Equilibration of Kaolinite in AqueousInorganic and Surfactant Solutions!

H. S. HANNA! AND P. SOMASUNDARANH~"" Krumb School of M;n~.f. Columbia Univ~r.f;ty. N~w YoI-k. New York 10017

Received October 6, 1978; accepccd November 27. 1978:-

Equilibradon of a aatura1 kaolinite sample and its purified sodium fonn in water and aqueous solu-tions ofNaC and sodium dodecyl beuzcoesulfonate (SDDBS) and sodium dodecyl sulfonate (SDDS)involves a fast ioa-eXchaDle and/or electrOStatic adsorption step and a slow step possibly due to dis-solution of aluminum species upon prolonged contact of kaolinite with water. Equihoration proc-esses were found to depeud on ionic StfenJth. pH. and t~ent of the sample. Past studies usingkaolinite appear not to have considered the possibility of an intennediate metastable condition whichcould be responsible for a number of contradictina results found in the literature. Ex2~i~tion of re-sults obtained for the sulfonate under various ionic Streasths and hydrogen ion concentrations sug-Jests a complex adsorption mechanism involvina ion-excbange. electrOStatic. metal activated modesof adsorption and precipitation dependial on the solution pH.

swfactant system have in fact shown a closerelationship between the adsorption of ani-onic surfactants and the suuctural propertiesof the water layers in the interfacial region.In this work, the clay/alkylsuJfonates sys-tem was studied under relevant pH and ionicstrength conditions and the results wereanalyzed to obtain information of the natureof interaction of clay with aqueous inorganicand swfactant solutions.

INTRODUcnON

The time of contact of clay minerals withwater or aqueous solutions may range froma few minutes, as in the case of flotation, toseveral months, as in the case of tertiary oilrecovery. Considerable differences in theresponse of the mineral owing to changes insuliace and rheological properties can oc-cur during such times (1-10). Equiliorationof mineral particles with aqueous solutionsis a complex process even for simple oxideand salt-type minera1s(11-16). The slow ap-proach of equiliorium that is often observedhas been attributed to the relatively low sur-face mobility of some of the dissolved species,particularly hydrolyzable surface cationsor anions t7), and the presence of orderedwater layer on the mineral that could affectthe rate of diffusion of large complex hy-droxy species to and from the bulk solution(17-21). Recent studies (22, 23) on clay!

MATERIALS AND METHODS

Kaolinite. A "well-crystallized" sampleof Georgia kaolinite purchased from the clayrepository at the University of Missouri wasused for the present tests. The surface areadetermined by nitrogen adsorption was 9.8mZ/g. From this sample, designated as"kaolinite," the homoionic "Na-kaolinite"was prepared in the following manner: (a) Thedry clay was treated with water for 10 min ina high-speed mixer at a solid to liquid ratioof 1 :2. The product was diluted with dis-tilled water to 2 to 3% solids, allowed tosettle, and the supernatant was discarded.This process of washing was repeated 7 to 10

'\.,

I Paper presented at the S2nd conoid and Surface

Science Symposium. Knoxville. June 1978.2 Present addre3S: Mineral ResoW'Ccs Institute. Uni-

versity of Alabama. P.O. Drawer AY, University,AJabama3S486. ,

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182 HANNA AND SOMASUNDARAN

and pH were of A.R. grade. Triple-distilledwater was used for all tests.

Adsorption. Adsorption tests were con-ducted in Pyrex vials by precontacting S to20 g of clay with water or salt solution for2 hr and then adding the surfactant solution.The sealed vials were then agitated on awrist-action shaker in an incubator main-tained at the desired temperature. At the endof the test, a sample of the supernatant solu-tion was centrifuged at 15008 for 20 min,and the liquid above the mineral layer wasthoroughly mixed and analyzed for residualconcenttation of 'the sulfonate. From thedifference between initial and final values,adsorption of the surfactant was calculated.The concenttation of the surfactant wasdetermined by the two phase tittation tech-nique using a mixed indicator of dimidiumbromide and disulfine blue (26).

