Tank bioleaching of low-grade chalcopyrite concentrates using redox control

Bioleaching tests were carried out in bench-scale piloting facilities, comprising fully controlled multi-stage continuously operated reactor systems using moderate thermophile and thermophile consortia under both uncontrolled and controlled redox potential conditions to assess the effect of temperature and redox control on chalcopyrite leach kinetics. The bench-scale studies demonstrated that copper recoveries > 95% could be achieved without redox control, using a thermophilic culture at 70 °C. Acceptable copper extractions could not be achieved under similar conditions at 45 °C. A significant increase in the copper leach kinetics and copper extractions was, however, achieved by controlling the redox potential in the 45 °C system at 420 mV. Final copper extractions increased from 64% at high redox potential to 97% under controlled redox conditions and as a result of the improvement in the Cu leach performance there is potential to reduce the overall residence time of the process. A key advantage of the process is that the bioleaching process costs are minimized, since the pyrite was not oxidized.