Mobility Of Actinides Research Articles

Impact of a Biological Chelator, Lanmodulin, on Minor Actinide Aqueous Speciation and Transport in the Environment.

Minor actinides are major contributors to the long-term radiotoxicity of nuclear fuels and other radioactive wastes. In this context, understanding their interactions with natural chelators and minerals is key to evaluating their transport behavior in the environment. The lanmodulin family of metalloproteins is produced by ubiquitous bacteria and Methylorubrum extorquens lanmodulin (LanM) was recently identified as one of nature's most selective chelators for trivalent f-elements. Herein, we investigated the behavior of neptunium, americium, and curium in the presence of LanM, carbonate ions, and common minerals (calcite, montmorillonite, quartz, and kaolinite). We show that LanM's aqueous complexes with Am(III) and Cm(III) remain stable in carbonate-bicarbonate solutions. Furthermore, the sorption of Am(III) to these minerals is strongly impacted by LanM, while Np(V) sorption is not. With calcite, even a submicromolar concentration of LanM leads to a significant reduction in the Am(III) distribution coefficient (Kd, from >104 to ∼102 mL/g at pH 8.5), rendering it even more mobile than Np(V). Thus, LanM-type chelators can potentially increase the mobility of trivalent actinides and lanthanide fission products under environmentally relevant conditions. Monitoring biological chelators, including metalloproteins, and their biogenerators should therefore be considered during the evaluation of radioactive waste repository sites and the risk assessment of contaminated sites.

Thermodynamic Study of Am(III)-Isosaccharinate Complexation at Various Temperatures Implicating a Stepwise Reduction in Binding Denticity.

Isosaccharinic acid, a major final product of cellulose degradation under highly alkaline cement porewater conditions, is known to increase the mobility of actinides via strong complex formation. In this study, the formation of Am(III) complexes with α-d-isosaccharinate (ISA) was studied in terms of thermodynamics and coordination structures by combining spectrophotometry, time-resolved laser fluorescence spectroscopy (TRLFS), and density functional theory (DFT) calculations. The formation constants of the Am(III)-ISA complexes were determined by absorption spectroscopy at temperatures in the range of 15-70 °C. The measured reaction enthalpy and entropy changes indicate that the formation of a 1:1 Am(III)-ISA complex is driven by an increase in entropy. By contrast, the 1:2 complex formation is exothermic with a much less increase in entropy. DFT calculations predict that C2- and C4-hydroxyl groups, along with the carboxyl group, participate in the tridentate chelate binding of the primary ISA. The thermodynamic, TRLFS, and DFT results collectively suggest the tridentate binding of the primary ISA to Am(III) via a carboxylate and C2- and C4-hydroxyl groups in the protonated state and reduced dentate binding of the secondary ISA, such as bidentate binding, forming a four-membered ring structure via the carboxylate group.

Sixty years of Radiochimica Acta: a brief overview with emphasis on the last 10 years

Abstract On the occasion of the diamond jubilee of Radiochimica Acta (RCA), this article briefly describes the progress made by the journal during the last 10 years; a detailed account of the developments during the first 50 years having been given earlier ( Radiochimica Acta 2012, 100, 483–492). Publishing responsibility for the journal was taken over in 2014 by Walter De Gruyter, a traditional German publishing company founded in 1749. This allowed RCA also to maintain its established traditional standard of publishing. Being broad-based, the journal encompasses all chemical aspects of nuclear science and technology. It has kept pace with the changing trends in radiochemical research. Today, besides fundamental nuclear chemistry, applied topics, such as chemical behaviour and mobility of actinides and fission products, accelerator-based radiochemistry, development of novel radiochemical techniques, study of radiation chemical effects, etc., are well represented. The journal is supported by a group of international Editors and Advisors who are distinguished radiochemists themselves. It follows a strict peer-review system and is assisted by a network of about 500 referees. About 200 manuscripts are received per year, out of which 40–45% are rejected. The impact factor (IF) of RCA is comparable to those of other radiochemistry-related journals, but the cited half-life (CHL) of RCA is by far the highest of all related journals. A list of top highly cited 100 articles has been provided alongside this article. In the past, most of the articles originated from Europe and North America, but in recent years the number of contributions from China and several developing countries has been increasing. All articles are published in English, and the journal is presently available to read both online and in a printed format.

