Synthesis of Na-A zeolite from coal gangue with the in-situ crystallization technique

Harnessing coal and coal waste for environmental conservation: A review of photocatalytic materials

Fossil fuels, especially coal, have played a pivotal role in driving technological and economic advancements over the past century, though accompanied by numerous environmental challenges. Rapid progress in green and sustainable energy sources, including tidal, wind, and solar energy, coupled with growing environmental concerns, the conventional coal industry is experiencing a sustained decline in both size and financial viability. This situation necessitates the urgent adoption of advanced approaches to coal utilization. Beyond serving as an energy source, coal and its by-products, known as coal waste, can serve as valuable resources for the development of advanced materials, including photocatalysts. The advancement of photocatalytic materials derived from coal and coal waste can capitalize on these natural carbon and mineral sources, providing a viable solution to numerous environmental challenges. Currently, research in this domain remains in its early stages, with existing studies primarily focusing on specific types of photocatalysts or particular aspects of the fabrication process. Therefore, available coal-based and coal waste-based photocatalytic materials were systematically examined and categorized into six types according to their composition and dimensional/structural characteristics. Each type of photocatalytic material was introduced, along with common fabrication and characterization technologies. Representative works were discussed in detail to highlight the unique features of different types of coal-based and coal waste-based photocatalytic materials. Furthermore, the promising applications of these materials in environmental protection and pollution treatment were summarized, while also addressing the challenges and prospects in this research field. This review comprehensively overviews the fundamental knowledge and recent advancements in photocatalytic materials derived from coal and coal waste, with the goal of catalyzing the development of next generation photocatalysts and contributing to the transformation of the conventional coal industry.

Opportunities, challenges and modification methods of coal gangue as a sustainable soil conditioner-a review

The persistent reliance on coal has resulted in the accumulation of substantial coal gangue, a globally recognized problematic solid waste with environmental risks. Given the coal gangue properties and global land degradation severity, the resourceful utilization of coal gangue as soil conditioners is believed to be a universally applicable, cost-effective, high-demand and environment-friendly model with broad application prospect. The direct application of raw coal gangue faces challenges of low active beneficial ingredients, inadequate water and fertilizer retention, presence of potentially toxic elements, resulting in limited efficacy and environmental contamination. This paper provided a comprehensive review of various modification methods (including mechanical, chemical, microbiological, thermal, hydrothermal and composite modifications) employed to enhance the soil improvement performance and reduce the environmental pollution of coal gangue. Furthermore, an analysis was conducted on the potential application of modified coal gangue as a muti-function soil conditioner based on its altered properties. The modified coal gangue is anticipated to effectively enhance soil quality, exhibiting significant potential in mitigating carbon emissions and facilitating soil carbon sequestration. This paper provided innovative ideas for future research on the comprehensive treatment of coal gangue and restoration of degraded soil in order to achieve the dual goals of zero-coal gangue waste and sustainable agriculture.

Subcritical hydrothermal treatment of municipal solid waste incineration fly ash: A review

Municipal solid waste incineration fly ash (MSWI-FA) is a hazardous waste generated from the incineration process, and the harmless treatment of MSWI-FA has attracted widespread attention. Subcritical hydrothermal treatment is competitive in achieving the harmless treatment and resource recycling of MSWI-FA. It exhibits excellent performance in degrading dioxins, stabilizing heavy metals, and converting MSWI-FA into zeolite or tobermorite at low temperatures. This paper clearly introduces the characteristics of MSWI-FA, roundly summarizes the current research status of treating MSWI-FA by subcritical hydrothermal methods, and deeply clarifies the mechanisms of dioxins degradation, zeolite/tobermorite synthesis, and heavy metals stabilization. Considering the research status of handling MSWI-FA by subcritical hydrothermal methods, future research directions are proposed. Owing to the advantages of high efficiency, energy-saving, and environmental sustainability, subcritical hydrothermal treatment of MSWI-FA exhibits promising prospects for industrialization.

