Influence of Preoxidation Treatment on the Reduction Behavior and Reaction Kinetics of Vanadium Titanomagnetite by Hydrogen

Hydrogen is a potential alternative reducing agent, which can greatly reduce CO₂ emission in the ironmaking process of vanadium titanomagnetite. This paper investigated the reaction process and kinetic characteristics of the hydrogen reduction of both untreated and preoxidized vanadium titanomagnetite using a thermogravimetric analyzer (TG). The effects of different preoxidation temperatures (T_oxi = 500 °C, T_oxi = 700 °C, and T_oxi = 900 °C) on the reduction characteristics of vanadium titanomagnetite were compared at a reduction temperature of 1000 °C. It was found that the reduction degree and reduction rate of low-temperature (T_oxi = 500 °C and T_oxi = 700 °C) preoxidized vanadium titanomagnetite are higher than those of high-temperature (T_oxi = 900 °C) preoxidized vanadium titanomagnetite. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses show that the low-temperature preoxidation process separates the Fe/Ti in vanadium titanomagnetite and forms micropores on the surface of the vanadium titanomagnetite, while the high-temperature preoxidation process allows the separated hematite and ilmenite to recombine and form pseudobrookite. The isothermal reduction experiments on untreated and preoxidized vanadium titanomagnetite were carried out, with reduction temperatures ranging from 600 to 1000 °C. The obtained results were subjected to kinetic analysis using conventional model-fitting and iso-conversional methods. The fitting results of different kinetic models show that the activation energies of the preoxidized vanadium titanomagnetite reduction reaction are lower than those of untreated vanadium titanomagnetite. In the entire range of the reduction reaction, the contracting area model (R₂) can best describe the reaction between hydrogen and untreated and preoxidized vanadium titanomagnetite. After the preoxidized treatment, the reduction energy barrier of vanadium titanomagnetite decreases by about 38.0%.