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Sorption Reactions

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Sorption Reactions

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    1. Sorption Reactions Pierre Glynn, USGS, March 2003

    2. Sorption processes Depend on: Surface area & amount of sorption “sites” Relative attraction of aqueous species to sorption sites on mineral/water interfaces Mineral surfaces can have: Permanent structural charge Variable charge

    3. Semi-empirical models

    9. Thermodynamic Speciation-based Sorption Models

    10. Sorption on permanent charge surfaces: “Ion exchange” Occurs in clays (smectites), zeolites Sorption on variable charge surfaces: “Surface complexation” Occurs on Fe, Mn, Al, Ti, Si oxides & hydroxides, carbonates, sulfides, clay edges.

    11. ION EXCHANGE MODELS

    12. Ion Exchange Calcs. (#1)

    13. Ion Exchange (#2)

    14. Ion Exchange (#3)

    17. Exercise S2

    18. S2 Questions What happens to the brine as a result of the mineral equilibration? What is the Na/Ca mole ratio in the brine before and after mineral equilibration? What is the Na/Ca mole ratio on the exchanger in equilibrium with the calcite and dolomite equilibrated brine? Bonus: What about the Mg/Ca ratios? What about proton exchange? Are the pH and aqueous concentrations affected by the exchange equilibrium? pH drops to 5.35 from 5.7. Dolomite dissolves. Calcite precipitates. 11.60; 11.63 43 ??; it occurs; nopH drops to 5.35 from 5.7. Dolomite dissolves. Calcite precipitates. 11.60; 11.63 43 ??; it occurs; no

    19. S2 Questions (cont) Re-equilibrate the calcite-and-dolomite equilibrated brine (trhe saved solution 1) with an exchanger that has 0.125 moles CaX2, 0.125 moles MgX2 and 0.5 moles NaX. How is the aqueous solution affected by the equilibration with the exchanger? What is the ionic strength of the brine? Is PHREEQC appropriate for this type of calculation? How are the activities of Na+ and Ca+2 species related to their total concentrations What is the model assumed for the activity coefficients of the sorbed species? ?? ??

    20. Ion Exchange: thermo. concepts (#1)

    21. Ion Exchange: thermo. concepts (#2)

    22. Ion Exchange: thermo. concepts (#3)

    23. Ion Exchange: thermo. concepts (#4)

    26. Ion Exchange & Transport (#1)

    27. Ion Exchange & Transport (#2)

    31. Ionic strength & sorbent effects on ion exchange

    34. Ion exchange: final remarks

    36. Surface Complexation Models

    37. Fully considers variable charge surfaces. # of sorption of sites is constant but their individual charge, & total surface charge, vary as a function of solution composition Similar to aqueous complexation/speciation A mix of anions, cations & neutral species can sorb Accounts for electrostatic work required to transport species through the “diffuse layer” (similar to an activity coefficient correction) ? Gouy-Chapman theory Surface Complexation Principles

    46. Gouy-Chapman Double-Layer Theory

    52. Surface complexation equations

    54. Surface Complexation Calcs. (#1)

    55. Surface Complexation (#2)

    56. Surface complexation (#3)

    57. Sorption parameters for HFO (from Dzombak & Morel, 1990)

    62. Thermodynamic and printing toolbars

    63. USER_PUNCH keyword

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