Critical Review of the Equilibrium Constants for Kaolinite and Sepiolite

19 Critical Review of the Equilibrium Constants for Kaolinite and Sepiolite R. L. BASSETT—U.S. Geological Survey, Denver, CO 80225 Y. K. KHARAKA—U.S. Geological Survey, Menlo Park, CA 94025

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D. LANGMUIR—Pennsylvania State University, University Park, PA 16802

Clay m i n e r a l s g e n e r a l l y form i n three ways: 1) p r e c i p i t a t i o n from s o l u t i o n ; 2) a l t e r a t i o n through weathering of primary minerals which have become unstable i n a given environment; and 3) d i a g e n e t i c or hydrothermal a l t e r a t i o n of other m i n e r a l s . In the l a s t two cases, r e s u l t a n t c l a y - m i n e r a l chemistry u s u a l l y r e f l e c t s parent m i n e r a l composition. Chemical v a r i a b i l i t y among c l a y m i n e r a l s of a given group poses a formidable problem when one wishes to determine the thermodynamic p r o p e r t i e s of a given c l a y . Other f a c t o r s must a l s o be considered i n the experimental d e t e r mination of f r e e energies of formation. F i r s t , p a r t i c l e s i z e may be a s i g n i f i c a n t p r o p e r t y , because most c l a y s range from a few microns i n e f f e c t i v e diameter to c o l l o d i a l dimensions. In t h i s s i z e range, the f r e e energy r e q u i r e d to form the s u r f a c e per mole of m a t e r i a l can e a s i l y be two to three k i l o c a l o r i e s ( 1 ) . Second, isomorphus s u b s t i t u t i o n of aluminum f o r s i l i c o n i n the t e t r a h e d r a l l a y e r , or i r o n , magnesium, t i t a n i u m , l i t h i u m , and so f o r t h , f o r aluminum i n the o c t a h e d r a l l a y e r , w i l l a f f e c t the energ e t i c s of formation of the m i n e r a l . Such s u b s t i t u t i o n s may vary from t r a c e i m p u r i t y to complete replacement. T h i r d , the degree of c r y s t a l l i n i t y or extent of d i s o r d e r should be e v a l u a t e d , whether due to (a) mode or c o n d i t i o n s of f o r mation, f o r example, low temperature as opposed to hydrothermal p r e c i p i t a t i o n , or (b) techniques employed to prepare the sample for i n v e s t i g a t i o n , such as mechanical g r i n d i n g . These f a c t o r s tend to i n c r e a s e the s o l u b i l i t y and make the m a t e r i a l l e s s s t a b l e than an ordered m a c r o s c o p i c a l l y c r y s t a l l i n e sample. F i n a l l y , c l a y s such as the smectites almost i n v a r i a b l y have a net negative s t r u c t u r a l charge because of isomorphous s u b s t i t u t i o n of c a t i o n s of lower charge than would be present i n a balanced s t r u c t u r e . In k a o l i n i t e , the amphoteric nature of the hydrated aluminum and s i l i c a s u r f a c e c o n t r i b u t e s more to s u r f a c e charge than does s u b s t i t u t i o n . As a r e s u l t of e i t h e r s u b s t i t u t i o n or surface d i s s o c i a t i o n , a r e g i o n of counter ions (exchangeable and

0-8412-0479-9/79/47-093-389$05.00/0 This chapter not subject to U.S. copyright Published 1979 American Chemical Society Jenne; Chemical Modeling in Aqueous Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


