Adsorption Kinetics of Methylene Blue from Aqueous Solutions onto Palygorskite

The adsorption kinetics of methylene blue from aqueous solutions on purified palygorskite was investigated. The kinetics data related to the adsorption of methylene blue from aqueous solutions are in good agreement with the pseudo-second order equation in ranges of initial concentration of 120-210 mg/L, oscillation speed of 100-200 r/min and temperature of 298-328K. The experimental results show that methylene blue is only adsorbed onto the external surface of purified palygorskite, and the apparent adsorption activation energy is 13.92 kJ/mol. The relatively low apparent adsorption activation energy suggests that the adsorption of methylene blue involves in not only a chemical, but also a physical adsorption process, and it is controlled by the combination of chemical adsorption and fiquid-film diffusion.

Improvement of CO2 capture performance of calcium-based absorbent modified with palygorskite

Limestone can be used for CO_2 capture and sequestration(CCS) in flue gas effectively. However, its CCS capability will dramatically decline after several cycles due to the surface "sintering". In this work, the limestone was modified with palygorskite to reduce sintering phenomenon between the absorbent particles during the CCS process and the carbonation rate of the limestone can be enhanced effectively. Palygorskite is a natural mineral with nano-fibrous structure which can reduce the mutual contact of limestone particles during the CCS process. The results were detected by TGA, SEM, MIP, FTIR and particle size analyzer respectively. The best CO_2 capture performance of modified absorbent was 13.11% improvement with only 5 wt% palygorskite added during the CCS process after 15 cycles compared with natural absorbent. It was found that excellent microscopic structures of absorbent modified with palygorskite was created, and the surface sintering was postponed leading to CO_2 capture performance enhanced under the same conditions.

Enhanced adsorptive removal of Cr(VI)in aqueous solution by polyethyleneimine modified palygorskite

Polyethyleneimine(PEI)modified palygorskite(Pal)was used for the adsorption of Cr(VI)in aqueous solution.The absorbent was characterized by Fourier transform infrared spectroscopy(FT-IR)and thermogravimetric analysis(TGA).Characterized results confirmed that the Pal has been successfully modified by PEI.The modification of PEI increased the Cr(VI)adsorption performance of the Pal by the adsorption combined reduction mechanism,and amino groups of the adsorbent play the main role in the enhanced Cr(VI)adsorption.The maximum adsorption capacity was 51.10 mg·g^-1 at pH4.0 and 25°C.The adsorption kinetics of Cr(VI)on the adsorbent conforms to the Langmuir isotherm model.The maximum adsorption occurs at pH3,and then the adsorption capacity of PEI-Pal was decreased with the increase of p H values.The adsorption kinetics of Cr(VI)on PEI-Pal was modeled with pseudo-second-order model.The addition of Cl^-,SO4^2-and PO4^3-reduced the Cr(VI)adsorption by competition with Cr(VI)for the active sites of PEI-Pal.The Cr(VI)saturated PEI-Pal can be regenerated in alkaline solution,and the adsorption capacity can still be maintained at 30.44 mg·g^-1 after 4 cycles.The results demonstrate that PEI-Pal can be used as a potential adsorbent of Cr(VI)in aqueous solutions.

Preparation of Palygorskite-based Phase Change Composites for Thermal Energy Storage and Their Applications in Trombe Walls

Palygorskite/paraffin phase-change composites were prepared by the combination of purified palygorskite clay and sliced paraffin. Then, this composite was used in the Trombe wall to improve its energy storage ability. Further, its energy storage ability was compared to that of ordinary concrete wall through contrastive test. The experiments show that palygorskite clay is a type of clay mineral with strong adsorption ability, and the purity of natural palygorskite clay can reach up to 97.1% after certain purification processes. Paraffin is well adsorbed by palygorskite, and the test results show that the optimal adsorption ratio is palygorskite： paraffin = 2：1（mass ratio）. Palygorskite/paraffin phase change composites can be obtained by using palygorskite as the adsorbing medium to adsorb paraffin. The composite materials exhibit good heat storage（release） performance, which can store heat with increasing environment temperature and release heat with decreasing temperature. This property not only increases the inertia to environment temperature change, but also promotes the energy migration in different time and space, thus achieving a certain energy-saving effect. The application of palygorskite/paraffin phase change composite materials to the Trombe wall can significantly reduce the fluctuation of indoor temperature and enhance the thermal inertia of indoor environment. From the aspect of energy storage effect, the Trombe wall fabricated using PCMs is significantly superior to the concrete wall with the same thickness.

