Experimental determination of ion interaction (Pitzer) parameters for the TcO4-ion in the sea water salt system Na+/K+/Mg2+/Ca2+/Cl-/SO42-/H2O at 25 C

Isopiestic vapor pressure experiments were performed at 25 C with binary NaTcO4 and Mg(TcO4)2 solutions and with mixtures 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 Cφ for NaTcO4 and Mg(TcO4)2. The binary parameters for KTcO4 are evaluated from its solubility in KCl solutions and those for Ca(TcO4)2 from the solubility of KTcO4 in CaCl2 solutions. The mixing parameters θTcO4-/Cl-, ΨM/TcO4-/Cl-, ΨM/M'/TcO4-, θTcO4-/SO42- and ΨM/TcO4-/SO42- are calculated either from osmotic coefficients or from solubilities in the corresponding ternary mixtures. The evaluated set of Pitzer parameters predict well the activity coefficients and solubilities of KTcO4 in multicomponent systems. (orig.)