mercury and istd: research overview and...

Mercury and ISTD: Research Overview and Perspectives

Lynn Katz, Justin Davis and Howard Liljestrand

University of Texas at Austin

Mercury is one of the most common metals identified at Superfund sites

Mercury Exposure & Toxicity

MeHg Biomagnification

SpeciesImportant

Exposure Pathway

Hg0 Inhalation

MeHg Ingestion

• Hg0 and MeHg are NEURO- and NEPRHOTOXINS

• Facile tissue transport of MeHg:• Causes biomagnification up the food chain• Makes MeHg an important teratogen

Sakamoto, M. et al. (2012), Environmental chemistry and toxicology of mercury, 501‐516.

Chemical Propertie

s

Inorganic Mercury Organic Mercury

Hg0 HgCl2 HgS CH3HgCl (CH3)2Hg

M.W. [g/mol] 200.59 271.50 232.65 251.08 230.66

Melting Point [°C] -38.87 276 583.5 170 ─

Boiling Point [°C] 356.9 302 ─ ─ 93

Density at 20°C [g/mL] 13.546 5.44 at 25°C 7.73 – 8.10 4.06 at 20°C 3.07

Vapor Pressure [mmHg] 1220 at 20°C 834000 at 25°C ─ 4700 at 20°C58.6 at 23.7°

C

Solubility in H2O [g/L] 5.6 x 10-5 at 25°C 69 at 20°C 10-5 at 18°C 0.1 at 21°C 1 at 21°C

KOW 4.15 3.33 ─ 1.7 182

Common Forms of Hg

• Elemental Hg is a DNAPL• Elemental Hg and HgCl2 are

volatile• HgCl2 is soluble• Hg speciation includes both

inorganic and organic forms• Organic mercury bioaccumulates

Key Points that affect remediation

Aqueous Speciation of Hg(II) in Aerobic Environments

With DOM

With [S=] + DOM

freshwater conditions

marine conditions

polysulfides absent

DOM speciationDominates except at high [S2‐]

Skyllberg, U. (2012), Environmental chemistry and toxicology of mercury, pg 219

Inorganic Speciation in Water

USGS, http://infotrek.er.usgs.gov/doc/mercury/images/mercury_cycle.gif

Biogeochemical Cycling

Hg(HS)20

FeOOH

OM

FeS

Hg2+

KFeO

KOM

KFeSHgS0

HgS2H-

Nano- HgS

CH3Hg+

Cl-

OM

24 SO

-HS

Solid phase

Aqueous phase

Non-bioavailable Bioavailable

• Methylation is an accidental byproduct of microbial activity – sulfate reducing bacteria

• Mercury-sulfur speciation is the key to understanding mercury methylation and affects a) bioavialability and b) mercury solubility

HgS(s)(cinnabar)

Mercury Speciation (Sulfate Reduction)

• Mercury vs. methyl mercury (MeHg)

• Methylation is an accidental byproduct of microbial activity

Inorganic Mercury Methyl Mercury

Solid

Pha

seA

queo

us p

hase

Hg2+

OM

FeOOH

FeS

– sulfate reducing bacteria

Methylation Paradigm

Solid

Pha

seA

queo

us p

hase

Hg2+

OM

FeOOH

FeS

Hg-NOM

Hg(SH)20

HgS0

HgS2H-

HgS22-

uncharged, bioavailable

mercury-sulfide

Methylation Paradigm

• Mercury vs. methyl mercury (MeHg)

• Methylation is an accidental byproduct of microbial activity

Inorganic Mercury Methyl Mercury

– sulfate reducing bacteria

Sources of Hg to Aquatic Systems

Sources of Hg emission

USGS, http://infotrek.er.usgs.gov/doc/mercury/images/hg_deposition.gif

US EPA Mercury Study Report to Congress, 1997

Atmospheric Deposition

Sources of Mercury Emissions in the U.S.

Industrial Category 1990 Emissions (tpy)

2005 Emissions (tpy)

Percent Reduction

Power Plants 59 53 10%

Municipal Waste Combustors 57 2 96%

Medical Waste Incinerators 51 1 98%

• Chlor-alkali plants have phased out Hg cells in favor of membranes

• More stringent regulations promoting control technologies such as:o Selective catalytic reduction with flue-gas desulfurization (SCR-

FGD)o Activated carbon injection (ACI) with fabric filter (FF) or

electrostatic precipitators (ESP)

• Medical industry phase-out of mercury thermometers

http://www.ehjournal.net/content/8/1/2http://www.epa.gov/mats/powerplants.html

Emission Reductions

Atmospheric deposition has decreased…

Provide constant flux to ground & surface waters

But legacy deposition and mining sites have left

contaminated soils & sediments

Stumm, W., & Morgan, J.J. (1996), Aquatic chemistry: chemical equilibria and rates in natural wat

