Electrochemical precipitation of chromium (Cr⁶⁺) from an electroplating wastewater

Abstract

This research was conducted in the laboratory to investigate an alternative of Cr removal from an electroplating wastewater using the electrochemical precipitation (ECP) process. The ECP unit consisted of an electrolytic cell made of two steel plates representing anode and cathode. The DC power source applied to the ECP unit had current (I) and electrical potential (E) of 3-6 A and 30-75 V, respectively. Electroplating wastewater used in the experiments contained Cr⁶⁺ in the range of 215-3860 mg/l, and the pH was 1.5. The parameters varied during the ECP experiments were: E, hydraulic retention time (HRT), Cr⁶⁺ concentration, conductivity and initial pH. The optimum ECP conditions found were electrical potential, 75 V; current, 4.8 A; HRT, 50 min; initial pH, above 3.2. Under these conditions, the Cr⁶⁺ concentrations remaining in the effluent were less than 0.2 mg/l. Sludge produced in the ECP unit had a sludge volume index (SVI) of 60-80, an indication of sludge settleability. X-ray fluorescence analysis of the ECP sludge revealed formation of Fe₂O₃ and FeCr₂O₄ as the main products. Power consumption of the ECP unit was found to be in the range of 14.7 - 20 kWh/m³ of wastewater. The economics of the ECP process was evaluated and compared with some conventional treatment processes for Cr removal.