Measurement and modelling of reactive transport in geological barriers for nuclear waste containment

Unit cell illustrating potential diffusion paths (bonds, yellow and red) in the neighbourhood of central particle (green); these join neighbouring cell faces and show where elongated pores may be assigned to the experimental pore system information.</p

Investigation of the complexation and the migration of actinides and non-radioactive substances with humic acids under geogenic conditions : complexation of humic acids with actinides in the oxidation state IV Th, U, Np ; final report

[no abstract available

Joint project: Migration of actinides in the system clay, humic substance, aquifer - migration behavior of actinides (Uranium, Neptunium) in clays: Characterization and quantification of the influence of humic substances : final report

[no abstract available

Influence of humic acids on the migration behavior of radioactive and non-radioactive substances under conditions close to nature : synthesis, radiometric determination of functional groups, complexation ; final report ; Laufzeit des Vorhabens: 01.11.1995 bis 28.02.1999

[no abstract available

Influence of humic acids on the migration behavior of radioactive and non-radioactive substances under conditions close to nature Synthesis, radiometric determination of functional groups, complexation

The interaction behavior of humic acids with uranium(VI) and the influence of humic substances on the migration behavior of uranium was investigated. A main focus of this work was the synthesis of four different humic acid model substances and their characterization and comparison to the natural humic acid from Aldrich. A radiometric method for the determination of humic acid functional groups was applied in addition to conventional methods for the determination of the functionality of humic acids. The humic acid model substances show functional and structural properties comparable to natural humic acids. Modified humic acids with blocked phenolic OH were synthesized to determine the influence of phenolic OH groups on the complexation behavior of humic acids. A synthesis method for &quot;1&quot;4C-labeled humic acids with high specific activity was developed. The complexation behavior of synthetic and natural humic acids with uranium(VI) was investigated by X-ray absorption spectroscopy, laser-induced fluorescence spectroscopy and FTIR spectroscopy. The synthetic model substances show an interaction behavior with uranium(VI) that is comparable to natural humic acids. This points to the fact that the synthetic humic acids simulate the functionality of their natural analogues very well. For the first time the influence of phenolic OH groups on the complexation behavior of humic acids was investigated by applying a modified humic acid with blocked phenolic OH groups. The formation of a uranyl hydroxy humate complex was identified by laserspectroscopic investigations of the complexation of Aldrich humic acid with uranium(VI) at pH7. The migration behavior of uranium in a sandy aquifer system rich in humic substances was investigated in column experiments. A part of uranium migrates non-retarded through the sediment, bound to humic colloids. The uranium migration behavior is strongly influenced by the kinetically controlled interaction processes of uranium with the humic colloids. The influence of humic acids on the sorption of uranium(VI) onto phyllite was investigated in batch experiments using two different humic acids. The uranium(VI) sorption onto the phyllite is influenced by the pH-dependent sorption behavior of the humic acids. (orig.)Im Rahmen des Forschungsvorhabens wurde das Wechselwirkungsverhalten von Huminsaeuren mit Uran(VI) sowie der Einfluss von Huminstoffen auf das Migrationsverhalten von Uran untersucht. Einen Schwerpunkt der Arbeiten bildete die Synthese von vier verschiedenartigen Huminsaeuremodellsubstanzen sowie deren Charakterisierung im Vergleich zur natuerlichen Huminsaeure von Aldrich. Eine radiometrische Methode zur Bestimmung funktioneller Gruppen wurde neben herkoemmlichen Methoden zur Bestimmung der Huminsaeurefunktionalitaet eingesetzt. Die Modellhuminsaeuren zeigen mit natuerlichen Huminsaeuren vergleichbare funktionelle und strukturelle Eigenschaften. Zur Bestimmung des Einflusses phenolischer OH-Gruppen auf das Komplexbildungsverhalten von Huminsaeuren wurden modifizierte Huminsaeuren mit blockierten phenolischen OH-Gruppen synthetisiert. Ein Syntheseverfahren fuer &quot;1&quot;4C-markierte Huminsaeuremodellsubstanzen mit hoher spezifischer Aktivitaet wurden entwickelt. Das Komplexbildungsverhalten synthetischer und natuerlicher Huminsaeuren mit Uran(VI) wurde mittels Roentgenabsorptionsspektroskopie, laserinduzierter Fluoreszenzspektroskopie und FTIR-Spektroskopie untersucht. Es wurde nachgewiesen, dass die synthetischen Huminsaeuremodellsubstanzen ein mit natuerlichen Huminsaeuren vergleichbares Wechselwirkungsverhalten gegenueber Uran(VI) zeigen und somit die Funktionalitaet der natuerlichen Analoga gut simulieren. Erstmals wurde unter Verwendung einer modifizierten Huminsaeure der Einfluss phenolischer OH-Gruppen auf das Komplexbildungsverhalten von Huminsaeuren untersucht. Im Rahmen von laserspektroskopischen Untersuchungen zur Komplexierung von Aldrich Huminsaeure mit Uran(VI) bei pH7 wurde die Bildung eines Uranylhydroxyhumat-Komplexes nachgewiesen. Das Migrationsverhalten von Uran in einem sandigen huminstoffreichen Grundwasserleiter wurde in Saeulenexperimenten untersucht. Ein Teil des Urans wird ungehindert, huminstoffgebunden durch das Sediment transportiert. Das Migrationsverhalten von Uran wird stark durch kinetisch kontrollierte Wechselwirkungsprozesse mit den Huminstoffkolloiden beeinflusst. Der Einfluss von Huminsaeuren auf die Sorption von Uran an Phyllit wurde in Batchexperimenten mit zwei verschiedenen Huminsaeuren untersucht. Die Sorption von Uran an Phyllit wird durch das vom pH-Wert abhaengige Sorptionsverhalten der Huminsaeure beeinflusst. (orig.)SIGLEAvailable from TIB Hannover: RR 1847(290) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman

Investigation of the complexation and the migration of actinides and non-radioactive substances with humic acids under geogenic conditions Complexation of humic acids with actinides in the ocidation state IV Th, U, Np

Objective of this project was the study of basic interaction and migration processes of actinides in the environment in presence of humic acids (HA). To obtain more basic knowledge on these interaction processes synthetic HA with specific functional properties as well as &quot;1&quot;4C-labeled HA were synthesized and applied in comparison to the natural HA Aldrich. One focus of the work was on the synthesis of HA with distinct redox functionalities. The obtained synthetic products that are characterized by significantly higher Fe(III) redox capacities than Aldrich HA were applied to study the redox properties of HA and the redox stability of U(VI) humate complexes. It was confirmed that phenolic OH groups play an important role for the redox properties of HA. However, the results indicate that there are also other processes than the single oxidation of phenolic OH groups and/or other functional groups contributing to the redox behavior of HA. A first direct-spectroscopic proof for the reduction of U(VI) by synthetic HA with distinct redox functionality was obtained. The complexation behavior of synthetic and natural HA with actinides (Th, Np, Pu) was studied. Structural parameters of Pu(III), Th(IV), Np(IV) and Np(V) humates were determined by X-ray absorption spectroscopy (XAS). The results show that carboxylate groups dominate the interaction between HA and actinide ions. These are predominant monodentately bound. The influence of phenolic OH groups on the Np(V) complexation by HA was studied with modified HA (blocked phenolic OH groups). The blocking of phenolic OH groups induces a decrease of the number of maximal available complexing sites of HA, whereas complex stability constant and Np(V) near-neighbor surrounding are not affected. The effects of HA on the sorption and migration behavior of actinides was studied in batch and column experiments. Th(IV) sorption onto quartz and Np(V) sorption onto granite and its mineral constituents are affected by the pH value and the presence of HA. HA exhibits a significant influence on the transport of U(IV) and U(VI) in a laboratory quartz sand system. In order to provide the basis for a more reliable modeling of the actinide transport, the metal ion complexation with HA has to be integrated into existing geochemical speciation codes. Within this project the metal ion charge neutralization model was embedded into the geochemical modeling code EQ3/6. In addition to that, a digital data base was developed which covers HA complexation data basing on the charge neutralization model. (orig.)Available from TIB Hannover: RR 1847(399) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Wirtschaft und Arbeit (BMWA), Berlin (Germany)DEGerman

The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution

The coordination of U(VI) sulfate complexes has been investigated by uranium L-III-edge EXAFS and HEXS measurements with the aim to distinguish monodentate and bidentate coordinated sulfate in aqueous solution. UV-vis absorption spectroscopy has been used to differentiate the species and to determine the species distribution as a function of the [SO42-]/[UO22+] ratio. A monodentate coordination prevails in solutions with [SO42-]/[UO22+] ratio of 1, where UO2SO4 is the dominant species. Besides the dominating monodentate sulfate a small amount of bidentate sulfate could be observed, indicating that two isomers may exist for UO2SO4. With increasing [SO42-]/[UO22+] ratio the UP2(SO4)(2)(2-) species becomes the main species. The uranium atom of this species is coordinated by two bidentate Sulfate groups