Showing papers on "Vermiculite published in 2009"

Plant-driven fungal weathering: Early stages of mineral alteration at the nanometer scale

Abstract: Plant-driven fungal weathering is a major pathway of soil formation, yet the precise mechanism by which mycorrhiza alter minerals is poorly understood. Here we report the first direct in situ observations of the effects of a soil fungus on the surface of a mineral over which it grew in a controlled experiment. An ectomycorrhizal fungus was grown in symbiosis with a tree seedling so that individual hyphae expanded across the surface of a biotite flake over a period of three months. Ultramicroscopic and spectroscopic analysis of the fungus-biotite interfaces revealed intimate fungal-mineral attachment, biomechanical forcing, altered interlayer spacings, substantial depletion of potassium (~50 nm depth), oxidation of the biotite Fe(II), and the formation of vermiculite and clusters of Fe(III) oxides. Our study demonstrates the biomechanical-chemical alteration interplay at the fungus-biotite interface at the nanometer scale. Specifically, the weathering process is initiated by physical distortion of the lattice structure of biotite within 1 μm of the attached fungal hypha. Only subsequently does the distorted volume become chemically altered through dissolution and oxidation reactions that lead to mineral neoformation.

Rapid Clay Weathering in the Rhizosphere of Norway Spruce and Oak in an Acid Forest Ecosystem

Abstract: The mineralogy of bulk and rhizosphere soils was compared to assess the effect of roots on mineral weathering in a Typic Dystrochrept supporting Norway spruce (Picea abies (L.) Karst) and oak (Quercus sessilifl ora Smith). In an experimental forest site (Breuil-Chenue, France), systematic soil sampling was performed in forty pits. The soil adhering to the roots was considered as rhizosphere soil. The remaining material was regarded as bulk soil. The mineralogy of the clay-sized particles of both fractions was determined by x-ray diffraction (XRD). Amorphous solid phases were estimated by extracting Fe and Al with hot Na-citrate and dithionite-citrate-bicarbonate. Total chemical analyzes were performed on the clay-sized particles via BaCl 2 -saturation and an iso-zirconium weathering balance was calculated. The XRD demonstrated an increase of illite-like minerals in the rhizosphere of both species and the selective extractions revealed a decrease in the amorphous phases. The total chemical analyzes showed that the rhizosphere clay-sized fraction contained signifi cantly more Si and K (for oak only) and less Fe and Al than the bulk soil. By way of the iso-zirconium weathering balance, these losses of Fe and Al in the rhizosphere were estimated at several tens of kilograms by hectare for the surface horizon (0-3 cm). This study demonstrates that, despite the short duration of the contact between the active part of a root and the solid mineral phase, the intensity of the processes occurring in the rhizosphere signifi cantly increases mineral weathering. Abbreviations: B, bulk soil; BS, base saturation; subscript c, hot Na-citate treatment; CEC, cation exchange capacity; subscript d, dithionite-citrate-bicarbonate treatment; EA, exchangeable acidity; EG, ethylene glycol treatment; HIS, hydroxy-interlayered smectite; HIV, hydroxy-interlayered vermiculite; ICP-AES, inductively coupled plasma spectrometry-atomic emission spectrometry; ICP-MS, inductively coupled plasma spectrometry- mass spectrometry; R, rhizosphere; subscript (tot), total; XRD, x-ray diffraction.

Montmorillonite, vermiculite and saponite based porous clay heterostructures modified with transition metals as catalysts for the DeNOx process

Abstract: Porous clay heterostructures (PCHs) were synthesized from natural montmorillonite and vermiculite as well as synthetic saponite using the surfactant directed method. The direct synthesis of PCHs from saponite and montmorillonite was possible, while the pre-treatment of parent vermiculite with acids was necessary prior to the intercalation step. The PCH samples were characterized with respect to their composition (EPMA), structure (XRD, UV–vis-DRS), texture (BET), surface acidity (FT-IR) and chemical nature of the deposited transition metal species (UV–vis-DRS). Porous clay heterostructures as well as their derivatives modified by deposition of transition metal (Cu, Fe) oxides were tested as catalysts for the DeNOx process. The transition metal containing PCH samples were found to be active, selective and stable catalysts of this process. Their catalytic performance depended on the kind of the parent clay used for the PCH synthesis as well as deposited transition metals.

