ORGANO-BENTONITES WITH QUATERNARY ALKYLAMMONIUM …minersoc.org/pages/Archive-CM/Volume_26/26-1-19.pdf · ammonium (TMTD) ions, and only ... highly charged vermiculites do not exchange

Clay Minerals (1991) 26, 19-32

O R G A N O - B E N T O N I T E S WITH Q U A T E R N A R Y A L K Y L A M M O N I U M IONS

H . F A V R E AND G . L A G A L Y

Institut fiir anorganische Chemic der Universitiit Kiel, OlshausenstraJ3e 40, D-2300 Kiel, Germany

(Received 5 March 1990; revised 28 May 1990)

A B S T R A C T: Three bentonites, from Bavaria, Wyoming and Brazil, were separated into various fractions. The layer charge was determined by alkylammonium ion exchange and increases with particle size from 0.25 Eq/(Si,A1)4Ol0 (<0.06 gm) to 0-28 Eq/(Si,Al)4010 (l-10 #m). The charge density corresponds to an interlayer cation density of 0-75-0.80 mEq/g silicate. Total amounts of 0.90-1-0 mEq of different surfactant cations (dimethyl dioctadecylammonium, trimethyl tetradecylammonium, alkylammonium ions) are bound per gram silicate. The difference between the total and the interlayer amount of surfactant ions decreases with increasing particle size. The amounts exceeding the interlayer CEC are bound at the edges. Tetramethylammonium (TM) ions restrict the interlayer adsorption of long-chain quaternary alkylammonium ions such as trimethyl tetradecylammonium (TMTD) ions, and only monolayers of flat-lying surfactants are formed. A ratio of TMTD and TM is attained which leads to densely packed monolayers of organic ions. The collapsing effect is smaller for tetraethylammonium ions so that considerable amounts of TMTD ions are adsorbed in bilayers. When bentonites are reacted with quaternary alkylammonium ions of technical quality some selectivity is observed according to particle size and layer charge. Smaller particles with lower charge density preferentially bind the longer chain compounds, whereas large particles with higher charge density select smaller sized surfactants.

Organophi l ic bentoni tes are used in a wide range of practical applications (Jones, 1983; Lagaly & Fahn, 1983). Fo r practical and industrial uses quaternary a lkylammonium ions are prefer red to pr imary a lkylammonium ions because effects due to hydrolysis (a lkylammonium/alkylamine equil ibrium) are absent , and desorpt ion of free a lkylamine is strongly reduced. A further advantage is that the large amount of organic mater ia l (30--40 wt%) reduces the density of the dispersed particles.

Organo-bentoni tes are excellent gelling agents (Vold & Phansalkar , 1962; Granquis t & McAtee , 1963). High gel strengths in non-polar solvents require addi t ion of small amounts of a polar additive (Granquis t & McAtee , 1963; Jones, 1983). Di luted dispersions of organophil ic bentoni tes in benzene/alcohol show maxima and minima of sedimentat ion rates and sediment volumes with increasing alcohol content (Sz~int6 & Veres, 1963; Sz~int6 et al., 1972). Adsorp t ion studies from binary solutions (for instance hydrocarbons/alcohol) by D6k~iny et al. (1986) have contr ibuted to a be t te r unders tanding of the effect of polar additives.

A further advantage of bentoni tes sa turated with quaternary a lkylammonium ions is the high adsorpt ion capacity toward organic compounds. Even from aqueous solutions, bentoni tes adsorb various organic compounds including phenols , amines and acids (Street & White , 1963; Lee et al., 1989). The use of bentoni tes with quaternary a lkylammonium ions as possible adsorbents for gas-sol id chromatography has been tested (Taramasso &

�9 1991 The Mineralogical Society

20 H. Favre and G. Lagaly

Veniale, 1969; Taramasso, 1971; Slabaugh & Vasofsky, 1975; Vasofsky & Slabaugh, 1976; McAtee & Robbins, 1980; Stul & Uytterhoeven, 1983).

In industrial production, bentonites are treated with quaternary alkylammonium salts at low water contents (paste-like materials) or in more diluted dispersions. Fine products are produced from diluted dispersions of Na-bentonite or soda-activated bentonite. The amount of alkylammonium salt added corresponds to the experimental cation exchange capacity (CEC) or thereabouts (80-100 mEq/100 g). Most of the alkylammonium ions are bound by exchanging the cations in the interlayer space and at the edges. Some amounts of alkylammonium salt are also retained, and these can be of great influence on the properties of the gels and dispersions. (This will be discussed in a subsequent paper.)

It is important to note that quaternary alkylammonium salts of technical quality often consist of a mixture of alkylammonium derivatives with different alkyl chain lengths and different degrees of quaternization. The possibility must be considered that the montmorillonite particles react preferentially with certain components of this mixture whereas other components are excluded from the interlayer space.

Whereas primary alkylammonium ions are strong agents which successfully compete with other cations for exchange positions, reaction of quaternary alkylammonium ions with clay minerals is more delicate. The reactivity decreases with increasing layer charge. More highly charged vermiculites do not exchange quaternary alkylammonium ions for interlayer cations. Another observation (McAtee, 1962, 1963) is that cations displace quaternary alkylammonium ions more easily from the interlayer space than primary alkylammonium ions which are held very tightly between the layers. A further consequence concerns the competition between short-chain and long-chain quaternary alkylammonium ions. It is to be expected that the long-chain alkylammonium ions are preferentially adsorbed when a mixture of short-chain and long-chain quaternary alkylammonium ions is reacted with montmorillonite as occurs for primary alkylammonium ions. However, quite different observations can be made.

M A T E R I A L S AND M E T H O D S

Bentonites

Wyoming bentonite (M 40, Greenbond) was supplied by Si~d-Chemie AG, Germany, as was sample M 39, a bentonite from Bavaria (Niedersch6nbuch). Bentonite "25 de Maio" is a Brazilian bentonite, supplied by Bentonit Uniao Nordeste SA, Brazil.

The bentonites were purified by removing organic materials by oxidation with H202, and iron oxides by citrate-dithionite extraction. Fractions <2/~m were prepared by sedimentation in the centrifugal field (details: Samii & Lagaly, 1987).

The particle-size distribution was derived from the sedimentation velocity in the gravitational and centrifugal field (Tributh & Lagaly, 1986).

Alkylarnmonium salts

The technical dimethyl dioctadecylammonium chloride (DMDO) as used in the production of organo-bentonite (Siid-Chemie AG) had a chain length composition of 1.5% Cl4, 0.8% C15, 27-5% C16, 2% C17 , 67.0% Cls and 1.2% C20.

Organo-bentonites with quaternary alkylammonium ions 21

Trimethyl tetradecylammonium (TMTD) bromide, tetramethylammonium (TM) chloride, and tetraethylammonium (TE) chloride (purum quality) were obtained from Hoechst AG and Merck AG, Germany.

DMDO derivatives

Aqueous solutions of the technical DMDO were added to the dispersions of various fractions of Na-montmoriUonite. The salt concentration was --0.1 mol/1, and the quantity of DMDO was 1.5 mEq/g bentonite (calculated for bentonite dried at 110~ After 72 h at 70~ the solution was removed, and the DMDO-montmorillonite was washed with ethanol/ water, re-dispersed in a fresh DMDO salt solution, and allowed to react again for 72 h at 70~ The samples were washed several times with ethanol/water (60 vol% ethanol) and dialysed at 70~ until the C/N content was virtually constant. The organo-montmorillonite was dried at 80~ milled, sieved to <200 mesh, and dried once more at 70~ in vacuum (<0.1 Pa) for 24 h.

Competitive cation exchange

The dispersions of Na-montmorillonites were reacted with TMTD chloride and TM or TE ammonium bromide in the following quantities per g bentonite: 4 mEq TMTD; 1 mEq TMTD + 3 mEq TM; 2 mEq TMTD + 2 mEq TM; 3 mEq TMTD + 1 mEq TM; 4 mEq TM; 2.5 mEq TMTD + 2.5 mEq TE; 5 mEq TE. The salt concentration was again 0.1 mol/1, and the period of reaction was 72 h at 70~ The samples were washed several times with ethanol/water (60 vol% ethanol) until the C/N ratio was nearly constant, and dried at 70~ in vacuum (<0-1 Pa).

Layer charge determination

The layer charge and charge distribution of the raw bentonites and the fractions were measured by the alkylammonium method (Lagaly, 1981, 1982; Stul & Mortier, 1974; Malla & Douglas, 1987a,b). Free alkylammonium salts and alkylamines were removed by careful washing and dialysis in the same way as described for the DMDO derivatives.

Precision of the layer charge determination was _+0-005 Eq/(Si,A1)4010 and --2% for the interlayer exchange capacity, Ci (eqn. 1).

Other analyses

The C, N-content of the samples was determined by combustion (Heraeus Elementaranalysator CHN-O Rapid). The data reported are average values of at least three parallel determinations. Deviations from the average value were in the range 2-5% which gives a precision of 3-7% for Ct (eqn. 9).

The basal spacings dE of the washed and dried samples were measured by X-ray diffraction using Debye-Scherrer cameras (diameter 114-6 mm, Cu-Ko~, Ni filter). For non- integral 001 reflections, dE = d00l.


100 -

.-z

r r

1:7"

5O

I I I I J I I I

0.01 0.06 0.2 0.6 2 6 20 particte size d/~um

F1G. 1. Par t ic le -s ize d i s t r ibu t ion of b e n t o n i t e f rom B a v a r i a ( A ) , W y o m i n g ( A ) and Braz i l ( 0 ) .

R E S U L T S A N D D I S C U S S I O N

Particle-size distribution

The bentonites from Wyoming and Bavaria consist of large amounts of fine particles (Fig. 1), - 6 0 wt% being <0.06/~m. The size distributions are similar, but different from the distribution for Brazilian bentonite which contains 35% of particles <0-06/an, and the cumulative curve increases more steeply. The distribution has a maximum for particles 0.064).2 ~m. The different distribution below 0.6/~m illustrates the great importance of particle size determinations at small particle sizes (Lagaly & Fahn, 1983; Lagaly et al., 1985).

