SEMINAR REPORT ON
Recovery of Precious Metals from Electronic Waste
By: Hemant Gaule (U04CH115) B.Tech-IV, CHEMICAL ENGINEERING
CONTENTS
1. Introduction 1.1 Quantity of e-waste 1.2 composition of e-waste 1.3 sources of e-waste 1.3.1 Generators of e-waste 1.4 Destination of E-waste:
2. Hazards of E-Waste 3. E-Waste Management 3.1 Industrial Management 3.1.1 Inventory management 3.1.2 Production-process modification 3.1.3 Volume reduction 3.1.4 Recovery and reuse 3.2 Responsibilities of Government/Industries/Public 3.2.2 Responsibility of Industries: 3.2.3 Responsibilities of the Citizen
4. Recycling of e-waste 4.1 Recycling/Recovery System 4.2 Bifurcation of electronic scrap 4.2.1 Characteristics of PCB Scrap 4.2.1.1 Density Differences 4.2.1.2 Magnetic and Electrical Conductivity Differences 4.2.1.3 Polyformity 4.2.1.4 Liberation Size 4.2.1.5 Chemical Reactivity 4.2.1.6 Electropositivity 4.3 Disassembly 4.3.1 Mechanical/physical recycling process 4.5 Mechanical Approaches of recycling electronic scrap 4.6 Hydrometallurgical Approaches 4.7 Extraction of IC/ other components from PCB 4.7.1 Recovery of Gold 4.7.2 Monitors 4.8 Disposal 4.9 Advantages of Recycling e-waste:
5. Conclusion
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1. Introduction E-waste is a popular, informal name for discarded and end-of-life electronic / electrical products. Such products include Computers, Equipment for Information and Communication Technology (ICT), Home Appliances (e.g., TV, Washing Machines, Air Conditioners, and Refrigerators etc.), Audio & Video Products and all of their peripherals. Given the escalating sales and rapid obsolescence of the products, ewaste is emerging as a risk to society. The use of electronic devices has proliferated in recent decades, and proportionately, the quantity of electronic devices, such as PCs, mobile telephones and entertainment electronics that are disposed of, is growing rapidly throughout the world. As new technologies and hardware replace the old ones, consumers get a wider choice of, better and relatively cheaper range of electronic goods to buy from. This generates huge amounts of E-Waste. Unfortunately, despite of its hazardous content, the waste is treated in such a way that most of the hazardous constituents get easily exposed to the environment. This is mainly because most of the electronic circuits contain valuable elements, which are simply stripped away from the waste, and the residue is simply dumped/burned away. Consequently the flora and fauna get affected. If recycled properly, E-Waste is more of a raw material than junk. The waste contains many valuable substances, like gold, platinum and copper, and that too in larger concentrations than their own respective ores. If appropriate means are employed to extract these substances, they can produce huge revenues. In other words, recycling is perhaps the most lucrative of all the management options for EWaste. A recent survey shows that about 80 percent of the E-Waste generated in the US is exported to India, China and Pakistan and unorganised recycling and backyard scrap-trading forms close to 100 percent of total E-Waste processing activity, most of which is burned in the open by these corporations. If these wastes are recycled properly, they could be a huge source of revenue. This report reviews the hazards and the possible management techniques used to handle e-waste. 1.1 Quantity of E-waste European studies estimate that the volume of E-waste is increasing by 3% - 5% per year, which is almost three times faster than the municipal waste stream is growing generally. Today, electronic waste likely comprises more than 5% of all municipal solid waste; that’s more than disposable diapers or beverage containers, and about the same amount as all plastic packaging [2]. Taking computers for instance, newer software rendering the old ones obsolete (software pushing), and cheaper, attractive hardware cause rapid obsolescence of computers. In 1994, it was estimated that approximately 20 million PCs (about 7 million tons) became obsolete. By 2004, this figure was to increase to over 100 million PCs. Cumulatively, about 500 million PCs reached the end of their service lives between 1994 and 2003. 500 million PCs contain approximately 2,872,000 tonnes of plastics, 718,000 tonnes of lead, 1363 tonnes of cadmium and 287 tonnes of mercury [3]. This fast growing waste stream is accelerating because the global market for PCs is far from saturation and the average lifespan of a PC is decreasing rapidly; for instance for CPUs from 4–6 years in 1997 to 2 years in 2005 [4]. As in the case of India, it is estimated that obsolete personal computers (PC’s) were around 2.25 million units in 2005, which are expected to touch a figure of 8 million obsolete units by the year 2010 at an average annual growth rate of 3
approximately 51%. Considering an average weight of 27.18 kg for a desktop/personal computer approximately 61,155 tonnes of obsolete computer waste would have been generated in India in 2005, which would increase to about 217,440 tonnes by the year 2010 at the projected growth rate [5]. Similarly, for US, it was estimated that 20 million computers became obsolete in 1998, and the overall E-waste volume was estimated at 5 to 7 million tons. The figures are projected to be higher today and rapidly growing. A 1999 study conducted by Stanford Resources, Inc. for the National Safety Council projected that in 2001, more than 41 million personal computers would become obsolete in the U.S. Analysts estimate that in California alone more than 6,000 computers become obsolete every day. In Oregon and Washington, it is estimated that 1,600 computers become obsolete each day [6]. To make matters worse, solid waste agencies and recyclers are anticipating a major increase in the volume of computer and TV monitors discarded in the next 5 years. As cathode-ray tube (CRT) monitors currently in use will be replaced by smaller, and more desirable liquid crystal display (LCD) screens, this could mean massive dumping of CRT monitors at an even higher rate. Add to this the fact that new federal rules for high-definition televisions (HDTV) will become effective in 2004. This leap in technology is also expected to lead to a significant increase in television disposal. So is the case with every other category of E-Waste, which indicates that it is very likely that the quantity of this waste will only increase. 1.2 Composition of E-waste Eectronic waste contains the following elements [7]: • • •
Elements in bulk: Tin, Copper, Silicon, Carbon, Iron and Aluminum Elements in small amounts: Cadmium and Mercury, Elements in trace amounts: Germanium, Gallium, Barium, Nickel, Tantalum, Indium, Vanadium, Terbium, Beryllium, Gold, Europium, Titanium, Ruthenium, Cobalt, Palladium, manganese, Silver, Antimony, Bismuth, Selenium, Niobium, Yttrium, Rhodium, Platinum, Arsenic, Lithium, Boron, Americium.
List of examples of devices containing these elements Almost all electronics contain lead & tin (as solder) and copper (as wire & PCB tracks), though the use of lead-free solder is now spreading rapidly [7]. Some of these substances and the components where they are found are described in Table 1. Recently the Swiss ordinance has been amended (June 2004) to match the EU Directive’s definition of the ten categories listed in Table 2, Categories 1–4 account for almost 95% of the E-waste generated (Fig. 1). According to the definitions in the Directive 2002/96/EC of the European Parliament and of the Council (January 2003) on Waste Electrical and Electronic Equipment [9], (WEEE/E-waste) consists of the ten categories listed in Table 2. This categorization seems to be in the process of becoming a widely accepted standard. The Swiss Ordinance on the Return, the Taking Back and the Disposal of Electrical and Electronic Equipment (ORDEE) of 1998 differentiates between the following categories of E-waste: •
Electronic appliances for entertainment; 4
•
Appliances forming part of office, communication and information technology; • Household appliances • Electronic components of the (above) appliances Fig. 2 categorizes the waste by the types of materials in it. Metals, as may be expected, form the majority of it. A study by the European Topic Center on Resource and E-Waste Management indicates that iron and steel form almost the half of the metals present in E-Waste, though they’re not at hazardous as many other metals present in it. Fig. 3 further shows the fraction of individual categories of materials present in E-Waste [1].
Table 1: Hazardous Contents of E-waste [7] Substance
Found in Solder, CRT Monitors (Lead in glass), Lead-acid battery. Solder. Copper wires, Printed circuit board tracks. Nearly all electronic goods using more than a few watts of power (heatsinks). Steel chassis, cases & fixings. Glass, transistors, ICs, Printed circuit boards. Nickel-cadmium rechargeable batteries. Lithium-ion battery. Plating for steel parts. Connector plating, primarily in computer equipment. Smoke alarms (radioactive source). 1950s & 1960s transistorised electronics (transistors). Fluorescent tubes (numerous applications), tilt switches (pinball games, mechanical doorbells). Lead-acid battery. Steel, plastics, resistors, in almost every electronic equipment.
