垃圾焚烧氯对重金属迁移特性的影响

在管式反应炉上，通过加入有机氯（PVC）和无机氯（NaCl）研究了垃圾焚烧时氯对重金属迁移特性的影响。结果表明，在低温下，氯对重金属的挥发几乎没有影响，只有在较高的反应温度下氯才会对重金属的挥发特性产生影响，且垃圾焚烧过程中氯的存在使重金属更易向飞灰或烟气中迁移，垃圾中有机氯对重金属迁移特性的影响要大于无机氯。氯的存在会显著改变分布在飞灰和烟气或底渣和飞灰之间的重金属的分布特性。     

垃圾焚烧炉飞灰熔融特性及重金属的分布

对垃圾焚烧炉飞灰进行了差热分析及熔融实验,探讨了不同熔融温度对试样的灼烧减量及重金属分布特性的影响。结果表明,飞灰试样在1132℃时熔融,在1252℃～1290℃发生二次熔融。灼烧减量在1200℃达到最低值27.5％; Cr、Ni、Cu在熔融体中的固溶率随着沸点的升高而依次升高。重金属Pb、Cd、As、Hg挥发率均超过95％,挥发性依次为Pb>Cd>As>Hg;飞灰中Zn的氧化物熔融后转化为Zn2SiO4、ZnSiO3和ZnAl2O4等不易挥发的化合物,且Zn在1200℃时挥发率最低仅有66.7％。     

固体添加剂对垃圾掺烧污泥焚烧飞灰高温过程中重金属挥发特性的影响

在研究垃圾与污泥掺烧后焚烧飞灰中重金属浸出特征的基础上,重点研究了飞灰在1 000 ℃条件下高温处置过程中重金属(Cu、Zn 、Pb、Cd)随不同停留时间的挥发特性及添加剂(CaO、Al₂O₃、SiO₂、高岭土、粉煤灰)对重金属转化与挥发特性的影响。研究结果表明,飞灰中重金属Zn、Pb、Mn含量较高,Ni的含量较低,而毒性较大的Cd达到29.4 mg/kg。浸出液中七种金属都满足危险废物鉴别标准(GB5085.3-1996),并且重金属的浸出浓度受浸取时间及浸取液pH值影响较大。在同样的高温处置条件下,焚烧飞灰中不同重金属的挥发特性有较大的差别。其中,Pb表现出易挥发的特性,其挥发率超过80%,而Cu挥发性较小,其挥发率小于30%。综合来看,飞灰中重金属的挥发性大小依次为Pb>Cd>Zn>Cu。飞灰中添加Al₂O₃和高岭土可以抑制Cd的挥发,添加Al₂O₃后Pb的挥发率有所减少,添加SiO₂、CaO、高岭土、粉煤灰均使Zn的挥发率降低,而对Cu的挥发率没有抑制作用,这与飞灰中高Cl含量及各痕量元素化合物对固体添加剂活性位选择性的竞争吸附有关。     

高分子螯合剂和垃圾焚烧飞灰中重金属的稳定化技术

简单介绍了垃圾焚烧飞灰的理化特性和垃圾焚烧飞灰中重金属稳定化技术。依据螯合剂的结构特点及分类,结合高分子螯合剂合成方法,简述了高分子螯合剂稳定重金属的原理。认为高分子螯合剂处理垃圾焚烧飞灰后短期内是有效的。但是,螯合剂与重金属形成的螯合物的长期稳定性有待进一步的实验验证。二硫代羧酸盐类高分子螯合剂研究较多,含其他配位基团的螯合剂有待研究。     

生活垃圾焚烧飞灰中重金属的稳定化及其机理研究

以中国西南某垃圾焚烧发电厂所产生的飞灰为研究对象,分别考察了二乙基二硫代氨基甲酸盐(DTC)和磷酸钠单一添加处理以及混合联用处理对飞灰中重金属的稳定化效果,运用X射线衍射(XRD)、傅里叶转换红外线光谱(FTIR)、扫描电子显微镜(SEM)和分级提取等分析方法对飞灰中重金属的稳定化机理进行研究.研究结果表明,DTC能有效稳定Cd、Cu和Ni,磷酸钠则对Pb的稳定化效果较好,用1%的DTC和8%的磷酸钠混配来处理飞灰,能使其中Cd、Cu、Ni和Pb的浸出浓度都达到生活垃圾填埋标准.稳定化药剂与飞灰中重金属结合没有生成晶体,而是重金属进入螯合剂有效基团内,反应生成絮状沉淀穿插、附着在飞灰颗粒物的孔隙和表面,并且处理后飞灰中Cd、Cu、Ni和Pb的形态均呈现出由不稳定态向稳定态转化的趋势,使飞灰中重金属的浸出浓度降低.     

