【作者】 田书磊；

【导师】 汪群慧； 王琪；

【作者基本信息】 哈尔滨工业大学 ， 环境工程， 2007， 博士

【摘要】 垃圾焚烧飞灰因含有高浸出浓度的重金属被视为危险废物,必须经水泥固化、化学药剂稳定化、熔融固化、高温烧结等技术将重金属固化后方可填埋或资源再利用。从环境长期的安全性考虑,经这些方法处理后残留在飞灰产品中的重金属不但会对环境构成潜在的危害,而且也是一种金属资源的浪费。为此,本文充分利用飞灰中重金属在高温处理过程中易挥发这一特性,对飞灰中高含量的Pb、Cd、Cu、Zn等重金属进行高温热分离研究,重金属挥发物随烟气一起冷凝形成二次飞灰。经高温热分离技术处理后的飞灰可作为普通废物填埋或建筑原材料,而二次飞灰中的重金属含量较高,相当于一种特殊的重金属富矿,可作为冶金原料。通过热分离工艺参数优化,确定了温度和时间为焚烧飞灰高温热处理的主要影响因素,而气氛和进气流量对重金属的挥发影响不显著。从重金属挥发效率和节能角度考虑,其最佳挥发温度和时间分别为1000℃和120min,此时重金属Pb的挥发率高达99.7%,Cd和Cu的挥发率达89.7%和77.9%,Zn仅为53.2%;若提高温度和延长热处理时间,可使Pb的最大挥发率接近100%,Cd、Cu分别高达98%和95%以上,而Zn也能达到90%以上。实验通过添加不同种类的氯制剂(CaCl2、MgCl2、AlCl3、FeCl3和NaCl)和“飞灰水洗预处理工艺”等研究方法,对重金属热分离的氯化反应机理进行了深入地探讨,并以氯制剂“平衡分压”和“反应的吉布斯自由能函数变”两种理论对氯化反应机理进行了解释。为了进一步验证氯化反应机理的正确性和科学性,本文采用人工配灰模拟实验对氯化反应机理进行了验证,结果发现模拟实验曲线与飞灰实验曲线非常拟合,从而验证了氯化反应机理的正确性。在飞灰“热重分析”实验数据的基础上,利用Friedman和Ozawa法对飞灰热重测试结果进行了分析,并采用三步连串反应模型:A --(Fn)--> B --(Fn)--> C --(Fn)--> D对飞灰热力学进行模拟,得到模型v=kcn=Ae-E/RTcn;并在氯化反应机理的基础上,建立了重金属热分离动力学模型C=Cg(1-e-kt/h)。二次飞灰理化特性分析表明:在宏观上,干燥的二次飞灰为黄褐色粉末,吸潮后逐渐形成粘稠浆状体,颜色由黄色渐变为天蓝色,随着水分的增加变为蓝绿色或浅绿色;在微观上(SEM),二次飞灰颗粒形状大小不一,多以不规则块状、棒状体居多,不规则形状的大颗粒表面上附着了一些形状各异的小颗粒。与原灰相比,二次飞灰中重金属Pb、Cu、Zn和Cd的含量大幅度提高,其中Pb的质量百分含量高达10%,是原灰的5倍;Cu和Zn的质量百分含量也高达5.7%和8.7%,与矿石的工业品位相近,说明二次飞灰可作为金属矿藏。物相分析表明二次飞灰中主要由Cl、Pb、Cu、Zn、K组成,占总量的98.1%,其中Cl约占了40%左右;二次飞灰中还存在大量金属氯化物,如PbCl2,这进一步验证了飞灰中重金属在高温热处理过程中主要以氯化物形式挥发的反应机理。总之,飞灰中重金属的高温热分离是可行的,可解决传统的飞灰处理方法给环境造成的隐患问题。更多还原

【Abstract】 Municipal solid waste incineration (MSWI) fly ash is classified as a special hazardous waste world-widely for the presence of leachable heavy metals, high concentrations of soluble salts. These hazardous substances in fly ash can pollute groundwater and soils, some of them are difficult to degrade and could accumulate, thus they are harmful to organisms when exposes to organisms. Thus, fly ash must be detoxified or decontaminated prior to disposal or reuse. At present, various approaches have been used to solidify/stabilize fly ash, such as cement fixation, acid extraction, stabilization with chemical agents and vitrification. From the long term view of environmental security, these heavy metals remained in fly ash will not only threaten the environment, but also cause waste of metal resources.Some heavy metals, such as Pb, Cu, Zn, Cd will evaporate during the heat-treatment, then formed solid again during cooling process. On the basis of these,“Thermal separation process (TSP)”was presented firstly and“Second fly ash(SFA)”was defined in this paper. During thermal separation, heavy metal will evaporate and be enriched in SFA. This method not only has solved environment security problem but also recoveried metals source.Optimization of TSP parameters determined that temperature and time were the main influence factors with the optimum values 1000℃and 120min, respectively. The evaporation rate of Pb can reach as high as 99.7% under the optimum conditions,and the Cd, Cu, Zn were 89.7%, 77.9% and 53.2%, respectively. If temperature and time are further enhanced, the evaporation of Cd and Cu can reach 98% and 95%, and Zn also achieve above 90%.The addition of different types of chlorides such as CaCl2、MgCl2、AlCl3、FeCl3 and NaCl, as well as“wash-ash”method were adopted to investigate the chlorination mechanism. Two theories, equilibrium partial pressure of chlorides and Standard Gibbs Free Energy Change for reaction, were brought out to explain the chlorination mechanism. In order to test the mechanism artificially synthetic fly ash was used in the experiment , the result showed that the simulating results were in fine identity with the experimental data ,which verified the mechanism validity.Thermodynamic Model and Kinetic Model were established based on the results of TG-DTG analysis. Friedman and the Ozawa law were used to calculate“Energy”and the pre exponential factor“A”. By three-step reaction mechanisms, A --(Fn)-> B --(Fn)--> C --(Fn)--> D, the thermodynamic Model of fly ash was simulated asv=kcn=Ae-E/RTcn. On the basis of chlorination mechanism, Kinetic Model for heavy metal thermal separation was proposed as C=Cg(1-e-kt/h)。Physico - chemical analysis indicated that the dry SFA was a kind of filemot powder, it would change gradually from filemot to azure after moisture absorption, with the moisture further increased, the azure powder would become cyan or aqua slurry in the end. The result of SEM demonstrated that shape and size of particles in SFA varied differently, mostly in the form of irregular block and clava. Lots of different shape small particles were clinged to big granules. Compared with the original fly ash, the content of heavy metals in SFA raised greatly. The mass percentage of Pb was 10%, which was 5 times of original one, the content of Zn and Cu were 8.7% and 5.7%, respectively. The SFA was mainly composed of Cl, Pb, Cu, Zn, K, accounted for the total quantity 98.1%, and Cl accounted for about 40%. Therefore, SFA can be reused as metallurgy materials or enriched into metal ore. Analysis of X-ray diffraction(XRD) indicated the SFA was mainly composed of metal chlorides, such as PbCl2、KPb2Cl5, et al. The result further confirmed that the heavy metal were evaporized with chlorides during the heat-treatment.In conclusion, the result of experiment shows that the method of TSP is feasible to treat the fly ash. It can solve the environment potential hazard problem which was created by the tradition methods for fly ash treatment.更多还原