A NOVEL APPROACH FOR TRACKING CO2 LEAKAGE INTO GROUNDWATER USING CARBONATE MINERAL DISSOLUTION

The stability of different carbonate minerals is pH-dependent and their rates of dissolution vary. In the case of CO₂ leakage and upward migration from geologic carbon storage (GCS) sites, the reaction of available metal carbonates in bedrock may release specific metals useful as tracers in shallow groundwater aquifers. In this study, we used laser induced breakdown spectroscopy (LIBS) to examine in situdissolution rates of various mineral carbonates (MgCO₃, CaCO₃, SrCO₃, and MnCO₃) in the presence of increasing CO₂ pressure ranging from 25 - 350 bar. The experiments were carried out using both pressed-carbonate and hydrogel-carbonate pellets. The gel pellets were formed by drying mixed suspensions of carbonate powder and 4% agarose gel. A pulsed Nd:YAG laser at 1064 nm was used to produce gaseous plasma in the fluid surrounding pellets. The ensuing plasma emission was spectrally analyzed, and the intensity of the Mg, Ca, Sr, and Mn emission lines were used to monitor their respective concentrations in aqueous solution. The dissolution of carbonates in CO₂-free aqueous HCl was also measured at ambient pressure over a pH range of 2 to 6 under the same experimental conditions. A kinetic model incorporating both results has been developed to represent the selective dissolution rates of carbonates used in this study. The results demonstrate that in situ monitoring of carbonate dissolution by LIBS may provide a useful indirect detection system indicative of CO₂leakage from some storage sites.