高分子螯合剂稳定垃圾焚烧飞灰中的重金属

建立了用电感耦合等离子体质谱仪测定飞灰浸出液中重金属浓度的方法。该方法线性范围宽,0~500 ppb;检出限低,0.005~2.1 ppb;准确度高,加标回收率在86%~103%;可同时测定多种元素。以聚乙烯亚胺基黄原酸钠处理垃圾焚烧飞灰,考察高分子螯合剂添加量、反应时间和浸提剂的pH值对螯合效率的影响。螯合剂添加量为飞灰质量的2%时,高分子螯合剂对铜、镉的螯合效率大于99%,对铅、镍、铬的螯合效率大于96%,对锌、硒的螯合效率大于92%。经稳定化处理后,飞灰中所有重金属元素的浸出浓度均低于《生活垃圾填埋场污染控制标准》中的限值。     

垃圾焚烧飞灰熔融污染物排放研究

在40℃-1400℃,升温速率为10℃/min,N2气氛下,利用热重分析仪,研究了飞灰熔融过程中污染物排放特点。实验发现,飞灰熔融过程中有分布在800℃-1000℃和1000℃-1200℃的两个主要失重峰;进一步在小试实验装置上收集并测定了熔融失重挥发物及气体污染物,讨论熔融过程中的质量分布规律。研究结果表明,飞灰熔融过程中在上述两个温度段的重金属和气体污染物均超标,如果处理不当会造成严重的二次污染。     

酸洗污泥与煤共燃烧过程中重金属的迁移分布研究

采用高温管式炉系统进行酸洗污泥与煤共燃烧实验。对共燃烧后As、Cr、Ni、Cd、Cu、Mn、Pb、Zn、Sb、Se重金属元素在烟气、飞灰及炉渣中的分配率进行分析。结果表明,Cd、Se、Zn是易挥发重金属,主要分布在烟气和飞灰中。Cd在烟气中的最大分配率为61%;Se在烟气中的分配率为38.58%~94.612%;Zn在低、高温段分别主要分布在烟气和飞灰中。As、Cu、Pb、Sb是半挥发重金属,Pb在炉渣中的分配率较稳定,分配率为42.67%~64.76%,在烟气和飞灰中的分配率波动较大,其分配率分别是14.176%~45.79%和9.78%~32.55%;Sb在烟气中的最大分配率为37.64%;温度升高反而会抑制As、Cu挥发,这与高温下As、Cu易与矿物质反应生成络合物有关。Ni、Cr、Mn属于难挥发重金属,绝大部分残留在炉渣中,且分配率对温度变化不敏感。赋存于炉渣中的Cr、Ni分别超过95%和97%;随着温度升高,Mn在炉渣中的分配率由71.46%增加到96.89%。     

生活垃圾流化床热处置中重金属迁移分布研究

在流化床实验装置上研究模拟生活垃圾热解、气化、焚烧等热处置过程中重金属Cd、Pb、Zn及Cu的迁移转化,分析氧化还原气氛及温度对重金属挥发特性的影响。结果表明,高温及还原性条件促进了Cd、Pb及Zn的挥发;而氧化性气氛有利于Cu的迁移。热力学平衡模拟结果表明,金属在氧化和还原气氛下的转化途径不同。在还原性气氛下,金属主要以元素态单质或硫化物的形式存在,其熔沸点高低决定了金属挥发程度。反之,CuCl_3等氯化物的生成促进了Cu在氧化性气氛下的挥发。金属基反应在氧化性气氛下得到加强,提高了Cd、Pb及Zn向气相产物转化的起始温度。进一步考察重金属在不同组分的分布及富集规律,大部分以气相形式挥发的重金属易在降温过程中冷凝并富集于飞灰。气流夹带亦是导致重金属迁移的重要原因,流化床的高气速特性对重金属分布有显著影响。     

