The Distribution of Cobalt Between Co-Cu Alloys and Alumina-Saturated MnO-SiO2-Al2O3 Slags

To obtain fundamental information on the dissolution of cobalt into alumina-saturated MnO-SiO 2 -Al 2 O 3 slags in the smelting reduction of spent lithium-ion batteries, the equilibrium distribution of cobalt between Co-Cu alloys and alumina-saturated MnO-SiO 2 -Al 2 O 3 slags was measured at 1573 K and 1623 K under a controlled CO-CO 2 atmosphere. The results show that (i) the solubility of cobalt in the slag increased with increasing concentration of cobalt in the alloy and increasing oxygen partial pressure in the atmosphere at a fixed concentration of cobalt in the alloy, and (ii) the activity coefficient of CoO in the slag increased with increasing cobalt oxide in the slag. The activity coefficient of CoO in the slag, γ CoO, referred to as solid CoO, can be described as a function of the concentration of CoO in slag as follows: γ CoO  = 11.2957(wt pct CoO in slag) + 12.0944 (1573 K, (wt pct MnO)/(wt pct SiO 2 )= 0.76–0.83); γ CoO  = 2.2286(wt pct CoO in slag) + 4.5232 (1623 K, (wt pct MnO)/(wt pct SiO 2 )= 0.78–0.85).