The shapes, sizes and settling velocities of flocs of kaolinite particles coagulated in 0.1 M NaCl solution at pH 10 were measured and the porosity of the flocs was calculated using the obtained data and Stokes' law. The results were as follows:
(1) Although the diameters of the flocs ranged from 30 μm to 180 μm, their shapes were almost all spherical.
(2) The porosity of the flocs was in the range of 97% to 99%.
(3) The face to face coagulation model can not explain the results of (1) and (2). Only the point to point coagulation model proposed by the authors can reasonably account for the results.

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Todorokite, one of the major Mn minerals, is less common and distinguishing the todorokite from lithiophorite and other associated Fe/Mn minerals is important. For many years, the crystal structure of todorokite was a subject of considerable conjecture and controversy. Therefore, the study was conducted to (a) distinguish todorokite from lithiophorite and iron oxide minerals, and (b) investigate the detailed micromorphological structures of todorokite and its associated Fe/Mn minerals. Fe/Mn brittle (MN-12) and nodule (MN-15) samples were collected from Shinzato, Sashiki-cho and Onna, Onna-son areas, respectively. Their surrounding soils were developed from Ryukyu limestone. They were analyzed using the successive selective dissolution procedure (SSDP) in combination with X-ray diffraction technique (XRD), while detailed micromorphology of todorokite and its associated minerals were observed using scanning electron microscopic technique (SEM). The NaOH treatment of the SSDP dissolved kaolinite and gibbsite, concentrating birnessite (Bs), todorokite (Td), lithiophorite (Lp), and goethite (Ge), specially in MN-12 sample. The HAHC treatment at 25°C effectively dissolved both birnessite and todorokite, but lithiophorite and goethite remained undissolved. A subsequent extraction with HAHC at 60°C dissolved lithiophorite without disturbing goethite. Finally, the DCB treatment dissolved goethite. Thus, extraction with HAHC at 25°C and 60°C were useful in distinguishing todorokite from lithiophorite and iron oxide minerals. Elemental analysis with respect to SSDP proved the presence of Fe/Mn minerals in semi-quantitative basis. Micromorphological observation explained that well crystallized todorokite minerals spread throughout the sample of MN-12 collected from the Sinzato area, Okinawa. Micrographs clearly show the detailed crystal nature of natural birnessite, todorokite, lithiophorite, gibssite, goethite and their association with other silicate minerals.

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The study was carried out in order to characterize and identify oxide and layer silicate minerals present in terrestrial Fe/Mn nodules and their surrounding soils occurring in Okinawa, Japan, with respect to the genesis of these materials. Ferrous-manganese nodules were found in Okinawan soils derived from parent material of Ryukyus limestone. Mineral composition was characterized using the successive selective dissolution procedure (SSDP) by treatments of sodium hydroxide (NaOH), hydroxylamine hydrochloride (HAHC) at 25°C and 60°C and dithionite-citrate-bicarbonate (DCB) in combination with X-ray diffraction and SEM techniques. Detailed micro-morphology of manganese minerals, observed in most of the nodules, showed pseudo-hexagonal platelets for high crystalline lithiophorite while poor crystalline birnessite exhibited globular shape like structure. Goethite and gibbsite as iron and aluminum oxide minerals respectively, were detected in all samples. Lepidocrocite, an iron oxide mineral found in one of the samples, was dissolved by NaOH treatment. Major layer silicate minerals detected in all samples were kaolinite (Kt) and illite (It). In addition, intergraded mineral vermiculite-chlorite (Vt-Ch) was observed in most of the samples. All nodule samples and their surrounding soils used in this work had almost same composition for layer silicate minerals. According to the similarity on mineralogy of layer silicate minerals in both nodule and its correlated surrounding soil, it is suggested that Fe/Mn nodules might be developed in the surrounding soils.

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Bangladesh has been divided into 30 Agroecological Regions (AEZs) on the basis of physiography, inundation land types, soils, and agroclimate. The applied agricultural research has currently been conducted on this basis. In context of the lack of enough information on mineralogy on the AEZ basis, an attempt has been taken to study on the mineralogy of important soils from all AEZs of Bangladesh. The present experiment was carried out in order to clarify the mineralogy of soils from Region 1: Old Himalayan Piedmont Plain. Eleven soil samples consisting of eight soil series were analyzed. The clay content of the surface soils ranged from 9.1 to 18.2% and the texture was loam or silt loam by the USDA soil textural class. The 2-20 μm silt fraction was dominated by quartz, with some mica, chlorite and plagioclase, and with small amounts of K-feldspar. The <2 μm clay fraction was dominated by mica and chlorite and in most cases by the interstratified mineral of mica and chlorite. These minerals were supposed to be inherited from the parent material of metamorphic rocks. The impact of mineralogy on agriculture or land use has been discussed.

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Bangladesh has been divided into 30 Agroecological Regions (AEZs) and the applied agricultural research has currently been conducted on this basis. In context of the lack of enough information on mineralogy on the AEZ basis, an attempt has been taken to study on the mineralogy of important soils from all AEZs of Bangladesh in order to provide basic information for applied research. As a part of this attempt, the mineralogy of soils from ten representative soil series of AEZ 3, Tista Meander Floodplain, has been reported in this paper. The clay content of the surface soils ranged from 11.5 to 22.1% and the texture was mostly silt loam. The 2-20 μm fraction was found to dominate over other fractions in all soils. This fraction was composed mainly of quartz, followed by mica, chlorite and plagioclase. The <2 μm clay fraction was dominated by mica and chlorite and in most cases by the interstratified mineral of mica and chlorite. These minerals were supposed to be inherited from the parent material of metamorphic rocks derived from the Himalayans. The impact of mineralogy on the inherent potentiality of soils regarding crop production has been discussed.

