Zeolite Adsorption Research Articles

Examining the influence of sintering temperatures on the efficiency of 3D-printed natural zeolite for methylene blue dye adsorption

Additive manufacturing technology, with its potential for improved material efficiency, cost reduction, and capability to fabricate complex structures, is increasingly being leveraged in environmental engineering applications. This study harnesses this technology for fabricating natural zeolite adsorbents using an extrusion-based 3D printer, examining the influence of different sintering temperatures (300, 600, 900, and 1200 °C) on the adsorbents' properties. The study finds that samples sintered at 300 °C disintegrated in water, while those at 1200 °C underwent melting, changing their shape. Focus was then shifted to samples sintered at 600 °C (3D-Ze-600) and 900 °C (3D-Ze-900), with the former displaying a remarkable methylene blue (MB) adsorption efficiency of 82.5%, significantly higher than the latter's 20.1%. This disparity in adsorption performance is closely linked to the difference in porosity; the 600 °C samples exhibited a notably higher apparent porosity, which was instrumental in their enhanced adsorption capability. In contrast, the 900 °C samples, despite their lower porosity, showed diminished adsorption efficiency. XRD analysis further revealed that the superior performance of the 600 °C samples could be attributed to their preserved crystalline structure, which was altered in the 900 °C samples. These findings highlight the critical role of sintering temperature in determining the structural and functional properties of 3D-printed zeolites, demonstrating their potential as efficient adsorbents in wastewater treatment and offering valuable insights for optimizing the fabrication process for environmental applications.

Separation of 2,3-Butanediol from Fermentation Broth via Cyclic and Simulated Moving Bed Adsorption Over Nano-MFI Zeolites.

The biomass-based platform molecule 2,3-butanediol (2,3-BDO) has a wide range of applications in production of sustainable fuels, chemicals, synthetic rubber, and others. However, the selective separation of 2,3-BDO from multicomponent fermentation broths presents challenges due to its low concentration, high solubility in water, high boiling point, and presence of many other species. Here, we demonstrate remarkably selective enrichment and recovery of 2,3-BDO from a corn stover hydrolysate fermentation broth by a pure-silica nano-MFI-type zeolite adsorbent. By means of cyclic and simulated moving bed adsorption processes, we obtained concentrated aqueous 2,3-BDO streams from the fermentation process stream with ∼93% purity and 3-fold enrichment, and >98% purity and 8-fold enrichment, respectively. These findings provide strong support for large-scale adsorptive separation for biobased 2,3-BDO production.

Molecular Insight into the Electric Field Regulation of N2 and CH4 Adsorption in the Trapdoor ZSM-25 Zeolites.

Controlling gas admission by regulating pore accessibility in porous materials has been a topic of extensive research. Recently, the electric field (E-field) has emerged as an external stimulus to alter the adsorption behavior of some microporous adsorbents. However, the mechanism behind this phenomenon is not yet fully understood. Here, we demonstrate the crucial role of the trapdoor cations of zeolite molecular sieves in E-field-regulated gas adsorption. The E-field activation caused framework expansion and cation deviation, significantly reducing the energy barrier for gas molecules passing through the pore aperture gated by the trapdoor cation. This led to an increase in the N2 adsorption capacity of ZSM-25 and a 60% improvement in N2/CH4 selectivity in the quest for nitrogen rejection for natural gas processing. By combining experimental and computational approaches, we elucidated the influence of E-field activation as a concurrent effect of the reduced heat of adsorption caused by framework expansion and the decrease in the energy barrier resulting from promoted cation oscillation. These findings pave the way for the material design of E-field-regulated adsorption and its application in molecular separation.

