EXPERIENCE WITH ALTERNATIVE LEACHING PROTOCOLS FOR MERCURY-BEARING WASTE

1. Department of Civil and Environmental Engineering Vanderbilt University Nashville, TN Nuclear Science and Technology Div. EXPERIENCE WITH ALTERNATIVE LEACHING PROTOCOLS FOR MERCURY-BEARING WASTE Florence Sanchez, Ph.D. David S. Kosson, Ph.D. Catherine H. Mattus Michael I. Morris Breaking the Mercury Cycle: Long Term Management of Surplus & Recycled Mercury and Mercury-Bearing Waste Boston, May 1st, 2002

2. Context • Mixed wastes • RCRA: treatment by BDAT prior to disposal • Wastes containing elemental Hg > 260 ppm • BDAT: Thermal desorption and reclaimation of Hg for recycling • Hg recovered from mixed wastes cannot be recycled • Need for alternative treatment processes acceptable as BDAT for Hg-contaminated mixed wastes • Side-by-side comparison of four vendor provided treatment processes (EPA/DOE)

3. Objectives • Evaluate a new leaching framework for assessing the efficacy of treatment processes for Hg-contaminated mixed wastes • Provide long-term Hg release estimates over a range of management scenarios • Provide insight into selection of acceptable management scenarios for each treatment process

4. Alternative Approach to Leaching Evaluation Define release modes Design test methods to and fundamental measure fundamental Test waste leaching parameters parameters Calculate release based on Evaluate acceptance based management scenario(s) • on projected impact • default criteria • site-specific impact estimate • and field conditions • default scenarios • site-specific conditions

5. 4.6 mg Hg/kg 1840 mg Hg/kg 997 mg Hg/kg Th. desorpt: Vendor 1 Untreated Am soil S/S: Vendor 2 SPC: Vendor 4 Materials • Two Hg-contaminated soils (~4500 mg/kg) containing radionuclides (Am-241 & Eu-152) • Four candidate treatments • Vacuum thermal desorption (Vendor 1) • Two forms of solidification/stabilization (Vendors 2 and 3) • Sulfur polymer cement encapsulation/amalgamation (Vendor 4)

6. Approach • Measurement of fundamental leaching parameters • Hg solubility as a function of pH • Hg release rate • Use of assumed management scenarios to estimate the release of Hg over 100-year time frame • Disposal under a percolation-controlled scenario (20cm infiltration/year) • Disposal under a diffusion-controlled scenario (100% precipitation frequency) • Disposal in the context of municipal waste landfill, hazardous waste landfill and industrial co-disposal landfill • Compare results to release estimates based on TCLP

7. Equilibrium CharacterizationAlkalinity, Solubility and Release as a Function of pH (SR002.1) • 11 parallel solubility extractions • DI with HNO3 or KOH addition • Size reduced material • Contact time based on size • LS ratio: 10 mL/g dry • Endpoint pH • Distributed 3≤pH≤12 • Titration curve and constituent solubility curve

8. Hg solubility as a function of pH Thermal desorption: Vendor 1 S/S: Vendors 2, 3 SPC: Vendor 4

9. Mass Transfer Rate Characterization (MT00x.0) • Two protocols • Monolithic (MT001.1) • Compacted granular (MT002.1) • Deionized water leachant • Liquid-surface area ratio • 10 cm3/cm2 • Refresh periods • Cumulative times of 2, 5, 8 hr, 1, 2, 4, 8 days (may be extended) • 7 leachates • Cumulative release as a function of time

10. Hg Release Rates(Untreated & SPC treated Hg-contaminated Soil) • Dobsuntreated Am soil = 9.8 10-16 m2/s • DobsSPC treated Am soil = 8.9 10-18 m2/s

11. Material Release Assessment: General Approach No Treatment Option Yes Mgmt Scenario Percolation Flow-around Fundamental leaching propertiesEquilibrium data Site information* Assessment model • Fundamental leaching properties • Availability data, Equilibrium data, Mass Transfer data • Site information* • Assessment model Release Estimate No Yes AcceptableImpact? Exit * Site-specific information or Default scenarios

12. V Sx Seepage Basins Release Scenario: Percolation • Scenario characteristics • Granular or highly permeable material • Low infiltration rate • Low liquid-solid ratios [mL/g] • Site information • Infiltration rate Inf • Fill density • Fill geometry H • Field pH r • Local equilibrium at field pH is rate limiting

13. Csat Cs0 Roadbase material V S a Release Scenario: Flow-around • Scenario characteristics • Low permeability material • High infiltration rate • High liquid-surface area ratios • Site information • Fill density • Fill geometry , • Fill porosity • Masstransport within solid matrix is rate limiting

14. Release Estimates for Different Management Scenarios Vendor 3 treated Am soil

15. Release Estimates for Different Management Scenarios Vendor 4 treated Am soil

16. Comparison of Treatment Processes S/S: Vendors 2, 3 SPC: Vendor 4

17. Field pH and LS distribution for Industrial Co-disposal Landfills (USA)

18. Comparison of Treatment Processes – Scenario: Industrial Co-disposal Landfill S/S: Vendors 2, 3 SPC: Vendor 4

19. Conclusions • The proposed leaching framework allowed • A good assessment of the efficacy of treatment processes for Hg contaminated mixed wastes • Comparison of estimated Hg release for a variety of management scenarios • Consideration of site-specific conditions • Insight into selection of acceptable management scenarios for each treatment process • The use of testing results in conjunction with assumed management scenarios and simple models leads to more realistic long-term release estimates than single batch test results

20. Acknowledgements • USEPA • Office of Solid Waste • Northeast Hazardous Substances Research Center • USDOE • TRU and Mixed Waste Focus Area (TMFA) • Consortium for Risk Evaluation with Stakeholder Participation (CRESP)