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Metal reclamation and recycling of electronic waste

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Currently, the majority of electronic waste is disposed of in a landfill. The remainder is either processed in energy inefficient method that only recovers a small amount of the available metals or burned to recover saleable metals such as copper, aluminum and iron. This is a problem for a number of reasons.

  • This waste contains recoverable trace amounts of precious metals, and larger quantities of a variety of other metals and alloys, especially copper, aluminum and steel.
  • Electronic waste contains high concentrations of heavy metals, brominated flame retardants and other plastic additives that have proven adverse effects on humans. Note: more information can be found at Electronic waste.
  • The volume of electronic waste produced is high, and growing fast [1]. In 2005, the United States alone disposed of was at least 1.5 million tons of electronic waste, and at most one quarter of that was recycled [2]. The situation is similar in Canada, with more than 71 000 tonnes of waste being disposed of in 2005, with just 26% being recycled [3]. In the province of Ontario, Canada, the percentage recycled in 2004 was just 2% [4].

Materials involved

There are a wide variety of materials involved in the multitude of items that can be classified as electronic waste. Each component adds to the complexity of any recycling effort. Below is an exploration of a number of the most common components, by weight.

Printed circuit boards

A printed circuit board, or PCB, is the piece of hardware acts as a base and provides electrical connections to the mounted components. They are present in many types of electronic waste, including cellphones, computers, TVs, and printers. A PCB is made of a number of components. Each step of the productions process is outlined below, to give an idea of the variety of materials involved.

picture of a circuit board here

FR-4 is the most common base material [5] for printed FR-4 is an abbreviation of Flame Retardant 4, referring to its flame resistance and self-extinguishing properties. It is a brittle material formed by hardening a woven fiberglass sheet with an epoxy resin, usually created from ethylene clorohydrin and bisphenol-A [6]. To give it the aforementioned self extinguishing properties, a brominated flame retardant is incorporated in the epoxy. Some flame retardants can be incorporated at the molecular level, like TBBPADEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD. [7]. It can be easily coloured, with common colours including green, blue, red, and black.

The type glass used to create the fiberglass sheets is S-glass. Content ranges, by weight are, 52-56% silicon dioxide, 16-25% calcium oxide, 12-16% aluminum oxide, 5-10% boron oxide, 0-2% sodium oxide or potassium oxide, 0-5% magnesium oxide, 0.05-0.4% iron oxide, 0-0.8% titanium oxide, and 0-1% fluorides [8].

Surface mounted components

A wide variety of components are soldered to printed circuit boards. A resistor is comprised of copper leads attached to a painted ceramic or carbon core [9]. Microchips are composed of small amounts of silicon, aluminum, and copper, [10] with plastic coatings. CPUs today have aluminum heatsinks as well.

Casings

Most consumer electronic devices have plastic casings, such as a TV or a cell phone. Household appliances also have aluminum or steel cases. Other products, such as computer cases have both metallic and plastic components to them.

CRT and LCD screens

CRT, or cathode ray tubeDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD., monitors are currently being phased out in favour of LCDDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD. monitors.

A CRT monitor consists of the electron gun and focusing equipment, a plastic casing and leaded glass. An analysis of the glass resulted in the following results, by weight, are 49.61% silicon dioxide, 24.17% lead oxide, 7.79% potasium oxide, 5.32% sodium oxide, 3.63% aluminum oxide, 2.99% strontium oxide, 2.30% calcium oxide, 1.96% barium oxide, 1.49% magnesium oxide, 0.58% zirconium oxide, 0.07% iron oxide and 0.07% phosphorous oxide [11]. The lead and phosphorous oxide [12] are most difficult to deal with. Most of the lead (up to 98.6%) can be recovered through a pyrovacuum process, where high heat and low pressure allow the lead to be vaporized and later recovered, with the aid of carbon powder[13].

Wire

Wire is a common element in electronic waste, as it has a method of connecting to a household wall socket, either through a power cord or charger. Internal wiring is common especially in desktop computers and older audio and video equipment.

Batteries

Batteries are a staple for portable electronic devices, whether in lithium ionDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD., rechargable NiCdDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD. or NiMHDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD., AAA or AA alkaline cellDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD. form. While batteries are electronic waste, they will not be covered in this analysis. There are numerous battery recycling programs; see [1][2][3].

Precious metals

Precious metals are used in electronics for their superior conductivity and resistance to oxidation. They are used as A study undertaken by Cui, J. et Al., at the Norwegian University of Science and Technology showed that there are recoverable amounts of precious metals, such as silver, gold and palladium. For typical electronic scrap, they found and average of 2000 ppm silver, 1000 ppm gold and 50 ppm palladium. Outliers include printed circuit boards with 3300 pm silver and cell phones with 210 ppm palladium[14]. This is significant, as this means that in the United States, using 2005 data [15], these numbers show that there was up to 1500 tons of gold and 3000 tons of silver in the electronic waste that was disposed of.

