EPA/600/3-91/021
March 1991
MINTEQA2/PRODEFA2, A GEOCHEMICAL ASSESSMENT MODEL
FOR ENVIRONMENTAL SYSTEMS: VERSION 3.0 USER'S MANUAL
by
Jerry D. Allison"1", David S. Brown, and Kevin J. Novo-Gradac*
"""Computer Sciences Corporation
Environmental Research Laboratory
Athens, Georgia 30613
Assessment Branch
Environmental Research Laboratory
Athens, Georgia 30613
*AScI Corporation
Environmental Research Laboratory
Athens, Georgia 30613
ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATHENS, GEORGIA 30613
U.S. Environs?'-'ri^ .' , > . ; iTO'aqy $$ Printed on Recycled Paper
P.5gior. 5, Libra
S. Dearborn .," - ~-> loVQ
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DISCLAIMER
The information in this document has been funded wholly or in part by
the United States Environmental Protection Agency. It has been subject to the
Agency's peer and administrative review, and it has been approved for
publication as an EPA document. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use by the U.S.
Environmental Protection Agency.
ii
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FOREWORD
As environmental controls become more costly to implement and the
penalties of judgment errors become more severe, environmental quality
management requires more efficient management tools based on greater
knowlege of the environmental phenomena to be managed. As part of this
Laboratory's research on the occurrence, movement, transformation, impact
and control of environmental contaminants, the Assessment Branch develops
management or engineering tools to help environmental officials achieve
pollution control goals.
The attention of environmental decision makers is increasingly being
focused on the movement of pollutants into ground water. Of particular
importance is the transport and speciation of metals. The MINTEQA2 model
is a versatile, quantitative tool for predicting the equilibrium behavior
of metals in a variety of chemical environments. Designed for convenient
use by environmental scientists and engineers, the model should be a
valuable tool for environmental risk assessment and hazard evaluation.
Rosemarie C. Russo, Ph.D.
Director
Environmental Research Laboratory
Athens, Georgia
iii
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ABSTRACT
MINTEQA2 is a geochemical equilibrium speciation model capable of
computing equilibria among the dissolved, adsorbed, solid, and gas phases in
an environmental setting. MINTEQA2 includes an extensive database of reliable
thermodynamic data that is also accessible to PRODEFA2, an interactive program
designed to be executed prior to MINTEQA2 for the purpose of creating the
required MINTEQA2 input file.
This report describes how to use the MINTEQA2 model. The chemical and
mathematical structure of MINTEQA2 and the structure of the database files
also are described. The use of both PRODEFA2 and MINTEQA2 are illustrated
through the presentation of an example PRODEFA2 dialogue reproduced from
interactive sessions and the presentation of MINTEQA2 output files and error
diagnostics. The content and format of database files also are explained.
IV
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TABLE OF CONTENTS
DISCLAIMER ii
FOREWORD iii
ABSTRACT iv
LIST OF FIGURES vii
LIST OF TABLES vii
ACKNOWLEDGMENT viii
CHAPTER 1. INTRODUCTION 1
CHAPTER 2. CHEMICAL AND MATHEMATICAL CONCEPTS 3
Component and Species Definitions 3
Components 3
Type I Components as Species in Solution 3
Type II Other Species in Solution or Adsorbed 3
Type III Species with Fixed Activity 4
Type IV Finite Solids 4
Type V Possible (Undersaturated) Solids 4
Type VI Excluded Species 5
The Pre-Defined Set of Components 5
Oxidation/Reduction Reactions 5
General Problem Formulation 6
Example Problem without a Solid Phase 9
Example Problem with a Solid Phase and with a Gas Phase 13
Adjustments to Equilibrium Constants 17
Temperature Corrections of Equilibrium Constants 17
Activity Coefficient Corrections of Equilibrium Constants 18
Activity of H20 20
Obtaining Total Dissolved Carbonate from Alkalinity 20
CHAPTER 3. ADSORPTION MODELS 24
Naming and Numbering Surface Species 24
Non-Electrostatic Adsorption Models 26
Activity Kd Adsorption Model 26
Activity Langmuir Adsorption Model 27
Activity Freundlich Model 28
Ion Exchange Adsorption Model 29
Electrostatic Adsorption Models 30
General Implementation of Electrostatic Models in MINTEQA2 . 32
Constant Capacitance and Diffuse-Layer Models 34
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Triple-Layer Model 38
CHAPTER 4. USING MINTEQA2 AND PRODEFA2 44
General Features and Organization of MINTEQA2 and PRODEFA2 .... 44
Running PRODEFA2 for the First Time 47
Detailed Explanation of PRODEFA2 Options 50
Main Menu Option 1: Edit Level I 50
Main Menu Option 2: Edit Level II 56
Main Menu Option 3: Edit Level III 67
Main Menu Option 4: Edit Level IV 70
Main Menu Option M: Multi-Problem Generator 74
Main Menu Option X: Exit 74
CHAPTER 5. THE MINTEQA2 OUTPUT FILE AND ERROR DIAGNOSTICS 76
Error Diagnostics 77
MINTEQA2 Error Codes and Messages 77
REFERENCES 82
APPENDIX A. THE THERMODYNAMIC DATABASE USED BY MINTEQA2 84
The Component Database File 85
Format of Database Species Entries 87
Examples of Entries in the Thermodynamic Database Files 93
APPENDIX B. NEWTON-RAPHSON APPROXIMATION METHOD 96
APPENDIX C. MINTEQA2 MODEL DISTRIBUTION 97
Introduction 97
Microcomputer Version 97
DEC VAX/VMS Version 98
Obtaining a Copy of the MINTEQA2 Model Package 98
CEAM Electronic Bulletin Board System (BBS) 99
Technical support 99
Disclaimers 99
APPENDIX D. EXAMPLE MINTEQA2 FILES 100
vi
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LIST OF FIGURES
Figure 3.1. Schematic representation of the surface charge/potential
relationships used in the constant capacitance and diffuse-
layer models
Figure 3.2. Schematic representation of surface species and
charge/potential relationships in the triple-layer model.
36
40
Table 2.1.
Table 2.2.
Table 2.3.
LIST OF TABLES
Reactions and log equilibrium constants for soluble species
in a 0.001 M solution of CaC03 at 25 °C
Stoichiometric matrix representing the 0.001 M CaC03
solution
Mass action expressions applicable to the CaC03 solution
using mixed equilibrium constants
10
11
12
vii
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ACKNOWLEDGMENT
The authors would like to thank Dr. John Westall, Oregon State
University, Corvallis, OR, for openly sharing his wisdom on metal speciation
modeling and for his criticisms and encouragement in the continued development
of MINTEQA2 and PRODEFA2. The many discussions we've had at MINTEQA2
workshops sponsored by the Athens Environmental Research Laboratory (AERL)
have contributed much to the enhancements in version 3.0.
We also extend thanks to Dr. Nick Loux of AERL for his shared insight in
environmental geochemistry, especially in modeling real-world systems. The
work of his colleagues, Ms. Claudia Chafin and Dr. Sayed Hassan of Technology
Applications, Inc., in validating the diffuse-layer model iron-oxide database
is also acknowledged. Mr. Bob Ambrose of AERL, Mr. Dave Disney, Ms. Catherine
Green, Ms. Lisa Sealock of Computer Sciences Corporation, and Ms. Joyce Wool
of ASci have contributed to the organization of MINTEQA2 into a form suitable
for public distribution through the AERL Center for Exposure Assessment
Modeling and have fostered its use by their assistance in the presentation
of MINTEQA2 workshops.
For helpful comments and suggestions arising from their review of this
document, we thank Mr. Robert Ryans, and Dr. George Bailey of AERL and
Ms. Angelica Schnieder-Graziosi of Ismes-Italy, Rome.
Research contributing to the development of the MINTEQA2/PRODEFA2 model
has been supported in part by the US EPA Office of Solid Waste.
Vlll
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CHAPTER 1
INTRODUCTION
Technical understanding of the physical, chemical, and biological
processes controlling the behavior of pollutants in the environment has
increased significantly in the past two decades. Many of the important
advances are reflected in the quantitative mathematical models now being used
to describe the influences of competing processes or reactions on the overall
behavior of pollutants. A variety of mathematical models encompassing years
of research are now available for predicting the behavior of pollutants in
various environmental settings. The metal speciation model MINTEQA2,
described in this manual, is a versatile, state-of-the-art example of the
equilibrium solution chemistry programs now available.
MINTEQA2 is a geochemical equilibrium speciation model for dilute
aqueous systems. The original MINTEQ (8) was developed at Battelle Pacific
Northwest Laboratory (PNL) by combining the fundamental mathematical structure
of MINEQL (23), a derivative of REDEQL (11), with the well-developed
thermodynamic database of the U.S. Geological Survey's WATEQ3 model (1).
MINTEQA2 is substantially different from the original MINTEQ in the features
and options available, in the manner in which calculations are implemented,
and in its thermodynamic database. Also, MINTEQA2 is complemented by
PRODEFA2, an interactive program used to create input files. The original
PRODEF also was a product of Battelle PNL and has undergone extensive
modification and development as PRODEFA2. The model can be used to calculate
the equilibrium composition of dilute aqueous solutions in the laboratory or
in natural aqueous systems. It can be used to calculate the mass distribution
between the dissolved, adsorbed, and multiple solid phases under a variety of
conditions including a gas phase with constant partial pressure.
The data required to predict the equilibrium composition consists of a
chemical analysis of the sample to be modeled giving total dissolved
concentrations for the components of interest and any other relevant invariant
measurements for the system of interest, possibly (but not necessarily)
including pH, pe, or the partial pressures of one or more gases. A measured
value of pH and/or pe may be specified as equilibrium values or MINTEQA2 can
calculate equilibrium values. Also, a mineral may be specified as presumed
present at equilibrium, but subject to dissolution if equilibrium conditions
warrant, or definitely present at equilibrium and not subject to complete
dissolution.
MINTEQA2 has an extensive thermodynamic database that is adequate for
solving a broad range of problems without need for additional user-supplied
equilibrium constants. The standard database can be easily modified if it is
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found to be incomplete or inadequate for a particular problem. The empirical
nature of the available metal adsorption data reflects the fact that natural
adsorbent phases often occur as mixtures of impure amorphous substances that
vary widely in chemical behavior from site to site. For this reason,
adsorption data are left to the discretion and problem-specific knowledge of
the user. Seven adsorption models are available in MINTEQA2 to match the type
of data available for specific problems.
The application of a geochemical equilibrium model to an environmental
problem involves four steps:
1) Formulate one or more precise and relevant chemical questions that
can be answered if one knows the equilibrium composition of the system.
The formulation of the chemical questions must respect the inherent
limitations in the site-specific data such as incomplete sampling or
incomplete chemical analyses of samples.
2) Pose the chemical questions to the model in terms of those symbols
and formats that it is programmed to understand and from which it may
interpret a mathematical problem.
3) Cause the computer program that is the geochemical equilibrium model
(in this case, MINTEQA2) to solve the mathematical problem.
4) Interpret the output from the model in terms of the original
environmental problem.
The first step is almost always the most difficult; the ability to do
this well is not obtained from reading a user manual. The authors anticipate
the writing of a companion "applications" volume in which several case studies
will be presented and the logic of step 1 will be emphasized. PRODEFA2 is
designed to perform step 2 by asking questions about the chemical system to be
modeled and building the appropriate MINTEQA2 input file from the answers.
Step 3, the actual execution of MINTEQA2, is usually rather automatic, not
requiring user intervention once initiated. Occasionally, computational
problems will occur during execution that will require the user to make
adjustments to the input file and re-execute MINTEQA2. This is discussed
later in Chapter 5. Step 4 is performed as the user examines the MINTEQA2
output file and relates the result to the initial problem.
Chapter 2 is a presentation of the chemical and mathematical concepts
employed in MINTEQA2 with the exception of those concepts that are peculiar to
the adsorption models that are presented separately in Chapter 3. The
mechanics of using PRODEFA2 and MINTEQA2 are presented in Chapter 4. Chapter
5 provides information about error conditions and their resolution.
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CHAPTER 2
CHEMICAL AND MATHEMATICAL CONCEPTS
This chapter provides a brief review of the important concepts used to
solve the general chemical equilibrium problem. The emphasis here is on how
MINTEQA2 works, rather than how to work MINTEQA2 (the subject of chapter 4).
After developing some definitions, we provide the relevant mass action and
mole balance equations and describe their solution using an example problem
first without, then with a solid phase. Other equations and algorithms used
in MINTEQA2 for correcting equilibrium constants, computing total dissolved
carbonate concentration from alkalinity, and obtaining other values are also
presented. The material presented in this chapter also applies to adsorption
reactions but the additional concepts that distinguish adsorption algorithms
are presented in chapter 3.
Component and Species Definitions
Components - These are the basis entities or building-blocks from which
all species in the system can be built. MINTEQA2 has an associated
component database file containing more than 100 components (see
Appendix A) from which the user selects only those needed in the
specific problem of interest. The components used in MINTEQA2 form a
pre-defined set, e.g., the component for calcium is Ca+2 and not some
other species such as CaOH+. The thermodynamic database, written in
terms of these components, is searched automatically to retrieve only
those species relevant to a specific problem. Components represent an
accounting system and, while it is not required that they be actual
chemical species, nearly all MINTEQA2 components except certain of those
used to represent electrostatic terms in adsorption models are
physically realizable species.
Type I Components as Species in Solution - These are the components
themselves defined as actual chemical species. As mentioned above, in
the general case, a component need not be an actual chemical species.
The set of available components in MINTEQA2 happens to include
components that are all bona fide chemical species (excepting the
electrostatic components). Thus, all (non-electrostatic) components in
a MINTEQA2 problem will also be defined as Type I species.
Type II Other Species in Solution or Adsorbed - These are all dissolved
species other than those that are Type I. These may be complexes or
free ions, for example, Cr3+ (the component for Cr3"1" is Cr(OH)2+).
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Insofar as components may be thought of as reactants, Type II species
may be considered aqueous and adsorption reaction products.
Type III Species with Fixed Activity - Generally, these are either
species that are present at fixed equilibrium activity or are mock
species that define a fixed equilibrium activity relationship between
two real species. In earlier MINTEQ documentation as well as in
documentation on related models (8,23), Type III species were referred
to as Fixed Solids because all Type III species are treated
mathematically in the same way as a solid. This terminology was a
source of confusion since Type III species are not necessarily solids.
Examples of a Type III species are any solids that are explicitly
constrained to be present at equilibrium (not subject to complete
dissolution; an infinite solid), any components whose activities are
explicitly constrained to a given equilibrium value (e.g. fixed pH or
pe), any gases whose partial pressures are explicitly constrained to a
given equilibrium pressure, or any mock species whose equilibrium
activity is explicitly constrained to an equilibrium value (such as a
redox couple that fixes the equilibrium activity ratio of two components
that form a redox pair.)
Type IV Finite Solids - These are solid phases that are presumed present
initially or precipitate from the solution. In the latter case, the
appropriate components are depleted in the aqueous phase to "create" the
precipitated solids. With MINTEQA2, it is also possible to specify one
or more precipitated solids as present initially at some given amount
(per liter basis). For those Type IV solids that are specified as
present initially, the entire amount may dissolve if equilibrium demands
it and the concentrations of the appropriate components will then be
supplemented in the aqueous phase. The reader should realiz:e that, in
theory, it doesn't matter to MINTEQA2 whether the system totals for
various components are specified at the outset as all dissolved or all
bound in precipitated solid(s) of given amount(s). In practice, it
helps to avoid phase rule violations (discussed later) if Type IV solids
are entered with a concentration of zero. In that case, the total
dissolved concentrations of the components of the solid represent total
system concentrations. MINTEQA2 will shift mass from the dissolved to
precipitated phases or vice versa as required by equilibrium.
Type V Possible (Undersaturated) Solids - These are solid phases that
are defined in MINTEQA2; however, they are not oversaturated, do not
physically exist, and thus have no direct impact on the chemical
equilibrium problem. When the solution becomes oversaturated with
respect to a particular possible solid, and if that solid is more
oversaturated than any other possible solid composed of the same
components, MINTEQA2 will precipitate that solid depleting the aqueous
phase concentrations of the appropriate components. The newly
precipitated solid is then re-assigned as a Type IV species. If any
Type IV solid dissolves completely so that its entire mass is shifted to
the aqueous phase, that solid is re-assigned as Type V. Note that in
PRODEFA2 and in the listing of input data that MINTEQA2 includes in its
output file, Type V solids are referred to as POSSIBLE solids. In the
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listing of equilibrated results however, Type V species are referred to
as UNDERSATURATED solids.
Type VI Excluded Species - These are species that would ordinarily be
Type I, II, III, or V but are assigned as Type VI to exclude them from
mass balance calculations. Reasons for wanting to impose such
exclusions are varied. For example, the mass of the component
representing the electron (e~) is entered as zero in the database. For
obvious reasons, one would not want to impose the condition of mass
balance on e". Therefore, unless an equilibrium pe is imposed, e" is
excluded from mass balance calculations by designating it as Type VI.
When MINTEQA2 reads the input file for a specific problem, it searches
the database to find all species that can be reaction products of the
specified reactants (components). Of these possible species, all gases
and redox couples are entered as Type VI unless they are explicitly
designated in the input file as Type III. Unless a flag in the input
file directs otherwise, all solid phases are treated as Type VI by
default. All electrostatic components used in adsorption reactions are
entered as Type VI in the input file because they are not real chemical
entities; they have no mass. Finally, any species that the user wishes
to explicitly exclude may be so designated in the input file. For
example, a solid phase that is suspected to be unrealistic for kinetic
reasons, but which would otherwise precipitate may be explicitly
excluded. PRODEFA2 has the logic to properly assign species to the Type
VI category as necessary and provides for explicitly assigning any
species to Type VI as desired by the user.
The Pre-Defined Set of Components
The pre-defined set of components available in MINTEQA2 (see Appendix A)
includes naked ions such as Na+ and neutral and charged complexes (e.g.
H4SiOA, Cr(OH)2+). In general, the species chosen to serve as components are
those that are expected to be the dominant dissolved species in natural
waters, i.e., H4SiOA as opposed to some other species of dissolved silica. Of
course, for a specific problem, the species which represents the component may
not always be the dominant equilibrium species, whatever components are
selected, it is only necessary that they linearly combine to produce every
species in the system and that it be impossible to produce any component
through another combination of components (multiple oxidation states of the
same chemical element being exempted from this latter requirement; i.e, the
fact that component Fe3+ can be produced from a combination of components Fe2"1"
and e" is acceptable).
Oxidation/Reduction Reactions
Redox reactions are represented in either of two ways in MINTEQA2. One
way is the designation of separate components to represent the oxidation
states of interest. For example, in the current database, there are separate
components for Fe2+ and Fe3+. Thus, separate reactions can be written for each
of these components; in fact, this has been done and those reactions are
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available in the thermodynamic database. Also, as mentioned earlier in
defining Type III Species with Fixed Activity, mock species are defined to
represent the activity ratio between two members of a redox couple. When such
a species is assigned as Type III and the equilibrium pe is also specified,
mass is shifted from one member of the couple to the other in such a way as to
cause their activity ratio to honor the Nernst Equation at the equilibrium pe
specified. The other way to represent different oxidation states requires
only one oxidation state to be defined as a component. Then any reaction that
would involve a different oxidation state of that same component is written to
include the gain or loss of electrons and the log K for the formation of the
product is adjusted accordingly. Had this scheme been used for the iron
system, Fe3+ might have been chosen as a component and Fe2"1" would have been a
Type II species with Fe3"1" and e" as reactants. While most of the redox
chemistry in MINTEQA2 is represented by the components of separately defined
oxidation states, the electron appears in many reactions as well.
General Problem Formulation
Two general approaches are commonly used to formulate and solve
multiple-component chemical equilibrium problems: 1) minimization of the
system free energy under mass balance constraints or 2) simultaneous solution
of the nonlinear mass action expressions and linear mass balance
relationships. MINTEQA2 uses the latter approach, frequently referred to as
the "equilibrium constant method". This method also is used in several other
geochemical equilibrium programs including PHREEQE (15), EQ3NR (24), and
MICROQL II (21). Van Zeggeren and Storey (20) have shown the two approaches
to be mathematically equivalent.
To solve the chemical equilibrium problem, MINTEQA2 uses an initial
guess for the activity of each component to calculate the concentration of
each species according to mass action expressions written in terms of
component activities. The total mass of each component is then calculated
from the concentrations of every species containing that component. The
calculated total mass for each component is then compared with the known input
total mass for each component. If the calculated total mass and the known
input total mass for any component differ by more than a pre-set tolerance
level, a new estimate of the component activity is made and the entire
procedure is repeated. The aqueous phase equilibrium composition is that set
of species concentrations which gives a mass imbalance less than the tolerance
level for every component.
After equilibrating the aqueous phase, MINTEQA2 computes the saturation
index (SI) for each possible solid with respect to the solution. The solid
with the most positive SI is allowed to precipitate by depleting the dissolved
concentrations of those components comprising the solid in accordance with the
known stoichiometry of each component. The reverse process occurs if an
existing solid is found to be undersaturated with respect to the solution. In
either case, it is necessary to re-equilibrate the solution after mass has
been added to or depleted from the aqueous phase. Thus the aqueous solution
is re-equilibrated just as before except with one less degree of freedom if
precipitation has occurred or one more if dissolution has occurred. The
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entire computational loop of iterating to equilibrium, checking for
precipitation or dissolution, and shifting mass from the aqueous to the solid
phase or vice versa is repeated until equilibrium is achieved and there are no
oversaturated possible solids and no undersaturated existing solids.
The number of degrees of freedom of the system is the number of
independent variables. These would ordinarily include temperature, pressure,
and all the component activities that can be independently varied. Several
constraints are used in MINTEQA2 that modify the usual phase rule
relationship. Because temperature and pressure are both specified to be
invariant by the user, the phase rule expression that applies to MINTEQA2
calculations is
f = C - P 2.01
Where:
f = the number of degrees of freedom
C - the number of components
P = NN(III) + NN(IV)
NN(III) - the number of Type III Species with Fixed Activity
NN(IV) = the number of Type IV Finite Solid Species
MINTEQA2 calculates f at the outset of each problem and if f is greater
than zero, proceeds with the calculations. One additional degree of freedom
is lost for each new solid phase that forms, that is, each species that is re-
assigned from Type V to Type IV. Conversely, each existing solid that
dissolves (Type IV species re-assigned to Type V) adds one degree of freedom.
Examples of constraints that result in reducing the number of degrees of
freedom, that is, that contribute to P in equation 2.01, are the fixed
activity of the component H20 or of other components with fixed activities.
As is evident above, each solid phase present (Type III or IV) also
contributes to P. This follows from the solubility product constraint imposed
by the presence of a solid phase. To see why the precipitation of a solid
results in the loss of one degree of freedom, consider the example
Ag+ + Cl~ ^± AgCl(s) log K = 9.75 2.02
By convention, the activity of the pure precipitated AgCl(s) is 1.0. Thus,
K = 109-75 - {AgCl(s)}/(Ag+}{Cl-} 2.03
or
= io-9-75 (err1
Thus, when pure AgCl(s) exists {Ag+} and {Cl~} are no longer independent
variables .
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A system of n independent components that can combine to form m species
is represented by a. set of mass action expressions of the form
K, - {SJ H X/aiJ 2.04
J
Where:
Ki - equilibrium constant for the formation of species i
(Si) - activity of species i
Xj - activity of component j
a^ - stoichiometric coefficient of component j in species i
II - indicates the product over all components in species i
The concentration of species i, [Si], is related to the activity {S^ by the
activity coefficient, 7A
(Si) - 7JSJ 2.05
Substituting this expression for {S^ in equation 2.04 and rearranging gives
[SJ - iq/Ti nX/iJ 2.06
j
Now, if we define K.\ such that
K'i - Ki/Tfi 2.07
then
Cj. - [SJ - K't UXjaiJ 2.08
j
For notational convenience, we will use Cj and [SL] interckangeably; both mean
the concentration of species i. In equation 2.08, the activity coefficient
term is incorporated into the equilibrium constant K\ and ideal conditions
(ionic strength 0; activity coefficients 1) correspond to the condition
K'i - K±.
In logarithmic form, equation 2.08 becomes
log Ci - log K'i+ 2 aAJ log Xj 2.09
J
In addition to the mass action expressions, the set of n independent
components is governed by n mass balance equations of the form
Yj - Z aij q - Tj 2.10
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Where:
Tj = total dissolved concentration of component j (also referred
to as the total analytical concentration because Tj is generally a
known measured input parameter)
YJ - the difference between the calculated total dissolved
concentration of component j and the known analytical total
dissolved concentration of component j
The solution (in the mathematical sense) is that set of component
activities X (using matrix notation for brevity) which results in the set of
concentrations C such that each individual of the set of mass balance
differences Y is equal to zero. In practice, it is only necessary to find X
such that each individual of Y is made less than some tolerance value. The
general procedure is to first guess X (PRODEFA2 makes this guess and puts it
in the input file), then calculate C and Y. If any individual of Y exceeds
(in absolute terms) its prescribed tolerance value, a new guess is made for X,
C and Y are recalculated, and the test is repeated. This iterative procedure
is continued until all the individuals of Y are less than the tolerance value.
Like MINEQL, MINTEQA2 uses the Newton-Raphson approximation method to estimate
the new X at each iteration (see Appendix B). The tolerance value or
convergence criteria for MINTEQA2 is pre-set to 1CT* times Tj for each
component j.
Example Problem without a Solid Phase
To illustrate the generalized mathematical formalisms used to solve
chemical equilibrium problems, it is instructive to consider a simple problem
in detail. The example problem formulation that follows is based on a simple
calcium carbonate (CaC03) solution. This solution has served as the classical
example for many chemical equilibrium models and has been discussed in great
detail elsewhere (7, 8, 21). A 0.001 molar solution of CaC03 that has no
access to atmospheric gases is considered. No solid phases are considered.
Furthermore, no adsorbent phases are present, no redox reactions occur, and no
Type III species are included.
The CaC03 solution at equilibrium will contain ten soluble species:
Ca2+, CaOH+, CaC03°, CaHC03+, H2C03, HC03", C032', H+, OH", and H20. (Note CaC03°
refers to the soluble complex, not the solid which is designated CaC03(s).)
The set of 6 independent reactions involving these species is shown in Table
2.1. The choice of components to represent a given solution, in general, is
not unique; however, the component set used in MINTEQA2 is pre-set (See
Appendix A).
The required number of components is equal to the number of species
minus the number of independent reactions. Thus, for this problem we need
four components. Some general guidelines for choosing components are:
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1) Always choose H20 as a component; this is required in MINTEQA2 and,
in fact, H20 is chosen automatically.
2) Always choose H"1" as a component; this is not required but, except
for certain problems of academic interest, H"1" should always be a
component.
3) If redox transformations are involved in this problem, include the
electron as a component. Remember that those database reactions that
involve the electron as a component, such as CH4(g), will not be brought
into the problem if e" is not a component. Even so, do not include e"
unless it's necessary.
