characterization of clays by organic...

Clay Minerals (1981) 16, 1-21.

C H A R A C T E R I Z A T I O N OF CLAYS BY O R G A N I C C O M P O U N D S

G. L A G A L Y

Institut fffr anorganische Chemie der Universitgit Kiel, Olshausenstr. 40/60, 23 Kiel, West Germany.

(Received 30 June 1980)

A B S T R ACT: Many problems--from soil research to ceramics--require a reliable characterization of the clay minerals involved. This can be done using four clay-organic reactions: (i) staining tests and dye adsorption; (ii) glycerol and glycol adsorption; (iii) intercalation; (iv) alkylammonium ion exchange. Dye adsorption (staining tests) and glycerol adsorption allow a preliminary identification of the clay mineral groups. Intercalation reactions indicate minute differences between kaolins which cannot be detected by XRD and DTA. Alkylammonium ion exchange provides the best method for characterizing smectites and is sensitive to changes in the layer charge.

About 1840, staining techniques were introduced in biological investigations. The availability of suitable staining tests was the decisive requirement for the detection of virus and bacillus infections. In 1882 Robert Koch detected the tubercle bacillus by staining with methylene blue. The importance of staining methods in biology and medicine induced some scientists to apply the tests in a quite different field of investigation, i.e. for identifying clay minerals. The first results were reported by Behrend in 1881; methylene blue rapidly became one of the most important dyes and has remained so until the present day.

The staining tests developed in the 19th century may be considered the basis for the identification of clays by organic reactions. Today, three additional reactions allow a very detailed characterization of clay minerals. These are: the adsorption of neutral molecules, commonly ethylene glycol and glycerol (Bradley, 1945; McEwan, 1948), the intercalation of neutral molecules in kaolins (Wada, 1961; Weiss, 1961) and the exchange of interlayer cations by alkylammonium ions in three-layer clay minerals (Weiss & Kantner, 1960).

F O U R R E A C T I O N S F O R C H A R A C T E R I Z I N G C L A Y M I N E R A L S

Adsorption o f dyes and staining tests

Various organic substances change colour on interaction with clays. Frequently the colour varies depending on the identity of the clay minerals. Identifying the clay mineral components of clay materials by staining tests is rapid and simple, but their applicability is restricted because of the mutual interference of the common components of clay materials. Many colour reactions are redox processes and the colour is determined by other factors, e.g. pH. Typical dyes used are benzidine, safranine, malachite green or fluorescent dyes (Grim, 1968; Fahn & Gennrich, 1955). In addition to a comprehensive account of clay-dye interactions (Theng, 1971), there are several more recent papers on

0009-8558/81/0300-0001502.00 �9 1981 The Mineralogical Society

2 G. Lagaly

the mechanism of dye adsorption, especially benzidine adsorption (Furukawa & Brindley, 1973; Tennakoon et al., 1974; Yariv et al., 1976; McBride, 1979).

Methylene blue adsorption was introduced by Gieseking & Janny in 1936. Experiments of Hang & Brindley (1970) and Brindley & Thompson (1970) showed that methylene blue adsorption can be used for the measurement of both surface areas and exchange capacities of clay minerals. The exchange capacities are determined from the plateaux of the adsorption isotherms. CECs ofmontmorillonites are obtained correctly only when the Na form is used. When the Na ions are fully exchanged the methylene blue molecules have their 17x3 .25=55A 2 face on the surface. In the presence of Na salts sorption of methylene blue is considerably increased. This is explained by additional adsorption of methylene blue hydroxide molecules due to the alkaline reactions of most Na salts. K ions retard the sorption of methylene blue and K salts do not increase the methylene blue adsorption above the CEC (Hofmann & Dammler, 1969; Brindley & Thompson, 1970). In industry, methylene blue adsorption is used as a simple and rapid method for estimating the smectite content of bentonites.

Ethylene glycol and glycerol adsorption

A second widely applied clay-organic reaction is the reaction of three-layer clay minerals with ethylene glycol or glycerol. A detailed account has been given by Brindley (1966). Recent papers (e.g. Chassin, 1976a,b) indicate that this clay-organic reaction has not lost its attractiveness for clay scientists.

Fig. 1 shows the relationships between the basal spacings and the layer charge of smectites, vermiculites and mica after ethylene glycol saturation. The plateaux indicate two-layer glycol complexes at basal spacings of 16-17 ,~ and monolayer complexes at 13-14 A.

18

~5 u cJ

tn

g

x x Na §

\ \

S m e c t i t e s V e r m i c u l i t e s B e ~ d e l t i t e 3 t t i t e s

i i I i I I 0 3 04- 05 0.(5 37 0.8

layer charge ~- (eq / (ShA l l / 010 )

K §

Mica I

o.g

F I G . 1. Basal spacings of homoionic clay minerals under ethylene glycol (most of the data from Brindley, 1 9 6 6 ) .

