Search Results (46)

Radium and barium are hazardous contaminants that frequently occur in wastewater, posing significant risks to human health and the environment. This study provides a comparative evaluation of five synthetic zeolites—3A, 4A, 5A, 13X (commercial), and NaP1 (synthesized from fly ash)—representing three distinct framework types (LTA, FAU, and GIS) for the removal of radium from real saline mine water (Upper Silesia Coal Basin, Poland) and barium from synthetic water. The zeolites were characterized by XRD, SEM-EDS, and N₂ adsorption, and tested in both granular and fine-powder forms using sequential batch adsorption experiments. For radium removal from mine water, zeolite NaP1 demonstrated superior performance, maintaining low ²²⁶Ra effluent activity (<1 Bq/L), even after treating ~50 L of water. Zeolites 3A, 4A, 5A, and 13X exhibited significantly lower performance than NaP1, showing poor selectivity for radium. In the barium batch tests, all tested zeolites achieved removal efficiencies exceeding 95% at low initial concentrations (100 mg/L). At higher concentrations (2000 mg/L), zeolites 3A, 4A, and 13X exhibited the highest adsorption capacities, with zeolite 4A achieving the maximum value of approximately 239.9 mg/g. The experiments demonstrated that idealized laboratory conditions can substantially overestimate sorbent performance relative to real water systems. Full article

This study addresses the challenge of separating powdered zeolite adsorbents by developing biomass-supported composites via in situ crystallization of zeolites NaA (LTA) and NaX (FAU) within lead tree wood. Wood was mixed with precursor gels and subjected to hydrothermal treatment, yielding composites and external zeolite powders. Phase formation and morphology were confirmed by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The zeolite content in the composites was estimated from TGA to be approximately 10 wt.% for LTW–NaA and ~2 wt.% for LTW–NaX. Cu(II) adsorption was evaluated under controlled conditions and analyzed using Langmuir and Freundlich models together with Giles classification. The NaA powder showed the highest capacity (q_m ≈ 210 mg g⁻¹), while composite performance reflected zeolite loading. When normalized by zeolite mass, the composites exhibited comparable or enhanced capacities relative to powders, suggesting improved accessibility of active sites. NaA-based materials displayed H-type isotherms, whereas NaX-based materials showed L-type behavior, indicating different adsorption mechanisms. These results demonstrate that framework topology and biomass confinement jointly influence adsorption and that the composites are promising, easily recoverable adsorbents, with further work required to assess regeneration and long-term stability. Full article

Despite global efforts to reduce landfill use for municipal waste, many sites remain active, and older closed sites still require management, particularly regarding leachate. Landfill leachate contains varying levels of organic and inorganic pollutants, generated through biological and physicochemical processes following water infiltration. Its complex composition—including COD, inorganic macro-components, heavy metals, and xenobiotics—necessitates effective treatment technologies to enable safe discharge into surface waters. This study compares low-cost, eco-sustainable adsorbents for the removal of ammonium, trace elements (Cd, Be, Fe, Cu, Ni, Pb, Cr, As, Sn, Sb, Se), and color (as an indirect measure of organic compounds) from urban landfill leachate. In more detail, six biochars from different biomass feedstocks and pyro-gasification conditions as well as natural chabazite and synthetic zeolite 13X (FAU-type) were investigated. After characterization, biochars were characterized and adsorption performance was assessed. Removal performance was comparatively evaluated after 24 h batch contact under fixed experimental conditions. Results showed that gasified biochars achieved high removal efficiency for metals and color but were ineffective for ammonium. Instead, both zeolites demonstrated efficient ammonium removal (~50%) but were less efficient for metals, reflecting the mechanism-driven selectivity of the adsorbents studied. Finally, a principal component analysis (PCA) revealed correlations between biochar physicochemical properties and contaminant retention, providing insight into key factors governing adsorption and informing the design of sustainable leachate treatment strategies. Full article

