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  1. Science & Tech
14 June 2016

Turning carbon dioxide into rocks – a new hope in the fight against climate change

A research project in Iceland has found a way of reducing carbon dioxide levels, potentially opening up a new way of tackling global warming. 

By Hasan Chowdhury

Can anyone deny climate change at this point? As global levels of the greenhouse gas carbon dioxide continue to soar higher than they’ve been for more than 400,000 years, it would seem illogical to.

A new forecast from the UK Met Office put the concentration of carbon dioxide atop Hawaiian volcano Mauna Loa – a significant atmospheric marker of climate change  at a sustained level of 400 parts per million over the year. For context, this unusually high concentration of carbon dioxide in the air was last matched three to 5m years ago, showing just how much change the climate has undergone, and how difficult it has been to contain the gas.

The process of finding ways to reduce carbon emissions has been a tricky one. Recommendations for individuals to reduce their carbon footprint have included advice on everything from travel to home energy expenditure, but the continuous creeping up of carbon dioxide levels means greater efforts are required.

However, a recent research project in Iceland may have found a way to cut carbon dioxide concentrations down to healthier levels. The CarbFix Project, initiated by Reykjavik Energy and whose goal was to “imitate the natural storage process of CO2” observed in Icelandic geothermal fields, has found a way to turn carbon dioxide into rocks.

In the journal Science, the researchers detailed their method of carbon capture and storage which involves the injection of carbon dioxide into basaltic rocks – a “highly reactive” type of rock which can commonly be found from a quick trawl of the ocean floor.

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At a site near the Hellisheidi geothermal power plant just outside Reykjavik, 230 tons of carbon dioxide was injected over the course of two phases to a depth between 400m and 800m below the surface – a level at which basaltic lavas flow and cool into basaltic rock.

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A previous difficulty in containing carbon dioxide has been as a result of gas leakage, which is why during the injection process the carbon dioxide was dissolved into water. The idea was that a reaction between the water-dissolved carbon dioxide and basaltic rock would form a carbonate, mineralising the gas to turn it into a rock. The result? More than 95 per cent of the injected gas was successfully converted into a chalky rock in the space of two years.

Speaking to the BBC, Dr Juerg Matter, leader of the project and associate professor in geoengineering from the University of Southampton said: “It was a huge surprise to all the scientists involved in the project, and we thought, ‘Wow! That is really fast.’”

It was originally thought that this type of stabilisation of carbon dioxide into rock, a naturally occurring part of the Earth’s carbon cycle, would take thousands of years. It’s why this particular experiment, and its acceleration of the longest phase of the carbon cycle to create a way of permanently storing carbon dioxide, has been such a success. The study’s co-author Martin Stute confirms that this method would allow “large amounts of CO2” to be stored in a “very safe way”.

The injection process was observed from eight different monitoring wells located between 150m and1300m below the surface. The dissolved carbon dioxide was tagged with a type of carbon called carbon-14, a radioactive form of the element which would allow researchers to follow the movement of the gas dissolved in the water, as well as its reactivity with basalts.

Given the ubiquity of basalts on ocean floors and some presence of the substance on land, the results from the project could pave the way for this type of carbon capture to be scaled up and across the globe, seriously improving the chances of combating the climbing levels of carbon dioxide. Previous attempts have been made to turn carbon dioxide into stone involving sandstone; however sandstone does not react anywhere near as well with carbon dioxide as basaltic rock.

The results of the project are promising, but its status as a pilot run means that cost effectiveness and scalability need to be measured on a larger stage. It’s not clear which factors specifically contributed to the rapid mineralisation of the carbon dioxide, and whether it’s a rate of conversion that can be replicated elsewhere. Around 25 tons of water are required for each ton of carbon dioxide dissolved, which amounts to a tremendous amount of water, but the elimination of the risk of escaping carbon dioxide means this method could still be viable.

The threat posed by untamed carbon emissions is real. Global warming, the spread of wildfires and indirect influences upon rising sea levels are just some of the consequences. Though the CarbFix project’s results may be looked at as a standalone success, any success should be expanded upon in order to win the fight against climate change.