Cr(VI) recovery from chromite ore processing residual using an enhanced electrokinetic process by bipolar membranes

An electrokinetic (EK) system improved by a bipolar membrane (BPM) (BPM-EK) was used to recycle hexavalent chromium (Cr(VI)) from the chromite ore processing residual (COPR) in the form of H2CrO4. The results showed that electrolyte concentrations in anode chamber (AC) and cathode chamber (CC) influenced the cell voltage and that 0.6 mol/L HNO3 in the AC and 1.0 mol/L NaNO3 in the CC were the optimal electrolyte concentrations. The current density also affected cell voltage, pH value of the COPR chamber (COPRC), Cr(VI) recovery efficiency, current efficiency (CE), and specific energy consumption (SEC). The optimal current density was 3.0 mA/cm(2). Compared to traditional EK processes, a higher CE and a lower SEC were obtained when two and three COPRC were equipped in the BPM-EK system and the Cr(VI) recovery efficiencies of all COPRCs were higher than 82%. With the increase in the number of equipped COPRC from one to two and three, CE increased from 0.60% to 1.67% and 2.30% and SEC decreased from 0.906 to 0.433 and 0.395 kW h/g, respectively. Experimental results showed that the BPM-EK process is an effective method for the recovery of Cr(VI) from COPR.