Can we turn carbon dioxide to stone to fight climate change?

"This is like a major war ... But we're going to win."
It's estimated that human activities are responsible for emitting about 40 billion tons of carbon dioxide a year.Athit Perawongmetha / Reuters file
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By Lynne Peeples

As more heat-trapping carbon dioxide continues to concentrate in our atmosphere — and to wreak havoc on our climate — scientists are desperately seeking solutions. Some are looking for ways to limit the greenhouse gas we spew from smokestacks, tailpipes and the like; others, whose efforts remain largely under the radar, are aiming to thin the layer of gas that already blankets our planet.

One group of researchers in Canada, taking the latter approach, may have hit upon a novel yet ancient idea: harness and accelerate the carbon-absorbing power of rocks.

"We have to learn how to remove carbon dioxide from the atmosphere, because we've already put too much into it," said Roger Aines, a senior scientist at Lawrence Livermore National Laboratory's energy program, who was not involved in the research. "Just making everything electric. Just making everything renewable. We have to do that, but that's not enough."

Throwing rocks at the problem, in other words, could make a significant dent.

The oceans, soils and trees aren't the only tools nature employs to capture and store away carbon dioxide. Minerals soak up the gas, too. Just one cubic kilometer of rock laden with magnesite and other carbonate minerals — about the size of a medium-sized mountain — could lock down a billion tons of carbon dioxide.

But this occurs over extremely long time frames — far too slow to keep up with the rate at which the world emits carbon dioxide, which is estimated to be about 40 billion tons a year.

Now, the Canadian team has devised a recipe to speed up the formation of magnesite, or magnesium carbonate, from hundreds or thousands of years in nature down to just 72 days in the lab. The key ingredient: tiny polystyrene microspheres — essentially latex beads — coated with charged molecules that help magnesium ions bond with carbonate ions to create magnesite.

In this photo, taken with a scanning electron microscope, tiny crystals of magnesite are forming. Ian Power

Compared to other carbonate minerals common near the Earth's surface, magnesite is particularly reluctant to form, and is therefore an apt target for the chemical cajoling. And once formed, the mineral is very stable. One ton of magnesite securely holds about a half ton of carbon dioxide.

"It's a great way of storing carbon dioxide for a long period of time," said Ian Power, an environmental geochemist at Trent University in Canada, who presented his team's research at the Geochemical Society's Goldschmidt Conference in Boston on Aug. 14.

Climate models suggest that by 2050, the world will need to remove 10 billion tons of carbon dioxide annually from the atmosphere, or about 20 times the weight of all humans on Earth. As such, scientists have been working on a myriad of carbon-sequestering strategies.

A team at the University of California, Berkeley, for example, is targeting reforestation and the restocking of carbon into soils. Engineers at Harvard University are testing machines that suck the greenhouse gas directly out of the air. Each strategy has merits, noted Aines, along with hefty price tags. "But if you can take a process that already wants to happen, and just encourage it to happen a little faster, you may be able to afford to do this," he said.

What's more, the latex beads catalyzed the creation of magnesite at room temperature in the lab — and they stayed intact, ready to be used again. (Higher temperatures are known to speed up the production of magnesite, but added heat means added cost and energy, likely yielding the counterproductive release of more carbon dioxide.)

"The opportunity to do it is definitely worth investigating," said Aines. "And it's going to work. The question is how well and how fast."

Greg Rau, a researcher in the Institute of Marine Sciences at the University of California, Santa Cruz, was more cautious about the magnesite research. While the results are "revealing," Rau said, "it is less obvious how this is a real breakthrough for carbon storage." The jury is out, he suggested, until further details come in regarding how the technique might be applied beyond the lab.

Possibilities, according to Power and Aines, include using the beads to increase the speed and decrease the cost of making magnesite in an industrial reactor. The beads may also speed up the underground formation of carbonate minerals, especially if combined with emerging technologies such as an injection method piloted by the CarbFix project in Iceland. While also speculative at this point, Power and Aines noted the potential for resulting rock to be put to use, perhaps as building material or in roads, which would increase the strategy's viability.

"The big challenge is to do this economically and to have the political will," said Power, emphasizing the importance of putting a price on carbon to drive innovation and large-scale implementation of carbon capture and storage ideas. "I'm a strong believer that we need to have many, many solutions to really tackle climate change. I don't think there will be one silver bullet solution."

"This is like a major war," added Aines. "There's going to be an enormous amount of damage along the way. But we're going to win."

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