SYNTHETIC INORGANIC IONEXCHANGERS

Reetha Nanu Cheruvalath “Studies on some ion exchangers” Thesis. Department of Chemistry, Sree Narayana Post Graduate College, University of Calicut, 2006

CHAPTER I1

SYNTHETIC INORGANIC ION

EXCHANGERS

Many natural and synthetic substances are capable of ion exchange.

The three important groups of ion exchangers are inorganic, natural organic

bases and synthetic ion exchangers. Among the inorganic ion exchangers the

aluinino-silicates, both natural and synthetic, are suitable for technical

purposes. Zeolites are naturally occurring cation exchangers and apatite is a

naturally occurring anion exchanger. Hydrate gells of aluminium, iron(II1)

38,39 and zirconium hydroxide act as synthetic inorganic anion exchangers .

Cellulose based ion exchangers containing phosphoric- and sulphonic acid-

and diethylainine groups come under natural organic base ion exchangers.

Synthetic ion exchange resins consist of a large organic molecular network to

which active groups able to ionise are fixed. The active groups of cation

exchange resins can be phenolic hydroxyl (-OH), carboxyl (-COOH) or

phosphoric acid [-PO(OH)2]. While for anion exchange resins, the active

groups are usually primary, secondary, tertiary or quaternary basic groups.

The ion exchangers in the liquid form are known as liquid ion

exchangers. The behaviour of liquid ion exchangers are similar to that of

resin ion exchangers in both techniques, an exchange of ions of like sign

occurs between two immiscible liquids in contact with each other. Analogous

to resin ion exchangers, there are both liquid anion and cation exchangers.

The liquid anion exchangers are mainly primary, secondary, tertiary amines or

quaternary ammonium salts of high inolecular weight. The liquid cation

exchangers are usually phosphoric acid esters or carboxylic acids.

The behaviours of analogous functional groups in liquid - and in resin

ion exchange are siinilar and it is possible to predict the likely course of liquid

ion exchange extraction by comparing with similar separations using solid ion

exchangers.

The development of synthetic inorganic ion exchangers during the last

two decades has attracted the attentions of analytical chemists. This is due to

their stability towards high temperature and ionising radiation. These are

superior to cominercially available organic or natural organic exchangers and

are suitable for uses in nuclear industry, preparation of ultra pure materials,

the recovery of valuable materials from industrial waste, hydrometallurgy,

etc.

A good number of papers dealing with the synthesis and ion exchange

properties of inorganic ion exchangers have been published. The informative

book by C. B. ~ i n ~ h l e t t ~ ~ and the reviews by Churins and at er ova^^." deal

with various types of ion exchangers and their uses. These authors reviewed

the uses of various types of clay minerals as ion exchangers and their

properties, the molecular sieve properties of zeolites and their exchange

isotherms and kinetics of exchange synthesis, properties and applications of

various types of heteropolyacid salts.

A systematic classification of inorganic ion exchangers was made by

Vesely and ~ a k a r e k ' ~ as follows.

1. Hydrated oxides of metals.

2. Acidic salts of polyvalent metals

3. Insoluble salts of hetero poly acids.

4. Insoluble hydrated metal ferro- and ferri cyanides

5. Miscellaneous type

2.1. Hydrated oxides of metals

An exhaustive survey covering the preparation, properties, uses and

theory of hydrous oxides of bivalent, trivalent, quadrivalent, quinquivalent

and sexivalent metals have been made by Vesley and Paltarelc. Similar

studies on hydrated oxides of metals, such as, Al, Si, Sn, Zr, antimonic acid,

Ce and tungsten were given by De and ~ e n ' ~ . walton4' has reviewed the

studies on antimony pentoxide, tin oxide and activated carbon impregnated

with tin oxide used in chromatography.

Hydrous a l ~ i n i n a " ~ ~ samples are constantly used in analytical

separation as adsorbent and desorbent. The results of the investigation show

that ion exchange capacity of alumina is enhanced by pre-treatment with

hydrochloric acid. Among the hydrous oxides, those of antiinonic acid, both

4734 crystalline and amorphous forms have found several uses . They are used

in the mutual separation of alkali metals. The other oxides studied include

55-57 hydrous titanium dioxide , stannic oxide5*, hydrous manganese 59,60

hydrated ferric oxide and hydrous cerium(1V) oxide6'.

