Mercury Speciation in FGD: Assessing Transport and Bioavailability Risk

1. Mercury Speciation in FGD: Assessing Transport and Bioavailability Risk Kirk Scheckel1, Souhail Al-Abed1, Thabet Tolaymat1, Gautham Jegadeesan2, Aaron Williams1 & Bruce Ravel3 1 US EPA 2 Pegasus Technical Services 3 MR CAT

2. Atomic Molecular Microscopic Macroscopic Field The Research Continuum • XRF • XPS • XAS • Requires • synchrotron • radiation. • XRD • TGA • FTIR • DRS • Enhanced • Visual • Analysis: • 1. SEM • 2. TEM • 3. AFM • Field Plots • Equilibrium • Studies • Kinetic • Studies • Extractions • Visual/ • Intuitive • Insight • Field Plots Adaptation of Bertsch and Hunter, 1996.

3. Samples • FGD samples were provided from locations with historically high levels of Hg (up to ~ 2 ppm) • Simple density separation method to concentrate the Hg • Employed XAS and Mössbauer spectroscopies

4. Advanced Photon Source (Argonne National Laboratory, Argonne, IL)

5. Surface Reactions As3+ Principal Synchrotron Techniques Used in Environmental Science Arsenic on Bangladesh Biotite • X-ray Fluorescence (XRF): chemical composition (quantification, mapping) • X-ray Absorption Fine Structure (XAFS) Spectroscopy: chemical speciation (oxidation state, coordination, nearest neighbors) • Surface Scattering and Diffraction: surface structure, sorption processes • Microtomography: 3D imaging of internal microstructure (porosity, fluid flow, composition) Cl 495oC Copper Speciation in Fluid Inclusions 2.09Å Cu1+ Arsenic in Cattail Root Plaque

6. X-ray Absorption Spectroscopy: Measure energy-dependence of the x-ray absorption coefficient m(E) [either log(I0 /I) or (If / I0 )] of a core-level of a selected element X-ray Absorption Spectroscopy Element Specific: Elements with Z>20 can be examined. Valence Probe: XANES gives chemical state and formal valence of selected element. Local Structure Probe: EXAFS gives atomic species, distance, and number of near-neighbor atoms around a selected element.. Low Concentration: concentrations down to 10 ppm for XANES, 100 ppm for EXAFS. Natural Samples: samples can be in solution, liquids, amorphous solids, soils, aggregates, plant roots, surfaces, etc. Small Spot Size: XANES and EXAFS measurements can be made on samples down to ~5 microns in size. XANES = X-ray Absorption Near-Edge Spectroscopy EXAFS = Extended X-ray Absorption Fine-Structure

7. Cr(VI) is highly carcinogenic and highly mobile in ground water. Cr(III) is not carcinogenic or very toxic, and is not mobile in ground water. X-ray Absorption Near Edge Spectroscopy • Chemical state is critical in determining toxicity and mobility

8. Hg X-ray Absorption Spectroscopy Inflection point difference (IPD) Derivative

9. Hg X-ray Absorption Spectroscopy IPD = 6.3 - 6.5 eV Speciation: Hg(I)

10. sample mount Detector Sample Transducer 57 Fe* Mössbauer Spectroscopy

11. Isomer Shift Quadrupole Splitting Magnetic Splitting 298 K 4 K Nuclear Transitions Oxidation State Coordination # Oxidation State Site Symmetry Magnetic Properties Particles size Unperturbed Mössbauer Spectra What can we learn?

12. Fe Influence in FGD C. L. Kairies, K. T. Schroeder, C. R. Cardone. Mercury in gypsum produced from flue gas desulfurization. Fuel 85 (2006) 2530–2536

13. Fe Chemistry in FGD Top Layer 85% Ferrihydrite 15% Fe(III)-Clay

14. The 503 Rule

15. The 503 Rule

16. The 503 Rule Hazard Identification: Can this pollutant harm human health and/or the environment? Exposure Assessment: Who is exposed, how do they become exposed, and how much exposure occurs? Dose-Response Evaluation: If a person, animal or plant are exposed to this pollutant, what happens? Risk Characterization: What is the likelihood of an adverse affect in the population exposed to a pollutant under the conditions studied?

17. Consider the Amount of Hg 4’ X 8’ piece of drywall weighs 54 lbs (24.55 kg) Estimate 330 sheets of drywall for walls & ceilings Total drywall weight = 8106 kg If FGD contains 2 ppm Hgmax = 0.016 kg or 0.036 lbs of Hg The “what-if”Katrina Effect: 100,000 homes 640 Ac/mile2 Land Application: 40 Ac X 2 T/Ac = 80 tons of FGD Could have as much as 0.15 kg or 0.32 lbs of Hg 40 Ac

18. Consider the Amount of Hg Land Application of FGD with 2 ppm Hg: Application rate @ 2 tons/Ac yields 0.0036 kg Hg/Ac One acre furrow slice (20 cm) weighs 1,052,183 kg One application results in 0.00035 mg Hg/kg soil 347 applications would approach the non-residential clean-up standard of 0.12 mg Hg/kg soil. This does not account for Hg loss.

19. Hg Loss from Land Application Carpi, A., Lindberg, S.E. (1997) "Sunlight-Mediated Emission of Elemental Mercury from Soil Amended with Municipal Sewage Sludge," Environmental Science & Technology 31(7):2085-2091. Hourly Hgo emissions from a sludge amended soil plot over    24-hrs.  Hgo emissions were more strongly correlated with    solar radiation than soil temperature.  Peak background soil    Hgo emissions at the same site were < 25 ng m-2 hr-1.

20. Conclusions • Hg speciation can be characterized as Hg(I) in a high Fe matrix; perhaps a direct association with Fe oxides or a Hg-C-Fe oxide ligand bridge • Fe chemistry in FGD consists of ferrihydrite and clay-based Fe likely from the CaCO3 source • Can the addition of Fe enhance the FGD process? • Hg can be easily concentrated via water separation – Erosion? • The objectives of Rule 503 are not geared towards land application of FGD material • Loss from microbial, solar radiation, and dust must be understood

21. Discussion/Questions