The role of iron-hydroxy precipitates in the passivation of chalcopyrite during bioleaching

The bioleaching of chalcopyrite an acidic sulphate nutrient medium was inve stigated using Sulfobacillus thermosulfidooxidans, a moderately thermophili c iron- and sulphur oxidising bacterium. Copper release to solution was ini tially rapid but this slowed significantly after about 50 hours. The decrea se in chalcopyrite dissolution rate coincided with significant precipitatio n of jarosite on the mineral surface. Cultures of the moderately thermophil ic acidophilic bacteria Acidimicrobium ferrooxidans, Sulfobacillus acidophi lus and Sulfobacillus thermosulfidooxidans were grown in anaerobic media co ntaining chalcopyrite passivated by jarosite. The moderate thermophiles use d the ferric ion in the jarositic surface precipitate as a terminal electro n acceptor in place of oxygen in the anoxic environment. Despite extensive bioreduction of the iron-hydroxy precipitates, it was found that the jarosi te was not completely removed and that subsequent biooxidation of the treat ed concentrate achieved no significant increases in copper release compared with concentrate that had not been subjected to prior biooxidation or bior eduction. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.