Rocks could be harnessed to soak up huge quantities of CO2 from air

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Washington, Nov 6 : A new study by scientists has determined that a type of rock found at or near the surface in the Oman and other areas around the world could be harnessed to soak up huge quantities of globe-warming carbon dioxide (CO2).

Geologist Peter Kelemen and geochemist Juerg Matter, both from Columbia University's Lamont-Doherty Earth Observatory, made the discovery during field work in the Omani desert, where they have worked for years.

Their studies show that the rock, known as peridotite, reacts naturally at surprisingly high rates with CO2 to form solid minerals, and that the process could be speeded a million times or more with simple drilling and injection methods.

Peridotite comprises most or all of the rock in the mantle, which undergirds earth's crust.

It starts some 20 kilometers or more down, but occasionally pieces are exhumed when tectonic plates collide and push the mantle rock to the surface, as in Oman.

Geologists already knew that once exposed to air, the rock can react quickly with CO2, forming a solid carbonate like limestone or marble.

However, schemes to transport it to power plants, grind it and combine it with smokestack gases have been seen as too costly and energy intensive.

The researchers said that the discovery of previously unknown high rates of reaction underground means CO2 could be sent there artificially, at far less expense.

"This method would afford a low-cost, safe and permanent method to capture and store atmospheric CO2," said Kelemen.

Their study area, a Massachusetts-size expanse of largely bare, exposed peridotite, is crisscrossed on the surface with terraces, veins and other formations of whitish carbonate minerals, formed rapidly in recent times when minerals in the rock reacted with CO2-laden air or water.

Up to 10 times more carbonates lie in veins belowground; but the subterranean veins were previously thought to be formed by processes unconnected to the atmosphere, and to be nearly as old as the 96-million-year-old rock itself.

However, using conventional carbon isotope dating, Kelemen and Matter showed that the underground veins are also quite young- 26,000 years on average-and are still actively forming as CO2-rich groundwater percolates downward.

Many underground samples were conveniently exposed in newly constructed road cuts.

Kelemen and Matter estimate that the Omani peridotite is naturally absorbing 10,000 to 100,000 tons of carbon a year, which is far more than anyone had thought.

According to scientists, the process of locking up carbon in the rocks could be speeded 100,000 times or more simply by boring down and injecting heated water containing pressurized CO2.

ANI

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