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

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 degrees C temperature range. The model coherently extends to Li the temperature-variable H-Na-K-OH-Cl-H2O model of Christov and Moller (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 (beta((0)), beta((1)), beta((2)), and C-phi), and (2) with 3 ion interaction binary parameters (beta((0)), beta((1)), and C-phi) 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 degrees C. Therefore, this approach was used to parameterize lithium chloride mixed systems. Temperature functions for the thermodynamic solubility product (as log K-sp(o)) of 5 simple lithium salts (LiCl center dot 2H(2)O(cr), LiCl center dot H2O(cr), LiCl(cr), LiOH center dot H2O(cr), and LiOH(cr)) are determined. The log K-sp(o) values of 3 double lithium basic salts precipitating in the LiOH-LiCl-H2O system at 50 degrees C (3LiOH center dot LiCl(cr), LiOH center dot LiCl(cr), and LiOH center dot 3LiCl(cr)) are also estimated using solubility data.