Relation Between Dual 

Acidity and Structure 

of H-Montmorillonite

GEOLOGICAL SURVEY PROFESSIONAL PAPER 386-C

Prepared on behalf of the

U.S. Atomic Energy Commission
Relation Between Dual 

Acidity and Structure 

of H-Montmorillonite

By ALFRED M. POMMER

CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

GEOLOGICAL SURVEY PROFESSIONAL PAPER 386-C

Prepared on behalf of the

U.S. Atomic Energy Commission

An experimental and theoretical study of relations 

between montmorillonite composition and structure 

and a discussion of their application to problems of 

radioactive waste disposal

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington 25, D.G.
CONTENTS

Abstract.._ ________________________________________

Introduction.______________________________________

Acknowledgments__ ___________________________

Implications of montmorillonite structure______________

Experimental data__________________________________

Experimental plan._____________________________

Material used-_____________________________

Preparation of the H-form___________________

Titration with NaOH_____________________

Analysis of filtrates.________________________

pH readings_ __ _ _________________________

Presentation of potentiometric and analytical data__ 

Semilogarithmic plotting of titration curves- ___ 

Evaluation of electrode data.________________

Page

Cl

1

1

1

2

2

3

3

3

4

4

4

4

5

Page 

Experimental data Continued

X-ray diffraction studies_______________________ C9

X-ray diffraction procedure.____________ __ 9

Presentation of data_________________----___ 9

Determination of exchangeable aluminum in hydrogen clay_ ____________--___-_---___-_--------- 16

Discussion.________________________________________ 16

Total acidity of the clay____________ _______ 16

The "first" acid________________-__ 17

The "second" acid______________________ 17

Montmorillonite and the problem of ionic specificity,. 17 

Montmorillonite and beidellite__________________ 19

Relation of alkali ion selectivity of clay to radioactive waste disposal__-_______-_'_____---___-_- 22

References cited-___-_-_-_--------_---_-_----------- 22

ILLUSTRATIONS

Page

FIGURE 1. Simplified montmorillonite structure-_____-___________________________-_----_---_-------------_---___- C2

2. Second series plot of pH for the titration of H-montmorillonite with sodium hydroxide.________-_----__--__ 6

3. Semilogarithmic plot of pH for the titration of H-montmorillonite with sodium hydroxide _______________ 7

4. Comparison of a corrected pH titration curve constructed from a semilogarithmic plot with one constructed

from a linear plot_-_-___________________________________________________-_____---_-__-_--------- 10

5. Comparison of experimental pH data of first series and second series_---_---__-----_------_--_-----_------ 11

6. Comparison of pH curve of first series based on averaging of four determinations with the pH curve of second

series after correction for C02-------_------_-_------_-_--------__-----_----___________-----__--_- 12

7. First series relation between flame photometric and potentiometric sodium values in a discontinuous montmorillonite titration_ _ ___________________________________________-________--__---_--_-------------- 13

8. Comparison of sodium electrode readings pooled for both series with analytical sodium values of the second series. _ 14

9. The relation between the acid dissociation constant pK0, the anionic radius r~, and cation specificity for oxyanions_-____--_-____________________________________________-__-____---_---_------_-----_------ 18

10. Simplified beidellite structure________________________________________-___________----__-__----------- 19

11. Semilogarithmic plot of titration of bentonite with NaOH and KOH_____________--__------_---_-_-------- 20

12. Semilogarithmic plot of titration of Putnam beidellite with NaOH and KOH_____________________--__-_---_ 21

TABLES

Page 

TABLE 1. Comparison of material used with original clay reference sample (API No. 23)___-_---__-___--_-------- C3

2. Titration of montmorillonite (Chambers, Ariz.) with 0.1 N NaOH________------_------------------_-------- 5

3. First series A comparison of readings, in millivolts (as determined by calomel and sodium-sensitive glass electrodes), with sodium values determined by flame photometry.___________________________-_-_------------ 5

4. First series A1203 found in filtrates from the titration of H-montmorillonite with 0.1 _V NaOH______________ 8

5. Second series Titration of montmorillonite (Chambers, Ariz.) with 0.1 N NaOH with provision for reaction

blanks ____________________________________________________________________________________________ 8

6. Second series pH values of solutions to which increments of 0.1 N NaOH were added______________________ 8

7. X-ray diffraction data on montmorillonite specimens recovered after discontinuous titration (first series)________ 15

8. X-ray diffraction data on montmorillonite specimens recovered after discontinuous titration (second series) __ __ 15

ra

CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

RELATION BETWEEN DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE

By ALFRED M. POMMER

ABSTRACT

Potentiometric studies with hydrogen-sensitive and cationsensitive glass electrodes supplemented by chemical determinations and X-ray diffractions on a hydrogen-montmorillonite 

prepared from API Reference Clay No. 23 (Chambers, Ariz.) 

indicate that the clay behaves as a mixture of two acids, resulting from the presence of two types of exchange sites, interlayer and edge, both occupied by hydrogen ions. The interlayer 

sites, which hold the hydrogen ions less tightly, cause the stronger 

acid function, and the edge sites, which form stronger hydrogen 

bonds, are responsible for the weaker acid function.

Correlation of these data with information from the literature 

indicates that in the case of beidellites the pattern is reversed 

and the interlayer positions represent the weaker acid function. 

Application of Eisenman's theory of atomic selectivity to the clay 

leads to the prediction that the stronger acid sites are more likely 

to hold cesium preferentially. This has bearing upon the 

problem of waste disposal of radioactive cesium-137.

INTRODUCTION

Garrels and Christ (1956), using original data of 

Marshall and Bergman (1942) for the titration of the 

clay mineral (beidellite) in the Putnam silt loam soil, 

have shown that the neutralization curve of pH plotted 

against concentration of potassium hydroxide appears 

similar to that of two independent ciay acids. They 

termed the two substrates the C~ (center or interlayer) 

site and the E~ (edge) site. Hauser (1955) published 

titration curves of bentonite that show the dibasic 

character of this material very strikingly. Thompson 1 

reviewed and summarized the extensive literature in 

this field.

The picture is complicated by the fact that hydrogen 

clays spontaneously alter to hydrogen-aluminum clays. 

The literature pertaining to this phenomenon has been 

recently summarized by Coleman and Craig (1961). 

Of great importance in this respect is the finding of Low 

(1955) that in bentonites the initial inflection point or 

break in the "curve represents the point at which the 

titration of exchangeable hydrogen is completed and

1 Thompson, A. C., 1956, Acidic properties of bentonite. Ph.D. Thesis, State 

College of Washington, Pullman, 101 p.

the titration of exchangeable aluminum begins. This 

leads immediately to the question whether there is a 

conflict between the findings of Garrels and Christ and 

those of Low. It is intended here to propose a model 

capable of accommodating both of these concepts and 

to report on experimental work which, it is hoped, will 

eventually lead to a resolution of the problem.

AC KNO WLED GMENTS

Special thanks are due to Dorothy Carroll, who 

contributed greatly to this work by performing a considerable part of the laboratory work, by making calculations, and by teaching me much clay mineralogy. 

The discussions of R. O. Fournier and E-an Zen were 

very helpful, and I am also grateful to them for their 

help and instruction in the use of the X-ray diffractometer. Thanks are also due to T. Tamura, Oak Ridge 

National Laboratories, for his help in reviewing the 

paper.

The study was supported by the Division of Reactor 

Development, U.S. Atomic Energy Commission.

IMPLICATIONS OF MONTMORILLONITE STRUCTURE

Ross and Hendricks (1945) gave the following 

idealized formula for montmorillonite:

[Ali.w Mg.«i!Si40ioIOH],

Nao.ss

In this simplified formula the aluminum and magnesium are coordinated octahedrally and the silicon is 

tetrahedrally coordinated. The mineral may be represented by a sandwichlike structure (fig. 1).

The tetrahedral layer is essentially silica and is electrically neutral in this idealized structure. The octahedral layer would be hydrated alumina and also 

electrically neutral if there were no magnesium present. The substitution of the bivalent magnesium for 

the tervalent aluminum in this layer, however, 

causes a charge deficiency which is neutralized by

Cl
C2 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

cations entering exchange positions on the surface of 

the material, and the cation-exchange capacity of the 

clay results from this charge deficiency. The clay is 

an insulator and the charge deficiency may be considered distributed over its surface according to the laws 

of electrostatics. As may be seen by inspection of figure 1, octahedrally coordinated layers are exposed in 

the "edge" positions. Elsewhere they are covered by 

an insulating layer of tetrahedral silica. It follows 

that the charge density in the interlayer positions 

must be less than that in the edge position, because 

the charge is attenuated by the silica interposed between the surface of the octahedral unit and the 

surface of the clay.

The implications of this concept in terms of the acid 

strength of a hydrogen clay are simple and straightforward. Hydrogen ions in the edge positions are held 

by a relatively strong electrostatic field, are ionized 

with difficulty, and the part of the acid represented by 

these positions must be weaker than the part represented by the interlayer positions. At the interlayer 

positions the field is attenuated, the hydrogen ions are 

more readily ionized, and the acid is stronger than at 

the edge positions.

