Clay-Water Interactions

Schmidt, D.D. Roos, A.F. Cline,J.T., "Interaction of Water with Organophylic Clay in Base Oils to Build Viscosity, SPE Paper 16683, 1987 SPE Annual Technical Conference and Exhibition, Dallas, 311-326. 

Newman, A. C. D. (1987), "The Interaction of Water with Clay Mineral Surfaces" in A. C. D. Newman, Ed., Chemistry of Clays and Clay Minerals, Longman, Essex, England, 237-274. 

It is difficult to reconcile these very different views of the interaction of water and clay surfaces. Sposito (8.) has attempted this. He points out that the thermodynamic properties have an essentially infinite time scale, whereas the spectroscopic measurements look at some variant of the vibrational or a predecessor of the diffusional structure of water. It is possible that the thermodynamic properties reflect a number of cooperative interactions which can be seen only on a very long time scale. Still, the X-ray diffraction studies seemingly also operate on as long a time scale as the thermodynamic properties. There is still not a clear choice between the short-range and long-range interaction models. 

In general, the 2 1 clays are not very simple systems in which to study the interaction of water and surfaces. They have complex and variable compositions and their structures are poorly understood. Water occurs in several different environments zeolitic water in the interlayer regions, water adsorbed on the external surfaces of the crystallites, water coordinating the exchangeable cations, and, often, as pore water filling voids between the crystallites. Thus, there are many variables and the effects of each on the properties of water are difficult to separate. 

Of particular interest for chemical transport into a predominantly smectite medium is the shrink-swell property of the clay material. The swelling properties of smectites are explained by two concepts. The first one, developed by Sposito (1973), shows that smectite swelling is caused by the hydration and mobility of the cations, which in turn balance the negative charge of the layer silicates. The second concept, presented by Low (1981), emphasizes the direct interaction of water molecules with the silicate surface. Both viewpoints fit the common observation that smectite swells in a high-hydration environment and at low electrolyte concentrations and shrinks when water is lost and salt is added to the bulk solution. 

Green, R. E. (1974). Pesticide-clay-water interactions. In Pesticides in Soil and Water, ed. W. D. Guenzi, pp. 3-37. Madison, WI Soil Science Society of America. 

Gtiven, N. (1992). Molecular aspects of clay/water interactions. In N. Gtiven and R.M. Pollastro, eds., Clay-Water Interface and Its Rheological Implications, Vol. 4. CMS Workshop Lectures. Boulder, CO Clay Minerals Society, pp. 2-79. 

Several researchers have found that suspensions of charged particles, especially clays, can have surface tensions that are several mN/m greater than that of pure water [139,146-148]. In much the same way as for solutions of inorganic electrolytes, the increased surface tension is probably due to strong interactions between water molecules and the ionic solutes. Figure 3.15 shows some examples, including... 

Therefore, the energetic materials could interact with water molecules or with exchangeable cations in the interlayer space of mineral. These interactions are considered as one of many possibilities for the remediation of highly contaminated soils by energetic materials [31]. This is the reason why the understanding of phenomena of hydration of clay minerals is the crucial aspect, which could help to find a possible way of decontamination. 

The experimental studies of water interactions with clay minerals are very extensive. The structure, dynamics and interactions of interlayer water with the surface of clay minerals were reviewed in several papers [32, 33] and described in a number of books [15, 34, 35]. Therefore, we will review only the most important studies concerning experimental investigations of the structure and interactions of water molecules on clays. 

In addition to diffraction methods, also spectroscopic techniques, especially NMR spectroscopy, are extensively used to study the complex interaction of water and the clay mineral surfaces. NMR spectroscopy has become a valuable tool to investigate the dynamics of water [41, 48-54]. The study of interaction of water with clays using NMR techniques has primarily involved measurements of H and 2H spin-lattice relaxation and lineship analysis of H and 2H in water molecules adsorbed on clays [32, 41, 51-54], Based upon the results of such studies, it is possible to calculate the distribution, orientation, and diffusion rates of water molecules bound to clays. It was found that water molecules have a preferential orientation on clays with low water contents at temperatures near 298K [52, 54]. 

Van der Waals interactions are noncovalent and nonelectrostatic forces that result from three separate phenomena permanent dipole-dipole (orientation) interactions, dipole-induced dipole (induction) interactions, and induced dipole-induced dipole (dispersion) interactions [46]. The dispersive interactions are universal, occurring between individual atoms and predominant in clay-water systems [23]. The dispersive van der Waals interactions between individual molecules were extended to macroscopic bodies by Hamaker [46]. Hamaker s work showed that the dispersive (or London) van der Waals forces were significant over larger separation distances for macroscopic bodies than they were for singled molecules. Through a pairwise summation of interacting molecules it can be shown that the potential energy of interaction between flat plates is [7, 23]... 

The clay-water interactions and the quantity of water present in the interlayer space strongly depend on the nature of exchangeable cations. The water in the clay may be acting as hydrate water or additional absorbed water. 

Surface chemistry of the oxide-water interface is emphasized here, not only because the oxides are of great importance at the mineral-water (including the clay-water) interface but also because its coordination chemistry is much better understood than that of other surfaces. Experimental studies on the surface interactions of carbonates, sulfides, disulfides, phosphates, and biological materials are only now emerging. The concepts of surface coordination chemistry can also be applied to these interfaces. This chapter is designed... 

Thompson, H. A., Parks, G. A., and Brown, G. E., Jr., (1999b). Dynamic interactions of dissolution, surface adsorption, and precipitation in an aging cobalt(II)-clay-water system. Geochim. Cosmochim. Acta 63, 1767-1779. 

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