In this study, we investigated on how the salt concentration influenced the mechanism of flocculation for Na-montmorillonite-water system based on rheological method under extremely diluted and alkaline state suspension.
Oue conclusions are as follows:
1) The montmorillonite-water system showed stable dispersion without dependence on the salt concentration when the salt concentration was less than 1.2 ×10^-2 mol/l.
2) When the salt concentration exceeded 1.2 ×10^-2 mol/l, dispersed particles started to flocculate under stable conditions and gelation occured; the gel structure developed further by increasing salt concentration from 1.2×10^-2 mol/l to3.0×10^-1 mol/l.
3) On the other hand, floc was formed by the bonding of dispersed particles in the flow state when the salt concentration exceeded 1.2 ×10^-2 mol/l. The effective volume of floc increased as the salt concentration increased within the range of 1.20times;102-5.6×10^-2 mol/l/.
4) However, for salt concentration between 5.6 ×10^-2 mol/l and 1.8 ×10^-1 mol/l, the effective volume of floc decreased with increasing salt concentration. This fact can be explained using the flocculation model proposed by Keren et al, starting that montmorillonite platelet is the flexible structure

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Experimental syntheses of kaolinite from powdered volcanic glass were performed using distilled water, 0.01N acetic acid solution, 0.01N, 0.05N, and 0.1N HCl solutions, and the same concentrations of HCl containing Al ions at 200°C for a period of 1 to 30 days. X-ray powder diffraction confirmed that kaolinite was formed in all acid solutions of acetic acid and HCl, and smectite was produced in distilled water. The amount of kaolinite formed in HCl solutions containing Al ions reached above 50% of the residual solid, whereas that formed in solutions without Al ions was relatively less than 40%. Based on the stability diagram for the system of Si0₂-Al₂0₃-Na₂0-H₂O, it was observed that the compositions of acid solutions agree with the stable field of kaolinite, whereas that of the distilled water changed to a stable field of smectite due to rapid increase in pH. The pH values of acid solutions at which kaolinite was formed went down from 4.42 to 1.04 range The morphology and crystallinity of kaolinite appeared to be strongly dependent on the pH values. Spherical kaolinite was formed in acid solution with the highest pH value of 4.42, however irregular or lath shaped kaolinites tend to appear with decreasing pH, and hexagonal platy kaolinite was produced at the lowest pH value of 1.04. The spherical and hexagonal platy kaolinites formed at both conditions of the highest and lowest pH exhibited extremely high crystallinity, whereas kaolinites formed at pH values between 4.42 to 1.04 showed quite lower crystallinity.

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The study of the properties of ion exchange by means of potentiometric titration and the measurement of the basal spacings under various conditions were carried out for both kenyaite and magadiite minerals to determine the similarities and differences regarding their surface properties and structure. Kenyaite and magadiite are layered silicates with useful properties such as ion exchange and intercalation. From cation exchange measurement, it could be presumed that these silicates are essentially the same as in the surface profiles, e.g., the arrengiment of the silanol groups and ≡-Si-0^- groups pairing up with Na⁺ as counter ion. When basal spacings of these silicates expanded (e. g., in the presence of interlayer cation and interlayer water, or with the intercalation of etylene glycol in the interlayer of silicates), the interlayer spaces of kenyaite and magadiite were observed to have the same interlayer distance for (001) direction. It was believed then that this interlayer distance was controlled only by the configuration of interlayer molecules. On the other hand, when the basal spacings of these silicates shortened (e.g., in the course of the dehydration by heating, or in the cource of the ion-exchange of interlayer Na⁺ ion by H⁺ ion), the shortening proceeded stepwise, and their interlayer distances observed in each step have different respecti vevalues. These results disclosed that interlayer surface of both silicates differs from one another in fine structure, and their differences bring about a respective characteristic toothing between adjacent layers during shortening.

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A hydrotalcite-type (HT) layered double hydroxide Al₂Li (OH) ₆ (NiC14) _1/2 was synthesized by an ionic exchange of Al₂Li (OH) ₆NO₃ and its thermal changes under oxidizing and reducing atmospheres were investigated. The synthesized NiCl₄^2- type HT compound was found to have a hexagonal cell with a=5.10 and c=23.08 Å. From the observed interlayer spacing, the NiCl₄^2-anions in the interlayers considerably form a planar square structure. Since the ion exchange was not complete, the amount of NiCl₄^2-anions in the interlayers was rather low and a fair amount of NO₃^-and/or Cl-anions remained in the interlayers. The intercalation of NiCl₄^2- anions influenced the thermal stability of the HT compound and its decomposition temperature increased to about 70°C compared with that of NO₃^-type HT compound. By firing under an oxidizing atmosphere, the Ni component which formed from the decomposition of NiCl₄^2-anions was incorporated with LiAl₅O₈, which then formed from the decomposition of the HT compound. On the other hand, Ni metal particles were also found in the samples fired under a reducing atmosphere. Two different types of Ni metal particles were found in the samples:(1) very uniform and fine particles with an average particle size of 4 nm and (2) fine particles with submicron meter in size. They were dispersed in the matrix of LiAl₅O₈ and formed nanocomposites.

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