Fundamental Chemistry, Characterization, and Separation of Technetium Complexes in Hanford Waste

Abstract

The ultimate goal of this project is to separate technetium from Hanford tank waste. Our prior work with Hanford waste has shown that a large portion of the technetium in some tanks is not pertechnetate (TcOd) and is not easily oxidized to it. This has serious repercussions for technetium partitioning schemes because they are designed to separate this chemical form. Rational attempts to oxidize these species to Tc04* for processing or to separate the non-pertechnetate species themselves would be facilitated by knowing the identity of these 5 complexes and understanding their fundamental chemistry. Tank characterization work has not yet identified any of the non-pertechnetate species. However, based on the types of ligands available and the redox conditions in the tank, a reasonable speculation can be made about the types of species that may be present. 3 Thus, this project was synthesizing relevant model complexes of Tc(III), Tc(IV), and Tc(V) that may form under tank waste conditions. The complexes were to be characterized and used as standards for characterizing the nonpertechnetate species in actual waste using instrumental techniques such as XAS and subsequent EXAFS and XANES analysis. We had hoped to study the redox chemistry of the technetium complexes so that more efficient and selective oxidative methods can be used to bring the tank non-pertechnetate species to TcOd for processing purposes. We were to study the ligand substitution chemistry of the synthesized complexes, which could be used to develop separation methods for non-pertechnetate species. Understanding the fundamental chemistry of these technetium complexes hopefully will enable technetium to be efficiently removed from the Hanford tank waste and help DOE to fulfill its remediation mission.