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

Abstract

The distribution behavior of Pb between molten copper and FetO-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 (LPb) 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 LPb, whereas a minimum value is observed at about 4 mass pct Al2O3 at Fe/SiO2 = 1.3. The log LPb 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 LPb 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.