l

RESULTS

Aging of Natural Kaolinite

Results obtained for the change in pH ofwater and NaCI solutions on adding drykaolinite 3J'e given in Fig. 1 as a function ofthe time of contact of the solid with solutions.Generally, addition of kaolinite to the aque-ous solutions produced a sharp drop in thepH during the first few minutes, followedby a slow. increase of pH. It appears fromthese data that equilibration of dry kaoliniteparticles with the aqueous phase involves atleast two steps, i.e., a fast step that wasfound to depend on NaCl concentration anda slow step that may be governed by variousdissolution processes.

times until there was no change in the con-ductivity of the supernatant. (b) The washedkaolinite was agitated with 2 M NaCl solu-tion at high solid to liquid ratio for 15 min;the suspension was diluted and reagitatedfor 2 hr before sedimentation and decanta-tion; this procedure was repeated 7 to 10times until a pH of 7 was reached and theconductivity of the supernatant remainedconstant. (c) The NaCl-treated product wasagitated at high solids concentration with1 M NaCl and at pH 3 to remove Al(OH)asurface contAminAtion. The product wasdiluted and washed until a constant conduc-tivity. and a supernatant pH of 7 were ob-tained. (d) This washed product was treatedwith 0.1 M NaCl and washed several timesuntil constant conductivity was reached.During the last washing steps the fine clayparticles were separated from the coarseimpurities by decantation. The Na-kaoliniteproduct thus obtained was filtered and driedat 500C for 3 to 5 days and stored dry.

Surfactants and chemicals. Sodium do-decyl su)fonate (SDDS) from Aldrich Chem-ical Company specified to be 99+% purewas used as received. Surface tension ver-sus concentration curve obtained for thedodecyl sulfonate showed it to be surfacechemically pure.

A sample of sodium dodecyl benzenesul-fonate (SDDBS) from Lacbat Chem. (spec-ified to be 95% but analysed to be 85%) waspurified as follows. The material was driedunder reduced pressure over phosphoruspentoxide at 50 to 6QOC, followed by extrac-tion with dry distilled diethylether in a soxh-let apparatus. The first fraction (20-30% byweight) was discarded and from the laterfraction (30-40%) the ether was evaporatedand the residue was recrystallized threetimes from acetone. A 98.1% SDDBS prod-uct and showing no minimum in surface ten-sion vs concentration curve was obtained.Infrared spectra of the purified material in-dicated predominance of p-DDBS isomerwith trace amounts of the ortho-isomer. Theinorganic salts used to adjust the ionic strength

I'

Equilibration of Prewetted Kaolinite inSurfactant Solutions

The results obtained for the adsorptionof sodium dodecyl sulfonate on prewettedkaolinite samples at 30"C and an ionic strengthof 10-1 M NaO are given in Fig. 2. The ad-sorption kinetics curves obtained are char-acterized by the presence of two plateaus,one at an adsorption density of about 1.4

J--.4I/c.--a41.~$cNIOCW. Vol.,., No. 1.J_l. 1979

EQUILIBRATION OF KAOLINITE 183

KAOUNITE I HoC.

\~~SOLIOS . 1~

~ . 30~ o.I"CN2 GAS

-~-~

--\'- T.O.W.

