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Waste Management 32 (2012) 1566–1574

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Waste Management

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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 article info abstract

Article history: It is estimated that approximately 6000,000 scrap TVs and 10,000,000 personal computers are generated Received 31 July 2011 each year in China. Cathode ray tubes (CRTs) from these machines consist of 85% glass (65% panel, 30% Accepted 14 March 2012 funnel and 5% neck glass). The leaded glass (funnel-24%, neck-30%) may seriously pollute the environ- Available online 28 April 2012 ment 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 Keywords: technology for waste CRTs in China is still immature. While the conventional CRT dismantling technolo- CRTs gies have disadvantages from both economic and environmental viewpoints, some of the new and emerg- Panel glass ing treatments such as automatic optical sorting facilities that have been applied in developed countries Funnel glass Dismantling offer advantages, and therefore should be transferred to China in the next few years to solve the CRT pre- Recycling processing 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 CRTs are recycled, 59% will be landﬁlled and 14.75% will be incinerated (Domingos, 2008). Even fewer CRTs are recycled in Due to rapid advances in television (TV) manufacturing technol- developing countries such as China and India. ogies, more and more conventional TVs have been replaced by new CRTs consist of 85% glass and constitute 65% of the entire products such as Liquid Crystal Displays (LCDs) and Plasma Display weight of a TV or monitor (Andreola et al., 2005a, 2007b). CRTs Panel (PDPs). Concurrently, computer life span is decreasing with are made up of different glass components each with different time. Data on the United States academic and business sectors chemical composition: (1) panel (65%), a barium strontium glass; suggest a lifespan of 6 years from 1985 to 2000, 5–4 years in (2) funnel (30%), a lead glass; (3) frit, a low melting temperature 2000, and 3 years in 2007 (Babbitt et al., 2009). As a result, a lead glaze; and (4) neck (5%), a very rich lead glass (Andreola growing fraction of the increasing stock of TVs and personal com- et al., 2007a; Mear et al., 2006b). The previous toxicity characteris- puters becomes obsolete each year. In 2006, 163,420 computers tic studies of the CRTs have demonstrated that the neck and funnel and TVs in North America were expected to become obsolete every glasses of CRT are hazardous waste, while the panel glass exhibits day (Yang and Williams, 2009). Approximately 2.9 million TVs little toxicity (Jang and Townsend, 2003; Musson et al., 2000, (74,000 tons) and 3.2 million computer monitors (48,000 tons) 2006). So it may create signiﬁcant potential health and environ- are currently stockpiled in California alone (Kim et al., 2005). In mental risks if they are not properly disposed of. Many studies con- the United Kingdom it is estimated that in 2002, 104,532 tons of ducted in the areas of Guiyu and Taizhou of China, which are CRT glass were generated out of which televisions contributed involved in the primitive e-waste dismantling and recycling activ- 69,000 t and computer monitors contributed 26,000 tons (Recy- ities, have found very high levels of the lead content in samples of cling, 2004). The recycling of CRTs appears to be uneconomical, dust, soil, river sediment, and water sources compared with the with few reuse options for the recycled glass (BAN, 2004). From a control area (Leung et al., 2007; Wang and Guo, 2006). The lead global perspective, it is estimated that only 26.75% of the discarded 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 ⇑ Corresponding author at: College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China. Tel.: +86 021 55966051. enormous quantities of e-waste devices imported from overseas, in E-mail address: [email protected] (G. Li). combination with the rising awareness of the problems caused by

Q. Xu et al. / Waste Management 32 (2012) 1566–1574 1567 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). Mean- while, 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 Fig. 2. The collection of five categories of WEEE in TES-AMM facility, Shanghai, resource utilization of the waste materials. China (Year: 2010).

