Recovery iron from cyanide tailings by anaerobic roasting-persulfate leaching: effect of roasting temperature.

Abstract

Anaerobic roasting combined with the persulfate-leaching process was used to treat cyanide tailings. In this study, the effect of the roasting conditions on the iron leaching rate was investigated by the response surface methodology. Additionally, this study was focusing on the effect of roasting temperature on the physical phase transformation of cyanide tailings and the persulfate-leaching process of roasted products. The results showed that roasting temperature had significant influences on the leaching of iron. The roasting temperature determined the physical phase changes of iron sulfides in roasted cyanide tailings, which in turn affected the leaching of iron. At the temperature of 700°C, all pyrite was converted to pyrrhotite, and the leaching rate of iron reached a maximum of 93.62%. At this point, the weight loss rate of cyanide tailings and the recovery rate of sulfur were 43.50% and 37.73%, respectively. The sintering of the minerals became more severe when the temperature raised to 900°C, and the iron leaching rate gradually decreased. The leaching of iron was mainly attributed to the indirect oxidation by SO4-˙ and OH˙ rather than the direct oxidation by S2O82-. The oxidation of iron sulfides by persulfate produced iron ions along with a certain amount of SO4-˙. Iron ions continuously activated persulfate to produce SO4-˙ and OH˙ under the mediation of sulfur ions in iron sulfides.