Pyrite-promoted dissolution of arsenopyrite in the presence of Sulfobacillus thermosulfidooxidans

The weathering of arsenopyrite in mine wastes is crucial for the formation of arsenic-containing acid mine drainage (AMD). Arsenopyrite is always associated with pyrite. In this study, the influence of pyrite on the biooxidation of arsenopyrite in the presence of Sulfobacillus thermosulfidooxidans was investigated by leaching experiments and surface characterizations. Bioleaching experiments of 5 days showed that the presence of pyrite increased the ferric concentration, and then accelerated arsenopyrite bioleaching, but increasing the mass ratio of pyrite to arsenopyrite above 1 had no obvious impact on further arsenopyrite dissolution. Synchrotron X-ray diffraction (S-XRD) and scanning electron microscopy (SEM) provided a direct understanding of arsenopyrite-pyrite galvanic interaction, and confirmed the formation of elemental sulfur and jarosite clusters, which did not passivate the arsenopyrite surface. Iron arsenate was detected by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). Additionally, the bioleaching experiments of 18 days indicated that the presence of pyrite facilitated the oxidation of As(III) to As(V) since most of arsenopyrite had been bioleached, and the increase of pyrite addition triggered the further oxidation of As(III).