Evidence for Carbonate Surface Complexation during Forsterite Carbonation in Wet Supercritical Carbon Dioxide

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• 作者：John S. Loring ; Jeffrey Chen ; Pascale B茅n茅zeth ; Odeta Qafoku ; Eugene S. Ilton ; Nancy M. Washton ; Christopher J. Thompson ; Paul F. Martin ; B. Peter McGrail ; Kevin M. Rosso ; Andrew R. Felmy ; Herbert T. Schaef
• 刊名：Langmuir
• 出版年：2015
• 出版时间：July 14, 2015
• 年：2015
• 卷：31
• 期：27
• 页码：7533-7543
• 全文大小：629K
• ISSN：1520-5827

文摘

Continental flood basalts are attractive formations for geologic sequestration of carbon dioxide because of their reactive divalent-cation containing silicates, such as forsterite (Mg₂SiO₄), suitable for long-term trapping of CO₂ mineralized as metal carbonates. The goal of this study was to investigate at a molecular level the carbonation products formed during the reaction of forsterite with supercritical CO₂ (scCO₂) as a function of the concentration of H₂O adsorbed to the forsterite surface. Experiments were performed at 50 掳C and 90 bar using an in situ IR titration capability, and postreaction samples were examined by ex situ techniques, including scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), focused ion beam transmission electron microscopy (FIB-TEM), thermal gravimetric analysis mass spectrometry (TGA-MS), and magic angle spinning nuclear magnetic resonance (MAS NMR). Carbonation products and reaction extents varied greatly with adsorbed H₂O. We show for the first time evidence of Mg-carbonate surface complexation under wet scCO₂ conditions. Carbonate is found to be coordinated to Mg at the forsterite surface in a predominately bidentate fashion at adsorbed H₂O concentrations below 27 渭mol/m². Above this concentration and up to 76 渭mol/m², monodentate coordinated complexes become dominant. Beyond a threshold adsorbed H₂O concentration of 76 渭mol/m², crystalline carbonates continuously precipitate as magnesite, and the particles that form are hundreds of times larger than the estimated thicknesses of the adsorbed water films of about 7 to 15 脜. At an applied level, these results suggest that mineral carbonation in scCO₂ dominated fluids near the wellbore and adjacent to caprocks will be insignificant and limited to surface complexation, unless adsorbed H₂O concentrations are high enough to promote crystalline carbonate formation. At a fundamental level, the surface complexes and their dependence on adsorbed H₂O concentration give insights regarding forsterite dissolution processes and magnesite nucleation and growth.