Detection of U(VI) on the surface of altered depleted uranium by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the surface of a depleted uranium (DU) disc immersed in a Ca-phosphate solution for 182 days. The weathering solution contained 2.49·10− 3 M calcium and 1.05·10− 3 M phosphate, representing enhanced pore water concentrations of agricultural soils. The TRLFS results clearly show that meta-autunite, a U(VI) phosphate, has formed during low temperature alteration of the DU disc. This secondary U(VI) mineral phase was identified using a fingerprinting procedure by comparing it with TRLFS-spectra from an in-house U(VI) TRLFS database, including U(VI) oxides, U(VI) hydroxides, U(VI) sulphates and U(VI) phosphates. Its TRLFS spectrum is characterized by six fluorescence emission bands at 486, 501, 522, 546, 573, and 601 nm, and two fluorescence life times of 50 ± 5 ns and 700 ± 25 ns.