monitors and TVs) proportion have exceeded 90% among the five 2. Domestic generation and transboundary shipments categories of home appliances (namely TVs, refrigerators, washing machines, air conditioners, and personal computers) as shown in Reliable data on waste CRT quantities are lacking for China in Fig. 2. Through May 2011, statistics show that over 18 million general, so this article presents a forecast of future household items of waste home appliances have been recalled in 28 provinces waste CRT quantities for the time span of 2003–2020 based on his- in China, about 82% of which are waste CRT TVs (MOFCOM, 2011). torical sales data (NBSC, 2010; AVC, 2010; MIITC, 2009) and aver- According to the ‘‘Old-for-new Home Appliances’’ polices, the high age lifetime values for Chinese household TVs (10 years) and subsidies (up to 400 RMB/unit TV) have stimulated much more out computer monitors (5 years) (Li, 2005)(Fig. 1). Data on in-stock of used and in storage CRT TVs entering into the e-waste stream CRTs are not considered in this prediction. It is concluded that than expected. although the CRT market share is shrinking, because of time delays, Because of the environmental and occupational risks and costs the quantity of waste CRT TVs and monitors will keep increasing involved in handling the leaded glass, the collapsing market for rapidly until the year 2015, at least. manufacturing new CRTs in U.S, Europe and Japan, non-working In China, TV sets are the dominant contributors to WEEE gener- CRTs are likely to being shipped to developing nations (BAN, ation and account for 47.7% of the total mass of WEEE, estimated at 2004). Although data on the actual quantity of CRT imports are 1.76 million tons, generated in 2003 (Lee et al., 2010). a formal unavailable, China is still the destination for a large proportion of e-waste recycling plant named TES-AMM in Shanghai is surveyed CRT shipments from developed countries, even though this is in on the reclamation of four typical WEEE constitution, since the violation of existing international laws and/or Chinese regulations. ‘‘Old-for-new Home Appliances’’ polices were implemented in At least 30 cases of illegal shipment of WEEE were caught by the October 2009, and this follow-up survey covered 6 months. The Chinese government during 1994–2007 (Basel Convention coordi- survey results show that CRT-containing devices (e.g., computer nating 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

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 Fig. 1. Prediction of annual amounts of CRT televisions and computer monitors in China. Sales data source: China Statistical Yearbook (2000–2010); AVC; China disposal problem created by scrap monitors and TVs. In this sec- Information and Industry Technology Statistical Yearbook (2000–2010). tion, we discuss the CRT dismantling technologies used in China. Author's personal copy

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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 Fig. 3. Dismantling and reclaim e-waste plants distribution in China. Data source: e-waste recycling practice in China. Most of the recycling sectors China Home Appliances ‘‘Old-for-new’’ Management and Information System, are small firms operating outside government regulations (Yan http://jdyjhx.mofcom.gov.cn/website/archives.shtml. 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 force abundant. In recent years, some Chinese companies have also and Taizhou of Zhejiang province. In these informal sectors manual developed various semi-automatic or automatic CRT dismantling dismantling and sorting operations are still prevailing. Primitive machines based on the technology of the electric wire heating technologies such as physical dismantling by using tools such as method (Deng, 2008; Hu et al., 2007). Normally, these apparatus hammers, chisels, screw drivers and bare hands are adopted to require about 3–5 min to process a CRT, and at least 3 operators separate different materials aimed to get their most valuable and are required. However, the electric wire heating method also has easily extractable components such as electron gun, deflection limitations; it cannot be used for all sizes of CRTs. It is most appro- unit, mask and implosion protection band. Then the plastic and priate for dismantling CRTs from 14 to 25 inches, furthermore, the iron are sold to local secondary recyclers, while the panel and fun- noise and dust emissions can have adverse effects on the health nel glass together with fluorescent materials are mixed and then and safety of the employees. The thermal acid bath method is rel- disposed in landfills or dumped illegally (China Central Television, atively simple and cheap. However, this method cannot achieve a 2004; Liu et al., 2006). These treatment methods are very ‘cost-effi- clean separation between the panel and funnel glass. Waste water cient’, due to the use of non-skilled manual labor and disregard