Consistency issues of aqueous solubility data and solution thermodynamics of electrolytes (original) (raw)
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Fluid Phase Equilibria, 2015
A new high pressure cell was developed to measure the high pressure phase behavior of gas + aqueous salt solutions and validated through the measurement, and comparison against literature data, of two systems, the H 2 O + CO 2 and H 2 O + CO 2 + NaCl, at temperatures up to 363 K and pressures up to 13 MPa. As previously reported by others, a salting out effect on the carbon dioxide solubility in water by NaCl is observed, decreasing its solubility as the salt concentration increases.
Journal of Chemical Education, 2014
The heterogeneous equilibrium of the solubility of calcium hydroxide in water is used to predict both its solubility product from solubility and solubility values from solubility product when inert salts, in any concentration, are present. Accepting the necessity of including activity coefficients to treat the saturated solution of calcium hydroxide (and by extension, all electrolyte solutions) and the inadequacy of any general or nonspecific equation (such as the Debye−Huckel limiting law or Davies equations) to calculate activity coefficients of 1:2 electrolytes, our results uncover (i) how the inclusion of ion pairs in the last mentioned equations makes them adequate for low ionic strength solutions and (ii) the need of sophisticated models, such as the ion-interaction Pitzer equations, for calculating the activity coefficients when ionic strength is high. In addition, we have developed a set of MATLAB scripts and propose the use of the free code PHREEQC version 3 to perform all the calculations described in the article. The tasks proposed here can be complemented with the experimental determination of the solubility of calcium hydroxide in water along with the experimental checking of its solubility in aqueous salt solutions during several lab sessions. Experimental guidance is provided as Supporting Information.
Journal of Physical and Chemical Reference Data, 2012
The alkaline earth carbonates are an important class of minerals. This volume compiles and critically evaluates solubility data of the alkaline earth carbonates in water and in simple aqueous electrolyte solutions. Part 1, the present paper, outlines the procedure adopted in this volume in detail, and presents the beryllium and magnesium carbonates. For the minerals magnesite (MgCO 3), nesquehonite (MgCO 3 Á3H 2 O), and lansfordite (MgCO 3 Á5H 2 O), a critical evaluation is presented based on curve fits to empirical and=or thermodynamic models. Useful side products of the compilation and evaluation of the data outlined in the introduction are new relationships for the Henry constant of CO 2 with Sechenov parameters, and for various equilibria in the aqueous phase including the dissociation constants of CO 2 (aq) and the stability constant of the ion pair MCO 0 3 ðaqÞ (M ¼ alkaline earth metal). Thermodynamic data of the alkaline earth carbonates consistent with two thermodynamic model variants are proposed. The model variant that describes the Mg 2þ ÀHCO À 3 ion interaction with Pitzer parameters was more consistent with the solubility data and with other thermodynamic data than the model variant that described the interaction with a stability constant. V
Chemical engineering transactions, 2015
The electrolyte thermodynamic models have been extensively studied for carbon dioxide – water system for the prediction of vapour liquid equilibrium at low pressures. However, no guidelines are available for selection of electrolytic models which are applicable at high pressure for prediction of thermodynamic properties. In this study, solubility prediction of limited Debye Huckel (DH), Pitzer Debye Huckel (PDH) and modified Three Characteristic Parameter Correlation (mTCPC) electrolyte models have been tested for a wide range of temperature (273 – 453 K) and pressure (0.1 – 7.2 MPa).The comparative study shows that introduction of electrolyte model improves the prediction accuracy when physical solubility of gas is low, either in high temperature or low pressure region. The mTCPC model gives improved prediction than nonelectrolyte model but requires additional parameters and complex calculations. New values for binary interaction parameters of UNIFAC for carbon dioxide – water syst...
The Journal of Physical Chemistry, 1990
The semiempirical specific-interaction model developed by Pitzer is applied to aqueous salt solutions that also contain a dissolved nonelectrolyte. Pitzer's model is used to describe phase equilibria for aqueous solutions containing either sodium chloride and carbon dioxide to 600 bar or sodium sulfate and carbon dioxide to 200 bar at several temperatures. In contrast to predictions reported by previous authors, we find that over wide ranges of pressure and temperature, Pitzer's equations provide an excellent description of salt solubilities in these ternary systems.
