Yes most scrap metal recycling yards will buy old aluminum license plates from you without a problem as long as they are not stolen.
I have scraped several junk cars in my life and have always remove the old aluminum license plates from the scrap cars and trucks and placed in them in a barrel.
Then when I got the barrel full I took the license plates in with another car and sold the license plates and made $20.00 off of them.
It wasn't much money but it paid for my gasoline in my vehicle to haul the scrap car or truck in.
Just never deface the old license plate when you bring them to the scrap yard as that looks suspicious but if you just have some old license plates that you got legit then scrap yards should take them for clean aluminum without a problem.