Layer charge and charge distribution

The three unfractionated montmorillonites have the same interlayer cation density = 0.28 Eq/(Si,Al)4010 and similar charge distributions with a maximum at

0.23~1.26 Eq/(Si,Al)4Oa0. A charge density of ~ Eq/(Si,A1)4010 corresponds to an interlayer exchange capacity, Ci (Lagaly, 1981):

Ci = ~/360 (Eq/g silicate) (1)

As the average molecular mass of the (Si,A1)aOm unit of montmorillonites is 360 g, the charge density ~ = 0.28 Eq/(Si,A1)4010 produces an interlayer exchange capacity of 0.78 mEq/g silicate.

Full details are shown for the Brazilian bentonite. The basal spacings of the alkylammonium derivatives (no = 8-18) (Fig. 2) are highest for the 1-0-10/~m fraction and decrease with decreasing particle size. The 0-06-0-2 #m fraction gives almost the same spacings as the unfractionated bentonite. The large differences in the spacings between the


particles >0.06/~m and the smaller particles indicate dramatic changes in the charge density. The steeper increase of the spacing with the alkyl chain length for particles <0.06 ~tm reveals a narrower charge distribution.

The charge distribution of the different particle-size fractions was calculated under consideration of a particle-size correction (Lagaly & Weiss, 1971; Stul & Mortier, 1974; Lagaly, 1981). This correction is based on the assumption that the alkyl chains of the alkylammonium ions lying very near the edges are squeezed out of the interlayer space. The effective area per charge, Ae', is then somewhat larger than the equivalent area, Ae, which is calculated for very large particles by

Ae = aobo/2~ (2)

An alkylammonium ion (diameter 4.5 ,&) near the crystal edge may occupy only an area of Ae/2. The number of chains in the edge region of a particle with a diameter d = 2r is 2n-r/4.5. The effective area per cation in the interlayer space is then

:rr 2 - (2:rr/4-5) x Aft2 1 - 2Af14.5d

A~' = :rre/Ae - 2Jrr/4.5 = A~I - 4Ae/4"5d (3)

In the interlayer space the alkylammonium ions are close packed when

A c = Ae'

where A c is the area occupied by a flat-lying alkylammonium ion (Lagaly & Weiss, 1971):

Ac = 1-27 x 4.5nc + 14 (/~k 2) (4)

20-

~15 ff l

El ~q CJ

..121

10 J L I I I i I 1 i I i I J

10 15 20

n c

Flo. 2. Basal spacings of the alkylammonium derivatives (nc carbon atoms in the alkyl chain) of bentonite from Brazil. Fractions (/~m): <0.02 (�9 0.02~).06 (O); 0.064)-2 (A); 0.2-1.0 (1);

1.0-10 (~'); unfractionated ([2).


I 10

50[

10

<0,02Fm ~=0249 ~ 2 - 1pro

=0276

, J

0_02- O.06p m ~:o2~s

i i I I i 1 I

I- 1OHm

0.06- 0,2)um

I

0,22 26 .30 .3& .38

un fractionated ~:0275

0'22 .26 .30 3/., .38 ~/eq/(SiA[)4.Qo

Fro. 3. Charge distribution of various fractions of bentonite from Brazil.

With Ae' = A c we obtain from eqn. (3):

Ae = A c + 4-5d/4 - (Ac 2 + (4-5dI4)2) ~

and with eqn. (2)

aobo aobo 1 - - - x ( 5 )

2A~ 2 A c + 4-5d/4 - ~ /Ac 2 + (4-5d/4) 2

The charge density and charge-density distribution is then obtained from Ac , and Ac is calculated using eqn. (4) from the alkyl chain length nc at the mono/bilayer transition.

On the basis of the same correction, Stul & Mortier (1974) developed an iteration process which leads to slightly higher charge densities for particles <0.04/~m. For larger particles, both methods give identical results. A particle size correction is not necessary for particles >0-2 #m.

The study of various fractions of several montmorillonites has shown that the particle-size correction probably produces too high charge densities for particles <-0-02 #m. A simple reason is that the particle-size fraction is given in Stokes equivalent diameters, but the real diameter of the particle is certainly larger. The charge densities for particle-size fractions <0-06 ~m were calculated on the basis of an apparent particle diameter of 0.04/*m. For the fractions 0-06~)-2, 0.2-1 and 1-10/~m, values of d = 0.1, 0.6 and 2/~m were used. Particles >0-06 ~m have a broad charge distribution (Fig. 3) with a maximum at

Organo-bentonites with quaternary alkylammoniurn ions

TABLE 1. Layer charge and CEC of bentonite 25 de Maio, Brazil.

