Treatment of raffinate generated via copper ore hydrometallurgical processing using a bipolar membrane electrodialysis system

Abstract

The raffinate generated during copper ore hydrometallurgical processing is difficult to be treated because it is strongly acidic, and has high concentrations of heavy metals (Iron, Zinc, Copper etc). In this study, a bipolar membrane electrodialysis (BMED) system was studied for treatment of this challenging stream because in which salts can be converted into their corresponding acids and bases, which enables resource recovery in raffinate. The target was to reuse the raffinate as a leaching influent, to achieve zero discharge of wastewater. It was found that 85.9% of SO42− in the raffinate could be recovered by the formation of H2SO4. The removal rates of heavy metals were 99.3% (iron), 99.1% (zinc), 99.0% (copper), 84.9% (nickel), 70.6% (chromium), 95.8% (cadmium), and 94.8% (arsenic). The heavy metal cations were mainly removed in the heavy metals chamber (HMC) and anions were mainly removed in the acid compartment. A current density of 3.0 mA/cm2, a volume ratio between the raffinate chamber (RC) and the HMC 1:15, and a duration of 40 h were the optimal experimental parameters. Increasing the RC number from one to two and three increased the current efficiency from 54.0% to 106.9% (two) and 157.9% (three), and decreased the specific energy consumption from 0.160 to 0.108 and 0.089 kWh/L of raffinate. It was concluded that the raffinate can be used as a leaching solution after treatment and the studied BMED process is an effective technique for the treatment of raffinate.