THn AMERICAx M INERA LOGISTJOURNAL OF THE MINERALOGICAL SOCIETY OF AMERICA

JULY_AUGUST 1958 Nos. 7 and 8

ADSORPTION AND RETENTION OF AN ORGANIC "MATERIAL BY MONTI,TORILLONITE IN THE

PRESENCE OF WATERX

G. W. BnrNorBv awo Manlrout Rusrov, Department of CeramicT echnolo gy, T he P ennsyl,vania S tate U n'iaer sity.

Assrnncr

The adsorption of a polyethylene glycoi ester of oieic acid on montmorillonite is studied

in relation to the water content of the system. At low concentrations of organic material

to clay mineral, T0/6 oI the organic material is adsorbed on the clay and' 30/6 remains in

solution. The lattice spacings of the clay-organic complexes, when dried at 110' C, are

studied for clays saturated with Na, Ca and Mg ions. Ordered complexes are found con-

taining one layer or two layers of organic material between silicate layers, and in the

appropriate composition ranges mixtures of lJayer and 2Jayer types are observed rather

than mixed sequences. Repeated washings reduce 2-layer to lJayer type sequences, but

a single organic layer between silicate sheets is firmly held.

h.rrnolucrroN

The adsorption of organic molecules by montmorillonite and the re-sultant expansion of the crystalline lattice have been intensively studiedand general surveys have been given by MacEwan (1951) and by Grim(1953). These studies have been made mainly with l iquids, either organicIiquids or solutions in water, but in a few instances with organic vapors.Glaeser and Mering (1952, 1954), and Barrer and Macleod (1955)

have studied the adsorption and desorption isotherms of montmoril-lonite for a number of gases and vapors in relation to the relative vaporpressure; comparable studies'for organic materials dissolved in waterappear not to have been made.

In the present investigation an attempt has been made to study equi-librium in a system comprising montmorillonite, an organic material,

and water. fn particular, attention has been given to (i) the partition

of the organic material between the clay and the liquid phase, (ii) thechange in character of the clay-organic complex as the organic com-

x Contribution No. 57-20 from the College of Mineral Industries, The Pennsylvania

State University, University Park, Pennsylvania.

627

628 G. W. BRINDLEY AND M. RUSTOM

ponent is increased from small amounts up to saturation, and (iii) theretention or fixation of the organic material by the clay.

In recent years much attention has been given to the adsorption ofcationic organic complexes on clays (see Gieseking (1939), Hendricks(1941), Jordan (1949,1954), Franzen (1955), Tal ib-Udeen (1955),Barrer and Macleod (1955), Haxaire and Bloch (1956)). The resultsindicate that in addition to a cation exchange reaction, physical adsorp-tion processes also occur. It seemed desirable, therefore, to study theadsorption of a non-ionic complex before considering situations in whichexchange reaction take place,

MerBnrars

Organic material,

The experiments have been carried out with a commercial wettingagent, "Nonisol 250", supplied by the Geigy Chemical Corporation,the choice of which was partly fortuitous. This is an ester of polyethyleneglycol and oleic acid, with the following chemical formula:

ICHz' CHz(OCH:. CH)*6. 911,. CH,O-C-(CHz) zCH:CH (CH:) zCHs

(polyethylene glycol) (oleic acid)

The material is normally a paste, readily soluble in water and in mostorganic solvents. It is recoverable from solution in water by drying at105'C. with less than a 1/oweight loss, and with no significant changein the r-ray powder diagram. The material is therefore chemicallystable to solution in water and re-drying.

Clay material

Montmoril lonite has advantages over non-swell ing clays since the ex-pansion of the crystal lattice can be measured by r-rays and this pro-vides an accurate method of studying adsorbed surface layers which isnot applicable to the non-swell ing clays.

A purif ied Wyoming bentonite was suppiied by Dr. J. L. McAtee, ofthe Baroid Sales Division, National Lead Company, Houston, Texas.This is a relatively well-crystall ized form of montmoril lonite. Theprecise purif ication process is not known but is believed to be one ofsedimentation and/or centrifugation. The sample supplied had Na andCa ions as exchangeable cations and contained a trace of cristobaliteimpuritv.

IOH

ADSORPTION OF ORGANIC MATERIAL BY MONTMORILLONITE 629

Expnnrlrewrer Pnocnounn s

Clay mineral preporation

By repeated treatment with 1-N solutions of the respective chiorides,clay samples were prepared saturated with Ca, Na and Mg ions. Follow-ing sedimentation and repeated washings of the clays with disti l ledwater, the remaining traces of excess chloride were removed by dialysisthrough cellophane tubing, using the silver nitrate test. The clay sampleswere then dried in air at 110" C. and stored in a dessicator over activatedalumina.

