First question is : How can you prove that the item is associated to black magic only and has nothing to do with other purposes like any other item?
Second question: Do you know for sure the owner of the item or not? If you know the owner of the item, then you must give it to him/her. If you do not know the owner and there is no considerable value for it, then you can throw it away provided that there is no possibility to know the owner.
Protection from black magic is by reciting Sura Falaq and Sura An Naas and Ayatul Kursi along with Du'a and Sadaqa.