Conversion Of Coal Fly Ash Research Articles

Coal fly ash to Y zeolite of great purity and crystallinity: A new and green activation method of combined in situ microwave and ultrasound

Highly crystalline and pure Y (FAU) zeolite were synthesized from coal fly ash (CFA) using a combined in situ microwave and ultrasonic irradiation-assisted method, improving the extraction efficiency of silicon and aluminum from coal fly ash with limited energy usage relative to conventional microwave or ultrasound methods. Significant improvement in the combined method was evident following activation in 4 mol/L sodium hydroxide solution for 1 h at 100°C whereby 39.80 wt% conversion of CFA was attained along with 70.26 mol.% conversion of Si and 68.03 mol.% conversion of Al. Solid-state 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra were used to investigate the framework chemical coordination environment, while the temperature-programmed desorption of NH3 (NH3-TPD) and pyridine-Fourier transform infrared (Pyridine-FTIR) spectra were employed to quantitatively detect the acidity and types of acid sites of the sample. The Si to Al ratio (SAR) of the as-obtained CFA-based Y zeolite was 4.65 with a specific surface area of 916.10 m2/g, leading towards excellent CO2 adsorption (107.14 cm3/g at 0 °C). Furthermore, the thermocatalytic performance of the CFA-Y sample was analyzed in the conversion of cumene, with high silica commercial ultra-stable Y (USY) zeolite as a reference.

Optimization of the Hydrothermal Activation Treatment with Sodium Hydroxide Solution for the Conversion of Coal Fly Ash to Zeolite and Its Adsorption Capability of Lead (II) Ions from the Liquid Phase.

Coal fly ash (FA) was treated by hydrothermal activation with sodium hydroxide solution at different concentrations to optimize the conversion method. Zeolite of the sodium type is prepared from coal FA by 1, 1.5, and 3 mol/L sodium hydroxide solutions (ZE1, ZE1.5, and ZE3). These adsorbents' morphology, crystal structure, scanning electron microscopy, Fourier transform (FT)-IR spectra, cation exchange capacity (CEC), specific surface area and pore volumes, and pHpzc were determined. An adsorption experiment was performed to evaluate the effects of contact time, pH, temperature, and coexistence. From the results, the values of CEC and specific surface area of prepared samples was in the order ZE3 < ZE1.5 < ZE1. The similar trends were observed in lead ions adsorption. In addition, our obtained data elucidate that the ion exchange with sodium ions in the interlayer ZE1 is one of the adsorption mechanisms of Pb2+ from water layer. Finally, lead ions adsorbed on ZE1 could be desorbed using a hydrochloric acid solution, showing that ZE1 could be reused as a water purification agent.

Green Conversion of Coal Fly Ash into Soil Conditioner: Technological Principle and Process Development

White mud is residue discharged during the acid method in the aluminum extraction process from coal fly ash, and this material is harmful to the environment. The implementation of an environmentally friendly and valuable way to use white mud is a key factor restricting the commercial application of the acid method in the fly ash alumina extraction technology. An analysis of white mud revealed the following: (1) it was highly enriched in SiO2 (70–80%) while concentrations of acid-soluble elements, such as Na, Al, and Fe, and some hazardous heavy metals, including Pb and Cr, were significantly lower than raw fly ash; (2) approximately 80% of SiO2 had relatively high reaction activity because of the foregoing Al-extraction treatment. Through an ingenious green chemical process, the complete conversion of white mud into silicon–calcium fertilizer (SCF) was achieved under very mild reaction conditions (approximately 100 °C and atmospheric pressure). Waste liquor was totally recycled, and no secondary solid waste was generated. The SCF had an available silicon content (ASC) of 35%, significantly higher than the commercial standard (20%). Converting them into soil conditioners or ecological remediation materials with the lowest possible energy consumption and secondary pollution may be the most promising approach for the future disposal of aluminosilicate industrial solid wastes.

