Review Article History, Introduction, and Kinetics of Ion ...A. Skogseid Preparation of potassium-speci c polystyrene cation exchanger chelating resin. J. A. Marinsky, L. E. Glendenin,

Hindawi Publishing CorporationJournal of ChemistryVolume 2013 Article ID 957647 13 pageshttpdxdoiorg1011552013957647

Review ArticleHistory Introduction and Kinetics of Ion Exchange Materials

Sanjeev Kumar and Sapna Jain

University of Petroleum and Energy Studies Dehradun Uttarakhand 248007 India

Correspondence should be addressed to Sapna Jain sapnaj22gmailcom

Received 20 May 2013 Revised 14 August 2013 Accepted 15 August 2013

Academic Editor Roberto Comparelli

Copyright copy 2013 S Kumar and S JainThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

During the last few decades ion exchange materials have evolved from laboratory tool to industrial products with significanttechnical and commercial impact The current paper briefly summarizes the history of the development of the ion exchangematerialsThe paper defines the ion exchangematerials and their typesThe paper signifies the kinetics involved in the ion exchangeprocess with description of factors affecting the rate of ion exchange The mechanism of ion exchange has also been delineatedthrough schematic diagram illustrating that there are two types of diffusion film and particle controlled diffusion A brief ofmathematical approach for kinetics of ion exchange has also been incorporated

1 Introduction

11 Historical Background Whenever an ion is removed outof an aqueous solution and is replaced by another ionicspecies it is generally referred to as ldquoion exchangerdquo It is anancient technique in cultural heritage Renaissance potteryof Mediterranean basin consisting of glass thin film had het-erogeneous distribution of silver and copper nanoparticles ofvaried sizes deposited on ceramic substrate [1ndash3] The cop-persilver deposition was obtained by putting a mixture ofcopper and silver salts and oxides together with vinegarochre and clay on the surface of a previously glazed potteryThen the whole systemwas heated to about 600∘C in a reduc-ing atmosphere produced by the introduction of smokingsubstances in the kiln In these conditions an ion exchangeprocess between metal ions and alkali ions in the glass wasinduced Later on the metal ions followed by a reductionaggregated remaining trapped within the first layer

Even before the sunup of the human civilization the ionexchange technique can be traced back to the Holy biblementioning the preparation of drinking water by ldquoMosesrdquofrom brackish water

Although the exchange of cations as a phenomenon wasfirst discovered slightly more than hundred years ago twoEnglish agricultural chemistsThompson andWay noted thatcertain soils had a greater ability than others to absorb ammo-nia from fertilizers [4 5] They found that complex silicates

in the soil performed an ion exchange function They wereable to prepare materials of this type in the laboratory fromsolutions of sodium aluminate and sodium silicate In 1906RoberGans usedmaterials of this type for softeningwater andfor treating sugar solutions [6]The first organic ion exchang-ers were synthesized in 1935 Adams and Holmes foundthat the crushed phonograph records exhibit ion exchangeproperties [7] In the middle 1940rsquos ion exchange resins weredeveloped based on the copolymerization of styrene cross-linked with divinylbenzeneThese resins were very stable andhad much greater exchange capacities than their predeces-sorsThe polystyrene-divinylbenzene-based anion exchangercould remove all anions including silicic and carbonic acidsThis innovationmade the complete demineralization ofwaterpossible

The discovery of ion exchangers was predetermined bythe overall progress in fundamental science in the middle(Michael Faraday concept of ions) and late (Svante Arrhe-nius theory of electrolytic solutions) eighteenth centuryThese ideas were crucial for the scientific discovery of ionexchangers because such materials both organic and inor-ganic are essentially polyelectrolytesThismeans that they canbe considered as consisting of two ions of opposite chargeContrary to conventional electrolytes ions of one charge arefixed to a polymeric (organic ion exchangers) or crystal-line (inorganic ion exchangers) structure Like any ioniccompound an ion exchange material can dissociate and

2 Journal of Chemistry

participate in ion exchange reactions However dissociationdoes not result in dissolving of the material This causesmany specific phenomena and many possibilities to designheterogeneous systems with ionic properties (Table 1)

12 Ion Exchange Materials Ion exchange is a chemical reac-tion in which free mobile ions of a solid the ion exchangerare exchanged for different ions of similar charge in solutionThe exchanger must have an open network structure eitherorganic or inorganic which carries the ions and which allowsions to pass through it

An ion exchanger is a water-insoluble substance whichcan exchange some of its ions for similarly charged ionscontained in a medium with which it is in contact thisdefinition is all embracing Referring to a ldquosubstancerdquo ratherthan a compound includes many exchangersmdashsome of themare natural products which do not have awell defined compo-sition The term ldquomediumrdquo acknowledges that ion exchangecan take place in solution both aqueous and nonaqueous inmolten salts or even in contact with vapours The definitionis not limited to solids since some organic solvents which areimmiscible withwater can extract ions from aqueous solutionby an ion exchange mechanism [10]

The definition also indicates something about the processof ion exchange Basically it consists of contact between theexchanger and themedium inwhich the exchange takes placeThese are usually a solid ion exchanger and an aqueous solu-tionThe fact that ions are exchanged implies that the exchan-ger must be ionized but only one of the ions in the exchangeris solubleThat ion can exchange while the other being insol-uble cannot do so

If we represent the ion exchanger as M+Xminus to show that itis ionizedmdashM+ being the soluble ionmdashand imagine it placedin a solution of the salt NY which ionizes to give the ions N+and Yminus the exchange reaction can be written as follows

M+Xminus +N+ + Yminus 997888rarr N+Xminus +M+ + Yminus (1)

This resembles a simple displacement reaction between twosalts MX and NY Since the ion Yminus takes no part in the reac-tion it can be omitted from both sides of the equation whichthen simplifies to

M+Xminus +N+ 997888rarr N+Xminus +M+ (2)

In this example cations are exchanged similarly an analogousequation can be written for an ion exchange when the insol-uble ion in the exchanger is the cation

There is no strict difference between ion exchange resinand chelating resins because some polymers can act as chelat-ing or nonchelating substance depending on the chemicalenvironment Ion exchange resembles sorption because bothare surface phenomenon and in both cases a solid takes up adissolved speciesThe characteristic difference between thesetwo phenomena is in stoichiometric nature of ion exchangeEvery ion removed from the solution is replaced by an equiv-alent amount of same charge (Figure 1) In sorption on theother hand a solute is usually taken up nonstoichiometricallywithout being replaced

Conventionally ion exchange materials are classified intotwo categories cation exchangers and anion exchangersbased on the kind of ionic groups attached to the material

Cation exchange materials containing negatively chargedgroups like sulphate carboxylate phosphate benzoate andso forth are fixed to the backbone material and allow the pas-sage of cations but reject anions while anion exchange mate-rials containing positively charged groups like amino groupalkyl substituted phosphine (PR

3

+) alkyl substituted sul-phides (SR

2

+) and so forth are fixed to the backbone materi-als and allow passage of anions but reject cations There arealso amphoteric exchangers that are able to exchange bothcations and anions simultaneously However the simultane-ous exchange of cations and anions can be more efficientlyperformed inmixed beds that contain a mixture of anion andcation exchange resins or passing the treated solution throughseveral different ion exchange materials There is one otherclass of ion exchanger known as chelating ion exchangerMany ions accept lone pair of electrons from ligands estab-lishing covalent like bonds called coordination bondsDepending on the number of coordination bonds the ligandis called monodentate bidentate or polydentate Coordina-tion interactions are highly specific An example of a coor-dination compound is the coordination of a metal ion withethylene diamine tetra acetic acid (EDTA) (Figure 2)

Organic structure of functional groups often containsnitrogen oxygen and sulphur atoms which are electrondonor elements (Figure 3)

