Low Cost Adsorbents

8/18/2019 Low Cost Adsorbents

1/62

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/248944639

Low Cost Adsorbents: Growing Approach toWastewater Treatment—A Review

ARTICLE in CRITICAL REVIEWS IN ENVIRONMENTAL SCIENCE AND TECHNOLOGY · OCTOBER 2009

Impact Factor: 3.47 · DOI: 10.1080/10643380801977610

CITATIONS

433

READS

551

4 AUTHORS:

Vinod K Gupta

Indian Institute of Technology Roorkee

640 PUBLICATIONS 33,084 CITATIONS

SEE PROFILE

Peter Carrott

Universidade de Évora


SEE PROFILE

M. M. L Ribeiro Carrott

Universidade de Évora


SEE PROFILE

Dr Suhas

Gurukula Kangri Vishwavidyalaya


SEE PROFILE

Available from: Peter Carrott

Retrieved on: 21 March 2016


2/62

PLEASE SCROLL DOWN FOR ARTICLE

This article was downloaded by: [B-on Consortium - 2007] On: 14 October 2009 Access details: Access Details: [subscription number 908038079] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Critical Reviews in Environmental Science and TechnologyPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713606375

Low Cost Adsorbents: Growing Approach to Wastewater Treatment—a Review

V. K. Gupta a; P. J. M. Carrott b; M.M.L. Ribeiro Carrott b; Suhas ba Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, India b Centro de Química deÉvora and Departmento de Quimica, Universidade de Évora, Colégio Luís António Verney, Évora, Portugal

Online Publication Date: 01 October 2009

To cite this Article

Gupta, V. K., Carrott, P. J. M., Ribeiro Carrott, M.M.L. and Suhas(2009)'Low-Cost Adsorbents: Growing Approach toWastewater Treatment—a Review',Critical Reviews in Environmental Science and Technology,39:10,783 — 842

To link to this Article: DOI:

10.1080/10643380801977610

URL: http://dx.doi.org/10.1080/10643380801977610

Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf

This article may be used for research, teaching and private study purposes. Any substantial orsystematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply ordistribution in any form to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss,actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directlyor indirectly in connection with or arising out of the use of this material.


3/62

Critical Reviews in Environmental Science and Technology, 39:783–842, 2009Copyright © Taylor & Francis Group, LLCISSN: 1064-3389 print / 1547-6537 onlineDOI: 10.1080/10643380801977610

Low-Cost Adsorbents: Growing Approach to Wastewater Treatment—a Review

V. K. GUPTA,1 P.J.M. CARROTT,2 M.M.L. RIBEIRO CARROTT,2

and SUHAS21 Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India

2Centro de Quı́mica de ´ Evora and Departmento de Quimica, Universidade de ´ Evora, Col´ egio

Lu´ ıs Ant ́ onio Verney, 7000-671 ´ Evora, Portugal

Industrial, agricultural, and domestic activities of humans have affected the environmental system, resulting in drastic problems

such as global warming and the generation of wastewater con-taining high levels of pollutants. As water of good quality is a pre-cious commodity and available in limited amounts, it has become highly imperative to treat wastewater for removal of pollutants. Inaddition, the rapid modernization of society has also led to the

generation of huge amount of materials of little value that have no fruitful use. Such materials are generally considered as waste, and their disposal is a problem. Also, there are some materials that are available in nature that have little or no use. The utilization of all

such materials as low-cost adsorbents for the treatment of wastew-ater may make them of some value. An effort has been made to

give a brief idea of an approach to wastewater treatment, partic-ularly discussing and highlighting in brief the low-cost alternative adsorbents with a view to utilizing these waste/low-cost materials.

KEY WORDS: activated carbon, adsorption, low-cost adsorbents,

pollutants, wastewater treatment

INTRODUCTION

Nature has provided plenty of resources that are used to sustain and developlife on the planet. One of the most important resources available to us is

Address correspondence to V. K. Gupta, Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, 247667, India; Tel.: +91-1332-285801; Fax: +91-1332-273560;

E-mail: [email protected]

783


4/62

784 V. K. Gupta et al.

FIGURE 1. (a) Water distribution1 on earth and (b) fresh water consumption3 in variousactivities (b).

water, which was present long before the evolution of life and without which life is not possible. The available water is distributed in an unevenmanner (see Figure 1). According to a World Health Organization fact sheetand other sources,1,2 of the total amount of water present on the earth,97.5% is salt water and cannot be used without treatment. The remaining water (2.5%) is generally fresh but most of it (70%) is locked in polar icecaps and glaciers, and the rest is mostly present as soil moisture or lies inunderground aquifers. Overall, the fresh water that is available for use is 1%or 0.007% of the total water on earth, which is really very little. The search forclean, fresh, and potable water has always been one of mankind’s priorities.

In olden times, when there was no industrial activity, the water availablefrom lakes, rivers and underground reservoirs was pure and suitable forhuman life. However, with rapid industrialization and modern methods of agricultural and domestic activities, the demand for water3 (see Figure 1)has increased tremendously, and this has resulted in the generation of largeamounts of wastewater4−6 containing a number of pollutants that are harmfulto both human and animal life. According to the United Nations World WaterDevelopment Report,7 some 2 million tons of waste per day are disposed of within receiving waters, including industrial wastes and chemicals, human

waste, and agricultural wastes (fertilizers, pesticides, and pesticide residues).In addition, according to the World Water Council and the World HealthOrganization,1,8 there is already more wastewater generated and dispersedtoday than at any other time in the history of our planet, and more thanone out of six people lack access to safe drinking water. Also, accordingto a WHO report,9 there were an estimated 2.6 billion people in the world without proper sanitation facilities, representing close to 42% of the world’spopulation, and approximately 1.1 billion people did not have access toany type of improved drinking water facility. It is also estimated that by themiddle of this century, at worst 7 billion people in sixty countries and at best

2 billion people in forty-eight countries will be water-scarce.7


5/62

Low-Cost Adsorbents 785

The UN policy on sustainable development, established by Agenda 2110

and the Rio Declaration on Environment and Development,11 is based onthe synergy between economic development, social development, and environmental protection. The use of low-cost adsorbents, particularly if they

are based on local natural materials or rural or industrial waste products,for pollution control and management and for securing potable water sup-plies, can make a significant contribution towards achieving the objectivesof Agenda 21 and the Rio Declaration.

