Kinetic analysis of non-isothermal hydrogen reduction of manganese ores: experimental investigation and combined chemical reaction-diffusion modeling

Abstract

Abstract Hydrogen-based reduction of manganese ores offers a promising route to reduce CO 2 emissions in manganese processing; however, the kinetics under non-isothermal conditions remain insufficiently understood. In this study, the non-isothermal hydrogen reduction behavior of two industrial manganese ores, Gloria and Zambian, was investigated using thermogravimetric analysis under 100% H 2 at heating rates of 2.5 and 5 K min − 1 up to 973 K (700 °C) from room temperature 293 K (20 °C). Calcination significantly modified the microstructure of the ores, increasing porosity from 1.6 to 32.66% for Gloria and from 19.12 to 28.07% for Zambian. The onset of reduction occurred between 611 and 689 K for Gloria and 625–653 K for Zambian depending on the heating rate, with final conversions of approximately 91–97%. A combined non-isothermal kinetic model based on the shrinking-core framework, incorporating interfacial chemical reaction and product-layer diffusion control, successfully described the reduction behavior. The model showed excellent agreement for Gloria ore (R 2 = 0.997 and 0.994) and reasonable agreement for Zambian ore (R 2 = 0.916 and 0.910). The apparent activation energies were 67.70 and 47.95 kJ mol − 1 for Gloria and Zambian ores, respectively. These results provide insight into the reduction mechanisms of manganese ores under hydrogen atmospheres and contribute to the development of hydrogen-based manganese processing technologies.