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 CO 2 -induced dissolution of minerals during geologic CO 2 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 CO 2 pressure (i.e., 95 °C and 100 bar CO 2 ). 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.