Fungal big-leaching of low grade laterite ores

In this study, the mineral leaching ability of heterotrophic fungi, through secretion of organic acids, of various laterite ores was studied. Ores sub jected to the leaching process included saprolite, weathered saprolite, lim onite and nontronite. Strains of Aspergillus and Penicillium were found to be the most efficient organisms. Nickel extraction of up to 36wt%, cobalt o f 54wt% and iron of 0.76wt% were achieved using a direct leaching where met als were leached in the same phase where bio-acids were produced. Extractio ns were compared with chemical leaching, where leaching up to 79.5wt % Ni, 71 wt% Co and 50wt% Fe were leached. The variation in recovery was found to be strongly influenced by the ore mineralogy and the metal loss through el ectro-sorption properties of the ores. Effective and selective leaching by certain strains for cobalt and nickel, which was not otherwise observed in the chemical leaching process, suggest that microbiological activity, apart from bio-acid production is participating in the leaching process. (C) 200 1 Elsevier Science Ltd. All rights reserved.