Systematic screening and evaluation for an optimal adsorbent in a facade-integrated adsorption-based solar cooling system for high-rise buildings

Solar-powered adsorption chillers are a climate-friendly solution for building cooling, but costs and space requirements limit their widespread adoption. Recently developed adsorption cooling facade systems (ACFS) save installation space and further reduce CO2 emissions. The performance of ACFS depends on the implemented adsorbent. To achieve low costs and high performance of ACFS, this study systematically screened and scored adsorbents using the analytic hierarchy process (AHP) method, focusing on price, stability, driving temperature and adsorption capacity. This method narrowed down 293 adsorbents to top 10 scored adsorbents including 4 silica gels, 4 active carbons and 2 molecular sieves. The adsorbent-specific performance is evaluated by numerical simulation, revealing silica gel Type A++, Type 2560, Siogel and molecular sieve AQSOA-FAM-Z02 have peak adsorber temperatures 1.5–9.3 °C lower and increase solar cooling efficiency (SCE) by 25–27 % compared to reference adsorbent Zeolite 13X. A sensitivity analysis of the Dubinin-Astakhov equation shows increasing E and decreasing V leads to an only minor adsorber temperature decrease and minor system efficiency increase. Lower temperatures and higher capacity cannot guarantee better system performance. This underscores that improving system performance cannot be achieved solely through adsorbent optimization but requires system optimization in parallel.

Faujasite/graphene nanoribbon hybrid adsorbent pellet for carbon dioxide capture

Pelletizing zeolite adsorbents is essential for practical applications, but conventional pelletization methods involve binders that can alter material properties. This study presents a one-pot approach to synthesizing FAU-type zeolite/graphene oxide nanoribbon (GONR) composite powders that can be pelletized by simple pressing without binders. This one-pot synthesis can be conducted without structure-directing agents, making the process simpler and more efficient. During zeolite crystallization, the particles decorate the strands of GONRs, effectively generating additional macropores and enhancing the pellets’ mechanical strength. Additionally, GONR suppresses water adsorption while maintaining good CO₂ adsorption, which improves the material’s performance under humid conditions. The FAU/GONR pellets exhibited enhanced mass transport properties compared to neat FAU pellets, as demonstrated by 10 times higher CO₂ permeability. The highest CO₂/N₂ selectivity of 76.5 was observed with 12 wt% GONR-containing pellet, and the performance was comparable to conventional pellets, while the fabrication procedure remained simple.

Robust Imidazopyridinium Covalent Organic Framework as Efficient Iodine Capturing Materials in Gaseous and Aqueous Environment.

The development of a high-performing adsorbent that can capture both iodine vapor from volatile nuclear waste and traces of iodine species from water is an important challenge, especially in industrially relevant process conditions. This study introduces novel imidazopyridinium-based covalent organic frameworks (COFs) through post-modification of a picolinaldehyde-based imine COF. These COFs demonstrate excellent iodine adsorption capacity, adsorption kinetics, and a high stability/recyclability in both vapor and water phases. Notably, one imidazopyridinium COF exhibits gaseous iodine uptake of 21wt.% under dynamic adsorption conditions at 150°C and a relative humidity of 50%, surpassing the performance of the currently used silver-based zeolite adsorbents (Ag@MOR (17wt.%)). Additionally, the same imidazopyridinium COFs can efficiently remove iodine species at a low concentration from aqueous solution. Seawater containing triiodide ions treated under dynamic flow-through conditions resulted in decreased concentrations down to the ppb level. The adsorption mechanisms for iodine and polyiodide species are elucidated for the imine COF and imidazopyridinium COFs; involving halogen bonding, hydrogen bonding, and charge-transfer complexes.

Application of natural zeolite adsorption in cooperation with photosynthesis for the post-treatment of microbial fuel cells.

Microbial fuel cells (MFCs) are a promising technology that directly converts organic matter (OM) in wastewater into electricity while simultaneously degrading contaminants. However, MFCs are insufficient for the removal of nitrogenous compounds. Therefore, the post-treatment of MFCs is essential. This study was the first to use natural zeolite adsorption integrated with photosynthesis (ZP) for post-treating MFCs. In this system, no external energy was required; instead, natural light was used to promote the growth of photosynthetic microorganisms, thereby enhancing contaminants removal through the photosynthesis process. To assess the effectiveness of the method, comparisons were conducted under two conditions: dark (no photosynthesis) and light (with photosynthesis). In darkness, extending hydraulic retention time (HRT) enhanced COD and BOD removal by 19.8% and 28.9%, respectively. When exposed to natural light, improvements were even more notable, with COD and BOD removal reaching 32% and 40%, respectively. In both conditions, the method effectively removed NH4 +, achieving 60% efficiency in darkness and 84.5% in light. This study showed that the adsorption capacity of the zeolite reached saturation when the cumulative liquid volume per unit weight of the zeolite exceeded 0.2 L g-1. The key functional photosynthetic microbes were investigated using 16S rRNA and 18S rRNA. This revealed the presence of microorganisms such as Chlorobium, Acidovorax, Novosphingobium, and Scenedesmus, which likely play a role in enhancing the efficiency of photosynthesis in removing contaminants. The study findings indicated that the integration of MFCs-ZP represents an eco-friendly approach capable of resource recovery from wastewater while also meeting discharge standards.

