Straw biomass

A new way to decarbonise steelmaking

Tackling a global challenge

Last updated: 4 June 2024

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

BioIron™ uses raw biomass and microwave energy instead of coal to convert Pilbara iron ore to iron and has the potential to support low carbon dioxide (CO2) steelmaking. Our modelling shows that when combined with renewable energy and carbon-circulation by fast-growing biomass, BioIron has the potential to reduce CO2 emissions by up to 95% compared with the current blast furnace method. 

We have proven the process works at a small-scale pilot plant, and now we’re planning to test it on a larger scale at our new BioIron Research & Development Facility.

Why is decarbonising steelmaking 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 – steelmaking is responsible for around 8% of all global CO2 emissions.  

Most of these emissions are created during the industrial process of 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 CO2 emissions.  

We worked with experts from the University of Nottingham, England and Metso Corporation (formerly known as Metso Outotec), a specialist in sustainable technologies, to prove BioIron works on a small batch scale, and now at our new facility we’ll be able to produce one tonne of iron per hour.

Rio Tinto BioIron

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

BioIron – one possible solution

It avoids the direct use of fossil fuel

In this new process, iron ore fines are mixed with 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. One main attraction of the BioIron process is that, as studies have demonstrated, it uses less than a third of the electricity needed by other new technologies currently being trialed such as those using hydrogen.

Fast-growing biomass offers a low CO2 energy source

BioIron still releases CO2, however by using fast-growing plants, these emissions are offset by the CO2 absorbed during photosynthesis when the plants regrow. 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 biomass source is important.

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.

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. Rio Tinto is aware of the complexities around the use of biomass supply and is working to ensure only sustainable sources of biomass are used. Through discussions with environmental groups, as the first step we have ruled out sources that support the logging of old growth and High Conservation Value forests. 

It could help our customers and the wider steel industry

To produce iron and steel with a smaller carbon footprint, we’ll need many technological breakthroughs. But there’s no single and obvious pathway to producing steel with low or no emissions. BioIron is one of the promising solutions we are developing and it works well with our Pilbara iron ores, the world’s largest iron ore region.

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 global 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 raw 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.

Raw biomass can be sourced from agricultural by-products, like wheat straw or canola stalks, 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.

BioIron still releases CO2, however by using fast-growing plants, these emissions are offset by the CO2 absorbed during photosynthesis when the plants regrow– 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 at our new BioIron R&D Facility 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. We’ve come a long way from the very first tests we did almost a decade ago. It’s new territory for us all, including Metso Corporation, 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 way is using electricity like in aluminium production. But we will need a variety of solutions to support sustainable steelmaking, and biomass could be a good option for Pilbara iron ores. Through this research, we’re not only able to find a way to process Pilbara iron ore with fewer emissions, we can also contribute to an industry-wide challenge and help our customers reduce their emissions, too. 

Related content

Water atomised steel powder

A new steel powder for 3D printing

Something infinitely small is making a big change
Yarwun Alumina Refinery from the air

Could hydrogen help reduce emissions in the aluminium industry?

A new pilot program will help us find out
Pilbara - Gudai-Darri site, 2020

Our first solar plant to power new iron ore mine

Gudai-Darri will be our most technologically advanced mine yet