Search

Abstract: The Bolkardağı bauxite province is located in the Tauride Belt of southern Turkey. The region hosts many lateritic- and karstic-type bauxite deposits within the Bolkardağı Unit (BU), the Namrun Tectonic Unit (NTU) and the Aladağ Unit (AU). The lateritic-type deposits occur on the Upper Triassic sericite-chlorite schist of the BU, on the Lower Triassic slates, and on the Upper Triassic phyllites of the NTU. The gradual transition from the protolith to saprolite and, eventually, to bauxite is observed in the lateritic-type deposits in the field. The karstic-type deposits occur in the carbonates of the BU, the NTU and the AU and were accumulated by clastic transportation from the lateritic material. The deposits within the BU and the NTU are metamorphosed and consist mainly of diasporite, haematite, pyrophyllite, chlorite, chamosite, and anatase; the deposits within the AU are not metamorphosed and consist mainly of boehmite and kaolinite, haematite, goethite, chlorite and anatase. The mean compositions of the deposits are 53% Al2O3, 19% Fe2O3, 12% SiO2, and 3% TiO2. The lateritic-type deposits have higher silica content (e.g., Camızalanı Bauxite Zone; mean 21% SiO2) than the karstic-type, indicating higher mobilisation of silica in the karstic-type deposits because of alkaline pH conditions. The ΣREE content varies between 273ppm and 1693ppm, and the ΣREE content increases with an increase in the content of La, Ce and Nd. The mass change calculations according to the Ti index element show that Rb, K, Ba, Ce, Si, Y, Sr, P, Ca, Mg and U were mobile during the bauxitisation processes. The Zr, Ta, Nb and Hf elements are relatively immobile in the first stage of bauxitisation in the saprolite zone but were slightly mobile at a later stage of bauxitisation. Fe, V, Pb, Ni, and Cr are the elements that were gained in the bauxite zone. From field evidence and geochemical data, it is concluded that the first stages of bauxitisation in the Bolkardağı Bauxite Province started during the post-Upper Triassic by the formation of a kaolinite-rich bauxitic soil via chemical weathering of the Lower Triassic pelitic rocks and Upper Triassic shales under acidic conditions. The kaolinite-rich bauxitic soil was transformed to boehmite during low water activity in hot and humid climatic conditions. The Aalenian–Bajocian transgression submerged the bauxite, causing burial diagenesis. At the time of the closure of the Tethyan Ocean during the Upper Cretaceous, ophiolite obductions over the continent gave rise to imbrication and further burial of the bauxite-bearing units. During this time, the bauxite deposits and their host units underwent a very low grade metamorphism in relation to their burial depths and thrusting. Thus, kaolinite was transformed to dickite, nacrite and pyrophyllite at 240–260°C in the saprolite zone, and boehmitic bauxite was transformed to diasporite in the deeply buried BU and the NTU. The boehmite was preserved as a primary bauxite mineral in the deposit which avoided burial metamorphism in the uppermost tectonic unit, the AU. [Copyright &y& Elsevier]

In Aubrecht et al. (2011) we brought new data showing that the arenitic caves in the Venezuelan tepuis did not necessarily originate through quartz cement dissolution (‘arenization’) but the main portion of the caves originated because of poor lithification prior to erosion. An additional important process is lateritization which is responsible for at least 30% of the caves' volume. Sauro et al. (2012) in their comment support the ‘arenization’ theory (quartz cement dissolution) and provide several arguments against some points of our research. Their main objections and arguments relate to the following topics: 1) the validity of the arenization theory, 2) the origin and importance of the ‘finger-flow’ pillars, 3) the importance of the Schmidt hammer measurements and, 4) metamorphism of the Matauí Formation. In our reply we present further documentation that: [1)] The quartz cement dissolution theory of cave evolution was far less documented petrographically than the new theory presented by us. Although the presence of quartz dissolution is evident, there is no current evidence that it is widespread or that it plays a trigger role. Many of the presented examples of corrosion on quartz grains could have been caused by local alkalization. In addition, the hydrogeochemical data presented in the comment to support the ‘arenization’ theory do not in fact contradict our speleogenetic interpretations. [2)] ‘Finger-flow’ pillars are speleogenetic indicators and not speleogenetic factors. Their absence in some caves provides no evidence against our theory. [3)] Schmidt hammer measurements only objectivize the data on contrasting hardness in the Matauí Formation beds. They do not say anything about the origin of this difference. [4)] The arguments of Sauro et al. (2012) involve the metamorphic overprint of the Matauí Formation shown by the presence of pyrophyllite and quartz mobilizations. Because quartz mobilization also occurs in hypergenic conditions, it may be neglected as a metamorphic indicator. Pyrophyllite is mentioned as a metamorphic indicator in the literature (anchizone to epizone) but it does not explain why there is still a vast quantity of kaolinite that did not undergo this reaction in the soft arenitic beds. There is an evidence that pyrophyllite may originate at lower temperatures. Some phases of the alumino-silicate mineral phases existing at atmospheric pressure and 25°C temperature show that H4SiO4 concentration is a critical factor in kaolinite/pyrophyllite transition. An increase in this concentration can theoretically cause transformation of kaolinite to pyrophyllite without increased temperature or pressure. [ABSTRACT FROM AUTHOR]

