CO2 sequestration into saline aquifers is considered to be one of the most promising options for reducing industrial CO2 emissions to the atmosphere. However, there are still many uncertainties regarding the storage of CO2 in the subsurface because of a lack of knowledge about CO2–water–rock interaction within CO2 reservoirs and the potential risk of CO2 leakage. In this study, we construct a semi-open type experimental system that can reproduce the interactions under conditions close to those of actual CO2 reservoirs. Using the system, we conduct CO2–water–rock interaction experiments for 8 months to monitor the long-term reaction and the mobilization of harmful metal elements. Altered tuffaceous rock is used in the experiment because these tuffaceous rock formations (called “Green Tuff”) are a potential candidate for CO2 storage in Japan. The results show that the major-element water composition will converge to the point where host rock dissolution and secondary mineral precipitation are balanced; then, the interaction will proceed under a certain groundwater composition. In addition, we found that groundwater contamination by some metal elements (Ni, Ba, and Mn) may reach unsafe levels for drinking water as a result of CO2-water–rock interaction.
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