δ-MnO2 Drives the Green Decomposition of Arsenopyrite by Mediating the Fate of Arsenic to Generate FeAsO4

Arsenopyrite (FeAsS) is a typical gold-bearing sulfide mineral. It usually encapsulates the gold particles and seriously inhibits the leaching of gold, so oxidation pretreatment of arsenopyrite is prerequired for the effective leaching of gold. However, the oxidation of arsenopyrite is accompanied by arsenic mobility, potentially resulting in serious environmental issues. An eco-friendly oxidant, δ-MnO2, was herein used to effectively oxidize arsenopyrite and control the fate of arsenic under acidic conditions. Via characterization of the variation of leaching parameters, morphology change, and elemental speciation transformation on the mineral surface, it was found that adding δ-MnO2 significantly provoked the oxidation of Fe(II) and As(−I) to Fe(III) and As(V), and mediated the speciation transformation of Fe/As to FeAsO4. δ-MnO2 dosage remarkably controlled the oxidation efficiency of arsenopyrite and arsenic speciation transformation, efficiently regulating arsenic fate. These results suggest that δ-MnO2 could simultaneously promote the dissolution of arsenopyrite and the immobilization of arsenic, which could have implications for the oxidation pretreatment of refractory gold minerals and the source management of arsenic-contaminated environments.