Palygorskite Fibers Research Articles

Assessment of excavation slurry produced clayey mineral from the Bahr Al-Najaf region

AbstractThis study targeted to investigate a type of excavation slurry by local available material in Najaf region. On the other hand, chief practises is supported the deep sides of foundation in particular pile foundation and, drilling oil wells. The results of slurries are checking, for seven properties, which includes the viscosity (apparent plastic and funnel Marsh), yield stress, density, acidity, and gel power (10–0 min). Which are 11.7367, 8.8733, 38.1667, 11.5467 mPa·s, 1.1045 kg m−3, 10.9067, and 11.2683 mPa·s, respectively. On the basis of the results tests for the above properties, that is possible to produce a product that conforms to the specifications of American Petroleum Institute specifications, and according to the requirements of the standard ACI 336.3R-93:2006 without additives. The rheological behavior improvement is achieved through the breakdown of the bundles of palygorskite fibers that normally make up the texture of these mudstones by increasing the time and speed of the shear force as soon as increasing the concentration of clay powder.

Monolithic Cu/Al2O3-palygorskite composite aerogel for high-efficiency iodine elimination in a multimedia environment

Radioactive iodine has highly radioactive and biological toxicity, and its effective recovery is of primary importance. However, few materials can show good iodine adsorption in different media. Herein, Cu/Al2O3-Pal aerogels with improved mechanical properties and hierarchical pore structures were prepared by constructing the three-dimensional support skeleton of the aerogel with palygorskite fibers. The Cu/Al2O3-Pal aerogel exhibited excellent adsorption properties for I− (aqueous phase, 264–411 mg/g) and I2 (organic phase, 503–744 mg/g), I2 vapor (459–1122 mg/g), and CH3I vapor (559–1032 mg/g). Notably, the aerogel also exhibited ultra-high removal rates for trace iodide in solution (>90 %) and was able to efficiently convert to stable CuI. Importantly, the Cu/Al2O3-Pal aerogel can be prepared directly for use as a monolithic material, allowing for an easy recovery process. Overall, our work demonstrates the great potential of Cu/Al2O3-Palx wt% aerogels for radioactive iodine elimination.

Stabilization of calcareous subgrade soils with polyelectrolytes: mechanisms and mechanical properties

ABSTRACT Organic polyelectrolytes, i.e. anionic poly(sodium 4-styrenesulphonate) (PSS), cationic poly(diallyldimethylammonium chloride) (PDADMAC) and their polyelectrolyte complexes (PECs) were evaluated for stabilisation of calcareous sandy subgrade soil. This paper investigated the effects of polymer type, surface charge type of PEC, concentrations of PEC solutions and dosages of polymer solutions added to the soil on improvement of soil mechanical properties. We found that anionic polymers, for both PECs and individual polyelectrolytes, were superior to their cationic counterparts in improving soil strength. Besides, the constituent polyelectrolytes, PSS and PDADMAC, worked better than their PECs for the specific soil investigated. The strength of polymer-treated soils was also found to increase with the increase in dosages of the polymer solutions as well as curing periods. Furthermore, polymer-treated soil specimens exhibited significant toughness improvement, which was higher than cement-treated samples. Scanning electron microscopy images revealed the abundance of long palygorskite fibres covering the surfaces of larger calcite and dolomite particles and linking surrounding aggregates after adding polymers. This observation suggests the interconnection of palygorskite fibres and their linking networks between and among coarse aggregates as the likely mechanism of polymer stabilisation of the soil studied.

