Vaporization behavior of zinc from the FeO-CaO-SiO_2-Al_2O_3 slag system

摘要

Vaporization behavior (1000-1300 deg C) of zinc in the slag system FeO-CaO-SiO_2-Al_2O_3 has been examined, including the formation ratio of vapor species and their partitioning, along with the effect of process factors such as temperature, duration time, slag composition, addition of reductive agents, and chlorine content. A thermodynamic estimation with the principle of Gibbs free energy minimization shows that the major vapor species from the sample of FeO-CaO-SiO_2-Al_2O_3 system+ZnO + CaCl_2 are metallic Zn, ZnCl_2 and FeCl_2 at the experimental temperature range. The results suggest that the formation ratio of metallic Zn and FeCl_2 increases, while that of ZnCl_2 decreases, with an increase in temperature. The evaporation of sample is initially fast and becomes steady after holding for 10min. Gaseous ZnCl_2 is mainly formed during heating period, at the holding stage it reacts with FeO to produce gaseous FeCl_2. With regard to slag compositions, Fe~(2+)/Fe~(3+) ratio and basicity significantly affect the evaporation of zinc. The former governs the types of vapor species and the latter affects the total volatile ratio of zinc. The evaporation ratio of zinc can be enhanced by the addition of reductants such as carbon powder. It also increases with the increasing ratio of CaCl_2/ZnO and levels off above 2.