The effect of additives such as CaO, SiO₂, MnO, MgO, Na₂O, P₂O₅, Al₂O₃, TiO₂, FeS, CaF₂ and CaCl₂ on the reduction rate of liquid iron oxide contained in an iron crucible with CO has been measured using a thermobalance as a fundamental study for the smelting reduction process. The effect of mass transfer in both the gas and liquid phase on the overall reduction rate was carefully estimated to learn the rate of chemical reaction on the surface.
It was found that the reduction rate was greatly affected by the ratio of Fe³⁺ /Fe² in the melts. An empirical rate equation was derived to express the rate of chemical reaction on the surface as follows :
r= (N²_FeO1.5/N³_FeO) ^1/3 (P_CO-P_CO2/K'_C)exp(-138000/RT-6.37)(kg/m²s)
Where, K'_C=(P_CO2/P_CO)_eq.. Since phosphate acted like a surface active species and retarded the reduction rate markedly, the rate equation mentioned above could not be applied to the liquid iron-phosphate system. The reduction rate of liquid iron oxide containing FeS, CaF₂ or CaCl₂ was also investigated to discuss the effect of coexisiting anions on the chemical reaction rate. It was concluded that the reduction rate was mainly affected by cations and the effect of anions was very small.