城市污水污泥与固体垃圾混烧过程中重金属迁移特性的研究

通过城市污水污泥与固体垃圾合成样品在小型管式焚烧炉内的混烧实验,采集灰渣样品进行XRF化学成分分析和浸出毒性鉴别测试,结合污水污泥焚烧过程中热力学平衡计算,定量表征了污水污泥中Cu、Pb、Zn、 Mn、Ni在焚烧过程中向底灰、飞灰和烟气迁移的特性及对灰渣的毒性影响。研究结果表明,污水污泥混烧显著提高了飞灰和底灰中重金属含量,其中Zn和Pb增加量最大,而Ni、Mn、Cu依次减少;随着有机氯的加入,飞灰中重金属含量呈现递增趋势,其中Zn表现最明显。毒性测试结果显示,污水污泥的混烧也导致了垃圾焚烧飞灰中Zn和Pb的浸出浓度超过中国对危险废物浸出的控制标准值。同时,重金属迁移的热力学平衡模型预测结果与实验结果差距较大。这表明热力学平衡计算方法还需进一步考虑影响重金属氯化物形成的其他因素,如在焚烧过程中反应动力学、焚烧室内氧气含量变化、与其他元素间的化学反应等。     

Evaluation of a mixed chelator as heavy metal stabilizer for municipal solid‐waste incineration fly ash: Behaviors and mechanisms

This paper compares the stabilization performances of three dithiocarbamate and three phosphate chemical stabilizing agents, selects the best agents from each group, combines them as a mixed heavy metal stabilizer for municipal solid‐waste incineration (MSWI) fly ash, and investigates the effectiveness of the mixed chelator in stabilizing heavy metals in MSWI fly ash from southwest China. The mechanism of stabilization is also analyzed. Results indicate that piperazine dithiocarbamate can stabilize Cd, Cu, and Ni effectively, while sodium dihydrogen phosphate can stabilize Pb better. With the addition of the mixed chelator (2% sodium dihydrogen phosphate and 1% piperazine dithiocarbamate), all the targeted heavy metal concentrations in the leachate were below the standards for pollution control on municipal solid waste landfill sites in China. The stabilizing agents combined with the heavy metals in fly ash could not generate insoluble crystals; however, the heavy metals could combine with the agents' effective groups, generating flocs in the pores or on the surfaces of the fly ash and offering significant densification. The mixed chelator could transfer heavy metals from unstable fractions to stable fractions, so the leaching of heavy metals from the fly ash was greatly decreased.     

垃圾焚烧中氯化物对重金属Pb迁移转化特性的影响

采用管式炉和模拟垃圾对垃圾中氯化物对重金属Pb迁移转化特性的影响进行了研究,使用ICP-AES(美国EPA消解方法)、SEM、EDS和XRD等对重金属浓度、灰渣表面形貌、成分和灰渣X射线衍射物相等进行了分析。结果表明,氯化物含量的增加使得Pb生成更多易挥发性物质,从而向飞灰迁移分布,但有机氯PVC的影响比无机氯NaCl的大。无机氯NaCl和有机氯PVC对焚烧中Pb迁移转化作用机理不同,NaCl易与Pb反应生成PbCl2,而PVC与Pb反应除了生成PbCl2外,还生成了Pb(ClO4)2、PbCl2O4和PbO2。同时焚烧温度和停留时间也是焚烧中Pb迁移分布的两个主要影响因素。     

A Sequential Extraction Method Measures the Toxic Metal Content in Fly Ash from a Municipal Solid Waste Incinerator

The purpose of this research was to develop an optimized pretreatment procedure for toxic metals (Pb, Cd, Zn and Cu) content in fly ash from a municipal waste incinerator. In addition, modified sequential extraction procedures were used to characterize the chemical composition of the fly ash samples. The sequential extraction resolved the fly ash elements into the following chemical forms: soluble, exchangeable, carbonate, oxide, organic, and silicate compounds. Certified reference city waste incineration ash (BCR.176) was used as target ash samples. A H₂O₂+HNO₃+HF mixed acid digestion solution with a low temperature evaporation procedure was selected as optimal for the fly ash digestion. The digested solution was analyzed by inductively coupled plasma mass spectrometry (ICP‐MS), which effectively determined the concentrations of the toxic metal elements in BCR.176. Except for Cd, the recovery of Pb, Zn, and Cu under H₂O₂+HNO₃+HF digestion and their sequential extraction procedures were higher than 95%. The relative standard deviations (RSD) for recoveries of the four elements were within 10%. Furthermore, the sequential extraction procedure's results provided information on the potential mobility of the studied elements. Most of the Cd was bound to water‐soluble and carbonate material in the fly ash samples. Most of the Pb, Zn, and Cu was released to carbonates and bound to organic matter in the fly ash samples.     

