A study in the thermodynamic behavior of nickel in the MgO-SiO ₂-FeO slag system

The dissolution behavior of nickel in the MgO-SiO₂-FeO slag system was investigated by using the thermodynamic equilibrium technique. Nickel distribution ratio between molten MgO-SiO₂-FeO slag and molten Fe-Ni alloy at 1773K and 1873K was measured to understand the dissolution mechanism of nickel into the slags. In particular, the effect of oxygen potential and basicity on the distribution of nickel was investigated. Nickel distribution between slag and Fe-Ni alloy increased with higher oxygen potential showing a slope of 1/2. For basic slag systems near the olivine saturated composition, the nickel distribution ratio increased with higher basicity and for acidic slag systems near the cristobalite saturated composition, the nickel distribution ratio decreased with higher basicity. Thus, the nickel dissolution into the MgO-SiO₂-FeO slag system showed two independent mechanisms similar to that found in the CaO-SiO₂-CaF₂ system. Ni + 1/2 O ₂(g) + O^2- = NiO₂^2-(slag) (Olivine_satd:) Ni + 1/2 O₂(g) = Ni²⁺(slag) (Cristobalite_:satd.f ) The contour of the iso distribution ratio was represented in the MgO-SiO₂-FeO ternary phase diagram. From the results, an optimum slag composition was determined to be near the olivine saturated with approximately X_MgO/X_SiO2 of 0.8 at 1773K and 1.0 at 1873K.