In the decay of a hydrogen clay to a hydrogenaluminum clay the alumina of the octahedral unit releases aluminum ions which then occupy exchange 

positions, replacing hydrogen ions. Inspection of figure 

1, in conjunction with the electrostatic concept presented here, makes it reasonable to assume that the 

aluminum can be released from the octahedral unit 

only at the edge positions, because this unit has a surface only at the edges. It is then likely that, to the

extent that sites are available, the aluminum ions occupy these sites. The forces holding the aluminum to 

the edge sites are stronger than the attenuated forces 

at the interlayer positions and the aluminum remains 

in place. Hence the exchangeable aluminum is in the 

E~ positions and the hydrogen in the C~ positions. If 

such a clay is titrated, it should behave as a dibasic 

acid, the first acid representing H+ in C~ positions and 

the second acid Al+3 in E~ positions. This model accommodates the concepts of Low (1955) and Carrels 

and Christ (1956). Although it is possible to introduce 

aluminum interlayers in montmorillonite by treatment 

with A1C13 solutions, this results in a product with 

an interplanar basal spacing of 14A (Sawhney, 1960). 

The X-ray data on titrated clays presented later in 

this paper show that this does not occur under the 

experimental conditions discussed here.

EXPERIMENTAL DATA

EXPERIMENTAL PLAN

It is known (Barshad, 1950) that the interplanar 

basal spacing of montmorillonite varies with the cation 

in the exchange position, and that this variation is related to the degree of hydration in the interlayer position. It is difficult to see how the type of cation in 

the edge position or its degree of hydration could affect 

the (001) spacing of a clay the same way. Accordingly, 

it might be expected that the change in this spacing 

during the replacement of H+ (or A1+3 ) with Na+1 in a 

clay should depend on the type of position affected by 

the exchange. It was decided to investigate this 

aspect.

INTERLAYER

TETRAHEDRALLY 

COORDINATED SILICON

INTERLAYER

INTERLAYER + *

OCTAHEDRALLY 

COORDINATED ALUMINUM

WITH MAGNESIUM

SUBSTITUTION

///// CHARGE DEFICIENCY 

FIGURE 1. Simplified montmorillonite structure.
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE C3

Discontinuous or "bottle" titrations (see p. 3) were 

used for reasons discussed elsewhere (Pommer, 1960), 

and an attempt was made to correct for the effect of 

atmospheric CO2 on pH for reasons discussed by Carroll (1960). Unfortunately it was not possible in this 

work to follow the change in exchangeable aluminum 

in the clay, as it was desired to keep the whole sample 

in the solution for a long time to complete the bottle 

titration, and then to use it for X-ray determinations 

ncluding ethylene glycol treatment and firing.

MATERIAL USED

A sample of montmorillonite from Chambers, Ariz. 

(API Reference Clay No. 23), was obtained from 

Ward's Natural Science Establishment. This reference 

sample has been described by Kerr and Kulp (1949). 

The clay contained 2.4 volume percent quartz and 0.6 

percent other impurities (Dorothy Carroll, written 

communication, 1960). Table 1 shows a comparison 

of analytical results obtained on this clay by this laboratory and those published by Kerr and others (1950). 

It -can be seen that the montmorillonite studied here is 

not identical with the sample reported on by the AmerTABLE 1. Comparison of material used with original clay 

reference sample (API No.'28)

SiO2 _________ ___ ...

A12O3------.-----. ------------

Fe2O3- __ -_.---.-_-_-__-_-_-_.

FeO -_-_---__-_--_-__-_-_. _.

MgO ________________________

CaO _________________________

Na2O

K2O_-_-___-_----_--.._. _._-...

H2O._--.______. .._. ______-__---

Ti02 ____ .._._._.__._._...._... .

MnO-___-__--_-.__________ __ .

C______________________________

co_____________________________

Original sample 

API No. 23 

(Kerr and 

others 1060) » 

(in weight 

percent)

_LQ O1

17.20

2. 17

.26

3.45

2.31

. 14

.28

23.47

.24

.04

Trace

Material used * 

(In weight 

percent)

53.4

15.9

1.5

<. 05

4 5

2.2

. 11

.28

21.6

.20

.10

<. 05

Exchangeable cations

(meq per 100 g) 

Ca 3..._-----__-._-_._.___._.._ * 87. 5

Mg»_____________________________ * 18. 2

Na 3.------______________________ 6 5. 9

K«______________________________ 8. 4

Total exchange capacity.._________ 7 120. 0

i Formula of original sample: 

(Ali.5iPeo.i3Mgo.*HAlo.o7Si3.M)Oio(OH)j(Nao.ojCa/2o.»7).

»Elmore, P. L. D., Barlow, I. H., Botts, S. D., and Chloe. Q. W., analysts. No 

corrections for impurities were made. Formula of material used (corrected for 

quartz impurity, Dorothy Carroll, written communication, 1960): 

(Ali.«Feo.MMgo.47)(Alo.MSis.M)Oio(OH1 8(Nao.MKo.MCa/2o.s!Mg/2o.o7). 

The charge deficiency is 0.474 in the tetrahedral layer and -0.065 in the octahedral 

layer, for a total of -0.629. The exchangeable cations neutralizing the charge, on the 

other hand, total 0.433 charge units.

»Not reported by Kerr and others (1950). They reported total exchange capacity of 147.5.

4 Brannock, W. W., analyst.

 Budinsky, J. W., analyst.

 Carroll, Dorothy, analyst.

7 Calculated sum of exchangeable cations. Exchange capacity determined by 

ammonium extraction was 104 meq. per 100 mg (Dorothy Carroll, analyst).

ican Petroleum Institute Project; however, the differences as shown in the clay formulas are not significant 

for the purpose of this investigation. X-ray diffraction 

studies on a nonoriented slide of the original material 

and on an oriented slide of the H-clay-disclosed no 

significant abnormalities. A total-cation-exchangecapacity determination by saturation with ammonium 

acetate and Kjeldahl distillation (modification of the 

procedure of Association of Official Agricultural Chemists, 1950) yielded a total base-exchange capacity of 

104 meq. per lOOg (Dorothy Carroll, written communication). The clay was converted to the hydrogen (H) 

form by the method of Aldrich and Buchanan (1958) 

as modified by Dorothy Carroll, who made the preparation as outlined here.

PREPARATION OF THE! H-FORM

A sample of montmorillonite was crushed to pass a 

230-mesh (0.06 mm) sieve, and a 1 percent suspension 

was made in distilled water. Sufficient HC1 was added 

to make the suspension 1 N. The suspension was 

placed in a 1-liter cylinder and shaken in an end-overend shaker for about 1 hour. The montmorillonite was 

removed from the acid solution by repeated centrifugation and washing until a negative chloride test with 

AgNO3 showed that all the acid had been removed. 

The quartz impurity was separated during centrifugation and discarded. The sample was finally dried at 

about 60° C, finely ground, and stored in a glass vial 

until required. The exchangeable cations remaining on 

the clay after its conversion to the hydrogen form were 

determined (Dorothy Carroll, analyst). They were in 

meq. per 100 g (milliequivalents per 100 grams): calcium 

11.5, magnesium 16.7, sodium 5.7, and potassium 0.6. 

In addition to the exchangeable hydrogen ions there 

were 34.5 meq. per 100 g of other exchangeable cations; 

from the original total exchange capacity of 120.0 

(obtained by additioja of the exchangeable cations of 

the original clay) we can estimate the exchangeable 

hydrogen ions of this clay as 85.5 meq. per 100 g. 

Almost all the potassium and more than 85 percent of 

the calcium was replaced by hydrogen, whereas the 

magnesium and the sodium were almost completely retained during the process. The role of exchangeable 

aluminum will be discussed later. As the hydrogen 

clay decayed, some exchange positions originally occupied by hydrogen ions became filled with aluminum ions. 

As this section is concerned with how good a hydrogen 

clay was produced by the treatment originally, the exchangeable aluminum is immaterial here.

TITRATION WITH NaOH

A discontinuous titration was made using small 

hydrogen-montmorillonite samples (65 mg to which 

increments of 0.1 N NaOH were added. Each 65-mg
C4 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

sample was weighed into a separate weighing bottle and 

sufficient water was added to make a constant volume. 

The increments were 0.02 ml for samples 2 through 13 

and 0.04 ml for samples 14 through 37. The largest 

volume of NaOH was in sample 37 which contained 

1.20 ml. The total volume for all samples was 6.20 ml. 

Sample 1 contained only montmorillonite with water. 

Reagent blanks without clay were run for samples 1, 6, 

12, 18, 24, 30, and 37 to measure the effect of CO2 

absorption. All samples were shaken gently after 

being prepared and allowed to stand 1 day before pH 

readings were taken. The concentration of montmorillonite was a little more than 1 percent. The 

increments of NaOH were added by an automatic 

microtitrator. Results are summarized in table 2.

ANALYSIS OP FILTRATES

The solutions in contact with the samples were 

removed by centrifugation and repeated washing in 

distilled water. The samples were returned to the 

weighing bottles and kept for X-ray examination. 

The filtrates were made up to 100 ml in volumetric 

flasks. Sodium and aluminum were determined in 

separate aliquots.

The titration was arranged so that the total exchange 

capacity of the montmorillonite in the H-form would 

be taken up at about sample 24 (0.68 ml 0.1 N NaOH, 

table 2). It was expected that the montmorillonite 

would absorb all the sodium added to it up to the 

equivalence point. Sodium in the filtrates was determined by flame photometer, with the results given in 

table 3. Sodium activities were measured in the solutions above the montmorillonite samples with a special 

Beckman sodium electrode. The millivolt readings are 

also given in table 3.

Aluminum in the filtrates was determined with 

alizarin red-S by the rapid method of Shapiro and 

Brannock (1956, p. 34). The aluminum found is 

given in table 4. This determination was made to see 

whether aluminum was released from the montmorillonite during the titration.

