Bergaya F. Handbook of Clay Science

Подождите немного. Документ загружается.

(Ioannou and Dimirkou, 1997). Anions can be adsorbed in larger amounts by ligand

exchange than by counterion binding because ligand exchange also operates when

the surface is uncharged or even negatively charged.

In the case of multivalent anions, the dominance of a certain species in solution at

a distinct range of pH values does not imply that this species is the major surface

species. The presence of the differently charged anions in the aqueous solution is

determined by the dissociation constants (pK

values), whereas the formation of the

surface species also depends on the surface complexing constants. The constant

capacitance model, one of the models used to describe surface complexation

(Goldberg, 1992), indicates that the proportion of neutral species [SH

](S¼ sur-

face) decreases to zero at pH 7, while the proportion of [SHPO

–

] species increases to

a maximum at pH 5.5, and [SPO

2–

] is the sole species at pH>8 (Ioannou and

Dimirkou, 1997). Arsenate adsorption showed a maximum around pH 6(Manning

and Goldberg, 1996).

Multivalent cations may form insoluble salts with anions, making it uncertain

whether the adsorption of the anions proceeds as a true anion exchange or by

precipitation (Rao and Murti, 1987).

Weiss et al. (1956) found that the anion exchange capacity depends on the di-

ameter of the montmorillonite particles if their shape is assumed to be almost reg-

ular. This would be expected if the anion exchange occurs on the edges. From the

adsorption of ﬂuoride ions, the authors derived average diameters of montmorillo-

nite particles of 300–450 mm. By contrast, most of the ﬂuoride ions are adsorbed at

the basal (planar) surface of kaolinite particles, and the anion exchange capacity

depends on the thickness of these particles.

Although the an ion exchange capacity of clay minerals is small compared to their

CEC, the adsorption of anions is of great importance to soil fertility and plant

nutrition. The adsorption of phosphate by soil and soil minerals recei ved particular

attention (Parﬁtt, 1978; Bowden et al., 1980; Fox, 1980; Theng et al., 1982). Wend-

elbo and Rosenqvist (1987) observed that sulphate can exert a dispersive effect on

clay soils, intermediate between chloride and phosphate. Phosphate, oligopho s-

phates, polyphosphates, and many other polyanions are capable of stabilising clay

mineral dispersions against coagulation and ﬂocculation (see Chapters 5 and 10.1).

Methods for determining the adsorption of phosphate and chloride were de-

scribed by Bain and Smith (1987).

12.10.2. DEFINITION OF CEC AND FACTORS INFLUENCING ITS

MEASUREMENT

The CEC of clays and clay minerals may be deﬁned as the quantity of cations

available for exchange at a given pH (Table 12.10.3), and is traditionally expressed in

milliequivalents (meq)/100 g of calcined clay (Bergaya and Vayer, 1997). Thus, the

Chapter 12.10: Cation and Anion Exchange988

pH value during the exchange reaction has to be speciﬁed. Various units were used in

the literature to express CEC. Although CEC values are often given in terms of dried

clay, the drying conditions (105, 110, 140 1C, or higher temperature) are not always

speciﬁed (van Olphe n, 1951a, 1977; van Olphen and Fripiat, 1979). The unit of CEC

recommended by the IUPAC is cmol(+)/kg, which is numerically equivalent to meq/

100 g. Only a few papers mention the pH during the exchange reaction.

The exchange capacity is usually determined at neutrality (pH ¼ 7). Table 12.10.3

lists the CEC of some clay minerals, showing the broad range of values. This is

because cation exchange is inﬂuenced by many factors, such as the nature of the

exchangeable cations, particle size (grinding can change the CEC), temperature, and

phase conditions (dilute or concentrated aqueous solutions, organic solvents, solid-

state reactions). As a result, CEC is difﬁcult to determine accurately. In any case,

CEC determination requires the complete replacement of all exchangeable cations by

‘index’ cations that are not present in the clay mineral sample.

