Performance of a Functionalised Polymer-Coated Silica at Treating Uranium Contaminated Groundwater from a Hungarian Mine Site

The performance of an active material for treating uranium contaminated groundwater within a permeable reactive barrier (PRB) is reported. This material, called PANSIL, has a tailored ligand system that selectively removes the uranyl (UO22+) cation from solution. The active uranyl ligand in PANSIL is a polyacryloamidoxime resin derived from polyacrylonitrile, which is deposited from solution onto the surface of quartz sand to form a thin film coating. PANSIL is effective at sequestering cationic and neutral uranyl species when the solution pH is above 4, due to the stability of the polyacryloamidoxime-uranyl complex formed. However the rate of sequestration decreases rapidly when the pH exceeds about 8 where neutral uranyl species are present only at very low concentrations. It can preferentially sequester UO22+ in the presence of typical divalent groundwater cations. In mildly alkaline conditions the sequestration performance in groundwater is sensitive to the concentration of uranyl complexing ligands, such as bicarbonate. Such behaviour has important consequences for PRB design as it will determine the barrier thickness required to treat a particular groundwater flow rate

Molecular Structure of the Uranyl Mineral Zippeite - An XRD, SEM and Raman Spectroscopic Study

Raman spectra at 298 and 77 K and infrared spectra of the uranyl sulfate mineral zippeite, K2[(UO2)6(SO4)3O(OH)6]. 4 H2O, were studied. Observed bands were tentatively attributed to the (UO2)2+ and (SO4)2- stretching and bending vibrations, the OH stretching vibrations of water molecules and hydroxyls, H2O bending vibrations and libration modes, and ￤ U-OH bending vibrations. Empirical relations were used for calculation of U-O bond lengths in uranyl R = f(￮3 or ￮1 (UO2)2+) Å. This was found in agreement with U-O bond lengths from the single crystal structure analysis. The number of observed bands supports the conclusion from single crystal structure analysis that at least two symmetrically distinct U6+ (in uranyl) and S6+ (in sulfate), and water molecules and hydroxyls may be present in the zippeite crystal structure. Some O-H…O bond lengths were attributed to the hydrogen-bonding network in zippeite crystal structure

Chemical Transformations of Hydrated Uranyl Fluoride

The chemical behavior of uranyl fluoride (UO2F2), a byproduct of the nuclear fuel cycle, is of significant interest for nuclear security applications. Two phases of uranyl fluoride (UO2F2 and [(UO2F2)(H2O)]7·4H2O) have been previously identified; these structures and the phase transition between them are further characterized in this work. In addition, the stability of uranyl fluoride is assessed under varying environmental conditions. While previous studies have suggested that uranyl fluoride may degrade upon exposure to high humidity, the chemical pathway of degradation was not well understood. This work demonstrates that uranyl fluoride undergoes a chemical reaction with water vapor to form a novel uranyl hydroxide hydration product. This species, shown to be structurally similar to the uranyl hydroxide mineral schoepite, can be further hydrated to form a uranyl peroxide species. The unexpected and novel nonphotochemical formation of uranyl peroxide from multiple uranyl hydroxide species is explained by unusually high uranyl ion reactivity in these reactant species. While the uranyl ion is typically fairly inert, strong sigma-donating equatorial ligands and strong interactions between uranyl oxygens and interlayer water molecules weaken the uranyl ion in these species such that an increase in the water vapor pressure can induce a redox reaction that is normally dependent on the photoexcitation of the uranyl ion

Uranyl phthalocyanines show promise in the treatment of brain tumors

Processes synthesize sulfonated and nonsulfonated uranyl phthalocyanines for application in neutron therapy of brain tumors. Tests indicate that the compounds are advantageous over the previously used boron and lithium compounds

Simple colorimetric method determines uranium in tissue

Simple colorimetric micromethod determines concentrations of uranium in tissue. The method involves dry ashing organic extraction, and colorimetric determination of uranyl ferrocyanide. This uranium determination technique could be used in agricultural research, tracer studies, testing of food products, or medical research

Thermal and Photochemical Reduction and Functionalization Chemistry of the Uranyl Dication, [U VI O2] 2+