The aluminum values in table 4 are quite high for 

the more alkaline solutions. This is so because the 

solutions were in contact with the clay for almost 4 

months prior to filtering. This was necessary to 

provide time for the 115-day reading considered 

desirable in a discontinuous titration. In order to 

obtain correlative analytical results bearing on the 

decomposition of the clays replicate runs of samples 10, 

20, and 30 were made, filtered after 7 and 12 days, 

respectively, and analyzed for alumina by Leonard 

Shapiro by methods similar to those described by 

Shapiro and Brannock (1956). As before, 65-mg 

samples were used, and total A12O3 in the solutions 

ranged from 0.06 to 0.11 mg. No trend was apparent,

and it seems reasonable to state that, although there 

was significant decomposition of the clays exposed to 

more concentrated sodium hydroxide solutions over 

a longer time, at the time of the pH and glass-electrode 

readings taken during the first 2 weeks, the clay may 

be considered as virtually intact, provided no new 

solid phase formed. No crystalline phase was apparent 

on X-ray diffraction.

pH READINGS

The neutralization of the acid montmorillonite was 

measured by pH readings made with a Beckman Model 

GS meter using a glass electrode. The readings were 

made in the supernatant solutions in contact with the 

montmorillonite samples that had settled to the 

bottom of the weighing bottles. The bottles were 

kept covered at all times except when making pH 

determinations. Clay in contact with electrodes will 

cause irregular pH values. These irregularities have 

been ascribed generally to the "suspension effect." 

This is discussed elsewhere (Pommer, 1961). Except 

for the most acid solutions no difficulty was experienced 

in getting the clay to settle, and the shape of the 

curves indicated that the slight turbidity involved in 

those few reaction mixtures did not cause a detectable

error.

PRESENTATION OF POTENTIOMETBIC 

AND ANALYTICAL DATA

Two separate series of determinations were run at 

different times. The results of the first series are shown 

in tables 2-4 and those of the second series in tables 5 

and 6.

SEMILOGARITKMIC PLOTTING OP TITRATION CURVES

Sillen (1959) discussed the literature, theory, and 

application of the logarithmic diagram with a master 

variable, a very useful graphic presentation of equilibrium data which was originally presented by Bjerrum 

(1914). The application of this technique to acid-base 

equilibria was illustrated by Sillen (1959). Mainly it 

involves the equivalent of plotting titration curves 

semilogarithmically, the volume being entered on the 

logarithmic axis. Such plots were found useful previously (Pommer and Breger, 1960a, 1960b; Pommer 

and Carroll, 1960; Pommer, 1960; Carroll and Pommer, 

1960) in producing reasonably straight lines if the values 

obtained in discontinuous titrations were thus treated. 

The nearness of the points of intersection of these lines 

to the equivalence points was verified in most cases by 

Gran's method (1952). The plotting method may be 

expected to be effective for the reasons given below.

If increments of a strong base solution are added to 

an aqueous neutral salt solution, the hydroxyl-ion 

concentration of the solution is a linear function of the 

titrant volume, and hence the solution pH is a linear
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE C5

TABLE 2. Titration of montmorillonite (Chambers, Ariz.) with 

0.1 N NaOH

[65-mg samples in a total volume of 6.20 ml]

Sample

I..... ___ ..

3.--- .... ..

4.. . ..........

5...... .... 

6..-. ...

7.. .. .........

8.. 

9.. ....... ....

W.. ..........

n.. ..........

12............

IS.. ...... ....

14.-. 

15.. .. ........

16-- 

n. .. .........

18,. ..........

1Q

20--- 

21-. ........ ..

22............

23... ...... ...

24-- 

25 

26... 

97

28.-. 

29--- 

30 

31 

32............

34-- 

35-. 

36. 

37-.. 

38 « ......

NaOH 

(ml)

nil 

0.02 

.04 

.06 

.08 

.10 

.12 

.14 

.16 

.18 

.20 

.22 

.24 

.28 

.32 

.36 

.40 

.44 

.48 

.53 

.56 

.60 

.64 

.68 

.72 

.76 

.82 

.86 

.90 

.94 

.98 

1.06 

1.10 

1.14 

1.16 

1.20 

1.20

pH readings at times (in days) and at stated temperatures 

(in degrees C) after mixing

1

25°

'4.05 

'4.60 

5.60 

5.70 

5.90 

6.20 

'6.30 

86.40 

6.35 

6.40 

6.60 

6.65 

6.70 

37.05 

'7.40 

37.70 

38.25 

'9.15 

39.50 

9.85 

10.05 

10.13 

10.25 

10.30 

10.40 

10.60 

10.73 

10.70 

10.85 

11.02 

11.00 

11.15 

11.35 

11.30 

11.20 

11.40 

11.70

2

24°

4.40 

5.22 

5.30 

5.70 

5.93 

6.20 

6.20 

6.02 

6.40 

6.32 

6.70 

6.70 

'6.85 

6.75 

6.70 

6.85 

7.37 

7.95 

8.65 

9.10 

9.40 

9.60 

9.65 

9.80 

10.15 

10.40 

10.30 

10.50 

10.75 

10.85 

10.79 

11.02 

11.25 

11.00 

11.05 

11.15 

11.65

3

25°

4.60 

5.08 

5.22 

'5.29 

5.91 

»6.05 

6.12 

5.90 

6.40 

6.45 

6.50 

6.58 

6.65 

6.70 

6.80 

7.08 

7.50 

7.95 

8.25 

8.59 

9.10 

9.40 

9.42 

9.62 

9.85 

9.85 

10.02 

10.11 

10.40 

10.55 

10.60 

10.88 

10.98 

11.10 

10.91 

11.01 

11.61

6

25°

4.55 

5.15 

5.50 

5.75 

5.89 

86.00 

6.19 

5.90 

'6.23 

6.35 

6.49 

6.43 

6.58 

6.75 

6.90 

7.20 

7.50 

8.05 

8.21 

8.50 

8.65 

8.80 

8.85 

9.15 

9.25 

9.60 

9.75 

9.65 

'9.85 

10.20 

' 10. 10 

10.70 

10.80 

10.90 

310.60 

10.85 

11.65

Average i

4.51 

5.15 

5.40 

5.71 

5.90 

6.20 

6.17 

5.94 

6.38 

6.38 

6.57 

6.60 

6.64 

6.73 

6.80 

7.04 

7.45 

7.98 

8.37 

9.01 

9.30 

9.48 

9.54 

9.71 

10.13 

10.11 

10.20 

10.24 

10.66 

10.65 

10.79 

10.93 

11.09 

11.07 

11.05 

11.10 

11.65

*48

29°

4.55 

5.10 

4.75 

5.20 

5.45 

5.70 

6.22 

5.20 

6.35 

6.50 

6.60 

6.65 

6.70 

6.80 

6.90 

7.35 

7.80 

7.95 

8.25 

8.90 

8.60 

8.60 

8.50 

8.63 

8.90 

8.95 

8.85 

8.90 

8.95 

8.92 

8.91 

8.95 

9.10 

9.10 

9.10 

9.05 

9.45

50

26°

4.80 

5.35 

5.15 

5.45 

5.95 

6.01 

6.10 

5.95 

6.39 

6.45 

6.58 

6.55 

6.80 

6.90 

6.95 

7.40 

7.80 

8.40 

8.29 

8.15 

8.40 

8.62 

8.70 

8.65 

8.88 

8.90 

8.98 

9.01 

9.00 

9.02 

8.95 

9.10 

9.10 

9.15 

9.10 

9.16 

9.50

115

25°

4.95 

5.30 

5.03 

5.58 

5.70 

5.75 

5.85 

5.75 

6.02 

6.12 

6.20 

6.30 

6.38 

6.51 

6.60 

7.10 

7.35 

7.75 

7.90 

8.00 

8.25 

8.33 

8.48 

8.48 

8.60 

8.70 

8.80 

8.82 

8.88 

8.92 

8.91 

9.00 

9.05 

9.08 

9.05 

9.11 

9.30

i The average was made up of the readings for the first four figures, but only those 

not differing by more than half the difference between the highest and the lowest 

reading for any sample were used to calculate the average. This value is plotted in 

fig. 2 and was published by Pommer and Carroll, 1960.

* Dilutions to constant volume (6.20 ml) made 1 day prior to this reading.

3 Reading omitted from calculation of average.

4 Sample 38 contained no clay sample, only 1.20 ml 0.1 N NaOH.

function of the logarithm of the titrant volume. The 

only requirement is that the initial volume be large 

enough to assume constant volume. This situation 

applies at the end of most acid-base titrations. If 

acid is present, the change in pH as a function of the 

logarithm of volume of base added may be linear 

under some conditions, as when the hydrogen ion 

concentration due to free acid is negligible. Under 

these conditions the slope of this part of the linear 

titration curve will be less. This is typical of most 

acid-base titrations before the end point is reached. 

Hence, semilogarithmic plotting of titrations can indicate end points; it can also yield dissociation constants 

of weak acids.

EVALUATION OF ELECTRODE DATA

Plots of pH and sodium-sensitive electrode data on 

the first series have been presented previously. 

Originally the average of the first four pH readings 

was plotted semilogarithmically (Pommer and Carroll, 

1960), and these values were then compared with 

sodium-sensitive electrode readings (Pommer, 1960). 

