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Metals Modeling

Metals Modeling. Summary of Process Equations and Model Input Data. Summary of Significant Heavy Metal Reactions. From Schnoor, et al., 1987. Free Ion. Soluble Complexes with Organic Ligands. Total Metal. Precipitates. Soluble Complexes with Inorganic Ligands. Adsorbed Species

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Metals Modeling

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  1. Metals Modeling Summary of Process Equations and Model Input Data

  2. Summary of Significant Heavy Metal Reactions WASP7 Course From Schnoor, et al., 1987.

  3. Free Ion Soluble Complexes with Organic Ligands Total Metal Precipitates Soluble Complexes with Inorganic Ligands • Adsorbed Species • Adsorption/Coprecipitation on hydrous iron/manganese oxides • Ion Exchange • Adsorption to clays, silicates, other minerals • Adsorption to organic solids From Felmy, et al., 1985. Speciation of Metals in Aquatic Environment WASP7 Course

  4. Metals Adsorption • An “adsorption reaction” is a reaction between a solute ion and a functional group (site) on a solid surface. • Important in attenuating dissolved metal concentration. • Use MINTEQA2 with adsorption reactions to calculate the distribution coefficient between adsorbed and dissolved phases. From Allison and Allison, 2004. MINTEQ course notes. WASP7 Course

  5. Adsorption in MINTEQA2 In MINTEQA2, adsorption reactions: • Are analogous to coordination reactions in solution. • Obey mass laws (mass action) • Include both physical and chemical solute-surface interactions (van der Waals forces, electrostatic attraction, valency forces). • Can be written as chemical “reactions” regardless of the mechanism. • Are thermodynamically distinct from solution reactions only when an electrostatic term is computed and applied separately. From Allison and Allison, 2004. MINTEQ course notes. WASP7 Course

  6. Adsorption Options in MINTEQA2 • Linear Partitioning model • Freundlich Isotherm • Langmuir Isotherm • Surface Complexation models: • Diffuse layer (i.e., MIT Two-Layer model) • Constant Capacitance • Triple Layer • Ion Exchange model From Allison and Allison, 2004. MINTEQ course notes. WASP7 Course

  7. Linear, Freundlich, and Langmuir Equations for: • Linear Partitioning: • Activity Kd Model • Freundlich Isotherm: • Activity Freundlich Model • Langmuir Isotherm: WASP7 Course From Allison and Allison, 2004. MINTEQ course notes.

  8. Sorption Model Comparison Comparison of Linear, Freundlich, & Langmuir Isotherms (after Stumm and Morgan, 1996; Morel, 1983) From Allison and Allison, 2004. MINTEQ course notes. WASP7 Course

  9. Free Ion Soluble Complexes with Organic Ligands Total Metal Precipitates Soluble Complexes with Inorganic Ligands • Adsorbed Species • Adsorption/Coprecipitation on hydrous iron/manganese oxides • Ion Exchange • Adsorption to clays, silicates, other minerals • Adsorption to organic solids Lumped Metals Partition Equation Cd, mg/L Cs, mg/L M, kg/L WASP7 Course

  10. ( ) calibration high flows NPS QNPS CNPS PS T or PS QT (hard inputs) CT MPS surface water Q KD ( ) adsorption/ precipitation hard input in headwaters QOUT QIN (calibration) CD CP hard input or fcn of v and size ( ) calibration high flows desorption/ dissolution scour deposition dispersion (calibration) adsorption CP CD bed sediment pore water desorption KD (calibration) ( ) calibration low flows GW QGWhard input CGW WASP Non-Reactive Metals Processes WASP7 Course From Caruso, 2005. CREM presentation

  11. Selection of TOXI Module for Simulating Metals • Non-Reactive Metals: Simple Toxicant Module • Ag, Ba, Be, Cd, Co, Cu, Mo, Ni, Pb, Sb, Tl, V, Zn • As, Cr, Se, Sn (if redox kinetics data unavailable) • Reactive Metals: Non-Ionizing Toxicant Module • As, Cr, Se, Sn (if redox kinetics data available) • Mercury: Mercury Module WASP7 Course

  12. Metals Data SpecificationSimple Toxicant Module • Constants • Log 10 partition coefficient to DOC, log (L/kg) • Partition coefficient to silts and fines, L/kg • Partition coefficient to sands, L/kg • Partition coefficient to organic solids, L/kg • Parameters • Dissolved organic carbon, mg/L • Partition coefficient to silts and fines, L/kg • Partition coefficient to sands, L/kg • Partition coefficient to organic solids, L/kg (KD values for constants, if any, take precedence over parameters) WASP7 Course

  13. Metals Data SpecificationNon-Ionizing Toxicant Module • Constants • Log 10 partition coefficients to DOC, log (L/kg) • Partition coefficients (to silts and fines, to sands, and to organic solids), L/kg • Oxidation rate constants (diss, sorb, DOC), M-1day-1 (or 1.0) • Oxidation mass yield coefficient (g/g) • Reduction rate constants (diss, sorb, DOC), M-1day-1 (or 1.0) • Reduction mass yield coefficient (g/g) • Parameters • Dissolved organic carbon, mg/L • Oxidant concentration, M, (or rate constant, day-1) • Reductant concentration, M, (or rate constant, day-1) WASP7 Course

  14. Partition Coefficients by Media (log KD in L/kg) From Allison and Allison, 2005 * Low / Median / High

  15. Partition Coefficients by Media (log KD in L/kg) From Allison and Allison, 2005 * Low / Median / High

  16. Partition Coefficients by Media (log KD in L/kg) From Allison and Allison, 2005 * Low / Median / High

  17. Partition Coefficients by Media (log KD in L/kg) From Allison and Allison, 2005 * Low / Median / High

  18. References • Allison, J.D., and Allison, T.L. 2004., MINTEQA2 Geochemial Speciation Workshop. Allison Geoscience Consultants, Inc., Buford, GA. • Allison, J.D., and Allison, T.L., 2005. Partition Coefficients for Metals in Surface Water, Soil, and Waste. U.S. EPA, Athens, GA. EPA/600/R-05-074. • Caruso, B. S., 2005. Modeling Metals Fate and Transport in the Upper Tenmile Creek Watershed Mining Area, Montana. CREM Presentation. • Felmy, A. et al., 1985. MINTEQ – A Computer Program for Calculating Aqueous Geochemical Equilibria. U.S. EPA, Athens, GA. EPA/600/3-84-032. • Schnoor, J.L., et al., 1987. Processes, Coefficients, and Models for Simulating Toxic Organics and Heavy Metals in Surface Waters. U.S. EPA, Athens, GA. EPA/600/3-87-015. WASP7 Course

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