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Physical Chemistry

Rock chemistry could solidify CO2 for storage

Reactions with basalt mineralize greenhouse gas to carbonate in two years

by Elizabeth K. Wilson
June 9, 2016 | APPEARED IN VOLUME 94, ISSUE 24

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Credit: Annette K. Mortensen
Carbon dioxide reacted with this section of basalt to form white mineralized calcium carbonate.
Credit: Annette K. Mortensen
Carbon dioxide reacted with this section of basalt to form white mineralized calcium carbonate.

Chemical reactions in common basalt rock can convert carbon dioxide into solid minerals in less than two years—dramatically faster than the hundreds or thousands of years previously estimated (Science 2016, DOI: 10.1126/science.aad8132). The discovery gives scientists another option to explore for the sequestration of excess atmospheric CO2 as a means to battle climate change.

Scientists are already investigating the possibility of storing CO2 deep underground in sandstone. But, in those rocks, the gas would simply sit and could potentially leak back into the atmosphere.

The new discovery comes from an international team led by Juerg M. Matter, geoengineering professor at the University of Southampton, as part of an Icelandic project called CarbFix. The project is a partnership with Reykjavik Energy, the University of Iceland, the Earth Institute at Columbia University, and France’s National Center for Scientific Research.

Several years ago, at a site near Reykjavik, the team injected 250 metric tons of CO2 mixed with water 400 to 800 meters down into basalt formations.

Within two short years, the CO2 completely incorporated into the rock as solid carbonate minerals.

Stuart Gilfillan, a geoscientist studying CO2 capture and storage at the University of Edinburgh, calls the work promising, noting that although the discovery is not hugely surprising given that basalts are much more chemically reactive with CO2 than sandstones, “it is very interesting to see that you can get such fast and complete mineralization.”

The team has now started injecting 5,000 metric tons of CO2 per year at the site and is finding the mineralization rates are still just as fast.

Nevertheless, the scientists caution that this process isn’t a quick fix for CO2 sequestration. For example, it requires 25 metric tons of water for every metric ton of CO2 stored. And transporting CO2 to the nearest basalt-rich region won’t be easy or cheap, Gilfillan says.

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Comments
JM Hatch (June 9, 2016 9:25 PM)
What tests are they using to determine if the CO2 incorporated into the basalt may cause structural issues in the integrity of the basalt? or with the mobility of other mineral/chemicals into the injected water, and where this water and associated minerals/chemicals will migrate?
EE Büllesbach (July 1, 2016 11:13 AM)
CO2 capture and storage is not the answer to our problem. Several valid points are made by the comment of JM Hatch that also reflects my concerns.

Another consideration is that burning fossil fuel takes oxygen from the atmosphere, which CO2 capture buries underground. This disturbs the atmosphere oxygen level, which may be neglectable at this point but cannot be done indefinitely. We have to be aware: the only sustainable way to remove CO2 is by photosynthesis.

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