A comparison of bioleaching of covellite using pure cultures of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans or a mixed culture of Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans

The aim of this investigation was to determine the efficacy of covellite bioleaching using pure cultures of Acidithiobacillus ferrooxidans or Acidithiobacillus thiooxidans and a mixed culture composed of At. thiooxidans and Leptospirillum ferrooxidans. The experiments were carried out in shake flasks with or without iron(II) (1 g/L as ferrous sulphate) at pH 2.0. Inocula of both iron-oxidising bacteria were obtained from cultures with iron(II) as the sole energy source, whereas At. thiooxidans inoculum was taken from a culture growing on sulphur. The solubilisation of copper in flasks inoculated with At. thiooxidans was greatly enhanced in the presence of additional iron(II) achieving 62% copper extraction in 30 days. This result agrees with a mechanism proposed recently. On the other hand, the effect of supplemental iron was not so important for covellite leaching by the At. ferrooxidans culture and the mixed culture. Copper solubilisation by the At. ferrooxidans culture was nearly the same as that for the mixed culture (51% versus 55%). (C) 2003 Elsevier B.V. All rights reserved.