390

CHEMICAL MODELING IN AQUEOUS SYSTEMS

adsorbed i o n s ) surrounds the c l a y to balance the charge. Whether v a r i a t i o n s i n the chemical composition of the l a y e r of counter ions a f f e c t s the f r e e energy of formation, AG^, of the c l a y i s a question that has not yet been r e s o l v e d . I n i t i a l l y i n t h i s study, i t was planned to c r i t i c a l l y e v a l u ate AG^ data f o r complex c l a y s , i n c l u d i n g c h l o r i t e , i l l i t e , and the s m e c t i t e s . However, there i s much evidence that these c l a y s d i s s o l v e i n c o n g r u e n t l y so t h a t the apparent e q u i l i b r i a i n s o l u t i o n are determined by secondary phases, such as g i b b s i t e , boehmite, amorphous s i l i c a , and f e r r i c oxyhydroxides. The smectites are f r e q u e n t l y the dominant c l a y s i n the c o l l o i d a l s i z e f r a c t i o n i n n a t u r a l sediments. They have very l a r g e exchange c a p a c i t i e s , and e x h i b i t wide chemical v a r i a t i o n s . U s u a l l y , one or more of these f a c t o r s have not been considered i n the experimental s o l u b i l i t y work. Even i f a p p r o p r i a t e c o r r e c t i o n s could be made, i t i s u n c e r t a i n whether a AG^ v a l u e so obtained would have a p p l i c a b i l i t y to n a t u r a l systems. In p a r t to avoid such problems, we have r e s t r i c t e d t h i s study to an a p p r a i s a l of the s t a b i l i t i e s of k a o l i n i t e and s e p i o l i t e ; compared, f o r example, to c h l o r i t e and the s m e c t i t e s . These c l a y s are w e l l d e f i n e d both c h e m i c a l l y and s t r u c t u r a l l y . Despite these c h a r a c t e r i s t i c s , the p u b l i s h e d AG_ f o r k a o l i n i t e ranges o n o

Ί

Γ , Zyo . l->

from -900 kcal/mol to -908.07 k c a l / m o l , and f o r s e p i o l i t e , -1101.8 kcal/mol to -1105.6 k c a l / m o l . Methods and Computational Scheme Thermodynamic data, whether determined through c a l o r i m e t r y or s o l u b i l i t y s t u d i e s , are subject to refinement as more exact values f o r the components i n the r e a c t i o n scheme, or more complete d e s c r i p t i o n of the s o l u t i o n phases, become a v a i l a b l e . Many of the s o l u b i l i t y s t u d i e s on c l a y s were done before d i g i t a l - c o m p u t e r chemical e q u i l i b r i u m programs were a v a i l a b l e . One such program, SOLMNEQ, w r i t t e n by one of the authors (2) s o l v e s the mass-action and mass-balance equations f o r over 200 species simultaneously. SOLMNEQ was employed i n t h i s i n v e s t i g a t i o n to convert the chemical a n a l y t i c a l data i n t o the a c t i v i t i e s of a p p r o p r i a t e i o n s , i o n p a i r s , and complexes. To d e r i v e f r e e energy of formation data from s o l u b i l i t y i n v e s t i g a t i o n s , the s o l u t i o n phase must be i n e q u i l i b r i u m w i t h the s o l i d phase and the a c t i v i t i e s of the ions must be known. The d i s s o l u t i o n r a t e f o r c l a y minerals i s extremely slow at 25 C; consequently, most s t u d i e s have allowed e q u i l i b r a t i o n times of s e v e r a l years. Because of the requirement f o r a long e q u i l i b r a t i o n time, a number of researchers have f i t t e d k i n e t i c expressions to the r a t e of d i s s o l u t i o n and e x t r a p o l a t e d to the e q u i l i b r i u m v a l u e . In a l l cases i n t h i s study, the chemical a n a l y t i c a l data measured at what appeared to be e q u i l i b r i u m , r a t h e r than

Jenne; Chemical Modeling in Aqueous Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

19.

