For many years it has been known that pore-solution chemical compositions have pronounced effects on the physical and chemical behavior of frozen ground. Until recently, the inability to model accurately thermophysical properties of aqueous electrolyte solutions at subzero temperatures has persuaded most researchers to assume expediently, but perhaps wrongly, that the thermophysical properties of frozen-ground pore solutions were identical to those of pure liquid water. Recent theoretical and experimental developments suggest that vastly improved quantitative estimates are possible for the thermophysical properties of aqueous electrolyte solutions in frozen porous media. Two theoretical developments have been responsible: The Pitzer equations and thermoporometry. The Pitzer equations allow estimation of mixed aqueous electrolyte solution thermophysical properties for wide ranges of temperatures, pressures, and compositions. When fully parameterized, the Pitzer equations allow the calculation of mean-ionic and single-ion activity coefficients, osmotic coefficients, enthalpies, entropies, Gibbs energies, heat capacities, and molal volumes of highly concentrated aqueous electrolyte solutions to temperatures below - 50oC. The thermodynamic treatment justifying thermoporometric measurements can be modified for complex pore-solution compositions allowing accurate estimation of capillary pressures of geochemical solutions in frozen ground. Applications include calculation of (1) mineral solubilities in cold-regions terrestrial environments and (2) capillary pressures in frozen soils having a range of pore-solution compositions.
Giles M. Marion USACRREL 72 Lynme Road Hanover, NH 03755 Tel: 603-646-4676 Email: gmarion@hanover-crrel.army.mil