Abstract
The transition from carbon-based reductants to hydrogen represents a paradigm shift for decarbonization in the ferroalloy industry. Processes such as HAlMan (Hydrogen and Aluminum use for Manganese and its alloys production) enable the replacement of solid carbon with hydrogen, offering a viable route to significantly reduce the environmental footprint of manganese and ferromanganese production. Having progressed from laboratory to pilot scale, the HAlMan concept demonstrates the potential to cut CO2 emissions by up to 1.5 tonnes per tonne of ferromanganese produced, positioning hydrogen-based metallurgy as a key enabler of sustainable ferroalloy manufacturing. In this study, the thermochemical behavior and hydrogen reduction kinetics of a high-grade and a low-grade European manganese ore was investigated under controlled laboratory conditions. To obtain reliable kinetic data, the ores were first calcined at 900°C to remove carbonates and hydroxides and to stabilize their microstructure followed by isothermal hydrogen reduction in a vertical thermogravimetric furnace at 600°C, 700°C, and 800°C. Mass loss and reduction rates were quantified using thermogravimetric analysis, while wet chemical analysis, XRD and porosity measurements were used to assess compositional and mineralogical evolution. The results indicate that hydrogen reduction kinetics of manganese and iron oxides are strongly temperature-dependent, with higher temperatures accelerating reduction and phase transformation. Sintering and densification effects were observed above 700°C, reflected by reductions in porosity (%). These results show that controlled thermal pre-treatment and temperature optimization are key to enabling efficient hydrogen reduction and advancing climate-neutral ferromanganese production.