Groundwater Communication

Davis, J. (2012), EWRE Seminar, University of Texas at A

Davis, J (2012)

Diverse Site Speciation: Solid & Liquid Phases

Ligand binding strength: Hg–S >> Hg–N ≈ Hg–O > Hg–Cl

Enhanced stability of NOM:

strong linear bridge with weaker contributions from C, N or O ligands

NOM is important in both pore water and solid speciation:WHENEVER ORGANIC MATTER IS PRESENT, IT TENDS TO DOMINATE

Hg(SR)2, α‐HgS, β‐HgS & thermodynamically favored

Skyllberg, U. (2006), Environmental Science & Technology, 40(13), 4174‐4180

Binding Strength & Stability of Hg–S

1. Electro-remediation• Description

o Uses electrodes to form and extract metal complexeso Electromigration, electroosmosis and electrophoresis

• Advantageso In-situ, chemical-free treatabilityo Permanent removal of Hgo Simultaneous treatment of other metalso Effective for soils of low hydraulic permeability

• Disadvantageso Interference by non target ionso Separation of HgS, generating larger waste volumeso May require chemical addition if Hg0 dominates speciation

(low solubility in soils)

Cabrejo, E., et al. (2010), http://www.clu-in.org/download/contaminantfocus/mercury/mercury-cabrejo-2010.pdfWang, J. ,et al.(2012). Journal of Hazardous Materials, 221–222(0), 1–18.

Potential Remediation Technologies

2. Stabilization/solidification• Description

o Promotes formation of stable HgS or solidified in sulfur polymer cement

• Advantageso In-situ, low cost treatabilityo Waste volume reduction

• Disadvantageso Hg is not removed from the soil columno Long-term monitoring may be required



3. Nanotechnology• Description

o Uses FeS nanoparticles to immobilize Hg

• Advantageso In-situ, low cost, low energy treatabilityo No additional waste volume

• Disadvantageso Effects of soil pH need to be determinedo Effects on soil microorganisms need to be determined



4. Phytoextraction• Description

o Uses living plant roots to extract Hg from contaminated soils

• Advantageso In-situ, low cost, low energy treatabilityo Permanent removal of Hgo No additional waste volume reduction

• Disadvantageso Effective only remediates surface soilso No hyperaccumulator plant species have been identifiedo Chemical additives may be required for effective removal



From 1950-1982 estimates of 240,000 pounds of mercury released from Y-12 to Upper East Fork Poplar Creek. An estimated 2 million pounds of mercury was unaccounted for.

0.00 – 0.99 mg/kg

1.0 – 9.9 mg/kg

10.0 – 99.9 mg/kg

100.0 – 7700 mg/kg

Oak Ridge Y-12

Wang, J. ,et al.(2012). Journal of Hazardous Materials, 221–222(0), 1–18.

Thermal Desorption

[1] M. Morris, et al., Bench‐and Pilot‐Scale Demonstration of Thermal Desorption for Removal of Mercury from the Lower East Fork Poplar Creek Floodplain Soils CONF‐950216‐129, Martin Marietta Energy Systems, Oak Ridge, TN, 1995.[2] C. George et al. Evaluation of steam as a sweep gas in low temperature thermal desorption processes used for contaminated soil clean up, Waste Manage. 15 (1995) 407–416.[3] C.R. Palmer, Removal of mercury using the X‐TRAX thermal desorption system,in: Proceedings of the International Conference on Incineration and Thermal Treatment Technologies, University of California, OEHS,, Irvine, CA, 1996.[4] ITRC, Technical Guidelines for On‐Site Thermal Desorption of Solid Media andLow Level Mixed Waste Contaminated with Mercury and/or Hazardous ChlorinatedOrganics Final Report, ITRC Work Team of Low Temperature ThermalDesorption, Washington, DC, 1998.[5] P. Massacci et al., Applications of physical and thermal treatment for the removal of mercury from contaminated materials, Miner. Eng. 13 (2000) 963–967.[6] DOE, The SepradyneTM‐Raduce System for Recovery of Mercury from MixedWaste DOE/EM‐0633, DOE Office of Environmental Management and Officeof Science and Technology, Washington, DC, 2002.[7] C. Washburn and E. Hill, Mercury retorts for the processing of precious metals and hazardous wastes, JOM J. Min. Met. Mater. Soc. 55 (2003) 45–50.

Wang, J. ,et al.(2012). Journal of Hazardous Materials, 221–222(0), 1–18.

