Langmuir 1992,8, 2730-2739
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Mechanism of Adsorption and Desorption of Water Vapor by Homoionic Montmorillonite. 1. The Sodium-Exchanged Form J. M. Cmes,*'t I. Bbrend,t G. Besson,t M. Fran ois,t J. P. Uriot,QF, Thomas,? and J. E. Poirier
F
Laboratoire Environnement et Minkralurgie et UA 235 du CNRS, B.P. 40, 54501 Vandoeuvre Cedex, France, Laboratoire de Cristallographie, UA 841, Universitk d'Orlkans, 45046 Orlkans Cedex, France, and Centre de Recherches Pktrographiques et Gkochimiques, B.P. 20,54501 Vandoeuure Cedex, France Received March 6,1992. In Final Form: July 1,1992
The structural changeswhich occur during the intracryatallineswellingof a well-characterizedWyoming sodium montmorillonite have been investigated using controlled-ratethermal analyeis,nitrogen adsorption volumetry, water adsorption and desorption gravimetry, immersion microcalorimetry in water, and X-ray diffraction under controlled humidity conditions. The experimental X-ray powder patterns of the 001 reflections have been compared with the theoretical simulationsto determine the structural change of the montmorillonite during hydration and dehydration. At relative water vapor pressures lower than 0.16, water absorbs only on the external surfaces of the tactoids. During this stage, the size of the tactoids decreases in order to reach a state identical to that determined after immersion in water (six clay layers thick) and the specific surface area increases from 43 to 105 m2/g. Between 0.16 and 0.50 relative HzO pressure, after the monolayer capacity has been reached on external surfaces, a first-layer hydrate ie formed on about 40% of the interlamellar space. For water pressures higher than 0.5 and up to 0.93,a two- and a three-layer hydrate are formed after the bilayer capacity is obtained on the external surface and the effective internal specific surface area reaches a value of about 710 m2/g. The osmotic swelling of the montmorillonite from the two-layer hydration state is an isoenthalpic process. The differenthydrates are never homogeneous, and never do H2O molecules completely fill the interlamellar spaces. Heat of hydration of exchangeable cations and the surface pressure on the external surface of tadoids are the driving forces of intracrystalline swelling of sodium montmorillonite. During desorption, the external surfaces mainly lose water down to a relative vapor pressure of 0.72. About 70% of the interlamellar space is occupied with a monolayer hydrate between 0.5 end 0.26 relative pressure of HzO. At a relative vapor pressure of 0.05, the initial dry state is reached again. It was also possible to distinguish different stages of hydration correspondingto the solvation of exchangeablecations and the accumulationof water molecules adsorbed on the silicate surface in the interlamellar space. Introduction The rheology and the colloidal properties of swelling clays play an important role in many industrial processes such as soil science, hydrogeology, and civil and petroleum engineering.'I2 For instance, during hydrocarbon exploration and production, serious problems are often encountered in smectite-rich m~drocks.~ In studying the swelling of clays in relation to hydration, it is necessary to distinguish between two kinds of swelling, namely, the intracrystalline swelling caused by the hydration of the exchangeablecationsin the interlayersof montmorillonite, vermiculite-like, and in some of the hydrous mica clay mineralsand osmotic swelling which results from the large difference between ion concentrations close to the clay surface and in the pore water. The essential features of osmotic swelling are not only the large spacings observed between individual clay layers"13 but also the different nature of the forces between the layers. These forces are t Laboratoire Environnementet Min6ralurgieet UA 235 du CNRS.
* Universite d'Orl6ane.
Centre de Recherches P6trographiquee et GBochimiquee. (1) h e , T.; Low, P. F. J. Colloid Interface Sci. 1988, 124, 624. (2) Moan, M. Rheological Propertiea of Montmorillonite Suspension. VI th I.F.P. Reeearch Conference on Exploration and Production, St. Raphael, France, September 1991. (3) Hall,P. L.;h i l l , D. M. Clays Clay Miner. 1989,37, 355. (4) Norrish, K. Tram. Faraday SOC.1954, 18, 120. (5) Ben -em, H.;Tessier,D.; Pone, C. H. Clay Miner. 1986,21,9. (6)Ben Rhaiem, H.;Pone, C. H.;Tessier, D. In Proceedings of the International Clay Conference,Denver,1985;Schultz,L. G.,Van Olphen, H., Mumpton, F. A., Eds.; The Clay Minerah Society Publisher: Blwmington, IN, 1987; p 292.