In order to solve the problems of low calorific value and pipeline corrosion caused by high concentration of CO₂ in oil-associated gas, and promote the resource utilization of associated gas, this study used validated grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation to investigate the adsorption characteristics of 11 different topological structures (straight-channel MFI/BEA, cage-channel LTA/FAU/CHA) and cation types (Ca²⁺, Na⁺, H⁺) of commercial zeolites for CO₂ and alkanes (CH₄, C₂H₆, C₃H₈) at 0%~90% RH. The results showed that the CO₂ adsorption capacity of all zeolites decreased with increasing humidity, but straight-channel zeolites (ZSM5-300, BETA-25) had excellent moisture resistance, with only a 20.8% and 30.6% decrease in capacity at 90% RH, respectively. The performance of cage-channel zeolite drops sharply under high humidity. Topology structure and cation synergistically regulate separation efficiency, maintaining stable diffusion order in straight channels. Ca²⁺ enhances dry state capacity but is prone to hydrophilic failure. The adsorption heat of CO₂ on straight-channel zeolite is 25–38 kJ/mol, resulting in lower regeneration energy consumption. ZSM5-300 is preferred for PSA (CH₄/CO₂ kinetic separation coefficient of 809.52 at 90% RH), and NaFAU is preferred for TSA (CO₂ adsorption capacity of 3.6 mmol/g and selectivity of 502.6 at 90% RH). This study clarifies the core structure-activity relationship and provides key theoretical support for the decarbonization of oil-associated gas. Full article

This study explores a sustainable synthesis route for FAU-type zeolite X using acid-treated ladle slag as a silicon source and waste aluminum cans as an alternative aluminum precursor. Conventional zeolite synthesis relies on high-purity reagents, which are costly and environmentally intensive to produce. Previous research has rarely addressed the valorization of ladle slag and metallic aluminum waste for zeolite formation, leaving their potential largely unexplored. The study focuses on the effective utilization of industrial and post-consumer wastes—acid-treated ladle slag and aluminum cans—as precursors for FAU-type NaX zeolite, demonstrating their feasibility as alternative silicon and aluminum sources. Here, zeolite X was synthesized hydrothermally from treated slag combined with either dissolved aluminum cans and commercial sodium aluminate at 90 °C for 6 h. FAU-type zeolite X was successfully synthesized using both aluminum sources, with a SiO₂/Al₂O₃ ratio of approximately 1.4. The results demonstrate that waste-derived precursors can effectively replace conventional chemicals, yielding predominantly NaX zeolite with high crystallinity and minor NaA impurity (as observed by XRD), with experimental yields of 1.47 g for aluminum cans and 1.266 g for sodium aluminate. The obtained zeolite X samples were structurally and texturally characterized by XRD, FTIR, XRF, BET surface area analysis, and thermogravimetric analysis (TG). Full article

Pervaporation is a compelling alternative to azeotrope-breaking and solvent dehydration due to lower energy demand and strong selectivity compared with distillation. FAU-type zeolite membranes combine large pore openings and hydrophilic frameworks with robust chemical stability, enabling water-selective separations from alcohols such as isopropanol and ethanol. Despite numerous synthesis routes, the role of seed crystal size in secondary growth, controlling nucleation density, intergrowth, and defect formation remains insufficiently quantified for FAU membranes under identical growth conditions. Here, FAU layers were fabricated on α-Al₂O₃ supports via secondary growth with varying seed sizes in the nanometer-to-micrometer range (72 nm to 6 μm). Zeolite crystal phase purity and morphology of membranes were assessed by XRD and SEM, with pervaporation of IPA/water 80 wt% at 75 °C quantified flux, separation factor, and permeance. We show that smaller seeds (95.51 nm) increase nucleation density, yielding thinner, more intergrown FAU layers with a higher separation factor but a modest trade-off in flux. Full article