Effects of clay activation and amine chain length on silica–palygorskite heterostructure properties

AbstractVarious approaches have been used for the preparation of heterostructured materials based on clay minerals, with numerous potential applications offered by the resulting functional materials. In this study, a fibrous clay mineral (palygorskite) and a tetraethyl orthosilicate reagent were used to obtain silica–palygorskite heterostructures. The aim was to highlight the influence of two factors during the preparation process: the effect of acid activation pre-treatment of the palygorskite with HCl and the effect of varying the length of the amine chains used – dodecylamine and butylamine – on the formation and development of silica nanoparticles on the surface of the palygorskite fibres. The silica–palygorskite heterostructures were obtained after the removal of the organic templates by calcination at 500°C. The textural and structural properties of the silica–palygorskite heterostructured samples were determined using various experimental characterization techniques, such as X-ray diffraction, transmission electron microscopy, gas adsorption and Fourier-transform infrared spectroscopy. The experimental variables targeted in this study appeared to have a significant effect on the textural properties of the silica–palygorskite heterostructure obtained. The great specific surface area and the mesoporous, microporous and ultramicroporous volumes as determined using nitrogen and/or carbon dioxide gas adsorption confirm the benefit of combining the acid activation pre-treatment of the fibrous clay mineral with the use of a long-chain amine co-surfactant (dodecylamine). The resulting silica–palygorskite heterostucture has a great specific surface area (628 m2 g–1) and a well-developed total pore network (VN2 = 0.24 cm3 g–1; Vultra (CO2) = 0.18 cm3 g–1). This material will be tested for the removal of volatile organic compounds at low concentrations.

Neoformation of palygorskite in Calcids of Central Iran

Palygorskite has been reported in alluvial sediments and in soil clays in Central Iran, but it is not known if it is inherited or formed in situ. Here, we sampled Calcids developed from Triassic and Cambrian dolomitic formations in the southwestern part of Yazd and performed soil and clay characterization by X-ray diffraction and fluorescence, optical and scanning electron microscopy and energy dispersive X-ray spectrometer analyses. Our results suggested palygorskite neoformation in the calcic soil horizons in Calcids. The soils with aridic soil moisture regime and high Mg concentration, during the formation of a calcic horizon by precipitation of secondary calcite, conditions were suitable for authigenic palygorskite crystals of long size (>10–20 μm) and their stability. In addition, the occurrence of short-size (about 2 μm) palygorskite fibers in the lower gypsic horizon probably resulted from its translocation from the upper horizons. Therefore, such results suggested palygorskite neoformation in the calcic soil horizons in these Calcids of Iran.

Nafion/SiO2@TiO2‐palygorskite membranes with improved proton conductivity

AbstractThis work deals with the synthesis of SiO2@TiO2 supported palygorskite fibers and their use as a filler for proton exchange membrane fuel cells in order to improve their performance. SiO2@TiO2‐palygorskite nanostructured particles were synthesized separately with original route to ensure the growth of TiO2 and then of SiO2 on the surface of the clay. Accordingly, the introduction of the synthetic filler (SiO2@TiO2‐paly) into the electrolyte membrane (Nafion) aims to improve mechanical, thermal, and proton conductivity properties. The TiO2 nanoparticles were generated via a sol–gel process on the external surface of palygorskite. Then, SiO2 nanoparticles were synthetized using a similar sol–gel process, onto the TiO2‐palygorskite particles to produce the final SiO2@TiO2‐palygorskite particles. The physico‐chemical properties of the nanostructured particles were studied by X‐ray diffractometry, Fourier transform infrared, scanning electron microscopy, and transmission electron microscopy. Nafion based composite membranes were prepared using SiO2@TiO2‐palygorskite and TiO2‐palygorskite as a control standard. The composite membranes show improved mechanical properties, thermal stability, water retention, and proton conductivity compared to the neat Nafion membrane. Proton conductivities (at 100°C and 100% relative humidity) increased from 65.0 mS/cm for neat Nafion to 70.4 mS/cm and to 128.6 mS/cm when incorporated TiO2‐Paly (6% in weight) and SiO2@TiO2‐Paly (6% in weight), respectively.

