Dross forms on the surface of molten aluminium as metal reacts with air. Skimmed off during melting and casting, it is a mixture of aluminium oxide, trapped metallic aluminium and, if fluxes are used, salts. White dross comes from primary and clean melting with little salt and has relatively high metal content. Black dross comes from secondary melting with salt flux and has lower metal content. Salt cake is the residue left after dross is processed in rotary furnaces.
Why it matters when buying
- Dross is priced on metal content %, so agree how it will be measured, for example by trial melt or lab analysis of a representative sample.
- Particle size and how quickly the dross was cooled affect recovery; hot dross keeps burning and loses metal.
- Dross can react with water to release flammable and toxic gases; it must be kept dry and handled under the applicable hazardous waste rules.
- Ask about state pollution control board authorisations of both seller and processor.
Typical uses
Dross is processed to recover metal for remelting or deoxidiser products, and residues may go to cement or other uses where permitted. See the dross selling guide and sell aluminium dross.