Cathode ray tube (CRT) recycling: Current capabilities in China and research progress

Cathode ray tube (CRT) recycling: Current capabilities in China and research progress

Waste Management 32 (2012) 1566–1574 Contents lists available at SciVerse ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/w...

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Waste Management 32 (2012) 1566–1574

Contents lists available at SciVerse ScienceDirect

Waste Management journal homepage: www.elsevier.com/locate/wasman

Review

Cathode ray tube (CRT) recycling: Current capabilities in China and research progress Qingbo Xu, Guangming Li ⇑, Wenzhi He, Juwen Huang, Xiang Shi College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China The State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China

a r t i c l e

i n f o

Article history: Received 31 July 2011 Accepted 14 March 2012 Available online 28 April 2012 Keywords: CRTs Panel glass Funnel glass Dismantling Recycling

a b s t r a c t It is estimated that approximately 6000,000 scrap TVs and 10,000,000 personal computers are generated each year in China. Cathode ray tubes (CRTs) from these machines consist of 85% glass (65% panel, 30% funnel and 5% neck glass). The leaded glass (funnel-24%, neck-30%) may seriously pollute the environment if it is not properly disposed of. In this paper, the past, current and future status of CRT dismantling technologies as well as the CRT glass recycling situation in China are presented and discussed. Recycling technology for waste CRTs in China is still immature. While the conventional CRT dismantling technologies have disadvantages from both economic and environmental viewpoints, some of the new and emerging treatments such as automatic optical sorting facilities that have been applied in developed countries offer advantages, and therefore should be transferred to China in the next few years to solve the CRT preprocessing problem. Meanwhile, because the demand for CRT glass closed-loop recycling is extremely limited, the authorities should take effective measures to improve CRT glass recycling rates and to facilitate a match to local conditions. Moreover, we also provide a broad review of the research developments in recycling techniques for CRT cullet. The challenge for the future is to transfer these environmentally friendly and energy-saving technologies into practice. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction Due to rapid advances in television (TV) manufacturing technologies, more and more conventional TVs have been replaced by new products such as Liquid Crystal Displays (LCDs) and Plasma Display Panel (PDPs). Concurrently, computer life span is decreasing with time. Data on the United States academic and business sectors suggest a lifespan of 6 years from 1985 to 2000, 5–4 years in 2000, and 3 years in 2007 (Babbitt et al., 2009). As a result, a growing fraction of the increasing stock of TVs and personal computers becomes obsolete each year. In 2006, 163,420 computers and TVs in North America were expected to become obsolete every day (Yang and Williams, 2009). Approximately 2.9 million TVs (74,000 tons) and 3.2 million computer monitors (48,000 tons) are currently stockpiled in California alone (Kim et al., 2005). In the United Kingdom it is estimated that in 2002, 104,532 tons of CRT glass were generated out of which televisions contributed 69,000 t and computer monitors contributed 26,000 tons (Recycling, 2004). The recycling of CRTs appears to be uneconomical, with few reuse options for the recycled glass (BAN, 2004). From a global perspective, it is estimated that only 26.75% of the discarded ⇑ Corresponding author at: College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China. Tel.: +86 021 55966051. E-mail address: [email protected] (G. Li). 0956-053X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.wasman.2012.03.009

CRTs are recycled, 59% will be landfilled and 14.75% will be incinerated (Domingos, 2008). Even fewer CRTs are recycled in developing countries such as China and India. CRTs consist of 85% glass and constitute 65% of the entire weight of a TV or monitor (Andreola et al., 2005a, 2007b). CRTs are made up of different glass components each with different chemical composition: (1) panel (65%), a barium strontium glass; (2) funnel (30%), a lead glass; (3) frit, a low melting temperature lead glaze; and (4) neck (5%), a very rich lead glass (Andreola et al., 2007a; Mear et al., 2006b). The previous toxicity characteristic studies of the CRTs have demonstrated that the neck and funnel glasses of CRT are hazardous waste, while the panel glass exhibits little toxicity (Jang and Townsend, 2003; Musson et al., 2000, 2006). So it may create significant potential health and environmental risks if they are not properly disposed of. Many studies conducted in the areas of Guiyu and Taizhou of China, which are involved in the primitive e-waste dismantling and recycling activities, have found very high levels of the lead content in samples of dust, soil, river sediment, and water sources compared with the control area (Leung et al., 2007; Wang and Guo, 2006). The lead exposure may threaten the health of people working and living in these regions (Liu et al., 2011; Turbini et al., 2001). In response to the rapid increase in e-waste generation and the enormous quantities of e-waste devices imported from overseas, in combination with the rising awareness of the problems caused by

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potential lead leaching from CRTs, China’s Central government has introduced a set of e-waste management regulations concerning the collection systems, standards, technical guidance and norms, recycling facilities etc. (Yang, 2008; Wilson et al., 2009). Meanwhile, different local administrative measures to control e-waste have also been put into effect in several regions including Beijing, Shanghai, Jiangsu province, Zhejiang province and Guangdong province. In this paper, based on the investigation of China’s CRTs treatment infrastructure, the current status of waste CRT treatment is introduced, and the existing dismantling technologies and their limitations are analyzed. Also, identification of existing problems during recycling process is presented. Moreover, in the last section of this paper, we also give a broad review of the research development of recycling techniques on CRT cullet. It is expected that new environmentally-friendly integrated recycling processes with less pollution and high efficiency for managing waste CRTs should be applied and developed to alleviate bottlenecks in waste CRT recycling. These conclusions may guide the development and implementation of a circular economy for complete recycling and resource utilization of the waste materials.

