Electrochemical techniques were conducted to clarify the role of solution potential and temperature under a variety of experimental conditions similar to those found during the mesophilic and thermophilic biooxidation of chalcopyrite (CuFeS2). Despite a large number of publications dealing with the bacterial leaching of CuFeS2, three central aspects remain unclear: How to dissolve preferentially copper from CuFeS2, the effect of temperature on the extent of CuFeS2 passivation, and the behavior of ferric ions on a polarized CuFeS2 surface. Anodic characteristics showed that CuFeS2 passivation was more severe in the potential range 0.45-0.65 V saturated calomel electrode at 25 degreesC. However, there was no evidence of CuFeS2 passivation at higher temperatures (45 and 65 Cu was preferentially dissolved from CuFeS2 at lower potentials and high temperatures at a ratio copper to iron of about 3:2. Cathodic characteristics showed that the ferric ions inhibited the leaching process when the CuFeS2 surface was polarized at high potentials and low temperatures. (C) 2002 Elsevier Science Ltd. All rights reserved.