Study on the Kinetic Behavior and Mechanism of Ilmenite Reduction with Starch
摘要
The reduction process of ilmenite was studied in a high-temperature tube furnace using starch (ST) as a reducing agent. Gas chromatography (GC), X-ray diffraction (XRD), and scanning electron microscope with energy-dispersive spectrometer (SEM-EDS) were used to analyze the effects of reduction time (10, 20, 30, 60, and 90 minutes), temperature (1000, 1100, and 1200 °C), and starch ratio (20, 25, and 30 pct) on the reduction degree, gas product concentration, solid product phase and micromorphology of ilmenite. The reduction mechanism was revealed by establishing an isothermal kinetic model. The results showed that the reduction degree increased with the increase of reduction time, temperature, and starch proportion, and the reduction temperature had the greatest effect on the reduction degree. When the starch proportion was 30 pct, the reduction temperature was 1200 °C, and the reduction time was 90 minutes, the reduction degree could reach 91.39 pct. In the reduction process, FeTiO3 and Fe3O4 experienced the transformation from FeTiO3 → Fe + ferrous-pseudobrookite [(Fe, Mg)Ti2O5] + TiO2 → Fe + ferrous-pseudobrookite [(Fe, Mg)Ti2O5] + Ti3O5 and Fe3O4 → FeO → Fe, respectively. As the reduction degree increased, the reduced iron mainly existed in the form of white particles, strips, or lumps in the cracks and pores generated on the ilmenite particles. In the isothermal reduction kinetics, the fixed carbon in the carbon source produced by starch pyrolysis and the CO gas produced by carbon gasification serve as the primary reducing agents, interacting with the ilmenite surface. The reduction rate was controlled by the carbon gasification reaction, and the reduction rate increases with the increase of the starch proportion. The fitted apparent activation energies were 265.9, 257.3, and 254.9 kJ/mol, respectively. The results provide a theoretical basis for directly reducing ilmenite using starch.