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Monday-Tuesday. Solutions Thermodynamics of aqueous solutions Saturation indices Mineral equilibria Cation exchange Surface complexation Advective transport Diffusive transport Acid mine drainage. 1. Carbonate reactions 2. Ion exchange 3. Organic carbon oxidation

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Monday tuesday
Monday-Tuesday

  • Solutions

    • Thermodynamics of aqueous solutions

    • Saturation indices

  • Mineral equilibria

  • Cation exchange

  • Surface complexation

  • Advective transport

  • Diffusive transport

  • Acid mine drainage


Processes that control major element chemistry

1. Carbonate reactions

2. Ion exchange

3. Organic carbon oxidation

O2/Nitrate reduction

Iron oxyhydroxide reduction

Sulfate reduction

Methanogenesis

4. Pyrite oxidation

5. Gypsum dissolution

6. Seawater evaporation

7. Silicate weathering

Processes that Control Major Element Chemistry


Processes that control minor element chemistry

  • 1. Redox

  • Oxyanions

  • Trace metals

  • Nitrate

  • 2. Surface complexation

    • Phosphate

  • Oxyanions

  • Trace metals

  • 3. Cation exchange

  • 4. Solid solutions

  • 5. Minerals

  • Processes that Control Minor Element Chemistry


    Phreeqc programs
    PHREEQC Programs

    • PHREEQC Version 3

      • PHREEQC: Batch with Charting

      • PhreeqcI: GUI with Charting

      • IPhreeqc: Module for programming and scripting

    • PHAST

      • Serial—soon to be Multithreaded

      • Parallel—MPI for transport and chemistry

      • TVD (not done)

      • 4Windows—GUI just accepted

    • WEBMOD-Watershed reactive transport


    Solution definition and speciation calculations

    Na

    SO4

    Ca

    Mg

    Fe

    Cl

    HCO3

    Reactions

    Saturation Indices

    Inverse Modeling

    Transport

    Solution Definition and Speciation Calculations

    Speciation calculation




    Initial solution 1 questions
    Initial Solution 1. Questions

    • What is the approximate molality of Ca?

    • What is the approximate alkalinity in meq/kgw?

    • What is the alkalinity concentration in mg/kgs as CaCO3?

    • What effect does density have on the calculated molality?

    PHREEQC results are always moles or molality


    Initial solution 1
    Initial Solution 1.

    For most waters, we can assume most of the mass in solution is water. Mass of water in 1 kg seawater ~ 1 kg.

    • 412/40 ~ 10 mmol/kgw ~ 0.01 molal

    • 142/61 ~ 2.3 meq/kgw ~ 0.0023 molal

    • 2.3*50 ~ 116 mg/kgw as CaCO3

    • None, density will only be used when concentration is specified as per liter.


    Default gram formula mass
    Default Gram Formula Mass

    Default GFW is defined in 4th field of SOLUTION_MASTER_SPECIES in database file.


    Databases
    Databases

    • Ion association approach

      • Phreeqc.dat—simplest (subset of Wateq4f.dat)

      • Amm.dat—same as phreeqc.dat, NH3 is separated from N

      • Wateq4f.dat—more trace elements

      • Minteq.dat—translated from minteq v 2

      • Minteq.v4.dat—translated from minteq v 4

      • Llnl.dat—most complete set of elements, temperature dependence

      • Iso.dat—(in development) thermodynamics of isotopes

    • Pitzer specific interaction approach

      • Pitzer.dat—Specific interaction model (many parameters)

    • SIT specific interaction theory

      • Sit.dat—Simplified specific interaction model (1 parameter)


    Phreeqc databases

    Other data blocks related to speciation

    SOLUTION_MASTER_SPECIES—Redox states and gram formula mass

    SOLUTION_SPECIES—Reaction and log K

    PHASES—Reaction and log K

    PHREEQC Databases


    Solutions
    Solutions

    • Required for all PHREEQC calculations

    • SOLUTION and SOLUTION _SPREAD

      • Units

      • pH

      • pe

      • Charge balance

      • Phase boundaries

    • Saturation indices

      • Useful minerals

      • Identify potential reactants


    What is a speciation calculation
    What is a speciation calculation?

    • Input:

      • pH

      • pe

      • Concentrations

    • Equations:

      • Mass-balance—sum of the calcium species = total calcium

      • Mass-action—activities of products divided by reactants = constant

      • Activity coefficients—function of ionic strength

    • Output

      • Molalities, activities

      • Saturation indices


    Mass balance equations

    Analyzed concentration of sulfate = (SO4-2) + (MgSO40) + (NaSO4-) + (CaSO40) + (KSO4-) + (HSO4-) + (CaHSO4+) + (FeSO4) + (FeSO4+) + (Fe(SO4)2-) + (FeHSO4+) + (FeHSO4+2)

    () indicates molality

    Mass-Balance Equations


    Mass action equations
    Mass-Action Equations

    Ca+2 + SO4-2 = CaSO40

    [] indicates activity


    Activity
    Activity

    WATEQ activity coefficient

    Davies activity coefficient


    Uncharged species
    Uncharged Species

    bi, called the Setschenow coefficient

    Value of 0.1 used in phreeqc.dat, wateq4f.dat.


    Pitzer activity coefficients
    Pitzer Activity Coefficients

    ma concentration of anion

    mc concentration of cation

    Ion specific parameters

    F function of ionic strength, molalities of cations and anions


    Sit activity coefficients
    SIT Activity Coefficients

    mk concentrations of ion

    Interaction parameter

    A = 0.51, B = 1.5 at 25 C


    Aqueous models
    Aqueous Models

    Ion association

    • Pros

      • Data for most elements (Al, Si)

      • Redox

    • Cons

      • Ionic strength < 1

      • Best only in Na, Cl medium

      • Inconsistent thermodynamic data

      • Temperature dependence


    Aqueous models1
    Aqueous Models

    • Pitzer specific interaction

      • Pros

        • High ionic strength

        • Thermodynamic consistency for mixtures of electrolytes

      • Cons

        • Limited elements

        • Little if any redox

        • Difficult to add elements

        • Temperature dependence


    Aqueous models2
    Aqueous Models

    • SIT

      • Pros

        • Possibly better for higher ionic strength than ion association

        • Many fewer parameters

        • Redox

        • Actinides

      • Cons

        • Poor results for gypsum/NaCl in my limited testing

        • Temperature dependence

        • Consistency?




