Mechanism Of Zeolite Research Articles

Removal of NH3-N from wastewater by novel zeolite X: adsorption behavior and removal mechanism

This study utilized a straightforward method to fabricate zeolite X, demonstrating high adsorption performance for the removal of NH3-N from wastewater. The adsorption behavior of zeolite X towards NH3-N was investigated through various methods including adsorption kinetics, isothermal adsorption, and thermodynamic models. The mechanism of zeolite X for removing NH3-N were analyzed using techniques such as SEM, EDS, XRD, BET, and XPS. The results indicated that when t = 30 min, pH = 6, zeolite dosage was 20 g/L and initial NH3-N concentration was 100 mg/L, the removal efficiency of NH3-N could reach 95.5%. The adsorption process followed Freundlich model and were endothermic. The enthalpy change (ΔH), entropy change (ΔS) and Gibbs function (ΔG(308.15 K)) were 10.66 kJ/mol, 28.81 J/(mol･K), and 1.78 kJ/mol, respectively. SEM and XRD analysis show that the crystal shape of zeolite X is octahedral, which is a typical morphology of FAU-type zeolite. The specific surface area of zeolite X was as high as 643 m2/g. The results of XPS analysis show that after Na+ exchange with NH4+, hydrogen bonds were formed between ammonia nitrogen and oxygen in zeolite X. This study introduces a novel adsorbent, offering a fresh approach to tackling ammonia nitrogen pollution in wastewater.

Rapid and high efficient synthesis of zeolite W by gel-like-solid phase method

Abstract Zeolite W was synthesized rapidly and efficiently by gel-like-solid phase method using silica-alumina xerogel as the silica-alumina source and potassium hydroxide as the alkali source. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and N2 adsorption-desorption. The results exhibited that zeolite W can be synthesized with silica-alumina gel (n(Al2O3)/n(SiO2) = 0.2) under a wide range of synthesis conditions: n(K2O)/n(SiO2) = 0.125–0.5, n(H2O)/n(SiO2) = 5.55–14.81, crystallization temperature T = 125–150 °C, and crystallization time t = 6–18 h. Among them, a batch of uniform and well crystallized zeolite W was synthesized under 150 °C for 12 h with the mole ratio of n(K2O)/n(SiO2) = 0.375 and n(H2O)/n(SiO2) = 7.40. The specific surface area of optimal sample is 221.98 m2 g−1, and NH4+ exchange capacity in exchange fluid is up to 38.12 mg g−1 and the highest recovery amount of K+ is 51.21 mg g−1 in artificially simulated seawater. The mechanism of zeolite W synthesized by gel-like-solid phase method is liquid-solid two phases transformation mechanism. Compared with the conventional hydrothermal synthesis system, the gel-like-solid phase synthesis method greatly reduced the amount of water, shortened the crystallization time, improved the utilization rate of raw materials and simplified the recovery process of mother liquor.

Mechanism of zeolite X crystallization from diatomite

Here we systemically investigated the crystallization process of zeolite X using diatomite, a natural cost-effective silica precursor by the hydrothermal method. To decipher the mechanism, solids were separated from the mixtures at various stages of crystallization and were characterized by XRD, SEM, solid state NMR, FT-IR, UV-Raman and XRF. The XRD patterns revealed that the crystallization started between 3 and 3.5 h and ended by 5 h. The SEM images showed that the intermediate species of zeolite X appear on the surface of particles. The FT-IR and UV-Raman spectra suggested the presence of double six-membered rings (D6R) in the framework of zeolite X and they played a critical role in the crystallization process. Furthermore, the UV-Raman spectra indicated that the secondary building units of β cages formed the intermediate species and they were interconnected via double six-membered rings to form the framework of zeolite X.

A candidate of mechanical energy mitigation system: Dynamic and quasi-static behaviors and mechanisms of zeolite β/water system

Abstract Zeolite β/water system is experimentally explored under both quasi-static and dynamic conditions to give insights into its potential as a protection system. Its energy absorption density, E under quasi-static condition is investigated, including its dependence on three influential parameters: the pretreatment temperature of zeolite β, T (room temperature to 1100 °C), concentration of sodium chloride, CNaCl (0–6 mol kg H 2 O - 1 , i.e., moles of salt/kg of water), and mass ratio of zeolite β to water, rM (0–1:1). Results show that higher content of zeolite β with a treatment lower than 1000 °C is preferable while two competing effects co-exist for the influence of CNaCl. Furthermore, dynamic impact tests based on drop weight device are conducted to demonstrate the cushioning effect of zeolite β/water system under low-speed impact. It shows that the peak force Fmax can be decreased by 42.82% and reaction duration time t can be extended by 79.16%. To conclude, results prove that zeolite β/water system can serve as impact mitigation system for protections with decent performance and shed lights on the future engineering for the system.

