CARBON DIOXIDE EMISSIONS ARE CAUSING CLIMATE CHANGE—SO RATHER THAN SENDING CO2 INTO THE SKY ICELAND IS TURNING IT INTO STONE
In conventional carbon capture and storage, CO2 is injected at high pressure into sedimentary basins in a gaseous, liquid or supercritical phase (where the liquid is at a temperature and pressure beyond the point it usually turns into a gas). An impermeable cap rock ordinarily prevents the CO2 from leaking back to the surface. But in Iceland, there is no such impermeable cap. Here, an alternative method is being developed where CO2 is dissolved in water prior to or during injection into the porous basalt rock. Dissolving the CO2 makes it less buoyant, and the CO2-charged fluid tends to sink down through the rock, lessening the risk of the CO2 escaping into the atmosphere.
In Iceland, the dissolved gas is injected into basalts and reactive rock formations at a depth of about 500m the dissolved gas is injected into basalts and reactive rock formations at a depth of about 500m where the CO2 can turn rapidly into minerals. At Hellisheiði, it takes about two years for 95% of the CO2 to be mineralised. The process can take more or less time at other sites, depending on a few factors. One is the depth at which the carbon is injected, and another is the temperature of the rock formation – the rate of the mineralisation process is generally faster at higher temperatures. Carbon Dioxide capture and storage (CCS) has a fundamental role in achieving the goals of the Paris Agreement to limit anthropogenic warming to 1.5–2?°C. Most ongoing CCS projects inject CO2 into sedimentary basins and require an impermeable cap rock to prevent the CO2 from migrating to the surface. Alternatively, captured carbon can be stored through injection into reactive rocks (such as mafic or ultramafic lithologies), provoking CO2 mineralization and, thereby, permanently fixing carbon with negligible risk of return to the atmosphere. Although in situ mineralization offers a large potential volume for carbon storage in formations such as basalts and peridotites (both onshore and offshore), its large-scale implementation remains little explored beyond laboratory-based and field-based experiments. In this Review, we discuss the potential of mineral carbonation to address the global CCS challenge and contribute to long-term reductions in atmospheric CO2. Emphasis is placed on the advances in making this technology more cost-effective and in exploring the limits and global applicability of CO2 mineralization.
- Carbon capture and storage has a key role in achieving the goals of the Paris Agreement.
- CO2 storage through mineral carbonation extends the applicability of carbon capture and storage by enabling storage in areas previously not considered feasible.
- The rapid mineralization of CO2 through injection into reactive rock formations increases storage security.
- Carbon mineralization in basaltic rocks offers a global storage potential that exceeds anthropogenic emissions.
- The method can be used for the subsurface storage of CO2, and potentially other environmentally important gases, through water capture, although this approach is water-intensive.
- Considerable efforts are needed to accelerate the deployment of CO2 storage through mineral carbonation, including more widespread operation in diverse conditions.