CARBON CAPTURE:

Scientists ponder methods to turn CO2 into stone

Mineral carbonization promises to store away carbon dioxide in a much more stable form than simply pumping it into an underground geologic formation, and scientists have long known about its potential, but the carbon sequestration method is resource intensive.

Still, a handful of scientists around the world are exploring ways to capture the greenhouse gas and prevent it from leaking out after injection by quickly turning it into minerals that occur naturally, like calcium carbonate, the main component in limestone.

A pilot project will begin next month in Reykjavík, Iceland, where, for the first time, carbon dioxide-saturated water will be injected into a basalt formation to study how quickly the carbon dioxide and water mixture reacts with the rock to form calcium carbonate. In the laboratory, mineralization begins within four to six weeks and occurs extensively within months.

In most sequestration projects, compressed carbon dioxide is injected into a geologic formation already filled with water. The gas must first dissolve into the water for mineralization to begin, and scientists do not know how long that process takes. In the meantime, scientists worry about what keeps the buoyant gas from working its way up through fractured rock and back into the atmosphere.

But the practical considerations for mineral carbonization are steep. Capturing the gas and injecting it dry into the ground takes large amounts of energy and money. But to start the mineralization process faster by first injecting carbon dioxide into water would require large amounts of water. Another potential problem occurs after injection. Carbonate minerals precipitate from the water solution into the porous rock, but in doing so, they may plug up areas where the water solution is migrating and spur the need for more injection wells (Victoria Schlesinger, Christian Science Monitor, Feb. 5). -- KJH

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