12.10.3. ORIGIN OF CEC

The CEC of clay minerals is generally related to the layer charge. The measured

CEC is eq uivalent to the layer charge only when all the charge-compensating cations

are exchangeable. The CEC corresponds to the summation of two types of charges

arising from

(i) Layer (isomorphous) substitution if the compensating cations are not ﬁxed on the

clay mineral and are exchangeable by other cations. This structural charge is also

called constant or permanent and is generated by ion substitutions or site va-

cancies in the octahedral and/or tetrahedral sheets (Gast, 1977) (see Chapter 2).

In most cases, the compensating cations are exchangeable. Speciﬁc interactions

with the silicate layers can impede quantitative exchange of the compensating

cations. An example is potassium ions in illites and micas, which are ‘ﬁxed’ in the

ditrigonal cavities (Verburg and Baveye, 1994). Some cations undergo chemical

reactions altering the expected classical exchange behaviour (see Chapter 5).

Table 12.10.3. CEC of clay minerals in cmol(+)/kg( ¼ meq/100 g) (Weiss, 1958b; Grim,

1968)

Kaolinite 3–15

Halloysite 2H

O 5–10

Halloysite 4H

O 40–50

Montmorillonite 70–120

Vermiculite 130–210

Illite 10–40

Micas (biotite, muscovite) up to 5

Chlorite 10–40

Sepiolite, palygorskite 20–30

12.10.3. Origin of Cec 989

(ii) Coordination of the cations at the edges of the silicate layers is, depending on the

pH, completed by H

O, or OH



(see Chapter 5). This pH-dependent

charge varies with the nature of the solution (ionic strength, pH) due to the

reactions:

MOH þ H

O$MO



þ H

MOH þ H

$MOH

þ H

with M ¼ Si

,Al

,orMg

. For other possible reactions, see Tournassat

et al. (2004). The contribution of the variable charge to the total charge depends

on particle morphology and the ratio of the edge/basal surface area. In case of

smectites, the pH-dependent charge varies between 10 and 20% of the total

charge (Anderson and Sposito, 1991). In kaolinites, the layers are aggregated to

larger particles, and the edges represent a larger fraction of the total surface area

(see Chapter 12.9). As kaolinites have little layer substitution, their structural

charge is relatively low, and the CEC is mainly attributed to the edge charges

(Gast, 1977).

12.10.4. CEC MEASUREMENTS

The CEC of clay minerals can be determined by a variety of established methods

(Van Olphen, 1951a, Weiss, 1958a, 1958b; Grim, 1968; Bain and Smith, 1987).

The choice of technique depends on the magnitude of the expected CEC, the nature

of the charge-compensating cations, and the available quantity of the sample. Some

methods are tedious and entail theoretical uncertainties and practical difﬁculties. It is

difﬁcult to recommend a universal method for different clays and clay minerals.

The most widely used methods involve the displacement of the interlayer cations

with the index cations in a known volume of solution and the analytical determi-

nation of the cations by standard techniques such as atomic absorption, spectro-

photometry, or titration.

A. Classical Methods

These methods are based on the exchange between the cations at the clay mineral

surface and the index cations in solution. The measurements are inﬂuenced by a

number of experimental variables, including pH, temperature, solution ionic

strength, and nature of the index cation as well as by factors relating to the clay

mineral such as nature of the compensating cations, particle morphology and size,

and surface area/volume ratio of the particles (Grim, 1968). The two last factors are

important when the pH-dependent charge is high compared with the permanent

charge.

Chapter 12.10: Cation and Anion Exchange990

B. Inﬂuence of Exchangeable and Index Cations

The exchange reaction of clay minerals is stoichiometric in relation to the charges.

As discussed above, the different cations have neither the same replaceability nor the

same replacing power. For measuring CEC, it is important to use cations that are

preferred or held more tightly on the surface than the cations being replaced. In some

cases, the cations are ﬁx ed on the clay mineral and are not displaced by other cations

even when an excess of highly preferred cations is added. Typical examples are

potassium ions in micas (see Section 12.10.1) and many organic cations.

Clay minerals show a strong preference for organic cations (Theng et al., 1967).