Column adsorption of Rhodamine 6G over Na–P/SOD zeolite synthesised from aluminosilicate secondary waste

Waste stream management for the conversion of coal fly ash into potential value-added aluminosilicate products has attracted intensive research in recent years. However, these valorisation processes generate secondary solid and liquid waste, thereby challenging the efficient recycling process, environmental sustainability, and industrial scalability. This study successfully utilised the secondary waste recovered after the extraction process of nanosilica from coal fly ash to synthesise Na–P/SOD zeolite adsorbent. The secondary solid waste was composed mainly of SiO2>Na2O > Al2O3 with mineral phases of thenardite, burkeite, and sodium carbonate sulphate. Upon thermal treatment of the secondary solid and liquid wastes, a high fraction of zeolite Na–P phase was formed and the characterised Si–O–Si or Si–O–Al bonds increased with increasing treatment period. Fixed-bed column studies were conducted for the adsorption of Rhodamine 6G over the synthesised adsorbents. High efficiency (71%) of Rhodamine 6G removal was achieved over the adsorbent with the highest fraction of Na–P/SOD zeolite phases. This adsorbent exhibited an extended utility before ultimate breakthrough and exhaustion time, which only occurred after prolonged uptake of the dye. The column adsorption data fitted the Thomas and Adams-Bohart model, thus, confirming the suitability of the adsorbents for the removal of dye from wastewater.

Effect of calcium on enhanced carbon capture potential of coal fly ash zeolites. Part II: a study on the adsorption mechanisms.

Coal fly ash zeolites (CFAZs) of type X with low (Na-X) and medium (Na-Ca-X) content of calcium were synthesized by alkaline conversion of lignite coal fly ash generated by combustion of lignite with lower and higher limestone amounts, extracted from different coal deposits and burned in separate thermal power plants. The concentration and state of Ca in the zeolites were investigated by energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS). CFAZs Na-Ca-X with a medium Ca-content were found to outperform their lower calcium counterparts Na-X in terms of carbon capture capacity. This provoked our research interest in elucidating the role of Ca in the CO2 retaining mechanism. CFAZs Na-X and Na-Ca-X were studied in consecutive dynamic adsorption cycles, after thermal regeneration at a temperature of 80 °C, at which only the physically adsorbed CO2 molecules can be released. Desorption was investigated by thermogravimetric TG-DTG analyses over a wide temperature range. In situ Fourier-transform infrared (FTIR) spectroscopy was performed to elucidate the structural features of Na-X and Na-Ca-X CFAZs and the types of their accessible adsorption sites. It was found that the role of Ca is to increase the number of accessible Na+ cations in SII and SIII positions in the zeolites where they can simultaneously adsorb two CO or CO2 molecules, which benefits their adsorption capacity. This study raises an issue on coal ash classification for the synthesis of zeolites with carbon capture applications.

Acetone-Sensitive Thin Films Comprising Coal Fly Ash Na-X Zeolites and Sol-Gel Nb2O5 Matrix.

In this study, thin composite films of a sol–gel Nb2O5 matrix doped with coal fly ash Na-X zeolites were deposited by the spin-coating method. Fly ash of lignite coal collected from the electrostatic precipitators of one of the biggest TPPs in Bulgaria was used as a raw material for obtaining zeolites. Zeolite Na-X was synthesized by ultrasonic-assisted double stage fusion-hydrothermal alkaline conversion of coal fly ash. In order to improve the optical quality and sensing properties of the deposited thin films, synthesized zeolites were wet-milled for 60, 120, and 540 s prior to film deposition. The surface morphology of zeolite powders was studied both by scanning electron microscopy and transmission electron microscopy, while their porosity was investigated by N2-physisorption. Refractive index, extinction coefficient, and thickness of the films were determined through fitting of their reflectance spectra. The sensing ability of thin films towards acetone vapors was tested by measuring the reflectance spectra prior to and during exposure to the analyte, and the change in the reflection coefficient ∆R of the films was calculated. The influence of milling time of zeolites on the sensing and optical properties of the films was assumed and confirmed.

