Environmetally Friendly Disassembly Of Electronic Components From Waste Printed Circuit Boards And Resources Recovery Of Aluminum Electrolytic Capacitors And Transistors

A printed circuit board?PCB?is an integral part of any electronic product.The waste PCB?WPCB?has the characteristics of huge amount,high toxicity,and high value content.Appropriate recycling and disposal of the WPCB is recognized as demands of both resources sustainable utilization and environmental protection.The recycling of WPCBs mainly contains three parts:disassembly of electronic components?ECs?from WPCBs,resources recovery and disposal of ECs,and resources recovery and disposal of waste printed wiring boards?WPCBs without ECs?.At present,the former two are weak links among WPCBs recycling chain.ECs should be recycled separately according to their material composition via disassembly since the uneven distributions of the kinds and contents of metals and hazardous substances in WPCBs,contributing to both the enhancements of the separation of metals and the cost reducing for pollution controlling.Hence,efficient disassembly of ECs from WPCBs is important for enhancement of high added-value products recovering and pollution eliminating.Currently,manual disassembling methods are used widely in practice,in the meantime,most of ECs have not been treated by efficient recycling approaches,demanding to research on and develop the disassembling technology and equipment of scientificity,high efficiency,and environmetal benignity.In this paper,the method of disassembling ECs from WPCBs was proposed,the system of ECs disassembly from WPCBs was established,and the disassembling parameters were optimized.In the meantime,the emission charateristics of gaseous pollutants and PM10 generated during the diassembling process were analyzed,and the deposition characteristics of the PM10 in the human respiratory system were studied.In addtion,the aluminum electrolyte capacitor?AECs?and the transistors,which were disassembled from the WPCBs,were recycled.On the basis of the analysis of the material characteristics of the AECs and the transistors,the recycling technological roadmaps were explored,and the experimental parameters were optimized.In addition,the environmental impacts were analyzed.On the basis of the analysis of soldering characteristics between ECs and base boards,with the guidance of reverse-assembly of ECs,this article proposed the methods of providing heat source for ECs disassembling from WPCBs by combining the electric heat tube and heated air,providing vibaration force for ECs disconnecting from WPCBs by falling from high-order position to low-order position,and ensuring the leak tightness of the dismantling machine during feeding and discharing by double-deck sealing flap valve.Based on the above designs,an environmetally friendly ECs automatic disassembling machine was originally created,and a lab-scale ECs disassembling system was established.The actual difference of temperature distribution inside the disassembling machine was about±15?.The investigation on the diassembling parameters showed that there were significant influences of the diassembling temperature and the disassembling period on the disassembling rates and appearances of ECs.The optimal conditions for disassembling ECs from WPCBs were at a diassembling temperature of 260?and a disassembling period of 479 s?inclination angle of 0.05°?,and vabration time of 5 times?roration speed of disassembling cylinder of 5 rpm?.Under the above optimum conditions,the disassembling rate of ECs from WPCBs?withhout any pretreatment?of computer reached100%.The applicability tests for the disassembling machine showed that,under the above optimal conditions,the disassembling rate of ECs from WPCBs?withhout any pretreatment?of mobile could reach 100%.The solder could be removed completely from the WPCBs of television,however,the line output transformers?LOTs?should be removed before the WPCBs entered into the disassembling machine.The results of the composition analysis of the disassembling off-gas showed that the composition of the off-gas after purification was basically the same as that of the air,indicating that the off-gas purification device proposed in this research had a good performance for purification of the dismantling off-gas and there was no gaseous pollutant detected.The emission characteristics analysis of PM10 which was sampled and analyzed by a electrical low pressure impactor?ELPI?indicated that the number concentration emission coefficient and mass concentration emission coefficient of PM10 were 2.14E+02cm^-3·s^-1 and 1.39E-02 mg/m³·s,respectively;and the number concentration emission coefficient and the mass concentration emission coefficient of PM2.5 were 2.13E+02cm^-3·s^-1 and 1.11E-03 mg/m³·s,respectively,accounting for 99.53%and 7.99%of the each PM10 emission coefficient,respectively.The deposition characteristics of PM10 in human respiratory system were evaluated using the simplified model provided by International Commission on Radiological Protection?ICRP?,and results demonstrated that deposition fluxes of PM10 in the nose and throat,the trachea-bronchia,and the pulmonary alveoli were 5.05E-03,2.06E-04,and 3.00E-04 mg·h^-1,respectively.The particles with the particle sizes 2.5¹0?m dominantly contributed to the above three deposition fluxes with the percentage of 96.5%,91.3%,and 81.9%,respectively.Comparing with the technology used in the existing enterprises,PM10 emission coefficient of the present ECs-ADM decreased by 2 to 3 orders of magnitude,and the theoretical calculation value of the deposition fluxes of PM10 in the workers'respiratory system was only 0.15⁰.16%of the current level of the relevant production enterprises.It was of great significance for reducing damages to the environment and workers'health.The aluminum electrolytic capacitors?AECs?,disassembled from WPCBs,were recycled via heat treatment,mechanical-physical separation,and the analysis of the pollutant discharging.The results showed that the pyrolysis-magnetic separation was better to recycle waste AECs since its advantages of short technological process,simple device,and cost-efficiency.The nonmetallic components were thermal decomposed completely under the conditions of 500 ^oC and 60 min.Then,the residue was treated by the processes of simple crushing,seiving?0.224 mm of mesh size?,and magnetic separation?350 rpm of feeding speed?.As a result,96.52%of aluminum and 98.68%of iron were recovered;and the purity of the recovered aluminum and iron were 99.03%and98.24%,respectivly.The analysis of the composition of the pyrolysis gas and the leaching toxicity of the pyrolysis residue demonstrated that the gaseous product was dominantly composed of the elements of C,H,and O,which could be disposed by burning and,the residue generated during the process of pyrolysis-magnetic separation process was not hazardous waste,which could end up directly in landfills safely or be further re-utilized.The researh on waste transistors recycling demonstrated that the liberating of metals and nonmetals and the concentrating of metals could be realized via the process of“crushing-pyrolysis-crushing-seiving”.The optimized conditions were that the pyrolysis temperature,the pyrolysis period,and the mesh size of screen were 600 ^oC,30 min,and0.6 mm,respectively.Finally,the grade of Cu increased from 54.57%?raw material?to92.75%,and its recovery rate reached 99.16%.The linear fitting analysis showed that the method of Flynn-Wall-Ozawa was suitable for the thermo-kinetics analysis of the epoxy molding compound in waste transistors.The average apparent activation energy of the epoxy molding compound was 134.33 kJ/mol.This study provide theoretical basis for the improvement of WPCBs recycling system and e-waste management.