Study of the Redox Stability of Uranium(VI) in Presence of Humic Substances

We studied the stability of the oxidation state of U(VI) in the presence of natural humic acid from Aldrich and synthetic acids Hyd-Glu and Cat-Gly representing humic acid model substances with pronounced redox functionalities. Using laser-induced photoacoustic spectroscopy we obtained the first spectroscopic proof for the reduction of U(VI) to U(IV) by the applied synthetic humic acids. In contrast to that, no spectroscopic indications for an Aldrich humic acid-mediated reduction of U(VI) were found. From that we concluded that both humic acid-like products show higher U(VI) redox capacities than Aldrich humic acid.