We applied the Modified Spectral Angle Mapper (MSAM) and continuum-removal methods to reflectance data obtained in the shortwave infrared regions by the airborne hyperspectral sensor, HyMap, to delineate distribution of the minerals related to hydrothermal alteration and pegmatite. The combination of these two methods was applied to remotely sensed hyperspectral data for the first time in this study. The effectiveness of this method, ‘continuum-removal MSAM’, was confirmed by comparing our mineral index maps with existing mineral maps of the Cuprite region, Nevada, USA. We then produced mineral index maps of southern Namibia using newly observed hyperspectral data. The existence of many pegmatite- and porphyry-type deposits is reported in this study area, where detailed mineralogical mapping based on remote-sensing data has not previously been conducted. Our mineral index maps are consistent with our field survey results, and also with X-ray diffraction analyses and spectral measurements of rock samples. In this study, the continuum-removal MSAM method successfully discriminated hydrothermal alteration minerals such as kaolinite and pyrophyllite, and pegmatite-related minerals such as high-aluminium muscovite and lepidolite in southern Namibia for the first time. The main advantages of our classification method are simplicity and high-precision identification of alteration minerals. [ABSTRACT FROM PUBLISHER]

The changes occurring when composites based on pyrophyllite raw material, obtained from the Kul'-Yurt-Tau deposit, with phosphate binder are heated are studied. Their compaction and hardening are strongly affected by processes associated with the interaction of the ancillary rocks with the phosphate binder. The deformations of composites in two temperature regimes are studied: heating with the temperature changing at a constant rate and with isothermal soaking. The experimental results make it possible to predict the behavior of the materials during operation in the thermal units of different systems and optimize materials preparation in the process of manufacturing articles with prescribed characteristics. [ABSTRACT FROM AUTHOR]

The basic technical characteristics of composites based on pyrophyllite and raw rocks from the Kul'-Yurt-Tau deposit and using phosphate binders are determined. While these materials have satisfactory strength their thermal expansion and thermal conductivity are low while the frost resistance and thermal stability are high. Such materials can be recommended as refractories and building materials for use at temperatures to 1250 - 1350°C depending on the composition of the initial batch. The technology for obtaining these materials is described. Parts and refractory mixes have found applications at certain enterprises. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the adhesion of bacteria (Escherichia coli) to pyrophyllite clay using batch and flow-through column experiments. Batch results demonstrated that pyrophyllite was effective in removing bacteria (94.5±2.0%) from aqueous solution (1 mM NaCl solution; pyrophyllite dose of 1 g/ml). At solution pH 7.1, negatively-charged bacteria could be removed due to their adhesion to positively-charged surfaces of pyrophyllite (point of zero charge=9.2). Column results showed that pyrophyllite (per cent removal of 94.1±2.3% ) was far more effective in bacterial adhesion than quartz sand (53.6±5.3%) under the given experimental conditions (flow rate of 0.3 ml/min; solution of 1 mM NaCl + 0.1 mM NaHCO3). Bacterial removal in pyrophyllite columns increased from 90 to 100% with decreasing flow rate from 0.6 to 0.15 ml/min due to increasing contact time between bacteria and filter materials. In addition, bacterial removal remained relatively constant at 94–97% even though NaHCO3concentration increased from 0.1 to 10 mM (flow rate of 0.3 ml/min). This could be related to the fact that pyrophyllite remained positively-charged even though the solution conditions changed. This study demonstrates that pyrophyllite could be used as adsorptive filter materials in the removal of bacteria. [ABSTRACT FROM AUTHOR]

