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According to the most recent listing reported by the European Commission, rare-earth elements (REEs) are the critical raw materials with the highest supply risk, whereas their recycling rates remain very low in the European Union [1]. End-of-life fluorescent lamps are a promising secondary source of REEs, but their recycling requires innovative separation processes [2,3]. By using phage surface display, Lederer and co-workers identified selectively surface-binding peptides that specifically bind to fluorescent lamp phosphors [4]. In a following study, Schrader et al. immobilized these peptides on coated well plates to investigate their binding to various REE phosphors [5]. The immobilization was facilitated by an activation with benzotriazole-1-yl-oxytripyrrolidinophosphonium-hexafluorophosphate (PyBOP) in the aprotic solvent N-Methyl-2-pyrrolidone (NMP) in the presence of the sterically hindered base diisopropylethylamine (DiPEA), a coupling reaction commonly used for chemical peptide synthesis. Recently, we investigated the immobilization method presented by Schrader et al. for the functionalization of Dynabeads [6]. Dynabeads are highly spherical and monodisperse composite magnetic beads, consisting of superparamagnetic iron oxide nanoparticles dispersed in a polystyrene matrix. They are commercially available with various surface coatings. The functionalization of amine coated Dynabeads with phosphor binding peptides, immobilized with the coupling reaction described above, did not change the Dynabeads’ zeta potential and had no significant effect on the interaction with REE phosphors [6]. On the other hand, we found that the immobilization onto carboxylic acid coated Dynabeads changed the Dynabeads’ zeta potential and isoelectric point. We also observed that this immobilization had a detrimental effect on the interaction of the beads with the targeted phosphor particles and suggested that this may be an indication of polymerization of the peptides on the Dynabea

Increased reactivity of radiation-damaged quartz in the alkaline pore water of concrete and its role in radionuclide transport is a subject that is becoming increasingly important as nuclear power plants (NPPs) around the world reach end-of-life. Quartz contributes more than half the weight of most concretes and up to 40 % of the total radioactive waste volume associated with the dismantling of an NPP. The gamma-emitting radionuclides are the major contributors to the radiation dose rate in the concrete biological shield in the intermediate term after NPP shut-down. The appreciable activity and associated half-lives of these radionuclides pose a problem not only during the safe dismantling of NPPs, but also in terms of processing the concrete to reduce the active waste volume for final disposal in a repository. While thermal neutrons are captured by atomic nuclei according to their thermal neutron cross-sections, fast neutrons undergo collision cascades, which cause defects in the structure of materials. The concentration of defects accumulates as a function of neutron energy and fluence. The high covalency and the density of Si-O bonds in tectosilicates, primarily quartz, followed by feldspars, makes these minerals very susceptible to radiation damage. In this study, two inactive concrete powder samples were placed inside an instrumentation channel passing through the first biological shielding of an operating German NPP, respectively for a half- and a full fuel cycle. Using a plant-specific 3D-reactor model in conjunction with Monte Carlo neutron transport calculations, neutron fluences at the sample positions and the resulting gamma activities are calculated. We compare the measured and calculated activities of the gamma-emitting radionuclides Synchrotron X-ray powder diffractometry was used to examine structural changes on sub-nanoscale. The local structure of the silicate aggregate minerals was investigated by solid-state magic angle spinning nuclear magnetic r

The interfacial mechanism of uranyl electroreduction at Au-electrodes in HCl solutions was discussed on the light of systematic studies of cyclovoltammetry, normal pulse voltammetry, UV-vis spectroscopy and published electroanalytical research. Voltammetric waves were numerically deconvoluted on the basis of a reaction model consisting of a first masscontrolled, quasi-reversible first electron transfer and a subsequent reduction of interfacial U(V) intermediate species with adsorption of generated U(IV) products. The dependence of the kinetic parameters on [HCl] indicates an electron transfer following an inner-sphere type mechanism assisted by electrosorption of chloride ligands. The interfacial accumulation of chloride exerts a strong electrostatic repulsion of complexed uranyl and a consequent edged drop of electron transfer rates at [HCl] ∼ 0.5 mol l-1. The electron transfer steps are followed by a chemical desorption reaction of the unstable tetravalent uranyl in U(H2O)94+ species. It is shown that the numerical reproduction of voltammetric waves suits as a method for calculating kinetic parameters in multi-steps electrochemical reactions.

