Large swaths of the Sierra Nevada and Appalachian mountain ranges could someday lock away vast amounts of carbon dioxide -- but not necessarily in the sense envisioned by "clean coal" advocates.
Scientists recently published a report and map identifying 6,000 square miles of ultramafic rocks -- those that formed from cooling magma and have very low silica content. Those rocks, scientists say, are ideal for carbon sequestration at or near the earth's surface.
Ultramafic rocks, which in the United States are primarily found on the East and West coasts, have the potential to store 500 years worth of CO2 production, said the study's lead author, Sam Krevor, who was just awarded his doctorate from Columbia University's Earth Institute.
"The take-home from this is that there is so much material out there to use ... that we are not limited by capacity," Krevor said. "It could be used to mitigate as many greenhouse gas emissions as could be imagined."
The sequestration method, known as mineral carbonation or mineral sequestration, that Krevor and his co-authors are studying is by no means fully developed or ready for commercial implementation, but several test projects are under way around the globe (ClimateWire, Feb. 9).
Certain rocks -- like the ultramafic ones mapped in Krevor's study -- contain minerals that react naturally with carbon dioxide in the air to form solid minerals that effectively turn the gas into stone, but that process can take thousands of years to lock away sizable quantities of greenhouse gases. Scientists, including Krevor, are studying ways to speed up the mineral carbonation process so it can also be used to store CO2 from power plants and other polluters and to curb the artificial process’s energy use. If the technology takes off, rocks like these around the world could be used as carbon dioxide traps -- without the worry of leaks.
Artificial mineral carbonation can be induced in two ways, Krevor said. The first is by injection, which is similar to the common testing that has occurred in saline limestone aquifers, depleted oil wells and porous coal seams. Carbon dioxide is captured from power plant smokestacks or other industrial facilities, combined with water and piped into the ground where it can react with the rock to form common rocks like limestone and chalk.
The other method involves mining the ultramafic rock, grinding it up and combining it with carbon dioxide and a reacting agent to spur the chemical reaction that locks the greenhouse gas into rocks.
The report was spurred by a 2005 Intergovernmental Panel on Climate Change special report on carbon sequestration that noted a significant gap in mineral carbonation knowledge about potential sources of the rocks that can store the greenhouse gas. The new report, which Krevor collaborated on with another Columbia student and two U.S. Geological Survey scientists, attempts to plug that gap.
"It's a really big step forward," said Klaus Lackner, who directs the Earth Institute's Lenfest Center for Sustainable Energy and helped originate the idea of mineral sequestration in the 1990s.
For decades, large U.S. ultramafic peridotite formations were mined for asbestos, which was later linked to cancer. The substance was banned for most uses and the mines were closed, but potentially hazardous mine tailings were left behind. Mineral carbonation could render those tailings harmless, Krevor said.
"This process would take advantage of those rocks that are already ground up and the remnant asbestos would be destroyed," Krevor said. "It's a double benefit of remediating hazardous waste and locking away carbon dioxide."