Industrial & Engineering Chemistry Research, 2017
Calcite and barite are two of the most common scale minerals that occur in various geochemical and industrial processes. Their solubility predictions at extreme conditions (e.g., up to 250 o C and 1,500 bars) in the presence of mixed electrolytes are hindered by the lacks of experimental data and thermodynamic model. In this study, calcite solubility in the presence of high Na 2 SO 4 (i.e., 0.0407 m Na 2 SO 4) and barite solubility in a synthetic brine at up to 250 o C and 1,500 bars were measured using our high temperature high pressure geothermal apparatus. Using this set of experimental data and other thermodynamic data from a thorough literature review, a comprehensive thermodynamic model was developed based on the Pitzer theory. In order to generate a set of Pitzer theory virial coefficients with reliable temperature and pressure dependencies which are applicable to a typical water system (i.e., Na-K-Mg-Ca-Ba-Sr-Cl-SO 4-CO 3-HCO 3-CO 2-H 2 O) that may occur in geochemical and industrial processes, we simultaneously fitted all available mineral solubility, CO 2 solubility, as well as solution density. With this model, calcite and barite solubilities can be accurately predicted under such extreme conditions in the presence of mixed electrolytes. Furthermore, the 95% confidence intervals of the estimation errors for solution density predictions are within 4×10-4 g/cm 3. The relative errors of CO 2 solubility prediction are within 0.75%. The estimation errors of the saturation index mean values for gypsum, anhydrite, and celestite are within ± 0.1, and that for halite is within ± 0.01, most of which are within experimental uncertainties.
Monatshefte f�r Chemie Chemical Monthly, 1993
The stoichiometric solubility constant of eitelite (NaMgo.sC03 + 2H + ~_ Na* + 05Mg 2 § + COz(g) + 1t20, log */(ps0 = 14.67+0.03 was determined at I= 3 m (tool kg "1) (NaCl04) and 25~ The stability of magnesium (hydrogen-)earbonato complexes in this ionic medium was explicitely taken into account. Consequently, trace activity coefficients of free ionic species, calculated from the Pitzer model with ion-interaction parameters from the literature, were sufficient for an evaluation of the thermodynamic solubility constants and Gibbs energies of formation for eitelite (-1039.88 +_ 0.60), magnesite (-1033.60 + 0.40), hydromagnesite (-1174.30 + 0,50), nesquehonite (--1724.67 +_ 0.40), and brucite (-835.90 + 0.80 kJ-mort). The increasing solubilities of nesquehonite and eitelite at higher sodium carbonate molalities were explained by invoking a magnesium dicarbonato complex (Mg z+ + 2C0Z3 -~_~ Mg(CO3)Z2 -, log 62 = 3.90+0.08). A set of ion-interaction parameters was obtained from solubility and dissociation constants for carbonic acid in 1 to 35m NaCl04 media (0FICO~ ,cao4 = 0.081, 0c03Z-,ao~ -= 0.071, VNa +, HCO3, ca04 = --0.019, VN~, +, co32-, ao~-= --0.006, ~cao-~, coz = -0.076) which reproduce these constants to 0.02 units in log K. The following Pitzer parameters are consistent with the previously studied formation of magnesium (hydrogen-)carbonato complexes in 3m NaCl04 (~ggg2+ nco~-, cao4 = -0.36, Lcao'~co3 = 0.081). The model and Gibbs functions of solid phases derived here reproduce original solubility data (-log [H+], [MgZ+]toO measured in perchlorate medium within experimental uncertainty.
Iranian Journal of Oil and Gas Science and Technology, 2017
In this work, the performance of four electrolyte models for prediction the osmotic and activity coefficients of different aqueous salt solutions at 298 K, atmospheric pressure and in a wide range of concentrations are evaluated. In two of these models, (electrolyte Non-Random Two-Liquid e-NRTL and Mean Spherical Approximation-Non-Random Two-Liquid MSA-NRTL), association between ions of opposite charges for simplification purposes is ignored and in the other two ones, (Associative Mean Spherical Approximation-Non-Random Two-Liquid AMSA-NRTL and Binding Mean Spherical Approximation BiMSA) association and solvation effects are considered. The predictions of these four models for the osmotic and activity coefficients of electrolyte solutions at 298 K and atmospheric pressure are compared with the experimental data reported in the literature. This comparison includes, 28 different aqueous salt solutions including thio-cyanates, perchlorates, nitrates, hydroxides, quaternary ammonium sal...