Search

Pyrophyllite has a significant role in both geophysics as a hydrous phase, which can recycle water into the Earth's mantle, and many industrial applications, such as petroleum and civil engineering. However, very few works have been proposed to fully characterize the thermodynamic properties of this mineral, especially at atomic scale. In the present work, we report structural, vibrational, thermochemical and thermophysical properties of pyrophyllite, calculated at the density functional theory level with the hybrid B3LYP functional, all-electron Gaussian-type orbitals and taking into account a correction to include dispersive forces. V( P, T) data at 300 K fit with isothermal third-order Birch-Murnaghan equations of state and yield K = 46.57 GPa, K′ = 10.51 and V = 213.67 Å, where K is the thermal bulk modulus at 0 GPa, K′ is the first derivative and V is the volume at zero pressure, in very good agreement with recent experimental results obtained by in situ single-crystal synchrotron XRD. The compressional behaviour is highly anisotropic, with axial compressibility in ratio β( a):β( b):β( c) = 1.218:1.000:4.188. Pyrophyllite bulk modulus, thermal expansion coefficients and heat capacity at different P- T conditions are provided. The results of this kind of analysis can be useful in both geophysical and technological applications of the mineral and expand the high-temperature and high-pressure knowledge of this phase at physical conditions that are still difficult to obtain by experimental means. The simulated vibrational spectrum can also be used as a guideline by other authors in their experimental investigation of pyrophyllite. [ABSTRACT FROM AUTHOR]

Mass movements associated with abandoned mines are dangerous and destructive. Local communities near abandoned mine sites are often threatened by the effect of extreme precipitation events on these sites. In this study, the geotechnical and rheological characteristics of mine deposits were examined to delimit the hazardous areas near abandoned mines. Waste rock materials were collected from a pyrophyllite mine deposit in the mountainous region of Korea, and a sieve analysis was performed to determine the grain size distribution. The yield stress in the debris flow modeling was determined using fall cone and rheometric tests. Rheological tests were performed on materials finer than 4.75 mm using a ball-measuring system rheometer. These samples were mainly composed of gravels and sands with small clay content. The waste materials typically exhibited a shear-thinning behavior within a given shear rate ranging between 10 and 10 s. The yield stresses obtained from the rheometric tests agreed well with those obtained from the fall cone tests. For the input parameter, we selected the yield stresses ranging from 100 to 500 Pa. As a case study, the debris flow mobility associated with the abandoned mine was examined using a one-dimensional flow dynamic model. The runout distance and velocity of the waste materials are strongly dependent on the yield stress; both factors significantly increase with decreasing yield stress. However, even under the highest yield stress (i.e., 500 Pa), the failed mass can flow into the mountain stream. Thus, the physico-chemical contaminations of areas downslope of abandoned mines may be unavoidable with respect to extreme rainfall events. [ABSTRACT FROM AUTHOR]

Iron as an impurity in pyrophyllite ore affects pottery, ceramics and tile quality. We carried out the characterization of a pyrophyllite ore sample using optical microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and wet chemical analysis. The study revealed the presence of 2.15% iron oxide (Fe2O3 ) along with silica and alumina as the major components, which constituted around 90% of the total sample. We carried out the removal of iron from the pyrophyllite using magnetic separation and acid leaching and found that wet high-intensity magnetic separation (WHIMS) could remove 28% of iron values while oxalic acid leaching could remove up to 99.3%. The leaching kinetics of iron removal and the effects of pulp density, acid concentration, leaching time and temperature were also investigated. The optimum conditions for leaching were found to be leaching time of 60 minutes, temperature of 90°C, pulp density of 5%, oxalic acid concentration of 0.3 M, and particle size below 100 microns. Iron dissolution from the pyrophyllite sample can be best described by the diffusion of ions through the product layer of constant-size spherical particles. The breakdown of the pyrophyllite structure was evident from the FTIR and TGA studies. The activation energy of the leaching process over the temperature range was calculated to be 43.47 kJ/mol. [ABSTRACT FROM AUTHOR]