Geochemical mobility of rare earth elements (REEs) and actinides (U and Th) originating from Kusatsu acid thermal waters during neutralization and river transport: Effect of aqueous speciation on sorption onto suspended materials and fractionation among REEs and actinides

Acidic thermal water originating from the Kusatsu geothermal area of Gunma Prefecture, Japan is introduced into rivers, where there are many anthropogenicobjects such as a neutralization plant, a dam and water channels for hydroelectric power plants. We have investigated changes in the physico-chemical nature and fractionation mechanisms of rare earth elements (REEs) including Y and actinides (Th and U) by artificial and natural neutralization processes during river transport.The geochemical behavior of these elements and fractionation among them are mainly controlled by pH-dependent sorption and/or precipitation, once the pH increases up to 5.5. Dissolved Th is nearly completely removed, and hydrous Fe and Al oxides (HFO and HAO) sorbing Th or Th(SO4)2s settle onto the reservoir's bed. On the other hand, REEs and U remain as dissolved species. The effect of temperature on removal of these metals is limited.At pH values of ~5.5, REEs and U are removed by HFO and/or HAO, resulting in less fractionation among them. As pH increases to greater than 6.5, dissolved REEs continue to be removed by HFO and/or HAO, whereas U largely remains as a dissolved species in river water. Formation of UO2‑carbonate complex species prevents removal of dissolved U. When pH approaches 8, U is desorbed from suspended materials.Fractionation of REEs including Y occurs during sorption onto suspended materials and is strongly pH-dependent. REEs are less fractionated, when sorption occurs under pH less than ~6.2. As pH increases, heavier REEs tend to be removed by sorption onto suspended materials, and lighter REEs tend to remain in river water. Compared to fractionation between MREE and HREE, fractionation between LREE and MREE is larger. Yttrium is sorbed more effectively than LREE but less effectively than HREE. REE fractionation may occur significantly under pH 6.2–7.5.

Characterization of Americium and Curium Complexes with the Protein Lanmodulin: A Potential Macromolecular Mechanism for Actinide Mobility in the Environment.

Anthropogenic radionuclides, including long-lived heavy actinides such as americium and curium, represent the primary long-term challenge for management of nuclear waste. The potential release of these wastes into the environment necessitates understanding their interactions with biogeochemical compounds present in nature. Here, we characterize the interactions between the heavy actinides, Am3+ and Cm3+, and the natural lanthanide-binding protein, lanmodulin (LanM). LanM is produced abundantly by methylotrophic bacteria, including Methylorubrum extorquens, that are widespread in the environment. We determine the first stability constant for an Am3+-protein complex (Am3LanM) and confirm the results with Cm3LanM, indicating a ∼5-fold higher affinity than that for lanthanides with most similar ionic radius, Nd3+ and Sm3+, and making LanM the strongest known heavy actinide-binding protein. The protein's high selectivity over 243Am's daughter nuclide 239Np enables lab-scale actinide-actinide separations as well as provides insight into potential protein-driven mobilization for these actinides in the environment. The luminescence properties of the Cm3+-LanM complex, and NMR studies of Gd3+-LanM, reveal that lanmodulin-bound f-elements possess two coordinated solvent molecules across a range of metal ionic radii. Finally, we show under a wide range of environmentally relevant conditions that lanmodulin effectively outcompetes desferrioxamine B, a hydroxamate siderophore previously proposed to be important in trivalent actinide mobility. These results suggest that natural lanthanide-binding proteins such as lanmodulin may play important roles in speciation and mobility of actinides in the environment; it also suggests that protein-based biotechnologies may provide a new frontier in actinide remediation, detection, and separations.

