Distribution of Minor Elements between Metallic Lead and PbO-FeOx-CaO-SiO2 or PbO-FeOx-CaO-SiO2-ZnO Slag

In order to clarify the behavior of minor elements in the oxidation zone of the QSL lead smelting process, the distribution ratio of the impurity element M (M = Cu, Ag, As and Sb) between the metallic lead phase and the PbO-FeOx-CaO-SiO2 or PbO-FeOx-CaO-SiO2-ZnO slag phase, as defined by LMS/Pb = (mass % M in slag)/[mass % M in lead], was investigated at 1,423 K. It was found that the iso-LMS/Pb lines of Cu, As and Sb for the PbO-FeOx-CaO-SiO2 slag with Q (mass % CaO/(mass % CaO + mass % SiO2)) = 0.4 in the PbO-FeOx-(CaO + SiO2) quasi-ternary composition diagram were almost parallel to the axis of the PbO composition in the range of the FeOx mole fraction less than 0.5 while the iso-LMS/Pb line for silver at a given PbO composition represented a tendency to increase with the FeOx content of the slag. The distribution ratios of As and Sb were found to increase with increasing Q from 0.3 to 0.4 while those of Cu and Ag decreased. It was clarified that the addition of ZnO to the PbO-FeOx-CaO-SiO2 slag did not give any serious effect to the distribution ratios. By using the determined LMS/Pb, the Raoultian activity coefficients of CuO0.5, AgO0.5, AsO1.5 and SbO1.5 were derived for the PbO-FeOx-CaO-SiO2 slag and they are 12, 1.1, 0.9, and 18 for the slag with NPbO = 0.1 and Q = 0.3 and 14, 3.4, 0.3 and 2.4 for the slag with NPbO = 0.1 and Q = 0.4, respectively. Based on the obtained LMS/Pb, the fractional distributions of As and Sb between the metallic lead, slag and gas phases were evaluated thermodynamically, and it was found that the fractional distribution in the slag phase increased drastically with increasing lead content of the slag.