SAED and HRTEM Investigation of Palygorskite

The microstructure of palygorskite from Longwang Mountain of Xuyu County, Jiangsu Province, was studied by energy dispersive X-ray analysis （EDX）, selected-area electron diffraction （SAED） and high-resolution transmission electron microscopy （HRTEM）. The average composition of the palygorskite studied is （Si7.38A10.62） （A10.96Fe^3＋ 0.62Mg2.86 0.56）Ca0.03K0.06O20（OH）2（OH2）4, which is rich in Mg. Several SAED patterns from a single crystal of palygorskite were obtained with different zone axes. The polymorphs （monoclinic and orthorhombic） are unequivocally distinguished by distant interplanar angles, even though they possess similar sets of d-values. High-resolution images of three principal zones （[010], [100] and [110]） were obtained. The lattice fringes on HRTEM images along [010] have spacings of 0.319 nm. These fringes are interpreted as periodic alterations of two tetrahedral （T） sheets and one octahedral （O） sheet （-TT-O-TT-O-）. We have directly observed trioctahedral and dioctahedral individual palygorskite particles along [100]. They are all presented as dark lines along [001], but the width of dark lines corresponding to trioctahedral crystals （0.913 nm） is twice that of the dioctahedral ones （0.456 nm）. This is because the trans.sites are occupied by cations in trioctahedral palygorskite. The width of dark lines along [110] is 1.024 nm, a bit thinner than the theoretical spacing （1.044 nm）. This is because water molecules quickly leave the structure upon the irradiation by the electron beam.

Distribution of Palygorskite in the Lingtai Profile of Chinese Loess Plateau:Its Paleoclimatic Implications

Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate. In this paper, field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai, Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma, but no occurrence has been found in eolian sediments since 3.2 Ma. Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis, and transformed from iilite-montmorilionite under the pore water action. In the Lingtai profile, the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility, dust flux and depositional rate. The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon, when changes took place in the East Asia paleoclimate pattern, i.e. a high-frequency strong fluctuation alternative evolution of the environment. Therefore, palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time.

Structures and Properties Characterization of Acrylonitrile-butadiene-styrene /Organo-palygorskite Clay Composites

Palygorskite （PGS） and vinyl tris-（2-methoxyethoxy） silane （KH-172） modified palygorskite （OPGS） were used to prepare acrylonitrile-butadiene-styrene （ABS）/clay composites. Thermal stability of the composites was evaluated by using thermogravimetric analysis （TGA）. The morphology of the fractured surface and the degree of dispersion of the clay in the ABS matrix were observed by scanning electron microscopy （SEM）. X-ray diffraction （XRD） analysis results showed the variation of the crystal structure. Measurements of the tensile properties of the ABS/clay composites proved that the ABS/OPGS composited material represented the most excellent tensile property, because of good compatibility and dispersion of ABS with OPGS.

Preparation and properties of a low-cost porous ceramic support from low-grade palygorskite clay and silicon-carbide with vanadium pentoxide additives

Alow-cost porous ceramic support was prepared from low-grade palygorskite clay(LPGS) and silicon carbide(SiC)with vanadium pentoxide(V_(2) O_(5)) additives by a dry-press forming method and sintering.The effects of SiC-LPGS ratio,pressing pressure,carbon powder pore-forming agent and V_(2) O_(5) sintering additives on the microstructure and performance of the supports were investigated.The addition of an appropriate amount of SiC to the LPGS can prevent excessive shrinkage of the support during sintering,and increase the mechanical strength and open porosity of the supports.The presence of SiC(34.4%) led to increases in the open porosity and mechanical strength of 40.43% ± 0.21% and(17.76 ± 0.51) MPa,respectively,after sintering at 700℃ for 3 h.Because of its low melting point,V_(2) O_(5) can melt to liquid during sintering,which increases the mechanical strength of the supports and retains the porosity.Certainly,this can also encourage efficient use of the LPGS and avoid wasting resources.

