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.     

粉煤灰基沸石处理氮磷废水的研究进展

近年来,粉煤灰因其价格低廉、产量高,且与沸石结构相似,常被用来作为合成沸石的原材料。在水处理方面,粉煤灰基沸石处理氮磷废水的研究颇受广大学者青睐。本文简介了粉煤灰的理化性质及利用现状,概述了粉煤灰基沸石因其独特的内部结构所具有的三个特性:离子交换性、吸附性、催化性。介绍了粉煤灰基沸石除氮、磷的机理,重点论述了粉煤灰基沸石对低、中、高不同浓度的氨氮废水、含磷废水、氮磷共存废水处理的进展情况。最后分析了该领域目前存在的问题及未来发展趋势。     

Synthesis of zeolite from coal fly ashes with different silica–alumina composition

Coal fly ashes can be converted into zeolites by hydrothermal alkaline treatment. This study focuses on the effect of Si/Al molar ratio of the fly ash source on the type of formed zeolite, which also is affected by the alkaline condition. The fly ashes were mixed with an aqueous NaOH solution and hydrothermally treated at about 100 °C. Zeolite Na–P1 and/or hydroxy-sodalite appeared after the treatment. Zeolite Na–P1 predominantly formed from silica-rich fly ash at a low-NaOH concentration. The cation exchange capacity of the product with a large content of zeolite Na–P1 reached a value of 300 meq/100 g. The type of the product was controlled by addition of aerosil silica or alumina. It was found that silica addition effectively enhances the formation of zeolite Na–P1, even at a high-NaOH concentration. These results were discussed on the basis of a formation mechanism of zeolite from coal fly ash through dissolution–precipitation process.     

Zeolite synthesis from coal fly ash for the removal of lead ions from aqueous solution

Fly ash samples from the Bayswater and Eraring power plants, located in New South Wales, Australia, were used in a preliminary study on zeolite synthesis by hydrothermal treatment with sodium hydroxide under various conditions. The treated fly ash was tested for the ability to remove lead ions from aqueous solution. Both fly ashes were partially converted to zeolite. The zeolites formed under the experimental conditions were zeolite Na‐P1 and sodalite octahydrate for the Bayswater ash and phillipsite, zeolite X, zeolite Na‐P1 and sodalite octahydrate for the Eraring ash. The type of zeolite formed was dependent on the treatment time and sodium hydroxide concentration. In the case of the Bayswater ash, zeolite Na‐P1 was formed by treatment with 4 mol dm^?3 NaOH for 48 h while treatment with 5 mol dm^?3 NaOH for 96 h produced sodalite octahydrate at the expense of zeolite Na‐P1. In the case of the Eraring ash, phillipsite was formed following treatment with 3 mol dm^?3 NaOH, zeolite X and zeolite Na‐P1 were formed following treatment with 4 mol dm^?3 NaOH and sodalite octahydrate was formed following treatment with 5 mol dm^?3 NaOH. A maximum cation exchange capacity of ～400 meq/100 g was achieved by both treated ash samples. Treatment of a solution with a lead ion concentration of 120 ppm using 0.5 g of both treated ash samples (S/L ratio = 0.25 g/100 cm³) achieved complete removal in 5 min, whereas treatment with 0.1 g of each material (S/L ratio = 0.05 g/100 cm³) achieved complete lead ion removal after 24 h. © 2001 Society of Chemical Industry     

不同钙含量粉煤灰合成沸石对污水中磷的去除

进行了以不同钙含量的粉煤灰为原料合成的3种沸石对污水中磷去除的试验,探讨了表面交换性阳离子种类、投加量以及磷浓度对除磷的影响。结果表明：最佳投加量为8g／L,磷去除率可达到70％以上合成沸石除磷能力均高于粉煤灰,钙饱和处理又可明显进一步提高粉煤灰合成沸石的除磷效果。粉煤灰合成沸石钙含量越高,对磷的去除率越高。因此,采用高钙粉煤灰为原料合成沸石并进行钙饱和处理,可以获得除磷能力强的合成沸石材料。     

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.     

粉煤灰合成沸石脱氮除磷的应用及展望

介绍粉煤灰合成沸石在氮磷废水处理中的应用。指出了粉煤灰合成沸石在处理氮磷废水方面具有处理效果好、占地少、便于管理控制等优点。粉煤灰来源广泛,价格低廉,将粉煤灰合成沸石处理氮磷废水可以以废治废,具有广阔的发展前景。     

