Showing papers on "Vermiculite published in 1998"

Mineralogical Transformation of Bioweathered Granitic Biotite, Studied by HRTEM: Evidence for a New Pathway in Lichen Activity

Abstract: The question of whether clay minerals can be biogenically transformed as a result of lichen activity at the lichen-rock interface remains unresolved. We applied several microscopical and analytical techniques—scanning electron microscopy-back-scattered electron (SEM-BSE), energy dispersive spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM)—in an attempt to address this issue. Unaffected granitic biotite and bioweathered material from the granitic biotite and Parmelia conspersa lichen thalli interface were examined using HRTEM after ultrathin sectioning. The n-alkylammonium treatment of ultrathin sections was carried out in order to study the biogenous mineralogical transformation of the biotite. Microsamples proceeding from unaffected biotite zones demonstrated homogenous 10-A d(001)-value biotite phase. HRTEM images of lattice fringes of samples taken from the lichen-biotite contact zone reveal large areas of both unexpanded (10-A) and randomly and R = 3 distributed expanded (from 14- to 30-A) layers of phyllosilicates identified as interstratified biotite-vermiculite. Results of artificial biotite weathering (replacement of K by Ca ion) also revealed the biotite-vermiculite phase formation, indicating that K release in biotite is one of the mechanisms responsible for interstratified mineral phase formation. Two parallel processes, physical exfoliation of biotite and inter-layer ionic exchange of K and subsequent vermiculite formation, are the mechanisms for biotite bioweathering induced by lichens.

An evaluation of clay minerals as support materials in anaerobic digesters

Abstract: The use of different clay minerals as support materials in anaerobic digestion has been studied. The support materials were evaluated in a batch microdigester and their effect on the digestion process was measured at the beginning of the process (startup) and at an intermediate point of the digestion process when the maximum differences between support materials were observed (working digester). All the systems with support were more efficient than the control (support-free). The following order of purification was established: STARTUP: Bentonite > talc > vermiculite > nontronite > montmorillonite > pyrophyllite > stevensite > sepiolite. WORKING DIGESTER: Sepiolite > stevensite > talc > nontronite > bentonite > montmorillonite > vermiculite > pyrophyllite. Bentonite, montmorillonite, talc and vermiculite were favourable for startup, as they rapidly released Ca2+ or Mg2+ to the medium. The best COD removal efficiencies were obtained with sepiolite and stevensite which release Mg2+ progressively to the medi...

The Formation of Sulfides During Alteration of Biotite to Chlorite-Corrensite

Abstract: Transmission electron microscopy/analytical electron microscopy (TEM/AEM) were utilized to study pyrite and sphalerite inclusions in chlorite or mixed-layer chlorite-corrensite from an analcimized ash bed in the Etalian stage (Middle Triassic), South Otago, New Zealand. These sulfide inclusions occur as elongated crystals up to 1 × 15 µm in size, within lens-shaped voids between separated, deformed (001) layers of (primarily) chlorite and mixed-layer chlorite-corrensite grains of typical detrital shape or chlorite packets in chlorite-mica stacks (intergrowths of chlorite and phengite packets) up to 40 × 150 µm in size. Relict biotite layers within chlorite, mixed-layer chlorite-corrensite and berthierine have textures implying replacement of the former by the latter, whereas in other unaltered samples only fresh biotite was observed. Anatase occurs in otherwise Ti-free chlorite, whereas relict biotite contains significant Ti (0.3 moles per 22 oxygen atoms). No sulfide minerals have been found in fresh biotite and phengite. Mass balance considerations indicate that S and Zn were introduced via pore fluids and that the Fe was provided by the decomposition of biotite to secondary phyllosilicates. The alteration of biotite and the reaction of biotite to form chlorite and pyrite is controlled by aH+/aK+ as well as oxidation of reduced S species or reduction of oxidized S species from solution. Simple calculations with the observed compositions of chlorite and biotite suggest that some of the Fe in biotite was actually removed in solution rather than precipitated in pyrite and chlorite. Similar textures are abundant in ferroan phyllosilicates elsewhere, implying that the mechanism may apply widely to precipitation of sulfides in phyllosilicates during early diagenesis of sediments.

