New geochemical simulations suggest that it is possible to sequester carbon dioxide in the Earth’s crust at a scale that would bring down global atmospheric concentrations of CO2, according to researchers at the University of Calgary.
Their research, conducted as part of the PICS Solid Carbon feasibility study, explores the consequences of directly injecting large quantities of captured CO2 into basalt aquifers that underlie the world’s oceans.
Previous pilot-scale field studies in Iceland have shown that vast basalt aquifers under the oceans are capable of storing CO2 in a durable mineral form through basalt carbonation – a process whereby CO2 is injected into porous, permeable sub-seafloor basalt, where it then reacts with minerals (calcium, magnesium and iron silicates) and forms a solid carbonate rock. Laboratory studies have found that by controlling the alkalinity and temperature of CO2-charged solutions, mineralization can be achieved in as little as just a few hours or days.
A new series of thermodynamic calculations and basalt dissolution simulations demonstrate that gigaton (Gt)-scale carbon dioxide storage is possible without such rigorous controls, even eliminating the onerous extra step of dissolving captured CO2 in huge quantities of water, according to the article in the journal Environmental Science & Technology, Alkalinity Generation Constraints on Basalt Carbonation for Carbon Dioxide Removal at the Gigaton-per-year Scale.
Lead author and UCalgary Associate Professor Benjamin Tutolo says very quick mineralization – which is water-intensive, costly, and difficult to scale up – may be unnecessary. He says their simulations demonstrate Gt-scale carbon mineralization, “if basalts are given time to react.”
“It’s not going to be incredibly fast the way it has worked in Iceland, but the reaction needn’t be completed in days or even months as long as the CO2 doesn’t escape before the process is complete, even if it takes centuries”, he said. Aquifers beneath the ocean floor are typically topped with more than 300 metres of “very impermeable” sediment, and residence times of water in these aquifers are inferred to be on the order of thousands or tens of thousands of years.
Siting CO2 mineralization projects offshore – think ocean-based platforms that combine direct air capture and injection - would enable exploitation of the vast quantity of sub-seafloor basalts, with the theoretical capacity to store 100,000 to 250,000 gigatons of CO2.
“The unique and awesome thing about this technology is that basalts are everywhere,” said Dr. Tutolo. “If this technology can be proven via a pilot program at sea, the capacity is far more than we could ever need.”
Building on the work published in this study, the Solid Carbon researchers are currently studying further aspects of large-scale CO2 injection into oceanic basalts; devising monitoring strategies, and the possibility of technologies such as water-alternating-gas injection to speed up mineralization.
This research was supported by the PICS Solid Carbon Theme Partnership, and the Natural Sciences and Engineering Research Council of Canada (NSERC).
Animations of Solid Carbon’s proposed technology can be viewed at solidcarbon.ca
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The climate significance of this research
Human activity adds around 51 gigaton (Gt) of GHGs to the atmosphere each year, driving us toward tipping points at which dire consequences of climate change will be inevitable.
Climate scenarios that keep global warming within the 2 degrees Celsius upper limit of the Paris Agreement rely on large-scale CO2 removal and sequestration.
Crucially, NETs such as Solid Carbon do not replace the need for urgent emissions reductions but are needed alongside deep decarbonization if we are to limit average global temperature increase to 1.5 degrees Celsius above pre-industrial levels.