An experiment in Iceland has confirmed that carbon dioxide, a major factor in global climate change, can be trapped in basalt rocks. Over 95 percent of CO2 pumped underground near Reykjavik turned into solid carbonate in less than two years.
Called CarbFix, the experimental injection of CO2 dissolved in water was described by researchers in a paper published by the Science magazine this week.
"This opens another door for getting rid of carbon dioxide or storing carbon dioxide in the subsurface that really wasn't seen as a serious alternative in the past," Martin Stute, study co-author and hydrologist at the Lamont-Doherty Earth Observatory at Columbia University in New York, said.
Capturing greenhouse gases instead of allowing them to be released into the atmosphere and pumping them into underground storage is a solution that has long been debated by environmentalists. Its biggest drawback, however, is that the gases are likely to escape eventually and seep through cracks or erupt catastrophically after a seismic event or a terrorist attack, even if stored in liquid or "slurry" form.
The researchers working at the Hellisheidi geothermal power plant, which produces some CO2 in the form of volcanic gases, proved that an alternative solution is feasible. Basalt formations are rich in calcium, magnesium, and iron. They can react with carbon dioxide and turn it into chalk-like carbonates.
Previously scientists thought the reaction would take decades or even centuries and wouldn’t make geologic CO2 storage any safer. The experiment in Iceland has proven that a couple of years do the trick.
The CarbFix experiment used a 2,000-meter injection well at a site about 25km east of Reykjavik. The target basalt formation is between 400 and 800 meters underground. Eight monitoring wells ranging in depth from 150 to 1300 meters were used to keep track of the CO2.
The experiment involved two phases. During the first, pure carbon dioxide dissolved in freshwater was injected underground. Phase two involved a mixture of carbon dioxide and hydrogen sulfide (H2S), a common component of volcanic gases. The second phase was designed to see if the storage technique was feasible for impure CO2, thus avoiding the high cost of gas separation.
The scientists spiked the carbon dioxide with carbon-14, an isotope chemically and physically identical to regular carbon-12. This allowed them to distinguish the CO2 they had injected from that already present in the formation.
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During the 550 days of the experiment, over 95 percent of the carbon dioxide was mineralized, the researchers wrote. The limit coincides with the breakdown of a pump in one of the monitoring wells, which was clogged and coated with calcite.
The method can be used not only to dispose of anthropogenic carbon dioxide produced by plants, but also to trap CO2 that has already been released into the atmosphere, potentially reversing the impact already made on climate.
However, more research is needed to explain why the mineralization happened much faster than expected and whether it would work with any basalt formation, as the scientists hope it will. They also want to see whether saltwater can be used instead of freshwater to dissolve the gas and store it underground.