【作者】 李佳；

【导师】 周尧和； 许振明；

【作者基本信息】 上海交通大学 ， 环境工程， 2007， 博士

【摘要】 目前,我国的家电及电子产品已达到淘汰报废的高峰期,报废量每年达100多万吨,而且国外又有大量的电子垃圾流向国内。但国内缺少无污染和全部资源化处理电子垃圾的技术和装备,落后的处理方法造成严重的环境污染和大量的资源浪费。印刷电路板是电子工业的基础,其中部分贵金属的含量是天然矿藏品位的几十倍甚至几百倍,具有很高的回收价值。电路板是玻璃纤维强化树脂和多种金属的混合物,其中金属和非金属紧密结合,分离难,是电子垃圾中最复杂、最难处理的,处理时要求技术含量高。目前国内处理废旧印刷电路板主要采用破碎后利用密度差的气流风选和水选进行金属与非金属的分离,存在效率低和二次污染等问题。因此,急需研究对废旧印刷电路板无害化处理和资源化利用的技术与装备。本研究通过理论分析,自主研发破碎机与高压静电分选机并对废旧印刷电路板进行无害化、资源化处理。首先研究电路板的破碎特性,利用MATLAB模拟分选空间的高压静电场分布,并通过MATLAB编程模拟金属颗粒的运动轨迹;由非金属颗粒的动力学分析得到电选机转辊的临界转速模型;对电选机应用于分离混合金属颗粒领域进行了探索;最终实现可工业应用的处理废电路板的成套生产线,为废旧印刷电路板无害化处理与资源化技术的开发提供理论依据,并为推动该技术走向工业应用奠定了基础。自行研制破碎机与高压静电分选机,确定剪切式旋转破碎机和冲击式旋转破碎机相结合的两级破碎方式对废旧印刷电路板进行破碎,使电路板中金属成分和非金属基板有效解离。剪切式旋转破碎机的工作转速为1440 rpm,转子半径为0.25 m,冲击式破碎机工作转速为2000 rpm,转子半径为0.2 m。高压静电分选机的供电系统最高电压达30 kV;电极结构为丝状电晕极与柱状静电极相结合的复合电极结构;电极位置可调;接地转辊表面镀铬处理,转速可调（10 rpm-1000 rpm）。Type-A（来自废旧电器）物料破碎后颗粒尺寸在1.2 mm以下达到完全解离,Type-B（来自电路板厂废料）物料破碎后颗粒尺寸在0.6 mm以下完全解离。破碎后电路板物料颗粒形状以球状和片状及多棱角状为主。MATLAB模拟高压静电分选空间电场强度分布,发现电场强度最大值位置偏向于静电极方向。不同工艺参数下电场强度分布表明,加大电压、采用复合电极结构、减小电极与接地转辊间的距离、增加静电极半径、减小静电极角度、加大电晕电极角度等参数变化可以提高电场强度,改善分选效果。当电选机工艺参数为以下范围时,可以得到较好的分选效果:U = 20 kV-30 kV, L = L₁ = L₂ = 0.21 m, R₁ = 0.114 m, R₂ = 0.019 m,θ₁ = 20°,θ₂ = 60°。建立了金属颗粒运动轨迹模型。该模型适用于多组电选机工艺参数的优化组合,为提高高压静电分选机的金属回收效率及扩展分选机的应用领域提供理论依据。应用模型对颗粒尺寸与受力关系的分析得到:小尺寸颗粒（r0 < 0.1 mm）受到外界因素影响更大,易出现特殊运动轨迹,破坏分选过程,在分选前应调整电选机的工艺参数,避免碰撞现象发生。在非金属颗粒的带电过程与受力模型基础上,建立高压静电分选机转辊的临界转速模型,得到颗粒饱和荷电判定方程。同时提出了“临界荷电转速n*”、“临界脱离转速n’”与“临界转速N”的概念。并得到提高临界脱离转速的方法:1)增加电晕极数量可增大电晕区宽度和电晕电场强度,从而提高临界荷电转速（n*）;2)避免火花放电的前提下,提高电压并减小电极之间的距离,以提高电晕电场强度及颗粒的荷电量;3)改变转辊的曲率和电晕极位置,以减少颗粒在转辊表面的电荷损失。高脱离转速可同时提高非金属回收率与金属纯度,对高压静电分选机参数设置具有重要的指导意义。计算机模拟混合金属颗粒的运动轨迹,拓展了高压静电分选机的应用领域。通过分析高压静电因素,机械因素,物料因素对混合金属颗粒分选的影响效果,得到一组优化工艺参数用于分选铜铝混合颗粒:U = 30 kV, R₂ = 0.025 m,α= 30°, L = 0.07 m, H = 0.28 m, R₁ = 0.125 m, n = 60 rpm, r₀ = 0.2 mm。在对废旧印刷电路板的破碎及高压静电分选的理论研究基础上,设计制造了一套处理废旧印刷电路板的生产线。生产线处理量可达300 kg/h,分选效率达到90%。为我国废旧电路板处理与资源化达到国际先进水平,提供绿色处理技术和先进的装备,对我国经济、社会和环境的可持续发展战略具有重要意义。更多还原

