management of crt glass from discarded computer monitors and tv sets
TRANSCRIPT
Waste Management 28 (2008) 1499
lable at ScienceDirect
2 Contents lists avaiWaste Management
journal homepage: www.elsevier .com/locate /wasman
Editorial
Management of CRT glass from discarded computer monitors and TV sets
E-waste disposal, especially of Cathode Ray Tubes (CRT), has be-come a global environmental problem. News of suspicious ship-ments of discarded computer monitors and TV sets fromdeveloped countries in Europe and North America to the lessdeveloped countries are not uncommon. Due to rapid develop-ments in technology, electronic products are being replaced bynewer models at a much faster rate (e.g., the continuous replace-ment of CRT monitors by LCD displays and the recent introductionof high resolution/definition TV sets). Predictions indicate thathuge numbers of CRTs will need to be disposed of in the comingdecades. With little handling alternatives, discarded CRTs derivedfrom computer monitors and televisions are frequently sent tolandfills. But the impacts of heavy metals in the discarded CRTsto the environment cannot be neglected, and the high concentra-tion of lead in the CRT creates the biggest problem.
Generally, glasses in a CRT can be classified into three maintypes: the relatively lead-free panel glass and the lead-laded funneland neck glasses. While basically immobile in the solid phase, po-tential leaching of lead from discarded CRTs in landfills has becomean environmental concern. The Toxicity Characteristics LeachingProcedure (TCLP) is currently adopted commonly to determinethe leaching toxicity of wastes, and wastes would be classified ashazardous if the elemental concentration in the leachate exceedsthe thresholds listed. A number of studies have demonstrated thatthe neck and funnel glasses of CRT are hazardous wastes, while thepanel glass exhibits little toxicity.
With rising awareness of the problems caused by potential leadleaching from CRT, legislation in Europe and North America im-poses stringent controls on CRT disposal. In addition, the recentgreen movement in many countries facilitates the introduction ofproducers’ responsibility legislation (such as the WEEE Directivein Europe), which requires producers of new E-products to beresponsible for the management, recycling and eventual disposalof the out-dated models. Therefore, alternatives other than landfilldisposal are needed to manage the end-of-life CRTs. Reuse byredistribution, for example, resale or donation to the less devel-oped world, can delay the rate of CRTs requiring disposal, but envi-ronmental friendly methods are still required for recycling andtreatment of the CRTs at the end of their life cycles.
Reuse of materials from CRTs requires dissembling and sortingprior to re-utilization. According to the recycling experiences in anumber of countries, electric wires, plastic casings, and otherexternal electronic and metallic parts are first required to be re-
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moved from the computer monitors and TV sets to isolate the CRTs.The glass components of CRTs are then separated into funnel andpanel glasses. Separation of the funnel and the panel glass is per-formed by laser cutting or by a hot wire separation method. Thepanel glass, being almost lead-free, has been reused as glass aggre-gate after crushing in construction products. But special arrange-ment is needed for the management the funnel glass, due to itshigh lead content.
Ideally, the lead glass derived from CRT should be best re-uti-lized for new CRT manufacturing. But with the introduction ofLCD, plasma and other flat-screen technologies, the demand fornew CRTs has dropped significantly. Other alternative recyclingoutlets are needed. Another common method is the re-utilizationof CRT glasses as a flux either in metal smelting or in brick, tilesand ceramic manufacturing. But the CRT glass must be free fromcontamination and be ground to sand-like consistency; such recy-cling outlets are only applicable in places where they have anindustry infrastructure to accommodate the CRT waste.
Methods have been developed by various researchers to removelead from the funnel glass of CRTs using a process of crushing, acidleaching and washing. Its has been demonstrated that the leach-able lead in the crushed glass particles can be effectively removed,rendering the treated glass a non-hazardous waste. The treatedglass should be able to be reused as aggregate for making special-ized indoor construction products (e.g., partition blocks) providedthat an outlet can be secured for the manufactured products.
Potential users (e.g., construction product manufacturers) of theCRT glass are still quite reluctant to use the recycled materialbecause of the worry about the marketability of the product as itstill contains a large amount of lead. Therefore, there is an urgentneed to develop technologies to utilize the lead content in the glassso that the recycled product can have an added value to enhance tomarketability of the recycled products.
Associate EditorC.S. Poon
Department of Civil and Structural Engineering,The Hong Kong Polytechnic University,
Hung Hom, Kowloon, Hong Kong, ChinaTel.: +852 2766 6024; fax: +852 2334 6389
E-mail address: [email protected]
Available online 20 June 2008