Synthesis and characterization of magnetic adsorbent prepared by magnetite nanoparticles and zeolite from coal fly ash

Magnetite nanoparticles were prepared by partial oxidation of Fe(II) ions of an aqueous suspension of hydroxysulfate green rust which was obtained by precipitation of Fe(II) ions. This magnetite was mixed with zeolite synthesized from coal fly ash to obtain the magnetic adsorbent and the final product characterization was made. By analysis of scanning electron microscopy and X-ray diffraction, images of clusters of magnetite nanoparticles were observed and crystallite sizes of 17 nm were determined, respectively. In thermal analysis, the weight ratio of 1:3 for magnetite-zeolite in the magnetic adsorbent was measured and a non-magnetic product at 974 °C was found in both magnetite and magnetic adsorbent. Magnetization measurements described small hysteresis from the clusters of magnetite nanoparticles. Fourier Transform Infrared spectroscopy analysis indicated that the synthesized zeolite is a hydroxy sodalite and evidences of formation of the magnetic adsorbent were observed. The performance of magnetic separation technique was evaluated and it was comparable to the centrifugation process. The magnetic adsorbent indicated a potential application for adsorption of dye Reactive Orange 16 from aqueous solution.     

Formation process of Na-X zeolites from coal fly ash

In order to synthesize Na-X zeolite from coal fly ash (Fa), Fa was pretreated under stirring condition at various temperatures of 20–50°C for 72 h and then aged at 85°C for a given period with NaOH solutions. The resulting materials were characterized by various means. When Fa was aged for 72 h without pretreatment, species P were formed. As the pretreating temperature raised from 20 to 50°C, the degree of crystallinity of faujasite increased, while that of species P decreased. The faujasite species formed was identified as Na-X zeolite with molar ratio SiO₂/Al₂O₃ = 2.4. When Fa was pretreated at 50°C and aged for 60 h, the only species formed was Na-X zeolite. Increasing the pretreating temperature up to 50°C results in the increase of Si⁴⁺ and Al³⁺ concentrations in the treating solution by dissolution of amorphous material in Fa. With the conditions used, the crystalline phase, such as -quartz and mullite, was poorly dissolved during the treatment. Hence, the higher pretreating temperature would give the uniform nucleation and crystal growth of Na-X zeolite during the aging.     

Comparison of the properties of glass, glass-ceramic and ceramic materials produced from coal fly ash

Glass, glass-ceramic and ceramic materials were produced from thermal power plant fly ash without any additives. X-ray diffraction (XRD) analysis revealed the amorphous phase of the glass sample. Augite phase was detected in the glass-ceramic sample, while the enstatite and mullite phases occurred in the ceramic samples. Scanning electron microscopy (SEM) investigations showed that tiny crystallites homogeneously dispersed in the microstructure of the glass-ceramic sample and elongated crystals formed in the ceramic samples. Density values of the obtained samples are comparable to those of the commercially produced glass, glass-ceramic and ceramic samples. Toxicity characteristic leaching procedure (TCLP) results indicated that the produced samples could be taken as non-hazardous materials. Produced samples showed high resistance to alkali solutions in contrast to acidic solutions. Microstructural, physical, chemical and mechanical properties of the produced glass-ceramic samples are better than those of the produced glass and ceramic samples.     

Coal fly ash and synthetic coal fly ash aggregates as reactive media to remove zinc from aqueous solutions

Coal fly ash (CF) and synthetic coal fly ash aggregates (SCFAs) were evaluated as low-cost reactive media for the remediation of groundwater contaminated with Zn. The SCFAs were prepared by mixing CF, sodium silicate, and deionized (DI) water. Serial batch kinetic and static tests were conducted on both CF and SCFAs, under various conditions (i.e., pH, initial Zn concentration, reaction time, and solid dosage), using Zn(NO(3))(2).6H(2)O solutions. Serial column tests were also conducted on both CF and SCFAs. The final rather than the initial pH of the solution had a greater effect on the removal of Zn. At pH>7.0, the removal of Zn was due to precipitation, whereas at <7.0, the removal of Zn was due to adsorption onto the reactive media. The removal of Zn increased with increasing dosage of the reactive medium and decreasing initial Zn concentration. The results of the column and batch tests were comparable. Preferential flow paths were observed with CF, but not SCFA. The hydraulic conductivity of CF was more significantly decreased than that of SCFA with increasing dry density of the specimen.     

