Mechanism of calcium oxide promoting the separation of zinc and iron in metallurgical dust under reducing atmosphere

Abstract

Based on the processes of recovering Zn from metallurgical zinc-bearing dust, it found that CaO could promote the separation of zinc and iron. The effect of CaO on phase evolution and reaction mechanism of zinc and iron oxide was studied. ZnO and Fe3O4 were reacted into zinc ferrite and Fe0.85-xZnxO, restricting the volatilization of Zn without CaO. So only at a high CO proportion, zinc can be reduced and volatilized thoroughly. In the presence of CaO, no significant phase of zinc ferrite was found in the roasting products, while plenty of calcium ferrite phases were generated and the generation of Fe0.85-xZnxO was inhibited. The reaction mechanism can be derived as Fe0.85-xZnxO+CaO→FeO+Ca2Fe2O5+ZnO and ZnFe2O4+CaO→Ca2Fe2O5+ZnO. Both of reactions promoted the volatilization of Zn. Therefore, for separating the zinc and iron in zinc-iron dust, the atmosphere of CO content can be reduced to 50 vol.% from 70 vol.% by adding CaO, and the volatilization rate of Zn reached above 80 wt.%. Keywords: Zinc-bearing dust, Zinc volatilization, Reducing atmosphere, Phase evolution