    Solution composition
    Solution Composition

    Set units!

    Default is mmol/kgw

    Select elements

    Set concentrations

    “As”, special units

    Click when done


    Run speciation calculation
    Run Speciation Calculation

    Run

    Select files


    Seawater exercise
    Seawater Exercise

    Units are ppm

    • Use phreeqc.dat to run a speciation calculation for file seawater.pqi

    • Use file seawater-pitzer.pqi

      or copy input to a new buffer

      • Ctrl-a (select all)

      • Ctrl-c (copy)

      • File->new or ctrl-n

        (new input file)

      • Ctrl-v (paste)



    Results of 2 speciation calculations
    Results of 2 Speciation Calculations

    Tile

    Ion Association

    Pitzer


    Questions
    Questions

    • Write the mass-balance equation for calcium in seawater for each database.

    • What fraction of the total is Ca+2 ion for each database?

    • What fraction of the total is Fe+3 ion for each database?

    • What are the log activity and log activity coefficient of CO3-2 for each database?

    • What is the saturation index of calcite for each database?


    Initial solution 2 answers
    Initial Solution 2. Answers

    () indicates molality

    1a. Ca(total)= 1.066e-2 = (Ca+2) + (CaSO4) + (CaHCO3+) + (CaCO3) + (CaOH+) + (CaHSO4+)

    1b. Ca(total) = 1.066e-2 = (Ca+2) + (CaCO3)

    2a. 9.5/10.7 ~ 0.95

    2b. 1.063/1.066 ~ 1.0

    3a. 3.509e-019 / 3.711e-008 ~ 1e-11

    3b. No Fe+3 ion.

    4a. log activity CO3-2 = -5.099; log gamma CO3-2 = -0.68

    4b. log activity CO3-2 = -5.091; log gamma CO3-2 = -1.09

    5a. SI(calcite) = 0.76

    5b. SI(calcite) = 0.70


    Saturation index the thermodynamic state of a mineral relative to a solution
    SATURATION INDEXThe thermodynamic state of a mineral relative to a solution

    IAP is ion activity product

    K is equilibrium constant


    Saturation index
    SATURATION INDEX

    SI < 0, Mineral should dissolve

    SI > 0, Mineral should precipitate

    SI ~ 0, Mineral reacts fast enough to maintain equilibrium

    Maybe

    • Kinetics

    • Uncertainties


    Rules for saturation indices
    Rules for Saturation Indices

    • Mineral cannot dissolve if it is not present

    • If SI < 0 and mineral is present—the mineral could dissolve, but not precipitate

    • If SI > 0—the mineral could precipitate, but not dissolve

    • If SI ~ 0—the mineral could dissolve or precipitate to maintain equilibrium


    Saturation indices
    Saturation Indices

    • SI(Calcite)

    • SI(CO2(g))

      = log(PCO2)


    Useful mineral list minerals that may react to equilibrium relatively quickly
    Useful Mineral ListMinerals that may react to equilibrium relatively quickly


    Data tree
    Data Tree

    • Files (double click to edit)

      • Simulation (END)

        • Keywords (double click to edit)

          • Data


    Edit screen
    Edit Screen

    • Text editor


    Tree selection
    Tree Selection

    • Input

    • Output

    • Database

    • Errors

    • PfW


    Keyword data blocks
    Keyword Data Blocks

    Also right click in data tree—Insert keyword



    Alkalinity

    Total Inorganic Carbon

    Alkalinity

    • Number of moles of carbon of valence 4

    • Approximately

      HCO3- + 2xCO3-2 + OH- - H+

    • Alkalinity is independent of PCO2



    Carbon and alkalinity solution spread pqi
    Carbon and Alkalinitysolution_spread.pqi

    SOLUTION_SPREAD

    SELECTED_OUTPUT

    USER_GRAPH



    Ph and pe
    pH and pe

    Keywords

    SOLUTION—Solution composition

    END—End of a simulation

    USE—Reactant to add to beaker

    REACTION—Specified moles of a reaction

    USER_GRAPH—Charting



    USE

    REACTION

    Solution 1

    CO2 1.0

    1, 10, 100, 1000 mmol

    -axis_titles "CO2 Added, mmol" "pH" "Alkalinity"

    -axis_scale x_axis auto auto auto auto log

    -axis_scale sy_axis 0 0.002

    -start

    10 GRAPH_X rxn

    20 GRAPH_Y -LA("H+")

    30 GRAPH_SY ALK

    -end

    USER_GRAPH


    Input file ph pqi
    Input filepH.pqi

    SOLUTION 1

    temp 25

    pH 7

    pe 4

    redox pe

    units mmol/kgw

    density 1

    Alkalinity 1

    Na 1 charge

    -water 1 # kg

    END

    USE solution 1

    REACTION 1

    CO2 1

    1 10 100 1000 millimoles

    USER_GRAPH 1

    -axis_titles "CO2 Added, mmol" "pH" "Alkalinity"

    -axis_scale x_axis auto auto auto auto log

    -axis_scale sy_axis 0 0.002

    -start

    10 GRAPH_X rxn

    20 GRAPH_Y -LA("H+")

    30 GRAPH_SY ALK

    -end

    END


    Ph is the ratio of hco3 to co2 aq
    pH is the ratio of HCO3- to CO2(aq)

    Alkalinity is independent of PCO2


    What is ph
    What is pH?

    pH = 6.3 + log[(HCO3-)/(CO2)]

    pH = 10.3 + log[(CO3-2)/(HCO3-)]

    Questions

    1. How does the pH change when CO2 degasses during an alkalinity titration?

    2. How does pH change when plankton respire CO2?

    3. How does pH change when calcite dissolves?

    pH = logK + log[(PO4-3)/(HPO4-2)]