Lead Tin Copper Aluminium Iron Silicon Nickel & cadmium Lithium Zinc Gold Americium Germanium Mercury Sulphur Carbon
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Table 2: E-Waste Categories [1] No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Category Large household appliances Small household appliances IT and telecommunications equipment Consumer equipment Lighting equipment Electrical and electronic tools (with the exception of large-scale stationary industrial tools) E & E tools Toys, leisure and sports equipment Medical devices (with the exception of all implanted and infected products) Monitoring and control instruments Automatic dispensers
Toys , 0.20%
Medical, 1.90%
Label Large HH Small HH ICT CE Lighting E & E tools Toys Medical equipment M&C Dispensers
M&C, 0.10% Dispensers, 0.70%
E&E Tools, 1.40% Lighting, 1.40% CE, 13.70%
Large HH, 42.10%
Small HH, 4.70%
ICT, 33.90%
Fig. 1. Composition of WEEE for Western Europe [1]
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Printed Circuit Boards, 1.71%
Others, 1.38% Pollutants, 2.70%
Screens (CRT and LCD), 11.87%
Cables, 1.97%
Metal-Plastic Mixture, 4.97% Metals, 60.20%
Plastics, 15.21%
Fig. 2. Material Fraction in E-waste [10]
Composition (Weight %) Iron and Steel
47.9
Components
Non-flame retarded plastic
15.3
Copper
7
Glass
5.4
Flame retarded plastic
5.3
Aliminum
4.7
Printed circuit boards
3.1
Other
4.6
Wood and plywood
2.6
Concrete and ceramics
2
Other metals (Non-ferrous)
1
Rubber
0.9 0
10
20
30
Fig. 3. E-waste Composition [9].
7
40
50
60
1.3 Sources of E-waste Developed countries like US, a few West Asian and European countries, produce enormous amounts of E-waste every year. And most of this is exported to developing nations like India, China, Pakistan, Malaysia etc. this is because those countries produce so much E-Waste themselves, that exporting it would be much cheaper than managing it themselves. Also, these developing nations have a workforce willing to dispose off the hazardous waste for very low wages. 1.3.1 Generators of Electronic Waste: Electronic waste is generated by three major sectors Individuals and Small Businesses: In India, this sectors accounts for about 24% of the total E-Waste generation [18,19]. Electronic equipment and computers in particular, are often discarded by households and small businesses, sometimes not because they are broken but simply because new technology has left them obsolete or undesirable. Large corporations, institutions, and government: Large users upgrade employee computers regularly. For example, Microsoft, with over 50,000 employees worldwide (some of whom have more than one computer) replaces each computer about every three years. Factories and industries replace the older of their equipment with new ones, causing more E-Waste and so on. Consequently, this sector contributes to about 74% of the total waste generation in India alone [18,19]. Original equipment manufacturers (OEMs): OEMs generate E-waste when units coming off the production line don’t meet quality standards, and must be disposed of. It is estimated that around 1050 tonnes per year of waste comes form this sector [19]. 1.4 Destination of E-waste: The waste is imported by over 35 countries, which include India, China, Pakistan, and Malaysia etc. Fig. 4 shows the global E-waste traffic routes across Asia. The waste generated by the consumers of electronic goods gets collected by scavengers or garbage collectors, and usually gets deported to backyard stripping houses etc, where the potentially valuable substances are separated from the waste and the residue, which may still contain many hazardous (or useful) substances, is dumped or incinerated.
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Fig. 4 Asian E-Waste Traffic [2]
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2. Hazards of E-Waste When e-waste is disposed of or recycled without any controls, there are predictable negative impacts on the environment and human health. E-waste contains more than 1000 different substances, many of which are toxic, such as lead, mercury, arsenic, cadmium, selenium, hexa-valent chromium, and flame retardants that create dioxins emissions when burned. Generally after being stripped off its valuable content, the residue that’s left behind ends up being burned or thrown away in landfills. Burning the waste exposes its harmful contents directly into the atmosphere, in other words, endangering the plant and animal life living in that atmosphere, whereas, landfill dumping may result in the elements being leached into the soil, and then into the surface/ground water. This affects the flora and the fauna of that environment. The substances liberated in the environment by E-Waste have the following affects on plant and animal lives. • Affect central and peripheral nervous system • May cause brain damage • Affect circulatory system • Show detrimental signs on the growth in plants • Affect the kidneys, reproductive and the endocrine system • Shows negative effect on brain development. According to the European Topic Centre on Resource and Waste Management [16], over time, the metal content has remained the dominant fraction, well over 50%, as compared to pollutants and hazardous components, which have seen a steady decline. E-Waste consists of a large number of components of various sizes and shapes, some of which contain hazardous components. Major categories of hazardous materials and components of E-waste are shown in Table 3. Some of the hazardous compounds liberated by E-wastes are listed in Table 4
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Table 3: Material used in a desktop computer and the efficiency of current recycling processes [11]. Name Plastics Lead Aluminum
Content (% of total weight) 22.9907 6.2988 14.1723
Recycling Efficiency % 13.8 3.8 8.5
Weight of Material (lb) 20 5 80
Germanium Gallium Iron
0.0016 0.0013 20.4712
< 0.1 < 0.1 12.3
0 0 80
Tin Copper Barium Nickel
1.0078 6.9287 0.0315 0.8503
0.6 4.2 < 0.1 0.51
70 90 0 80
Zinc Tantalum Indium Vanadium Terbium
2.2046 0.0157 0.0016 0.0002 0
1.32 < 0.1 < 0.1 < 0.1 0
60 0 60 0 0
Beryllium Gold
0.0157 0.0016
< 0.1 < 0.1
0 99
Europium Titanium
0.0002 0.0157
< 0.1 < 0.1
0 0
Ruthenium Cobalt
0.0016 0.0157
< 0.1 < 0.1
80 85
Palladium
0.0003
< 0.1
95
Manganese
0.0315
< 0.1
0
Silver Antinomy Bismuth Chromium Cadmium
0.0189 0.0094 0.0063 0.0063 0.0094
< 0.1 < 0.1 < 0.1 < 0.1 < 0.1
98 0 0 0 0
Selenium Niobium Yttrium Rhodium Platinum Mercury Arsenic Silica
0.0016 0.0002 0.0002 0 0 0.0022 0.0013 24.8803
0.00096 < 0.1 < 0.1
70 0 0 50 95 0 0 0
< 0.1 < 0.1 15
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Use/Location Includes organics, oxides other than silica Metal joining, radiation shield/CRT, PWB Structural, conductivity/housing, CRT, PWB, connectors Semiconductor/PWB Semiconductor/PWB Structural, magnetivity/(steel) housing, CRT, PWB Metal joining/PWB, CRT Conductivity/CRT, PWB, connectors In vacuum tube/CRT Structural, magnetivity/(steel) housing, CRT, PWB Battery, phosphor emitter/PWB, CRT Capacitors/PWB, power supply Transistor, rectifiers/PWB Red phosphor emitter/CRT Green phosphor activator, dopant/CRT, PWB Thermal conductivity/PWB, connectors Connectivity, conductivity/PWB, connectors Phosphor activator/PWB Pigment, alloying agent/(aluminum) housing Resistive circuit/PWB Structural, magnetivity/(steel) housing, CRT, PWB Connectivity, conductivity/PWB, connectors Structural, magnetivity/(steel) housing, CRT, PWB Conductivity/PWB, connectors Diodes/housing, PWB, CRT Wetting agent in thick film/PWB Decorative, hardener/(steel) housing Battery, glu-green phosphor emitter/housing, PWB, CRT Rectifiers/PWB welding allow/housing Red phosphor emitter/CRT thick film conductor/PWB Thick film conductor/PWB Batteries, switches/housing, PWB Doping agents in transistors/PWB Glass, solid state devices/CRT,PWB
Table 4: Products and Health Effects of E-Waste [12]. Source of E-Waste Constituent Chip resistors and Cadmium (Cd) semiconductors.
