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Tantalum is a metal found in some capacitors and is easily sold as scrap for a decent price.
Basic building blocks of a tantalum capacitor
The capacitor is made from a plug of metallic tantalum powder often with an anode pin of tantalum wire sticking out. The powder is sintered at high temperature (1500-2000 °C) under vacuum to create a solid metal piece. The plug is porous and have a large surface area. Then via electrochemical processes an oxide surface is built up, this is the dielectric layer and the thickness decides the voltage rating. Next up is the cathode, it is built up by a thin layer of manganese dioxide. After the manganese oxide layer is formed a graphite layer is added. It is needed to separate the manganese oxide from the silver contacts that is next.
Some capacitors have silver in the contacts or casing. There are some older metal can type where the can is made of silver. On newer surface mounted capacitors there are silver filled epoxy between the solder pad and the tantalum plug. When incinerating surface mounted types the silver ends up in the ash.
Tantalum capacitors can be sold as is or incinerated and the plug is extracted and sold. After incineration the plug would consist mainly of tantalum oxide and tantalum, before incineration the capacitors contain around 30% weight of Ta. Tantalum metal and oxide is resistant to nitric acid so the silver can easily be leached with nitric acid.
Yield numbers for silver from tantalum caps are, red capped = 40%, green capped 25%.
Eric no longer propose incineration as a treatment since it will oxidize the tantalum.
- Eric buys Ta, good thread with lots of pictures
- Tantalum Recycling, good thread with lots of pictures
- GRF : Silver tantalum capacitors (pictures)
- The technology behind tantalum capacitors (pdf)
- University of Tokyo : Recycling Process for Tantalum and Some Other Metal Scraps (pdf)
- Safety concerns with tantalum caps, smoke from incineration
- Pictures of some Ta-capacitors before and after incineration
- Good introduction to tantalum extraction, chemistry, politics and trade
- Pictures of various tantalum capacitors