INVESTIGATION OF ION SEPARATION BY MICROPOROUS NANOFILTRATION MEMBRANES

Two new nanofiltration membranes, an organomineral (titania-Nafion) me dium and an inorganic (gamma Al2O3) medium, were studied using single or mixed solutions of monovalent or divalent ions. The experimental re sults not only confirm previous findings concerning the treatment of e lectrolytic solutions using charged nanofiltration membranes, but prov ide additional data notably for microporous membranes. A simple model based on the Nernst-Planck equation is proposed; ifs simplicity is rel ated to the nature of the two membranes tested for which the diffusion terms may easily be disregarded. It highlights the importance of the potential difference that forms on the membrane and explains most of t he observed rejection results. In addition, ionic plugging of micropor es may play a part with regards to rejection and flow depending on wor king conditions.