原料粒度对粉煤灰成型吸附剂结构和性能的影响(英文)

In this paper, different particle sizes of coal fly ash FA-R (D50=15.75μm), FA-A (D50=3.61μm) and FA-B (D50=1.73μm) were treated with NaOH solution to prepare the forming adsorbents FFA-R, FFA-A and FFA-B. The structure and adsorption properties of the forming adsorbents for methylene blue (MB) from aqueous solu-tion were examined. The results showed that the specific surface areas and adsorption capacities of the forming adsorbent for MB increased with decreasing particle size of raw coal fly ashes. The adsorption kinetic data of MB on FFA-R, FFA-A and FFA-B fitted the second-order kinetic model very wel with the rate constants (k2) of 3.15 × 10?2, 3.84 × 10?2 and 6.27 × 10?2 g·mg?1·min?1, respectively. The adsorption process was not only con-trol ed by intra-particle diffusion. The isotherms of MB on FFA-R, FFA-A and FFA-B can be described by the Lang-muir isotherm and the Freundlich isotherm, and the adsorption processes were spontaneous and exothermic. ? 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.     

Effect of particle size and alkali activation on coal fly ash and their role in sintered ceramic tiles

We focus on fly ashes of different sizes and their alkali-activation on ceramic products. Backscattered electron imaging-energy dispersive X-ray spectroscopy was used to classify coal fly ash particles according to particle size and to study the pre-activation of particles with different sizes. Secondary electron imaging-energy dispersive X-ray spectroscopy was used to study the role of coal fly ash particles of different sizes in ceramic bodies before and after alkali-activation. Ash particles can be divided into three classes based on size: clay-, quartz- and feldspar-like particles, which act as clay, quartz and feldspar, respectively, in ceramic bodies. The pre-activation process contributes to the plasticity of ash particles, the crystal skeleton role of clay-like particles and the fluxing agent role of feldspar-like particles, so preprocessing can improve the performance of ash-based ceramic tiles significantly. This research provides a new pretreatment method for coal fly ash in ceramic fields.     

Effects of particle size on microstructure and mechanical strength of a fly ash based ceramic membrane

Recycling fly ash for ceramic membrane fabrication not only reduces solid waste discharge, but also decreases the membrane cost. Now, fly ash is becoming a promising substitute material for ceramic membrane preparation. A significant difference between fly ashes from different plants is the particle size, which makes performances of fly ash membranes unpredictable. The novelty of this work is to clarify the effects of the particle size of fly ash on ceramic membranes, thereby giving practical suggestions on fly ash selection for ceramic membrane preparation. Ceramic membranes were fabricated with different sizes of fly ashes. Effects of particle size on porosity, pore size, microstructure, mechanical strength and gas permeability of the membrane were investigated. Results indicate that a broader particle size distribution of fly ash leads to a denser structure of membrane with a lower porosity. Pore size and gas permeability of membrane increase while bending strength decreases with the particle size increasing. Bending strength of a fly ash membrane is largely determined by large particles in the fly ash because the large particles lead to cracks in the membrane. This work provides experimental bases for developing high performance ceramic membranes from fly ash.     

Hydrothermal synthesis of zeolites from coal fly ash

The fly ash, from the combustion of coal to produce energy and heat, is an industrial waste, in which large accumulations represent a serious environmental threat. To reduce the environmental burden and improve the economic benefits of energy production, the science and industry focus on the transformation of coal combustion byproducts into new functional materials. The fly ash was studied by modern analytical methods. As a result of the hydrothermal reaction, several types of zeolites were synthesised from the fly ash: analcime, faujasite (zeolite X) and gismondine (zeolite P). It was shown that the experimental conditions (temperature, reaction time and alkali concentration) have a significant influence on the type of zeolite and its content in the reaction products. The series of experiments resulted in building approximate crystallisation field of zeolites and other phases as the first stage of the formation of ceramic membrane and other materials.     

