The construction industry crushes about 50 million metric tons of rock every year for various uses. If done in the presence of carbon dioxide gas, this common activity could capture 0.5 percent of global carbon dioxide emissions, a new study suggests.
The paper published in Nature Sustainability suggests that this would require almost no additional energy. And the amount of carbon captured would be equivalent to planting a forest the size of Germany.
The construction industry today creates 11 percent of global carbon emissions. If the industry would conducted rock-crushing in a stream of carbon dioxide gas, such as that produced from cement manufacture, it would drastically reduce the carbon footprint of buildings and infrastructure, researchers from the University of Strathclyde in Glasgow, UK write in the paper.
Rocks naturally trap carbon dioxide. When rain absorbs carbon dioxide from the atmosphere and becomes slightly acidic lands on rocks, it gradually breaks down the rock and reacts with minerals in the rocks that are rich in calcium and magnesium, forming carbonate. The carbonate minerals permanently lock up carbon dioxide.
A few companies and organization are trying to speed up this process. Some are injecting carbon dioxide into suitable rock formations where they will turn into carbonate minerals. Others are crushing basalt rock and spreading it on forests and farmlands. Recent studies have found that spreading rock dust—a byproduct of mining—on farmland could soak up two billion tons of carbon dioxide from the air every year, and almost half the carbon dioxide required to help the UK meet its 2050 net-zero targets.
Some studies have also explored milling pure calcium- or magnesium-rich minerals to trap carbon dioxide. But those reactions are slow, so researchers have tried to speed things up by adding heat.
In the new work, researchers from the University of Strathclyde show that milling granite and basalt, which have multiple minerals in them, traps carbon dioxide more efficiently. The researchers crushed two rock samples at room temperature in the presence of pure carbon dioxide. They found that each gram of basalt and granite can capture up to 15.4 and 13.9 milligrams of carbon dioxide respectively.
But at the end, they did not detect any carbonate minerals in the rock samples. This implies that carbon trapping is happening via a different mechanism. With further investigation, they found that the carbon dioxide is being taken up at the boundaries between the crystals of the different minerals.
Unlike the carbon dioxide captured on pure minerals, which can dissolve in water, the gas trapped in the crushed rocks is more stable. The carbon dioxide-laced milled rocks can be stored and then used for construction and other purposes.
“If the technology were adopted worldwide in [crushed rock] production, it could potentially capture 175 million tons of carbon dioxide annually,” said Strathclyde professor of civil and environmental engineering Rebecca Lunn in a press release. “Future research can pin this down, as well as optimize the process to trap more carbon.”
Source: Mark Stillings et al, Mechanochemical processing of silicate rocks to trap CO2, Nature Sustainability, 2023.
Image by PublicDomainArchive from Pixabay