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The directing effect of coordinating ligands in the formation of uranium molecular complexes has been well established, but the role of counterions in metal-ligand interactions remains ambiguous and requires further investigation. In this work, we describe the targeted isolation, through the choice of alkali-metal ions, of a family of tetravalent uranium sulfates, showing the influence of the overall topology and, unexpectedly, the UIV nuclearity upon the inclusion of such countercations. Analyses of the structures of uranium(IV) oxo/hydroxosulfate oligomeric species isolated from consistent synthetic conditions reveal that the incorporation of Na+ and Rb+ promotes the crystallization of 0D discrete clusters with a hexanuclear [U6O4(OH)4(H2O)4]12+ core, whereas the larger Cs+ ion allows for the isolation of a 2D-layered oligomer with a less condensed trinuclear [U3(O)]10+ center. This finding expands the prevalent view that counterions play an innocent role in molecular complex synthesis, affecting only the overall packing but not the local oligomerization. Interestingly, trends in nuclearity appear to correlate with the hydration enthalpies of alkali-metal cations, such that the alkali-metal cations with larger hydration enthalpies correspond to more hydrated complexes and cluster cores. These findings afford new insights into the mechanism of nucleation of UIV, and they also open a new path for the rational design and synthesis of targeted molecular complexes.

We report separation data indicating that 99Mo can be separated from a vast excess of either uranyl sulfate or uranyl nitrate in irradiated dilute acid solutions. These results suggest that, if medical isotope 99Mo is produced during fission of high concentrations of low enriched uranium sulfate solution fuel, it is feasible to both recover >90% of the 99Mo for further purification and the uranium for recycle.

In situ leaching of uranium ores with sulfuric acid during active uranium mining activity on the Gessenheap has caused longstanding environmental problems of acid mine drainage and elevated concentrations of uranium. To study there remediation measures the test site Gessenwiese, a recultivated former uranium mining heap near Ronnenburg/East Thuringia/Germany, was installed as a part of a research program of the Friedrich-Schiller University Jena to study, among other techniques, the phytoremediation capacity of native and selected plants towards uranium. In the first step the uranium speciation in surface seepage and soil pore waters from Gessenwiese, ranging in pH from 3.2 to 4.0, were studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS). Both types of water samples showed mono-exponential luminescence decay, indicating the presence of only one major species. The detected emission bands were found at 477.5, 491.8, 513.0, 537.2, 562.3, and 590.7 nm in case of the surface water samples, and were found at 477.2, 493.2, 513.8, 537.0, 562.4, and 590.0 nm in case of the soil water samples. These characteristic peak maxima together with the observed mono-exponential decay indicated that the uranium speciation in the seepage and soil pore waters is dominated by the uranium (VI) sulfate species UO2SO4(aq). Due to the presence of luminescence quenchers in the natural water samples the measured luminescence lifetimes of the UO2SO4(aq) species of 1.0–2.6 μs were reduced in comparison to pure uranium sulfate solutions, which show a luminescence lifetime of 4.7 μs. These results convincingly show that in the pH range of 3.2–4.0 TRLFS is a suitable and very useful technique to study the uranium speciation in naturally occurring water samples. Electronic supplementary material The online version of this article (doi:10.1007/s10967-011-1389-z) contains supplementary material, which is available to authorized users.

The subsurface acid mine drainage (AMD) environment of an abandoned underground uranium mine in Konigstein/Saxony/Germany, currently in the process of remediation, is characterized by low pH, high sulfate concentrations and elevated concentrations of heavy metals, in particular uranium. Acid streamers thrive in the mine drainage channels and are heavily coated with iron precipitates. These precipitates are biologically mediated iron precipitates and related to the presence of Fe-oxidizing microorganisms forming copious biofilms in and on the Fe-precipitates. Similar biomineralisations were also observed in stalactite-like dripstones, called snottites, growing on the gallery ceilings. The uranium speciation in these solutions of underground AMD waters flowing in mine galleries as well as dripping from the ceiling and forming stalactite-like dripstones were studied by time resolved laser-induced fluorescence spectroscopy (TRLFS). The fluorescence lifetime of uranium species in both AMD water environments were best described with a mono-exponential decay, indicating the presence of one major species. The detected positions of the emission bands and by comparing it in a fingerprinting procedure with spectra obtained for acid sulfate reference solutions, in particular Fe(III) – SO42− – UO22+ reference solutions, indicated that the uranium speciation in the AMD environment of Konigstein is dominated in the pH range of 2.5–3.0 by the highly mobile aquatic uranium sulfate species UO2SO4(aq) and formation of uranium precipitates is rather unlikely as is retardation by sorption processes. The presence of iron in the AMD reduces the fluorescence lifetime of the UO2SO4(aq) species from 4.3 μs, found in iron-free uranium sulfate reference solutions, to 0.7 μs observed in both AMD waters of Konigstein and also in the iron containing uranium sulfate reference solutions. Colloids were not observed in both drainage water and dripping snottite water as photon correlation spectroscopy analyses and centrifugation experiments at different centrifugal accelerations between 500g and 46000g revealed. Thus transport and uranium speciation at the investigated AMD sites is neither influenced by U(IV) or U(VI) eigencolloids nor by uranium adsorbed on colloidal particles. This study shows that TRLFS is a suitable spectroscopic technique to identify the uranium speciation in bulk solutions of AMD environments.

