Carbon sequestration may not, according to researchers at MIT, be the panacea that some had hoped. A recent study, partially funded by the United States Department of Energy, has found that far less carbon dioxide than the ideal prediction of 90 percent may be turned into rock when sequestered. This means much might eventually escape back into the atmosphere.
The University of Illinois recently celebrated reaching its goal of capturing and storing one million tons of carbon dioxide underground, but the process may not be as rock solid as thought.
"If it (CO2) turns into rock, it’s stable and will remain there permanently," says Yossi Cohen, a postdoc working on the study. "However, if it stays in its gaseous or liquid phase, it remains mobile and it can possibly return back to the atmosphere."
The findings almost contradict the central tenet of how the process works, which sounds charmingly elegant and simple. CO2 from coal fired power plants is collected (tricky in itself) and injected into rock at 7,000 feet below ground level then stored in large pockets of brine – or deep-saline aquifers – where it reacts with the liquid and turns from gas to solid. However the scientists found in their modelling of the process that very little gas may actually become solid. Though it does solidify, it only does so at the interface where the CO2 enters the brine pool. It then reacts to build a "wall" the rest of the gas cannot get through.
"The expectation was that most of the carbon dioxide would become solid mineral. Our work suggests that significantly less will precipitate," explains Cohen.
The scientists say that these predictions require further experimental studies. "There are many factors, such as the porosity and connectivity between pores in rocks, that will determine if and when carbon dioxide mineralizes," says Cohen. Once this is known there will be a better understanding of which kinds of rock formation will be best suited for the job.
The study, authored by Professor Daniel Rothman of the MIT’s Department of Earth, Atmospheric, and Planetary Sciences and Yoshi Cohen, was published this week in the Proceedings of the Royal Society A.
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