Studies on the Potential of Nonmodified and Metal Oxide-Modified Coal Fly Ash Zeolites For Adsorption of Heavy Metals and Catalytic Degradation of Organics for Waste Water Recovery

The potential of zeolite nanocomposites in removing microplastics, ammonia, and trace metals from wastewater and their role in phytoremediation

Nanocomposites are emerging as a new generation of materials that can be used to combat water pollution. Zeolite-based nanocomposites consisting of combinations of metals, metal oxides, carbon materials, and polymers are particularly effective for separating and adsorbing multiple contaminants from water. This review presents the potential of zeolite-based nanocomposites for eliminating a range of toxic organic and inorganic substances, dyes, heavy metals, microplastics, and ammonia from water. The review emphasizes that nanocomposites offer enhanced mechanical, catalytic, adsorptive, and porosity properties necessary for sustainable water purification techniques compared to individual composite materials. The adsorption potential of several zeolite-metal/metal oxide/polymer-based composites for heavy metals, anionic/cationic dyes, microplastics, ammonia, and other organic contaminants ranges between approximately 81 and over 99%. However, zeolite substrates or zeolite-amended soil have limited benefits for hyperaccumulators, which have been utilized for phytoremediation. Further research is needed to evaluate the potential of zeolite-based composites for phytoremediation. Additionally, the development of nanocomposites with enhanced adsorption capacity would be necessary for more effective removal of pollutants.

Fusion-Assisted Hydrothermal Synthesis of Technogenic-Waste-Derived Zeolites and Nanocomposites: Synthesis, Characterization, and Mercury (II) Adsorption

This study presents the synthesis of zeolites derived from coal fly ash (CFA) using the fusion-assisted alkaline hydrothermal method. The zeolites were synthesized by combining CFA and NaOH at a molar ratio of 1:1.2 under fusion temperatures of 500, 600, and 700 °C. Subsequently, the obtained zeolites were subjected to further modifications through the incorporation of magnetic (Fe₃O₄) and silver (Ag⁰) nanoparticles (NPs). The Fe₃O₄ NPs were introduced through co-precipitation of Fe(NO₃)₂ and FeCl₃ at a molar ratio of 1:1, followed by thermal curing at 120 °C. On the other hand, the Ag⁰ NPs were incorporated via ion exchange of Na⁺ with Ag⁺ and subsequent reduction using NaBH₄. The synthesized porous materials exhibited the formation of zeolites, specifically analcime and sodalite, as confirmed by X-ray diffraction (XRD) analysis. Additionally, the presence of Fe₃O₄ and Ag⁰ NPs was also confirmed by XRD analysis. The elemental composition analysis of the synthesized nanocomposites further validated the successful formation of Fe₃O₄ and Ag⁰ NPs. Nitrogen porosimetric analysis revealed the formation of a microporous structure, with the BET surface area of the zeolites and nanocomposites ranging from 48.6 to 128.7 m²/g and pore sizes ranging from 0.6 to 4.8 nm. The porosimetric characteristics of the zeolites exhibited noticeable changes after the modification process, which can be attributed to the impregnation of Fe₃O₄ and Ag⁰ NPs. The findings of this research demonstrate the effectiveness of the fusion-assisted method in producing synthetic zeolites and nanocomposites derived from CFA. The resulting composites were evaluated for their potential application in the removal of mercury ions from aqueous solutions. Among the samples tested, the composite containing Ag⁰ NPs exhibited the highest adsorption capacity, reaching 107.4 mg of Hg²⁺ per gram of composite. The composites modified with Fe₃O₄ NPs and Ag/Fe₃O₄ nanocomposites displayed adsorption capacities of 68.4 mg/g and 71.4 mg/g, respectively.

Zeolite A powder and beads from sugarcane bagasse fly ash modified with iron(III) oxide-hydroxide for lead adsorption