2. Domestic generation and transboundary shipments Reliable data on waste CRT quantities are lacking for China in general, so this article presents a forecast of future household waste CRT quantities for the time span of 2003–2020 based on historical sales data (NBSC, 2010; AVC, 2010; MIITC, 2009) and average lifetime values for Chinese household TVs (10 years) and computer monitors (5 years) (Li, 2005) (Fig. 1). Data on in-stock CRTs are not considered in this prediction. It is concluded that although the CRT market share is shrinking, because of time delays, the quantity of waste CRT TVs and monitors will keep increasing rapidly until the year 2015, at least. In China, TV sets are the dominant contributors to WEEE generation and account for 47.7% of the total mass of WEEE, estimated at 1.76 million tons, generated in 2003 (Lee et al., 2010). a formal e-waste recycling plant named TES-AMM in Shanghai is surveyed on the reclamation of four typical WEEE constitution, since the ‘‘Old-for-new Home Appliances’’ polices were implemented in October 2009, and this follow-up survey covered 6 months. The survey results show that CRT-containing devices (e.g., computer

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Fig. 2. The collection of five categories of WEEE in TES-AMM facility, Shanghai, China (Year: 2010).

monitors and TVs) proportion have exceeded 90% among the five categories of home appliances (namely TVs, refrigerators, washing machines, air conditioners, and personal computers) as shown in Fig. 2. Through May 2011, statistics show that over 18 million items of waste home appliances have been recalled in 28 provinces in China, about 82% of which are waste CRT TVs (MOFCOM, 2011). According to the ‘‘Old-for-new Home Appliances’’ polices, the high subsidies (up to 400 RMB/unit TV) have stimulated much more out of used and in storage CRT TVs entering into the e-waste stream than expected. Because of the environmental and occupational risks and costs involved in handling the leaded glass, the collapsing market for manufacturing new CRTs in U.S, Europe and Japan, non-working CRTs are likely to being shipped to developing nations (BAN, 2004). Although data on the actual quantity of CRT imports are unavailable, China is still the destination for a large proportion of CRT shipments from developed countries, even though this is in violation of existing international laws and/or Chinese regulations. At least 30 cases of illegal shipment of WEEE were caught by the Chinese government during 1994–2007 (Basel Convention coordinating Center for Asia and the Pacific, 2009). Green Peace (2008) reported that many e-waste ‘‘hidden flows’’ unaccounted for from industrialized countries are likely to be exported to the newly industrialized countries such as China and India with large informal recycling sectors. All of these factors lead to a growing volume of unwanted TVs and PCs that find their way to different available postconsumer management options such as storage, reuse, recycle, incineration, or landfill. 3. The current status of technology options for dismantling CRTs in China

Fig. 1. Prediction of annual amounts of CRT televisions and computer monitors in China. Sales data source: China Statistical Yearbook (2000–2010); AVC; China Information and Industry Technology Statistical Yearbook (2000–2010).

Before recycling a CRT, the case must be removed and the tubes depressurized at the Materials Recycling Facility (MRF). Metals are separated and plastics are shredded and then the CRTs are sent to CRT recyclers where they proceed through either glass-to-glass or glass-to-lead recycling (Kang and Schoenung, 2005). CRT glass recycling is the most costly unit operation compared with other materials such as metals and plastics in electronic waste recycling. Hence the successful recycling of scrap CRT glass was identified by Ladou and Lovegrove (2008) as an important option in relieving the disposal problem created by scrap monitors and TVs. In this section, we discuss the CRT dismantling technologies used in China.