25

Particle ~ Ae G I Ct size ~m Eq(Si,A1)4010 A 2 mEq/g mEq/g Ci/C~

<0.02 0.2492 93 0.69 0.94 0-73 0.02-0-06 0.255 91 0.71 0.94 0.76 0.06-0.2 0.276 84 0.77 0.96 0.80 0.2-I 0.276 84 0.77 0.97 0.79 1-10 0.282 82 0.78 0.57 -- Unfractionated 0-275 85 0.76 0-95 0,80

C,, ct in mEqtg silicate, Ct [rom the decy~ammonium derivative. 2 Three decimal digits are given only to reveal the variation in layer charge more clearly.

0.23-0-25 Eq/(Si,A1)4010 and an almost even par t ic ipat ion of charge densities between 0-25 and 0.35 Eq/(Si,Al)4Ol0. The very narrow charge distr ibution of part icles <0.06/~m produces the impression that these part icles are of different origin or have been produced by different al terat ion processes.

The total amount of the a lkylammonium ions bound is calculated from the ni trogen (cN) or the carbon content (cc) when adsorbed a lkylammonium salt is removed by washing. The quantit ies cN and cr are usually obta ined in wt%. The total exchange capacity, Ct, is then

CN/14 Ct = (Eq/g silicate) (6)

100 - M • CN/14

when Ct is re la ted to the silicate skeleton (amount of inorganic material) . The molecular mass of the a lkylammonium ion is M, the total amount of organic mater ial is M x cN/14, and 100 - M x CN/14 is the amount of inorganic mater ia l (silicate).

The corresponding expression from the carbon content , co, is

cc/12nc Ct = (Eq/g silicate) (7)

100 - M x cc/12nc

The total exchange capacity from the N and C content of the a lkylammonium derivatives varies between 0-94 and 0.97 mEq/g silicate (Table 1). The inter layer cation density increases with the particle size from Ci = 0.69 to 0.78 mEq/g, and the ratio Ci/Ct from 0.73 to 0.80. Thus, 20% of the cations are held at the crystal edges of the particles >0-06/~m.

The largest fraction contains high amounts of admixed minerals and materials; the total exchange capacity, Ct, is 0.57 mEq/g. For the pure fraction, Ct is assumed to be --0.97 mEq/g so that the montmori l loni te content of the largest fraction is - 5 9 % .

DMDO derivatives

The total amount of the D M D O ions bound per gram silicate, G , is calculated from the N and C content (Table 2). As the D M D O is of technical quality, the mean molecular mass, 3), is es t imated from the C/N ratio:


TABLE 2. DMDO derivatives of three bentonites.

c i Elementary analysis Ct d00a Bentonite Eq/(Si,Al)4010 mEq/g CN CC ~( mEq/g Ci/Ct ]~

Brazil 0-28 0.78 0-906 28.72 36.9 0.98 0.80 23-0 Wyoming 0-28 0-78 0-896 28.34 36.9 0.97 0-80 23-5 Bavaria 0-28 0.78 0.880 28.47 37.7 0.96 0-81 24.2

M'~( I x 14)+(Xx 14)+4 (8) 1 nitrogen + X methylene groups + 4 hydrogens of 4 methyl groups

An amount of 100 g D M D O bentoni te contains CN/14 mol D M D O (CN is the N content in wt%) and an amount of ~r x CN/14 organic material (in g). The amount of organic material

per g silicate is then

CN/14 C~ = (gq/g silicate) (9)

100 - ~r • CN/14

The bentonites bind 0.96--0.98 mEq DMDO/g silicate (Table 2). Comparison with Ci

(from the alkylammonium exchange, eqn. 1, Table 1) indicates that 80% (81% for Bavarian bentonite) of the total amounts of D M D O replace the exchangeable cations in the interlayer space. This ratio is the same as for decylammonium ions (Table 1).

An important observation is reported in Tables 2 and 3. The molar ratio C/N = Z of the D M D O derivatives of the unfractionated Brazilian and Wyoming bentonite is almost the same as in D M D O chloride (C/N = 36.7) but is enhanced for the Bavarian bentonite . The bentonites reveal a tendency to enrich the longer chain compounds with decreasing particle size (Table 3). For very small particles (<0.06 gm), the C/N ratio of 38 is distinctly larger than in the D M D O chloride. Larger particles (>0.2 #m) have C/N ratios smaller than in the

TABLE 3. Binding of DMDO (technical quality) by different fractions of three bentonites,

Particle Elementary analysis d f~31 Bentonite size/~m ~1 Cia cN Cc Z 32 Ct 2 Ci/Ct A

Brazil <0.06 0.25 0.70 0.905 29.48 38.1 551 bOO 0.70 23.9 0.0602 0.27 0.77 0.915 28.48 36-3 526 0.97 0.79 23-5 0.2-1-0 0-28 0.78 0.895 26.98 35.2 510 0-95 0-82 25.2

Wyoming 3 <0.06 0-28 0.77 0.873 28.29 37.8 547 0-95 0-81 22.4 0.06-0.2 0-27 0.74 0-882 27-18 36.0 521 0.94 0-79 21.3 0.2-1.0 0-29 0.81 0.849 25.89 35-6 516 0.89 0-91 23.6

Bavaria 3 <0.06 0.27 0.74 0.917 30.06 38-2 553 1.03 0-72 24.5 0-06-0-2 0.29 0-79 0.887 27.70 36.4 528 0.95 0-83 24.5 0.2-1-0 0-28 0.79 0.893 27.20 35-5 516 0.95 0-83 23-6

t In Eq/(Si,Al)4Oi0. 2 G, C, in mEq/g silicate. 3 Westfehling, 1987.


quaternary salt. The general conclusion is that very small particles enrich the longer chain compounds, and larger particles the cations with smaller C/N ratios.

