Philip b. Lorenz-surface Conductance and Electrokinetic

8/2/2019 Philip b. Lorenz-surface Conductance and Electrokinetic

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Clays and Clay Minerals, 1 9 6 9 , V o l . 1 7 , p p . 2 2 3 - 2 3 1 . P e r g a m o n P re s s . P r i n t e d i n G r e a t B r i t a i n

S U R F A C E C O N D U C T A N C E A N D E L E C T R O K I N E T I CP R O P E R T I E S O F K A O L I N I T E B E D S

P H I L I P B . L O R E N ZBartlesville Petroleum Research Center, Bureau of MinesU.S. Department of the Interior, Bartlesville, Oklahoma( R e c e i v e d 1 M a r c h 1969)

Abstract-A technique was developed for forming clay beds of uniform porosity between 48 and62 per cent. The surface conductance and streaming potential of sodium kaolinite were determinedover a range of values. Zeta potential as calculated from the classical formula was about - 30 mV atneutral pH and changed sign at pH 4. The surface conductivity of the sodium clay at various pH valueswas directly proportional to the zeta potential and from 12 to more than 30 times as large as thecalculated electrokinetic surface conductivity. Similar measurements were made on kaolinite in theacid (hydrogen-aluminum) and calcium forms. The acid clay fitted the experimental correlation foundfor the sodium series, but the calcium clay, with less than one-tenth of the zeta potential of the sodiumclay at neutral pH, had half its surface conductance. The results are interpreted as showing thatexchangeable ions on kaolinite are mostly in a condensed layer on the surface where the mobilitydetermines surface conductance. The surface mobilities for Na, Ca and H-A1 are 20, 8 and 0 per centof normal, respectively. Apparently hydrogen ion from the solution is very effective in replacingsodium, which exhibits its electrokinetic and conductive properties in proportion to its concentrationon the surface.I N T R O D U C T I O N

THE SURFACEconduct ance of clays and the stream-ing potentials they generate are important in petro-leum production because of their influence onelectric logs. The two properties are closely as-sociated, but agreement has not been reached onhow far the two can be quantitatively related.Experimental values of the surface conductance ofclays and related materials are usually largerthan the predictions of the classical theory in-volving zeta potential (Overbeek, 1952; Street.1956, 1960; Holmes e t a l . , 1965; James. 1966).This disagreement with theory has been ex-plained in various ways. Bikerman (1942) suggest-ed that materials such as clays, which are capableof swelling in aqueous media, form a gel la3,eron the surface that is conductive but electrokin-etically inactive. Other theories have suggestedmobility of ions in the Stern layer (Urban e t a l . ,1935) and conduction by ionizable surface hy-droxyl groups (Holmes e t a l . , 1965). These ideasare not mutually exclusive. It should also be re-member ed that calculations of zeta potentialdepend on the dielectric constant and viscosity,which may have abnormal values near the surface:that the compression of double layers in finepores (e.g., Oldman e t a l , 1963) is often not takeninto account; and that the effect of surface con-

ductance on streaming potential in randomlyinterconnected pores cannot be evaluated pre-cisely (Overbeek and Wijga, 1946). The resultof these uncertainites is to make calculated zetapotentials too low, which tends to accentuate thediscrepancy between calculated and measuredsurface conductivities. This error is partly com-pensated for by the fact that measured surfaceconductivity values are also too low, since thetortuosity of the pores is usually assumed to bethe tortu osity effective for the surface as well.The present work was designed to study thefunctional relation between surface conductivityand zeta potential on kaolinite. Measurementsmade over a range of zeta potential indicate theform of the function, and comparison of thiswith the theory is more reveal ing than a compari-son of individual values. It is of particular interestto determine whether surface conductance dis-appears when the zeta potential becomes zero.In this way, information should be gained aboutthe properties of the kaolinite surface.Rutgers and De Smet (1953), working withglass, and Street (1958), working with an ionexchange resin, varied the zeta potential and founda minimum in surface conductance at the iso-electric point. However, the results were notfurther analyzed.

223


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224 PHI LIP B. LORE NZE X P E R I M E N T A L

Preparation of clay bedsThe kaolinite used was Peerless No. 2,*a pro-duct of R. T. Vanderbilt Co. It was converted by

leaching with NaCI, CaCI2, or HCI to the sodium,*Reference to specific brand names is made for identi-fication only and does not imply endorsement by theBureau of Mines.

calcium, or acid form, and equilibrated at the de-sired concentration and pH. The equilibrated sus-pension was centrifuged in small batches to forma paste. After the batches were mixed, the claywas placed in the side chamber, No. 11 in theapparat us shown in Fig. I. The cell portion (No. 1),made of Plexiglas, was evacua ted with an aspiratordown to the vapor pressure of water (about 25 mmof mercury). The clay was extruded through a

/2

/ /

4Fig. 1. Schematic section of cylindrical Plexiglas cell and fillingapparatus. 1. Measuring cell with lower electrodes in place; 2. Tapfor solution access; 3. Lower cap; 4. Tap for electrode lead; 5.Flanges, bolted together and sealed by O-ring; 6. Tap for vacuum;7. Electrode; 8. Perforated Plexiglas disk (with filter paper); 9.Extrusion attachment. Replaced after extrusion by upper cap andelectrode; 10. ~" hole for extrusion; 11. Clay reservoir; 12. Piston,screw-driven (with sliding O-ring seal).


