Abstract  A robust analytical method has been developed in our laboratory for the separation of radionuclides by means of extraction chromatography using an automated separation system. The proposed method is both cheap and simple and provides the advantageous, rapid and accurate separation of the element of interest. The automated separation system enables a shorter separation time by maintaining a constant flow rate of solution and by avoiding clogging or bubbling in the chromatographic column. The present separation method was tested with two types of samples (water and urine) using UTEVA-, TRU- and Sr-specific resins for the separation of U, Th, Am, Pu and Sr. The total separation time for one radionuclide ranged from 60 to 100 min with the separation yield ranging from 68 to 98% depending on the elements separated. We used ICP-QMS, multi-low-level counter and alpha spectroscopy to measure the corresponding elements.

Abstract  Laser optogalvanic spectrometry (LOGS) is being developed at the Diagnostic Instrumentation and Analysis Laboratory (DIAL) to measure the concentration of uranium present in the off-gases of mixed hazardous waste thermal-treatment systems, where metal species occur as airborne metal oxide and/or metallic particles rather than as free, single atoms. Limits of detection for uranium and selected volatile, toxic trace metal particles are reported. This study demonstrates the feasibility of using LOGS to detect uranium in off-gases at concentrations significantly lower than can currently be achieved using other real-time, on-line technologies, such as radioactive disintegration counting methods or air inductively coupled plasma-atomic emission spectrometry (air ICP-AES).

Abstract  An effective potentiometric sensor had been fabricated for the rapid determination of Pb2+ based on carbon paste electrode consisting of room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6), multiwalled carbon nanotubes (MWCNTs), nanosilica, synthesized Schiff base, as an ionophore, and graphite powder. The constructed nanocomposite electrode showed better sensitivity, selectivity, response time, response stability, and lifetime in comparison with typical Pb2+ carbon paste electrode for the successfully determination of Pb2+ ions in water and in waste water samples. The best response for nanocomposite electrode was obtained with electrode composition of 18% ionophore, 20% BMIM-PF6, 49% graphite powder, 10% MWCNT, and 3% nanosilica. The new electrode exhibited a Nernstian response (29.76 +/- 0.10 mV decade(-1)) toward Pb2+ ions in the range of 5 x 10(-9)-1.0 x 10(-1) mol L-1 with a detection limit of 2.51 x 10(-9) mol L-1. The potentiometric response of prepared sensor is independent of the pH of test solution in the pH range of 4.5-8.0. It has quick response with response time of about 6 s. The proposed electrode show fairly good selectivity over some alkali, alkaline earth, transition, and heavy metal ions.

Abstract  Schiff bases were obtained using p-trimethoxy benzaldehyde, p-hydroxyl benzaldehyde and 2-amino pyridine to prepare new complexes of thorium(IV) and dioxouranium(VI) metals by various anions. The synthesized ligands and complexes were analytically studied through spectral studies, elemental analysis conductance measurements along with semi empirical and thermogravimetric methods. The complexes were assigned various coordination numbers ranging from 6-10 on the basis of these studies.

Abstract  Prior to this study, phosphogypsum (PG) stockpiles at the Eshidiya mine in Jordan were thought to be potentially enriched with potentially toxic metals and radionuclides, resulting in possible environmental degradation of the surrounding ecosystem. In order to investigate this phenomenon, enrichment levels and distribution patterns of metals (e.g. Zn, Cd, V) and radionuclides in the underlying soils, alluvium, and yellow marl bedrock were determined and compared against those in the PG stockpiles. The Ra-226, Pb-210, and U-238 in soil reached peak concentrations of 1.5 pCi/g, 2.0 pCi/g, and 1.1 pCi/g, respectively. These elemental concentrations are similar to their concetrations in the uncontaminated soils, whereas the concentrations of these elements exhibit higher concentrations in PG and are as follows: Ra-226= 18 pCi/g, Pb-210= 19 pCi/g, and U-238= 4 pCi/g. The elements Cd, Zn, and V have maximum concentrations of 3 mg kg(-1), 69 mg kg(-1) and 62 mg kg(-1), respectively, in the soil's layer. These elemental concentrations are relatively lower than in uncontaminated soil and the PG. The degrees of mobility of the determined elements in soils were classified into three categories: elements with high mobility are Se, Mn, Pb, and Cr; those with moderate mobility are Co, Ni, As, Hg, Cu, V, and Zn; and those with low mobility are U, Cd, Pb-210, Ra-226, and U-238. Following correlation analysis, R-mode factor analysis was applied in conjunction with mineralogy to understand the geochemical variability of the soil. Four main meaningful factors were extracted: a detrital quartz factor, a clay minerals factor, a carbonate factor, and a terrigenous minerals factor. To investigate the spatial distribution patterns of the elements, a contour mapping technique was applied, allowing the following conclusions: (1) The elements Pb-210, Ra-226, and U exhibit similar distribution patterns; (2) Cd and Cu show similar distribution patterns; (3) As and V exhibit similar distribution patterns; and (4) no observed trend was observed for Cr. Generally, the results revealed that potentially toxic metals and radionuclides are not contaminated in soils related to the phosphogypsum stockpiles, and the soils of the Eshidiya area do not contain potentially toxic metals and radionuclide concentrations that threaten the surrounding ecosystem.

Abstract  Direct dating of fossil coral reefs using the U-series chronometer provides an important independent test of the Milankovitch orbital forcing theory of climate change. However, well-dated fossil corals pre-dating the last interglacial period (>130 thousand years ago; ka) are scarce due to, (1) a lack of sampling localities, (2) insufficient analytical precision in U-series dating methods, and (3) diagenesis which acts to violate the assumption of closed-system U-series isotopic decay in fossil corals. Here we present 50 new high-precision U-series age determinations for fossil corals from Henderson Island, an emergent coral atoll in the central South Pacific. U-series age determinations associated with the Marine Isotope Stage (MIS) 9 interglacial and MIS 7.5 interstadial periods are reported. The fossil corals show relatively little open-system U-series behaviour in comparison to other localities with fossil coral reefs formed prior to the last glacial cycle, however, open-system U-series behaviour is still evident in most of the dated corals. In particular, percent-level shifts in the [(230)Th/(238)U](act) composition are observed, leading to conventional U-series ages that are significantly younger or older than the true sample age. This open-system U-series behaviour is not accounted for by any of the open-system U-series models, indicating that new models should be derived. The new U-series ages reported here support and extend earlier findings reported in Stirling et al. (2001), providing evidence of prolific coral reef development on Henderson Island at 320 ka, most likely correlated with MIS 9.3, and subsequent reef development at similar to 307 ka during MIS 9.1, while relative sea-level was potentially similar to 20 m lower than during MIS 9.3. The U-series ages for additional well-preserved fossil corals are suggestive of minor reef development on Henderson Island during MIS 7.5 (245-230 ka) at 240.3 +/- 0.8 and 234.7 +/- 1.3 ka. All U-series observations are consistent with the Milankovitch theory of climate change, in terms of the timing of onset and termination of the dated interglacial and interstadial periods. The best preserved samples also suggest that the oceanic (234)U/(238)U during MIS 9 and MIS 7.5 was within five permil of the modern open ocean composition. (C) 2010 Elsevier Ltd. All rights reserved.

