[ Sustainability ]
[ Sustainability ]
Green steel from toxic red mud
An economical process with green hydrogen can be used to extract CO 2 - free iron from the red mud generated in aluminium production .
Text & images by Max-Planck-Institut für Eisenforschung
The production of aluminium generates around 180 million tonnes of toxic red mud every year . Scientists at the Max-Planck-Institut für Eisenforschung , a centre for iron research , have now shown how green steel can be produced from aluminium production waste in a relatively simple way . In an electric arc furnace similar to those used in the steel industry for decades , they convert the iron oxide contained in the red mud into iron using hydrogen plasma . With this process , almost 700 million tonnes of CO 2 -free steel could be produced from the four billion tonnes of red mud that have accumulated worldwide to date – which corresponds to a good third of annual steel production worldwide . The process would also be economically viable .
180 MT of mud per year According to forecasts , demand for steel and aluminium will increase by up to 60 % by 2050 . Yet the conventional production of these metals has a considerable impact on the environment . The aluminium industry produces around 180 million tonnes of red mud every year , which is highly alkaline and contains traces of heavy metals such as chromium . In Australia , Brazil and China , among others , this waste is at best dried and disposed of in gigantic landfill sites , resulting in high processing costs . When it rains heavily , the red mud is often washed out of the landfill , and when it dries , the wind can blow it into the environment as dust . In addition , the highly alkaline red mud corrodes the concrete walls of the landfills , resulting in red mud leaks that have already triggered environmental disasters on several occasions , for example in China in 2012 and in
In October 2010 , the dam of a red mud landfill site near the Hungarian town of Ajka burst ; over one million m3 flowed into the environment and three villages . Such environmental disasters could be avoided if the mud was used for steel production . Photo © Balazs Mohai / dpa / picture alliance .
Hungary in 2010 . Large quantities of red mud are also simply disposed of in nature .
Saving 1.5 billion tonnes of CO 2 “ Our process could simultaneously solve the waste problem of aluminium production and improve the steel industry ’ s carbon footprint ,” says Matic Jovičevič-Klug , who played a key role in the work as a scientist at the Max-Planck-Institut für Eisenforschung . In a study published in the journal Nature , the team shows how red mud can be utilised as a raw material in the steel industry . This is because the waste from aluminium production consists of up to 60 % iron oxide . The Max Planck scientists melt the red mud in an electric arc furnace and simultaneously reduce the contained iron oxide to iron using a plasma that contains 10 % hydrogen . The transformation , known as plasma reduction , takes just ten minutes , during which the liquid iron separates from the liquid oxides and can then be extracted easily . The iron is so pure that it can be processed directly into steel . The remaining metal oxides are no longer corrosive and solidify on cooling to form a glass-like material that can be used as a filling material in the construction industry , for example .
Other research groups have produced iron from red mud using a similar approach with coke , but this produces highly contaminated iron and large quantities of CO 2 . Using green hydrogen as a reducing agent avoids these greenhouse gas emissions . “ If green hydrogen would be used to produce iron from the four billion tonnes of red mud that have been generated in global aluminium production to date , the steel industry could save almost 1.5 billion tonnes of CO 2 ,” says Isnaldi Souza Filho , Research Group Leader at the Max-Planck-Institut für Eisenforschung .
An economical process The heavy metals in the red mud can also be virtually neutralised using the process . “ After reduction , we detected chromium in the iron ,” says Matic Jovičevič-Klug . “ Other heavy and precious metals are also likely to go into the iron or into a separate area . That ’ s something we ’ ll investigate in further studies . Valuable metals could then be separated and reused .” Furthermore , heavy metals that remain in the metal oxides are firmly bound within them and can no longer be washed out with water , as can happen with red mud .
22 Stainless Steel World May 2024 www . stainless-steel-world . net