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SURFACE CONDUCTANCE AND ELECTROKINETIC PROPERTIES 225~in. hole, No. 10, into the evacua ted region. Thevertical piston, No. 12, was used to apply justenough pressure to compress the clay into bedsfree of visible voids. Bed thicknesses varied from1.2 to 2.4cm. The cell had cross section of 35cm2. The vac uum was br oken by admitting equi-librium solutions. Beds were permeated by severalpore volumes of solutions, with a head of about2 m of water upstream before meas urements weremade. It is assumed that during the equilibrationperiod (several weeks) the acid clay exchan ge sitesacquired a substantial population of aluminumions.Fractional pore volumes ranging from 0.48 to0.62 were obtained by using different speeds onthe centrifuge. With the sodium clay, measure-ments were made with solutions of NaCI in twoseries of co ncent ratio ns, 0.6 and 2.0 meq/1. Withineach series the pH was varied between 4 and 11by substitu ting HCI or Na OH for part of the NaC1without significantly changing the ionic strength.After measurements on the beds, the solutionconductivity and pH values were measured andused to calculate the final actual concentrations ofNa +, CI-, H +, OH- , and sometimes HCO3-. Thecalcium clay was measu red in equilibrium withCaC12 at c oncen trat ion 1-4 meq /l, and the hydro-gen- alumi num clay in 0.01 meq/ l of HC1. Allmeasurements were made with the cell maintainedat 25.00~ in an oil bath.

S u r f ( I c e a r e (lFractional pore volume (porosity) and hydraulicpermeability were measured for use in calculatingsurface area from the Kozeny -Carm an equation.Permeability was measured by the pressure-declinetechnique (Dodd e t a l . , 1951) with a maximumpressure of 30 cm of water. Linear uniformit y ofthe beds was tested by slicing the beds in to sectionsand measuring the porosity of the sections. The

maxi mum variation in porosity was onl y 4 per centof the overall bed porosity. Therefore, the presenttechnique of preparing the clay beds avoids thepitfall of nonuniform beds, a condition generatedwhen clay is compacted to different porosities witha piston. Separate beds formed from the same claypreparat ion were identical in porosity, and differedby abo ut 1 per cent in permeability. The s tandarddeviation of the calculated surface areas forsamples of sodium clay at the same pH was7 per cent.Particle-size distributions were measured witha Coulter Counter on the most dispersed and themost flocculated clay. The peaks of the curveswere at 1.5 and 2.5/~, respectively.

S u r f a c e c o n d u c t a n c eConductance (or resistance) was measured bythe two-electrode method with a Foy-Martellconductance bridge (Foy and Martell, 1948) and

checked by Eastman's (1920) four-electrodemethod. The current through the bed neverexceeded 30/~-amp/cm2.Silver gauze electrodes, lightly chloridized be-fore each run, were used in all of the experiments.One pair was in contact with the bed (separatedfrom the clay by filter paper). Electrode polariza-tion corrections were obtained after each run bymeasuring the resistance of the cell filled with asolution of kno wn conductivity.Measurements were made at eight frequenciesbetween 83 and 500 c/s. As usually observed withsuch systems, the resistance decreased continu-ously with increasing frequen cy. The total spreadof values amounted to several per cent of the re-sistance in many cases. The resistance at zerofrequency (Ro) was estimated by extrapolationby use of the impedance function of an analogcircuit shown in Fig. 2. The data fitted this functionempirically with a standard deviation of 0.3per cent.The surface conductance is evaluated from themeasured conductanc e of the bed by a comparisonwith that expected fr om the conduc tivit y of thepermeant solution. The expected ratio of solutionconductivity to bed conductivity was computedfrom the porosity, 6, by means of the empiricalexpression 1.76 d, -117 (Winsauer e t a l . , 1952). Theconstants in this expression were obtained bymeasurement over the experimental range of por-osity on beds permeated by 0.1 N NaCI solutions.At this concentratio n the surface condu ctance isnegligible. The standard deviation of the datafrom the exp ressio n was 1-6 per cent.E l e c t r o k i n e t ic p r o p e r t i e s

Figures 3 and 4 show examples of streamingpotential and electroosmosis measurements.Figure 3 is a tracing of data plotted directly by anX - Y recorder, with the output of a pressure trans-ducer on the X-axis and the output from electrodesin the cell on the Y-axis. The input impedance ofthe recorder was 1 MI); the beds ranged from 150to 12 00~ . Pressure (+ 20 cm of water) was cali-

R0

R I CFig. 2. Circuit analogue for clay bed.C C M V o l . 1 7 N o . 4 - C


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2 26 P H I L I P B . L O R E N Z

.m 1 6 . 9 c m

F i g . 3. A s t r e a m i n g p o t e n t i a l m e a s u r e m e n t .

