电子垃圾拆解区甲基硅氧烷溴代产物的排放机理及其在土壤中的转化行为研究

Recently, environmental behavior of methylsiloxanes has attracted increasing attention. Due to their usage in printed circuit boards (PCBs) as encapsulating and insulating agents, methylsiloxanes may be brominated by free bromine (arising from brominated flame retardants in PCBs) during e-waste thermo-treatment. As brominated organic compounds were always more toxic than their parent compounds, generation/emission of brominated methylsiloxanes attributed to e-waste dismantling and their environmental fates deserve dedicated attention. However, relative studies were scarce. During one pre-research in 2017, brominated methylsiloxanes were found in soil samples from an e-waste dismantling industrial park located in Zhejiang Province. Following the pre-research, the current project will systematically analyze dust and soil samples from e-waste dismantling areas located in Taizhou City, Zhejiang Province and Xinle City, Hebei Province, and then select typical brominated methylsiloxanes contaminated areas; combining with simulated experiments, investigate the emission characteristics and influencing factors (temperature, time, oxygen and metal content) of brominated methylsiloxanes emission during PCBs thermo-treatment ; by comprehensively analyzing intimidate products, illuminate specific differences on hydrolysis/rearrangement of homologues and isomers of brominated methylsiloxanes in soils; The current project will provide a preliminary understanding of resources and environmental behavior of brominated methylsiloxanes, and contribute to establishing potential control and abatement strategies for these compounds in e-waste dismantling.

近年来，甲基硅氧烷的环境行为引起了科研人员的关注。甲基硅氧烷应用于电路板的封装材料和绝缘漆中，其在废旧电路板热处理过程中可能与溴系阻燃剂产生的游离溴发生溴代反应。鉴于溴代有机物的生物毒性通常高于母体，电子垃圾拆解过程中溴代甲基硅氧烷的排放和环境行为需要引起重视，然而目前缺乏相关研究。在2017年的预研中，项目申请人在浙江某电子垃圾拆解工业园土壤中检出溴代甲基硅氧烷。在此基础上，本项目将考察浙江台州和河北新乐多个电子垃圾拆解工业园的灰尘/土壤样本，从而筛选溴代甲基硅氧烷污染的典型区域；结合模拟实验，揭示典型区域电路板热拆解中溴代甲基硅氧烷的排放特征及影响因素（温度、时间、氧气和金属含量）；基于全面分析中间产物，阐明区域土壤中溴代甲基硅氧烷同系物和异构体在水解/重排反应中的差异性机制。该项目有助于深入了解溴代甲基硅氧烷污染来源和环境归趋，为电子垃圾拆解中此类化合物的控制和消减策略提供科学依据。

本项目系统研究了电子垃圾拆解地甲基硅氧烷及其溴化产物的来源和归趋。在电子垃圾热拆解实验中，除挥发性甲基硅氧烷 （D4、D5 和 D6）以外，通过 Q-TOF GC/MS 检测技术还发现了甲基硅氧烷溴代产物的生成，即D3D(CH2Br)、D4D(CH2Br)和 D5D(CH2Br)。总体而言， 甲基硅氧烷和溴代甲基硅氧烷分别在 300-400°C 和 400-500°C 时排放速率最快， 占其总排放量的 35-51%和 39-82%。在电子垃圾拆解地土壤样品中 D4-D6 的浓度比对照区域的土壤高出 3 个数量级，拆解地土壤样品中都检测到了 D3D(CH2Br)—D5D(CH2Br)，浓度<LOD-70.3 ng/g dw （df = 23-77%），而在对照区域中未检出。模拟实验表明，土壤中溴代甲基硅氧烷的水解（9.0-378 d）和挥发（8.5-1007 d）半衰期比其母体甲基硅氧烷长 1.6-5.0 倍，表明硅氧烷溴代产物的环境持久性明显强于其母体。在溴代硅氧烷研究的基础上，进一步拓展特殊支链硅氧烷的环境归趋研究。首次发现油田采油废水中氯离子在电化学处理工艺产出活性氯进而诱导甲基硅氧烷生成一/二氯代产物，转化率0.2-28%，单氯代产物在土壤中的降解和挥发半衰期比母体长 1.1—2.4 倍，二氯代产物的降解速率比单氯代产物的慢 1.12—4.66 倍。揭示了污水/渗滤液中苯基和乙烯基等改性硅氧烷支链的氧化、加成等特异性反应途径，为有机硅化学品的污染控制和风险评估提供重要基础数据。本项目为有机硅化学品的污染控制和风险评估提供重要基础数据。 项目标注 SCI 论文 10篇，发表于ES&T、Water Research、Environment International 等知名期刊。