| With rapid development of economy and electronic manufacturing technologies, higher performance requirements and greater demands of electric and electronic equipment (EEE) make the replacement of EEE become more and more frequent, which results in large quantities of electronic waste need to be disposed of. Printed circuit boards (PCBs), the base of electronic industry, is an essential part of almost all of the electronic products. Therefore, developing non-polluting, efficient, and low-cost processing technologies for recycling WPCBs can not only avoid environmental pollution, but also help recycle valuable resources, which has a great practical significance for continuous improvement of the human living environment and resources recycling.In this study, we focused on the recycling of WPCBs.Centrifugal separation technology for separating solder from WPCBs was put forward firstly; new processes of "centrifugal separation + vacuum pyrolysis" and "vacuum pyrolysis+ centrifugal separation" for the combined recovery of solder and organic materials from WPCBs were investigated; a novel technology entitled "vacuum pyrolysis-centrifugation coupling technology" for recycling WPCBs was investigated, which integrated the processes of vacuum pyrolysis and centrifugal separation in order to improve the efficiency and decrease the recovery cost significantly.An overview of the current technologies for treating WPCBs was discussed, and then the advantages and problems of different methods were analyzed and evaluated. Solder was separated from WPCBs previously, which is very important in the process of recovering metals from WPCBs. Therefore, we used oil as medium to heat WPCBs until the solder melted into a liquid state, and then recycled it from WPCBs by the centrifugal force, which was carried out on the self-made equipment. The WPCBs used in this study are the two most common types.One was made from cellulose paper reinforced phenolic resin (referred to commercially as FR-2), and the other one was made from glass fiber reinforced epoxy resin (FR-4).The results showed that the major influence factors are rotating speed, oil temperature, rotating time and rotating times, and solder was effectively separated from WPCBs under the following conditions:the oil temperature was 240℃,and the rotating drum was rotated for 6 min intermittently with a rotational speed of 1400 rpm.Based on the centrifugal separation technology, a new process of "centrifugal separation + vacuum pyrolysis" for the combined recovery of solder and organic materials from WPCBs was investigated. The results of centrifugal separation indicated that the separation of solder from WPCBs was complete when WPCBs were heated at 240℃, and the rotating drum was rotated at 1400 rpm for 6 min intermittently. After centrifugal separation, the two types of WPCBs without solder were pyrolysed under vacuum condition at 600℃for 30 min. The results of vacuum pyrolysis showed that the type-A of WPCBs without solder pyrolysed to form an average of 69.5 wt% residue, 27.8 wt% oil,and 2.7 wt% gas;and pyrolysis of the type-B of WPCBs without solder led to an average mass balance of 75.7 wt% residue,20.0 wt% oil,and 4.3 wt% gas.The recycling process was further ameliorated based on our former work, aiming at recycling organic materials and solder from WPCBs with higher efficiency and lower cost. A recovery process consisting of vacuum pyrolysis and vacuum centrifugal separation was used to separate and recover materials from WPCBs.The two types of WPCBs were pyrolysed under vacuum condition at 600℃for 30 min. The type-A of WPCBs pyrolysed to form an average of 67.97 wt%residue,27.73 wt% oil, and 4.30 wt% gas, and pyrolysis of the type-B of WPCBs led to an average mass balance of 72.20 wt% residue,21.45 wt% oil, and 6.35 wt% gas.After vacuum pyrolysis, the pyrolysis residue was sent to the vacuum centrifugal separation process.The results indicated that the separation of solder was complete when the residue was heated at 400℃under vacuum condition, and the rotating drum was rotated at 1200 rpm for 10 min.Based on our previous work, a novel technology entitled "vacuum pyrolysis-centrifugation coupling technology" for recycling WPCBs was investigated in this study, which integrated the processes of vacuum pyrolysis and centrifugal separation in order to improve the efficiency and decrease the recovery cost significantly. The two types of WPCBs were pyrolysed at 600℃for 30 min under vacuum condition. The type-A of WPCBs pyrolysed to form an average of 67.91 wt% residue,27.84 wt% oil, and 4.25 wt% gas; and pyrolysis of the type-B of WPCBs led to an average mass balance of 72.22 wt% residue,21.57 wt% oil, and 6.21 wt% gas. During the pyrolysis process, the solder of WPCBs was separated and recovered when the temperature range was 400-600℃, and the rotating drum was rotated at 1000 rpm for 10 min.The pyrolysis residues contain various metals, glass fibers and other inorganic materials, which could be recycled for further processing.The pyrolysis oils can be used for fuel or chemical feedstock and the pyrolysis gases can be collected and recycled. |
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