Extreme temperatures and pressures were applied to systems based on stabilized zirconia, ZrO2, doped with Ce4+ ions as surrogate for tetravalent Actinides in order to conclude on their long term stability in deep geological underground. Both tetragonal and cubic Yttrium-stabilized ZrO2 (YSZ) exhibit excellent phase and structural stabilities up to 1150 K. In addition, incorporated guest Ce4+ did not show any increase in their mobility at elevated temperatures. Application of external pressure did not induce any structural or phase changes in cubic YSZ doped with 5 at.% Ce as well. However, a corresponding tetragonal analogue with lower Yttrium content exhibits a 2nd order phase transition towards higher cubic symmetry around 9 GPa. Remarkably, no discharge of the guest Ce4+ ions was observed throughout the transition and further upon increase in pressure. This together with T-dependent data indicates excellent affinity of guest Ce atoms with the host YSZ matrices. The parent YSZ phases are, therefore, promising candidates as host materials for long term underground immobilization for radiotoxic tetravalent elements like U, Th or Pu.

Novel separation processes for end of life fluorescent lamp phosphors could greatly contribute towards a more sustainable rare-earth element market. Furthermore, surface-binding peptides bound to magnetic carriers are a promising biotechnological tool for selective particle separation processes. In this work, we investigate the magnetic carrier separation of the three most common rare-earth fluorescent lamp phosphors, facilitated by Dynabeads functionalized with previously identified selectively surface-binding peptides. We present an active ester-mediated coupling to chemically immobilize the peptides on amine and carboxylic acid coated beads. We report on the impact of the peptide functionalization on the surface properties of the beads, based on zeta potential investigations of variously functionalized beads and a Raman spectroscopic structural study of the investigated peptides. Fluorometrically, we show that the phosphor removal strongly depends on the medium and the surface coating of the beads. Furthermore, the Raman spectroscopic evidence of various simultaneously present disulfide bond conformations indicates an equilibrium of multiple peptide conformations and/or the presence of intermolecular disulfide bonds. Moreover, we found that carboxylic acid coated Dynabeads have a high affinity for the red phosphor Y2O3:Eu3+ and based on the determined isoelectric points we hypothesize that this is driven by electrostatic surface interactions. This work can contribute towards novel rare-earth phosphor separation processes and towards a better understanding of magnetic carrier separation processes facilitated by surface-binding peptides.

Y-stabilized zirconia (YSZ) phases were found to incorporate Th atoms and the corresponding solubility ranges depend on the relative Y content. For the tetragonal phases with lower Y concentration of 14 at.% a maximal possible Th intake on the Zr/Y metal site reached ca. 10.3 at.%. Cubic phases with higher Y content could dissolve 11 at.% Th in equilibrium state and up to ca. 12.3 at.% Th under non-equilibrium conditions. Larger Th-Zr/Y solubility range for phases with higher Y concentration was found to be related to the associated symmetry increase, as concluded from synchrotron radiation powder diffraction data. Specifically, introduction of Th into tetragonal YSZ induces evolution towards higher cubic symmetry via flattening of the Zr/YO8 polyhedra. In addition, tetragonal YSZ crystal lattice exhibits strongly anisotropic expansion with concomitant decrease in tetragonality upon the intake of Th. This results in easier accommodation of bigger Th atoms via structural stabilization of longer Zr/Y-O bonding distances which yields more symmetrical coordination of central Zr/Y metal ions by surrounding O atoms. Cubic symmetry is, therefore, more favorable to incorporation of large tetravalent Actinide elements.