"1 ~~~=;~:::::::::::::::~:- - ~'JM NIQ- Vi" M '-C1

~~~::::=:--- 3.~"::iM N8C1- 5~-aMN8C1

am . ~1 . ~O . ~ . 1~TIME, IOriR.

FIG. 1. Eft'ec:t of addition of dry kaotiDite au !be pH of deaeratcd tripie-<tistiDed water at various NaCtcoaceDtratiODS as a function of tbe time of contact of the solid with solutions.

of SDDS/kaolinite system. However, theinitial rate of adsorption in this case is muchhigher and only 5 to 10 min are needed toreach the first apparent equihorium condi-tion.

.u.moles/m2 and the other at 1.8 lJ.1I1oles/m2.Adsorption increases rapidly during the first40 min, remains at an apparently constantvalue for the next 5 hr, and then increasesagain to reach another limiting value in about100 hr.

The kinetics curves for the sodium do-decyl benzenesulfonate adsorption on Na-kaolinite at different solid/liquid ratios aregiven in Fig. 3. These isotherms also showthe two step behavior observed for the case

\

F.ffect of Pretreatment of Kaolinite onSulfonate Adsorption

Results obtained for tbe adsorption ofdodecyl benzenesulfonate under constant

J-.-afC", ~SN", V... 70. No. I.J_/. tm

184 HANNA AND SOMASUNDARAN

OODECYI.8£NZEPCSUI.FONArt / No -KAOI.INIT£

2.0'N

....'I

1

,......z

'!

z1.QaGo!!c

--.e--'. ...-10.. SQ.JOS

m.. ~IOSt . 1O~N8CI -8-40.. SOUOS

,.. . S.7.t o.z.~ . 3O.t o.S.C

IMTiAi. SRCGc. . S.I.M/I. .. .. ..- 0-1 Q.5 1 5 10 ~ ~

AOSOR~TION TlMC. ~--

FIG. 3. Adsorptioa kiDetics of dodecyl beazeaesulfoaace on prewetted Na-kaoliDite at differentsoIid/Iiquid ratios.

0.0'

ionic strength conditions and at three dif-ferent pH values on prewetted Na-kaoliniteand prewetted as received kaolinite sam-ples are given in Figs. 4-6. The adsorptionisotherms are characterized by the presenceof maximum under all conditions. It mightbe noted that in the case of as received sam-

pies. the adsorption tended toward zero oreven negative values in concentrated sur-factant solutions.

The adsorption capacity of purified Na-kaolinite samples was higher than that of theoriginal as received sample at all pH values.

Effect ofpH

The results in Fig. 7 show clearly thatadsorption of dodecyl benzenesulfonate onNa-kaolinite sample is highly sensitive tohydrogen ion concentration. To obtain in-

,.

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185EQUIUBRATION OF KAOLINITE

formation on adsorption as a function offinal pH under constant equilibrium con-centration of the surfactant. the data givenin Figs. 4-6 were treated to generate theplots given in Fig. 8. It can be seen that sul-fonate adsorption increases markedly withincrease in hydrogen ion concentration. par-ticularly in the acidic pH range. but the gen-eral shape of the adsorption isotherm is un-altered. In the acidic pH range the maximumamount of SDDBS adsorbed was found to

correspond to a compact monolayer with amolecular area of 33.7 As/SDDBS mole-cule. This value is in agreement with the re-ported values for close packed monolayersof dodecyl benzenesulfonate on CaCOs andCa,(POJ, (25, 26). The adsorption densitiesin the neutral and alkaline pH range, how-ever, were found to correspond to only 25

5 . . 10,"FIG. 8. EB'ect oCpH on SDDBS adsorption on the untreated original kaolinite and Na-kaolinite samples.

;-.- II{ ~.. J-.,f8e- sa voL ,., No. I. J- I. 1979

186 HANNA AND SOMASUNDARAN

OO«~~IU\.FOU~ I ~-KAQ.INI~

eo~ - 10" M N8CIi _1O-a.~ #I -M)N8CI~ .~ ,

)."2.0~ . I4OKI U:r SIt u ~

8 ~:!:~=::i=-~~~=: i.. 1.0 , 11,0 I

.. Uru~JU . . . 'w

0 10 ~ 30 40 50

~~IM~M ~CENTR&TI<*. ~I

PIG. 9. E&ct o(icmi!: ItreIIIIh ~ the ~ 0( SDDBS oa N~~i.e at D8tIIn1 pH ofthc pulp

precipitation of resultant complexes. Thepossible role of the above processes in de-termining the equilibration of kaolinite withaqueous solutions is examined here with thehelp of data obtained under various condi-tions of pH. ionic strenam. and sulfonateconcenttatioos.

and 12% of close packed monolayer, respec-tively.