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3.1. The current status of dismantling waste CRTs in China Generally, conventional CRT dismantling involves the following steps: removing the CRT from the plastic casing, releasing the vacuum in the tube, separating the panel glass from the funnel glass, removing various metals and non-glass metals including the electron gun, and removing the phosphor coatings from the panel glass (Weitzman and IEEE, 2003). Since the composition and hazardous characteristics of the panel and the funnel glass are different, it is necessary to separate these components in order to treat and recycle each (Lee et al., 2004). However, the dismantling process can be somewhat dependent on the final destination for cullet. In many destinations, particularly where the glass will be treated as hazardous waste, it is unnecessary to separate the two types of glass. Among the steps listed above, separation of the panel glass from the funnel glass is the key step in the CRT dismantling process. Therefore, in this section, we focus on the technologies used for this step and give an overview of the past, current, and future status of CRT dismantling and technology development in China. Over the past decade informal recycling has been the prevalent e-waste recycling practice in China. Most of the recycling sectors are small firms operating outside government regulations (Yan and Liu, 2006), mainly located in coastal areas such as Guangdong, Zhejiang, Jiangsu, Shandong, Hebei and Beijing provinces (Eugster M, 2004). The most notable area is Guiyu of Guangdong province and Taizhou of Zhejiang province. In these informal sectors manual dismantling and sorting operations are still prevailing. Primitive technologies such as physical dismantling by using tools such as hammers, chisels, screw drivers and bare hands are adopted to separate different materials aimed to get their most valuable and easily extractable components such as electron gun, deflection unit, mask and implosion protection band. Then the plastic and iron are sold to local secondary recyclers, while the panel and funnel glass together with fluorescent materials are mixed and then disposed in landfills or dumped illegally (China Central Television, 2004; Liu et al., 2006). These treatment methods are very ‘cost-efficient’, due to the use of non-skilled manual labor and disregard of any hazards to environment or health. These businesses are selforganizing. In 2007, about 0.7 million people were employed in the e-waste recycling industry (Duan, 2007), with 98% employed in informal recycling sectors. It is thought that nearly 60% of the generated e-waste in China is passed through these informal recycling processes (Eugster M, 2004). Since 2003, along with the execution of policies and regulations for e-waste recycling, Registered formal recyclers (including foreign invested ones) have been undertaken by the Chinese National Development and Reform Commission in different provinces (MOFCOM, 2011). A list of officially certified e-waste treatment plants in China is shown in Fig. 3 (NDRS, 2010). Among these plants, Hangzhou Dadi, Beijing Huaxing, Qingdao Haier and Tianjin Datong are four national pilot projects that were launched sequentially since 2004 (Yang, 2008). Regarding formal dismantling technologies, at present, there is no single dismantling strategy being implemented within China that performs CRT glass separating task more economically, effectively and efficiently, which might affect the recovery rate of the CRT cullet. According to our investigation into the WEEE formal factories in China, the data illustrate that separation of the funnel and the panel glass is mainly performed by the thermal acid bath method and the electric wire heating method. The former are mainly applied in China’s new CRT manufacturers as well as in some of the small-scale e-waste factories in Guangdong Province and Fujian (Jiang and Guan, 2006), and the latter are more commonly used in most of China’s e-waste factories. The electric wire heating method is preferred in developing countries because the labor cost is comparatively low and the work

Fig. 3. Dismantling and reclaim e-waste plants distribution in China. Data source: China Home Appliances ‘‘Old-for-new’’ Management and Information System, http://jdyjhx.mofcom.gov.cn/website/archives.shtml.

force abundant. In recent years, some Chinese companies have also developed various semi-automatic or automatic CRT dismantling machines based on the technology of the electric wire heating method (Deng, 2008; Hu et al., 2007). Normally, these apparatus require about 3–5 min to process a CRT, and at least 3 operators are required. However, the electric wire heating method also has limitations; it cannot be used for all sizes of CRTs. It is most appropriate for dismantling CRTs from 14 to 25 inches, furthermore, the noise and dust emissions can have adverse effects on the health and safety of the employees. The thermal acid bath method is relatively simple and cheap. However, this method cannot achieve a clean separation between the panel and funnel glass. Waste water management is also an important issue with this method. The laser cutting and diamond saw methods are efficient CRT separation techniques that are commercially used in developed countries such as Japan and Europe (Yin et al., 2008). In these processes a clean separation can be achieved and it can cut about one to two CRTs per-minute depending on their size, so the process can be utilized for large-scale operation. A single laser-based facility can achieve up to an annual processing capacity of 500,000 CRTs (PETEC, 2008). However, because laser cutting is energy intensive, has a high processing cost and requires significant investment capital, these facilities are not used in China’s e-waste treatment plants. 3.2. Automatic technologies for CRT shredding and glass sorting Instead of the aforementioned separating techniques, the separation of panel glass from funnel glass can be achieved by using sensor guided automatic sorting. A complete process description for this type of CRT treatment method has been previously published (Zumbuehl, 2006). In summary, the stripped CRTs are first crushed, sieved and partly separated into coarse and fine glass cullet, and then the ferrous metals are separated from the glass fraction. The fluorescent layer on the screen glass as well as the iron oxide coating from the funnel glass is mechanically removed by tumbling the cullet. After washing off the dust, the cullet is dried using electric oven. Then the separation step using a detection system to specify the density of the cullet takes place. On a conveyor belt the cullet arrive at a detection unit. After blowing out the denser cullet with air jets a fraction of funnel glass as well as the

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Fig. 4. Flow-sheet of Sims e-waste company CRT glass sorting line (Source: SIMS, 2010).

