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Ways to Recover Metals from Electronic Waste

December 5th, 2012 · No Comments

Here are important ways to recover metals from electronic waste. E-waste recycling is important processes which involve conversion electronic devices to usable metals.

E-waste recycling is one of the important processes which involve conversion of used electronic devices to usable metals. Every year millions of tons of E-waste get exported from countries like U.S and Australia to developing countries like India and China where it gets dumped as landfills which cause pollution to the environment owing to their toxic nature.

Recover Metals from Electronic Waste

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Shredding

It is a process which is generally referred to as mechanical recycling of E-waste where the used electronic materials are shredded with help of specialized equipment. Once the E-waste is shredded, the individual materials are separated by using Eddy currents and magnetic fields or with help of novel technology like vertical vibration separation.

It is one of the latest techniques that are considered to be very effective for separation of metals like copper and iron from plastics. The metallic portion will be sold for smelters and additional shredded waste will get separated as landfills.

Another byproduct of using this method of separation is fine dust. The resulting dust could be used for production of Portland cement and compensate 30% of the weight.

The analysis of the dust particles indicated that it could mainly aluminum and calcium oxide with smaller amount of copper and lead. This process is very good for separation of plastics from metals but is not suitable for separation of low concentration metals taken from PCBs.

Municipal Incineration

Municipal incineration is dumping all the used electronic products in a furnace where the high metal concentration gets diluted. Using heat, the metals are separated individually based on different densities and then filtered out.

Usually metals, halogens, dioxins, SVOCs and VOCs are filtered separately. But there are some risks with this process as certain dangerous gases like hydrogen bromide can get emitted during the process while burning Printed circuit boards.

Pyrometallurgical Recovery

This process is carried out by addition of copper ore concentrate with shredded electronic waste which is later refined by using heat. It can be used for successful separation of metals from electronic waste. One such example is the  Noranda process used at a Copper Smelter in Canada where they treated electronic waste with 24% copper in liquid metal bath at temperate of 1250 degree Celsius.

It can convert lead, zinc and iron to oxides that are later separated with silicon dioxide based slag. They use an anode furnace for refining such metals which result in an alloy containing 99.1 percent copper and reminder of metals like nickel, tellurium, and selenium, palladium, platinum, gold and silver.  This process is quite efficient for electronic waste which contains high quantity of metal content. But it won’t be useful for separation of aluminum and other dioxins because it uses brominated flame retardants.

Thermal Depolymerization

This process makes use of thermal energy with high pressure and water for decomposition of organic molecules. It could be used for rendering epoxies and plastic into usable oil and the solids obtains as residue will contain greater concentration of metals. The process can be used for recovery of metals and plastics from electronic waste which contains high concentration of oxides.

Bioleaching

It is an advanced process used for recovery of metals from electronic waste with help of Fungi and Bacteria. Organisms like Bacillus Sp, Yarrowia lipolytica and Sacchormyces Cerelisiae can separate metals like tin, copper and lead from printed circuit boards when shredded to smaller sizes.

Also bacteria like T.Thiooxidans and T.Ferrooxidans can mobilize ninety percent of copper, nickel, zine and aluminum present in electronic waste.

A bacterium called C.Violaceum is used for separation of Gold from electronic waste and based on experiments it was observed to dissolve fourteen percent of gold from 10 mg of dicyanourate.  These organisms can separate metals from electronic waste after they are broken to small pieces through process like shredding.

Open Flame Incineration

This involves use of Acids to dissolve and recover metals from E-waste. This process is mainly followed in China, India and Asian countries where E-waste gets exported form developed nations like US, UK and Australia. It can mainly recover metals like copper, gold, lead and iron from E-waste like printed circuit boards, used mobile phones etc.

Plasma Arc Gasification                                                 

This process involves recovery of metals with help of electrically charged and superheated air stream. The air is heated up to 13900 degree Celsius and then exposed to electronic waste stored in huge containers.

It produced molten glass and SyngasW from E-waste which includes metals and many impurities. It is used mainly in small scale to recover metals and energy from municipal waste. It is not very efficient to recover high concentration of metals.

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