【作者】 吴江；

【导师】 许振明；

【作者基本信息】 上海交通大学 ， 环境工程， 2009， 博士

【摘要】 电路板是电子和信息工业的基础,几乎所有电子产品中都含有电路板。随着现代社会对电子产品的广泛使用和技术革新导致的产品快速更新换代,废旧电路板急剧增加。废旧电路板中含有大量的贵金属,具有很高的资源利用价值。同时,由于废旧电路板结构和成分复杂、含有大量有毒有害物质,若不采用环境友好方式处理,将对自然环境和人体健康造成严重威胁。目前,废旧电路板回收处理技术比较落后,对自然环境造成了严重的污染,急需研发科学、高效、环境友好的处置和回收技术和装备。高压静电分选技术可以实现破碎废旧电路板中金属和非金属的物理分离,并具有高效、低耗、环境友好等显著优点,是目前废旧电路板无害化处理和资源化利用的先进技术之一。为此,本文在建立高压静电分选过程理论模型的基础上,系统研究了高压静电方法分离破碎废旧电路板中金属与非金属的规律,提出了静电分选过程中的关键技术和存在的问题,并针对这些关键技术和问题进行了分析和优化设计,为废旧电路板的无害化处理与资源化利用提供了理论基础和新方法。通过对破碎废旧电路板高压静电分选过程进行因子设计和响应曲面设计,分别建立了分选过程的线性-交互作用模型和二阶非线性模型。得出了电压、辊速、电晕电极角度、电晕电极距离和静电极角度等因素的主效应、交互作用和二阶作用,及其对分选过程金属、中间体和非金属的影响规律;并通过模型对分选过程参数进行了优化,得到了满足不同生产要求的最优参数匹配。线性-交互作用情况下的最优设置为U=30 kV、N=60 rpm、α1 =25°、s1 =70 mm、α2=75°、s2 =90 mm;二阶非线性情况下的最优设置为U=28.5 kV、N=60 rpm、α1 =25°、s1 =70 mm、α2=75°、s2 =90 mm。研究发现“中间体-分选效率”评价指标无法解释物料金属含量对分选效率的影响,并针对这一问题提出了破碎废旧电路板颗粒荷电的正态分布假设。根据假设,讨论了“中间体-分选效率”评价指标的适用范围:当分选过程仅受静电分选系统因素影响时该指标完全适用,即中间体量越小分选效率越高;当分选过程受到物料金属含量影响时,必须结合金属产品纯度对分选效率进行判断。通过引入空气阻力和提出金属颗粒在离子化区域中的“临界荷电状态”假设的基础上,对破碎废旧电路板金属颗粒的轨迹模型进行了修正,修正后的轨迹模型比原有模型更加与实际情况吻合。提出了“稳定颗粒”和“不稳定颗粒”的概念,将10 kV电压降范围内,落点差小于5 cm的颗粒定义为“稳定颗粒”,将落点差大于5 cm的颗粒定义为“不稳定颗粒”。同时,研究了多粒度混合颗粒对高压静电分选过程的影响,发现单一电场对多粒度混合颗粒体系无法进行有效分选。在研究非金属粉末对高压静电分选过程影响的基础上,提出了非金属粉末在高压静电分选时的填充效应、包裹效应和粘着效应,并研究了其对分选效率和金属回收率造成的影响。发现了非金属粉末在物料颗粒中的不均匀分布所造成的分选过程的不稳定性和积尘现象,当物料颗粒中的非金属粉末含量超过10%时,将对分选过程造成显著的影响。研究了环境湿度对于破碎废旧电路板高压静电分选过程的影响,发现由于潮湿环境中非金属颗粒表面导电性的增大和粘附力的增强,导致分选过程的效率随相对湿度的增加而降低。对破碎废旧电路板高压静电分选,物料的存放以及运行过程的环境湿度不能超过70%,控制在60%以内最佳,以降低湿度造成的影响。在传统辊式分选设备(RTS)的基础上,提出了破碎废旧电路板“多级分选”的概念,构建了实验性的新型双辊式两级分选设备(T-RTS)。通过和RTS的比较实验,发现T-RTS在提高分选质量、减少中间体量、提纯非金属产物、分选过程的稳定性以及提高处理能力方面,都比传统的RTS有了显著的进步:中间体减少了45%,金属产物提高了8.9%,非金属产物中残余金属含量降低了81.3%,处理量提高了1倍。更多还原

【Abstract】 As the core of electronics and information industrial, printed circuit boards (PCBs) used in almost all electrical and electronic products. The waste PCB is sharply increasing with the extensive use of electronic products and the rapid replacement of product caused by technological innovation. Waste PCB has considerable economic value for its high content of noble metals and rare metals. At the same time, its toxic and harmful substances will make a serious threat to the natural environment and human health if there are not appropriate methods for its treatment. However, the efficiency of present recycle technology is low and leads to some serious second-pollutions for the natural environment. Therefore, it is urgent to develop a scientific, efficient, and environmentally friendly recycling technology. High-voltage electrostatic separation is an excellent waste PCB recycling technology for its high efficiency, low energy consumption and environmentally-friend. This paper provides a systemic study on recycling metals and nonmetals from waste PCB, presents the key technologies and problems, optimizes the separation process and promotes the technology and theoretical support for recycling waste PCB.The study analyzes the factors’main effect, interaction through fractional factorial design and response surface methodology. The experimental data are discussed and some liner-interaction models and quadratic models are derived to describe the mass of middling, conductor and nonconductor products, respectively. The optimum setting of linear-interaction model is U=30 kV, N=60 rpm,α1 =25°, s1 =70 mm,α2=75°and s2 =90 mm. The optimum setting of quadratic non-linear models is U=28.5 kV, N=60 rpm,α1 =25°, s1 =70 mm,α2=75°and s2 =90 mm.The study found that the classical criterion can not make a reasonable explain for the relationship between the metal content of feeding materials and the separation efficiency. This paper puts forward a“normal distribution assumptions”to overcome this problem. According to the assumption, the study makes a more precise definition for the criterion and its application scope.The study establishes an improved model for the theoretical trajectory of conductive particle through the introduction of air resistance and a "critical charge state" assumption for the metal particles in the ionization area. Compared with the previous one, the improved model shows a good agreement with the practices. The paper presents "stable particles" and "unstable particle". For the former, the particle’s landing displacement is less than 5 cm when the voltage drop is 10 kV. For the latter, the particle’s landing displacement is more than 5 cm.The study analyzes the impact of nonconductive powder (NP) caused by over-grinding on the electrostatic separation process. The paper presents NP’s filling, enfolding and adherring effects, analyzes the relationship between these three effects and the separation efficiency, and discusses the instability and powder-accumulation. The separation process will be strongly influenced by NP when NP’s content is more than 10%.The study explores the impact of ambient humidity on the electrostatic separation for recycling waste PCB. The results show that the separation efficiency will degrade for the increase of nonconductive particle’s surface conductivity and adhesive force in the humid ambient. For the electrostatic separation, the ambient humidity in storage and operation area should not exceed 70%, preferably less than 60%. The study summarizes the traditional roll-type separator’s (RTS) various problems due to its inherent structural in dealing with waste PCB, presents a concept about "Multi-step separation", and builds a new two-roll type separator (T-RTS). Compared with RTS, T-RTS makes notable progresses in improving quality, reducing the middling products, purifying the nonconductive product, increasing the stability and enhancing the treatment capability: the middling product decreases 45%,the metallic product increases 8.9%,the residual metals decreases 81.3% and the capacity increases 100%。更多还原