Elsevier

Science of The Total Environment

Volumes 463–464, 1 October 2013, Pages 1124-1132
Science of The Total Environment

Toxic metals in WEEE: Characterization and substance flow analysis in waste treatment processes

https://doi.org/10.1016/j.scitotenv.2012.07.078Get rights and content

Abstract

Waste electrical and electronic equipment (WEEE) has received extensive attention as a secondary source of metals. Because WEEE also contains toxic substances such as heavy metals, appropriate management of these substances is important in the recycling and treatment of WEEE. As a basis for discussion toward better management of WEEE, this study characterizes various types of WEEE in terms of toxic metal contents. The fate of various metals contained in WEEE, including toxic metals, was also investigated in actual waste treatment processes. Cathode-ray tube televisions showed the highest concentration and the largest total amount of toxic metals such as Ba, Pb, and Sb, so appropriate recycling and disposal of these televisions would greatly contribute to better management of toxic metals in WEEE. A future challenge is the management of toxic metals in mid-sized items such as audio/visual and ICT equipment because even though the concentrations were not high in these items, the total amount of toxic metals contained in them is not negligible. In the case of Japan, such mid-sized WEEE items as well as small electronic items are subject to municipal solid waste treatment. A case study showed that a landfill was the main destination of toxic metals contained in those items in the current treatment systems. The case study also showed that changes in the flows of toxic metals will occur when treatment processes are modified to emphasize resource recovery. Because the flow changes might lead to an increase in the amount of toxic metals released to the environment, the flows of toxic metals and the materials targeted for resource recovery should be considered simultaneously.

Highlights

► Appropriate management of toxic metals contained in WEEE is important during recycling and treatment of WEEE. ► CRT TVs contain large amount of toxic metals with high concentration and thus appropriate management is highly important. ► Mid-sized equipment is a future target for managing toxic metals in WEEE because the total amount is not negligible. ► Changes in the flows of toxic metals will occur when treatment processes are modified to emphasize resource recovery. ► The flows of toxic metals and valuable materials should be managed simultaneously in recycling and treatment of WEEE.

Introduction

Waste electrical and electronic equipment (WEEE), or e-waste, has recently received extensive attention as a secondary resource (UNEP, 2009), and recovery of materials such as valuable metals contained in WEEE is currently popular in both developed and developing countries. At the same time, the hazardous nature of WEEE is also widely recognized (Tsydenova and Bengtsson, 2011), so WEEE is an important target for appropriate management for the prevention of environmental pollution.

European countries have increased their recycling of WEEE under the directive on WEEE (European Council, 2003), which covers all electrical and electronic equipment for consumer and professional use (Huisman et al., 2007). Since the properties of different types of WEEE differ and the mixture of end-of-life products is highly heterogeneous, sorting WEEE by specific characteristics is necessary to optimize processes for resource recovery (Chancerel and Rotter, 2008). Similarly, sorting is also useful for appropriate hazard management in the recycling and treatment of WEEE, because the characteristics regarding contained toxic materials are also different by types of WEEE.

In the United States, WEEE is commonly managed in municipal solid waste (MSW) treatment systems, although several types of electronics are covered in WEEE legislation and producer take-back programs in some states (Electronics Takeback Coalition, 2011). In Japan, several schemes for the separate collection and recycling of WEEE have been introduced either through legislation or on a voluntary basis (Aizawa et al., 2008, Murakami et al., 2008, Yoshida et al., 2009) as shown in Table 1. Many other types of WEEE, however, are not covered by recycling laws and are generally subject to MSW treatment. According to an estimate by Oguchi et al. (2008), those types of WEEE account for one-third of the total generation of WEEE in Japan on a weight basis. Better management of toxic substances in these items is therefore also needed. Overall, a better understanding of substances contained in various types of WEEE is necessary to improve systems of collection and recycling according to each item's specific characteristics.

An understanding of the fate of substances in WEEE recycling and treatment processes is also important for appropriate hazard management as well as for improved resource recovery. Several experimental studies have been conducted on substance flows of selected metals and brominated flame retardants associated with dismantling, shredding, and separation of WEEE in Europe (Chancerel and Rotter, 2009, Chancerel et al., 2009, Morf et al., 2005, Morf et al., 2007). Oguchi et al. (2012) investigated the fate of 55 metals contained in WEEE in shredding and separation processes at an MSW plant in Japan. Residue from such processes, however, is often landfilled either directly or after being incinerated. Further study is needed on the fate of substances throughout the entire recycling and treatment system for WEEE, including the treatment of residues.

As a basis for discussion toward better management of substances in WEEE, this article presents a characterization and substance flow analysis of toxic metals in WEEE. First, by using data on product composition and the amount of end-of-life products generated, this study examined the relative importance of various types of WEEE in terms of managing both toxic and valuable metals. Second, this study investigated the distribution behavior of metals in a typical process for MSW thermal treatment in Japan. Based on that, a case study was conducted to estimate the final destinations of selected metals contained in WEEE under different treatment scenarios.

Section snippets

Characterization of WEEE in terms of contained valuable and toxic metals

The authors, along with other colleagues, previously discussed the relative importance of various types of WEEE as targets for metal recovery (Oguchi et al., 2011). From an analogy between natural resource development and metal recovery from WEEE, it was pointed out that not only metal concentration but also the total amount of metals contained in WEEE should be considered in the characterization of WEEE as secondary metal resources. In the analysis, various types of WEEE were categorized into

WEEE characteristics in terms of contained toxic metals

Table 2 shows the median weight fractions of the materials in 24 types of WEEE, and Table 3 shows the concentrations of six toxic metals in printed circuit boards in these items. Note that the concentrations for Cr were those of total chromium, not hexavalent chromium. The median concentrations for Ba in CRT panel glass and Pb in CRT funnel glass were 79,000 and 215,000 mg/kg-glass, respectively. Concentrations of selected common metals and precious metals that were reported in Oguchi et al.

Characteristics of WEEE in terms of contained valuable and toxic metals

Table 4 summarizes the characteristics of each WEEE item based on the categorization results for toxic metals. The relative characteristics of the examined items may be similar in other countries because the compositional breakdown of WEEE items was found not to be very different between Japan and other countries from the comparison of the estimates by Oguchi et al. (2008) and Huisman et al. (2007). It would, of course, be possible to conduct similar characterizations in other countries as data

Conclusions

This study discussed the relative importance of various types of WEEE in managing toxic metals from the viewpoint of both the concentration and the total amount of contained toxic metals. Appropriate recycling and disposal of CRT televisions should notably contribute to better management of toxic metals contained in WEEE. A future challenge is discovering how to manage toxic metals in mid-sized items such as audio/video and ICT equipment because, although they contain moderate concentrations of

Acknowledgments

The authors thank the city of Hitachi for the cooperation in the investigation. The authors thank the editor and two anonymous reviewers for their helpful comments. This work was partly supported by the Environment Research and Technology Development Fund from the Ministry of the Environment, Japan (K113011) and the Japan Society for the Promotion of Science KAKENHI (22360387).

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