We have investigated the complexation behavior of natural humic acids (HA) with model substances. Our synthetic HA model substance, prepared from glutamic acid and xylose, shows operational properties comparable to those of natural 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 U O r ion by time-resolved laser-induced fluorescence spectroscopy. For comparison, we used purified natural HA from Fluka and Aldrich. The experimental data were evaluated applying the metal ion charge neutralization model developed by Kim and Czerwinski. For our synthetic product, we determined a loading capacity of 23 ± 4% and a complexation constant of log β = 6.16 ± 0.22 (pH 3.90 ± 0.05; / : 0.1 Μ NaC104). The obtained values are comparable with experimental results determined for Fluka and Aldrich HA. These results lead to the conclusion that our synthetic product appropriately models the functionality of natural HA.

The use of the OPO technique in laser induced spectroscopic instrumentation is a new and improved spectroscopic technique. Solid crystals for the tunable laser allows one to perform laser spectroscopy over a wide wavelength range without the use of a dye laser. We have demonstrated that the laser output of the OPO-system (in our case 270 nm) is suitable for time-resolved laser-induced fluorescence measurements. The uranyl sulfate complexation was investigated for the first time by fluorescence measurements. Compared to spectrophotometric methods, lower uranyl concentrations can be investigated and therefore measurements could be made in seepage waters of uranium mine tailing piles.The measured lifetimes of the 1:1, 1:2, and 1:3 uranyl sulfate complexes are 4.3 +/- 0.5 mu s, 11.0 +/- 1.0 mu s and 18.8 +/- 1.0 mu s, respectively. The main fluorescence bands of the sulfate complexes are centered at 498 nm, 515 nm and 538 nm and no significant shift of the fluorescence maxima was found between the three complexes. The complex formation constants of the first two uranyl sulfate complexes at an ionic strength of 0.2 M were measured as log beta(1(0.2 M)) = 2.42 and log beta(3(1.0 M)) 3.30, respectively. The complex formation constants for the three uranyl sulfate complexes at an ionic strength of 1 M were measured as log beta(1(1.0 M)) = 1.88, log beta(2,(1.0 M)) = 2.9 and log beta(3(1.0 M)) 3.2, respectively. A speciation diagram was calculated from the results of the time resolved measurements.

An artificial humic acid (HA) from xylose, phenylalanine and glycine was synthesized to investigate its interaction with UO22+. This substance was characterized by different analytical methods, e.g., elemental analysis, radiometric determination of functional groups (carboxylic, phenolic OH and ester groups), calcium acetate exchange for the determination of carboxylic groups, IR spectroscopy and capillary electrophoresis. The interaction of this synthetic HA with UO22+ was compared to the natural HA from Fluka by extended X-ray absorption fine structure (EXAFS) spectroscopy. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was used for characterizing the fluorescence behavior of the HA's. These investigations reveal structural and functional similarities between the synthetic HA and the natural HA.