Secondary smelters produce low-magnesium-containing aluminum alloys for the die casting industry by demagging scrap of high magnesium content from mill products. Inefficiency of halogenation leads to a major problem of air pollution. Metallurgical considerations of reactions involved in demagging indicate that the process can be made 100 percent efficient. This article reviews commercially available methods to achieve efficient demagging, including the use of molten metal pumps developed by the author's company for controlling the demagging process by establishing closed-loop recirculation.