Differences in coating mechanism of structurally different aluminosilicates observed through the thermal analysis

Systematic modification of three structurally different minerals (zeolite, mica, and vermiculite) was carried out with the aim of determining the modification mechanism and exposing the hydrophobic surface that can be used as a sorbent for many organic compounds. Mechanism of modification with cationic surfactant depends strongly on the mineral type. In order to identify the influence of aluminosilicates structural differences on the modification process, adsorption experiments with organic matter and water vapor, supplemented with the DTA/TG analysis, were performed. The cation exchange capacity (CEC) value was 1454?>?560?>?28 meq kg^?1 for zeolite (clinoptilolite), vermiculite, and mica (muscovite), respectively. Despite its CEC value, vermiculite adsorbed three times the amount of organic matter than did clinoptilolite due to the porous structure of zeolite, which acted to limit the adsorption only on the external exchangeable cations. If the loading amount is equal to the CEC or the external cation exchange capacity for clinoptilolite (ECEC?≈?10% CEC), the monolayer will form while mineral surface will have hydrophobic character. Only one active center exists at the surface of the clinoptilolite that was identified by DTA curves with a sharp and defined peak around 300 °C and by the mass loss at the TG diagrams. Two significant and equal active centers were observed in vermiculite, one for the exchange of the surface cations and the other for the interlayer cations and H₂O molecules. Muscovite CEC is negligible, and due to the absence of any other functional groups, the modification of this mineral was impossible.     

Adsorption of arsenic (V) from a water solution onto a surfactant-modified zeolite

In this study a surfactant-modified zeolite (SMZ) was prepared by adsorbing the cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide on a clinoptilolite. The adsorption of the surfactant modified the surface properties of the clinoptilolite and enhanced the anionic capacity of the SMZ. The adsorption equilibrium data of As(V) from the water solution on the SMZ were obtained in a batch adsorber, and the Langmuir isotherm matched the data reasonably well. The As(V) adsorption capacity of the SMZ was 12.5 times greater than that of the clinoptilolite. The adsorption of As(V) on SMZ was mainly due to the interactions between the anionic sites of the SMZ and the As(V) anions in water solution. The adsorption capacity of the SMZ was dependent on the solution pH. The adsorption capacity was increased and decreased by augmenting the pH from 5 to 7 and from 7 to 12, respectively. This unusual behavior was due to the fact that the affinity of the As(V) for the SMZ was dependent on the As(V) species that were present in solution. The adsorption capacity of the SMZ was slightly favored by decreasing the temperature from 25 to 15 °C. The heat of adsorption was estimated to be ΔH _ads=−46.82 KJ/mol, indicating that the adsorption was exothermic and the As(V) was chemisorbed on the SMZ.     

Thermal Study of Surfactant and Anion Adsorption on Clinoptilolite

The mechanism of surfactant adsorption on various forms of clinoptilolite was studied by DTA, TG and DTG analyses. The examined series of surfactant modified clinoptilolite (SMC) was previously prepared by the adsorption of the surface-active oleylamine on Ca²⁺, Na⁺, H⁺ and mechanochemically treated forms of clinoptilolite. The oleylamine was most strongly adsorbed on H⁺-forms of clinoptilolite due to the largest number and strength of adsorption sites. The surfactant adsorption mechanism on H⁺-form of clinoptilolite was studied by recording the series of variously surfactant-loaded samples. The products of sulphate, dihydrogenphosphate and hydrogenchromate adsorption on SMC were analyzed by DTA, TG and DTG in order to investigate the mechanism of anion adsorption.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermal treatment of zeolitic tuff

In this study, the zeolitic tuffs having clinoptilolite obtained from Bigadic region of western of Anatolia, Turkey were investigated as regards to whether it is possible to be transformed into amorphous phase from them. At first, the zeolite tuffs rich in clinoptilolite were characterized using XRD, DTA, TG, DSC, and FTIR standard methods. All the samples were heated at 110 °C for 2 h and then were expanded within 5 min between the temperatures 1200 and 1400 °C. In addition, porosity and density were determined. The resistance values of all the samples were measured in acidic and basic media. These samples were also analyzed. As a result of this study, zeolitic tuffs in clinoptilolite were transformed into amorphous phase, and especially in chemical industry were found convenient.     

