THE MEASUREMENT OF ELECTRICAL CONDUCTANCE OF SUB- AND SUPERCRITICAL AQUEOUS ELECTROLYTE SOLUTIONS - METHOD TO DETERMINE SPECIATION, DISSOCIATION CONSTANTS AND LIMITING ION MOBILITIES. SYSTEM Li₂SO₄ – K₂SO₄ – Na₂SO₄ – H₂SO₄ – H₂O

Applying of modern physico-chemical theory to electrical conductance data of electrolyte dilute solutions and their mixtures allows the determination of the ion association model, dissociation constants and limiting ion equivalent conductances. The main parts of the method are 1) Turq – Blum - Bernard – Kunz (1992, 1995) (TBBK) equation for conductance of a single strong electrolyte as a function of concentration; 2) a mixing rule that predicts the conductivity of a mixture of strong electrolytes from the conductances of the single electrolytes; 3) a model for the activity coefficients of the ions and neutral species so that the equilibrium concentrations of all species in solution can be calculated from the dissociation constants and mass balance equations. The electrical conductivities of aqueous solutions of Li₂SO₄, K₂SO₄, and Na₂SO₄, H₂SO₄, and their mixtures have been measured at 100 - 400⁰ C at 12 to 28 MPa in dilute solutions for molalities up to 10^-2 mol kg^-1. These conductivities have been fit to the TBBK conductance equation with a consensus mixing rule and Mean Spherical Approximation (MSA) activity coefficients. Provided the concentration is not too high all of the data can be fitted by a solution model which includes ion association to form MeSO4^- (aq), Me₂SO₄⁰ (aq), HSO₄^- (aq), H₂SO₄⁰ (aq) and MeHSO₄⁰ (aq), where Me is Li, K, or Na. The adjustable parameters of this model are the dissociation constants of SO4 - species and the H⁺, SO4^2- , HSO4^- conductances (ion mobilities) at infinite dilution.