The impacts of pyrite/pyrrhotite on aqueous arsenic species in arsenopyrite pressure leaching: An XAS study

In this study, the impact of pyrite and pyrrhotite on the arsenic solution species in arsenopyrite pressure leaching were investigated by in-situ synchrotron X-Ray Absorption Spectroscopy (XAS). At an oxygen pressure of 28 bar and room temperature, the solution As existed as As(V) (0.5 M H2SO4 coexisting with arsenopyrite (Aspy), arsenopyrite/pyrite or arsenopyrite/pyrrhotite). At higher temperatures, the As(III) appeared and contributed to an increasing portion of the As species with the increase of temperature, which was re-oxidised to As(V) in the cooling stage. The addition of pyrrhotite (Po) facilitated the reduction of As(V) and stabilised As(III) in the solution. On the other hand, the addition pyrite in the leaching system favoured the presence of As(V) in the solution. This result could be explained by the catalysing effect of pyrite on As oxidation. The S k-edge XANES showed significant surface oxidation happened in arsenopyrite/pyrrhotite system but not in the other two systems, which further proved the high stability of As(III) in Aspy/Po system was because of the high reactivity of pyrrhotite that created a more reductive environment in the solution.