In the Pötürge (Malatya, Turkey) area pyrophyllite occurrences are common in the shear zones, mostly in the form of lenses along faults. Mineralogical investigations (XRD, FTIR and SEM) revealed that pyrophyllite, kaolinite (dickite) and quartz are present in the form of major phases and muscovite (sericite), kyanite, chlorite, and alunite are only present in the form of minor phases. This study revealed that the existence of the kyanite phase points out to high pressure and temperature conditions which the rocks were underwent. On the other hand, the minerals such as pyrophyllite, kaolinite, and alunite are products of a low degree metamorphism (retrograde). The mineral paragenesis in the pyrophyllite deposits suggests that the formation of minerals took place in two ways: (1) the transformation of kyanite into pyrophyllite and quartz through retrograde metamorphism by a high degree temperature, (2) then pyrophyllite and probably muscovite were transformed into kaolinite and alunite through reactions with relatively low temperature hydrothermal fluids. The geochemical data indicate that during the retrograde metamorphism the elements K, Rb, Sr, Ba, S, and Fe were mobile, the elements Si, Al, P moderately mobile to immobile and the HPS elements (Zr, Ti, and Nb) were immobile. It was shown that the formation of pyrophyllite, kaolinite and alunite was associated with depletion in alkalis, Mg, Fe and enrichment of elements including Sr, Ba, and S. Mineralogical and geochemical data suggest that parent rocks (pre-metamorphism) of the Pötürge pyrophyllite were probably kaolinite, Al-rich clays or bauxites. [ABSTRACT FROM AUTHOR]

In this study, possibility of the use of WPC 42.5 containing pyrophyllite in the production of white concrete was investigated. Normal and light-weight concrete samples were produced with WPC. In normal-weight concrete mixture, WPC and white aggregate were used. In light-weight concrete mixtures, WPC, FA, SF and SP were used. Setting time and soundness of cement paste specimens and compressive strength of light and normal weight white concrete specimens were determined. According to the test results, normal weight white concrete can be used in the construction of frames and light-weight white concrete can be used in the production of concrete/reinforce concrete panels. [ABSTRACT FROM AUTHOR]

Changes of the phase and chemical compositions as well as the course of strengthening on heating of mixtures of pyrophyllitic raw material from the Kul'-Yurt-Tau deposit and, for comparison, the Ovruchskoe deposit with a phosphate binder are studied. It is shown that these materials exhibit similar behavior. The optimal amount of binder to obtain a strong pressed intermediate product is determined. The composites must be heat-treated at temperatures 500 - 600°C in order to attain water resistance and the required strength. [ABSTRACT FROM AUTHOR]

Results are provided for a study of high-temperature deformation and creep of composites based on corundum, pyrophyllite raw material, and phosphate binder. Data are obtained making it possible to predict material behavior during operation. [ABSTRACT FROM AUTHOR]

Research demonstrates that at the start of mullitization the mullite crystal lattice exhibits a large number of defects, and then as firing temperature increases it is completed. At 1100°C there is formation of primary (lamellar), short-prismatic, and short-columnar mullite. [ABSTRACT FROM AUTHOR]

A hybrid pressure cell of pyrophyllite and magnesium oxide (HPCPM) used in large volume cubic presses is presented. In the HPCPM, a cubic frame which is made of pyrophyllite with face-centered square holes works as gaskets, and a heteromorphosis magnesium oxide works as the pressure-transmitting medium. Our experimental results indicated that the pressure-generation efficiency using the HPCPM was improved by about 40% than that using the traditional pyrophyllite pressure cell without decreasing the anvil truncation size (without sacrificing the sample volume). The HPCPM could pressurize samples of 1000 mm3 volume up to about 8 GPa, which is significantly higher than that available using the traditional pressure cell, which reports a highest pressure of about 6 GPa. [ABSTRACT FROM AUTHOR]

Pyrophyllite deposit at Madrangjodi is a large lensoidal massif overlain unconformably by Dhanjori quartzite and underlain by the parent Singhbhum granite (Phase - II). Pyrophyllite and quartz are the major minerals with minor to trace amounts of muscovite, chloritoid opaques and tourmaline. It is broadly divisible into lamellar, granular and schistose varieties. SiO (66.90-74.36%) and AlO (20.80-27.54%) are the major oxides. The major elements data indicate its derivation from Singhbhum granite with depletion of SiO and increment of AlO. Trace and REE data are discussed to corroborate its genesis. [ABSTRACT FROM AUTHOR]

Features are established for the occurrence of thermal processes, making it possible to control them, and use the data obtained in developing ceramic acid-resistant material firing regimes. The least coefficient of effective thermal conductivity of acid-resistant materials lies in a temperature range within which the intensity of physicochemical processes is more marked. These zones correspond to the most complex firing conditions, since the lower thermal conductivity, the slower an object heats up. [ABSTRACT FROM AUTHOR]

