NESC0886 EQ3/6.

1. NAME OR DESIGNATION OF PROGRAM:  EQ3/6

3. DESCRIPTION OF PROBLEM OR FUNCTION

The EQ3/6 release 3230B software package is a set of computer programs and supporting data files, used in modeling aqueous geochemical systems. The two main programs are EQ3NR and EQ6. EQ3NR is a geochemical aqueous speciation-solubility program which models the thermodynamic state of an aqueous solution by calculating the distribution of aqueous species, such as simple ions, ion-pairs, and aqueous complexes. The EQ6 program, which must be initialized by an EQ3NR calculation, computes either reaction paths of reacting aqueous systems or heterogeneous equilibrium with fixed masses of chemical elements. Two auxiliary programs, MCRT and EQTL, are included in the package. MCRT is a database building program used to process thermo- dynamic input data files into a form suitable for the EQ3/6 thermodynamic database and to perform temperature extrapolation of 25 degree C data. The primary data file that supports EQ3/6 contains thermodynamic data corresponding to the temperatures 0, 25, 60, 100, 150, 200, 250, and 300 degrees C, a pressure of 1.013 bar (1 atmosphere) up to 100 degrees C, the steam/liquid water equilibrium pressure at higher temperatures, and other necessary supporting data. EQTL, a database preprocessor, reads this primary data file, checks each reaction for mass and charge balance, fits interpolating polynomials to all data on temperature grids, and reformats the data into suitable form in three secondary data files  read directly by EQ3NR or EQ6.

4. METHOD OF SOLUTION

EQ3NR uses a modified Newton-Raphson algorithm  to calculate the distribution of aqueous species. Input primarily consists of data derived from total analytical concentrations of dissolved components and can also include pH, alkalinity, electrical balance, phase equilibrium (solubility) constraints, and a default value for Eh, pe, or the logarithm of oxygen fugacity. The program evaluates the degree of disequilibrium for various reactions and computes either the saturation index or thermodynamic affinity for minerals. Individual values of Eh, pe, equilibrium oxygen fugacity,  and Ah (redox affinity) are computed for aqueous redox couples. EQ3NR can be used alone. It is required to initialize reaction-path  calculations performed by EQ6, its companion program.

EQ6 first checks that the input system is in homogeneous equilibrium If not, the system is "equilibrated" according to the specified mass balance constraints. This will yield a single Eh for  the solution and alter to some extent all the other solution parameters, including the pH. If there are any supersaturated phases, EQ6 then "precipitates" a set so that no supersaturations remain. This may result in still different values for the pH and other solution parameters. Any such initial precipitates may be retained in the system or deleted before the reaction progresses. Calculations may then be performed to model simple titration or irreversible reaction with "reactants" in systems that are either closed to solids or open (flow-through) systems. EQ6 solves at each  point of reaction progress the algebraic equations describing mass and charge balance, mass action, and non-ideality. Finite-difference expressions of high order are used to estimate derivatives with respect to reaction progress and predict the values of a basis set of unknowns at a subsequent point. The predicted values are then corrected by using the Newton-Raphson method. Convergence is aided by optimizing starting estimates and by under-relaxation techniques.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

The temperature range of the thermodynamic data in the primary data file is 0 to 300 degrees C. The activity coefficient approximations for aqueous solutes are not dependable at ionic strengths of greater than roughly one molal.

6. TYPICAL RUNNING TIME

On a CDC7600 the EQ3NR test cases requires about 2 seconds to run and the EQ6 test cases about 10 seconds.

NEADB executed the test cases included in this package  on a VAX 8810 computer. The following CPU times were required: EQPT(standard option): 47 secs; EQPT(pitzer option): 33 secs; EQ3NR(nacldot.3i data): 5 secs; EQ3NR(swpar1.3i data): 10 secs; EQ3NR(sylvite1.3i data): 4 secs; EQ6(pyrite1.6i data): 15 minutes; EQ6:( sylvite1.6i data): 8 secs.

7. UNUSUAL FEATURES OF THE PROGRAM

The programs were developed for the FTN and CFT FORTRAN compiler language on the CDC7600 and CRAY1 computers with specific conventions adopted to facilitate transportability to UNIVAC, IBM, DEC VAX, and other systems.

8. RELATED AND AUXILIARY PROGRAMS

Other well-known geochemical codes  for the EQ3 distribution-of-species problem are SOLSAT (Helgeson), SOLMNEQ (Kharaka and Barnes), the WATEQ series (Ruesdell, Plummer, Ball), REDEQL (Morel and Morgan), and MINEQL (Westall). Similar in modeling function to EQ6 are Helgeson's PATH1 and PATHCALC programs.

