The laid down tailings accumulated during more than 40 year operation of the Gecamine's concentrator at Kipushi, Democratic Republic of Congo present nowadays a reprocessing challenge with both economic and environmental implications. An experimental study aimed at reflotation of this material to bring sulphide concentrate suitable for further processing by hydrometallurgical means has been realized. The results from a bioleaching route chosen to accomplish the later task by use of moderate thermophilic and mesophilic microorganisms are reported. It has been found that due to the complexity of the treated material, the leaching pattern of the two principal metals of interest, copper and zinc vary. Whilst the copper bearing minerals have been leached relatively fast by direct mechanism, the leaching kinetics for the zinc minerals has been moderate involving predominantly an indirect mechanism. The effects of pH and temperature variations and ferrous ions addition upon the extent of copper and zinc dissolution have been examined. The presence of ferrous ions has been found beneficial for the leaching of sphalerite, however the concomitant formation of jarosite precipitates has led to copper leaching hindrance. Similarly, the rapid zinc solubilisation has been counterbalanced by decrease in rate of copper dissolution. It has been found that the increased leach temperatures associated with use of moderately thermophilic microorganisms, have limited the passivation phenomena and have brought better extraction especially for zinc.
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