1. Why mineralogical storage of CO2?
In geological CO2 storage, CO2 is stored in deep underground formations, such as depleted oil and gas reservoirs and deep saline aquifers. Oil and gas reservoirs have naturally stored CO2 and other gases and fluids for millions of years without significant leakage. However, nothing is absolutely sure. Therefore, mineralogical CO2 storage is aimed at permanently storing CO2 in form of carbonate minerals. By bringing CO2 to its thermodynamic ground state, which is a carbonate mineral, potential health, safety and environmental risks are minimized.
2. Why basalt and why Iceland?
Basaltic rocks are one of the most reactive rock types of the Earth’s crust. Basaltic rocks contain reactive minerals and glasses with high potential for CO2 sequestration. More than 90% of Iceland is made of basalt. The process where CO2 from solidifying magma reacts with calcium from the basalt and forms calcite, occurs naturally and the mineral is stable for thousands of years in geothermal systems. Chemical weathering of basalts at the surface of the Earth is another example of carbon fixation in nature. The proposed experiment will aim at accelerating these natural processes.
3. What happens chemically when the injected CO2 enters the basaltic bedrock?
CO2 dissolves into the groundwater and the pH of the groundwater decreases as a first consequence of injedting CO2. This low pH groundwater leads to a large number of coupled chemical reactions including the dissolution of basalt which both neutralizes the acidic groundwater and leads to the precipitation of stable carbonate minerals and thus the permanent storage of the injected CO2.
4. How fast is the CO2 mineralization in the lab vs. field?
In the lab, McGrail et al. (2006) showed that exposing basalt samples from the Columbia River Basalt (USA) to CO2-saturated water yielded calcium carbonate mineral formation in four to six weeks and extensive mineralization within several months. The CO2 mineralization rate in the field is unknown today. This is the main motivation for the CarbFix project, to conduct the field injection experiment and to monitor the CO2 mineralization rate in situ in the field.
5. How do we know that the CO2 injected will stay captured and not leak into the atmosphere?
The injected CO2 will be monitored and the storage safety will be verified by a set of technologies. These monitoring technologies (e.g. CO2 detectors, soil gas analysis, seismic survey, pressure monitoring, geochemical tracers in groundwater etc.) are critical to measure the amount of CO2 stored at a specific sequestration site, to monitor potential leaks, to track the location of the underground CO2 plume, to detect chemical reaction between CO2, groundwater and rocks, and to verify that the CO2 is stored in a permanent way.
6. What is the status of CO2 mineral storage in the world, is it only happening in Iceland?
Iceland is the ideal place to develop the technology to store CO2 in the subsurface as stable carbonate minerals for several reasons including:
1) Iceland is made up of basalt, a rock that contains abundant divalent metal cations, such as Ca (calsium), Fe (iron) and Mg (magnesium), which are the building blocks for making stable carbonate mineral.
2) Iceland is among the few countries that has the scientific and engineering know-how, due to their long experience in geothermal energy to perform a successful field scale test and develop the technology to export the new technology developed from the CarbFix program.
Besides the CarbFix project in Iceland, the Big Sky Regional Partnership, one of the seven U.S. Department of Energy partnerships for carbon capture and sequestration, is conducting a CO2 injection pilot test in the Columbia River Basalt in NW of the United States to study the in situ mineralization of CO2 (http://www.bigskyco2.org/).
7. Where are the good mineralogical CO2 storage sites?
The mineralization of CO2 requires the availability of divalent cations such as Ca (calsium) , Mg (magnesium), and Fe (iron). Basaltic and peridiotic rocks consist of minerals rich in Ca, Mg and Fe and are therefore ideal for mineralogical storage of CO2. Basalt is the one of the common rock type in Earth’s crust. Over 10% of the continental crust is made up of basalts. Perhaps even more exciting is that most continents are surrounded by massive basalt formations (oceanic crust), just offshore, providing local CO2 storage sites easily accessible for most countries. Basalt formations onshore and offshore together have sufficient storage capacity to contain all human produced CO2 for the foreseeable future.