- 5 0 / l amps

brated with a manometer in the line, and potentialwas calib rated by inserting a 1-mV signal from thepotentiometer used to oppose the asymmetrypotential of the electrodes.As a check on the streaming potential, electro-osmosis was measured on one bed with positivestreaming potential and on another with negative.The rate of pressure-decline due to flow under ahead of a few centimeters of water was observedin a vertical precision bore tube of inner diameter0-2007 cm. T he change in rate on application ofa constant current was used to calculate electro-osmosis. The results are compared with the stream-ing potential in Table 1.

Table 1. Electroosmosis and streaming potentialElectro- Streamingosmosis potentialp H ( c m 3 s e c - l a m p - l ) v o l t . dyne-lcm2 107

3.5 --0.22 --0.245 0.462 0.473

The numerical agreement is within the repro-ducibility of the two sets of measurements. (Thefactor of 10 r occurs becaus e of the use of practicalelectrical units). Both streaming potential andelectroosmosis have the same value for flow ineither direction, which is another indication of theuniformity of the beds (Tikhomolova, 1960;Kede m and Katchal sky, 1963).

RE SULT SS u r f a c e a r e a sThe area, So, in m2lcm3 of solid was calculated

3 0 n l / s e c

Appl ied currentI I I I+ 5 0 ) J. arnps

- - 3 0 n l / s e cFig. 4. An Electroosmosis measurement.

from the Ko zeny- Carma n equation in the formSo = [6/(1 --q,)] V(6/5"00 k) x 104

where k is the specific permeabilit y in cm 2. Valuesranged from 35 for the bed in the most basicsolution to 20 in the most acid solution. The valuefor the hydrogen -aluminum clay was 21. Thus,flocculation in the acid solution reduced the sur-face effective in flow by 40 per cent. This corres-ponds with the particle sizes reported above whichshowed an equi valent increase. As shown in Fig.5, there is a small variation with porosity, some-what less than that found on beds compacted witha piston (Michaels and Lin, 1954; Ballou, 1955).The Kozen y-Ca rman values of surface areawere used to calculate surface conductivity. The ywere considered to be more representative of theareas in an aqueous medium than Brunauer-Emmett-Teller (B.E.T.) values from nitrogenadsorption, which are about 30 per cent higher andshow little variation with ionic type (Johansen andDunning, 1959; Keenan, Mooney, and Wood,1951).


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S U R F A C E C O N D U C T A N C E A N D E L E C T R O K 1 N E T I C P R O P E R T IE S 227

oE

I.dn.-IJJLt.n.,O~

4 0 m

3 Q

2C

D ~ xx

I I I0 " 5 0 0 " 5 5 0 ' 6 0F R A C T I O N A L P O R E S P A C E

F ig . 5. S o v s . ~ b : e p H l l ; Z e t a p o t e n t ia l s

T h e e l e c t r o k i n e t i c p r o p e r t i e s o f c l a y s a m p l e sp r e p a r e d i n d if f er e n t w a y s w e r e c o m p a r e d b yc o n v e r t i n g s t r e a m i n g p o t e n t i a ls , E p , t o " z e t ap o t e n t i a l s " a s c a l c u l a t e d f r o m t h e c l a s s ic a lH e l m h o l t z - S m o l u c h o w s k i e x p r e s s i o n 4rw h e r e -q is v i s c o s i t y , E is d i e l e c t r i c c o n s t a n t o f t h es o l u t i o n s , a n d K ' i s t h e e f f e c t i v e c o n d u c t i v i t yw i t h i n t h e p o r e s . T h e l a t t e r w a s c a l c u l a t e d f ro m1 - 7 6~ b - l" ] T L /R A , w h e r e L i s b e d t h i c k n e s s , a n d Ai t s c r o s s s e c t i o n a l a r e a . A s d i s c u s s e d e a r l i e r , s u c h" z e t a p o t e n t i a l s " a r e p r o b a b l y s o m e w h a t l o w e rt h a n t h e r e a l z e t a p o t e n t i a l o f th e s u r f a c e . I n f a c t ,i t w a s e x p e c t e d t h a t v a l u e s c a l c u l a t e d i n t h i s w a yw o u l d s h o w a v a r i at i o n w i t h p o r o s i t y , si n c e th em e a n h y d r a u l i c r a d i u s , So (1 -qb ) l ch , r a n g e d f r o m0 .0 3 3 t o 0 . 0 7 1 / x , a n d i ts r a t i o t o t h e D e b y e - H i i c k e lr a d i u s ( " d o u b l e - l a y e r t h i c k n e s s " ) r a n g e d f r o m2 . 4 t o 7 - 4 f o r t h e s o d i u m c l a y . N o s u c h v a r i a t i o n i n" z e t a p o t e n t i a l s " w a s o b s e r v e d a s l o n g a s p H w a sc o n s t a n t . I n v i e w o f th i s , it d i d n o t s e e m a p p r o p r i -a t e t o a p p l y r a d i u s c o r r e c t i o n s .T h e r e s u l t s w e r e l i t t le a f f e c t e d b y c o n c e n t r a t i o n