As table 2 shows a lowering of pH with time, it was 

felt that, in addition to the aging of the clay, carbon

678823 O 63 2

dioxide absorption might play a part. Carroll (1960) 

discussed some implications of this factor. Because 

the effect of carbon dioxide upon pH values in the 

first run could not be determined from the availabe 

data, the experiment was repeated.

The results of the second titration are presented in 

figures 2 and 3. Here line A represents the curve on 

the day after mixing (the alternate A' line indicates 

equivocal indications of a second end point), line B 9 

days later, and lines D and E represent the titration 

curves of the reagent blanks on these days. It may 

be observed that, whereas line A shows two equivalence 

points, the problematic second equivalence point has 

been lost in line B. A pronounced shift to the left 

from A to B and D to E shows the lowering of pH 

owing to CO2 absorption from the air. All bottles 

received the same handling at all times, and for this 

reason it appeared that NaOH solutions of identical pH 

should exhibit the same acid shift, whether or not 65 

mg of clay were suspended in them. A corrected curve 

was made, adjusted for the effects of CO2 absorption. 

This was done graphically by taking a point at B,

TABLE 3. First series A comparison of readings, in millivolts 

(as determined by a calomel and sodium-sensitive glass electrodes), 

with sodium values determined by flame photometry

[Modified from Pommer, 1960]

Sample

1 ________ _ __ _ ___ _

2. ._._-...__ _ __________

3____ --- _-_-_-_

4.---------- __ _________

5__--------_____-_-______

6 __ _._-_ __.__..

7

8_____ _____ ______

9___----_-__-_-__________

11_______________________

12________-__-.__________

13_----_-_--__---_-______

14..- __ ___ _ _ . ______

15__ ____ _ ___ __________

16____-____---___-___-___

17_______________________

19_____._----__--___-____

20-______-_-._____-_--_-_

21_--_-__--_-__--________

22_______-___-_._________

23-_____-_-___--_____-.__

24__________-__-__--_-.__

25______----_----__---.__

26_________.-_-______----

27___.___--_-__--_-_---_-

28___--__-_-______ _______

29______. ..__-_.-_---_--_

30____________--.___---__

31-. ___-____-_----------_

32_______. __._-_____. ___.

34___-___._____--_-------

35.-. -___.__-_--____-----

36 _ . _ . __--

37_______________________

38___-__----.__ ._._.__-_-

pH

4.80

5.30

5.25

5.80

6.00

6. 10

6. 15

6.00

6.40

6.55

6.65

6.70

6.80

7.00

7.40

7.60

8.25

8.35

8.50

8.60

8. 60

8.65

8.75

8.80

8.90

8.90

8.75

9.05

9.05

9. 10

9. 10

9.05

9.20

9.20

9.45

Na» 

(millimoles 

per liter)

0.53

.55

.60

.55

.55

.69

.70

.70

.76

.70

.90

.98

1.4

1.8

2.0

2.4

2.4

2.5

3.5

3.8

4. 2

4.2

4.8

5.7

6.4

7.0

7.0

7.8

7.2

8.8

9. 1

11

11

11

19

Electrode 

reading 

(millivolts)

89

109

104

120

120

120

122

104

118

118

118

118

116

113

104

91

69

61

53

51

45

42

38

35

31

31

31

24

25

22

20

18

18

15

7

i Dorothy Carroll, analyst.
C6 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

180 -

170 - Line 4: Clay swnplas 1 day after mixing

IJneS: Clay samples 10 days after mixing

LinaC: Clay samples 10 days after mixing; pH corrected

for CO 2 absorption

UneO: Reagent blanks 1 day after mixing 

Una C: Reagant blanks 10 days eftar mixing

11.0 12.0

FIGURE 2. Second series Plot of pH for the titration of H-montmorillonite with sodium hydroxide (with correction

for carbon dioxide absorption).
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE C7

200

175

150

125

100

90

80

70

60

50

40

30

20

15

10

3 9 

O

1.5

1.0 

0.9 

0.8

Line A-A': Clay samples 1 day after mixing 

Line fi. Clay samples 10 days after mixing

Clay samples 10 days after mixing; pH corrected

for CO 2 absorption

Reagent blanks 1 day aftar mixing

Reegent blenks 10 days after mixing

Line C:

LineO: 

Line £:

- 10.5

- 1.05

10.0 11.0

- at05

12.0

PH

FIGURE 3. Semilogarithmic plot of pH for the titration of H-montmorillonite with sodium hydroxide (with correction for carbon

dioxide absorption).
C8 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

going down vertically to the intersection with E, then 

horizontally to the right (to counteract the shift to the 

left caused by CC>2 absorption) to the intersection with 

D, then up vertically to the ordinate of the original 

point on line B. This point was plotted and the procedure repeated until line C was constructed. It may 

be noted that D and E join at a pH of 5.6, a not too 

unreasonable value for distilled water saturated with 

10~4 atmospheres of CO2 ; below pH 5.6, lines B and 

C are therefore identical. In the linear plot the lines 

join at pH 5.0, an experimentally determined value. 

It was decided not to use this point in the semilogarithmic plot for two reasons: The proper ordinate for 

the experimental point would be located at minus 

infinity; also the adopted procedure illustrates that the 

plotting method has limitations. The difference of 0.6 

pH units is not excessive for such an unbuffered system. Comparison of A and B then gives the overall 

effect of standing upon the titration, whereas a comparison of A and C shows the effect on standing with 

the CO2 absorption effect removed.

Figure 4 shows the corrected curves derived from the 

linear and semilogarithmic plots and shows them to be 

similar enough to indicate the validity of both plots

TABLE 4. First series Al^Os found in filtrates from the titration

of H-montmorittonite with 0.1 N NaOH 

[Reprinted from Carroll, I960. 65 mg samples in a total volume of 6.2 ml]

Sample

1__ _.--.__-. __ -_-.._-._...__..

2___ __ ._-. ___ . ______ _ _

3___. _______________

4. -__-_------__-_._____________

5__ ___.__.__._. _.._._.... _.__.

6_. _....__- _ .__. ______ ....

7_ ______________________ _____

8.. ______________________ ......

9. ......__- _ ___.... _ . ......

10... _______________ .

11_. _ ._ ____ _ .

12_._____ _ ...... ____ _ _ . .

13...... .___.__.......__.....__

14...... _____ -__.._. ___ . _

15. -.-_.._._._._._..._......._ 

16... -_._.....-._..______...._.

17... _._._.._....._........_...

18. ..._.... ____ .... ___ ... .

19. ____________________________

20___________________________ _

21_____________________ _

22____ ____________ ___

23__________________________ _

24_____ _ _ _ __________ _

25_-________. _ _______

26___________________________ _

27__. _____________________ _

28_________ _ _____ _

29_. _.__._,..___._______.___.. _

30____________________ _

31__ _ _ .

32_ ________________ _

34__ ___________________________

35____________________ . _

36_. ______________ _

37____________________

NaOH added 

(ml)

nil

0.02

O4

.06

no

.10

. 12

. 14

. 16

10

.20

.22

.24

00

.32

.36

4.O

.44

AQ

KO

.56

.60

.64

.68

.72

.76

.82

.86

.90

.94

.98

1.06

1.10

1. 14

1.16

1. 20

Al»Os (mg)

0.06

nil

nfi

nil

nil

nil

OK

0.7

.50

oo

QQ

no

1.75

2.75

4. 13

3.92

3.69

87

2

00

2 87

a

KO

0 QC

3.11

3.95

3.95

3. 11

2 QQ

2.39

4.31

0 KO

3.05

4 1Q

4.31

5

00

4 84

5.26

TABLE 5. Second series titration of mpntmorittonite (Chambers,

Ariz.) with 0.1 N NaOH with, provision for reaction blanks !

[60-mg samples in total volume of 6.20 ml]

Sample

1 

2 

3 .......

4... . 

5.. __ .

6... .

7 

8. ___

9.. .....

10 

11 

12 

13. .....

14 

15 

16 

17 

18 

19 

20 

21 

22 _ 

23 

24 

25.. 

26 

27 

28 

29 

30... 

31 

32 

33 

34. ..... 

