Showing papers on "Vermiculite published in 1993"

Root-induced release of interlayer potassium and vermiculitization of phlogopite as related to potassium depletion in the rhizosphere of ryegrass

Abstract: SUMMARY The ability of roots to weather phlogopite as shown by the release of interlayer-K and by the concomitant vermiculitization of the mica was investigated in the rhizosphere of Italian ryegrass (Lolium multiflorum), grown for 1 to 32 d on 2–105 μm mica as sole source of both K and Mg. The K-balance showed that ryegrass was able to induce a significant release of interlayer-K from phlogopite after 8 d of cropping. After 32 d, this root-induced release of K amounted to 191 g Kg−1 of total-K and contributed a major part of plant nutrition. Concurrently, the concentration of K in solution decreased markedly in the rhizosphere and X-ray diffractometry showed a strong vermiculitization of the phlogopite. The transformation of phlogopite into vermiculite was detected when the K-concentration in the rhizosphere decreased below a threshold of about 80 μmol dm−3. That suggests that the roots act by depleting the rhizosphere-K, and thus shifting the exchange equilibrium, so as to release interlayer-K and expand the interlayer space of the phyllosilicate leading to the transformation of the phlogopite into vermiculite.

Root‐induced irreversible transformation of a trioctahedral mica in the rhizosphere of rape

Abstract: '' ! ! SUMMARY The ability of the roots of rape (Brassica napus) to promote the transformation and dissolution of a phlogopite mica was studied in the rhizosphere. Rape was cropped for 1 to 32 d on 2-105 ~m phlogopite as sole source ofboth K and Mg. The chemical balance of K and Mg revealed that rape was able to induce a significant release ofinterlayer-K after 4 d, and even a significant release of octahedral- Mg after 8 d of cropping. After 32 d, the root-induced release amounted to 80 and 21 gkg-1 of total-K and -Mg, respectively. The weathering products sampled in the close proximity of the roots were analysed by X-ray diffractometry (XRD), and by energy dispersive X-ray (EDX) microanalysis of resin-embedded samples prepared for transmission electron microscopy. The XRD analysis ofK-saturated, oriented plates showed that part of the vermiculite formed by root activity behaved as a typical hydroxy-aluminous interlayered vermiculite (HIV). The EDX microanalysis revealed that the release of interlayer-K which occurred during the vermiculitization was compensated mostly by Al and Mg originating from the octahedral sheet of the phlogopite. Such crystallographic and crystallochemical changes necessarily involved an acid dissolution of the mica structure, which may be related to the rootinduced pH decrease encountered simultaneously in the rhizosphere. Proton excretion by rape roots was thus the probable mechanism involved in the root-induced irreversible transformation of the phlogopite.

Characterization of Hydroxy-Interlayered Vermiculite and Illite/Smectite Interstratified Minerals from the Weathering of Chlorite in a Cryorthod

Abstract: X-ray diffraction, FTIR, and chemical analyses were performed on clay fractions (1-2/~m, <0.1 pm), separated by means of size fractionations and high-gradient magnetic separation techniques, from a Cryorthod developed in a chlorite-mica schist saprolite. Weathering of large phyllosilicates pre- existing in the saprolite involves physical fragmentation and mineralogical transformations. Chloritic minerals in the coarse fractions were the most affected by physical breakdown, while micas were generally preserved. As a consequence, a concentration of mica layers occurred in the coarse clay fraction, while chloritic residues accumulated in the fine clays. These residues exhibited the typical XRD pattern of hydroxy-interlayered intergrade minerals, but the interlayered contaminants were found to be mainly hydroxy-Mg cations. Further mineralogical transformations of the intergrade minerals involved the pro- gressive removal of the hydroxide interlayered sheet and dissolution of chloritie layers. Illite/smectite mixed-layers were formed in the surface horizon of the soil profile. These processes were associated with a strong decrease in Fe and Mg contents in the clay fractions.

Calcium-zinc and Calcium-cadmium Exchange in Suspensions of Various Types of Clays

Abstract: Calcium-cadmium and calcium-zinc exchange equilibria were studied at 20-degrees-C and constant ionic strength (0.015) on four clay minerals, viz. montmorillonite, bentonite, illite and vermiculite. Vermiculite and, to a lesser extent, illite and bentonite showed the strongest affinity for Cd2+ or Zn2+ over Ca2+ ions, whereas on the Camp Berteau montmorillonite nearly non-preferential exchange isotherms were observed. With this one exception, selectivity for the heavy metals was greatly enhanced in the trace Cd or Zn regions, suggesting the presence of specific adsorption sites in these clays. Generally, the adsorption increased with the polarizing power of the exchangeable cation. Thermodynamic equilibrium constants and standard free energy changes for the complete exchange of Ca-clay to Cd- or Zn-clay were calculated.

