A-type Zeolite Research Articles

Preparation of fly ash zeolite supported ZnO/Co3O4 catalyst for the photocatalytic degradation of xanthate under visible light

The development of high-value utilization technology of fly ash plays an important role in promoting environmental protection and social and economic development. In this paper, a novel composite photocatalyst Z-ZnO/Co3O4 is synthesized by loading ZnO/Co3O4 on the surface of fly ash zeolite. In addition, the properties of Z-ZnO/Co3O4 are characterized by variety of methods. The results show that the surface of cubic A-type zeolite is coated with ZnO/Co3O4 composite, forming an open spherical flower-like structure with a typical p-n heterostructure, which plays a positive role in reducing the band gap and the recombination rate of photogenerated electrons and holes of the composite catalyst, thus improving the degradation efficiency of xanthate. The degradation rate toward xanthate of Z-ZnO/Co3O4 is 97.62 % after simulated sunlight irradiation for 120 min under the optimum conditions, which is higher than that of Z-ZnO and Z-Co3O4, respectively. Meanwhile, the experimental results indicate that h+ plays a leading role in the catalytic reaction system. Furthermore, degradation rate toward xanthate of Z-ZnO/Co3O4 decreases slightly from 97.62 % to 88.24 % after five cycles, indicating its remarkable durability and stability.

Soil improved with a hybrid alkali-activated cement from waste stone wool and OPC

The use of OPC as a construction material is currently being reconsidered owing to the generation of greenhouse gases during production. Geopolymers or alkali-activated cement (AAC) have been proposed as partial replacements because of their excellent chemical and mechanical properties, which are equal to or superior to those of OPC. The use of these alkaline types of cement in soil stabilization has also gained significant interest in the academic community because of the possibility of it being derived from industrial waste. In this study, clay soil stabilized with AAC using waste stone wool fiber (SW) as a precursor and stabilized with hybrid alkali-activated cement (HAAC) using SW and OPC was prepared and subsequently evaluated mechanically and chemically after 28 days of curing. The results showed a significant increase in soil strength with both stabilization processes. The maximum achieved unconfined compressive strength (UCS) in the soil stabilized with AAC was 0.9 MPa (15 % SW), while the strength achieved with HAAC was 1.7 MPa (10.5 % SW - 4.5 % OPC). The California Bearing Ratio (CBR) of the latter combination was also determined, finding a value of 133 %, well above that of the soil without treatment (3.32 %). Through XRD, the A-type zeolite was identified as a product of the alkaline reaction, whereas the formation of N-A-S-H and C-A-S-H gels was observed via SEM. EDS mapping showed an increase in the atomic percentages of Si and Al in the soil specimens with HAAC, indicating the formation of Si-O-Si and Si-O-Al bonds. In addition to the potential application of this material in civil infrastructure related to soils (e.g., embankments and wall fillings), a sustainable construction material using industrial waste SW with a lower percentage of OPC is proposed.

Lithium leach residue synthesis process of high crystallinity hydroxysodalite, NaX, NaA zeolites and solidification and migration of potentially toxic elements

Converting lithium leach residue (LLR) into zeolite can reduce environmental impacts while also producing high value-added products. However, the synthesis of zeolites by LLR under alkali fusion may result in the solidification and migration of potentially toxic elements with secondary environmental impacts. Systematic research into this subject is rare in the open literature and the mobility of toxic elements from LLR derived zeolites is yet to be understood. In this paper, we have investigated the highly crystalline synthesis of hydroxy sodalite, X-type zeolite (NaX), and A-type zeolite (NaA) without stencil agent and crystal species, which can be achieved by modulating the alkali fusion temperature, all three zeolites have greater than 90 % conversion of the major elements aluminum and silicon. Meanwhile, the leachability of thallium (Tl), beryllium (Be), and potentially toxic elements (lead (Pb), mercury (Hg), cadmium (Cd), chromium (Cr), arsenic (As), barium (Ba), copper (Cu), nickel (Ni), cobalt (Co), zinc (Zn)) was monitored by pH-dependent leaching test for LLR and three kinds of synthesized zeolites according to the Chinese standard and the emission of toxic elements during the synthesis process was analyzed, to investigate the migration and quantify the distribution of the toxic elements in the LLR to the product zeolites and the cleaning wastewater. The migration efficiency of potentially toxic elements from LLR to the product zeolite and cleaning wastewater was explored. It was found that most of the toxic elements Tl, Be and potentially toxic elements were solidified in the structure of the zeolites by ion exchange (solidification rate > 90 %), and a small portion flowed into the cleaning wastewater. Although there are toxic elements solidified in the structure, there is no significant leaching under various pH conditions, which is in line with the Chinese standard (GB/T 5085.3–2007). Therefore, it is considered that LLR realizes environmentally friendly zeolite production and does not cause secondary pollution to the environment. This work demonstrates great potential for green recycling of LLR from the lithium extraction process and introduces an environmentally friendly slag treatment technology.

