Stability constant determinations for technetium (IV) complexation with selected amino carboxylate ligands in high nitrate solutions

The stability constants for Tc(IV) complexation with the ligands IDA, NTA, HEDTA, and DTPA were determined in varied nitrate concentrations using liquid-liquid extraction methods. The determined log beta(101) stability constants at 0.5 M NaNO3 were found to be 9.2 +/- 0.3, 10.3 +/- 0.3, and 15.3 +/- 0.3 for IDA, NTA, and HEDTA, respectively. The log beta(111) stability constant for DTPA was determined to be 22.0 +/- 0.6. These determined stability constants show a slight decrease in magnitude as a function of increasing NaNO3 concentration. These stability constants were used to model the total dissolution of Tc(IV) in acidic aqueous solutions in the presence of each ligand. The results of these predictive models indicate that amino carboxylic ligands have a high potential for increasing the aqueous dissolution of Tc(IV); at pH 2.3, 0.01 M ligand yield dissolved Tc(IV) concentrations of 1.42.10(-5) M, 1.33.10(-5) M, 6.07.10(-6) M, 9.65.10(-7) M, for DTPA, HEDTA, NTA, and IDA, respectively.