I 1.0

Characterization of clays by organic compounds 3

The data in Fig. 1 can be used for recognition of, or distinction between, the different three-layer clay minerals if the clays are saturated with Ca or K ions. However, the positions of the steps cannot be fixed exactly and it is impossible to distinguish between the clay species at layer charges in the range of the dotted lines in Fig. 1. It should be emphasized further that the boundaries, e.g. the smectite/vermiculite boundary as determined by glycol adsorption, do not coincide with the official structural definitions provided by AIPEA. (The glycol test tends to overestimate, and the glycerol test to underestimate, smectite as compared with the AIPEA definition (Srodofi & Eberl, 1980).) The small step at the vermiculite/illite boundary in the presence of potassium ions should not be used to distinguish vermiculites and illites; spacings of about 10 A in the vermiculite area can also result from interstratification with expanding interlayer species. If glycerol is used rather than glycol it should be noted that the boundaries between the different interlayer structures (plateaux in Fig. 1) are shifted to other layer charges. For routine identification Srodofi & Eberl (1980) suggest using ethylene glycol rather than glycerol. Pretreatments of soil clays for removing organic matter may either improve identification of the clay species or render this more difficult (Perez-Rodriguez & Wilson, 1969). This should be kept in mind when XRD patterns of soils rich in organic matter are interpreted.

Glycol adsorption is the standard method for investigating interstratified minerals with smectitic interlayer spaces (Reynolds & Hower, 1970; Cradwick, 1975; Cradwick & Wilson, 1978; Srodofi, 1980). The proportion of expanding layers in randomly interstratified smectite-illite can be estimated by the method of Weir et al. (1975) based on the measurement of the shape of the first order basal reflections. An alternative method is to match the X-ray pattern against a set of computer-simulated traces from models composed of varying proportions of 16.9 A smectite layers and 10 A illite layers (Weir & Rayner, 1974; Weir et al. 1975; cf. Jones & Greenland, 1980).

A further application of glycol adsorption is in the determination of the total surface area ofsmectites from the amount of glycol adsorbed (Diamond & Kinter, 1956; Moore & Dixon, 1970; Chassin, 1976b). Madsen (1977) proposed determining the amount of glycol adsorbed by TG. Eltantawy & Arnold (1972) suggest using ethylene glycol monoethyl ether for surface area measurements rather than glycol (cf. Jones & Greenland, 1980).

Glycol or glycerol adsorption can also be used for a rough estimation of the proportion of smectites in clays. For this purpose the application of polymeric molecules may be of advantage. Levy & Francis (1975) recommend the quantitative determination of smectites in soils from the intensity of the basal spacings after adsorption of polyvinylpyrrolidone.

'Reaction types' o f kaolins

Some organic molecules can be intercalated as 'guest molecules' between the layers of kaolin (Fig. 2). The reaction provides a simple method for distinguishing between halloysite, dehydrated halloysite and kaolin (Range et al., 1970; Wilson & Tait, 1977). Differentiation between different types of kaolin is based on the maximum degree of reaction, am, with some selected guest compounds (Fernandez-Gonzales et al., 1976). The value of �9 is taken from the intensity of the (001) reflections of kaolin and the intercalation compound (Fig. 3) (Fenoll Hach-Ali & Weiss, 1969). The maximum degree of reaction is

4 G. Lagaly

f

FIG. 2. Intercalation of DMSO into kaolinite.

not always 100~o (am = 1) even after very long reaction times, as this depends on the type of kaolin.

Weiss and co-workers concluded that kaolins in general are mixtures of different types of kaolinites with different chemical reactivity. Using dimethylsulfoxide (or hydrazine) and urea as guest molecules, three types were distinguished*: (i) a highly reactive type A which reacts with a large number of guest molecules; (ii) type B with low, but detectable, reactivity; (iii) type C, which is unable to form intercalation compounds.

The experimental procedure is very simple: the maximum degree of reaction of a kaolin with dimethylsulfoxide (or hydrazine) and urea (concentrated aqueous solution) is measured. The ratio of types A,B and C in the kaolin specimen is calculated from a m with dimethylsulfoxide (or hydrazine ) (am, DMSO) and urea (am, urea) (Table 1). Kaolins with high proportions of type A are China clays. Ball clays are kaolins with larger amounts of type B. High contents of type C characterize flint clays and fire clays (Range et al., 1970; Fernandez et al., 1976).

111

E

Powder Diffroction

* ! i i i i I

I t

J I

I

A * i I i

I I

- . - -*20

Degree of Reoction

o~ =- 1 (100%)

{001) a f t e r in tercat tx t ion ( in tens i ty I i )

(001) of k o o t i n I i (intensity I k) ~ =

I i § I k

= 0 ( 0 % )

FIG 3. Intercalation o f DMSO into kaolinite and determination of the degree of reaction from the intensity of the basal spacings.

* A classification into four types can be based on the behaviour ofhydrazine-kaolins with water (Range et al., 1970; Bartz & Range, 1979).

Characterization of clays by organic compounds

TASL~ 1. Classification of kaolins by 'reaction types' after Range et al. (1970)

Degree o f reaction Reaction type

with DMSO with urea c t : l cr A u = l ct=0 B cr ct=0 C

Kaolins as micromixtures of different kaolinites A, B, C:

Experimentally observed: 0~DMSO, ~urea (in %) Then: %A = Cturea,

~ooB = ~ D M S O - - ~u rea ,

%C = 1 - ~tDMSO.

In a paper containing magnificent scanning electron micrographs of kaolins from all over the world, Keller & Haenni (1978) showed kaolins to be commonly and intimately intermixed in microdimensions. Such variability in kaolin mineralogy is common in natural deposits and is widespread in occurrence. It is difficult to detect such mixing by X-ray powder diffractograms. Even diffractograms of artificial mixtures do ~ not necessarily reveal the crystallinities of the end members.

