The aluminum industry produces around 198 million tons (180 million tonnes) of bauxite residue – 'red mud' – yearly, which is extremely corrosive because it has high alkalinity and is rich in toxic heavy metals. In countries such as Australia, China and Brazil, the leftover red mud is usually disposed of in gigantic landfills, with high processing costs. The steel industry is equally environmentally damaging, responsible for 8% of global carbon dioxide emissions. Yet, the demand for steel and aluminum is forecast to increase by up to 60% by 2050.

However, scientists from the Max-Planck-Institut für Eisenforschung, Germany, a center for iron research, may have a solution to turn the toxic red mud by-product left over from aluminum production into green steel.

"Our process could simultaneously solve the waste problem of aluminum production and improve the steel industry's carbon footprint," said Matic Jovi?evi?-Klug, the study's lead author.

Red mud consists of up to 60% iron oxide. Melting the mud in an electric arc furnace using a plasma containing 10% hydrogen reduces it to liquid iron and liquid oxides, allowing the iron to be easily extracted. The plasma reduction technique takes 10 minutes and produces iron so pure, say the researchers, it can be processed directly into steel. And the no-longer-corrosive metal oxides solidify on cooling, so they can be transformed into glass-like material that could be used as a filling material in the construction industry.

Other researchers have produced iron from red mud using a similar approach, but with coke; however, it results in highly contaminated iron and large quantities of carbon dioxide. The approach taken in the new study, using green hydrogen as a reducing agent, avoids these greenhouse gas emissions.