Conventional hydrothermal synthesis of Na-A zeolite from cupola slag and aluminum sludge

Aluminosilicate and zeolitic materials synthesis using alum sludge from water treatment plants: Challenges and perspectives

Alum sludge (AS) is a by-product generated from drinking water treatment and produced in large amounts around the world. Its chemical composition makes this waste an emerging alternative source of silicon and aluminum for aluminosilicates or zeolite material production, which can add value to residues and contribute to the circular economy process on a global scale. In this sense, and considering the scarcity of information about AS, this review shows data collection about AS in different countries, including generation, chemical composition, and disposal information. The reuse of AS is discussed based on circular economy and the environmental gains derived from such approaches are highlighted, including the possibility of utilization with other residues (e.g., ash, bioproducts, etc). Moreover, this review shows and discusses the benefits and challenges of AS reuse in the synthesis process and how it can be a sustainable raw material for aluminosilicates and zeolite synthesis. The most common conditions (conventional or non-conventional) in zeolite synthesis from AS are mentioned and advantages, limitations and trends are discussed. The discussions and data presented can improve the AS management and reuse legislations, which certainly will collaborate with sustainable AS use and circular economy processes.

Waste Symbiosis through the Synthesis of Highly Crystalline LTA and SOD Zeolites

In recent years, the demand for natural and synthetic zeolites has surged due to their distinctive properties and myriad industrial applications. This research aims to synthesise crystalline zeolites by co-recycling two industrial wastes: salt slag (SS) and rice husk ash (RHA). Salt slag, a problematic by-product of secondary aluminium smelting, is classified as hazardous waste due to its reactive and leachable nature, though it is rich in aluminium. Conversely, RHA, an abundant and cost-effective by-product of the agro-food sector, boasts a high silicon content. These wastes were utilised as aluminium and silicon sources for synthesising various zeolites. This study examined the effects of temperature, ageing time, and sodium concentration on the formation of different zeolite phases and their crystallinity. Results indicated that increased Na+ concentration favoured sodalite (SOD) zeolite formation, whereas Linde type-A (LTA) zeolite formation was promoted at higher temperatures and extended ageing times. The formation range of the different zeolites was defined and supported by crystallographic, microstructural, and morphological analyses. Additionally, the thermal behaviour of the zeolites was investigated. This work underscores the potential to transform industrial waste, including hazardous materials like salt slag, into sustainable, high-value materials, fostering efficient waste co-recycling and promoting clean, sustainable industrial production through cross-sectoral industrial symbiosis.

The Removal of Strontium Ions from an Aqueous Solution Using Na-A Zeolites Synthesized from Kaolin

Sr2+ ions in an aqueous solution were removed using Na-A zeolites synthesized from kaolin, a natural mineral. Na-A zeolites with high crystallinity were synthesized using NaOH/kaolin mass ratios of 0.6 (ZK06) and 0.9 (ZK09). The adsorption reached equilibrium within 120 min. The adsorption data obtained from experiments for Sr2+ using ZK06 and ZK09 were appropriately analyzed with pseudo-second-order kinetic and Langmuir isotherm models. Comparing the maximum adsorption capacities (qm) of ZK06 and ZK09 for Sr2+, the highest values were obtained at 1.90 and 2.42 mmol/g, respectively. Consequently, the Na-A zeolites synthesized from kaolin can be evaluated as adsorbents with high adsorption capacities for the removal of Sr2+, proportional to the degree of their crystallinity.

Optimization of preparation of NaA zeolite from fly ash for CO2 capture

The green synthesis method of fly ash-based NaA zeolite was explored to reduce the synthesis cost and environmental hazards. For the prepared NaA samples, the effects of crystallization time, solid-liquid ratio, and Si/Al ratio were systematically studied. CO2 adsorption isotherm is used for adsorption model fitting analysis and adsorption selectivity determination. According to the experimental results, the optimized NaA zeolite synthesis conditions are as follows: the Si/Al ratio of NaA zeolite is 1.4, the solid-liquid ratio is 10, and the crystallization time is 6 h. The green synthesis method reported in this study can successfully prepare NaA zeolite and exhibit excellent CO2 adsorption performance, reaching 4.34 mmol/g, with high CO2 selective adsorption ability, reaching 89.2 for N2, 257.1 for O2, and 45.8 for CH4. The adsorbed CO2 can be released for further utilization, and NaA zeolite also has strong adsorption and regeneration performance, with a ten cycle adsorption capacity only decreasing by 1.17%. In addition, the use of cheap raw materials synthesis methods will promote the large-scale industry application of green synthesis technology in the future.