Solder in printed circuit boards, glass panels and gaskets in computer monitors.
Lead (Pb)
Relays and switches, printed circuit boards.
Mercury (Hg)
Plastic housing of electronic equipments and circuit boards. Front panels of CRTs
Brominated flame retardants (BFR)
Motherboards
Beryllium (Be)
Cabling and computer housing
Plastics including PVC
Corrosion protection of untreated and galvanized steel plates, decorator or hardner for steel housing
Hexavalent Chromium VI (Cr)
Barium (Ba)
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Health Effects Toxic irreversible effects on human health. Accumulation in kidney and liver. Causes neural damage Teratogenic. Damage to central and peripheral nervous system and kidney damage. Affects brain development of children Chronic damage to the brain Respiratory and skin disorders due to bioaccumulation in fishes. Disrupts endocrine system functions. Short term exposure causes: Muscle weakness; Damage in heart liver and spleen Carcinogenic (lung cancer) Inhalation of fumes and dust. Causes chronic beryllium disease or beryllicosis. Skin diseases such as warts. Burning produces dioxins, it causes: Reproductive and developmental problems; Immune system damage; Interference with regulatory hormones. Asthmatic Bronchitis DNA damage
2.1 Products of E-waste Following are some of the compounds liberated by E-Wastes [9]. Lead: Lead can cause damage to the central and peripheral nervous systems, blood systems, kidney and reproductive system in humans. Effects on the endocrine system have been observed and its serious negative effects on children’s brain development are well documented. Lead accumulates in the environment and has high acute and chronic effects on plants, animals and microorganisms [4]. The main applications of lead in computers are: glass panels and gasket (frit) in computer monitors (3-8 pounds per monitor), and solder in printed circuit boards and other components. Cadmium: Cadmium compounds are toxic with a possible risk of irreversible effects on human health, and accumulate in the human body, particularly the kidneys . Cadmium occurs in certain components such as SMD chip resistors, infra-red detectors, and semiconductor chips. Cadmium is also a plastics stabilizer and some older cathode ray tubes contain cadmium. Mercury: Mercury can cause damage to various organs including the brain and kidneys, as well as the fetus. Most importantly, the developing fetus is highly susceptible through maternal exposure to mercury. When inorganic mercury spreads out in the water, it is transformed to methylated mercury in the bottom sediments. Methylated mercury easily accumulates in living organisms and concentrates through the food chain, particularly via fish. It is estimated that 22 % of the yearly world consumption of mercury is used in electrical and electronic equipment. It is used in thermostats, sensors, relays, switches (e.g. on printed circuit boards and in measuring equipment), medical equipment, lamps, mobile phones and in batteries. Mercury, used in flat panel displays, will likely increase as their use replaces cathode ray tubes. Hexavalent Chromium/Chromium VI: Chromium VI is still used as corrosion protection of untreated and galvanized steel plates and as a decorative or hardener for steel housings. It easily passes through cell membranes and is then absorbed— producing various toxic effects in contaminated cells. Chromium VI can cause damage to DNA and is extremely toxic in the environment (15). Plastics including PVC: Plastics make up 13.8 pounds of an average computer. The largest volume of plastics (26%) used in electronics has been poly-vinyl-chloride (PVC). PVC is mainly found in cabling and computer housings, although many computer moldings are now made with the somewhat more benign ABS plastics. PVC is used for its fire-retardant properties. As with many other chlorine-containing compounds, dioxin can be formed when PVC is burned within a certain temperature range. Barium: Barium is a soft silvery-white metal that is used in computers in the front panel of a CRT, to protect users from radiation. Studies have shown that short-term exposure to barium has caused brain swelling, muscle weakness, damage to the heart, liver, and spleen. There is still a lack of data on the effects of chronic barium exposures to humans. Animal studies, however, reveal increased blood pressure and changes in the heart from ingesting barium over a long period of time.
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Beryllium: In computers, beryllium is commonly found on mother-boards and “finger clips”. Beryllium has recently been classified as a human carcinogen as exposure to it can cause lung cancer. The primary health concern is inhalation of beryllium dust, fume or mist. Workers who are constantly exposed to beryllium, even in small amounts, and who become sensitized to it can develop what is known as Chronic Beryllium Disease (beryllicosis), a disease which primarily affects the lungs. Exposure to beryllium also causes a form of skin disease. Toners: One of the ubiquitous computer peripheral scraps and post consumer E-waste is the plastic printer cartridge containing black and color toners. The main ingredient of the black toner is a pigment commonly called, carbon black. The general term used to describe the commercial powder form of carbon. Inhalation is the primary exposure pathway, and acute exposure may lead to respiratory tract irritation. The International Agency for Research on Cancer has classified carbon black as a class 2B carcinogen, possibly carcinogenic to humans. Little information exists on the hazards of colored toners. Phosphor and additives: Phosphor is an inorganic chemical compound that is applied as a coat on the interior of the CRT faceplate. The hazards of phosphor in CRTs are not well known or reported, but the U.S. Navy has not minced words about the hazards involved in some of their guidelines: “NEVER touch a CRT’s phosphor coating: it is extremely toxic. If you break a CRT, clean up the glass fragments very carefully. If you touch the phosphor seek medical attention immediately.” The phosphor coating contains heavy metals, such as cadmium, and other rare earth metals, e.g. zinc, vanadium, etc. as additives. These metals and their compounds are very toxic. This is a serious hazard posed for those who dismantle CRTs by hand.
3. E-Waste Management It is estimated that 75% of electronic items are stored due to uncertainty of how to manage it. These electronic junks lie unattended in houses, offices, warehouses etc. and normally mixed with household wastes, which are finally disposed off at landfills. This necessitates implement able management measures. However, some already existing modes of disposal cause significant amount of harm to the surrounding ecosystem. Some of these and their consequent harms are listed below [12]: Incineration: Municipal incineration is the largest source of dioxins, and heavy metal contamination. E-wastes on incineration liberate huge quantities of metals, mostly heavy metals in the slag, fly ash, flue gas and in the filter cake of an incinerator. For example, more than 90% of Cadmium put to an incinerator is found in the fly ash and more than 70% of Mercury in the filter cake. Electro-scrap also contains Copper, which is a catalyst for dioxin formation. Hence the incineration may result in generation of extremely toxic polybrominated dioxins (PBBDs) and furans (PBDFs). Landfills: Even highly efficient landfills show signs of leaking. Mercury and certain PCBs from certain electronic devices may leach from landfills, into the soil and groundwater. Lead ions have been found to dissolve when mixed with acid waters, which generally occur in landfills. Moreover, vaporization of metallic mercury, dimethyl mercury may also occur from landfills. Uncontrollable fires are a frequent 14
occurrence in many landfills. When exposed to fires, metals and other chemical substances, such as extremely toxic dioxins and furans are also emitted. Recycling: Recycling E-Waste can be a big source of many valuable substances, but they are worth only if they are extracted by proper means. Most of the methods used today for recycling the waste simply moves the hazards into secondary products that eventually have to be disposed of too. Unless the goal is to redesign the product to use non-hazardous materials, such recycling is a false solution. Due to halogenated substances found in plastics, both dioxins and furans are generated as a consequence of recycling the metal content of E-waste. Hazardous emissions to the air also result from recycling of E-waste containing heavy metals such as lead and cadmium. These can be significantly reduced by pre-treatment operations. Hence, most of the methods used today for dismantling and disposal of electronic waste are causing more contamination and hazards to the ecosystem, contrary to what their purpose is. Therefore a suitable alternative is required for these processes. Various factors can play a significant role in managing the e-waste. Discussed below are the roles of few of these major factors. 3.1 Industrial Management In industrial management of e-waste it should begin at the point of generation. This can be done by waste minimization techniques and by sustainable product design. Waste minimization in industries involves the following: [12] 3.1.1 Inventory management: Proper control over the materials used in the manufacturing process is an important E-Waste Management way to reduce waste generation. By reducing both the quantity of hazardous materials used in the process and the amount of excess raw materials in stock, the quantity of waste generated can be reduced. This can be done in two ways i.e. establishing material-purchase review and control procedures and inventory tracking system. 3.1.2 Production-process modification: Changes can be made in the production process, which will reduce waste generation. This reduction can be accomplished by changing the materials used to make the product or by the more efficient use of input materials in the production process or both. Potential waste minimization techniques can be broken down into three categories: i) Improved operating and maintenance procedures, ii) Material change and iii) Process-equipment modification; in short creating a sustainable product design. This can be done by: Rethinking the product design: Efforts should be made to design a product with fewer amounts of hazardous materials. For example, the efforts to reduce material use are reflected in some new computer designs that are flatter, lighter and more integrated. Other companies propose centralized networks similar to the telephone system. Here consumers would have only a simple screen and keyboard at home or in the office and we would pay a monthly fee based on the level of software complexity we would want to access. Use of renewable materials and energy: Bio-based plastics are plastics made with plant-based chemicals or plant-produced polymers rather than from petrochemicals. Bio-based toners, glues and inks are used more frequently. Solar computers also exist but they are currently very expensive.
