HR: 1340h
AN: B33A-1017    [Abstracts]
TI: Inhibited Carbonate Precipitation in Seawater Allows Carbon Dioxide Storage as Carbonate Alkalinity
AU: * Rau, G H
EM: rau4@llnl.gov
AF: IMS/UCSC, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Caldeira, K
EM: kcaldeira@globalecology.stanford.edu
AF: Carnegie Inst., 260 Panama Street, Stanford, CA 94305 United States
AB: As we have previously described, contacting flue gas (from fossil fuel combustion) with water and limestone presents a simple way of spontaneously reacting CO₂ out of point-source waste gas streams to form a bicarbonate-rich solution via the reaction: CO₂ + CaCO₃ + H₂O <--> Ca²⁺ + 2HCO₃^-. This process, we term Accelerated Weathering of Limestone (AWL), can provide a low-tech, inexpensive, high-capacity, environmentally friendly CO₂ capture and sequestration technology in locations where limestone and abundant water are in close proximity to CO₂ sources. Coastal locations are especially attractive because the ocean provides a source of water as well as a receptacle for the resulting bicarbonate solution. However, as evident in the preceding equation, the reaction will be driven to the right and hence excess bicarbonate will theoretically remain in solution only so long as excess CO₂ is present. If the solution's excess CO₂ is allowed to contact and thus degas to the atmosphere, carbonate ions will become supersaturated and solid carbonate will precipitate, thus reversing the original reaction and the CO₂ mitigation potential of the process. Yet in the case of seawater, an important caveat is that carbonate precipitation is chemically hindered by the presence of phosphate, organic compounds, magnesium ions, and possibly other solutes. Indeed, the surface ocean is typically 6X supersaturated in calcite and 4X in aragonite, and it has been experimentally shown that seawater can tolerate >18X supersaturation before carbonate precipitation is chemically initiated. This means that: i) a substantial fraction of AWL-captured and -converted carbon will stay in solution in the form of carbonate alkalinity even if the solution's CO₂ is fully equilibrated with the atmosphere, ii) significant CO₂ mitigation can be achieved regardless of depth or location of solution disposal in the ocean, and iii) the resulting elevation in solution pH following CO₂ degassing would be helpful in offsetting the ongoing ocean acidification via passive anthropogenic CO₂ invasion, and could also enhance marine biotic calcification.
DE: 0428 Carbon cycling (4806)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 4806 Carbon cycling (0428)
DE: 4835 Marine inorganic chemistry (1050)
SC: Biogeosciences [B]
MN: Fall Meeting 2005