Bioleaching of chalcopyrite by pure and mixed cultures of Acidithiobacillus spp. and Leptospirillum ferriphilum

Bioleaching is an economical method for the recovery of metals that requires low investment and operation costs. Furthermore, it is generally more environmentally friendly than many physicochemical metal extraction processes. The bioleaching of chalcopyrite in shake flasks was investigated with pure and mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Acidithiobacillus caldus, and Leptospirillum ferriphilum. The mixed cultures containing both iron- and sulfur-oxidizing bacteria were more efficient than the pure culture alone. The presence of sulfur-oxidizing bacteria positively increased the dissolution rate and the percentage recovery of copper from chalcopyrite. Mixed cultures consisting of moderately thermophilic L. ferriphilum and A. caldus leached chalcopyrite more effectively than mesophilic A. ferrooxidans pure and mixed cultures. The decrease of the chalcopyrite dissolution rate in leaching systems containing A. ferrooxidans after 12–16 days coincided with the formation of jarosite precipitation as a passivation layer on the mineral surface during bioleaching. Low pH significantly reduces jarosite formation in pure and mixed cultures of L. ferriphilum and A. caldus.