The discharging of lead-contaminated wastewater is a concern because of its toxicity to living organisms and water quality resulting in dangerous water consumption, so it is highly recommended to remove lead from wastewater to be below water quality standards for a safe environment. Zeolite A sugarcane bagasse fly ash powder (ZB), zeolite A sugarcane bagasse fly ash powder mixed iron(III) oxide-hydroxide (ZBF), zeolite A sugarcane bagasse fly ash beads (ZBB), zeolite A sugarcane bagasse fly ash powder mixed iron(III) oxide-hydroxide beads (ZBFB), and zeolite A sugarcane bagasse fly ash beads coated iron(III) oxide-hydroxide (ZBBF) were synthesized and characterized in various techniques. Their lead removal efficiencies were investigated by batch experiments, adsorption isotherms, and kinetics. The specific surface area, pore volume, and pore size of ZB were close values to zeolite A standard (STD), and ZBF had the highest specific surface area and the smallest pore size than others. ZB and ZBF demonstrated crystalline phases whereas ZBB, ZBFB, and ZBBF were amorphous phases. The surface morphology of ZB was a cubic shape similar to STD. ZBF demonstrated an agglomerated formation of ZB and iron(III) oxide-hydroxide whereas ZBFB and ZBBF had sphere shapes with coarse surfaces. Si, Al, O, Fe, Na, Ca, O-H, (Si, Al)-O, H₂O, and D₄R were detected in all materials. The surface charges of all zeolite A materials had negatively charged at all pH values, and their surfaces increased more negatively charged with increasing pH value which pH 5 illustrated as the highest negatively charged in all materials. Their lead removal efficiencies were higher than 82%. Langmuir isotherm and pseudo-second-order kinetic models were well explained for their adsorption patterns and mechanisms. Finally, ZBBF is a good offer for applying in industrial wastewater treatment systems because of its easy operation and saving costs than ZBF.

Special Issue “Sustainable Remediation Processes Based on Zeolites”

Zeolites are microporous tectosilicates characterized by a three-dimensional network of tetrahedral (Si, Al)O4 units with the general formula: Mx+Ly2+[Al(x+2y)Si1−(x+2y)O2n]·mH2O where M+ and L2+ are monovalent and divalent cations [...]

Fly Ash Coated with Magnetic Materials: Improved Adsorbent for Cu (II) Removal from Wastewater

Fly ash/magnetite material was used for the adsorption of copper ions from synthetic wastewater. The obtained material was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) surface area, and vibrating sample magnetometer (VSM). Batch adsorption experiments were employed in order to investigate the effects of adsorbent dose, initial Cu (II) concentration and contact time over adsorption efficiency. The experimental isotherms were modeled using Langmuir (four types of its linearization), Freundlich, Temkin, and Harkins-Jura isotherm models. The fits of the results are estimated according to the Langmuir isotherm, with a maximum adsorption capacity of 17.39 mg/g. The pseudo-second-order model was able to describe kinetic results. The data obtained throughout the study prove that this novel material represents a potential low-cost adsorbent for copper adsorption with improved adsorption capacity and magnetic separation capability compared with raw fly ash.

Quasi Natural Approach for Crystallization of Zeolites from Different Fly Ashes and Their Application as Adsorbent Media for Malachite Green Removal from Polluted Waters

Worldwide disposal of multi-tonnage solid waste from coal-burning thermal power plants (TPPs) creates serious environmental and economic problems, which necessitate the recovery of industrial waste in large quantities and at commercial prices. Fly ashes (FAs) and slag from seven Bulgarian TPPs have been successfully converted into valuable zeolite-like composites with various applications, including as adsorbents for capturing CO2 from gases and for removal of contaminants from water. The starting materials generated from different types of coal are characterized by a wide range of SiO2/Al2O3 ratio, heterogeneous structure and a complex chemical composition. The applied synthesis procedure resembles the formation of natural zeolites, as the raw FAs undergo long-term self-crystallization in an alkaline aqueous solution at ambient temperature. The phase and chemical composition, morphology and N2 adsorption of the final zeolite products were studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-Ray Diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses. The growth of faujasite (FAU) crystals as the main zeolite phase was established in all samples after 7 and 14 months of alkaline treatment. Phillipsite (PHI) crystals were also observed in several samples as an accompanying phase. The final products possess specific surface area over 400 m2/g. The relationships between the surface properties of the investigated samples and the characteristics of the raw FAs were discussed. All of the obtained zeolite-like composites were able to remove the highly toxic dye (malachite green, MG) from water solutions with efficiency over 96%. The experimental data were fitted with high correlation to the second-order kinetics.

Recent Advances in Magnetic Nanoparticles and Nanocomposites for the Remediation of Water Resources

Water resources are of extreme importance for both human society and the environment. However, human activity has increasingly resulted in the contamination of these resources with a wide range of materials that can prevent their use. Nanomaterials provide a possible means to reduce this contamination, but their removal from water after use may be difficult. The addition of a magnetic character to nanomaterials makes their retrieval after use much easier. The following review comprises a short survey of the most recent reports in this field. It comprises five sections, an introduction into the theme, reports on single magnetic nanoparticles, magnetic nanocomposites containing two of more nanomaterials, magnetic nanocomposites containing material of a biologic origin and finally, observations about the reported research with a view to future developments. This review should provide a snapshot of developments in what is a vibrant and fast-moving area of research.