Paleoenvironmental conditions during deposition of Kolosh and Gercus formations in northern Iraq as deduced from clay mineral distributions

A mineralogical study using X-ray diffraction supported by scanning electron microscopic examination on the Paleocene- Eocene Kolosh and Gercus formations from northern Iraq is conducted to show the distribution of clay minerals and their paleoenvironmental implications. Smectite palygorskite, kaolinite, illite, and chlorite are commonly present in varying proportions within the Kolosh and Gercus formations. Association of smectite and chlorite in the claystone of the Paleocene Kolosh Formation refers to marine environment of this formation, whereas development of palygorskite fibers from smectite precursor may relate to post-depositional diagenesis. In addition, the abundance of illite and kaolinite in the Eocene Gercus Formation suggests a greater influence of terrigenous input in humid conditions, affecting the distribution of these clay minerals. The study shows vertical change in clay minerals distribution when illite and kaolinite dominate in the Eocene Gercus Formation, in comparison to chlorite and smectite abundance in the Paleocene Kolosh Formation which may relate to global warming in the Eocene.

Interactions among TiO2 and palygorskite revealed: Boost for stability of well-known photocatalyst

Anatase, is widely used in photocatalysis because it is environmentally friendly, low-cost and presents good catalytic activities. Nevertheless, the anatase nanoparticles tend to agglomerate resulting in degradation of catalysis efficiency. The agglomeration problem can be resolved, using the fibrous clay mineral palygorskite via TiO2 particles dispersion on its fibers. Hence, it should be possible the efficient photocatalytic activity to derive from the strong interactions among the initial compounds. Palygorskite–TiO2 nanocomposites were synthesized and characterized by X-ray diffraction, Fourier transform-infrared spectroscopy and transmission electron microscopy, while the exact interactions and possible spontaneous bonding between palygorskite and the anatase sphere were investigated by molecular simulations. Three different supercells of palygorskite were built, which were further interacted with the TiO2 sphere with suitable surfaces. The optimal TiO2-palygorskite connection takes place among the Ti atoms of the curved TiO2 part with the O atoms from palygorskite’s fibers surface via electrostatic interactions and the potential strong covalent bonds. The molecular simulations results are in good agreement with transmission electron microscopy data. Based on simulation we can see the curved part of anatase which interacts with the Ti atoms and is connected to the palygorskite fibers through several types of its surfaces via the O atoms.

Degradation of sulfamethoxazole by Co3O4-palygorskite composites activated peroxymonosulfate oxidation

In this study, a simple hydrothermal method was used to synthesize Co3O4-palygorskite composites. Transmission electron microscopy, X-ray spectroscopy and X-ray diffraction analysis showed that Co3O4 nanoparticles with diameters of approximately 3–5 nm were uniformly distributed on the surface of palygorskite fibers. Co3O4-palygorskite composites were outstanding catalyst for activating peroxymonosulfate (PMS) to degrade the antibiotic sulfamethoxazole (SMX). Complete removal of 30 μM SMX at pH 3–5 was achieved with doses of 0.3 mM PMS and 125 mg/L Co3O4-palygorskite composites. The composites exhibited higher catalytical activity than unsupported Co3O4. The removal rate of SMX was accelerated under acidic conditions (pH 3–5), while was significantly inhibited under basic conditions (pH 11–12). Radical quenching tests revealed that SO4− and OH were responsible for the degradation. The oxidative degradation was initiated at either isoxazole or aniline moiety of the SMX molecule. Using solid phase extraction-liquid chromatography-time-of-flight-tandem mass spectrometry, a total of six transformation products formed from benzene ring hydroxylation, S-N bond cleavage, aniline moiety oxidation and coupling reactions were identified. Based on the products, three transformation pathways are proposed for the catalytic degradation of SMX in the Co3O4-palygorskite/PMS system.

