HABILITATION THESIS HEAVY METALS REMOVAL FROM … abilitare_L. Tofan.pdf · De asemenea, sunt...

“GH. ASACHI” TECHNICAL UNIVERSITY OF IASI

“ CRISTOFOR SIMIONESCU’’ FACULTY OF CHEMICAL ENGINEERING AND

ENVIRONMENTAL PROTECTION

DEPARTMENT OF ENVIRONMENTAL ENGINEERING AND MANAGEMENT

HABILITATION THESIS

HEAVY METALS REMOVAL FROM

WASTEWATERS BY SORPTION PROCESSES

PhD Lavinia TOFAN

IASI

2017

REZUMAT 5

2 Habilitation Thesis

1.ACADEMIC AND SCIENTIFIC ACHIEVEMENTS 12

1.1.Significant aspects of the teaching activities 12

1.2.Scientific contributions 14

2. RETENTION OF HEAVY METAL IONS FROM AQUEOUS SOLUTIONS BY

SORPTION ON FUNCTIONALIZED POLYMERS AND WASTE MATERIALS

19

2.1.Sorption– a method of choice in concentration/ recovery of heavy metal

ions from aqueous solutions

19

2.1.1. Removal of heavy metals from aquatic environments– a critical

need

19

2.1.2. Description and characterization of the sorption methods 21

2.1.3. Types of sorbents 25

2.1.3.1. Sorbents based on polymer materials 27

2.1.3.2.Sorbents based on waste materials 29

2.1.3.2.1. Low – cost sorbents 29

2.1.3.2.2. Low – cost sorbents from natural materials 31

2.1.3.2.3. Agricultural and industrial wastes as sorbents for

remediation of heavy metal ions

33

2.1.4. An overview of the sorbents targeted in my research work 34

2.2. Removal/recovery of heavy metal ions from aqueous solutions by using

polymeric sorbents

36

2.2.1. New chelating polymers as selective sorbents of heavy metal

ions

38

2.2.1.1. Background 38

2.2.1.2. Chelating sorbents with grafted groups 40

2.2.1.2.1. Synthesis and characterization 40

2.2.1.2.2. Chelating sorbents based on acrylic copolymers 43

2.2.1.2.2.1 New chelating sorbents based on acrylic

copolymers bearing amidoethylenamine and thiol groups

for the selective recovery of platinum(IV) from chloride

solutions

43

2.2.1.2.2.2. A new acrylic copolymer with

dimethylaminobenzaldehyde functional groups as a good

performance material for gold(III) separation from

wastewaters

52

2.2.1.3. Ion exchangers modified with chelating reagents 62

2.2.1.3.1. Anionic exchangers modified with chelating

reagents

62

2.2.1.3.1.1.Macroporous anion exchanger Purolite A-

500 loaded with Ferron for palladium (II) recovery

62

2.2.1.3.1.2. Determination of trace amounts of Rh(III)

by a new procedure based on the reaction product of

Nitroso-R salt previously loaded on Dowex 1x1 anion

exchanger

68

2.2.1.3.2.Cationic exchangers modified with chelating

reagents

72

Heavy metals removal from wastewaters by sorption processes 3

2.2.1.4. Impregnated sorbents 72

2.2.1.5. Conclusions 73

2.2.2. Advances in preconcentration/ removal of environmentally

friendly relevant heavy metal ions from water and wastewater by

sorbents based on polyurethane foams

73

2.2.2.1. Synthesis, physical and chemical properties of

polyurethane foams

74

2.2.2.2. Preconcentration of pollutant metal ions from

environmental aqueous media by different types of polyurethane

foams

75

2.2.2.2.1. Sorbents based on unloaded polyurethane

foams

75

2.2.2.2.2. Sorbents based on loaded polyurethane foams 76

2.2.2.2.3. Chemically modified(reacted) polyurethane

foams

81

2.2.2.3. The applicability of sorbents based on polyurethane

foams in water and wastewater treatment

82


2.3. Sorption removal of heavy metal ions from aqueous media by waste

materials

84

2.3.1. Removal/ recovery of heavy metal ions from aqueous solutions

by sorption on hemp fibers

87

2.3.1.1.Background 87

2.3.1.2. Batch studies on the removal of heavy metal by using

natural hemp fibers

88

2.3.1.3. Hemp fibres with improved performances in batch

sorption systems

90

2.3.1.3.1 Sorbents based on impregnated hemp 91

2.3.1.3.2. Sulphydryl hemp fibers 93

2.3.1.3.3. Concentration of Cd(II) trace amounts from large

volumes of aqueous samples on chemically modified femp

fibers

95


2.3.2. Waste of rapeseed from biodiesel production as appropriate

sorbent for Cu(II), Cd(II) and Zn(II) ions

98


2.3.2.2. Rapeseed characterization 100

2.3.2.3. Batch studies of Cu(II), Cd(II) and Zn(II) sorption on

rapeseed

101

2.3.2.4. Comparison of rapeseed waste with other low – cost

sorbents for Cu(II), Cd(II) and Zn(II) ions removal

105

2.3.2.5. Thermogravimetric investigations 106

2.3.2.6. Fixed bed column studies on the removal of Pb(II) ions by

using rapeseed biomass

110



2.3.3. Sorption removal of Cu(II), Zn(II) and Cd(II) ions from aqueous

effluents by Romanian bark wastes

114


2.3.3.2. Romanian pine bark as low – cost sorbent for Cu(II), Zn(II)

and Cd(II) from aqueous solutions

117

2.3.3.2.1. Characterization of the pine bark under investigation 117

2.3.3.2.2. Assessment of kinetic, equilibrium and thermodynamic

parameters of Cu(II), Zn(II) and Cd(II) sorption by Romanian pine

bark

118

2.3.3.3. Sorption of Cu(II) and Cd(II) from aqueous solutions by

Romanian silver fir (Abbies alba Mill.) bark wastes

125


2.3.4. Thermal power plants ash as sorbent for the removal of Cu(II),

Zn(II), Pb(II) and Cd(II) ions from wastewaters

131


2.3.4.2.Batch sorption capability of the tested fly ash as function

of initial pH, sorbent dose, metal ion concentration, temperature

and contact time

133

2.3.4.3. Thermodynamic description of the heavy metal ions

sorption on energy pit coal ash

142

2.3.4.4. Kinetic description of some heavy metal ions sorption on

energy pit coal ash

143


3. PROPOSAL FOR THE ACADEMIC AND SCIENTIFIC CAREER

DEVELOPMENT

146

3.1. Future prospects in the teaching career 146

3.2. Future prospects in the scientific career 147

4. REFERENCES 150


REZUMAT

De-a lungul celor 30 de ani de când fac parte din corpul profesoral al Universității

Tehnice ‖Gheorghe Asachi‖ din Iași, Facultatea de Inginerie Chimică și Protecția Mediului,

mi-am desfășurat activitatea didactică și științifică în cadrul colectivului de Chimie

Analitică. În ultimul deceniu, colectivul de Chimie Analitică a devenit parte integrantă a

departamentului de Ingineria și Managementul Mediului.

Teza de abilitare intitulată „Eliminarea metalelor grele din apele uzate prin

procese de sorbție ” constituie o imagine de ansamblu a activității profesionale,

academice și științifice din perioada ulterioară susținerii tezei de doctorat (1998–2017).

Această teză este structurată în 4 capitole al căror conținut reflectă experiența

acumulată, principalele contribuții științifice și direcțiile de perspectivă în cariera

academică.

În capitolul 1 sunt prezentate în 2 subcapitole cele mai importante realizări din

activitatea didactică (1.1) și științifică (1.2).

Am absolvit în anul 1984 Facultatea de Tehnologie Chimică din cadrul Institutului

Politehnic ‖Gh. Asachi‖ Iași, secția Tehnologia Compușilor Macromoleculari (1984), iar în

perioada 1984-1987 am efectuat perioada de stagiu de 3 ani în producție la Combinatul

de Fire Sintetice Iași, în cadrul Atelierului de Cercetare și Proiectare Uzinală. După

încheierea perioadei de stagiu, m-am transferat la Institutul Politehnic ‖Gh. Asachi‖ Iași,

Facultatea de Tehnologie Chimică, unde mi-am început activitatea didactică și de

cercetare, fiind asistent suplinitor la catedra de Chimie și Tehnologie Anorganică,

colectivul de Chimie Analitică. În anul 1990 am ocupat, prin concurs, postul de asistent

titular la Universitatea Tehnică „Gh. Asachi‖ din Iași, Facultatea de Chimie Industrială,

Catedra de Chimie Analitică, iar, ulterior, parcursul meu profesional în învățământul

superior a fost următorul: asistent universitar- 1990–1999; șef de lucrări–1999– 2013;

conferențiar universitar–din 2013–până în prezent. Din 1999, în calitate de conferențiar

universitar(din 2013) și șef lucrări (1999–2013) am fost titulară de curs și aplicații la

următoarele discipline: Chimie analitică I (Inginerie Chimică); Chimie analitică și analiză

instrumentală (Ingineria Mediului); Chimie analitică I (colegiu); Tehnici de analiză și

calitatea produselor chimice (colegiu Tehnici de laborator); Controlul analitic al calității

produselor (Inginerie și Management); Chimia și fizica mediului ambiant (Masterat Energie

–Mediu); Evaluarea indicatorilor de calitate a poluării mediului (Masterat Ingineria

Procedeelor Nepoluante); Ecologie și protecția mediului (Masterat Managementul

Mediului). Activitatea didactică a fost susținută prin publicarea unui număr de 18 cărți,

după cum urmează: 6 cursuri/ manuale (dintre care prim autor/ unic autor:5) publicate în


edituri recunoscute CNCS; 1 curs editat la Litografia Universității Tehnice „Gh. Asachi‖ din

Iași (prim autor); 10 îndrumare de laborator/ culegeri de probleme (dintre care prim

autor/unic autor:3) publicate în edituri recunoscute CNCS; 1 îndrumar de laborator

publicat la Litografia Universității Tehnice „Gh. Asachi‖ din Iași.

In perioada 1990–1998 mi-am desfășurat activitatea doctorală în cadrul

Universității Tehnice ―Gh. Asachi‖ din Iași–Facultatea de Inginerie Chimică și Protecția

Mediului, sub conducerea conducerea prof. dr. chim. Al. Nacu. În urma susținerii publice,

în ianuarie 1998, a tezei de doctorat cu titllul „Metode combinative (hibride) pentru

determinarea concentrațiilor mici de substanțe din sisteme tehnologice și mediile ce le pot

polua‖ am obținut titlul de doctor în Chimie, specializarea Chimie Analitică.

Metodele combinate de analiză a unor ioni metalici poluanți în concentrații mici,

studiate și elaborate în cadrul cercetării doctorale, s-au bazat pe îmbinarea concentrării/

separării prin sorbție pe diferite tipuri de materiale cu determinarea prin metode

spectrometrice.

Direcțiile de cercetare pe care le-am abordat prioritar după obținenerea titlului de

Doctor au fost o continuare și o aprofundare a tematicii doctorale. Acestea vizează:

concentrarea/ recuperarea unor ioni de metale grele prin sorbție pe materiale

polimerice (rășini organice sintetice și spume poliuretanice);

studii privind fezabilitatea conversiei unor deșeuri industriale și agricole în sorbenți

cu valoare adăugată, aplicabili în epurarea avansată a apelor uzate;

adaptarea și elaborarea unor metode analitice pentru determinarea unor specii

chimice în concentrații mici.

Contribuția mea științifică se reflectă în publicarea a 80 de articole, dintre care 32

de articole în reviste cotate ISI Thomson-Reuters, 39 de articole în reviste BDI și 9 articole

publicate în volumele unor manifestări ştiinţifice internaţionale și naţionale. La

17(53,12%) dintre articolele publicate în reviste cotate ISI am calitatea de autor principal.

De asemenea, sunt prim autor la 21 (53,84%) dintre articolele publicate în reviste BDI.

Articolele mele au acumulat un număr de 212 citări în reviste cotate ISI . În acest context,

îmi corespunde un coeficient Hirsch a cărui valoare este egală cu 7 (Scopus)

De asemenea, sunt co–autor la 1 monografie („Biomateriale–Biotehnologii-

Biocontrol” -660 pagini) publicată într-o editură din țară, recunoscută CNCS și la 5 capitole

în cărţi de specialitate publicate în edituri recunoscute din străinătate (4) și din țară(1).

Un alt aspect important al activității mele de cercetare este legat de participarea

mea la proiecte de cercetare- dezvoltare pe bază de contract/ grant (53), în calitate de

coordonator (5) sau membru în diferite echipe de cercetare (48).


Capitolul 2,cel mai extins al tezei, reprezintă o abordare integrată a principalelor

contribuții științifice pe direcțiile de cercetare menționate mai sus. Sub denumirea de

„Reținerea ionilor de metale grele din medii apoase prin sorbție pe diferite tipuri de

materiale‖, rezultatele studiilor realizate sunt descrise succint în 3 secțiuni care se

succed după cum urmează:

În subcapitolul 2.1 este evidențiată superioritatea metodelor sorbtive în

concentrarea/ recuperarea ionilor de metale grele din soluții apoase. După sublinierea

imperativului eliminării ionilor de metale grele din medii apoase (2.1.1), sunt descrise și

caracterizate metodele sorbtive (2.1.2) și principalele tipuri de sorbenți (2.1.3).

Coroborând rezultatele obținute în cadrul cercetării doctorale cu actualitatea și

perspectiva necesității de a elabora noi sorbenți, cu performanțe superioare, mi-am

concentrat atenția asupra sorbenților pe bază de materiale polimerice și de deșeuri.

Subcapitolele 2.1.3.1 și, respectiv 2.1.3.2 conțin o prezentare generală a acestor tipuri

de sorbenți. În subcapitolul 2.1.4. se face referire distinctă la materialele sorbtive efectiv

investigate (rășini chelatizante, spume poliuretanice, deșeuri de cânepă, rapiță, scoarță

de pin și cenușă de termocentrală), a căror alegere este riguros justificată.

Subcapitolul 2.2. pune accentul pe prezentarea rezultatelor studiilor privind

reținerea ionilor metalici din soluții apoase pe sorbenți pe bază de polimeri chelatizanți

(2.2.1) și spume poliuretanice (2.2.2).

În secțiunea 2.2.1. sunt descrise succint elementele actuale și de

perspectivă din literatura de specialitate din domeniul sorbenților chelatizanți și sunt

sistematizate cele mai relevante rezultate ale cercetărilor proprii pe această tematică.

Aspectele abordate au vizat, în special, sinteza și caracterizarea unor noi polimeri

chelatizanți ca sorbenți selectivi pentru ionii de metale grele; evaluarea abilităților sorbtive

ale polimerilor propuși prin stabilirea condițiilor optime de sorbție a unor ioni metalici în

cadrul unor studii asupra influenței unor parametri experimentali (pH–ul soluției inițiale,

concentrația inițială a ionului metalic, doza de sorbent, timpul de contact, temperatura) în

sisteme statice de sorbție; modelarea la echilibru a proceselor de sorbție; modelarea

cinetică și caracterizarea termodinamică a acestora. După unele considerații generale

(2.2.1.1), secțiunea 2.2.1 este subdivizată în 3 părți, corespunzătoare principalelor clase

de sorbenți chelatizanți propuși și investigați.

- 2.2.1.2. – Sorbenți chelatizanți cu grupări grefate

Conturarea unei imagini de ansamblu asupra metodelor de sinteză a sorbenților

chelatizanți cu grupări grefate este urmată de evidențierea proprietăților distinctive ale

acestora prin prezentarea succintă a caracteristicilor a 2 polimeri funcționalizați (rășina

comercială Purolite S–940 și schimbătorul de ioni chelatizant cu două tipuri de grupări


funcționale- acid hidroxamic și amidoximă), pe care i-am studiat din punct de vedere al

potențialei lor aplicabilități în reținerea unor ioni de metale grele [Pd(II); Pb(II)] din efluenți

industriali. În continuare au fost evidențiate perspectivele extrem de favorabile pe care le

poate deschide utilizarea unor noi sorbenți chelatizanți (copolimeri acrilici funcționalizați

cu grupări de amidoetilenamină și dimetilaminobenzaldehidă) pentru recuperarea

selectivă a Pt(IV) și, respectiv Au(III) din soluții clorhidrice.

- 2.2.1.3. – Schimbători de ioni modificați cu reactivi chelatizanți

Metodele specifice laborioase de preparare a sorbenților chelatizanți cu grupări

grefate, costul ridicat și dificultățile lor de regenerare au stimulat cercetările pentru găsirea

de noi proceduri simple și rapide, aplicabile în sinteza acestora. O alternativă viabilă este

reprezentată de sorbția unor reactivi organici chelatizanți pe anioniți sau cationiți. În acest

context, în scopul lărgirii gamei de sorbenți chelatizanți cu performanțe superioare în

recuperarea Pd(II), răşina anionică puternic bazică Purolite A-500 în forma Cl- a fost

modificată cu acidul 7-iodo–8-hidroxichinolin-5-sulfonic (Feron). Rezultatele cercetării

efectuate, în condiții statice, în 2 etape (studiul reținerii Feronului pe rășina

anionică→studiul sorbției Pd(II) pe anionitul modificat cu reactivul chelatizant) au arătat

că anionitul macroporos Purolite A–500 modificat cu Feron îndeplinește toate condițiile

pentru o aplicare eficientă în recuperarea sorbtivă a Pd(II) din soluții apoase.

Anioniții modificați cu reactivi chelatizanți pot fi eficienți utilizați atât pentru

separarea și concentrarea selectivă a unor microelemente, cât și pentru elaborarea unor

noi metode de analiză care îmbină concentrarea ionilor metalici din medii apoase cu

determinarea ulterioară a acestora direct în faza rășină. Prin valorificarea acestei

oportunități, am propus metode de determinare a ionilor de Pd(II) și Rh(III) prin

spectrometrie în fază solidă. Metodele propuse s-au bazat pe reținerea ionilor de metale

platinice pe schimbătorul anionic Dowex 1x1 impregnat cu sarea disodică a acidului 1-

nitrozo- 2-hidroxinaftalen-3,6-disulfonic (sare R-Nitrozo) și măsurarea absorbanței

complecșilor de culoare roșie formați în faza solidă.. Prin compararea datelor obţinute la

determinarea ionilor de metale platinice prin spectrometrie în fază solidă cu cele ale

spectrofotometriei clasice, s-a observat că metoda elaborată este mult mai sensibilă, mai

simplă, rapidă şi precisă.

- 2.2.1.4. Sorbenți impregnați

O variantă simplă și rapidă de preparare a unui sorbent impregnat se bazează pe

‖impregnarea mecanică‖ a unei matrici inerte cu agenți complexanți. În acest scop,

suportul inert este tratat cu o soluție a reactivului chelatizant într-un reactiv organic, care

este apoi îndepărtată prin filtrare sau evaporare. Astfel, prin impregnarea cu 5,7- dibromo-


8- hidroxichinolină (bromoxină) a suportului polistirenic nepolar Purasorb s-a preparat un

sorbent chelatizant, particularizat printr-o mare selectivitate faţă de ionii de Pd(II).

Secțiunea 2.2.2. se axează pe descrierea comparativă a performanțelor

unor sisteme statice și dinamice de separare/ preconcentrare în care am utilizat sorbenți

ai ionilor metalici pe bază de spume poliuretanice netratate și spume poliuretanice

impregnate.

Subcapitolul 2.3 este consacrat prezentării rezultatelor studiilor originale privind

fezabilitatea conversiei unor deșeuri industriale și agricole în sorbenți cu valoare

adăugată, aplicabili în epurarea avansată a apelor uzate. Pornind de la conceptul de

Green Chemistry, care guvernează noua generație de produse și procese, în ultimii ani,

atenția mea în activitatea de cercetare s-a concentrat asupra evaluării compatibilității unor

deșeuri indigene (fibre de cânepă, rapiță, scoarțe de conifere , cenușă de termocentrală)

cu funcția de sorbenți ai unor ioni de metale de grele din soluții apoase. În cadrul

subcapitolului 2.3., rezultatele cercetărilor pe această direcție au fost descrise și

sistematizate, după cum urmează:

Secțiunea 2.3.1. se concentrează pe eliminarea/ recuperarea unor ioni de

metale grele din soluții apoase prin sorbție pe fibre de cânepă - deșeuri din industria

textilă. Mai întâi, sunt prezentate succint și încadrate în contextul științific actual,

rezultatele unei serii de articole publicate începând din anul 1999, când am raportat

pentru prima oară posibilitatea utilizării fibrelor de cânepă naturală (2.3.1.2) și modificată

prin tratamente fizice și chimice (2.3.1.3) în eliminarea ionilor de metale grele din ape

uzate. Impactul rezultatelor obținute în urma acestor studii trebuie considerat din

perspectiva aplicabilității practice a cânepii în eliminarea ionilor de metale grele din medii

apoase.

Din această perspectivă, am prezentat succint și investigațiile care au vizat

concentrarea unor cantități în urme de Cd(II) din volume mari de probe apoase pe cânepă

funcționalizată cu grupări mercapto (2.3.1.4). Pe lângă aspectele legate de managementul

produselor secundare şi remedierea mediului ambiant, rezultatele acestui studiu pot fi

importante, în contextul necesității menţinerii procesului de epurare a apelor uzate la un

preţ de cost cât mai scăzut şi deschid posibilitatea recuperării metalului extras în faza

lichidă.

În secțiunea 2.3.2. sunt sistematizate rezultatelor studiilor care au arătat

viabilitatea utilizării alternative a deșeurilor de rapiță din producția de biodiesel ca sorbent

pentru reținerea ionilor de Cu(II), Cd(II) și Zn(II) din soluții apoase. După prezentarea

datelor reprezentative din literatura științifică internațională recentă, care fundamentează

cercetarea aplicativă efectuată și descrierea succintă a metodologiei experimentale


(2.3.2.1), se caracterizează sorbentul înainte și după procesul de sorbție a ionilor metalici

(2.3.2.2). În continuare sunt sintetizate și explicate rezultatele studiilor statice axate pe

evaluarea influenței pH–ului soluției inițiale, a dozei de sorbent, a concentrației ionului

metalic (compatibilitatea cu ecuațiile Langmuir și Freundlich) și a timpului de contact

(corelația datelor experimentale cu ecuațiile modelelor cinetice de ordin pseudo–unu și de

ordin pseudo–doi) asupra reținerii ionilor de Cu(II), Cd(II) și Zn(II) pe rapiță (2.3.2.3).

Analiza comparativă efectuată sugerează posibilitatea aplicării deșeurilor de rapiță în

tratarea efluenţilor cu un conţinut scăzut de cupru, cadmiu sau zinc (2.3.2.4). În urma

investigațiilor termogravimetrice (2.3.2.5) s-a constatat că rapița încărcată cu ioni de zinc

manifestă o stabilitate termică sporită, datorată, probabil, reticulării generată prin

complexarea intermoleculară a ionilor de Zn(II).

Secțiunea 2.3.3. raportează rezultatele originale obținute în urma studiilor

statice de sorbție a ionilor de Cu(II), Zn(II) și Cd(II) din soluții apoase pe deșeuri indigene

de scoarță de pin (Pinus sylvestris L ) și de scoarță de brad(Abbies alba Mill.). Potențialul

sorbtiv al scoarței de pin a fost evaluat în funcție de pH – ul soluției inițiale, doza de

sorbent, concentrația ionilor de Cu(II), Zn(II) și Cd(II) în soluția inițială, timpul de contact

al fazelor și temperatură. Au fost detaliat discutate echilibrul, cinetica și termodinamica

proceselor de sorbție considerate. Echilibrul de reținere este bine descris prin modelul

Langmuir, indicând faptul că sorbţia ionilor de Cu (II), Zn(II) și Cd(II) pe scoarța testată

este restricţionată la un monostrat. Valorile capacităţilor maxime de sorbție au fost de

17,46 mg Cu(II)/ g scoarță, 15,73 mgZn(II)/ g scoarță și 27,32 mg Cd(II)/ g scoarță, fiind

comparabile cu date raportate în literatura de specialitate pentru reținerea Cu(II),Zn(II) și

Cd(II) pe alţi sorbenţi neconvenționali. Cinetica sorbției corespunde unui modelul cinetic

de ordinul pseudo-doi. Această corelație sugerează că reținerea ionilor testați urmează

un mecanism de ordin doi, iar stadiul determinant de viteză poate fi sorbţia chimică.

Parametrii termodinamici au evidențiat natura endotermă a proceselor de sorbție a ionilor

de metale grele pe scoarța de Pinus sylvestris L. și de Abbies alba Mill.

În secțiunea 2.3.4. sunt abordate aspecte legate de potențiala utilizare a

cenușii provenite din arderea huilei energetice într-o termocentrală din Iași pentru

reţinerea unor ioni ai metalelor grele din medii apoase. S-a constatat că asupra sorbției

ionilor de Cu(II), Zn(II), Pb(II) and Cd(II) pe cenușa studiată își pun amprenta o serie de

factori (pH–ul inițial, doza de cenușă, concentrația cationului în soluția inițială,

temperatura, timpul de contact), a căror influență este evaluată în subcapitolul 2.3.4.2. În

continuare, sorbția ionilor metalici testați pe cenușa de termocentrală este descrisă din

punct de vedere termodinamic (2.3.4.3) și cinetic (2.3.4.4). Rezultatele originale

sistematizate în această secțiune trebuie considerate din prisma evoluției sorbției ionilor


de metale grele din soluții apoase pe cenușă de termocentrală către o metodă de

perspectivă.

Capitolul 3 al tezei de abilitare se referă la direcțiile viitoare de dezvoltare în

cariera academică și științiifică. Sunt prezentate succint elementele de continuitate și de

noutate și modul în care îmbinarea lor armonioasă se va reflecta în evoluția carierei mele

profesionale.

Teza de abilitare se încheie cu „Bibliografie‖ (Capitolul 4), în care sunt incluse

referințele care fundamentează cercetările efectuate. De asemenea sunt inserate și

lucrările științifice personale aferente studiilor prezentate în această teză de abilitare.


1. ACADEMIC AND SCIENTIFIC ACHIEVEMENTS

1.1. Significant aspects of the teaching activities

After the graduation of the Faculty of Chemical Technology from the "Gh. Asachi"

Polytechnic Institute of Iasi, Macromolecular Compounds Technology specialization

(1984), I was assigned to the Research Institute for Rubber and Plastics Processing of

Bucharest, with an internship of 2 years at the Factory of Synthetic Fires and Fibres in

Vaslui. I completed the internship period of 3 years (1984-1987) at the Factory of

Synthetic Fibers in Iasi, where I was detached from the Factory of Synthetic Fires and

Fibres in Vaslui. At the Factory of Synthetic Fibers in Iasi, I performed at the Workshop of

Factory Research and Design, where I dealt with the following issues: industrial-scale

achievement of an installation for producing sintered alumina thread guides; the

assimilation and the approval of the thread guides. After the end of the internship, I was

transferred to the "Gh. Asachi" Polytechnic Institute of Iasi, the Faculty of Chemical

Technology, where I began my teaching and research activity as substitute assistant at

the Department of Inorganic Chemistry and Technology, team of Analytical Chemistry. In

1990 I occupied by contest the position of assistant professor at the "Gh. Asachi‖

Technical University of Iasi (TUIASI), Faculty of Industrial Chemistry, the Analytical

Chemistry Department. Later my academic career has been evolved as follows: 1990 -

1999 - assistant professor; 1999 - 2013 – lecturer; associate professor from 2013 until the

present.

Throughout the 30 years since I am part of the teaching staff of TUIASI, Faculty of

Chemical Engineering and Environmental Protection, all my professional activity unfolded

within the Analytical Chemistry team. During the last decade, the team of Analytical

Chemistry has become part of the Department of Engineering and Environmental

Management.

Between 1987 and 1999 I conducted laboratory teaching activities at the

disciplines of Analytical Chemistry and Analytical Chemistry and Instrumental Analysis,

which I taught to the students from the educational programs for engineers,

specializations on Chemical Engineering and Environmental Engineering and to the

college students. In these activities my permanent concern was the care for the smooth

running of the laboratory classes, the training and evaluation of the students‘ knowledge

both in theoretical and practical terms. I tried to impress to students the laboratory sense

of duty and I helped them to learn correctly the techniques of chemical analysis so that


they could cope with the issues that they would encounter in the superior years and those

for the development of graduate work.

Since 1999 until the present, as Associate Professor (since 2013) and Lecturer

(1999-2013) I taught the following courses: Analytical Chemistry I (Chemical Engineering

BSc specialization); Analytical Chemistry and Instrumental Analysis (BSc Specialization

on Environmental Engineering); Analytical Chemistry I (College); Analysis Techniques and

Quality of Chemical Products (College of Laboratory Techniques); Analytical Control of

Product Quality (BSc Specialization on Engineering and Management); Environmental

Chemistry and Physics (Master of Science Program on Energy and Environment);

Assessment of Quality Indicators of Environmental Pollution (Master of Science Program

on Engineering of Clean Procedures); Ecology and Environmental Protection (Master of

Science Program on Environmental Management). Of the 8 courses that I taught, 3 were

new, dealing with directions not addressed before, on BSc (Analysis Techniques and

Quality of Chemical Products) and MSc programmes (Environmental Chemistry and

Physics and Assessment of Quality Indicators of Environmental Pollution). In addition, at

2 disciplines from the MSc programmes I was titular of applications and I introduced

new works. During my whole career I was guided by the principle of the continuous self-

improvement of my teaching and professional activity. In this context, I was in a constant

competition with myself in order to improve the teaching act and the ways to transfer the

knowledge to the students with whom I have interacted in the various forms of activity. I

tried and constantly try to be both a facilitator of learning and a fellow of students actively

involved in their training. I learned the importance of continuous updating of the teaching

materials for BSc and MSc students. Thus, my publishing activity was materialized in the

contribution as first author/ sole author or co-author to the development of a number of 18

books as follows:

- 6 courses / books (including first author/ sole author: 5) published in CNCS rated

publishing houses;

- 1 course published at the Lithography of TUIASI (as first author);

- 10 handbooks/exercise books (including first author/sole author: 3) published by

CNCS rated publishing houses;

- 1 handbook published by the Lithography of TUIASI.

The published books cover in a clear and concise manner the curriculum content

of the taught courses and the laboratory works. It should be mentioned that the "Analytical

Biochemistry, volume I: Chemical Analysis Methods. Methods of Separation and

Concentration of Biomolecules" and "Analytical Biochemistry, volume II: Biological

Applications of Biosensors" monographs, of which I am the first author, were developed in


an attempt to fill a gap in the Romanian literature that refers to the application of the

analytical chemistry methods in the biochemical analysis.

Also during this period, I coordinated many graduation and dissertation theses of

the Bsc and MSc students in the specializations on Chemical Engineering and

Environmental Engineering. I guided the students works for student events organized at to

faculty level.

I was member (2013) of the target group of the ‖DidaTec‖ project (POSDRU /

87/1.3/S 60891) of the Cluj – Napoca Technical University.

I participated as expert in education sciences at 2 POSDRU projects:

- New approaches in the training of specialists in the field of environmental

engineering for the sustainable regional development and the correlation to the

current requirements of the labor market (REGIOSIM)–POSDRU/ 156/1.2/G/

136423 (13.05.2014-12.11.2015);

- The national network of ongoing training for teachers in secondary technical

professional education system (CONCORD) - POSDRU/87/1.3/S /61.397 (2012 -

2013).

I was deeply involved in the academic community through activities that have

resulted in:

the participation as member in bachelor committees;

the participation in committees for promotion contests;

contribution to the development of the documents for the ARACIS accreditation of

educational programs

Also, I was head of the "Analytical Chemistry and Environmental Control" team

from the Environmental Engineering and Management Department and I was member of

the Teaching Council of the Faculty of Chemical Engineering and Environmental

Protection.

.

1.2. Scientific contributions

Between 1990 and 1998 my doctoral work was performed at "Gh. Asachi"

Technical University of Iasi, the Faculty of Chemical Engineering and Environmental

Protection, under the coordination of Prof. Ph.D. Chemist Al. Nacu. After the finalization

(January 1998) of the Ph.D thesis entitled "Combinative (Hybrid) Methods for the

Determination of Low Concentrations of Substances in Technological Systems and

Environments that They can Pollute”, I obtained the PhD in Chemistry, specialization of

Analytical Chemistry (diploma - P series no. 0006339, MEC Order 4090 / 3.07.1998).


The combined methods for the analysis of the pollutant metal ions in low

concentrations studied and developed during the doctoral research were based on the

combination of the concentration/ separation by sorption on different types of materials

(Dowex 2x4 and Vionit AT-14 anionite synthetic styrene–divinylbenzene resins;

aminoethyl- , diethylaminoethyl- and triethylaminoethyl- anionites celluloses modified with

5– sulphosalicylic acid; "SPUMATIM" polyurethane foam modified by physical adsorption

of dimethylglyoxime and tri-n–butylphosphate; natural hemp fibers; physically and

chemically modified hemp fibers) with determination by spectrometric methods.

The research directions that I have addressed as a priority since I obtained the

PhD title were a continuation and a deepening of the doctoral theme. The research topics

targets:

sorption removal/recovery of heavy metal ions by using polymeric materials

(organic synthetic resins and polyurethane foams);

studies concerning the feasibility of the conversion of industrial and agricultural

wastes into value-added sorbents, applicable in the advanced wastewater

treatment;

the adaptation and development of analytical methods for the determination of

chemical species in low concentrations.

My scientific contribution is reflected in the publication of 80 papers of which 32

papers in ISI Thomson-Reuters journals (Journal of Hazardous Materials, Microchimica

Acta, Applied Surface Science, Journal of Environmental Management, Process Safety

and Environmental Protection; Reviews in Chemical Engineering; Reviews in Analytical

Chemistry; BioResources; Journal of the Iranian Chemical Society; Desalination Water

Treatment, Environmental Engineering and Management Journal, Materiale Plastice,

Journal of the Serbian Chemical Society; Croatica Chemica Acta, Cellulose Chemistry

and Technology, Journal of Optoelectronics and Advanced Materials; Revue Roumaine

de Chimie), 39 papers in BDI journals and 9 papers published in the proceedings of

international and national scientific meetings. I have the status of first author/

corresponding author at 17 (53.12%) of the papers published in ISI journals. Also, I am

the first author of 21 (53.84%) of the papers published in BDI journals. These

observations support my ability to work at a significant scientific level and to coordinate

the research activity.

The results of researches dealing the sorption removal / recovery of heavy metal

ions by using polymeric materials have been published in 30 papers of which 11 ISI

papers and 19 papers published in BDI journals.


The studies on the feasibility of the conversion of industrial and agricultural waste

into value-added sorbents, applicable in advanced treatment of wastewater have been

validated by the 15 papers (11 as first author / corresponding author) published in ISI

journals and the 11 published in BDI journals.

The research direction targets to the adaption and development of analytical

methods for the determination of chemical species in low concentrations is supported by

the 7 published articles: 3 (1 as sole author) in ISI journals and 4 papers published in BDI

journals.

My papers have received a number of 198 citations in ISI journals (Scopus) and I

have an Hirsch index of 7.

