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Lead: Secondary Lead Smelter

Raw Materials Processing > Handling and Transport                   

Tempered Air Cab Diagram
Click for larger view of air cab diagram

Handling and transportation of feed materials is an essential part of the secondary lead smelting process. Material is primarily transported through the use of mobile equipment (forklifts, front-end loaders). Proper operator training, prudent work practices, and good housekeeping are key in minimizing lead emissions during mobile equipment operation. Conversely, careless equipment operation coupled with inadequate housekeeping can lead to serious lead exposure throughout the plant. Certain material transporting operations call for mechanical conveyance. Some common mechanical conveyance methods used in secondary lead smelters include:

Mobile Equipment
Fig. 1. Forklift transporting materials
Fig. 1. Forklift transporting materials

Potential Sources of Exposure:
  • Lead dust from feed materials can become airborne during handling and transport (Fig. 1).

  • Settled lead dust on surfaces and equipment may become airborne by vehicle traffic and wind.

  • Dust may be generated while mixing feed materials outside ventilated areas prior to charging.

Possible Engineering and Work Practice Controls:
  • Provide vehicles with enclosed cabs that have positive-pressure, HEPA-filtered air.
    arrow Tempered Air Cab Diagram

  • Keep all surfaces wet and clean through the use of water supply systems and central vacuum cleaners.
    arrow Central Vacuum System Diagram

  • Maintain positive-pressure, HEPA-filtered air system on mobile equipment to ensure effective operation. Check and change air filters regularly as part of an effective scheduled preventative maintenance program.

  • Remain inside the vehicle and keep doors and windows shut during mobile equipment operation in contaminated areas.

  • Reduce vehicle speeds to minimize the stirring up of settled dust.

  • Vacuum the inside of mobile equipment frequently.

  • Pave all roadways to facilitate housekeeping.

  • Wet down raw materials storage to suppress the dust generation.

  • If it is determined that lead dust is coming from mobile equipment or is coming from adjacent areas, evaluate material handling patterns and practices and area isolation.

Video Exposure Monitoring: Material Transport
Video Exposure Monitoring: Material Transport

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, workplace activities are recorded on a videotape. The right hand bar indicates changes in total dust concentrations over time.

As the employee moves slag from the furnace to the slag pot cooling area with a front-end loader, the increasing red bar indicates that employee exposure may be from the stirring up of settled lead dust from the floor or possibly fugitive emissions from the furnace.

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.

Belt Conveyors
Belt conveying systems can be used to transport furnace feed material from storage to battery shredders and the furnace charging area.

Potential Source of Exposure:
  • Lead dust may be emitted from open conveyor systems:
    • At the receiving end
    • At the discharge end
    • At the underside of conveyor
    • From spillage along the conveyor belt

Toxic material belt conveying head pulley
Click for larger view of belt conveying head pulley diagram

Toxic material conveyor belt loading
Click for larger view of conveyor belt loading diagram

Possible Engineering and Work Practice Controls:
  • Provide an enclosed conveying system, such as a screw conveyor, in place of a chain-drag or open conveyor belt where possible.

  • Totally enclose and exhaust ventilate the conveyor from loading to transfer points.
    arrow Conveyor Belt Ventilation Diagram

  • Provide a trough belt and conveyor skirting to minimize spillage.

  • Provide a baffle to ensure the unloading of conveyor at transfer point.

  • Provide a belt scraper at the discharge end to dislodge dust particles that may adhere to the belt surface.

  • Provide access doors to conveyor and transfer point enclosures to facilitate maintenance, wash down, and other activities.

  • Use top-hinging doors for inspection to prevent spillage of leaded material.

  • Provide drains and sumps in conveyor trench to collect wash water and mud.

  • Provide hose bibs for manually washing the conveyor equipment.

  • Wet down materials to suppress dust generation.

Screw Conveyors
Screw conveyors are commonly used in the secondary lead smelting industry to transport flue dust from the baghouse to an agglomeration furnace or a storage area (Fig. 2).

Potential Sources of Exposure:
  • Lead dust may be emitted from leaking screw conveyors and at furnace discharge points.

Fig. 2. Screw Conveyor
Fig. 2. Screw conveyor

Possible Engineering and Work Practice Controls:
  • Enclose screw conveyor systems that transport leaded materials.
    arrow Screw Conveyor Components

  • Enclose and exhaust ventilate screw conveyor transfer points.

  • Maintain cover gaskets and repair leaks immediately.

Note: The screw conveyor can not be used for charging smelting furnaces.

Bucket Elevators and Drag Chains/Lines
Commercially available bucket elevators and drag chains may be used in conjunction with some material handling operations.

Bucket elevator ventilation diagram
Click for larger view of bucket elevator ventilation diagram
Potential Sources of Exposure:
  • Leaded materials may leak from the feed or discharge end of the elevator.

Possible Engineering and Work Practice Controls:
  • Provide a properly-designed and exhaust-ventilated bucket elevator.
    arrow Bucket Elevator Ventilation Diagram
    arrow Bin and Hopper Ventilation Diagram

  • Minimize dust generation when feeding the bucket elevator by keeping the height of the material free-fall to a minimum and by gently loading material into the bucket elevator.

  • Enclose and exhaust ventilate the chutes between the elevator discharge and the receiving furnace.

  • Repair any holes or openings in the casings of the bucket elevator or chutes.


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