Zeolite P synthesis based on fly ash and its removal of Cu(II) and Ni(II) ions

Preparation and characterization of P-type zeolite for adsorption of Cr3+, Ni2+, and Co2

Acid-washed coal fly ash (AW-CFA) was subjected to wet grinding activation followed by hydrothermal crystallization to synthesize P zeolite (FAZ-P). The FAZ-P obtained at 120 °C for 24 h exhibited a maximum relative crystallinity of 93.15% and was employed for the adsorption of Cr3+, Ni2+, and Co2+ from aqueous solutions. The zeolitization of coal fly ash (CFA) leads to an increase in specific surface area to 44.00 m2/g, resulting in the formation of nano-sized P zeolite crystals with uniformly narrow fissures and sizes within the range of 10-30 nm. Adsorption experimental results indicate that FAZ-P exhibits maximum adsorption capacities of 49.03 mg/g for Cr3+, 22.20 mg/g for Ni2+, and 27.25 mg/g for Co2+. The adsorption equilibrium data for both mixed and single-metal ion solutions conform to the Langmuir model, with the affinity sequence for heavy metal ions being Cr3+  > Co2+  > Ni2+. The pseudo-first-order and pseudo-second-order kinetic models effectively described the adsorption behavior of Cr3+, Ni2+, and Co2+. Increasing the initial pH value of the solution significantly enhanced the adsorption capacity of the adsorbent for heavy metal ions. The removal mechanism of metal ions involves both adsorption and ion exchange processes. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic.

Simultaneous adsorption of Cu(II), Zn(II), Cd(II) and Pb(II) from synthetic wastewater using NaP and LTA zeolites prepared from biomass fly ash

Herein, NaP and LTA zeolites were successfully synthesised from woody biomass ash with alkali fusion-assisted hydrothermal method by altering the NaOH/ash ratio, crystallisation time and crystallisation temperature. In order to reduce the synthesis costs, NaP zeolite was synthesised with no additional source of aluminium and silicon. The synthesised zeolites were utilized for the monocomponent and simultaneous adsorption of Cu(II), Cd(II), Pb(II) and Zn(II) ions. The maximum adsorbed amount of metals had the trend Pb(II) > Cu(II) > Cd(II) > Zn(II) for both NaP and LTA zeolite. The kinetic data fit well to the pseudo-second order model indicating that chemisorption is the rate-limiting step. The isotherm data were well described with Sips and Redlich-Peterson models indicating a non-ideal heterogeneous adsorption process. Maximum adsorption capacity of NaP zeolite was 42.9 mg/g for Cu(II) and 117.3 mg/g for Cd(II), while LTA had 140.1 mg/g and 223.5 mg/g for Cu(II) and Cd(II) ions, respectively.

Emerging waste-to-wealth applications of fly ash for environmental remediation: A review

The considerable increase in world energy consumption owing to rising global population, intercontinental transportation and industrialization has posed numerous environmental concerns. Particularly, in order to meet the required electricity supply, thermal power plants for electricity generation are widely used in many countries. However, an annually excessive quantity of waste fly ash up to 1 billion tones was globally discarded from the combustion of various carbon-containing feedstocks in thermoelectricity plants. About half of the industrially generated fly ash is dumped into landfills and hence causing soil and water contamination. Nonetheless, fly ash still contains many valuable components and possesses outstanding physicochemical properties. Utilizing waste fly ash for producing value-added products has gained significant interests. Therefore, in this work, we reviewed the current implementation of fly ash-derived materials, namely, zeolite and geopolymer as efficient adsorbents for the environmental treatment of flue gas and polluted water. Additionally, the usage of fly ash as a catalyst support for the photodegradation of organic pollutants and reforming processes for the corresponding wastewater remediation and H₂ energy generation is thoroughly covered. In comparison with conventional carbon-based adsorbents, fly ash-derived geopolymer and zeolite materials reportedly exhibited greater heavy metal ions removal and reached the maximum adsorption capacity of about 150 mg g^-1. As a support for biogas reforming process, fly ash could enhance the activity of Ni catalyst with 96% and 97% of CO₂ and CH₄ conversions, respectively.

