pH가 낮은 탄산수의 CO2 탈기에 따른 용존탄소동위원소 변화 (Changes of carbon-13 Isotope of Dissolved Inorganic Carbon Within Low-pH CO2-rich Water during CO2 Degassing)

서지정보

· 발행기관 : 한국지하수토양환경학회
· 수록지 정보 : 지하수토양환경 / 24권 / 3호 / 24 ~ 35페이지
· 저자명 : 채기탁, 유순영, 김찬영, 박진영, 방하은, 이인혜, 고동찬, 신영재, 오진만

초록

It is known that δ13CDIC (carbon-13 isotope of dissolved inorganic carbonate (DIC) ions) of water increases when dissolved CO2 degases. However, δ13CDIC could decrease when the pH of water is lower than 5.5 at the early stage of degassing. Laboratory experiments were performed to observe the changes of δ13CDIC as CO2 degassed from three different artificial CO2-rich waters (ACWs) in which the initial pH was 4.9, 5.4, and 6.4, respectively. The pH, alkalinity and δ13CDIC were measured until 240 hours after degassing began and those data were compared with kinetic isotope fractionation calculations. Furthermore, same experiment was conducted with the natural CO2-rich water (pH 4.9) from Daepyeong, Sejong City. As a result of experiments, we could observe the decrease of DIC and increase of pH as the degassing progressed. ACW with an initial pH of 6.4, δ13CDIC kept increasing but, in cases where the initial pH was lower than 5.5, δ13CDIC decreased until 6 hours. After 6 hours δ13CDIC increased within all cases because the CO2 degassing caused pH increase and subsequently the ratio of HCO3 − in solution. In the early stage of CO2 degassing, the laboratory measurements were well matched with the calculations, but after about 48 hours, the experiment results were deviated from the calculations, probably due to the equilibrium interaction with the atmosphere and precipitation of carbonates. The result of this study may be not applicable to all natural environments because the pressure and CO2 concentration in headspace of reaction vessels was not maintained constant as well as the temperature. Nevertheless, this study provides fundamental knowledge on the δ13CDIC evolution during CO2 degassing, and therefore it can be utilized in the studies about carbonated water with low pH and the monitoring of geologic carbon sequestration.

영어초록

It is known that δ13CDIC (carbon-13 isotope of dissolved inorganic carbonate (DIC) ions) of water increases when dissolved CO2 degases. However, δ13CDIC could decrease when the pH of water is lower than 5.5 at the early stage of degassing. Laboratory experiments were performed to observe the changes of δ13CDIC as CO2 degassed from three different artificial CO2-rich waters (ACWs) in which the initial pH was 4.9, 5.4, and 6.4, respectively. The pH, alkalinity and δ13CDIC were measured until 240 hours after degassing began and those data were compared with kinetic isotope fractionation calculations. Furthermore, same experiment was conducted with the natural CO2-rich water (pH 4.9) from Daepyeong, Sejong City. As a result of experiments, we could observe the decrease of DIC and increase of pH as the degassing progressed. ACW with an initial pH of 6.4, δ13CDIC kept increasing but, in cases where the initial pH was lower than 5.5, δ13CDIC decreased until 6 hours. After 6 hours δ13CDIC increased within all cases because the CO2 degassing caused pH increase and subsequently the ratio of HCO3 − in solution. In the early stage of CO2 degassing, the laboratory measurements were well matched with the calculations, but after about 48 hours, the experiment results were deviated from the calculations, probably due to the equilibrium interaction with the atmosphere and precipitation of carbonates. The result of this study may be not applicable to all natural environments because the pressure and CO2 concentration in headspace of reaction vessels was not maintained constant as well as the temperature. Nevertheless, this study provides fundamental knowledge on the δ13CDIC evolution during CO2 degassing, and therefore it can be utilized in the studies about carbonated water with low pH and the monitoring of geologic carbon sequestration.

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