I'm really rooting for the Stanford University researchers working on this carbon removal method. They've found a way to activate materials commonly found in rocks to capture carbon dioxide out of the air at room temperature. It's not exactly the fastest way to hoover up CO2, but the team believes it could be a relatively inexpensive affair, and can easily scale to help sort our emissions problem worldwide.
The novel carbon removal method builds on a natural process known as weathering, where common minerals called silicates react with water and atmospheric CO2 to form solid carbonate minerals over thousands of years. You can see what weathered rocks look like in the picture at the top of this article.
The Stanford team used its lab furnace to heat a mixture of calcium oxide – derived from commonly available limestone that's used to make cement – with another mineral containing magnesium and silicate ions. The minerals transformed into alkaline magnesium oxide and calcium silicate, both of which react quickly with acidic CO2 in the air.
When the resulting minerals were exposed to water and pure CO2, they trapped carbon from the CO2 over the course of two hours and transformed it into new carbonate minerals.
In another test, wet samples of calcium silicate and magnesium oxide were simply exposed to air. This time around, the carbonation process took several weeks given the significantly lower concentration of CO2 in the atmosphere. However, it occurred at room temperature, and even at this pace, ended up being thousands of times faster than natural weathering.
To make this work at scale, researcher and Stanford chemistry professor Matthew Kanan explained this could be implemented on farms, with multiple beneficial effects.
"You can imagine spreading magnesium oxide and calcium silicate over large land areas to remove CO2 from ambient air," said Kanan. "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."
"Adding our product would eliminate the need for liming," Kanan explained, referring to a process of using calcium carbonate to help balance soil pH levels. He added, "... 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."
According to the researchers, tackling carbon removal at a global scale using their process could already be within reach. The same kilns we use to make cement could produce carbon-trapping rocks from easily available and plentiful minerals like olivine or serpentine.
"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,” said researcher Yuxuan Chen. He added that more than 400 million tons of mine tailings with suitable silicates for the team's carbon capture method are generated worldwide annually, so there should be enough to get this going.
It's worth noting that the mineral activation process involves heating the materials up to 2,370 °F (1,300 °C). That sounds energy-intensive, but the researchers believe their process is still a good bet.
We're already using a process called Direct Air Capture (DAC) to suck CO2 out of the air in purpose-built facilities around the world, but it currently costs between US$600-$1,000 to remove 1 ton of carbon dioxide from the atmosphere.
“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.
Hopefully, that will work out to less than $200 a ton, which is what the World Economic Forum estimates we'll need to get to before DAC is widely adopted around the world. We might also see several competing methods and technologies at play, including using large fans to draw ambient air through a filter and selectively capturing CO2, and passing air over porous crystalline materials like COF-999 for quick CO2 adsorption.
The research has been published in the journal Nature.
Source: Stanford University