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.     

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.     

Preparation of low melting temperature glass-ceramics from municipal waste incineration fly ash

Glass-ceramics have been prepared from air pollution control residues (fly ash) of a municipal solid waste incineration (MSWI) plant in southern China. The use of additives was investigated in order to decrease the melting temperature of the waste and thus to reduce the costs of production of glass-ceramics from the vitrified waste. Results showed that the melting temperature can be decreased significantly from 1500 to 1200 °C, which was achieved by combining the MSWI fly ash with silica sand powder and a Fe₂O₃-rich and CaO-rich iron slag to form a glass in the SiO₂-CaO-Al₂O₃-Fe₂O₃ quaternary phase system. Sodium carbonate and borax were used as fluxing agents and TiO₂ of chemical grade was added as a nucleation agent. The main crystalline phase in both high and low melting temperature glass-ceramics was found to be diopside (Fe-bearing), and the microstructure exhibited the presence of fine crystals of size in the range 100-200 nm which developed at crystallization temperatures in the range 800-900 °C for 1-2 h. The leaching behaviour of the glass-ceramic materials was tested, and it was found to be lower than that of a cement-stabilized body that was fabricated using the same waste for comparison. The results demonstrate the feasibility of reusing MSWI fly ash for glass-ceramic production at relatively low melting temperature, e.g. in a less energy-intensive process, as a viable approach for tackling the problem of hazardous MSWI residues.     

Bulk and sintered glass-ceramics by recycling municipal incinerator bottom ash

Glass-ceramics were produced using an Italian municipal incinerator bottom ash and glass cullet coming from a community glass recycling program. The capability of three different mixtures to be vitrified and subsequently devitrified by both bulk and sintering process was investigated by means of differential thermal analysis, X-ray diffraction, hot stage microscopy, firing shrinkage, water absorption and bulk density measurements, as well as scanning electron microscopy observations. High ash contents favour the growth of crystallised fraction volume and the formation of crystals of the pyroxene group, and anorthite in addition to wollastonite. Since the nucleation mechanism starts from the surface and sintering occurs before crystallisation, all the compositions humidified with a water solution are easily sinterable in dense materials at the relatively low temperature of about 850°C, in such way as to render the process economically advantageous     

Analysis of mechanism on water-reducing effect of fine ground slag, high-calcium fly ash, and low-calcium fly ash

The addition of ultrafine powder (UFP) to concrete can improve the fluidity of concrete, showing a water-reducing effect. The aim of this article was to analyze the water-reducing mechanism of UFP both experimentally and theoretically. Three UFPs—fine ground slag, high-calcium fly ash, and low-calcium fly ash—were chosen for the study. The contrastive experiments were done to investigate the fluidity of mortars with 30%, 45%, 60%, and 75% equivalent cement replaced by fine ground slag, high-calcium fly ash, and low-calcium fly ash, respectively. The results showed the physical and chemical characteristic of the powders, such as their grain morphology, glass phase activities, densities, specific areas, and their grain cumulating conditions, can strongly affect their water-reducing effect.     

粉煤灰的超细粉磨及其性能的研究

在建立的半工业化球磨系统中对多种粉煤灰进行了超细粉磨，探讨了粉磨系统的工艺参数和粉磨电耗，并对超细粉煤灰的颗粒形貌和性能进行了测定和分析。结果表明，利用该系统能够对粉煤灰进行超细粉磨处理，粉煤灰的比表面积可达11000cm^2／g左右，中位粒径可以〈4．0μm，这种超细粉煤灰不仅具有很高的活性，对砂浆和混凝土的工作性也有显著的促进作用，可以减水10％左右，能够用来生产大流动度、大掺量粉煤灰高强砂浆或者混凝土。     

Aggregation mechanism of fine fly ash particles in uniform magnetic field

Aggregation of fly ash particles with size range of 0.023-9.314 μm in a uniform magnetic field was investigated for removing them. A binary collision-aggregation model evaluating particle aggregation coefficient was developed. Based on the model, particle removal efficiency was calculated by solving the General Dynamic Equation. The comparison was done between the calculated and experimental data. The modeling aggregation coefficient shows that the aggregation coefficient increases with particle size, and the bigger the size difference between two particles is, the more strongly the gravity difference promotes aggregation. For the mid-sized particles, their removal efficiencies are higher than those of the smaller and bigger ones. The effect of the magnetic flux density on total particle removal efficiency is similar to that on aggregation coefficient. Before particles are saturatedly magnetized, their total removal efficiency increases with an increase in the magnetic flux density. Higher removal efficiency can also be caused by prolonging the particle residence time in the magnetic field or increasing their mass concentration. The particle number median diameter decreases with an increase in the total removal efficiency. Calculation results are found to coincide essentially with the experimental data.     

