Mineral carbonation

Mineral carbonation is the term for naturally-occurring chemical reactions that bind carbon dioxide (CO2) from the atmosphere, with minerals.  In nature these processes typically occur at very slow rates, taking hundreds or even thousands of years. Our research aims to develop technologies to rapidly accelerate these processes to permanently store more CO2 in less time, as benign, inert minerals. 

Our research will focus on technology both in-situ and ex-situ. Ex-situ mineral carbonation refers to processes that take place at the Earth’s surface (involving mine-waste materials for example), whereas in-situ processes take place underground. We estimate that our research will rapidly accelerate naturally occurring mineral carbonation and enhance its capacity for CO2 storage.

What we know

Rock weathering has played a key role in the global carbon cycle for millions of years, through chemical reactions that convert atmospheric CO2 to minerals and soluble ions. This confirms the potential of these processes for secure carbon removal from the atmosphere. If enhanced these processes have the potential to securely remove large amounts of carbon.  

Suitable minerals for mineral carbonation exist within the earth but by-products from mining, already crushed and accessible above ground also show promise. Mine waste and tailings are a legacy issue for the mining industry. Utilising these waste materials for carbon storage could help solve this legacy issue. Many of these rocks are ultramafic, or high in magnesium, which increases their utility in the carbonation process.

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

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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.

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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.

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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.

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

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

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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.

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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.

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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.

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

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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.

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

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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.

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

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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.

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Key research challenges

Our main priority is to develop the means to accelerate mineral carbonation processes to a matter of weeks or a few years. Each carbon mineralisation pathway (ex-situ and in-situ) also has its own challenges. Our research will seek to:

  • Better identify and understand the rocks and minerals with the greatest mineral carbonation potential.
  • Enhance our understanding of the micro-structure of the mineral-water interface during mineral carbonation reactions, the reaction mechanisms and the factors that influence mineral dissolution-precipitation reactions. Further, we need to determine the thermodynamic and kinetic properties during these reactions in order to establish reliable geochemical modelling.
  • Identify the most effective ex-situ processes and the unit operations required to achieve them; examine the carbon storage potential/capacity using various types of tailings or mine waste materials.
  • For ex-situ mine waste and tailings it is important to ensure accelerated carbonation processes do not themselves create tailings and a further legacy problem.
  • Develop modelling of the mineral carbonation process in order to predict the possible site and time where the carbonation process occurs. This allows us to assess the speed at which it is occurring and the potential for different kinds of rocks and tailings.
  • Define the best strategy to inject CO2 fluids into in-situ rocks to minimize the operational risks such as injectivity loss due to mineralisation in near injection wellbore.
  • Assess several risks including reservoir engineering, rock geomechanics, and CO2 containment due to the changes of mineral volume as a result of mineral carbonation reactions.

If successful, what might this program achieve?

Success will see this technology utilised by a range of high-emissions industries in order to draw down atmospheric carbon dioxide and store it at much higher rates than is currently possible. The true potential of this technology will be realised through integration with other carbon dioxide removal technologies being developed through the CarbonLock Future Science Platform.