The differential effect of amorphous ?-S and orthorhombic a-S8 on chalcopyrite bioleaching by Acidithiobacillus ferrooxidans

Elemental sulfur (S0), as one of the most important intermediates formed during chalcopyrite bioleaching, can exist in a variety of allotropic forms, among which amorphous mu-S and orthorhombic a-S8 are the most common forms. Although previous studies have focused on the effect of S0 on chalcopyrite bioleaching, how S0 allotropes affect chalcopyrite bioleaching is unclear. Therefore, in this work, the differential effect of a-S8 and mu-S on chalcopyrite bioleaching by Acidithiobacillus ferrooxidans (A. ferrooxidans) was studied at the molecular and atomic levels by combining synchrotron radiation-based X-ray absorption near edge structure (XANES) spectroscopy, comparative transcriptome analysis and density functional theory (DFT) calculations, accompanied by the determination of solution behaviors and mineral surface morphologies. The results showed that mu-S was favorable for bacterial adsorption and that the addition of mu-S could promote the copper extraction rates by A. ferrooxidans, while the addition of a-S8 inhibited the copper extraction rates. The XANES results showed that both cases with the addition of a-S8 and mu-S could affect the formation and evolution of secondary minerals during bioleaching by A. ferrooxidans. The comparative transcriptome analysis showed that the gene expression of A. ferrooxidans was much more affected by the addition of mu-S, with more genes upregulated than a-S8. The DFT results indicated that both a-S8 and mu-S could adsorb on the CuFeS2 (001) surface easily, and mu-S could make the CuFeS2 surface obviously change, while a-S8 hindered the adsorption of bacterial cells. Of note, mu-S could enhance the interaction between the CuFeS2 (001) surface and bacterial cells with stronger bonding and more transferred electrons than a-S8.