I have been putting my Ali heatsinks with transistors aside, but sorting them into extruded & sheet Ali first.

The copper on a transistor back is worth about 2 cents, just my 2 cents.
They all get put into one container, in which it will get burnt off one day, & cement mixer rumble to sort the copper & the carbon dust apart. Then tru a microwave door sieve. Coppers $7 a kg here.