Critical Review pubs.acs.org/est
Disposing and Recycling Waste Printed Circuit Boards: Disconnecting, Resource Recovery, and Pollution Control Jianbo Wang and Zhenming Xu* School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, People’s Republic of China ABSTRACT: Over the past decades, China has been suffering from negative environmental impacts from distempered ewaste recycling activities. After a decade of effort, disassembly and raw materials recycling of environmentally friendly e-waste have been realized in specialized companies, in China, and law enforcement for illegal activities of e-waste recycling has also been made more and more strict. So up to now, the e-waste recycling in China should be developed toward more depth and refinement to promote industrial production of e-waste resource recovery. Waste printed circuit boards (WPCBs), which are the most complex, hazardous, and valuable components of e-waste, are selected as one typical example in this article that reviews the status of related regulations and technologies of WPCBs recycling, then optimizes, and integrates the proper approaches in existence, while the bottlenecks in the WPCBs recycling system are analyzed, and some preliminary experiments of pinch technologies are also conducted. Finally, in order to provide directional guidance for future development of WPCBs recycling, some key points in the WPCBs recycling system are proposed to point towards a future trend in the e-waste recycling industry.
1. INTRODUCTION The speed of information and communication technological (ICT) progress has proved Moore’s law, the observation that the number of transistors that can be packed into an integrated circuit doubles every 18 months.1,2 There is no doubt that ICTs are transforming societies and economies around the world. ICT is an example of a ‘general-purpose technology’3 due to its convenience and functionality, meaning that it interacts with and enhances other technologies. Not surprisingly, large quantities of e-waste, which have fundamentally restructured human interactions with the environment, are discarded continuously.2,4 According to the United Nations Environment Programme (UNEP), about 50 million tons of e-waste is generated annually nowmore than 70% of that ends up in China.5,6 For the last decades, China has suffered serious pollution caused by improper e-waste recycling activities. A number of papers have been reported focusing on this phenomenon.4,7−14 Actually, the problem caused by e-waste increasingly becomes an international issue due to the characteristics of e-waste of large quantity, discarding continuously, high value materials content, and, most of all, pollutants migration. Great attention has been drawn by researchers and governments all over the world, especially in China. After a decade of efforts, tremendous progress in e-waste recycling technology has been achieved in China,15−27 such as integrated recycling processes for crushed printed circuit boards (PCBs), waste nickel−cadmium batteries, waste refrigerators, waste washing machines, and so on. In addition, a series of laws and © XXXX American Chemical Society
supporting measures have been enacted to promote regularization and environmental friendliness of e-waste recycling by the government of China.15,28,29 Consequently, recycling and resource recovery activities for e-waste have been developed more and more normally and scientifically. At present, some processes like open incineration and open acid washing are prohibited strictly in China. For example, the town of Guiyu, Guangdong province, China, is well-known around the world after a report by Nongovernmental organizations (NGOs), the Basel Action Network and Silicon Valley Toxics Coalition in 2002, on improper waste electrical and electronic equipment (WEEE) recycling and serious pollution.15 According to the report of the Guangdong news broadcast,30 64 tons of illegal sulfuric acid, hydrochloric acid, and nitric acid, which were intended for improper e-waste recycling activities, were seized; 31 self-employed entrepreneurs involved were captured recently in 2014 in Guiyu, said by Kai Xu, the vice mayor of Shantou city. Now, there are about 300 enterprises and 3207 self-employed entrepreneurs for e-waste recycling in Guiyu, and all of them have a license for e-waste recycling. In October 2010, the town of Guiyu was selected by the National Development and Reform Commission (NDRC) and the Chinese Ministry of Environmental Protection (MEP) to implement a pilot program of an integrated e-waste recycling Received: October 2, 2014 Revised: December 17, 2014 Accepted: December 19, 2014
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DOI: 10.1021/es504833y Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 1. Influence of the improper recycling activities on the environment and human health.
Figure 2. Integrated process for WPCBs recycling.
system. As designed, the 2500 acres industrial park of e-waste recycling in Guiyu will be divided into six districts and run for recycling waste appliances and will be planned to be built and put into production before December 2015.31 Hence, up to now, the e-waste recycling in China should be developed toward more depth and refinement to promote industrial production of e-waste resource recovery. In this article, waste PCBs (WPCBs) are selected as one typical example. Although the Chinese government and a number of researchers have made great efforts to improve WPCBs recycling, there are still some obstacles that limit the industrial application of WPCBs recycling techniques. PCBs are integral parts of any electrical and electronic equipment (EEE);17 the percentage of WPCBs is very huge (about 4%)32 among the e-waste amount and even more in some EEEs,33 like color TV (7.04%), PC control unit (18.76%), and mobile phone (21.30%). Meanwhile, WPCBs are the most complex and hazardous components among e-waste,34 which contain more than 60 elements35,36 including plenty of toxic heavy metals (such as Pb, Cr, Cd, Hg, As) and toxic organic substances (such as brominated flame retardants, polycyclic aromatic hydrocarbons, dechlorane plus). Most of these substances are potential for bioaccumulation and high environmental persistence and enough to cause serious harm to various parts of the body.37 If WPCBs could not be disposed or recovered properly, these toxic materials would be released into the environment and jeopardize human health via direct contact and the food chain,11,38 as presented in Figure 1. The triggering consequence to human society of both the quantity and the toxicity of these materials is absolutely a disaster which is totally beyond economic compensation. For example, about 76 000 t of polybrominated dipheny1 ethers (PBDEs), which have been shown to disrupt endocrine hormones in lab animals and wildlife alone, are released into the environment each year at e-waste sites in China.37 However, PBDEs are the main additives as brominated flame retardants (BFRs) in PCBs.39
