Leaching of chalcopyrite with ferric ion. Part IV: The role of redox potential in the presence of mesophilic and thermophilic bacteria

This paper reports a study on the effect of redox potential in chalcopyrite bioleaching in the presence of iron- and sulphur-oxidizing bacteria. Bioleaching tests were carried out in stirred Erlenmeyer flasks at 180 rpm, with 0.5 g of chalcopyrite mineral, 99 ml of a sulphate solution of Fe³⁺/Fe²⁺ (with the redox potential ranging between 300 and 600 mV Ag/AgCl) at pH 1.8 and 1 ml of a mesophilic (35 °C) or thermophilic (68 °C) culture. The overoxidation of the leaching solution, due to the activity of iron-oxidizing microorganisms (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Sulfolobus BC), favoured the precipitation of jarosite on chalcopyrite surfaces followed by passivation. Iron- and sulphur-oxidizing microorganisms, such as A. ferrooxidans and Sulfolobus BC adapted for 4 months to elemental sulphur as the sole energy source, recovered their iron-oxidizing ability after being in contact with Fe²⁺.