Abstract
Weathering of arsenopyrite is a main cause of arsenic ions in acid mine drainage, and establishing the mechanism of arsenopyrite dissolution is important to design and develop methods for suppressing the dissolution. However, the factors affecting the oxidation state of arsenic formed by arsenopyrite dissolution are not established.
This study investigated the effect of Fe(II) and Fe(III) concentrations as well as the presence of dissolved oxygen on the oxidation states of arsenic ions formed from arsenopyrite in sulfuric acid solutions by a shaking-flask method. Dissolved oxygen or Fe(III) was required as oxidant for dissolving arsenopyrite. When only Fe(III) was present as the oxidant, arsenic extracted from arsenopyrite was As(III). In the presence of dissolved oxygen, both As(III) and As(V) were formed and the concentrations of these ions were varied depending on the solution composition: As(V) was dominant when Fe(II) or Fe(III) were not added, and As(III) was dominant with high concentrations of Fe(III) and Fe(II). It was also found that under aerobic conditions arsenopyrite acts as a catalyst for the oxidation of As(III) to As(V), and that Fe(II) and Fe(III) inhibit the As(III) oxidation. Based on the results, the mechanism for arsenopyrite dissolution and the oxidation state of extracted arsenic are discussed.
