A New Direction for Biomining: Extraction of Metals by Reductive Dissolution of Oxidized Ores

Biomining, the biotechnology that uses microorganisms to extract metals from ores and concentrates, is currently used exclusively for processing reduced ores and mine wastes. Metals of economic value also occur extensively in oxidized ores, such as nickel laterites. While these are not amenable to oxidative dissolution, the ferric iron minerals they contain can, in theory, be disrupted by iron reduction, causing associated metals to be released. We have harnessed the ability of the facultatively anaerobic, acidophilic bacterium Acidithiobacillus ferroooxidans to couple the oxidation of elemental sulphur to the reduction of ferric iron in the goethite fraction of a limonitic nickel ore at 30 degrees C. Nickel and other metals (Co, Cr and Mn) were effectively solubilised and maintained in solution due to the low pH (1.8) of the leach liquor. The results highlight the potential for the bioprocessing of oxidized, iron-rich ores using an approach that is energy-saving and environmentally-benign compared with metallurgical processes currently applied to the extraction of Ni from lateritic ores.