Thermodynamic behavior of nickel in CaO-SiO2-FetO slag

Abstract

The distribution ratio of nickel between Ag-Ni alloy and CaO-SiO2-FetO slag at high temperatures was measured to clarify the dissolution mechanism of nickel in this melt. Also, the nickel oxide capacity was suggested and was compared to phosphate and sulfide capacities. The dissolution mechanism of nickel into the CaO-SiO2-FetO slags could be described by the following equation from the effect of oxygen potential and slag basicity on nickel dissolution behavior: $$Ni(1) + \frac{1}{2}O_2 (g) + O^{2 - } (slag) = NiO_2^{2 - } (slag)$$ The nickel oxide capacity increases with increasing CaO/SiO2 ratio at a fixed FetO content. When the ratio of XCaO to \(X_{SiO_2 } \) (C/S) is about 1.1 to 1.3, log \(C_{NiO_2^{2 - } } \) increases with increasing FetO content up to about 35 mol pct, followed by a nearly constant value of \(C_{NiO_2^{2 - } } \cong 10^3 \). In the composition of C/S=0.5 to 0.7, log \(C_{NiO_2^{2 - } } \) exhibits a maximum value at about 50 mol pct FetO. From the iso-\(C_{NiO_2^{2 - } } \) trends in ternary phase diagram, nickel oxide capacity dominantly depends on FetO content in slags; it exhibits a maximum value of \(C_{NiO_2^{2 - } } \cong 10^3 \) at \(X_{Fe_t O} \cong 0.5\). The relationship between nickel oxide capacity and phosphate (sulfide) capacities exhibit linear correlations, as expected from theoretical equations.