Abstract  Robust, independent age constraints on the absolute timing of climate events based on the U-series dating of fossil coral are sparse before the last glacial cycle. Using multiple-collector inductively coupled plasma mass spectrometry with multiple- Faraday protocols, we are able to date similar to 600 ka samples with an uncertainty of better than +/- 15 ka (2 sigma), representing a three-fold improvement in precision compared with previous techniques. Using these methods, we report U-series measurements for a suite of >500 thousand year old (ka) corals from Henderson Island, an emergent atoll in the south-central Pacific Ocean. The fossil corals show extraordinarily little diagenetic alteration for their age and the best-preserved sample yields a U-series age of 600 15 ka (2 sigma), which overlaps with the timing of the warm Marine Isotope Stage (MIS) 15 interglacial. The open-system model of Villemant and Feuillet [Villemant B. and Feuillet N. (2003) Dating open systems by the (238)U- (234)U-(230)Th method: application to Quaternary reef terraces. Earth and Planetary Science Letters 210(1-2), 105-118.] and the linear regression (or open-system isochron) is clearly limited for such old samples. However, the open-system model developed by Thompson et al. [Thompson W.G., Spiegelman M.W., Goldstein S.L., and Speed R.C. (2003) An open-system model for U-series age determinations of fossil corals. Earth and Planetary Science Letters 210(1-2), 365- 381.] appears to reliably correct for open-system effects in roughly half of the corals, giving a MIS 15 origin for these. Thus the data provide evidence that the systematic addition of (230)Th and (234)U through alpha-recoil is a dominant open-system process occurring in the Henderson Island fossil reef system. Several coral samples yield significantly older Thompson et al. open- system ages between 650 and 750 ka. The uncertainty on these ages (typically +/- 30 kyrs) is too great for precise assignment but most data overlap with the MIS 17 interglacial. The reliability of these ages is currently unclear. It is shown that separate aliquots of the same coral can yield different Thompson model ages. Therefore, there appear to be additional diagenctic mechanisms that create further anomalous excursions in the U-series systematics, limiting the reliability of the Thompson et al. open-system model. (c) 2007 Elsevier B.V. All rights reserved.

Abstract  We evaluated authigenic changes of Fe, Mn, V, U, Mo, Cd and Re in suboxic, periodically remobilized, tropical shelf sediments from the Amazon continental shelf and the Gulf of Papua. The Cd/Al, Mo/Al, and U/Al ratios in Amazon shelf sediments were 82%, 37%, and 16% less than those in Amazon River suspended sediments, respectively. Very large depletions of U previously reported in this environment were not observed. The Cd/Al ratios in Gulf of Papua sediments were 76% lower than measurements made on several Papua New Guinea rivers, whereas U/Al ratios in the shelf sediments were enriched by approximately 20%. Other metal/Al ratios in the Papua New Guinea river Suspended sediments and continental shelf sediments were not distinguishably different. Comparison of rnetal/Al ratios to grain size distributions in Gulf of Papua samples indicates that out, observations cannot be attributed to differences in grain size between the river Suspended sediments and continental shelf sediments. These two shelves constitute a source of dissolved Cd to the world ocean equal to 29-100%, of the dissolved Cd input from rivers, but only 3% of the dissolved Mo input and 4% of the dissolved U input. Release of Cd, Mo, and U in tropical shelf sediments is likely a result of intense Fe and Mn oxide reduction in pore waters and resuspension of the sediments. Since we do not observe depletions of particulate Fe and Mn in the shelf sediments most of these dissolved metals must reoxidize in the overlying waters and reprecipitate. As Cd exhibits the largest losses on these tropical shelves, we examined the ability of newly formed Fe and Mn oxides to adsorb dissolved Cd using a geochemical diffuse double-layer surface complexation model and found the oxide surfaces are relatively ineffective at readsorbing Cd in seawater due to surface-site competition by Mg and Ca. If the remobilization and reoxiclation of Fe and Mn Occurs frequently enough before sediment is buried significant amounts of Cd may be removed from the oxide surfaces. Because a much greater percentage of Mn than Fe becomes remobilized in these shelf sediments, metals closely associated with Mn oxides (like Cd) are more likely to show losses during deposition. (c) 2005 Elsevier Ltd. All rights reserved.