of management is also an important issue with this method. any hazards to environment or health. These businesses are self- The laser cutting and diamond saw methods are efficient CRT organizing. In 2007, about 0.7 million people were employed in separation techniques that are commercially used in developed the e-waste recycling industry (Duan, 2007), with 98% employed countries such as Japan and Europe (Yin et al., 2008). In these pro- in informal recycling sectors. It is thought that nearly 60% of the cesses a clean separation can be achieved and it can cut about one generated e-waste in China is passed through these informal recy- to two CRTs per-minute depending on their size, so the process can cling processes (Eugster M, 2004). be utilized for large-scale operation. A single laser-based facility Since 2003, along with the execution of policies and regulations can achieve up to an annual processing capacity of 500,000 CRTs for e-waste recycling, Registered formal recyclers (including for- (PETEC, 2008). However, because laser cutting is energy intensive, eign invested ones) have been undertaken by the Chinese National has a high processing cost and requires significant investment cap- Development and Reform Commission in different provinces ital, these facilities are not used in China’s e-waste treatment (MOFCOM, 2011). A list of officially certified e-waste treatment plants. plants in China is shown in Fig. 3 (NDRS, 2010). Among these plants, Hangzhou Dadi, Beijing Huaxing, Qingdao Haier and Tianjin 3.2. Automatic technologies for CRT shredding and glass sorting Datong are four national pilot projects that were launched sequen- tially since 2004 (Yang, 2008). Regarding formal dismantling tech- Instead of the aforementioned separating techniques, the sepa- nologies, at present, there is no single dismantling strategy being ration of panel glass from funnel glass can be achieved by using implemented within China that performs CRT glass separating task sensor guided automatic sorting. A complete process description more economically, effectively and efficiently, which might affect for this type of CRT treatment method has been previously pub- the recovery rate of the CRT cullet. According to our investigation lished (Zumbuehl, 2006). In summary, the stripped CRTs are first into the WEEE formal factories in China, the data illustrate that crushed, sieved and partly separated into coarse and fine glass cul- separation of the funnel and the panel glass is mainly performed let, and then the ferrous metals are separated from the glass frac- by the thermal acid bath method and the electric wire heating tion. The fluorescent layer on the screen glass as well as the iron method. The former are mainly applied in China’s new CRT manu- oxide coating from the funnel glass is mechanically removed by facturers as well as in some of the small-scale e-waste factories in tumbling the cullet. After washing off the dust, the cullet is dried Guangdong Province and Fujian (Jiang and Guan, 2006), and the using electric oven. Then the separation step using a detection sys- latter are more commonly used in most of China’s e-waste facto- tem to specify the density of the cullet takes place. On a conveyor ries. The electric wire heating method is preferred in developing belt the cullet arrive at a detection unit. After blowing out the den- countries because the labor cost is comparatively low and the work ser cullet with air jets a fraction of funnel glass as well as the Author's personal copy

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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 dismantling processes, especially completely automated systems mixed glass is manually separated into pure front glass and mixed (e.g., automatic crushing and on-line sorting techniques), will be glass. The mixed glass consists of cullet of front glass frit- and fun- preferred in some Chinese large-scale formal e-waste recycling nel glass. Only 0.5% of waste is produced. It contains the fluores- enterprises. A few efforts have been launched around China to be- cent coating as well as the iron oxide coating and glass dust. This gin to research the semi- or auto-dismantling technologies, for fraction has to be disposed of in an incineration plant. Water is example, both the Ministry of Science and Technology of the Peo- kept in a closed loop cycle thus no wastewater is produced. A rep- ple’s Republic of China and the Committee of Science and Technol- resentative facility can produce approximately 5 tons of CRT cullet ogy of Shanghai have set up CRT recycling research programs in per hour (Zumbuehl, 2006). Presently, there are some facilities 2009 and 2010, respectively (MSTC, 2009; STCSM, 2010). The main using this method to separate lead glass by this crushing and sort- objectives of these projects are to design and develop automatic ing techniques, such as at the SwissGlas in Switzerland (Zumbuehl, recognition and separation technology for CRT glass. It is hoped 2006), RTG GmbH in Germany (RTG, 2010) and SIMS in UK (SIMS, that such efforts will promote technology transfer to create a more 2010). One example of this type of process is that developed by the sustainable CRT recycling sector. However, social attributes (e.g. Sims Mirec group (SIMS Mirec 2007) (Fig. 4). 