粉煤灰组成与其胶砂活性的灰色关联分析

采用不同化学成分的粉煤灰试样,通过遴选试样及粉磨,使它们的细度及颗粒群分布基本一致,以50％的比例掺入纯硅酸盐水泥中,制成粉煤灰硅酸盐水泥。参照水泥标准测其各龄期的胶砂强度。采用灰色关联分析的方法,以粉煤灰水泥各龄期胶砂抗压强度为母序列,以相应的粉煤灰各组分含量为子序列,分析了粉煤灰各组分与其水泥胶砂宏观强度的关联度。本文进一步以XRD物相鉴定、酸溶解法等测试手段研究了粉煤灰矿物成分以及玻璃体含量与化学成分的关系,证实了灰色关联的分析结果。     

分选与磨细加工对粉煤灰物化性质以及颗粒特性的影响

在半工业化分选与粉磨工艺系统中对粉煤灰进行了分选与磨细处理,并测定了不同粉煤灰样品的物化性质及颗粒特性。结果表明,分选与磨细处理对粉煤灰的化学成分影响不大,但能够明显改善粉煤灰的物理性质,如:需水量比下降、密度增加、活性指数增加。两种处理方式相比较,分选更有利于粉煤灰需水量比的降低而磨细更有利于粉煤灰活性指数的提高;分选灰的颗粒分布范围较窄而磨细灰的颗粒分布范围较宽。     

Mineralogical and elemental composition of fly ash from pilot scale fluidised bed combustion of lignite, bituminous coal, wood chips and their blends

The chemical and mineralogical composition of fly ash samples collected from different parts of a laboratory and a pilot scale CFB facility has been investigated. The fabric filter and the second cyclone of the two facilities were chosen as sampling points. The fuels used were Greek lignite (from the Florina basin), Polish coal and wood chips. Characterization of the fly ash samples was conducted by means of X-ray fluorescence (XRF), inductive coupled plasma-optical emission spectrometry (ICP-OES), thermogravimetric analysis (TGA), particle size distribution (PSD) and X-ray diffraction (XRD). According to the chemical analyses the produced fly ashes are rich in CaO. Moreover, SiO₂ is the dominant oxide in fly ash with Al₂O₃ and Fe₂O₃ found in considerable quantities. Results obtained by XRD showed that the major mineral phase of fly ash is quartz, while other mineral phases that are occurred are maghemite, hematite, periclase, rutile, gehlenite and anhydrite. The ICP-OES analysis showed rather low levels of trace elements, especially for As and Cr, in many of the ashes included in this study compared to coal ash from fluidised bed combustion in general.     

Effect of particle size distribution of fly ash-cement system on the fluidity of cement pastes

This paper investigates the effect of particle size distribution of fly ash-cement system on the fluidity of the cement pastes using class F fly ash collected from the hopper attached to an electrostatic precipitator when the burning conditions and types of coal are changed at a coal-fired power plant. The unburned carbon content of fly ashes used in the experiment is less than 1.5%. To prevent the unburned carbon in fly ashes from affecting the fluidity of the pastes, polycarboxylic acid plasticizer with more saturation amount is added into the pastes for experimentation. The particle size distribution of fly ash-cement system is analyzed using n value of Rosin-Rammler function and the n value is derived with a nonlinear least squares fitting method. As the result, it is shown that the fluidity increases as the particle size distribution becomes wider, i.e., as n value gets smaller.     

不同炉型潞安煤灰理化及酸/碱溶解特性

对潞安煤经循环流化床、煤粉炉和气化炉处理后得到的煤灰进行了化学组成、矿物组成、特征基团、粒径分布、比表面积及微观形貌等理化性质的对比研究,并考察了其在酸浸和碱浸过程中Al^3+,Si^4+,Fe^3+,Ca^2+,K^+和Ti^4+等离子的溶解特性。结果表明:不同炉型潞安煤灰中铝、钙、硫等元素的含量有明显的差异;矿物组成包括晶相的鳞石英、方石英、莫来石、硬石膏及非晶相的偏高岭石、假莫来石、无定型二氧化硅等;相比较而言,气化炉灰中铝硅酸盐矿物结构更加不稳定。循环流化床灰颗粒呈具有一定孔洞结构的不规则状,而煤粉炉灰和气化炉灰均为光滑球形颗粒,循环流化床灰的粒径>煤粉炉灰的粒径>气化炉灰的粒径,循环流化床灰的比表面积>气化炉灰的比表面积>煤粉炉灰的比表面积。在HCl溶液中,Al^3+,Fe^3+,Ca^2+,K^+,Ti^4+的溶出率均较高;在NaOH溶液中,仅Si^4+和K^+的溶出率较高。不同炉型潞安煤灰中各元素的溶出率具有较大差异,主要与其矿物组成、结构稳定性、粒径和比表面积等相关。     