Abstract  Human health risk assessments for depleted uranium art common for Department Of Defense (DOD) sites since the metal has various military uses. At a training and experimental site, DU was evaluated in soil in order to make decisions regarding cleanup and future use of the site. At this site, concentrations were found to be protective of human health; DU is less toxic than uranium. Other data important to this decision were the type of receptors likely to be exposed, the amount of time spent by the receptor on-site, the acceptable yearly radiation dose, and other non-radiation associated effects to the kidney. Total uranium concentrations in soil were calculated,for the 90th percentile and the 50th percentile. The highest soil concentration used as all exposure point was 3500 ug/g (90th percentile). Short exposure timeframes contributed to the risk results.

Abstract  Radiological emergencies may occur either, as an accident or as a result of an intentional and malevolent use of radioactive sources. In the last few years, concerns about the potential use of radioactive materials in a ""dirty bomb"" or in an improvised nuclear device have increased. Although such an incident has not occurred up to now and experience in dealing with such a situation has not been acquired, there have been accidents with radioactive sources and radiation facilities that posed similar threats and challenged the capabilities of emergency responders and radiation protection infrastructures. Cases such as the deliberate poisoning of Litvinenko with Po-210, the accident in Goiania with a radioactive source taken from a medical facility by metal scrappers, the Chernobyl nuclear accident, and the Balkan's syndrome related to depleted uranium, are reviewed in order to extract lessons relevant to radiological protection and radiological emergency management.

Abstract  The objective of this study was to assess selected bioassays and ecological screening tools for their suitability in a weight of evidence risk screening process of acidic metal contaminated soil. Intact soil cores were used for the tests, which minimizes changes in pH and metal bioavailability that may result from homogenization and drying of the soil. Soil cores were spiked with ZnCl2 or CaCl2. Leachate collected from the soil cores was used to account for the exposure pathways through pore water and groundwater. Tests assessed included MetSTICK in soil cores and Microtox in soil leachate, lettuce (Lactuca sativa), red fescue (Festuca rubra) and red clover (Trifolium pratense) in the soil cores and lettuce and red clover in soil leachate. Hyallella azteca in soil leachate, and an ecological soil function test using Bait Lamina in soil cores. Microtox, H. azteca, lettuce and red fescue showed higher sensitivity to low pH than to Zn concentrations and are therefore not recommended as tests on intact acidic soil cores and soil leachate. The Bait Lamina test appeared sensitive to pH levels below 3.7 but should be investigated further as a screening tool in less acidic soils. Among the bioassays, the MetSTICK and the T. pratense bioassays in soil cores were the most sensitive to Zn, with the lowest nominal NOEC of 200 and 400 mg Zn/kg d.w., respectively. These bioassays were also tolerant of low pH, which make them suitable for assessing hazards of metal contaminated acid soils. (C) 2012 Elsevier Inc. All rights reserved.

Abstract  Se-79 is a long-lived (1.1x10(6) yrs) fission product which is chemically and radiologically toxic. Under Eh-pH conditions typical of oxidative alteration of spent nuclear fuel, selenite, seO(3)(2-) or HSeO3-; or selenate, SeO42-, are the dominant aqueous species of selenium. Because of the high solubility of metal-selenites and metal-selenates and the low adsorption of selenite and selenate aqueous species by geological materials under alkaline conditions, selenium may be highly mobile. However, Se-79 released from altered fuel may become immobilized by incorporation into secondary uranyl phases as low concentration impurities, and this may significantly reduce the mobility of selenium. Analysis and comparison of the known structures of uranyl phases indicate that (SeO3) may substitute for (SiO3OH) in structures of alpha-uranophane and boltwoodite that are expected to be the dominant alteration products of UO2 in Si-rich groundwater. The substitutions (SeO3)<-> (SiO3OH) in sklodowskite, Mg[(UO2)(SiO3OH)] (2)(H2O)(6) and (SeO3) tt (PO4) in phurcalite, Ca-2[(UO2)(3)(PO4)(2)O-2](H2O)(7), may occur with the eliminated apical anion being substituted for by an H2O group, but experimental investigation is required. The close similarity between the sheets in the structures of rutherfordine, [(UO2) (CO3)] and [(UO2)(SeO3)] implies that the substitution (SeO3) tt (CO3) can occur in rutherfordine, and possibly other uranyl carbonates. However, the substitutions: (SeO3) <-> (SiO4) in soddyite and (SeO3) <-> (PO4) in phosphuranylite may disrupt their structural connectivity and are, therefore, unlikely. (C) 1999 Elsevier Science B.V. All rights reserved.