Adsorption isotherms obtained under var-ious ionic strength conditions for kaolinite!SDDBS system at the natural pH of the pulpare shown in Fig. 9, which sugest that theadsorption of sulfonate on kaolinite is en-hanced by the addition of salt. In these testspH was found to decrease from an initialvalue of about 6.8 to 5.9 and 5.3 in 10-1 and10-1 M NaCl, respectively. and from 6.8 toabout 5.8 with 5 x 10-1 M SDDBS alone. Toderive the effect of ionic strength alone twoseries of adsorption experiments were con-ducted at constant pH values and a summaryof these results is given in Fig. 10 as a func-tion of pH at constant equiliorium surfactantconcentration levels. It is evident from thisfigure that adsorption of sulfonate on kaolin-ite is enhanced but only slightly with increasein ionic strength.

HydrolysisThe process of equih"bration of dry kaolin.

ite with the aqueous pbase involves at least

DISCUSSION

Several physicochemical processes canbe expected to take place when clays arecontacted with electrolyte solutions and tocontribute toward determining the overallbehavior of the resulting suspemions. Majoramon. such processes are recognized to behydrolysis of surfaces species. ion-exchaDge,electtostatic adsorptibns and dissolution ofthe clay constituents, and adsorption or

10

FIG. 10. EffKt OD ionic streDItb OD Ibe ads«pbODof SDDBS at CODstaat equilibrium CODcentraUOD as afuDdioa 0( pH It 30 ~ O.SOC.

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EQUIUBRATION OF KAOLINITE 187

two steps (Fig. 1). The fast step can partly beaccounted for by hydrolysis reactions in-volving surface species on kaolinite. Paststudies (24,27 -29) have suggested the sourceof acidity on kaolinite to be the terminalbonds and sttuctural coordination acrossthe edge faces either due to the siIanol groupsor due to aluminol groups at the strainedgibbsite layer. In aqueous solutions, thebroken bonds at the edge surface of drykaolinite will be hydrated and converted toa hydroxylated surface. Bronsted acid gen-eration, which is likely under these condi-tions can result from one of the followingdeprotonation processes (fast) (6):

ite/SDDBS system under various pH condi-tions (Fig. 7 and 8). In this case while thefinal pH of this system in the acidic rangewas always higher than the initial value (ini-tial pH of3.1 shifted to a final pH of 4.6), theopposite was true in the neutral and alkalinepH range (initial pH values of7 and 11 shiftedto 6.5 and 9.6, respectively). These observa-tions can be explained in terms of the ampho-teric character of the terminal aluminumions on the kaolinite surface and its anionicand cationic exchange properties. In theacidic pH range, the sulfonate ions can ex-change with the surface OH- ions leading toan increase in the pH of the solution. Such amechanism is widely accepted by many in-vestigators for the adsorption of phosphateson clays. The drop in the pH of the clay sus-pension from 11 to 9.6 in the alkaline regioncan also be explained in te~s of the ex-change of the negatively charged sulfonateions with aluminate anions. The formationof aluminate ions is accompanied by OH-consumption as shown by the following re-action (31):

l'0I .

m-U-O-SL-o -.I I. .

-..+--

~

t-oI .

ao-U-O-SL-o .. + ...I 1(_)

. ~ 0t-OI .

8-U-O-U-o-++",I I0(-) ~

V1AltSitO,(OH).(s) + 'hHtO

+ OH-;:t Al(OH). + ~SiO4

pK = -5.7

Ion-ExchangeThis process is characteristic of clay min-

erals since exchangeable cations are presentas counterions in the clay (5, 30). This pos-sibility is supported by the fact that increasedacidity resulted upon adding NaO to thesystem (see Fig. 1):H - Kaolinite + Na+ # Na

- Kaolinite + H+ (fast)

The hydrogen ions released under suchconditions should be related to the ion-ex-change capacity of the clay. The decreasein pH observed here at 5 x 10-1 M NaOcorresponds to about 63 iJ.Eq/g of clay. Suchan ion-exchange process is expected to befast and therefore can partly explain the fastpH drop observed.

Additional possibilities for ion-exchangeexist in the presence of sulfonate in the sys-tem. Information on these can be obtainedby examining the pH changes in the kaolin-

The surface coverage of7 to 8% monolayercalculated from the ion-exchange reactionis close to the 12% observed at pH 9.6.

