Structure and Dynamics of Forsterite-scCO2/H2O Interfaces as a Function of Water Content

Journal Article · Tue May 01 04:00:00 EDT 2012 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/j.gca.2012.01.038· OSTI ID:1039834

Kerisit, Sebastien N; Weare, John H; Felmy, Andrew R

Molecular dynamics (MD) simulations of forsterite surfaces in contact with supercritical carbon dioxide (scCO2) fluids of varying water content were performed to determine the partition of water between the scCO2 fluid and the mineral surface, the nature of CO2 and H2O bonding at the interface, and the regions of the interface that may be conducive to HxCO3(2-x)- formation. Calculations of the free energy of the associative adsorption of water onto the (010) forsterite surface from the scCO2 phase indicated that the formation of a water film up to three-monolayer thick can be exothermic even for water contents below the water saturation concentration of the scCO2 fluid. In MD simulations of scCO2/H2O mixtures in contact with the (010) forsterite surface, H2O was found to readily displace CO2 at the surface and, therefore, CO2 directly contacted the surface only for water coverages below two monolayers. For thicker water films, a two-monolayer hydration layer formed that CO2 could not penetrate. Simulations of the hydroxylated (010) surface and of the (011) surface suggested that this conclusion can be extended to forsterite surfaces with different surface structures and/or compositions. The density, diffusion, and degree of hydration of CO2 as well as the extent of CO2/H2O mixing at the interface were all predicted to depend strongly on the thickness of the water-rich film, i.e., on the water content of the scCO2 fluid.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1039834
• Report Number(s): PNNL-SA-81856; 39937; KC0303020
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Vol. 84; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ADSORPTION
BONDING
CARBON DIOXIDE
DIFFUSION
Environmental Molecular Sciences Laboratory
FREE ENERGY
HYDRATION
MIXTURES
THICKNESS
WATER
WATER SATURATION