Solubility and Pitzer model parameters in thallium(I) chloride systems, TlCl–MgCl2–H2O and TlCl–CaCl2–H2O

Abstract

The solubility of thallium(I) chloride has been determined in aqueous solutions of magnesium chloride and calcium chloride at concentrations up to 1.5 mol kg^–1. The data were fitted to Pitzer's equations without explicit assumption of ion association. Here the β⁽¹⁾ term for TlCl is essentially equivalent to the β⁽²⁾ term for 2 : 2 electrolytes, but with α= 3, instead of α= 2. ‘Best values’ of β⁽⁰⁾ and β⁽¹⁾ for TlCl are recommended together with K_s, the activity solubility product. These were used to derive the mixture parameters perataining to the systems, θ_TIN and ψ_TINCI(N = Ca, Mg). The fit of the experimental data was found to be worse if higher-order mixing terms were included in the analysis. Best values of θ_TIM and ψ_TIMCI for M = H, NH₄, Li, Na, K, Rb and Cs are also given to complete the parameter base. Activity coefficients for thallium(I) chloride in the mixtures are derived.