ELECTROCHEMICAL OXIDATION OF ARSENOPYRITE IN ACIDIC MEDIA

Arsenopyrite (FeAsS) is a common sulfide mineral in base metals and pr ecious metals ores and concentrates. The treatment of these kinds of o res involves frequently an oxidation step to improve metal recoveries. The study of the mechanisms occurring during the arsenopyrite oxidati on is then necessary to optimize industrial processes, like bioleachin g of arsenopyrite-bearing concentrates using autotrophic acidophilic b acteria. In this work, an electrochemical approach was used to study t he arsenopyrite oxidation in acidic media. Cyclic voltammetry and chro noamperometry techniques were performed using a carbon paste electrode (CPE) and an acidic growth medium as electrolyte solution. This elect rochemical study allows to determine that the oxidation of arsenopyrit e in an acidic growth medium is performed in two steps. The first step corresponds to the initial surface oxidation of arsenopyrite to produ ce realgar (As2S2) and ferrous ions in solution (E < 0.55 V/SCE). Duri ng the second step, a catalytic oxidation of these interfacial product s appears to solubilize finally H3AsO4 and ferric ions (E > 0.55 V/SCE ). The presence of elemental sulfur on the arsenopyrite surface was no t detected in this study. This fact is associated to the potential zon e where this electrochemical study was performed. However, the study h ere reported allows to have some advances in the understanding of the arsenopyrite oxidation in acidic media.