Removal of bromide ions from an aqueous solution by Donnan dialysis with anion-exchange membranes

Abstract

Abstract The potential of Donnan dialysis to remove the bromide ions and associated ions (nitrates and bicarbonates) from a model solution was examined, using three anion-exchange membranes (AMEs) differing in their ion-exchange capacity and water content: Selemion AMV, Neosepta AFN and Neosepta ACS. Selemion AMV provided the most advantageous exchange of bromide ions for chloride ions and effectively limited co-ion transport, thus contributing to the lowest salt leakage into the feed observed in this study. The efficiency of bromide exchange ranged from 70 to 78% (for 500 μg Br−/L) at a salt concentration in the receiver of 100 and 300 mM NaCl, respectively. Anion exchange with Neosepta AFN (characterized by a loose structure) proceeded at a faster rate and provided a slightly lower efficiency of bromide removal (68–70%). The a major advantage that Neosepta AFN offered was the short duration of the process (the time required for achieving minimal bromide concentration in the feed). Nonetheless, the loose membrane structure was responsible for the relatively high salt leakage into the feeding solution. The use of the monoanion-selective membrane Neosepta ACS brought about a concomitant decrease in the rate of anion removal, which extended the time required for obtaining a similar extent of bromide exchange (70–77%). It was observed with all the membranes examined that the rise in the initial concentration of bromides in the feed (from 200 to 1000 μg/L) enhanced the efficiency of their exchange for chloride ions.