Water Remediation by Adsorption of Phenol onto Hydrophobic Modified Clay

Abstract: In this work we studied the phenol sorption from contaminated water onto modified clay mineral vermiculite and bentonite by insertion of hexadecyltrimethylammonium in the interlayer of clays. The non modified clays showed negligible interaction with phenol. The experimental data were treated using the Freunlich equation which had a good fit. The removal percentages were higher than 35% for modified vermiculite and for modified bentonite, 30%. Vermiculite and bentonite were compared for the removal of phenol from an aqueous solution based on the maximum adsorption capacity of each adsorbent, and no significant difference was found. The adsorption mechanism for both is the same, according to the results. Although, there is a lack of studies using vermiculite for this purpose, it can be concluded that hydrophobic modified vermiculite is very effective for removing phenol from water. Hydrophobic modified bentonite also remove phenol, but in lower proportions.

Effects of Modified Vermiculite on Water Absorbency and Swelling Behavior of Chitosan-g-Poly (Acrylic Acid)/Vermiculite Superabsorbent Composite

Abstract: In this study, a series of chitosan-g-poly(acrylic acid)/vermiculite (CTS-g-PAA/VMT) superabsorbent composites containing VMT, acid-activated, ion-exchanged, and organic modified VMT were synthesiz...

Terahertz Time-Domain Spectroscopy of Selected Layered Silicates

Abstract: Micaceous layer silicate clay minerals are attractive materials for applications involving non-linear optics because of their low cost and ability to form well ordered, platy aggregates, but such applications require precise knowledge of the dielectric behavior of the clay. The purpose of the present study was to use Terahertz time-domain spectroscopy (THz-TDS) to determine the dielectric properties of certain cleavable layered clay minerals, including muscovite, vermiculite, phlogopite, and biotite. The samples were characterized by X-ray diffraction and Fourier transform infrared spectroscopy as well as chemical analysis by Energy dispersive X-ray spectroscopy. The THz frequency window investigated was the far-infrared region of 3.3 to ∼40.0 cm−1 corresponding to 0.1 and 1.2 THz, respectively. The samples were selected so that the hydrated form of the interlayer cation, e.g. Mg2+ present in the interlayer gallery of vermiculite, could be compared to species such as phlogopite, biotite, and muscovite with the dehydrated form of interlayer cations such as K+ or Na+. The frequency-dependent complex index of refraction of these natural materials was determined to vary between 2.50 and 2.80. The presence of water in the interlayer space of vermiculite was reflected in the detection of increased values of the absorption index in comparison with the muscovite, phlogopite, and biotite.

Efeito da dose de nitrogênio e de formulações de substratos na miniestaquia de Eucalyptus dunnii maiden

Abstract: The aim of this study was to determine the influence of different nitrogen doses and substrate formulations on the minicutting technique of Eucalyptus dunnii Maiden. The clonal minigarden of 90-day- old seedlings was cultivated in the commercial substrate of pine bark and vermiculite (tubes of 55 cm3). The dose test used a unique source (NH4NO3) in the following concentrations of N: 0.2; 0.4 and 0.6 g L- 1. Each ministump was weekly watered with 10 mL of the tested solution. Five different substrate mixtures were tested: a commercial substrate with pine bark special, medium size vermiculite, carbonized rind of rice and incorporated fertilization. The survival of ministumps in the nitrogen doses tested was 100% until the 10th collection, after which, it was observed mortality in 0.4 treatment (1 ministump). All the evaluated characteristics showed direct relation to the N doses tested. The higher values were achieved with higher doses. The substrates presented statistical differences in the survival and formation of seedlings (collar diameter and height) and vegetative vigor of seedlings. In conclusion, the minicutting technique of E. dunnii is influenced by the nitrogen fertirrigation and the substrate. It is suggested the dose of 0.6 g L-1 and the substrate formed by the commercial substrate with pine bark and vermiculite + medium size vermiculite + carbonized rind of rice (1:1:1) + incorporated fertilization.

Heat resistant phosphate cement

Abstract: A phosphate cement composition is provided. The cement composition comprises about 10 to 40 percent by weight calcium or magnesium oxide, about 10 to 40 percent by weight acid phosphate, and about 10 to 50 percent by weight vermiculite or perlite or mixture thereof.

