Effects of chemical composition and temperature of heating on the infraredspectra of Li-saturated dioctahedral smectites. (I) Mid-infrared region

Infrared spectroscopy in the mid-IR region was used to follow the structura l changes occurring in five Li-saturated dioctahedral smectites upon heatin g. The smectites included three montmorillonites, an Fe-beidellite and a fe rruginous smectite. Fixation of Li+ ions in the structure even upon heating at 120 degreesC caused the appearance of an AlMgLiOH-stretching band near 3670 cm(-1) in the spectra of all three montmorillonites. This band confirm ed the presence of Li(I) in the previously vacant octahedral positions in m ontmorillonites. No similar band was observed in the spectra of ferruginous heated smectites with prevailing tetrahedral charge. A gradual upward freq uency shift and decrease in intensity of the AlAlOH-bending band showed tha t Li(I) present in the hexagonal cavities causes pronounced perturbation of this OH-bending mode. The Li(I) present in the octahedral sheets causes sm all perturbations of the OH-bending mode near 850 cm(-1) and activation of a new OH-bending mode near 803 cm(-1). Reversible changes in the positions of the stretching Si-O and bending OH bands in the spectra of Fe-beidellite and a ferruginous smectite proved that Li was present in these minerals pr imarily in the hexagonal holes of the tetrahedral sheets.