BASSETT

Kaolinite

ET AL.

and

Sepiolite

391

e x t r a p o l a t e d values derived from systems s t i l l changing i n c o n c e n t r a t i o n w i t h time, were used i n the computation. For the d i s s o l u t i o n of k a o l i n i t e and s e p i o l i t e , the f o l l o w i n g r e a c t i o n schemes were employed: Kaolinite f

Al Si 0 ,(0H)4 o

Z

o

[

Ζ J

N

+ 6H 5 2 A 1

3 +

+ 2H.SiO° + H 0 o

4

(Cj

Κ Downloaded by UNIV OF PITTSBURGH on May 13, 2016 | http://pubs.acs.org Publication Date: March 19, 1979 | doi: 10.1021/bk-1979-0093.ch019

/

eq

-^

4

' X °4 ' V

ΐ 3 +

(1)

Ζ

Si

(2)

4*

Sepiolite Mg Si 0 2

3

y

5

(0H).3H 0 2

+ 4.5 H 0 ί 2 M g

( c )

2+

Κ

2+

+ 3H SiO° + 40H

2

( 3 )

4

a

- 4

' H S i O ^ ' 4~ 4

eq a

( 4 )

4.5 H 0 2

where a denotes a c t i v i t y of species i , and the a c t i v i t y of the s o l i d phase i s defined to be u n i t y . Reaction schemes used by s e v e r a l authors (_3, 40 were w r i t t e n to i n c l u d e the dominant aluminum complex present at the pH of the experiment. In this way the a c t i v i t y could be estimated, n e g l e c t i n g the other complexes. The approach taken i n our study, u t i l i z i n g the chem i c a l e q u i l i b r i u m computer program, o f f e r s the advantage that r e g a r d l e s s of the pH, the a c t i v i t i e s of a l l the i d e n t i f i e d ions are computed through the use of an i n t e r n a l l y c o n s i s t a n t s e t of s t a b i l i t y constants f o r the complexes and i o n p a i r s . This being the case, a l l data were analyzed according to the equations shown below: AG° = -RT I n Κ R eq where R = the gas constant, Τ = temperature, i n degrees k e l v i n , and AG = standard Gibbs f r e e energy of r e a c t i o n . AG° = EAG^ (Products) - EAG°. (reactants) « Κ.

r

r


392


For k a o l i n i t e : AG

?,298.15

(A1

Si

2 2°5

(OH

V

3+

= -AG° + 2AG°(A1 ) + 2AG°(H.SiO?) + AG°(H„0). Κ

r

r

4

r

H

ζ

The second m o d i f i c a t i o n performed on the o r i g n i a l data was the s u b s t i t u t i o n of more r e c e n t l y determined values f o r the f r e e energy of formation of the components. Hemingway and Robie Ç5, J3, 7) have r e c e n t l y r e v i s e d the f r e e energy of formation f o r the Downloaded by UNIV OF PITTSBURGH on May 13, 2016 | http://pubs.acs.org Publication Date: March 19, 1979 | doi: 10.1021/bk-1979-0093.ch019

,3+

,3+

aqueous A l i o n to -116.97 + 0.33. I n most cases, the A l value i s -1.9 kcal/mol more negative than that p r e v i o u s l y used. The data employed i n the computations are given i n Table I , and i n p a r t represent a c r i t i c a l review of the e x i s t i n g thermodynamic data f o r aqueous species being conducted by one of the authors (D. Langmuir). Table I . — A P a r t i a l L i s t Of The Thermodynamic Data Employed I n Computing The Revised Values For The Free Energy Of Formation Of K a o l i n i t e And S e p i o l i t e Components

AG

f,298.15 (kcal/mol)

ΔΗ° _ „ f,298.15 (kcal/mol)

S° " (cal/deg mol)

Reference

Aluminum Al

3 +

A10H

(aq) 2+

(aq)

-116.97

-126.9

-73.3

-166.8

-183.3

-40

(A) 1/

A1(0H>2 (aq)

-217.7

A1(0H)°(aq)

-266.66

A1(0H)~ (aq)

-312.0

-356.1

35

1/

H Si0° (aq)

-312.6

-348.30

45.1

1/

R^SiO^ (aq)

-299.18

-342.18

20.7

(10)

H SiO^"(aq)

-281.31

-330.7

-.7

1/

(£>

Silicon 4

2

Others H0

-56.688

-68.315

16.71

(ID

OH H+

-37.60 0

-54.98 0

-2.56 0

-108.70

-111.58

-32.98

(8) (8) (8)

2

Mg

2+ 1/

Langmuir, Donald, Pennsylvania State Univ. unpublished data,

1978).