I am also co-author of 1 monograph („Biomaterials – Biotechnologies - Biocontrol”

- 660 pages) published by a CNCS rated publishing house in Romania and 5 chapters in

books published by publishing houses rated both abroad (4) and in Romania (1).

Another important aspect of my research work is related to the participation in

research and development projects upon grants / contract (53), as coordinator (5) or as

member of various research teams (48).

Between 2004 and 2010 I was director of 3 contracts with industry. I was project

manager (partner P1 TUIASI) to the Contract no. 223/2012 "Inquiry-Based Education in

Science and Technology" (total value per partner P1- TUIasi- 207 500 RON)(2012 –

2016). This project was coordinated by the National Institute for Laser, Plasma and

Radiation Physics and running through the PNCD II Partnerships Program.

The project „Inquiry–Based Education in Science and Technology” (http://

education. inflpr.ro/ro/ IBEST.htm) addresses various aspects of science teaching in order

to have a long term impact. The project aims to: the development of a participatory model

of teaching science, based upon the inquiry-based learning and problem-based learning

methods. The model was and will be tested and validated by applying it to a real problem,

easily identifiable and perceived by ordinary citizens, for example, weather and

meteorological parameters / environmental pollution / monitoring of risks; the development

of a set of teaching materials such as experimental kits and educational films and books;

the development of students' skills such as: creativity, the ability to innovate and provide

answers to new challenges, the rigor in scientific inquiry.

As member of different research teams, I was involved in 11 national grants

dealing with:

- advanced porous materials with applicability in separation processes and in biomedicine;

- expertise for the sustainable exploitation of ecosystems: Case Study: Terrestrial and

aquatic peri-urban ecosystems in the basin of the river Ciric, at north of the Iasi city;


- intelligent photosensitive nanomaterials applicable to the biotechnology processes

monitoring, food, cosmetic and pharmaceutical biocontrol or medical and cytogenetic

tests;

- antioxidant plant compounds and synthesis succedaneum;

- biotechnological applications of the sorbents functionalized with dyes or fluorochromes;

- sorbents modified with reactive dyes recovered from wastewaters with applications in

trace analysis, remediation processes and separations of ecological and biotechnological

interest;

- methods of separation and concentration; methods of analysis and control with superior

performances.

Also, I was involved as member of research team in 37 contracts with industry, in

which I studied issues related to the pollution prevention and control: monitoring, process

analysis, wastewater treatment; investigation of advanced wastewater treatment

processes for wastewater recycling and reuse.

During this period I performed 3 proposals for CNCS projects. I applied the latest

proposal for a project in 2012 at a competition for the IDEI program- Exploratory Research

Projects. Although it has been declared eligible, the project "Treatment and valorization of

waste materials for the removal of toxic and carcinogenic pollutants from aqueous

effluents", unfortunately, did not receive funding.

In 2008 I organized the conference "Application of Laser to on - line analysis of

particulate matter", supported by Prof. PhD. Israel Schechter from the Technion- Israel

Institute of Technology, at TUIASI, Faculty of Chemical Engineering and Environmental

Protection (21.08.2008).

The acquired experience and the obtained results have led to:

- my cooptation as member of the Environmental Engineering and Impact Assessment

Research Center( Water& Wastewater Engineering Research Group),which works at the

Faculty of Chemical Engineering and Environmental Protection, TUIASI;

- my request as scientific reviewer for various ISI journals;

- my participation as scientific reviewer in commissions for analysis of 4 PhD thesis;

- receiving of medals and awards: the 2014 Excellence Award and the "Gheorghe

Asachi" Medal for the category "The group that has contributed to attracting most funds

for research" (group coordinator: Prof.dr.ing. Carmen Teodosiu); the Silver Medal and the

Excellence Diploma at the Jubilee International Exhibition of Research, Invention and

Technology Transfer, INVENTICA 2008, for the work entitled "The assessment of the

eutrophication stage of the Ciric lake (a study performed under the CEXDUREC-CEEX

contract no.634/2005);


- my cooptation as analyst at the Laboratory for Analysis and Control of Environmental

Factors–LACMED, accredited by the Romanian Accreditation Association - RENAR.

Founded in 2013 in TUIASI and coordinated by prof.dr.ing. Carmen Teodosiu,

LACMED performs servicies for analysis-consultancy- research related to water and

wastewater quality.


2. RETENTION OF HEAVY METAL IONS FROM AQUEOUS

SOLUTIONS BY SORPTION ON FUNCTIONALIZED POLYMERS

AND WASTE MATERIALS

2.1. Sorption- a method of choice in the concentration/recovery of heavy

metal ions from aqueous solutions

2.1.1. Removal of heavy metals from aquatic environments– a critical need

Heavy metals are defined as metallic elements that have a high atomic weight and

a density at least 5 times greater than that of water [Tchounwou et al. 2012]. Heavy

metals can be classified into three different types, including toxic metals (such as Hg, Cr,

Pb, Zn, Cu, Ni, Cd, Co, Sn etc.), precious metals (such as Pd, Pt, Ag, Au, Ru etc) and

radionuclides( such as U, Th, Ra, Am etc.) [Wang and Chen 2009].

The rapid development and changing technologies, industrial products and

practices of the present day has led to tremendous increase in the use of heavy metal

over the past few decades and inevitably resulted in an increased flux of metallic

substances in the aquatic environment and surrounding soils. The ubiquitous nature of

heavy metals, their toxicity even in trace quantities, their tendency for bioaccumulation in

food chain, their non–biodegradability, their ability to undergo transformations, the

economic impact and the stricter environmental regulations related to heavy metals

discharges (Table 2.1.) have prompted the development of processes for the removal of

heavy metals from wastewaters and soils. In addition, the increasingly high demand for

heavy metals drive the increase in the research into efficient recovery of heavy metals

from all waste materials, especially wastewaters.

The treatment of heavy metals contaminated effluents is a process that is

sometimes more complicated that any other manufacturing process, because especially

industrial wastewaters can have a widely variable composition in terms of organic or

inorganic compounds, extreme acidity or alkalinity, presence of volatile substances and so

on. Several methods were developed for the removal and recovery of toxic and/or

valuable heavy metals from water or municipal/industrial wastewater, i.e. reverse osmosis,

electrodialysis, ion exchange, coagulation/ flocculation, phytoremediation, chemical

precipitation/ neutralization, sorption on various media [Fu and Wang 2011; Barakat 2011;

Ahluwalia and Goyal 2007; Wang and Chen 2009; Wan Ngah et al. 2011; Abdel Salam et

al. 2011; Qdais and Moussa 2004; Wan Ngah and Hanafiah 2008; Katsou et al. 2011].


Table 2.1. Some heavy metals and their effects on human health with their permissible

limits [Singh et al. 2011]

Pollutant

Major source

Effects on human health

Permissible level

(mg/ L)

Arsenic Pesticides, fungicides, metal smelters

Bronchitis, dermatitis, poisoning 0.02

Cadmium Welding, electroplating, pesticide, fertilizer, Cu and Ni batteries, nuclear fission plant

Renal dysfunction, lung disease, lung cancer, bone defects, increased blood pressure, kidney damage, bronchitis, gastrointestinal disorder, bone marrow, cancer

0.06

Lead Paint, pesticides, smoking and mobile emissions, mining, burning of coal

Mental retardation in children, developmental delay, fatal infant encephalopathy, paralysis, sensor neural deafness and acute or chronic damage to the nervous system, liver, kidney, gastrointestinal disorder

0.1

Mercury Pesticides, batteries, paper industry

Tremors, gingivitis, minor psychological changes, damage to nervous system

0.01

Zinc Refineries, brass manufacture, metal plating, plumbing

Zinc fumes have corrosive effects on skin, cause damage to nervous membrane

15

Chromium Mines, mineral sources

Damage to the nervous system, fatigue, irritability

0.05

Copper Mining, pesticide production, chemical industry, metal piping

Anemia, liver and kidney damage, stomach irritation

0.1

These methods have disadvantages, such as: incomplete metal removal,

increased economic costs (energy, reagents), generation of toxic sludge or other heavy

metal wastes, lack of flexibility in terms of treated effluent volumes and concentrations,

need of thorough supervision/ maintenance of equipment (Table 2.2).

Since the last decades, sorption by sorbents has been found to be one of the

most popular processes for the removal of heavy metals from aquatic environment due to

its low complexity, straightforward implementation in field conditions and sludge- free

operation. The sorption process offers flexibility in design and operation and, in many

cases, produces treated effluents suitable for re-use, free of color or odor. Furthermore,

because the sorption is sometimes reversible, the regeneration of the sorbent with

resultant economy of operation is possible [O‘ Conell et al.2008]. Additionally, another

significant advantage of the sorption process in removing or minimizing the heavy metal

ions even at very low concentration enhance the application of sorption as one practical

treatment.


Table 2. 2. Comparison among wastewater treatment technologies [Zwain et al. 2014]

Technique Advantages Disadvantages

Chemical precipitation

-Simplicity; -Inexpensive; -Adapted to treat high heavy metal ions concentrations

-Ineffective when metal ion concentration is low; -Not economical; -Produce large amounts of sludge

Ion exchange -Widely applied for heavy metal

removal; - Ion exchange resins can be regenerated

- Secondary pollution can be caused due to regeneration by chemical reagents; - Expensive when treating a large amount of wastewater so cannot be used at large scale

Membrane filtration High heavy metal ions removal efficiency

-High cost and complex process; -Membrane fouling has limited heavy metal removal

Coagulation –

flocculation Good sludge settling and dewatering characteristics

-It involves chemical consumption; -Increased sludge volume generation

Flotation - High metal selectivity;

- High removal efficiency; - High overflow rates; - Low detention periods

- High initial capital cost; - High maintenance and operation cost

Electrochemical -Regarded as rapid and well

controlled which required fewer chemicals; -Provide good reduction yields and produce less sludge

Involving high initial capital investment; Expensive electricity supply

Sorption -Flexibility and simplicity of design;

- Ease of operation and insensitivity to toxic pollutants

Efficiency depends on the type of sorbents

2.1.2. Description and characterization of the sorption methods

Sorption is a physicochemical process by which one substance becomes

attached to another [Michalak et al. 2013]. Sorption is a term that is used for both

absorption and adsorption.

Absorption is the incorporation of a substance in one state into another of a

different state (e.g. liquids being absorbed by a solid or gases being absorbed by water),

i.e. into a three-dimensional matrix. Adsorption is the physical adherence or bonding of

ions and molecules onto the surface of another molecule, i.e. onto a two-dimensional

surface[Barakat 2011]. Adsorption is the most common form of sorption involved in

―traditional‘‘ clean-up technologies, but unless it is clear which process (absorption or

adsorption) is operative, sorption is the preferred term, and can be used to describe any


system where a sorbate (e.g. an atom, molecule, a molecular ion) interacts with a sorbent

(i.e. a solid surface) resulting in an accumulation at the sorbate–sorbent interface [Fomina

and Gadd 2014]. Many researchers consider biosorption as a subcategory of adsorption,

where the sorbent called biosorbent is a biological matrix [Michalak et al. 2013]. In last

years, biosorption has been proposed as one of the most promising technologies for the

removal of heavy metal ions from wastewaters [Wang and Chen 2009; Park et al. 2010;

Lim and Aris 2014; Mishra 2014].

The nature of bonding between the sorbate and the surface of the sorbent

distinguishes between the types of sorption. Based on the nature of bond or sharing of

electrons, the sorption of metal ions is categorized as physical adsorption or chemical

adsorption (Table 2.3).

Table 2.3. General characteristics of the adsorption types [Rutven 1984].

Physical adsorption Chemical adsorption

Low heat of adsorption (<2 or 3 times the latent heat of evaporation);

Relatively low temperatures, always under the critical temperature of the sorbate;

Non–specific;

Adsorption takes place in monolayer or multilayer;

No dissociation of sorbed species;

Rapid, non- activated, reversible;

Low activation energy;

No electrons transfer, although polarization of sorbate may occur

- High heat of adsorption ( >2 or 3 times the latent heat of evaporation); - High temperature; - Type of interaction: strong; covalent bond between sorbate and surface takes place only in a monolayer; - High activation energy; - Increase in electron density in the sorbent – sorbate interface; - Reversible only at high temperature.

Sorption mechanisms are complicated as no simple theory adequately explains

the retention of metal ions on the sorbent surface [Abas et al. 2013].

Quantification of the sorption interactions is fundamental for the evaluation of

potential implementation strategies. The sorption phenomena can be expressed as batch

equilibrium isotherm curves. The graphical representation of the dependence between the

amount of species adsorbed per unit mass of sorbent (q) and its residual equilibrium

concentration (C) in the solution phase, q= f(C), at a given temperature, is called sorption

isotherm. These can be modeled by mechanistic or empirical equations; the former can

explain, represent and predict the experimental behavior, while the latter do not reflect the

experimental curves [Manohar et al. 2002]. Empirical models involving 2, 3 or 4

parameters can be used to fit batch equilibrium isotherm curves. [Manohar et al.2002].

Among these, the Langmuir and Freundlich (Table 2.4) are the most commonly used, with

a high rate of success [Park et al. 2010].


Kinetics studies provide important information about the possible mechanism of

sorption that involves the diffusion (bulk, external and intraparticle) and chemical

reactions. In general, it is assumed that the metal ion transport occurs in the following

steps: external diffusion (from the bulk solution to the external surface of the sorbent) →

the transport across the boundary layer → the transfer in the pores to the internal parts of

the sorbent and uptake by the active sites → sorption and desorption [Michalak et al.

2013]. Among the various models that are available in the reported literature, the models

based on the number of chemical reaction are of particular interest. Thus, the most

attention is focused on the Lagergren (pseudo– first order) and Ho (pseudo– second

order) models which are based on the assumption that the rate of sorption is proportional

to the number of free sites on the surface of the sorbent in the proper power (first or

second). The equations of the pseudo-first order and pseudo-second order kinetic model

are summarized in Table 2.4.

In order to fully understand the nature of the sorption, the thermodynamic

parameters such as free energy (∆G), enthalpy (∆H) and entropy (∆S) changes could be

calculated (Table 2.4). Free energy change (∆G) is considered as the spontaneity

indicator of the sorption process. ΔH positive values are characteristic for endothermic

processes, favored by temperature increasing. The positive value of entropy change (∆S)

shows an increase in the degree of freedom (or disorder) of the sorbed species [Al– Anber

2011].

Table 2.4. A brief presentation of the most used models for the description of batch sorption systems

a) SORPTION

Langmuir equation [Langmuir 1916]

CK

CKqq

L

L

10

Langmuir constants : q0 is the maximum capacity of sorption, corresponding to the sorbent surface and KL is the equilibrium constant (Langmuir) Determination of the Langmuir constants: from the intercept and slope of the corresponding linear Langmuir plot, expressed by the following equation:

00

111

qCKqq L

Assumptions : - the sorption is limited to monolayer coverage; - all surface sites are alike and can only accommodate one sorbed species; - the ability of a species to be sorbed on a given

ISOTHERMS Freundlich equation q = KF ∙ C

1/n

[Freundlich 1906] Freundlich constants KF and n are related to all factors affecting the retention process: sorption capacity (KF) and energy of sorption (n), respectively. Determination of the Freundlich constants: - from the plot of the logarithmic Freundlich equation:

lg q = lg KF + Cn

lg1

Assumptions : - the sorption occurs on heterogeneous surface of an sorbent with interaction between the sorbate molecules


site is independent from its neighboring sites occupancy; - sorption is reversible; - the sorbed species cannot migrate across the surface or interact with neighboring molecules

b) SORPTION Pseudo-first order model (Lagergren

model)[Lagergren 1898]

Equation:

log (qe – qt) = log qe - tk

303.2

1

where qe and qt are the amounts of cation (mg/ g)

sorbed at equilibrium and at time t, respectively

Kinetic parameters

k1- rate constant of pseudo–first order model

sorption(min−1

).

Remark: is based on adsorption capacity

KINETICS Pseudo-second order model (Ho model)[Ho

1999]

Equation: tqhq et

111

where qe and qt are the amounts of cation (mg/

g) sorbed at equilibrium and at time t,

respectively

Kinetic parameters

k2- the rate constant of the pseudo–second

order model

h = k2∙qe2 (mg/ g ∙min) can be regarded as

initial sorption rate constant of the pseudo–

second–order sorption (g./mg∙min).

Remark : is based on adsorption capacity

c) THERMODYNAMIC Free energy change, ΔG = - RT ln KL R is the gas constant; T is the absolute temperature; KL is Langmuir constant

PARAMETERS Enthalpy change (ΔH), ln KL = constant = -ΔH / RT R is the gas constant;T is the absolute temperature

Entropy change (ΔS) ΔS = (ΔH- ΔG)/T ΔH and ΔS values can be obtained from the slope and intercept of Van‘t Hoff plots of the ln KL (from the Langmuir isotherms) versus 1/T.

The sorption process of heavy metal ions from aqueous media is strongly

influenced by the several physical and chemical factors, such as:

initial pH:

Common finding Explanation

In a particular pH range, most metal sorption is enhanced with initial pH increasing to a certain value, followed by a reduction when further pH increases.

The initial pH plays a vital role in the removal of metal ions from aqueous media by sorption due to its impact on both the surface functional groups on sorbents and the metal chemistry in solution.

initial metal concentration : Common finding Explanation

The amount of heavy metal ion retained on the sorbent increased with increasing metal ion concentration.Conversely, the increase of initial metal concentration leads to a decrease of the removal efficiency.

This finding is due to the fact that the initial concentration acts as a driving force to overcome mass transfer resistance for metal ion transport between the solution and the surface of the sorbent [Arief et al. 2008]


sorbent dose


The removal percentages of heavy metal increase with the increase of the sorbent dose.

This behavior can be attributed to the increase in surface area resulting from the increase in sorbent mass, thus increasing the number of active sorption sites [Nguyen et al. 2013].

contact time


In the initial stages of the sorption process the amounts of heavy metal retained on sorbent increased sharply with increasing contact time of the phases, reaching values that remained then almost constant. It can be considered that the retention of metal ions on the sorbent takes place in two distinct steps, a relatively fast phase followed by a slower one

This two-phases sorption may be explained by taken into account the fact that the active sites in a system is a fixed number and each active site can sorb only one ion in a monolayer, the metal uptake by the sorbent surface will be rapid initially, showing down as the competition for decreasing availability of active sites intensifies by the metal ions remaining in solution [Li et al. 2008]

temperature


Temperature of solution can change the sorption equilibrium depending on the endothermic or exothermic nature of the process.

The change in temperature affects not only the diffusion rate of metal ions, but also the solubility of metals.[Park et al. 2010]

These factors determine the overall sorption through affecting the uptake rate,

selectivity and amount of heavy metals removed.

2.1.3. Types of sorbents

The sorbents researched for the removal of heavy metal ions rely on the

interaction of the metal ions with the functional groups present on the surface of the

materials, and hence, the functional groups play a leader role in determining the

effectiveness of the sorption process. As such, the performance of the sorption depends

strongly on the nature of the sorbent.

The importance of sorption in heavy metal clean – up technologies is reflected by

the ever increasing range of types of sorbents that are employed. The materials used as

sorbents of heavy metal ions are versatile. This versatility allows the sorbent to be of

mineral, organic or biological origin, zeolites, polymeric materials, industrial and

agricultural wastes and biomasses (Figure 2.1). The sorbents can be used under different

forms from insoluble beads, to gels, sponges, and fibers (Figure 2.1). Materials are

available in a variety of structures and a variety of properties [Khalaf 2015].


Figure 2. 1. Classification of sorbents

A suitable sorbent for the sorption processes of heavy metal ions should meet

several requirements:

high ability to reduce the concentration of heavy metal ion below the acceptable

limits;

efficient for the removal of a wide range of targeted heavy metals [Shemshadi et

al. 2012];

high porosity and consequently larger surface area with more specific sorption

sites [Khalaf 2015];

high capacity and rate of sorption;

important selectivity for different concentrations;

high physical strength;

able to be used in continuous sorption–desorption cycles [Mahmood et al. 2010],

meaning that:

- the sorbent should be cheap and reusable;

- both uptake and release of metal ions should be efficient and rapid;

- desorption of metal ions from the sorbent should be metal-selective and

economically feasible [Mishra S.P. 2014].

tolerant for a wide range of wastewater parameters;

fit to purpose, durable, environmentally friendly and cost effective [Abu Al-Rub

et al. 2002].


Heavy metal sorption has been studied on various materials such as activated

carbon [Jusoh et al. 2007; Kang et al.2008; Rahman et al. 2014; Manjuladevi and

Manonmami 2015]; carbon nanotubes [Wang et al. 2007; Pillay et al. 2009; Li et al. 2010];

oxide minerals, natural and synthetic polymers, low cost sorbents and so on [Bhatnagar

and Minocha 2006; Crini and Badot 2010]. Among them, activated carbon is the most

popular.

Despite the prolific use of activated carbon, the biggest barrier of its industrial

applications is the cost–prohibitive and the difficulties associated with the regeneration

[Foo and Hameed 2010]. Realizing the complication, a growing exploitation to evaluate

the feasibility and suitability of conventional and non–conventional sorbents in heavy

metal ions removal from inorganic effluents has been exerted.

In the endeavor to explore more and more materials in accessing an ideal sorption

system, I focused my research on following types of sorbents for heavy metal ions:

1. polymeric materials;

2. waste materials as low–cost sorbents.

2.1.3.1. Sorbents based on polymer materials

Polymeric materials play an important role in the sorption of heavy metal ions

because of their superior properties. They are comparable to other methods of polluted

water treatment in terms of technical and economical feasibility.

Polymeric sorbents also designated as chelating polymers, functionalized

polymers, chelating sorbents, chelating resins or chelating ion exchangers have been

known for a long time [Erlemneyer and Dahn 1939]. These materials are usually

polyelectrolytes possessing very large number of sorption sites per molecule. The

coordination bonds and electrostratic forces in metal ion chelating groups are the reasons

for the high metal ion selectivity of the chelating ion exchangers. They can be of varying

configurations, but mainly consist of two components: the chelate forming functional

groups and the polymeric matrix (support) [Tofan and Paduraru 2012]

The key mechanism of the remediation of wastewater using chelating polymers

depends on the nature of functional groups and/or donor atom (O, N, S) capable of

forming chelate rings. The desired features of a ligand function for polymer complex

formation are: capability of easy incorporation into a polymer matrix; sufficiently stability to

withstand the polymerisation or resinification process; compactness so that its chelating

ability is not hindered by the dense polymeric matrix; presence of both arms of a chelate

structure on the same monomer unit in proper spatial configuration.The common chelate

functionalities incorporated in polymers are: iminodiacetic acid, 8–hydroxyquinoline,


polyamines, cyclic polyamines, guanidine, dithiocarbamate, mercapto groups, hydroxamic

acid, aminophosphoric acid, crown ethers, Schiff bases, alcohols. The hard and soft acid–

base theory is the foundation upon which the choice of appropriate ligands is derived.

[Tofan and Păduraru 2012]. Thus, the functional groups in chelating sorbents usually act

as bases: oxygen containing functional groups have hard, sulphur–containing groups

have soft and nitrogen- containing groups have an intermediate character.

Generally, the restrictions imposed by the interactions with the polymeric matrix,

which appear in the process of incorporation of complexing agents into solid support

provided increased reagent selectivity. The series of stability for metal complexes on

chelating sorbents and in solutions (in free state) are similar but the values of the stability

constants of complexes formed by metal ions with macromolecular and low molecular–

weight functional ligands are not completely analogous [Bilba, Tofan et al. 1998].

The other analytical properties of the chelating sorbents, namely the sorption

capacity, kinetic features, mechanical and chemical strength and regeneration depend on

the polymeric matrix. The various polymeric materials used for the chelating groups

immobilization can be ordered as follows:

Most of the chelating sorbents are based on synthetic organic matrices. These

sorbents have high sorption capacity, good kinetic properties and high selectivity. Among

these sorbents, the most widely used are based on copolymers of styrene with

divinylbenzene [Rao et al. 2004]. Their better permeability to the reaction medium

facilitates the synthesis of sorbents based on them and ensures rapid sorption kinetics.

Other matrices include hydrophilic macroporous copolymers of glycidyl–

methacrylate–ethylene–dimethacrylate (GMA–EDMA),hydroxyethylmethacrylate–ethylene

dimethacrylate, polyetylene polyamine, polyvinyl alcohol, acrylonitrile etc.

Numerous studies and reviews concerning the design, synthesis and

characterization of chelating polymers and their wide applicability in the removal of toxic

Polymer matrices

Inorganic: silica gel, Kieselgur, controlled pore glass,

hydrated metal oxides

Organic

natural: cellulose, chitin, starch and their derivatives (chitosan, cyclodextrin)

synthetic: polymeric resins, fibrous materials, foamed plastics.

Inorganic- organic hybrid materials


metals and complex ions as well as in the selective metal ion recovery processes have

been published [Myasoedova et al. 1986; Liu 1989; Kantipuly et al. 1990; Bilba, Tofan et

al. 1998; Beauvais and Alexandratos 1998; Mandal and Das 2004; Alexandratos 2009].

The reviewed literature highlights that the chelating polymers as sorption media for the

removal/ recovery of heavy metal ions provides the following advantages [Tofan and

Păduraru 2012]:

they have high selectivity and high capacity;

they have long usable lifetimes;

they are re-usable and feasible;

they have good mass transfer kinetics and rapid equilibrium with the solutions

containing metal;

they can be used at high temperatures(chemical and thermal stability).

2.1.3.2. Sorbents based on waste materials

2.1.3.2.1. Low – cost sorbents

The need for cheaper and greener alternatives to polymer sorbents has resulted in

the search for nonconventional materials that may be useful in reducing the levels or

accumulation of heavy metals in the environment. [Tofan and Toma 2015]. A vast array of

natural materials and waste products from another production like agricultural, industrial

and food production in their raw form or after some physical or chemical modification has

been explored as low–cost sorbents of heavy metal ions. Bailey et al.(1999) defines low–

cost sorbent as a product that requires little processing, is abundant in nature or is a by-

product or waste material from another industry, also referring cost as an important

parameter for comparing sorbent material.

In recent years, applying low–cost sorbents in removal of heavy metals from

aqueous solution and wastewater has been paid much attention and gradually becomes

hot topic in the field of metal pollution control [Wang and Chang 2009]. The main

attractiveness of the use of this kind of technology is based on three aspects. The first one

is the intrinsic low cost of these materials, because they are either natural widely available

materials or by –products of agricultural and industrial processes. The second is the wide

range of these materials with different origin which can be used either on its raw form or

after a previous treatment to enhance their sorption capacity or to improve their

mechanical or mass transfer properties. The third is the fact that this application convert

agricultural and industrial by–products into added–value, environmentally sustainable

sorbents. [Kyzas and Kostoglou 2014].

http://ro-en.ro/index.php?d=e&q=attractiveness


Low –cost sorbents for treatment of heavy metals contaminated waters mainly

come under the categories systematized in Figure 2. 2.

Figure 2.2. General scheme of different kinds of materials used as low- cost sorbents for

heavy metals removal from aqueous media

Whatever the material used, it is obvious from all the reported data that the

application of low–cost sorbents for the environmental clean–up has the following

advantages [Vijayaraghavan and Yun 2008; Lim and Aris 2015]:

the cost, which involves mainly transportation and other simple processing

charges, is usually low;

they are easy to store and use;

the selectivity is poor, but can be significantly improved by modification/

processing;

the versatility is reasonably good;

the uptake of heavy metal is usually rapid;

high possibility of sorbent regeneration, with possible reuse over a number of

cycles.

Despite the huge number of papers published on sorbents based on natural and

waste materials for heavy metals removal, there is yet little literature containing a full

study comparing various sorbents.


Performance comparison of different low-cost sorbents is difficult because of

inconsistencies in data, principally due to different experimental conditions (pH,

temperature, initial concentration, ionic strength, particle size, presence of competitive

ions, etc.). A comparison between the reported results show that low-cost sorbents

present outstanding removal capacities for heavy metal ions, such as Cd(II) (Figure 2.3).

Figure 2.3. Cd(II) sorption capacity(q) of different low – cost sorbents [Tofan et

al., 2016]

Activated sludge of milk factory [Khosravan and Lashari 2011]; ground pine cone [Izanlov and Nasseri 2005]; industrial waste product Morus alba L. pomace [Serencam et al. 2013]; grape stalk waste [Villaescusa et al. 2006]; Eleocharis acicularis biomass [Miretzky et al. 2010]; clarified sludge [Naiya et al. 2008]; Chlamydomonas reinhardtii [Tuzun et al. 2005]; olive cake [Al-Anber and Matong 2008]; algal biomass Oedogonium sp. [Gupta and Rastogi 2008]; Nostoc commune (cyanobacterium) [Morsy et al. 2011] Tamrix articulata wastes [Othman et al. 2011]; chemically modified orange peel [Feng et al. 2011].

The sorption capacities vary depending on the characteristics of individual sorbent,

the extent of surface modification and the initial concentration. In general, technical

applicability and cost–effectiveness are the key factors that play major roles in the

selection of the most suitable low – cost sorbent to treat aqueous effluents [Kurniawan et

al. 2005].

2.1.3.2.2. Low–cost sorbents from natural materials [Tofan and Toma 2015].

Natural materials are locally available in bulk quantities and possess large surface

area and high cation exchange capacity that are essential requisite for a sorbent


[Bhatnagar and Minocha 2006]. Depending upon their origin, they can be classified as

mineral, organic and biological materials [Sabreen Alfarra et al. 2014]

Mercury (Hg) is one of the most toxic heavy metals commonly found in the global

environment; its toxicity is related to the capacity of its compounds to bioconcentrate in

organisms and to biomagnifie through food chain [Miretzky and Fernandez Cirreli 2009].

In this context, the natural materials as low-cost sorbents for heavy metal ions are

presented by referring strictly to mercury removal [Tofan and Toma 2015].

Due to its metal– binding capacity, natural mineral materials such as clays, mainly

composed of silica, alumina, iron, calcium and magnesium oxides have been explored for

treating mercury–contaminated waters. Thus, the sorption of mercury on Tunisian

smectitic clays was characterized as an exothermic process [Eloussaief et al. 2013]. The

results of the study concerning the sorption of mercury on laterite showed that the

different mineral compositions in the laterite caused significant differences in the Hg(II)

adsorption capacity of this environmental material [Yu et al. 2008].

Potent metal biosorbents under the class of bacteria include genre of Bacillus,

Pseudomonas and Streptomyces [Vijayaraghavan and Yun 2008; Michalak et al. 2013;

Fomina and Gadd 2014; Gupta et al. 2015]. Nonviable biomass of an estuarine Bacillus

sp. was successfully employed for the remediation of man – impacted coastal ecosystems

with mercury [Green–Ruiz 2006]. Pseudomonas aeruginosa was observed to uptake 80%

and Brevibacterium casei 70% of Hg(II) from the medium after 24 hours of incubation at

370C, suggesting the possibility of using these bacterial strains for removal of mercury

from Hg(II) contaminated wastewater [Rehman et al. 2007].

Fungi, especially filamentous form, have been recognized as a promising class of

low-cost sorbents for the removal of heavy metals from contaminated waters [Wang and

Chen 2009; Dhankhar and Hooda 2011; Michalak et al. 2013; Fomina and Gadd 2014;

Gupta et al. 2015]. Important fungal sorbents include Aspergillus, Rhizopus and

Penicillium. The inorganic mercury (Hg2+) exhibited more rapid sorption on a sorbent

from Aspergillus niger than methyl mercury(CH3Hg+ ); removal of both mercury species

from spiked ground water samples was efficient and not influenced by other ions; the

sorbent from Aspergillus niger was reusable up to six cycles without serious loss of

binding capacity [Karunasagar et al. 2003].The sorption of mercury by the fungus

Penicillium purpurogenum reached a plateau value at around pH 5.0; the maximum

sorption capacity of Hg(II) ions onto the fungal biomass under noncompetitive conditions

was 70.4 mg/g; the fungus Penicillium purpurogenum could be used for ten cycles for

mercury sorption [Say et al. 2003].


Marine algae, popularly known as seaweeds are biological resources, which are

available in many parts of the world [Tofan and Toma 2015]. Algal divisions include red,

green and brown seaweed; of which brown seaweed are found to be excellent eco–

friendly sorbents [Melita and Gaur 2005; Gupta et al. 2015]. For instance, at pH 5,

maximum mercury sorption capacities of 170.3 and 145.8 mg/g were recorded for the

brown seaweeds T. conoides and Sargassum sp., respectively, compared with

138.4 mg/g for the green seaweed Ulva sp.; reusing T. conoides biomass in three

successive sorption-desorption cycles resulted in only 8.8% reduction in Hg(II)biosorption

capacity compared with its original uptake[ Vijayaraghavan and Joshi 2012]. Metal

sorption involves binding on the cell surface and to intracellular ligands; the sorbed metal

is several times greater than intracellular metal; carboxyl group is most important for metal

binding; various pretreatments enhance metal sorption capacity of algae; CaCl2

pretreatment is the most suitable and economic method for activation of algal

biomass[Melita and Gaur 2005].The studies on the ability of Cystoseira baccata algal

biomass to remove Hg(II) from aqueous solutions indicated that the salinity exhibited two

opposite effects depending on the electrolyte added; an increase in concentration of

nitrate salts (NaNO3, KNO3) slightly enhances the mercury uptake, on the contrary, the

addition of NaCl salt leads to a drop in the sorption: the addition of different divalent

cations to the mercury solution, namely Ca(II), Mg(II), Zn(II), Cd(II), Pb(II) and Cu(II),

revealed that their effect on the uptake process is negligible [Herrero et al. 2005].

2.1.3.2.3. Agricultural and industrial wastes as sorbents for

remediation of heavy metal ions

Widespread agricultural and industrial activities generate huge amounts of solid

waste materials as by–products. One of the main subjects of today is to develop new

applications of these wastes. The use of agricultural and industrial wastes as sorbents for

heavy metal ions provides a two – fold advantages to environmental pollution. Firstly, the

volume of waste material is partially reduced into an eco–friendly way and secondly, the

sorbents developed from such wastes can reduce the cost of wastewater treatment

[Ahmaruzaman 2011].

Sorption removal of heavy metal ions by waste materials is considered now a

promising replacement strategy for existing conventional systems [Kurniawan et al. 2006;

Bhatnagar and Sillanpa 2010]. Hundred of agricultural and industrial wastes were reported

as potential sorbents for heavy metals remediation. Some sorbents can bind ions on a

wide range of heavy metals with no specific priority, whereas others are specific for

certain types of metals [Abdoli et al. 2014].


Agricultural waste materials being economic, eco–friendly and cost

effective, due to their unique chemical composition, availability in abundance and

renewable nature are a viable option for water and wastewater remediation [Sud

et.al.2008]. The basic components of the agricultural waste materials include cellulose,

hemicellulose, lignin, extractives, lipids, proteins, simple sugars, water hydrocarbons and

starch containing a variety of functional groups (hydroxyl groups, acetamido, carboxyl,

phenolic, amido, amino, sulphydryl, carbonyl groups, alcohols and ester). The actual

mechanism of the metal sorption is not fully understood, though many mechanisms

(chemisorption, complexation and chelation, ion exchange, diffusion through cell wall and

membranes) have been proposed for the heavy metal ions retention [Nguyen et al. 2013].

