Carbon Storage in the Earth's Crust
Calcium and magnesium silicon oxides, which are prevalent in certain rocks (like wollastonite, olivine, or serpentine), react spontaneously with CO2 to produce mineral carbonates such as limestone (CaCO3) or magnesium carbonate (MgCO3) in a process known as natural mineral carbonation. Mineral carbonates offer long-term storage because they are stable under ambient temperatures and pressures and can serve as construction materials or as fillers in abandoned mines. To fix a metric ton of CO2 into carbonates requires between 1.6 metric tons and 3.7 metric tons of silicon oxide rock. [1] Nonetheless, Earth’s crust contains more than enough of these silicon oxides to react with all of the CO2 released from combusting the planet’s entire reserves of fossil fuels. Natural mineral carbonation, however, is prohibitively slow.
Accelerating this process to acceptable rates involves mining rocks containing silicon oxides, crushing and grinding them into a powder, and removing impurities (e.g., iron compounds, via magnetic extraction). The silicon oxide powder is then dissolved in a mild acid solution, and CO2 is bubbled through the solution at high temperature and pressure (approximately 185°C and 15 MPa). The reaction forms particles that are smaller in size than the original silicon oxide particles. Finally, the process sieves the fine carbonate particles from the larger silicon oxide particles, disposes of the carbonates, and returns the unreacted silicon oxides to the reaction vessel.
These procedures consume 30% to 50% of the energy generated by a power plant. [1] Together with the 10% to 30% energy penalty for CO2 capture, a power plant equipped CO2 capture and storage (CCS) capability via mineral carbonation expends nearly double the energy for operations than a plant without CCS. As a result, costs for mineral carbonation CCS are several times that of other methods, explaining why mineral carbonation CCS has yet to be implemented on a commercial scale.
Other carbon dioxide storage methods include pumping CO2 into the ocean and burying CO2 in deep geological formations.
[1] IPCC (2005) IPCC Special Report on Carbon Dioxide Capture and Storage prepared by Working Group III of the Intergovernmental Panel on Climate Change, Metz, B., O. H. Davidson, C. de Coninck, M. Loos, and L. A. Meyer, eds. Cambridge University Press, New York.
This is an excerpt from the book Global Climate Change: Convergence of Disciplines by Dr. Arnold J. Bloom and taken from UCVerse of the University of California.
©2010 Sinauer Associates and UC Regents
