Chemical oxidation of arsenopyrite using a novel oxidant—Chlorine dioxide

Arsenopyrite is a typical arsenic-containing mineral, and gold is generally hosted by arsenopyrite mineral which adversely affects gold leaching. In this study, a novel environmentally friendly oxidant, chlorine dioxide (ClO 2 ), was used for the first time to efficiently oxidize arsenopyrite under acidic conditions, preventing the adverse effect of arsenopyrite on gold leaching. The addition of solid NaClO 2 to acidic arsenopyrite slurry made the oxidation of arsenopyrite feasible for practical purposes, as NaClO 2 generates ClO 2 under acidic conditions, which then oxidizes arsenopyrite. For a 400 mL sample of arsenopyrite pulp with the initial concentration of 4.07 g/L (0.025 M), the oxidation efficiencies of Fe and As in arsenopyrite reached 94.25% and 85.39%, respectively for NaClO 2 and H 2 SO 4 concentrations of 0.125 M each, under magnetic stirring for 1 h at 30 °C in a constant-temperature water bath. At the end of the reaction, both the acidity and oxidation-reduction potential of the system increased, and the ClO 2 concentration correspondingly decreased. Chemical composition analysis, X-ray diffraction analysis, particle size distribution measurements, scanning electron microscopy combined with energy dispersive spectrometer analysis, and X-ray photoelectron spectroscopy of arsenopyrite mineral ore and its oxidized residues were performed under different reaction conditions. Analysis results indicated that tiny amorphous precipitates of the oxidation by-products, such as FeAsO 4 ·7H 2 O, H 3 AsO 3 , Fe 2 (SO 4 ) 3 ·7H 2 O, and hydrated ferric oxides would cover the surface of unreacted arsenopyrite at low H 2 SO 4 concentration, which prevented the oxidation-reduction reaction from proceeding. As the concentrations of H 2 SO 4 and NaClO 2 increased, fine arsenopyrite particles were oxidized first, and ClO 2 gradually eroded the surface of the unreacted arsenopyrite minerals to form cracks, defects, and pores, until arsenopyrite was fully oxidized. ClO 2 presents several advantages: it can be easily prepared, it is a strong oxidant, and is non-polluting. Therefore, the procedure in this study is expected to be used as a novel method for preventing the effect of arsenopyrite enwrapping gold in refractory gold ores and for directly leaching gold.