Kaolinite Flakes Research Articles

Corkit a metatorbernit z uranového výskytu Kosobody u Jesenice

Corkite and metatorbernite occur in the supergene zone of uranium mineralization at an abandoned exploration shaft No 36 situated about 1 km NW from the village of Kosobody at Jesenice in the Rakovník District. The locality was explored for uranium in 1954–1959 and subsequently in 1970–1972 (Mrázek 1972). The mineralization is confined to discordant mm–cm thick veinlets in brecciated phyllite. The veinlets are composed of quartz, barium-rich K-feldspar, “limonite” (goethite), kaolinite, metatorbernite and corkite. The country rock is Neoproterozoic phyllite of the Teplá-Barrandian Zone (Chlupáč – Štorch 1992, Kopecký et al. 1997, Klomínský et al. 2010). The samples were collected in 2021 and studied by PXRD and in carbon-coated polished sections by EMPA. Metatorbernite forms apple-green, thin tabular to lamellar crystals 0.1–1 mm in size (Fig. 1a, b). In the thin section, it also forms more massive fillings and radiating aggregates up to several millimeters (Fig. 2a–c, Fig. 3a). EMPA showed good agreement with the theoretical formula. The content of barium fluctuates in the range of 0.0–5.51 wt. % BaO, which corresponds up to 36 mol. % of metauranocircite component. The mean empirical formula is: (Cu0.79Ba0.12Ca0.03) (UO2)2.03(PO4)1.98 · 8 H2O, see Table 1. The lattice parameters calculated for the Space Group P4/n: a = 6.9647(8) A, c = 17.322(2) A, V = 840.2(2) A3 are in good agreement with published data (compare Table 2). Corkite forms isometric or irregular accumulations up to 1 mm in size of yellow colour, which are mostly brown cloudy, intergrown ith metatorbernite and are often surrounded by aggregates of “limonite” (goethite) and kaolinite flakes (Fig. 2a–c). In BSE, corkite aggregates show irregular darker and lighter domains (Fig. 3b). Lighter domains have slightly higher Pb contents, otherwise the differences in chemical composition are negligible. To calculate the empirical formula, the numbers of atoms were normalized to the sum T-site elements = 2. The mean empirical formula: (Pb0.99U0.04)(Fe2.85Al0.26) [(PO4)1.46 (SO4)0.49] (OH)6, displays a significant predominance of P over S. The data are thus plotted near the corkite – kintoreite boundary in the ternary P – As – S diagram (Fig. 4). The Al, which partly replaces Fe3 , indicates 4–12 mol. % of isomorphic admixture of hinsdalite, ideally PbAl3(PO4)(SO4)(OH)6. There is also low but omnipresent content of uranium (0.03–0.05 U apfu, see Table 3), which was not reported among minerals of the crandallite group (Fig. 5). The lattice parameters a = 7.265(3) A, c = 16.87(1) A, V = 771.5(6) A3, calculated for the Space Group R3m, are in the agreement with the published data (compare Table 4).

Biomimetic Tremelliform Ultrathin MnO2/CuO Nanosheets on Kaolinite Driving Superior Catalytic Oxidation: An Example of CO.

Highly efficient three-dimensional (3D) kaolinite/MnO2-CuO (KM@CuO-NO3) catalysts were synthesized by a mild biomimetic strategy. Kaolinite flakes were uniformly wrapped by ultrathin tremelliform MnO2 nanosheets with thicknesses of around 1.0-1.5 nm. Si-O and Al-O groups in kaolinite hosted MnO2 nanosheets to generate a robust composite structure. The ultrathin MnO2 lamellar structure exhibited excellent stability even after calcination above 350 °C. Kaolinite/MnO2 exhibited abundant edges, sharp corners, and interconnected diffusion channels, which are superior to the common stacked structure. Open channels guaranteed fast transportation and migration of CO and O2 during CO oxidation. The synthesized KM@CuO-NO3 achieved a 90% CO conversion efficiency at a relatively low temperature (110 °C). Furthermore, the abundant oxygen vacancies on KM@CuO-NO3 assisted the adsorption and activation of oxygen species and thus enhanced the oxygen mobility and reactivity in the catalytic process. The mechanism results suggest that CuO introduced to the catalyst not only acted as CO active sites but also weakened the Mn-O bond, subsequently improved the mobilities of the oxygen species, which was found to contribute to its high activity for CO oxidation. This study provides new conceptual insights into rationally regulating structural assembly between transition metal oxides and natural minerals for high-performance catalysis reactions.