Vermiculite composition with improved thermal expansion properties

Abstract: A vermiculite composition capable of exhibiting a high degree of volume increase upon subjection to thermal exfoliation composed of vermiculite mineralogical species having specific gravity of from 2.5 g/cm 3 to 2.9 g/cm 3 . Further, intumescent sheets formed with said vermiculite composition exhibit low initial expansion temperature and very high maximum expansion properties.

Vermiculite composition with improved chemical exfoliation

Abstract: A vermiculite composition composed of particulate vermiculite mineral species having a density of 2.3 g/cm 3 to 2.7 g/cm 3 which has intercalated cations of lithium or organo ammonium and to dispersions obtained therefrom.

Thermal study of vermiculites and mica-vermiculite interstratifications

Abstract: Simultaneous DTA-TG has been carried out on a set of natural vermiculite samples. Based on their dehydration behaviour the samples can be divided in two groups: (a) those with DTA endothermic peak temperatures at 140°–150°C and 240°–270°C (pure vermiculties) and (b) those with peak temperatures at 95°–115°C (vermiculite with mica or mica-vermiculite interstratifications). The low temperature at which the endothermic effect in group (b) appears is discussed on the basis of dilution due to the inert layers of mica, differences in chemical composition, and lowering of interlamellar water bond energy.

Charge heterogeneity and nanostructure of 2:1 layer silicates by high-resolution transmission electron microscopy

Abstract: Several soil and reference smectites and vermiculites and one reference illite were examined by high-resolution transmission electron microscopy (HRTEM) to decipher the nanostructure and layer charge heterogeneity in these minerals. HRTEM results were compared with those obtained from powder X-ray diffraction (XRD) analysis. Samples were either exchanged with Na+ ions followed by equilibration with a very dilute solution of NaCl in a pressure membrane apparatus at 316 hPa (pF = 2.5) to see the effect of hydration and applied pressure on layer organization, or exchanged with dodecylammonium ions to see the expansion behavior. Oriented samples were embedded in a low viscosity resin and cut approximately 500 A thick perpendicular to d(001) using an ultramicrotome fitted with a diamond knife. In general, Na-saturated soil clays possessed crystallites that were thinner (c-direction) and shorter (ab-direction) as compared with reference clays. In all cases, samples treated with dodecylammonium chloride exhibited nanostructures that were more disintegrated as compared with Na-saturated samples. In a soil vermiculite, dodecylammonium ion exchange showed frayed edges indicating the initiation of mica transformation to vermiculite from edge toward core. In a reference vermiculite (Transvaal) treated with dodecylammonium ions, in addition to completely expanded crystallites, a regular interstratification between expanded vermiculite and mica (phlogopite) layers was clearly observed in some crystallites. Such nanostructural details were not detected by XRD. HRTEM of the Na-treated illite showed thick crystallites having 10 A layer separations, whereas the dodecylammonium-exchanged illite showed three types of layers with different degrees of expansion indicating charge heterogeneity in illite: 1) unexpanded (10 A, highest charge) crystallites; 2) expanded high-charge vermiculite-like (24 A) crystallites; and 3) occasionally expanded high-charge vermiculite-like (24 A) layers interspersed in the matrix of 10A crystallites.

Intumescent sheet material

Abstract: Intumescent sheets are having improved expansion characteristics are disclosed The intumescent sheets comprise an inorganic fibrous material, a binder, and a heat expandable layer mineral composition containing at least 875% by weight of heat expandable interstratified layer minerals comprising interstratified layers of vermiculite and biotite

Ammonium fixation by soil and pure clay minerals

Abstract: Fixation of the ammonium ion (NH4 +) by clay minerals is an alternate way of building the nitrogen (N) pool in soil to optimize N crop recovery and minimize losses. Clay minerals (illite, montmorillonite, and vermiculite) and an illitic Portnoeuf soil were used to compare NH4 + fixation abilities. Total N determination and X‐ray diffraction analysis were performed on each of the minerals and the Portnoeuf soil controls, and NH4 + saturated batches were subsequently desorbed by potassium chloride (KCl) after 4096 hours. Total N was determined for each employing either Kjeldahl digestion only, or pretreating with hydrofluoric‐hydrochloric acid (HF‐HCl) before the Kjeldahl digestion. The total N for the soil was 38% more after pretreatment with HF‐HCl. The total N determined after pretreatment with HF‐HCl for the NH4 + saturated and subsequently KCl desorbed minerals was found to be highest in vermiculite. The cation exchange acapacity (CEC) of each of the minerals was determined, and highest CEC wa...

