A determination of the sign of charge of asymmetric finely porous membranes from ion transport numbers through the membrane under electrodialysis

A method for determining the sign of the charge of fixed ion-exchange group s of finely porous membranes from the data on the electrodialysis of a bina ry electrolyte solution in a multicompartmental electromembrane cell is pro posed. The principle of the method is that the behavior of a charged finely porous membrane in the electrodialysis cell is similar to that for an ion- exchange membrane. Consequently, the sign of the charge of the membrane can be determined from the concentrations of the binary electrolyte solution m easured on both sides of the membrane upon the passing of a current, Ultraf iltration, nanofiltration, and reverse-osmotic charged membranes were inves tigated, Weakly charged ultrafiltration and highly charged ion-exchange mem branes were used as reference membranes, The experimental results showed th at, among the investigated membranes, the UPM-type ultrafiltration membrane s and the nanofiltration membranes were negatively charged. The reverse-osm otic composite membranes were found to be positively charged.