4) For all other components, the choices are obvious; PRODEFA2 can
provide a listing of all available components but there's only one that
can represent As3+, one that can represent Ca2"1", etc.
The four components that are applicable to the CaC03 solution are H20, H+,
Ca2+, and C032". H20 is presumed to exist at constant activity. This is a
good assumption for all dilute solutions because the mass of H20 present is
several orders of magnitude greater than the other components. The small mass
of water consumed (or generated) by reactions with other components is
justifiably neglected; there is no mole balance on H20.
Table 2.1. Reactions and log equilibrium constants for soluble species in a
0.001 M solution of CaC03 at 25 °C .
Reactions log K
H20 - H+ a=± OH' -14.0
C032- + H+ «=* HC03- 10. 2
C032- + 2H+ «=± H2C03 16 .5
Ca2+ + H20 - H+ ^z± CaOH+ -12.2
Ca2+ + C032- + H+ ^± CaHC03+ 11.6
Ca2+ + C032- j=± CaC03° 3.0
For any species, the stoichiometric coefficients for each component are
given by the corresponding reaction written with the components all on the
left side of the reaction and the species as the sole reaction product on the
right side. For example,
Ca2+ + H20 - H+ j=± CaOH+
10
-------
Thus, the stoichiometric coefficient for the component H+ in the species CaOH"1"
is -1. Similarly for H2C03
C032' + 2H+ *=± H2C03
the stoichiometric coefficient for the component H+ in the species H2C03 is
+2. If MINTEQA2's component list had been chosen differently (we have already
observed that the selection of components in our pre-defined list is
arbitrary) so that 02~ were a component, then the reaction for H2C03 in the
database would have been:
C032" + H20 - O2' +=± H2C03
In that case, the components C032~, H20, and O2" would have stoichiometries 1,
1, and -1 respectively. Of course, the equilibrium constant for this reaction
would be different from that of the former H2C03 reaction.
The stoichiometric coefficients and log equilibrium constants for all
species in the CaC03 problem are shown in Table 2.2. Note that the
equilibrium constants are for the formation of the species from the components
with the corresponding stoichiometries and that these are thermodynamic
database constants. Before they are used in MINTEQA2, they will each be
corrected by the species activity coefficient as in equation 2.07.
Table 2.2. Stoichiometric matrix representing the 0.001 M CaC03 solution.
Species
H20
H+
Ca2+
co32-
OH"
HC03"
H2C03
CaOH+
CaHC03+
CaCO,°
H20
1
0
0
0
1
0
0
1
0
0
Components
H+ Ca2+
0
1
0
0
-1
1
2
-1
1
0
0
0
1
0
0
0
0
1
1
1
K
C032'
0 K!
0 K2
0 K3
1 -\7
*- "4
0 K5
1 K
IV
7
0 K8
1 V
*XQ
Irr
Jx-i rt
11
-------
Note that Table 2.2 includes several identity relationships. The
generalized nature of the computational algorithm is such that to make the
species H+ for example, requires that the stoichiometry of the component H+
be one and that of all other components be zero.
The set of mass action constraints that apply to the reactions in Table
2.2 are given in Table 2.3. Note that because we are expressing species
concentrations in terms of component activities, we must use the mixed
equilibrium constants as given by equation 2.07.
Table 2.3. Mass action expressions applicable to the CaC03 solution using
mixed equilibrium constants.
(1) [H20] - {H20} K'i
(2) [H+] = {H+} K'2
(3) [Ca2+] - (Ca2+) K'3
(4) [C032-] = {C032-} K\
(5) [OH'] = {H20} {HV1 K'5
(6) [HC03-] = {C032-} {H+} K'6
(7) [H2C03] = {C032-} {H+}2 K'7
(8) [CaOH+] - {Ca2+} {H20} {H*}'1 K'8
(9) [CaHC03+] = {Ca+2} {C032'} {H+} K'9
(10) [CaC03°] - {Ca+2} {C032~}
10
Three mole balance expressions are required to complete the set of
equations that define the CaC03 system (recall that mass balance is neglected
on H20). The mole balance expressions corresponding to equation 2.10 are
generated by summing the concentrations of all species involving a particular
component and subtracting the respective analytical input concentration for
that component. The resulting expressions are:
YCa2t = [Ca2+] + [CaOH+] + [CaHC03+] + [CaC03°] - TCa2+ 2.11
YC02- = [C032'] + [HC03-] + [H2C03] + [CaHC03+] + [CaC03°] - Tco 2- 2.12
3 3
YH+ = [H+] + [HC
-------
The ultimate goal is to solve these mole balance equations under the
constraints of the mass action expressions in Table 2.3. To do this, the
species concentration terms in those equations are replaced with their
corresponding mass action expressions from the table. The final set of mole
balance equations then becomes :
YCa2+ - K'3{Ca2+} + K'8{Ca2+}{H20}{H+}-1 + K' 9{Ca2+) (H+)
+ K'10{Ca2+}{C032-} - TCa2+ 2.14
YC02- = K'A{C032-} + K'6{H+}{C032-} + K'7{H+}2{C032-}
3
+ K'9{Ca2+}{H+HC032~} + K'10{Ca2+HC032-} - Tco 2- 2.15
YH+ = K'2{H+) + K'6{H+HC032~} + 2K' 7{H+}2{C032"} + K' 9{Ca2+) {H+} {C032-}
- K'8{H20}{Ca2+}{H+}"1 - K'stHaOHHV1 - TH+ 2.16
These three equations are now expressed in terms of three unknowns,
{H+}, {Ca2"1"}, and {C032~}. The adjusted equilibrium constants, analytical
component total dissolved concentrations, and the activity of H20 are known.
(Recall that the analytical input concentrations (TCa2+, TC02-, and TH+) are
supplied by the user when the problem is specified and H20 3always has activity
fixed at approximately 1.0). The mathematical solution is that set of
component activities which gives YCa2+, Yco 2- , and YH+ all equal to zero, or
more practically, all less than some acceptably small error (convergence
criteria). From final component activities, the equilibrium concentrations of
all species can be calculated using the mass action expressions in Table 2.3.
Example Problem with a Solid Phase and with a Gas Phase
Let us consider the same calcium carbonate system as before except with
a solid phase, calcite, present at equilibrium. In that case, we would add
the following reaction to Table 2 . 1
Ca2+ + C032" ^=± CaC03(s) Kn
and the stoichiometric coefficients for CaC03(s) in Table 2.2 would be the
same as for the dissolved species CaC03°. The appropriate mass action
expression (equation 2.08) that would be added to Table 2.3 is
[CaC03°] = {Ca+2} {C032-} K'n 2.17
Now, because CaC03(s) is a pure phase,
[CaC03(s)j = (CaC03(s)} = 1
13
-------
and we can solve equation 2.17 for either {Ca2"1"} or {C032 }; let us choose
{C032~}. Then,
{C032-} =
2.18
K'n (Ca2+)
Thus , the three unknowns of equations 2 . 14 thru 2 . 16 have been reduced to only
two by making use of the fact that a pure phase has activity of 1. If we make
this substitution (equation 2.18) in the three mole balance equations, we
obtain
K'3{Ca2+} + K'8{Ca2+}{H20}{H+}-1 + K' 9{H+)
- TCa2+
2.19
Yco2-
O
+
-1 + K' 7{H+}2(K'u{Ca2+} )'1
TC032-
2.20
- K'2{H+)
2K' 7{H+)2(K'u{Ca2+} r1
+r1 - K' 5{H20) {H+T1 - TH+ 2-21
Note that Equations 2.19 through 2.21 now contain only {Ca2"1"} and {H+}
as unknowns. Carbonate ion activity has been eliminated as a component and
the dimensions of the Jacobian matrix that must be calculated to estimate new
component activities at each succeeding iteration during the Newton- Raphson
iteration sequence have been reduced.
For more complicated systems that may contain a number of solids (Types
III or IV), the process of eliminating variables is more complicated. A
priority order of thermodynamic stabilities of each solid is established by
comparing the appropriate ion activity products (IAP) with the corresponding
formation constant after the aqueous phase has been equilibrated. The
logarithmic ratio of these terms (saturation index) is calculated and used to
establish the stability order for precipitation or dissolution of solids.
Saturation Index = log
IAP
K
2.22
If the saturation index for a particular mineral is negative, the system
is undersaturated with respect to that mineral. If the index is positive, the
solution is supersaturated and, if the user has selected the appropriate
14
-------
precipitation option, MINTEQA2 will precipitate the solid in question until
the equilibrium condition is satisfied, i.e., until:
IAP
log - 0 2.23
K
Undersaturation for a given mineral can arise from three situations: a) a less
soluble mineral phase could be controlling the activities of one or more
common ions, b) the component input concentrations are insufficient to exceed
the formation constant, or c) free solution ion activities are limited by
sorption reactions.
MINTEQA2 re-evaluates the saturation indices for each solid each time
the aqueous phase is equilibrated. The user may choose to:
1) Allow no solids to precipitate regardless of saturation state,
2) Allow the precipitation of explicitly designated solids but only if
they become oversaturated,
3) Allow all oversaturated solids to precipitate, or
4) Allow all oversaturated solids to precipitate except for those
explicitly designated as excluded (Type VI).
In cases where precipitation is allowed, the entire computational loop
of iterating to equilibrium, checking for precipitation or dissolution, and
shifting mass from the aqueous to the solid phase or vice versa is repeated
until equilibrium is achieved with no oversaturated Type V Possible Solids and
no undersaturated Type IV Finite Solids.
Because the formation of solid phases changes the equilibrium species
distributions, the inclusion of a large number of Type IV or V solids in
MINTEQA2 executions requires that the species distribution equilibria problem
be re-solved several times during the iteration sequence for precipitating
solids. The difficulty of obtaining convergence is increased accordingly.
For this reason, model systems should be spared unnecessary detail. The user
should note that usually only a small number of solids control the free
solution activities of species representing a given metal. It may be useful
to perform a run with all solids prohibited from precipitating; examination of
the saturation indices will provide information as to the dominant solids.
The initial rule is, "If in doubt leave it out." The saturation index listings
can be used to detect first-pass mistakes. All unprecipitated
(supersaturated) solids will be represented by a positive saturation index.
If any positive values are found, the user may then add the omitted solid and
repeat the execution. In the final analysis, all controlling solids (those
that actually precipitate) will be identified with saturation indices equal to
zero.
Specifying a gas phase at a fixed partial pressure in the example CaC03
system would have much the same effect mathematically as did the solid calcite
15
-------
phase. When a C02(g) gas phase is present, the following reaction would
apply
C032- + 2H+ - H20 j=± C02(g) K'12 2.24
The corresponding mass action expression would be represented by
PCO = {COa'-HHVtHzO}-1 K'12 2.25
where Pco = the partial pressure of C02 in atmospheres. For systems open to
the atmosphere, Pco is fixed at 10"3-5 atmospheres. The new equilibrium
constant would be : 2
K'ia = K'i2/pco, 2.26
2
Then,
{H+} = [{C032-} K'i2]-* 2.27
If the solid phase is present as before, the expression for {C032~} (equation
2.18) can be substituted in equation 2.27 to give
{H+} - [{Ca2+}K'11(K'i2)-1]% 2.28
This expression for (H"1"} can be substituted into the mole balance equations
(2.19 through 2.21) which are then expressed in terms of the only remaining
unknown, namely {Ca2"1"}.
Note that PRODEFA2 computes the adjusted equilibrium constant from the
user-specified partial pressure. The database log K is 18.16 and if
Pco - 10"3-5atm, then the adjusted log K is computed from
2
log K'i2 = 18.16 - (-3.5) - 21.66 2.29
It is possible to over -cons train a system (eliminate all degrees of
freedom) by entering too many fixed species. If, for instance, a user
simultaneously fixed Pco and (H+) in the CaC03 problem above and then if a
solid phase is precipitated (by MINTEQA2 in computing the equilibrium or by
the user specifying an initial solid) , there would be no remaining variables
in the mole balance equations and the system would be over -cons trained.
MINTEQA2 would report a phase rule violation and execution would end with an
error.
In introducing the CaC03 problem originally, the gas phase reactions
were excluded. If this problem had been executed using MINTEQA2 , the user
would have been reminded of this exclusion in the output listing for Type VI
Excluded Species.
16
-------
Adjustments to Equilibrium Constants
The equilibrium constants in equations 2.14 through 2.16 are functions
of the system temperature and ionic strength. The values supplied in
MINTEQA2's thermodynamic database are referenced to 25°C and an ionic strength
of zero. If the temperature is not at 25°C, a new set of equilibrium
constants must be calculated before solving the equations. The ionic strength
affects activity coefficients which in turn affect the adjusted equilibrium
constants (equation 2.07). MINTEQA2 allows the option of specifying a fixed
ionic strength or of recalculating the ionic strength from the new estimates
of species concentrations at each iteration.
Temperature Corrections of Equilibrium Constants
MINTEQA2 incorporates two schemes for adjusting the equilibrium
constants for temperature. If the necessary data are available in the
thermodynamic database, MINTEQA2 uses a power function of the form
log KT = A + BT + C/T + D Log(T) + ET2 + F/T2 + GT1/2 2.30
Where:
T - temperature (K°)
A,B G = empirical constants stored in the thermodynamic database
Only 25 of the more than 1000 species in the database have these constants
available.
For any species that does not have the constants needed for equation
2.30, the equilibrium constant is corrected for temperature variations from
25°C by the van't Hoff equation
AHr° ( 1 1 1
log KT - log KT - 2.31
1 2.303R [ T TrJ
Where:
Tr = reference temperature, 298.16°K
log KT = logarithm of the equilibrium constant at the reference
r temperature
R = molar gas constant
T - temperature of the system to be modeled (Kelvin)
AHr° - standard enthalpy change of the reaction
17
-------
Caution should be used in attempting to apply MINTEQA2 to high
temperature systems. The van't Hoff equation implicitly assumes the
enthalpies of reaction to be independent of temperature. This assumption is
not always valid and significant errors can result at temperatures far above
25°C. For this reason, MINTEQA2 calculations should be restricted to a
temperature range below 100°C. Applications to high temperature geothermal
systems should definitely not be attempted unless empirical temperature
correction data are available.
If the standard enthalpy change is not available in the database,
MINTEQA2 uses the uncorrected log K's (25°C) . Users are encouraged to become
familiar with the database and to evaluate the impacts of these limitations on
their systems. Missing enthalpy data can be permanently added to the database
or, alternatively, temporarily entered into a given model execution using
instructions provided by PRODEFA2. The latter option is convenient for
testing a given system's sensitivity for individual reaction enthalpies.
Activity Coefficient Corrections of Equilibrium Constants
Activity coefficients for all species are functions of solution ionic
strength (I) and vary as species distributions alter the ionic strength.
Unless a fixed ionic strength is specified, successive sets of activity
coefficients are calculated for all solution species with each iteration.
These are used to generate corrected values of the equilibrium constants (see
equation 2.07) that appear in the mole balance expressions (equation 2.10).
Initial activity guesses for the input components are provided in the input
file for a given problem. These initial component activity guesses are used
to "crudely" estimate the concentrations of each dissolved species so that the
solution ionic strength can be calculated. Each succeeding iteration provides
improved estimates of species concentrations and activity corrections. The
solution ionic strength is used in either the modified Debye-Huckel equation
(19) or the Davies equation (3) to calculate activity coefficients (7) for all
charged species. If the user selects the modified Debye-Hiickel equation, it
will be used for those species that have the necessary parameters in the
database. For any species lacking the necessary parameters, the Davies
equation will be used to estimate the activity coefficient for that species.
If the user selects the Davies equation at the outset, it will be used
throughout the problem because it requires no species-specific data other than
charge. The activity coefficients are used in equation 2.07 to compute
adjusted equilibrium constants.
The modified Debye-Huckel expression used to calculate the activity
coefficients is
-Ad Z,2 I1/2
log 7l + bi I 2.32
1 + Bd a, I1/2
18
-------
Where:
Ad and Bd - constants that depend on the dielectric constant
and temperature
Zi the charge on each species i
&i " ion size parameter
b£ = ion specific parameter that accounts for the decrease in
solvent concentration in concentrated solutions
I solution ionic strength
The ionic strength (I) is calculated from
m
I = 4 S Z^ Cj. 2.33
i-l
Where:
Ci - concentration of ion species i
m - number of charged species present in the solution
Zi - charge on species i
The modified Debye-Huckel relation above is used only when the
parameters at and bt are available in the database . The current database
contains ai and b± parameters for many major inorganic ion species and a few
important trace metals . The values used were taken largely from the WATEQ3
data compilation (1). Where data are not available or if the user selects it,
the Davies equation will be used.
The Davies equation as implemented in MINTEQA2 is
f I% 1
log 7t - -AZ^ -- 0.241 2.34
in which the variables are defined as in equation 2.32.
With the exception of H20, activity coefficients of neutral species are
calculated using the development of Helgeson (10) ,
log 7i = ai I 2.35
where the constant QX is set equal to 0.1 in MINTEQA2 .
19
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Users are cautioned that the activity correction models presented here
are generally not intended for use at ionic strengths greater than 0.5. At
higher ionic strengths, as in marine conditions (ionic strength - 0.7 m),
these correction equations may still provide usable results; this should be
verified for the specific system to be modeled. Alternatively, one should
consider adding expanded versions of the Debye-Huckel equation, which include
terms to account for ion interactions occurring in more concentrated
solutions. The work of Pitzer and coworkers (16-18) provides some useful
alternative equations.
Successive sets of log K values that reflect the temperature corrections
(van't Hoff) and activity coefficient corrections (Debye-Huckel or Davies)
above are computed and substituted into the mole balance expressions. If no
solids are specified, the Jacobian matrix relating changes in mass balance to
changes in component activities is used to calculate that set of component
activities that will simultaneously minimize the mass imbalance for all
species. The procedure used is an iterative Gaussian elimination and back
substitution with a convergence test following each iteration.
Activity of H,0
The activity of water is estimated from
n
(H20) = 1 - 0.017 2 CA 2.36
1=1
where the C^'s represent the concentrations of individual ion species.
Equation 2.36 is applicable only in dilute solutions and is based on a
derivation using Raoult's law. The proportionality constant (0.017) is
derived from a plot of H20 activity versus the number of solute ions (9) .
Obtaining Total Dissolved Carbonate from Alkalinity
Most geochemical equilibria of the natural environment are in some way
dependent upon the total dissolved carbonate concentration, Tco 2-. Water
analyses frequently provide an alkalinity measurement rather tlfan an
analytical measurement of dissolved carbonate. MINTEQA2 can compute Tco 2-
from alkalinity. Implicit in the method used to compute Tco 2- are the 3
assumptions that the titration used to determine alkalinity was to the C02
equivalence point and that there exists no solid phase in the titrated
solution possessing additional acid-neutralizing capacity, all isolids having
been dissolved. This last assumption means that no solids should be allowed
in a MINTEQA2 run that uses alkalinity. If modeling of solid phases is
desired, do a preliminary model run without solids solely for calculating
Tco 2- , then use that calculated value in further modeling with solids rather
than alkalinity.
20
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Alkalinity as used here means that the value supplied represents the
acid-neutralizing capacity of the solution as determined by titrating the
solution to the C02 equivalence point. This corresponds to an operational
definition implemented in MINTEQA2 which is: The alkalinity is given by the
negative of the TOTH expression when the components are the principal
components at the C02 equivalence point. Beyond this, the exact definition of
alkalinity as used in a particular problem depends upon the content of the
database file, ALK.DBS. The content of that file is entirely the
responsibility of the user; it is not to be thought of as a database file,
but rather as an auxiliary input file. The definition of alkalinity as the
negative of the equation for TOTH and the use of ALK.DBS are illustrated
below.
In general, the principal components of an aqueous solution at the C02
equivalence point are H20, H+, and the most abundant soluble species of each
chemical entity. MINTEQA2 has a pre-defined set of components not all of
which are the principal components at the C02 equivalence point, but this does
not invalidate the applicability of the operational definition of alkalinity.
It simply means that the alkalinity expression will incorporate species that
may also be components. Practically, the procedure for determining the
alkalinity factors needed for carbonate containing species in THERMO.DBS and
for entries in ALK.DBS is to write (outside of MINTEQA2) the TOTH expression
derived using the principal components at the C02 equivalence point. The
negative of the coefficient for each species as it occurs in the TOTH equation
is the alkalinity factor for that species. Stated differently, the
contribution of each species in solution to the alkalinity is given by the
negative of the stoichiometry of H+ in that species times the species
concentration. The only species that are implicitly included as contributors
to the entered alkalinity is the Type I species (C032~) and those Type 2
species for which there is a non-zero entry for the alkalinity factor in
THERMO.DBS (such as for HC03") . For these species, it is not necessary for
the user to know the alkalinity factor; the appropriate factor is already in
THERMO.DBS. If other species are to be included as contributors to
alkalinity, the ID number and the proper alkalinity factor, as given by the
TOTH expression derived using the principal components at the C02 equivalence
point, must be entered in ALK.DBS. Entries for species containing C032~ MUST
NOT be included in that file. Suppose for example that the sample you wish to
model and for which you've measured the alkalinity contains appreciable
dissolved phosphate. You may wish to account for the phosphate contribution
to the measured alkalinity so as to arrive at a more correct value for total
dissolved carbonate. The procedure for doing this is:
1) Determine the principal components at C02 equivalence point:
H+, H2C03, H2P04-
2) Write out a mole balance equation for H+ including all species for
which the stoichiometry of the component H+ is non-zero. This is done
by first writing the reactions to produce all the species using the
components above as reactants. For example,
21
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H2P(V + H+ ^-> H3P04
and
H2C03 - H+ ^z± HC03-
The stoichiome tries of H+ in HC03" and H3POA, respectively, are 1 and -
1. The complete TOTH expression then is
TOTH - [H+] - [OR-] - [HC03-] - 2[C032-] + [H3POJ - [HP042'] - 2[P043'] 2.37
3) Noting that the piq for H3P04 is 2.2, we might choose to omit that
species altogether due to its negligible concentration above pH 4.
Retaining it here for illustration, entries in ALK.DBS would be:
3305802 -1.00
3305800 1.00
580 2.00
3300020 1.00
330 -1.00
where the 7-digit and 3-digit numbers are species ID numbers and the
rightmost digit in each ID number is in column 7 and the first line in
the file holds the first entry. The ID numbers correspond to species:
3305802 - H3POA
3305800 - HP042"
580 - P043'
3300020 - OH"
330 - H+
The alkalinity equation to which the value input for alkalinity corresponds is
alk - -TOTH or:
alk - -[H+] + [GIT] + [HC03-] + 2[C032-] - [H3PO<] + [HPO,,2'] + 2[P043'] 2.38
In most natural systems, the phosphate species are at much lesser
concentration than the carbonate and can be neglected. In any case, the user
controls the alkalinity equation by preparing ALK.DBS.
If this same file is used in a MINTEQA2 run for which component ID # 580
(P043~) is not included, then those entries in ALK.DBS that involve component
580 are simply ignored and the alkalinity equation that would be used is:
alk - -[H+] + [OH"] + [HC03-] + 2[C032'] 2.39
Let the contribution of non- carbonate containing species to the input
alkalinity be called non- carbonate alkalinity. Then, the dissolved total
inorganic carbon Tco 2- is given by
3
Tco 2 -- alk - excrb - noncrb + [H2C03] 2.40
3
22
-------
where
alk - input alkalinity value converted to eq/L.
excrb - total number of excess equivalents of acid consumed per mole of
carbonate containing species, (summed over all such species). For each
carbonate species, the alkalinity factor gives the total number of
equivalents of acid consumed per mole. Therefore, the excess
equivalents for each such species is given by the difference between the
alkalinity factor and the stoichiometry of C032" in that species times
the number of moles, that is, times the concentration (per liter basis).
noncrb total number of equivalents of non-carbonate alkalinity (summed
over all species contributing to non-carbonate alkalinity). For each
non-carbonate species, the alkalinity factor is the number of
equivalents of acid consumed per mole. Therefore, the number of
equivalents of non-carbonate alkalinity for each such species is the
alkalinity factor times the species concentration (per liter basis).
Since the alkalinity as given by equation 2.40 is a function of the
speciation and thus, so is TC02-, MINTEQA2 re-computes the Tco 2- with each
iteration. The user is reminded that the measured alkalinity3assumes that
there is no additional acid-neutralizing capacity in the form of solids. The
measured alkalinity value cannot be used to compute an accurate value of Tco 2-
if solid phases are specified or allowed to precipitate. If the problem befng
modeling involves solids, use the alkalinity value in a preliminary run with
no solid phases present or allowed. Then, in subsequent runs with solid
phases, use the computed total dissolved carbonate concentration (Tco2-) from
that preliminary run rather than the measured alkalinity. 3
23
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CHAPTER 3
ADSORPTION MODELS
Seven options are currently available in MINTEQA2 for modeling surface
reactions. These include: 1) the activity Kd model, 2) the activity Langmuir
model, 3) the activity Freundlich model, 4) the ion exchange model, 5) the
constant capacitance model, 6) the triple-layer model, and 7) the diffuse-
layer model. Thermodynamic database files of surface reactions are generally
not provided for these models as for aqueous and solid species; the user must
provide the set of surface reactions and their equilibrium constants. An
exception is a database of several surface reactions relevant to the diffuse-
layer model for trace metal adsorption onto an iron oxide surface.
Mathematical formalisms and input data requirements of the individual
adsorption models are discussed in separate sections below.
In the implementation of adsorption models in MINTEQA2, five different
surfaces may be simultaneously defined for a single program execution. Each
surface may have up to two types of sites. Only one adsorption model may be
specified in a single execution e.g., it is not possible to define one
surface undergoing adsorption in accordance with the Freundlich model and
another surface undergoing Langmuir adsorption in the same MINTEQA2 run. The
general modeling approach is to create a component to represent a particular
type of site on. a particular surface and then to write reactions between other
components and that site. The reactions are introduced to MINTEQA2 through
its input file and the solution is equilibrated with the surface species
treated mathematically as aqueous species except with certain peculiarities
pertinent to the adsorption model specified. When the equilibrium composition
is determined, the equilibrated mass distribution between the dissolved,
sorbed, and solid phases is computed and reported. When comparing MINTEQA2
equilibrated results with experimental Kd values, the MINTEQA2 adsorbed and
precipitated species should be grouped together because these two phases are
not experimentally distinguishable. There is no intrinsic difference within
MINTEQA2 that distinguishes one surface from another nor one site, on a surface
from another. The user establishes the difference between any two surfaces
and between the two sites on a surface by specifying the surface concentration
and other surface specific parameters, such as specific surface area, and by
specifying the reactions that each site may undergo.
