Thermodynamics of water sorption in clay

Experimental data on desorption isotherms of three types of clay at different temperatures (40, 50 and 60°C) were determined using a static method. The results were fitted by the famous Guggenheim-Anderson-deBoer (GAB) model. The thermodynamic functions, differential heat of sorption, net integral enthalpy and entropy, were evaluated at several moisture contents. Heat of sorption decreased with the moisture content and the trend became asymptotic as the moisture content of 0.01 (d.b.) was approached.

In this study, we have determined experimentally the desorption isotherms of three types of clay at different temperatures. Then we have used the GAB model to smooth the experimental data: the results are generally acceptable. The GAB model is retained for the description of the experimental sorption data with a weak standard error and a relative error Fig. 5. Sorption enthalpies for the 3 clays.