Presentation on theme: "Mercury Speciation in FGD: Assessing Transport and Bioavailability Risk Kirk Scheckel 1, Souhail Al-Abed 1, Thabet Tolaymat 1, Gautham Jegadeesan 2, Aaron."— Presentation transcript:
Mercury Speciation in FGD: Assessing Transport and Bioavailability Risk Kirk Scheckel 1, Souhail Al-Abed 1, Thabet Tolaymat 1, Gautham Jegadeesan 2, Aaron Williams 1 & Bruce Ravel 3 1 US EPA 2 Pegasus Technical Services 3 MR CAT
AtomicMolecularMicroscopicMacroscopicField Field Plots Equilibrium Studies Kinetic Studies Extractions Enhanced Visual Analysis: 1. SEM 2. TEM 3. AFM Visual/ Intuitive Insight Field Plots XRD TGA FTIR DRS XRF XPS XAS Requires synchrotron radiation. Adaptation of Bertsch and Hunter, 1996. The Research Continuum
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
Advanced Photon Source (Argonne National Laboratory, Argonne, IL)
Principal Synchrotron Techniques Used in Environmental Science 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) Surface Reactions Arsenic on Bangladesh Biotite As 3+ Arsenic in Cattail Root Plaque 495 o C Cl 2.09Å Cu 1+ Copper Speciation in Fluid Inclusions
X-ray Absorption Spectroscopy: Measure energy-dependence of the x-ray absorption coefficient (E) [either log(I 0 /I) or (I f / I 0 )] of a core-level of a selected element Element Specific: Elements with Z>20 can be examined. EXAFS = Extended X-ray Absorption Fine-Structure XANES = X-ray Absorption Near-Edge Spectroscopy Valence Probe: XANES gives chemical state and formal valence of selected element. Natural Samples: samples can be in solution, liquids, amorphous solids, soils, aggregates, plant roots, surfaces, etc. Low Concentration: concentrations down to 10 ppm for XANES, 100 ppm for EXAFS. Small Spot Size: XANES and EXAFS measurements can be made on samples down to ~5 microns in size. Local Structure Probe: EXAFS gives atomic species, distance, and number of near-neighbor atoms around a selected element.. X-ray Absorption Spectroscopy
X-ray Absorption Near Edge Spectroscopy Chemical state is critical in determining toxicity and mobility 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.
SampleDetectorTransducer 57 Fe* sample mount Mössbauer Spectroscopy
What can we learn? Mössbauer Spectra Isomer Shift Quadrupole Splitting Magnetic Splitting Oxidation State Coordination # Oxidation State Site Symmetry Unperturbed Magnetic Properties Particles size 298 K 4 K Nuclear Transitions
C. L. Kairies, K. T. Schroeder, C. R. Cardone. Mercury in gypsum produced from flue gas desulfurization. Fuel 85 (2006) 2530–2536 Fe Influence in FGD
Fe Chemistry in FGD Top Layer 85% Ferrihydrite 15% Fe(III)-Clay
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? The 503 Rule
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 Hg max = 0.016 kg or 0.036 lbs of Hg The what-ifKatrina Effect: 100,000 homes 640 Ac/mile 2 40 Ac 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
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.
Hourly Hg o emissions from a sludge amended soil plot over 24-hrs. Hg o emissions were more strongly correlated with solar radiation than soil temperature. Peak background soil Hg o emissions at the same site were < 25 ng m-2 hr-1. 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.Environmental Science & Technology Hg Loss from Land Application
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 CaCO 3 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
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