Sorption of NiCl2 and FeCl3 or di- and trivalent cation salt mixtures on polysulfone or polysulfone polyester-supported cation exchange membranes was investigated as a function of pH and concentration. The sorption of Fe(III) was higher than that of Ni(II) for both types of membranes. The maximum sorption for Fe(III) and Ni(II) ions was observed at pH 2.8 and 4.4, respectively. The selectivity coefficient of Fe(III) was also higher than that of Ni(II). The results were explained by considering the hydration effect and ionic valence.