Genesis of monazite-rich, orthopyroxene-bearing veins in the Kliphoog area of the Concordia Granite, Springbok, Namaqualand, South Africa: Sources, fluids, and the mobility of actinides and REE

A network of monazite-rich, coarse-grained veins and fine-grained veins permeating the mid-Proterozoic Concordia Granite in the Kliphoog area near Springbok, Namaqualand, North Cape Province, South Africa, are described with respect to their whole-rock chemistry, petrography, mineralogy, and mineral chemistry along with zircon and monazite geochronology. Chondrite-normalized trace element data indicate that the coarse-grained veins are enriched in LREE relative to the Concordia Granite with HREE enrichment being somewhat variable. HREE in altered Concordia Granite, at the contact with the coarse-grained vein, are heavily depleted compared to unaltered Concordia Granite while the LREE show the same approximate abundances. Chloritization is common in the coarse-grained veins along mineral grain boundaries with chlorite replacing most of the orthopyroxene megacrysts, though occasional remnants of orthopyroxene remain in the core. A traverse across one of the coarse-grained veins showed no obvious mineral chemical trends between the vein and surrounding granite. Relic Fe-rich megacryst orthopyroxene has an Al2O3 content of around 2.0 wt% suggesting formation at around 700 °C. The Fe-rich biotite has mean Ti values ranging from TiO2 = 4.1 to 1.2 wt% indicating formation at 700–800 °C. The coarse-grained veins and fine-grained veins are characterized by abundant accessory Th-rich monazite, heterogeneously distributed in the veins. Lesser amounts of monazite are found in the granite. Other accessory minerals in the veins and granite include zircon and rare fluorapatite. Back-scattered electron imaging shows that the anhedral to euhedral monazite grains (up to more than 1500 μm in size) tend to be complexly zoned with light and dark areas. Lighter areas are more enriched in Th and/or Ce than darker areas. This complex zoning can occur as magmatic/sector zoning and more commonly as a complex series of metasomatic alteration events. Metasomatic textures, which are due to variable fluid-induced mobility of Th, U, and REE, are the result of a coupled dissolution-reprecipitation process and have been reproduced experimentally using high pH alkali-bearing fluids. The analysis of seven zircon cores from the Concordia Granite yields a concordia age of 1173 ± 15 Ma suggesting that an age of ca. 1170 Ma most likely represents the true emplacement age of the Concordia Granite. The mean 207Pb/206Pb age of 1042 ± 9 Ma obtained on zircon from the main coarse-grained vein is interpreted as the crystallization age of the vein. 207Pb/235U monazite ages are highly variable in the veins and Concordia Granite host, ranging from ca. 1050 to 1000 Ma. This supports the petrographic and mineral chemistry evidence that the monazite U--Pb system was variably affected by a continuous or multi-pulse metasomatic/metamorphic event(s) occurring between 1050 and 1000 Ma. U--Pb analyses of deformed monazite crystals from a radioactive sinistral shear zone of the Kliphoog area yield a mean 207Pb/235U age of ca. 1006 ± 9 Ma, indicating that the late circulation of Th-LREE-rich fluids synchronous with strike-slip deformation occurred at ca. 1000 Ma. On a regional scale, the intrusion of the Kliphoog coarse-grained vein is contemporaneous with granulite-facies metamorphism as well as the A-type granitoid magmatism of the Spektakel Suite, mafic magmatism of the Koperberg Suite, and emplacement of the monazite vein-type deposit at Steenkampskraal. Therefore, a genetic relationship between the formation of monazite-rich Kliphoog veins and these metamorphic, magmatic, and metallogenic events is proposed.

