Small-angle X-ray scattering measurements were performed on zirconium acidic aqueous solutions to investigate the structure and the size of polynuclear species larger than the previously identified tetrameric species. Solutions with [H+]added and [OH-]added ranging from 0.0 to 1.0 M and 0.0 to 0.02 M, respectively, were analyzed. This study demonstrates that an octameric species, Zr8(OH)20(H2O)24Cl12, exists in equilibrium with the tetrameric species, Zr4(OH)8(H2O)16Cl6 2+, such that, for 0.05 M Zr(IV) in highly acidic solutions ([H+]added ≥ 0.6 M), the tetramer is the dominant species; and at conditions with [H+]added ≤ 0.05 M, the octameric species becomes predominant. The estimated value of the equilibrium quotient obtained for the tetramer/octamer equilibrium is 0.20 ± 0.05 M3. The tetramer and octamer have radii of gyration of 3.8 and 5.1 ± 0.2 Å and a hydrolysis ratio of 2.0 and 2.5, respectively. The octamer forms by stacking two tetramers on top of each other. At conditions where small amounts of NaOH are added, unidentified polymeric Zr(IV) species larger in size than the octameric species appear.

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Publication costs assisted by the Oak Ridge National Laboratory Raman spectrum measurements were performed with molten LiF-NaF-ZrF4 mixtures at 650°in an investigation of the coordination chemistry of zirconium(IV) in alkali metal fluoride melts. The spectra of several MxZryF4y+;r polycrystalline compounds were also examined to assess the utility of using crystalline spectra as a means of identifying species present in molten fluoride solution. Octahedral coordination for Zr(IV) in a 31-36-33 mol % LiF-NaF-ZrF4 melt was established by comparing its Raman spectrum with that of crystalline Li2ZrFe where X-ray diffraction measurements have shown the presence of unbridged ZrFe2-ions. The occurrence of eight-, seven-, and five-coordinated zirconium in molten fluoride was inferred from frequency shifts accompanying changes in "free" fluoride ion concentration caused by varying the mole per cent ZrF4.

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The structures of Pu(IV) hydrous polymers were measured by small-angle neutron scattering (SANS) in aqueous media and after solvent extraction in organic phases. The scattering data from polymers occurring as aqueous colloidal suspensions indicate long, thin, rodlike particles. Pu(IV) hydrous polymers formed in the presence of uranium were shorter than those produced in the absence of uranium; this is consistent with earlier observations that uranium reduces the rate of Pu(IV) polymer formation. The Pu(IV) polymers were extracted into C6D6 solutions by alkyl esters of phosphoric acid. The extractant-Pu polymer geometries were shorter than those in the aqueous media; their radii were increased by the lengths of the extended alkyl substituents of the extractants. Comparable extractions of Pu(IV) monomers were also examined. X-ray scattering measurements exhibit well-defined Bragg diffraction lines for the Pu polymer in both the aqueous and organic phases. All of the lines could be identified with those of PuOz.Spectrophotometeric measurements monitored the polymeric nature of the aqueous and organic suspensions.