Naming and Numbering Surface Species
Developing a coherent notational scheme for the naming of surface sites
and the species that pertain to them is a difficult task. The notation
frequently used in the literature for the electrostatic models seems to be
24
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primarily applicable to oxide surfaces. Nevertheless, it does provide a
coherent system and we have used "SOH" to designate a surface site throughout
this chapter. Within MINTEQA2, a more elaborate but generic scheme is used
both for naming and numbering surface species. The explanation that follows
is not intended as a guide on how to name or number surface reactions. In
fact, PRODEFA2 is aware of the rules described below so that specifying
surfaces, sites, the parameters that define them, and the reactions in which
they are involved is rather automatic. MINTEQA2 does not really care about
the names; they are for the benefit of the user in organizing the problem and
interpreting the results. ID numbers do have significance within MINTEQA2.
The cardinal rule is: Do not change the component or species ID numbers
assigned by PRODEFA2.
As for all MINTEQA2 components, the pre-defined adsorption components
have 3 digits - they span the range 811 through 859. The middle digit
designates the surface number (1-5) and the meaning of the rightmost digit is:
1 = surface site 1
2 = surface site 2
3 - electrostatic component for the o-plane
4 - electrostatic component for the ^-plane
5 = electrostatic component for the d-plane
6 = not used
7 - not used
8 = not used
9 = not used
Thus, component 834 represents the electrostatic component for the ^-plane for
the surface number 3, etc, (It is not really necessary to have defined
surfaces 1 and 2 in order to have a surface with the number 3 although
PRODEFA2, which would ordinarily be used to design the input file, will define
the surfaces beginning with number 1. Also, as will be seen below, the
electrostatic component for the /3-plane is relevant to the triple-layer model
only; this component would never be used for any of the other models.) The 3-
digit ID number of a site and the 3-digit ID number of another component that
reacts with that site are combined by suffixing the former with the latter and
then an arbitrary digit is suffixed to that result to give a 7-digit number to
represent the reaction product. For example, 8123301 would represent a
surface species resulting from a reaction between site 2 on surface 1 and H+
(whose 3-digit number is 330). The rightmost digit (1) is arbitrary and is
there to insure that the 7-digit number is unique (there could be other
reactions between this site and H+) .
The names assigned to those surface species that are reaction products
are left to the discretion of the user (PRODEFA2 will query for the name).
However, the names of the surface components themselves are pre-determined.
These names are of the form ADSnTYPl, ADSnTYP2, ADSnPSIO, ADSnPSIB, ADSnPSID
where n refers to surface number. For example, ADS1TYP1 corresponds to site 1
on surface 1 (component ID number 811), ADS4PSID corresponds to the
electrostatic component representing the d-plane on surface number 4.
25
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For the explanation and discussion of the adsorption models that
follows, we have used the simpler notation of SOH to designate a surface site
and electrostatic terms are referred to in accepted notation of a and ij) to
represent surface charge and potential, respectively.
Non-Electrostatic Adsorption Models
The seven adsorption models in MINTEQA2 are conveniently grouped into
those that involve electrostatic terms and those that do not. The non-
electrostatic models have been in common use and certain conventions as to
their use have become accepted (14). The specifics of each model and
departures from accepted model conventions in MINTEQA2 are explained below.
Activity Kd Adsorption Model
The activity Kd adsorption model implemented in MINTEQA2 differs in two
respects from the usual definition of the Kd model. For an adsorbing metal M,
Kd is conventionally defined as the ratio of the concentration of metal bound
on the surface to total dissolved metal concentration at equilibrium. That
is,
;SOH«M]
[M]T
Kd 3.01
where [SOH-M] represents the concentration of adsorption sites occupied by an
ion M or surface-bound metal and [M]T is the total dissolved equilibrium
concentration of M.
In the MINTEQA2 activity Kd model,
(SOH-M)
K(jact 3 02
{M}
where {M} is the free activity of M in the equilibrium solution. Following
convention and because there is no generally accepted method of computing
activity coefficients for unreacted or reacted adsorption sites, we define
those coefficients as unity so that {SOH-M} = [SOH-M]. Then in terms of
concentrations, equation 3.02 becomes
[SOH-M]
3 03
where 7m is the activity coefficient of dissolved species M and Kdact may be
thought of as the equilibrium constant of the surface reaction
26
-------
SOH + M ^± SOH.M 3.04
SOH represents unreacted surface sites and is present at a fixed activity (or
fixed concentration if we insist that the activity coefficient pertaining to
SOH is unity). Taking the activity of SOH as 1.0 equation 3.03 may be thought
of as a mass action expression for reaction 3.04. This is implemented in
MINTEQA2 by assigning the component representing unreacted sites, SOH, as a
Type III species. The constraint is that there is an unlimited supply of
fresh unreacted sites; the surface cannot approach saturation no matter how
much M adsorbs. The reader will note that this constraint also renders
competition between different metals (M1, M2,...) meaningless. Equation 3.02
defines the equilibrium constant actually used for an activity Kd reaction in
MINTEQA2; the reader will observe that this is a unitless ratio. However,
PRODEFA2 calculates this value from the more common expression of Kd in I/kg
and solid concentration in kg/1 (e.g., the number of kg of soil with which one
liter of solution is equilibrated) .
Activity Langmuir Adsorption Model
In the Langmuir adsorption model, the number of surface sites available
for adsorption must be specified at the outset. The surface reaction can be
written identically as for the activity Kd model
SOH + M *=t SOH-M KLact 3.05
and where we again express the equilibrium constant in terms of activities
(SOH«M)
KLact -- 3.06
{M} {SOH}
If, as is the case for every adsorption model in MINTEQA2 , we arbitrarily
assign the value of unity to the activity coefficients pertaining to unreacted
and reacted surface sites, we can re-write the mass action equation 3.06 as
;SOH«M]
. ict _
XL
KTact 3.07
7m[M] [SOH]
To see the correspondence between this implementation of the Langmuir
model and the defining equation to which that model is commonly ascribed, we
note that the mass balance equation written for the surface sites is
[SOH]T = [SOH-M] + [SOH] 3.08
where [SOH]T = total concentration of surface sites available. The combined
mass balance and mass action expressions yield the Langmuir relationship in
terms of activities
27
-------
KLact [SOH]T 7m[M]
[SOH-M] 3.09
1 + Vct 7ra[M]
To express 3.09 in terms of concentrations, replace KLact with KL and let jm -
1.
The so-called competitive Langmuir model for the competing metals Hit
M2,... is derived in a similar manner with additional reactions defined:
SOH + Mj. ^ SOH.M1 KL1act
SOH + M2 ^± SOH.M2 KL2act
SOH + ^ ^± SOH-M,, KLnact
All that is required to model such competition in MINTEQA2 is to define these
separate reactions on the surface.
The only difference between the Langmuir and activity Kd treatments is
that the Langmuir equation accounts for the finite concentration of surface
sites. It is also important to remember that the KL used is an "activity" KL
rather than the conventional concentration-based constant.
A meaningful way to employ commonly available "concentration" KL data is
to model the experimental supernatant solution in which the KL was determined
and replot the data in terms of the MINTEQA2 activities of the sorbate. To do
this, the Langmuir isotherm is first rewritten in the linear form.
[M] 1 [M]
+ 3.10
[SOH-M] KL [SOH]T [SOH]T
If the Langmuir isotherm accurately describes the system, a plot of
[M]/[SOH»M] will yield a straight line of slope 1/[SOHT] and intercept
1/KL[SOHT] . Conventionally, the constant KL is obtained by dividing the slope
by the intercept. The KLact can be derived from an analogous plot in which the
MINTEQA2 sorbate activities {M} are plotted in place of the sorbate
concentration terms [M].
Activity Freundlich Model
The mass action equation representing the Freundlich model can be
written
SOH + (l/n)M *=* SOH'M Kfact 3.11
28
-------
{SOH-M}
Kfact = - 3.12
n {SOH}
Like the activity Kd model, an unlimited supply of unreacted sites is assumed
and the activity and concentration of surface species are considered to be
equal. Imposing the condition {SOH} = 1.0.
[SOH-M] = Kfact {Mm+}1/n 3.13
[SOH«M] = equilibrium concentration of reacted sites or surface-
bound metal
{M} = equilibrium activity of the free metal species M
1/n = mass action stoichiometric coefficient pertaining to M
This is similar to the activity Kd relationship except that the
stoichiometric coefficient of the reacting species M is 1/n. For the special
case where n - 1, the Freundlich and activity Kd mass action equations are
identical. Note that the mass balance stoichiometry for M is 1.0, just as it
is for the activity Kd model. It is only the mass action stoichiometry that
is 1/n.
Kfact may be derived from conventional concentration Kf data in a manner
similar to obtaining Kdact from conventional Kd data. The logarithmic form of
the Freundlich mass action equation (3.13) is
log [SOH-M] = log Kfact + 1/n log {M} 3.14
If the Freundlich model is applicable to a given system, a plot of log [SOH-M]
versus log {M} will yield a straight line of slope 1/n and intercept log Kfact.
Experimental isotherms usually involve concentration rather than activity
plots. The Kf values from these plots can be converted to Kfact's by using
MINTEQA2 to speciate the equilibrium solution at each point along the
adsorption isotherm and re-plotting the isotherm in terms of log {M} rather
than log [M]. The resulting intercept will be the Kfact required by MINTEQA2.
Alternatively, one can simply guess the activity coefficient of the adsorbing
metal M for each concentration along the curve.
Ion Exchange Adsorption Model
Ion exchange sorption is defined as the process by which an ion from
solution is exchanged for one on the solid surface. The relative abilities of
solute ion species to compete for surface sites is governed by intrinsic
factors and their solution activities. The ion exchange model assumes that
the surface site is initially occupied by an exchangeable ion that is released
29
-------
into solution during the exchange process. The ion exchange reaction and its
corresponding mass action equation can be expressed as
*i ' Mi + M2 ^ SOH-M2 3.15
(Mi) {SOH-M2}
Kex = 3.16
{M2}
where Mx is the ion initially occupying the exchange site, M2 is the replacing
ion to be adsorbed, and SOti'M^ SOH«M2 are surface sites occupied by the
respective ions. As for the previous models, no attempt is made to calculate
activity coefficients for the occupied sites; they are arbitrarily taken as
unity and Kex is written in terms of concentrations by replacing activity of
each species in equation 3.16 with the product of concentration and activity
coefficient.
Earlier versions of MINTEQ implemented the ion exchange model in such a
way as to require an infinite supply of solid of constant composition. This
condition implied a fixed solution phase activity ratio between the two
exchanging ions. Also, there was no mass balance on the ion that initially
occupied the surface and was expelled during the exchange reaction. Beginning
with MINTEQA2 version 3.00, these features are no longer model constraints;
the model conforms to conventional and accepted usage as given by equations
3.15 and 3.16.
Selectivity coefficients (Kex's) can be derived from the literature for
most common ions such as Na+, K+, Ca2+, Mg2+, etc., but are seldom available
for trace metals. In using the ion exchange algorithm, users must supply the
reaction stoichiometries and selectivity constants and specify the ion that
initially occupies the exchange sites. Note also that reaction
stoichiometries may be related to ion charge. For example, a single Ca2+ ion
may replace two Na+ ions and thus occupy two sites.
Electrostatic Adsorption Models
All four adsorption models discussed thus far neglect the electrostatic
influences of charged surfaces on the solution and the counter influences of
changes in surface charge due to solution composition. Many colloidal
particles carry a significant surface charge that creates electrostatic
potentials extending into the suspending solutions. Solution ions with charge
of the same polarity as the surface are repelled and ions of opposite charge
are attracted. Because of this, the electrostatic potentials associated with
charged surfaces may greatly influence the adsorptive behavior of charged
species. This influence is incorporated in electrostatic adsorption models by
including terms in the mass action equations that modify the activities of
sorbate ions approaching charged surfaces by the electrical work necessary to
penetrate the zone of electrostatic potentials (V"'s) extending away from the
surface.
30
-------
Several models are available to account for these effects in various
degrees of detail. Readers are referred to Westall and Hohl's (22) excellent
review for clear comparisons of the presently available surface complexation/
electrostatic models. The discussion that follows will be limited to brief
descriptions of the three surface complexation model options provided in
MINTEQA2: the constant capacitance, diffuse-layer, and triple-layer models.
These three models are closely related in many ways. Each treats adsorption
as a surface complexation reaction (that is, the reaction is treated as
analogous to a solution phase complexation reaction governed by a mass action
equation) and each accounts for the electrostatic potentials at the charged
surface. They differ primarily in the types of surface species that are
allowed within specific physical locations or layers extending away from the
surface and in the parameters of the electrostatic model that each employs.
The surface complexation models available in MINTEQA2 were developed to
describe surface reactions in amorphous metal oxide systems (2,4,5) and have
also been applied to clay systems (12). The large body of experimental
evidence that has accumulated from laboratory bench studies of pure oxide
systems indicates that surface complexation models can predict adsorption
behavior (6). Few data exist for applying these models to natural systems
where complex mixtures of impure amorphous oxides, clays, and humic materials
provide the reactive surfaces. Recent work by Loux et.al. (13) demonstrated
good model agreement with experimental results on an aquifer material spiked
with trace metal cations. The adsorbing surface was modeled as amorphous iron
oxide using MINTEQA2 with the diffuse-layer model using surface reactions and
their associated stability constants as given by Dzombak (6). In general,
freshly prepared laboratory oxide systems often behave differently from the
aged, impure mixtures found in the environment. The interactions are such
that properties of the mixture as a whole are not necessarily those obtained
by summing the properties of the individual components. Care must be used in
selecting input parameters for natural systems using MINTEQA2's surface
complexation models.
The constant capacitance, diffuse-layer, and triple-layer models all
treat trace metal surface reactions as complexation reactions analogous to the
formation of complexes in solution. Surface sites are represented as SOH
groups where S's are metals associated with the solid structure and located at
the solid-liquid interface. Some ions, such as H+, OH", and a variety of
trace metal ions are presumed to be specifically adsorbed at the surface via
complexation with the surface sites. In all three models, a charge (CT)
associated with the surface is assumed to be balanced by a charge (crd)
associated with a diffuse layer of counterions. These charges are such that a
+ crd = 0. In the constant capacitance and diffuse-layer models, all
specifically adsorbed ions contribute to the surface charge (CT). However, in
the triple-layer model, the net charge due to adsorption is the sum of the
charges associated with two adsorbing planes rather than one. The innermost
of the two planes (the o-plane) specifically adsorbs H+ and OH" and is
characterized by charge a0. The other plane (^3-plane) has charge a^ resulting
from the adsorption of other ions. The net surface charge is given by a = a0
+ Op and is balanced by the charge in the diffuse layer such that a + aA = 0.
Because the electrical potential gradients extending away from the surface are
the direct result of the surface charge, the specifically adsorbed potential
31
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determining ions also govern distributions of counterions in the diffuse
layer.
Activities of ions in solution and near the surface are influenced by
the presence of electrostatic potentials arising from the surface charge. The
activity difference between ions near the surface and those far away is the
result of electrical work in moving the ions across the potential gradient
between the charged surface and the bulk solution. The activity change
between these zones is related to the ion charge (z) and the electrical
potential (VO near the surface and can be expressed using the exponential
Boltzmann expression,
{Xsz} - {Xz} [e/RT]z 3.17
Where:
z = charge of ion X
{Xsz} = activity of an ion X of charge z near the surface
{Xz} = corresponding activity of X in bulk solution outside
the influence of the charged surface
e-^F/RT _ Boltzmann factor
F = Faraday constant
R - ideal gas constant
T - absolute temperature
General Implementation of Electrostatic Models in MINTEQA2
The general algorithm is similar for all three of the electrostatic
models. Specific details for each model are discussed separately below. As
mentioned above, for the constant capacitance and diffuse- layer models, there
is only one layer or plane within which specifically adsorbed ions define the
surface charge a. Accordingly, that plane is commonly referred to as the o-
plane and the surface charge and potential are denoted a0 and ^>0. We will
retain that notation here as well as the notation ad and Va f°r their
counterparts in the diffuse layer. We point out, however, that the o -plane is
defined differently in the triple -layer model and those parameters subscripted
with "o" in that model should not be regarded as equivalent to the o-plane
parameters of the former two models. Also, with regard to the constant
capacitance and diffuse -layer models, we may refer to a0 and V0 as "surface"
charge and "surface" potential. This is not true of the triple-layer model
because there are two planes ("o" and "/3") associated with the surface. Thus,
the charge at the beginning of the diffuse layer is defined in terms of
subscripted
to indicate the layer to which it applies) is incorporated as a scaling factor
32
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by assigning it a component ID number and writing the surface reaction so as
to include it as a reactant of appropriate stoichiometry . The reader should
realize that this is only a mathematical way to incorporate the parameters of
the desired model into an existing computational scheme. The mass action
equations for surface reactions will contain those fake components (which we
shall refer to as electrostatic components) that are really the Boltzmann
factors. Also, because they are not real chemical entities, there is no
analytical total to ascribe as input for the electrostatic components, rather
the total charge is calculated via expressions that are unique to each model
and are mathematically related to the potential. Still, we will refer below
to Ta referenced to a specific plane as the total charge for that plane but
note that we do not imply a measured input value as was the case with earlier
references to T. Also, MINTEQA2 will seek to perform mass balance
calculations on all components. It is necessary, therefore, to direct
otherwise for the electrostatic components by designating them as Type VI
(excluded from mass balance) . Charge balance equations that are analogous to
mass balance (see equation 2.10) are defined for the electrostatic components
and have the form
- T 3.18
,
where aia is the stoichiometry of the electrostatic component pertaining to a
in species i.
The overall sense of the electrostatic calculations for a given plane is
this:
1) Calculate the total charge Ta from the potential on the plane by
using a functional relationship appropriate for the model (see below) .
Initial guesses for the potential of each plane are provided in the
input file.
2) Calculate the total charge on the plane by a different method,
namely, by summing the charges of all species specifically adsorbed on
that plane. Operationally, this becomes a summation of the charge
contribution from all species in which the stoichiometry of the
component representing the plane is non-zero.
3) Obtain the difference in the total charge pertaining to the plane as
in equation 3.18. Test whether the difference is less than some small
tolerance value. If not, adjust the potential for that plane and
repeat. Of course, the potentials are adjusted simultaneously with the
activities of other components .
Calculations involving the surface sites themselves are exactly as
described for other real chemical entities by the mass action equations (2.08)
and mass balance equations (2.10).
33
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As for all MINTEQA2 adsorption models, the activity coefficients of both
the reacted and unreacted surface sites are always taken as unity. The
artificial contrivance whereby we have created components to represent the
Boltzmann factors demands that we create activity coefficients for them as
well. Imaginary though they be, we make them innocuous by setting them to
unity .
All surface reactions in MINTEQA2 are written in terms of the neutral
surface site SOH (components 8nl or 8n2; n - 1,2 ..... 5) and the equilibrium
constants appropriate for MINTEQA2 are formation constants. The constants for
many reactions found in the literature are intrinsic constants, which
sometimes are referenced to the protonated surface site SOH2+ (for adsorbing
anions) and to the deprotonated site SO" (for adsorbing cations) . Such
reactions must be re-written in terms of MINTEQA2 components and their
equilibrium constants adjusted accordingly before use in MINTEQA2. The
surface reactions, which are generally model specific, must be provided to
MINTEQA2 through its input file; there is no permanent database of adsorption
reactions. Version 3.00 includes a separate file containing surface reactions
that are applicable to the diffuse-layer model for an iron oxide surface. To
be used, that file (FEO-DLM.DBS) must be appended to a previously prepared
input file. Instructions for doing this are provided in PRODEFA2 . For other
surface reactions that the user may wish to create for an input file, PRODEFA2
is capable of computing the correct stoichiometry for the electrostatic
components. In fact, this is done automatically without user intervention.
The user may be asked to supply an initial activity guess for the
electrostatic components (for use in item 1 above) . Specifically, a seed
value representing the negative of the exponent in the Boltzmann factor of
equation 3.17 is requested and a guess of zero will usually work.
The analytical input concentration for the surface site, TSOH, is
expressed in moles of sites per liter and is calculated from
Cs
3.19
Where:
Ns = the analytically determined surface site density (number of
sites/m2)
SA = specific surface area of the solid (m2/g)
Cs = concentration of solid in the suspension (g/L)
NA = Avogadro's number (6.02 X 1023)
Ns, SA, and Cs are requested from the user by PRODEFA2. From these
parameters, TSOH is calculated.
34
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Constant Capacitance and Diffuse-Layer Models
The constant capacitance and diffuse -layer models have many
similarities. Both define specific adsorption of all ions on the "o" plane.
Also, their mass action and charge balance equations are identical (except for
the numerical value of the equilibrium constants) . The difference in these
two models is in the function relating total surface charge a0 to surface
potential ^0. For the diffuse -layer model,
Jo
- 0.1174 I% sinh(ZV>0F/2RT) 3.20
where Z is the valency of the symmetrical electrolyte (which we take as
unity), I is ionic strength, and all other parameters are defined as in
equation 3.17. This expression is used in evaluating equation 3.18.
The constant capacitance model is a special case of the diffuse-layer
model for solutions of high ionic strength and surfaces of low potential. In
such systems, equation 3.20 can be approximated by
T,0 - <7*0 3.21
where C is a constant capacitance term. Equation 3.21 is used to evaluate
equation 3.18 for the constant capacitance model. Although the models are
similar in implementation, the capacitance term C is often treated as a
fitting parameter rather than as a measured characteristic of the system and
the constant capacitance model can be applied to systems of all ionic
strengths. Outside the range of ionic strength where the approximation of
equation 3.21 is valid, the constant capacitance and diffuse-layer models are
not the same.
As mentioned, the assignment of specifically adsorbed species to the
o-plane, the mass action equations, and the charge balance equations for the
constant capacitance and diffuse-layer models are the same. Figure 3.1 shows
a conceptual structure of an oxide surface as represented by either of these
two models. The discussion of surface reactions that follows applies to
either model.
35
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o
-OH
0"
OM
-
X
X
CONSTANT CAPACITANCE MODEL
DIFFUSE LAYER MODEL
Figure 3.1. Schematic representation of the surface charge/potential
relationships used in the constant capacitance and diffuse-layer models.
36
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Surface reactions are represented by mass action expressions with
Boltzmann factors represented as components (see equation 3.17).
Stoichiometries of those components are included in the definition of surface
reactions provided to MINTEQA2. Several examples of such reactions and their
corresponding mass action expressions are given below to illustrate the use of
Boltzmann factors. Consider the protonation reaction
SOH + Hs+
-------
The stoichiometry in MINTEQA2 corresponds to:
SOH - H+ - e^°F/RT ^z± SO" 3.29
For multivalent species, both charge and stoichiometry of the adsorbing
ion must be considered in writing the mass action expression. Consider the
surface reaction involving the divalent cation M2+
SOH + MS2+ - Hs+ *=+ SO-M+ 3.30
The corresponding mass action expression is
{SO-M+} {Hs+}
K =
{SOH} {MS2+}
{SOH} {M2+} [e~
{SO-M+} {H+}
3.31
{SOH} {M2+} [<
In this case, the Boltzmann factor in the numerator can be canceled and the
stoichiometry in MINTEQA2 corresponds to:
omj 4. M2+ H"1" 4- o"^oF/RT * on M+ T TO
&\jn T ii - n ~ c u ^ jU*n 3 . 3Z.
Mass action expressions for other surface reactions are formulated in a
similar manner.
In addition to the surface reactions with their equilibrium constants
and the parameters of equation 3.19, the constant capacitance model requires
an input value for the capacitance, C. This is the capacitance (farads/m2)
between the o-plane and the diffuse layer of counterions.
Triple-Layer Model
The triple-layer model is generally more complex than the constant
capacitance and diffuse-layer models. In the MINTEQA2 implementation of the
triple-layer model, only protonation and deprotonation of surface sites are
assigned to the o-plane. Other specifically adsorbed ions are assigned to the
/3-plane and determine the charge o^ and potential V/j i-n that zone. Non-
specifically adsorbed ions are envisioned as residing in the diffuse layer or
'd' plane and are influenced by V"a potentials. The capacitance between the o-
plane and the /3-plane is denoted C± and between the /J-plane and d-plane, C2.
Both are treated as user-supplied constants in MINTEQA2. Background
electrolytes are allowed to adsorb. Also, note that the potential gradients
38
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in the inner and outer zones are linear, but potentials decay exponentially in
the diffuse layer zone. A schematic diagram of the triple-layer model surface
is shown in Figure 3.2.
The input parameters for the triple-layer model are similar to those for
the constant capacitance model except that two capacitance terms and three
electrostatic components are required. As with the other electrostatic
models, the first of these components (id number 8n3) pertains to the charge
and potential on the o-plane. The second (id number 8n4) pertains to the
charge and potential on the /3-plane and the third (id number 8n5) to the d-
plane.
Total charges associated with the triple-layer model o-, ft-, and d-
planes are related to the potential differences between planes.
1^ - C-L (V>0 - V'fl) 3.33
T0 - Cl (V>fl - V"0) + ^2 ($6 ' V>d) 3.34
3.35
Where:
Ta , T , and Tff total charges associated with the o-, ft-, and d-
planes
GI and C2 = capacitances associated with the zones between the o- and /?-
planes and y3- and d-planes, respectively
V>0, i>p, and V"d = electrostatic potentials at the o-, ft-, and d-planes
The total charge on the o- and /3-planes are used in equation 3.18 along with
the summation of species that are specifically adsorbed on each plane and have
non-zero stoichiometry in the appropriate electrostatic component.
Recalling that the d-plane has no specifically adsorbed ions and thus
has zero stoichiometry in all species, we replace equation 3.18 for that plane
only with
Y,d=ad-Tad 3.36
where the diffuse layer charge (erd) for a monovalent symmetric electrolyte is
given by the Gouy-Chapman relationship
ad = - (ee0RIT)1/z sinh(FV>d/2RT) 3.37
Where:
e = dielectric constant
e0 = permittivity in free space (8.85 x 10~12 (coulombs)2/j°ule-ni
39
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I - ionic strength
MINTEQA2 also uses Equation 3.37 as an approximation for non-symmetric
electrolytes.
X
X
X
X
B
Figure 3.2. Schematic representation of surface species and charge/potential
relationships in the triple-layer model.
40
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Surface reactions in the triple -layer model are represented in a manner
similar to the other two electrostatic models except that mass action
expressions must have the proper stoichiometry for the electrostatic component
representing the /3-plane as well as the o-plane. No stoichiometry is needed
for the d-plane because no specific adsorption occurs on that plane.
