Dissolution and Precipitation of Clay Minerals under Geologic CO2 Sequestration Conditions: CO2−Brine−Phlogopite Interactions

To ensure efficiency and sustainability of geologic CO2 sequestration (GCS), a better understanding of the geochemical reactions at CO2-water-rock interfaces is needed. In this work, both fluid/solid chemistry analysis and interfacial topographic studies were conducted to investigate the dissolution/precipitation on phlogopite (KMg3Si3AlO10(F,OH)2) surfaces under GCS conditions (368 K, 102 atm) in 1 M NaCl. Phlogopite served as a model for clay minerals in potential GCS sites. During the reaction, dissolution of phlogopite was the predominant process. Although the bulk solution was not supersaturated with respect to potential secondary mineral phases, interestingly, nanoscale precipitates formed. Atomic force microcopy (AFM) was utilized to record the evolution of the size, shape, and location of the nanoparticles. Nanoparticles first appeared on the edges of dissolution pits and then relocated to other areas as particles aggregated. Amorphous silica and kaolinite were identified as the secondary mineral phases, and qualitative and quantitative analysis of morphological changes due to phlogopite dissolution and secondary mineral precipitation are presented. The results provide new information on the evolution of morphological changes at CO2-water-clay mineral interfaces and offer implications for understanding alterations in porosity, permeability, and wettability of pre-existing rocks in GCS sites.