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 [4], 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 [5]. Isotope exchange and luminescence studies allow for the quantification of kinetic interaction studies between metal and humic/fulvic acids and additional competing system components [6].
The formation of U(IV)-silica colloids (<20 µm) and their significant stability in natural waters was described for the first time [7].
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 [8].
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 [9], 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].

References

[1] Schmeide, K., et al.: Np(V) reduction by humic acid: Contribution of reduced sulfur functionalities to the redox behavior of humic acid. Sci.Tot.Environ. 419(2012), 116-123
[2] 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
[3] Lippold, H., et al.: Competitive effect of iron(III) on metal complexation by humic substances: Characterisation of ageing processes. Chemosphere 67 (2007) 1050-1056
[4] Hennig, C., et al.: The relationship of monodentate and bidentate coordinated uranium(VI) sulfate in aqueous solution. Radiochim.Acta 96(2008), 607-611
[5] Lippold, H., Lippmann-Pipke, J.; Effect of humic matter on metal adsorption onto clay materials: Testing the linear additive model. J.Cont.Hydrol. 109(2009) 40-48
[6] Lippold, H., et al.: Diffusion, degradation or on-site stabilisation – identifying causes of kinetic processes involved in metal-humate complexation. Appl.Geochem. 27(2012), 250-256
[7] Dreissig, I., et al.: Formation of uranium(IV)-silica colloids at near-neutral pH. Geochim.Cosmochim.Acta 75, 2 (2011), 352-367.
[8] Schierz, A.; Zänker, H. Aqueous Suspensions of Carbon Nanotubes: Surface Oxidation, Colloidal Stability and Uranium Sorption.Environ.Poll. 157(2009), 1088-1094
[9] Franke, K., et al.: A new technique for radiolabelling of humic substances. Radiochim. Acta 92 (2004) 359 – 362.
[10] Hildebrand, H.; Franke, K. A new radiolabeling method for commercial Ag⁰ nanopowder with ^110mAg for sensitive nanoparticle detection in complex media.  J. Nanopart. Res. 14 (2012), 1142
[11] Hildebrand, H., Schymura, S., Holzwarth, U., Gibson, N., Dalmiglio, M., Franke, K.: Strategies for radiolabeling of commercial TiO2 nanopowder as a tool for sensitive nanoparticle detection in complex matrices. J. Nanopart. Res. 17 (2015) 278ff
[12] M. Richter, M. et al.: cc, Radiochim.Acta 93 (2005), 643-651.
[13] M. Gründig, M. et al.: Tomographic radiotracer studies of the spatial distribution of heterogeneous geochemical transport processes. Appl.Geochem. 22, 2334-2343.
[14] Kulenkampff, J., Gründig, M., Richter, M. and Enzmann, F. Evaluation of positron emission tomography for visualisation of migration processes in geomaterials. Phys.Chem.Earth 33 (2008), 937-942.
[15] Kulenkampff, J., Gründig, M., Lippmann-Pipke, J. Quantitative observation of tracer transport with high-resolution PET. Solid Earth 7, 1217-1231.
[16] Kulenkampff, J., Gründig, M.; Zakhnini, A.; Lippmann-Pipke, J. Geoscientific process monitoring of molecular diffusion in clay with positron emission tomography (GeoPET). Solid Earth 7, 1207-1215.
[17] Lippmann-Pipke, J., Gerasch, R.; Schikora, J.; Kulenkampff, J. Benchmarking PET for geoscientific applications: 3D quantitative diffusion coefficient estimation in clay rock. Comp. Geosci. 101, 21-27.
[18] Schymura, S., Fricke, T., Hildebrand, H., Franke, K. Elucidating the Role of Dissolution in CeO₂ Nanoparticle Plant Uptake by Smart Radiolabeling Angew. Chem. Int. Ed., 56(26) (2017) 7411–7414.