Chalcopyrite Bioleaching at High Sulfate Concentrations

The efficiency of chalcopyrite bioleaching in a high sulfate background was evaluated using acidophilic microorganisms adapted to sulfate. The concentration of magnesium sulfate added to mesophilic, moderately thermophilic and thermophilic bioleaching tests was equivalent to 100, 40 and 80 g L-1SO42-, respectively. Biological copper extraction was highest at 45 °C (67 %), followed by 60 °C (54 %) and 30 °C (16 %). Quantitative x-ray diffraction (QXRD) analysis of the ROM ore and bioleached residues revealed the complete disappearance of pyrrhotite and a significant reduction of pyrite at all temperatures. Significant chalcopyrite was leached at 45 and 60 °C; however, no chalcopyrite was leached at 30 °C. As the bioleach did not plateau after 31 days, it is possible that higher copper yields may have been achieved with prolonged leaching.