Thermodynamic modeling of aqueous aluminum chemistry and solid-liquid equilibria to high solution concentration and temperature.: I.: The acidic H-Al-Na-K-Cl-H2O system from 0 to 100°C

In this paper, we describe the development of a thermodynamic model that calculates solute/solvent activities and solid-liquid equilibria in the acidic aluminum system, H-Al3+-Na-K-Cl-H2O, to high molality from 0 degrees to approximate to 100 degrees C. The model incorporates the concentration-dependent, specific interaction equations for aqueous solutions of Pitzer (Activity Coefficients in Electrolyte Solutions, 2nd edn., pp. 75-153, CRC Press, Boca Raton, 1991). Parameterization of this model adds Al3+ specific interactions in the binary Al-Cl-H2O and ternary Al-H-Cl-H2O, Al-Na-Cl-H2O and Al-K-Cl-H2O systems as well as the standard chemical potentials of AlCl3 center dot 6H(2)O(s) and Al(OH)(3)(s) (gibbsite) in the 0 degrees to 100 degrees C range to our variable temperature (0-250 degrees C) model of acid-base reactions in the H-Na-K-OH-Cl-HSO4-SO4-H2O system (Christov and Moller in Geochim. Cosmochim. Acta 68:1309, 2004). In constructing our aluminum model, we used Emf, osmotic, equilibrium constant and solubility data. New Emf measurements using the cell Pt broken vertical bar H-2(g, 101.325 kPa)broken vertical bar HCl(m (1)), AlCl3(m (2))broken vertical bar AgCl(s)broken vertical bar Ag broken vertical bar Pt at temperatures ranging from 0 to 45 degrees C and at total ionic strength ranging from 0.1 to 3 mol kg(-1) are presented. Gibbsite and boehmite, AlOOH(s), solubility data are used in testing the model. Limitations of the model due to data insufficiencies are discussed.