October 4, 2012: Time Scales of Carbonate Mineral Sequestration of CO2 in the Subsurface

Carl Steefel
Lawrence Berkeley Laboratory

Mineral trapping of CO2 in the subsurface is acknowledged to be the most secure form of sequestration, but some studies have suggested that the process is extremely slow, perhaps on the order of 10,000 years or more. But what are the arguments for these long time scales based on? Certainly part of it has to do with the slow dissolution rates of silicates needed to provide a source of cations (Ca2+, Mg2+, and Fe2+) and alkalinity for carbonate precipitation. Rates of dissolution for many silicates are very slow (e.g., albitic plagioclase and chlorite), while othersilicate minerals (anorthitic feldspar, olivine) dissolve appreciably faster. Determining which mineral is rate-limiting in the case of the faster dissolving silicates (dissolving silicate or precipitating carbonate), however, is not always straightforward without a careful analysis of dissolution and precipitation as a coupled process. We are investigating coupled dissolution and precipitation in microfluidic experiments Preliminary experiments and modeling both suggest that carbonate precipitation can be significant on the time scale of tens of years.

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