Abstract
The recovery and reuse of waste printed circuit boards (PCBs) has attracted more and more attention from global researchers, as recycling of waste PCB metals is of great significance to the rational utilization of metal material resources. This study puts forward a clean and economical method in which enhanced gravity separation and wet high-gradient magnetic separation were combined to recover waste PCBs with heat treatment at a temperature of 240 °C. The heat treatment could improve the metal liberation effect of the PCBs, and the thermal behavior was measured by thermogravimetric analysis (TGA). The pyrolysis of the non-metal fraction (NMF) began around 300 °C, and the glass transition temperature of epoxy resin was 135.17 °C. The enhanced gravity separation technique was used for the separation of metals and NMF under the compound force field. The metals grade of the gravity concentrates fraction (GRF) was 82.97% under the optimal conditions, and the metals recovery reached 90.55%. A wet high-gradient magnetic separator was applied to classify the GRF into magnetic (MA) and non-magnetic (NMA) fractions, which could achieve iron and copper enrichment. After the three stages combined process, the copper and iron grades of the NMA and MA fractions were 70.17% and 73.42%, and the recovery reached 74.02% and 78.11%, respectively.
Highlights
With the rapid development of the global electronic information industry, the requirement for electrical and electronic equipment is sharply increasing
Before the printed circuit boards (PCBs) heat treatment and separation experiments, the elemental composition should be confirmed. For this a sample was ground to less than 0.074 mm by using a ring pulverizer (FW400A, Maike, Taian, China), and dried in the oven (105 ◦ C) for two hours, the elemental composition of the waste PCBs was analyzed by XRF (S8 Tiger, Bruker, Karlsruhe, Germany) with the elements analysis ranging from 4 Be to 92 U
Epoxy resin is the adhesive of PCB, and its glass transition and thermal decomposition occur at a high temperature [26,27].The waste PCBs was subjected to heat treatment for the better metal liberation, but thermal decomposition should be avoided due to the potential release of noxious gases [28,29,30]
Summary
With the rapid development of the global electronic information industry, the requirement for electrical and electronic equipment is sharply increasing. Electrostatic separation technique utilizes the different electrical properties of the NMF and metals, whereby the organic particles were negatively charged while the metal particles are positively charged during the triboelectrification process These mechanical-physical methods have the advantage of being economical and generating less secondary pollution. The mechanical-physical approaches of enhanced gravity separation and high-gradient magnetic separation were combined to recover the metals from waste computer PCBs. The heat treatment of waste PCBs was performed before the recovery tests. This is the first study of a combined process including heat treatment, enhanced gravity separation and wet high-gradient magnetic separation for metal recovery and the enrichment of copper and iron It provides an economical, efficient and environmentally friendly method for the recycling of waste PCBs and provides significant guidance for the recycling of metal materials
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