Analysis of fly ash heavy metal content and disposal in three thermal power plants in India

The study investigates the heavy metal content of fly ash and bottom ash from three major power plants in North India, using flame atomic absorption spectrometry. It also studies the prevalent disposal methods used at these sites. The ashes were analysed for the presence of Cr, Mn, Pb, Zn, Cu, Ni and Co and detectable levels of all were found in both fly ash and bottom ash. The concentrations of Cr and Zn were highest while Co concentration was less. The wet disposal method is used in two of the power plants (site 1 and site 3). Neither of the sites uses ash pond lining in the construction of the ash ponds, hence leaching of the heavy metals is possible. Site 2 has adopted 100% dry disposal system which allows better utilization but incurs additional costs. Better management practices, increased utilization and proper disposal practices need to be undertaken to minimize the adverse environmental impact.     

粉煤灰处理含重金属废水试验研究

本文比较了粉煤灰及酸活化粉煤灰处理重金属离子的性能 ,着重探讨了酸活化粉煤灰去除工业电镀废水中重金属离子铬、铅、铜、镉的适宜条件 ,经处理后的废水可达到排放标准。同时提出了一套成功的粉煤灰活化工艺 ,具有较好的社会效益和经济效益。     

Characterization of an alkali activated lagoon ash and its application for heavy metal retention

The wet disposal of ash, from the coal-fired thermal power plants, involves its mixing with water and its impoundment in the ash ponds or lagoons. This causes the interaction of ash and the alkalies present in it with water over a period and the formation of ash zeolites (i.e. zeolitization of the ash) takes place. In order to simulate such ash-water interactions, alkali activation of a typical lagoon ash, from India, has been conducted. Investigations have been conducted to identify the effect of zeolitization of the ash on its physical, chemical and mineralogical characteristics. Such studies are essential to explore the possibility of application of the lagoon ash, and the zeolitized ash, for various environmental applications, viz. retention and removal of heavy metals from the industrial sludge.     

The leachability of heavy metals in hardened fly ash cement and cement-solidified fly ash

The effect of mix proportion, leachant pH, curing age, carbonation and specimen making method etc. on the leaching of heavy metals and Cr(VI) in fly ash cement mortars and cement-solidified fly ashes has been investigated. In addition, a method for reducing the leaching of Cr(VI) from cement-solidified fly ashes is proposed. The results mainly indicate that: (1) either Portland cement or fly ash contains a certain amount of heavy and toxic metals, and the leaching of them from hardened fly ash incorporated specimens exists and is increased with fly ash addition and water to cement ratio; (2) the leachability of some heavy metals is greatly dependent on leachant pH; (3) when carbonation of cement mortars occurs the leaching of chromium ions is increased; (4) the amount of heavy metals leached from cement-solidified fly ashes depends more on the kind of fly ash than their contents in fly ash; and (5) with ground granulated blast furnace slag addition, the leaching of Cr(VI) from solidified fly ashes is decreased.     

垃圾焚烧飞灰水洗脱氯及重金属浸出特性研究

系统研究了机械炉排炉垃圾焚烧飞灰水洗过程中氯化物和重金属的浸出特性,并采用Visual MINTEQ模拟分析水洗液中重金属的存在形态。结果表明：飞灰中的氯主要以可溶性氯化钠（NaCl）、氯化钾（KCl）、氯化钙（CaCl₂）、碱式氯化钙（CaClOH）的形式存在,飞灰水洗浸出成分97%以上为氯离子（Cl^-）、钠（Na）、钾（K）、钙（Ca）,其中氯离子占比高达60%;重金属及其他成分的浸出量很少,不足1%。水洗对氯离子的去除效果非常明显,可达92%以上,但是重金属的浸出量极低。飞灰单次水洗最佳条件：液固体积质量比为6 mL/g,洗涤时间为10 min。Visual MINTEQ模型分析表明,pH是控制飞灰水洗液中铅（Pb）、铜（Cu）、锌（Zn）、镉（Cd）形态的重要因素,氯离子（Cl^-）对镉的形态分布也有着重要的影响。飞灰水洗液电导率与氯离子质量浓度具有极好的线性相关性,其可作为监测滤液中氯离子质量浓度变化的有效间接指标。     