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Bangladesh has been divided into 30 Agroecological Regions (AEZs) and the applied agricultural research has currently been conducted on this basis. In context of the lack of enough information on mineralogy on the AEZ basis, an attempt has been taken to study on the mineralogy of important soils from all AEZs of Bangladesh in order to provide basic information for applied research. As a part of this attempt, the mineralogy of twelve soils from six representative soil series of AEZ 9, Old Brahmaputra Floodplain, has been reported in the present paper. The clay content of the surface soils ranged from 10 to 33%. Nine soils were medium-textured (7 loam and 2 silt loam), while two soils were sandy loam and the remaining one was clay loam. The 2-20 μm fraction was dominated by quartz, and then by mica and chlorite; plagioclase and K-feldspar were also identified. The <2 μm clay fraction was dominated by mica and chlorite with some vermiculite and/or vermiculite-chlorite intergrade. The impact of mineralogy on the inherent potentiality of soils regarding crop production has been discussed.

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Dihexadecylviologen (1, 1'-dihexadecyl-4, 4'-bipyridinium: 2C₁₆V²⁺)-montmorillonite intercalation compound was synthesized by an ion exchange reaction, and used as a support to accommodate mesotetraphenylporphine. The photoinduced electron transfer from the adsorbed porphine to the 2C₁₆V²⁺ was observed by visible light irradiation. The amphiphilic viologen acted as an electron accepter as well as surface modifier to introduce the porphine into the interlayer space of montmorillonite.

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Talc was treated with acid under a variety of conditions to obtain porous silica by selective leaching. Aliquots of the powder (1g) were leached with 50 ml of 2-4 M strong acids (HCl, HNO₃ and H₂SO₄) at 80°and 150°C for 0.5 h-14 days. Since the chemical compositions of the resultant products showed little change after acid treatment at 80°C for 2 h, which conditions are generally sufficient to prepare a silica-rich product by selective leaching from a variety of other clay minerals, it is concluded that talc is more resistant to acid attack than other clays. The products obtained at 150°C using an autoclave showed an increased SiO₂ content (up to>90 mass%) with longer leaching times. The specific surface areas of the resultant products were<40 m²/g and are lower than those from other clay minerals. This low surface area of the product is discussed with respect to the chemical compositions and structures of the various clay mineral reactants. Since the products preserved the original flaky particle shape after selective leaching and also after firing to 1000°C, the selective leaching of talc provides a method for preparing amorphous silica with a platy particle shape.

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Structural changes and thermal conductions in kaolinite suspensions were examined as a function of the solid fraction and freezing temperatures. Solid fractions ranging from 20 to 50% were tested, and each sample was prepared with freezing temperatures of-30°C, -50°C (in a freezer) and-196°C (with liquid nitrogen). Effective thermal conductivities were calculated using the equation of heat conduction. As a result, it was found that the effective thermal conductivity ratio of kaolinite suspension slightly decreases with an increasing solid fraction. Applying Fricke's model to these results, we predict that an increasing solid fraction promotes orientation of platy particles in kaolinite suspensions.
Particle arrangement in freeze-dried suspensions was examined with SEM. Consequently, the particle arrangement in the kaolinite suspension with a 20% solid fraction and a freezing temperature of-30°C takes on a honeycomb structure, and the other samples prepared in a freezer have a halfpipe-like structure. On the other hand, the particle arrangement of samples lyophilized by liquid nitrogen is similar to a sponge structure. According to an additional observation with an ESEM, namely an environmental scanning electron microscope, it becomes evident that the freeze-drying method with liquid nitrogen is one of the best sample preparations to keep particle structure in kaolinite suspensions for SEM observation.

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The hybridization of poly (ethylene terephthalate)(PET) with montmorillonite (Mont) clay was investigated using anchor monomers, i.e., hydroxyethyl isonicotinamide (HENA) or hydroxypentyltrimethylammonium iodide (HPTA), which have cationic substituents to adsorb onto clay surfaces and a hydroxyethyl moiety (-CH₂CH₂OH) to react with the polymer chain terminal of PET. The condensation of the mixtures of the intercalation compounds, bis (2-hydroxyethyl) terephthalate (BHET) and HENA/Mont or HPTA/Mont, led to a homogenous and transparent PET hybrid in which the Mont clay particles were scattered homogenously. The HPTA/Mont hybrid films copolymerized with BHET exhibited a dramatic improvement in such characteristics as tensile strength and optical transparency.

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The effect of kaolinite on the growth of hydrocarbon-utilizing indigenous microorganisms in high concentration of heavy oil (i.e., approximately 150 g/l) was studied. Microorganisms were able to grow well in such an extremely high concentration in the presence of yeast extract as co-substrate in direct contact with kaolinite. The presence of kaolinite was not toxic but stimulant for the microbial growth associated with the formation of biofilms at pH values of 5-6 after 36 days of incubation. Bacterial growth predominated when the pH of solutions was neutral-alkaline condition, while fungal growth was predominant as the pH of solutions decreased to be as low as 5 or lower. TEM observation of the kaolinite-oil-microorganism complexes showed that the microbial cells tended to be primarily bound on the edges of kaolinite, and XRD analysis confirmed that their complexes were the adsorption of the cells and heavy oil to the external surfaces of kaolinite. The results may contribute to what environmental factors having a great influence on the bioremediation process is therefore fundamental to many areas contaminated with oil spills, primarily marine and coastal environments. To our knowledge, there are no previous reports on the use of the clay minerals (i.e., kaolinite) in the bioremediation of the Nakhodka oil spill in combination with biofilm formation.

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