Showing papers in "Clay science in 2005"

Molecular orbital analysis on the dissolution of nano-ball allophane under alkaline condition

Abstract: Reaction mechanism between hydroxide ion (OH - ) and pore region of nano-ball allophane was analyzed by molecular orbital method (MOPAC-PM3) with a model cluster including the pore Many Si atoms with silanol groups (Si-OH) are exposed as broken edge at the pore region, and nucleophilic OH - may attack the positively charged Si atoms When Na + , as a counter ion of OH - , was held on the silanol group by cation exchange reaction (Si-ONa), calculated positive charge of the Si atom increased from that of Si-O - This may promote nucleophilic attack and adsorption of OH - toward the Si atom In model cluster with an OH - adsorbed on the Si atom to form five-fold coordination, decreases in calculated bond orders, bond strengths, of some Si-O and Al-O bondings were observed near the OH - adsorption site This bond weakening will lead to dissolution of one Si and three Al atoms from the pore region of fundamental allophane structure, which is consistent with experimental observation The increase in positive charge on Si atom and decrease in bond order of Si-O and Al-O bondings were also observed in calculations with one to six water molecules added to simulate reactions in aqueous system

Crystal Structure of Mixed-Layer Minerals and Their X-ray Identification : New Insights from X-ray Diffraction Profile Modeling(Interstratified Minerals)

Abstract: Modeling of experimental X-ray diffraction (XRD) patterns represents the optimum approach to the structure determination of mixed-layer structures (MLSs) that are commonly found in natural clay-rich samples. This approach allows for a detailed structural characterization of both pure and mixed-layer clay phases and for a semi-quantitative phase analysis in complex mixtures. The two informations are essential to gain new insight into the actual nature of reactions taking place in geological environments. Significant new findings obtained at different scales (from that of the particle to that of the elementary layer) on the actual structure of MLSs by modeling XRD profiles are reported.

Clay mineralogical composition of alluvial soils from different river systems/agro-ecological regions in vietnam in reference to origin, regional distribution and soil quality

Abstract: Sixteen profiles of alluvial soils of Vietnam were collected throughout the country and subjected to clay mineral analysis. Alluvial soils from different river systems/agro-ecological regions had different clay mineralogical compositions due to differences in sediment sources. Mica and kaolinite were found to be predominant clay minerals in alluvial soils. Other major minerals detected were vermiculite, smectite, chlorite, and the mica/vermiculite/smectite∼mica/smectite mixed-layer mineral, depending on the river systems. The clay mineralogical composition was remarkably similar within soil units belonging to the same river system and in a profile. However, the clay mineralogical composition greatly varied with river systems; therefore, the regional variation existed and was mainly controlled by the mineralogical features of the sediment sources. Mica was found to be altered to mixed-layer minerals in some soils under specific conditions. The soil quality was assessed from the viewpoint of inherent potentiality based on the type and amount of clay minerals as plant-nutrient sources. Alluvial soils distributed in the Red River and Mekong River systems were evaluated to be in the high level of inherent potentiality. Those from the Trakhuc River and Ba River systems were classified to have low inherent potentiality, while those from the remaining ones were to be at an intermediate level.

INTERCALATION OF POLYHYDRIC ALCOHOLS INTO Mg-Al LAYERED DOUBLE HYDROXIDE BY CALCINATION-REHYDRATION REACTION

Abstract: Layered double hydroxide (LDH) has an anion exchange property, and the intercalation of various organic molecules into LDH has been investigated in recent years. We have reported the intercalation of non-ionized guests such as pentose, hexose and cyclodextrin, into Mg-Al LDH by the calcination-rehydration reaction. In this paper, the intercalation behavior of non-ionized guests, various straight chain polyhydric alcohols (carbon number 3-5), into Mg-Al LDH by the same reaction has been examined. According to the XRD patterns and FT-IR spectra, the solid product was found to contain polyhydric alcohol and to show the restorable LDH structures. The amount of polyhydric alcohols intercalated was as follows: glycerin (C3) < erythritol (C4) < ribitol (C5) < arabitol (C5) < xylitol (C5) and greatly influenced by the conformation of C5 polyhydric alcohol isomers. It was confirmed that these polyhydric alcohols were intercalated into the LDH interlayer space by the formation of hydrogen bond between hydroxyl groups of guest polyhydric alcohols and the host LDH basal layer.

Crystal Structure of Mixed-Layer Minerals and Their X-ray Identification: New Insights from X-ray Diffraction Profile Modeling

Abstract: Modeling of experimental X-ray diffraction (XRD) patterns represents the optimum approach to the structure determination of mixed-layer structures (MLSs) that are commonly found in natural clay-rich samples. This approach allows for a detailed structural characterization of both pure and mixed-layer clay phases and for a semi-quantitative phase analysis in complex mixtures. The two informations are essential to gain new insight into the actual nature of reactions taking place in geological environments. Significant new findings obtained at different scales (from that of the particle to that of the elementary layer) on the actual structure of MLSs by modeling XRD profiles are reported.

