| 题名 | 再生金属冶炼过程中多氯萘的排放特征与 生成机理研究 |
| 作者 | 姜晓旭 |
| 学位类别 | 博士 |
| 答辩日期 | 2016-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 郑明辉 ; 刘国瑞 |
| 关键词 | 多氯萘，影响因素，生成机理，再生金属冶炼，氯化反应。 Polychlorinated naphthalenes, Influencing factor, Formation mechanism, Secondary metal smelting, Chlorination reaction. |
| 其他题名 | Formation of Polychlorinated Naphthalenes during Secondary Metal Smelting Processes |
| 学位专业 | 环境科学 |
| 中文摘要 | 多氯萘（polychlorinated naphthalenes, PCNs）是 2015年 5月被列入《关于持久性有机污染物的斯德哥尔摩公约》受控名单中 的新型持久性有机污染物（persistent organic pollutants, POPs），我国将履行该公约所规定的义务，尤其亟需开展对我国重点排放源的污染控制和削减研究。本课题组前期初步识别了我国的几类典型 PCNs污染源，发现再生金属冶炼过程是我国最重要的 PCNs排放源之一。为了源头上控制 PCNs的生成和排放，还需对影响 PCNs排放的关键因素进行研究，深入认识 PCNs的生成机理，为开发减排技术提供理论依据。 本研究以再生金属冶炼过程作为重点排放源，结合现场研究和实验室模拟研究，对影响 PCNs排放的关键因素和生成机理进行了系统研究，得到了一些新的发现和认识，主要结果如下： （1）通过现场研究，阐明了我国典型再生铜冶炼过程不同工艺段 PCNs的分布特征。研究发现烟道气中 PCNs的排放水平为477.0–762.5ng m-3，毒性当量（toxic equivalent, TEQ）范围为4.4–8.3 pg TEQ m，不同冶炼阶段的排放浓度由-3高到低为：氧化段>加料熔化段>还原段。各阶段排放量在总排放量中的贡献顺序为：加料熔化段（65%）>氧化段（27%）>还原段（8%），因此加料熔化段是再生铜冶炼过程 PCNs排放的主要工艺阶段。其次，揭示了再生铜冶炼过程中PCNs的排放特征，发现一氯萘到三氯萘是主要的同类物，毒性同类物也以低氯代同类物（CN-1、CN-2和 CN-5/7）为主，这些指纹图谱为环境中 PCNs的源解析提供了数据支持。上述结果为针对再生铜冶炼重点工艺段进行 PCNs的排放控制提供了重要依据。 （2）选取我国 4家典型再生铝企业，系统地考察了 PCNs在不同排放介质中的分配比例以及影响PCNs排放水平的关键因素。研究发现再生铝冶炼过程中，99.99%以上的 PCNs分布于气相介质并排放到周边环境中，表明传统的布袋除尘技术对气相介质中 PCNs的去除效果并不理想。发现原料组成、燃料类型和含氯添加剂的使用是影响 PCNs排放的关键因素。值得关注的是，一般在冶炼的后期PCNs的排放水平会因有机杂质的消耗而降低，而本研究发现在冶炼后期的调质阶段和出铝阶段 PCNs排放浓度却明显升高，这与冶炼后期含氯添加剂的使用有关。以上的结果可以为关键冶炼工艺的改进提供科学依据，从而有效控制和削减PCNs的生成和排放。 （3）在现场研究的基础上，选取再生铜冶炼过程中产生的飞灰作为反应基质，搭建了实验室模拟反应平台，进一步地探索 PCNs的生成机理和影响因素。研究发现飞灰在 30 min内可生成高浓度的 PCNs，生成量（33.40–73.94 μg g）-1最高可达原始含量的 104倍。在250–450°C温度区间内，PCNs生成浓度在450°C下达到最高，高温更利于低氯代向高氯代同系物转化的氯化反应的发生。通过相关性分析、同系物分布变化趋势分析、特征同类物比较分析以及关键中间产物的定性定量分析，发现氯化反应是再生金属冶炼过程中PCNs生成的重要机理之一。 上述研究结果将有助于了解研究再生金属冶炼过程中PCNs排放的变化规律，识别其主要排放介质、主要排放工艺段、影响排放水平和特征的关键因素以及生成机理，这些成果将为优化工艺技术和污染控制技术提供科学依据，以达到控制和削减再生金属冶炼过程中 PCNs的生成和排放的目的。 |
| 英文摘要 | olychlorinated naphthalenes (PCNs) have been classed as new persistent organic pollutants under the Stockholm Convention on Persistent Organic Pollutants since May 2015. The inclusion of PCNs in the Stockholm Convention means that the Chinese Government has certain obligations and responsibilities, particularly to develop strategies and techniques for controlling PCN emissions. The manufacture and use of PCNs as industrial chemicals ceased in many countries in the 1980s, so emissions of unintentionally produced PCNs during industrial activities are now the main sources of PCNs. Most recent studies have been focused on determining the amounts of PCNs that are emitted by industrial sources. Secondary metal smelting processes have been found to be some of the most important sources of PCNs in China. However, the mechanisms through which PCNs are formed and the factors that influence the amounts of PCNs emitted during industrial processes in China are still poorly understood. Studies should be conducted to improve our understanding of the mechanisms through which PCNs are formed and to characterize PCN emissions. An intensive study of PCN formation mechanisms and the factors that influence the formation of PCNs during secondary metal smelting processes in China was performed in both field scale and laboratory scale. The results of the study are presented below. (1) Field studies were conducted elucidating the distribution amounts of PCNs emitted during different smelting stages of the secondary copper smelting process. The mass