Search Results (55)

Implementing efficient strategies for the circular recovery and reuse of nutrients from wastewaters is mandatory to meet the Green Deal objectives and Sustainable Development Goals. In this context we investigated the use of zeolitic tuff (containing chabazite and phillipsite) in the selective recovery and reuse of N from various anaerobic liquid digestates in view of their implementation in farm-scale treatment plants. We tested the method on three livestock digestates and two municipal organic solid waste digestates. Adsorption isotherms and kinetics were assessed on each digestate, and a large set of parameters, including (i) contact time, (ii) initial NH₄⁺ concentration, (iii) presence of competing ions, (iv) total solids content, and (vi) separation methods (microfiltration and clarification), were considered in the experimental design. Our results showed that the adsorption mechanism can be explained by the Freundlich model (R² up to 0.97), indicating a multilayer and heterogeneous adsorption, while the kinetic of adsorption can be explained by the pseudo-second-order model, indicating chemical adsorption and ion exchange. The efficiency in the removal of NH₄⁺ was indirectly related to the K⁺ and total solids content of the digestate. Maximum NH₄⁺ removal exceeded 90% in MSW-derived digestates and 80% within 60 min in livestock-derived digestates at a 5% solid/liquid ratio. Thermodynamic parameters confirmed favorable and spontaneous adsorption (ΔG up to −7 kJ⋅mol⁻¹). Farm-scale projections estimate a nitrogen recovery potential of 1.2 to 16 kg N⋅day⁻¹, depending on digestate type and process conditions. These findings support the application of natural zeolitic tuffs as a low-cost, chemical-free solution for ammonium recovery, contributing to sustainable agriculture and circular economy objectives. Full article

Chabazite, a tectosilicate mineral, belongs to the zeolite group and has been widely used for the adsorptive removal of a number of cationic contaminants from the aqueous phase. However, a negatively charged chabazite surface can be altered by chemical modification in order to change its adsorption abilities towards anions. This study reports the potential for the removal of hexavalent chromium ions from aqueous solutions by modified chabazite. In this regard, natural chabazite was modified by the immobilization of HDTMA-Br to achieve double-layer coverage on its surface, defined as the double external cation exchange capacity. Next, a batch adsorption system was applied to study the adsorption of inorganic Cr(VI) anions from aqueous solutions. The process equilibrium was described by 11 theoretical isotherm equations, while 6 adsorption kinetics were represented by four models. Among those tested, the most appropriate model for the description of the studied process kinetics was the pseudo-second order irreversible model. The obtained results suggest that Cr(VI) adsorption takes place according to a complex mechanism comprising both Langmuir-type sorption with the maximum adsorption capacity of modified chabazite, approx. 9.3–9.9 mg g⁻¹, and the trapping of Cr(VI) inside the capillaries of the amorphous sorbent, making it a viable option for water treatment applications. Full article

We report the occurrence of natural calcium silicate hydrates (C-S-H) from the Grolla quarry in the Lessini Mountains of Northern Italy. These minerals are formed by basic and ultrabasic magma interacting with carbonate rocks. The mineral assemblage includes thaumasite, xonotlite, tobermorite, and plombierite, often intergrown with other silicates, as well as minor amounts of carbonates and sulfates. Common zeolites in this area include chabazite, phillipsite/harmotome, natrolite, and thomsonite. Although less abundant, these zeolites are typically associated with calcite, fluoroapophyllite, and barite. The Grolla quarry outcrop allows for the study of the in situ complex crystalline overgrowths and specific crystal chemistry of rare natural mineral phases, such as C-S-H minerals, formed under metasomatic to hydrothermal conditions. Full article

