粉煤灰农业利用研究进展

评述粉煤灰农业利用研究进展情况,并讨论其中存在的问题.对未来研究工作进行了展望.     

Characteristics of coal fly ash and adsorption application

Several fly ash samples were collected and their physico-chemical properties were characterised using N₂ adsorption, XRD, SEM, and pH titration. These fly ash samples were applied as low-cost adsorbents for removal of methylene blue and humic acid from aqueous solution. It is found that the adsorption has a close relationship with surface area and pore volume. Higher surface area and pore volume of fly ash will result in higher adsorption of methylene blue (MB) and humic acid (HA). The adsorption of MB and HA on various fly ash samples can reach 7 and 10 mg/g, respectively. Solution pH will also influence humic acid adsorption on fly ash and higher pH will result in lower adsorption. Ionic strength will also influence HA adsorption.     

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.     

Heavy metal characterization of CFB-derived coal fly ash

The present study investigates the heavy metal content of coal fly ash (FA) samples coming from three different sampling points (secondary cyclone, cooler and filter) of a pilot plant combustion facility. The combustion experiments were carried out in a 0.1 MW Circulated Fluidized Bed (CFB) boiler using South African coal, with the addition of limestone for sulfur capture. FA was tested for the presence of selected heavy metals using inductively coupled plasma optical emission spectrometry (ICP-OES); batch leaching tests were conducted as well. The samples were also characterized in terms of their microstructure, chemical and mineralogical composition, total surface area and particle size distribution. Most of the studied metals (Cd, Cr, Cu, Ni, Mn, Zn) showed enrichment in the fine, filter FA particles, while Pb was mostly concentrated in the cooler sample. Regarding leaching characteristics of the examined samples, Cr was found to occur in considerable amounts. Although the use of CFB technology for the combustion of solid fuels steadily gets bigger worldwide, only a very limited number of studies have environmentally assessed CFB-coal FAs to date. Thus, the current study aims to contribute toward building a more integrated knowledge on the environmental impact of this abundant power production by-product.     

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.     

Preparation and characterization of fully waste-based glass-ceramics from incineration fly ash,waste glass and coal fly ash

Municipal solid waste incineration (MSWI) fly ash (FA) is a typical hazardous waste due to its high contents of toxic heavy metals, and hence its disposal has attracted global concern. In this work, it was recycled into environmental-friendly CaO–Al₂O₃–SiO₂ system glass-ceramics via adding coal fly ash (CFA) and waste glass (WG). The effects of CaO/SiO₂ ratios and sintering temperatures on the crystalline phases, morphologies, mechanical and chemical properties, heavy metals leaching and potential ecological risks of glass-ceramics were investigated. The results showed that wollastonite (CaSiO₃), anorthite (CaAl₂Si₂O₈) and gehlenite (Ca₂Al₂SiO₇) were the dominant crystals in the glass-ceramics, which were not affected by CaO/SiO₂ ratio and sintering temperature. The compressive strength increased, while the Vickers hardness and microhardness decreased as increasing the sintering temperatures from 850 to 1050 °C, which reached their maximum values of 660.69 MPa, 6.14 GPa, and 7.43 GPa, respectively. However, the increase of CaO/SiO₂ ratio resulted into the reduction of the three mechanical parameters. As varying CaO/SiO₂ ratio from 0.48 to 0.86, the maximum compressive strength, Vickers hardness and microhardness were 611.80 MPa, 5.43 GPa, and 6.56 GPa, respectively. Besides, all the glass-ceramics exhibited high alkali resistance of >97%. The extremely low heavy metals leaching concentrations and low potential ecological risk of glass-ceramics further revealed its environmentally friendly property and potential application feasibility.     

Mineralogy and geochemistry of Greek and Chinese coal fly ash

In this paper the mineralogy and geochemistry of Greek and Chinese coal fly ash are examined. Annual production of fly ash in China is around 160 Mt while in Greece lignite fly ash accounts around 10 Mt. Even though the mineralogical and chemical composition of the fly ashes coming from these two countries differs, there are common questions on the utilization of this material. The variation of the Greek fly ash’ chemical composition, from Ca-poor to Ca-rich fly ash, has resulted to applications such as dam construction, use in cement and possibly in concrete and road construction. The Chinese fly ash, which is rich in mullite, is broadly applied for brick making.     