Removal and kinetics of cadmium and copper ion adsorption in aqueous solution by zeolite NaX synthesized from coal gangue

Zeolite can remove the heavy metals in wastewater, but the removal efficiency was determined by the types of zeolites and the treatment conditions. In this study, a kind of zeolite NaX synthesized from the coal gangue, a by-product of coal production, was used and the removal efficiency of Cd²⁺ and Cu²⁺and the kinetic models were studied. The effects of its dosage, initial pH value of wastewater, and adsorption temperature on its adsorption of heavy metals Cd²⁺ and Cu²⁺ in the simulated wastewater were studied through the indoor experiments in laboratory, and the adsorption mechanism was analyzed by the adsorption kinetic model based on its adsorption efficiency and its structures. The results show that the zeolite NaX synthesized from coal gangue has a good adsorption effect on Cd²⁺ and Cu²⁺. The adsorption reaches the best effect when the dosage of zeolite is 2 g/L, the initial pH of simulated wastewater is 5, the adsorption temperature is room temperature (25 ℃), and the removal efficiency of Cd²⁺ and Cu²⁺ (100 mg/L) is more than 90%. Additionally, the Langmuir, Freundlich, and Temkin isothermal adsorption models were used to compare and analyze the adsorption effects. The equilibrium data was better fitted by the Langmuir model with the maximum adsorption capacities of 100.11 mg/g (Cd²⁺) and 95.29 mg/g (Cu²⁺), and both separation coefficients were 0-1, which shows that the process was the favorable adsorption. Weber Morris diffusion model shows that the adsorption process at 120 min was more consistent with the pseudo-second-order kinetics model, and the adsorption efficiency was simultaneously controlled by the liquid diffusion step and intraparticle diffusion step. Moreover, the removal mechanism of Cd²⁺ and Cu²⁺ mainly includes physical adsorption and ion exchange. Therefore, the adsorption effect of zeolite synthesized from coal gangue is remarkable, which will provide a feasible and potential alternative for its resource application.

Cost-effective microwave-assisted hydrothermal rapid synthesis of analcime-activated carbon composite from coal gangue used for Pb2+ adsorption

Heavy metal contamination of water has brought about serious harm to the ecological environment and also threatens human health to a certain extent. In this study, a composite structure comprised of analcime-activated carbon (ANA-AC) was synthesized in situ via a microwave-assisted hydrothermal method using coal gangue (CG) for the potential treatment of Pb²⁺ from aqueous solution. The products were systematically characterized using XRD, SEM, BET, FTIR, and XPS. The results showed that activated carbon was successfully integrated with the structure of the analcime and the BET surface area of the ANA-AC (20.82 m²/g) was much greater than that of the CG (9.33 m²/g) and ANA (10.04 m²/g) independently. The relationship between Pb²⁺ adsorption capacity and the initial solution concentration, adsorbent dosages, contact time, pH, and temperature was studied. Under optimal conditions (Pb²⁺  = 100 mg/L, dosage = 0.1 g, contact time = 6 h, pH = 5.4-6, temperature = 298 K), the maximum adsorption capacity of ANA-AC can reach 100%, which was higher than that of CG and ANA. The Langmuir isotherm model was in good agreement with the data obtained for Pb²⁺ adsorption, and the pseudo-second-order kinetic model was more suitable for describing the experimental data, showing that chemical adsorption was the controlling step during the adsorption process. In summary, analcime-activated carbon composite prepared from coal gangue could be used as an appropriate adsorbent for Pb²⁺ adsorption from an aqueous solution.

Synthesis of coal-analcime composite from coal gangue and its adsorption performance on heavy metal ions

An innovative adsorbent, "coal-analcime composite", was converted from coal gangue directly, that combined the adsorption effect of analcime and residual coal in coal gangue. The gangue was added silicon and alkali source, composite was synthesized under saturated steam pressure of 1 Mpa(187 °C) for 3 h. Moreover, the products generation mechanism and property have been explored by XRD, FTIR, Ar adsorption measurement. The characterization results showed that residual coal was modified after the hydrothermal alkali activation process, higher specific surface area and more extensive pore size distribution were obtained compared with pure analcime. Modified coal loaded on the surface of analcime enhanced the adsorption capacity of analcime, adsorption experiments showed that the chemo-adsorption occurred between heavy metal ions and composite, the maximum Pb²⁺ exchange capacity reached as high as 268 mg/g.

