The complexation of Tc(IV) with EDTA and picolinic acid at high pH

Abstract

AbstractIn the UK, technetium may be disposed of in a high pH, low Eh cementitious repository. In such a scenario, its chemistry would be dominated by TcO4−, in aerobic conditions and the sparingly soluble TcO2(s)in anaerobic conditions. Repository heterogeneity could mean that both Tc(VII) and Tc(IV) are present simultaneously. The anthropogenic ligands EDTA and picolinic acid are commonly used as decontamination agents and are likely to be present in intermediate-level waste (ILW). They could complex with Tc(IV) increasing its aqueous concentration and mobility in the cement porewaters and beyond. The conditional stability constants (measured in 0.3 mol dm−3NaOH) for the Tc(IV)–EDTA and Tc(IV)–picolinic acid complexes have been determined to be: βTc(IV)−EDTA= 1.6 × 1026, which corresponds to log β = 25.2±0.6; and βTc(IV)−PA= 8.65 × 1026, which corresponds to log β = 26.9±0.1, respectively.