Type C kaolinites do not intercalate guest molecules directly. However, Jackson & Abdel-Kader (1978) reported lattice expansion of nearly all types of kaolins after dry grinding with cesium chloride. Dry grinding disorders and delaminates the kaolinite particles and, together with cesium chloride, evidently improves the inner-crystalline reactivity. The mechanism of this reaction is still unclear.

Alkylammonium ion exchange

Smectites. Quantitative exchange of the interlayer cations of smectites by alkylammonium ions (Fig. 4) provides the best method for characterization of smectites and

iiiii!iiii__iiiiiiiiiiiiiiiiiii iiiiiil

iiiiiiiii iiiiiiiiiiiiiiiiiii iiiiil Ca 2+ Ca 2+

iii ii !i!iii i i i i i i Ca 2+ Ca 2+

I{iiiii iiiiiiii!iiiill Co z+ Co 2§

ti iiiiiiiiiiiiiii 1

+ alkylammoni um .... v

ions

Iill iiiiiii!ilii!ii!i FIG. 4. Alkylammonium ion exchange in three-layer clay minerals.

6 G. Lagaly

determination of their layer charge. Fig, 4 only gives an example of the interlayer structure. The structure depends on the layer charge ~ (=interlayer cation density = packing density of the alkylammonium ions) and the alkyl chain length (Fig. 5). Short- chain alkylammonium ions are arranged in monolayers, long-chain alkylammonium ions in bilayers (Jordan, 1949; Brindley & Hoffmann, 1962; Lagaly & Weiss, 1971). Three-layers of kinked alkyl chains are only observed with highly charged smectites (e.g. beidellite, Lagaly et al., 1970, 1976).

The different types can easily be detected by their basal spacings. The basal spacing of alkylammonium smectites increases in steps with the alkyl-chain length (Fig. 5). The monolayer has a basal spacing of 13.6 A, the bilayer a spacing of 17.7 A.

The monolayer rearranges into the bilayer if the area of the flat-lying alkylammonium ion becomes larger than the equivalent area. The equivalent area is the area available for a monolayer cation in the interlayer space: Ae=aobo/2~. At the monolayer/bilayer transition (Fig. 5) the area of the alkylammonium ion Ac (Ac=5-7 • 14 (A2)) * becomes equal to the equivalent area Ae. The layer charge is then calculated from the ratio aobo/2Ac = 4. For small particles a particle size correction has to be made (Lagaly & Weiss, 1971; Stul & Mortier, 1974; Lagaly et al., 1976) because alkylammonium ions near the crystal edges are pressed out of the interlayer spaces. The relation between critical chain length n~ at the monolayer/bilayer transition and the interlayer cation density ~ (layer

19

.~17

13

i i~!iiiiiiii~iiiiiiiiiiii~ii!iiiiiiii~iiiiiiiiiiiiiiii~iiiiiiiiii!~iiiiiiiii~iiiiiiiiiiii~iiiiiiiiii~

I, / A C < A e

1 i i I l ~ i =

n C

A C > A e

A C" A e

/ \ 5.7n c . 14 = a6bo12

= ao bo 5.7n C + I/,

FIG. 5. Alkylammonium monolayers and bilayers in a lkylammonium smectites and calculation of the cation density ~ from nc at the monolayer/bilayer transition.

* nc = number of carbon atoms in the alkyl chain.

C har ac t e r i z a t i on of clays by organic compounds

TABLE 2. Relations between chain length nr and interlayer cation density ~ (dioctahedral smectites,

aobo = 46-5 A 2, Ac= 5.7 nc+ 14)

nc Ac(~k 2) Particle diameter (k)

400 600 1000 > 1000

(eq/(Si,A1)4Olo) 6 48 0.51 0.50 0.50 0.49 7 54 0.46 0-45 0-44 0.44 8 59 0-42 0.41 0-40 0.39 9 65 0-39 0.38 0.37 0.36

l0 71 0.36 0.35 0-34 0.33 11 76 0.34 0.33 0.32 0.31 12 82 0.31 0-30 0.29 0.29 13 88 0.29 0-29 0"28 0.27 14 93 0"28 0.27 0"26 0-25 15 99 0"27 0.26 0.25 0.24 16 105 0-255 0'245 0"235 0.22 17 110 0.246 0.234 0-225 0.21 18 116 0"235 0"224 0"214 0.20

charge) for montmorillonites is given in Table 2 for particles of different size. Values for very highly charged smectites with probably beidellitic charge distribution and the experimental details for preparation and investigation of the alkylammonium derivatives are reported by Lagaly et al. (1976).