Conversion of coal fly ash into advanced crystalline materials

In recent years, coal fly ash disposal has become one concerning environmental problems in Indonesia. Although coal fly ash is remains categorized as hazardous solid waste in several countries, it is also widely known as a valuable material used in various fields, including as a precursor for the synthesis of advanced crystalline materials such as zeolite and geopolymer. Previous studies mainly focused on the utilization of coal fly ash originated from the thermal power plant. This research done to acknowledge the potency of coal fly ash originated from the textile industry to be further converted into new advanced materials through several procedures, such as (1) modification using NaOH solution (FA-Na), (2) synthesized into geopolymer (Geo), and (3) synthesized into zeolite-A (FA-LTA). Characterization of synthesized products conducted using various techniques, i.e., X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), and cation exchange capacity (CEC). The results show that increasing crystallinity, specific surface area, and CEC in the samples are directly proportional to the increasing alkali concentration used. This research has proven that coal fly ash originated from the textile industry and could also synthesize zeolite and geopolymer.

Studies on the thermochemical energy storage in the coal ash zeolite/water system

Deterioration of the air quality and the greenhouse effect requires replacement of the conventional fuels with renewable energy sources (RES). The main disadvantage of RES is the intermittent production of energy during the day and the different seasons. This requires efficient energy storage solutions. Affordable technologies applicable to household-scale heating are thermochemical energy storage systems (TES). TES are usually applied for concentration and storage of solar energy. TES based on zeolites as heat storage media use the exothermic effect of water adsorption. The preferred storage medium is commercial zeolite 13X, which is characterized by high porosity and a large specific surface area. In these systems, the charging is carried out at 130-180 °C and the energy storage efficiency is over 90 %. In the present study, storage media of zeolite X synthesized by the alkaline conversion of coal fly ash was studied in a laboratory assembled TES as a possible substitute of zeolite 13X. The results revealed a micro-mesoporous structure for coal fly ash zeolites (CFAZ) in contrast to the microporous 13X. The charge of TES with CFAZ can be carried out at lower temperatures, while its discharge is enough exothermic. The utilization of coal ash as raw materials for synthesis of heat storage media contribute to many environmental benefits.

Conversion of coal fly ash into nanozeolite Na-X by applying ultrasound assisted hydrothermal and fusion-hydrothermal alkaline activation

This research is emphasized on the synthesis of micro-mesoporous nanozeolite Na-X from coal fly ash wastes (CFA) by ultrasound assisted hydrothermal and double stage fusion-hydrothermal alkaline activation. The products from CFA zeolitization were studied with respect to their morphology by scanning electron microscopy (SEM), chemical and phase composition by energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), respectively. Their thermal properties were investigated by thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) and surface characteristics by nitrogen adsorption. The effects of the ultrasound agitation and additives on the zeolitization process were studied. Sonicated CFA Na-X zeolites possess nanocrystalline morphology and mixed micro-mesoporous structures with higher external specific surface area as compared to microcrystalline zeolite Na-X prepared by magnetic stirring. CFA nanozeolites of Na-X type are expected to behave excellent adsorption potential and catalytic activity due to the enlarged surface and fine morphology with uniformly distributed particles of iron oxides transferred from the raw material.

Sulphates removal from AMD using CFA hydrothermally treated zeolites in column studies

