Comparative FT-IR study of the removal of octahedral cations and structural modifications during acid treatment of several silicates

The acid activation of different silicates of the clay group has been carried out. Sepiolite, palygorskite and two saponites, one having a high iron content, have been studied. Thus, different structures (layered or fibrous) and different chemical compositions (aluminic, magnesic and ferromagnesic) of the clays can be compared. The FT-IR spectra of solids obtained after the acid treatment permit the observation of structural changes occurring during the acid treatment. Thus, the depopulation of the octahedral sheet can be clearly observed from the change in intensity of bands related to octahedral cations. The changes result in the formation of amorphous silica gel, which can be observed from the change in the bands corresponding to the SiO bonds and in new bands corresponding to free silica.