Researchers turn CO2 into stone using natural processes

limestoneA new paper published this week shows it’s possible to turn carbon dioxide into limestone, but the price tag isn’t cheap. Scientists pumped large amounts of carbon dioxide (CO2) and water into underground basalt rocks, and the resulting chemical mix reacted with the rocks’ calcium magnesium to form limestone. Limestone is considered a more permanent solution for storing CO2 because it’s now been converted to stone. The technique was published in a new in the journal Science.

“It’s no longer a gas,” said Juerg Matter, a co-author of the study at the University of Southampton in England. “Basically carbon dioxide converted it into stone.” Previous experiments done in the lab showed it could take thousands or hundreds of thousands of years for this process to occur. In this study, it took about two years and converted 95 percent of the gas.

Another process is known as carbon capture sequester (CCS), where large amounts of CO2 are pumped and stored deep underground to slow down global warming. Once the gas is pumped into the ground, it can be stored in into depleted oil wells, but it runs the risk of escaping. With this new method, the gas is converted to stone. Previous efforts to store large amounts of CO2 in the ground using CCS have made little progress.

The entire process described in the new paper is natural, as carbon dioxide mixed with water forms a weak acid. This acid breaks down the calcium magnesium, bonds with it, and forms limestone made of calcium carbonate (not the same as sedimentary limestone). But the cost of $17 per ton may be cost-prohibitive. That’s more than a couple times more expensive than shooting CO2 into old wells using CCS.

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