Pyrophyllite, AlSiO(OH), a layered aluminosilicate material, has several properties which suggest that it might exhibit desirable frictional properties for solid-state lubrication. These include a lamellar structure and a low-energy basal plane. Here, we utilize atomic force microscopy to investigate the tribological performance of mineralogical pyrophyllite samples and compare the results to those of other minerals and solid lubricants. The results indicate that pyrophyllite exhibits low friction forces and shear stresses, on the same order of other commonly used solid lubricant materials, and a high resistance to deformation within a single layer. These fundamental findings highlight the potential use of pyrophyllite as a possible tribological material and alternative solid lubricant. [ABSTRACT FROM AUTHOR]

Rehydroxylation of the previously dehydroxylated dioctahedral 2:1 layer clay mineral occurs preferentially in specific sites within the former octahedral sheet. The rehydroxylation of dehydroxylated A1-rich and A1,Mg-rich 2:1 layers occurs as trans-vacant (tv) structural arrangements, regardless of whether the initial structure was tv or cis-vacant (cv). In nontronite (Fe-rich 2:1 layer clay), the dehydroxylate pseudo-cv structure is probably directly reconstructed into the rehydroxylated cv structure without migration of octahedral cations. Rehydroxylation occurs preferentially in the R3+-Or-R3+ former octahedral structural arrangements (Or = residual oxygen) over R2+-Or-R (R = R3+ or R2+ = A13+, Fe3+ or Mg2+, Fe2+). In the case of the R2+ octahedral substitution, the interlayer cation is attracted to the electrostatically undersaturated residual oxygen of the R2+-Or-R arrangement, which blocks the ability of water molecules to pass through the ditrigonal cavity and rehydroxylate the previously dehydroxylated local arrangement. The pyrophyllite-like type of octahedral R3+-Or-R3+ arrangements, formed due to the lack of tetrahedral substitution and resulting in the absence of interlayer cations, is thus favored for rehydroxylation over the mica-like R3+-Or-R3+ arrangements where Al occurs in the tetrahedral sheet. The valence of the interlayer cation and the charge density of the 2:1 layer clay mineral, which controls the interlayer cation content, also affect the degree of rehydroxylation.Dehydroxylated 2:1 layer minerals with a high-rehydroxylation potential, including beidellite and illite, use all the adsorbed water molecules that persist above 200 °C for rehydroxylation; the water vapor from the ambient environment also becomes a source of H2O molecules for rehydroxylation. The high demand for water molecules to use for rehydroxyltion results in a noticeable gain of mass in the temperature interval between 200 and 350 °C even during heating. [ABSTRACT FROM AUTHOR]

The physical-mechanical properties and the chemical and mineralogical compositions of pyrophyllitic rocks from the Kul'-Yurt-Tau deposit in the Republic of Bashkortostan were analyzed from the standpoint of using these materials as the principal component of the refractory composites based on a phosphate binder. The characteristics of the mineral pyrophyllite and surrounding rocks in the deposit indicated were examined. The initial materials for research were chosen on the basis of the information obtained. [ABSTRACT FROM AUTHOR]

The UV irradiation aging behaviors of PVC composites with several inorganic fillers were studied through Fourier transform spectroscopy (FTIR), ultraviolet spectroscopy (UV-Vis), differential scanning calorimeter (DSC), scanning electron microscopy (SEM), and mechanical property test. It was found that incorporation of a small amount of the inorganic fillers such as CaCO3, talc and SiO2 could hold up the UV aging behaviors of PVC. Those filler-filled PVC composites sheets after 20 days UV irradiation maintain lower carbonyl index (CI) and good appearance of surfaces, as compared with the corresponding neat PVC sheets, ascribed to high reflection of those fillers to UV light. While montmorillonite (MMT) and pyrophyllite fillers could accelerate the UV aging behaviors of PVC, which could be concluded from both the sharp increase of the CI and lower T g due to the chain scission reactions because of their high absorbance of these fillers to UV light in 290-400 nm. In these two PVC composites, UV irradiation caused the deterioration of their mechanical properties and the appearance of rough, cracked and chalked surfaces after 20 days UV irradiation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

