At the end of the sorting operation, equipment fit for dismantling (i.e. equipment that cannot be refurbished nor repaired) is put together and sent to be processed. The dismantling operation consists in extracting reusable spare parts, removing all polluting substances from the equipment and sorting materials so that they can be sent to the proper recovery industries.
It is essential to conduct this activity in accordance with the regulations, to ensure worker safety and environmental protection. All handling operations are potential sources of injury. To avoid accidents, it is recommended that a procedure is established to describe all movements appropriate to every operation. Meanwhile, staff must be trained in issues relating to the hazardous equipment that they work with. Safety notices should be pinned up in the premises to remind employees of all hazards and the instructions to be followed. The risks of being cut or of inhaling dust must be monitored, and emissions must be controlled to avoid damaging the environment and the health of the handlers.
Dismantling a central unit
The dismantling operation consists in extracting the various materials used in the CU, to put them into homogeneous batches that will then be recovered by the appropriate industries. However, it is not always necessary to dismantle all the components of the computer. Indeed, some components may be recovered as they are, if they are sent to the appropriate industry.
When dismantling a CU, the first thing to do is to open and remove the case, to get access to the internal components. The case, mainly made of plastic or metal, is then sorted according to the type of material (plastic or metal). However, due to the complex composition of plastics, it is often difficult to identify the types of plastics and to sort them out to make homogeneous batches. Since the enactment of the ISO 11469:2000 standard, plastics composing new pieces of equipment can be identified thanks to pictograms. According to a study carried out by the ADEME, CU cases are mainly composed of either ABS plastic (acrylonitrile butadiene styrene), of ABS/PC (polycarbonate) plastic composite, or of ABS/HIPS (high impact polystyrene) plastic composite.
The power pack consists of a radiator, a fan, some cables and connectors, a printed circuit and a transformer. Several colored cables go from the power pack to various parts of the computer. To dismantle a power pack, the technician disconnects all these cables and removes the few screws holding the pack to the computer. Then, he has to sever the white connectors with cutters, and cut the bundle of cables to recycle each of them separately. Afterwards, the various components must be put into homogeneous batches. Some components, such as printed circuits or external electric cables, are classified as hazardous waste by the WEEE Directive and must therefore be treated accordingly.
The hard drive is made up of a lid, a metal case, a data disk and a printed circuit. The technician undoes six to eight screws to remove the little aluminum lid and the computer board which is beneath it. The other parts of the drive may be dispatched into containers of mixed aluminum. If hard drives are pierced to secure the data disposal, this operation should be carried out under an aspirating hood, as the smoke resulting from it may contain harmful substances. Some other drives (CD-ROM, etc.) have a similar composition and can be dismantled in the same manner.
There are numerous printed circuit boards in a computer. The most important is the motherboard, as all the components of the computer are connected to it. Three types of pieces must be removed from this board: the memory modules, the microprocessors and the batteries. Batteries are considered to be hazardous waste and must undergo specific treatment. The other boards are smaller and are inserted into the motherboard and are called daughterboards. They include video boards, network boards, sound boards, etc. They all have at least one connector and golden contacts. All these boards must be collected into homogeneous batches to be recovered separately.
In a computer, there is usually only one microprocessor, inserted in the motherboard. A microprocessor is generally two inches long, two inches wide and half an inch thick. In most cases, it is beneath an aluminum radiator and a fan, which must be removed before the microprocessor can be recovered. When removing these pieces, the technician must be careful not to cut wire connectors, or the pieces would become unusable.
Extraction of pollutants
According to European regulations, there are three particularly polluting components in a CU: the coin cell, the small electrolyte capacitors and the LEDs. The coin cell is often inserted into a mechanical holder or sometimes soldered to the board. It should be removed from the motherboard because otherwise, during the shredding operation, the cell could be opened, thus exposing the lithium anode. Small electrolyte capacitors can be found on old printed circuits of larger computer equipment, such as mainframes and large printers. They have to be collected separately because they can be considered as hazardous. Indeed, capacitors may contain corrosive liquids. Therefore, the removal of capacitors larger than 25 cm² must be carried out prior to shredding and recovery because printed circuits are considered hazardous waste. LEDs present on some printed circuits may need to be removed from the printed circuit boards, due to their gallium arsenide content.
