Thermal and volumetric properties of complex aqueous electrolyte solutions using the Pitzer formalism – The PhreeSCALE code

Abstract

International audienceThe thermal and volumetric properties of complex aqueous solutions are described according to the Pitzer equation, explicitly taking into account the speciation in the aqueous solutions. The thermal properties are the apparent relative molar enthalpy (L_ϕ) and the apparent molar heat capacity (C_(p,ϕ)). The volumetric property is the apparent molar volume (V_ϕ). Equations describing these properties are obtained from the temperature or pressure derivatives of the excess Gibbs energy and make it possible to calculate the dilution enthalpy (〖∆H〗_ ^D), the heat capacity (c_p) and the density (ρ) of aqueous solutions up to high concentrations. Their implementation in PHREEQC V.3 (Parkhurst and Appelo, 2013) is described and has led to a new numerical tool, called PhreeSCALE. It was tested first, using a set of parameters (specific interaction parameters and standard properties) from the literature for two binary systems (Na2SO4-H2O and MgSO4-H2O), for the quaternary K-Na-Cl-SO4 system (heat capacity only) and for the Na-K-Ca-Mg-Cl-SO4-HCO3 system (density only). The results obtained with PhreeSCALE are in agreement with the literature data when the same standard solution heat capacity (C_p^0) and volume (V^0) values are used. For further applications of this improved computation tool, these standard solution properties were calculated independently, using the Helgeson-Kirkham-Flowers (HKF) equations. By using this kind of approach, most of the Pitzer interaction parameters coming from literature become obsolete since they are not coherent with the standard properties calculated according to the HKF formalism. Consequently a new set of interaction parameters must be determined. This approach was successfully applied to the Na2SO4-H2O and MgSO4-H2O binary systems, providing a new set of optimized interaction parameters, consistent with the standard solution properties derived from the HKF equations

Thermodynamic evidence of giant salt deposit formation by serpentinization: an alternative mechanism to solar evaporation

“…The Pitzer coefficients are one of the main potential sources of uncertainty in this thermodynamic approach. For the sensitivity tests, we compared the results obtained with the Pitzer database 50 (distributed with PhreeqC) and those obtained with the PhreeSCALE code 55 and its associated thermodynamic database at 25 °C (data are not available at higher temperatures in the database associated with PhreeSCALE) 8,55 but found no considerable difference. Furthermore, elements such as aluminium, ferric iron or sulfur were not considered at either ambient temperature or temperatures above ambient temperature.…”

An improved model for CO2 solubility in aqueous Na+–Cl−–SO42− systems up to 473.15 K and 40 MPa

“…In this work, the chemical equilibrium is described with PhreeSCALE (Lach et al, 2016). In this software, the solubility of gas CO 2 is calculated using a geochemical model present by Appelo (2015) and Appelo et al (2014) :…”

“…c and a stand for cations and anions, respectively. For the temperature dependence for the interaction parameters, the following expression is assumed (which is the combination of equations of Møller (1988) and Christov and Møller (2004a)) as propose by Lach et al (2016):…”

“…We determined a new set of interaction parameters to address the chemical behavior of CO 2 -H 2 O-salt systems. All the calculations were performed with the PhreeSCALE geochemical simulation software (Lach et al, 2016). This code is an extension of the well-known PHREEQC code widely used by the geochemist community (Appelo, 2015;Appelo et al, 2014;Parkhurst and Appelo, 2013).…”

“…The software also uses the standard properties of solutes computed from the HKF theory (Helgeson et al, 1981;Tanger and Helgeson, 1988), which is widely acknowledged by the geochemists community. The input files are similar for the two codes, only some additional output keywords are declared in PhreeSCALE to write the corresponding properties in the output files (Lach et al, 2016). The thermodynamic database is regularly increasing with new chemical systems and it is available on demand (André et al, 2020).…”