Red mud is a hazardous waste from aluminium production and research is underway to extract the steel from aluminium waste. Using waste product from the aluminium industry to produce valuable green steel is promising. Can it scale from lab scale to production in a timely manner – technically and economically?

The world’s most-produced metals, iron and aluminium, have high environmental costs. The production of steel (1,600mt from 2,500mt of ore) requires fossil fuel (coal) and generates approximately 2 tonnes of carbon dioxide per tonne of steel. Green steel production is underway, albeit slowly. Aluminium production of about 60 million tonnes production (from 380mt of ore) generates 2–4 tonnes of environmentally problematic waste per tonne of aluminium produced. Steel production accounts for about 11% of global emissions.

In 2019 researchers showed iron extraction from red mud using roasting with sodium salt but in 2024, Jovičević-Klug et al. in Nature, report a process that has the potential not only to address this waste but also to achieve carbon-neutral steel production thereby increasing the sustainability of two major metal industries.

Red Mud – from Waste to Steel

Aluminium Production Process

• The first step is a hydrometallurgical extraction and refinement of alumina from bauxite ore. Needs temperatures of up to 240 °C and includes digesting crushed bauxite in strong sodium hydroxide solutions, resulting in alumina and an insoluble residue (red mud).
• The second part (Hall–Heroult process) is electrolysis refinement and consists of the decomposition of alumina dissolved in an electrolyte (Na₃AlF₆) at 950–970 °C followed by a purification stage, producing the metallic aluminium.
• Reduction of emissions from alumina smelters is underway – using renewable energy but with changes in the processes.

Red Mud

• Red mud is the main solid waste.
• About 4–5 tons of red mud is discarded per 1 ton of aluminium metal produced.
• More than 120m tonnes per year.
• Global inventory of red mud over 4 billion tonnes.
• Cheapest disposal method is transport to a dam, then go through dehydration and drying process to reduce its volume and maintenance costs. 
• Red mud method has a high potential for environmental impact.
• The sludge represents an environmental and economic problem.
• Red mud contains iron but the extraction process has been not as economically viable as mining iron ore directly.

Any process that takes waste, and turns it into a product is an opportunity.

Conventional Steel Mining and Production

Iron ore is a crucial raw material in the production of iron and steel, and its availability and quality play a significant role in determining the economic viability of steel manufacturing. Visually compare here. About 2,600 million tonnes are mined annually. Total world crude steel production was 1,878.5 Mt in 2022, a 4.2% decrease compared to 2021. 

Hematite

Hematite is the most abundant and widely mined iron ore. It is a reddish-black, heavy and relatively hard oxide mineral, ferric oxide (Fe₂O₃) has high iron content (70 percent).  Australia, Brazil, and China are the major producers. Only needs simple crushing, screening and blending process before shipped off for steel production. It accounts for a significant portion of the global iron ore output.

Magnetite

Magnetite primary component is an iron oxide that contains equal amounts of iron(II) and iron(III). The empirical formula, Fe3O4, is also expressed as iron(II,III) oxide. Previously called ferrous–ferric oxide and triiron tetraoxide. Known for its magnetic properties and high iron content. Australia, Russia, and Sweden are main suppliers. Magnetite’s production volume is lower than hematite’s, but is still a valuable resource in the iron and steel industry.

Limonite

Limonite, a lesser-known type of iron ore, consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. Colour is yellowish brown. The generic formula is FeO·nH₂O. The ratio of oxide to hydroxide can vary quite widely. It has a range of industrial and scientific uses, including as a pigment in paints and coatings, a source of iron oxide in cement production, a soil conditioner, and a filter medium in water treatment systems.

Primarily mined in Australia, Brazil, and China.

References

1. Ding Wei, Xiao Jun-Hui, Peng Yang, Shen Si-Yue & Chen Tao (2021) Iron Extraction from Red Mud using Roasting with Sodium Salt, Mineral Processing and Extractive Metallurgy Review, 42:3, 153-161, DOI: 10.1080/08827508.2019.1706049
2. Silveira, N.C.G.; Martins, M.L.F.; Bezerra, A.C.S.; Araújo, F.G.S. Red Mud from the Aluminium Industry: Production, Characteristics, and Alternative Applications in Construction Materials—A Review. Sustainability 2021, 13, 12741. https://doi.org/10.3390/su132212741
3. Jovičević-Klug, M., Souza Filho, I.R., Springer, H. et al. Green steel from red mud through climate-neutral hydrogen plasma reduction. Nature 625, 703–709 (2024). https://doi.org/10.1038/s41586-023-06901-z

Red Mud – Steel from aluminium waste

Considering iron content is betwen 35% to 48% iron ore, there is scope to recover this from the 2 billion already mined.

Info from Nature Paper

Source https://www.nature.com/articles/s41586-023-06901-z/figures/1