Adsorption of herbicides on coal fly ash from aqueous solutions

Development of low cost adsorbent for pesticide retention is an important area of research in environmental sciences. The present study reports the sorption potential of coal fly ash, a waste from power stations, for removal of metribuzin, metolachlor and atrazine from water. Batch sorption method was used to study the sorption of herbicides from water. The amount of herbicides sorbed increased with increase in the amount of fly ash in the suspension. The maximum capacity of the fly ash to adsorb metribuzin, metolachlor and atrazine was found to be 0.20, 0.28 and 0.38 mg/g by Freundlich equation and 0.56, 1.0 and 3.33 mg/g by Langmuir equation. Freundlich adsorption equation better explained the results of herbicides sorption in fly ash as regression coefficient (R²) values were higher from Freundlich equation than the Langmuir equation. Adsorption isotherms were L-type suggesting that the herbicide sorption efficiency of fly ash depend on the initial concentration of herbicide in the solution and maximum removal of herbicide was observed at concentrations less than 10 μg/ml. The results of this study have implications in using the fly ash for removal of these herbicides from industrial and agricultural waste water and can find use as a material in the preparation of biobeds to minimize environmental contamination from pesticide use.     

Heavy metal accumulation from coal fly ash by cyanobacterial biofertilizers

Bioleaching of heavy metals (Cu, Zn, Cr and Pb) from coal fly ash by cyanobacterial strains (Nostoc muscorum, Anabaena variabilis, Tolypothrix tenuis and Aulosira fertilissimia), that are commonly used as biofertilizers in rice cultivation was studied to assess utilization of fly ash while mitigating its environmental metal toxicity. Cyanobacteria were grown at different concentration of fly ash at 0, 5, 10, and 20% was treated with different blue green algal strains (Nostoc muscorum, Anabaena variabilis, Tolypothrix tenuis, and Aulosira fertilissimia) in suitable growth medium (BG-11) and distilled water to observe their growth and metal accumulation. Nostoc muscorum (ARM 442?mg?g^?1) showed maximum uptake of Cr (3.65?mg?g^?1), Pb (2.12?mg?g^?1) at BG 11(-N) medium amended with 10% fly ash, respectively. Anabaena variabilis (ARM 441) showed maximum uptake of Cu (0.313?mg?g^?1) and Pb (2.01?mg?g^?1) in BG 11 (–N) medium amended with 5% fly ash whereas Cr uptake (1.21?mg?g^?1) at 10% fly ash and Zn uptake (0.697?mg?g^?1) at 20% fly ash grown in BG 11(-N) medium. Increased accumulation of metals in blue green algae biomass grown in BG 11(-N) medium amended fly ash confirms that metal concentration was balanced between the algal strains.     

Dielectric properties of fly ash

This paper reports the dielectric properties of fly ash. The dielectric measurements were performed as a function of frequency and temperature. The sample of fly ash shows almost similar behaviour in the frequency and temperature range studied. The large value of dielectric constant in the typical frequency range is because of orientation polarization and tight binding force between the ions or atoms in the fly ash. The sample of fly ash is of great scientific and technological interest because of its high value of dielectric constant (10⁴).     

