Formation of Hydrotalcite-like Compounds During R7T7 Nuclear Waste Glass and Basaltic Glass Alteration

A. Abdelouas1, 2, J. L. Crovisier2, W. Lutze1, *, B. Fritz2, A. Mosser3 and R. Müller1
1 Kernforschungszentrum Karlsruhe, INE, Postfach 3640, 76021 Karlsruhe, Deutschland
2 Centre de Géochimie de la Surface, C.N.R.S. 1, rue Blessig, 67084 Strasbourg Cedex, France
3 IPCMS Groupe Surfaces-Interfaces, 4, rue Blaise Pascal 67070 Strasbourg Cedex, France
* Present address: University of New Mexico, 209 Farris Engineering Building, Albuquerque, New Mexico 87131.

Abstract: Alteration experiments have been performed using RTT7 and synthetic basaltic glasses in MgCl2-CaCl2 salt solution at 190°C. The duration of experiments ranged from 0.25 to 463 days. The alteration products were studied by Scanning Electron Microscope (SEM), Scanning Transmission Electron Microscope (STEM), X-ray diffraction (XRD) and Electron Spectrometry for Chemical Analysis (ESCA). For both glasses, the early alteration product is a hydrotalcite-like compound [Mg6Al2CO3(OH)16·4H2O] in which HPO42−, SO42− and Cl substitutes for CO32−. The measured basal spacing is 7.68 Å for the hydrotalcite formed from R7T7 glass and 7.62 Å for the hydrotalcite formed from basaltic glass which reflect the high Al/Al + Mg ratios x (0.34 ≤ x ≤ 0.46). The chemical microanalyses show that the hydrotalcite is subsequently covered by a silica-rich gel which evolves into saponite after a few months. These results support the use of basaltic glasses alteration patterns in Mg-rich solution, to understand the long-term behavior of R7T7 nuclear waste glass.

Key Words: Basaltic glass • Experimental alteration • Hydrotalcite-like compounds • MgCl2-CaCl2 salt solution • R7T7 nuclear waste glass • Saponite

Clays and Clay Minerals; October 1994 v. 42; no. 5; p. 526-533; DOI: 10.1346/CCMN.1994.0420503
© 1994, The Clay Minerals Society
Clay Minerals Society (www.clays.org)