Investigation of structural changes during hydrogen-based direct reduction of iron ore fines under pressure using in-situ XRD and SEM

Abstract

The steel industry is a significant contributor to global carbon dioxide emissions, necessitating the development of alternative ironmaking processes to meet climate targets. This study investigated the direct reduction of iron ore fines using pure hydrogen as a reductant, focusing on the influence of pressure and temperature on structural changes. In-situ X-ray diffraction (XRD) was employed to monitor the phase transformations during the reduction process, while scanning electron microscopy (SEM) was used to characterize the surface morphology of the reduced samples. Additionally, X-ray fluorescence (XRF) analysis was conducted to determine the chemical composition of the original iron ore. The experiments were performed up to 700 °C and at 1 bar and 3 bar absolute pressure. Increasing the pressure from 1 bar to 3 bar accelerated the formation of metallic iron, lowering the onset temperature by about 20 °C from 280 °C to 260 °C and promoting faster phase transformation. SEM analysis revealed that higher pressure leads to more compact microstructures and finer cracks, reflecting a more uniform reduction. Even gangue-rich, low-grade ore exhibited good reducibility under hydrogen, particularly at elevated pressure. These findings provide valuable insights for the optimization of hydrogen-based direct reduction and support the development of sustainable, energy-efficient ironmaking technologies with reduced CO2 emissions.