Abstract: The invention relates to an apparatus for carrying out a process for separating electrolysis bath residues on used anode units removed from electrolysis cells for the production of aluminum by the Hall-Heroult process, said units comprising a cabon residue 5 or "butt", in which are sealed discs 3 interconnected by flanges 2 welded to a suspension rod 13, the axes of the discs 3 being parallel to the axis of the suspension rod 13, said process comprising passing at least one rotary milling cutter 9, of which the axis of rotation 10 in the working position is substantially parallel to the axis of the rod 13, through the space situated between the discs and around the discs 3 and defined by the upper face of the carbon butt 5 on the one hand and the flanges 2 on the other hand.