Neutron Scattering Study of Vermiculite−PEO Mixtures

Abstract: A four component clay−polymer−salt−water system, consisting of n-butylammonium vermiculite, poly(ethylene oxide), n-butylammonium chloride, and heavy water, was studied by neutron scattering. The volume fraction of clay in the system and the salt concentration were held constant, at r = 0.01 and c = 0.1 M, respectively, and the volume fraction of polymer v was varied between 0 and 0.04. The addition of polymer, up to v = 0.04, had no effect on the phase transition temperature between the tactoid and gel phases of the clay system. However, even for v values as low as 0.001, the clay plates in the gel phase were more parallel and more regularly spaced than in the system without added polymer. In the gel phase, the lattice constant d along the swelling axis of the clay colloid decreased as a function of the polymer volume fraction, from 12 nm at v = 0 to 6 nm at v = 0.04. This behavior is qualitatively similar to that observed in the vermiculite system with added poly(vinyl methyl ether). Possible mechanisms...

Evaluation of the test-mineral method for studying minesoil geochemistry

Abstract: The test-mineral method was evaluated as a means of assessing the chemical environment and soil processes in mine soils. This study was carried out on lignite mine tailings at As Pontes (northwestern Spain). The spoils are heterogeneous and mainly consist of carbonaceous and noncarbonaceous clays and slates, often containing pyrite. Vermiculite was used as a reference mineral and placed in ion-permeable polyamide bags that were then buried in various reclaimed minesoils. One bag was recovered from each soil after 13,26, and 52 wk and analyzed for pH, elemental composition, exchangeable cations, cation-exchange capacity (CEC), extractable Al and Fe, and mineralogy (x-ray diffractometry [XRD], differential thermal analysis [ DTA ], and thermogravimetry [TGA]). Vermiculite rapidly underwent geochemical and mineralogical changes (in <13 wk). The greatest changes took place in soils developed from minespoils rich in sulfides; exchangeable Na on the vermiculite was replaced with Ca, Mg, Al, or H and there was an important decrease in CEC due to interlayer Al-polymerization. This behavior is typical of an acid environment. By contrast, the CEC of vermiculite in the low-sulfide soils did not change and exchangeable Na (principal cation in original vermiculite) was displaced by Ca, with virtually no involvement of other cations. This test vermiculite proved to be an excellent indicator of the chemical environment of minesoils.

Stability of N-butylammonium vermiculite in powder and flake forms

Abstract: Interaction between n-butylammonium (BA) chloride and vermiculite from Santa Olalla (Spain) has been studied in large flake (5  5  0.1 ram) or ground powder (~<80 txm) samples. The differences in adsorption and decomposition of BA ions in both particle sizes have been established. In the interlamellar space, the BA ion remains unaltered in powder samples, but is degraded in flakes. The experimental results suggest decomposition of the BA in the interlamellar space of vermiculite flakes by breaking of the C-N bond. The degradation of BA takes place over a short period. The variety with BA in the interlamellar space is transformed into a new one, due to the degradation of alkylammonium. The transformation occurs through an interstratified phase formed between BA-vermiculite and NH:vermic- ulite, and finally a phase appears in which only ammonium is present in the interlamellar space. Due to the many industrial applications of alkylammonium-clays, determination of the stability of alkylammo- nium in the interlamellar space of clay minerals is of great importance.

Changes in kaolinite, vermiculite, and smectite clays after adsorption by hydroxy-chromium species

Abstract: Kaolinite, vermiculite, and montmorillonites were treated with solutions containing hydroxy-chromium (OH-Cr) species. The OH-Cr solution was prepared by adding 0·2 М NaOH to 0·1 М chromium nitrate solution and allowing the solution to stand at 60°C for 1 day. The samples were characterised by chemical analyses, N2 adsorption-desorption isotherms, and X-ray diffraction. The textural and structural behaviours of kaolinite, vermiculite, and the montmorillonites were analysed in the original samples and after treatment with the polymeric OH-Cr species. The montmorillonites showed higher retention of chromium (19·20%), higher basal spacing (2·06 nm), and higher micropore surface area (276 m2/g) than the vermiculite (3·70%, 1·49 nm, 13 m2/g) and kaolinite (1·15%, 0·73 nm, ~1 m2/g) clays after treatment with the OH-Cr species. In contrast, the external surface area increased from 6 to 9 m2/g for kaolinite and from 18 to 24 m2/g for vermiculite, and decreased from 7 to 4 m2/g for montmorillonite after treatment with the OH-Cr solution. The residual chromium, basal spacing, and texture of the clays after treatment with the OH-Cr species were primarily related to the magnitude of the negative charge originating from the octahedral sheet.

