Activity coefficient of NiO in SiO2-saturated MnO-SiO2 slag and Al2O3-saturated MnO-SiO2-Al2O3 slag at 1623 K

As a part of the fundamental study related to the reduction smelting of spent lithium-ion batteries and ocean polymetallic nodules based on MnO-SiO2 slags, this work investigated the activity coefficient of NiO in SiO2-saturated MnO-SiO2 slag and Al2O3-saturated MnO-SiO2-Al2O3 slag at 1623 K with controlled oxygen partial pressure levels of 10−7, 10−6, and 10−5 Pa. Results showed that the solubility of nickel oxide in the slags increased with increasing oxygen partial pressure. The nickel in the 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 nickel in the slag and increased the activity coefficient of NiO. Furthermore, the activity coefficient of NiO (γNiO), which is solid NiO, in the SiO2 saturated MnO-SiO2 slag and Al2O3 saturated MnO-SiO2-Al2O3 slag at 1623 K can be respectively calculated as γNiO = 8.58w(NiO) + 3.18 and γNiO = 11.06w(NiO) + 4.07, respectively, where w(NiO) is the NiO mass fraction in the slag.