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14 February 2024 7 min read

What if you could accelerate a process that naturally takes carbon dioxide from the air and locks it away? 

Geologist, Renee Birchall, is the CSIRO Lead for Mission Innovation Engagement and part of the CarbonLock Future Science Platform.

Enhanced mineralisation – EM for short – does exactly that, speeding up the natural but slow geological process of mineral carbonation.

Scientists around the world say EM – or enhanced mineral carbonation – is one of the methods we need to deploy to reduce carbon dioxide (CO2) in the atmosphere to combat climate change.

EM replicates a range of natural geochemical processes, such as weathering (ex-situ) and hydrothermal processes (in-situ).

Weathering of surficial rocks reacts negatively charged CO2 (dissolved in rainwater) with positively charged alkaline elements – such as magnesium and calcium – to form carbonate minerals.

Similarly, CO2 -rich hydrothermal fluids from the deep crust can react with magnesium-oxide-bearing minerals such as olivine and serpentine to form Mg carbonate (magnesite) and silica.

EM is about engineering and accelerating these natural processes.

Australia is co-leading the EM technical track for Carbon Dioxide Removal (CDR), one of several missions being run by the global initiative Mission Innovation (MI-CDR).

The 2023-26 work plan was co-developed by CSIRO and colleagues from the Kingdom of Saudi Arabia and released at COP28 in Dubai.

"One of the really exciting parts of the work plan is developing a CDR roadmap, which will help inform policy to develop the industry around carbon dioxide removal," says geologist Renee Birchall, CSIRO Lead for MI-CDR Engagement and part of CSIRO’s CarbonLock Future Science Platform.

"Our work can show policymakers where we need to go regarding the technologies and science and how it will benefit countries' commitments to reach net zero. We're also signalling to markets and investors the potential of this industry."

The MI-CDR collaboration is vital knowledge exchange between nations as we all race to net zero.

"It's the greatest challenge of our time, and we can’t be doing this R&D work individually – to achieve the outcome we need to, we all need to work together," says Renee.

[Music plays and a split circle appears, and photos move through on either side of the circle showing various CSIRO activities, and then the circle morphs into the CSIRO logo]

[Image changes to show a blue screen, and text appears: Carbonlock: Research Project Spotlight, Mineral Carbonation]

[Image changes to show Renee Birchall talking to the camera, and text appears: Renee Birchall, CSIRO]

Renee Birchall: I’m Renee Birchall and I’m a geoscientist working on carbon sequestration in rocks.

[Images move through to show a close view of Renee talking to the camera, a view looking down over a mountain to the sea, and a close view of water dripping off the rocks]

I’m working on something called mineral carbonation which is a naturally occurring process in nature that sequesters CO2 by reacting with the minerals in the rocks.

[Image changes to show dark clouds scudding across the sky above farming land, and then the image changes to show a close view of Renee talking to the camera]

This is one of the ways that the Earth’s been managing its climate through the natural rock weathering cycle, and this has been happening for millions of years.

[Image changes to show a medium and then close view of Renee talking to the camera, and then the image changes to show dark clouds moving over the mountains and then the sea]

One of the ways we know carbonation works in nature is rainwater reacts with the carbon dioxide in the atmosphere effectively sucking it out of the air and creating carbonic acid.

[Image changes to show close views of rain falling on trees, and then on to rocks]

The rainwater then falls to Earth and weathers rocks forming bicarbonate and then stable carbonate.

[Images move through to show rain falling on to rocks, an aerial view of a river, and then a river mouth joining into the sea]

The carbonate is permanently and safely stored and stays in the soil then washes into the waterways and eventually the ocean.

[Image changes to show a medium and then a close view of Renee talking to the camera]

We’re looking at speeding up those natural cycles and engineering the specific mineral reactions so we can scale up and increase the amount of carbon dioxide sequestered.

[Images move through to show rocks moving through a crusher, and an aerial view of a mine tailings dam]

By engineering mineral carbonation, we can imitate this process using crushed rocks from industrial waste, including toxic mine tailings that can’t just be released into the environment.