In aquatic environments, the presence of iodine species, including radioactive isotopes like ¹²⁹I and I₂, poses significant environmental and health concerns. Iodine can enter water resources from various sources, including nuclear accidents, medical procedures, and natural occurrences. To address this issue, the use of natural occurring nanoporous minerals, such as zeolitic materials, for iodine removal will be explored. This study focuses on the adsorption of iodine by silver-modified zeolites (13X-Ag, 5A-Ag, Chabazite-Ag, and Clinoptilolite-Ag) and evaluates their performance under different conditions. All materials were characterized using scanning electron microscopey (SEM), energy-dispersive X-ray spectroscopy (EDS), powdered X-ray diffraction (P-XRD), Fourier-transform infrared spectrometry (FTIR), and nitrogen adsorption studies. The results indicate that Chabazite-Ag exhibited the highest iodine adsorption capacity, with an impressive 769 mg/g, making it a viable option for iodine removal applications. 13X-Ag and 5A-Ag also demonstrated substantial adsorption capacities of 714 mg/g and 556 mg/g, respectively, though their behavior varied according to different models. In contrast, Clinoptilolite-Ag exhibited strong pH-dependent behavior, rendering it less suitable for neutral to slightly acidic conditions. Furthermore, this study explored the impact of ionic strength on iodine adsorption, revealing that Chabazite-Ag is efficient in low-salinity environments with an iodine adsorption capacity of 51.80 mg/g but less effective in saline conditions. 5A-Ag proved to be a versatile option for various water treatments, maintaining its iodine adsorption capacity across different salinity levels. In contrast, Clinoptilolite-Ag exhibited high sensitivity to ionic competition, virtually losing its iodine adsorption ability at a NaCl concentration of 0.1 M. Kinetic studies indicated that the pseudo-second-order model best describes the adsorption process, suggesting chemisorption mechanisms dominate iodine removal. Chabazite-Ag exhibited the highest initial adsorption rate with a k₂ value of 0.002 mg g⁻¹ h⁻¹, emphasizing its superior adsorption capabilities. Chabazite and Clinoptilolite, naturally occurring minerals, provide eco-friendly solutions for iodine adsorption. Chabazite superior iodine removal highlights its value in critical applications and its potential for addressing pressing environmental challenges. Full article

The study presents experimental results on the adsorption of endosulfan in new natural zeolite deposits from Mexico. The adsorption of this herbicide was evaluated using inverse gas chromatography with a thermal conductivity detector and helium as the carrier gas. The experimental adsorption data were analyzed using the Langmuir and Freundlich equations in their linear form over a temperature range of 413–573 K. The study also estimated thermodynamic parameters such as the Free Energy of Gibbs (ΔG), isosteric enthalpy of adsorption (ΔH), and entropy change (ΔS) within this temperature range. The results indicated that the zeolites studied had a low adsorption capacity for this herbicide under the experimental conditions. The study also quantitatively determined the presence of starting minerals, with Na-Mordenite and Na-Clinoptilolite being the most prevalent, followed by Ca-Chabazite, Ca-Clinoptilolite, and Montmorillonite, with Quartz being present in low amounts. The NMOR zeolite underwent ion exchanges with AgNO₃ to produce the Ag-MOR zeolite and assess its herbicide adsorption capacity. Another mineral, Ca-Stilbite, was present in higher quantities than Ca-Clinoptilolite and Quartz. Full article

A serious risk that harms the safe use of water and affects aquatic ecosystems is water pollution. This occurs when the water’s natural equilibrium is disrupted by an excessive amount of substances, both naturally occurring and as a byproduct of human activities, that have varied degrees of toxicity. Radiation from Cs isotopes, which are common components of radioactive waste and are known for their long half-lives (30 years), which are longer than the natural decay processes, is a major source of contamination. Adsorption is a commonly used technique for reducing this kind of contamination, and zeolite chabazite has been chosen as the best adsorbent for cesium in this particular situation. The purpose of this research is to investigate a composite material based on magnesium phosphate cement (MPC). Magnesium oxide (MgO), potassium dihydrogen phosphate (KH₂PO₄), and properly selected retarders are used to create the MPC. The optimal conditions for this composite material are investigated through the utilization of X-ray diffraction, scanning electron microscopy, BET surface area analysis, and atomic absorption spectroscopy. The principal aim is to enable innovations in the elimination of radioactive waste-contaminated water using effective cesium removal. The most promising results were obtained by using KH₂PO₄ as an acid, and MgO as a base, and aiming for an M/P ratio of two or four. Furthermore, we chose zeolite chabazite as a crucial component. The best adsorption abilities for Cs were found at Q_ads = 106.997 mg/g for S₂ and Q_ads = 122.108 mg/g for S₁. As a result, zeolite is an eco-friendly material that is a potential usage option, with many benefits, such as low prices, stability, and ease of regeneration and use. Full article