Facile activation of lithium slag for the hydrothermal synthesis of zeolite A with commercial quality and high removal efficiency for the isotope of radioactive 90Sr

Zeolite A with commercial quality and high removal efficiency for Sr2+ was hydrothermally synthesized from lithium slag after mild and facile activation.

Efficiency in Ofloxacin Antibiotic Water Remediation by Magnetic Zeolites Formed Combining Pure Sources and Wastes

In this work, red mud (RM) and spinel iron oxide nanoparticles (SPIONs) were added to pure silica/alumina sources (SAs) and fly ash (FA) with the aim of synthesizing and investigating the magnetic behavior of different zeolites. SAs were used to synthesize zeolite with LTA topology (zeolite A) with the addition of both red mud and spinel iron oxide nanoparticles. FA and RM were mixed to synthesize sodalite whereas only FA with the addition of SPIONs was used to form zeolite with FAU-topology (zeolite X). All the synthetic products showed magnetic properties. However, zeolites with spinel iron oxide nanoparticles (zeolites A and X) showed ferromagnetic-like behavior. Sodalite was characterized by a reduction in saturation magnetization, whereas zeolite A with red mud displayed antiferromagnetic behavior. For the first time, all the synthetic products were tested for polluted water remediation by a persistent emerging contaminant, ofloxacin (OFL) antibiotic. The four zeolite types showed good adsorption affinity towards OFL under actual conditions (tap water, natural pH). All materials were also tested for OFL removal in real waters spiked with OFL 10 µg L−1. Satisfactory recoveries (90–92% in tap water, 83–87% in river water) were obtained for the two zeolites synthesized from industrial waste materials.

Effects of Si/Al Ratios on the Bulk-Type Zeolite Formation Using Synthetic Metakaolin-Based Geopolymer with Designated Composition

In this paper, synthetic metakaolin with fixed composition (Al2O3·2SiO2) was produced by a simple chemosynthetic route. The chemosynthetic metakaolin can eliminate the influence of impurities in metakaolin from natural kaolin minerals. The synthetic metakaolin together with NaOH and SiO2-sol were used to prepare Na-based geopolymer precursors with various molar ratios of Si/Al. The molar ratios of Si/Al from 1 to 2 were tailored by adding different contents of SiO2-sol. Zeolite/geopolymer composites or monolith-type zeolite were successfully fabricated from synthetic metakaolin-based geopolymer through a hydrothermal process. The effects of Si/Al ratios on the phase composition and microstructure of the produced zeolite/geopolymer composites or zeolites were studied. The results proved that the composition of synthetic metakaolin and geopolymer precursors can be facilely tuned, and the monolithic geopolymer precursors can be mostly, or even totally, transformed into zeolite after hydrothermal treatment.

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.

Applicability of weathered coal waste as a reactive material to prevent the spread of inorganic contaminants in groundwater

It is necessary to determine an environmentally friendly method of reusing the vast amount of coal waste that is generated during coal preparation. This study evaluates the applicability of using weathered coal waste in a permeable reactive barrier to prevent groundwater contamination. Coal waste, with different weathering degrees, was obtained from two coal mining sites in South Jeolla Province, Korea. The reactivities of the coal waste with inorganic contaminants, such as copper, cadmium, and arsenic, were examined in batch and column experiments. The batch experiment results indicate that the coal waste removal efficiencies of copper (99.8%) and cadmium (95.4%) were higher than those of arsenic (71.0%). The maximum adsorption capacities of coal waste for copper, cadmium, and arsenic calculated from the Langmuir isotherm model were 4.440 mg/g, 3.660 mg/g, and 0.718 mg/g, respectively. The equilibrium of adsorption was attained within 8 h. The column experiment results reveal that the coal waste effectively removed inorganic contaminants under flow-through conditions. Faster breakthrough times were observed in single solute system (As(V) = 19.3 PV, Cu(II) = 47.6 PV) compared with binary solute system (As(V) = 27.8 PV, Cu(II) = 65.4 PV). To confirm the applicability of using coal waste in a groundwater environment, its decontamination ability was analyzed at low concentrations and under various pH conditions. To examine the potential ecological risks in the subsurface environment, a test to determine acute toxicity to Daphnia magna and a toxic characteristic leaching procedure (TCLP) test were conducted. The coal waste was found to satisfy appropriate standards. The acute toxicity test also confirmed the ecological safety of using coal waste in a groundwater environment. The acceptably high capacity and fast kinetics of inorganic contaminant sorption by the coal waste indicate it could potentially be employed as a reactive material. The recycling and application of this abundant waste material will contribute to solving both coal waste disposal and water pollution problems.

