When we think of combating climate change and reducing global carbon dioxide emissions, we often envision renewable energy sources, electric vehicles, and rewilding projects. However, there is another powerful tool to combat climate change right under our feet – rocks. 

The concept of using rocks to remove CO2 from the atmosphere is based on the fundamentals of mineral carbonation. This process occurs naturally over thousands of years as carbon dioxide reacts with certain types of rocks to form stable minerals. By accelerating this process, we can harness the power of rocks to remove carbon dioxide on a much faster timescale. 

The $100M XPRIZE Carbon Removal competition incentivizes innovation in carbon dioxide removal (CDR), including rock-based methods, and encourages innovators to join this global movement and help move the needle on CDR solutions. In this way, XPRIZE hopes to pave the way for a more sustainable future and mitigate the impacts of climate change.

Rock-Based CDR Solutions

Rock-based methods can be divided into two broad categories: those that happen deep underground (known as in situ mineralization) and those that happen above ground by exposing crushed rocks to CO2‐bearing gases (known as ex-situ or surficial mineralization). 

Underground mineralization involves injecting CO2 deep underground where it can be stored permanently. Wells are drilled deep into geologic formations where the rock is reactive - the CO2 forms durable minerals and is locked away for millennia. The trick with these methods is making sure that the CO2 does not escape, so projects are monitored closely to ensure the CO2 remains sequestered.

Above-ground mineralization is also commonly referred to as enhanced rock weathering (ERW). This technique involves crushing rocks and spreading them over large land areas. Rocks commonly used for this include basalt and olivine. As rainwater and carbon dioxide interact with the crushed rocks, a chemical reaction takes place. This converts carbon dioxide into stable minerals throughout the process. The resulting salts - carbonates - are then stored in the ground, effectively removing excess carbon dioxide from the atmosphere. 

Enhanced weathering is beneficial to the environment on a secondary level as it’s able to replenish vital nutrients in the soil and promote healthier plant growth on the land. This contributes to the sustained, overall health of the area and its ecosystem.

Basalt, shown here in a columnar formation, can be crushed and spread for enhanced weathering CDR.

Impact of CDR Methods

The most notable benefits of using rock-based CDR methods are their scalability and permanence. Unlike other carbon removal solutions that rely on complex infrastructure, rock-based CDR can be implemented in various locations around the world. Additionally, once the carbon dioxide is converted into stable minerals, it remains locked away for geological timescales, providing a long-term solution to carbon storage

It's important to note that rock-based carbon dioxide removal, like all CDR methods, is not a singular solution to our climate challenges. To be effective, it’s necessary that these methods complement other mitigation strategies and emission reductions. Large-scale implementation of these methods will require significant investment in research, development, and infrastructure - areas in which XPRIZE Carbon Removal is working to facilitate growth.

Moving Forward

Rock-based methods offer a promising and innovative approach to not only remove carbon dioxide from the atmosphere but also contribute to the creation of sustainable and resilient ecosystems. By harnessing the power of rocks, we can pave the way for a more sustainable future and mitigate the impacts of climate change.

Teams participating in XPRIZE Carbon Removal are using a variety of these methods in the competition. To learn more about rock-based CDR, check out the video below on XPRIZE Carbon Removal top 60 team, SIlicate, and their process of weathering silicate minerals to remove excess carbon dioxide from the atmosphere and store it over geological timescales.

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