LOCAL ENVIRONMENT OF LANTHANUM IONS IN MONTMORILLONITE UPON HEAT ING

ABSTRACT: Structural differences which occur on heating La-montmorillonite have been studied and compared with those for montmorillonite saturated with Na(I) and Li(I). Rehydration experiments show that La-montmorillonite swells after preheating up to 500 ~ However, FT-IR spectra suggest partial migration of the La(III) cations from the interlamellar region to the structural sheets and(or) deprotonation f hydrated La(III) cations, followed by migration of the resulting protons to vacant octahedral sites. Additional measurements of X-ray absorption spectra (EXAFS, XANES) and heating to 700 ~ suggest that interlamellar hydrated La(III) partially deprotonates producing polyoxocations. Smectites and their pillared derivatives made with trivalent lanthanide cations have recently attracted much attention as catalysts (Shabtai et al., 1984). In addition, La simulates Am in studies on the interaction of the latter with clay minerals. Determination of the interaction mechanism upon heating is important for the design of safe repositories for high-level nuclear wastes. Their storage in continental or marine repositories usually involves clay-bearing packing materials that act as a barrier. The aim of this paper is to study significant structural differences upon heating Na-, Li