MSW fly ash stabilized with coal ash for geotechnical application

The solidification and stabilization of municipal solid waste (MSW) fly ash for the purpose of minimizing the geo-environmental impact caused by toxic heavy metals as well as ensuring engineering safety (strength and soaking durability) are experimentally evaluated. The mixtures of MSW fly ash stabilized with cement and fluidized bed combustion coal fly ash (FCA) were used for unconfined compressive strength tests, leachate tests, and soaking tests. The behavior of soluble salts contained in the MSW fly ash significantly affects strength development, soaking durability, and the hardening reaction of the stabilized MSW fly ash mixtures. The cement stabilization of the MSW fly ash does not have enough effect on strength development and soaking durability. The addition of cement only contributes to the containment of heavy metals due to the high level of alkalinity. When using FCA as a stabilizing agent for MSW fly ash, the mixture exhibits high strength and durability. However, the Cd leachate cannot be prevented in the early stages of curing. Using a combination of cement and FCA as a MSW fly ash stabilizer can attain high strength, high soaking durability, and the containment of heavy metals. The stabilized MSW fly ash with cement and FCA can be practically applied to embankments.     

Copper and cadmium adsorption on pellets made from fired coal fly ash

Studies on the utilization of low cost adsorbents for removal of heavy metals from wastewaters are gaining attention. Fired coal fly ash, a solid by-product that is produced in power plants worldwide in million of tonnes, has attracted researchers' interest. In this work, fly ash was shaped into pellets that have diameter in-between 3-8mm, high relative porosity and very good mechanical strength. The pellets were used in adsorption experiments for the removal of copper and cadmium ions from aqueous solutions. The effect of agitation rate, equilibration time, pH of solution and initial metal concentration were studied. The adsorption of both cations follows pseudo-second order kinetics reaching equilibrium after an equilibration time of 72 h. The experimental results for copper and cadmium adsorption fit well to a Langmuirian type isotherm. The calculated adsorption capacities of pellets for copper and cadmium were 20.92 and 18.98 mg/g, respectively. Desorption experiments were performed in several extraction media. The results showed that both metals were desorbed substantially from pellets under acidic solutions. For this reason, metal saturated pellets were encapsulated in concrete blocks synthesized from cement and raw pulverized fly ash in order to avoid metal desorption. The heavy metals immobilization after encapsulation in concrete blocks was tested through desorption tests in several aqueous media. The results showed that after 2 months in acidic media with pH 2.88 and 4.98 neither copper nor cadmium were desorbed thus indicating excellent stabilization of heavy metals in the concrete matrix. As a conclusion, the results showed that fly ash shaped into pellets could be considered as a potential adsorbent for the removal of copper and cadmium from wastewaters. Moreover, the paper proposes an efficient and simple stabilization process of the utilized adsorbents thus guarantying their safe disposal in industrial landfills and eliminating the risk of pollution for groundwater and other natural water receivers.     

The surface chemistry of leaching coal fly ash

The utilization of coal fly ash in the construction and non-construction areas has seen a rapid growth in the last decade. As production outweighs the utilization of fly ash, its disposal as a dilute or dense slurry is still practiced in coal fired power stations. In this review the surface chemistry of leaching coal fly ash is presented to highlight the role of mass transfer in providing resistance and consequently delayed leaching of elements, when fly ash is disposed or used for value addition.     

A study of physico-chemical and mineralogical properties of Talcher coal fly ash for stowing in underground coal mines

This study examines the suitability of Talcher coal fly ash for stowing in the nearby underground coal mines based on their physico-chemical and mineralogical analysis. The physical properties such as bulk density, specific gravity, particle size distribution, porosity, permeability and water holding capacity etc. have been determined. From the chemical characterization it is found that the ash samples are enriched predominantly in silica (SiO₂), alumina (Al₂O₃) and iron oxides (Fe₂O₃), along with a little amount of CaO, and fall under the Class F fly ash category. In addition, the mineral phases identified in the ash samples are quartz, mullite, magnetite, and hematite. The particle morphological analysis revealed that the ash particles are almost spherical in shape and the bulk ash porous in nature. From the particle size and permeability point of view, pond ash may be considered a better stowing material than fly ash.     