35 

36 

37 

NaOH 

added 

(ml)

nil 

0.02 

.04 

.06 

.08 

.10 

.12 

.14 

.16 

.18 

.20 

.22 

.24 

.28 

.32 

.36 

.40 

.44 

.48 

.52 

.56 

.60 

.64 

.68 

.72 

.76 

.80 

.84 

.88 

.92 

.96 

1.00 

1.04 

1.08 

1.12 

1.16 

1.20

Meq. 

ofNa 

per 

100 g 

(100 

mg 

day)

3.08 

6.16 

9.24 

12.32 

15.40 

18.48 

21.56 

24.64 

27.72 

30.80 

33.88 

36.96 

43.12 

49.28 

55.44 

61.60 

67.76 

73.92 

80.08 

86.24 

92.40 

98.56 

104.72 

110.88 

117.04 

123.20 

129.36 

135.52 

141.68 

147.84 

154.00 

160.16 

166.32 

172.48 

178.64 

184.80

pH value after number of days 

indicated

1

4.05 

4.55 

5.20 

5.51 

5.45 

5.61 

5.78 

5.85 

5.73 

6.15 

6.70 

6.32 

6.82 

7.50 

7.65 

8.08 

8.50 

8.65 

9.15 

9.15 

9.25 

9.65 

9.85 

9.85 

10.05 

10.00 

10.30 

10.50 

10.60 

10.65 

10.65 

10.78 

11.00 

11.00 

11.05 

11.15 

11.18

2

4.45 

4.75 

5.00 

5.30 

5.40 

5.55 

5.80 

5.75 

5.90 

6.05 

6.15 

6.20 

6.75 

6.70 

6.55 

6.60 

6.85 

7.15 

7.80 

7.95 

8.05 

8.80 

9.05 

9.15 

9.38 

9.60 

9.60 

9.95 

10.00 

10.38 

10.30 

10.48 

10.51 

10.68 

10.80 

10.85 

10.88

5

5.10 

4.75 

5.15 

5.10 

5.15 

5.20 

5.80 

5.50 

5.72 

5.78 

5.85 

5.80 

6.15 

6.15 

6.25 

6.30 

6.55 

6.80 

7.05 

7.25 

7.50 

7.75 

8.05 

8.35 

8.83 

9.25 

9.30 

9.51 

9.63 

9.95 

9.80 

10.11 

10.35 

10.45 

10.60 

10.71 

10.75

7

4.25 

4.80 

4.90 

5.20 

5.15 

5.30 

5.85 

5.55 

5.65 

5.80 

6.00 

5.90 

6.30 

6.35 

6.50 

6.50 

6.70 

6.85 

7.10 

7.40 

7.60 

7.75 

8.05 

8.35 

8.58 

9.02 

9.10 

9.30 

9.40 

9.80 

9.65 

9.90 

10.20 

10.25 

10.35 

10.45 

10.45

12

5.10 

4.80 

4.71 

4.80 

4.95 

4.95 

5.65 

5.20 

5.40 

5.45 

5.50 

5.50 

5.90 

5.75 

5.90 

6.00 

6.25 

6.60 

6.90 

7.20 

7.45 

7.55 

7.80 

8.25 

8.20 

8.40 

8.45 

8.75 

8.90 

9.45 

9.15 

9.55 

9.90 

10.05 

9.85 

10.10 

10.15

Na electrode 

reading after 

number of 

days indicated ( mv)

7

107 

125 

127 

129 

125 

125 

124 

122 

122 

122 

118 

122 

111 

109 

107 

100 

100 

93 

87 

78 

73 

71 

67 

62 

60 

58.1 

56.3 

52.7 

50.9 

50.2 

45.4 

46.5 

45.4 

41.8 

40.0 

38.2 

38.2

12

96 

122 

126 

133 

126 

131 

131 

122 

122 

129 

122 

124 

122 

116 

115 

111 

107 

98 

89 

78 

75 

69 

67 

60 

58 

56 

53 

49.1 

45.5 

45.5 

40.0 

41.8 

38.2 

36.4 

32.8 

32.8 

30.9

Na infiltrate* 

(ppm

1.0 

.7 

.5 

.6 

.7 

.7 

.7 

.7 

1.0 

.9 

.8 

.8 

1.0 

1.0 

1.0 

1.6 

2.0 

2.1 

2.4 

2.4 

3.6 

3.7 

4.1 

4.9 

5.2 

4.7 

5.6 

7.1 

7.2 

7.2 

8.9 

10.0 

10.2 

12.4 

12.4 

13.4 

13.3

i Shown in table 6.

* Dorothy Carroll, analyst.

TABLE 6. Second series pH values of solutions to which increments of 0.1 N NaOH were added 

[Reprinted from Carroll, 1960. Total volume of each is 6.2 ml]

Sample

la 

6a .......

12a

188. 

24a. 

30a. ... -

38.. 

NaOH 

added 

(ml)

0.02 

.10 

.22 

.44 

.68 

.92 

1.20

NaOH 

micromoles 

in solution

0.32 

1.61 

3.54 

7.10 

10.96 

14.83 

19.35

pH values alter number of days 

indicated

1

7.60 

9.85 

10.50 

11.00 

11.50 

11.75 

11.85

2

6.40 

9.50 

10.30 

10.95 

11.35 

11.58 

11.65

5

6.10 

7.80 

9.75 

10.90 

11.40 

11.52 

11.75

7

6.10 

7.45 

9.15 

10.60 

11.35 

11.65 

11.75

12

6.05 

7.20 

8.00 

9.70 

11.35 

11.65 

11.85

Difference in 

pHin 

11 days

1.55 

2.65 

2.50 

1.30 

.15 

.10 

nil

for the purpose. The line derived from the semilogarithmic plot appears to be slightly better at the 

lower end. In this connection it should be noted also 

that in figures 2 and 3 line C crosses line A. This is 

physically unreasonable and is probably caused by the 

inadvertent CO2 uptake of sample 18a. This sample 

contained twice as much NaOH as sample 12a and its 

pH was only 0.1 unit higher. Also, when plotted 

semilogarithinically, the pH of NaOH solutions at 

different concentrations should fall on a straight line. 

Inspection of curve D in figure 2 indicates that the 

point identified as 18a on table 6 deviates from the 

straight line by 0.15 pH unit and should be at pH 11.15 

if the line were straight. This is almost at the place 

where the buffering capacity of the solution is at a
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE C9

maximum and indicates, therefore, considerable CO2 

absorption, owing to a technical accident. The overcorrection probably does not affect the position of the 

end points or the conclusions presented here; however, 

it makes impossible an evaluation of the second pK 

and an interpretation of Henderson-Hasselbalch plots 

(Pommer and Carroll, 1960).

The results show that more blank solutions are required in a run to cancel out the effects of possible 

technical accidents. The graph, however, clearly 

shows the advantage of the procedure.

Figures 5 and 6 compare the value of the first series 

previously published (Pommer and Carroll, 1960) to 

the experimental and corrected value of the second 

series. Although the consistency of the experimental 

pH values of both series is clearly shown in tables 2 and 

5, figure 6 summarizes strikingly the effect of using a 

titration curve from average pH values compared to 

titration curves not corrected for CO2 absorption as 

they change with time. The figure also points out 

the difference between the two series not accounted 

for by the changed procedure. For instance, curve 

I should remain in the area bounded by A and B, as 

the averaging procedure used in its construction should 

yield an intermediate value. However, it crosses line 

A in the region where the sodium concentration is 

higher. The reason for this discrepancy is not known, 

but a possible explanation is that the CO2 uptake of the 

system in the first series was much less. This might 

explain the remarkable similarity of curves / and C in 

figure 6.

Experimental details for the measurement of sodium by cationic-sensitive electrodes (first series) have 

been reported elsewhere (Pommer, 1960, 1961). Figure 

7 compares flame photometric and potentiometric 

sodium values of the first series, and figure 8 compares 

the potentiometric data of both series with sodium 

values from flame photometry of the second series. 

A complete' enumeration of all sodium data is presented in tables 3 and 5. As the determination of 

sodium by cation-sensitive electrodes is relatively new, 

these data are given to indicate the powers and limitations of the electrode used.

It can be concluded that the clay takes up virtually 

all the sodium added during neutralization of the 

"first" acid and that it continues to take up a considerable fraction of the sodium added during the neutralization of the "second" acid. In the region of overtitration some sodium may be taken up, either by 

physical absorption or possibly by exchange for residual 

calcium in the hydrogen clay.

It is of interest to note that the second segment of 

the sodium electrode curve, in figure 8 is less steep than 

the third. Although this is physically unreasonable

it is to be expected in view of the abnormality of the 

response of the sodium electrode in clay titrations in 

this region. This is discussed elsewhere (Pommer, 

1961).

X-RAY DIFFRACTION STUDIES 

X-RAY DIFFRACTION PROCEDURE

Oriented aggregate mounts on glass slides were made 

of the montmorillonite samples that had been titrated. 

The clay suspensions were allowed to dry at room 

temperature. X-ray diffraction patterns were made 

of the (001) d spacing in order to show the change in 

this spacing from the H-form montmorillonite to 

that in which the interlayer exchange positions were 

filled with sodium. Copper Ka radiation was used 

throughout, and the chart was run at 1° per minute. 

Some of the slides were also treated at 35 percent 

humidity in a desiccator. Others were treated with 

ethylene glycol, and a few were heated. Slide preparation was done by Dorothy Carroll.

PRESENTATION OF DATA

The X-ray data are presented in tables 7 and 8. 

In effect, as the hydrogen in the clay is replaced by 

sodium, there is a systematic change in the (001) 

spacing completely in line with what might be expected in the light of Barshad's (1950) data. This 

change is most pronounced if the patterns are taken 

at room temperature and humidity. It is lessened if 

the slides are pretreated at 35 percent humidity, and 

it is totally obliterated if they are treated with glycol, 

or if they are fired. This is as must be expected. 

It is, however, important to note that almost the 

entire change in (001) spacing appears to take place 

during the neutralization of the "first" acid. This is 

precisely the result to be predicted from the concept 

of interlayer versus edge sites of Garrels and Christ 

(1956) in the light of Barshad's (1950) findings concerning the effect of the cations upon interplanar 

spacing. The data furnish experimental indications 

that the neutralization of the "first" acid is related to 

the exchange of Na+ for H+ in interlayer positions 

and that the neutralization of the second acid is 

related to the exchange of Na+ for H+ in positions 

which are not interlayer positions. Presumably these 

positions are edge sites.

