Selection of thermophiles for base metal sulfide concentrate leaching, Part I: Effect of temperature on copper concentrate leaching and silver recovery

•Copper-silver concentrate bioleaching was observed at 30, 48 and 76 °C.•S. thermosulfidooxidans displaced Acidithiomicrobium during leaching at 48 °C.•Bioleaching temperature influenced hydrometallurgical, post-leach silver extraction.•Thiosulfate was most effective Ag extractant with high temperature bioleach residue.

The influence of temperature on bioleaching of a copper-silver concentrate of a black shale-ore was observed at 30, 48 and 76 °C. Post-leach residues' weights and copper contents decreased with increase in leaching temperature while the iron contents increased through more iron precipitation. A designed, incremental increase in the concentration of copper in solution resulted in Sulfobacillus thermosulfidooxidans replacing a species of Acidithiomicrobium as the dominant iron-and mineral sulfide-oxidizing strain in the mixed culture used at 48 °C. The temperature of bioleaching influenced the hydrometallurgical extraction of silver from post-leach residues. Thiosulfate was most effective with a high temperature bioleach residue while ferric chloride and copper/ammonium/thiosulfate was most effective with a low temperature bioleach residue.