Infrared spectroscopy (IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray analysis (EDS) were used to investigate the evolution of mechanical destruction of the pyrophyllite structure and final ground products upon grinding with a laboratory planetary ball mill. The raw ore used in this present work was mainly composed of pyrophyllite and quartz. This pyrophyllite was more resistant toward mechanical destruction, and the crystalline order of pyrophyllite was not completely destroyed until grinding for 240 min with a 20:1 of weight ratio of the balls to powder. The existing crystalline phase in the final ground product was found to be quartz, which served as the associated phase in the original pyrophyllite mineral. The rate of destruction of pyrophyllite structure depended on the types of chemical bonds. Additionally, increasing the intensity of grinding resulted in acceleration of the mechanically induced amorphization of the pyrophyllite structure, whereas the associated quartz grains contributed to the deceleration of the amorphization of pyrophyllite. [ABSTRACT FROM AUTHOR]

The compressional behaviour of (triclinic) pyrophyllite-1 Tc was investigated by means of in situ synchrotron single-crystal diffraction up to 6.2 GPa (at room temperature) using a diamond anvil cell. Its thermal behaviour was investigated by in situ synchrotron powder diffraction up to 923 K (at room pressure) with a furnace. No evidence of phase transition has been observed within the pressure range investigated. The α angle decreases whereas the β and γ angles increase with P, with the following linear trends: α( P) = α − 0.203(9)·Δ P, β( P) = β + 0.126(8)·Δ P, and γ( P) = γ + 0.109(5)·Δ P (angles in ° and P in GPa). P- V data fits with isothermal Murnaghan and third-order Birch-Murnaghan Equations of State yield: K = 47(3) GPa and K′ = 6.6(14) for the M-EoS fit, K = 47(4) GPa and K′ = 7.3(19) for a III-BM-EoS fit, with the following anisotropic compressional scheme: β: β: β = 1.06:1:4.00. The evolution of the 'Eulerian finite strain' versus 'normalized stress' leads to: Fe(0) = 47(3) GPa as intercept value and regression line slope with K′ = 7.1(18). A drastic and irreversible change of the thermal behaviour of pyrophyllite-1 Tc was observed at 700 < T < 850 K, likely ascribable to the first stage of the T-induced de-hydroxylation. Between 298 and 700 K, the α angle shows a slight decrease whereas the β and γ angles tend to be unaffected in response to the applied temperature; all the unit-cell edges show a monotonic increase. The axial and volume thermal expansion coefficients of pyrophyllite were modelled between 298 and 773 K following the equation α( T) = α(1 − 10 T), with α = 2.2(2) × 10 K [with V = 424.2(1) Å and α = 5.5(3) × 10 K] and thermal anisotropic scheme α: α: α = 1.20:1:2.72. By linear regression, we obtained: V( T)/ V = 1 + α· T = 1 + 3.1(2) × 10 ( T − T). The thermal behaviour of talc-1 Tc was investigated by in situ synchrotron powder diffraction up to 1,173 K (at room- P) with a furnace. At 423 K, the diffraction pattern was indexable with a monoclinic unit-cell but with a doubling of the c-axis (as expected for the 2 M-polytype). At T > 1,123 K, an irreversible transformation occurs, likely ascribable to the first stage of the T-induced de-hydroxylation. Between 423 and 1,123 K, the β angle decreases in response to the applied temperature; all the unit-cell edges show a monotonic increase. The volume expansion coefficient of talc was modelled between 423 and 1,123 K by the linear regression, yielding: V( T)/ V = 1 + α· T = 1 + 2.15(3) × 10 ( T − T). The comparative elastic analysis of pyrophyllite and talc, using the data obtained in this and in previous studies, shows that pyrophyllite is more compressible and more expandable than talc. [ABSTRACT FROM AUTHOR]