POLLUTANTS

The term pollutant , in a broad sense, refers to a substance/material that

changes the natural quality of the environment by physical, chemical, orbiological means. Thus, we may have pollution in air, water, and soil. Asthis review article deals with ther removal of pollutants from wastewater, only pollutants generally present in effluents are described here. The three mainactivities that mankind indulges in are domestic, agricultural, and industrial.In all of these activities, a large amount of fresh water is used, which isdischarged as wastewater containing different pollutants depending on thetype of activity. These may be various inorganic and organic chemicals 12−14

and biological agents as well as heat and radiations. Some of the importantpollutants are discussed below.

Biological Agents

A number of biologically active agents,14 such as Vibrio comma, Salmonellatyphosa, Yersinia enterocolitica, Escherichia coli, and Shigella dysenteriae,may be present in domestic effluent and sewage water and need to beremoved. Some of the important waterborne diseases caused by biologicalagents are cholera, typhoid, dysentery, gastroenteritis, and jaundice.

Heat

Ideally, the temperature of water should be constant or undergo mini-mum variation. Because of its high heat capacity, water is used as a cool-ing medium. Thus, many industrial plants discharge water carrying away waste heat.15 The high temperature of this wastewater not only affectsaquatic life but is known to cause many chemical and bacteriological re-actions, such as formation of trihalomethane (THM) and higher corrosion

activity.


6/62


Dissolved and Non-Dissolved Chemicals

During the course of domestic, industrial, and agricultural operations, a num-ber of chemicals are used or produced and often get mixed up with fresh water, which is then discharged as wastewater. The chemicals present in

wastewater may be in a dissolved or non-dissolved state. Non-dissolvedsubstances are generally present as suspended solids in a dispersed form.The suspended solids make the water turbid and sometimes they may alsoslowly settle down with the formation of silt. The presence of suspendedsolids clogs waterways, fills up dams, and is harmful to aquatic life in many ways.16 The most common chemicals14 found in wastewater in a dissolvedstate and considered as potential pollutants are heavy metals, dyes, phenols,detergents, pesticides, polychlorinated biphenyls (PCBs), and a host of otherinorganic and organic substances.

HEAVY METALS

The wastewater generated from many industries may contain a number of heavy metals which have significant toxic effects17,18 and they are thereforeconsidered as pollutants19,20 requiring removal. The various industries thatgenerate such water include the tanning, battery, glassware, ceramics, elec-troplating, mining, paints, and photographic industries. These wastewaterscontain heavy metals such as chromium, lead, cadmium, arsenic, copper,iron, manganese, vanadium, nickel, mercury, cobalt, molybdenum, and bis-

muth, among others. The amount and the number of metals present in any wastewater is related directly to the operations carried out in an industry. Forexample, tanneries discharge chromium in wastewater; copper, chromium,zinc, and cadmium are widely generated from metal plating; the productionof electrical equipment and mining, smelting, and fossil fuel combustioncontribute to mercury pollution; and lead is generated from a number of in-dustrial and mining sources. In most wastewaters, the concentration of heavy metals present is much larger than the safe permissible limits and, therefore,they need to be removed.

D YES

Dyes are important materials that are currently in use both for domestic andindustrial purposes. Since the invention of synthetic dyes21 in 1856, severalforms of dyes are now available, and more than 8000 dyes are being man-ufactured and consequently used for specific purposes. The dyes in use areboth water soluble and insoluble. The big consumers of dyes are textile,dyeing, paper and pulp, tannery, and paint industries. Hence, the effluentsof these industries as well as those from plants manufacturing dyes tend tocontain dyes in sufficient quantities for them to be considered an objection-

able type of pollutant for two reasons: they impart color to water, which is


7/62


not acceptable on aesthetic grounds, and they are toxic and adversely affectlife.22−24

PHENOLS

Like dyes and metals, phenols are also considered priority pollutants,25,26

as they impart bad taste and odor to water and are also toxic,27−29 even atlow concentrations. The determination and removal of phenols from water istherefore important. Phenols present in wastewater are generated from paperand pulp, chemical, paint, resin, pesticides, gas and coke manufacture, anddyeing industries.

MISCELLANEOUS SUBSTANCES

A wide variety of other substances generated from different industries may also be present in wastewaters in dissolved or non-dissolved forms. Some of

them are summarized here:

Radioactive substances. Radioactive substances14 should be handled withconsiderable precaution in view of the harmful nature of the radiationsemitted by them. In spite of this, radioactive materials are often foundin effluents coming from research laboratories, hospitals, nuclear powerplants, and ore processing industries.

Detergents. Synthetic and natural detergents are widely used for cleaningand emulsification purposes. Thus, domestic wastewater and effluents of pharmaceutical and other industries may contain them.14

PCBs. One class of organic water pollutants of considerable interest isthe family of polychlorinated biphenyls (PCBs). PCBs are made by sub-stituting 1 to 10 hydrogen atoms of biphenyl with chlorine atoms. They show high chemical, thermal, and biological stability, as well as low vaporpressure and high dielectric constants. They do not cause a biochemicaloxygen demand problem in aquatic ecosystems but are extremely toxic.16

PCBs are generated in a variety of manufacturing processes, which in-clude the manufacture of brake linings, glass ceramics, grinding wheels, various types of coatings, flame proof paints, varnishes, sealants, electrical

equipments, and plastic coatings, etc. Pesticides. Whereas many other pollutants are only important in the urbansetting, pesticides are preeminently a problem arising from rural activities.Depending on their function, pesticides30 are subclassified as insecticides,molluscides, nematicides, rodenticides, avicides, piscides, fungicides, bac-tericides, slimcides, algicides, and herbicides. Among these, insecticidesand fungicides are important pesticides with respect to human exposurein food because they are applied shortly before or even after harvesting.Herbicide production has increased significantly, as chemicals are beingincreasingly used during the cultivation of land for controlling weeds and

now accounts for the majority of agricultural pesticides. Although DDT has


8/62


been banned, various substitutes such as toxaphene, lindane, parathion,malathion, heptachlor, and endrin can also cause environmental pollu-tion. The problem of pesticide pollution arises not only due to agriculturaloperations but also from pesticide manufacturing plants.

Other organic chemicals. A host of other organic chemicals may also bepresent in effluents generated from different industries. These include:trihalomethanes, such as chloroform and bromoform; trichloroethylene;tetrachloroethylene; aromatic hydrocarbons, such as benzene, toluene,xylene, and biphenyls; halogenated aromatics, such as choloroben-zene, dicholorobenzene, cholorotoluene, and chloroxylene; halogenatedaliphatic compounds, including bromocholoromethane, dibromomethane,and tetrachloromethane; halogenated ethers; polycyclic aromatic hydro-carbons, such as naphthalene, acenaphthene, fluorene, and phenan-therene; aldehydes; esters; alicyclic hydrocarbons; and ketones.

