Stability and Redox Behavior of Plutonium-EDTA and Mixed Pu(IV)-EDTA-L (L = Hydroxide, Carbonate, Citrate) Complexes

摘要

Amino-carboxylate ligands are nonspecific chelating agents with a strong binding affinity for a variety of metal ions. Upon binding to metal ions, the chelating agents changes the composition of the inner coordination hell of the metal ions and thereby alter their chemical speciation and behavior. Because of these properties, ethylenediaminetetra-acetic acid (EDTA) and other amino-carboxylate ligands have been extensively used in the processing of radionuclides. As a consequence, EDTA is codisposed with radionuclides and colocated with radionuclide contamination. If EDTA is released to the environment, it has the potential to significantly affect the solubility and overall behavior of radionuclides. This is particularly true for low-valent actinides, such as plutonium, that would generally hydrolyze and precipitate or sorb to mineral surfaces in water and soils in the absence of strong chelators. The first step in predicting how EDTA would affect the environmental behavior of plutonium and impact the safe disposal of nuclear waste is determining the nature of the complexes formed. Previous work on EDTA complexation of plutonium was focused on acidic conditions and interpretation of bulk solubility studies. Our approach was to determine the speciation and thermodynamic stability of species formed, more directly and under near-neutral pH and excess EDTA conditions.