Preferential adsorption (longer chain compounds by small particles, compounds with lower C/N ratio by large particles) is caused by the charge density variation and the particle size. A larger equivalent area Ae (smaller ~) promotes binding of longer chain compounds, in particular as the area of the dimethyl dioctadecyl ammonium ion ( -230 A~ 2, McAtee, 1962) is much larger than the equivalent area (Table 1). The particle size effect results from the enrichment of the longer chain compounds near the particle edges. As the long alkyl chains are squeezed out of the interlayer space, larger amounts of longer chain compounds are bound by smaller particles.

It is clear that the total amount of quaternary cations which decreases with increasing particle size, is not decisive in determining the basal spacing which increases (Brazil, Wyoming) or decreases (Bavaria) with particle size (Table 3). Rather, the spacing is determined by the interlayer cation density Ci which increases with particle size.

A pseudotrimolecular arrangement (Lagaly, 1982) may be expected from the relation between the area per molecule (230 &2 for the widely extended conformation) and the equivalent areas of 82-93 A2/charge. A spacing of - 2 2 A is typical of this arrangement. The larger spacings are indicative of more complicated conformations with gauche-bonds in the alkyl chains. The number of possible conformations with one, two or even more gauche bonds per alkyl chain is large so that details of the interlayer alkyl chain arrangements cannot be deduced. It is evident from the data in Table 3 that small changes in the interlayer cation density can induce conformations with distinctly higher spacings (d001 = 23.5 ---> 25-2/~).

Competitive adsorption

An important observation is that the adsorbed amount of long-chain quaternary alkylammonium ions can be strongly reduced in the presence of short-chain alkylammonium ions. This is exemplified for TMTD ions and TM or TE ions.

Various particle-size fractions of the three bentonites were reacted with mixtures of both surfactants. The interlayer amounts of TMTD and TM or TE were calculated from the C and N contents and the C/N ratio.

The N content, CN (in %), gives the total amount of interlayer surfactants

ct = 0.01 CN/14 (Eq/g organo-bentonite) ct = cl + c2 (10)

The quantities cx and c2 are the amounts of TM or TE and TMTD ions in Eq/g organo- bentonite. The number of C atoms in the surfactants is no(l) and nc(2), X is the molar ratio C/N, so that

C t X ~ = C 1 • nc(1) + C 2 X nc(2) = Ca • nc(1) + ( G - el)no(2)

G(X- nc(2)) cl - (11)

nc(1) - nc(2)

The total amount of surfactants, Ct (in Eq/g silicate) is then


Ca + c2 ct = ( E q / g s i l icate) (12)

1 - (c~M1 + c2M2)

w h e n M1 a n d M2 a re t he m o l e c u l a r m a s s e s of s u r f a c t a n t 1 ( T M or T E ) a n d s u r f a c t a n t 2

( T M T D ) .

T h e to t a l a m o u n t of T M T D a n d T M ions (G = 0 -90-0 .97 m E q / g ) is in t he s a m e r a n g e as

for a l k y l a m m o n i u m ions ( T a b l e 1) or D M D O ions (Tab le s 2,3) . T h e a m o u n t s of T E ions

(ct = 0 -83-0 .88 m E q / g ) a re s o m e w h a t s m a l l e r b u t still g r e a t e r t h a n t h e ci va lues .

T h e smal l e s t pa r t i c les w h i c h ca r ry t he sma l l e s t nega t i ve c h a r g e dens i ty , s h o w a

p r e f e r e n t i a l a d s o r p t i o n of T M T D ions o v e r T M ions (c2/G = 0 .82-0 -94) , w h e r e a s l a rge r

pa r t i c les ( > 0 . 0 2 / ~ m ) b i n d a l m o s t e q u a l a m o u n t s of b o t h s u r f a c t a n t s (c2/G ~ 0 .5 -0 -6 ) . T h e

ra t io c2/G t h e n c h a n g e s less wi th t he pa r t i c l e size, a n d is also no t so d e p e n d e n t o n t he r a t io of

the s u r f a c t a n t s in so lu t ion . A s t r o n g e r d e p e n d e n c e is o b s e r v e d for T E ions . Smal l pa r t i c les

( < 0 - 0 6 ~m) a d s o r b exc lus ive ly T M T D ions . F o r l a rge r par t ic les t he p r o p o r t i o n of the long-

cha in ca t ions d e c r e a s e s f r o m 0.84 to 0.43 ( T a b l e 4).