Fabrication of Ag3PO4/TiO2@molecular sieve (MS) ternary composites with remarkably enhanced visible light-responded photocatalytic activity and mechanism insight

In this study, Ag₃PO₄/TiO₂@molecular sieve (MS) ternary composites were fabricated via in-situ deposition and hydrothermal growth method for photocatalytic degradation of formaldehyde and sodium isobutyl xanthate (SIBX) under visible light irradiation. XRD, PL, UV-vis, UPS, SEM-EDS and XPS techniques were adopted to characterize the composite. The results show that the MS material was indexed as zeolite P and Ag₃PO₄-TiO₂ hybrid structure could improve the absorption of visible light and greatly inhibit the recombination of photogenerated charge carriers by introducing 3 times TiO₂. After evaluating the photocatalytic activity and kinetics model, it is found that photocatalytic activity is consistent with the apparent first-order kinetic model. The Ag₃PO₄/TiO₂-3@MS ternary composite under visible light irradiation appears the highest removal rate with 97.9% of formaldehyde and 96.7% of SIBX, respectively. Furthermore, the reusability of the photocatalyst was investigated by successive reuse. After five reuses, the removal rates reached 97.3% and 94.6% within 105 min for formaldehyde and SIBX, respectively. At last, the proposed mechanism of the photocatalytic reaction and the degradation routes of formaldehyde and SIBX were systematically discussed.

Effect of H2O Activity on Zeolite Formation

In an effort to understand the effects of H₂O activity on zeolite formation, we have synthesized LTA zeolite using a combination of freezing processes and varying drying temperatures. Sodium aluminate and sodium silicate were used to form LTA zeolite, according to the IZA (International Zeolite Association) protocol. The synthesis steps were modified by adding the precursor frozen process by a rapid liquid nitrogen (-196 °C) treatment or slow conventional freezer treatment (-20 °C). The samples were subsequently sonicated and then dried at 80 °C or 40 °C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed on the samples immediately after the drying process as well as after 2 weeks and 1 month of aging the solid products. The results indicated that LTA zeolite does not form. The silica-alumina precursor after both freezing processes and after being dried at 80 °C showed the presence of sodalite displaying stable behavior over time. Both sets of samples dried at 40 °C and did not show the presence of zeolite immediately after the drying process. However, after 2 weeks, the liquid nitrogen-frozen precursor was characterized by the presence of EMT whereas zeolites never formed in the -20 °C samples. These results suggest that freezing processes differently control the H₂O activity during the drying and aging processes in the solid state. Thus, although the precursor chemical composition is the same, the type of zeolite formed is different.

Sorption and mechanism studies of Cu2+, Sr2+ and Pb2+ ions on mesoporous aluminosilicates/zeolite composite sorbents

