【作者】 卫樱蕾；

【导师】 严建华； 李晓东； 岑可法；

【作者基本信息】 浙江大学 ， 工程热物理， 2010， 博士

【摘要】 我国作为一个发展中国家,持久性有机污染物(Persistent Organic Pollutants,简称POPs)污染问题十分严峻,加入斯德哥尔摩公约并切实履行公约符合我国的长远利益。公约要求,到2015年,实现对重点行业已识别的含二恶英废物实施环境无害化管理与处置；到2028年,完成所有含多氯联苯废物环境无害化管理与处置。本文针对这两种代表性的POPs,采用机械化学(Mechanochemistry, MC)法对二恶英(PCDD/Fs)和多氯联苯(PCBs)的无害化处置进行了一系列的基础性研究工作,研究内容主要包括：(一)对影响机械化学法降解效率的参数进行研究,以球磨时间、球磨转速、球磨介质材料、球料比和填充系数、还原剂的类型和添加比例这几个典型参数为例,研究含氯有机物的脱氯速率与参数之间的关系。并将MC法用于含溴电路板的处理,取得了最佳27.6%的脱溴率,MC法对于含溴有机物有一定的降解作用。(二)以典型的二恶英生成前驱物五氯酚(PCP)为研究对象进行机械化学降解实验。结果表明：PCP和CaO混合比例n(Ca)：n(C1)=4,球磨公转转速400r/min的情况下,PCP含量随反应时间延长而迅速减少,球磨6h后,残留的PCP含量少于1%,球磨8h以上,无机Cl离子浓度达到99.9%。PCP在降解过程中,Cl从有机相中脱除,转变为无机Cl离子。使用石英砂(SiO2)辅助研磨、采用不锈钢磨球均可提高降解效率。对降解后的产物进行气相色谱／质谱、X射线多晶体衍射光谱、傅里叶红外光谱、热重、离子色谱等多种仪器表征,对降解机理推测如下：PCP首先发生的是还原脱氯的过程,PCP得到电子的同时去掉一个氯取代基并释放一个Cl阴离子。Cl阴离子与-CaO接触反应,形成CaOHCl中间体,PCP的氯取代基逐步从苯环上脱除下来,最终发生开环降解,再经过一系列复杂的反应,形成无定形C和CaCl2·nH2O。(三)废弃鸡蛋壳等作为钙基添加剂,对实际医疗废物飞灰中的二恶英进行机械化学无害化处理。研究了球磨时间、球磨转速对二恶英总量和毒性当量降解的影响。利用扫描电镜(SEM)对球磨后样品的结构、尺寸进行分析和表征。实验结果表明,蛋壳作为添加剂可以有效地降解飞灰中的二恶英,通过8h以上的球磨,二恶英的总含量和毒性当量都降低到50%以下。相同条件下,球磨转速越高,二恶英的降解率也越高。对于规模化的应用,选取转速在300-400 r/min之间较为合理。脱氯反应以及分解反应是机械化学法降解二恶英的主要途径。(四)在水平滚动式球磨试验台上对高浓度PCBs污染土壤进行机械化学降解,处理20 h后,PCBs总量的降解率达到74%,毒性当量(WHO-TEQ)的降解率达到78%。水平滚动式低速球磨对土壤中高浓度的PCBs有降解效果,是一种较有商业应用前景的、成本低廉且有效的含卤化合物无害化处置方法。对降解前后的PCDD/Fs生成量进行了比较,结果表明,机械化学法处理高浓度PCBs污染物的同时,其产物中PCDD/Fs总量及毒性当量呈现下降趋势,几乎不存在PCDD/Fs的二次合成问题。(五)通过密度函数理论计算获得了13种PCBs的分子结构,电离能和电子亲和能。采用了目前最常用的三参数混合密度函数(B3LYP)结合6-31G(d)和6-311G(d,p)基组。非邻位氯代的PCBs相对于邻位氯代的PCBs有更小的扭转角。所有13种PCBs的阴离子和阳离子的结构相对于对应的中心分子更加平面。其中非邻位氯代PCBs的阴离子的结构近似于共平面结构。增加一个电子使得PCBs的C-Cl键长变长。除一氯联苯(MoCBs)外,其余的PCBs的电子亲和能都是正的。PCBs的电离能和电子亲和能都随氯代水平上升而增加。这说明高氯代的PCBs更易于被还原脱氯,而低氯代PCBs更容易被氧化。更多还原

