Pitzer Parameters for the Pertechnetate Ion in the System Na⁺/K⁺/Mg²⁺/Ca²⁺/Cl⁻/SO ⁴₂ ⁻/TcO ⁴₋ /H₂O at 25°C

Abstract

Isopiestic vapor pressure experiments are performed at 25°C with aqueous Mg(TcO₄)₂ solutions and with ternary mixtures containing various combinations of NaTcO₄, Mg(TcO₄)₂, NaCl, MgCl₂, Na₂SO₄, and MgSO₄. The osmotic coefficients of the binary solutions are used to evaluate the binary Pitzer parameters β⁽⁰⁾, β⁽¹⁾, and C^Φ for Mg(TcO₄)₂. We previously reported these parameters for NaTcO₄. The binary parameters for KTcO₄ and Ca(TcO₄)₂ are evaluated from solubilities of KTcO₄ in KCl and CaCl₂ solutions, respectively. The mixing parameters Θ _TcO ⁻_{4 /Cl} ⁻, Ψ_M/TcO ⁻_{4 /Cl} ⁻, Θ _TcO ⁻_{4 /SO} ²⁻₄ , Ψ_M/TcO ⁻_{4 /SO} ²⁻₄ , and Ψ_Na ⁺ _/Mg ²⁺ _/TcO4 ²⁻ are calculated from either osmotic coefficients or solubilities in the corresponding ternary mixtures. The evaluated set of Pitzer parameters predicts well the activity coefficients and solubilities of KTcO₄ in multicomponent systems.