remaining panel and mixed glass is produced. Then the remaining mixed glass is manually separated into pure front glass and mixed glass. The mixed glass consists of cullet of front glass frit- and funnel glass. Only 0.5% of waste is produced. It contains the fluorescent coating as well as the iron oxide coating and glass dust. This fraction has to be disposed of in an incineration plant. Water is kept in a closed loop cycle thus no wastewater is produced. A representative facility can produce approximately 5 tons of CRT cullet per hour (Zumbuehl, 2006). Presently, there are some facilities using this method to separate lead glass by this crushing and sorting techniques, such as at the SwissGlas in Switzerland (Zumbuehl, 2006), RTG GmbH in Germany (RTG, 2010) and SIMS in UK (SIMS, 2010). One example of this type of process is that developed by the Sims Mirec group (SIMS Mirec 2007) (Fig. 4). 3.3. The CRT dismantling technology options in China In short, effective recycling of CRT glass requires an economical disassembly process that results in well-identified and separated glass that meets quality needs for glass recycling. Until now, only a few papers refer to operation research models used to assess the economics of CRT dismantling operations. Based on technical feasibility, processing cost, and eco-friendly criteria, various panel-funnel separating techniques for end-of-life CRT glass were assessed and sequenced systematically by Yan et al. (2008). The results of this work show that the preferred separation techniques for CRT glass in China are the electric wire heating method, the thermal acid bath method, and mechanical cutting. From the investigations into China’s officially certified e-waste treatment plants, we know the conventional approach for treating CRTs has been for the panel glass to be separated from the funnel glass using a variety of technologies. This carries a number of key disadvantages - most notable being high environmental and occupational hazard, low volumes and poor resulting quality with high reject rates. The advantage of crushing and sorting techniques is that one does not have to separate the whole panel and funnel glass, but rather these are crushed together and then sorted. By combining this with magnetic and eddy current techniques, fully automatic CRT pre-processing can be realized. So this innovative technology is able to take broken cathode ray tubes, in bulk tippers, saving time, energy and transport costs (CRT Recycling Ltd, 2011). However, state-of-the-art apparatus are highly dependent on capital investment. Furthermore, it must be considered that the use of X-ray equipment in a plant requires appropriate shielding and must follow strict rules to protect workers from exposure, with an obvious increase in cost and environmental and safety problems. To our knowledge, large-scale CRT pre-processing by crushing and sorting methods do not exist and is therefore still a challenge for the China CRT recycling industry. With the rapid growth in waste CRTs and its environmental hazard concern, after establishing the initial capital investment, the more competitive

dismantling processes, especially completely automated systems (e.g., automatic crushing and on-line sorting techniques), will be preferred in some Chinese large-scale formal e-waste recycling enterprises. A few efforts have been launched around China to begin to research the semi- or auto-dismantling technologies, for example, both the Ministry of Science and Technology of the People’s Republic of China and the Committee of Science and Technology of Shanghai have set up CRT recycling research programs in 2009 and 2010, respectively (MSTC, 2009; STCSM, 2010). The main objectives of these projects are to design and develop automatic recognition and separation technology for CRT glass. It is hoped that such efforts will promote technology transfer to create a more sustainable CRT recycling sector. However, social attributes (e.g. job creation), or economic ones (e.g. like capital intensiveness) will play the most crucial role and could hamper the effectiveness of the innovative technologies. We can still easily imagine that manual labor could be economically competitive with automated systems. So it is concluded that the primitive technologies (informal sectors), traditional technologies (formal sectors), automated technologies (few large-scale factories) will co-exist for a long time in China. 4. The recycling of CRT glass 4.1. The current status of recycling CRT glass in China According to China Environmental Protection Ministry, both black-and-white and color CRT TVs and computer monitors have been declared ‘hazardous’ and subsequently banned from landfills and incinerators(The Chinese Environmental Protection Ministry, 2010). These products contain toxic materials that present challenges at end-of-life: the CRTs contain not only glass, but also plastics treated with flame retardants that can produce dioxins in the gas mixture during incineration process; the landfilling is avoided because of the lead, which has the potential to leach into the ground water. Although the CRT glass can be disposed of in areas licensed for hazardous waste, the cost of disposal at such locations is extremely expensive and is increasing in cost at a rate of 20–25% per year. No e-waste dealers are willing to pay the CRT glass disposal fee for the hazardous waste landfilling. Although reliable data on waste CRT glass treatment are lacking for most of the countries in general, especially for the region of developing countries, the currently available data from government reports (US EPA, 2008; UNU, 2008; METI, 2010; BCRC China, 2009) and websites (Yoshida A, 2010; Greenpeace, 2005; BAN and SVTC, 2002; CRT Recycling Ltd, 2011)as well as several published articles (Oguchi, 2010; Liu, 2006; Li, 2010; Xianbing, 2006; Wang, 2007), are aggregated in Fig. 5. In Europe, prior to the implementation of extended producer responsibility (EPR) in electronic waste management, the disposal route had been landfilling and incineration (Nnorom et al., 2011). Because of the high recycling costs and low secondary

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Fig. 5. The CRT glass recycling situation in selected countries in the year 2007 (Unit: 10,000 tons). Note: Europe-15 and Japan Stockpile data is not available. Source: USEPA (2009), Greenpeace (2005) , United Nations University (2008), BCRC China (2009); METI (2010), Wang (2007); Liu, (2006); Li (2010); Xianbing (2006); Oguchi (2010).