Most of the chemicals present in wastewater are toxic above certain con-centration levels and are therefore considered as pollutants. The toxic effectsof the pollutants are well documented in the literature.17,18,22−24,27−30 In viewof the general awareness created by modern methods of communication andinformation, it has become an imperative for governments, industries, andmunicipal authorities to work out methods for pollution control. A num-ber of methods are of course available, but sometimes cost factors are of overriding importance in the choice of the pollution control methods to beimplemented. Hence, the search for cost-effective technology for the safe

and effective treatment of wastewater is always on.

METHODOLOGIES FOR POLLUTION CONTROL

In order to meet the growing demand for potable water and water of goodquality for industrial use, it has become necessary to treat wastewaters forrenovation, reuse, and pollutant removal before mixing with natural wa-ter bodies containing good quality water. The methods that are adopted to

treat wastewater for pollution control can be broadly classified in four cat-egories: physicochemical processes, biological processes, nuclear treatment,and acoustical, electrical, and electromagnetic processes.

The various useful methodologies adopted under these are filtration31;ultrafiltration and dialysis32; reverse osmosis33,34; ion exchange35; sol- vent extraction36; oxidation37,38 using chlorine, ozone, hydrogen peroxide,and chlorine dioxide; evaporation39; adsorption40,41; coagulation42; foamflotation43 and photochemical reactions44; activated sludge45; aerobic andanaerobic treatment46−48; microbial reduction49; bacterial treatment50; irradi-ation by nuclear radiations51,52 and electrodialysis53; electrolysis54; ultrasonic

treatment55

; and magnetic separation.56


9/62


Many of the listed methods are employed for the control of specific pol-lutants. On the other hand, adsorption processes are generally non-specificand can be used to remove or minimize a wide variety of pollutants. They are also among the most effective and easy to operate and thus show wider

applicability.

ADSORPTION AND ION EXCHANGE

The versatility and wide applicability of adsorption in pollution control hasbeen recognized.40,57−62 The importance of adsorption62−65 in the chemical,food, petroleum, and pharmaceutical industries is also well established.

The term adsorption refers to a process wherein a material is con-centrated at a solid surface from its liquid or gaseous surroundings. The

phenomenon of adsorption65,66 was observed by C. W. Scheele in 1773for gases exposed to carbon. This was followed by observations made by Lowitz in 1785 of the reversible removal of color- and odor- producing com-pounds from water by wood charcoal. Larvitz in 1792 and Kehl in 1793observed similar phenomenon with vegetable and animal charcoals, respec-tively. However, it was Kayser who introduced for the first time in 1881 theterm adsorption to differentiate surface accumulation from intermolecularpenetration. He postulated that the basic feature of an adsorption processis surface accumulation of material. It is now customary to differentiate be-tween two types of adsorption. If the attraction between the solid surface and

the adsorbed molecules is physical in nature, the adsorption is referred to asphysical adsorption. Generally, in physical adsorption, the attractive forcesare van der Waals forces, and as they are weak, the resulting adsorptionis reversible in nature. On the other hand, if the attraction forces betweenadsorbed molecules and the solid surface arise due to chemical bonding, theadsorption process is called chemisorption. In view of the higher strength of the bonding in chemisorption, it is difficult to remove chemisorbed speciesfrom the solid surface.

Along with adsorption, ion exchange67 shares various common features

in regard to application in batch and fixed-bed processes, and they can begrouped together as “sorption processes” for a unified treatment to havehigh water quality. Thus, it is appropriate to also refer to ion exchange inthis review. Ion exchange is basically a reversible chemical process whereinan ion from solution is exchanged for a similarly charged ion attached to animmobile solid particle. By far the largest application of ion exchange68 todrinking water treatment is in the area of softening, that is, the removal of calcium, magnesium, and other polyvalent cations in exchange for sodium.

Both adsorption and ion exchange involve the transfer and resultingequilibrium distribution of one or more solutes between a fluid phase and

solid particles. In most cases, adsorption and ion exchange are modeled and


10/62


discussed using similar equations, which bring up a mixture of concepts.However, it is also worthwhile noting that ion exchange is a stoichiometricreaction whereas adsorption is a non-stoichiometric phenomenon.

A variety of solid adsorbents have been developed and used for remov-

ing solutes from solution by adsorption or ion exchange and also for theadsorption of gases. Some of these are discussed here.

ADSORBENTS

The most important property that a good adsorbent66,69 should possess is aporous structure resulting in high surface area. In addition, the time taken foradsorption equilibrium to be established should be as small as possible sothat it can be used to remove contaminants in lesser time. Thus, for removal

of pollutants, one looks to adsorbents with high surface area and porosity and showing fast adsorption kinetics. Some of the important adsorbents which are generally used in industry and for pollution control are discussednow.

Alumina and Bauxite

Alumina is a synthetic porous crystalline gel, which is available in the formof granules of different sizes. It is found to have a surface area70 ranging

from 200–300 m2

g−1

and is used in industries requiring the removal of waterfrom gas streams, decolorization, and refining of petroleum oils and waxes.On the other hand, bauxite is a naturally occurring porous crystalline alu-mina contaminated with kaolinite and iron oxides in varying proportions,depending on the place of origin. It is widely used in place of alumina, andit has been experimentally demonstrated that it removes most aerobic andanaerobic bacteria. Its surface area65 ranges from 25 to 250 m2g−1.

