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

Abstract

Abstract--Alteration experiments have been performed using RTT7 and synthetic basaltic glasses in MgC1E-CaClz salt solution at 190~ 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 [MgrAlzCO3(OH)~6' 4H20] in which HPO42 , SO42-and C1-substitutes for CO32-. The measured basal spacing is 7.68 A for the hydrotalcite formed from R7T7 glass and 7.62 ~ for the hydrotalcite formed from basaltic glass which reflect the high A1/A1 + 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.

Microbial and inorganic control on the composition of clay from volcanic glass alteration experiments

“…Mg-containing systems (Thomassin et al 1989;Abdelouas et al 1994). The silicate particles with compositions consistent with clays also had the typical flaky clay morphology, usually with irregular outlines (Fig.…”

Modelling the alteration gel composition of simplified borosilicate glasses by precipitation of an ideal solid solution in equilibrium with the leachant

“…The researches were focused on glasses (basalt glasses essentially) considered as natural analogues of nuclear glasses [1][2][3][4][5][6][7] as well as on the R7T7 borosilicate (SON68) glass, used as the French confinement matrix for the light water reactor (LWR) high level nuclear waste [2,8,9].…”

Electron Microscopy Study of Volcanic Tuff Alteration to Illite-Smectite Under Hydrothermal Conditions

“…Kinetic effects (e.g., low temperatures, short alteration times) influence the formation of poorly crystalline phases such as hydrotalcite (Abdelouas et al, 1994) and allophane Tomita, 1992, 1995;Kawano et al, 1993). Low pH promotes the formation of halloysite and kaolinite (Nagasawa, 1978;Kawano and Tomita, 1995), neutral and slightly basic conditions favor smectite formation Ghiara et al, 1993;, and basic pH values promote zeolite formation (Mariner and Surdam, 1970;Hall, 1998).…”