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Dross is a mass of solid impurities floating on a molten metal bath. It appears usually on the melting of low melting point metals or alloys such as tin, Lead, zinc or aluminum, or by oxidation of the metal(s). They can also consist of impurities such as paint leftovers. It can easily be skimmed off the surface before pouring the metal into a mold or casting flask. With tin and Lead the dross can also be removed by adding sodium hydroxide pellets, which dissolve the oxides and form a slag. Dross is distinguished from slag, which is a (viscous) liquid floating on the alloy, by being solid.
Lead Dross shall consist of slag, dross, skimming or spilling from Lead melting operations. A scum formed on the surface of molten metal. Dross refers to the Lead oxides, copper, antimony, and other elements that float to the top of the molten Lead.
The waste material skimmed from the surface of the Lead-tin pot is commonly referred to as "Lead dross." As the name might suggest, Lead dross has a high percentage of Lead, causing it to be classified as a hazardous waste.
Drossing: During drossing operations, dross is skimmed to the rim of the kettle and manually shoveled or "spooned" into a container. Mechanical drossing methods, such as vacuum drossing, are used by some secondary Lead smelters. Significant levels of Lead fume and dust may be released during drossing.
- Lead dust and fume may be emitted during manual or vacuum dross removal.
- Lead dust may be emitted when depositing dross into a waste container.
- Emissions may be released while charging dross to the storage bin via pneumatic conveyance system.
- Lead dust may be spilled and emitted while handling, transporting, and storing dross.
- Eliminate or minimize the use of manual drossing. Use automated dross machines where ever possible.
- Provide an exhaust ventilated barrel or bin in which dross can be deposited before transfer to the storage area.
- Provide portable local exhaust ventilation or enclosure to control emissions from dross which is manually deposited in ladles
- Provide enclosure and exhaust ventilation for dross storage.
- Use local exhaust ventilation at drossing access locations.
- Do not overfill dross containers.
- Eliminate or minimize the use of a torch for dross cleanup.
- If a torch must be used provide portable local exhaust ventilation or a ventilated torch.