To develop a humidity self-control material in living quarters, the water vapor adsorption-desorption properties of porous clay minerals and related materials were studied. Based on Kelvin's capillary condensation theory, suitable pore diameters for the adsorption of water vapor at 0.4 and 0.7 of relative vapor pressure were calculated to be 3.2 and 7.4nm, respectively. The adsorption-desorption isotherms of sepiolite, allophane, diatomite, and selectively leached clay minerals were measured and considered as candidates for humidity self-control materials.

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Several commonly used adsorption isotherms were applied to phosphate adsorption data for 24 different complexes of hydroxyaluminum (HyA) or hydroxyaluminosilicate (HAS) ions with montmorillonite (Mt) or vermiculite (Vt) clays. The applied isotherms were evaluated with regards to their goodness of fit utilizing different criteria adopted by several earlier workers for this purpose. Relative merits and limitations of those criteria were discussed on statistical ground. The isotherm equations were found to describe the phosphate adsorption data with different levels of success. The two surface Langmuir equation was found to be the best in describing the adsorption data suggesting the existence of two different populations of adsorption sites on the HyA/HAS-Mt/Vt complexes that have varying affinities for phosphate ions. The OH or OH₂ groups coordinated with Al atoms at the broken edges of HyA or HAS polymers fixed on the external planner surfaces, and/or in the interlayer spaces of Mt/Vt were assumed to be predominantly involved in the ligand exchange reaction of phosphate adsorption in Region I. Ligand exchange predominantly with OH groups linking Al atoms inside the polymeric structure of the fixed HyA or HAS ions was assumed to be the principal adsorption process in Region II. The Temkin equation, however, was almost equally successful which was followed by the Freundlich equation in terms of their goodness of fit. The estimated adsorption parameters of different equations fitted were although numerically different but were positively and significantly correlated with each other at 1% level of significance suggesting that these parameters are relevant to describe phosphate adsorption behavior of the complexes as well as possess wide confidence limits.

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Intercalation property was investigated by insertion of dimethyl sulfoxide and its removal for four types of synthesized kaolinite samples. All the synthetic kaolinites with platy morphology formed intercalation compounds with different ratios and rates. The intercalation with the well-crystallized synthetic kaolinite was completed. However, the intercalation ratios and rates were independent of the degree of stacking disorder of the synthetic kaolinites. On the other hand, no intercalation compound was formed with the spherical synthetic kaolinite.

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Manganese nodules were found in Java soils which is located in the humid tropical region and influenced by volcanic environment. The objective of this research was to study the mineralogy of the soil manganese nodules developed in the different parent materials. Both samples of manganese nodule and soil were collected from soil profiles developed from limestone (Semanu), tuff-agglomerate (Patuk), and tuff (Cikopomayak). Mineral composition of the manganese nodule was identified with combination of successive selective dissolution and X-ray diffraction. The predominant soil clay mineral in all samples was kaolinite; while in Semanu soil there was also intergrade mineral (Vt-Ch); and vermiculite, illite and Vt-Ch were also identified in Cikopomayak soil. In the manganese nodules, manganese-oxide minerals were almost amorphous minerals and iron-oxide minerals were goethite. Birnessite was only present in Semanu, and Mn was concentrated 23 times in this sample. Some heavy metals were also enriched from the soil to manganese nodule. As for the similarity in the mineralogy of layer silicate on both manganese nodule and soil, it was suggested that the manganese nodules were developed in the soil.

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On the basis of recent information on the chemical structure of allophane with nano-ball morphology, a new mechanism was proposed for phosphate adsorption on the allophane: replacement of weakly bonded silicon with phosphorus. First experimental ground for the mechanism was linear relationship between silicon release and phosphate adsorption. Second was much more silicon release upon the adsorption for allophane with higher Si/Al ratio which contains much weakly bonded silicon in its chemical structure than for allophane with the low ratio. The replacement mechanism was formulated as:
≡Si-O-(OH) ₃+H₂PO₄^-→≡Si-O-PO (OH) O^-+Si (OH) ₄.
Possibility of the reaction was proven by negative value of the change in heats of formation, ΔH, obtained by molecular orbital calculation. The replacement mechanism is not a kind of usual adsorptions, but regarded as one of chemical reactions between allophane and phosphate. We also found that high phosphate concentration in aqueous solution (>1.5mM) caused partial destruction of allophane structure even around pH 6, and that Ca²⁺ ion enhanced phosphate adsorption by bridging effect between allophane and phosphate.

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The argillic subsoil B-horizon in the calcareous alluvial plain of Pacabit-Madulao area contains soil clay materials dominated by smectite with occasional association of kaolinite. X-ray diffraction and chemical data demonstrated that smectite is Fe-montmorillonite which is characterized by mainly Ca²⁺ of the interlayer cation reflecting the parent material of basic rocks. This clay contains more octahedral Fe³⁺ than ordinary montmorillonite, exhibits no substitution of Al to Si in the tetrahedral layer and dehydroxylates below 600°C. The morphology showed both detrital and euhedral habits suggesting a neo-formed origin.
Clay illuviation and redeposition of translocated clay materials are considered to be significant processes ultimately responsible for the accumulation of this nearly monomineralic clay assemblage. Large amounts of smectite produced initially by the weathering of basic rocks were transported in suspension in soil water and redeposited at deeper zones in the soil profile. The genesis of smectite speculated here is supported by the absence of mixed layer minerals or any transitory weathering products of the original detrital clay in the samples. The possibility of neo-formed smectite in this soil environment is also considered as several hints of authigenic clay formation were observed in some clay mineralogical examinations.

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