According to the most recent listing reported by the European Commission, rare-earth elements (REEs) are the critical raw materials with the highest supply risk, whereas their recycling rates remain very low in the European Union [1]. End-of-life fluorescent lamps are a promising secondary source of REEs, but their recycling requires innovative separation processes [2,3]. By using phage surface display, Lederer and co-workers identified selectively surface-binding peptides that specifically bind to fluorescent lamp phosphors [4]. In a following study, Schrader et al. immobilized these peptides on coated well plates to investigate their binding to various REE phosphors [5]. The immobilization was facilitated by an activation with benzotriazole-1-yl-oxytripyrrolidinophosphonium-hexafluorophosphate (PyBOP) in the aprotic solvent N-Methyl-2-pyrrolidone (NMP) in the presence of the sterically hindered base diisopropylethylamine (DiPEA), a coupling reaction commonly used for chemical peptide synthesis. Recently, we investigated the immobilization method presented by Schrader et al. for the functionalization of Dynabeads [6]. Dynabeads are highly spherical and monodisperse composite magnetic beads, consisting of superparamagnetic iron oxide nanoparticles dispersed in a polystyrene matrix. They are commercially available with various surface coatings. The functionalization of amine coated Dynabeads with phosphor binding peptides, immobilized with the coupling reaction described above, did not change the Dynabeads’ zeta potential and had no significant effect on the interaction with REE phosphors [6]. On the other hand, we found that the immobilization onto carboxylic acid coated Dynabeads changed the Dynabeads’ zeta potential and isoelectric point. We also observed that this immobilization had a detrimental effect on the interaction of the beads with the targeted phosphor particles and suggested that this may be an indication of polymerization of the peptides on the Dynabea

Autoluminescence CO2 BET Elemental analysis Leaching test results Powder XRD TGA-DSC UV/vis

Structural characterization of actinide nanoparticles (NPs) is of primary importance and hard to achieve, especially for non‐homogeneous samples with NPs below 3 nm. By combining High Energy X‐ray Scattering (HEXS) and High‐Energy‐Resolution Fluorescence Detected X‐ray Near‐Edge Structure (HERFD XANES), we characterized for the first time both short‐ and medium‐range order of ThO₂ NPs obtained by chemical precipitation. With this methodology, a novel insight into the structure of NPs at different steps of their formation process is achieved. The Pair Distribution Function (PDF) reveals a high concentration of ThO₂ small units similar to Th hexamer clusters mixed with 1 nm ThO₂ NPs in the initial steps of formation. Drying the precipitates at ⁓150 °C promotes recrystallization of the smallest units into more thermodynamically stable ThO₂ NPs. HERFD XANES at Th M₄ edge, a direct probe of the f states, shows variations that we correlate to the break of the local symmetry around Th atoms, which most likely concerns surface atoms. Together, HEXS and HERFD are a powerful methodology to investigate actinide NPs and their formation mechanism.

The uptake of the fission product technetium (Tc) by chukanovite, an Fe(II) hydroxy carbonate mineral formed as a carbon steel corrosion product in anoxic and carbonate-rich environments, was studied under anoxic, alkaline to hyperalkaline conditions representative for nuclear waste repositories in deep geological formations with cement-based inner linings. The retention potential of chukanovite towards Tc(VII) is high in the pH range 7.8 to 12.6, evidenced by high solid-water distribution coefficients, log Rd ~ 6, and independent of ionic strength (0.1 or 1 M NaCl). Using Tc K-edge X-ray absorption spectroscopy (XAS) two series of samples were investigated, Tc chukanovite sorption samples and coprecipitates, prepared with varying Tc loadings, pH values and contact times. From the resulting 37 XAS spectra, spectral endmembers and their dependence on chemical parameters were derived by self-organizing (Kohonen) maps (SOM), a neural network-based approach of machine learning. X-ray absorption near-edge structure (XANES) data confirmed the complete reduction of Tc(VII) to Tc(IV) by chukanovite under all experimental conditions. Consistent with mineralogical phases identified by X-ray diffraction (XRD), SOM analysis of the extended X-ray absorption fine-structure (EXAFS) spectra revealed the presence of three species in the sorption samples, the speciation predominately controlled by pH: Between pH 7.8 and 11.8, TcO₂-dimers form inner-sphere sorption complexes at the surface of the initial chukanovite as well as on the surface of secondary magnetite formed due to redox reaction. At pH ≥11.9, Tc(IV) is incorporated in a mixed, chukanovite-like, Fe/Tc hydroxy carbonate precipitate. The same species formed when using the coprecipitation approach. Reoxidation of sorption samples resulted in a small remobilization of Tc, demonstrating that both the original chukanovite mineral and its oxidative transformation products, magnetite and goethite, contribute to the immobilization