Potential utilization of oil sludge incineration bottom ash for glass-ceramics: Crystallization kinetics,properties and toxicological evaluation

The bottom ash (OIBA) generated from the incineration of hazardous oil sludge is classified as a hazardous waste. In this work, the OIBA was applied as raw material to prepare SiO₂-Al₂O₃-CaO system glass-ceramics by melt-sintering with the addition of waste glass wool (GW). The effects of basicity (CaO/SiO₂ ratio, 0.52-1.05) and sintering temperature (900–1050 °C) on the crystallization kinetics, properties, microstructure, leaching concentrations of heavy metals and potential toxicity of glass-ceramics were investigated. The results showed that the crystallization pattern was two-dimensional crystallization, and with the decrease of basicity, the main crystalline phase evolved from gehlenite to diopside. And the glass-ceramics with basicity of 0.88 and sintering temperature of 950 °C exhibited the best comprehensive properties, including density (2.72 g/cm³), water absorption (0.06%), compressive strength (452.45 MPa) and chemical corrosion resistance. In addition, the reduction of heavy metal leaching concentration indicates that produced glass-ceramics showed excellent solidification effect on heavy metals, the low toxicity of glass-ceramics leaching solution to the wheat seeds and Artemia suggests the environmental protection characteristics of OIBA-based glass-ceramics. These findings proved that the glass-ceramics produced by OIBA and GW could be a promising method to dispose hazardous waste with preparing high value-added construction materials.     

粉煤灰中重金属元素砷的赋存状态与分离方法

粉煤灰中重金属元素在环境中的迁移转化和累积效应是粉煤灰综合利用过程中面临的壁垒问题,明晰粉煤灰中重金属元素的赋存状态并探索一种高效脱除方法是解决粉煤灰大宗利用的关键。利用改进的BCR连续提取法发现,粉煤灰中重金属元素砷的水溶态和酸可溶态占比较高,证明重金属砷容易在环境中迁移,从而影响周边环境。基于粉煤灰中重金属砷的赋存状态特征,建立了硫酸一步脱除重金属元素砷的新方法,考察了硫酸浓度、反应温度和反应时间对重金属砷脱除率的影响。结果表明,砷的脱除率随硫酸浓度增大而增大,随反应温度升高而降低,随反应时间增加而增大。综合考虑重金属砷的脱除率、粉煤灰中常量元素的损失率和球形颗粒的破坏程度,确定硫酸一步法脱除粉煤灰中重金属砷的最佳条件为硫酸溶液物质的量浓度2.0 mol/L、反应温度20℃、反应时间60 min,此时重金属砷的脱除率达75.21%。     

垃圾焚烧底渣中重金属的研究

采用Tessier四步分级提取法对垃圾焚烧飞灰中的4种重金属(锌、镍、铜、镉)的化学形态进行了研究。结果表明,金属Cd主要以底渣态的形式存在(占总镉质量的61.22%~62.41%),Ni,Zn以底渣态和铁锰氧化态为主,Cu主要以有机结合态为主(占总铜质量的60.97%~62.29%)。同时4种金属的生物有效性由高到低顺序依次为Ni,Cd,Zn,Cu。     

The effects of agglomeration/defluidization on emission of heavy metals for various fluidized parameters in fluidized-bed incineration

