Principles, caveats and improvements in databases for calculating hydrogeochemical reactions in saline waters from 0 to 200 degrees C and 1 to 1000 atm

摘要

Databases distributed with PHREEQC may give widely different results for concentrated solutions. Only the database that uses Pitzer's interaction coefficients provides both correct solubilities and mean activity coefficients. The applicability of this database for predicting scaling by mineral precipitation is extended by fitting interaction coefficients for the Na-K-Mg-Ca-Ba-Cl-CO2-HCO3-SO4-H4SiO4 system from isopiestic and solubility data at high temperatures. The pressure dependence of equilibrium constants is calculated from the reaction volume, in which the apparent molar volume of the solutes is derived from density measurements. The apparent volumes are a function of temperature, pressure, and ionic strength, and incorporate complicated changes of the partial molar volumes of the water molecules.