Fundamental chemistry and thermodynamics of hydrothermal oxidation processes. 1997 annual progress report

'The objective of this research program is to provide fundamental scientific information on the physical and chemical properties of solutes in aqueous solutions at high temperatures needed to assess and improve the applicability of hydrothermal oxidation (HTO) to the remediation of US Department of Energy (DOE) hazardous and mixed wastes. Investigators in two divisions at Oak Ridge National Laboratory (Chemical and Analytical Sciences, and Chemical Technology) and at the University of Tennessee are focused on the solubility and speciation of actinides and surrogates in model HTO process streams at high temperatures, on the experimental and theoretical development of equations of state for aqueous mixtures containing noncondensible gases under HTO process conditions ranging above the critical temperature of water, and on achieving a predictive level of understanding of the chemical and physical properties of HTO process streams through molecular-level simulations of aqueous solutions at high temperatures. Specific tasks in these three efforts over the past year include measurements of solubility and identification of stable solid phases for UO{sub 3} in aqueous carbonate solutions at temperatures above 100 C, measurements of fluid-phase coexistence boundaries and densities of mixtures in (H{sub 2}O + N{sub 2} + CO{sub 2}) mixtures at high temperatures and pressures, and molecular dynamics simulations of water and aqueous solutions addressing the speciation of simple ionic solutes and the structure of water and aqueous solutions as functions of temperature and density. Research in this project has been divided into individual tasks, each addressing a particular scientific question and each contributing to a unified understanding of HTO processing problems related to the treatment of DOE hazardous and mixed wastes. The three primary tasks are (1) the determination of solubilities of inorganic compounds including actinides and surrogates to determine their likely fate during HTO processing, (2) experimental and modeling studies of the density and phase behavior of (water + gas) mixtures at high temperatures to determine the physical state of the process fluid, and (3) simulations of water and aqueous solutions at high temperatures and comparison with experimental results as a method for the development of accurate, comprehensive descriptions of the properties of aqueous fluids.