Effect of Pre-reduction of Manganese Ore by Hydrogen on Its Smelting Behavior and Interaction with Stable Oxides

The conventional ferromanganese production process is driven by coal/coke utilization and constitutes a substantial source of greenhouse gas emissions. Hydrogen-based pre-reduction process stands out for its substantial carbon reduction capabilities and established technological maturity. Regarding this, a process called HAlMan is proposed, where the manganese ore is pre-reduced with hydrogen and then fed in the smelting furnace for complete reduction with aluminum. As the pre-reduced ore becomes the charge material (feed) it becomes quite necessary to understand how the pre-reduced ore behaves when it meets other stable oxides and refractories for that matter. The present work studies the interaction of Nchwaning Manganese ore with Al₂O₃, SiO₂ and MgO substrates before and after reduction with hydrogen, using sessile drop wettability approach. The formed slag droplet on the substrate was cut through center and the cross-sectional analysis for diffusion depth and microstructure was done using SEM, EDS and mapping. In addition, FactSage thermodynamic software was used to correlate and understand the experimental observation and possible phase formed at elevated temperatures. The study found that both pre-reduction and substrate types significantly influence softening and smelting behavior of ore particles. Pre-reduced ore melted at 1350 °C with a wetting angle of 24.32° on SiO₂ and 1544 °C with 13.62° on Al₂O₃. While the unreduced ore melted at 1285 °C with of 32.15° on SiO₂ and at 1485 °C with 16.12° on Al₂O₃. No complete melting was observed on MgO substrate in either case. Giving an idea that MgO could be a better refractory for smelting of pre-reduced ore. The addition of Al₂O₃ to the pre-reduced and unreduced Nchwaning ore has opposing effects, as studied using FactSage. The melting temperature of pre-reduced decreases while that of unreduced ore increases on Al₂O₃ addition. This shows that the aluminothermic reduction of pre-reduced ore is better as the dissolution of Al₂O₃ would decrease the overall melting temperature during operation in the HAlMan process.