NESC1101 MINTEQ.

1. NAME OR DESIGNATION OF PROGRAM:  MINTEQ.

3. DESCRIPTION OF PROGRAM OR FUNCTION

MINTEQ is a geochemical program to model aqueous solutions and the interactions of aqueous solutions with hypothesized assemblages of solid phases. It was developed for  the Environmental Protection Agency to perform the calculations necessary to simulate the contact of waste solutions with heterogeneous sediments or the interaction of ground water with solidified wastes. MINTEQ can calculate ion speciation/solubility, adsorption, oxidation-reduction, gas phase equilibria, and precipitation/dissolution of solid phases. MINTEQ can accept a finite mass for any solid considered for dissolution and will dissolve the specified solid phase only until its initial mass is exhausted. This ability enables MINTEQ to model flow-through systems. In these systems the masses of solid phases that precipitate at earlier pore volumes can be dissolved at later pore volumes according to thermodynamic constraints imposed by the solution composition and solid phases present. The ability to model  these systems permits evaluation of the geochemistry of dissolved traced metals, such as low-level waste in shallow land burial sites. MINTEQ was designed to solve geochemical equilibria for systems composed of one kilogram of water, various amounts of material dissolved in solution, and any solid materials that are present. Systems modeled using MINTEQ can exchange energy and material (open  systems) or just energy (closed systems) with the surrounding environment. Each system is composed of a number of phases. Every phase is a region with distinct composition and physically definable boundaries. All of the material in the aqueous solution forms one phase. The gas phase is composed of any gaseous material present, and structurally distinct solid forms a separate phase.

4. METHOD OF SOLUTION

MINTEQ applies the fundamental principles of thermodynamics to solve geochemical equilibria from a set of mass balance equations, one for each component. Because the mass action constraints are nonlinear in the components, the problem reduces to  the solution of a system of nonlinear equations. In MINTEQ when a solid enters the equilibrium assemblage, the system of mass balance  equations is modified to incorporate the additional solubility constraint. The system is then solved directly using the Newton-Raphson technique. MINTEQ is composed of four submodels. The  speciation submodel computes the activities of complexed and uncomplexed cationic and anionic species, neutral ion pairs, and the activities of cationic and anionic redox species. These activities are then fed to the solubility submodel, which calculates ion activity products for solids and minerals. The results from these calculations are used by the mass transfer submodel to calculate the mass of solid that precipitates or dissolves. In the fourth or adsorption submodel MINTEQ models adsorption onto solid surfaces via several mechanisms: an activity Langmuir isotherm, an activity Freundlich isotherm, an ion exchange model, a constant capacitance surface complexation model, and a triple-layer surface complexation  model. The calculations completed by each submodel are dependent on  the thermodynamic data stored in the MINTEQ database.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

MINTEQ assumes that  the system is at equilibrium and will not explicitly consider kinetics. The equilibrium constants in the MINTEQ data base are given for 25 degrees C. MINTEQ should not be used to model solutions at temperatures greater than 100 degrees C. In addition, no capability exists to consider solid solutions or to model high ionic strength brine solutions. It is impossible to automatically vary the composition of a precipitating solid as the solution composition changes. MINTEQ computes the final equilibrium of a given system in  a "single-step" neglecting reaction path calculations.

6. TYPICAL RUNNING TIME

NESC compiled and executed the sample problem in 129 CPU seconds on a DEC VAX11.

The test case included in this package ran at NEADB on  a VAX8810 computer in 16 seconds of CPU time.

7. UNUSUAL FEATURES OF THE PROGRAM:

8. RELATED AND AUXILIARY PROGRAMS

MINTEQ integrates many of the capabilities of its two immediate predecessors, MINEQL and WATEQ3, and is a member of the REDEQL family of codes. It is recommended along with EQ3/6 (NESC 886) for modeling reactions that effect solute geochemistry.

10. REFERENCES

- MINTEQ, NESC No. 1101, MINTEQ Tape Description and Implementation
  Information,
  National Energy Software Center Note 88-74, June 3, 1988.
- S.R. Peterson, B.E. Opitz, M.J. Graham and L.E. Eary
  An Overview of the Geochemical Code MINTEQ: Applications to
  Performance Assessment for Low-Level Wastes,
  PNL-6112, March 1987.
- A.R. Felmy, S.M. Brown, Y. Onishi, S.B. Yabusaki and R.S. Argo
  MEXAMS - The Metal Exposure Analysis Modeling System,
  EPA-600/3-84-031, 1984.
- J.W. Ball, D.K. Nordstrom and E.A. Jenne
  Additional and Revised Thermochemical Data and Computer Code for
  WATEQ2-A Computerized Chemical Model for Trace and Major Element
  Speciation and Mineral Equilibria of Natural Waters,
U.S. Geological Survey, Water Resources Investigations WRI-78-116,    1980.

- S.R. Peterson, C.J. Hostetler, W.J. Deutsch, and C.E. Cowan:
  MINTEQ User's Manual
  NUREG/CR-4808 (PNL-6106) (February 1987).
- A.R. Felmy, D.C. Girvin and E.A. Jenne:
  MINTEQ - A Computer Program for Calculating Aqueous Geochemical
  Equilibria
  EPA-600/3-84-032 (February 1984).

11. MACHINE REQUIREMENTS:  255 Kbytes are required on a DEC VAX11/785.

About 800K bytes of main storage are required to run the test case on a VAX 8810.

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  VMS 4.2, 4.5.

VMS V5.1 (VAX 8810).

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:

15. NAME AND ESTABLISHMENT OF AUTHORS

          K.M. Krupka
          Pacific Northwest Laboratory

File name	File description	Records
NESC1101_01.001	MINTEQ information file	100
NESC1101_01.002	MINTEQ FORTRAN source	2650
NESC1101_01.003	Alkalinity factors	11
NESC1101_01.004	Polyn. coeff. to comp. log K	28
NESC1101_01.005	COMMON file for the subroutines	18
NESC1101_01.006	Component data library	53
NESC1101_01.007	Sample problem input	42
NESC1101_01.008	Sample problem input, same as file 7	42
NESC1101_01.009	Thermodynamic data, TYPE 6 solids	650
NESC1101_01.010	Thermodynamic data for aqueous species etc.	1230
NESC1101_01.011	Sample problem output	1203