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eTools Home :Lead: Secondary Lead Smelter Scope | Definitions | References | Credits
Lead: Secondary Lead Smelter



Refining and Casting > 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. Mechanical screw drossing diagram
Click for larger view of mechanical drossing diagram


Drossing

Fig. 1. Manual removal of dross may expose workers to lead dust and fume
Fig. 1. Manual removal of dross may expose workers to lead dust and fume
Potential Sources of Exposure:
  • Lead dust and fume may be emitted during manual or vacuum dross removal (Fig. 1).

  • 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.

Slag/dross/skim pot hooding
Click for larger view of dross pot hood diagram





Fig. 2. Portable dross hood with flexible duct attachment port
Fig. 2. Portable dross hood with flexible duct attachment port




Fig. 3. Mechanical dross vacuum
Fig. 3. Mechanical dross vacuum

Possible Engineering and Work Practice Controls:
  • Eliminate or minimize the use of manual drossing. Use automated dross machines where ever possible (Fig. 2).
    Mechanical Drossing Diagram Mechanical Drossing Diagram

  • Provide an exhaust ventilated barrel or bin in which dross can be deposited before transfer to the storage area.
    Dross Hood Diagram

  • Provide portable local exhaust ventilation or enclosure to control emissions from dross which is manually deposited in ladles (Fig. 3).
    Moveable Exhaust Hood Diagram

  • Provide enclosure and exhaust ventilation for dross storage.
    Dross Storage Diagram

  • Use a drossing shovel, which allows molten lead to drain prior to removal of dross.

  • 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.
    Portable Tool Exhaust Diagram
 


Video Exposure Monitoring: Manual Dross Removal
Video Exposure Monitoring: Manual Dross Removal

low bandwidth video feed
Dial up Modem, ISDN

high bandwidth video feed
LAN, DSL, T1, T3

With video exposure monitoring (VEM), worker exposures to lead are monitored and recorded with a direct reading instrument. At the same time, work place activities are recorded on a video tape. The right hand bar indicates changes in total dust concentrations over time.

As the employee skims dross (oxide and other impurities) from the kettle, the increasing red bar indicates that the local exhaust ventilation is inadequate to effectively capture lead dust generated during  the transfer of dross from the kettle to the ventilated dross receiving vessel. 


Note: This example illustrates the level and duration of exposure to total dust and is used to show how VEM can be used for determining sources of employee exposure. Other sources of employee lead exposure can be determined by using VEM sampling for a full work shift. 
 


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