Abstract  Groundwater and soil contamination with depleted uranium (DU) is an important public concern because of its long-term toxicity. In this study, the DU risk in groundwater was assessed through modeling of its sorption equilibrium and kinetics, as well as modeling of its transport in natural subsurface systems. Whenever possible, simulation results were compared with published experimental and field data. Equilibrium modeling studies showed that DU sorption increased sharply from 0 to 100% in the pH range of 3.5 to 5.0 and maximum immobilization was established at pH > 5. Kinetic simulations indicated that the sorption of DU in subsurface systems is a rapid process. Simulations of DU mobility due to groundwater flow and due to infiltration, as well as modeling of DU fate, were carried out by using a metal ion transport model, which included aqueous speciation, redox, precipitation, and sorption reactions. The results showed that the DU mobilization is a relatively slow process. Precipitation, redox, and sorption reactions resulted in the immobilization of DU. Among these reactions, sorption played a major role, and the pH of soils was critical in the immobilization; higher pH in soils resulted in greater immobilization of DU. The impact of DU transport from infiltration was estimated based on four extreme cases of climate and existing conditions of uranium penetrator fragments. The simulations demonstrated that the transport of DU in groundwater is slow due to the low infiltration rate and low DU concentration resulted from the penetrators. Finally, modeling of DU fate showed that the natural cleanup of the DU-contaminated sites is a slow process.

Abstract  The paper describes the results of experimental investigations and instrumental realization of remote method of laser induced breakdown spectroscopy (LIES) for express diagnostics of highly toxic and radioactive elements in the water. As an example the samples of oxides of non-ferrous metals and uranium are used. The emission spectrum of materials is excited in non-equilibrium plasma of a laser spark. A laser source provides in the radiation focusing range at a wavelength of 10.6 mm the peak radiation density 10(8) - 5x10(7) W/cm(2), the pulse duration at half-altitude is 0.3 ms. On the atmospheric experiments the radiation focusing is performed using the Cassegrainian telescope with a large mirror 0.45 m diameter. Statistical data an laser spark initiation have been obtained at distances up to 250 m - on the solid and liquid targets.

Abstract  The Athabasca Basin hosts many world-class unconformity related uranium deposits. Recently, uranium reserves for the Eagle Point basement-hosted deposit have increased with the discovery of new mineralized zones within secondary structures. A paragenetic study of Eagle Point reveals the presence of three temporally distinct alteration stages: a pre-Athabasca alteration, a main alteration and mineralization comprised of three substages, and a post-main alteration and mineralization stage that culminated in remobilization of uraninite from primary to secondary structures. The pre-Athabasca alteration stage consists of minor amounts of clinochlore, followed by dolomite and calcite alteration in the hanging wall of major fault zones and kaolinitization of plagioclase and K-feldspar caused by surface weathering. The main alteration and uranium mineralization stage is related to three temporally distinct substages, all of which were produced by isotopically similar fluids. A major early alteration substage characterized by muscovite alteration and by precipitation Ca-Sr-LREE-rich aluminum phosphate-sulfate minerals, both from basinal fluids at temperatures around 240A degrees C prior to 1,600 Ma. The mineralization substage involved uraninite and hematite precipitated in primary structures. The late alteration substage consists of dravite, uranophane-beta veins, calcite veins, and sudoite alteration from Mg-Ca-rich chemically modified basinal fluids with temperatures around 180A degrees C. The post-main alteration and mineralization stage is characterized by remobilization of main stage uraninite from primary to secondary structures at a minimum age of ca. 535 Ma. U-Pb resetting events recorded on primary and remobilized uraninites are coincident with fluid flow induced by distal orogenies, remobilizing radiogenic Pb to a distance of at least 225 m above the mineralized zones.

