A new Pitzer parameterization for the Na-OH-Cl-NaOH0(aq)-H2O system up to high concentrations (30 M), from 0 to 250°C at water saturation pressure

Adeline Lach (1) , Laurent André (1) , Arnault Lassin (1) , Mohamed Azaroual (1) , Pierre Cézac (2) , Jean-Paul Serin (2)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 LATEP - Laboratoire de Génie Thermique Énergétique et Procédés (EA1932)

The aim of this study is to represent the thermodynamic excess properties (osmotic coefficient, aqueous species and solvent activities) of Na-OH-Cl-H2O systems from dilute to highly concentrated aqueous solutions within a 0 to 250°C temperature range at water saturation pressure. Pitzer's theory [1] was successfully used as a thermodynamic model. Binary (NaOH-H2O) and ternary (NaOH-NaCl-H2O) systems are successively studied in the model parameterization procedure. The binary system was already studied but not within the temperature and concentration conditions explored in this work. For the binary system two different approaches were used: (1) NaOH is completely dissociated, which requires four interaction parameters (β0, β1, β2 and Cϕ), and (2) NaOH is only partially dissociated and the neutral aqueous species NaOH0(aq) and its related equilibrium dissociation constant (KNaOH) are introduced in the model. Our parameterization procedure includes the following steps: first the development of the simplest model, and then progressively the increase of its complexity as long as the model is not satisfactory. Initially, we started parameters fitting using the approach (1) considering only β0, β1 and Cϕ. Since model failed in reproducing the experimental thermodynamic properties correctly, we added the supplementary adjustable interaction parameter β2 and varied the values of the associated parameter, α2. But this last model could not still describe satisfactorily the experimental values over the whole range of concentrations and temperature of interest. Finally, we successfully applied approach (2) by introducing the temperature dependent ternary ζNa+/OH-/NaOH and binary λNaOH/NaOH interaction parameters in addition to β0, β1, Cϕ and the thermodynamic equilibrium constant (KNaOH). The second approach fits better the osmotic coefficient and solvent activities up to 30 mol.kg-1 and to 250°C. The resulting model also allows describing the solubility of NaOH in H2O with a very good confidence, taking into account the five hydrated states of the solid salts (NaOH:nH2O with n=1,2,3.11,3.5 and 4) [2]. The thermodynamic solubility products of the five salts were also determined in this study. Then, we studied the solubility of NaCl in NaOH solutions and thus optimised two new temperature dependent ternary interaction parameters ψNa+/Cl-/OH- and ζNa+/OH-/NaCl, which are consistent with the θCl-/OH- interaction parameter estimated by Christov and Moller [3]. The final model is able to correctly represent aqueous properties and salt solubilities in the Na-OH-Cl-NaOH0(aq)-H2O system at high concentrations and temperatures and consistently extends the model of [3].

Mots clés: base brine; modelling; Pitzer approach

Domaines: Sciences de l'environnement

Adeline Lach, Laurent André, Arnault Lassin, Mohamed Azaroual, Pierre Cézac, et al.. A new Pitzer parameterization for the Na-OH-Cl-NaOH0(aq)-H2O system up to high concentrations (30 M), from 0 to 250°C at water saturation pressure. 21st International Congress of Chemical and Process Engineering CHISA 2014 Prague, Aug 2014, Prague, Czech Republic. ⟨hal-00967366⟩