Fundamental chemistry, characterization, and separation of technetium complexes in Hanford waste. 1998 annual progress report

Abstract

'The ultimate goal of this proposal is to separate technetium from Hanford tank waste. The recent work has shown that a large portion of the technetium is not pertechnetate (TcO{sub 4}{sup -}) and is not easily oxidized. This has serious repercussions for technetium partitioning schemes because they are designed to separate this chemical form. Rational attempts to oxidize these species to TcO{sub 4}{sup -} for processing or to separate the non-pertechnetate species themselves would be facilitated by knowing the identity of these 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. Thus, this proposal will synthesize and characterize the relevant model complexes of Tc(III), Tc(IV), and Tc(V) that may have formed under tank waste conditions. Once synthesized, these complexes will be used as standards for developing and characterizing the non-pertechnetate species in actual waste using instrumental techniques such as capillary electrophoresis electrospray mass spectrometry (CE-MS), x-ray absorbance spectroscopy (EXAFS and XANES), and multi-nuclear NMR (including {sup 99}Tc NMR). The authors study the redox chemistry of the technetium complexes so that more efficient and selective oxidative methods can be used to bring these species to TcO{sub 4}{sup -} for processing purposes. They will also study their ligand substitution chemistry which could be used to develop separation methods for non-pertechnetate species. Understanding the fundamental chemistry of these technetium complexes will enable technetium to be efficiently removed from the Hanford tank waste and help DOE to fulfill its remediation mission. This report summarizes the first 8 months of a 3-year project.'