Effect of H₂/CO ratio on non-isothermal reduction behavior and kinetics of vanadium titanomagnetite

Hydrogen-based direct reduction of vanadium titanomagnetite is crucial for developing clean and efficient hydrogen metallurgy technology, while existing studies lack systematic research on the impact of H₂/CO ratios on the reduction of vanadium titanomagnetite under non-isothermal conditions. This study examines the influence of varying H₂/CO ratios on the non-isothermal reduction behavior and kinetics of vanadium titanomagnetite through thermogravimetric analysis (TGA). The results of thermogravimetric experiments show that raising the H₂ ratio can significantly lower the initial reduction temperature and accelerate the reduction rate. When H₂/(H₂+CO) rises from 0 to 1, the initial reduction temperature can be lowered by around 150 °C at a heating rate of 10 °C/min. As the heating rate decreases, the reduction curve shifts to the low-temperature region, and the reduction reaction becomes easier to proceed. The vanadium titanomagnetite reduction activation energy was calculated using the Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) model-free kinetic methods, and the activation energy of vanadium titanomagnetite reduction under pure CO atmosphere (H₂/(H₂ + CO) = 0) was the highest (120.74 kJ/mol by FWO and 107.82 kJ/mol by KAS). As the H₂/(H₂+CO) ratio increases, the activation energy continuously decreases, effectively reducing the reduction energy barrier of vanadium titanomagnetite. In contrast to an environment of pure CO, the activation energy for the reduction of vanadium titanomagnetite was reduced by 25.47 % (FWO method) or 28.73 % (KAS method) in a pure H₂ atmosphere (H₂/(H₂ + CO) = 1), indicating that an elevated H₂ ratio significantly enhanced the reduction of vanadium titanomagnetite. XRD analysis showed that, after the non-isothermal reduction, unreduced iron oxide was still present within the vanadium titanomagnetite under a pure CO atmosphere, while the final reduction product was mainly metallic iron under different H₂/CO ratios. Increasing the hydrogen ratio can accelerate the reduction of the intermediate phase (wüstite/FeO), and promote the conversion of intermediate phase to metallic Fe. The reduction path of vanadium titanomagnetite is: Fe_3-xTi_xO₄→FeO + FeTiO₃→Fe + TiO₂. This research establishes a theoretical foundation for the industrial application of H₂/CO reduction technology of vanadium titanomagnetite.