Determining the kinetic rate constants of Fe3O4-to-Fe and FeO-to-Fe reduction by H2

Abstract

Steel production using coal accounts for ∼ 8% of global carbon emissions. “Green Steel” is a new grand concept proposed recently to make steel from iron ores using renewable derived “Green Hydrogen” to achieve zero carbon emission. The kinetics and rate-limiting steps of iron ore reduction into iron with H2 as a reducing agent is critically important to the success of this new technology. While reduction of Fe2O3 into Fe by H2 follows multiple steps, the past research on this topic mainly deals with the overall averaged kinetics, giving little information on the elemental and rate-limiting steps. Here we report a kinetic study specifically design to attain kinetic rate constants of one-step reduction of Fe3O4-to-Fe and FeO-to-Fe. Guided by thermodynamics, we show first how to create in situ the desirable starting oxide phases, i.e., Fe3O4 and FeO, with precisely controlled the ratio of partial pressures of H2O and H2. We then show time-dependent raw H2O content data collected by a mass spectrometer and the processed reduction data to extract kinetic rate constants. We found that the kinetics of the two one-step reduction reactions follows nicely the Johnson-Mehl-Avrami (JMA) phase transformation model. The one-step reduction mechanisms and activation energy are also discussed.