Bioprocessing of a Low-grade Chalcopyrite Ore by the Isolate of Acidithiobacillus Ferrooxidans

Bioprocessing for copper recovery from a lean grade chalcopyrite ore of Malanjkhand Copper Project (MCP) is reported. This ore with 0.3-0.4% copper, which is adjacent to the rich grade ore (09-1.0% Cu), available in large amount is untouched for want of a suitable option, can be utilized to meet the growing demand of the metal in the country. Different leaching parameters such as pH, temperature, pulp density, particle size, etc; were optimised in shake flask experiments using Acidithiobacillus ferrooxidans (A.ferrooxidans) isolated from the source mine water. Sterile sets were also run to assess the contribution of chemical leaching in parallel with bioleach sets. The leaching under sterile control conditions recorded poor metal recoveries. In bioleach experiments, leaching of copper showed increasing trend with dissolved ferric iron in solution indicating the role of indirect leaching mechanism also. A high redox potential (674mV) observed during the bioleaching may be attributed to the enhanced bacterial oxidation thereby resulting in 72% Cu bio-recovery in 35 days at 35℃, pH 2, 5%PD and with <50μm ore particles. With the coarser size of the ore, the copper recovery was comparatively lower under the similar conditions. XRD phase identification of the ore and the leach residue showed the formation of jarosite limiting the bio-dissolution of the metal.