Evaluating the potential of the membrane technology for copper recovery from effluents and wastewater generated at copper mines and processing facilities in South Africa

Abstract

Membrane separation is a well-known and widely used method in water treatment. It finds applications in mining and metallurgical processes and offers many potential benefits to the mining industry, such as significant water recovery from mine wastewater, excellent metal upgrades, and reagent recycling from process streams. This study evaluated membrane technology for the recovery of copper and recycling clean water from an aqueous effluent stream generated from copper mines. The copper content in the test work was 639 mg/L copper (Cu) in a synthetic solution and 427 mg/L copper in a real solution. Seven commercial flat sheets (FS) membranes were tested at a laboratory scale, and at the pilot scale, one spiral-wound membrane was tested. The performance of membranes was assessed, as well as the effect of various process parameters. It was demonstrated that nanofiltration (NF) technology could be effectively used to treat wastewater generated by copper mines. Five of seven evaluated membranes (AMS A3011, A3012, A3014, B4021, and DOW N90) were found to reject >90% of copper into the concentrate at operating pressure of 20, 30, and 40 bar at ambient temperatures. In all the evaluated membranes the following was observed; o An increase in the operational pressure increased operational flux; o However, as pressure and temperature increased, the rejection of copper and other metals decreased. During the optimisation of DOW N90 operational parameters, the following trends were identified: o Operational pressure is required as it improved operational flux, increased the rejection of copper, and minimized flux depreciation with time. o The temperature had a negative impact on flux; however, the optimum operating temperature has to be found because copper rejection can be compromised at higher temperatures. The DOW NF90, which was tested on a pilot rig, was also found to be suitable for treatments of the diluted copper solution, with a high copper rejection achieved. And a permeate recovery of 53.64% was achieved, but this value can be improved by increasing copper in the concentrate for further recovery.