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In this work, we present an electrochemical study using a carbon paste electrode modified with chalcopyrite (CuFeS 2) in solution A of T&K medium with different ferrous ion concentrations, in the absence and presence of the bacterium Acidithiobacillus ferrooxidans. The aim was to evaluate the influence of ferrous ions and bacteria on the electrochemical behavior of chalcopyrite. Electrochemical impedance spectroscopy (EIS) was used to investigate the processes occurring at the electrode/solution interface in the different systems, considering the charge transfer reactions involving chalcopyrite and ferrous ions, the presence of a multicomponent layer, and diffusion. The main changes in the chalcopyrite response occurred before 67 h or 43 h of immersion, in the absence or presence of ferrous ions, respectively, indicating that the surface oxide layer present on chalcopyrite was dissolved faster in the presence of ferrous ions. The addition of bacteria decreased the charge transfer reaction resistance, especially when ferrous ions were present. In the presence of Fe 2+ , sulfur and jarosite were detected in the solid residues after leaching, while only jarosite was detected in the bioleaching experiment. The results suggested that ferrous ions accelerated the dissolution of chalcopyrite, and that overlayers including biofilms did not halt chalcopyrite dissolution, indicating that there was no passivation.

ABSTRACT:Copper is one of the metals with great economic interest and about 70% of it is found in nature as chalcopyrite mineral (CuFeS 2 ). Due to its slow dissolution kinetics, chalcopyrite dissolution is still a challenge for industries and researchers. Control of redox potential though has been said to be the key for increasing dissolution rate in chalcopyrite leaching systems. The current work investigated the effect of redox potential by ferrous ions addition on chalcopyrite (bio)leaching experiments. In abiotic systems, 90% of copper was leached into solution when redox potential was kept low (around 420 mV/Ag/AgCl) whereas in bacterial systems (610 mV/Ag/AgCl) low copper dissolution was observed. SEM analysis suggested presence of new phases that were confirmed by XRD to be elemental sulfur and jarosites and a significant decrease of chalcopyrite peak heights in these analyses was also observed. Jarosite was the only new phase detected in bacterial systems. Passivation of chalcopyrite surface did not occur in either conditions. The results clearly show that low redox potential along with presence of ferrous ions has positively influenced copper recovery, confirming the existence of a critical redox potential range where chalcopyrite dissolution is favored.