concentrations and toxic equivalent concentrations of PCNs in stack gases produced during different smelting stages were 477.0–762.5 ng m−3 and 4.4–8.3 pg toxic equivalents m−3, respectively. The PCN concentrations in the stack gases produced during the three smelting stages that were studied decreased in the following order: oxidation stage>feeding-fusion stage>deoxidation stage. The amounts of PCNs emitted during the stages decreased in the order feeding-fusion stage>oxidation stage>deoxidation stage. The feeding-fusion stage was found to dominate PCN emissions, contributing 65% of the total amount of PCNs emitted. The characteristics of the PCNs in the stack gases were also studied. The less-chlorinated homologues (mono- to tri-chloronaphthalenes) were found be dominant, and the dominant congeners were CN-1, CN-2, and CN-5/7. Identifying the key stage of the smelting process in which PCN emissions occur, as achieved in this study, will help in improving smelting techniques, allowing PCN emissions to be controlled and eliminated. (2) The PCN concentrations in different discharges produced during the secondary aluminum smelting process and the factors influencing the PCN concentrations in the discharges were investigated. More than 99.99% of the PCNs were found to be emitted to the atmosphere in stack gases. Traditional air pollution control devices used by the secondary aluminum smelting industry are therefore insufficient for controlling gaseous PCN emissions. The compositions of the aluminum scrap used in secondary aluminum smelters, the types of fuel used, and the addition of chloride additives were found to affect the amounts of PCNs that were formed and emitted. Variations in the PCN concentrations in the discharges produced during different smelting stages were compared. The concentration generally decreased as the smelting process proceeded because organic impurities became exhausted during the smelting process. However, high PCN concentrations were found in emissions produced during the refining and casting stages. The results of the study will allow both air pollution control devices and smelting techniques to be improved, so that PCN emissions can be brought under control. (3) On the basis of the results of the field studies, a series of laboratory-scale experiments to simulate the thermal formation of PCNs in a secondary copper smelter were performed using fly ash as the reaction matrix. The mechanisms involved in the formation of PCNs were investigated under different thermal conditions. High PCN concentrations (33.40–73.94 μg g−1), which were about two orders of magnitude higher than the initial PCN concentrations in the fly ash, were found after the fly ash had been heated for less than 30 min. The formation of PCNs was found to occur at between 250 and 450 °C, but more PCNs were formed at 450 °C than at lower temperatures. Correlation, homologue profile, and congener pattern analyses were performed and key intermediate products were quantified, and the results indicated that the chlorination mechanism was an important PCN formation pathway. A detailed PCN formation pathway (from naphthalene to PCNs) was proposed. |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/36868]  |
| 专题 | 生态环境研究中心_环境化学与生态毒理学国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 姜晓旭. 再生金属冶炼过程中多氯萘的排放特征与 生成机理研究[D]. 北京. 中国科学院研究生院. 2016. |
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