Several authors (see Section 12.10.5) used organic cations such as methylene blue

and crystal violet as index cations. Such cations are strongly adsorbed by clay min-

erals, their binding coefﬁcients (Nir et al., 1986) are very high compared with alkali

or alkali-earth cations (Table 12.10.1).

When exchanging cations such as NH

or Ba

are used, the procedure needs

several incubation and separation cycles. In this case the CEC measurements are also

inﬂuenced by further factors like the number of washings and the nature of the

washing solvent.

C. Inﬂuence of pH

The pH of the solution has two impacts:

(i) The pH at which the exchange reaction takes place as well as the nature of the

unbuffered or buffered solution determine the type of measured charge: perma-

nent or pH dependant charge. Thus, the pH during the exchange has to be

carefully measured and controlled. Grim (1968) proposed to determine the CEC

at pH ¼ 7 assuming that only the exchangeable cations on permanent sites will

participate in the exchange reaction. Amacher et al. (1990) proposed to deter-

mine the CEC in soils at different conditions in order to determine not only the

exchangeable cations but also the exchangeable cations at acidic sites.

(ii) The pH de termines also the form of the ions present in solution. Depending on

pH, many multivalent cations form oligomeric and polymeric hydroxo meta l

ions (see Chapter 5) and also at pH ¼ 7 the cations form different complexes.

The estimation of CEC from analytically determined amounts of cations pre-

supposes that the charge of these cations is known. If different forms of cations

are bound, the numerical value of the CEC is not correct (Bache, 1976 ).

12.10.5. ANALYTICAL TECHNIQUES

The basic steps of CEC determination starting from an X-clay are illustrated in

Fig. 12.10.5. We distinguish two kinds of determinations: the ﬁrst is based on

quantitative analysis (E) after the replacement of exchangeable cations X by the

index cation A or B; the second consists of titrations (T) performed during the

12.10.5. Analytical Techniques 991

addition of the index cation A or B and supposes that the replacement of the initial

exchangeable cations X by the index cations A or B occurs immediately.

The ﬁrst step is the replacement of all cations X on the clay mineral by the index

cations A when the solution containing cations A is added to the clay miner al.

During this step, the CEC is evaluated (T1) by following some physical properties of

the dispersion or the supernatant solution (after sedimentation) such as conductivity

(Dakshinamurti and Bhavanarayana, 1982), surface tensi on when a cationic surfact-

ant is the index cation (Burrafato and Miano, 1993), or the appearance of ﬂocculat-

ion (Pleysier et al., 1986).

When all cations X are replaced (in some cases, total exchange needs several cycles

and thus is very time consuming), the CEC is derived by analysing either the excess

of cations A in solution (E1), the released cations X in solution (E2), or the index

cations A retained by the clay mineral (E3). E1 and E2 are complementary methods.

If E2 is used, the total volume of washing solution must be collected and considered.

Generally, it is the same for E1; in this case we consider the quantity and not the

concentration. Method E3 needs the complete removal of the non-adsorbed index

cations A by washing. The sampl es are generally washed with organic solvents. Small

amounts of salts can be retained if the organic solvent is not carefully chosen, in

which case the CEC is not correctly measured (Francis and Grigal, 1971). All E3

methods cited in the literature require sophisticated instruments such as radioactivity

counters or microwave equipment, or are completely destructive.

Other methods are based on the replacement of the cations A by the index cations

B in a second step. During this step, the CEC can be evaluated (T2) in the same way

as by T1. Either the excess of cations B remaining in solution (E4) is measured, or the

amount of the index cations A released into the solution is determined (E5). CEC

determination by measuring the amount of index cations B ﬁxed on the clay mineral

(E6) was never reported. For both steps, classical analytical techniques such as

Addition of a solution with A-cations

T1: Titration of A-cations

X-clay

Solution with A-cations and X-cations

E1: analysis of A-cations in excess

E2: analysis of released X-cations

Solution with A-cations and B-cations

E4: analysis of B-cations in excess

E5: analysis of released A-cations

A-clay

E3: analysis of the A-cations

B-clay

E6: analysis of the B-cations

Addition of a solution with B-cations

T2: Titration of B-cations

Fig. 12.10.5. Basic steps of CEC determinations.