Solution Blowing of Palygorskite-Based Nanofibers for Methylene Blue Adsorption

Palygorskite(PG)adsorbent with superior adsorption property and ion-exchange ability is highly desired in the field of dye removal.However,it generates high amounts of precipitation due to the granular form,resulting in secondary pollution after adsorption.Herein,the novel high porosity PG-based nanofibers that are easy for operating and retrieving have been fabricated using effective solution blowing and subsequent calcination.The obtained highly efficient adsorption nanofibers exhibit large specific surface area about 170.50 m^(2)/g with average diameter from 243 nm to 365 nm.Based on the abovementioned nanofibrous structure and negatively charged PG,the solution blowing of PG-based nanofibers(SBPNs)showed high adsorption capacity for methylene blue(MB)(112.36 mg/g).In addition,the adsorption of SBPNs is well described by the Langmuir isotherm model.This work provides new SBPNs forming process for the fields of dye removal,which may achieve the production of PG adsorbents at the industrial level.

Solar Photocatalysis of TiO2 Supported Natural Palygorskite Nanofibers Elaborated by a One_Pot Mechanochemical Route

This study reports the successful synthesis of supported TiO2_Palygorskite nanocomposites by a one-pot dry mechanochemical route. Indeed, the elaboration procedure involved an in-situ reaction between accessories carbonates present in raw fibrous palygorskite clay and titanyl sulfate (TiOSO4) precursor under variable grinding conditions, essentially ball/solid matter mass ratio and rotation velocity. This yielded after air annealing at 600%C for 1 h to the immobilization of anatase TiO2 nanoparticles (≈8 nm of average size) as evidenced by XRD and TEM analyses. Once the conditions of elaboration were optimized, the photocatalytic properties were evaluated under 3 conditions: artificial UV radiation, artificial solar radiation (UV + visible range) and under dynamic solar illumination taking into account the discontinuities of the solar resource. The results allowed the estimation and comparison of the catalyst’s capabilities and showed its ability to work under natural irradiation. The so developed supported photocatalysts TiO2/Palygorskite exhibited a good activity towards the removal of Orange G (OG) dye from aqueous media under artificial UV and natural solar radiations.

Direct evidence of transformation from smectite to palygorskite:TEM investigation

Palygorskite clays sampled from palygorskite clay deposits in Jiangsu and Anhui provinces were investigated by transmission electron microscopy (TEM). Many intergrowth phenomena of special ultra-microstructure between smectite and palygorskite were found. The ultra-microstructure indicates that palygorsite fiberrous crystals grow along (001) of primary smectite through structural transformation and decomposition of the primary smectite. According to field investigation and X-ray diffraction (XRD) analyses, the transformation mechanism and process can be described as: formation of smectite from basalt weathering deposited in localiza- tion basin; evaporation of lake water in aridity environment causing pH increase and concentra- tion of magnesium ion in interstice water of sediment smectite in the lake basin. Under alkaline conditions, magnesium ion occupied interlayer positions of the smectite. Because of the misfit between magnesium octahedral sheet and smectite layer, magnesium ion interaction with smec- tite layers caused the smectite to transform into palygorskite, and resulted in the formation of smectite and palygorskite complex particulates, and even smaller secondary smectite crystal plates. The transformation of smectite structure resulted in the formation of nanometer minerals with large specific surface area and excellent property of physics and chemistry in smec- tite-palygorskite mixing clay. The results from TEM investigation are important for understanding properties of palygorskite clay and application.

Activated carbon coated palygorskite as adsorbent by activation and its adsorption for methylene blue

An activation process for developing the surface and porous structure of palygorskite/carbon（PG/C） nanocomposite using ZnC l2 as activating agent was investigated. The obtained activated PG/C was characterized by X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FTIR）, field-emission scanning electron microscopy（SEM）, and Brunauer-Emmett-Teller analysis（BET） techniques. The effects of activation conditions were examined,including activation temperature and impregnation ratio. With increased temperature and impregnation ratio, the collapse of the palygorskite crystal structure was found to accelerate and the carbon coated on the surface underwent further carbonization. XRD and SEM data confirmed that the palygorskite structure was destroyed and the carbon structure was developed during activation. The presence of the characteristic absorption peaks of C_C and C-H vibrations in the FTIR spectra suggested the occurrence of aromatization. The BET surface area improved by more than 11-fold（1201 m2/g for activated PG/C vs. 106 m2/g for PG/C） after activation, and the material appeared to be mainly microporous. The maximum adsorption capacity of methylene blue onto the activated PG/C reached 351 mg/g. The activated PG/C demonstrated better compressive strength than activated carbon without palygorskite clay.