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osmotic and result from a balance of electrostatic forces, van der Waals forces, and the osmotic pressure exerted by the interlamellar cations.1+22 Many studies have shown that sorption of water into the interlamellar space is governed both by the size and charge of the saturating cation as well as by the value and localization of the layer charge of the adjacent silicate (7) Pone, C. H.;Ben Brahim, J.; YBcel, A.; Tchoubar, D.; Tchoubar,
C. Clay Miner. 1980,15,111.
(8)Pone, C. H.; Rouslleaux, F.; Tchoubar, D. Cloy Miner. 1981,16,23. (9) Pone, C. H.;Rouseeaux, F.; Tchoubar, D. Clay Miner. 1982,17, 327. (10) Pone, C. H.;Teasier, D.; Ben W e m , J.; Tchoubar, D. In A Compahon between X-ray Diffraction Studiea and ElectronMicrorcopy Observation of Smectite Fabric: in Development in Sedimentology, International Clay Conference,Bologna, 1981; van Olphen, H.,Veniale, F., Eds.;&vier Publisher: Amsterdam, 1982; Vol. 36, p 177.
(ll)Ramsay,J.D.F.;Swanton,S.W.;Bunce,J.J.Chem.Soc.,Faraday Tram. lsSo,86,3919. (12) Slade, P. G.;Quirk, J. P. J. Colloid Interface Sci. 1891,144,18. (13) Slade, P. G.;Quirk, J. P.; Norrish, K. Clays Clay Miner. 1991,39, 234. (14) Barahad, I. Clays Clay Technol. Diu. Mines Bull. 19M,169,70. (15) Oliphant, J. L.;Low, P. F. J. Colloid Interface Sei. 1982,89,968. (16) Low, P. F. The Clay-Water Interface. In Proceedings of the International Clay Conference,Denver, 1985,Schultz,L.G.,Van Olphen. H.,Mumpton, F. A., Eds.; The Clay Minerale Society Publirher: Blwmingon, IN,1987; p 247. (17) Low, P.F. Clay Miner. 1987,26,255. (18) Madsen,F.T.; Mtiller-Vonmooe, M. Appl. Clay Sci. 1989,4,143. (19) Rauaeell-Colom, J. A.;Saez-Aunon, J.; POM,C. H. Clay Miner. 1989,24,459. (20) Delville, A.; Laszlo, P. Langmuir 1990,6,1289. (21) Denis, J. H.Clays Clay Miner. 1991,39,35. (22) Denia, J. H.;Keal, M. J.; Hall,P. L.;Meeten, G. H.Clay Miner. 1991,26, 255.
Q 1992 American
Chemical Society
Water Vapor Adsorption and Desorption by Montmorillonite
It is clear, on the basis of IFt spectroscopic experiments, that the location of the deficit of positive layer charge plays an important role in determining the spatial arrangement of the water solvating the exchangeable cations. If, as in montmorillonite, the charge occurs mainly in the octahedral sheet, the negative charge on the surface oxygena t o m is delocahd and the adsorbed water molecules form only weak hydrogen bonds with this surface. On the other hand, if the charge deficit occurs in the tetrahedral sheet, there is a greater localization of the negative charge on the surface, and the formation of relatively strong hydrogen bonds between the adsorbed water molecules and surface oxygen atoms near sites of isomorphous substitution is favored. The different stages of hydration have been studied under controlledconditions using sodium beidellib,% sodium nontronite,n sodium rectorite,28sodium saponite,*U or sodium or lithium vermiculite" because these minerals, due to tetrahedral substitutions, present several homogeneous hydration states, namely, zero, and two la~ers.~~138-40 Recently, high-resolution solid-state NMR of exchangeable cations present in 23Na-and ll'Cd-exchanged vermiculite have shown that each state of hydration is characterized by one specific value of the chemical shift." In addition, deuterium NMR studies of water moleculeshave described the different geometries for heavy molecules squeezed between charged aluminosilicate sheets and condensed counterions, revealing the real influence of the charge of the exchangeable cation on the spatial arrangement of water molecules.42 The nature of the exchangeable cations in clay mineral and interlayer water also plays a central role in the adsorption processes. The use of smectites in heterogeneous catalysis is almost as old as the catalyst itself. Interlamellar water adjacent to cations of high field strengthUM is much more dissociated than water in the (23) MacEwan, D. M.C.; Wilson, M. J. Interlayer and Intercalation Complexea of Clay minerale. In Crystal Structures of Clay Minerals and their X-Ray Identification; Brindley, G. W., and Brown, G., Eds.; Mineralogical Society Publisher: London, 1980. Mon. 5, p 197. (24) Spoaito, G.; Prost, R. Chem. Rev. 1982,82,564. (26) Newman, A. C. D.The Interaction of Water with Clay Mineral Surfaces. In Chemistry of Clays and Clay minerals; N e w " , A. C. D., Ed.; Longman Scientific k Technical Publisher: Birmingham, AL, 1987; p 237. (26) Kawano, M.; Tomita, K. Clays Clay Miner. 1991,39,77. (27) Suquet, H.; Malard, C.; P h r a t , H. Clay Miner. 1987,22, 157. (28) Kawano, M.; Tomita, K. Miner. Mag. 1989,14,361. (29) Suquet, H.; de la Calle, C.; Pezerat, H. Clays Clay Miner. 1976, 23, 1.
