Bioleaching of a Chalcopyrite Concentrate with Mesophile and Thermophile Microorganisms: A Pilot Scale Approach

This technical contribution aimed at extracting copper from a flotation concentrate comprising copper sulphides such as chalcopyrite (CuFeS2), at a content of nearly 70%, and bornite (Cu5FeS4) as 30%, amounting a copper content of 28.8%. The pilot column was loaded with around 1 ton of a mix of a support rock coated with flotation concentrate in a ratio of 9:1, respectively (890kg of support rock to 96.2 kg of flotation concentrate). The coating operation was done pouring the flotation concentrate slurry, with 70% of solids, on top of the support rock on a rotating mixer. The aqueous phase of the slurry was a mix of sulphuric acid solution, at a pH 1.5, with the mesophile, moderate and extreme thermophile microorganisms at 106 cells per gram of flotation concentrate. During the leaching process a period of 7 days were used to make the mesophile microorganisms from acting at 30 oC, where the copper concentration in solution started levelling out. At that time the temperature was raised gradually up to 50 oC, where the moderate thermophile microorganisms reach their optimum temperature, remaining there for 14 days levelling out the copper concentration as such. Finally, the temperature was raised up to 66 oC, which is the extreme thermophile temperature, remaining at that value for 83 days. Therefore, the copper extraction reached, considering the contribution of the three consortium used, was of 90.6%, which was really high bearing in mind the considerable chalcopyrite content of that concentrate. We are expecting to enhance such extraction with optimization of the experimental parameters.