Removal of Ammonia and Colour from Landfill Leachate using Integrated Electrocoagulation-Zeolite Adsorption Processes

The amount of waste generated in Malaysia had increased annually due to both economic and population accelerations. This resulted in an increase in leachate production that contains a high amount of ammonia nitrogen (NH3-N) and colour, which is a severe problem for both environments as well as for human health. Therefore, this study aimed to determine the potential of Electrocoagulation (EC) – zeolite adsorption for removing NH3-N and colour from landfill leachate. In the experimental works, two batch studies consist of batch EC using aluminium (Al) cylindrical electrode and batch adsorption study using clinoptilolite zeolites adsorbent were conducted using leachate sample collected from Pulau Burung Sanitary Landfill (PBSL). The batch EC experiment was carried out to determine the optimum removal of NH3-N and colour by the effect of current density (7 - 35 mA/mm2), initial pH (5 - 9), electrolysis time (0 - 90 minutes) and inter-electrode distance (5 - 25 mm). An integrated EC - zeolite adsorption was carried out under the optimum condition of 2.0 g/150 mL adsorbent dosage, contact time of 100 minutes and an initial pH value of 8. Based on the experiment, almost 50% of NH3-N and 95% of colour were removed using a single EC under the optimum current density of 14.0 mA/mm2, pH 5, electrolysis time of 75 minutes and 15 mm of inter-electrode distance. A comparison of colour removal between single EC and EC-Zeolite showed the same degradation performance. The interaction of hydrogen ion (H+) with aluminium hydroxide ion (Al (OH)3) produces during EC stabilises small particles forming larger sludge that reduces colour concentration. The removal of NH3-N increased from 50.0% to 93% when EC was integrated with clinoptilolite zeolite adsorption. In conclusion, the results show that both processes can potentially remove colour while the integrated process effectively removes NH3-N from landfill leachate. The proposed treatment helps optimise process performance while minimising the operational cost of the treatment. Thus, the proposed integrated EC – zeolite adsorption processes can be an alternative to landfill leachate treatment which aligns with the 12thMalaysia Plan to reduce pollution and carbon emissions to become a carbon neutral nation as early as 2050.

Highly efficient recovery of phosphate and fluoride from phosphogypsum leachate: Selective precipitation and adsorption

Phosphogypsum, a typical by-product in the phosphorus chemical industry, could generate a large amount of leachate containing phosphate and fluoride in the process of rainfall and long-term stacking, which not only causes serious environmental pollution, but also leads to a waste of resources. In this study, a united treatment of calcium hydroxide precipitation and lanthanum zeolite (La-ZFA) adsorption was proposed to achieve the recovery of phosphate and fluoride from phosphogypsum leachate. In phosphogypsum, most phosphorus could be leached except P in the residual occurrence form, while for fluoride, only water-soluble F could be effectively leached. The optimum leaching amounts of phosphate and fluoride were 22.59 and 4.64 mg/g, respectively, at liquid-solid ratio of 400:1, leaching time of 120 min, pH of 6.0, particle size of >200 mesh (<0.075 mm), and leaching temperature of 25°C. Using Ca(OH)2 as the precipitant, the phosphate could be precipitated selectively from phosphogypsum leachate by controlling pH and time, and the concentrations of it decreased significantly to 0.29 mg/L at pH 10.0, with a removal efficiency of 99.48%. XRD, SEM and Visual MINTEQ software analysis proved that the main component of the precipitate was hydroxyapatite (Ca5(PO4)3(OH)). After P precipitation, a series of sorbents for fluoride were investigated, and La-ZFA sorbent was chosen and utilized to recover the fluoride from the leachate through a cyclic fixed-bed column. The efficiency of La-ZFA was basically not affected by the high concentration sulfate, and it can selectively adsorb fluoride from phosphogypsum leachate, leading to a final fluoride concentration of 0.29 mg/L in the effluent. The characterization demonstrated that fluoride might be adsorbed onto the La-ZFA via ligand exchange with hydroxy groups. The proposed method in this study is expected to sequentially recover phosphate and fluorine from the leachate of phosphogypsum, and it has great guiding significance for resource utilization and management of phosphogypsum.

