Study of the water-bentonite system by vapour adsorption, immersion calorimetry and X-ray techniques: II. Heats of immersion, swelling pressures and thermodynamic properties

A B S T R A C T: A number of thermodynamic properties were obtained from the determination of adsorption isotherms and enthatpies of immersion for systems with water and Na- and Ca-bentonites. Entropy differences were calculated by combining the enthalpies of immersion and the changes in free energy derived from the adsorption isotherms. The swelling pressures, also calculated from the water adsorption isotherms, are in satisfactory agreement with the experimental data. In the second part of this study of the water-bentonite system for well characterized natural Na- and Ca-bentonites, the changes in the adsorption entropy, the enthalpy of immersion and the swelling pressure are examined as the amount of water increases (for the first part of the study see Kraehenbuehl et al., 1987). The transport of water in unsaturated clays and in soils depends on various potentials and on transport coefficients (diffusion coefficients, permeabilities, etc.). The potentials are thermodynamic quantities which can be derived from measurements performed at equilibrium, and they are usually defined in terms of partial specific potentials, for example g,w = ( 6Gw/bmw)T,p and