几种不同产地粉煤灰水热法合成沸石性能探究

利用粉煤灰合成沸石的方法很多,其中水热法合成沸石因操作简单、能耗低被认为是将粉煤灰基沸石商业化最可行的手段。采用水热法将国内外不同产地的几种粉煤灰合成沸石,并通过X射线衍射（XRD）、X射线荧光光谱（XRF）、热重分析（TG-DTA）、扫描电镜（SEM）等手段对合成的沸石产品进行表征,并在同一水热合成参数下考察不同粉煤灰合成沸石在品质上的差异。XRD谱图表明,原料中有80%~90%的成分转化为沸石,且沸石主要结晶类型为Na-P1型,也有少量的A型;XRF分析表明,3种粉煤灰基沸石硅铝物质的量比分别为1.61、1.35、1.45,符合XRD谱图的分析结论;TG-DTA表明,合成沸石在500 ℃以上几乎没有质量损失,具有良好的热稳定性;由SEM照片可见,合成的沸石为非球形,表面的纹理可增加沸石比表面积,结晶状态好。整个实验过程简单、成本低、合成沸石样品品质较高,由此可见通过水热法将粉煤灰合成沸石产品具有巨大的商业化潜力。     

碱熔融粉煤灰合成沸石分子筛的影响因素分析

评述了碱熔融粉煤灰合成沸石的方法;分析了该法合成沸石过程中的影响因素,这些因素主要包括粉煤灰的组成、碱灰比、焙烧温度及时间、晶化温度及时间;探讨了目前研究的情况及未来研究的方向,这些分析为碱熔融法今后的应用提供理论依据.     

粉煤灰为原料水热合成ZSM-5沸石的工艺条件

以工业废弃物粉煤灰为初始原料,经酸处理除杂、碱处理活化后,采用常规水热法合成高纯ZSM-5沸石。考察酸处理过程的温度、时间和酸浓度等对酸浸取效果的影响,以及碱处理过程的焙烧温度和碱灰质量比等对碱熔活化的影响,采用XRF、XRD、SEM以及N2吸附-脱附等手段对各阶段样品进行表征。结果表明,盐酸处理可以除去粉煤灰中氧化钙、氧化铁等绝大部分碱性氧化物杂质,最适宜酸处理条件下所得粉煤灰中氧化硅和氧化铝质量分数之和由51.51%上升到处理后的85.37%;以最适宜高温氢氧化钠碱熔活化条件下所得活性硅铝溶液为原料,水热合成类似球状结构并具有较高比表面积和相对结晶度的高纯ZSM-5沸石,进而获得粉煤灰水热合成ZSM-5沸石的最佳工艺条件。     

水泥、粉煤灰及其硬化体中Cr(Ⅵ)溶出条件与其影响因素

分析了国内外现行的溶出试验方法,研究了不同溶出试验条件对水泥、粉煤灰及其硬化体中Cr(Ⅵ)溶出的影响,探讨了粉煤灰中可溶性Cr(Ⅵ)最大溶出量的测定方法.结果表明:静置时间、温度、液固比、颗粒细度、振荡频率及振荡容器尺寸对水泥和粉煤灰及其硬化体中Cr(Ⅵ)的溶出及测定都具有一定的影响,其中振荡时间和浸提液pH值的影响较为显著.粉煤灰中Cr(Ⅵ)的溶出是一个缓慢连续的过程,其可溶性Cr(Ⅵ)最大含量的测定以多级萃取溶出试验为宜.     

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.     

粉煤灰吸附剂的最新研究进展

概述了近几年国内外粉煤灰吸附剂研究情况,讨论了粉煤灰吸附剂在去除水体中氮、磷、重金属离子,净化烟气中SO2、NOx、Hg等有毒有害污染物的应用,此外,还阐述了粉煤灰负载壳聚糖和制备沸石分子筛的应用研究,分析总结了粉煤灰吸附剂目前存在的问题,为粉煤灰吸附剂未来的发展方向和资源化利用奠定了理论基础.     

Removal of mercury in aqueous solution by fluidized bed plant fly ash

Coal combustion in power plant produces fly ash. Fly ash may be used in water treatment to remove mercury (Hg²⁺) from water or to immobilize mercury mobile forms in silts and soils. Experiments were carried out on two kinds of fly ashes produced by two circulating fluidized bed plants with different chemical composition: silico-aluminous fly ashes and sulfo-calcic fly ashes. For the two kinds of fly ashes, adsorption equilibrium were reached in 3 days. Furthermore, removal of mercury was increased with increasing pH. Sulfo-calcic fly ashes allow us to remove mercury more efficiently and more steady. The chemical analysis of fly ash surface was carried out by electron spectroscopy. The results show that mercury is bound to ash surface thanks to several chemical reactions between mercury and various oxides (silicon, aluminium and calcium silicate) of the surface of the ashes.     

