FORMATION OF HYDROXY-AI AND-Fe INTERLAYERS IN MONTMORILLONITE AND VERMICULITE: INFLUENCE OF PARTICLE SIZE AND TEMPERATURE

Abstract--Hydroxy-Al and-Fe interlayers were prepared in "mono-mineralic " fine and coarse clay montmorillonite and coarse clay and silt vermiculite at 3 ~ and 21 ~ The formation of hydroxy interlayers was evaluated by X-ray diffraction, cation exchange capacity, and chemical analyses. At comparable particle size and regardless of temperature, the amounts of hydroxy-Al and-Fe interlayers in montmorillonite exceeded by far those formed in vermiculite. Likewise, the aluminum systems exhibited ahigher degree of interlayering than iron systems. Within montmorillonite, the amount of hydroxy-A1 and-Fe interlayers increased as the particle size decreased, regardless of temperature. The aluminum interlayered montmorillonite equilibrated at 3 ~ was characterized by basal spacings of about 17, ~ after Ca-saturation plus 54 per cent relative humidity. These spacings are larger than those normally observed for smectites. Within vermiculite systems equilibrated at 3 ~ more hydroxy-AI interlayers were recorded in coarse clay than in silt fraction, whereas at 2 I ~ about equal amounts of interlayers were formed. By contrast, hydroxy-Fe interlayer was favored by the silt fraction at both temperature levels. The formation of aluminum interlayers in both minerals increased with increasing temperature. The formation of hydroxy-Fe interlayers in montmorillonite was generally not temperature d pendent, whereas the formation of such interlayers in vermiculite increased slightly with increasing temperature. These data may partially explain the formation of chloritic intergrades in soils as a function of type of minerals, kind of ions, and thermal variations