material value, in China only a small fraction of the waste CRT glass is recycled and a large fraction of the waste flows do not get proper treatment but are kept in storage or discarded via open dumping (He et al., 2006; Li, 2010). So appropriate disposal routes are required in China in the management of CRTs in order to mitigate environmental contamination and human exposure to toxins. Generally, closed-loop recycling (for manufacturing new CRT glass) and open loop recycling (the glass for other applications) are two principal ways of recycling CRT glass (ICER, 2004). The reuse of recovered CRT glass can achieve the following results: save the energy, substitute raw materials, and decrease pollution. To date, the preferred process for the management of waste CRT glass is to recycle it into new CRT glass (Kang and Schoenung, 2005), however, due to the significant declining market for new CRTs, the manufacturers no longer have the capacity to utilize the increasing amount of waste CRT glass. According to our investigation, in China, only three CRT manufacturers (IRICO, Shanxi; AnCai and AnFei, Henan) have the capacity to absorb a volume of 100,000 tons of the recycled glass per year, which only represents a small fraction of generated waste. As a result, large quantities of CRT glass are being stored and accumulated in the dismantling facilities throughout of China. According to a report from Qinghua University, it is estimated that the total waste CRT glass will exceed 5.2 million tons, including 3.5 million tons of color CRT panel glass, 1.7 million tons of funnel glass and 0.7 million tons of

black-and-white CRT glass (Li, 2010). The huge amount of CRT glass would bring about great treatment pressure for the current recycling facilities. When the supply of recovered CRT glass exceeded the demand of the reuse market, there was therefore a need for other outlets, a number of which have been discussed in earlier studies (Shi X., 2011; Herat, 2008) as summarized in Table 1., From the table we can see that the open-loop recycling method can be classified into two broad technologies: glass-to-glass recycling and glass-to-lead recycling. Recycling the CRT glass is possible, and some processes such as use as fluxing agents for lead or copper smelters have been developed and commercialized in USA and German companies for many years (Kang and Schoenung, 2005; Menad, 1999). In China, among the feasible recycling methods, using the CRT glass to produce foam glass has drawn considerable attention (Gao et al., 2007; Zhang Y., 2002). Meanwhile, a survey on potential domestic consumption of CRT glass was also conducted by Basel Convention Coordinating Centre for Asia and the Pacific (abbreviated as BCRC China) (Table 2). Data demonstrates that even though the recycling systems operate at full capacity; the recycling rate of these materials is still not satisfactory compared to the rapid generation of CRT glass that may result from efforts to increase collection of CRTs. The funnel glass recycling rate is even lower compared with the panel glass. And the total capacity of the potential Chinese CRT glass recycling companies is about 700,000 t/year compared to an estimated total of 1000,000 t/year expected to be treated per year in the country considering the domestic collection and importing from overseas per year. This indicates that available recycling infrastructure is grossly inadequate. However, not all of the recycling methods are cost-efficient; furthermore, the CRT glass collection rate, transportation cost, technology barriers, treatment cost, market-demand, and the secondary pollution during the processing are also important factors that can influence their feasibility. In a bid to achieve proper disposal of CRTs in China, the following recommendations are suggested: Firstly, different CRT glass recycling routes should be adopted according to local conditions, the government and society should implement strong supportive policy and economic measures to boost the development of CRT recycling factories. Secondly, as a feasible route to produce construction materials using CRT glass as raw material, the related standards and polices should be introduced for guiding the market. Last, but most important, accelerate the R&D technology and there applications for CRT glass recycling by related organizations such as knowledge centers, recycling companies and authorities, etc. 4.2. The research progress on recycling of CRT glass worldwide In contrast to the recycling of plastic, metal, and other components, the recycling of CRT glass is quite problematic. This is due

Table 1 The technique-economic-environmental comparison of recycling methods for CRT glass. Item

As fluxing material

Foam glass

Glass products

Construction materials

Glass type

Funnel glass Or Mixing glass Metallurgy

Panel glass

Panel, or Mixing glass

Complex Lead pollution in dust and slag is serious Reduce energy consumption and the virgin materials Low High

Common Greenhouse gas emission

Panel, funnel, or Mixing glass Functional glass production Complex No significant environmental problems Lead crystal glassware, Radiation Protection Materials High Low

Applied field Technology Environmental impacts Additional value

Disposal costs[1,2] Market demand[3,4,5]

Architecture field

Foam glass is an excellent bulk material for civil construction and insulation purposes Medium High

Note: [1]: Kang and Schoenung, 2005; [2]: Weitzman, 2001; [3]: Li, 2010; [4] Shi et al., 2011; [5] Yan et al., 2008.

Road, Building Complex The lead materials is potential hazardous As a substitute for natural aggregates in concrete manufacture High Medium

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Q. Xu et al. / Waste Management 32 (2012) 1566–1574 Table 2 The scenario of recycling capacities of CRT glass by feasible recycling technologies in China (unit: 10,000 tons). Application for CRT glass

Glass type

Expected additive proportion

Consuming annually (10,000 tons)

The Production Scale of recycling factories

Locations of the recycling factories

CRT glass manufacturing

Panel Funnel Panel Or BW Pane Or BW Pane Or BW Pane Or BW Pane Or BW Funnel Panel + BW Funnel

30% 25% 20–90%

19 9 1

3 factories. 40 million units/a 20 factories. 150,000 m3/a

Shanxi, Henan

20%

30

30 million m3/a

Guangdong, Fujian

20%

8

Guangdong

5%

10

150 factories. 500,000 tons glaze/a 50 million tons/a

<90%

2

100,000 tons/a

Around China

60–70%

2.5 70 11.5

50,000 tons/a

Zhejiang, Shanghai

Foam glass Glass ceramics Glaze Fluxing agent in Clay bricks, ceramic products; Domestic glass products (except container glass and packaging glass) Crystal glass, handicraft, X-ray shield Total