Synthesis of high-quality NaP1 zeolite from municipal solid waste incineration fly ash by microwave-assisted hydrothermal method and its adsorption capacity

The Si and Al in municipal solid waste incineration fly ash (MSWI FA) can be utilized for zeolite fabrication, which can improve the application value of the products. This study focuses on the fabrication of zeolite from MSWI FA by microwave-assisted hydrothermal (MH) treatment. The effects of magnetic stirring time, Na₂SiO₃ dosage, MH time, and NaOH solution concentration on the crystallization of zeolite NaP1 from MSWI FA are systematically analyzed. The synthetic products are analyzed through spectroscopic and mineralogical methods. The results show that zeolite NaP1 with high crystallinity (51.68 %) can be fabricated by magnetic stirring and MH treatment, and the cation exchange capacity (CEC) of the product can reach a value of 2.58 meq/g, which is approximately 133 times that of the CEC of MSWI FA. The Si/Al ratio plays a decisive role in the zeolite NaP1 synthesis, and a Na₂SiO₃ dosage of 30 wt% is adopted for zeolite NaP1 fabrication. A NaOH concentration of 1 M is sufficient for zeolite NaP1 synthesis. Additionally, the zeolite NaP1 content is found to obviously increase with increasing MH time from 0.5 h to 2 h. To demonstrate the feasibility of the method provided in this study, the optimal experimental condition is employed for various MSWI FAs, and zeolite NaP1 and analcime are fabricated successfully. The leachability of heavy metals for the synthetic products was evaluated, which met the requirements for pollution control. The BET surface area and total pore volume of zeolite NaP1 fabricated at optimal condition are 61.42 m²/g and 0.44 cm³/g, respectively. The adsorption capacity of zeolite NaP1 for Cu²⁺ ion and methylene blue are determined to be 84.65 mg/g and 84.55 mg/g, respectively, indicating zeolite NaP1 is a potential adsorbent for cation ion and dyes. This study provides an environmentally friendly scheme for the utilization of MSWI FA.

Management of solid waste after used motor oil recovery via production of zeolite A

The attempt of the current study is to find an eco-friendly method for managing the solid waste deposited in the landfill of used motor oil recovery factories through the fabrication of zeolite-based compounds. This toxic waste is originated from the application of natural bentonite, traditionally used as an effective adsorbent in the recovery process. The black waste was converted to zeolite structures through the fusion technique. Firstly, the collected powder was mixed with sodium hydroxide, and boehmite followed by the thermal treatment at different temperatures, 600-800 °C. Then, the obtained precursors were hydrothermally converted to zeolite A or hydroxysodalite. The effects of processing factors like alkalinity, boehmite, and sodium aluminate ratios (respect to solid waste mass), fusion temperature, and aging time on the structural characteristics, and cation exchange capacity (CEC) were studied in detail. In order to achieve a cation exchange capacity of about 190 mg g^-1, the alkali and boehmite ratios should be adjusted at 2.00 and 0.53, respectively. Based on the morphological observations, the fusion at 800 °C caused the formation of cubic particles with sharp edges. Besides, the hydrosodalite powder with the extended surface area, 77 m² g^-1, could be produced by fixing the boehmite, and sodium aluminate ratios at the levels of 0.13 and 0.40, respectively.

Cost Profile of Membranes That Use Polymers of Intrinsic Microporosity (PIMs)

Assessing the financial impact of polymers of intrinsic microporosity, otherwise known as PIMs, at the lab scale has been impeded by the absence of a holistic approach that would envelop all related financial parameters, and most importantly any indirect costs, such as laboratory accidents that have been consistently neglected and undervalued in past assessments. To quantify the cost of PIMs in relation to the risks befalling a laboratory, an innovative cost evaluation approach was designed. This approach consists of three stages. Firstly, a two-fold “window of opportunity” (WO) theory is suggested, dividing the total cost profile into two segments, followed up by a qualitative risk analysis to establish the potential cost components. The last stage builds on a total cost of ownership model, incorporating the two types of WO. The total cost of ownership (TCO) approach was selected to ascertain the costs and construct the cost profile of PIMs, according to laboratory experimental data. This model was applied to the synthesis and physicochemical characterization processes. The quantitative analysis revealed that the most influential parameters for synthesis are accidents and energy costs. This is in contrast with the physicochemical characterization process, where the most important determinant is the energy cost.

Hydrothermal Synthesis and Characterization of Zeolite A from Corn (Zea Mays) Stover Ash

This study deals with the impact of calcination, alkalinity, and curing time parameters on the hydrothermal synthesis of zeolite A. The zeolite A sample, produced from corncob-stalk-and-leaves (corn stover) ash was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that calcination, alkalinity, and curing time have significant effects on the crystallization and the morphology of zeolite A. In addition, these parameters also impacted the cation exchange capacity. Furthermore, the synthesized zeolite A was obtained using a calcination temperature of 500 °C within two hours of airflow, which is much lower than the temperatures previously reported in the literature for an agricultural waste and other waste materials. A fusion ratio of corn stover ash:NaOH of 1.0:1.5 and a curing time of nine hours were achieved. This is a major result as this curing time is much lower than those featured in other studies, which can reach up to twenty-four hours. In this paper, cubic crystal with rounded edge of zeolite A, having a cation exchange capacity of 2.439 meq Na⁺/g of synthesized anhydrous zeolite A, was obtained, which can be a good candidate for ion-exchange separation.

