Spectroscopic characterization of synthetic becquerelite, Ca[(UO2)6O4(OH)6]•8H2O, and swartzite, CaMg[UO2(CO3)3]•12H2O

Becquerelite, Ca[(UO2)(6)O-4(OH)(6)].8H(2)O, and swartzite, CaMg[UO2(CO3)(3)].12H(2)O, have been synthesized and identified by X-ray powder diffraction (XRD). Chemical compositions were verified by ICP-MS and AAS. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) and Fourier-transformed infrared spectroscopy (FTIR) were used for the first time to characterize these phases. In becquerelite, there are four fluorescence emission bands, at 518.9, 535.6, 553.4, and 578.9 nm, and a characteristic fluorescence lifetime of 3.1 +/- 0.21 mus. Swartzite shows six characteristic fluorescence emission bands, at 472.3, 488.9, 509.0, 531.1, 554.7, and 578.9 nm, and a fluorescence lifetime of 59.4 +/- 0.1 mus. The FTIR spectra of becquerelite are characterized by an intense asymmetric stretching vibration (nu(3) UO22+ mode) band at 946 cm(-1), with shoulders at approximately 925 and 902 cm(-1). Swartzite shows its characteristic nu(3) UO22+ mode of the uranyl cation at 898 cm(-1). As natural U6+-bearing samples commonly form thin coatings on rock or mineral surfaces or as a component mixed with other solids, it is generally difficult to identify small quantities of these secondary phases. Spectroscopic methods like TRLFS and FTIR spectroscopy are found to be promising methods to identify such secondary phases.