- 5 0 m v - 7 -1 . r~

I a . ~ /

i

.~ /~ S I I I I ] I8 2 u 5 6 8 9 I 0 I Ip H

+ 1 0 -Fig. 6 . Ze ta p otent ia l of sodium kao l in i te .

i n th i s r an g e , i n a g r e e m e n t w i t h t h e m e a s u r e m e n t so f ~ o n t h e s a m e c l a y b y t h e C o r n e l l U n i v e r s i t yP r o j e c t ( 1 9 5 1 ) . C o n s e q u e n t l y , a l l t h e d a t a f o r t h es o d i u m c l a y a r e p l o t t e d t o g e t h e r i n F ig . 6 . T h es t a n d a r d d e v i a t i o n o f p o in t s f ro m t h e c u r v e i s3 .6 m V . T h e v a l u e a t p H 7 ag r e e s w i t h s e v e r a lp u b l i s h e d v a l u e s o f ~ f o r t h is k a o l i n i t e , b a s e d o ns t r e a m i n g p o t e n t i a l ( M . I . T . , 1 9 5 3 ) , e l e c t r o o s m o s i s( M i c h a e l s a n d L i n , 1 9 5 5 ), a n d e l e c t r o p h o r e s i s( C o r n e l l U n i v e r s i t y , 1 9 5 1 ). I t w a s i n d e e d l o w e rt h a n s o m e r e p o r t e d v a l u e s ( B a l l o u , 1 9 5 5 ; S t r e e ta n d B u c h a n a n , 1 9 5 6 ), b u t s u c h d i f f e r e n c e s c a ne a s i l y b e c a u s e d b y d i f f e r e n c e s i n t h e c o n d i t i o n so f p r e p a r a ti o n . T h u s , t h e r e i s c o n s i d e r a b l e v a r i a -t io n i n th e r e p o r t e d p H f o r t h e i s o e l e c tr i c p o i n t o fk a o l i n i t e ( e. g ., S t r e e t a n d B u c h a n a n , 1 9 5 6 ; S m i t ha n d N a r i m a t s u , 1 9 6 7 ), w h i c h c a n n o t b e a t tr i b u t e dt o a n y p a r t i c u l a r a s s u m p t i o n s i n c a l c u l a t io n . I ti s t h e r e fo r e b e l i e v e d t h a t t h e " z e t a p o t e n t i a l s "r e p o r t e d h e r e r e p r e s e n t t h e t r u e v a l u e s w i t h i n af a c t o r o f 3 o r 4 .S u r f a c e c o n d u c t i v i t y

S t r e e t ' s ( 1 9 5 6 ) f o r m u l a f o r s u r fa c e c o n d u c t i v i t ya p p l i e d t o t h e p r e s e n t s y s t e m b e c o m e sKs = (1.7 6 q~-mTL/AR - - K) (v~k~)

w h e r e K i s t h e c o n d u c t i v i t y o f t h e s o l u t i o n o u t s i d et h e p o r e s . A s p r e v i o u s l y m e n t i o n e d , t h is f o r m u l ag i v e s a n u n d e r e s t i m a t e o f Ks. L i k e g , t h e e x p e r i -m e n t a l v a l u e o f K s w a s n o t s i g n i f i ca n t l y d i f f e r e n ta t t h e t w o c o n c e n t r a t i o n s . T h e r e s u l t s o n t h es o d i u m c l a y ( s o l i d c i r c l e s i n F i g . 7 ) i n d i c a t e al i n e a r r e l a t i o n b e t w e e n z e t a p o t e n t i a l a n d s u r f a c ec o n d u c t a n c e . T h e r e i s n o r e s i d u a l s u rf a c e c o n d u c -t a n c e a t t h e i s o e l e c t r i c p o i n t : t h e l e a s t - s q u a r e sl i n e p a s s e s w i t h i n a d i s t a n c e l e s s t h a n 0-1 s t a n d a r dd e v i a t i o n f r o m t h e o r i g i n . I t w a s t h o u g h t t h a t t h el i n e a r p r o p o r t i o n a l i t y b e t w e e n Ks a n d g m i g h t b es p u r i o u s d u e t o t h e i n f l u e n c e o f s u r f a c e c o n d u c -t a n c e o n t h e c a l c u l a ti o n o f z e t a p o t e n t i a ls f r o m


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2 2 8 P H I L I P B . L O R E N Z

streaming potentials. The correction implied in theuse of K' is not strictly correct in porous media(Overbeek and Wijga, 1946). Therefore, a test wasmade with the equation of Ghosh e t a l . (1954),~ t = ~ , , ( 1 + B l ~ s / a t z ) .

