FORMATION AT 300-DEGREES-C OF A HIGH-TEMPERATURE DISILICATE FROM HYDRATED LUTETIUM IN A LAYERED ALUMINOSILICATE

The interaction between interlamellar Lu(III) cations and the layered silicate structure has been studied by means of MAS-NMR, XRD and EDX. Irreversible fixation of exchangeable Lu(III) cations upon hydrotherma l treatment at 300 degrees C of Lu-saturated montmorillonite is report ed, through the formation of the crystalline phase Lu2Si2O7 It is show n that the lowest temperature previously described for this reaction, 400 degrees C, does not indicate a thermodynamic boundary. This basic solid-state finding is relevant for some clay applications such as tho se related to the safety of nuclear waste repositories with engineerin g barriers.