As discussed earlier, exchange betweenNai- and Hi- ions is an important processthat explains the results presented in Fig. 9.The decrease in pH is the direct result of ion-exchange between the surface H+ ions onkaolinite by Na+ ions from all the addedsalts. The resulting change in pH will haveits own effect on the adsorption of sulfonateon the mineral. This indirect effect can infact predominate the direct effect of changesin ionic strength (Fig. 10).

From the above discussion it can be con-cluded that ion-exchange can be a majormechanism responsible for adsorption.

J-- 0/ ~ lN~~ Sd V.. 7Q. No. I. S- I. 1979

188 HANNA AND SOMASUNDARAN

molecules associated with each edge proton,one completing with coordination sphereof the edge octahedron and the other closelyassociated with the silanol group (6). Pro-ton mobility from silanol groups to the alu-minum octahedra is considered to produceexchangeable aluminum ions after longperiods of time. The decre3Se in the acidityof kaolinite suspension with time is attrib-uted to the release of such exchangeablealuminum ions into the system. The highlycharged Al3+ species could readsorb on themineral surface in different fonns after aseries of hydrolysis reactions that producecomplex ions such as Al(OH)Z+, A1.<Offi.++,Al(OH)" and Al(O~)-. Such a process canbe expected to be very slow in comparisonto the dissociation of the weakly acidicgroups on kaolinite surface. The adsorptionthat results from the slow release of alumi-num species during the initial period will beof a smaller magnitude than that due to elec-trostatic or ion-exchange reactions and anapparent equilibrium could therefore be at-tained (Figs. 2 and 3). At longer contacttimes. however, the slow release of increas-ing amounts of charged aluminum speciesfrom the basal kaolinite surfaces into thesolution followed by their adsorption on thekaolinite surface will be an important processparticularly in the acidic and basic pH rangeswhere concentration of dissolved aluminumspecies is considerably higher than in theneutral range (see Fig. 11). This will increasethe affinity of the negatively charged sulfo-nate toward kaolinite surface and hence anincrease in adsorption, especially at low pHvalues. Under such conditions a new equi-librium is obtained in time intervals thatwould be dictated essentially by the kineticsof release of aluminum species and theirsubsequent hydrolysis and readsorption.

Past studies (36-40) using kaolinite donot appear to have considered this possibil-ity of an intennediate metastable condition.Implications of such a metastable conditionin the interpretation of adsorption datashould be noted.

Electrostatic Adsorption

The presence of charge at the edges aswell as faces of the kaolinite particles canindeed be expected to influence the adsorp-tion of both organic and inorganic species.In addition to the fact that the nature of thesecharges will vary considerably from edge tosurface of a particle, complications arisealso due to readsorption of dissolved chargedmineral species such as that of aluminum.

The abnormal two-step adsorption kineticscurve obtained for kaolinite (Figs. 2 and 3)reflects the complex solution chemistry andthe resultant interfacial behavior of thismineral.

The amounts adsorbed at the first plateaucorrespond only to about 5% of compactmonolayer suggesting that the adsorption ofthe sulfonates in this region is limited to thepositively charged edge surfaces of the kao-linite particles, which were reported in cer.tain cases to be about 2 to 5% of the totalarea (6). H+ and OH- ions are considered tobe the potential detennining ions for thecharged edge surfaces and therefore With adecrease in pH the number of positive siteson the mineral and the adsorption of theanionic surfactant will increase.

While such a simple mechanism prevailsfor adsorption of sulfonates on simple oxideminerals (32, 33), its role is expected to belimited in the case of kaolinite because thesurface area occupied by the positivelycharged edge groups does not exceed 2 to5% of the total surface (6). From the datagiven in Fig. 3 it has been shown that thetotal coverage of sulfonate does exceed thatof 5% monolayer.