    USE

    REACTION

    Solution 1

    FeCl2 1.0

    1, 10, 100, 1000 mmol

    -axis_titles "FeCl2 Added, mmol" "pe" ""

    -axis_scale x_axis auto auto auto auto log

    -start

    10 GRAPH_X rxn

    20 GRAPH_Y -LA("e-")

    -end

    USER_GRAPH


    Input file
    Input file

    SOLUTION 1

    temp 25

    pH 3

    pe 4

    redox pe

    units mmol/kgw

    density 1

    Cl 1 charge

    Fe(3) 1

    -water 1 # kg

    END

    USE solution 1

    REACTION 1

    FeCl2 1

    1 10 100 1000 millimoles

    USER_GRAPH 1

    -axis_titles "FeCl2 Added, mmol" "pe" ""

    -axis_scale x_axis auto auto auto auto log

    -start

    10 GRAPH_X rxn

    20 GRAPH_Y -LA("e-")

    -end

    END



    What is pe
    What is pe?

    Fe+2 = Fe+3 + e-

    pe = log( [Fe+3]/[Fe+2] ) + 13

    HS- + 4H2O = SO4-2 + 9H+ + 8e-

    pe = log( [SO4-2]/[HS-] ) – 9/8pH + 4.21

    N2 + 6H2O = 2NO3- + 12H+ + 10e-

    pe = 0.1log( [NO3-]2/[N2] ) –1.2pH + 20.7

    pe = 16.9Eh, Eh in volts (platinum electrode measurement)


    Redox and pe in solution data blocks
    Redox and pe in SOLUTION Data Blocks

    • When do you need pe for SOLUTION?

      • To distribute total concentration of a redox element among redox states [e.g. Fe to Fe(2) and Fe(3)]

      • A few saturation indices with e- in dissociation reactions

        • Pyrite

        • Native sulfur

        • Manganese oxides

    • Can use a redox couple Fe(2)/Fe(3) in place of pe

    • Rarely, pe = 16.9Eh. (25 C and Eh in Volts).

    • pe options can only be applied to speciation calculations; thermodynamic pe is used for all other calculations




    Seawater initial solution
    Seawater Initial Solution

    Fe total was entered. How were Fe(3) and Fe(2) concentrations calculated?

    For initial solutions

    For “reactions”


    Final thoughts on pe
    Final thoughts on pe

    • pe sets ratio of redox states

    • Some redox states are measured directly:

      • NO3-, NO2-, NH3, N2(aq)

      • SO4-2, HS-

      • O2(aq)

      • Sometimes Fe, As

    • Others can be assumed:

      • Fe, always Fe(2) except at low pH

      • Mn, always Mn(2)

      • As, consider other redox elements

      • Se, consider other redox elements

      • U, probably U(6)

      • V, probably V(5)


    Berner s redox environments
    Berner’s Redox Environments

    • Oxic

    • Suboxic

    • Sulfidic

    • Methanic

    Thorstenson (1984)



    Summary
    Summary

    SOLUTION and SOLUTION _SPREAD

    • Units

    • pH—ratio of HCO3/CO2

    • pe—ratio of oxidized/reduced valence states

    • Charge balance

    • Phase boundaries

  • Saturation indices

    • Uncertainties

    • Useful minerals

  • Identify potential reactants


  • Summary1
    Summary

    Aqueous speciation model

    • Mole-balance equations—Sum of species containing Ca equals total analyzed Ca

    • Aqueous mass-action equations—Activity of products over reactants equal a constant

    • Activity coefficient model

      • Ion association with individual activity coefficients

      • Pitzer specific interaction approach

    • SI=log(IAP/K)


    Phreeqc reactions in a beaker

    SOLUTION

    EXCHANGE

    SURFACE

    KINETICS

    MIX

    REACTION

    EQUILIBRIUM_PHASES

    GAS_PHASE

    SOLUTION

    EXCHANGE

    SURFACE

    GAS_PHASE

    EQUILIBRIUM_

    PHASES

    +

    PHREEQC: Reactions in a Beaker

    REACTION BEAKER

    REACTION_TEMPERATURE

    REACTION_PRESSURE


    Reaction simulations
    Reaction Simulations

    • SOLUTION, SOLUTION_SPREAD, MIX, USE solution, or USE mix

      Equilibrium

      Nonequilibrium

    • EQUILIBRIUM_PHASES

    • EXCHANGE

    • SURFACE

    • SOLID_SOLUTION

    • GAS_PHASE

    • REACTION_TEMPERATURE

    • REACTION_PRESSURE

    • KINETICS

    • REACTION

    • END



    Keywords
    Keywords 100 to 1000 atm

    SOLUTION 1

    END

    USE solution 1

    REACTION_PRESSURE

    USER_GRAPH

    END


    Use item on shelf
    USE—Item on shelf 100 to 1000 atm

    To the beaker

    Item number on shelf


    Use all of these reactants are numbered
    USE 100 to 1000 atmAll of these Reactants are Numbered

    • SOLUTION

    • EQUILIBRIUM_PHASES

    • EXCHANGE

    • GAS_PHASE

    • KINETICS

    • SOLID_SOLUTIONS

    • SURFACE

    • REACTION

    • REACTION_PRESSURE

    • REACTION_TEMPERATURE


    Reaction pressure
    REACTION_PRESSURE 100 to 1000 atm

    • List of pressures

      100 200 300 400 500 600 700 800 900 1000

      Or

    • Range of pressure divided equally

      100 1000 in 10 steps


    User graph
    USER_GRAPH 100 to 1000 atm

    10 GRAPH_X PRESSURE

    20 GRAPH_Y SI(“Calcite”)

    30 GRAPH_SY expr

    • Expressions are defined with Basic functions

    • Basic—+-*/, SIN, COS, EXP,…

    • PHREEQC—PRESSURE, SI(“Calcite”), MOL(“Cl-”), TOT(“Cl-”), -LA(“H+”),…


    Plot the si of calcite with temperature seawater p pqi
    Plot the SI of Calcite with Temperature 100 to 1000 atmSeawater-p.pqi