Chapter 12.10: Cation and Anion Exchange992

volumetry, atomic absorption spectrometry, inductively coupled plasma emission

spectrometry (ICPES), etc. are used.

The selection of a particular method is determined (i) by the choice of the index

cations and (ii) more simply, by the techniques available in the laboratory. CEC

determinations using different index cations are described below.

A. Exchange with Protons

Hissink (1924) measured the acidity of soils, and derived their CEC from titration.

Later, Glae ser (1946) and Grim (1968) proposed methods based on the acid–base

titration of H

-exchanged clay minerals. These methods are no longer in use because

the preparation of H

-clay miner als needs special care. Further, it is impossible to

reach constant pH because the presence of protons leads to autotransformation of

the minerals (see Chapter 5).

B. Exchange with Organic Cations

Since organic cations are preferentially exchanged over inorganic cations, they (es-

pecially methylene blue) were widely used for determining CEC as well as speciﬁc

surface areas (Brindley and Thompson, 1970; Hang and Brindley, 1970; API, 1990;

Rytwo et al., 1991; Kahr and Madsen, 1995) (see Chapter 7.3). Although total

exchange of the inorganic cations needs only one incubation cycle, the determination

of CEC by adsorption of methylene blue (MB) seems questionable because the

adsorbed MB cations can assume more than one orientation at the clay miner al

surface (Hang and Brindley, 1970). The surface area of the ﬂat-lying monovalent MB

cation is about 1.32 nm

. For highly charged clay minerals, the interlayer area per

charge can be smaller than the area occupied by M B, and hence the amount ad-

sorbed may no longer be equal to the CEC.

Brindley and Thompson (1970) and Hang and Brindley (1970) derived the CEC of

clay minerals from saturation adsorption of MB but this is only valid for the Li

-and

-exchanged forms. Rytwo et al. (1991) and Kahr and Madsen (1995) showed that

clay minerals adsorb MB in excess of the CEC. Accordingly, Rytwo et al. (1991)

proposed to determine the CEC from the amount of cations released into solution, while

Kahr and Madsen (1995) used the point where the MB added to the clay dispersion is

no longer adsorbed. This method requires the clay minerals to be in the Na

form.

C. Exchange with Ammonium Ions

Several methods use NH

as the index cation. The method involving leaching

with ammonium acetate and subsequent replacement of the NH

ions from ex-

change sites is widely used, and often serves as a standard or reference procedure

(Peech, 1945; Mackenzie, 1951; Fraser and Russell, 1969; Busenberg and Clemen cy,

1973; Greenhill and Peverill, 1977; Gillmann et al., 1983). However, the method is

12.10.5. Analytical Techniques 993

time-consuming because the exchange with NH

involves ﬁve to six steps. In ad-

dition, the CEC is generally determined by analysing the washed clay using tech-

niques that are sometimes laborious. However, the method has the following

advantages: (i) the exchange can be accomplished at a well-deﬁned pH using buffered

solutions (pH 7 for NH

OAc and pH 8.5 for NH

Cl/NH

) and (ii) several techniques

can be used to determine the nitrogen content (Kjeldahl titration, acidimetry, am-

monium sensitive electrodes, colorimetry).

D. Exchange with Alkali or Alkaline-Earth Cations

The use of alkali or alkaline earth cations such as Cs

(Hillier and Clayton, 1992),

(Bache, 1970), Ca

,Na

, and Sr

as index cations A or B is also very

time-consuming as several cycles are needed to reach complete exchange. Different

analytical techniques are used such as conductivity (Mortland and Mellor, 1954),

electrochemical measurements with speciﬁc electrodes (Malcolm and Kennedy, 1969;

Chiu et al., 1990), nephelometry for small quantities (Adams and Evans, 1979), or

isotopic techniques (Bache, 1970; Francis and Grigal, 1971; Brouwer et al., 1983;

Maes et al., 1985) all of which are not commonly available in laboratories.

