Microbial dissolution of a low grade Indian chalcopyrite ore using mixed culture of Mesophiles

An enriched culture of mesophiles namely, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans derived from mine water of Malanjhkhand Copper Project (MCP), India in the ratio of 4:1, and adapted on 5%(w/v) ore at 35oC was used for the bioleaching of a low grade chalcopyrite ore (0.27% Cu). Optimum copper recovery of 91% was achieved at 1.5pH and 10% (w/v) pulp density in 30days using <50μm particles. Copper recovery decreased to 82% when pH was raised to 2.5 under similar conditions. Higher copper recovery at pH 1.5 may be attributed to the improved bacterial activity (7.0x108 cells/mL), higher redox potential (666mV) and formation of minimum amount of hydronium jarosite, which was prominent at higher pH. Copper recovery was 41.2% in sterile control leaching conditions at 1.5pH. However, unadapted bacterial consortium yielded copper recovery of 69.4% only in 30 days at pH 1.5 under the above conditions. Higher metal recovery with adapted mixed culture may be attributed to increased rate of iron bio-oxidation. The biorecovery of copper from the MCP lean grade ore appeared to follow direct as well as indirect mechanism.