Complexation of Tc(IV) with SO42- in NaCl Medium

This work reports the experimental determination of the stability constant for the complexation of the Tc(IV) cation by SO42- at 1.0 mol.kg(-1) ionic strength (NaCl) and pcH 1.51 +/- 0.05, using a solvent extraction method. The data herein represent a first step in determining unknown thermodynamic parameters for the complexation of Tc(IV) by simple polyatomic anions. Radiotracer studies were carried out with Tc-99 and S-35, using both HDEHP and TOPO as extractants, to characterize the mechanism of the solvent extraction and to examine the extraction of the competing species, TcO(HSO4)(+) and TcOSO4, into the organic phase. The apparent stability constant log(10) beta(app) for the complexation of Tc(IV) by sulfate was found to be 1.13 +/- 0.04.