What is carbon capture and storage (CCS)?
CCS broadly refers to technologies that can capture and store carbon dioxide to mitigate climate change. Mitigation can happen in one of two ways- preventing emissions from entering the atmosphere by capturing CO2 from emissions sources and storing it permanently, or removing CO2 directly from the atmosphere and storing it. The latter pathway is referred to as carbon dioxide removal (CDR).
The only way to combat human-caused climate change is to drastically cut emissions and decarbonize immediately.
The IPCC reports since 2018 have been crystal clear: to meet the goals of the Paris Agreement, we need a zero-emissions world AND we need massive amounts of CDR. CCS can help prevent emissions while we decarbonize globally, and CDR is needed to remove “legacy carbon” that we’ve already put into the atmosphere. There is a wide variety of CDR approaches being developed, and frankly we need all of them. Basalt weathering is currently being researched in two main ways as a method to remove and store atmospheric carbon dioxide.
1. Enhanced weathering.
Part 1 of the long-term carbon cycle is the basis for enhanced rock weathering, which generally involves the crushing of basaltic rocks or the mafic minerals within these rocks (such as olivine) and dispersing the powder either in terrestrial (e.g., agricultural soils) or coastal settings. By crushing rocks, reactive mineral surfaces are exposed, and weathering can proceed much faster than it would naturally. Because agricultural soils have high CO2 concentrations (and we learned above that elevated CO2 levels accelerates weathering), croplands are being researched as enhanced weathering sites, and there may be co-benefits beyond CO2 drawdown. Enhanced weathering draws down atmospheric CO2, and it enters rivers as bicarbonate, that eventually flows into the oceans where Part 2 proceeds naturally. Additionally, lots of waste materials from industrial operations are rich in divalent cations needed for CO2 mineralization, thus there is an active area of research on the subject of repurposing mine tailings for carbon removal and mineralization. Because the weathering reactions are being accelerates at the surface Earth, these technologies are often referred to as “ex-situ”. Ex-situ technologies aren’t limited to enhanced weathering, but rather many researchers have come up with innovative ways to leverage weathering and precipitation reactions to both draw CO2 out of the air to be stored elsewhere, as well as directly precipitate carbonate minerals from atmospheric CO2 for permanent storage.
2. Mineral Carbonation.
Unlike enhanced weathering, mineral carbonation of basalts is a carbon storage technology, not a carbon removal. It is important to note that a “removal” constitutes drawdown from the atmosphere PLUS permanent storage. Some technologies, like enhanced weathering and ex-situ mineralization, both remove and store in one step. Other CDR technologies such as Direct Air Capture (DAC), need somewhere to put the CO2 once it’s captured. Capturing CO2 from emissions sources also relies on access to storage. Mineral carbonation, or in-situ mineralization, is a geologic carbon storage technique where captured CO2 is injected underground into basaltic rocks. Chemical weathering (Part 1) dissolves the basaltic minerals in the subsurface, and causes the subsequent precipitation carbonate minerals (Part 2) underground. Mineral carbonation combines Part 1 and Part 2 of the long term carbon cycle, and mineralizes the carbon into a solid form. Because the carbon is eventually stored as a mineral (aka “mineralization” or “mineral storage/trapping”), this method of carbon storage is durable and secure. Mineral carbonation has been proven to be successful in two pilot field studies, and when scaled, mineral carbonation can serve as a leading carbon storage method.
One Icelandic company, founded by scientists who pioneered mineral carbonation, is already actively turning CO2 into stone. CarbFix has a fantastic website where you can extensively learn about mineral carbonation, how and where it works, and the potential scalability of their method as a major solution to climate change. The CarbFix method uses fresh water and CO2, where CO2 is dissolved into water (essentially the same way that soda is carbonated), and the CO2-charged water is injected into the basaltic subsurface. This method requires about ~25 tons of water per ton of CO2 stored, but is very effective at rapid mineralization. Water availability is an obvious limitation to scaling mineral carbonation to gigaton/year scales, which is the absolute minimum of what is needed to reverse climate change (again, in combination with drastic emission reductions). Seawater has been proven to be effective in experimental settings, and CarbFix is gearing up to test it in the field.
In order to reach massive scales, we need to find a way to inject supercritical CO2 as opposed to dissolved. At Cella, we are developing a novel technology for in-situ mineralization that incorporates the injection of pure-phase CO2.The Wallula Basalt Pilot Project in Washington, USA, demonstrated a successful injection of supercritical CO2 into basalt, and our technology is building on what’s known to design a new injection method that optimizes mineralization during scaled injections, cuts water demand, and lowers cost. The entire ocean floor is made of basalt, and Cella’s method is ideal for offshore injections, paving the way towards accessing the limitless storage capacity of offshore reservoirs.
Photo of the Hellisheiði geothermal power plant in Iceland, where the first CarbFix projects are in operation. Photo source: CarbFix.