pubs.acs.org/Langmuir © 2010 American Chemical Society
On the Cation Dependence of Interlamellar and Interparticular Water and Swelling in Smectite Clays ,^
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F. Salles,*,†,‡ O. Bildstein,*,† J. M. Douillard,‡ M. Jullien,† J. Raynal,§ and H. Van Damme
CEA, DEN, DTN Cadarache, F-13108 Saint Paul Les Durance, France, ‡Institut Charles Gerhardt, Universit e Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5, France, §CEA, DEN, DEC Cadarache, F-13108 Saint Paul Les Durance, France, ESPCI-Paris Tech, UMR 7615, CNRS-UPMC-ESPCI, 10 rue Vauquelin, 75231 Paris Cedex 05, France, and ^Universit e Paris Est - Laboratoire Central des Ponts et Chauss ees, 58 boulevard Lefebvre, 75232 Paris Cedex 15, France )
†
Received July 12, 2009. Revised Manuscript Received February 25, 2010 The osmotic character of long-range interlamellar swelling in smectite clays is widely accepted and has been evidenced in the interlayer space by X-ray diffraction. Such a behavior in mesopores was not experimentally confirmed until the determination of the mesopore size distribution in Na-montmorillonite prepared from MX80 bentonite using thermoporometry experiments. This is confirmed here for other montmorillonite samples where the interlayer cations are alkaline and Ca2þ cations. The nature of the interlayer cation is found as strongly influencing the behavior of the size and the swelling of mesopores. These results are supported by the BJH (Barrett, Joyner and Halenda) pore radius values issued from the nitrogen adsorption-desorption isotherms at the dry state. Thermoporometry results as a function of relative humidity ranging from 11% to 97% have shown an evolution of the mesopore sizes for a purified Na-montmorillonite. New thermoporometry data are presented in this article and confirm that the interparticle spaces in K-, Cs-, or Ca-montmorillonites are not strongly modified for all the range of relative humidity: the swelling is not observed or is strongly limited. It appears in contrast that only Li- and Na-montmorillonites undergo a mesopore swelling, distinct from the interlayer swelling. More generally, our results confirm the possibility to use thermoporometry or differential scanning calorimetry to study the structure and the evolution of swelling materials in wetting conditions such as natural clays or biological cells. In this paper, we describe the different key steps of the hydration of swelling clays such as montmorillonites saturated with alkaline cations. Using thermoporometry results combined with X-ray diffraction data, we distinguish the evolution of the porosity at the two different scales and propose a sequence of hydration dependent on the interlayer cation. From this study, it is shown that the interlayer spaces are not completely filled when the mesopores start to fill up. This implies that the swelling observed in the mesopores for Li and Na samples is due to an osmotic swelling. For the other samples, it is difficult to conclude definitively. Furthermore, we determine the different proportion of water (interlayer water and mesopore water) present in our samples by the original combination of (1) X-ray diffraction data, (2) the pore size distribution obtained by thermoporometry, and (3) recent adsorption isotherm results. It is found that the interlayer space is never completely filled by water at the studied relative humidity values for all samples except for the Cs sample.
1. Introduction The purpose of this paper is to describe the influence of the exchangeable cations on the nano- and mesoscale swelling of smectite clays in the solid state. Smectite clays, often called swelling clays, are negatively charged lamellar silicate colloids which interact readily with cations and water, leading to a variety of physical states going from compact solid rocks (shales) to pasty muds, gels and finally to dilute sols. They are used or considered for use in a wide range of applications, including engineered barrier systems for nuclear wastes repository.1-3 In this case, the role of the clay is to (1) limit water fluxes toward the waste package, (2) reduce technological gaps as a result of swelling, and (3) slow down the migration of radio-nuclides into the surrounding porous media once the waste package has been attacked.1-3 At the macroscopic scale, the swelling of a solid smectite sample may be described
as the increase of its apparent sample volume by absorption of water from a liquid or a vapor source.4-6 At the microscopic scale, it is much less simple due to the multiscale structure of smectite clays and to the sensitivity to water and to cations of the many intermolecular and surface forces - van der Waals, ion dipole, hydrogen bonds, Coulomb, double layer repulsion, and ion correlation attraction, to name a few - which determine the attractive and repulsive interactions in the material.1,7-9 The basic structural units of smectite clays are negatively charged 0.96 nm thick lamellae, separated by cations and water molecules.1,6 However, the description of the structure of a macroscopic sample as a simple collection of individual and quasi-independent lamellae is far from being satisfying, except in some special situations like in very dilute aqueous suspensions of Li- or Na-exchanged montmorillonite, hectorite or nontronite for instance.4,7,10-14 In most situations, at least one
*Corresponding authors. E-mail: (F.S.)
