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Smectite stability in acid salt solutions and the fate of Eu, Th and U in solution

Published online by Cambridge University Press:  09 July 2018

A. Bauer*
Affiliation:
Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgungstechnik, AK Chemie der Versatzmaterialien, PO Box 3640, D-76021 Karlsruhe, Germany
T. Schäfer
Affiliation:
Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgungstechnik, AK Chemie der Versatzmaterialien, PO Box 3640, D-76021 Karlsruhe, Germany
R. Dohrmann
Affiliation:
BGR, Tonforschung, Stilleweg 2, D-30655, HannoverGermany
H. Hoffmann
Affiliation:
Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgungstechnik, AK Chemie der Versatzmaterialien, PO Box 3640, D-76021 Karlsruhe, Germany
J. I. Kim
Affiliation:
Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgungstechnik, AK Chemie der Versatzmaterialien, PO Box 3640, D-76021 Karlsruhe, Germany
*

Abstract

The alteration and transformation behaviour of Ceca smectite in two acid and saline solutions (NaCl and KCl) was studied in batch experiments. This type of smectite is proposed as potential backfill material for nuclear waste storage sites. The initial solution was enriched with 500 ppm of U, Th and Eu. The evolution of pH and solution concentrations were measured over a period of 25 months. The mineralogical and chemical evolution of the clays was also studied. X-ray diffraction revealed a significant loss of diffraction intensity and the clays became amorphous to Xrays with increasing reaction time. Deconvolution of the XRD data indicated a continuous collapse of the smectite layers but no illitization. Infrared spectroscopy revealed unchanged smectite spectra at the end of the experiment. Thorium precipitated as amorphous ThO2, but showed an incipient crystallization after 500 days. The Th, Eu and U were neither adsorbed onto the clays nor incorporated into a secondary phase.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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