斜長石-CO_2反応による地中固定化の実験的研究

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Experiments on CO2-water-rock interaction at hydrothermal conditions have been performed to investigate mineral dissolution and precipitation phenomena, mainly focusing on calcite deposition from the alteration of plagioclase and rocks during CO2 sequestration into geothermal fields. Plagioclase from Shiga and granodiorite from the Ogachi hot/dry rock field (7 g; grain size is 0.5 to 2 mm) were independently enclosed with Kyoto tap water in a Teflon reaction container. The container is filled with CO2 (10 MPa) or N2 gas after evacuating and heated up to 150 °C in an electric furnace with rotation (1 rpm). After 1 to 15 days, the solutions were analyzed for their chemical compositions after filtration and the mineral surfaces were observed by using SEM-EDS. The concentration of Ca in the solutions reacted with CO2 quickly increases within 1 day and is+∼50 mg/L higher than those without CO2 (with N2 gas). The saturation index shows that the solutions with CO2 are saturated with respect to carbonate such as calcite and aragonite during the reaction. Newly formed calcium carbonate (possibly calcite) was detected by SEM-EDS observation on the plagioclase surfaces, but the other minerals such as kaolinite were not. These results indicate that Ca can be released from rocks (silicates) easily and might be removed as CaCO3 during CO2 sequestration into relatively high temperature (geothermal) fields. Also, Ca-rich plagioclase has a high potential of CO2 fixation as carbonate.
2009-07-30

斜長石-CO_2反応による地中固定化の実験的研究

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