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White Dross, what is white dross? white dross definition

 

White Dross is a mixture of aluminum oxide and aluminum metal with the metal content varying from 15 to 80%. It is produced during the melting of aluminum in a furnace hearth or the transporting of molten aluminum between furnaces or crucibles.

 

The dross is collected in a “skimming operation” where an operator either manually removes the floating mixture from the furnace, or in the case of modern large furnaces, an operator on a motorized piece of equipment skims the floating dross. In either case the dross mixture is removed from the furnace and into a” skim pan” for containment and cooling. As will be discussed in more detail later, the dross removed from the furnace may not be of the same composition and quality as the dross shipped off to a processor at a later date.

 

In addition to the two major dross components, aluminum metal and aluminum oxide, smaller amounts of other compounds can be present depending upon the conditions in the furnace (as well as the subsequent dross pan), the metal source, and the alloys being processed. These other compounds include aluminum nitride (AlN), aluminum carbide (Al4C3), and possibly cryolite (Na3AlF6). The last compound is often associated with molten metal coming from electrolysis cells, while the two former compounds are associated with “thermite” reactions occurring in the furnace or dross skim pan.

 

White dross can include oxide compounds not directly formed in the furnace such as metallic skim removed from cooled transfer troughs, skulls from crucibles, and spills. Finally, white dross contains little or no salt flux.

 

 The related information

Aluminum dross processing machine

white dross, what is white dross, white dross definition