In last several decades, various agricultural wastes have been tested in their raw or

modified form as low–cost sorbents for heavy metal ions [Alluri et al. 2007; Demirbas

2008; Sud et al.2008; Hubbe et al. 2011; Nguyen et al. 2013; Dhir 2014]. Among these,

the following are included: olive cake, olive pomace, Neem olive cake, rice husk, rice

straw, rice polish, mustard husk, sugarcane bagasse, maize corncob, wheat, bran, green

coconut shell powder, almond shell, coconut copra meal, orange waste, peels of different

fruits (mandarin, banana, grapefruit, orange), egg shells, buckwheat hulls, coffee husk,

sunflower stalks, rapeseed waste.

Industrial wastes are also potentially low-cost sorbents for the removal of

heavy metal ions from wastewaters. Generally, industrial wastes are generated as by-

products and are available almost for free of cost and require little processing to increase

the sorptive capacity [Ahmaruzzaman 2011; Bhatnagar and Sillanpa 2010; Zwain et al.

2014]. The availability of industrial wastes is regulated by the production of industrial

processes that in turn is regulated by demand. Various types of industrial wastes such as

fly ash, waste slurry, red mud, bark tree, sawdust have been explored for their technical

feasibility to remove heavy metal ions from contaminated waters.

2.1.4. An overview of the sorbents targeted in my research work

Corroborating the results obtained in my doctoral research with the current and

future need to develop novel sorbents with enhanced performances. I oriented my

research towards polymeric materials (organic synthetic resins and polyurethane foams)

and waste materials as sorption media for heavy metal ions. From my literature survey, it

is evident that these kinds of sorbents offer unique advantages in rapid, versatile and

effective removal and/or recovery of heavy metal ions from aqueous solutions, as

presented in Table 2.5.


Table 2.5. Assessment of sorbents with wide scale use in heavy metal ions removal from wastewaters [Teodosiu, Tofan et al. 2014]

Sorbent Advantages Disadvantages References

Activated carbons Excellent sorption performances which allows a high quality of the treated effluents Large surface area Strong interaction with a wide range of trace elements ions High sorption capacity High rate of sorption

Low reproductibility Non-selectivity High reactivity Ability to act as catalyst of undesirable chemical reactions Drastic conditions for analyte elution Difficulty in removal of heavy metals at ppb levels

[Zhao et al.2011] [Fu and Wang 2011]

Silica gel Good mechanical strength Possibility to undergo heat treatment Resistance to swelling caused by solvent change High sorption capacity Chelating agents can be easily loaded or bound chemically

Low selectivity Hydrolysis at basic pH

[Zougagh et al. 2005] [Lemos et al.2007]

Chelating resins (typically based on cross – linked polymers having polystyrene or acrylate matrices)

Wide range of structure and physicochemical characteristics High capacity of sorption High rate of sorption Important selectivity for different concentrations Able to be regenerated and used in many cycles of sorption - desorption Tolerant for a wide range of wastewater parameters

High operational costs Limited use in specialized environmental applications such as treatments of industrial wastewaters to the parts per billion levels. Non– environmentally friendly

[Asouhidou et al.2004] [Crini 2005] [Pan et al.2009]

Polyurethane foams

Very low cost Simplicity of preparation Easy to purchase Resistance to changes in pH Provides high preconcentration factors Versatile applicability in multi – element preconcentration procedures or in specific procedure Easy use in automatic and on – line preconcentration systems

Unable to retain metal ions without prior complexation Relatively low sorption capacity

[Lemos et al.2007] (Lemos et al. 2012]

Unconventional low – cost sorbents (waste materials)

Low cost Local availability Good cost – effectiveness ratio Renewability

Low sorption capacity Difficulty to recover Mechanisms of sorption are not fully understood

Nanosorbents Unique structure Special structure characteristics High sorption capacity High selectivity Infinite recyclability

Expensive Non– environmentally friendly

[Wang et al.2012]

For a better argumentation, Figure 2.4 is shown based on data from literature

studies and my research work: chelating resins [Bilba, Tofan et al.1998; Rengaraj et


al.2007; Asouhidou et al. 2004; Pandey and Thakkar 2004; Reddy and Reddy 2003; Shah

et al.2011; Ngeontae et al. 2007], polyurethane foam [Alhakawati and Banks 2004;

Moawed 2004; Saeed et al. 2007; Abdel Salam et al. 2011; Tofan et al.1996; El-Shahawi

et al. 2008], hemp [Tofan et al.2000; Tofan et al.2009; Tofan et al. 2010; Paduraru and

Tofan 2008; Tofan et al. 2001], pine bark [Amalinei, Tofan et al.2012; Tofan et al.2012;

Mohan and Sumitha 2008; Acemioglu et al. 2004; Gonçalves et al. 2012; Vijayakumaran

et al. 2009], fly ash [Tofan et al.2011; Tofan et al.2008; Tofan et al. 2009; Özkök et al.

2013; Gupta et al. 2003], zeolites [O‘Connell et al. 2008], cellulose powder [Wan Ngah

and Hanafiah 2008; O‘Connell et al. 2008].

Figure 2.4. Comparison of sorbents for heavy metal ions removal [Teodosiu, Tofan et al.

2014]

It can be observed from Figure 2.4 that the sorbents on which I focused are very

suitable for the removal and recovery of heavy metal ions from large volumes of industrial

wastes.

2.2. Removal/ recovery of heavy metal ions from aqueous solutions by using

polymeric sorbents

My research efforts have been directed towards the development and

implementation of new selective sorbents based on organic synthetic resins and

polyurethane foam to target precious and toxic heavy metal ions (Figure 2.5.).


Figure 2.5. Focus on my studies concerning polymeric materials as sorption media

In this context, I addressed issues related to the setting of optimized conditions of

sorption and understanding of the sorption process by:

- investigating the effectiveness of the developed polymers under various

experimental conditions (solution pH, metal ion concentration, sorbent dose,

contact time and temperature);

- modeling the heavy metal sorption process (isothermic, kinetic and thermodynamic

models).

A major part of the research results on this subject have been published in

significant journals, as follows:

1.Tofan, L., Bunia, I. Păduraru, C. Teodosiu,C., Synthesis, characterization and

experimental assessment of a novel functionalized macroporous acryilc copolymer

for gold separation from wastewater, Process Saf. Environ. Prot., 106(2017), 150 –

162

2. Teodosiu, C., Wenkert, R., Tofan, L., Păduraru, C., Advances in preconcentration/

removal of environmentally relevant heavy metal ions from water and wastewater by

sorbents based on polyurethane foam, Rev.Chem. Eng. (2014), 30, 403–420.

3.Tofan, L. Solid – phase spectrophotometry use for the determination of trace amounts

of Rh(III), Rev. Anal. Chem., 30 (2011), 171–175.


4. Tofan, L., Păduraru,C., Creţescu,I., Ceica,A., Neagu, V., Chelating sorbent containing

two types of functional groups- hydroxamic acid and amidoxime for lead(II) ions

effluent management, Environ. Eng. Manag. J., 9(2010), 113-118.

5. Bilba, D., Paduraru, C., Tofan, L., Macroporous anion exchanger Purolite A-500 loaded

with Ferron for palladium(II) recovery, J. Iran. Chem. Soc. (2010), 7, 608-614.

6. Neagu, V., Păduraru, C., Bunia, I., Tofan, L., Platinum (IV) recovery from chloride

solution by functionalized acrylic copolymers, J. Environ. Manage.(2009) 91, 270–

276.

7. Tofan, L., Bîlbă, D., Păduraru, C., Toma, O., Sorption of Ga(III) on flexible open-cell

polyurethane foam of polyether type impregnated with tri-n-buthyl phosphate,

Chem.J. Mold. (2007), 2, 51–57.

8. Păduraru, C., Bîlbă, D., Sârghie, I.,Tofan, L., A sorption study of Pd(II) on

aminomethylphosphonic Purolite resin S–940, J.Serb. Chem. Soc. (2005), 70, 1205-

1212

9. Bîlbă, D., Păduraru, C., Tofan,L., Determination of trace amounts of palladium (II) by

solid phase spectrophotometry, Microchim. Acta (2004), 144, 97-101.

10. Bilba, D., Bejan, D., Tofan, L., Chelating sorbents in inorganic chemical analysis,

Croat. Chem. Acta (1998), 71, 155–178

11. Bîlbă, D., Tofan, L., Păduraru, C., Nacu, A., The sorption study of Fe(III) on

„SPUMATIM” polyurethane foam pretreated with tri-n-butyl phosphate, Rev. Roum.

Chem. (1998), 43, 493–498.

2.2.1. New chelating polymers as selective sorbents for heavy metal ions 2.2.1.1. Background

The chelating polymers are very efficient in the removal of certain targeted heavy

metal ions as well as in their multi–removal. Furthermore, they have a strong capability to

retain heavy metal ions at very low pH.

A chelating sorbent is made up of a polymer network (support) containing active

functional groups, able of interactions with metal ions by forming coordinate bonds.

The versatility of these polymers is attributed to the triple function of ion exchange,

chelate formation and physical adsorption. Thus, a chelating polymer is distinguished from

a conventional ion exchanger by the following essential properties [Tofan and Păduraru

2012]:


1. Selectivity. The selective properties of chelating ion exchangers to particular

metal ions are mainly based on the nature of functional groups and depend to a

minor extent on the size, charge and other physical features of the cations.

2. Bond strength. If in the conventional ion exchangers, the bond is of electrostatic

nature and with a strength of 2–3 kcal/mole, the bond energy in the chelating

resins is about 15–25 kcal/ mole.

3. Sorption capacity. It is determined by the content of immobilized functional

groups and is, generally, lower than that of the conventional ion exchangers. The

sorption capacity varies within sufficiently large limits (<0.1->1mmole/ g),

depending on the matrix nature and synthesis conditions of the sorbent.

4. Kinetics. The sorption rate is, generally, slower than that in the ion exchange and

is controlled either by a particle diffusion mechanism or by a second order

chemical complexation reaction. Kinetic characteristics of chelating sorbents

depend mainly on the nature and properties of the polymeric matrix (cross– linking

degree).

The sorption of metal ions on chelating polymers is mainly due to complex

formation within the resin. The advantage of this chemistry is that a selective removal can

be achieved by choosing a suitable functionality.

Incorporation of functional groups able to form complexes with metal ions into the

support can be accomplished by the following methods:

- formation of a covalent bond between the organic reagent and support(chelating

resins with grafted groups);

- formation of an ionic bond between the chelating reagent and the functional group

of an ion exchange resin( modified resins);

- impregnation and physical adsorption of the organic reagent on support

(impregnated sorbents).

Although the large number of reported studies demonstrates the high efficiency of

the chelating polymers for the removal/recovery of heavy metals, still there are some gaps

to be filled in order to introduce this type of materials as un ideal solution for such

application. For instance, a gap is the lack of selectivity for some chelating polymers

which has been experienced in means of high competition between some elements.

In light of above, my work followed to fulfill these gaps and enhance the

performances of the functionalized polymers for the removal/recovery of heavy metal ions

in order to introduce them as feasible materials. The targeted issues in my research were:

preparation and properties of new chelating sorbents with improved

performances;


the use of these new chelating sorbents in selective processes of precious heavy

metal recovery;

the applicability of these resins in the removal of toxic heavy metals ions from

industrial effluents;

development of new methods of analysis which combine the concentration of

precious metal ions from aqueous samples with their subsequent determination

directly in the resin phase.

2.2.1. 2. Chelating sorbents with grafted groups

2.2.1.2.1. Synthesis and characterization

Chelating resins with grafted groups can be synthesized either by the direct

polymerization of a monomer containing chelating groups with a crosslinking agent or by

the chemical transformation of a preformed polymer.

Direct polymerization of ligand–containing monomers is usually carried out by

formaldehyde polycondensation reactions or radical polymerization in the presence of

cross–linking agents [Ahamed et al. 2010; Singru and Gurmule 2010; Singru et al. 2010;

Gurnule and Patle 2011; Gurnule and Katkamwar 2012; Shah et al. 2011; Manivannan et

al. 2010]. Although the polycondensation method is extensively used because of its

simplicity, condensation polymers can undergo hydrolytic and cleavage reactions and

have a poor chemical and mechanical stability.[Gorduza,Tofan et.al. 2002].

Polymerization of vinylic derivatives containing chelating groups is less used due

to the difficulties connected with the synthesis of starting substances [Bilba, Tofan et al.

1998].

The main synthesis method of chelating sorbents proves to be the incorporation of

an active functional group into polymeric matrix by ―reactions on polymers‖ - the grafting

procedure (Table 2.6.).


Table 2.6. Removal of some heavy metal ions from wastewaters by chelating sorbents

prepared by a grafting procedure [Tofan and Paduraru 2012]

Chelating resin Synthesis method Remarks Reference

Novel chelating resin with cyanoguanidine groups

Functionalizing reaction of a macroporous bead based on chlormethylated copolymer of styrene – divinylbenzene with dicyandiamide in the presence of phase transfer catalyst.

The maximum Hg(II) sorption capacity was 1077 mg/g at 45

0C.

[Ma et al.2011]

Polystyrene – bound pyridine – 2,6 – dicarboxilate

Chloromethylated polystyrene (cross – linked with 2% divinylbenzene) was treated with an appropriate quantity of pyridine – 2,6 – dicarboxylic acid in refluxing DMF for 24 hours.

Maximum Hg(II) sorption capacity was about 41.5 mg/g. The regeneration of resin was feasible and desorption was very high (up to 96%)

[Iravani et al. 2010]

Chelating fiber having amine functional group

Grafting copolymerization of acrylic acid onto polypropylene fiber, consequently aminating with diethylenetriamine.

99% removal efficiency would be achieved when feed concentration of mercury was 1 mg/L.

[Ma et al. 2012]

Chelating resins (PS – DEG–3 AP and PS– TEG–3–AP ) containing 3 – aminopyridine and hydrophilic spacer arm

Inserting spacer ethylene oxide and ethylene sulfide, respectively, with 3-aminopyridine (3-AP) into polystyrene-co-divinylbenzene.

The adsorption properties of the resins for Hg(II), Ag(I), Fe(III), Pb(II), Co(II), Cu(II), Ni(II), Cd(II) and Zn(II) had been studied, and the results revealed that the resins had higher adsorption capacities and adsorption selectivity for Hg(II).

[Ji et al. 2010]

Poly(AGE/IDA-co-DMAA)-grafted silica gel.

Surface grafting of polymer containing a functional monomer for metal chelating, poly[1-(N,N-bis-carboxymethyl)amino-3-allylglycerol-co-dimethylacrylamide] (poly(AGE/IDA-co-DMAA) onto silica modified by silylation with 3-mercaptopropyltrimethoxysilane. Monomer 1-(N,N-bis-carboxymethyl)amino-3-allylglycerol (AGE/IDA) was synthesized by reaction of allyl glycidyl ether with iminodiacetic acid.

The Pb(II) sorption capacity of functionalized resin was 15.06 mg/ g. The chelating sorbent can be reused for 15 cycles of sorption–desorption without any significant change in sorption capacity. A recovery of 96.2% was obtained for the metal ion with 0.5 M nitric acid as eluting agent.

[Panahi et al. 2010]

Generally, the chelating sorbents are characterized, after their synthesis, by: IR

spectra; sorptive properties(estimated based on the retention capacity of metal ions); acid

– base properties (assessed by means of dissociation constants of functional groups);

chelating properties (expressed quantitatively by the values of stability constants of the

complexes formed in the resin phase); kinetic properties (strongly dependent on the

nature, concentration and accessibility of functional groups; the nature and concentration

of the metallic ion under study; features of the polymer matrix: particle size, cross-linking

degree, swelling degree, porosity, hydrophobic or hydrophilic nature [Bilbă, Tofan et.al.


1998]. For instance, the main features of the two of the chelating sorbents that I studied

in terms of their potential applicability for the removal of heavy metal ions from industrial

effluents are systematized in Table 2.7.

Table 2.7. Characterization of two of the chelating sorbents that I investigated in my

research

Sorbent Physical and chemical characteristics

Characterization of the resin behavior in the sorption process

Reference

Commercial aminomethylphos-phonic resin Purolite S – 940

Polymer matrix structure: styrene – divinylbenzene copolymer Functional group: –CH2NHCH2PO3H2

Ionic form: Na

+

Moisture: 60–65% Retention form :Na

+

Bead size: 20 – 40 mesh Total exchange capacity: 5 meq /g of dry resin (determined by potentiometric titration

Maximum operating conditions: 90

0C

Morphological structure: macroporous resin

The performed study concerns the behavior of the Purolite S- 940 resin in the process of selective retention of Pd(II)ions from aqueous solutions. The yield of Pd(II) recovery was maximum in buffer solution of pH 3-5. The retention percentage showed a decreasing trend from 85.8% to 73.3% to an increase in the initial concentration of the Pd(II) from 22.2 to 83.3 mg / L. The raising of solution temperature from 5

0C to 50

0C leads

to an enhancement of the process of Pd(II) sorption. The experimental data fitted very well with the Langmuir model. The maximum capacity of sorption, determined on the basis of Langmuir isotherm, was 53.2 mg Pd(II)/ g of resin (25

0C). The thermodynamic

parameters (free energy changes, ∆G=- 18,5 KJ/mol / 278K; -22KJ/mol/298K; -24,8 KJ/mol/ 323 K; enthalpy change, ∆H =+ 24,5 KJ/mol; entropy change ∆S= +152.7 J/ mol K) suggest an affinity of the Purolite resin S – 940 for Pd(II) ions .

[Păduraru, Tofan et.al.

2005].

New chelating ion exchanger with hydroxamic acid and amidoxime groups synthesized by the aminolysis reaction of ethylacrylate(EA)/ acrylonitrile(AN)/ divinylbenzene copolymer with hydroxylamine in presence of sodium ethoxilate [Neagu et al.2003]

Polymer matrix structure: ethylacrylate:acrylonitrile: divinylbenzene copolymers Functional groups:

Cross– linking degree: 10% divinylbenzene Exchange capacity : 4.06 meq /g (1.38 meq / mL) Diameter of beads: 0.3 – 0.8 mm Morphological structure: macroporous resin

I studied the potential applicability of the proposed sorbent for the removal of Pb (II) from industrial effluents. The retention process of Pb(II) by the solid support depends on pH, attaining the maximum value in unbuffered solutions with initial pH of 4.5. From aqueous solutions with Pb(II) initial concentration of 82.96 μg/mL the sorption percentage is 98.64%. The values of the Langmuir maximum capacity of Pb(II) sorption showed an increasing trend with temperature being of 0.9378, 1.0085 and 1.162 mmole/g at 4

0C, 25

0C and 50

0C,

respectively. The macroporous structure enhances the kinetic performance as it allows more rapid diffusion within the resin: the Lagergren constant rate of Pb(II) sorption was 2.533 x 10

-3 min

-1; the value of

half-life of sorption which characterizes the relative rate of the retention process was 273.58 min.

[Tofan et al.2010]

-CH2-CH-CH2-CH-

C O

NH

OH

C NOH

NH2


The main disadvantages of chelating sorbents with grafted functional groups are

determined by the synthesis difficulty and include: low reversibility of sorption –

desorption processes and, sometimes, unsatisfactory kinetic features [Tofan and

Păduraru 2012].

2.2.1.2.2. Chelating sorbents based on acrylic copolymers

Acrylic copolymers represent interesting macromolecular supports because of their

higher physicochemical stability and their structure more hydrophile than that of styrene

copolymers. The modification of the acrylic matrices is a possible method of obtaining

compounds with ionic or ionizable functional groups and high hydrophilicity of the

structures [Neagu et al., 2009]. In this context, my work was focused on the synthesis,

characterization and sorption properties of a new acrylic copolymers bearing:

a) amidoethylenamine and thiol groups for platinum(IV) sorption from chloride solution;

b) dimethylaminobenzaldehyde functional groups for gold(III) recovery from chloride

solutions.

2.2.1.2.2.1. New chelating sorbents based on acrylic copolymers bearing

amidoethylenamine and thiol groups for the selective recovery of platinum(IV) from

chloride solutions [Neagu, Tofan et al. 2009]

Platinum is one of the precious metals with many applications, including in

catalysis, electronic devices and jewelry [Nikolski et al. 2015]. However, its limited

resources are becoming depleted. To meet the future demand and conserve resources, it

is necessary to recover platinum not only from primary sources (minerals), but also from

secondary sources (waste materials such as spent automotive catalysts, catalysts from

the chemical industry, electronic scrap, exhausted nuclear fuel, military equipment and

even tailings from ore-dressing plants for noble metals-containing deposits) [Nikolski et al.

2015].

The use of chelating resins is, in many cases, the most suitable method for

platinum preconcentration–recovery from natural, technological and waste solutions

[Cortina et al. 1998; Jermakowicz-Bartkowiak et al. 2005]. For this purpose, coordinating

polymers containing donor N, O and S atoms in their functional groups are the most

promising chelating compounds.

Acrylic copolymers represent interesting macromolecular supports because of their

higher physico -chemical stability and their more hydrophilic structure than that of the

styrene copolymers. The modification of the acrylic matrices is a possible method of


obtaining compounds with ionic or ionizable functional groups and enhanced

hydrophilicity of the structures [Neagu et al. 2009].

Starting from these premises, two acrylic sorbents with different morphological

structures and bearing amidoethylenamine and thiol groups were obtained and used for

platinum sorption from chloride solution by the batch method.

Synthesis of the chelating sorbents

The synthesis of the proposed chelating sorbents (AA1 and AA 2) with O, N and S

as donor atoms were performed by the chemical transformations of the acrylic

copolymers, prepared in a previous step. Thus, the two steps involved in the synthesis of

the AA1 compound are: the free radical suspension copolymerization in water of

ethylacrylate (EA) with 8% divinylbenzene (DVB), in the presence of toluene as diluent

and benzoyl peroxide as initiator→ chemical transformation of EA:8% DVB copolymer

with thiourea for a copolymer:thiourea ratio of 1:1.5. Synthesis of AA2 sorbent may be

described by the following sequence of reactions: the free radical suspension

copolymerization in water of ethylacrylate (EA), acrylonitrile (AN) with 2% DVB→the

aminolysis–hydrolysis reaction of EA: AN: 2% DVB copolymer with ethylenediamine

(EDA) at a copolymer: amine ratio of 1:3 ( Scheme 2.1).

Scheme 2.1. Synthesis of the AA2 chelating polymer

The characteristics of the yielded compounds are presented in Table 2.8.


Tabelul 2.8. Main features of the synthesized sorbents

Sample

code

Functional group Crosslinking

content

(% in feed)

Volume

weight

(g/mL)

Weak exchange

capacity

meq/mL meq/g

AA1 a

O ∥ - C – NH- C - NH2

∥ S

8 0.2355 0.65 2.80

AA2b

O

∥ - C – NH(- CH2)2- NH2

2 0.0374 0.29 7.86

aEA: DVB copolymer obtained in the presence of toluene, at a dilution D= 0.3.

bEA:AN: DVB copolymer obtained in the presence of toluene, at a dilution D= 0.4.

As can be seen from Table 2.8., the yielded sorbents contain functional groups

known to have chelating properties towards platinum group metals.

Studies of Pt(IV) sorption

Sorption studies of Pt(IV) were selected with regard to potential application of the

prepared sorbents in hydrometallurgical separation procedure and recovery processes

The Pt–chlorocomplexes are the most well studied and important as aqueous chloride

solution is the only cost effective medium in which Pt can be brought into solution and

concentrated. Against this background, the Pt(IV) sorption studies were carried out in

chloride solutions by the batch method under non-competitive conditions (Figure 2.6.)

The sorption ability of the investigated sorbents bearing amino and thiol groups

towards Pt(IV) was investigated in monocomponent solution. Table 2.9 shows the

retention capacity values for the synthesized compounds.


Figure 2.6. Schematic

representation of the Pt(IV)

sorption studies performed by

batch procedure

Table 2.9. Sorption capacity(q) of Pt(IV) for the acrylic sorbents

C0a (mg/L)

q, (mg/g)

AA1 AA2

164 211 246 290 328 375

0.95 1.43 3.12 6.85 9.28

12. 05

56 77 88 104 110 114

aInitial concentration of Pt(IV).

It is evident that only the metal ion which forms the strongest chloride complexes

may be retained on the yielded sorbents. The best sorption capacity of Pt(IV) is exhibited


by AA2 sample (obtained by the aminolysis–hydrolysis of EA:AN:2% DVB with EDA).

Therefore, the sorption experiments of Pt (IV) were performed on this polymeric material.

Experimental factors that influence the sorption process such as solution pH, initial Pt(IV)

concentration, sorbent amount, contact time and temperature were investigated. In

addition, the equilibrium, kinetic and thermodynamic parameters of Pt (IV) sorption at pH =

1 have been determined.

1. Effect of pH, initial Pt(IV) concentration and sorbent amount

The influence of pH, initial Pt (IV) concentration and sorbent amount in the batch

sorption system Pt(IV) – AA2 is described briefly in Table 2.10.

Table 2.10. Factors with major influence on the Pt(IV) sorption by the AA2 sorbent

Factor Influence Explanation

Solution pH

Sorption conditions: initial concentration of Pt(IV), 245.76 mg/L; amount of sorbent, 0.05 g; volume of sorption medium, 25 mL; temperature, 25±1

0C; sorption

time, 4 h

In very acidic solution (pH= 1) the sorption has the highest level, whereas it decreased with the increasing of pH up to pH= 5.

At pH = 1 the sorption capacity is the best due to the total protonation of nitrogen atom. The ability of Pt(IV) sorption can be caused by some factors which are connected with hydrophilicity or hydrophobicity of the sorbents, the structures of their matrices and the steric hindrance around ligands. In the same time, there are other factors such as, charge, size and geometry of the complex anions and properties of the central atom which can affect the retention of the complex anions [Iglesias et al. 2000].

Pt(IV) initial concentration Sorption conditions: initial concentration of Pt(IV), 164–375 mg/L; amount of sorbent, 0.05 g; volume of sorption medium, 25 mL; temperature, 25±1

0C; sorption

time, 4 h; pH= 1).

The increasing of the initial concentration of platinum led to the increase of the sorption

capacity [(q)(•)] and decreasing of the recovery yield [ (R%) (▲)]

To explain these opposite trends it can assume that in the Pt(IV) sorption process the superficial amidoethylenamine groups play a leading role. The highest initial concentration of Pt(IV) determines the high values of ratio between the initial number of moles of Pt and the number of the available functional groups which are located at the surface of the sorbent and therefore, the enhancing of the metal sorption capacity occurs. The loading of the total active sites of the sorbent with Pt leads to the access hindrance of the metal to the functional groups and consequently, the decreasing of the recovery yield occurs.

Sorbent


amount Conditions: initial concentration of Pt(IV), 312 mg/L; volume of sorption medium, 25 mL; temperature, 25± 1

0C; sorption

time, 4 h; pH = 1).

The sorption efficiency increased with increasing

amount of sorbent due to the increased availability of sorption

sites. It was observed that at the concentration of 312 mg/L,

8 g/L are needed for the sorption efficiency of 90%.

2. Effect of contact time and kinetic modeling

Figure 2.7 shows the effect of contact time on the recovery of platinum by AA2

sorbent for two concentrations of K2[PtCl6] namely, 211 mg/L and 328 mg/L.

Figure 2.7.

Effect of contact time on the sorption of Pt(IV) by AA2

(sorption condition – initial concentrations of Pt(IV),

211 mg/L (∙) and 328 mg/L

(▲); amount of sorbent,0.05 g; volume of sorption

medium, 25 mL;temperature,

25∓ 10C; sorption time, 4 h; pH= 1).

For both concentrations used in these experiments the recovery capacities

increased with time and reach the equilibrium in 4 h. High sorption rate of platinum for the

sorbent are observed at the onset and then plateau values are gradually reached within 3

h. The increasing contact time increased the Pt(IV) sorption and it remains constant after

equilibrium reached in 4 h for both concentrations. In each case the decreasing

concentration of Pt (IV) remaining in the solution, indicates that platinum was sorbed

strongly by AA2.

In order to analyze the sorption rate, the kinetic data were modeled using

Lagergren pseudo-first-order [Rudzinski and Plazinski 2006] and pseudo- second- order

[Azizian 2004] equations:

Kinetic equation of pseudo-first-order (Lagergren): qt = qe tke 11


Kinetic equation of pseudo-second -order: tqk

tqkq

e

et

2

2

2

1

where qt and qe are the amounts of Pt(IV) sorbed (mg/g) at time and at equilibrium,

respectively and k1(min-1) and k2 (mg/g min) are the rate constants of pseudo-first-order

and pseudo-second order sorptions, respectively.

The values of the constants are calculated and listed in Table 2.11. The data in

Table 2.11 indicate the increase of the sorption rate with the increase of the concentration

of Pt(IV). The correlation coefficient (R2) values of the pseudo-first- and second order

equations for the concentration of 211 mg/L and 328 mg/L suggest that sorption kinetics

can be well described by both equations.

Table 2.11. Kinetic parameters derived from pseudo-first-order and pseudo-second-order

plots for Pt(IV) sorption.

Initial concentration,

C0 (mg/L)

Pseudo – first order

Pseudo-second order

k1(min-1

) R2 k2(mg/g min) h

a(mg/g min) R

2

211 0.967x10-2

0.9928 0.362x10-3

3.00 0.9979

328 1.289x10-2

0.9974 0.428x10-3

8.74 0.9999

ah=k2qt

Both applied models led to the conclusion that the most important step in the sorption

of Pt(IV) could be both the particle diffusion and chemical reaction of [PtCl6]2─ with amine

functional groups.

3. Isothermic modeling

The equilibrium amount of Pt(IV) sorbed per unit mass of sorbent, q (mg/g) and its

final concentration in solution C (mg/L) are related by means of sorption isotherms. The

most common mathematical models for describing the sorption isotherms in aqueous

solutions such as, Langmuir and Freundlich equations were tested to fit the experimental

data obtained for Pt(IV) sorption (Figure 2.8.).

Langmuir: 00

1

qKq

C

q

C

L

Freundlich: log q = log KF+ Cn

log1


where q and C are the amount of Pt(IV) sorbed(mmol/g) and concentration of platinum at

equilibrium(mg/L), respectively; q0 is the is the maximum capacity of sorption; KL is a

constant related to the binding energy of sorption; KF and 1/n are Freundlich constants

related to the sorption capacity and heterogeneity factor, respectively.

Figure 2.8. Sorption

isotherms of Pt(IV) on

AA2 (conditions – initial

concentration of Pt(IV),

245.76 mg/L; amount of

sorbent, 0.05 g; volume

of sorption medium,

25 mL; temperature:

(∙)4, (◆) 25 and

(▲) 50 0C; sorption time,

4 h, pH= 1).

The isotherm constants were determined from the intercept and slopes of the

corresponding linear Langmuir plots for the sorption of Pt(IV) and presented in Table 2.12.

Table 2.12. Various isotherm parameters for the sorption of Pt(IV) by AA2 chelating sorbent.

T(K)

Langmuir isotherm Freundlich isotherm

R

2 q0

(mmole/g) KL(L/mol) R

2 KF n

277 0.9975 0.8302 1296 0.9936 2.713 1.440 297 0.9908 1.1027 1512,4 0.9765 5.112 1.585 323 0.9982 1.3616 1833,5 0.9870 8.094 1.668

From the data presented in Table 2.12., it can seen that the Langmuir model fit

very well the sorption equilibrium of Pt(IV) on the studied sorbent. The high values of the

sorption constants suggest a strong interaction between platinum and amine functional

groups with the increase of the temperature.

4. Thermodynamic parameters

Based on Langmuir‘s constants the thermodynamic parameters such as, free

energy change (ΔG), enthalpy changes (ΔH,) and entropy change (ΔS) have been

calculated and are presented in Table 2.13.

0

20

40

60

80

100

120

140

160

0 25 50 75 100 125 150 175C, mg/L

q,

mg

/g


Table 2.13. Thermodynamic parameters values of the sorption of Pt(IV) by AA2 sorbent.

Thermodynamic parameter Equations T, K Obtained values

Free energy change (ΔG) ΔG = - RT ln KL

R is the gas constant; T is the absolute temperature

277 297 323

- 16.48 kJ/mol - 18.066kJ/mol - 20.157 kJ/mol

Enthalpy change (ΔH) ln KL = constant =

-ΔH / RT R is the gas constant;

T is the absolute temperature

277 297 323

5.70 kJ/mol 5.70 kJ/mol 5.70 kJ/mol

Entropy change (ΔS) ΔS = (ΔH- ΔG)/T

277 297 323

0.080 J/mol.K 0.080 J/mol.K 0.080 J/mol.K

The negative ΔG indicates the process for AA2 to be spontaneous in nature of

sorption. The positive ΔH shows that the sorption process is an exothermic reaction and

the strong interaction between Pt(IV) and amine groups occurred. The positive values of

the entropy described the more disordered state at the molecular level.

5. Sorption mechanism

The sorption of platinum chlorocomplexes by sorbents containing nitrogen ligands

can take place according to the mechanism of ion exchange when nitrogen atoms are

protonated or can occur through the formation of platinum complexes when nitrogen acts

as a coordinating atom.

An additional proof of this assertion are the FT-IR spectra of the AA2 and AA2+

Pt(IV) samples (Figure 2.9).

From Figure 2.9. the major modifications are observed in spectrum b for AA2+

Pt(IV), as follows:

- strong broad bands in the region of 1749–1559 cm-1 which are attributed to amino and

carboxyl groups have been appeared;

- stretching vibration of –C–N– bonds at 1262 cm-1 appear when Pt(IV) is loaded on

sorbent;

- major difference was observed in the range of 3400–3100 cm-1 due to –N–H bond;

- upon metal sorption the new clear peaks appear at 613 cm-1 which can be attributed to

N-metal vibration [Simanova et al. 2001; Nakamoto 1986].


Figure 2.9. IR spectra of AA2(a) and AA2 + Pt (b)

CONCLUDING REMARK:

The results of this study suggest that the proposed sorbent is a promising candidate for

the sorptive preconcentration and recovery of Pt(IV) from acidic chloride media

2.2.1.2.2.2 A new acrylic copolymer with dimethylaminobenzaldehyde functional

groups as a good performance material for gold(III) separation from wastewaters

[Tofan et al., 2017]

Gold (Au) is the most noble of all metals with unique chemical and physical

properties [Syed, 2012]. The growing number of gold uses and its limited availability result

in an imperious necessity to recover this precious metal from aqueous and waste

solutions. Among the traditional methods, the sorption has been considered as the most

significant and promising method for gold separation and preconcentration, because of its

high efficiency and easy handling [Syed, 2012; Das, 2010].


The uptake of gold by sorption is mainly carried out from hydrochloric solutions in

which this metal exists as sorption-active chloride or aqua-chloride anionic complexes

[Myasoedova et al., 2007]. A wide range of sorbents have been used in this respect

[Pyrzynska, 2012]. But the selectivity for gold is proved only by the chelating resins or

polymers with functional groups. Especially the polymers functionalized with groups

containing nitrogen or sulfur donor atoms are preferred in the sorption of gold ions,

because of the Hard-Soft Acid-Base (HSAB) principle introduced by Pearson [Erim et al.,

2013; Pearson, 1968].