CATION EXCHANGE REACTIONS OF VERMICULITE WITH Cu-TRIETHYLENETETRAMINE AS AFFECTED BY MECHANICAL AND CHEMICAL PRETREATMENT

Abstract: The cation exchange capacity (CEC) is a characteristic property of expandable clay minerals, such as smectites and vermiculites. The aim of this work was to examine the cation exchange behavior of vermiculite using the Cu-triethylenetetramine (Cu-trien) CEC method and the influence of mechanical and chemical pretreatment, with the ammonium acetate method serving as a reference. The Cu-trien method makes rapid and direct CEC measurements possible. Three different kinds of mill were used to grind a vermiculite sample from Russia, in order to reduce the particle size to <10 μm. The Netzsch CGS 10 dry mill reduced the particle size more effectively than the other grinding methods. Chemical pretreatments were used to remove carbonates, organic matter, Fe oxides, and divalent exchangeable cations from vermiculite samples prior to CEC measurements. Subsamples of ground and chemically pretreated vermiculite samples were saturated with Na, Li, Mg, Ca, and Cu cations to determine the effect of exchangeable cations on measured CEC values. Chemical pretreatment, monovalent cation pretreatment, and 48 h of shaking time were needed to measure vermiculite CEC values effectively using the Cu-trien method.

Enhanced Biodegradation of Naphthalene and Anthracene by Modified Vermiculite Mixed with Soil

Abstract: Hydrophobic modified vermiculite mixed with soil was investigated in biodegradation experiments of naphthalene and anthracene. The experiments had been carried out on mixtures of soil and vermiculite at a proportion of 2%, 10%, and 15% and also in the absence of clay used for control. Biodegradation of the pollutants was followed by the decline of naphthalene and anthracene concentration, measured by CG. Compound mineralization was also proved by the evolution of CO2. The results showed that in the mixture with a higher proportion of vermiculite biodegradation is enhanced compared to that performed in the absence of vermiculite. In general, when vermiculite proportions are increased, the rate of degradation increases, which may account for the bioavailability of compounds. Bioavailability is an important factor for the degradation of compounds with low solubility. Comparison of biodegradation rates shows that naphthalene is degraded faster than anthracene. The chemical structure could be responsible for this observation. However, although we did not identify the microorganism that was in the soil, we can conclude that vermiculite could be an alternative for the bioavailability of such compounds. Vermiculite in the modified form could also be very useful as a barrier to retain organic pollutants in accidental spills.

Equilibrium and Thermodynamic Studies of Cesium Adsorption on Natural Vermiculite and Optimization of Operation Conditions

Abstract: Removal of cesium from synthetic aqueous solution through adsorption on vermiculite, under batch equilibrium experimental condition at six initial values of pH (3, 4, 6, 9, 11 and 12) and five temperatures (25, 50, 75, 85 and 95 °C) has been investigated. It is necessary to propose a suitable model for a better understanding of the mechanism of cesium adsorption on vermiculite. For this propose the suitability of the Langmiur, Freundlich and Redlich-Peterson (R-P) adsorption models for equilibrium data were investigated. The parameters in the adopted adsorption isotherm models were determined by Eviews software. The study of equilibrium isotherm shows that the best model for analysis of experimental data is Redlich-Peterson model with correlation coefficient higher than 0.99(both for temperature and pH). The results showed that increasing of pH and temperature increased the adsorption ability of vermiculite. Optimum conditions for adsorption were determined as T=75 °C, pH=9, vermiculite dose=1.5 g and contact time of 24 hr. Finally the thermodynamic constants of adsorption phenomena, DH° and DS° were found to be 2.672 kJ/mol and 0.563 kJ/mol K in the range of 25-95 °C respectively. The negative value of the Gibbs free energy DG demonstrates the spontaneous nature of cesium adsorption onto vermiculite.

Thermal characterization of polypropylene/vermiculite composites

Abstract: Vermiculite clay (VMT) was organically modified with a quaternary organic salt and added to polypropylene (PP). The compounds were prepared by melt intercalation using a twin extruder. The morphology of the composites was investigated through wide-angle X-ray diffraction (WAXD). The WAXD results suggested that exfoliation phenomena were found for the composites with modified clay. The thermal properties of the obtained composites were studied by means differential scanning calorimetry (DSC) and thermogravimetry (TG) measurements. A variation in the crystallinity of PP was found. A significant increase of the thermal stability of PP was achieved in the presence of the modified VMT.

Mineralogical composition of shallow soils on basic and ultrabasic rocks of East Fennoscandia and of the Ural Mountains, Russia.