D
(30)Suquet, H.; de la Calle, C.; Pezerat, H. C. R.Acad. Sciences, Ser.
1977,284, 1489. (31) Suquet, H.; Prost, R.; PBzerat, H. Clay Miner. 1982,17,231. (32) Suquet, H.; Pezerat, H. Clays Clay Miner. 1987,35,353. (33) Kawano, M.; Tomita, K. Clays Clay Miner. 1991,39, 174. (34) DelaCalle,C.; Suquet, H. Vermiculite. InHydrousPhyllosilicates (erclusioe of Micas); Bailey, S. W., Ed.; Review in mineralogy 1% MineralogicalSociety American Publisher: Washington DC, 1988, p 455. (36) Glaeaer, R.;MBring, J. C. R. Acad. Sci. Ser. D 1968,267,463. (36) Pone, C. H.; Pozzuoli, A.; Rauseel-Colom,J. Pa.; de la Calle, C. Clay Miner. 1989,24,479. (37) Ben Brahim, J.; Armagan,N.; Beeeon,G.; Tchoubar, C. ClayMiner. 1986,21,111. (38)Ben Brahim, J.; Armagan, N.; Besson,G.;Tchoubar, C. J. Appl. Crystallogr. 1989, 16, 264. (39) Ben Brahim, J.; Beaeon, G.; Tchoubar, C. J. Appl. Crystallogr. 1984,17, 179.
(40)Ben Brahim, J.; Beeeon, G.; Tchoubar, C. 5th Meeting of the European Clay Groups; Charlea University Publisher: Prague, 1985; p 66.
(41) Laperche, V.; Lambert,J. F.; Prost, R.;Fripiat, J. J. J. Phys. Chem. 1990,94,8821. (42) Grandjean, J.; Laszlo, P. Clays Clay Miner. 1989,37,403. (43) Poimiion, C.; Caeea, J. M.Bull. Mineral. 1978,101,469. (44)Poimiion, C.; Cases, J. M.;Fripiat, J. J. J. Phys. Chem. 1978, 82, 1866.
Langmuir, Vol. 8, No. 11, 1992 2731
bulk state-ome studies indicate a factor of lo7*iLand is capable of protonating organic molecules. Moreover, the interlamellar water is not rigidly bound. The dynamic structure of water layers on hectorite, bentonite, and vermiculitehas been investigated by quasielasticneutron scattering. For instance, for the planar hydrate Li+*3Hs0, the water molecules were found to be involved in two uniaxial motions: a slow motion of the entire hydrate around an axis parallel to the c asis of the clay layer and a fast rotation of water molecules around their cp axis. Both motions persist with increasing water content, but their rotation is slowed. For water contents greater than that necessary to form two layers of HpO, pore water becomes predominantand its diffusionbehavior was found to be similar to that of bulk ~ a t e r ~ ~ ~ 9 Much is known about the mechanisms of adsorption and desorption of water molecules on homoionic montmorillonitesin the undersaturated but it is neverthelessstill a controversialsubject. Amongthe issues that remain unresolved are the actual distribution and the organization of water adsorbed on the external eurface and in the interlamellarspace of the montmorillonite.Thie is mainly because the different stages of hydration depend (i) on the ability of the exchangeable cations to solvate (therefore, hydration is not necessarily accompanied by the formation of complete monolayers of water molecules in the interlayer space), (ii)the possiblechange in external surface area during the increase of the HpO vapor relative pressures, and (iii) the suitable conditions to determine thermodynamic properties from adsorption isotherms. In the past, it was possible to obtain a good knowledge from particular systems. For instance, the amount of methanol adsorbed in the interlamellar space of chargedeficient lithium, sodium, calcium, and barium montme rillonites, the amount occluded in the microporosity due to the organization of the and the tendency of methanol to form on the clay surface hydrogen-bonded zigzag chains, analogous to those in crystalline CHsOH, can be determined. The exchangeablecations,more (Ca2+) and lees (Li+), perturb this organizati~n.~~ (45) Fripiat, J. J.; Jelli,A.; Poncelet, G.; AndrB, J. J.Phys. Chem. 1965, 69,2186.