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 man- 3.3. The CRT dismantling technology options in China ual labor could be economically competitive with automated systems. So it is concluded that the primitive technologies (informal In short, effective recycling of CRT glass requires an economical sectors), traditional technologies (formal sectors), automated tech- disassembly process that results in well-identified and separated nologies (few large-scale factories) will co-exist for a long time in glass that meets quality needs for glass recycling. Until now, only China. 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 4. The recycling of CRT glass panel-funnel separating techniques for end-of-life CRT glass were assessed and sequenced systematically by Yan et al. (2008). The 4.1. The current status of recycling CRT glass in China results of this work show that the preferred separation techniques for CRT glass in China are the electric wire heating method, the According to China Environmental Protection Ministry, both thermal acid bath method, and mechanical cutting. black-and-white and color CRT TVs and computer monitors have From the investigations into China’s officially certified e-waste been declared ‘hazardous’ and subsequently banned from landfills treatment plants, we know the conventional approach for treating and incinerators(The Chinese Environmental Protection Ministry, CRTs has been for the panel glass to be separated from the funnel 2010). These products contain toxic materials that present chal- glass using a variety of technologies. This carries a number of key lenges at end-of-life: the CRTs contain not only glass, but also plas- disadvantages - most notable being high environmental and occu- tics treated with flame retardants that can produce dioxins in the pational hazard, low volumes and poor resulting quality with high gas mixture during incineration process; the landfilling is avoided reject rates. The advantage of crushing and sorting techniques is because of the lead, which has the potential to leach into the that one does not have to separate the whole panel and funnel ground water. Although the CRT glass can be disposed of in areas glass, but rather these are crushed together and then sorted. By licensed for hazardous waste, the cost of disposal at such locations combining this with magnetic and eddy current techniques, fully is extremely expensive and is increasing in cost at a rate of 20–25% automatic CRT pre-processing can be realized. So this innovative per year. No e-waste dealers are willing to pay the CRT glass dis- technology is able to take broken cathode ray tubes, in bulk tippers, posal fee for the hazardous waste landfilling. Although reliable saving time, energy and transport costs (CRT Recycling Ltd, 2011). data on waste CRT glass treatment are lacking for most of the coun- However, state-of-the-art apparatus are highly dependent on cap- tries in general, especially for the region of developing countries, ital investment. Furthermore, it must be considered that the use of the currently available data from government reports (US EPA, X-ray equipment in a plant requires appropriate shielding and 2008; UNU, 2008; METI, 2010; BCRC China, 2009) and websites must follow strict rules to protect workers from exposure, with (Yoshida A, 2010; Greenpeace, 2005; BAN and SVTC, 2002; CRT an obvious increase in cost and environmental and safety prob- Recycling Ltd, 2011)as well as several published articles (Oguchi, lems. To our knowledge, large-scale CRT pre-processing by crush- 2010; Liu, 2006; Li, 2010; Xianbing, 2006; Wang, 2007), are aggre- ing and sorting methods do not exist and is therefore still a gated in Fig. 5. In Europe, prior to the implementation of extended challenge for the China CRT recycling industry. With the rapid producer responsibility (EPR) in electronic waste management, the growth in waste CRTs and its environmental hazard concern, after disposal route had been landfilling and incineration (Nnorom et al., establishing the initial capital investment, the more competitive 2011). Because of the high recycling costs and low secondary Author's personal copy