TABLE 4. Competitive binding of tetramethylammonium ions (TM) or tetraethylammonium ions (TE) (= q) and trimethyl tetradecylammonium ions (TMTD) (= c2) by different fractions of bentonite from Brazil.

Fraction (/~m) cN Z c, cl 1 C21 Ct 2 C2[Ct dora (A)

3 mEq TM + 1 mEq TMTD/g bentonite <0.02 1.13 15-59 0.80 0-09 0.71 0-99 0.89 14-8 0.024).06 1.15 10-44 0.82 0.41 0.40 0-95 0.49 13-8 0.0643.2 1.10 9.84 0.78 0.43 0-35 0-90 0.45 13-7 0-24)-6 1.10 9.20 0.78 0-47 0.31 0.89 0.40 13.6 0.6-2 0-98 10-66 0.70 0.34 0-36 0-80 0.52 13.7 2-6 0-65 11.11 0-46 0.21 0.25 0-50 0.55 14.1

2 mEq TM + 2 mEq TMTD/g bentonite <0-02 1-09 14.72 0-77 0.14 0-64 0.94 0-82 14.0 0.024)-06 1.14 12.30 0.81 0-29 0.52 0.96 0-64 13.8 0.064).2 1.16 12.01 0-82 0.32 0.51 0.98 0.62 13.9 0-24).6 1.15 1t-64 0.82 0-34 0-48 0-97 0-59 14.1 0.6--2 0.93 12.14 0.66 0.25 0.41 0.76 0.63 13.7 2-6 0.64 11.60 0.45 0-19 0.27 0.50 0-58 15.2

1 mEQ TM + 3 mEq TMTD/g bentonite <0.02 1.08 16-20 0.77 0-05 0.72 0.96 0.94 15.2 0.024).06 1.11 12-89 0.79 0-25 0.54 0.95 0-68 13.9 0.064).2 1.16 12.53 0.83 0-29 0.54 0.99 0.66 13.9 0-2-0-6 1.12 12.07 0.80 0.40 0-50 0-95 0-62 14.2 0.6-2 0.98 11.98 0.70 0.27 0.43 0.81 0.61 13.7 2-6 0.64 12.34 0.46 0-16 0.29 0.50 0.64 15.5

2-5 mEq TE + 2-5 mEq TMTD/g bentonite <0-02 1.05 17.00 0.75 0 0.75 0.93 1.00 15.9 0.024).06 1.07 17.14 0.76 0 0.76 0.96 1.00 16.0 0-064).2 1.10 15-37 0.79 0-13 0.66 0.97 0.84 15.9 0-24)-6 1-11 14-98 0-79 0-18 0-62 0-97 0-78 16-0 0.6--2 0.99 13.24 0.71 0.30 0.41 0.83 0.58 15-6 2-6 0.79 11.86 0.56 0.32 0.24 0.62 0.43 13.9

1 In mEq/g organo-bentonite. 2 In mEq/g silicate.


Most basal spacings of the TM/TMTD derivatives are in the monolayer range (13.6.14.0 A). The surfactants are arranged in monolayers, and the TMTD ions assume a conformation as fiat as possible. The surfactants are closely packed when a distinct ratio of TM and TMTD ions is attained. This ratio can be calculated in the following way. The monolayer area per formula unit is aobo/2 = 23.25 A 2. There are, per formula unit, ~1 TM ions (38 ~2/ion; Barrer et al., 1967) and ~2 TMTD ions (112 A2/ion) (~1 + ~2 = ~). The monolayers are closely packed for

38~1 + 112(~ - ~1) = 23-25 (A2/unit) (13)

Thus, ~1 can be calculated as a function of the layer charge ~. With increasing particle size, ~1 increases strongly from 0.06 TM ions/unit for ~ = 0.25 to 0.11 ions/unit for

= 0.28 (Table 5). The ratio ~2/~ decreases from 0.74 to 0-61. The ratio TMFFMTD at the external surfaces may be different from that in the interlayer space but data cannot be obtained. If the differences are not too large, ~2/~ should be similar to c2/ct. This is in fact observed when the concentration of TMTD in solution is sufficiently high (->2 mEq/g bentonite).

Formation of dense monolayers of TM and TMTD ions in the interlayer space is unexpected. The reason for the stability of monolayers is the strong tendency of the TM ions to hold the silicate layers at close distances (13.6-13.9 A; Barrer & Kelsey, 1961; Clementz & Mortland, 1974). The driving force is the keying of the methyl groups into the six-membered rings of surface oxygen atoms (Barter & Kelsey, 1961). For very small particles the number of these links is too small, and the TMTD ions can prise apart the layers to some extent (dL > 13.8 ~ ) .

With mixtures of TE and TMTD ions, the montmorillonites react as expected. Small particles (<0.06/~m) bind only TMTD ions. The ratio c2/ct decreases with increasing particle size but is still large (20.8) for the 0.2-0-6/~m particles. Adsorption of the small cations is preferred over the long-chain ions only for larger particles.

