Dissociation constants and speciation in aqueous Li2SO4 and K2SO4 from measurements of electrical conductance to 673 K and 29 MPa

The electrical conductivities of aqueous solutions of Li2SO4 and K2SO4 have been measured at 523-673 K at 20-29 MPa in dilute solutions for molalities up to 2 x 10(-2) mol kg(-1). These conductivities have been fitted to the conductance equation of Turq, Blum, Bernard, and Kunz with a consensus mixing rule and mean spherical approximation activity coefficients. In the temperature interval 523-653 K, where the dielectric constant, e, is greater than 14, the electrical conductance data can be fitted by a solution model which includes ion association to form MSO4-, M2SO40, and HSO4-, where M is Li or K. The adjustable parameters of this model are the first and second dissociation constants of the M2SO4. For the 673 K and 300 kg m(-3) state point where the Coulomb interactions are the strongest (dielectric constant, epsilon = 5), models with more extensive association give good fits to the data. In the case of the Li2SO4 model, including the multi-ion associate, Li-16(SO4)(8)(0), gave an extremely good fit to the conductance data. (c) 2006 Elsevier Inc. All rights reserved.