In this context, the present study deals with the synthesis, characterization and

sorption properties of a new acrylic copolymer with dimethylaminobenzaldehyde functional

groups (AS- 5BA) for gold(III) recovery from chloride solutions.

The synthesis of the proposed chelating resin takes place in three steps (Scheme

2.2):

a) preparation of the etylacrylate/acrylonitrile/divinylbenzene (EA/AN/DVB) copolymer by

radical copolymerization;

(b) synthesis of the AS-127 acrylic anion exchanger by the aminolysis reaction of

EA/AN/DVB copolymer with triethylenetetramine (TETA);

c) synthesis of the AS-5BA functionalized copolymer by the aminolysis reaction of AS-

127 acrylic anion exchanger with dimethylaminobenzaldehyde (DMABA)


H2C CH

C N

CH2C

CHH2C

H2C CH

C O

OH2C CH3

x y z

POB

HC

H2C

CH

H2C

H2C

HC

H2C

C O

OH2C CH3

HC

C N

x y z

radical copolymerization

TETAC2H5OH

NH2

HC

H2C

CH

H2C

H2C

HC

C O

HNH2C

x y z

HN

2H

3

HC

H2C

CH

H2C

H2C

HC

C O

HNH2C

x y z

HN

2 2

N CH

N CH3H3C

DMABA

H2O

(a)

(b) (c)

Scheme 2.2. Synthesis of the acrylic sorbent The characteristics of the compounds are summarized in Table 2.14

Table 2.14. Characteristics of the synthesized compounds

Sample Functional group Volume

weight,

g/ mL

Exchange capacity Swelling

coefficient

mequiv/mL mequiv/g

AS-127

3NH

C=O

NH2CH2

( )2

0.093

0.960

10.317

380

AS-5BA

C O

NH CH2 NH

2 2

CH2

2

N CH

N

CH3H3C

0.102

0.969

9.488

500


The AS – 5BA functionalized copolymer was used for Au sorption from chloride

solution by the batch method (Figure 2.10.) The complete gold desorption from the tested

acrylic copolymer functionalized with dimethylaminobenzaldehyde was carried out using

5% thiourea solution in 0.1M HCl

Figure 2.10. Scheme of Au(III) sorption – desorption in batch conditions

The structure of the developed material was characterized by infrared

spectroscopy (IR) and scanning electron microscope (Figure 2.11). The SEM images in

Figure 2.11 clearly show the morphological changes occurring on the surface of the

sorbent after the reaction with a chloride solution containing Au(III) ions. The SEM

micrographs show the presence of gold particles bound to the surface and inside the


polymer matrix. The micrographs also indicate the scattered particles present on the

surface in high concentrations around the microfissures. Figure 2.11.c was obtained by

sectioning granules of polymer and indicates the penetration and retention of gold inside

the polymer particle

(a)

(b)

(c)

Figure 2.11. SEM images of: (a) AS–5BA sorbent; (b) AS-5BA+Au(III); (c) section on the

granules AS-5BA+Au(III).

X-ray photoelectron spectroscopy (XPS) was used in this study to investigate the

presence of gold in the chemical composition of the acrylic functionalized copolymer

before (a) and after Au (III) retention (b), as depicted in Figure 2.12.

a

b


c

Figure 2.12. XPS spectra for: a. AS–5BA sorbent; b. AS-5BA+Au(III);

c. Au 4f photoelectron peak

The most important peaks are those of carbon (C 1s), oxygen (O 1s) şi nitrogen (N

1s), which are indicated qualitatively and quantitatively in the probe composition. These

peaks were identified through the binding energy value (BE). For example, the peak C1s

appears at BE =285 eV and is the specific enegy for–C-O bond, N 1s appears at BE =

399 eV, O 1s appears at BE =531 eV and is specific to the C=O bond (Qi et al, 2016). In

Fig. 2.12 (c) appears the peak Au 4f at BE = 87 eV. In this spectra, Au 4f doublet peaks

(in the interval 82 and 90 eV), responsible for Au(III) form, are dominating. These energies

have been assigned to the HAuCl4 used for the sorption process.

Batch sorption capability of the tested acrylic copolymer with

dimethiyaminobenzaldehyde groups for the recovery of gold(III) ions from chloride

solutions was investigated as respect to the function of acidity, metal ion concentration

and contact time:

the gold retention is maximum (24.11mg/g) in HCl concentration of 0.1M (pH =1)

The gold removal efficiencies decreased from 98.85% to 80% by increasing HCl

concentration up to 6 M. ( Figure 2.13)


Figure 2.13. Effect of acidity on the sorption of Au(III) by AS – 5BA (initial concentration of

Au(III) is 57 mg/L; dose of sorbent 2g/L)

the amount of Au(III) retained on the functionalized copolymer under study

increased with increasing metal ion concentration, while the Au(III) sorption

percentage decreased;

the dependence between the equilibrium concentrations of Au(III) in the sorbent

phase and chloride solution phase was described by Langmuir, Freundlich and

Dubinin–Radushkevich models (Table 2.15)

Table 2.15 Isotherm models parameters

Langmuir isotherm (Langmuir, 1916)

Equation Quantitative parameters Isotherm parameters, significance

q = KL.C. q0/ (1 + KL. C)

KL, q0 KL – binding energy (relative sorption affinity), q0 – maximum capacity of sorption

L/mol mg/g mmol/g R2 χ2

7042 87.75 0.4456 0.9909 0.0716

Freundlich isotherm (Freundlich, 1906)

Equation Quantitative parameters Isotherm parameters, significance

log q = log KF + (1/n)log C

(linearised form)

KF n R2 χ2

KF - sorption capacity n–energy of sorption

5.53 1.16 0.9837 1.2911

Dubinin-Radushkevich isotherm (Dubinin, 1960)

Equation Quantitative parameters Isotherm parameters, significance 2

Dq = q exp(-Bε )

1RT ln 1

C

1E=

-2B

E, kj/mol

q0 R2 χ

2

qD is the maximum sorption capacity (mg/g); B is the activity

coefficient related to mean sorption energy; ε is the Polanyi potential and E is the mean free

energy of sorption (kJ/ mol)

mg/g mmol/g

11.97

141.41

0.718

0.9817 2.8952


in order to establish the best fitting for the isotherms under evaluation, the Chi-

square test was applied. The advantage of using the chi-square test is the

possibility to make a comparison of all isotherms on the same abscissa and

ordinate. The Chi-square statistic test is calculated as follows:

where: p is the number of experimental data; qcalc is the equilibrium capacity

calculated from each model (mg/g) and qmeas is the equilibrium capacity (mg/g)

measured from experimental data. If data from the model are similar to the

experimental data, χ2 will be a small number while, if they differ χ2 will be a bigger

number (Brdar et al., 2012). The values χ2 obtained in Table 2.15 for the three

isotherms shows that Langmuir isotherm model describes best the sorption

process under study at equilibrium. This situation showed that a homogeneous

and monolayer sorption occurred.

the sorption of Au(II) ions on the tested functionalized acrylic copolymer follows

better the pseudo-second-order kinetic model which includes different sorption

mechanisms such as surface complexation or ion exchange.

A comparison of the Langmuir maximum capacity of gold sorption of AS – 5BA

synthesized functional copolymer with that of other reported chelating sorbents is shown

in Table 2.16. It is clear from Table 2.16 that the tested acrylic copolymer with

dimethylaminobenzaldehyde groups is competitive against other reported sorbents with

groups containing nitrogen donor atoms, being very suitable for the recovery of gold ions

from large volumes of industrial wastes.


Table 2.16. Comparison of sorption capacity of various polymers functionalized with

groups containing nitrogen donor atoms for gold(III) recovery from chloride solutions

Sorbent Au(III)

sorption

capacity, mg/g

pH Reference

Aminoguanidine derivative

of gel expanded

poly(vinylbenzyl chloride – co –

divinylbenzene) copolymer

68.0

[Jermakowicz-

Bartkowick and

Kolarz,

2002]

L – lysine modified crosslinked chitosan resin 70.34 2.0 [Fujiwara et al.

2007]

Silica – gel with hydroxyl- or amino-

terminated polyamine

106.36 –

169.39

[Qu et al.,

2008]

Thiourea – formaldehyde chelating resin

Urea - formaldehyde chelating resin

21.46

17.33

2.0 [Ertan and

Gulfen, 2009]

Cotton fiber/ chitosan composite sorbents

SCCH(4.49% chitosan)

RCCH(4.25% chitosan)

76.81

88.63

[Qu et al.,

2009]

1,8 – diaminonaphtalene – formaldehyde chelating

resin

119.0 1.0 [Erim et al.,

2013]

Acrylic copolymer with dimethylaminobenzaldehyde

groups

87.75 1.0

The investigation of the sorption selectivity showed that AS-5BA functionalized

copolymer exhibited very high selectivity for gold in the presence of Co(II), Mn(II) and

Cd(II) ions (Figure 2.14.). This behavior shows that the developed AS–5BA copolymer can

be applied to recover and separate Au(III) from aqueous solutions.

Figure 2.14. The sorption selectivity of the tested functionalized copolymer for Au(III)


In this context, the acrylic copolymer under study was tested for the batch recovery

of gold from a wastewater collected from a gold jewelry manufacturing plant The

quantitative sorption of the gold was found for a contact time of 4 hours with wastewater

(Figure 2.15 a,b).

a

b

Figure 2.15. Composition of wastewater collected from: a. the gold jewelry manufacturing

plant, b. after sorption by AS–5BA copolymer

The acrylic copolymer functionalized with dimethylaminobenzaldehyde is suitable

for multiple processes of gold sorption–desorption from chloride solutions (Figure 2.16).

Figure 2.16. Sorption of gold from HCl solution after its desorption from AS – 5BA resin

by using 5% thiourea solution in 0.1M HCl


2.2.1.3. Ion exchangers modified with chelating reagents A simple way of great interest for preparation of modified resins with high

selectivity is the ―sorption‖ of chelating organic reagents on ion exchangers. The polymer

matrix is represented by a conventional ionic resin that keeps its properties (porosity,

swelling and granulation).The resin is equilibrated with solutions of chelate forming

reagents that must be organic molecules with a strongly dissociated anionic (for example

sulfonic) or cationic (quaternary nitrogen) group. By different analytical methods (infrared

spectroscopy, potentiometric titration of released chloride) it was established that the

―sorption‖ of these reagents on ion–exchange resins take place mainly by an ion–

exchange mechanism. Thus, the retention of 5- sulphosalicylic acid (SSA) on the anionic

exchangers Dowex 2x4 and Vionit AT -14 in their chloride form is based on ion– exchange

reactions which can be described as follows:[Tofan and Paduraru 2012]:

Low saturation degree of resin High concentrations of SSA

RClm ⁺ -O3SC6H4(OH)COO- =

[RClm-2]2+ [OSC6H4(OH)COO]2- + 2Cl-

RClm ⁺ -O3SC6H4(OH)COOH=

[RClm-1]+ [OSC6H4(OH)COO]2- + Cl-

Also, the interaction between resin matrix and chelating reagent molecule, i.e. van

der Waals forces, molecular adsorption, hydrogen bonds cannot be neglected, even their

effect is a minor one [ Bilba, Tofan et al. 1998]

2.2.1.3.1. Anionic exchangers modified with chelating reagents

The anion exchangers modified with chelating reagents may be efficiently used not

only for the selective separation and concentration of some microelements, but also for

the development of new methods of analysis which combine the concentration of metal

ions from various samples with their subsequent determination directly in the resin phase.

2.2.1.3.1.1. Macroporous anion exchanger Purolite A-500 loaded with Ferron for

palladium (II) recovery [Bîlbă, Tofan et al. 2010]

Background

Owing to its corrosion resistance nature and alloying ability, palladium, one of

precious metals is, technologically speaking, highly important. On the other hand,

palladium is one of the most expensive metals. Many processes have been developed to

recover this metal in complex solutions or aimed at its recovery from spent catalysts.


Sorption by chelating resins is one of the most important and modern methods for

the separation and preconcentration of the platinum metals traces [Bîlbă, Tofan 1998;

Păduraru, Tofan et al. 2005; Venkatesan et al. 2007; Jermakowicz – Bartkowiak 2007;

Parodi et al. 2008; Garcia et al. 2008; Kumaresan et al. 2008]. Among the chelating

sorbents with wide applicability in the recovery of palladium, is highlighted those based on

ion exchangers modified with chelating agents [Kolarik and Renard 2003; Goodlewska –

Zylkiewicz 2004; Bilba, Tofan et al. 2004; Myasoedova et al. 2007; Ojeda et al. 2007;

Mokhodoeva et al. 2007].

Materials with excellent sorptive properties have been obtained by loading 8-

hydroxyquinoline on different solid supports [Achterberg et al. 2001; de Jong et al. 1998;

Vlašánková and Sommer 1999]. Similarly, by the sorption of a sulfonic acid derivative of

8-hydroxyquinoline, namely Ferron, on anion exchange resins, chelating sorbents with

good applicability in separation and preconcentration of some metal cations from aqueous

media have been obtained [Moldovan and Neagu 2002].

In order to broaden the range of chelating sorbents with improved performance in

the recovery of Pd (II), I prepared a material based on macroporous anion exchanger

Purolite A-500 (in chloride form) loaded with 7-iodo-8-hydroxyquinoline-5-sulfonic acid

(Ferron) and I studied its complexing properties towards the Pd (II) ions.

The selection of Ferron as a modifier agent was determined by the presence, in its

structure, of two ligand groups: a sulfonic one, able to interact with the anion exchange

resin and the 8-hydroxyquinoline group able to chelate with Pd(II).

Sorption studies

My research was conducted under batch conditions in 2 stages: (1)preparation of

the anionic resin loaded with Ferron; (2)study of Pd(II) sorption on the anion exchanger

loaded with the chelating reagent, according to the procedures presented in Figure 2.17.


Purolite A500 (Cl

─ form)

0.05g

Solution containing determined amounts of Ferron (25 mL)

Equilibration for 24 hours with intermittent stirring

Filtration and washing Filtrate was analysed to evaluate the unretained amount of Ferron

Drying until constant weigh (ambiental conditions)

Resin loaded with Ferron (0.73 mmole Ferron/ g A-500)

Contact between sample of ca. 0.05g loaded resin and 25 mL sample of aqueous solution containing defined amounts of Pd(II) ions for a

determined time

Filtration of mixture

Spectrophotometric determination of the final Pd(II) concentration in filtrate (with KI, λ= 420 nm)

Calculation of the parameters characteristic to metal ion sorption on the loaded resin

Sorption percentage, R (%) R = [(C0- C)/C0].100

Retained amount of metal ion, q (mg g)

q = [(C0-C)/G].V

where: C0 = initial concentration of metal ion (mg/ L)

C = cation concentration after sorption (mg/ L) V = volume of solution (L)

G = weight of resin (g)

Figure 2.17. Schematic representation of the analytical procedures involved in the

preparation of the loaded resin and in the subsequent studies of Pd(II) retention.


1. Sorption study of Ferron on the anionic resin Purolite A-500 To establish the proper conditions of the chelating ion exchanger preparation, the

interaction of anion exchange resin with Ferron, in different conditions of acidity and

organic reagent concentration was studied.

The study regarding the pH effect on the retention of Ferron by anion exchange

resin Purolite A-500 leads to the experimental results given in Table 2.17.

Table 2.17. Immobilization of Ferron on the anion exchanger Purolite A-500 as function of solution pH

pH q, mmole/g R% a

lg Kdb

2 0.206 68.66 3.039

4 0.257 88.6 3.578

4.8-5 0.252 85.33 3.456

5.8-6 0.28 93.33 3.845

7 0.284 96.66 4.152

9 0.276 95 3.963

aR is the retention degree;

bKd is the the distribution coefficient calculated as the ratio:

mmol Ferron/ resin/ mmol Ferron/ mL solution at equilibrium

It can be noted that the immobilization of Ferron on the anion exchanger Purolite

A-500 easily increased with the increase of the solution pH. The retention degree was

maximum (R≥95%) in neutral (Ferron solution neutralized with NaOH) to slightly alkaline

(ammoniacal buffer) medium. Such a behavior could be explained by taking into account

the dissociation of hydroxyl group in this pH domain.

The low sorption level in acidic region (pH < 4) is probably due to a protonation

process, according to the equation [Hseu and Tsai 1978]:

NH+

OH

I

SO3 H+

-H+

pK1=3, 4

N

OH

I

SO3 H+

-H+

pK2=8,35

N

O

I

SO3 H+

By the addition of ammoniacal buffer, the concentration of Cl─ ions increases and

the exchange equilibrium of Ferron is retrograded

The influence of Ferron concentration was investigated for values of initial ratio

Ferron/resin ranging from 0.15-0.70 mmole/g.The Ferron distribution at equilibrum


between the solution and resin phases, represented in Figure 2.18., indicates that the

reagent is retained on ion exchanger almost quantitatively.

Figure 2.18. Sorption

isotherm of Ferron on anion-

exchanger Purolite A-500

(t = 20 °C; time = 24 h; 0.05

g resin).

To elucidate the sorption mechanism of Ferron on anionic resin Purolite A-500, the

correlation between the amount of retained reagent and the amount of removed chloride

was studied. The obtained results suggest a retention mechanism of ion-exchange (1:1)

type, involving electrostatic interaction between the resin matrix and the anionic form of

Ferron (sulphonic group) [Bîlbă, Tofan et al. 1998; Liu1989]

In order to verify this assumption, the ion-exchange constant (KCl/Ferron) and the

value of Gibbs free energy were calculated: ΔG = -RT ln KCl/Ferron, where

KCl/Ferron= rs

sr

ClFerron

ClFerron

(amounts from square brackets represent the concentrations

of Ferron and Cl - ions in phases of resin (r) and solution (s) at equilibrium). The average

value KCl/Ferron of 3.53, is relatively low, though characteristic of an ion-exchange process.

The low value of ΔG = -3.07 kJ/ mole corresponds to a spontaneous process of ion-

exchange.

Ferron-loaded resin has a high chemical stability; the amount of desorbed Ferron

does not exceed 10% by treatment with HCl 0.5 M or HNO3 0.2 M. These findings imply

that the interaction between the polymeric matrix resin (PSt-DVB) and the condensed

rings of the organic reagent could not be ignored, even though their effect is a minor one.

2.Sorption study of Pd(II) on Ferron-loaded resin

In order to avoid the possible blocking of sorbed ligand functional groups, a resin

with a low Ferron saturation degree of 18.7% and a sorption capacity of 0.73 mmol


Ferron/ g A-500 was selected for my study. The Pd(II) sorption process was investigated

at the 1:500 (g sorbent/ mL solution) ratio of phases and initial concentration of 11.36 mg

Pd(II)/L, corresponding to a value of [loaded Ferron]/[Pd] molar ratio of 6.83.

The results obtained by studying the effect of pH, initial concentration and

temperature on the sorption of Pd (II) by the selected resin are summarized in Table 2.18.

Table 2.18. Systematization of the results of the study concerning Pd(II) sorption on the

Ferron- loaded resin

The performed study

The obtained results Remarks

Effect of pH The sorption of Pd(II) became higher as the pH of the analyzed solution increased, attaining values that stay almost constant in the pH range ~5-9. This is in good agreement with the range of pH corresponding to Pd-Ferron complex formation in solution.

Taking into account the real samples requiring Pd(II)recovery from acidic media, the subsequent investigations were made with solutions of initial pH equal to 5.6 wherein the retention percentage has a high value (74.69%).

Effect of Pd(II) concentration in initial solution

At the investigated pH of 5.6 (acetate buffer),the amount of Pd(II) retained on Ferron-loaded resin (0.73 mmol Ferron/g) increases by increasing the metallic ion initial concentration. Conversely, as the Pd(II) concentration increases, the sorption percentage decreases.

Ferron-loaded resin under study can be efficiently used for the quantitative recovery of Pd(II) from aqueous diluted solutions (R ≈ 80%).

Effect of temperature

Increasing the temperature of initial solution (pH = 5.6) has a favorable effect on Pd(II) sorption by Ferron-loaded resin (0.73 mmol/g).

For one degree of rise in temperature, the increase of Pd(II) sorption percentage is about 1.2%.

Sorption isotherms

The sorption isotherms of Pd(II) on Ferron-loaded resin at different temperatures fit well the Langmuir model.

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50

C, mg/L

q, m

g/g

The Pd(II) sorption isotherms on Ferron-loaded resin A-500 at (∙)- 5

0C; (♦) – 15

0C; (▲)27

0C

The values of maximum capacity of sorption (q0) increase with the increase in temperature, being of 0.919 mmol Pd/ g resin at T = 300 K. The explanation for this trend is based on the assumption that the interaction between Pd(II) and the functional group of sorbent takes place with a 1:1 molar ratio of 1 Pd(II):Ferron The high values of the sorption constants, KL(1777.02 L/mol- 5

0C;

2095.76L/mol-150C; 2573.74 - 27

0C

L/mol) reflect the strength of sorbed Pd(II)-sorbent bonds and confirm the existence of a complexation reaction.

Thermodyna-mic parameters

Negative values of apparent Gibbs energy at all working temperatures (ΔG= - 17.286 kJ /mol at 5

0C; - 18.303 kJ /mol at 15

0C; - 19.773 kJ /mol at

270C.Positive value of apparent enthalpy of sorption

, ΔH= + 11.69 kJ /mol Positive value of entropy, ΔS= 104.15 kJ /mol

The values of thermodynamic quantities ΔG, ΔH and ΔS, suggest a strong affinity between Ferron-loaded resin and the tested cation.


CONCLUDING REMARK:

The results of this study emphasize that the macroporous anion exchanger Purolite A-

500 loaded with Ferron is eligible as good sorbent for Pd(II) recovery.

2.2.1.3.1.2. Determination of trace amounts of Rh(III) by a new procedure based on

the reaction product of Nitroso-R salt previously loaded on Dowex 1x1 anion

exchanger [Tofan, 2011]

Background

Rhodium, known for its stability in corrosive environments, physical beauty and

unique physical and chemical properties, is a valuable and rare metal of special

importance for many industrial processes and products [Bosch Ojeda et al. 2006]. Today,

approximately 73% of the world production of rhodium is consumed in the production of

autocatalysts, leading to its emission into the environment; here it can be deposited along

roadways, on vegetable and soil surfaces adjacent to roadways and in the streams, rivers

and waterways either directly or as runoff and can possibly enter the food chain [Ravindra

et al. 2001]. Rhodium and its complex salts, such as Rh(III) chlorides have been reported

as potential health risk to human, causing asthma, allergy, rhino-conjunctivitis and other

serious health problems [Rauch and Morrison 2008].

The heterogeneous composition of environmental samples and the low

concentration level of rhodium make its determination really difficult. Among the analytical

techniques currently used for rhodium determination, the spectrophotometric methods

have a wide applicability [Bosch Ojeda et al. 2005]. In general, a separation and/or

preconcentration step is necessary prior to the rhodium determination by

spectrophotometry. In this context, a significant improvement might be represented by the

use of solid- phase spectrophotometry (SPS).

Applied since 1976, the solid phase spectrophotometry involves techniques in

which the spectrophotometric reagent is used simultaneously for preconcentration and

determination of the analyte [Yoshimura et al.1976]. Solid-phase spectrophotometry

(SPS) combines the preconcentration of the species of interest on a solid substrate with

subsequent measurement of the absorbance in solid phase [Brykina et al. 1995; Yadalloh

et al. 2002; Pascual-Reguera et al. 2004; Liu et al. 2004].

Due to the preconcentration effect and the selectivity of sorption on the ion

exchanger, the solid-phase spectrophotometry provides increased sensitivity and

selectivity than the solution methods and has been successfully applied to the


determination of a wide variety of inorganic or organic species in real samples [Bilba,

Tofan et al. 2004; Pellerano et al. 2007; Amin 2009; Saputro et al. 2009; Koga et al. 2010;

Richter et al.2011].

I performed a study which deals with development of a procedure for the

determination of trace amounts of Rh(III) from aqueous samples by solid-phase

spectrophotometry (Table 2.19). The solid phase is represented by the Dowex 1x1 anion

exchanger loaded with disodium1-nitroso-2-hydroxynaphthalene-3,6 disulphonate (Nitroso

– R salt) ( 20μmol/g of resin).

Table 2.19. A brief description of the experimental part

Chemicals --Stock solution of 1000 mg/L was prepared by dissolution of analytical grade reagent RhCl3 in 0.1 M HCl solution. Working solutions of Rh(III) were prepared by the appropriate dilutions of the stock solutions at 50 mL volume. - Dowex 1x1 (50–100mesh) anion-exchange resin (Suchuchardt, Germany) in chloride form was used as solid support without any preliminary treatment. The beads are spherical, colorless and optically transparent in the visible region of the spectrum. - A 5x10

-3mol/L aqueous solution of Nitroso-R salt (disodium 1-nitroso-2-

hidroxynaphthalene-3,6-disulphonate; NRS) was prepared freshly

Analytical procedure

To a 50 mL sample solution containing Rh(III) (up to 100 μg) of pH value adjusted as required were added 0.06 g of Dowex 1x1 (50–100 mesh) beads previously loaded with NRS (20 μmol NRS/g dry resin). The mixture was moderately heated for 30 min. and then cooled at room temperature while stirring (1 hour). The colored resin beads were collected by filtration and packed into a glass cell of 1mm thickness together with a small portion of filtrate using a pipette. The light absorption of the red-colored beads was measured against a 1 mm cell packed with the exchanger loaded with NRS and equilibrated with water. The apparent values of absorbance were measured at 500 nm (the absorption maximum of the colored species) and 750 nm (the background absorbance). Thus, the errors due to the variation of filling of the resin beads into cells (the change in path-length or scattering) are eliminated. The net absorbance ARC of the complex species sorbed on the resin phase was calculated using Yoshimura‘s equation [Yoshimura et al.1985]: ARC= ∆A-∆A*, where ∆A= A500-A750 (for the sample) and ∆A*= A500-A750 (for the blank).

Immobilization of Nitroso–R–salt (NRS) from neutral solutions on Dowex resin

beads takes place due to an anion–exchange mechanism, but the interactions between

the polymeric matrix of the exchanger and the condensed rings of the organic reagent are

very important [Bilba, Tofan et al.1998]. The loaded NRS resin was found to be

chemically stable in strongly acidic, neutral and weakly alkaline solutions and has a good

thermal stability at 600C [Bilba, Tofan et al. 2004].


Absorption spectra

The Dowex 1x1 beads loaded with NRS have a yellow color with an absorption

maximum at 400 nm [Bilba, Tofan et al.2004]. Their reaction with Rh(III) resulted in a

complex of red color, the color being stable at least 48 hours. This complex formed in the

solid phase exhibits an absorption maximum at λ=500nm. The electronic spectra of the

reagent and its complex with Rh(III) in the solid phase are shown in Figure 2.19. It can be

seen from Figure 2.19 that the spectra have a shape similar to that of corresponding

aqueous solution spectra at the same pH, the slight displacement of absorption bands

being explained by the molecule deformation in the resin phase (a bathochromic shift from

the solution to the solution phase).

Figure 2.19. Absorption spectra in Dowex 1x1 resin phase: (1) Nitroso-R salt, 20 μmol/g

resin; (2) Rh(III)–NRS complex, 2.25 μmol/g of resin.

Influence of experimental variables

In order to find the best analytical conditions for the determination, the

experimental variables (wavelength, pH, amount of resin, sample solution volume) were

optimized:

The optimum pH value for the method was selected as 4.8, considering also that

the swelling of the resin is strongly pH dependent;

The absorbance decreases with increasing the amounts of the resin beads

impregnated with NRS. From an experimental point of view, the minimum amount

of dry resin required to obtain sufficiently high absorbances values is 50 mg;

The sensitivity of the method can be increased by decreasing the ratios of solution

volume/resin amount.

2


Analytical performances of the proposed method

Under the optimum conditions selected, the calibration curve is linear in the

concentration range of 0.5–2 μg/mL, for the system with 50 mL of sample volume

(pH=4.8) and 60 mg of Dowex impregnated with NRS (20 μmol/g resin). The analytical

parameters are recorded in Table 2.20.

Table 2.20. Analytical parameters

Parameter Value

Linear dynamic range (μg/mL)

Correlation coefficient (R2)

RSD (%)

Detection limit (k=3) (μg/L)

Molar absorptivity (L/mol.cm)

0.5–2

0.9991

1.18

3.842

3. 0356.104

A comparison with conventional spectrophotometric methods revealed that the

proposed method is simple, reproductibile and accurate and can be an inexpensive tool

for trace analysis. Due to the preconcentration effect, the sensitivity of the solid-phase

spectrophotometric method under study, expressed as molar absorptivity, is about 4–12

times higher than that of other spectrophotometric methods for rhodium(III) determination.

Application of the proposed method

The proposed method was successfully applied to the determination of Rh(III) from

different synthetic samples containing other platinum metals over a wide range of

concentrations (Table 2.21.)

Table 2.21 Determination of 80 μg Rh(III) /L in synthetic samples

Sample Found*±Sn-1

μg /L

Relative error

(%)

Recovery

(%)

A 78 ± 2 2.5 97.5

B 81± 1.5 1.25 101.25

C 77 ± 2.8 3.75 96.25

*n = 3; sample A: Pd(II), 500 μg/L; sample B: Os(VIII), 500 μg/L; sample C: Pt(IV), 500 μg/L

CONCLUDING REMARK:

The results obtained on synthetic solutions clearly indicate the feasibility of the proposed

method for real sample analysis


2.2.1.3.2.Cationic exchangers modified with chelating reagents [Bilba, Tofan et

al.1998; Tofan and Păduraru 2012].

By the sorption of Alizarin Red–S on cation exchanger stannic silicate a chelation

ion exchange material has been prepared [Rawat et al. 2012]. This material has been

used for the selective separation of Cd(II) and Pb(II) from a mixture of several cations,

viz. Cr(III), Hg(II), Fe(III), Co(II) and Ni(II) using nitric acid solution of pH 1 and 6 as

eluents. While all other metal ions in the mixture were eluted first by nitric acid solution of

pH 6, Cd(II) and Pb(II) ions were eluted by solution of pH 1 with a recovery of 99% and

98.03% for Cd(II) and Pb(II), respectively [Rawat et al. 2012].

Removal of heavy metal ions from synthetic and real mixtures was studied by a

new sorbent based on the cation exchange resin Amberlite IR–120 modified with

Rhodamine B [Nabi et al. 2011]. On the basis of distribution coefficients (Kd), Ni(II) and

Fe(III) metal ions from binary mixtures have been separated. The limit detection for the

Ni(II) and Fe(III) metal ions was 0.81 and 0.60μg/L and the limit of quantification was

found to be 2.272 and 2.0 μg/L [Nabi et al. 2011].

2.2.1.4. Impregnated sorbents

Impregnated sorbents are chelating resins whose functional groups are not

chemically bounded to the matrix, but fixed on the surface with physical weak forces

[Zagordini 2007].

A simple and rapid technique of impregnated sorbent preparation is based on ―the

mechanical impregnation‖ of the inert matrix with complexing reagents. For this reason,

the support is treated with the solution of the complexing reagent in an organic reagent,

which is then removed by filtration or evaporation. Sometimes, the inert support is utilized

for the direct sorption (noncovalent binding) of the metal – complexes of analytical reagent

[Bilba, Tofan et al. 1998; Tofan and Păduraru 2012].

Thus, by impregnation of 5, 7–dibromo–8 – hydroxyquinoline (bromoxine) on the polystyrenic non–polar support Purasorb (specific surface area of 800 m2/g; pore volume 0.8 mL/g; bead size 20–60mesh), I have been developed a chelating sorbent, particularized by a high selectivity towards Pd (II) ions [Păduraru, Tofan et al. 2002].The content in bromoxine of impregnated support was of 0.1 mmol/g. It has been found that the formation of Pd(II)–bromoxine complex on impregnated Purasorb is favored by the methanol presence in the solution (≥ 20% v/v) and by the increase of the pH values. The equilibrium sorption data fitted well to the Langmuir isotherm. The values of Langmuir parameters were of 0.0756 mmol/g and 1000.87 L/mole for the maximum capacity of sorption (q0) and Langmuir constant (KL), respectively [Păduraru, Tofan et al. 2002].


Impregnated sorbents have been used in various applications for the treatment of

metal effluents containing heavy metal ions [Thharanitharan and Srinivasan 2009; Harun

2010; Hosein et al. 2010; Hosseini–Bandegharari et al. 2011; Mahmoud et al. 2010;

Gawin et al. 2011]

Unfortunately, the main disadvantage of the impregnated sorbents is the loss of

chelating reagent due to its solubility in aqueous phase. Leakage of the chelating agent

from the polymeric support leads to a steady loss of the sorption capacity after several

cycles of application. This problem is thought to be the main reason why the impregnated

resins technology has not evolved into large–scale applications [Gupta et al. 2006].

2. 2.1.5. Conclusions

Retention of heavy metal ions by chelating polymers is, in many cases ,the

method of choice for their removal/ recovery. Selective sorption can be achieved via

functionalizing the polymer support with desirable chelating groups. Chelating sorbents

have higher selectivity and sorption capacity, good physical and chemical stability, being

reusable and easily separable.

Chelating sorbents have been one of my major research interest. I have been

prepared some new chelating sorbents by covalent immobilization of desired groups, also

by some special, noncovalent methods. The proposed polymer sorbents have enhanced

efficiency and good selectivity towards targeted precious and toxic heavy metal ions. They

have been used in the selective processes of precious heavy metal recovery; the removal

of toxic heavy metals ions from aqueous media and for development of new methods of

analysis which combine the concentration of precious metal ions from aqueous samples

with their subsequent determination directly in the resin phase.

The results of my studies are significant for the future development of the

proposed sorbents into beneficial materials for industrial and environmental applications.

2.2.2. Advances in preconcentration/removal of environmentally relevant

heavy metals from water and wastewater by sorbents based on polyurethane

foams [Teodosiu, Tofan et al. 2014]

The potential possibilities of polyurethane foam (PUF) as a suitable sorbent for

wastewater treatment have been pointed out in 1970 [Bowen 1970]. Braun and Farag

verified that open–cell type resilient polyurethane foams have remarkable mass–transfer

properties and rapid sorption owing to their quasi–geometric membrane [Braun and Farag


1975; Braun and Farag1978]. These features allowed their utilization in separation and

preconcentration procedures with relatively high flow rates in batch and dynamic systems.

These initial studies have resulted in others by using unloaded and physically or

chemically modified polyurethane foams for environmental applications [Tofan et al.

1994;Tofan et al. 1995; Tofan et al.1996; Bilba, Tofan et al. 1998; Braun et al.2000;

Lemos et al. 2007; Türker 2012].

With the aforementioned, as a continuation of my research during doctoral thesis,

I choose to further evaluate the sorbents based on polyurethane foams in more realistic

conditions. For this reason, I performed a bibliographic review which attempts to be a

platform in describing the synthesis, characterization and applicability of different types of

polyurethane foams for the removal of heavy metals, as well as the comparison of these

sorbents with other sorbents effective for such processes.