粉煤灰在酸性废水处理中的应用

粉煤灰是燃煤电厂排放的固体废弃物。近年来,人们开始致力于粉煤灰在环境保护方面的开发利用,其处理废水已经成为研究的热点之一。本文综述了近年来国内粉煤灰处理工业酸性废水的研究进展,并介绍了粉煤灰处理酸性废水的机理、存在的问题及其应用前景。     

Adsorptive removal of thiophene and benzothiophene over zeolites from Mae Moh coal fly ash

Zeolites have been hydrothermally synthesized using Thai coal fly ash from Mae Moh Power Plant as silica and alumina sources. The synthesis conditions, i.e., SiO₂/Al₂O₃ ratio, amount of water, amount of base, and aging temperature, were varied to prepare different topologies of zeolitic products. The zeolites attained were sodalite (SOD), gismondine (GIS), and cancrinite (CAN). The zeolites have been applied to adsorption of thiophene and benzothiophene in n-hexane solution. It was found that GIS with higher specific surface area and average pore volume had superior performance to other synthesized materials. Adsorption capacity of our developed zeolites was compared to those of commercial zeolites, i.e. NaY, HUSY, beta, and ZSM-5 obtained via the conventional synthesis methods. The results suggested a potential of zeolites derived from Mae Moh coal fly ash for removal of refractory sulfur compounds, such as benzothiophene.     

Investigations on Cr mobility from coal fly ash

Coal fly ash, which is a source of metals emission to environment, was researched. Investigations on Cr chemical fractions and their environmental mobility in ash-solution system were carried out. In order to obtain results repeatedly, the conditions of sequential extraction of Cr from coal fly ash were optimized. It was found that Cr in coal fly ash occurs in the following fractions (mg kg⁻¹): exchangeable (2.5), associated to carbonates (4.0), associated to organic matter and sulfides (8.5), associated to Fe-Mn oxides (16.0), and residual (41.6). Mobility fractions of Cr contain 8.2% of its total concentration in the fly ash in environmental conditions. The obtained results indicate that coal fly ash is a source of environmental contamination by Cr especially, in soils where its utilization is inadequate.     

分选与磨细粉煤灰对水泥胶砂性能的影响

研究了分选与磨细粉煤灰的颗粒分布与形貌的差异及对水泥胶砂性能的影响。研究结果表明:当勃氏比表面积相近,磨细粉煤灰的中位粒径大于分选细粉煤灰,其圆珠状颗粒较少,表面较为粗糙。在相同水胶比的条件下,掺分选粗粉煤灰的水泥胶砂流动度及强度均低;分选粗粉煤灰磨细后,不仅减少了颗粒的粘连,增加了比表面积,而且提高了粉煤灰的反应活性和水泥胶砂流动度及强度,虽其水泥胶砂流动度仍小于掺分选细粉煤灰的水泥,3d水泥胶砂强度也略低,但其28d水泥胶砂强度略高于掺分选细粉煤灰的水泥;在相同水泥胶砂流动度的条件下,掺磨细粉煤灰配制的水泥胶砂3d强度低于掺分选细粉煤灰的水泥,但随着水化龄期的增长,其差距逐步缩小,至60d时可超过后者。     

Production of glass from coal fly ash

The coal fly ash from a Chinese thermal power plant was vitrified after the addition of ∼10 wt% Na₂O. The glass products have suitable viscosity at 1200 °C and displayed a good chemical durability. The heavy metals of Pb, Zn, Cr and Mn were successfully immobilized into the glass as determined by the toxicity characteristic leaching procedure method. Results indicate an interesting potential for the coal fly ash recycling to produce useful materials.     

Influence of trace metal distribution on its leachability from coal fly ash

The risks associated with the reuse of coal fly ash in natural environmental settings in terms of their mobility and ecotoxicological significance is largely determined by: (1) the physicochemical conditions the fly ash is placed under; (2) the total leachable metal content in fly ash and; (3) the distribution or mineralogical fractionation of metals. In this study, we report the mobility of As, Cr, Pb, Fe, Cu and Zn from a single Class F fly ash (CFFA). The influence of pH on metal release was compared to the total leachable metal content, as determined by single and sequential chemical extractions. The results show that the CFFA sample is environmentally safe under natural pH conditions, with metal leaching less than the mandated RCRA limits. The elements Fe, Pb and Cr were moderately soluble at acidic pH and sparingly soluble beyond neutral pH. Arsenic release from CFFA was higher under aggressive pH conditions (pH < 4 and pH > 9) and consistent with its oxyanionic behavior. Partial dissolution of the acid soluble (exchangeable) fraction at acidic pH; desorption of oxyanions at alkaline pH; adsorption and or co-precipitation of metals with iron (hydr) oxides at neutral pH appeared to be the probable mechanisms controlling metal release. While simple EDTA extractions provided good indications of the total leachable amounts, a direct correlation with pH leaching data was impossible as the mineralogical distribution of the metals in the fly ash appeared to play a significant role in their leachability. In the case of Class F fly ash, metal association with Fe-oxide appeared to play a more dominant role in metal release.     

