Environmental Engineering Reference
In-Depth Information
•
Resistance to microbial degradation.
•
Good mechanical integrity of final waste forms (compressive strengths
typically ≥ 14 MPa).
•
Resistance to radiation degradation (in doses up to 10
8
rad). Compressive
strength of polyethylene waste forms improves with radiation doses up
to 10
8
rad.
•
Relatively low leachability. Leach indices of 8 to 11, depending on type
of waste and waste loading.
In addition, other advantages associated with polyethylene encapsulation
include:
•
One process amenable for both micro- and macroencapsulation. Both
technologies can share similar process equipment, so one facility can be
equipped for processing both micro- or macroencapsulated waste forms.
•
Physical encapsulation process with no chemical reactions required for
solidification; i.e., not subject to interactions with waste chemistry and
solidification of waste forms is assured.
•
Ability to remelt and reform processed waste forms. Waste forms can be
melted and recast if needed based on disposal performance and require-
ments.
•
Lower cost of polymer matrix (e.g., $0.50/lb for virgin polyethylene).
•
Ability to use recycled plastics. Industrial and consumer recycling pro-
grams generate large volumes of plastic materials to reduce disposal loads
on municipal landfills and provide feedstock for polyethylene products.
However, many manufacturers cannot use recycled feedstock due to prod-
uct variability issues such as coloration. Availability of these waste prod-
ucts to encapsulate hazardous, radioactive, and mixed wastes provides an
ideal market for recycled plastics.
Several vendors, offering services for the treatment of mixed waste lead and
debris to both DOE and commercial clients, have successfully commercialized
polyethylene macroencapsulation. Each offers a different processing technique. The
standard and most commonly used method involves compacting waste within an
inner container, placing it within a larger overpack, and then extruding clean poly-
ethylene to fill the space between containers. Millions of pounds of mixed waste
lead from across the DOE complex have been treated using this technique. Mac-
roencapsulation can also be conducted by inserting compacted waste into precast
polyethylene cylinders and then “welding” plastic caps on each end to make the
final seal. This method was recently used to treat metal debris from the Y-12 Plant
in Oak Ridge, TN. A third method involves placing the waste in preengineered plastic
boxes or containers and then sealing the lid using imbedded electric resistance wires.
Polyethylene microencapsulation using both single-screw extrusion and kinetic
mixer-based processing has been commercialized, but has not been used to treat
large quantities of waste, to date.
Search WWH ::
Custom Search