Phase Behavior of Aqueous Na-K-Mg-Ca-CI-NO3 Mixtures: Isopiestic Measurements and Thermodynamic Modeling

A comprehensive model has been established for calculating thermodynamic properties of multicomponent aqueous systems containing the Na{sup +}, K{sup +}, Mg{sup 2+}, Ca{sup 2+}, Cl{sup -}, and NO{sub 3}{sup -} ions. The thermodynamic framework is based on a previously developed model for mixed-solvent electrolyte solutions. The framework has been designed to reproduce the properties of salt solutions at temperatures ranging from the freezing point to 300 C and concentrations ranging from infinite dilution to the fused salt limit. The model has been parameterized using a combination of an extensive literature database and new isopiestic measurements for thirteen salt mixtures at 140 C. The measurements have been performed using Oak Ridge National Laboratory's (ORNL) previously designed gravimetric isopiestic apparatus, which makes it possible to detect solid phase precipitation. Water activities are reported for mixtures with a fixed ratio of salts as a function of the total apparent salt mole fraction. The isopiestic measurements reported here simultaneously reflect two fundamental properties of the system, i.e., the activity of water as a function of solution concentration and the occurrence of solid-liquid transitions. The thermodynamic model accurately reproduces the new isopiestic data as well as literature data for binary, ternary and higher-order subsystems. Because of its high accuracy in calculating vapor-liquid and solid-liquid equilibria, the model is suitable for studying deliquescence behavior of multicomponent salt systems

Fundamental Chemistry And Thermodynamics Of Hydrothermal Oxidation Processes

Hydrothermal oxidation (HTO) is a promising technology for the treatment of aqueous-fluid hazardous and mixed waste streams. Waste streams identified as likely candidates for treatment by this technology are primarily aqueous fluids containing hazardous organic compounds, and often containing inorganic compounds including radioisotopes (mixed wastes). These wastes are difficult and expensive to treat by conventional technologies (e.g. incineration) due to their high water content; in addition, incineration can lead to concerns related to stack releases. An especially attractive potential advantage of HTO over conventional treatment methods is the total containment of all reaction products within the overall system. The potential application of hydrothermal oxidation (HTO) technology for the treatment of DOE hazardous or mixed wastes has been uncertain due to concerns about safe and efficient operation of the technology. In principle, aqueous DOE wastes, including hazardous an d mixed waste, can be treated with this technology. Oxidation reactions are carried out in the aqueous phase at high temperatures ({approx}600 C), effectively converting organic waste constituents to nonhazardous materials (e.g., CO2). Inorganic materials which become insoluble in supercritical water may precipitate as scales adhering to components of the reactor, limiting reactor availability and necessitating frequent cleaning of the system. Also, most hazardous organic compounds contain heteroatoms (other than carbon, hydrogen, and oxygen). These heteroatoms, including halides (F, Cl, Br, I), sulfur, phosphorus, and some nitrogen groups, form strong mineral acids on oxidation of the organic compounds, resulting in a solution having low pH and high oxidation potential. This combination, in conjunction with the high temperatures and high fluid densities attained in both the heating and cooling regions of an HTO reactor, can lead to corrosion of structural materials (usually metal s) anticipated for use in HTO reactor construction. Methods have been suggested for mitigating the problems arising from the production of mineral acids and insoluble solids in HTO processes (Barnes et al., 1993). Previous work in this Laboratory centered on the problems arising from the presence of corrosive or insoluble inorganic compounds in HTO fluids (Simonson et al., 1993, 1994, 1995). However, significant gaps in our knowledge of process chemistry remained at the initiation of this project. It was not possible to determine accurately the properties of coexisting fluid phases; the solubilities of radioactive components of mixed wastes were unknown at high temperatures; and molecular level understanding of interparticle interactions was needed for reliable extrapolation of phenomenological equations for solution behavior beyond the range of experimental results. The present project was undertaken to address these deficiencies. The project was undertaken to provide fundamental information needed to support deployment decisions related to HTO technology, and no innovations in the technology per se were anticipated. Rather, the innovations of this project involved applying new or existing experimental and modeling approaches to studies of aqueous inorganic reactions and properties under the rigorous anticipated HTO operating conditions. This work was made possible in part through the support of researchers at ORNL and the University of Tennessee, Knoxville, by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences of the Department of Energy. This support has allowed significant, unique experimental and 2 computational resources to be developed for studies of aqueous solution chemistry at high temperatures and pressures

Liquid-vapor partitioning of NaCl(aq) from concentrated brines at temperatures to 350{degrees}C

Compositions of coexisting liquid and vapor phases have been determined at temperatures from 250 to 350°C for brines containing NaCl and either HCI or NaOH by direct sampling of both phases from a static phase-equilibration apparatus. In these experiments, NaCl concentrations in the liquid phase ranged to 6.5 mol-kg{sup -1}, with corresponding vapor-phase NaCl concentrations varying strongly with temperature and brine composition. Acid or base was added to the brines to suppress unknown contributions of NaCl(aq) hydrolysis products to the observed volatilities. Thermodynamic partitioning constants for NaCl have been determined from the observed compositions of the coexisting phases combined with the known activity coefficients of NaCl(aq) in the liquid phase. An apparent dependence of the values of these partitioning constants on brine concentration is explained by considering the effect of decreasing pressure on the density of the vapor phase. Concentrations of HCI and NaCl in steam produced from various natural brines may be calculated as hnctions of temperature and brine composition based on these new results coupled with our previous determinations of the partitioning constants for HCl(aq). Application of these results to The Geysers will be discussed in terms of the composition of postulated brines which could be in equilibrium with observed steam compositions at various temperatures

Measurements of water vapor adsorption on The Geysers rocks

One of the goals of this project is to determine the dependence of the water retention capacity of the rocks as a function of temperature. The results show a significant dependence of the adsorption and desorption isotherms on the grain size of the sample. The increase in the amount of water retained with temperature observed previously between 90 and 30{degrees}C for various reservoir rocks from The Geysers may be due to the contribution of slow chemical adsorption and may be dependent on the time allowed for equilibration. In contrast with the results of Shang, some closed and nearly closed hysteresis loops on the water adsorption/desorption isotherms were obtained in this study. In these cases the effects of activated processes were not present, and no increase in water adsorption with temperature was observed