【Abstract】 New technological innovation continues to accelerate the replacement of equipment leading to a significant increase of waste electrical and electronic equipments （WEEE）. At present, the discarding and eliminating peak of electrical appliances and the electronic products has arrived in China. The annual discarding quantity was more than 1 million tons and large quantities of WEEE flows to the nation from foreign countries. Because there is lack of technology and equipments for recycling WEEE in domestic, backward processing methods caused serious environmental pollution and wasted large quantity of resources. The production of printed circuit boards （PCB） is the basis of the electronic industry as it is the essential part of all most electrical and electronic equipments （EEE）. PCBs contain nearly 28% metals which have abundant nonferrous metals such as Cu, Pb, Sn etc, and the purity of precious metals which is about more than 10 times of rich-content mineral. Therefore, recycling of PCB is an important subject not only from the treatment of waste but also from the recovery of valuable materials. The PCBs contain glass fiber, reinforced resin and metals. Their special physical and chemical characteristics make it difficult to recycle them. At present, the major processing method in domestic was density-based separation, which was time-consuming and emits waste to the environment. So, it is necessary to have research on recycling resources from waste PCBs without impact to the environment.On the basis of theoretical analysis, the scraping machines and corona electrostatic separator （CES） were originally created to research the harmless and resources processing for the waste PCBs in this study. At first the scraping characteristic of waste PCBs was studied. The software of MATLAB was used to simulate the distribution of electric field strength in the CES and the program was written to compute the trajectory of metal particle from scraped waste PCBs. The critical rotational speed model of CES was established from the analysis of dynamics of nonmetal particle. The method of applying the CES to separate mixture metal particles was explored. Finally, the complete equipment was manufactured. The complete equipment provided theoretical basis and industrial application experiences for recycling resources from waste PCBs without impact to the environment.The scraping machines and CES for researching the methods of processing the waste PCBs were originally created. Two-step scrapping process which was combined with shearing machine and hammer grinder was adopted. The metal parts were completed striped from base boards of waste PCBs during scraping. The parameters of shearing machine were: Rotational speed （n） was 1440 rpm and the radius of rotor was 0.25 m; the parameters of hammer grinder were: Rotational speed （n） was 2000 rpm and the radius of rotor was 0.2 m. The peak value of direct current power of CES was 30 kV. the electrodes include the filar type corona electrode and the columnar electrostatic electrode. The position of electrodes can be adjusted freely. The surface of rotating roll has chromate treatment and the rotational speed can be adjusted from 10 rpm to1000 rpm.When the particle size of scraped Type-A materials （from waste electronic equipments） was below 1.2 mm and the particle size of scraped Type-B materials （from local PCBs factory） was below 0.6 mm, the metal parts were completely striped from the base boards. The shapes of particles from scraped waste PCBs were spherical, flaky and polyhedral.The PDE tool box from software of MATLAB was used to simulate the distribution of electric field strength in the CES. It was found that the position of maximum value of electric field strength closed to the direction of electrostatic electrode. The way of increasing the applied voltage, radius of static electrode, angle of corona electrode and decreasing center distance, angle of electrostatic electrode were good for the separation. Through the correlation of simulated and experimental results, the good separation results were got under the optimized operating parameter: U= 20KV-30KV, L = L₁ = L₂ = 0.21m, R₁ =0.114, R₂ = 0.019m,θ₁ = 20°andθ₂ = 60°.The program wrote by MATLAB was used to establish the trajectory model for metal particle from scraped waste PCBs. The model was suitable for multi-compositions of operating parameters and provided theoretical support to enhance recycling efficiency and expand the applied domain of CES. From the analysis of relation between the particle size and particle stress, it was found that the small particles （r0 < 0.1 mm） were easy to be impacted from outside factors and broke the separation. So the operating parameters of CES should be adjusted to avoid colliding phenomenon.The charging process and stress of nonmetal particle were analyzed. The critical rotational speed model was established. From the model, the judgment equation of charging critical rotational speed was got. The concepts of the charging critical rotational speed （n^*）, the detaching critical rotational speed （n’） and the critical rotational speed （N） were proposed from the model. The method of increasing n’are: 1) increasing the number of corona electrodes, width of corona field and electric field strength to increase the charging critical rotational speed （n^*）; 2) under the premise of avoiding spark discharge, increasing applied voltage and decreasing discharge gap to increase corona electric field strength and charging value of particles; 3) changing the curvature of rotating roll electrode and position of corona electrodes to decease the loss of charge value on the surface of rotating roll electrode. Large n’could simultaneously improve the purity of metal parts and recycle percentage of nonmetal parts. The critical rotational speed model has the important guiding significance to the setting of operating parameters of CES.The computer simulation was used to compute the trajectories of mixture metal particles and the applied domain of CES was expanded. The impacts of electrical, material and mechanical factors to the particle trajectory were analyzed and the optimized operating parameters for separating copper and aluminum particles were got: U = 30 kV, R₂ = 0.025 m,α= 30°, L = 0.07 m, H = 0.28 m, R₁ =0.125 m, n = 60 rpm, r₀ = 0.2 mm.On the basis of study the theory of scraping and corona electrostatic separating waste PCBs, a set of production line for recycling resources from waste PCBs was manufactured. The products of the line were metal particles, glass fiber powders. The capacity of production line was 300 kg/h and the separating efficiency was 90%. The green processing technology and advanced equipments were provided to make our treatment methods and recovery of waste PCBs reaching the international advanced level, which has great signification for China’s economic, social and environmental sustainable development strategies.更多还原