Study on the Effects of Mg–Si Gangue Compositions within Magnetite on Iron Oxide Crystallization during Pellet Roasting

This article investigates the consolidation performance of high-magnesium content pellets under varying roast temperatures and Mg–Si elemental contents. The study reveals that as the proportion of high-Mg–Si ore increases, the strength of preheated pellets decreases from 546 to 470 N at a constant preheating temperature. The rise in magnesium and silicon phases diminishes the oxidation degree of the pellets, requiring a higher sintering temperature to achieve optimal consolidation. The research indicates that at 1200 °C pellets exhibit the highest average compressive strength with the best level of oxidation and secondary crystallization. However, over-roasting leads to a reduction in pellet strength due to excessive liquid phase interference at 1250 °C. When the high-Mg–Si raw material proportion is 50 wt%, the pellets with the highest compressive strength of 2843 N are yielded at the sintering temperature of 1200 °C and preheating temperature of 850 °C, which is attributed to the high oxidation, secondary crystallization of magnetite, and the MgO content facilitating the formation of CaO·Fe₂O₃ liquid phase, resulting in the best pellet consolidation strength.