Eleven soils from different Ganges Floodplains of Bangladesh were studied to investigate the clay mineralogical composition and to clarify the relationship between disappearance of smectite and decalcification of calcareous floodplain soils occurring in these areas. In general, mineralogical composition of calcareous floodplain soils were dominated by mica and smectite, and in some cases by vermiculite. Chlorite and kaolinte were also present in minor amounts.
Amjhupi and Gangni soils on ridges and Ghior (1) soil in a basin had the lower smectite as well as carbonate contents in Ap and B2 horizons than in the corresponding C horizon. However, all horizons having low carbonate content did not always show the lower smectite content, possibly due to near-neutral reaction or due to difference in the rate between decalcification and disappearance of smectite. Complete disappearance of smectite was observed in Tahirpur soil and partial disappearance in Baradi soil; both are situated on the non-flooded highland and thoroughly decalcified and considered to be in the oldest soil formation in Ganges Floodplains of Bangladesh. Based on the assigned age of the soils, smectite disappearance was estimated to be in the order of 2500-3000 years.

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Reduction and oxidation reactions of chromium (Cr) have attracted the interest of environmental scientist because the toxicity and mobility of Cr in soils and geologic materials are depending on its oxidation state. In this study, the oxidation of immobile and nontoxic Cr (III) to mobile and toxic Cr (VI) by a series of synthesized birnessites (σ-MnO₂) with different crystallinity in aqueous environment was tested. The oxidation rates were initially fast and followed by a sharp rate decline after 1 hour equilibration. The oxidation of Cr (III) to Cr (VI) by birnessites favored lower pH, higher initial Cr (III) concentration, and higher ratio of birnessite surface area to solution volume when the other two factors are fixed. The combination of high pH and high initial Cr (III) concentration reduced Cr oxidation rate. Chromium oxidation capacity of birnessite increased with a decreased crystallinity.

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Mineralogical studies of some Meghna Floodplains soils, in which the sediments as parent materials were possibly transported by the Meghna, Old Brahmaputra, Jamuna (Brahmaputra), and/or Ganges Rivers, were carried out to determine the contribution of different river sediments in Lower Meghna River Floodplain, Young Meghna Estuarine Floodplain, and the part of Old Meghna Estuarine Floodplain which is surrounded by Ganges Floodplains. In general, mica, smectite, vermiculite, chlorite and kaolinite were the major clay minerals in these soils. Soils of Lower Meghna River Floodplain were dominated by mica, vermiculite and chlorite, and were estimated to be developed from the Jamuna (Brahmaputra) sediments while the contribution of the Meghna/Old Brahmaputra sediments increased towards the surface. The Ganges sediments had apparently no contribution. In contrast, soils of Young Meghna Estuarine Floodplain contained good amounts of smectite and chlorite in addition to mica, and were estimated to be developed from the Ganges and Meghna/Old Brahmaputra sediments. Due to the predominance of smectite in the Ap and B horizons or Ap horizon, soils of the part of Old Meghna Estuarine Floodplain which is surrounded by Ganges Floodplains were estimated to consist of the Ganges sediments in the upper horizons and of the Meghna/Old Brahmaputrta sediments in the lower horizons.

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The natural Na-montmorillonite (Tsukinuno mine, Yamagate Prefecture, Japan) was treated under hydrothermal conditions. Temperature ranged between 250 and 500°C at 100MPa, and run durations ranged between 1 and 150 days. The identification of phases was carried out by the X-ray powder diffraction method. The Greene-Kelly test was applied to distinguish among montmorillonite, beidellite and saponite. The phases identified in the products were plotted in a time-temperature diagram. The diagram showed that montmorillonite below 350°C reacted to the assemblage of mixed-layered phase of smectite and the 1:1 regular interstratification of montmorillonite/beidellite (S/r.i.M-B) +montmorillonite+quartz+analcime, and with increasing temperature transformed to the assemblage of Na-rectorite+quartz+feldspar, through the intermediate phase assemblage of beidellite+ saponite+ quartz+ feldspar. The diagram indicated also that montmorillonite and S/r.i.M-B might be stable clay minerals below 300°C, and that the decomposition of montmorillonite to an assemblage of beidellite, saponite and quartz can proceed in nature below the temperature where rectorite is formed.

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Smectite was formed from some clays, such as pyrophyllite, kaolinite, sericite and talc by reaction with NaOH solution at 100°C under atmospheric pressure. Smectite was formed well under the condition that the concentration of NaOH was near 2M-3M. Furthermore, when the reaction time involved is within 50 days, the amount of starting material should be less than 0.5g in 100ml solution to form smectite.

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Organized organic-inorganic ultrathin films have been constructed from the fabrication of smectite unit layers and an amphiphilic ruthenium (II) complex monolayer using the conventional Langmuir-Blodgett (LB) technique. According to the method, a chloroform solution of an amphiphilic ruthenium (II) complex, [Ru (phen) ₂ (dC18bpy)] ²⁺ (phen=1, 10-phenanthroline, dC18bpy=4, 4'-dioctadecyl-2, 2'-bipyridyl as shown in Figure. 1), was spread onto an aqueous subphase containing either exfoliated saponite or hectorite suspension. Brewster angle microscopy (BAM) observation showed that Ru (II) complex molecules formed a self-assembled monolayer on a water surface and that clay particles were adsorbed by the monolayer from an aqueous subphase. A composite film of a Ru (II) complex and a clay particle thus formed was transferred onto a hydrophilic glass plate by the vertical dipping method. The surface structure of a deposited film was studied with an atomic force microscope (AFM). As a results, a glass substrate was covered with the single sheet of a clay on which amphiphilic metal complexes were attached

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Crystal structure of dehydroxylated 2M₁ sericite from Goto mine, Nagasaki Prefecture, Japan was investigated, and was compared with the crystal structure of unheated 2M₁ sericite. The crystal structure of the dehydroxylated 2M₁ sericite showed different site cation occupancies in interlayers. Density distribution in interlayers showed alternating different densities. It was confirmed that the formation of regularly interstratified mica/smectite from the dehydroxylated 2M₁ sericite is attributed to the crystal structure of dehydroxylated 2M₁ sericite.

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