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Reductive roasting and ammonia leaching of high iron-bearing zinc calcines

ABSTRACT The separation of iron and zinc is a considerable challenge in the zinc smelting processes. A reduction roasting-ammonia leaching process is proposed in this paper. In roasting experiments, the apparent active energy of the reductive roasting of zinc ferrite is 31-35kJmol−1, and the diffusion of the reactant is the rate-determining step. Zinc ferrite was well decomposed into ZnO and Fe3O4 in reductive roasting. However, byproducts including FeO and Fe0.85−xZn xO were also detected. To achieve a high zinc recovery and to avoid the leaching of FeO, ZnO was selectively extracted via ammonia leaching, while magnetite and ferrous oxide were left in residues and recovered through magnetic separation (MS). The optimal operations of the proposed process were 750°C for 45min under a CO concentration of 8% and a CO intensity of 20%, and leached at 30°C for 1 h with a solid/liquid ratio of 1:7 and a stir speed of 200 revmin−1. A total of 88.56% of the zinc was extracted, and just 1.2% of the iron was extracted. The recovery and grade of iron reached 86.46 and 46.5%, respectively, after MS. This reduction roasting-ammonia leaching process is a favourable option for efficient zinc recovery from high iron-bearing zinc ores.