    Arsenic in the central oklahoma aquifer
    Arsenic in the Central Oklahoma Aquifer 100 to 1000 atm

    • Arsenic mostly in confined part of aquifer

    • Arsenic associated with high pH

    • Flow:

      • Unconfined

      • Confined

      • Unconfined


    Geochemical reactions
    Geochemical Reactions 100 to 1000 atm

    • Brine initially fills the aquifer

    • Calcite and dolomite equilibrium

    • Cation exchange

      • 2NaX + Ca+2 = CaX2 + 2Na+

      • 2NaX + Mg+2 = MgX2 + 2Na+

    • Surface complexation

      Hfo-HAsO4- + OH- = HfoOH + HAsO4-2


    More reactions and keywords
    More Reactions and Keywords 100 to 1000 atm

    EQUILIBRIUM_PHASES

    SAVE

    EXCHANGE

    SURFACE


    Equilibrium phases minerals and gases that react to equilibrium
    EQUILIBRIUM_PHASES 100 to 1000 atmMinerals and gases that react to equilibrium

    Calcite reaction

    CaCO3 = Ca+2 + CO3-2

    Equilibrium

    K = [Ca+2][CO3-2]


    Equilibrium phases data block
    EQUILIBRIUM_PHASES Data Block 100 to 1000 atm

    • Mineral or gas

    • Saturation state

    • Amount

      Example EQUILIBRIUM_PHASES 5:

      CO2 Log PCO2 = -2, 10 moles

      Calcite equilibrium 1 moles

      Dolomite equilibrium 1 moles

      Fe(OH)3 equilibrium 0 moles


    Let s make a carbonate groundwater
    Let’s Make a Carbonate Groundwater 100 to 1000 atm

    • SOLUTION—Pure water or rain

    • EQUILIBRIUM_PHASES

      • CO2(g), SI -1.5, moles 10

      • Calcite, SI 0, moles 0.1

      • Dolomite, SI 0, moles 1.6

    • SAVE solution 0


    Oklahoma rainwater x 20 ignoring no3 and nh4
    Oklahoma Rainwater x 20 100 to 1000 atmIgnoring NO3- and NH4+

    SOLUTION 0 20 x precipitation

    pH 4.6

    pe 4.0 O2(g) -0.7

    temp 25.

    units mmol/kgw

    Ca 0.191625

    Mg 0.035797

    Na 0.122668

    Cl 0.133704

    C 0.01096

    S 0.235153 charge


    Limestone groundwater
    Limestone Groundwater 100 to 1000 atm


    Brine
    Brine 100 to 1000 atm

    • Oil field brine


    Solution data block
    SOLUTION Data Block 100 to 1000 atm

    • SOLUTION 1: Oklahoma Brine

      units mol/kgw

      pH 5.713

      temp 25.

      Ca 0.4655

      Mg 0.1609

      Na 5.402

      Cl 6.642

      C 0.00396

      S 0.004725

      As 0.03 (ug/kgw)


    Ion exchange calculations 1

    Ion Exchange Calculations (#1)

    • PHREEQC “speciates” the “exchanged species” on the exchange sites either:

      • Initial Exchange Calculation: adjusting sorbed concentrations in response to a fixed aqueous composition

      • Reaction Calculation: adjusting both sorbed and aqueous compositions.


    Ion exchange 2

    • PHREEQC uses 3 keywords to define exchange processes 100 to 1000 atm

      • EXCHANGE_MASTER_SPECIES (component data)

      • EXCHANGE_SPECIES (species thermo. data)

      • EXCHANGE

    • First 2 are found in phreeqc.dat and wateq4f.dat (for component X- and exchange species from Appelo) but can be modified in user-created input files.

    • Last is user-specified to define amount and composition of an “exchanger” phase.

    Ion Exchange (#2)


    Ion exchange 3

    • “SAVE” and “USE” keywords can be applied to “EXCHANGE” phase compositions.

    • Amount of exchanger (eg. moles of X-) can be calculated from CEC (cation exchange capacity, usually expressed in meq/100g of soil) where:

    • where sw is the specific dry weight of soil (kg/L of soil), q is the porosity and rB is the bulk density of the soil in kg/L. (If sw = 2.65 & q = 0.3, then X- = CEC/16.2)

    • CEC estimation technique (Breeuwsma, 1986):

    • CEC (meq/100g) = 0.7 (%clay) + 3.5 (%organic carbon)

    • (cf. Glynn & Brown, 1996; Appelo & Postma, 2005, p. 247)

    Ion Exchange (#3)


    Exchange cation exchange composition
    EXCHANGE “EXCHANGE” phase compositions.Cation exchange composition

    Reaction:

    Ca+2 + 2NaX = CaX2 + 2Na+

    Equilibrium:


    Exchange data block
    EXCHANGE Data Block “EXCHANGE” phase compositions.

    • Exchanger name

    • Number of exchange sites

    • Chemical composition of exchanger

      Example EXCHANGE 15:

      CaX2 0.05 moles (X is defined in databases)

      NaX 0.05 moles

      Often

      X 0.15 moles, Equilibrium with solution 1


    Exchange
    EXCHANGE “EXCHANGE” phase compositions.

    • Calculate the composition of an exchanger in equilibrium with the brine

    • Assume 1 mol of exchange sites


    Input file1
    Input File “EXCHANGE” phase compositions.


    Exchange composition
    Exchange Composition “EXCHANGE” phase compositions.

    -------------------------------------------------------

    Beginning of initial exchange-composition calculations.

    -------------------------------------------------------

    Exchange 1.

    X 1.000e+000 mol

    Equiv- Equivalent Log

    Species Moles alents Fraction Gamma

    NaX 9.011e-001 9.011e-001 9.011e-001 0.242

    CaX2 4.067e-002 8.134e-002 8.134e-002 0.186

    MgX2 8.795e-003 1.759e-002 1.759e-002 0.517


    Sorption processes
    Sorption processes “EXCHANGE” phase compositions.