Ca treated Palygorskite and Halloysite clay minerals for Ferrous Iron (Fe+2) removal from water systems

Abstract Palygorskite fibers and halloysite nanotubes (HNT) were used for the Fe (II) uptake from aqueous solutions under various experimental conditions. Palygorskite and halloysite samples were characterized using XRD, FTIR, SEM, BET and CEC and then were saturated by exchanging Ca + 2 cations. The Ca-Palygorskite (Ca-Pal) and Ca-Halloysite (Ca-Hall) were characterized as well, and applied in batch kinetic experiments series. It was shown that both Ca-treated clay minerals were more efficient adsorbents for the lowest ferrous concentrations removal (5 mg/L), especially when the highest solid: liquid ratio (20 g/L) have been applied, reaching 99.8% and 91.2% removal with Ca-Pal and Ca-Hall respectively, within 10 min at the optimal room temperature (20 ± 1 °C). The pH value affected the adsorption’s efficiency, as Ca-Pal was more efficient adsorbent at acidic values (4–6), while Ca-Hall efficiency is positively correlated with pH increase (7 ). Moreover, the competitive ions found to prohibit Ca-Hall capacity for Fe (II), following the order Mn K Cu Zn Ba Mg Na, but Ca-Pal is slightly affected by K Na=Mn Zn Cu Mg Ba, highlighting its preference to a Fe cations. According to the thermodynamic analysis the Fe (II) uptake is a physical and spontaneous process, while both Ca-Pal and Ca-Hall fit in Langmuir isotherm instead of Freundlich, indicating monolayer sorption. The exact mechanism of Ca-Pal efficient adsorption was verified and further explained with molecular simulation optimization by Material Studio 4.3.

Effects of pH on the gel properties of montmorillonite, palygorskite and montmorillonite-palygorskite composite clay

The effects of pH on the structures, compositions, morphologies, Zeta potential, and gel properties of montmorillonite, palygorskite and their composite clays were investigated in the study. With the increase in pH, the above properties of montmorillonite, palygorskite and their composite clays showed different changing trends. The compositions of montmorillonite and palygorskite basically remained unchanged in the pH range of 1–13. The dissociation and dispersion degrees of montmorillonite sheets, the separation and dispersion degrees of palygorskite fiber cluster and the absolute value of Zeta potential increased. The viscosity of palygorskite sample firstly increased and then decreased. The viscosity of montmorillonite and composite clay samples increased and the increase was rapid especially at pH above 12. The viscosity of montmorillonite and composite clay samples reached 9151 mPa·s at pH 13, but the viscosity of composite clay sample was lower than that of montmorillonite at the same pH value. The influencing factors of viscosity mainly included the dissociation degree of montmorillonite sheets, the separation degree of palygorskite fibers and the Zeta potential. The higher degrees of dissociation and dispersion corresponded to the higher viscosity. With the increase in the absolute value of Zeta potential, the viscosity of montmorillonite and composite samples increased, but the viscosity of palygorskite increased firstly and then decreased. The potential mismatch between palygorskite and montmorillonite was responsible for the lower actual viscosity of the composite sample compared to the calculated viscosity.

Excellent flame retardant and thermal insulated palygorskite/wood fiber composite aerogels with improved mechanical properties

Clay aerogels have many attractive properties, such as low thermal conductivities, good thermal stabilities and low flammability. But the generally weak mechanical property severely restrains their practical applications. Incorporation of polymers into clay aerogel could achieve desirable strength, unfortunately, the fire resistance or insulating properties were sacrificed to some extent. In this work, fire-resistant palygorskite/wood fiber composite aerogels with low densities were prepared by an eco-friend freeze-drying method. In the aerogels, palygorskite contents were up to 80 wt% while only a small amount of wood fiber were used as reinforced filler. The composite aerogel had an array of porous structure with intertwined palygorskite fibers as pore walls, which resulted in a low thermal conductivity of 0.033 W/mK. In addition, the composite aerogel exhibited good mechanical strength with the Young's modulus up to 4.7 MPa while the density was lower than 0.08 g/cm3. Overall, an outstanding combination of excellent machinability, thermal stability, high limiting oxygen index, and prominent flame-retardant properties has been achieved in the composite aerogels. This work represents a significant progress of porous materials development and makes the practical applications of clay-based aerogel insulators realistic.