Influence of Basic Red 1 dye adsorption on thermal stability of Na-clinoptilolite and Na-bentonite

Influence of physically adsorbed basic red 1 (BR1) dye on the physicochemical properties of natural zeolite (clinoptilolite) and clay (bentonite) was compared using adsorption, FTIR, and TG/DTA methods. A larger adsorption of the dye was observed for bentonite (0.143 mmol/g) than for clinoptilolite (0.0614 mmol/g) per gram of an adsorbent. However, the adsorption values are the same per surface unit (1.8 μmol/m²). The result (per gram) is due to location of dye molecules in interlayer and interparticle space of bentonite with much larger specific surface area than that of clinoptilolite. The dye adsorption leads to a decrease in the specific surface area and the pore volume of both minerals. The adsorption changes also a character of active sites and thermal stability. A TG study shows that the dye adsorption on bentonite changes adsorbed water amounts, weight loss, and decomposition temperature. In the case of zeolite, the dye adsorption insignificantly influences the thermal stability. The dehydration energy distributions calculated from the Q-TG and Q-DTG data demonstrate a complex mechanism of water thermodesorption and the influence of adsorbed dye on this process.     

Investigation of clinoptilolite rich natural zeolites from Turkey: a combined XRF,TG/DTG,DTA and DSC study

Turkey clinoptilolite-rich tuffs from Gördes and Bigadiç regions of western of Anatolia and their exchanged forms (K⁺, Na⁺, Mg²⁺ and Ca²⁺) were characterized by TG/DTG-DTA, DSC and XRF methods and the surface areas were also determined for both tuffs. TG-DTG and DTA curves of all clinoptilolite samples were measured in the temperature range 30–1000 °C. All clinoptilolite samples had major, rapid mass losses between 30 and 200 °C, with slower and less significant mass losses at higher temperatures. The mass loss of the Natural-G is 9.54% while that of the Natural-B sample is 10.50%. Water content increases in the order of K < Na < Ca < Mg for Bigadiç clinoptilolite samples and in the following sequence K < Na < Mg < Ca for Gördes clinoptilolite samples. One mass loss step for all clinoptilolite samples was observed using differential scanning calorimeter (DSC) in the range of 30–550 °C.     

Thermal stability of Ag-exchanged clinoptilolite rich mineral

Thermal stability of clinoptilolite rich mineral from Western Anatolia, Turkey and its Ag-exchange forms was investigated. Parent mineral of different sizes were heated up to 1000°C with heating rate of 2 and 10°C min^-1 using differential thermal analyzer (DTA) and thermogravimetric analyzer (TG). Ag exchange was conducted both in conventional constant temperature waterbath and microwave at 40, 60 and 80°C. The exchanged minerals were then characteized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), DTA and TG. The particle size and heating rate do not have significant effect on the thermal behavior of the parent mineral and no structural changes were observed with Ag exchange, only decomposition temperature was lowered. It was finally concluded that, Ag-exchanged clinoptilolite rich minerals were less thermally stable compared to parent mineral that does not affect their use for possible applications.     

TG and DTA Study of the Thermal Dehydration of Metal-exchanged Zeolite-4A Samples

Zeolite-4A is a hydrated aluminosilicate which becomes more hydrated when exchanged with transition metals. In this work, the dehydration kinetics of cobalt, nickel and copper(II)-exchanged zeolite-4A were studied by means of TG and DTA over the temperature range from 20 to 500°C, and the numbers of water molecules in the metal-exchanged zeolite samples were calculated. It was observed that, as the ionic radius of the hydrated metal increased, the number of water molecules also increased. The loss of water from the zeolite samples generally occurred in the temperature range 100–300°C and was manifested in the DTA graphs by an extended endothermic effect. The DTA curves demonstrated that the peak position shifted towards lower temperatures as the metal concentration increased or, in other words, the water of hydration increased. The kinetic parameters (order of reaction and activation energy) were calculated via the Coats and Redfern method. The process of dehydration was found to follow first-order kinetics. This revised version was published online in August 2006 with corrections to the Cover Date.     