13 Types of Ion Exchange Material Based on origin the ionexchange materials can be classified as natural and synthetic(Figure 4)

14 Natural Organic Products Several natural organic mate-rials possess ion exchange properties or can be given to themby simple chemical treatment Plant and animal cells act asion exchangers by virtue of the presence of carboxyl groups ofamphoteric proteins These carboxyl groups (ndashCO

2H) and

phenolic groups (ndashOH) are weakly acidic and will exchangetheir hydrogen ions for other cations under neutral or alka-line conditionsThehumins and humic acids found in naturalsoil ldquohumusrdquo are examples of this class of exchanger thepartially decayed and oxidized plant products contain acidgroupings Several organic products are marketed which arebased on treated cellulose either in fibre form for use in ionexchange columns or as filter papers for ion exchange sepa-rations on paper Many ion exchangers have been preparedfrom other natural materials such as wood fibres peat andcoal by oxidation with nitric acid or better still with concen-trated sulphuric acid when the strongly acid sulphonic acidgroup (ndashSO

3H) is introduced into the material The latter

process was particularly successful with sulphonated coalsThese can exchange in acid solution because the exchanginggroup itself is ionized under these conditions whereas theweaker carboxylic and phenolic groups are not All thesematerials have certain disadvantages however they tend tocolour the solutions which are treated and their propertiesare difficult to reproduce because of the difficulty of control-ling the treatment they are given

Journal of Chemistry 3

Table 1 The main development steps of ion exchange [8 9]

Scientist namesource Breakthrough in field of ion exchange YearBible Moses experiments water debitteri sim1400 BC

Aristotle Aristotle finds that sea water loses part of its salt contents when percolated throughcertain sand sim330 BC

H S Thompson Thompson passed a solution of manure through a filter made of ordinary gardensoil and found that the ammonia was removed from solution 1845

H S Thompson and JT WayJ Spence

Recognition of the phenomenon of ion exchange and a description of its basiccharacteristicsThe ion exchange property of soils was found to be based on their containing smallamounts of zeolites

1848ndash1852

H Eichorn Proved that the adsorption of ions by clays and zeolites constitutes a reversiblereaction 1858

J Lemberg Zeolites recognized as carriers of base exchange in soils equivalence of exchange ofbases proved 1876

F Harm A RumpherS Mayert and KHalse

Artificial zeolites used for removal of potassium from sugar juices First syntheticindustrial ion exchanger Manufacture of sulphonated coals and suggestion for theremoval of potassium from sugar juices

1901ndash1902

R GansDiscovered that the zeolites could be used to soften hard water He also inventedprocesses for synthesizing zeolites and designed the equipmentmdashthe zeolite watersoftner used for the recovery of gold from sea water

1905

O Folin R Bell The first analytical application of ion exchange 1917J Whitehorn The first use of ion exchange in column chromatography 1923A Bahrdt The first use of ion exchange column for anion analysis 1927

O Leibknecht

The entirely new types of cation exchangers were developed Not only could they beused in the sodium cycle when regenerated with salt but also in the hydrogen cyclewhen regenerated with an acid One group of these cation exchangers was thecarbonaceous type which was made by the sulphonation of coal

1934ndash1939

B A Adams and E LHolmes Synthesis of the first organic ion exchanger 1934ndash1935

GF Drsquoalelio Invention of sulphonated polystyrene polymerization cation exchangers 1942G E Boyd JSchubert and A WAdamson

Demonstration of the applicability of ion exchange for adsorption of fissionproducts in traced amounts 1942

C H Mcburney Invention of aminated polystyrene polymerization anion exchangers 1947A Skogseid Preparation of potassium-specific polystyrene cationmdashexchanger chelating resin 1947J A Marinsky L EGlendenin and C DCoryell

The discovery of promethium an element found in nature is attributed to ionexchange 1947

D K Hale DReiechenberg N ETopp and C GThomas

Development of carboxylic addition polymers as weak acid cation exchangers 1949ndash1956

R M Barrer and DW Breck New zeolites as molecular sieves with ion exchange properties 1951ndash1956

H P Gregor K WPepper and L RMorris

Invention and development of chelating polymers 1952ndash1971

M A Peterson H ASober Development of cellulose ion exchangers 1956

F Helfferich Foundation laid for the new theoretical treatment of ion exchange 1959T R E Kressmannand J R Millar Invention and development of isoporous ion exchange resins 1960

J Weiss Thermally regenerable ion-exchange and water desalination based on them 1964


minus minus minus minus minus minus minus minus minus minus minus minus


Y+2Y+2Y+2Y+2Y+2Y+2

Y+2 Y+2 Y+2 Y+2 Y+2 Y+2

X+

X+X+X+X+X+X+X+X+X+X+X+X+

X+X+X+X+X+X+X+X+X+X+X+

(a)


minus minusminus minus minus minus minus minus minus minus minus minus


X+ X+ X+ X+ X+ X+ X+ X+ X+ X+ X+ X+

Z+3Z+3Z+3Z+3

Z+3

Z+3 Z+3

Z+3

(b)

Figure 1 ((a) and (b)) Equivalent character of ion exchange The following reactions are considered RX + Y2+ = RY + 2X+ and RX + Z3+ =RZ + 3X+

M

N

C

O

N

O

O

OOminus

Ominus

Ominus

H2C

Figure 2 Coordination of a metal ion with ethylene diamine tetraacetic acid (EDTA)

15 Natural Inorganic Products Many natural mineral com-pounds such as clays (eg bentonite kaolinite and illite)vermiculite and zeolites (eg analcite chabazite sodaliteand clinoptilolite) exhibit ion exchange properties Naturalzeolites were the first materials to be used in ion exchange

N

N N

N

CH2

CH2CH2

CH2CH2

CH2

CH2

COOH

CH2 COOH

COOH

COOH

COOH

Cu+2

COOminus

COOminus

COOminus

Na+

N

CH2

CH2

COOminus Na+

COOminus Na+N

CH2

CH2 COOH

COOminus Na+

+ Cu+2

+ Na+

+ Na+

+ 2H+

+ 2H+

+ 2H+

Figure 3 Functional groups containing oxygen as electron donor

processes Clay materials are often employed as backfill orbuffer materials for radioactive waste disposal sites becauseof their ion exchange properties low permeability and easy


Ion exchangers

NaturalModified

naturalSynthetic

OrganicInorganic OrganicInorganic

Vermiculite

Zeolites

Clays

Polysaccharide

Protein

Carbonaceous materials

Zeolites

Titanates and silicotitanateTransition metal hexacyanoferrate

Polystyrenedivinyl

benzenePhenolic

Acrylic

Figure 4 Classification of ion exchangers

workability Clays can also be used in batch ion exchangeprocesses but are not generally suited to column operationbecause their physical properties restrict the flow through thebed

16 Modified Natural Ion Exchangers To improve exchangecapacity and selectivity some naturally occurring organicion exchangers are modified for example cellulose basedcation exchangers may be modified by the introduction ofphosphate carbonic or other acidic functional groups

The sorption parameters of naturalmaterials can bemod-ified by a chemical andor thermal treatment for example bytreating clinoptilolite with a dilute solution of acids or somesalts a more selective form of sorbent can be developed for aparticular radionuclide [11]

In Japan natural minerals treated with alkaline solutionsunder hydrothermal conditions have been proposed for thesorption of caesiumand strontium from solutionThese treat-ments have provided materials with distribution coefficientsof 1000 to 10000 Good results have been reported for theremoval of caesium and strontium by neoline clays modifiedwith phosphoric acid [12]