Abstract  Knowledge of the ability of an aquifer to retard the groundwater transport of toxic or radioactive ions can be inferred from the analysis of groundwater for the radionuclides of the U-238- and Th-232-decay chains. Groundwaters of varying chemical composition were analyzed from wells in Long Island, New York, and Connecticut. Aquifer lithologies are arkose, quartz sandstone, granite, and glacial drift. Adsorption (k1) and desorption (k2) coefficients for Ra and Pb were calculated using Rn-222 activity as a measure of the supply of other alpha-recoil nuclides. Laboratory tests of the validity of this assumption were made by measuring the flux of Ra-224 and Rn-222 from aquifer solids. The ratio k1/k2 is the distribution coefficient, K, which is effectively equal to R(f), the retardation factor. The average value of K for Ra is 6 x 10(2) in Long Island aquifers and 5 x 10(4) in Connecticut. The distribution coefficient for Pb is 10(4) in Long Island and 10(5) in Connecticut. Results from this and other studies reveal a strong dependence of retardation on pH, f(O2), and ionic strength that tends to overwhelm any dependence of retardation on lithology.

Abstract  The response of an aquatic environment to the decrease of phosphate discharges from a technologically improved transhipment terminal, situated at the Croatian Adriatic coast in the port of Sibenik, has been assessed based on uranium activity and concentration in sediment, seawater and mussels Mytilus sp. The highest 238 U activities (485 +/- 16 Bq kg(-1) dry weight) were found in the sediment sample collected from the sampling site closest to the terminal. The maximum concentrations in the sediment samples are above the natural ranges and clearly indicate the harbour activities' influence. The U-238/Ra-226 activity ratios in sediment samples demonstrate the decreasing trend of phosphate ore input. Mussel samples showed levels of U-238 activities in the range from 12.1 +/- 2.9 to 19.4 +/- 7.2 Bq kg(-1) dry weight, thus being slightly higher than in normally consumed mussels. Only the seawater, taken just above the bottom sediment at the sampling site closest to the terminal, shows a slightly higher uranium concentration (3.1 +/- 0.2 mu g L-1) when compared to the samples taken in upper seawater layers (2.1 +/- 0.2 mu g L-1) but is in the range of the concentration level of uranium in natural seawater. Since the transhipment terminal in the port of Sibenik was modernised in 1988, discharge of phosphate ore into the seawater was drastically reduced and, consequently, uranium concentration levels in seawater have decreased. However, enhanced uranium activity levels are still found in deeper sediment layer samples and in mussel. (c) 2005 Elsevier Ltd. All rights reserved.