Layer Silicates from Serpentinite-Pegmatite Contact (Wiry, Lower Silesia, Poland)

Abstract: Highly tectonized contact between serpentinite and younger pegmatite in the magnesite mine of Wiry contains various layer silicates. Vermiculite, chlorite, smectite, and interstratified mica-vermiculite were recognized by means of routine XRD examination. Two three component interstratifications of mica-vermiculite-chlorite and chlorite-swelling chlorite-smectite were identified by a combined procedure of deconvolution of the XRD patterns and simulation of XRD tracings. A mineral with large diffraction maxima, displaying “chlorite intergrade” characteristics, appeared to be a mixture of chlorite, mixed layer chlorite-smectite, and vermiculite. Polytypes of phyllosilicates were determined by the X-ray transmission method. Due to the heritage of parent mineral polytype structure by transitional products of alteration, two distinct sequences of layer silicates were observed: one formed from trioctahedral mica (vermiculite, mixed layer mica-vermiculite); and one evolved from chlorite (e.g., mixed layer chlorite-swelling chloritesmectite). A tentative scheme of the primary contact zone structure, not obscured by subsequent brittle tectonics either by transformation of layer silicates, is proposed.

Influence of geogenesis and pedogenesis on clay mineral distribution in northern vietam soils

Abstract: This is a study of a sequence of five soils developed in the Red River valley of Vietnam along a transect extending from the foothills to old terraces. Most of these soils are chemically depleted, having, in particular, a very low CEC. The mineralogical study shows that the <2-μm fraction is made up of a mixture of vermiculite, illite, kaolinite, quartz, and iron oxyhydroxides. Other minerals, such as pyrophyllite in the foothills and chlorite and gibbsite in the old terraces, are present in small quantities. The major mineralogical differences among these soils lie in the relative abundance of quartz in the <2-μm fraction, the vermiculite/illite ratio, and the degree of the intergrade character of vermiculites, which is variable not only within each profile but also from one region to another. The amount of quartz generally increases toward the foothills, indicating the greater weathering of foothill materials relative to old terraces, which have been less weathered during geogenesis. The vermiculite/ illite ratio, which also increases toward the foothills, indicates an increasing transformation of 2:1 minerals. The effects of pedogenesis are characterized by the difference in vermiculite/illite ratios between the surface and 1-m-deep horizon. Nevertheless, the intensity of pedogenesis cannot be evaluated in profiles developed on highly weathered sediments because illite of the parent material has been completely transformed into vermiculite during a preweathering stage. Alternate wet and dry conditions apparently lead to an increase in illite content by the collapse of vermiculite sheets in surface horizons. The creation of a plow pan in these hydromorphic conditions may have favored the dissolution of clay by ferrolysis and the lateral leaching of fine clay particles out of the profile, increasing quartz content in the <2-μm fraction of the plow pan.

Coated substrates and laminate structures comprising organic solvent-based dispersions of organocation- modified vermiculite

Abstract: Coated substrates, and laminate structures made with intermediate layers provided by organic solvent-based dispersions of organocation-modified delaminated vermiculite are disclosed. The laminates display better peel strength compared to laminates made from water-based dispersions, and can be used in a number of applications.

Synthesis of nitrogen ceramics from a new vermiculite–polyacrylonitrile intercalation compound by carbothermal reduction

Abstract: In the preparation of Si–M–O–N ceramics (M = Al, Mg), liquid acrylonitrile was intercalated in an alkylammonium vermiculite, polymerized in situ and carboreduced under a nitrogen flow. Magnesium silicon nitride, β-silicon nitride and β-sialon with fibre morphology were produced at 1400 °C.

Asbestos-free porous mass for acetylene cylinders

Abstract: Monolithic porous mass free from asbestos, for filling acetylene cylinders, the mass being based on calcium silicate obtained from lime and crystalline quartz powder, characterised in that the binder consists of inorganic synthetic fibres based on carbon and/or of vermiculite, with the optional addition of one or more dispersing and densifying agents.

