Distribution of Rhodium between SiO₂–CaO–CrO_x Slag System and Molten Copper

In the hydrometallurgical process used for the recycling of platinum group metals (PGMs), a residue containing Cr₂O₃ and PGMs is generated. In this study, a pyrometallurgical process was applied, in which PGMs from the residue generated in the hydrometallurgical processes were concentrated in a molten Cu phase as a collector metal, and Cr₂O₃ was separated into a slag phase with SiO₂ and CaO as the flux. To reduce the loss of PGMs into the slag, the dissolution of PGMs into the slag must be reduced. Therefore, the distribution ratio of Rh, as a representative PGM, between the liquid SiO₂–CaO–Al₂O₃–CrO_x or the liquid SiO₂–CaO–CrO_x slag and molten Cu were measured at 1773 K under an oxygen partial pressure of p_O2 ¼ 10^-10. The experimental results revealed that the distribution of Rh in the slag increased with increasing CrO_x concentration. At a constant Cr₂O₃ concentration in the slag, the solubility of Rh increased with increasing slag basicity, which is defined as B = (mass%CaO)/(mass%SiO₂). Furthermore, compared with the distributions of Rh and Pt between the slag system and molten Cu, Rh was more easily lost to the slag, and the dependence of Rh on basicity was greater than that of Pt.