Alteration of smectites by treatments with hydrochloric acid and sodium carbonate solutions

Modeling description and spectroscopic evidence of surface acid–base properties of natural illites

“…6, the heights of several 0 0 l diffraction lines, such as basal reflection d(0 0 1) at 912y, d(0 0 2) at 1812y and d(0 0 3) at 26.512y, which are usually regarded as the diagnostic reflections for natural illites (Sroden, 1984), sharply decreased relative to those of hydrated samples during the acidic titration procedure. This situation is in accord with that in other reports (Komadel et al, 1990), though stronger experimental conditions were applied in their cases, such as concentrated acid and heating. To some extent, the intensities of certain diffraction peaks resumed after hydroxide back titration up to around pH 5.5-6, especially for the Surface acid-base nature of natural illites 4119 reflection line at 26.512y with a d-spacing of 3.34-3.37 Å .…”

“…This situation differs from the results of other studies, where intensity reduction and band shift of infrared vibrations for the specific functional groups accounted for the extent of dissolution, were remarkable, possibly due to the use of relatively acute reaction conditions (Komadel et al, 1990(Komadel et al, , 1996. However, a new IR absorption band lying in the range of 1370 and 1385 cm @1 , appeared for both illite samples after acid-base potentiometric titration.…”

“…In some cases, however, the basal planes inside the layer structure are also highly reactive, which is ascribable to shallow step edges, structural defects and impurities (Johnsson et al, 1992). Komadel et al (1990) also indicated that after a part of octahedral sheets had been dissolved during acid attack, an amorphous form of silicic acid could be produced from the silicon tetrahedra.…”

“…Acid treatment is a common means to modify the surface/catalytic properties of clay minerals via activation of surface sites, and therefore has miscellaneous applications in industry (Komadel et al, 1990(Komadel et al, , 1996Tka`c et al, 1994). Since the aforementioned reactions generally occur in the region of the solid/aqueous interface, numerous studies have been performed in the relevant aspects, e.g., mechanistic interpretation, model refinement and simulation strategy (Katz and Hayes, 1995;Hiemstra and Van Riemsdijk, 1996;Borkovec, 1997;Lu¨tzenkirchen, 1998).…”

An environmentally friendly preparation of iodohydrins from alkenes mediated by clay-minerals

“…The corresponding clay-mineral peak of a smectite group was more pronounced in the natural clays than in the acid clays, suggesting that the previous acid treatment of KSF and K-10 disarranges the smectite structure. 10,11 These facts show the importance of the clay-mineral structure to the formation of the iodohydrins, once the better yields were obtained with the natural Brazilian clays.…”