New process gets common rocks to trap carbon rapidly and cheaply

Stanford College chemists have developed a sensible, low-cost approach to completely take away atmospheric carbon dioxide, the principle driver of world warming and local weather change.

The brand new course of makes use of warmth to rework frequent minerals into supplies that spontaneously pull carbon from the ambiance and completely sequester it. These reactive supplies could be produced in standard kilns, like these used to make cement.

“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,” stated Matthew Kanan, a professor of chemistry within the Stanford College of Humanities and Sciences and senior creator of the study in Nature. “Our work solves this problem in a way that we think is uniquely scalable.”

Enhanced weathering

In nature, frequent minerals known as silicates react with water and atmospheric CO₂ to kind secure bicarbonate ions and strong carbonate minerals—a course of referred to as weathering. Nevertheless, this response can take lots of to hundreds of years to finish. Because the Nineteen Nineties, scientists have been looking for methods to make rocks take in carbon dioxide extra quickly via enhanced weathering methods.

Kanan and Stanford postdoctoral scholar Yuxuan Chen developed and demonstrated of their lab a brand new course of for changing slow-weathering silicates into rather more reactive minerals that seize and retailer atmospheric carbon shortly.

“We envisioned a brand new chemistry to activate the inert silicate minerals via a easy ion-exchange response,” stated Chen, lead creator of the examine, who developed the method whereas incomes a chemistry Ph.D. in Kanan’s lab. “We didn’t expect that it would work as well as it does.”

Many consultants say that stopping extra world warming would require each slashing the usage of fossil fuels and completely eradicating billions of tons of CO₂ from the ambiance. However applied sciences for carbon removing stay pricey, energy-intensive, or each—and unproven at giant scale. One of many applied sciences getting a lot curiosity and even early-stage funding currently is direct air seize, which makes use of panels of enormous followers to drive ambient air via chemical or different processes to take away CO₂.

“Our course of would require lower than half the power utilized by main direct air capture applied sciences, and we predict we could be very aggressive from a price viewpoint,” stated Kanan, who can be a senior fellow on the Precourt Institute for Vitality within the Stanford Doerr College of Sustainability.

Spontaneous carbonation

The brand new method was impressed by a centuries-old method for making cement.

Cement manufacturing begins by changing limestone to calcium oxide in a kiln heated to about 1,400 levels Celsius. The calcium oxide is then combined with sand to supply a key ingredient in cement.

The Stanford group used an identical course of of their laboratory furnace, however as an alternative of sand, they mixed calcium oxide with one other mineral containing magnesium and silicate ions. When heated, the 2 minerals swapped ions and reworked into magnesium oxide and calcium silicate—two alkaline minerals that react shortly with acidic CO₂ within the air.

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

As a fast take a look at of reactivity at room temperature, the calcium silicate and magnesium oxide have been uncovered to water and pure CO₂. Inside two hours, each supplies had utterly reworked into new carbonate minerals with carbon from CO₂ trapped inside.

For a extra lifelike take a look at, moist samples of calcium silicate and magnesium oxide have been uncovered on to air, which has a a lot decrease focus of CO₂ than pure CO₂ from a tank. On this experiment, the carbonation course of took weeks to months to happen, nonetheless hundreds of occasions sooner than pure weathering.

The Stanford group says their method can be utilized past the laboratory to seize CO₂ at an industrial scale.

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

Kanan stated this method may have co-benefits for farmers, who sometimes add calcium carbonate to soil to extend the pH if it is too low—a course of known as liming.

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

Cementing the longer term

Kanan’s lab can produce about 15 kilograms (about 33 kilos) of fabric per week. However trapping CO₂ on the size required to meaningfully have an effect on world temperatures would require annual manufacturing of tens of millions of tons of magnesium oxide and calcium silicate.

The researchers say the identical kiln designs used to make cement may produce the wanted supplies utilizing considerable magnesium silicates similar to olivine or serpentine, which is present in California, the Balkans, and lots of different areas. These are additionally frequent leftover supplies—or tailings—from mining.

“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 stated. “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.” (A gigaton equals 1 billion metric tons, or about 1.1 billion tons.)

After accounting for emissions related to burning pure fuel or biofuel to energy the kilns, the researchers estimate every ton of reactive materials may take away one ton of carbon dioxide from the ambiance. Scientists estimate world emissions of carbon dioxide from fossil fuels exceeded 37 billion tons in 2024.

Kanan can be collaborating with Jonathan Fan, affiliate professor {of electrical} engineering within the College of Engineering, to develop kilns that run on electrical energy as an alternative of burning fossil fuels.

“Society has already figured out how to produce billions of tons of cement per year, and cement kilns run for decades,” Kanan stated. “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.”