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. CO${}_2$ addition enhances stability, increasing gas temperature from approximately 1900 K (pure H${}_2$) to 2900 K at 50% CO${}_2$ driven by exothermic H${}_2$ oxidation. Particle rapidly reach gas temperature ($>$2000 K within 5 ms). The highest metallization degree ($\approx$37%) achieved at 30% CO${}_2$, corresponds to an optimal reductant gas composition balancing hydrogen, carbon monoxide, and atomic hydrogen availability. Higher dilution (50% CO${}_2$) significantly decreased the reductant gas availability, lowering the degree of reduction despite higher temperatures. These insights demonstrate that controlled CO${}_2$ 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 CO${}_2$ closed loop.