Fixed-bed adsorption of methylene blue using granular NaX zeolite/attapulgite composite: efficiency, mechanism and reusability of saturated G-NaX/A

A novel granular NaX zeolite/attapulgite (G-NaX/A) composite was developed to address the challenges of high pressure drop in fixed beds with powder synthetic zeolite and low adsorption capacity of natural zeolite. The synthesized G-NaX/A retains the micropores of NaX and the mesoporous of attapulgite. The BET specific surface area reached 481.17 m2/g, and the total pore volume was 0.3549 cm3/g. The G-NaX/A maximum methylene blue (MB) adsorption capacity was 1.56 times that of commercial granular activated carbon (7.41 mg/g). The breakthrough time and adsorption capacity improved with lower influent flow rate and MB concentration and higher pH. Under optimal conditions (flow rate: 150 mL/min, MB concentration: 25 mg/L, pH = 8), it achieved a maximum adsorption capacity of 11.51 mg/g and a breakthrough time of 2.54 h. The adsorption behavior of G-NaX/A was well-fitted by the Yoon–Nelson and Thomas models at different operating conditions. The mechanism studies revealed that MB (cation: C16H18SN3+) removal by G-NaX/A occurred through electrostatic attraction, ion exchange with Na+/Mg2+, surface coordination with ≡Al/SiOH, and surface physical adsorption. The regeneration studies confirmed the reusability potential of G-NaX/A by calcining at 500 °C for 2 h, and significantly improved adsorption capacity reaching about 14.39 mg/g, 16.31 mg/g and 14.07 mg/g across the three adsorption-regeneration cycles respectively. The findings support G-NaX/A technical feasibility, high adsorption capacity and potential for further scaling in fixed bed adsorption studies.

Landfill leachate treatment using sequential natural zeolite adsorption and peroxymonosulfate activated by UV/Fe2+ system: Effects of main operating parameters and application of fluorescence EEM to monitor organic matters’ transformation

The significant increase in global Landfill Leachate is a pressing challenge directly linked to the growing global population. Among the strategies for landfill leachate treatment, advanced oxidation processes using sulfate radical (SR-AOP) have gained considerable interest, despite the challenge of nitrate generation during ammonia oxidation. This study introduces a sequential treatment method that combines adsorption and a UV/PMS/Fe2+ system to assess its impact on COD (Chemical Oxygen Demand) and ammonia removal efficiencies.The results show that the sequential process achieves optimal COD and ammonia removal rates of 88 % and 88.3 % respectively. The increase in UV254 absorbance removal during the adsorption phase indicates the removal of UV quenching substances (UVQS), supporting the effectiveness of using adsorption as a pretreatment for the UV-assisted systems (UV/PMS/Fe2+). Additionally, analysis using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) reveals that the adsorption treatment before the SR-AOP process not only enhances COD and ammonia removal efficiencies, but also eliminates heavy metals such as vanadium (V), titanium (Ti), zinc (Zn), and aluminum (Al) present in leachate.Moreover, the higher BOD/COD ratio suggests improved biodegradability of the effluent. When compared to other systems at optimal conditions, the sequential adsorption and UV/PMS/Fe2+ systems demonstrate superior performance, focusing on removing refractory matter and reducing ammonia content, especially effective at a pH level of 7.25. Analysis using Excitation-Emission Matrix (EEM) shows a shift from primary peaks in raw leachate spectra associated with humic and fulvic acid-like compounds to lower-intensity peaks from fulvic-like small molecule materials in the treated effluent.

Odors Adsorption in Zeolites Including Natural Clinoptilolite: Theoretical and Experimental Studies.