Insights into uranium sequestration by coal fly-ash-derived zeolites: Understanding via wet chemistry, and advanced spectroscopies

The operation of nuclear power plants requires a supply of nuclear fuel where uranium plays a substantial role as a primary fissile material. Its extraction from U-bearing minerals and handling may cause a leakage of heavily toxic radioactive pollution, which ends up in water bodies and soil. Therefore, tackling U-contaminated water is crucial to preserve water integrity and quality. Zeolites are known as profound ion exchangers with great affinity towards cationic species present in polluted waters. Various zeolite synthesis routes have made this group of aluminosilicates even more promising to be applied as water purification materials. Here, the synthetic gismondite, faujasite, and Linde type-A zeolites from coal fly-ash were synthesized via tailored, coupled fusion-hydrothermal method and applied to remove aqueous uranium (primarily as 238U) under varying pH, time (sorption kinetics), and initial U concentrations (sorption isotherms). The maximum U uptake was observed for Na–P1 (GIS) zeolite, which equals 48.72 mg U/g, the highest reported value on maximum U adsorption capacity for zeolitic materials. The U adsorption kinetics showed that equilibrium is reached after approximately 3 h of adsorption and that the removal process follows a Freundlich isothermal model for all zeolites, thus preferential adsorption onto heterogeneous surfaces. Advanced spectroscopic studies, including laboratory-scale X-ray Photoelectron Spectroscopy with synchrotron light X-ray Absorption Near Edge Structure in High Energy Resolution Fluorescence Detection mode, revealed that at acidic pH, predominantly an ion exchange between Na+ ions with hexavalent uranyl species takes place. In contrast, in the neutral pH region, the U is immobilized via precipitation in the form of μm-scale mineral aggregates of Na-schoepite: Na[(UO2)4O2(OH)5](H2O)5↓. The outcomes of the research study has demonstrated that synthetic zeolites, obtained from industrial by-products such as coal fly-ash, can be successfully valorized to efficient U adsorbents while unveiling the insights to understand the zeolites/U interactions at the nanoscale level.

Synthesis and Characterization of Alginate Gel Beads with Embedded Zeolite Structures as Carriers of Hydrophobic Curcumin.

Alginate-based beads containing a porous zeolite filler were developed as carriers of bioactive compounds with a hydrophobic nature, such as curcumin (Cur). Curcumin, a natural pigment extracted from the turmeric (Curcuma longa) plant, exhibits antioxidant, anti-inflammatory, anticarcinogenic, and antiviral properties. To enhance the bioavailability of the drug, curcumin needs to be encapsulated in a suitable carrier that improves its dispersibility and solubility. Commercial A-type zeolites (Z5A) were used as curcumin-binding agents and they were immobilized within the alginate gel beads by cross-linking in calcium chloride solution during an extrusion dripping process. The process parameters (alginate and CaCl2 concentrations, needle gauge, collecting distance) were optimized to fabricate beads with good sphericity factor and 1.5-1.7 mm diameter in their hydrated state. The chemical structure of the gel beads was assessed using FTIR spectroscopy, while their thermal stability was evaluated through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Due to the alginate matrix, the composite Alg/ZA5-Cur beads possess pH-responsive properties. In addition, the gel beads were modified by chitosan (CS) to enhance the stability and control the degradation behavior of the gel matrix. The swelling behavior and the degradation of the beads were analyzed in physiological solutions with different pH values. Results demonstrate the stabilizing and protective effect of the chitosan coating, as well as the reinforcing effect of the zeolite filler. This makes the pH-responsive alginate gel beads good candidates for the delivery of lipophilic drugs to specific inflammatory sites.