煤气化飞灰特性的研究进展

在对煤气化飞灰的物理化学性质、微观形貌、气化反应活性和粘附特性归纳分析的基础上,讨论了气化飞灰的形成机理及其气化过程中的结渣倾向性,并对气化过程中避免飞灰在气化炉内的结渣和在合成气冷却器积灰结垢的措施进行了介绍。最后对气化飞灰的研究热点问题进行了展望。     

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.     

Mineralogy and microstructure of sintered lignite coal fly ash☆

Lignite coal fly ash from the ‘Nikola Tesla’ power plant in Yugoslavia has been characterised, milled, compacted and sintered to form monolithic ceramic materials. The effect of firing at temperatures between 1130 and 1190 °C on the density, water accessible porosity, mineralogy and microstructure of sintered samples is reported. This class C fly ash has an initial average particle size of 82 μm and contains siliceous glass together with the crystalline phases quartz, anorthite, gehlenite, hematite and mullite. Milling the ash to an average particle size of 5.6 μm, compacting and firing at 1170 °C for 1 h produces materials with densities similar to clay-based ceramics that exhibit low water absorption. Sintering reduces the amount of glass, quartz, gehlenite and anhydrite, but increases formation of anorthite, mullite, hematite and cristobalite. SEM confirms the formation of a dense ceramic at 1170 °C and indicates that pyroplastic effects cause pore formation and bloating at 1190 °C.     

改性粉煤灰在水处理方面的研究

随着电力工业的发展,燃煤电厂中粉煤灰排放量逐年增加,粉煤灰的有效利用逐渐引起人们的重视。由于粉煤灰表面多孔,且其上所含有氧化铝和氧化硅能与吸附质通过化学键结合,经过改性后,其吸附性能更加得到提高,因此,在废水处理领域具有良好的应用。本文介绍了粉煤灰在水处理方面的作用机理,归纳了粉煤灰的改性方法,阐述了改性粉煤灰在NH3-N废水、含磷废水、重金属废水、酸性矿井污水和染料废水中的应用进展。     

Preparation of zeolitic adsorbents from waste coal fly ash

Power plants burning coal generate a large amount of fly ash as waste matter. The objective of this study is to produce zeolitic adsorbents that possesses high adsorptive capacity for toxic cations. The sample was first pretreated with a High Intensity Magnetic Separator for the removal of iron and magnetic materials (mainly Fe₂O₃ and TiO₂). The zeolitic adsorbents were prepared under the various conditions of NaOH concentration (1–5 N), reaction time from 3 to 96 hours and at the various temperatures of 60, 80 and 100°C. The results of the experiment showed that the coal fly ash should be synthesized with 4 N NaOH for 48 hours at 100°C in order to have good adsorptive capacity. The zeolitic adsorbents showed higher cation exchange capacity values than the natural zeolite in removing NH ₄ ⁺ , Pb²⁺, Ca²⁺and Cd²⁺ions.     

火力发电厂燃煤飞灰润湿性能

化学团聚是控制燃煤电厂细微颗粒排放最有效的方法之一。颗粒物被团聚剂润湿是化学团聚的首要步骤。以小龙潭电厂燃煤飞灰为对象,采用激光粒度仪研究了燃煤飞灰在十二烷基硫酸钠(SDS)、十二烷基苯磺酸钠(SDBS)和Triton X 100(TX100)三种润湿剂溶液中的润湿性能,考察了润湿剂浓度、温度对燃煤飞灰润湿性能的影响。结果表明：水仅能将飞灰颗粒中的PM^₁₀+部分全部润湿,0.25%的SDS溶液中PM_2.5⁺可全部润湿,1%的SDS及0.4%的SDBS溶液中PM₁⁺可全部润湿;TX100溶液在低浓度条件下具有较强的润湿飞灰颗粒的能力,且0.1%的TX100溶液对细微颗粒的润湿性能较好;温度从20℃上升到60℃,润湿剂溶液表面张力降低,飞灰的润湿性能增强。鉴于飞灰在三种润湿剂中良好的润湿性能,三种润湿剂均可作为团聚剂组分以促进燃煤飞灰中的细微颗粒润湿进而被团聚成为容易脱除的大颗粒。     

Adsorption of an acid dye onto coal fly ash

In this study, we found the raw coal fly ash (CFA) that had not been subjected to any pretreatment process had superior adsorbing ability for the anionic dye Acid Red 1 (AR1) than did two modified coal fly ashes (CFA-600 and CFA-NaOH). The adsorption capacities followed the order CFA > CFA-600 > CFA-NaOH, and they each increased upon increasing the temperature (60 °C > 45 °C > 30 °C). The adsorptions of AR1 onto CFA, CFA-600, and CFA-NaOH all followed pseudo-second-order kinetics. The isotherms for the adsorption of AR1 onto the raw and modified coal fly ashes fit the Langmuir isotherm quite well; the adsorption capacities of CFA, CFA-600, and CFA-NaOH for AR1 were 92.59–103.09, 32.79–52.63, and 12.66–25.12 mg g^?1, respectively. According to the positive values of ΔH° and ΔS°, these adsorptions were endothermic processes. The ARE and EABS error function methods provided the best parameters for the Langmuir isotherms and pseudo-second-order equations, respectively, in the AR1–CFA adsorption system.     