The following surface reactions and mass action expressions illustrate
the determination of stoichiometric coefficients for those components. For
the surface protonation and de-protonation reactions, the triple-layer model
results are identical to those obtained for the constant capacitance and
diffuse-layer models in equations 3.26 and 3.29 (although one could expect the
numerical value of the equilibrium constants to be different) . For the
monovalent metal ion M+
SOH - Hs+ + Ma+ ;j=* (SO-M) 3.38
With the substitution for Hs+
{Hs+} - {H+} [e-*°F/RT] 3.39
(see equation 3.17) and a similar substitution for the metal ion near the
surface (except the effective potential refers to the ^-plane because that is
where M"1" is specifically adsorbed)
{Ms+} - {M+} [e~^F/RT] 3.40
the mass action expression is
{SO.M} {H+} [e^°F/RT]
K -- 3.41
{SOH} {M+J [
The reaction written in terms of MINTEQA2 components and including the
electrostatic components is
SOH - H+ - e-*°F/RT + M+ + e^F/RT *=+ SO-M 3.42
For a surface reaction involving a divalent metal, M2+
SOH - Hs+ + MS2+ ^± (SO-M)+ 3.43
the substitution of equation 3.39 together with
{MS2+} - {MS2+} [e'^F/RT]2 3.44
provides the mass action expression
K -- 3.45
{SOH} {M2+} [
41
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The corresponding MINTEQA2 reaction is
SOH - H+ - e-*°F/RT + M2+ + 2e-^F/RT ^± SO-M+ 3.46
The combined hydrolysis/sorption reaction for an M2+ ion is expressed
SOH + MS2+ + H20 - 2HS+ +=* SOMOH 3.47
and the corresponding mass action expression is written
(SO-MOH) {H+}2 [e-
K - - 3.48
{SOH} {M2+} {H20} [e-^F/RT]2
The corresponding MINTEQA2 reaction is
SOH + M2+ + 2e'^F/RT + H20 - 2H+ - 2e^°F/RT ^z± SO-M+ 3.49
For the reaction of a monovalent anion (A") , a neutral surface species
can result
SOH + As" + Hs+ ^ SOH2«A 3.50
With the substitution
{A/} = {A'} [e-W]-1 ^ 3.51
the mass action expression is
{SOH2.A} [
K -- 3.52
{SOH} {A'} {H+} [e^°F/RT]
and the MINTEQA2 reaction is written
SOH + A' - e- + H+ + e-°/ ^z* SOH2-A 3.53
Finally, for a divalent anion,
SOH + A,2' + Hs+ ^± SOH2.A' 3 . 54
the mass action expression is
{SOH2.A-} [
K -- 3.55
{SOH} (A2'} {H+}
42
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The MINTEQA2 reaction is written
SOH + A2' - 2e^F/RT + H+ + e^°F/RT +=± SORA' 3.56
The reader is reminded to write adsorption reactions in terms of
MINTEQA2 components and to adjust the equilibrium constants accordingly before
entering the reaction through PRODEFA2 . The electrostatic components are of
no concern in this procedure. PRODEFA2 will add the appropriate electrostatic
components at the correct stoichiometry when the reaction is entered.
43
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CHAPTER 4
USING MINTEQA2 AND PRODEFA2
The purpose of this chapter is to inform the reader how to use MINTEQA2
from an operational point of view. There is another level of understanding
how to use the model - - a level that embodies knowledge of chemical,
geological, and other physical parameters of the system to be modeled and from
which a chemical question or problem is developed. Before addressing that
level, it is necessary to learn to pose the chemical problem to the model.
Largely, this consists of learning to use the interactive program PRODEFA2 to
create input files for MINTEQA2. An effective way of becoming familiar with
PRODEFA2 and the options it provides is to run through several interactive
sessions and note the changes in the resulting files as you change your
responses to the prompts. The following pages provide a "walk through" of a
PRODEFA2 session. Because of the many options available and numerous
branching of prompts; however, it is not practical to include every
permutation of possible prompts and responses. Therefore, before beginning
the "walk through," some general facts about both programs are discussed.
These are points that would certainly become apparent after several sessions.
Knowing about them beforehand will help the new user to anticipate the flow of
logic and many of the prompts.
Appendix C describes the content of the distribution diskettes and
general computer system requirements. There are several test files included
on the diskettes that are helpful as learning aids. These are named
TESTxx.HLP (PRODEFA2 dialogue file), TESTxx.INP (MINTEQA2 input file), and
TESTxx.LST (MINTEQA2 output file). The "xx" represents additional numbers or
characters of the name. The PRODEFA2 dialogue files (.HLP) provide a record
of the prompts and responses that occurred during the interactive session in
which the MINTEQA2 input files (.INP) were created and the MINTEQA2 output
files (.LST) show the results when those files were executed with MINTEQA2. A
useful approach to becoming familiar with PRODEFA2 is to print a particular
.HLP file, and with the printout in hand, to run PRODEFA2 and respond to the
prompts as shown on the printout. You should choose a different name for the
input file you are creating so that the .INP file is not superseded and
compare the new file with the .INP file. The .INP and .LST files for a
problem using the triple-layer adsorption model are reproduced in Appendix D.
General Features and Organization of MINTEQA2 and PRODEFA2
The following features will become obvious after using the programs
several times, but it is helpful to know them in advance:
44
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The two programs are completely separate. The sequence of their
execution is generally PRODEFA2 followed by MINTEQA2. Execution of the
former begins when the user types "PRODEFA2" at the DOS (or DCL) prompt.
MINTEQA2 is executed by typing "MINRUN" and answering the filename
prompts.
Both programs use the same thermodynamic database files (their names
are listed in Appendix C). These files contain the pre-defined set of
components and the reactions in which those components serve as
reactants.
Because the model has its own database, the primary information that
must be conveyed through the input file to model a particular system is
the total dissolved concentration or fixed activity of each component of
the system. Components are selected from the pre-defined set by
specifying either the first letter of the component name or the 3-digit
component ID number. In general, it is not necessary to identify the
species that are reaction products of the selected components. MINTEQA2
will search the database to find the species that can be formed from the
specified components. Exceptions are specifying that a particular
species is to be excluded, specifying the disposition of a particular
solid with regards to oversaturation (explained below), or for any
database species, specifying a different equilibrium constant than that
provided in the thermodynamic database. When it is necessary to do so,
aqueous species that are reaction products are identified by specifying
the components that represent the major cation and major anion. Solids
are identified to PRODEFA2 by specifying the component that represents
the major cation and the main mineral group to which the solid belongs
(e.g. carbonate, sulfide). Alternatively, one may specify the 7-digit
ID number for any aqueous or solid species if it is known. Menus and
prompts within PRODEFA2 allow all of these things to be done with
relative ease.
- New components may be defined by editing the component database file,
COMP.DBS. Of course, new components are of little use unless reactions
incorporating them as reactants are also provided. New reactions
between new or existing components may be permanently added to the
database files (see Appendix A) or may be added for a particular
execution by including them in the input file. PRODEFA2 will prompt for
the information needed to do this.
MINTEQA2 solves the equilibrium problem iteratively by computing mole
balances from estimates of component activities, that is, activities of
the free species represented by the components (see Chapter 2). Hence,
it is necessary to provide an initial estimate or guess for the activity
of each component. PRODEFA2 makes this guess automatically for every
component as equal to the component total dissolved concentration but
also provides the means for the user to change the guess.
It is possible for the user to insist that certain conditions prevail
at equilibrium. For example, it may be desired to equilibrate the
solution to a specified pH. This is done by specifying that the
45
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activity of H+ is fixed as dictated by the selected pH. The pe may be
fixed in a similar manner. It is also possible to insist that a given
solid is present at equilibrium. This is done by specifying it as an
INFINITE solid in PRODEFA2. Likewise, the equilibrium partial pressure
of a gas may be specified.
The user has four options with regard to allowing oversaturated
solids to precipitate (not including the infinite solids option above).
1) No solids are allowed to precipitate, 2) No solids are allowed
except for those explicitly specified in the input file, 3) All
oversaturated solids are allowed, or 4) All oversaturated solids are
allowed except for those explicitly excluded in the input file.
The process of picking the correct set of solids so that equilibrium
is attained without phase-rule violations is also an iterative procedure
within MINTEQA2. This means that a particular solid may precipitate and
then may dissolve in a later iteration. The user can assist the model
in arriving at the proper set of solids by designating those presumed to
be present at equilibrium as FINITE solids. PRODEFA2 provides the means
of doing this.
There are four choices for units of concentration for the input data:
1) Molal (approximately the same as molar for the dilute systems
appropriate for MINTEQA2), 2) mg/1, 3) PPM (parts per million), or
4) meq/1 (milliequivalents per liter). PRODEFA2 can convert from one to
another so that you may, for example, enter a portion of the total
dissolved concentration data in molal and then convert to mg/1.
Regardless of the units chosen for input data, the units of
concentration used for the MINTEQA2 output data are always molal.
At start-up, PRODEFA2 asks for the name of the MINTEQA2 input file to
be created. It also asks for the name of an existing MINTEQA2 input
file to use as a seed file or "template." If the user does not wish to
use a seed file, program defaults are used for all system variables and
program flags and the single component H"1" is entered automatically. If
a seed file is used, all system variables, program flags, and species
definitions become identical to those of the seed file. Note that the
seed file itself is not modified by this procedure unless the filename
selected for the MINTEQA2 file to be created and the seed file's name
are the same.
- PRODEFA2 is divided into four distinct sections called edit levels.
After inquiring for file names, PRODEFA2 goes automatically to EDIT
LEVEL I to display the settings and parameters of the default problem or
the seed problem represented by a seed file if one has been specified.
Upon the users acceptance of the EDIT LEVEL I settings, a main menu
screen is displayed from which the user may choose to enter any of the
four edit levels, to use the current problem as a seed for another
similar problem to be included in the same MINTEQA2 input file, or to
exit the program. Upon returning from any edit level, this MAIN MENU is
always displayed.
46
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Running PRODEFA2 for the First Time
The following pages provide a basic introduction to PRODEFA2 by
"walking-through" a short session where only the problem title is changed.
This session also demonstrates the "default problem" built-in to PRODEFA2.
After that session, each edit level is explored separately in greater detail.
If you have never used PRODEFA2 or MINTEQA2 before, you should first read the
information supplied with your copy of the MINTEQA2 and PRODEFA2 software.
The program is currently distributed in a compacted form which requires that
you stringently adhere to the installation procedure. You should read the
documentation distributed with the software thoroughly since it will also
contain information on changes that have been made to the code since the
release of this manual as well as corrections to this document. Once you have
loaded your copy of MINTEQA2 onto your computer you should then proceed
through the short example that follows.
The steps presented below will familiarize you with the basic operation
of the PRODEFA2 preprocessor and the files that it creates. This practice
session will terminate with the preparation of an input file that you can then
run through MINTEQA2. This final step is recommended as an initial test of
your installation of the MINTEQA2 routine and datasets.
In order to execute PRODEFA2, you must change to the MINTEQA2 sub-
directory and type PRODEFA2 at the prompt. PRODEFA2 will begin by prompting
you for the name of the MINTEQA2 input file you will create during this
session. PRODEFA2 allows you to create an input file by beginning with the
standard default values or by using an existing MINTEQA2 input file as a seed
file. The following is a sample listing of the opening dialogue with
PRODEFA2. Lines that are indented and appear in the smaller characters
represent what actually appears on your computer screen. Items that are
underlined are examples of entries made by the program user.
PRODEFA2
Version 3.00 09-01-90
PRODEFA2 is an interactive program used to build
input files for MINTEQA2 v3.00.
If you encounter errors, please print the file named SAMPLE.QUE
or copy it to a diskette and send along with a description of the
problem you were attempting to model to: Jerry D. Allison,
USEPA Environmental Research Lab, College Station Rd., Athens, 6A
30613.
In responding to prompts, use: Y or y = Yes, N or n = No,
R or r = Return to previous prompt (where applicable).
Enter the name of the MINTEQA2 input file to be created.
Use up to 8 characters PLUS from 0 to 3 characters for an
extension.
ENTER FILENAME (enter "X" to exit PRODEFA2) > TESTA.INP
47
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If you want to use an existing MINTEQA2 input file as a "seed" file to be
copied into PRODEFA2 and modified, enter the filename. Otherwise:
Enter an R to return to the previous question, or
Simply press ENTER to start a new file from scratch.
ENTER filename, R, or press ENTER >
The MINTEQA2 input file to be created is called TESTA.INP. No seed file
is specified, so PRODEFA2's default values will be used for all system
parameters and program flags and the component H+ will be entered
automatically with a total concentration of l.OOOe-07 m. Had an existing
filename been entered at the second prompt, the parameters, flags, and species
entries of that file would be entered automatically. Note that in the VAX
environment, the name of the existing file must be different from the name of
the file to be created. When the two names are identical in a PC environment,
the existing file is overwritten by the one being created. An accessory file
called LAST.DAT is periodically updated throughout the PRODEFA2 session so
that if an abnormal termination occurs, some portion of the work will be
recoverable.
As previously mentioned, PRODEFA2 has four sections called edit levels.
By default, you will automatically be placed in EDIT LEVEL I after responding
to the filename prompts.
EDIT LEVEL I PROB # I
1 Title 1:
2 Title 2:
3 Temperature (Celsius): 25.00
4 Units of concentration: MOLAL
5 Ionic strength: TO BE COMPUTED
6 Inorganic carbon is not specified.
7 Terminate if charge imbalance exceeds 30Z ? NO
8 Oversaturated solids ARE NOT ALLOWED to precipitate. EXCEPTIONS: Solids
listed in this file as TYPE -III (Infinite), -IV (Finite) or -V (Possible).
9 The maximum number of iterations is: 40
10 The method used to compute activity coefficients is: Davies equation
11 Level of output: INTERMEDIATE
12 The pH is: TO BE COMPUTED
13 Neither pe nor Eh has been specified.
14 Adsorption phenomena are not to be modeled.
15 Display on-screen status messages during MINTEQA2 execution? YES
99 Choose a different file to modify OR return to output filename prompt.
To change any of the above entries or to explore other possible values,
enter the number to the left of the entry. Enter zero when you are finished.
ENTER CHOICE >
In EDIT LEVEL I, a screen of information is displayed on your computer, as
shown above. In this example, PRODEFA2's default settings for system
parameters, and program flags are displayed. If you had selected a previously
existing input file as the starting point, its values would be displayed
instead. In order to change any of the entries on this screen, enter the
number to the left of the entry and respond to the questions presented. For
example, to change the first line of title information for the run, enter a
"1" as shown below. The program will then prompt you to enter the first line
of the title for this problem.
48
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ENTER CHOICE > 1
Enter problem title (1 of 2 lines),
OR press ENTER to omit title,
OR enter "R" to return to previous prompt:
This exercise illustrates PRODEFA2's "default problem".
After any option is selected and changes are specified, the EDIT LEVEL I
screen is updated to reflect the changes. The remainder of the EDIT LEVEL I
options are discussed in a subsequent section. To exit EDIT LEVEL I enter a
"0" at the "ENTER CHOICE >" prompt in the EDIT LEVEL I menu.
After exiting from EDIT LEVEL I, the MAIN MENU is displayed. From the
MAIN MENU the user may choose to enter any of the four edit levels, to use the
current problem as a seed for a another similar problem to be included in the
same MINTEQA2 input file, or to exit the program. Upon returning from any f
edit level, this MAIN MENU is always displayed. The options presented in each
edit level will be the subject of the remainder of this chapter. For the
moment, let us exit PRODEFA2.
MAIN MENU: SELECT OPTION PROB # 1
1 = EDIT LEVEL I (Change ionic strength, pH, Eh, temperature, adsorption
parameters, number of iterations, precipitation options, etc.)
2 - EDIT LEVEL II (Specify components, gas, redox, aqueous, and mineral
species, adsorption sites and reactions, add new species of all types)
3 - EDIT LEVEL III (Check, individually edit all entries)
4 = EDIT LEVEL IV (Sweep a range of pH, pE, or dissolved concentration;
Designate an auxiliary MINTEQA2 output file to receive equilibrated
mass distribution data.)
M = MULTI-PROBLEM GENERATOR
X = EXIT (Write the current problem to the new MINTEQA2 input file
and EXIT PROGRAM)
ENTER CHOICE > X
This causes the file "testa.inp" to be written to the directory that you are
currently connected to and PRODEFA2 reminds you of the filename as you exit
the program.
A Problem File Named TESTA.INP Has Now Been Generated.
It Can Be Modified By This Same Program By Recalling It As The Old File.
The contents of the file TESTA.INP are shown below. Note that the
default values for system parameters, program flags, and species entries in
PRODEFA2 really define a default chemistry problem, namely, to calculate the
pH of a solution that is l.OE-07 molal in H+. The file TESTA.INP created
above is thus a legitimate MINTEQA2 input file. You might like to use MINRUN
to submit this problem to MINTEQA2.
49
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This exercise illustrates PRODEFAZ's "default problem".
25.00 MOLAL 0.000
0010000011100
000
330 l.OOOE-07 -7.00 /H+l
Detailed Explanation of PRODEFA2 Options
The primary options available in PRODEFA2 are explained and illustrated
below. The specific settings associated with each option are not necessarily
default values; most were chosen for illustration only. Default values in
program start-up are discussed above. Others are mentioned where appropriate.
Main Menu Option 1: Edit Level I
EDIT LEVEL I displays the current settings of system parameters such as
temperature as well as program flag settings such as the number of iterations
allowed. The user may change any of these settings by selecting the option
number and responding to the resulting prompts.
This section contains a more detailed explanation of EDIT LEVEL I
options and suggestions for using them. For most options, the explanation
provided by PRODEFA2 will prove adequate. You are encouraged to experiment
with all of the options available to become familiar with the capabilities of
the program. Below is a sample of the display that appears when you enter
EDIT LEVEL I.
EDIT LEVEL I PROS # I
1 Title 1:
2 Title 2:
3 Temperature (Celsius): 25.00
4 Units of concentration: MOLAL
5 Ionic strength: TO BE COMPUTED
6 Inorganic carbon is not specified.
7 Terminate if charge imbalance exceeds 30% ? NO
8 Oversaturated solids ARE NOT ALLOWED to precipitate. EXCEPTIONS: Solids
listed in this file as TYPE -III (Infinite), -IV (Finite) or -V (Possible).
9 The maximum number of iterations is: 40
10 The method used to compute activity coefficients is: Davies equation
11 Level of output: INTERMEDIATE
12 The pH is: TO BE COMPUTED
13 Neither pe nor Eh has been specified.
14 Adsorption phenomena are not to be modeled.
15 Display on-screen status messages during MINTEQA2 execution? YES
99 Choose a different file to modify OR return to output filename prompt.
To change any of the above entries or to explore other possible values,
enter the number to the left of the entry. Enter zero when you are finished.
ENTER CHOICE >
50
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Edit Level I Options 1 and 2: Titles
These two entries allow you to enter a two line title for the MINTEQA2
run. The titles will appear in PART 1 of the MINTEQA2 output file and serve
as a reminder of the purpose of the run.
Edit Level I Option 3: Temperature
Many of the parameters used in MINTEQA2 are temperature dependent and we
recommend that you set this value to the actual conditions. MINTEQA2 will
automatically correct as many values as possible to the temperature that you
specify. See Chapter 2 for a description of temperature corrections to
equilibrium constants.
Edit Level I Option A: Units of Concentration
Values for component total dissolved concentrations are later requested
in whatever units are specified here. When the units parameter is changed,
values that are already present in the input file are converted to the new
units. The available choices for units are listed below as they appear in
PRODEFA2.
Select units for concentration. Because these are dilute solutions,
you can approximate molal concentrations with molar concentrations
with negligible error.
1 - molal
2 - mg/1
3 - ppm
4 " meq/1
ENTER CHOICE >
Edit Level I Option 5: Ionic Strength
Two choices are available, the ionic strength can either be computed by
MINTEQA2 from the solution chemistry or it can be fixed at a molal value
specified by the user. Fixing the ionic strength will generally improve
convergence times since changes in ionic strength also change the activity
coefficients and hence the solution composition. When the ionic strength is
fixed, it becomes independent of the solution chemistry. Fixing the ionic
strength implies that there are certain rather inert ions present in large
enough concentration for their impact on ionic strength, and hence on activity
coefficients, to be important. However, because these ions are not very
reactive, they need not be included as actual components. Examples are Na+
and Cl" in many surface water problems (though it is not true that they should
always be represented solely by fixing the ionic strength). An example of the
dialogue when Option 5 is selected is shown below.
Should the ionic strength be fixed? (Y,N,H) > Y
Enter fixed ionic strength (molal) > .01
51
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Edit Level I Option 6: Inorganic Carbon
MINTEQA2 needs the total dissolved concentration of each component for
use in the mole balance equations. Frequently, the dissolved total for
carbonate (C032~) is not available but alkalinity is. PRODEFA2 allows you to
enter the alkalinity in your choice of several commonly used units. The
alkalinity value is stored in the data location ordinarily used for total
dissolved carbonate and a special program flag is set in the input file so
that MINTEQA2 will know to treat this value as alkalinity. MINTEQA2 computes
the total dissolved carbonate concentration from the alkalinity value by the
method described in Chapter 2. You should read that portion of Chapter 2
carefully before using this option. When the alkalinity option is not used,
total dissolved carbonate concentration may be entered just as any other
component. Alternatively, you may set the total dissolved carbonate
concentration to zero and specify that carbonate is in equilibrium with a
fixed partial pressure of C02(g) in EDIT LEVEL II. The PRODEFA2 dialogue for
entering alkalinity is shown below.
Do you want to specify dissolved inorganic carbon
in this problem ? (Y,N) > Y
When alkalinity is specified, no solids are allowed, (set EDIT LEVEL I Option 8
to zero and specify no TYPE III,IV, or V solids.)
Also, the titration used to determine alkalinity is assumed to be to the
pH that is the equivalence point of the solution). Otherwise the alkalinity,
factors in the database will not be applicable.
You have the option of specifying alkalinity as a measure of
dissolved inorganic carbon. Alternatively, you may specify dissolved
inorganic carbon explicitly. Your choice will generally depend upon the way
carbonate concentration is expressed in the chemical analysis of the
sample you are modeling.
Do you want to specify alkalinity ? (Y,N) > Y
Select alkalinity units:
0 - Return to previous question
1 - mg/1 C03-2
2 - mg/1 CaC03
3 - eq/1
ENTER CHOICE > 2
Enter alkalinity in mg/1 CaC03 > 0.500E+02
Alternatively, if you choose to entered total dissolved carbonate directly,
the dialogue is:
Do you want to specify alkalinity ? (Y,N) > N
Do you want to enter total inorganic carbon as total dissolved concentration
of the MINTEQA2 component for inorganic carbon C03-2 ? (Y,N) > Y
Enter total inorganic carbon as total dissolved concentration of
COS-2 in MOLAL > 0.3500E-03
The same result could have been achieved by entering total carbonate as you
would any other component in EDIT LEVEL II.
Edit Level I Option 7: Termination on Charge Imbalance
Generally, it is not important for MINTEQA2 to terminate if the charge
balance exceeds 30%. There are some cases when a large charge imbalance would
52
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indicate improper data, however. When a large charge imbalance occurs, the
user should consider whether it results from omitting a relatively inert
species such as Na"1" or from omitting a more reactive species such as S042". In
the former case the equilibrium composition will be affected very little
(provided the effect on ionic strength is accounted for by fixing it as if Na+
were present), but in the latter, the omission might be important.
Edit Level I Option 8: Precipitation
This entry allows you to turn precipitation on or off for the solids in
the database except those which you explicitly specify as "POSSIBLE" or
"EXCLUDED." These special designations for solids can be made in EDIT LEVEL
II. Sometimes, it is better to not allow any precipitation for the first run
of a complex system and then to incorporate precipitation into a second run.
When precipitation is not allowed, MINTEQA2 will still compute the saturation
indices for all the solids. Indices greater that zero indicate oversaturation
with respect to the solution and indices less than zero indicate
undersaturation. The indices are printed in the output file and may be used
to decide which of the solids may be important in your problem.
In a model run with solid precipitation not permitted, many solids may
be listed as oversaturated at equilibrium. It is important to realize that if
a solid is listed as oversaturated, it may not actually precipitate when
precipitation is permitted in a subsequent run. For a given cation, the most
oversaturated solid will precipitate first. After it does so, others that
were also oversaturated with respect to the pre-precipitation solution may not
be oversaturated. When precipitation is allowed, it is generally best to also
set the number of iterations to a large number (100 or 200) depending on the
number of solids you expect to precipitate. MINTEQA2 allows you to obtain the
saturation indices each time the solution is provisionally equilibrated during
the program execution by specifying the solids print option as shown below.
(Here, the term "provisional equilibration" means that the solution is
equilibrated but not with the complete or correct set of solids.) Generally,
print option 1 is sufficient. With print option 1, provisional equilibration
results are not written to the MINTEQA2 output file. Print option 2 causes
provisional as well as final equilibrated results to be written to the output
file.
Are all oversaturated solids to be allowed to precipitate? (Y,N,H) > Y
Select the solids output print option:
0 = Return to previous question
1 = Only after the final answer is reached
2 = Each time a mineral precipitates or dissolves
ENTER CHOICE >
Edit Level I Option 9: Maximum Number of Iterations
The default number of iterations is 40. Generally this is sufficient
for relatively simple problems or those that do not allow solids to
precipitate. More iterations may be necessary if the problem is very complex
and/or poor activity guesses are provided for the species present. Also, if
53
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you suspect that multiple solids will precipitate, then a larger number of
iterations will be required.
Select maximum number of iterations:
0-40 iterations
1-10 iterations
2 - 100 iterations
3 - 200 iterations
ENTER CHOICE > 0
Edit Level I Option 10: Calculation of Activity Coefficients
There are two choices for calculating activity coefficients, the
modified Debye-Huckel equation or the Davies equation (consult Chapter 2 for
details). It should be noted that only a fraction of the species present in
the database have the necessary constants for the modified Debye-Huckel
equation. When the Debye-Huckel equation is selected, the Davies equation
will be substituted for those species lacking the required constants. By
selecting option "1" you will cause all the activity coefficients to be
calculated in a consistent manner by with Davies equation.
Select an activity coefficient algorithm:
0 - Extended Debye-Huckel
1 - Davies Equation
ENTER CHOICE >
Edit Level I Option 11: MINTEQA2 Output File Options
You can control the amount of information written to the MINTEQA2 output
file. Option 1 is the most complete and Option 3 provides the least
information. You should experiment with these to determine how much of the
information you really need to obtain. In general, Option 2 provides the best
combination of brevity and completeness. Care should be used in selecting
Option 1 and simultaneously choosing the solids print Option 2 (see EDIT LEVEL
I OPTION 8) and using the sweep option (see EDIT LEVEL IV OPTION 1). Very
large output files may result.
Select the output option:
0 Return to previous question
1 - FULL output file
2 = INTERMEDIATE (omit some of the thermodynamic data
read from the database uncorrected log K values, gfw, etc.)
3 = ABBREVIATED (mass distribution at equilibrium only)
ENTER CHOICE >
Edit Level I Option 12: pH
The hydronium ion concentration can be entered as a measured pH, or as
total hydrogen. Each of these options also allows you the choice of fixing
the pH or letting MINTEQA2 calculate the equilibrium value. If you choose to
let MINTEQA2 calculate the value.