Factors affecting the suitability of fly ash as source material for geopolymers

The suitability of fly ash stock piles for geopolymer manufacturing was studied. The results of chemical analyses, X-ray diffraction (XRD) and particle size distribution (PSD) of five sources of fly ash obtained from coal-fired power generating plants in the US are presented. Geopolymer paste and concrete specimens were prepared from each stock pile. The specimens were subjected to an array of chemical and mechanical tests including XRD, RAMAN spectroscopy, setting time and compressive strength. A correlation study was undertaken comparing the fly ash precursor chemical and crystallographic compositions as well as particle size distribution, with the mechanical and chemical characteristics of the resulting geopolymer. Factors inherent to the fly ash stockpile such as particle size distribution, degree of vitrification and location of the glass diffraction maximum were found to play an important role in the fresh and hardened properties of the resulting geopolymer.     

Size fraction characterization of highly-calcareous fly ash

The chemical and mineralogical composition of lignite fly ash (FA) varies as a function of the prevalent conditions in both the processes of power production and lignite mining. The differentiation of the qualitative and quantitative composition of the highly-calcareous lignite fly ash, as a function of its particle size distribution, is verified in this paper. According to the results of the conducted research, a fine-grained fraction of considerable amount presents properties that obstruct the sustainable exploitation of calcareous lignite fly ash in cement industry applications. On the other hand, the same grain fraction (because of its hydraulic properties) can be utilized in other sort of applications, based on different criteria, i.e. in road constructions. The coarse-grained fraction (which reflects a low proportion to the total fly ash output) presents the same undesired characteristics as well. Rather, the intermediate grain fraction (75-150 μm) presents the highly desirable properties when fly ash is utilized as a pozzolanic additive. In addition, the mechanism of the formation of the intermediate grain fraction strongly prevents the factors that cause the variation of fly ash-quality. It is therefore the optimum part of the whole amount of lignite FA, to be utilized as additive in cement manufacturing. The outcomes of this paper will hopefully contribute towards the crucial goal of the expansion of the utilization of calcareous lignite fly ash by proposing a more effective way of using this material, basically by taking advantage of its fundamental chemical and mineralogical properties.     

Burning and physico-chemical characteristics of carbon in ash from a coal fired power plant

The paper addresses the relationship between the chemico-physical properties and the residual combustion reactivity of fly ashes from a full-scale front fired PF coal boiler. Ashes collected at different rows of electrostatic precipitators (EP) have been characterized for their particle size distribution, morphology, chemical composition and combustion reactivity. The combustion time of carbon in ash has been estimated for a wide range of temperatures using a thermobalance and a heated strip reactor.Results showed the existence of marked differences in the content of both carbon and inorganic elements according to the row of EP and the granulometric size of the samples. In contrast with this, the combustion reactivity of all ash samples was similar regardless of their collection point and particle size. Ash reactivity resulted to be approximately 100 times lower than that of the parent coal.The role of thermal annealing on the low reactivity of fly ashes and their propensity to undergo additional thermodeactivation upon further heat treatment has also been investigated. To this end coal and fly ashes have been heated under inert conditions up to 2000 °C and then characterised for their residual combustion reactivity. These tests showed that heat treatment does reduce the reactivity of coal but does not reduce any further the already low reactivity of fly ashes.     

