This question has been asked before here, but most of the comments were removed, and the one that's left is about Lumumba, so the question is still unanswered: https://www.reddit.com/r/AskHistorians/comments/2itjl3/has_belgium_ever_acknowledged_or_apologized_for/ Thanks!
There was an AMA by /u/Matthew_G_Stanard about Selling the Congo and Belgian imperialism. I don't remember that your precise question has been asked then as part of that AMA, but waiting for a more complete answer it should give you some context about the transition from the so called Congo Free State to a Belgian colony.