Modified Synthetic Humic Acids for the Investigation of Humic Acid Complexation Behavior with Urany(IV) Ions

The influence of humic substances on the speciation of actinide ions and their migration behavior in natural aquifer
systems is of great interest within environmental research. Specified knowledge about this is required, for instance, to
develop strategies of risk assessment for long-time safety in the regions of the former uranium mining in Saxony and
Thuringia. Due to the complex and heterogeneous nature of humic substances a thermodynamic founded 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. Therefore, it is necessary to
investigate the complexation process with well defined model substances.
We synthesize and characterize humic acid functionality models from reducing sugars and  -amino acids, with functional
properties comparable to those of natural humic acids with respect to type and number of functional groups. Former
measurements have shown that this synthetic humic acids mimic the interaction humic acid - metal ion very well.
This work deals with the possibilities to synthesize modified humic acids, e.g., humic acids with blocked phenolic OH
groups. With this model substances we investigate the influence of phenolic OH groups on the complexation behavior
of humic acids with uranyl ions by time-resolved laser-induced fluorescence spectroscopy. We expect to get a better
understanding of the humic acid - metal ion interaction process and to gather information regarding geochemical
modeling in the presence of humic acids.