Synergistic oxidation of dissolved As(III) and arsenopyrite in the presence of oxygen: Formation and function of reactive oxygen species

•As(III) can be heterogeneously oxidized on arsenopyrite surface by ROS.•ROS is mainly formed by the interaction of O2 with Fe(II) on arsenopyrite surface.•Dissolved As(III) promotes the oxidation of arsenopyrite at pH 3.0.•The oxidation rate of dissolved As(III) decreases with increasing pH. As an important source of arsenic (As) pollution in mine drainage, arsenopyrite undergoes redox and adsorption reactions with dissolved As, which further affects the fate of As in natural waters. This study investigated the interactions between dissolved As(III) and arsenopyrite and the factors influencing the geochemical behavior of As, including initial As(III) concentration, dissolved oxygen and pH. The hydrogen peroxide (H2O2) and hydroxyl radical (OH•) generated from the interaction between Fe(II) on arsenopyrite surface and oxygen were found to facilitate the rapid oxidation of As(III), and the production of As(V) in the reaction system increased with increasing initial As(III) concentration. An increase of pH from 3.0 to 7.0 led to a gradual decrease in the oxidation rate of As(III). At pH 3.0, the presence of As(III) accelerated the oxidation rate of arsenopyrite; while at pH 5.0 and 7.0, As(III) inhibited the oxidative dissolution of arsenopyrite. This work reveals the potential environmental process of the interaction between dissolved As(III) and arsenopyrite, and provides important implications for the prevention and control of As(III) pollution in mine drainage. [Display omitted]