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

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.