Resolving the kinetics of individual aqueous reaction steps of actinyl (AnO2 + and AnO2 2+; An=U, Np, and Pu) tricarbonate complexes with ferrous iron and hydrogen sulfide from first principles

Abstract The solubility and mobility of actinides (An), like uranium, neptunium, and plutonium, in the environment largely depends on their oxidation states. Actinyls (AnV,VIO2 +/2+ (aq)) form strong complexes with available ligands, like carbonate (CO3 2−), which may inhibit reduction to relatively insoluble AnIVO2(s). Here we use quantum-mechanical calculations to explore the kinetics of aqueous homogeneous reaction paths of actinyl tricarbonate complexes ([AnO2(CO3)3]5−/4−) with two different reductants, [Fe(OH)2(H2O)4]0 and [H2S(H2O)6]0. Energetically-favorable outer-sphere complexes (OSC) are found to form rapidly, on the order of milliseconds to seconds over a wide actinyl concentration range (pM to mM). The systems then encounter energy barriers (E a), some of which are prohibitively high (>100 kJ/mol for some neptunyl and plutonyl reactions with Fe2+ and H2S), that define the transition from outer- to inner-sphere complex (ISC; for example, calculated E a of ISC formation between UO2 + and UO2 2+ with Fe2+ are 35 and 74 kJ/mol, respectively). In some reactions, multiple OSCs are observed that represent different hydrogen bonding networks between solvent molecules and carbonate. Even when forming ISCs, electron transfer to reduce An6+ and An5+ is not observed (no change in atomic spin values or lengthening of An–Oax bond distances). Proton transfer from bicarbonate and water to actinyl O was tested as a mechanism for electron transfer from Fe2+ to U6+ and Pu6+. Not all proton transfer reactions yielded reduction of An6+ to An5+ and only a few pathways were energetically-favorable (e. g. H+ transfer from H2O to drive Pu6+ reduction to Pu5+ with ΔE = −5 kJ/mol). The results suggest that the tricarbonate complex serves as an effective shield against actinide reduction in the tested reactions and will maintain actinyl solubility at elevated pH conditions. The results highlight reaction steps, such as inner-sphere complex formation and electron transfer, which may be rate-limiting. Thus, this study may serve as the basis for future research on how they can be catalyzed by a mineral surface in a heterogeneous process.

Determining the kinetics of discrete aqueous redox reaction sub-steps using computational methods: Application to reactions of plutonyl (PuO2+/2+) with Fe2+, Fe3+, and hydroxyl radical (•OH)

The solubility and mobility of actinides, such as plutonium, are highly-dependent on their oxidation state, with the penta- and hexavalent species forming soluble actinyl ions (for example, PuO2+/2+). While significant data exist on the equilibrium thermodynamics of these species, the kinetic datasets for actinide reactions are less robust. To understand these reactions in greater detail, this study assesses the degree to which different sub-steps affect the overall rate of an aqueous reaction. In this approach, reactions are broken into three steps: (1) the diffusion of reactants toward each other in solution to form an outer-sphere complex, (2) the transition from outer- to inner-sphere complex, and (3) the transfer of an electron. We address encounter frequency using collision theory and the last two steps using quantum-mechanical modeling to analyze the energy, as well as atomic charges and spins, as a function of distance between the two reactants. This approach is applied to the reactions of PuO22+ and PuO2+ hydrolysis species with Fe2+, Fe3+, and hydroxyl radical (•OH) at high pH. Regardless of the hydration treatment scheme or spin configuration (explicit vs. explicit with an implicit continuum model; ferromagnetic vs. antiferromagnetic), once species are within distances of 7.3 to 11.0 A, the formation of an outer-sphere complex is found to be energetically favorable. This process proceeds rapidly even at low, environmentally-relevant plutonyl concentrations. The half-life of plutonyl in the bulk solution (that is, that which has not yet formed an outer-sphere complex) is found to be From the quantum-mechanical calculations, changes in system energy versus reactant distance reveal the transition from outer- to inner-sphere complex, along with specific changes to the physical and electronic structure. The energy gain associated with hydrogen bonding between the first hydration spheres drives the reaction to form progressively interconnected complexes. In the models with Fe2+, charge and spin analysis confirms the formation of the inner-sphere complex is coincident with the reduction of Pu5+ and Pu6+. Since there is no change in angular (spin) momentum of the overall system when the spins of Fe and plutonyl assume opposite directions (antiferromagnetic case) during this redox process, such a spin configuration is more likely to further electron transfer. Overall, the derived kinetics of the conversion between different complex configurations indicate that collision and outer-to-inner sphere conversion of these reactions proceed quickly and are likely not rate-limiting for these systems. This methodology can provide insight into rate-limiting sub-processes and allow us to explore the redox behavior of Pu and other metals in greater detail. The computational scheme can now be reasonably extended to determine the kinetics of complex formation at mineral-solution interfaces and also combined with Marcus theory calculations to determine explicit electron transfer rates for complex-dependent redox processes.

