Additional software information

[AnnaJulIQ]

Hello, I am doing an investigation in which I use this software and I would like to find more information in addition to what the manual has on the operation of the software, what thermodynamic models it uses and how it calculates these models.

[dlparkhurst]

The 1999 manual for version 2 gives most of the equations and derivatives for the Newton-Ralhson numerical method. Equations added in version 3 are given in the version 3 manual.

Latest input is given in the version 3 manual with extensions in the release notes. This manual  has 22 examples that demonstrate most of the programs capabilities. Additional examples and other resources can be found at https://hydrochemistry.edu and of course this forum.

The text Applo and Postma Geochemistry, Groundwater and Pollution covers most of the geochemical processes that can be used in Phreeqc. The text includes many Phreeqc examples and exercises.

For a different take on geochemical modeling, consider Bethke's text Geochemical  and Biochemical Reaction Modeling. Many geochemical processes are discussed with examples using Geochemist's Workbench.

Tony Appelo teaches courses on Phreeqc regularly in Amsterdam.

[AnnaJulIQ]

Thank you very much, I would like to know if phreeqc uses algorithms for minimizing the Gibbs free energy of the system and which algorithms it uses.

[dlparkhurst]

Phreeqc does not use free energy minimization, although it does use an optimization technique described at about page 31 of the 1999 manual. Basically, the method requires saturation indices of minerals in EQUILIBRIUM_PHASES to be less than or equal to zero.