A thermodynamic study on cobalt containing calcium ferrite and calcium iron silicate slags at 1573 K

Redox equilibria, activities of cobalt, iron and their oxides in calcium ferrite and calcium iron-silicate slags, were measured through metal-slag-gas equilibrium experiments under controlled oxygen potentials (10(-7) to 3 X 10(-7) atm) at 1573 K. Results on the redox equilibria show that addition of CoO to calcium ferrite slag increases the equilibrium Fe3+/Fe2+ ratio in these melts. Measured activities of CoO and FeO showed positive deviations from ideal behavior, while that of Fe2O3 showed negative deviation. Partial substitution of CaO by SiO2, by up to 4 wt pct SiO2 in the calcium ferrite based melts, resulted in increases in the activity coefficients of CoO and Fe2O3. Phase equilibria studies on the cobalt containing CaO-FeO-Fe2O3-SiO2 slags were also carried out using the drop-quench technique. Good agreement between the activity data and the liquidus temperature with respect to magnetite solid solution containing CoO was observed.