In the meantime, WPCBs contain tons of value metals (30− 40%), including Cu (∼16%), Sn (∼4%), Fe (∼3%), Ni (∼2%), Zn (∼1%), and many precious metals, like Au (∼0.03%), Ag (∼0.05%), Pt, Pd, etc.,40 which are the main targets for the recyclers, and nonmetals (mainly resin) derived from petroleum, a nonrenewable resource.41−43 Grossman44 (an environmental writer based in Portland, Oregon) who delves deeply in copper points out that about two-thirds of the world supply is obtained from open-pit mines. A quarter of the annual global production is destined for digital devices 0.96%− 1.12% in PCBs. Therefore, it is not only for economic benefit but also the need of resource sustainable development to recover these metals.15,45 However, 90% of discarded electronics end up in landfills or incinerations, although numerous illegal recyclers commonly exist nowadays in China, India, and many African countries.44 This may be attributed to their low efficiency and regulatory governments. As a matter of fact, several supporting measures have also been launched in China.15,46,47 For example, disposal and resource recovery technology for WPCBs has been listed as the key technology of resources comprehensive utilization technology of the major national industry technology development project by NDRC since 2004 in China; and a great number of researchers have made their best efforts, which mainly focus on disassembly of electronic components (ECs) from WPCBs48,49 and recovery of waste printed wiring boards (WPWBs, WPCBs without ECs),50−53 to solve this problem for the past many years. Despite the achievements being remarkable, a complete technical system cannot be developed for lack of investigations of disposal and recovery for ECs, which is one of the most important and difficult processes in the overall system. As a consequence, there is no one company that has a license for disposing and recovering WPCBs for technical obstacles until now in China. In order to explore and complete a thorough system of disposal and resource recovery for WPCBs from the standpoint of industrial application, this article reviews and analyzes the B
DOI: 10.1021/es504833y Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Critical Review
Environmental Science & Technology
Figure 3. Disassembling system of WPCBs: (a) experimental system and photos of (b) WPCB before the experiment, (c) WPCB after the experiment, and (d) dismantled ECs.
Figure 4. WPCBs dismantling system for production level application.
of which are functional and usable at the time of disposal as ewaste, based on a thesis the average end-of-life for ECs is 20 000 h, of which less than 5% of its designed lifespan (500 000 h).16,58 Therefore, dismantling ECs from WPCBs is a crucial step from both standpoints of materials recovery and ECs reuse in the WPCBs recycling chain to conserve scare resources, reuse functioning ECs, and eliminate potential exposure to hazardous materials.16,33 Many studies aiming at ECs dismantling from WPCBs have been conducted, where WPCBs are mainly processed in two steps: (1) damage solder joints between base boards and ECs, including wearing down the solder joints on the back-side of PCBs by grinders,56 dissolving solders by chemical reagents,59 infrared heaters,60 electronic heating tubes,61,62 hot air,63,64 and hot fluids65−68 like molten solder, diesel, paraffinic oil, and silicon oil, to melt solders; (2) certain external force applied to make ECs dislodge from WPCBs, including mechanical sweep,69 gas jet,16,63,64 and centrifugal force.19 In summing up experiences of these existing techniques, a process which is suitable and potential to industrial application,16 as presented in Figure 3, developed by Chen and his colleagues from Southwest University of Science and Technology, China, satisfies requirements of a sound system for WPCBs dismantling: (1) widespread applicability for all sizes and shapes of WPCBs, due to without the need of fixing of WPCBs; (2) high efficiency, attributes to automatic feeding and automatic discharging, as well as no strict requirements for position and the layer number stacked up of WPCBs; (3) low cost and low energy consumption, for the simple structure of
status of related technologies and then optimizes and integrates the proper approaches in existence, consequently, an integrated process for WPCBs recycling is supposed, as provided in Figure 2. Meanwhile the bottlenecks in the complete recycling system are analyzed, and some preliminary experiments of ECs (aluminum electrolytic capacitors, AECs) are conducted. In addition, some suggestions are also proposed.
2. WPCBS DISMANTLING SYSTEM PCBs are always mounted with ECs.16 However, the contents of different metals and various toxic substances are very disparate in printed wiring boards (PWBs, i.e., PCBs without ECs) and different ECs.54 For example, PWBs mainly contain54 copper (∼28%) and a small amount of lead, tin, and BFRs, while electrolytic capacitors mainly contain aluminum (35− 50%), electrolytic paper, and hazardous electrolyte. Moreover, integrated chips (ICs) mainly contain55 silicon, silver, indium, germanium, and other rare and precious metals. It is very difficult and expensive not only to concentrate on minor metals and recover them individually but also to dispose the diverse hazardous substances caused by the processes when all these substances mix up.56 Even illegal recovery processes (like Guiyu and Taizhou, China) also begin with dismantling and classification, except for the differences that the dismantling process is manual33 and the toxic substances are released without environmental controls.57 In addition, an idea is proposed by many researchers that the ECs disassembled from WPCBs could be reused in some new products, because most C
DOI: 10.1021/es504833y Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 5. Process of separation for metals and nonmetals from WPWBs.
Figure 6. Process of vacuum metallurgy separation for metals from WPWBs.
the interior diameter of the inlet pipe is too small (15 mm) compared to the relative big disassembling machine (Ø 450 × h 500 mm). So it can be supposed that the essential temperature of this system would be reduced with the increase of the inside diameter of the inlet pipe. Hence, the further study about this problem is necessary.
equipment and industrial waste heat adoption; (4) environmentally friendly, for no pollution to ECs and WPWBs which are dismantled during the disassembly process and the close dismantling system adopted. In this process, hot air is used to melt solders, and pulse jet, using hot air, is used to separate the components and base boards. As a result, the disassemble rates of small surface mount components (SSMCs, side length
