Silver-catalysed bioleaching of a chalcopyrite concentrate with mixed cultures of moderately thermophilic microorganisms

Bioleaching of a chalcopyrite concentrate was studied using two mixed cultures of moderately thermophilic microorganisms, one from the drainage of Rio Tinto mines and the other obtained by raising the growth temperature of a mixed culture of mesophilic bacteria. Both cultures were adapted to different concentrations of silver (0.1-0.5 g of silver/kg of concentrate) to test their leaching capacity in the presence of this catalyst. The results showed the important role of silver in the chalcopyrite leaching process carried out at 45 degrees C. Copper yields increased around 3-fold over the control experiment without silver. At 50 degrees C, however, only one of the cultures remained active and the effect of silver was masked by strong jarosite precipitation, which increased with the amount of silver used. The 9K medium played a key role in this respect, and it was clear that more diluted media should be used to avoid this problem. Despite this drawback, the amount of copper extracted using the catalyst was double than that obtained without it. (C) 1999 Published by Elsevier Science B.V. All rights reserved.