The uranyl ion, [UVIO2]2+, possesses rigorously trans, strongly covalent, and chemically robust U-oxo groups. However, through the use of anaerobic reaction techniques, both one- and two-electron reductive functionalization of the uranyl oxo groups has been discovered and developed. Prior to 2010, this unusual reactivity centered around the reductive silylation of the uranyl ion which entailed conversion of the oxo ligands into siloxy ligands and reductive metalation of the uranyl oxo with Group 1 and f-block metals. This review surveys the large number of new examples of reductive functionalization of the uranyl ion that have been reported since 2010, including reductive borylation and alumination, metalation with d- or f-block metals, and new examples of reductive silylation. Other examples of oxo-group functionalization of [UVIO2]2+ that do not involve reduction, mainly with Group 1 cations, are also covered, along with new advances in the photochemistry of the uranyl(VI) ion that involve the transient formation of formally uranyl(V) [UVO2]+ ion

Ligand-Promoted Dissolution of Uranyl Phosphate Across Scales

The formation of uranyl phosphate precipitate is a remediation strategy because the low solubility of uranyl phosphate minerals, like chernikovite, limits the mobility of uranium in contaminated soils. However, organic ligands can complex with aqueous metal cations to form more soluble species. For example, citrate is a commonly occurring organic ligand produced by plants and microbes that increases the solubility of uranium and therefore the dissolution of uranyl phosphate minerals in the uranyl phosphate-citrate system. This effect is an important control on the mobility of uranium in organic-rich, and near-surface vegetated environments. Nevertheless, key aspects of the citrate-uranyl phosphate system remain poorly understood, and this limits the ability to assess risks of exposure and strategies for remediating uranium contaminated soils. The goals of this research are to determine the mechanism, extent, and rate of citrate-promoted dissolution of uranyl phosphate and evaluate how ligand-promoted dissolution and solid-phase transformations of uranyl phosphate affect macro-scale uranium transport. Batch dissolution, continuously stirred tank reactor (CSTR), soil column, and field lysimeter experiments were conducted to span across spatial scales ranging from Ångstrom to the meter scale. The results from all experiments indicate that the concentration of uranium dissolved from a chernikovite source increases with the concentration of citrate. However, this study determined that the rate of increase in uranium concentration diminishes at higher citrate concentrations and longer residence times and provided evidence of a uranyl-citrate alteration layer on the surfaces of uranyl phosphate grains after citrate exposure. These findings suggest that a combination of secondary-phase precipitation and ligand surface saturation hinder the release of uranium into solution. In the presence of soil, cations from the soil compete with uranium from the chernikovite to form citrate-complexes, slowing the dissolution of chernikovite. Soil cations, like potassium and calcium, can also integrate into the uranyl phosphate structure, altering the original chernikovite to a less soluble uranyl phosphate phase that is more resistant to citrate-promoted dissolution at lower citrate concentrations. The findings presented in this work show that although citrate promotes the dissolution of uranyl phosphate, other mechanisms hinder the release of uranium in the environment from a uranyl phosphate source

Neodymium as an alternative contrast for uranium in electron microscopy

Uranyl acetate is the standard contrasting agent in electron microscopy (EM), but it is toxic and radioactive. We reasoned neodymium acetate might substitute uranyl acetate as a contrasting agent, and we find that neodymium acetate indeed can replace uranyl acetate in several routine applications. Since neodymium acetate is not toxic, not radioactive and easy to use, we foresee neodymium will replace uranyl in many EM sample preparation applications worldwide

PHYSICO-CHEMICAL PROPERTIES OF PHOSPHATE CATION-EXCHANGE RESIN

There are investigated sorption and desorption characteristics of phosphate cation-exchange resin among metals: copper, nickel, cobalt, an uranyl-ion depending on pH-environment, the ionic form of cation-exchange resin, concentration of investigated cations. Interaction of cation-exchange resin in Na- and H-forms with solutions of salts sulphate of copper, nickel, cobalt, chloride sodium, calcium and nitrate of uranyl is studied. It is shown, that ions of copper, nickel, cobalt and an uranyl-ion by phosphate cation-exchange resin sorb at the expense of an ionic exchange and partially at the expense of formation of coordination communications with ionogenic group of cation-exchange resin. A study of the sorption of uranyl ions depending on the concentration of uranyl nitrate in the range of 0.01-0.1 N showed that with an increase in the concentration of uranyl in the studied interval, the value of sorption of uranyl increases slightly. The studied phosphate cation exchanger has a sufficiently high sorption and desorption ability to the ions of the tested metals