Experiment of limestone dissolution under high CO_2 concentration and high pressure

在1 ~ 100大气压条件下，采用高CO_2浓度海水与石灰石样品反应的实验方法，估算了石灰石的溶解速率。这是通过向珊瑚礁基岩中注入CO_2来中和海水，分离海洋中以碳酸氢离子形式存在的CO_2的技术基础实验（见下图化学方程式）。CO_2 + CaCO_3 + H_2O→Ca^<2+> + 2HCO^<3->为本研究新研制了两个与常压和高压条件相对应的实验装置。前一个实验是在高压实验前准备的初步研究，对于分析海洋酸化对有孔虫、珊瑚等碳酸盐壳海洋生物的影响也是有效的。通过实验对浅海地区几种矿物的溶蚀速率进行了量化，与前人的研究结果一致。从高压实验的结果来看，注入的CO_2在几分钟的时间内通过石灰岩的溶解被海水隔离。此外，还证实了CO_2溶解和CO_2分压降低对海水酸化的抑制作用。结果表明，石灰石分离CO_2是一种有效的技术。当海水CO_2分压较高时，石灰石溶解分离的效率降低。计算得出，当CO_2分压在总压的几~ 10%范围内时，CO_2隔离效果最好，因此在1m^3的海水中，CO_2分压条件下隔离的CO_2量在10^<-1> ~ 100 kg量级。此外，溶解速率取决于反应容器内的流速，这一点在以往的研究中尚未得到证实。这一结果对分析实际注CO_2在地下或水下石灰岩地层中CO_2隔离和石灰岩溶蚀的分布和变化具有重要意义。少

The purpose of this study is to estimate limestone dissolution rate by an experiment with high CO_2 concentration seawater reacting with limestone samples under 1 to 100 atm pressure conditions. This is fundamental experiment for technology to isolate CO_2 as hydrogen carbonate ion in the ocean (see the following chemical equation) by neutralization of seawater with injected CO_2 into the coral reef basement rock.CO_2 + CaCO_3 + H_2O → Ca^<2+> + 2HCO^<3->Two experimental devices corresponding to the atmospheric pressure and high pressure conditions were newly developed for this study. The former experiment was prepared preliminary study before the high-pressure experiment, and was also efficient for analysis of an impact of ocean acidification to marine biota with carbonate shell such as foraminifera and corals. The dissolution rate of several kinds of minerals in the shallow marine area is quantified from the experiment and is confirmed to be consistent with the former studies.From th … More e result of the high-pressure experiment, injected CO_2 was confirmed to be isolated in seawater by dissolution of limestone within short time period of about several minutes. In addition, restraint of the acidification of the seawater by CO_2 dissolution and decrease of the CO_2 partial pressure were also confirmed. These results indicate that the CO_2 isolation method using limestone is an effective technique. The efficiency of the isolation by the limestone dissolution was confirmed to decrease when CO_2 partial pressure of seawater was high. We calculated that the CO_2 isolation is the most effective when CO_2 partial pressure is within the range of several to tens percent of the total pressure, and thus the quantity of isolated CO_2 under the CO_2 partial pressure conditions was within an order of 10^<-1> to 100 kg in 1m^3 seawater. In addition, dissolution rate depends on flow speed in reaction vessel, which has not been confirmed in previous studies. This result should give important knowledge for the analysis of distribution and change of CO_2 isolation and limestone dissolution during actual CO_2 injection into underground or underwater limestone strata. Less