CHARGED MEMBRANES FOR LOW-PRESSURE REVERSE-OSMOSIS PROPERTIES AND APPLICATIONS

Experimental data on properties and applications of charged reverse osmosis (RO) membranes have been reviewed. Experimental findings concerning membrane rejection as a function of concentration and the valency type of feed electrolyte solutions, ion-exchange capacity of membrane matrix, pH value of feed solutions and transmembrane volume flux have been shown to be in qualitative agreement with a simple theory based on Donnan's ideas, though remarkable quantitative deviations have also been observed. A number of new explanations to those deviations has been suggested. Areas of the optimum charged RO membrane applications have been shown to be the treatment of dilute electrolyte solutions at low working pressures (nanofiltration), namely: conditioning brackish waters, water softening, removing small amounts of toxic ions and recovery of valuable metals from industrial waste waters, purification of water from dissociating organics. Recently, the separation of amino acids and proteins according to their pK values has also been becoming an ever more promising application.