The relation of interplanar spacing to the type of 

exchangeable cation can be utilized in an attempt to 

determine the position of some of the cations. It will 

be recalled that the clay used in this work had not been 

completely converted to the hydrogen form and that it 

contained 28 meq. per 100 g of bivalent cations (Ca 

and Mg) and about 6 meq. per 100 g univalent alkali 

cations (Na and K) in addition to about 90 meq. per 100 

g hydrogen ions. It is now of interest to determine 

whether the exchangeable alkali and alkaline earth
CIO CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

190, -

180

170

130

120

< 90

5 

o

50

30

10

4.05 4.25

Ox 

JO

a

Ox

a 

a 

a 

ox

a 

o x

a

xo

Ox

Ox

O

x O 

x O 

x O 

x O

5.0 6.0 7.0 8.0

PH

10.0 11.0 120

FIGURE 4. Comparison of a corrected pH titration curve constructed from a semilogarithmic plot (x-x-x-x) with one 

constructed from a linear plot (0-0-0-0-0). (For purposes of clearness the points of the curves are not connected 

by lines.)
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE Cll

200

175

150

125

100

90

80

70

60

50

40

30

20 

oo 

§

i l5

a 

a

z

i-

| 10

I 9

1.5

1.0 

0.9 

0.8

MONTMORILLONITE

l i

5.0 6.0 7.0 8.O 

PH

9.0 10.0

10.5

1.05

0.105

11.0 12.0

FIGUEE 5. Comparison of experimental pH data of first series (7) and second series (lines A and A' and B same as shown in fig. 3). 

The alternate A and A' lines show that the second inflection point is based on equivocal evidence.
012 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

200

175

150

125

IOO 

90 

8O

70

60

50

40

30

» 20

8

I

£ 15

IUJ

I

S 10

d 9 

8

7

1.5

1.0 

0.9 

0.8

O,

MONTMORILLONITE

I I II I I

5.0 6.0 7.0 8.0 

pH

9.0 10.0

1.0 

0.9 

0.8 

0.7

0.6 

0.5

0.4 

0.3

0.2

i

0.1 Z

ss

0.09 ~ 

6

0.08 g 

UJ

0.07 3

Zi

0.06 I 

0.05

0.04

0.03

0.02

11.0 12.0

FIOUBE 6. Comparison of pH curve of first series based on averaging of tour determinations with (line /) with the pH curve of second

series after correction for C Oj (line C).
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE CIS

1.2 

I.I 

1.0

0.9 

0.8

o: 0.7

LU 

CL

JJ 0.6

y 0.5 

o

I 0.4

O 

O

0.3 

0.2 

O.I 

0

-O.I

-0.2

-0.3

I I

-20 -40 -60 -80 -100 -120

MILLIVOLTS

-140

FIQUBB 7. First series Relation between flame photometric and potentiometric sodium values in a discontinuous montmorillonite titration

(Pommer,1861).
C14 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

SODIUM, IN PARTS PER MILLION, OF FILTRATE 

DILUTED TO 100 (CORRECTED FOR BLANK)

Analytical sodium values of second series

Represents a sodium electrode value, in

millivolts,of a clay sample

Represents the electrode value of a sodium

hydroxide solution blank

Symbols referring to the first series are

marked with a dot in their center

Sodium electrode readings are in millivolts

(refer to bottom scale) and analytical

sodium values are in parts per million

(refer to top scale). Top and bottom

scales are not related to each other

-130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 -0

MILLIVOLTS

FIGUEE 8. Comparison of sodium electrode readings pooled for both series with analytical sodium values of the second series (x-x-x).
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE C15

TABLE 7. X-ray diffraction data on montmorillonite specimens 

recovered after discontinuous titration (first series)

[CuKa radiation, 1° per minute]

Sample

Na 

added 

(meq. 

per 

100 g)

Na 

taken up 

by clay 1 

meq. per 

100 g)

d(001) A > <J(001) A » d(001) A « d(001) A t

Neutralization of first clay acid

1..... ________

2.. ............. .... 

Z.. ................. 

4.. ................. 

5... ___ ..... _ ..

6...... _ .......... 

7. ....... _ .. ___ 

8.... __ . _ ..... _ 

9.. ................. 

10....... _ . _ .... 

11... ...............

12.. ________ ... 

13..................

14.... ____ . _ ..

0 

3.1 

6.2 

9.3 

12.3 

15.4 

18.4 

21.6 

24.6 

27.7

on o

33.9 

37.0 

43.1

0 

3.1 

6.2 

9.3 

12.3 

13.9 

16.9 

20.0 

23.1

OQ O

30.8 

32.3 

33.9

14.73 

13.92

13.39 

13.39 

13.81 

13.19 

13.39 

12.99 

13.29 

12.62

14.48 

14.48 

14.48

14.85

14.37

14.26 

14.37

13.59

16.99 

16.67

16.67

16.67

14.26 

14.26

14.03 

14.48

14.26 

14.26 

13.81 

13.60 

13.81 

13.39 

13.39 

13.19 

13.19

Neutralization of second clay acid

15... ...............

16... ...............

17..................

18..................

19--..-.... ......

20..................

M ___________

49.3 

55.4 

61.6 

67.8 

73.9 

80.1 

86.2

37.0 

40.0 

43.1 

53.9 

55.4 

61.6 

72.4

12.81 

12.45 

12.53 

12.27 

12.45 

12.45

13.81

13.59 

13.57 

13.49 

13.55 

13.59

16.67

16.67

13.00 

13.00 

13.00 

12.63 

12.63 

12.81

Over titration

22... . __ .

23..................

24..................

25

26...... ........

27......... ......

28...... .....

29

30.... _____ .....

31........ ..........

32.. __ _ . _ 

33--...-..... . 

34... 

35... 

36.......... ........

37......... ......

92.4 

98.6 

104.7 

110.9 

117.0 

123.2 

129.4 

135.5 

141.7 

147.8 

154.0 

160.2

166.3 

172.5 

178.6 

184.8

75.5 

63.1 

69.3 

69.3 

66.2 

66.2 

66.2 

72.4 

72.4 

77.0 

73.9

83.2 

80.1 

81.6 

86.2

12.63

12.63

12.36

13.49

1Q KK

13.59

16.83

(«)

16.83

12.63

12.81

12.63

12.63 

12.63 

12.63 

12.63 

12.63 

12.81

12.63

TABLE 8. X-ray diffraction data on montmorillonite specimen8 

recovered after discontinuous titration

[CuKa radiation, 1° per min]

Sample

Na added 

(meq. per 

lOOg)

Na taken 

up by clay1 

(meq. per 

lOOg)

d (001) A> d (001) A> d (001) A»

Neutralization of first clay acid

1.. 

2. ___ - ______ 

3. _______ . __ - 

4.... _________ 

5 __ 

T.. .................. 

8 _ ... _ . 

9 

10 

11 

12. 

13 

14 

0 

3.1 

6.2 

9.3 

12.3 

15.4, 

18.4 

21.6 

24.6 

27.7 

30.8 

33.9 

37.0 

43.1

0 

3.1 

6.2 

9.3 

12.3 

15.4 

18.4 

21.6 

24.6 

27.7 

30.8 

33.9 

37.0 

43.1

14.98 

14.98 

14.73 

14.73 

14.73 

14.26 

14.26 

14.26 

14.03 

14.23 

14.03 

13.81 

13.81 

13.81

14.23 

14.48 

14.26 

14.03 

13.60 

13.81 

14.03 

13.81 

13.81 

13.81 

13.60 

13.39 

13.39

16.99 («)

16.99

16.99

16.99

Neutralization of second clay acid

15 ___ - 

16 

17. __________

1*

20 

91

49.3 

55.4 

61.6. 

67.8 

73.9 

80.1 

86.2

49.3 

52.4 

55.4 

60.1 

64.7 

70.8 

67.8

13.60 

13.39 

13.39 

13.19

13.00

13.39 

13.19 

13.00 

12.81

12.80

16.99

16.99

OTCT titration

09

24. . 

25 

Oft

97

Oft

OQ

30 __ . _ . _____

O-f

39

QQ

34

35... .

Oft

Q7

92.4 

98.6 

104.7 

110.9 

117.0 

123.2 

129.4 

135.5 

141.7 

147.8 

154.0 

160.2 

166.3 

172.5 

178.6 

184.8

73.9 

78.5 

78.5 

83.2 

92.4 

92.4 

89.3 

93.9 

101.6 

95.5 

93.9 

100.1 

90.9 

97.0 

97.0 

103.2

12.63

12.81

12.81

12.81

12.81

12.63

12.63

12.63

12.63

12.63

16.99

16.99

16.99

1 Calculated from analysis for Na in toe filtrate (Dorothy Carroll, analyst).

> Allowed to dry on slide at room temperature and humidity (Dorothy Carroll, 

written communication).

1 Same as * but kept at humidity of 35 percent for 24 hr.

* Same as 2 but treated with ethylene glycol at 60° C.

s Allowed to dry on slide at room temperature and humidity (on different day than').

< After ethylene glycol treatment this sample was fired at 300°C for 2.5 days; it 

bad a (001) spacing of 10.16A.

cations are located in interlayer or edge positions. 

Because the edge positions exhibit lower acidity and 

hold hydrogen ions more tightly, it may be predicted 

that hydrogen ions will first replace other cations in 

these positions, and that the remaining exchangeable 

ions most likely will be found in interlayer positions.

This hypothesis may easily be supported by the 

following consideration. A pure hydrogen montmorillonite has an interplanar basal spacing of 14.5 A 

(Barshad, 1950), whereas the values of the hydrogen 

montmorillonite used in this work tend to be slightly 

higher (tables 7 and 8). Similarly, as the spacing of the 

sodium montmorillonite produced by titration tends 

to be slightly more than the 11.9 A for magnesium and 

calcium montmorillonite, respectively, increased spacing 

for hydrogen or sodium clay containing some of these

1 Calculated from analysis for Na in the filtrate (Dorothy Carroll, analyst).

* Allowed to dry on slide at room temperature and humidity. Determinations 

made on different days. 