Silica Gel

It is prepared by the coagulation of colloidal silicic acid, which results in theformation of porous and noncrystalline granules of different sizes. It showsa higher surface area70 as compared to alumina, which ranges from 250 to900 m2g−1. The gel is considered a good adsorbent and is used in many industries for drying of gases and liquids, purifying of hydrocarbons, etc.71,72

Zeolites and Ion Exchange Resin

Zeolites are important microporous adsorbents that occur naturally and

are also prepared synthetically. They are also considered to be selective


11/62


adsorbents and show ion exchange property 73−75 as well as molecularadsorption.73,76,77 Zeolites are crystalline tectosilicates capable of undergoingreversible base-exchange reactions. Earlier zeolites were formed by fusing weighed amounts of feldspar, clay, and soda ash. Later on, synthetic zeolites

obtained from mixtures of caustic soda, sodium silicate, and bauxite werealso developed. Natural zeolites generally show low surface area; however,the apparent surface area78 of some synthetic zeolites can be as high as 700m2g−1. The textural characterization78 of zeolites is usually carried out by measuring surface area, pore volume, and pore size distribution by low tem-perature N2 adsorption and applying various techniques such as X-ray andneutron diffraction, IR, Raman, NMR, and scanning electron microscopy. Anumber of zeolites have been used for the removal of pollutants as well.79 – 81

Besides zeolites, it was shown in 1934 by Adams and Holmes thatphenol-formaldehyde resins exhibit cation exchange properties. This led

to the development of a different type of resin that is used as adsor-bents through a cation or anion exchange mechanism. Cation exchangeresins67 generally contain bound sulfonic acid groups or, less commonly,carboxylic, phosphonic, or phosphinic groups. Examples are polystirenesulfonate, sulfonated phenolic resin, phenolic resin, polystirene phospho-nate, and polystirene amidoxime. Anionic resins,67 on the other hand, gen-erally have quaternary ammonium groups (strongly basic) or other aminogroups (weakly basic) and include polystirene-based trimethyl benzyl am-monium, epoxy-polyamine, and aminopolystirene. A number of exchangeresins has been used quite efficiently for the removal of specific organiccompounds.35,82

Although the first ion exchangers used to soften water on a commer-cial scale were the natural zeolites, the most common ion exchangers usedpresently on a large scale are based on synthetic resins due to their fasterexchange rates, longer life, and higher capacity.

Activated Carbon

Activated carbon83 is the oldest adsorbent known and is usually prepared

from source material, such as coal, coconut shells, lignite, and wood, usingone of two basic activation methods:

1) Physical activation. This is a process in which the precursor is developedinto activated carbons83−86 using gases. The precursor is usually subjectedto carbonization followed by activation or using either. Carbonizationis the first stage where the precursor is pyrolyzed in the temperaturerange 600–900◦C, in an inert atmosphere (nitrogen, argon) resulting inthe formation of char, which is normally non-porous. The activation is

the process in which the material is exposed to oxidizing atmospheres


12/62


(carbon dioxide, oxygen, or steam) usually in the temperature range 600– 1200◦C, which results in the removal of the more disorganized carbonand the formation of a well-developed porous structure, leading to highsurface area.

2) Chemical activation. This is the other method used for the preparationof activated carbons83,84,86,87 and involves impregnation with chemicalssuch as H3PO4, KOH, or NaOH, followed by heating under a gas (usu-ally nitrogen) flow in the temperature range 450 to 900◦C. It is believedthat carbonization and activation steps proceed simultaneously in chem-ical activation. Generally, chemical activation is preferred over physicalactivation owing to the lower temperature and shorter time needed foractivating the material.

The product formed by either of the methods is known as activatedcarbon and generally has a very porous structure with a large surface arearanging from 500 to 2000 m2 g−1.88 It has been found that adsorption onactivated carbon is not usually selective, as it occurs through van der Waalsforces. The ability of charcoal to remove odor and taste was recorded cen-turies ago. The literature66,89 shows that according to a Sanskrit manuscriptfrom circa 200 BC, “it is good to keep water in copper vessels, to expose itin sunlight and to filter it through charcoal.”

The credit of developing commercial activated carbon,90 however, goesto Raphael von Ostrejko, whose inventions were patented in 1900 and 1901.

Hassler84 has summarized in his book the successful application of activatedcarbon in providing potable water. In the United States, for the first timein 1928, activated carbon was used for the water supplies, and within ten years, the number of plants treating water with activated carbon increased tothe thousand mark. The applicability of activated carbon for water treatmenthas been demonstrated by Weber et al.91 In his article, Stenzel92 describesadsorption with granular activated carbon to be a proven technology for water purification. Besides these and other workers, Bansal and Goyal62

have also discussed activated carbon and its applications in their book.

Activated carbon for water treatment is available in two main forms:powdered activated carbon (PAC) and granular activated carbon (GAC). Mostof the work on the removal of pollutants from water has been on GAC, due tothe fact that the granular form is more adaptable to continuous contacting,and there is no need to separate the carbon from the bulk fluid. On theother hand, the use of PAC presents some practical problems because of therequirement to separate the adsorbent from the fluid after use. However, inspite of these problems, PAC is also used for wastewater treatment due tolow capital cost and lesser contact time requirement.93

Activated carbon is used for wastewater treatment because of its

ability to adsorb different types of pollutants such as metal ions,94−98


13/62


phenols,25,99−102 dyes,103−106 pesticides,59,107,108 chlorinated hydrocarbons,109

humic substances,110 PCBs,111 detergents,112,113 organic compoundsthat cause taste and odor,114,115 and many other chemicals andorganisms.60,116−122 Activated carbons are not low-cost materials; hence, in

spite of their good efficiency and applicability for adsorbing a wide vari-ety of materials, their use can sometimes be restricted due to economicconsiderations

R EGENERATION OF SPENT ACTIVATED C ARBON

Activated carbons are generally used to purify water, and this is mostly done with column or fixed bed operations using GAC. After use, the columns areexhausted and are no longer capable of further adsorbing pollutants. Oncethe GAC has been exhausted, it has to be regenerated for further use inpurifying water. A number of methods are used for this purpose. The mostcommon technique practiced in regeneration is thermal.89,123 Besides this,chemical regeneration of spent activated carbon has also been tried. Martinand Ng124 used acetic acid and formic acid to regenerate carbon exhaustedby adsorption of commercial humic acid and reported high regenerationefficiencies. The regeneration of exhausted carbon has been reported by using NaOH by Newcombe and Drikas,125 acetone by Kilduff and King,126

methanol by Rollar and coworkers,127 and through oxidation by Notthakumet al.128 The regeneration of exhausted activated carbon using electrochem-ical techniques has also been investigated by various workers.129−131 They

also reported good regeneration efficiency for activated carbons.It should be pointed out that the regeneration of activated carbon is oftencarried out in installations belonging to the manufacturer or distributor of the activated carbon, and this can obviously create serious logistic problemsif the end-user is localized at a significant distance from the regenerationfacility. Furthermore, any regeneration process results in a loss of carbonand the regenerated product may have a slightly lower adsorption capacity in comparison with the virgin activated carbon. For this reason, activatedcarbon producers add about 10% of virgin carbon (paid for by the end-user) to the regenerated product in order to maintain the product within its

specification.