A record of uranium-series transport at Nopal I, Sierra Peña Blanca, Mexico: Implications for natural uranium deposits and radioactive waste repositories

Studies of uranium-series (U-series) disequilibria within and around ore deposits provide valuable information on the extent and timing of actinide mobility, via mineral-fluid interaction, over a range of spatial and temporal scales. Such information is useful in studies of analogs of high-level nuclear-waste repositories, as well as for mining and mineral extraction sites, locations of previous nuclear weapons testing, and legacy nuclear waste contamination. In this study we present isotope dilution mass spectrometry U-series measurements for fracture-fill materials (hematite, goethite, kaolinite, calcite, dolomite and quartz) from one such analog; the Nopal I uranium ore deposit situated at Peña Blanca in the Chihuahua region of northern Mexico. The ore deposit is located in fractured, unsaturated volcanic tuff and fracture-fill materials from surface fractures as well as fractures in a vertical drill core have been analyzed. High uranium concentrations in the fracture-fill materials (between 12 and 7700ppm) indicate uranium mobility and transport from the deposit. Uranium concentrations generally decrease with horizontal distance away from the deposit but in this deposit there is no trend with depth below the surface.Isotopic activity ratios, 238U–234U-230Th–232Th linear age trends, and U-Th-Pa model ages indicate an actinide mobility evolution that can be characterized as complex and varied. There is evidence of both open and closed system behavior for uranium, depending on both sample and time-scale. The 234U/238U activity ratios indicate U mobility from 1.2–0.2Ma. In the last 0.2Ma there is isotopic evidence for some U mobility but mostly U immobility. In almost all cases the Th‐Pa radionuclides studied here have been immobile for the past 200ka. Radium appears to have been recently (0.1–8ka) mobile due to ongoing fluid flow in the fractures. Overall, the mainly closed system behavior for U-Th-Pa over the past ~200ka provides an indicator of the geochemical immobility of these actinides over time-scales relevant for potential nuclear waste repositories situated in fractured, unsaturated tuff.

Decreased Salinity and Actinide Mobility: Colloid-Facilitated Transport or pH Change?

Colloids have been implicated in influencing the transport of actinides and other adsorbed contaminants in the subsurface, significantly increasing their mobility. Such colloid-facilitated transport can be induced by changes in groundwater chemistry that occur, for example, when high ionic strength contaminant plumes are displaced by infiltrating rainwater. We studied the transport and mobility of Th(IV), as an analogue for Pu(IV) and other tetravalent actinides [An(IV)], in saturated columns packed with a natural heterogeneous subsurface sandy sediment. As expected, decreases in ionic strength both promoted the mobilization of natural colloids and enhanced the transport of previously adsorbed Th(IV). However, colloid-facilitated transport played only a minor role in enhancing the transport of Th(IV). Instead, the enhanced transport of Th(IV) was primarily due to the pH-dependent desorption of Th(IV) caused by the change in ionic strength. In contrast, the adsorption of Th(IV) had a marked impact on the surface charge of the sandy sediment, significantly affecting the mobility of the colloids. In the absence of Th(IV), changes in ionic strength were ineffective at releasing colloids while in the presence of Th(IV), decreases in ionic strength liberated significant concentrations of colloids. Therefore, under the conditions of our experiments which mimicked acidic, high ionic strength groundwater contaminant plumes, Th(IV) had a much greater effect on colloid transport than colloids had on Th(IV) transport.