The agglomeration/defluidization may be produced to generate the secondary pollutant during incineration. However, the effects of agglomeration/defluidization on heavy metal distribution have rarely been examined. Therefore, the effects of the agglomeration/defluidization process on heavy metal emission in flue gas are studied. The artificial waste is employed to simulate municipal waste and to form agglomerates, which contain alkali metals, earth alkali metals, a mixture of metals (Pb, Cr and Cd) and sawdust. The fluidized parameters (including gas velocity, sand particle size and static bed height) are varied to determine their influences on heavy metal emission. The results indicate that addition of Na increases the risk of agglomeration/defluidization, but the emission concentration of heavy metals decreases during agglomeration/defluidization. The heavy metals may react with Na to form the eutectics or are covered and adhered by the liquid-phase eutectics of Na to stay in sand particle and lead to a decrease in the emission of heavy metals.The system was operated at a low gas velocity that not only easily resulted in agglomeration/defluidization but also increased the emission concentration of heavy metals. Large particles (920 μm), which have a poor fluidized quality, had the highest emission concentration. Small particles (645 μm) were uniformly fluidized to enhance the fluidization quality and to decrease the emission concentration. Additionally, adding Ca did not decrease the heavy metal emission concentration, but maintained the fluidization during eutectic accumulation. The Ca prevented the sand bed from quickly achieving defluidization and prolonged the increased emission of heavy metals after defluidization.     

Influence of heavy metal contaminants at variable pH regimes on rheological behaviour of bentonite

Long-term competent performances of clays as barrier and liner systems for waste landfills are dependent on both the physico-mechanical properties and attenuation characteristics of the clay soils. The presence of heavy metal ions in the pore water will alter the physico-chemical characteristics of the clay–water system, resulting in changes in the short- and long-term mechanical and chemical behaviour of the clay soil barrier materials. This study investigates bentonite–contaminant interaction at different pH levels and heavy metal ion concentrations, and their resultant effect on the mechanical behaviour of bentonite soil. A set of physico-chemical experiments including Atterberg limits, precipitation testing, pH measurement and consolidation were performed to investigate the fundamental mechanism of soil–contaminant interaction from a rheological point of view. Consolidation tests were performed to study volume change behaviour with respect to the control exercised by mechanical and osmotic stresses. The impact of multiple aspects of heavy metal ion interaction on the osmotic compressibility and consolidation of bentonite is investigated. It is shown that while the selectivity phenomenon governs the adsorption characteristics of contaminated bentonite, the microstructural change due to the lower pH level and the high concentration of HMs, the different onset of precipitation for Zn and Pb, and the osmotic phenomenon control the rheological performance of compacted bentonite. The theoretical aspect of the experimental investigation is addressed and the restrictions of classical double layer theory for heavy metal/clay soils interaction are illustrated.     

Simulation study on the melting process of nano-corundum

When the shape of α-Al₂O₃ product is very complicated, 3D printing technology based on laser or ion beam energy would be the best choice. But it is very difficult at present because of the high melting point and low thermal conductivity of α-Al₂O₃. So studying the melting process of nano α-Al₂O₃ with the different particle size can help to provide a guidance for 3D printing of α-Al₂O₃. In this paper, the melting point and melting process of nanosized α-Al₂O₃ with the radius of 1–2.2 nm were studied by molecular dynamics simulation. Results showed that: The melting points of nano-particles increased along with the radii increased. The melting point of 1.8 nm particle was 2200 K. Its melting process could be divided into four stages: the thermal expansion stage 300–700 K, the surface activation stage 700–1600 K, the pre-melting stage 1600–2200 K, and the melting stage 2200 K. Dominantly due to the migration of O atoms during the melting process, the bond broke at the sites 2.55 Å (1 nm = 10 Å), etc. away from the central atom. The heating rate had a great influence on the melting process of α-Al₂O₃ nanoparticles. The higher the heating rate, the higher the melting point. The nanoparticle could be superheated and the superheating phenomenon had the dynamic stability limit temperature.     

Studies of Cd, Pb and Cr distribution characteristics in bottom ash following agglomeration/defluidization in a fluidized bed boiler incinerating artificial waste

