Structures and Reactivity at the Water/Mineral Interface
The Helmholtz-funded Young Investigator Group "Structures and Reactivity at the Water/Mineral Interface" works on understanding the reactions of the actinides (particularly Pu, Am, and Cm) at mineral surfaces on the molecular level. The work is embedded in our institute's efforts to provide reliable information as a basis for the safety case of a potential nuclear waste repository, where the mobility of the actinides will depend on their retention by the surrounding mineral phases.
The ternary system consisiting of actinide, solution, and mineral surface may host a wide range of chemical reactions (see figure). The retention potential of these reactions will vary significantly, which is why a quantification without understanding of the underlying mechanisms of retention is insufficient. As an example, a structurally incorporated ion will only be remobilized, if the host mineral phase dissolves macroscopically, on the other hand "outer sphere" sorption complexes may become unstable by a mere change in ionic strength.
Accurate description of such a system requires the use of cutting edge techniques capable of acquiring molecular information selectively from the mineral surface. To this end, our group focuses on applying surface X-ray diffraction techniques (crystal truncation rods - CTR und resonant anomalous X-ray reflectivity - RAXR) as well as site-selective time-resolved laser-induced fluorescence spectroscopy (TRLFS). Both techniques allow us to determine the speciation of actinides at an interface in situ at environmentally relevant trace concentration levels. The techniques are complementary, in that TRLFS yields information on the local structure surrounding an adsorbate, while CTR and RAXR yield a full structural picture of the interface from bulk crystal to bulk solution.
This fundamental research will help to make long-term, safe disposal of nuclear waste possible.
- Dr. Moritz Schmidt
- Sophia Hellebrandt
- Stefan Hellebrandt
- Dr. Canrong Qiu
- Dr. Bin Xiao
- Konrad Molodtsov
- Dr. Erik V. Johnstone
- Dr. Sascha Hofmann
Sorption und interfacial reactions (Stefan Hellebrandt, Dr. Canrong Qiu)
This project is focused on the interaction of actinides and their homologues with surfaces of alumino-silicate minerals (micas and feldspars), where weak sorption of strongly hydrated cations leads to a successive interfacial reactions, e.g. formation of nanoparticles. These processes are studied in dependence of the aqueous chemistry of the elements (redox properties, complexation, background electrolyte interactios,...) with the goal to develop an in depth understanding of the chemical reactions, and the associated effects on the mobility of the actinides.
Structural incorporation (Sophia Hellebrandt, Dr. Bin Xiao)
This project studies the retention of actinides by structural incorporation in mineral phases relevant to nuclear waste disposal (e.g. calcite CaCO3). The work focuses both, on the effects of the solution conditions on the incorporation process, as well as the impact of the incorporated ion on the local structure of the mineral phase. For example, we are investigating surface destabilization processes by background electrolytes, and differences in the incorporation process close to equilibrium and during mineral precipitation, as well as using polarization-dependent TRLFS for detailed characterization of local distortions induced in single crystal host materials to evaluate lattice strains.
TRLFS-Microscopy (Konrad Molodtsov)
Natural rock is rarely composed of a single mineral phase, but rather a complex mixture of various minerals. To enable us to selectively characterize the interaction of the actinides in such a system with all its complexity spatial resolution needs to be implemented into the TRLFS technique. The aim in this project is to develop the capability to perform full spectroscopic characterization of Eu(III), Cm(III), and possibly U(VI)O22+ on single mineral grains within a natural rock sample. However, the same technique will also be useful in microbiological and biomineralization studies.
Structural incorporation into bio-minerals
This project investigates the retention of actinides by mineral phases which have been formed under the influence of or directly controlled by microorganims (biomineralization). During this process the mineral phase itself, as well as the incorporating ion are influenced by significant amounts of biogenic organics. This may cause changes in the formation of the mineral phase, e.g. in the preferred expression of a particular mineral face, and/or affect the speciation of the radionuclides in the growth solution. Comparison of the biominerals to their inorganic counterparts, and the characterization of the incorporated ions, allows us to deduce which consequences the formation pathway has for the retention of the radionuclides.