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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 (abbrevi- ated as BCRC China) (Table 2). Data demonstrates that even though 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. the recycling systems operate at full capacity; the recycling rate of Source: USEPA (2009), Greenpeace (2005) , United Nations University (2008), BCRC these materials is still not satisfactory compared to the rapid gen- China (2009); METI (2010), Wang (2007); Liu, (2006); Li (2010); Xianbing (2006); eration of CRT glass that may result from efforts to increase collec- Oguchi (2010). tion of CRTs. The funnel glass recycling rate is even lower compared with the panel glass. And the total capacity of the poten- material value, in China only a small fraction of the waste CRT glass tial Chinese CRT glass recycling companies is about 700,000 t/year is recycled and a large fraction of the waste flows do not get proper compared to an estimated total of 1000,000 t/year expected to be treatment but are kept in storage or discarded via open dumping treated per year in the country considering the domestic collection (He et al., 2006; Li, 2010). So appropriate disposal routes are re- and importing from overseas per year. This indicates that available quired in China in the management of CRTs in order to mitigate recycling infrastructure is grossly inadequate. However, not all of environmental contamination and human exposure to toxins. the recycling methods are cost-efficient; furthermore, the CRT Generally, closed-loop recycling (for manufacturing new CRT glass collection rate, transportation cost, technology barriers, treat- glass) and open loop recycling (the glass for other applications) ment cost, market-demand, and the secondary pollution during the are two principal ways of recycling CRT glass (ICER, 2004). The re- processing are also important factors that can influence their feasi- use of recovered CRT glass can achieve the following results: save bility. In a bid to achieve proper disposal of CRTs in China, the fol- the energy, substitute raw materials, and decrease pollution. To lowing recommendations are suggested: Firstly, different CRT glass date, the preferred process for the management of waste CRT glass recycling routes should be adopted according to local conditions, is to recycle it into new CRT glass (Kang and Schoenung, 2005), the government and society should implement strong supportive however, due to the significant declining market for new CRTs, policy and economic measures to boost the development of CRT the manufacturers no longer have the capacity to utilize the recycling factories. Secondly, as a feasible route to produce con- increasing amount of waste CRT glass. According to our investiga- struction materials using CRT glass as raw material, the related tion, in China, only three CRT manufacturers (IRICO, Shanxi; AnCai standards and polices should be introduced for guiding the market. and AnFei, Henan) have the capacity to absorb a volume of Last, but most important, accelerate the R&D technology and there 100,000 tons of the recycled glass per year, which only represents applications for CRT glass recycling by related organizations such a small fraction of generated waste. As a result, large quantities of as knowledge centers, recycling companies and authorities, etc. CRT glass are being stored and accumulated in the dismantling facilities throughout of China. According to a report from Qinghua 4.2. The research progress on recycling of CRT glass worldwide 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 In contrast to the recycling of plastic, metal, and other compo- glass, 1.7 million tons of funnel glass and 0.7 million tons of nents, 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 Panel glass Panel, funnel, or Mixing Panel, or Mixing glass Or Mixing glass glass Applied field Metallurgy Architecture field Functional glass Road, Building production Technology Complex Common Complex Complex Environmental impacts Lead pollution in dust and Greenhouse gas emission No significant The lead materials is potential slag is serious environmental problems hazardous Additional value Reduce energy Foam glass is an excellent bulk material for Lead crystal glassware, As a substitute for natural consumption and the civil construction and insulation purposes Radiation Protection aggregates in concrete virgin materials Materials manufacture Disposal costs[1,2] Low Medium High High Market demand[3,4,5] High High Low Medium

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

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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 Consuming annually The Production Scale of Locations of the proportion (10,000 tons) recycling factories recycling factories CRT glass manufacturing Panel 30% 19 3 factories. Shanxi, Henan Funnel 25% 9 40 million units/a Foam glass Panel Or 20–90% 1 20 factories. 150,000 m3/a Jiangsu, Zhejiang BW Glass ceramics Pane Or 20% 30 30 million m3/a Guangdong, Fujian BW Glaze Pane Or 20% 8 150 factories. Guangdong BW 500,000 tons glaze/a Fluxing agent in Clay bricks, ceramic products; Pane Or 5% 10 50 million tons/a Around China BW Domestic glass products (except container Pane Or <90% 2 100,000 tons/a Around China glass and packaging glass) BW Crystal glass, handicraft, X-ray shield Funnel 60–70% 2.5 50,000 tons/a Zhejiang, Shanghai Total Panel + BW 70 Funnel 11.5