2.2. Acidic salts of polyvalent metals

Details of various acidic salts of polyvalent metals having different

anionic parts such as phosphate, arsenate, antimonite, selenate, ferrocyanides,

molybdate, tungstate were given by Vesley and ~ a k a r e k ~ ~ , De and ~ e n ' ~ and

~ a l t o n ' ~ . Other exchangers of special uses reported4' are hafnium- and

thoriuin phosphate, cerium oxalate, zirconium tungstate and -1nolybdate.

Molecular sieves of aluminium silicate were used to separate glucose and

fructose45.

Crystalline phosphates of zirconium and titanium as ion exchangers

were reviewed by ~ o b a ~ a s h i ~ ' . Industrial applications of ion exchangers

include, ways of increasing the efficiency of ion exchange method for

separation of mixtures, substance purification and preparation.

Characteristics and properties of group (IV) acid salts as ion exchanges had

62-65 been studied . The catalytic properties and applications of ion exchangers,

and super ionic conductivity in cubic potassium antimonite(V) zirconium

phosphate and exchange of alkali metals, thermal, redox and catalytic

characterisation of inorganic ion exchangers were discussed by Ruvarac,

66-73 Howe, Clearfield, Besse, Garicia Laginestra, Alberti and Abe .

Alberti et al.74 studied the synthesis and preliminary characterisation of

ion exchange behaviour of zirconiuin phosphate and -phosphite with layered

structures of a-type. Tetramineplatinum(I1)-H ion exchange on a-zirconium

75,76 phosphate . The conduction, the preparation and ion exchange properties of

77,78 y-NH4Zr H(PO4)2 and Y - Z ~ ( H O P ~ ) ~ were reported .

Synthesis, ion exchange characteristics and application of zirconium

79,80 antiinonate , zirconium molybdate8' and zirconium t ~ n ~ s t a t e ~ ~ were

studied. Anion exchange characteristics of zirconium tellurite were

thoroughly studied by Srivastava et aL8' Thorium tellurite acted as a cation

exchanger in alkaline medium and as an anion exchanger in acidic medium83.

The exchanger is useful in the separation of NO3 from NO2 and Moo4 from

PO4. The reaction mechanism involved and the stabilities of a- and y-

titanium phosphates have been investigated8" The complex ion exchanger,

titanium phosphate aininoniuin inolybdophosphate was used for the recovery

of 1 3 7 ~ s from power reactor fuels85 and H+/N~'+ ion exchange in a-

86,87 Ti(HP04)2H20 at 5°C and 25OC was determined .

Chroinatographic and photon conduction behaviour of 44 metal ions in

DMSO-HN03 and DMSO-H20 systems on thin layers of stannic phosphate

55,56 have been described . Also the stability of composition during the sorption

of traces of I< from 2-7 M K1 solution was noted8'. Similar studies based on

stannic arsenates9 and stannic pyrophosphate was also c o n d u ~ t e d ~ ~ ~ ~ ' .

A new inorganic ion exchanger prepared by mixing solutions of

cerium(1V) aininonium sulphate and tellurous acid at different concentrations

and different pH, namely cerium(1V) telluriteg2 were studied. Ceric phosphate

was used as ion exchanger in the separation of carrier free bismutch-2 10 from

lead-210, yttrium-90 from ~r-gog3. Cerium(1V) selenite was synthesised and

93,94 its ion exchange properties were studied by Hussain et al. A preliminary

study on the selectivity of ceric antimonite as ion exchange material for

various metal ions other than alkali metal ions has been reportedg5.

Cation exchange study, effect of y-irradiation on ion exchange

behaviour, separations of cadmium(I1) from Zn(I1) and Mn(II), Mg(I1) from

Ba(II), Cu(I1) and Sr(I1) were achieved on a crystalline thermally stable phase

of antimony(II1) silicateg6. Separation of cd2+ from pd2+ and from cu2+

and ~ i ~ ' were carried out on a column of amorphous lanthanum tungstateg7.

