【作者】 刁智俊；

【导师】 赵跃民；

【作者基本信息】 中国矿业大学 ， 环境工程， 2013， 博士

【摘要】 废弃电路板的回收利用是实现资源循环利用的有效途径，能够在防治环境污染的同时获得可观经济效益。而破碎是制约废弃电路板资源化利用的关键因素。本文基于高压电脉冲的选择性破碎作用，实现了电路板中金属与非金属的有效解离以及金属的富集，并通过对破碎产物的粒级分布、解离特性和表面形态的分析，研究了高压电脉冲的作用机理和破碎能耗；利用X射线荧光光谱仪（XRF）对破碎产物进行了表征；利用扫描电子显微镜附加电制冷能谱仪（SEM/EDS）及气相色谱/质谱联用仪（GC/MS）对破碎产物进行了分析；借助ReaxFF反应分子动力学模拟研究了高压电脉冲破碎过程中环氧树脂热解的反应机理和反应产物，并分析了环氧树脂的热解在电路板的破碎以及金属与非金属解离过程中的作用。电路板的高压电脉冲破碎结果表明，破碎产物中+2mm粒级产率大，2mm以下各粒级的产率小，该结果与机械破碎的结果不同。另一方面，高压电脉冲能够在破碎电路板的同时实现对电路板中金属的富集。随着电压和脉冲个数的增加，2mm以下各粒级中铜纯度逐渐增加。当电压为170kV脉冲个数为600时，虽然-2+0.5mm粒级产率为32.39wt%，但是电路板中88.67wt%的铜都集中在该粒级。破碎产物的平均粒径随单位质量电路板能耗的增加而减小，而平均单体解离度主要由单个脉冲能量即电压决定；电压主要影响+2、-2+1.5mm粒级单体解离度。不同实验条件所得破碎产物中1.5mm以下各粒级的单体解离度均为100%，表明该部分细颗粒的产生过程几乎都是在铜箔与环玻布板解离过程之后。采用高压电脉冲进行破碎时，破碎能耗与破碎产物颗粒数量的平方根的增量成正比，建立了数量方程：E=KN（D-1.5-d-1.5）。模拟结果表明，经验公式数量方程适用于高压电脉冲破碎电路板的能耗研究，另一方面也说明在热能作用下电路板中有机物发生的化学反应是高压电脉冲破碎电路板的主要作用机理之一。采用SEM观察固体破碎产物表面形貌，结果表明在高压电脉冲作用下环氧树脂发生了熔融和热解反应。用GC/MS对热解过程中产生的溶于水的有机物进行了分析，结果表明高压电脉冲破碎产生的可溶有机物的种类较少，产生的二次污染较小。ReaxFF反应分子动力学模拟结果表明，温度和升温速率对环氧树脂和固化环氧树脂模型化合物的热解反应有较强的影响。升高反应终温和提高升温速率都能缩短引发时间。因所需活化能最低，醚键的断裂是环氧树脂模型化合物分解的引发反应，并且在所有反应条件下CH₂O皆为优先生成的产物，其它主要的小分子化合物还包括H₂O、CH₄和H₂。固化环氧树脂模型化合物的热解引发反应为含N和含O桥键的断裂。温度较低时，固化环氧树脂模型化合物热解的主要产物为H₂O，而温度较高时，H₂为主要产物，并且高温促进了含石墨烯结构且分子量较大的碳团簇的形成。在固化环氧树脂模型化合物的热解反应中，H₂O为最先生成的小分子产物，主要的小分子产物还包括CO、CH₄、CH₂O和H₂。ReaxFF反应分子动力学模拟首次证实了高压电脉冲破碎过程中电路板热解生成大量气体所造成的局部压力增加也是导致金属与非金属解离的主要原因。ReaxFF反应分子动力学模拟所得环氧树脂热解机理和化学反应现象与实验结果一致，说明ReaxFF反应分子动力学方法为从分子水平上研究有机物高温热解反应提供了一种有效的途径。更多还原