粉煤灰合成人造沸石除磷效果的研究

以粉煤灰为原料,在微波场下水热合成人造沸石,可缩短结晶时间.将这种人造沸石应用于污水处理实验,处理城市景观用水,控制水体富营养化的氮、磷指标.氨氮的去除机理主要为离子交换,而磷的去除机理的研究目前尚缺乏相关资料.合成沸石中含磷量较低时,不影响在污水处理中的应用.     

Application of B MAS-NMR to the characterization of boron in coal fly ash generated from Nantun coal

Boron and its compounds are environmentally hazardous substance and are well-known condensed products that appear in coal fly ash during combustion of coal in coal-fired electric power stations. In a previous study, we suggested that boron in coal fly ash obtained from Nantun coal in China, identified as Ash-N, may exist on the surface of relatively large coal fly ash particles or as very fine particles generated by homogeneous nucleation. Although the characterization of boron in coal fly ash is important for its effective stabilization or removal, its detection is quite difficult because of its low concentration in coal fly ash and its light atomic weight. In the present work, solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) technique has been applied to reveal the local chemical structures of boron in Ash-N. In the ¹¹B MAS-NMR spectrum of Ash-N, two peaks which are attributed to a three-oxygen coordinated boron unit (BO₃) and a four-oxygen coordinated boron unit (BO₄) were observed with high resolution. We have estimated quadrupole parameters of the BO₃ unit in Ash-N using computer simulation, and we have fingerprinted these moieties with the parameters of borates. The result of the present analysis shows that calcium- or magnesium-bearing orthoborate or pyroborate are the most likely forms of boron in Ash-N.     

不同粒径改性粉煤灰对磷酸根吸附性能的影响

废水排放过量的磷导致水体污染日益严重,将粉煤灰通过化学改性制备成了水化硅酸钙吸附剂,研究了改性吸附剂对磷酸根的吸附效果。利用XRD, SEM及BET比表面积等手段对粒度分级前后的吸附剂进行表征,研究不同粒级吸附剂对磷酸根的吸附性能,并考察其吸附机理。结果表明,不同粒级的吸附剂其化学成分出现了明显的偏析现象,孔隙结构也差异显著。相比其他粒径下的吸附剂颗粒,颗粒粒径在50?75 μm时,吸附剂中钙和硅含量较多,铝、铁和镁含量较低,水化硅酸钙组分含量最高,且伴有含铝的托贝莫来石晶体出现,钙离子的增加使其可以与更多的磷酸根结合形成沉淀。同时此粒径下具有较高的比表面积及孔隙度,疏松多孔的结构为钙离子提供更多活性位点。当使用粒径在50?75 μm的吸附剂吸附磷酸根时,磷的饱和吸附量可达到17.1 mg/g,比未分级的吸附剂高19.58%。     

Ceramic tiles derived from coal fly ash: Preparation and mechanical characterization

Coal fly ash (CFA) accounts for a large fraction of the solid waste produced in China. Hence, there is an urgent need for the effective utilization of CFA, for example, as a raw material for ceramics production. In this study, clay- and feldspar-like materials fabricated by alkali activation pre-treatment of CFA were mixed with untreated CFA (regarded as a quartz-like material) and sintered to prepare fully ash-based ceramic tiles. The obtained tiles exhibited excellent sintering properties, e.g., low firing temperature and a wide sintering range; further, they showed better green strength (due to hydrogen bonding) and post-sintering performance (due to fluxing and mullite skeleton effects) than ceramic tiles produced exclusively from untreated CFA. The fully ash-based ceramic tiles sintered at 1100 °C exhibited optimal post-sintering properties (bulk density, 2.5 g/cm³; rupture modulus, 50.1 MPa; and water absorption, 0%). Thus, the proposed method is well suited for preparing a novel kind of ceramic tiles completely derived from CFA, highlighting its importance in the field of fly ash ceramics.     