The fact that TE ions are not as strong competitors for interlayer sites as TM ions probably follows from the reduced keying of the ethyl groups between the surface oxygen atoms. Tetraethylammonium ions do not hold together the silicate layers as strongly as TM ions and admit the binding of larger amounts of TMTD.

The spacings of --16 ~ are too small to be caused by conformations distinctly different from a flat arrangement. The layer separation only allows insertion of a kink into the alkyl

TABLE 5. Interlayer composition of close-packed monolayers of surfactant cations. Number of cations per (Si,Al)4010 unit: ~1 tetramethylammonium ions; ~2 trimethyltetradecylammonium

ions; ~1 + ~2 = ~.

0.25 0-06 0-74 0-26 0.08 0-69 0.27 0.09 0.65 0.28 0.11 0.61 0.29 0-12 0-57 0-30 0.14 0.53


chain (Lagaly, 1976), which increases the spacing by 1-6-2 A. (The theoret ical displace- ment of the chain sections in the zig-zag plane by a kink is 1-8 A . ) I t is more l ikely that as a consequence of charge heterogenei ty , bilayers are interstratif ied with monolayers of TE /TMTD ions. The short-chain and long-chain ions will not be distr ibuted uniformly between monolayers and bilayers. Monolayers evolve in inter layer spaces with higher charge densities and contain higher amounts of TE ions. More lowly charged interlayers enrich T M T D ions in bilayers. Consequent ly the most highly charged part icles (2-6 ~m fraction) contain surfactant monolayers , and the ratio Cz/Ct is low.

C O N C L U S I O N S

Bentoni tes develop a certain selectivity against distinct quaternary a lkylammonium ions when reacted with mixtures of such surfactants. The extent of selectivity depends on the particle size. As technical surfactants are general ly mixtures of several compounds , two impor tant practical consequences arise. The real composi t ion of the organo-bentoni te depends not only on the layer charge, but also on the particle-size distr ibution. I t also depends on the technical quality of the surfactant used in industrial product ion. Thus, organo-bentoni tes from different product ions or manufacturers may differ considerably in their proper t ies .

Organo-bentoni tes are often produced by addi t ion of the organic cations to paste-l ike materials , and the product is dr ied without removal of excess salt by washing. When the surfactants are added to more or less di luted bentoni te dispersions, some of the excess salt is removed by the filtration steps but some of the salt may adhere to the dr ied material . Even if these amounts are relat ively small, they can strongly affect the proper t ies of the organo-bentoni te .

Differences between similar organo-bentoni tes can be detected by the C and N contents and C/N ratios. Even small differences can be indicative of widely differing propert ies . Very sensitive are rheological proper t ies (examples will be repor ted in a subsequent paper) .

The use of different bentoni tes , surfactant mixtures, levels of adsorpt ion and amounts of excessive salts thus constitute the main confidential ways by which manufacturers produce organo-clays with different propert ies .

ACKNOWLEDGMENT

The authors are indebted to the Alexander-von-Humboldt-Stiftung for a fellowship to Henry Favre during his stay in Kiel. We also thank Mrs Gallay for an enormous number of C/N determinations.

REFERENCES

BARRER R.M., PAPADOPOULOS R. & REES L.V.C. (1967) Exchange of sodium in clinoptilolite by organic cations. J. Inorg. Nucl. Chem. 29, 2047-2063.

BARRER R.M. & KELSEY K.E. (1961) Thermodynamics of interlamellar complexes. 1. Hydrocarbons in methylammonium montmorillonites. Trans. Farad. Soc. 57, 452-462.

CLEMENTZ D.M. & MORTLAND M.M. (1974) Properties of reduced charge montmorillonite: tetra-alkylammonium ion exchange forms. Clays Clay Miner. 22, 223-229.

DI~I~ANY I., SZ,~NT6 F. & NAGY L.G. (1986) Sorption and immersional wetting on clay minerals having modified surface. J. Coll. Interf. Sci. 109, 376-384.

GRANQU1ST W.T. & MCATEE J.L. (1963) The gelation of hydrocarbons by montmorillonite organic complexes. J. Coll. Sci. 18, 409-420.

JONES T.R. (1983) The properties and uses of clays which swell in organic solvents. Clay Miner. 18, 399-410.

Organo-bentonites with quaternary a l k y l a m m o n i u m ions 31

LACALY G. & WEISS A. (1971) Anordnung und Orientierung kationischer Tenside auf Silicatoberfl~ichen. Teil IV Anordnung von n-Alkylammoniumionen bei niedrig geladenen Schichtsilicaten. Kolloid Z.Z. Polymere 243, 48-55.

LAGALY G. (1976) Kink-block and gauche-block structures of bimolecular films. Angew. Chem. Int. Ed. Engl. 15, 575-586.

