Pure hydrogen and hydrogen-carbon dioxide for plasma iron oxide smelting reduction

Hydrogen plasma is an emerging technology for carbon-free iron oxide reduction, offering enhanced reactivity. Most studies utilize inert noble gases for plasma stabilization, but their high-cost limits industrial applications. This study explores pure hydrogen and hydrogen–carbon dioxide mixtures for in-flight iron oxide smelting reduction in atmospheric elongated plasmas. CO₂ in plasma dissociates into reactive CO, enabling exothermic iron oxide reduction and subsequent CO₂ regeneration. CO₂ addition improved plasma stability and resulted in increased plasma load from current and voltage measurements. Particle addition reduced plasma load slightly at 100% H₂, indicating minimal dissociation, while a notable reduction occurred with CO₂ dilution. Gas temperature measurements via spectroscopy (H₂ Fulcher-α, OH A-X) ranged from 2000–2700 K, rising with increased CO₂. Particle temperatures increased linearly with CO₂ concentration, matching gas temperature above 30% CO₂. X-ray diffraction with Rietveld refinement showed more hematite (Fe₂O₃) at 100% H₂, attributed to lower plasma stability. The metallization degree increased with CO₂ addition up to 30% CO₂ but declined at 50% CO₂. No carbon was detected in treated particles, indicating CO₂ improves plasma stability process temperature, and reactivity, presenting an alternative to noble gases. Recirculating remaining gases could achieve net-zero carbon emissions.