Synthesis of NaA zeolite from foundry dust and its adsorption capacity of ammonia

Synthesis and Application of LTA Zeolite for the Removal of Inorganic and Organic Hazardous Substances from Water: A Review

Industrialization and human activities have caused significant environmental challenges, with water pollution posing severe risks to human health. This underscores the urgent need for effective water treatment solutions. Zeolites, known for their high specific surface area and stability, have gained increasing attention as adsorbents for water treatment. Among zeolites, LTA varieties stand out due to their low Si/Al ratio, which enhances ion-exchange capacity, and their cost-effectiveness. This review focuses on the synthesis of low-silica LTA zeolites, particularly zeolite A, using natural materials and solid wastes without relying on organic-structure-directing agents (OSDAs). Common pretreatment processes for such synthesis are also highlighted. The review further explores the applications of LTA zeolites in water treatment, emphasizing their exceptional performance in adsorbing inorganic and organic pollutants. In particular, LTA zeolites are highly effective at removing inorganic cation pollutants through ion exchange. An updated ion-exchange selectivity order, based on previous studies, is provided to support these findings. Overall, this review aims to guide future research and development in water treatment technologies.

Preparation of NaA zeolite with graphite tailings and its adsorption of ammonia nitrogen

Environmental pollution caused by the accumulation of graphite tailings (GT) is a significant global challenge. In this study, GT was utilized as a raw material to synthesize NaA zeolite (GTA), with synthesis conditions optimized. The synthesized GTA was characterized by SEM, EDS, BET, XRD, and FTIR, and its ammonia nitrogen (AN) adsorption performance was investigated under varying conditions, including dosage, pH, adsorption time, and temperature. The optimized synthesis conditions were an alkali melting temperature of 700 °C, alkali-ore ratio of 1.2:1, aging time of 8 h, hydrothermal temperature of 90 °C, liquid-solid ratio of 6:1, and hydrothermal time of 8 h, yielding a specific surface area of 36.62 m2/g. In a 100 mg/L AN solution at pH 7 and 30 °C, GTA exhibited an adsorption capacity of 13.88 mg/g within 1 h. The adsorption process follows a pseudo-second-order kinetic model. The adsorption isotherm conforms to the Langmuir model, suggesting that the mechanism involves uniform monolayer adsorption on the surface. The adsorption of AN on zeolite is primarily controlled by chemical rather than physical adsorption. This study provides a foundation for the resource utilization of GT and AN treatment, with practical environmental implications.

Efficient removal of ammonia-nitrogen in wastewater by zeolite molecular sieves prepared from coal fly ash

Zeolite molecular sieves are potential adsorbents for wastewater treatment, characterized by high efficiency, simple process, easy regeneration, and low treatment cost. In this study, zeolite A molecular sieves were prepared using coal fly ash (CFA), which is an effective method for the utilization of CFA. The results showed that the CFA-based zeolite molecular sieves synthesized under optimized conditions exhibited excellent adsorption and removal rates (> 40%) for ammonia-nitrogen in wastewater of different concentrations and properties. The analysis of adsorption kinetics revealed that the adsorption process followed pseudo-second-order kinetics model, indicating that the adsorption of ammonia-nitrogen on zeolite is primarily controlled by chemisorption rather than physisorption. The adsorption process can be divided into two stages, with a higher adsorption rate and a smaller diffusion boundary layer thickness in the first stage, and a lower adsorption rate and an increased diffusion boundary layer thickness in the second stage. This indicates that as the adsorption proceeds, the internal diffusion resistance within the particles gradually increases, leading to a decrease in the adsorption rate until reaching equilibrium, where both the diffusion and adsorption become stable. The adsorption isotherms of ammonia-nitrogen on zeolite A conformed to the assumptions of the Langmuir model, suggesting that the adsorption mechanism primarily involves uniform monolayer adsorption on the surface without intermolecular interactions.

Copper supported Dowex50WX8 resin utilized for the elimination of ammonia and its sustainable application for the degradation of dyes in wastewater

To obtain high efficient elimination of ammonia (NH4+) from wastewater, Cu(II), Ni(II), and Co(II)) were loaded on Dowex-50WX8 resin (D-H) and studied their removal efficiency towards NH4+ from aqueous solutions. The adsorption capacity of Cu(II)-loaded on D-H (D-Cu2+) towards NH4+ (qe = 95.58 mg/g) was the highest one compared with that of D-Ni2+ (qe = 57.29 mg/g) and D-Co2+ (qe = 43.43 mg/g). Detailed studies focused on the removal of NH4+ utilizing D-Cu2+ were accomplished under various experimental conditions. The pseudo-second-order kinetic model fitted well the adsorption data of NH4+ on D-Cu2+. The non-linear Langmuir model was the best model for the adsorption process, producing a maximum equilibrium adsorption capacity (qmax = 280.9 mg/g) at pH = 8.4, and 303 K in less than 20 min. The adsorption of NH4+ onto D-Cu2+ was an exothermic and spontaneous process. In a sustainable step, the resulting D-Cu(II)-ammine composite from the NH4+ adsorption process displayed excellent catalytic activity for the degradation of aniline blue (AB) and methyl violet 2B (MV 2B) dyes utilizing H2O2 as an eco-friendly oxidant.

