Spectroscopic verification of the mineralogy of an ultrathin mineral film on depleted uranium

The alteration of a depleted uranium (DU) disk in contact with a synthetic pore water, as a simulant for fertilized agricultural soil, was studied by exposing the DU to a calcium phosphate solution (2.5 × 10 M Ca, 1 × 10 M P). Within 12 months this contact resulted in the formation of a thin film of a secondary uranium mineral on the metallic DU. The reaction product was analyzed with both time-resolved laser-induced fluorescence spectroscopy (TRLFS) and infrared spectroscopy. Both techniques identified the reaction product on DU as a uranium(VI) phosphate phase, but only TRLFS provided its unequivocal identification as meta-autunite based on the positions of the fluorescence emission maxima at 487.8, 502.0, 523.6, 547.0, 572.1, and 600.6 nm and fluorescence lifetimes of 410 ± 15 and 3300 ± 310 ns. These results highlightthe enhanced performance and sensitivity of the TRLFS technique for mineralogical characterization of thin surface films. Furthermore, they demonstrate that the dissolution of uranium from DU projectiles under the conditions described here is limited by the development and solubility of a meta-autunite secondary phase. The findings have helped clarify the interactions of DU ammunition with phosphate-rich soil-water. © 2008 American Chemical Society.