Ternary Ag-deposited TiO2/palygorskite composites with synergistic effect for enhanced photocatalytic activity

Ternary Ag-deposited TiO2/palygorskite (AgTP) composites were facilely prepared by a one-step method. The crystal phases, morphology and photoelectric performances were characterized, and the results indicated that Ag-deposited TiO2 nanoparticles with size of 12–15 nm were adequately immobilized on the palygorskite fibers surface. Compared with anatase TiO2 and TiO2/palygorskite, the AgTP composites exhibited enhanced photocatalytic activity in degradation of methylene blue. Especially, the optimal sample (6.0AgTP) showed the highest photocatalytic activity, achieving 99.48% and 95.27% degradation efficiency after 60 min of UV–vis (350 ≤ λ ≤ 780 nm) or 210 min of visible-light (λ ≥ 420 nm) irradiation, respectively. Trapping tests with different scavengers revealed that not superoxide radicals but hydroxyl radicals and photogenerated holes were highly responsible for the degradation process. The enhanced photocatalytic activity was ascribed to the synergetic effect of palygorskite support effects (provide large surface area, optimize nanoparticles dispersibility and increase adsorption capacity), surface plasmon resonance of Ag, and efficient separation of charge carriers.

The effect of support on the structure and photocatalytic activity of ternary ZnO-ZnFe2O4/palygorskite composite photocatalysts

The ternary ZnO-ZnFe2O4/palygorskite composite photocatalysts were fabricated via a solvothermal method followed by thermal treatment. The structure, morphology and photoelectric performances of samples were characterized, and the results indicated that ZnO/ZnFe2O4 nanoparticles with size of 25–30 nm were adequately anchored on the palygorskite fibers surface. Compared with ZnO, ZnFe2O4, ZnO/ZnFe2O4 and ZnO/palygorskite, the ZnO-ZnFe2O4/palygorskite composite photocatalysts exhibited significantly improved photocatalytic activity in degradation of methylene blue (MB). Especially, the optimal photocatalyst (ZF1.5) displayed the highest photocatalytic activity, achieving 99.68% and 99.48% degradation efficiency after 90 min of UV–vis (350 ≤ λ ≤ 780 nm) and 100 min of visible-light (λ ≥ 420 nm) irradiation, respectively. The photocatalysis degradation process matched well with the Langmuir-Hinshelwood kinetics. The obtained improvement of photocatalytic activity was ascribed to the synergetic effect of superior visible-light utilization; effective charge carrier separation and palygorskite support effect (optimize nanoparticles dispersibility, developed mesoporous structure, enlarge specific surface area and increase adsorption capacity).

Design of solid foams for flame retardant based on bionanocomposites systems

Bionanocomposites are hybrid materials obtained from the interaction between two or more components. The construction of this type of material comes from a continuous phase, usually organic, and the dispersed phase, usually inorganic. Both phases are naturally occurring and at least one of them has a nanoscale structure. The bionanocomposites in this work were synthesized from the biopolymers rice starch and pectin reinforced by the clay mineral palygorskite. During synthesis, the freeze-drying method was used for production of low-density solid foams. Spectroscopic techniques were applied in order to identify the interaction mechanism established between the inorganic fibers and the polysaccharide chains, which is established between the hydroxyl groups in the biopolymers and the silanol groups at the external surface of the palygorskite fibers. Besides, X-ray diffraction showed that the structure of palygorskite was not affected during the synthesis and Energy-Dispersive X-ray spectroscopy (EDX) revealed a good dispersion of palygorskite on biopolymers. Horizontal burning tests were carried out based by ASTM D4986–03 for a preliminary study of flame-retardant materials, revealing that bionanocomposite foams based on rice starch with palygorskite content > 5% behave as auto-extinguishable materials.