17 Synthetic Organic Ion Exchangers In 1935 two chemists attheNational Chemical Laboratory in Teddington Adams andHolmes [7] demonstrated that organic ion exchange resinscould be synthesized in a manner similar to the well iden-tified resin ldquoBakeliterdquo which was prepared by Baekelandin 1909 ldquoBakeliterdquo is a hard insoluble condensation resinpolymer and can be easily made by heating together phe-nols and formaldehyde in the presence of acid or basewith the elimination of water Basically the reaction takesplace in two stages (Figure 5)

The repeat of the pervious reactions will generate a three-dimensional structure containing weakly acidic phenolicndashOH or OR groups (Figure 6)

OH

OH

OH

O

OH

O

OH OH

H

HO

minusH+

Ominus

Ominus

Ominus

Ominus

OminusOminus

CH2

CH2

CH2

CH2

OHminus

n

n

Figure 5 Mechanism of formation of Bakelite

Adams and Holmes showed that these exchanged theirhydrogen ions in alkaline solution they also prepared cationexchanger which worked in acid solution by introducingstrongly acidic sulphonic acid groups ndashSO

3H into the struc-

tureThiswas done either by sulphonation of the final productor by using as starting material not a phenol but a phenolsul-phonic acid in which the sulphonic acid group was alreadypresent


OH

OH OH OH

OH OH

CH2CH2CH2

Figure 6 Cross-linked polymer of phenol and formaldehyde

CH2

Figure 7 Styrene

By a suitable modification of their synthesis they werealso able to introduce basic groups derived from amines andso prepare synthetic anion exchangers For the first time itbecame possible to prepare under controlled conditions bothcation and anion exchange resins the behaviour and stabilityof which were considerably in advance of other materials

Until the development of modern techniques of highpolymer chemistry the condensation resins were used suc-cessfully In 1944 drsquoAlelio in the United States producedsuperior materials DrsquoAleliorsquos resins as well as most of theirdescendants were based on a regular three-dimensional net-work formed by polymerizing the benzene derivative styrene(see Figure 7)

The double bond in the side chain may be opened andstyrene units linked end to end to give the polymer chain(Figure 8)

Here the repeating unit based on the styrene moleculeoccurs millions of times Styrene may also be regarded asa derivative of ethylene in which one hydrogen atom hasbeen replaced by a phenyl group ndashC

6H6 Just as ethylene

may be polymerized to polyethylene (polythene) styrenereadily polymerizes to polystyrene The chains may belinked together into two- and three-dimensional structures ifstyrene is mixed with a small proportion of divinyl benzene(Figure 9) which resembles styrene in its properties but hastwo unsaturated side chains throughwhich it can polymerize

The polymer formed from a mixture of styrene and div-inyl benzene consists of chains like those mentioned previ-ously linked to another chain wherever the unit is a divinylbenzene molecule instead of styrene (Figure 10)

In the areas enclosed by the broken lines the chains arelinked together and if we imagine this occurring in threedimensions it is easy to see that the resulting polymer willform a fairly regular network (Figure 10) The links between

n

Figure 8 Polystyrene

CH2

H2C

Figure 9 Divinyl benzene

Figure 10 Polymer of divinyl benzene

chains are termed ldquocross-linksrdquo and the resin is generallycharacterized by the percentage of divinylbenzene (DVB)used in its preparation thus a 2 percent cross-linked resincontains 2 percent of DVB and 98 percent of styrene

DlsquoAlelio prepared such resins by emulsion polymeriza-tion using suitable emulsifiers from which the resin settlesas spherical beads The polymer itself does not work as ionexchanger but it can be sulphonated just as can the conden-sation resins introducing the strongly acidic group like ndashSO3H into the benzene rings of the polymer The hydrogen

ions of this groupwill exchangewith other cations in solutionRemembering that one benzene ring is repeated many

times throughout the polymer the basic steps in the introduc-tions of the exchanging groups (or ldquofunctionalrdquo groups as theyare usually called) are as shown in Figure cation exchange (a)and anion exchange (b) (Figure 11)

The second of these reactions gives a quaternary ammo-nium salt which is strongly ionized and is readily convertedto the corresponding base The anion readily exchanges withother anions at all pH values The cation forms part of aninsoluble polymer chain or network so that the exchanger asa whole is insoluble in water


Polymeric chain

H HO

Polymeric chain

SO3HSO3H

+ H2O

(a)

Polymeric chain Polymeric chain

+

CH2Cl

(CH3)3NCH2N+(CH3)3Clminus

(b)

Figure 11 (a) Cation exchange (b) anion exchange

The synthetic ion exchangers like polystyrene-basedresins which form the basis of most resins available commer-cially today possess numerous advantages over earlier naturalorganic exchangers

(1) the method of synthesis is more controlled and theend product is more uniform in particle size degreeof cross-linking and the content of functional groups

(2) by suitable variation of these factors a wide range ofdifferent products may be prepared

(3) the product is spherical unlike the irregular particlesformed when the solid mass of condensation resin iscrushed and sieved This minimizes waste in addi-tion spherical particles pack more uniformly intobeds than do irregularly shaped particles This influ-ences the flow pattern of solutions through the bedsand makes it easier to control their behavior

(4) the physical and chemical stability of these resins aresuperior to that of the condensation resins

18 Synthetic Inorganic Ion Exchangers

181 Synthetic Zeolites Zeolites are crystalline hydrated alu-minosilicates of alkali and alkaline earth metals having infi-nite three-dimensional atomic structures [13] They are fur-ther characterized by the ability to lose and gain water revers-ibly and to exchange certain constituent atoms also withoutmajor change of atomic structure Alongwith quartz and feld-spar minerals zeolites are three-dimensional frameworks ofsilicate (SiO

4) tetrahedra in which all four corner oxygens of

each tetrahedron are shared with adjacent tetrahedra If eachtetrahedron in the framework contains silicon as its centralatom the overall structure is electrically neutral as is quartz(SiO2) In zeolite structures some of the quadricharged sili-

con is replaced by triply charged aluminum giving rise to adeficiency of positive charge The charge is balanced by thepresence of singly-and doubly-charged atoms such assodium (Na+) potassium (K+) ammonium (NH4+) calcium(Ca2+) and magnesium (Mg2+) elsewhere in the structureThe empirical formula of a zeolite is of the type

M2119899

O sdot Al2O3sdot 119909SiO

2sdot 119910H2O (3)

whereM is any alkali or alkaline earth atom 119899 is the charge onthat atom 119909 is the ratio of silica and alumina varies numberfrom 2 to 10 and 119910 is a number from 2 to 7 The chemicalformula for clinoptilolite a common natural zeolite is

(Na3K3) (Al6Si40)O96sdot 24H2O (4)

Atoms or cations (ie charged metal atoms) within thesecond set of parentheses are known as structural atomsbecause with oxygen they make up the rigid framework ofthe structure Those within the first set of parentheses areknown as exchangeable ions because they can be replaced(exchanged) more or less easily with other cations in aqueoussolution without affecting the aluminosilicate frameworkThis phenomenon is known as ion exchange or more com-monly cation exchange The exchange process involvesreplacing one singly-charged exchangeable atom in the zeoliteby one singly-charged atom from the solution or replacingtwo singly-charged exchangeable atoms in the zeolite by onedoubly-charged atom from the solution The magnitude ofsuch cation exchange in a given zeolite is known as its cationexchange capacity (CEC) and is commonly measured interms of moles of exchangeable cation per gram (or 100grams) of zeolite or in terms of equivalents of exchangeablecations per gram (or 100 grams) of zeolite

182 Polybasic Acid Salts These are the acidic salts of multi-valent mainly quadrivalent metals formed by mixing acidicoxides of metals belonging to IV V and VI groups of periodictable They have nonstoichiometric composition based oncondition of precipitation Specially tetravalent metal acid(tma) salts [14 15] are gaining importance due to their excel-lent thermal stability and chemical resistivityThey are cationexchangers possessing the general formula M(IV)(HXO

