Zeta (ζ) potential of clay minerals, which affects the dispersion and the flocculation in their water suspension, is generally determined by an electrophoresis method. This method is, however, required the diluted suspension system which is thoroughly dispersed, and needs considerably long times for the measurement. An electrokinetic sonic amplitude (ESA) method for the ζ-potentials was applied to four kinds of Na⁺-saturated clay minerals, kaolinite, halloysite, montmorillonite and allophane. The pH-dependence of ζ-potential was discussed comparing with the changes of their mean particle or aggregate sizes determined by a laser scattering method. The ζ-potential of kaolinite, halloysite, montmorillonite and allophane was 22, -15, -25 and -50 mV in the clay samples saturated with Na⁺ at about pH 7.0, respectively. These approximated to the values reported in the previous studies. The ζ-potential of clay minerals estimated with the ESA method was clearly related with the dispersibility of their suspension at various pHs. The ESA method was effective for the estimation of ζ-potential of clay minerals, in conclusion.

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Adsorption of zinc on two nano-ball allophane samples, namely one with low Si/ Al ratio (KyP) and one with high Si/Al ratio (KnP) was found to increase with increasing solution pH, with highest adsorption occurring at initial pH 7. The adsorption was found to be higher in the high Si/Al allophane sample (KnP) due to its relatively higher amount of silanol groups per unit mass. It seemed that the surface OH^- groups bonded to Al and/or Si atoms in nano-ball allophane structure, particularly those ionised at higher pH, retain zinc very strongly. For most cases, the Langmuir and Freundlich parameters were found to increase with increasing initial solution pH. Adsorption of zinc by allophane sample (KnP) at initial pH 6-7 fi tted with Langmuir equation. All zinc adsorption data of low Si/Al ratio (KyP) sample conformed to the Freundlich model. From the observed changes in solution pH after zinc adsorption, reaction mechanism was proposed as release of H+into the bulk solutio

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In order to predict the effect of acid precipitation on building stone, artificial chemical weathering of polished plates of Kitagi Granite, Okayama, southwestern Japan, was conducted. An improved Soxhlet extraction apparatus was used with distilled water and HNO₃, H₂SO₄ and HCI solutions of pH 3 at 55°C for different periods of time up to 824 days. The granite was composed mainly of quartz, plagioclase (Ab₈₆An₁₂Or₂), alkali feldspar (0r₉₂Ab₈) and biotite. The leached sample solutions were analyzed for major and minor elements using ICP, ICP-MS and ionchromatography. Morphological and chemical changes of each mineral surface were studied by SEM, EPMA and microscopic techniques. Alteration products were collected from the surface of each mineral on the polished plates by hand picking and examined using an XRD.
Molar ratios of each element in the leached solutions to those in the fresh granite varied depending on the experimental period. The ratios of elements such as Mn, Fe, Mg, Sc and Zn, which reflect the dissolution of biotite, were relatively high. Similarly, the ratios of Ca, Na, Gd, Sm, Nd, La and Sr, which reflect the dissolution of plagioclase, were relatively high. It seems, therefore, that plagioclase and biotite are easily weathered. It was also estimated from the ratios that the reactivity order of the acid solutions for plagioclase is H₂SO₄, HCI and HNO₃, and for biotite is HNO₃, H₂SO₄, and HCl.
It is evident that biotite changed into mica-clay minerals and/or interstratified minerals of mica and vermiculite by exposure to the various acid solutions used in the experiment. Smectite appeared to be formed from plagioclase during the artificial chemical weathering. However, altered products from quartz and alkali feldspar, were not detected.

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High silica ZSM-5 zeolites were synthesized by using microporous silica derived from kaolin and were characterized by XRD, FTIR, SEM and N₂ adsorption. The microporous silicas were prepared by calcining kaolinite at 600°C and selectively leaching with H₂S0₄ solution for different times. Microporous silicas with Si0₂/ Al₂0₃ ratios of 70 and 710 were used as the starting materials. These powders were then converted into ZSM-5 by hydrothermal treatment at 150° in the presence of the templating agent tetrapropylammonium hydroxide. ZSM-5 zeolite formation was observed as early as 3h in the both samples. The growth rates of the crystals were found to depend on the Si0₂/Al₂0₃ ratios of the starting materials. A high Si0₂/Al₂0₃ ratio resulted in more uniform and well-crystallized ZSM-5 zeolite. The change of crystal morphology was examined as a function of hydrothermal treatment using XRD and SEM, showing that the preferential growth of (020) plane resulted in thick platy ZSM-5 crystals in the high silica batch. The specfiic surface areas obtained were 300-340 m²/g and the pore size distributions showed a considerable change due to differences in the size and morphology of the ZSM-5 crystals.

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Vermiculite (Vt) was found in the clay fraction of sandy volcanic ash soils around Mt. Pinatubo, Philippines. Origin of the clay-size Vt was examined selecting two horizons from two pedons with different land use, from a paddy rice and a sugarcane field. In order to concentrate Vt, 2-0.4 μm fraction was taken because halloysite and a small amount of smectite and quartz were also included in these clay fractions. Regarding (060) diffraction spacing, two major peaks were found at 0.153 and 0.149 nm in both samples. With heating at 600°C, intensity of the diffraction peak at 0.149 nm was greatly reduced and that at 0.153 nm remained almost unaffected, indicating that the diffraction peak at 0.149 nm was mostly due to halloysite. Overlap between diffraction peaks at 0.154 nm of quartz and that at 0.153 nm was only partial in these samples. Thus, it was concluded that the diffraction peak at 0.153 nm was assigned to trioctahedral Vt. Weathered particles of biotite were found with the naked eye and under an optical microscope in the sand fractions of these soils. In the silt fractions, Vt and biotite were suggested by X-ray diffraction (XRD) analysis. XRD peak intensity indicated that vermiculitization of biotite in the sand fractions was more advanced in the paddy field than in the sugarcane field. However, Vt was dominant in the silt and clay fractions of both soils. From these results, it was strongly suggested that claysize Vt was inherited from biotite in these soils.

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The structure of an anhydrous 2: 1-Na layer silicate (NLS), which was synthesized by heating a mixture of talc and Na₂SiF₆ at 800°C for 2 h, was estimated by MD simulation based on a 1 M mica structure (C2/m). The results of MD simulation showed that the top and bottom silicate layers moved in mutually opposite direction along the a- and b-axes, and the silicate layer stacking of NSL was similar to that of talc structure. The trajectory of the Na⁺ ions in the NLS structure from the MD simulation clearly shows two different movements as follows: one Na+ ion near the Mg²⁺ vacant site in the octahedral sheet was especially localized in the upper silicate layers, but the other Na⁺ ion apart from the Mg²⁺ vacant site in the octahedral sheet was placed in the middle position between the silicate layers. The ²³Na MAS NMR spectra of the NLS and Mg²⁺ ion-exchanged NLS also showed that the NLS had two different kinds of Na⁺ ions, one was exchangeable and the other was nonexchangeable. However, the MD simulation could not explain quantitatively the mass balance of the exchangeable and non-exchangeable Na⁺ ions in the NLS structure.

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