(46)Touillaux, R.; Salvador, P.; Vandermeereche, C.; Fripiat, J. J. Isr. J. Chem. 1968,6,337. (47) C o d , J.; &trade-Smarckopf, H.;Dmoux, A. J.; Poimignon, c. J. Phj'S. 1984,45,1361. (48) Poimiion, C.; &trade-Szwarckopf, H.; Conard, J.; Dianoux, A. J. Water Dynamic in the Clay-Water System: A Qusaiehtic Neutron ScatteringStudy. In Proceedings of the International Clay Conjemnce, Denver, 1985, Schultz, L.G., Van Holphen, H., Mumpton, F. A,Edr.; T h e Clay Minerals Society Publiaher: Bhmington, IN, 1987, p 284. (49) Poinaignon, C.; &trade-Szwarckopf, H.; C o d , J.; Dianoux,A. J. Physica B 1989,166,167,140. (60)Ta"it.ch, J.1.;Ovchnrenko,F. D. Adsorption m r d w minhux argileux. Naukoua Dumka; Kiev, 1975; p 361. (61) Del Pennino, U.; M e w , E.; Valeri, S.; Alietti, A; Brigatti, M. F.; Poppi, L. J. Colloid Interface Sci. 1981,84,301. (62) Poirier, J. E.;Franpoie, M.; C a m , J. M.; Rouquerol, J. Study of Water Adsorption on Na-Montmorillonite: New Data Owing the UIO of Continuow Procedure. In Fundamental of Adsorption; Liaph, A. I., Ed.; AIChE Publieher: New York, 1987; p 473. (63) Krahenbuehl, F.; Stoeckli, H. F.; Brunner, F.; Kahr, G.; MuellerVonmooa, M. Clay Miner. 1987,22, 1. (64)Tdlo, J. M.;Poyato, J.; Tobias, M. M.; Ca~tro,M. A. Clay Miner. 1990,26,486. (66) Kahr, G.; Kraehenbuehl, F.; Stoeckli, H. F.; Muellor-Vonmm, M. Clay Miner. 1987,22,1. (MI) Annabi- Bergaya, F.; Cruz, M. I.; Gatineau, L.;Fripiat, J. J. Cloy Miner. 1979,14, 249. (67) Annabi- Bergaya, F.; Cruz, M. 1.; Gatineau, L.;Fripiat, J. J. Cloy Miner. 1980,15, 219. (68)Annabi- Bergaya, F.; Cruz, M. I.; Gatineau, L.;Fripiat, J. J. Clay Miner. 1980,16,226. (69) Annabi- Bergaya, F.; Cruz, M. I.; Gatineau, L.;Fripiat, J. J. Clay Miner. 1981,16, 116.
2732 Langmuir, Vol. 8, No. 11, 1992 T h e present study on the mechanisms of water adsorption-desorption of sodium montmorillonite was undertaken with the above aspecta in mind and is novel in t h a t several parallel characterization techniques have been applied, which include controlled-transformation-rate thermal analysis (CTRTA), nitrogen adsorption volumetry, and X-ray diffraction (XFtD) to determine the state of the adsorbentin t h e initial (dry) state;continuous water adsorption-desorption gravimetry in order to know the total amount of water adsorbed as a function of relative pressure; immersion microcalorimetry in water which allows the surface area to be determined by the so-called "absolute" method of Harkins and JuralBoin order to determinethe sizeof tactoidsimmersedin water;and X-ray diffraction in order to compare the experimental 001 reflection obtained from a powder pattern with those calculated from models and to permit investigation of the different states of hydration.
Experimental Section Materials. Montmorillonite belongs to the family of dioctahedral layer lattice silicates with a 2 1 structure. Because of its layered morphology,thisclay has a tendency to form aggregates of elementaryparticles called tactoids. The turbostratic stacking of tactoids originah from random rotations and translations between adjacent layers. It may be compared to a disorganized deck of cards. The materialused in both sets of experimentswas the Wyoming montmorillonite Clay Spur 26 supplied by Ward's Natural Science. A size fraction of
