Raw Palygorskite Research Articles

Structural, electrokinetic and surface properties of activated palygorskite for environmental application

Unlike smectite, the surface characteristics of palygorskite remain underexplored for its potential application in environmental remediation. In this study, palygorskite from Western Australia was activated through thermal (300°C for 4h), acid (4M HCl for 2h at 70°C) and acid-thermal (acid treatment followed by heating at 300°C for 4h) treatments, and the structural and physico-chemical characteristics were examined against the raw clay mineral. The influence of activation was systematically investigated using X-ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) spectroscopy, N2 adsorption-desorption measurements and solid state 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy. The XRD patterns indicated preservation of the crystalline structure of palygorskite following all the treatments. These findings were supported by the Al (IV) and Al (VI) coordination peaks (chemical shift ~55 and 2.9ppm, respectively) which were unaltered in the 27Al MAS NMR spectra of the samples. The acid-thermal activated palygorskite exhibited the highest specific surface area (152.7m2g−1) and pore volume (0.2137cm3g−1) which respectively were 3-fold and 69% greater than the raw palygorskite. The potentiometric titration analyses highlighted the possible role of Al derivatives towards development of the surface charge of the activated palygorskites. Electrokinetic studies described the stability of the activated products (zeta potential values ranging from -5mV to -32mV) at different electrolyte (NaNO3) concentrations. Combined acid-thermal activated palygorskite displayed a stronger specific adsorption of multivalent cations, and held a direct relevance to environmental remediation. Findings of this study will assist in the development of palygorskite-based adsorbents for heavy metal contaminants remediation.

From naturally low-grade palygorskite to hybrid silicate adsorbent for efficient capture of Cu(II) ions

A new eco-friendly hybrid Mg, Al-silicate adsorbent with superior adsorption properties for Cu(II) was prepared by a one-step hydrothermal process using earth-abundant low-grade palygorskite (PAL) as the starting materials and non-toxic sodium carbonate as the assistant. The structural characterizations by scanning electronic microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), BET adsorption-desorption isotherms and Zeta potential analyses confirm that part of rod-like PAL crystals were in-situ transformed as smectite sheets, and the hybrid silicate adsorbents with rod/sheet transition formulation were formed. Under the action of alkaline, some inert SiOSi(or M) bonds were broken as –Si–O− groups, which not only make the adsorbent having extremely negative surface charge (−46.4mV), but also strengthen the chelating and holding capability of the adsorbent to Cu(II). The silicate adsorbent shows high adsorption capacity of 229.9mg/g for Cu(II), which can capture 98.95% of Cu(II) from 200mg/L of Cu(II) solution at the dosage of 2.6g/L (only 64.5% for raw PAL). The intensified electrostatic attraction, ion-exchange, and chemical association of Si-O− surface groups with Cu(II) primarily contribute to the improved capture capability for Cu(II).

A functionalized hybrid silicate adsorbent derived from naturally abundant low-grade palygorskite clay for highly efficient removal of hazardous antibiotics

As promising eco-friendly materials, natural silicates have received great attention as abundant, low-cost, non-toxic, stable, and environmentally benign adsorbents. Inspired by the idea of “from nature, for nature”, a series of highly efficient hybrid silicate adsorbents were synthesized via a simple one-step hydrothermal process, using naturally abundant low-grade palygorskite (PAL) as the initial material in the presence of sodium silicate (SS), magnesium sulfate (MS), and monochloroacetic acid (MCA). As expected, the PAL crystal and the associated minerals were restructured as amorphous and multi-porous Mg, Al-silicates, while the active COOH groups were simultaneously introduced into the silicate to form a hybrid adsorbent with a specific surface area of 410.61m2/g (compared to 52.87m2/g for raw PAL). The hybrid silicate adsorbent showed excellent adsorption capabilities for the antibiotics chlortetracycline (CTC) (329.84mg/g) and oxytetracycline (OTC) (207.47mg/g), which were enhanced by 218.9% and 107.9%, respectively, in contrast to that of raw PAL. The adsorption of the hybrid adsorbent for CTC and OTC was pH-dependent, and the pH values of 3.56–7.82 (for CTC) and 3.45–7.57 (for OTC) favored the adsorption. The dynamic adsorption process was well described by a pseudo second-order model, which suggested that chemical adsorption was the prominent driving force. The thermodynamic adsorption pattern agreed well with the Redlich–Peterson model, revealing that the heterogeneous surface was the main adsorption site and that removal of antibiotics occurred mainly by multi-layer adsorption.

