Elbow grease is my preferred way to do it. :wink:
To use chemicals to dissolve the plastic at a hobby level would become expensive really fast, mechanical separation of the black epoxy that contains the bond wires is best, then treat them as the black top from plastic top BGA chips. Incineration and panning.
In larger quantities I think smelting, possibly with a collector metal together with similar scrap would be most effective, making refiners bars.
Göran