The carbonic acid system and calcite solubility in aqueous Na-K-Ca-Mg-Cl-SO 4 solutions from 0 to 90°C

Abstract

CO 2 solubility, and the first and second stoichiometric dissociation constants of carbonic acid ( K 1 ∗ and K 2 ∗ ), have been determined in aqueous solutions containing Cl and SO 4 salts of Na, K, Ca and Mg over a wide range of ionic strength from 0 to 90°C at 0.1032 MPa (1 atm) pressure. Activity coefficients for CO 2(aq), HCO 3 − and CO 3 2 − ions were calculated from m co 2, K 1 ∗ and K 2 ∗ . These activity coefficients were then used to derive Pitzer parameters for the interaction between these carbonate species and other ions between 0 and 90 °C. The resulting Pitzer model for the carbonic acid system was verified by its ability to accurately predict experimentally determined calcite solubility in brines from 0 to 90°C. However, calcite solubility measurements in complex brines initially supersaturated with respect to calcite indicate that Na +, Mg 2+ and SO 4 2− ions are probably incorporated into calcite lattice and significantly increase calcite solubility in brines.