This publication presents the results of combined theoretical and experimental research for the potential use of natural clinoptilolite zeolite (CLI) as an odor-adsorbing material. In this study of adsorption capacity, CLI of various granulation was used and its modifications were made by ion exchange using Sn and Fe metals to check whether the presence of metals as potential active centers does not lead to catalytic processes and may lead to enhanced absorption of odorous substances through their adsorption on the created metallic forms. Additionally, in order to increase the specific surface area, modifications were made in the form of hierarchization in an acidic environment using hydrochloric acid to also create the hydrogen form of zeolite and thus also check how the material behaves as an adsorbent. To compare the effect of CLI as a sorption material, synthetic zeolite MFI was also used-as a sodium form and after the introduction of metals (Sn, Fe). The above materials were subjected to adsorption measurements using odorous substances (including acetaldehyde, dimethylamine, pentanoic acid and octanoic acid). Based on the measurements performed, the most advantageous material that traps odorants is a natural material-clinoptilolite. Depending on the faction, its ability varies for different compounds. In the case of acetaldehyde, an effective material is clinoptilolite with a grain size of up to 2 mm. In the case of carboxylic acids, it is material after hierarchization with a fraction of 3-4 mm. In the case of theoretical calculations, information was obtained to show that metallic centers are more stable above oxygen, which is associated with the skeletal aluminum in clinoptilolite.

Theory guided engineering of zeolite adsorbents for acaricide residue adsorption from the environment.

Zeolites have attracted attention for their potential in adsorbing environmental contaminants. However, contaminants, such as acaricides used extensively in livestock production to control ticks and mites, have received limited exploration regarding their adsorption onto zeolite surfaces. This study aimed to identify the most appropriate zeolite frameworks for the adsorption of acaricide residues, deduce the mechanism underlying the adsorption process, and evaluate the impact of surface modification on the adsorption capabilities of zeolites. Grand Canonical Monte Carlo (GCMC) was used to screen the entire zeolite database to analyze their adsorption properties, where the cloverite zeolite framework (CLO) exhibits the highest adsorption capacity (percentage weight, 54%). Machine learning was employed to rank structural feature importance on adsorption. Density and helium void fraction appeared to be the most important structural features. Thus, engineering these features is of utmost significance in harvesting the desired acaricides. The second step involved engineering the structural and electronic properties of the shortlisted zeolite frameworks via cation substitution with suitable atoms. DFT calculations involving natural bond orbital (NBO) analysis and quantum theory of atoms in molecules (QTAIM) have been done to understand the influence of cation substitution on the electronic structure.

Study on adsorption and purification materials for ethylene in cold storage

In view of the lack of systematic quantitative and comparative studies on the purification effect of ethylene adsorbent in cold storage, starting from the selection of purification materials, this paper analyzed the purification effect of different zeolite materials on ethylene through a small test chamber, and screened out the best zeolite adsorbents used in self-made purification device. Combined with characterization analysis, purification efficiency evaluation and adsorption capacity of zeolite material, the removal performance of ethylene was investigated. The results showed that the zeolite samples with rough and porous surface showed better adsorption performance for ethylene. The larger the specific surface area and total pore volume, the stronger the adsorption capacity to ethylene. In addition, the presence of Na elements and mesoporous increased the exchange capacity and pore volume, which also played a certain role in the ethylene adsorption process. Experimental result demonstrates that clean air volume (CADR) of ethylene is 232 m3/h, the ethylene removal rate at 30 min is 98.19%, and the purification energy efficiency is 1.39. At the same time, the adsorption capacity of the selected zeolite sample is 1380.5 μg/g by dynamic adsorption experiment, and the service life of the filter element of the self-made purification device is estimated to be 166 days. This study can provide a theoretical basis for ethylene purification in cold storage.

Adsorption studies on synthetic lentil-like mordenite for column and batch removal of cadmium and lead ions: investigating isotherms and kinetics

