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User's Guide to PHREEQC


PHREEQE (Parkhurst and others, 1980) has been a useful geochemical program for nearly 15 years. PHREEQE is capable of simulating a wide range of geochemical reactions including mixing of waters, addition of net irreversible reactions to solution, dissolving and precipitating phases to achieve equilibrium with the aqueous phase, and effects of changing temperature. Concentrations of elements, molalities and activities of aqueous species, pH, pe, saturation indices, and mole transfers of phases to achieve equilibrium can be calculated as a function of specified reversible and irreversible geochemical reactions, provided sufficient thermodynamic data are available.

However, PHREEQE suffers from a number of deficiencies. As a speciation code, it lacks flexibility in defining mole balances on valence states and in distributing redox elements among their valence states. As a reaction path code, it does not keep track of the mass of water in solution nor the moles of minerals in contact with the solution. Surface complexation, ion exchange, or a fixed-pressure gas phase can not be modeled without program modification. Determining reaction paths and thermodynamically stable mineral assemblages is time consuming and tedious. The numerical method fails for some redox problems, which causes the program not to converge to the correct solution to the algebraic equations. Perhaps most importantly, the fixed format input and reliance on index numbers is cumbersome and prone to errors. There are also many Fortran-imposed limits, such as limits on the numbers of elements, aqueous species, phases, solutions, and lengths of character strings (mineral names for instance) that are inconvenient and time consuming to modify.

Program Capabilities
Program Limitations
How to Obtain the Software and Manual
Installation and Setup of the DOS Version
Installation and Setup of the Unix Version
Purpose and Scope

User's Guide to PHREEQC - 07 MAY 96
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