Explorations on efficient extraction of uranium with porous coal fly ash aerogels

In order to explore a suitable uranium adsorbent with the advantages of low-cost, recyclability and high efficiency, porous coal fly ash aerogels with different size of coal fly ash were synthesized. Among them, PCFAA-1250 (prepared with 1250 mesh coal fly ash (CFA)) showed better adsorption performance and the maximum adsorption efficiency even approached 96.5% (C₀ = 10 mg L^-1, m/V = 1.0 g L^-1, T = 298 K, t = 24 h and pH = 3.0), which was higher than most of previous adsorbents. Langmuir and pseudo-second-order models were more likely to be used to determine the removal behavior of uranium on PCFAA, illustrating that the adsorption reaction was uniform chemisorption. Meanwhile, the adsorption process on PCFAA was spontaneous. Notably, the desorption efficiencies of all of PCFAA were more than 80% after five cycles, which suggested that PCFAA possessed good recyclability, especially PCFAA-1250. Besides, the adsorption mechanism was further revealed via XPS and the uranium ions were immobilized on the surface of adsorbents through complexation. Based on above conclusions, it could be concluded that PCFAA-1250 had the potential to be a candidate for the extraction of uranium from wastewater.

Interzeolitic Transformation of Clinoptilolite into GIS and LTA Zeolite

A natural clinoptilolite zeolite was transformed into other zeolites of greater industrial interest, such as zeolites with GIS and LTA structures. The synthesis conditions were studied, and the interzeolitic transformation was characterized by X-ray diffraction (XRD), X-ray fluorescence (FRX), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). From the results, it was possible to observe that the GIS and LTA zeolites were successfully synthesized. Furthermore, the results revealed that a synthesis time of 4 days was enough to obtain the GIS structure, and 4 h was sufficient to obtain LTA. The interzeolitic transformation can be explained by the RBU (Ring Building Unit) approach using C4 units from the HEU topology. The use of clinoptilolite in the synthesis of other zeolites is an innovative, economically viable, and environmentally sustainable process that exploits a material that exists in large quantities and is still little explored by industry.

Hydrothermal transformation of geopolymers to bulk zeolite structures for efficient hazardous elements adsorption

This paper reports a facile route to prepare bulk zeolites with tunable phase compositions and microstructures by combining hydrothermal treatment and geopolymer precursor technique. Amorphous Na-based geopolymer (NaGP) is transformed into crystalline analcime following hydrothermal treatments. By systematically investigating the effects of hydrothermal conditions on the phase compositions and microstructures of the products, the optimal hydrothermal procedure is screened as treating NaGP in 1 M NaOH solution at 160 °C for 6 h. Furthermore, we achieve control over phase compositions of the resulting bulk zeolites by tailoring the initial Na/K ratio of geopolymer precursors. For instance, treating the geopolymer precursor with a Na/K ratio of 9: 1 under the optimal hydrothermal procedure leads to the formation of zeolite consisting of analcime and zeolite-P. The as-prepared adsorbents exhibit outstanding adsorption performance for the hazardous elements, among which analcime-zeolite-P shows an adsorption efficiency of 93.3% for Cs⁺, and NaGP exhibits an adsorption efficiency of 99.6% for Sr²⁺. Moreover, we reveal the mechanisms underlying the adsorption of Cs⁺ and Sr²⁺ in the adsorbents to be chemisorption. Meanwhile, ion exchanges also occur in NaGP and analcime-zeolite-P during Cs⁺ adsorption. These results render geopolymers and their derived bulk zeolites promising for hazardous elements adsorption.

Conversion of silica by-product into zeolites by thermo-sonochemical treatment

The fine powdered silica by-product of processing of aluminum fluoride (fertilizer plant, Lithuania) was used for zeolite synthesis as silica and aluminum source. The effect of sonication time and the time of hydrothermal synthesis on crystallinity of the synthesized zeolite were studied. This allowed the transformation of the by-product to the mixture of Na-P zeolite and Na-X zeolite. It was determined that ultrasonic-assisted hydrothermal action effected the "diamond" shape formation of Na-P zeolite with clear crystal edges. Na-P zeolite had the morphology of pseudo-spherical forms constituted by small plates when hydrothermal treatment (without sonication) was use for the preparation of zeolites. Moreover, it was determined that ultrasonic-assisted hydrothermal method effected a reduction in the crystal size compared with the zeolites which were synthesized only by using hydrothermal synthesis. The total amount of zeolites as high as 88-93% was achieved after 24 h of hydrothermal treatment followed or unfollowed by sonication. By using longer duration (20 min) of ultrasound pretreatment it is possible to reduce the duration of hydrothermal synthesis: from 24 h to 12 h of hydrothermal treatment. In this case, similar results of total amount of zeolites were detected. In the present work, low-cost raw materials, such as silica by-product have been investigated for the production of zeolites.

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.