When the mean hydraulic radius was used for a,the values of the empirical geometrical factor B.necessary to convert apparent values ~


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SURFACE CONDU CTAN CE AND ELECTROKIN ETIC PROPERTIES 229parallel path independent of the electrokineticproperties. It seems more fitting to speak simply ofa condensed layer. Table 2 illustrates the distri-bution and mobility of ions on the surface of kaoli-nite, as calculated from Stem's model. Both themodel and the data are approximations, but thecalculations are of qualitative interest. Even forthe sodium clay, most of the exchangeable ionsare in a condensed layer; in the model onlyabout 1 per cent are set in motion by the streamingof the liquid. The calculated adsorption potential is

Apart from the effect of continuous changes insurface composition, there is no direct correlationof surface conductivity of kaolinite with the zetapotential. The zeta potential regulates the mobilepart of the double layer, The surface conductanceis dominated by the condense d part of the doublelayer and the mobility of the ions there. Table2 illustrates that these factors are independent.The surface conductance is therefore dependenton specific properties of the ions and not on thesimple existence of a zeta pot entia l

Table 2. Calculations on homoionic kaolinitesSodium in Calcium in0.6 meq/1 1-4 meq/lNaCI CaClz

Cation exchange capacity, meq/I 3-1 3.1Surface area, m'-'/g 13 9.3Total surface charge density.* tzC/cm z 23ion/unit cell area 0-66Zeta potential, mV 36 1Ratio, (mobile/total) surface charge density 0.006 0.0005Stern adsorption potential,t ev 0-23 0.24Cation mobility on surface, ohm-~cm~equiv 1 9 4.6*Calculated from exchange capacity and surface area for dispersedsodium clay and assumed to be the same for calcium clay.t Based on 2 exchange site/unit cell area.

rather large, and the mobility of the adsorbe dsodium ions is about 20 per cent of its normalvalue. For the calcium ions, the figure is about8 per cent of normal.Previous work has indicated that calcium is lessmobile than sodium on the surface of montmoril-lonite (Van Olphen, 1957), and that sodium issomewhat less mobile on kaolinite than on mont-morillonite (Cremers and Laudelot, 1966). The9present work confirms the low mobility on kaoliniteand shows that calcium is less mobile than sodiumin this case too. Aluminum is not mobile at all,and the decrease of both conduction and electro-kinetic effects in the order Na, Ca, A1 is no doubtpartly a valence effect.

The hydrogen does not fall into this valencesequence, in fact, it is unique in several ways, suchas its influence on cation exchange capacity, andits role in the de velopmen t of positive edge chargesin competition with negative face charges. It alsohas a very high replacing power. In the experimentsdescribed above, the process of replacement ofNa was virtually complete at pH 3-8, where theH :N a ratio was 1:2 for the dilute series and only1 : 10 for the conce ntrat ed. Thus the low mobilit yand electroki netic activity of hydrogen on kaolinitemust be due to the nat ure of the bond to the surfacerather than to a steric blocking by aluminum.

Acknowledgments-Thanks are due to three of mycolleagues: to F. E. Armstrong for building the con-ductance bridge; to R, T. Johansen for suggestions onthe design of the extruding apparatus; and to R. D.Thomas for making the particle-size measurements.R E F E R E N C E SBallou, E. Vernon (1955) Electroosmotic flow in homo-ionic kaolinite: J. ColloidSci. 10, 450-460.Bikerman, J. J. (1942) Electrokinetic equations from gelsand the absolute magnitude of electrokinetic potentials:J. Phys. Chem. 46,724-730.Cornell University (1951) Fundamental Properties,Clay-Water Systems: Soil Solidification Research,Final Report, Vol. I1.Cremers, A. E., and Laudelot, H. (1966) Surface mobil-ities of cations in clays: Proc. Soil Sci. Soc. Am. 30,570-576.Dodd, Charles G., Davis, James W, and Pidgeon,Frances D. (1951) Measurement of specific surfaceareas of nonporous powders by a pressure-declineliquid-permeability method: J. Phys. Chem. 55,684-698.Eastman, E. D. (1920) Conductivity and frequency: J.Am. Chem. Soc. 42, 1648-1655.Foy, Walter L. and Martell, Arthur E. (1948) An improv-ed conductance bridge: Rev. Sci. Instrum. 19,628-632.Ghosh, B. N., Choudbury, B. K., and De, P. K. (1954)Evaluation of true zeta potential of the particles ofglass forming a diaphragm from measurements of


