Materials recovery from waste cathode ray tubes (CRTs)
This is the second interim report of this project being carried out by ICER with support from Glass Technology Services. The project is examining potential markets for waste CRT glass. In this second stage five potential applications have been investigated, three for screen glass which does not contain lead and two for lead-containing funnel glass or mixed glass. The technology for separating the leaded funnel glass from the non-leaded screen glass has also been explored. This stage of the project also looked at current practice in collecting CRTs for recycling.
Use of CRT screen glass in bricks and tiles
Bricks and cladding tiles can be manufactured by pressing together glass particles and firing the resulting product to increase density and strength. The project analysed two products made with CRT glass. The first was a brick product developed by Staffordshire University. Tests showed that the physical properties of the product make it suitable for a range of non-engineering applications e.g. decorative bricks, cladding tiles. Chemical durability tests showed that likely levels of toxic leachates were below the levels set for drinking water. The manufacturing process has a reduced environmental impact in terms of CO2 emissions compared to standard clay bricks and also compares well in terms of cost. This application has the potential to use significant quantities of the UK’s waste CRT screen glass but considerable market research is needed to understand and develop a market for this niche product.
The second product was a cladding tile manufactured by Innolasi Oy. This was found to be expensive to produce compared to imported natural stone. It is therefore unlikely that there would be substantial demand for this product in the UK.
Use of CRT screen glass as flux in brick and ceramic manufacture
Research by CERAM into the use of container glass as flux in brick manufacture indicates that a 5% addition of glass could save between 3 and 5% of the energy used in the firing process. CERAM has undertaken further research which shows that additional energy savings could result from the use of CRT glass. It may also be a more effective fluxing agent than container glass because of its higher alkali content. This application has the potential to use a significant amount of the UK’s waste CRT screen glass. If all UK brick manufacturers used 5% some 370,000 tonnes of CRT glass would be required, over 5 times the annual arisings of waste CRT screen glass in the UK. The use of glass as flux will, however, add some cost to brick manufacture because of the need to grind the glass very finely. Further work is needed to raise awareness among brick manufacturers of the potential for using CRT glass and to explore the collection and processing infrastructure needed to ensure consistent supply
There is a similar potential for using CRT glass as flux in the manufacture of ceramic-ware but further research is needed and demand has not been quantified.
Use of CRT screen glass in ceramic glaze
Because the metal oxide content of waste CRT screen glass varies from batch to batch it would be technically difficult to incorporate CRT glass in ceramic glazes and glass frits. Furthermore, these applications would use only a fractional amount of UK arisings of waste CRT glass.
Use of CRT Screen glass in foam glass
Foam glass is an insulating material which can be made from post-consumer waste glass. Experience in Norway indicates that it is technically feasible to incorporate at least 20% CRT screen glass. There are no known technical barriers to using CRT glass and no adverse environmental impacts compared to using other types of waste glass. Demand for foam glass in the UK, however, is limited and there is currently no production capability. Production facilities are being considered but the projected demand for CRT glass in this application is low starting at 3,000 tonnes per annum and rising to a maximum of 9,000 tonnes per annum.
Use of CRT glass (screen and funnel) in the manufacture of new CRTs
There is potential to use 10% of the UK’s total annual arising of waste CRT glass (14% of screen glass arisings) in the manufacture of new screens in the UK. Demand for waste CRT glass – screen and funnel - across the 15 EU member states is currently between 8% and 10% of estimated arisings and could increase to as much as 20% if it proves technically and commercially feasible to use over 50% glass cullet in the manufacture of new funnel glass and 30% in screen glass. The glass must be separated, sorted and cleaned to meet glass manufacturers strict quality requirements Further work is needed to explore the technical limits on using post-consumer cullet and to raise awareness of the demand from glass manufacturers for waste CRT glass. Use of cullet in the manufacture of new CRT glass is an important application for waste CRT glass particularly for lead-containing funnel glass for which recycling options are limited.
Use of CRT glass (screen and funnel) in smelting operations
In some types of smelting operations, CRT glass (mixed or separated) can replace sand which is used as a flux. Copper smelters have the greatest potential to use CRT glass but lead smelters such as Imperial Smelting Furnaces (ISFs) used for primary lead and zinc may also have potential to use this material. In order to use CRT glass in smelting operations it is necessary to establish that the lead in the glass can be recovered and that the resulting slag is sufficiently non-toxic to be used in secondary applications such as road aggregate. Smelting is potentially an important application for lead-containing funnel glass for which other recycling options are limited.
Methods of separating CRT glass
There are two approaches to separating the screen glass from the lead-containing funnel glass. The first is to manually remove the CRT from its casing and split it. Established techniques in commercial operation include hot-wire, laser-cutting, diamond-sawing and thermal shock. The second approach is to shred whole TVs and monitors, recover the glass from the remaining material and separate it into different types. This approach is still under development in the UK.
The next stage of the project will put together a business development plan to identify commercial operators and take forward the four applications which have been identified as having potential to use significant amounts of the UK’s arisings of waste CRT glass i.e. to make bricks, to make new CRTs, as flux in brick and ceramics manufacture and as flux in smelting operations.