Complexation of Tc(IV) with EDTA at varying ionic strength of NaCl

Summary. The stability constant for Tc(IV) / EDTA com-plexes were determined using a solvent extraction technique atvarying ionic strength (NaCl) and the specific ion interactiontheory model allowed for calculating stability constants at zeroionic strength. The stability constants at zero ionic strengthfor the formation of the TcOEDTA 2− and TcOHEDTA − com-plexes are 10 20 . 0±0 . 4 and 10 25 . 3±0 . 5 , respectively. The modeledTc(IV) solubility was calculated to be 3 . 9×10 −7 M at near-neutral pH and in presence of 2 . 5 mM EDTA, a result found tobe in good agreement with published solubility experimentaldata. Speciation calculations showed that TcOEDTA 2− is thepredominant species between pH 4 and 7.5 in presence of0 . 171mM EDTA, while TcO(OH) 20 is predominant in basicsolution. These studies show that EDTA has a very strongaffinity for complexation with Tc(IV) and can increase theenvironmental mobility of Tc(IV). 1. Introduction Technetium-99 ( 99 Tc ) , a pure beta emitter ( E max