The hydroxyl stretching frequencies of four phyllosilicates have been measured at high pressures and temperatures using an externally heated diamond-anvil cell and synchrotron infrared spectroscopy. Spectra were measured up to 26, 31, 21 and 8 GPa at room temperature for samples of talc, pyrophyllite, muscovite and 10-Å phase, respectively. Spectra were also measured in the range 273-500 K at ambient pressure for all samples and at 8-9 GPa for talc and pyrophyllite. The frequency of the MgOH band in talc increases with pressure due to the absence of hydrogen bonding. The different orientation of the hydroxyl group in pyrophyllite and muscovite leads to hydrogen bonding and a decrease in the frequency of the AlOH band with pressure. 10-Å phase is approximately equivalent to talc with the addition of interlayer HO. In a spectrum of a sample synthesised for 143 h, two hydroxyl stretching bands are clearly resolved on compression. One is the same as the MgOH band in talc, indicating the presence of intra-layer hydroxyl in a talc-like environment with no hydrogen bonding. The other, which separates from the talc-like band at 1 GPa, is associated with intra-layer hydroxyl that is hydrogen bonded to interlayer HO. There are equivalent bands in high-pressure spectra of a sample of deuterated 10-Å phase, synthesised for 400 h. This sample shows a greater extent of hydrogen bonding at ambient pressure than the 143 h sample. For all of the phases studied, increasing temperature leads to a decrease in frequency for every hydroxyl stretching vibration, both at low and high pressures. The shifts in frequency with temperature are an order of magnitude greater than the shifts with pressure when normalised to previously measured structural parameters. [ABSTRACT FROM AUTHOR]

Quantitative measurements of pressure gradients have been made in the pyrophyllite and magnesium oxide (MgO) pressure-transmitting mediums using large-volume cubic apparatus. The relationships of pressure gradients along the axis of symmetry of the pyrophyllite and MgO cubes versus corresponding cell pressures have been established at room temperature. Our experimental results indicated that the pressure gradients increase as the cell pressure increases and that the pressure gradient in the MgO pressure-transmitting medium is about twice as high as that in the pyrophyllite pressure-transmitting medium at the same cell pressure. When the cell pressure reaches 5.5 GPa, the pressure gradient along the axis of symmetry of the pyrophyllite cube is about 50 MPa/mm. When the cell pressure reaches 7.7 GPa, the pressure gradient along the axis of symmetry of the MgO cube is about 140 MPa/mm. The experimental data obtained in the present work not only adapt to the cubic apparatus but also provide reference for the tetrahedral press and the double-stage multi-anvil apparatus (the octahedral compression). [ABSTRACT FROM PUBLISHER]

The article focuses on the aspects of the mineral pyrophyllite. It states that mineral pyrophyllite is abundant in nature its main deposits are found in the U.S., South Africa and China. It says that mineral pyrophyllite is seldom used in ceramic system despite its abundance as it is seldom in a pure state like kaolinite, associated minerals can influence its properties and it is difficult to beneficiate for commercial purposes.

Abstract: A scaled-up version of a 6–8 Kawai-type multianvil apparatus equipped with 47-mm WC anvils has been developed at the Institute for the Study of the Earth’s Interior for operation over pressure ranging up to 19 and 24GPa using the conventional system with larger compressional volumes between 1.2 and 0.4cm3, respectively. This system is used under uniaxial compression along cube diagonal of the Kawai-cell up to the press load of 19MN. Experiments are performed using octahedral pressure media (PM) made of MgO- and ZrO2-based semi-sintered ceramics and unfired pyrophyllite gaskets. In this study we used “Toshiba-F” grade WC anvils allowing pressure generation up to 24GPa. We perform pressure calibrations at room and high temperatures, with octahedron/anvil truncation edge-length ratios (a 0/b, mm) of 12.2/6, 14/6, 14/7, 16/7, 18/7, 18/9, and 18/10. Different configurations show that an increase in edge-length ratio of permits the achievement of higher pressure, which agrees with the results of Frost at al. (Frost, D.J., Poe, B.T., Tronnes, R.G., Liebske, C., Duba, A., Rubie, D.C., 2004. A new large-volume multianvil system. Phys. Earth Planet. Inter. 143, 507). However, it also shifts the pressure maximum to higher press loads, in some cases exceeding the capacity of a press. Our and data reveal that the 14/6, 18/8, and 18/10 assemblies are the most suitable in generating pressures of up to 19–24GPa at 19MN press load limits. The assemblies with a low a 0/b ratio have a lower upper pressure limit; however, they exhibit a systematically higher efficiency in pressure generation at low press loads. Consequently, assemblages with high and low a 0/b ratios should be used in high and low pressure experiments, respectively. For example, the 18/12 assembly is suitable for 5–11GPa pressure range (Stoyanov, E., Haussermann, U., Leinenweber, K., 2010. Large-volume multianvil cells designed for chemical synthesis at high pressures. High Pressure Res., 30, 175), whereas the 14/6, 18/8 (), and 18/10 assemblies are suitable for 22–24, 19–23, and 11–19GPa pressure ranges, respectively. The maximum pressure generation achieved in the present study is 24GPa, using the 14/6 assembly. This appears to be the maximum pressure level attainable by using WC anvils. [Copyright &y& Elsevier]

