Eric H. Oelkers

The steady-state dissolution rates of basaltic glass and labradorite were measured in the presence of 10 to 700 × 10−3 mol·kg−1 aqueous NaCl, KCl, CaCl2, and MgCl2 at 25 °C. All rates were measured in mixed flow reactors, and at pH~3.6 by the addition of HCl to the reactive fluids. The steady-state basaltic glass dissolution rates, based on Si release, increased by ~0.3 log units in the presence of 10−3 mol·kg−1 of either CaCl2 or MgCl2 compared to their rates in 10−3 mol·kg−1 of NaCl or KCl. In contrast, the steady-state dissolution rates of labradorite decreased by ~0.4 log units in the presence of 10−3 mol·kg−1 of either CaCl2 or MgCl2 compared to their rates in 10−3 mol·kg−1 of NaCl or KCl. These contrasting behaviours likely reflect the varying effects of these cations on the stability of rate controlling Si-rich activated complexes on the surface of the dissolving solids. On average, the Si release rates of these solids are similar to each other and increase slightly with increasing ionic strength. As the pH of water charged with 10 to 30 bars CO2 is ~3.6, the results of this study indicate that both basaltic glass and labradorite dissolution will likely be effective at increasing the pH and adding Ca to the aqueous phase in saline fluids. This observation supports potential efforts to store carbon through its mineralization in saline aquifers containing Ca-bearing feldspar and in submarine basalts.