The handling of dross is an unfortunate but necessary activity of melting aluminum in a reverberatory (reverb) furnace. Recyclers have been working on ways to minimize melt loss and improve metal recovery for over 100 years. Even so, as much as 3% of the scrap can still end up as dross. Big savings can accrue if this metal can be recovered, but this is only possible if dross is properly collected and handled. A side benefit of proper dross handling is that the workplace environment is improved and disposal costs are minimized.
Aluminum melt shops produce three types of dross. First is white dross, which is mainly a mixture of aluminum oxide and aluminum skimmed from the melt surface before tapping the furnace. White dross may contain up to 80% metallic aluminum. Second is black dross from the charging well, which is a mixture of salt flux, aluminum oxide and metal. The salt flux must be replenished because impurities in the scrap create sludge in the salt, which accumulates and hinders the settling of small droplets of molten aluminum. Third is salt cake, which arises from the treatment of white and black dross to recover their metal content. Most melt shops collect their dross and send it out to recyclers for treatment to recover the metal values.