Genesis and possible applications of Lwamondo and Zebediela Kaolins, Limpopo Province, South Africa

ABSTRACT The genesis and potential industrial applications of Lwamondo and Zebediela Kaolins in South Africa were determined. Selected physico-chemical characteristics were determined. Mineralogical characteristics were determined using XRD and SEM; and geochemical characteristics were determined using XRF and LA-ICP-MS. Kaolin colours were generally light (Lwamondo) and brown (Zebediela). Both kaolins had low pH (<6.5) and EC (<50 µS/cm). The texture of Lwamondo Kaolin was generally loam and clay loam, whereas that of Zebediela was clayey, silty and loamy. Major mineral phases were kaolinite, smectite and plagioclase in Lwamondo Kaolin, and kaolinite in Zebediela Kaolin. The morphology of the kaolins consisted mainly of stacks of kaolinite flakes. The most dominant major oxides were SiO2, Al2O3 and Fe2O3, and the kaolins were slightly depleted in light rare earth elements. The studied characteristics indicated that the kaolins (i) formed in a supergene environment and (ii) are suitable for hollow bricks.

Kaolinite flakes and coal fines production in lignite core under ambient conditions: A case study of Neyveli Lignite Field at Cauvery Basin, Southern India

Coal fines production and structural collapse during waterflooding process was widely observed and reported in several coalbed methane (CBM) fields. Besides, fines migration also plays a major role in the destruction of coal cleats and consequently, declining the gas recovery. This paper presents the coal fines production in lignite core as a function of kaolinite. Actually, it is a clay fine particle that rests on coal surface under the dominances of the four forces, namely, lift, drag, gravity, and electrostatics. Under hydrodynamic and thermodynamic forces these fines detach from the rock surface and migrate in the porous interspace, and at a certain point it is captured, and thereby deteriorating the well productivity and structural collapse as well. Many researchers have investigated these fines migration mechanisms in anthracite and bituminous coals, but to best of our knowledge till date this research was not carried out in lignite coals. In order to successfully demonstrate this mechanism in lignite, three sets of coreflood experiments have been conducted under ambient conditions for analyzing the coal and kaolinite fines transport and their impact on gas recovery. Lignite samples are procured from Neyveli Mines at Cauvery Basin in Southern India and then the simulated version is used for the analysis. The coreflood results revealed that the gas recovery increases for increasing PVI and that there is an observation of pressure drop across the core for increasing PVI and this phenomenon is attributed to enhancing concentration of fines. Additionally, the water flow velocity elevates the velocity of coal fines and the microstructural analysis indicated the presence of kaolinite flakes among coal fines. The entire experimental model was tested against the statistical model in SPSS and showed good agreement. Overall, it is understood that even lignite reservoirs are prone to fines migration and permeability decline.

Lanthanum-doped kaolinite for hierarchical bi-modal porous inorganic membrane

Porous inorganic membranes can function in corrosive or high-temperature environments for prolonged duration without significant degradation in performance. Their high fabrication and material cost, however, outweigh their advantages. Here, adding lanthanum (La) to kaolinite, a cheaper inorganic material, enables a stronger and more permeable membrane sintered at 1150°C; A 11wt% La-doped kaolinite displays strength of ∼10MPa and Darcy’s permeability of 1.5×10−13m2–2.5 and 3 times higher than the pristine sintered kaolinite matrix respectively. The La-doping technique disrupts the randomly oriented stack of kaolinite flakes and increases the particle-particle contacts during sintering. Consequently, “pot-holes” are created to give a bi-modal porous structure, which reduces the tortuosity and improves the pore connectivity. It is concluded that La interacts with Al of the kaolinite during sintering based on XRD and EDX analysis. Finally, a carbon nanotube network (CNTN) is incorporated into the porous channel of La-doped membrane and is used as a membrane to purify emulsified oily water with a 100% rejection.

