Reduction disintegration behavior and crystallographic transformation of vanadium–titanium magnetite pellets during hydrogen-based reduction

：There are many advantages of the smelting of vanadium-titanium magnetite pellets by hydrogen-based shaft furnace pre-reduction and electric arc furnace process, including high reduction efficiency, low carbon dioxide emission and high recovery of titanium and so on. The preparation of qualified vanadium-titanium magnetite pellets with low reduction disintegration index (RDI) is prerequisite of this process. The reduction disintegration behavior of vanadium-titanium magnetite pellets during hydrogen-based reduction was systematically investigated in this work, and the crystallographic transformations during the reduction were dig into as well. The RDI +6.3 mm of vanadium-titanium magnetite pellets reached 43.28% after 60 minutes of reduction at 500 °C in a Midrex atmosphere (36% CO, 5% CO 2 , 55% H 2 , and 4% CH 4 ). During the reduction of trigonal titano-hematite [(Fe,Ti) 2 O 3 ] to cubic titano-magnetite, both the single unit cell volume and the total number of unit cells increased dramatically. The total titanium-iron oxide cell volume expanded nearly sevenfold, from 8.75×10 22 ų to 5.99×10 23 ų, causing considerable pellet swelling. Conversely, the reduction of rhombohedral Fe 2 TiO 5 to trigonal FeTiO 3 resulted in a decrease in cell volume. Studying the crystalline transformation is crucial for developing effective methods to inhibit low-temperature reduction disintegration, thereby enhancing the comprehensive utilization of vanadium-titanium magnetite resources.