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An Ion-association Model for Highly Saline, Sodium Chloride-dominated Waters¹

ABSTRACT

An empirical ion-association model for concentrated aqueous solutions in which NaCl is the principal solute was developed for incorporation into the computer program GEOCHEM. The model involved the use of the Davies equation to calculate the activity coefficients of charged species and other semiempirical equations based in statistical mechanics to calculate the activity coefficients of neutral complexes. Model validation was initiated through prediction of the solubilities of gypsum, amorphous silica, and barite in NaCl solutions and other Na-salt solutions. Predicted solubilities usually agreed with measured values to within ±5% at ionic strengths up to 2 kmol m^–3 (mol L^–1). These encouraging results suggest that the model, although limited in scope and validation, will be useful for chemical speciation calculations on highly saline soil solutions and brines.

Key Words: aqueous solutions • brines • chemical speciation • mineral solubility • salinity • salt-affected soils

¹ Contribution from the Dep. of Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521 and Dep. of Agronomy, The Ohio State Univ., Columbus, OH 43210. Salaries and research support provided partially by state and federal funds, appropriated to the Ohio Agricultural Research and Development Center, The Ohio State Univ., Wooster, OH 44691. Journal article 86-86.

² Professor of Soil Science and Assistant Professor of Soil Physical Chemistry, respectively.