recycling of non-metallic fractions from waste printed circuit boards_ a review

1、Journal of Hazardous Materials 168 (2009) 567–590Contents lists available at ScienceDirectJournal of Hazardous Materialsjournal homepage: www.elsevier.com/locate/jhazmatReviewRecycling of non-metallic fractions from wast

2、e printed circuit boards: A reviewJiuyong Guo, Jie Guo, Zhenming Xu ?School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, PR Chinaa r t i c l e i n f oArtic

3、le history:Received 16 September 2008Accepted 17 February 2009Available online 26 February 2009Keywords:Printed circuit boards (PCBs)Non-metallic fractions (NMFs)RecyclingHazardous substancesa b s t r a c tThe major econ

4、omic driving force for recycling of waste printed circuit boards (PCBs) is the value ofthe metallic fractions (MFs) of PCBs. The non-metallic fractions (NMFs), which take up almost 70 wt% ofwaste PCBs, were treated by co

5、mbustion or land filling in the past. However, combustion of the NMFswill cause the formation of highly toxic polybrominated dibenzodioxins and dibenzofurans (PBDD/Fs)while land filling of the NMFs will lead to secondary

6、 pollution caused by heavy metals and brominatedflame retardants (BFRs) leaching to the groundwater. Therefore, recycling of the NMFs from waste PCBsis drawing more and more attention from the public and the governments.

7、 Currently, how to recycle theNMFs environmental soundly has become a significant topic in recycling of waste PCBs. In order to fulfillthe better resource utilization of the NMFs, the compositions and characteristics of

8、the NMFs, methodsand outcomes of recycling the NMFs from waste PCBs and analysis and treatment for the hazardoussubstances contained in the NMFs were reviewed in this paper. Thermosetting resin matrix composites,thermopl

9、astic matrix composites, concrete and viscoelastic materials are main applications for physi-cal recycling of the NMFs. Chemical recycling methods consisting of pyrolysis, gasification, supercriticalfluids depolymerizati

10、on and hydrogenolytic degradation can be used to convert the NMFs to chemicalfeedstocks and fuels. The toxicity characteristic leaching procedure (TCLP) and synthetic precipitationleaching procedure (SPLP) can be used to

11、 determine the toxicity characteristic (TC) of the NMFs and toevaluate the environmental safety of products made from the recycled NMFs. It is believed that physi-cal recycling of the NMFs has been a promising recycling

12、method. Much more work should be done todevelop comprehensive and industrialized usage of the NMFs recycled by physical methods. Chemicalrecycling methods have the advantages in eliminating hazardous substances in the NM

13、Fs. The trend inchemical recycling of the NMFs is to make the best of advantages over physical recycling of the NMFs tocompensate its higher cost. Removing and treating the hazardous substances in the NMFs is an ultimate

14、method to eliminate the pollution.© 2009 Elsevier B.V. All rights reserved.Contents1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

15、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5682. Compositions of waste PCBs and characteristics of the NM

16、Fs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5692.1. Compositions of waste PCBs . . . . .

17、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5692

18、.2. Characteristics of the NMFs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19、 . . . . . . . . . . . . . . . . . . . 5693. Physical recycling of non-metallic fractions from waste PCBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5703.1. Recycling the NMFs from waste PCBs as a filler for thermosetting resin matrix composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

21、 . . . . . . . . . . . . . . 5713.2. Recycling the NMFs from waste PCBs as a reinforcing filler for thermoplastic resin matrix composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5753.3. Recycl

22、ing the NMFs from waste PCBs as a raw material for concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5773.4. Recycling

23、the NMFs from waste PCBs as a modifier for viscoelastic materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5783.5. Perspectives on physical

24、 recycling of the NMFs from waste PCBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5794. Chemical recycling of non-m

25、etallic fractions from waste PCBs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5794.1. Recycling

26、the NMFs from waste PCBs by pyrolysis processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5804.2. Recycli

27、ng the NMFs from waste PCBs by gasification processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5834.3. Recycli

28、ng the NMFs from waste PCBs by depolymerization in supercritical fluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584? Corresponding author. Tel.: +8

29、6 21 54747495; fax: +86 21 54747495.E-mail address: zmxu@sjtu.edu.cn (Z. Xu).0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.jhazmat.2009.02.104J. Guo et al. / Journal of Hazard

30、ous Materials 168 (2009) 567–590 569Fig. 4. Recovering gold from waste PCBs using acid baths [2].driving force for recycling of waste PCBs is the value of the MFscontained in PCBs. The NMFs were treated by combustion or

31、landfilling in the past. However, combustion of the NMFs will causethe formation of highly toxic polybrominated dibenzodioxins anddibenzofurans (PBDD/Fs) while land filling of the NMFs will lead tosecondary pollution cau

32、sed by heavy metals and BFRs leaching tothe groundwater. Therefore, the NMFs must be recycled in an envi-ronmentally sound way, which has become a great challenge facedby recycling of waste PCBs. At present, recycling of

33、 the NMFs fromwaste PCBs is drawing more and more attention from the publicand the governments. In order to give a fundamental understand-ing of recycling of the NMFs from waste PCBs and provide a detailedresearch status

