Distribution Equilibria of Fe, Co and Ni between MgO-saturated FeO_x–MgO–SiO₂ Slag and Ni Alloy

Abstract

As a fundamental study related to the recycle of Ni–Fe–Co alloy, the distribution equilibrium of Fe, Co and Ni between MgO saturated FeO_x–MgO–SiO₂ slag and nickel alloy was investigated at 1 773, 1 823 and 1 873 K with controlled oxygen partial pressure between 10^-4 to 10² Pa. The distribution ratios of Fe, Co and Ni at 1 773 K vary from 0.61 to 26, 0.040 to 4.2 and 0.0030 to 0.34 respectively with increasing oxygen partialpressure.
The distribution ratios of Fe, Co and Ni between MgO saturated FeO_x–MgO–SiO ₂ slag and nickel alloy suggest that most of nickel and cobalt can remain in the alloy phase with lower oxygen partial pressure, and iron can be eliminated adequately from nickel alloys with higher oxygen partial pressure. However, the solubility of nickel and cobalt oxide in the slag also increases with increasing the oxygen partial pressure. Lower oxygen partial pressure and higher temperature are favorable for decreasing the loss of nickel and cobalt into slag. An oxygen partial pressure at which the separation coefficients show minimum was observed.
The MgO solubility in the FeO_x–MgO–SiO₂ slag decreases when the NiO content exceeds about 25% at higher oxygen partial pressure.
The activity coefficients of NiO and CoO in slags were calculated and found that their values increased with increasing of the NiO and CoO contents in slag respectively.