Hybrid hydro-pyrometallurgy route for green steel: Design and cost analysis of innovative and negative carbon dioxide emissions industrial-scale plants with different iron ore grades

Abstract

To ensure a sustainable future for the steel industry, it is crucial to develop decarbonization solutions that enable steel production from low-grade iron ores. This article presents a techno-economic assessment of an innovative industrial-scale process for producing green steel from low-grade ores with net-negative carbon dioxide (CO₂) emissions. The process includes a hydrometallurgical stage, where iron oxides are selectively dissolved by oxalic acid into ferric salts (Fe³⁺). These salts are then reduced to ferrous iron (Fe²⁺) through a photoreduction process using only light energy. In the subsequent pyro-reduction stage, the iron salts are converted into metallic iron with carbon monoxide and hydrogen as reducing agents. The oxalic acid used in the process is regenerated through the electrolytic reduction of CO₂, requiring an external CO₂ supply, while hydrogen is produced via alkaline water electrolysis. Results indicate that green steel can be produced with a levelized cost of production of 1093.32 $/t_STEEL, assuming renewable energy costs of 30 $/MWh. The main limitation of the process is its high energy demand, primarily due to the endothermic nature of metal oxide dissolution and the energy consumption of the electrolyzers. However, with expected improvements in electrolyzer efficiency, energy consumption is anticipated to decrease, further lowering production costs.