19.

Kaolinite

BASSETT E T A L .

and

Sepiolite

393


Thermochemical Studies of K a o l i n i t e .

The e a r l i e s t reported

Gibbs f r e e energy of formation (AG°,298.15) f o r k a o l i n i t e i s -888.1 +0.7 k c a l / m o l , as computed by Barany and K e l l e y (12). Two k a o l i n i t e s were employed i n t h e i r study, one from a deposit near Murfreesboro, Ark., and the second from A l t a Mesa, N. Mex. The free-energy value was obtained by combining the heat of s o l u t i o n measurements from h y d r o f l u o r i c a c i d s o l u t i o n c a l o r i m e t r y of Barany and K e l l e y (12), w i t h heat c a p a c i t y determinations f o r k a o l i n i t e by King and Weller (13). The free-energy value i s much too p o s i t i v e and can be made more r e a l i s t i c by i n c o r p o r a t i n g r e v i s e d and updated thermodynamic data i n t o the r e a c t i o n scheme. In the same study, Barany and K e l l e y a l s o determined the heat of format i o n f o r g i b b s i t e ; Hemingway and others (5) redetermined the enthalpy and heat c a p a c i t y of g i b b s i t e Ç5, 7^) and re-evaluated Barany and K e l l e y s r e s u l t s . Hemingway and others d i s c u s s the experimental work i n d e t a i l and p o i n t out t h a t the heat of s o l u t i o n measurements f o r both g i b b s i t e and k a o l i n i t e appear to be c o r r e c t ; however, the heat of s o l u t i o n of H 0(1) + HF and H 0(1) + HC1 i n HF i s i n e r r o r . In a d d i t i o n , the r e a c t i o n scheme o r i g i n a l l y employed r e q u i r e d that the heat of s o l u t i o n f o r A1C1 *6H 0 (aluminum c h l o r i d e hexahydrate) be known; that value was i n c o r r e c t because of the technique used i n emplacing the sample i n the ampules and l o a d i n g them i n t o the c a l o r i m e t e r . To avoid these sources of e r r o r , Hemingway and Robie (7) used only the h e a t - o f - s o l u t i o n measurement of Barany and K e l l e y and wrote the r e a c t i o n scheme to i n c l u d e g i b b s i t e , which has well-known thermodynamic p r o p e r t i e s . Their r e c a l c u l a t e d value f o r the f r e e energy of formation of k a o l i n i t e at 298.15°K i s -908.07 kcal/mol (7), which i s the most negative f r e e energy reported to date and represents the only c a l o r i m e t r i c value a v a i l a b l e . I t should be noted that the m i n e r a l o g i c a l p u r i t y and c r y s t a l l i n i t y of the two k a o l i n i t e s used by Barany and K e l l e y (12) i s not known, as an X-ray examination was not conducted; however, the chemical a n a l y s i s of the bulk m a t e r i a l i n d i c a t e d that the S i 0 and ΑΙ,^Ο^ content was w i t h i n l h percent of the t h e o r e t i c a l composition of kaolinite. S o l u b i l i t y Studies of K a o l i n i t e . There have been numerous attempts to determine the f r e e energy of formation of k a o l i n i t e from s o l u b i l i t y s t u d i e s (Table I I ) . P o l z e r and Hem (3) reacted an API standard k a o l i n i t e from Lewistown, Mont., f o r 2 years w i t h an a c i d i c s o l u t i o n approaching e q u i l i b r i u m from unders a t u r a t i o n . The sample appears to have been very near to e q u i l i b r i u m , and these authors r e p o r t a AG^ ^ g ^ = -903 kcal/mol. 1

2

2

3

2

2

2

Using SOLMNEQ to recompute the a c t i v i t i e s of the d i s s o l v e d species from t h e i r experimental data, and employing the most recent thermodynamic data, the r e c a l c u l a t e d value i s -907.76 kcal/mol. This i s very c l o s e to -908.1 kcal/mol, which i s the c a l o r i m e t r i c value of Robie and others (8). A d d i t i o n a l confidence may be placed i n t h i s value because the p a r t i c l e s



