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Iceland turns carbon dioxide to stone

The Hellisheiði geothermal plant in southwest Iceland The Hellisheiði geothermal plant in southwest Iceland Columbia University
09 Jun
Project to turn carbon dioxide into stone works faster than ever imagined

Carbon. It is an essential building block of rocks, plants and people, but can become a notorious greenhouse gas when chemically converted into carbon dioxide. Finding ways to lock up CO2 has become a modern kind of alchemy, with a growing body of science looking at putting the stuff back into the ground, sequestering it in tree plantations or even turning it into graphene and other useful materials. The need is great; the Intergovernmental Panel on Climate Change reported in 2014 that effective carbon capture and storage is crucial to the effort to temper global warming.

Out in the steaming hills of western Iceland, the latest attempt has been to turn CO2 into stone. Studies had estimated that such a chemical reaction could take hundreds – if not thousands – of years. A project called Carbfix has done it in just two. ‘People thought it couldn’t happen that fast,’ says Edda Aradottir, who leads the project. Even she had estimated that the process would take longer, between eight and 12 years. ‘Then it happened much faster and it was a very welcome surprise,’ she says.

The pilot project involved dissolving 250 tons of CO2 in water and injected it into underground basalt. The volcanic rock, which makes up 90 per cent of Iceland’s geology, contains the vital calcium, iron and magnesium needed to precipitate the mixture into carbonate minerals. Sooner than anyone expected, core samples of the rock started coming up laced with a solid, whitish substance, giving the basalt the appearance of crumbly black marble. Scientists now conclude that 95 per cent of the CO2 has ‘mineralised’ into porous basalt in just two years.

11Analysing core samples of the Basalt (Image: Columbia University)

A hydrologist at the University of Columbia, Martin Stute, believes the project’s success could change the game for carbon capture efforts. ‘This means that we can pump very large amounts of CO2 and store it in a very safe way over a very short period of time,’ he says. In Iceland, Carbfix has increased its ambitions, and since 2014 has been injecting carbon into the ground at a rate of 5,000 tons per year. Because the mineralisation process is keeping up, the company plans to double that again this summer.

The reaction is taking place at the island’s Hellisheiði geothermal power plant, the third-largest in the world. It can generate 300 Megawatts of electricity out of steam, at the price of 40,000 tons of CO2 per year. Though this is only roughly five per cent of the emissions of the average coal plant, Hellisheiði's operator, Reykjavik Energy, wanted to improve the quality of its air emissions and rein in its carbon footprint. With an abundance of basalt and water aplenty, the plant has the ideal conditions for the carbon capture process to take place.

12A University of Iceland geologist shows the solid carbonate minerals (Image: Columbia University)

However, these same conditions could prove to be limitations for other power plants looking to solidify their emissions. Basalt aside, the reaction requires a large amount of water, to the tune of 25 tons for every one ton of CO2 (in the future, it could be that the process is adapted for the sea). Another limitation is the standalone cost of separating and injecting the CO2 – Hellisheiði can do it cheaply with its own existing technology.

Nevertheless, lead author of the paper, Juerg Matter, feels the benefits still outweigh the potential costs. ‘We need to deal with rising carbon emissions,’ he says. ‘This is the ultimate permanent storage.’

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