34、 for further investigation in this paper, the recyclingmethods and outcomes of the NMFs from waste PCBs and analysisand treatment for the hazardous substances contained in the NMFsare reviewed on the basis of our previou

35、s study.In general, the recycling methods of the NMFs from wastePCBs can be summarized as physical recycling methods andchemical recycling methods. Physical recycling methods of theNMFs are adopted after the MFs and the

36、NMFs have been sep-arated from waste PCBs by using mechanical processing [10].Mechanical processing for the separating the MFs and the NMFsfrom waste PCBs includes shape separation, magnetic separation,electric conductiv

37、ity-based separation, density-based separationand corona electrostatic separation, all of which have been wellreviewed by Cui [11] and Huang et al. [12]. Corona electrostaticseparation (CES) for the MFs and the NMFs from

38、 waste PCBs hasbeen intensively studied by Xu and his colleagues from Shang-hai Jiao Tong University in China [13–24] and has been proved tobe a highly efficient and environmental friendly process. Chemi-cal recycling me

39、thods of the NMFs are adopted during and afterthe stage of the chemical separating process for the MFs and NMFsin chemical recycling methods for waste PCBs. Chemical recyclingmethods [25] include pyrolysis, gasification,

40、 depolymerization pro-cess using supercritical fluids and hydrogenolytic degradation. Theenvironmental safety analysis and evaluation of the products madefrom the recycled NMFs from waste PCBs is also an importantissue.

41、The hazardous substances contained in the NMFs are mainlyBFRs (tetrabrombisphenyl-A (TBBA), etc.) and residual heavy met-als (lead, chromium, mercury, cadmium, etc.) [26]. The fate andsubstance flows of these hazardous s

42、ubstances are important dur-ing the recycling of the NMFs from waste PCBs. Removing andtreating BFRs and heavy metals contained in the NMFs is an ulti-mate method to eliminate the pollution caused by the hazardoussubstan

43、ces.Table 1Typical composition of printed circuit boards (PCBs) [7].Element Ag Al As Au SContent 3300 g/t 4.7% <0.01% 80 g/t 0.10%Element Ba Be Bi Br CContent 200 g/t 1.1 g/t 0.17% 0.54% 9.6%Element Cd Cl Cr Cu FConte

44、nt 0.015% 1.74% 0.05% 26.8% 0.094%Element Fe Ga Mn Mo NiContent 5.3% 35 g/t 0.47 0.003% 0.47%Element Zn Sb Se Si02 SnContent 1.5% 0.06% 41 g/t 15% 1.0%Element Te Ti Sc I HgContent 1 g/t 3.4% 55 g/t 200 g/t 1 g/tElement Z

45、r SrContent 30 g/t 10 g/t2. Compositions of waste PCBs and characteristics of theNMFs2.1. Compositions of waste PCBsThe choice of manufacturing materials used for PCBs dependson the application, for example, difunctional

46、 epoxy resins are ade-quate for simple two-sided circuit boards but more sophisticatedmultifunctional epoxy resins or cyanate esters are required for thickmulti-layered boards [27,28]. Two common type PCBs are made ofgla

47、ss fiber reinforced epoxy resin (referred to commercially as FR-4) or cellulose paper reinforced phenolic resin (FR-2). FR-4-typePCBs are used in high-value EEE and FR-2 types are used in televi-sions and home electronic

48、s [29]. PCBs contain significant quantitiesof metals such as copper, iron, nickel, silver, gold, and palladium.Other metals that are present in waste PCBs include the electri-cal components themselves and the solder used

49、 to attach them tothe boards [30]. The Rönnskar smelt plant of Sweden analyzed thetypical compositions (Table 1) of waste PCBs [31].The components mounted on PCBs generally include chips,connectors, capacitors, etc.

50、 [32]. Different components have a dif-ferent material composition [33,34]. Material composition of PCBsis, therefore, quite complex and causes problem for the recyclingof waste PCBs. The materials present in PCBs can be

51、 categorizedin three groups: organic, metals, and ceramics. In general, PCBsmounted with components consist of approximately 40% metals,30% plastics, and 30% ceramics [7]. For waste PCBs without mountedelectronic parts,

52、the material composition is made up about 28 wt%metals (mainly copper) and 72 wt% non-metallic materials [35].2.2. Characteristics of the NMFsThe NMFs consist of cured thermosetting resins, glass fiber(cellulose paper),

53、ceramics, BFRs, residual metals and other addi-tives. The material compositions vary with the source and type ofwaste PCBs and the separation processing. In a study carried out byYokoyama and Iji [36], the NMFs consisted

54、 of glass fiber (65 wt%),cured epoxy resin (32 wt%), and impurities (copper: <3 wt%, solder:<0.1 wt%). The residual metal (mainly copper) in the NMFs, whichwere separated from waste PCBs without mounted electronic

55、partsby using the CES, was characterized by Guo et al. [37] and the resultsTable 2Component of non-metallic fractions (NMFs) from waste PCBs [37].Size range (mm) wt% wt% of Cu vol% of Cu (volume fraction)0.3–0.15 11.8 0.