Yes, as others have said, they will take empties away for free, but you will only get any money for them if you trade them in within so long of actually 'buying' them in the first place. IIRC it was something like within 1 year 75%, 2 yrs 50% etc etc, but even then, you have to have the original lease paperwork with you, which it doesn't sound as though you have in this case.
Perhaps you'll just have to think of another use for them?: