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

Advective-diffusive/dispersive transport of chemically reacting species in hydrothermal systems. Final report, FY83-85

A general formulation of multi-phase fluid flow coupled to chemical reactions was developed based on a continuum description of porous media. A preliminary version of the computer code MCCTM was constructed which implemented the general equations for a single phase fluid. The computer code MCCTM incorporates mass transport by advection-diffusion/dispersion in a one-dimensional porous medium coupled to reversible and irreversible, homogeneous and heterogeneous chemical reactions. These reactions include aqueous complexing, oxidation/reduction reactions, ion exchange, and hydrolysis reactions of stoichiometric minerals. The code MCCTM uses a fully implicit finite difference algorithm. The code was tested against analytical calculations. Applications of the code included investigation of the propagation of sharp chemical reaction fronts, metasomatic alteration of microcline at elevated temperatures and pressures, and ion-exchange in a porous column. Finally numerical calculations describing fluid flow in crystalline rock in the presence of a temperature gradient were compared with experimental results for quartzite

Evaluation of the solubility constants of the hydrated solid phases in the H2O-Al2O3-SO3 ternary system

International audienceDuring the acid processing of aluminosilicate ores, theprecipitation of a solid phase principally consisting of hydratedaluminium hydroxysulfates may be observed. The experimentalstudy of the H2O-Al2O3-SO3 ternary system at 25◦C and 101 kPaenabled to describe the solid-liquid equilibria and to identify the nature,the composition and the solubility of the solid phases which mayform during the acid leaching. To predict the appearance of thesealuminium hydroxysulfates in more complex systems, their solubilityconstants were calculated by modelling the experimental solubilityresults, using a geochemical reaction modelling software, CHESS.A model for non-ideality correction, based on the B-dot equation,was used as it was suitable for the considered ion concentrationrange. The solubility constants of three out of four solid phaseswere calculated: 104.08 for jurbanite (Al(SO4)(OH).5H2O), 1028.09for the solid T (Al8(SO4)5(OH)14.34H2O) and 1027.28 for the solidV (Al10(SO4)3(OH)24.20H2O). However the activity correction modelwas not suitable to determine the solubility constant of alunogen(Al2(SO4)3.15.8H2O), as the ion concentrations of the mixtures weretoo high and beyond the allowable limits of the model. Another ionicactivity correction model, based on the Pitzer equation for example,must be applied to calculate the solubility constant of alunogen