394

Table I I . — O r i g i n a l And Recomputed Data For The Free Energy Of Formation Of K a o l i n i t e And S e p i o l i t e Material

Original Size


source

AG

Murfreesboro, Ark. A l t a Mesa, N. Mex. Lewiston, Mont. England Georgia 1 Georgia 2 Idaho North C a r o l i n a Georgia 3 South C a r o l i n a Montmorillonite Dry Branch, G a . — Keokuk, Iowa Varied 3

5

Bulk Bulk

f,298.15

Recomputed

Recomputed

log Κ

AG

eq

f,298.15

1

^ β δ δ . ι

2.0-149.0 urn -903.0 (3) Bulk -903.8 (19) Bulk -903.6 (19) Bulk -903.4 (19) Bulk -902.9 (19) Bulk -902.9 (19) Bulk -902.7 (19) Bulk -902.5 (19) .2-5.0 ym -904.2 (20) Bulk -905.8 Bulk -903.6 (4) Bulk -897.5 to -903.6 (4) 4

2

(12) 5.92 6.70 6.88 7.08 7.36 7.33 7.37 7.61 6.20 7.38 7.54

5

Selected value

5.96

3

-908.1

-907.8 -906.7 -906.4 -906.1 -905.7 -905.8 -905.7 -905.4 -907.4 -905.8 -905.5 -901.1 to -907.5 -907.7

Sepiolite Precipitated Balmut, N.Y. Amboseli, K e n y a — Selected v a l u e

0.5-10 ym 63-124 urn

-1101.0 (24) -37.4 -1105.6 (25) -40.2 -1105.6 (26) -40.4 -40.4

3

-1101.0 -1105.4 -1105.6 -1105.6

Average v a l u e from f i v e experimental runs on each c l a y . Accepted v a l u e of Hemingway (7) computed from the heat of s o l u t i o n data of Barany and K e l l e y (12). See t e x t . ^Average value f o r 16 sample runs on same m a t e r i a l (May, Η. Μ., U n i v e r s i t y of Wisconsin, p e r s o n a l communication, 1978). Range of values f o r k a o l i n i t e from 26 l o c a t i o n s . 2

3

5



19.

BASSETT E T A L .

Kaolinite

and

Sepiolite

395

l e s s than 2 ym diameter were removed to e l i m i n a t e p a r t i c l e - s i z e effects. Reesman (4) i n v e s t i g a t e d the s o l u b i l i t y of numerous standard c l a y minerals, monitoring the approach to e q u i l i b r i u m from unders a t u r a t i o n f o r s e v e r a l months. The a n a l y t i c a l data have been re-evaluated by us and y i e l d f r e e energies of formation ranging from -900.4 to -907.4 kcal/mol f o r k a o l i n i t e (Table I I ) . Reesman employed a w e l l c r y s t a l l i z e d k a o l i n i t e (Keokuk), which i s g e n e r a l l y a s s o c i a t e d with geodes found i n Iowa. Even though the Keokuk k a o l i n i t e has been proposed as a reference mineral, due to i t s well-ordered and h i g h l y c r y s t a l l i n e nature (14), the samples used by Reesman were bulk samples and probably contained very small p a r t i c l e s which increased the s o l u b i l i t y . An i n d i c a t i o n of t h i s i s the f a c t that he chose to c e n t r i f u g e h i s samples f o r 8 hours to s e t t l e a l l the suspended c o l l o i d a l m a t e r i a l (4). The recomputed value obtained f o r Keokuk k a o l i n i t e i s -905.5 kcal/mol (Table I I ) . This value i s s l i g h t l y greater than 2 kcal/mol more p o s i t i v e than the c a l o r i m e t r i c value, or the f r e e energy of forma t i o n determined f o r P o l z e r and Hem*s data, which had the d^ and a shape f a c t o r ( r a t i o of p a r t i c l e surface to p a r t i c l e volume m u l t i p l i e d by d, a value of 14 i s used here). There are no published values f o r the s u r f a c e - f r e e energy f o r c l a y minerals; however, the value f o r hydrated s i l i c a g e l i s approximately 120 ergs/cm (17). Smith and Hem (18) report sur face energies f o r the edge and face f o r g i b b s i t e c r y s t a l s as 483 and 140 ergs/cm , r e s p e c t i v e l y . Parks determined that a surface energy of 270 ergs/cm would be a l l that i s r e q u i r e d to e x p l a i n the free-energy discrepancy i n the g i b b s i t e data that he evaluated which was due to 0.010 ym p a r t i c l e s (1). Employing the same reasoning, assuming that 0.015 ym p a r t i c l e s are present i n the bulk samples used by Reesman i n h i s study, then the 2.2 kcal/mol d i f f e r e n c e between the data of Reesman (4) and that of Polzer and Hem (3) would r e q u i r e a s u r f a c e - f r e e energy f o r k a o l i n i t e of 150 ergs/cm . T h i s i s c e r t a i n l y w i t h i n the range of values one would expect f o r a surface composed of hydrated aluminum and silica. Because the exact value f o r the s u r f a c e - f r e e energy and the minimum p a r t i c l e s i z e i n the bulk samples are not known, the p o s i t i o n taken i n t h i s paper i s that a f r e e energy of formation f o r 9

