discovered_02_2015

WWW.HZDR.DE 14 15 TITLE // THE HZDR RESEARCH MAGAZINE Start Young... Since October 2013, Moritz Schmidt has led a Helmholtz junior researcher group at the HZDR focusing on the topic "Structures and Reactivity at the Aqueous/Mineral Interface." For five years he receives on average a quarter of a million euros each year from the Helmholtz Association for the purpose of building his group. With this funding, the Helmholtz Association aims to support the early independence of exceptional junior scientists. Three doctoral candidates and one post-doc scientist work in the junior research group. Currently, Moritz Schmidt, who previously researched at the Karlsruhe Institute of Technology (KIT), is expanding his team. He regularly gives lectures on the chemistry of actinides at the TU Dresden, hoping to thus draw new junior researchers to Rossendorf. From the group of actinides, Schmidt and his young colleagues are focusing mainly on the four elements of plutonium, americium, curium, and neptunium. "These transuranic elements are especially long-lived and radiotoxic," the chemist explains. But there have also been experiments with the homologous elements europium or yttrium. "Curium fluoresces very strongly," Schmidt says. "This enables us to identify it even at very low concentrations and determine how it interacts with the mineral." Yttrium, however, is not radioactive, but displays similar chemical behavior to that of actinides and is therefore a good alternative for basic investigations. How curium bonds to calcite In experiments with the radionuclide curium, scientists were able to use TRLFS to determine that curium bonds with calcite in three different ways. "We see three bands that occur for different excitation wavelengths. Each belongs to a different species, and these differ from each other in the type of coordination, symmetry, and water content," Schmidt explains. His work group also discovered that minimal traces of nitrate drastically change adhesion behavior. If nitrate is present, a soft, gel-like layer will form on the calcite's surface. "This weakens the radionuclide's bond considerably," according to Schmidt. Now researchers want to study the mechanism of surface modification in order to see if the ions of other materials such as sulfate or phosphate could experience a similar effect. Another analysis method used frequently by HZDR scientists is surface X-ray diffraction. While X-ray diffraction is normally used to determine the regular three-dimensional arrangement of atoms in a crystal, the method used by Schmidt and his colleagues is especially sensitive to surface effects - the atoms inside the mineral are faded out so to say. Using this process, researchers can precisely observe how the presence of nitrate fosters the formation of a gel-like layer on calcite. The process requires highly intense X-rays from a synchrotron source. "We currently take our measurements in Chicago at the Advanced Photon Source of the Argonne National Laboratory," Moritz Schmidt reports. "It will soon be somewhat easier, because we are currently constructing a measuring station for the ROBL Beamline at the European Synchrotron Radiation Facility ESRF in Grenoble. Then it won't be necessary to transport samples as far from the lab in order to measure them and we will get results back more quickly." PUBLICATIONS: M. Schmidt et al.: "Effects of the background electrolyte on Th(IV) sorption to muscovite mica", in Geochimica et Cosmochimica Acta 2015 (DOI: 10.1016/j.gca.2015.05.039) H. Geckeis, J. Lützenkirchen, R. Polly, T. Rabung, M. Schmidt: "Mineral–water interface reactions of actinides", in Chemical Reviews 2013 (DOI: 10.1021/cr300370h) CONTACT _Junior research group "Structures and Reactivity at the Aqueous/Mineral Interface" at HZDR Dr. Moritz Schmidt moritz.schmidt@hzdr.de JUNIOR SCIENTIST GROUP: Chemists Erik Johnstone, Stefan Hellebrandt, Sascha Hofmann, Moritz Schmidt and Sophia Hellebrandt (left to right) will soon be getting backup.

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