    • 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

    • Sorption can occur even when a surface is neutrally charged.


    Some simple models

    Linear Adsorption (constant K “EXCHANGE” phase compositions.d):

    where q is amount sorbed per weight of solid, c is amount in solution per unit volume of solution; R is the retardation factor (dimensionless), q is porosity, rb is bulk density. Kd is usually expressed in ml/g and measured in batch tests or column experiments.

    Some Simple Models

    • Assumptions:

      • Infinite supply of surface sites

      • Adsorption is linear with total element aqueous conc.

      • Ignores speciation, pH, competing ions, redox states…

      • Often based on sorbent mass, rather than surface area


    Thermodynamic speciation based sorption models
    Thermodynamic “EXCHANGE” phase compositions.Speciation-based Sorption Models



    Surface charge depends on the sorption/surface binding of potential determining ions, such as H+. Formation of surface complexes also affects surface charge.


    Examples of Surface Complexation Reactions potential determining ions, such as H

    outer-sphere complex

    inner-sphere complex

    bidentate inner-sphere complex


    pH “edges” for cation sorption potential determining ions, such as H


    Surface complexation

    • PHREEQC uses 3 keywords to define exchange processes potential determining ions, such as H

      • SURFACE_MASTER_SPECIES (component data)

      • SURFACE_SPECIES (species thermo. data)

      • SURFACE

    • First 2 are found in phreeqc.dat and wateq4f.dat (for component Hfo and exchange species from Dzombak and Morel) but can be modified in user-created input files.

    • Last is user-specified to define amount and composition of a surface.

    Surface Complexation


    Surface surface composition trace elements zn cd pb as p
    SURFACE—Surface Composition potential determining ions, such as HTrace elements Zn, Cd, Pb, As, P

    Reaction:

    Hfo_wOH + AsO4-3 = Hfo_wOHAsO4-3

    Equilibrium:


    Surface data block
    SURFACE Data Block potential determining ions, such as H

    • Surface name—Hfo is Hydrous Ferric Oxide

    • Number of surface sites

    • Chemical composition of surface

    • Multiple sites per surface

      Example SURFACE 21:

      Hfo_wOH 0.001 moles, 600 m2/g, 30 g

      Hfo_sOH 0.00005 moles

      Often

      Hfo_w 0.001 moles, Equilibrium with solution 1


    Surface
    SURFACE potential determining ions, such as H

    • Calculate the composition of a surface in equilibrium with the brine

    • Assume 1 mol of exchange sites

    • Use the equilibrium constants from the following slide


    Dzombak and morel s model
    Dzombak and Morel’s Model potential determining ions, such as H

    SURFACE_MASTER_SPECIES

    Surf SurfOH

    SURFACE_SPECIES

    SurfOH = SurfOH

    log_k 0.0

    SurfOH + H+ = SurfOH2+

    log_k 7.29

    SurfOH = SurfO- + H+

    log_k -8.93

    SurfOH + AsO4-3 + 3H+ = SurfH2AsO4 + H2O

    log_k 29.31

    SurfOH + AsO4-3 + 2H+ = SurfHAsO4- + H2O

    log_k 23.51

    SurfOH + AsO4-3 = SurfOHAsO4-3

    log_k 10.58

    SOLUTION_MASTER_SPECIES

    As H3AsO4 -1.0 74.9216 74.9216

    SOLUTION_SPECIES

    H3AsO4 = H3AsO4

    log_k 0.0

    H3AsO4 = AsO4-3 + 3H+

    log_k -20.7

    H+ + AsO4-3 = HAsO4-2

    log_k 11.50

    2H+ + AsO4-3 = H2AsO4-

    log_k 18.46


    Input file2
    Input File potential determining ions, such as H


    Surface composition
    Surface Composition potential determining ions, such as H

    ------------------------------------------------------

    Beginning of initial surface-composition calculations.

    ------------------------------------------------------

    Surface 1.

    Surf

    5.648e-002 Surface charge, eq

    3.028e-001 sigma, C/m**2

    4.372e-002 psi, V

    -1.702e+000 -F*psi/RT

    1.824e-001 exp(-F*psi/RT)

    6.000e+002 specific area, m**2/g

    1.800e+004 m**2 for 3.000e+001 g

    Surf

    7.000e-002 moles

    Mole Log

    Species Moles Fraction Molality Molality

    SurfOH2+ 5.950e-002 0.850 5.950e-002 -1.225

    SurfOH 8.642e-003 0.123 8.642e-003 -2.063

    SurfHAsO4- 9.304e-004 0.013 9.304e-004 -3.031

    SurfOHAsO4-3 6.878e-004 0.010 6.878e-004 -3.163

    SurfH2AsO4 2.073e-004 0.003 2.073e-004 -3.683

    SurfO- 2.875e-005 0.000 2.875e-005 -4.541


    Modeling the geochemistry central oklahoma
    Modeling the Geochemistry Central Oklahoma potential determining ions, such as H

    • Reactants

      • Brine

      • Exchanger in equilibrium with brine

      • Surface in equilibrium with brine

      • Calcite and dolomite

      • Carbonate groundwater

    • Process

      • Displace brine with carbonate groundwater

      • React with minerals, exchanger, and surface


    Explicit approach
    Explicit Approach potential determining ions, such as H

    • Repeat

      • USE carbonate groundwater

      • USE equilibrium_phases

      • USE exchange

      • USE surface

      • SAVE equilibrium_phases

      • SAVE exchange

      • SAVE surface


    1d solute transport
    1D Solute Transport potential determining ions, such as H

    • Terms

      • Concentration change with time

      • Dispersion/diffusion

      • Advection

      • Reaction


    Phreeqc transport calculations

    1 potential determining ions, such as H

    2

    3

    4

    5

    6

    n

    1

    1

    2

    2

    3

    3

    4

    4

    5

    5

    6

    6

    n

    n

    Advection

    PHREEQC Transport Calculations

    Dispersion

    Reaction


    Advection data block

    1 potential determining ions, such as H

    2

    3

    4

    5

    6

    n

    1

    2

    3

    4

    5

    6

    n

    Brine

    ADVECTION Data Block

    Carbonate groundwater

    Reaction

    Minerals, Exchange, Surface


    Advection
    ADVECTION potential determining ions, such as H

    • Cells are numbered from 1 to N.