On the key role of the surface of palygorskite nanofibers in the stabilization of hexagonal metastable β-Ag2CO3 phase in palygorskite-based nanocomposites

This study reports an original remarkable effect of fibrous palygorskite clay mineral in the stabilization at the ambient temperature of the metastable hexagonal β-phase of Ag2CO3 along with the stable monoclinic one (m-Ag2CO3) and the refinement of their particles size (≈5–10 nm). These structural and microstructural features likely arise owing to heterogeneous nucleation induced by the surface of palygorskite fibers between CO32– anions in solution and Ag+ exchanged palygorskite (Ag+-Pal) as reactants kept maturing for short periods, which should not exceed 1 h. Besides, the phase composition of Ag2CO3 supported on palygorskite, namely β- and m-structures can be monitored by carrying on appropriate low temperature treatments under CO2 atmosphere coupled with aging during several months in such a way that either pure β or m single-phases as well as biphased mixtures with controlled composition can be obtained. Taking into account experimental results and literature data, a growth mechanism is discussed.

Dolomite dissolution: An alternative diagenetic pathway for the formation of palygorskite clay

AbstractPalygorskite is a fibrous, magnesium‐bearing clay mineral commonly associated with Late Mesozoic and Early Cenozoic dolomites. The presence of palygorskite is thought to be indicative of warm, alkaline fluids rich in Si, Al and Mg. Palygorskite has been interpreted to form in peritidal diagenetic environments, either as a replacement of detrital smectite clay during a dissolution–precipitation reaction or solid‐state transformation, or as a direct precipitate from solution. Despite a lack of evidence, most diagenetic studies involving these two minerals posit that dolomite and palygorskite form concurrently. Here, petrological evidence is presented from the Umm er Radhuma Formation (Palaeocene–Eocene) in the subsurface of central Qatar for an alternative pathway for palygorskite formation. The Umm er Radhuma is comprised of dolomitized subtidal to peritidal carbonate cycles that are commonly capped by centimetre‐scale beds rich in palygorskite. Thin section, scanning electron microscopy and elemental analyses demonstrate that palygorskite fibres formed on both the outermost surfaces of dissolved euhedral dolomite crystals and within partially to completely dissolved dolomite crystal cores. These observations suggest that dolomite and palygorskite formed sequentially, and support a model by which the release of Mg2+ ions and the buffering of solution pH during dolomite dissolution promote the formation of palygorskite. This new diagenetic model explains the co‐occurrence of palygorskite and dolomite in the rock record, and provides valuable insight into the specific diagenetic conditions under which these minerals may form.

Mineralogy and physicochemical features of Saharan dust wet deposited in the Iberian Peninsula during an extreme red rain event

