Search

When radionuclides (RN) enter the food chain and are ingested by humans, they pose a potential health risk due to their radio- and chemotoxicity. To minimize the health risk, decorporation agents (DA), which are usually strong complexants, are used after the accidental incorporation of RN to increase their excretion. In order to accurately assess the health risk after oral ingestion and to apply effective decontamination methods, it is essential to understand the processes of (bio)chemistry and speciation of RN at the molecular and cellular level. Within the joint research project RADEKOR: “Speciation and transfer of radionuclides in the human organism especially taking into account decorporation agents”, molecular speciation studies of RN in artificial biofluids of the digestive system of humans and cytotoxicity studies with respective human and rat renal cell lines in vitro both in the absence and presence of DA were performed. As DA we investigated i) aminopolycarboxylate diethylenetriaminepentaacetic acid DTPA as the only approved and commercially used DA and ii) some promising new chelators like the hydroxypyridinone 3,4,3-(LI-1,2-HOPO) (HOPO) and 1-hydroxy-ethylidene-1,1-diphosphonic acid (HEDP), which was formerly used as a pharmaceutical. First, the complex formation of the non-radioactive An(III) analogue Eu(III) with HEDP in aqueous solution and cell culture medium was studied. Second, Eu(III) and Am(III) cytotoxicity onto kidney cells was investigated in absence and presence of DTPA and HOPO. Finally, the molecular speciation of Eu(III) and Am/Cm(III) with and w/o DTPA and HOPO was studied in both cell culture medium and exposed renal cells. The results of this work contribute to a better understanding of the effect of DA after RN incorporation at the molecular level and support making them more effective in the future.

The ingress of water into an underground nuclear repository, described as a worst-case scenario, can lead to the degradation of cement-based engineered barriers and thus to the release of organic cement additives that can affect radionuclide immobilisation. The additive 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) is one of the most commonly used long-term retarders in cement, and also used as a corrosion inhibitor in reinforced concrete and steel. PBTC is an organophosphonate ligand with one phosphonate and three carboxyl groups [1]. These functional groups make PBTC an effective dispersant and strong complexing agent for various metal ions (e.g. Ca2+, Al3+, Fe3+). However, neither the complexation of radionuclides by PBTC nor the influence of PBTC on radionuclide retention in cement phases has been investigated. Therefore, both the complexation of U(VI) with PBTC in solution (binary system) and the influence of PBTC on the U(VI) retention by cementitious materials (ternary system) were investigated for the first time. The U(VI) complexation studies were performed by different series varying the pH from 2 to 11 and/or the U(VI) to PBTC ratio. The structure-sensitive methods NMR, IR and Raman spectroscopy were used to characterize the complex structure. Complementary DFT calculations were carried out. The U(VI) speciation in presence of PBTC was determined by UV-Vis and TRLFS spectroscopy. In the case of PBTC excess, soluble complex species are formed up to pH >10, which is relevant for cementitious systems due to degradation processes. For the U(VI) retention studies both calcium (aluminate) silicate hydrate (C-(A-)S-H) phases of different compositions, representing different cement degradation stages, as well as hardened cement paste were applied. TRLFS was applied to characterize the U(VI) binding. The PBTC retention was quantified by 1H and 31P solution NMR.

In a nuclear waste repository, cement-based materials are to be used for waste conditioning and as an engineered barrier. The ingress of water into the nuclear waste repository, described as a worst-case scenario, leads to increased aging and degradation of the concrete. These processes are associated with a leaching of diverse organic substances usually added to the cement to realize the desired physicochemical and mechanical properties of the cement-based materials. The impact of the additives is based on their excellent ability to complex metal ions. Consequently, the complexation behavior of such additives towards radionuclides (RN) and thus their impact on RN mobilization and migration into the environment is essential for a comprehensive risk assessment. One of the additives commonly used for long-term retardation of cement hardening is 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC). PBTC is a polyfunctional ligand possessing three carboxyl groups and one phosphonate group, which have been shown to make PBTC a strong complexing agent for various metal ions (e.g. Ca2+, Zn2+, Al3+, Fe3+) [1,2]. However, to date, there are no studies on PBTC interaction with radionuclides. Therefore, the complexation of PBTC with U(VI) was investigated for the first time, using different spectroscopic methods over a wide pH range (2 through 11) to identify and characterize possible complex species. U(VI)-PBTC species with solubility as high as 100 mM were observed throughout the entire pH range studied, especially when PBTC is in excess. This allowed the convenient application of structuresensitive methods such as NMR, IR, and Raman spectroscopies. Furthermore, time-resolved laserinduced fluorescence spectroscopy (TRLFS) and UV-Vis titration studies provided insight into U(VI)–PBTC system’s speciation.

