Determination and comparison of uranyl complexation constants with naturaland model humic acids

We have investigated the complexation behavior of natural humic acids (HA) with model substances. Our synthetic HA model substance, prepared from glut amic acid and xylose, shows operational properties comparable to those of n atural HA in terms of water solubility at different pH and in the type and number of its functional groups. We investigated its complexation behavior with the UO2(2)(+) ion by time-resolved laser-induced fluorescence spectros copy. For comparison, we used purified natural HA from Fluka and Aldrich. T he experimental data were evaluated applying the metal ion charge neutraliz ation model developed by Kim and Czerwinski. For our synthetic product, we determined a loading capacity of 23 +/- 4% and a complexation constant of l og beta = 6.16 +/- 0.22 (pH 3.90 +/- 0.05; I: 0.1 M NaClO4). The obtained v alues are comparable with experimental results determined for Fluka and Ald rich HA. These results lead to the conclusion that our synthetic product ap propriately models the functionality of natural HA.