Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The complex formation of U(VI) with humic acid (HA) in the presence of carbonate was studied by time-resolved laser-induced fluorescence spectroscopy at low temperature (cryo-TRLFS) at pH 8.5. In the prescence of HA, a decrease of the luminescence intensity of U(VI) and no shift of the emission band maxima in compari-son to the luminescence spectrum of the UO₂(CO₃)₃ ^4- complex, the dominating U(VI) species under the applied experimental conditions in the absence of HA, was observed. The formation of a ternary U(VI) carbonato hu-mate complex of the type UO₂(CO₃)₂HA(II)⁴⁻ starting from UO₂(CO₃)₃ ^4- was calculated from the luminescence data. A complex stability constant of log K = 2.83 ± 0.17 was determined and the result of the slope analysis with a slope of 1.12 ± 0.11 verifies the postulated complex reaction. These results agrees very well with literature data. Speciation calculations show, that the formation of the ternary U(VI) carbonato humate complex can significantly influence the U(VI) speciation under environmental conditions.