Isothermal kinetics of zinc ferrite reduction using a CO-CO2-Ar gas mixture

•The isothermal reaction kinetics of ZnFe2O4 in a CO−CO2-Ar mixture were studied.•The CO intensity impacts reaction rate more significantly than CO concentration.•The nucleation of ZnO is determined as the rate-controlling step.•The migration of Zn2+ together with O2− causes the slow nucleation of zinc oxide. The isothermal kinetics of zinc ferrite in a COCO2-Ar atmosphere were investigated by using thermogravimetric analysis (TGA). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were applied in studying the mechanism of reduction roasting. Linear-fitting of the measured data indicates that the growth of nuclei model is the kinetic model, and the overall Ea was 72.75 kJ/mol; the kinetic equation was derived as follows: [−ln(1−α)]32=3.1054×106⋅PCO0.766⋅VCO1.135⋅e−72.75×103RT⋅t. The CO intensity impacts the reaction rate more significantly than the CO concentration. The XRD and XPS results of the roasted products reveal that due to the migration of zinc ions together with oxygen ions during reductive roasting, the generation of magnetite is much faster than zinc oxide, indicating that the nucleation of zinc oxide is the rate-determining step.