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Use of non-renewable materials that are safer: Because many of the materials used are non-renewable, designers could ensure the product is built for re-use, repair and/or upgradeability. 3.1.3 Volume reduction: Volume reduction includes those techniques that remove the hazardous portion of a waste from a non-hazardous portion. These techniques are usually to reduce the volume, and thus the cost of disposing of, a waste material. For example, an electronic component manufacturer can use compaction equipments to reduce volume of waste cathode ray-tube. 3.1.4 Recovery and reuse: This technique could eliminate waste disposal costs, reduce raw material costs and provide income from a salable waste. Waste can be recovered on-site, or at an off-site recovery facility, or through inter industry exchange. For example, a printed-circuit board manufacturer can use electrolytic recovery to reclaim metals from copper and tin-lead plating bath. 3.2 Responsibilities of Government/Industries/Public Considering the severity of the problem, following are some of the suggestions for the government, industries and the public [12]. a) Governments should set up regulatory agencies in each district, which are vested with the responsibility of co-coordinating and consolidating the regulatory functions of the various government authorities regarding hazardous substances. b) Governments should be responsible for providing an adequate system of laws, controls and administrative procedures for hazardous waste management. Existing laws concerning e-waste disposal be reviewed and revamped. Such a law should empower the agency to control, supervise and regulate the relevant activities of government departments. c) Governments must encourage research into the development and standard of hazardous waste management, environmental monitoring and the regulation of hazardous waste-disposal. d) Governments should enforce strict regulations against dumping e-waste in .the country by outsiders. Where the laws are flouted, stringent penalties must be imposed. In particular, custodial sentences should be preferred to paltry fines, which these outsiders / foreign nationals can pay. e) Governments should enforce strict regulations and heavy fines levied on industries, which do not practice waste prevention and recovery in the production facilities. f) Polluter pays principle and extended producer responsibility should be adopted. g) Governments should encourage and support NGOs and other organizations to involve actively in solving the nation's e-waste problems. h) Governments should explore opportunities to partner with manufacturers and retailers to provide recycling services. i) Every country should follow the Basal Convention, which bans exports of hazardous waste destined for final disposal in developing countries.
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3.2.2 Responsibility of Industries: a) Extended Producer Responsibility (EPR) Some countries are implementing policies and programs to prevent pollution and promote waste minimization. Key among these approaches is the "Extended producer Responsibility" [2]. Its objective is to make manufactures (financially) responsible for the entire life-cycle of their products, especially when they become obsolete. The underlying assumption is the company's interest in easier recycling and decomposition, and as such resource use limitation, pollution prevention and waste avoidance through ecological ("green") design, re-use, re-manufacturing and efficient recycling. b) Generators of wastes should take responsibility to determine the output characteristics of wastes and if hazardous, should provide management options. c) All personnel involved in handling e-waste in industries including those at the policy, management, control and operational levels, should be properly qualified and trained. Companies can adopt their own policies while handling E-wastes. Some are given below: • Use label materials to assist in recycling (particularly plastics). • Re-evaluate 'cheap products' use, make product cycle 'cheap' and so that it has no inherent value that would encourage a recycling infrastructure. • Create computer components and peripherals of biodegradable materials. • Utilize technology sharing particularly for manufacturing and de manufacturing. • Encourage / promote / require green procurement for corporate buyers. • Look at green packaging options. • Manufacturers of computer monitors, television sets and other electronic devices containing hazardous materials must be responsible for educating consumers and the general public regarding the potential threat to public health and the environment posed by their products. At minimum, all computer monitors, television sets and other electronic devices containing hazardous materials must be clearly labeled to identify environmental hazards and proper materials management. • Electronic equipment manufacturers should encourage their customers to play their role in proper disposal of used electronics. If the manufacturer follows EPR, it will be easier for the same to practice it by providing incentives to its costumers to help the manufacturer out with used electronics. n: Waste prevention is perhaps more preferred to any other waste management option including recycling. Donating electronics for reuse extends the lives of valuable products and keeps them out of the waste management system for a longer time. But care should be taken while donating such items i.e. the items should be in working condition. E-Waste Management Reuse, in addition to being an environmentally preferable alternative, also benefits society. By donating used electronics, schools, non-profit organizations, and lower-income families can afford to use equipment that they otherwise could not afford. E-wastes should never be disposed with garbage and other household wastes. This should be segregated at, the site and sold or donated to various organizations.
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While buying electronic products opt for those that: • Are made with fewer toxic constituents. • Use recycled content. • Products that are energy efficient; • Are designed for easy upgrading or disassembly. • Utilize minimal packaging • Offer leasing or take back options • Have been certified by regulatory authorities. Customers should opt for upgrading their computers or other electronic items to the latest versions rather than buying new equipments. • Have been manufactured by companies who ensure proper disposal of used electronics. This will encourage other manufacturers to have a proper plan for used electronics’ disposal. 3.3 Life Cycle of E-waste. To ensure proper and nearly complete collection of used electronic equipments after they are rendered useless, it is important to study the processes, which the equipment has undergone. That is to say, the study of the life cycle of the equipment is equally relevant. The Fig. 5 shows the life span of electronic equipments, taking into account that it may have switched users during the course of its operational life. This course will have to be considered for effective collection so that maximum or all of the E-Waste can be recycled. For instance, computer hardware would appear to have up to 3 distinct product lives: the original life or first product life (when it is being used by the primary user) and up to 2 further lives depending on reuse. Fig. 5 depicts the flow of computer hardware units from point-of-sale to the original purchaser and on to the reuse phases. The duration of the product’s first life is estimated to be between 2 and 4 years for corporate users and between 2 and 5 years for domestic users. The life cycle of computer waste is defined as, the period from when it is discarded by the primary user to when it goes for recycling or is disposed of in a landfill.
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Product Manufacturer Material Recycle
Primary User
Reuse
Second User
Reuse
Third/ Fourth User
Landfill
Residue
Life Cycle Of Waste
Fig. 5. Flow of E-waste During Its Life Cycle [13]
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3.4 E-Waste Mining This is the name given to the process where valuable materials such as gold, copper, iron and plastics are extracted from circuitry of computers and cell phones, by using the same techniques that miners use to process metal ores. In a study conducted by Toxic Link in 2007, it was estimated that the junk thrown away as E-Waste contains more gold, aluminum and copper than found in the ores. In fact, stats show that one tonne of scrap from discarded computers contains more gold than can be produced from 17 tonnes of gold ore. This is not very surprising as E-Waste is often richer in other rare metals as well, containing 10 to 50 times higher copper content than copper ore. A cell phone contains 5 to 10 times higher gold content than a gold ore. Multiply this with 150,000 tonne of E-Waste generated annually and the numbers are pretty lucrative. According to the same study, about 5 tonnes of E-Waste, which could come from about 183 computers, gives a huge profit of Rs 1,78,308. The math is simple: taking a very conservative estimate of the materials recovered, total value of the recoverable materials from 183 computers will be Rs 2,88,108. The input cost of 183 computers (friom various market sources) is approx 183*600 (inclusive of logistics) = Rs 1,09,800. This means a good profit margin of almost Rs 1.8 lacs for the recycler. Considering that countries like India not only produce, but import E-Waste, this could be a huge source of revenue. [20] Considering that the figures only for computers are so impressive, it is evident that all the E-Waste combined will generate even more profit. This implicates that a recycling industry or “E-Waste Mining” is a lucrative arena.
