Showing papers on "Vermiculite published in 1999"

Fixation of radiocaesium traces in a weathering sequence mica vermiculite hydroxy interlayered vermiculite

Abstract: Radiocaesium fixation in soils is reported to occur on frayed edge sites of micaceous minerals. The weathering of mica in acid soils may therefore influence the Cs+ fixation process and thereby the mobility of the radiopollutant. We produced a laboratory weathering model biotite --> trioctahedral vermiculite --> oxidized vermiculite --> hydroxy interlayered vermiculite (HIV) and quantified the Cs' fixation of each mineral both in a fixed K+-Ca2+ background and in acid conditions. The transformation process was achieved through K depletion by Na-tetraphenylboron, oxidation with Br-2 and Al-intercalation using NaOH and AlCl3. In a constant K+-Ca2+ background, vermiculite fixed 92-95% of the initial Cs-137(+) contamination while biotite and HIV fixed only 18-33%. In acid conditions, the interlayer occupancy by either potassium (biotite) or hydroxy-Al groups (HIV) strongly limited Cs+ fixation to 1-4% of the initial Cs-137(+) contamination. Cs+ fixation occurred on vermiculitic sites associated with micaceous wedge zones. Though both oxidized and trioctahedral vermiculites fixed similar Cs+ amounts in a constant K+-Ca2+ background (92-95%), the oxidized vermiculite retained much more radiocaesium in acid conditions (78-84% against 54-59%), because of its dioctahedral character.

Influence of the nature of clay minerals on the fixation of radiocaesium traces in an acid brown earth-podzol weathering sequence

Abstract: The magnitude of radiocaesium fixation by micaceous clay minerals is affected by their transformation, which depends on weathering in soil The net retention of radiocaesium traces was quantified by sorption-desorption experiments in the Various horizons of four sandy soils forming an acid brown earth-podzol weathering sequence derived from sandy sediments and characterized by marked changes in mineral composition The features of the 2:1 minerals of the four soils, resulting from an aluminization process in depth and a desaluminization process towards the surface, had a strong influence on Cs+ fixation Beneath the desaluminization front, which deepens from the acid brown earth to the podzol, hydroxy interlayered vermiculite was dominant and the Cs-137(+) fixation was the weakest At the desaluminization front depth, vermiculite was responsible for the strongest Cs-137(+) fixation In the upper layers, smectite appeared in the podzolized soils and the Cs-137(+) fixation decreased The magnitude in Cs+ fixation therefore appeared as a tracer of the transformation process affecting the 2:1 clay minerals in the acid brown earth-podzol weathering sequence This magnitude was positively correlated with the vermiculite content of the studied soil materials estimated by the rubidium saturation method

Mixed-layer kaolinite-illite-vermiculite in North Sea shales

Abstract: The finest fractions of Upper Jurassic shales from the North Sea and onshore Denmark contain 80 90% of an illite-smectite-vermiculite (I-S-V) mixed-layer mineral and, in addition a phase which has X-ray diffraction (XRD) peaks at 7.20-7.26 A and 3.56-3.58 ,~ in air- dried and glycolated specimens. This phase may be a fine kaolinite with a small thickness of coherent scattering domains (CSDs) or alternatively a mixed-layer mineral which has kaolinite as the dominant component. For one sample from the Norwegian well 9/4-3, these alternatives are investigated using the multi-specimen method by which agreement between the experimental pattern and the pattern calculated for one and the same structure is obtained for each of several specimens saturated with different cations and with/without glycolation. It is demonstrated that the modelled XRD patterns for a kaolinite-illite-vermiculite (K-I-V) structure having 0.94 kaolinite, 0.03 illite and 0.03 vermiculite layers and random alternation fit the experimental patterns.

Mineralogy Of B Horizons In Alpine Forest Soils Of Taiwan

Abstract: The nature of minerals in the B horizons of alpine forest soils in subtropical and tropical areas remains to be identified. The objective of this study was to investigate the distribution of Fe-oxides and hydroxy-interlayered vermiculite (HIV) in typical alpine forest soils of Taiwan. Five pedons at roughly 2000 m elevation of Taiwan were selected as example for this study. High gradient magnetic separation (HGMS), conventional X-ray diffraction (XRD), differential X-ray diffraction (DXRD), and transmission electron microscopy (TEM) were employed to characterize the clay minerals. The content of crystalline Fe-oxides increased sharply from E to B horizons. Only Al-substituted lepidocrocite and goethite were identified by differential X-ray diffraction (DXRD) analysis in magnetic clay fractions of the B (or placic) horizons; no substantial hematite peaks appeared in the XRD patterns of any pedons. These observations are quite different from those of Spodosols or Spodosol-like soils developed in the temperate and frigid zones of North America. Hydroxy-interlayered vermiculite (HIV) was characterized by collapse of the 1.42-nm peak in the XRD diagrams toward 1.0 nm when the K-saturated clay samples were heated to 350°C. In the surface horizons, only vermiculite could be identified in the coarse clay fractions. The distribution patterns of acid ammonium oxalate extractable Fe and Al in these pedons indicate that Al and Fe were leached from the A horizons and accumulated in the B horizons when forming Al-substituted lepidocrocite, goethite, and HIV. This is attributed to the combined effect of organic acids, Al, and Fe in the pedogenic environments. The present findings are of fundamental significance in understanding the formation of Spodosol-like soils in alpine forest soils in the subtropics and tropics.