【Abstract】 Resource utilization of waste printed circuit board （WPCB） is an effective way forrecycling of resources, protecting environment and obtaining considerable economicbenefits. However, the crush is the main reason for restricting resource utilization ofWPCB. On the basis of the selective crushing characteristic of high voltage pulse（HVP）, the fragmental experiments were performed. The metals in WPCB wasseparated from nonmetals effectively and metal enrichment was also realized.Furthermore, the energy consumptions of various theories of comminutionmechanisms of crushing were studied, according to the distribution of size fractions,characteristic of degree of liberation and surface features of crushed products obtainedunder different experiment conditions. The crushed products were characterized by XRay Fluorescence Spectrometry （XRF） and analyzed with SEM/EDS and GC/MS. Inorder to investigate the products and detailed pyrolysis mechanisms for WPCB duringHVP crushing process, we used ReaxFF reactive force field to perform a series ofmolecular dynamics simulations （MDSs） on model compound of. According to theMDSs results, we studied the effects of pyrolysis on the fragmentation of WPCB andliberation of metals from nonmetals.The results show that the yield is prominent for+2mm size fraction but not for-2mm, which is different from the results of mechanical crushing process. On the otherhand, The WPCB can be crushed and the metals in WPCB can be concentratedsimultaneously. The pureness of copper in-2mm size fraction increased with thevoltage and the number of pulses of HVP. Although the yield of-2+0.5mm sizefraction was32.39wt%, in total88.67wt%of copper in WPCB was concentrated inthis fraction with voltage of170kV and600pulse.The average particle size decreased with the increase in energy consumption perweight of WPCB. And the average monomer dissociation degree is decided by thepulse energy of voltage.The voltage influences mainly the monomer dissociationdegree of+2,-2+1.5mm size fraction.The degree of liberation of-1.5mm size fractionfrom crushed products is100%under different experiment conditions. The resultindicate that the-1.5mm size fraction is almost produced after the separation betweencopper foil and epoxy-glass cloth laminate.Broken WPCB by high voltage pulse, energy consumption of fragmentation isproportional to the increment of the square root of the quantity of crushed product particles. The Number equation was established: E=KN（D-1.5-d-1.5）. The result ofnon-line fitting demonstrate that the empirical formula, Number equation, applies toresearch energy consumption of process that crushed WPCB by high voltage pulse. Onthe other hand, the result show that The Chemical Reaction of organics in WPCB hasoccurred under the action of thermal energy, which could also be the main mechanismto crush WPCB.The surface features of solid products were studied with SEM. The results exhibitthat under the high temperature condition caused by HVP, modeling and thermaldecomposition reaction of epoxy has occurred. The compounds, which were producedin thermal decomposition, dissolved in water were analyzed with GC/MS. The resultsshow that few soluble organic matters were generated during HVP crushing process.ReaxFF molecular dynamics simulations （MDSs） results show that both thetemperature and the heating rate strongly affect the decomposition of epoxy resins andcured epoxy resins. both increased in final temperature and heating rate shorten theinitiation time. The results show that the decomposition of epoxy resins modelcompound is initiated by ether linkage cleavage reaction with the lowest activationenergy. We found CH₂O formation to be the first reaction to occur. Other mainsmall-molecule products observed in our simulations include H₂O, CO and H₂. ReaxFFMDSs results show that the cleavages of nitrogen-and oxygen-bridge bonds areinitiation reaction of the decomposition of cured epoxy resins model compound. Theresults show that the cleavages of nitrogen-and oxygen-bridge bonds are initiationreaction. We found that at lower temperatures the primary product is H₂O, whereas athigh temperatures H₂is dominant one and the larger carbon cluster containinggraphene-related structure prefers to formation. Furthermore, other small molecularproducts found include CH₄, HCN, NH₃and CO₂.ReaxFF MDSs provide that the increase of local pressure in discharge channelscaused by the pyrolysis gas during HVP crushing process is also the main factor forliberation between metals and nonmetals. The agreement of these results with availableexperimental observations demonstrates that ReaxFF can provide useful insights intothe complicated bulk thermal decomposition of organic materials under extremeconditions at the atomistic level.更多还原