Content of a CRT
Old CRTs can contain 2 to 3 kg of lead, whereas new models generally contain no more than 1 kg. CRT screens consist of a plastic case (ABS/PC), a cathode ray tube, an electron gun, a printed circuit and cables. The CRT contains by far the greatest amount of all substances of concern in a PC.
The inner side of the faceplate is covered with a fluorescent coating, also known as luminophore, which emits light radiation when excited by electron impact. The composition of this fluorescent and phosphorescent coating varies from one manufacturer to the other. The luminophore is generally made of materials which are difficult to recycle, such as rare earth oxides, phosphorus, iron oxide, graphite, lead, silicates, cadmium sulphides and cadmium tungstates. According to the OECD , the cone glass (or funnel glass) contains about 20-24% of lead, the neck glass about 28-30 % of lead and the glass frit about 80% of lead. The screen glass may contain encapsulated lead that can be released when the glass is broken.
CRT screen dismantling
Apart from the removal of the plastic cases, no dismantling operation should be conducted on monitors without adequate facilities. Only industrial channels that have adequate facilities should process cathode ray tubes. Such facilities can isolate hazardous materials contained in tubes in a confined environment.
To dismantle CRTs, the technician must recover the plastic cases and sort them according to their hazard symbol, and recover the electronic boards. Once the lid has been removed, all the internal cables must be cut so that the internal components can be removed (display adaptor, metal components, screen cable, etc.). Once sorted, the plastic cases are assembled in batches. To remove the electron gun, the dismantling technician has to take out the screw holding it to the end of the CRT. The technician continues to remove components one by one until only the CRT remains.
CRTs are then processed in a treatment unit specially designed to meet the strictest requirements regarding environmental protection and occupational health and safety.
Dismantling sites may consider investing in the installation of an industrial unit specialising in the mechanical separation of the cone glass containing leachable lead and the panel glass containing lead in its matrix. Such an installation enables the tubes to be dismantled while protecting technicians from dust they might inhale, and efficiently controlling air emissions. The installation should be equipped to clean the glass and to remove the phosphor coatings. Once it has been separated from lanthanides, the cleaned lead and barium glass (with assayed lead concentrations), can be sent to a specialised industry for recovery. Moreover, the staff must be protected against inhaling the phosphorus contained in the fluorescent coating. This is why wet processes are often used to remove the phosphorus.
Flat screen dismantling
LCD screens are progressively replacing CRT screens on the market. Flat panel displays consist of a plastic case and a coat of liquid crystal contained between two glass panels covered with conductive materials. The liquid crystal is derived from butylaniline, and can be considered as harmful to human health and the environment if handled improperly. There are few existing technologies to process them, but flat panel screens containing liquid crystal displays could still be sent for recovery operations. There is mercury in flat screens and therefore they should be handled and treated with particular precaution.
Peripherals et cables processing
There are two kinds of cables in a computer: flat cables and small colored cables which come from the power pack. Connectors should be extracted prior to separating cables. Black plastic connectors are collected separately, and cables are recycled to recover non-ferrous metals (copper, aluminum), which are then sent to refiners. If possible, insulated electrical wires (e.g. power cables) should be separated from PCs. Insulated wires require particular treatment because their PVC coating contains chlorine and therefore they are classified as hazardous waste.
As batteries used in portable computers are recognised as hazardous waste, they must be manually removed and sorted according to their category: nickel-cadmium (Ni-Cd), nickel metal hydride (NiMeH, corrosive), or lithium ion batteries (recyclable). Some lead-acid batteries are also used. Batteries must be handled carefully, to avoid short circuits and untimely external current flows. It is advised not to keep too many batteries in stock and to send them to specialised metal recovery facilities. Once sorted, batteries should be stored in small quantities, and physically separated from each other, to avoid any risk of explosion or fire.