E. Exchange with Transition Metal Ions or Organo-Metal Complexes

The last group of methods used hydrates or complexes of transition metal cations as

index cations, such as [Co(H

]

(Rhodes and Brown, 1994) or [Co(NH

)

]

(Mantin and Glaeser, 1960), silver thiourea cations (Chhabra et al., 1976; Pleysier

and Juo, 1980; Pleysier et al., 1986; Searle, 1986) and [Ni(en)

]

(en ¼ ethylene

diamine) (Cornell and Aksoyoglu, 1991).

Mantin (1969) proposed a novel method to determine the CEC of clay minerals. It

consists of saturating the samples with metal cations (Cu

,Ni

,Zn

,Mn

,Fe

), and then adding varied quantities of ethylene diamine to the clay

mineral dispersion. As a result, the complex [M(en)

]

is formed in the interlayer

space. The CEC is derived from the quantity of ethyl ene diamine required for

transforming the metal cation completely into the complex. Mantin further sug-

gested the use of [M(en)

]

complexes such as [Ni(en)

]

for CEC determinations.

The method based on [Cu(en)

]

was developed by Bergaya and Vayer (1997),

while Meier and Kahr (1999) proposed the use of [Cu(trien)

]

complex to deter-

mine CEC. Ammann et al. (2005) found good agreement between the two methods if

the pH-dependence of the photometric determinations is taken into account.

12.10.6. OTHER TECHNIQUES

The CEC of smectites and vermiculites can be calculated from the layer charge

determined by the alkylammonium method ( Lagaly, 1994). The CEC values so

Chapter 12.10: Cation and Anion Exchange994

derived correspond to the permanent negative layer charge that in the case of

smectites, are 10–20% smaller than the (total) exchange capacity (Lagaly, 1981,

1994). The CEC can also be estimated from the colloidal properties and the sediment

values of clay dispersions in the presence of surfactants (Janek an d Lagaly, 2003). On

the rare occasion when the clay miner al sample is non-interstratiﬁed and very pure,

or when its mineralogi cal composition is exactly known, the CEC may be deduced

from chemical analysis.

12.10.7. CONCLUSIONS

The determination of CEC of clay minerals, using [Cu(en)

]

and [Cu(trien)]

complexes, is presently the most versatile method.

(1) The procedure is very simple and well suited for routine analysis. No sophis-

ticated chemicals and materials are required. Only glass vessels, stirring devices, a

centrifuge, an d possibly a photometer are needed.

(2) The exchange reaction is fast.

(3) The Cu

complexes can displace all kinds of cations from exchange sites on the

clay minerals, including heavy metal cations. Full quantitative exchange can be

obtained with Na

- and Ca

-montmorillonites (Bergaya and Vayer, 1997;

Ammann et al., 2005). This accords with the high equilibrium constant of the

/Na

exchange reaction, indicative of ideal ion-exchange behaviour

(Fletcher and Sposito, 1989).

(4) The results are reproducible over a wide range of CEC values, and good accuracy

may be obtained even with small amounts of samples or clays with low CEC.

(5) The measurement is not restricted to a particular pH (Ammann et al., 2005).

Although the use of metal complexes as index cations may not be universally

applicable, the method allows the CEC of many types of clays and clay minerals to

be determined simply and reliably.

REFERENCES

Abollino, O., Aceto, M., Malandrino, M., Sarzanini, C., Mentasti, E., 2003. Adsorption of

heavy metals on Na-montmorillonite. Effect of pH and organic substances. Water Re-

search 37, 1619–1627.

Adams, J.M., Evans, S., 1979. Determination of the cation-exchange capacity (layer charge) of

small quantities of clays minerals by nephelometry. Clays and Clay Minerals 27, 137–139.

Altin, O., O

zbelge, H.O

., Dog

u, T., 1998. Use of general purpose adsorption isotherms for heavy

metal–clay mineral interactions. Journal of Colloid and Interface Science 198, 130–140.

Amacher, M.C., Henderson, R.E., Breithaupt, M.D., Seale, C.L., Labauve, J.M., 1990. Un-

buffered and buffered salt methods for exchangeable cations and effective cation exchange

capacity by potentiometric titration using divalent cation electrodes. Soil Science Society of

America Journal 54, 1036–1042.