Clay-or ganic adsor ption pr oced.ure

The experiments were designed mainly on a volumetric basis. A sus-pension of montmoril lonite containing I gm. clay/l iter water, and anorganic solution containing 1 gm./liter water were prepared. Requisitevolumes of clay suspension, organic solution, and water were mixedand agitated intermittently for 4 hours. After centrifugation, an aliquotof the clear solution was analysed for organic material, and the clay wasremoved for x-ray examination.

Organic analysis

To determine the organic matter left in solution, a direct weighingmethod was tried using very thin Pyrex bulbs as evaporating dishes.The method was found to be capable of giving reasonable accuracy butwas very lnconvenrent.

A titration method was developed making use of the C:C bond inthe oleic acid part of the molecule. Adsorption of bromine by the doublebond was determined by measuring excess bromine with a thiosulphatetitration. A calibration curve was obtained using organic solutions ofknown concentration. The conditions for the bromine absorption and thesubsequent titration were standardized precisely. The method was foundto be accurate and measurements could be repeated.

X-roy onalysis

The clay samples were prepared as thin, oriented layers on glass slidesand were examined with a Philips Norelco difiractometer with CuKaradiation. The atmosphere surrounding the specimen was controlled byair circulation, either dry air or air of humidity approaching 100/6. Thelatter was used with wet clay films prior to any drying treatment andensured that the clay film remained wet during the r-ray examination,usually about 30 min.-l hr.

G. W BRINDLEY AND W. RUSTOM

Re sur,rs

(a) Partition oJ organic material between clay and, water for constant initialconcentration oJ organic material

The three components, clay, organic material and water, were mixedto provide an initial concentration of 300 mg. organic material,/literwater, and to cover a range of values for the ratio of organic material toclay.

In Fig. 1, the organic material adsorbed per gm. clay is plotted againsttotal organic material in the system per gm. clay. The adsorption eurvetends smoothly to an asymptotic l imit of about 0.6 gm. adsorbed organic

o6

o.4

o2

- ' >E c 'o rE

.dec ctloE D L

b3!tq,

.ct

o@

!t

o.2 o.4 l 2t.oo.8

Totol orgonic in sYslem, gm,per gm c loy

Frc. 1 . Adsorption ;l,ilir#HTn_r#i$il:

oreic acid on

material per gm. clay. fn the region of about half maximum adsorptiona large number of observations were made to check for a possible de-parture from the smooth curve, but within the accuracy of the deter-minations, no deviations were found.

Up to about SO/e of maximum adsorption, the curve is linear with agradient corresponding to about 70/6 of the total organic materialbeing adsorbed on the clay. At about 90/6 of maximum adsorption,the clay adsorbs about 50/6 of the total organic material.

(b) X-ray examination oJ the.wet clay-organic f,lms prior to d'rying

A{ter centrifugation, the clear liquid was drained from the clay, afew ml. of water were added, and several drops of the clay suspensionplaced on a glass slide. Evaporation in air was allowed to proceed unti l

ADSORPTION OF ORGANIC MATERIAL BV MONTMORILLONITE 631

a coherent but sti l l moist clay fi lm was obtained. This was placed in the

diffractometer enclosure and kept moist by passing air of almost 10070

R.H.The lattice spacing d(001) was 18.5-19 A largely irrespective of the

exchangeable cations and the amount of adsorbed organic material. The

results are set out in Table 1. For Na-montmoril lonite, the spacing

ranged up to 22 A for small quantit ies of adsorbed organic material, but

otherwise conformed to the values found for Ca- and Mg-montmoril-

Ionites. These results suggest that prior to drying the lattice spacing is de-

termined principally by water remaining between the silicate sheets.

Tenle 1. Larrrce Specrucs ol WBr MoNruonrr,r-oNrtE Frlus ConrnrNrNc

Aosonson Polvernvr,nNr Gr,vcor Esrrn or Or-arc Acro (NoNrsor- 250);

Vlr.uns or d(001) rN A

Exchangeable cations

Clay films prior to any drying treatment

Clay 61ms re-wetted af ter drying at

1 1 0 ' c .

