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-SiO 2 slags, this work investigated the activity coefficient of NiO in SiO 2 -saturated MnO-SiO 2 slag and Al 2 O 3 -saturated MnO-SiO 2 -Al 2 O 3 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-SiO 2 slag and MnO-SiO 2 -Al 2 O 3 slag existed as NiO under experimental conditions. The addition of Al 2 O 3 in the MnO-SiO 2 slag decreased the dissolution of nickel in the slag and increased the activity coefficient of NiO. Furthermore, the activity coefficient of NiO ( γ NiO ), which is solid NiO, in the SiO 2 saturated MnO-SiO 2 slag and Al 2 O 3 saturated MnO-SiO 2 -Al 2 O 3 slag at 1623 K can be respectively calculated as γ NiO = 8.58 w (NiO) + 3.18 and γ NiO = 11.06 w (NiO) + 4.07, respectively, where w (NiO) is the NiO mass fraction in the slag.