Extraction of nickel and cobalt from over-burden sample of chromite ore mines of orissa mining corporation

Abstract

Nickeliferrous laterite and chromite ores are located in the Sukinda region of Cuttack district in Orissa. The nickeliferrous over-burden generated from the chromite mines is in the order of 9 million tonnes per annum averaging about 0.7% Ni. The department of mines has shown an interest in exploring the possibility of extracting nickel and cobalt from laterite ore and the over-burden for future needs in the country. The National Metallurgical Laboratory, Jamshedpur and Regional Research Laboratory, Bhubaneswar, Council of Scientific and Industrial Research, Delhi are the two organisations involved in the recovery of nickel and cobalt by reduction-roast-ammoniacal leach solvent-extraction electrowinning process. In this process different type of reductants, such as fuel oil, reducing gas, coal, saw dust could be used for metallisation of nickel and cobalt. Reduction roasting experiments were carried out in horizontal tube furnace in batch and in continuous 1 Kg/hr. scale in vertical retort furnace using coal as a reductant. Characterization studies of the overburden were done by X-ray powder diffraction and thermal analysis. X-ray powder diffraction results showed the presence of goethite phase (a - FeO OH) and was confirmed by D.T.A. peak around 300-degrees-C, TG curve showed some weight loss upto 450-degrees-C and no further loss in weight indicating the complete transformation of goethite to a - Fe2O3 and no other phase transformation beyond this temperature range of study (450-degrees-C-1000-degrees-C). Reduction roasting studies in horizontal tube furnace were initially carried out on 50 gm of pellets. About 10% coal was found to be the optimum where percent recoveries of nickel and cobalt were maximum (90% Ni and 70% Co). Variation of reduction time, leaching period were studied. In vertical retort furnace reduction of the sample (pellets) was done in a moving bed at 1 Kg/hr. Leaching was done batchwise on 50 gm, 200 gm and 5 Kg scale. Recoveries of around 90% Ni and 70% Co were achieved. From these experimental trials on batch and continuous moving bed reactor, it can be concluded that coal is a cheap and very effective reductant for the overburden sample