MgCa

18.4-18 . 8

18. 8 -19 . 2

1 8 . 4 - 1 9 . 0

(c) X-ray er.amination oJ the d'ried clay-organic f'lms

The clay-organic films were now dried at 110" c. and maintained in a

dry atmosphere during storage and during r-ray examination with the

diffractometer.The results vary according to the exchangeable cation and the total

organic/clay ratio. Typical difiractometer recordings for selected or-

ganicf clay ratios are shown in Figs. 2,3, and 4, and the lattice spacings,

d(001), are shown in Figs. 5, 6, and 7'

Figs. 5, 6, and 7 show that the lattice spacing expands to nearly sta-

tionary values of about 14 A and 17.5 A as the total organic content is

increased. The detailed results, see Table 2, show'that the mean lattice

expansions with respect to clays dried at 250' C. and without organic

material are 4.2o A and 7.7o L. These expansions are regarded as cor-

responding to one and two Iayers of organic material respectively be-

tween the montmoril lonite sheets.It is of particular interest to consider whether, with increasing organic

content, the clay-organic complexes form regular structures at certain

compositions, and irregular or interstratified structures at intermediate

compositions. The evidence in Figs. 2-7 points to the formation of regu-

Iar structures as the main feature of these olganic complexes. Although

there is some evidence for irregular stratifications of the clay-organic

layers, this does not appear to be a major characteristic of the present

system.

632 G, W. BRINDLEY AND M. RUSTOM

Frc. 2' Difiractometer recordings of ca-montmorillonite-organic complexes. The ratioof total organic material in the system to the amount of clay is shown by the value at theright hand side of each diagram.

The breaks in the curves at about 20:10" arise from a change of the intensitv scalefor the higher order reflections.

ADSORPTION OF ORGANIC MATERIAL BY MONTMORILLONITE 633

2{t

Fro. 3. Diffractometer recordings of Na-montmorillonite-organic complexes' The ratio

of total organic material in the system to the amount of clay is shown by the value at the

right hand side of each diagram.

The breaks in the curves at about 20:t0" arise from a change of the intensity scale

for the higher order reflections'

6s4 G, W. BRINDLEY AND M. RUSTOM

Frc' 4. Difiractometer recordings of Mg-montmorillonite-organic complexes. The ratioof total organic material in the system to the amount of clay is shown bythe value at theright hand side of each diagram.

The breaks in the curves at about 20:10" arise from a change of the intensity scalefor the higher order reflections.

oE

" EE o lg t g

o_: cL'eouro

oo)-oooo

o.?

20

t8o<

: t 6ooE t 4

t2

ADSORPTION OF ORGANIC MATERIAL BY MONTMORILLONITE 635

A d s o r b e d o r g o n i c , 9 m , P e r g m c l o Y

o l o z o . 3 0 4 0 5

0.6

t ' A

lo l-

o6 o.8

Totol orgonic in sYsfem in gm

Per gm c loY

Ftc. 5. Lattice spacings in A of dried Ca-montmorillonite-organic complexes with

increasing organic material in the reacting system.

Curve A is the adsorption curve of Fig' 1'

Regularity of a layer structure is indicated by the formation of an inte-

gral series of Bragg reflections; the lattice spacing calculated from each

reflection with its assumed integral order should then have a constant

Toto l orgonic in sYslem,gm'per gm c loy

Frc. 6. Lattice spacings in A of dried Na-montmorillonite-organic complexes with increasing

organic material in the reacting system'

o.4

o.4o.?

r8

t 6o {

inoo; t 2

to

8

636 G. W, BRINDLEY AND M. RUSTOM

o.2 0.4 0.6 0.8 I .O t .2

Tolo l orgonic in system, gm,pe r gm c loy

Frc. 7. Lattice spacings in A of clried Mg-montmorillonite-organic complexes withincreasing organic material in the reacting system.

value. l\'Iixed-layer sequences do not give truly integral orders of reflec-tion and if inlegral orders are assumed, then the lattice spacings derivedon this basis do not have a constant value. fn Figs. 5, 6, and 7, mean val-ues of d(001), obtained from the observed reflections with the assump-tion of integral orders, are recorded and the short vertical lines indicatethe mean deviations of individual values from the average values. Thefact that the mean deviations are generally small means that, for themost part, the integral Bragg law is obeyed, i.e., the structures are regu-lar.