Alteration is recorded throughout much of the 3 km thick Upper Witwatersrand succession in South Africa, and extends for 300 km around the basin and 50 km into the basin. The evidence for this alteration comes from petrography, mineralogy, geochemistry, rock fabrics and stratigraphy. The alteration, conceived as a giant halo enveloping each major goldfield, requires a major hydrothermal event focused on the auriferous Upper Wits (Central Rand Group). The scale and nature of the alteration, and its relationship to gold distribution on various scales, strongly support a hydrothermal model for gold deposition. Such a model can account for the 50,000 t of gold mined from the Witwatersrand goldfields. The model works within the context of the major advances in understanding of the geological framework of the Witwatersrand Basin including the recognition of the importance of post-burial processes. It is highly significant that the age of Witwatersrand sedimentation is much older than 2700 My, and thus the host rocks for gold were deposited at least 100 My before the major global Archean greenstone gold event. The shale units from 40 major mines covering the seven goldfields are examined to establish the nature and distribution of the alteration, and to make the connection between the fluid infiltration that caused the alteration, and the introduction of gold into the Witwatersrand Basin. In the hydrothermal model described here, an auriferous low salinity fluid is produced at about 500 °C during the metamorphism of mafic material that was below and adjacent to the Witwatersrand Basin. Large shear zones in the footwall of goldfields are the inferred fluid pathways into the Upper Wits succession, and then unconformities, smaller shear zones, veins and the reef packages guide local fluid flow. In this model, gold precipitation occurs in response to the reaction of the fluid with carbon- and iron-bearing rocks that are abundant in the reef packages immediately overlying unconformity surfaces. Gold precipitation occurred at about 350 °C and 10 km depth with the implication of a high geothermal gradient approaching 35 °C per km. The alteration of the shales, but lack of abundant gold in them, is predicted from the paucity of appropriate rocks or minerals in the shale units to precipitate gold, but fluid infiltration still changed their composition fundamentally. The source of the Witwatersrand gold, its present distribution and the alteration are explained within this hydrothermal model, with similarities to the models invoked for other major gold provinces. It is worth noting that quartz-pebble conglomerate is a poor term for this gold type and has almost certainly limited exploration opportunities globally. [ABSTRACT FROM AUTHOR]

To address the problem of depleting reserves of raw materials for the manufacture of porcelain tiles a comparative analysis is made between two possible alternatives. The recycling of waste generated during tile manufacturing and the use of pyrophyllite in the composition were compared in relation to process parameters such as firing temperature and manifested properties such as linear shrinkage, porosity, bulk density and the sequence of sintering in a dilatometric study. It was found that the use of pyrophyllite in such systems is a better proposition. The conclusion was supported by microstructural and XRD phase analysis. The better ceramic properties in the pyrophyllite containing system are attributed to higher mullite formation at comparative firing temperature and a possible explanation for the same has been put forward. The use of pyrophyllite will open up an opportunity to utilize this non-conventional material in the commercial production of different porcelain products. [ABSTRACT FROM AUTHOR]

In this study, anthracene was employed as a probe to explore the potential catalytic effect of clay minerals in soil environment. Clay minerals saturated with various exchangeable cations were tested. The rate of anthracene transformation follows the order: Fe-smectite >> Cu-smectite > Al-smectite ≈ Ca-smectite ≈ Mg-smectite ≈ Na-smectite. This suggests that transition-metal ions such as Fe(III) play an important role in anthracene transformation. Among Fe(III)-saturated clays, Fe(III)-smectite exhibits the highest catalytic activity followed by Fe(III)-illite, Fe(III)-pyrophyllite, and Fe(III)-kaolinite, which is in agreement with the interlayer Fe(III) content. Moreover, effects by two common environmental factors, pH and relative humidity (RH), were evaluated. With an increase in pH or RH, the rate of anthracene transformation decreases rapidly at first and then is leveled off. GC-MS analysis identifies that the final product of anthracene transformation is 9,10-anthraquinone, a more bioavailable molecule compared to anthracene. The transformation process mainly involves cation-π bonding, electron transfer leading to cation radical, and further oxidation by chemisorbed O. The present work provides valuable insights into the abiotic transformation and the fate of PAHs in the soil environment and the development of contaminated land remediation technologies. [ABSTRACT FROM AUTHOR]

