Researchers create green steel from toxic red mud in 10 minutes

Researchers create green steel from toxic red mud in 10 minutes
Researchers have turned the red mud waste from aluminum production into green steel
Researchers have turned the red mud waste from aluminum production into green steel
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Researchers have turned the red mud waste from aluminum production into green steel
Researchers have turned the red mud waste from aluminum production into green steel

Researchers have devised an economically viable way of reducing the environmental impact of both the steel and aluminum industries by using hydrogen to melt down the toxic red mud left over from aluminum production to produce green steel in around 10 minutes.

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 Jovičević-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.

“If green hydrogen would be used to produce iron from the four billion tonnes of red mud that have been generated in global aluminum production to date, the steel industry could save almost 1.5 billion tonnes of CO2," said Isnaldi Souza Filho, corresponding author of the study.

The toxic heavy metals originally found in the red mud are “virtually neutralized” using this process. Any heavy metals that remain are firmly bound within the metal oxides and can’t be washed away with water, as can happen with red mud left in a landfill site.

“After reduction, we detected chromium in the iron,” Jovičević-Klug said. “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.”

The researchers say that producing iron from red mud directly using green hydrogen benefits the environment “twice over " and is economically beneficial. Using their calculations, if the red mud contains 35% iron oxide, this is enough to make the process economical. Taking the cost of green hydrogen and electricity to power the arc furnace at today’s prices and including the cost of landfilling the red mud, a proportion of 30% to 40% iron oxide in the mud would be needed for the resulting iron to be competitive in the market.

“These are conservative estimates because the costs for the disposal of the red mud are probably calculated rather low,” said Souza Filho.

In addition, electric arc furnaces are widely used in the metal industry – including in aluminum smelters – which would require industries to make only limited investments to become more sustainable.

“It was important for us to also consider economic aspects in our study,” said Dierk Raabe, a study co-author. “Now it’s up to the industry to decide whether it will utilize the plasma reduction of red mud to iron.”

The study was published in the journal Nature.

Source: Max-Planck-Gesellschaft

Gregg Eshelman
This looks like an ideal use case for a small nuclear reactor to produce the electricity to split water into hydrogen and oxygen and to power the arc furnace. More electricity could be generated by using fuel cells to recombine hydrogen and oxygen into water, which would reduce the amount of additional water used for hydrogen production.
They should proceed with using any hydrogen and let the hydrogen industry green by themselves.
Jim B
@Gregg - how big would the reactor need to be? Are small blast arc furnaces moveable?
If the red mud is 60% iron oxide, I'm surprised it hasn't been used as an ore using the standard coke process. It might be lower in iron content, but it doesn't need expensive mining. Just guessing that government intervention (subsidies, etc) gets in the way of common sense.
It’d be nice to get rid of all that crappy red mud but what’s the environmental cost of all the required electricity? And where does it come from? Nobody would ever get more nuclear power plants licensed or coal either. So while interesting, sadly it’s just academic pie in the sky. Maybe next century.
Expanded Viewpoint
Exactly right there, Tech Gazer! If something is 60% of your feedstock, that is quite the find! If there really are any precious metals in the red mud, what are they and what percentage?
Your comment Gregg, makes no sense. If a nuke plant is splitting water apart to get the Hydrogen, then why recombine it with Oxygen again to get some electricity out of the reaction? Have you ever taken any classes in chemistry?
It would be lovely to see the cost-benefit analysis for this. In particular, it would be interesting to see what the energy costs are, precisely. Electricity has a fairly stable cost per kWhr. The process "as described" would require energy to hydrolyze water into hydrogen, the energy required to strip hydrogen of its electrons (turn it into a plasma), the energy required to strike and maintain a substantial arc (already available, as the article notes, in the aluminum plant itself so this is stable/standard technology), the energy needed to take red "mud" from a slurry to molten metal temperatures, and finally the downstream energy costs of separating out the iron, smelting out anything in the iron you don't want to leave there as you make steel with it (possibly things of value as well), and the costs of turning the residual sludge into "stable fill" as it cools, if any. In addition to energy costs there would be some capital costs for infrastructure and humans and any additional chemistry required, but if the ENERGY costs make sense relative to traditional steel (which also requires a lot of energy to make from iron ore) then the rest of it will likely take care of itself.

Obviously, if one could skip the entire "store the red mud in a wet slurry" step, and incorporate this INTO the hot process involved in making aluminum, one might save the energy burden of heating up everything to molten metal temperatures more than once, and might even be able to build an "assembly line" with bauxite in at one end, aluminum and iron/steel/chromium/etc coming out at various intermediate points, and chunks of cooling inert silicates at the far end with the valuable metals removed and leftover toxic metals bound up in a more or less inert form. This is the kind of pilot program they need to demonstrate at a small scale, but a SCALABLE small scale.,
Why not try the hydrogen arc furnace on native bauxite, containing both iron and aluminum? Wouldn't that simply both processes?
Gregg Eshelman
@Expanded Viewpoint obviously there would be hydrogen left over from using it in smelting the iron so rather than let it go to waste it should be captured for re-use. One way to do that would be running it through a fuel cell if the amount of it, pressure or other reasons don't make it practical to store as-is to pump back into the furnace. Instead it would be "stored" as part of water. Water is easily kept in tanks.
Enough with ridiculous, totally redundant Imperial units!
One ton = 1000kg
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