Chemical Composition Of Smectites Research Articles

Expansion of Smectite by Hexadecyltrimethylammonium

AbstractThe adsorption of hexadecyltrimethylammonium (HDTMA) in smectite was studied by adsorption isotherms, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Smectites that had reacted for 48 h with HDTMA cations equivalent to 0.2–3.0 times the cation exchange capacity (CEC) were converted to HDTMA-exchanged smectites with various d-spacings. Study of HDTMA-smectites by HRTEM suggests that the HDTMA adsorption results in interlayer expansion with various d-spacings and irregular wavy layer structures. We believe that HDTMA loading beyond the CEC of smectite affects the structure of clay by the additional adsorption of HDTMA-Br− via hydrophobic bonding. Surfactant orientation probably depends on the quantity of surfactant in the interlayer. Our TEM study shows that the structure of the adsorbed HDTMA layer in the interlayers of smectite depends on the charge distribution and chemical composition of smectite.

Smectite in weathered hyaloclastite of the Shakotan Peninsula, Hokkaido, Japan: significance of clay mineralogy in engineering geology

The occurrence and chemical composition of smectite in hyaloclastite from the Toyohama rock fall site of 10 February 1996 and the Oshoro Bay area were examined by using optical microscope, X-ray diffractometer, electron probe microanalyser and analytical transmission electron microscope. Frequently, smectite occurs as fillings and linings of pores in various forms, and sporadically as the replacement of volcanic glass in hyaloclastite. The analytical results show that smectite is of dioctahedral and Fe-rich type. Its compositional field varies extensively between montmorillonite and nontronite. Moreover, interlayer cations of smectite vary intensively in relation with the type of weathering in hyaloclastite. Na-smectite occurs characteristically in discoloured hyaloclastite affected by superficial weathering, whereas Ca- and K-smectite occurs dominantly in the hyaloclastite collected from the inner part of the rock mass. These features of smectite in hyaloclastite can be attributed to its formational and weathering environments. Mineralogical characterisation of hyaloclastite provides detailed information on engineering properties of this type of rock mass and rock materials.

THE NATURE OF SMECTITES IN SOME FINE TEXTURED LACUSTRINE PARENT MATERIALS IN SOUTHERN SASKATCHEWAN

Detailed mineralogy and chemistry of the clay fraction of five glacio-lacustrine deposits and of one Cretaceous marine shale (Ashville) were studied. Fine clay separates (< 0.2 μm) of the five parent materials were predominantly smectite with an average chemical composition:[Formula: see text]X-ray diffraction, dehydration, infrared, and chemical analyses, and the Greene-Kelly test showed that the smectite was an iron rich montmorillonite. Similarities in the crystal structure of the five soil parent material clays suggest that they were likely transported from the same source. Despite the differences in percentage of clay minerals, similarities between chemical composition of the coarse and the fine clays is interpreted as an indication of close diagenetic relationships between the predominant smectite and soil mica. High silicate bound iron may have caused a distortion in the crystal lattice and a slightly favorable weathering condition of smectites. However, presence of high exchangeable and soluble magnesium in the soil complex is likely retarding the smectite alteration. Thus, weathering by elemental substitution may have been restricted to the smectite end member only. Key words: Swelling clay soils, iron montmorillonite, chemical composition of smectites, dehydration of smectites