Some advanced engineering materials like B4C, CaB6, SiC, Si3N4, Si or Al2O3 are obtained by thermal treatment methods as calcination roasting or carbothermic reduction. In this study, intensive planetary ball milling was employed to mechanically activate selected minerals such as colemanite (Ca2B6O11.5H2O), pyrophyllite (Al2Si4O10(OH)2) and quartz (SiO2) in order to alter their thermal behaviour in the high temperature processes. Unmilled and milled mineral samples were then roasted to determine high temperature phases of the minerals. Minerals were also analysed using thermogravimetry. By comparing the crystal structures and thermal behaviors of the minerals investigated, the footprints of the mechanical activation were investigated. It was concluded that mechanical activation of these industrial minerals can provide more useful outputs in the production of the advanced materials at low costs. [ABSTRACT FROM AUTHOR]

In this work, the main world deposits of pyrophyllite are indicated according to the literature, showing the available production data. It is emphasized the research focusing on mining and characterization of raw materials containing pyrophyllite, which shows a marked applied interest. It is described and reviewed the most relevant applications of pyrophyllite and pyrophyllite raw materials, in especial refractories and ceramics, fillers, building materials, catalysts and as a high-pressure medium for synthesis of materials. Finally, it is also described and reviewed its use as raw material for the preparation of advanced materials, such as sialon, emphasizing the possibilities of application of pyrophyllite raw materials in our country as a result of distinct investigations of relevant interest performed by several Research Institutes and University Departments. It is deduced that pyrophyllite and pyrophyllite raw materials are increasing in relative importance in many applied fields, as compared with other layer silicates, such as talc and kaolinite.En este trabajo se indican los principales yacimientos mundiales de pirofilita según la bibliografía, los datos de producción disponibles, además de revisar las investigaciones más destacadas sobre prospección y caracterización de materias primas que contienen pirofilita y que presentan un marcado interés aplicado. Se realiza una amplia revisión de las principales aplicaciones a las que se destinan dichas materias primas, en especial para la preparación de materiales cerámicos y refractarios, su uso como carga, en la construcción, obtención de catalizadores y síntesis de materiales a alta presión debido a sus propiedades. Por último, se describen y revisan sus aplicaciones en la preparación de nuevos materiales y materiales avanzados, como son los sialones, destacando su potencial de utilización en nuestro país como resultado de diversas investigaciones de interés, realizadas por distintos Institutos y Departamentos universitarios. Se deduce que la pirofilita adquiere una importancia relativa cada vez mayor en relación a otros silicatos laminares, como son talco y caolinita.

Potassium silicate fertilizer grade were successfully produced by direct fusion of silica (SiO2) and potasium (KOH and K2CO3) in furnaces at temperatures up to melting point of mixture. The geothermal sludge (98% SiO2) and the pyrophyllite (95% SiO2) were used as silica sources. The purposes of the study was to synthesise potassium silicate fertilizer grade having solids concentrations in the range of 31-37% K2O, and silica in the range of 48-54% SiO2. The weight ratio of silicon dioxide/potasium solid being 1:1 to 5:1. Silica from geothermal sludge is amorphous, whereas pyrophylite is crystalline phase. The results showed that the amount of raw materials needed to get the appropriate molar ratio of potassium silicate fertilizer grade are different, as well as the fusion temperature of the furnace. Potassium silicate prepared from potassium hydroxide and geothermal sludge produced a low molar ratio (2.5: 1 to 3: 1). The potassium required quite small (4:1 in weight ratio), and on a fusion temperature of about 900 °C. Meanwhile, the potassium silicate prepared from pyrophyllite produced a high molar ratio (1.4 - 9.4) and on a fusion temperature of about 1350 °C, so that potassium needed large enough to meet the required molar ratio for the fertilizer grade. The product potassium silicate solid is amorphous with a little trace of crystalline.