10. REFERENCES

- T.J. Wolery and L.J. Walters, Jr.,
  Calculation of Equilibrium Distributions of Chemical Species by
  Means of Monotone Sequences, Mathematical Geology, Vol. 7, pp.
  99-115, 1975.
- H.C. Helgeson,
  Evaluation of Irreversible Reactions in Geochemical Processes
  Involving Minerals and Aqueous Solutions-I.
Thermodynamic Relations, Geochimica et Cosmochimica Acta, Vol. 32,    pp. 853-877, 1968.
- T.J. Wolery and K.J. Jackson:
  Chapter 2: Activity Coefficients in Aqueous Salt Solutions -
  Hydration Theory Equations
  ACS Symposium Series 416; developed from a symposium sponsored by
  the Division of Geochemistry at the 196th National Meeting of the
American Chemical Society, Los Angeles, CA (September 25-30, 1988)  - U. Vuorinen and H. Leino-Forsman:
Solubility and Speciation Calculations (EQ3/6) for the Elements of    Importance in TVO-92
  YJT-92-11 (Auhust 1992).

- K.J. Jackson:
  Verification and Validation Studies of the Addition of Pitzer's
  Equations to the EQ3/6 Brine Model
  UCRL-53841 (July 20, 1988).
- S.A. Daveler and B. Bourcier:
  EQ3NR - Input File User's Guide
  LLNL (Version EQ3NR R114) (July 7, 1989).
- S.A. Daveler and B. Bourcier:
  EQ6 - Input File User's Guide
  LLNL (Version EQ6R104) (June 22, 1989).
- T.J. Wolery and S.A. Daveler:
  EQ6 A Computer Program for Reaction Path Modeling of Aqueous
  Geochemical Systems - User's Guide and Documentation
  LLNL (March 30, 1989).

11. MACHINE REQUIREMENTS

About 136,000 (octal) words of SCM and 157,000 (octal) words of LCM are required on a CDC7600 for EQ3NR, about 124,000 (octal) words of SCM and 165,000 (octal) words of LCM  for EQ6. Three units in addition to the standard input/output units  used by EQ3NR, 11 units in addition to the standard I/O units by EQ6.

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  SCOPE 2.1.5 (CDC7600).

VMS V5.1-1 (VAX 8810) with compiler VAX FORTRAN V5.0-1.

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

The program is written in FORTRAN 66, but FORTRAN 77 compatible. Central memory must be preset to zero when running EQ6.

15. NAME AND ESTABLISHMENT OF AUTHOR

   T.J. Wolery
   Earth Sciences Division
   Lawrence Livermore National Laboratory
   P.O. Box 808
   Livermore, California 94550

File name	File description	Records
NESC0886_04.001	Information file	156
NESC0886_04.002	Data file data0; the eq3/6 data base	25704
NESC0886_04.003	Pitzer coefficient data file	4196
NESC0886_04.004	Harvie,Moller,Weare coefficient data file	3140
NESC0886_04.005	eq3nr include file	190
NESC0886_04.006	eq3nr source file	6763
NESC0886_04.007	eq6 include file	377
NESC0886_04.008	eq6 source file	15985
NESC0886_04.009	eqpt output file with pitzer data	695
NESC0886_04.010	second eqpt output file with pitzer data	737
NESC0886_04.011	eqpt short output file with pitzer data	179
NESC0886_04.012	eqpt output file with standard data	1546
NESC0886_04.013	eqpt short output file with standard data	569
NESC0886_04.014	eqpt include file	279
NESC0886_04.015	eqpt source file	4714
NESC0886_04.016	eqlib include file	625
NESC0886_04.017	eqlib source file	10368
NESC0886_04.018	the program to decompose *.inc file	73
NESC0886_04.019	eq3nr input file	37
NESC0886_04.020	eq3nr output file	481
NESC0886_04.021	eq6 input file	141
NESC0886_04.022	eq6 output file	5462
NESC0886_04.023	eq3nr input file	115
NESC0886_04.024	eq3nr output file	1099
NESC0886_04.025	eq3nr input file	50
NESC0886_04.026	eq3nr output file	542
NESC0886_04.027	eq6 input file	112
NESC0886_04.028	eq6 output file	2289
NESC0886_04.029	history file for eq3nr	417
NESC0886_04.030	history file for eq6	804
NESC0886_04.031	history file for eqpt	114
NESC0886_04.032	history file for eqlib	410