Lead oxide-montmorillonite complex (LMC), Pb_2.90O_2.73 (Si_3.77Al_0.23)-Al_1.69 Mg_0.15 Fe_0.17O₁₀ (OH) ₂, was prepared by heating a basic lead carbonatemontmorillonite complex at 400°C. The properties of the LMC were characterized by X-ray powder diffractometry, infrared absorption spectroscopy and X-ray photoelectronic spectroscopy. The electron density obtained by a one-dimensional Fourier synthesis method showed that the LMC had a crystal structure in which lead oxide having two lead atomic planes intercalated between the 2: 1 silicate layers.

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Fluorescent xanthenc dyes having carboxyl or hydroxyl group in their molecular structures were found to he dissociatively adsorbed on chrysotilc as carhoxylatc or phenolate. The dyes were preferentially adsorbed on chrysotilc more than on kaolinite because of the anionic adsorption. Fluorescence excitation and infrared spectra showed that deprotonated umbelliferone (7-hydroxycoumarin) was adsorbed on magnesium of chrysotile. Strong fluorescence intensities of these dyes adsorbed on chrysotile are expected to he utilized for a selective detection method of chrysotile asbestos.

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The formation process of kaolinitc in the hydrothermal reaction of an amorphous calcium silicate with aluminum chloride was studied by XRD, IR, DTA-TG, TEM, and high-resolution solid state ²⁹Si-MAS/NMR. The amorphous calcium silicate prepared from diatomite and calcium hydroxide was hydrothermally treated with an aluminum chloride solution in a Teflon pressure vessel at 220°C for a reaction period varying from 1 to 144 h. As the first step of the reaction, the Q² state component of the starting material changed into an intcrmcdiate amorphous with the Q³ state. The degree of silica-polycondensation of this state is identical to that of the intermedicate phase observed in the kaolinitization from the amorphous mixture of silica and alumina. The intermediate amorphous phase was then converted directly into the crystalline kaolinite with a platy shape (the Q³ state), without forming a spherical kaolinite. The latter was observed in the reaction system started from an amorphous mixture of silica and alumina.

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In ambient air having 60 relative humidity (RH) at 25°C, the adsorption of methanethiol by sepiolite was studied by comparison with that by coconut-shell active carbon. The amount of methanethiol adsorbed by sepiolite was as small as 0.12μmol/g in the air with 1 ppm methanethiol, while, the amount by active carbon was as large as>1.1μmol/g in the air with <0.03ppm methanethiol. Methanethiol was converted into dimethyldisulfide on active carbon.
In ambient air having 60% RH at 25°C, the removal of methanethiol by the sepiolite-metal complexes was also studied by comparison with that by thc corresponding metal compounds. The removal rate of methanethiol on the sepiolite-metal complexes was larger than that on the corresponding metal compounds. In the oxidation reaction of methanethiol to dimethyldisulfide in the presence of the sepiolite-metal compound complexes, sepiolite much enhances the catalytic action of metal compounds such as metal chloride and oxalate, and metallophthalocyanine.

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Ferrihydrite and feroxyhyte were synthesized at room temperature from 0.1M FeSO₄. Fcrrihydrite, with 6 to 7 diffraction lines, formed at pHs 5-11 in the presence of Si (Fe:Si=10:1). The use of Ge, in place of Si, resulted in the same, with the same d-spacings of the diffraction peaks. This indicates that the Si or Ge is not in the structure of ferrihydrite, but forms Fe-O-Si (or Ge) at the periphery of “domain” of ferrihydrite. The presence of Si or Ge was a requisite for the formation of ferrihydrite, because their absence led, at the pHs investigated, to the formation of goethite or lepidocrocite. Synthetic products at pH 7 from Fe (NO₃) ₃ and Fe (CIO₄) ₃ were 2-line ferrihydrites irrespective of the presence of Si, and those from FeCl₂ were lepidocrocitc in the presence and magnetite in the absence of Si.
The products from FeSO₄ at pH 12 yielded 4 diffraction lines for feroxyhyte. Either Si or Gc seemed to effect the formation of the mineral, because, in the absence of these cations at the same pH, the oxidation of Fe (II) never proceeded from the stage of green rust. Electron microscopic examination showed that ferrihydrite appears as shapeless assemblies of granular texture, and feroxyhyte consists of numerous “rod-like” particles about 4 nm wide and 70 nm long.

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