The stacking parameters, lattice constants, bond lengths, and bulk moduli of pyrophyllite and montmoriflonites (MMTs), with alkali and alkali earth metal ions, are investigated using density functional theory with and without dispersion corrections. For pyrophyllite, it is found that the inclusion of the dispersion corrections significantly improves the agreement of the calculated values of the lattice parameters and bulk modulus with the experimental values. For the MMTs, the calculations predict that the interlayer spacing varies approximately linearly with the cation radius. The inclusion of dispersion corrections leads to sizable shirts of the interlayer spacings to shorter values. In Li-MMT, compaction of the interlayer distance triggers migration of the Li ion into the tetrahedral sheet and close coordination with basal oxygen atoms. Analysis of electron density distributions shows that the isomorphic octahedral Al3+/Mg2+ substitution in MMT causes an increase of electron density on the basal oxygen atoms of the tetrahedral sheets. [ABSTRACT FROM AUTHOR]

The experimental and computational methods have been applied for assessing mixed soil characteristics. To enhancement bearing capacity of the mixed soil the mineralogy and soil mechanic testing techniques have been used. The result indicated that for improving a mixed soil characteristics it has to be embedded with appropriate minerals, and due to presence of Pyrophyllite mineral, the negative correlation between compaction technique with enhancement of soil mechanical properties has been observed, it could be suggested that in landslide mitigation or any subsoil improvement if Pyrophyllite mineral presence, the compaction technique could not be apply, it will result reverse, and it is observed that gathering Illite, Muscovite and Sauconite in a soil lead to achieving maximum level of density, and also some other minerals may have same affect on mixed soil compaction that is required to be more investigate. [ABSTRACT FROM AUTHOR]

Batch adsorption study was carried out to remove excess fluoride from water using pyrophyllite. Result showed that adsorption of fluoride was rapid in first 20 min and thereafter increased slowly to reach the equilibrium in about 2 hrs. About 85% removal efficiency was obtained within 2 hrs at an adsorbent dose of 4 g/L for initial fluoride concentration of 10 mg/L. Maximum fluoride adsorption takes place at pH 4.9. Thermodynamic parameters such as Gibb's free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes were determined for the adsorption process. Negative ΔH° value signified that the adsorption process was exothermic in nature. From the kinetic study it was found that fluoride adsorption by pyrophyllite followed pseudo-second-order kinetics with an average rate constant of 0.92 g/mg · min. Intraparticle diffusion model was studied to determine the rate limiting step of the adsorption process. The system followed the Langmuir isotherm with maximum adsorption capacity of 2.2 mg/g of fluoride. [ABSTRACT FROM AUTHOR]

A multi-cycle heating and cooling thermogravimetric (TG) method was used to study the kinetic behavior of two partially dehydroxylated pyrophyllite samples. In the original state, the S076 sample contains only trans-vacant (tv) layers, whereas in sample S037 tv and cis-vacant (cv) layers are randomly interstratified. The method consists of consecutive heating cycles (rate 2 °C/min) separated by intervals of cooling to room temperature, with the maximum cycle temperature set (MCT) incrementally higher than in each previous cycle. The activation energy (Ea) values were calculated for the S037 and S076 samples for all cycles in terms of a homogeneous zero-order reaction with the regression coefficients r² ≥ 0.9997. The S076 sample had Ea values that varied from 40 to 42 kcal/mol within a partial dehydroxylation (DT) range from 19 to 63%. However, at DT values <19% and >63% the Ea values are slightly lower at 38-39 kcal/mol and drop below 30 kcal/mol at DT = 90%. A bimodal distribution of the S037 sample Ea values exists with increasing MCT and DT. In the first cycles of intense dehydroxylation from tv layers the Ea values increase sharply from 34 kcal/mol at DT = 7% to 45 kcal/mol within the MCT interval from 525 to 575 °C and then decrease to 36-38 kcal/mol at the cycles with MCT = 650-700 °C. In the second portion of cycles corresponding to the dehydroxylation of cv layers, the Ea values increase from 36-37 kcal/mol at MCT = 700 °C to 44-46 kcal/mol at MCT = 775 °C. These results show that both tv and cv layers require exactly the same energy for dehydroxylation and have similar variation of the Ea values with MCT and DT. The pyrophyllite particle size distribution is a major factor that is likely responsible for a broad interval of dehydroxylation temperature. This implies that the lower the temperature, the smaller the particles that can be dehydroxylated. Therefore, the activation energy values at the beginning of the reaction are lower than those at higher degrees of dehydroxylation because of the combination of a slow experimental heating rate and thin crystallites, which both contribute to lower temperatures at which the reaction starts. The decrease in activation energy observed at the end of the dehydroxylation reaction of sample S076, and of the tv layer portion of sample S037 is accompanied by an increase in the "induction" temperature interval during which an accumulation of additional thermal energy decreases the activation energy. The kinetic parameters determined for the samples in this study correspond to a homogeneous reaction and are used to predict a general pattern of the structural transformations of pyrophyllite at different stages during dehydroxylation. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper examines the mechanochemical activation of starting minerals (kaolin, pyrophyllite, and talcum) and their effect on the solid-phase synthesis and properties of cordierite. Binary oxide compounds (spinel, mullite, enstatite, forsterite) are synthesized. It is established that binary compounds and crystalline silica should be minimized to decrease the synthesis temperature of cordierite. Processes for synthesis and production of cordierite ceramics with lower thermal expansion coefficient ((1.0-1.2) ⋅ 10 °C) are developed. [ABSTRACT FROM AUTHOR]

