The ability of bacteria to catalyse the oxidation of sulphide minerals is well known. This paper presents the results of the bacterial leaching of flotation tailings from a complex sulphide ore containing pyrite, chalcopyrite and sphalerite, with an assay of 5.4percent copper. The objectives of this study were to investigate the recovery of copper from the waste material which was not possible by physical methods. The laboratory scale tests were performed using a 5 litre stirred reactor on a continuous basis. Leaching was performed in several stages, with the residue from each run being releached to simulate a multistage process. The cooper level in the residue from the first stage of leaching was found to have increased from 5.4percent to 8.5percent, releaching this residue increased its copper content from 8.5percent to 13.3percent and a third stage test enhanced this to 18percent copper. The experiments revealed that the rate of bacterial oxidation of sphalerite was the most raipid and similar to theat pyrite, while chalcopyrite leached at a much reduced rate. After two stages of leaching approximately 84percent of the sphalerite, 80percent of the pyrite and 30percent of the chalcopyrite from the feed material had been oxidised. The results indicated that if the copper in solution was recovered and combined with the leach residue, a product could be obtained which would be suitable as a feed for a copper smelter.
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