| 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%。... |
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