Reduction mechanism of Fe₂O₃-Cr₂O₃-NiO system by carbon

Abstract

Isothermal experiments on the reduction of Fe₂O₃-Cr₂O₃-NiO (molar ratio of Fe-to-Cr-to-Ni is 3:2:2) by graphite were carried out at 1350–1550°C, and effects of various factors on reduction degree were studied. The results show that the reaction rate of the Fe₂O₃-Cr₂O₃-NiO system is fast during the initial period (reduction degree, α<38%), and then the rate decreases until the end of the reduction. Factors such as temperature, carbon content, sample size have a more significant effect during the final stage (α>38%). The metallic product formed at the initial stage (a Fe-Ni alloy) greatly promotes the reduction of Cr₂O₃ at the final stage. Further, during the reduction of Fe₂O₃-Cr₂O₃-NiO by carbon, interfacial reaction is the rate-controlling step and g(α)=1-(1-α)^0.5 is the reaction mechanism for the initial stage, whereas two-dimensional diffusion is the rate-controlling step and f(α)=α+(1-α)ln(1-α) is the reaction mechanism for the final stage. The apparent activation energies are 55.43 kJ/mol and 174.54 kJ/mol for the initial and the final stages, respectively.

Keywords

Fe₂O₃-Cr₂O₃-NiO system / isothermal reduction / reduction degree / kinetics / reaction mechanism

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