Abstract

In this study, a series of autoclave experiments were conducted in order to investigate the geochemical and mineralogical effects of carbon dioxide on deep subsurface environments. High pressure and temperature conditions of 50°C and 100 bar, which are representative environments for geological CO₂ sequestration, were created in stainless- steel autoclaves for simulating the interactions in the scCO₂-groundwater-mineral reaction system. Zeolite, a widespread mineral in Pohang Basin where many researches have been focused as a candidate for geological CO₂ sequestration, and groundwater sampled from an 800 m depth aquifer were applied in the experiments. Geochemical and mineralogical alterations after 30 days of scCO₂-groundwater-zeolite sample reactions were quantitatively examined by XRD, XRF, and ICP-OES investigations. The results suggested that dissolution of zeolite sample was enhanced under the acidic condition induced by dissolution of scCO₂. As the cation concentrations released from zeolite sample increase, H⁺ in groundwater was consumed and pH increases up to 10.35 after 10 days of reaction. While cation concentrations showed increasing trends in groundwater due to dissolution of the zeolite sample, Si concentrations decreased due to precipitation of amorphous silicate, and Ca concentrations decreased due to cation exchange and re-precipitation of calcite. Through the reaction experiments, it was observed that introduction of CO₂ could make alterations in dissolution characteristics of minerals, chemical compositions and properties of groundwater, and mineral compositions of aquifer materials. Results also showed that geochemical reactions such as cation exchange or dissolution/precipitation of minerals could play an important role to affect physical and chemical characteristics of geologic formations and groundwater.

Keywords carbon dioxide, zeolite, high pressure and temperature, geochemical reaction, dissolution