Research Article
Jhider N and Bagane M
Abstract
This work is based on data from adsorption isotherms and isosteric enthalpies of El Hamma raw clay at different temperatures (30, 40, 50 and 60°C). These previously obtained data were used here to show the variation of the thermodynamic properties of water adsorbed on the surface of the clay: Gibbs energy, enthalpy and entropy. Then we present a model of solid solution based on a polynomial expression of degree 7. This model was applied to calculate the excess quantities: excess Gibbs energy of mixing, entropy term and Gibbs energy of mixing. The variations of free energy, enthalpy and entropy of adsorbed water show fluctuations that characterize three areas. For low water contents the entropy of the adsorbed water is greater than that of liquid water. As the amount of adsorbed water increases the entropy gradually approaches the normal value. Close to saturation, the model shows that the term of excess energy of mixing is always positive, although the water remains bound to the solid. Since the term of enthalpy of mixing is negative this means that the solution is stable.