Nature of nano-sized plutonium particles in soils at the Hanford Site

The occurrence of plutoniumdioxide (PuO2) either from direct deposition or from the precipitation of plutonium-bearing solutions in contaminated soils and sediments is well described, particularly for the Hanford site in Washington State. However, past research has suggested that plutonium at the Hanford site may exist in chemical forms in addition to PuO2. Although the majority of the plutonium is present as oxide, we present evidence for the formation of nano-sized mixed plutonium-iron phosphate hydroxide structurally related to the rhabdophane group minerals in 216-Z9 crib sediments from Hanford using both transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS). The iron-plutonium phosphate formation may depend on the local microenvironment in the sediments, availability of phosphate, and hence the distribution of these minerals may control long-term migration of plutonium in the soil.