Phase relations in ferromanganese production through the aluminothermic reduction of a pre-reduced manganese ore

High-carbon ferromanganese is commercially produced via a carbothermic reduction route which generates a metal typically with 70-80% Mn,1-2% Si and 7.5% C along with significant amount of slag. An alternative sustainable approach to produce ferromanganese is the pre-reduction of the ore by hydrogen followed by an aluminothermic reduction-smelting process, the HAlMan process. In this work, extensive study on aluminothermic reduction of hydrogen based pre-reduced Nchawning manganese ore was done. The study was conducted with varying Al, and the quantity of added lime to obtain molten ferromanganese and slag in a flux-smelting process. The study further extends to find the possibility of forming leachable calcium aluminate slag, to recover further Al2O3 used in the process. The experimental study has shown that a metal with 75-80 % Mn, 0.5-1% Si and rest Fe, could be obtained. Moreover, a slag with SiO2 < 7 wt% , Al2O3 > 47 Wt.% and CaO<42 wt.% could be formed, and it was characterized using XRD, SEM and XRF analysis. The slag was found to mostly contain calcium aluminate phase with small amount of unreduced MnO and significantly lower amount of gehlenite phase. It is shown by experimental and theoretical work that the new approach will provide high quality metal product with high yield.