Mechanism analysis of effect of MgO on reduction swelling behaviour of iron pellets in CO/H₂ atmosphere based on first-principles calculations

To explain the influence mechanism of MgO on the consolidation and reduction characteristics of roasted iron pellets, the properties and structure of pellets were investigated from multi-dimensions. It indicated that the MgO addition decreased the reduction swelling index (RSI) and reduction degree of pellets in both CO and H₂ atmospheres. During the stepwise reduction process of Fe₂O₃ → Fe₃O₄ → FeO, the reduction behaviour of pellets in CO and H₂ was similar, while the reduction rate of pellets in H₂ atmosphere was almost twice as high as that in CO atmosphere. During the stepwise reduction process of FeO → Fe, the RSI of pellets showed a logarithmic increase in CO atmosphere and a linear decrease in H₂ atmosphere. As investigated by first-principles calculations, C and Fe mainly formed chemical bonds, and the CO reduction process released energy, promoting the formation of iron whiskers. However, H and Fe produced weak physical adsorption, and the H₂ reduction process was endothermic, inhibiting the generation of iron whiskers. With Mg²⁺ doping in Fe_xO, the nucleation region of iron whiskers expanded in CO reduction process, and the morphology of iron whiskers transformed from “slender” to “stocky,” reducing RSI of the pellets.