Organophosphonates are used multipurpose in the chemical industry. One of the most commonly used organophosphonates is 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC).[1] The functional groups of PBTC consist of one phosphonate and three carboxylate groups, which make PBTC not only an effective dispersant, but also a very good complexing agent for various metal ions (e.g. Ca2+, Al3+, Fe3+).[2,3] Due to these properties, PBTC is used, for example, as an efficient long-term retarder in cement, as a corrosion inhibitor in reinforced concrete and steel, or as a scale inhibitor in water treatment plants or cooling water circulation systems.[4,5] However, this ubiquitous use can also lead to anthropogenic discharge into the environment, where PBTC can complex heavy metals or even radionuclides. Complexation can increase the solubility of metal ions and thus their bioavailability. As a result, there is an increased risk of toxic metal ions being distributed in the environment and thus also being absorbed into the human food chain. However, to date there have been no studies on the complexation of PBTC with radionuclides. For this reason, the complexation of PBTC with U(VI) in the pH range from 1 to 11 was investigated for the first time using various spectroscopic methods. The studies were performed by different series varying the pH or the U(VI) to PBTC ratio. For the methods used, U(VI) concentrations in the mM range were employed, which was possible due to the very good water solubility of the U(VI)-PBTC complexes. The structure-sensitive methods NMR, IR and Raman spectroscopy were used to characterise the complex structure. Supporting DFT calculations were carried out. The stability constants of the complex species were determined by UV-Vis spectroscopy. By applying the different spectroscopic methods, it was possible to determine chelation of U(VI) by the phosphonate group and one of the carboxyl groups. Furthermore, by means of factor analysis, the distribution of

Although 2-phosphonobutane-1,2,4,-tricarboxylic acid, PBTC, has manifold industrial applications, relevant and reliable data on the protonation of PBTC are poor. However, these data are critical parameters for ascertaining PBTC speciation, especially with regard to a sound structural and thermodynamic characterization of its metal ion complexes. A rigorous evaluation of pH-dependent 1H, 13C, and 31P chemical shifts along with accessible scalar spin–spin coupling constants (J) was performed in order to determine the pKa values of PBTC in 0.5 molal NaCl aqueous solution by means of nuclear magnetic resonance (NMR) spectroscopy. The phosphonate group revealed pKa values of 0.90 ± 0.02 and 9.79 ± 0.02, and the pKa values associated with the carboxylic groups are 3.92 ± 0.02, 4.76 ± 0.03, and 6.13 ± 0.03. Supported by DFT-calculated structures revealing strong intramolecular hydrogen bonding, the sequence of deprotonation could be unambiguously determined.

Air pollution remains a major environmental and health concern in urban environments, especially in street canyons that show increased pollution levels due to a lack of natural ventilation. Previous studies have investigated the relationship between street canyon morphology and in-canyon pollution levels. However, these studies are typically limited to the scale of a single street canyon and city-wide assessments on this matter are scarce. In 2018, NO2 concentrations were measured in 321 street canyons in the city of Antwerp (Belgium) as part of the large-scale citizen-science project “CurieuzeNeuzen”. In our research, this data was used to study the correlation between morphological indices (e.g. aspect ratio (AR), lateral aspect ratio (LAR), presence of trees) and the traffic volumes on a city-wide scale. The maximum hourly traffic volume (TVmax) and AR correlated significantly with the measured NO2 values, making them useful indicators for air quality in street canyons. For street canyons with AR > 0.65, a TVmax of 300 vehicles/hour was found as a threshold value to guarantee acceptable air quality. No significant correlations were found for the other parameters. Finally, a number of typical street canyon types were defined, which can be of fundamental interest for further research and spatial policy making., BT/Environmental Biotechnology

