The activity coefficient of nickel oxide in SiO₂ saturated MnO-SiO₂ slag and Al₂O₃ saturated MnO-SiO₂-Al₂O₃ slag at 1623K

As a part of the fundamental study related to the reduction smelting of both spent lithium-ion batteries and polymetallic sea nodules based on MnO-SiO₂-based slags, the activity coefficient of nickel oxide in SiO₂ saturated MnO-SiO₂ slag and Al₂O₃ saturated MnO-SiO₂-Al₂O₃ slag at 1623 K was investigated with controlled oxygen partial pressure of 10^-7, 10^-6, and 10^-5 Pa. The results show that the solubility of nickel oxide in the slags increased with increasing the oxygen partial pressure. The nickel in both MnO-SiO₂ slag and MnO-SiO₂-Al₂O₃ slag existed as NiO under experimental conditions. The addition of Al₂O₃ in the MnO-SiO₂ slag decreased the dissolution of Ni in the slag, and increased the activity coefficient of NiO. Furthermore, the activity coefficient of NiO, referred to solid NiO, can be calculated as: γ_NiO=8.58(wt% NiO in slag) + 3.18 (SiO₂ saturated MnO-SiO₂ slag, 1623K);γ_NiO=11.06(wt% NiO in slag) + 4.07 (Al₂O₃ saturated MnO-SiO₂-Al₂O₃ slag, 1623K).