FEATURE

The Carbon Eaters

One Columbia researcher thinks a solution to global warming could lie beneath our feet.

by Douglas Quenqua Published Fall 2013
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Peter Kelemen and his daughter Sarah, a college freshman, map rock formations in Wadi Fins, Oman, where veins of carbonate fill every crack that has been exposed to water.For example, pools of water that emerged from the rock and came in contact with air would develop a cloudy white film. Disturb that film, and it would grow back almost immediately. “I’d throw a pebble in the pool and knock the little scum of carbonate down, and a day later, a new one would have formed,” says Kelemen, who is the Arthur D. Storke Memorial Professor in the Department of Earth and Environmental Sciences. “For a geologist, that’s just superfast. That’s supersonic.”

So when he and fellow Columbia geochemist Juerg Matter returned to Oman on a field trip for students in 2007, they collected samples of the carbonate and had them dated using carbon-14 analysis. “I thought a lot of these deposits would be millions of years old, but they weren’t,” Kelemen says. “It turned out they were all less than 50,000 years old.” Their tender age was a strong indication that the carbonate deposits were still forming. This seemed to happen when the mountains’ topsoil eroded to expose fresh peridotite and when new cracks appeared in the rock, permitting carbonate deposits to form deep inside.

Finding a way to store carbon dioxide in a mineral form has always been the Holy Grail of sequestration research.

Kelemen and Matter estimated that the peridotite was absorbing about 100,000 tons of carbon annually, far more than geologists had previously believed. Kelemen and Matter soon published a study theorizing that this natural process could be accelerated a million-fold in some places. Their idea was to pierce the Hajar Mountains, a range the size of Massachusetts, with boreholes and then pump huge quantities of CO2-infused water into the ground. Even considering the economic and engineering challenges involved, Kelemen and Matter concluded that it would be feasible to store several billion tons of CO2 per year, or roughly 10 percent of all of the CO2 that humans are now producing. Alternatively, they proposed drilling boreholes off the coast, which would permit seawater to permeate the mantle rock beneath the ocean floor and deposit its CO2 there.

Finding a way to store carbon dioxide in a mineral form has always been the Holy Grail of sequestration research, says Greg Dipple, a professor of geology at the University of British Columbia. “It’s been recognized since the early 1990s as the optimal way to store carbon, but it hadn’t been feasible,” he says. “What Peter came up with is a novel way to do it on a large scale.”

Rock-Tight Storage?

This past January, Kelemen spent a month in Oman collecting more samples.

“We’re now interested in learning how to maximize the amount of CO2 that a certain volume of rock absorbs,” he says. “What nature can do in this regard is amazing — we’ve found pieces of the rock that literally have carbonate attached to every single one of the magnesium and calcium atoms. It’s permeated. Maxed out. And we want to learn how to make more of the rock like that.”

In recent years, Kelemen has learned more about the mechanism by which peridotite absorbs CO2. For example, he has discovered that when carbonate forms within the cracks of peridotite it presses out against the surrounding rock, forming new, microscopic fissures. These clefts allow more air and water inside the peridotite, which kick-starts a self-perpetuating cycle of carbonate formation and splintering.

“This rock from the earth’s interior is out of equilibrium with our atmosphere, and hungry for carbon dioxide,” Kelemen says. “We want to take advantage of that. This is chemical potential energy, as a geochemist would say. It’s there to be harnessed on a massive scale, if we can learn how to do it.”

Carbon dioxide reacts with peridotite in this region, turning it into a chalky substance that resembles limestone.Kelemen is now collaborating on the project with several other Columbia scientists. Among them is Heather Savage, a geophysicist who studies earthquakes. She is now applying everything she knows about how rock formations near tectonic faults naturally slip, crumble, and crack in order to help Kelemen figure out a way to initiate new fissures within peridotite, thereby exposing more of its surface area to CO2. Alissa Park, a climate scientist and engineer who has done extensive research on novel methods of carbon sequestration, is working with Kelemen to understand the optimal conditions for CO2 to chemically combine with elements in the peridotite.

“One trick is to circulate the water as deep into the ground as possible, because heat from the earth’s interior is going to make the chemical reactions occur at a faster rate,” says Kelemen.

Kelemen’s next goal is to dig a single borehole and experiment with the injection and removal of large quantities of CO2-rich water. The operation would cost roughly $10 million, and so far he has not convinced anybody to put up the money. Part of the challenge in funding his work, Kelemen says, is that private companies don’t yet see commercial potential in storing carbon dioxide, especially when scientists are still searching for an economically viable way to remove it from the air.

He is prepared to be patient. “Maybe in ten or twenty years, after we’ve had catastrophes that are clearly attributable to global warming, there will be more urgency surrounding the development of these technologies,” Kelemen says. “When the time comes, we want to have the basic concepts ready to go.”

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