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User's Guide to PHREEQC


The input for PHREEQC is arranged by keyword data blocks. Each data block begins with a line that contains the keyword (and possibly additional data) followed by additional lines containing data related to the keyword. The keywords that define the input data for running the program are listed alphabetically: END, EQUILIBRIUM_PHASES, EXCHANGE, EXCHANGE_MASTER_SPECIES, EXCHANGE_SPECIES, GAS_PHASE, INVERSE_MODELING, KNOBS, MIX, PHASES, PRINT, REACTION, REACTION_TEMPERATURE, SAVE, SELECTED_OUTPUT, SOLUTION, SOLUTION_MASTER_SPECIES, SOLUTION_SPECIES, SURFACE, SURFACE_MASTER_SPECIES, SURFACE_SPECIES, TITLE, TRANSPORT, and USE. Keywords and their associated data are read from a database file at the beginning of a run to define the aqueous model. Then data are read from the input file until the END keyword is encountered, after which the specified calculations are performed. The process of reading data from the input file until an END is encountered followed by performing calculations is repeated until the last END keyword or the end of the input file is encountered. The set of calculations, defined by keyword data blocks terminated by an END, is termed a "simulation". A "run" is a series of one or more simulations that are contained in the same input data file and calculated during the same invocation of the program PHREEQC.

Each simulation may contain one or more of five types of speciation, reaction, and transport calculations: (1) initial solution speciation, (2) determination of the composition of an exchange assemblage in equilibrium with a fixed solution composition, (3) determination of the composition of a surface assemblage in equilibrium with a fixed solution composition, (4) calculation of chemical composition as a result of chemical reactions, which include mixing; net addition or removal of elements from solution, termed "net stoichiometric reaction"; equilibration with an assemblage of exchangers; equilibration with a gas phase at a fixed total pressure; equilibration with an assemblage of surfaces; dissolution or precipitation of pure phases; or variation in temperature, and (5) advective transport through a series of cells in combination with any of the available chemical processes. This combination of capabilities allows the modeling of very complex geochemical reactions and transport processes by using one or more simulations.

In addition to speciation, reaction, and transport calculations, the code may be used for inverse modeling, by which net chemical reactions are deduced that account for differences between one or a mixture of initial water compositions and a final water composition.

Conventions for Data Input
Reducing Chemical Equations to a Standard Form
Conventions for Documentation
Overview of Data Files and Keyword Data Blocks

User's Guide to PHREEQC - 07 MAY 96
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