|December 11, 2013|
Abandoned mine could yield clues to stopping global warming
|An abandoned mine in California is providing scientists with important data that could lead to a possible new weapon to fight global warming.|
Massive amounts of the greenhouse gas carbon dioxide vacuumed from smokestacks or the air could be permanently locked up in a type of tight, magnesium-rich rock found in the mine, according to scientists. One tricky part is to break up the rock to make room for the greenhouse gas. And that may require violence.
This type of violent breakup happened in a burst of geologic activity millions of years ago in a coastal mountain range in California near the infamous San Andreas Fault, Pablo Garcia del Real, a graduate student at Stanford University in California, explained.
An abandoned mine at a mountain there contains some of the world's largest veins of a chalky mineral made of magnesium and carbon dioxide known as magnesite. He and colleagues are studying the magnesite deposits to determine how they formed so they can replicate the process to store carbon dioxide produced in places such as coal-fired power plants.
"The potential is great," del Real told NBC News. The Red Mountain mine where he and his colleagues are working once held the equivalent of 140,000 metric tons of carbon in mineral form before the magnesite was mined in the early 20th century, he said.
All told, the magnesium-rich rocks in this particular mountain area in California could hold 13 gigatons of carbon, he added, "and there are hundreds more" areas with magnesium-rich rocks "around California and massive ones in Oregon."
For perspective, human activity has put more than 500 gigatons of carbon into the atmosphere. According to climate scientists, irreversible climate change is likely to occur somewhere around 1,000 gigatons, a threshold that humanity is on course to cross by the middle of this century.
Del Real presented research on Tuesday at the annual meeting of the American Geophysical Union in San Francisco on the formation of the magnesite deposits at the abandoned mine and how it relates to their own efforts to store carbon dioxide.
"Nature does it very well, does it quickly and violently," he said.
When the San Andreas Fault formed about 29 million years ago, it created a gap between the Earth's crust and the underlying mantle. This allowed heat to rise to the surface, raising the temperature of the water and liquid carbon dioxide trapped in the magnesium-rich rocks, according to the researchers.
The rising temperature caused the volume of the liquid to increase, which added sufficient pressure to break up the rock, del Real explained. Once broken apart, this increased the surface area for the magnesium and carbon dioxide to chemically bind, forming the magnesite deposits.
The deposits are "composed of very, very tiny crystals --- millions of them," del Real said. "So that tells us a clue that the magnesite is forming very quickly, meaning that the crystals are not growing too big."
Analysis of chemical signatures in the rock suggests the magnesite formed as temperatures rose from about 53 degrees to 86 degrees Fahrenheit, which is sufficiently low for scientists to efficiently convert atmospheric carbon dioxide into magnesite. However, replicating the process in the lab has proven elusive.
"What you have is just a stagnant solution with magnesium and carbon dioxide, but the magnesium and carbon dioxide would never bind, which is a problem," del Real said. "What I'm trying to do in the lab is use different media ... to grow magnesite and that is still an ongoing process."
The magnesium-rich rock that del Real and colleagues are working with is known as ultramafic rock. In addition to growing the crystals, the scientists need to overcome the engineering challenge of efficiently breaking apart the rock to increase the surface area for the magnesite to form.
"The ultramafic rocks have very low porosity and they are not permeable, fluid cannot flow through these things at the times that we need for carbon sequestration," del Real said.
The approach of storing carbon dioxide in ultramafic rocks, which make up about 1 percent of the Earth's surface, is similar to an ongoing project supported by the U.S. Department of Energy to permanently store the greenhouse gas in basalt rocks.
"Probably the most significant difference is that basalts generally have structures with natural permeability where large volumes of fluids can be injected or extracted," Pete McGrail, a research fellow at the energy department's Pacific Northwest National Laboratory in Richland, Wash., told NBC News in an email.
"Ultramafic rocks lack anything equivalent; permeability would have to be created artificially," added McGrail, who leads the basalt storage project. "Whether that could be done at the required scale and cost effectively are very challenging problems."