Iceland's known for the ability to tap vast reserves of natural volcanic heat for electricity and power. Its largest geothermal power plant, Hellisheidi, puts out just 5 percent of the planet-warming carbon dioxide that a comparable coal-fired plant would.
Still, that 5 percent amounts to 40,000 tons of carbon dioxide every year—that's like having more than 7,000 extra cars on the road.
Hellisheidi's operators set out to get that number to zero, and they've hit upon an unusual way to do it: By turning the pollution into stone. Their project, Carbfix, is a promising new idea for neutralizing the climate impact of producing energy.
The carbon dioxide at the power plant comes up along with the hot water it pumps from underground. The research team, which included people from plant operator Reykjavik Energy, Columbia University, University of Iceland and elsewhere, mixed the carbon dioxide with water and injected it back underground, where basalt reacted with the mixture and crystallized it within two years.
While scientists expected the mineralization to happen, they didn't think it would be that fast: "“The conventional wisdom has been that these reactions would be slow. They would take 100 years, maybe a thousand," study co-author Martin Stute of Columbia University told National Geographic.
Turning Carbon Emissions to Stone in Iceland Turning Carbon Emissions to Stone in Iceland
Other projects around the world are making a similar attempt to suck away pollution before it reaches the atmosphere and then inject it underground. But some of those projects use the carbon to mine more fossil fuel; they also run the risk that carbon gas or liquid could leak back out. Because Carbfix is turning the carbon into a solid, it could be more effective at locking it away for good.
Though the technology does use a lot of water, Stute says there's a possibility that water could be recycled. As for basalt, there's plenty to go around—Columbia University's statement notes, "Basically all the world’s seafloors are made of the porous, blackish rock, as are about 10 percent of continental rocks."
Though the Carbfix test was small—just under 250 tons of gas was solidified—the plant has already scaled up to 5,000 tons a year and is aiming to eventually put all of its emissions underground.