The denudation processes in abandoned mines pose environmental and social problems. Insufficient remediation and cleanup modify the physicochemical properties near the mine sites. In addition, large amounts of sediment and debris can flow downward due to heavy rainfall. Here, the shear characteristics of mine deposits are presented rather than their chemical contaminants, which include heavy metals. Drained and undrained ring shear tests were performed on waste rock materials that were collected from pyrophyllite mine deposits in the mountainous region of Korea. These samples were classified as gravelly sandy soils (i.e., with an effective grain size of D = 0.3 mm and a uniformity coefficient of c = 5). The following three tests were performed: (i) shear stress measurement with shearing time for a given shear velocity (i.e., 0.1 mm/sec), (ii) shear stress as a function of shear velocity, and (iii) shear stress as a function of normal stress. The fully saturated samples were subjected to different normal stresses (i.e., 25 and 100 kPa) and shear velocities (i.e., 0.01, 0.1, 1, and 100 mm/sec). The waste materials exhibited a strain-softening behavior regardless of the drainage and shear velocity condition. In addition, the shear stress was strongly influenced by the shear velocity and increased with increasing shear velocity and normal stress in the post-failure stage. Using grain size distribution analyses, we show that significant grain crushing occurs in the shear zone during shearing. Under relatively high shear velocity conditions (i.e., >;100 mm/sec), the grain crushing effect is more significant and results in rapid mass movements. [ABSTRACT FROM AUTHOR]

A detailed petrographic, structural and morphometric investigation of different types of caves carved in the quartz–sandstones of the “tepui” table mountains in Venezuela has allowed identification of the main speleogenetic factors guiding cave pattern development and the formation of particular features commonly found in these caves, such as funnel-shaped pillars, pendants and floor bumps. Samples of fresh and weathered quartz–sandstone of the Mataui Formation (Roraima Supergroup) were characterised through WDS dispersive X-ray chemical analyses, picnometer measurements, EDAX analyses, SEM and thin-section microscopy. In all the caves two compositionally different strata were identified: almost pure quartz–sandstones, with content of silica over 95% and high primary porosity (around 4%), and phyllosilicate-rich quartz–sandstone, with contents of aluminium over 10% and low primary porosity (lower than 0.5%). Phyllosilicates are mainly pyrophyllite and kaolinite. SEM images on weathered samples showed clear evidence of dissolution on quartz grains to different degrees of development, depending on the alteration state of the samples. Grain boundary dissolution increases the rock porosity and gradually releases the quartz grains, suggesting that arenisation is a widespread and effective weathering process in these caves. The primary porosity and the degree of fracturing of the quartz–sandstone beds are the main factors controlling the intensity and distribution of the arenisation process. Weathering along iron hydroxide or silt layers, which represent inception horizons, or a strata-bounded fracture network, predisposes the formation of horizontal caves in specific stratigraphic positions. The loose sands produced by arenisation are removed by piping processes, gradually creating anastomosing open-fracture systems and forming braided mazes, geometric networks or main conduit patterns, depending on the local lithological and structural guidance on the weathering process. This study demonstrates that all the typical morphologies documented in these quartz–sandstone caves can be explained as a result of arenisation, which is guided by layers with particular petrographic characteristics (primary porosity, content of phyllosilicates and iron hydroxides), and different degrees of fracturing (strata-bounded fractures or continuous dilational joints). [ABSTRACT FROM AUTHOR]

Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) data were analyzed for the Nohwa deposit area, Korea. The data were calibrated to reflectance using crosstalk correction and atmospheric correction and then used to map pyrophyllite distribution in surface by using band math, combination of Spectral Angle Mapper (SAM), and Matched Filtering (MF) technique. Results from two methods show generally close agreement with the existing alteration map. However, some pixels extracted by band math were vegetation areas not associated with pyrophyllite. In contrast, combination of SAM and MF could detect more accurately areas associated with pyrophyllite than band math. Furthermore, the regional distribution of high-grade and low-grade pyrophyllite in the Nohwa deposit area could be differentiated by combination of SAM and MF. Classification map, according to pyrophyllite grade, using ASTER data is likely to provide ancillary information in development of open-pit mine. [ABSTRACT FROM AUTHOR]

Thermochemical behavior of pyrophyllite was characterized by using XRD, FTIR, TG-DTA and MAS NMR techniques. Pyrophyllite experiences a series of solid-state phase transformations during thermal treatment. Dehydroxylation of pyrophyllite is completed at 880 °C, and the original layered framework is inherited in dehydroxylated pyrophyllite. Up to 1100 °C, the layered framework is collapsed thoroughly, with formation of amorphous SiO 2 and mullite. Above 1200 °C, cristobalite crystallizes from amorphous SiO 2 , and mullitization is promoted dramatically. The alkali leaching results show that amorphous SiO 2 in the thermally activated pyrophyllite is soluble in caustic soda liquor, while mullite is not, and the formation of sodium aluminosilicate hydrate of 0.95Na 2 O·Al 2 O 3 ·3.25SiO 2 ·4.79H 2 O during alkali leaching diminishes the dissolution ratio of silica. The alkali dissolution behavior of silicon demonstrates an innovative process for removing silica from pyrophyllite by using thermochemical activation (TCA) followed by alkali leaching, which can be applied to desilication of bauxite ore and preparation of alumina-base porous material. A desilication of 84% was obtained from the tested ore containing 90% pyrophyllite at the optimal thermochemical activation conditions of temperature 1100–1150 °C and time 90–20 min. The good alkali dissolution characteristic of silica also is a cogent evidence on the formation of amorphous silica during the thermal treatment of pyrophyllite. [ABSTRACT FROM AUTHOR]

In this paper, β-Sialon ceramic was formed with pyrophyllite as raw material and coke as reductant by carbothermal reduction and nitridation in flowing nitrogen atmosphere. Then, the erosion wear property of β-Sialon ceramic was measured. When the pre-synthesized temperature was 1400°C, the effects of carbon additions (with theoretical carbon addition and carbon in excess of 10–50wt.%) on the phase compositions of the products were studied by X-ray diffraction. β-Sialon ceramic was sintered at 1600°C, and its erosion wear behavior was examined with the use of a self-designed, liquid–solid, two-phase flow erosion equipment. Results show that the optimum carbon addition to fabricate the β-Sialon ceramic powders was in excess of 10wt% at 1400°C. Under these conditions, the pre-synthesized powders were composed of β-Sialon as the main crystalline phase and β-SiC as the secondary phase. The relationship between volume erosion amount per area of the specimens and erosion time can be explained by two exponential equations— and in two stages. [ABSTRACT FROM AUTHOR]

We study the influence of the ultrasonic treatment of pyrophyllite in different media on its structure and charge transfer and analyze the dependences of changes in the Gibbs free energy, resistance to charge transfer, and capacitance of the Helmholtz layer caused by the acoustic action on the amount of 'guest' lithium x. It is shown that abnormally high diffusion coefficients of lithium cations for all investigated values of x represent a specific feature of the kinetics of intercalation in LiAL(OH)[SiO]. [ABSTRACT FROM AUTHOR]