Synthesis of Linde A-type zeolite from ball clay with incorporated ruthenium and application in hydrogenation catalysis

The Linde A-Type zeolite (LTA zeolite) was synthesized from ball clay through two steps of calcination at 600 °C with the addition of NaOH/Al(OH)3 in a mass ratio of 1:1.2/0.43 and hydrothermal treatment at 60 °C for 48.0 h. A certain amount of 3.0 wt% Ru3+ was introduced before the hydrothermal treatment, and the Ru0-nanoparticles were in-situ fixed in the zeolite in a facile way. The synthesized materials were characterized by X-ray diffraction, infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The zeolite with LTA structure was successfully synthesized from ball clay, and the catalytic performance was checked by using hydrogenation of benzene at 150 °C and PH2 = 5.0 MPa, and the turnover frequency (TOF) of cyclohexane reached 4000 mol/(mol·h). The good stability was demonstrated by the high conversion of 94.0% and 98.0% of benzene after cycling use for many runs of catalysis and calcination at 550 °C.

The Influence of Ultrasound on Fly Ash Zeolitisation Process Efficiency

ABSTRACT The zeolitisation of fly ash originating from hard coal combustion in a Polish power plant was conducted using the alkaline hydrothermal method with and without the application of ultrasound. The output ash primarily contained glass, mullite, quartz and hematite, and its dominant chemical components included SiO2 (over 50 wt.%) and Al2O3 (over 28 wt.%). The synthesis of two zeolitic materials was conducted under the following conditions: 3 M NaOH solution, synthesis time – 8 hours, temperature – 80°C. For one of the syntheses, ultrasound with a frequency of 40 kHz and power of 480 W was applied for the first two hours. The identification of mineral components of initial ash and post-synthesis products was conducted using following methods: X-ray diffraction, X-ray energy dispersive spectroscopy, scanning electron microscopy, differential thermal analysis and thermogravimetric analysis. The obtained zeolitic materials varied greatly in phase composition. The product phase composition for the non-ultrasound-assisted synthesis was practically identical to the initial fly ash (mullite, quartz and hematite). The glass underwent minor chemical metamorphosis, recognizable by the presence of new phases in small quantities, typically mutually interlayered, mostly in the form of thin incrustation on the ash grains. The phases included: hydrosodalite, NaP-type zeolite, LTA-type zeolite and A-type zeolite. These phases, where Na+ cations should be dominant, contained K+, Ca2+ and Mg2+ cation substitutions. The zeolitic material obtained with the application of ultrasound, apart from initial fly ash phase residues, contained new phases in significant quantities, such as hydrosodalite and NaP-type zeolite, and A-type zeolite in smaller quantities.

Synthesis of X- and A-Type Zeolites from Waste Stone Powder and Aluminium Dross Using Alkali Fusion

Zeolites A and X, well-known as practical materials, were successfully synthesized with high cation exchange capacity (CEC) using two industrial wastes, waste crushed stone powder and aluminum dross, by alkali fusion treatment. Waste stone powder and aluminum dross are industrial wastes, and effective utilization of these wastes has been highly expected. Since the main components of the two wastes are Si, Al and O, those wastes can be used as starting materials for synthesis of zeolites. In this study, these industrial wastes were converted into crystalline zeolite-X and –A using alkali fusion. The stone powder, dross and the mixture of these wastes were transformed into a soluble phase via alkali fusion, and then agitated in distilled water at room temperature to give an intermediate gel-like solid, followed by synthesis at 80 °C to give the final product. The zeolites were successfully synthesized via the alkali fusion process, and selective synthesis of zeolites A and X was achieved by controlling the mixing ratio of aluminium dross to stone powder.

