Distribution Behavior of Nickel between Liquid Copper and CaO–SiO2–FetO–MgO Slag

The distribution ratio of nickel (\({L}_{Ni}\)) between Cu-1 mass pct Ni alloy and CaO–SiO₂–Fe_tO–MgO slag was measured to explore the possibility of refining nickel from molten copper for increased use of copper scrap. Slag-metal equilibrium experiments were carried out at temperatures from 1598 K (1325 °C) to 1673 K (1400 °C) with an oxygen partial pressure of \({p}_{{\text{O}}_{2}}={10}^{-6}\text{atm}\) over a wide range of slag compositions. At a fixed temperature, \({L}_{Ni}\) increased with increasing basicity for the relatively basic regime near the monoxide (Mg, Fe)O-saturated slags, whereas it decreased with increasing slag basicity for the relatively acidic regime near the olivine (Mg, Fe)₂SiO₄-saturated slags. Thus, the dissolution mechanism of nickel into the CaO–SiO₂–Fe_tO–MgO slag can be described by the following two independent dissolution reactions: \(\left[ {Ni} \right] + \frac{1}{2}O_{2} \left( g \right) + \left( {O^{2 - } } \right) = \left( {NiO_{2}^{2 - } } \right)\) (at monoxide saturation); \(\left[ {Ni} \right] + \frac{1}{2}O_{2} \left( g \right) = \left( {Ni^{2 + } } \right) + \left( {O^{2 - } } \right)\) (at olivine saturation). The distribution ratio of nickel increases with increasing Fe_tO content. Under constant temperature and oxygen partial pressure, the redox equilibrium of iron in Fe_tO-containing slag is influenced by the chemical composition of the slag. The activity coefficient of NiO (\({\gamma }_{NiO}\)) in the olivine-saturated slag is higher than those in the monoxide-saturated slag in the observed compositions. Consequently, in terms of copper loss and stability of nickel oxide, monoxide-saturated slag system is recommended as an optimal slag window compared to olivine-saturated slag system.