TRLFS-investigations of uranium(VI) sorbed on gibbsite and ferrihydrite


TRLFS-investigations of uranium(VI) sorbed on gibbsite and ferrihydrite

Baumann, N.; Arnold, T.; Geipel, G.; Bernhard, G.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is a useful tool to study the speciation of uranyl in solution and at mineral surfaces. Sorption experiments of U(VI) adsorbed on ferrihydrite samples were carried out under ambient atmosphere for pH 5.8 and 7.8 in 0.1 N NaClO4 solution. A ferrihydrite suspension with an iron concentration of 1 mM was used. The total U(VI) concentration used in these experiments were 5·10-5, 1·10-5, and 1·10-6 M. The contact time of U(VI) with the mineral was two to three days.
TRLFS measurements in the ferrihydrite system were carried for the supernatant. Characteristic fluorescence spectra of the remaining U(VI) in solution were found for the samples with 5·10-5 and 1·10-5 M at pH 5.8. No uranium fluorescence signal could be obtained for all samples at pH 7.8 indicating that the sorption at this pH was stronger than at pH 5.8. The emission bands for the detected fluorescence signal of the two pH 5.8 samples were found at 486, 502, 522, and 546 nm. These emission bands and the determined respective lifetime of 28500 ± 1000 ns and 4600 ± 100 ns are indicative for UO2OH-5 and UO2(OH)2.
Batch sorption experiments of U(VI) adsorbed on gibbsite samples were carried out under ambient atmosphere for pH 3.5 to 9.5 in 0.1 N and 0.01 N NaClO4 solution. The solid concentration for the gibbsite samples was 12.5 g/L. The total U(VI) concentration used in these experiments was 1·10-6 M. The gibbsite was separated from solution by centrifugation at 3500 rpm for 15 minutes. The residue was then taken up with a solution of the same ionic strength and pH and subsequently measured the suspension by TRLFS. This procedure guarantees that the detected signal was exclusively attributed to adsorbed U(VI) on the gibbsite surface.
The detected emission bands for the adsorbed U(VI) surface species on gibbsite were observed at 495, 518, 543, and 568 nm. The fluorescence spectrum was best described with one lifetime of 2400 ± 660 ns indicating that one U(VI) surface species on gibbsite has formed.

  • Lecture (Conference)
    TRLFS-investigations of uranium(VI), Bochum, Sept. 2003
  • Beiheft zum European Journal of Mineralogy 15 (2003) S. 16

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Publ.-Id: 5589