2.2.2.1. Synthesis, physical and chemical properties of polyuretahane foams

Polyurethane foams can be defined as plastic materials in which a proportion of

the solid phase is replaced by gas in the form of numerous small bubbles [Braun and

Farag 1978]. From the geometrical point of view, if the gas bubbles occupy a volume

larger than 76%, those will be distorted into quasi– spherical polyhedral [Braun and Farag

1978].

Polyurethane foams can be prepared in soft, flexible and rigid form using a variety

of polyethers and polyesters. The two most important reactions in the preparation of

urethane foams are those between hydroxyl compounds (polyester or polyether polyols)

and isocyanate and those between isocyanate and water. The second reaction is

responsible for the foaming process due to the liberation of carbon dioxide [Tofan et al.

1994].

The flexible polyurethane foam of polyether type has the most significant

environmental applications. To prepare this type of polyurethane foam, propylene oxide

adduct (average molecular mass of 3000 and 90% content in terminal secondary hydroxyl

groups) and 2, 4 and 2,6- isomers of toluene diisocyanate in 80/20 and 65/35 molar ratios

are frequently used.

The majority of feedstock for polyurethane foams is still based on crude oil, but in

recent years, alternatives based on renewable resources have been developed, like

polyols based on vegetable oils [Tanaka et al.2008; Campanella et al. 2009; Zou et al.

2012]. The properties of these vegetable oil-based polyurethane foams are often

comparable to, or even better than those prepared from petroleum [Pfister et al. 2011].


The properties of polyurethane foams depend on various structural factors

(crystallinity, cross–linking degree, chain rigidity, constraints to its rotation, intermolecular

bonds) and can be changed in wide range by a proper selection of raw materials [Tofan et

al.1994].The main physical and chemical features of the polyurethane foams with

application in separation/ preconcentration of heavy metals can be systematized as

follows:

hydrophobic character;

large porosity; bulk density of 10–35 kg/m3; surface area of 7.6–92.5 m2/kg;

reversible swelling in: water, HCl until 8M, H2SO4 until 4M, HNO3 until 2M, glacial

CH3COOH, NH4OH 2M, NaOH 2M, organic solvents (benzene, carbon

tetrachloride, chloroform, acetone, alcohols);

dissolution in concentrated H2SO4 and concentrated HNO3;

degradation by heating to 180–2200C and UV exposure;

low anionic exchange capacity; relatively fast sorption rate of chemical species

[Braun and Farag 1978].

These special properties make the open–cell polyurethane foam an ideal inert

support for immobilization by physical adsorption of different modifying agents (organic

extractants, ion exchangers, precipitates).

In batch and dynamic systems of separation/preconcentration are used sorbents of

heavy metal ions based on:

1. unloaded polyurethane foams;

2. loaded polyurethane foams;

3. chemically modified polyurethane foams

2.2.2.2. Preconcentration of pollutant metal ions from environmental aqueous

media by different types of polyurethane foams

2.2.2.2.1. Sorbents based on unloaded polyurethane foams

Unloaded polyurethane foam retains heavy metal ions after complex formation

(thiocyanate, chloride, iodide complexes). Generally, unloaded polyurethane foam

functions according to the succession of steps shown in Figure 2.20 [Teodosiu, Tofan et

al. 2014].

The saturation sorption capacity of unloaded polyurethane foam varies in wide

range from about 0.04 mmol/g to over 1.5 mmol/g of unloaded foam, depending on the

nature of the cation under study [Tofan et al.1994].


Thus, the critical capacity of Se(IV) from aqueous media(spiked to fresh waters)

containing bromide ions onto unloaded foam column was found to be equal to 0.3 mg/g.

The value of the breakthrough capacity of selenium uptake was calculated as 0.65 mg/g.

[Bashammakh 2010].

Figure 2.20. The succession steps involved in the sorption of heavy metal ions by

unloaded polyurethane foam [Teodosiu, Tofan et al. 2014].

The quantitative recovery of Cu(II) from various water samples (tap water, mineral

water and seawater) was achieved in a medium containing 60 mg/L of Eriochrome Black

and pH 1.5. The minimum time required to obtain total recovery of Cu(II) from solution

was 30 min, when 200 mg of PUF were stirred with 100 mL of the samples [Soriano and

Cassela 2013].

Future research is focused on testing the ability of unloaded polyurethane foam

and its performances for on–line preconcentration, separation and determination of heavy

metal ions. For instance, a proposed method could be applied to on column packed

unloaded polyurethane foam for simple, reliable and low cost procedure for quantitative

and chemical speciation of Au(I) and Au(III) on- site analysis [Bashammakh et al.2009].

2.2.2.2.2. Sorbents based on loaded polyurethane foams

Flexible open cell polyurethane foams can be physically modified with various

organic extracting and chelating reagents.The loading process (Figure 2.21) offers a wider

range of applications which improves the selectivity and the capacity of the sorbents.


Figure 2.21. Schematic representation of the loading process [Teodosiu, Tofan et al.

2014]

By swelling into organic extractants, polyurethane foam can be loaded with large

amounts of tri–n–butyl–phosphate (TBP), methyl iso-butyl ketone, diethyl ether. A detailed

study revealed that the flexible open–cell polyurethane foams retained tri–n–butyl–

phosphate much more efficiently than other known bead supports. On the other hand, the

polyurethane foams of polyether type have an increased capacity of TBP retention than

the polyester foam [Tofan et al. 1995].

By impregnation of solid foams, the selectivity of the hydrophobic organic

extraction agents and the fastness of the kinetics of the sorption process between the

metal ions in aqueous solution and the loaded polyurethane foams are combined.

A special attention should be given to the tri–n–butyl–phosphate–loaded

polyurethane foam, due to the double function of tri–n–butyl–phosphate: a) plasticizer

which significantly increased the foam permeability and b) extracting agent with high

solvation power in ionic association systems. Thus, the excellent properties of the flexible

open–cell polyurethane foam of polyether type impregnated with tri–n–butyl–phosphate


allowed quantitative separation of silver, gold, bismuth, cadmium, cobalt, chrome, copper,

mercury, nickel, lead, palladium, tin, tantalum, thorium [Tofan et al. 1995], calcium

[Mondall and Kundu 2005], and the concentration of iron [Bilba, Tofan et al.1998] and

gallium from chloride media [Tofan et al.2007]. The main factors with significant influence

on the retention of pollutant metal ions by polyurethane foams impregnated with

extractants are the solution acidity, time of contact, initial concentration and temperature

of solution. Thus, the Ga(III) sorption from hydrochloric solutions(3M) is favored by the

increase of time of phases contact( Figure 2.22), Ga(III) concentration in external solution(

Figure 2.23.) and temperature ( Figure 2.24) [Tofan et al. 2007].

Figure 2.22. Effect of

contact time on the Ga(III)

retention by polyurethane

foam impregnated with tri–

n–butyl–phosphate (C0(initial

concentration)= 0.1584 mg

Ga(III)/mL) [Tofan et al.

2007]

Figure 2.23. Effect of initial

concentration in the Ga(III)–

TBP– polyurethane foam

batch system of sorption, at

different temperatures (●)-

278 K; (▲)- 313 K [Tofan et

al. 2007]

0

10

20

30

40

50

60

70

0 30 60 90 120 150 180 210time, min

R, %

0

10

20

30

40

0 20 40 60 80

Co, mg/L

q, m

g/g


Figure 2.24. Effect of

temperature on the Ga(III)

retention by polyurethane foam

impregnated with tri–n–butyl–

phosphate, at different initial

concentrations: (●)-C0 = 19

mg/L; (♦)- C0 = 31.7 mg/L; (▲)-

C0= 44.3 mg/L [Tofan et al.

2007]

The experiments carried out on a column filled with polyurethane foam loaded with

tri–n–butyl–phosphate indicated the quantitative retention of Fe (III) (99.3 - 99.9%) from

hydrochloric solutions (4M) with an initial concentration of 5.6 – 39.2 mg Fe(III)/L. In order

to estimate the efficiency of the used chromatographic column, the number of theoretical

plates, N, and the height equivalent to a theoretical plate, H, have been calculated. The

average values were found to be: N= 59.07 and H= 0.846; these values pointing out the

feasibility and efficient use of the column packed with tri–n–butyl–phosphate loaded foam

for Fe(III) retention from hydrochloric solutions (4- 6M). The properties of the packed

column did not change significantly with time, the sorption capacity of Fe (III) being almost

constant over 10 repeated cycles of sorption – desorption [Bilba, Tofan et al. 1998]

The chelating agent–loaded polyurethane foam can be prepared in two ways

[Tofan et al. 1995]:

by the direct contact between a certain amount of spongious material and a

solution of the organic reagent in a volatile solvent. The efficiency of these polyurethane

sorbents in selective and quantitative separation of metal ions from very diluted aqueous

solutions is mainly due to the feasibility of the polyurethane foam to act as ―solvent‖ for the

formed complexes, for instance the colloidal particles of nickel and palladium

dimethylglyoximates [Tofan et al. 1996]. Thus, the polyurethane foam loaded with

dimethylglyoxime(6.3866 mg dimethylglyoxime/g foam) could be efficiently used for

concentration of Ni(II) and Pd(II) ions and their separation each other and from Cu(II),

Cd(II), Zn(II) and Co(II) ions [Tofan et al.1996].

0

0,5

1

1,5

2

2,5

3

3,5

270 280 290 300 310 320

T, K

log

Kd


through the plasticizers (dissolution of a chelating reagent into a plasticizer

followed by the swelling of the polyurethane foam in the obtained solution).

Some chelating reagents (dithizon, diethylammonium diethyldihiocarbamate, 1–

(2–pyridylazo)–2–naphtol) dissolve in different plasticizers (tri–n-butyl–phosphate, α–di–

n–nonylphatalate, α–n–octyl-phatalate) and the polyurethane foam matrix swells in their

solutions. The plasticized chelating polyurethane foams are characterized by superior

permeabilities, ensuring increased mobilities of the metallic ions. In this context, the

possibilities of cation–complexing agent interaction are more varied, the plasticized

polyurethane foams having an increased sorption efficiency as compared to the unloaded

foams [Tofan et al. 1995].

The sorption process of heavy metal ions on loaded polyurethane foams is

evaluated and characterized by Langmuir and Freundlich isotherms [Saeed 2008]. A

comparison between Langmuir and Freundlich isotherm models for the sorption of some

metal ions on two kind of loaded polyurethane foam is presented in Table 2.22.

The applicability of the Langmuir isotherm for the batch sorption systems as

presented in Table 2.22 suggests the formation of a monolayer covering on the surface of

the loaded – polyurethane foams. Also, it can be seen from Table 2.22 that the values of

the n Freudlich constant are above unit, indicating favorable sorption of gallium (III) by

polyurethane foam impregnated with TBP at all working temperatures [Tofan et al. 2007].

Despite the fact that these materials can suffer from poor selectivity and leaching

out the reagents, physically modified polyurethane foams are extensively used [Dos

Santos et al. 2006; Garna et al. 2006; Rashid and Munir 2008; Anjaneyulu and Rao 2009;

Saeed et al. 2005; Burham 2009; Saeed and Ahmad 2005].

Current and future studies consider the development of new strategies and the

improvement of the analytical performances of the previous reported methods for fast and

selective removal of heavy metal ions onto loaded polyurethane foams. Thus, a method

based upon the use of the ion pairing reagent tetraheptylammonium bromide (THA+.Br−)

immobilized polyurethane foams sorbent in packed columns for the retention of ultra trace

concentrations of gold (III) from aqueous chloride medium of pH 3–4 at 5 mL/ min flow

rate has been developed [El–Shahawi et al. 2011]. The capacity data (17 ± 0.7 and

19.5 ± 065 mg/ g) of the developed sorbent are better than the data (11.21 ± 1.8 and

5.29 ± 0.9 mg/g) previously reported. The method was applied satisfactorily (> 95%) for

the analysis of total inorganic gold (I) and/or gold (III) ions in wastewater samples and

anodic slime [El–Shahawi et al. 2011].

A novel sorbent based on chitosan impregnated polyurethane foam (maximum

sorption capacity of 76.6 mg/g and 96.01 mg/g for copper(II) and nickel(II), respectively)


has been successfully used for the removal of heavy metal ions from wastewaters

[Prakash et al. 2011]. One of the most important results of this study was the fact that the

polyurethane foam provided enough sorption sites to overcome mass transfer limitations

and thus the process of Cu(II) and Ni(II) sorption on chitosan impregnated polyurethane

foam could provide extra–value for practical applications [Prakash et al. 2011].

Table 2.22. Quantitative description of some metal ion – loaded polyurethane foam batch

sorption systems on the basis of the Langmuir and Freundlich models.

Langmuir isotherm [Langmuir1916]

Polyurethane foam

impregnated with

tri–n–butyl–phosphate

(5.1714 TBP/ g foam)

Polyurethane

foam loaded with dimethylglyoxime

(6.3866 mg DMG/g foam)

Freundlich isotherm [Freundlich 1906]

Polyurethane foam

impregnated with

tri–n–butyl–phosphate

(5.1714 TBP/ g foam)

Ga(III) [Tofan et al.

2007]

Ni(II) [Tofan

Pd(II) et al. 1996]

Ga(III)

q =

KL.C.q0/(1+KL.C), q - the amount of metal ion sorbed on solid phase (mmol/g of foam); C - the equilibrium concentration of the metal ion in solution(mmol/mL); KL – Langmuir constant related to the sorption capacity (L/mol) q0 is the maximum capacity of sorption(mmol/g)

1262.87(278K) 2216.2 (295K) 3424 (313K) 0.5301(278K) 0.5535 (295K) 0.5835 (313K)

4.762 (295K)

5.366 (295K)

log q = log KF+(1/n)log C where q is the amount of metal ion taken up per 1gram of loaded foam (mg/g), C is the cation concentration left in solution at equilibrium (mg/mL); KF is the Freundlich constant related to the sorption capacity; n is the Freundlich constant relating to the energy of sorption

1.820(278K) 3.88(295K) 6.76(313K) 1.886(278K) 2.430(295K) 3.10(313K)

2.2.2.3. Chemically modified (reacted) polyurethane foams

The reacted polyurethane foams are characterized by the fact that the chelating

reagent is bonded to the backbone of the polymer via chemical bonds. The synthesis

method differentiates between two types of reacted polyurethane foams. [Dmitrienko and

Zolotov 2002].

The first type is represented by the functionalized polyurethane foams. They are

obtained by covalently linking chemical reagent to the side group in the prepared

polyurethane foam material (Dmitrienko and Zolotov 2002). There are some functional


groups (terminal amino, isocyanate in the toluene diisocyanate moiety, carbonyl and imino

of the urethane groups, hydroxyl groups in the polyol residues) in the polymer chain that

can be used for this purpose. However, the only way known so far is performed by using

the terminal amino groups. The modification by azo coupling of the terminal amino groups

to different organic compounds results in selective polyurethane sorbents with improved

sorption capacity [Burham et al. 2008; Burham et al. 2009; Azeem et al. 2010; Burham et

al.2013; Abdel–Azeem et al. 2013; Moawed et al.2013]

The second type corresponds to the grafted polyurethane foams. In this case, the

reagent, carefully selected, is added during the manufacturing process of the

polyurethane foam and acts as monomer which participates in the polymerization

reaction. Thus, the reagent should contain side groups necessary for polymerization and

chelation and must be soluble in the mixture of the polymerization reaction [Moawed et al.

2013; Oliveira and Lemos 2012; Moawed and El–Shahat, 2013].

There is a continuous and increased interest in the synthesis of new sorbents

based on chemically modified polyurethane foams and their use as solid phase extractor

of heavy metal ions in water and wastewater samples. In this context, the novel resins of

polyurethane foam linked with aminophenol or o–hydroxyphenylazonaphtol can be

mentioned. These resins have been recently synthesized and used for preconcentration of

nickel, cadmium and zinc ions from natural water samples prior to their atomic absorption

spectrometric determination [Burham et al.2011]. The content of lead in well water and

drinking water samples was determined after its separation and preconcentration on a

new sorbent based on polyurethane foam functionalized with 4,5–dihydroxy–1,3–

benzenedisulphonic acid [Lemos et al. 2012]. Under optimum conditions, the proposed

system presented enrichment factors of 38 (50 mL) and 114 (500 mL) [Lemos et al. 2012].

2.2.2.3. The applicability of sorbents based on polyurethane foams in water and

wastewater treatment

The open cell polyurethane foams have been succesfully used in column studies

regarding the treatment of large volumes of effluents containing heavy metals, as

presented in Table 2.23. These materials can be efficiently applied over a wide range of

metal ions concentration and do not lose their efficiency even for repeated cycles of

sorption–desorption.Furthermore, the sorbed metal can be almost quantitatively recovered

by a relatively easy desorption (Table 2.24.). Regarding the economical feasibility, it was

found that the operational costs for the removal of 1kg of mercury ions from 20 KL of the

effluent using one time ammonium pyrrolidine dithio carbamate loaded polyurethane foam


as sorbing medium were of USD 5000 and can be significantly reduced by increasing the

number of recycles [Murthy and Marayya 2011].

Table.2.23. Practical uses of polyurethane foams in water and wastewater treatment [Teodosiu, Tofan et al. 2014]

Type of polyurethane Wastewater Collected metal ions

Removal efficiency

Reference

Immobilized ion exchange polyurethanes

Synthetic primary coolant of a nuclear power plant

Co(II) 98% [Yeon et al. 2004]

2-aminophenol – bonded PUF, hydroxyphenylazoacetylacetone – bonded PUF and hydroxyphenylazonaphtol– bonded PUF

Cooling water of a sulfuric acid unit

Cu(II), Ni(II), Pb(II), Mn(II), Zn(II), Fe(III)

89.3 – 106.66

[El–Shahat et al. 2008]

3- sulfonamoyl – phenyl – spiro –[4- oxo – thiazolidin- 2,2‘- steroid] physically immobilized onto polyurethane foam

Industrial wastewater of electroplating industry (samples of 0.5L)

Cd(II) (5,10 μg/ml)

~ 100%

[Tawfiqmakki et al. 2011]

Ammonium pyrrolidine dithio carbamate loaded polyurethane foams

Municipal sewage Chloro – alkali industrial wastes

Pb(II), Hg(II), Cd(II), Ni(II), Cu(II) and Cr(VI) Hg(II)

70 –82% 95– 98%

[Murthy and

Marayya 2011]

Table 2.24. Desorption and multiple sorption/ regeneration cycles for heavy metal ions

removal by sorbents based on polyurethane foams [Teodosiu, Tofan et al. 2014]

Sorbent

Retained

metal ions

Desorbing solution

Metal

recovery percentages

Number of sorption/

desorption cycles

Reference

1-( 2 – thiazolylazo)- 2 – naphtol imbedded polyurethane foam

Pb(II) 0.03 N perchloric acid 96 -99.7%

[Saeed et al.2007]

Tetraphenylarsonium chloride and tetraphenylphosphonium bromide loaded polyurethane foams

Cr(VI) 2M sodium hydroxide 97.5∓2.6% 5 [El – Shahawi et al.2008]

Alginate/polyurethane composite foams

Pb(II) Disodium salt of ethylenediaminetetra

~ 100% 4 [Sone et al. 2009]


acetic acid Alizarin complexone functionalized polyurethane foam

Cu(II) Zn(II) Cd(II)

0.1 M nitric acid ~ 100% [Azeem et al.2010]

Rhodamine B grafted polyurethane foam

Bi(III) Sb(III) Fe(III)

2M sodium hydroxide 96 – 100% [Moawed et al. 2013]

Acetylacetone chemically anchored to polyurethane foam

Cu(II) Mn(II) Zn(II)

0.4 M hydrochloric acid

93.6% 97.2% 93.5%

70 [Abdel – Azeem et al. 2012]

2.2.2.4. Conclusions

Sorbents based on unloaded polyurethane foam work generally in batch conditions

according to the following succession of steps: the reaction between the metal ion and a

complexing agent → addition of unloaded polyurethane foam→ retention of the formed

complex on polyurethane foam. The extraction or chelating reagents loaded polyurethane

foams were developed so as to increase the sensitivity and specificity of the foams for the

removal of heavy metal ions. The resistance of the loaded foams towards reagent

leaching out limits their applicability. This observation has led to the synthesis of new

polyurethane foam sorbents which are prepared by building up chelating groups on the

terminal amino groups in the polyurethane foam. The open cell polyurethane foams can

be efficiently applied in the treatment of large volumes of effluents containing a wide

range of heavy metal ions concentrations and do not lose their efficiency even for

repeated cycles of sorption–desorption.

2. 3. Sorption removal of heavy metal ions from aqueous media by waste

materials

A very wide range of low cost waste materials has received growing attention

among the environmental community as an innovative and economical technology in

removing heavy metal ions in place of the conventional costly methods. [Demirbas 2008;

Sud et al.2008; Faroog et al. 2010; Ray et al. 2010; Ahmaruzzaman 2011; Nguyen et

al.2013]. However, their adoption at large scale industrial wastewater treatment is still a

distant reality. The necessity for investigating more and more materials is still of stringent

actuality in order to obtain the best material for industrial applications.

Against this background, a significant part of my research work deals with:

assessment of recovery and treatment possibilities of different indigenous wastes

acting as low-cost sorbents;


studies on the sorption performances of newly prepared sorbents in the removal of

heavy metals from aqueous effluents (Figure 2.25)

modelling, optimization and simulation of the process behaviour and

performances, with applications in water and wastewater treatment.

Figure 2.25. Waste materials explored as low – cost sorbents in my research The most targeted heavy metal ions in my researches are Cu (II), Zn(II) and

Cd(II). I have chosen Cu(II) and Zn(II) because their presence in the environment, even

in relatively low concentrations, is responsible for producing a variety of illnesses related

with the risk of derma damage, respiratory problems, and several kinds of cancer [Rao et

al. 2009]. One the other hand, Cd (II) is listed as the sixth most poisonous substances

jeopardizing human health [Zavvar Mousavi and Seyedi 2011].

The results from my research are distinguished by the following originality elements:

- the waste materials (hemp, rapeseed, Romanian pine bark) have been less

investigated; most existing studies up to date belong to me;

- in order to improve the retention performances, hemp was physically and

chemically treated( impregnation and/or functionalization);

- investigating the performance of the fixed bed columns filled with fibers of natural

and modified hemp;

- the recovery of metals, with the possibility of their re –use in the economic circuit

and sorbent regeneration.


A list of significant papers published on this subject is following:

1.Tofan,L., Păduraru,C., Bunia,I. Mihăilescu Amălinei,R.L., Miron,A. Removal of

cadmium(II)from aqueous effluents by sorption on Romanian silver fir tree

bark(Abbies alba Mill.)wastes, Global NEST J. (2017), 19(1), 107 – 114

2.Moroșanu,I. ,Teodosiu,C., Păduraru,C., Ibănescu,D., Tofan,L., Biosorption of lead ions

from aqueous effluents by rapeseed biomass, New Biotechnology,(2017), 39PA,

110- 124

3. Tofan, L., Păduraru,C., Mihăilescu Amălinei,R.L., Bunia,I., Miron, A., Valorization of

Romanian silver tree bark (Abies alba Mill.)wastes as low –cost sorbent of Cu(II)

ions from polluted waters, Water Sci.Technol. (2016), 74(10), 2314 – 2324

4.Paduraru, C., Tofan, L., Teodosiu, C., Bunia, I., Tudorachi, N., Toma, O., Biosorption of

zinc(II) on rapeseed waste:Equilibruim studies and thermogravimetric investigations,

Process Saf. Environ. Prot. (2015), 94, 18 – 28

5.Tofan, L., Păduraru,C., Wenkert, R., Characterization of pit coal fly ash as sorbent for

Cd(II) ions from aqueous solutions, J.Optoelectron. Adv.Mater, (2013), 15, 899– 904

6.Tofan, L., Paduraru, C., Volf, I.,Low cost resources such as maize bran for Cu(II) ions

removal , Cellulose Chem.Technol.(2012), 45, 275–280

7.Tofan, L., Paduraru, C., Robu, B., Miron, A., Amalinei Mihailescu, R.L.,Removal of

Cd(II) ions from aqueous solution by retention on pine bark, Environ. Eng. Manag. J.

(2012),11, 199 – 205.

8.Amălinei, R.L., Miron,A., Volf,I., Păduraru,C., Tofan,L., Investigations on the feasibility

of Romanian pine bark wastes conversion into a value– added sorbent for Cu(II) and

Zn(II) ions, BioResources (2012), 7,148-160

9.Tofan, L.,Paduraru, C., Volf, I., Toma, O., Waste of rapeseed from biodiesel production

as a potential biosorbent for heavy metal ions, BioResorces(2011), 6, 3727-3741.

10.Tofan, L., Păduraru, C.,Volf,I., Wenkert,R., Comparative study concerning the kinetic

and thermodynamic description of some heavy metal ions sorption on fly ash, J.

Optoelectron. Adv.Mater. (2011), 13, 896–900

11.Tofan, L. Paduraru, C., Bilba, D., Rotariu,M., Thermal power plants ash as sorbent for

the removal of Cu(II)and Zn(II) ions from wastewaters, J.Hazard. Mater.(2008), 156,

1-8.

12. Păduraru, C., L. Tofan, L., Investigations on the possibility of natural hemp fibers use

for Zn(II) removal from wastewaters, Environ.Eng. Manag. J. (2008), 7, 687- 693

13.Tofan, L., Păduraru,C., Sorption studies of Ag (I), Cd (II) and Pb (II) ions on sulphdryl

hemp fibers, Croat. Chem. Acta (2004), 77, 581-586


14. Păduraru, C., Tofan, L., Equilibrium studies for the sorption of metal ions onto hemp,

Cell. Chem. Technol.(2002), 36, 375–380.

2.3.1. Removal/ recovery of heavy metal ions from aqueous solutions by

sorption on hemp fibers

2.3.1.1.Background

Hemp (Cannabis sativa L) is a fast growing plant almost anywhere and requires no

pesticides or fertilizer. The potential for hemp is vast, including sustainable biomass

(power) and biodiesel (fuel). Hemp also makes an excellent source for textile and paper

[Amaducci and Gusovius 2010]. The fiber of hemp is one of the inexpensive and readily

available bast natural fibers and hemp – fiber reinforced polymer composite products have

gained considerable attention in last years [Kalia et al. 2009; Summerscales et al. 2010;

Ku et al. 2011 ]. Recently, special interest has been observed for the use of hemp-based

materials for the removal of different pollutants [Pejic et al. 2009; Zou et al. 2012; Kulkarni

et al. 2014; Vukcevic et al. 2014; Kyzas et al. 2015].

The performances of hemp as sorbent for heavy metals is based on its remarkable

fundamental features:

low cost;

availability

high mechanical strength;

high porosity;

hydrophilic character;

fast sorption;

tolerance to biological structures;

easiness in functionalization;

possibility of being used as fibers and filters.

In comparison with other natural and waste materials, plant fibers as sorbent have

some advantages: they function at low pH level, they are resistant at toxic levels of metal

ions and they are chemically and physically more robust [Bailey et al 1999; Demirbas

2008; Pejic et al. 2011]. The metal ion sorption by agricultural fibers, unmodified and

modified coir, jute, kenaf, agave and ramie have been studied in many laboratories [Mahvi

2008; Ben Hamissa et al. 2010; O‘Conell et al. 2008; Conard and Bruun Hansen 2007;

Shukla and Pai 2005]. However, only a few publications were found so far about the


sorption of heavy metals by hemp fibers. Except of two studies published by Serbs

researchers, all other results belong to me.

Hemp fibers consist mainly of cellulose, lignin, some pectin and extractives (fat,

waxes, etc.) (Table 2.25).

Table 2.25. Chemical composition of hemp used in the performed studies[Paduraru and

Tofan 2008]

Cellulose(%)

Hemicellulose(%)

Lignin(%)

Waxs(%)

74 – 75

18.4- 15.4

3.7

4.04

Ash(%)

Xylans(%)

Proteins(%)

Pectines(%)

0.82

3.0 – 7.0

0.5 – 1.0

4.0-8.0

Strong bonding of heavy metal ions by carboxylic (primarily present in

hemicelluloses, pectin and lignin) phenolic (lignin, extractives and pectin) and carbonyl

groups(lignin) often involves complexation and ion exchange [Pejic et al. 2011]. In my

studies I have been shown that unmodified and modified hemp fibers, waste material from

textile industry, have a significant feature that highly recommends their use for the

removal of heavy metals from wastewaters.

2.3.1.2. Batch studies on the removal of heavy metal ions by using natural hemp

fibers

The thick and rigid fibers of hemp (resulting as waste from a textile factory in the

north–east region of Romania) were explored as sorbent for the removal of Cr(III), Cu(II),

Ag(I) , Cd(II), Zn(II), Pb(II) ions from aqueous solutions in batch conditions (Table 2.26).


Table 2.26. Batch sorption experiments

Hemp

purification

Hemp fibers were purified by boiling for 4h in a solution containing

soap and soda ash, followed by washing several times with water,

rinsing with bidistilled water and drying in an oven at 450C.

SEM image of natural hemp

fibers

Chemicals

Stock solutions of the tested cations were prepared through

dissolution of analytical grade reagent Cr(NO3)3⋅9H2O, CuCl2⋅2H2O,

AgNO3, Cd(CH3COO)2⋅2H2O, ZnSO4⋅7H2O and Pb(NO3)2,

respectively. The working solutions were prepared through

appropriate dilutions of the stock solutions.

Sorption

procedure

Samples of about 0.25g of natural hemp were equilibrated with 50

mL of each aqueous solution containing defined amount of metal ions,

for 24 h, with intermittent stirring. The mixture was then filtrated and

the filtrates were analyzed for the final ion concentration. The metal

ion concentration in the filtrate samples was determined by atomic

absorption spectrometry.

Calculation of the

parameters characteristic

to the metal ions sorption

by natural hemp

retention percentage, R (%)= [(C0- C)/C0].100;

retained amount of metal ion, q = [(C0-C)/G,

where C0 is the initial concentration of metal ion (mg/ L),C is the cation

concentration after sorption (mg/ L),V is the volume of solution (L); G

is the weight of hemp(g)

The most significant results of the performed studies are systematized in Table

2.27.


Table 2.27. A review on the results of my batch sorption studies concerning the removal

of heavy metal ions from aqueous solutions by natural hemp fibers

Retained

cations

Type of study

Remarks

References

Cr(III), Cu(II), Ag(I) , Cd(II)

Equilibrium data have been analyzed using the Langmuir and Freundlich isotherm models.

The monolayer sorption capacity is of 367.124, 1157.407, 89.180 and 140.313 mg/g for Cr(III), Cu(II), Ag(I) and Cd(II) ions, respectively.The following relative affinity of cations sorption on natural hemp: Cu(II)>Cr(III)>Cd(II)>Ag(I) has been established

[Tofan and Paduraru 2000; Paduraru and Tofan 2002]

Cd(II), Cu(II), Cr(III)

Thermodynamic parameters, free energy change (∆G), enthalpy change(∆H) and entropy change (∆S) have been calculated.

The retention of Cr(III) ions on natural hemp is a process of endothermic chemisorption. In the hemp – alizarine S – Cr(III) sorption system the physical interactions play a major role. The process of Cu(II) sorption by hemp and bleached hemp loaded with α- benzoinoxime is feasible spontaneous and of endothermic nature.

[Tofan et al. 2010a]

Zn(II) The effect of experimental factors was studied in batch conditions. Equilibrium (Langmuir and Freundlich isotherm), kinetics and thermodynamics of the considered sorption processes were discussed.

The Langmuir maximum sorption capacities were determined as being of 0.2545, 0.3238 and 0.3754 mmol/g at 5

0C, 20

0C and 50

0C. The

constant of the pseudo first sorption rate, k‘, determined by means of Lagergren equation is 6.678x10

-3

min-1

. The values obtained for the thermodynamic parameters point out the spontaneous and endothermic nature of the Zn (II) sorption process, favoured by temperature increasing.

[Paduraru and Tofan 2008]

Pb(II) Equilibrium, kinetic and thermodynamic studies

The highest Pb(II) retention is reaching at pH=5 from unbuffered solutions. The pseudo – first order equation is better obeyed than the kinetic pseudo – second order.

[Tofan et al. 2010b; Tofan et al. 2010c]

As can be seen from Table 2.27, the batch sorption capacity of natural hemp is

significant and comparable, so that the hemp can be considered as a valuable alternative

for use in the treatment of industrial effluents.

2.3.1.3. Hemp fibers with improved performances in batch sorption systems

Taking into account the fact that the efficiency of natural and waste materials in

heavy metal ions retention is strongly dependent on their capacity to form chelates, it has

been imposed the need to increase the affinity of these cellulosic materials towards

metallic cations.


As the main constituent of the hemp is cellulose, whose functional groups can be

physically and chemically modified, I tried the improvement of the waste material

analytical performances in the concentration and separation of Cr(III), Cu(II), Ag(II) and

Cd(II) by achievement of new fibrous sorbents with loaded and grafted functional

groups( Table 2.28).

Table 2.28. A review on the results of my sorption studies concerning the removal of

heavy metal ions from aqueous solutions by modified hemp fibers

Type of hemp Retained

cations

Type of study

Remarks

References

Natural hemp and hypochlorite bleached hemp fibers physically modified with α- benzoinoxime

Cu(II) Equilibrium and thermodynamic studies

The analytical potential of natural and bleached hemp fibers in batch retention of Cu(II) has been significantly improved by impregnation with α- benzoinoxime.

[Tofan and Paduraru 1999; Tofan et al. 2001a]

Hemp fibers impregnated with alizarin S

Cr(III) From a potential practical use, the influence of pH, contact time, metal ion concentration and temperature has been studied in batch conditions

An increase in solution temperature tends to reduce the maximum Cr(III) sorption capacity of hemp impregnated with alizarin S from 8.632mg/g at 4

0C to 4.726mg/g at

400C

[Tofan et al.2001b]

Sulphydryl hemp fibers

Ag(I), Cd(II), Pb(II)

Sorption characteristics and kinetic properties of the chemically modified hemp fibers have been investigated.

The monolayer sorption capacity of chemically modified hemp is 10.75, 14.05 and 23.00 mg/g for silver, cadmium and lead ions, respectively, at 18

0C.

[Tofan and Paduraru 2004]

2.3.1.3.1. Sorbents based on impregnated hemp

In order to obtain fibrous sorbents with improved selectivity for Cu(II) and Cr(III)

ions, the hemp was pretreated with α- benzoinoxime and - alizarin S, respectively(Figure

2.26).


Natural and hypochlorite

bleached hemp fibers

Methanol solutions of -α- benzoinoxime; - alizarin S

Equilibration for 24 hours with intermittent stirring

Filtration and washing until the the complete elimination of the reagent solution excess

Filtrate was analysed to evaluate the unretained amount of chelating reagent

Drying until constant weigh

Physically modified hemp fibers

α- benzoinoxime impregnated hemp

alizarin S impregnated hemp

Figure 2.26. Scheme of hemp loading

The choice of α- benzoinoxime and alizarin S as modifier agents for hemp fibers

was based on the major role of chelating reagent in the selective retention of trace

pollutants on natural polymeric substrates.