Non-hydrothermal synthesis of mesoporous materials using sodium silicate from coal fly ash

Siliceous mesoporous materials with pores of ordered 2-D hexagonal structure were successfully prepared without hydrothermal treatment from condensation–polymerization of various concentration of quaternary ammonium salt as structure directing agents and silica precursor from the supernatant of coal fly ash (CFA) in the presence of catalyst. The synthesized materials had high surface area of ca. 740 m² g⁻¹ and pore volume of ca. 0.42 mL g⁻¹. The synthesized material exhibited a narrow size pore distribution and the mean pore diameter as measured by Dollimore–Heal method was about 2.3 nm. The formation of ammonium salt that act as precipitant during the synthesis enable the hydrolysis and co-condensation of the sodium silicate at room temperature.     

热处理粉煤灰及其胶凝性

在适当煅烧温度下,分别运用Na2CO3、CaO和CaF2等材料对二级低钙粉煤灰进行了改性研究,从而促进了粉煤灰活性的发挥.运用XRD、TGA等测试方法,研究了热处理粉煤灰的晶相组成及其水化特性.研究表明,粉煤灰能够和这些组分发生化应,形成NaAlSiO4、CaO·Al2O3·SiO2、α-Ca2SiO4和Na,Ca)(SiAl4)4O8等晶相,玻璃态网络结构也发生了相应的变化.热处理粉煤灰表现出了良好的胶凝性能.上述3种组分对粉煤灰活性的影响不尽相同,其中CaF2对粉煤灰的活性有更加积极的影响.     

燃煤锅炉灰渣中可燃碳含量的分析方法

采用工业分析法、元素分析法和热重质谱联用加等效特征图谱法,对循环流化床锅炉的飞灰及炉渣中可燃碳含量进行分析。结果表明:工业分析法和元素分析法无法完全排除水分、消石灰、碳酸盐和硫酸盐等物质的影响,热重质谱联用加等效特征图谱法可排除水分、消石灰、碳酸盐和硫酸盐等物质的影响,可精确测量飞灰及炉渣中可燃碳含量。     

Removal of trivalent chromium from aqueous solution by zeolite synthesized from coal fly ash

The capability of 14 zeolites synthesized from different fly ashes (ZFAs) to sequestrate Cr(III) from aqueous solutions was investigated in a batch mode. The influence of pH on the sorption of Cr(III) was examined. ZFAs had a much greater ability than fly ash to remove Cr(III), due to the high cation exchange capacity (CEC) and the high acid neutralizing capacity (ANC) of ZFAs. The mechanism of Cr(III) removal by ZFAs involved ion exchange and precipitation. A high-calcium content in both the fly ashes and ZFAs resulted in a high ANC value and, as a result, a high immobilization capacity for Cr(III). The pH strongly influenced Cr(III) removal by ZFAs. Inside the solubility range, removal of chromium increased with increasing pH. Hydroxysodalite made from a high-calcium fly ash had a higher sorptive capacity for Cr(III) than the NaP1 zeolite from medium- and low-calcium fly ashes. On the other hand, at pH values above the solubility range, the efficiency of chromium removal by the ZFAs approached 100% due to the precipitation of Cr(OH)3 on the sorbent surfaces. It is concluded that ZFAs and high-calcium fly ashes may be promising materials for the purification of Cr(III) from water/wastewater.     

Utilization of coal fly ash in the glass-ceramic production

Manufacturing the glass-ceramic has been proposed as a useful choice to recycle coal fly ash from power plants. In this work, a glass-ceramic of SiO2-Al2O3-Fe2O3-CaO family was synthesized by mixing 90 wt% of coal fly ash, from a power plant in west of China, with Na2O, and then melted at 1350 degrees C. The ceramization of the obtained glass was carried out at 770 degrees C for 2h. Esseneite and nepheline were found present as major crystal phases. The produced glass-ceramic exhibited good chemical durability as well as good mechanical properties. The toxicity characteristic leaching procedure (TCLP) method found that the glass-ceramic was non-hazardous.