4. Recycling of e-waste The conventional e-waste processing and recycling is basically a five-step process [21]: 1. Generation and Stockpiling Many different “economic actors” purchase, use, and then stockpile or discard electronic waste. These range from manufacturers such as MNCs to large and small businesses, households, institutions, and non-profit organizations. 2. Collection There are a wide variety of possible collection alternatives for this e-waste. A variety of entities are providing these services including the electronics industry, private or nonprofit recycling services, and the public sector through the solid waste management and recycling infrastructure. 3. Handling & Brokering The next link in the cycle is the handling and brokering services. Here computers, TVs, monitors and other collected electronics are consolidated and made ready for processing and/or sorted to determine what equipment can be refurbished or reused as whole units and what equipment must be disassembled for commodity processing. 4. Processing After electronic equipment is dismantled, it is then processed into either feedstock for new production or refurbished into new equipment. Outputs from demanufacturing activities include scrap commodities such as glass, plastics, and metals 20
– the primary elements from which all electronic hardware is made. For export, and to a lesser extent national processing markets, there are significant issues associated with the environmental and health practices of current service providers in this part of the cycle. 5. Production The final step in this cycle is to turn the processed commodities or refurbished whole electronics back into new products for sale and consumption by end users. There are many different players and industries involved in this production process. The recycling fraction is miniscule compared with the production of product using virgin materials. The substances procured by recycling may be used for several purposes, even for manufacturing the very same equipments they were derived from. 4.1 Recycling/Recovery System First of the operations involves dismantling and rapid separation of primary materials. The following materials are separated for further recycling: • Material containing copper: Including printer and other motors, wires and cables, CRT yokes, circuit boards, etc • Steel: Including internal computer frames, power supply housings, printer parts, washing machines, refrigerator, etc. • Plastic: Including housings of computers, printers, faxes, phones, monitors, keyboards, etc. • Copper: Extracted from transformer and CRT after their dismantling • Circuit Boards: These come from many applications including computers, phones, disc drives, printers, monitors, etc. Each of these processes has been described below. Following describes the conventional way of recycling a personal computer [21]. 4.2 Bifurcation of electronic scrap Printed Circuit Boards (PCBs) The printed circuit boards contain heavy metals such as antimony, gold, silver, chromium, zinc, lead, tin and Copper. According to some estimates, there is hardly any other product for which the sum of the environmental impacts for raw material, industrial refining and production, use and disposal is as extensive as for printed circuit boards. The methods of salvaging material from circuit boards are highly destructive and harmful as they involve heating and open burning for the extraction of metals. Even after such harmful methods are used, only a few of the materials are recovered. The recycling of circuit boards, drawn from monitors, CPU, disc and floppy drives, printers, etc. involves a number of steps [21]. 4.2.1 Characteristics of PCB Scrap PCB scrap is characterised by significant heterogeneity and relatively high complexity, although with the levels of complexity being somewhat greater for populated scrap boards1. As has been seen in respect of materials composition, the levels of inorganics in particular are diverse with relatively low levels of precious metals being present as deposited coatings of various thicknesses in conjunction with
21
copper, solders, and various alloy compositions, non ferrous and ferrous metals. In spite of the inherent heterogeneity and complexity, there are too many differences in the intrinsic physical and chemical properties of the many materials and components present in scrap PCBs, and indeed electronic scrap as a whole, to permit recycling approaches that separate such into their individual fractions. The following characteristics ultimately govern mechanical and hydrometallurgical separation and it is based upon such that current and potential recycling techniques and infrastructures have been envisaged, developed and implemented [22]. 4.2.1.1 Density Differences Differences in density of the materials contained within scrap PCBs have formed the basis for separation methods subsequent to their liberation as free constituents. The specific gravity ranges of typical materials are as shown below. Materials Gold, platinum group, tungsten Lead, silver, molybdenum Magnesium, aluminium, titanium Copper, nickel, iron, zinc GRP
Specific Gravity Range (g/cm3) 19.3 - 21.4 10.2 - 11.3 1.7 - 4.5 7.0 - 9.0 1.8 - 2.0
With these densities not being significantly affected by the addition of alloying agents or other additives, it is predictable that the deployment of various density separation systems available within the raw materials process industry may be utilized to effect separation of liberated constituents of a similar size range. The utilization of density differences for the recovery of metals from PCB scrap has been investigated on many occasions and air classifiers have been used extensively to separate the non metallic (GRP) constituents, whilst sink-float and table separation techniques have been utilised to generate non ferrous metal fractions4. Air techniques that effectively combine the actions of a fluidised bed, a shaking table and an air classifier, have been successfully implemented in applications involving a diversity of electronic scrap separations. It is essential, as has been noted, that the feed material must be of a narrow size range to guarantee effective stratification and separation. 4.2.1.2 Magnetic and Electrical Conductivity Differences Ferrous materials may be readily separated with the application of low intensity magnetic separators that have been well developed in the minerals processing industry. Many non-ferrous materials in respect of their high electrical conductivity may be separated by means of electrostatic and eddy current separators. Eddy current separation has been developed within the recycling industry since strong permanent magnets, such as iron boron- neodymium, have become available. Rotating belt type eddy current separation is the most extensively used approach for the recovery of nonferrous metal fractions. In application, the alternating magnetic fields caused by the rapidly rotating wheel mounted with alternating pole permanent magnets result in the generation of eddy currents in non ferrous metal conductors, which in turn, generate a magnetic field that repels the original magnetic field. The resultant force, arising from the repulsive force and the gravitational force permits their separation from nonconducting materials.
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4.2.1.3 Polyformity One of the important aspects of both PCB and electronic scrap is the polyformity of the various materials and components and the effect this can have on materials liberation. It is essential that any shredding and separation processes take this into account. In eddy current separation, the shape of conducting components, in addition to their particle sizes and conductivity/density ratios, has a significant effect on the generated repulsive forces that ultimately govern the separation efficiency. For instance, multiple induced current loops may be established in conductors with irregular shapes with the induced magnetic fields counteracting each other and reducing the net repulsive force. 4.2.1.4 Liberation Size The degree of liberation of materials upon shredding and comminution is crucial to the efficiency and effectiveness of any subsequent separation process in respect of yield, quality of recovered material and energy consumption of the process. This is especially critical in mechanical separation approaches. The comminution of scrap PCBs has been shown to generate a high level of material liberation and levels as high as 96% to 99% have been reported for metallic liberation after comminution to sub 5 mm particulates. It must noted, however, that a continual observation from recyclers is that liberation levels such as these are atypical of actual yields and that a fundamental constraint on mechanical processing is the loss, particularly of precious metal content, that appears to be inherent due primarily to the nature of many plasticmetal interfaces. 4.2.1.5 Chemical Reactivity Hydrometallurgical approaches depend on selective and non selective dissolution to achieve a complete solubilisation of all the contained metallic fractions within scrap PCBs. Although all hydrometallurgical approaches clearly benefit from prior comminution this is primarily undertaken to reduce bulk volume and to expose a greater surface area of contained metals to the etching chemistry. Selective dissolution approaches may utilise high capacity etching chemistries based on cupric chloride or ammonium sulphate for copper removal, nitric acid based chemistries for solder dissolution and aqua regia for precious metals dissolution, where as non selective dissolution may be carried out with either aqua regia or chlorine based chemistry. Electropositivity Dissolved metals generated via chemical dissolution are present as ionised species within an aqueous media and may be recovered via high efficiency electrolytic recovery systems. In the instance of selective dissolution, a single metal is recovered as pure electrolytic grade material, usually in sheet form; from the spent etching solution with certain etching chemistries permitting regeneration of the liquors for reuse as etch chemistries. In the instance of selective dissolution, use may be made of the differing electropositivities of the contained ionised metallic species to selective recovery metals at discrete levels of applied voltage.
