THE EFFECTS OF ACETATE on DISSOLUTION AND PRECIPITATION OF ANORTHITE UNDER GEOLOGIC CO2 SEQUESTRATION CONDITIONS

Understanding of the super critical carbon dioxide (scCO₂)-brine-mineral interactions and their effects on the aqueous compositional and mineral morphological changes is critical to ensure the efficiency and sustainability of CO₂ sequestration. In this study, both aqueous/solid chemistry analysis and interfacial topographic studies were conducted to investigate the effects of acetate on anorthite dissolution and precipitation under conditions relevant to geological carbon dioxide sequestration (308 K, 74.85 atm). Anorthite is the calcium end-member of feldspar, abundant in earth’s crust, and acetate is the most abundant organic compound existing in oil-field brines, which can be present at many CO₂ sequestration sites. After a short induction period, dissolution and precipitation occur simultaneously, resulting in non-monotonical changes in aqueous metal compositions. The effect of acetate was element-specific and in general lowered metal concentrations in the solution. The effect of acetate on dissolved cation concentration decreased in the order: Al > Mg > Si >=Ca. In addition, morphological changes were identified using atomic force microscope and scanning electron microscopy. Nanoparticles stemming from the precipitation of secondary mineral phases were observed and grow heteroepitaxially at scCO₂-water-Anorthite interfaces. Clear facets were formed on reacted substrates (within 30 hours) in the presence of 10^-2 M acetate, which is different from unreacted substrates. The results provide new information on the aqueous geochemistry evolution as well as morphological changes at CO₂-water-feldspar interfaces in presence of organic compounds. This can offer implications for understanding alterations in porosity, permeability, and wettability of pre-existing rocks and changes in aqueous compositions in geological carbon sequestration sites.