Evaluating the performance of flow-electrode capacitive deionization for cadmium removal from aqueous solution

Abstract

Cadmium (Cd2+) polluted water causes harmful impact to human beings, life and the natural ecological environment. It is necessary to develop environmentally friendly treatment process for Cd2+ removals. In this study, flow-electrode capacitive deionization (FCDI) technology was proposed to treat Cd2+-containing aqueous solutions. The performance of FCDI in removing Cd2+ under various operating conditions was investigated, including the initial Cd2+ concentration, pH values and applied voltage, as well as the long-term operation behavior. The results showed that 50% of Cd2+ was removed at an initial concentration of 10 mg/L, and increased initial Cd2+ concentrations resulted in lower removal efficiencies. The pH of the solution significantly influenced removal efficiency, and the highest Cd2+ removal (54%) was observed at pH of 3. With the increase of applied voltage, the removal efficiency of Cd2+ by FCDI system increased, with a peak of 46.6% at 2.4 V. Then, the multi-cycle operation experiments demonstrated that a stable Cd2+ removal was achieved using FCDI. Multiple characterizations of activated carbon electrode before and after the experiment showed that the surface functional groups of activated carbon did not change after adsorbing Cd2+. The results obtained in this work indicated that FCDI can remove Cd2+ effectively and stably.