Thermal Desorption

[8] T. Chang et al., On‐site mercury‐contaminated soils remediation by usingthermal desorption technology, J. Hazard. Mater. 128 (2006) 208–217.[9] A.M. Kunkel et al., , Remediation of elemental mercury using in situ thermal desorption (ISTD), Environ. Sci. Technol. 40 (2006) 2384–2389.[10] F. Taube, L. et al. Soil remediation – mercury speciation in soil and vapor phase during thermal treatment, Water Air Soil Pollut. 193 (2008) 155–163.[11] R. Kucharski, et al., A method of mercury removal from topsoil using low‐thermal application, Environ. Monit. Assess. 104 (2005) 341–351.[12] B. Lesa et al. Bench‐scale tests on ultrasoundassisted acid washing and thermal desorption of mercury from dredging sludge and other solid matrices, J. Hazard. Mater. 171 (2009) 647–653.[13] A. Navarro et al. , Application of solar thermal desorption to remediation of mercury‐contaminated soils, Sol. Energy 83 (2009) 1405–1414.[14] Y. Busto, X. Cabrera, F.M.G. Tack, M.G. Verloo, Potential of thermal treatmentfor decontamination of mercury containing wastes from chlor‐alkali industry,J. Hazard. Mater. 186 (2011) 114–118.[15] Y.T. Huang et al. Influences of thermal decontamination on mercury removal, soil properties, and repartitioning of coexisting heavy metals, Chemosphere 84 (2011) 1244–1249.

Why thermal desorption works:

1.E-071.E-061.E-051.E-041.E-031.E-021.E-011.E+001.E+011.E+021.E+03

1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9

PRES

SUR

E (m

m H

g)

1000/T [1000/K ]

PCB 1242TCDD

PCB 1260

Water

Mercury

BenzeneTCE

Naphthalene

PCE

n-C16H34

n-C29H60

PCP

As

n-C10H22

Dieldrin

Pb Zn

TELB(a)Pyrene

CdCl2

As2O3

Sb

SbCl3

T oC

Hg0 HgCl2pVap (mm

Hg)1.22E3 @ 20

°C8.34E5 @ 25

°CStegemeier, G. L., & Vinegar, H. J. (2000), Hazardous and radioactive waste treatment technologies handbook (pp. 4.6–1 – 4.6–38)

In-situ Thermal Desorption

Experimental Evaluation

Thermal Remediation

Off‐Gas Treatment

Courtesy of George Stegemeier

Influent Flow Meter

Pressurized Air Source

Mechanical Connect ionsInsulated RegionTemperature

Logger

Heater

Heater

Heater

Sample Vialcontains

5% HNO3/10%H2O2

Silica Gel

Impinger 3 4% KMnO4/10%H2SO4

Impinger 15% HNO3/10% H2O2

Impinger 24% KMnO4/10%H2SO4

HeaterCondenser

Influent Flow Meter

Pressurized Air Source

Mechanical Connect ionsInsulated RegionMechanical Connect ionsInsulated RegionTemperature

Logger

Heater

Heater

Heater

Sample Vialcontains

5% HNO3/10%H2O2

Silica Gel

Impinger 3 4% KMnO4/10%H2SO4

Impinger 15% HNO3/10% H2O2

Impinger 24% KMnO4/10%H2SO4

HeaterCondenser

Experimental Evaluation

Thermal Remediation

Off‐Gas Treatment

Courtesy of George Stegemeier

0.001

0.01

0.1

1

10

1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5Temperature (1000/°K)

Vapo

r Pre

ssur

e (a

tm)

C10F18correlation (29)

Mercury data(30)

C10F18 data

Temperature (°C)

394 315 253 203 162 127 97 72 49 30 13

Vapor Pressure-Temperature Correlations

Perfluorodecalin can be used as a surrogate for elemental mercury

Kunkel, A. M. et al. (2006), Environmental Science & Technology, 40(7), 2384‐2389.

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8Normalized Cumulative Volume (L/mmol)

Nor

mal

ized

Mas

s Fr

actio

n R

ecov

ered

Experiment PFD7

Experiment PFD11

Experiment Hg3

Experimental Evaluation: Controlled Experiments

T = 69.5 C

T = 69.7 C

T = 244 C

Elemental mercury removal compared to STARS simulation

Kunkel, A. M. et al. (2006), Environmental Science & Technology, 40(7), 2384‐2389.

Experimental Evaluation: Controlled Experiments

Two approaches:

1. Thermodynamic modeling

2. Standard thermo-desorption curves

Experimental Approach: Field Samples

Speciation determined by comparing thermal desorption of field soils to thermodynamic modeling (FactSage)

Taube, F. et al. (2008), Water, Air, & Soil Pollution, 193(1), 155–163.

