Fundamental Research On Selective Separation Of Valuable Metals From Typical Electronic Wastes By Supergravity

With the continuous improvement of science and technology,the electronic industry is facing rapid changes.Its product renewal cycle is shortening year by year.The number of eliminated electronic related products is increasing year by year,which poses a serious threat to the ecological environment.There are many valuable metals and organic substances in electronic wastes(e-wastes),and it is of great significance to recycle and utilize.However,due to the variety and complexity of e-wastes,how to recycle kinds of metals in e-wastes cleanly and efficiently is still an urgent problem to be solved.In this paper,based on the differences of physical properties of metals in e-wastes,a novel selective separation process of valuable metals from e-wastes by supergravity technology was proposed.The separation mechanism,key process parameters and device structure design of new process were systematically studied.In this paper,two typical printed circuit boards(PCBs),computer and television PCBs,were selected as experimental samples for separation.The physical properties,phases and metal compositions in the samples were analyzed by using various high-precision detection devices.A variety of metals(e.g.Cu,Zn,Pb,Sn,Fe)were obtained from the PCBs.Most of metals were in the element and alloy state,precious metals Au,Ag,Pt,and Pd were dispersed in the form of aggregates in the PCBs.Based on the melting point differences of metals in the PCBs,two separation methods,pressure melting and supergravity melting,for separating low-melting-point metals(Pb and Sn)and high-melting-point metals(Cu)in the PCBs were detailedly compared and investigated.The results show that the separation effect of supergravity melting is more obvious than pressure melting.The organic matter in the PCBs were studied by pyrolysis technology.The main components of pyrolysis gases were Hz,CO,CO2,CH4,benzene compounds,H2O,small molecular alkanes and a small amount of bromine volatile components;the main components of liquid products were phenol,o-cresol,4-methylphenol,3-(1-methylethyl)phenol,triphenyl phosphate and a small amount of bisphenol A,furfural formaldehyde,nitrogenous(4-phenylbutyronitrile)and bromine(2,6-dibromophenol and 4-bromo-2,6-dimethylaniline)organic substances;the main components of solid products were glass fiber and coke.The selective separation process of low-melting-point and high-melting-point metals by supergravity was systematically investigated.Three kinds of alloys with different compositions were obtained by three-step separation process from metal-rich particles of PCBs and the enrichment of precious metals Au,Ag and Pd was realized by supergravity.The results show that gravity coefficient and heating temperature were the main factors affecting the separation and recovery of valuable metals in the PCBs.Gravity coefficient improved the metal recoveries,and heating temperature affected the alloy compositions.Under the temperature of 410 ℃,gravity coefficient of 1000 and separation time of 5 min,Pb-Sn alloy was obtained and the recoveries of Pb and Si were 54.41%and 41.94%,respectively,and the total contents of Pb and Sn in the Pb-Sn alloy was 94.84 wt%.Sn and Cu as the main alloy components was separated at 800 ℃ with gravity coefficient 1000 and separation time 5 min.The recoveries of Cu,Zn,Pb,and Sn were 19.72%and 18.94%,17.78%and 23.25%,respectively.The total contents of Sn and Cu in the Sn-Cu alloy were 83.18 wt%.Subsequently,Cu-Zn alloy was separated at 1300 ℃,gravity coefficient of 1000 and separation time of 5 min.The recoveries of Cu,Zn,Pb and Sn are 79.12%,68.28%,26.14%,and 27.43%,respectively and the total contents of Cu and Zn in the Cu-Zn alloy were 89.23wt%.In the complete three-step separation process,the total recoveries of Cu，Zn,Pb,and Sn were 98.84%,86.96%,98.33%and 92.62%,respectively.Precious metals Au,Ag,and Pd were mainly distributed in the Cu-Zn alloys and the final residues.Under these conditions,compared with the contents of Au,Ag,and Pd in the original PCBs,those in the Cu-Zn alloy increased by 2.05,1.65 and 1.54 times,respectively,while those in the final residues increased by 1.02,0.63,and 2.62 times,respectively.Based on the basic research on the selective supergravity separation process of valuable metals from e-wastes,the conceptual design and principle verification of the industrial device for selective supergravity separation of valuable metals from e-wastes were carried out,which provided theoretical guidance for the engineering application process and efficient utilization of electronic waste resources.