[email protected]; (O.B.)
[email protected].
(5) Norrish, K.; Quirk, J. P. Nature 1954, 173, 255–256. (6) Norrish, K. Discuss. Faraday Soc. 1954, 18, 120–134. (7) Salles, F.; Beurroies, I.; Bildstein, O.; Jullien, M.; Raynal, J.; Denoyel, R.; Van Damme, H. Appl. Clay Sci. 2008, 39, 186–201. (8) Delville, A. Langmuir 1991, 7, 547–555. (9) Laird, D..A. Appl. Clay Sci. 2006, 34, 74–87. (10) Van Duijneveldt, J. S.; Klein, S.; Leach, E.; Pizzey, C.; Richardson, R. M. J. Phys.: Condens. Matter 2005, 17, 2255–2267. (11) Warr, L.; Berger, J. Phys. Chem. Earth 2007, 32, 247–258.
(1) Handbook of clay science; Bergaya, F., Theng, B. K. G., Lagaly, G., Eds.; Developments in clay science series; Elsevier Science: Amsterdam, 2006; Vol. 1. (2) Madsen, F. T. Clay Miner. 1998, 33, 109–129. (3) Push, R.; Yong, R. Appl. Clay Sci. 2003, 23, 61–68. (4) Tessier, D. Etude experimentale de l’organisation des materiaux argileux, hydratation, gonflement et structuration au cours de la dessiccation et de la rehumectation. Ph.D. Thesis, Universite Paris 7, 1984.
5028 DOI: 10.1021/la1002868
Published on Web 03/05/2010
Langmuir 2010, 26(7), 5028–5037
Salles et al.
Figure 1. Representation of the multiscale structure of swelling clays: layer, particle, and aggregate and corresponding porosities.13
or two intermediate (“meso”) structural features have to be introduced.13-16 For instance, the dilute suspensions of most ion-exchanged smectites (except the Na- or Li-exchanged ones) are actually suspensions of orientationally and translationally ordered lamellae aggregates, first called “quasi-crystals” by Aylmore and Quirk, in which the lamellae are separated by a few layers of water molecule.10,17 The number of lamellae in a quasi-crystal is a function of the cation properties (mainly charge and radius) and the crystal chemical properties of the clay lamellae (charge density, charge localization).4,10,18,19 These ordered - yet still deformable - stacked structures at mesoscale are also recognizable in solid clay samples, where they are often called “particles” (see Figure 1). However, those (12) Likos, W. J.; Lu, N. Clays Clay Miner. 2006, 54, 515–528. (13) Jullien, M.; Raynal, J.; Kohler, E.; Bildstein, O. Oil Gas Sci. Technol. 2005, 60(1), 107–120. (14) Van Damme, H. C.-R. Acad. Sci. Paris 1995, t320, serie IIA, 665-681 (15) Bihannic, I.; Michot, L. J.; Lartigues, B. S.; Vantelon, D.; Labille, J.; Thomas, F.; Susini, J.; Salome, M.; Fayard, B. Langmuir 2001, 17, 4144–4147. (16) Guggenheim, S.; Martin, R. T. Clays Clay Miner. 1995, 43, 255–256. (17) Aylmore, L. A. G.; Quirk, J. P. Soil Sci. Soc. Am. Proc. 1971, 35, 652–654. (18) Lantenois, S.; Nedellec, Y.; Prelot, B.; Zajac, J.; Muller, F.; Douillard, J. M. J. Colloid Interface Sci. 2007, 316, 1003–1011. (19) Berend, I. Les mecanismes d’hydratation de montmorillonites homoioniques pour des pressions relatives inferieures a 0.95. Ph.D. Thesis, Nancy, France, 1991.
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particles are not independent structural units.4,14,18 They should more appropriately be considered as locally ordered domains in an otherwise orientationally and translationally disordered continuum. Thanks to its deformability, a single lamella may be part of a “particle” at some place, leave it, and be inserted in another particle at another place. This entangled organization is responsible for the structural continuity and mechanical strength of even larger structural units, which are powder grains when the clay is in powdered form, or aggregates in soft soils, or else pieces of rock when the clay is part of a geological deposit.13 The swelling process which, starting from a dry solid sample expands it all the way to a suspension of individual or aggregated lamellae is obviously a multiscale process. At least two hydration and expansion processes should be considered.7,20 The first one is the increase of the distance between the lamellae within each particle. The second one is the increase of the wall-to-wall distance in the mesoscale voids between particles.7 The expansion of the interlamellar and intra-particular distances is easily evidenced by the shift of the 001 X-ray diffraction line toward smaller scattering angle.19,21,22 In IUPAC nomenclature terms, the interlamellar space belongs to the category of micropores (spacing
