Mineralogical characteristics and isothermal oxidation kinetics of Hongge chromium containing vanadium and titanium magnetite pellets

The isothermal oxidation kinetics and mineralogical characteristics of Hongge chromium containing vanadium and titanium magnetite (HCVTM) pellets were investigated. The experiments related to the isothermal oxidation kinetics were performed over a temperature range of 1073 to 1373 K and a time range of 10 to 60 min. First, the microstructure and variations in the mineral composition of the pellets were analyzed. Further, the oxidation rate and its change regulation were calculated and analyzed by combining the defined oxidation rate function, and the effects of the mineral phase structures on the rate of oxidation were determined. Finally, the modified oxidation rate function, Arrhenius equation, reaction rate constant, correction factor, and reaction activation energy were calculated by combining the shrinking core model, and the restrictive step in the oxidation reaction was determined. The results depict that an increase in temperature causes an increase in the low melting point liquid phase; formation, growth, and recrystallization of hematite grains; and formation of a bonding phase. Additionally, it causes a decrease in the number of interspaces. With an increase in time, the bonding and growth of hematite grains are promoted due to the generation of a liquid phase. However, the structure of pellets is observed to deteriorate due to the formation of silicate and perovskite phases. Meanwhile, perovskite, and pseudobrookite phases are also generated. Oxidation rate decreased with increasing time due to the decrease in the number of interspaces and bonding phases. In HCVTM pellets, the oxidation reaction is controlled by diffusion. The activation energy of the initial reaction is 13.74 kJ·mol^-1 while that of the latter reaction is 3.58 kJ·mol^-1. Further, the corrected parameter for the oxidation rate function is observed to be 0.03.