The prereduction reactions in the submerged arc furnace (SAF) are highly decisive of the total carbon, and energy consumption of the ferromanganese process. Therefore, understanding the dependency of prereduction behavior on ore characteristics and furnace conditions is of paramount importance. Prereduction behavior of Comilog, Nchwaning and UMK ores with solid carbon was studied in an open 75 kVA induction furnace set up simulating the conditions of an industrial SAF. In addition, the ores were thermogravimetrically studied with non-isothermal heating to 1000 °C in a flowing 70/30 CO/CO₂ atmosphere. Gasification of carbon according to Boudouard reaction was considered significant for carbonate ores in induction furnace setup. UMK had a greater extent of prereduction compared to Nchwaning which is low in carbonates and Comilog which is known to have a higher CO reactivity at similar CO contents. TGA rate curves shows that prereduction of UMK ore occurred with two major distinctive steps. The first one was a combination of prereduction reactions and decomposition of carbonates with a peak temperature of 700 °C, and the second peak was the decomposition of calcite at 900 °C. The O/Mn ratio for UMK shows that prereduction is already completed prior to the second decomposition peak at 900 °C. In addition to prereduction reactions, Nchwaning is also characterized by an endothermic step which is decomposition of carbonates at 900 °C. Comilog ore produced the most fines followed by Nchwaning and lastly UMK on decrepitation.

Phase development during slag formation and reduction of Comilog and Assmang ores in a setup that simulates the conditions in an industrial SAF process under different coke bed temperatures, 1473 K (1200 °C), 1673 K (1400 °C) and 1773 K, (1500 °C) was investigated. Graphite crucibles were utilized to contain the charge and as a heating element in an induction furnace. A temperature profile was established, cross-sectional excavations were made, and samples were core drilled at selected positions. The resultant phases, i.e., slag and metal, were examined in an electron probe microanalyzer (EPMA) coupled with wavelength-dispersive spectrometry (WDS). The equilibrium phase relations in the MnO–SiO₂–CaO–MgO–Al₂O₃ oxide system were calculated using FactSage 7.3 thermochemical software. Differences in ore compositions revealed significant differences in phase development during slag formation and reduction behavior of these manganese sources. The phase development is highly influenced by temperature and position in relation to the coke bed, with a two-phase region, i.e., manganosite + liquid, dominant on top of the coke bed and a dominant liquid slag inside the coke bed. The solid monoxide phase in Comilog has been found to be purely MnO. In contrast to Comilog, the solid monoxide solution phase in Assmang has significantly high FeO content and forms a (Mn,Mg,Fe)O solid solution, which becomes more enriched in MgO with increases in temperature and reduction extent. Due to lower concentration of CO gas for prereduction in this experimental setup, iron oxides are reduced to FeO instead of Fe and subsequently FeO is stabilized in the monoxide solid solution.

Three pilot-scale experiments have been conducted at SINTEF/NTNU in a 440 kVA AC electric furnace to demonstrate the process operation, energy requirements and CO2 emissions in the production of high carbon ferromanganese alloys. Comilog, UMK and Nchwaning (Assmang) ores blended with other materials, such as sinter and flux, thus achieving different charge mixtures have been utilized in the experiments. In the prereduction zone, higher manganese oxides in the ore are reduced to MnO through solid-gas exothermic reactions and at a temperature around 800oC, the unwanted endothermic Boudouard reaction is also active. As such, the total coke and energy consumption is highly dependent on if the prereduction occurs by CO gas or solid C. The pilot furnace has been excavated after each experiment and the extent of prereduction of the ore has been investigated by collecting samples from specific regions in the prereduction zone. In addition, material, and energy balance calculations for the three pilot experiments have been calculated using HSC Chemistry software. The HSC material and energy balance calculations have shown that the slag/alloy ratios, metal analyses, carbon consumption and the overall energy consumption are mainly affected by the composition of the charge mixtures. The relationship between the specific carbon consumption, the off-gas CO2/(CO2+CO) ratio and energy consumption to produce 1 tonne of HCFeMn alloy is discussed for the three different pilot-scale scenarios.