Microbial mobilization of plutonium and other actinides from contaminated soil

We examined the dissolution of Pu, U, and Am in contaminated soil from the Nevada Test Site (NTS) due to indigenous microbial activity. Scanning transmission x-ray microscopy (STXM) analysis of the soil showed that Pu was present in its polymeric form and associated with Fe- and Mn- oxides and aluminosilicates. Uranium analysis by x-ray diffraction (μ-XRD) revealed discrete U-containing mineral phases, viz., schoepite, sharpite, and liebigite; synchrotron x-ray fluorescence (μ-XRF) mapping showed its association with Fe- and Ca-phases; and μ-x-ray absorption near edge structure (μ-XANES) confirmed U(IV) and U(VI) oxidation states. Addition of citric acid or glucose to the soil and incubated under aerobic or anaerobic conditions enhanced indigenous microbial activity and the dissolution of Pu. Detectable amount of Am and no U was observed in solution. In the citric acid-amended sample, Pu concentration increased with time and decreased to below detection levels when the citric acid was completely consumed. In contrast, with glucose amendment, Pu remained in solution. Pu speciation studies suggest that it exists in mixed oxidation states (III/IV) in a polymeric form as colloids. Although Pu(IV) is the most prevalent and generally considered to be more stable chemical form in the environment, our findings suggest that under the appropriate conditions, microbial activity could affect its solubility and long-term stability in contaminated environments.

Geochemical association of Pu and Am in selected host-phases of contaminated soils from the UK and their susceptibility to chemical and microbiological leaching

Understanding the biogeochemical behaviour and potential mobility of actinides in soils and groundwater is vital for developing remediation and management strategies for radionuclide-contaminated land. Pu is known to have a high Kd in soils and sediments, however remobilization of low concentrations of Pu remains a concern. Here, some of the physicochemical properties of Pu and the co-contaminant, Am, are investigated in contaminated soils from Aldermaston, Berkshire, UK, and the Esk Estuary, Cumbria, UK, to determine their potential mobility. Sequential extraction techniques were used to examine the host-phases of the actinides in these soils and their susceptibility to microbiological leaching was investigated using acidophilic sulphur-oxidising bacteria. Sequential extractions found the majority of 239,240Pu associated with the highly refractory residual phase in both the Aldermaston (63.8–85.5 %) and Esk Estuary (91.9–94.5%) soils. The 241Am was distributed across multiple phases including the reducible oxide (26.1–40.0%), organic (45.6–63.6%) and residual fractions (1.9–11.1%). Plutonium proved largely resistant to leaching from microbially-produced sulphuric acid, with a maximum 0.18% leached into solution, although up to 12.5% of the 241Am was leached under the same conditions. If Pu was present as distinct oxide particles in the soil, then 241Am, a decay product of Pu, would be expected to be physically retained in the particle. The differences in geochemical association and bioleachability of the two actinides suggest that this is not the case and hence, that significant Pu is not present as distinct particles. These data suggest the majority of Pu in the contaminated soils studied is highly recalcitrant to geochemical changes and is likely to remain immobile over significant time periods, even when challenged with aggressive “bioleaching” bacteria.

Interactions of the Mont Terri Opalinus Clay Isolate Sporomusa sp. MT-2.99 with Curium(III) and Europium(III)

Bacterial cell walls have great potential to influence the speciation and mobility of actinides and lanthanides in the environment. In this study we explored the unknown interaction between Cm(III)/Eu(III) and cell-suspensions of Sporomusa sp. MT-2.99, a novel isolate recovered from Opalinus Clay (Mont Terri, Switzerland). The Cm(III)/Eu(III) binding by the cell surface functional groups was studied by potentiometry combined with time-resolved laser-induced fluorescence spectroscopy (TRLFS). This article provides stability constants of Cm(III)/Eu(III) complexed by cell surface functional groups. We could show that as a function of pH Cm(III)/Eu(III) binding occurred to hydrogen phosphoryl, carboxyl and deprotonated phosphoryl sites. Both metals showed a similar interaction process consisting of surface complexation (major) with high thermodynamic stability and an irreversible binding within the cell envelope (minor).