54
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Select pH option:
1 - Measured pH
2 - Measured total hydrogen
3 = Neither
ENTER CHOICE > 1
Enter pH > 6.600
Should H+l Be Independently Fixed? (Y,N) > Y
Edit Level I Option 13: pe or Eh
Redox potential can be entered as either Eh or pe. If you choose to
enter either value you will also be asked whether to fix the electron
activity, that is, whether to consider the pe or Eh entered an equilibrium
value. Systems containing redox chemistry can be very sensitive to the
initial activity guesses made for the electron (if the pe is to be calculated)
or for the components of redox couples (if pe is fixed). Be prepared to
assist MINTEQA2 by making improved guesses.
Select redox potential option:
E = You want to specify Eh
P - You want to specify pE
N - You prefer not to specify either
H = You want more explanation
ENTER CHOICE > E
Enter Eh (millivolts) > -Q.1560
Should E- (ENTERED AS EH) Be Independently Fixed? (Y,N) > Y
Edit Level I Option 14: No Adsorption Modeling
This is not a real option, but rather a display line that lets you see
which adsorption model has been implemented in this file. You can change the
sorption model in EDIT LEVEL TWO, described below.
Edit Level I Option 15: On Screen Status Messages
MINTEQA2 is capable of generating status screens during execution as a
means of reporting on progress in a problem. It is sometimes useful to
display these screens if an error is occurring, but writing them out does slow
the calculations considerably, causing significantly longer execution times.
If you are working in an AT environment it is recommended that you turn this
option off. You can perform timing tests on your problems to determine if the
time savings is significant on your machine.
Edit Level I Option 99: Change Seed File or Change Name of File to be Created
This option allows you to abandon any work up to the point it is
selected and choose a different existing file to use as a seed file. Once you
arrive at the prompt that allows this adjustment, you have the option of
returning to the very first prompt of the PRODEFA2 session and specifying a
different filename for the MINTEQA2 input file to be created, or to exit the
program.
55
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Main Menu Option 2: Edit Level II
EDIT LEVEL II is used to specify the chemistry of the system. Total
dissolved concentrations or fixed activities of components are specified by
selecting the appropriate option from the EDIT LEVEL II menu. Infinite
solids, gases, redox couples, finite solids, and other possible solids may
also be specified. Many of the options involving aqueous species and solids
provide a facility for searching the database if the user is uncertain whether
that species is included. New species may be defined by following the
prompts. EDIT LEVEL II also provides for choosing an adsorption model,
specifying its parameters, and defining adsorption reactions. (There are no
adsorption reactions in the standard database; see Chapter 3.) The menu
screen for EDIT LEVEL II appears below.
SELECT OPTION
Specify AQUEOUS COMPONENTS: TOTAL CONCENTRATIONS or FIXED ACTIVITIES
Specify AQUEOUS SPECIES not in the database, search the database,
or alter a database AQUEOUS SPECIES equilibrium constant
Specify an ADSORPTION MODEL and REACTIONS
Specify GASES at FIXED partial pressures
Specify REDOX COUPLES with FIXED activity ratios
Specify INFINITE SOLID phases
Specify FINITE SOLID phases
Specify POSSIBLE SOLID phases
Specify EXCLUDED SPECIES of any type
RETURN to MAIN MENU
All choices allow you to browse and return without changing anything;
Most allow you to search or view a directory of the relevant database.
ENTER CHOICE > 1
Each of these selections will prompt you for information in
approximately the same way and you will find some repetition in the discussion
of the different options that follow.
Edit Level II Option 1: Specify an Aqueous Component
This option is used to select the basic components that you will need in
the MINTEQA2 input file. Components are the building blocks for all other
species in the database. A complete list of all components and their ID
numbers can be found in Appendix A. When a component is selected, you must
specify either its total dissolved concentration or the fixed activity of the
free component.
Components are identified to PRODEFA2 by specifying the first letter of
the component name or the 3-digit component ID number. In the example below,
Ca+2 is selected from the list of components starting with the letter "C."
For Ca+2 this ID number would be 150 as shown below. To signal that you are
finished entering components, enter a zero. You may toggle between the first
letter mode of entry and the ID number mode by entering -1 as directed. Note
that the names of some components are written as acids. For example, an entry
of "S" in the first letter mode will produce a numbered list of components
that begin with the letter "S" but the component for silicon will not be among
them. That component, H4SiOA, is listed under "H" . Also, when you enter a
total dissolved concentration, an activity guess is made by PRODEFA2 unless
56
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the entered concentration is zero. In that case you will be asked to supply
the activity guess (read the prompt carefully; you may be asked for the "log
activity" which should be taken to mean the common logarithm of the free
component activity). For components that you specify as having fixed
activity, you will likewise be asked to specify the fixed activity. Note that
activities, whether fixed or guessed, are always in units of molal
(approximately molar) regardless of the concentration units specified in EDIT
LEVEL I.
EDIT LEVEL II PROB # 1
DEFINE COMPONENT SPECIES
Specify components for which you know the:
1 - TOTAL DISSOLVED CONCENTRATION
2 - FIXED EQUILIBRIUM ACTIVITY
R - Return to previous options menu (EDIT LEVEL II)
ENTER CHOICE > 1
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > c
1 C03-2 2 CN- 3 Ca+2 ~ 4 Cd+2 5 Cl-1
6 Cr+2 7 Cr(OH)2+ 8 Cr04-2 9 Cu+1 10 Cu+2
11 Citrate
Select the number of the appropriate component (0 - NONE) > 3
Enter the TOTAL DISSOLVED CONCENTRATION (MOLAL) of COMPONENT:
Ca+2 ID # 150 > 0.10000E-03
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > 0
Specify components for which you know the:
1 - TOTAL DISSOLVED CONCENTRATION
2 - FIXED EQUILIBRIUM ACTIVITY
R Return to previous options menu (EDIT LEVEL II)
ENTER CHOICE > R
Edit Level II Option 2: Specify an Aqueous Species
There are two reasons for selecting this option. One is to change the
equilibrium constant associated with a particular species from the database
value to some other that you have reason to believe more appropriate. The
other reason is to search the database to see whether a particular species is
included and, if it is not, to define that species as an added reaction. The
series of prompts that assist you in defining the new aqueous species are
similar to those encountered in defining a new solid or an adsorption reaction
in other EDIT LEVEL II options. You should have the reaction already written
out in terms of MINTEQA2 components so that you can provide the stoichiometry
and you should have the log K for the reaction as written as well as the
species charge and molar mass. Other entries (enthalpy, Debye-Huckel
constants, alkalinity factor) can be entered as zero if you do not have good
values.
57
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In identifying the species of interest, the user is asked for both the
major cation and anion in a manner that is similar to EDIT LEVEL II OPTION 1
above. The database is searched for complexes that contain both components.
If any matches are found, the reactions that contain them and their products
are displayed on the screen. You may select any of these reactions. If no
match is found or the species you want is not among those found, you are given
an opportunity to add a new reaction. Note that you may skip the database
search when a new species is to be added, but do this ONLY if you are sure the
species is not in the database already. It is generally best to first search
the database by choosing the search option (1) first. An example dialogue for
adding a reaction is shown below.
Specify AQUEOUS SPECIES ? (Y,N) > Y
Choose an option:
0 = Return to the previous question.
1 = Search the thermodynamic database for the species you want.
If it is in the database, display its log K and enthalpy values for
you to change if desired. If not in the database, assist you in
defining and adding the species.
2 - Assist you in defining and adding a species that you already know
is not in the thermodynamic database.
ENTER CHOICE > 1
The idea of the next series of prompts is to identify the species you
want to PRODEFA2. The 7-digit ID number could be used for an existing species
(assuming you want to check or change its equilibrium constant).
EDIT LEVEL II PROB~?I
DEFINE AQUEOUS SPECIES
Is the ID f known for AQUEOUS SPECIES ? (Y,N) > N
Define MAJOR cation component
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > c
1 Ca+2 2 Cd+2 3 Cr+2 ~ 4 Cr(OH)2+ 5 Cu+1
6 Cu+2
Select the number of the appropriate component (0 - NONE) > 3
Define MAJOR anion component
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > c
1 C03-2 2 CN- 3 Cl-1 ~ 4 Cr04-2 5 Citrate
Select the number of the appropriate component (0 = NONE) > 3_
Once you have completed choosing the major ions, the computer will
search the entire database for entries that contain those two major
components. In this case, no matches were found. Had one or more species
been found that included both of these components, a numbered menu would
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appear from which to choose. If none were the species of interest, you would
be given opportunity to define a new species just as the case where no
matching species was found, as in this example. The dialogue which informs
you that no matches were detected and proceeds to prompt you for information
for the new species follows.
PATIENCE..Thermodynamic database file 7 is being searched !
No NEAR match found in the database for ID 2101800
Do you want to define a new species comprised at least partly of those
constituents you have already specified ? (Y,N) > Y
Is ID » 2101800 acceptable for a new AQUEOUS SPECIES ? (Y,N,H) > Y
Now Add Reaction Not Yet In Data Base For AQUEOUS SPECIES
Enter Name For AQUEOUS SPECIES . > CrCl+
Enter Charge On Species > 1.00
Enter Debye-Huckel A Parameter > 0.00
Enter Debye-Huckel B Parameter > 0.00
Enter Alkalinity Factor > 0.00
Enter Molecular Wt. (GFW) > 87.S
THE REACTION THUS FAR CREATED IS :
0.000 Cl-1 + 0.000 Cr+2 < > CrCl+
Specify MASS ACTION and MASS BALANCE stoichiometry
Enter the stoichiometric coefficient for Cl-1
Remember that REACTANTS have positive stoichiometry while PRODUCTS have
negative stoichiometry. ENTER stoichiometry > 1.
THE REACTION THUS FAR CREATED IS :
1.000 Cl-1 + 0.000 Cr+2 < > CrCl+
Specify MASS ACTION and MASS BALANCE stoichiometry
Enter the stoichiometric coefficient for Cr+2
Remember that REACTANTS have positive stoichiometry while PRODUCTS have
negative stoichiometry. ENTER stoichiometry > !_._
Are there any other components in this reaction ? (Y,N,H) > N
THE REACTION THUS FAR CREATED IS :
1.000 Cl-1 + 1.000 Cr+2 < > CrCl+
Should Cl-1 Be Independently Fixed? (Y,N,H) > N
Should Cr+2 Be Independently Fixed? (Y,N,H) > N
For The Request That Follows, K Must Be Consistent With Molal Concentrations.
Enter Log K For Reaction To Form CrCl+ > 5.6
Enter Enthalpy For Reaction To Form CrCl+ > -20.2
ID # 2101800 CrCl+ Chosen. Current LOG10(KEQ)= 0.56000E+01
EDIT LEVEL TWO PROB * 1
DEFINE AQUEOUS SPECIES
Specify AQUEOUS SPECIES ? (Y,N,H) > N
59
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Note that the stoichiometry coefficients requested are for the mass action
expression. MINTEQA2 supports the option of having mass balance stoichiometry
that differs from that of the mass action expression. For added reactions
with this characteristic, the mass balance stoichiometry can be specified in
EDIT LEVEL III. Also, note that we can tell by examination of the above
example that the components Cl" and Cr2"1" had not been selected as components
for this problem when this reaction was defined. The query, "Should Cl- Be
Independently Fixed?" clues us in that Cl" has been added to the list of
components in this problem with a total dissolved concentration of zero and a
log activity of -16.0 (both program default values). The question indicates
that PRODEFA2 wants to know whether the activity is to be fixed. Similarly
for Cr2+. These default values may be changed in EDIT LEVEL III if not
satisfactory.
Edit Level II Option 3: Specify Adsorption Definition
This option is chosen when you want to specify an adsorption model and
add adsorption reactions to the problem. Descriptions of input parameters for
the available models are provided in Chapter 3. In the following example,
Ca+2 is allowed to adsorb to surface 1 site type 1 by a simple activity Kd
sorption algorithm. The adsorption reactions are created and treated
similarly to aqueous complexation reactions in the above example.
EDIT LEVEL II PROB f I
DEFINE Adsorption Problem
Specify ADSORPTION DEFINIT'N? (Y,N) >
Select an adsorption algorithm:
0 - None
1 = Activity Kd
2 ~ Activity Langmuir
3 = Activity Freundlich
4 = Ion Exchange Model
5 = Constant Capacitance Model (CCM)
6 = Triple Layer Model (TLM)
7 = Diffuse Layer Model (DLM)
ENTER CHOICE > 1
A maximum of five adsorbing surfaces, each with one or two types of binding
sites may be defined. Opportunity to define multiple surfaces is presented
in a succession of prompts. The identifying surface numbers 1 through 5
serve only to distinguish one surface from another when specifying surface
reactions. There is no intrinsic difference between surfaces of different
identifying numbers. Similarly, there is no intrinsic difference between
sites 1 and 2 on a surface. For both surfaces and sites YOU establish any
differences by assigning different characteristics and parameters for
different surfaces and different reactions and equilibrium constants for
the different sites on a surface.
PRESS ENTER TO CONTINUE
Enter the mass of soil (kg) to which one liter of solution is exposed > 3.177
Once you have selected the adsorption model, a screen displaying the
status of currently defined surface and site definitions will appear. This
screen will be updated as you set additional parameters. You may define one
or more reactions involving each site. The procedure is almost identical to
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that required to enter a new aqueous species as shown in EDIT LEVEL II OPTION
2. For the electrostatic models, note that the components that represent
electrostatic terms are entered with the proper stoichiometry automatically.
ADSORPTION STATUS
The following binding-site types are defined for 0 surface(s):
NO SURFACES CURRENTLY DEFINED
ADSORPTION OPTIONS
Select an option:
1 - ADD a NEW SURFACE with a site
2 - ADD a NEW SITE on a currently defined surface
3 - ADD a NEW REACTION at a currently defined site
4 - ATTACH an auxiliary database of adsorption reactions
5 - DELETE a currently defined site
R - RETURN without changing anything
Enter Choice: > 1.
Enter the site type number (1 or 2) > 1.
SPECIFICATION OF ADSORPTION REACTIONS ON Site Type 1_
SURFACE NUMBER ONE
**** PROCEED TO DEFINE REACTION * 1 ****
Select An Aqueous Metal Or Ligand To Make Up ID For ADSORP'N PRODUCT
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > £
1 C03-2 2 CN- 3 Ca+2 * Cd+2 5 Cl-1
6 Cr+2 7 Cr(OH)2+ 8 Cr04-2 9 Cu+1 10 Cu+2
11 Citrate
Select the number of the appropriate component (0 - NONE) > 3.
Is ID - 8111500 acceptable for a new ADSORBED SPECIES ? (Y,N) > Y
Now Add Reaction Not Yet In Data Base For ADSORBED SPECIES
Enter Name For ADSORP'N PRODUCT . > X-Ca
THE REACTION THUS FAR CREATED IS :
0.000 ADS1TYP1 + 0.000 Ca+2 < > X-Ca
Specify MASS ACTION and MASS BALANCE stoichiometry
Enter the stoichiometric coefficient for ADS1TYF1
Remember that REACTANTS have positive stoichiometry while PRODUCTS have
negative stoichiometry. ENTER stoichiometry > 1.00
THE REACTION THUS FAR CREATED IS :
1.000 ADS1TYP1 + 0.000 Ca+2 < > X-Ca
Specify MASS ACTION and MASS BALANCE stoichiometry
Enter the stoichiometric coefficient for Ca+2
Remember that REACTANTS have positive stoichiometry while PRODUCTS have
negative stoichiometry. ENTER stoichiometry > 1.00
Are there any other components in this reaction ? (Y,N) > N
THE REACTION THUS FAR CREATED IS :
1.000 ADS1TYP1 + 1.000 Ca+2 < > X-Ca
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For The Request That Follows, K Must Be Consistent With Molal Concentrations.
Enter Log K For Reaction To Form X-Ca > 0.50000E+00
Enter Enthalpy For Reaction To Form X-Ca > O.OOOOOE+00
ID # 8111500 X-Ca Chosen. Current LOGIO(KEQ)- 0.50000E+00
Any MORE ADSORPTION REAC'NS for Site Type 1? (Y,N) > N
ADSORPTION STATUS
The following binding-site types are defined for 1 surface(s):
Surface Site Type Number Component Number Site Cone (moles/1)
1 1 811 Infinite Supply
ADSORPTION OPTIONS
Select an option:
1 ADD a NEW SURFACE with a site
2 ADD a NEW SITE on a currently defined surface
3 ADD a NEW REACTION at a currently defined site
ATTACH an auxiliary database of adsorption reactions
DELETE a currently defined site
RETURN without changing anything
Enter Choice: > R
Note that a currently defined site and all added reactions in which it is
involved may be deleted by choosing Option 5.
Edit Level II Option 4: Specify a Fixed Gas Species
When this option is chosen, you are prompted with a complete list of the
gases present in MINTEQA2's database. You then make a selection and enter the
fixed equilibrium partial pressure of the gas. You are allowed to change the
log K if you desire; otherwise, it is automatically corrected to the partial
pressure you have specified (in atm). All gases are automatically defined as
EXCLUDED species in MINTEQA2 unless explicitly entered here.
EDIT LEVEL II PROB
DEFINE GASEOUS SPECIES
Specify FIXED GASES ? (Y,N) > Y
1-CH4 (g) 2-C02 (g) 3-02 (g) 4-Hg (g)
5-Hg2 (g) 6-Hg(CH3)2(g) 7-HgBr (g) 8-HgCl (g)
9-HgF (g) 10-HgI (g) H-HgBr2 (g) 12-HgF2 (g)
13-HgI2 (g)
Enter the number corresponding the gas you want. Enter zero to abort tha
specification of a gas.
ENTER CHOICE > 2
PATIENCE..Thermodynamic database file 9 is being searched !
1 3301*03 C02 (g) <- 1.0 C03-2 + 2.0 H+l + -1.0 H20
Enter the non-zero partial pressure (atm) of C02 (g) > 0.10000E-02
Corrected log K is 21.160
Want To Change Log K For C02 (g) From 0.2116E+02 ? (Y,N) > N
Specify FIXED GASES ? (Y,N) > N
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Edit Level II Option 5: Specify a Redox Couple
When this option is selected, PRODEFA2 will scan the list of components
that have thus far been selected. For each of those components, if a redox
couple exists in the thermodynamic database, that couple will be displayed in
a numbered menu from which you may choose those you want to include in the
MINTEQA2 problem. If no components have been specified that have a
corresponding reduced or oxidized form that is also available as a MINTEQA2
component, no such numbered menu will be displayed. Therefore, if you plan to
implement redox chemistry, specify the components of interest first in EDIT
LEVEL II OPTION 1. It is also a good idea to specify the pe or Eh either as a
guess at the equilibrium value (if the true pe or Eh is to be computed) or as
a fixed value (if the solution is to be equilibrated to a given pe or Eh). In
the example that follows, either Fe+2, Fe*3, or both could be specified as
components first. If neither is specified, the Fe redox couple would not
appear on the numbered menu.
EDIT LEVEL II PROB
DEFINE REDOX SPECIES
Specify FIXED-RATIO REDOX ? (Y,N) > Y
1-FE+3/FE+2 2-CR+2/CR(OH)2
This menu displays only those redox couples for which you have already
specified at least one aqueous component. Enter the index corresponding
to the couple you want. Enter zero to abort redox specification.
ENTER CHOICE > 1
PATIENCE..Thermodynamic database file 8 is being searched !
1 2812800 FE+3/FE+2 <- 1.0 Fe+3 + -1.0 Fe+2 + 1.0 E-l
Want To Change Log K For FE+3/FE+2 From 0.1303E+02 ? (Y,N) > N
Want To Change Enthalpy For FE+3/FE+2 From -0.1000E+02 ? (Y,N) > N
EDIT LEVEL II PROB » 1
DEFINE REDOX SPECIES
Specify FIXED-RATIO REDOX ? (Y,N) > N
Note that had the electron not already been entered as a component (by
specifying the pe or Eh in EDIT LEVEL I OPTION 13 or by simply selecting it as
a component in EDIT LEVEL OPTION 1 above), PRODEFA2 would have entered it as a
component with total dissolved concentration of zero and inquired whether to
fix its activity (at the program default value of log activity = -16.0).
Edit Level II Option 6: Specify an Infinite Solid
An infinite solid is one that is not subject to complete dissolution.
As such, the solution is required to be at equilibrium with the infinite
solid. All precipitated solids, whether infinite or finite, reduce the
degrees of freedom by 1 (see Chapter 3). As was shown above for EDIT LEVEL II
OPTION 2 (Specify Aqueous Species), PRODEFA2 provides means of searching the
database to see whether a particular solid is present, allowing you to specify
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an equilibrium constant different from the database value if desired, and
allowing you to define a new solid species if the one you seek is not found in
the database. The method of identifying the solid species you want is the
primary difference between the aqueous species procedure and that shown below
(which applies to INFINITE, FINITE and POSSIBLE solids). In general, the
major cation and major mineral group as given by a numbered menu are
specified. For solids that are known to be included in the database, the 7-
digit ID number may be specified instead.
EDIT LEVEL II PROB * 1
DEFINE MINERAL SPECIES
Specify INFINITE SOLIDS ? (Y,N) > Y
Choose an option:
0 - Return to the previous question.
1 - Search the thermodynamic database for the species you want.
If it is in the database, display its log K and enthalpy values for
you to change if desired. If not in the database, assist you in
defining and adding the species.
2 " Assist you in defining and adding a species that you already know
is not in the thermodynamic database.
ENTER CHOICE > 1
Is the ID # known for MINERAL ? N
1 Elemental 10 Sulfide 11 Cyanide
12 Selenide 14 Antimonide 20 Oxide or Hydroxide
30 Multiple Oxide 40 Bromide 41 Chloride
42 Fluoride 43 Iodide 50 Carbonate
SI Nitrate 52 Borate 60 Sulfate
61 Selenate or Selenite 70 Phosphate 72 Arsenate
73 Vanadate 80 Orthosilicate 82 Chain Silicate
84 Framework Silicate 86 Sheet Silicate
Enter the number corresponding to the class to which this mineral belongs.
ENTER CHOICE (0 - none) > 10
****** Specify the major cation or cation donor ******
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > f
1 Fe+2 2 Fe+3
Select the number of the appropriate component (0 - NONE) > 1
PATIENCE..Thermodynamic database file 19 is being searched !
1 1028000 FES PPT <- -1.0 H+l + 1.0 Fe+2 + 1.0 HS-1
2 1028001 OREIGITE <- -4.0 H-H + 2.0 Fe+3 + 1.0 Fe+2
+ 4.0 HS-1
3 1028002 MACKINAWITE <- -1.0 H+l + 1.0 Fe+2 + 1.0 HS-1
4 1028003 PYRITE <- -2.0 H+l + -2.0 E-l + 1.0 Fe+2
+ 2.0 HS-1
Enter the number aligned with the species you want. (0 - None of above) > 4.
Should HS-1 Be Independently Fixed? (Y,N) > N
Want To Change Log K For PYRITE From 0.1848E+02 ? (Y,N) > N
Want To Change Enthalpy For PYRITE From -0.1130E+02 ? (Y,N) > N
64
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Remember that each solid specified, as well as each gas, each redox couple,
each finite solid, and each component with fixed activity reduces the number
of degrees of freedom for solving this problem by 1. If the degrees of
freedom is reduced to zero, phase-rule violation will occur in MINTEQA2 (see
Chapter 2 for details). PRODEFA2 checks the degrees of freedom upon
attempting to exit the program and warns if it is zero at the outset due to
the presence of more fixed species than variable components. It may be
necessary to remove some constraints such as one or more infinite solids if
such a warning occurs.
Edit Level II Option 7: Specify a Finite Solid
A finite solid is presumed present at equilibrium and, as an aid to
MINTEQA2 in picking the correct set of solids, is noted as such by specifying
it here. Unlike the infinite solid above, a solid designated as finite may
dissolve if equilibrium conditions warrant. It is entered in the same manner
as the infinite solid, with the exception that you may specify an amount
present (in moles present in one liter of solution). The amount can be
entered as zero because you really do not know how much is present at
equilibrium, if any; it is MINTEQA2's job to figure that out! If you choose
to enter a non-zero amount, be aware that the total system concentration of
the components of the solid will be changed unless you also deplete the total
dissolved concentrations of those components by a corresponding amount (with
proper respects to the stoichiometry of each component of the solid). To see
how this works, do a simple MINTEQA2 run using the default values for all EDIT
LEVEL I parameters except the pH which is fixed at 7.0. In EDIT LEVEL II,
specify Ca2"1" and C032"as components, each with total dissolved concentration of
l.OOOe-03 m, not fixed. Using this option, specify calcite as a finite solid
with a concentration of zero. Submit this problem to MINTEQA2 and save the
output file. Next use PRODEFA2 to create a second file using that first one
as a seed file. Change nothing except in EDIT LEVEL III, change the total
dissolved concentration of both Ca2+ and C032" to zero, and change the
concentration of the finite solid calcite to l.OOOe-3. Exit and submit this
problem to MINTEQA2. Compare the output file from the second run with the
first. You will see that the equilibrated results are identical. Now imagine
what the results would have been if, in the second run, you had changed the
amount of calcite from zero to l.OOOe-03, but had not changed the total
dissolved concentration of the constituent components. In that case, the
results could not be the same because the total system concentration of both
Ca2+ and C032~ would be 2.000e-03 m; the problem would be fundamentally
different.
Edit Level II Option 8: Specify a Possible Solid
POSSIBLE SOLIDS are solids that are permitted to precipitate if
equilibrium conditions warrant. All database solids become POSSIBLE SOLIDS
when the precipitation flag in EDIT LEVEL I OPTION 8 is so set. In that case
there is no need for this option. However, the other setting of the EDIT
LEVEL I flag dictates that all solids be EXCLUDED SPECIES except those
explicitly designated as POSSIBLE SOLIDS through this option. Note that
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within MINTEQA2, when a POSSIBLE SOLID precipitates it is re-defined as a
FINITE SOLID. Conversely, when a FINITE SOLID dissolves, it is re-defined as
a POSSIBLE SOLID. Chapter 2 provides more details. The manner of identifying
POSSIBLE SOLIDS is identical to that for INFINITE SOLIDS above and is not
repeated here.
Edit Level II Option 9: Specify an Excluded Species
This option allows you to exclude any type of species from mole balance.
In the case of solids, one setting of the precipitation flag in EDIT LEVEL I
provides for all database solids to be excluded from precipitating (the
equivalent of defining them as EXCLUDED SPECIES). Another provides for all to
be permitted to precipitate if equilibrium conditions warrant. This option
can be used in conjunction with the latter EDIT LEVEL I option to explicitly
exclude certain solids (see EDIT LEVEL II OPTION 8). Any aqueous species may
also be excluded including any component as an aqueous species. The user will
note that certain species appear in the list of EXCLUDED SPECIES automatically
when MINTEQA2 is executed. These include the electron unless its activity is
fixed, all electrostatic components of the adsorption models, all database
gases and redox couples not explicitly defined as SPECIES WITH FIXED ACTIVITY.
EXCLUDED solids do not appear in the list unless explicitly defined as
EXCLUDED SPECIES in MINTEQA2.
