X-Ray Absorption Fine Structure Spectroscopic Determination of the Speciation of Pu(IV/IV+d ) in the Environment and Under Environmentally Relevant Conditions
Rinat I. Gabitov1,2,3, Steven D. Conradson1, and Mei Ding1
(1)-Los Alamos National Laboratory, Los Alamos NM 87545
(2)-Rensselaer Polytechnic Institute, Troy NY 12180
(3)-Institute of Experimental Mineralogy, Russia 142432
In this study, the X-ray absorption fine structure (XAFS) spectroscopy has been used to determine Pu speciation in the samples from the different sites. The chemical speciation of an element is the primary determinant of its reactivity, and is therefore the best predictor of its solubility and transport behavior and subsequent tendency to accumulate in water and soil. Thus, speciation is a much more critical parameter than the concentration by itself in evaluating the level of risk posed by residual amounts of Pu in soil. However, speciation is also much more difficult to identify, particularly at trace levels. Extended XAFS (EXAFS) and X-ray Absorption Near Edge Structure (XANES) spectroscopy were used to characterize the speciation of Pu in concrete and soil samples from Rocky Flats Technology Site (RFETS) in Denver Colorado, Hanford cribs in Washington, and Waste Isolation Pilot Plant (WIPP) simulants in Carlsbad New Mexico. The results demonstrate that XAFS is easily capable of identifying the Pu speciation at very low concentrations (down to a few ppm) in solids. XAFS analysis identified multiple types of Pu speciation and structural modes within the Pu-O2-H2O system, including PuO2 or Pu(IV) hydrated-protonated oxides, and Pu(IV/V) hydrated-protonated oxides. All of these species appear to be stable under the range of conditions found in storage and within the environment.