Examination of a large number of smectites has shown that the layer charge is an average value. The interlayer cation density is not constant in all interlayer spaces but varies from interlayer space to interlayer space within certain limits. The charge heterogeneity is recognized by a more or less broad transition between the monolayer (13.6 A) and the bilayer plateau (17.7 A, Fig. 6) and by the non-integral nature of the basal reflections (13.6 A < d00] < 17.7 A). The cation density calculated from the largest

_ - _

"I - - . - . - I I ' 9 "~

. . . . l - - / ~17 ' . . _ �9 @ �9

�9 ~ _ . ~ . { J #'~ czT.~., ) 4, �9 - _ * �9 _.-( - ! o15

. . . . . ? - - -: - I , ,_,..., t ~ �9 , �9 �9 - �9 �9 . . . . . . . s = u . , , ~ . ( . _ . _

�9 E * ~ �9

l i h

B /

/ /

/ /

/ /

/ /

I I I i I t i t t I , i i

1o 15

c h a i n l e n g t h ( r ~ )

FIG. 6. Monolayer/bilayer transition of alkylammonium smectites with charge heterogeneity: from nc at A-,highest interlayer cation density, from nc at B~lowest interlayer cation density.

8 G. Lagaly

value of nc at the monolayer plateau (point A, Fig. 6) is the highest interlayer cation density; the density calculated from the smallest nc at the bilayer plateau (point B, Fig. 6) is the lowest interlayer cation density.

The atkylammonium ion exchange corroborates the assumption of charge heterogeneity in some previous investigations (Byrne, 1954; McAtee, 1958; Jonas & Roberson, 1966; Tettenhorst & Johns, 1966; cf. Clementz & Mortland, 1974; Tettenhorst & Grim, 1975).

Determination of the charge density limits provides a simple and reliable method for characterizing smectites. In addition, the transition can be analysed in more detail and charge distribution diagrams can be constructed (Stul & Mortier, 1974; Lagaly & Weiss, 1976). An example is shown in Fig. 7. This gives the frequency of the interlayer spaces with distinct cation densities: 59~o of the interlayer spaces have a cation density of around 0'3, 18~o of around 0.35 and 23~ densities up to 0.4 eq/(Si,AlhOi0. No other method gives such detailed information on the charge distribution in three-layer clay minerals.

In order to construct the charge distribution histograms, the fractions of 17.6 A layers

E

10

5O

C O

O"

10

Q

Bentonite New Zealand

I I

03 0/+ 05 0.6 ,. cation densityleq(Si,Ailt.010l

l soda activation

b

i

(12 O3 O.4 0.5 06 - cation density (eq(Si, AI)~O)0)

FIG. 7. Charge distribution of the montmorillonitic component in a bentonite from New Zealand: a, original sample; b, after industrial soda activation.


(bilayers ofalkylammonium ions) are determined from the apparent d0ot for each value of nc using peak migration curves (Table 3). The spacings of the bentonite from New Zealand (Fig. 7)for nc= 8, 9, 10, 11, 12 and 13 are 13.6, 14.5, 15.0, 15.4, 16.4 and 17-7 A. The peak migration curve (Table 3) indicates for spacings of 13.6 A, (nc= 8) and 14.5 A (nc= 9) a fraction of bilayers of 0% (nc = 8) and 23% (nc = 9). Therefore, 23% of all the interlayer spaces have cation densities between 0.40 and 0-37 (read from Table 2 for nc = 8 and 9, particle diameters about 1000 A). Since 15.0 A at nc=10 indicate 32% bilayers, 3 2 - 2 3 % = 9% of the interlayer spaces have cation densities between 0.37 and 0.34 (for no---9 and 10 from Table 2). The spacings for nc= 11- 13 are evaluated by the same procedure and the histogram shown in Fig. 7 is constructed.

Vermiculites and interstratified minerals. The determination of the layer charge of vermiculites from the basal spacings of the alkylammonium derivatives requires a slightly different approach from that used for smectites. It is based on comparison with calculated spacings (Fig. 8a). Comparison with two theoretical curves indicates that the cation density of a Young River vermiculite varies between 0.45 and 0.55 eq/(Si,A1)4Ot0. Higher charged vermiculites (charge density ~0.7 eq/(Si,Al)40~0) are recognized by a nearly linear increase of the basal spacings of the alkylammonium derivatives (Fig. 8b). An odd/even alternation of the spacings can be observed if the heterogeneity is small and the stacking order high (Lagaly & Weiss, 1970).

The procedure for analysing regularly interstratified minerals has been published for rectorite (allevardite) and more recently for rectorite-like minerals from Japan (Weiss et al., 1970; Lagaly, 1979). An interesting point is that 50% of the 300 or so smectites examined exhibited a pronounced mixed-layer character, i.e. the charge distribution diagrams had two maxima. Histograms such as that shown in Fig. 9c were very often observed (Lagaly & Weiss, 1976). This charge distribution apparently is the end member of the series: 'ideal' interstratified minerals with regular structure (Fig. 9a)--interstrati- fled minerals with two different smectitic interlayers (Fig. 9b)--heterogeneous smectites (Fig. 9c). It would appear that the weathering process favours the formation of mixed-layer like charge distributions in the way that groups of lower-charged and groups of higher-charged interlayer spaces are formed. This may be a consequence of the

TABLE 3, Peak migration curve for the evaluation of charge distribution histograms from the first order basal reflections of the alkylammonium smectites (fraction p of 17.6 A layers as function of d001 deduced from peak migration curves of McEwan et al.