Parameters Affecting the Synthesis of X and A Zeolites from Coal Fly Ash

This paper summarizes the investigation results on the main parameters affecting the synthesis of type X and A zeolites using coal silicious fly ash (FA) as raw material. The synthesis was performed by dissolution of alkali-fused alumino-silicates, followed by hydrothermal treatment. The experimental data confirm that fly ash SiO2/Al2O3 ratio, NaOH/FA ratio, acid treatment of pre-fused fly ash, salinity of solution have a significant effect on type and properties of newly formed zeolites. In summary, the results show that A and X-type zeolite form with FA SiO2/Al2O3 ratio < 1.12 and > 1.86, respectively. Moreover, FA characterized by SiO2/Al2O3 mole ratio of 3.15 is suitable for X-type zeolite synthesis while A-type zeolite does not form without NaAlO2 addition. The crystallization occurs faster at higher temperatures although above 90°C X-type zeolite evolves into more stable phases whereas increasing the crystallization time from 1 to 72 hours, the yield of the synthetic products enhances from 60 to 75%. The use of seawater is responsible for the synthesis of X-type showing both lower purity and specific surface area. However, the synthetic products are characterized by high exchange capacity (> 320 meq/100 g), thus suggesting their successful application as adsorbents and catalysts in different types of wastewater and industrial waste treatments.

Ultrafine tuning of the pore size in zeolite A for efficient propyne removal from propylene

Abstract The removal of trace propyne (C3H4) from propyne/propylene (C3H4/C3H6) mixtures is a technical and challenging task during the production of polymer-grade propylene in view of their very similar size and physical properties. While some progress has been made, it is still very challenging to use some highly stable and commercially available porous materials via an energy-efficient adsorptive separation process. Herein, we report the ultrafine tuning of the pore apertures in type-A zeolites for the highly efficient removal of trace amounts of C3H4 from C3H4/C3H6 mixtures. The resulting ion-exchanged zeolite 5A exhibits a large C3H4 adsorption capacity (2.3 mmol g−1 under 10−4 MPa) and high C3H4/C3H6 selectivity at room temperature, which were mainly attributed to the ultrafine-tuned pore size that selectively blocks C3H6 molecules, while maintaining the strong adsorption of C3H4 at low pressure region. High purity of C3H6 (>99.9999%) can be directly obtained on this material under ambient conditions, as demonstrated by the experimental breakthrough curves obtained for both 1/99 and 0.1/99.9 (V/V) C3H4/C3H6 mixtures.

Removal of cesium ions from A-type zeolites using sodium tetrakis(4-fluorophenyl)borate and sodium tetraphenylborate

With the ultimate aim of reducing the volume of radioactive-cesium-contaminated soil generated by the nuclear power plant accident in Fukushima Prefecture in 2011, this study focuses on the desorption of Cs+ ions from minerals that strongly adsorb Cs+, such as clay, using the ion-association reagents sodium tetrakis(4-fluorophenyl)borate hydrate (NaTFPB) and sodium tetraphenylborate (NaTPB) under mild conditions. A-type zeolite was selected as a representative aluminosilicate mineral with a high cesium adsorption capacity. NaTFPB exhibits stronger hydrophobic interactions with Cs+ and improved Cs+ compared to NaTPB; a desorption efficiency of 89.4% was achieved at a 10:1 NaTFPB/cesium molar ratio.

Adsorption of hydrogen and deuterium on A-type zeolites at 77 K after various heat treatments

Abstract Molecular sieves (MSs) are a potentially useful means of hydrogen isotope recovery as well as the temporary storage and supply of such isotopes. In this study, the hydrogen adsorption isotherms for various MS samples were acquired after applying different water removal processes to activate the MSs. MS-3A sample was found not to adsorb hydrogen regardless of the activation conditions. MS-4A sample adsorbed hydrogen at 77 K after heating at 473, 513, and 673 K. However, the adsorption amount after heating at 473, 513 K was considerably less than that at 673 K. Consequently, heating at 673 K was required to activate this type of MS. In the case of an MS-5A sample, the presence of residual water had little effect on hydrogen isotope adsorption at 77 K. From these results, it is evident that MS-5A is the most suitable hydrogen adsorption material because it is readily activated and is less affected by water adsorption.