Exposure to trivalent lanthanides (Ln) and actinides (An) poses a serious health risk to animals and humans. Since both Ln and An are mainly excreted with the urine, we investigated the effect of La, Ce, Eu, and Yb (as representatives of Ln) as well as Am (as representative of An) exposure on a rat kidney cell line (NRK-52E) for 8, 24, and 48 h in vitro. Cell viability studies using the XTT assay and fluorescence microscopic investigations were combined with solubility and speciation studies using ICP-MS and time-resolved laser-induced fluorescence spectroscopy (TRLFS). Thermodynamic modeling was applied to predict the speciation of Ln and Am in cell culture medium. All Ln show a concentration- and time-dependent effect on NRK-52E cells with Ce being the most potent element. Effective Ln concentrations reducing the cell viability to 50 % (EC50 values) range from 340 µM for Ce to 1.1 mM for Eu. In general, light and heavy Ln seem to exhibit a greater effect than middle Ln. In cell culture medium with 10 % fetal bovine serum (FBS), the Ln are completely soluble and complexed with proteins from FBS. Ln speciation is time-independent. Comparative experiments with Am are ongoing and will reveal analogies and/or differences in the effect of trivalent Ln and An on rat kidney cells. This is the first study revealing the effects of Ln onto mammalian kidney cells. Furthermore, our laboratory is one of the few worldwide, which is able to perform cell culture studies using radioactive elements like Am. The results of this study underline the importance of combining biological, chemical, and spectroscopic methods in studying the effect of Ln and An on cells in vitro and may contribute to the improvement of the current risk assessment for Ln in the human body. Furthermore, they demonstrate that Ln seem to have no effect on rat renal cells in vitro at environmental trace concentrations. Nevertheless, especially Ce has the potential for harmful effects at elevated concentrations ob

Exposure to trivalent lanthanides (Ln) and actinides (An) poses a serious health risk to animals and humans. Since both Lan and An are mainly excreted with the urine, we investigated the effect of La, Ce, Eu, and Yb (as representatives of Ln) as well as Am (as representative of An) exposure on a rat renal cell line (NRK-52E) for 8, 24, and 48 h in vitro. Cell viability studies using the XXT assay and fluorescence microscopic investigations were combined with solubility and speciation studies using ICP-MS and time-resolved laser-induced fluorescence spectroscopy (TRLFS). Thermodynamic modeling was applied to predict the speciation of Ln and Am in cell culture medium. All Ln show a concentration- and time-dependent effect on NRK-52E cells with Ce being the most potent element. Effective Ln concentrations reducing the cell viability to 50 % (EC50 values) range from 340 µM for Ce to 1.1 mM for Eu. In general, light and heavy Ln seem to exhibit a greater effect than middle Ln. In cell culture medium with 10 % fetal bovine serum (FBS), the Ln are completely soluble and complexed with proteins from FBS. Ln speciation is time-independent. Comparative experiment with Am are ongoing and will reveal analogies and differences in the effect of trivalent Ln and An on rat kidney cells. The results of this study underline the importance of combining biological, chemical, and spectroscopic methods in studying the effect of Ln and An on cells in vitro and may contribute to the improvement of the current risk assessment for Ln in the human body. Furthermore, they demonstrate that Ln seem to have no effect on rat renal cells in vitro at environmental trace concentrations. Nevertheless, especially Ce has the potential for harmful effects at elevated concentrations observed in mining and industrial areas. References: [1] A. Heller, Ecotox. Environ. Safe. 2019, 173.

The similar chemical properties of f-block elements are still a challenging task in the separation of nuclear fuel waste material by hydrometallurgical methods. Extractants based on phosphorus (e.g. D2EHPA, PC88A, TBP) are typically used in industrial recovery processes.1, 2 Chelating agents, such as 4-acylpyrazolones received remarkable attention as extractants for rare earth elements.3 Our approach is to achieve suitable reagents for selective separation of lanthanides and actinides by implementing the phosphoryl group in the backbone of pyrazolones. This is the first publication on 4-phosphorylpyrazolones4, 5 with respect to their coordination behaviour towards f-block elements.

