Mercury Treatability Studies: an Overview

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Mercury Treatability Studies an Overview

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• Mary Cunningham, EPA
• John Austin, EPA

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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.

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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.

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Study Outline, Continued

• Treated wastes were exposed to fixed pH
  conditions for 14 days.
• leachate to solids 201
• -9.5 mm solids
• The treated wasteforms were required to pass
  TCLP to be included in the study.

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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)

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Constant pH Leaching Protocol

• Treated wastes exposed to fixed pH conditions (pH
  2 12) for 14 days.
• Leachate to solids 201
• 9.5 mm solids
• Duplicate leach experiments at pH 2, 8, and 12.
• Leachates were analyzed using extensive
  laboratory QA/QC.

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Metal Solubility is controlled by

• pH
• Liquid/solid ratio
• Redox conditions
• Major ions
• Particle size
• Exposure time
• Our studies focus on pH.

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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

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Vendor A
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Vendor B
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Vendor C
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Vendor D
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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

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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.

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Bulk Elemental Treatment Study

• Same leaching protocol
• Same Vendors
• Treated bulk mercury product

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Vendor A Bulk Elemental
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Vendor B Bulk Elemental
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Vendor C Bulk Elemental
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Reagent HgSe
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Mercury Loading
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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).

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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.