The research aimed to develop a novel mesoporous aluminosilicate/zeolite composite by the template co-precipitation method. The effect of aluminosilicate (AlSi) and zeolite (NaY) on the basic properties and adsorption capacity of the resultant composite was conducted at different mass ratios of AlSi/NaY (i.e., 5/90, 10/80, 15/85, 20/80, and 50/50). The adsorption characteristics of such composite and its feedstock materials (i.e., aluminosilicates and zeolite) towards radioactive Sr²⁺ ions and toxic metals (Cu²⁺ and Pb²⁺ ions) in aqueous solutions were investigated. Results indicated that BET surface area (S_BET), total pore volume (V_Total), and mesopore volume (V_Meso) of prepared materials followed the decreasing order: aluminosilicate (890 m²/g, 0.680 cm³/g, and 0.644 cm³/g) > zeolite (623 m²/g, 0.352 cm³/g, and 0.111 cm³/g) > AlSi/NaY (20/80) composite (370 m²/g, 0.254 cm³/g, and 0.154 cm³/g, respectively). The Langmuir maximum adsorption capacity (Q_m) of metal ions (Sr²⁺, Cu²⁺, and Pb²⁺) in single-component solution was 260 mg/g, 220 mg/g, and 161 mg/g (for zeolite), 153 mg/g, 37.9 mg/g, and 66.5 mg/g (for aluminosilicate), and 186 mg/g, 140 mg/g, and 77.8 mg/g for (AlSi/NaY (20/80) composite), respectively. Ion exchange was regarded as a domain adsorption mechanism of metal ions in solution by zeolite; meanwhile, inner-surface complexation was domain one for aluminosilicate. Ion exchange and inner-surface complexation might be mainly responsible for adsorbing metal ions onto the AlSi/NaY composite. Pore-filling mechanism was a less important contributor during the adsorption process. The results of competitive adsorption under binary-components (Cu²⁺ and Sr²⁺) and ternary-components (Cu²⁺, Pb²⁺, and Sr²) demonstrated that the removal efficacy of target metals by the aluminosilicate, zeolite, and their composite remarkably decreased. The synthesized AlSi/NaY composite might serve as a promising adsorbent for real water treatment.

Extraction of alumina from alumina rich coal gangue by a hydro-chemical process

Vast quantities of gangue from coal mining and processing have accumulated over the years and caused significant economic and environmental problems in China. For high added-value utilization of alumina rich coal gangue (ARCG), a mild hydro-chemical process was investigated to extract alumina. The influences of NaOH concentration, mass ratio of alkali to gangue, reaction temperature and reaction time were systematically studied. An alumina extraction rate of 94.68% was achieved at the condition of NaOH concentration 47.5%, alkali to gangue ratio of 6, reaction temperature of 260°C and reaction time of 120 min. The obtained leaching residues were characterized through X-ray diffraction, scanning electron microscopy and energy-dispersive spectrometer. Research confirmed that kaolinite the main alumina-bearing phase of ARCG can be decomposed and transformed to Na₈Al₆Si₆O₂₄(OH)₂(H₂O)₂ and Ca₂Al₂SiO₆(OH)₂ at relatively low temperature and short reaction time. Additionally, Na₈Al₆Si₆O₂₄(OH)₂(H₂O)₂ and Ca₂Al₂SiO₆(OH)₂ are unstable and will transform to alumina-free phase NaCaHSiO₄ under the optimal conditions, which is the major reason for high alumina extraction rates.

Highly effective removal of Pb2+ in aqueous solution by Na-X zeolite derived from coal gangue

The present study aimed to synthesize Na-X zeolite from coal gangue powder (CGP) via the alkali fusion hydrothermal method. The optimal synthetic conditions were investigated, the mass ratio of CGP/NaOH(s) was 1:1.25, and crystallization reaction time was 12 h. X-ray powder diffraction, scanning electron microscopy energy-dispersive X-ray spectrum, and Fourier transform infrared spectrometer techniques were used to test the properties of resultant zeolite product, which was highly identical to that of commercial zeolite. The efficiencies of the synthetic zeolite for Pb²⁺ adsorption were analyzed on factors including solution pH, adsorbent dosage, temperature, and contact time. Compared with the pseudo-first-order, Elovich, Freundlich, and Temkin models, the pseudo-second-order and Langmuir models were fitted more satisfactorily with the dynamic data and adsorption equilibrium data, respectively. The maximum Pb²⁺ adsorption capacity of synthetic zeolite (457 mg/g) could be reached when the pH, contact time, temperature, and initial Pb²⁺ concentration was 6, 40 min, 45 °C, and 200 mg/L. The adsorption capacity was higher than many of the natural and synthetic zeolites reported in previous literature.

