- © The Mineralogical Society Of America
Sulfate minerals participate in a variety of mineral-water reactions with waters containing elevated concentrations of dissolved solids. Reliable prediction of sulfate-mineral solubility in concentrated waters is required for a multitude of geological, hydrogeological, industrial, and meteorological applications. Precipitation of pure sulfate minerals or sulfate-bearing solid solutions can limit concentrations of dissolved metals, radionuclides, and other cations at waste-disposal sites, in marine and other naturally occurring saline waters, in industrial waters, and in smog. Formation of these solids can control the major-ion geochemistry of water and, in turn, influence the behavior of trace constituents.
One of the most widely used and robust approaches for predicting mineral solubility in concentrated waters is the Pitzer ion-interaction approach as first introduced by Pitzer (1973), as applied to geological systems by Harvie and Weare (1980) and Harvie et al. (1980), and as summarized by Weare (1987). Clegg and Whitfield (1991) and Pitzer (1979a,b; 1991) provided further comprehensive discussions on the developments and application of the ion-interaction approach to predict mineral solubility in natural waters. This chapter focuses on the application of the ion-interaction approach, or its variations, for predicting sulfate-mineral solubility in a variety of geochemical settings. Included are a summary of the Pitzer approach as applied to predictions of mineral solubility, a summary of the available constants for modeling sulfate-mineral solubility, and examples of applications for natural and contaminated sites. The discussion focuses on recent additions to earlier models developed for application to near-Earth-surface temperature and pressure conditions. Applications outside this temperature and pressure range are described only briefly.
Compositions of concentrated waters
The majority of concentrated waters in nature form as a result of solar evaporation of marine and continentally-derived waters. The evaporation of seawater leads to predictable sequences of mineral formation, including precipitation of several common sulfate minerals (e.g. gypsum, …