Use of H2 in Mn-Ferroalloy Production

Abstract

The use of H2 as a reductant in the iron and steel industry is an obvious choice towards carbon neutrality. For pyrometallurgical processes like Mn and Si, H2 cannot be the only solution, as the stability of the oxides of these elements is higher compared to Fe. H2 can, however, be used in the Mn-process together with other low CO2 emission mitigations. In the Mn-ferroalloy process, H2 can be used to reduce higher manganese oxides to MnO, and the last part of the reduction to metallic Mn can be done with biocarbon or with electrolysis. In studies from NTNU, the reduction of higher manganese oxides to MnO has been investigated with pure H2 or with CO/H2 mixtures. It is shown that the H2 containing gases will give higher reduction rate compared to CO/CO2 gases with the same reduction potential. The reduction rate will be increased in the order of 20–100%, and H2 has a larger impact on the reduction rate for high oxygen pressures. In H2 gas, it is seen that the final degree of reduction is higher than using CO gas, and this is believed to be due to the formation of metallic iron. The reduction rate in H2 gases varies for various ores, and as for CO containing gases, the reduction rate of Comilog ore is faster than the Nchwaning ore, and activation energies of 23 kJ/mol versus 68 kJ/mol are, respectively, found for isothermal experiments in CO, H2, and CO2 gases.