Significance of the Effect of Mineral Alteration on Nuclide Migration

Abstract: In order to clarify the effect of mineral alteration on nuclide migration, we examined the processes, mechanisms, and kinetics of chlorite weathering, and the uranium concentrations in minerals and rocks at Koongarra, Australia. The observed concentrations of uranium in rocks were compared to those calculated. The sequence of chlorite weathering may be simply expressed as a chlorite → vermiculite → kaolinite conversion. These minerals occur as a function of depth, which corresponds well to uranium concentrations on the meter scale. Iron minerals, closely related to the uranium redistribution, are released during the weathering. The first-order kinetic model of the weathering process suggests that the weathering rate is not constant but time-dependent. The uranium concentrations are qualitatively proportional to the extent of the weathering; the weathered part having higher uranium concentration. Uranium mainly occurs with iron minerals, and sub micron sized saleeite, a uranyl phosphate, is one of the most probable uranyl phases associated with the iron minerals. The uranium fixation mechanisms are probably saleeite microcrystal coprecipitation and sorption to the iron minerals. Our model, which describes uranium concentrations in rocks as a function of time, shows that the transition zone (a vermiculite dominant area) plays an important role in the uranium migration. We have established that weathering of chlorite has affected the redistribution of uranium for more than one million years. The present study demonstrates the significance of mineral alteration when we estimate nuclide migration for geologic time.

Purifying method for vermiculite

Abstract: PURPOSE:To easily provide high purity and high quality by heat-treating vermiculite at high temperature to foam it and thereafter removing impurities by elutriation CONSTITUTION:Vermiculite of 1-10mm particle diameter is introduced into a furnace at about 700 degC and foamed to obtain foamed vermiculite 1 Then this foamed vermiculite 1 is introduced into a vessel A which is filled with water 4 and opened in the upper part A foamed vermiculite layer B is obtained by floating the foamed vermiculite 1 so that thickness thereof is regulated to 1-50mm Then, after water is violently agitated for 1-2 minutes so that the vermiculite 1 is sunk underwater, it is allowed to stand for 1-2 minutes to sink impurities 3 such as pyroxene and feldspar and unfoamed vermiculite in the bottom part Such states (C), are obtained that only purified and foamed vermiculite 2 of high purity remains on the water surface 5 Then only the purified vermiculite 2 floated on the water surface is recovered by using elutriation The obtained vermiculite is dried at 400-800 degC to produce the purified vermiculite

Mineralogy of a Few Entisols

Abstract: Study on mineralogy of sand, silt and clay fractions of a few Entisols of West Bengal show that quartz,feldspar and mica are the major silicate minerals in sand and siltfractions. In the clay fractions, the dominant clay mineral is mica in association with minerals like kaolinite, smectite, vermiculite, chlorite, microcline coupled with considerable amount of amorphous mineral. Mica, feldspar and chlorite are considered as partly inherited from parent materials and weathering sequence of mica has been shown. Minerals are in vermiculite weathering stage calculated from weathering means.

Soil improver having plant growth promoting action and soil improving action

Abstract: PURPOSE:To obtain the subject improving material exhibiting plant-growth promoting action and soil improving action and having draining, adsorbing, wetting and water-retaining properties by impregnating a specific acidic additive to pumice stone, etc., formed by the eruption of a volcano. CONSTITUTION:The objective improving material is produced by impregnating (A) an acidic additive composed mainly of various kinds of metal salts and non-metal salts obtained by dissolving vermiculite which is an efflorescence of a mica mineral (preferably black mica) in an aqueous solution of an inorganic acid in (B) a porous pumice rock, pumice gravel or pumice sand formed by the eruption of a volcano. The component A is produced e.g. by mixing 1 pt.wt. of vermiculite with 1 pt.wt. of dilute hydrochloric acid produced by diluting concentrated hydrochloric acid to 1/2-1/4 under stirring, reacting at 20-30 deg.C for 1 week under stirring and filtering the reaction product.

Thermal study of vermiculites and mica-vermiculite interstratifications

Abstract: Simultaneous DTA-TG has been carried out on a set of natural vermiculite samples. Based on their dehydration behaviour the samples can be divided in two groups: (a) those with DTA endothermic peak temperatures at 140~176 and 240~176 (pure vermiculites) and (b) those with peak temperatures at 95~176 (vermiculite with mica or mica-vermiculite interstratifications). The low temperature at which the endothermic effect in group (b) appears is discussed on the basis of dilution due to the inert layers of mica, differences in chemical composition, and lowering of interlamellar water bond energy.