    • Index numbers (of SOLUTION, EQUILIBRIUM_PHASES, etc) are used to define the solution and reactants in each cell

    • SOLUTION 0 enters the column

    • Water is “shifted” from one cell to the next


    Advection1
    ADVECTION potential determining ions, such as H

    • Number of cells

    • Number of shifts

    • If kinetics—time step


    Advection2
    ADVECTION potential determining ions, such as H

    • Output file

      • Cells to print

      • Shifts to print

    • Selected-output file

      • Cells to print

      • Shifts to print


    Complete simulation
    Complete simulation potential determining ions, such as H

    • Define As aqueous and surface model

    • Define brine (SOLUTION 1)

    • Define EXCHANGE 1 in equilibrium with brine

    • Define SURFACE 1 in equilibrium with brine

    • Define EQUILIBRIUM_PHASES 1 with 1.6 mol dolomite and 0.1 mol calcite

    • Define carbonate groundwater (SOLUTION 0)

      • Pure water

      • EQUILIBRIUM_PHASES calcite, dolomite, CO2(g) -1.5

      • SAVE solution 0


    Complete simulation continued
    Complete simulation (continued) potential determining ions, such as H

    • Define ADVECTION

    • Define USER_GRAPH

      X—step or pore volume

      Y—ppm As, and molality of Ca, Mg, and Na

      SY—pH

      USER_GRAPH Example 14

      -headings PV As(ppb) Ca(M) Mg(M) Na(M) pH

      -chart_title "Chemical Evolution of the Central Oklahoma Aquifer"

      -axis_titles "PORE VOLUMES OR SHIFT NUMBER" "Log(CONCENTRATION, IN PPB OR MOLAL)" "pH"

      -axis_scalex_axis 0 200

      -axis_scaley_axis 1e-6 100 auto auto Log

      10 GRAPH_X STEP_NO

      20 GRAPH_Y TOT("As")*GFW("As")*1e6, TOT("Ca"), TOT("Mg"), TOT("Na")

      30 GRAPH_SY -LA("H+")


    Keywords in input file
    Keywords in Input File potential determining ions, such as H

    SURFACE_MASTER_SPECIES

    SURFACE_SPECIES

    SOLUTION_MASTER_SPECIES

    SOLUTION_SPECIES

    SOLUTION 1 Brine

    END

    EXCHANGE 1

    END

    SURFACE 1

    END

    EQUILIBRIUM_PHASES 1

    END

    SOLUTION 0

    EQUILIBRIUM_PHASES 0

    SAVE solution 0

    END

    ADVECTION

    USER_GRAPH Example 14

    END


    Advection results
    Advection Results potential determining ions, such as H


    Geochemical reactions1
    Geochemical Reactions potential determining ions, such as H

    • Cation exchange

      • 2NaX + Ca+2 = CaX2 + 2Na+

      • 2NaX + Mg+2 = MgX2 + 2Na+

    • Calcite and dolomite equilibrium

      • CaCO3 + CO2(aq) + H2O = Ca+2 + 2 HCO3-

      • CaMg(CO3)2 + 2CO2(aq) + 2H2O = Ca+2 + Mg+2 + 4 HCO3-

    • Surface complexation

      Hfo-HAsO4- + OH- = HfoOH + HAsO4-2


    Diffusive transport and kinetics
    Diffusive TRANSPORT and Kinetics potential determining ions, such as H

    • Potomac River Estuary data

    • KINETICS

      • Non-equilibrium reactions

      • Biogeochemical

      • Annual cycle of sulfate reduction

    • TRANSPORT capabilities


    Thermodynamics vs kinetics
    Thermodynamics vs. Kinetics potential determining ions, such as H

    • Thermodynamics predicts equilibrium dissolution/precipitation concentrations

    • Probably OK for “reactive” minerals (Monday’s useful minerals list) and groundwater

    • Need kinetics for slow reactions and/or fast moving water


    Kinetics is concentration versus time
    Kinetics is potential determining ions, such as HConcentration versus Time

    Dissolution “half-life”

    Appelo and Postma, 2005


    Half life ph 5 dissolution of the solid phase
    Half-life potential determining ions, such as H(pH 5 dissolution of the solid phase)

    • Gypsum – hours

    • Calcite – days

    • Dolomite – years

    • Biotite, kaolinite, quartz – millions of years

    • If half-life is << residence time then equilibrium conditions can be used

    • If half-life is >> residence time then kinetics will need to be considered


    Appelo and Postma, 2005 potential determining ions, such as H


    Rate laws
    Rate Laws potential determining ions, such as H

    • Mathematically describes the change in concentration with time (derivative)

    • Simple if constant rate (zero order - linear)

    • Complex if rate constant changes with time due to multiple factors (i.e., concentration, temperature, pH, etc.), thus higher order, non-linear

    • Remember that experimental data may not represent real world conditions


    Kinetics nonequilibrium reactions
    KINETICS—Nonequilibrium Reactions potential determining ions, such as H

    • Monod Kinetics

    • Radioactive decay

    • Silicate hydrolosis

    • Biological processes


    Kinetics and rates data blocks
    KINETICS and RATES Data Blocks potential determining ions, such as H

    • Kinetic reaction name

    • Stoichiometry of reaction

    • Rate expression (RATES)

      Example

      KINETICS 21:

      DOC_decay

      formula Doc -1 CH2O +1

      RATES

      10 Rate = 0.01*TOT(“Doc”)

      20 SAVE rate*TIME


    Organic decomposition kinetics
    Organic decomposition KINETICS potential determining ions, such as H

    • 2CH2O + SO4-2 = 2HCO3- + H2S

    WRONG!

    -formula

    CH2O -2

    SO4-2 -1

    HCO3- +2

    H2S +1

    • RIGHT!