4)2

times 119899H2O where M(IV) = Zr Ti Sn Ce Th and so forth and

X = P W As Mo Sb and so forth These materials possessstructural hydroxyl groups the H of the ndashOH being theexchangeable sites They possess an appreciable ion exchangecapacity as well as high selectivity for certain metal ionsTma salts can be obtained in both amorphous and crystallineforms Though structures of crystalline materials are wellknown they have not been found to be suitable in columnoperations as they are obtained in powder forms Amorphousmaterials on the other hand can be obtained in granular formvery suitable for column operations [16] Tma salts being syn-thesized by solndashgel routes materials with varying watercontent composition ion exchange capacity and crystallinitycan be obtained by varying parameters such as stoichiometryand concentration of the reagents used temperature at whichthey aremixed rate of addition mode ofmixing and pH Ionexchange materials with higher selectivities are continuouslybeing investigated [17]

183 Hydrous Oxides The hydrous oxides of some metalions are also used as ion exchange materials like freshlyprecipitated trivalent metal oxides


184 Metal Ferrocyanides Insoluble metal ferrocyanides arealso used as inorganic ion exchange materials commonlyknown as scavengers for alkali metals They are easy to pre-pare and are used widely in radioactive waste treatment

185 Insoluble Ion Exchange Materials They are of greatinterest as ion exchangers and are being prepared largely byprecipitation from metal salt solution with sodium sulphideand hydrogen sulphide

186 Heteropolyacids HPAs are complex proton acids thatincorporate polyoxometalate anions (heteropolyanions) hav-ing metal-oxygen octahedra as the basic structural units [10]The heteropoly compounds are quite strong oxidizing agentHeteropoly acids are used as ion exchangers derived from 12HPAswith general formulaH

119899XY12O40sdot119899H2OThefirst char-

acterized and the best knownof these is theKeggin heteropol-yanion typically represented by the formula XM

12O119909minus840

whereX is the central atom (Si4+ P5+ etc) 119909 is its oxidation stateand M is the metal ion (Mo6+or W6+)

2 Mechanism of Ion Exchange Process

Amost common ion exchange system includes a water swol-len ion exchangematerial and surrounding aqueous solutionIon exchange like any heterogeneous process is accomplishedby transfer of ions to and from the interphase boundary thatis the chemical reaction itself diffusion inside the materialand diffusion in the surrounding solution should be con-sidered as ion exchange Beside the two major phases thethin film of solution at surface of the exchanger should beconsidered separately The film properties differ from prop-erties of the surrounding bulk solution Formation of thinfilm is unavoidable Even rigorous agitations only reduce thethickness of the interphase film

Figure 12 shows the simplest illustration of the masstransfer at ion exchange Ions B diffuse from the solu-tion through the film into beads and ions A diffuse outof the beads crossing the film into the solution Thisinterphase diffusion of counterions is called ion exchangeCounterions are exchangeable ions carried by ion exchangersCounterions can freely move within the frame work buttheir movement has to be compensated by correspondingcountermovements of other ions of the same change fulfillingthe electroneutrality principle The term counterion has twointerpretations

(a) It can be used exclusively for ions inside the ionexchanger

(b) It can be used in a broad sense whether in the exchan-ger or in the external solution all ionic species withcharge sign opposite to that of the functional groupscan be called counterions

Coion is a term used for ionic species with the samecharge sign as the functional group Ionic form is the termdefining which counterion is present in the ion exchange

The solutionThe film

A B A B

A B

A B

C

C

C

C

Figure 12 Mass transfer during ion exchange the material isinitially bonded with counterion A Solution initially containscounterion B and coionC During the process ions B are transferredinside the exchanger replacing ions A When transferred betweentwo phases the ions pass through the film which cannot be removedwith agitation

Any counterion which leaves the ion exchanger isreplaced by an equivalent amount of other counterions Thisis a consequence of the electroneutrality requirement Whena counterion crosses the interphase boundary an electricpotential is created between two phases This potential mustbe compensated by the movement of another counterion inopposite direction (ion exchange) or by the movement ofco-ion in the same direction In many systems particularlyin diluted solution Donnan exclusion (Donnan exclusionreduction in concentration of mobile ions within an ionexchange membrane due to the presence of fixed ions of thesame sign as the mobile ions) restricts entering of coions intothe exchanger during the whole process In this case coionsdo not participate in the reaction and have little effect on therate However an indirect influence can occur

From Figure 13 it is clear that initially the dissolved saltdissociates containing the first ion step (1) followed bydiffusion of the first ion from solution towards the interphasefilm step (2) Then the ion diffuses out of the film step (3)towards the material phase step (4) The ion associates withthe functional group step (5) and then dissociation of secondion and the functional group occurs in step (6) The secondion diffuses inside thematerial phase towards the surface step(7)The second ion diffuses inside the interphase film step (8)followed by diffusion and randomdistribution in the solutionstep (9)Thus the formation of second ion pair completes step(10)

21 Selectivity of Ion Exchange Materials Selectivity is aparameter that is defined at specific solution conditionsOther equilibrium associated with the ion of interest mayaffect the selectivity of the ionThree general classes ofmodelshave been invoked for explaining exchange selectivity

Nonmechanistic models were derived using principlesof mass action and thermodynamics mechanistic modelsbased on diffuse double layer theory andmechanistic models


minus

minus

minus

minus

minus

Ion pair

Dissociation of ion pair

Diffusion in solution

FilmDiffusion in film

(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger

Formation of ion pair

(5)

(6)(7)

(8)


(9)

(10)

Diffusion in exchanger

Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +

Figure 13 Schematic representation of various steps involved in ion exchange process [10]

derived from the energetics of hydration and electrostaticinteractions

Calculation of mass action selectivity coefficients frommeasured ion exchange data is perhaps the most com-mon treatment of cation exchange selectivity Ideally suchcoefficients estimate thermodynamic equilibrium constants(119870sim) This treatment of ion exchange does not distinguishbetween the solid and liquid phases and therefore requiresthat activities be determined for adsorbed ions Vanselow(1932) suggested that activities of adsorbed ions are closelyapproximated by mole fractions of the ions adsorbed ontothe solid [18] Measured Vanselow coefficients (119870V) howeveroften vary with the ionic composition of the exchanger andthe total ionic strength of the equilibration solution [19]Gaines andThomas (1953) proposed integration of measuredselectivity coefficients over the full compositional range as ameans of estimating thermodynamic equilibrium constants[20]Under theGaines-Thomas approach variations inmeas-ured selectivity coefficients with the ionic composition of theexchanger are arbitrarily attributed to variations in activitiesof the adsorbed ionsThe Gaines-Thomas approach explicitlyincludes changes in chemical potential for water that mayoccur during an ion exchange reaction

The thermodynamic treatment of cation exchange selec-tivity has 2 fundamental problems (1) hysteresis is some-times observed in ion exchange reactions involving 2 1 phyl-losilicates [21] and when hysteresis is observed the thermo-dynamic treatment of ion exchange is invalid because revers-ibility is a requirement of equilibrium (2) The standard ther-modynamic approach is inherently nonmechanistic onemaypredict the outcome of an ion exchange reaction but one willnever know the cause of ion exchange selectivity

Eriksson proposed a mechanistic model for cationexchange selectivity that is based on diffuse double layer(DDL) theory [22] With various modifications the Erikssonmodel has been shown to estimate selectivity coefficients for

heterovalent exchange reactions that are within an order ofmagnitude of measured coefficients [19 23] The Erikssonmodel considers only electrostatic interactions and treats allcations as point charges therefore it does not distinguishselectivities for exchange reactions involving cations of likecharge Several authors have proposed modifications of theEriksson model in an effort to overcome this problem Nealand Cooper for example assumed that an ion could comeno closer to a charged surface than its hydrated radius[24] and Nir used specific binding coefficients to accountfor differences in selectivity for cations of like charge [25]For a given clay the Eriksson model can be adjusted tofit measured data However no amount of adjustment willchange the fundamental prediction of the Eriksson modelthat higher charged cations will be increasingly preferred aslayer charge of the clay increases Although this relationshiphas been qualitatively demonstrated forNa-Ca exchange [23]the opposite relationship is observed for K-Ca exchange[26 27] Failure of the Eriksson model to account for therelationship between layer charge and selectivity in K-Caexchange reactions suggests a major flaw in the Erikssonmodel

