Acid leaching of a copper ore by sulphur-oxidizing microorganisms

This study examines the potential for use of biogenic sulphuric acid for leaching of a low-grade Brazilian ore containing 0.64% copper occurring as brochantite, Cu4SO4(OH)6, and as malachite, Cu2CO3(OH)2. Ore was agglomerated with elemental sulphur and sulphur-oxidizing microorganisms. Copper extraction was more efficient from inoculated ore amended with 6.67 kg So/t of ore, compared to uninoculated ore with no added So and leached with an acid solution maintained at pH 2.0 with sulphuric acid. The rate and extent of copper bioleaching were proportional to the amount of added So. A maximum of 88% copper was extracted after 9 weeks of bioleaching with 13.3 kg S added/t of ore. Cu extraction was more efficient if sulphur was uniformly mixed with the ore than if the sulphur was added only to the upper zone of the ore column. There was no evidence that acid leaching of Cu from this ore was far more efficient in ore crushed by a high pressure grinding rolls (HPGR) compared to a conventional jaw crusher.