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 compo- (Swartling, 2006).So only a small amount of CRT funnel glass is sent nents and each is chemically different. Glasses as funnel and neck to lead smelters as fluxing agents to substitute the silica-materials. contain principally lead, whereas panel glass contains other heavy In the last decade, attention has been moved from pyrometallurgi- metals (Ba, Sr, etc.) that forbid their recycling in the glass industry cal processes to hydrometallurgical processes for recovery of for the production of containers, domestic glassware and glass fi- metals from electronic waste. Compared to pyrometallurgical pro- ber. For these reasons, there is an increasing urgency to develop cessing, hydrometallurgical methods are more exact, more predict- new applications for CRT glass. In the last few years; many studies able, and more easily controlled (Andrews et al., 2000). have been carried out on CRT glass treatments. Laboratory tests have been carried out to study the possibilities to recover the lead from the funnel glass through hydrometallurgi- 4.2.1. Lead recovery cal method. Saterlay et al. (2001) reported the use of power ultra- With respect to prospects for metal recovery, recycling is quite sound to facilitate the removal of lead from the heavily-leaded CRT slow for hazardous heavy metals; for instance, only 5% of lead is glass via an accelerated leaching protocol, with the aim of produc- recycled, and most heavy metals have little value, except for pre- ing a lead-free product for greener disposal or more ideally for cious metals such as gold (99% recycling rate) and silver (98% recy- glass recycling purposes. Pruksathorn and Damronglerd (2005) cling) from integrated circuit boards (Basel Action Network (BAN), aimed to recover lead from frit glass waste of electronic plants 2004, Basel Action Network and Silicon Valley Toxics Coalition by using the electrochemical method comprising two successive (SVTC) 2002). Recently, the entire circle of heavy metals has at- steps of lead leaching and electrodeposition. In the leaching step, tracted considerable interest because it is strongly related to envi- it was found that nitric acid and acetic acid were better solutions ronmental protection and resource shortages. Waste CRT glass for the dissolution of lead oxide compared with sodium hydroxide, contains high content of lead in the funnel glass (15%-25% PbO).It hydrochloric acid, and sulfuric acid. More than 95% of the lead was can be recovered by hydro-metallurgical and pyro-metallurgy pro- leached by 0.1 M nitric acid or 0.5 M acetic acid at 0.5% weight by cesses. Pyro-metallurgy processing has been a traditional technol- solid volume. In the electrodeposition step, more than 95% of lead ogy for recovery of precious metals from waste electronic can be removed with high current efficiency from the leaching equipment. Lead and copper smelting operations use, depending solution at an optimum current density. Miyoshi et al.(2004) utiliz- on operation practices,, a large amount of silica flux. Discarded ing a subcritical hydrothermal treatment at 628 K and 24 MPa fol- CRT glass can potentially be used to replace silica (Huisman J, lowed by acid leaching at 373 K to remove lead from the silicate 2004; United Nations University, 2007).Although there are a lim- glass. This process may be used to prevent disposal of lead contain- ited number of smelters for CRT glass, for example, the Doe Run ing waste glass into landfills, and to reduce environmental risks in and Noranda in U.S.A as well as Xstrata’s Horne smelter in Canada, the future. Because Lead atoms contained in a lead glass are firmly how to treat the slag in an environmentally friendly way is still a fixed by encapsulation in the cavity of the glass network, it is very problem. To gain knowledge on the materials treated to assure that difficult to dissociate the SiO2 glass network structure and dissolve no adverse effects occur, research has been carried out with the lead ions into acid solution at room temperature. Thus, some aim to investigate the influence of using WEEE glass as additional researchers have attempted to remove lead atoms from lead-glass silica flux on the properties of slag from the copper smelting pro- powder by using the chelate reagent sodium ethylenediamine- 0 0 cess (Mostaghel and Samuelsson, 2010). Because metallic silicon N,N,N ,N -tetraacetate (Na2EDTA) dehydrate during the wet ball- is a contaminant in steel, the glass cannot be used as flux in ferrous milling process at room temperature. This method not only sepa- smelting (ICER, 2004). rates the heavy metals from metal-EDTA but also allows for the However, the presence of halogenated flame retardants (HFR) in recycling of the EDTA chelate reagent (Sasai et al., 2008). the smelter feed can lead to the formation of dioxins unless special A novel process for lead nanopowder synthesis from this type of installations and measures are present. State of-the-art smelters are glass was developed by combining vacuum carbon–thermal reduc- highly depended on investments (Cui and Zhang, 2008). Also, since tion and inert-gas consolidation procedures (Xing M. and Zhang F. the overall lead content in CRT glass (5%) is too low to use it eco- S., 2011). Experimental results showed that the maximum lead nomically in their smelting process, CRT glass would substantially evaporation ratio was 96.8% and particles of 4–34 nm were suc- increase the amount of the silica-slag which leads to extra losses cessfully obtained by controlling the temperature, holding time, Author's personal copy

