PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations; (2) batch-reaction and onedimensional (1D) transport calculations involving reversible reactions, which include aqueous, mineral, gas, solidsolution, surface-complexation, and ion-exchange equilibria, and irreversible reactions, which include specified mole transfers of reactants, kinetically controlled reactions, mixing of solutions, and temperature changes; and (3) inverse modeling, which finds sets of mineral and gas mole transfers that account for differences in composition between waters, within specified compositional uncertainty limits. New features in PHREEQC version 2 relative to version 1 include capabilities to simulate dispersion (or diffusion) and stagnant zones in 1D-transport calculations, to model kinetic reactions with user-defined rate expressions, to model the formation or dissolution of ideal, multicomponent or nonideal, binary solid solutions, to model fixed-volume gas phases in addition to fixed-pressure gas phases, to allow the number of surface or exchange sites to vary with the dissolution or precipitation of minerals or kinetic reactants, to include isotope mole balances in inverse modeling calculations, to automatically use multiple sets of convergence parameters, to print user-defined quantities to the primary output file and (or) to a file suitable for importation into a spreadsheet, and to define solution compositions in a format more compatible with spreadsheet programs. This report presents the equations that are the basis for chemical equilibrium, kinetic, transport, and inverse modeling calculations in PHREEQC; describes the input for the program; and presents examples that demonstrate most of the program's capabilities.

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User's guide to PHREEQC (Version 2)-a computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations

Ion-exchange isotherms between hydrotalcite-like (HT) of the NO3-, CI-, and SO4- forms and F , 0% Br , I , OH-, SO42-, CO3 z-, and Naphthol Yellow S (NYS 2-) ions were determined, and the spacing and the width of the 003 reflection were measured as a function of HT composition The ion-exchange equilibrium constant for HTs of monovalent anions are in the sequence OH- > F > Cl > Br- > NO3- > I , those for divalent anions are in the sequence CO3 ~- > NYS z- > SO42- The ion-exchange equilibrium constants tend to increase as the diameters of the anions decrease, and the crystallite size in the 001 direction tends to increase with anions having higher selectivity The OH-form of HT has the smallest basal spacing and the largest crystallite size in the 001 direction

Anion-exchange properties of hydrotalcite-like compounds

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User's guide to phreeqc a computer program for speciation, reaction-path, advective-transport, and inverse geochemical calculations

Lateral pressure in membranes

The behavior of colloid systems is governed primarily by their large interfacial area. The interface is defined as the boundary region between the adjoining bulk phases that comprise the colloid system. When one of the phases is a gas or a vapor, the term surface is commonly used for the boundary region. The foundation for thermodynamic treatment of surfaces was established in the last century by Gibbs, who published a considerable contribution to the field in 1878. His work still forms the basis of modern thermodynamics (Gibbs, 1928).

Physical Chemistry of Surfaces

Expressions for thermodynamic equilibrium constants are set up for the ion‐exchange equilibria of models defined in terms of operational variables. Formulas summarizing the methods for the computation of the requisite activity coefficients are given. In particular, the effects of the solvent, which is considered as an independently variable component, are taken explicitly into account.

Adsorption Studies on Clay Minerals. II. A Formulation of the Thermodynamics of Exchange Adsorption

The applicability of a thermodynamic equation of state to the Π–A curves of insoluble monolayers is examined. The equation of state is based on the Gibbs dividing surface formalism and takes explicit account of the subphase water. It is found that the entire course of the Π–A isotherm can be accounted for qualitatively with an activity coefficient for the water in the surface region. In particular, the expanded film Π–A curves of many compounds can be quantitatively reproduced with a surface‐pressure independent activity coefficient which is evaluated from the measured value of the surface vapor pressure. This result implies that compression in the expanded film regime corresponds only to a reduction in the water content of the film. When the equation of state is applied to mixed‐surfactant monolayers, it is shown that only if the activity coefficient of water is the same in both single component films and the mixed film do we obtain the surface area additivity, which has been used as a criterion of ideal...

The thermodynamic equation of state for insoluble monolayers. I. Uncharged films

Ion‐exchange equilibria for the pair cesium‐strontium between aqueous chloride solutions and a montmorillonite clay have been studied in the temperature range 5°—75°. Data from chromatographic elution experiments have been found to be unreliable because of nonequilibrium effects, and a method independent of rate behavior has been applied. From the data obtained, equilibrium constants, solid‐phase activity coefficients, heat content and entropy changes for the reaction have been evaluated.

Adsorption Studies on Clay Minerals. V. Montmorillonite‐Cesium‐Strontium at Several Temperatures

A thermodynamic equation of state for the Π–A curves of insoluble monolayers is extended to ionized surfactant species. It is shown that at infinite dilution on a pure water subphase, the limiting law ΠA=νskT (where νs is the number of ions into which the surfactant dissociates) is obtained. For monolayers spread on salt solutions with a common counterion, it is shown that the adsorption of soluble salt appears explicitly in the equation of state. If the Gibbs dividing surface is placed such that this adsorption is taken as zero, the form of the equation becomes similar to, and can be applied in the same manner as, that used for uncharged films. In some cases, this permits fitting experimental Π–A curves with surface‐pressure independent activity efficients. When this is not possible, it suggests that the relative salt and water adsorptions change as the film is compressed. Additional experimental information will be required to evaluate this possibility, and to permit application of the general equation ...

George L. Gaines

Papers

Adsorption Studies on Clay Minerals. II. A Formulation of the Thermodynamics of Exchange Adsorption

The thermodynamic equation of state for insoluble monolayers. I. Uncharged films

Adsorption Studies on Clay Minerals. V. Montmorillonite‐Cesium‐Strontium at Several Temperatures

The thermodynamic equation of state for insoluble monolayers. II. Ionized films