Researchers have designed a new system to capture carbon dioxide from shipping exhaust after studying how limestone naturally dissolves in the ocean
Ships could capture their own carbon dioxide emissions by bubbling exhaust through seawater and limestone, then pouring the water back into the ocean. This could save space and energy compared with other systems, but it is unclear what the environmental impacts might be.
The system takes advantage of a natural reaction between CO2 and calcium carbonate, also known as limestone. “The ocean has been running exactly this reaction for billions of years,” says Jess Adkins at Calcarea, the start-up behind the technique.
When seawater absorbs CO2, it becomes acidic enough to break down limestone. The dissolved rock then reacts with CO2 in the water to form bicarbonate minerals, which can remain stable in the ocean for millennia. This is one of the primary ways the planet removes CO2 from the atmosphere over long timescales.
For decades, Adkins and his colleagues studied how this dynamic affects organisms with shells or skeletons made of calcium, like corals, as the oceans become more acidic due to rising levels of atmospheric CO2. They realised that speeding up the rate at which limestone dissolved would transform more CO2 into stable bicarbonate – and one way to do this was to increase the concentration of carbon dioxide exposed to limestone. “You can make [the reaction] go an order of magnitude faster if you use pure CO2,” says Adkins.