Jiangsu, Zhejiang

Around China

Note: Consuming annually refers to CRT glass consuming; BW refers to the black-and-white CRT glass. Source: (Li J H., 2010) the research on waste CRT glass utilizing way (report). Qinghua University, China.

to the fact that CRTs are normally made of several glass components and each is chemically different. Glasses as funnel and neck contain principally lead, whereas panel glass contains other heavy metals (Ba, Sr, etc.) that forbid their recycling in the glass industry for the production of containers, domestic glassware and glass fiber. For these reasons, there is an increasing urgency to develop new applications for CRT glass. In the last few years; many studies have been carried out on CRT glass treatments. 4.2.1. Lead recovery With respect to prospects for metal recovery, recycling is quite slow for hazardous heavy metals; for instance, only 5% of lead is recycled, and most heavy metals have little value, except for precious metals such as gold (99% recycling rate) and silver (98% recycling) from integrated circuit boards (Basel Action Network (BAN), 2004, Basel Action Network and Silicon Valley Toxics Coalition (SVTC) 2002). Recently, the entire circle of heavy metals has attracted considerable interest because it is strongly related to environmental protection and resource shortages. Waste CRT glass contains high content of lead in the funnel glass (15%-25% PbO).It can be recovered by hydro-metallurgical and pyro-metallurgy processes. Pyro-metallurgy processing has been a traditional technology for recovery of precious metals from waste electronic equipment. Lead and copper smelting operations use, depending on operation practices,, a large amount of silica flux. Discarded CRT glass can potentially be used to replace silica (Huisman J, 2004; United Nations University, 2007).Although there are a limited number of smelters for CRT glass, for example, the Doe Run and Noranda in U.S.A as well as Xstrata’s Horne smelter in Canada, how to treat the slag in an environmentally friendly way is still a problem. To gain knowledge on the materials treated to assure that no adverse effects occur, research has been carried out with the aim to investigate the influence of using WEEE glass as additional silica flux on the properties of slag from the copper smelting process (Mostaghel and Samuelsson, 2010). Because metallic silicon is a contaminant in steel, the glass cannot be used as flux in ferrous smelting (ICER, 2004). However, the presence of halogenated flame retardants (HFR) in the smelter feed can lead to the formation of dioxins unless special installations and measures are present. State of-the-art smelters are highly depended on investments (Cui and Zhang, 2008). Also, since the overall lead content in CRT glass (5%) is too low to use it economically in their smelting process, CRT glass would substantially increase the amount of the silica-slag which leads to extra losses

(Swartling, 2006).So only a small amount of CRT funnel glass is sent to lead smelters as fluxing agents to substitute the silica-materials. In the last decade, attention has been moved from pyrometallurgical processes to hydrometallurgical processes for recovery of metals from electronic waste. Compared to pyrometallurgical processing, hydrometallurgical methods are more exact, more predictable, and more easily controlled (Andrews et al., 2000). Laboratory tests have been carried out to study the possibilities to recover the lead from the funnel glass through hydrometallurgical method. Saterlay et al. (2001) reported the use of power ultrasound to facilitate the removal of lead from the heavily-leaded CRT glass via an accelerated leaching protocol, with the aim of producing a lead-free product for greener disposal or more ideally for glass recycling purposes. Pruksathorn and Damronglerd (2005) aimed to recover lead from frit glass waste of electronic plants by using the electrochemical method comprising two successive steps of lead leaching and electrodeposition. In the leaching step, it was found that nitric acid and acetic acid were better solutions for the dissolution of lead oxide compared with sodium hydroxide, hydrochloric acid, and sulfuric acid. More than 95% of the lead was leached by 0.1 M nitric acid or 0.5 M acetic acid at 0.5% weight by solid volume. In the electrodeposition step, more than 95% of lead can be removed with high current efficiency from the leaching solution at an optimum current density. Miyoshi et al.(2004) utilizing a subcritical hydrothermal treatment at 628 K and 24 MPa followed by acid leaching at 373 K to remove lead from the silicate glass. This process may be used to prevent disposal of lead containing waste glass into landfills, and to reduce environmental risks in the future. Because Lead atoms contained in a lead glass are firmly fixed by encapsulation in the cavity of the glass network, it is very difficult to dissociate the SiO2 glass network structure and dissolve lead ions into acid solution at room temperature. Thus, some researchers have attempted to remove lead atoms from lead-glass powder by using the chelate reagent sodium ethylenediamineN,N,N0 ,N0 -tetraacetate (Na2EDTA) dehydrate during the wet ballmilling process at room temperature. This method not only separates the heavy metals from metal-EDTA but also allows for the recycling of the EDTA chelate reagent (Sasai et al., 2008). A novel process for lead nanopowder synthesis from this type of glass was developed by combining vacuum carbon–thermal reduction and inert-gas consolidation procedures (Xing M. and Zhang F. S., 2011). Experimental results showed that the maximum lead evaporation ratio was 96.8% and particles of 4–34 nm were successfully obtained by controlling the temperature, holding time,

