What do we do with a problem like carbon dioxide? We want to remove the excess from our atmosphere, but how? In Iceland, geologists are burying the greenhouse gas with water, so that basic chemistry can turn it into solid rock inside what the New York Times calls "a geological soda machine".
Storing carbon dioxide underground is not a new idea, but CarbFix in Iceland uses an unique approach. Conventionally, liquid carbon dioxide is injected into porous rock — like at Sleipner in Norway — where we hope the carbon dioxide will (eventually) turn into carbonate minerals after thousands or tens of thousands of years. Over that long stretch of time, the pressurised gas could escape through cracks into the air, leaving us right back where we started.
CarbFix wants to speed up the process of mineralisation, using something as simple as water. But lots of it. Carbonated water is acidic — just like your Diet Coke hence the wonderful phrase "geological soda machine" — which helps release elements like calcium with which carbon dioxide can react. In Iceland's volcanic fields, the carbon dioxide is injected into basalt, where it should turn to calcite.
CarbFix began their first test field injection in 2012, and they're now analysing their cores of rock for calcite. They have also scaled up their operations to inject 10,000 tons of carbon dioxide captured from a nearby power plant each year. It appears promising, but there is a big dollar sign hanging out next to a question mark over everything. The Times explains why:
But injecting huge amounts of water along with the CO2— 25 tons of liquid for each ton of gas — adds to the cost. CarbFix scientists have estimated that transportation and injection could cost about $US17 per ton of CO2, about twice the cost of transporting and injecting the gas alone. (These costs are on top of the much higher costs of capturing and separating CO2from a power plant smokestack.)
Without economic incentives, energy companies have no reason to invest in burying their carbon dioxide with water, especially if there are other cheaper solutions. The irony, though, is that over tens of thousands of years, CarbFix's solution might actually be cheaper if it truly works as promised without leaking. But we humans are not so good at thinking in tens of thousands of years. [New York Times]
Picture: Cores containing calcite believed to contain carbon dioxide injected in 2012, via CarbFix