As Gold Drops .........

Originally Posted by eesakiwi

The 'low grade - brown boards' will only have one side with Copper traces, maybe both sides and that's it.

Green boards and such are made up of several layers of boards, I have read of up to 7 layers, so that's a minimum of 8 layers of (thin) Copper traces.
Also they want the traces to contact between the boards and they often have Gold plating lining the 'thru board' holes. The Gold plating is a easy to plate metal and the Copper plating plates onto Gold really easy to make good connections between boards.

I expect they are acid etching off as much Copper as they can from the boards, then mincing them to a paste and using Cyanide to remove the rest of the Copper and Gold.
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They use Cyanide to get Gold from soil, the Golds so fine you cannot see it. That's how they do it at a Gold mine in NZ.
They spread out huge plastic sheets and cover it with ballmilled soil (the 'rich soil' only) then cover that with Cyanide solution and let the rain carry the Cyanide down thru the soil, then they collect the outgoing water from the pits and remove the Cyanide, with the Gold stuck to it, and separate the Cyanide off to get the Gold.
The washed soil is not allowed to have more than 4 parts per million of Cyanide in it afterwards, often its got more Cyanide than that in it before they process it !
Any Cyanide left in it is a waste, as its holding the Gold in there as well.
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Also, the boards have other metals in/on them that the refiners get, Silvers a good one as its in the solder, along with Bismuth(?), Tin and Platinum.
The tiny brown SMD blocks, the capacitors, have Silver and Platinum(?) In them.
Lotsa Gold and Silver in the surface mounted switches, contacts and SAW devices.
It all adds up when you do it by the Ton....

Large refiners almost always incinerate boards, and then recover the values from what is left over, or the filters in the flue/exhaust.

You are right about other metals, many times the components also have silver, palladium (MLCC for example), platinum, gold, etc.

Scott