It is established that the use of an ammonium fluoride treatment on quartz-pyrophyllite rock (45% pyrophyllite and 53% quartz) at 650°C changes the traditional mechanism by which mullite is synthesized; it is formed not from metapyrophyllite but from fluoridated pyrophyllite, with the formation of aluminum trifluoride and topaz being intermediate stages of the synthesis process. The optimum ratio of quartzpyrophyllite rock to ammonium hydrodifluoride is 1:1.6, which at 1300°C increases the yield of acicular mullite (with particles 20 - 30 μm long and 3 - 5 μm in cross section) from 12 to 68 wt.%. The content of residual quartz in the mullite is no greater than 15 - 18 wt.%. [ABSTRACT FROM AUTHOR]

The Longmen kaolinite deposit is one of the largest hydrothermal clay deposits of Ganxi volcanic basin (northern Wuyi Mountain area, China). The pristine host rocks are rhyolitic crystal-vitric tuff and minor lapilli tuff from the Late Jurassic Ehuling Formation. The ore consists of kaolin-group minerals (kaolinite, dickite), pyrophyllite with minor quartz, sericite, pyrite, etc.. From the host rocks to the transition zones (altered rocks) then to the vein ores, contents of SiO and TFeO decrease, whereas AlO and LOI increase, consistent with the contents increase of kaolin minerals and pyrophyllite in the samples. The total REE abundances of the ores are much lower than that of the host and altered rocks, Rb, Nb, Nd, Zr, Ti and Y are significantly depleted. Apparent zoning features of bulk geochemistry and mineral component reflect that the kaolinite deposit occurred at the expense of the host rock by ascending hydrothermal fluids with distinct removal of SiO, TFeO, NaO, KO. According to the mineral assemblage, the formation temperature of this deposit falls within the range of 270-350 °C. With regard to the industrial applications, the kaolinized ores are suitable for use in ceramics and gemologic materials crafted for seal stones. Moreover, in mineralogical terms, this deposit is also proved to be an excellent example for studying channeled hydrothermal alterations of rhyolitic tuff. [ABSTRACT FROM AUTHOR]

The possibility of directly using the natural mineral pyrophyllite for the efficient generation of Li intercalation current is demonstrated experimentally. The dependences of changes in the Gibbs energy and the entropy of the intercalation reaction on the degree of the guest lithium load are analyzed. A distinctive feature of the intercalation kinetics in LiAl(OH)[SiO] is the anomalously high diffusion coefficients of lithium cations at x > 0.3. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical activation of the 2:1 layer lattice aluminosilicate pyrophyllite is investigated, with particular regard to the implications of this process for gold preg-robbing behaviour. Short-term grinding in a high energy laboratory ring mill increases the adsorption of gold by pyrophyllite in an acidic chloride medium, which would be problematic in the operation of a hydrometallurgical process. However, prolonged grinding (30minutes or more) inhibits the sorption of gold anions onto the surface of pyrophyllite, reducing the extent of gold losses from solution. Analysis of surface chemistry and structure of ground pyrophyllite reveals significant distortion of the mineral by grinding. The dehydration and dehydroxylation of pyrophyllite during prolonged grinding are accompanied by changes in Al coordination number and the formation of an amorphous Al-rich phase covering the surface of pyrophyllite to a depth of around 50nm. Approximately 41% coverage of the pyrophyllite surface by this newly formed Al-rich phase is calculated from XPS data after 30minutes of intense grinding. The local structural alteration of Si tetrahedra as well as Al octahedra is directly identified for the first time in our experimental results, indicating some incorporation of Si in the newly formed amorphous phase on the surface of intensely ground pyrophyllite, and this plays a significant role in influencing gold sorption. The highly reactive amorphous material on the surface of particles cements the particles together, which results in lower surface reactivity and preg-robbing. These findings demonstrate the important role of surface activation of ore constituents during fine grinding and the need for careful adjustment of grinding parameters to achieve the highest overall recovery. [Copyright &y& Elsevier]