The ethanol dehydration process is studied regarding protonic and Ag-loaded chabazite zeolite in advanced FT-IR and UV-vis operando spectroscopic studies with simultaneous mass spectroscopy and gas chromatography analyses of products. The spectroscopic investigation provides information on the species formed on the surface of catalysts, while mass spectrometry and gas chromatography methods identify the desorbed products. These studies are also supported by spectroscopic, chromatographic, and thermogravimetric analyses of coke species formed over the catalyst’s surface during ethanol conversion. The Ag-chabazite catalyst shows higher selectivity for ethylene and propylene; the slower formation of coke species; and, thus, a longer lifetime. Full article

The olive fruit fly (Bactrocera oleae Rossi) is the most dangerous pest of olive fruits and negatively influences the chemical and sensory quality of the oil produced. Organic farms have few tools against this pest and are constantly looking for effective and sustainable products such as geomaterials, i.e., zeolite. Since a particle film covers the canopy, a study was carried out on the olive tree’s responses to zeolite foliar coating. The tested treatments were natural zeolite (NZ), zeolite enriched with ammonium (EZ), and Spintor-Fly^® (SF). EZ was associated with higher photosynthetic activity with respect to the other treatments, while no differences were found between SF and NZ. Foliar treatments affect the amount of BVOC produced in both leaves and olives, where 26 and 23 different BVOCs (biogenic volatile organic compounds) were identified but not the type of compounds emitted. Foliar treatment with EZ significantly affected fruit size, and the olive fruit fly more frequently attacked the olives, while treatment with NZ had olives with similar size and attack as those treated with Spintor-Fly^®; no difference in oil quantity was detected. Oil produced from olives treated with NZ presented higher values of phenolic content and intensities of bitterness and spiciness than oils from those treated with EZ and SF. According to the results of this study, using zeolite films on an olive tree canopy does not negatively influence plant physiology; it has an impact on BVOC emission and the chemical and sensory characteristics of the oil. Full article

A study was conducted to assess the efficacy of chabazite zeolite in mitigating ammonia levels in wastewater from a land-based marine fish farm in southern Tuscany (Italy). The fish farm discharges effluent into a lagoon, constituting an important eutrophication source. The experimental setup involved a pond/canal that received wastewater from three sea bream tanks (40 L/s). A 50 m canal section was divided into two parallel halves (T and B), each about 3 m wide. In T, a chabazite bed (granules about 3 cm ϕ) was placed that was about 6 cm thick; B was untreated and used as a control. Five sampling trials were conducted in both T and B to determine N-NH₄, N-NO₃, and P-PO₄ levels, in surface and near-bottom waters at both input and output. Prior to the zeolite addition, T and B sediments were sampled for TN and TP determination. Results indicated the not-managed canal system released nutrients and the output values were higher than the input, overshadowing the zeolite effects. Significant zeolite effects were observed by comparing B and T for differences between input and output: in T, nitrate increased (p = 0.05), demonstrating a resumption of nitrification, and ammonium (p = 0.07) and SRP (p = 0.06) decreased, in contrast to B. Full article

Volcanic tuffs rich in chabazite zeolites have been extensively examined for their potential to enhance soil properties and increase fertilizer efficiency, both in their natural state and when enriched with nitrogen (N). However, there is a scarcity of data regarding their utilization in acidic sandy soil, particularly when used alongside organic fertilizers. This paper presents the findings of a 50-day laboratory incubation study that investigated the dynamics of N pools in an acidic sandy-loam agricultural soil treated with various N sources. These sources included urea, N-enriched chabazite zeolite tuff, and pelleted composted manure applied at a rate of 170 kg N/ha. Additionally, the N sources were tested in combination with chabazite zeolite tuff mixed into the soil to assess its role as a soil conditioner. The results revealed distinct behaviours among the tested N sources, primarily impacting soil pH and N dynamics. Soil fertilized with manure exhibited slow N mineralization, whereas N-enriched zeolite displayed a more balanced behaviour concerning net NO₃⁻-N production and NH₄⁺-N consumption. Both N-enriched zeolite and urea temporarily altered the soil pH, resembling a “liming” effect, while pelleted manure facilitated a prolonged shift towards neutral pH values. Considering the water adsorption capacity of zeolite minerals, caution is advised when adjusting water content and employing combustion methods to measure soil organic matter in zeolite-treated soil to avoid potential inaccuracies. In summary, N-enriched chabazite zeolite tuff emerged as a valuable N source in acidic sandy-loam soil, offering a promising alternative to synthetic fertilizers and showcasing a sustainable means of N recycling. Full article

