Thermodynamic analysis and experimental verification of the direct reduction of iron ores with hydrogen at elevated temperature

• Published in: Journal of materials science Vol. 57; no. 43; pp. 20419 - 20434
• Main Authors: Li, Shaofei, Gu, Huazhi, Huang, Ao, Zou, Yongshun, Yang, Shuang, Fu, Lvping
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.11.2022; Springer; Springer Nature B.V
• Subjects: Air pollution; Analysis; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Coagulation; Crystallography and Scattering Methods; Diffusion barriers; Direct reduced iron; Disproportionation; Emissions (Pollution); Emissions control; Energy conservation; Greenhouse gases; Hematite; High temperature; Hydrogen; Hydrogen reduction; Iron compounds; Iron ores; Magnetite; Materials Science; Metallurgical analysis; Metals & Corrosion; Nonmetallic inclusions; Phase composition; Polymer Sciences; Solid Mechanics; Thermodynamics
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-022-07855-9

Hydrogen-based direct reducing iron production (H-DRI) possesses great potential for energy saving and emission reduction of greenhouse gas in metallurgical industries. Although the relevant research has been studied since long, the thermodynamics and process of reduction by pure H 2 in a broad temperature range are not well understood. Hence, we conducted a thermodynamic analysis of different iron ores (hematite and magnetite) reduced by H 2 at 300–1700 K to study the phase-composition variation with temperature. Subsequently, we explored the reduction process of iron ores by pure H 2 at 1173 K and 1673 K, respectively, to further investigate the influence of ore species and temperature on the microstructure evolution of ultimate metallic iron. The results reveal that excessive H 2 favors the transition from FeO to Fe in the last reduction step, and the magnetite achieves a higher reduction extent than hematite. Temperature above 837 K is beneficial for avoiding the occurrence of the disproportionation reaction and promoting the FeO → Fe transition to improve the reduction extent. Meanwhile, the higher volume mismatch and the associated stresses between hetero-phases at 1673 K contributed to the formation of large-size pores or cracks. The higher content of dense Fe layers formed in magnetite at relatively lower temperature served as barriers against the diffusion of O, leading to the retention of abundant closed pores in the iron matrix. The oxide impurities cannot be reduced by H 2 at 1673 K instead translated into oxide inclusions due to their low oxide-formation free energies, of which the coagulation was facilitated by increasing temperature as the higher velocity of migration and movement. With this study, we aim to provide theoretical direction for the practical application development of H-DRI.