Abstract  A model of rabbit muscle phosphoglucomutase was refined at 2.7-angstrom resolution by using two heavy atom derivatives for initial phasing and standard refinement procedures, including molecular replacement averaging about a 2-fold axis and dynamic simulation: final R-factor, 0.223 (no solvent modeling); RMS deviation from standard bond lengths and angles, 0.020 angstrom and 3.6-degrees, respectively (all 8658 nonhydrogen atoms plus 36,953 reflections (F/sigma greater-than-or-equal-to 3) between 8- and 2.7-angstrom resolutions); average of individually refined atomic B-factors, 40 angstrom2 (all atoms) and 30 angstrom2 (all atoms in domains I-III). An H-bonding scheme with 538 main chain H-bonds for the two monomers in the asymmetric unit and probable ligands for six uranyl ions in one heavy atom derivative is given. The monomer contains 42 strands/helices arranged into four alpha/beta-domains. Each of the first three domains contains an alpha-3-beta-4-alpha-1 motif, where the topology of beta-4 is 2,1,3,4:up up up down, which is a topology not encountered in an extensive search among known protein structures. A spatial similarity is observed between corresponding residues in the three repetitions of this motif per monomer, but the minimal mutational distance between spatially corresponding residues is not statistically significant. The loop between the antiparallel strands in each of these domains is an important feature of the active site. In domain IV, beta-sheet topology is 2,1,3,4,6,6:down up up up down up. Non-covalent domain/domain interactions within the monomer are greatest between adjacent domains along the polypeptide chain, which are not substantially interdigitated and can be cleanly disengaged by altering the phi/psi-torsional angles of three uniquely positioned residues in the model. The observed hierarchy of noncovalent interactions between structural units within the crystal, based on a semi-empirical paradigm, suggests that monomer-monomer contacts within the asymmetric unit are formed during growth of the lattice and provides a rationale for some of the diffraction characteristics of phosphoglucomutase crystals. An unusually deep crevice involving 58 residues is formed by the head-to-tail, twisted semicircular arrangement of the four domains of the monomer that places no atom more than 12 angstrom from the water-accessible surface. The active site of the enzyme is extensively buried at the bottom of this crevice, at the approximate confluence of the four domains. Other features of the active site, including the surrounding helical dipoles, and the metal-ion binding pocket are described, together with structure/function comparisons with a number of other enzymes.

Abstract  The effect of mercury and some other heavy metals on the ferrous iron oxidizing ability of Thiobacillus ferrooxidans was studied using redox potential measurement, UV-VIS and atomic absorption (AA) spectroscopy, and electron microscopy, Results obtained suggest that the presence of some cations (e.g. Hg(II), Ag(I), Pb(II) and Cd(II) at a concentration level of 10 mg/l), inhibits the microbial oxidation of Fe(II). The presence of 10 mg/l of As(III), Mn(II), Sn(II), Co(II), Cu(lI) and Zn(II) and anions such as Cl- and NO3- did not have an observable effect on Fe(II) oxidizing activity of the bacteria. Our results also suggest that Hg(II) inhibits the microbial oxidation of Fe(II) in an uncompetitive mechanism, suggesting that it may bind with the enzyme-Fe(II) complex. In the presence of 10 mg/l Hg(II), microbial oxidation of Fe(II) is likely to be controlled by the rate of diffusion of Fe(II) into the periplasmic space of the T. ferrooxidans cells.

Abstract  The predominant form of technetium under oxic conditions is the pertechnetate anion (TcO4-), which is highly soluble in water and readily mobile in the environment. Technetium-99 is of particular concern because of its persistence and mobility. Various equipment decontamination and uranium recovery operations at the Portsmouth Gaseous Diffusion Plant generate a ''raffinate'' waste stream characterized by toxic heavy metals, high concentration of nitric acid, and low levels of radionuclides (U-235 and Tc-99). Dilution and adjustment of solution pH to a value of 8.2 to 8.5 precipitates a heavy-metals-sludge and a filtrate. The removal of Tc-99 from these waste streams and from contaminated groundwater can be accomplished using anionic ion-exchange resins. Batch equilibrium and packed column breakthrough and regeneration studies were performed using inorganic sorbents and organic ion-exchange resins (Dowex SRB-OH and Reillex resins). These studies were performed on actual and surrogate raw raffinates, filtrates, and surrogate groundwater samples. The experimental conditions were chosen to closely represent the actual process.

Abstract  Actinide chemistry and electronuclear cycle: contribution of synchrotron radiation The topics related to actinide chemistry involved in the civil nuclear industry follow the electronuclear cycle: mining-enrichment, physical chemistry of the nuclear fuel, behavior in reactors, selective extraction for fuel reprocessing, storage, environmental impact, and human toxicology. In order to characterize the actinide properties, dedicated synchrotron beam lines are necessary, although scarce. This article focuses on synchrotron studies related to the elaboration of the nuclear fuel, its reprocessing, the storage in glass matrices and the bio-environmental impact.

