Chemical oxidation of arsenopyrite using a novel oxidant—Chlorine dioxide

Abstract

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 (ClO2), 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 NaClO2 to acidic arsenopyrite slurry made the oxidation of arsenopyrite feasible for practical purposes, as NaClO2 generates ClO2 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 NaClO2 and H2SO4 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 ClO2 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 FeAsO4·7H2O, H3AsO3, Fe2(SO4)3·7H2O, and hydrated ferric oxides would cover the surface of unreacted arsenopyrite at low H2SO4 concentration, which prevented the oxidation-reduction reaction from proceeding. As the concentrations of H2SO4 and NaClO2 increased, fine arsenopyrite particles were oxidized first, and ClO2 gradually eroded the surface of the unreacted arsenopyrite minerals to form cracks, defects, and pores, until arsenopyrite was fully oxidized. ClO2 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.