Dissolution of Surface Species

The slow pH changes following the initialfast pH drop observed (Fig. 1) during equil-ibration of kaolinite with the aqueous phasesuggest occurrence of slow processes suchas dissolution and hydrolysis of surfacespecies of aluminum and silicon. It has beenpointed out recently tba~ there are two water

J~ "'~ ""~ ScM_. Va'" No. 1. ~ 1. 1m

EQUlUBRATlON OF KAOLINITE 189

from clay by an ion-exchange mechanismhas been found to cause precipitation ofsulfonate at low concentrations; precipitatesubsequently redissolved at higher sulfonateconcentrations (34). This pbenomenon basbeen shown to contnoute toward the ad-sorption maximum observed for the kaolin-ite/alkyl sulfonate systems (35).

17I~W

Pretreatment of Clay>-...0:zc5

i...

!

§

I

" ~ I

I . 8. . 10 .. I.

The role of aluminum species and thechange in their relative concenttations uponpretreatment of kaolinite in controlling theadsorption of sulfonate can in fact be verysignificant. For example. the actual cover.lie obtained for sulfonate adsorption 011alumina is found to corTespond to a closepacked monolayer under acidic pH condi~tions and such coverage is made possiblepartly by the generation of secondary posi.tive sites owing to specific adsorption ofAl'+ ion and its complexes to the basal nega-tive kaolinite crystal. Acid leaching studiesof Buchanan and Oppenheim (7) and Conelyand Althoff (6) have in fact confinned thepresence of conoidal aluminum hydroxide invarying quantities on aged kaolinite par-ticulates. Also. the dissolved Al3+ and itshydroxy complexes can be expected to reactwith the bulk surfactant species to formaluminum sulfonate complexes that caneasily adsorb on the kaolinite surface. PR.cipitation of aluminum sulfonates in bulksolution is also a ~or contributing factor.In addition. the presence of other importantmultivalent cations such as CaJ+ released

,"Flo. 11. Solubility-pH dia&ram of kaolinite [after

~a and Oppenheim (7)].

"--"c..- ~ ' r $~. Va 7Q. No. I. "- I. 1m

The observed difference in adsorptioncapacity between the "kaolinite" and "Na-kaolinite" suggests that the kaolinite sur-face, during the purification process, wassubjected to certain physicochemical changessuch as removal or introduction of swfacecomplexes or impurities and alterations inthe hydration properties of the solids. Pro-longed treatment of kaolinite with water forthe purpose of removing associated solublesalts can result in the generation of ex-changeable aluminum species on the min-eral surface as discussed before (5-8). It basbeen shown recently that even the so-called"At-free" homoionic sodium kaolinite gen-erates as much as 10-' M At3+ in 10-1 M NaOsolutions. Surface contamination by hydro-lyzed silicon species is also possible (7).

It is of interest to note that in the case ofas received sample, adsorption of sulfonatetends toward even negative values in con-centrated surfactant solution. Such behav-ior is characteristic for minerals ofhigb watersorption capacity such as montmorilloniteand suggests presence of this type of min-erals as impurity in the original sample. Ap-parently the impurities were removed fromthe Na-kaolinite sample during the washingand decantation steps due to their fine par-ticle size and resultant slow settling. An in-crease in the effective surface area of thepurified Na-kaolinite during the process oftreatment may also be partially responsiblefor its higher adsorption capacity as themeasured nitrogen surface area is only a fewpercent of the theoretical value of this miD-erall073 m%/g(41). Changes in surface prop-

190 HANNA AND SOMASUNDARAN

enies can also occur during storage of the 3. Hurd, B. G., Paper SPE Sl18, Improved Oil Re-purified clay for long periods. Stored sam- covery Symp. of SPE AlME, Tulsa, MarcbI xhib ' d I ads . . . 22-24 1976