(1961) and Ruiz Amil et al. 0967)

dool (A) p (%) dool (A) p (%)

13-6 0 16.0 49 14-0 13 16.5 58 14-5 24 17.0 70 15-0 33 17.3 80 15-5 40 17.7 100

10 G. Lagaly

25

20

15"

BASAL SPAC ING

[I,I

VERMICULITE

YOUNG RIVER

r . . . . i o i o i

Io I

A A mt J

(o)

- e - - e - -

LAYER CHARGE: - - GAS - - - - 0S$ (00l)- SERIES:

IN TEeRAL NON INTEei~AL

30

25

20

15

- BASAL SPACING

Iltl J jJ

/ o

S J

/o LLANO VERMICULITE

(TMMI

C-ATOMS IN THE CHAIN 10 (1:3) C-ATOMS IN THE CHAIN i I , , , , i t , , t i , , i , , , , i , , , , t

5 10 1 5 5 10 15

F I G . 8 . a . B a s a l s p a c i n g s o f a Y o u n g R i v e r V e r m i c u l i t e ( . , o o b s e r v e d , , c a l c u l a t e d f o r

c a t i o n d e n s i t i e s o f 0 . 4 5 a n d 0 . 5 5 e q / ( S i , A 1 ) 4 0 ] 0 ) , b . B a s a l s p a c i n g s o f a h i g h - c h a r g e v e r m i c u l i t e

( L l a n o , T e x a s ) .

olA ~.. 3C 30 30 U e'-

GI 2C" 20 20

tD 1( ~ 10 10

" i _ . _ F 1 o3, 33 3~ 39% .9 10,1 a ~ 33 36.39 o ~ ~ 26 ~ ~ 31 33 3~

cat ion densi ty (eq/(Si, At)4010)

i d e a [ m i x e d - l . a y e r Lo P e t o t e r a ( M e x i c o ) P o n z a ( I t a l y )

a b c FIG. 9. Interstratification and charge heterogeneity: a, ideal case of interstratification; b, interstratification with two types of smectitic interlayers (La Petatera, Mexico); c, heterogeneous

smectite (Ponza, Italy).


cooperative nature which is typical for many reactions proceeding in layer crystals (Lagaly, 1976, 1979).

APPLICATION OF A L K Y L A M M O N I U M ION EXCHANGE

Investigation of bentonites

Bentonites contain different amounts of smectites. Determination of the layer charge by chemical analysis requires, as a first step, the complete separation of the smectite or an exact quantitative determination of the components present. In the second step the chemical composition has to be evaluated. This can be difficult and time-consuming. These drawbacks are avoided by the alkylammonium ion exchange. Since the mean layer charge and the charge distribution are determined solely by X-ray measurements, separation or concentration of the smectite is not necessary: the charge distribution is determined directly in the samples picked from the deposit. In addition, the proportion of montmorillonite in the sample can be estimated from the carbon content of alkylammonium derivatives (usually measured by combustion).

Small amounts of smectite (< 5~o), not observed in the X-ray patterns, are detected after conversion into the alkylammonium derivatives. The sensitivity is increased if the alkylammonium derivatives are swollen in alcohols (Fig. 10). Displacement of the inorganic interlayer cations by organic cations and swelling with organic compounds

20C

>-

(n z 14.1

10~

Q|kytom moniu rn ion exchonge qnd swe[ting

ORIGINAL

t * , * , t

10 15 - 29

FIG. tO. Intensity of the basal reflections of a smectite after alkylammonium ion exchange and swelling.

12 G. Lagaly

increase the intensity of the (001) reflections by factors of 100 and more so that even small amounts of smectite are detected (Weiss et al., 1971).

"Layer charge" and CEC

The alkylammonium ion exchange measures the interlayer cation density and, thus, the CEC due to the interlayer cations. For conversion of cation density to CEC, the molecular weight of the formula unit is needed. For montmorillonites this is a relatively constant value of about 360. The interlayer CEC is then 1000 • ~-/360 (mEq/g) or 278 x ~-(mEq/100 g). Thus the interlayer CEC can be obtained from simple basal spacing measurements.

The CEC usually measured by cation exchange is the total exchange capacity. I t exceeds the interlayer CEC by the number of cations bound at the crystal edges (Fig. 11) (cf. Peigneur et al., 1975). At pHs > 4-5 the crystal edges develop negative charges and carry exchangeable cations. The number of cations at the crystal edges can be estimated by comparing the total CEC with the interlayer CEC (from the alkylammonium ion exchange). For many smectites the interlayer CEC is about 80~o of the total CEC; 20~o of the CEC results from cations at crystal edges (cf. Vogt & K6ster, 1978). The variability between total and interlayer CEC is demonstrated in Fig. 12. The ratio interlayer CEC: total CEC ranges from 0.6 to 0.9. The variability of the edge charge density may be the reason for some unexpected technical properties, which are found during the industrial application of bentonites. There should be a relation between edge charge density and rheological properties. To date, our studies are too fragmentary to draw reliable conclusions but it is noteworthy that highly thixotropic bentonites contain smectites with high edge charge densities, i.e. smectites with a low ratio of interlayer CEC to total CEC.

