EFFECTS OF GALVANIC INTERACTIONS OF SULFIDES ON EXTRACTION OF PRECIOUS METALS FROM REFRACTORY COMPLEX SULFIDES BY BIOLEACHING

A process employing bioleaching was conceptually developed and tested for the recovery of precious metals from complex sulfide ores and tailings. Since the precious metals were associated with the sulfide minerals, a bulk sulfide flotation concentrate was produced and then subjected to bioleaching using Thiobacillus ferrooxidans, before final treatment of residues by cyanidation to extract the gold and silver. In agreement with the galvanic series of sulfides, our experimental results demonstrate that in a mixed sulfide concentrate containing pyrite (FeS2), galena (PbS), sphalerite (ZnS), and chalcopyrite (Cu FeS2), the biooxidation-leaching of chalcopyrite, sphalerite and galena proceeded preferentially, while that of pyrite was retarded compared with bioleaching of a chiefly pyrite concentrate. This was reflected in the recovery of precious metals also. A recovery of over 95% of gold and 98% of silver from the complex sulfide ore concentrate could be achieved after bioleaching ahead of cyanidation extraction.