pes e rte ower orp~on capac~tI.es 4. Trushens'ki, s.' P., DaubeD, D. L., and Parrish.than freshly prepared purified kaolinite, D. R.,Soc. Petro En,. J. 633-642 (Dec. 1974).samples (see Fig. 7). Similar observations 5. Swanzeu-ADen. S. L., and Matijevic, E.. Chem.have also been made by Martin (30) who Rev. 74.3,385 (1974).emphasized the need for extreme care in the 6. Conley, R. F., and Althoff. A. C.. J. Conoidpreparation of kaolinite and suggested that Inter/ace Sa. 37. I, 186 (1971).

. . . Jar . be 1. Buchanan. A. S., and Oppenheim. R. C..AllSt. J.expenments on a paniCU specImen C/rem. 11 2361 (1968) and 15. 18S1 (1972)completed within a few weeks to obtain 8. Rand, B., ~ Melton, I. E.. J. 'Colloid Inteifaceconsistent and meaningful results. Sci. 60.2.308 (1977).

9. Swartzeo-AlleD, S. L., and MatijeviC, E.. J. Co/-CONCLUSIONS laid Inter/ace Sci. 58. t, 143 (1975).

Both the equilibration of the kaolinite with 10. Davey, B. G., and Low, P. F.. Soil Sci. Soc. Amer.d th ad . f alk I 1£' Proc. 35. 230 (1971).

~er an e so.rpUon 0 y Suuonates 11. Kultami. R. D.. and Somasundarao. P..in "Oxide-on It were found to mvolve at least two major Electrolyte Interfaces" (R. S. Awiu, Ed.),stepS. Also the final adsorption obtained p. 31. ~hem. Soc.. 1973.was dependent strongly on the pretreatment 12. SomasuDdalan, P .,J. Colloid Inter/ace Sci. 17.659

that the clay had unde~one as well as the 13. So=~aran, P., and Apr, G. E.. J. Colloidextent of subsequent aging. Inter/ace Sci. 14.433 (1967).

Changes in pH of water due to its con- 14. Parks, G. A., in "Chemical OceanOlraPhy" (1. P.tacting with kaolinite are attributed mainly Riley and G. SkirTOw, Eds.), 2nd ed., p. 241.to the ion-exchange propenies of the clay Academic Press. New York. 1975.and reactions of dissolved aluminum and 15. 1ohansen, P. G.. and Buchanan, A. S.. Au"t. J.-:'1:- . .th th bulk S..1~ Ch,m. II. 392. 3M (1957).3u.a#on s~s WI e ~r. uuonate 16. SchuyleDborlb. J.. Ames, P. L., and K:ock.adsorption. on the other hand. IS the result J. G. J., R,c. Trav. CMm. 69. 1m (1950);ofacombined mechanism involving electro- SchuYIeDOorlt1. J., Traa. 4tlt Int. Con,r. Soilstatic adsorption. ion-exchange. metal acti- Sci., Amsterdam 1.89 (1950) and 1, 63 (19$0).vated adsorption and p~ipitation. Dis- 11. ADdersoD. D. M., aM Low, P. E., Soil Sci. Soc.

I . f al " of Amer. Proc. n. 99 (1958).souuon 0 ummum specIes appears to 18. Derjaauin,B.W..andSamypn,M.M.,Acad.Sci.playa major role in determining the inter- SSSR. cited in Ch. 75, Acta Poly. $ca., p. 34.facial propenies of the system particularly 1968.through the latter two modes of adsorption, 19. Udstrom. L., Acta Poly. Sca. Cb. 75, 34 (1968).

20. Drost.HaoseD, W.,J. Conoid Inter/ace Sci. 15. 131(1968).

ACKNOWLEDGMENTS 21. Benlbe, Y. G., and deBnsyn, P. L., J. Colloid

Support of the National &ience Foundation. Amoco Inter/ace Sci. 18. 92 (1968).Production Company, Chevron Oil Field R~h 22. Somasundarao, P., and Hanna. H. S.,SPE 7059.Company, Exxon R~b and EDliDeerinl Co.. Paper presented at the SPE/AIME Fifth Symp.GuifResean:b and Development Company, MaradKJa on Improved Oil Recovery, Tulsa. April 1978.Oil Company. Mobil ~b and Development D. Hanna. H. S., and Somasundarao. P.. Paper pre-Compaoy, SheU DevelopmeD1Company. Texaco, Inc., seated at the AIChE Natiodal Meetina. Phil.and Union Oil Company of California is aratefuDy adeipbia. June 1978.acknowledaed. 24. Reid. V. W., Longman, G. F., and Heinen.h; E.,

Tenside 4.9, 292 (1967); 5. 3, 90 (1968).REFERENCES 25. Hanoa. H. S., and Saleeb, R. ZO, Paper presented

at 14th ACS Midwest RePonaI Meedng. Fayette-1. Somasu!!'i-.!-wan. P., "Re~ Needs in Mineral vUle. Arkansas, Oct. 26-27, 1978.

Processing," NSF Workshop Report, Columbia 26. Hanna. H. S., Ph.D. Thesis, Aim Shames Uni-University. New York, 1975, p. 125 (1976). vemty, Cairo, 1968.

2. Trahar,W.1.,andWarren,L.1.,Int.J.Min/.Proc- 27. Uoyd, M. K., and Conley, R. F., Clays Clayess. 3. 103 (1976). Miner. Is. 37 (1970).

l-- ..c~ I"~ Scil~. "w. 70. No. 1. ~ I, 1979

,.

191EQUIUBRATION OF KAOUN1TE

28. Mukherjee. S. K.. and GanguUy. A. K.. Ind: J.Phys. 14,223(19-'2).

29. Grim. R. E.. "Clay Mineralosy." 2nd ed.. p. 193.McGraw-HiD. New York. 1968.

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