A lot of experiments were investigated to show the behaviour of an ultrafiltration membrane during the filtration of pure salt solutions. What happens when the filtered solution contains several ions? In this paper, results are given concerning the filtration of mixtures of two salts solutions, salts with a common anion: NaCl + CaCl2 and Na2SO4 + CaSO4. The surface charge of the membrane is characterized by streaming potential measurements and rejection rates by means of chromatography. These results confirm the adsorption of divalent ions on the surface and a good selectivity for divalent cations. (C) 2007 Elsevier B.V. All rights reserved.