Analysis of Ethanol Dehydration using Membrane Separation Processes.

After the biomass pretreatment and fermentation processes, the purification step constitutes a major task in bioethanol production processes. The use of membranes provides an interesting choice to achieve high-purity bioethanol. Membrane separation processes are generally characterized by low energy requirements, but a high capital investment. Some major design aspects for membrane processes and their application to the ethanol dehydration problem are addressed in this work. The analysis includes pervaporation and vapor permeation methods, and considers using two types of membranes, A-type zeolite and amorphous silica membrane. The results identify the best combination of membrane separation method and type of membrane needed for bioethanol purification.

Coal fly ash derived zeolite for highly efficient removal of Ni2+ inwaste water

A novel efficient Ni2+ adsorbent A-type zeolite is successfully synthesized. It is worth noting that the raw material used is the waste coal ash produced by local power plants. The ability of A-type zeolite to remove Ni2+ from wastewater is up to 94%. In the study, the physical properties of zeolite are systematically characterized. In addition, we study in detail the effect of the external environment on the adsorption capacity of A-type zeolite. Moreover, the pseudo secondary kinetic model and Langmuir isothermal model evaluate the kinetic performance and isothermal equilibrium adsorption ability are better. The synthetic zeolite not only effectively uses the coal fly ash, but also realizes the sewage recycling. Therefore, the use of power plant coal fly ash to make adsorbent zeolite has potential practical significance.

Improving the biocidal activity of outdoor coating formulations by using zeolite-supported silver nanoparticles

Zeolite/nanoparticle composites are synthesized and used as additive for waterborne formulations in replacement of traditional isothiazolinone-based biocides. Silver nanoparticles dispersed onto micrometer-sized crystals of A-type zeolite were prepared by thermal treatment or chemical reduction methods applied to the Ag-exchanged zeolite. The antifungal efficiency against Trichoderma sp. of waterborne outdoor coatings containing the supported silver nanoparticles, measured in terms of inhibition halo development, shows similar results to those obtained by using traditional organic biocides, the type, size and size distribution of the nanoparticles being the main factors affecting the biocidal action of the prepared coatings.

Preparation, characterization and performance evaluation of supported zeolite on porous glass hollow fiber for desalination application

A-type zeolite membranes were synthesized on porous glass hollow fibers that prepared using the in-situ hydrothermal process. The porous glass hollow fibers were prepared using the phase inversion and sintering technique with the addition of yttria stabilized zirconia (YSZ) to improve their porosity. The glass hollow fibers were characterized using the scanning electron microscope (SEM), Fourier transform infrared (FTIR), mechanical properties and water permeability. The porosities of pure glass hollow fiber were improved by the addition of YSZ particles, which lead to an increase in the pure water permeability. The water permeability shows that the glass hollow fiber prepared form spinning suspension E, which has 30 wt% zeolite particles and 20 wt% YSZ particles, has the highest permeability of 155.65 L m−2 hr−1 bar−1 compared to the previous work, which was only 4.0 L m−2 hr−1 bar−1. This glass hollow fiber was later used as the support for the incorporation of zeolite membrane for the desalination application. The performance of membranes is separating sodium chloride (NaCl) salt solution were tested using two different setups, namely pressure driven reverse osmosis (RO) and sweeping liquid assisted reverse osmosis (SLRO). The solute flux for 5,000 and 10,000 ppm NaCl salt solutions were 24.45 and 17.86 L m−2 hr−1, respectively. Both operations enabled the solute rejection up to 98%.