The properties of biogenic elemental selenium (BioSe) need to be studied in order to understand its environmental fate. In this paper, the magnetic properties of biogenic elemental selenium nanospheres (BioSe-Nanospheres) and nanorods (BioSe-Nanorods) obtained via the reduction of selenium(IV) using anaerobic granular sludge were investigated. The study indicated that the BioSe nanomaterials have a strong paramagnetic contribution with some ferromagnetic component due to the incorporation of Fe(III) (high spin and low spin species) as indicated by Electron Paramagnetic Resonance (EPR). X-Ray Photoelectron Spectroscopy (XPS) also confirmed the weak presence of Fe(III) and combined with EPR data, the Fe(III) availability through the nanomaterial was established. It is likely that Fe(III) being abundantly present in sludge got entrapped in the extracellular polymeric substances (EPS) coating the biogenic nanomaterials. The presence of Fe(III) in BioSe nanomaterials increases the mobility of Fe(III) and can have an effect on phytoplankton growth in the environment. Further, there is a potential to exploit the magnetic properties of BioSe nanomaterials in drug delivery system as well as in space refrigeration.

INTRODUCTION Safe disposal of spent nuclear fuel (SNF) requires matrix materials with strong resistance against corrosion and dissolution over a period of 106 years. Derivatives of zirconium-based ceramics, in particular zirconia, ZrO2, are promising materials for these applications since these phases are known to remain stable in geological cycles of up to 109 years. Here scientific and technological goals are to obtain zirconium-based ceramic materials containing maximum possible tetravalent actinides (An) without Zr/An phase separation. In addition, structural stability of these phases under various external parameters, e.g. temperature (T), pressure (P), irradiation and leaching resistance is essential in order to exclude possible discharge of the incorporated radioactive elements over a long time scale. Five different structural modifications of zirconia are known to exist. At ambient pressure undoped ZrO2 phase exhibits three different polymorphs as a function of temperature - low-temperature (LT) monoclinic (7-fold coordination of Zr atoms, P21/c ) and parent HT tetragonal (T > 1440 K), and cubic (T > 2640 K) forms (8-fold coordination, P42/nmc and Fm-3m, respectively) [1]. Upon application of high pressure (HP) monoclinic modification of zirconia transforms into orthorhombic-I phase (Pbca, 7-fold coordination of Zr atoms similar to that observed for the parent monoclinic P21/c phase) at pressure of ~ 4 GPa [2]. Upon further compression at P > 25 GPa orthorhombic-I modification transforms into orthorhombic-II phase (Pnma, 9-fold coordination) [3] and this phase was found to be stable up to at least 100 GPa [4]. Various properties of ZrO2 can be efficiently controlled by doping. In particular, introduction of Y3+ ions is known to significantly influence phase stability range of zirconia and to stabilize desired HT modifications. Specifically, tetragonal Y-stabilized zirconia (YSZ) phases, denoted as t′, can be obtained at ambient temperature for Y content of ~

