User:Shiny.spoon/Geochemical modeling

Software programs in common use
The USGS website provides free access to many of the software listed above.

PHREEQC
The name PHREEQC, for the geochemical modeling computer program, is an abbreviation for PH REdox EQuilibrium in C language. PHREEQC is used to model multiple different types of aqueous geochemistry reactions and processes that occur in the natural world and in a laboratory. Different model capabilities include speciation from solutions with or without gases and solids, exchange and surface complexation, batch reactions, inverse-modeling, advective-transport, advective-dispersive transport, and cell batch-reactions.

PHREEQC was originally derived from a Fortran program PHREEQE in 1980, which was able to model the mixing of waters, the dissolving and precipitating of solids from aqueous solutions, and the effects of changing temperature. PHREEQC version 1 was a new program, based on PHREEQCE created in 1995, but being written in the C programming language. Version 1 could compute ion-exchange equilibria, completion equilibria, fixed pressure gas-phase equilibria, advective transport, and inverse modeling. PHREEQC version 2, also written in C, improved upon version 1 by adding kinetically controlled reactions, solid solution equilibrium, fixed volume gas equilibria, variation of number of exchange sites, and isotope balance of inverse modeling. PHREEQC version 3 improved upon version 2 by adding the ability to simulate results from both laboratory and field experiments. IPhreeqc allows PHREEQC to be utilized with other software programs.

Available PHREEQC databases are listed in the table, and each database can be used to model different types of geochemical reactions.

Limitations
Some limitations of PHREEQC are associated with differences of in the database content, lack of complicated ion exchange models, solid solution models that assume ideality (which make it impossible to model more than two solid solutions), and the inability to solve more complex Raleigh Fractionation calculations for inverse modeling of isotopes.