The procedure for explicitly excluding a species amounts to little more
than identifying it to PRODEFA2. The procedures for doing that are basically
the same as for identifying species of the various types as shown above. The
same questions and rules follow here as well, except a little less information
is required. Please refer to the options above for examples of the selection
dialogue. An example of excluding a component follows.
EDIT LEVEL II PROB~j1
DEFINE Excluded Species
-- This section allows you to specify component, aqueous, mineral, or
adsorbed, species that you want to be excluded from mass balance
calculations. Note that all redox and gas species except those you entered
above are excluded automatically as are components used for
electrostatic potentials.
Specify EXCLUDED SPECIES ? (Y,N) > Y
1-COMPONENT SPECIE 2-AQUEOUS SPECIES 3-MINERAL SPECIES
4-ADSORBED SPECIES 5-REDOX SPECIES 6-GASEOUS SPECIES
Enter the number that corresponds to the desired class > 3
Is the ID # known for EXCLUDED SPECIES ? (Y,N) > N
1 Elemental 10 Sulfide 11 Cyanide
12 Selenide 14 Antimonide 20 Oxide or Hydroxide
30 Multiple Oxide 40 Bromide 41 Chloride
42 Fluoride 43 Iodide 50 Carbonate
51 Nitrate 52 Borate 60 Sulfate
61 Selenate or Selenite 70 Phosphate 72 Arsenate
73 Vanadate 80 Orthosilicate 82 Chain Silicate
84 Framework Silicate 86 Sheet Silicate
Enter the number corresponding to the class to which this mineral belongs.
ENTER CHOICE (0 = none) > 10
66
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****** Specify the major cation or cation donor ******
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > f
1 Fe+2 2 Fe+3
Select the number of the appropriate component (0 NONE) > JL
PATIENCE..Thermodynamic database file 19 is being searched !
<- -1.0 H+l + 1.0 Fe+2 + 1.0 HS-1
1 1028000 FES PPT
2 1028001 GREIGITE <- -4.0 H+l
+ 4.0 HS-1
3 1028002 MACKINAWITE <- -1.0 H+l
4 1028003 PYRITE
<- -2.0 H+l
+ 2.0 HS-1
+ 2.0 Fe+3
+ 1.0 Fe+2
+ -2.0 E-l
1.0 Fe+2
1.0 HS-1
1.0 Fe+2
Enter the number aligned with the species you want. (0 = None of above) >
Specify EXCLUDED SPECIES ? (Y,N) > N
Main Menu Option 3: Edit Level III
EDIT LEVEL III functions as a "line editor" in displaying by category or
TYPE of data (see Chapter 2) line by line entries of those species that have
been explicitly entered through EDIT LEVEL II. The order of data presentation
is: 1) COMPONENTS, 2 ) TYPE II - AQUEOUS SPECIES, 3) TYPE III -SPECIES WITH
FIXED ACTIVITY, 4) TYPE IV - FINITE SOLIDS, 5) TYPE V - POSSIBLE SOLIDS, and
6) TYPE VI - EXCLUDED SPECIES. Finally, any new species for which the
reaction has been entered in PRODEFA2 (referred to as TYPE VII in this
listing) is displayed. Note that TYPE I - COMPONENTS AS SPECIES IN SOLUTION
are omitted because displaying the components themselves is sufficient here.
Also, if no species have been explicitly entered for a particular type, that
listing is omitted. For all the data types, the user is given opportunity to
change entered values or to delete an entry altogether.
As each screen is displayed, the user is given opportunity to edit
specific entries by specifying the number displayed to the left of each entry.
Upon selecting an entry for editing, that entry is isolated and a menu of
change operations is displayed. The change commands are rather
straightforward. The example below illustrates simple change commands.
Entry
1
2
3
4
8
I.D.
330
150
180
210
280
Verify or
Name
H+l
Ca+2
Cl-1
Cr+2
Fe+2
EDIT LEVEL III
PROB #
1
change listing of COMPONENTS
Total Cone.
l.OOOOOE-07
l.OOOOOE-04
O.OOOOOE-01
O.OOOOOE-01
l.OOOOOE-05
Log Activity
-7.00000E+00
-4.00000E+00
-1.60000E+01
-1.60000E+01
-5.00000E+00
Enter entry # to change, add or delete (0 NONE) > 1^
You may edit parameters for any of the components present in a variety
of ways, as shown here for entry 1.
67
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Entry
1
I.D.
330
Name
H+l
Total Cone.
l.OOOOOE-07
Log Activity
-7.00000E+00
Select:
-1 = Delete this component
0 Return; no more changes
1 - Change ID number
2 = Change name
3 Change total concentration
4 = Change log activity guess
Enter Choice: > 0
Enter entry t to change, add or delete (0 = NONE) > 0
EDIT LEVEL III
PROB
Entry
1
I.D.
1501401
Verify or change listing of AQUEOUS SPECIES
Name
CaC03 AQ
Log K
3.45000E+00
Enthalpy
4.03000E+00
Enter entry # to change.
Entry I.D. Name
1 1501401 CaC03 AQ
add or delete (0 - NONE)
Log K
3.45000E+00
> j.
Enthalpy
4.03000E+00
Select:
-1 = Delete this species
0 " Return; no more changes
1 - Change the ID number
2 = Change the name
3 - Change the log K
4 = Change the enthalpy
Enter Choice: > 3
Enter Log K For Reaction To Form CaC03 AQ > 3.150E+00
Entry I.D. Name Log K Enthalpy
1 1501401 CaC03 AQ 3.15000E+00 4.03000E+00
Select:
-1 = Delete this species
0 = Return; no more changes
1 = Change the ID number
2 Change the name
3 - Change the log K
4 = Change the enthalpy
Enter Choice: > 0
EDIT LEVEL III
PROB
Verify or change listing of FIXED SPECIES
Entry
1
2
3
4
I.D.
3301403
2812800
1028003
811
Name
C02 (g)
FE+3/FE+2
PYRITE
ADS1TYP1
Log K
2.11600E+01
1.30320E+01
1.84790E+01
O.OOOOOE-01
Enthalpy
-5.30000E-01
-l.OOOOOE+01
-1.13000E+01
O.OOOOOE-01
Enter entry # to change, add or delete (0 - NONE) >
No FINITE SOLIDS
No POSSIBLE SOLIDS
(TYPE 4) have been defined.
(TYPE 5) have been defined.
EDIT LEVEL III
PROB # 1
Verify or change listing of EXCLUDED SPECIES
Entry I.D. Name
1 1028000 FES PPT
2 1 E-l
Enter entry # to change, add or delete (0 = NONE)
68
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Note that there is seldom a need to change the ID number associated with
a species. If you had mistakenly entered K+ rather than Na+, you could
correct that mistake by changing the ID number from 410 to 500 and changing
the names (although MINTEQA2 does not use the names read from the input file
anyway, it uses the ID number and finds the name in the database files). EDIT
LEVEL III has been designed to give you maximum control over the data that
finally appears in the output file. Use it to replace PRODEFA2 generated data
such as "activity guesses" with your own. "Activity guesses" are the common
logarithm of the free component species activity in molal. PRODEFA2 usually
guesses that the free component activity is equal to the component's total
dissolved concentration. This is usually an adequate guess. The exception is
for any component that has not yet been entered when a species that requires
it is explicitly entered in one of the other categories. In that case,
PRODEFA2 enters the component automatically at a total dissolved concentration
of zero and with a log activity guess of -16.0. EDIT LEVEL III allows you to
change such entries if desired. DO NOT USE EDIT LEVEL III TO CREATE NEW
COMPONENT ID NUMBERS.
The change command menu for added species includes the option of
changing the mass action stoichiometry of any component and designating those
components that have different mass balance stoichiometry. The mass balance
stoichiometry is denoted "*stoichiometry" for brevity. The example below
illustrates this menu.
EDIT LEVEL III
Verify or
Entry
1
2
I.D.
2101800 CrCl+
Stoichiometry
8111500 X-Ca
Stoichioraetry
Name
: < 1.
: ( 1.
change listing of ADDED SPECIES
Log K Enthalpy Charge
5.600 -20.20 1.0
.000)180 (
0.500
.000)811 (
1.000)210
0.00
1.000)150
0.0
PROB # 1
gfw
87.500
0.000
Alk. Factor
0.00
0.00
Enter entry # to change, add or delete (0 = NONE) > 2
Entry I.D. Name Log K Enthalpy Charge gfw Alk. Factor
2 8111500 X-Ca 0.500 0.00 0.0 0.000 0.00
Stoichiometry: ( 1.000)811 ( 1.000)150
Select:
-1 = Delete this species
0 = Return; no more changes
1 = Change ID number
2 = Change name
3 - Change log K
4 = Change enthalpy
5 = Change charge
6 = Change gram formula wt.
7 = Change alkalinity factor
8 = Change stoichiometry
Enter Choice: > 8
There are two groups of stoichiometry/component ID pairs for each reaction.
The main group, which allows up to 12 pairs, ordinarily represents the
stoichiometry of each component for both mass action and mass balance, these
being equal. Sometimes however, it is useful to specify a mass balance
stoichiometry for one or more components that is not equal to its mass
action counterpart. The second group of stoichiometry/component ID pairs,
which allows up to 3 pairs, represents the mass balance stoichiometry
for those components. The main group is labeled "Stoichiometry" in the
listing of added species while the second group, present only in special cases
such as a Freundlich adsorption reaction, is labeled "*Stolchiometry".
69
-------
Select an option:
0 - Return; no more changes
1 - Change, add to, delete from Stoichiometry
2 = Change, add to, delete from *Stoichiometry
Enter Choice: > 0
Entry I.D. Name Log K Enthalpy Charge gfw Ali. Factor
2 8111500 X-Ca 0.500 0.00 0.0 0.000 0.00
Stoichiometry: ( 1.000)811 ( 1.000)150
Select:
-1 - Delete this species
0 - Return; no more changes
1 - Change ID number
2 = Change name
3 - Change log K
4 « Change enthalpy
5 - Change charge
6 - Change gram formula wt.
7 = Change alkalinity factor
8 Change Stoichiometry
Enter Choice: > ()
Main Menu Option 4: Edit Level IV
EDIT LEVEL IV is concerned with certain utility functions rather than
with chemistry. There are two primary options in EDIT LEVEL IV. One is to
set certain parameters so that the MINTEQA2 run becomes a series of multiple
runs as in a titration or "sweep." The total concentration or fixed activity
of one (and only one) user selectable component may be designated as the sweep
parameter. A starting value and incremental value may be specified along with
the number of titration points or the value of the sweep parameter may be
entered explicitly for up to 20 points. The second option allows the user to
direct that the equilibrated mass distribution among dissolved, sorbed, and
solid phases be written to a special file for up to three components. The
format of that special file is such that it can be imported by popular
spreadsheet programs. The components H+ and e" are written automatically when
this option is used; the three selectable components are in addition to these.
Combined use of these two options can produce plottable results, say dissolved
Cd2+ as a function of pH, in a single MINTEQA2 run. An example of the
dialogue for these two options is shown below.
Edit Level IV Option 1: Sweep Option
In the example that follows, a demonstration of how to set up an
incremental sweep over the total dissolved concentration of the component Ca2"1"
is shown. The starting concentration is l.OOOe-05, the incremental
concentration is l.OOOe-06, and there are six titration points in the sweep.
The dialogue begins after having selected option 1 from the EDIT LEVEL IV
menu.
SPECIFY THE SWEEP COMPONENT:
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > f
1 F-l 2 Fe+2 3 Fe+3 ~ 4 Formate 5 Fulvate
70
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Select the number of the appropriate component (0 " NONE) > 2
Indicate what the values are to represent:
1 - Total Concentration
2 - Fixed Equilibrium Activity (values entered as negative log activity,
e.g., pH, pE, or in general, p[XJ)
R Return to previous question,
ENTER CHOICE > 1
Enter the number of values. Range: 2 to 20 values;
An entry of one (1) or zero (0) ABORTS sweep.
Enter number of values > 6
Choose the method of entering the 6 Total Concentration values:
1 » Specify a starting value and a constant incremental value
2 - Specify the values explicitly
R - Return to previous question
ENTER CHOICE > 1
Enter the increment between desired values.
An entry of zero (0) ABORTS sweep.
Enter increment > 0.100E-Q5
EDIT LEVEL IV PROB
"SWEEP UTILITY
>»»» CURRENT SETTINGS for Sweep Component Fe+2
Series of values represent: TOTAL CONCENTRATION
Number of values: 6
Starting value: l.OOOE-05
Incremental value: l.OOOE-06
OPTIONS
1 = Change the SWEEP COMPONENT
2 - Change the NUMBER OF VALUES or the VALUES
3 - Change whether the values represent TOTAL DISSOLVED CONCENTRATION
or FIXED EQUILIBRIUM ACTIVITY (values entered as negative log activity,
e.g., pH, pE, or in general, p[X])
R = ACCEPT current settings and RETURN to EDIT LEVEL IV main menu
C - CANCEL current settings and RETURN to EDIT LEVEL IV main menu
ENTER CHOICE >
You can change the sweep component, the number of values, or the type of
sweep from a total concentration to fixed activity or vice versa at any time
during a PRODEFA2 session. Below is an example of changing the Ca2* component
total dissolved concentrations to just four explicitly given values.
ENTER CHOICE > 2
EDIT LEVEL IV PROB »]~
SWEEP UTILITY
>»»» CURRENT SETTINGS for Sweep Component Fe+2
Series of values represent: TOTAL CONCENTRATION
Number of values: 6
Starting value: l.OOOE-05
Incremental value: l.OOOE-06
OPTIONS
Enter the number of values. Range: 2 to 20 values;
An entry of one (1) or zero (0) ABORTS sweep.
Enter number of values > 4
71
-------
Choose the method of entering the 4 Total Concentration values:
1 = Specify a starting value and a constant incremental value
2 - Specify the values explicitly
R ~ Return to previous question
ENTER CHOICE > 2
The current starting value is l.OOOE-04.
Is this correct (Y/N) ? N
Enter the new starting total concentration > 5E-06
Enter the next 3 successive values separating them from one another
with commas or spaces > 6E-06. 7E-06. 8E-06
Note that you are given opportunity to re-affirm or change the original
value for the sweep component's total dissolved concentration. That value
becomes the starting value for the sweep and the next three values are entered
explicitly. You may cancel the sweep entirely or accept the current settings
as shown below.
_ EDIT LEVEL IV PROB
SWEEP UTILITY
»»»> CURRENT SETTINGS for Sweep Component Fe+2
Series of values represent: TOTAL CONCENTRATION
Number of values: 4
VALUES
5.000E-06 6.000E-06 7.000E-06 8.000E-06
OPTIONS
1 - Change the SWEEP COMPONENT
2 - Change the NUMBER OF VALUES or the VALUES
3 - Change whether the values represent TOTAL DISSOLVED CONCENTRATION
or FIXED EQUILIBRIUM ACTIVITY (values entered as negative log activity,
e.g., pH, pE, or in general, p[X])
R " ACCEPT current settings and RETURN to EDIT LEVEL IV main menu
C - CANCEL current settings and RETURN to EDIT LEVEL IV main menu
ENTER CHOICE > R
Edit Level IV Option 2: Special Output File from MINTEQA2
The following section shows how to tell PRODEFA2 to create a spreadsheet
importable file and how to specify the information you want. In this example,
the file to be appended to (or created if it doesn't already exist) is
TESTD.PRN. Each line within that file represents the equilibrated results
from a separate MINTEQA2 run or from an individual sweep or titration point of
a run where the sweep option is used. The first two entries on each line of
the file are time and date ID numbers that allow you to associate the results
with the run or sweep to which they pertain (those same ID numbers are written
to PART 5 of the MINTEQA2 output file). When this option is used, the pH will
be written automatically without having been designated as a component to be
written. The same is true of pe if it is defined in your run. The
equilibrated mass distribution for the other components selected (up to 3) is
written to the special file just as it appears in PART 5 of the MINTEQA2
output file. Information on Fe2"1" and HS" is requested as shown in the example
below.
72
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_ EDIT LEVEL IV PROB # 1
SELECT OPTION
1 = Specify that the total concentration or fixed log activity of
one component only is to be systematically varied in a series of
otherwise identical problems.
2 = Specify that the equilibrated mass distribution (computed by
MINTEQA2) of up to three user selected components, pH, and
Eh (if applicable) be written to a user designated file in a
format appropriate for import by popular spreadsheet programs.
R - Return to MAIN MENU
ENTER CHOICE > 2
EDIT LEVEL IV PROB
"IMPORT UTILITY
1 = Filename to which the equilibrated data for spreadsheet import
is to be written:
2 - Currently specified component(s) whose equilibrated mass distributions
are to be written:
C « Cancel current settings and reset so as to NOT generate importable output
R = Return to previous menu without changing anything
ENTER CHOICE > 1
Enter the name of the file to which the importable MINTEQA2 output data is
to be written. Use up to 8 characters plus an optional filename extension
of up to 3 characters.
ENTER FILENAME > TESTD. PRN
_ EDIT LEVEL IV PROB
IMPORT UTILITY
1 - Filename to which the equilibrated data for spreadsheet import
is to be written: TESTD.PRN
2 - Currently specified component(s) whose equilibrated mass distributions
are to be written:
C " Cancel current settings and reset so as to NOT generate importable output
R = Return to previous menu without changing anything
ENTER CHOICE > 2
STEP 1 - ENTER THE NUMBER OF COMPONENTS whose equilibrated mass distributions
are to be written (from 1 to 3; 0 to cancel) > 2
STEP 2 - Follow instructions to SPECIFY COMPONENT 1 of the 2 to be written
to the importable ASCII file.
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > f
1 F-l 2 Fe+2 3 Fe+3 ~ 4 Formate 5 Fulvate
Select the number of the appropriate component (0 - NONE) > 2
73
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*********************************************************************
Component ID number 280, Fe+2 is now flagged for special
output by MINTEQA2.
STEP 2 - Follow instructions to SPECIFY COMPONENT 2 of the 2 to be written
to the importable ASCII file.
- Enter the FIRST LETTER for the COMPONENT:
To identify the component you want, enter the first letter in its
chemical symbol (inorganic) or name (organic),
OR enter a minus one (-1) to switch to component entry by ID number,
OR enter a zero (0) to terminate component entry.
ENTER your choice > h
1 H20 2 H3As03 3 H3As04 ~ 4 H3B03 5 H+l
6 Hg2+2 7 Hg(OH)2 8 HS-1 9 HSe-1 10 HSe03-l
11 H4Si04 12 Hexam 13 Humate
Select the number of the appropriate component (0 - NONE) > 8
*********************************************************************
Component ID number 730, HS-1 is now flagged for special
output by MINTEQA2.
EDIT LEVEL IV PROB # 1
"IMPORT UTILITY
1 = Filename to which the equilibrated data for spreadsheet import
is to be written: TESTD.PRN
2 = Currently specified component(s) whose equilibrated mass distributions
are to be written: Fe+2 HS-1
C ** Cancel current settings and reset so as to NOT generate importable output
R Return to previous menu without changing anything
ENTER CHOICE > R
Main Menu Option M: Multi-Problem Generator
MINTEQA2 will also accept multiple problems that are submitted back-to -
back in one input file. PRODEFA2 supports this feature and allows you to
create input files which contain multiple problems. This feature is most
useful when you need to make subtle changes to a standard input file in a
fashion that the sweep option does not support. These back-to-back problems
do not generate a time savings over running separate files (separate files
have the advantage of flexibility and can be strung together with batch files
for sequential execution.) The time savings which can be realized is the
result of a shortened setup time for the additional problems in PRODEFA2.
Main Menu Option X: Exit
Upon selecting the EXIT option, PRODEFA2 re-orders the list of TYPE III
- SPECIES WITH FIXED ACTIVITY so that fixed components are last in the list.
It also checks to be sure that the electron is excluded if it is not a FIXED
SPECIES. Finally, as mentioned in the explanation above for EDIT LEVEL II
OPTION 4 (infinite solids), PRODEFA2 determines the initial degrees of
74
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freedom. If found to be zero or less, the user is advised to add more
components or remove some of the species from the TYPE III list. Finally,
upon exiting PRODEFA2 reminds the user of the name of the MINTEQA2 input file
just created.
75
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CHAPTER 5
THE MINTEQA2 OUTPUT FILE AND ERROR DIAGNOSTICS
The MINTEQA2 output file is divided into six parts. Some of these parts
may appear several times in one file depending on the combination of solid
print option, general output file detail, and whether the sweep option is
used. The designations of PARTS 1 through 6 are designed to lend organization
rather than sequential ordering although there is logic in the ordering as
well.
PART 1 - Reproduction and interpretation of the input file.
PART 2 - Detailed listing of species read from the database files
including log K values, enthalpy, molar mass, charge, Debye-Huckel
constants, etc.
PART 3 - Iteration information and detailed information for each species
including calculated concentration, activity, adjusted log K values,
etc.
PART 4 - Percentage distribution of components among dissolved and
adsorbed species.
PART 5 - Provisional or equilibrated mass distribution, provisional or
equilibrium ionic strength, equilibrium pH and pe, electrostatic surface
potential and charge for electrostatic adsorption models.
PART 6 - Saturation indices of all database solids with respect to the
solution.
The "provisional" designation in PART 5 pertains to the use of solids print
option 2 where provisional results are written to the output file each time a
solid precipitates. The final results will be designated "equilibrated" in
the output file. Only equilibrated results are written when the solids print
option is set to 1.
The FULL OUTPUT option in PRODEFA2 results in an output file that
includes all six parts. The INTERMEDIATE OUTPUT option causes PART 2 to be
omitted. The ABBREVIATED OUTPUT option causes PART 2, most of PART 3, and all
of PART 6 to be omitted. Appendix D contains an example output file.
76
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Error Diagnostics
The README.1ST document included with the MINTEQA2 diskettes explains
how to configure your system for properly executing MINTEQA2. If an error
occurs while attempting to use MINRUN, consult that document to be sure you
have set the CONFIG.SYS parameters as instructed.
Occasionally, errors occur during the execution of MINTEQA2 that are
unrelated to the installation of the model. Whatever the cause, the output
file will contain an error code of the form MVx.xx-yy where x.xx is the
MINTEQA2 version number and yy refers to an error message code. All error
message codes are written to the output file along with a suggested REMEDY and
sometimes with an ALTERNATIVE remedy. The complete set of error message codes
and their corresponding remedies are listed below along with additional
explanation and remedial suggestions if appropriate.
MINTEQA2 Error Codes and Messages
MV3.00-01
The number of COMPONENTS specified exceeds the maximum allowed, NXDIM.
REMEDY: Eliminate unnecessary components (those that are chemically
non-reactive in this system, the reduced members of redox couples when
the pe is very high or vice versa, etc.).
ALTERNATIVE: Re-compile MINTEQA2 with a larger value for parameter NXDIM
in the file MINTEQA2.INC.
Too many components are specified in the MINTEQA2 input file. Eliminate those
that would probably remain as free species at equilibrium anyway. If
eliminating such components adversely affects the ionic strength, fix it at
the appropriate value. The effect of Na+, Cl", N03", and K+ on the final
equilibrium composition can frequently be adequately modeled by merely fixing
the ionic strength.
MV3.00-02
The number of species read from the database exceeds the maximum
allowed, NYDIM.
REMEDY: Eliminate unnecessary components (those that are chemically
non-reactive in this system, the reduced members of redox couples when
the pe is very high or vice versa, etc.). This will result in fewer
species.
ALTERNATIVE: Re-compile MINTEQA2 with a larger value for parameter NYDIM
in the file MINTEQA2.INC.
Same comment as for MV3.00-01.
77
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MV3.00-03
A species included in the input file as TYPE 3, 4, 5, or 6 was not in
the thermodynamic database.
REMEDY: Check to make sure that the ID numbers of TYPE 3, 4, 5, and 6
entries in the input file are valid.
If the input file ID numbers are all legitimate database species, check to be
sure you have not inadvertently changed the database.
MV3.00-04
The number of adsorption parameters entered is insufficient for the
adsorption model specified.
REMEDY: Check the input file to be sure that the solid sorbent
concentration, specific surface area, and capacitance parameters are
entered as appropriate for the model specified. PRODEFA2 inserts the
appropriate parameters for each model.
Use PRODEFA2 to set-up input files for adsorption runs; do not try to insert
adsorption parameters by using an editor. Also, do not attempt to change the
adsorption model of an input file in PRODEFA2; that characteristic of a file
cannot be changed with PRODEFA2.
MV3.00-05
The input file is interpreted to have a species TYPE greater than six.
REMEDY: This usually results from having used an editor to modify the
input file outside PRODEFA2. Check for misplaced blank lines or the
wrong number of entries specified for TYPE 3, 4, 5, or 6 in the input
file.
There is no legitimate type number greater than six. If things are out of
place in the input file, MINTEQA2 may misinterpret an input field.
MV3.00-06
A component ID listed in the input file is not a valid MINTEQA2
component ID number.
REMEDY: This error may be a typo resulting from using an editor to
modify the input file. If it is not a typo but rather is an attempt to
use a new component previously unknown to MINTEQA2, be aware that you
must edit the component database file COMP.DBS and insert the new
component therein. Consult the documentation file DATABASE.DOC for more
info.
78
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New components cannot be defined by specifying them in PRODEFA2. The
component database COMP.DBS file must be edited to define a new component.
MV3.00-07 RESERVED - NOT CURRENTLY USED
MV3.00-08
As requested via an input option, execution is halted due to charge
imbalance.
REMEDY: Obtain more accurate or complete analyses of total dissolved
concentrations or reset the input option via PRODEFA2 to continue in
spite of charge imbalance.
MV3.00-09 06
Computations have resulted in a singular matrix.
REMEDY: Check initial activity guesses. Poor guesses may lead to
divergence rather than convergence. If this is a fixed pH or fixed pe
run, use the sweep option starting at a pH or pe where you can make good
guesses to compute the equilibria at a difficult pH or pe by specifying
a small increment with each sweep.
This error is generated by the routine that estimates the change in component
activities with each successive iteration. It indicates that the problem is
not converging and results either from poor initial activity guesses or from
an improperly posed chemical problem. Re-think the chemical problem in terms
of a laboratory system and make sure it is formulated properly for MINTEQA2.
If it seems to be a reasonable chemical problem, try making better initial
activity guesses.
MV3.00-10 07
Computations have resulted in an estimate of zero for the activity of
some component.
REMEDY: Check initial activity guesses. Poor guesses may lead to
divergence rather than convergence. For fixed pH or fixed pe runs, use
the sweep option starting at a pH or pe where you can make good guesses
to compute equilibria at a difficult pH or pe by specifying a small
increment with each sweep.
ALTERNATIVE: Eliminate the component whose activity has become zero.
Same comment as MV3.00-09.
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MV3.00-11 02
A phase rule violation has occurred.
REMEDY: Too complex to explain here. See the User's Manual.
Phase rule violations are more likely when a FINITE solid with non-zero
concentration is specified in the input file. This is because the solid
specified may not be the most insoluble at equilibrium. If it is not,
MINTEQA2 will dissolve it in favor of the more insoluble form. Should the
replacing mineral precipitate before the initial one has dissolved, a phase
rule violation may occur. The remedy is to either remove the FINITE solid
from the input file or set its concentration to zero. In either case, the
total dissolved concentrations of its constituent components must be
supplemented as discussed in Chapter 4 (EDIT LEVEL II OPTION 7).
