A Computer Program Incorporating Pitzer's Equations for Calculation of
Geochemical Reactions in Brines

By L.N. Plummer, D.L. Parkhurst, G.W. Fleming, and S.A. Dunkle

U.S. Geological Survey Water-Resources Investigations Report 88-4153, 1988.

ABSTRACT

The program named PHRQPITZ is a computer code capable of making
geochemical calculations in brines and other electrolyte solutions to
high concentrations using the Pitzer virial-coefficient approach for
activity-coefficient corrections. Reaction-modeling capabilities
include calculation of (1) aqueous speciation and mineral-saturation
index, (2) mineral solubility, (3) mixing and titration of aqueous
solutions, (4) irreversible reactions and mineral-water mass transfer,
and (5) reaction path. The computed results for each aqueous solution
include the osmotic coefficient, water activity, mineral saturation
indices, mean activity coefficients, total activity coefficients, and
scale-dependent values of pH, individual-ion activities, and
individual-ion activity coefficients. A data base of Pitzer
interaction parameters is provided at 25 C for the system
Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O, and extended to include
largely untested literature data for Fe(II), Mn(II), Sr, Ba, Li, and
Br with provision for calculations at temperatures other than 25 C. An
extensive literature review of published Pitzer interaction parameters
for many inorganic salts is given. Also described is an interactive
input code for PHRQPITZ called PITZINPT.