Phosphate removal in marine electrolytes by zeolite synthesized from coal fly ash

The aim of this study was to examine the influence of seawater electrolytes on removal of phosphate by zeolite synthesized from fly ash (ZFA). A low-calcium ZFA was initially saturated with Na⁺, Mg²⁺, Ca²⁺, Al³⁺, and Fe³⁺. Al- and Fe-ZFA showed nearly complete removal of phosphate regardless of the major seawater electrolytes, pH, and salinity. This result was explained primarily on the basis of the adsorption mechanism through the formation of inner-sphere complexes. The remaining ZFAs showed lower phosphate removal performance, in general with the order of Ca-ZFA > Mg-ZFA > Na-ZFA. Compared with pure water, increase of electrolyte concentration or salinity initially enhanced phosphate uptake but then reduced phosphate removal. The individual presence of major seawater electrolytes all facilitated the retention of phosphate, with CaCl₂ being the most effective. The mechanism for phosphate removal by Na-, Mg-, and Ca-ZFA was due mostly to precipitation. Repeated batch equilibration experiments indicated that, compared with pure water, ZFA had greater sorptive capacity for phosphate (except for Ca-ZFA, whose capacity decreased slightly) and had lower reversibility for sorbed phosphate in marine electrolytes. In conclusion, our results suggest that presence of seawater electrolytes had roughly no effect, or even positive effects, on the removal of phosphate by ZFA.     

Preparation and characterization of mullite whisker reinforced ceramics made from coal fly ash

Ceramics with mullite whiskers were prepared from coal fly ash and Al₂O₃ raw materials, with AlF₃ used as an additive. The phase structures and microstructures of the ceramics were identified via X-ray diffraction and scanning electron microscopy, respectively. The results show that pickling of coal fly ash is an effective method for enhancing the flexural strength of ceramics. Sintering temperature and AlF₃ addition were also key factors influencing the creation of ideal ceramics. The ceramic made from pickled coal fly ash, 6?wt% AlF₃, and sintered at 1200?°C, exhibited the highest flexural strength of 59.1?MPa, and had a bulk density of 1.32?g/cm³ and porosity of 26.8%. The results show that ceramic materials made under these conditions are ideal candidates for manufacturing ceramic proppants for the exploitation of unconventional oil and gas resources.     

Adsorption of heavy metal cations using coal fly ash modified by hydrothermal method

In this study, the adsorption properties of synthetic zeolite produced from Brazilian coal fly ash were investigated for some heavy metal cations (Zn, Cu, Mn and Pb). The batch method has been employed, using metal concentrations in solution ranging from 100 to 3000 mg/l. Preliminary statistical analysis has indicated that temperature and time of synthesis of zeolites were the most important variables that affect the their adsorption capacity. Results lead to the conclusion that a hydrothermal treatment can increase from 2 to 25 times the adsorption capacity (CA) of the coal ash comparing to its original capacity. The ion-exchange characteristic of the zeolites was determined using Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich isotherms. The adsorption increases as cation concentrations in aqueous solution increases. The preference order observed for adsorption is Pb > Cu > Zn > Mn.     

煤粉炉粉煤灰与循环流化床粉煤灰矿物学性质比较

为了提高粉煤灰的利用率,通过化学成分分析、扫描电子显微镜(SEM)分析、X射线衍射光谱(XRD)分析和核磁共振分析,对煤粉炉和流化床2种粉煤灰的形貌、物相组成和活性进行了表征,研究了2种粉煤灰矿物学性质的差别。试验结果表明:2种粉煤灰在形貌和物相上存在较大的区别。形貌上,煤粉炉粉煤灰中存在大量的玻璃微珠,而流化床粉煤灰由于成灰温度低不存在玻璃微珠;物相上,煤粉炉粉煤灰中存在较大量的结晶类矿物,而流化床粉煤灰多为非晶玻璃态物质。通过核磁共振分析发现煤粉炉粉煤灰中硅氧结构和铝氧结构的聚合度较高,不利于活性组分溶出。     

Removal of boron from coal fly ash by washing with HCl solution

Boron as an environmentally regulated substance is well known to condense in the coal fly ash generated from coal combustion plants. Since boron in the coal fly ash tends to elute into the soil easily, a technology for its stabilization or removal from fly ash is required. An acid washing process is proposed and studied as one of the candidate technologies for the removal of boron from coal fly ash. A laboratory-scale investigation is conducted on the dissolution behavior of boron in the coal fly ash in a diluted HCl solution. The dissolution of boron and alkaline species is considerably fast and exhibits a behavior different from that of aluminum and silicon, which are major components of the ash. From the kinetic model, it is expected that boron in the ash may mainly be in the form of alkaline or alkaline earth borates that are deposited on the surface of relatively large ash particles of alumino-silicate or may be precipitated as fine particles during coal combustion. This acid washing process is extended to a bench-scale plant and boron is successfully removed from the coal fly ash until its content is less than the regulation limit.