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Reference : UMR5275-FABCAR-028
Workplace : GRENOBLE
Date of publication : Monday, November 25, 2019
Type of Contract : FTC Scientist
Contract Period : 12 months
Expected date of employment : 1 February 2020
Proportion of work : Full time
Remuneration : 2617€ gross salary
Desired level of education : PhD
Experience required : Indifferent
Among the essential micronutrients, selenium has one of the narrowest ranges between dietary deficiency and toxic levels (one order of magnitude difference in daily intake), and is hence often described as 'double‐edged sword' (Levander and Burk, 2006). Since both Se toxicity and deficiency have dramatic effects on the health of people, understanding Se bioavailability is of paramount importance for society. However, it is not an easy task to decipher the physico‐chemical and biological processes that govern selenium bioavailability. In the environment, a variety of redox states and associated chemical forms, and their interaction with organic and inorganic natural phases, result in a complex behavior, with different species being present at the same time in one environment. Furthermore the radioisotope 79Se poses a substantial risk for the safe disposal of nuclear waste due to its long half life (~1.1 Mio a) and suspected high mobility. At corroding waste canisters, the surrounding compacted clay liners and in deep anoxic aquifers, however, complex redox reactions may initiate the precipitation of selenium nanoparticles from seleniae, which are challenging predictive geochemical models (Breynaert et al., 2008; Charlet et al., 2007; Scheinost and Charlet, 2008; Scheinost et al., 2008). The safety assessment of advanced radwaste programs must demonstrate a detailed understanding of the physical–chemical phenomena governing the effects of RN speciation and diffusion-driven transport within the geological barrier system. (Charlet et al., 2017). Among critical points to such performance assessment are, as pointed out by Altmann (2008), the poor ability of certain highly to moderately mobile, long half-life radionuclides (e.g. 79Tc, 79Se) to be sorbed in their more oxidized form and to be reductively precipitated by Fe(II) containing clay or oxides. In fact increasing the Kd value from 0 to only 1 mg/L was shown to have a great effect (orders of magnitude) on the total fluxes (mol/year) of 129I, 36Cl and 79Se potentially released after 103 to 106 years from a geological barrier system such as the Callovo- Oxfordien formation (Altmann, 2008). In a variety of previous studies we have investigated chemically and spectroscopically the reduction of selenite by a variety of Fe(II) containing minerals (pyrite, mackinawite, magnetite, Fe(II) containing calcite and clay).
- In the present project, our goal is to quantify the reductive precipitation of selenate (Se(VI)) and perrhenate (Re(VII), another recalcitrant Tc-model oxyanion, by Fe(II) containing minerals, and to évaluate the stability of this process in case of pH or composition change perturbations via break through curves (BTCs)
- We will compared these static and dynamic sorption studies to spectroscopic investigations and possibly molecular dynamics, in order to quantify and understand Se & Re reduction mechnaisms in micro and nanoporous model claystone systems.
1. The postdoc researcher will measure selenate(Se(VI))and perrhenate (Re(VII) anion adsorption by nano-magnetite, either in « barch » or in microfluidic dynamic experiments, the device being coupled to a liquid chromatography with measurements performed in 50 µL samples. This will be compared to the reactivity of goethite suspended in H2-rich water. In previous work we have studied the sorption of H2 on clays (Mondelli et al., 2015, Didier et al., 2014; Bardelli, 2014) and shown that the reduction of selenite ions (Se (IV)) at the surface of clay in presence of Fe2+ was going through an hypothetic sorbed H2 intermediate (Charlet et al., 2007). Recent studies from our Institute have shown that clayrock can also contain up to 500 ppm H2 in water saturated conditions (Truche et al., 2018). One of the co-advisors, F. Brunet, is presently conducting H2 sorption experiments onto goethite and mercury reductive volatilisation (as Hg°(g)) by goethite in presence of H2(g). The effect of competitive redox inactive anion, and of pH varations will also be investigated.
2. Based on the large experience of our team in synchrotron based spectroscopy, the postdoc will perform XAFS measurements, and interpret the data, possibly with the help of computational molecular dynamics, in order to study the reductive precipitation mecanisms in claystone systems. Kinetic macroscopic models will also be applied to macroscopic batch data and BTCs.
Techniques to be used include: wet heterogeneous chemical kinetics (and modeling) ; use of glovebox (N2 atmosphere) ; microfluidic BTCs ; Ion chromatograhy and ICP-AES ; XRD/SEM/TEM/TEM/FTIR measurements, XAFS spectroscopy, and computational chemistry.
The research is part of an ISTerre (Grenoble, France) research programme, done in collaboration with synchrotron ROBL beamline at ESRF (Grenoble, France). The two teams will share their experience to study the adsorption of Se(VI) or Re(VII) on nano magnetite or on goethite H2-rich suspension.
This position is part of a European research program on Radioactive wate disposal (https://cordis.europa.eu/project/rcn/223662/factsheet/en), the EURAD project, funded by the EU (H2020).
General informations on ISTerre and ROBL are available http://isterre.fr and http://www-robl.ec). ISTerre is ranked 4th worldwide in Geochemistry/Geophysics according to CWUR World University Ranking 2018-2019 (https://cwur.org/2017/subjects.php#Geochemistry%20&%20Geophysics).
The candidate must have completed his/her PhD by October 2019.
We are looking for a highly motivated scientist, interested in material physics and chemistry, Fe(II) mineralogy and redox chemistry, wet chemistry and analytical lab work.
The candidate must furthermore have a strong background in spectroscopy (XAFS, FTIR).
Knowledge of French language is not required. An excellent level in English is required (both written and oral) .
The choice of the candidate will be based on his academic record and demonstrated skills during the interviews.
Candidates must provide a detailed CV with academic diploms, skills, research and personnal interests, employment history, and a complete list of publications / abstracts / conferences, as well as name, position, email and phone of 2 referents.
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