Also, phase rule violations are more likely when all oversaturated
solids of the database are allowed to precipitate (see Chapter 4,EDIT LEVEL I
OPTION 8). If this option is used and a phase rule violation occurs, execute
the model a second time with no solids allowed. The saturation indices of
database solids will be printed out and can be used as a guide for deciding
which solids to specifically allow.
A general observation regarding this type of phase rule violation is
illustrated by imagining a model run with several metal components. In such a
run, imagine that after converging several times and precipitating a solid
each time, a solid of metal "M" precipitates. Iterations continue and several
more solids precipitate, none involving metal "M." Finally, a second solid of
metal "M" precipitates and execution ends with a phase rule violation. It is
usually the case that the correct remedy is to run the model again with that
solid of metal "M" that precipitated first explicitly EXCLUDED. That this is
the correct remedy can be verified by examining the listing of saturation
indices in PART 6 of the output file. If no phase rule violation occurs and
the index calculated for the EXCLUDED solid is less than zero, the problem has
been correctly resolved. It may be that the first phase rule violation will
be eliminated, but a new one involving a different solid (which has taken the
place of the one you excluded and is now the first precipitate of metal "M")
now occurs. Try applying the same procedure again, excluding the new
offending solid as well as that which was formerly excluded. It may be
necessary to repeat the procedure several times before the most insoluble
solid is finally the first to precipitate.
MV3.00-12 04
The number of degrees of freedom is zero. This problem is
over-cons trained.
REMEDY: Specify additional components or reduce the number of fixed
species. Remember that each solid that precipitates introduces an
additional fixed constraint on the system.
80
-------
There are too many fixed species for computations to continue. If, for
example, Ca+, C032", and H+ are the only components (other than H20) and if the
pH is fixed and a C02(g) phase with fixed partial pressure is imposed, and if
solids are allowed to precipitate, this error will occur when a solid
containing calcium precipitates. In that case, there will be four components
and four fixed species and no variables remaining in the problem. Add inert
components to allow computations to continue or restrict certain solids from
precipitation.
MV3.00-13 04
The number of iterations has reached the maximum allowed as specified in
the input file.
REMEDY: Use PRODEFA2 to re-set this to a larger value or else make
better initial activity guesses to produce convergence in fewer
iterations.
Most well-formulated problems take fewer than 100 iterations unless there are
many solid phases.
81
-------
REFERENCES
1. Ball, J.W., E.A. Jenne and M.W. Cantrell. 1981. WATEQ3: A Geochemical
Model with Uranium Added. U.S. Geological Survey, Washington, DC, Open
File Report 81-1183.
2. Benjamin, M.M. and J.O. Leckie. 1981. Multiple-Site Adsorption of Cd,
Cu, Zn, and Pb on Amorphous Iron Oxyhydroxide. J. Coll. Inter. Sci.
79:209-221.
3. Davies, C.W. 1962. Ion Association. Butterworths Pub., Washington, DC.
190 pp.
4. Davis, J.A., R.O. James and J.O. Leckie. 1978. Surface lonization and
Complexation at the Oxide/Water Interface: I. Computation of Electrical
Double Layer Properties in Simple Electrolytes. J. Coll. Inter. Sci.
63:480-499.
5. Davis, J.A. and J.O. Leckie. 1978. Surface lonization and Complexation
at the Oxide/Water Interface: II. Surface Properties of Amorphous Iron
Oxyhydroxide and Adsorption of Metal Ions. J. Coll. Inter. Sci.
67:90-107.
6. Dzombak, D.A. 1986. Toward a Uniform Model for the Sorption of
Inorganic Ions on Hydrous Oxides. Ph.D. Thesis, Massachusetts Institute
of Technology, Cambridge Massachusetts.
7. Felmy, A.R., S.M. Brown, Y. Onishi, S.B. Yabusaki andR.S. Argo. 1984.
MEXAMS--The Metals Exposure Analysis Modeling System. U.S. Environmental
Protection Agency, Athens, GA. EPA-600/3-84-031.
8. Felmy, A.R., D.C. Girvin, and E.A. Jenne. 1984. MINTEQ--A Computer
Program for Calculating Aqueous Geochemical Equilibria. U.S.
Environmental Protection Agency, Athens, GA. EPA-600/3-84-032.
9. Garrels, R.M. and C.L. Christ. 1965. Solutions, Minerals, and
Equilibria. Freeman, Cooper and Company, San Francisco, CA.
10. Helgeson, H.C. 1969. Thermodynamics of Hydrothermal Systems at Elevated
Temperatures and Pressures. Amer. J. of Sci. 267:729-804.
11. Ingle, S.E., M.D. Schuldt and D.W. Shults. 1978. A Users Guide for
REDEQL.EPA. A Computer Program for Chemical Equilibria in Aqueous
Systems. U.S. Environmental Protection Agency, Corvallis, OR.
EPA600/3-78-024.
82
-------
12. James, R.O. and G.A. Parks. 1982. Characterization of Aqueous Colloids
by Their Electric Double-Layer and Intrinsic Surface Chemical
Properties. Surface Colloid Sci. 12:119-216.
13. Loux, N.T., D.S. Brown, C.R. Chafin, J.D. Allison and S.M. Hassan, 1989.
Chemical Speciation and Competitive Cationic Partitioning on Sandy
Aquifer Material. Journal of Chemical Speciation and Bioavailability.
1: 111-125.
14. Morel, F.M.M. 1983. Principles of Aquatic Chemistry. John Wiley and
Sons, New York, NY, 446 pp.
15. Parkhurst, D.L., D.C. Thortenson and L.N. Plummer, 1980. PHREEQE--A
Computer Program for Geochemical Calculations. U.S. Geological Survey,
Water Resources Investigations 80-96, 210 pp.
16. Pitzer, K.S. 1973. Thermodynamics of Electrolytes. I. Theoretical Basis
and General Equations. Jour. Phys. Chem. 77:268-277.
17. Pitzer, K.S. and J.J. Kim. 1974. Thermodynamics of Electrolytes. IV.
Activity and Osmotic Coefficients for Mixed Electrolytes. J. Am. Chem.
Soc. 96:5701-5707.
18. Pitzer, K.S. and G. Mayorga. 1973. Thermodynamics of Electrolytes. II.
Activity and Osmotic Coefficients for Strong Electrolytes with One or
Both Ions Univalent. Jour, of Phys. Chem. 77:2300-2308.
19. Truesdell, A.H. and B.F. Jones. 1974. WATEQ, A Computer Program for
Calculating Chemical Equilibria in Natural Waters. U.S. Geological
Survey J. Res., Washington, DC, 2:233-248.
20. Van Zeggeren, F. and S.H. Storey. 1970. The Computation of Chemical
Equilibria. Cambridge University Press, London, England.
21. Westall, J.C. 1986. MICROQL. A Chemical Equilibrium Program in BASIC.
Report No. 86-02, Oregon State University, Corvallis, OR.
22. Westall, J.C. and H. Hohl. 1980. A Comparison of Electrostatic Models
for the Oxide/Solution Interface. Adv. Coll. Inter. Sci. 12:265-294.
23. Westall, J.C., J.L. Zachary and F.M.M. Morel. 1976. MINEQL, A Computer
Program for the Calculation of Chemical Equilibrium Composition of
Aqueous Systems. Tech. Note 18, Dept. Civil Eng., Massachusetts
Institute of Technology, Cambridge, MA.
24. Wolery, T.J. 1982. Computer Program for Geochemical Aqueous
Speciation--Solubility Calculations. Lawrence Livermore Laboratory,
Livermore, CA, 224 pp.
83
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APPENDIX A
THE THERMODYNAMIC DATABASE USED BY MINTEQA2
The thermodynamic database used by MINTEQA2 contains over 1000 species.
The best way to search the database for a species of interest is to use
PRODEFA2 or an editor with a search/find utility. If the latter option is
used, you must know how the species ID number or names are derived and
expressed. Because FORTRAN does not support the use of super- or subscripts,
the customary method of writing chemical formulas cannot be accommodated
without modification. The following naming rules are used in MINTEQA2.
1) Stoichiometric coefficients are written with parentheses and brackets
enclosing the elements in the formula to which the stoichiometry applies.
2) Species charge numbers will always be preceded with a sign (+/-) The one
(1) in (+1) and (-1) may be omitted. If a species name ends with an unsigned
number, that number represents stoichiometry.
3) Species names involving organics may be shortened by leaving out letters.
Examples:
H20 means H20
CR(OH)2+ means Cr(OH)2+
HG(OH)2 means Hg(OH)2
S04-2 means S042"
TARTRAT means Tartrate
The following is an explanation of MINTEQA2's thermodynamic database
files. This information is useful for adding new reactions to any of the four
database files: THERMO.DBS, TYPE6.DBS, REDOX.DBS or GASES.DBS. Before
attempting to add to or modify these files, note the following.
- You should make a backup copy of the file you are going to modify
before you start. Give the copy a name such as TYPE6.SAV. This is just
in case things do not go as planned.
- When adding to or modifying the thermodynamic database, if the
reaction is an AQUEOUS species, you need only edit THERMO.DBS. If the
reaction is a SOLID (mineral), REDOX couple, or GAS, you must edit two
files as explained below. The main file, THERMO.DBS, is divided into
84
-------
several sections delineated by blank lines and lines that contain a zero
in column 7. The first section is for AQUEOUS species and is followed
by three lines with zeroes separated by blank lines. After these
separator lines, the next section is for SOLIDS and that section is
followed with one blank line and one line with a zero. The next section
is for REDOX couples and is followed immediately by the GAS section.
The file is terminated with a blank line then a line with a zero. YOU
MUST HONOR THE SECTIONAL DIVISIONS WHEN MAKING ADDITIONS--DO NOT DELETE
OR CHANGE THE SEPARATOR LINES. The arrangement of these sections serves
to signal MINTEQA2 as to the nature of the species (AQUEOUS species,
SOLID, etc.).
- To add a new AQUEOUS species, it need only be entered in THERMO.DBS.
The other files remain unchanged.
- To add a new SOLID (MINERAL), it must be entered in THERMO.DBS and in
TYPE6.DBS.
- To add a new REDOX couple, it must be entered in THERMO.DBS and in
REDOX.DBS.
- After all desired changes are made to THERMO.DBS and TYPES.DBS, new
versions of the corresponding files that are actually used by MINTEQA2
and PRODEFA2 must be created. This is easily accomplished by executing
the program UNFRMT.EXE (included on the distribution media). Before
executing UNFRMT, rename the current THERMO.UNF and TYPE6.UNF to
something else for safe keeping. UNFRMT creates unformatted versions of
THERMO and TYPE6 that can be read faster than their formatted
counterparts. The unformatted files cannot be edited directly because
they are unintelligible. The program FRMT.EXE does exactly the inverse
of UNFRMT so that THERMO.DBS and TYPE6.DBS can be recreated from the
unformatted files if desired.
- To add a new GAS, it must be entered in THERMO.DBS and in GASES.DBS.
- Constants for all entries are referenced to a temperature of 25
degrees C. AQUEOUS species constants are for ionic strength of zero,
REDOX couple constants are for zero potential, and GAS constants are for
a partial pressure of one atmosphere.
The Component Database File
The component database file is shown below. The 3-digit ID number,
MINTEQA2 name, and real chemical name are shown for each component. Note that
ID numbers 240 through 259 are reserved and should not be used for newly
created components. Also, note the adsorption components are numbered 811
through 859.
001 E-l e" 030 Al+3 Al"1"3
002 H20 H20 060 H3As03 H3As03
020 Ag+1 Ag"1"1 061 H3As04 H3As04
85
-------
090 H3B03
100 Ba+2
130 Br-1
140 C03-2
143 CN-
144 CCN-
150 Ca+2
160 Cd+2
180 Cl-1
210 Cr+2
211 Cr(OH)2+
212 Cr04-2
230 Cu+1
231 Cu+2
240-259
270 F-l
280 Fe+2
281 Fe+3
330 H+l
360 Hg2+2
361 Hg(OH)2
380 1-1
410 K+l
440 Li+1
460 Mg+2
470 Mn+2
471 Mn+3
490 NH4+1
491 N02-1
492 N03-1
500 Na+1
540 Ni+2
580 P04-3
600 Pb+2
680 Rb+1
730 HS-1
731 S
732 S04-2
740 Sb(OH)3
741 Sb(OH)6-
760 HSe-1
761 HSe03-l
762 Se04-2
770 H4Si04
800 Sr+2
811 ADS1TYP1
812 ADS1TYP2
813 ADS1PSIO
H3B03
Ba+2
Br'1
Cog'2
CN"
OCN"
Ca+2
Cd+2
Cl"1
Cr"1"2
Cr(OH)2+
Cr04"2
Cu+1
Cu+2
RESERVED
F'1
Fe+2
Fe*3
H+1
Hg2+2
Hg(OH)2
1-1
K+1
Li+1
Mg+2
Mn+2
Mn+3
NH4+1
NC^"1
NOg'1
Na"1"1
Ni+2
P04"3
Pb+Z
Rb*1
HS'1
S
SO.-2
Sb(OH)3
Sb(OH)6"
HSe"1
HSe03-1
Se04'2
H4Si04
Sr+2
Adsorban
Adsorban
Adsorban
surface layer
814 ADS1PSIB Adsorbant 1, electrostatic
layer
815 ADS1PSID
821 ADS2TYP1
822 ADS2TYP2
823 ADS2PSIO
824 ADS2PSIB
825 ADS2PSID
831 ADS3TYP1
832 ADS3TYP2
833 ADS3PSIO
834 ADS3PSIB
835 ADS3PSID
841 ADS4TYP1
842 ADS4TYP2
843 ADS4PSIO
844 ADS4PSIB
845 ADS4PSID
851 ADS5TYP1
852 ADS5TYP2
853 ADS5PSIO
854 ADS5PSIB
855 ADS5PSID
870 Tl+1
871 T1(OH)3
891 U+4
890 U+3
892 U02+1
893 U02+2
900 V+2
901 V+3
902 VO+2
903 V02+1
950 Zn+2
955 Dietham
956 Nbutyam
958 Methatn
959 Dimetham
960 Trbutph
961 Hexam
963 EN
Adsorbant 1, electrostatic d
layer
Adsorbant 2, type 1
Adsorbant 2, type 2
Adsorbant 2, electrostatic
surface layer
Adsorbant 2, electrostatic ft
layer
Adsorbant 2, electrostatic d
layer
Adsorbant 3, type 1
Adsorbant 3, type 2
Adsorbant 3, electrostatic
surface layer
Adsorbant 3, electrostatic ft
layer
Adsorbant 3, electrostatic d
layer
Adsorbant 4, type 1
Adsorbant 4, type 2
Adsorbant 4, electrostatic
surface layer
Adsorbant 4, electrostatic ft
layer
Adsorbant 4, electrostatic d
layer
Adsorbant 5, type 1
Adsorbant 5, type 2
Adsorbant 5, electrostatic
surface layer
Adsorbant 5, electrostatic ft
layer
Adsorbant 5, electrostatic d
layer
T1(OH)3
+3
U
UO;
uo,
+1
+2
+3
+2
V0
diethylamine
n-butylamine
methylamine
dimethylamine
tributylphosphate
hexylamine
ethylenediamine
86
-------
964 Npropam
965 Ipropam
966 Tmetham
967 Citrate
968 NTA-3
969 EDTA-4
971 Prpanot
972 Butanot
973 Isobuty
980 ZMetpyr
981 3Metpyr
982 AMetpyr
983 Formate
984 Isvaler
985 Valerat
990 Fulvate
991 Humate
992 Acetate
993 Tartrat
994 Glycine
995 Salicyl
996 Glutama
997 Phthala
n-propylamine
iso-propylamine
tri-methylamine
citrate
nitrilotriacetate
EDTA'4
propanoate
butyrate
iso-butyrate
2-methyl pyridine
3-methyl pyridine
4-methyl pyridine
formate
iso-valerate
valerate
fulvate
humate
acetate
tartrate
glycine
salicylate
glutamate
phthalate
Format of Database Species Entries
Each reaction in THERMO.DBS, TYPE6.DBS, GASES.DBS, and REDOX.DBS is specified
by a two or three line entry. The explanation of each line is as follows:
FIRST line
Column(s)
I - 7
Meaning
Format
Species reaction product ID number. If
you are adding a new reaction, you create this
number.
For AQUEOUS and GAS species, the 7-digit ID
is formed from the 3-digit component ID # of
the major cation suffixed by the 3-digit
component ID # of the major anion suffixed
by a single digit to ensure that the
resulting 7-digit number is unique within
the entire database.
For SOLID species, the 3-digit component
ID # of the major cation is prefixed with
a 2-digit code that represents the class
17
87
-------
to which the solid belongs. The 2-digit
class codes are listed below. The resulting
5-digit number is suffixed with 2-digits to
ensure that the final 7-digit number is
unique within the entire database.
2-Digit Codes for Classes of Solids
Code Class
00 Elemental
10 Sulfide
11 Cyanide
12 Selenide
14 Antimonide
20 Oxide and Hydroxide
30 Multiple Oxide
40 Bromide
41 Chloride
42 Fluoride
43 Iodide
50 Carbonate
Code Class
51 Nitrate
52 Borate
60 Sulfate
61 Selenite.Selenate
70 Phosphate
72 Arsenate
73 Vanadate
80 Orthosilicate
82 Chain Silicate
84 Framework Silicate
86 Sheet Silicate
For REDOX couples, the 3-digit component
ID # of one member of the redox pair is
prefixed by the other and the resulting
6-digit number is suffixed by a single
digit to ensure that the final 7-digit ID
number is unique within the entire database.
8 blank
9-20 Species reaction product name. With only 12 A12
spaces, it may be necessary to abbreviate.
Subscripts aren't possible but do use parentheses
where appropriate. If the species is charged,
always hang the charge on the end of the name
prefixed with the appropriate algebraic sign.
For SOLIDS, mineral names are preferred to
chemical formula names.
21 - 30 Enthalpy change, i.e., delta H for the F10.4
reaction (kcal/mole). MINTEQA2 uses this
value to adjust the equilibrium constant for
temperatures other than 25 degrees C.
31 - 40 Log K. Common logarithm of the equilibrium F10.4
constant for this reaction.
88
-------
For AQUEOUS species, this is a thermodynamic
stability or formation constant, i.e., for
the reaction
wA + xB < > yC + zD
{C}y {D}z
K -
(A}w
where braces { } denote activity.
For MINTEQA2, this reaction would be written
wA + zB - yC < > zD
in the thermodynamic database where A, B, and
C are MINTEQA2 components and D is an AQUEOUS
species and is referred to here as the species
reaction product.
For SOLIDS, K is the reciprocal (log K is the
negative) of the solubility product. This is
because MINTEQA2 treats precipitation reactions as if
written with reactants on the left and precipitates
on the right which is reversed compared with the
solubility product rule. A representative MINTEQA2
precipitation reaction is
Ag+ + Cl~ < > AgCl(s)
{AgCl}
K -
where brackets { } again denote activity. The
activity of solid AgCl is 1.0 because it is a
pure phase so that we may write
K -
Now, the solubility product rule applied to the
silver chloride reaction gives
Ksp - (Ag+) {el'}
Therefore, the K needed in MINTEQA2 is related to the Ksp
89
-------
K -
log K - -log K,
sp
In summary, the log K value for a SOLID in the
database is the negative of log K .
For REDOX couples , the value entered for log K
is computed from the Nernst equation
E - E° - 2.303 RT/nF log Q
where E is the potential, E° is the standard
reduction potential at 25 degrees C, R is the molar
gas constant, T is the absolute temperature, F is
the Faraday constant, n is the number of electrons
in the half -reaction, and Q is that function of
concentrations (activities) of products and reactants
that occurs in the equilibrium constant which is sought.
For potentials measured in volts at 25 degrees C
E - E° - (1/n) (0.05916) log Q .
Just as log K's for AQUEOUS species are referenced
to an ionic strength of zero, the log K's for
REDOX couples are referenced to a potential of
zero. So, with rearrangement and taking E = 0,
the above equation becomes
log Q - 16.903 nE°
For the Fe3+/Fe2+ couple (species ID # 2812800),
Fe3+ + e~ ...... >
for which the standard reduction potential is 0.771
and n = 1, the above expression gives
log Q - 13.032.
This is the value entered for log K in that reaction.
For GASES , the log K entered is log Kp where the
partial pressure of the gas is in atmospheres. The
values currently in the database files are for a
partial pressure of one atmosphere. If you want to
compute equilibria at pressures other than one atm,
90
-------
you will need to adjust the log Kp accordingly. PRODEFA2
makes this adjustment for you by asking for the desired
partial pressure, obtaining the constant for one atm
from the database, and entering the corrected log K
in your input file . An example of a gas reaction
and the partial pressure adjustment is species
3301403
C03"2 + 2H+1 - H20 < ..... > C02 (g)
The log Kp at one atm is 18.16. The log of the partial
pressure of C02 (g) in the atmosphere is about -3.5.
Therefore, the corrected log Kp is
log Kp - log Kp - log 10"3-5
- 18.16 - (-3.5)
- 21.66
MINTEQA2 requires that the partial pressures of all
gases be fixed for a given problem.
41 - 48 Maximum reported log K. This entry is made F8 . 3
only for SOLID species and is not actually
used in MINTEQA2's equilibria calculations.
It is intended to provide a means of judging
the reliability of the log K given in columns
31 - 40.
49 - 56 Minimum reported log K. This entry is made F8.3
for SOLID species only and is not actually
used in MINTEQA2's equilibria calculations.
It is intended to provide a means of judging
the reliability of the log K given in columns
31 - 40.
57 - 61 Charge of species reaction product. F5.2
62 - 66 Debye-Huckel a parameter for species reaction F5.2
product.
67 - 71 Debye-Hiickel b parameter for species reaction F5 . 2
product.
72 - 80 Gram formula weight of species reaction F9.4
product . No entry for REDOX couples .
91
-------
SECOND line
Column(s) Meaning Format
1-5 Carbonate alkalinity factor. This entry is F5.2
made only for AQUEOUS species that have
carbonate (ID # 140) as a component. In cases
where the user has chosen to specify the
inorganic carbon as alkalinity (this is an option
when executing MINTEQA2), the carbonate alkalinity
factor is used to determine total dissolved inorganic
carbon concentration from a measure of alkalinity.
To compute the carbonate alkalinity factor for a
new species, use the formula:
alkalinity factor = 2 x STOIC(C032~) - STOIC(H+)
where STOIC(x) is the stoichiometry of component
x in the reaction.
6 blank
7 Number of components (as reactants or II
products) in this reaction. Maximum = 9.
8 - 10 blank
11 - 17 Stoichiometry of the first component. F7.3
Negative if the component is a reaction product,
that is, if it occurs in the left-hand side of
the chemical equation with a negative coefficient.
18 blank
19 - 21 ID number of the first component.
22 - ? Additional stoichiometry/component ID # pairs
with separating spaces so that the total
number of pairs is equal to the number of
components as specified in column 7. These
are entered in the same manner as the first
pair in columns 8-21. That is, 3 blank
columns followed by seven columns for the
stoichiometry in F7.3 format, one blank
column and finally, three columns for the
component ID # in 13 format. The remainder
of the second line will hold 4 additional
pairs through column 77. If the total number
of components is greater than 5, continue on
a third line with the 3 columns 78 - 80 of
92
-------
the second line counted as the 3 blank columns
for the sixth pair. Use columns 1 - 7 of the
third line for the stoichiometry of the sixth
pair. Column 8 should be blank and columns
9-10 should contain the component ID #.
Continue with the 3X.F7.3,1X,I3 format for
up to three additional pairs on the third line.
Examples of Entries in the Thermodynamic Database Files
The following are excerpts from the thermodynamic database files . Each
excerpt is followed by an explanation of all entries. The explanation is
presented with the component names just as they appear in MINTEQA2 .
AQUEOUS Species
3300020 OH- 13.3A5 -13.998
2 1.000 2 -1.000 330
1501401 CAC03 AQ 4.0300 3.1500
2.00 2 1.000 150 1.000 140
2113300 CR+3 -20.1400 9.62
0.00 3 1.000 211 2.000 330 -2.000
EXPLANATION:
-1. 3.5 0.0 17.0074
0. 0.0 0.0 100.0890
3.00 0.00 0.00 51.9960
First reaction --
Species ID number:
Species name:
Delta H:
Log K:
Maximum Log K:
3300020
OH"
13.345 kcal/mol
-13.998
not used
Minimum Log K:
Species charge:
Debye-Hiickel a:
Debye-Huckel b:
Gram Formula Wt.
not used
-1
3.5
0 or unknown
17.0074
Alkalinity factor: none Number of components: 2
Chemical Equation (from stoichiometry/components):
H20 - H"1"1 < > OH"
or, in terms of (stoichiometry)component ID #'s:
1(002) - 1(330) < > 3300020
Second reaction - -
Species ID number:
Species name:
Delta H:
Log K:
Maximum Log K:
1501401
CaC03 (aq)
4.03 kcal/mol
3.15
not used
Minimum Log K:
Species charge:
Debye-Huckel a:
Debye-Huckel b:
Gram Formula Wt. :
not used
0
0 or unknown
0 or unknown
100.089
Alkalinity factor: 2.0 Number of components: 2
Chemical Equation (from stoichiometry/components):
93
-------
Ca
C0
"2
CaC03
or, in terms of (stoichiometry)component ID #'s:
1(150) + 1(140) < ..... > 1501401
Third reaction --
Species ID number:
Species name:
Delta H:
Log K:
Maximum Log K:
2113300
Cr+3
-20.140 kcal/mol
9.62
not used
Minimum Log K:
Species charge:
Debye-Huckel a:
Debye-Huckel b:
Gram Formula Wt.
not used
+3
0 or unknown
0 or unknown
51.996
Alkalinity factor: none Number of components: 3
Chemical Equation (from stoichiometry/components):
,.+3
Cr(OH)2+ + 2H+1 - 2H20 < > Cr+
or, in terms of (stoichiometry)component ID #'s:
1(211) + 2(330) - 2(002) < > 2113300
SOLID (Mineral) species
6010000 BARITE
2 1.000 100
-6.280 9.976
1.000 732
.000 9.773
EXPLANATION:
Species ID number: 6010000
Species name: Barite
Delta H: -6.280 kcal/mol
Log K: 9.976
Maximum Log K: unknown
Alkalinity factor: none
233.4016
Minimum Log K:
Species charge:
Debye-Huckel a:
Debye-Huckel b:
Gram Formula Wt,
9.773
0
unknown
unknown
233.4016
Number of components: 2
Chemical Equation (from stoichiometry/components):
Ba+2 + S04"2 < > BaS04 (Barite)
or, in terms of (stoichiometry)component ID #'s:
1(100) + 1(732) < > 6010000
94
-------
REDOX Couple
2812800 FE+3/FE+2 -10.0 13.032
3 1.000 281 -1.000 280 1.000 1
EXPLANATION:
Species ID number: 2812800 Minimum Log K: not used
Species name: Fe+3/Fe+2 Species charge: not used
Delta H: -10.0 kcal/mol Debye-Huckel a: not used
Log K: 13.032 Debye-Huckel b: not used
Maximum Log K: not used Gram Formula Wt.: not used
Alkalinity factor: none Number of components: 3
Chemical Equation (from stoichiometry/components):
Fe+3 - Fe+2 + E"1 < > activity ratio of Fe+3/Fe+2
or, in terms of (stoichiometry)component ID #'s:
1(281) - 1(280) + 1(001) < > 2812800
GAS species
3301403 C02(GAS) -0.53 18.16 41.0100
3 1.000 140 2.000 330 -1.000 2
EXPLANATION:
Species ID number: 3301403 Minimum Log K: not used
Species name: C02 (g) Species charge: 0
Delta H: -0.53 Debye-Hiickel a: unknown
Log K: 18.16 Debye-Huckel b: unknown
Maximum Log K: not used Gram Formula Wt.: 41.010
Alkalinity factor: none Number of components: 3
Chemical Equation (from stoichiometry/components):
C03'2 + 2H+1 - H20 < > C02 (g)
or, in terms of (stoichiometry)component ID #'s:
1(140) + 2(330) - 1(002) < > 3301403
95
-------
APPENDIX B
NEWTON -RAPHSON APPROXIMATION METHOD
The Newton-Raphson approximation method is an iterative technique for
finding a value x such that y(x) - 0. When only one variable is involved,
successive (improved) values of x (x,,, x,,+1, Xn+j,--.) are obtained from the
difference quotient.
dy
- - - z B1.01
*n+l ' *n d*
where the derivative evaluated at x,, is denoted by zn.
