Hydrogen plasma in extractive metallurgy application

Metal production have long been using carbon sources as both reducing agents and energy sources. Consequently, the global extractive metal sector contributes significantly to greenhouse gas emissions, accounting for approximately 9.5 per cent. Hydrogen gas offers as a promising ecofriendly alternative to carbon in metallurgical processes, serving as both a reductant and energy supplier with a by-product being only water vapour. However, the implementation of molecular hydrogen faces certain challenges related to the thermodynamics and kinetics of metal oxide reduction. In addressing these challenges, researchers have explored the application of hydrogen plasma, generated by subjecting molecular hydrogen to high energy to produce atomic, ionic and excited hydrogen species. Hydrogen plasma offers thermodynamic and kinetic advantages over molecular hydrogen and carbon-based reductants, exhibiting lower standard Gibbs free energy of reaction and activation energy. Therefore, hydrogen plasma can produce metal in fewer steps, process any oxide feed and feed size and even be used to refine metals. Despite these advantages, challenges exist in utilising hydrogen plasma in extractive metallurgy, including electricity costs, potential reverse reactions and industrial-scale implementation. This study provides a mini review of prior research on hydrogen plasma for metal oxides reduction, particularly iron oxide, as well as state-of-the-art techniques for its use in extractive metallurgy applications by mentioning several reactor types. Future prospects and scale-up possibilities of the hydrogen plasma in extractive metallurgy will also be presented.