The carbonic acid system and solubility of calcium carbonate and sulfate in aqueous solutions over a wide range of solution composition, temperature and pressure

The stoichiometric Henry's law constant and dissociation constants for the carbonic acid system were experimentally determined in various aqueous solutions from 0 to 90{dollar}spcirc{dollar}C to high ionic strengths by the solubility method and the EMF method. The experimental results are in good agreement with previous measurements in dilute solutions available in the literature. Stoichiometric activity coefficients for CO{dollar}sb{lcub}rm 2(aq){rcub},{dollar} HCO{dollar}sb{lcub}3sp-{rcub},{dollar} and CO{dollar}sb3sp{lcub}2-{rcub}{dollar} were calculated from these experimental data. Pitzer parameters for interactions between the carbonic acid species and major ions Na{dollar}sp+,{dollar} K{dollar}sp+,{dollar} CA{dollar}sp{lcub}2+{rcub},{dollar} Mg{dollar}sp{lcub}2+{rcub},{dollar} Cl{dollar}sp-,{dollar} and SO{dollar}sb4sp{lcub}2-{rcub}{dollar} were obtained by regression analysis.; Experimental data at 25{dollar}spcirc{dollar}C and 1 atm were used to evaluate Pitzer parameters in the literature. The Pitzer model, in association with the ion-pairing model and Pitzer parameter data sets from both Harvie's group and Pitzer's group, provides proper estimates of activity coefficients within the range of experimental uncertainty.; The new Pitzer parameters for the carbonic acid system were consistent with parameters for other systems from either Harvie's group or Pitzer's group. A chemical model based on thermodynamic constants, and osmotic and activity coefficients estimated from Pitzer equations were found to predict accurately calcite solubility in the literature.; Calcite solubility in synthetic brines (Na-K-Ca-Mg-Cl-SO{dollar}sb4){dollar} was measured from 0 to 90{dollar}spcirc{dollar}C in open systems from both undersaturation and supersaturation. It was found that calcite solubilities predicted using Pitzer model were generally in good agreement with experimental solubility data obtained from undersaturation. However, this was not the case when equilibrium was approached from supersaturation. The discrepancy between experimental data and predicted data may result from the fact that adsorbed and/or coprecipitated ions (such as Mg{dollar}sp{lcub}2+{rcub}{dollar} and SO{dollar}sb4sp{lcub}2-{rcub}){dollar} on calcite surfaces tend to maintain a metastable equilibrium between the surface and bulk solution.; Pitzer parameters for correcting the pressure effect on activity coefficients were obtained for NaHCO{dollar}sb3{dollar} and {dollar}rm Nasb2COsb3{dollar} from 0 to 45{dollar}spcirc{dollar}C. The solubility of CaSO{dollar}sb4{dollar} can be predicted by the chemical model up to 200{dollar}spcirc{dollar}C and 1000 bars. However, CaCO{dollar}sb3{dollar} solubility can be only predicted up to 1000 bars from 0 to 25{dollar}spcirc{dollar}C.