Soda activation of bentonites

Soda activation is an economic method for changing a natural Ca-clay into one which has Na ions as the predominant exchangeable cations, so that all the applications of the Na-clay come within the scope of the original Ca-clay. Na-bentonites form stable

| | |

total @I-( - - - - exchange 0 | | | Q | | capaci ty L, . . . . 4 I_l -,I

interlayer -- - - exchange ~- G G 0 Q • ~)

c~ If- - I | | | g | 1 7 4 |

| - -I | Q Q~'- interlayer cations

o/_ I , - - - l | FIG. 1 1. Exchangeable cations of smectite crystals.

outer surface cat ions

Character&ation of clays by organic compounds 13

dispersions in water at low solid contents and also thixotropic gels. They find wide application in industry as suspension aids, binding agents and plasticizers.

Fig. 7 shows the charge distribution of an original bentonite from New Zealand, which is completely changed after soda activation. There is now a broad distribution around 0.32 and 0.45 eq/(Si,A1)4Oi0. The mean layer charge is only slightly increased from 0.32 to 0.34 (Lagaly, 1980).

In water or dilute electrolyte solutions, the layers of Na-smectites are separated from each other and form a colloidal dispersion. During drying the layers are aggregated again but in a different manner to those in the original clay. To demonstrate disintegration and reconstitution of clay crystals with layers of different charge, Fig. 13 shows two kinds of layers, high-charged ones (in black) and low-charged ones. These are regularly mixed and the interlayer cation density is constant in all interlayer spaces. After disintegration and reconstitution the layer sequence differs from the original one and the cation density is heterogeneous.

It can be proved that the process discussed above is really possible (Frey & Lagaly, 1979). Mixed colloidal solutions of montmorillonite layers (Fig. 14a) as low-charged layers and of beidellite layers (Fig. 14c) as high-charged layers were prepared. The nature of the coagulates after addition of NaCI was investigated by the alkylammonium ion exchange. Two different products were obtained depending on the particle size of the original smectites. Using a > 0.1/~m fraction the particles with similar charge aggregated together: high-charged particles with high-charged ones, low-charged particles with low-charged ones. The coagulate of the < 0.1 #m fraction, however, contained one kind of particle only. Beidellite and montmorillonite layers were mixed, the crystals were built up by montmorillonite and beidellite layers in random sequence. The charge distribution

13 1.0 UJ 13

"609

13 (~8 UJ 13

O

o) 0s .c:

05

' 90' ' " ' ' 100' ' ' ' ' 1101 i ' ' ' 1201 , , , ' 1/30 ' to ta l CEC (rneq7100g)

FIG. 12. Total and interlayer CEC of smectites (x: Miiller-Vonmoos et al., unpublished data; o: Vogt & K6ster, 1978).

14 G. Lagaly

I

)

V//A~ J

I 3 FIG. 13. Disintegration and reconstitution of smectite crystals with high- and low-charged layers

in presence of Na ions.

differs from the distribution of both starting materials (Fig. 14b). The process described can be understood on the basis of the DLVO-theory.

Particle size and layer charge

3oil scientists, especially those concerned with soil genesis and weathering processes of micas, are interested in the variation of the layer charge with particle size. In the fractions of a chernozem (Fig. 15) the layer charge of the three-layer minerals decreases with decreasing particle size, indicating transformation of illite into smectite. In contrast, the layer charge of smectites in bentonites is more or less independent of particle size.

If weathering of mica to smectite proceeds from crystal edges to the core, one could assume that the charge density in smectites decreases from the interior to the edges (Fig. 16a). Another process should not be overlooked, i.e. that the weathering reaction proceeds in different ways in succeeding silicate layers. In this case, the layers obtain a more uniform charge distribution and the charge density varies from layer to layer (Fig. 16b).

Smectites were carefully treated with hydrofluoric acid to make the particles smaller. Changes in the layer charge were followed by the alkylammonium ion exchange. Typical results are plotted in Fig. 17. With decreasing particle size the charge density only slightly increases but the charge heterogeneity decreases. The charges are more uniformly


30

20

10

Beidettite

C

30

A

2o

U C | 10

mixed- [ayer coagutate

b

30

20

10

Montmoritlonite

Q

025 31 ./~2 eq/(SijAl.)/O10 93 12 17 pCbcm-2

FIG. 14. Charge distribution: a, montmorillonite (from Cyprus); b, mixed-layer crystals prepared from mixed colloidal solutions of Na-montmorillonite and Na-beidellite; c, beidellite (Unterrups-

roth, Germany).

distributed in the centre of the particles than in the outer region. It is also evident that the charge distribution changes in the first step and remains constant with further decrease in particle size. Therefore, a small region at the crystal edges exists which contributes most to the charge heterogeneity. The distribution in the core is more uniform than in the small outer region but still exhibits some random variability. This signifies that the charge heterogeneity results predominantly from different charge densities in succeeding interlayer spaces. It also indicates that the weathering reactions proceed at different rates or to different extents in succeeding layers. The mixed-layer like charge distribution of most smectites may be judged as another indication of such processes.

16 G. Lagaly

0.8

o ,..t

.~-0.6 ( :T

0

u

~0.~

02

I ( . Otoy (2/,, APJ)

Schwaiba-- ~ Wy~1~il~ 1 - - - e - - . . . . . . ~ - - - - - - , - - e - - - - Amory(22b)

t I I i

0.01 0.1 1 10 : part ic le s i z e (jura)

FIG. 15. Variation of the mean layer charge with particle size (*Tributh, 1976; **Rengasamy et al., 1976).

i

b

FIG. 16. Weathering of micas proceeding from edges to the core (a) or proceeding in different ways in succeeding layers (b).