Characterisation of the glass fraction of a selection of European coal fly ashes

Fly ash largely consists of the inorganic content of coal that remains after combustion. The crystalline phases present in fly ash may form upon cooling of a molten alumino‐silicate glass. This view is supported by the spherical shape of many fly ash particles, inferring that they have gone through a viscous fluid state. The amorphous content in fly ash is believed to dominate reactivity behaviour, under both alkaline and acid conditions, because glasses have a higher potential energy than the equivalent crystal structure and the variation of bond angles and distances in a glass makes the bond breakage easier. It is the degradation behaviour under alkaline conditions, and the subsequent release of silica from the glass phase, that is important in the use of fly ash for conversion to zeolites and for pozzolanic applications in cement. This research comprehensively studies the composition, quantity and stability of the glass phase in a series of nine fly ashes sourced from Spanish and Italian power plants. The quantitative elemental composition of the glass phase in each fly ash was determined. Samples of the ashes then underwent a series of tests to determine the internal structure of the ash particles. Heat treatment of most of the ashes results in mullite crystallising from the glass phase; this is the crystalline phase that is predicated to form by both the relevant phase diagrams and also by NMR spectroscopy. In the ashes, mullite is present as a spherical shell, tracing the outline of the particle but in some specific cases the mullite skeleton is made up of coarse crystals reach also the internal parts of the particles. The morphology and density of the mullite crystals in these shells varies greatly. This work has supported the view that some crystalline phases present in fly ashes, such as mullite, form upon cooling of the amorphous glass melt as opposed to direct conversion from existing mineral phases in the coal during the combustion process. Copyright © 2004 Society of Chemical Industry     

粉煤灰基沸石的制备及应用研究进展

粉煤灰是燃煤电厂产生的固体废弃物,其主要成分中包含大比例的SiO2、Al2 O3,是合成沸石的理想原料.粉煤灰合成沸石的方法随着研究的深入而逐渐成熟,从起初的一步水热法到现在的复合水热法,从以未经处理的粉煤灰为原料到现在使用预处理过的粉煤灰为原料,粉煤灰合成沸石的工艺一直在进步.从粉煤灰的预处理、合成沸石方法、产物应用...     

粉煤灰沸石及Pd改性沸石脱除煤气中单质汞的研究

以粉煤灰为原料,采用超临界水热法制备了一系列的粉煤灰沸石.首先,考察了不同种类粉煤灰制备的沸石的煤气脱汞性能,以及由同一种粉煤灰制备的不同晶型沸石的脱汞活性.其次,考察了活性评价温度和H2 S气体对粉煤灰沸石煤气脱汞性能的影响.结果表明,其中的两种粉煤灰制备的沸石有较好的脱汞活性,具有方钠石晶型的粉煤灰沸石(Z5s)的脱汞性能优于具有钙霞石晶型的粉煤灰沸石(Z5c),Z5s沸石的脱汞率在360 min内保持在90%以上.气氛中的H2 S气体有利于单质汞的脱除,而温度升高时脱汞率降低.粉煤灰沸石(Z5s)采用贵金属Pd改性后,其脱汞活性在中高温时高于Z5s沸石.     

Microwave-assisted zeolite synthesis from coal fly ash in hydrothermal process

Coal fly ashes, which include much amount of silica and alumina, can be converted into zeolite by hydrothermal alkaline treatment. In the present work, the effect of microwave irradiation on the zeolite formation was investigated with emphasis on the change in yield of zeolite during the reaction. The fly ash was mixed with 2 M NaOH solution and heated by oil bath or microwave for 2 h. Zeolite Na-P1 formed after the conventional treatment using oil bath, but no zeolitic product was obtained by microwave heating. When microwave was applied in the course of hydrothermal treatment, zeolitization was promoted by the early-stage irradiation. This is due to the stimulated dissolution of SiO₂ and Al₂O₃ from coal fly ash. On the other hand, the microwave irradiation in the middle to later stage retarded the crystallization of zeolite. The microwave is effective to produce the zeolite from coal fly ash in a short period by control of irradiation schedule in the early stage.     

The effect of mechanically and chemically activated fly ashes on mortar properties

Fly ash is a waste material from coal-burning power plants that consume pulverized solid fuels. Two fly ashes from Asturias (Spain) were activated mechanically by wet milling and chemically by leaching with sulfuric acid. The activated fly ashes were characterized in terms of physico-chemical characterization, granulometry, density, blaine, BET, XRD and SEM.A comparative study was carried out of several mortars, in some cases using different additions of silica fume or activated fly ash. The influence that these additives have on the mechanical resistance of the mortars was studied. As well as the possible use of these activated fly ashes as a replacement for silica fume in producing high-strength mortar or concrete. It was found that mortars containing activated fly ash presented higher compressive strengths.A mercury intrusion porosimetry study was carried out on cement mortars made with mineral additives such as silica fume and activated fly ashes. In general, the porosities values of these mortars showed that mineral admixtures improved mechanical resistance due to the decrease in pore size.     

国外利用粉煤灰合成沸石的研究现状

对国外利用粉煤灰合成沸石型矿物材料的研究现状从几个方面进行了综合评述。这些方面包括原料组成、碱加入量、温度对合成沸石的影响;沸石相在粉煤灰颗粒中的形成过程机理;合成物质的处理或非处理工序对合成沸石的影响;以及合成沸石在环保方面的应用等。