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4.3 Disassembly Disassembly in practice In the practice of recycling of waste electric and electronic equipment, selective disassembly (dismantling) is an indispensable process since: (1) The reuse of components has first priority, (2) Dismantling the hazardous components is essential, (3) It is also common to dismantle highly valuable components and high-grade materials such as printed circuit boards, cables, and engineering plastics in order to simplify the subsequent recovery of materials [22]. Most of the recycle plants utilize manual dismantling. Ragn-Sells Elektronikåtervinning AB in Sweden is a typical electronics recycling operation. A variety of tools is involved in the dismantling process for removing hazardous components and recovery of reusable or valuable components and materials. A study of potential future disassembly and recycling technologies for the electronics and the automotive industry was carried out by Boks and Tempelman between November 1996 and March 1997 [23]. The results reflect the opinions of a panel of approximately 70 specialists pre-selected by the authors. Concerning the technical feasibility of full automation Fig. 3. Recycling process developed by RagnSells Elektronikåtervinning AB. J. Cui, E. Forssberg / Journal of Hazardous Materials B99 (2003) 243–263 251 (90–100%) disassembly of electronic equipment, 65% of the panel members thought a breakthrough in automated disassembly will occur by 2010; and 57% of the panel thought it will be in Germany, while only 35% of the German panel members agree. In addition, 32% of the panel thought full automation disassembly of both brown goods (e.g. TVs, audio and video equipment) and white goods (e.g. freezers, washing machines) will not be economically attractive by 2020. In their opinion, the main obstacles preventing automated disassembly from becoming a commercially successful activity are: (1) too many different types of products, (2) the amount of products of the same type is small, (3) general disassembly-unfriendly product design, (4) general problems in return logistics and (5) variations in returned amounts of products to be disassembled. Fortunately, research in the field of product design for disassembly has gained momentum in the past decade. One good idea is self-disassembly, which is called active disassembly using smart materials (ADSM). Chiodo [24] reported the application of shape memory polymer (SMP) technology to the active disassembly of modern mobile phones. The smart material SMP of polyurethane (PU) composition was employed in the experiments. This method provides a potential dismantling scenario for the removal of all components if this material was to be developed for surface mount components. Research into using ADSM in other small electronics also has been done to handle units such as telephones, cell phones, PCB/component assemblies, cameras, battery chargers, photocopier cartridges, CRTs, computer casings, mice, keyboards, game machines nd stereo equipment [24]. 4.3.1 Mechanical/physical recycling process 1. Screening: Screening has not only been utilized to prepare a uniformly sized feed to certain mechanical process, but also to upgrade metals contents. Screening is necessary because the particle size and shape properties of metals are different from
24
that of plastics and ceramics. The primary method of screening in metals recovery uses the rotating screen, or trommel, a unit, which is widely used in both automobile scrap and municipal solid waste processing. This unit has a high resistance to blinding, which is important with the diverse array of particle shapes and sizes encountered in waste. Vibratory screening is also commonly used, in particular at non-ferrous recovery sites, but wire blinding is a marked problem [25]. 2. Shape separation: Shape separation techniques have been mainly developed to control properties of particles in the powder industry [26-29]. The separation methods were classified into four groups by Furuuchi [26]. The principles underlying this process makes use of the difference: (1) the particle velocity on a tilted solid wall, (2) the time the particles take to pass through a mesh aperture, (3) the particle’s cohesive force to a solid wall, and (4) the particle settling velocity in a liquid. Shape separation by tilted plate and sieves is the most basic method that has been used in recycling industry [30,31]. An inclined conveyor and inclined vibrating plate were used as a particle shape separator to recover copper from electric cable waste [31] printed circuit board scrap [30] and waste television and personal computers in Japan [32]. 3. Magnetic separation: Magnetic separators, in particular, low-intensity drum separators are widely used for the recovery of ferromagnetic metals from non-ferrous metals and other non-magnetic wastes. Over the past decade, there have been many advances in the design and operation of high-intensity magnetic separators, mainly as a result of the introduction of rare earth alloy permanent magnets capable of providing very high field strengths and gradients. In Table 5, we can see that the use of high-intensity separators makes it possible to separate copper alloys from the waste matrix. An intense field magnetic separation is achievable at least for the following three alloy groups [33]: • Copper alloys with relatively high mass susceptibility (Al multi-compound bronze); • Copper alloys with medium mass susceptibility (Mn multi-compound bronze, special brass); • Copper alloys with low mass susceptibility and/or diamagnetic material behavior (Sn and Sn multi-compound bronze, Pb and Pb multi-compound bronze, brass with low Fe content). 4 Electric conductivity-based separation: Electric conductivity-based separation separates materials of different electric conductivity (or resistivity) (Tables 6 and 7). As shown in Table 8, there are three typical electric conductivity-based separation techniques: (1) Eddy current separation, (2) corona electrostatic separation, and (3) triboelectric separation [34-38]. In the past decade, one of the most significant developments in the recycling industry was the introduction of Eddy current separators whose operability is based on the use of rare earth permanent magnets. The separators were initially developed to recover non-ferrous metals from shredded automobile scrap or for treatment of municipal solid waste [25,39-41], but is now widely used for other purposes including foundry casting sand, polyester polyethylene terephthalate (PET), electronic scrap, glass cullet, shredder fluff, and spent potliner [42-48]. Currently, Eddy current separators are almost exclusively used for waste reclamation where they are particularly suited to handling the relatively coarse sized feeds.
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The rotor-type electrostatic separator, using corona charging, is utilized to separate raw materials into conductive and non-conductive fractions. The extreme difference in the electric conductivity or specific electric resistance between metals and non-metals supplies an excellent condition for the successful implementation of a corona electrostatic separation in recycling of waste. To date, electrostatic separation has been mainly utilized for the recovery of copper or aluminum from chopped electric wires and cables [34,35,49-52], more specifically the recovery of copper and precious metals from printed circuit board scrap [34-36,53]. Triboelectric separation makes it is possible to sort plastics depending on the difference in their electric properties (Table 5). For the processing of plastics waste, research has shown many obvious advantages of triboelectric electrostatic separation, such as independence of particle shape, low energy consumption, and high throughput [38]. Table 5 Mechanical separation processes based on electric characteristics of materials [54] Processes Separation Principles of separation Sorting task Workable criteria particle size ranges Eddy current Electric Repulsive forces exerted Non-ferrous >5mm separation conductivity in the electrically metal/nonand density conductive particles due metal to the interaction separation between the alternative magnetic field and the Eddy currents induces by the magnetic field (Lorentz force) Corona Electric Corona charge and Metal/non0.1–5mm electrostatic conductivity differentiated discharge metal (10mm separation lead to different charges separation for of particles and this to laminar action of different forces particles) (particularly, image forces) Triboelectric separation
Dielectric constant
Tribo-charge with different charges (+ or −) of the components cause different force directions
Separation of Plastics (nonconductors)
<5 (10) mm
5 Density-based separations: Several different methods are employed to separate heavier materials from lighter ones. The difference in density of the components is the basis of separation. Table 6 shows that density-based separation processes have found widespread application in non-metal/metal separation [55]. Gravity concentration separates materials of different specific gravity by their relative movement in response to the force of gravity and one or more other forces, the latter 26
often being the resistance to motion offered by a fluid, such as water or air [56]. The motion of a particle in a fluid is dependent not only on the particle’s density, but also on its size and shape, large particles being affected more than smaller ones. In practice, close size control of feeds to gravity processes is required in order to reduce the size effect and make the relative motion of the particle specific gravity dependent. Table 6 Density separation processes utilized for non-metal/metal separation [55] Density Workable Utilized for following sorting tasks separation piece Process Sizes Plastics Aluminum Lead Cable Electronic (mm) waste scrap battery scrap scrap scrap Light steel scrap In liquids In heavy media Gravity 5–150 separator Hydrocyclone + <50 In aerosuspensions In aero0.7–3 chutes In fluidized 0.7–5 bed Trough separators
Sink-float separation * * *
*
*
* *
*
* *
Sorting by jigging Hydraulic 2–20 jigs Pneumatic <3 jigs Sorting in chutes and on tables Aero-chutes 0.6–2 Aero-tables <4 Up-stream hydraulic Separation Up-stream pneumatic Separation
5–150
* * * * Up-stream separation * *
<300
* *
