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Vermiculite
About: Vermiculite is a research topic. Over the lifetime, 2320 publications have been published within this topic receiving 37142 citations.
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TL;DR: In this paper, the metal adsorption properties of vermiculite were investigated and the batch sorption kinetics can be described by a first-order reversible reaction and equilibria follow the Freundlich adsorptive isotherm.
30 citations
TL;DR: The kinetics and thermodynamics of Pb(II) adsorption on vermiculite have been studied by the sets of experiments at various conditions (temperature, initial lead concentration and adorption time) as discussed by the authors.
Abstract: The kinetics and thermodynamics of Pb(II) adsorption on vermiculite have been studied by the sets of experiments at various conditions (temperature, initial lead concentration and adsorption time). The structures of the vermiculite before and after Pb(II) adsorption were measured using X‐ray diffraction (XRD), thermogravimetric analysis (TA), and X‐ray photoelectron spectroscopy (XPS). Adsorption of Pb(II) was strongly affected by pH. First order kinetics model best described the reaction rate, and the adsorption capacity calculated by the model was consistent with that actual measurement. Isotherms for the adsorption of Pb(II) on vermiculite were developed and the equilibrium data fitted well to the Langmuir and Freundlich models. Thermodynamic parameters such as enthalpy, entropy, and free energy were calculated using the Van't Hoff equations. The thermodynamics of Pb(II) on vermiculite indicates the spontaneous and endothermic nature of adsorption. Quantitative desorption of Pb(II) from vermic...
30 citations
TL;DR: In this article, the alkylammonium adsorption method for the determination of layer-charge density was slightly modified and applied to mixtures of expandable clay minerals (i.e. predominantly 18 A minerals after glycerol sorption) from two loess samples and two soils (Haplaquept and Aquentic Chromudert) having different K-adsorption properties.
Abstract: A B S T R A C T : The alkylammonium adsorption method for the determination of layer-charge density was slightly modified and applied to mixtures of expandable clay minerals (i.e. predominantly 18 A minerals after glycerol sorption) from two loess samples and two soils (Haplaquept and Aquentic Chromudert) having different K-adsorption properties. The layer-charge density of the so-called 18 A minerals from these sediments and soil samples varied between --0.23 and -0.85 per formula unit, which suggested the presence of different amounts of vermiculite within the 18 A minerals. The amounts of these vermiculites were related to K-fixing and K-buffering properties of the different samples. High-resolution electron micrographs of vermiculites saturated with tetradecylammonium exhibited a basal spacing of 25 .A. It was confirmed, that the alkylammonium ions in the interlayers of the vermiculites formed a paraffin-type structure. In the fine clay from the loess samples an interstratification of vermiculite and illitic layers was observed. In order to understand the cation exchange behaviour of soils containing smectites and vermiculites it is important to quantify these two mineral species. The direct measurement of the expansion of layer-silicates may help to explain the adsorption/desorption behaviour of expandable clay minerals in sediments and their relation to clay mineral transformation in soils. Knowledge of the layer charge is also essential to differentiate smectites from vermiculites. Glycerol and ethylene glycol methods are probably not adequate for this purpose, though they have been in common use for some time (Brindley, 1966). Adsorption of n-alkylammonium ions offers a way of measuring the layer-charge density of smectites and vermiculites and also the charge heterogeneity of low-charge vermiculites (Lagaly & Weiss, 1971; Lagaly et al., 1976; Lagaly, 1981, 1982). The alkylammonium ions are arranged with their chains lying flat or tilted (paraffin-type), the former being typical for low-charge silicates and the latter for high-charge ones (Stul & Mortier, 1974; Lagaly & Weiss, 1975). Special embedding and sectioning procedures (Vali, 1983) allow n-alkylammonium-saturated silicates to be cut perpendicular to the a-b plane; because of the stability of expanded n-alkylammoniumsaturated layer-silicates, the layer distances are preserved. Electron micrographs show clearly the layer-sequence in clay mineral mixtures from sediments and soils. Although some information on the use of the n-alkylammonium procedure for the determination of layer-charge heterogeneity of pure clay minerals is available, such information on mixed clay fractions from soils and sediments is scanty. The purpose of the present investigation was to determine the layer charge of the 'glycerol 18/~ clay mineral
30 citations
TL;DR: In this paper, the radioactivity cochromatographed with 4-(or 6-)chloroindolyl-3-acetic acid and its methyl ester was found near these chlorinated indolyl acetic acid markers.
Abstract: Immature seeds were harvested from 15 species grown in perlite/vermiculite containing 36Cl-, but with very low levels of cold Cl-. Autoradiograms of one- and two-dimensional thin layer chromatograms of butanol extracts of lyophilized seeds indicated several radioactive compounds besides the 36Cl- in many species. In pea the radioactivity cochromatographed with 4-(or 6-)chloroindolyl-3-acetic acid and its methyl ester; in other species radioactivity was found near these chlorinated indolyl-acetic acid markers.
30 citations
TL;DR: In this article, it is demonstrated that X-ray photoelectron diffraction can be used to differentiate between equivalent, near-equivalent, and nonequivalent sites occupied by two elements either in one single crystal or in crystals of closely similar structure, even when the element(s) concerned comprise only a small fraction of the crystal and when the sub-lattice lacks both long and short-range order.
Abstract: Angle-resolved X-ray photoelectron spectra of freshly exposed cleavage planes of muscovite, lepidolite, phlogopite, and both natural and Pb-exchanged vermiculite are interpreted to yield both quantitative elemental analyses relating to the outermost 100 A of the crystals and a wealth of structural information, the latter from consideration of phenomena resulting from diffraction of the photo-emitted electrons. It is demonstrated that X-ray photoelectron diffraction can be used to differentiate between equivalent, near-equivalent, and non-equivalent sites occupied by two (or more) elements either in one single crystal or in crystals of closely similar structure, even when the element(s) concerned comprise only a small fraction of the crystal and when the sub-lattice lacks both long- and short-range order. These studies are complemented by extensive chemical analyses, by energy-dispersive X-ray (K-emission) analyses performed in an electron microscope (an elementary calibration procedure for which is outlined) and by X-ray diffraction studies. The muscovite and lepidolite are shown to cleave in regions exhibiting typical bulk composition, whereas the phlogopite and vermiculite both cleave in regions rich in aluminium, and deficient in magnesium (relative to their silicon content). The principal interlayer cations in the vermiculite, potassium and calcium, could be entirely replaced with lead by prolonged refluxing in lead nitrate solution: the lead and calcium are shown to retain their hydration spheres whereas potassium coordinates directly (without hydration) to the layer oxygen, as in the true micas. Some structural implications of these data are evaluated and discussed.
30 citations