Study on the Effectiveness of Sulfate-Reducing Bacteria Combined with Coal Gangue in Repairing Acid Mine Drainage Containing Fe and Mn

In view of the characteristics of the high content of SO42−, Fe2+ and Mn2+ in acid mine drainage (AMD) and low pH value, based on adsorption and biological methods, coal gangue was combined with sulfate-reducing bacteria (SRB). On this basis, four dynamic columns, including Column 1 (SRB combined with spontaneous combustion gangue from the Gaode coal mine), Column 2 (SRB combined with spontaneous combustion gangue from Haizhou), Column 3 (SRB combined with gangue from Haizhou), and Column 4 (SRB combined with gangue from Shanxi), were constructed. The efficacy of four columns was compared by the inflow of AMD with different pollution load. Results showed that the repair effect of four columns was: Column 3 > Column 2 > Column 1 > Column 4. In the second stage of the experiment, the repair effect of Column 3 was the best. The average effluent pH value and oxidation reduction potential (ORP) value were 9.09 and –262.83 mV, the highest removal percentages of chemical oxygen demand (COD) and SO42− were 84.41% and 72.73%, and the average removal percentages of Fe2+, Mn2+ were 98.70% and 79.97%, respectively. At the end of the experiment, when deionized water was injected, the fixed effect of AMD in the four columns was stable and no secondary release appeared.

Synthesis of zeolite SSZ-13 from coal gangue via ultrasonic pretreatment combined with hydrothermal growth method

SSZ-13 zeolite has been widely used in catalysis and adsorption because of good hydrothermal stability and pore structure. However, long crystallization time is the main challenge limiting its industry application. As increased emissions and ineffective treatment, coal gangue not only occupies land, but also pollutes the waterbody and farmland. Using coal gangue as raw material to synthetize zeolite has been considered as an environmentally friendly and effective alternative to solve the issues of accumulation and pollution, which also improves the added value of coal gangue. The ultrasonic assistance has been proven to be one of the potential pretreatment methods to promote the dissolution of crystalline silicon aluminum and reduce the crystallization time of molecular sieve. In this work, SSZ-13 was synthesized by coal gangue via ultrasonic pretreatment combined with hydrothermal growth method. The ultrasonic frequency and power were 20 kHz and 120 W, respectively. The synthesized samples were characterized by XRD, SEM, EDS, BET. The results showed that the crystallization time was shorten to 18 h, which was about 12 h lower than the same conditions of conventional chemicals synthesis. Furthermore, the specific surface area of the synthesized sample was more than 620 m²/g, which also indicated over 95% NO_x conversion across a broad range from 180 to 400 °C and over 94% NO_x conversion at 200-400 °C after hydrothermal treatment 6 h. This study provides a reference for the environmentally friendly utilization of coal gangue and the low-cost rapid synthesis and application of SSZ-13.

Synthesis of X-Zeolite from Waste Basalt Powder and its Influencing Factors and Synthesis Mechanism

Traditional hydrothermal method (TH) and alkali fusion-assisted hydrothermal method (AFH) were evaluated for the preparation of zeolites from waste basalt powder by using NaOH as the activation reagent in this study. The synthesized products were characterized by BET, XRD, FTIR and SEM. The effects of acid treatment, alkali/basalt ratio, calcination temperature and crystallization temperature on the synthesis process were studied. The results showed that AFH successfully synthesized zeolite X with higher crystallinity and no zeolite was formed by TH. The specific surface area of synthetic zeolite X was 486.46 m²·g⁻¹, which was much larger than that of original basalt powder (12.12 m²·g⁻¹). Acid treatment and calcination temperature had no effect on zeolite types, but acid treatment improved the yield and quality of zeolite. Alkali/basalt ratio and crystallization temperature not only affected the crystallinity of synthesized zeolites but also affected its type. The optimum synthesis condition of zeolite X are as follows: acid treatment of 5 wt% HCl solution, NaOH/basalt ratio of 1:1, a calcination temperature of 650 °C and crystallization temperature of 120 °C. The work shows that basalt can be used as a raw material to prepare zeolite.

