Cement production (shown) accounts for a fourth of the world’s carbon emissions. But a new technique using seawater splitting might make its production carbon-negative.
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A new cement-making process could shift production from being a carbon source to a carbon sink, creating a carbon-negative version of the building material, researchers report March 18 in Advanced Sustainable Systems. This process might also be adaptable to producing a variety of carbon-stashing products such as paint, plaster and concrete.
Cement production is a huge contributor to global carbon dioxide emissions, responsible for about 8 percent of total CO2 emissions, making it the fourth-largest emitter in the world. Much of that carbon comes from mining for the raw materials for concrete in mountains, riverbeds and the ocean floor.
So, researchers at Northwestern University in Evanston, Ill., partnered with cement manufacturer Cemex’s innovation development branch, located in Brügg, Switzerland, to develop a “greener” cement.
The team used seawater electrolysis, a technique that zaps seawater with electricity to split its molecules. The process generates hydrogen gas, chlorine gas and oxygen, and also produces some minerals, including calcium carbonate, the primary raw material for cement manufacture.
Researchers who use seawater electrolysis for hydrogen gas production have found those precipitated minerals to be an annoyance, because they can clutter up the electrolysis equipment, says Northwestern environmental engineer Alessandro Rotta Loria. But that mineral production might be a feature, not a bug, when it comes to sustainable cement production.
The rate of electrolysis-based mineral production is too slow to meet industrial demand. So Rotta Loria and his colleagues investigated in the laboratory how these minerals form during electrolysis and whether it’s possible to expedite the process and increase the yield.
In their experiments, the team inserted their electrodes into seawater. They then adjusted the applied voltage and injected carbon dioxide gas into the water at different rates and volumes to fine-tune the water’s pH. Varying these factors turned out to change the volumes, chemical compositions and crystal structures of the precipitating minerals, making them flakier or more porous or denser.
These experiments suggest it’s possible to tailor seawater electrolysis to make a variety of minerals and aggregates that the construction industry could use, the team says. And, if the energy source for the electricity is renewable, these materials could be not just carbon-neutral, but carbon-negative — trapping some of the atmosphere’s carbon dioxide for up to thousands of years.