Improved thermodynamic model for interaction of EDTA with trivalent actinides and lanthanide to ionic strength of 6.60 m

The dissociation constants of ethylenediaminetetraacetic acid (H4EDTA), and the stability constants of Am3+, Cm3+and Eu3+ with EDTA4− have been determined at 25°C, over a range of concentration varying from 0.1 to 6.60m NaClO4 using potentiometric titration and an extraction technique, respectively. The formation of only 1:1 complex, M(EDTA)−, where (M=Am3+, Cm3+ and Eu3+), was observed under the experimental conditions. The observed ionic strength dependencies of the dissociation constants and the stability constants have been described successfully over the entire ionic strength range using the Pitzer model. The thermodynamic stability constant: logβ1010=20.55±0.18 for Am3+, logβ1010=20.43±0.20 for Cm3+ and logβ1010=20.65±0.19 for Eu3+ were calculated by extrapolation of data to zero ionic strength in an NaClO4 medium. In addition, logβ1010 of 20.05±0.40 for Am3+ was obtained by simultaneously modeling data both in NaCl and NaClO4 media. For all stability constants, the Pitzer model gives an excellent representation of the data using interaction parameters β(0), β(1), and Cϕ determined in this work. The improved model presented in this work would enable researchers to model accurately the potential mobility of actinides (III) and light rare earth elements to ionic strength of 6.60m in low temperature environments in the presence of EDTA.

Complexation of Uranium(VI) by Gluconate in Alkaline Solutions

Gluconate (C6H11O7) is a polyhydroxycarboxylic acid that can be assumed as a representative model compound for a wide variety of additives in cement formulations. It can play an important role in the cementitious environments characteristic of radioactive waste disposal sites, as actinides (such as U(VI)) may form stable complexes with gluconate. As a consequence, the presence of the organic ligand can lead to an enhancement of actinide mobility. The results presented in this work show that gluconate increases significantly the uranium solubility at pHc = 12; the study of U(VI) speciation in alkaline solutions is complex, mainly due to formation of sparingly soluble uranates of varying compositions (e.g. sodium and potassium uranates). UV–Vis measurements in the alkaline pH range have been used to determine the stability constant for the formation of a 1:1 U(VI):gluconate complex. The results obtained with spectroscopic techniques allow explaining the results from solubility experiments, from both over- and under-saturation conditions.

Curium(III) Speciation Studies with Cells of a Groundwater Strain of Pseudomonas fluorescens

Ubiquitous Pseudomonads have great potential to influence the speciation and mobility of actinides in the environment. This study explores the unknown interaction between curium(III) and cell-suspensions of Pseudomonas fluorescens (CCUG 32456) isolated from the Äspö site, Sweden. The interaction between curium(III) and P. fluorescens cells was studied at trace curium(III) concentrations (0.3 μM) using time-resolved laser-induced fluorescence spectroscopy. Extraction studies have shown that the biosorption of curium(III) is a reversible process. Two Cm3+−P. fluorescens (CCUG 32456) species were identified, R−O−PO3H−Cm2+ and R−COO−Cm2+, having emission maxima at 599.6 and 601.9 nm, respectively. The corresponding surface complexation constants were determined to be log β111 = 12.7 ± 0.6 and log β110 = 6.1 ± 0.5, respectively.

Degradation of Organic Complexing Agents by Halophilic Microorganisms in Brines

The potential use of geologic salt beds as terminal repositories for nuclear waste has necessitated research on the interaction of the waste with indigenous microbiota. Microorganisms may affect actinide solubility by degrading organic complexing agents present in the waste. A halophilic bacterium and Archaea indigenous to a salt formation in New Mexico were examined for their ability to degrade acetate, oxalate, citrate, and ethylenediamine tetraacetate under aerobic conditions in low and high-magnesium brines. All complexing agents, except EDTA, were utilized, suggesting that microorganisms indigenous to such repositories can potentially play a beneficial role in mitigating actinide mobility.