Kaolinization of saprolite developed on pan african granite of batie district, west province of cameroon

Abstract: The weathering process of the Pan African granitic rock of Batie was mineralogically investigated by means of Microprobe analysis (EPMA), X-ray diffraction (XRD), X-ray fluorescent (XRF), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The porphyritic granite is composed of biotite, feldspar and quartz as main minerals, whereas epidote, chlorite, kaolinite and mica clay mineral are secondary products. Mica clay mineral and kaolinite are main constituent clay minerals in the granite saprolite (weathered granite). Mica clay mineral predominantly occurs at the lower part of the investigated profile associating with a small amount of kaolinite. The granite saprolite at the top part of the profile consists mainly of platy kaolinite with a small amount of lath shape mica clay mineral. Mica clay mineral was formed in the hydrothermal clay veins occurring in the weathering profile. It is inferred that mica clay mineral occurred in the altered granite was formed by hydrothermal activity. Detailed observations of morphological variation by TEM with X-ray analysis revealed that crystal size and shape reasonably explain the transformation sequence of kaolinite as weathering proceeds. Close relationship between crystal size and morphology is obtained. Etch pits developed on quartz and K-feldspar grains are commonly observed. However, shape and size of the etch pits are quite complicated suggesting none monotonous micro-weathering condition. Etch pits found in the upper part are much rougher than those of the lower part. Based on the results obtained, weathering condition of the Batie granite was discussed mainly from the standpoint of clay mineralogy.

Mineralogy of soils from different agroecological regions of bangladesh : region 28-madhupur tract

Abstract: 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 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 28, Madhupur Tract, has been reported in this paper. The soils were acidic in nature, had moderate to high amounts of clay, and the texture was medium (silt loam) to heavy (clay). The 2-20 μm silt fraction was composed mainly of quartz, with small amounts of mica, plagioclase, K-feldspar and chlorite. Mica, kaolinite and the interstratified mineral of kaolinite and smectite were the predominant minerals in the <2 μm clay fraction. The impact of mineralogy on the inherent potentiality of soils regarding crop production has been discussed.

Artificial chemical weathering of gabbro under earth surface conditions- - : The influence of acid rain on rocks and minerals (part 4)

Abstract: In order to predict the effect of acid precipitation on building stone, artificial chemical weathering of polished plates of Muroto Gabbro from Kochi, Shikoku Island, Japan, was conducted. An improved Soxhlet extraction apparatus was used with distilled water and HNO 3 , H 2 SO 4 and HCl solutions at pH 4 at 55°C for different periods of time up to 780 days. The gabbro was composed mainly of olivine (Fo 66 Fa 34 ), plagioclase (Ab 33 An 66 Or 1 ), and clinopyroxene (En 47 Fs 13 Wo 40 ). Morphological and chemical changes of each mineral surface were studied by SEM, EPMA and optical microscopic techniques. Alteration products were collected from the surface of each mineral on the polished plates by hand picking and examined using XRD. The leached sample solutions were analyzed for major and minor elements using ICP-AES, ICP-MS and ion-chromatography. It is evident that olivine changed into smectite, chlorite and talc 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 clinopyroxene were not detected. Molar ratios of each element in the leached solutions to those in the fresh gabbro varied depending on the experimental period. The ratios of elements such as Mg, Mn, Fe, Ni, Zn and Co, which reflect the dissolution of olivine, were relatively high. Similarly, the ratios of Ca, Na, Sr, Ce, Sm and La, which reflect the dissolution of plagioclase, were relatively high. It seems, therefore, that olivine and plagioclase are easily weathered. It was also estimated from the molar ratios that the reactivity order of the acid solutions for olivine and plagioclase is H 2 SO 4 , HNO 3 and HCl.

Mineralogy of soils from different agroecological regions of bangladesh : region 26-high barind tract

Abstract: 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 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 ten soils from seven important soil series of AEZ 26, High Barind Tract, has been reported in this paper. The soils were slightly acidic in nature, had moderate to high amounts of clay, and the texture was medium (silt loam) to heavy (silty clay). The 20-53 μm fraction was found to dominate over other fractions in most soils. The 2-20 μm fraction was composed mainly of quartz, followed by mica, plagioclase, K-feldspar and chlorite. Mica was the predominant mineral in the <2 μm clay fraction followed by kaolinite. The interstratified minerals of kaolinite and smectite and of mica, vermiculite and smectite were present indicating the highly weathered nature of these soils. The impact of mineralogy on the inherent potentiality of soils regarding crop production has been discussed.

Orientational Order in Clay Gels

Abstract: This article describes the nematic-like orientational order of exfoliated platelets in concentrated smectite clay gels. At concentrations larger than a few percent (w/w), clay gels are strongly birefringent, which is usually associated with nematic liquid-crystalline ordering. This means that the clay platelets tend to align parallel to each other in a cooperative way. Indeed, very oriented samples can easily be prepared and their SAXS patterns are strongly anisotropic, resulting in nematic order parameters of S 0.55 quite comparable to those of common organic liquid crystals used for display applications. Even though the sol/gel transition occurs at concentrations lower than the isotropic/nematic one, nematic ordering appears in concentrated clay gels and it must be considered in most practical situations.

