Study on hydrogen reduction behavior of Hainan Hematite: Kinetic and microstructural evolution from a green resource processing perspective

Abstract

Hainan hematite is a typical refractory iron ore with low porosity and high structural compactness, which severely limits its reactivity during hydrogen-based reduction. To address this challenge, a comprehensive investigation was conducted to examine its reduction behavior from multiple perspectives. Unlike conventional hematite, Hainan hematite exhibited a distinct two-stage kinetic behavior, which could not be fully described using traditional models. A segmental kinetic analysis was therefore applied, revealing a transition from chemical reaction control to diffusion control. The transformation from hematite to magnetite proceeded slowly at low temperatures but was significantly accelerated by elevated temperatures or extended reduction durations. Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometry (VSM) analyses revealed that the formation of internal cracks and the development of porous product layers enhanced hydrogen diffusion and magnetic phase enrichment, particularly at higher degrees of reduction. Brunauer–Emmett–Teller (BET) analysis further confirmed the progressive evolution of the pore network and highlighted the interplay between fine pore formation and crack propagation. These findings provide, for the first time, a detailed kinetic and microstructural interpretation of hydrogen-based reduction behavior in Hainan hematite, offering new insight into the reduction mechanism of refractory iron ores. The results contribute to a better understanding of the coupling among reaction kinetics, phase transformation, and pore structure evolution, and offer theoretical guidance for the advancement of low-carbon metallurgical technologies.