A keyboard is composed of several printed circuits. The keyboard’s frame and keys are made either of ABS plastic or of ABS/PC plastic composite (about 1 kg, or 2.2 lbs).
Directing materials to the proper recovery channel
This stage comes after dismantling and sorting. It requires heavy industrial investments to be carried out in the best conditions of safety and environmental protection. It is generally outsourced, as the recycling centre does not have the appropriate technologies. If pieces of computer equipment are dumped or incinerated, the hazardous substances they contain may pose risks for human health and the environment. These risks can be reduced thanks to appropriate work practices, the control of combustion and the use of air emissions control devices. As far as occupational health and safety matters are concerned, the most important thing is to be aware of the potential risks of the activity, and to implement measures to control and reduce these risks. To prevent these risks the entrepreneur must find the most appropriate companies to treat and recover the batches of homogeneous materials resulting from the dismantling operation. He must find companies that offer economical and ecological advantages.
To reduce logistics costs, once plastic has been extracted, it is possible to reduce volumes by using tools such as a mechanical press or shears for iron or balers for plastics and master cartons. This can be secondhand equipment. For larger volumes, it is possible to use comminuting machines such as pelletizers. After identification and homogenization, plastic will be sent for recovery in the form of plastic batches weighing about 150 kg. This operation requires neither specific skills nor expensive equipment. The operation is interesting for the recycler as it generates homogeneous materials that can be negotiated with scrap dealers and industrial traders.
Even though there is a plastic recovery market, it is hindered by a number of obstacles. First, recovery is complicated by the presence of flame retardants (bromine) in plastics which are therefore non-homogeneous. Then, the presence of labels and metal pieces reduces the homogeneity of plastic batches. And finally, plastic recovery requires large quantities of homogeneous plastics to be a profitable activity. Therefore, it is in the entrepreneur’s interest to carefully carry out the dismantling operation, to form high quality batches of homogeneous plastics that will be sold at the best prices to industries.
To maximize profits, it is in the entrepreneur’s interest to sell metal batches which are as homogeneous as possible. The iron in the structure of the CU represents the largest quantity of metal used in a computer. It can be sold to iron and steel industries or to scrap dealers. Computer equipment also contains non-ferrous metals, such as copper (up to 1.5 kg) and aluminium, or lead and pewter in smaller quantities. However, these metals are often mixed to form other components, such as printed circuits. In these cases, the separation of these metals requires advanced technologies.
The recovery of these materials is very interesting to the entrepreneur, as he can sell them as they are (mixed) or in homogeneous batches.
In a used PC, printed circuit boards are among the most valuable components. Firstly, they may contain chips that can be removed and sold for reuse. But above all they contain valuable metals that can be sold to a smelter. Electronic boards that cannot be reused as spare parts still have value. To optimize the value of these boards, it is necessary to sort them according to their precious metal content. The boards are then sold to refineries. Their price depends on the market price of precious metals, on the homogeneity of batches and on the quantity. The recovery of circuit boards must be carried out by specialised industries, to avoid any health or environmental risk.
Some circuit boards (such as power supply boards and electronic boards found in monitors) contain on average less than 100 g of gold per tonne. They are «low grade» boards. However, some boards (e.g. graphic boards, audio boards and network boards) contain a lot more precious metal. «high grade» boards contain between 400 and 500 g/tonne, and are found in laptops and mobile phones. «Very high grade» boards, containing more than 500 g/tonne, come from large mainframe computers or phone centres.
Once at the smelter, the different metals (gold, copper, silver, selenium, tellurium, lead, palladium, etc.) are recovered through complex processes. Due to the complexity of the technologies used and given that recovery practices can be highly polluting, the entrepreneur must sell the printed circuits to appropriate industries that can conduct recovery operations in an environmentally sound manner.
