Slag-copper matte equilibria in CaO modified Fe-O-Al₂O₃-SiO₂ slags at fixed p(O₂), p(S₂), p(SO₂), and 1200 °C for mixed concentrate-WEEE feed

Lime modification of alumina-bearing iron silicate slags in copper matte production was studied at 1200 °C. The experimental p(SO₂) and p(O₂) conditions were fixed to produce about 60 wt% Cu matte grade. The behaviour of the slag and matte, containing trace elements silver, indium, lead, and tin, was studied as a function of lime concentration in the slag (2–––11 wt% CaO). Lime modification had a clear effect on the chemical dissolution of copper in the slag, and it also clearly decreased the deportment of silver and indium in the slag. The deportments of copper and the trace elements between the slag and magnetite (‘spinel’) phase were measured by electron probe microanalysis and laser ablation-ICP-mass spectrometry. The obtained results imply that a reductive slag cleaning technology should be employed at smelters treating high-silver feeds, such as WEEE (waste electric and electronic equipment). As indicated by the significant volatilization of many of the studied trace elements during the experiments, flue dust treatment is essential in smelters using feed mixtures with volatile elements, such as indium, lead, and tin.