Copper Biodissolution from a Low Grade Chalcopyrite Ore by Unadapted /Adapted Acidithiobacillus ferrooxidans S. C. Pale, K. D. Mehta', Abhilash ', V . Kumar', B. D. Pandey' and T. R. Mankhand2 1 M.E.F. Division, National Metallurgical Laboratory, Jamshedpur - 831007 2 Metallurgical Engineering Dept., I.T., B.H.U., Varanasi - 221005 ABSTRACT The depletion of high-grade deposit of copper around the world has drawn attention for the utilisation of low-grade reserves . Malanjkhand Copper Project ( MCP) in India is a low- grade ore containing -0.3% Cu in which copper metal is found to be present as chalcopyrite associated with pyrite in quartz veins and granitic rocks. In order to extract copper from this material , an alternate processing option such as bioleaching has been followed. Bench scale bioleaching experiments were carried out using Acidithiobacillus ferrooxidans (Ac. Ti) isolated from mine water . On using unadapted Ac. Tf isolate directly at pH 2.0 and 35°C, the optimum leaching conditions in shake flask were found to be 5% pulp density ( PD), 2.OpH , 35°C temperature for <50p . m particles , yielding 72% Cu biorecovery in 35days. The Tf isolate when adapted to the ore and employed for the bioleaching of the ore at 5% PD (w/v), 2.OpH and 25 ° C with three particle sizes viz.150 - 76μm, 76-5011m and < 50μm , resulted in recovery of 38 . 31%, 29.68 % and 47 . 5% Cu respectively with a rise in Eh from 530 to 654 mV in 35 days. Under similar conditions , the unadapted strain gave maximum recovery of 44. 0 % for <50pm ore size with rise in Eh from 525 to 650mV . Copper biorecovery increased to 75.3 % with the adapted isolates at 35°C for the finer particles of <50gm at 2.OpH with a rise in cell count from lx l 07 cells/mL to 1.13x109 cells/mL in 35 days. The biodissolution of copper from chalcopyrite with the involvement of adapted Ac. Tf species resulted in the improvement of iron oxidation rate ( Fe2+ to Fe'`) and consequently higher redox potential. INTRODUCTION With the depletion of high grade resources of ores, there is a need to process low grade discarded ores and tailings to meet the current demand of metals. The existing conventional processes are not suitable to recover the metals from such resources due to high energy consumption and cause environmental pollution. The biohydrometallurgy is one such approach which can recover metals economically without affecting environment with the application of microbes. The process has been initiated in isolation of a mesophilic and acidophilic bacteria from mine waters and its usage in bioleaching of copper ores. These bacteria have been used for dissolution of copper from different low grade ores and tailings and metal recovered 1-4. Various researchers globally worked in elucidating the role of bacteria in bioleaching in catalyzing the oxidation of metal sulphides 5'10. Two mechanisms of bacterial action have been suggested: (a) a direct attack of the bacteria on the mineral surface and its oxidation through enzymatic reactions; and (b) an indirect attack, where the bacteria regenerate the oxidizing agent of the mineral by means of the oxidation of Fe(II) to Fe(III) via thiosulphate or poly- sulphide depending on the type of mineral. In India the demand for copper is also increasing with industrialisation and to meet the requirement of copper, low grade ores / tailings located in Malanjkhand (M.P.), Khetri ( Rajasthan ) and Singhbhum (Jharkhand ) regions can be important source. The Malanjkhand Copper Project ( MCP) is the largest open-cast mine having copper deposits of 22 million T of low grade ores (-4.26%). Biohydrometailurgical processing can be an alternative route to recover copper from these low grade reserves 11, 12. At NML, R & D studies have been carried out on bench scale for bio-leaching of lean MCP ore. This paper explains the optimizing of process parameters in bio-dissolution of copper metal from the ore using Acidithiobacillus ferrooxidans (Ac.Tf), initially derived from mine water of MCP. A series of experiments have been carried out using Ac. Tf unadapted and the adapted isolates to compare the efficiency of bio-leaching.