Recycling of Zinc and Iron from Smelting Waste Containing Zinc Ferrite via Sulfating Roasting Using SO2: Transformation Effects and Mechanisms

It is critical to recycle valuable elements such as zinc and iron from smelting waste containing zinc ferrite because of the resource crisis and environmental sustainability. Sulfating roasting followed by water leaching has been considered a promising approach. In this study, a novel sulfating roasting method using SO 2 has been developed to treat zinc ferrite for the efficient separation of zinc and iron. Moreover, the conversion mechanism of zinc ferrite and SO 2 was investigated in detail. The results showed that the transformation rate of zinc ferrite reached 95.47% at 600°C for 30 min under SO 2 /SO 2  + O 2 of 60% (v/v). The mechanism studies revealed that O in SO 2 combined with the O vacancy of \( {\text{Zn}}_{{{\text{A}} - {\text{site}}}}^{{2 + }} - {\text{O}} - {\text{Fe}}_{{{\text{B}} - {\text{site}}}}^{{3 + }} \) , while the S in SO 2 combined with the \( {\text{Fe}}_{{{\text{B}} - {\text{site}}}}^{{3 + }} \) of \( {\text{Zn}}_{{{\text{A}} - {\text{site}}}}^{{2 + }} - {\text{O}} - {\text{Fe}}_{{{\text{B}} - {\text{site}}}}^{{3 + }} \) for electron migration. S (IV) was oxidized to S (VI) while Fe 3+ was reduced to Fe 2+ . Importantly, zinc ferrite transformed into zinc-deficient magnetite intermediate ( \( {\text{Zn}}^{{2 + }} ({\text{Fe}}^{{2 + }} )_{{{\text{A}} - {\text{site}}}} - {\text{O}} - {\text{Fe}}^{{3 + }} ({\text{Fe}}^{{2 + }} )_{{{\text{B}} - {\text{site}}}} \) ) via reduction of Fe 3+ and migration of Fe 2+ . The transformation of zinc ferrite was a catalyst-free redox reaction. This study provided a new insight into the utilization of smelting waste and a theoretical basis for the efficient separation of zinc and iron from smelting waste containing zinc ferrite.