Spectroscopic Characterization of the Uranium Carbonate Andersonite Na₂Ca[UO₂(CO₃)₃]·6H₂O

Abstract

The uranium carbonate andersonite Na2Ca[UO2(CO3)3] x 6H2O was synthesized and identified with classical analytical and spectroscopic methods. The classical methods applied were powder X-ray diffraction (XRD), nitric acid digestion, and scanning electron microcopy combined with energy-dispersive spectroscopy (SEM/EDS). To characterize andersonite spectroscopically, time-resolved laser-induced fluorescence spectroscopy (TRLFS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) were used. Natural and synthetic andersonite samples were characterized with the nondestructive TRLFS by six fluorescence emission bands at 470.6, 486.1, 505.4, 526.7, 549.6, and 573.9 nm. In addition, andersonite was characterized by FT-IR measurements by the appearance of the asymmetric stretching vibration of the uranyl cation [v3(UO2(2+))] at 902 cm(-1) with a shoulder at 913 cm(-1). XPS measurements verified the composition of the synthetic andersonite sample. The measured intensity ratios of the XPS lines agree with the stoichiometry of Na2Ca[UO2(CO3)3] x 6H2O. The XPS features of the inner valence molecular orbitals are characteristic of the [UO2(CO3)3]4- structural moiety. These spectroscopic methods can be used to identify in a fingerprinting procedure secondary U(VI) phases in mixtures with other phases or as thin coatings on mineral and rock surfaces.

Uranyl sorption onto gibbsite studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

“…TRLFS measurements were carried out on the above described samples to obtain spectroscopic information on the adsorbed uranyl(VI)-gibbsite surface species. These investigations on fluorescent uranium(VI) species yield two kinds of characteristic information: the position of the fluorescence emission bands and the fluorescence lifetime [29]. Here the positions of the fluorescence emission bands are primary features of the TRLFS spectrum, whereas the fluorescence lifetime is a secondary one, because it is more dependent on the sample preparation (wet or dry) and temperature of the experiment [30].…”

X‐ray photoreduction of U(VI)‐bearing compounds

“…Several U5f valence region spectra are reported in the literature for U(VI) compounds, such as UO 2 X 2 (with X = F, Cl or Br), [40] UO 3 , [41] and Na 2 Ca[UO 2 (CO 3 ) 3 ]. 6H 2 O, [42] and the U5f peak is always found very weak. Moreover, Fig.…”

Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids

“…This observation was made at pH 5.5 and 8.0. Given the degree of splitting (Dm as/s ) as a criterion to differentiate between monodentate mononuclear (single-corner sharing), bidentate mononuclear (edgesharing), and monodentate binuclear (double-corner sharing) complexes (Lefèvre, 2004), the increase of Dm as/s in the presence of adsorbed uranyl (152-176 cm À1 at pH 5.5 and pH 8.0) ranges between the Dm as/s value of the UO 2 ðCO 3 Þ 3 4À complex (Dm as/s = 140 cm À1 ) and the mineral andersonite (Na 2 Ca[UO 2 (CO 3 ) 3 ] AE 6H 2 O, Dm as/s $ 190 cm À1 ; Amayri et al, 2004). In both complexes the carbonate group is bidentately coordinated to UO 2 2þ in the equatorial plane.…”