Increasing the recovery of copper from a chalcopyrite concentrate in bioleaching by electrochemical controlling of the redox potential on a continuous scale

One of the main limitations and the reason for the slow dissolution kinetic of chalcopyrite in acidic ferric sulfate solutions is surface passivation at potentials higher than critical values. In order to optimize the operating parameters of chalcopyrite bioleaching, the effect of redox controlling on the recovery of copper from chalcopyrite concentrate was evaluated. The used flotation concentrate was mainly contained chalcopyrite (45.7%), pyrite (23.4%) and secondary copper sulfides (10.8%). Bioleaching and electrobioleaching experiments were performed in a continuous set-up containing a preparation tank and three bioreactors using moderate thermophile bacteria. Results of conventional bioleaching experiments indicated that the recovery of copper was low. To increase the copper recovery, the effect of redox potential on the leaching of chalcopyrite was investigated by electrochemically controlling of redox potential. The results of experiments conducted in different redox potential ranges showed that reducing the redox potential from high levels to optimum window (420-440mV Ag/AgCl) caused a 75% increase in copper recovery compared to conventional bioleaching. In the best conditions studied in this research (7-days residence time, 420-440 mV redox window, acidity of 55 Kg/ton and 30μm particle size) copper recovery was approximately 94%.