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Metal reclamation and recycling of electronic waste

2,955 bytes added, 03:04, 21 November 2008
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== Current solutions ==
Solutions is a misnomer for this category. Electronic waste processed in a manor shown below either does not recover usable materials, is selective of feedstock, or processes the electronic waste in a manner that has measured environmental effects.
It should be noted that the bromine in brominated flame retarded plastics and printed circuit boards was found to mainly produce a gas made of two dangerous compounds: {{WP|hydrogen bromide}} and {{WP|bromobenzene}}.<ref>Chien, Y. et Al., 1999, "Fate of bromine in pyrolysis of printed circuit board wastes," Chemosphere, '''40''', (4).</ref>
===Open flame incineration===
The waste that is shipped to India, China and other Asian countries is burned, cut up, or dissolved in acids to recover metals, mainly copper that can be sold to scrap dealers. Components that have no resale value are dumped. Numerous written [] and video accounts [][] are available.
It is believed that the majority of the waste treated in this way is exported from the United States of America, as it remains one of the few countries where the export of electronic waste remains legal. See [[Electronic waste legislation and practices]].
== Proposed solutions ==
Below are detailed the proposed solutionsby recycling companies and researchers. It should be noted that none of them are complete solutions to the current problemproblems faced.
===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. No other solution It would, in theory, render plastics and epoxies present into usable oil. The resulting solids would have much higher concentrations of metals.
This process is effective in dealing with plastics, but offers no method of bromine recovery. Also the metal-laden slag generated would increase the metal content by weight, but would likely complicate the metal recovery process due to the high concentration of oxides. Therefore, no overall increase in recycling efficiency is expected. This process is widely lauded as the solution to organic waste, but does not suit
===Plasma arc gasification===
Plasma arc gassification is the process of incinerating waste with the use of a superheated (up to 13 900 C at initiation), charged stream of air. This produces {{WP|syngas}} and molten glass, which includes all of the metals and other impurities. This process is in use on a small scale, worldwide, for recovering energy from municipal waste. This process is self sustaining, as only two thirds of the energy extracted from cooling the syngas is required to meet the energy requirements of the process. The remainder can be sold as electricity.
While this is an economically viable method of disposing of municipal waste, it is a very energy inefficient step in recovering metals. The oxide output contains the metals diffused throughout itself, rendering the metals harder to recover than the original waste.
Bioleaching is the process of using bacteria and fungi to separate metals from electronic waste. It promises to be very energy efficient. Organisms such as ''Bacillus'' sp., ''Saccharomyces cereÍisiae'', and ''Yarrowia lipolytica'' leach lead, copper, and tin from printed circuit boards when shredded into sub-milimeter sizes. Under ideal conditions, ''T. ferrooxidans'' and ''T. thiooxidans'' were able to mobilize at least 90% of the aluminum, copper, nickel and zinc present <ref>Brandl, H. et Al., 1999, "Computer-munching microbes: metal leaching from electronic scrap by bacteria and fungi," Hydrometallurgy, '''2001''', (59).</ref>. One type of bacteria, C. violaceum, was able to leach gold from larger pieces of electronic waste (5 x 10 mm). It disolved dissolved 14.9% of the approximately 10 mg of gold present as dicyanoaurate <ref>Cui, J. et Al., 2007, "Metallurgical recovery of metals from electronic waste: A review," Journal of Hazardous Materials, '''2008''', (158), p. 18.</ref>. The conditions required for the organisms to survive and leach these metals dictates that the electronic waste piece sizes are extremely small and have a low spacial density. This means that this process would be useful only for recovering metals from the dust generated by shredding.  ===Exhaust gas scrubbing to recover bromine===There have been a number of demonstrations of bromine recovery, either through the use of acidic and base gas scrubbers<ref>Boerrigter, H. et Al., "Bromine Recovery From The Plastics Fraction of Waste of Electrical and Electronic Waste (WEEE) With Staged Gassification," European Brominated Flame Retardant Industry Panel, 2002.</ref>, or just a sodium hydroxide scrubber<ref> Accessed November 20, 2008.</ref>.
== Progress towards a sustainable future ==
* 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.
* Lead free solder. The {{WP|RoHS}} Directive of the European Union currently specifies that products that are sold in their jurisdiction must contain no more than trace amounts of lead. Fortunately, this has had an impact on products availible available in North America, with the RoHS logo adorning many of the relevant electronic products in N.A. as well. This, along with the move to LCD based monitors and TVs will cause a large reduction in percentage lead composition of electronic waste.
* Elimination of halogens. Simply by reading this page, the complications that halogens such as bromine cause are made apparent. An alternative to brominated flame retardants would have a very positive effect on the environmental release of halogens due to electronic waste.
===Comprehensive processing plan===
From all of the processes outlined so far, an attempt at a comprehensive plan for the recovery of metals and ultimately the recycling of electronic waste can be made.
# When the waste is collected, batteries and CRT monitors are diverted to specialist recyclers.
# The remaining waste is shredded, with care that the dust is collected.
This process increases efficiency over single processes in a number of ways.
== References ==


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