Retention of selenium by calcium aluminate hydrate (AFm) phases under strongly-reducing radioactive waste repository conditions

Dalton Transactions : an International Journal of Inorganic Chemistry
H RojoJ Tits

Abstract

Safety assessment studies of future nuclear waste repositories carried out in many countries predict selenium-79 to be a critical radionuclide due to its presence as anion in three relevant oxidation states (vi, iv, -ii) resulting in weak retardation by most common rock minerals. This assumption, however, ignores its potential uptake by AFm phases, positively charged anion exchangers, which are present in significant quantities in the cementitious materials used in artificial barriers. Here we report for the first time wet chemistry and spectroscopic data on the interaction of the most relevant selenium anion species under the expected strongly reducing conditions, i.e. HSe-, with two AFm phases commonly found in cement, monocarbonate (AFm-MC) and hemicarbonate (AFm-HC). Batch sorption experiments showed that HSe-is retained much more strongly by AFm-HC (solid-liquid distribution ratio, Rd, of 100 ± 50 L kg-1) than by AFm-MC (Rd= 4 ± 2 L kg-1) at the equilibrium pH (∼12). X-ray absorption fine-structure (XAFS) spectroscopy revealed that the larger d-spacing in AFm-HC (d-spacing = 8.2 Å) provides easy access for HSe-to the AFm interlayer space for sorption, whereas the smaller d-spacing of AFm-MC (d-spacing = 7.55 Å) hinders int...Continue Reading

References

Jul 24, 2003·Environmental Science & Technology·Min Zhang, Eric J Reardon
Sep 12, 2003·Environmental Science & Technology·Isabel Baur, C Annette Johnson
Mar 15, 2006·Waste Management·Barbara Lothenbach, Erich Wieland
May 12, 2006·Journal of Synchrotron Radiation·T Ressler
Apr 16, 2008·Environmental Science & Technology·Andreas C Scheinost, Laurent Charlet
Nov 4, 2008·Journal of Contaminant Hydrology·Andreas C ScheinostLaurent Charlet
Apr 10, 2012·Journal of Contaminant Hydrology·A DienerD Schild
Sep 21, 2012·Acta Crystallographica. Section B, Structural Science·Tomče RunčevskiHerbert Pöllmann
Jun 17, 2014·Environmental Science & Technology·Daniela SoltermannMaria Marques Fernandes
Oct 30, 2015·Chemical Communications : Chem Comm·U PachmayrD Johrendt
Mar 25, 2016·Journal of Contaminant Hydrology·Nicolas Finck, Kathy Dardenne

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Citations

Aug 25, 2018·Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials·Jakub PlášilJiří Čejka

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Methods Mentioned

BETA
X-ray

Software Mentioned

ITFA
AFm
FDMNES
WinXAS
SixPACK
MC
FEFF8

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