Dissociation constants and speciation in aqueous Li 2SO 4 and K 2SO 4 from measurements of electrical conductance to 673 K and 29 MPa

Abstract

The electrical conductivities of aqueous solutions of Li 2SO 4 and K 2SO 4 have been measured at 523–673 K at 20–29 MPa in dilute solutions for molalities up to 2 × 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, ε, is greater than 14, the electrical conductance data can be fitted by a solution model which includes ion association to form MSO 4 - , M 2 S O 4 0 , and HSO 4 - , where M is Li or K. The adjustable parameters of this model are the first and second dissociation constants of the M 2SO 4. For the 673 K and 300 kg m −3 state point where the Coulomb interactions are the strongest (dielectric constant, ε = 5), models with more extensive association give good fits to the data. In the case of the Li 2SO 4 model, including the multi-ion associate, Li 16 ( SO 4 ) 8 0 , gave an extremely good fit to the conductance data.