Low-Cost Alternative Adsorbents

Activated carbon remains the most widely studied adsorbent, and it has beenfound to adsorb a variety of materials such as metals, dyes, phenols, and ahost of other organic compounds and bio-organisms, and is therefore usedfor the removal of pollutants from wastewaters by adsorption. The designand operation of the process is convenient and can be handled easily, and

the operational costs are therefore comparatively low. As a result, the cost


14/62


of the adsorbent, and the additional costs of regeneration if required, canbe a significant fraction of the overall process costs. Attempts have thereforebeen made by many research workers132 in the field of waste managementand pollution control to look for alternative adsorbents that are cheaper than

activated carbons. The materials that have been investigated for this purposeinclude both natural materials and wastes and byproducts generated frommany industries. These materials have been used as such and sometimesafter some minor treatment, and are widely known as low-cost adsorbents(LCAs). A schematic diagram showing solid liquid pollutant generation andutilization of low-cost adsorbents is shown in Figure 2. In addition, fromthe numerous studies already carried out, a protocol for the development,utilization, and application of low-cost adsorbents generally adopted by re-searchers has been suggested and is given in Figure 3. It is worthwhilenoting here that these materials are usually called substitutes for activated

carbons because of their wide use and especially for their application intreating wastewater, which is usually done by activated carbons; however,in a broad and clearer way, they are basically substitutes for all expensiveadsorbents. These low-cost alternative adsorbents may be classified in two ways, either on basis of their availability (i.e., natural materials such as wood,peat, coal, lignite, etc.; industrial/agricultural/domestic wastes or byproductssuch as slag, sludge, fly ash, bagasse flyash, red mud, etc.; and synthesizedproducts) or depending on their nature (i.e., inorganic and organic). Thoughboth classifications are good, we are adopting the first for discussing the ma-terials in brief. It is important to point out that some materials may lie in two

as well as all three categories we are discussing. Though some review articlesdiscussing low-cost alternatives133−143 are already available, they are gener-ally either adsorbate-specific (metals, dyes, etc.) or are adsorbent-specific.For example, Bailey et al.135 presented a nice review of the removal of met-als by low-cost adsorbents; similarly, an overview of low-cost adsorbentsfor heavy metal removal has been presented by Babel and Kurniawan.136

Heavy metal removal by metabolically inactive non-living biomass of mi-crobial or plant origin has been reviewed by Ahluwalia and Goyal137; theapplication of biosorption using fungi, yeasts, and bacteria for the removal

of organic pollutants has been reviewed by Aksu

143

; Crini

138

reviewed thefeasibility of various non-conventional low-cost adsorbents for removal of dyes; chromium removal by various low-cost adsorbents has been discussedby Mohan and Pittman139; the possible use of sawdust for removal of variouscontaminants such as dyes and metals has been discussed by Shukla et al.140;the use of polysaccharide-based materials as adsorbents have been reviewedby Crini141; and application of chitosan for metal removal has been discussedby Gerente et al.142

Without going into too much detail, a summary of some relevant pub-lished data with some of the latest important results and giving a source

of up-to-date literature on the adsorption properties of some alternative


15/62

− A l u m i n a a n d b a

u x i t e

− S i l i c a g e l

− Z e o l i t e s a n d i o n

e x c h a n g e

r e s i n

− A c t i v a t e d c a r b o

n

−

L o w - c o s t a l t e r n a t i v e

a d s o r b e n t s

I n d u s t r i a l , a g r i c u l t u r a l

a n d d o m e s t i c a c t i v i t i e s

S o

l i d p o l l u t a n t s ,

b y p r o d u c t s

P h y s i c o c h e m i c a l

p r o c e s s e s

B i o l o g i c a l p r o c e s s e s

N u c l e a r t r e a t m e n t

A c o u s t i c a l , e l e c t r i c a l

a n d e l e c t r o m a g n e t i c

p r o c e s s e s

D i s s o l v e d a n d n o n -

d i s s o l v e d c h e m i c a l s

H e a t

B i o l o g i c a l a g e n t s

−

A d s o r p t i o n

− F i l t r a t i o n

− U l t r a f i l t r

a t i o n a n d d i a l y s i s

− R e v e r s e

o s m o s i s

− I o n e x c h

a n g e

− S o l v e n t e x t r a c t i o n

− O x i d a t i o

n u s i n g c h l o r i n e ,

o z o n e , h y d

r o g e n p e r o x i d e ,

c h l o r i n e d i

o x i d e ,

− E v a p o r a t i o n

− C o a g u l a t i o n , f o a m f l o a t a t i o n

− P h o t o c h e m i c a l r e a c t i o n s

L i q

u i d p o l l u t a n t s /

b y

p r o d u c t s

O n e o f t h e u t i l i z a t i o

n m e t h o d s

S o u r c e

P o l l u t a n t / p o l l u t i o n

T r e a t m e n t

m e t h o d o l o g y

F

I G U R E 2 . S c h e m a t i c d i a g r a m o f

s o l i d l i q u i d p o l l u t a n t g e n e r a t i o n

a n d t h e i r r e m o v a l .

795


16/62


Organic precursors Inorganic precursors

Industrial, agricultural,

and domestic activities

Physical activation

Carbonization

Activation

Washing and drying

Sieving and storage

Chemical activation

Mixing precursor withchemical

Activation

Washing and drying

Sieving and storage

Chemical treatment

Washing and drying

Sieving and storage

Characterization of

adsorbent

Adsorption and testing of

adsorbent by batch process

Removal of pollutants by

small scale column

Removal of pollutants by

large scale column

FIGURE 3. Protocol for development of low-cost adsorbents and their utilization for wastew-ater treatment.

adsorbents is presented in Table 1, and some of the results are dis-cussed here. It is worthwhile mentioning here that a critical directcomparison135,136,138,139 of adsorbents is difficult because of the many in-consistencies in data presentation, and also (mainly) due to the differ-ent laboratory conditions, materials, and methodologies (which includesdifferent concentrations, pH, temperature, adsorbent dose, particle size, gas


17/62

T

A B L E 1 . R e p o r t e d a d s o r p t i o n c a

p a c i t i e s a n d o t h e r p a r a m e t e r s f o r d i f f e r e n t a d s o r b e n t s

M a t e r i a l

A d s o r b

a t e s

A d s o r p t i o n

c a p a c i t y

C o n c e n t r a t i o n

r a n g e

C

o n t a c t

t i m e

P e r c e n t a g e

a d s o r p t i o n

R e f e r e n c e

W o o d

T e l o n b l u e

7 . 0 – 1 1 . 6 m g g − 1

—

—

—

1 4 4

W o o d

A s t r a z o n e b l u e

1 0 0 . 1 m g g − 1

—

2 h

—

1 4 5

J u n i p e r w o o d

C d ( I I )