Tetravalent actinides form colloids at near neutral pH in the presence of silicic acid. This may have significant impact on actinide mobility in the far field of a nuclear waste repository or the case of accidental release of actinides into the environment as silicate is ubiquitous in natural waters and is of special importance in the case of nuclear waste repositories in crystalline rock formations. We investigated the formation, stability and mobility of such colloids employing the tetravalent actinide analog zirconium and the radiotracer Zr-89. The radiotracer was produced at the in-house IBA Cyclone 18/9 cyclotron at the HZDR Research Site Leipzig. A foil of metallic yttrium was irradiated with 14.5 MeV protons to trigger the nuclear reaction Y-89(p,n)Zr-89. The target was subsequently dissolved and the radiotracer was isolated via ion chromatography methods using UTEVA resin. The radiotracer was employed to synthesize zirconium oxyhydroxy silicate colloids that form spontaneously at near neutral pH at Si concentrations between 0.5 – 2 mM. In contrast to the Zr(O)(OH)2 particles that precipitate without silicates these colloids remain in stable dispersion. Column experiments in model porous media reveal a potentially massively increased mobility of these colloids due to very low affinities for the geomatrix surface. The stability of these colloids was further investigated by producing particles from solutions containing various Zr : Si ratios. Homoaggregation affinity measurements on these systems by dynamic light scattering reveal an increasing stabilization of the colloids with increasing silica content hinting at (electro-)steric stabilization mechanisms due to polymeric silicic acid structures at the colloid surface. Consequently an increased mobility of low concentration tetravalent actinides through colloid formation may occur in environments with silicic acid presence.

Y-stabilized zirconia (YSZ) is one of the reference materials for immobilization of actinide elements for long-term and secure storage of radioactive waste. YSZ adapts different structural modifications, namely monoclinic, tetragonal (unstable) and cubic [1]. Changes in relative Y content and synthesis temperature can be used to obtain specific structural form. However, for an intermediate Y content of ~5-17 at.% a mixture of cubic and unstable tetragonal modifications can form thus compromising corresponding long-term structural integrity. Nevertheless, for this Y concentration range a stabilized tetragonal (t′) phase can be obtained through a rapid quenching of the parent cubic modification. Addition of Th was shown to influence phase composition and stability in the YSZ system as well [2]. In this work we report studies of solubility of Th in 14%Y- stabilized zirconia phase. Series of 14%Y-ZrO2 compounds with Th at. % content of 3, 6, 9 and 12 were synthesized by sol-gel method from salts of Zr(IV), Y(III) and Th(IV). Subsequent powder synchrotron radiation diffraction measurements were performed in order to study underlying phase and structural evolutions. It was found that the cell parameters increase nearly linearly for the Th content from 3 to 9% and no cell increase is observed for the end-member with 12%Th. Additionally, ThO2 was found to precipitate in this sample. This may indicate that Th solubility limit in the 14%Y-ZrO2 system situates near 9%. Interestingly, Th content was reported to exceed 15% for the 25%Y-ZrO2 system, as concluded from electron microscopy data [3]. Studied samples, however, were found to be 25%Y-ZrO2–ThO2 phase separated. Considering that in the current study traces of ThO2 have been found already in the 9%Th sample, conditions of thermal treatment with the resulting phase equilibria may impact Th solubility. Further details on structural and phase properties in the Th-14%Y-ZrO2 system will be presented. [1] Scott H G 1975 J. Mater

