Complexation of Aquatic Humic Substances from the Bog "Kleiner Kranichsee" with Uranium(VI)

As a contribution to Task 1 (Sampling and Characterization), we have characterized Derwent Reservoir fulvic acid by means of FTIR spectroscopy and capillary zone electrophoresis and compared to Kranichsee humic and fulvic acid and Aldrich humic acid.
Our contribution to Task 2 (Complexation) consists of two parts. First, we studied the complexation of Kranichsee humic acid (HA) and fulvic acid (FA) with uranyl(VI) ions by laser-induced fluorescence spectroscopy at pH 4 and an ionic strength of 0.1 M (NaClO4). The loading capacities were determined to be 14 ± 1 % and 13 ± 1 % for humic acid and fulvic acid, respectively. The complexation constants for Kranichsee humic acid and fulvic acid were found to be log ß = 6.35 ± 0.22 and log ß = 6.21 ± 0.20, respectively. These results were compared to the uranyl complexation behavior of other natural humic acids such as Aldrich HA and GoHy-573 HA. Second, we investigated original bog water of the mountain bog 'Kleiner Kranichsee' by ultrafiltration to determine the hydrodynamic particle size distribution, i.e., the 'apparent molecular weight' distribution of the organic substances in the bog water. Furthermore, the influence of uranyl complexation on this particle size distribution of humic colloids was investigated. No significant influence of the uranyl ions on the molecular weight distribution of the humic substances was found.