This study focused on the effects of agglomeration/defluidization on the Cd, Pb and Cr distribution in bottom ash particles of different sizes. In this study we have incinerated artificial waste, which was a mixture of sawdust, polypropylene, selected metal solutions, and polyethylene. The experimental parameters included Na concentration, addition of Ca and Mg and operating temperature. The results indicated that particle size decreased by attrition and thermal impact in the absence of added Na. When Na was added to the system, this metal reacted with silica sand to form eutectics, which increased particle size. Further addition of Ca and Mg was found to prolong the operating time, with greater amounts of liquid eutectic accumulating, leading to increase particle size.The heavy metal concentrations in coarse and fine particles were greater than those present in particles of intermediate sizes over a range of experimental conditions. As the particle size decreased below 0.59 mm or increased above 0.84 mm, the heavy metal concentrations increased. As Ca and Mg were added, the heavy metal concentrations in particles of all sizes increased relative to those present in identical particles when no metals or only Na were added. Additionally, the ratio of Cd sorption to silica sand decreased with increasing Na concentration, but Cr sorption had the opposite tendency. Therefore, while the addition of Na tended to increase agglomeration, it also increased the tendency for heavy metals to remain in the sand bed of fluidized bed incinerators. Addition of Ca and Mg not only inhibited the agglomeration/defluidization process, resulting in increased operating time, but also enhanced the removal of heavy metals by silica sand, decreasing the concentration of heavy metals in reactor exhaust.     

添加秸秆类生物质对长平煤灰熔融特性的影响

借助高温热台显微镜、扫描电子显微镜-能谱仪、灰熔点仪和X射线衍射仪考察了添加稻草和棉秆两种秸秆对长平煤灰熔融特性的影响.研究结果表明添加两种秸秆都能有效地降低长平煤灰的熔融温度.在高温弱还原性气氛下,长平煤灰主要矿物组成为耐熔性石英和莫来石,而添加秸秆后产生了白榴石、尖晶橄榄石、钙长石等低温共熔化合物,使长平煤灰熔点降低.不同灰的高温熔融图像表明,煤灰在熔融过程中由于受热而使固相持续软化,形成了不利于难熔物分解的高黏度熔体.而煤和稻草的混合灰在熔融时形成了易发生流动的低黏度熔体,能够促进矿物质发生反应而更易熔融.     

粉煤灰对水泥中重金属存在形式的影响

本文对添加不同含量的粉煤灰后,熟料水化过程中重金属元素（Cr、Mn、Cu、Pb、Zn）存在形式及其浸出毒性进行了实验和探讨。随着粉煤灰掺入量由0%提升至10%,水化产物形貌中微细孔增多,重金属元素在C-S-H中富集程度增加,熟料重金属元素浸出毒性呈现不同程度下降趋势,最大下降幅度达到56.1%,主要因为微细孔对重金属有较好的吸附作用,且重金属元素在水化产物周围的富集程度增加,有助于重金属离子以较为稳定的形态固化在水化产物中。     

重金属螯合剂处理垃圾焚烧飞灰的稳定化技术

引言随着我国社会经济的发展、城市化进程的加快以及人们物质生活的提高,全国城市生活垃圾年产生量已达1.5亿吨以上,并以每年8%～10%的速率增加[1-3]。城市垃圾焚烧是我国垃圾处置的重要手段,在焚烧过程中将产生大量飞灰,飞灰产量与垃圾种类、焚烧条件、焚烧炉型及烟气处理工艺有关,一般约占被焚烧垃圾量的3%～5%。分析表     

电感耦合等离子体原子发射光谱法测定工厂废酸液中重金属元素含量

工厂废酸液经过处理后,采用电感耦合等离子体原子发射光谱法测定其中铅、镉、铬、砷、铜、镍、锌等7种重金属元素的含量。对仪器的工作条件进行了优化,选择各元素的分析线,测定各元素的检出限。对2个工厂废酸液样品进行分析,7种重金属元素测定的相对标准偏差RSD(n=9)在0.10%～6.8%之间。     

高灰熔点煤灰熔融特性的可控调整研究进展

我国高灰熔点煤占煤炭储量的57%左右,直接用于气流床气化时将面临"积灰和堵渣"的问题,探索高灰熔点煤灰熔融特性的调控方法对气流床的稳定运行意义重大。主要分析了助熔剂和配煤对灰熔融温度的影响规律;并从矿物质演变机理的角度综述了助熔剂(Fe2O3,Ca O,Mg O,Na2O,K2O和复合助熔剂)、配煤和软件分析(FactSage软件热力学计算和Gaussian量子化计算)如何分析和实现高灰熔点煤灰熔融特性的可控调整;最后阐述了采用支持向量机进行煤灰熔融温度的预测存在精度高的优势。提出了寻找新型助熔剂以增强灰熔融温度调控的准确性和基于支持向量机模型建立煤灰成分与灰熔融温度的关联式,进而指导和优化气化配煤煤种和比例的选择,为高灰熔点煤的清洁高效利用提供理论支持。     

