Vacuum purification of liquid metals

A process for removing metallic impurities from a metal having a low vapor pressure, comprising,

• selecting an apparatus provided with a receptacle containing a bath of a molten metal having a low vapor pressure and a vacuum chamber and at least one conduit extending from below the surface of the molten metal to a point above the molten metal in the vacuum chamber, to provide for a metal fall under vacuum, condensing means in the upper reaches of the vacuum chamber for condensing rising metallic gases,
• continuously injecting a lifting gas into a lower part of said conduit whereby liquid metal is lifted therethrough by the action of the expanding rising gases and discharged in finely divided form by the explosive release of lifting gas to drop in a metal fall onto the surface of the molten metal in the receptacle and a mixture is formed of said lifting gas and gases evaporating from said molten metal,
• subjecting the vacuum chamber to a vacuum effective, in the presence of the lifting gas, to cause a bulk flow of rising gases between the molten metal surface and the condensing means, said vacuum being lower than that which would cause a bulk flow of rising gases in the absence of lifting gas,
• continuously condensing the metallic rising gases on the condensing means to prevent reflux of impurities into the molten metal, thereby to increase the speed of removal of metallic impurities,
• restoring the pressure to normal, and
• recovering the treated metal.