2

2

2

2


396

C H E M I C A L M O D E L I N G IN

AQUEOUS SYSTEMS


1

k a o l i n i t e of -905.5 kcal/mol d e r i v e d from Reesman s data i s the most p o s i t i v e v a l u e one should use f o r w e l l - c r y s t a l l i z e d k a o l i n i t e . There are numerous u n c e r t a i n t i e s i n the s o l u b i l i t i e s determined by Reesman (40 f o r the other k a o l i n i t e s ; many samples contained other c l a y m i n e r a l i m p u r i t i e s ; most were bulk samples; and some were mechanically crushed, which may have d i s t o r t e d the c r y s t a l l i n i t y and increased the s o l u b i l i t y . K i t t r i c k (19, 20) performed two separate s t u d i e s to determine the s t a b i l i t y of k a o l i n i t e . In the f i r s t i n v e s t i g a t i o n , samples of b u l k k a o l i n i t e from seven l o c a l i t i e s were e q u i l i b r a t e d w i t h a d i l u t e a c i d s o l u t i o n f o r 2 years. Recomputed AG^ values f o r the seven k a o l i n i t e s based on h i s f i n a l s o l u t i o n compositions range from -905.4 to -906.7 kcal/mol. In the second study, K i t t r i c k (20) reacted the 0.2 to 5 ym f r a c t i o n s of three m o n t m o r i l l o n i t e c l a y s w i t h low pH (

an e x t r a p o l a t e d value (25). Recent d i s s o l u t i o n experiments at 25°C by S t o e s s e l l (26) using n a t u r a l l y o c c u r r i n g s e p i o l i t e from Amboseli, Kenya, suport the e x t r p o l a t e d value of C h r i s t and others -40.4 (23). S t o e s s e l l obtained a Keq e q u i v a l e n t to 10 * f o r the r e a c t i o n described by expression (4) y i e l d i n g a AG ( s e p i o l i t e ) = -1105.6 kcal/mol. Conclusions The experimental values f o r the f r e e energies of formation of k a o l i n i t e and s e p i o l i t e are given i n Table I I . The value of -907.7 +1.33 kcal/mol recommended f o r k a o l i n i t e , i s the mean of three recomputed f r e e energies of formation weighed e q u a l l y i n the computation, and was obtained from c a l o r i m e t r y , d i s s o l u t i o n , and p r e c i p i t a t i o n data. S e v e r a l values i n the -905 to -906.0 kcal/mol range probably r e f l e c t the more s o l u b l e nature of small p a r t i c l e s t y p i c a l l y present i n bulk samples. A f r e e energy of formation f o r s e p i o l i t e of -1105.4 kcal/mol i s based on e x t r a p o l a t i o n to 25°C of r e s u l t s from measurements made at 51, 70, and 90°C by C h r i s t and others (25). In support of t h i s , S t o e s s e l l (26) has determined a Κ at 25°C which y i e l d s a — eq AG^ at 25°C, only 200 c a l o r i e s more negative than that computed from the r e s u l t s of C h r i s t and o t h e r s . The value recommended here f o r the f r e e energy of formation f o r s e p i o l i t e i s -1105.6 +0.4 kcal/mol.