2 4 . 8 – 2 8 . 3 µ

m o l g − 1

—

3 0 m i n

—

2 7 1

H a

r d w i c k i a b i n a t a

b a r k

H g ( I I )

5 . 3 8 – 9 . 5 8 m g g − 1

5 – 4 0 0 m g L − 1

2 h

—

2 7 2

P i n k b a r k

C u ( I I ) , C d ( I I ) , N i

( I I )

0 . 1 4 9 , 0 . 1 2 6 , 0 . 1 0 7

m m o l g − 1

≤

4 0 0 m g L − 1

2 4 h

—

2 7 3

P i n u s s y l v e s t r i s b a r k

C r ( I I I )

9 . 7 7 m g g − 1

5 – 2 0 m g L − 1

2 4 h

≥ 9

1 6 5

E u

c a l y p t u s b a r k

C r ( V I )

4 5 m g g − 1

2 5 0 m g L − 1

—

—

2 7 4

C o

a l

M e t o m e g a c

h r o m e

o r a n g e ( M

C O )

0 . 7 6 9 1 m g g − 1

1 0 m g L − 1

8 0 m i n

9 7 . 6 6 %

2 7 5

S a m l a c o a l

P h e n o l ,

p - n i t r o p h e n o l ,

p - c h l o r o p h e n o l

1 3 . 2 8 , 5 1 . 5 4 , 5 0

m g g − 1

—

7 2 h

—

2 7 6

C h

a r fi n e s , l i g n i t e

c o a l , b i t u m i n o u s

c o a l

D i r e c t b r o w n

6 . 4 , 4 . 1 , 2 . 0 4 m g g − 1

5 0 m g L − 1

6 0 m i n

—

1 4 7

L i g

n i t e - I l g ı n

C u ( I I ) , P b (

I I ) , N i ( I I ) 1 7 . 8 , 5 6 . 7 , 1 3 . 0

m g g − 1

—

4 0 – 7 0 m

i n f o r C u

( I I ) , N

i ( I I ) , 1 0 – 3 0

m i n f o r P b ( I I )

6 7 %

2 7 7

L i g

n i t e - B e y s e h i r

C u ( I I ) , P b (

I I ) , N i ( I I ) 1 8 . 9 , 6 8 . 5 , 1 2 . 0

m g g − 1

—

4 0 – 7 0 m

i n f o r C u

( I I ) , N

i ( I I ) , 1 0 – 3 0

m i n f o r P b ( I I )

6 0 %

2 7 7

L i g

n i t e

F e ( I I ) , M n ( I I ) , F e

( I I I )

3 4 . 2 2 , 2 5 . 8 4 , 1 1 . 9 0

m g g − 1

—

4 8 h

—

2 7 8

P e a t


0 . 4 3 – 0 . 9 1 g g − 1

2 0 0 m g d m − 3

5 d a y s

—

2 7 9

P e a t

P b

2 7 – 1 0 6 m g g − 1

1 0 0 – 5 0 0 m g d m − 3

4 h

—

2 8 0

( C o n t i n u e

d o n n e x t p a g e )

797


18/62

T


p a c i t i e s a n d o t h e r p a r a m e t e r s f o r d i f f e r e n t a d s o r b e n t s ( C o n t i n u e d )

M a t e r i a l

A d s o r b

a t e s

A d s o r p t i o n

c a p a c i t y


r a n g e

C

o n t a c t

t i m e

P e r c e n t a g e

a d s o r p t i o n

R e f e r e n c e

S p h a g n u m p e a t m o s s P b , C u , N i

2 4 . 6 , 1 4 . 3 , 7 . 5 m g g − 1

3 5 – 2 1 0 ,

2 5 – 2 0 0 , 1 0 – 1 0 0

m g L − 1

—

—

2 8 1

C h

i t i n

H g

1 0 0 m g g − 1

—

—

—

2 8 2

C h

i t o s a n

H g

4 3 0 m g g − 1

—

—

—

2 8 3

C h

i t o s a n b e a d

( c h e m i c a l l y

c r o s s l i n k e d )

R e a c t i v e b l u

e 2 ,

r e a c t i v e r e d 2 ,

r e a c t i v e y e l l o w 2 ,

r e a c t i v e y e l l o w 8 6

2 4 9 8 , 2 4 2 2 , 2 4 3 6 ,

1 9 1 1 m g g − 1

—

5 d a y s

—

2 8 4

C h

i t o s a n b e a d



A c i d o r a n g e

1 2 , a c i d

r e d 1 4 , a c i d o r a n g e

7

1 9 5 4 , 1 9 4 0 , 1 9 4 0

m g g − 1

—

5 d a y s

—

2 8 4

C h

i t o s a n b e a d



D i r e c t r e d 8 1

2 3 8 3 m g g − 1

—

5 d a y s

—

2 8 4

S t a

r c h g r a f t

c o p o l y m e r

C u ( I I ) , P b ( I I )

2 . 1 2 , 2 . 0 9 m m o l g − 1

—

2 h

—

1 8 0

S q u i d p e n s

R e a c t i v e g r e

e n 1 2 ,

d i r e c t g r e e n 2 6

3 9 . 8 , 4 . 8 3 m g g − 1

—

1 5 d a y s

—

1 5 5

S e p i a p e n s


e n 1 2 ,


3 . 4 6 , 5 6 . 0 m g g − 1

—

1 5 d a y s

—

1 5 5

A n

o d o n t a s h e l l


e n 1 2 ,


0 . 4 3 6 , 1 1 . 3 m g g − 1

—

1 5 d a y s

—

1 5 5

G a

n o d e r m a

l u c i d u n a

C u ( I I )

0 . 3 8 3 m m o l g − 1

0 . 2 – 1 m M

6 0 m i n

—

2 8 5

R .

a r r h i z u s a n d C .

v u l g a r i s

I r o n ( I I I ) - c y a n i d e

c o m p l e x

6 1 2 . 2 , 3 8 7 m g g − 1

1 9 9 6 . 2 , 3 8 7 m g L − 1

—

—

2 8 6

D .