Clay minerals of clayey subsoils of weichselian age in the zealand-funen area, denmark

Abstract: The distribution of clay mineral constituents of clay-size particles (<2 p) from weathered and unweathered clayey subsoils of Weichselian age were studied at 8 sites within the Zealand-Funen area, Denmark. At a large regional scale, four classes (C1 to C4) of clay mineral assemblages of unweathered grey CaC0,-rich till and melt-water clay were identified. The regional distribution of each of these classes revealed a close association with the movement of the glaciers during the Weichselian glaciation. Post-depositional processes (oxidation and leaching) had formed two weathenng zones; an upper brownish CaC0,-free zone down to depths of 1-3.5 m, and a lower brownish CaC0,-rich zone down to 3-6.5 m. The composition of the clay minerals of weathered CaC0,-rich clayey subsoils studied at a regional scale suggested a total-transformation process of chlorite, illite, and illite-smectite to smectite and vermiculite. The diversity of clay minerals, typically 5, impeded a more thorough characterization of the transformation of individual clay mineral constituents. Nevertheless, at the Havrebjerg site separate phases of the chlorite transformation were identified within a 0.6 m wide weathering sequence: lowest, a grey zone with unaltered inherited chlonte, followed by a greyish brown zone with slightly transformed chlorite, a brown zone with hydroxy-interlayered vermiculite/smectite, and a yellowish brown coloured zone with hydroxy-interlayered vermiculite/smectite and vermiculite/smectite (but no chlorite). Also, the weathering sequence reflected changes in the cation exchange capacities of the clay fraction and ratio of stmctural Fe(I1) in clay minerals to total Fe.

Oxygen-generating material for soil and its production

Abstract: PROBLEM TO BE SOLVED: To produce an oxygen-generating material capable of sustaining the generation of the oxygen for a long period without decomposing in a short period and to provide a method for producing the oxygen-generating material. SOLUTION: This oxygen-generating material for soil is produced by compounding 5-95wt.% volume-expanded vermiculite and 95-5wt.% calcium peroxide. The method for producing the oxygen-generating material comprises mixing 10-90wt.% vermiculite raw ore with 90-10wt.% calcium oxide and 5-60wt.% aqueous hydrogen peroxide, heating the resultant mixture at 50-130 deg.C and providing a mixture of the volume-expanded vermiculite with the calcium peroxide.

Comparison of Biotite Dissolution in the Laboratory and in the Field by High-Resolution Transmission Electron Microscopy

Abstract: The dissolution of minerals are generally explained by protonation, deprotonation and the subsequent detachment of metal species (e.g. Stumm, 1992) based on laboratory experiments under 'far from equilibrium' conditions. The process is considered to be applicable to the dissolution of sheet silicates in which Si and A1 ions dissolve from the edges of the 2:1 layers (e.g. Wieland and Stumm, 1992; Nagy, 1995). However, weathering in the field seems to be different from laboratory dissolution in terms of the saturation state with respect to primary minerals and the formation of secondary minerals. In particular, biotite weathering is usually accompanied by vermiculite overgrowth within a biotite grain (Banfield and Eggleton, 1988) partly because there is no significant differences between biotite and vermiculite except for the small differences in the interlayer cations and occupancies, and the compositions of the 2:1 layers. Thus, the process observed in the laboratory is not consistent with that in the field. Recently, Kogure and Murakami (1996) successfully identified biotite and vermiculite layers in hydrobiotite by high-resolution transmission microscopy (HRTEM) in the atomic scale. Using their technique, we compare the process of biotite dissolution in the laboratory with that in the field in the early stage of dissolution.

Composite clay material

Abstract: PROBLEM TO BE SOLVED: To obtain a composite clay material which can be uniformly dispersed in a vinyl polymeric material and has improved properties by making a clay mineral organic by treatment with an agent comprising a specified mol% hydroxy organic onium ions and mixing the mineral made organic with a vinyl alcohol copolymer SOLUTION: An agent used for making organic and comprising an organic onium ions having 10-80mol% hydroxyl groups is added to a clay mineral It is desirable that the organic onium ions used are derived from an acrylic oligomer having a number-average molecular weight of 1,000-15,000 The organic onium ions intercalated between the layers of the mineral are ionically bonded to the mineral to expand the interstice between them The clay mineral chiefly used are layered clay minerals (layered phyllosilicates, smectite layered clay minerals such as montmorillonite or saponite, vermiculite, halloysite, and swellable mica)

Method for treating industrial wastes coming from domestic use with the use of modified-treated vermiculite

Abstract: The invention refers to a method for treating wastes from cotton and synthetic fabric dye houses characterized in the use of vermiculite during the procces of treating the wastes.

