When rice husk is burnt, about 20wt% of the husk remains as ash. The rice husk ash has more than 95 wt% of silica with high porosity and large surface area, because it still retains the skeleton of cellular structure. These properties of the rice husk ash can be used to synthesize siliceous raw materials such as clay minerals. Syntheses of smectite from the rice husk ash were conducted by using a starting material of a mixture of rice husk ash, magnesium chloride and lithium chloride with a molar ratio of Si: Mg: Li=8: 5.34: 0.66. The optimal conditions of smectite synthesis is as follows. Burning condition of rice husk: 400°C-450°C for 5 hours after smouldered at 350°C for 4 hours, pH value of initial suspension: 13.2-13.5, Reaction temperature: 200°, Reaction time: 1 day-4 days. The rice husk ash as agro-waste can be therefore exploited readily for the hydrothermal synthesis of smectite.

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The adsorption of acetaldehyde by sepiolite combined with 2-aminobenzoic acid (sepiolite-OABA complex) was studied in comparison with that of the aldehyde by mere sepiolite. Experiments were carried out at 25°C in ambient air having relative humidity of 9.0, 30, 60, and 80%. Combination of 2-aminobenzoic acid (OABA) with sepiolite was found to give big enhancement on the adsorptive capacity of sepiolite. For example, in 9.0% relative humidity, the adsorptive capacity of sepiolite combined with 10% OABA was about 10 times larger than that of mere sepiolite. In 30, 60, and 80% relative humidity, that of sepiolite combined with 10% OABA was about 30, 50, and over 100 times larger than that of mere sepiolite, respectively.
Removal rate of the aldehyde by sepiolite from the air was decreased proportionally with elevating relative humidity regardless of the initial concentration (C_o=19.9-345ppm). But that of the aldehyde by the sepiolite combined with 10% OABA was nearly constant (≥99.5%) in 9.0-60% relative humidity range and decreased slightly (≅1 %), when relative humidity was lowered (≅80%) in the relatively high initial concentration (C_o=924-2506 ppm). The removal of the aldehyde was discussed on the basis of reaction and adsorption.

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Clay mineralogical composition of a Yellow-brown soil of China was examined. Common to the A and C horizons, micas and their transformation products dominated the clay fraction. The transformation products of micas were, however, different between the fine (<0.2μm) and coarse (0.2-2μm) clay fractions. Irregularly interstratified mica/smectite or mica/vermiculite/smectite of the smectite-rich phase was found in the fine clay fraction, while smectite and regularly interstratified mica/smectite were detected in the coarse clay fraction. The endo-type and exo-type K-replacement models were proposed to explain the different transformation products between the two clay fractions.

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