Calcined Post-Production Waste as Materials Suitable for the Hydrothermal Synthesis of Zeolites

The zeolite production process is currently being very intensively researched. Due to environmental protection, as well as issues related to the guidelines of a zero-waste economy, all activities aimed at obtaining such materials from post-processed waste are extremely important. This article presents an innovative method of utilising calcined carboniferous shale in order to produce synthetic zeolites. The raw material for testing came from two Polish hard coal mines. Both the chemical and phase composition of the coal shale were characterised. Based on the recorded thermal analysis results coupled with the mass spectrometer, the processes occurring during the heating of raw materials were interpreted and the calcination temperatures were determined. The changes in the phase composition of raw materials resulting from the calcination process used were also analysed. The heat-treated raw materials were subjected to the synthesis of zeolites in an aqueous solution of sodium hydroxide by means of the hydrothermal method at a concentration of 2.75 M. The results of water leaching and structural parameters are presented for both raw materials, as well as the produced synthesis. The conducted research confirmed that after the application of the synthetic process on coal shale, a zeolite with a surface area of S_BET equal to 172 m²/g can be obtained.

Preparation, characterization, and performance of 4A zeolite based on opal waste rock for removal of ammonium ion

In this study, 4A zeolite was prepared from opal waste rock by hydrothermal method and applied in ammonium ion adsorption. To optimize synthesis conditions, the effect of crystallization time (1–8 h), crystallization temperature (65–115°C), Na2O/SiO2 (0.6–2.0), H2O/Na2O (20–70), and SiO2/Al2O3 (1.0–3.5) was investigated. X-ray diffraction, scanning electron microscope imaging, cation exchange capacity, static water adsorption, Fourier transform infrared spectroscopy, and N2 adsorption–desorption isotherm were used for assessing properties of 4A zeolite. Adsorption experiments were performed by 1.0 g l−1 4A zeolite with NH4+ solution (5–300 mg l−1) for 4 h at room temperature. The experiment results revealed with a crystallization time of 3 h, a crystallization temperature of 85°C, Na2O/SiO2=1.0, H2O/Na2O = 40, and SiO2/Al2O3=2.0, the 4A zeolite synthesized had excellent performance with cation exchange capacity of 2.93 mmol (g dry zeolite)−1 and static water adsorption of 22.3%. The adsorption process was described by Freundlich model (R2>0.99) and the maximum adsorption capacity could reach to 53.11 mg g−1. The experimental results provided a novel approach for the utilization of opal waste rock, which is produced during the mining of opal-rich palygorskite, and for the synthesis of 4A zeolite and the removal of ammonium ion.

One-Step Hydrothermal Synthesis of Zeolite X Powder from Natural Low-Grade Diatomite

Zeolite X powder was synthesized using natural low-grade diatomite as the main source of Si but only as a partial source of Al via a simple and green hydrothermal method. The microstructure and surface properties of the obtained samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), wavelength dispersive X-ray fluorescence (XRF), calcium ion exchange capacity (CEC), thermogravimetric-differential thermal (TG-DTA) analysis, and N₂ adsorption-desorption technique. The influence of various synthesis factors, including aging time and temperature, crystallization time and temperature, Na₂O/SiO₂ and H₂O/Na₂O ratio on the CEC of zeolite, were systematically investigated. The as-synthesized zeolite X with binary meso-microporous structure possessed remarkable thermal stability, high calcium ion exchange capacity of 248 mg/g and large surface area of 453 m²/g. In addition, the calcium ion exchange capacity of zeolite X was found to be mainly determined by the crystallization degree. In conclusion, the synthesized zeolite X using diatomite as a cost-effective raw material in this study has great potential for industrial application such as catalyst support and adsorbent.

Hydrothermal synthesis of mixtures of NaA zeolite and sodalite from Ti-bearing electric arc furnace slag

NaA and sodalite zeolites were synthesized from Ti-bearing EAF slag and the removal capacity of prepared zeolite for Cu²⁺ can reach 1.346 mmol g⁻¹ for 180 min.