Effect of Slag Composition on the Distribution Behavior of Pb between Fe_tO-SiO₂ (-CaO, Al₂O₃) Slag and Molten Copper

The distribution behavior of Pb between molten copper and Fe_tO-SiO₂ (-CaO, Al₂O₃) slags was investigated at 1473 K (1200 °C) and \( p_{{{\text{O}}_{2} }} = 10^{ - 10} \,{\text{atm}} \) in view of the reaction mechanism of Pb dissolution into the slag. Furthermore, the lead capacity of the slag was estimated from the experimental results. The distribution ratio of Pb (L _Pb) decreases with increasing CaO content (~6 mass pct) irrespective of Fe/SiO₂ ratio (1.4 to 1.7). However, the addition of alumina into a slag with Fe/SiO₂ = 1.5 linearly decreases the L _Pb, whereas a minimum value is observed at about 4 mass pct Al₂O₃ at Fe/SiO₂ = 1.3. The log L _Pb continuously decreases with increasing Fe/SiO₂ ratio, and the addition of Al₂O₃ (5 to 15 mass pct) into the silica-saturated iron silicate slag (Fe/SiO₂ < 1.0) yields the highest Pb distribution ratio. This is mainly due to a decrease in the FeO activity even at silica saturation. The log L _Pb linearly decreases by increasing the log (Fe³⁺/Fe²⁺) value. The Pb distribution ratio increases and the excess free energy of PbO decreases with increasing Cu₂O content in the slag. However, from the viewpoint of copper loss into the slag, the silica-saturated system containing small amounts of alumina is strongly recommended to stabilize PbO in the slag phase at a low Cu₂O content. The lead capacity was defined in the current study and shows a linear correlation with the activity of FeO in a logarithmic scale, indicating that the concept of lead capacity is a good measure of absorption ability of Pb in iron silicate slags, and the activity of FeO can be a good basicity index in iron silicate slag.