Particle-mediated transport in geosystems
The mobility of metals and non-metal elements in hydro-geosystems is often determined by the mobility of their likely carriers that occur in broad varieties in nature (geogenic) or are introduced into nature by technological and/or anthropogenic activities. A further deepened, fundamental research based understanding of such particle-mediated transport in geosystems (process understanding) and the likely subsequent risks for the environment is the aim our past, current and future research activities.
Current and past Projects:
- NuWaMa: Visualization of PET-labelled SiO2 particles in a fracture and porous flow (Co-ordinator). BMBF (2016-2018)
- NetFlot: Network of infrastructure: Modeling the Flotation Process (Co-ordinator). H2020, EIT KIC RawMaterial (2016-2018)
- nanoSuppe: Fate of nanoparticles in waste water: TiO2, MWCNT, CeO2, Quantum Dots (Co-ordinator). BMBF (2014-2017)
- cntTrack: Transport of technical carbon nanoparticles in geomatrices´s. DFG FR1643/3-1 (2012-2015)
- Quality-Nano projects: Radiolabelling of nanoparticles with cyclotron facilities. JRC (2013, 2014, 2015)
- nanoTrack: Investigation of the life cycle of nanoparticles be means of [45Ti]TiO2 and [105Ag]Ag0 (Co-ordinator). BMBF (2011-2014)
Occurrence, characterization and modification of nanoparticles and colloids
Natural aqueous humic and fulvic acids, partly extracted from geosystems (surface water and soils), are characterized and used in (kinetic) metal-humate complexation and sorption studies. Metals and non-metals under investigation include Al, Fe, Co, Cu, Zn, Sn, Y, Tl, Eu, Tb, Th, U, Np, Pu, Am, Cm and Se [e.g. 1-3]. Spectroscopic methods (XAS, HEXS, and DLS) allow for the speciation , microscopic (TEM and SEM) allow elucidating their complex structures and polymerization/aggregation mechanism. Radiolabelling methods for the impact assessment of geochemical parameter variations on the metal or metal-humate mobility in geosystems . Isotope exchange and luminescence studies allow for the quantification of kinetic interaction studies between metal and humic/fulvic acids and additional competing system components .
The formation of U(IV)-silica colloids (<20 µm) and their significant stability in natural waters was described for the first time .
The capacity of modified, primarily water-insoluble multiwall carbon nanotubes as U(IV) carrier was uncovered and their significant stability in systems near to nature was demonstrated .
Currently, the characterization of technical nanoparticles (metal oxides and carbon nano tubes) by means of dynamic light scattering, SEM, and ICP-OES, and their modification for better solubility in aquatic systems is studied in detail.
Radiolabelling of system components
Radiolabelling strategies of dedicated system components (humic/fulvic acids , technical nanoparticles, EDTA-coated SiO2) aim at gaining an advanced understanding of processes related to the particle-mediated transport in geosystems. An increasing portfolio of suitable radionuclides (half-life, chemistry, decay mode) is – if not commercially available – produced via neutron activation or at an in-house cyclotron. Effective and stable particle-labelling strategies (complexation, in-diffusion, isotope exchange) are prerequisites for the monitoring of their transport behaviour in geosystems under conditions near to nature and are continuously under development and are regularly published [10,11].
Methods for the 1-4 dimensional visualization and quantification of (particle-mediated) transport in synthetic and natural heterogeneous geologic media were developed in the past decade [12-16]. A basic principle is the application of radionuclide-labelled system components, detectable at very low concentrations and – ideally - chemical identical with non-labelled system components. A specific distinctive feature is the application of the GeoPET-method that allows the visualization of the movement of a PET-nuclide-labelled system component during its passing through the connected pore space/ or fracture in a natural, heterogeneous geological media. So far, complementing tomographic and numerical methods allow for the quantification and verification of the proposed, underlying conceptual models for fluid dynamics and non-reactive (conservative) transport [16,17].
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 Joseph, C., et al.: Sorption of uranium(VI) onto Opalinus Clay in the absence and presence of humic acid in Opalinus Clay pore water. Chem.Geol. 284(2011), 240-250
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