Electrophoretic deposition of kaolin: effects of Al/(Al + Si) ratio, surface charge, mineral, structural and morphological properties

Aluminosilicate compounds such as zeolite and kaolin and their coatings can be useful as a support of sensors and absorbers. In this study, electrophoretic deposition (EPD) of four types of kaolin has been reported. Various types of kaolin differ from each other in Al/(Al + Si) ratio, mineral compositions, surface charge and size of kaolinite flakes. EPD in aqueous and non-aqueous (ethanol) suspensions were compared. Quality of deposition and yield of non-aqueous suspension was higher due to the higher current density which can be resulted from lower polarity index of ethanol. It was found that the kaolin sample with the highest ability of ion extracts, higher zeta potential in the wide range of pH (−20 to −60 mV) and larger diameter of basal surfaces with respect to edge size of kaolinite flakes were essential factors to obtain completely coverage of aluminum substrate below 15 min. This kaolin coating can be useful in sensors and catalysts, because of high surface area in contact with gas molecules.

Trace element (Th, U, Pb, REE) behaviour in a cryptokarstic halloysite and kaolinite deposit from Southern Belgium: importance of “accessory” mineral formation for radioactive pollutant trapping

Hectometer wide cryptokarsts in Paleozoic limestone from Southern Belgium have been studied, to determine to what extent U, Th, Pb and rare earth elements (REE) have been mobilized in the karst sedimentary filling, during a Miocene weathering event. The weathering process resulted in the massive halloysite/kaolinite formation at the karst wall. As with most fossil systems, data on weathering fluid chemistry are lacking, hence it is difficult to quantify relevant parameters such as pH, Eh, and to address solution chemistry. However, on the basis of both field studies of more recent systems, and of geochemical modeling, it is proposed that moderately acid fluids percolated through a multi-layer sedimentary filling, in near-surface conditions and in a temperate/warm climate. Special attention is paid to the trace element immobilization/trapping processes, in newly crystallized REE phosphates, at the karst wall. Analytical methods used include major/trace element geochemistry (emission ICP, ICP–MS) and mineralogy (XRD, SEM, TEM, microprobe). The results suggest that both the sandy sediments that are in contact with the karst carbonate wall, and the carbonate wall itself acted as a kind of geochemical “barrier”. Mineralization cells settled there, at the decimeter to meter scale. This results in sequential trace element (Pb, Th, REE, U) trapping, according to the affinity of these elements for the aqueous solution. At the end of the sequence, minute U-rich automorphic (Ce, Nd) monazite crystals (from 3 nm upwards) formed on kaolinite flakes. Though the analogy between the studied cryptokarst and planned surface-based repositories for low-level radioactive waste (LLW) in argillaceous context is far from complete, the results outlined here are relevant because they show that even in natural—i.e. intrinsically uncontrolled and unmonitored—systems, “pollutant” radionuclide (U, Th, REE, Pb) migration paths are often limited in space. Various processes converge towards trapping of these elements, that are present in the radioactive waste.

Depositional and diagenetic signatures of Late Eocene–Oligocene sediments, South Carolina