Silica-alumina molar ratio and some factors effect on the synthesis of zeolites from fly ash

In order to improve the activity and eliminate some impurities, pretreatment was used before hydrothermal synthesis. The fly ash was mixed with an aqueous NaOH solution, the alkali melted fly ash was also adopted, which is hydrothermally treated at about 104 °C, and the liquid/solid ratio was controlled at 6:1. In order to control Si/Al molar ratio, SiO2 or Al2O3 powers were added to the fly ash. The results of XRD and SEM show that the alkali melted can activate fly ash and eliminate its quartz and mullite, along with the improvement of Si/Al molar ratio and alkalinity. In addition, zeolite Na-A changes into sodalite gradually, and nepheline is the synthesized intermediate product. Those results were discussed on the basis of a formation mechanism of zeolite from fly ash.

Mechanism of zeolite A nanocrystal growth from colloids at room temperature.

The formation and growth of crystal nuclei of zeolite A from clear solutions at room temperature were studied with low-dose, high-resolution transmission electron microscopy in field emission mode and with in situ dynamic light scattering. Single zeolite A crystals nucleated in amorphous gel particles of 40 to 80 nanometers within 3 days at room temperature. The resulting nanoscale single crystals (10 to 30 nanometers) were embedded in the amorphous gel particles. The gel particles were consumed during further crystal growth at room temperature, forming a colloidal suspension of zeolite A nanocrystals of 40 to 80 nanometers. On heating this suspension at 80 degrees C, solution-mediated transport resulted in additional substantial crystal growth.

Study on the mechanism of zeolite Y formation in the process of liquor recycling

Abstract Crystallization of zeolite Y formation in the process of mother liquor recycling (MLR) has been studied. The zeolite crystallization mother liquor comprises a little sodium silicate as well as minor zeolite, Upon addition of aluminum sulfate, the silicate existed in the mother liquor reacts to form finely divided silica–alumina hydrogel (MLHG) which can be utilized later in zeolite Y formation. The particle of MLHG is relatively small and Si/Al of the gel's framework is a little great. Since amorphous aluminosilicate gel passes through two stages of gelation, the pseudoequilibrium between solid phase and liquid phase of gel is attained rapidly and the time of zeolite Y formation is much reduced. In addition, experiments have also showed that the quantities and the properties of zeolite Y added affect the process of crystallization heavily. Minor quantities of zeolite in the mother liquor have detrimental effect on the zeolite Y formation. Based on studies of crystallization from recycling mother liquor, a model of two-phase transformation for zeolite Y formation has been proposed.

97/02566 Coking mechanism of zeolite for supercritical fluid alkylation of benzene

97/02566 Coking mechanism of zeolite for supercritical fluid alkylation of benzene

The Mechanism of Zeolite Y Destruction by Steam in the Presence of Vanadium

The mechanism of zeolite Y destruction by steam in the presence of vanadium is described. Electron spin resonance, UV–VIS diffuse reflectance, and sorption measurements are used to understand vanadium dynamics on the zeolite. Vanadium deposited on the external surface of the zeolite migrates into the channels by being heated in oxidizing atmosphere; although water helps vanadium reach the acid sites, it is not required. Vanadium is stabilized as VO2+cation near the acid sites. The strongest acid sites can stabilize V as VO2+cations, but experimental results show that VIVdoes not play any role in zeolite destruction. Extraframework aluminum competes with the zeolite for vanadium and delays its migration to the acid sites. In the presence of water vanadic acid is formed inside the zeolite according to the reaction VO2+–Y+2H2O ⇌H+– Y+2H3VO4. Since vanadic acid is a strong acid, it can destroy the zeolite by hydrolysis of the SiO2/Al2O3framework; in this way, vanadium can act as a catalyst for zeolite destruction. Synergistic action between sodium and vanadium is explained. A detailed mechanism for zeolite dealumination by steam is proposed.

Effect of Zeolite on the Dispersion Stability of Iron Oxide Particles

The mechanisms of zeolite that contribute to the dispersion stability of iron oxide were investigated. It was evident that an interaction exists between iron oxide and zeolite by the sedimentation method and absorbance measurements. Moreover, zeolite enhances the dispersion stability of iron oxide particles. This study proves that zeolite exerts an effect of increasing pH, which is one of the mechanisms that contributes to the dispersion stability of iron oxide particles.

Studies on the Mechanism of Zeolite X Crystallization. I. Effects of Silica Sources of Starting Materials on the Crystallization of Zeolite X

Abstract The crystallization mechanism for zeolite was investigated. Tetraethyl orthosilicate and silica sol were used as silica sources. Many kinds of solid phases were obtained at various reaction times. These solid phases were characterized by analyses for chemical compositions, X-ray diffraction, adsorption of nitrogen gas and water vapor, and IR spectroscopy. The results obtained suggest that the solid phase derived from tetraethyl orthosilicate at an early stage of reaction is composed of slightly ordered skeletons. In addition, during aging of gel at room temperature, the structure of the solid phase of gel undergoes a rearrangement to form a crystalline structure. On the other hand, the gel phase obtained from silica sol is predominantly made up by the coagulation of disordered aluminosilicate polymers or silicic polymers. These gel phases act as a precursor, and a part of the gel dissolved into the liquid phase and the dissolved species are converted into crystals in the liquid phase. Thus, the silica sources influence the structure of gel and crystals. In general, the crystallization mechanism is strongly influenced by the starting materials, especially by the silica sources.