p o t a t o r u m

C u , C d

1 . 3 0 , 1 . 1 2 m m o l g − 1

—

—

9 2 , 9 0 %

2 8 7

798


19/62

R . n i g r i c a n s b i o m a s s P b

7 4 . 6 8 m g g 1

1 0 0 – 1 0 0 0 m g L − 1

2 h

—

2 8 8

M o d i fi e d m y c e l i u m

N i ( I I )

2 6 0 m g g 1

2 0 0 – 8 0 0 m g L − 1

5 h

—

1 6 6

M o n t m o r i l l o n i t e

P b , C d

0 . 3 4 , 0 . 3 6 m e q g − 1

4 × 1 0 − 4 – 9 ×

1 0 − 3 M

2 4 h

—

2 8 9

K a o l n i t e

P b , C d

0 . 0 6 , 0 . 1 6 m e q g − 1

4 × 1 0 − 4 – 9 ×

1 0 − 3 M

2 4 h

—

2 8 9

N a t u r a l c l a y

N i ( I I )

1 2 . 5 m g g 1

1 0 – 5 0 p p m

4 5 m

i n

—

2 9 0

H e a t - t r e a t e d

b e n t o n i t e

C d

1 6 . 5 0 m g g − 1

—

—

—

1 7 4

A c i d - t r e a t e d

b e n t o n i t e

C d

4 . 1 1 m g g − 1

—

—

—

1 7 4

A c t i v a t e d c l a y

B B 6 9 , B R 2 2

5 8 5 , 4 8 8 . 4 m g g − 1

—

—

9 0 . 2 3 , 6 1 . 7 8 %

2 9 1

S p e n t a c t i v a t e d c l a y

C u ( I I )

1 0 . 9 m g g − 1

3 . 0 × 1 0 − 5 M

6 0 m

i n

—

1 7 3

B e n t o n i t e

C r ( V I ) , P b

0 . 5 1 2 , 6 . 0 m g g − 1

—

—

—

2 9 2

W o l l a s t o n i t e

M e t o m e g

a c h r o m e

o r a n g e

0 . 6 9 5 7 m g g − 1

1 0 m g L − 1

1 5 0 m i n

7 3 . 0 4 %

2 9 3

K a o l n i t e

M e t o m e g

a c h r o m e

o r a n g e

0 . 6 5 0 6 m g g − 1

1 0 m g L − 1

1 2 0 m i n

8 4 . 2 3 %

2 9 3

K a o l i n i t e

C r ( I I I )

0 . 1 0 8 m e q g − 1

0 . 6 2 – 8 . 2 7 m m o L − 1

—

—

2 9 4

B e n t o n i t e

C u ( I I )

4 . 7 5 m g g − 1

1 0 0 µ g m l − 1

1 8 0 m i n

8 5 %

2 9 5

B e n t o n i t e

M e t h y l e n

e b l u e

1 6 6 7 m g g − 1

1 0 0 – 1 0 0 0 m g L − 1

6 0 m

i n

—

2 9 6

B e n t o n i t e

B a s i c r e d

2

2 7 4 m g g − 1

5 0 – 4 5 0 m g L − 1

6 0 m

i n

—

2 9 7

A l u n i t e

P h o s p h a t e

1 3 2 . 4 m g g − 1

—

6 0 m

i n

—

2 9 8

D i a t o m i t e

M e t h y l e n

e b l u e

1 9 8 m g g − 1

1 0 0 – 4 0 0 m g d m − 3

4 8 h

—

1 7 0

J o r d a n i a n p o t t e r y

C u ( I I )

7 . 5 5 m g g − 1

5 0 – 5 0 0 p p m

—

—

2 9 9

P e a n u t h u l l c a r b o n

H g ( I I )

1 0 9 . 8 9 m g g − 1

1 0 – 2 0 m g L − 1

5 – 1 8

0 m i n

—

1 8 2


C d ( I I )

8 9 . 2 9 m g g − 1

2 0 m g L − 1

6 0 m

i n

∼

1 0 0 %

1 8 3


P b ( I I )

2 1 0 . 5 3 m g g − 1

1 0 – 5 0 m g L − 1

8 0 m

i n

9 8 %

1 8 4

P e a n u t h u l l

P b ( I I ) , C

u ( I I ) , C d

( I I ) , Z n

( I I )

3 0 , 8 , 6 , 9 m g g − 1

≤

1 0 0 0 m g L − 1

4 h

—

1 8 6

( C o n t i n u e d o n n e x t p a g e )

799


20/62

T



M a t e r i a l

A d s o r b

a t e s

A d s o r p t i o n

c a p a c i t y


r a n g e

C

o n t a c t

t i m e

P e r c e n t a g e

a d s o r p t i o n

R e f e r e n c e

P e a n u t p e l l e t s

P b ( I I ) , C u ( I I ) , C d

( I I ) , Z n ( I I )

3 0 , 1 0 , 6 , 9 m g g − 1

≤

1 0 0 0 m g L − 1

4 h

—

1 8 6

H a

z e l n u t s h e l l

C d 2 + , Z n 2 + ,

C r ( I I I ) ,

C r ( I V )

5 . 4 2 , 1 . 7 8 , 3 . 0 8 , 3 . 9 9

g K g − 1

0 . 1 – 2 . 0 m m o L − 1

5 h

9 2 . 4 , 8 7 . 9 , 9 4 . 6 , a

n d

9 7 . 8

3 0 0

H a


M e t h y l e n e b

l u e , a c i d

b l u e 2 5

7 6 . 9 , 6 0 . 2 m g g − 1

5 0 – 1 0 0 0 , 5 0 – 5 0 0

m g L − 1

6 0 – 1 8 0 m i n

—

1 8 7

H a


a c t i v a t e d c a r b o n

N i ( I I )

5 . 7 5 7 – 1 1 . 6 4 0 m g g − 1

—

1 8 0 m i n

—

3 0 1

S a w d u s t : w a l n u t

M e t h y l e n e b

l u e , a c i d

b l u e 2 5

5 9 . 1 7 , 3 6 . 9 8 m g g − 1

5 0 – 1 0 0 0 , 5 0 – 5 0 0

m g L − 1

6 0 – 1 8 0 m i n

—

1 8 7

S a w d u s t : c h e r r y

M e t h y l e n e b

l u e , a c i d

b l u e 2 5

3 9 . 8 4 , 3 1 . 9 8 m g g − 1

5 0 – 1 0 0 0 , 5 0 – 5 0 0

m g L − 1

6 0 – 1 8 0 m i n

—

1 8 7

S a w d u s t : o a k

M e t h y l e n e b

l u e , a c i d

b l u e 2 5

2 9 . 9 4 , 2 7 . 8 5 m g g − 1

5 0 – 1 0 0 0 , 5 0 – 5 0 0

m g L − 1

6 0 – 1 8 0 m i n

—

1 8 7

S a w d u s t : p i t c h p i n e

M e t h y l e n e b

l u e , a c i d

b l u e 2 5

2 7 . 7 8 , 2 6 . 1 9 m g g − 1

5 0 – 1 0 0 0 , 5 0 – 5 0 0

m g L − 1

6 0 – 1 8 0 m i n

—

1 8 7

A l k a l i - t r e a t e d s t r a w

C r ( I I I )

