In-Flight Reduction of Iron Ore Particles in an Atmospheric Pressure Hydrogen Microwave Plasma

CO₂ emission from the steel industry, which accounts for ~7-9% of the global anthropogenic CO2 emissions, is a key challenge for achieving a carbon-neutral future. To overcome this challenge, the steel industry must reduce its dependence on blast furnaces for iron ore reduction, i.e., the conversion of iron oxide to iron, and adopt new technologies that drastically lower carbon emissions. This contribution presents a plasma process for reducing iron ore particles with an atmospheric pressure hydrogen plasma. The plasma is maintained by coupling microwave power of 1.5 kW into an argon-hydrogen gas mixture. The iron ore particles with a size of about 50 µm are aerosolized and passed through the active plasma zone. After the treatment, the collected particles are observed to follow three distinct populations: i) unreduced particles with the shape and size of the original feedstock, ii) partially (15%) reduced spheres, larger than the feedstock, and iii) fully reduced nanoparticles. It is found that the nanoparticles are likely formed from previously evaporated material, and the reduction happens either on the surface of the particles before evaporation or in the gas phase after evaporation. The plasma temperature is estimated to be more than 2000 K, which enables the rapid evaporation and reduction of these particles within residence times of only a few 10 milliseconds. The technology has the potential to become a zero-carbon process. It overcomes some major problems encountered in competing technologies, such as the need for pelletizing, vacuum operation, and the lifetime of electrodes/plasma torches.<br/>This work was supported by the University of Minnesota under the Ronald L. and Janet A. Christenson Chair in Renewable Energy and by the Minnesota Environment and Natural Resources Trust Fund under project 2023-171.