398



Abstract Clay minerals are present i n almost all surface-water and ground-water systems, and i n many instances may be controlling the concentration of aluminum, s i l i c a , iron, magnesium, or other cations i n solution. The thermodynamic data necessary to evaluate the state of reaction (saturation) are not available for some clay minerals, and for those minerals with published values, the data are i n disagreement by as much as 10 kilocalories per mole for the same clay mineral. A c r i t i c a l review of the available data for kaolinite and sepiolite, incorporating both the most recent thermo dynamic data for the components in the reaction schemes and a more complete computation for the solubility data, yields the values of -907.7 ± 1.3 and 1105.6 ± 0.4 kilocalories per mole for the free energy of formation of kaolinite and sepiolite, respectively. Literature Cited 1.

2.

3. 4. 5.

Parks, G. A. Free energies of formation and aqueous solu b i l i t i e s of aluminum hydroxides and oxide hydroxides at 25°C. Am. Min. 57, 1163-1189 (1972). Kharaka, Υ. Κ., and Barnes, I. SOLMNEQ: Solution-mineral equilibrium computations. U.S. Geol. Survey Computer Contr. Report PB-215 899, 81 p. (1973). Polzer, W. L., and Hem J. D. The dissolution of kaolinite. J. Geophys. Research 70, 6233-6240 (1965). Reesman, A. L. "A Study of Clay Mineral Dissolution." Ph. D. thesis, Univ. Missouri, 215 p., 1966. Hemingway, B. S., Robie, R. Α., Fisher, J. R., and Wilson, W. H. Heat capacities of gibbsite, Al(OH) , between 13 and 480 Κ and magnesite, MgCO , between 13 and 380 Κ and their standard entropies at 298.15 K, and the heat capacities of calorimetry conference benzoic acid between 12 and 316 K. U.S. Geol. Survey J. Research 5, 797-806 (1977). Hemingway, B. S., and Robie, R. A. The entropy and Gibbs free energy of formation of the aluminum ion. Geochim. Cosmochim. Acta 41, 1402-1404 (1977). Hemingway, B. S., and Robie, R. A. Enthalpies of formation of low albite (NaAlSi O ), gibbsite (Al(OH) ), and NaAlO ; revised values for AH°f,298 and AG°f,29 8 of some aluminosili cate minerals. U.S. Geol. Survey J. Research 5, 413-429 (1977). Robie, R. Α., Hemingway, B. S., and Fisher, J. R. Thermo dynamic properties of minerals and related substances at 298.15 Κ and 1 bar (10 pascals) pressure and at higher temperatures. U.S. Geol. Survey Bull. 1452, 456 p. (1978). Baes, C. F., and Mesmer, R. E. "The Hydrolysis of Cations." 496 p. Wiley-Interscience, New York, 1976. 3

3

6.

7.

3

8.

8

3

5

9.


2

19.

10. silicic

11.

12.


13. cities

14.

15.

16.

17. 18.

19. solubility 20. 1 21. 22.

23. 24.

25. in

BASSETT E T A L .

