Researchers have developed a way to capture and store carbon dioxide by turning it into stone. Their technique, described in a paper published this week in the journal Science, could provide a safer, faster way to sequester CO2 and limit global warming.
Scientists have long seen carbon capture and sequester, or CCS, as a potentially significant way to combat climate change. The idea is that storing CO2 emissions underground would prevent the greenhouse gas from entering the atmosphere, but previous efforts have made little progress. Most experiments involve pumping CO2 into sandstone or deep aquifers, though there are concerns that the gas could eventually escape and reenter the atmosphere — whether through human error or seismic activity.
Promising (and fast) results
The approach announced this week aims to reduce this risk by dissolving CO2 with water and pumping the mixture into volcanic rocks called basalts. Once that happens, the CO2 turns into a solid mineral (calcite), which can then be stored.
Researchers from Columbia University's Lamont-Doherty Earth Observatory and other institutions tested this approach as part of a pilot program called the CarbFix project, which launched in 2012 at the Hellisheidi power plant in Iceland — the world's largest geothermal facility. Previous studies suggested that it would take hundreds or even thousands of years for the calcite to form, but the researchers' technique worked much faster. In 2012, they injected 250 tons of CO2 (mixed with water and hydrogen sulfide) into basalt about 1,500 feet below ground. Within two years, 95 percent of the carbon injected into the basalt below the plant had solidified into stone.
"This means that we can pump down large amounts of CO2 and store it in a very safe way over a very short period of time," Martin Stute, a hydrologist at the Lamont-Doherty Earth Observatory and a coauthor of this week's study, said in a statement. "In the future, we could think of using this for power plants in places where there’s a lot of basalt — and there are many such places."
It's not yet clear whether this approach could be viable on a large scale. The process requires a significant amount of water — 25 tons for every ton of CO2 — and some question whether it could be easily applied to other parts of the world.
"Here, they injected into reactive rocks and the minerals precipitated relatively quickly and are then unable to migrate anywhere," Christopher Rochelle, a CSS expert who was not involved in the study, tells the BBC. "That's great, but the rocks under Iceland are different to those under the North Sea, for example. So the approach that is taken is going to have to vary depending on where you are. We are going to need a portfolio of techniques."
But at Hellisheidi, at least, operators are moving forward with the approach. In 2014, the plant's operator, Reykjavik Energy, began pumping CO2 underground at a rate of 5,000 tons per year. The company plans to double that rate this summer.