Batteries and accumulators are not necessarily hazardous as they are. However their content can have an impact on the environment. Therefore, the enterprise must be careful to ensure the security of the storage area before disposal. In a PC, the coin cell is often composed of a lithium anode. If some of the lithium is exposed, it may react with oxygen or moisture, generating heat and possibly hydrogen gas. A fire can occur during the shredding operation. A lithium coin cell can be recovered, after it has been fully discharged to eliminate potential reactivity, by shredding and gravity separation. The entrepreneur is therefore advised to resell these batteries to industries that possess the equipment and technologies necessary to recover them. However, some batteries do not have any value and the entrepreneur is responsible for having them recycled by a specialised industry.
Cables can be shredded before being sent to specialised industries or burned in a facility where every measure is taken to prevent the formation of harmful substances, such as chlorinated dibenzofurans and dibenzodioxins. Those cables (or cable residue) can be recovered by industries specializing in the separation of copper wires from their plastic sheaths. These industries usually use various physical means to separate these materials in order to obtain perfectly homogeneous pieces of copper and plastics.
There are two main industries that recycle CRT glass. First, there are the manufacturers making new CRT screens from recycled CRT glass. They often require the panel glass to be separated from the cone glass, so that they can proportion correctly the quantities of lead in the glass they produce. And then there is the lead-glass recycling industry. In this case, glass is sent to lead smelters, to be used as a fluxing agent in the smelting process. Then, smelters can recover the lead contained in the glass.
Cathode Ray Tubes are made of a faceplate (containing lead or barium) welded to a cone glass by a frit. The tubes contain lead encapsulated in glass that can be released if the glass is broken. Therefore, the entrepreneur is advised to leave the responsibility of treating tubes to specialised enterprises. Indeed, the staff carrying out the mechanical separation of glass must be protected from inhaling the dust released when the tubes are broken, because they may contain lead or barium oxide. Moreover, the fluorescent coating on the faceplate may present inhalation risks if they are handled in a dry state. This is why wet processes are often used to remove the phosphor particles.
CRT Electron guns
The electron gun of the CRT contains a small getter plate (about 1-2 grams including frame), and bears barium and barium compounds (barium oxide is considered as a harmful substance). During the shredding operation, the CRT screen getter can release harmful barium dust. Therefore, several countries require its removal. Once removed, the getters should be stored separately, away from any source of moisture since barium is a leachable and easily solvable substance. They must be sent to a specialised industry that can incinerate them in an environmentally sound manner. The electron gun itself can be sent to a recycling facility that can reclaim the copper it contains.
Flat screen monitors
According to a document issued by the OECD working group on waste prevention and recycling, entitled “Technical Guidance for the Environmentally Sound Management of Specific Waste streams: Used and Scrap Personal Computers” LCD screens can be sent to a smelter for recovery of non-ferrous metals on the condition that the smelter is equipped with flue gas cleaning systems (to minimise dioxin emissions), and prepared to carry out the separation or immobilisation of mercury. Flat panel screens should be sent for either recovery operation or thermal treatment at an environmentally sound and appropriately authorised incinerator with modern flue gas cleaning systems. When discharge lamps are removed, they should be sent to a specialised mercury recovery facility or to an environmentally sound and appropriately authorised hazardous waste incinerator with modern flue gas cleaning systems that guarantees the proper separation or immobilisation of mercury. The WEEE Directive requires that liquid crystal displays of a surface area greater than 100 cm2 are managed separately, as they are back lighted with gas discharge lamps containing mercury.
Pollution control and disposal
In a piece of computer equipment, some components cannot be recycled. These components, mainly plastics and resins containing flame retardants, must be burned or buried in and environmentally sound manner. However, in some countries, the burial of waste is prohibited. According to the Basel convention, these materials should preferably be burned for energy recovery rather than buried or incinerated without energy recovery. The incinerator or the combustion unit must be designed to limit the formation and emission of furans and dioxins and must be equipped with state-of-the-art flue gas cleaning systems. Ashes resulting from the combustion of materials, or materials that cannot be valorised “should be disposed of in an environmentally sound and appropriately authorised landfill”.