Current solutions

Solutions is a misnomer for this category. Electronic waste processed in a manor shown below either does not recover usable materials or processes the electronic waste in a manner that has measured environmental effects.

Shredding

In this process, commonly known as mechanical e-waste recycling, electronic waste is shredded by specialized equipment. An example of a shredder used in Kansas, U.S.A.[16] may be found here. This waste is then sorted mechanically, by magnetic fieldDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD. or eddy currentDEPRECATED TEMPLATE - PLEASE USE {{W}} INSTEAD. separators, or novel means such as vertical vibration separation[17]. This last method has demonstrated effective for separating metals from plastics, especially copper[18].

Another product of this method is fine dust. Research has been conducted into possible uses of this dust. In a study conducted by Kakimoto, K et Al., it can be successfully incorporated into Portland cement, without the loss of strength, up to %30 by weight. An analysis of this dust found to that it was mainly silicon dioxide, calcium oxide and aluminum oxide, with trace amounts of lead and copper.

This process is effective at separating metals from plastics, but fails to address the separation of low concentration metals from printed circuit boards.

Municipal incineration

Pyrometallurgical recovery

Open flame incineration

Proposed solutions

Thermal depolymerization

Thermal depolymerization is a process in which thermal energy, under high pressure conditions and with the aid of water, is used to decompose organic molecules. This would not be true solution for recycling electronic waste, but a step in the process. It would, in theory, render plastics and epoxies present into usable oil. The resulting solids would have much higher concentrations of metals.

Plasma arc gasification

Bioleaching

Alternative materials and manufacturing

A number of alternatives have been proposed to the materials and processes currently used. These initiatives are detailed below.

  • An alternative to FR-4 is a circuit board composed of chicken feathers with a soy-based epoxy. If this technology becomes commonplace, this would have a massive effect on the composition of the average electronic waste. It would render

References

  1. http://www.epa.gov/epawaste/conserve/materials/ecycling/manage.htm Accessed Nov. 11, 2008
  2. http://www.epa.gov/epawaste/conserve/materials/ecycling/docs/fact7-08.pdf Accessed Nov. 11, 2008
  3. http://www.ec.gc.ca/wmd-dgd/default.asp?lang=En&n=F3852FB1-1 Accessed Nov. 11, 2008.
  4. http://www.ene.gov.on.ca/en/news/2007/061201.php
  5. Coombs, C., 2001, Printed Circuits Handbook Fifth Edition, McGraw-Hill, New York, section 6.
  6. http://www.p-m-services.co.uk/how%27s_fr4_made_.htm Accessed Nov. 7, 2008.
  7. Coombs, C., 2001, Printed Circuits Handbook Fifth Edition, McGraw-Hill, New York, section 6.4.2 and 6.2.3.
  8. Coombs, C., 2001, Printed Circuits Handbook Fifth Edition, McGraw-Hill, New York, section 6.5.1
  9. http://www.ecawa.asn.au/home/jfuller/electronics/resistors.htm Accessed Nov. 11, 2008.
  10. http://www.intel.com/education/makingchips/index.htm Accessed Nov. 11, 2008.
  11. Chen, M. et Al., 2008, "Lead recovery and the feasibility of foam glass production from funnel glass of dismantled cathode ray tube through pyrovacuum process," Journal of Hazardous Materials, currently unprinted, p. 2.
  12. http://avogadro.chem.iastate.edu/MSDS/P2O5.htm Accessed Nov. 12, 2008.
  13. Chen, M. et Al., 2008, "Lead recovery and the feasibility of foam glass production from funnel glass of dismantled cathode ray tube through pyrovacuum process," Journal of Hazardous Materials, currently unprinted, pp. 1-5.
  14. Cui, J. et Al., 2007, "Metallurgical recovery of metals from electronic waste: A review," Journal of Hazardous Materials, 2008, (158), p. 3.
  15. http://www.epa.gov/epawaste/conserve/materials/ecycling/docs/fact7-08.pdf p. 1, Accessed Nov. 11, 2008
  16. http://www.prlog.org/10046578-automated-waste-shredding-system-operational.html Accessed Nov. 12, 2008.
  17. Mohabuth, N. et Al., 2006, "Investigating the use of vertical vibration to recover metal from electrical and electronic waste," Minerals Engineering, 2007, (20).
  18. Mohabuth, N. et Al., 2006, "Investigating the use of vertical vibration to recover metal from electrical and electronic waste," Minerals Engineering, 2007, (20), pp. 3-6.