Abstract: A simple model for estimating the rate constant between CO₂-CO gas and molten slag containing iron oxides was developed using optical basicity only. In this model, the temperature dependence of the rate constant can be described by the Arrhenius law, and the activation energy can be expressed with a linear function of the slag's optical basicity. The model was applied to some molten slag systems, such as FeO, FeO-CaO, FeO-SiO₂, FeO-Na₂O, FeO-CaO-SiO₂, FeO-SiO₂-P₂O₅, FeO-SiO₂-Na₂O, and FeO-CaO-SiO₂-P₂O₅. A comparison between the predicted results and measured data showed that the model worked well.