Fly ash from coal-fired power plants is a promising precursor for zeolite synthesis due to its aluminosilicate-rich composition. However, its direct utilization is often limited by impurities and a low silicon-to-aluminum ratio (SAR). This study demonstrates the conversion of Class C fly ash from the Soma thermal power plant (Turkey) into FAU- and CHA-type zeolites through optimized acid leaching and hydrothermal synthesis. Acid treatment increased the SAR from 1.33 to 2.85 and effectively reduced calcium-, sulfur-, and iron-bearing impurities. The SAR enhancement by acid leaching was found to be reproducible among Class C fly ashes, whereas Class F materials exhibited a limited response due to their acid-resistant framework. Subsequent optimization of alkaline fusion-assisted synthesis enabled selective crystallization of FAU and CHA, while GIS and MER appeared under prolonged crystallization or higher alkalinity. SEM revealed distinct morphologies, with MER forming rod-shaped clusters, and CHA exhibiting disc-like aggregates. Water sorption analysis showed superior uptake for metastable FAU (~23 wt%) and CHA (~18 wt%) compared to stable GIS and MER (~12–13 wt%). Overall, this study establishes a scalable and sustainable route for producing high-performance zeolites from industrial fly ash waste, offering significant potential for adsorption-based applications in dehumidification, heat pumps, and gas separation. Full article

This study focuses on the exchange of mono- and divalent metal cations in FAU-type zeolite and their behavior in gas-phase CO₂ adsorption measurements and liquid-phase methylene blue (MB) adsorption in the absence of oxidizing agents under dark conditions. Firstly, zeolites exchanged with different cations were characterized by several techniques, such as XRD, SEM, XRF, XPS, and N₂ adsorption–desorption, to reveal the impact of the cations on the zeolite texture and structure. The adsorption studies revealed a positive effect of cation exchange on the adsorption capacity of the zeolite, particularly for silver-loaded FAU zeolite. In liquid-phase experiments, Ag-Y zeolite also demonstrated the highest MB removal, with a value of 79 mg/g. Kinetic studies highlighted that Ag-Y could reach the MB adsorption equilibrium within 1 h, with its highest rate of adsorption occurring during the first 5 min. In gas-phase adsorption studies, the highest CO₂ adsorption capacity was also achieved over Ag-Y, yielding 10.4 µmol/m² of CO₂ captured. Full article

This work focuses on the effectiveness of removing ammonium from real municipal wastewater using synthetic faujasite (FAU-type) and β (BEA-type) zeolites and a commercial β (BEA-type) sample. The results demonstrated that synthetic samples presented enhanced performance on ammonium removal in comparison with commercial zeolite due to higher Al content and larger specific surface area, promoting better accessibility to active adsorption sites of the adsorbents. Synthetic FAU-type and BEA-type zeolites achieved a maximum adsorption capacity of 28.87 and 12.62 mg·g⁻¹, respectively, outperforming commercial BEA-type zeolite (6.50 mg·g⁻¹). Adsorption assays, associated with kinetic studies and adsorption isotherms, were better fitted using the pseudo-second order model and the Langmuir model, respectively, suggesting that chemisorption, involving ion exchange, and monolayer formation at the zeolite surface, was the main mechanism involved in the NH₄⁺ adsorption process. After ammonium adsorption, the NH₄⁺-loaded zeolite samples were used to stimulate the growth of tomato seedlings; the results revealed a change in the biomass production for seedlings grown in vitro, especially when the BEA_C_NH₄ sample was employed, leading to a 15% increase in the fresh mass in comparison with the control sample. In contrast, the excess of ammonium adsorbed over the BEA_S_NH₄ and FAU_NH₄ samples probably caused a toxic effect on seedling growth. The elemental analysis results supported the hypothesis that the presence of NH₄⁺-loaded zeolite into the culture medium was important for the release of nitrogen. The obtained results show then that the investigated zeolites are promising both as efficient adsorbents to mitigate the environmental impact of ammonium-contaminated water bodies and as nitrogen-rich fertilizers. Full article