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2 3 0 P H I L I P B . L O R E N Zs t r e a m i n g p o t e n t i a l : T r a n s . F a r a d a y S o c . 5 0 , 9 5 5 -9 5 8 .H o l m e s , H . F . , S h o u p , C h a r l e s S . , J r ., a n d S e c o y , C .H . ( 1 9 6 5) E l e c t r o k i n e t i c p h e n o m e n a a t th e t h o r i u mo x i d e - a q u e o u s s o l u t i o n i n t e r f a c e : J . P h y s . C h e m .6 9 , 3 1 4 8 - 3 1 5 5 .J a m e s , S . D . ( 1 9 6 6 ) E l e c t r o c h e m i s t r y o f t h e i n t er f a c eb e t w e e n s o m e a l u m i n o s i l ic a t e c r y s t a ls a n d s a l t so l u -t i o n s . I . S u r f a c e c o n d u c t i v i t y : J . P h y s . C h e m . 7 0 ,3 4 4 7 - 3 4 5 4 .J o h a n s e n , R o b e r t T ., a n d D u n n i n g , H . N . ( 1 9 5 9 ) W a t e r -v a p o r a d s o r p t i o n o n c l a y s : C l a y s a n d C l a y M i n e r a l s 6 ,2 4 9 - 2 7 8 .K e d e m , O . , a n d K a t c h a l s k y , A . , ( 1 9 6 3 ) P e r m e a b i l it y o fc o m p o s i t e m e m b r a n e s . P a r t 3 . S e r i es a r r a y o f e l e-m e n t s : T r a n s . F a r a d a y S o c . 59, 1941 - 1953 .K e e n a n , A . G . , M o o n e y , R . W . , a n d W o o d , L . A . ( 1 9 5 1 )T h e r e l a ti o n b e t w e e n e x c h a n g e a b l e i o n s a n d w a t e ra d s o r p t i o n o n k a o l i n i te : J . P h y s . C h e m . 5 5 , 1 4 6 2 - 1 4 7 4 .M i c h a e l s , A l a n S . , a n d L i n , C . S . ( 1 9 5 4 ) P e r m e a b i l i t yo f k a o l i n i te : I n d , E n g . C h e m . 4 6 , 1 2 3 9 - 1 2 4 6 .M i c h a e l s , A . S . a n d L i n , C . S . ( 1 9 5 5 ) E f f e c t s o f c o u n t e r -e l e c t r o o s m o s i s a n d s o d i u m i o n e x c h a n g e o n p e r m e a b i l -i t y o f k a o l i n i t e : I n d . E n g . C h e m . 4 7 , 1 2 4 9 - 1 2 5 3 .M . I . T . , S o il S ta b i l iz a t i o n L a b . R e p . V I , O c t o b e r 1 9 53 .O l d h a m , 1 . B . , Y o u n g , F . J . , a n d O s t e r l e , J . F . ( 1 9 6 3 )S t r e a m i n g p o t e n t i a l i n s m a l l c a p i l l a r i e s : J . C o l l o i dS c i . 1 8 , 3 2 8 - 3 3 6 .O v e r b e e k , J . T h . G . ( 1 9 5 2 ) I n H . R . K r u y t ( E d i t o r )C o l l o i d S c i e n c e , V o l . I . , p . 2 3 5 . E l s e v i e r , A m s t e r d a m .

O v e r b e e k , J . T h . G . , a n d W i j g a , P . W . O . ( 1 9 4 6 ) O ne l e c t r o - o s m o s i s a n d s t r e a m i n g - p o t e n t i a l s i n d i a -p h r a g m s : R e c . T r a y . C h i m . 6 5 , 5 5 6 -5 6 3 .R u t g e r s , A . J . , a n d D e S m e t , M . ( 1 9 5 3 ) N a t . B u r . S t d .C i r c u l a r 5 2 4 , p . 2 6 3 .S m i t h , R . W . , a n d N a r i m a t s u , Y . ( 1 9 6 7 ) : M i n i n g E n g r .1 9 , 3 4 ( a b s t r . ) .S t r e e t , N . ( 1 9 5 6 ) T h e r h e o l o g y o f k a o l in i t e s u s p e n s i o n s :A u s t r a l i a n J . C h e m . 9 , 4 6 7 - 4 7 9 .S t r e e t , N . , a n d B u c h a n a n , A . S . ( 1 9 5 8 ) T h e , ~ - po t e nt i al o fk a o l i n i t e p a r t i c l e s : A u s t r a l i a n J. C h e m . 9 , 4 5 0 - 4 6 6 .S t r e e t , N o r m a n , J . ( 1 9 5 8 ) S u r fa c e c o n d u c t i v i t y o f a na n i o n - e x c h a n g e r e s i n : J . P h y s . C h e m . 6 2 , 8 8 9 - 8 9 0 .S t r e e t , N o r m a n J . ( 1 9 6 0 ) S u r f a c e c o n d u c t a n c e o f s u s -p e n d e d p a r t i c l e s : J . P h y s . C h e m . 6 4 , 1 7 3 - 1 7 4 .T i k h o m o l o v a , K . P . , ( 1 9 6 0 ) E l e c t r o o s m o s i s a n d s t r e a m -i n g p o t e n t i a l o n t w o - l a y e r p o w d e r m e m b r a n e s : V e s t n .L e n i n g r . U n i v . 15, no . 4 . S e r . F i z . i K h i m . n o . 1 , 1 0 6 -116.U r b a n , F r a n k , W h i t e , H . L . , a n d S t a s s n e r , E . A . ( 1 9 3 5 )C o n t r i b u t i o n t o t h e t h e o r y o f s u r f a c e c o n d u c t i v i t y a ts o l i d - l i q u i d i n t e r f a c e s : J . P h y s. C h e m . 3 9 , 3 1 1 - 3 3 0 .V a n O l p h e n , H . ( 1 9 5 7 ) S u r fa c e c o n d u c t a n c e o f v a r i o u si o n f o r m s o f b e n t o n i t e i n w a t e r a n d t h e e l e c tr i c al d o u b l el a y e r : J . P h y s . C h e m . 6 1 , 1 2 7 6 - 1 2 8 0 .W i n s a u e r , W . A . , S h e a r i n , H . M . , J r . , M a s s o n , P . H . , a n dW i l l i a m s , M . ( 1 9 5 2 ) R e s i s t i v i t y o f b r i n e - s a t u r a t e ds a n d s i n r e l a t i o n t o p o r e g e o m e t r y : B u l l . A m . A s s o c .P e t r o l . G e o l . 3 6 , 2 5 3 - 2 7 7 .

