Abstract:

Hydrogen (H₂) gas has been proposed as an attractive candidate to replace carbon in metal production. Oxide reduction with H₂ releases water (H₂O) as the off-gas rather than carbon dioxide (CO₂). This has been shown to be feasible for e.g. iron oxides and some manganese oxides. However, common, more stable oxides, such as manganese monoxide (MnO), are subject to thermodynamic limitations, which prohibit reduction with H₂. Utilizing monoatomic or ionized hydrogen (H or H⁺), abundant in hydrogen plasma, makes the hydrogen-oxide reactions more favourable and allows reactions such as:

2H + MnO → H₂O + Mn

H⁺ + MnO → OH + Mn⁺

The current work demonstrates experimentally the production of metallic manganese by exposing sintered MnO to hydrogen plasma. The hydrogen plasma was generated by passing H₂ through a plasma torch. This paper will present the experimental setup and method, as well as characterisation of the reaction products. Hypotheses for the reaction paths are presented and discussed in the context of thermodynamics and solidification theory. Furthermore, computational fluid dynamics is used to support the discussions via mathematical modelling of temperature- and flow fields.

Although substantial research is still needed, the presented results demonstrate that hydrogen plasma allows for reduction of more stable oxides than is possible with H₂, and that hydrogen plasma-based technologies can be used for manganese production.

Keywords: Plasma, manganese production, MnO reduction, hydrogen

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Dr. Halvor Dalaker