Mixed Waste Encapsulation in Polyester Resins at the Hanford Site

Site Name:

Hanford Site


Richland, WA

Period of

Not identified


Treatability study

Microencapsulation by Polyester Resin
- Four polyester resins tested - polymer (trade name) - orthophthalic (S2293), isophthalic (Aropol™ 7334), vinyl ester (Hetron® 922-L25), and water extendable (Aropol™ WEP 662 - proprietary)
- WEP resin was tested on aqueous wastes; other three were tested on dry waste
- Initiator (catalyst) - cobalt naphthenate
- Mixer equipped with a variable speed paddle and sample molds for curing
- Dry waste added as free-flowing powder; aqueous waste was slurried
- Mixing time - 5 to 10 minutes at a low rate to homogenize waste; additional 2 to 5 minutes at a high rate after initiator added (until the temperature rises indicating the onset of curing)
- Curing molds placed in adiabatic chambers
- Three tests using surrogate wastes; one test using a Hanford waste stream

Cleanup Authority:

Principal Investigator:
Rabindra Biyani
COGEMA Engineering Corporation
P.O. Box 840
Richland, WA 99352
Telephone: 509-376-1004
E-mail: biyani@COGEMA-Engineering.com
MWFA Product Line Manager:
Vince Maio, Advisory Engineer
Mixed Waste Focus Area
Lockheed Martin
Idaho Technologies Company
Idaho National Engineering
and Environmental Laboratory
P.O. Box 1625
Idaho Falls, ID 83415
Telephone: 208-526-3696
Fax: 208-526-1061
E-mail: vmaio@inel.gov

Metals and radionuclides
- Spiked metals concentrations in treatability study wastes - arsenic (159.3 mg/kg), barium (154.1 mg/kg), cadmium (119 mg/kg), chromium (151.3 mg/kg), lead (132.7 mg/kg), and selenium (140.9 mg/kg)
- Spiked radionuclide concentrations in treatability study wastes - cesium (1.2x105 pCi/L), cobalt (1.1x105 pCi/L), strontium (1.1x105 pCi/L), and tecnetium (1.3x105 pCi/L)

Waste Source:
Salt-containing mixed wastes from DOE processes and surrogate wastes

Type/Quantity of Media Treated:
Process waste streams

Purpose/Significance of Application:
Treatability study of various polyester resins to stabilize high salt-containing mixed waste

Regulatory Requirements/Cleanup Goals:
RCRA Land Disposal Restriction (LDR) and NRC disposal criteria
- Treatability test targeted to TCLP levels for RCRA heavy metals - cadmium (1.0 mg/L), hexavalent chromium (5.0 mg/L), lead (5.0 mg/L) and mercury (0.2 mg/L)
- NRC leachability indices - target of 6 or higher

Orthophthalic, isophthalic, and vinyl ester resins:
- For RCRA metals, TCLP results for resins were below the target levels for all metals except cadmium. Failure was attributed to the sampling method which required the mold be cut to a smaller size (9mm), possibly destroying the polyester coating. To counter the effect, fully coated polyester waste form molds of 9mm were specifically prepared for TCLP testing; this sample passed for all metals including cadmium
- Results were also compared to the UTS criteria - most samples failed for RCRA metals.
- Polyester microencapsulation was validated for salt loadings of 30-wt% for all three resins, and for salt loadings of up to 70% for the orthophthalic resin

WEP resin:
- For RCRA metals, TCLP results were below the targeted levels for all metals
- Results were also compared to the UTS criteria - samples passed for all metals expect for cadmium
- For radionucides, the leachability indices ranged from 10.1 to 10.8

Cost Factors:
- Projected full-scale cost for the polyester resin encapsulation process - capital cost of $2 million including equipment design and development and operating cost of $5,940/cubic meter of waste form
- Disposal cost of $2,100/cubic meter of waste form

The Mixed Waste Focus Area, a DOE Environmental Management (EM) -50 program, sponsored the development of five low-temperature stabilization methods as an alternative to cement grouting to stabilize salt-containing mixed waste. One of the alternative methods is microencapsulation using polyester resins. COGEMA Engineering Corporation performed a series of treatabilitiy studies and developmental tests of the technology at the Hanford site. The studies included encapsulation of salt-containing mixed wastes from the Handford site and with surrogate wastes spiked with contaminants. Four types of resins were tested: orthophthalic polyester, isophthalic polyester, and vinyl ester for dry waste, and a water-extendible polyester resin for aqueous wastes. The cured waste forms were evaluated against the RCRA LDR and NRC disposal criteria.

The results of the studies showed that the encapsulation of salt-containing mixed waste using polyester resins is applicable to inorganic, relatively homogeneous low-level mixed wastes containing high levels of salt. Further development is needed to identify chemical additives to reduce the solubility and toxicity of the RCRA metals. Other factors to be considered in future development of the process include safety controls to address potential flammable and unstable conditions when using polyester encapsulation, and additional research into the long-term effectiveness of the technology.