The title compound, poly[N,N,N′N′-tetramethylpropane-1,3-diaminium [aquatetraoxotri-μ3-sulfatodiuranate(VI)]], (C7H 20N2)[(UO2)2(SO4) 3(H2O)]n, contains two-dimensional [(UO 2)2(SO4)3(H20)] 2~ layers that are unprecedented in uranium chemistry. The layers in this compound are separated by C7H20N22+ cations, forming the basis of an extensive hydrogen-bonding network. An independent intralayer hydrogen-bonding network is also observed, involving water molecules bound directly to a uranium centre. © 2005 International Union of Crystallography Printed in Great Britain - all rights reserved.

The uranium mine in Konigstein (Germany) is currently in the process of being flooded. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO2SO4) and UO2++ speciation as well as of the solid uranium species Uranophane [Ca(UO2)(2)(SiO3OH)(2)center dot 5H(2)O] and Coffinite [U(SiO4)(1-x)(OH)(4x)], which are defined in the stability field of pH>4.8 and Eh < 960 mV and pH>0 and Eh4.8. Even analysis by Energy-filtered Transmission Electron Microscopy (EF-TEM) and electron energy loss spectroscopy (EELS) within the biofilms did not provide any microscopic or spectroscopic evidence for the presence of uranium immobilization. In laboratory experiments the first phase of the flooding process was simulated by increasing the pH of the AMD water. The results of the experiments indicated that the F. myxofaciens dominated biofilms may have a substantial impact on the migration of uranium. The AMD water remained acid although it was permanently neutralized with the consequence that the retention of uranium from the aqueous solution by the formation of solid uranium species will be inhibited.

Three different continuous processes were developed for the recovery of uranium from sulfate-containing simulated mill solutions. In all cases, a high-quality product, low in molybdenum and vanadium, which could be filtered and dried easily, was obtained. The presence of sulfate slows the precipitation rate and results in larger precipitated particles, which is an advantage in filtering and drying the precipitate. The morphologies of the large particles produced in the processes described in this report suggest that crystal growth predominated over nucleation in the precipitator. At 60 °C, the uranium peroxide precipitated as the dihydrate, but below 50 °C to 60 °C, the tetrahydrate was formed, and this knowledge led to important conclusions regarding the rate of the precipitation. A variety of particle morphologies was found, the most unusual being spherulitic aggregates consisting of needles radiating from a common point at the center of the particle.

The effect of employing hydrofluoric acid as a mineraliser in the formation of organically templated uranium sulfate materials has been studied. Variable amounts of HF((aq)) were added to a series of reaction gels in which all other reactant concentrations were invariant, resulting in the formation of three different phases, depending upon the fluoride concentration. Two of these phases are novel; [N(2)C(4)H(14)][UO(2)(H(2)O)(SO(4))(2)] is a new templated uranium sulfate, containing anionic [UO(2)(H(2)O)(SO(4))(2)](2-) chains that hydrogen bond to one-another forming pseudo-layers, and [N(2)C(4)H(14)][UO(2)F(SO(4))](2) is the first example of a templated uranium sulfate fluoride, which consists of uranium fluoride chains linked by sulfate groups to form [UO(2)F(SO(4))](-) layers. The role of F(-) in these reactions is two-fold; it acts as a mineraliser when present in small concentrations, while it is incorporated into the reaction product when present in larger mole fractions. Both of the new materials have been characterised using a range of physical techniques including single crystal X-ray structure analysis.