Aromatic polyamides. II. Synthesis,wet-spinning,and fiber thermal characterization of poly(4,4′-oxanilideterephthalamide) and copolymers with 4,4′-oxydianiline or isophthalic acid

Poly(4,4′-oxanilideterephthalamide) (coded A-202) was prepared from 4,4′-diaminooxanilide (DAO) and terephthaloyl chloride (TCI) in N,N-dimethylacetamide (DMAc)/5% LiCl and DMAc (5% LiCl)/hexamethylphosphorictriamide (HMPA) solvents. Fiber with tenacity/elongation/modulus at 1% extension (t/e/m) of 5.2 grams per denier (gpd)/1.9%/316 gpd was obtained. The all-para A-202 tended to precipitate from solution. More soluble copolyamides were prepared from DAO and TCl in combination with either 4,4′-oxydianiline (A-202/ODA) or isophthaloyl chloride (A-202/I) in DMAc (5%LiCl). A-202/ODA solutions were spun to fiber with t/e/m of 11.2 gpd/6%/217 gpd; A-202/I gave fiber with t/e/m of 6.4 gpd/1.3%/432 gpd. Dynamic mechanical analyses (Vibron) and dilatometric measurements of A-202, A-202/ODA, and A-202/I showed no glass transition temperature below 200°C. Differential thermal analyses (DTA) revealed no transitions below 400°C. Thermogravimetric analyses (TGA) at 15°C/min exhibited substantially no weight loss in air at temperatures up to 400°C.     

Removal of thorium from aqueous solutions by sodium clinoptilolite

Adsorptive behavior of natural clinoptilolite was assessed for removal of thorium from aqueous solutions. Natural zeolite was characterized by X-ray diffraction and X-ray fluorescence. The zeolite sample composed mainly of clinoptilolite. Na-exchanged form of zeolite was prepared and its sorption capacity for removal of thorium from aqueous solutions was examined. The effects of relevant parameters, including initial concentration, contact time, solid to liquid ratio, temperature and initial pH on the removal efficiency were investigated in batch studies. The pH strongly influenced thorium adsorption capacity and maximal capacity was obtained at pH 4.0. Kinetics and isotherm of adsorption were also studied. The pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models were used to describe the kinetic data. The pseudo-second-order kinetic model provided excellent kinetic data fitting (R ² > 0.999) with rate constant of 1.25, 1.37 and 1.44 g mmol⁻¹ min⁻¹ respectively for 25, 40 and 55 °C. The Langmuir and Freundlich models were applied to describe the equilibrium isotherms for thorium uptake and the Langmuir model agrees very well with experimental data. Thermodynamic parameters were determined and are discussed.     

Influence of acid treatment on structure of clinoptilolite tuff and its adsorption of methane

This study presents the results of the methane adsorption properties of clinoptilolite tuff from Bigadic, Turkey and that of acid treated forms at 273 and 293 K up to 100 kPa using volumetric apparatus. In order to assess changes in structural and gas adsorption properties of clinoptilolite, zeolite sample was treated with acid solutions of varying concentrations (0.1, 0.5, 1.0 and 2.0 M) at 70 °C during 3 h. Structural and thermal characterization of natural and acid treated clinoptilolite samples were carried out using a combination of techniques such as X-ray diffraction, X-ray fluorescence, thermogravimetric, differential thermal analysis and nitrogen adsorption methods. At both temperatures, uptake of methane (CH₄) increased in the following order: CLN < CLN-H2 < CLN-H1 < CLN-H05 < CLN-H01. CH₄ adsorption capacities of the original and acid treated clinoptilolites were found in the range of 0.476–0.910 mmol/g and 0.398–0.691 mmol/g at 273 and 293 K, respectively.     