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process pressure, argon gas flow rate at 1000 °C, 2–4 h, 500– 2000 Pa, 50–200 ml/min, respectively. All of the experimental results illustrate that it is feasible to remove lead from the funnel or neck glass through leaching processes, which can protect environment. However, only limited previous reports discussed the lead recovery from the funnel glass. Therefore, further studies on commercially viable options and lead recovery from the funnel glass should be developed in the future work. 4.2.2. Detoxification Stabilization/consolidation is also one of the usual environmentally benign disposal methods for hazardous wastes. This is reflected in a sound depollution of WEEE with appropriate disposal of hazardous components and substances and high worker health and safety standards. Recently, the exploitation of self-propagating reactions for hazardous waste consolidation has received considerable attention. Chen et al. (2009a) reported a novel process of detoxification for CRT glass by a self-propagating process. In the process, various types of CRT glass powders were blended with suitable amounts of ferric oxide and magnesium, and the mixtures could generate self-propagating reactions once locally ignited by a thermal source. X-ray photoelectron spectroscopy (XPS) experiments showed that heavy elements in the final products became more stable and were solidified during the process. Leaching tests demonstrated that heavy metals in the final products fulfilled the environmental regulations of USEPA. And the final detoxified products have the potential to be used as foundation and building materials for construction. Kim et al.(2009) used commercially available microbial biopolymers of xanthan gum and guar gum to encapsulate lead from hazardous CRT glass waste using biopolymer cross-linked concrete systems, This CRT–biopolymer–concrete (CBC) composite showed higher compressive strength than the standard concrete and a considerable decrease in lead leachability. It is believed that the pyrovacuum process is an applicable option for CRT funnel glass detoxification and reutilization. The dramatic effect of pyrovacuum reduction on the detoxification and reutilization of lead-containing funnel glass was demonstrated in a study by Chen et al. (2009b), TCLP test result indicated that lead leached from the foam glass was below the regulated value at optimum conditions. In China, although detoxification is a sound method in the recycling process of WEEE, recyclers do not face economic incentives for sound depollution and appropriate disposal of the toxics. In contrary, strong economic disincentives to do so exist. 4.2.3. Foam glass Foam glass or cellular glass is mainly used for thermal and sound insulation purposes and for ground stabilization. Foam glass is manufactured by generating a gas in glass at a temperature between 700 °C and 900 °C. As a result the gas expands producing a structure of cells within the glass to form a porous body. The present day foam glass industries are using up to 98% post-consumer waste glass in their products (ICER, 2004). Using CRT glass to produce the foam glass instead of flat glass and container glass can decrease the energy consumed, for the softening temperature of the CRT glass is about 60–100 °C less than that of flat glass and container glass. The feasibility of using recycled CRT glass in foam glass manufacture has been investigated by several researchers. Mear et al. (2006c) studied the characterization of foam glass produced from CRT glass powder and the reducing agents nitride (TiN) and carbide (SiC).They measured the parameters such as density, porosity, thermal and mechanical properties and found that reutilization of CRT glass in the form of foam glass is a recycling process with high potential. Several

other studies have investigated the effects of parameters such as reaction time, temperature and mass percentage of reducing agents on the reaction process and the physical and chemical properties of foam glass produced from CRT glass to determine the optimum conditions (Bernardo and Albertini, 2006; Mear et al., 2006a; Mear et al., 2005; Mear et al., 2007). Recently an alternative route for preparing porous glasses was reported, which use waste panel glass as a starting material for hydrothermal hot-pressing (HHP) conditions, followed by a conventional heating of the compact. This method does not require any additive agents to generate gas in the glass, Furthermore, the value of this product is similar to that of other foamed glasses that have closed cell networks and low thermal conductivity (0.0021 W/cm/°C) (Matamoros-Veloza et al., 2008). 4.2.4. Other glass products It is difficult to use funnel glass in many open-recycling systems due to its lead content. In glass products such as container glass and tableware, raw materials with high lead content are not allowed. However, in some special industry, it is possible to use both panel and funnel glass from CRTs as the restrictions are much lower. A case study by Andreola et al. (2005b) investigated the potential of using CRT glass in glass–ceramics manufacture. Glasses were melted at a temperature of about 1500 °C and transformed into glass–ceramics by different thermal treatments (900 °C to 1100 °C temperature range and 0.5 to 8 h soaking time). By using the evaluation of thermal, mineralogical and microstructural data it has been pointed out that a good degree of crystallization is reached at about 1000 °C and with a high proportion of waste glass (50–75%) if 40–45% of CaO and MgO bearer (dolomite) is introduced. Dondi et al.(2009) studied the feasibility of re-using lead-containing glass is in the manufacturing of clay bricks and roof tiles. The effect of both funnel and panel glasses on the technological behavior and technical performance of heavy-clay products was assessed. Previous work has also evaluated the feasibility of using end-of-life CRT glass as the main component for porcelain stoneware tiles (Raimondo et al., 2007; Rambaldi, 2004), ceramic glazes(Andreola et al., 2007b), X-ray radiation-shielding applications (Boccaccini et al., 1997; Ling and Poon, 2011) and glass–alumina platelet composite materials (Minay et al., 2003). However, some of these potential applications that have been proposed are quite problematic or less attractive from a social-economic and environmental point of view than innovative technologies. Therefore, it is urgent to develop a recycling technology without negative impact to the environment to resolve the problems of waste CRTs. 5. Conclusions Generation of waste from WEEE is increasing at a rapid rate worldwide surpassing the rate of generation of normal municipal waste. Used televisions and computer monitors form a significant portion of this waste stream. The increasing domestic generation and illegal trans-boundary shipment of e-waste have created great challenges to the environment and formal recycling infrastructure. Dismantling the CRTs is a key step to realize the separation of panel glass and funnel glass for improving the CRT glass value. Through the analysis and investigation of the Chinese e-waste recycling plants, for solving the current problem, the more costeffective and eco-friendly separation methods such as crushing and automatic sorting techniques could be applied in some formal recyclers from the national pilot project. As the availability of opportunities for closed-loop recycling declines in the coming

