Iceland is Taking Notes From Medusa by Turning CO2 Into Stone

The answer to our climate change prayers?

To deal with anthropogenic (human-caused) carbon dioxide (CO₂) emissions, an international team of scientists has been investigating a way to physically remove some of our emissions from the atmosphere — a process known as “carbon capture and storage.”

The study, published in the journal Science, has shown for the first time that carbon dioxide can be permanently, and surprisingly quickly, locked away from the atmosphere — by turning it into stone.

Sealing CO₂ gas in voids underground, such as in abandoned oil and gas reservoirs, was previously considered as a solution to carbon emissions, but these are susceptible to leakages, and even explosions (although unlikely). Attention is now turned to the mineralization of carbon so we can say “hasta la vista” to excess CO₂.

This process was thought to take several hundreds to thousands of years, which is impractical, but the current study, led by Columbia University, University of Iceland, University of Toulouse, and Reykjavik Energy, has shown that it can take just two years.

"Our results show that between 95 and 98 per cent of the injected CO₂ was mineralised over the period of less than two years, which is amazingly fast," explained lead author Juerg Matter, Associate Professor in Geoengineering at the University of Southampton, in a University of Southampton press release.

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How did they do it? Since Iceland is a volcanic island, it is made up of 90 percent basalt — a rock rich in calcium, magnesium, and iron. The 250 tons of captured CO₂ gas, which was dissolved in water, was injected into a deep well. When the mixture contacted the basalt rocks located 400-800 meters (1310-2620 feet) below the surface, the solution began to form carbonate minerals — a white, chalky, environmentally-benign mineral.

^{Section of rock from the CO₂ storage reservoir showing basalt as well as a fracture containing calcium carbonate. Photo credit: Annette K. Mortensen}

"Carbonate minerals do not leak out of the ground, thus our newly developed method results in permanent and environmentally friendly storage of CO₂ emissions," said Matter. "On the other hand, basalt is one of the most common rock type on Earth, potentially providing one of the largest CO₂ storage capacity."

Since the size of the study was small, the team has already upscaled the experiment at the Reykjavik Energy Hellisheidi geothermal power plant, located in Iceland, where up to 5,000 tons of CO₂ per year are being captured and stored.

But the technology is not without its problems. First, the process uses a lot of water — about 25 tons for every ton of CO₂. However, seawater, rather than fresh, could be used. Second, a study published in May identified subterranean microbes that appear to feed off carbonate minerals and use them to release methane — a more potent greenhouse gas.

However, the interest in the technology is growing. As Matter concluded in a Columbia University press release, "We need to deal with rising carbon emissions. This is the ultimate permanent storage—turn them back to stone."

The investigation is part of the CarbFix project, a European Commission and U.S. Department of Energy funded program to engineer ways to capture and store anthropogenic CO₂ in basaltic rocks.

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