The treatment of chabazite (CHA), a natural zeolite, with the alkaline hydrothermal method to improve its ion-exchange capacity is a widely adopted route by environmental scientists for the purpose of better ammonium (${\mathrm{N}\mathrm{H}}_4^{+}$) removal from wastewater. This work addresses a noteworthy trend in environmental science, where researchers, impressed by the increased ion-exchange capacity achieved through alkaline hydrothermal treatment, often bypass the thorough material characterization of treated CHA. The prevalent misconception attributes the improved features solely to the parent zeolitic framework, neglecting the fact that corrosive treatments like this can induce significant alterations in the framework and those must be identified with correct nomenclature. In this work, alkaline-mediated hydrothermally treated CHA has been characterized through X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), solid-state magic-angle spinning nuclear magnetic resonance (MAS-NMR), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDS) and it is concluded that the treated samples have been transformed into a desilicated, aluminum (Al)-dense framework of analcime (ANA) with a low silica–alumina ratio and with a strikingly different crystal shape than that of parent CHA. This treated sample is further examined for its ${\mathrm{N}\mathrm{H}}_4^{+}$ removal capacity from synthetic wastewater in a fixed-bed column arrangement. It achieved a maximum ${\mathrm{N}\mathrm{H}}_4^{+}$ removal efficiency of 4.19 meq/g (75.6 mg/g of ${\mathrm{N}\mathrm{H}}_4^{+}$), twice that of the parent CHA. Moreover, the regeneration of the exhausted column yielded a regenerant solution, with 94% reclaimed ${\mathrm{N}\mathrm{H}}_4^{+}$ in it, which could be used independently as a nitrogenous fertilizer. In this work, the meticulous compositional study of zeolitic materials, a well-established practice in the field of material science, is advocated for adoption by environmental chemists. By embracing this approach, environmental scientists can enhance their comprehension of the intricate changes induced by corrosive treatments, thereby contributing to a more nuanced understanding of zeolitic behavior in environmental contexts. Full article

Cu-CHA zeolites have proven to be effective for NO_x reduction, but a drawback in using CHA zeolites is the cost associated with using expensive organic structure-directing agents. To overcome this drawback, we are reporting here the synthesis of Cu-CHA zeolite catalysts in both their NH₄-form as well as K-form that do not require the use of organic structure-directing agents. After comprehensive characterization by XRF, XRD, ²⁷Al NMR spectroscopy, FE-SEM, SEM/EDS, N₂-adsorption/desorption, NH₃-TPD, H₂-TPR, and XPS, the zeolite catalysts were tested for NO_x conversion by NH₃-selective catalytic reduction (NH₃-SCR). Cu-NH₄-CHA zeolite catalysts exhibited remarkable activity and thermal stability over a wide temperature window, outperforming their counterpart K-forms. Among the NH₄-forms of CHA zeolite catalysts, the 0.1 M Cu-NH₄-CHA showed the best catalytic performance, achieving 50% NO_x conversion at a temperature as low as 192 °C, and reaching full conversion of NO_x at 261 °C. These Cu-based CHA zeolite catalysts are promising thanks to their environmentally friendly synthesis and offer the opportunity of maximizing DeNO_x strategies in applications for NO_x pollution abatement. Full article