In the presence of polyborates (detected by 11B-NMR) a weak Eu(III) borate complex formation (lg beta ~ 2, estimated) was observed with time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation progress of this solid was investigated by TRLFS in dependence on the total boron concentration: The lower the total boron concentration the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD, solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.

The latest results in the Eu-B(OH)3-Organic System are presented: 1) New approach to determine the formation constant of a Eu borates 2) Formation of the solid Eu borate in NaCl medium 3) Quantitative synthesis of Eu borate and structure characterization

Boric acid (B(OH)3) and (poly)borates are of great interest regarding the mobilization of trivalent actinides in nuclear waste repositories, particularly in salt deposits. This work describes approaches to determine the stability constant in the Eu(III)-borate system. The stability constant between Eu(III) and borates is in the order of magnitude of 1...2, and with it the borate complexation is very weak. Furthermore, in presence of polyborates at pH 6 the formation of a solid Eu borate species is observed. The formation rate of the solid Eu borate species depends on the polyborate concentration and salt concentration/type (NaClO4/NaCl). Some structural information of the solid Eu borate were provided from IR spectroscopy, solid-state NMR (11B) and solid-state TRLFS.

Boric acid (B(OH)3) and (poly)borates are of great interest regarding the mobilization of trivalent actinides in nuclear waste repositories, particularly in salt deposits. This work describes the influence of boric acid on the Eu salicylate complexation due to the formation of a borate ester of salicylate, which could be the key to determine the stability constants of Eu-borate complexes. Furthermore, at pH 6 the formation of a solid Eu borate species in presence of polyborates is observed. The formation progress of the solid Eu borate species depends on the polyborate concentration and salt concentration. The solid formation could be an interesting possibility for the immobilization of trivalent actinides in a nuclear waste repository.

no abstract for this material

Presently, argillaceous rock formations are under investigation as potential host rocks for nuclear waste repositories. In addition to the diffusion the sorption of radionuclides on mineral phases is an important physicochemical process in a nuclear waste repository in the case of a water inleakage. Concerning the required long-term safety and risk assessment of the storage of high-level radioactive waste the understanding of these processes is essential. The investigations concentrated on the sorption of Eu(III) on OPA under realistic OPA pore water conditions (medium: pH 7.6; ionic strength 0.4 mol•L-1; presence of chloride, sulfate, carbonate) up to 50°C. In addition to the temperature dependent investigations the influence of tartrate and citrate (representatives of NOM) on the Eu(III) sorption was studied. The sorption is characterized by a very strong binding of Eu(III) to the clay surface and a significant temperature dependency. With rising temperature the Rd value rises, showing that the Eu(III) sorption increases. In the presence of tartrate or citrate the Eu(III) sorption decreases with rising ligand concentration.

Concerning the safety and risk assessment for a nuclear waste repository the interaction between trivalent lanthanides and actinides and borates is interesting to study. Borates occur in salt deposits (possible host rock for nuclear waste repositories) and can be release due to corrosion of vitrified waste block (borosilicate glass) and storage containers. The investigations concentrate on the reaction between Eu(III) and borates in aqueous solution. At pH 6 the formation of a Eu borate solid species in presence of polyborates is observed. The formation of the solid Eu borate species depends on the polyborate concentration and ionic strength.

Borates are ubiquitous compounds in the environment (rocks, soils, natural waters) and are used in many applications. Thus, there are many sources for the release of borates in the environment. Another aspect is the occurrence of borates in salt formations, which is important concerning the search of a proper nuclear waste repository. But although there is a relevance of borates the Ln(III)/An(III)-borate system is investigated insufficiently. The investigations concentrated on the complexation between Eu(III) and borates in aqueous solution. First results show a small influence of borates on the Eu(III) speciation.

