The Geochemist’s Workbench

Bethke, C. M., 2007, The Geochemist s Workbench Release 7.0 (four volumes). Hydrogeology Program, University of Illinois, Urbana, Illinois. 

This book provides a comprehensive overview of reaction processes in the Earth s crust and on its surface, both in the laboratory and in the held. A clear exposition of the underlying equations and calculation techniques is balanced by a large number of fully worked examples. The book uses The Geochemist s Workbench modeling software, developed by the author and installed at over 1000 universities and research facilities worldwide. The reader can, however, also use the software of his or her choice. The book contains all the information needed for the reader to reproduce calculations in full. 

In 1992, we bundled these programs together into a package called The Geochemist s Workbench which is owned by The Board of Trustees of the University of Illinois and can be licensed inexpensively for educational or commercial purposes. Within a few months of its completion the software was in use at dozens of universities and companies around the world. 

Figure 4.11 Simulated reaction pathway between 25 cm3 ceramic and 1 kg seawater, at STP, showing the predicted alteration of the minerals in the ceramic. Total corrosion rate = 104.62 mg/year. [From Wilson, 2004 199, generated using The Geochemist s Workbench (Bethke, 1996), with permission of the author.]...

The Geochemist s Workbench http //hercuies.geoiogy.uiuc.edu/ bethke/... 

Figure 7.2. Plot of log activity of Al3+ or Fe3+ in solution vs. pH for the common Al- and Fe(III)-oxides and oxy(hydroxides). Calculations were made using The Geochemist s Workbench.

A set of five programs known as The Geochemist s Workbench or GWB was developed by Bethke (1994) with a wide range of capabilities similar to EQ3/6 and PHREEQC v. 2. GWB performs speciation, mass transfer, reaction-path calculations, isotopic calculations, temperamre dependence for 0-300 °C, independent redox calculations, and sorption calculations. Several electrolyte databases are available including ion association with Debye-Huckel activity coefficients, the Pitzer formulation, the Harvie-M0ller-Weare formulation, and a... 

Bethke C. M. (1994) The Geochemist s Workbench A User s Guide to Rxn, Act2, Tact and Gtplot. Urbana-Champaign, University of Illinois Hydrogeology Program. 

Bethke C. (2002) The Geochemist s Workbench User Guide, University of Illinois. 

Limitations and problems additional to those of the speciation codes The models do not consider solid-solution mass transfer and provide only limited information on ion exchange/adsorption mass transfer. All the programs except PHREEQE, PHRQPITZ, and MINTEQA2 keep track of water mass. Except for EQ3/6 and the Geochemist s Workbench, rate laws for mass transfer kinetics cannot be specified. Convergence problems occur more often than for the speciation codes. 

The thermodynamic data bases of most geochemical models are only occasionally corrected and updated. Updated data bases for the Geochemist s Workbench (Bethke 1994, 1996) and EQ3/6 (Wolery 1992a, 1992b) may be obtained by anonymous ftp from ftp //s32.es.llnl.gov/johnson where they are located in the files gwb and eq36. For further information contact Jim Johnson at his e-mail address jviJohnson llnl.gov. 

Bethke, C. M. 1994. The geochemist s workbench, version 2.0, A users guide to Rxn, Act2, Tact, React, and Gtplot. Hydrogeology Program. Urbana, IL Univ. of Illinois. 

In addition to these programs, which are freely available and very widely used, there are a few others we will mention from time to time, which are also useful. The first two are available at relatively nominal cost from their authors. The Geochemist s Workbench group of programs are available on a commercial basis. 

The Geochemist s Workbench . A collection of five geochemical programs by C.M. Bethke and his group at the University of Illinois, capable of performing virtually all options we discuss (except coupled reactive transport), with graphical output (Bethke, 1994, 1996). Inquiries should be directed to... 

For example, the database for the The Geochemist s Workbench programs looks like the following. We choose this one because it is relatively readable. Databases for other programs contain essentially the same kind of information, but usually in a more condensed format which is harder for humans to understand. 

For example, here is a phreeqc input file which would give results very much like those of Figure 8.6 (which was actually created with The Geochemist s Workbench ). 

Figure 6.11. The same curves as drawn by The Geochemist s Workbench and from the data in minteqa2, at 25°C.

Table 7.1. Some ways of representing surface complexes on HFO. In programs such as The Geochemist s Workbench and phreeqc, the user may define other types of notation and other surfaces. The default ones are shown.

Programs rxn and react in The Geochemist s Workbench can account for the sorption of aqueous species onto mineral surfaces by several methods, including the two layer surface complexation model of Dzombak and Morel (1990), the constant... 

Table 7.2. A react script to calculate the amounts of various ions adsorbed by 1 g of HFO. From The Geochemist s Workbench User s Guide.

To show how these programs work, we consider a couple of examples from The Geochemist s Workbench User s Guide, then repeat them with phreeqc. Examples of more complex systems are considered in later chapters. 

The Geochemist s Workbench Consider a dilute solution containing several ions in contact with the adsorbing surfaces of hydrous ferric oxide (HFO). A script for program react is shown in Table 7.2. 

The Geochemist s Workbench stores the Dzombak and Morel data in a file called FeOH. dat. The program calculates the sorbing surface area and available sites from the mass of mineral (1 g) and data in FeOH. dat. 

Note that to model redox disequilibrium in phreeqc, a new species must be defined for each disequilibrium redox species (Parkhurst and Appelo, 1999, Example 15). Program react (The Geochemist s Workbench ) has a simpler decouple command. 

The Geochemist s Workbench In program react, part of The Geochemist s Workbench , equation (11.29) is implemented by using the kinetic command to set the variables (key words) required. The format is... 

This example is modified from one in the GWB User s Guide (Bethke, 1994). Program REACT in The Geochemist s Workbench also implements several other equations for rate laws, catalyzing and inhibiting species, nucleation, catalysis, and so on. 

A recent release of The Geochemist s Workbench adds the ability to program any rate law, much as in this phreeqc example. 

The Geochemist s Workbench program react now includes procedures to calculate reaction kinetics of biotransformations, and the phreeqc documentation gives an example of similar calculations in phreeqc. 

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