Showing papers in "Clay science in 1998"

Boron Adsorption on Allophane with Nano-ball Morphology.

Abstract: Two types of reaction scheme were proposed for boron (B) adsorption at equilibrium B concentrations of less than 2 mM on nano-ball shaped allophane with its fundamental structure of aluminum orthosilicate. (i) Al-OH + B(OH) 3 → Al-O-B(OH) 2 + H 2 O (ii) Al-OH + B(OH) 4 - → Al-(OH)-B(OH) 3 + OH - With the aluminol groups (Al-OH) included in the structure, the reaction (i) occurs below equilibrium pH of about 10, whereas the reaction (ii) does at equilibrium pH of higher than about 8. Calculated Langmuir parameters suggested that the aluminol groups of nano-ball allophane had higher affinity for B(OH) 4 - than B(OH) 3 . Because the content of the aluminol groups increase with decreasing Si/Al ratio of allophane, B adsorption maxima were higher for KyP sample (Si/Al=1.34:2) than for KnP sample (Si/Al =1.98:2) irrespective of equilibrium pH. Release of Si from allophane samples during B adsorption on them was much smaller than the case of phosphate P) adsorption previously studied. This indicates that B has less ability than P for replacing Si in the structure of nanoball allophane and the main B adsorption site is the aluminol group at the pore of the allophane nano-ball.

Formation of layer-by-layer composite films by the Langmuir-Blodgett technique : Smectite-amphiphilic ruthenium(II) complex systems

Abstract: Organized organic-inorganic ultrathin films have been constructed from the fabrication of smectite unit layers and an amphiphilic ruthenium (II) complex monolayer using the conventional Langmuir-Blodgett (LB) technique. According to the method, a chloroform solution of an amphiphilic ruthenium (II) complex, [Ru(phen) 2 (dC18bpy)] 2- (phen = 1.10-phenanthroline, dC18bpy = 4,4'-dioctadecyl-2,2'-bipyridyl as shown in Figure. 1), was spread onto an aqueous subphase containing either exfoliated saponite or hectorite suspension. Brewster angle microscopy (BAM) observation showed that Ru(II) complex molecules formed a self-assembled monolayer on a water surface and that clay particles were adsorbed by the monolayer from an aqueous subphase. A composite film of a Ru(II) complex and a clay particle thus formed was transferred onto a hydrophilic glass plate by the vertical dipping method. The surface structure of a deposited film was studied with an atomic force microscope (AFM). As a results, a glass substrate was covered with the single sheet of a clay on which amphiphilic metal complexes were attached.

OXIDATION OF CHROMIUM (III) TO CHROMIUM (VI) BY A SERIES OF SYNTHESIZED BIRNESSITES (σ-MnO2): KINETICS AND OXIDATION CAPACITY

Abstract: Reduction and oxidation reactions of chromium (Cr) have attracted the interest of environmental scientist because the toxicity and mobility of Cr in soils and geologic materials are depending on its oxidation state. In this study, the oxidation of immobile and nontoxic Cr (III) to mobile and toxic Cr (VI) by a series of synthesized birnessites (δ-MnO 2 ) with different crystallinity in aqueous environment was tested. The oxidation rates were initially fast and followed by a sharp rate decline after 1 hour equilibration. The oxidation of Cr (III) to Cr (VI) by birnessites favored lower pH. higher initial Cr (III) concentration, and higher ratio of birnessite surface area to solution volume when the other two factors are fixed. The combination of high pH and high initial Cr (III) concentration reduced Cr oxidation rate. Chromium oxidation capacity of birnessite increased with a decreased crystallinity.

Crystal structure of dehydroxylated 2M1 sericite and its relationship with mixed-layer mica/smectite

Abstract: Crystal structure of dehydroxylated 2M 1 sericite from Goto mine, Nagasaki Prefecture, Japan was investigated, and was compared with the crystal structure of unheated 2M 1 sericite. The crystal structure of the dehydroxylated 2M 1 sericite showed different site cation occupancies in interlayers. Density distribution in interlayers showed alternating different densities. It was confirmed that the formation of regularly interstratified mica/smectite from the dehydroxylated 2M 1 sericite is attributed to the crystal structure of dehydroxylated 2M 1 sericite.