Hydrothermally treated zeolites were synthesized from a coal combustion waste by-product, coal fly ash. Synthesis of this material involved dissolution of the coal fly ash matrix followed by crystallization of the slurry. Characterization of coal fly ash using BET indicated that the coal fly ash had a surface area of 3.141 m2 g−1. The XRD patterns on coal fly ash showed dominance of the mullite and quartz peaks and was observed to be amorphous. The optimized parameters for dissolution of the coal fly ash matrix was a concentration of 3 M NaOH aged for 24 h at a solid/ liquid ratio of 15 g/120 mL. The second stage was focused on optimization of crystallization conditions of the CFA/NaOH slurries for synthesis of zeolite. The effect of variation of water content, crystallization time and crystallization temperature were studied where the optimized conditions obtained were a H2O/SiO2 ratio of 0.53, crystallized at 140 °C for a duration of 24 h. Powder x-ray diffraction studies indicated successful conversion of coal fly ash into zeolites as the dominant coal fly ash minerals such as mullite and quartz diminished while the zeolitic hydroxysodalite phase was formed. Fourier transform infra-red studies showed formation of zeolitic bands at 948 cm−1 due to Al–O and Si–O asymmetric stretching, indicating conversion of the CFA aluminosilicate phase. Thereafter, the adsorption performance of hydrothermally treated zeolites for SO42 was evaluated. The parameters evaluated included, zeolite bed height, flow rate and concentration where the optimized conditions were 4.0 cm, 0.45 mL min−1 and 5.0 mg L−1 respectively. Application studies on AMD derived water from Fleurhof dam indicated an anion selectivity with an increasing order of Cl− < NO3– < Br− < NO2– < SO42−.

Green synthesis of mesoporous γ-Al2O3 from coal fly ash with simultaneous on-site utilization of CO2.

Mesoporous Al2O3 with crystalline framework walls has expanded all over the world due to the various potential applications especially in catalysis. Here, we develop a green and facile approach for the conversion of coal fly ash (CFA) into ordered mesoporous γ-Al2O3. The practical and promising lime-sinter method was comprehensively studied for the extraction of aluminum from CFA as a first step. The extraction efficiency of aluminum could reach up to 87.42%, through calcining with CaCO3 at 1390°C for 1 h and then dissolving in Na2CO3 solution at 70°C for 0.5 h. Combined with the urgent demand for CO2 emission reduction, simulated purified flue gas was introduced to precipitate the Al(OH)3 precursors without structure-directing agents for just 1 h, followed by calcining at only 400°C or 550°C. A series of characterizations were conducted to discuss the effect of precipitation temperature and calcination temperature, resulting the superior product (Al2O3-65/550) with high surface area (230.3 m2 g-1), crystalline γ-Al2O3 phase and ordered mesostructure. This proposed strategy, integrating the on-site recycling of CFA and utilization of CO2, appears to be promising for scalable production of mesoporous γ-Al2O3.

Conversion of Coal Fly Ash into Zeolite Materials: Synthesis and Characterizations, Process Design, and Its Cost-Benefit Analysis

In this work, coal fly ash (CFA) – a byproduct of coal combustion, has been successfully converted into a value-added product— zeolite. This study focuses on the production of the Na-A zeolite phase via the fusion method. The effects of fusion reaction temperature, hydrothermal reaction temperature, reaction time, and the concentration of alkaline were investigated. The synthesized products were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) and studied for their purity and yield. A fusion temperature of 550 °C, fusion duration of 1.5 h, and a subsequent hydrothermal temperature of 100 °C for a reaction of 12 h were found to be the optimal conditions. Based on the synthesis conditions found, an up-scale production process was designed and simulated with aid from the Aspen Plus program. It was found that zeolite production via the fusion method obtained high profitability. For a 5000 kg/h coal fly ash feed, a payback period of 7.1 years is feasible over a 20-year ope...

An Efficient Cost-Effective Removal of Ca2+, Mg2+, and Cu2+ Ions from Aqueous Medium Using Chlorosodalite Synthesized from Coal Fly Ash

Fly ash is one of the coal combustion solid wastes which causes environmental problems around the world. In this context for the first time, this paper reports the conversion of coal fly ash (CFA) into aluminosilicate chlorosodalite, Na8[AlSiO4]6Cl2. The synthesized chlorosodalite was analyzed by X-ray diffraction, Fourier transform infrared, scanning electron microscopy, and Brunauer–Emmett–Teller surface area measurements. The synthesized aluminosilicate chlorosodalite material was tested for potential applications for the removal of calcium, magnesium, and copper from their aqueous medium. The catch method was successfully used to study the effect of the initial concentration of metal ions, adsorbent dose, and contact time. The equilibrium data obtained were fitted by the Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models and showed the affinity order Cu2+ > Ca2+ > Mg2+. The well-known thermodynamic aspects such as the variation in Gibbs free energy (ΔG), entropy (ΔS), and enthalpy ...