Abstract  In oxidizing environments, the toxic and radioactive element uranium (U) is most soluble and mobile in the hexavalent oxidation state. Sorption of U (VI) on Fe-oxides minerals (such as hematite [alpha-Fe2O3] and goethite [alpha-FeOOH]) and occlusion of U(VI) by Fe-oxide coatings are processes that can retard U transport in environments. In aged U-contaminated geologic materials, the transport and the biological availability of U toward reduction may be limited by coprecipitation with Fe-oxide minerals. These processes also affect the biological availability of U(VI) species toward reduction and precipitation as the less soluble U(IV) species by metal-reducing bacteria. To examine the dynamics, of interactions between U(VI) and Fe oxides during crystallization, Fe-oxide phases (containing 0.5 to 5.4 mol% U/(U + Fe)) were synthesized by means Of Solutions of U(VI) and Fe (III). Wet chemical (digestions and chemical extractions) and spectroscopic techniques were used to characterize the synthesized Fe oxide coprecipitates after rinsing in deionized water. Leaching the high mol% U solids with concentrated carbonate solution (for sorbed and solid-phase U(VI) species) typically removed most of the U, leaving. on average. about 0.6 mol% U. Oxalate leaching of solids with low mol% U contents (about I mol% U or less) indicated that almost all of the Fe in these solids was crystalline and that most of the U was associated with these crystalline Fe oxides. X-ray diffraction and Fourier-transform infrared (FT-IR) spectroscopic studies indicate that hematite formation is preferred over that of goethite when the amount of U in the Fe-oxides exceeds 1 mol% U (similar to4 wt% U). FT-IR and room temperature continuous wave luminescence spectroscopic studies with unleached U/Fe solids indicate a relationship between the mol% U in the Fe oxide and the intensity or existence of the spectra features that can be assigned to UO22+ species (such as the IR asymmetric nu(3) stretch for O = U = O for uranyl). These spectral features were undetectable in carbonate- or oxalate-leached solids, suggesting solid phase and sorbed U(VI)O-2(2+) species are extracted by the leach solutions. Uranium L-3- edge x-ray absorption spectroscopic (XAFS) analyses of the unleached U-Fe oxide solids with less than 1 mol% U reveal that U(VI) exists with four O atoms at radial distances of 2.19 and 2.36 Angstrom and second shell Fe at a radial distance at 3.19 Angstrom. Because of the large ionic radius of UO22+ (similar to1.8 Angstrom) relative to that of Fe3+ (0.65 Angstrom), the UO22+ ion is unlikely to be incorporated in the place of Fe in Fe(Ill)-oxide structures. Solid-phase U(VI) can exist as the uranyl [U(VI)O-2(2+)] species with two axial U-O double bonds and four or more equatorial U-O bonds or as the uranate species (such as gamma-UO3) without axial U-O bonds. Our findings indicate U6+ (with ionic radii of 0.72 to 0.8 Angstrom, depending on the coordination environment) is incorporated in the Fe oxides as uranate (without axial O atoms) until a point of saturation is reached. Beyond this excess in U concentration, precipitating U(VI) forms discrete crystalline uranyl phases that resemble the uranyl oxide hydrate schoepite [UO2(OH)(2).2H(2)O]. Molecular modeling studies reveal that U6+ species could bond with O atoms from distorted Fe octahedra in the hematite structure with an environment that is consistent with the results of the XAFS. The results provide compelling evidence of U incorporation within the hematite structure. Copyright (C) 2002 Elsevier Science Ltd.

Abstract  Since the first commercial extraction of uranium in the early 1940s, the range of feasible process alternatives has greatly increased. This paper reviews process options to reduce extraction costs, improve efficiencies, effect safer operations, and lessen environmental impacts. Equipment and processes used in the past, in use now, and that could be considered for future use are described.