  • -formula

  • CH2O 1

  • Or perhaps,

  • -formula

  • CH2O 1

  • Doc -1


  • Organic decomposition in phreeqc
    Organic Decomposition in PHREEQC potential determining ions, such as H

    • Mole balance of C increases

    • H and O mole balances increase too, but equivalent to adding H2O

    • If there are electron acceptors, C ends up as CO3-2 species

    • Electron acceptor effectively gives up O and assumes the more reduced state

    • The choice of electron acceptor is thermodynamic


    Organic decomposition
    Organic Decomposition potential determining ions, such as H

    • Sequential removal of electron acceptors, usually in the sequence:

      • O2

      • NO3-

      • MnO2

      • Fe(OH)3

      • SO4-2

      • Organic carbon


    Rate equation ch 2 o
    RATE EQUATION CH potential determining ions, such as H2O

    RATES

    CH2O

    -start

    10 sec_per_yr = 365*24*3600

    20 k = 1 / sec_per_yr

    30 pi = 2*ARCTAN(1e20)

    40 theta = (TOTAL_TIME/sec_per_yr)*2*pi

    50 cycle = (1+COS(theta))/2

    60 rate = k*TOT("S(6)") * cycle

    70 moles = rate*TIME

    80 SAVE moles

    -end

    END


    1 cos theta 2
    (1+COS(theta))/2 potential determining ions, such as H


    Kinetics
    KINETICS potential determining ions, such as H

    KINETICS 1-4

    CH2O

    -formula (CH2O)8NH3

    END


    Transport
    TRANSPORT potential determining ions, such as H

    • 20 cells

    • 100 shifts

    • 0.1 y time step


    Transport1
    TRANSPORT potential determining ions, such as H

    • Diffusion only

    • Diffusion coefficient

    • Constant boundary (1/2 seawater)

    • Closed boundary


    Transport2
    TRANSPORT potential determining ions, such as H

    • Cell lengths

      0.025 m

    • Dispersivities

      0.0 m


    Transport3
    TRANSPORT potential determining ions, such as H

    • Output file

    • Selected output file and USER_GRAPH


    Transport options
    TRANSPORT Options potential determining ions, such as H

    • At end of exercise we will try multicomponent diffusion, where ions diffuse at different rates

    • Capability for diffusion in surface interlayers


    Transport charge balanced diffusion
    TRANSPORT—Charge-Balanced Diffusion potential determining ions, such as H

    TRANSPORT

    -multi_d true 1e-9 0.3 0.05 1.0

    SOLUTION_SPECIES

    H+ = H+

    log_k 0.0

    -gamma 9.0 0.0

    -dw 9.31e-9

    • Multicomponent diffusion—true

    • Default tracer diffusion coefficient—1e-9 m2/s

    • Porosity—0.3

    • Minimum porosity—0.05

    • (Diffusion stops when the porosity reaches the porosity limit)

    • Exponent of porosity (n) –1.0.

    • (Effective diffusion coefficient–De = Dw * porosity^n)

    • -dw is tracer diffusion coefficient in SOLUTION_SPECIES


    Transport options1
    TRANSPORT Options potential determining ions, such as H

    • Stagnant cells/dual porosity

      -One stagnant cell

      -Multiple stagnant cells

    • Dump options


    V3 pqi
    V3.pqi potential determining ions, such as H

    • Check periodic steady state

    • Adjust parameters

      • More SO4 consumption

      • Greater depth range


    Adjust parameters so envelope is like the green curves
    Adjust parameters so envelope is like the green curves potential determining ions, such as H

    • Rate expression

      • K controls rate of reaction

      • Cycle controls periodicity

      • Rate is overall rate of reaction (mol/s)

    • TRANSPORT

      • Diffusion coefficient

    • KINETICS

      • Cells with kinetics


    One choice
    One Choice potential determining ions, such as H

    • Diffusion coefficient

    • RATES k

    • RATES cycle

    • Cells


    So 4 2
    SO potential determining ions, such as H4-2

    Multicomponent diffusion

    Fixed diffusion coefficient


    NH potential determining ions, such as H4+

    Fixed diffusion coefficient

    Multicomponent diffusion


    H 2 s
    H potential determining ions, such as H2S

    Fixed diffusion coefficient

    Multicomponent diffusion


    Acid mine drainage
    Acid Mine Drainage potential determining ions, such as H


    Sulfide oxidation
    Sulfide Oxidation potential determining ions, such as H

    • Pyrite/Marcasite are most important reactants

    • Need Pyrite, Oxygen, Water, and bugs

    • Oxidation of pyrite and formation of ferric hydroxide complexes and minerals generates acidic conditions


    Iron mountain california
    Iron Mountain, California potential determining ions, such as H

    • Sulfide deposits at the top of a mountain

    • Lots of rain and snow

    • Unsaturated conditions

    • Tunnels drain


    Picher oklahoma
    Picher, Oklahoma potential determining ions, such as H

    • Flat topography

    • Mines 200 to 500 ft below land surface

    • Saturated after dewatering ceased

    • Cut off the supply of oxygen


    Simplified reactions
    Simplified Reactions potential determining ions, such as H

    High pH

    FeS2 + 15/4O2 + 4HCO3- = Fe(OH)3 + 2SO4-2 + 4CO2 + 1/2H2O

    Or

    FeS2 + 15/4O2 + 7/2H2O = Fe(OH)3 + 2SO4-2 + 4H+

    Low pH

    FeS2 + 15/4O2 + 1/2H2O = Fe+3 + SO4-2 + HSO4-


    Additional reactions
    Additional reactions potential determining ions, such as H

    • Hydrous ferric oxides

      • Ferrihydrite

      • Goethite

      • Jarosite

    • Aluminum hydroxides

      • Alunite

    • Carbonates

    • Gypsum


    Modeling pyrite oxidation
    Modeling Pyrite Oxidation potential determining ions, such as H

    FeS2 + 15/4O2 + 7/2H2O = Fe(OH)3 + 2SO4-2 + 4H+

    • Pick the irreversible reactant: FeS2

      • Oxygen rich environment of a tailings pile

      • We are going to react up to 50 mmol FeS2

    • Equilibrium reactions


    Reaction exercise
    REACTION Exercise potential determining ions, such as H

    • React pure water with 10 mmol of pyrite (REACTION) in 20 steps, maintaining equilibrium with atmospheric oxygen (log PO2 = -0.7) and goethite.

