Stepwise Oxygen-Enriched Sintering of Vanadium-Titanium Magnetite: Linking Oxygen Potential Distribution, Mineral Phases Evolution, and Metallurgical Properties

Vanadium–titanium magnetite (VTM) typically exhibits poor bed consolidation and unfavorable mineral-phase development during sintering. Oxygen-enriched sintering improves thermal conditions, accelerates oxidation kinetics, and optimizes the mineral-phase assemblage. This study evaluated the effects of oxygen enrichment applied during the heating stage, the cooling stage, and across the full process on VTM-sinter performance. Infrared thermography, X-ray diffraction (XRD), reflected-light mineral microscopy, and field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FE-SEM/EDS) were used to relate oxygen-potential distributions to mineralogy and metallurgical properties. Oxygen enrichment during heating narrowed the combustion zone, concentrated the heat flux, and accelerated liquid-phase formation, yielding a sintering productivity (utilization coefficient) of 2.37 t/(m 2 ·h). It also promoted the formation of dense, acicular silico-ferrite of calcium and aluminum (SFCA), strengthening the bonding phase and thereby improving sinter strength and the low-temperature reduction-degradation index (RDI). By contrast, oxygen enrichment during cooling or throughout the process increased perovskite (CaTiO 3 ), produced skeletal hematite (Fe 2 O 3 ), and induced microcracking and porosity, thereby weakening the bonding phase and worsening RDI. Overall, oxygen enrichment confined to the heating stage was the most effective strategy for simultaneously improving VTM-sinter quality and process efficiency.