Reduction of MnO Using a Thermal Hydrogen Plasma

Hydrogen (H₂) plays an important role in meeting the demand for carbon-free steels. When reduction is done with H₂, harmless water is released as the off-gas, instead of CO₂ generated by reduction with carbon. While steel can be produced using H₂, many of its alloying elements cannot. As a result, fully carbon-free steel production necessitates a carbon-free production of its alloying elements. An important alloying element for steel, manganese (Mn), is subject to thermodynamic limitations that makes reduction with H₂ infeasible. If instead a much more reactive hydrogen plasma is used these thermodynamic limitations would disappear. The current work shows an in-depth investigation into the reduction of manganese oxide (MnO) by a thermal hydrogen plasma under various conditions. By passing H₂ through a plasma torch before it contacts an MnO-containing slag, formation of metallic Mn was achieved with a hydrogen-based reductant. Investigating the reduced samples with an electron probe micro analyser (EPMA) the amount of Mn formation in different conditions is mapped out. The reduction was found to be favoured when the torch was operated with a transferred arc mode, and for slags high in MnO, if the melting point was not too high. While the research into reduction of stable oxides with thermal hydrogen plasmas is still in an early stage and there are many unanswered questions, the work presented demonstrates the possibility of hydrogen-based manganese production.