Vaporization behavior of lead from the FeO-CaO-SiO2-Al2O3 slag system

Vaporization behavior (1163–1463 K) of lead in the slag system of FeO-CaO-SiO₂-Al₂O₃ with CaCl₂ was examined. A thermodynamic estimation with the principle of Gibbs free energy minimization showed that the major vapor species from the sample of the FeO-CaO-SiO₂-Al₂O₃ system+PbO+CaCl₂ were metallic Pb, PbCl, PbCl₂, and FeCl₂, at the experimental temperature range. The experimental results show that the mole ratio of vaporized Cl in lead chlorides to vaporized Pb, simply expressed as Cl/Pb, decreases with increasing temperature. The larger Cl/Pb means a larger ratio of gaseous PbCl₂, since metallic Pb and PbCl vapors are formed in a similar reduction atmosphere. The evaporation is initially rapid and becomes steady after holding for 10 min. Gaseous PbCl₂ is mainly formed during the heating period, and at the holding stage, it reacts with FeO to produce gaseous FeCl₂. With regard to slag composition, FeO content and basicity significantly affect the evaporation of lead. High FeO content and high basicity promotes the formation of metallic Pb and PbCl, whereas, it prohibits PbCl₂ evaporation.