How it works
Trees and vegetation are not the only form of carbon drawdown from the atmosphere. Vast quantities of carbon are naturally stored in rocks. Carbfix imitates and accelerates these natural processes, where carbon dioxide is dissolved in water and interacts with reactive rock formations, such as basalts, to form stable minerals providing a permanent and safe carbon sink. The Carbfix process captures and permanently removes CO2. The technology provides a complete carbon capture and injection solution, where CO2 dissolved in water – a sparkling water of sorts – is injected into the subsurface where it reacts with favorable rock formations to form solid carbonate minerals via natural processes in about 2 years. For the Carbfix technology to work, one needs to meet three requirements: favorable rocks, water, and a source of carbon dioxide.
Carbonated water is acidic. The more carbon you can pack into water, the more acidic the fluid will become. Carbfix's carbonated water reacts with rocks underground and releases available cations such as calcium, magnesium and iron into the water stream. Over time, these elements combine with the dissolved CO2 and form carbonates filling up the empty space (pores) within the rocks. The carbonates are stable for thousands of years and can thus be considered permanently stored. The timescale of this process initially surprised scientists. In the CarbFix pilot project, it was determined that at least 95% of the injected CO2 mineralizes within two years, much faster than previously thought.
The injected carbonated water is denser than the surrounding water in the geological formation and therefore has the tendency to sink after it has been injected. This differs from more conventional methods of carbon capture and storage, which depend on cap rock to prevent possible leakage of gaseous CO2 injected into deep formations. Young basaltic rocks are highly fractured and porous such that water seeps easily through the interconnected cracks and empty spaces underground.
Detailed description can also be found in our scientific papers.
Why is mineralisation so quick?
Dissolution of CO2 prior to or during injection ensures that chemical reactions between the host rock and injected fluid take place immediately after injection. The high reactivity and chemical composition of the basaltic host rock (up to 25% of the weight of calcium, magnesium and iron) can combine with the injected CO2 to form stable carbonate minerals, efficiently and permanently storing emissions as minerals within basaltic rocks.
What is so special about basalts?
Basaltic rocks are highly reactive and contain the elements needed for permanently immobilising CO2 through the formation of carbonate minerals. They are often fractured and porous, containing storage space for the mineralised CO2. Furthermore, basalt is the most common rock type on the surface of Earth, covering ~5% of the continents and most of the oceanic floor. Check out our mineral storage atlas to see where it works.
It has been estimated that the active rift zone in Iceland could store over 400 Gt CO2 (400 billion tonnes CO2). The theoretical storage capacity of the ocean ridges is significantly larger than the estimated 18,500 Gt CO2 stemming from the burning of all fossil fuel carbon on Earth. The question remains, how much of this theoretical storage capacity is feasible to use for mineral storage of CO2.
The pore space, chemical composition, and wide distribution of basalts makes it the perfect candidate to develop the Carbfix process. However, other reactive rocks such as andesites, peridotites, breccias and sedimentary formations containing calcium, magnesium and iron rich silicate minerals could also be suitable. Studies on the storage suitability of these rocks are mainly undertaken in the related GECO project.
How is mineralization measured?
The mineralization of the injected gases has been proven and is observed using tracers and by following geochemical signals, both of which are monitored by the sampling of fluids from wells in the vicinity of the injection point. Known amounts of tracers and known amounts of CO2 are injected into the injection well. Measured tracer concentration and chemical composition in monitoring wells enable the evaluation of CO2 mineralization through mass balance calculations. The mineralization has also been quantified using different isotopes.
Is it possible to use seawater?
Carbfix has developed the scientific basis for using seawater to dissolve CO2, prior to injection, thus expanding the applicability of the technology to water scarce regions, coastal and offshore areas. Reaction path modelling and laboratory studies have showed the use of seawater instead of fresh water. A field site demonstration of mineral storage using seawater will follow in 2022: Project CO2-Seastone.
A recent review article by our team in Nature Reviews summarizes the science and the current state of play of mineral carbonation.
The legal framework for the capture and injection of CO2 underground in Icelandic ground, including the Carbfix technology, is in accordance with directive 2009/31/EC on the geological storage of carbon dioxide, that has been implemented into Icelandic law (Act No 7/1998, with later amendments).