Novel synthesis of ultramarine blue from waste coal fly ash via thiocyanate aluminosilicate sodalite

ABSTRACTThis paper for the first time reports the conversion of coal fly ash into intense blue ultramarine via thiocyanate aluminosilicate sodalite Na8[AlSiO4]6(SCN)2. The possibility of stepwise and systemic conversion of thiocyanate aluminosilicate sodalite into intense blue ultramarine had never been previously demonstrated. The ultramarine analogs of various colors have been prepared by structure conversion of thiocyanate aluminosilicate sodalite by calcination (500–950°C). The products obtained are characterized by various investigative techniques including Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), UV-visible spectroscopy, scanning electron microscopy (SEM), electron spin resonance (ESR) spectroscopy. Surface morphology is studied by the SEM technique. Elemental analysis is carried out with the help of EDAX. Results of ESR have been reported and interpreted. Ultraviolet and Raman spectroscopic analysis gave clear evidence of conversion of SCN− to and further on into . These extensive characterizations showed that the ultramarine pigment is good enough and that the sodalite framework is thermally highly stable with its structure undisturbed even at 950°C.

Developing a zero liquid discharge process for zeolitization of coal fly ash to synthetic NaP zeolite

Successful conversion of coal fly ash (CFA) to synthetic NaP zeolite with zero liquid discharge is reported in this article. The process eliminates the need for large amounts of water and the need for a huge wastewater treatment unit. The need for water, as a make-up stream, is only to compensate water losses during sampling and drying. Savings associated with minimizing make-up water and eliminating wastewater treatment unit can be substantial. Water and sodium hydroxide consumption is reduced by 90% and 50%, respectively. Furthermore, quality of the NaP zeolite (CFA-ZP) obtained is comparable to conventional method. The zeolitized product shows high crystallinity and leach resistance toward heavy metal and trace element content of the product. Leaching tests revealed that the concentrations of most of trace elements in leachate of CFA-ZP were less than threshold limit for landfill leachate and wastewater effluent for discharging into river and surface water.

Conversion of coal fly ashes into faujasite under soft temperature and pressure conditions: Influence of additional silica

The hydrothermal conversion of a French coal fly ash (FA) into NaX zeolite (faujasite) was studied under soft conditions (30 °C, atmospheric pressure). One used molar composition had previously been found during a preliminary study aiming to determine an optimal composition for the synthesis of NaX from this FA, i.e., 1SiO 2:0.36Al 2O 3:3.8NaOH:72.7H 2O, the Al 2O 3/SiO 2 ratio corresponding to the one of the FA, and the zeolitisation procedure consisting only in adding a NaOH solution to the FA. As this composition is much poorer in silica than the one given in the literature for the synthesis from commercial reactants, new experiments were performed with addition of external soluble silica, leading to the following composition: 1SiO 2:0.17Al 2O 3:4.0NaOH:75.5H 2O. The zeolitisation kinetics – followed mainly by XRD and N 2 adsorption – were compared in presence or absence of additional silica. The addition of silica leads to a final higher content in faujasite (30 wt.% instead of 20–25 wt.%), a higher purity of the zeolitic fraction (co-formation of traces of other more stable zeolites avoided). In presence of external silica, the faujasite crystals are also smaller and display a slightly higher Si/Al framework ratio (1.2 instead of 1.1). One significant point is that the addition of soluble silica leads to a better solubilisation of the FA, about 20% more Al being mobilised. Finally, the zeolisation reaction is delayed when silica is added, the maximum faujasite content being reached after about 50 days instead of about 20 days.

