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Digger gold is the common slang term for gold recovered from electronics components such as board fingers, CPUs, and connector pins.
Methods
For the gold fingers on boards or circuits, often a stripping solution is used to remove the gold from the board material, nitric acid also works well in this regard as many gold components are soldered to boards with silver-based solders that are soluble in nitric acid (which gold is not). After dissolving all other metals in solution, the digger gold is recovered by dissolution of the gold in aqua regia and subsequent selective precipitation of the gold using ferrous sulfate or another selective reducing agent such as hydrazine.
References
Digger gold Wikipedia(Text) CC BY-SA