Microstructure-transport coupling in titaniferous magnetite pre-reduction: Porosity evolution, Ti-phase effects, and modelling for low-carbon ironmaking

Titaniferous magnetite (TTM) is among the largest reserves of underexploited iron ore resources. Titanium-bearing minerals including ilmenite, pseudobrookite, and enriched titanium spinel phases alter reduction mechanisms, pore structure development, and transport phenomena in ways that traditional iron oxide models cannot capture. This review addresses that gap by consolidating recent developments in the solid-state, packed-bed pre-reduction of TTM, a process whose literature remains comparatively scarce relative to conventional hematite, with emphasis on the coupling between microstructural evolution and transport processes across particle, pellet, and reactor scales. Topics covered include porosity transitions from uni-modal to bi-modal pore structures, the competing roles of sintering and pore formation in controlling permeability, the effect of Ti-phase enrichment on the transition from chemical to diffusion control, reaction-front progression, the influence of carbonaceous and gaseous reductants, and multiphysics computational fluid dynamics modelling of heat, gas-phase transport, and phase transformation across scales. Since direct TTM evidence remains sparse relative to conventional ore, this review also develops testable, semi-quantitative hypotheses linking Ti-phase persistence to permeability loss, percolation-threshold shifts, and whisker-versus-dense-shell morphology, alongside three outstanding gaps: the absence of data linking titanium-phase formation to permeability under realistic flowing-gas conditions, the lack of pore-scale investigation under titaniferous conditions, and the absence of a multiphysics CFD model incorporating Fe-Ti-O multicomponent thermochemistry in packed-bed reactors. Insights from synchrotron visualization, thermogravimetric kinetics, and reactor simulation provide a foundation for efficient, low-carbon pre-reduction of titaniferous magnetite.