Title: Management of CRT glass from discarded computer monitors and TV sets
Publication Type: Journal Article
Year of Publication: 2008
Author Poon CS
Journal Title: Waste Management
Pages – 1499
E-waste disposal, especially of Cathode Ray Tubes (CRT), has become a global environmental problem. News of suspicious shipments of discarded computer monitors and TV sets from developed countries in Europe and North America to the less developed countries are not uncommon. Due to rapid developments in technology, electronic products are being replaced by newer models at a much faster rate (e.g., the continuous replacement of CRT monitors by LCD displays and the recent introduction of high resolution/definition TV sets). Predictions indicate that huge numbers of CRTs will need to be disposed of in the coming decades. With little handling alternatives, discarded CRTs derived from computer monitors and televisions are frequently sent to landfills. But the impacts of heavy metals in the discarded CRTs to the environment cannot be neglected, and the high concentration of lead in the CRT creates the biggest problem.
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Generally, glasses in a CRT can be classified into three main types: the relatively lead-free panel glass and the lead-laded funnel and neck glasses. While basically immobile in the solid phase, potential leaching of lead from discarded CRTs in landfills has become an environmental concern. The Toxicity Characteristics Leaching Procedure (TCLP) is currently adopted commonly to determine the leaching toxicity of wastes, and wastes would be classified as hazardous if the elemental concentration in the leachate exceeds the thresholds listed. A number of studies have demonstrated that the neck and funnel glasses of CRT are hazardous wastes, while the panel glass exhibits little toxicity.
With rising awareness of the problems caused by potential lead leaching from CRT, legislation in Europe and North America imposes stringent controls on CRT disposal. In addition, the recent green movement in many countries facilitates the introduction of producers’ responsibility legislation (such as the WEEE Directive in Europe), which requires producers of new E-products to be responsible for the management, recycling and eventual disposal of the out-dated models. Therefore, alternatives other than landfill disposal are needed to manage the end-of-life CRTs. Reuse by redistribution, for example, resale or donation to the less developed world, can delay the rate of CRTs requiring disposal, but environmental friendly methods are still required for recycling and treatment of the CRTs at the end of their life cycles.
Reuse of materials from CRTs requires dissembling and sorting prior to re-utilization. According to the recycling experiences in a number of countries, electric wires, plastic casings, and other external electronic and metallic parts are first required to be removed from the computer monitors and TV sets to isolate the CRTs. The glass components of CRTs are then separated into funnel and panel glasses. Separation of the funnel and the panel glass is performed by laser cutting or by a hot wire separation method. The panel glass, being almost lead-free, has been reused as glass aggregate after crushing in construction products. But the special arrangement is needed for the management the funnel glass, due to its high lead content.
Ideally, the lead glass derived from CRT should be best re-utilized for new CRT manufacturing. But with the introduction of LCD, plasma and other flat-screen technologies, the demand for new CRTs has dropped significantly. Other alternative recycling outlets are needed. Another common method is the re-utilization of CRT glasses as a flux either in metal smelting or in brick, tiles and ceramic manufacturing. But the CRT glass must be free from contamination and be ground to sand-like consistency; such recycling outlets are only applicable in places where they have an industry infrastructure to accommodate the CRT waste.
Methods have been developed by various researchers to remove lead from the funnel glass of CRTs using a process of crushing, acid leaching and washing. Its has been demonstrated that the leachable lead in the crushed glass particles can be effectively removed, rendering the treated glass a non-hazardous waste. The treated glass should be able to be reused as aggregate for making specialized indoor construction products (e.g., partition blocks) provided that an outlet can be secured for the manufactured products.
Potential users (e.g., construction product manufacturers) of the CRT glass are still quite reluctant to use the recycled material because of the worry about the marketability of the product as it still contains a large amount of lead. Therefore, there is an urgent need to develop technologies to utilize the lead content in the glass so that the recycled product can have an added value to enhance to the marketability of the recycled products.