A tool for predicting the integrity of Y zeolite crystalline structure

The purpose of this work was to employ the differential thermal analysis technique (DTA) to compare variations in the collapse energy of the Y zeolite crystalline structure in a fresh sample and in the sample after temperature treatment and impregnated with 3,000 ppm of vanadium and nickel. A small exothermic signal in the DTA curve at 950–1,150 °C indicated the collapse of the crystalline structure. The areas of the exothermic signals in the DTA curves of the samples indicated a 20% reduction in the exothermic area peak of sample treated 600 °C for 3 h and 25% reduction in same peak in the metal impregnated Y zeolite. These results were compared with X-ray data leading to the conclusion that metal impregnation affects the Y zeolite crystalline structure and that the DTA technique is a potentially useful tool for measuring the integrity of Y zeolite in catalysts.     

Removal of Rhodamine-B from Aqueous Solution by Adsorption onto Crosslinked Alginate Beads

The biosorption of rhodamine-B from aqueous solution using crosslinked alginate beads was studied by contact method at fixed pH ?3 and room temperature (28 ± 0.2°C). Both the Freundlich and Langmuir isotherm models could describe the adsorption equilibrium of the rhodamine-B onto crosslinked alginate beads. The influence of various experimental parameters such as pH, temperature, effect of concentration and time were evaluated. It was observed that the adsorption capacity of rhodamine-B onto alginate beads decreased with increase in pH and temperature above room temperature.     

Desorption of stearic acid upon surfactant adsorbed montmorillonite

Thermal analysis and differential thermal analysis offers a novel means of studying the desorption of acids such as stearic acid from clay surfaces. Both adsorption and chemisorption can be distinguished through the differences in the temperature of mass losses. Increased adsorption is achievable by adsorbing onto a surfactant adsorbed montmorillonite. Stearic acid sublimes at 179 °C but when adsorbed upon montmorillonite sublimes at 207 and 248 °C. These mass loss steps are ascribed to the desorption of the stearic acid on the external surfaces of the organoclays and from the de-chemisorption from the surfactant held in the interlayer of the montmorillonite.     

Thermal analyses of four adsorption materials for environmental pollution by DSC and TG

In view of loss prevention and hazard control, traditional engineers use adsorbents to adsorb volatile organic compounds (VOCs) in the semiconductor, photonics, and petrochemical industries. To save funds and promote green energy application, industries usually apply a zeolite processing desorption step under high temperature in the zeolite rotor-wheel system. Many thermal runaway accidents and flame incidents have occurred in the desorption step. Zeolite has been used to adsorb VOCs and applied in the processing desorption step in a reactor without considering oxygen concentration situation, which could easily lead to a flame followed by thermal explosion. Nitrogen is a critically important purge gas regarding passive action for avoiding an accident. Home-made zeolite was investigated for the best manufacturing ratio, which was 20. Brunauer–Emmett–Teller of zeolite (Si/Al = 20) was analyzed to be 400 m² g^?1, which is easy for adsorbing pollutants. According to our previous studies, home-made zeolite has prominent adsorption capacities on VOCs. Zeolite rotor-wheel system was developed to desorb the pollutants of interest. Zeolite was applied to analyze the thermal stability, runaway reaction under various oxygen concentrations, reuse rates, etc. Zeolite is a thermally stable material under room temperature to 650 °C. An endothermic reaction (30–100 °C) of home-made zeolite was analyzed by differential scanning calorimetry and thermogravimetric analyzer. Clearly, water has a significant effect on deteriorating for the zeolite adsorption. Home-made zeolite is a suitable adsorbent and catalyst in the petrochemical and environmental industries. As far as pollution control and loss prevention are concerned, versatility in the analysis of recycled adsorbents is required and is useful for various industrial applications.     

Dechlorination of molten chloride waste salt from electrorefining via ion-exchange using pelletized ultra-stable H-Y zeolite in a fluidized particle reactor

Dechlorination of eutectic LiCl–KCl based electrorefiner (ER) salt is reported via ion-exchange reaction with protonated ultrastable Y-type (USHY) zeolite bound into mechanically fluidized 45–250 μm diameter particles. Evidence of exchange of cations from the salt (Li⁺, K⁺, and fission product cations) into the zeolite lattice replacing H⁺ ions was found based on a change in unit cell size, ICP-MS, XRD and TEM–EDS in addition to detection of HCl off gas. Ion exchange reaction was carried out at 625 and 650 °C, temperatures above the melting point of eutectic LiCl–KCl. Experiments were carried out to optimize zeolite drying temperature, estimate maximum ion-exchange capacity, and determine the thermal stability of USHY zeolite. The results indicate over 90% dechlorination can be achieved without zeolite structure collapse at 625 °C. This provides a promising route to stabilizing waste from radioactive chloride salts into dechlorinated waste forms for permanent geologic disposal.