The chemical process involved in the separation and purification of 99 Mo from the liquid fuel of a water-boiler reactor (WBR) has been established. The process includes separation of 99 Mo from uranium sulfate fuel solution with α-benzoin oxime precipitation and purification of 99 Mo by chelating ion exchanger, alumina, and calcium phosphate hydroxide as adsorbents. Recycling of uranium fuel solution to WBR was performed by purification with anion exchanger and hydrogen peroxide precipitation. Parameters affecting the recovery yield and purity of 99 Mo and uranium in each process step were examined by batch study. Synthetic fuel solution experiments under the established optimum process conditions were also carried out. The experimental results conclude that the overall recovery of 99 Mo product solution is 81.0±1.5% and that its radionuclide purity is quite satisfactory for the preparation of 99m Tc generator for nuclear medical diagnosis applications. The recovery yield of uranium fuel was found to be 98.5±0.3%.

Batch 316-type cellulose acetate membranes were characterized in terms of pure water permeability constant, solute transport parameter, and mass transfer coefficient with a reference system of aqueous sodium chloride solution. These membranes were used in the determination of reverse osmosis characteristics such as product rate and solute separation in the case of uranium sulfate solutions of different concentrations (100 to 8000 ppm) in the feed solutions. A long-term test extending over a week has been carried out with dilute uranium solutions. Reverse osmosis treatment of synthetic mine water sample showed satisfactory performance of the membranes in the separation of metal ions.

Reactions between sulfides of heavy metals and solutions of hexavalent uranium sulfate at pH about 2, in the range of 200-360°C, led to replacement of pyrrhotite by marcasite-pyrite aggregate, development of bornite and pyrite after chalcopyrite, growth of regenerated chalcopyrite on the periphery of uranium oxides, replacement of chalcopyrite by bornite (with the accompanying complications, fig. 3), redepositions of chalcocite and native copper, and, in experiments with pyrite-galena and galena-marmatite pairs, redepositions of the minerals with the corresponding growth of pyrite. —V.P. Sokoloff.

Solutions of copper and uranium sulfate can be analyzed with relative standard deviations of about 0.1% by controlled-potential coulometric titration if both ions are reduced at -0.3 volt and copper only is reoxidized at plus or minus 0.175 volt. The method is not affected by the copper-uranium ratio. (auth)

The technique of high-frequency titrimetry was applied to the determination of thorium, uranium, sulfate, and free acid. In Part I, the reproducibility of the method for the titration of standard solutions that contained 50 rag of thorium in the absence of interferences is established. Under these conditions, the coefficient of variation of the method was

Only fifty-four years ago the French physicist Becquerel announced the discovery of the phenomenon which we now term radioactivity. In those fifty-four years many scientists of many different disciplines have contributed an immense store of knowledge to this rapidly expanding field. Chief among the contributions, however, have been those of physicists and of chemists. Two of the previous papers in this series have dealt with the physical aspects of radioactivity. We shall discuss here a small part of the chemists' contributions to the knowledge of radioactivity, as well as applications of the phenomenon to the solution of problems in chemistry. In 1896 Henri Becquerel, engaged in a general study of phosphorescence of natural materials, noted that certain uranium minerals were capable of fogging photographic plates even through heavy black paper. This property was not dependent upon the amount of previous solar irradiation, hence was different from the phosphorescence Becquerel was studying. It was an entirely new and independent phenomenon, seemingly unique to uranium containing minerals. At just this time the young Polish chemist, Marie Sklodowska Curie, was casting about for a research problem suitable for a doctoral thesis. She was immediately interested by Becquerel's results, and soon with the complete approval of her physicist husband, Pierre, she began to study the phenomenon. After developing means such as the electroscope to measure the activity, she showed that the activity was proportional to the amount of uranium present, and that it was also independent of the state of chemical combination of the uranium. That is, a definite weight of uranium was associated with a definite amount of activity, whether the uranium was present as elementary metal, or combined with other elements to form such compounds as uranium oxide or uranium sulfate. Radioactivity, as Mme. Curie named the phenomenon, was thus shown to be an atomic property. It must have seemed to Mme. Curie quite unlikely, perhaps even unreasonable, that such an interesting property as radioactivity should be exhibited by compounds of only one element, uranium. At any rate, she undertook an exhaustive investigation of all minerals of which she could obtain samples. One result of this Edisonian research was the discovery of the radioactivity of thorium and thorium compounds. A more impor