Effect of the surface potential on the cation exchange capacity of kaolin minerals

Abstract: The characteristics related to surface charge were investigated for various kind of kaolin minerals. Two types of kaolin minerals were used, one from weathering and sedimentary origins, Shinagawa-kibushi and Hara-gairome, and the other from hydrothermal origins, Georgia-kaolin and dickite. They were chemically treated in order to remove the organic species and ion-exchanged with Na + . The surface potential obtained from the variation of zeta potential and the cation exchange capacity (CEC) were studied for neutral kaolin minerals. A positive correlation exists between the surface potential and the CEC, and the CEC depends directly on the surface potential on the particle. The surface potential was larger for clays of weathering and sedimentary origins, Shinagawa-kibushi and Hara-gairome, than that of the hydrothermal originated Georgia-kaolin and dickite. The surface potential among kaolin minerals depends on the thickness of the edge plane and increases with a decrease in the crystallite size. Therefore, Shinagawa-kibushi and Hara-gairome which have large surface potential, have a large water film thickness due to the large amount of absorbed cations.

Characterization of microporous silica prepared by selective leaching of calcined kaolinite : effect of calcining temperature

Abstract: Microporous silica was prepared by selective leaching of the Al 2 O 3 component from calcined kaolinite. The kaolinite was calcined at various temperatures from 400 to 1000°C for 24 h. It was then chemically treated with a 20 mass% H 2 SO 4 solution at 90°C for 2h and the effect of the calcining temperature was studied. The chemical composition of the acid leached product changed largely by elevating the calcining temperatures from 425 to 475°C owing to selective leaching of Al 2 O 3 from metakaolinite and became almost SiO 2 composition above this calcining temperatures. With decreasing of Al 2 O 3 content in the products, the specific surface area increased and became higher than 300 m 2 g -1 . It further increased gradually with higher calcining temperature up to 700°C because of the increase of efficiency of selective leaching. The pore size distribution was calculated by the Horvath-Kawazoe method based on Ar gas isotherms and the slit-shaped pore size was about 0.6 nm in width for all the products with irrespective to the calcining temperatures. Since the particle shape was preserved after the leaching treatment, those pores are considered to be formed in the interlayers of the SiO 4 tetrahedral layers largely preserving the original metakaolinite structure.

Disappearing trend of smectite in ganges floodplains soils of bangladesh

Abstract: Eleven soils from different Ganges Floodplains of Bangladesh were studied to investigate the clay mineralogical composition and to clarify the relationship between disappearance of smectite and decalcification of calcareous floodplain soils occurring in these areas. In general, mineralogical composition of calcareous floodplain soils were dominated by mica and smectite, and in some cases by vermiculite. Chlorite and kaolinte were also present in minor amounts. Amjhupi and Gangni soils on ridges and Ghior (1) soil in a basin had the lower smectite as well as carbonate contents in Ap and B2 horizons than in the corresponding C horizon. However, all horizons having low carbonate content did not always show the lower smectite content, possibly due to near-neutral reaction or due to difference in the rate between decalcification and disappearance of smectite. Complete disappearance of smectite was observed in Tahirpur soil and partial disappearance in Baradi soil; both are situated on the non-flooded highland and thoroughly decalcified and considered to be in the oldest soil formation in Ganges Floodplains of Bangladesh. Based on the assigned age of the soils, smectite disappearance was estimated to be in the order of 2500-3000 years.

Characterization of kaolin/smectite mixed layer mineral in paleudult of Java Island

Abstract: In a Paleudult of Java Island, there was a clay mineral indicating a mixed layer mineral which gave 15.51 A peak (in the range of 14.63 A and 16.37 A) on Mg 2+ -air dry and a 20.55 A peak on Mg 2+ -glycerol solvation. On K - -saturation, the mineral showed an 11.87 A peak and this peak was continuous to 7.53 A. Furthermore, on sequential heating, the peak gradually shifted and finally shifted completely to 10.05 A at 550°C in X-ray diffraction (XRD). A peak of 7.53A was also observed in both Mg 2+ - and K + -saturated clays which disappeared after heating at 550°C. The objective of this study was to investigate the characteristics of this mineral. The 060 peak was 1.50 A and suggests the dioctahedral smectite. The Greene-Kelly test on the clay sample suggests beidellite. Formamide solvation that caused a swelling of the 7.53 A peak to 10.05 A suggests the presence of halloysite. The 5M NaOH treatment resulted in a collapse of the 7.53A peak and remained at a sharp peak of 15.50 A (in Mg 2+ -saturated clay). The presence of halloysite was also supported by a SiO 2 /Al 2 O 3 molar ratio of NaOH extractable materials. The NaOH treatment also resulted in an increase of the 11.87 A peak (in K + -saturated clay) to 13.49 A. According to the mineralogical and chemical properties of the clay sample we consider that the mineral is halloysite/beidellite mixed layer mineral.

