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

Abstract

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 μ-S and orthorhombic ɑ-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 ɑ-S8 and μ-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 µ-S was favorable for bacterial adsorption and that the addition of µ-S could promote the copper extraction rates by A. ferrooxidans, while the addition of ɑ-S8 inhibited the copper extraction rates. The XANES results showed that both cases with the addition of ɑ-S8 and µ-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 µ-S, with more genes upregulated than ɑ-S8. The DFT results indicated that both ɑ-S8 and µ-S could adsorb on the CuFeS2 (001) surface easily, and µ-S could make the CuFeS2 surface obviously change, while ɑ-S8 hindered the adsorption of bacterial cells. Of note, µ-S could enhance the interaction between the CuFeS2 (001) surface and bacterial cells with stronger bonding and more transferred electrons than ɑ-S8.