ELECTROCHEMICAL-BEHAVIOR OF CHALCOPYRITE IN THE PRESENCE OF SILVER AND SULFOLOBUS BACTERIA

The electrochemical behaviour of massive chalcopyrite electrodes has b een studied in an acid medium (pH 1.5) containing silver ions (0.02 g dm(-3) Ag+) and thermophilic bacteria (68 degrees C). Preliminary test s on particulate electrodes made from graphite, elemental sulfur and A g2S were included to determine the electrochemical response of reactan ts (Ag+) and products (S degrees and Ag2S) associated with the dissolu tion of chalcopyrite in the presence of silver. Massive chalcopyrite e lectrodes under potential scan showed a dependence on the dissolution of the Ag2S film with both the time of contact with the silver solutio n and [Ag+]. As well as Ag2S, metallic silver was detected on the chal copyrite surface. It has been demonstrated that Fe3+ and bacteria play an important role in the regeneration of the Ag2S film. The breakdown of this film is a requirement for the further dissolution of chalcopy rite. The bioleaching of chalcopyrite with thermophilic microorganisms in the presence of silver decreased the decomposition potential of th e electrode and favoured its electrodissolution. Bioleaching treatment in the presence of silver ions for periods of time longer than two we eks did not improve the surface reactivity. However, in the initial st ages of the process, the lower reactivity of the bioleached electrodes was probably related to a toxic effect of silver on the microorganism s.