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4.5 Mechanical Approaches of recycling electronic scrap As may be anticipated, all of the work undertaken on mechanical systems has been with the primary objective of enhancing separation yield of the various fractions, particularly the precious metal bearing ones. The basic mechanical techniques deployed in the treatment of scrap PCBs and electronic assemblies have been adapted or adopted from the raw materials processing sector and refinement has sought to address both yield constraints and ultimately cost effectiveness of the approaches, either used singly or in an integrated manner. The problems associated with yield were apparent from early attempts to produce a model methodology for handling all types of electronic scrap as instanced by the US Bureau of Mines (USBM) approach in the late 1970s and early 1980s [57-59]. The separation route, developed up to a 250 kg per hour pilot plant, comprised shredding, air separation, and magnetic, eddy current and electrostatic separation to generate aluminium rich, copper rich (including major precious metal fraction), light air classified and ferrous fractions [59]. The yield, however, was such that no commercial uptake of this approach has been instanced. The relatively poor yields or levels of separation obtained from this approach were undoubtedly a result of the use of a standard hammer mill having no provision, or levels of refinement, to cope with clear comminution of aluminium, the use of a ramp type eddy current separator of low capacity and selectivity and the use of a high tension separator for metals/non metals, which has been since demonstrated as having low capacity and high susceptibility to humidity. There was little further meaningful development work on the implementation of mechanical treatment approaches until the early 1990s when Scandinavian Recycling AB in Sweden implemented their mechanical concept for electronic scrap handling which did not specifically address the treatment of scrap PCBs but rather removed PCBs for specialist treatment as part of the pre sorting stage. Subsequent to this development, work in both Germany and Switzerland has seen the implementation of mechanically based approaches for the handling and separation of electronic scrap with the work at FUBA dedicated to scrap PCBs being a notable example of this activity. In 1996, Noell Abfall and Energietechnik GmbH in Germany implemented a 21,000 tonnes per annum plant with the capability of handling a wide variety of electronics scrap but specifically intended for redundant telecommunications scrap [60]. The system again involves PCB scrap and the inherent precious metal content being subject to prior manual disassembly. The overall methodology deploys a three stage liberation and sequential separation route with ferromagnetic removal via overhead permanent magnets and eddy current techniques because of their ability to optimise the handling of fractions in the 5 to 200 mm particle size range. Air table techniques were utilised for the separation of particulate fractions in the 5 to 10 mm, 2 to 5 mm and less than 2 mm ranges respectively. Mechanical and physico mechanical approaches to the treatment of scrap PCBs may be deployed as stand alone treatment stages, (i.e. pulverisation, magnetic separation, or integrated into a complete treatment system with the output being metallic and non-metallic fractions). The metallic output would be destined for pyrometallurgical refinement via smelting where as the nonmetallic output would find applications in the secondary plastics marketplace or be utilised within dedicated developed applications. As reported, FUBA has developed
28
its total mechanical treatment system, albeit only currently utilised for nonpopulated board scrap or ancillary laminate waste through this latter route. There are commercially available turnkey mechanical systems for the treatment of a wide range of electronic scrap materials including populated and non-populated PCBs. One such is that developed by hamos GmbH in Germany which is an automated integrated mechanical system comprising the following stages: • Primary coarse size reduction, accomplished with a shredder having multi-use rotational knives; • Coarse ferrous metal separation, accomplished with rare earth magnets sited above an oscillating conveyor belt feed to allow high efficiency ferrous separation across a range of particle sizes; • Pulverisation in which circuit board assemblies are pulverised within a hammer mill utilising high abrasion resistance hammers and liners and proprietary grates with the action of the mill inducing a 'spherising' effect on the metallic articulates; • Classification, utilising self-cleaning sieves; • Electrostatic separation, allowing virtually complete separation of metallic fractions with recirculation of mid-range particulate fractions • Further size reduction, cosisting of secondary pulverisation to effect size reduction on oversized particulates. The hamos system can additionally incorporate density separation for aluminium extraction and dust generation treatment of any such outfall from the hammer mills via secondary electrostatic separators. The complete conveyor based systems are operated at negative pressures to eliminate any airborne pollution and are currently available with treatment capabilities up to 4 tonnes per hour of input feed. All products from the system viz mixed plastic, metallic and extracted ferrous and aluminium is bagged automatically for onward shipment. Considerable work has been undertaken on enhancing the effectiveness of mechanical treatment systems. For example, the development of newer pulverising process technology via the application of multiple pulverising rotors and ceramiccoated systems has enabled the generation of sub-millimetre particulate comminution. This in turn has enabled the efficiency of subsequent centrifugal separation techniques to realize 97% copper recovery yields. The effectiveness of the pulverising process has been improved by the adoption of dual pulverising stages: a crushing process and a fine pulverising process. The crushing process combines cutting and shearing forces and the fine pulverising process combines shearing and impact forces. With such effective particulate comminution both screen separation and gravity separation have been investigated and conclusions drawn that the most effective approach was by gravity using a centrifugal classifier with a high air vortex system. Researchers at Daimler-Benz in Ulm, Germany, have developed a mechanical treatment approach that has the capability to increase metal separation efficiencies, even from fine dust residues generated after particulate comminution in the treatment of scrap PCB assemblies. They considered a purely mechanical approach to be the most cost effective methodology and a major objective of their work was to increase the degree of purity of the recovered metals such that minimal pollutant emissions would be encountered during subsequent smelting. Their process comprises the initial coarse size reduction to ~2 cm x 2 cm dimensioned fractions followed by magnetic separation for ferrous elements. A low temperature grinding stage then follows this. The embrittlement of polymeric components at temperatures less than 70°C was found to enable enhanced
29
separation from non-ferrous metallic components when subjected to grinding within a hammer mill. In operation the hammer mill was fed with liquid nitrogen at minus 196°C, which served to both impart brittleness to the plastic feedstock constituent and to effect process cooling. Additionally, the grinding of material within such an inert atmosphere eliminated any 17 likelihood of oxidative by product formation from the plastics, such as dioxins and furans. Subsequent to this enhanced grinding stage the metallic and non metallic fractions were separated via sieving and electrostatic stages. Cost analyses undertaken by Daimler-Benz engineers have indicated that such a process may be economically viable even when dealing with relatively low grade PCB scrap having little precious metal content. Ongoing activities are concerned with development of the treatment of separated polymeric fractions in conjunction with Mitsubishi Heavy Industries that have set up a gasification and methanolysis plant to such effect. Air table separation systems have been researched with a view to effecting separation of metallic and plastic components from an input feed of screened 7 mm shredded particulate scrap PCBs post ferromagnetic separation. Recovery rates for copper, gold and silver of 76%, 83% and 91% respectively were considered to validate the approach, but only for low-grade PCB scrap or general electronic scrap. 4.6 Hydrometallurgical Approaches A number of hydrometallurgical approaches have been developed through to pilot plant stage with preliminary cost studies indicating the potential recovery of all materials, with the exception of discrete components, at an operational profit of some US$200 per tonne. In the USA, a methodology based on solvolysis has been developed to enable both the more efficient recovery of metals and the recovery of plastic materials such as epoxides at high quality and with the additional benefit of having the capability to extract both halogens and brominated hydrocarbon derivatives. On a relatively small scale there have been a number of hydrometallurgical approaches traditionally pursued in the recovery specifically of gold from pins and edge connectors. Such methodologies have usually been deployed on discrete edge connectors and gold-coated assemblies that have been manually separated from the scrap board via the use of air knives etc. The approaches have either liberated gold as metal flake via acidic dissolution of the copper substrates or dissolution of the gold in cyanide or thiourea based leachants followed by electrowinning or chemical displacement or precipitation with powdered zinc. The use of non-selective leachants to dissolve the non precious metal content of scrap PCBs has also received attention. Various studies have been undertaken into the viability of utilising dilute mineral acids in conjunction with subsequent metal recovery techniques based on concentration and separation such as solvent extraction, ion exchange, adsorption and cementation [61]. In the UK, there have been two potentially significant development projects undertaken on hydrometallurgical approaches to the recycling of scrap PCBs with both having demonstrated viability to a pre pilot plant stage. Both of these are reported in some detail within Section 8. The first of these approaches is from a Cambridge University led consortium, which deploys a selective dissolutionelectrolytic recovery route for discrete metal constituents [62]. The solder recovery stage employs a solder selective (non copper etching) regenerable leachant based on fluoroboric acid. This may or may not be deployed prior to mechanical pre treatment,
30
from which the dissolved solder can be electrolytically recovered in pure metallic form. Subsequent selective leaching of copper and PMG metals is then carried out. The ability to remove selectively solder prior to mechanical comminution has specific advantages in enabling disassembly and component integrity and recovery. Mechanical pre treatment methodologies followed by the Cambridge group have
PWB Waste
Crushing Process Pulverising Process Fine Pulverising Process
Gravity Separation
Copper Rich Powder
Glass Fibre & Resin Powder
Recycling of Copper
Filler in Construction Materials
97% Copper Recovery 31
Figure 6. 97% recovery of Copper from PWBs [59]
included shredding, magnetic separation, eddy current separation and classification. The second development is that of the Imperial College, London (ICL) consortium which has taken shredded and classified sub 4mm PCB populated PCB scrap through a single leachate route comprising electro-generated chlorine in an acidic aqueous solution of high chloride ion activity [63-65]. This has produced a multi metal leach electrolyte containing all of the available metal content at generally mass transport controlled rates with respect to dissolved chlorine. The viability of subsequent metal recovery via electrolytic membrane cells with discrete metal separation has also been demonstrated. To summarize the above discussions: • Hydrometallurgical approaches offer a viable methodology in maximising the recovery of intrinsic metal value, particularly precious metals, and should be further developed through pilot plant stages to commercialisation. • No single treatment approach will be appropriate for the handling of all scrap PCBs because of their diversity and varying intrinsic worth. Rather, an integrated hierarchy of approaches that encompasses disassembly and mechanical and hydrometallurgical methodologies will be needed to generate either materials or components for direct reuse or downstream application or a non-toxic feedstock for pyrolytic refining. 4.7 Extraction of IC/ other components from PCB IC/other components from PCBs are manually extracted as shown in Figure 7. This process is common for PC, TV and cell-phone. The E-waste stream from cellphone joins the E-waste stream of PC and TV [21].