12.10.7. Conclusions 995

Ammann, L., Bergaya, F., Lagaly, G., 2005. Determination of the cation exchange capacity of

clays with copper complexes revisited. Clay Minerals 40, 441–453.

Anderson, S.J., Sposito, G., 1991. Cesium-adsorption method for measuring accessible struc-

tural surface charge. Soil Science Society of America Journal 55, 1569–1576.

API, 1990. Recommended practice standard procedure for laboratory testing drilling ﬂuids.

API Recommended Practice 13, 1.

Auboiroux, M., Melou, F., Bergaya, F., Touray, J.C., 1998. Hard and soft acid–base model

applied to bivalent cation selectivity on a 2:1 clay mineral. Clays and Clay Minerals 46,

546–555.

Bache, B.W., 1970. Barium isotope method for measuring cation-exchange capacity of soils

and clays. Journal of the Science of Food and Agriculture 21, 169–171.

Bache, B.W., 1976. The measurement of cation exchange capacity of soils. Journal of the

Science of Food and Agriculture 27, 273–280.

Bain, D.C., Smith, B.F.L., 1987. Chemical analysis. In: Wilson, M.J. (Ed.), A Handbook of

Determinative Methods in Clay Mineralogy. Blackie, Glasgow, pp. 248–274.

Beneke, K., Lagaly, G., 1982. The brittle mica-like KNiAsO

and its organic derivatives. Clay

Minerals 17, 175–183.

Bereket, G., Arog

uz, A.Z., O

zel, M.Z., 1997. Removal of Pb(II), Cd(II), Cu(II), and Zn(II)

from aqueous solutions by adsorption on bentonite. Journal of Colloid and Interface

Science 187, 338–343.

Bergaya, F., Vayer, M., 1997. CEC of clays: measurement by adsorption of a copper ethylene-

diamine complex. Applied Clay Science 12, 275–280.

Bergseth, H., 1980. Selektivita

t von Illit, Vermiculit und Smectit gegenu

ber Cu

,Pb

,Cd

und Mn

. Acta Agricultura Scandinavica 30, 460–468.

Bergseth, H., 1985. Selektierungsvermo

gen eines Eisenoxidhydroxids und einiger Ton-

minerale gegenu

ber Phosphat und Sulfationen. Acta Agricultura Scandinavica 35,

375–388.

Bowden, J.W., Posner, A.M., Quirk, J.P., 1980. Adsorption and charging phenomena in

variable charge soils. In: Theng, B.K.G. (Ed.), Soils with Variable Charge. New Zealand

Society of Soil Science, Lower Hutt, pp. 147–166.

Brindley, G.W., Thompson, T.D., 1970. Methylene blue adsorption by montmorillonite: de-

termination of surface areas and exchange capacity with different initial cation saturations.

Israel Journal of Chemistry 8, 409–415.

Brouwer, E., Baeyens, B., Maes, A., Cremers, A., 1983. Cesium and rubidium ion equilibria in

illite clay. Journal of Physical Chemistry 87, 1213–1219.

Burrafato, G., Miano, F., 1993. Determination of the cation exchange of clays by surface

tension measurements. Clay Minerals 28, 475–481.

Busenberg, E., Clemency, C.V., 1973. Determination of the cation exchange capacity of clays

and soils using an ammonia electrode. Clays and Clay Minerals 21, 213–218.

Chhabra, R., Pleysier, J., Cremers, A., 1976. The measurement of CEC and exchangeable

cations in soils: a new method. In: Bailey, S.W. (Ed.), Proceedings of the International Clay

Conference 1975. Applied Publishing, Wilmette, IL, pp. 439–449.

Chiu, Y.C., Huang, N.L., Uang, C.M., Huang, J.F., 1990. Determination of cation exchange

capacity of clays minerals. Colloids and Surfaces 46, 327–337.

Cornell, R.M., Aksoyoglu, E.S., 1991. Simultaneous determination of the cation exchange

capacity and the exchangeable cations on marl. Clay Minerals 26, 567–570.

