Fig. 2. The reflection coefficient, 
, according to the Fritz-Marine Membrane Model (FMMM); top as a function of the porosity at an average concentration of 0.1 mol L-1, and bottom as a function of the average concentration at a given porosity of 0.5. Curves were calculated using Eq. [4] for monomineral membranes made of kaolinite, illite or montmorillonite with values for the cation-exchange capacity (CEC) of respectively 15, 25, and 100 cmolc kg-1. For the frictional coefficient, Rwm, an initial value of 0.1 was taken which decreased linearly in the porosity range between 0 and 0.4. Above a porosity of 0.4 the value of Rwm was taken to be zero. Values of the other frictional coefficients are given in the text.