Packing effect and pozzolanic reaction of fly ash in mortar

This research is to study the effect of particle size of fly ash on packing effect and pozzolanic reaction of mortar when 20% of fly ash is used to replace Portland cement type I. Both effects can be determined by using fly ash and insoluble material which have almost the same particle size to replace Portland cement type I. Normally, the compressive strength of fly ash mortar is contributed from hydration reaction, packing effect, and pozzolanic reaction. For mortar mixed with insoluble material, the compressive strength is due to hydration reaction and packing effect. Thus, compressive strength due to pozzolanic reaction can be determined from the difference in compressive strength between fly ash mortar and insoluble material mortar. The results show that the strength activity index of fly ash mortar depends on the median particle size of fly ash and curing ages of mortar samples. At early ages, the strength activity index of fly ash mortar due to packing effect is higher than that due to pozzolanic reaction. At the ages of 3 to 90 days, the difference in strength activity index due to packing effect of fly ashes with median particle size of 2.7 and 160 μm is almost constant about 22% of the strength of standard mortar (STD). The differences in strength activity index due to pozzolanic reaction of fly ashes with median particle size of 2.7 and 160 μm are 3%, 20%, and 27%, respectively, at the ages of 3, 28, and 90 days.     

循环流化床粉煤灰理化特性及元素溶出行为研究进展

综合论述了循环流化床（CFB）粉煤灰粒度、微观形貌、化学及物相组成、化学结构等理化特性,并与煤粉炉（PC）粉煤灰进行对比分析,突出了CFB灰在理化特性方面的独特性。其次,总结了CFB灰在酸碱体系中主要元素溶出行为及浓度、液固比、反应时间和温度等因素对溶出行为的影响。结果表明,CFB灰中铝硅聚合度低于PC灰,物相以无定形硅铝酸盐为主,晶体矿物质质量分数之和仅为灰质量的20%~30%。同等条件下CFB灰中铝在酸溶液的溶出活性高于PC灰,使得CFB灰在有价元素提取方面更具优势。然而,随着铝在酸溶液中的溶出,硅逐渐累积并附着在颗粒表面,阻碍了铝的进一步溶出。因此,综合考虑CFB灰有价元素温和提取及酸浸渣利用可大幅提高技术经济性。在碱性体系中CFB灰主要溶出元素为硅和铝,目前对CFB灰无定形硅铝酸盐中硅铝在碱性体系溶出行为缺乏深入的认识,加强该方面研究可提高对CFB灰碱激发过程胶凝机理的认识,从而促进CFB灰制备胶凝材料方面的发展。     

Colour measurement as a proxy method for estimation of changes in phase and chemical composition of fly ash formed by combustion of coal

Influence of technology on colour changes of fly ashes was studied in relationships with their chemical and phase composition. Dry bottom boilers at the Detmarovice Power Plant (the Czech Republic) were selected for this study. Combustion tests were performed using mixture of coal and mineral oil residues at the minimum and maximum output of the power plant. Fly ashes for chemical analysis, phase analysis and colour measurements were sampled from the four sections of electrostatic fly ash precipitator. Colour parameters indicate relationships with concentrations of elements which are preferentially bound in silicate matrix. The maximum output of power plant increases the concentration of glass which has decisive influence on values of colour parameters. The changes of colour parameters can indicate the conditions of the technological process. Relationships between colour and constituents of the fly ash are expressed by CIE Lab colour parameters.     

Suitability of Sarawak and Gladstone fly ash to produce geopolymers: A physical,chemical, mechanical,mineralogical and microstructural analysis

Two types of fly ash sourced from Sarawak, Malaysia and Gladstone, Australia reflect differences in chemical compositions, mineral phase and particle size distributions. In this paper, the Sarawak fly ash was used to produce geopolymer in comparison to the well-developed Gladstone fly ash-based geopolymer. Characteristics of fly ash and mixtures proportions affecting compressive strength of the geopolymers were investigated. It is found that the variations of both fly ash types on particle size distributions, chemical compositions, morphology properties and amorphous phase correspond to the compressive strength. The results obtained show that after 7 days, geopolymer using Sarawak fly ash has lower compressive strength of about 55 MPa than geopolymer using Gladstone fly ash with strength of about 62 MPa. In comparison with Gladstone fly ash-based geopolymer, it showed that Sarawak fly ash-based geopolymer can be a potential construction material. Moreover, the production of Sarawak fly ash-based geopolymer aids to widen the application of Sarawak fly ash from being treated as industrial waste consequently discharging into the ash pond.     