Fabrication of CuO-doped catalytic material containing zeolite synthesized from red mud and rice husk ash for CO oxidation

In this study a series of the CuO-doped materials containing zeolite with varying CuO contents were synthesized from red mud (RM) and rice husk ash (RHA). The rice husk ash/red mud with the molar ratio of , and being 1.8, 2.5 and 60, respectively, were maintained during the synthetic process of materials. The characteristic structure samples were analyzed by x-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET) surface area and H2 temperature program reduction (H2-TPR). The catalytic activity of samples was evaluated in CO oxidation reaction in a microflow reactor at temperature range 200 °C–350 °C. The obtained results showed that all synthetic samples there exist the A-type zeolites with the average crystal size of 15–20 nm, the specific surface area of , and pore volume of . The material synthesized from RM and RHA with the zeolite structure (ZRM, undoped CuO) could also oxidize CO completely at 350 °C, and its activity was increase significantly when doped with CuO. CuO-doped materials with the zeolite structure exhibited excellent catalytic activity in CO oxidation. The ZRM sample loading 5 wt% CuO with particle nanosize about 10–30 nm was the best one for CO oxidation with complete conversion temperature at 275 °C.

Semi-clathrate hydrate process of methane in porous media-microporous materials of 5A-type zeolites

Porous media can significantly promote the kinetics of hydrate formation by reducing the barrier of physical chemistry, where zeolites are typical microporous minerals. In this paper, the formation process and the reaction kinetics of the methane hydrate were investigated in A-type zeolite with tetrahydrofuran (THF) and tetra-n-butyl ammonium bromide (TBAB) aqueous solution in a long tubular reactor. The results showed that good kinetic characteristics of methane hydrate formation can be achieved with A-type zeolite. At initial pressure of 1.5 MPa and 1.8 MPa at 285.15 K, the aqueous solution of tetrahydrofuran (THF) and tetra-n-butyl ammonium bromide (TBAB) with 5A-type zeolite can form methane hydrate with gaseous methane in 10 h. The temperature raised significantly during the formation process of the system with 5A-type zeolite. Throughout the reaction, there was an obvious temperature rising region which was located in the inlet side of tubular reactor. The gas uptake increased rapidly in the beginning of 100 min and then maintained stable increasing during the hydrate formation. The final gas uptake capacity raised with the reaction pressure but was little affected by the type of promoter. From 1.5 MPa to 1.8 MPa the final gas uptake of hydrate increased 6.48% and 6.15% in the THF and TBAB solution respectively. The reaction rate quickly reached the peak after the reaction began and then rapidly dropped to decays. Simultaneously the average of reaction rate of THF solution was 13.2–30.8% higher than that of TBAB solution when the pressure was 1.5 MPa and 1.8 MPa at the same experimental conditions.

Synthesis of Zeolite A from Mongolian Coal Fly Ash by Hydrothermal Treatment

Raw coal fly ash and acid pretreated fly ash were used to synthesize A-type zeolite by hydrothermal treatment. In order to synthesize zeolite A an aqueous gel having a molar batch composition of Na2O:Al2O3:1.926SiO2:128H2O was utilized. Fly ash and zeolitic products were characterized by SEM, XRF, XRD and cation exchange capacity (CEC). After hydrothermal treatment, several types of zeolites were formed: zeolite A, analcime, faujasite and hydroxy-sodalite. The highest content of zeolite A was formed in the mixture treated at 80°C for 8 hours. CEC values of the zeolitic products were 28-38 times higher than that of in raw fly ash. Acid pretreatment which leads to low calcium and iron content is preferable method for processing of fly ash for the zeolite synthesis. Synthesized zeolite can be used for ion exchangers for water treatment.

Ultrasonic vs hydrothermal method: Different approaches to convert fly ash into zeolite. How they affect the stability of synthetic products over time?

The action of direct sonication (US) versus conventional hydrothermal method (HY) was investigated to determine the differences in the crystallization mechanism of zeolite formed from fly ash. The results showed that ultrasonic energy is decisive in very fast faujasite and A-type zeolite transformation into more stable sodalite phase. The data display the main presence of sodalite together with a low amount of faujasite and zeolite A after the first 3 h of sonication. The full transformation of the latter two phases into sodalite takes place after 1 h more of treatment. The samples incubated by hydrothermal process for 3 h, instead, are characterized by the main presence of faujasite and A-type zeolites. The progressive synthesis of sodalite at the expense of the other two phases begins only after 4 h of treatment. The conclusion is that the crystallization of zeolites by ultrasonic and hydrothermal method proceeds via two different mechanisms. The data also show that the two approaches affect the stability of the synthetic products in a different way over the years.