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New Approach To Cathode Ray Tube Recycling October 2003

© Copyright 2003 Icer Page 1 of 34

The main barrier to recycling CRTs is the perceived lack of applications for glass

which contains high levels of lead oxide and other undesirable metal oxides.

The objective of this project was to test two techniques – smelting and electrolysis - for

removing metal oxides from waste CRT glass. The project was led by ICER. The experimental

work was designed and carried out by Glass Technology Services.

The project also estimated arisings of waste CRTs in 2002, forecast arisings over the next 10

years and identified the environmental and legislative drivers for CRT recycling. In addition, it

surveyed current approaches to CRT recycling in the UK.

A CRT is composed of two different types of glass. One — used for the funnel and neck

sections — is characterised by high levels of lead oxide and the other — used for the screen —

is typically a non-leaded glass that contains high levels of barium oxide. There is considerable

variation in the composition of glass, especially screen glass, made by different manufacturers.

In addition to glass, there are other materials in a CRT, including ferrous and non-ferrous

metals, and coatings to the screen and funnel sections. CRTs are usually housed in a plastic

casing.

Arisings of waste CRTs in the UK in 2002 are estimated at 105,000 tonnes. This includes waste

glass from TVs, PC monitors, monitors used in specialist applications and waste from the CRT

assembly process.

Arisings of waste CRT glass from the same sources are forecasted to be 100,000 tonnes in

2012. This figure assumes a decline in waste glass from PC monitors because of the shift to flat

screen display technology but an increase in glass from TVs because of larger screen sizes in

later models. Waste CRTs from all sources except PC monitors are likely to continue to enter

the waste stream for at least 25 years.

Studies have shown that when CRTs are disposed of in landfill sites, lead can leach from the

crushed glass and contaminate ground water. This is a major driver for CRT recycling. It is also

important to reclaim the other materials, such as ferrous and non-ferrous metals and plastics,

which are associated with CRTs.

The WEEE (Waste Electrical and Electronic Equipment) Directive sets targets for material

recycling and recovery of equipment containing CRTs. It is to be implemented in national

regulations by 13 August 2004.

New Approach To Cathode Ray Tube Recycling October 2003

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The European Waste Catalogue classifies CRTs as hazardous waste. This makes it more costly

to dispose of CRTs under the Landfill Directive and also limits potential for exporting waste

CRTs to non-OECD countries.

Mixed CRT glass (funnel, neck and screen glass) contains on average 5% lead oxide, 10%

barium oxide and 2% strontium oxide. Waste glass of this composition is unsuitable for

applications where metal oxides could leach into food products or ground water.

Currently in the UK, recycling of CRT glass is restricted to glass from the CRT assembly

process and glass from some post-consumer PC monitors. This is because recycling of postconsumer

CRT glass has a cost. The economic barriers to increased recycling of CRT glass are

expected to decline when the WEEE Directive comes into force, requiring producers to pay the

costs of recycling WEEE from households from August 2005.

Post-production waste CRT glass from the assembly process is mostly shipped to Europe for

use in the manufacture of new CRTs. Some CRTs from end-of-life PC monitors are sent to a

copper-lead smelter in Europe where the glass acts as a substitute for sand in the smelting

process. Other CRT glass from monitors is used to make ceramic products. Little postconsumer

CRT glass is sent for manufacture of new CRTs. This is because of the high cost of

separating, sorting and processing the glass to meet the standards required by glass

manufacturers.

This project reviewed the possible technologies to extract the lead oxide and to a lesser extent

barium and strontium oxide from the glass matrix, to render the glass non-toxic and suitable for

use in other applications. Whole CRT units were crushed and used in the experimental work;

this resulted in a mixed glass that contained approximately 5 weight % lead oxide, 10.8 weight

% barium oxide and 2.4 weight % strontium oxide.

The two known technologies for extracting metal oxides from glass are:

smelting to reduce the metal oxides to metal by melting the glass mixture in reducing

conditions using reactants such as carbon or aluminium so that the metal forms into spheres

and falls to the bottom of the glass melt

electrolytic separation by applying a voltage across a molten bath of mixed glass so that the

metal ions are attracted to the positive electrode and form metal from the oxide.

Experiments indicated that the glass smelting technique with the use of 0.5 weight %

aluminium addition resulted in a glass with a 50% reduction of lead oxide from the mixed CRT

waste, with metallic spheres of less than 1mm diameter suspended in the glass. In addition, the

barium and strontium oxide were reduced by 30% and 35% respectively. Although the

experiments showed that it was possible to reduce the lead oxide content in waste CRT glass by

50%, there was no indication that it would be possible to remove all the lead compounds from

waste CRT glass.

New Approach To Cathode Ray Tube Recycling October 2003

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The experiments also showed that electrolytic separation is not a practical technique for

extracting metals from waste CRT glass. No measurable amounts of lead were removed from

the glass structure during the course of the experiments.

However, the waste CRT glass used in both sets of experiments was coarsely crushed. If finely

ground waste glass was used instead, it might be possible to further reduce the lead and metal

oxide levels. This would involve additional cost.

Because of the residual lead, barium and strontium oxide content in the smelted waste CRT

glass, this glass could not be used in applications where there are strict limits on permitted

levels of these oxides, for example, in food and drink glass containers or water filtration media.

This work indicated that the removal of lead, barium and strontium oxide to an acceptably low

level from mixed waste CRT glass was not practical under the experimental conditions

investigated. It is therefore recommended that further work on waste CRT glass recycling

should be directed at seeking suitable applications, either for mixed waste CRT glass or for lead

oxide glass and barium oxide glass. However, if suitable and economic applications for waste

CRT glass are not found, it is recommended that the approach of heavy metal oxide reduction

be revisited