Clay-water Interactions Research Articles

Clay—water interactions and the mechanism of soil swelling

The examination of micropore structure in swollen systems such as wet clay soils must be preceded by removal of the enmeshed water. For such mechanically weak systems the drying process used to remove this water is of the utmost importance. This paper discusses the problem in connection with the elucidation of soil swelling mechanisms. The pore size distributions of compressed cores and natural aggregates of a clay soil have been measured over the range 2 nm–50 μm for samples which have been rapidly frozen and freeze-dried from a wide range of water potentials. These results are discussed in relation to an earlier proposal that the swelling of divalent clay systems results from the water-initiated release of stresses, accumulated as particle distortion during drying and leads to the formation of discontinuities in the soil fabric in which water is retained by surface tension forces. The observation of pores in the 1-μm range is thought to be largely an artifact from the freeze-drying process. A preliminary result based on solvent exchange and critical point drying suggests that this drying method may give a more reliable indication of the pore structure of the swollen soil.

Hydraulic conductivity in surface active soils

Kozeny's equation based on a capillary tube model with constant viscosity does not give satisfactory results for fine-grained soils. When surface forces dominate over gravity forces, the pore water behaves abnormally and the physical properties of this pore water are found to be quite different from free water. Flow through saturated fine-grained soils is known to be affected by the properties and thickness of loosely and strongly bound water, whose viscosity is observed to be higher because of the modified water structure induced by clay-water interaction. An analytical solution based on a capillary tube model taking into account the changed viscosity of bound water and variation of viscosity within the bound water in relation to its thickness is attempted. The derived equation appears to be general in nature and is applicable for both surface active and inactive soils. It is shown that Kozeny's equation turns out to be the particular case of the derived equation when the thickness of the bound water is zero or when the variation of viscosity is not taken into account.

Equilibrium Theory of the Kaolinite-Water System at Low Moisture Contents, with Some Remarks Concerning Adsorption Hysteresis

AbstractA microscopic theory of the kaolinite-water system is presented, based upon the assumption that the clay-water interaction may be envisioned as partly hydration of the exchangeable cations and partly adsorption by the oxygen and hydroxyl surfaces. The theory treats exchangeable cation hydration quantum-mechanically as an ion-dipole phenomenon and considers water adsorption by the mineral surface as a problem in hydrogen bonding. A statistical mechanical model incorporating the quantum-theoretical results is then invoked to find the contribution of each component interaction to the initial portion of the adsorption isotherm for homoionic kaolinite. Good agreement between the theoretical calculations and available experimental data is achieved for water vapor adsorption by Li-, Na-, K-, and Mg-kaolinite, without the use of ad hoc empirical parameters. The concordance, in turn, is used to suggest that the basis for adsorption hysteresis in kaolinite-water vapor systems is the irreversible transition: mineral surface water → cation hydration water.

Non-Darcy flow behavior in liquid-saturated porous media

Velocity-gradient data for water-saturated porous media were considered in some detail. Deviations from Darcy's law were found in data originally presented in support of the law. Recent data were analyzed on the basis of a postulated three-parameter equation, in contrast with the one-parameter Darcy proportionality. The equation contains Darcy's law as a special case and in general fits the data quite well for water and electrolyte solutions flowing in sandstones and clays. The fitted parameters behave consistently, and are capable of reasonable interpretation. Possible mechanisms giving rise to non-Darcy behavior are suggested, including that of non-Newtonian liquid effects caused by clay-water interaction.

INTRINSIC PERMEABILITY OF CLAY AS AFFECTED BY CLAY-WATER INTERACTION

INTRINSIC PERMEABILITY OF CLAY AS AFFECTED BY CLAY-WATER INTERACTION

The role of water in minerals

The interaction of water with clay minerals is central to a wide range of disciplines that span from fundamental particles used in materials science and engineering to applied aspects in soil science and geotechnical engineering. Because water is the most abundant molecule on the surface of the Earth, and clay minerals are ubiquitous mineral phases, it follows that clay–water interactions play many important roles in the biosphere. In fact, water is an integral component of many clay mineral structures. This chapter reviews key elements of the structure of water, its interaction with ions, and the interaction of water with clay minerals. Surface interactions include hydrogen bonding, ion–dipole, dipole–dipole, and van der Waals interactions involving both neutral and charged clay mineral surfaces. Recent spectroscopic and molecular modelling studies of clay mineral–water interactions are presented in the framework of molecular probes and reporter groups.