EXPERIENCE WITH ALTERNATIVE LEACHING PROTOCOLS FOR MERCURY-BEARING WASTE

Florence Sanchez, Ph.D.David S. Kosson, Ph.D.

Catherine H. MattusMichael I. Morris

Breaking the Mercury Cycle: Long Term Management of Surplus & Recycled Mercury and Mercury-Bearing Waste

Boston, May 1st, 2002

Nuclear Science and Technology Div.

Department of Civil and Environmental Engineering

Vanderbilt UniversityNashville, 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 modesand fundamentalleaching parameters

Design test methods tomeasure fundamentalparameters

Test waste

Calculate release based onmanagement scenario(s)and field conditions• default scenarios• site-specific conditions

Evaluate acceptance basedon 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 14.6 mg Hg/kg

S/S: Vendor 2

1840 mg Hg/kg

SPC: Vendor 4

997 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 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

Particle size Contact time

< 300 m 18 hr

< 2 mm 48 hr

< 5 mm 8 days

Hg solubility as a function of pH

Thermal desorption: Vendor 1S/S: Vendors 2, 3SPC: Vendor 4

SR002

TCLP

0.00001

0.0001

0.001

0.01

0.1

1

10

100

0 2 4 6 8 10 12 14pH

Hg

[mg

/L]

--- DL=0.05g/L--- TCLP limit=0.2mg/L

pH 8.4

Vendor 1 treated Am soil

0.00001

0.0001

0.001

0.01

0.1

1

10

100

0 2 4 6 8 10 12 14pH

Hg

[mg

/L]

pH 12.7

--- DL=0.05g/L--- UTS TCLP limit=0.025mg/L

Vendor 2 treated Eu soil

0.00001

0.0001

0.001

0.01

0.1

1

10

100

0 2 4 6 8 10 12 14pH

Hg

[mg

/L]

-- TCLP limit=0.2mg/L

pH 6.8

--- DL=0.05g/L

Untreated Am soil

0.00001

0.0001

0.001

0.01

0.1

1

10

100

0 2 4 6 8 10 12 14pH

Hg

[mg

/L]

pH 10.2

--- DL=0.05g/L--- UTS TCLP limit=0.025mg/L

Vendor 3 treated Am soil

0.00001

0.0001

0.001

0.01

0.1

1

10

100

0 2 4 6 8 10 12 14pH

Hg

[mg

/L]

pH 9.7

--- DL=0.05g/L-- UTS TCLP limit=0.025mg/L

Vendor 4 treated Am soil

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

GranularMonolithic GranularMonolithic

Cumulative release as a function of time

Hg Release Rates (Untreated & SPC treated Hg-contaminated Soil)

Dobs untreated Am soil = 9.8 10-16 m2/s Dobs SPC treated Am soil = 8.9 10-18 m2/s

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0.1 10 1000 100000

t [hr]H

g F

lux

[mg

/m2 s]

Vendor 4 treated Am soil

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

0.1 10 1000 100000

t [hr]

Hg

Flu

x [m

g/m

2 s]

Untreated Am soil

Release Assessment: General Approach

Treatment Option

MgmtScenario

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

AcceptableImpact?

Release Estimate

ExitYesNo

Flow-aroundPercolation

* Site-specific information or Default scenarios

Release Scenario: Percolation

Seepage Basins

V

Sx

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

Csat

Cs0

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

VaS

Release Estimates for Different Management Scenarios

0.009%0.208 mg/kg

100%2410 mg/kg

0.002%0.06 mg/kg

0.0003%0.007 mg/kg

7.7%185 mg/kg

0.004%0.09 mg/kg

0.0001

0.001

0.01

0.1

1

10

100

1000

10000

Total content TCLP Nat pH 10.2(LS_exp=10)Percolation-Controlled

Nat pH (LS_exp=0.5)Percolation-Controlled

pH 4.4 (LS_exp=10)Percolation-Controlled

pH 9.1 (LS_exp=10)Percolation-Controlled

Masstransfer-Controlled

Me

rcu

ry r

ele

as

e [

mg

/kg

]

% of total content released

a b c

0.005%0.12 mg/kg

a'

Vendor 3 treated Am soil

0.2%1.9 mg/kg

0.4%4.1 mg/kg

0.5%5.1 mg/kg

0.09%0.85 mg/kg

100%997 mg/kg

0.01

0.1

1

10

100

1000

10000

Total content TCLP Nat pH 9.7(LS_exp=10)Percolation-Controlled

Nat pH 10.1(LS_exp=0.5)Percolation-Controlled

pH 4.8(LS_exp=10)Percolation-Controlled

pH 9.7(LS_exp=10)Percolation-Controlled

Masstransfer-Controlled

Me

rcu

ry r

ele

as

e [

mg

/kg

]

% of total content released

a b

0.5%5.1 mg/kg

0.1%1.2 mg/kg

a' c

Vendor 4 treated Am soil

Release Estimates for Different Management Scenarios

Comparison of Treatment Processes

S/S: Vendors 2, 3SPC: Vendor 4

Min-Max0.3-1.7% Min-Max

0.4-0.5%

Min-Max0.2-3.2%

0

5

10

15

20

25

30

Untreat.Am soil

Untreat.Eu soil

Vendor3

Vendor4

Vendor2

%

Min-Max0.0003-7.7%

Min-Max0.001-29.6%

Percolation scenario

0.4%0.4%

0.004%0

0.2

0.4

0.6

0.8

1

1.2

1.4

Untreat.Am soil

Untreat.Eu soil

Vendor3

Vendor4

Vendor2

%

1.2%

0.2%

Diffusion scenario

0.04%

0.002%0

0.05

0.1

0.15

0.2

0.25

0.3

Untreat.Am soil

Untreat.Eu soil

Vendor3

Vendor4

Vendor2

%

0.2%

0.04%

0.09%

TCLP

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

Distribution for Field pHScenario: Industrial Codisposal Landfill -

n = 455

Mean = 6.9

X <= 5.75%

X <= 7.695%

0

0.2

0.4

0.6

0.8

1

4.5 5 5.5 6 6.5 7 7.5 8

pH

Pro

bab

ility

Distribution for LS_Site [L/kg] (100 years)Scenario: Industrial Codisposal Landfill -

n = 41

Mean = 21.6

X <= 93.595%

X <= .065%

0

0.2

0.4

0.6

0.8

1

0 25 50 75 100 125 150 175 200

LS ratio [L/kg]

Pro

bab

ility

Comparison of Treatment Processes – Scenario: Industrial Co-disposal Landfill

S/S: Vendors 2, 3SPC: Vendor 4

0.01

0.1

1

10

100

1000

10000

0 20 40 60 80 100

Percentile

Mer

cury

rel

ease

[m

g/k

g]

Vendor 2 Vendor 3 Vendor 4 Untreated Am soil

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)