Abstract: The present invention relates to a ladle for the chlorination in co-flow mode of aluminium alloys in a molten state.It is divided by a vertical partition (6) which, with the bottom, leaves a space (7) for the flow of the metal, into a feed compartment (8) and a treatment compartment (9) in which a chlorinated gas distributor rotor (10) is immersed. It is characterized in that the treatment compartment is closed at its base by a horizontal wall (13) which extends at the level of the bottom of the partition and which is apertured at its center by an opening whose axis coincides with the axis of rotation of the rotor.It is used in the removal of magnesium from aluminium alloys and, with ladles of a capacity of close to 1 m.sup.3 and which can therefore be easily maneuvered, it makes it possible to attain treatment capacities of the order of 20 T/hour with suitable levels of efficiency in regard to the removal of magnesium.