Exfoliation of Layered Transition Metal Oxides: Formation of Functional Oxide Nanosheets and Their Applications

Abstract: Unilamellar two-dimensional crystallites of transition metal oxides, Tio .9102, Ca2Nb3O10 and Mn02, have been derived by delaminating layered host precursors via intercalation of quaternary ammonium ions. The nanosheets are characterized by their high two-dimensional anisotropy with a molecular thickness, and this structural feature yields novel physicochemical properties. A range of useful nanostructured materials can be fabricated by organizing these nanosheets as a building block through various wet processes. Flocculation induced by the addition of appropriate cationic species can produce restacked lamellar aggregates, through which functional materials, e.g. porous or fluorescent materials, can be designed by the selection of the nanosheets and combined flocculating agents. The sequential adsorption procedure via electrostatic self-assembly can be employed to deposit the nanosheets layer-by-layer with polycations, which can lead to multilayer ultrathin films and hollow nanospheres.

HYDROTHERMAL SYNTHESIS AND PHYSIOCHEMICAL PROPERTIES OF Ni-HECTORITE

Abstract: Hectorite containing Ni 2+ instead of Mg 2+ in the trioctahedral sheets has been synthesized at 300°C for 12 h under autogenous water vapor pressure by hydrothermal reaction of four kinds of starting slurry with the initial molar ratios Na:Ni:Li:Si = 07:54:06:80, 14:54:12:80, 14:48:12:80 and 14:48:12:75 made from Ni-Si homogeneous precipitates, lithium fluoride and sodium hydroxide The resulting Ni-hectorite has been characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrophotometry (FT-IR), thermogravimetry and differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry The Ni-hectorite is relatively large massive plate-like particles with a characteristic tint of green and has similar structure to other hectorites, a smaller cation exchange capacity (CEC) and lower adsorptive ability of methylene blue (MB) compared to a commercial Mg-hectorite and a synthetic Zn-hectorite as reference It has also been clarified that the Ni-hectorite modified electrode shows a redox reaction Ni 2+ to Ni 3+ and Ni 3+ to Ni 2+ in cyclic voltammetry

Clay mineralogy of red-yellowish soils distributed in hilly mountain area neighboring the eastern part of fukui plain, central japan

Abstract: The clay-mineralogical characteristics were examined in two Yellow Brown Forest soils distributed in the hilly mountain area neighboring the eastern area of Fukui plain, Central Japan. The subsoil in one of the two soils was the buried horizons considered to be the paleosol. The results were summarized as follows: In those two soils, chlorite-vermiculite intergrade was predominant in the clay fractions, and the chlorite contents were increased in the surface soils, which were characterized by the Yellow-Brown Forest soils. The presence of chlorite-vermiculite intergrade accompanied by small amounts of chlorite and mica minerals suggested that they were influenced by the eolian dust transported from the Asian continent. Halloysite was found in the clay fractions of those soils and was derived from the autochthonous material which is the weathered tuffaceous rock. Gibbsite derived from the autochthonous material was also present in the clay fractions, and its content was especially high in the KZP soil.

Evaluation of egyptian glauconitic clay

Abstract: Samples of Egyptian glauconitic material from El Gidida area were investigated. The characterization study included the mineralogical and chemical composition, crystal morphology, surface area and porosity. The effect of heat treatment and acid activation on the surface area, pore volume and microporosity of glauconitic clay was also investigated. Data obtained by using Scanning Electron Microscope (SEM), X-ray diffraction (XRD), X-ray Fluorescence (XRF), and Infrared (IR) spectroscopy, reveal that the studied glauconitic material is di-octahedral with an iron-rich illite-smectite mixed layer composed of a range of expandable layers (<10 to 40%), in addition to variable percentages of kaolin and quartz. As the relative amounts of kaolin and quartz increased, illite-smectite mixed layers decreased. Low K 2 O content in glauconitic material is related to the composition of the parental glaucony mineral phase as well as to destabilization of glauconite. Morphologically, glauconite pellets consist of spheroidal aggregates of very fine particles, arranged parallel to each other, and separated by debris. However, many of the platelets are bent and curly, generating numerous mesopores. The surface area and pore volume ranged between 80-147 m 2 /g and 0.164-0.341 cm 3 /g, respectively. Details of the above characterization studies are given in this paper.

Mineralogy of soils from different agroecological regions of bangladesh : region 12-low ganges river floodplain

Abstract: 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 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 ten soils consisting of nine representative soil series of AEZ 12, Low Ganges River Floodplain, has been reported in this paper. The clay content of the surface soils ranged from 18.6 to 35.7% and the texture was mostly silt loam. The 2-20 μm silt fraction was found to dominate over other fractions in almost all soils. This fraction was composed mainly of quartz, followed by mica, plagioclase and chlorite. Mica and smectite were predominant minerals in the <2 μm clay fraction. The impact of mineralogy on the inherent potentiality of soils regarding crop production has been discussed.