Reduction of iron oxides with hydrogen: pathways towards sustainable metallurgy

Dierk Raabe, Max-Planck Institut für Eisenforschung, Düsseldorf, Germany

This lecture presents challenges and measures targeting the improvement of the sustainability of metallic alloys, specifically steels. Metals have enabled technological progress over millennia and have an enduring importance in our society. They paved the path of human civilization with load-bearing and functional applications that can be used under the harshest environmental conditions, from the Bronze Age onwards. Only metallic materials encompass such diverse features as strength, hardness, workability, damage tolerance, joinability, ductility and toughness, often combined with functional properties such as corrosion resistance, thermal and electric conductivity and magnetism [1,2]. Today we produce and consume about 2.1 billion tons of metals every year, with steels alone standing for an annual production of currently 1.85 billion tons.
This lecture therefore focusses on steels: it presents and discusses methods for improving the sustainability of steels, in areas including reduced-carbon-dioxide primary production by direct reduction and plasma [3,4], recycling and scrap-compatible alloy design. Steel production alone causes about a third of all industrial CO2 emissions, due to the use of carbon-carriers as reductants for iron ores, making it a major cause of global warming. Therefore, current research efforts aim at replacing carbon by hydrogen as reductant. Among several possible processing pathways, hydrogen-based direct reduction, in which solid iron ore pellets are exposed to gaseous hydrogen at temperatures between 600 and 1000°C, is a potentially attractive method, as it has been successfully used in industry with CH4 as reductant. In principle, hydrogen diffuses much faster through shaft furnace pellet agglomerates then conventional reductant cases such as CH4 or CO. However, the overall reduction kinetics and metallization achieved in hydrogen based direct reduction are rather sluggish, imposing challenges for meeting the high-throughput steel production required by markets. The lecture will therefore address some of the basic pending research questions in the field of hydrogen-based direct reduction of iron oxides. The lecture will also address other techniques for sustainable iron-ore reduction and the underlying scientific challenges such as plasma reduction [4].

[1] youtube: Sustainable Metallurgy and Green Metals

[2] Raabe D, Tasan CC, Olivetti EA. Strategies for improving the sustainability of structural metals. Nature. 2019 Nov; 575 (7781): 64-74.

[3] SH Kim, X Zhang, Y Ma, IR Souza Filho, K Schweinar, et al. Influence of microstructure and atomic-scale chemistry on the direct reduction of iron ore with hydrogen at 700° C, Acta Materialia, 2021

[4] IR Souza Filho, Y Ma, M Kulse, D Ponge, B Gault, et al. Sustainable steel through hydrogen plasma reduction of iron ore: Process, kinetics, microstructure, chemistry, Acta Materialia, 2021