Abstract

The electrochemical response of a massive chalcopyrite electrode at two different temperatures, 25°C and 68°C, were compared. The electrolyte used in the experiments was an acidic medium (0.4 g · 1-1 (NH4)2SO4, 0.5 g · 1-1 MgSO4 · 7H2O, 0.2 g · 1-1 K2HPO4 at pH = 2) which is suitable for the growth of the microorganisms involved in the bioleaching process. The chosen temperatures were optimum for the growth of the mesophilic (Thiobacillus ferrooxidans) and thermophilic (Sulfolobus) microorganisms. The experimental results at both temperatures were similar and confirmed that, during the anodic dissolution of chalcopyrite, a passive film is formed on the surface which restricts the oxidation reactions in the medium by diffusional control of the film. The different responses at the temperatures tested were due to the differing physical structure of the complex films of the electrochemically formed sulphides, polysulphides and elemental sulphur.