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Lawrence Berkeley National Laboratory Recent Work Title EXAFS Determinations of Uranium Structures : Uranyl Complexed with Tartaric , Citric , and Malic Acids Permalink

The uranium Lmedge extended x-ray absorption fine structure (EXAFS) was measured for 1: 1 mixtures of uranyl with tartaric, malic, and citric acids. The room temperature EXAFS of these mixtures at pH = 3 show the characteristic short uranium-oxygen interactions of the uranyl ion, U022+, at 1.80 A along with -5 oxygen near neighbors around the uranyl equator at 2.40 A. In addition, the EXAFS of each solution reveal a U-U interaction at 3.92 A, indicating the presence of a uranyl dimer structure. Based on models proposed by earlier potentiometric titration experiments, it is concluded that the dimer is the ligand bridged species, (U02)2(L)2, in which bridging occurs through the a-hydroxyl groups of the polycarboxylate ligands.