A sustainable reduction roasting technology to upgrade the ferruginous manganese ores

Reduction roasting of manganese ores is a known process; however, it is not yet commercialized mainly due to various techno-economic issues. The current research work presents results of a large-scale plant trial performed at a commercial Direct Reduced Iron making plant to upgrade low-grade ferruginous manganese ores (Mn: 25–32%, Mn/Fe: ∼1). Trials were carried out using a lot of 2000 of tons low grades ferruginous manganese ores of three different types. Experiments were designed to test 3 levels of two different variables for each type of ore. Raw material feed rate (3, 4.5, and 6tph) and feed coal proportion (25, 29,33% of ore) were the prime process variables. Process settings were identified and fixed to limit the occurrence of undesired chemical reactions to restrict the formation of complex Mn_xFe_3-xO₄ phases and dilution of reducing atmosphere. Ores were crushed into 0–15 mm size, reduce-roasted at 950 °C in a rotary kiln, crushed into <3 mm size, and passed through a magnetic separator. The technology can enhance the Mn content of the ores by > 15 units (Mn: 30%→46%) and can bring down the Fe content by > 15 units (Fe: 27%→12%) in the produced ore concentrate. The developed process could achieve product yield ∼50% and Mn Recovery>70%. The Mn-rich concentrate was successfully converted into extrusion briquettes and consumed in a submerged arc furnace for ferroalloy making. The iron-rich by-product was successfully used as a sinter mix for steelmaking process. Techno-economic evaluation and sensitivity analysis have also been carried out. Studies indicated that roasting of ferruginous manganese ores at a commercial Direct Reduced Iron plant is an adaptable and sustainable solution to upgrade the low-grade Mn resources in the dynamic global Mn ore market.