Activity coefficients and pitzer parameters in the systems Na+/Cs+/Cl-/TcO 4 - or ClO 4 - /H2O at 25°C

Isopiestic vapor pressure experiments are performed at 25°C with aqueous NaTcO₄, mixed NaTcO₄-NaCl, and NaCl reference solutions. The solubility of CsTcO₄ is determined in 0–7.4m CsCl and in 0–5.6m NaCl solutions. The osmotic coefficients of the binary and ternary solutions are used to evaluate the binary Pitzer parameters Β⁰, Β^l, and C^Φ for NaTcO₄ and the mixing parameters θ_{TcO 4} ^- /cl^- and ψ_Na ⁺/TcO ₄ ^- /cl^-. The binary Pitzer parameters for the sparingly soluble CsTcO₄ and CsC1O₄ are calculated together with ψ_Cs ⁺/mo ₄ ^- /cl^- from their solubilities in CsCl solution. The solubilities of CsTcO₄ in NaCl and CsClO₄ in NaClO₄ solution are also included in the parametrization of the reciprocal salt systems Na⁺/Cs⁺/Cl^-/MO ₄ ^- . The parameters Β⁰ and Β^l of pertechnetate and perchlorate salts correlate well with the ionic radii.