1572 Q. Xu et al. / Waste Management 32 (2012) 1566–1574 process pressure, argon gas flow rate at 1000 °C, 2–4 h, 500– other studies have investigated the effects of parameters such as 2000 Pa, 50–200 ml/min, respectively. reaction time, temperature and mass percentage of reducing All of the experimental results illustrate that it is feasible to re- agents on the reaction process and the physical and chemical prop- move lead from the funnel or neck glass through leaching pro- erties of foam glass produced from CRT glass to determine the opti- cesses, which can protect environment. However, only limited mum conditions (Bernardo and Albertini, 2006; Mear et al., 2006a; previous reports discussed the lead recovery from the funnel glass. Mear et al., 2005; Mear et al., 2007). Therefore, further studies on commercially viable options and lead Recently an alternative route for preparing porous glasses was recovery from the funnel glass should be developed in the future reported, which use waste panel glass as a starting material for work. hydrothermal hot-pressing (HHP) conditions, followed by a conventional heating of the compact. This method does not require 4.2.2. Detoxification any additive agents to generate gas in the glass, Furthermore, the Stabilization/consolidation is also one of the usual environmen- value of this product is similar to that of other foamed glasses that tally benign disposal methods for hazardous wastes. This is re- have closed cell networks and low thermal conductivity flected in a sound depollution of WEEE with appropriate disposal (0.0021 W/cm/°C) (Matamoros-Veloza et al., 2008). of hazardous components and substances and high worker health and safety standards. Recently, the exploitation of self-propagating 4.2.4. Other glass products reactions for hazardous waste consolidation has received consider- It is difficult to use funnel glass in many open-recycling systems able attention. Chen et al. (2009a) reported a novel process of due to its lead content. In glass products such as container glass detoxification for CRT glass by a self-propagating process. In the and tableware, raw materials with high lead content are not al- process, various types of CRT glass powders were blended with lowed. However, in some special industry, it is possible to use both suitable amounts of ferric oxide and magnesium, and the mixtures panel and funnel glass from CRTs as the restrictions are much could generate self-propagating reactions once locally ignited by a lower. thermal source. X-ray photoelectron spectroscopy (XPS) experi- A case study by Andreola et al. (2005b) investigated the poten- ments showed that heavy elements in the final products became tial of using CRT glass in glass–ceramics manufacture. Glasses were more stable and were solidified during the process. Leaching tests melted at a temperature of about 1500 °C and transformed into demonstrated that heavy metals in the final products fulfilled the glass–ceramics by different thermal treatments (900 °Cto environmental regulations of USEPA. And the final detoxified prod- 1100 °C temperature range and 0.5 to 8 h soaking time). By using ucts have the potential to be used as foundation and building the evaluation of thermal, mineralogical and microstructural data materials for construction. it has been pointed out that a good degree of crystallization is Kim et al.(2009) used commercially available microbial biopoly- reached at about 1000 °C and with a high proportion of waste glass mers of xanthan gum and guar gum to encapsulate lead from haz- (50–75%) if 40–45% of CaO and MgO bearer (dolomite) is ardous CRT glass waste using biopolymer cross-linked concrete introduced. systems, This CRT–biopolymer–concrete (CBC) composite showed Dondi et al.