Enhanced chalcopyrite dissolution in stirred tank reactors by temperature increase during bioleaching

Primary copper sulfides, such as chalcopyrite, represent the most important copper resource and are currently mainly exploited by pyrometallurgy. Bioleaching is considered as environmental-friendly and economic alternative, and the technical feasibility of stirred tank reactor (STR) bioleaching of copper ore concentrates using acidophilic, iron- /sulfur-oxidizing microorganisms was proven. In case of copper concentrates from Kupferschiefer-type ore the copper recovery at temperatures suitable for moderately thermophilic acidophiles was, however, incomplete due to inefficient chalcopyrite dissolution. The presented study therefore aimed to enhance chalcopyrite dissolution by decoupling of growth and bioleaching activity of the acidophiles. This was achieved by a controlled temperature increase in laboratory bioreactor experiments with copper concentrate from Kupferschiefer-type ore. Total cell number and microbial activity monitoring allowed to define three stages of the bioleaching process: (i) growth phase, (ii) bioleaching phase and (iii) resting phase. The total residence time was close to seven days, according to copper recovery and iron oxidation activity. Experiments at constant temperatures (42 degrees C, 48 degrees C, 50 degrees C) and a controlled temperature increase at the end of the growth phase of 42/46 degrees C, 44/48 degrees C and 46/50 degrees C, showed that metal recovery was enhanced by incremental temperature increase and resulted in a lower redox potential. Copper recovery was improved from originally 86% to 97% by only 4-8 degrees C temperature increase. Mineralogical analysis confirmed an almost complete absence of chalcopyrite in the residues after the 46/50 degrees C bioleaching experiments. These results indicate a distinct temperature effect on copper recovery. The study defines parameters to make STR bioleaching of chalcopyrite-rich ores more efficient and economically feasible and ensures an optimal control of the process for upscaling.