Plutonium and neptunium speciation bound to hydrous ferric oxide colloids

The speciation of plutonium and neptunium in colloid suspension collected from the contaminated aquifer of the “Mayak” site was studied by nano-SIMS, XPS and XANES. At tracer level concentration found in original groundwater sample Pu is sorbed onto hydrous ferric oxide colloids, while at higher concentration relevant to near-field conditions it forms intrinsic PuO2 × nH2O colloids. The formation of such colloids occurs through the reduction of Pu(V) to Pu(IV) upon its sorption.