Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The complexation of neptunium(V) with humic acids at pH 7 was studied by EXAFS and UV-Vis spectroscopy using a natural humic acid from Aldrich as well as a synthetic humic acid model substance (type M42) with well defined functional properties. In addition, we studied the influence of phenolic OH groups on the complexation between humic acids and neptunium(V) in the neutral pH range using Aldrich humic acid in a modified form, i.e., with blocked phenolic OH groups.
The formation of neptunium(V) humate complexes was confirmed for all investigated humic acids by UV-Vis spectroscopy. Neptunium LIII-edge EXAFS spectra were recorded in fluorescence mode at the Rossendorf Beamline (ROBL) at the ESRF in Grenoble. For the first two coordination shells of neptunium(V) the EXAFS spectra were analyzed. The obtained structural information for the axial and equatorial oxygen atoms surrounding the neptunium atom will be presented and compared with results for neptunium(V) hydrates.