Aluminum is the fastest growing mass-produced material group, a prerequisite for lightweight design of cars, airplanes as well as civil engineering structures. For its primary production through the Hall–Héroult process, alumina is used as the primary feedstock that is extracted through refinement of bauxite ore. During this process, the by-product bauxite residue or colloquially named red mud is formed. Due to the large scale of alumina production, red mud is produced in massive amounts of about 180 million tons per year that is mostly disposed into large ponds due to its low utilization in other industries (only 4 % of yearly production). As a result, red mud has amassed to one of the largest environmentally hazardous waste products on the planet, reaching a staggering global amount of 4 billion. Due to its high alkalinity and presence of heavy metals with it, red mud waste is environmentally highly hazardous and generally toxic to flora and fauna. However, red mud can hold large amounts of iron oxide, namely, up to 60 wt.%, making it a potential source for sustainable production of iron and other materials, if properly processed and neutralized.

In this presentation we demonstrate how red mud can be turned into valuable and sustainable feedstock for iron production using fossil-free hydrogen plasma-based reduction. (HPR) This on the one hand provides a solution to reducing the amount of red mud deposited on the planet and on the other it provides new means of mitigating part of the steel-related CO2 emissions through the production of green steel. Additionally to iron extraction, the processing of red mud with HPR also provides means to neutralize the remaining portion of the red mud residue by lowering its pH value close to neutral levels. In turn, this enables the complete utilization of the processed red mud by using the residual oxides for construction purposes such as cements. The presented process proceeds through rapid liquid-state reduction that simultaneously allows reduction of the iron oxides and chemical partitioning of the oxide melt into individual inert and stable oxides. The process also benefits from density and viscosity-driven separation of the different portions of the melt that enable easy extraction of high-grade iron in the form of macroscopic spheres ranging into the cm scale. With microstructural and chemical analysis of the reduced material we reveal the underlying chemical reactions, pH neutralization processes and phase transformations during this simple and fast single-step reduction process. A techno-economical and life-cycle assessment is also performed to evaluate the feasibility and long-time environmental impact of the process in relation to the different iron content within red mud. The approach provides a novel and efficient pathway towards sustainable treatment of environmentally-hazardous red mud into valuable products thus delivering a bridging solution for the waste and CO2 challenges of both aluminium and steel industry.