In situ Remediation of Petroleum Contaminated Groundwater by Permeable Reactive Barrier with Hydrothermal Palygorskite as Medium

The permeable reactive barrier（PRB） has proven to be a costeffective technique to remediate the petro leum contaminated groundwater at a northeast field site in China. In this study, the geology, hydrogeology and con tamination characterization of the field site were investigated and the natural hydrothermal palygorskite was chosen as a reactive medium. Furthermore, the adsorption of the total petroleum hydrocarbons（TPH） in the groundwater onto hydrothermal palygorskite and the adsorption kinetics were investigated. The results indicate that the removal rates of TPH, benzene, naphthalene and phenantharene could all reach up to 90% by hydrothermal palygorskite with a diameter of 0.25-2.00 mm that had been thermally pretreated at 140 ℃. The adsorption of TPH onto hydrothermal palygorskite after pretreatment followed a pseudosecondorder kinetic model and a Langmuir adsorption isotherm, suggesting that the theoretic adsorption capacity of hydrothermal palygorskite for adsorbate could be 4.2 g/g. Scan ning electron microscopy（SEM）, infrared spectroscopy（IR）, Xray diffraction（XRD） and Xray fluorescence spec troscopy（XRF） were carried out to analyze the adsorption mechanism. The results reveal that hydrothermal palygors kite is a fibrous silicate mineral enriched in Mg and A1 with large surface area and porosity. The dense cluster acicular and fibrous crystal of hydrothermal palygorskite, and its effect polar group OH played an important role in the physical and chemical adsorption processes of it for contaminants. This study has demonstrated hydrothermal paly gorskite is a reliable reactive medium for in situ remediation of petroleum contaminated groundwater at field sites.

Tribological properties of novel palygorskite nanoplatelets used as oil-based lubricant additives

Layered palygorskite(PAL),commonly called attapulgite,is a natural inorganic clay mineral composed of magnesium silicate.In this study,an aqueous miscible organic solvent treatment method is adopted to prepare molybdenum-dotted palygorskite(Amo-PMo)nanoplatelets,which greatly improved the specific surface area of PAL and the dispersion effect in an oil-based lubricant system.Their layered structure and size were confirmed using transmission electron microscopy(TEM)and atomic force microscopy.Following a tribological test lubricated with three additives(PAL,organic molybdenum(SN-Mo),and Amo-PMo),it was found that the sample of 0.5 wt%Amo-PMo exhibited the best tribological properties with a coefficient of friction of 0.09.Moreover,the resulting wear scar diameter and wear volume of the sliding ball surface were 63%and 49.6%of those lubricated with base oil,respectively.Its excellent lubricating performance and self-repairing ability were mainly attributed to the generated MoS2 adsorbed on the contact surfaces during the tribochemical reaction,thereby effectively preventing the direct collision between asperities on sliding solid surfaces.Thus,as-prepared Amo-PMo nanoplatelets show great potential as oil-based lubricant additives,and this study enriches the existing application of PAL in industry.

Ammonium sulfide-assisted hydrothermal activation of palygorskite for enhanced adsorption of methyl violet

Herein,palygorskite（PAL）was activated via a simple hydrothermal process in the presence of ammonium sulfide,and the effects of activation on the microstructure,physico-chemical feature and adsorption behaviors of PAL were intensively investigated.The hydrothermal process evidently improved the dispersion of PAL crystal bundles,increased surface negative charges and built more active –Si–O-groups served as the new＂adsorption sites＂.The adsorption property of the activated PAL for Methyl Violet（MV）was systematically investigated by optimizing the adsorption variables,including p H,ionic strength,contact time and initial MV concentration.The activated PAL exhibited a superior adsorption capability to the raw PAL for the removal of MV（from 156.05 to 218.11 mg/g）.The kinetics for MV adsorption followed pseudo second-order kinetic models,while the isotherm and thermodynamics results showed that the adsorption pattern well followed the Langmuir model.The structure analysis of PAL before and after adsorption demonstrated that electrostatic interaction and chemical association of –X–O-are the prominent driving forces for the adsorption process.