On a more fundamental level the validity of the Erikssonmodel for describing the ion exchange selectivity exhibitedby smectites may be questioned because the Eriksson modelis based on DDL theory In aqueous systems smectites existas quasicrystals Each quasicrystal consists of 1 to severalhundred lamellae stacked with parallel 119888 axes but randomlyoriented 119886 and 119887 axes Diffuse double layers may form in thebulk solution adjacent to external surfaces of the quasicrys-tals however DDLs do not form between lamellae within aquasicrystalWithin a quasicrystal the lamellae are separatedby 4 or fewer discrete layers of water molecules and anionsare excluded from the interlayer spaces [28] Assuming thatan average quasicrystal consists of 10 coordinated lamellaewith layer charge distributed uniformly over all surfaces then


90 of the exchangeable cations are retained on internal sur-faces and only 10 are retained on external surfaces Diffusedouble layer theory and the Eriksson model are relevant fordescribing selectivity exhibited by the 10 of cations sorbedon the external surfaces but have no bearing on selectivity forthe 90 of cations retained on internal surfaces

Another approach to understanding cation exchangeselectivity is based on Eisenmanrsquos theory which was devel-oped to explain the behavior of ion selective electrodes [29]Eisenman argued that the molar free energy of exchange(AGex) is determined by the net change in Coulombic andhydration energies for the exchanging cations Eberl appliedEisenmanrsquos theory to 2 1 phyllosilicates for exchange reac-tions between Cs and other alkali cations [30] To do so heassumed that Cs was unhydrated both in solution and whenadsorbed onto a clay However he was unable to use theEisenman approach for partially hydrated 2 1 clays becausethe hydration states of partially hydrated interlayer cationswere unknown Instead he assumed that the interlayer waterin a 2 1 clay was analogous to water in a concentrated alkalihalide solutionWith this assumption he was able to estimate119860119866sim as a function of both interlayer molarity and layercharge Consistent with experimental data the analysis indi-cated that preference for the lesser hydrated cation increasesas interlayer water decreases and as layer charge densityincreases

3 Kinetics of ion Exchange Materials

Kinetics is dependent on these considerations

(i) Mass transfer (diffusion) in the solution or in otherexternal medium is an unavoidable step in any ionexchange interaction The process is well known Itcan be easily assisted by hydrodynamic turbulencesand thus cannot be considered as a limiting step forion exchange

(ii) The film is a solution zone of certain thickness withno convectionThemass transfer in the film is definedsolely by the diffusion coefficients The film thicknesscan be reduced by an agitation

(iii) Mass transfer in the exchange phase depends on thephysiochemical properties of the system and cannotbe enhanced without altering the chemical systemitself

(iv) Reaction between counterions and fixed groups arethe only chemical interaction that can affect the over-all rate of the ion exchange

(v) Complexes dissociation and formation of ion pairsin solution is not considered as a part of the ionexchange

As followed from these considerations most of the ionexchange processes are purely diffusion phenomenon that is

they are controlled by diffusion of the counterions rather thanby actual chemical reaction

Two main rate determining steps are considered in mostof the cases diffusion of ions inside the material or diffusionof ions through the liquid film In both cases migration ofions is defined solely by properties of the system Rate ofthese steps cannot be enhanced or slowed downwith externalaction without altering the system itself

Diffusion inside the material is referred as particle diffu-sion and diffusion through film is referred as film diffusionIn simple cases the rate of ion exchange is determined by theslower of these two processes Dominance of one of thesemechanisms can be predicted using approximate [31ndash33] Forparticle diffusion control see [32ndash34]

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)

And for film diffusion control see [34] where 119876 is theconcentration of fixed group and 119862 is solution concentra-tion 119863 is the interdiffusion coefficient in the ion exchan-ger 119863 is the interdiffusion coefficient in the film 119903

0is the

bead radius 120575 is the film thickness and 120572119860119861

is the separatefactor

According to criterion all factors which tend to increasethe rate of interdiffusion in the beads and to reduce the rate inthe film favor the film diffusion control and vice versaThusthe film diffusion control may prevail in system characterizedby the following properties [31]

(i) high concentration of exchange sites

(ii) low degree of cross-linking

(iii) small particle size

(iv) dilute solution

(v) inefficient agitation

The simplest technique for distinguishing between par-ticle and film diffusion control is interruption test Theion exchange interaction is performed in batch mode Theconversion degree is monitoredThe beads are removed fromthe solutionmuch before the completion of the process Aftera brief period thematerial is reimmersed in the same solutionIf the concentration gradient is created inside the beadsthese gradients level out when supply of fresh ions from thesolution is interrupted If the process is controlled by theparticle diffusion the rate immediately after the reimmersionis greater prior to the interruption In case of the film dif-fusion the amount of the ions unevenly distributed in thefilm at themoment of the interruption is almost undetectableand no concentration gradient in the bead exists Thus theinterruption does not affect this process and the rate beforeand after the interruption in the same


4 Mathematical Approach toKinetics of Ion Exchange

The general approach to metal ion exchange kinetics is toapply conventional diffusion equations Due to accounting ofinteraction for ion exchange makes modeling highly compli-catedThese interactions are diffusion induced electric forcesselectivity specific interactions changes in swellingThe basisfor description of diffusion processes is Fickrsquos first law [35]

119869119894= minus119863119894grad119862

119894(6)

(see [35]) For phase of ion exchange

119869119894= minus119863119894grad119862

119894

(7)

(see [35]) where 119869119894is the flux of the ion in molestime and

unit cross-section119863 is the diffusion coefficient and 119862119894is the

concentration in moles per unit volumeIn the simplest case the diffusion coefficient is taken as

constant and thus the flux is proportional to the concentra-tion gradient 119863 being constant means that the species is notsubject to any forces beside the concentration inhomogeneityThis is not common case when ion exchange is consideredbecause of electrocoupling of ionic fluxes Influence of cou-pling can be neglected only when fluxes are equal There canbe exception in ion exchangeAn example of such exception isdiffusion controlled isotope in systems where concentrationof others are leveled The corresponding diffusion coefficient(same for both isotopes) is referred as the self-diffusion coef-ficient Its value is constant throughout any single phase of thesystem but of course depends on the nature and compositionof the particular phase and on the temperature

In most of the other cases the diffusion coefficient is notconstant It means that the variation of the diffusion coeffi-cient must be taken into account The influence of electricfield can be accounted by using the Nernst-Planck equationinstead of Fickrsquos equation

119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)

(see [35]) where 120576 is electric potentialIf two exchanged ions are present in the phase with

different concentration their diffusion is affected by the elec-trocoupling interaction unequally As shown in (7) the flux ofdiffusion species depends only on the concentration gradientand does not depend on the concentration itself (first term in(7)) because the diffusion is purely statistical phenomenoninvolving no physical force on the molecular level

In contrast the electric field causes a true physical forceacting on every ion and producing a flux proportional to theconcentration of the respective ion (second term in (8)) Asa result the electric field mainly affects the ions present as inmajority For those in the minority the second term is smalland thus (8) approaches (6) As a result the ions present insmall concentration migrate essentially at the rate of theirordinary diffusion For the interdiffusion of two counterions

in the absence of a significant co-ion transfer the two fluxesare rigorously coupled Diffusion of the majority ion is notmuch affected by the action of electric field and thus controlsthe rate

