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 Fe 3 O 4 –MgO in different roasting atmospheres were investigated in this study. The results showed that Fe 2+ preferentially diffused to the MgO layer and combined with Mg 2+ to form Mg y Fe 1− y O in inert atmosphere, and then, Fe 3+ and Fe 2+ binded to Mg 2+ to form [(MgO) x (FeO) 1− x ]·Fe 2 O 3 (0 ≤  x  ≤ 1). The increase of roasting temperature was favorable for the entry of Mg 2+ into the spinel phase. In air atmosphere, Fe 3 O 4 was first oxidized to Fe 2 O 3 . Fe 3+ and Mg 2+ counter-diffused and then combined to Mg x Fe 3− x O 4 ( x  = 1). Fe 3 O 4 reacted more readily with MgO in inert atmosphere than in air atmosphere. It was favorable to increase the oxygen partial pressure for Mg x Fe 3− x O 4 ( x  = 1) generation. The diffusion rate of Mg 2+ at the interface of Fe 3 O 4 –MgO system in inert atmosphere was 1.88  µ m/min at 1200 °C, which was faster than that of 1.49  µ m/min in air atmosphere. Graphical Abstract