Uranium uptake onto Magnox sludge minerals studied using EXAFS

AbstractAround the world large quantities of sludge wastes derived from nuclear energy production are currently kept in storage facilities. In the UK, the British government has marked sludge removal as a top priority as these facilities are nearing the end of their operational lifetimes. Therefore chemical understanding of uranium uptake in Mg-rich sludge is critical for successful remediation strategies. Previous studies have explored uranium uptake by the calcium carbonate minerals, calcite and aragonite, under conditions applicable to both natural and anthropogenically perturbed systems. However, studies of the uptake by Mg-rich minerals such as brucite [Mg(OH)2], nesquehonite [MgCO3·3H2O] and hydromagnesite [Mg5(CO3)4(OH)2·4H2O], have not been previously conducted. Such experiments will improve our understanding of the mobility of uranium and other actinides in natural lithologies as well as provide key information applicable to nuclear waste repository strategies involving Mg-rich phases. Experiments with mineral powders were used to determine the partition coefficients (Kd) and coordination of UO22+ during adsorption and co-precipitation with brucite, nesquehonite and hydromagnesite. The Kd values for the selected Mg-rich minerals were comparable or greater than those published for calcium carbonates. Extended X-ray absorption fine structure analysis results showed that the structure of the uranyl-triscarbonato [UO2(CO3)3] species was maintained after surface attachment and that uptake of uranyl ions took place mainly via mineral surface reactions.

Fifty years of Radiochimica Acta: a brief overview

Abstract This paper provides a brief account of the development of this journal over the last fifty years. Having started in 1962 as a modest outlet for reporting research results in radiochemistry, Radiochimica Acta soon became a respected specialist journal. There has been long-term continuity both in editorial activity and publishing management, resulting in welldefined publishing policies. Starting with the Founding Editors, the Board of Editors was changed only in 1977 and 1996. Similarly the original Publisher, Akademischer Verlag, published the journal until 1983. Since then OldenbourgWissenschaftsverlag has been managing the publication process. The journal has been broad-based, encompassing all chemical aspects of nuclear science and technology. It has played a significant role in the dissemination of new knowledge, occasionally by bringing forth special issues in fast emerging areas. It has kept pace with the changing trends in worldwide radiochemical research. Whereas by about the middle of 1980s all areas of radiochemistry were equally represented, today the emphasis is more on applied topics, such as chemical behaviour and mobility of actinides and fission products, accelerator-based radiochemistry, medical applications of radioactivity, etc. The number of published scientific contributions to date amounts to about 5100, covering about 30 000 printed pages. The total number of authors is around 7000. The journal follows a strict peer-review system and is supported by a network of about 400 referees. About 200 manuscripts are received per year, out of which 30-35% are rejected. The impact factor (IF) of the journal is almost the highest among the radiochemistry related journals, and the cited half-life (CHL) among the highest of all chemistry and physics oriented journals. In short, today Radiochimica Acta is a well established, internationally recognised periodical. Presently, approximately 50 percent of the published contributions originate from Europe, 25 percent fromNorth- and South America and the remaining 25 percent from Asia, Australia and Africa together. All articles are published in English, and the journal is available to readership both on-line and in printed form.

Radioactive contamination in the Belarusian sector of the Chernobyl Exclusion Zone

This article summarises some key activities undertaken as part of a NATO-funded project to map and improve our understanding of the behaviour and fate of radionuclides in the Belarusian Sector of the Chernobyl Exclusion zone. Data are presented concerning activity concentrations of 137 Cs, 90 Sr and selected actinides and how these data have been used to produce contour maps of contamination densities. Factors affecting the transfer of radionuclides to plants and animals at selected study sites are considered and the geochemical phase association of radionulcides in soils and implications for actinide mobility commented upon. A final important subject for elaboration has been the transboundary transport of contamination by natural phenomena. The influence of forest fires on remobilisation of radionuclides, for example, has been addressed through the application of a bespoke probabilistic model.