Common rocks turned into great carbon trappers with new technology

Scientists have devised an affordable way to permanently remove carbon dioxide from the atmosphere by converting common minerals into highly reactive substances that spontaneously lock away CO2.

This breakthrough could play a critical role in curbing global warming by addressing one of its primary causes.

The new technique was developed by chemists at Stanford University Matthew Kanan, a professor of chemistry and senior author of the paper, explained the motivation behind the carbon capture research.

“The Earth has an inexhaustible supply of minerals that are 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.”

Rapid carbon removal with new chemistry

In nature, silicate minerals gradually bind with CO2 through weathering, forming stable carbonates over hundreds or thousands of years. 

Researchers worldwide have long sought methods to accelerate this slow process, often referred to as enhanced weathering.

Kanan and Stanford postdoctoral scholar Yuxuan Chen found a way to make silicates rapidly absorb carbon, thanks to what Chen describes as a “new chemistry.”

“We envisioned a new chemistry to activate the inert silicate minerals through a simple ion-exchange reaction,” said Chen, who led the lab work. “We didn’t expect that it would work as well as it does.”

By speeding up mineral reactions that would otherwise unfold over centuries, this approach has the potential to remove significant amounts of carbon dioxide from the air in a fraction of the time.

More efficient mineral transformation

Existing carbon removal strategies – such as direct air capture – often rely on energy-intensive equipment, including large fans, chemicals, and other methods to filter out CO2. They can be both costly and difficult to scale. In contrast, the Stanford scientists point to the energy savings of their approach.

“Our process would require less than half the energy used by leading direct air capture technologies, and we think we can be very competitive from a cost point of view,” said Kanan, who is also a senior fellow at the Precourt Institute for Energy in the Stanford Doerr School of Sustainability.

In their experiments, the team heated limestone (calcium carbonate) in a kiln to produce calcium oxide, then combined this material with silicate minerals containing magnesium. 

When the two substances were heated together, they exchanged ions and yielded magnesium oxide and calcium silicate – both of which readily take up carbon from the air.

“The process acts as a multiplier,” Kanan noted. “You take one reactive mineral, calcium oxide, and a magnesium silicate that is more or less inert, and you generate two reactive minerals.”

Trapping carbon with simple chemistry

Cement manufacturers have used kilns for centuries, processing limestone at high temperatures to create key ingredients for concrete. The Stanford method adapts this time-tested approach but substitutes part of the cement mixture with magnesium silicates.

When these newly formed minerals are exposed to water and carbon dioxide – even at the relatively low concentrations found in ambient air – they spontaneously convert CO2 into stable carbonates. 

Laboratory tests showed that wet samples of magnesium oxide and calcium silicate could trap carbon in weeks to months, far outpacing natural weathering.

“You can imagine spreading magnesium oxide and calcium silicate over large land areas to remove CO2 from ambient air,” Kanan said. 

“One exciting application that we’re testing now is adding them to agricultural soil. As they weather, the minerals transform into bicarbonates that can move through the soil and end up permanently stored in the ocean.”

Potential benefits for farmers

Soil treatments commonly include calcium carbonate (lime) to raise pH when it is too acidic. In principle, farmers could switch to these new reactive minerals instead of conventional lime. 

“Adding our product would eliminate the need for liming, since both mineral components are alkaline,” Kanan explained. 

“In addition, as calcium silicate weathers, it releases silicon to the soil in a form that the plants can take up, which can improve crop yields and resilience. Ideally, farmers would pay for these minerals because they’re beneficial to farm productivity and the health of the soil – and as a bonus, there’s the carbon removal.”

Scaling up for global impact

According to Kanan’s team, ramping up production to a meaningful scale would require converting millions of tons of silicate minerals each year. 

“Each year, more than 400 million tons of mine tailings with suitable silicates are generated worldwide, providing a potentially large source of raw material,” Chen said. 

“It’s estimated that there are more than 100,000 gigatons of olivine and serpentine reserves on Earth, enough to permanently remove far more CO2 than humans have ever emitted.”

Nature’s carbon solution

After factoring in emissions from heating kilns using natural gas or biofuel, the researchers estimate that each ton of their final material can remove one ton of CO2 from the atmosphere. 

For context, fossil fuel emissions of carbon dioxide surpassed 37 billion tons in 2024, demonstrating the pressing need for large-scale solutions.

“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.”

Work is also underway to develop electric-powered kilns in collaboration with electrical engineering associate professor Jonathan Fan.

If successful, this innovation could reduce or eliminate the carbon footprint of the heating process, further boosting the climate benefits.

By combining well-established industrial methods with a novel chemical reaction, this approach could offer a promising and relatively low-cost way to draw down billions of tons of CO2 from the atmosphere – and help mitigate the accelerating effects of climate change.

The study is published in the journal Nature.

Image Credit: Renhour48 via Wikimedia

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