The operation of nuclear power plants generates a large amount of low- and intermediate-level radioactive waste liquid. Zeolite-rich geopolymers, which are synthesized under hydrothermal conditions from industrial waste fly ash, can effectively immobilize radioactive nuclides. In this study, the synthesis law of zeolite-rich geopolymers and the adsorption/desorption performances of radioactive nuclide Cs⁺ were researched using XRD, SEM and ICP. The results show that the increase in curing temperatures and NaOH concentrations leads to the transformation of Y-type zeolite to chabazite and cancrinite at low NaNO₃ concentrations. However, at high NaNO₃ concentrations, NaOH above 2 M has no obvious effect on the phase transformation of the main zeolite of chabazite and cancrinite. In the adsorption and desorption experiment of Cs⁺ on the chabazite/garronite-rich geopolymer, it was found that the adsorption of Cs⁺ in the low initial concentration range is more suitable for the Freundlich equation, while the Langmuir equation fits in the adsorption process at the high initial concentration range. Moreover, the desorption kinetics of Cs⁺ are in good agreement with the pseudo-second-order rate equation. Thus, the adsorption of Cs⁺ on chabazite/garronite-rich geopolymers is controlled by both physical and chemical reactions, while desorption is a chemical process. Full article

The gas-to-liquid (GTL) process is a catalytic technology for achieving carbon neutrality during fuel production. Fischer–Tropsch synthesis (FTS), a core step in this process, converts synthesis gas (CO + H₂) to high-value hydrocarbon products. This study synthesized a chabazite-shaped zeolite and a Co/γ-alumina catalyst by using conventional hydrothermal and wet impregnation methods, respectively. Hybrid FTS catalysts were then prepared by mixing the Co/γ-alumina catalyst with supports, including the synthesized and commercial zeolites alone and mixed at various ratios. The effects of these zeolites on the FTS conversion and selectivity were investigated. Additionally, the physicochemical properties of the supports and prepared catalysts were analyzed. The bifunctional hybrid catalyst performance was evaluated in a fixed-bed reactor, and the FTS products were analyzed using online and offline gas chromatography. The hybrid catalysts produced lighter hydrocarbons than the Co/γ-alumina catalyst alone. Meanwhile, heavy hydrocarbons produced over the Co/γ-alumina catalyst were hydrocracked at the acid sites of the silicoaluminophosphate zeolite (SAPO-34) to yield lighter, fuel-range hydrocarbons. Cobalt-based hybrid FTS catalysts were also investigated to determine the optimum support ratio for high carbon conversion and C₅₊ selectivity. The hybrid catalyst supported on SAPO-34:ZSM-5 (2:8) exhibited the highest CO conversion and favorable C₅₊ selectivity. Full article

DeNO_x activity in a NSR–SCR hybrid system of two copper-containing chabazite-type zeolitic catalysts was addressed. A Pt-Ba-K/Al₂O₃ model catalyst was used as the NSR (NO_x storage and reduction) catalyst. For the SCR (selective catalytic reduction) system, two Cu-CHA zeolites were synthesized employing a single hydrothermal synthesis method assisted with ultrasound and incorporating Cu in a 2 wt.%, 2Cu-SAPO-34 and 2Cu-SSZ-13. The prepared catalysts were characterized, and the crystallinity, surface area, pore size, HR-TEM and EDX mapping, coordination of Cu ions and acidity were compared. The NH₃ storage capacity of the SCR catalysts was 1890 and 837 ${\mathsf{\mu }\mathrm{mol} \mathrm{NH}}_3{·\mathrm{g}}_{\mathrm{cat}}^{-1}$ for 2Cu-SAPO-34 and 2Cu-SSZ-13, respectively. DeNO_x activity was evaluated for the single NSR system and the double-bed NSR–SCR by employing alternating lean (3%O₂) and rich (1%H₂) cycles, maintaining a concentration of 600 ppm NO, 1.5% H₂O and 0.3% CO₂ between 200 and 350 °C. The addition of the SCR system downstream of the NSR catalyst significantly improved NO_x conversion mainly at low temperature, maintaining the selectivity to N₂ above 80% and reaching values above 90% at 250 °C when the 2Cu-SSZ-13 catalyst was located. The total reduction in the production of NH₃ and ~2% of N₂O was observed when comparing the NSR–SCR configuration with the single NSR catalyst. Full article