Changes in soil mineralogy and exchangeable cation pools in stands of Norway spruce planted on former pasture land

Abstract: Chemical and mineralogical properties of the soils in 35- and 70-year-old stands of Norway spruce (Picea abies (L.) Karst), planted on former pasture and were studied at Asa Experimental Forest, southern Sweden. Remnant deciduous forests bordering the spruce stands were used as controls to assess possible tree-species-related effects on soil development. All soils are acid with little difference in soil pH between the spruce and deciduous stands. However, the saturation of the exchange complex with Mg is lower beneath spruce and the total exchangeable Mg pool in the upper meter of these soils is one third of the Mg store beneath the deciduous stands. Amphibole, biotite and chlorite are the major sources of Mg in the parent soil. The clay fraction of the topsoil beneath spruce has been depleted of all these easily weatherable ferromagnesian minerals. Apart from weathering-resistant primary silicates, the clay fraction consists almost exclusively of expandable, smectitic mixed-layer minerals, which are believed to be the products of advanced stages of biotite weathering. In contrast, vermiculite is the dominant secondary mineral in the A-horizon in the deciduous stands, and some chlorite has survived. Moreover, a greater depth of in situ weathering is indicated for the soil of the old spruce stands where biotite/vermiculite mixed-layers have formed in the C-horizon as products of early stages of biotite weathering. Thus, differences between the paired sites in soil solution chemistry are supported by the qualitative differences in soil mineralogy, and are believed to reflect divergent biotic and/or abiotic processes in the different stand types.

Structural Study of Monomethylammonium and Dimethylammonium-Exchanged Vermiculites

Abstract: Vermiculite crystals from Santa Olalla, Spain, were first Na exchanged and then intercalated with monomethylammonium (= NH3(CH3)+, MMA) and dimethylammonium (= NH2(CH3)2+, DMA) molecules, respectively, by immersion in 1 M ammonium-chloride solutions at 65°C for 2–3 wk. MMA-and DMA-exchange with vermiculite resulted in crystals with near perfect three-dimensional stacking, suitable for single crystal X-ray diffraction analysis. Unit cell parameters are: a = 5.353(2) A, b = 9.273(3) A, c = 11.950(6) A, and s = 98.45(4)° for MMA-exchanged vermiculite and a = 5.351(2) A, b = 9.268(4) A, c = 12.423(8) A, and s = 98.33(5)° for DMA-exchanged vermiculite. Refinement results are R = 0.059 and wR = 0.073 (MMA-exchanged vermiculite) and R = 0.059 and wR = 0.064 (DMA-exchanged vermiculite). The results are based on structures which show substitutional disorder, and thus the presented models are derived from average structures. There are two distinct sites for the MMA molecule in MMA-exchanged vermiculite. One crystallo-graphically unique MMA is oriented such that the N-C axis of the molecule is perpendicular to the basal oxygen plane, with the N ion offset from the center of the interlayer by 1.04 A. The other MMA is located such that the N ion is at the center of the interlayer between adjacent 2:1 layers, presumably with the N-C axis of the molecule oriented parallel to the basal oxygen plane. This represents the first known occurrence of an organic molecule located exactly between the two adjacent 2:1 layers. Both sites are located between hexagonal cavities of adjacent layers. DMA molecules in DMA-exchanged vermiculite are located such that the N ion is offset from the central plane in the interlayer by 0.95 A. A static model is proposed with two orientations of DMA to produce a DMA “zigzag” orientation of molecules parallel to the (001) plane. The plane defined by the C-N-C atoms in the molecule is perpendicular to the (001) plane. An alternate model is more dynamic, and it involves the rotation of DMA molecules about one C-N axis. Identical starting material was used in previous studies on tetramethylammonium (TMA)-exchanged vermiculite and tetramethylphosphonium (TMP)-exchanged vermiculite. The effect of onium-ion substitutions on the 2:1 layer shows that the tetrahedral rotation angle, α, is significantly smaller for MMA-and DMA-exchanged vermiculite vs. TMA and TMP-exchanged vermiculite. Tetrahedral and octahedral bond distances of the 2:1 layer of the TMA, TMP, MMA, and DMA-exchanged structures may be explained by the location of the organic cation relative to the basal oxygen atom plane and by the differences in the geometries of the organic molecule. Thus, the 2:1 layer is affected by the interlayer molecule, and the 2:1 layer is not a rigid substrate, but interacts significantly with the onium ions.

