Inorganic species in geologic fluids: Correlations among standard molal thermodynamic properties of aqueous ions and hydroxide complexes

Abstract

Correlations among experimentally determined standard partial molal thermodynamic properties of inorganic aqueous species at 25°C and 1 bar allow estimates of these properties for numerous monatomic cations and anions, polyatomic anions, oxyanions, acid oxyanions, neutral oxy-acid species, dissolved gases, and hydroxide complexes of metal cations. Combined with correlations among parameters in the revised Helgeson-Kirkham-Flowers (HKF) equation of state (Shock et al., 1992), these estimates permit predictions of standard partial molal volumes ( V° ), heat capacities ( C° P ), and entropies ( S° ), as well as apparent standard partial molal enthalpies ( Δ H° P,T ) and Gibbs free energies (ΔḠ° P,T) of formation to 1000°C and 5 kb for hundreds of inorganic aqueous species of interest in geochemistry. Data and parameters for more than 300 inorganic aqueous species are presented. Close agreement between calculated and experimentally determined equilibrium constants for acid dissociation reactions and cation hydrolysis reactions supports the generality and validity of these predictive methods. These data facilitate the calculation of the speciation of major, minor, and trace elements in hydrothermal and metamorphic fluids throughout most of the crust of the Earth.