Predicting Sulfate-Mineral Solubility in Concentrated Waters

Abstract

INTRODUCTIONSulfate minerals participate in a variety of mineral-water reactions with waters containing elevated concentrations of dissolved solids. Reliable prediction of sulfatemineral 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 and , 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. BACKGROUND

Acid‐sulfate weathering of synthetic Martian basalt: The acid fog model revisited

“…In the less acidic solutions (i.e., C and D), much lesser amounts of only gypsum (Figure 4b) were identified. The presence of these phases results from high levels of Ca present in the fluids prior to evaporation and also because gypsum and anhydrite are among the most insoluble sulfate phases and commonly precipitate first in evaporite sequences [Ptacek and Blowes, 2000].…”

Coupled thermal, hydraulic and geochemical evolution of pyritic tailings in unsaturated column experiments

“…The Pitzer ion-interaction equations, in their original form, assume complete dissociation of all ions and represent the interaction between ions solely with ion-interaction equations with parameters derived from experimental data (Ptacek and Blowes, 2000). The only exception to this treatment is the complex HSO À 4 .…”

“…The only exception to this treatment is the complex HSO À 4 . This aqueous complex is generally included in models using the Pitzer interaction approach in waters with low pH and high sulfate concentrations (Reardon and Beckie, 1987;Ptacek and Blowes, 2000). Solubility products and reactions were taken from the WATEQ4f database (Ball and Nordstrom, 1991) except in the cases detailed in Table 3.…”

Thermodynamic equilibrium of the O2–ZnSO4–H2SO4–H2O system from 25 to 250°C

“…The solubility of minerals has been reviewed by Pitzer [13] and Ptacek and Blowes [22]. Most of the work either focused on selected chloride systems like NaCl and KCl, or limited to low temperatures and in pure water in sulphate systems like NiSO 4 , CuSO 4 , FeSO 4 , etc.…”