Development of a tank bioleaching process for the treatment of complex Cu-polymetallic concentrates

The development of a bioleaching process for the treatment of complex Cu-polymetallic concentrates, containing chalcopyrite, sphalerite, galena and silver, using a moderately thermophilic culture operating at 45 °C is described. Initial development work and subsequent research for process improvements was carried out in bench-scale piloting facilities comprising a fully controlled multi-stage continuously operated reactor system. This facility was employed to assess the effect of a range of process parameters such as pH, redox potential, feed grind and solids concentration on microbial performance and metals extractions. The copper occurred mainly as chalcopyrite and it has been found that temperatures in the mesophilic range (35–37 °C) were not sufficient to achieve acceptable Cu extractions. However, Cu recoveries of > 95% could be achieved using a moderately thermophilic culture at 45 °C after fine milling of the concentrate, by operating at low pH levels and in some cases by operation at controlled redox potential levels. The high levels of Ag and base metals such as Cu, Fe and Zn present in the concentrates did have an inhibitory effect on microbial performance, but the ability of the micro-organisms to adapt and improve their performance after a long-term adaptation programme has been demonstrated.