Abstract. The mineralogy and physicochemical features of Saharan dust particles help to identify source areas and determine their biogeochemical, radiative, and health effects, but their characterization is challenging. Using a multianalytical approach, here we characterized with unprecedented level of detail the mineralogy and physicochemical properties of Saharan dust particles massively wet deposited ( ∼ 18 g m−2) following an extreme red rain event triggered by a northern African cyclone that affected the southern Iberian Peninsula during 21–23 February 2017. Abundant palygorskite and illite, and relatively high carbonate contents, well-known northern and north-western Saharan dust indicators, along with low chlorite content and significant amounts of smectites and kaolinite, whose abundance increases southwards in the western Sahara, complemented by satellite imagery and back/forward trajectories, show that the most probable dust source areas were (i) southern/central Algeria, northern Mali, and northwestern Niger, and (ii) northern Algeria, southern Tunisia, and northwestern Libya. Scanning and transmission electron microscopy analyses, including Z-contrast high angle annular dark field (HAADF) imaging and analytical electron microscopy (AEM), show that clay minerals include abundant structural Fe (55 % of the total Fe) and typically form nanogranular aggregates covered or interspersed with amorphous/poorly crystalline iron oxyhydroxide nanoparticles (ferrihydrite), which account for ∼ 18 % of the free Fe, the rest being goethite and hematite. These nanogranular aggregates tend to form rims lining large silicate and carbonate particles. Such internally mixed iron-containing phases are the main contributors to the observed absorption of solar and thermal radiation, and along with the abundant coarse/giant particles ( > 10 µm) strongly affect the dust direct radiative forcing. The lack of secondary sulfates in aggregates of unaltered calcite internally mixed with clays/iron-rich nanoparticles shows that iron-rich nanoparticles did not form via atmospheric (acid) processing but were already present in the dust source soils. Such iron-rich nanoparticles, in addition to iron-containing clay (nano)particles, are the source of the ∼ 20 % soluble (bioavailable) iron in the studied desert dust. The dust particles are a potential health hazard, specifically the abundant and potentially carcinogenic iron-containing palygorskite fibers. Ultimately, we show that different source areas are activated over large desert extensions, and large quantities of complex dust mixtures are transported thousands of kilometers and wet-deposited during such extreme events, which dwarf any other Saharan dust event affecting southwestern Europe. The past, present, and future trends, as well as impacts, of such extreme events must be taken into account when evaluating and modeling the manifold effects of the desert dust cycle.

Adsorption of linuron by an Algerian palygorskite modified with magnetic iron

Abstract Three types of palygorskite nanoparticles for the retention of the herbicide linuron in water were tested: purified palygorskite (Pur Pal), palygorskite modified by magnetic iron oxides (FeO Pal 1 ) and this one synthesized by hydrothermal treatment (FeO Pal 2 ). The adsorbents were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), electron microscopy (TEM) and chemical analysis (XRF). XRD patterns indicate the presence of a magnetic Fe 2 O 3 compound, and TEM images evidence how these crystals cover the palygorskite fibers' surface with different crystallite sizes (7–15 nm in FeO Pal 1 and 30-50 nm in FeO Pal 2 ). The adsorbent mass, the contact time, the initial adsorbate concentration and the effect of temperature were evaluated for linuron retention. Adsorption kinetics revealed that adsorption followed a pseudo-second order equation. Adsorption isotherms were better fitted to the Freundlich than to the Langmuir equation. Removed linuron amounts were ranged as FeO Pal 2 (83%) > FeO Pal 1 (55%) > Pur Pal (27%). The adsorbents could be used as a cheap alternative for pesticide removal in environmentally-contaminated waters.

Palygorskite occurrences and genesis in calcisol and groundwater carbonates of the Tensift Al Haouz area, Central Morocco

Palygorskite has been identified as a major constituent of the clay fraction in carbonate soils of arid and semi-arid regions. This fibrous clay has a great significance as a paleoclimatic indicator and is of fundamental importance for a more complete understanding of conditions under which petrocalcic horizons and groundwater carbonates precipitate. The present study was undertaken in order to evaluate the occurrence, the genesis as well as the micromorphological aspects of palygorskite in calcisol and groundwater carbonates. The samples were analyzed by X-ray Diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis (XRF). Two modes of genesis for palygorskite were identified: (1) In the petrocalcic horizons, the palygorskite is the dominant clay mineral; palygorskite fibers and fiber bundles extend from euhedral or subhedral calcite crystals showing an authigenic origin of palygorskite. The palygorskite is formed in the vadose environment from infiltrating soil water through the intense evaporation of subsurface water after calcite precipitation. (2) In the groundwater carbonates, smectite flakes appear to terminate palygorskite fibers suggesting formation of palygorskite through the alteration of precursor smectite. The increasing aridity would have caused the intense evaporation conducive to the precipitation of calcite and an increase in pH, which lead to dissolution of smectite and formation of palygorskite.