     

Separation of BTEX compounds (benzene,toluene, ethylbenzene and xylenes) from aqueous solutions using adsorption process

A commercial synthetic zeolite (Na-ZSM-5) was modified with an organic surfactant, HDTMA-Br. Then both unmodified and modified zeolite (SMZ-100) were tested to adsorb Benzene, Toluene, Ethylbenzene and Xylene (BTEX) compounds from water solution. Adsorption tests were done in batch conditions at the ambient temperature (20?°C) and pressure. Adsorbents were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N₂ adsorption-desorption isotherms and field emission scanning electron microscopy (FE-SEM) and characterization results proved the existence of surfactant on the surface of the adsorbent. In all cases, the modified zeolite sample, because of increasing the hydrophobicity of its surface, exhibited higher adsorption capacity in comparison with unmodified zeolite. Also, for each adsorbent, the adsorption capacity follows the order: E?>?X?>?T?>?B. In equilibrium experiments, Langmuir isotherm model fitted the equilibrium data better than the Freundlich model. In kinetic experiments, the pseudo-second order model described the kinetic data better than the other models.     

Characterization and pozzolanic activity of thermally treated zeolite

Summary The pozzolanic reactivity of thermally treated zeolites was studied on the basis of the Chapelle test combined with X-ray diffraction (XRD) and Fourier Transform (FTIR) spectroscopy, as well as thermogravimetric analysis (TG/DTG) and differential thermal analysis (DTA). The raw zeolite samples are from the Pentalofos area, Thrace, NE Greece. Their main mineral constituent is 'heulandite type-II', an intermediate type of the heulandite-clinoptilolite isomorphous series. Calcination of the samples was carried out up to 400, 500, 600, 700 and 1000°C for 15 h. The changes were recorded using the above methods. The deformation of the zeolite crystal lattice starts at about 400°C and proceeds as the temperature of thermal treatment rises. The thermal treatment of zeolite at 400°C improves its pozzolanic reactivity and accelerates the reaction with Ca(OH)₂.     

Modification of Polyethylene with Activated Natural Zeolite

Abstract

In an attempt to improve its main physical and mechanical characteristics, the modification of high density polyethylene (HDPE) with activated (dehydrated) natural zeolite clinoptilolite, in an attempt to improve its main physical and mechanical characteristics is investigated. After dehydration at 350°C and cooling in an atmosphere of dry air, about 30% of the entire volume of the zeolite particle is freed. This free volume and the ensuing from the specific structure sorption processes-the possibility for sorption of the polymer chain on the surface channel of the zeolite particle-determine the active modification function of dehydrated clinoptilolite.     

Adsorption and thermodynamic behavior of uranium on natural zeolite

Adsorptive behavior of natural clinoptilolite-rich zeolite from Balikesir deposites in Turkey was assessed for the removal of uranium from aqueous solutions. The uranium uptake and cation exchange capacities of zeolite were determined. The effect of initial uranium concentrations in solution was studied in detail at the optimum conditions determined before (pH 2.0, contact time: 60 minutes, temperature: 20 °C). The uptake equilibrium is best described by Langmuir adsorption isotherm. Some thermodynamic parameters (ΔH°, ΔS°, ΔG°) of the adsorption system were also determined. Application to fixation of uranium to zeolite was performed. The uptake of uranium complex on zeolite followed Langmuir adsorption isotherm for the initial concentration (25 to 100 μg/ml). Thermodynamic values of ΔG°, ΔS° and ΔH° found show the spontaneous and exothermic nature of the process of uranium ions uptake by natural zeolite. This revised version was published online in August 2006 with corrections to the Cover Date.