Equation (6) is not only possible way to describe diffusionprocess The theory of irreversible thermodynamics statesthat the driving force for diffusion is not the concentrationgradient but the gradient chemical potential

In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)

(see [35]) where 120583119894is the chemical potential and 1198631015840

119894

isinterconnected with 119863 by equation

119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)

(see [35]) while 119863119894depends on the concentration and

thus can differ in different points of the nonhomogenousmedium 1198631015840

119894

can be assumed to be having a constant valueIf the system contains more than two compounds (9) shouldbe replaced with

119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)

(see [35]) where 119899 is the number of compounds Howeverdue to the electrocoupling of ionic fluxes only one diffusionflux can be considered as independent and thus (9) could beused for most of the ion exchange [10]

In conclusion the concentration of the external solutioncan be decisive for the rate determining step that is a simpleincrease of solution concentration could alter the mechanismfrom film diffusion to particle diffusion control

5 Conclusion

Ion exchange is an ancient technique documented more thanhundred years ago Since then they were used for softeningwater to an incomparable wider scale of applications andhas become an integral part of new technical and industrialprocessesThere is a wide diversity of ion exchange materialsThey have many appearances natural and synthetic organicand inorganic cationic anionic and amphoteric and soforth A most common ion exchange system includes a waterswollen ion exchange materials and surrounding systemsIn all cases the mechanism involves formation of thin filmDuring the interphase diffusion the electroneutrality is main-tained The kinetics of ion exchange involves mass transferwhich is solely defined by the diffusion coefficients Thisdepends upon physicochemical properties of systemThe twomain steps considered to be influencing the rate are diffusionof ions inside the material or diffusion of ions through liquidfilmThe most simple technique for distinguishing the two isinterruption test


The paper suggests about steps targeting to enhance therates of the ion exchange process The most straightforwardway to get faster diffusion inside the exchanger beads is toselect materials with low density of the gel Overall the rateof process can be enhanced even without replacement ofthe materials Reducing the bead size can reduce the time ofthe equilibrium achievement for particle controlled processElevated temperature enhances the rates independent of therate controlling step

References

[1] J Perez-Arantegui J Molera A Larrea et al ldquoLuster potteryfrom the thirteenth century to the sixteenth century a nanos-tructured thin metallic filmrdquo Journal of the American CeramicSociety vol 84 no 2 pp 442ndash446 2001

[2] S Padovani C Sada P Mazzoldi et al ldquoCopper in glazes ofrenaissance luster pottery nanoparticles ions and local envi-ronmentrdquo Journal of Applied Physics vol 93 no 12 pp 10058ndash10063 2003

[3] S Padovani I Borgia B Brunetti et al ldquoSilver and coppernanoclusters in the lustre decoration of Italian Renaissance pot-tery an EXAFS studyrdquoApplied Physics A vol 79 no 2 pp 229ndash233 2004

[4] H S Thompson ldquoOn the absorbent power of soilsrdquo Journal ofthe Royal Agricultural Society of England vol 11 pp 68ndash74 1850

[5] J T Way ldquoOn the power of soils to absorb manurerdquo Journal ofthe Royal Agricultural Society vol 11 pp 313ndash379 1850

[6] R Gans ldquoZeolites and similar compounds their constitutionand meaning for technology and agriculturerdquo Jahrbuch derKoniglich Preussischen Geologischen Landesanstalt vol 26 p179 1905

[7] B A Adams and E L Holmes ldquoAdsorptive properties of syn-thetic resinsrdquo Journal of Chemical Society vol 54 pp 1ndash6 1935

[8] httpdardelinfoIXother infohistoryhtml[9] C A Lucy ldquoEvolution of ion-exchange frommoses to theman-

hattan project to modern timesrdquo Journal of Chromatography Avol 1000 no 1-2 pp 711ndash724 2003

[10] A A Zagorodni Ion Exchange Materials Properties and Appli-cations Elseiver Oxford UK 1st edition 2007

[11] N B Chernjatskaja ldquoSorption of strontiumon clinoptilolite andheulanditerdquo Radiochemistry vol 27 pp 618ndash621 1988

[12] N Yamasaki S Kanahara and K Yanagisawa ldquoAdsorptions ofstrontium and cesium ions on hydrothermally altered mineralsof feldsparrdquo Lithia-Mica and Bauxite Nippon Kagaku Kaishivol 12 pp 2015ndash2018 1984

[13] M Naushad ldquoInorganic and composite ion exchange materialsand their applicationsrdquo Ion Exchange Letters vol 2 pp 1ndash142009

[14] K G Varshney and A M Khan ldquoAmorphous inorganic ionexchangersrdquo in Inorganic Ion Exchangers in Chemical AnalysisM Qureshi and K G Varshney Eds pp 177ndash270 CRC Press1991

[15] A Clearfield ldquoInorganic ion exchangers a technology ripe fordevelopmentrdquo Industrial and Engineering Chemistry Researchvol 34 no 8 pp 2865ndash2872 1995

[16] G Alberti U Costantino andM L Luciani ldquoCrystalline insol-uble acid salt of tetravalent metals IIComparison of ion-exchange properties of crystalline 120572-zirconium phosphate and

120572-titaniumphosphaterdquoGazzetta Chimica Italiana vol 110 p 611980

[17] T Moller Selective crystalline inorganic materials as ion exchan-gers in the treatment of nuclear waste solutions [Academic Dis-sertation] University of Helsinki Helsinki Finland 2002

[18] A P Vanselow ldquoEquilibria of the base-exchange reactions ofbentonites permutites soil colloids and zeolitesrdquo Soil Sciencevol 33 no 2 pp 95ndash113 1932

[19] H Laudelout R van Bladel G H Bolt and A L Page ldquoTher-modynamics of heterovalent cation exchange reactions in amontmorillonite clayrdquo Transactions of the Faraday Society vol64 pp 1477ndash1488 1968

[20] G L Gaines Jr and H C Thomas ldquoAdsorption studies on clayminerals II A formulation of the thermodynamics of exchangeadsorptionrdquo The Journal of Chemical Physics vol 21 no 4 pp714ndash718 1953

[21] K Verburg and P Baveye ldquoHysteresis in the binary exchangeof cations on 21 clay minerals a critical reviewrdquo Clays amp ClayMinerals vol 42 no 2 pp 207ndash220 1994

[22] E Eriksson ldquoCation exchange equilibria on clay mineralsrdquo SoilScience vol 74 no 2 pp 103ndash113 1952

[23] A Maes and A Cremers ldquoCharge density effects in ionexchange I Heterovalent exchange equilibriardquo Journal of theChemical Society Faraday Transactions vol 73 pp 1807ndash18141977

[24] C Neal and D M Cooper ldquoExtended version of Gouy-Chap-man electrostatic theory as applied to the exchange behavior ofclay in natural watersrdquo Clays amp Clays Minerals vol 31 no 5 pp367ndash376 1983

[25] S Nir ldquoSpecific and nonspecific cation adsorption to clays solu-tion concentrations and surface potentialsrdquo Soil Science Societyof America Journal vol 50 no 1 pp 52ndash57 1986

[26] B L Sawhney ldquoCesium uptake by layer silicates effect on inter-layer collapse and cation exchange capacityrdquo in Proceedings ofthe International Clay Conference L Heller Ed pp 605ndash611Israel University Press Tokyo Japan September 1969

[27] I Shainberg N I Alperovitch and R Keren ldquoCharge densityand Na-K-Ca exchange on smectitesrdquo Clays amp Clay Mineralsvol 35 no 1 pp 68ndash73 1987

[28] AM Posner and J PQuirk ldquoThe adsorption ofwater fromcon-centrated electrolyte solutions by montmorillonite and illiterdquoProceedings of the Royal Society A vol 278 no 1372 pp 35ndash561964