粉煤灰和矿渣粒度分布对混凝土微观结构和抗氯离子渗透性的影响

针对胶凝材料比表面积和粒度分布等物理性质存在的差异,将P·Ⅱ水泥,Ⅰ级、Ⅱ级粉煤灰和S95级、S105级矿渣进行互掺,固定水泥用量,设计了4种粉煤灰和矿渣的组合方式,通过流动度试验分析了组合方式对净浆流动性的影响,并将粒度分布曲线与Fuller分布曲线进行了比较。在净浆配合比的基础上,对不同组合方式的混凝土进行了工作性、力学性能及自由氯离子浓度测试,探讨了粉煤灰和矿渣的粒度分布对混凝土强度和抗氯离子渗透性的影响,并对硬化浆体水化产物的微观形貌和化学组成进行了分析,揭示了影响机理。研究结果表明,矿物掺合料的粒度分布是决定颗粒级配优劣的重要因素。Ⅰ级粉煤灰具有更强的滚珠效应,在提高流动性方面起了关键性作用。粉煤灰和矿渣的水化及火山灰反应程度影响着混凝土的力学性能和耐久性能,由于Ⅰ级粉煤灰有更大的比表面积,火山灰活性也较高,因此Ⅰ级粉煤灰和S95/S105级矿渣组合的净浆流动度,混凝土的工作性、抗压强度和抗氯离子渗透性均明显高于Ⅱ级粉煤灰和S95/S105级矿渣组合。其中Ⅰ级粉煤灰和S95级矿渣组合的胶凝材料粒度分布曲线与Fuller曲线最为接近,粒度分布最优,水化浆体中Ca(OH)₂含量最低,火山灰反应最为充分,对应的混凝土微观结构致密,抗氯离子渗透性最好。     

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.     

Microscopic single particle characterization of zeolites synthesized in a soil polluted by copper or cadmium and treated with coal fly ash

In the perspective of the development of new soil remediation technologies, zeolites can be directly synthesized in soil from fused coal fly ash to reduce heavy metal mobility and availability. Such a process promotes the formation of metal hydroxide/oxide precipitates which can be also occluded inside the structure of the forming minerals. In this study, different types of zeolites (zeolite X, P, and A) were synthesized by treating soil samples, artificially contaminated by high concentrations of Cu or Cd ions, with fused coal fly ash at 30 and 60 °C. The formed zeolites were characterized for their amount, structure, chemical composition and size. To accomplish this survey, besides quantitative X-ray diffraction analyses (XRD), an automated single particle analysis (ASPA) method using electron probe X-ray microanalysis (EPXMA) was employed for the first time for direct zeolite characterization in soil samples. The obtained results provide new information for assessing the role of heavy metals in zeolite crystallization in coal fly ash-treated soils. Heavy metal contamination, while not significantly hindering the zeolite formation process, can influence crystal size and preferentially drive zeolite synthesis toward the formation of sodalite unit-based zeolite X and zeolite A, even at 60 °C. The presence and nature of metal precipitate occlusions inside the forming zeolite minerals might have also favored the preferential synthesis of certain zeolitic structures.     

Determination of glass content and estimation of glass composition in fly ash using quantitative X-ray diffractometry

The proportion of amorphous or glassy material in a series of fly ashes has been evaluated by X-ray powder diffraction (XRD) using the Rietveld-based SIROQUANT software package. Several different sample preparation and processing methods were investigated, including XRD analysis of samples spiked with known masses of synthetic corundum and zinc oxide as well as techniques based on analysing the raw or unspiked fly ash directly using the SIROQUANT process. In the latter case, two different poorly crystallised silicate mineral patterns, metakaolin and tridymite, were used in the SIROQUANT processing of the raw ash XRD data to represent the amorphous constituents. The results of the different methods based on XRD of spiked samples were found to be mutually consistent, and also consistent with other published data for an international reference fly ash sample. SIROQUANT analysis of the unspiked fly ashes gave similar results, although different poorly crystallised silicate reference patterns seem to be more suited for ashes from Australian and North American sources.The mineralogy of the ashes, including the proportions of quartz, iron oxide and glassy constituents, appears to be related to the nature of the mineral matter in the relevant feed coals. Calculations based on subtracting the inferred chemistry of the crystalline minerals in the fly ashes from the total fly ash chemistry were also used to estimate the overall chemical composition of the glass fraction in each ash. The results indicate that ashes derived from lower-rank coals in the samples studied have different glass compositions to those derived from higher-rank (bituminous) materials. These different glass compositions appear to be related to several other ash properties, including particle density and particle surface area. Evaluation of glass content and composition may be significant in different aspects of ash utilisation, and also in evaluating interactions with water at ash disposal sites.     

