Spectroscopic and structural studies of environmentally relevant Neptunium(V) and Plutonium(V) complexes

Carbonate and bicarbonate are common anions in natural waters, consequently carbonate complexes of the actinides may play an important role in their migration from a nuclear waste repository. Due to the relatively high solubility and redox stability of Np(V) and Pu(V), these ions are particularly important to consider. Carbonate complexation reactions were examined for NpO2+ and PuO2+ using a variety of techniques, including 13C and 17O NMR and UV-Vis-NIR spectroscopies, EXAFS studies have been performed on both solid state and solution species. Previously, NpO2+, carbonates have been difficult to observe by UV-Vis-NIR spectroscopy due to the formation of insoluble NaNp2O2(CO3) or Na3NpO2(CO3)2 salts. However, by employing tetrabutylammonium as the counter cation, millimolar concentrations have been obtained and utilized for temperature dependent carbonate complexation studies by NMR and UV-Vis-NIR spectroscopy