Mineralogical approach to alternation of different river sediments in meghna floodplains soils of bangladesh

Abstract: Mineralogical studies of some Meghna Floodplains soils, in which the sediments as parent materials were possibly transported by the Meghna, Old Brahmaputra. Jamuna (Brahmaputra), and/or Ganges Rivers, were carried out to determine the contribution of different river sediments in Lower Meghna River Floodplain, Young Meghna Estuarine Floodplain, and the part of Old Meghna Estuarine Floodplain which is surrounded by Ganges Floodplains. In general, mica, smectite, vermiculite. chlorite and kaolinite were the major clay minerals in these soils. Soils of Lower Meghna River Floodplain were dominated by mica, vermiculite and chlorite, and were estimated to be developed from the Jamuna (Brahmaputra) sediments while the contribution of the Meghna/Old Brahmaputra sediments increased towards the surface. The Ganges sediments had apparently no contribution. In contrast, soils of Young Meghna Estuarine Floodplain contained good amounts of smectite and chlorite in addition to mica, and were estimated to be developed from the Ganges and Meghna/Old Brahmaputra sediments. Due to the predominance of smectite in the Ap and B horizons or Ap horizon, soils of the part of Old Meghna Estuarine Floodplain which is surrounded by Ganges Floodplains were estimated to consist of the Ganges sediments in the upper horizons and of the Meghna/Old Brahmaputrta sediments in the lower horizons.

Reaction sequence of sodium montmorillonite under hydrothermal conditions

Abstract: The natural Na-montmorillonite (Tsukinuno mine, Yamagate Prefecture, Japan) was treated under hydrothermal conditions. Temperature ranged between 250 and 500°C at 100 MPa, and run durations ranged between 1 and 150 days. The identification of phases was carried out by the X-ray powder diffraction method. The Greene-Kelly test was applied to distinguish among montmorillonite, beidellite and saponite. The phases identified in the products were plotted in a time-temperature diagram. The diagram showed that montmorillonite below 350°C reacted to the assemblage of mixed-layered phase of smectite and the 1:1 regular interstratification of montmorillonite/beidellite (S/r.i.M-B) + montmorillonite + quartz + analcime, and with increasing temperature transformed to the assemblage of Na-rectorite + quartz + feldspar, through the intermediate phase assemblage of beidellite + saponite + quartz - feldspar. The diagram indicated also that montmorillonite and S/r.i.M-B might be stable clay minerals below 300°C, and that the decomposition of montmorillonite to an assemblage of beidellite, saponite and quartz can proceed in nature below the temperature where rectorite is formed.

Origin of smectite in basin soils surrounded with the miocene hill in imadate, fukui, japan

Abstract: Clay mineral composition of the Holocene soils in the narrow basin of Hattori river, Imadate, Fukui, Central Japan, was compared with that of the Miocene soils on the surrounding hill by means of XRD, DTA, TG and chemical analyses. The results led to a following conclusion: Smectite in the Holocene soils of this basin hardly originated in the Miocene sediments located at both side hills, but in the Miocene ones at the upper stream of Hattori river. This smectite was derived directly from parent materials. Or it was altered secondarily from vermiculite or its related minerals, which had been formed previously in the Miocene soil located at the upper stream, in the Holocene soil exposed alternately to the reductive and oxidative conditions. Smectite in this Holocene soils inside of this basin was brought from the Miocene materials in the upper stream, in either case.

Synthesis of smectite from some clays at atmospheric pressure

Abstract: Smectite was formed from some clays, such as pyrophyllite, kaolinite, sericite and talc by reaction with NaOH solution at 100°C under atmospheric pressure. Smectite was formed well under the condition that the concentration of NaOH was near 2M ∼ 3M. Furthermore, when the reaction time involved is within 50 days, the amount of starting material should be less than 0.5g in 100ml solution to form smectite.