Between the composition ianges in which only one basal spacing

TesrB 2. Larncn SeacrNcs, rw A, on Dnrro Frr,us ol MoNruonrrroNrrrC o NrarnrNc An s o nnno Por;;:ilrr"Trfiiycol Es :rr n or Oln rc

t 8

t6

l 4

t2

to

oo!t

Expanded clays

Exchange ion Fully driedclay

9 . 6 a

o 7 .

10 .0

Seccnd sta3e of explnr i r r

7 . 8 s

/ . J 6

Ld

Na

Ca

First stage of expansion

Mg

7 . 7 0

ADSORPTION OF ORGANIC MATERIAL BY MONTMORILLONITE 637

cate sheets.

(d,) X-ray eramination of re-wetted' clay-orgonic flms

(e) Stebitily oJ the clay-organic flms to uashing

The effect of repeated washing of the clay-organic complexes was

studied. both before and alter a drying treatment' After each washing the

clay was centrifuged, the l iquid removed' fresh water added and a further

the single adsorbed laYer.

DrscussroN

G. W. BRINDLEY AND M. RUSTOM

Tasrr 3. Lerrrcr SnecrNcs, rx A, or. Dnrnn Monruonrrlolurn-NoNrsolCouplnxns Arrnn Rrpnarnn WlsrrrNcs rx Warnn

Na-Montmorillonite Mg-Montmorillonite Ca-Montmorillonite

No. ofwashings

10l . )

d(001)

77.2 (2-layers)13.9 ( lJayer)

13.7 ( l - layer)

13.8 ( lJayer)

13.7 (l-layer)

13.8 ( lJayer)

No'.of d(ool)wasnlngs

No'.of d(oo1)wasnmgs

17.8 (2Jayers)

10 13.7 ( l - layer)

20 13.8 ( lJayer)

14.2 (l-layer)8 14.2 (lJayer)

12 13.8 ( l- layer)76 13.9 ( lJayer)

77.3 (2-layers)4 17 2 (2Jayers)

12 17.2 (2-Iayers)20 14.0 ( lJayer)

41 22025

13.8 ( lJayer)

13.9 ( lJayer)

13.9 ( lJayer)

13.8 ( lJayer)

13.8 ( lJayer)

lated to the adsorbed organic material and to the totar organic materialin the system.

rt has already been noted that there is a marked tendency towards theformation of ordered complexes containing either one layer or two layersof organic material between successive silicate sheets. It p(n) denotesa regular phase containing n organic layers between successive silicatesheets, andP(n,m) an irregular sequence in which n or ln organic layersoccur randomly between successive silicate sheets, then the sequence ofphases observed as the amount oI organic material increases in the claylattice, is as follows:

P(0), P(0, 1), P(1), P(1) + P(2), P(2).

P(0) symbolizes the pure montmorillonite. p(0, 1) appears as an irreg_ular sequence extending from zero to about 0.07 gm. adsorbed organicmaterial per gm. clay which corresponds to about 12/s ol the saturationvalue.

The ordered phase P(1) extends from about 0.07-0.17 gm. adsorbedorganic per gm. clay, i.e., l27o-307o of the saturated value. The lattice

range 0.17-0.25 gm. adsorbed organic per gm. clay, i.e., 30/6-aZ/6 ofthe saturation value.

This symbol, P(1)+P(2), implies that the co-existing phases are regu-

ADSORPTION OF ORGANIC MATERIAL BY MONTMORILLONITE 639

Iar structures, which is essentially the case, but the regularity is some-

what less perfect than in the single phase ranges. One may therefore pic-

ture the P(1) phase as containing a small proportion of two-layer com-

plex and the P(2) phase a small proportion of one-layer complex, but the

proportions are too small to make any appreciable change in mean lat-

tice spacing except perhaps in the case of the Na-clay' see Fig. 6.

When the adsorbed organic exceeds 0'25 gm. per gm' clay (42/6 ol

saturation), then P(2) alone is formed. This means that even though the

organic material is not quite sufficient to fill one layer to maximum ca-

pacity, a regular two-layer structure is formed. From 42/6-100/6 satura-

tion, the two-layer complex becomes increasingly filled with organic mol-

ecules. Adsorption beyond a two-layer complex does not occur'

In order to visualize how the adsorption complexes are formed, it

must be remembered that the adsorption takes place initially when the

silicate layers are separated in water. The spacing of the dried films is

the result of bringing two adsorbing surfaces together. If each surface

had,50/6 of its maximum adsorption, then it might be expected that the

molecules adsorbed on one surface could be accommodated in vacant

positions on the adjacent surface, thereby producing one completely

filled layer. The results show that for Ca-clay when each surface ad-

sorbs 42/6 of its maximum capacity, a regular two-layer structure is

formed. It must be concluded that the organic molecules are held rather

tightly and are not sufficiently mobile to give a close-packed single layer.

