Study of the reduction rate of FeO in slag by solid carbon

The reduction reaction of FeO in slag by carbon plays an important role in bath smelting reduction processes. In this study, the rate of this reaction was measured to understand the kinetic behavior of FeO reduction in slag by using the mass spectrometer technique. The present experimental results implied that the rate-determining step would change from the mass transfer of FeO at a low FeO content (<5 wt pct) to the chemical reaction at the gas/carbon interface at a high FeO content (>30 wt pct), while the total reduction rate would increase with an increasing FeO content in the slag. Based on the results of this study and comparisons with thermodynamical data for FeO in slag, the reduction rate of FeO can be expressed by the following equation: r = 4.4×10^-5 (a_FeO)^1.34 or r = 1.67×10^-7 (wt pct FeO)^1.26. The activation energy of the present reaction was measured to be 60.0 kcal/mol for 10 wt pct FeO. The large value of the activation energy suggested that the chemical reactions at the gas/carbon interface would be the rate-limiting step for FeO contents higher than 30 wt pct. In the meantime, the reduction mechanism would change from a chemical reaction at the carbon surface to a mixed controlling step of chemical reactions and mass transfer of FeO in slag for FeO contents lower than 5 wt pct.