Borates and organic matter (humic and fulvic acids, small organic molecules) are ubiquitous compounds in the environment (rocks, soils, natural waters). Concerning the safety and risk assessment for a nuclear waste repository the interaction between trivalent lanthanides and actinides and borates is interesting to study. Borates occur in salt deposits (possible host rock for nuclear waste repositories) and can be release due to corrosion of vitrified waste block (borosilicate glass) and storage containers. The investigations concentrate on the reaction between Eu(III) and borates in aqueous solution. For boric acid (B(OH)3) no and for polyborates weak complexation properties concerning Eu(III) are observed. The complexation between Eu(III) and salicylate is influenced by boric acid due to the formation of a borate ester. Furthermore at pH 6 the formation of a solid Eu borate species in presence of polyborates is observed. The formation of the solid Eu borate species depends on the polyborate concentration and ionic strength.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) has been extensively used as a sensi-tive and selective technique to analyze actinide complexation with inorganic and organic ligands in trace metal concentrations. However, the application of TRLFS onto Am(III) complexation systems was up to now limited because of the much lower luminescence intensity and much shorter lifetime of Am(III) in comparison to U(VI) or Cm(III). We investigated the complexation behavior of Am(III) complexes with lactate (Lac) and substituted benzoic acids like pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) at ambient and ele-vated temperatures with TRLFS. Using the emission of the 5D1-7F1 transition at around 691 nm, spectral data like luminescence life-times, luminescence maxima and complex stability constants were calculated. Temperature dependent stability constants were determined to estimate thermodynamic data (reaction enthalpy, reaction en-tropy). The Am(III) aquo ion shows at pH 4-6 a luminescence lifetime of 23 ns, corresponding to approxi-mately 9 coordinating water molecules. Complexation with BTC shows no change of the excitation and emission maximum but an increase of the luminescence intensity and lifetime. The luminescence lifetime was prolonged to 27 ns, corresponding to 8 remaining water molecules in the first coordina-tion shell. This indicates an exchange of 1 water molecule with 1 coordination site of the ligand, re-sulting in an Am-BTC 1:1 complex [1]. In contrast, complexation with lactate causes a red shift of the excitation wavelength of Am(III) (Fig. 1), resulting in a red shift of the luminescence emission maxi-mum of about 5 nm. The luminescence lifetime is prolonged up to 37 ns which corresponds to 5-6 re-maining water molecules. This indicates an exchange of about 3-4 water molecules with coordination sites of ligand molecules which implies the formation of 1:1, 1:2 and 1:3 complexes. The stability con-stants increase slightly with ris

Clay minerals which are components of potential host rock formations for nuclear waste repositories can contain small organic molecules like formate, citrate or lactate. Such small organic molecules can like the ubiquitous humic acids influence the migration behavior of radionuclides. Different substituted benzoic acids can mimic the main functionalities and are often used as model compounds for humic substances. The understanding of the complex behavior of radionuclides with such natural organic matter and the thermodynamic quantification of the interaction especially at elevated temperatures is of great importance to simulate and predict their migration behavior in the environment, particularly in the near field of nuclear waste disposals where higher temperatures are prevailing. We present the investigation of the complex behavior of Am(III) and Eu(III) with lactate and salicylate at ambient and elevated temperatures with time-resolved laser-induced fluorescence spectroscopy (TRLFS) and the resulting thermodynamic data (reaction enthalpy, reaction entropy). Whereas the complexation with lactate is for both cations nearly temperature independent, is the complexation with salicylate clearly an endothermic reaction.