Optimisation of zeolite LTA synthesis from alum sludge and the influence of the sludge source

Generation of alum sludge (AS) at drinking water treatment plants represents an environmental liability and adds to the cost of water purification. Consequently, this study explored the feasibility of using low and high carbon containing alum sludge from two water treatment plants to synthesize zeolite LTA. The hypothesis was that zeolite LTA synthesis was dependant upon alum sludge source and that a range of strategies may be required to optimize zeolite crystallinity. Zeolite characteristics such as morphology, phase composition, crystallinity, and particle size distribution were recorded. "One pot" hydrothermal synthesis of precursor gel with molar composition 4.2Na₂O:Al₂O₃:1.2SiO₂:168H₂O at 80°C for 3 hr resulted in 25 and 46 wt.% zeolite LTA from high and low carbonaceous sludge, respectively. Prior to hydrothermal reaction stage it was discovered that ageing of the gel, addition of zeolite LTA seeds, ultrasonic treatment and calcination all promoted zeolite LTA formation. Calcination of the alum sludge at 700°C for 2 hr before hydrothermal synthesis resulted in particle size reduction and the highest amount of crystalline zeolite LTA: 79 wt.% from low carbon sludge and 65 wt.% from high carbon sludge. Notably, the zeolite crystallinity reported in this study was the higher than previous studies on this topic. The outlined approach may allow value adding of alum waste and produce a commodity which could be used locally by the water treatment plant as a water softener.

Comprehensive Understanding of the Eco-Friendly Synthesis of Zeolites: Needs of 21st Century Sustainable Chemical Industries

Zeolites have taken a leading position in petrochemical, fine, and bulk chemical industries due to their porous architecture, pore sizes, tunable acidity, and thermal stability. Various strategies of zeolites preparation, including template-free, solvent-free, and toxic mineral-free strategies are summarized. Moreover, the zeolite synthesis using naturally occurring minerals and sustainable natural templates is also discussed, which involves the synthesis of nanocrystalline zeolites of different framework structures using plant-based natural templates and biomass-derived renewable chemicals. Overall this personal account provides the fundamentals of various sustainable synthetic strategies reported in the literature for the synthesis of zeolites with suitable examples that will be useful for the students and will motivate experienced researchers to develop various novel sustainable methods for the synthesis of zeolites and other inorganic materials of industrial relevance.

Investigation of reducing particulate matter (PM) and heavy metals pollutions by adding a novel additive from metallurgical dust (MD) during coal combustion

In this study, a novel additive from metallurgical dust(MD)was applied to reduce particulate matter (PM) emissions and heavy metals pollutions during coal combustion. PM samples were collected and divided into 13 stages from 0.03 μm to 10 μm. Results showed that the irregular morphology of fine particles with equal to/less than 2.5 μm (PM_2.5), fine particles with equal to/less than 4 μm (PM₄) and fine particles with equal to/less than10 μm (PM₁₀) gradually became dense with increasing of MD content. The PM₁₀ concentration with 10% MD dosage was about 3 times higher than that of raw coal. Zn, Ti, Cu and Cr were the most abundant elements in all particulate matters (PMs), meanwhile, heavy metals accumulated into large particles with increasing MD content. The mechanism of reducing PM emissions indicated that MD reacted with nucleation elements (Pb, Cd, etc.) and trapped a large amount of alkali metal (Na/K), which aggregated into large particles. The study highlights the potential of adding MD into coal to prevent the attachment of heavy metals onto ultrafine particles, thereby reducing the heavy metals emissions.

Effects of ultrasonic treatment on zeolite NaA synthesized from by-product silica

The synthesis of zeolite NaA from silica by-product was carried out in the presence of 20 kHz ultrasound at room temperature. Zeolites obtained in this type of synthesis were compared to zeolites obtained by performing conventional static syntheses under similar conditions. The sonication effects on zeolite NaA synthesis were characterized by phase identification, crystallinity etc. The effects of different parameters such as crystallization time and initial materials preparation methods on the crystallinity and morphology of the synthesized zeolites were investigated. The final products were characterized by XRD and FT-IR. It was possible to obtain crystalline zeolite NaA from by-product silica in the presence of ultrasound.

Zeolites in Wastewater Treatment

The world consumption of natural zeolites is approximately 6.0 Mt annually and is increasing at a fast rate. Natural zeolites are crystalline hydrated aluminosilicates with a framework structure containing pores. The porous zeolite is host to water molecules as well as a variety of positively charged ions. One important property of zeolites is the ability to exchange cations. Owing to their high cation-exchange ability as well as to their molecular sieve properties, natural zeolites have been widely used as adsorbents in separation and purification processes in recent decades. In this chapter we review the recent developments of natural zeolites as adsorbents in wastewater treatment, specifically for the removal of ammonia from wastewater.