Experimental Approach: Field Samples

Speciation using thermodynamic modeling

Mod

el p

aram

eter

s:

Model species

Soil composition

Mercury (M) Inorganic ligands (M) Redox condition

Hg2+ Hg22+ Cl‐ S as HS‐ S as SO42‐ pe

Hg(l) 2.4 9.0e‐7 < 1.0e‐1 ‐ ‐ < 4.4

HgS(s) 2.4 1.0e‐8 ‐ 1.0e‐3 ‐ ‐5

HgCl2(s) 2.4 1.0e‐8 8.9 ‐ ‐ > 15

Phase transition simulation of Hg(ℓ)

0.00E+00

4.00E-07

8.00E-07

1.20E-06

1.60E-06

2.00E-06

273.15 293.15 313.15 333.15 353.15 373.15

mol

es o

f Hg

in v

apor

pha

se

Temperature (K)

Hg(l) → Hg(g)Hg(l)→ Hg(g)

(a)

0.0E+00

2.0E-04

4.0E-04

6.0E-04

8.0E-04

1.0E-03

1.2E-03

273.15 303.15 333.15 363.15 393.15 423.15

mol

es o

f Hg

in v

apor

pha

se

Temperature (K)

HgS(s) → Hg(g)HgS(s)→ Hg(g)

(b)

Phase transition simulation of HgS(s)

Park, C. M. (2011), http://repositories.lib.utexas.edu/handle/2152/ETD‐UT‐2011‐12‐4533

Experimental Approach: Environmental Samples

Speciation using thermodynamic modeling

33

Phase transition simulation of HgCl2(s)

0

0.1

0.2

0.3

0.4

273.15 293.15 313.15 333.15 353.15 373.15

mol

es o

f Hg

in v

apor

pha

se

Temperature (K)

HgCl2(s) → HgCl2(g)HgCl2(s)→ HgCl2(g)

(c)

Park, C. M. (2011), http://repositories.lib.utexas.edu/handle/2152/ETD‐UT‐2011‐12‐4533

Experimental Approach: Environmental SamplesM

odel

par

amet

ers:

Model species

Soil composition

Mercury (M) Inorganic ligands (M) Redox condition

Hg2+ Hg22+ Cl‐ S as HS‐ S as SO42‐ pe

Hg(l) 2.4 9.0e‐7 < 1.0e‐1 ‐ ‐ < 4.4

HgS(s) 2.4 1.0e‐8 ‐ 1.0e‐3 ‐ ‐5

HgCl2(s) 2.4 1.0e‐8 8.9 ‐ ‐ > 15

Speciation using standard thermo-desorption curves

Probability distributions of thermally desorbed standards

Biester, H. et al. (2002), Science of The Total Environment, 284(1–3), 191–203.



Biester, H., & Nehrke, G. (1997), Fresenius’ Journal of Analytical Chemistry, 358(3), 446–452.Biester, H., & Scholz, C. (1997), Environmental Science and Technology, 31(1), 233–239.



Eddy-Dilek, C. et al. (2012), Remediation of Chlorinated and Recalcitrant Compounds Conference


Traditional scrubbing techniquesWet scrubbing

Activated carbon injectionSulfur-impregnated activated carbon

Gold amalgamation

Advanced scrubbing techniquesSilver-promoted molecular sieves

Metal-sulfide systems

Soelberg, N. et al.. (2007), http://www.inl.gov/technicalpublications/Documents/3693725.pdfEckersley, N. (2010). Hydrocarbon processing, 89(1).;Chambers, A. et al. (1997), http://www.osti.gov/bridge/product.biblio.jsp?osti_id=663460

Post-treatment: Scrubbing

Thermal desorption kiln

Cooling water

recycle

Condensation water separation

Sulfur-impregnated

activated carbon

Air effluent

Coagulation Dewatering

Buffer

Sulfur-impregnated

activated carbon

Water effluent

Chang, T. C., & Yen, J. H. (2006), Journal of Hazardous Materials, 128(2–3), 208–217.

Post-treatment: Schematic

Post-treatment Remediation: Hg(II) Adsorbtion to Fe Oxides

Where do we go from here?1. Obtain more experimental data regarding:

• Speciation effects• Matrix-binding effects (e.g. FeS–Hg, NOM–Hg)• Mixed-Waste

2. Perform mechanistic analyses, account for variation among similar species

3. Validate and improve thermodynamic models

4. Improve field characterization methods

5. Perform optimization studies

6. Construct pilot projects

Future Work

Acknowledgements

Gary Pope, PGE

Graduate Students: Anna Kunkel, Ricci Lampert, Jeremy Siebert, Chang Min Park, Jeremiah Mangold

Terratherm, George Stegemeier, Harold Vinegar