What can I do with old locks?
Make sure they are complete

Both knobs, core assembly, latches (latches are not standard/universal), and the screws.   

The screws that hold the latch on are not nearly as important, and one can subsitute a plain old wood screw or drywall screw.  

Worn out ones, straight into recycle bin or trash, it is metal, they will separate it out with magnets or eddy currents. 

Once I verify it is complete, I  throw each knob or deadbolt (complete) into a gallon Ziploc and then throw the Ziplocs into a box.  And then, the keys.  If you have enough keys, throw one in each Ziploc.  

Then the kaboodle either goes on eBay or to the Habitat for Humanity store.    Because that's where people go when they want lock sets, not Goodwill.  Also Goodwill won't get that this is a set, HfH will.