Some unconvetional sorbents obtained by loading of natural and hypochlorite

bleached hemp fibers with α- benzoinoxime can be efficiently used as selective materials

for Cu(II) ions [Tofan and Paduraru 1999; Tofan et al. 2001a]. Although both materials


possess important sorptive properties, there is significant differences between Cu(II)

sorption capacity of hemp - α- benzoinoxime(13.8072mg/g) and bleached hemp fibers

impregnated with the same organic reagent(8.0378 mg/g)[Tofan and Paduraru 1999;

Tofan et al. 2001a]. The decreased sorption capacity of the bleached hemp fibers loaded

with α- benzoinoxime may be considered as an effect of the hypochloride oxidation on

hemp fibers.

The feasibility of the chromium (III) enrichment capability of the natural hemp was

ascertained by its impregnation with alizarin S. The effect of most significant process

parameters (pH, contact time, initial concentration of Cr(III) and temperature) on the

sorption equilibrium was studied by batch method [Tofan et al 2001b].The study of the

medium acidity influence revealed that the maximum Cr(III) removal by its sorption on

alizarin S pretreated hemp occurred at pH 5.8. On the basis of the obtained results it was

assumed that the sorption takes place by the formation of a 1:1 chrome (III): alizarin S

complex in the impregnated hemp phase. It was shown that the pseudo–second order

model could best describe the sorption kinetics.The Langmuir and Freundlich, model

isotherms were used to elucidate the observed Cr (III) sorption phenomena. As it was

expected, alizarin–S impregnated hemp exhibited higher Cr(III) sorption capacity (6.340

mg/g impregnated hemp) than the natural hemp fibers (4.006mg/g). The obtained values

of the isothermal thermodynamic parameters showed that the Cr (III) sorption is an

exothermic process of physical nature [Tofan et al.2001b].

2.3.1.3.2. Sulphydryl hemp fibers

From the data presented in literature according to which the sulfur ligands are

more selective towards heavy metals than their analogues with nitrogen and oxygen, I

tried the improvement of the waste hemp fibers performances by their chemical

modification with β – mercaptopropionic acid and acetic anhydride ( Figure 2.27).


Figure 2.27. Scheme of sulphydryl hemp fibers preparation [Tofan and Paduraru

2004].

Although by introducing sulphydyl functional groups into hemp fibers a

considerable change in the cellulosic fibrous material was made, their fundamental

physical – chemical properties were unaffected( Figure 2.28).

(a)

(b)

Figure 2.28. SEM images of a) natural hemp fibers; b) natural hemp fibers

functionalized with β – mercaptopropionic acid


The sorption and kinetic properties of the material prepared by introducing

sulphydyl( - SH) functional groups into hemp fibers in the batch retention of Ag(I), Cd(II)

and Pb(II) ions have been reported [Tofan and Paduraru 2004]. The results of this

systematic study are recorded in Table 2.29.

Table 2.29. Quantitative description of the batch sorption systems based on hemp - SH

Sorption system Langmuir

constants

Freundlich

constants

Sorption rate

constant(min-1)

q0(mmol/g) KL KF n

Hemp – SH – Ag(I) pH =5.10

0.100 8.648 2.30 4.68 5.806x10-2

Hemp – SH – Cd(II) pH = 5.75

0.125 7.547 2.37 7.76 1.632x10-2

Hemp – SH – Pb(II) pH=3.03

0.111 4.687 2.34 1.71 4.078x10-2

According to Table 2.29, the systems under study offer some new attractive

possibilities of selective sorption of various pollutants from aqueous effluents.

2.3.1.3.3. Concentration of cadmium(II) trace amounts from large volumes of

aqueous samples on chemically modified hemp fibers [Tofan et al.2009]

In order to emphasize the practical usefulness of the sulphydryl hemp fibers, the

concentration of trace amounts of cadmium(II) from large amounts of aqueous solutions

have been carried out. The

desorption studies were also

performed to see the desorption

of cadmium from the point of view

of its recycling/safe disposal( with

or without treatment)(Figure 2.29)

Figure 2.29. Scheme of Cd(II)

sorption – desorption in batch

conditions


The results of these experiments are listed in Table 2.29. It must be noticed that

the values of the concentration factor in Table 2.29 were calculated by means of the

following equation [Tofan et al.2009]:

Concentration factor = ksample

samplek

Vq

Vq

where qk and qsample are the absolute amounts of Cd(II) in concentrate and sample,

respectively; Vk is the volume of the concentrate; Vsample is the volume of the sample.

The batch experiments were conducted in replicates (n=4) and the data listed in

Table 2.30 represents the mean value. Furthemore, the following statistical parameters

have been calculated [Tofan et al.2009]:

X = n

xxxx n.....321 the arithmetic mean

1

1

2

2

n

xX

s

n

i

i

the selection variance

n

xX

s

n

i

i

1

2

the mean square deviation

n

ss

x the mean square deviation of the selection mean

E%=X

sx

100 the relative error

n

stX

the confidence interval ( t is Student coefficient(95%) = 3.18

The obtained values for these statistical parameters are given in Table 2.31.

Table 2.30. Concentration of Cd(II) in traces by hemp – SH(Vk = 25 mL)

Experiment Vsample,

mL Initial

amount of Cd(II),

μg

Cd(II)

μg/mL

Cd(II) found

μg/mL

Concentration factor

Remarks

1. 200 112 0.560 88.1 6.29 Desorption with HNO3 2M

2. 200 112 0.560 109.4 7.81 Calcinining SH-

3. 500 112 0.224 96.8 17.29 hemp and dissolution of the

4. 1000 112 0.112 87.7 30.27 obtained residue with HCl 1:1


Table 2.31. Statistical analysis

Experiment s2

s x

s E% Confidence interval

1. 0.0300 0.1732 0.0866 1.37 6.29∓ 0.2753

2. 0.0300 0.0550 0.0275 0.35 7.81 ∓ 0.0875

3. 0.6819 0.8257 0.4128 2.38 17.29∓ 2.6250

4. 0.5679 0.7535 0.3767 1.24 30.27∓ 1.1979

The data from Table 2.30 and Table 2.31 show that by optimizing experimental

factors and errors minimization, the use of sulphydryl hemp fibers can lead to the

decrease of the cadmium concentration from large volumes of wastewaters below

allowable discharge limits. As can be seen from Table 2.30, the achieved values of the

cadmium concentration factors ranged between 6.29 and 30.27. The loaded cadmium

was subsequently desorbed with HNO3 2M, when a desorption of 78.66% was attained.

However, an almost quantitative recovery of the sorbed cadmium(II)(97.67%) was

possible by calcining Cd loaded sulphydryl hemp fibers at 8000C and dissolution of the

obtained residues with HCl 1:1.


The batch sorption of six toxic and polluting metal ions, viz. Cr(III), Cu(II), Ag(I),

Cd(II), Zn(II) and Pb(II) has been studied. The results of batch studies pointed out that the

sorption of the tested cations on natural hemp fibers is very well described by the

Langmuir isotherm model and follows a pseudo–second order kinetics. In order to improve

the sorption performances of this material, the hemp fibers have been physically and

chemically modified. By using sulphydryl hemp fibers the concentration of Cd(II) in

wastewaters might be reduced below allowable discharge limits. The recovered cadmium

was greater than 95% and cadmium concentration factors over 30 have been achieved.

The results of the performed studies strongly suggest that natural and modified

hemp fibers may be promising sorbents provided for environmental technologies in the

future. However, the possibility to use hemp fibers as an alternative in the heavy metal

ions wastewater treatment should be studied under pilot scale applications so as

complete the studies concerning the removal efficiencies with technical and economic

factors that influence process scale-up.


2.3.2.Waste of rapeseed from biodiesel production as appropiate sorbent for

Cu(II), Cd(II) and Zn(II) ions

2.3.2.1. Background Some studies have demonstrated that seed press cakes can be used to remove

toxic pollutants. Examples include sorption of copper by mustard oil seed cake [Ajmal et

al. 2005], methylene blue sorption by oil palm fiber [Tan et al.2007] and sunflower oil cake

[Karagoz et al. 2008], biosorption of pesticides in cold-pressed rapessed, moringa and

soybean cakes [Boucher et al.2007] and removal of cadmium and chromium by Jatropha

oil cake [Garg et al. 2008]. Another study has emphasized the feasibility of employing

degreased coffee beans for adsorption of metal ions, including copper(II), zinc(II), lead(II),

iron(III), and cadmium(II) [Kaikake et al.2007]. However, the successful application of

seed press cakes at industrial scale for the removal of heavy metals from wastewater

needs to be fundamented on laboratory work and pilot scale applications.

Rapeseed (Brassica napus) is a bright yellow flowering member of the mustard

family. It has greatly improved its competitive position in the world, being actually a major

crop in many countries, including Romania [Bassam 2010]. The seeds of this plant, with

very high level of oil, are one of the principal components of the crop. They can be ground

into nutritional meals used in animal fodder, or pressed for the oil, which can be used for

human food or in the production of biodiesel [Bassam 2010]. At present there are few

studies regarding the potential treatment of wastewaters containing heavy metal ions by

sorption on rapeseed [Al-Aseh and Duvnyak 1999; Nemeth et al. 2011; Stefusova et al.

2012; Amouei 2013]. The findings of these studies strongly suggested that the waste of

rapeseed could be efficiently used in the removal of heavy metals from wastewaters with

low contents in Cu(II), Cd(II) or Pb(II).

In view of the aforementioned, the aim of my studies was to use the rapeseed

waste from biodiesel production as a sorbent for the removal of copper(II), cadmium(II)

and zinc(II) ions from aqueous systems in order to find alternative applications for this

low-cost biomaterial and thus increase its added value. (Figure 2.30.).


Figure 2.30.

Scheme of the batch

procedure performed

for Cu(II), Cd(II) and

Zn(II) ions sorption by

rapeseed waste

The evaluation

of rapeseed waste as

biosorbent was done

after running batch

experiments for the

effect of initial pH,

sorbent dose metal ion concentration, contact time and temperature (Table 2.32).

Langmuir and Freundlich's isotherm equations were applied to the experimental data.

Mathematical models were used to investigate the sorption kinetics in batch systems. The

rapeseed was characterized before and after the metal sorption processes. The thermal

stability of the rapeseed before and after Zn(II) biosorption was studied by

thermogravimetric analysis.

Table 2.32. Sorption experimental conditions

Studied influence

Tested cations

Initial pH

Rapeseed dose (g/ L)

Metal ion concentration

(mg/ L)

Temperature (0C)

Contact time

(hours)

Effect of initial pH of solution

Cu(II) Cd(II) Zn(II)

1-5 1-5 1-6

10 10 10

92.48 90.44

72; 119

20 20 25

24 24 24

Effect of rapeseed dose


4.5-5 4.5-5 4.5-5

5-30 5-30 5- 30

69.36 90.44

72; 119

20 20 25

24 24 24

Effect of initial concentration


4.5-5 4.5-5 4.5-5

10 10 10

21.38-231 22.61-271 24 – 191

20 20 25

24 24 24


Cu(II) Cd(II)

4.5-5 4.5-5

10 10

23.12-138.72 22.61-135.66

4; 20; 60 4; 20; 60

24 24

Effect of contact time


4.5-5 4.5-5 4.5-5

10 10 10

92.48 90.44

48; 119

18 18 25

0.50-24 0.50-24 0.50-24


2.3.2.2. Rapeseed characterization

The chemical composition of the rapeseed waste under study was determined by

conventional methods [Budoi 2000]. The following relevant results have been obtained:

nitrogen 3.61%, crude proteine 22.57 %, fat 48.19 %, and ash 4.65 % [Tofan et al. 2011].

The pHzpc ( zero point of charge ) value of rapeseed has been determined as being 5

[Paduraru, Tofan et al. 2015].

FTIR spectroscopy was applied to identify the functional groups of rapeseed

responsible for metal adsorption [Tofan et al. 2011; Paduraru, Tofan et al. 2015]. To

reveal the systematic changes in the spectral features upon reaction with metal ions, FTIR

spectra were obtained for the sample before and after reacting with Cu(II) and Cd(II), as

presented in Figure 2.31.

A comparison between these spectra shows that the intensity and position of peaks

assigned to carboxyl, -NH and -OH groups from rapeseed were either minimized or

slightly shifted after sorption of Cu(II) and Cd(II) ions (Table 2.33.). These changes can be

attributed to electrostatic interactions between functional groups in the rapeseed structure

and the metallic cations, confirming the chemical nature of the sorption of Cu(II) and

Cd(II).

Figure 2.31. IR-spectra for (1) rapeseed, (2) rapeseed-Cu(II), and (3) rapeseed-Cd(II)

systems[Tofan et al. 2011]

4000 3000 2000 1000Wavenumber (cm-1)

3358

3009

2926

2855

2345 2170

1746

1656

15441517

14551402

134013151302

1139 1096 1056

866 831 781

665608

3422

30333008

2925

2855

2170

1746

1655

1543 14581390

1315

1240

11621095

853

722671

530

3413

3007

2926

2855

2366

2170

1746

1655

1542 14571402

1318

12381162 1102

807 780722

613

531469

1

2

3


Table 2.33. The main FTIR spectral characteristics of rapeseed before and after sorption of Cu(II) and Cd(II)

Transmission band (cm-1

) Assignment Before

adsorption After

adsorption Cu(II)

After adsorption

Cd(II)

3358

3413

3424

Strong band indicates the presence of –OH and –NH groups

2855 2855 2855 Aliphatic C-H group

1656

1655

1655

Double bands of carboxylic group

1456 1457 1458 Aromatic groups

1056 1110 1095 Assigned to alcoholic group

The morphological structure of rapessed and Zn(II)- rapessed was studied by

scanning electron microscopy, SEM (Scanning Electron Microscope type Quanta 200,

operating at 20 kV with secondary electrons) [Paduraru, Tofan et al. 2015]. Figure 2.32

shows the images of rapessed (a) and rapessed loaded with Zn(II) ions (b). The SEM

images clearly show the morphological changes occurring on the surface of the rapessed

after the treatment with a solution containing Zn (II) ions.

a) b)

Figure 2.32. SEM images of: (a) rapessed, (b) rapessed loaded with Zn(II) ions[Paduraru,

Tofan et al. 2015]

Furthermore, the EDX analysis was performed to highlight the zinc ion. The

elemental composition from the peak areas is calculated and it is as follows: oxygen-

23,95%; carbon- 67,61%; nitrogen- 2,84%; zinc- 4,52%. [Paduraru, Tofan et al. 2015]

2.3.2.3. Batch studies of Cu(II), Cd(II) and Zn(II) sorption on rapeseed

A series of batch sorption experiments was carried out to determine the effect of


(i) initial solution pH; (ii) sorbent dose; (iii) metal ion concentration (fitting to Langmuir and

Freundlich equations); (iiii) contact time (kinetics fitted to linear pseudo-first, -second order

equations) on the retention of copper(II), cadmium(II) and zinc(II) ions from aqueous

effluents by rapeseed waste. The obtained results can be briefly described as follows:

Effect of initial pH

The optimum value of initial pH for Cu(II), Cd(II) and Zn(II) sorption on rapeseed

was found to be 4.5 to 5 (Table 2.34).

Table 2.34. The influence of initial pH on the retention of the heavy metal ions under study by rapeseed waste

(●)Cu(II) and Cd(II) (■) [Tofan et al. 2011]

Zn(II) (C0= 72mg/L(), C0= 119mg/L(▲)

[Paduraru, Tofan et al. 2015]

The effect of pH can be explained in terms of pHzpc (zero point of charge ) of rapeseed which has been determined as being 5. The surface charge of the sorbent is positive when the media pH is below the pHzpc value, while it is negative at a pH over the pHzpc. [Ahmaruzzaman 2011]. On the oher hand, at pH below the pHzpc, the predominant metal species M

2+ are positively

charged. Therefore, it can be considered that the sorption of metal ions on the tested rapeseed in the pH range below pHzpc is H

+ - M

2+ exchange

process.

This finding is confirmed by other literature data that proposed the ion exchange as predominant mechanism of heavy metals sorption at pH<5[Michalak et al. 2013]. With an increase in pH above pHzpc, the surface of the sorbent is negatively charged and the sorption still increases as long as the metal species are still positively charged, due to electrostatic attraction[Ahmaruzzaman 2011].

Effect of sorbent dose

The percentages of Cu(II), Cd(II) and Zn(II) sorption increased with increasing

rapeseed doses. At a maximal rapeseed dose of 30 g/ L, the values of the retention

percentage exceeded 90%. (Table 2.35)


Table 2.35.The influence of sorbent dose on the retention of the heavy metal ions under study by rapeseed waste


Zn(II) (C0= 72mg/L(), C0= 119mg/L(▲) [Paduraru, Tofan et al. 2015]

Effect of metal ion concentration in initial solutions [Tofan et al. 2011;

Paduraru, Tofan et al. 2015].

The amount of cation retained on rapeseed (q) waste increased with increasing

initial metal ion concentrations(C0), while the Cu(II), Cd(II) and Zn(II) removal efficiency

(R%)decreased ( Table 2.36).

Table 2.36. Influence of initial concentration on Cu(II) Cd(II) and Zn(II) sorption by

rapeseed waste

C0, mg/L q, ( mg/g) R%

Cu(II) Cd(II) Zn(II) Cu(II) Cd(II) Zn(II) Cu(II) Cd(II) Zn(II)

21.38 42.76 69.36 92.48 115

138.72 185 231

22.61 45.22

67 91 113 136

180.88 271

24 48 72 95 119 142 167 191

2.10 3.79 4.46 6.50 7.79 9.76 13.71 17.00

1.89 4.09 6.26 7.64 10.67 12.45 15.27 19.36

2.11 4.27 6.24 8.02

10.78 12.63 14.21 16.78

93.00 90.20 86.20 81.50 78.30 73.24 65.00 59.30

95.79 92.53 90.60 88.11 82.00 76.00 69.00 62.00

90.5 88 86 84 81 78 76 72

Sorption isotherms

The dependence between the equilibrium concentrations of Cu(II), Cd(II) and

Zn(II) in the rapeseed phase(q) and aqueous solution phase(C) was very well described

by Langmuir isotherm model (Table 2.37). The Langmuir model is only limited by the

following four postulates (i) the sorption sites are evenly distributed on the rapeseed

surface, (ii) there is a stoichiometric interaction between one metal ion and one sorption


site, (iii) equilibrium leads to the formation of a monolayer, and (iiii) sorption of one metal

ion on one site is independent of the binding state of the surrounding ones. [Saadi et al.

2015]. The Langmuir parameters (q0 and KL)(Table 2.37) are of high importance since

they provide valuable information that could contribute to improving the understanding of

metal uptake mechanisms onto rapeseed.

As can be seen from Table 2.37, the relative sorption affinity of the rapeseed is

higher for cadmium(II) than for copper(II) ions. Langmuir constants increased with

increasing temperature, showing that the sorption capacity and the intensity of sorption

are enhanced at higher temperatures.

Table 2.37. Quantitative description of the batch sorption systems under study on the

basis of Langmuir isotherm model [Tofan et al. 2011; Paduraru, Tofan et al. 2015].

Sorption system

T,K Equation [Langmuir, 1916]

Isotherm parameters q0,

mg/g KL ,

L/mol

Cu(II)-

rapeseed

waste

277

293

333

q0–maximum capacity

of sorption

13.88

15.55

19.52

878

1310

1736

Cd(II)-

rapeseed

waste

277

293

333

q = CK

qCK

L

L

1

0

KL – binding energy

(relative sorption

affinity)

17.53

21.80

25.06

1799

2418

3649

Zn(II)–

rapeseed

waste

297

13.85

2085

Effect of contact time

In the initial stages of the sorption process the amounts of Cu(II), Cd(II) or Zn(II)

retained on rapeseed increased sharply with increasing contact time of the phases,

reaching values that remained then almost constant (Table 2.38)


Table 2.38.The influence of contact time on the sorption of the heavy metal ions under

study by rapeseed waste


Zn(II) (● C0= 48mg/ L; ▲ C0= 119/ mg L) [Paduraru, Tofan et al. 2015]

Explanation

Kinetic modeling

It can be considered that the retention of the tested ions on rapeseed takes place in two distinct steps, a relatively fast phase followed by a slower one. This two-phases sorption may be explained by taken into account the fact that the active sites in a system is a fixed number and each active site can adsorb only one ion in a monolayer, the metal uptake by the sorbent surface will be rapid initially, showing down as the competition for decreasing availability of active sites intensifies by the metal ions remaining in solution [Li et al. 2008]

The pseudo-first-order and pseudo-second-order rate equations were used to test the experimental data. The sorption of Cu(II), Cd(II) and Zn(II) ions on the tested rapeseed follows better the pseudo-second-order kinetic model, which is in agreement with chemisorption being the rate-controlling step [Ho and McKay 1999]. Furthermore, the sorption rate depends on the concentration of Zn(II) ions on the rapeseed surface.

2.3.2.4. Comparison of rapeseed waste with other low- cost sorbents for Cu(II),

Cd(II) and Zn(II) ions removal

The maximum Cu, Cd(II) and Zn(II) sorption capacity of the tested rapeseed (q0)

is compared in Table 2.39 with other low – cost sorbents that were used for the removal

of Cu(II), Cd(II) or Zn(II). It may be noticed that a direct comparison between different

low- cost sorbents is difficult because of inconsistencies in data, principally due to different

experimental conditions (pH, temperature, initial concentration, ionic strength, particle

size, presence of competitive ions etc.) [Nguyen et al. 2013].


Table 2.39. Comparison of maximum sorption capacity of Cu(II), Cd(II) and Zn(II) on

different low-cost sorbents

Low – cost sorbent

Initial pH

Sorbent dose, g/ L

Maximum capacity

of sorption, mg/ g

Reference

Cu(II)

Maize bran 5 20 8.38 [Tofan et al. 2012] Peach stones 5.0 25 10 – 15 [Hansen et al.2010] Chestnut shell 5.0 10 12.56 [Yao et al. 2010] Peanut hulls 5.0 4 13.84 [Oliveira et al.2010]

Rapeseed waste 4.5-5 10 15.43 [ Tofan et al. 2011] Wheat shell 5.0 17.42 [At and Olunbenga

2015] Sour orange waste 5.0 23.47 [ Khormaei et al. 2007] Banana peel 6.0 5 28.57 [ Hossain et al. 2012] Ground pine cone 7.0 6 13.5 [Izanlov and Nasseri

2005]

Pomelo peel 5.0 1 21.83 [Saikaew et al.2009] Rice husk 6.0 2.5 21.28 [Senthil Kumar et

al.2010]

Cd(II)

Rapeseed waste 4.5-5 10 21.72 [ Tofan et al. 2011] Grape stalk waste 5.5 - 27.77 [Villaescisa et al.2006]

Banana peel 8.0 - 35.52 [Memon et al.2008] Olive cake 6.0 - 65.4 [Al-Anber and Matong

2008]

Cattle manure of vermicompost

2 100 2.49 (kaolin wastewater)

20.48 (synthetic solution)

[Jordao et al. 2009]

Zn(II)

Olive oil mill solid residues 5 4 5.63 [Hawari et al. 2009] Dried animal bones 5 4 11.55 [Banat et al., 2000]

Neem bark 5 10 13.29 [ Naiya et al. 2009] Waste of rapeseed 5 10 13.859 [ Paduraru, Tofan et

al. 2015] Rice bran 5 14.17 [Wang et al. 2006]

Tectona grandis L.f. 5 0.1 16.42 [Kumar et al. 2006] Streptoverticillium

cinnamoneum 5.5 2.0 21.3 [Puranik and Paknikar

1997]

It can be seen from Table 2.39 that the heavy metal ions sorption capacity of

rapeseed is significant and comparable, so that the rapeseed waste can be considered as

a valuable alternative for use in the treatment of industrial effluents.

2.3.2.5. Thermogravimetric investigations [Paduraru, Tofan et al., 2015]

In order to highlight the thermal stability of the blank sample (rapeseed) and that of

the Zn(II) ions loaded sample and the degree of Zn(II) removal from aqueous solution, the

thermogravimetric analysis in inert gas atmosphere (nitrogen) has been used. Figure 2.33

shows the TG and DTG curves on weight losses by thermal decomposition performed

with a heating rate of 100C min-1for the rapeseed–Zn(II) and rapeseed samples. The


thermal decomposition behavior of plant biomass frequently is assumed to be

approximated by the sum of the contributions of the respective components. From

chemical point of view, the most samples of plant biomass can be regarded as a mixture

of hemicellulose, cellulose, and lignin (20-40 wt.%, 40-60 wt.%, 10-25 wt.% respectively)

and some minor components [Raveendran et al. 1996; Ramiah 1996; Mc Kendry 2002].

Previous studies showed that the biomass thermal degradation can be divided in several

stages: moisture evolution, hemicellulose decomposition, cellulose decomposition and

lignin decomposition [Raveendran et al. 1996].

The thermal parameters of both samples present three stages of thermal

degradation. In the first stage (up to 120oC) the weight losses are of approximately 4 wt.%

and are due to humidity and release of the bound water molecules. In general, the

humidity of lignocellulosic materials ranged between 4 and 8 wt.%. In the second stage

(200-250oC), the weight losses are higher than 14 wt.% (rapeseed Zn(II) and 18 wt.%

(rapeseed) due to volatile materials (CO2, CH4, CO, H2,). At this stage, was degraded the

hemicellulose and also a part of cellulose which is found in rapeseed waste. In the third

stage, at higher temperatures (300-450 oC), the weight losses are of 47-49 wt.% , and

these can be attributed of the cellulose decomposition and a lignin part much more

thermostable [Mothe and de Miranda 2013]. These findings are based on the results

achieved by thermogravimetric analysis coupled with FT-IR spectrophotometry and mass

spectrometry (TG-FT-IR-MS) that are later presented. By comparing the two samples it is

obvious that the thermal stability is different, the zinc loaded rapeseed exhibits a better

thermal stability than the original rapeseed, presumably due to the cross linking generated

by the intermolecular complexation of the Zn(II) ions. [Volenski and Holan 1995; Michalak

et al. 2013]. The T10 temperatures at which the weight losses are of 10 wt% were 220 oC

and 238 oC for rapeseed and rapeseed–Zn(II), respectively. On the other hand, the T50

temperatures at which the weigh losses are of 50 wt.% were 359 oC for rapeseed and

370oC for rapeseed-Zn(II). The analysis of the residue amount remaining at the

temperature of 550 oC leads to the determination of the amount of retained metal (32.61

%- 30.29 % = 2.32 %). This result is in good agreement with that obtained by batch

sorption studies [Paduraru, Tofan et al. 2015]


Figure 2.33. TG and DTG curves: - rapeseed sample; - rapeseed-Zn(II) sample

The FT-IR and MS spectra of the evolved gases were recorded continuously

during the thermal degradation of the rapeseed sample by TG- FT-IR- MS equipment with

a heating rate of 10oC/min. In Figure 2.34 a, the FT-IR-3D spectrum resulted from the

thermal decomposition of rapeseed, is presented. A good evolution of gases in time and a

correlation with thermal decomposition processes is noticed. From the FT-IR-3D

spectrum, the bi-dimensional spectra at 223 oC and 330oC corresponding to DTG peaks,

were extracted (Figure 2.34 b), and in Figs. 2.34c and 2.34d, the corresponding mass

spectra, are presented. As it can be seen from FT-IR spectrum at 223 oC and the

corresponding MS spectrum, there are few signals with a low intensity, such as: water

(m/z=18) with FT-IR absorption bands at 3587-3600cm-1 and 1500-1600cm-1, methane

(m/z=16) at 3300-3400cm-1. The wide absorption band from 3200cm–1 is a characteristic

of the MCT detector (cooled with liquid-nitrogen) of the TGA-IR external module. Also,

another signal which appear to 2358cm1, belongs to CO2 (m/z=44).

At temperatures over 300°C, more compounds occur due to the thermal

degradation reactions and breaking of the bonds associated with the functional groups of

the cellulose and lignin. The strongest specific signals for the resulted products can be

observed in the FT-IR spectrum from 330oC and the corresponding MS spectrum. Some

absorption bands at 1515cm-1 and 3736cm-1 are registered as a result of rotation-vibration

frequencies of water in the vapor phase (m/z=18). CO2 (m/z=44) presents an adsorption

band of great intensity at 2358 cm-1.

The adsorption bands at 1752 cm-1 and 1164 cm-1 are attributed to νC=O non-ionic

carboxyl groups (–COOH) from carboxylic acids. Also, the presence of an absorption

100 200 300 400 50020

30

40

50

60

70

80

90

100

-6

-4

-2

0

2

Mas

s, %

Temperature, oC

Rapeseed Zn (II)

Rapessed

DT

G,

% /

min


band at 965 cm-1 belongs to ammonium derivative (m/z=16) may be remarked. Also, the

presence of the absorption bands from 2936 and 2880 cm-1 (CH3 asymmetric stretching

vibrations) and 965 cm-1 (CH3 deformation vibrations) belongs to aliphatic fragments

CH4+ (m/z=16), C2H5

+ (m/z=29). The significance of the signals (m/z), was attributed using

the NIST spectral libraries (http://webbook.nist.gov/chemistry/name-ser.html.).

Figure 2.34.. a) - FTIR stacked plot diagrams, b) - 2D FTIR spectra, c) - MS spectrum at

223 oC, d) – MS spectrum at 330 oC of evolved gases at thermal degradation of rapeseed.

In both cases, the thermal decomposition takes place according to some

reassembling kinetic models, in two phases with order n reactions.

http://webbook.nist.gov/chemistry/name-ser.html


2.3.2.6.Fixed bed column studies on the removal of Pb(II) ions by using rapeseed

biomass[Moroșanu, Tofan et al.,2017]

The sorption capacity of the rapeseed biomass was evaluated through batch

experiments, which as a rule, present information about the effectiveness of the sorbent-

metal sorption systems. However, the information obtained from batch studies is not

sufficient for designing a wastewater treatment system for continuous operation. Taking

this fact into account, the dynamic behavior of a fixed bed column filled with rapeseed

biomass was studied in terms of breakthrough curve, which underlies the description of

the column performances. In a fixed bed sorption system, the sorbent situated near the

influent solution saturates first where maximum sorption takes place initially. This sorption

zone moves further as time proceeds and approaches towards the end of the bed. When

the sorption zone reaches the exit of the bed the effluent concentration becomes equally

to the influent concentration [Bhaumick et al. 2013] A plot of effluent concentration as a

function of time or volume of solution processed is known as breakthrough curve.The

shape of brekthrough curves is a very important feature for the evaluation of the operation

and the dynamic response of a sorption column.

The experimental breakthrough data were processed using the Thomas and Yoon-

Nelson models

The Thomas solution is one of the most general and widely used model in column

performance theory. This model is based on the assumption of Langmuir's kinetics of

adsorption–desorption, without axial dispersion. Its main hypothesis is that the rate driving

force obeys second–order reversible reaction kinetics [Thomas, 1948].

The following linearized form of Thomas equation has been used in my studies

[Al–Ghouti et al.2007]:

ln

F

CK

F

mqK1

C

C 0TT0T

t

0 V

where C0 is the initial metal ion concentration (mg/L); Ct is the equilibrium concentration

(mg/L) at time t (min); kT is the Thomas constant (L/min∙mg); F is the volumetric flow rate

(L/min); q0(T) is the maximum column capacity (mg/g), determined by the Thomas model;

m is mass of sorbent (g) and V is the volume (L).

Yoon and Nelson have proposed a less complicated model based on the

assumption that the rate of decrease in the probability of sorption for each sorbate

molecule is proportional to the probability of sorbate breakthrough on the sorbent [Yoon

and Nelson 1984]. The linear form of the Yoon–Nelson model used in my studies is

represented as follows [Sivakumar and Palamisamy 2009]


YNYNt0

t ktkCC

Cln

where Ct is effluent concentration at time

t (mg/L); C0 is metal ion initial concentration(mg/L); kYN is Yoon–Nelson rate constant (min-

1) ; τ is time required for 50% sorbate breakthrough; t is sampling time (min). A plot of ln

0t

t

CC

C versus t gives a straight line with a slope of kYN and intercept of - τ ∙ kYN

According to the Yoon–Nelson model, the amount of metal ion sorbed in a fixed bed

is half of the total metal ion entering the adsorption bed within 2τ period [Gupta et al.

2000]. In this context, for a given bed, the column sorption capacity in the Yoon–Nelson

model, q0(YN) can be computed with the following equation:

m1000

rC

m

2x1000/rC2

1

m

qq 0

0total

Yn0

where C0 is the initial concentration (mg/L); r is flow rate (mL/min) ; m is weight of sorbent

(g) and τ is time required for 50% sorbate breakthrough. Fixed bed column studies on the

removal of Pb(II) ions by using rapeseed biomass were performed according to the

procedure presented in Table 2.40.

Table 2. 40. Dynamic sorption experiments

Rapeseed preparation

The rapeseed was washed several times with Grade I water (Adrona Crystal E), dried at 40

0C for 24 h and crushed to obtain particle sizes

between 0.1 and 0.2 mm

Chemicals Stock solution of 1000 mg/ L were prepared through dissolution of analytical grade reagent Pb(NO3)2 in deionised water(Adrona Crystal E, Grade I) The actual Pb (II) solutions for testing were prepared through appropriate dilutions of the stock solution.

Dynamic sorption studies

The dynamic studies were carried out in a flow glass column of 1.5 cm inner diameter and 15 cm in length. A 0.7 g of rapeseed was mixed with a commercially available resin (Purolite MN200) in a ratio 1:2 to avoid column clogging. To ensure that no adsorption phenomena occurs on the used polymer, tests with Pb(II) solutions (50 and 100 mg/L) were done. There was no significant change in lead concentration after the experiments.Therefore, the mentioned resin can be considered an inert material for the studied process. The bed height of the mixture rapeseed/resin achieved was 6 cm. A layer of wadding glass was fitted at the bottom of the column to support the sorbent during studies. The influent feed flow was established at 2.5 mL/min.The initial Pb(II) concentrations in test solutions were 50 and 100 mg/L.The working temperature was 20

0C.

The initial pH of the solution was around 5.2 and it wasn‘t controlled during the experiment. Effluent samples were collected at the bottom of the column at certain time intervals and analysed for Pb(II) ions content.

Dynamic experiments with industrial wastewater

The wastewater sample was obtained from a factory located near Iasi, Romania. A volume of 200 mL of industrial effluent was treated through the column at a bed height of 6 cm and a flow rate of 2.5 mL/min. The physico-chemical characteristics of the wastewater used in the experiment were analysed before and after the column by standard methods and the concentration of lead ions was determined by spectroscopy


The results for the sorption of Pb(II) in a fixed bed column filled with rapeseed

biomass are systematized in Table 2.41.

Table 2.41. Description of the Pb(III)- rapeseed biomass dynamic sorption system

Breakthrough curves

Experimental parameters of the breakthrough curves

C0 (mg/L) tb (min) Vb (L) ts (min) Vs (L) qt (mg/g)

50 100.78 0.25 188.48 0.47 20.37

100 89.91 0.22 181.63 0.45 40.04

C0 (mg/L) – influent concentration, tb (min)– breakthrough time (Ct/C0 = 0.1), Vb (L) – breakthrough volume, ts (min) – saturation time (Ct/C0 = 0.9), Vs (L) – saturation volume, qdyn (mg/g) - total dynamic uptake capacity.

