Theoretic model and computer simulation of separating mixture metal particles from waste printed circuit board by electrostatic separator

doi:10.1016/j.jhazmat.2007.09.089

Journal of Hazardous Materials

Volume 153, Issue 3, 30 May 2008, Pages 1308-1313

https://doi.org/10.1016/j.jhazmat.2007.09.089 Get rights and content

Abstract

Traditionally, the mixture metals from waste printed circuit board (PCB) were sent to the smelt factory to refine pure copper. Some valuable metals (aluminum, zinc and tin) with low content in PCB were lost during smelt. A new method which used roll-type electrostatic separator (RES) to recovery low content metals in waste PCB was presented in this study. The theoretic model which was established from computing electric field and the analysis of forces on the particles was used to write a program by MATLAB language. The program was design to simulate the process of separating mixture metal particles. Electrical, material and mechanical factors were analyzed to optimize the operating parameters of separator. The experiment results of separating copper and aluminum particles by RES had a good agreement with computer simulation results. The model could be used to simulate separating other metal (tin, zinc, etc.) particles during the process of recycling waste PCBs by RES.

Introduction

The waste printed circuit board (PCB) is increasing worldwide. Recycling of PCB is an important subject not only from the treatment of waste but also from the recovery of valuable materials [1], [2]. The corona electrostatic separation was proved to be an efficient and environmental way for recovering metals from PCB scraps [3]. The separated metal particles after corona electrostatic separation always mixed with different metals (such as copper, aluminum, tin, zinc, etc.). Traditionally, the mixture metals was sent to smelt factory and refined to pure Copper. Some valuable metals (aluminum, zinc and tin) with low content in PCB were lost during smelt and waste these resources.

Simple and reliable roll-type electrostatic separation (RES) has been investigated extensively in the minerals processing industry for recycling metals. But there is not relevant research about using RES to separate different metals. A study [4] only established a theoretic model for computing the trajectory of solo conducting particle from waste PCB in RES. However, the metal particles from waste PCBs were mixture (such as copper, aluminum, tin, zinc, etc.). How to separating and recycling these resources was an important object. The aim of this paper is to show that the RES can be successfully employed for separating different metal particles. On the basis of theoretic model [4], a program by MATLAB language was wrote. The program was designed to simulate the process of separating mixture metal particles. The operating parameters of RES: electrical, material and mechanical factors were analyzed to optimize the operating parameters of separator.

Section snippets

Principle of proposed method

The separator consists of a rotating roll, connected to the ground, and a high-voltage electrode (Fig. 1). The materials were fed on the rotating roll by an electric shaker. Apart from the electric force involved in the electrostatic separation system, the gravitational force, centrifugal force and other mechanical forces are also present. At first, the metal particles were moved with rotating roll. When the co-acting forces on them satisfied special condition, the particles detached from the

Trajectories analysis

The theoretic model [4] has been established from computing electric field and the analysis of forces on the particles. However, some particles were acicular, filar or flat, not spherical and the charging value of the particle was correlated with it is surface area. Then, the surface equivalent radius (r_s) is used. The particle's r_s is $r_{s} = \frac{\sqrt{S / π}}{3}$ where S is the surface area of particle.

As shown in Fig. 2, when the particle was acicular, the particle was regarded as ellipsoid and the S is $S = 2 π a^{2} (1 + F G)$

Results and discussion

Fig. 5 shows the particle trajectories of mixture material (copper and aluminum) in the RES with the general operating parameters. The difference between d_(Cu) and d_(Al) (X_d) was only 14.8 mm. This distance barely supports industrial application. Single factor changing method was used to prove if a series optimized operating parameters could be applied in practical production. On the basis of general operating parameters, only one factor was changed and other factors were unchanged. In this

Conclusions

It has been shown in present study that, the collecting points of metal particles can be computed by Eq. (6). 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. The experimental results of separating copper and aluminum particles by roll-type electrostatic separator (RES) had a good agreement with computer simulation results, which proved the model could

Acknowledgements

This project was supported by the National High Technology Research and Development Program of China (863 program 2006AA06Z364), Program for New Century Excellent Talents in University and the Research Fund for the Doctoral Program of Higher Education (20060248058).

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Application of corona discharge and electrostatic force to separate metals and nonmetals from crushed particles of waste printed circuit boards
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