Plutonium(III) complexation by humic substances studied by X-ray absorption fine structure spectroscopy

We determined structural parameters for the near-neighbor surrounding of plutonium(III) in complexes with humic and fulvic acids at pH 1 and for the purpose of comparison also for the plutonium(III) aquo ion by means of X-ray absorption fine structure (XAFS) spectroscopy. It could be shown that in the complexes with humic substances as well as in the Pu3+ aquo ion sample the trivalent oxidation state of plutonium was stable within the time of the experiment. In the humate and fulvate complexes, the plutonium(III) is surrounded by about 8 oxygen atoms with an average Pu-O distance of 2.48 ± 0.02 Å. The structural parameters determined for plutonium(III) humate and fulvate complexes were compared to structural parameters of plutonium(III) and plutonium(IV) aquo ions given in the literature.