Interfacial alteration of pyrite caused by bioleaching

Abstract Bioleaching, an environmentally friendly and economical method to oxidize metal containing minerals and gold extracted from refractory gold ores, has been extensively studied over the past few decades. During bioleaching, pyrite surfaces are modified using a mixed culture and the biofilm that affects the surface properties of the material. We characterized the pyrite interface during bioleaching using confocal laser scanning microscopy and spectroscopy, and further calculated the interfacial energy to study the interfacial alteration during bioleaching at 45 °C with an initial pH of 1.5 and a cell density of 2 ± 0.2 × 108 cells/mL. The results show that pyrite dissolution can be separated into three stages based on dissolution rates of 0.43, 0.89, and 2.26 mg/cm2·d, respectively. Surface roughness increased from 0.041 ± 0.023 to 13.587 ± 5.767 μm and corrosion pit depth from 0.331 ± 0.270 to 84.356 ± 35.623 μm. Ferric ions can increase the bond length and the biotic action can promote bond breakage. A small amount of elemental sulphur can be detected on pyrite surface on the sixth day, which increased the interfacial energy from 43 to 61 ± 6 mJ/m2. If covered with biofilms, the hydrophilicity of pyrite surfaces increased, while hydrophobicity increased in the absence of biofilms. The interfacial energy of pyrite decreased to 2 ± 1 mJ/m2 when covered by biofilms because of the combination of Fe O bonds and phosphodiester groups in the extracellular polymeric substances.