If you absolutely feel they can serve no further use , the proper way to dispose of them would be the way which errs on the side of caution. IOW, blessed religious objects should never be just thrown into the garbage. They need to either be buried or burned. If you’re unsure as to whether they are blessed , it’s better to bury (or burn) them.
There are some other interesting alternatives that came up in this CAF thread from 2007 - Properly Disposing of a Blessed , Broken Rosary . Unfortunately the link posted to the couple who needs broken rosaries and repairs rosaries as part of their apostolate no longer appears to be active (post # 13).
Then there’s that post about Mother Angelica (# 16).