Two pyrophyllite samples, one S037, from the Coromandel region of New Zealand and the other, S076, from Berosovska, Ural, Russia, were studied by thermogravimetric (TG and DTG), infrared (IR), and X-ray diffraction (XRD) methods to investigate structural transformations of these samples at different stages of their partial dehydroxylation. The samples were heated at different temperatures during 45 min and the degree of dehydroxylation was estimated as a ratio of mass loss of each particular heated specimen to the total mass loss of the sample during total dehydroxylation. Sample S076 consists only of trans-vacant (tv) layers because its DTG curve and IR spectrum contain a single dehydroxylation maximum at Tmax = 723 °C and an OH stretching band 3675 cm-1, respectively. In sample S037 tv and cis-vacant (cv) layers are interstratified at random and its DTG and IR spectrum contain, respectively, two dehydroxylation maxima at 595 and 760 °C and two stretching bands at 3675 and 3668 cm-1. The positions and intensities of the reflections in the experimental powder XRD patterns of sample S037, as well as the refined parameters of the unit cell, almost coincide with those determined for 1A pyrophyllite. However, the XRD patterns contain an "additional" peak with d = 4.454(6) Å, which is absent in normal 1A pyrophyllite. This peak can be considered as an indicator of a structure in which tv and cv layers are interstratified. The XRD patterns from the oriented specimens of the studied samples heated above 500 °C show splitting of the basal reflections. Simulation of the XRD patterns from oriented specimens of the S076 sample show that the phase composition of the specimens is the same independent of the heating temperature and represents a physical mixture of a non-treated original pyrophyllite and an almost completely dehydroxylated phase, which contains 5% of non-dehydroxylated layers. The higher the temperature, the higher the content of the dehydroxylated-rich phase in the heated sample. Simulation of the XRD patterns from the heated S037 samples show that the phase composition of each specimen is a physical mixture of low-and high-dehydroxylation phases, referred to as LD and HD phases, respectively. Each of these phases is a mixed-layered structure in which the original non-dehydroxylated (ND) and completely dehydroxylated (CD) layers are interstratified at random. The main difference between these phases is that in the LD phase the content of ND layers prevail, whereas in the HD phase CD layers dominate. The increase in temperature and degree of dehydroxylation change the relative content of the LD and HD phases as well as the relative amount of ND and CD layers in these phases. Interstratification of ND and CD layers in the LD and HD phases is not consistent with the commonly accepted model according to which during dehydroxylation of pyrophyllite and related layer silicates, non-dehydroxylated and dehydroxylated domains can coexist within one layer. As a result of this inconsistency, the model explaining the wide temperature interval of pyrophyllite dehydroxylation needs to be reconsidered. A similar inconsistency arises with the model predicting the formation of several intermediate semi-dehydroxylated structures during pyrophyllite dehydroxylation because evidence for such phases was not observed. A new model of pyrophyllite dehydroxylation is presented, which is consistent with the hypothesis, that the reaction is homogeneous and spontaneous nucleation and growth of completely dehydroxylated layers takes place during pyrophyllite dehydroxylation. In terms of this model, the large temperature interval of pyrophyllite dehydroxylation is related to particle size distribution as well as to structural disorder. A mechanism for the formation of the mixed-layered structures of the LD and HD phases is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Garin Hawal area, Kebbi State, NW Nigeria is part of the Neoproterozoic to Early Phanerozoic terrane separating the west African and Congo Cratons. Three main gold-bearing shear zones were detected in the study area from the processed Landsat ETM+ images and extensive ground investigation. Field and petrographical studies indicate that the Neoproterozoic rocks are represented by a highly folded and faulted belt constituted of hornblende, muscovite and graphite schist. They are intruded by granondiorites and late to post granitic dykes. Extensive alteration zones were identified using high resolution QuickBird image along Garin Hawal shear zone. The alteration zones and associated quartz veins are generally concordant with the main NE–SW regional structural trend and are dipping to the NW. Geochemical studies indicate that the gold content reaches 8g/t in the alteration zones, while it reaches up to 35g/t in the quartz veins. Mineralogical studies indicate that the alterations are strongly potassium-enriched. Pyrophyllite, kaolinite, illite, gypsum and quartz also occur. The main ore minerals are gold, chalcopyrite, arsenopyrite, pyrite, galena and iron oxides. This study indicates that the alteration zones and the associated quartz veins in the muscovite schist are promising and need more detailed exploration for Au and Ag mineralization to evaluate their potential. [Copyright &y& Elsevier]

