Quickfire carbon capture method turns CO2 into solid rock within two years

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Could a new method of carbon sequestration hold the key to battling climate change?(Credit: lady_lbrty/Creative Commons)

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Carbon capture and storage, or carbon sequestration, is one approach proposed to offset mounting C02 emissions, but the possibility of gas seeping out and escaping into the atmosphere is one of the factors holding the technology back. Researchers have now come up with a technique that promises to overcome this problem, finding that injecting CO2 into volcanic rocks can turn the gas solid within two years, which is a drastically shorter timeframe than the centuries or millennia the current scientific consensus suggests.

It would be a hugely significant breakthrough, but the prospect of an effective carbon sequestration method would also present its share of questions. Does it hand big polluters a get out of jail free card? How will we wean ourselves off fossil fuels if there is little incentive to do so? Would the money involved be better funneled into renewable energy research? Let's park these reservations for a minute and take a look at a technology that the International Energy Agency describes as a "critical component" in combating climate change.

Carbon sequestration is a process whereby CO2 is pulled from the chemical processes in power plants and pumped into underground reservoirs before it can enter the atmosphere. Generally, the gas is compressed to decrease its volume beforehand, resulting in what is known as supercritical C02. But the trouble with supercritical CO2 is that it is buoyant, which means storing it underground raises the risk of leaks, which is something certain countries have responded to by banning sequestration altogether.

Of course, one way to stop a gas leak is to remove gas from the equation. So much of the research into carbon sequestration has centered on how the gas can be converted into a solid. Coffee grounds and sea urchins have inspired some of the more imaginative approaches, but largely the focus remains on pumping it into rock formations that react with the gas and turn it into solid carbonate minerals.

But this mineralization process takes hundreds or even thousands of years, meaning that the sequestration sites would need to be monitored for leaks which would make for quite an expensive exercise. So while all of the necessary technological components are already available and in use in various sectors, carbon sequestration is yet to be applied on a scale that would make any meaningful difference to global carbon emissions.

Since 2007, an international team of scientists has been investigating how basaltic rocks in Iceland's geothermal fields can naturally store C02. Dubbed the CarbFix project, the researchers have happened upon a method of stowing carbon away that could seriosuly fast-track the mineralization process.

Instead of compressing the gas to form supercritical CO2, the researchers used it to make carbonated water, pumping 248 tons of it into an underground well fed by a fresh-water aquifer. The basalt rock in the aquifer is rich in elements such as calcium, magnesium and iron, which were released into the water and reacted with the dissolved CO2 to form solid carbonate minerals.

What really surprised the researchers was not just how much of the CO2 was converted, but how quickly all of this happened. Through observations at downstream monitoring wells and the earlier addition of tracer chemicals, the researchers found that more than 95 percent of the CO2 had formed into solid carbonate minerals within just two years.

A fractured basalt rock reveals the white calcium carbonate crystals that formed after the addition of CO2 to the underground well

"Our results show that between 95 and 98 per cent of the injected CO2 was mineralized over the period of less than two years, which is amazingly fast," says Dr Juerg Matter, Associate Professor in Geoengineering at the University of Southampton and lead author on the study.

The team is already ramping up the carbon capture method at Reykjavik Energy's Hellisheidi geothermal power plant, where the original study took place. It says up to 5,000 tons (4,535 tonnes) of CO2 are now being stowed away each year.

This sure sounds like a lot, but it is a mere drop in the ocean compared to the billions of metric tons emitted globally each year. The good news is that basalt rock is present beneath the Earth's surface more than any other rock. It's not so common on land, with only around 10 percent of the continents made up of basalt, but almost all of the ocean floors contain the material. So while it won't be simple, replicating the process in other locations is a real possibility.

"Carbonate minerals do not leak out of the ground, thus our newly developed method results in permanent and environmentally friendly storage of CO2 emissions," says Matter. Noting how common basalt rock is, Matter also points out that it could potentially provide one of the largest capacity options for CO2 storage.

The team's research was published in the journal Science.

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