PbO solubility in lead-blast furnace slags

A series of slags in the PbO-CaO-FeO-Fe₂O₃-SiO₂ system has been equilibrated in contact with molten Pb and Pb-Ag alloys in a closed system at 1473 K. The influences of lead activity and the CaO/SiO₂ and ferric/ferrous ion ratios on PbO solubility in slag have been examined. The PbO content is proportional to the lead activity and the ferric/ferrous ratio, but decreases with increasing values of the CaO/SiO₂ ratio. The solubility of lead in the slag can also be characterized by the following empirical equation, whereX _PbO is the lead oxide mole fraction,K ₂ the equilibrium constant for the formation of liquid PbO at 1473 K, andF andG are the calcia/silica and iron/silica weight ratios, respectively. This equation, developed from data in the literature, has been used with the experimental results of this investigation for comparison with values ofp _{O 2}predicted by Hollitt’s structural model. Further comparison with Hollitt’s model has been made with other experimental data in the literature. The values ofp _{O 2}predicted with the structural model are an order of magnitude lower than those predicted by the empirical equation and the values ofp _{O 2} used by other investigators. The reason for this discrepancy may lie in part in the use of questionable assumptions about the behavior of FeO in slag systems; reevaluation of the structural model to include more “basic” FeO improves agreement between the values ofp _{O 2}obtained with the structural model and those obtained with the empirical equation and the partial pressures of O₂ used by other investigators. In addition, the structural model has also been tested with regard to the influence of CaO and FeO additions on the solubility of PbO. The possible effect of interaction between the equilibrating slag melt and the calcia-stabilized zirconia crucible on the system equilibria has also been examined; such an effect may not be as negligible as previous researchers have claimed.