LAGALY G. (1981) Characterization of clays by organic compounds. Clay Miner. 16, 1-21. LAGALY G. (1982) Determination of layer charge heterogeneity in vermiculites. Clays Clay Miner. 30, 215-222. LAGALY G. & FAHN R. (1983) Ton und Tonminerale. Pp. 311-326 in: Ullmann's Eneyklopiidie der technischen

Chemie, 4. Auflage, Band 23. LAGALY G., TRIBUTH H . , SANDER H. & CRACIUN C. ( 1 9 8 5 ) Die Korngr6genverteilung von Bentoniten und ihr EinluB

auf r/Sntgenographische und rheologische Eigenschaften. Keram. Z. 37, 75-79. LEE J.F., MORTLAND M.M. & BOYD, ST.A. (1989) Shape selective adsorption of aromatic molecules from water by

tetramethylammonium-smectite. J. Chem. Soc. Faraday Trans. 1, 85, 2953-2962 MALLA P.B. & DOUGLAS L.A. (1987a) Identification of expanding layer silicates: layer charge vs. expansion

properties. Proc. Int. Clay Conf. Denver, 277-283. MALLA P.B. & DOUGLAS L.A. (1987b) Problems in identification of montmorillonite and beidellite. Clays Clay

Miner. 35, 232-236. McATEE J.L. (1962) Cation exchange of organic compounds on montmorillonite in organic media. Clays Clay

Miner. 9, 444-450. MCATEE J.L. (1963) Organic cation exchange on montmorillonite as observed by ultraviolet analysis. Clays Clay

Miner. 10, 53-162. MCATEE J.L. & ROBB1NS R.C. (1980) Gas chromatographic separation of cresols by various quaternary ammonium

substituted montmorillonites. Clays Clay Miner. 28, 61-64. SAMn A.M. & LAGALY G. (1987) Adsorption of nuclein bases on smectites. Proc. Int. Clay Conf. Denver, 343-351. SLABAUGH W.H. & VASOFSKY R.W. (1975) Adsorption of xylene by organo-clays. Clays Clay Miner. 23,458-461. STREET G.B. & WHITE D. (1963) Adsorption by organo-clay derivatives. J. Appl. Chem. 13, 288-291. STUL M.S. & MORTtER W.J. (1974) The heterogeneity of the charge density in montmorillonites. Clays Clay Miner.

22, 391-396. STUL M.S. & UYTTERHOEVEN J.B. (1983) Monotrimethylammoniumdodecane clay--benzene, hexane vapor

interactions. J. Colt. Interj" Sci. 91,286-288. SZ,~NT6 F. & VERES S. (1963) Stability of organophilic bentonite suspensions in mixtures of apolar and polar liquids.

Acta Physica Chemica, Szeged, nova series IX, 157-167. SZ,~NT6 F., G1LDE F. & Swos E. (1972) Sedimentation organophiler Bentonite. Kolloid-Z.Z. Polymere, 250,

683-688. TARAMASSO M. & VENIALE F. (1969) Gas-chromatographic investigations on dimethyldioctadecyl ammonium

derivatives of different clay minerals. Contr. Mineral. Petrol. 21, 53-62. TARAMASSO M. (1971) Adsorbents for gas-solid chromatography prepared by epitacial modification of clay minerals

with quaternary ammonium ions. J. Chromatogr. 58, 31-38. TRJBUTH H. & LAC, At.V G. (1986) Auf'oereitung und ldentifizierung von Boden- und Lagerstfittentonen. II.

Korngr/~13enanalyse und Gewinnung yon Tonsubfraktionen. GIT Fachzeitschrift fiir das Laboratorium, 30, 771-776.

VASOFSKV R.W. & SLAaAUGH W.H. (1976) Dimethyldiocatadecyl-ammonium clay xylcne vapor interactions. J. Coll. Interj. Sci. 55, 342-357.

VOLD R.R. & PHANSALKAR V.K. (1962) Dispersion of alkylammonium montmorillonites in organic liquids. J. Coll. Sci. 17, 589-600.

WESTFErtUNG R. (1987) Uber den Ladungsnullpunkt yon Tonmineralen. Thesis, Univ. Kiel, Germany.

A P P E N D I X

List of symbols:

A~ = equivalent area, for montmorillonite Ae = 23-25/~ (/~2) CN, CC = nitrogen and carbon content (in %) cl, c2 = amounts of surfactant cations 1 and 2 (Eq/g organo-bentonite)

C t = C 1 + C 2

Ci = amount of interlayer cations = interlayer exchange capacity (Eq/g silicate) C, = amount of cations (internal and external) = total exchange capacity (Eq/g silicate)


dL= basal spacing (.~) M, M1, Me = molecular masses

nc = number of carbon atoms in the organic cation = average charge density (layer charge) (Eq/(Si,A1)4Olo unit)

~1, ~2 = number of tetramethyl or tetraethylammonium ions ( e ) and trimethyl tetradecylammonium ions (~2) per unit (Si,Al)4Olo, ~a + ~2 =

Z = molar ratio C/N

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ORGANO-BENTONITES WITH QUATERNARY ALKYLAMMONIUM …minersoc.org/pages/Archive-CM/Volume_26/26-1-19.pdf · ammonium (TMTD) ions, and only ... highly charged vermiculites do not exchange