Vaporization behaviors of Zn in Fe_tO-CaO-SiO₂-Al₂O₃ slag system

Vaporization behavior of zinc in the slag system Fe_tO-CaO-SiO₂-Al₂O₃ was examined, including the formation ratio of vapor species and their partitioning as well as the effect of process factors such as temperature, holding time, slag composition, and addition of reductive agents. A thermodynamic estimation with the principle of Gibbs free energy minimization shows that the major vapor species from the sample of FeO-CaO-SiO₂-Al₂O₃ system + ZnO + CaCl₂ are metallic Zn, ZnCl₂ and FeCl₂ in the experimental temperature range. The results suggest that the formation ratio of metallic Zn and FeCl₂ increases with temperature increasing, while that of ZnCl₂ decreases. The evaporation of sample is initially fast and becomes steady after holding for 10 min. Gaseous ZnCl₂ is mainly formed during heating period, at the holding stage it reacts with FeO to produce gaseous FeCl₂. With regard to slag compositions, FeO and basicity significantly affect the evaporation of zinc. The evaporation ratio of zinc can be enhanced by the addition of reductants such as carbon powder.