Tailoring the properties of palygorskite by various organic acids via a one-pot hydrothermal process: A comparative study for removal of toxic dyes

Naturally abundant palygorskite (PAL) has been frequently used as an efficient, stable, low cost and environment-benign adsorbent to remove toxic pollutants for alleviating their harm to human health. However, the adsorption capacity of natural PAL is limited, which restricts its applications as an efficient adsorbent. As the aim to improve the adsorption capability of natural PAL and develop a high-efficient silicate adsorbent, the organic acids with different structures (i.e., acetic acid, glycolic acid, glycine, chloroacetic acid, benzoic acid, oxalic acid and citric acid) were employed to modify natural PAL via a simple one-step hydrothermal process. The effect of hydrothermal process in the presence of organic acids on the microscopic structure, physico-chemical features and adsorption properties of the PAL-derived adsorbent was studied comparatively using the dyes methylene blue (MB), methyl violet (MV) and malachite green (MG) as the model pollutants. It was found that the structural evolution of PAL and the introduction of functional groups positively contribute to improve the adsorption capacity. The PAL-derived adsorbents in the presence of chloroacetic acid (CAA-PAL) and citric acid (CA-PAL) show excellent adsorption capacity, which could almost completely remove the MB, MV and MG dyes from 200mg/L of the solution, but the raw PAL can only remove 59% (for MB), 63% (for MV) and 88% (for MG). The intensified electrostatic attraction, hydrogen-bonding interaction and chemical association of –Si–O− groups with dyes, resulting from the hydrothermal evolution of PAL crystal, are primarily responsible for the enhancement of adsorption capacity.

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 pH, 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 218.11mg/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.

Effects of solvothermal process on the physicochemical and adsorption characteristics of palygorskite

Palygorskite (PAL) was treated with various organic solvents including methanol (MT), ethanol (ET), isopropanol (IPA), dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) via a facile solvothermal process. The effects of various solvents and reaction parameters on the microstructure, morphology and adsorption properties of PAL were intensively investigated. Fourier transformation infrared spectrometry (FTIR) and thermogravimetric (TG) analyses confirmed that some solvent molecules could be encapsulated in the tunnels of PAL and the polarity of solvent molecules plays an important role for their interaction with PAL. Field-emission scanning electron microscopy (FESEM) shows that the solvothermal treatment results in a better dispersion of PAL crystal bundles. The treated PAL by various solvents has relatively higher adsorption capacity (from 119mg/g to 154mg/g) and removal efficiency for methylene blue (MB) than the raw PAL, and the improved electrostatic and hydrogen-bonding interactions between MB and PAL are mainly responsible for the enhancement of adsorption properties. The adsorption properties of PAL for MB were greatly affected by the characters of solvents, and DMF-treated PAL gives the best adsorption and removal capabilities for MB.

A simple hydrothermal approach to modify palygorskite for high-efficient adsorption of Methylene blue and Cu(II) ions

Silicate materials have been frequently used as stable, low-cost and efficient adsorbents for the removal of dyes and heavy metal ions from aqueous solution. Herein, at the aim of designing new adsorbent with higher adsorption capacity, natural palygorskite (PAL) was modified via a one-step hydrothermal process by introducing sodium silicate and magnesium salts. The effect of Si/Mg dosage ratio on the structure and physico-chemical features of the adsorbent was investigated, and its adsorption capability for Methylene blue (MB) and Cu(II) ions was intensively evaluated. It was found that Si/Mg dosage ratio is the key to control the adsorption properties of the adsorbent. The active magnesium silicate could be formed around PAL at the moderate Si/Mg dosage ratio, and even the undesirable quartz impurities without adsorption activity in the natural PAL minerals may transform as amorphous magnesium silicate with higher adsorption activity in this process. The adsorbent shows greater BET specific surface areas (407.3m2/g), ideal surface charge distribution and superior adsorption capacity to MB and Cu(II) ions, with the maximum adsorption capacity of 527.22mg/g for MB and 210.64mg/g for Cu(II) ions at the Si/Mg dosage ratio of 2:1. The MB molecules and Cu(II) ion could be almost completely removed from 100mg/L of MB solution and 25mg/L of Cu(II) solution by the adsorbent, respectively, which is far away higher than that of raw PAL. The electrostatic attraction, ion exchange and chemical association of –Si–O− groups contribute to the enhanced adsorption for MB or Cu(II) ions.

