Induration Process of MgO Flux Pellet

The induration process of oxidized pellet, containing the oxidation of magnetite phase (Fe3O4) and the sintering of oxidized magnetite phase (hematite–Fe2O3), is significant to obtain sufficient pellet strength. The current study focuses on the induration mechanisms of MgO flux pellet in terms of the oxidation process of Fe3O4 and densification process of the pellet. It is found that MgO dosage negatively affects the oxidation of Fe3O4 into Fe2O3. The number of recrystallized grain of Fe2O3 in the MgO flux pellet is less than that in the Non-MgO flux pellet. Additionally, an unreacted core model was applied to consider and clarify the oxidation of Fe3O4. According to the verification experiments, the experimental data and calculated results fit well. Therefore, the unreacted core model can describe the oxidation of Fe3O4 in the pellet induration process. Moreover, based on the development of pore parameters during the pellet induration process, a new index, the so-called oxide densification index (ODI) was defined to profoundly specify the densification degree of the pellet. The results show that the ODI of the MgO flux pellet maintains at a lower level compared with that of the Non-MgO flux pellet. It illustrates that MgO can substantially restrain the pellet densification process.

Phases Transition and Consolidation Mechanism of High Chromium Vanadium-Titanium Magnetite Pellet by Oxidation Process

Based on the fundamental characteristics of high chromium vanadium-titanium magnetite (HCVTM), the effects of roasting temperature and roasting time on the phase transition and oxidation consolidation during the oxidation were investigated systematically. It was shown that the oxidation of HCVTM pellet was not a simple process but complex. With increasing roasting temperature and time, the compressive strength of oxidized pellet was improved. The phase transition during oxidation was hypothesized to proceed as follows: (1) Fe3O4 → Fe2O3; (2) Fe2.75Ti0.25O4 → Fe9TiO15 + FeTiO3 → Fe9TiO15 + Fe2Ti3O9; (3) Fe2VO4 → V2O3 → (Cr0.15V0.85)2O3; (4) FeCr2O4 → Cr2O3 → Cr1.3Fe0.7O3 + (Cr0.15V0.85)2O3. The oxidation consolidation process was divided into three stages: (1)oxidation below 1,173 K; (2) recrystallization consolidation at 1,173 – 1,373 K; (3) particle refining recrystallization-consolidation by the participation of liquid phase at 1,373 – 1,573 K. To obtain the HCVTM oxidized pellet with good quality, the rational roasting parameters included a roasting temperature of 1,573 K and a roasting time of 20 min.