» Same as » but treated with ethylene glycol at 60° C.

* After ethylene glycol treatment this sample was fired at 300° C for 2.5 days; it has 

a (001) spacing of 10.40 A.

cations is to be expected, provided these cations are in 

interlayer positions where they can affect the d spacing. 

An evaluation of the interlayer expansion in 

montmorillonite by Barshad (1949) showed that in 

a montmorillonite containing one layer of water the 

thickness of the unit cell may be expected to be 

10.16+2.76=12.92A if the centers of the oxygens of 

the water molecules are vertically above and below the 

centers of the oxygens of the lattice. If, however, the 

water molecules form tetrahedra with the bases of 

the linked silica tetrahedra of the lattice, the interplanar 

basal spacing would be 10.16+1.78=11.94A, a value 

closely comparing with the value of 11.9 A for sodium 

montmorillonite, a unimolecular layer of water being 

associated with sodium in the interlayer position 

(Barshad, 1950). According to the same author a 

bimolecular water layer is associated with hydrogen,
C16 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

calcium, or magnesium ions in the interlayer positions 

of montmorillonite at normal temperature and humidity, and Barshad (1949) considered the thickness of a 

montmorillonite with two water layers under various 

assumptions. The values for hydrogen, calcium, and 

magnesium montmorillonite given here fit best the 

value of 10.16+1.78+2.76 = 14.70A, a value expected 

when the water molecules form tetrahedra at the wateroxygen interface but are vertically above each other at 

the water-water interface. A change from a pure 

hydrogen montmorillonite to a pure sodium montmorillonite then would be expected to produce a decrease of 

2.76A in interplanar basal spacing.

It is now desirable to calculate the expected decrease 

in interplanar basal spacing, if the hydrogen clay used 

in this work is titrated with a sodium hydroxide 

solution. For clarity, all the assumptions made are 

summarized as follows: 

a. The remaining exchangeable alkali and alkaline earth

cations are in interlayer positions, 

b. Only cations in interlayer positions affect this

spacing.

c. Water molecules form tetrahedra with the bases of 

the linked silica tetrahedra of the lattice, but in 

the case of two layers the water molecules are 

vertically above each other at the water-water 

interface.

d. As the determination of interplanar basal spacings 

by X-ray diffraction is in effect an averaging 

procedure, replacement- of a fraction, /, of all 

cations causing expansion by two molecular layers 

of water by cations causing expansion by only one 

such layer will cause a decrease in the thickness of 

the unit cell amounting to 2.76X/.

If the hydrogen clay used here has a total exchange 

capacity of 120 meq. per 100 g, and the remaining 

alkali ions on the clay total 6 meq. per 100 g, there are 

114 meq. per 100 g ions causing expansion by two 

alkali ions on the clay total 6 meq. per 100 g, there are 

114 meq. per 100 g ions causing expansion by two 

molecular layers of water. Of these, the calcium and 

magnesium are not replaced during the titration, and 

the exchangeable hydrogen ions which are replaced then 

amount to 114-28 or 86 meq. per 100 g. The fraction, 

/, then is 86/114 or 0.754, and the expected decrease in 

interplanar basal spacing is 0.754X2.76 or 2.08A.

As can be seen in tables 7 and 8, there is considerable 

spread in the d spacings. This may be expected in view 

of the sensitivity of the clay to atmospheric humidity 

changes, and also in view of the difficulty in having to 

work at very low angles of incidence. The hydrogen 

clays, having principally two molecular water layers on 

C~ positions, are more sensitive to variations in humidity, and it may be observed that the sequence of decreasing d spacings with increasing sodium content of the 

clay is more often disturbed in the high-hydrogen region. 

For this reason the decrease in the four series at room 

temperature and humidity shown in -tables 7 and 8 was 

determined by taking the difference between the highest 

and the lowest rather than the first and the last member 

of each series. These decreases in interplanar spacings, 

in angstroms, amount to 2.10, 1.85, 2.17, and 1.85, or 

1.99±0.29A, a value well compatible with the expected 

decrease in d spacing of 2.08A. Therefore, the X-ray 

data furnish a reasonable indication that the remaining 

exchangeable cations on the hydrogen clay used in this 

work were in interlayer positions.

It must be borne in mind that the explanation of the 

change in d spacings by Barshad is not necessarily correct. Other interpretations may be found in the literature. It is important to note that this does not necessarily affect the validity of the argument, because the 

numerical values appear to be correct. In view of the 

high standard deviation of the data reported here, not 

too much confidence should be placed in their interpretation. All the information supports the trend of 

reasoning but does not prove it uniquely by any means. 

It must also be pointed out that the columns in tables 

7 and 8 indicating the calculated sodium in the clay 

are based on the assumption that the clay was not decomposed during the run. As table 4 shows, this is 

clearly not true for the samples with higher numbers. 

In view of the fact that data on dissolved silica were not 

available, corrections could not be made. The numerical sodium values indicate that the error is not 

unreasonably high, because the values go as high as 

86.2 meq. per 100 g, a value easily within experimental 

error of the expected value of 90 meq. per 100 g (Pommer and Carroll, 1960).

DETERMINATION OF EXCHANGEABLE ALUMINUM 

IN HYDROGEN CLAY

For the purpose of determining the probable maximum spontaneous alteration of the hydrogen clay to 

hydrogen-aluminum clay, a sample was stored in a 

closed vessel under air for 2 years, extracted by the 

method of Low (1955) and the aluminum in the extract 

was determined by the method of Shapiro and Brannock 

(1962). The exchangeable aluminum in the hydrogen 

montmorillonite was 47 meq. per 100 g (Leonard

Shapiro, analyst).

DISCUSSION

TOTAL ACIDITY OF THE CLAY

The total acidity of the hydrogen clay can be 

evaluated from the last "break" in the titration curve. 

This gives, from pH measurements, 90 meq. per 100 g 

(Pommer and Carroll, 1960). The pH curve was constructed by taking the average of four pH readings
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE C17

taken over a period of 10 days; "outlying" values being 

eliminated by a statistical procedure; another pH 

curve, corrected for CO2 absorption as explained 

previously, yielded a total acidity of 84 meq. per 100 g 

(fig. 3, line C). From a plot of analytical sodium 

values in the filtrates (fig. 8), the total acidity is 93 

meq. per 100 g; a plot of sodium-electrode readings 

gives a very questionable end point at about 100 meq. 

per 100 g (fig. 8). If the total cation-exchange capacity 

is calculated at 120 meq. per 100 g by summing the 

exchangeable cations (table 1) and the exchangeable 

cations actually found on the hydrogen clay are subtracted from this value (34.5 meq. per 100 g, Pommer 

and Carroll, 1960), the difference of 86 meq. per 100 g 

gives the total acidity. Disregarding the very questionable "break" in the sodium-electrode curve of 

figure 8, a series of four determinations done by four 

different approaches gives a total acidity of 88 ±7 

meq. per 100 g clay.

THE "FIRST" ACID

Although the quality of the data varies significantly, 

it is not difficult to determine a reasonable value. 

Here the pH curves are not good, owing to the CO2 

absorption effect. The value obtained by simply 

averaging a series of pH measurements obtained over a 

period of time, 50 meq. per 100 g (Pommer and Carroll, 

1960), is considerably higher than the 35 meq. per 100 g 

obtained from figure 3, using the graphical correction 

for CO2 absorption. The limitations of the data 

obtained here have been discussed. The best values 

are probably obtained from the sodium values (fig. 8). 

These are 44 meq. per 100 g for the analytical sodium 

values and 45 meq. per 100 g obtained from the X-ray 

diffraction spacings of the first series, both at room 

humidity and at a humidity of 35 percent. These 

values, however, could not be reproduced satisfactorily 

in the second series.

THE "SECOND" ACID

The difference between the average total acidity and 

the best values of the "first" acid is 44 meq. per 100 g; 

individual segments of this part of the curve range 

from 40 to 49 meq. per 100 g in the pH and analytical 

sodium curves. If in accordance with the theory of 

Low (1955) and the considerations proposed in the 

section of implications of montmorillonite structure the 

exchangeable aluminum (47 meq. per 100 g) is assigned 

to the second acid, a very consistent pattern is obtained 

which indicates that the experimental evidence produced in this work supports the postulates presented 

here. The results also are consistent with those re2 Thompson, A. C., 1956, Acidic properties of bentonite: Ph. D. Thesis, State 

College of Washington, Pullman, 101 p.

ported in the literature. Typical values for the two 

acids are given by Bradfield (1931) as 45 and 50 meq. 

per 100 g; by Thompson 2 as 41 and 43 meq. per 100 g; 

and by Hauser and Colombo (1954) as 42 and 43 meq. 

per 100 g.

MONTMORILLONITE AND THE PROBLEM 

OF IONIC SPECIFICITY

Eisenman (1961) has shown that the anionic field 

strength of the protoplasmic and membrane components of living cells governs the sequence and magnitude of specificity among the alkali metal cations and 

hydrogen ion. He has explained that in biological 

material this field strength is controlled by the energy 

interactions between the nearest neighbor to the cations, 

generally oxygen, as modulated by the next adjacent 

atom, generally carbon or phosphorus. In clays a 

generally similar mechanism must be involved, but 

here the relations between the oxygen atoms must be 

controlled by silicon and aluminum.