Preparation of activated carbon–zeolite composite materials from coal fly ash

Composite materials consisting of activated carbon and zeolites, which are expected to be suitable for environmental applications, were successfully prepared using coal fly ash with unburned carbon of ca. 8.0 mass% as a source material. The main components (SiO 2 and Al 2O 3) along with unburned carbon were activated by NaOH fusion treatment at 750 °C in a N 2 atmosphere, and subsequently converted into zeolites Na–X and/or Na–A with good crystallinity by hydrothermal treatment. The type of zeolite phase formed was dependent on the hydrothermal treatment conditions including NaOH concentration. In this report, the influence of preparation parameters and the presence or absence of unburned carbon on the chemical conversion of coal fly ash into composite materials consisting of activated carbon and zeolites is described.

Conversion of coal fly ash to composite materials with zeolite and activated carbon

Conversion of coal fly ash to composite materials with zeolite and activated carbon

Conversion of coal fly ash to Na-X zeolites

Coal ash is formed by combustion of coal in coal-fired power station as a waste product. In the world and Japan, the amounts of coal ash formed are approximately 500 and 5 million tons per year, respectively, and are predicted to increase [1]. The coal ash can be separated into two forms: one is fly ash (Fa) and another is clinker ash. The Fa is collected at the top of burner using cyclones, electric precipitators, or mechanical filters. Whereas, the clinker ash is obtained from bottom of furnace as a mass of fused rock. The proportion of Fa generated is occupied 84% of total coal ash [2]. In the world, only 15% of the Fa are used as a raw material of cement and concrete, and the remaining Fa is disposed of for reclamation [1]. Although, Fa contains various hazardous heavy metals, for instance, As, Pb, Sn and Cd [3]. Therefore, resource recover of Fa is of concern at present. It has been known that Fa is mainly composed of amorphous aluminosilicate with some crystals such as α-quartz (SiO2), mullite (2SiO2 · 3Al2O3), hematite (α-Fe2O3) and magnetite (Fe3O4) [4] and can be converted to zeolites in alkali solutions by hydrothermal treatment [5–10]. Since the faujasite possesses large pore openings and large cavities, this material is used as catalysts, washing builder, cation exchangers, adsorbents and so forth. The conversion of Fa to faujasite has been studied by Henmi [5] and LaRosa et al. [8]. They treated Fa in NaOH aqueous solutions at 80–90 ◦C to produce faujasite. However, not only faujasite but also other type zeolites such as zeolite P and phillipsite were formed. Recently, a single phase of faujasite has been synthesized from Fa fused with NaOH at 550 ◦C [11–13]. The disadvantage of this technique is that fusion of Fa requires a high temperature. In this study, we report the synthesis of a single phase of faujasite from Fa by treating in NaOH aqueous solutions below 100 ◦C without fusion process. The chemical composition of Fa supplied from Nippon Steel Co. was determined by a Rigaku X-ray fluorescence spectrometer (XRF) and is listed in Table I.

Formation of Na-A and -X zeolites from waste solutions in conversion of coal fly ash to zeolites

Na-A and -X zeolites were synthesized from waste solutions in conversion of coal fly ash (Fa) to zeolite. The amorphous SiO 2 and Al 2O 3 of Fa were completely dissolved to form Po, Pt, and Pc type zeolites in NaOH solutions at 85°C. Only 24% of Si 4+ eluted from Fa were converted to the zeolites and the remaining waste solutions contained high Si 4+ concentrations. When molar ratio SiO 2/Al 2O 3 of the waste solutions was modified at 1.0≤SiO 2/Al 2O 3≤2.0 by addition of NaOH–NaAlO 2 solutions and the solutions were agied at 85°C, a single phase of Na-A zeolite was formed. The Na-X zeolite was formed at SiO 2/Al 2O 3≥2.5 and its crystallinity was increased with increasing the SiO 2/Al 2O 3 ratio, whereas the crystallinity of Na-A zeolite was decreased. At SiO 2/Al 2O 3=7.3, a single phase of Na-X zeolite was produced.