Abstract Surficial and near-surface soils of the South Carolina Coastal Plain reflect a variety of lithologies and depositional environments that are difficult to differentiate because of intense leaching and abrupt or laterally inconsistent facies changes. Binocular microscopic examination, scanning electron microscopic/energy dispersive X-ray (SEM/EDX) observations, and X-ray diffraction (XRD) analyses indicate that onshore Late Eocene to Late Oligocene Barnwell Group sediments are transitional facies ranging from high-energy fluvial deposits to offshore siliciclastic shelf sands. Interfingering of the units results in alternation of mineralogic signatures within a low-gradient fluvial/transitional/marine depositional system. Late Eocene and Early Oligocene offshore sediments were deposited in a mixed carbonate–siliciclastic, middle- to outer-shelf environment that was subjected to periods of erosion or non-deposition during transgressive events. Detrital and diagenetic characteristics of the onshore kaolinite-enriched, Late Oligocene Upland Unit sediments reflect deposition in a high- to low-energy fluvial system. Differentiation between these uppermost sediments and the underlying low-energy fluvial deposits of the Late Eocene Tobacco Road Sand is based on distinctive hydroxy-interlayered vermiculite (HIV) signatures. Intervals of HIV-enrichment are coincident with accumulations of carbonaceous material and identified as paleosols; these “soils” are used to infer offshore transgressive periods. Onshore sediments of the Late Eocene Dry Branch Formation contain high concentrations of smectite and flocculated, relatively poorly crystallized kaolinite flakes reflective of marine depositional conditions. At the base of this unit, authigenic Ca-minerals (Ca-zeolites and calcite) and quartz lepispheres (opal-CT) form coatings on and between sand grains. Late Eocene siliceous microfossils that contribute to opal-CT formation are identified in southwestern North Atlantic continental margin shelf, slope and rise deposits and are a valuable correlation tool for onshore sediments.

Supergene Origin of the Lastarria Kaolin Deposit, South-Central Chile, and Paleoclimatic Implications

AbstractThe residual kaolin deposits near Lastarria, South-Central Chile, were formed by weathering of subvolcanic quartz porphyry stocks, which intruded the metamorphic basement of the Coastal Cordillera. The clay fractions (&lt;2 µm) consist mainly of poorly-ordered, very fine-grained kaolinite and lath-shaped illite (17–38 wt. %) with minor amounts of quartz, sanidine, and goethite. A sample from the top of the deposit contains major quantities of gibbsite morphologically indistinguishable from kaolinite flakes. The gibbsite-free clays contain 35.5–36.6 wt. % Al2O3, 0.4–2.6 wt. % Fe2O3, 1.3–3.9 wt. % K2O, and have low TiO2 concentrations (&lt;0.02 wt. %). The absence of quartz veining, the abundance of melt inclusions, and the scarcity of secondary fluid inclusions in quartz phenocrysts from altered rocks imply a lack of significant hydrothermal activity in the quartz porphyries. The δ 18O and δD values of the kaolins indicate formation in a weathering environment at significantly higher annual mean air temperatures (∼12°C) than present mean temperatures of ∼9.4°C. Uplift of the region alone probably cannot account for the change in climate. The stable isotope composition of gibbsite is consistent with an origin of desilication of kaolinite at superficial temperatures. Various criteria proposed to distinguish supergene from hypogene kaolins are discussed.

Depositional environment and diagenesis of the lower part of the Kurnub Sandstone Formation (lower cretaceous), Mahis area, Jordan

The lowest part of the Kurnub Sandstone Formation (Lower Cretaceous) in the Mahis area was deposited in a fluvial environment. Kaolinite is the major clay mineral associated with quartz. The transformation of feldspars and mica to sericite and finally to kaolinite was a major degradation process and was the result of intensive action of acidic circulating water. Most of the kaolinite flakes, however, are believed to be detritally deposited under freshwater conditions.

St. Peter Sandstone: A Closer Look

ABSTRACT At low magnifications, the St. Peter Sandstone from working quarries in northeastern Illinois was found to be subangular to rounded, frosted in appearance, and occasionally covered with localized, relatively large, terminated quartz overgrowths. At higher magnifications, however, the frosted surface of the quartz grains was found to consist of a layer of micron-sized, coprecipitated quartz crystals and kaolinite flakes. The delicate nature of the crystals suggests that these surface features are secondary, having a postdiagenetic origin. Based on the scanning electron microscope data presented, it is impossible to tell the state or nature of the original sand surface before deposition.