Thomas and Yoon – Nelson parameters

C0,

mg/L

Thomas model model Yoon- Nelson model

KT 10-3,

L/min/mg

q0(T),

mg/g

R2 kYN,

1/min

τ, min q0(YN),

mg/g

R2

50 1.55 23.98 0.930 0.0367 197.47 35.17 0.916

100 0.58 48.81 0.947 0.0479 143.11 51.11 0.927

As depicted in Table 2.41, the breakthrough curve obtained for Pb(II) biosorption

on rapeseed has a characteristic ―S‖ shape and is dependent on the inlet concentration.

At lower lead concentration, the curve is more lengthened and the breakthrough point

occurs later. This behaviour can be explained by the fact that at higher initial

concentration the active sorption sites are more rapidly covered by the metal ions.

The experimental breakthrough data are verified by both Thomas and Yoon-

Nelson models (Table 2.40). The time required to accomplish 50% retention in Table 2.41

decreases with the inlet Pb(II) concentration of tested solutions, implying a faster column

saturation at higher concentration.Thomas model, as well as Yoon-Nelson model, has

given sorption capacities which are higher than the one provided by Langmuir equation,

i.e. 21.29 mg/g at room temperature[Moroșanu, Tofan et al.,2016].

The physical-chemical characteristics of the industrial wastewater before and after

column treatment are presented in Table 2.42. After 200 mL of the water has passed


through the rapeseed/resin packed column, the content of Pb(II) was reduced with over

94%. This fact clearly indicates the affinity of rapeseed biomass for lead ions even in the

presence of other compounds. In addition, the other quality indicators considered in this

experiment, like chemical oxygen demand (COD), total suspended solids (TSS), chloride

and water hardness showed a significant improvement (Table 2.42). In conclusion, these

results reflect the ability of rapeseed to remove Pb(II) ions and organic compounds from

real wastewater.

Table 2.42. Treated water characteristics

Quality indicator Treated water R%

pH 7.01 9.89%

TSS (mg/L) 48 30.43%

COD (mg/L) 256 50.35%

Pb2+ (mg/L) 0.27 94.47%

Cl- (mg/L) 124 17.33%

Total hardness (°G) 3.52 71.61%

*Calculated as R (%)= (Cinitial – Cfinal)*100/Cinitial


The results of the works give the evidence of the possible benefits of using the

rapeseed waste from biodiesel production for the removal of heavy metals from aqueous

media. The rapeseed, in the batch experiments, was found to be very efficient in removing

copper, cadmium or zinc ions from aqueous solutions. The process is strongly affected by

several parameters such as: initial pH of the solution, sorbent dose, initial metal ion

concentration and contact time. The thermal stability of the rapeseed before and after

Zn(II) biosorption was studied by thermogravimetric analysis. It was found that the zinc

loaded rapeseed exhibits a better initial thermal stability than the original rapeseed,

presumably due to the cross linking generated by the intermolecular complexation of

Zn(II) ions. The amount of retained metal determined on the basis of the residue amount

remaining at the temperature of 550oC was in good agreement with that obtained by batch

sorption studies. Pb(II) sorption capacity for 50 mg/L and 100 mg/L feed concentration of

lead ions were higher than the batch conditions for the same initial concentrations,

indicating the prefference of the biosorbent to column mode operation. Column studies

with real industrial wastewater presented a removal efficiency of 94.47% for Pb(II) and a


general improvement of the other quality indicators from the effluent showed the practical

utility of the biosorbent.

Further work needs to be performed in order to establish the optimum conditions

(technical and economical) for applying such a process to municipal/industrial

wastewaters.

2.3.3. Sorption removal of Cu(II), Zn(II) and Cd(II) ions from aqueous effluents

by Romanian bark wastes

2.3.3.1. Background

Tree bark is a low–value wood by–product of sawmills and paper mills, which is a

readily available and renewable resource, amounting to about 7% of a total weight of a

tree and 12% of the total volume of tree [Durat et al. 2013].

Statistics on bark production are scarce, and the production is usually estimated

indirectly from total round wood production. In 2008, about 1.542 million m3 of round

woods were produced worldwide that generated approximately 200 million m3 of bark

[FAO 2011].

Currently wood bark is disposed via burning or waste disposal, generating

atmospheric pollutants harmful to the environment and to human health [Zhang et al.

2015].

In recent years, there has been a renewed interest in biomass utilization as a raw

material for production of chemicals, materials and energy, and studies have been

developed focusing on the concept of biorefineries, i.e., to use biomass more efficiently by

extracting valuable chemicals and materials [Tuck et al. 2012]. Under this biorefineries

concept, the main utilization possibilities of bark are [Sen et al. 2015]:

o energy generation by incineration or other thermochemical processes (such as

charcoal production or pyrolysis);

o composting;

o materials production using either the whole bark or only fractions (e.g. cork and

fibers);

o chemicals production by extraction of soluble materials or by chemical

modification;

o adsorption resin from a biological origin for the removal of pollutants.

Many studies have shown that bark of different Pinus species (Pinus brutia; Pinus

densiflora; Pinus pinaster; Pinus ponderosa; Pinus sylvestris; Pinus strobus; Pinus

thunberghii) has great potential for the removal of toxic metal ions [Pb(II); Cr(VI); Cr(III),


Cd(II); Cu(II); Zn(II); Ni(II)] and organic pollutants (17β-estradiol; phenol; 2,4,6–

trinitrotoluene) and consequently, it can be used as a substitute for commercial sorbents

such as active carbon [Gundogdu et al.2009; Ozdes et al. 2014; Seki et al. 1997; Kumar

2006; Braga et al.2011; Vasquez et al.2006; Oh and Tshabalala 2007; Nehrenheim et al.

2011; Martin – Dupont et al. 2006].

Pinus sylvestris L. (Pinaceae, Scots Pine) is a coniferous species that is widely

spread across Europe and Asia. In Romania it grows naturally in the Carpathian

Mountains, but it is also planted due to its economic importance. Pinus sylvestris L. bark is

rich in polyphenols, particularly condensed tannins (procyanidins) [Karonen et al. 2004].

Procyanidins are pentahydroxyflavan oligomers and polymers. These molecules bear

ortho-dihydroxy phenolic groups that are able to chelate metal ions, leading to stable

complexes [Chin et al. 2009].Despite the large amounts of pine bark wastes generated in

Romania from the industrial processing of pine wood, no studies on the sorption

capabilities of Romanian pine bark have been carried out. The aim of my work was to

investigate the possibility of conversion of pine bark residues into a low-cost sorbent for

removal of Cu(II), Zn(II) and Cd(II) ions from aqueous solutions.

The silver fir tree (Abies alba Mill.) is a coniferous species in the family of

Pinaceae that is widely spread across Europe. In Romania it grows naturally in the

Carpathian Mountains, but it is also planted due to its economic, environmental and social

importance. The silver fir tree occupies 5% of the Romanian forest area, being the second

coniferous tree, as percentage, after spruce. The wood of mature Abies alba Mill tree is

used as raw material in furniture industry or as building material. The main waste from the

industrial processing of the wood of mature silver fir trees is the bark. The possible

therapeutic applications of Romanian Abies alba bark waste and its antioxidant potential

have been emphasized (Vasincu et al.2013). The performed studies proposes another

way of Romanian Abies alba bark waste valorization, with the scope of providing a low –

cost sorbent, with good performances in the removal of Cu(II) and Cd(II) from

wastewaters.

The batch studies undertaken (Table 2.43) include an evaluation of the effects of

various process parameters such as pH, initial metal ion concentration, sorbent dosage,

contact time and temperature. The kinetic models, equilibrium isotherm models and

thermodynamic parameters related with the process were performed.


Table 2.43. A brief description of the experimental part

Plant material

Patches of Pinus sylvestris L. bark were collected in the Calimani Mountains

(Romania) in February 2008. A full-grown tree was randomly selected for collection.

The species was identified and authenticated by specialists from Botanical Garden,

Iasi, Romania. The bark was shade-dried at room temperature for two weeks and

powdered in a knife mill. A voucher sample was deposited in the Department of

Pharmacognosy, Faculty of Pharmacy, ―Gr. T. Popa‖ University of Medicine and

Pharmacy, Iasi, Romania. Before use, the natural material was washed with

deionized water several times and then dried at 40 °C for 24 h.

Patches of Abies alba Mill bark were collected in the Calimani Mountains

(Romania). A full-grown tree was randomly selected for collection. The species was

identified and authenticated by specialists from Botanical Garden, Iasi, Romania. The

bark was shade-dried at room temperature for two weeks and powdered in a knife

mill. A voucher sample was deposited in the Department of Pharmacognosy, Faculty

of Pharmacy, ―Gr.T. Popa‖ University of Medicine and Pharmacy, Iasi, Romania.

Before use, the natural material was washed with deionized water several times and

then dried at 40 °C for 24 h.

Chemicals

Stock solutions of 1202 mg/ L, 1000 mg/ L and 1130 mg/L were prepared by

dissolution of analytical grade reagents CuSO4‧5H2O, ZnSO4‧7H2O and

CdSO4‧8H2O, respectively in deionized water and were complexonometrically

standardized. Working solutions of Cu(II), Zn(II) and Cd(II) ions were prepared by the

appropriate dilutions of the stock solutions

Sorption

procedure

(batch

conditions)

Contact between sample of ca. 0.3g bark and 50 mL sample of aqueous solution

containing defined amounts of metal ion for a determined time→ removal of bark

from the aqueous solutions by centrifugation→ determination of the final metal ion

concentration in filtrate [Cu(II) and Zn(II) by atomic absorption spectrometry; Cd(II)-

by spectrofotometric method with xylenol orange (λ=580 nm) or by atomic absorption

spectrometry]→calculation of the parameters characteristic to the metal ions sorption

by bark [retention percentage, R (%)= [(C0- C)/C0].100; retained amount of metal ion,

q = [(C0-C)/G], where C0 is the initial concentration of metal ion (mg/ L), C is the

cation concentration after sorption (mg/ L), V is the volume of solution (L); and G is

the weight of bark (g)]


2.3.3.2. Romanian pine bark as low cost sorbent for Cu(II), Zn(II) and Cd(II) from aquous effluents

2.3.3.2.1. Characterization of the pine bark under investigation [Amalinei, Tofan et al.

2012]

Previous studies showed that the major chemical components of raw pine bark

are cellulose and lignin [Argun et al. 2009]. Pine bark proved to be a material of very low

porosity, low specific surface area, and strong carbon aromatic content, probably due to

its content of polyphenols and lignin [Bras et al. 2005].

IR spectra of the pine bark under investigation before and after Cu(II) and Zn(II)

ion sorption are given in Figure 2.35. The broad and strong band ranging from 3000 to

3600 cm-1 indicates the presence of –OH and –NH groups, which is consistent with the

peaks at 1035 and 1159 cm-1 assigned to alcoholic C-O and C-N stretching vibration. The

peaks observed near 2921 cm-1 can be assigned to C-H group. Bands near 1614 and

1635 cm-1 are indicative of carboxyl groups (C=O). The IR spectra indicate that the

carbons possess different surface structure (aliphatic, aromatic, cyclic), as one observe

the bands at 1447 cm-1 and over the 1371 to 1276 cm-1 range [Gundogdu et al. 2009].

Figure 2.35. IR-spectra for 1-pine bark; 2-pine bark-Cu(II) ions; 3-pine bark-Zn(II) ions

[ Amalinei, Tofan et al., 2012]

4000 3000 2000 1000Wavenumber (cm-1)

457.11523.65

560.3587.3620.09

670.24692.42

780.18818.75

883.37

1035.741058.88

1107.11157.25

1279.72

1371.34

1447.531515.03

1614.36

1737.8

2169.84

2360.79

2851.65

2921.09

3411.95

1

2

3


2.3.3.2.2. Assessment of kinetic, equilibrium and thermodynamic parameters of

Cu(II), Zn(II) and Cd(II) sorption on Romanian pine bark

The sorption characteristics of tested heavy metal ions on the pine bark was

investigated with respect to well-established effective factors including the effects of initial

pH, dose of bark, initial cation concentration ( Table 2.44), contact time and temperature.

Table 2.44. The impact of major experimental factors on the sorption of Cu(II), Zn(II),

Cd(II) ions on the Romanian pine bark

Factor Influence Description

Initial pH

Effect of initial pH on Cu(II) ions (▲) and Zn(II) ions (●); retention by pine bark (C0= 72 mg Cu(II)/ L; C0=60 mg Zn(II)/L)

[Amalinei, Tofan et al.2012]

This major dependence was investigated in solutions with initial pH in the range of 1 to 5(6) where all metals exist in their double positively charged ionic forms (Cu

2+;Zn

2+;Cd

2+)

and their precipitation as metal hydroxides is avoided. The sorption for all metal ions under study decreased with reducing the initial pH. [Amalinei, Tofan et al.2012; Tofan et al. 2012] Thus, Cu(II) ions showed a maximum sorption of 6.98 mg/ g at pH 4.5 to 5, which decreased progressively to 4 mg/ g at pH 3 and 0.68 mg/g at pH 1. The respective values for Zn(II) ions are 6.24 mg/ g at pH 4.5 to 5, 3.3 mg /g at pH 3 and 0.54 mg/ g at pH 1.

Pine bark dose

Removal percentage of Cd(II) retention on pine bark as function of sorbent dose (C0=60 mg/L; pH=5-5.5; time=24h; t= 20

0C) [Tofan et al. 2012]

The Cd(II) removal presented a significant improvement with increase in pine bark dose. This behavior can be attributed to the increase in surface area resulting from the increase in sorbent mass, thus increasing the number of active sorption sites[Tofan et al. 2012]


Initial Cd(II) concentration

Influence of initial solution concentration on Cd(II) retention by pine bark under study[Tofan et al. 2012]

C0 (mg/L) q (mg/g) R%

20 40 60 80 100 120 140 160

3.00 5.01 8.25 10.3 11.2 12.00 13.01 14.00

87 80 78 68 60 55 47 43

The increase in initial metal ion concentration enhances the cadmium uptake. On the other hand, the Cd (II) sorption percentage decreased as the initial concentration of metal ions was increased. [Tofan et al. 2012]

Effect of contact time and kinetic parameters

The kinetic data for the sorption of Cu(II), Zn(II) and Cd(II) ions by pine bark are

shown in Figure 2.36( a and b) Amalinei, Tofan et al.2012; Tofan et al. 2012].

a) b)

Figure 2.36. Effect of the contact time on a)Cu(II) ) [() C0= 72 mg/ L;(▲)C0= 96 mg/ L

and Zn(II) [(■) C0=60 mg/L; (♦) C0=100 mg/L] and b) Cd(II) (C0 = 60 mg/L)

retention by pine bark. [Amalinei, Tofan et al.2012; Tofan et al, 2012].

According to Figure 2.36 (a,b), the kinetics of Cu(II) Zn(II) and Cd(II) ions removal

by pine bark under study presents a shape characterized by a strong capacity of tested

metal ions removal by pine bark during the first few minutes, followed by a slow increase

until the state of equilibrium is reached. In this context, it can be considered that the

retention of Cu (II), Zn(II) and Cd(II) ions on Pinus sylvestris L. bark takes place in two


distinct steps, a relatively fast phase followed by a slower one. The optimum time to reach

equilibrium is about 4 hours, and an increase of the sorption time to 24 hours did not show

notable effects. These findings are in good agreement with those reported in literature for

removal of Pb(II) ions from aqueous solution by sorption on Pinus brutia Ten. bark

[Gundogdu et al. 2009].

Kinetics of Cu(II) and Zn(II) ions sorption on pine bark under study was modeled

by the pseudo-first order and pseudo-second order equations, summarized in Table 2.45.

Table 2.45. Mathematical form and parameters of the used kinetic models

Kinetic model Equation form Kinetic parameters Remarks Reference

Pseudo-first

order model

(Lagergren

model)

log (qe – qt) =

log qe - tk

303.2

1

where qe and qt are the

amounts of cation (mg /g)

sorbed at equilibrium and

at time t, respectively

k1-rate constant of

pseudo–first order model

sorption(min−1

).

Based on

adsorption

capacity

[Lagergren

1898]

Pseudo-

second

order model

(Ho model)

tqhq et

111

k2- the rate constant of

the pseudo–second

order model

h = k2∙qe2 (mg/ g ∙min)

can be regarded as

initial sorption rate

constant of the pseudo–

second–order sorption

(g/mg∙min).

Based on

adsorption

capacity

[Ho and

McKay

1999]

The kinetic parameters derived from the plots of the linearized form of the pseudo-

first order and pseudo-second order equations are recorded in Table 2.46, along with the

corresponding correlation coefficients (R2).

Table 2.46. Kinetic characterization of the sorption systems based on pine bark.[Amalinei,

Tofan et al.2012]

Metal Initial

concentration

C0 (mg/ L)

Pseudo-first-order Pseudo-second-order

k1,

min-1

R2

k2,

g/ mg⋅ min

h,

mg/ g ⋅min

q0, (mg/ g)

R

2

Cu(II) 72 0.64 x10-2

0.9748 1.35x10-3

0.0828 7.82 0.9944

96 0.78x10-2

0.957 0.809x10-3

0.1943 10.83 0.9948

Zn(II) 60 0.62x10-2

0.9811 1.16 x10-3

0.0687 7.037 0.9975

100 0.713x10-2

0.9709 1.36x10-3

0.0968 8.42 0.9929


According to R2 values, it is obvious that the experimental results of Cu(II) and

Zn(II) ions sorption on the tested pine bark show a better compliance with pseudo–second

order kinetic model. A similar behavior has been observed on the sorption of Cu(II) and

Zn(II) ions onto a cone biomass of Pinus sylvestris L. [Ucun et al. 2010] and of Pb(II) ions

from aqueous solutions by Pinus brutia Ten. bark [Gundogdu et al. 2009]. According to

literature data, the pseudo-second order kinetic model includes different sorption

mechanisms such as surface complexation or ion exchange. The model is based on the

assumption that the rate-limiting step is chemical sorption (chemisorption) involving

valence forces through the sharing or exchange of electrons between the sorbent and the

sorbate [Lazarevic et al. 2011]. Furthermore, the sorption rate depends on the

concentration of Cu(II) and Zn(II) ions on the pine bark surface (Table 2.46). [Amalinei,

Tofan et al.2012]

Sorption isotherms

The experimental data were processed in the light of Langmuir and Freundlich

models (Table 2.47).

Table 2.47. Concise description of the applied isotherm models

Sorption

isotherm

model

Equation

Isotherm

parameters,

significance

Assumptions

Reference

Langmuir q =

CK

qCK

L

L

10

KL – binding

energy (relative

sorption affinity)

q0 – maximum

capacity of

sorption

Formation of a monolayer

coverage of metallic ion at the

sorbent surface containing a

finite number of

homogeneous sites of

sorption

[Langmuir

1916]

Freundlich log q = log KF +

(1/n)log C

(linearised form)

KF - sorption

capacity

n–energy of

sorption

Logarithmic decrease in the

enthalpy of sorption with the

increase in the fraction of

occupied sites

[Freundlich

1906]

Figures 2.37, 2.38 and 2.39 illustrate the Langmuir isotherms for Cu(II),Zn(II) and

Cd(II) ions sorption on the investigated pine bark at three different temperatures. The

Cu(II) Zn(II) and Cd(II) ions retention on the pine bark under study is characterized in

Table 2.48 by means of Langmuir constants obtained from the corresponding linear

Langmuir plots.


Figure 2.37. Langmuir

isotherms of Cu(II) ions sorption on pine

bark at (▲) 600C; () 200C;(♦) 40C (pH=

4.5-5; sorbent dose=6 g/ L) [Amalinei,

Tofan et al.2012]

Figure 2.38.

Langmuir isotherms of Zn(II) ions

sorption on pine bark at (▲) 600C;

() 200C;(♦) 40C

(pH= 4.5-5; sorbent dose=6 g/ L)

[Amalinei, Tofan et al.2012]

Figure 2.39.

Langmuir isotherms of Cd(II)

sorption on pine bark at(♦) 40C; () ;

200C (▲); 600C(▲) (pH= 5-5.5;

sorbent dose=6g/L) [Tofan et al.

2012].


Table 2.48. Quantitative description of batch sorption systems under study on the basis

of Langmuir [Amalinei, Tofan et al.2012; Tofan et al. 2012] and Freundlich [Amalinei,

Tofan et al.2012]

It can be seen from Table 2.48 that the conversion of pine bark waste under study

to value-added sorbent for Cu(II), Zn(II) and Cd(II) ions is viable. The KL values in Table

2.48 derived from the Langmuir model suggest the following order of the metal binding

affinity: Cu>Zn. The same metal sorption sequence (Cu>Zn) has been reported for Cu(II)

and Zn(II) ions uptake by other silvichemical biomass materials [Yu et al. 2008]. The

values for q0 are comparable with those reported in literature for some other low-cost

sorbents based on tree barks (Table 2.49). This comparison reveals that sorption capacity

of Pinus sylvestris L. bark under study is not very high, however quite sufficient for waste

materials. The regeneration and reuse of pine bark may play also an important role in

making this a practical process. The cost of regeneration/disposal of the spent sorbent

would have to be considered in any detailed economic analysis required to determine the

most economical sorbent [Anwar et al. 2010].

The empirical values of the Freundlich constants for Cu(II) ion-pine bark and Zn(II)

ion-pine bark batch sorption systems are recorded in Table 2.48 and point out again that

the sorption process is strongly dependent on the nature of the metal ion. [Amalinei,

Tofan et al.2012]. The n values are above unity, indicating favorable sorption of KF values

determined in this study are higher than those determined in previous studies using other

low-cost sorbents such as peanut hulls [Oliveira et al. 2010). This finding strongly

indicates that the pine bark under study is a promising material for heavy metal ions

removal from waste streams. However, future experiments should be performed with

industrial wastewaters to investigate pine bark sorption behavior of these metals in co-

presence of other metals and organic matter.

To compare the Langmuir and Freundlich isotherm models, the experimental data

were statistically processed by linear regression. High values of the linear regression

Metal

ion

Langmuir isotherm Freundlich isotherm

T, K R2 q0,

(mg/g)

KL

(L/ mol)

R2 KF n

Cu(II)

277 0.9832 13.32 1892 0.9873 0.768 1.64 293 0.9967 17.46 3591 0.9967 1.89 2.21 333 0.9899 21.90 4543 0.9974 3.41 2.70

Zn(II)

277 293 333

0.9922 13.37 648.9 0.9799 0.1688 1.20 0.9948 15.73 1319 0.968 0.529 1.47 0.987 16.70 2320 0.9957 1.39 1.954

Cd(II)

277 0.9898 22.06 709 293 0.9940 27.32 1210 333 0.9848 32.59 1550


correlation coefficients (R2) for both Langmuir and Freundlich plots (Table 2.48) suggest

that monolayer sorption, as well as heterogeneous surface conditions may co-exist under

applied experimental conditions. A similar behavior has been reported in the literature for

the sorption of Pb(II) ions on Pinus brutia Ten. bark [Gundogdu et al. 2009].

Table 2.49. Comparison of the sorption capacity for Cu(II), Zn(II) and Cd(II) ions of some tree barks

Sorbent q0, mg/g Reference

Cu(II)

Coniferous barks Hardwood bark Casuarina equisetifolia L. bark Natural radiata bark pine (Pinus radiata D. Don) Pine bark Douglas fir barks (Pseudotsuga sp.) Romanian Pinus sylvestris L. bark

5.08 – 9.525 20.574(pH= 5)

22.796(pH = 6) 16.58 (pH = 5) 20 – 50 9.46 7.0485 17.46

[Yu et.al 2008] [Jang et al. 2005]

[Mohan and Sumitha 2008] [Montes et al. 2003] [Zacaria et al. 2002] [Dupont et al. 2002] [Amalinei, Tofan et al. 2012]

Zn(II)

Coniferous barks Hardwood bark Azadirachta indica A. Juss. Bark Douglas fir barks (Pseudotsuga sp.) Pelletized ponderosa pine bark (Pinus ponderosa) Romanian Pinus sylvestris L. bark

7.4 12.025(pH = 5) 12.155(pH = 6) 33.49 4.0625 20.6(pH = 5.1) 15.73

[Conrad and Hansen 2007] [Jang et al. 2005] [King et al. 2008] [Dupont et al. 2002]

[Oh and Tshabalala

2007] [Amalinei, Tofan et al. 2012

Cd(II)

Juniperus monosperma bark Bark of Eucalyptus (globulus) Harwickia binata bark Eriobotrya japonica Loquat Bark Romanian Pinus sylvestris L. bark

10.08 14.56 33.60 28.802(pH=4) 27.32

[Shin et al. 2005] [Ghodbane et al. 2008] [Seki et al.1997]

[ Salem et al.2012]

[Tofan et al. 2012]

Effect of temperature and thermodynamic parameters

It is obvious from Figures 2.37, 2.38 and 2.39 that the temperature has a favorable

effect within the sorption systems under study. Both Langmuir and Freundlich constants

(Table 2.48) increase with increasing temperature, showing that the sorption capacity and

the intensity of sorption are enhanced at higher temperatures.

The thermodynamic parameters, free energy change (ΔG), enthalpy change (ΔH)

and entropy change (ΔS) were calculated on the basis of Langmuir constant KL at different

temperatures by using the following equations [Park et al. 2010]:


ΔG = - RT ln KL ln KL = constant = RT

H

T

GHS

where R is the gas constant and T is the absolute temperature.

The thermodynamic description of the sorption systems under study on the basis

of experimental data is given in Table 2.50 [Amalinei, Tofan et al.2012; Tofan et al.2012].

Table 2.50. The thermodynamic parameters of the sorption process of Cu(II) and Zn(II) ions on pine bark

The negative values of ΔG at all working temperatures indicated the spontaneous

nature of the sorption process of Cu(II), Zn(II) and Cd(II) ions by pine bark. Like in other

cases of heavy metal ions retention on low- cost sorbents, the change in free energy

increases with increase in which exhibits an increase in sorption with rise in temperature.

This could be possibly because of activation of more sites on the surface of pine bark with

increase in temperature or that the energy of sorption sites has an exponential distribution

and a higher temperature enables the energy barrier of sorption to be overcome [Ayhan

Sengil and Ozacar 2008].

The ΔH positive values are characteristic for endothermic processes, favored by

temperature increase.The endothermic process shows that the diffusion from bulk solution

to sorbent surface may require energy to overcome interaction of dissolved ions with

solvation molecules [Zakaria et al. 2009].

The positive value of entropy change ΔS shows increased randomness at the

solid–solution interface during the sorption of Cu(II), Zn(II) and Cd(II) ions on pine bark.

2.3.3.3. Sorption of Cu(II) and Cd(II) from aqueous solutions by Romanian silver fir

tree (Abies alba mill.) bark wastes[ Tofan et al., 2016 ;Tofan et al., 2017]

Previous studies have been emphasized that Romanian silver fir cone powder and

sawdust (Abies alba) are able to retain cadmium(II) ions from aqueous solutions, the

maximum sorption capacity having low values of 3.74 mg Cd/g of cone powder and 2.159

T, K ΔG ΔH ΔS

(KJ/ mol) (KJ /mol) (J/ mol K)

Cu(II) 277 293 333

-17.35 -19.78 -23.3

10.54 0.102 0.104 0.101

Zn(II) 277 293 333

-15.031 -17.362 -21.418

8.48 0.084 0.088 0.089

Cd(II) 277 293 333

-15.10 -17.28 - 20.30

10.07 0.090 0.093 0.091


mg Cd/g of sawdust, respectively (Manzatu et al.,2014; Nagy et al.,2013). But among tree

biomass components, bark has the highest capacity for heavy metal sorption, followed by

cones, needles and wood (Sen et al., 2015). In these studies, wastes of Romanian silver

tree (Abies alba) bark were explored for first time as green and economical sorbent for

the removal of Cu(II) and Cd(II) ions from aqueous solutions.

The bark from softwood Abies alba is structurally heterogeneous. According to

previous studies, the major chemical components of the raw Romanian Abies alba bark

are cellulose (48.24–58.32%) and lignin (29.20–33.30%) (Nagy et al.2013). Its ash

content (as a measure of the concentrations of the inorganic components) is 0.12 – 0.46%

(Nagy et al.2013).

To identify the chemical structure, infrared spectrometry has been used. IR spectra

of the bark of Romanian Abies alba Mill. before (S1) and after Cu(II) ions sorption(S2)

are presented in Table 2.51. FTIR spectroscopy was employed to identify the functional

groups that may be involved in the studied process. The morphological structure of the

bark and Cu(II)-bark was also studied by scanning electron microscopy (Table 2.51). The

SEM images (Table 2.51) clearly show the morphological changes occurring on the

surface of the sorbent after the reaction with a solution containing Cu(II) ions. After

biosorption roughness attenuation was observed, this can be due to the effective

adsorption of Cu (II) ions in the cavities and pores of Abies alba bark. FTIR studies

revealed that several functional groups present in the Abies alba bark are able to bind the

Cu (II) ions and sorption process occurs predominantly by chemical interactions. Physical

and chemical characteristics of the Romanian bark suggest the fact that this material

could be a good biosorbent for heavy metal ions.


Table 2.51. The main FTIR spectral characteristics of Abies alba bark (S1) and Abies alba

bark-Cu(II)(S2) and SEM micrographs

Transmission band (cm-1

)

4000 3000 2000 1000Wavenumber (cm-1)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tra

nsm

itta

nce

460

521.7

2562.2

3592.1

2616.2

3665.4

1781.1

4818.7

5891.0

81033.8

1058.8

81107.0

91159.1

71276.8

21315.4

1371.3

31448.4

81515.0

2

1624.9

6

1737.7

9

2056.0

3

2344.3

82371.3

8

2852.6

2922.0

4

3424.4

7

(a)

- 3600-3200cm-1

- corresponding

to the deformation of O-H and

N-H groups. The stretching of

O–H bonds results in vibrations

within a range of

requencies/wavenumbers which

specify the presence of O–H

bonds of carboxylic acids and/or

free hydroxyl groups.

- 2950-2800 cm-1

- attributed to

C-H asymmetrical and

symmetrical stretching;

- The peaks observed at 2950-

2800 cm-1

can be assigned to

CH2 group.

- 1650-1550cm-1

- Represents

the stretching vibration of C=O

bonds.

-1375-1200cm-1

corresponding

to the stretching vibrations of C–

O from phenolic groups.

-1107-1033cm-1

- assigned to

alcoholic C-O and C-N

stretching vibration.

4000 3000 2000 1000Wavenumber (cm-1)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tra

nsm

itta

nce

456.1

5563.1

9588.2

6611.4

1617.2

665.4

1782.1

820.6

8887.2

21034.7

71058.8

81107.0

91158.2

1

1278.7

5

1368.4

4

1448.4

81515.0

2

1622.0

7

1736.8

3

2344.3

82371.3

8

2852.6

2921.0

7

3425.4

4

(b)

IR-spectra for: (a) S1- silver fir bark; (b) S2- silver fir bark-Cu(II) ions


SEM image of Abies alba bark

SEM image of Abies alba bark-Cu(II)

The effect of various experimental parameters such as initial solution pH, sorbent

dose, initial metal ion concentration, temperature and contact time on the Cu(II)- Abies

alba bark and Cd(II) - Abies alba bark sorption systems has been investigated under

batch conditions ( Table 2.52.)

Table 2.52. Systematization of the results of batch the studies concerning the Cu(II)

and Cd(II) sorption on the Abies alba bark

The performed study

Remarks

Effect of pH The optimum value of initial pH for Cu(II) and ions sorption was found to be 4.5 to 5.

Effect of bark dose

The heavy metal removal efficiency increased rapidly: - from 19% to 83%, in the case of Cu(II) - from 32% to 87.8%, for Cd(II)

with increasing of silver fir tree bark concentration from 4g/L from 20g/L.

Effect of metal ion concentration in initial solutions

The amount of metal ions retained on the bark under study under increased with the increasing of metal ion concentration, while the metal ions sorption percentage decreased. On the basis of this behavior it can be concluded that the wastes of Romanian silver fir bark may be a sustainable material for the efficient removal of Cu(II) and Cd(II) from industrial effluents with low content in the tested cation.


Sorption isotherms

The sorption isotherm studies clearly indicated that the sorptive behavior of Cu(II) and Cd(II) ions on Romanian Abies alba bark under study satisfies not only the Langmuir assumptions, but also the Freundlich assumption.

Langmuir isotherms and Freudlich isotherms for the sorption of Cu(II) ions

sorption on Romanian Abies alba bark at different temperatures (♦) 40C; () 20

0C;

(▲) 600C.


The calculated values for the isothermal thermodynamic parameters show that Cu(II) and Cd(II) ions retention by silver fir tree bark is a spontaneous process of endothermic and chemical nature.

Effect of contact time and kinetic modeling

The removal rate of the tested cations was rapid at the beginning and it became slow with increase of the contact time. It was observed that the process of Cu(II) and Cd(II) sorption on Romanian Abies alba bark reached equilibrium at 120 minutes.The sorption kinetics for Cu(II) and Cd(II) ions removal from aqueous solutions with initial pH of 4.5 to 5 followed by pseudo-second order model.

Comparison study

Comparing with other sorbents based on bark wastes in the aspect of capacity, Romanian Abies alba bark has a reasonable sorption capacity , and even if not the best for Cu(II) or Cd(II) removal, it is a viable and promising alternative.

Sorbent Maximum Cd(II) sorption capacity,

mg/g

Reference

Abies sachalinensis bark

6.72 (Seki et al.,1997)

Pinus pinaster bark 7.84 (Kumar, 2006)

Juniperus monosperma bark

10.08 (Shin et al., 2007)

Ceratonia siliqua bark 14.27 (Farhan et al., 2012)

Bark of Eucalyptus (globulus)

14.56 (Ghodbane et al., 2008)

Romanian Pinus sylvestris L. Bark

27.32 (Tofan et al., 2012)

Eriobotrya japonica Loquat bark

28.80 (Salem et. al, 2012)

Harwickia binata bark 33.60 (Seki et al.,1997)

Cassia siamea bark 37.70 (John et al., 2011)

Romanian Abies alba Mill. bark

11.98 (Tofan et al., 2017)


The applicability of Romanian Abies alba bark as sorbent for the removal of Cu(II)

ions from industrial wastewaters was evaluated in batch conditions. Table 2.53 gives the

details on the composition of the industrial electroplating wastewater sample applied for

this study before and after the sorption experiments. The results in Table 2.53 show that

Cu(II) ions removal from the effluent is 90.29%. Other species present in the industrial

electroplating wastewater were significantly minimized though to a lesser extent.

Table 2.53. Sorption removal of Cu(II) from industrial wastewater by batch process.

Parameters of wastewater Before sorption After sorption

100 mL sample, 1g bark, 4 hours

pH 3.74 5.40

COD 29.15 16.24

Turbidity (NTU) 0.60 0.51

Total hardness (0G) 22 15

Chloride 40 36

Cu(II) 5.25 0.51

Zn(II) 2.75 0.42

Ni(II) 2.15 0.56


The potential of Romanian pine (Pinus sylvestris L ) and silver fir (Abies alba Mill.)

bark wastes as green and economical sorbent for copper(II), zinc(II) and cadmium (II)

ions removal from aqueous solutions has been tested in batch conditions as function of

initial pH, sorbent dose, metal ion concentration, contact time, and temperature.

