Kinetics and reduction mechanism of non-isothermal analysis carbothermal reduction of zinc ferrite

The amount of zinc-containing EAF dust has increased due to the increased proportion of galvanized steel scrap used in the electric arc furnace (EAF) steelmaking process. If the zinc in the EAF dust is not recycled, it will not only lead to a waste of valuable metal resources but also results in environmental pollution. Zinc is mainly present in the EAF dust in the form of zinc ferrite (ZnFe₂O₄). Zinc ferrite is a kind of spinel mineral that exhibits a crystal lattice of greater stability, which increases the difficulty of recycling valuable elements such as zinc and iron from zinc-containing EAF dust. To further clarify the carbothermic reduction process of zinc ferrite, this paper studies the kinetics of the non-isothermal carbothermal reduction of zinc ferrite and its reduction reaction mechanism. The phase transition process of the zinc ferrite carbothermal reduction reaction was analyzed via the XRD results of the reduced zinc ferrite. FeO_0.85·xZnO was found at 950 °C when Fe³⁺ was reduced to Fe²⁺. The relationship between the conversion and conversion rate of the zinc ferrite carbothermal reduction process is discussed. The reduction process can be divided into three stages, and the conversion of the second stage changes greatly (0.085–0.813). Finally, the kinetics of the second stage of the carbothermic reduction of the zinc ferrite at different heating rates was evaluated through the isoconversional method and the master curve fitting method. The activation energy of the second stage is between 331.01–490.04 kJ·mol⁻¹, and the average activation energy is 362.16 kJ·mol⁻¹. The large change in the activation energy in the second stage indicates that the reactions in this stage are more complicated, and there are obvious differences in the activation energy between the reactions. The secondary chemical reaction is the main rate-controlling link in the second stage, and the kinetics equation of the second stage is determined.