Clay mineralogy and potassium status of selected soils in the glacial Lake Agassiz region of central Manitoba

Abstract: The clay mineralogy of the soil is important in that it can affect potassium (K) availability, particularly if vermiculite is present. Large areas of Glacial Lake Agassiz in Manitoba contain fine-grained lacustrine sediments that support boreal forest vegetation. The purpose of this investigation was to identify the clay mineralogy of several commonly occurring soils and document its influence on soil fertility, particularly K availability. The soils were classified as either Eluviated Eutric Brunisols or Orthic Eutric Brunisols. X-ray diffraction analysis verified that vermiculite, hydrous mica and kaolinite were the principal clay minerals in these soils. Vermiculite was demonstrated to have hydroxy Al-interlayers and the amount of vermiculite decreased in the deeper soil horizons. Smectite was present in the Btj horizons of the Eluviated Eutric Brunisols, while trace amounts of chlorite were present in every inorganic horizon. Quantity/intensity curves for K and an experimental estimate of the K-fixati...

The Effect of Humic Substances on Pb(II) Adsorption on Vermiculite.

Abstract: Adsorption of lead ion from aqueous solutions containing humic substances on vermiculite was investigated. Humic substances exhibited a strong influence on lead adsorption on vermiculite. The adsorption of humic acids on vermiculite plays an important role in lead ion distribution between the clay mineral and aqueous solution. There are remarkable differences in adsorption behaviors of humic acid itself among the humic acids taken from different origins. Adsorption behaviors of lead from aqueous solution containing fulvic acids were found to be less dependent on their origins, which may be attributable to negligible adsorption of fulvic acids on vermiculite.

Effect of reducing conditions on the weathering of Fe3+-rich biotite in the new lahar deposit from Mt. Pinatubo, Philippines

Abstract: Biotite in the new lahar (volcanic mud flow) deposit from Mt. Pinatubo, Philippines (hereafter referred to as P-Bt) was easily converted to vermiculite during lowland rice-cultivation in pots. The K 2 O content of the P-Bt gradually decreased, and the peak intensity of the X-ray diffraction (XRD) at 1.4 nm increased during seven cultivations of the paddy rice. The amount of K + release from the P-Bt with Na 2 S 2 O 4 treatment was about 1.2 times greater than that released with a NaCl treatment when they were compared at the same pH and Na + concentration. This result was considered to be a characteristics of biotite containing a large amount of Fe 3+ because the amount of K + released from two reference biotites having a Fe 3+ /total Fe ratio of < 0.1 was smaller after the Na 2 S 2 O 4 treatment than after the NaCl treatment. Fe 3+ at the edge site of the P-Bt might react with the reducing agent, and released Fe 2+ and other polyvalent cations might replace the interlayer K + because a 1.4-nm reflection peak appeared after the Na 2 S 2 O 4 treatment. The reducing conditions during lowland rice cultivation could facilitate vermiculitization of the P-Bt and contribute to the K + supply for the rice plants. The characteristics of the P-Bt were confirmed by XRD, infrared absorption (IR) spectroscopy, and elemental analysis. The trioctahedral type was also confirmed from the (060) reflection peak at 0.153 nm. IR bands of P-Bt were observed in the 400-1400-cm -1 and 3400-3700-cm -1 region. The IR bands of P-Bt from 400 to 1400 cm -1 were very similar to those for the two reference biotites whereas the IR bands in the 3400 to 3700 cm -1 region of the P-Bt differed from those for the reference biotites. The atomic Mg/Fe ratio of the P-Bt was 1.56, which was in the range of biotite. The atomic Fe 2+ /total Fe ratio of the P-Bt was 0.47, and its average structural formula was K 0.74 ,Na 0.09 (Si 2.80 ,Al 1.20 )(Al 0.06 ,Fe 3+ 0.50 ,Fe 2+ 0.45 ,Mg 1.48 , Ti 0.21 )O 10 (OH) 2 .

