Interactions of Tc(IV) with citrate in NaCl media

This paper presents the experimental determination of the stability constant for the citrate complexes with TcO(OH)+ and TcO(OH)20 at different ionic strengths (NaCl), using a solvent extraction method. Data show that the stability constants for the formation of TcO(OH)Cit2- and TcO(OH)2Cit3- are 107.5±0.2 and 102.8±0.2, respectively, at zero ionic strength, with an average of 106.5±0.3 and 102.8±0.2, respectively, in the 1.0-3.0 M ionic strength range. PHREEQC calculations based on these stability constants show that the TcO(OH)Cit2- is the predominant species between pH 3 and 8 and that 50 mM citrate leads to a Tc(IV) solubility of 2 x 10-5 M at pH 5. (orig.)