Abstract: The influence of epigenetic (pre-pedogenetic) alteration of basic and ultrabasic rocks leading to the formation of phyllosilicate mineral associations is not well known The purpose of this study was to gain further understanding of the processes involved by investigating the mineral associations of shallow soils underlain by amphibolites and metamorphosed gabbro-diabases (East Fennoscandia) and by serpentinous dunites (olivinite) and metagabbro amphibolites (the Ural Mountains) Where phyllosilicates were absent from the bedrock, they were also absent from the sola The pedogenic alteration of the initial mineral soil matrix was very weak and did not result in a significant accumulation of phyllosilicates in the soils (East Fennoscandia) Pedogenesis enhanced the transformation of phyllosilicates, a process initiated by epigenic rock alteration Phyllosilicates in the sola from basic and ultrabasic rocks of the Polar Urals were largely inherited according to their origin The inherited phyllosilicate association of the sola from ultrabasic rocks included talc, serpentine, and chlorite Saponite resulted from pedogenesis; its distribution in various thin soils depending on the processes of neoformation and decomposition, the latter probably taking place under the influence of lichens and moss Chlorite and illite and products of their transformation, including vermiculite, comprise the phyllosilicate association of a solum from basic rock, and traces of talc were found The distribution of vermiculite and randomly interstratified chlorite-vermiculite (C-V) depended on the processes of chlorite vermiculitization and vermiculite decomposition

Physicochemical characteristics for adsorption of MTBE and cadmium on clay minerals

Abstract: Physicochemical characteristics relevant to the adsorption of MTBE and Cd on three types of clay minerals were investigated. The characteristics were examined through batch adsorption tests conducted under various experimental conditions such as adsorption time, ratio of solution-to soil, concentration of solutes, concentration of organic matters, pH, and zeta potential. The adsorption efficiency of MTBE or Cd on three types of clays decreased in response to an increase of the ratio of solution-to-soil; nevertheless, the adsorbed amounts inversely increased. MTBE was adsorbed on clays in an increasing order of vermiculite, bentonite, and CTAB-bentonite. However, Cd was adsorbed in a different order of bentonite, vermiculite, and CTAB-bentonite. The adsorption of MTBE was well fitted with the Freundlich model, whereas the Cd was more closely suited to a Langmuir equation. By adding humic acids of 1 and 5%, MTBE was significantly adsorbed on bentonite and vermiculite, respectively, but beyond that, its adsorption was diminished. In comparison, the adsorption on CTAB-bentonite was increased in proportion to the humic acids addition. Likewise, the addition of humic acids acted to increase the adsorption of Cd regardless of the types of adsorbent, where up to 90% of Cd was removed at pH 10. Further increase of pH declined the degree of zeta potential, while increasing Cd concentration also lowered the zeta potential, which consequently contributes in enhancing the adsorption efficiency of Cd on clays.

Preferential Sorption and Desorption of Organic and Inorganic Phospates by Soil Hydroxyinterlayered Minerals

Abstract: The purpose of this study was to assess the potential of soil clays rich in hydroxyinterlayered vermiculite (HIV) and smectite (HIS) minerals to adsorb and release P after interaction with a mixture of inorganic and organic P forms as compared with geologic reference gibbsite and goethite mi

Effect of Active Filler Addition on the Ionic Conductivity of PVDF-PEG Polymer Electrolyte

Abstract: A novel composite microporous polymer electrolyte based on poly(vinylidene fluoride), PVDF, poly(ethylene glycol), PEG, and Li-exchanged vermiculite(Li-VMT)was prepared by a simple phase inversion technique The prepared membrane was subjected to XRD, SEM, impedance spectroscopy The incorporation of Li-exchanged vermiculite greatly enhanced the ionic conductivity and solvent uptake as compared to the membrane without Li-exchanged vermiculite The Li-exchanged vermiculite plays a active role in ion transport since relatively large platelets serve as the anion and allowed for exceptionally large Li transference numbers

Method for preparing molecular self-assembly porous vermiculite air purification material

Abstract: The invention relates to a method for preparing a molecular self-assembly porous vermiculite air purifying material. The method comprises that: (1) vermiculite is subjected to acid cleaning, alkali cleaning and alcohol cleaning sequentially; and finally, the vermiculite is washed by deionized water and dried; (2) the vermiculite is soaked in a 0.01 to 0.1mol/l surfactant solution; after the surface of the vermiculite is assembled with a layer of organic unimolecule film, the vermiculite is taken out; a surface physical adsorption composition is washed out; and the vermiculite is dried in vacuum; (3) the vermiculite is soaked in 0.15 to 0.35 mol/L sol; an SnCl2 solution is taken out and injected to the sol; PdCl2 is taken out and dripped to the sol; the mixture is kept stand, stirred and separated; a loose layer is washed out; and the mixture is dried; and (4) the step (2) and the step (3) are repeated for three to four times; and the mixture is calcined to obtain the molecular self-assembly porous vermiculite air purifying material. The preparation method is simple, easy to operate and suitable for industrial scale production; and the prepared air purifying material has good air purifying effect.