Experiment of limestone dissolution under high CO_2 concentration and high pressure

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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