The influence of temperature up to 50°C and small organic ligands (citrate, tartrate) on the sorption of Eu(III) on the natural clay rock Opalinus Clay (OPA) under aerobic (p(CO2) = 10^(-3.5) atm) synthetic OPA pore water conditions (pH 7.6, I = 0.4 M) was investigated. Batch sorption experiments and time-resolved laser-induced fluorescence spectroscopy (TRLFS) were used to study these influencing factors on the Eu(III) sorption. Sorption isotherms and distribution coefficients Rd (15°C: log Rd = 4.50 ± 0.05 … 50°C: log Rd = 5.54 ± 0.06) at 2•10^(-9) M Eu(III) as a function of the solid-to-liquid ratio (up to 3 g•L^(-1)) and temperature were determined. A significant temperature dependency of the Eu(III) sorption was observed. With rising temperature the Eu(III) sorption increases. The surface reaction is endothermic (sorption enthalpy ~ 50 kJ•mol^(-1)). Using TRLFS, a surface species with a luminescence lifetime of (201 ± 9) microseconds was identified. In the presence of tartrate or citrate the Eu(III) sorption decreases with increasing ligand concentration due to a complex formation of Eu(III) in solution, with citrate having a more pronounced influence on the sorption than tartrate. With the batch sorption experiments it can be shown that at a citrate concentration larger than 10^(-5) M and at a tartrate concentration larger than 10^(-4) M an increasing Eu(III) desorption occurs. This result is supported by TRLFS measurements, which show the correlation between the complexation of Eu(III) by citrate or tartrate in solution and the Eu(III) desorption process. Possible Eu(III) citrate or Eu(III) tartrate surface species on OPA could not be detected using TRLFS.

Clay minerals which are components of potential host rock formations for nuclear waste repositories can contain small organic molecules like formate, citrate or lactate. Such small organic molecules can like the ubiquitous humic acids influence the migration behavior of radionuclides. Different substituted benzoic acids can mimic the main functionalities and are often used as model compounds for humic substances. The understanding of the complex behavior of radionuclides with such natural organic matter and the thermodynamic quantification of the interaction especially at elevated temperatures is of great importance to simulate and predict their migration behavior in the environment, particularly in the near field of nuclear waste disposals where higher temperatures are prevailing. We present the investigation of the complex behavior of Am(III) and Eu(III) with lactate and salicylate at ambient and elevated temperatures with time-resolved laser-induced fluorescence spectroscopy (TRLFS) and the resulting thermodynamic data (reaction enthalpy, reaction entropy). Whereas the complexation with lactate is for both cations nearly temperature independent, is the complexation with salicylate clearly an endothermic reaction.

Presently, argillaceous rock formations are under investigation as potential host rocks for nuclear waste repositories. The sorption of radionuclides on mineral phases is an important physicochemical process in a nuclear waste repository in the case of a water inleakage. Concerning the required long-term safety and risk assessment of the storage of high-level radioactive waste the understanding of this process is essential. Opalinus Clay (OPA) is a complex composed argillaceous rock. This natural occurring clay rock is discussed as host rock formation for nuclear waste repositories. In a repository based on argillaceous rock an initial temperature of around 100°C is expected. But although elevated temperatures are able to influence the sorption behaviour of radionuclides on mineral phases the temperature effect is still investigated insufficiently. Due to the fact that natural organic matter was found in the OPA the influence of organic matter on the radionuclide sorption hast to be investigated. The investigations concentrated on the sorption of Eu(III) and U(VI) on OPA under realistic OPA pore water conditions (OPA pore water medium, pH 7.6, I = 0.4 mol•L-1) up to 50°C. In addition to the temperature dependent investigations the influence of small organic molecules (e.g. lactate, acetate, propionate, tartrate, citrate) on the Eu(III) and U(VI) sorption on OPA was studied up to 50°C. The Eu(III) sorption is characterized by a strong binding of Eu(III) and the U(VI) sorption is characterized by a weak binding of U(VI) to the clay surface. A significant temperature dependency for the Eu(III) and U(VI) sorption was observed. In the presence of the organic matter the Eu(III) and U(VI) sorption decreases with rising ligand concentration due to a complexation of the metal ions by the ligands in solution. The mobilization of Eu(III) and U(VI) correlates with the complex formation strength of the organic ligands.

Investigations to the mobilisation of radionuclides are essential in the risk assessment of radionuclides in the environment and the safety assessment of nuclear waste repositories. The mobilisation of radionuclides takes place for instance by the formation of water soluble complexes or sorption processes on mineral surfaces. Concerning the required risk and safety assessments a wide knowledge about the chemical and physical behavior of radionuclides, particularly actinides, is needed. Thus, interaction studies of radionuclides are carried out, e.g. complexation studies with components of the environmental compartments (humic acids, bioligands, inorganic ligands, bacteria, …). Borates (e.g. boric acid B(OH)3 and its salts or esters) are ubiquitous compounds in the environment (rocks, soils, natural waters) and are used in many applications, e.g. glass production, detergents, agriculture and nuclear technology. Thus, there are many sources for the release of borates in the environment. But although there is a relevance of borates in the environment and, perhaps, in nuclear waste repositories, the Ln(III)/An(III)-borate system is investigated insufficiently. The work concentrates on the complex formation in the An(III)/Ln(III)-borate system. The influence of temperature and ionic strength on the complexation will be investigated.