[29] G Eisenman ldquoCation selective glass electrodes and their modeof operationrdquo Biophysical Journal vol 2 no 2 pp 259ndash3231962

[30] D D Eberl ldquoAlkali cation selectivity and fixation by clay min-eralsrdquo Clays amp Clay Minerals vol 28 no 3 pp 161ndash172 1980

[31] F Helfferich Ion Exchange McGraw Hill New York NY USA1962

[32] F G Helfferich and Y L Hwang ldquoIon Exchange kineticsrdquo in IonExchangers K Dorfner Ed pp 1277ndash1309 Walter de GruyterBerlin Germany 1991

[33] F G Helfferich ldquoIon exchange kineticsevolution of a theoryrdquoin Mass Transfer and Kinetics of Ion Exchange L Liberti andF G Helfferich Eds pp 157ndash180 Martinus Nijhoff PublishersHague The Netherlands 1983

[34] F Helfferich ldquoKinetik des Ionenaustauschsrdquo AngewandteChemie vol 68 no 22 pp 693ndash698 1956


[35] G V Samsonov E B Trostyanskaya and G E Elrsquokin IonExchange Sorption of Organic Substances (Ionnyi ObmenSorbtsiya Organicheskikh Veshchestv) Nauka Leningrad Rus-sia 1969

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


participate in ion exchange reactions However dissociationdoes not result in dissolving of the material This causesmany specific phenomena and many possibilities to designheterogeneous systems with ionic properties (Table 1)

12 Ion Exchange Materials Ion exchange is a chemical reac-tion in which free mobile ions of a solid the ion exchangerare exchanged for different ions of similar charge in solutionThe exchanger must have an open network structure eitherorganic or inorganic which carries the ions and which allowsions to pass through it

An ion exchanger is a water-insoluble substance whichcan exchange some of its ions for similarly charged ionscontained in a medium with which it is in contact thisdefinition is all embracing Referring to a ldquosubstancerdquo ratherthan a compound includes many exchangersmdashsome of themare natural products which do not have awell defined compo-sition The term ldquomediumrdquo acknowledges that ion exchangecan take place in solution both aqueous and nonaqueous inmolten salts or even in contact with vapours The definitionis not limited to solids since some organic solvents which areimmiscible withwater can extract ions from aqueous solutionby an ion exchange mechanism [10]

The definition also indicates something about the processof ion exchange Basically it consists of contact between theexchanger and themedium inwhich the exchange takes placeThese are usually a solid ion exchanger and an aqueous solu-tionThe fact that ions are exchanged implies that the exchan-ger must be ionized but only one of the ions in the exchangeris solubleThat ion can exchange while the other being insol-uble cannot do so

If we represent the ion exchanger as M+Xminus to show that itis ionizedmdashM+ being the soluble ionmdashand imagine it placedin a solution of the salt NY which ionizes to give the ions N+and Yminus the exchange reaction can be written as follows

M+Xminus +N+ + Yminus 997888rarr N+Xminus +M+ + Yminus (1)

This resembles a simple displacement reaction between twosalts MX and NY Since the ion Yminus takes no part in the reac-tion it can be omitted from both sides of the equation whichthen simplifies to

M+Xminus +N+ 997888rarr N+Xminus +M+ (2)

In this example cations are exchanged similarly an analogousequation can be written for an ion exchange when the insol-uble ion in the exchanger is the cation

There is no strict difference between ion exchange resinand chelating resins because some polymers can act as chelat-ing or nonchelating substance depending on the chemicalenvironment Ion exchange resembles sorption because bothare surface phenomenon and in both cases a solid takes up adissolved speciesThe characteristic difference between thesetwo phenomena is in stoichiometric nature of ion exchangeEvery ion removed from the solution is replaced by an equiv-alent amount of same charge (Figure 1) In sorption on theother hand a solute is usually taken up nonstoichiometricallywithout being replaced

Conventionally ion exchange materials are classified intotwo categories cation exchangers and anion exchangersbased on the kind of ionic groups attached to the material

Cation exchange materials containing negatively chargedgroups like sulphate carboxylate phosphate benzoate andso forth are fixed to the backbone material and allow the pas-sage of cations but reject anions while anion exchange mate-rials containing positively charged groups like amino groupalkyl substituted phosphine (PR

3

+) alkyl substituted sul-phides (SR

2

+) and so forth are fixed to the backbone materi-als and allow passage of anions but reject cations There arealso amphoteric exchangers that are able to exchange bothcations and anions simultaneously However the simultane-ous exchange of cations and anions can be more efficientlyperformed inmixed beds that contain a mixture of anion andcation exchange resins or passing the treated solution throughseveral different ion exchange materials There is one otherclass of ion exchanger known as chelating ion exchangerMany ions accept lone pair of electrons from ligands estab-lishing covalent like bonds called coordination bondsDepending on the number of coordination bonds the ligandis called monodentate bidentate or polydentate Coordina-tion interactions are highly specific An example of a coor-dination compound is the coordination of a metal ion withethylene diamine tetra acetic acid (EDTA) (Figure 2)

Organic structure of functional groups often containsnitrogen oxygen and sulphur atoms which are electrondonor elements (Figure 3)

13 Types of Ion Exchange Material Based on origin the ionexchange materials can be classified as natural and synthetic(Figure 4)

14 Natural Organic Products Several natural organic mate-rials possess ion exchange properties or can be given to themby simple chemical treatment Plant and animal cells act asion exchangers by virtue of the presence of carboxyl groups ofamphoteric proteins These carboxyl groups (ndashCO

2H) and

phenolic groups (ndashOH) are weakly acidic and will exchangetheir hydrogen ions for other cations under neutral or alka-line conditionsThehumins and humic acids found in naturalsoil ldquohumusrdquo are examples of this class of exchanger thepartially decayed and oxidized plant products contain acidgroupings Several organic products are marketed which arebased on treated cellulose either in fibre form for use in ionexchange columns or as filter papers for ion exchange sepa-rations on paper Many ion exchangers have been preparedfrom other natural materials such as wood fibres peat andcoal by oxidation with nitric acid or better still with concen-trated sulphuric acid when the strongly acid sulphonic acidgroup (ndashSO

3H) is introduced into the material The latter

process was particularly successful with sulphonated coalsThese can exchange in acid solution because the exchanginggroup itself is ionized under these conditions whereas theweaker carboxylic and phenolic groups are not All thesematerials have certain disadvantages however they tend tocolour the solutions which are treated and their propertiesare difficult to reproduce because of the difficulty of control-ling the treatment they are given








1848ndash1852





1901ndash1902


1905


O Leibknecht


1934ndash1939

















Y+2Y+2Y+2Y+2Y+2Y+2

Y+2 Y+2 Y+2 Y+2 Y+2 Y+2

X+



(a)




X+ X+ X+ X+ X+ X+ X+ X+ X+ X+ X+ X+

Z+3Z+3Z+3Z+3

Z+3

Z+3 Z+3

Z+3

(b)


M

N

C

O

N

O

O

OOminus

Ominus

Ominus

H2C



N

N N

N

CH2

CH2CH2

CH2CH2

CH2

CH2

COOH

CH2 COOH

COOH

COOH

COOH

Cu+2

COOminus

COOminus

COOminus

Na+

N

CH2

CH2

COOminus Na+

COOminus Na+N

CH2

CH2 COOH

COOminus Na+

+ Cu+2

+ Na+

+ Na+

+ 2H+

+ 2H+

+ 2H+




Ion exchangers

NaturalModified

naturalSynthetic


Vermiculite

Zeolites

Clays

Polysaccharide

Protein


Zeolites


Polystyrenedivinyl

benzenePhenolic

Acrylic








OH

OH

OH

O

OH

O

OH OH

H

HO

minusH+

Ominus

Ominus

Ominus

Ominus

OminusOminus

CH2

CH2

CH2

CH2

OHminus

n

n



3H into the struc-



OH

OH OH OH

OH OH

CH2CH2CH2


CH2

Figure 7 Styrene









n


CH2

H2C









Polymeric chain

H HO

Polymeric chain

SO3HSO3H

+ H2O

(a)


