Multiple Ion Association versus Redissociation in Aqueous NaCl and KCl at High Temperatures

Abstract

The electrical conductivities of aqueous solutions of NaCl have been measured at 651 and 670 K at 28 MPa for molalities up to 1.0 mol kg-1. These conductivities as well as the results of Hwang et al. (High Temp. High Pres. 1970, 2, 651−669), Ritzert and Franck (Ber. Bunsen-Ges. Phys. Chem. 1968, 72, 798−808), and Mangold and Franck (Ber. Bunsen-Ges. Phys. Chem. 1969, 73, 21−27) for aqueous KCl have been fit to the conductance equation of Turq et al. (J. Phys.Chem. 1995, 99, 822−827) with a consensus mixing rule and either mean spherical approximation or Debye−Huckel activity coefficients. Except at one state point (NaCl at 670 K and 28 MPa), where the interactions are the strongest (β* = 17.8), the simplest model that fits the experimental results reasonably well (± 2−3%) at molalities up to 4.5 mol kg-1 is one with only the limiting equivalent conductance and a pair association constant adjusted. Activity coefficients calculated with either the MSA and ionic diameters or with the Debye−Huckel equation of...