Microbial assisted galvanic leaching of chalcopyrite concentrate in continuously stirred bioreactors

Abstract

The objective of this study is to combine two proven technologies, namely galvanic and microbial assisted leaching of chalcopyrite in a novel way. Using a commercial chalcopyrite-rich flotation concentrate and pure natural pyrite samples from an Iranian copper mining complex as well as mixed cultures of moderately thermophilic microorganisms, continuous electrochemical bioleaching tests were performed in stirred bioreactors at 50 °C as a first step towards a commercial application of microbially assisted galvanic leaching of chalcopyrite.From the results of this study, the importance of oxidation reduction potential (ORP) on the catalytic interaction between chalcopyrite and pyrite could be pointed out as a main parameter for successful bioprocessing of chalcopyrite concentrates. Optimization of the particle size of feed (D80) and adjusting the ORP in the range between 400 and 500 mV are important criteria, governing the electrochemical bioleaching rate of chalcopyrite concentrates. It is believed that the main reason for increased copper recovery could be the control of chalcopyrite passivation resulting from improved galvanic interaction between chalcopyrite and pyrite in the selected ORP range and the bacterial assisted oxidation of Fe2+ to Fe3+. Under optimum conditions of this study (T = 50 ± 2 °C, pH = 1.1 ± 0.2, ORP = 400–500 mV, solid load = 10%, stirring rate = 300 rpm) the copper extraction from chalcopyrite flotation concentrate during continuous electrochemical bioleaching operations in stirred bioreactors was >95%, which should be high enough to justify the process economically.