The technology that turns CO2 into rock

Iceland may have uncovered the first truly safe method for carbon capture and storage. Currently, the established carbon capture technology is to extract carbon dioxide (CO2) from the atmosphere, condense it, and pump it into underground chambers. This is the technique favoured by the oil and gas industry because they can suck an oil or gas reservoir dry, pump CO2 back in, and claim they are doing their bit for climate change. The problem with this method (beyond the hypocrisy) is that the CO2 can leak back out — it is only ever an earthquake away from seeping to the surface, and into the atmosphere. Much like nuclear waste, it doesn’t solve a problem, it simply passes the buck to future generations.

Here’s the Icelandic alternative: the CO2 reacts with mineral-rich rocks to turn into a solid, instead. In the mainstream carbon capture and storage scenario outlined above, this geological process would take well over 100,000 years (during which time the unstable CO2 would likely have leaked out anyway). But researchers in Iceland have developed a method by which CO2 is dissolved in water before being injected into the island’s mineral-rich, basaltic rocks. Here, it turns into solid white calcite crystals in far less than 100,000 years — in fact, it takes just two years.

This is not just theoretical or lab-based research. It has been happening on an industrial scale at CarbFix, part of the Hellisheidi geothermal power plant, near Reykjavik, since 2014. Waste CO2 is captured from the power plant’s steam, is dissolved into large volumes of water and injected into the basalt below, between 400m and 800m deep. There the basalt (which contains up to 25% of calcium, magnesium, and iron by weight) looks literally like a black sponge, filled with air holes that the CO2 settles in and forms calcite — or mineralized carbon — within just hundreds of days, not hundreds of thousands of years.

The Hellisheiði Geothermal Power Plant, site of the CarbFix project. Photo: Sigrg.

Juerg Matter, Associate Professor in Geoengineering at the University of Southampton, part of the original research group, tells me: “Since 2016, [CarbFix] has upscaled the CO2 storage and mineralization to industrial scale by injecting about 10,200 tonnes of CO2 per year… into basaltic subsurface storage”.

All the carbon in the atmosphere, in plants and animals, inside you and me, originates from rocks, and will eventually become rocks again: this is known as the ‘carbon cycle’. A 2014 paper in Science, by Institute of Earth Sciences, University of Iceland, explains that: “Humans have accelerated this cycle by mining and burning fossil fuel since the beginning of the industrial revolution, causing rising atmospheric carbon dioxide (CO2) concentrations that are the main cause of global warming. One option for mitigating high levels of global warming is to capture CO2 and safely store it for thousands of years or longer in subsurface rocks. By accelerating carbonate mineral formation in these rocks, it is possible to rebalance the global carbon cycle, providing a long-term carbon storage solution.”

University of Iceland’s Institute of Earth Sciences. Extracting CO2 from geothermal steam. Photo: Sigurður Reynir Gíslason.

Iceland is unusually blessed with basalt — more than 90% of the highly volcanic island is made up of it. But basalt isn’t exactly rare in the rest of the world, either: it is one of the most common rock types on Earth, covering approximately 10% of the surface and most of the ocean floor. Sandra Snaebjornsdottir, a geologist working for CarbFix, told the BBC: “Wherever there are basalt and water, this model would work. The storage capacity is such that, in theory, basalts could permanently hold the entire bulk of CO2 emissions derived from burning all fossil fuel on Earth.”

So why — given the world has abundant basalt and an apocalyptic atmospheric CO2 problem — isn’t the CarbFix model happening elsewhere? “Good question”, says Matter. “The CarbFix model is unique because it dissolves CO2 into water (waste water from the geothermal power plant) during injection into the storage reservoir. This is an ideal situation and it is not possible everywhere to co-inject water with CO2 because of [the lack of] water availability.” However, “it may be possible to inject pure CO2 into a deep basalt formation without co-injection of water”, informs Matter. Preliminary results published from a pilot CO2 injection project into the Columbia River Basalt in Washington State, have done just that.

Another reason for the dominance of mainstream carbon storage in underground reservoirs is that, “the oil and gas industry is dominating the field”, Matter tells me. “They have no knowledge and expertise with ‘unconventional’ reservoirs such as basalt.”

CarbFix, jointly run by Reykjavik Energy, explains on its website that “by capturing CO2 from variable sources and injecting it into suitable deep rock formations, the carbon released is returned back where it was extracted… This technology might help to mitigate climate change as injecting CO2 at carefully selected geological sites with large potential storage capacity can be a long-lasting and environmentally benign storage solution.” The leakage risk is zero. The problem it leaves for the next generation to solve? Also zero.

The priority must be to reduce carbon emissions in the first place. But a truly stable form of carbon capture is surely a useful addition to the arsenal in the fight against global warming.