Effect of pre-heating on the thermal dehydration of lanthanide montmorillonites

Abstract

Simultaneous DTA-TG, TPD-GC, BET specific surface area and FT-IR measurements have been carried out on Ln-montmorillonites (Ln  La, Nd, Gd, Ho or Yb) in order to study the effect of air-heating at 300°C on Ln III fixation and subsequent thermal dehydration. In the unheated samples, the hydration shell of the exchangeable 4f ions contains an average number of H 2O molecules which ranges from 20 (La) to 12 (Yb). This decrease can be ascribed to partial hydrolysis of interlamellar cations, which increases for all the samples on heating at 300°C. Deprotonation of the montmorillonites by reaction of their structural OH groups with the interlamellar 4f hydroxides is suggested.