Ternary uranium(VI) carbonato humate complex studied by cryo-TRLFS

摘要

The complex formation of U(VI) with humic acid (H ) 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 presence of HA, a decrease of the luminescence intensity of U(VI) and no shift of the emission band maxima in comparison to the luminescence spectrum of the UO_2(CO_3)_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 humate complex of the type UO_2(CO_3)_2HA(II)~4- starting from UO_2(CO_3)_3 ~4- was concluded from the luminescence data. For this complex a complex stability constant of log K = 2.83±0.17 was determined. Slope analysis resulted in a slope of 1.12±0.11, which verifies the postulated complexation reaction. The results agree 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.