Aggregation experiments on fine fly ash particles in uniform magnetic field

Aggregation experiments on three fly ash samples in the size range of 0.023-9.314 μm were conducted in a uniform magnetic field. The fly ash particles were produced from combustion of three different bituminous coals. The coals were originated Dongshen, Datong and Xuzhou of China, respectively. A fluidized bed aerosol generator was used to disperse the fly ash particles to generate a constant aerosol. The aerosol particles aggregated when passing through the magnetic field. The variation of particle number concentration caused by particle aggregation was measured in real time by an Electrical Low Pressure Impactor (ELPI). The effects of several parameters, such as particle size, magnetic flux density, particle residence time in the magnetic field, total particle mass concentration and average gas velocity, on particle aggregation were examined. Experimental results indicated that removal efficiencies are the highest for particles with sizes in the middle of the size ranges tested. Increasing magnetic flux density, total particle mass concentration, particle residence time in the magnetic field or by reducing average gas velocity can increase removal efficiencies of single-sized and total fly ash particles. When fly ash particle magnetization reached saturation state, further increase of the magnetic flux density will have no effect on particle aggregation. The single-sized and total particle removal efficiencies of the three fly ashes are different under the same operating conditions. The removal efficiency is the highest for fly ash generated from Dongshen coal, followed by fly ash from Datong coal, and then fly ash from Xuzhou coal. Particle number median diameters decreases with the increase in the total particle removal efficiencies. The model prediction of particle aggregation under high total particle mass concentrations conditions indicated that the single-sized and total particle removal efficiencies will increase greatly with the increase in total particle mass concentration. The model predicted total removal efficiencies of the three fly ash particles are 53%, 43% and 14%, for Dongshen, Datong and Xuzhou coals respectively when total particle mass concentration is 40 g/m³.     

Bulk magnetic susceptibility measurements for determination of fly ash presence in concrete

Reproducible measurements of magnetic susceptibility χ_m of laboratory and field extracted concrete core samples were achieved with simple instrumentation. There was a nearly linear relationship between χ_m and the mass of fly ash per unit volume, or its volume fraction. The magnetic response of a given FA was not significantly affected by the process of curing and subsequent evolution of the concrete over two years, or by carbonation of the concrete. Field extracted concrete cores exhibited a wide range of χ_m values. The group of specimens with the highest values of χ_m also had the lowest chloride ion diffusivity, consistent with the presence of admixed FA. Conversely, specimens with nil magnetic response included those from concrete with the highest chloride diffusivity. The magnetic measurements provided reasonable order-of-magnitude indications of FA presence in field extracted cores. However, precise determination of FA content from magnetic measurements of field cores does not appear feasible in the absence of additional information.     

粉煤灰细粉添加量对多孔莫来石材料的影响

为了提高粉煤灰的资源化利用,在m(漂珠):m(氢氧化铝):m(V2O5):m(AlF3)=45:55:4:3的混合料中分别添加不同量(每100 g混合料分别添加0、5、10、20、30 g)的粉煤灰细粉,以PVA溶液为结合剂,经干料混匀、泥料搅拌、泥料陈腐、挤制成型、1100℃保温2 h烧成制备莫来石试样,然后检测其致...     

以粉煤灰为原料制备高纯氧化铝

引言 粉煤灰是电厂排放的废弃物,到2000年我国排放量已达12000万吨[1],给环境造成了巨大的污染,因此开展粉煤灰的综合利用具有长远的战略意义.     

Ge extraction from gasification fly ash

Water-soluble germanium species (GeS₂, GeS and hexagonal-GeO₂) are generated during coal gasification and retained in fly ash. This fact together with the high market value of this element and the relatively high contents in the fly ashes of the Puertollano Integrated Gasification in Combined Cycle (IGCC) plant directed our research towards the development of an extraction process for this element. Major objectives of this research was to find a low cost and environmentally suitable process. Several water based extraction tests were carried out using different Puertollano IGCC fly ash samples, under different temperatures, water/fly ash ratios, and extraction times. High Ge extraction yields (up to 84%) were obtained at room temperature (25 °C) but also high proportions of other trace elements (impurities) were simultaneously extracted. Increasing the extraction temperature to 50, 90 and 150 °C, Ge extraction yields were kept at similar levels, while reducing the content of impurities, the water/fly ash ratio and extraction time. The experimental data point out the influence of chloride, calcium and sulphide dissolutions on the Ge extraction.     

陶瓷研磨体用于磨制超细粉煤灰的生产实践

山东某公司因地理位置原因,到厂矿渣价格较高,且不能保证稳定供货,影响公司正常生产经营。但该公司周围粉煤灰资源丰富,到厂价格也低。如何在保证水泥质量的前提下,最大限度提高水泥中粉煤灰掺加量,一直是努力的重点。同时,开辟超细粉煤灰在商品混凝土领域的应用,也可为公司增加新的利润增长点。为此,自2017年5月份起,利用一台Φ3.2 m×13 m闲置开路磨进行超细粉煤灰的试生产工作,至2018年4月31日已累计生产比表面积大于650 m2/kg的超细粉煤灰3万余吨,除了本公司生产水泥作混合材使用,还可销售给其他公司,取得了较好的效益,也为超细粉煤灰的球磨机工业化生产探索了一条新的可行的技术路径     