ABSTRACT The mordenite zeolite adsorbent, with a lentil-like structure, was synthesised using a one-step green hydrothermal method. Its textural, structural, and morphological properties were characterised through X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, and the Brunauer-Emmet-Teller (BET) method. The prepared adsorbent was employed in both continuous and batch adsorption processes to remove toxic Cd(II) and Pb(II) metal ions from aqueous solutions. Operational parameters such as flow rate, initial concentration, and bed height were varied to understand breakthrough time, mass transfer zone, adsorption capacity, and exhaustion time during continuous adsorption, which were investigated and optimised. Additionally, the study explored the influence of solid/liquid ratio, pH, assay time, and initial concentration on batch adsorption. The maximum adsorption capacities of the lentil-like mordenite zeolite in fixed-bed breakthrough experiments were determined to be 78.22 mg/g for Cd (II) ions and 80.82 mg/g for Pb (II) ions. In batch experiments, the capacities were 133.64 mg/g for Cd (II) ions and 239.57 mg/g for Pb (II) ions. Dynamic continuous adsorption isotherms exhibited an excellent fit with the Thomas and Yoon – Nelson models, while batch adsorption isotherms conformed well to the Langmuir model. This study presents a new approach for synthesising high surface area, engineered morphology, reusable, and stable zeolite for effectively adsorbing hard metal ions from wastewaters, contributing to environmental remediation.

High-efficiency lanthanum-modified zeolite adsorbents for phosphorus control and algal suppression: Preparation, characterization and mechanistic insights

The use of lanthanum (La)-based materials for phosphate removal from water has received increasing attention. However, challenges remain to enhance phosphate (P) sorption capacities and remove P at low concentrations. In this study, lanthanum modified zeolite materials loaded with different lanthanum types were synthesized by hydrothermal method. Based upon preliminary screening of synthesized La-modified zeolite materials in terms of phosphate sorption capacity and La content, lanthanum chloride-modified zeolite (LZ) is chosen for further study. Specifically, for these materials, phosphate sorption kinetics and isotherm behavior, and solution matrix effects (solution pH, and ionic strength) are reported. The developed LZ has a high sorption capacity of 124.38 mg/g, which exceeds that of most La-based adsorbents currently available. P uptake by LZ was pH-dependent with the highest sorption capacities observed over a pH range of 3 ∼ 9. The presence of coexisting ions (Cl-, SO42-, HCO3–) does not significantly affect the adsorption capacity of LZ. In a real treated wastewater effluent with phosphate concentration of 1.92 mg/L and 0.155 mg/L, 0.1 g/L and 0.01 g/L of LZ efficiently reduced the phosphate concentration to below 0.01 mg P/L. Electrostatic attraction and inner-sphere complexation were identified as the sorption mechanisms of phosphate by LZ. The acute toxicity test confirms that the addition of LZ has no acute toxicity effect on aquatic organisms. However, LZ shows indirect and direct inhibitory effects on algae growth, which is beneficial for the control of eutrophic water. Moreover, the exhausted LZ can be easily regenerated with over 70 % adsorption capacity remained during five recycles. Overall, LZ shows great application potential, and this work provides new insights into the molecular-level mechanism of phosphate sequestration by LZ.

Nanocrystalline sodium mordenite as an efficient low-concentration CO2 adsorbent

Systematic control of the crystal size and morphology of zeolites to enhance their CO2 adsorption performance is of great importance from both environmental and economic perspectives. Here we report the seeded synthesis of sodium mordenite (Na-MOR) with a Si/Al ratio of 4.9 and an average crystal length and width of 70 and 40 nm, respectively, using γ-aminobutyric acid as a crystal growth inhibitor in the absence of any organic structure-directing agent (OSDA). This nanozeolite shows an unprecedented CO2 capacity of 1.58 mmol g−1 under dynamic direct air capture (DAC) conditions at 25 °C, which is approximately 40 % greater than the value (1.15 mmol g−1) of the best zeolite adsorbent (an unidentified OSDA-directed Na-MOR (Si/Al = 5.0) zeolite with Na+ enrichment in 8-ring side pockets), mainly due to its nanocrystalline nature. It has also been characterized by much faster CO2 adsorption kinetics (ca. 5 vs. 50 min equilibration time) compared to a commercial Na-MOR zeolite with Si/Al = 5.0. Our study paves the way for developing a more efficient zeolite-based DAC adsorbent.

Adsorption of Cu(II) and Ni(II) from Aqueous Solutions Using Synthesized Alkali-Activated Foamed Zeolite Adsorbent: Isotherm, Kinetic, and Regeneration Study.

