Investigation of Humic Acid Complexation Behavior with UO2 2+ Ions using Modified Synthetic and Natural Humic Acids

Humic acids influence the speciation and migration behavior of actinide ions in the environment. Due to their complex and heterogeneous nature, a thermodynamically based description of their complexation behavior with metal ions is difficult. Numerous uncertainties exist in the description of the complexation process, e.g., the kind and number of complexing functional groups is uncertain.
We are investigating the influence of different functional groups on the complexation behavior of humic acids to improve the understanding of the humic acid - metal ion interaction. Such information is very important for a more precise modeling of geochemical processes in the presence of humic acids.
We synthesized and characterized synthetic and natural humic acids with blocked phenolic hydroxyl groups. With these humic acids, we investigate the influence of phenolic hydroxyl groups on the complexation behavior of humic acids with UO22+ ions. The investigations were carried out by laser-induced fluorescence spectroscopy and FTIR spectroscopy.
For the first time, we compared the complexation behavior of a modified and non-modified synthetic humic acid with UO22+ ions at pH 4 by laser-induced fluorescence spectroscopy. The spectroscopic results show that the blocking of the phenolic hydroxyl groups changes the interaction behavior between the humic acid and the UO2 2+ ion.