Thermal and chemical behaviour of different glasses containing steel fly ash and their transformation into glass-ceramics

Chemically inert and different coloured glasses were prepared by inserting up to 10 wt.% steel plant fly ash into different kinds of inorganic matrices. Three different matrices were tested: municipal incinerator grate ash, glass cullet and a low cost CMAS devetrifiable glass. The experimental techniques used to characterise both the starting and the heat treated (glass-ceramics) glasses were differential thermal analysis, durability and release tests, X-ray diffraction, scanning electron microscopy and colour analysis (CIELab method). The results reached suggest the possibility to recover the steel ash both as a starting material in glass and glass-ceramic formulations and as a colouring agent in place of a pure iron oxide into a colourless base system.     

粉煤灰提取氧化物研究进展

粉煤灰是目前世界上排放量最大的固体废弃物之一。研究表明,中国部分地区粉煤灰具有极高的利用价值。近年来,关于粉煤灰中硅、铝的提取和应用方面的研究逐渐升温。介绍了粉煤灰提取氧化物的4种主要方法：赤泥法、烧结法、酸法、碱法,详细介绍了烧结法、酸法、碱法并给出了其典型工艺路线。综述了目前中国粉煤灰提取氧化物的最新研究进展。总结了几种方法各自的优缺点,展望了中国粉煤灰提取氧化硅、氧化铝的前景。粉煤灰提硅提铝工艺的研究和开发,有良好的社会效益和经济价值。     

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.     

利用粉煤灰提取氧化物的研究进展

为了减轻粉煤灰对环境的污染以及提高其综合利用率,阐述了粉煤灰精细化利用的重要性,介绍了粉煤灰的化学组成及矿物组成,得出了粉煤灰中提取Al_2O_3和SiO_2的潜在价值及存在的问题。介绍了粉煤灰提取氧化物的3种主要方法:酸法、碱法、酸碱联合法,并探讨了各种方法的优缺点。在此基础上指出了目前我国实现粉煤灰提取Al_2O_3联产SiO_2工业化生产的不足:对设备要求较高、易造成二次污染以及成本过高。最后对粉煤灰的精细化利用进行了展望。     

Kinetics of carbon oxidation from fly ash

Thermal gravimetric analysis (TGA) and evolved gas mass spectroscopy were used to study the kinetics of carbon oxidation from a Class-F fly ash. A multi-process ignition loss schema is presented wherein carbon combustion is modeled as a series or discrete independent reactions. These processes were studied at temperatures up to 1000 °C (1832 °F), for oxygen partial pressures between 0.05 and 0.50 and for heating rates between 5 and 40 °C/min (9-72 °F/min). The results show that carbon combustion can be modeled by a series of at least three processes; the weights (fractions) of which are a function of temperature and not a function of oxygen partial pressure. Such detailed combustion kinetics are relevant for the post processing of fly ash to produce materials suitable for use as concrete admixtures or in the manufacture of sintered artificial aggregate or similar densified structures based on fly ash. Such are low temperature, low heating rate processes relative to coal combustion power generation applications.     

利用粉煤灰生产粉煤灰水泥的试验研究

随着我国工业的蓬勃发展,产生了大量的工业废渣和工业尾矿。据有关部门统计,1995年全国工业废渣为7.4亿t,累积堆存达65亿t,占地5～6公顷。我国是世界上的最大的煤炭生产国和消费国,煤炭的大量开采和利用伴生了大量的工业废弃物。1995年我国粉煤灰排放量达1.4亿t。由于粉煤灰是一种产量多、分布地区较广的工业废渣,因而用粉煤灰作水泥原料和混合材是粉煤灰综合利用和开发及发展水泥工业的一个重要方面。粉煤灰作水泥原料和混合材在国内外已经积累了较丰富的技术资料和生产经验,并取得了较为显著的社会效益。另外,国家的各项优惠政策也在向综合利用工业废渣倾斜,对于综合利用工业废渣的企业(项目、产品)实行减免税的优惠政策。     

Plerosphere and its role in reduction of emitted fine fly ash particles from pulverized coal-fired power plants

Fine particles (PM_2.5) emitted from the stacks of the coal-fired power plants are of environmental concern since they can easily enter the human respiratory track. The detailed study of the fly ash particles using scanning electron microscope/electron dispersive spectrometry (SEM/EDX) show that fine solid spherical particles (microspheres) are contained by the large cenosphere particles (>50 μm) during the combustion process. The resulting macro particles are known as “plerosphere”, which are typically impregnated by the fine microspheres. The coal-fired power plants’ particle control devices such as the electrostatic precipitators (ESP) and baghouse filters tend to capture the large plerospheres, more efficiently. Therefore, the result of this study suggests that the containment of the microspheres by plerospheres during the coal combustion process can effectively reduce the amount of fine particles and associated elements released into atmosphere.