Equilibrium (Langmuir and Freundlich isotherm), kinetics and thermodynamics of the

considered sorption processes were discussed in details. Equilibrium was best described

by the Langmuir isotherm, while the kinetics of the process was best described by the

pseudo-second-order model, suggesting monolayer coverage and a chemisorption

process. Thermodynamic parameters showed that heavy metal ions sorption process on

barks under study is an endothermic process. The utility of Romanian Abies alba bark

has been demonstrated by removing Cu(II) along with other species from industrial

electroplating wastewater. A concentration of Cu(II) as high as 5.25mg/L in wastewater

can be reduced to 0.51mg/g.

The results indicate that sorption can be a viable alternative for bark valorization

purposes.


2.3.4. Thermal power plants ash as sorbent for the removal of Cu(II), Zn(II),

Pb(II) and Cd(II) ions from wastewaters

2.3.4.1. Background

Fly ash, generated during the combustion of coal for energy production, is an

industrial by-product which is regarded as a problematic solid waste, due to its potentially

toxic trace elements (arsenic, lead, zinc, nickel, copper manganese cadmium, chromium

and selenium) and organic compounds (e.g. polycyclic aromatic hydrocarbons, PAHs)

content[Jayaranjan et al. 2014].

Since wide scale coal firing for power generation began in the 1920s, many

millions of tons of ash and related by-products have been generated. The current annual

production of coal ash worldwide is estimated around 600 million tones, with fly ash

constituting about 500 million tones at 75–80% of the total ash produced [Ahmaruzzaman

2010]. These estimates, however, are based on at least 10 years old data. A more up to

date estimate would mean that globally about 750 million tons of coal fly ash is

generated annually [Shaheen et al. 2014].

At present, fly ash (coal waste) disposal is a major issue worldwide due to its

possible adverse environmental impacts as well as due to its high volume of generation

which requires large land area for disposal. On the other hand, the present day utilization

of ash on worldwide basis varied widely from a minimum of 3% to a maximum of 57%, yet

the world average only amounts to 16% of the total ash [Ahmaruzzaman 2010]. Thus,

appropriate measures for its safe disposal and means of utilization are necessary for

sustainable management of this waste. [Shaheen et al.2014].

In recent years, utilisation of fly ash has gained much attention in public and

industry, which will help reduce the environmental burden and enhance economic benefit

[Wang and Wu 2006; Jayaranjan et al. 2014; Shaheen et al. 2014; Wdowin et al. 2014 ].

Possible uses of fly ash include: [Franus et al. 2014]

macro –leving, soil stabilization;

in mines as backfilling material and material for disposal wells;

ceramics ( brick manufacturing);

the production of building materials ( cement and concrete);

soil fertilization ( alkalization and increased sorption complexes);

geopolymer construction;

road construction;

CO2 sequestration;

zeolites synthesis


The search for new prospective economic uses of fly ash has led to investigations

into other possible utilizations. Thus, the sorption of pollutant species (heavy metals,

organics, dyes) on different kinds of fly ashes has been intensively studied [Sharma et al.

2007; Bayat 2002a; Bayat 2002b; Cho et al., 2005; Banerjee et.al.2003; Chaiyasith et

al.2006; Woolard et al. 2000; Wang and Wu 2006; Kao et al. 2000; Li et al. 2006; Yamada

et al. 2003; Vondrias et al. 2002; Albanis et al. 2000; Wang et al.2005].The results of all

studies suggest that fly ash sorption is a progression towards a perspective method.

Against this background, my research interest was to asses the potential of an

energy pit coal fly ash resulted from the combustion of an energy pit coal in a thermal

power plant in Iasi (Table 2.54) to be used in the removal of heavy metal ions from

aqueous solutions.

Table 2.54. Chemical composition and characteristic features of the fly ash under study

Chemical composition Main properties

Constituent Wt % Physical Chemical

Si as SiO2 Al as Al2O3

Fe as Fe2O3 Ca as CaO Na as Na2O

47.39 23.49 8.55 4.67 1.36

Aspect: fine powdery particles ; Morphology: spheroid; Colour: grey; Specific surface area: 170-250 m

2/kg [Harja et al. 2007]

They are influenced to a great extent by the coal burned and the techniques used for handling and storage.

The effect of the solution pH, ash dose, initial concentrations of solutions,

temperature and contact time on the removal of Cu(II), Zn(II), Pb(II) and Cd(II) ions was

studied under batch conditions (Figure 2.40). The conditions employed for the sorption

studies undertaken are systematized in Table 2.55.

The sorption isotherm and probable mechanism are explained. The

thermodynamic and kinetic parameters for the sorption of Cu(II), Zn(II), Pb(II) and Cd(II)

ions on the tested fly ash have also been computed and discussed.

The obtained results could be used for designing treatment plants for the treatment

of Cu(II), Zn(II), Pb(II) and Cd(II) rich waters and wastewaters.

Contacting samples of ca. 0.5g ash with 50 mL of aqueous solution containing defined amounts of metal ions for a determined time

Filtration of mixture

Spectrophotometric determination of the final ion concentration in filtrate of:


-Cu(II) with rubeanic acid (λ = 390 nm) -Zn((II) with xylenol orange (λ = 570 nm)

-Pb(II) with pyridyl-azo-resorcinol (λ= 570nm). Determination of the Cd(II) final concentration in filtrate by atomic absorption

spectrometry

Calculating the parameters characteristic of metal ion on fly ash

Sorption percentage, R (%)

R = [(C0- C)/C0].100

Retained amount of metal ion, q (mg/g) q = [(C0-C)/G].V

where: C0 = initial concentration of metal ion (mg/L), C = cation concentration after sorption (mg/L); V = volume of solution (L); G = weight of ash (g)

Figure 2.40. Scheme of Cu(II), Zn(II), Pb(II) and Cd(II) sorption on fly ash by batch

procedure

Table 2.55. Sorption experimental conditions

Nature of investigation

Cations Initial pH

Ash dose (g/L)

Metal ion concentration

(mg/L)

Temperature (0C)

Contact time (h)

Solution pH

effect

Cu(II) Zn(II) Pb(II) Cd(II)

2 – 5 2 – 5 1 – 5 1 – 5

10 10 10 10

50.00 50.00 97.50 80.00

18 18 18 25

24 24 24 24

Ash dose effect Cu(II) Zn(II)

4.5 – 5 4.5 – 5

5 – 35 5 – 35

50; 100 100

18 18

24 24

Initial concentration

effect


4.5 – 5 4.5 – 5 4.5 – 5 4.5 - 5

10 10 10 10

30 – 130 30 – 130 30 – 140 20 – 140

18 18 18 25

24 24 24 24

Temperature

effect


4.5 – 5 4.5 – 5 4.5 – 5 4.5 – 5

10 10 10 10

30 – 130 30 – 130 30 – 140 20 – 140

4; 18; 60 4; 18; 60 4; 18; 50 4; 25; 50

24 24 24 24

Effect of contact

time

Cu(II) Zn(II) Pb(II)

Cd(II)

4.5 – 5 4.5 – 5 4.5 – 5

4.5 - 5

10 10 10

10

50; 100 50; 100 54.175; 108.35 60; 120

18 18 18

25

0.25 – 24 0.25 – 24 0.25 – 24

0.25 - 24

2.3.4.2. Batch sorption capability of the tested fly ash as function of initial ph,

sorbent dose, metal ion concentration, temperature and contact time

Effect of initial pH [Tofan et al. 2008a; Tofan et al. 2008 b; Tofan et al. 2013]

The major purpose of this investigation performed with solutions whose initial

concentrations were of 50 mg/ L for Cu(II) and Zn (II) or 97.5 mg/L and 80 mg/L for Pb(II)

and Cd(II) ions, respectively, is to find out the fly ash maximal ability in the sorption of the


tested cations.This estimation is most reliable at pH values when no hydroxide

precipitation takes place and therefore the heavy metals pH dependence sorption on ash

was studied in the initial pH ranges of 2→ 5 for Cu(II) and Zn(II) or pH 1→ 5 in the case

of Pb(II) and Cd(II). It was found that the final pH of solutions after Cu(II) or Zn(II) sorption

differed significantly from initial pH. The pH changes are about 2–3.3 units of pH (e.g.

from 2.6 to 5.3 or from 3.1 to 6.4 in the case of Cu(II) or Zn(II), respectively). However, in

these two cases the final pH of solutions did not exceed the pH of beginning of metal

hydroxides precipitation. For the Cu(II) and Zn(II) solutions under study, pH of beginning

Cu(OH)2 (solubility product = 5x 10-20) and Zn(OH)2 (solubility product = 7.1×10-18)

precipitation was calculated as being 5.90 and 6.98, respectively. [Tofan et al. 2008 a]. In

this context, on the basis of speciation data from literature it is obvious that in solutions at

pH 1–5, all metals exist in their double positively charged ionic form (Cu2+, Zn2+, Pb2+ and

Cd2+) [Fergusson 1990]. The effect of initial pH on sorption of Cu(II), Zn(II),Pb(II) și Cd(II)

ions by fly ash is shown in Figure 2.41 a, b and c [Tofan et al. 2008a; Tofan et al. 2008

b; Tofan et al. 2013]

As follows from Figure 2.41 (a, b, c), the sorptive potential of the tested fly ash is

minimum in strongly acidic media. Thus, the percentage of Cu (II) and Zn(II) sorption was

only about 40% at pH 2 (reached by acidification with H2SO4 solution). In the case of

Pb(II), the smallest percentage of retention (around 30%) was found at pH ~1.5 (reached

by acidification with HNO3 solution). Subsequently, the retention percentages rapidly

increased to 81% for Cu(II), 90% for Zn(II) and 90% for Pb(II) in the initial pH range of 2–

3.5 for these three cations. The same trend was shown in the case of Cd(II) sorption on

the tested fly ash. At the initial pH values higher than 3.5, the percentage of sorption did

not increase further. This behaviour may be correlated with the variation of the charge of

the ash surface depending on pH. Taking into account that the major component of the

tested fly ash is SiO2 (pHPZC ≈ 2), a protonation of the superficial hydroxyl groups ( ≡ SiOH

+ H+ → ≡SiOH2+) takes place at pH<2.


a)

b)

c)

Figure 2.41. The influence of initial pH on the retention of ions: a) Cu(II)(∙) and

Zn(II)(▲) [Tofan et al. 2008a] ;b) Pb(II) [Tofan et al. 2008b] ; c) Cd(II) [Tofan et al. 2013]

on energy pit coal fly ash

This leads to a positive charge of the surface of fly ash. Under the circumstances,

the small Cu(II), Zn(II), Pb(II) and Cd(II) sorption corresponding to low pH (pH 1-2) is

caused by the repulsion between the surface charge and metal ions [Bayat 2002b; Scotti

et al. 1999].

In the pH range 2–5, as a result of superficial hydroxyl groups dissociation (≡SiOH

→≡SiO─ + H+; ≡AlOH → ≡AlO- + H+), the surface of fly ash is negatively charged. The

sorption increase with pH increasing may be due to these negative charges at the active

sites on the fly ash surface that would allow metallic ions (M2+) to be chemisorbed

[Chaiyasith et al. 2006]:

2(≡SiO-) + M2+ → (≡SiO)2M

2(≡AlO-) + M2+ → (≡AlO)2M


These findings are in good agreement with other literature data that proposed the

competitive adsorption with H+ as predominant mechanism of heavy metal ions retention

on fly ash at pH<5 [Ricou et al.1999a].

In this context, the influence of other experimental factors was performed with

solutions of initial pH 4.5 – 5.

Influence of ash dose [Tofan et al. 2008a]

Figure 2.42 illustrates the effect of the sorbent dose on the Cu(II) and Zn(II)

sorption from solutions with different initial concentrations (C0) onto fly ash of the pit coal-

fired power station. The dependences in Figure 2.42 shows that the Cu(II) and Zn(II)

percentages of retention increase with increasing ash doses. From Cu(II) and Zn(II)

solutions of initial concentration equal to 100 mg/L, the values of sorption percentages are

47.5% and 50.2% at 5 g ash/L and increase to 67.5% and 77.32% at 15 g ash/L, for Cu

(II) and Zn(II), respectively. At the maximal dose of 30 g ash/L, the Cu(II) and Zn(II)

retention percentages reached values of 89.5% and 93%, respectively. In the case of a

solution with initial concentration of 50 mg/L, Cu(II) is retained to an enhanced proportion,

R% increasing from 75% to 99%, at the increase of ash dose from 5 g/L to 30 g/L.

Figure 2.42. Removal

percentage of Cu(II) and

Zn(II) retention on fly ash

as function of sorbent

concentration (♦ ) Cu–C0

= 50 mg/L;() Cu–C0 =

100 mg/L; (▲) Zn- C0 =

100 mg/L [Tofan et al.

2008a]

Effect of heavy metal ions concentrations in initial solutions [Tofan et al. 2008a;

Tofan et al. 2008 b; Tofan et al. 2013]

The amount of cation retained on the studied fly ash (q) increased with increasing

metal ion concentrations, but the Cu(II), Zn(II), Pb(II) and Cd(II) sorption percentages

(R%) decreased (Table 2.56.).


The increasing trend may be attributed to the higher number of collisions between

metal ions and ash, as a result of increasing initial concentration of the analyzed solution.

The lower percentage of retention at higher initial concentrations of heavy metal ions can

be explained by the saturation of the superficial sorption sites or by lowering the rate of

metal ions transport from aqueous solution to the ash surface. [Wang and Wu 2006]. This

trend leads to the conclusion that the fly ash resulted by burning energy pit coal can be

efficiently used in the removal of heavy metals from wastewaters with low contents of

Cu(II), Zn(II), Pb(II) or Cd(II).

Table 2.56. Influence of initial solution concentration on Cu(II), Zn(II), Pb(II) and Cd(II)

retention by fly ash under study [Tofan et al. 2008a; Tofan et al. 2008 b; Tofan et al.

2013]

Cation

Initial

concentration, (C0), mg/L

q,

mg/ g ash

R%

Cation

Initial

concentration (C0), mg/L

q,

mg/g ash

R%

Cu(II)

30 50 70 90 110

2.54 3.64 4.23 4.65 4.77

85.41 65.00 56.25 52.14 43.71

Zn(II)

30 50 70 90 110

2.44 3.41 4.45 5.02 5.83

81.31 68.33 63.48 56.02 53.18

Pb(II)

31.11 51.81 72.59 93.94 114.00 135.00

3.05 5.16 6.94 8.87

11.18 13.23

98.60 90.50 87.20 78.20 67.60 60.80

Cd(II)

20 40 60 80 100 120 140

3.94 5.30 6.55 7.50 9.75

11.27 12.55

89.2 80.5 75

65.3 59

50.25 49

Sorption isotherms

In order to describe the qualitative and quantitative aspects of the interactions

between the metal ions and the energy pit coal ash, the equilibrium data at three different

temperatures have been processed by means of isotherm models of Langmuir [Tofan et

al. 2008a; Tofan et al. 2008 b; Tofan et al. 2013] and Freundlich [Tofan et al. 2009; Tofan

et al. 2013]‘

The Langmuir isotherms for Cu(II), Zn(II), Pb(II) and Cd(II) sorption on the

investigated energy pit coal at three different temperatures are presented in Figures

2.43– 2.46.



isotherms of Cu(II) sorption on

the tested fly ash at 40C (∙ );

180C(♦) și 600C( ▲); pH = 4-

4.5; fly ash dose = 10g/L


isotherms of Zn(II) sorption on

the tested fly ash at 40C (∙ );

180C(♦) și 600C( ▲); pH = 4-

4.5; fly ash dose = 10g/L


isotherms of Pb(II) sorption on

the tested fly ash at 40C (♦);

250C(♦);și 500C(▲)

0

1

2

3

4

5

6

7

8

9

0 20 40 60 80 100C (mg/L)

q (

mg

/g)

0

2

4

6

8

10

12

14

16

0 10 20 30 40 50 60 70C, mg/L

q,m

g/g

0

1

2

3

4

5

6

7

8

0 20 40 60 80 100

C (mg/L)

q (

mg

/g)



isotherms of Cd(II) sorption on

the tested fly ash at : (■) 40C;

() 250C; (▲) 500C; (pH= 4.5-5;

fly ash dose= 10g/L).

Table 2.57 characterizes the Cu(II), Zn(II), Pb(II) and Cd(II) sorption on fly ash

under study at three different temperatures by means of Langmuir constants, obtained

from the intercepts and slopes of the corresponding linear Langmuir plots. The

experimental data were statistically processed by linear regression. The regression

equations are of y = ax+b type and the values obtained for the correlation coefficients, R2,

are given in Table 2.57, too.

Table 2.57.Quantitative description of the Cu(II)–ash; Zn(II)–ash; Pb(II) ash; Cd(II)–ash

sorption systems on the basis of Langmuir model [Tofan et al. 2008 a; Tofan et al. 2008b;

Tofan et al. 2009; Tofan et al. 2013]

Langmuir equation

[Langmuir 1916]

Parameters

and significance

Assumptions

Cation

T

(K)

q0,

mg/g ash

KL

(L/mol)

R

2

q =

CK

qCK

L

L

1

0

KL – energy of sorption

formation of a monolayer coverage of metallic ion at the fly ash surface containing a finite number of homogeneous sites of sorption

Cu(II) 277 291 333

4.5943 4.7151 7.6128

4599 7800 20986

0.9972 0.9990 0.9917

Linearized form

00

1

qKq

C

q

C

L

(relative affinity of sorption)

Zn(II) 277 291 333

4.1052 5. 7525 7.6548

5518.7 8998.4 5110.3

0.9914 0.9990 0.9915

q0 – maximum capacity of

Pb(II) 277 297 323

11.6955 13.8433 15.9804

8071 17667 32154

0.9797 0.9945 0.998

sorption Cd(II) 277 298 323

6.45 10.15 13.75

6754 10131 19235

0.9931 0.9904 0.9904


It can be seen from Table 2.57 that the thermal power plant fly ash under study

may be considered as a reasonable sorbent for Cu(II), Zn(II), Pb(II) and Cd(II) ions

removal from aqueous solutions. It was found that the low values for q0 are in good

agreement with literature data (Table 2.58). The comparisons in Table 2.58 were made on

the basis that the maximum capacities of Cu(II), Zn(II), Pb(II) and Cd(II) sorption depend

strongly on the fly ash origin. The high values of KL constants in Table 2.57 involve strong

bonds between the heavy metal ions and the fly ash under study. Furthermore, the KL

values reflect that the relative sorption affinity of the investigated fly ash is higher for zinc

ions than for copper ions. [Tofan et al.2008a]. A similar order of the sorption affinity (Zn(II)

> Cu(II)) has been reported for two different Turkish fly ashes [Bayat 2002b].

Table 2.58. Comparison of maximum sorption capacity of Cu(II), Zn(II), Pb(II) and Cd(II)

on different kinds of fly ash

Maximum capacity of sorption(mg/g)

Ash Cu(II) Zn(II) Pb(II) Cd(II) Reference

Fly ash resulted from the combustion of South African coal in a 600MV pulverized-coal power

plant

2.2 (pH=5; C0= 500mg/L)

1.2 (pH= 5; C0=519.3mg/L)

[Ricou et al. 1999b].

Different kinds of fly ashes from pulverized-coal

power plants in France

5.7 – 6 1.6 – 2.2

[Hequet et al. 1999; Hequet et al. 2001]

Pellets made from fired coal fly ash

20.92 18. 98 [Papandreou 2008]

Modified fly ash 21.5 (pH = 6.4)

22 pH=6,4

[Allinor 2007]

High-calcium Turkish fly ash 2.778 0.714 [Bayat 2002a]

Treated fly ash from Thailand 14.33 [Chaiyasith et al. 2006]

Fly ash 18.0 [ Wang et al. 2008] Bagasse fly ash 2.5 1.267

(300C)

1.67 (40

0C)

2.00 (50

0C)

[Gupta et.al. 2003] [Gupta and Ali 2004]

Pit coal fly ash 4.7151

5.7525

13.8433

10.15

[Tofan et al. 2008a; Tofan et al. 2008 b; Tofan et al. 2013]

Effect of temperature [Tofan et al. 2008a; Tofan et al. 2009; Tofan et al. 2013]

The temperature has a favorable effect within the sorption systems under study

(Figures 2.43 – 2.46). Both Langmuir constants (Table 2.57) increase with increasing

temperature, showing that the sorption capacity and the intensity of sorption are enhanced

at higher temperatures. Furthermore, this trend indicates the endothermic and chemical


nature of the sorption of the studied metals on fly ash of pit coal. Another reason for the

observed influence of temperature may be the increased accessibility of the sorption sites

in the ash particles.

Effect of contact time [ Tofan et al. 2008a; Tofan et al. 2009; Tofan et al. 2013]

Figure 2.47 (a, b, c) demonstrates the influence of contact time on the Cu(II) , Zn(II),

Pb(II) and Cd(II) retention from solutions with initial pH of 4.5–5 and different initial

concentrations by the tested fly ash.

a)

0

1

2

3

4

5

6

7

0 2 4 6 8 10 12time (h)

q (

mg

/g)

b)

0

1

2

3

4

5

6

7

8

0 50 100 150 200 250 300 350 400

time, min

q, m

g/g

c)

Figure 2.47. Effect of contact time on:

a) Cu(II)(CCu = (●) 50 mg/L; (♦) 100mg/L) and Zn(II) ( CZn= (▲) 50mg/L; (○) 100 mg/L;

b) Pb(II) ( CPb - (●)54.175 mg/L; (▲) – 108.35 mg/L

c) Cd(II)( CCd - (●) 60mg/L; (▲)100mg/L)

retention by the fly ash under study (ash dose = 10g/L, initial pH = 4.5- 5)


The kinetic data in Figure 2.47 indicate that the extent of the heavy metal ion

sorption increased sharply with increasing contact time, attaining values that stay almost

constant. At all the tested ranges of concentration, the sorption equilibrium is reached in

around 120 minutes. This fact emphasizes that the equilibrium time is independent of the

initial concentration. This observation may be ascribed to the reduction in immediate metal

ions sorption, owing to lack of available active sites required for high initial concentration

of metal ions.[Chaiyasith et al. 2006].

2.3.4.3.Thermodymamic description of some heavy metal ions sorption on energy

pit coal ash [Tofan et al. 2011; Tofan et al.2009; Tofan et al. 2013]

In order to evaluate the thermodynamic feasibility of the sorption process and to

confirm its nature, the thermodynamic parameters, free energy change (ΔG), enthalpy

change (ΔH) and entropy change (ΔS) were calculated based on the values of the

Langmuir constants (KL) at different temperatures (Table 2.57). The obtained values are

reported in Table 2.59.

Table 2.59. The thermodynamic quantities of the sorption of Cu(II), Zn(II), Pb(II) and

Cd(II) on energy pit coal fly ash.

Thermodynamic parameter

Equations [Khazali et al., 2007]

T, K

Obtained values


Free energy change,ΔG,

(kJ/mol)

ΔG=-RTlnKL 277 291(298) 323(333)

-19.404 -21.660

-27.530

-19.832 -22.010 -26.629

-20.69 -24.137 -27.84

- 20.29 - 22.75 - 26.46

Enthalpy change, (ΔH), kJ/mol

ln KL = constant =

- RT

H

277 291 (298) 323(333)

20.98

13.84

22.40

26.73

Entropy change (ΔS), kJ/mol

ΔS =

T

GH

277 291(298) 323(333)

145 146

145.6

121 123

121

155 156

155

166,5 166 166

(R is the gas constant;T is the absolute temperature)

As can be seen in Table 2.59, the values of the negative free energy change are

negative in all studied systems. This feature shows that the sorption process is

spontaneous and that the degree of spontaneity of the reaction increases with increasing

temperature. In such cases, the adsorptive forces are strong enough to cross over the

potential barrier [Khan et al. 2009].


The ΔH positive values are characteristic for endothermic processes, favored by

temperature increasing. Although not very high these positive values of ΔH can be

interpreted on the basis of considerably strong interactions between the heavy metal ions

and the fly ash surface.

Table 2.59 also shows that the ΔS values for Cu(II), Zn(II), Pb(II) and Cd(II) sorption

by energy pit coal ash were positive. This can occur as a result of the redistribution of

energy between the heavy metal ions and the fly ash. Before the sorption occurs, the

heavy metal ions near the surface of the sorbent will be more ordered than in subsequent

sorbed state and the ratio of free heavy metal ions to ions interacting with the fly ash will

be higher than in the sorbed phase. As a result, the distribution of the rotational and

translational energy among a small number of molecules will increase with increasing

sorption by producing a positive value of ΔS and the randomness will increase during the

sorption process. [Hefne et al. 2008].

2.3.4.4. Kinetic description of some heavy metal ions sorption on energy pit coal

ash [Tofan et al. 2009; Tofan et al.2011; Tofan et al.2013]

In order to study the controlling mechanism of the Cu(II), Zn(II), Pb(II) and Cd(II)

sorption process on the tested fly ash, the obtained kinetic data were processed

according to the pseudo-first-order [Tofan et al. 2008a; Tofan et al. 2009; Tofan et

al.2011;Tofan et al. 2013] and pseudo-second-order kinetic models [Tofan et al. 2009;.

Tofan et al.2013]. The results point out that the Cu(II), Zn(II), Pb(II) and Cd(II) ions

sorption on the tested fly ash follows better the pseudo–first order kinetic model.

The pseudo-first-order model (Lagergren‘s equation) describes adsorption in

solid–liquid systems based on the sorption capacity of solids [Ho 2004]. On the basis of

this model one can assumes that one heavy metal ion is sorbed onto one sorption site on

the fly ash surface:

A + M2+ 1kAM solid phase

where A represents an unoccupied sorption site on the fly ash and k1 is the pseudo- first-

order rate constant (min-1).

The Lagergren pseudo-first-order kinetic model is represented by the following

equation [Lagergren 1898]:

log(qe – qt) = log qe - tk

303.2

1

where qe and qt are the amounts of cation (mg/g) sorbed at equilibrium and at time t,

respectively and k1 is the pseudo-first order sorption rate constant(min−1).


The kinetic parameters obtained from the linear Lagergren plots for the studies

undertaken are given in Table 2.60.

Table 2.60. Parameters of the Lagergren kinetic model for Cu(II), Zn(II), Pb(II) and

Cd(II) sorption on the thermal power plant ash under study.

Cation C0(mg/L) q e(mg/g) k 1(min-1

)

Cu(II) 30 50 100

2.72 3.46 4.89

0.00345 0.00484 0.00507

Zn(II) 50 100

4.46 7.32

0.00806 0.01013

Pb(II) 54.175 108.35

6.55 11.18

0.00299 0.00368

Cd(II) 60 120

5.28 7.25

0.00875 0.00936

The results in Table 2.60 are in good agreement with data of literature studies that

used the Lagergren pseudo–first order equation for the kinetic description of the same

heavy metal ions on different kinds of ashes (Table 2.61)

Table 2.61. A comparison of the Lagergren kinetic parameters for the sorption of

Cu(II), Zn(II), Pb(II)and Cd(II) ions on different ashes.

Type of ash

Cation q e (mg/g)

k1

(min-1

) Refe-

rences

Wood ash


8.8 5.7 5.14 6.8

0.0161 0.02

0.0343 0.022

[Chirenje et al. 2006]

Bituminuous coal fly ash


0.0140 0.0389 0.0239 0.0578

[Cho et al. 2005]

Waste tire rubber ash

Cu(II) Pb(II)

34.3 0.0012 0.0023

[Mousavi et al. 2010a; 2010b]

Coal fly ash Cu(II) Pb(II)

0.0177 0.0211

[Allinor 2007]

Bottom fly ash

Pb(II)

Cd(II)

0.08 (C0= 2mg/L) 0.148(C0= 4mg/L) 0.211(C0= 6mg/L)

[Khan et al. 2009]

Bagasse fly ash Cu(II) Zn(II)

2.41 2.39

[Taha 2006]

Furthermore, the results in Table 2.60 indicate the order of the sorption affinity,

Zn(II) ions being sorbed faster (k1 = 8.06x10-3 min-1 at an initial concentration C0 =50mg/L)

than copper ions( k1 = 4.836x10-3min-1 for the same initial concentration) and lead ions (k1

= 2.99x10-3min-1 at an initial concentration of 54.175 mg/L). In addition, it can be seen that

heavy metal concentrations have a significant influence on the rate of sorption. Thus, for


an increase in Cu(II) initial concentration from 30 mg/L to 100 mg/L, the values of the

pseudo–first rate constant increased from 3.454x10-3min-1 to 5.066x10-3min-1, respectively.

In the case of Cd(II), the values of the pseudo–first rate constant increased from 8.75x10-3

min-1 to 9.36x10-3min-1 for an increase in initial concentration from 60 mg/L to 120 mg/L,

respectively.


The results of my studies are good prospects for the sorption of toxic metals by fly ash in

practical applications. It is evident that pH, ash dose, initial Cu(II), Zn(II), Pb(II) and Cd(II)

ions concentration, temperature and contact time have marked effect on the sorption. The

equilibrium data are best explained by Langmuir sorption isotherm. Thermodynamic

parameters also favor the sorption of heavy metal ions under study on energy pit coal ash.

Kinetics of sorption follows pseudo – first order rate equation.It is necessary to investigate

the efficacy of energy pit coal to treat real industrial effluents. This valuable use of fly ash

will not only convert this waste material into low- cost effective sorbent, but also provide a

viable solution to its disposal.


3. PROPOSAL FOR THE ACADEMIC AND SCIENTIFIC CAREER

DEVELOPMENT

My future professional path will be guided by the principle of continuity, which

compliance will overlap with my short/medium/long term concern for the achievement of

the following priority objectives:

maintaining and enhancing of the standards of academic and professional

excellence;

direct collaboration with all fellows – teachers and students.

3.1. Future prospects in the teaching career

I will promote an autonomous, active and situational teaching of the students, in

the coordinates of a constructivist approach, which mainly involves:

the consideration of learning as an own construction;

the direct and interactive involvement and participation of the students;

the teaching of the courses and laboratory applications as a ―staging‖ in which

students learn a lot from the roles that they play;

the teacher gives up the roles of expert and organizer and become a student

and a observer;

providing knowledge as a resource of the learning process;

performing of the learning through experiments that favor the thinking, the

independent action and the active participation;

the stimulation of curiosity as the main purpose of the educational work;

the generating of curiosity and intrinsic motivation as a result of certain

stimulant situations especially created;

the students construct the learning content which no longer identifies with the

subject matter to be taught.

I think that the success of my future teaching career will be conditioned by the

extent to which I will be able to achieve the following objectives:

supporting of my teaching activities by the publishing of all courses that I teach

in rated publishing houses;

the modernization of the educational process by using IT solutions and multi-

media presentations;

the development of e-learning type publications for course and applications

materials;


the annual updating of the syllabuses;

the implementation of interactive teaching methods based on collaborative

creativity and educational partnership (inquiry based learning; problem based

learning);

the diversification of the evaluation methods;

the expanding of the relations of partnership with the students;

the elaboration of the bachelor and dissertation projects in tutelage with

specialized companies;

the correlation of the educational activities with the research activities;

the perfection by short stages in universities from abroad.

3.2. Future prospects in the scientific career

I propose that my scientific career development reflects the harmonious jointing

of the continuity and novelty elements. I was, I am and I intend to remain equally

enthusiastic in looking for new solutions and approaches to old problems and open to

knowledge and progress. I will try my professional perfection through the most efficient

valorization of the experience and expertise already gained. Being aware of the particular

importance of the collaboration and teamwork in the success achievement, I will insist on

the maintaining and strengthening of the relationships already established and I will

militate for the creation of new ones. In this context, I propose to perform the scientific

research activities on two levels:

1. The continuation and deepening of the studies on the scientific directions priority

addressed to the present

a) Future prospects in the research direction related to sorption removal/recovery

of heavy metal ions by using polymeric materials targets:

- the valorization of the results already obtained in order to find the most

effective possibilities of the tested materials application in real systems;

- studies on the possibilities of desorption of the heavy metals loaded on

sorbents, with a dual goal: the metals recovery, with their potential reintroduction in the

economic circuit and the recycling of the sorption material;

- fixed bed column studies;

- studies on the designed bifunctional sorbents for the simultaneous removal

of toxic metal cation and anions from wastewaters;


- the assessment of new chelating sorbents with improved performances for

precious metals recovery;

- investigations on the possibility to develop and asses the performances

of artificial materials which would imitate low cost sorbents but would not show the low

cost sorbents disadvantages.

b) The studies on the feasibility of industrial and agricultural wastes conversion

into value-added sorbents, applicable in advanced treatment of wastewater will be

continued and deepened from the following perspectives:

- the assessment of the performance of the waste materials already tested (hemp,

rapeseed, pine bark, fly ash) not only in a single metal solution system but also multi –

metal and multi – pollutant solution systems prior to their industrial applications;

- the previous studies deepening by the assessment of the chemism and mechanisms of

the retention processes of heavy metal ions on hemp, rapesed, tree bark and fly ash;

- the subsequent valorization of the results already obtained in order to find the most

efficient solutions for the sorption performances of the tested wastes improvement, by

different methods of physical and chemical treatment;

- comprehensive studies on the regeneration and reuse of the sorbents for further sorption

of heavy metal ions;

- novel achievment procedures of the pollutant retention on the proposed sorbents, as

improvment variants of the performances of the actual sorption process;

- comprehensive dynamic studies in order to use the tested waste materials for treating

complex industrial wastewaters and also for the simultaneous removal of heavy metal ions

and organic substances in solution;

- identification and assessment of better and more selective waste materials;

- development of novel low – cost sorbents with increasing robutness by immobilization

techniques.

c) Future researches related to the adaptation and development of analytical methods

for the determination of chemical species in low concentrations deals with:

• the adaptation of the solid phase spectrometry for the determination of other

precious metals (gold, iridium, platinum);

• the purchase of software for the determination of the elements in small

concentrations by derived spectrometry.


2) Addressing of new environmental research directions

In order to achieve this goal my attention will focus, especially, on the use of

lasers in pollution monitoring. The choice of this research direction is justified by the

following considerations:

- the actuality and the special interest in the global scientific community;

- the high novelty degree of this topic for Romania;

- the close cooperation with a group of researchers from the National Institute for

Laser, Plasma and Radiation Physics–Laser Metrology Laboratory, where exist

last generation equipments;

- the advantages of the laser spectroscopy application in environmental monitoring,

advantages resulting from the defining characteristics of this method:

high selectivity;

high sensitivity;

the possibility to detect many compounds with a single instrument;

the wide dynamic range that provides the monitoring of small or high

concentrations with a single instrument;

the rapid response;

the temporal resolution is good for on- line monitoring;

invasiveness and destructiveness.

I propose that the interest provoked by the performing of these researches should

not distract me from the achievement of following short term/medium term objectives:

- the continuation of the activities until the completion of contracts in which I am involved

as project manager or team member;

- the application of project proposals for national and international grants;

- the active involvement in the activities of the LACMED laboratory (RENAR rated) in

order to maintain and diversify them.

To improve the relevance and the impact of my scientific activity, I propose the

research results dissemination by the annual publication of scientific papers in ISI/

international data base journals and annual participation at international conferences.


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