Y-stabilized zirconia (YSZ) is one of the reference materials for immobilization of actinide elements for long-term and secure storage of radioactive waste. YSZ adapts different structural modifications, namely monoclinic, tetragonal (unstable) and cubic. Changes in relative Y content and synthesis temperature can be used to obtained specific structural form. However, for an intermediate Y content of ~5-17 at. % a mixture of cubic and unstable tetragonal modifications can form thus compromising corresponding long-term structural integrity. Nevertheless, for this Y concentration range a stabilized tetragonal (t′) phase can be obtained through a rapid quenching of the parent cubic modification. In this work we report studies of solubility of Th in 14%Y- stabilized (t′) zirconia phase. Series of 14%Y-ZrO2 compounds with Th at. % content of 3, 6, 9 and 12 were synthesized by sol-gel method using salts of Zr(IV), Y(III) and Th(IV) as starting materials with a final sintering temperature of 1400 K. Subsequent powder X-ray diffraction measurements were performed in order to study underlying phase and structural evolutions. It was found that the cell parameters increase nearly linearly for the Th content from 3 to 9% and no cell increase is observed for the end-member with 12%Th. Additionally, ThO2 was found to precipitate in this sample. This may indicate that Th solubility limit in the 14%Y-ZrO2 system lies within the 9-12% range. Interestingly, Th content was reported to exceed 15% for the 25%Y-ZrO2 system, as concluded from electron microscopy data. This sample, however, was found to be 25%Y-ZrO2–ThO2 phase separated. Considering that in the current study traces of ThO2 have been found already in the 9%Th sample, conditions of thermal treatment with the resulting phase equilibria may impact the Th solubility. Further details on structural and phase properties in the Th-14%Y-ZrO2 system will be presented.

A general strategy for the determination of Tc oxidation state by new approach involving X-ray absorption near edge spectroscopy (XANES) at the Tc L₃ edge is shown. A comprehensive series of ⁹⁹Tc compounds, ranging from oxidation states I to VII, was measured and subsequently simulated within the framework of crystal-field multiplet theory. The observable trends in absorption edge energy shift in combination with the spectral shape allow for a deeper understanding of complicated Tc coordination chemistry. This approach can be extended to numerous studies of Tc systems as this method is one of the most sensitive methods for accurate Tc oxidation state and ligand characterization.

The nanoscience field often produces results more mystifying than any other discipline. It has been argued that changes of the plutonium dioxide (PuO2) particle size from bulk to nano can have a drastic effect on PuO2 properties. Here we report a full characterization of PuO2 nanoparticles (NPs) at the atomic level, explore their stability and probe their local and electronic structure. The particles were synthesized from precursors with different oxidation states (Pu III, IV and V) under various environmentally and waste storage relevant conditions (pH 8 and pH 12). We demonstrate that well dispersed, crystalline NPs with a size of ~2.5 nm in diameter are always formed in spite of diverse chemical conditions. Identical crystal structures and the presence of only Pu(IV) oxidation state in all NPs indicate that their fundamental properties, rather than being fancy and exotic, are identical to those of the bulk PuO2.

We report here experimental evidence that the formation of PuO2 nanoparticles from oxidized Pu(VI) under environmentally relevant conditions proceeds through the formation of an intermediate Pu(V) solid phase, similar to NH4PuO2CO3, which is stable over a period of several months. State-of-the-art experiments at Pu M4 and L3 absorption edges combined with theoretical calculations unambiguously allowed us to determine the oxidation state and the local structure of this intermediate phase

Plutonium is one of the most significant elements among actinides due to its high radiotoxicity and long period of high-decay. The migration of plutonium in the environment is a challenging and global problem. Plutonium migrates at scale of kilometers from previously contaminated sites in the form of intrinsic colloids or “pseudocolloids”.1-2 In the last few years it was found that so called “colloidal Pu(IV) polymers” actually represents as aggregates of PuO2 nanoparticles with size ~ 2 nm.3-5 The revealing of the mechanism of these particles formation (including the consideration of different factors which may have an influence), as well as their characterization is a key to understanding the conditions for long-term storages for the nuclear waste. With the combination of different laboratory and synchrotron techniques it was found that small (2 nm) nanoparticles are formed from Pu(III), Pu(IV), Pu(V) aqueous solutions at pH 8-12, with the crystal structure close to PuO2, and with only Pu(IV) oxidation state present. Any other Pu-O contributions except Pu(IV)-O (in oxide) were not revealed.