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How it works

Trees and vegetation not only bind carbon from the atmosphere. Huge quantities of carbon are naturally stored in rocks. Carbfix imitates and accelerates natural processes, in which carbon dioxide is dissolved in water and interacts with reactive rock formations to form stable minerals providing a permanent and safe carbon sink. Carbfix dissolves CO2 in water, injects it into the subsurface and turns it into stone in less than two years through proprietary technology. For the Carbfix technology to work, one needs three things: favourable 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 the rock underground and elements such as calcium, magnesium and iron are released into the water. With time, these elements will combine with the dissolved CO2 and form carbonates filling up the empty space in the rocks underground. The carbonates are stable for thousands of years and can thus be considered permanently stored. The timescale of this process initially surprised the scientists. In the CarbFix pilot project, it was determined that at least 95% of the injected CO2 mineralises within two years, much faster than previously thought.

The injected carbonated water is both colder and has higher density than the surrounding water in the geological formation and therefore has the tendency to sink after it has been injected. This is in contrast with other more conventional methods of carbon capture and storage which depend on a layer of cap rock to prevent possible leakage of gaseous CO2 injected into deep formations. Young basaltic rocks are very fractured and porous so that water seeps easily through the interconnected cracks and empty spaces underground.

Detailed description can also be found in our scientific papers.

WHY IS MINERALIZATION SO QUICK?

Dissolution of CO2 prior to or during injection ensures that chemical reactions between host rock and injected fluid begin to take place immediately after injection. The high reactivity and chemical composition of the basaltic host rock (up to 25% by weight of calcium, magnesium and iron that can combine with the injected CO2 to form stable carbonate minerals) play an even larger role in the efficiency of permanent mineral storage in basalts.

WHAT IS SO SPECIAL ABOUT BASALTS?

Basaltic rocks are highly reactive and contain the elements needed for permanently immobilizing CO2 through the formation of carbonate minerals. They are often fractured and porous, containing storage space for the mineralized 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. 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 can also do the job. 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 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 evaluation of CO2 mineralization through mass balance calculations. The mineralization has also been quantified using different isotopes.

A recent review article by our team in Nature Reviews summarizes the science and the current state of play of mineral carbonation.