Hi Flavio,
This is definitively a spear blade from the Ngbandi tribe in Congo.
Here is a picture from the book 'Iron work from Central Africa' by H. Westerdijk. Unfortunately only available in the Dutch language.
Your spear blade is similar to the one in the top row, second from the left.
For those interested, these spear blades are attributed to :
A - Ngbandi
B - Ngbandi
C - Ngbandi and Bati
D - Ngbandi, Yakoma,Ngombe, Bati, Ngbaka
All these spear blades were used in the Northwestern part of Congo and were traded over a large area and used by different tribes. These were used for thrusting, but also as a means of showing ones wealth.