Hydrogen reduction kinetics of a high-carbonate manganese ore in raw and calcined forms under isothermal conditions

This study examines the hydrogen-based isothermal reduction behavior of high-carbonate UMK manganese ore in both raw and calcined forms, with the aim supporting cleaner manganese ferroalloy production. Comprehensive characterization was performed using XRF, XRD, optical microscopy, and EPMA to assess the impact of the calcination process on lumpy ore structure, composition, and H 2 -reduction kinetics. Results show that calcination significantly enhances mineral liberation by decomposing carbonate phases and increasing porosity. Thermogravimetric reduction experiments at 700 °C, 800 °C, and 900 °C under 100 % H 2 reveal that calcined samples exhibit higher reduction rates, and improved extent of reduction compared to raw ore. Kinetic modelling using the Avrami-Erofeev equation demonstrates a shift in the rate-controlling mechanism from surface-controlled (dried ore) to diffusion-controlled (calcined ore), with apparent activation energy decreasing from 58.72 kJ/mol to 33.23 kJ/mol. Thermodynamic analysis confirms the active role of hydrogen in enhancing carbonate decomposition via the reverse water-gas-shift reaction (RWGSR), especially aiding calcite decomposition at lower temperatures. These findings highlight that calcination of the ore prior to hydrogen reduction not only improves hydrogen reactivity but also promotes favorable gas-solid interactions and CO 2 removal. The study supports hydrogen pre-reduction as a viable pathway to decarbonize Mn-alloy production and optimize furnace performance in high-temperature systems. • Calcination improves the reduction kinetics of carbonate-rich UMK manganese ore. • Hydrogen enables Mn and Fe oxide reduction at lower temperatures. • Reverse Water Gas Shift Reaction (RWGSR) promotes CO 2 removal and enhances calcite decomposition in H 2 . • Avrami modelling confirms shift to diffusion control after calcination. • Pre-treatment lowers apparent activation energy and boosts reduction efficiency.