(2009) studied the feasibility of re-using lead-con- higher compressive strength than the standard concrete and a containing glass is in the manufacturing of clay bricks and roof tiles. siderable decrease in lead leachability. The effect of both funnel and panel glasses on the technological It is believed that the pyrovacuum process is an applicable op- behavior and technical performance of heavy-clay products was tion for CRT funnel glass detoxification and reutilization. The dra- assessed. Previous work has also evaluated the feasibility of using matic effect of pyrovacuum reduction on the detoxification and end-of-life CRT glass as the main component for porcelain stone- reutilization of lead-containing funnel glass was demonstrated in ware tiles (Raimondo et al., 2007; Rambaldi, 2004), ceramic a study by Chen et al. (2009b), TCLP test result indicated that lead glazes(Andreola et al., 2007b), X-ray radiation-shielding applica- leached from the foam glass was below the regulated value at opti- tions (Boccaccini et al., 1997; Ling and Poon, 2011) and glass–alu- mum conditions. mina platelet composite materials (Minay et al., 2003). In China, although detoxification is a sound method in the recy- However, some of these potential applications that have been cling process of WEEE, recyclers do not face economic incentives proposed are quite problematic or less attractive from a social-eco- for sound depollution and appropriate disposal of the toxics. In nomic and environmental point of view than innovative technolo- contrary, strong economic disincentives to do so exist. gies. Therefore, it is urgent to develop a recycling technology without negative impact to the environment to resolve the prob- 4.2.3. Foam glass lems of waste CRTs. 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 be- 5. Conclusions tween 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 pres- Generation of waste from WEEE is increasing at a rapid rate ent day foam glass industries are using up to 98% post-consumer worldwide surpassing the rate of generation of normal municipal waste glass in their products (ICER, 2004). waste. Used televisions and computer monitors form a significant Using CRT glass to produce the foam glass instead of flat glass portion of this waste stream. The increasing domestic generation and container glass can decrease the energy consumed, for the and illegal trans-boundary shipment of e-waste have created great softening temperature of the CRT glass is about 60–100 °C less than challenges to the environment and formal recycling infrastructure. that of flat glass and container glass. The feasibility of using recy- Dismantling the CRTs is a key step to realize the separation of pa- cled CRT glass in foam glass manufacture has been investigated nel glass and funnel glass for improving the CRT glass value. by several researchers. Mear et al. (2006c) studied the character- Through the analysis and investigation of the Chinese e-waste ization of foam glass produced from CRT glass powder and the recycling plants, for solving the current problem, the more cost- reducing agents nitride (TiN) and carbide (SiC).They measured effective and eco-friendly separation methods such as crushing the parameters such as density, porosity, thermal and mechanical and automatic sorting techniques could be applied in some formal properties and found that reutilization of CRT glass in the form recyclers from the national pilot project. As the availability of of foam glass is a recycling process with high potential. Several opportunities for closed-loop recycling declines in the coming Author's personal copy

Q. Xu et al. / Waste Management 32 (2012) 1566–1574 1573 years there is a definite need to invest in research and develop- Duan, H.B. et al., 2007. Employment analysis of WEEE recycling and disposal in ment for open-loop recycling to make it more environmentally China. Internal working paper of EMPA. St. Gallen, EMPA. Eugster, M., Fu, H., 2004. Waste assessment in P.R. China—A case study in Beijing. friendly. We summarize the studies that have been carried out to Swiss E-Waste Program, EMPA. Materials Science and Technology. recycle CRT glass for lead recovery, detoxification, foam glass and Greenpeace International, 2008. Toxic Tech: Not in Our Backyard-Uncovering the other glass products such as glass–ceramics, glass glaze, glass com- Hidden Flows of e-Waste. Greenpeace, 2005. Toxic tech: pulling the plug on dirty electronics. Greenpeace posites, X-ray resistant glass, showing that several experimental International. Greenpeace Toxics Campaign. techniques have demonstrated favorable results. The challenge Gao, S., Guo, H., Dong, X.F., Mu, K.L., 2007. Study on preparation of foam glass from for the future is how to transfer these results into practice given waste cathode ray tubes and its performance. construction material (in Chinese), 44–48. the preference to emphasize economic aspects over environmental Herat, S., 2008. Recycling of cathode ray tubes (CRTs) in electronic waste. Clean-Soil aspects in many situations. Through drivers such as legislation and Air Water 36, 19–24. practices such as cleaner production and design for environment it Hu, Y.C., Yang, J.X., Zhu, J., Wang, P.W., Liu, Z.X., 2007. The CRTs glass separating methods and device.CN101172770A, China. is hoped that high quality CRT glass is made available for efficient Huisman, J., 2004. 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