Surface Processes Division
A detailed knowledge of the molecular processes determining the migration behavior of heavy metal contaminants, namely long-lived radionuclides, in the environment is mandatory for the assessment of their dissemination and the risk involved for human health. A deep understanding of these processes, which in general are strongly related to the host rock in the in the near and far field of the considered site, is fundamental for the development of new detoxification, separation and remediation strategies but also for the design of a deep underground waste repository. Thus, a characterization and ranking of the most relevant interactions of radionuclides with mineral surfaces, but also the aqueous chemistry of these heavy metals, represents the central scope of the division “Surface Processes” of the Institute of Resource Ecology.
In this context, the exploration of complex systems, such as the sorption processes on naturally occurring mineral surfaces, the aqueous speciation and colloid forming processes within a wide range of environmental parameters becomes essential. From the results obtained, the identification of (surface) species and development of molecular models comprehensively describing the mechanisms of transport and retention of the radionuclides in the environment can be achieved. These models are expanded into the compilation of data bases providing reliable parameter sets for the assessment of the macroscopic migration behaviour of the long-lived radionuclides.
The actual major research topics of the division can be summarized as follows:
- Spectroscopic characterization of heavy metal species in aqueous solutions and at mineral surfaces as a function of pH, temperature, and salinity including the impact of redox active complexing compounds. (→)
- Development and parameterization of models describing surface complexation phenomena of heavy metal ions on mineral oxides and rock materials (e.g. natural clays). (→)
- Investigation of the complexation behavior of long-lived radionuclides with organic compounds and biomolecules in aqueous media.
- Identification and characterization of colloidal nanoparticles of actinides and their relevance for radionuclide transport in the environment (from the source of radionuclide to man’s food chain).(→)
- Set-up of thermodynamic data bases for prospective deep nuclear waste repositories. (→)
- In situ vibrational spectroscopy →
The molecular processes of dissolved metal ions at mineral-water interfaces are monitored in real time by reaction-induced difference spectroscopy using the ATR technique. Metal complexes of biomolecules in aqueous solution can be characterized. Complementary vibrational spectroscopic information can be obtained from FT-Raman spectroscopy.
- Time-resolved laser-induced fluorescence spectroscopy (TRLFS)
Emission spectra of aqueous solutions, suspensions, solids and flow cell experiments can be recorded with a Minilite laser system (Nd:YAG laser; λexc. = 266 or 532 nm from Continuum, Santa Clara, CA, U.S.A.). Detection is managed with an ICCD camera (Horiba Jobin Yvon) with iHR550 spectrometer in the wavelength range from 150 – 1500 nm. Time resolution is < 100 μs. Temperature of the samples can be controlled between −150°C and 70°C. The element specific limit of detection for U(VI) is 10−10 M.
- NMR spectroscopy
The interaction of lanthanides (as substitutes for actinides) with biologically and environmentally relevant complexing agents in solution are investigated with a Varian Unity inova 400 MHz NMR spectrometer. Multinuclear 1D- and 2D-NMR methods are applied.
- UV-Vis-NIR absorption spectroscopy
Absorption spectra of aqueous samples and flow cell experiments can be recorded in the wavelength range from 190 – 3300 nm with an Cary5G from Varian, Inc. Temperature control is optional between 0°C and 70°C. The element specific limit of detection for U(VI) and Np(V) is 10−4 M and 10−5 M, respectively.
- DFT calculations
Quantum chemical calculations (mainly DFT calculations) are used to predict the molecular structures of various uranium(VI) organic and inorganic complexes including calculations of IR spectra and luminescence properties. (→)
- THEREDA (→) offers evaluated thermodynamic data for all compounds of dose relevant elements according to the present state of research.
- RES³T (→) is a digitized version of a thermodynamic sorption database as required for the parameterization of Surface Complexation Models (SCM).
- Radioanalytical methods
α-spectrometry: Grid ionization chamber (GIK 800S, MAB) allows the analysis of thin layers up to ~300 cm2 (limit of detection ~10−2 Bq).
Semiconductor detector (PIPS: PH 450-21-100AM, Canberra) allows the analysis of thin layers up to ~4.5 cm2 (limit of detection ~10−3 Bq).
β-spectrometry: Liquid scintillation counting (LSC) with α/β discrimination (1400 Wallac Win Spectral, Tri-Carb 3100 TR, Perkin-Elmer).
γ-spectrometry: High Purity Germanium Detection (Gamma-X HPGe, Coaxial Photon Detector, Ortec).
- Colloid characterization techniques
Light scattering: Dynamic and static light scattering (ALV / CGS-3 and Brookaven BI-90) allows size distributions of colloidal nanoparticles and determination of molecular weights of macromolecules.
Zeta-Potential: The zeta potentials of nanoparticles in dependence on pH can be determined by laser Doppler velocimetry using a Zetasizer Nano ZS (Malvern).
- Mass spectrometry
Inductively coupled plasma-mass (ICP-MS) spectrometry is highly sensitive for the quantification of elements in solid and liquid samples.
- Batch sorption experiments
Sorption properties of different minerals towards inorganic and organic pollutants depending on various factors (e.g. pH, ionic strength, redox potential, temperature, presence of organic matter, microbes or competing species) are determined by batch experiments and thermodynamic parameters (Kd, ΔRH, ΔRS) are derived.
- Determination of transport parameters (De, Kd, porosity)
Small-scale stainless steel diffusion cells are used for investigation of radionuclide migration through minerals or rock materials.
- Specific surface area analysis
Determination of the specific surface area (m2/g) of solids based on the so-called BET (Brunauer, Emmett and Teller) method, by measuring N2(g) physical adsorption onto cleaned surfaces.
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