Aluminum production generates massive amounts of toxic, heavy metal-laden, corrosive red mud, which is typically dried and disposed of in huge concrete-lined basins or, worse, dumped in nature. Some 4 billion tons have accumulated in such landfills around the world. However, red mud is highly alkaline and corrodes the concrete landfill walls. In addition, heavy rains can cause overflows, spilling red mud into the surrounding environment, and when it dries, wind can spread it as airborne dust.

Matic Jovičević-Klug, Isnaldi R. Souza Filho, and colleagues, Max Planck Institute for Sustainable Materials, Düsseldorf, Germany, have studied ways to turn red mud into valuable resources. Focusing on its high iron oxide content of up to 60%, they developed a method to produce green steel by melting the red mud in an electric arc furnace. Using plasma with 10% hydrogen, they reduce iron oxide to iron, separating it from liquid oxides. The pure iron can then be processed into steel.

For decades, the steel and aluminum industries have used such furnaces to melt down scrap metal.  
The researchers say their process could solve the aluminum industry’s waste problem while improving the steel industry’s carbon footprint.  With around 4 billion tons of red mud worldwide, nearly 700 million tons of steel—about one-third of global annual production—could be extracted. If green hydrogen is used, the steel industry could save about 1.5 billion tons of CO₂, the researchers say.

The remaining metal oxides solidify into a non-corrosive, glass-like material that could be used in construction. Further research is being conducted to explore the recovery of additional valuable metals, but the residual material is stable and unlikely to leach harmful substances.

• Green steel from red mud through climate-neutral hydrogen plasma reduction,
  Matic Jovičević-Klug, Isnaldi R. Souza Filho, Hauke Springer, Christian Adam, Dierk Raabe,
  Nature 2024, 625, 703–709.
  https://doi.org/10.1038/s41586-023-06901-z