    • Limestone can neutralize acid mine drainage. Rerun assuming calcite equilibrium (maintain equilibrium with O2, goethite, and atmospheric CO2).

    • Add the possibility of gypsum precipitation in the treatment process.


    No buffering
    No Buffering potential determining ions, such as H


    Calcite buffering
    Calcite Buffering potential determining ions, such as H


    Picher oklahoma abandoned pb zn mine mg l
    Picher Oklahoma potential determining ions, such as HAbandoned Pb/Zn Minemg/L

    • Mines are suboxic

    • Carbonates are present

    • Iron oxidizes in stream


    Pyrite oxidation

    Pyrite Oxidation potential determining ions, such as H

    Requires

    Pyrite/Marcasite

    O2

    H2O

    Bacteria

    Produces

    Ferrihydrite/Goethite, jarosite, alunite

    Gypsum if calcite is available

    Evaporites

    Possibly siderite

    Acid generation

    Pyrite > FeS > ZnS


    Processes that control minor element chemistry1
    Processes that Control Minor Element Chemistry potential determining ions, such as H

    1. Carbonate reactions

    2. Ion exchange

    3. Organic carbon oxidation

    O2/Nitrate reduction

    Iron oxyhydroxide reduction

    Sulfate reduction

    Methanogenesis

    4. Pyrite oxidation

    5. Gypsum dissolution

    6. Seawater evaporation

    7. Silicate weathering


    Processes that control minor element chemistry2

    • 1. Redox potential determining ions, such as H

    • Oxyanions

    • Trace metals

    • Nitrate

    • 2. Surface complexation

      • Phosphate

    • Oxyanions

    • Trace metals

  • 3. Cation exchange

  • 4. Solid solutions

  • 5. Minerals

  • Processes that Control Minor Element Chemistry


    Other major keywords
    Other Major Keywords potential determining ions, such as H

    • Selected output

      • SELECTED_OUTPUT

      • USER_PUNCH

    • GAS_PHASE

    • SOLID_SOLUTIONS

    • MIX

    • REACTION_TEMPERATURE

    • INVERSE_MODELING

    • RUN_CELLS (not yet in PhreeqcI)

    • COPY, DELETE (not yet in PhreeqcI)


    Inverse geochemical modeling

    Inverse potential determining ions, such as HGeochemical Modeling


    Principles
    Principles potential determining ions, such as H

    • Objective: Describe the chemical and isotopic evolution observed on a hydrologic flow path in terms of sets (models) of balanced reactions.

    • Input:

      • Analytical data for one (or more if mixing occurs) “initial” solutions and one “final” solution

      • Stoichiometry of plausible reactants and products

    • Output:

      • Mass-balance models – heterogeneous reactive mass transfers (mineral/gas dissolution/exsolution, sorption/exchange) that account for changes in chemistry and isotopic composition.


    Simple mole balance equations
    Simple Mole Balance Equations potential determining ions, such as H

    Cfinal = Cinitial + DCO2 + DCaCO3

    Cafinal = Cainitial + DCaCO3


    Phreeqc equations
    PHREEQC Equations potential determining ions, such as H

    • Mole balance and valence state balance

    • Isotope mole balance

    • Electron balance

    • Solution charge balance

    • Alkalinity balance

    • Water balance

    • Uncertainty constraints (elements, pH, isotopes)


    Example equations
    Example Equations potential determining ions, such as H

    • Generalized mole-balance:

    • Solution charge balance:



    Mineralogical determinations
    Mineralogical Determinations the sets of

    • Thin Sections or ion microprobe or Scanning Electron Microscope with Energy Dispersive X-rays

      • Mineralogy and composition of specific minerals.

      • Poor job of fine grained secondary phases such as clays and oxy-hydroxides

    • X-ray diffraction

      • Gives mineralogy, including fine grained phases and clays.

      • Does not give the specific mineral compositions.

      • Quantitation techniques are improving

    • Knowledge of geologic framework, geochemistry and hydrology


    Tar creek problem
    Tar Creek problem the sets of

    • Evolution of a recharge water during pyrite and sphalerite oxidation, carbonate, albite and halite dissolution.

    • Use file “tarcreek.pqi”





    Tar creek inverse modeling3
    Tar Creek Inverse Modeling the sets of

    Summary of inverse modeling:

    Number of models found: 4

    Number of minimal models found: 1

    Number of infeasible sets of phases saved: 19

    Number of calls to cl1: 31


    Tar creek inverse modeling4
    Tar Creek Inverse Modeling the sets of

    Solution fractions: Minimum Maximum

    Solution 1 1.001e+000 0.000e+000 0.000e+000

    Solution 2 1.000e+000 0.000e+000 0.000e+000

    Phase mole transfers: Minimum Maximum

    Calcite 2.740e-003 0.000e+000 0.000e+000 CaCO3

    Dolomite 1.033e-002 0.000e+000 0.000e+000 CaMg(CO3)2

    CO2(g) -1.293e-003 0.000e+000 0.000e+000 CO2

    Sphalerite 2.306e-003 0.000e+000 0.000e+000 ZnS

    Pyrite 1.391e-002 0.000e+000 0.000e+000 FeS2

    O2(g) 5.542e-002 0.000e+000 0.000e+000 O2

    Albite 3.096e-003 0.000e+000 0.000e+000 NaAlSi3O8

    Quartz -6.245e-003 0.000e+000 0.000e+000 SiO2

    Kaolinite -1.522e-003 0.000e+000 0.000e+000 Al2Si2O5(OH)4

    Halite 7.936e-004 0.000e+000 0.000e+000 NaCl

    Fe(OH)3(a) -8.512e-003 0.000e+000 0.000e+000 Fe(OH)3


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