In situ detection of Cu2+, Fe3+ and Fe2+ ions at the microbe-mineral interface during bioleaching of chalcopyrite by moderate thermophiles

Abstract

Bioleaching of metal sulfides represents an interfacial process in which the spatial relationship of metal ions with microbial cells and extracellular polymeric substances (EPS) is complex. The dissolution of chalcopyrite, cell attachment, and biofilm formation patterns were assessed during bioleaching with mixed cultures at 45 °C. The analysis of confocal laser scanning microscopy (CLSM) indicated that EPS were laid flat on the surface of chalcopyrite coupons, forming monolayer biofilms, with significant amounts of Fe3+, Fe2+ and Cu2+ enriched at the cell-chalcopyrite interface. In addition, the metal ions from mineral surfaces were extracted by ultrasonication. The results showed that the mineral surface is enriched with large amounts of Fe3+ (12.07 mg/g) and Cu2+ (10.82 mg/g) during the final stage of bioleaching, and more Cu2+ ions and iron maters from bio-oxidizing maybe were enclosed in the EPS space. It was inferred that the EPS with jarosite on the surface of chalcopyrite gradually acted as a weak diffusion barrier for Cu2+, and Fe3+ ions transference during bioleaching. These results can provide important evidence to reveal the hypothesis of ''metal ions enrichment on the mineral surface'' and benefit a further understanding of the bioleaching mechanism.