Straw biomass

A new way to decarbonise steel making

Tackling a global challenge

Last updated: 23 November 2022


A new process could offer a solution to reducing carbon emissions in iron and steel making.

BioIron™ uses raw, sustainable biomass and microwave energy instead of coal to convert Pilbara iron ore to iron in the steelmaking process. BioIron has the potential to be carbon neutral and can result in net negative emissions when linked with carbon capture and storage.

We have proven the process works using a small-scale pilot plant, and now we’re planning to test it on a larger scale.

Why is low-carbon steel important?

Making steel – the process of converting iron ore into iron and iron into steel – uses a lot of energy. Because of this – and the fact it’s used in so many things – steel making is responsible for around 8% of all global emissions. 

Most of these emissions are created during the industrial process transforming iron ore – the raw material – into metal. Decarbonising the way iron (and therefore steel) is made could make a significant contribution to reducing global emissions. 

We worked with experts from the University of Nottingham, England and Metso Outotec, a specialist in sustainable technologies, to prove BioIron works on a small scale, and now we’re scaling it up to a continuous pilot plant with a capacity of one tonne per hour.

Warning: video contains flashing lights at 2.18

Steel making is responsible for around 8% of all global emissions and 66% of our Scope 3 emissions.

BioIron – one possible solution

  • It doesn’t create fossil fuel emissions.
    In this new process, iron ore fines are mixed with sustainable raw biomass material (like agricultural waste) and heated using a combination of gas released by the biomass and high efficiency microwaves powered by renewable energy, turning the iron ore into metallic iron.
  • Fast-growing biomass offers a carbon-neutral energy source.
    While the biomass will release carbon dioxide when it’s used, this is reabsorbed by using fast-growing plants as the biomass source. This is because about the same amount of carbon dioxide is absorbed in photosynthesis when the plants are regrown. If you just used plants and didn’t regrow them, or if the plants grew slowly – like trees in old growth forests – the CO2 would stay in the atmosphere. So using a fast-growing, sustainable biomass source is important.
  • If it’s done right, it could be a truly sustainable solution.
    We don’t want to solve one problem and cause another. We know from talking to environmental groups that we need to consider the kind of biomass we use and how it’s produced and transported. So, we’re including this as part of our research and we’re also undertaking a benchmarking study of biomass certification processes. And through our discussions with environmental groups, as a first step we have ruled out sources that support the logging of old growth and High Conservation Value forests.
  • The biomass used in this process doesn’t include food sources.
    Our process doesn’t, and can’t, use food such as sugar and corn. The parts you can’t eat – the straw, stalks and leaves – contain material called lignocellulose which has the type of carbon the process needs.
  • It could help our customers and the wider steel industry.
    It’s a global challenge and we want to play a part in finding solutions.
Michael, our iron man

Meet Michael

Our iron man

Michael Buckley likes the heat. As a materials engineer, he’s spent his career focusing on the high-temperature processes by which iron ore is converted into iron and steel:


“Steel is everywhere. It builds our cities, our homes, our cars, everything. But the process of making steel from iron ore takes a lot of energy, it accounts for about 8% of all global carbon dioxide (CO2) emissions. So, for over 10 years now, I’ve been trying to figure out how to decarbonise the process – I’m leading Rio’s scientific research into a new process for producing steel from Pilbara ores that would eliminate the use of coal, and potentially be a cost-effective way for the steel industry to cut its carbon emissions.

Our process uses sustainable biomass instead of coal. We briquette the biomass with the iron ore, preheat it and then zap it with microwaves – which can be powered by renewable energy – and this removes the oxygen from the iron ore, rapidly converting it into iron metal, which can then be turned into steel.

Sustainable biomass can be sourced from agricultural by-products, like wheat straw or sugarcane bagasse, or purpose grown energy crops on marginal agricultural land, or even micro and macroalgae. Importantly the process doesn’t – and can’t – use foodstuffs such as sugar and corn, and we would never use biomass that supports the logging of native forests.

Effectively the system is carbon neutral because the CO2 emitted by the process is reabsorbed by the fast-growing biomass that we use – and this is often referred to as “circular carbon”.

We know our process works in a small-scale pilot plant, and now we’re scaling it up further to a continuous pilot plant with a capacity of one tonne an hour.

It means a lot for our partners at the University of Nottingham as well to be taking it to this next stage. They’ve been with us on the journey all the way from those first two metal balls. It’s new territory for us all, including Metso Outotec, and we’re learning a lot and having a lot of fun.

It’s still early days and we have more work to do to prove it can work. But if we’re successful, it could play an important part in reducing carbon emissions across the steel industry.”


Why biomass?

Theoretically there are other ways you can produce iron from iron ore without using coal. One is to use hydrogen to react with the oxygen. Another is to zap it with a lot of electricity like in aluminium production. But we will need a variety of solutions to make sustainable steel, and this could be a good option for Pilbara iron ores. Through this research, we’re not only able to find a low-carbon way to process Pilbara iron ore, we can also contribute to an industry-wide challenge and help our customers reduce their emissions too.

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