Synthesis of zeolite from industrial wastes: a review on characterization and heavy metal and dye removal

Increasing world population, urbanization, and industrialization have led to an increase in demand in production and consumption, resulting in an increase in industrial solid wastes and pollutant levels in water. These two main consequences have become global problems. The high Si and Al content of solid wastes suggests that they can be used as raw materials for the synthesis of zeolites. In this context, when the literature studies conducted to obtain synthetic zeolites are evaluated, it is seen that hydrothermal synthesis method is generally used. In order to improve the performance of the hydrothermal synthesis method in terms of energy cost, synthesis time, and even product quality, additional methods such as alkaline fusion, ultrasonic effect, and microwave support have been developed. The zeolites synthesized by different techniques exhibit superior properties such as high surface area and well-defined pore sizes, thermal stability, high cation exchange capacity, high regeneration ability, and catalytic activity. Due to these specific properties, zeolites are recognized as one of the most effective methods for the removal of pollutants. The toxic properties of heavy metals and dyes in water and their carcinogenic effects in long-term exposure pose a serious risk to living organisms. Therefore, they should be treated at specified levels before discharge to the environment. In this review study, processes including different methods developed for the production of zeolites from industrial solid wastes were evaluated. Studies using synthetic zeolites for the removal of high levels of health and environmental risks such as heavy metals and dyes are reviewed. In addition, EPMA, SEM, EDX, FTIR, BET, AFM, and 29Si and 27Al NMR techniques, which are characterization methods of synthetic zeolites, are presented and the cation exchange capacity, thermodynamics of adsorption, effect of temperature, and pH are investigated. It is expected that energy consumption can be reduced by large-scale applications of alternative techniques developed for zeolite synthesis and their introduction into the industry. It is envisaged that zeolites synthesized by utilizing wastes will be effective in obtaining a green technology. The use of synthesized zeolites in a wide variety of applications, especially in environmental problems, holds great promise.

Synthesis of high-crystallinity Zeolite A from rare earth tailings: Investigating adsorption performance on typical pollutants in rare earth mines

The ecological restoration of rare earth mines and the management of rare earth tailings have consistently posed global challenges, constraining the development of the rare earth industry. In this study, Zeolite A is efficiently prepared from the tailings of an ion-type rare earth mine in the southern Jiangxi Province of China. The resulting Zeolite A boasts exceptional qualities, including high crystallinity, a substantial specific surface area, and robust thermal stability. The optimum conditions for Zeolite synthesis are experimental determination and the adsorption properties of Zeolite A for typical pollutants (Cd2+, Cu2+, NH4+, PO43- and F-) in rare earth mines. The synthesised Zeolite A material is found to have strong adsorption properties. The adsorption mechanism is mainly cation exchange, and the priority of adsorption of pollutants is Cu2+> Cd2+ > NH4+ > PO43- > F-. Notably, the sodium Zeolite A material synthesized at room temperature can be effectively recycled multiple times. In summary, we propose a method to synthesise low cost and high adsorption zeolites using rare earth tailings. This will facilitate the reduction of rare earth tailings and the rehabilitation of rare earth mines. Our method has great potential as a rehabilitation technology for rare earth mines.

Zeolite Composite Materials from Fly Ash: An Assessment of Physicochemical and Adsorption Properties

Waste fly ash, with both low (with the addition of vermiculite) and high contents of unburned coal, were subjected to hydrothermal syntheses aiming to obtain zeolite composite materials-zeolite + vermiculite (NaX-Ver) and zeolite + unburned carbon (NaX-C). The composites were compared with parent zeolite obtained from waste fly ash with a low content of unburned carbon (NaX-FA). In this study, the physicochemical characteristics of the obtained materials were evaluated. The potential application of the investigated zeolites for the adsorption of ammonium ions from aqueous solutions was determined. Composite NaX-Ver and parent zeolite NaX-FA were characterized by comparable adsorption capacities toward ammonium ions of 38.46 and 40.00 mg (NH₄⁺) g^-1, respectively. The nearly 2-fold lower adsorption capacity of composite NaX-C (21.05 mg (NH₄⁺) g^-1) was probably a result of the lower availability of ion exchange sites within the material. Adsorbents were also regenerated using 1 M NaCl solution at a pH of 10 and subjected to 3 cycles of adsorption-desorption experiments, which proved only a small reduction in adsorption properties. This study follows the current trend of waste utilization (fly ash) and the removal of pollutants from aqueous solutions with respect to their reuse, which remains in line with the goals of the circular economy.