Performance and Mechanisms of Fluoride Removal from Groundwater by Lanthanum-aluminum-loaded Hydrothermal Palygorskite Composite

Lanthanum-aluminum loaded hydrothermal palygorskite（La-Al-HP） composite was prepared and selected as adsorbent for the fluoride removal from simulated groundwater. The adsorbent was characterized by scanning electron microscopy（SEM）, Brunauer-Emmet-Teller（BET） analysis, X-ray diffraction（XRD） analysis and X-ray pho- toelectron spectroscopy（XPS）. SEM visualization shows that the dense surface structure of raw HP appeared loose and presented micro canals after modification. The BET analysis also proved the specific surface area of La-Al-HP composite（95.58 m^2/g） was higher than that of the raw HP（34.31 m^2/g）. Subsequently, the adsorption capacity of La-Al-HP composite was demonstrated in adsorption experiments. The kinetics of fluoride ion adsorption into La-Al-HP composite followed the pseudo-second order with a correlation coefficient of 0.997. The isotherm data was well fitted with the Langmuir model. The monolayer adsorption capacity of La-Al-HP composite was 1.30 mg/g. The XRD and XPS results reveal that the La^3＋ and Al^3＋ ions were loaded on the surface of modified HP and the fluoride ion was adsorbed onto the La-Al-HP composite. A large amount of La-Al-O composite oxide existing on the surface of La-Al-HP composite might be the immanent cause for the excellent adsorption capacity of fluoride ions.

Suspension Polymerization of Methyl Methacrylate Stabilized Solely by Palygorskite Nano Fibers

A kind of fibrous clay, palygorskite （PAL）, was used as the sole stabilizer in suspension polymerization without the using of any other stabilizer usually used, especially polymeric stabilizers. In order to improve the compatibility with the organic monomer, PAL nano fibers were organically modified with silane coupling agent methacryloxypropyltrimethoxysilane （MPS）. Transmission electron microscopy （TEM） and Fourier-transform infrared （FTIR） spectroscopy results show that the hydrolyzed MPS was attached onto PAL surface through Si--O--Si bonds formation without morphology change of PAL. At a loading amount of PAL to monomer as low as 0.36 wt%, effective stabilization could be achieved. After suspension polymerization, spherical poly（methyl methacrylate） （PMMA） particles were obtained. Scanning electron microscopy （SEM） analysis on both the outer surface and the inner cracked surface of the spherical PMMA particles indicates that the PAL particles reside on the surface of the PMMA spheres. The densely stacked PAL together with attached silane coupling agent stabilized the droplets throughout the suspension polymerization.

TiO_(2)@palygorskite composite for the efficient remediation of oil spills via a dispersion-photodegradation synergy

Removing spilled oil from the water surface is critically important given that oil spill accidents are a common occurrence.In this study,TiO_(2)@Palygorskite composite prepared by a simple coprecipitation method was used for oil spill remediation via a dispersion-photodegradation synergy.Diesel could be efficiently dispersed into small oil droplets by TiO_(2)@Palygorskite.These dispersed droplets had an average diameter of 20-30µm and exhibited good time stability.The tight adsorption of TiO_(2)@Palygorskite on the surface of the droplets was observed in fluorescence and SEM images.As a particulate dispersant,the direct contact of TiO_(2)@Palygorskite with oil pollutants effectively enhanced the photodegradation efficiency of TiO_(2)for oil.During the photodegradation process,·O_(2)^(−)and•OH were detected by ESR and radical trapping experiments.The photodegradation efficiency of diesel by TiO_(2)@Palygorskite was enhanced by about 5 times compared with pure TiO_(2)under simulated sunlight irradiation.The establishment of this new dispersion-photodegradation synergistic remediation system provides a new direction for the development of marine oil spill remediation.

Synthesis of Tributyl Acetate Catalyzed by Keggin Type Heteropolyacid Supported on Palygorskite

1 Results Industrially,the traditional process of synthesis of tributyl acetate is always carried out in liquid phase under H2SO4 which could not accord with "green chemistry".Heteropolyacids is considered good to replace it.But small specific surface area (1-5 m2·g-1)[1]and high solubility property in polar media limit their application.So great interests have focus on the various supports,which can carry and highly disperse them and such heterogeneous catalyst is easily separated from the reaction pro...

Study on the Synthesis and Adsorption Properties of KH-560 Modified PalygorskiteSupported β-Cyclodextrin

1 Results Palygorskite (PGS) is a chain-layer magnesium-aluminum silicate mineral. Because of its developed interior channels and large specific surface area, and thus considerable adsorption capacity, it has been studied for the application as one of environmental mineral adsorbents[1-3]. Cyclodextrins (CD) possess a hydrophilic exterior and a hydrophobic interior into which a variety of hydrophobic organic molecules maybe introduced. The CD molecule not only affects a hydrophilic cavity on the nanomet...