Chromium removal by a bipolar electro-chemical precipitation process

This research was conducted in laboratory to investigate an alternative for Cr removal from an electroplating wastewater using the electro-chemical precipitation (ECP) process. The ECP unit, operated in the bipolar mode, had six steel plates including the anode and cathode and was supplied with DC power. The electroplating wastewater used in the experiments contained Cr concentrations in the range of 570-2100 mg/l. The Cr removal efficiencies in the bipolar ECP units were higher than 99% and the Cr concentrations in the treated effluent were less than 0.5 mg/l. The acceptable conditions of the bipolar ECP unit treating the electroplating wastewater were found to be: I - 1.0 amp (or i - 6.70 amp/m²) and initial pH (pH_i) of 4.5. At these acceptable conditions, the electric power and steel electrode plate consumptions were 20.0 kWh/m³ and 1.1-2.8 kg-Fe/kg Cr removed, respectively. X-ray fluorescence and X-ray diffractometric analysis performed on the precipitated sludge revealed the main compounds to be maghemite (Fe₂O₃) and chromite (FeCr₂O₄). The percent Fe₂O₃ and FeCr₂O₄ contents of the dried ECP sludge were 68% and 25%, respectively. From the mass balance analysis, the percent of Cr removal by precipitation in the ECP unit and adsorption on the ECP sludge were 85.1 and 14.8%, respectively.