Oxygen concentrators (OCs) are essential medical devices providing oxygen in various settings, especially low-resource settings (LRSs). Despite their adaptability and cost-effectiveness, challenges arise in such environments due to factors like dust, temperature, and humidity, leading to premature OC failure. While efforts have been made to address these issues, understanding the primary contributing factor remains unclear. This study aims to shed light on this matter through the analysis of exhausted zeolite samples from Uganda, Ethiopia, and South Africa alongside a commercial virgin sample. The samples were comprehensively characterized through powder X-ray diffraction (PXRD) analysis, wavelength dispersive X-ray fluorescence (WDXRF) elemental analysis, Brunauer–Emmett–Teller (BET) surface analysis, and thermo-gravimetric analysis (TGA) coupled with mass spectrometry (MS). The characterization results confirmed a low silicon X-type framework (FAU-LSX) for all the samples. The maximum mass loss during TGA tests occurred at 130–160 °C, suggesting that water is the main component released from the zeolites. This was confirmed by MS analysis, which revealed the predominance of water in all the sample matrices. A correlation was found between OC efficiency and the amount of water adsorbed by the zeolites, proving that humidity has a key role in causing OC malfunctioning. No evidence for the presence of dust as a contaminant in the zeolites was found by the absence of the expected chemical elements in WDXRF. Since the outcomes of the study are independent of the geographical origin of the zeolites, its findings provide general guidance for engineers to modify OCs and prevent zeolite moisture poisoning. Full article

Entropies for alkane isomers longer than C₁₀ are computed using our recently developed linear regression model for thermochemical properties which is based on second-order group contributions. The computed entropies show excellent agreement with experimental data and data from Scott’s tables which are obtained from a statistical mechanics-based correlation. Entropy production and heat input are calculated for the hydroisomerization of C₇ isomers in various zeolites (FAU-, ITQ-29-, BEA-, MEL-, MFI-, MTW-, and MRE-types) at 500 K at chemical equilibrium. Small variations in these properties are observed because of the differences in reaction equilibrium distributions for these zeolites. The effect of chain length on heat input and entropy production is also studied for the hydroisomerization of C₇, C₈, C₁₀, and C₁₄ isomers in MTW-type zeolite at 500 K. For longer chains, both heat input and entropy production increase. Enthalpies and absolute entropies of C₇ hydroisomerization reaction products in MTW-type zeolite increase with higher temperatures. These findings highlight the accuracy of our linear regression model in computing entropies for alkanes and provide insight for designing and optimizing zeolite-catalyzed hydroisomerization processes. Full article

The purification and removal of polar impurities in olefin feedstocks is crucial for downstream deep processing, and adsorption is the main method for deep purification of such impurities. This article takes dimethyl ether, a typical oxygen-containing compound impurity in MTOs, as a polar impurity molecule, and LTA and FAU topological zeolites as research objects. The influence of zeolite topology, morphology, skeleton silicon–aluminum (Si/Al) ratio, and ion type on the adsorption and removal of trace dimethyl ether was investigated by XRD, SEM, XRF, and nitrogen adsorption–desorption methods. The FAU topological zeolites show a better adsorption performance for dimethyl ether owing to their larger specific surface area and unobstructed pores compared with LTA zeolites. Among FAU topological zeolites, the NaX zeolite a with lower framework silica–alumina ratio has the highest adsorption capacity for dimethyl ether. Magnesium ion exchange on NaX zeolites (MgNaX) reduce the specific surface area and adsorption capacity of the NaX zeolite. However, after forming with alumina as a binder, the adsorption capacity of the MgNaX–Al₂O₃ adsorbent is about 13% higher than that of the NaX–Al₂O₃ adsorbent without Mg ion exchange. This may be due to the decomposition of residual organic Mg salts in the Mg ion exchange samples during high-temperature calcination, resulting in a larger specific surface area for the formed adsorbent. Further characterization of NH₃–TPD and CO₂–TPD shows that Mg ion exchange weakens the acid–base active sites on the adsorbent surface. The reduction in acid–base sites reduces the occurrence of side reactions such as polymerization and isomerization caused by the exothermic adsorption of olefins on adsorbents. Repeated adsorption data show that the formed adsorbent has excellent regeneration–adsorption performance. Full article