Effect of inorganic materials on the solidification of heavy metal sludge

Portland cement, cement-fly ash and lime-fly ash binders were used to solidify a synthetic heavy metal sludge containing nitrates of Cr, Ni, Cd and Hg. The sludge to binder (cement, cement-fly ash and lime-fly ash) ratio was kept at 3.33, 1.43 and 1.25, respectively. In addition inorganic substances like Cu, Zn, Pb, Sodium hydroxide and sodium sulfate were added. The molded samples were cured at room temperature for 28 days. The solidified samples with and without interference were examined for the change in their bulk density and compressive strength at definite time intervals during curing. All the metals and sodium salts added increased the average bulk density of the final product with increase in concentration (2% to 8%) with all the binder systems. The samples containing copper and lead decreased the compressive strength at all the concentrations added with CFA and LFA binders. Zn had the largest effect on all the three binder systems, lowering the strength of all samples at all the days and concentrations except the 2% Zn with CEM binder. However, Pb had only minor effect on the compressive strength with CEM binder and values remained almost constant at all the times and concentrations studied. In contrast, the effect of sodium sulfate was less marked while sodium hydroxide increased the rate of set and 28-day compressive strength of samples containing cement as binder. These observations confirm the need for specific studies of the waste and binder prior to the selection of a solidification process for the treatment of hazardous wastes. The results provide a better understanding of materials that may interfere with the immobilization of waste constituents and provide information on the possible mechanism of the interfering effects.     

Flux mechanism of compound flux on ash and slag of coal with high ash melting temperature

The melting temperature of Z coal ash was reduced by adding calcium–magnesium compound flux(W_(CaO)/W_(MgO)=1). In the process of simulated coal gasification, the coal ash and slag were prepared. The transformation of minerals in coal ash and slag upon the change of temperature was studied by using X-ray diffraction(XRD). With the increase of temperatures, forsterite in the ash disappears, while the diffraction peak strength of magnesium spinel increases,and the content of the calcium feldspar increases, then the content of the amorphous phase in the ash increases obviously. The species and evolution process of oxygen, silicon, aluminum, calcium, magnesium at different temperatures were analyzed by X-ray photoelectron spectroscopy(XPS). The decrease of the ash melting point mainly affects the structural changes of silicon, aluminum and oxygen. The coordination of aluminum and oxygen in the aluminum element structure, e.g., tetracoordinated aluminum oxide, was changed. Tetrahedral [AlO_4] and hexacoordinated aluminoxy octahedral [AlO_6] change with the temperature changing. The addition of Ca~(2+) and Mg~(2+) destroys silica chain, making bridge oxide silicon change into non-bridge oxysilicon; and bridge oxygen bond was broken and non-bridge oxygen bond was produced in the oxygen element structure. The addition of calcium and magnesium compound flux reacts with aluminum oxide tetrahedron, aluminum oxide octahedron and silicon tetrahedron to promote the breakage of the bridge oxygen bond. Ca~(2+) and Mg~(2+) are easily combined with silicon oxide and aluminum oxide tetrahedron and aluminum. Oxygen octahedrons combine with non-oxygen bonds to generate low-melting temperature feldspars and magnesite minerals, thereby reducing the coal ash melting temperatures. The structure of kaolinite and mullite was simulated by quantum chemistry calculation, and kaolinite molecule has a stable structure.     

炼焦煤中灰分对焦炭热性能的影响

研究了炼焦煤的灰分和催化指数,通过小焦炉实验进行了焦炭的反应性和反应后强度的测定。结果表明,灰分催化指数对焦炭的反应性和反应后强度的影响显著。焦炭的反应性与灰分碱性催化指数呈正线性相关,焦炭的反应后强度与灰分碱性催化指数呈负线性相关。