Effect of Atmospheres on Transformation of Heavy Metals during Thermal Treatment of MSWI Fly Ash: By Thermodynamic Equilibrium Calculation

The vaporization behaviors of eight heavy metals (Pb, Zn, Cu, Cd, Cr, Co, Mn, and Ni) in municipal solid wastes incineration (MSWI) fly ash during thermal treatment under air atmosphere (21% O₂/79% N₂), an inert atmosphere (100% N₂), and a reducing atmosphere (50% CO/50% N₂) were evaluated based on a thermodynamic equilibrium calculation by FactSage 8.1. The results show that the reducing atmosphere promotes the melting of MSWI fly ash, resulting in a more liquid phase than in air or an inert atmosphere. Except for Cd, the formation of liquids can dissolve heavy metals and reduce their vaporization ratio. In the air and inert atmospheres, Pb, Zn, Cu, Co, Mn, and Ni vaporize mainly in the form of metallic chlorides, while Cd volatilizes in the form of metallic Cd (g) and CdO (g). In the reducing atmosphere, Co, Mn, and Ni still vaporize as chlorides. Zn and Cd mainly vaporize in the form of Zn (g) and Cd (g), respectively. In terms of Pb, in addition to its chlorides, the volatiles of Pb contain some Pb (g) and PbS (g). Cr has a low vaporization ratio, accounting for 2.4% of the air atmosphere. Cr, on the other hand, readily reacts with Ca to form water-soluble CrCaO₄, potentially increasing Cr leaching. Except for Cd, the results of this study suggest that the reducing atmosphere is used for the thermal treatment of MSWI fly ash because it promotes the melting of fly ash and thus prevents heavy metal vaporization.     

城市生活垃圾焚烧飞灰重金属的浸出特性

对用流化床焚烧炉混烧垃圾和煤的布袋飞灰进行了重金属的TCLP(Toxicity Characteristic Leaching Procedure)浸出特性实验，探讨了液固比、初始pH值及浸出时间对飞灰中重金属Pb、Cr、Cd、Ni、Cu、Zn的浸出影响。结果表明，重金属的浸出量都随着液固比的增加而增加，其中Cr、Cu一般呈上升趋势，Cd、Ni、Zn在液固比大于20时曲线变化较平缓，Pb的浸出规律比较特殊，有一个明显的波峰和波谷。重金属在浸取液的pH≤2.90时的浸出浓度远远大于pH≥4.03时的浸出浓度。Pb、Cr、Zn随着浸出时间的增加，浸出浓度下降，而Cd、Ni上升，Cu是先上升后下降。在液固比、初始pH值及浸出时间这三个影响因素中，pH值对重金属的浸出影响较大，重金属在酸性环境下较易浸出。     

模拟城市生活垃圾热处理过程中Cd与Pb挥发特性研究

以Cd与Pb为研究对象,在流化床反应器上对模拟城市生活垃圾Al₂O₃热处理过程中重金属的动力学挥发特性进行了研究。分析了氧化还原条件、H₂O、HCl、SO₂及基体Al₂O₃对重金属的挥发特性影响。研究结果表明,Cd具有较强的挥发性,尤其是在通入HCl的情况下,而Pb的挥发程度则较低,同时氧浓度的增加会降低重金属的挥发。Al₂O₃颗粒中重金属的物理化学吸附以及重金属的扩散效应则同样在一定程度上抵制了重金属的释放,而SO₂的通入则在一定程度上促进了Cd与Pb的释放。     

Innovative stabilization/solidification processes of fly ash from an incinerator plant of urban solid waste

Fly ash samples from an incineration plant of urban solid waste (USW) were submitted to a stabilization/solidification process based on encapsulation with a polyester resin. With this process, a very limited increase of about 25% in weight and a compressive strength as high as 1200 kg/cm² can be obtained. The efficiency of the process to stabilize/solidify the residues and to reduce the pollutant release was evaluated by performing both mechanical and leaching tests following the IRSA–CNR standard method. The leaching test was based on treating the sample with an acetic acid solution adjusted to pH 5.2 for 24 h under magnetic stirring. Toxic metals (Pb, Cd, and Cu) and organic pollutants (PAHs, PCBs, and OCPs) were determined in raw fly ash samples and in the leaching solutions of treated samples. Raw residues showed higher concentrations of trace metals than the regulatory limits, whereas the stabilized/solidified residues showed a concentration of all the pollutants lower than the regulatory limits and a compressive strength much higher than the suggested minimum value. Finally, a critical comparison with conventional stabilization/solidification processes based on the use of Portland cement highlighted that the polyester resin-based process performed much better in terms of the release of both organic and inorganic pollutants, thus substantially lowering the environmental impact of these residues.