The Breakthrough Institute

MIT's Technology Review has a very interesting article on the sequestration of carbon dioxide exploiting natural geologic processes as reported today in a paper paper from Columbia University, published by the Proceedings of the National Academy of Sciences (full paper available here).

Technology Review writes of the paper:

The researchers have shown that rock formations called peridotite, which are found in Oman and several other places worldwide, including California and New Guinea, produce calcium carbonate and magnesium carbonate rock when they come into contact with carbon dioxide. The scientists found that such formations in Oman naturally sequester hundreds of thousands of tons of carbon dioxide a year. Based on those findings, the researchers, writing in the current early edition of the Proceedings of the National Academy of Sciences, calculate that the carbon-sequestration rate in rock formations in Oman could be increased to billions of tons a year-more than the carbon emissions in the United States from coal-burning power plants, which come to 1.5 billion tons per year. . .

The researchers found that the natural peridotite formations in Oman captured carbon dioxide in a network of underground veins. Peridotite contains large amounts of olivine, a mineral composed of magnesium, silicon, and oxygen. As groundwater reacts with the olivine, the water becomes rich in dissolved magnesium and bicarbonate, with the latter effectively increasing the carbon concentration in the water by about 10 times. As this water seeps deeper into the rock and stops reacting with the air, the magnesium, carbon, and oxygen precipitate out of solution and form magnesium carbonate, also called magnesite. Dolomite, which contains calcium, magnesium, carbon, and oxygen, also forms. As the magnesite and dolomite form, they increase the total volume of the rock by about 44 percent, causing cracks to appear throughout it, which creates a network of fractures as small as 50 micrometers across. This opens up the rock and allows water to penetrate further. "It's a little bit like setting a coal seam on fire," says Peter Kelemen, a professor of earth and environmental studies at Columbia University. "You're taking rocks that haven't been exposed to the atmosphere, and you're oxidizing them very fast."

The researchers calculate that the natural process can be sped up dramatically. Using techniques commonly employed by the oil industry to increase oil production, the rock could be fractured further, increasing the surface area for the reactions. Carbon dioxide captured from power plants could then be pumped into the rock, where it would trigger the formation of carbonates. Heating the rock would increase the rate of the reactions. What's more, because the reactions themselves generate heat, once they reach a certain rate, they will be self-sustaining. Initiating this self-sustaining reaction would require heating the rock to 185 °C, the researchers say, which could be done during the process for fracturing the rock. They calculate that in such a system, one cubic kilometer of rock would store a billion tons of carbon dioxide per year.

The researchers are careful to note that the technology is not proven, and because it is not laboratory science, would need to be tested in the field. But the technology offers a large potential to sequester at low cost. Technology Review writes of the potential of carbon dioxide sequestration (available here):

The researchers propose a carbon-sequestration strategy that would eliminate the need to transport carbon dioxide, as well as the need to heat up the rock. In this scenario, they would access rock formations in shallow ocean waters off the coast of Oman and elsewhere by drilling into them and fracturing the rock using existing oil-industry techniques. The researchers would drill two holes. Into one, they'd pump cool seawater. Rock temperature increases with depth, so as the water is pumped into the holes, it will get hotter, until it reaches nearly 185 °C. Carbon dioxide naturally dissolved in the water would then precipitate out of the solution. The hot water would eventually make its way through the fractured rock to the second drilled hole, where it would rise to the surface via convection. This seawater would quickly absorb more carbon dioxide, since shallow waters and surf mix well with the atmosphere. Because "the atmosphere transports carbon dioxide all over the world for free," Kelemen says, this approach, if deployed on a grand scale, could be used to lower worldwide levels of carbon dioxide.

This scenario would be limited by the concentration of carbon dioxide in seawater, so a cubic kilometer of rock would only sequester about a million tons of carbon dioxide a year. But since it wouldn't be necessary to transport carbon dioxide or pay to heat the rock, Kelemen says, it would be possible to work with much larger areas of rock, and thereby reach a rate of billions of tons of carbon dioxide per year.

The publication of this paper shows that there are options not yet in the discussion of climate policy that may yet lead to low cost, politically tractable options that contribute significantly to stabilizing carbon dioxide concentrations in the atmosphere. Considerably more effort should be spent opening up the discussion to these new options, rather than continuing to follow failed strategies where ever they lead.