Comparison of heterogeneous anion-exchange membranes for nitrate ion removal from mixed salt solution

Nitrate concentration in surface and groundwater is becoming a global concern. The electrodialysis is a useful separation technique that uses ion-exchange membranes to treat the solution, and these membranes can possess certain selectivity towards different ions. The objective of this work was to compare the possibility of nitrate separation form a mixed salt solution by electrodialysis using three different anion-exchange membranes (AEMs). Characteristic properties of heterogeneous AEMs are mainly defined by their composition, a mixture of a polymer matrix and an anion-exchange resin. In this work, three different kinds of anion-exchange resins with distinct functional groups (trimethylamine and dimethylethanolamine) were used to prepare AEMs, in which selectivity towards nitrate ion was compared by desalination of mixed salt solution using laboratory electrodialysis unit. The solution used was composed of NaCl, NaNO3, NaH2PO4, and Na2SO4, every salt of concentration 0.05 mol L−1. Although the properties of individual AEMs and their courses of desalination differed significantly, all membranes had higher selectivity for nitrate ions than for the remaining ones; however, their selectivity towards nitrate and chloride was very similar. The affinity relationship of the AEMs was: nitrate > chloride > dihydrogen phosphate > sulfate.