Interface Diffusion and Reaction Mechanisms of Fe₃O₄–MgO System in Pellets Under Different Atmospheres

The proportion of pellets in the blast furnace charge structure is gradually increasing, among which magnesium-bearing fluxed pellets have been widely applied due to their excellent metallurgical properties. To further determine the consolidation mechanism in different reaction layers of magnesium-bearing fluxed pellets, the phase transformation and diffusion behaviors of Fe₃O₄–MgO in different roasting atmospheres were investigated in this study. The results showed that Fe²⁺ preferentially diffused to the MgO layer and combined with Mg²⁺ to form Mg_yFe_1−yO in inert atmosphere, and then, Fe³⁺ and Fe²⁺ binded to Mg²⁺ to form [(MgO)_x(FeO)_1−x]·Fe₂O₃ (0 ≤ x ≤ 1). The increase of roasting temperature was favorable for the entry of Mg²⁺ into the spinel phase. In air atmosphere, Fe₃O₄ was first oxidized to Fe₂O₃. Fe³⁺ and Mg²⁺ counter-diffused and then combined to Mg_xFe_3−xO₄ (x = 1). Fe₃O₄ reacted more readily with MgO in inert atmosphere than in air atmosphere. It was favorable to increase the oxygen partial pressure for Mg_xFe_3−xO₄ (x = 1) generation. The diffusion rate of Mg²⁺ at the interface of Fe₃O₄–MgO system in inert atmosphere was 1.88 µm/min at 1200 °C, which was faster than that of 1.49 µm/min in air atmosphere.