METHOD OF REMOVAL OF LIGHT METALS FROM ALUMINUM

Improved apparatus and method are described for the removal of light metals; sodium, lithium, calcium and magnesium, from virgin aluminum tapped from a Hall Heroult reduction cell using LiF-modified or LiF + MgF2 electrolyte. The method is performed i n a crucible or at a station intermediate between the cells and furnaces in a cast house. Fine particulate aluminum fluoride and/or sodium aluminum tetrafluoride are transported by a gas or ga s mixture into the molten aluminum in a manner such that the light metals are preferentially removed or their concentration substantially lowered through: 1) the axle of a specially designed spinning impeller; 2) partially through the axle of a specially designed spinning impeller and partially through one or more pipes equipped with dispersers for dispersing into the molten metal flow close to the spinning impeller; or 3) through one or more pipes equipped with dispersers for dispersing into th e molten metal flow close to the impeller fastened to a solid axle.