Efficient recovery of iron from anaerobic roasted cyanide tailings using advanced oxidation technology

Persulfate-mediated advanced oxidation process (AOP) has been used to oxidize iron and sulfur bearing minerals, but the iron leaching process and the activation of persulfate by minerals themselves has been neglected. In this study, AOP was used to leach iron from cyanide tailings, roasted in a nitrogen atmosphere. The oxidation behavior of pyrrhotite and the activation mechanism of persulfate were proposed through process optimization, product analysis, reactive species and degradation area. The iron leaching efficiency from roasted cyanide tailings was 97.1%, with a mass loss ratio of 32.5%. The gold grade in leach residues increased from 1.19 g/t to 2.07 g/t under the leaching conditions: sodium persulfate concentration of 0.3 mol/L, leaching temperature of 60 °C, slurry concentration of 30 g/L, and stirring speed of 300 rpm. The pyrrhotite in roasted cyanide tailings was oxidized by persulfate and the free radicals produced by its activation. Oxidation products were Fe3+, SO42−, and elemental sulfur. The oxidation of pyrrhotite was dominated by the indirect oxidation by the free radicals OH• and SO4−•, and their contributions to the iron leaching efficiency were 66.6% and 24.2%, respectively. The reason for the thermally enhanced iron leaching effect was the activation of persulfate to produce a certain amount of OH•. The Fe2+ produced by the oxidation of pyrrhotite activated persulfate to produce SO4−• and OH•. Besides, S(II) in pyrrhotite mediated the circulation of iron ions, thereby continuously producing Fe2+ to activate persulfate. •Iron in cyanide tailings was effectively leached in the persulfate system.•The oxidation of pyrrhotite was dominated by the indirect oxidation of SO4−• and OH•.•Proved that the SO4−• and OH• were produced by thermally activated persulfate and pyrrhotite self-activated persulfate.•Fe3+ could be regenerated to Fe2+ activated persulfate by the mediation of S(II) in pyrrhotite.