MgO solubility in BOF slag equilibrated with ambient air

The MgO solubility in the CaO‐MgO‐Fe₂O₃‐FeO‐SiO₂‐(MnO)‐(Al₂O₃) slag was measured under the condition of equilibrium with the ambient air at 1873 K as a fundamental study for precise slag coating control in BOF operation. The CaO/SiO₂ mass ratios of the main slag were 1, 1.5, 2, 3 and 4, and total iron content was in the range of 10 to 35 %. Moreover, 1 to 13 % of MnO and 2 to 12 % of Al₂O₃ were added to the melt to evaluate their effects on the MgO solubility. The effect of slag composition on the MgO solubility was discussed and quantified by means of a newly developed formula. As the basicity in slag increases, the MgO solubility decreases. The effect of iron oxide content is observed to be dependent on the basicity of slag. An increase in iron oxide content makes the MgO solubility higher for basic slag but lower for acidic slag. It is revealed that the MgO solubility in steelmaking slag is controlled by the complex anion formation reaction of iron oxide. Both Al₂O₃ and P₂O₅ increase the MgO solubility by diluting the basic oxides as SiO₂ does, while manganese oxide affects the MgO solubility in a similar manner as iron oxide. The MgO solubility can be described as a function of slag composition, X = (%CaO) + 0.45(%Fe₂O₃+ %FeO) + 0.55(%MnO), in the equation of (%MgO) = 0.00816X^2‐1.404X + 62.31. Based on the results, the guidance for addition of MgO‐containing material could be suggested for best slag coating practice.