R f s u m r - O n a d r v e l o p p 6 u n e t e c h n i q u e p o u r f o r m e r d e s c o u c h e s d ' a r g i l e d e p o r o s i t 6 u n i f o r m e , e n t r e4 8 e t 6 2 % . L a c o n d u c t a n c e e n s u r f a c e e t le p o t e n ti e l d ' g c o u l e m e n t d e k a o l in i t e a u s o d i u m o n t 6 t 6 d r -t e r m i n r s p o u r t o u t e u n e g a m m e d e v a l e ur s . L e p o t e n t i e l z& a , c a l c u l6 d ' a p r ~ s l a f o r m u l e c l a s s i q u e ,6 t a it d ' e n v i r o n - 3 0 m V p o u r p H n e u t r e e t c h a n g e a i t d e s ig n e p o u r p H 4 . L a c o n d u c t iv i t 6 e n s u r f ac ed e l ' a r g i l e d e s o d i u m 5. d i f f 6 r e n t es v a l e u r s d e p H 6 t a i t d i r e c t e m e n t p r o p o r t i o n n e l l e a u p o t e n t i e l z g t ae t d e 1 2 ~ p lu s d e 3 0 f o i s a u s s i g r a n d e s q u e l a c o n d u c t i v i t ~ e n s u r f a c e c a l cu l r , e p a r l ' 6 1 e c t r o c in & i q u e .D e s m e s u r e s s i m i l a i r e s o n t 6 t 6 f ai t e s s u r l e k a o l i n i t e s o u s l e s f o r m e s d ' a c i d e ( h y d r o g / ~ n e - a l u m i n i u m ) e td e c a l ci u m . L ' a r g i l e a c i d e c o r r e s p o n d a i t e x a c t e m e n t ~. l a c o r r r l a ti o n e x p e r i m e n t a l e t r o u v r e p o u r l a s r r i es o d i u m , m a i s l a c o n d u c t i v i t 6 d e s u r f a c e d e l ' a r g i l e d e c a l c i u m , a v e c m o i n s d ' u n d i z i / ~ m e d u p o t e n t i e lz r t a d e l ' a r g il e d e s o d i u m a u p H n e u t r e , 6 ta i t i n f r r i e u r e d e m o i t i r. L ' i n t e r p r r t a t i o n d e s r ~ s u l t a t s m o n t r eq u e l e s i o n s d ' r c h a n g e d u k a o l i n i te s e t r o u v e n t s u r t o u t d a n s u n e c o u c h e c o n d e n s r e d e l a s u r f a c e o h l am o b i li t6 d & e r m i n e l a c o n d u c t i v i t r . L e s m o b i l i t r s d e s u r f ac e p o u r N a , C a , e t H - A 1 s o n t r e s p e c t i v e m e n td e 2 0 % , 8 % e t 0 % d e l a n o r m a l e . A p p a r e m m e n t , l ' i o n d ' h y d r o g r n e d e l a s o lu t i o n e s t t r~ s e ff ic a ced a n s l e r e m p l a c e m e n t d u s o d i u m , q u i e x p o s e s e s p r o p r i r t r s 6 1 e c tr o c in & i q u e s e t d e c o n d u c t iv i t 6 p a rr a p p o r t 5 . s a c o n c e n t r a t i o n e n s u r f a c e .Kurzreferat-Es w u r d e e i n e M e t h o d e z u r B i l d un g v o n T o n b e t t e n g l e i c h f f r m i g e r P o ro s it S .t z w i s c h e n4 8 u n d 6 2 % e n t w i c k el t . D i e O b e r f l f ic h e n l ei t u n g u n d d a s S t r i S m u n g s p o te n t ia l v o n N a t r i u m k a o l i n i tw u r d e n i ib e r e i n en w e i t e n B e r e ic h v o n W e r t e n b e s t im m t . D a s n a c h d e r h e r k r m m l i c h e n F o r m e lb e r e c h n e t e Z e t a p o t e n t i a l w a r c i r c a - 3 0 m V b e i n e u t r a l e m p H u n d w e c h s e l t e V o r z e i c h e n b e i p H 4 .D i e O b e r fl S .c h e n le i tu n g d e s N a t r i u m t o n e s b e i v e r s c h i e d e n e n p H W e r t e n w a r d e m Z e t a p o t e n t i a l d i r e k tp r o p o r t i o n a l a n d 1 2 b is m e h r a l s 3 0 m a l g r /S s s er a l s d i e b e r e c h n e t e e l e k t r o k i n e t i s c h e O b e r f t ~ i c h en l e it -f ~i hi gk ei t. E s w u r d e n ~ in li ch e M e s s u n g e n a n K a o l i n i t in d e r s a u r e n ( W a s s e r s t o f f - A l u m i n i u m ) u n dC a l c i u m f o r m d u r c h g e f ii h r t. D e r s a u r e T o n s t i m m t e m i t d e r f i ir d ie N a t r i u m s e r i e g e f u n d e n e n e x p e r i -m e n t e l l e n K o r r e l a t i o n i i b e r e i n , d e r C a l c i u m t o n d a g e g e n , m i t w e n i g e r a l s e i n e m Z e h n t e l d e s Z e t a -p o t e n t i a l s d e s N a t r i u m to n e s b e i n e u t r a l e m p H, w ie sh a lb d i e Ob e rf l~ i ch e nl ei tf '~ .higk e it d e s se l b e n a u f.D i e E r g e b n i s s e w e r d e n d a h i n g e h e n d a u s g e d e u t e t , d a s s a u s t a u s c h b a r e I o n e n a m K a o l i n i t m e i s t i ne i n e r v e r d i c h t e t e n S c h i c h t a n d e r O b e r f l ~ ic h e s i n d , w o d i e B e w e g l i c h k e i t d i e O b e r f l ~ i c h e n le i t u n g b e s -t i m m t . D i e O b e r f l~ i c h e n b ew e g l i c h k ei t en f i ir N a , C a u n d H - A I s i n d 2 0 % , b z w , 8 % u n d 0 % d e s N o r m a l -w e r t e s . W a s s e r s t o f f i o n a u s d e r L t i s u n g i s t s c h e i n b a r s e h r w i r k s a m i m E r s a t z v o n N a t r i u m , d a s s e i n ee l e k t r o k i n e t i s c h e n u n d L e i t f ~ i h i g k e i t s e i g e n s c h a f t e n i m V e r h ~ i lt n i s z u s e i n e r K o n z e n t r a t i o n a n d e rO b e r f l~ i c he z u m A u s d r u c k b r i n g t .