【Abstract】 The Stockholm Convention (SC) on POPs is a global treaty designed to protect the environment and human health from POPs. As a developing country, China faces a more complex environmental problem than developed countries. The control and reduction of POPs is a significant problem in China’s environmental protection strategy. Take PCBs and PCDD/Fs for example:identified dioxin wastes released by key industries must be environmentally sound disposaled by 2015, and all PCBs-containing wastes must complete the environmentally sound disposal by 2028.This dissertation launched a series of fundamental experimental study, with aim to investigate the mechanochemical degradation mechanism of PCBs and PCDD/Fs. The main contents of this dissertation are formed by the five parts as follows.1. The relationship between the dechlorination rate of chlorinated organic and the parameters which affecting the mechanochemical degradation efficiency was experimentally studied. These parameters include:grinding time, revolution speed, materials of the milling media, ball-to-powder ratio(BPR), ball mill fill-factor, the type and ratio of the reducing agent. And organic bromine compounds were also treated by MC means, and the highest debromination rates was 27.6%.2. Mechanochemical treatment of typical dioxin precursor was experimentally studied. PCP was mixed with CaO in a molar ratio of 1:20. And the mixture was co-grinding in a planetary ball mill at the revolution speed of 400 r/min. The effects of the milling time and additives on the dechlorination rate were investigated. The results indicate more than 99% of the PCP concentration was reduced when 6 h grinding is conducted.The yield of Cl ion concentration reached 99% after 8 h grinding. Organic chlorine of PCP is gradually changed into inorganic ion-state chlorine as milling proceeding. The addition of quartz to the grinding mixture facilitated dechlorination. The resulting product was characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), thermogravimetric analysis (TG) and ion chromatography (IC). On the basis of the experimental results, the decomposition mechanism was derived that free radicals were induced by grinding on CaO surfaces and subsequently the charge transfer occurred on the organic PCP. C-Cl bonding in PCP tended to be cut off to produce some intermediates or products. Cl atom splited off from the C-Cl bond of PCP. At the same time, CaO reacted with the Cl atom to form Ca(OH)Cl intermediate. Cl substituents on PCP have been gradually removed from the structure of a benzene ring. PCP can be dechlorinated following the pathways of dechlorination and oxidation. With a series of complicated reactions induces, a mixture of CaCl2·nH2O and amorphous carbon are formed as the final products.3. The mechanochemical decomposition of the virulent polychlorinated dibenzo-p-dioxins and polychlorinated dibenzof urans (PCDD/Fs) in fly ash was studied by planetary mill. Calcium-based additives such as waste eggshell powder were added as reducing agent. Effects of milling time and rotation speed of the ball mill on degradation efficiency of PCDD/Fs for the total concentration and I-TEQ concentration were investigated. The grinding products were characterized with regard to their structure and size by scanning electron microscopy(SEM). The experimental results indicate that by using eggshell powders, more than 50%of the total concentration and I-TEQ concentration of PCDD/Fs were reduced when 8 h grinding is conducted. The degradation efficiency increases with an increase in rotation speed. It is reasonable to choose 300-400 r/min for large-scale utilization. The destruction and dechlorination reaction occoured simultaneously in mechanochemical treatment of PCDD/Fs.4. The mechanochemical decomposition of polychlorinated biphenyls (PCBs) in soil was studied using a horizontal mill. Grinding a mixture of PCBs and calcium oxide with or without quartz was conducted, and the addition of quartz facilitated dechlorination. Effects of milling time and additives on the degradation efficiency of PCBs were investigated:74%of the total concentration and 78%of the World Health Organization toxic equivalence quantity (WHO-TEQ) of PCBs were reduced after 20 hr of grinding. Formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) during mechanochemical destruction of PCBs was evaluated. The results demonstrate that the problem of PCDFs formation can be overcome.5. Density functional theory calculations were performed to obtain the structures, ionization potentials and electron affinities of 13 polychlorinated biphenyls. A popular three-parameter hybrid density functional, B3LYP, was utilized with the 6-31G(d) and 6-311G(d,p). The structures of non-ortho-chlorinated PCBs have small torsional angles. The optimized structures of the cations and anions of the all the selected PCBs tended to be more planar than the structures of the corresponding neutrals. The anions of non-ortho-chlorinated PCBs have nearly coplanar structures. The addition of an electron increases the C-Cl bond length. Except for MoCBs, the electron affinities of the selected PCBs were positive. The electron affinities and ionization potentials increase with the chlorination level of PCBs. This suggested that the higher chlorinated PCBs are inclined to be reductive dechlorinated, and the lower chlorinated PCBs tend to be oxided.更多还原