Membrane behavior of clay considering the effect of fixed charges.

Membrane efficiency coefficient of clay is evaluated with considering the effect of fixed charges adsorbed on clay mineral surfaces. By virtue of the concept of chemical potential, the ionic concentration of pore water is calculated. An equation is first proposed to calculate the Donnan osmotic pressure based on the activity of water (HO), and then a new method is developed to determine the membrane efficiency coefficient, based on the theoretical chemo-osmotic pressure difference. The proposed method is used to calculate the membrane efficiency coefficients of geosynthetic clay liners (GCLs) with different bentonite contents and porosities under different KCl concentrations. The calculated results are compared to those of van't Hoff equation, showing that if skeletal deformation is excluded, the proposed model and van't Hoff equation with average ion concentration difference yield practically the same results; if the deformation is considered, however, van't Hoff equation yields smaller membrane coefficients.