Research Program to Determine Redox Properties and Their Effects on Speciation and Mobility of Pu in DOE Wastes

Plutonium contamination is a major problem at many DOE sites. This project seeks to provide fundamental data and models for predicting plutonium speciation and environmental behavior that will allow evaluation of the many processes proposed for remediation of plutonium-containing DOE wastes. Basic to this prediction are (1) the complete fundamental data on aqueous complexation, solubility reactions, and geochemical conditions under which different plutonium oxidation states transform from one to another, and (2) a model containing this fundamental data that can predict site specific reactions. We propose to summarize existing data and develop additional fundamental data to measure the oxidation state (or states) in a variety of solid/solution systems in the presence and absence of chemicals likely to be present in DOE wastes and which can promote redox transformations and complexation reactions. Specifically, we will (1) develop methodology to determine complexation constants of Pu(IV) with strongly complexing ligands, (2) determine stability constants of Pu(IV) with strong complexants such as EDTA, (3) determine the geochemical conditions under which different reductants (e.g., Fe(0), Fe2+, H2O2) can reduce Pu(VI) to Pu(III)/Pu(IV) and oxidants (e.g., MnO2 and radiolytic products) that can oxidize Pu(IV) to Pu(V)/Pu(VI), and (4) summarize fundamental Pu data for use in a model for predicting Pu behavior under different geologic conditions