Indium distribution between FeO–CaO–SiO 2 slags and lead bullion at 1200°C

Indium is a valuable minor element in some zinc, lead and tin concentrates, and is used in flat panel displays as indium–tin oxide (ITO). Most primary indium is recovered from zinc ferrite residues which have been recycled to lead smelters for processing. Efforts to optimise the recovery of indium during lead smelting require an understanding of the distribution of indium between lead bullion and slag, and of the thermodynamics of indium oxide in slag. In this work, measurements of the indium metal/slag distribution ratio as a function of oxygen partial pressure at 1200°C in FeO–CaO–SiO₂–8 wt-%Al₂O₃ slags were used to show that indium exists in these slags as InO. The indium distribution ratio was mapped across the liquid field and found to be dependent on the FeO/SiO₂ ratio but independent of the CaO/SiO₂ ratio, being a maximum in FeO rich slags. This behaviour suggests that InO behaves as a ‘neutral’ metal oxide. The activity coefficient of InO(g) varied from approximately 4 × 10⁻⁸ to 3 × 10⁻⁷, with the value increasing as the FeO/SiO₂ ratio in the slag increased.