Local environment of iron and uranium ions in vitrified iron phosphate glasses studied by Fe K and U L_III-edge x-ray absorption fine structure spectroscopy

The local structure of iron and uranium ions in a series of iron phosphate glasses with the general composition (40 – x)Fe₂O₃–xUO₂–60P₂O₅ and (1–x–y)(40Fe₂O₃–60P₂O₅)– xUO_2–y(Na₂O or CaO) was investigated using Fe K-edge and U L_III-edge x-ray absorption fine structure spectroscopy. Replacing Fe₂O₃ by UO₂ in the glass caused more distortion in the coordination environment of Fe(III) ions. Extended x-ray absorption fine structure fits revealed that the Fe–P bonds observed in the base glass also existed in all the waste-loaded glasses. X-ray absorption near-edge structure showed that the uranium ions were predominantly present as U(IV) in the glasses. Uranium ions were coordinated to approximately 8 ± 1 oxygen atoms and 2.5 ± 0.6 phosphorus atoms at an average distance of 2.47 ± 0.02 and 3.8 ± 0.02 Å, respectively. There were no Fe–U or U–Fe neighbors observed, indicating that uranium ions occupied voids in the glass away from the PO₄ units. These conclusions were supported by Mössbauer, x-ray photoelectron, and Raman spectroscopic data.