Hydrogen plasma smelting reduction of Cr 2 O 3 /Chromite: challenges, insights, and initial results of direct and sustainable stainless-steel production

By the end of 2050, the European Union aimed to decrease the carbon footprint (CO and CO 2 ) considerably. It was targeted to achieve 80–95% less than the level of emissions in 1990. Hydrogen, as a clean reducing agent, can eliminate the carbon footprint from the steel industry considerably (up to 95%). However, some factors, such as the endothermic nature of H 2 reduction and the thermodynamic resistance of some high-temperature mineral oxides against reduction by H 2 , hinder such achievement. Hydrogen plasma smelting reduction (HPSR), as an alternative promising method compared to H 2 and conventional carbon-based reduction methods, has emerged both in the lab and on a pilot plant scale in the current years. The direct reduction of chromite ore by HPSR, containing both Cr 2 O 3 and Fe 2 O 3 (and FeO), enables single-step production of low-carbon ferrochromium or stainless steel. Chromium is the major alloyed element of stainless steel produced mainly through the primary metallurgy methods from chromite ore. The ore contains different mineral oxides in the spinel phases that complicate the reduction process. Therefore, the study of different factors on the reduction of pure Cr 2 O 3 is the first step in evaluating the feasibility of ferrochromium production by HPSR. The plasma state provides enough reactivity and heat via the excited species of hydrogen to overcome the mentioned kinetic (T HP = 5000-25000 K) and thermodynamic (ΔG° HP ≤ −1500 kJ/mol) obstacles. In this paper, the in-situ evaluation of reduction degree via hydrogen by optimizing gas flow rate, melting temperature, and activity on pure Cr 2 O 3 and the mixture of it with selective acidic and basic fluxes in different crucibles (structural steel and magnesia-chromite refractory) was studied. Moreover, the required thermodynamic assessments for the experiment were conducted to clarify the feasibility of the reduction process.