March 11, 2009 The debate about the benefits of using Carbon Capture and Sequestration (CCS) to fight against climate change is ongoing. One one hand there are reservations regarding suitable sequestration sites that provide sufficient security to store CO2 for centuries as well as the cost of implementing such a system, which could draw important funds away from the development of renewable energy technologies. On the other, we are still heavily reliant on burning fossil fuels to produce energy and this infrastructure can't be replaced overnight. CCS is obviously attractive to existing power generation companies as it allows them to keep hold of their existing infrastructure and for this reason, it is more than likely that CSS schemes will continue to gather momentum. So where to we can CO2 be stored? Scientists at Columbia University’s Earth Institute and the U.S. Geological Survey have produced a new report that maps large rock formations in the United States that can also absorb CO2 and are exploring ways to speed up the CCS process.

The report shows 6,000 square miles of ultramafic rocks at or near the surface that contain minerals that react naturally with carbon dioxide to form solid minerals in a process called mineral carbonation – not unlike the bacteria we looked at recently that converts CO2 into calcium carbonate. Because of their chemical makeup, when ultramafic rocks are exposed to carbon dioxide, they react to form common limestone and chalk. The bad news is that it normally takes thousands of years for the rocks to react with sizable quantities of CO2, but scientists are working on ways to speed up the process by dissolving CO2 in water and injecting it into the rock as well as capturing heat generated by the reaction to accelerate the process.

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So far, most work in CCS has focused on storing liquid or gaseous CO2 underground in saline aquifers, depleted oil wells and porous coal seams that are not commercially viable. Such approaches bring concerns about leaks so a system that can permanently remove the CO2 by converting the carbon into a solid proves very attractive. If the experiments prove successful and the technology takes off, geological formations around the world could provide a vast sick for heat-trapping CO2. The report’s lead author Sam Krevor, says the United States’ ultramafic rocks could be enough to stash more than 500 years of U.S. CO2 production, and with the bulk of the ultramafic rock formations located in strips along the west and east coasts are located close to high population and high CO2 emitting areas.

The U.S. survey is the first of what Klaus Lackner, who directs the Earth Institute’s Lenfest Center for Sustainable Energy, hopes will become a global mapping effort and work is also underway to map the locations of common volcanic basalt, which also reacts with CO2. In Iceland, Juerg Matter, a scientist at Columbia’s Lamont-Doherty Earth Observatory, is about to participate in the first major pilot study on CO2 sequestration in a basalt formation and in May he and three other Lamont-Doherty scientists will join Reykjavik Energy and others to inject CO2-saturated water into basalt formations there. Over nine months, the rock is expected to absorb 1,600 tons of CO2 generated by a nearby geothermal power plant. Matter and another Lamont-Doherty scientist, David Goldberg, are also involved in a study by Pacific Northwest National Laboratory, which will eventually inject 1,000 tons of C02 into formations beneath land owned by a paper mill near Wallula, Washington. Matter and another colleague, Peter Kelemen, are also currently researching peridotite formations in Oman, which they say could be used to mineralize as much as 4 billion tons of CO2 a year, or about 12 percent of the world’s annual output.

One model is to capture CO2 directly from power-plant smokestacks or other industrial facilities, combine it with water and pipe it into the ground, as in the upcoming Iceland project, but Lackner and his colleagues are also working on a process using “artificial trees” that would remove CO2 already emitted into the atmosphere. Aside from the obvious benefit of reduced CO2 in the atmosphere, Krevnor says combining rocks and CO2 could provide an added benefit. For decades, some large U.S. peridotite formations were mined for asbestos, but after a link between asbestos and cancer was proven, the substance was banned for most uses, and the mines were closed. Mine tailings left behind, at Belvidere Mountain in Vermont and various sites in California, provide a ready supply of crushed rocks. These potentially hazardous tailings would be rendered harmless during the mineralization process.

While the use of ultramafic rocks in CCS offers the promise of permanently removing CO2 from the atmosphere as part of the legacy system of existing fossil fuel fired power plants, it seems the viability of such a scheme rests on the ability of the scientists to speed up the natural mineral carbonation process. Without that we could be waiting a very long time to see any kind of worthwhile results.

Darren Quick

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