LOCAL ENVIRONMENT OF LANTHANUM IONS IN MONTMORILLONITE UPON HEATING

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-degrees-C. However, FT-IR spectra suggest partial migration of the La(III) cations from the interlamellar region to the structural sheets and(or) deprotonation of 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-degrees-C suggest that interlamellar hydrated La(III) partially deprotonates producing polyoxocations.