Nano-crystal glass-ceramics obtained from high alumina coal fly ash

Glass has been obtained by melting high alumina coal fly ash with fluxing additives. A thermal treatment was employed to convert the obtained glass into nano-crystal glass-ceramics. X-ray diffraction (XRD) patterns show that the main crystalline phases in both the glass-ceramics are anorthite (CaAl₂Si₂O₈) and wollastonite (CaSiO₃). The crystals are homogeneously dispersed within the parent glass. The average crystal size is below 200 nm. Physical and mechanical properties, such as density, thermal expansion coefficient, hardness, and bending strength, of the glass have been examined and the corresponding microstructures are discussed. The results demonstrate that the glass-ceramics have potential for a wide range of construction application.     

Utilising unprocessed low-lime coal fly ash in foamed concrete

This paper describes an extensive laboratory-based investigation into the use of unprocessed, run-of-station, low-lime fly ash in foamed concrete, as a replacement for sand. Foamed concrete with plastic densities ranging between 1000 and 1400 kg/m³ and cube strengths from 1 to 10 N/mm² were tested. It is shown that by using this type of fly ash in this way can significantly enhance many of the properties of foamed concrete, including rheology and compressive strength development, whilst providing almost complete immunity to sulfate attack. Given the high carbon content of this type of fly ash, however, it was found that there was a need to increase greatly the amount of foam required to achieve the specified design plastic density. However, given the relatively low cost of foam production, this is not likely to have significant implications for the use of material.     

粉煤灰沸石的合成及应用研究进展

将粉煤灰合成沸石是有效利用资源的途径之一。综述了以粉煤灰为原料合成沸石的方法、影响沸石合成的因素、沸石的潜在应用领域。合成粉煤灰沸石的方法主要有一步水热合成法、两步水热合成法、碱熔融水热合成法、微波辅助合成法、添加晶种法、盐热合成法。影响粉煤灰沸石合成的因素主要有粉煤灰种类、碱液的量及浓度、反应温度、反应时间等。水处理、气体分离与净化、土壤改良是粉煤灰沸石的潜在应用领域。     

活化粉煤灰/NR复合材料的制备与性能研究

采用硅烷偶联剂对粉煤灰进行活化处理,制备活化粉煤灰/NR复合材料并对其性能进行研究.结果表明,与未活化粉煤灰/NR复合材料相比,活化粉煤灰/NR复合材料的邵尔A型硬度、拉伸强度和拉断伸长率明显增大;活化粉煤灰用量为20份时,复合材料的拉伸强度和拉断伸长率达到最大值.随着活化粉煤灰用量的增大,活化粉煤灰/NR复合材料的耐热性能明显提高,燃烧速率减慢,阻燃性能逐渐提高.活化粉煤灰作为橡胶填料,可部分替代炭黑降低橡胶制品生产成本,同时有利于环保.     

煤粉工业锅炉底部粉煤灰沉降速度试验研究

为了加快煤粉工业锅炉底部粉煤灰的沉降速度和除灰速度,保障锅炉的稳定运行,采用试验的方法研究了粉煤灰特性、粉煤灰燃烧状况和落灰斗结构对粉煤灰沉降速度的影响,重点研究了粉煤灰颗粒的粒径、粉煤灰的燃烧充分性、落灰斗的高度和侧壁倾斜度对沉降速度的影响。结果表明:粒径较小的粉煤灰颗粒沉降速度较慢,粒径小于0.009 mm的粉煤灰颗粒容易造成炉底刮板机内细泥积聚;当煤粉不完全燃烧时,粉煤灰有少部分不溶于水且下降速度慢;粉煤灰的沉降速度随落灰斗侧壁倾斜度的增大和落灰斗高度的减小而减小,因此,设计的落灰斗在空间允许的情况下侧壁倾斜度应为10°以内,并且应该尽量加大落灰斗的垂直高度。     

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。