Kinetics and microstructural changes during fluidized reduction of magnetite with hydrogen at low temperatures

Hydrogen reduction has received much attention in reducing carbon dioxide emissions and becoming carbon neutral in the iron and steel industry. In this study, the low-temperature hydrogen reduction (H2: N2 = 80%: 20%) process of natural magnetite in a fluidized bed was investigated. The reduction kinetics, phase transformation, and microstructure changes were characterized using chemical analyses, X-ray diffraction, Brunauer–Emmett–Teller method, and scanning electron microscopy. The results revealed that the magnetite was reduced to metallic iron in one step in the temperature range of 495 °C to 570 °C, and the reaction rate increased with increasing temperature. The one-step reduction of magnetite was controlled by the phase boundary reaction, and the apparent activation energy was 29.76 kJ/mol. Microstructural analysis indicated that as the reduction reaction progressed, micropores and cracks on the surface of the solid particles gradually developed. The dense magnetite core was wrapped by the porous metallic iron, which promoted the penetration of hydrogen into the particles and continued the reaction.