High-Pressure Raman and X-Ray Scattering Studies on Vermiculite Layered-Silicate Intercalation Compounds

Abstract: Single crystals of vermiculite were studied by high-pressure Raman scattering and x-ray diffraction methods using diamond-anvil cells with distilled water and mineral oil as pressure-transmitting media. When water was used, intercalation of water molecules to vermiculite was observed (pressure-induced intercalation). High-pressure Raman spectra from vermiculite samples in various intercalation states revealed the roles of interlamellar intercalant molecules and atoms in the lattice dynamics of vermiculite.

The Influence of Water Pollution on the Slowed Weathering Rates and Accelerated Biomass Productions Observed in Two Portuguese Granitoid Areas

Abstract: Quantitative geochemical mole-balance studies were first applied by Garrels and Mackenzie (1967) in the study of a pristine area (Sierra Nevada, USA); using the so-called 'balance-sheet' method, they could envisage which natural processes were responsible for the composition of springs and groundwater in their area. More recently, other mole-balance models were developed to address problems such as the influence on mineral weathering rates caused by the growth of biomass (Taylor and Velbel, 1991) or to analyse the chemical evolution of water along a flow path caused by the mixing of different water types _ plus the reaction with solid phases (Parkhurst, 1997). In the present paper, we present a summary of the most important conclusions of two studies, carried out in two Portuguese granitoid areas (Pacheco and Van der Weijden, 1996; Pacheco et al., submitted), which, among other things, analysed the influence of soil, saprolite and ground water pollution on the intensity of mineral weathering (plagioclase and biotite) and on the rates pine growth in those areas. In these two studies, a different mole-balance algorithm was applied, the so-coined SilicaBicarbonate (SiB) algorithm, which is able to separate the contributions to water chemistry associated with natural sources from those associated with anthropogenic and other pollution sources. The type and abundance of secondary minerals present in the soils derived from a certain rock type depend primarily on the environmental parameters climate and topography, as early recognized by Tardy et al. (1973), on the local drainage conditions, and on the mineralogy and chemistry of that rock type; in the case of a granite under temperate climatic conditions, the most important weathering reactants are plagioclase (major) and biotite (minor), and the most common associated secondary products are vermiculite (low rainfall/stagnant drainage conditions), halloysite (moderate to high rainfall/favourable drainage conditions) and gibbsite (very high rainfall/excellent drainage conditions). But the formation of a certain weathering product may also be influenced by factors such as pollution, as pointed out by Pacheco and Van der Weijden (1996) in a study of the Fund~o granitoid plutonite (central Portugal); they suggested that, under stagnant leaching conditions and raised levels of soil/ saprolite water contamination caused by the application of manure and fertilizers on farmland, vermiculite could result from the weathering of biotite, instead of halloysite the most stable product under the local rainfall conditions. The influence of soil and saprolite water pollution on the intensity of mineral weathering was later corroborated by Pacheco et al. (submitted) in a study of the Chaves-Vila Pouca area (northern Portugal), a granitoid and forested area located along a large-scale Hercynian fault; in this case, it was noticed that two water types linked to the weathering of the same plagioclase type (andesine-An40) could be associated to the formation of mixtures with 50% gibbsite plus 50% halloysite, when the water type was less polluted, and to mixtures with 30% less gibbsite when the water type was definitely contaminated. In pristine forested areas, the rates of biomass production and of elemental uptake depend on factors such as climate, morphology, soil fertility, tree species, and stand maturity; for instance, regarding tree species, the response of elemental uptake to the demand of biomass production is different when considering coniferous or deciduous species (coniferous species appear to meet all of their annual requirement of nutrients via the uptake process, while deciduous species meet only about 70% of their needs throughout that process, the rest being provided by translocation of nutrients from older tissue). Besides, most of the annual uptake of elements is provided by recycling from decay of previous year's litter and only a small part is removed from the mineral compartment through weathering.