Electro chroinatographic studies of several metal ions were carried out on

98-99 paper impregnated with lanthanum antiinonate . Mukherjee et al."'

described the synthesis, physicochemical properties and applications of

lanthanum arsenate. Samples of iron(I11) molybdatelo1 were prepared by

mixing 0.05M aqueous solution of Fe(N03)3 and ammonium inolybdate at

various pH. Distribution coefficients for many metal ions were determined on

this material, and its structure was proposed tentatively on the basis of pH

titration, cheinical and thermal analysis, and IR and Mossbauer spectra.

Thind et a1.'O1 described the properties, application and the separation of

thoriuin on iron(II1) selenite exchanger. Composition and ion exchange

properties of K and Zn selective tantalum tungstate and basic tantalum

sulphate were reported by Qureshi et a1.1°2 A new inorganic ion exchanger,

tantalum selenite 103y104 was used for paper chromatographic separation of

different phenols. Ion exchange characteristics of lithium niobate crystals

were studied by Ganshin et al. 105,106

2.3. Insoluble salts of hetero poly acid salts

42,43 Vesely and Sen have reviewed various types of heteropoly acid

salts containing phosphorous, arsenic, silicon, germanium, boron,

molybdenum, tungsten, vanadium, etc, as hetero elements. CS selective

aininoniuin phosphomolybdate continues to be used as ion exchanger,

especially in the isolation of CS froin sea water. Using this, the separation of

Th, In, U and Se was also reported.

Synthesis, structure determination, chemical and thermal stability and

y-radiation stability of zirconium(1V) arsenophosphate and -arsenosilicate had

been reported lo7-11'. These exchangers are used for the separation of A1 and

Mg in some antacid drugs1l2. Other exchangers based on zirconiuin are

zirconium inolybdophosphate, zirconium tungstoarsenate, zirconiuin

iodophosphate, zirconium selenophosphate and zirconium(1V)

iodoinolybdate 113-117

A new mercury selective ion exchanger, thorium(1V) phosphosilicate

was synthesised and the effect of y-irradiation on its ion exchange property

was reported118. The results showed that the material was unaffected by doses

of 2 X 10' rad. Synthesis of titanium(1V) arsenophosphate, its ion exchange

property and utility in the analysis of certain alloys and rocks had been

107,109 published . Similarly, ion exchange behaviour of titanium(1V)

tungstoarsenate had been studied1I9. It is stable towards acids, salt solutions

and can be used up to 8-10 cycles without loss in efficiency. Titanium

inolybdoarsenate had been used for the separation of Pb(I1) and Hg(I1) from

La and cei20. Effect of y-irradiation on ion exchange characteristics of

titanium vanadophgsphate had also been reported12'. Study of stannic

selenophosphate with other heteropoly acid alts like stannic selenoarsenate

had been made 122,123 . Quantitative separation of binary mixtures of

manganese(I1) and Mg(I1); Ba(I1) and Cd(I1); and nickel(I1) and copper(I1) on

stannic arsenoantimonate column was reported12'. Preparation, properties,

analytical applications and comparative study on tin(1V) tungstoselenate,

tin(1V) boratomolybdate, tin(1V) iodophosphate, stannic vanadotungstate and

tin(1V) inolybdosilicate had been studied 115,125-129

Distribution and pH titration studies of alkali metal ions on amorphous

tin(1V) a r s e n ~ ~ h o s ~ h a t e ' ~ ~ has been reported. Tin(1V) tungstovanado-

phosphate'3' had been used for the separation of the following mixtures:

Mg(I1)-Cd(II), Cd(11)-Zn(II), Cd(11)-Pb(II), Mn(I1)-Hg(II), Ba(I1)-Ca(II),

Hg(I1)-P b(II), Ce(1V)-Th(1V) , Y (1V)-Th(1V)-Zr(1V) and Cd(I1)-Y (1V)-Zr(1V) .

Gupta et all3' reported the properties of stannic tungstophosphate towards

bivalent metal ions. Crystalline tin(1V) antimonophosphate was prepared and

its application in binary separation of metal ions were studied'32. Likewise,

synthesis and ion exchange characteristics of thermally stable tin(1V)

molybdophosphate had been reported by Qureshi et

Varshney et al.'" prepared cerium(1V) phosphosilicate and

chromium(II1) arsenophosphate exchangers and converted to H+ form. Their

ion exchange behaviours towards L?, ~ d , K' and NH; were investigatedI3O.