In montmorillonite, however, a rather unique situation is found. The anionic field strength with respect 

to exchangeable cations is a function of the charge 

deficiency. As montmorillonite has two types of exchange sites that can be distinguished by different 

charge densities, anionic field strength in the interlayer 

and edge sites is different, and for this reason the 

selectivity for alkali ions in these two types of sites 

may be expected to be different. It will be recalled 

from figure 1 and preceding discussion that the anionic 

field strength in the interlayer positions is significantly 

lower than that of the edge positions.

The selectivity rule of Eisenman (1961) is based on 

the assumption that with increasing negative electrostatic field strength the least strongly hydrated cation 

is the first to be desolvated. In brief, it can be presented as follows. For a typical cation exchange reaction,

IX+J+=JX+1++AF«,

where IX and JX represent a solid ion exchanger in an 

unspecified state of hydration which does not change 

during the reaction, and 7+ and J+ are dilute aqueous 

ions; the Gibbs free energy change, A-Fy, is a function 

of Ktj, the equilibrium constant of the reaction and 

hence related to the ease of dehydration and absorption of an ion in solution by the exchanger. The anionic field strength in turn is a function of the anionic 

radius, r_, which also, in an oxyanion, is a function of 

the acid dissociation constant pKa. Figure 9 summarizes Eisenman's calculations. The selectivity orders 

are indicated by vertical regions that are marked by 

Roman numerals. In this figure the cation most 

strongly selected from water by the anionic "site" is 

the lowest on the chart.
CIS CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

FIGUBE 9. The relation between the acid dissociation constant pKa , the anionic 

radius r-, and cation specificity for oxyanions whether in free solutions or polymerized, including the location of biological phenomena by their specific sequence 

(Reprinted from Eisenman, 1961).
DUAL ACIDITY AND STRUCTURE OF H-MONTMORILLONITE

+ + + + INTERLAYER + + + + + +

C19

TETRAHEDRALLY 

COORDINATED SILICON

OCTAHEDRALLY 

COORDINATED ALUMINUM

WITH MAGNESIUM

SUBSTITUTION

+ + INTERLAYER +

///// CHARGE DEFICIENCY

\\\\\ CHARGE DEFICIENCY (Different Value)

FIGTTBE 10. Simplified beidellite structure.

Puri and Ashgar (1938) have pointed out that, if soil 

acidoids are treated with different bases, the characteristic shape of the titration curve is maintained with 

every base, although different amounts of alkali are 

required to produce a particular pH value with various 

ions. These authors also pointed out that this was in 

agreement with observations made on weak acids such 

as phosphoric acid, that the actual course of the titration curve depends on the nature of alkali used, although 

the end point must be reached with the same amount 

of alkali, but at a different pH, in every case.

If Eisenman's theory is applied to a montmorillonite 

with approximately the structure shown in figure 1, it 

can be predicted that the characteristic shape of the 

titration curve will not be maintained if this material 

is titrated with different alkalis.

MONTMORILLONITE AND BEIDELLITE

Beidellite has been defined as a member of the 

montmorillonite group in which there is substantially 

no magnesium present and in which tervalent aluminum 

replaces quadrivalent silicon in the tetrahedral unit 

(Ross and Hendricks, 1945). This results in a clay 

where the entire charge deficiency resides in the tetrahedral unit. This clay and the type of montmorillonite 

represented in figure 1 form the end members of a solid 

solution series, which subsumes montmorillonites and 

beidellites; these derive their designation from whatever 

end member they more closely represent. It can be 

seen (table 1), however, that the montmorillonite used 

here approximates the theoretical charge relations of 

figure 1 satisfactorily.

Figure 10 represents a simplified beidellite structure 

representing, however, an actual situation. There are

charge deficiencies in both units and no statement is 

made on the illustration concerning their relative 

amounts. This is necessary to avoid classification 

difficulties in the middle of the series. For example, 

taking the montmorillonite-beidellite series of Ross 

and Hendricks (1945), sample 44 is a clay from Beidell, 

Colo., a beidellite, with a charge deficiency of 0.36 

in the tetrahedral unit and 0.08 in the octahedral unit, 

whereas sample 45, a clay from Embudo, N. Mex., 

has a charge deficiency of 0.43 in the tetrahedral unit 

and 0.72 in the octahedral unit.

This clay is clearly more aluminian than the Beidell 

clay and should be classified as beidellite; still, the 

charge deficiency relations between the two types of 

layers are reversed. Foster (1954) stated that the 

charge of beidellite is predominantly in the tetrahedral 

layer. Some modern authors object to the term beidellite (Grim, 1953, p. 40); however, as a true beidellite 

has been described (Weir and Greene-Kelly, 1962), it 

is not desirable to replace this term by another expression in this discussion.

The actual charge deficiencies of the beidellite of the 

Putnam soil are 0.64 charge per unit on the tetrahedral layer and 0.20 charge per unit on the octahedral layer. The charge relations support the argument that the more strongly bonded hydrogen ions 

occupy the interlayer positions, as the charge density 

on the layer bounding the clay is stronger; hence, in 

disagreement with the interpretation of Garrels and 

Christ (1956), the interlayer acid is the weaker of the 

two substrates and the edge acid is stronger.

In this connection it becomes apparent that the 

charge deficiencies of the two beidellite units do not 

differ as much from each other as those of a relatively
C20 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

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C22 CONTRIBUTIONS TO PROBLEMS OF RADIOACTIVE WASTE DISPOSAL

ideal montmorillonite. For this reason, if hydrogen 

beidellites of the Putnam type are titrated with different alkalis, it may be expected that their titration 

curves will show a similar relation to each other as the 

soil acidoids of Puri and Ashgar (1938). Putnam 

beidellite and a Wyoming montmorillonite have been 

titrated under similar conditions with KOH (Marshall 

and Bergman, 1942) and NaOH (Marshall and Krinbill, 

1942), and the titration curves, plotted on a semilogarithmic basis, are presented in figure 11 for bentonite (montmorillonite) and in figure 12 for Putnam 

beidellite. As predicted, the curves for Na+ and K+ 

titrations do not resemble each other in the case of the 

bentonite but are similar for the Putnam beidellite 

titration.

Blackmon (1958) calculated constants for the conversion of cation from the C exchange site to the E exchange 

site for beidellite and bentonite from the data of Marshall and Bergman (1942) and Marshall and Krinbill 

(1942) and reported for beidellite the logarithm of the 

exchange constant for conversion from the C to the E 

position to be 1.1 for potassium and 1.5 for sodium 

and for bentonite values of 0.5 for potassium and 1.4 

for sodium. As he neglected to take into account the 

charge relations of beidellite, the logarithms of the constants must be multiplied by ( 1) to yield a compatible 

picture. If this is done, however, it can be seen that 

the relative strength with which sodium and potassium 

are bound to these respective sites is similar in beidellite 

but quite different in bentonite. All this is consistent 

with the general postulate that in beidellite the selectivity of both types of exchange positions for sodium 

and potassium does not differ very much, but that this 

is not true for bentonites.

RELATION OF ALKALI ION SELECTIVITY OF CLAY 

TO RADIOACTIVE WASTE DISPOSAL

Among the alkali ions considered in the selectivity 

rule of Eisenman (1961) is cesium. The radioisotope of 

this element Cs137 is a product of nuclear fission which, 

on account of its long half life, is especially troublesome 

in the environmental contamination by radioactive 

fallout (Schulz and others, 1960) and in radioactive 

waste (Glueckauf, 1961). A brief review of nuclear 

technology including references to the literature on 

radioactive waste has recently been presented by Tomlinson (1961); among others, Theis (1956) and Barker 

(1958) have discussed the problem of radioactive waste.

A site of low anionic field strength is most likely to 

select cesium over other alkali metals. In other words, 

those clays or clay sites which form strong clay acids 

are the best cesium binders. Among clays examined 

by Tamura and Jacobs (1960) "illite" was the most 

effective for cesium sorption, and as shown by Carroll

and Pommer (1960), hydrogen "illite" after aging 

forms a very strong acid. Eisenman (1961) determined the anionic field strength of some materials including clay minerals. Among the materials listed, in 

decreasing order of cesium selectivity, are kaolin, Utah 

bentonite, Putnam clay, and montmorillonite. Eisenman's prediction, made from the anionic field strength, 

that feldspar should prefer rubidium over sodium, is in 

accordance with the experimental findings of Hechter 

and other (1959). Eisenman's findings also lead to the 

prediction that the two clay acids of the montmorillonite used here will differ by their cesium-binding property. Tamura and Jacobs (1961) find that heating of 

bentonites improves their selectivity for cesium, 

though the exchange capacity of this material, which 

consists almost entirely of montmorillonite, drops considerably. As it is likely that heating causes some of 

the exchangeable cations to migrate into the interior 

of the lattice and to neutralize a part of the charge deficiency, the loss in exchange capacity is easily understood. As the lessening of the charge deficiency 

decreases the anionic field strength, and increase in 

cesium selectivity is also expected and found.

It appears that clays of high-exchange capacity and 

low-charge density would be ideal for cesium sorption. 

Although in natural material those two requirements 

are somewhat but not altogether incompatible, synthetic ceramics could be made which contain only 

porous material of low-charge density and a large 

surface.

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U. & GOVERNMENT PRINTING OFFICE : 1963 O - 678-823