Susceptibility of Granite Rock to scCO 2 /Water at 200 o C and 250 o C DISCLAIMER Susceptibility of Granite Rock to scCO 2 /Water at 200°C and 250°C Susceptibility of Granite Rock to scCO 2 /Water at 200°C and 250°C

• Main Authors: Toshifumi Sugama, Simerjeet Gill, Lynne Ecker, Thomas Butcher, John Warren, Daniel Bour
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Carbonic acid
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1081.4566

Abstract Granite rock comprising anorthoclase-type albite and quartz as its major phases and biotite mica as the minor one was exposed to supercritical carbon dioxide (scCO 2 )/water at 250°C and 13.78 MPa pressure for 104 hours. For comparison purpose, four other rocks, albite, hornblende, diorite, and quartz, also were exposed. During the exposure of granite, ionic carbonic acid, known as the wet carbonation reactant, preferentially reacted with anorthoclase-type albite and biotite, rather than with quartz. The susceptibility of biotite to wet carbonation was higher than that of anorthoclase-type albite. All the carbonation by-products of anorthoclase-type albite were amorphous phases including Na-and K-carbonates, a kaolinite clay-like compound, and silicon dioxide, while wet carbonation converted biotite into potassium aluminum silicate, siderite, and magnesite in crystalline phases and hydrogen fluoride (HF). Three of these reaction by-products, Naand K-carbonates and HF, were highly soluble in water. Correspondingly, the carbonated top surface layer, about 1.27 mm thick as carbonation depth, developed porous microstructure with numerous large voids, some of which have a size of ≥ 10 µm, reflecting the erosion of granite by the leaching of these water-soluble reaction byproducts. Comparing with this carbonation depth, its depth of other minerals was considerable lower, particularly, for hornblende and diorite with 0.07 and 0.02 mm, while no carbonate compound was detected in quartz. The major factor governing these low carbonation depths in these rocks was the formation of water-insensitive scale-like carbonate by-products such as calcite (CaCO 3 ), siderite (FeCO 3 ), and magnesite (MgCO 3 ). Their formation within the superficial layer of these minerals served as protective barrier layer that inhibits and retards further carbonation of fresh underlying minerals, even if the exposure time was extended. Thus, the coverage by this barrier layer of the non-carbonated surfaces of the underlying rock was reason ...