Theoretical study of the permselectivity of an anion exchange membrane in electrodialysis

Abstract

Electrodialysis (ED) is one of the useful membrane processes to produce a drinking water from underground water, brine water and other water sources. In ED, the monovalent anion selectivity is a very important property of anion exchange membranes (AEMs) to remove harmful ions like NO3− and F− ions from feed solutions and to protect the precipitation of scale. In this paper, we theoretically discussed the effect of parameters on permselectivity and suggested ways to improve the monovalent anion selectivity of ED system using the equivalent circuit model. The results showed that a decrease in the thickness of diluted compartment was very important to properly reflect the membrane properties on the permselectivity. It was also shown that the multivalent anion selectivity of an AEM was increased by increasing the positive charge density of the AEM. On the other hand, the monovalent anion selectivity was improved by modifying the AEM with a negatively charged layer. Finally, we discussed a method for estimating the monovalent anion selectivity of ED system.