Collaborative effects of Acidithiobacillus ferrooxidans and ferrous ions on the oxidation of chalcopyrite

In recent decades, the bioleaching of chalcopyrite has been successfully developed and employed in copper hydrometallurgy. Understanding the decomposition mechanism of chalcopyrite is also of great significance for environmental remediation because the microbial oxidation of metal sulfides in mining waste and outcrop rocks commonly causes serious environmental contamination. This study investigates the influence of Acidithiobacillus ferrooxidans (A. ferrooxidans) and added Fe2+ ions on the oxidation of chalcopyrite. The results show that A. ferrooxidans and added Fe2+ ions can collaboratively promote the recovery of Cu from chalcopyrite. In the bioleaching system with added Fe2+ ions, A. ferrooxidans prefer to oxidize soluble Fe2+ ions rather than decompose chalcopyrite to acquire energy, which inhibits the release of Cu at the first stage but enhances the growth of A. ferrooxidans. After reacting for 18 days, however, the produced Fe3+ ions greatly promote decomposition and release more Cu than the bioleaching system free of Fe2+, which remained in the rest experiments. Both the oxidation of chalcopyrite and the release of Cu in the bioleaching system are greater than what occurs in the chemical leaching system. Chalcocite, covellite, bornite, and elemental sulfur were identified as intermediate products, and a sulfur transforming route of S2-/S-2(2-) -> Sn2-/S-0 -> SO32- -> SO42- can be recognized by X-ray photoelectron spectroscopy. As the principle end product, jarosite covered the chalcopyrite grains and consequently inhibited further oxidation. It is noteworthy that the released Cu2+ ions barely suppressed the growth of A. ferrooxidans because they tended to be enriched only in extracellular polymeric substance (EPS), while Fe3+ ions could be found on both the cell surfaces and the EPS, which implies a potential mechanism for the survival of cells in a high Cu2+ solution. Collectively, an integrated model of chalcopyrite oxidation, collaborated by both chemical and microbial oxidation, has been proposed to elucidate the bioleaching mechanisms and to give a perspective on its hydrometallurgical and environmental applications.