On an active volcanic ridge in Iceland’s southwest, researchers are pumping water charged with captured CO2 underground into basaltic rock. They are demonstrating to the world a new method of carbon storage – one that traps most of it as stable carbonate minerals within a year.

Current carbon storage techniques inject CO2 directly as a gas into rock. But the gas remains buoyant for thousands of years until it becomes mineralised and stable. Until then, the gas could leak upwards from where it is stored – posing a health risk.

The EU-funded project CarbFix has developed technology to reduce this risk by dissolving CO2 in water while it is injected underground into basalt. Once dissolved, the gas is no longer buoyant and the water accelerates the process of mineralisation.

Around 80% of the CO2 was trapped as a mineral within a year of being injected at the project’s pilot injection site in southwest Iceland, says project coordinator Edda Sif Aradóttir, a chemist and reservoir engineer with Reykjavik Energy. The pilot injection began operating in January 2012.

“This result suggests that the CarbFix method can shorten the timescale of mineral carbon trapping considerably – which normally takes tens of thousands of years within the sedimentary basins conventionally used for carbon storage,” Aradóttir says.

Closing a carbon loop

CarbFix’s pilot plant is located near Reykjavik Energy’s Hellisheidi geothermal power station. The station uses the geothermal fluids generated by a volcanic system in the region to produce electricity and hot water for heating.

The process also brings CO2 of volcanic origin to the surface. CarbFix’s pilot gas separation station captures around 2% of that CO2. At another site nearby, the gas is released as small bubbles – at depth – into water flowing down an injection well to the basaltic rock some 500 to 800 metres underground. The CO2 reacts with the calcium, magnesium and iron in the basalt, transforming into stable carbonate rock.

The CarbFix method costs more than other underground storage techniques and requires a substantial amount of water, Aradóttir says. Only 5% of the injected mass sent underground is CO2.

But on balance, the CarbFix method could also be cost effective as it reduces the need for long-term monitoring as the carbon is rapidly transformed into stable minerals, she adds.

What’s next?

The CarbFix technology was developed to be used by any industry capturing and storing carbon, not just power plants, Aradóttir says.

After the project ends in September 2014, the partners plan to continue working together to refine the injection technology and lower costs. They plan to start building an industrial-scale plant next to Hellisheidi in 2014; it will initially store up to 20% of the CO2 from the geothermal plant – around 5 000 tonnes of CO2 a year. The plan is to eventually capture all CO2 that the plant produces.

Carbon storage at sea

The pilot plant also demonstrates the advantage of storing CO2 in basaltic rocks, which are more common on the seafloor. Current underground storage methods use sedimentary rocks, more common on land. Instead of the fresh water used on land, the technology can use seawater.

European public opinion is currently moving against carbon storage on land due to the perceived risk, she says. This makes it more likely that future carbon storage will be done mostly under the seafloor – where capacity is potentially huge.

“The storage potential of all the ocean ridges is larger than the estimated CO2 emissions that would stem from burning all of the Earth’s fossil fuel resources,” Aradóttir says. “How much of this storage potential will be of practical use in the future may depend more on political will and economic realities than on scientific efforts.”