Re-Os analyses of pyrite from the Pueblo Viejo high-sulfidation epithermal deposit (both Monte Negro and Moore ore zones) yield an isochron age of 111.9 ± 3.7 Ma and initial 1870s/1880s ratio of 0.22 ± 0.18 (mean square of weighted deviates = 84, n = 21). Isochrons grouped by pyrite setting (layered versus vein) or locations yield ages within uncertainty of the overall isochron and with each other and, as such, do not yield temporally distinguishable ages. Sphalerite vein samples as well as shale source rocks show evidence of open system behavior and loss of Re and therefore are not included in the above regression. These results confirm that the Pueblo Viejo deposit is Early Cretaceous in age and coeval with the volcanic Los Ranchos Formation, which hosts the deposit. Recent paleontological age assignments for the Hatillo Formation, which overlies the Los Ranchos Formation, show that it is only slightly younger, opening the possibility that mineralization in the Hatillo Formation could also be related to late stages of Los Ranchos magmatism. Whether these revised Los Ranchos-Hatillo relations provide sufficient cover to account for the paragenetically late formation of pyrophyllite at Pueblo Viejo remains unclear. Recognition that Pueblo Viejo is coeval with the Los Ranchos Formation shows that large-scale, high-sulfidation epithermal mineralization can form from basal island-arc tholeiitic magmatism. A review of available experimental data confirms that these magmas can generate hydrothermal solutions of the necessary composition; favorability of the Los Ranchos Formation might have been enhanced by its bimodal composition. These results suggest that exploration for epithermal precious metal deposits should include basal island-arc tholeiite terranes. [ABSTRACT FROM AUTHOR]

Capillary forces between discrete colloid particles are of interest in many areas of science and engineering. This study used molecular dynamics (MD) to examine capillary phenomena that develop in a clay–water–air system, which requires an understanding of capillary forces, contact angles, and meniscus curvatures. The capillary formed between two parallel pyrophyllite clay particles and pure water was studied using MD for various system parameters which included particle separation, particle thickness, and strength of the clay–water van der Waals force. For a given set of potential energy parameters, the contact angle was independent of particle separation (≈550), the radius of curvature depended on particle separation, and particle thickness had a negligible influence on contact angles and meniscus radii. The van der Waals energy parameters, however, had a profound influence on contact angles and meniscus radii. In all cases, capillary forces on clay particles calculated by MD agreed with values calculated using the classical Young–Laplace equation. When the separation distance is 40Å, the force was calculated to be 9.87×10−10 N by Young–Laplace equation and 8.37×10−10 N by MD. [ABSTRACT FROM AUTHOR]

Some meteorites consist of a mix of components of various parent bodies that were presumably brought together by past collisions. Impact experiments have been performed to investigate the degree of target fragmentation during such collisions. However, much less attention has been paid to the fate of the impactors. Here, we report the results of our study of the empirical relationship between the degree of projectile fragmentation and the impact conditions. Millimeter-sized pyrophyllite and basalt projectiles were impacted onto regolith-like sand targets and an aluminum target at velocities of up to 960 m s−1. Experiments using millimeter-sized pyrophyllite blocks as targets were also conducted to fill the gap between this study and the previous studies of centimeter-sized rock targets. The catastrophic disruption threshold for a projectile is defined as the energy density at which the mass of the largest fragment is the half of the original mass. The thresholds with the sand target were 4.5 ± 1.1 × 104 and 9.0 ± 1.9 × 104 J kg−1, for pyrophyllite and basalt projectiles, respectively. These values are two orders of magnitude larger than the threshold for impacts between pyrophyllite projectiles onto aluminum targets, but are qualitatively consistent with the fact that the compressive and tensile strengths of basalt are larger than those of pyrophyllite. The threshold for pyrophyllite projectiles and the aluminum target agrees with the threshold for aluminum projectiles and pyrophyllite targets within the margin of error. Consistent with a previous result, the threshold depended on the size of the rocks with a power of approximately −0.4 (Housen and Holsapple 1999). Destruction of rock projectiles occurred when the peak pressure was about ten times the tensile strength of the rocks. [ABSTRACT FROM AUTHOR]