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years there is a definite need to invest in research and development for open-loop recycling to make it more environmentally friendly. We summarize the studies that have been carried out to recycle CRT glass for lead recovery, detoxification, foam glass and other glass products such as glass–ceramics, glass glaze, glass composites, X-ray resistant glass, showing that several experimental techniques have demonstrated favorable results. The challenge for the future is how to transfer these results into practice given the preference to emphasize economic aspects over environmental aspects in many situations. Through drivers such as legislation and practices such as cleaner production and design for environment it is hoped that high quality CRT glass is made available for efficient and economical reuse and recycling. Acknowledgments The authors gratefully acknowledge the financial support from the Key Research Project of Shanghai in China (Grant No. 10dz1205200) and the National Key Technology R&D Program of China (Grant No. 2008BAC46B02). The authors are thankful to Prof. J.M. Schoenung (from University of California, Davis) for the collaboration in e-waste recycling field. Reference Andreola, F., Barbieri, L., Corradi, A., Lancellotti, I., 2005a. Cathode ray tube glass recycling: an example of clean technology. Waste Management & Research 23, 314–321. Andreola, F., Barbieri, L., Corradi, A., Lancellotti, I., Falcone, R., Hreglich, S., 2005b. Glass-ceramics obtained by the recycling of end of life cathode ray tubes glasses. Waste Management 25, 183–189. Andreola, F., Barbieri, L., Corradi, A., Ferrari, A.M., Lancellotti, I., Neri, P., 2007a. Recycling of EOL CRT glass into ceramic glaze formulations and its environmental impact by LCA approach. International Journal of Life Cycle Assessment 12, 448–454. Andreola, F., Barbieri, L., Corradi, A., Lancellotti, I., 2007b. CRT glass state of the art – a case study: recycling in ceramic glazes. Journal of the European Ceramic Society 27, 1623–1629. Andrews, D., Raychaudhuri, A., Frias, C., 2000. Environmentally sound technologies for recycling secondary lead. Journal of Power Sources 88, 124–129. Babbitt, C.W., Kahhat, R., Williams, E., Babbitt, G.A., 2009. Evolution of product lifespan and implications for environmental assessment and management: a case study of personal computers in higher education. Environmental Science and Technology 43, 5106–5112. Basel Action Network, 2004. CRT Glass Recycling Survey Results. Basel Action Network (BAN) and Silicon Valley Toxics Coalition (SVTC), 2002. Exporting Harm: The High-Tech Trashing of Asia. Basel Convention Coordinating Center for Asia and the Pacific, 2009. The report on current status and development of national and international technology on e-waste recycling. Via: http://en.bcrc.cn. Bernardo, E., Albertini, F., 2006. Glass foams from dismantled cathode ray tubes. Ceramics International 32, 603–608. Boccaccini, A.R., Bucker, M., Trusty, P.A., Romero, M., Rincón, J.M., 1997. Sintering behavior of compacts made from television tube glasses. Glass Technology 38. China Statistics Bureau, China Statistical Yearbook (2000–2010). Beijing, China: China Statistical Press, in Chinese. Chen, M.J., Zhang, F.S., Zhu, J.X., 2009a. Detoxification of cathode ray tube glass by self-propagating process. Journal of Hazardous Materials 165, 980–986. Chen, M.J., Zhang, F.S., Zhu, J.X., 2009b. Lead recovery and the feasibility of foam glass production from funnel glass of dismantled cathode ray tube through pyrovacuum process. Journal of Hazardous Materials 161, 1109–1113. China Central Television, 2004. The prediction of WEEE in China. Website: http:// www.CCTV.com. Cui, J.R., Zhang, L.F., 2008. Metallurgical recovery of metals from electronic waste: a review. Journal of Hazardous Materials 158, 228–256. CRT Recycling Ltd, 2011.Via: http://www.crt-recycling.co.uk/2/About+CRT (accessed in February 2012). Committee of Science and Technology of Shanghai, 2010. Via: http:// www.stcsm.gov.cn/jsp/xxgk/zhtz/content.jsp?id=348 (accessed in October 2011). Deng, M.Q., 2008. A fast cutting apparatus of CRT glass. CN 201704210 U. China. Domingos, T., 2008. A discussion of the paper, Elshkaki et al., ‘‘Dynamic stock modeling: a method for the identification and estimation of future waste streams and emissions based on past production and product stock characteristics’’, Energy 2005; 30: 1353–63. Energy 33, 834. Dondi, M., Guarini, G., Raimondo, M., Zanelli, C., 2009. Recycling PC and TV waste glass in clay bricks and roof tiles. Waste Management 29, 1945–1951.

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