Assessment of Red Mud Recycling using Hydrogen Plasma Smelting Reduction

Steadily increasing global demand for industrial metals, particularly iron (Fe) and aluminium (Al), results in the annual emission of enormous amounts of carbon dioxide (CO2), thereby significantly contributing to anthropogenic climate change. In addition to CO2, the primary production of Al generates large quantities of environmentally harmful red mud (RM) (2 – 3 t RM/t Al). Treating this alkaline residue using hydrogen plasma smelting reduction (HPSR) contributes to a circular economy by enabling Fe to be recovered. This process not only conserves resources but also reduces CO2 emissions when powered by renewable electricity. The experiments conducted in this thesis focus on evaluating the feasibility of RM recycling through HPSR and optimising process conditions for the reduction of Fe oxides. This is done by adding fluxes and adjusting the hydrogen (H2) partial pressure. HPSR is based on removing oxygen (O) from Fe oxides in a liquid state using ionised hydrogen (H+) as a reducing agent, while an electric arc provides the thermal energy required for melting the input material and ionising hydrogen. A series of 18 experiments was carried out to identify the conditions that maximise Fe yield when using the available plasma reactor in combination with the investigated RM. Recycling unavoidable RM from primary Al production thus enables its use as a secondary raw material and facilitates the further processing of the residue. Consequently, landfilling and the associated demand for large disposal areas can be avoided.