Introduction to Carbon Capture Technology

Of all the planet-warming greenhouse gases released into the atmosphere through human activity, carbon dioxide is the most significant emission. As such, experts recommend drastically reducing fossil fuel use and actively removing carbon dioxide (CO2) from the atmosphere. However, carbon capture technology is often expensive and/or energy-intensive, requiring carbon storage solutions.

A Novel Approach: Utilizing Rocks for Carbon Capture

Now, researchers at Stanford University have proposed a surprisingly practical strategy: leveraging rocks to capture CO2. They have developed a process that uses heat to transform minerals into materials that absorb CO2 permanently. As detailed in a study published in the journal Nature, this process is practical, low-cost, and can satisfy the needs of a common agricultural practice, addressing two issues simultaneously.

The Science Behind the Process

According to Matthew Kanan, the senior author of the study, "The Earth has an inexhaustible supply of minerals capable of removing CO2 from the atmosphere, but they just don’t react fast enough on their own to counteract human greenhouse gas emissions. Our work solves this problem in a way that we think is uniquely scalable." For decades, scientists have studied ways to accelerate some rocks’ natural absorption of CO2, a process called weathering that can take hundreds or thousands of years. Kanan and his colleague Yuxuan Chen have cracked the code by converting common slow-weathering minerals called silicates into fast-weathering minerals.

The Role of Ion-Exchange Reaction

"We envisioned a new chemistry to activate the inert silicate minerals through a simple ion-exchange reaction," Chen explained. This process involves ions, which are atoms or groups of atoms with an electrical charge. "We didn’t expect that it would work as well as it does." The researchers drew inspiration from cement production, where a kiln converts limestone into a reactive chemical compound called calcium oxide. They replicated this process, swapping sand out for magnesium silicate, which contains two minerals that, with heat, exchanged ions and turned into magnesium oxide and calcium silicate – minerals that weather quickly.

Testing the Results

"The process acts as a multiplier," said Kanan. "You take one reactive mineral, calcium oxide, and a magnesium silicate that is more or less inert, and you generate two reactive minerals." To test their results, Kanan and Chen exposed wet calcium silicate and magnesium oxide to air, and they turned into carbonate minerals – the result of weathering – within weeks to months.

Potential Applications

"You can imagine spreading magnesium oxide and calcium silicate over large land areas to remove CO2 from ambient air," Kanan said. One exciting application being tested is adding them to agricultural soil, which could also be practical for farmers who add calcium carbonate to soil when it’s too acidic. "Adding our product would eliminate the need for liming, since both mineral components are alkaline, and as calcium silicate weathers, it releases silicon to the soil in a form that plants can take up, which can improve crop yields and resilience."

Efficiency and Scalability

Approximately one ton of magnesium oxide and calcium silicate could absorb one ton of CO2 from the atmosphere, accounting for the CO2 emitted by the kilns themselves, which still require less than half the energy used in other carbon capture technologies. Scaling this solution to an impactful level would require millions of tons of magnesium oxide and calcium silicate annually. Nevertheless, Chen points out that if estimates of natural reserves of magnesium silicates are accurate, they would be enough to remove all human-emitted atmospheric CO2 and more. Additionally, the silicates could be recovered from mine tailings.

Conclusion

"Society has already figured out how to produce billions of tons of cement per year, and cement kilns run for decades," Kanan said. "If we use those learnings and designs, there is a clear path for how to go from lab discovery to carbon removal on a meaningful scale." This novel approach offers a promising solution to the pressing issue of carbon capture, utilizing rocks to absorb CO2 in a practical, low-cost manner.