A nickel hydroxide-vermiculite complex; preparation and characterization

Abstract: A nickel hydroxide-vermiculite complex (NHVC) with csinbeta = 1.41 nm and particle sizes from 0.075 to 0.15 mm was obtained hydrothermally by adding nickel nitrate solution to vermiculite from Transvaal, South Africa. The quantity of nickel hydroxide included in NHVC was controlled by adjusting the concentration of the nickel nitrate solution. The thermal behavior of NHVC at 450 degrees C or above was independent of the Ni content. However, small differences exist in the dehydration behavior of NHVC below 450 degrees C. One-dimensional Fourier electron density analysis of the NHVC structure containing 2.43 mol of Ni per half unit cell showed that Ni cations occupy the interlayer of NHVC, and 10% of the total Ni cations is in the ditrigonal cavity of the basal-oxygen plane of the tetrahedral sheet.

Heat resistant product and method

Abstract: A heat resistant product comprises a ceramic binder and vermiculite, wherein between 35 % and 95 % of the dry weight of the product is vermiculite having a particle size such that more than 60 % of the vermiculite does not pass through a 1 mm sieve.

Mineralogical weathering of mudstone in western Shimane Peninsula, Japan.

Abstract: This paper describes the weathering of the Miocene mudstone in western Shimane Peninsula, from a standpoint of the outcrop occurrence and mineralogy. In this area, the mudstone is classified into three weathering zones (I, II and III zones from the bottom of the outcrops to the top), based on its color and hardness. This classification well agrees with the mineralogical characteristics in each zone : chlorite and pyrite have not been altered in the I zone ; chlorite has partly altered to chlorite-vermiculite interlayer (Ch-V) or vermiculite, and pyrite has partly altered to iron hydroxide (or oxide) in the II zone ; chlorite has mostly altered to Ch-V or vermiculite, and pyrite has mostly altered to iron hydroxide (or oxide) in the III zone. Alteration of chlorite and pyrite changes the color and hardness of mudstone, and plays an important role in forming the weathering zones in this area.

Vermiculite molding product and its production

Abstract: PROBLEM TO BE SOLVED: To obtain a molding product having the whole characteristics of low-temperature expanded vermiculite, capable of being sintered while retaining the shape of the molding product and changed into a porous ceramic by solidifying vermiculite expanded by a peroxide with a resin binder SOLUTION: A premix comprising vermiculite, a peroxide and a resin binder is put in a mold and heated usually at 70-220 degC The peroxide may be an inorganic peroxide or an organic peroxide The peroxide is generally suspended or dissolved in a solvent and used In the case of using hydrogen peroxide, >=15% aqueous solution of hydrogen peroxide is advantageously used A phenol resin, a furan resin, a polyvinyl alcohol, etc, are especially preferable as the resin binder The amount of the resin binder used is 10-100 g based on 100 g of vermiculite The amount of the peroxide used is generally about 001-5 mol based on 100 g of vermiculite

Summary: mineralogy of sodic soils in ceará

Abstract: Sand, silt and clay fraction mineralogy as well as the weathering processes of two soils with excess of sodium (SPL and SS) were studied in the state of Ceara, Brazil The sand coarse and silt were studied using polarized microscopy and phase contrast, while the fine silt and clay were analyzed by X-ray diffraction Additional information on the mineralogical transformations that occurred in the horizons of both pedons was obtained using scanning electron microscopy The Solodic Planosol showed in the clay fraction almost equivalent amounts of kaolinite and montmorillonite in the 2Btn horizon, the same occurring with the proportions of kaolinite and vermiculite in the A horizon In the other fractions, variable contents of quartz, plagioclase, hornblende and biotite were found On the other hand, the Solodized-Solonetz had essentially kaolinit clay fraction all over the profile, with variable contents of quartz, feldspar and biotite in the other fractions In both profiles, the clay enrichment of the argillic horizon seemed to be a result of the weathering of the primary minerals from the underlying parent material The assumption of alternate oxi-reduction processes in the A and, or, E horizons due to the low 2Btn horizon permeability, which induces a process of ferrolysis on those horizons, is also an alternative genesis which cannot be disregarded to explain the high textural contrast of these soils The weathering of albite, as well as of the other plagioclases rich in sodium, associated with the semi-arid climate and impeded drainage, are the factors that cause the high sodium percentage observed on both pedons Also on both soils, the contrasting quartz contents, the geomorphology of the region and the presence of a stone line separating the A or A + E horizons from the 2Btn one, reveal a duplicity of parent materials

Intercalation of Nickel Hydroxide into Large Crystal of Vermiculite

Abstract: Vermiculite of centimeter size was treated with a nickel nitrate solution under hydrothermal condition. A complex intercalated with nickel hydroxide was produced at the part within 100 μm from the edge and 10 μm from the surface under the conditions of 250 °C for 100 h. In the inner regions, nickel hydroxide was intercalated in the layers having no fixed K, but not intercalated in the region having fixed K.