A thermodynamic model of aqueous electrolyte solution behavior and solid-liquid equilibrium in the Li-H-Na-K-Cl-OH-H₂O system to very high concentrations (40 molal) and from 0 to 250 °C

Abstract

This paper describes a chemical model that calculates solute and solvent activities and solid-liquid equilibria in the Li-H-Na-K-Cl-OH-H₂O system from dilute to high solution concentration within the 0 to 250 °C temperature range. The model coherently extends to Li the temperature-variable H-Na-K-OH-Cl-H₂O model of Christov and Møller (2004b, p. 1309). The solubility modeling approach based on Pitzer's (1973, p. 268) specific interaction equations is used. All binary (LiCl-H₂O and LiOH-H₂O) and ternary (LiCl-HCl-H₂O, LiCl-NaCl-H₂O, LiCl-KCl-H₂O, LiOH-NaOH-H₂O, LiOH-KOH-H₂O, and LiOH-LiCl-H₂O) lithium subsystems are included in the model parameterization. The model for the LiCl-H₂O system is parameterized using two different approaches: (1) with 4 ion interaction binary parameters (β⁽⁰⁾, β⁽¹⁾, β⁽²⁾, and C^ϕ), and (2) with 3 ion interaction binary parameters (β⁽⁰⁾, β⁽¹⁾, and C^ϕ) and including neutral aqueous LiCl⁰(aq) species. Approach (2) provides a better fit of activity data in unsaturated binary solutions and accurately predicts solid solubilities up to 40 mol.kg⁻¹ and up to 250 °C. Therefore, this approach was used to parameterize lithium chloride mixed systems. Temperature functions for the thermodynamic solubility product (as log K^o_sp) of 5 simple lithium salts (LiCl.2H₂O(cr), LiCl. H₂O(cr), LiCl(cr), LiOH. H₂O(cr), and LiOH(cr)) are determined. The log K^o_sp values of 3 double lithium basic salts precipitating in the LiOH-LiCl-H₂O system at 50 °C (3LiOH.LiCl(cr), LiOH.LiCl(cr), and LiOH.3LiCl(cr)) are also estimated using solubility data.