Clay-organic complexes

Smectites in soils often exhibit very poor X-ray patterns. This is due mainly to weathering but it can also result from adsorption of organic materials. Some natural macromolecular compounds penetrate between the layers but often without regular expansion of the lattice (Talibudeen, 1954). Other compounds do not penetrate between the layers but are anchored at frayed edges (Fig. 18). Both reactions can much reduce the

Characterization of clays by organic compounds

original ~= 0.29

Q2 03

17

treatments with HF

oLl-- 02 03 02 0.3 0.2 0.3

--,,.co'Lion density

OLI__ 02 03 02 03 0.2 Q3

GR E E N BOND Id/.0, 1"/. HF

FXG. 17. Charge distribution of a montmorillonite (Greenbond) after decreasing the particle size by treatment with HF (1-6 days).

' ~ ~ ~ a _ ~

f ~ K ~ (a)

FIC~. 18, Clay protein interactions: a, protein penetrating between the layers; b, protein anchored at the edges or frayed edges.

intensity and sharpness of the basal reflections. In most cases the alkylammonium ion exchange is not prohibited but leads to some unusual features, as shown for an Andalusian Black Earth (Fig. 19, Perez-Rodriguez et al., 1977).

Similar changes are observed after protein adsorption (albumen, lysozyme). Basic principles of protein adsorption were evaluated by the work of Gieseking, Talibudeen and others. With short reaction times albumen does not penetrate between the layers but once the lattice is opened by alkylammonium ions, protein molecules press into the lattice and cause the unusual variation of the spacing with alkyl chain length. The Andalusian Black Earth smectites appear to be similar complexes: macromolecules are strongly attached at the external surfaces and frayed edges and penetrate partially between the layers after lattice expansion with alkylammonium ions. The amount of organic material is very small (carbon content ~< 1~o ) and it is impossible to determine its chemical nature. The example, however, confirms that external adsorbed macromolecules steal into the interlayer spaces during reactions which open the clay lattice. The surface properties and the reactivity of the smectite will then be quite different from those of a pure smectite. An instructive

18 G. Lagaly

.~1~

SOIL O- 160crn

/

t

a

I t i i I [ I i i i I i I i

10 15 chain length

20

15

pure SMECTITE

aHHHH~

#

, , * , L , , , , I , , ,

5 10 15

2C

15

Protein- SMECTI TE

/ 20 i f

t 1 - 1 . - O - O - O r

l

/ 15 ' C

J , ~ , l l ~ l , , i , , ,

5 ~ 15

SOIL > 160 cm

p v

i , . �9 i / . . . . a , . ,

5 10

FIG. 19. Basal spacings of alkylammonium derivatives: a, Soil smectite: Andalusian Black Earth, profile 0-160 cm; b (for comparison), pure smectite, charge density ~0.3 eq/(Si,A1)4O10; c, smectite (b) with protein adsorbed; d, soil smectite, Andalusian Black Earth, profile > 160 cm.

example was presented at the E u r o p e a n Clay Conference in Oslo by Mi i l l e r -Vonmoos & K a h r (1977). St r ik ing differences ( increasing plast ici ty, ion exchange capaci ty , in ternal surface and sed imenta t ion stabil i ty; decreas ing sediment vo lume and po ta s s ium content) were observed for a wea thered and unwea the red Opa l inus ton at the end and the top o f a landsl ide. In spite of these s t r ik ing var ia t ions , differences in the minera log ica l compos i - t ion o f the c lay f rac t ions could no t be found by the usual methods . I t turned out tha t a d s o r b e d organic mate r ia l interfered with the X- ray me thods (cf. Pe rez -Rodr iguez & Wilson, 1969). Wi th a l k y l a m m o n i u m exchange a h igh-charge smecti te cou ld be detected in the wea thered mater ia l . I t is assumed tha t the different p roper t ies result f rom a d s o r p t i o n o f the organic ma te r i a l a t the edges o f this smecti te.

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BRADLEY W.F. (1945) Molecular association between montmorillonite and some polyfunctional organic liquids. J. Am. Chem. Soc. 67, 975-981.

BRINDLEV G.W. (1966) Ethylene glycol and glycerol complexes of smectites and vermiculites. Clay Miner. 6, 237 259.

BRINDLEV G.W. & HOFraAr~N R.W. (1962) Orientation and packing of aliphatic chain molecules on montmorillonite. Clays Clay Miner. 9, 246-256.

BRINDLEY G.W. & THOMPSON T.D. (1970) Methylene blue absorption by montmorillonites. Determination of surface areas and exchange capacities with different initial cation saturations. Israel J. Chem. 8, 409-415.

Characterization o f clays by organic compounds 19

BVRNE P.J.S. (1954) Some observations on montmorillonite-organic complexes. Clays Clay Miner. 2, 241-253. CHASSIN P. (1976a) Influence de la st6r6o-chimie des diols sur la formation des complexes interfoliaires de la

montmorillonite calcique. Clay Miner. 11, 13-22. CHASSIN P. (1976b) Signification de la mesure des surfaces totales des argiles avec l'+thane 1 �9 2 diol. Clay Miner.