[Images move through to show mine tailings moving down through the rocks, a close view of rocks moving up a conveyer belt, rocks moving through a crusher, and then a barrel of cement being stirred]

Many of these industrial wastes and mine tailings already contain the necessary elements we need to react with carbon dioxide to create stable carbonates and even carbonate products like cement.

[Images move through to show Renee talking to the camera, a close view of hand spreading mulch between plants, and a rear view of a farmer walking through a field carrying a shovel]

Precipitation of carbonates through adding crushed rock to soils will improve the soil health raising the pH, and also improve farm productivity.

[Images move through to show Renee talking to the camera, a plane in the air, and views of large chimneys belching smoke into the air]

Engineered mineral carbonation can also be used as a stepping stone to assist fossil fuel-based industries in their pathway to net zero and in their emissions reduction strategies.

[Images move through to show clouds scudding over a lake and mountains, and then a close view of water dripping off some rocks]

Of course, there’ll be concerns especially about the potential environmental impacts of these new technologies. In responding to these challenges, communication is key.

[Image changes to show medium and close views of Renee talking to the camera]

Having conversations with communities early, getting the right people in the room and achieving social acceptance from the beginning will help us move forward together.

[Image changes to show a view of Parliament House, and then the image changes to show two people shaking hands]

That means having policy makers, First Nations representatives and the scientists, having those difficult conversations early in the piece.

[Image changes to show an eroded coastline, and then the image changes to show a close view of water moving around the rocks on the shore]

We also need to make sure that our negative emissions technologies are responsive to decarbonisation strategies so that the two can go hand in hand.

[Image changes to show the CSIRO logo, and text appears: CSIRO, Australia’s National Science Agency]

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Prospecting for mineral carbonation

"The first milestone in our three-year work plan includes producing a publicly available resource map," says Renee.

"This global map will help identify potential feedstocks for mineral carbonation technologies and assist industry with site selection and where to look at collaborative partnerships. CSIRO is responsible for the Australian part."

Her colleague Dr Jim Austin, a geophysicist and a CSIRO CarbonLock FSP Project Leader, is breaking rocks on that mapping work – literally.

Despite many decades of extensive geological mapping across the Australian continent by the state geological surveys, Geoscience Australia and CSIRO itself, Jim explains that there are plenty of holes in the hunt for EM-prospective sites.

Map of New South Wales showing major roads, cities and towns. Pink areas show regions containing recent basalts. Green areas refer to regions  containing serpentinite and ophiolite. Purple areas refer to regions ultramafic intrusions
A large part of our project is focussed on collating and interrogating state geological data to better categorise the different types of mafic and ultramafic rocks and estimate their volumes.

"The mineral carbonation potential is around a range of geological, logistical and environmental factors," says Jim.

He lists his 'Five Ms' for EM to be viable: magnesium oxide content, mineralogy, metamorphism, metasomatism, and the mechanics of fluid transport.

He and his team have already made five field trips.

"The reason this hasn’t been done before is because it's hard," says Jim.

"You need to travel – go out to the field, go to core yards, collect rocks, image their mineralogy and analyse them to find out if they contain the reactive minerals we're after, as well as the porosity and permeability needed. This new information can be applied to existing geological mapping."

"We're coming up with a rigid set of criteria around how you evaluate the potential of different geological formations," he says, adding that they'll be applicable globally for the rest of the MI-CDR team.

Our field team, Dr Sarath Patabendigedara (left) and Dr Jim Austin, on their travels through the Manning Valley to sample Serpentinites near Nundle, Tamworth and Manilla, NSW

Ex-situ or in-situ, it's all about locking away carbon dioxide

Engineering mineral carbonation to achieve EM is divided into ex-situ and in-situ.

Jim's detailed mapping for the CDR-EM technical track is the hunt for these CO2-reactive feedstocks – rocks rich in magnesium and calcium ions – with the right porosity and in viable areas.

