Decontamination of metal surfaces contaminated with low levels of radionuclides is a major concern at Department of Energy facilities. The development of an environmentally friendly and cost-effective decontamination process requires an understanding of their association with the corroding surfaces. We investigated the association of uranium with the amorphous and crystalline forms of iron oxides commonly formed on corroding steel surfaces. Uranium was incorporated with the oxide by addition during the formation of ferrihydrite, goethite, green rust II, lepidocrocite, maghemite, and magnetite. X-ray diffraction confirmed the mineralogical form of the oxide. EXAFS analysis at the U L III edge showed that uranium was present in hexavalent form as a uranyl oxyhydroxide species with goethite, maghemite, and magnetite and as a bidentate innersphere complex with ferrihydrite and lepidocrocite. Iron was present in the ferric form with ferrihydrite, goethite, lepidocrocite, and maghemite; whereas with magnetite and green rust II, both ferrous and ferric forms were present with characteristic ferrous:total iron ratios of 0.65 and 0.73, respectively. In the presence of the uranyl ion, green rust II was converted to magnetite with concomitant reduction of uranium to its tetravalent form. The rate and extent of uranium dissolution in dilute HCl depended on its association with the oxide: uranium present as oxyhydroxide species underwent rapid dissolution followed by a slow dissolution of iron; whereas uranium present as an inner-sphere complex with iron resulted in concomitant dissolution of the uranium and iron.

angle spinning ͑MAS͒ nuclear magnetic resonance ͑NMR͒ spectroscopy has been used to study the local structure of LiNi x Mn 2Ϫx O 4 (x ϭ 0.05,0.1,0.3,0.5) synthesized by solid-state reactions. When the extent of doping is small ͑x ϭ 0.05 and 0.1͒, several resonances are observed, which are assigned to lithium local environments containing different numbers of Mn 3ϩ and Mn 4ϩ ions. As the doping level increases and the average manganese oxidation state rises, the intensity of the resonances assigned to lithium environments containing a greater number of higher-oxidation state manganese ions increases; this results in a gradual shift of the center of mass of the spectrum to higher frequency. By x ϭ 0.5, only Mn 4ϩ ions are present, and only one major resonance, due to the lithium local environment Li͑ONi 2ϩ ͒ 3 ͑OMn 4ϩ ͒ 9 is observed; this is consistent with Mn/Ni ordering on the octahedral sites of the spinel structure. The variable temperature NMR behavior of these samples is indicative of different magnetic behavior for the undoped and doped materials. A plot of 1/␦ ͑␦ ϭ 6 Li NMR shift͒ vs. temperature is consistent with the predominance of antiferromagnetic correlations for low doping level samples, while Ni 2ϩ -O-Mn 4ϩ antiferromagnetic correlations clearly dominate the behavior of the x ϭ 0.5 sample, resulting in overall ferrimagnetic behavior. 6 Li MAS NMR spectra were also collected following various levels of charging. In the case of LiNi 0.1 Mn 1.9 O 4 , Li ϩ is deintercalated from the different local sites sequentially: lithium ions in the local environment containing manganese ions with an average oxidation state of ϩ3.5 are deintercalated first, followed by lithium ions in sites containing progressively more Mn 4ϩ ions. In contrast, for LiNi 0.5 Mn 1.5 O 4 , where the deintercalation process involves oxidation of Ni 2ϩ only, no changes in the lithium local environments were observed during the charging process: the shift position remained constant during the charging cycle and only a loss of the intensity of the lithium signal was observed.

structure structure (solids and liquids) D 2000 -010Cation Ordering and Electrochemical Properties of the Cathode Materials LiZnxMn 2−x O 4 , 0 ¡ x ≤ 0.5: A 6 Li Magic-Angle Spinning NMR Spectroscopy and Diffraction Study.-As revealed by 6 Li MAS NMR spectroscopy, powder XRD, and neutron powder diffraction Li is present in the octahedral sites of the spinal structure of the title compounds, indicating that Zn substitutes for Li in the tetrahedral sites. Ordered Li 0.5 Zn 0.5 [Mn 1.5 Li 0.5 ]O 4 crystallizes in the space group P2 1 3 and shows complete ordering on the octahedral site but some partial disorder or cation vacancies on the tetrahedral site. A gradual change in the nature of the magnetic interactions between Mn spins, from antiferromagnetic to ferromagnetic, is observed with increasing Zn concentration.