Figure 7 Extraction of IC/ other components from PCB
4.7.1 Recovery of Gold
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Gold pins are recovered from PCB manually as shown in Figure 8. First, there is manual removal of gold-plated pins. The core of each motherboard has a flat laminated gold plate. These laminated parts cut down and sold to gold-smiths for gold recovery.
Figure 8 Gold Recovery
Preheating of PCB and extraction of components The preheating process is applied to remove resalable components like ICs, condensers, bearings (pulleys) from floppy drive and hard drive. Pre-heating means simply putting the motherboard on a burning stove as shown in Figure 9. Low heat is maintained to loosen only the chemical bond between solder and plastic. Then resalable chips, condensers, etc, are plucked out from these pre-heated plates. After that, the pre-heated circuit boards are taken by other dealers for recovery of solder (which consists of lead and mercury). The method of solder recovery Figure 9 is very rudimentary. The lead extracted due to heat application goes into a water tub – it floats due to low density. 4.7.2 Monitors Monitors are much sought after by scrap dealers as they contain good quantity of copper yoke, besides circuit board and picture tube. The different recovery processes observed in MMR are given below. Dissembling of CRT and Extraction of Components The first step in monitor recycling involves physical removal of plastic casing, picture tube (cathode ray tube), copper yoke and plates as shown in Figure 5.4. The intact and functional CRT is used for the manufacture of colour and black & white televisions for local brands. Re-gunning is possible only for those monitors whose 33
terminal pin (diode pin) of electron gun has not broken in the process of removing yoke from gun.
Recovery of Glass from CRT Defective CRT is broken down to recover iron frames from the glass funnel as shown in Figure 10,11. The iron frames are found only in color CRTs and not in black & white monitors. The glasses and iron frames from picture tubes are given to waste traders.
Figure 10 Dissembling of CRT and Extraction of Components
Yoke Core, Metallic Core and Copper from Transformers The copper and yoke core recovered from yoke coils found around the picture tube end is sold to copper smelters and re-winders as shown in Figure 12 and Figure 13. Apart from the yoke, copper and metallic core is also recovered from transformers mounted on the circuit board of the computer. The circuit tray also contains a number of condensers of different sizes. Depending upon their condition and demand they again enter into the secondary market for reuse. If they are defective, they are sold along with the motherboard. 34
Figure 11: Glass Recovery by CRT Breaking
Figure 11: Extraction of Yoke Core and Copper 35
Figure 13 Extraction of Metallic Core of Transformer and Copper
Rare Earth Core of Transformer and Copper These small transistors and rare earth transformers are boiled in water with small amount of caustic soda, which results in loosing of joint between the core resulting in core and copper extraction as shown in Figure 14.
Figure 14: Extraction of Rare Earth Core of Transformer and Copper Copper Extraction from Wires
36
Two kinds of processes are being followed under this category as listed below: 1. Manual drawing of wires for copper 2. Extraction of copper by burning the wire Manual drawing of Wires for Copper Under this process with the use of knife the edge of wire is cut and then with the help of pliers the copper is extracted from PVC as shown in Figure 15. The process is as shown below copper goes for sale to copper smelters and PVC is used for plastic graining.
Figure 15: Computer Cable
Plastic Shredding and Graining The plastic casings of monitors are made either of PVC (polyvinyl chloride) or ABS (acrylonitrile-butadiene styrene). PVC was used more commonly in the early models of computers. Now computer-manufacturing companies have shifted to ABS plastic in the production of monitors. Though both types of plastics are currently being recycled as shown in Figure 16, the PVC one cannot be recycled. This is due to the high percentage of silicate being added for making it fire retardant. The silicate plastic often ends up at kilns as an alternate source of energy. The plastic casing is recycled into EBS or High Impact Plastic. These kinds of plastics are frequently used in manufacturing toys. Dismantling of compressor & segregation of compressor & cooling box Refrigerator is dismantled for metal recovery, plastic recovery, insulating material and compressor as shown in Figure 17.
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4.8 Disposal It has been observed in many parts of the world that the most common practice of disposing e-waste is simply throwing it away with domestic waste, which eventually ends up in landfills or gets incinerated. However, this may result in several environmental hazards and hence, the waste must be disposed off in a proper manner.
Figure 16: Plastic Shredding
Figure 17: Dismantling of Refrigerator and Segregation of Compressor and Cooling Box
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4.9 Advantages of Recycling e-waste: • • • • • • • •
It will give way to Perfect Management of E-Waste. As there will be virtually no landfilling or incineration, the hazards to the environment will be avoided. Waste disposal costs will be reduced for organizations handling their own EWaste. It will generate good quantity of raw materials for various other industries. Moreover, the cost of this raw material will be much less than that obtained from its original source. Widely used metals like copper, platinum have to be dug out from their ores. Acquiring them this way will not only be a cheaper, less time consuming mean, but will also result in reduction of waste, and its hazards by reuse. Plastics can be reused relatively many times. So recycling them from E-Waste makes use of this advantage of plastics. It will have better and safer working conditions relative to backyard stripping corporations. This means protected means of dismantling and recycling of EWaste. It will generate many employment opportunities for people from many disciplines.
5. Conclusion The requirement and usage of electronic equipments is increasing day by day, as new, cheaper and better technologies replace the old ones. This renders the old equipments totally useless, and leaving huge amounts of electronic waste behind. However, this waste still has valuable metals and substances that can be used. Consequently, the dismantling and reuse of E-waste components has become quite a lucrative industry. But a only a fraction of the total amount of E-Waste is found to be recycled, and the rest discarded along with domestic waste. By discarding the rest of the waste, not only is the environment being contaminated with hazardous substances, but also many reusable valuable materials get are wasted. The materials recovered from E-Waste are often in richer quantity than their original sources. In addition to that, their recovery is much cheaper as well. Hence EWaste can be considered to be a rich yet cheap source of many valuable substances like plastics, gold, copper etc. This implies that with better collection and processing techniques, an E-Waste recycling industry, set up with contributions from the government and the consumers, can generate remarkable revenue, at the same time providing a sustainable E-Waste management technique. .
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