Argillaceous rocks, like the Opalinus clay formation (OPA) in Switzerland are potential host rocks for nuclear waste repositories. The OPA can contain up to 1% dissolved organic matter. It consists of small organic molecules like formiate, citrate or lactate. Such small organic molecules can like the ubiquitous humic acid influence the migration behaviour of radionuclides. The understanding of the complex behaviour of radionuclides with such natural organic matter and the thermodynamic quantification of the interaction is of great importance to simulate and predict their migration behaviour in the environment. Additionally, it is crucial to study the complex behaviour of radionuclides at elevated temperatures, because especially in the near field of nuclear waste disposals higher temperatures are prevailing. We investigated the complex behaviour of Am(III) complexes with lactate and substituted benzoic acids like pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) which serve as model compounds for humic substances at ambient and elevated temperatures with time-resolved laser-induced fluorescence spectroscopy (TRLFS). TRLFS has been extensively used as a sensitive and selective technique to analyze actinide complexation with inorganic and organic ligands in trace metal concentrations. However, the application of TRLFS onto Am(III) complex systems was up to now limited because of the much lower luminescence intensity and much shorter lifetime in comparison to U(VI) or Cm(III). Using the emission of the 5D1-7F1 transition at around 690 nm, spectral data like luminescence lifetimes and maxima and complex stability constants were calculated. Temperature dependent stability constants were determined to estimate thermodynamic data (enthalpy, entropy). The Am(III) aquo ion shows at pH 4-5 a luminescence lifetime of 23 ns, corresponding to approximately 9 coordinating water molecules. Complexation with BTC shows no change of the emission maximum but an increase of

Presently, argillaceous rock formations are under investigation as potential host rocks for nuclear waste repositories. In addition to the diffusion the sorption of radionuclides on mineral phases is an important physicochemical process in a nuclear waste repository in the case of a water inleakage. Concerning the required long-term safety and risk assessment of the storage of high-level radioactive waste the understanding of these processes is essential. Opalinus Clay (OPA) is a complex composed argillaceous rock. This natural occurring clay rock is discussed as host rock formation for nuclear waste repositories. In a repository based on argillaceous rock an initial temperature of around 100°C is expected due to the radioactive decay and the release of geothermal energy. But although elevated temperatures are able to influence the sorption behaviour of radionuclides on mineral phases the temperature effect is still investigated insufficiently. The investigations concentrated on the sorption of Eu(III) on OPA under realistic OPA pore water conditions (pH 7.6, I = 0.4 mol•L-1) up to 50°C. In addition to the temperature dependent investigations the influence of organic matter (tartrate, citrate) on the Eu(III) sorption on OPA was studied up to 50°C. The Eu(III) sorption is characterized by a very strong sorption to the clay surface. A significant temperature dependency of the Eu(III) sorption was observed. In the presence of tartrate or citrate the Eu(III) sorption decreases with rising ligand concentration. A surface species, most likely a EuCO3 surface species, was detected using TRLFS. The formation of a surface species containing tartrate or citrate was not observed with TRLFS.

Americium contributes to the activity of radioactive waste to a certain extend. Until now, a little is known about the complexation with organic molecules. We analyzed the complexation of the trivalent ion (Am(III)) with Pyromellitic acid (Pyr) using UV-vis spectroscopy with a Liquid Waveguide Capillary Cell (LWCC) at different temperatures.

