Promoted acid leaching of Zn from hazardous zinc-containing metallurgical dusts: Focusing on transformation of Zn phases in selective reduction roasting

As hazardous wastes from metallurgical processes, high zinc dust (HZD) was considered as a potential alternative resource of Zn. The acid leaching of HZD was a principal step and therefore was highly relevant to efficient utilization. Unfortunately, zinc ferrite (ZnFe2O4) in HZD was difficult to be leached by hydrometallurgical methods. Therefore, in this study, to enhance the recovery of zinc, selective reduction roasting was used to decompose ZnFe2O4. The transformation of Zn phases during the reduction process was investigated by thermodynamic calculation, XRD analysis. The results showed that ZnFe2O4 was converted into acid-soluble ZnO in H2 at 600 °C, while the further reduction of ZnO to Zn(g) and the volatilization of ZnO was avoided. However, the soluble ZnSO4 in HZD was also reduced to acid-insoluble ZnS. Consequently, a novel method of reduction roasting combined with water leaching was proposed to pretreat HZD. In water leaching, the solid-liquid ratio was1:10 (g/mL). When H2SO4 concentration was 80 g/L, the leaching ratio of Zn was 94.24% after pretreatment, higher than that of direct leaching of HZD (87.76%). Therefore, acid leaching of Zn was promoted by water leaching and reduction roasting pretreatment, which will bring considerable benefits to the high zinc dust recycling enterprises.