Cr(III) recovery in form of Na2CrO4 from aqueous solution using improved bipolar membrane electrodialysis

Abstract

During the process of Cr(III) recovery from an aqueous solution using an electrodialysis or a bipolar membrane electrodialysis (BMED) system, the purity and recovery are often low because of the migration of co-existing cation ions, such as Na+, K+, Ca2+, and Mg2+. In this study, a modified BMED system was used to recycle Cr(III) from an aqueous solution in the form of Na2CrO4, which is a basic compound in the chromate chemical industry, after Cr(III) was oxidized to Cr(VI) by H2O2 under alkaline conditions. The electrolyte concentration in the Cr(III) solution and the current density influenced the chromium recovery, current efficiency, and specific energy consumption. Under optimal experimental parameters, i.e., 5.0 g/L Na2SO4 in Cr(III) solution and a current density of 0.5 mA/cm2, more than Cr(III) of 87.8% could be recycled. When the number of recovery chamber modules increased from one to two and then three, the current efficiency increased from 23.2% to 45.6% and 67.6%, and the specific energy consumption decreased from 1.19 to 0.89 and 0.73 kW∙h/g of chromium. The present technology was therefore found effective for recovering Cr(III) from aqueous solutions.