For the first time, the complexation of americium(III) with salicylic acid was studied at trace metal concentrations using a 2.0 m Long Path Flow Cell for UV–vis spectroscopy. The detection limit of Am(III) in aqueous solution at pH 3.0 was found to be 5 9 10-9 M. Two Am(III)-salicylate complexes were formed at pH 5.0 in 0.1 M NaClO4, indicated by a clear red shift of the absorption maximum. The absorption spectra obtained from spectrophotometric titration were analyzed by means of factor analysis and complex stabilities were calculated to be log b110 = 2.56 ± 0.08 and log b120 = 3.93 ± 0.19.

Im Vortrag werden Ergebnisse zur Temperaturabhängigkeit der Eu(III)-Sorption an Opalinuston sowie zum Einfluss kleiner organischer Moleküle auf das Sorptionsverhalten vorgestellt. Außerdem wird die Komplexierung von Am(III) mit Weinsäure, untersucht bei Raumtemperatur mit UV-vis mittels LWCC, präsentiert. Des weiteren werden die Temperaturabhängigkeit des Eu(III)-Pyromellitsäure-Komplexsystems, untersucht mit TRLFS und Mikrokalorimetrie, und strukturelle Aspekte dieses Systems, ermittelt mit FT-IR und DFT, diskutiert.

Die Komplexbildung von Am(III) und Eu(III) wurde mittels UV-vis Spektroskopie und TRLFS untersucht. Mit steigender Temperatur konnte ein Anstieg der Eu(III)-Lactat Komplexierung festgestellt werden. Die Stabilität logb des Am(III)-Lactat Komplexes konnte bei Raumtemperatur mit TRLFS, UV-vis mit LWCC und UV-vis mit Standardpfadlänge übereinstimmend auf 2,2 ± 0,2 beziffert werden und liegt damit in der Nähe des Eu(III)-Lactat Komplexes. Vorgestellt wurde außerdem der Einfluss von Temperatur, pH-Wert und Organik auf die Sorption von Eu(III) am Opalinuston im Porenwasser. Es konnte gezeigt werden, dass die Sorption mit steigender Citrat und Tartat Konzentration abnimmt. Über TRLFS konnten Eu(III)-Citrat Spezies im Überstand der Batch-Sorptionsversuche, nicht jedoch am Opalinuston nachgewiesen werden. Die Erhöhung der Temperatur führt zwischen 20 und 60°C zu einer Verstärkung der Sorption. Ein Einfluss der Liganden auf die Sorptionsenthalpie konnte nicht nachgewiesen werden.

The long-term safety analysis of nuclear waste disposals in clay formations requires detailed knowledge of the interaction of actinides at relevant temperatures (up to 100 °C). It is well known that the migration behaviour of the actinides is strongly influenced by natural organic matter (NOM) from the clay. However, the current thermodynamic database is lacking fundamental data about the temperature-dependent complexation of americium (and its analogue europium) with small organic acids, which are structural similar components of natural organic matter in the clay. We present our results for the complexation of both Am(III) and Eu(III) with 2-hydroxybenzoic acid (salicylic acid), 1,2,4,5-benzentetracarboxylic acid (pyromellitic acid) and 2,3-dihydroxbutanedioic acid (L-tartaric acid) in the temperature range from 20 to 50°C, at ionic strength of 0.1 mol/l NaClO4 and pH below 6. For the first time, temperature-dependent UV-Vis spectroscopic measurements with a Liquid Waveguide Capillary Cell were used for complexation investigations. Due to the long optical path length of the capillary cell (up to 2 m) very low americium and europium concentrations can be measured. Thus, the presented absorption measurements were carried out at Am(III) concentrations below 5e-7 mol/l and Eu(III) concentration below 5e-4 mol/l. For all investigated model ligands we observed a slight shift of the absorption maxima of Eu(III) (394 nm) and Am(III) (504 nm) spectra of 0.5 to 2 nm to higher wavelengths due to the complexation. We first validated the method with europium: at 25°C the determined constants for the 1:1 complexes of europium salicylate, europium pyromellitate and europium L tartrate with logß111=15.4+/-0.06, logß112 = 14.3 +/-0.2, logß111=7.9+/-0.3 respectively, are in good agreement with the literature values [1], [2]. For the americium salicylate system, both a 1:1 complex and a 1:2 complex were observed at pH 4. The stability constants of these complexes are logß111= 15.42+