Carbon sequestration is a process that injects carbon dioxide deep below the Earth’s surface where it solidifies into rock. However, researchers at the Department of Earth, Atmospheric and Planetary Sciences at Massachusetts Institute of Technology (MIT) have found that less carbon dioxide is converted to rock than was previously thought.

After studying the chemical reactions between carbon dioxide and its surroundings, the team found that a relatively small fraction of gas turns into rock—the remainder of the gas stays in a more tenuous form.

"If it turns into rock, it's stable and will remain there permanently," says Yossi Cohen, a post-doctoral researcher. "However, if it stays in its gaseous or liquid phase, it remains mobile and it can possibly return back to the atmosphere."

The team created a model of the chemical reactions between the carbon dioxide and brine, and found that the carbon dioxide solidifies, but only at the surface. The reaction creates a solid wall at the point where the two meet, but that wall doesn’t allow the rest of the carbon dioxide to react with the brine.

"This can basically close the channel, and no more material can move farther into the brine, because as soon as it touches the brine, it will become solid," Cohen says. "The expectation was that most of the carbon dioxide would become solid mineral. Our work suggests that significantly less will precipitate."

Cohen says these theoretical predictions require experimental study to determine the magnitude of this possible effect.

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