Kaolinite

and Sepiolite

399

Busey, R. Η., and Mesmer, R. E. I o n i z a t i o n e q u i l i b r i u m s of a c i d and p o l y s i l i c a t e formation i n aqueous sodium c h l o r i d e s o l u t i o n s to 300°C. J. Inorg. Chem. 16, 2444-2446 (1977). Robie, R. Α., and Waldbaum, D. R. Thermodynamic p r o p e r t i e s of minerals and r e l a t e d substances a t 298.15°K (25.0°C) and l atmosphere (1.013 bars) pressure and a t higher tempera tures. U.S. Geol. Survey B u l l . 1259, 256 p. (1968). Barany, R., and K e l l e y , Κ. K. Heats and f r e e energies of formation of g i b b s i t e , k a o l i n i t e , h a l l o y s i t e , and d i c k i t e . U.S. Bureau Mines Report Inv. 5825, 13 p. (1961). King, E. G., and Weller, W. W. Low-temperature heat capa and entropies a t 298.15°K of diaspore, k a o l i n i t e , d i c k i t e , and h a l l o y s i t e . U.S. Bureau Mines Report Inv. 5810, 6 p. (1961). K e l l e r , W., P i c k e t t , Ε. Ε., and Reesman, A. L. Elevated dehydroxylation temperature of the Keokuk geode kaolinite— a p o s s i b l e reference mineral, in Proceedings I n t e r n a t . Clay Conf. 1, 75-85 (1966). Enüstun, Β. V., and Türkevich, J. S o l u b i l i t y of f i n e p a r t i c l e s of strontium n i t r a t e . J . Am. Chem. Soc. 82, 45024509 (1960). S c h i n d l e r , P. Η., Hofer, F., and Minder, W. L o s l i c h k e i t s -produkte von metalloxiden und hydroxiden 10. L o s l i c h k e i t s produkte von Zinkoxyd, Kupfer Hydroxid und Kupferoxid i n Abhangigkeit von Teilchengrosse und Molarer Oberflache e i n B e i t r a g zur Thermodynamik von G r e n z f l a c h e n f e s t - f l u s s i n g . Helv. Chem. Act. 48, 1201-1215 (1965). Adamson, A. W. " P h y s i c a l Chemistry of Surfaces." 698 p. I n t e r s c i e n c e , New York, 1960. Smith, R. W., and Hem, J . D. E f f e c t of aging on aluminum hydroxide complexes i n d i l u t e aqueous s o l u t i o n s . U.S. Geol. Survey Water-Supply Paper 1827-D, 51 p. (1972). K i t t r i c k , J . A. Free energy of formation of k a o l i n i t e from measurements. Am. Min. 51, 1457-1466 (1966). K i t t r i c k , J . A. P r e c i p i t a t i o n of k a o l i n i t e a t 25°C and atm. Clays Clay Min. 18, 261-266 (1970). Velda, B. "Developments i n Sedimentology." 218 p. E l s e v i e r , Amsterdam, 1977. S i f f e r t , B. Quelques réactions de la silice en s o l u t i o n : La formation des a r g i l e s . Mem. Ser. Carte Geol. A l s a c e L o r r a i n e 21, 86 p. (1962). S i f f e r t , Β., and Wey, R. Synthese d'une s e p i o l i t e á temperature o r d i n a i r e . C. R. Acad. S c i . P a r i s 254, 1460-1462 (1962). Wollast, R., Mackenzie, F. T., and B r i c k e r , O. P. E x p e r i mental p r e c i p i t a t i o n and genesis of s e p i o l i t e a t earth surface c o n d i t i o n s . Am. Min. 53, 1645-1662 (1968). C h r i s t , C. L., H o s t e t l e r , P. B., and S i e b e r t , R. M. Studies the system MgO-SiO -CO -H2O ( I I I ) : the a c t i v i t y - p r o d u c t constant of s e p i o l i t e . Am. J . Sci. 273, 65-83 (1973). 2

2


400 26.


Stoessell, R. K. "Geochemical Studies of Two Magnesium Silicates, Sepiolite and Kerolite." Ph. D. thesis, Univ. Calif., Berkeley, 122 p., 1977.

Disclaimer: The reviews expressed and/ or the products mentioned in this article represent the opinions of the author(s) only and do not necessarily represent the opinions of the U.S. Geological Survey. November 16,

1978.


RECEIVED


Critical Review of the Equilibrium Constants for Kaolinite and Sepiolite

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