Electrochemical oxidation of arsenopyrite in acidic media

Arsenopyrite (FeAsS) is a common sulfide mineral in base metals and precious metals ores and concentrates. The treatment of these kinds of ores involves frequently an oxidation step to improve metal recoveries. The study of the mechanisms occurring during the arsenopyrite oxidation is then necessary to optimize industrial processes, like bioleaching of arsenopyrite-bearing concentrates using autotrophic acidophilic bacteria. In this work, an electrochemical approach was used to study the arsenopyrite oxidation in acidic media. Cyclic voltammetry and chronoamperometry techniques were performed using a carbon paste electrode (CPE) and an acidic growth medium as electrolyte solution. This electrochemical study allows to determine that the oxidation of arsenopyrite in an acidic growth medium is performed in two steps. The first step corresponds to the initial surface oxidation of arsenopyrite to produce realgar (As2S2) and ferrous ions in solution (E < 0.55 V/SCE). During the second step, a catalytic oxidation of these interfacial products appears to solubilize finally H3AsO4 and ferric ions (E > 0.55 V/SCE). The presence of elemental sulfur on the arsenopyrite surface was not detected in this study. This fact is associated to the potential zone where this electrochemical study was performed. However, the study here reported allows to have some advances in the understanding of the arsenopyrite oxidation in acidic media.