In this study the use of the kaolinite, which contains very low levels ofpyrophyllite, as a ceramic tiles material was studied. Chemical, mineralogical analysis and thermal behaviours of the clay were determined. After analysing the chemical, mineralogical content and thermal behaviour of the clay, the shaping properties were determined according to Atterberg and Pfefferkorn plasticity tests. The samples that had been shaped with vacuum extrusion were fired at between 600 °C to 1200 °C with 100 °C internals. Mineralogical, physical-mechanical properties and microstructure of fired samples were determined. As a result, it was seen that the grain size of the clay and its plasticity values are suitable for ceramic tile and formation of secondary mullite as well as lamellar shaped pore structure at low temperatures (1100 °C) has positive effect on mechanical properties. It was determined that ceramic tile can be produced at 1000 °C for Group Allb and at 1100 °C for Group Alla according to Turkish Standard (TS EN ISO 14411). The colour and aesthetic appearance of the fired products correspond the market demands with smooth surface. [ABSTRACT FROM AUTHOR]

A set of Silurian black shales from Sierra de Albarracín (NE Spain) corresponding to two different sections was studied to determine the relative influence of diagenesis, igneous activity, and regional tectonics on the clay-mineral genesis. The coexistence of pyrophyllite, I-S interstratifications (R1), ammonium-rich illite, potassium illite, kaolin, and chlorite is not the result of prograde evolution during diagenesis – very low-grade metamorphism. Three different stages may be inferred: (1) sedimentation of black shales (Aeronian, Lower Silurian, to basal Ludfordian, Upper Silurian) and the subsequent diagenetic process producing the coexistence of quartz, illite, kaolinite, organic matter, etc.; (2) intrusion of andesitic sills producing hydrothermal alteration and crystallization of pyrophyllite, ammonium-rich illites, smectite, I-S R1 phases and jarosite; and (3) and folding of shales and sills and development of penetrative schistosity during the late Variscan leading to illite and paragonite recrystallization reaching the anchizone grade. [ABSTRACT FROM AUTHOR]

Abstract: The experiment on the search for life under very high pressure done on small animal, tardigrade, has been extended to the moss Ptychomitrium. Several spore placentas of the moss Ptychomitrium were sealed in a small Teflon capsule together with fluorinate as liquid pressure medium. The capsule was put in the center of a pyrophillite cube. This cube was compressed by six tungsten–carbide second-stage anvils with a front edge length of 4.0mm. These anvils were compressed by a first stage, 250ton press. It was proven that 80–90% of the spores were alive and germinated after being exposed to the maximum pressure of 7.5GPa for up to 48h. Furthermore, a relatively high germination rate of about 35% was retained even after exposure to 7.5GPa for 6 days. The pressure tolerance of moss is found to be much stronger than tardigrades. [Copyright &y& Elsevier]

Pyrophyllite is a raw material of significant interest due to its large number of applications. Most of these applications require a thermal transformation of pyrophyllite; this thermal transformation implies the release of structural OH groups and the formation of new phases. In this paper, we report on the dehydroxylation of pyrophyllite and the reversibility of the process. A value of 224±16 kJ/mol for the dehydroxylation of pyrophyllite was obtained. In addition, it was observed that the partially or totally dehydroxylated pyrophyllite suffered a partial reversible rehydroxylation when cooled to room temperature. This rehydroxylation was substantiated by thermogravimetric measurements, while infrared spectroscopic studies showed that, during the rehydroxylation, the intensity of the OH band at 3675 cm−1 increased as two new bands at 3690 and 3702 cm−1 appeared. This rehydroxylation process was heavily influenced by the particle size of the pyrophyllite. Thus, smaller particles (<1 μm) showed a larger rehydroxylation percentage (about 12%), while the larger ones (20–40 μm) showed a smaller percentage (about 1.6%). The extent of rehydroxylation also depended on the dehydroxylation temperature and reached a maximum value at 750°C. [ABSTRACT FROM AUTHOR]