From Pure H2 to H2-CO2 Mixtures: A Study of Reductant Strategies in Plasma Iron Smelting Reduction

Hydrogen plasma offers an emerging route for carbon-free iron oxide reduction, but typical inert gas dilution limits industrial applicability. This study explores pure hydrogen and hydrogen–carbon dioxide plasma for in-flight hematite reduction in atmospheric elongated arc discharge. Pure hydrogen yields the lowest power consumption, but reduced plasma stability and limited conversion. CO2 addition enhances stability, increasing gas temperature from approximately 1900 K (pure H2 ) to 2900 K at 50% CO2 driven by exothermic H2 oxidation. Particle rapidly reach gas temperature (>2000 K within 5 ms). The highest metallization degree (≈37%) achieved at 30% CO2 , corresponds to an optimal reductant gas composition balancing hydrogen, carbon monoxide, and atomic hydrogen availability. Higher dilution (50% CO2 ) significantly decreased the reductant gas availability, lowering the degree of reduction despite higher temperatures. These insights demonstrate that controlled CO2 co-feeding and regeneration optimize plasma stability, temperature, and reductant gas chemistry, presenting a promising approach towards scalable and energy-efficient hydrogen plasma smelting reduction for sustainable metallurgy with a CO2 closed loop.