By Barbara Kessler
Green Right Now
Scientists have been studying a certain type of rock as a potential way to soak up carbon emissions. These ultramafic rocks, found in the United States, the Middle East and other locations, naturally react with carbon dioxide over thousands of years, turning the gas into solid minerals.
Geologists are exploring ways to exploit this natural tendency of the rock, and hurry it up a bit to help clean our carbon-addled atmosphere. The researchers include Columbia University graduate student Sam Krevor (and colleagues) who recently mapped the ultramafic rocks in the United States for his doctoral dissertation. The map shows a bounty of rock that they say could be enough to stash more than 500 years of U.S. CO2 production. That’s carbon scrubbing on an unheard-of scale.
Krevor (that’s him having a rocking good time in Oman) plans to pursue his research at Stanford University, looking at combining crushed ultramafic rock, leftover from closed asbestos mines, with organic salt catalysts to speed the carbon absorption process. Other scientists are developing ways of combining carbon with water and injected it into ultramafic rock formations.
We talked with Krevor, whose work was supported by the Lenfest Center for Sustainable Energy at the Earth Institute at Columbia and the U.S. Geological Survey, about these emerging technologies aimed at using rocks to absorb carbon.
Q: This field shows such promising prospects. What do you envision would be the possible trajectory of this technology? When might it be perfected and come to market?
A: There are many, but not too many, groups all taking different approaches to use these rocks to soak up the carbon. And this map, we were hoping to provide this research because we thought it would be useful to everyone.
My research has been on just one part of the process where you grind up the rocks, put them in a reactor and react them with CO2 and react them with optimal conditions, specific temperatures and pressures at which these reactions happen….
The main issue with mineral carbon sequestration in general is that people have struggled to get these reactions to happen fast enough, without using energy, so it could take place on scales useful to us. As of yet, the methods that have been tried out have been too energy intensive. So where the research is going now, there are groups of us looking at using catalysts to make the reaction go fast enough. Others are looking at injecting the CO2 into the rock.
We are at the basic research stage but there are many avenues being explored and many opportunities for it to develop in an economic way.
Q: So how many years away before we know if these processes could make economic sense?
A: I think you’ll know in a few years; three to four years, we’ll at least know if the current suite of approaches being taken will work out.
Right now the energy costs are at a factor of three to five. The cost of that is about $100 to $150 per ton of CO2 (sequestered). …That’s a factor of about 3 to 5 too costly…But in terms of energy development that’s not unreasonable.
We’re trying to bring it down to the $10 to $30 range (for each ton of CO2 sequestered). We think in that range it could be used commercially.
Q: One of the techniques being investigated involves first sinking the carbon into water then injecting it into rocks. That reminds me of the fracking process used to access natural gas – it’s very water intensive. Will this technology require a lot of water?
A: I wouldn’t want to comment on Yearg’s and Peter’s study. (Juerg Matter, a scientist at Columbia’s Lamont-Doherty Earth Observatory, and colleague Peter Kelemen are studying peridotite formations in Oman and exploring ways of injecting carbon dissolved in water into rocks.)
As for our process, we wouldn’t use a lot of water. It would have minimal impact on water resources and pollution.
Q: Tell me more about how the whole cycle would work. Will the rocks absorb just the ambient CO2. Wouldn’t the facilities need to be near the cities where carbon emissions are the worst?
A: There are many approaches. In each case you’ll be transporting CO2 to the rock. You’ll never be transporting rock, you be transporting CO2….
In the case of using catalysts, you can imagine transporting dilute CO2 from a power plant or just taking it from the air. You have to be in somewhat proximity to the sources of CO2. But 100 miles or 200 miles of pipeline is something people are expecting right now.Several sources of carbon could be transported to the pipeline to the rock formations. What we’ve mapped is rocks exposed at the surface. But they’re like the tip of the iceberg. There are very deep formations. Many are more than 5 km deep and a fair number reach half a mile in depth. That’s not atypical for these rock formations.
Q: Explain a bit more about the crushed rock approach that you’ll be investigating.
A: There’s many reasons that’s attractive. It’s already ground. It’s already disturbed as an industrial site. And we’d be cleaning up the pollution.
There’s a common misperception that the grinding of the rock is energy intensive. But it’s not. A relative small amount of CO2 is released in the grinding process, and several studies have been done looking at the mining. They look at it and worry about re-releasing 5 percent of that carbon…That’s manageable….If you can find the right catalyst to make this go quickly you could save a lot of energy.
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