Determination of Structural Parameters for Thorium(IV), Neptunium(IV), Neptunium(V) and Plutonium(III) Humate Complexes by Means of XAFS Spectroscopy


Determination of Structural Parameters for Thorium(IV), Neptunium(IV), Neptunium(V) and Plutonium(III) Humate Complexes by Means of XAFS Spectroscopy

Schmeide, K.; Sachs, S.; Reich, T.; Heise, K. H.; Bernhard, G.

Structural parameters for the near-neighbor surrounding of Pu(III), Th(IV), Np(IV) and Np(V) in complexes with various natural and synthetic humic and fulvic acids were determined by means of X-ray absorption fine structure (XAFS) spectroscopy. Furthermore, the interaction of the actinides with Bio-Rex70, a cation exchange resin having solely carboxylic groups as metal binding functional groups, was studied to determine structural parameters for the interaction of the respective actinide ions with carboxylic groups. Applying chemically modified humic acids with blocked phenolic/acidic OH groups, the influence of phenolic/acidic OH groups on the complexation of Np(V) by humic acids was studied in the neutral pH range. The structural parameters determined for actinide humate complexes were further compared with structural parameters of aqueous ions of the actinides and of solid actinide carboxylates given in the literature. The results indicate that the interaction between the actinide ions and humic acid is dominated by humic acid carboxylate groups. These carboxylate groups act predominantly as monodentate ligands. A contribution of phenolic/acidic OH groups to the complexation of Np(V) by humic acids at pH 7 cannot completely be excluded by EXAFS analysis.

Keywords: Thorium(IV); Neptunium(IV); Neptunium(V); Plutonium(III); Humic acid; Fulvic acid; EXAFS; XANES; Complexation; tetravalent

  • Contribution to external collection
    FZKA 6800, Wissenschaftliche Berichte, Forschungszentrum Karlsruhe, Karlsruhe 2003, S. 65-77.

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Publ.-Id: 5215