Reduction behavior and mechanism of Hongge vanadium titanomagnetite pellets by gas mixture of H2 and CO

Hongge vanadium titanomagnetite (HVTM) pellets were reduced by H2-CO gas mixture for simulating the reduction processes of Midrex and HYL-III shaft furnaces. The influences of reduction temperature, ratio of φ(H2) to φ(CO), and pellet size on the reduction of HVTM pellets were evaluated in detail and the reduction reaction kinetics was investigated. The results show that both the reduction degree and reduction rate can be improved with increasing the reduction temperature and the H2 content as well as decreasing the pellet size. The rational reduction parameters are reduction temperature of 1050 °C, ratio of φ(H2) to φ(CO) of 2.5, and pellet diameter in the range of 8 - 11 mm. Under these conditions (pellet diameter of 11 mm), final reduction degree of 95.51% is achieved. The X-ray diffraction (XRD) pattern shows that the main phases of final reduced pellets under these conditions (pellet diameter of 11 mm) are reduced iron and rutile. The peak intensity of reduced iron increases obviously with the increase in the reduction temperature. Besides, relatively high reduction temperature promotes the migration and coarsening of metallic iron particles and improves the distribution of vanadium and chromium in the reduced iron, which is conducive to subsequent melting separation. At the early stage, the reduction process is controlled by interfacial chemical reaction and the apparent activation energy is 60.78 kJ/mol. The reduction process is controlled by both interfacial chemical reaction and internal diffusion at the final stage and the apparent activation energy is 30.54 kJ/mol.