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This presentation will probably involve audience discussion, which will create action items. Use PowerPoint to keep track of these action items during your presentation In Slide Show, click on the right mouse button Select “Meeting Minder” Select the “Action Items” tab
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This presentation will probably involve audience discussion, which will create action items. Use PowerPoint to keep track of these action items during your presentation • In Slide Show, click on the right mouse button • Select “Meeting Minder” • Select the “Action Items” tab • Type in action items as they come up • Click OK to dismiss this box • This will automatically create an Action Item slide at the end of your presentation with your points entered. Mercury Treatability Studies: an Overview Mary Cunningham, EPA John Austin, EPA
Background • EPA has participated with DOE in 3 recent studies to evaluate waste stability. • A study of radioactively contaminated soils has been completed. • Studies of a surrogate waste and elemental mercury are near completion.
Study Outline for both Bulk Elemental and Mercury Surrogate Studies • Vendors received wastes for treatment and returned treated wasteforms for assessment. • The treatments entailed amalgamation and/or stabilization using proprietary reagents.
Study Outline, Continued • Treated wastes were exposed to fixed pH conditions for 14 days. • leachate to solids 20:1 • -9.5 mm solids • The treated wasteforms were required to pass TCLP to be included in the study.
Study Outline, continued • Treated and untreated forms characterized • bulk density, moisture content, percent organic matter, cation exchange capacity, particle size. • Total Hg, TCLP, Constant pH Leaching • Hg vapor pressure (ORNL)
Constant pH Leaching Protocol • Treated wastes exposed to fixed pH conditions (pH 2 – 12) for 14 days. • Leachate to solids 20:1 • 9.5 mm solids • Duplicate leach experiments at pH 2, 8, and 12. • Leachates were analyzed using extensive laboratory QA/QC.
Metal Solubility is controlled by: • pH • Liquid/solid ratio • Redox conditions • Major ions • Particle size • Exposure time Our studies focus on pH.
Mercury Surrogate Waste Study • Multiple forms of mercury (5000 mg/kg) in sludge of diatomaceous earth, aluminum hydroxide, ferric chloride, and sodium chloride. • Elemental mercury, Mercury chloride, Mercury nitrate, Mercury oxide, Phenyl mercuric acetate • TCLP 110 mg/L average
Surrogate Study - Significant Findings • Some vendors can treat ~ 5000 ppm Hg wastes to below 0.025 mg/L Hg in certain pH ranges. • Each treated waste form has an Achilles' heel. • Significant leaching at extreme pH acid or base. • Each treatment process produced a wasteform that responded differently at the various pH levels
Surrogate Waste Study: Conclusions • LDR standard of “amalgamation,” “stabilization” or even a number is not appropriate across the board • To allow treatment and disposal, we would need site specific data on the waste, the treatment process, and the disposal conditions (pH and redox of landfill), etc. • We think that site specific variances could be approved in limited instances, where data show stability in the expected disposal environment.
Bulk Elemental Treatment Study • Same leaching protocol • Same Vendors • Treated bulk mercury product
Elemental Study-Significant Findings • We have some general concerns about treating and disposing bulk elemental mercury: • Difficulty in getting elemental mercury to react with reagents, resulting in a heterogeneous wasteform • Leachate data alone cannot determine efficacy of treatment • Our test conditions are NOT a worst case. • More aggressive conditions could leach more. • Treatment would result in large volume increases of waste. • Additional barriers would be necessary to inhibit leachate attack (e.g., macroencapsulation).
Next Steps • Studies will be subjected to independent peer review. • The peer reviewer comments and study reports will be published in a Notice of Data Availability (NODA). • We are consulting with DLA on their EIS for disposition of the national stockpile. • We are working with ECOS in a partnership to address the issues with the long-term management of mercury.
