Structural identification of a trioctahedral smectite formed by the aqueous alteration of a nuclear glass

The precipitation of crystallized magnesium phyllosilicates appears to control the residual alteration rate, under aqueous oxidizing conditions, of nuclear waste containment glass from the French Vitrification Facility at Marcoule (AVM). As a consequence, the precise identification of the formed phyllosilicates is crucial for modeling the long-term behavior of glass. Morphological and chemical analysis (scanning electron microscopy, EDS, ICP-AES after caustic fusion), and structural analysis (X-ray diffraction, MAS NMR) were used to determine the nature and structure of the precipitated phase: a trioctahedral smectite intermediate between saponite and hectorite, with the formula: Na0.39(Mg2.25Li0.06Al0.38Fe0.06 M0.25)(Si3.23Al0.77)O10(OH)2.