Chapter 12.10: Cation and Anion Exchange996

Dakshinamurti, C., Bhavanarayana, M., 1982. An isoconductivity method for determining the

cation exchange capacity of soils and clays. Catena 9, 175–179.

Eberl, D.D., 1980. Alkali cation selectivity and ﬁxation by clay minerals. Clays and Clay

Minerals 28, 161–172.

El-Batouti, M., Sadek, O.M., Assaad, F.F., 2003. Kinetics and thermodynamic studies of

copper exchange on Na-montmorillonite clay mineral. Journal of Colloid and Interface

Science 259, 223–227.

Ferris, A.P., Jepson, W.B., 1975. The exchange capacities of kaolinite and the preparation of

homoionic clays. Journal of Colloid and Interface Science 51, 245–259.

Fletcher, P., Sposito, G., 1989. The chemical modelling of clay–electrolyte interactions for

montmorillonite. Clay Minerals 24, 375–391.

Fox, R.L., 1980. Soils with variable charge: agronomic and fertility aspects. In: Theng, B.K.G. (Ed.),

Soils with Variable Charge. New Zealand Society of Soil Science, Lower Hutt, pp. 195–224.

Francis, C.W., Grigal, D.F., 1971. A rapid and simple procedure using Sr 85 for determining

cation exchange capacities of soils and clays. Soil Science 112, 17–21.

Fraser, A.R., Russell, J.D., 1969. A spectrophotometric method for determination of cation

exchange capacity of clay minerals. Clay Minerals 8, 229–230.

Gast, R.G., 1972. Alkali metal exchange on Chambers montmorillonite. Soil Sience Society of

America Proceedings 36, 14–19.

Gast, R.G., 1977. Surface and colloid chemistry. In: Dixon, J.B., Weed, S.B. (Eds.), Minerals

in Soil Environments. Soil Science Society of America, Madison, WI, pp. 27–73.

Gast, R.G., Klobe, D., 1971. Sodium–lithium exchange equilibria on vermiculite at 25 1C and

50 1C. Clays and Clay Minerals 19, 311–319.

Gillmann, G.P., Bruce, R.C., Davey, B.G., Kimble, J.M., Searle, P.L., Skjemstad, J.O., 1983.

A comparison of methods used for determination of cation exchange capacity. Commu-

nications in Soil Science and Plant Analysis 14, 1005–1014.

Glaeser, R., 1946. De

termination de la capacite

d’e

change de base dans la montmorillonite.

Comptes Rendus de l

Acade

mie des Sciences, Paris, vol. 222, pp. 1179–1181.

Goldberg, S., 1992. Use of surface complexation models in soil chemical systems. Advances in

Agronomy 47, 233–329.

Goulding, K.W.T., Talibudeen, O., 1980. Heterogeneity of cation-exchange sites for K–Ca

exchange in aluminosilicates. Journal of Colloid and Interface Science 78, 15–24.

Greenhill, N.B., Peverill, K.I., 1977. Determination of cation exchange capacity of soils using

ammonia and chloride electrodes. Communications in Soil Science and Plant Analysis 8,

579–589.

Grim, R.E., 1968. Clay Mineralogy, 2nd edition. McGraw-Hill, New York.

Hang, P.T., Brindley, G.W., 1970. Methylene blue adsorption by clay minerals. Determination

of surface areas and cation exchange capacities (Clay—organic studies XVIII). Clays and

Clay Minerals 18, 203–212.

Hanna, M.T., Zaghloul, A.A., El-Batouti, M., El-Shazly, S.A., 1995. Solvent effect on the

kinetics of the exchange of copper ions on Na-montmorillonite. Journal of Colloid and

Interface Science 176, 418–421.

Hillier, S., Clayton, T., 1992. Cation exchange ‘staining ‘ of clay minerals in thin-section for

electron microscopy. Clay Minerals 27, 379–384.

Hirsch, D., Nir, S., Banin, A., 1989. Prediction of cadmium complexation in solution and

adsorption to montmorillonite. Soil Science Society of America Journal 53, 716–721.

References 997