Effects of Na+ and K+ Exchange in Interlayers on Biotite Dissolution under High-Temperature and High-CO2-Pressure Conditions.

Cations in formation brine can affect CO2-induced dissolution of minerals during geologic CO2 sequestration (GCS), affecting the GCS performance. This study investigated the dissolution of biotite with 0-4 M Na+ and 0-10 mM K+ under high temperature and high CO2 pressure (i.e., 95 °C and 100 bar CO2). At <0.5 M Na+ concentration, Na+ replaced K+ in the biotite interlayer and enhanced the biotite dissolution. In >0.5 M Na+, however, the enhancing effect of Na+ was mitigated by an inhibition caused by competing sorption between Na+ and protons. With 0.5 M Na+ concentration, coexisting K+ significantly inhibited the biotite dissolution with high sensitivity at even lower K+ concentrations, such as 0.1-0.5 mM. In this study, we also reported the dissolution of Na-treated biotite, mimicking biotite naturally equilibrated with Na+-abundant brine. Na-treated biotite dissolved faster than natural K-containing biotite, and during the dissolution, it transformed to vermiculite. Aqueous Na+ inhibited the dissolution of Na-treated biotite by suppressing the release of interlayer Na+, and aqueous K+ inhibited the dissolution of Na-treated biotite by replacing the interlayer Na+. These findings contribute to better understanding of biotite dissolution in the presence of potassium-containing clay-swelling inhibitors and different salinities at GCS sites.