12:00 PM - 1:00 PM
Numerous geologic environments, such as continental geothermal systems and submarine hydrothermal vents, involve circulation of aqueous fluids at elevated temperature (T) and pressure (P). At such conditions, aqueous fluids exhibit physical and chemical properties that differ dramatically from those at ambient T and P, leading to systematic variation in the complexing and, thus, solubility of electrolytes (salts). Our current understanding of the contrasting behavior of different salts in hydrothermal solutions at varying T and P is largely based on empirical observations, whereas underlying molecular-scale controls on hydrothermal salt behavior is largely inferred ex post. To identify strategies for predicting and modeling chemical properties and phase equilibria, we target molecular-scale interactions and their link to macroscopic thermodynamic properties using combined spectroscopy and molecular simulations. This presentation will focus on approaches and results pertaining to sodium ± potassium sulfate solutions. Spectroscopic analyses and simulation results provide a consistent picture of ion-ion interactions and pre-nucleation clustering, which heralds the onset of precipitation with increasing temperature and/or decreasing pressure. Moreover, the contrasting properties of sodium versus potassium ions in solution lead to solubility enhancement in ternary solutions. These results yield insights into the underlying controls on phase equilibria and properties of saline hydrothermal fluids, and provide a basis for predictive modeling of fluid-rock reactions in extreme environments.