Water pollution, particularly from heavy metals, poses a significant threat to global health, necessitating efficient and environmentally friendly removal methods. This study introduces novel zeolite-based adsorbents, specifically alkali-activated foamed zeolite (AAFZ), for the effective adsorption of Cu(II) and Ni(II) ions from aqueous solutions. The adsorbents' capabilities were comprehensively characterized through kinetic and isotherm analyses. Alkaline activation induced changes in chemical composition and crystalline structure, as observed via XRF and XRD analyses. AAFZ exhibited a significantly larger pore volume (1.29 times), higher Si/Al ratio (1.15 times), and lower crystallinity compared to ZZ50, thus demonstrating substantially higher adsorption capacity for Cu(II) and Ni(II) compared to ZZ50. The maximum monolayer adsorption capacities of ZZ50 and AAFZ for Cu(II) were determined to be 69.28 mg/g and 99.54 mg/g, respectively. In the case of Ni(II), the maximum monolayer adsorption capacities for ZZ50 and AAFZ were observed at 48.53 mg/g and 88.99 mg/g, respectively. For both adsorbents, the optimum pH for adsorption of Cu(II) and Ni(II) was found to be 5 and 6, respectively. Equilibrium was reached around 120 min, and the pseudo-second-order kinetics accurately depicted the chemisorption process. The Langmuir isotherm model effectively described monolayer adsorption for both adsorbents. Furthermore, the regeneration experiment demonstrated that AAFZ could be regenerated for a minimum of two cycles using hydrochloric acid (HCl). These findings highlight the potential of the developed adsorbents as promising tools for effective and practical adsorption applications.

Post-treatment of high-rate activated sludge effluent via zeolite adsorption and recovery of ammonium-nitrogen as alternative fertilising products

This study investigates the potential to connect nutrient flows between wastewater treatment and agriculture through a two-stage nitrogen (N) recovery system composed of high-rate activated sludge treatment in contact stabilisation mode (HRAS/CS) and column adsorption with zeolite. The HRAS/CS process removes organic matter and suspended solids in wastewater, leaving N behind in the effluent. The N was successfully recovered with the zeolite column under different scenarios, generating N and K-rich by-products. The regeneration effluent from the zeolite column with KCl contained 60–845 mg NH4+-N/L and 1.6–14.3 g K/L, having potential for use as fertigation water. The N-saturated zeolite contained 1.5–8.4 mg N/g and 14.3–19.3 mg K/g of the product fresh weight and low contaminant content, making it potentially eligible as various fertilising products. Adsorption can thus concentrate N from HRAS/CS effluent and produce by-products with potential agricultural value while meeting chemical oxygen demand and total nitrogen discharge standards.

Sorption-enhanced intensified CO2 hydrogenation via reverse water–gas shift reaction: Kinetics and modelling

Intensification of CO2 hydrogenation via the reverse water–gas shift (RWGS) reaction for CO production can be achieved through in situ removal of water when hydrophilic adsorbents are incorporated alongside the catalyst in the reaction bed. In this work, seeking to move a step closer to the industrial implementation of this innovative CO2 valorization process, a comprehensive reactor model, validated by experimental data obtained in a fixed-bed reactor, was developed to simulate the behavior of this sorption-enhanced (SE) RWGS process. Simulation and experimental data matched with good accuracy, demonstrating the striking benefits brought by the adsorbent addition, such as an almost doubling of the CO production rate at 300 °C. The kinetics of RWGS reaction over a Cu-based catalyst and H2O adsorption on a 13X zeolite adsorbent were studied both experimentally and theoretically and the kinetic models were integrated into the reactor model to assess the performance of SE-RWGS process. Fitting of the RWGS reaction rates by a Langmuir-Hinschelwood-Hougen-Watson-type heterogeneous kinetic model suggested that the rate-determining step of the reaction is the surface interaction between an adsorbed CO2 molecule and a H* species on catalytic sites of different nature. Meanwhile, the dynamic behavior of water adsorption was effectively simulated by a semi-empirical double-stretched exponential model combined with the Sips isotherm model. The results of this work could be applied to the design and scale-up of the SE-RWGS process, which offers considerable improvements over the thermodynamically constrained conventional process. The intensified approach represents a promising avenue for the effective conversion of carbon dioxide into CO, as well as into other value-added chemicals as part of a multi-stage CO2 reduction process.