Experimental Examination of the Coupled Dissolution-Precipitation Kinetics of Ca-Feldspar and Calcite at 80oC

The permanent trapping of carbon dioxide (CO₂) as carbonate minerals during geologic CO₂ storage relies on a steady supply of carbonate-forming cations (e.g., Ca⁺⁺, Mg⁺⁺, Fe⁺⁺), which must ultimately be sourced through the dissolution of co-occurring silicate minerals. In principle, reactive transport models (RTMs) are fully capable of simulating this coupled reaction. However, out of necessity, RTMs generally rely upon separate parameterizations for silicate mineral dissolution and carbonate mineral precipitation to calculate this inherently coupled process. Here, we take a fully-coupled experimental approach to examine the kinetics of coupled labradorite dissolution and calcite precipitation at 80°C. In the experiments, bicarbonate solutions at a range of saturation states with respect to both labradorite and calcite are passed through a stirred reactor containing one or both of the minerals. When present, calcite seeds the growth of secondary calcite precipitate, a process which has been verified through SEM imaging. Concentrations of Ca, Na, Al, Si and alkalinity in effluent solutions are monitored throughout the experiments and compared to inflowing solution concentrations in order to determine rates of mineral dissolution and growth. At steady-state, the observed change in concentration between the inflow solution and the effluent is used to calculate the coupled reaction rates. These results are then compared against those calculated using existing parameterizations of labradorite dissolution and calcite precipitation. In turn, these coupled-rate observations will help to improve RTM predictions of the efficacy of carbonate mineral trapping during geologic CO₂ storage.