Chemical Trapping of CO2 by Clay Minerals at Reservoir Conditions: Two Mechanisms Observed by in Situ High-Pressure and -Temperature Experiments

This paper presents the results of experiments performed in situ at temperature and pressure relevant to reservoir conditions (T = 323 K and Pfluid = 90 bar) to evaluate whether clay minerals can react with supercritical CO2 to produce carbonate phases by ion exchange–precipitation reactions and dissolution–reprecipitation reactions. The results show that both can occur on a time scale of hours under the conditions of our studies. The dissolution–reprecipitation mechanism was examined using Ca-, Cs-, and tetramethylammonium (TMA+) laponite, a synthetic smectite analogous to hectorite that has small particles (basal dimensions of ∼10 × 10 nm2) and a high fraction of edge sites where only two of the usual three bridging oxygen atoms are shared with other tetrahedra in the silicate sheet (Q2 sites), making it an excellent case for examining the role of T–O–T edges. The ion exchange–precipitation mechanism was observed for a Pb-exchanged natural low-Fe smectite (hectorite). Novel X-ray diffraction and NMR and...