Brazilian Palygorskite as Adsorbent for Metal Ions from Aqueous Solution—Kinetic and Equilibrium Studies

Natural palygorskite was used as an adsorbent for the removal of copper, cobalt and nickel from an aqueous solution. All assays were performed under controlled conditions to establish the adsorption capacity of the solid. Initially, the clay was characterized by chemical analysis, XRD, infrared spectroscopy and thermogravimetry. Adsorption experiments for the ions in aqueous solution were carried out by a batch method through which the reaction time, initial concentration of cations, temperature and pH of the aqueous solution were systematically varied. First-order, pseudo-second-order and intraparticle diffusion models were used to describe the kinetic data. The results show that the processes were fitted well by the pseudo-second-order model. Moreover, the equilibrium solid–cation systems followed the Langmuir isotherm model. The results indicate that raw palygorskite could be employed as a low-cost material for the removal of heavy metals from aqueous solution.

Thermal modified palygorskite: Preparation, characterization, and application for cationic dye-containing wastewater purification

Palygorskite has excellent sorption properties due to its porous structure and fibrous morphology. In this paper, the thermal modified palygorskite was prepared and characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), N2 adsorptiondesorption and thermogravimetric-differential scanning calorimetry (TG-DSC) analysis. The adsorption properties of the raw palygorskite and the thermal modified palygorskite were investigated by removal of methylene blue (MB) from aqueous solution. The effects of the calcination temperature, the initial MB concentration and the pH value on the MB removal were evaluated. The results show that the structure of palygorskite was destroyed gradually with increasing the calcination temperature, and the adsorption capacity of the palygorskite can be improved by thermal modification in appropriate temperature ranges. The isotherms and the kinetic data of the MB adsorption onto the modified palygorskite were studied by the Freundlich model and the pseudo-s...

Adsorptive Removal of 2,6-Dichlorophenol from Aqueous Solution by Surfactant-Modified Palygorskite Sorbents: Equilibrium, Kinetics and Thermodynamics

Raw palygorskite was modified by the addition of selected surfactants, viz. hexadecyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB) and octadecyldimethylbenzyl ammonium chloride (ODBAC). These modified clays were used as sorbents for the adsorptive removal of 2,6-dichlorophenol (2,6-DCP) from aqueous solution. Characterization of the sorbents was achieved by Fourier-transform infrared (FT-IR) analysis, nitrogen adsorption/desorption measurements and particle-size analysis. The adsorptive performance of the modified palygorskites towards the removal of 2,6-DCP from aqueous solution was studied by batch methods. In addition, the influence of contact time, pH and temperature on the adsorption process was investigated in detail.The equilibrium data for the three modified sorbents were well fitted by the Langmuir model. It was found that the monolayer adsorption capacity increased with increasing contact time and solution temperature, respectively. Application of the pseudo-first-order and pse...

Effect of Heat Treatment on Properties of Mineral Attapulgite

Mineral attapulgite powders were heat treated at different temperature from 100°C to 800°C. The effect of heat treatment on properties of attapulgite were studied by particle size distribution, surface free energy, and water vapor adsorption performance. The results show that the medium particle size and surface free energy of attapulgite increase and hygroscopic capacity promptly reduce with the increase of heat temperature .The medium particle size of the raw palygorskite is 3.09 μm, and it becomes 14.12 μm after heat treatment at 800 °C. The surface free energy, polarity component and dispersion component of the natural attapulgite are 45.16mN•m-1, 13.92mN•m-1, 31.24mN•m-1, respectively, and they become 116.22 mN•m-1，116.22 mN•m-1，0.0 mN•m-1 after heat treatment at 800°C. Moreover, the hygroscopic capacity of attapulgite in 24h decreases from 17.1 % to 5.6% after heat treatment at 800°C.

A facile 1,2 proton migration of chalcone epoxide using acid activated palygorskites

Different natural as well as modified palygorskite clays, Padappakkara blue (Kaolinite) and Zeolite 4A have been used to study the rearrangement of chalcone epoxide. Acid washed palygorskite clays have been identified as an excellent catalytic material for promoting a facile 1,2 proton migration of chalcone epoxide. The rearrangement of α-epoxyketone (chalcone epoxide) was found to yield E(−) enolic form of 1,3-diphenyl-1,3-propanedione indicating that the proton migration has taken place from the less favoured direction of the epoxide ring. It was observed that acid washed palygorskite gave higher yield of the compound. As the acidity and specific surface area of the clay increased, the rate of the reaction was found to increase. An attempt has been made to correlate the properties of the more active (4 M HCl activated) clay, an eco-friendly catalyst in the formation of the final product. 4 M HCl activated palygorskite clay catalysed a very high yield of 90% of E(−) enolic form of 1,3-diphenyl-1,3-propanedione. Raw palygorskite, Padappakkara blue clay as well as Zeolite 4A have no effect in the rearrangement of chalcone epoxide, even after increasing the epoxide/catalyst ratio to 1:1.