Comparison of two electrodialysis stacks having different ion exchange and bipolar membranes for simultaneous separation of boron and lithium from aqueous solution

Abstract

Two electrodialysis (ED) stacks having different ion exchange and bipolar membranes were compared for separation of boron and lithium simultaneously and their recoveries from an aqueous solution. As operational parameters, types and concentrations of the solutions employed in the acid and base chambers of ED stacks and their initial concentrations, types of the electrode solutions (NaOH, LiOH), the electrical potential applied (15, 20 V) on efficiencies of two stacks were investigated. When 0.05 mol/L of H3BO3 and 0.05 mol/L of LiOH were employed in the acid and base chambers, respectively along with 0.1 mol/L of LiOH as the electrode solution at 15 V, both ED stacks did not exhibit a remarkable difference with respect to separations and recoveries of both boron and lithium. However, the highest separations with the percent removals of 77.5% and 99.8% along with the percent recoveries of 54.0% and 86.4% were achieved, respectively for boron and lithium at 20 V of electrical potential when 0.05 mol/L of H3BO3 in the acid chamber and 0.05 mol/L of LiOH in the base chamber along with 0.1 mol/L of LiOH as the electrode solution were employed in ED-1 stack. The tests conducted with ED-2 stack using 0.05 mol/L of H3BO3 and 0.05 mol/L of LiOH as acid and base chambers solutions, respectively, with an electrode solution of 0.1 mol/L of LiOH at 20 V showed a greater performance for boron removal (81%) than with ED-1 stack. While lower boron and lithium recoveries (38.8 and 50.2%) in ED-2 system were achieved, there was almost no difference between two stacks in terms of lithium removal with a value of about 99.8%.