The maximum adsorption on each surface to give a single layer P(1)

complex occurs at 30/6 of its maximum adsorptive capacity. When the

adsorbed organic content exceeds 30/6 of saturation, the P(2) complex

makes its appearance along with the P(1) complex' It is difficult to ex-

plain why some clay particles contain wholly or almost wholly the P(1)

complex and others contain wholly or almost wholly the P(2) complex'

One is almost forced to conclude that there are minor differences be-

tween individual clay particles such that certain particles tend to build

up a P(2) complex at a lower organic content than do other clay parti-

cles. In consequence, as the organic content in the liquid phase is in-

creased, more and more particles pass over from the P(1) to the P(2)

type of complex.Presumably these differences between particles are not sufficient to

influence the initial organic adsorption, for here a mixed-layer phase

P(0,1) is produced rather than a mixture of pure montmorillonite P(0)'

plus a one-layer complex, P(1).One might hazard a guess that the hypothetical minor differences

arise from difierences in chemical composition giving rise to different

exchange capacities and difierent layer charges' On this basis it is con-

640 G. W. BRINDLEY AND M, RUSTOM

ceivable that when the organic content in the liquid phase approaches acertain range of values, some particles wil l be extended to P(2) com-plexes while others sti l i remain as P(1) complexes.

AcrNowrBoGMENrs

This work forms part of a program made possible by a Grant-in-Aidfrom the Gulf Research and Development Company, Harmarvil le, Pa.The purif ied montmoril lonite was kindly made available by Dr. J. L.\{cAtee, and the Baroid Sales Division, National Lead Company,Houston, Texas, and the organic agent by the Geigy Chemical Corpora-tion.

RBlonnNcos

Bannen, R. M., aNn Mecl,ron, D. M. (1955), Activation o{ montmorillonite by ion-exchange and sorption complexes of tetra-alkyl ammonium montmorillonites, TransFaraday Soc., 51, 1290-1300.

FnaNzeN, P. (1955), X-ray analysis of an adsorption complex of montmorillonite withcetyltrimethyl ammonium bromide (iissolamine), Clay Min. Bull, ,2,223-225.

Greserrrc, J. E. (1S39), Mechanism of cation exchange in the montmorillonite-beidellite-nontronite type of clay minerals, Soil 9ci.,47, l-74.

Gr..trsnn, R., exo MfnrNc, J. Q952), Les propri6t6s des associations organo-argileuses,Congris Geol. Inter , Alger.,18,117-127

Gr.ensnn, I{., ,r.Nl MfnrNc, J. (1954), Isothermes d'hydratation des montmorillonitesbi-ioniques (Na, Ca), Clay Min. BulI.,2, 188-193

Glarsrn, R. (1954), Complexes organo-argileux et r6le des cations 6changeables, 1-68,Thbse (Paris)

Grncvr-Knr,r,v, R. (1955), An unusual montmorillonite complex, CIay Min. BulL,2,226-232.

Gnru, R. E. (1953), "Clay Mineralogy", Ch. X, pp 25O-277, McGraw-Hill, New YorkHlxarno, A., exo Br.ocn, J. M. (1956), Sorption de mol6cules organiques azot6es par la

montmorillonite Etude du m6chanisme, Bull. Soc. FranE. Min. Crist.,79,464475.HnNDucrs, S B. (1941), Base-exchange of the clay mineral montmorillonite for organic

cations and its dependence upon adsorption due to Van der Waals forces. J. Phys.Ckem., 45, 65-87.

Jonnam, J W. (19.19), Organophilic bentonites, I Swetling in organic liquids, -r. P/zys.and CoIl. Chem ,53.29+306.

JoroaN, J W. (1949), Alteration of the properties of bentonite by reaction with amines,Min. Mag.,28, 598-605.

Jonr,ur, J. W., aNn Wrr.rrans, F. J. (1954), Organophilic bentonites. IIf Inherent proper-ties, Koll-Zei,t., 137, 40-48.

MacEwaN, D M. C. (1951), The montmorillonite minerals; Ch. IV, pp.86 137, in "X-ray Identification and Cr1's121 5,.u.,nres of Clay Minerals" Mineralogical Society,London.

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Manuscr'i,bt receiteil Oct. 5. 1957