The Reactivity of C109 Sand: A Closer Look

ABSTRACTIt was observed that standard ASTM C 109 sand (St. Peter Sandstone) from working quarries in the Ottawa area (northeastern Illinois) is nearly always sub-angular to rounded, frosted in appearance, and occasionally covered with localized, relatively large, terminated quartz overgrowths. At higher magnifications the frosted surface of the quartz sand was found to consist of a thin layer of micron-sized, coprecipitated quartz crystals and occasional kaolinite flakes. Upon reaction of the sand with either a saturated Ca(OH)2 solution or as part of a sand-cement paste, some of these features were preserved, whereas others were lost. Micrographs of sand cured in cement paste at 90°C are presented showing that the kaolinite flakes react and become “puffy” and rounded in appearance. Also, the smooth surfaces of the large, terminated quartz overgrowths are severely etched as a result of dissolution. Sand reacted at 38°C in saturated Ca(OH)2 solution demonstrated more subtle effects, perhaps obscured by precipitated CaCO3 and C-S-H on the surfaces of the quartz overgrowths. These results suggest that ASTM C 109 sand is not entirely inert, but exhibits a limited amount of temperature-dependent pozzolanic activity.

Dissimilar Fabrics by Scan Electron Microscopy of Sedimentary Versus Hydrothermal Kaolins in Mexico

AbstractDissimilar fabrics, observed by scan electron micrography (SEM) on freshly broken surfaces of kaolins from weathered, water-laid material vs hydrothermally altered material in Mexico are illustrated, contrasted, and tentatively related to their respective environments of genesis. Coarse, open-textured, well-preserved books and vermiforms of kaolinite characterize the kaolin from water-laid material at Jacal, Mexico. Hydrothermal kaolins tend to have more tightly compacted crystals of either kaolinite flakes (individuals or in packets) or elongates (halloysite morphology) or mixtures of both in the same deposit. Variations in porosity of parent rock whether sedimentary or igneous, and dissimilar permeation by meteoric water and by vapor and liquids of hydrothermal fluids are deemed to be significant in the processes producing distinctive fabrics. The question is raised as to the fundamental distinction between kaolinite and halloysite and their nomenclature.

THE RETENTION OF AMORPHOUS, COLLOIDAL ‘FERRIC HYDROXIDE’ BY KAOLINITES

SummaryThe sorption and distribution of amorphous colloidal ‘ferric hydroxide’1 particles on the surfaces of kaolinite flakes were studied by electron microscopy. The sorption reaction was crystallographically specific with particles observed only on basal plane surfaces and was unaffected by the presence of excess NH4+, Ca++, or Al+++ ions. Cationic surface‐active agents prevented the reaction. Differences observed in colloid distribution and density on the introduction of a competing surface indicated that only one surface of a flake was attracting colloid particles and similar experiments with quartz and gibbsite suggested the silicatetrahedra surface of kaolinites as the probable site of colloid fixation. The distribution of colloid was unaffected by pH variation, saturation with ammonium acetate, prolonged washing, or ultrasonic vibrations. The colloid was removed only by extraction with sodium dithionite.

The slaking of soil crumbs as influenced by clay mineral composition

The water adsorption and swelling of dry orientated flakes of a Ca-illite and a Ca-kaolinite have been measured at high relative vapour pressures and finally immersed in solution. Portions of the flakes equilibrated in the vapour phase were immersed in solution, either in air or under vacuum, and the degree of slaking observed. Whereas the pore space of illite was filled at p/po = 0.92 and slaking was inhibited, that of kaolinite was incompletely filled at p/po = 0.985 and the clay still slaked severely. Slaking of both clays only occurred if air was present initially in the flakes. The swelling of dry Ca-montmorillonite flakes in water was increased if the flakes were immersed in air rather than under vacuum. It is suggested that the pressures developed by entrapped air, and hence the amount of slaking due to this cause, depend not only on the initial size of the air-filled pores but also on how much the clay swells. Further, the thickness of the clay particles controls not only the pore size distribution but also how far the shear stresses due to swelling can be reduced by bending of the particles. Some of the observed properties of kaolinite flakes are explained in terms of a simple model. Two examples are given of kaolinitic soils which appear to slake and collapse to an appreciable depth on rapid wetting.

Note on Surface Smoothness of Kaolinite Flakes

Note on Surface Smoothness of Kaolinite Flakes