In each successive step, the function y(xn+1) is set to zero (because
this is the solution sought) and Equation B1.01 is solved for x,j+1 in terms of
the previously known values of x,,, y(x,,) and zn. When y(xn+1) in Equation
B1.01 is set to zero
zn Ax - y(xn) B1.02
where Ax - x,, - Xj^.
The new value of x is then found from:
- x,, - Ax B1.03
Similar reasoning applies to problems in more than one variable except
that the analog to Equation B1.02 becomes the matrix equation
Zn AX - Yn B1.04
where Zn is the Jacobian of Y with respect to X evaluated at Xp. A solution
for AX is found from Gaussian elimination and back substitution and ^n+1 is
calculated from:
- AX B1.05
96
-------
APPENDIX C
MINTEQA2 MODEL DISTRIBUTION
Introduction
The MINTEQA2 model, PRODEFA2 program, and all support files and programs are
available on diskette or 9-track magnetic tape from the Center for Exposure
Assessment Modeling (CEAM) at no charge.
Microcomputer Version
The CEAM has an exchange diskette policy. It is preferred that diskettes be
received before sending a copy of the model package. Included in the diskette
set are
Installation DOS batch command and documentation support files for the
latest release of the model package
Data base files and support programs and documentation
Test and help files in the form of PRODEFA2 dialogue (*.HLP) and
MINTEQA2 input (*.INP) and output (*.LST) files
Executable task image files for the MINTEQA2 model and the PRODEFA2
program; also the FRMT and UNFRMT data base support programs
FORTRAN source code files for IBM PC and compatible microcomputer
systems
Batch command files to compile, link, and run selected task image files
Please note that a FORTRAN compiler and a link editor are NOT required to
execute any portion of the model and/or any program as received on the
distribution diskette(s).
If the user wishes to modify the model or a program, it will be up to the user
to supply and/or obtain
An appropriate text editor that saves files in ASCII (text) format
FORTRAN program development tools to recompile and link edit any portion
of the model and/or any program
97
-------
The microcomputer release of the MINTEQA2 model and the PRODEFA2 program are
full implementations of the DEC VAX/VMS versions. The microcomputer
implementation of this model and program perform the same function as the U.S.
EPA mainframe/minicomputer versions.
DEC VAX/VMS Version
A copy of the DEC VAX/VMS version of the MINTEQA2 model package is also
available free of charge on one-half inch, 9-track magnetic tape in
DEC VAX files-11 (COPY)
ASCII non-labeled, or
EBCDIC non-labeled format.
The CEAM furnishes the tape and requests that it be returned to the Center
once the model package has be loaded onto the recipient's system. Tapes sent
outside the United States should NOT be returned. Included on the tape are
Installation VAX/VMS DCL batch command and documentation support files
for the latest release of the model package
Data base files and support documentation
Test and help files in the form of PRODEFA2 dialogue (*.HLP) and
MINTEQA2 input (*.INP) and output (*.LST) files
FORTRAN source code files for DEC VAX/VMS systems
VAX/VMS DCL batch command files to compile, link, and run task image
(*.EXE) files
Obtaining a Copy of the MINTEQA2 Model Package
To obtain a copy of the model package, send a cover letter requesting the
MINTEQA2 model to the address shown below. For the microcomputer version,
send three (3), 5.25 inch (360k, DS/DD), or one, 3.5 inch (1.44Mb, DS/HD) PC
DOS (tm) (Disk Operating System) formatted diskette(s). For a copy of the DEC
VAX/VMS version, state in the request letter the type of tape format preferred
(see list above).
Center for Exposure assessment Modeling (CEAM)
U.S. Environmental Protection Agency
Environmental Research Laboratory
College Station Road
Athens, Georgia 30613-7799
ATTN: Mr. David W. Disney
98
-------
CEAM Electronic Bulletin Board System (BBS)
To download a copy of the complete model package or check the status of the
latest release of this model and/or programs, or any other CEAM program, call
the CEAM electronic bulletin board system 24 hours a day, 7 days a week. To
access the BBS, a computer with a modem and communication software are needed.
The phone number for the BBS is 404/546-3402 or (FTS) 250-3402. Communication
parameters for the BBS are
300/1200/2400/9600 baud rate
8 data bits
No parity
1 stop bit
In order to access the BBS at 9600 baud, a US Robotics Courier HST modem must
be used.
Technical support
For questions concerning the installation of the MINTEQA2 model or the
PRODEFA2, FRMT, and/or the UNFRMT programs, contact Mr. David Disney in the
Athens ERL ADP Section at 404/546-3549 or (FTS) 250-3549. This number can
also be used for any questions concerning the Center for Exposure Assessment
Modeling. For questions concerning program and/or model content, application,
and/or theory, please contact Mr. Jerry D. Allison at the above address or at
404/546-3323 or (FTS) 250-3323.
Disclaimers
The CEAM cannot support, maintain, and/or be responsible for modifications
that change the function of any executable task image file (*.EXE) or DOS or
DCL batch command files (*.BAT, *.COM) supplied with this model package.
The MINTEQA2 model and the PRODEFA2, FRMT, and UNFRMT programs must be used at
the user's own risk. Neither the U.S. EPA nor the program authors can assume
responsibility for model and/or program content, output, interpretation, or
usage.
Mention of trade names or use of commercial products does not constitute
endorsement or recommendation for use by the United States Environmental
Protection Agency.
99
-------
APPENDIX D
EXAMPLE MINTEQA2 FILES
The following example files are included on the distribution diskettes
as TEST4.INP and TEST4.LST. The corresponding PRODEFA2 dialogue file,
TEST4.HLP, is too lengthy to include here; it can also be found on the
distribution diskettes.
TEST4.INP
TEST4 - Triple Layer Adsorption model with two adsorbing
surfaces.
25.00 MOLAL 0.000
/H+l
/K+l
/N03-1
/ADSlPSIo
/ADSlPSIb
/ADSlPSId
/ADS1TYP1
/ADS2PSIo
/ADS2PSIb
/ADS2PSId
/ADS2TYP1
/ H+l
/ADSlPSIo
/ADSlPSIb
/ADSlPSId
/ADS2PSIo
/ADS2PSIb
/ADS2PSId
000 0.000 0.00 0.00 0.00 0.0000
0.000 0 0.000 0 0.000 0
0 0.000 0 0.000 0
000 0.000 0.00 0.00 0.00 0.0000
0.000 0 0.000 0 0.000 0
0 0.000 0 0.000 0
000 0.000 0.00 0.00 0.00 0.0000
1.000 813 -1.000 814 0.000 0
0 0.000 0 0.000 0
000 0.000 0.00 0.00 0.00 0.0000
-1.000 813 1.000 814 0.000 0
0 0.000 0 0.000 0
000 0.000 0.00 0.00 0.00 0.0000
0.000 0 0.000 0 0.000 0
0 0.000 0 0.000 0
0010000011
326
8.174E+00 129.00 1.
4.087E+00 600.00 1.
330 l.OOOE-07
410 l.OOOE-01
492 l.OOOE-01
813 O.OOOE-01
814 O.OOOE-01
815 O.OOOE-01
811 1.320E-04
823 O.OOOE-01
824 O.OOOE-01
825 O.OOOE-01
821 1.370E-04
3 1
330 7.0000
6 6
813 0.0000
814 0.0000
815 0.0000
823 0.0000
824 0.0000
825 0.0000
2 8
8113300 =1SO-
0.00 3 1.000 811
0.000 0 0.000
0 0.000 0 0.000
8113301 =1SOH2+
0.00 3 1.000 811
0.000 0 0.000
0 0.000 0 0.000
8114920 =1SOH2N03
0.00 5 1.000 811
0.000 0 0.000
0 0.000 0 0.000
8114100 -1SOK
0.00 5 1.000 811
0,000 0 0.000
0 0.000 0 0.000
8213300 =2SO-
0.00 3 1.000 821
0.000 0 0.000
0 0.000 0 0.000
8213301 =2SOH2+
100
200 0.200 81
400 0.400 82
-7.00
-1.00
-1.00
0.00
0.00
0.00
-3.88
0.00
0.00
0.00
-3.86
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
-1.000 330
0 0.000
0 0.000
0.0000
1.000 330
0 0.000
0 0.000
0.0000
1.000 492
0 0.000
0 0.000
0.0000
1.000 410
0 0.000
0 0.000
0.0000
-1.000 330
0 0.000
0 0.000
0.0000
-9.3100 0
-1.000 813
0 0.000
0
7.3300 0
1.000 813
0 0.000
0
8.3300 0
1.000 330
0 0.000
0
-8.3100 0
-1.000 330
0 0.000
0
-6.5200 0
-1.000 823
0 0.000
0
7.0100 0
000
0.000 0.00 0.00 0.00 0.0000
100
-------
0.00 3 1.000 821
0.000 0 0.000
0 0.000 0 0.000
8214920 =2SOH2N03
0.00 5 1.000 821
0.000 0 0.000
0 0.000 0 0.000
8214100 =2SOK
0.00 5 1.000 821
0.000 0 0.000
1.000 330
0 0.000
0 0.000
0.0000
1.000 492
0 0.000
0 0.000
0.0000
1.000 410
0 0.000
1
0
5
1
0
-5
-1
0
.000
0.
0
.3500
.000
0.
0
.3100
.000
0.
823
000
0,
330
000
0,
330
000
0.
0
.000
1.
0
.000
-1.
0
000
0.
0
000
0.
0
000
0.
0
000
.000
823
000
.000
823
000
0.000
0 0.
0.00 0.
-1.000
0 0.
0.00 0.
1.000
0 0.
0
,000
00 0
824
000
00 0
824
,000
00 000 000
0 0
.000
0
.000
0
.000
0
.0000
0
.0000
0
TEST4.LST
PART 1 of OUTPUT FILE
PC MINTEQA2 v3.00 DATE OF CALCULATIONS: 2-AUG-90 TIME: 10:18:59
TEST4 - Triple Layer Adsorption model with two adsorbing
surfaces.
Temperature (Celsius): 25.00
Units of concentration: MOLAL
Ionic strength to be computed.
If specified, total carbonate concentration represents total inorganic carbon.
Do not automatically terminate if charge imbalance exceeds 30*
Precipitation is allowed only for those solids specified as ALLOWED
in the input file (if any).
The maximum number of iterations is: 40
The method used to compute activity coefficients is: Davies equation
Intermediate output file
Adsorption model: Triple Layer
Number of adsorbing surfaces: 2
8
4
. 174E+00
.087E+00
330
410
492
813
814
815
811
823
824
825
821
1.
1.
1.
0.
0.
0.
1.
0.
0.
0.
1.
129.00 1
600.00 1
OOOE-07
OOOE-01
OOOE-01
OOOE-01
OOOE-01
OOOE-01
320E-04
OOOE-01
OOOE-01
OOOE-01
370E-04
.200
.400
-7
-1
-1
0
0
0
-3
0
0
0
-3
0.200
0.400
.00
.00
.00
.00
.00
.00
.88
.00
.00
.00
.86
81
82
H20 has been inserted as a COMPONENT
3 1
0.0000
330
6 6
813
814
815
823
824
825
2 8
8113300
0.00 3
0.000
0.000
8113301
0.00 3
0.000
7.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
=1SO-
1.000 811
0 0.000
0 0.000
=1SOH2+
1.000 811
0 0.000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
,000 330
0.000
-9.3100
-1.000 813
0 0.000
0.000 0.000 0.00 0.00 0.00 0.0000
0.000 0 0.000 0 0.000 0
0 0.000 0 0.000 0
0.000 0 0.000
8114920 =1SOH2N03
0.00 5 1.000 811
0 0.000 0
0.0000 7.3300 0.000 0.000 0.00 0.00 0.00 0.0000
1.000 330 1.000 813 0.000 0 0.000 0 0.000 0
0 0.000 0 0.000 0 0.000 0 0.000 0
0 0.000 0
0.0000 8.3300 0.000 0.000 0.00 0.00 0.00 0.0000
1.000 492 1.000 330 1.000 813 -1.000 814 0.000 0
101
-------
0.000
0.000 0 0.000 0 0.000 0 0.000 0 0.000 0
0.000 0 0.000
8114100 -1SOK
0.00 5 1.000 811
0.000 0 0.000
0.000 0 0.000
8213300 -2SO-
0.00 3 1.000 821
0.000 0 0.000
0.000 0 0.000
8213301 -2SOH2+
0.00 3 1.000 821
0.000 0 0.000
0.000 0 0.000
8214920 =2SOH2N03
0.00 5 1.000 821
0.000 0 0.000
0.000 0 0.000
8214100 -2SOK
0.00 5 1.000 821
0.000 0 0.000
0 0.000 0
0.0000 -8.3100 0.000 0.000 0.00 0.00 0.00 0.0000
1.000 410 -1.000 330 -1.000 813 1.000 814 0.000 0
0 0.000 0 0.000 0 0.000 0 0.000 0
0 0.000 0
0.0000 -6.5200 0.000 0.000 0.00 0.00 0.00 0.0000
-1.000 330 -1.000 823 0.000 0 0.000 0 0.000 0
0 0.000 0 0.000 0 0.000 0 0.000 0
0 0.000 0
0.0000 7.0100 0.000 0.000 0.00 0.00 0.00 0.0000
1.000 330 1.000 823 0.000 0 0.000 0 0.000 0
0 0.000 0 0.000 0 0.000 0 0.000 0
0 0.000 0
0.0000 5.3500 0.000 0.000 0.00 0.00 0.00 0.0000
1.000 492 1.000 330 1.000 823 -1.000 824 0.000 0
0 0.000 0 0.000 0 0.000 0 0.000 0
0 0.000 0
0.0000 -5.3100 0.000 0.000 0.00 0.00 0.00 0.0000
1.000 410 -1.000 330 -1.000 823 1.000 824 0.000 0
0 0.000 0 0.000 0 0.000 0 0.000 0
0.000 0 0.000 0 0.000 0
INPUT DATA BEFORE TYPE MODIFICATIONS
ID
330
410
492
813
814
815
811
823
824
825
821
2
NAME
H+l
K-H
N03-1
ADSlFSIo
ADSlPSIb
ADSlPSId
ADS1TYP1
ADS2FSIO
ADS2PSIb
ADS2PSId
ADS2TYP1
H20
ACTIVITY GUESS
l.OOOE-07
l.OOOE-01
l.OOOE-01
l.OOOE+00
l.OOOE+00
l.OOOE+00
1.318E-04
l.OOOE+00
l.OOOE+00
l.OOOE+00
1.380E-04
l.OOOE+00
LOG GUESS
-7.000
-1.000
-1.000
0.000
0.000
0.000
-3.880
0.000
0.000
0.000
-3.860
0.000
ANAL TOTAL
l.OOOE-07
l.OOOE-01
l.OOOE-01
O.OOOE-01
O.OOOE-01
O.OOOE-01
1.320E-04
O.OOOE-01
O.OOOE-01
O.OOOE-01
1.370E-04
O.OOOE-01
CHARGE BALANCE: UNSPECIATED
SUM OF CATIONS- l.OOOE-01 SUM OF ANIONS - l.OOOE-01
PERCENT DIFFERENCE - 5.000E-05 (ANIONS - CATIONS)/(ANIONS + CATIONS)
102
-------
PC MINTEQA2 v3.00
PART 3 of OUTPUT FILE
DATE OF CALCULATIONS: 2-AUG-90~
TIME: 10:19: 5
PARAMETERS OF THE COMPONENT MOST OUT OF BALANCE:
ITER NAME
ID
821
410
492
813
814
815
811
823
824
825
2
330
0
1
2
3
4
5
6
ADS1TYP1
ADS2PSIO
ADSlPSId
ADSlPSId
ADSlPSId
ADSlPSId
ADSlPSId
NAME
ADS2TYP1
K+l
N03-1
ADSlPSIo
ADSlPSIb
ADSlPSId
ADS1TYP1
ADS2FSIO
ADS2PSIb
ADS2PSId
H20
H+l
TOTAL MOL
1.320E-04
-5.374E-05
O.OOOE-01
-9.265E-06
-2.080E-05
-2.963E-05
-3.271E-05
DIFF FXN
5.648E-04
-7.267E-05
-5.748E-04
-2.861E-04
-1.093E-04
-2.211E-05
-1.056E-06
LOG
-3
0
-0
-0
-0
-0
-0
ANAL MOL CALC MOL ACTIVITY
1,
1.
1.
8,
-5,
-3,
1.
-7,
5.
2
0,
1.
.370E-04 1.
.OOOE-01 9.
.OOOE-01 9.
.752E-05 3.
.462E-05 4.
.290E-05 8.
.320E-04 4.
.826E-05 1.
.817E-05 1.
.010E-05 1.
.OOOE-01 -1.
.OOOE-07 1.
670E-05 1.670E-05
994E-02 7.750E-02
995E-02 7.750E-02
650E-01 3.650E-01
733E-01 4.733E-01
504E-01 8.504E-01
290E-05 4.290E-05
228E+00 1.228E+00
127E+00 1.127E+00
044E+00 1.044E+00
291E-07 9.966E-01
290E-07 1. OOOE-07
ACTVTY
.88000
.02994
.99717
. 58694
.27410
.11052
.07223
LOG ACTVTY
-4.
-1.
-1.
-0.
-o.
-0.
-4.
0.
0.
0.
-0.
-7.
77721
11071
11069
43771
32489
07040
36750
08911
05193
01851
00148
00000
1
0
0
1
1
1
1
1
1
1
1
0
GAMMA
.000000
.775441
.775441
.000000
.000000
.000000
.000000
.000000
.000000
.000000
.000000
.775441
NEW LOCK
0.0000
0.1105
0.1105
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0015
0.1105
DIFF FXN
-2.711E-20
-1.037E-10
-8.512E-11
8.754E-11
3.957E-10
-2.370E-09
1.712E-11
O.OOOE-01
1.355E-20
-1.317E-13
O.OOOE-01
O.OOOE-01
Type I - COMPONENTS AS SPECIES IN SOLUTION
ID
330
410
492
811
821
NAME
H+l
K+l
N03-1
ADS1TYP1
ADS2TYP1
CALC MOL
1
9
9
4
1
.290E-07
.994E-02
.995E-02
.290E-05
.670E-05
ACTIVITY
0
0
0
0
0
.0000001
.0774988
.0775015
.0000429
.0000167
LOG ACTVTY
-7
-1
-1
-4
-4
.00000
.11071
.11069
.36750
.77721
GAMMA
0
0
0
1
1
.775441
.775441
.775441
.000000
.000000
NEW LOCK
0
0
0
0
0
.110
.110
.110
.000
.000
DH
0.000
0.000
0.000
0.000
0.000
Type II - OTHER SPECIES IN SOLUTION OR ADSORBED
ID
8214100
3300020
8113300
8113301
8114920
8114100
8213300
8213301
8214920
NAME
-2SOK
OH-
=1SO-
=1SOH2+
=1SOH2N03
=1SOK
=2SO-
-2SOH2+
=2SOH2N03
CALC MOL
5.
1.
5.
3.
5.
2.
4.
2.
3.
820E-05
291E-07
757E-07
348E-05
483E-05
112E-07
108E-05
098E-05
157E-08
ACTIVITY
0.
0.
0.
0.
0,
0,
0,
o,
o!
.0000582
.0000001
.0000006
,0000335
.0000548
.0000002
.0000411
.0000210
.0000000
LOG ACTVTY
-4.
-6.
-6.
-4.
-4.
-6.
-4.
-4.
-7.
.23510
.99948
.23979
47520
.26100
,67538
.38633
,67810
50072
GAMMA
1.
0.
1.
1.
1.
1.
1.
1.
1.
000000
775441
000000
000000
000000
000000
000000
000000
000000
NEW LOCK
-5
-13
-9
7
8
-8
-6
7
5
.310
.888
.310
.330
.330
.310
.520
.010
.350
DH
0.000
13.345
0.000
0.000
0.000
0.000
0.000
0.000
0.000
Type III - SPECIES OF FIXED ACTIVITY THAT DEFINE EQUILIBRIUM CONDITIONS
ID
2
330
NAME
H20
H+l
CALC MOL
-1.291E-07
-9.157E-06
LOG MOL
-6.889
-5.038
NEW LOCK
0.001
7.000
DH
0.000
0.000
Type VI - EXCLUDED SPECIES (not included in mole balance)
ID
823
815
814
813
825
824
NAME
ADS2PSIO
ADSlPSId
ADSlPSIb
ADSlPSIo
ADS2PSId
ADSZPSIb
CALC MOL
1.228E+00
8.504E-01
4.733E-01
3.650E-01
1.044E+00
1.127E+00
LOG MOL
0.089
-0.070
-0.325
-0.438
0.019
0.052
NEW LOOK
0.000
0.000
0.000
0.000
0.000
0.000
DH
0.000
0.000
0.000
0.000
0.000
0.000
103
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PART * of OUTPUT FILE
PC MINTEQA2 v3.00 DATE OP CALCULATIONS: 2-AUG-90 TIME: 10:19:16
PERCENTAGE
ADS2TYP1
K+l
N03-1
ADSlPSIo
ADSlPSIb
ADSlPSId
ADS1TYP1
ADS2PSIO
ADS2PSIb
ADS2PSId
H20
H+l
DISTRIBUTION OF COMPONENTS AMONG TYPE I and TYPE II (dissolved and adsorbed) species
ADS2TYP1
42.5
30.0
15.3
62.6
25.4
41.5
52.5
361.7
592.3
226.7
12.2 PERCENT BOUND IN SPECIES # 821
PERCENT BOUND IN SPECIES #8214100 -2SOK
PERCENT BOUND IN SPECIES #8213300 '^SO-
PERCENT BOUND IN SPECIES #8213301 -2SOH2+
99.9 PERCENT BOUND IN SPECIES # 410
99.9 PERCENT BOUND IN SPECIES # 492
38.3 PERCENT BOUND IN SPECIES #8113301
PERCENT BOUND IN SPECIES #8114920 =1SOH2N03
100.4
PERCENT BOUND IN SPECIES #8114920
32.5 PERCENT BOUND IN SPECIES # 811
PERCENT BOUND IN SPECIES #8113301 -1SOH2+
PERCENT BOUND IN SPECIES #8114920 -1SOH2NO3
74.4 PERCENT BOUND IN SPECIES #8214100
PERCENT BOUND IN SPECIES #8213300 -2SO-
100.1
100.0
PERCENT BOUND IN SPECIES #8214100
K+l
N03-1
=1SOH2+
-1SOH2N03
ADS1TYP1
-2SOK
=2SOK
PERCENT BOUND IN SPECIES #3300020 OH-
1.4 PERCENT BOUND IN SPECIES # 330
PERCENT BOUND IN SPECIES #8113301 -1SOH2+
PERCENT BOUND IN SPECIES #8114920 -1SOH2N03
PERCENT BOUND IN SPECIES #8213301 =2SOH2+
H+l
104
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PC MINTEQA2 v3.00
PART 5 of OUTPUT FILE
DATE OF CALCULATIONS: 2-AUG-9(f
TIME: 10:19:16
EQUILIBRATED MASS DISTRIBUTION
IDX
NAME
410 K+l
492 N03-1
2 H20
330 H+l
DISSOLVED
MOL/KG PERCENT
9.994E-02 69.9
9.99SE-02 99.9
1.291E-07 100.0
-1.548E-10 0.0
SORBED
MOL/KG PERCENT
5.841E-05
5.486E-05
O.OOOE-01
9.257E-06
0.1
0.1
0.0
100.0
PRECIPITATED
MOL/KG PERCENT
O.OOOE-01
O.OOOE-01
O.OOOE-01
O.OOOE-01
0.0
0.0
0.0
0.0
CHARGE BALANCE: SPECIATED
SUM OF CATIONS « 9.994E-02 SUM OF ANIONS 9.995E-02
PERCENT DIFFERENCE - 1.776E-03 (ANIONS - CATIONS)/(ANIONS + CATIONS)
EQUILIBRIUM IONIC STRENGTH (m) - 9.994E-02
EQUILIBRIUM pH = 7.000
TRIPLE LAYER ADSORPTION MODEL
**** Parameters For Adsorbent Number 1 ****
Electrostatic Variables: psiO - 0.025893 sigO - 0.008009
psib - 0.019219 sigb - -.004998
psid - 0.004165 sigd - -.003011
Adsorbent Concentration (g/1): 8.174
Specific Surface Area (sq. meters/g): 129.00
**** Parameters For Adsorbent Number 2 ****
Electrostatic Variables: psiO - -.005272 sigO =
psib - -.003072 sigb -
psid - -.001095 sigd -
Adsorbent Concentration (g/1): 4.087
Specific Surface Area (sq. meters/g): 600.00
-.003079
0.002289
0.000791
DATE ID NUMBER:
TIME ID NUMBER:
900802
10191682
105
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PART 6 of OUTPUT FILE
PC MINTEQA2 vS.OO DATE OF CALCULATIONS: 2-AUG-90 TIME: 10:19:17
Saturation indices and stoichiometry of all minerals
ID t NAME Sat. Index Stoichiometry (in parentheses) of each component
atl.S. GOVERNMENT PRINTING OFFICE: !991-5ii8.ie?2o58B
106
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