A big factor when looking for prospective EM sites in Australia, he explains, is considering the specific properties of our ancient geology.

"Iceland, where they’re working with in-situ EM, is a relatively new geological environment – there are rocks being formed today, so they're naturally porous and retain their original minerals," says Jim.

"Compare that to Australia, where the rocks we’re talking about have been sitting around for between 500 million years and three-and-a-half billion years. The chances are pretty slim that these rocks have not been cooked up, deformed, crunched up and had their mineralogy completely changed by either metamorphism or metasomatism. Those geological processes do affect the potential for in-situ EM in Australia."

On the other hand, ex-situ applications involve passive interaction with atmospheric CO2, for example, with crushed silicate such as ultramafic-rock mine tailings and industrial waste materials or adding crushed basalt to soil.

"For example, BHP's Mount Keith nickel mine in Western Australia has tailings that passively react with atmospheric CO2," says Renee.

The mine has one of Australia's largest tailings dams and has the right minerals to be a carbon sink by passively reacting with the CO2.

"BHP is looking at methods to enhance that. Enhanced rock weathering is another ex-situ type of mineral carbonation when you put silicate rocks – such as basalt – onto agricultural fields. Adding alkaline materials to the soil helps to improve the pH and soil health in general."

In-situ EM injects CO2 into mafic and ultramafic rock formations. Because in EM "is reacting CO2 with the rock, it's the best possible outcome", says Jim.

"We have huge volumes of rock that we can react with, and the CO2 is going to stay there for a long time."

Note that he’s talking about geology time, so that's millions of years.

Whichever the method, the challenge for EM is speed and scale.

"We know that it works; now we need to find ways to speed up the natural reaction rates, and to scale up the technologies in a way that's cost effective and sustainable," says Renee.

Dr Jim Austin, standing on a rock outrcrop near Marlborough, Qld, which illustrates the in situ carbonisation process (left image). Right hand side images shows olivine and serpentine in the ultramafic rock are being altered to siderite and magnetite, releasing silica which forms quartz in fractures.

Direct-air capture has the wind in its sails

Jim believes the most promising path for Australia to scale EM is in-situ using Direct Air Capture (DAC).

He agrees it has a bunch of hurdles but also compelling opportunities and his mapping for the MI-CDR work plan is finding the best rocks and locations across Australia.

"Our plans revolve around bringing together DAC with in-situ mineral carbonation," says Jim.

"We take it directly out of the air using DAC units, mix it with water, then pump it directly into reactive rocks at depth. Environmental and logistical factors also influence the efficiency and cost effectiveness of potential mineral carbonation sites."

The logistical issues include needing a water or brine source to mix with the CO2 that's been collected by the DAC unit.

He is also looking at climate data for areas where there are prevailing winds.

That gives you an opportunity to produce power, and you wouldn't need as much power to drive the system because nature pumps wind through the DAC for you," says Jim.

"You'd need a lot of these DAC units, so accessibility is another factor."

Once all that's all successfully navigated, a raft of economic benefits for Australia awaits.

"If you can get this up and going, there's potential for a lot of jobs," says Jim of in-situ EM using DAC.

"In this age of carbon offsets, for the same reasons mining companies come to Australia for minerals – politically stable, high-tech workforce, good services – Australia could be a very good opportunity for global companies figuring out their carbon offsets."

"Of course, there's a lot of work to do – first, to understand which methods and geological formations will provide the best outcomes, second, in developing technologies and methodologies suitable for Australian conditions, and third, in monitoring the effectiveness of decarbonisation sites into the future."

The science, technology and logistics don't make it easy, but EM will play a vital role in reaching net zero.

"Even after deep emissions reductions, CDR technologies will be absolutely necessary to reduce residual emissions and limit warming to two degrees or less by 2100," says Renee.

"We need to do everything that we possibly can to get there, and mineral carbonation provides some of the most permanent tools in the toolbox."

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