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 1 st, 2002 Nuclear Science and Technology Div. Department of Civil and Environmental Engineering Vanderbilt University Nashville, TN

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)

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

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

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) Untreated Am soil Th. desorpt: Vendor mg Hg/kg S/S: Vendor mg Hg/kg SPC: Vendor mg Hg/kg

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

Equilibrium Characterization Alkalinity, Solubility and Release as a Function of pH (SR002.1) 11 parallel solubility extractions DI with HNO 3 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 Particle sizeContact time < 300  m 18 hr < 2 mm48 hr < 5 mm 8 days

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

Mass Transfer Rate Characterization (MT00x.0) Two protocols  Monolithic (MT001.1)  Compacted granular (MT002.1) Deionized water leachant Liquid-surface area ratio  10 cm 3 /cm 2 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

Hg Release Rates (Untreated & SPC treated Hg-contaminated Soil)  D obs untreated Am soil = m 2 /s  D obs SPC treated Am soil = m 2 /s

Release Assessment: General Approach Treatment Option Mgmt Scenario Fundamental leaching properties Equilibrium data Site information* Assessment model Fundamental leaching properties Availability data, Equilibrium data, Mass Transfer data Site information* Assessment model Material No Yes Acceptable Impact? Release Estimate Exit YesNo Flow-aroundPercolation * Site-specific information or Default scenarios

Release Scenario: Percolation Seepage Basins V SxSx  Local equilibrium at field pH is rate limiting 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 

Release Scenario: Flow-around C sat Cs0Cs0 Roadbase material  Mass transport within solid matrix is rate limiting Scenario characteristics -Low permeability material -High infiltration rate -High liquid-surface area ratios Site information -Fill density -Fill geometry, -Fill porosity V a S

Release Estimates for Different Management Scenarios Vendor 3 treated Am soil

Vendor 4 treated Am soil Release Estimates for Different Management Scenarios

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

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

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

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

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)