Difference between revisions of "Electronic recycling"

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Electronic recycling involves the extraction of various elements, mainly precious metals or metalloids from waste electronics. Most notably, gold can be extracted from computer parts such as processors.

Overview

E-waste are a good source of materials for the amateur chemist or electronics hobbyist. Useful materials, such as magnets, copper wiring, coils, quartz, Nichrome wiring, aluminium heatsinks, mica sheets, etc. can be found in various scrap electronics. Working components, such as cooling fans, electromagnetic coils, switches, heating elements, relays, LEDs, phone cameras and even functional electronic parts (RAM boards, CPUs, etc.) can also be obtained from e-wastes.

The most known aspect of the electronic recycling is the extraction of precious metals, such as gold, silver, platinum or palladium from various electronic parts, such as computer motherboards, cellphones or old industrial boards. A dedicated recycler can also obtain usable amounts of tantalum, nickel, cadmium, tungsten and other metals or their compounds. Other useful elements that can be obtained are silicon, neodymium, lithium, etc.

Older electronics tend to contain heavy metals, so proper protection should be worn when handling them.

Most desired materials

Metals

Aluminium

CPU heatsinks, transistor plates and device frames tend to be made of high purity aluminium, though aluminium with traces of copper is also used. To obtain the aluminium simply unscrew the screws holding the aluminium components and then wash them to remove impurities.

Aluminium can also be obtained from electrolytic capacitors. Large capacitors can simply be cut open with pliers, and the inner roll tends to contain aluminium. To obtain aluminium from smaller capacitors, first crush them with a hammer, then heat them outside in a kiln to melt the aluminium and separate it from the waste plastic rubber. Note that this procedure, while quick, will generate lots of toxic smoke and soot, so make sure You do this in a remote location. It's mandatory to crush the capacitors before heating them, otherwise they will burst and spray their inner content everywhere.

Copper

Transistors, and sometimes heatsinks, tend to have thick copper plating to aid in heat dissipation. To remove it, simply unscrew the plate from the board and then remove the plastic body (if it has one). If there's any conductive paste on it, simply wash it off with a bit of isopropanol.

Copper wiring is another good source of copper. To remove the insulation, use a wire stripper.

Gold

Gold can be found in pin and finger connectors and can be extracted by dissolving the copper circuitry with a PCB etchant, like ferric chloride, in a beaker. The resulting gold will separate as powder or flakes and settle at the bottom of the beaker. Filter the solution through a filter (coffee filters are sufficient), rinse the gold with distilled water and dry it. After you obtained the gold flakes, ou can either purify it by dissolving it in aqua regia or just melt it.

Lead

Some weights found in some electronic components, like very old hard drives are made of metallic lead. They tend to be covered in a protective coating, which can be removed by using a paint stripper.

Spent lead car batteries contain plenty of metallic lead, as well as lead oxides

Mercury

Mercury tilt switches contain a small amount of mercury.

Palladium

Can be extracted from monolitic capacitors.

Silver

Silver can be extracted from depleted silver oxide batteries, or other electronic components like keyboard mylar sheets, varistors, crystal oscillators, by milling the electronic components and then dissolving them in nitric acid. Filter or decant the solution then precipitate the silver with copper to obtain silver powder, which you can melt it to make solid metal.

The best source of silver are the electric contacts. To obtain silver, remove the contacts from the copper/brass body and then dissolve the contacts in nitric acid. Purify the resulting silver nitrate, precipitate the silver metal with copper or another metal and then melt the silver powder to silver metal.

Tin

Tin can be extracted from PCBs by heating the solder with a heat gun, then collect the molten metal. The resulting tin isn't pure, and tends to contain lead or copper, though this isn't always a problem for most reactions.

Tungsten

Light bulb filaments are made of tungsten. Carefully break the bulb, and then pick the tungsten wire with tweezers.

Zinc

Zinc-carbon batteries contain a zinc outer casing, which can be easily removed using pliers. Some alkaline batteries contain zinc powder which can be removed by ripping apart the battery and dumping the zinc powder in water, decant it then dry it.

Some electronic cable fasteners use zinc as sealing metal.

Nonmetals

Carbon

Graphite electrodes can be extracted from Zn-C batteries. You will need to wash them thoroughly to remove any manganese

Germanium

Silicon

Can be extracted from silicon dies.

Compounds

Lithium compounds

Spent lithium batteries, like disposable lithium, lithium-ion or lithium-polymer batteries are a good source of lithium ions. To extract the lithium ions, you will need to carefully break the battery and remove away any plastic, then carefully tear apart the lithium ion sheets. Add the battery sheets in acid and then extract the lithium salts from the reaction product.

Nichrome

Nichrome wiring can be salvaged from a variety of heating elements.

Sulfuric acid

Lead batteries tend to contain 30% solution of sulfuric acid.

Components

Other

Handling

Safety

Extracting materials and components from scrap electronics carries the risk of injury, since wiring, broken ceramic and glass, connector pins and metal frames have sharp edges or gain sharp edges during the dismantling process. Most old electronic components contain toxic heavy elements, such as lead, antimony, cadmium or even mercury, that can enter the body via dermal contact, breathing, ingestion or through scratches. Always wear thick gloves and wear a mask. Use pliers or tweezers to collect small objects.

Extracting valuable metals from the scrap requires corrosive chemicals such as ferric chloride, acids. The extracting process must be performed in a well ventilated area or outside, while wearing proper protection attire.

Disposal

The leftover boards containing useless components should be taken to electronic recycling centers. Waste solutions must be reduced to less toxic compounds and taken to hazardous chemical disposal centers. DO NOT POUR THEM DOWN THE DRAIN!

Solutions containing copper ions can be reduced to metallic copper with iron, resulting iron solutions which are much less toxic that the copper ones. The copper can be reused.

Legal

Dumping e-waste with common trash is forbidden by law in many countries, as it contains materials that are more harmful than ordinary waste. Waste solutions from processing e-waste contains heavy metals which must not be dumped down the drain.

References

Relevant Sciencemadness threads

• gold from E-waste