3 . 9 1 m g g − 1

—

6 0 m i n

—

3 0 2

I n s o l u b l e s t r a w

x a n t h a t e

C r ( I I I )

1 . 8 8 m g g − 1

—

6 0 m i n

—

3 0 2

S u n fl o w e r s t a l k

M e t h y l e n e b

l u e ,

b a s i c r e d 9 , c o n g o

r e d , d i r e c t b l u e

2 0 5 , 3 1 7 , 3 7 . 7 8 , 2 6 . 8 4

m g g − 1

1 0 0 – 2 0 0 0 , 1 0 0 – 2 0 0 0 ,

5 0 – 1 0 0 0 , 5 0 – 1 0 0 0

m g L − 1

5 d a y s

8 0 %

1 9 2

S u n fl o w e r s e e d

s h e l l s , m a n d a r i n

p e e l i n g s

R e a c t i v e b l a

c k 5

—

5 0 m g L − 1

2 1 0 m i n

8 5 , 7 1 %

3 0 3

O r

a n g e p e e l

D i r e c t r e d 2 3 , d i r e c t

r e d 8 0

1 0 . 7 2 , 2 1 . 0 5 m g g − 1

—

1 5 m i n

—

3 0 4

800


21/62

M a i z e c o b

A c i d b l u e 2 5 , a c i d

r e d 1 1 4

4 1 . 4 , 4 7 . 7 m g g − 1

0 . 0 5 d m 3

5 d a y s

—

3 0 5

C o r n c o b

C u ( I I )

0 . 3 4 4 1 m m o l g − 1

6 . 0 × 1 0 − 3 – 0 . 5 ×

1 0 − 4

m o l L − 1

1 5 m

i n – 1 h

—

3 0 6

L i g n i n

P b ( I I ) , C

u ( I I ) , C d

( I I ) , Z n

( I I ) , N i ( I I )

0 . 4 3 2 , 0 . 3 6 0 , 0 . 2 2 6

,

0 . 1 7 2 , 0 . 1 0 2

m m o l / g

0 . 2 – 2 . 5 m M

2 4 h

—

3 0 7

O r g a n o s o l v l i g n i n

C u ( I I )

∼

1 . 7 m g g − 1

—

4 0 m

i n

4 0 . 7 4 %

1 9 4

K r a f t l i g n i n

C u ( I I )

3 . 3 8 m g g − 1

5 – 2 0 0 m g L − 1

3 h

—

1 9 5

S t r a w l i g n i n

C u ( I I )

4 . 2 m g g − 1

—

6 0 m

i n

—

1 9 6

L i g n i n : b e e c h

P b ( I I ) , C

d ( I I )

8 . 2 , 6 . 7 m g g − 1

—

4 – 5 h

—

1 9 7

L i g n i n : p o p l a r

P b ( I I ) , C

d ( I I )

9 . 0 , 7 . 5 m g g − 1

—

4 – 5 h

—

1 9 7

K r a f t l i g n i n

C u ( I I ) , C

d ( I I )

1 3 7 , 8 7 m g g − 1

1 × 1 0 − 5 – 5 ×

1 0 − 3 M

4 8 h

—

1 9 8

S o y m e a l h u l l

D i r e c t r e d 8 0 , d i r e c t

r e d 8 1 , a c i d b l u e

9 2 , a c i d r e d 1 4

1 7 8 . 5 7 , 1 2 0 . 4 8 ,

1 1 4 . 9 4 , 1 0 9 . 8 9

m g g − 1

5 0 – 1 5 0 m g L − 1

2 4 h

3 0 8

H a r d w o o d s a w d u s t


8 2 . 2 – 1 0 5 . 7 m g g − 1

2 0 0 m g d m − 3

3 h

—

3 0 9

S a w d u s t

C u ( I I )

4 . 4 0 – 0 . 1 6 m g g − 1

1 – 5 0 m g L − 1

6 0 m

i n

—

3 1 0

S a w d u s t

C r ( V I )

4 . 4 4 m g g − 1

5 0 m g d m − 3

4 5 – 7

5 m i n

—

3 1 1

P o l y a c r y l a m i d e -

g r a f t e d

s a w d u s t

C r ( V I )

1 2 . 4 m g g − 1

1 0 0 – 1 0 0 0 m g L − 1

4 h

9 1 %

3 1 2

B e e c h s a w d u s t

M e t h y l e n

e b l u e , r e d

b a s i c 2

2

9 . 7 8 , 2 0 . 2 m g g − 1

—

1 4 d a y s

—

2 0 0

C e d a r s a w d u s t ,

c r u s h e d b r i c k

M e t h y l e n

e b l u e

1 4 2 . 3 6 , 9 6 . 4 1 m g g − 1

—

5 h

—

3 1 3

( C o n t i n u e d o n n e x t p a g e )

801


22/62

T



M a t e r i a l

A d s o r b

a t e s

A d s o r p t i o n

c a p a c i t y


r a n g e

C

o n t a c t

t i m e

P e r c e n t a g e

a d s o r p t i o n

R e f e r e n c e

W o o l , o l i v e c a k e ,

s a w d u s t , p i n e

n e e d l e s , a l m o n d

s h e l l s , c a c t u s

l e a v e s , a n d

c h a r c o a l

C r ( V I )

4 1 . 1 5 , 3 3 . 4 4 , 1 5 . 8 2 ,

2 1 . 5 0 , 1 0 . 6 2 , 7 . 0 8 ,

6 . 7 8 m g g − 1

2 0 – 1 0 0 0 m g L − 1

2 h

8 1 %

2 5 1

P i n h ˜ a o w a s t e s

C u ( I I )

3 2 . 2 m g g − 1

1 0 – 1 0 0 0 m g L

Date post:	07-Jul-2018
Category:	Documents
Upload:	etelka-david
View:	253 times
Download:	0 times

Low Cost Adsorbents

Documents