Effect of Refractory Type on the Characteristics of Alloy and Slag Produced by Aluminothermic Reduction of a Prereduced Manganese Ore

The present study systematically investigates the influence of refractory crucible materials, Al 2 O 3 , MgO, SiC, and graphite on the metal and slag phases formed during the aluminothermic reduction of a hydrogen-based prereduced Nchwaning manganese ore. Laboratory-scale experiments revealed that the choice of refractory material of crucibles significantly affects metal recovery, phase evolution, and chemical composition of both metal and slag products. Manganese recovery was highest (~97%) in SiC and graphite crucibles, compared with ~93% in the Al 2 O 3 crucible. However, despite the higher recovery, metals produced in SiC and graphite crucibles exhibited contamination from crucible-derived impurities. In the SiC crucible, Si pickup led to the formation of Mn 5 Si 3 as a dominant phase, while in the C refractory crucible, carbon dissolution resulted in Mn 7 C 3 as the major phase. The targeted slag phase, krotite (CaAl 2 O 4 ), formed as the primary phase in all crucibles except MgO, where it was observed only as a minor phase. Overall, although SiC and graphite crucibles enhanced manganese recovery, the Al 2 O 3 crucible provided the optimal balance between metal purity and slag chemistry, producing ferromanganese low in C and Si content along with krotite-rich slag. Therefore, Al 2 O 3 emerges as the most suitable refractory material for laboratory-scale aluminothermic reduction of hydrogen-based prereduced Nchwaning manganese ore.