For industrial tail gas to be converted into high-purity hydrogen, the H₂-N₂ mixture needs to be separated efficiently. This work examined the adsorption characteristics and competitive mechanisms of H₂ and N₂ on LTA- and FAU-type zeolites, at 77 K, 298 K, and 0.1–10 bar by thoroughly analyzing results of adsorption capacity experiments and molecular simulations. In the Grand Canonical Monte Carlo (GCMC) simulations, the force field causing a molecular dipole of H₂ and the polarization force field of N₂ are first applied. The accuracy of the force field was experimentally verified. The findings indicate that N₂ and H₂ loading on Ca-FAU (Ca-LTA) are higher than Na-FAU (Na-LTA). On NaX at 77 K, the highest adsorption selectivity (N₂/H₂) is observed; on NaA at 298 K, it is the opposite. The GCMC data findings demonstrate that H₂ and N₂ have remarkably similar adsorption sites, with framework oxygen atoms and non-framework cations serving as the main adsorption sites for adsorbate molecules. Furthermore, the rate at which H₂ diffuses is higher than that of N₂. The study of redistribution charge before and after adsorption demonstrated that N₂ has a greater affinity for the framework oxygen atoms than H₂. This study provides a molecular theoretical foundation for the adsorption behavior of H₂-N₂ mixture in zeolites. Full article

At present, cobalt belongs to what are called critical raw materials due to its scarcity and its economic importance. Cobalt is a crucial element in the development of new technologies and applications for decarbonization, with around 40% of cobalt consumption being used for rechargeable battery materials. Additionally, cobalt-based catalysts are used in the production of hydrogen fuel cells, and this element is also employed in the production of superalloys for aerospace and power generation industries. For this reason, it is imperative to increase cobalt recycling by recovering from secondary sources, such as decommissioned lithium-ion batteries. Among the technologies for cobalt recovery, adsorption is a reliable alternative as it allows its recovery even at low concentrations in aqueous solutions and is relatively low in cost. Among the potential adsorbents for cobalt recovery, this paper reviews two of the most promising adsorbents for cobalt recovery from aqueous solutions: zeolitic and carbonaceous materials. Regarding zeolitic materials, the maximum adsorption capacities are reached by FAU-type zeolites. In the case of carbonaceous materials, the actual trend is to obtain activated carbons from a wide range of carbon sources, including waste, the adsorption capacities, on average, being larger than the ones reached with zeolitic materials. Additionally, activated carbons allow, in many cases, the selective separation of cobalt from other ions which are present at the same time in the aqueous solutions such as lithium. Full article

The impact of solvents on the efficiency of cationic dye adsorption from a solution onto protonated Faujasite-type zeolite (FAU-Y) was investigated in the prospect of supporting potential applications in wastewater treatment or in the preparation of building blocks for optical devices. The adsorption isotherms were experimentally determined for methylene blue (MB) and auramine O (AO) from single-component solutions in water and in ethanol. The limiting dye uptake (saturation capacity) was evaluated for each adsorption system, and it decreased in the order of MB–water > AO–water > AO–ethanol > MB–ethanol. The mutual distances and orientations of the adsorbed dye species, and their interactions with the oxygen sites of the FAU-Y framework, with the solvent molecules, and among themselves were inferred from Monte Carlo simulations and subsequently utilized to rationalize the observed differences in the saturation capacity. The dye–solvent competition and the propensity of the dyes to form compact pi-stacked dimers were shown to play an important role in establishing a non-uniform distribution of the adsorbed species throughout the porous space. The two effects appeared particularly strong in the case of the MB–water system. The necessity of including solvent effects in modeling studies is emphasized. Full article