Comparative assessment of Australian fly ash and conventional concrete bricks

A comparative study of the chemical composition, mineralogy, morphology and crushing strengths of fly ash bricks, conventional concrete bricks and fly ash samples has been undertaken. The main chemicals present in the products were silica and alumina while their main minerals were quartz, mullite, illite, vaterite, and calcite. Elemental analysis by XPS showed that the major elements in the samples were oxygen, silicon, carbon, calcium and aluminium; and scanning electron microscopy revealed that the fly ash samples consist of spherically‐shaped particles with surface attachment containing needle‐like particles. Compared with conventional concrete bricks, fly ash bricks generally have higher atomic silicon and crushing strengths but lower crystalline silica. The implication of the results on the suitability of fly ash bricks as replacements for conventional concrete bricks in the building industry is discussed from the point of view of human health and occupational safety. Copyright © 2004 Society of Chemical Industry     

Leaching characteristics of selected Korean fly ashes and its implications for the groundwater composition near the ash disposal mound

Currently only 20% of the fly ash produced in Korea is utilised for industry, and the remainder is disposed as waste in landfill sites. Both anthracite and sub-bituminous coals are burnt in Korea. Fly ash and coal samples were collected from five different coal-fired power stations in Korea and analysed for their chemistry and mineralogy. Batch leaching tests were also carried out to investigate the leaching behaviour of selected fly ashes. The fly ash leachate chemistry was compared with the groundwater taken directly from the monitoring well installed in one of the power stations. The anthracite coals contain illite, pyrophyllite and kaolinite whereas kaolinite is the representative clay mineral for the sub-bituminous coals. Anthracite coals were higher in Si, Al and K than the sub-bituminous coals, reflecting higher mineral matter contents in the anthracite coals. Mullite and quartz are the main mineral phases for two different types of the fly ashes, with some iron oxides. The chemical compositions of the anthracite and sub-bituminous fly ashes are comparable with each other, except for extraordinary high concentrations of Cr for one anthracite fly ash. Most of the trace elements in the ash were enriched in the finer fraction, indicating surface associations. Although, some elements including Na, K, Ca and Cu were released rapidly in the initial stage of leaching, measurable amounts of metals were still detectable in the fly ash leachate treated several times with distilled water. Such leaching behaviour indicates slow and long-term leaching of elements associated with the glass fractions of the ash particle. This was confirmed by leaching of weathered fly ash, which had been disposed of for several years. Comparison of the ash leachate, treated with 0.1N-HCl, fly ash slurry in the ash pond and the groundwater indicate the influence of the ash leachate from the ash disposal mound on the groundwater composition.     

Characterization of the coal fly ash for the purpose of improvement of industrial on-line measurement of unburned carbon content

The influence of selected properties of fly ash on the measurements of an on-line analyser was described. Fly ash studied in the research originated from the pulverized coal fired boiler. The samples were taken using an inspection method within a period of 3 months. Systematic observation of the properties of the ash allowed monitoring of the work of the industrial analyzer during a relatively long period of the power plant work. Samples of coal fly ash were examined for their chemical and physical properties. Morphology was analysed by scanning electron microscopy. Unburned carbon content in fly ash was determined by using loss-on-ignition (LOI) and thermogravimetry analysis (TGA). The particle size distribution of fly ash was examined. Correlation between laboratory and on-line industrial measurements of the unburned carbon content of ash was discussed.     

水煤浆气化炉内飞灰的形成机理

基于实验室规模的多喷嘴对置式水煤浆气化炉,利用SEM、马尔文激光粒度仪和XRD表征气化炉内飞灰的粒径分布和组成,并分析了气化炉内飞灰的形成机理。结果表明,喷嘴平面处飞灰与气化炉出口处飞灰的粒径分布及化学组成存在显著差异,不同气化阶段飞灰的形成机理也不同。气化燃烧阶段飞灰的形成机理为部分固定碳燃烧和外在矿物转化,而在焦炭气化反应阶段,飞灰的形成机理为焦炭破碎和内在矿物释放及转化。