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New Method For Trapping CO2 as Solid Rock Could Help to Fight Climate Change

A groundbreaking field test proves that carbon emissions can be safely stored as solid rock in basalt formations.
The white areas within the dark basalt rock core sample show where the CO2 has reacted with minerals in the basalt and converted into a carbonate mineral similar to limestone. Image: Pacific Northwest National Laboratory

There's no denying that 2016 has been a year of environmental extremes. Think "extraordinarily" hot Arctic temperatures, rapidly melting glaciers, unprecedented extinctions, and month-after-month of broken climate records. Now, perhaps more than ever, a bit of good news would be welcome.

So, here it is: A groundbreaking experiment out of Washington state has shown that pure carbon dioxide (CO2) can be injected into basalt rock and naturally converted into a stable, solid mineral. Earlier laboratory studies suggested this could take millennia to occur, but the recent field trial was successful in just two short years.

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This is hugely significant for a couple of reasons. For starters, as Motherboard previously pointed out, human activities emit around 40 billion tons of CO2 into the atmosphere each year. Climate scientists agree that greenhouse gas emissions are the primary driver of global warming, and to mitigate the progression of climate change, we'll need to find a way to reduce or capture much of that carbon.

Furthermore, the ability to sequester CO2 in basalt, specifically, is a tremendous bonus, according to Peter McGrail, a researcher at the US Department of Energy's Pacific Northwest National Laboratory and lead author of the new study published in Environmental Science & Technology Letters.

Basalt is a common type of volcanic rock that contains elements like calcium, magnesium, iron, and manganese, and is found all across the world. Much of the ocean floor is founded on basalt, and vast fields of it have even been identified on our moon.

"These continental-scale basalt formations are one of the largest geological formations on our planet. They're spread all across the globe both onshore and offshore, and in really important locations," McGrail told me over the phone. In India, for example, where fossil fuel emissions are high and carbon storage options are thin, local basalt flows known as the Deccan Traps could play a future role in sequestering greenhouse gases.

Because of its chemical composition, basalt can produce a unique carbonate mineral called "ankerite" when exposed to the acidic conditions enabled by CO2. While this all might seem like regular old chemistry, the implications of a solid hunk of CO2 are exciting.

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Traditionally, when carbon emissions are injected underground, they're flooded into wells of porous rock as a supercritical fluid, or gaseous liquid. But what goes in might also come back out, and some fear that CO2 explosions are a dangerous consequence of such technology. With a carbonate material, however, there's "no possibility for leakage," and the solidified carbon dioxide "will be there essentially forever," McGrail added.

Another similar project garnered attention this year when researchers with CarbFix, a group run by Iceland's geothermal power producer, Reykjavik Energy, managed to create calcite—a white, crystalline mineral—by injecting carbonated water into basalt rocks. Like the field test in Washington, this study proved that CO2 could be stored as a solid form between layers of basalt. But the project, which was described at length in Science, also had its drawbacks, claimed McGrail.

"From a commercial perspective, yes, CO2 is soluble in water. But it's not that soluble, so if you're going to inject a ton of CO2 into the subsurface, you've got to access about 10 to 100 times the volume of water that one might need compared to injections of supercritical fluid," he said. "It's not 100 percent clear if that's even physically possible for a larger scale commercial project."

The CarbFix study accessed CO2 from a nearby geothermal plant in Reykjavik, added water, and injected it up to 2,600 feet beneath the surface. Because the carbonated water solution can cause basalt to dissolve immediately, McGrail warned that injection wells could also clog up with key metal components. "With a supercritical injection, there's no worry at all," he said.

An isotopic analysis of the Washington ankerite exactly matched its "fingerprint" with the isotopic content of the injected CO2, meaning it could have only been produced by a chemical reaction with the basalt's primary minerals. The project's "real coup de grace" and "absolute proof" of its success, McGrail told me.

As for the practical application of this new method, that's one thing McGrail couldn't comment on. Someone will need to prove that it can be safely scaled up to larger quantities of CO2; "intermediate next steps" before the technique can become commercially viable. But for now, at least we know the possibilities are wide open.

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