EFFECT OF CATALYTIC IONS ADDITION ON THE BIOOXIDATION OF CHALCOPYRITE

The influence of C r and Ag + ions on lhe bacterial and chemical dissolution of chalcopyrite was evaluated by means of the electrochemical noise analysis (ENA). ENA is a generic term describing the phenomenon of spontaneous fluctuations of potential or current noise of electrochemical systems. lt provides a nondestructive condition for investigating corrosion processes and can be useful to understand the electrochemical oxidation of mineral. The dissolution of chalcopyrite electrode was evaluated at O and 24 hours contact time, in acidic medium and in the presence or absence of bacterium. lt was observed that the addition of silver ions does not improve the chalcopyrite dissolution rate during the course of the experiment, in chemical or bacterial attack. lt can be explained by fonnation of a passive silver sulfate film that modifies lhe mineral I solution interphase. However, the current noise fluctuations were much higher in the medium containing chloride ions. As a consequence, noise resistance, R11 , calculated from amplitude and frequencies of these oscillations, was about tive times lower in the presence of A. ferrooxidans . It indicates that cr ions improve the bacterial attack on lhe mineral sulfide, once increased the ionic strength of lhe leaching medi um decreasing lhe electrostatic repulsion between bactcria and electrode surface and facilitate the oxide, sulfur and/or sulfide passive film degradation. KEYWORDS: chalcopyrite, Acidithiobaci//usferrooxidans, electrochemical no i se analysis, bioleaching. 59 60 Daniela G. Horta, Heloísa A. Acciari, Denise Bevilaqua, Oswaldo Garcia Júnior, Assis V. Benedetti