Available thesis topics
The following is a list of topics available for master's and PhD thesis.
- Spectroscopic characterization (NMR, TRLFS) of the complexation of uronic acids with Cm(III) and Eu(III)
- Incorporation of Cm(III) into calcite under recrystallization conditions close to thermodynamic equilibrium
- Investigation of the incorporation of Cm(III) and Eu(III) into calcite formed by emiliania huxleyi using TRLFS
- E. V. Johnstone, S. Hofmann, A. Cherkouk, M. Schmidt (2016) "Study of the Interaction of Eu3+ with Microbiologically Induced Calcium Carbonate Precipitates using TRLFS", Environ. Sci. Tech., 50(22), 12411-12420.
- S. Hellebrandt, K. E. Knope, S. S. Lee, A. J. Lussier, J. E. Stubbs, P. J. Eng, L. Soderholm, P. Fenter, M. Schmidt (2016) "A Comparison of Adsorption, Reduction, and Polymerization of the Plutonyl(VI) and Uranyl(VI) Ions from Solution onto the Muscovite Basal Plane", Langmuir, 32(41), 10473-10482.
- S. E. Hellebrandt, S. Hofmann, N. Jordan, A. Barkleit, M. Schmidt (2016) "Incorporation of Eu(III) into Calcite under Recrystallization conditions", Sci. Rep., 6, 33137.
- S. S. Lee, M. Schmidt, T. T. Fister, K. L. Nagy, N. C. Sturchio, P. Fenter (2016) "Structural Characterization of Aluminum (Oxy)hydroxide Films at the Muscovite (001)–Water Interface", Langmuir, 32(2), 477-486.
- S. Hofmann, K. Voïtchovsky, P. Spijker, M. Schmidt, T. Stumpf (2016) "Visualising the molecular alteration of the calcite (104) – water interface by sodium nitrate", Sci. Rep., 6, 21576.
- M. Schmidt, S. Hellebrandt, K. E. Knope, S. S. Lee, J. E. Stubbs, P. J. Eng, L. Soderholm, P. Fenter (2015) "Effects of the Background Electrolyte on Th(IV) Sorption to Muscovite Mica", Geochim. Chosmochim. Acta, 165, 280-293.
- S. Hofmann, K. Voitchovsky, M. Schmidt, T. Stumpf (2014) “Trace concentration - huge impact: Nitrate in the calcite/Eu(III) system”, Geochim. Cosmochim. Acta, 125, 528-538.
- M. Schmidt, S. S. Lee, R. E. Wilson, K. E. Knope, F. Bellucci, P. J. Eng, J. E. Stubbs, L. Soderholm, P.Fenter, (2013) “Surface-Mediated Formation of Pu(IV) nanoparticles at the Muscovite-Electrolyte Interface”, Environ. Sci. Technol., 47(24), 14178-14184.
- S. S. Lee, M. Schmidt, N. Laanait, N. C. Sturchio, P. Fenter (2013) “Investigation of Structure, Adsorption Free Energy, and Overcharging Behavior of Trivalent Yttrium Adsorbed at the Muscovite (001) - Water Interface”, J. Phys. Chem. C, 117(45), 23738-23749.
- M. Schmidt, S. Heck, D. Bosbach, S. Ganschow, C. Walther, T. Stumpf (2013) “Characterization of powellite-based solid solutions by site-selective time resolved laser fluorescence spectroscopy”, Dalton Trans., 42(23), 8387 – 8393.
- H. Geckeis, J. Lützenkirchen, R. Polly, T. Rabung, M. Schmidt (2013) “Mineral–Water Interface Reactions of Actinides”, Chem. Rev., 113(2), 1016–1062.
Dr. Moritz Schmidt reads the lecture "Chemie der f-Elemente" (Chemistry of the f-elements) at the Technical University Dresden every winter term (in German). The lecture is part of the module Umwelt- und Radiochemie (Environmental and radiochemistry) as part of the master's degree in Chemistry.