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The migration of radionuclides in the subsurface depends strongly on their oxidation states and their solubility. Complexation with chelating agents generally stabilizes the radionuclide in a soluble form, which may increase migration. This study provides fundamental knowledge of the behavior of plutonium in the presence of nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA). These complexing agents have been identified as contaminants in the mixed organic-radionuclide waste at U.S. Department of Energy (DOE) sites.We studied the complexation behavior of the different oxidation states of plutonium: Pu(III), Pu(IV), Pu(V), and Pu(VI) in the presence of NTA and EDTA at various concentrations of plutonium and several Pu/organic-chelating ratios. We found that Pu(IV) is the predominant oxidation state at pH 5 to 8. Pu(III) was oxidized and Pu(V) and Pu(VI) were reduced. We found that the presence of NTA and EDTA in plutonium solution stabilizes* plutonium in soluble form and therefore enhances its potential migration in the subsurface.

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