Iron(II1) iodophosphate was synthesised and compared with tin(IV), Zr(1V)

iodophosphatel 15. A column packed with thalliuin tungstophosphate was used

for the separation of Sr(II), Co(II), Ce(II1) and Cs(1). Talati et1 all3' studied

uranyl zinc molybdophosphate as an ion exchanger.

2.4. Insoluble hydrated metal ferro- and ferri cyanides

A new type of inorganic ion exchanger aminetin(1V)-

hexa~~anoferrate(11)'~~ with seven different ainines was prepared. Based on

pH titration, elution curves, IR and therinograviinetric studies, a tentative

formula of the compound was proposed.

Copper ferricyanide ion exchanger was used for the separation of

caesi~rnl'~. Badik et aLn8 reported the ion exchange properties of mixed

uranyl - and alkaline earth ferrocyanides. A thermodynamic model for the ion

exchange of K, NH4 and CS on the exchanger was proposed138. Preparation,

properties and selectivity of rubidium on titanium(1V) ferrocyanide gel was

studied 139-141

2.5. Miscellaneous types

Recently, a variety of inorganic chelating ion exchangers were

prepared. A chelating ion exchanger prepared from SnC14 and

diethanolamine14* was used for the separation of various metal ions by

chromatography. Similarly, titanium diethanolamine and aluminium

triethanolamineI4' were prepared by modification of hydrated aluminium

oxide. Singh et synthesised iron(II1) diethanolainine and studied its ion

exchange behaviour.

Ion exchange and dehydration of layer of titanates, Na3T1307 and

K2T1409 had been reported14s. Studies on preparation and properties of

ineta aininophosphoinolybdate and molybdosilicophosphate had been

reported 146-147 . Poly acrylamide-zirconium phosphate148 shows a high affinity

137 for CS at given conditions offering a possible way for radioactive liquid

waste treatinent.

Distribution studies and selective ion exchange separation of inetal ion

on polytungstoantiinonate14g and sorption behaviour of collodinum

i n ~ l ~ b d o a r s e n a t e ~ ~ ~ had been made. Tin(1V) EDTA ion ex~hanger '~ ' had

been synthesised and cation exchange properties of activated carbon by

treatment with HN03 had been reportedls2. Liquid ion exchange

chroinatography and recovery of some inetal ions on PAN-sorbed tin(1V)

silicate had also been reportedls3.

New ion exchanging materials - organic and inorganic, continue to be

reported, but less frequently than before. A nuinber of ion exchangers, both

in amorphous and crystalline forins were synthesised. After preparation, they

were subjected to different physico-chemical investigations for elucidation of

structure, composition and nature. For selective sorption, the distribution

coefficient (Kd) of different cations and anions were measured. It has been

found that inorganic ion exchangers are selective for a particular inetal ions.

Inorganic ion exchangers impregnated on papers have been used for

chroinatography, electro chromatography and thin layer chroinatography.

2.6. Significance and scope of the investigation

The nuinber of materials which may be understood as inorganic ion

exchanging substances have grown enormously during the period. However,

because of the ion exchange processess in many substances are accompanied

by other phenomena, such as, physical adsorption, surface adsorption,

precipitation and CO-precipitation processes, lattice defects, etc. It is difficult

to find an exactly limited scope for the term "inorganic ion exchanger."

There appears to have been a marked trend towards providing a inore

exact explanation of ion exchange rectors rather than studying purely practical

separation applications. The basic studies of ion exchange mechanism have

been carried out on defined crystalline materials, the detailed structure of

which, along with the location of the exchanging ions in the crystal lattice, are

of great interest. This knowledge, accompanied by the determination of the

main therlnodynainic functions have permitted a full explanation of the ion

exchange process. It is interesting that the exchange processes in many

substances are connected with the formation of insoluble compounds of the

ingoing ion with the "matrix", and that the forination of two distinct solid

phases has been detected in some cases. These facts together with the other

observed phenonlena mentioned above suggest that the ion exchange process

in the case of inorganic ion exchangers are of colnplex character and that the

traditional treatment of these processes in terms of pure ion exchange does not

fully describe all aspects of the processes. In view of the above facts,

different types of exchangers have been prepared and their specificity towards

several metal ion have been studied.