Among the various greenhouse gases released by human activities, carbon dioxide (CO2) stands as the most impactful contributing to global warming. To combat this, experts have recommended not only reducing the use of fossil fuels but also actively extracting CO2 from the atmosphere. However, carbon capture technology is often costly and energy-intensive, requiring effective carbon storage solutions.
Researchers at Stanford University have introduced an innovative approach that leverages natural processes: utilizing rocks to absorb carbon dioxide. Chemists Matthew Kanan and Yuxuan Chen have developed a method that transforms minerals into CO2-absorbing materials through a heat-induced process. This method, detailed in a study published in the journal Nature, is described as both practical and economical. The process can also meet the requirements of a common agricultural practice, effectively addressing two challenges simultaneously.
Matthew Kanan, the senior author of the study, explained that Earth possesses an abundant supply of minerals capable of capturing atmospheric CO2, but these minerals react too slowly to effectively counteract human-generated greenhouse gas emissions. Their research offers a scalable solution to this issue.
For years, scientists have explored methods to accelerate the natural CO2 absorption of certain rocks— a process known as weathering that usually takes centuries. Kanan and Chen have developed a technique that converts slow-weathering silicate minerals into fast-weathering minerals.
Yuxuan Chen described their innovation as a new chemical approach that activates inert silicate minerals through a straightforward ion-exchange reaction involving electrically charged ions. The process, inspired by cement production, converts limestone into a reactive chemical compound called calcium oxide. The researchers adapted this process by replacing sand with magnesium silicate, inducing a reaction that produces fast-reacting magnesium oxide and calcium silicate.
The process is described as a multiplier by Kanan, as it generates two reactive minerals from one naturally reactive mineral and an inert magnesium silicate. The efficacy of their method was confirmed through tests where wet calcium silicate and magnesium oxide were exposed to air, forming carbonate minerals in weeks to months.
Kanan suggested the potential of spreading magnesium oxide and calcium silicate over large areas to remove CO2 from the air. A promising application currently being tested involves adding these minerals to agricultural soil, which could eliminate the need for traditional liming practices and simultaneously enhance crop productivity.
Approximately one ton of magnesium oxide and calcium silicate can absorb one ton of CO2 from the atmosphere, and this calculation considers the CO2 produced during the kiln process, which uses less than half the energy of other carbon capture technologies.
For this strategy to make a significant impact, millions of tons of magnesium oxide and calcium silicate would be required annually. Nonetheless, Chen notes that if natural reserves of magnesium silicates, such as olivine or serpentine, are sufficient as estimated, they could remove all man-made atmospheric CO2. Additionally, these silicates could be sourced from mining by-products.
Kanan emphasized that since society already knows how to produce billions of tons of cement annually with long-lasting kilns, there exists a clear trajectory from laboratory discovery to significant carbon removal.