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Real Sodi6dad espa~ola de Fisica y Quimica LXV, 769-790. FERNANDEZ-GONZALES M., WEISS A. & LAGALY G. (1976) Uber das Verhalten nordwestspanischer Kaoline bei

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and hectorite. Clays Clay Miner. 21,279-288. GR1M R.E. (1968) Clay Mineralogy. McGraw-Hill Book Company, New York. HANC P.H. & BRINDLEV G.W. (1970) Methylene blue adsorption by clay minerals. Determination of surface

areas and cation exchange capacities. Clay Clay Miner. 18, 203-212. HOFMANN U. & DAMMLER J. (1969) Die Methylenblauadsorption an Montmorillonit. Chimia 23, 476-480. JACKSON M.L. & AaDEL-KADER F.H. (1978) Kaolinite intercalation procedure for all sizes and types with XRD

spacing distinctive from other phyllosilicates. Clays Clay Miner. 26, 81-87. JONAS E.C. & ROBERSON H.E. (1966) Structural charge density as indicated by montmorillonite hydration. Clays

Clay Miner. 13, 223-230. JONES A.A. & GREENLAND D.J. (1980) Quantitative determination of the interlamellar volume in an

interstratified mica-smectite soil clay. Clay Miner. 15, 175-191. JORDAN J.W. (1949) Organophilic bentonites. I. Swelling in organic liquids, ol. Phys. Colloid Chem. 53, 294-306. KELLER W.D. & HAENNI R.P. (1978) Effects of micro-sized mixtures of kaolin minerals on properties of

kaolinites. Clay Clay Miner. 26, 384-396. LAGALY G. (1976) Kink-block and gauche-block structures of bimolecular films. Angew. Chem. Int. Ed. Engl. 15,

575-586. LAGALY G. (1979a) The 'Layer Charge' of regular interstratified 2/l-clay minerals. Clay Clay Miner. 27, 1-10. LAGALY G. (1979b) Crystalline silicic acids and their interface reactions. Advances Colloid Interface Sci. 11,

105-148. LAGALV G. & FAHN R. (1981) Vorgiinge bei der Sodaaktivierung von Bentoniten. Keram. Z. (in press). LAGALY G. & WEISS A. (1970) Anordnung und Orientierung kationischer Tenside auf Silicatoberflachen, Teil III

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20 G. L a g a l y

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Characterization o f clays by organic compounds 21

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Clay Miner. 24, 51-52.

R 1~ S U M I~: De nombreux p r o b l 6 m e s ~ e la science des sols 5, celle des c6ramiq ues--n6cessistent une caract6risation correcte des min6raux argileux concern6s. Pour cela on peut utiliser 4 r6actions: (i) les tests de coloration et l 'adsorption de colorants; (ii) l 'adsorption de glycol et de glyc6rol; (iii) l'intercalation; (iv) l'6change avec des ions alkylammonium. L'adsorption de colorants (test de coloration) et l 'adsorption de glyc6rol, permettent une identification pr~liminaire du groupe auquel appartient le min6ral argileux. Les r~actions d'intercalation indiquent de petites diff6rences entre les kaolins, impossibles fi d6tecter par DRX et ATD. L'6change avec les ions alkylammonium fournit la meilleure m&hode pour caract+riser les smectites; elle est sensible aux variations de la charge des feuillets.

K U R Z R E F E R A T : Eine zuverl~issige Charakterisierung der Tonminerale wird bei vielen Untersuchungen gefordert, die yon Untersuchungen von Bodentonen his zur Verwendbarkeit der Tonminerale in der keramischen Industrie reichen. Vier Reaktionen mit organischen Verbin- dungen k6nnen dazu herangezogen werden: (i) Adsorption von Farbstoffen; (ii) Adsorption yon Glyzerin und Glycol; (iii) Einlagerung organischer Verbindungen; (iv) Eintausch von Alkylam- moniumionen. Die Adsorption von Farbstoffen und Glycol (Glycerin) erlaubt eine grobe Identifizierung der einzelnen Gruppen der Tonminerale. Dagegen k6nnen durch Einlagerungs- reaktionen geringe Differenzen zwischen Kaolinen erkannt werden, die sich r6ntgenographisch und thermoanalytisch nicht bemerkbar machen. Der Eintausch von Alkylammoniumionen bietet die beste M6glichkeit Smectite zu charakterisieren und auch geringe Ver~inderungen in der Schichtladung zu erkennen.

R E S U M E N : La resoluci6n de diversos problemas que van desde el estudio del suelo hasta los estudios cerfimicos, requieren una caracterizaci6n precisa de los minerales de la arcilla contenidos en la muestra. Esta caracterizaci6n puede hacerse utilizando cuatro tipos de reacciones de compuestos orgfinicos con las archillas, a saber: (i) tests de color y adsorci6n de colorantes; (ii) adsorcion de glicerol y glicol; (iii) intercalaci6n; (iv) cambio i6nico con cationes alquilamonio. Le adsorci6n de colorantes (tests de color) y la adsorei6n de glicerol permiten una identificaci6n previa del grupo al que pertenecen los minerales. Las reacciones de intercalacion ponen de relieve pequefias diferencias entre caolines que no pueden ser detectados por DRX y ATD. El cambio i6nico con iones alquilamonio es el mejor m~todo de caracterizaci6n de esmectitas y es sensible a cambios en la densidad de carga de la 15.mina.

characterization of clays by organic...

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