Resource Utilization of Cyanide Tailings: Preparation of Ferrous Oxalate by a Combined Technique of Anaerobic Roasting-Persulfate Leaching Followed by Oxalic Acid Precipitation

The combined process of anaerobic roasting, persulfate leaching, and oxalic acid precipitation has been used to treat cyanide tailings, which achieved the harmless reduction and value-added utilization of the tailings while obtaining high-quality ferrous oxalate products. This paper focused on the main process and technical parameters of the resource utilization of cyanide tailings. The reaction mechanism of each step was further elucidated by analyzing and characterizing the various products. After roasting in a nitrogen atmosphere, the pyrite in the cyanide tailings was converted into pyrrhotite by removing elemental sulfur, and the sulfur removal ratio reached 37.73%. The iron leaching ratio of the roasted products reached 97.22% under the optimum leaching conditions. The oxidative decomposition of pyrrhotite in the leaching process mainly depended on persulfate and the free radicals generated by its self-activation. Iron entered the leaching solution in the form of Fe3+/Fe2+, while sulfur was oxidized to elemental sulfur and SO42-. After the small amount of Fe3+ remaining in leaching solution was reduced to Fe2+ by the iron powder, Fe2+ could be complexed by oxalate to obtain alpha-type ferrous oxalate, and the iron precipitation ratio could reach 82.54%. The total mass loss ratio reached 43.50%, with both gold and silver enriched in the leaching residue.