+

CH2Cl


(b)












M2119899


2sdot 119910H2O (3)





4)2










12O119909minus840









A B A B

A B

A B

C

C

C

C







minus

minus

minus

minus

minus

Ion pair




(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger


(5)

(6)(7)

(8)


(9)

(10)


Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +






















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of








1848ndash1852





1901ndash1902


1905


O Leibknecht


1934ndash1939

















Y+2Y+2Y+2Y+2Y+2Y+2

Y+2 Y+2 Y+2 Y+2 Y+2 Y+2

X+



(a)




X+ X+ X+ X+ X+ X+ X+ X+ X+ X+ X+ X+

Z+3Z+3Z+3Z+3

Z+3

Z+3 Z+3

Z+3

(b)


M

N

C

O

N

O

O

OOminus

Ominus

Ominus

H2C



N

N N

N

CH2

CH2CH2

CH2CH2

CH2

CH2

COOH

CH2 COOH

COOH

COOH

COOH

Cu+2

COOminus

COOminus

COOminus

Na+

N

CH2

CH2

COOminus Na+

COOminus Na+N

CH2

CH2 COOH

COOminus Na+

+ Cu+2

+ Na+

+ Na+

+ 2H+

+ 2H+

+ 2H+




Ion exchangers

NaturalModified

naturalSynthetic


Vermiculite

Zeolites

Clays

Polysaccharide

Protein


Zeolites


Polystyrenedivinyl

benzenePhenolic

Acrylic








OH

OH

OH

O

OH

O

OH OH

H

HO

minusH+

Ominus

Ominus

Ominus

Ominus

OminusOminus

CH2

CH2

CH2

CH2

OHminus

n

n



3H into the struc-



OH

OH OH OH

OH OH

CH2CH2CH2


CH2

Figure 7 Styrene









n


CH2

H2C









Polymeric chain

H HO

Polymeric chain

SO3HSO3H

+ H2O

(a)


+

CH2Cl


(b)












M2119899


2sdot 119910H2O (3)





4)2










12O119909minus840









A B A B

A B

A B

C

C

C

C







minus

minus

minus

minus

minus

Ion pair




(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger


(5)

(6)(7)

(8)


(9)

(10)


Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +






















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




Y+2Y+2Y+2Y+2Y+2Y+2

Y+2 Y+2 Y+2 Y+2 Y+2 Y+2

X+



(a)




X+ X+ X+ X+ X+ X+ X+ X+ X+ X+ X+ X+

Z+3Z+3Z+3Z+3

Z+3

Z+3 Z+3

Z+3

(b)


M

N

C

O

N

O

O

OOminus

Ominus

Ominus

H2C



N

N N

N

CH2

CH2CH2

CH2CH2

CH2

CH2

COOH

CH2 COOH

COOH

COOH

COOH

Cu+2

COOminus

COOminus

COOminus

Na+

N

CH2

CH2

COOminus Na+

COOminus Na+N

CH2

CH2 COOH

COOminus Na+

+ Cu+2

+ Na+

+ Na+

+ 2H+

+ 2H+

+ 2H+




Ion exchangers

NaturalModified

naturalSynthetic


Vermiculite

Zeolites

Clays

Polysaccharide

Protein


Zeolites


Polystyrenedivinyl

benzenePhenolic

Acrylic








OH

OH

OH

O

OH

O

OH OH

H

HO

minusH+

Ominus

Ominus

Ominus

Ominus

OminusOminus

CH2

CH2

CH2

CH2

OHminus

n

n



3H into the struc-



OH

OH OH OH

OH OH

CH2CH2CH2


CH2

Figure 7 Styrene









n


CH2

H2C









Polymeric chain

H HO

Polymeric chain

SO3HSO3H

+ H2O

(a)


+

CH2Cl


(b)












M2119899


2sdot 119910H2O (3)





4)2










12O119909minus840









A B A B

A B

A B

C

C

C

C







minus

minus

minus

minus

minus

Ion pair




(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger


(5)

(6)(7)

(8)


(9)

(10)


Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +






















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Ion exchangers

NaturalModified

naturalSynthetic


Vermiculite

Zeolites

Clays

Polysaccharide

Protein


Zeolites


Polystyrenedivinyl

benzenePhenolic

Acrylic








OH

OH

OH

O

OH

O

OH OH

H

HO

minusH+

Ominus

Ominus

Ominus

Ominus

OminusOminus

CH2

CH2

CH2

CH2

OHminus

n

n



3H into the struc-



OH

OH OH OH

OH OH

CH2CH2CH2


CH2

Figure 7 Styrene









n


CH2

H2C









Polymeric chain

H HO

Polymeric chain

SO3HSO3H

+ H2O

(a)


+

CH2Cl


(b)












M2119899


2sdot 119910H2O (3)





4)2










12O119909minus840









A B A B

A B

A B

C

C

C

C







minus

minus

minus

minus

minus

Ion pair




(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger


(5)

(6)(7)

(8)


(9)

(10)


Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +






















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


OH

OH OH OH

OH OH

CH2CH2CH2


CH2

Figure 7 Styrene









n


CH2

H2C









Polymeric chain

H HO

Polymeric chain

SO3HSO3H

+ H2O

(a)


+

CH2Cl


(b)












M2119899


2sdot 119910H2O (3)





4)2










12O119909minus840









A B A B

A B

A B

C

C

C

C







minus

minus

minus

minus

minus

Ion pair




(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger


(5)

(6)(7)

(8)


(9)

(10)


Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +






















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Polymeric chain

H HO

Polymeric chain

SO3HSO3H

+ H2O

(a)


+

CH2Cl


(b)












M2119899


2sdot 119910H2O (3)





4)2










12O119909minus840









A B A B

A B

A B

C

C

C

C







minus

minus

minus

minus

minus

Ion pair




(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger


(5)

(6)(7)

(8)


(9)

(10)


Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +






















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







12O119909minus840









A B A B

A B

A B

C

C

C

C







minus

minus

minus

minus

minus

Ion pair




(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger


(5)

(6)(7)

(8)


(9)

(10)


Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +






















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


minus

minus

minus

minus

minus

Ion pair




(1)

(2)

(3)First ion

(4)

Diffusionin

exchanger


(5)

(6)(7)

(8)


(9)

(10)


Diffusion in film


Complete formation

minus

Second ion

+

++

+

+

+

+

+ +






















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of















119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≪ 1

119876 sdot 119863 sdot 120575

119862 sdot 119863 sdot 1199030

sdot (5 + 2120572119860

119861

) ≫ 1

(5)


0is the













119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




119869119894= minus119863119894grad119862

119894(6)


119869119894= minus119863119894grad119862

119894

(7)






119869119868= minus119863119894grad119862

119894minus 119863119894119885119894119862119894(

119865

119877119879

) grad 120576 (8)






In this case

119869119894= minus1198631015840

119894

119862119894

119877119879

grad 120583119894 (9)


119894


119863119894= minus1198631015840

119894

(1 +

120575 ln 120574119894

120575 ln119862119894

) (10)



119894


119869119894= minus

119899

sum

119869=1

1198631015840

119869sdot119894

119862119894

119877119879

grad120583119895 (11)



5 Conclusion




References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



References















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of












Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Documents

Review Article History, Introduction, and Kinetics of Ion ...A. Skogseid Preparation of potassium-speci c polystyrene cation exchanger chelating resin. J. A. Marinsky, L. E. Glendenin,