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S U R F A C E C O N D U C T A N C E A N D E L E C T R O K I N E T I C P R O P E R T I E S 2 31

P e 3 m M e - - - P a 3 p a 6 o T a H a M e T O Il X K a n o J 1 y q e H H f l FI II 4H H C T~ ,I X I ] p e r i a p a T O B B B H ~ e C J IO e B C O ~ H o p o 2 1 H O ~HODHCTO CTblO OT 48 4 0 6 2 % . [ - [OBepXH OCTHa~[ HpOBO ~HMO CTI, H I 'IOTeHIXHflY[ TetIeHH~I HaTpHeBOFO~ a o n H H H T a o ~ p e ; l e n ~ f l H c h B m H p o K a x n p e ; l e n a x H x 3 H a q eH H i ~ . ~ 3 e T a - r I O T e H t t a a n , B b lq ll cJ le H Hb Il~ ln o K n a c c a a e c K o ~ d ~ o p M y Jl e, C O C T a B ~ O K On O-- 3 0 m y r i p H H ef iT p a~ q bH O M 3 H a q e H H H p H n M e l l o n3 H a K n p a p H 4 . I' ]O B e pX H O C T H a~ 3 J -l eK T p oH p o BO h H O C T b H a T p H e B O ~ r n a n b l n p p a 3H b ~ X 3 H a q e H ~ i g xp H 6 b m a n p a M O n p o n o p t t M o H a ~ b H a i 1 3 e T a - n o T e H u a a ~ y ~ n p e B b ~ t u a a a B 1 2 -- 30 p a 3 n 6 o h e e 8 b l -qM c.qeHHyrO 3J leKT pOKi lHeT r lSec lr noBepxH OCT Hy}O 3J l eKx por lpoB o~lHO CT b .

A a a ~ o r H a a b ~ e a 3 M e p e s n : a 6 b i J l n c / l e . qa H b l ~ .n ~l K n C n O fi ( B O a O p O iI H O - an ~ O M n H I 4e B O ~ ) H K a n b u a e B o ~r K a oJ IH H H Ta . ~ a H H b l e ~ n S ~ n c n o f i r n H H b l c o r n a c y m T c s c 3 K cH e pH M eH T aJ ~b H bl M CO O TH O III eH H eM ,yCT aHOBneHHbIM ~1~lf l t l aT pH eBb iX 0pOpM , HO KaYlbHHeBbl fi KaOYI HHHT , ~13eTa- rlOT CHL tHaYl KO T Op Or oc o c r a a a a a M e H e e q e M 0 , 1 B e ~I Hq lt Hb l s 8 a T p n e B o f i r n n n b l I lp I 4 H e ~ T p a J~ b r lO M3 H a q e H n n p H , o 6 a a ~ a e T T O n b g O n o n o B n n o f i e r o n o a e p x H O C T n O f i H pO BO 2114M OC TH . ][-Io p e 3 y n b T a T a M91r c~ l e~a r l Bb lBO~I, t lT O O6M eHH ble HOHbl B l Kn aae T 3 .qe l~T pOKt lHeT l lqecKl4e CBO~CT Ba 14 CBOHCT BO r IpOBO/II , M OCT I4r l p o n o p tl H o n a J l b a O e r o K o n u e n z p a u n I 4 H a n o a e p x H o c T n .

Philip b. Lorenz-surface Conductance and Electrokinetic

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