In Situ Observation of Sustainable Hematite–Magnetite–Wüstite–Iron Hydrogen Plasma Reduction

Abstract Hydrogen plasma smelting reduction (HPSR) is an energy efficient, electrified, and fast process route to reduce not only iron ores but also thermally stable oxide materials, such as steelmaking sidestreams, waste, lean metallic ores, and metals with strong oxygen bonds. Both basic research of the underlying redox reaction mechanisms and upscaling and piloting of HPSR has gained significant momentum during the past decade, shedding light on reaction kinetics, hydrogen utilization, and process optimization. Yet, many questions still remain unanswered, the most important of which are how the reduction actually works at the interface between the hydrogen plasma and the oxidic and metal melts and what the actual radical species distribution is at the interface. Here, we present for the first time an in situ observation series of hematite reduction to metallic iron with filtered plasma imaging and optical emission spectroscopy. With the aid of plasma imaging and the optical spectra, the hematite, magnetite, wüstite, and both near-complete and complete metallization phases could be identified. The atomic hydrogen, iron, and aluminum species together with molecular optical emissions of FeO molecules were used to further analyze the process. Here, we study specifically hematite reduction to metallic iron at 10 pct H 2 /90 pct Ar in 450 and 900 mbar, and at 20 pct H 2 /80 pct Ar in 450 mbar as a model system.