Mineral phase evolution of titanomagnetite (TTM) during the reduction process is not only important from the theoretical point of view, but also crucial to the practice of its direct reduction. Therefore, in the present study, the phase evolution pathway as well as the reduction mechanism and kinetics of TTM at 1323 K were investigated in hydrogen (H2) and carbon monoxide (CO) atmospheres, respectively. It was found that, regardless of the atmosphere, the phase evolution sequence is Fe3−xTixO4→2FeO·TiO2→FeO·TiO2→FeO·2TiO2→TiO2. For the transition of Fe3−xTixO4→2FeO·TiO2, it was identified as an exsolution process of wüstite (FetO), in which the crystal structure of TTM remained unchanged but with a continuous increase of Ti/Fe molar ratio to 0.5. For the transitions of 2FeO·TiO2→FeO·TiO2→FeO·2TiO2→TiO2, they were characterized by the structural change accompanied by the continued increase of Ti/Fe molar ratio and formation of product metal Fe. Concerning the kinetic behavior of these transitions, it was found that although the rate of each transition is distinct from each other, all of them complied with the regularity of a first-order interfacial chemical reaction. Furthermore, under a H2 atmosphere, the reduction rate constants for the Fe3−xTixO4 phase, 2FeO·TiO2 phase, FeO·TiO2 phase, and FeO·2TiO2 phase are 6.14 × 10−3, 2.00 × 10−3, 9.94 × 10−4, and 3.96 × 10−4 min−1, respectively. Under a CO atmosphere, the corresponding values for these phases are 6.07 × 10−3, 1.73 × 10−3, 8.01 × 10−4, and 2.95 × 10−4 min−1, respectively. This indicates that the rate of each transition is strongly correlated with the Ti/Fe molar ratio of the parent phase, and the larger the Ti/Fe molar ratio, the slower the transition rate. And, for each transition, its rate in H2 is higher than in CO, and the larger the Ti/Fe molar ratio, the bigger the difference.
