Scientists at the University of Strathclyde have discovered that crushing rock in carbon dioxide can result in trapping CO2 in a stable, insoluble form, thus reducing emissions.
A paper published in Nature Sustainability says that almost no additional energy would be required to trap the CO2.
The materials and construction industry accounts for 11% of global carbon emissions. More than 50 billion tonnes of rock is crushed worldwide every year and current crushing processes – standard in construction and mining – do not capture CO2.
Previous work has explored trapping carbon into single minerals by the same method, but the research at the University of Strathclyde shows this is unstable and dissolves out of the mineral when placed in water. The paper documents how a larger proportion of carbon dioxide can be trapped in a stable, insoluble form in rocks composed of multiple different minerals by grinding it in CO2 gas. The resulting rock powders can then be stored and used in the environment for construction and other purposes.
The abstract for the paper, called Mechanochemical processing of silicate rocks to trap CO2, reads: “Polymineralic rocks such as granite and basalt, whether high or low in carbonate-forming metals, are more efficient at trapping CO2 than individual minerals. This is because the trapping process is not, as previously thought, based on the carbonation of carbonate-forming metals. Instead, CO2 is chemically adsorbed into the crystal structure, predominantly at the boundaries between different minerals. Leaching experiments on the milled mineral/rock powders show that CO2 trapped in single minerals is mainly soluble, whereas CO2 trapped in polymineralic rocks is not. Under ambient temperature conditions, polymineralic rocks can capture >13.4 mgCO2 g−1 as thermally stable, insoluble CO2. Polymineralic rocks are crushed worldwide to produce construction aggregate. If crushing processes could be conducted within a stream of effluent CO2 gas (as produced from cement manufacture), our findings suggest that for every 100 Mt of hard rock aggregate sold, 0.4–0.5 Mt CO2 could be captured as a by-product.”
Principal investigator Rebecca Lunn, a professor in the University of Strathclyde’s Department of Civil & Environmental Engineering, said: “The hope is that the sector could reduce the emissions by adapting the current setups to trap carbon from polluting gas streams such as those from cement manufacture or gas-fired power stations.”
“If the technology was adopted worldwide in aggregate production, it could potentially capture 0.5% of global CO2 emissions – 175 million tonnes of carbon dioxide annually. Future research can pin this down, as well as optimise the process to trap more carbon.”
Co-investigator Dr Mark Stillings said: “Now we know that CO2 trapping in most hard rock can be done in a lab, we need to optimise the process and push the limits of how much can be trapped through the crushing technique. We then need to understand how this process can be scaled up from the lab to industry, where it can reduce global CO2 emissions.
“If this process was applied, the CO2 footprint associated with building houses and public infrastructure could be greatly reduced, helping to meet global objectives to combat climate change.”
Professor Lunn added: “In the future, we hope that the rock used in concrete to construct high-rise buildings and other infrastructure such as roads, bridges and coastal defences will have undergone this process and trapped CO2, which would otherwise have been released into the atmosphere and contributed to global temperature rise.”
The work was part-funded by the Engineering & Physical Sciences Research Council, whose deputy director Dr Lucy Martin said: “This breakthrough research from the University of Strathclyde, which EPSRC has proudly played a part in funding, is truly revelatory. It points to a new process for the construction industry that could significantly reduce global carbon emissions and help us meet our net zero goals.”