It won’t be a gas, stored indefinitely in a pressure vessel; the gas should react with the basalt to form limestone.
http://earthobservatory.nasa.gov/Newsroom/view.php?id=28622
[font face=Serif][font size=5]Western States to Host First Test of Carbon Sequestration in Lava Rock[/font]
November 4, 2005
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In the experiment, the researchers will compress pure carbon dioxide to form a liquid, which it will then inject more than a half-mile underground. There, the liquid will displace some water, explains Robert Smith, a geochemist at UI and the technical lead for Big Sky’s geologic sequestration. Based on their analyses, the researchers expect the carbon dioxide to dissolve over the next few months into the water “like in a can of soda,” he says. This mixture will produce a weak acid, roughly the acidity of orange juice. Minerals in the basalt will react with the acid to produce calcium carbonate (limestone, found in seashells), magnesium carbonate (a chalky substance, used by gymnasts and weightlifters to improve their grip) and other solid carbonates.
“It’s the same kinds of natural reactions that occur all the time, except that there’s so much more carbon dioxide that the reactions are going to occur much, much faster,” Smith explains. “You’re speeding up naturally occurring processes that take carbon out of the atmosphere.”
Other rock types convert carbon dioxide to solid form, but much more slowly. Because volcanic rock is young and reactive, the conversion happens tens to hundreds of times faster than in other types of rock, in just a few centuries. That’s a blink of an eye in geologic time.
“These rocks have a large capacity and they react very rapidly,” Smith says. “Because the final products are solids, they don’t come back to the surface. They’re not going to leak out.”
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