Rock chemistry could solidify CO₂ for storage

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.