Pitzer Ion Interaction Research Articles

Physical Properties of Aqueous Solutions of Ionic Liquid, 1-Propyl-3-methylimidazolium Methyl Sulfate, at T = (298.15 to 328.15) K

Osmotic coefficients, electrical conductances, densities, viscosities, and refractive indices of ionic liquid, 1-propyl-3-methylimidazolium methyl sulfate [PrMIm]MSO4, with water have been measured at T = (298.15 to 328.15) K and atmospheric pressure. Experimental osmotic coefficients have been measured using the vapor pressure osmometry (VPO) method and correlated with Pitzer-ion interaction and modified NRTL (MNRTL) electrolyte models. Molar conductances of this system have been correlated with the low concentration chemical model (lcCM) of conductance equation, and then ion association constants have been obtained at different temperatures. Ion association constant values increase with increasing temperature. The apparent molar volumes at infinite dilution are estimated by the Redlich−Mayer and Pitzer equations. Viscosity B coefficients have been calculated from Jones−Dole equation. It was found that in the investigated range of concentrations the values of viscosity B coefficients are positive. The B coefficient decreases with an increase in temperature. The results are explained in terms of hydrophobic hydration of ionic liquid.

Modeling of ammonia speciation in anaerobic digesters

Anaerobic digestion of high-nitrogen wastes such as animal manure can be inhibited by high concentrations of un-ionized ammonia, NH 3 (aq). Understanding the toxicity of NH 3 (aq) to anaerobic digestion requires a method for determining its concentration. Previous work on ammonia toxicity in anaerobic digesters has utilized a simple equilibrium calculation for estimating NH 3 (aq) concentration from total ammonia, temperature, and pH. This approach is not appropriate for concentrated solutions. In this work, a speciation model for major solutes in anaerobic digesters, based on Pitzer's ion-interaction approach, is presented. Model simulations show that the simple equilibrium calculation (without corrections for non-ideal behavior) substantially overestimates NH 3 (aq) concentration for all but dilute digesters. This error in concentration determination increases with total solids content and is estimated to be greater than 40% for a digester fed dairy manure with 5% total solids or swine manure with 3% total solids. However, including an estimate of the activity coefficient for NH 4 + in the simple equilibrium calculation results in much more accurate estimates of NH 3 (aq) concentration. In this case, the estimated error is less than 10% in the absence of struvite precipitation at the highest total solids contents considered.

Experimental investigation of the stability and evaporation of sulfate and chloride brines on Mars

We have investigated the evaporation of concentrated magnesium and ferrous sulfate, and magnesium and ferric chloride brines as possible sources for liquid water on the surface of Mars, with special emphasis on the effect of freezing and crystallization of solutions. Experimental evaporation rates range from 0.04 mm h − 1 for 25 wt.% MgSO 4 at 271.9 K, to 0.19 mm h − 1 for 18 wt.% FeSO 4 at 270.5 K. For chloride solutions, evaporation rates range from 0.09 mm h − 1 for 40 wt.% FeCl 3 at 261.34 K, to 0.43 mm h − 1 for 20 wt.% MgCl 2 at 267.2 K. These evaporation rates are significantly lower than for pure water, i.e. 1.35 mm h − 1 at 273 K. Using the Pitzer ion interaction model, we show that the decrease in evaporation rate is due to lower water activity in concentrated solutions, down to 0.91 for saturated MgSO 4 and 0.97 for saturated FeSO 4, at their eutectic temperatures. For saturated MgCl 2 and FeCl 3, the calculated water activities are 0.57 and 0.60 at their respective eutectic temperatures. In addition, we show that the water activity drops significantly when salts are crystallizing, down to 0.17 and 0.21 for MgSO 4 and FeSO 4, respectively. Our experiments and calculations show that the water activity and evaporation rate are dependent on the hydration state of the precipitating salt, which is in turn controlled by the temperature and the relative humidity. Low-hydration state salts precipitate at lower humidity, with lower evaporation rates. Our study suggests that martian brines could remain stable for longer periods of time, at low temperatures and low humidity, than previously thought. Brines formed from these salts would be a more stable source of water on Mars, thus beneficial for any putative martian life, past and/or present.

Thermophysical Properties of Ionic Liquid, 1-Pentyl-3-methylimidazolium Chloride in Water at Different Temperatures

Osmotic coefficients, \({\phi}\), electrical conductance data, Λ, and refractive indices, nD, of aqueous solutions of the ionic liquid, 1-pentyl-3-methylimidazolium chloride [PnMIm]Cl have been measured at T = (298.15, 308.15, 318.15, and 328.15) K. Measurements of osmotic coefficients were carried out by the vapor-pressure osmometry method (VPO). Osmotic coefficient values show that ion–solvent interactions are stronger at lower temperature. The osmotic coefficients were correlated to the Pitzer-ion interaction and modified NRTL (MNRTL) models. From these data, mean molal activity coefficients, γ±, and excess Gibbs free energies, GE, have been calculated. Electrical conductance data have been applied for determination of association constants, Ka, and limiting molar conductances, Λ0, using the low concentration chemical model (lcCM). Calculated ion-association constant, Ka, values show that ion-association effects increase at high temperatures which is in agreement with osmotic coefficient results. Experimental results of refractive indices for the binary system are reported, and have been fitted by a polynomial expansion.

High temperature and high pressure volumetric properties of (methanol + [BMIM+][OcSO− 4]) mixtures

The (p, ρ, T) and some derived volumetric properties such as excess, partial and apparent molar volumes of [BMIM+][] in methanol at temperatures T = (298.15–398.15) K and pressures up to p = 40 MPa have been measured with a vibrating-tube densimeter. Measurements were made at seven concentrations of x = (0.0388, 0.1351, 0.2785, 0.4961, 0.7497, 0.9312 and 1.0) mole fraction of [BMIM+][]. The total uncertainty of density, temperature, pressure and concentration measurements were estimated to be less than 0.15 kg m−3, 15 mK, 5 kPa and 10−4 mole fraction, respectively. The uncertainties reported in this article are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The effect of temperature, pressure and concentration on the density and derived volumetric properties was studied. The measured densities were used to develop a Tait-type equation of state (EOS) for the mixture and the pure components. The derived values of apparent molar volumes were extrapolated to zero concentration using Pitzer's ion-interaction model to calculate the values of apparent molar volumes (or partial molar volumes) at infinite dilution. The method of correlation function integrals is used to study the structural and thermodynamic properties of dilute methanol + ILs mixtures. The structural properties, such as direct and total correlation function integrals and cluster size (coordination number), were calculated using the Krichevskii function concept and EOS for the mixture at infinite dilution.

Osmotic Coefficients and Refractive Indices of Aqueous Solutions of Ionic Liquids Containing 1-Butyl-3-methylimidazolium Halide at T = (298.15 to 328.15) K

Experimental results of the osmotic coefficients and refractive indices of aqueous solutions of ionic liquids containing 1-butyl-3-methylimidazolium chloride, [BMIm]Cl, and 1-butyl-3-methylimidazolium iodide, [BMIm]I, have been measured over the composition range of 3 mol·kg−1 at T = (298.15 to 328.15) K. The determination of experimental osmotic coefficients was performed by the vapor pressure osmometry method. The results show that osmotic coefficients increase when the concentration of ionic liquid and temperature increase. The osmotic coefficients were correlated to the Pitzer ion interaction and modified NRTL (MNRTL) models. From these data, mean activity coefficients and excess Gibbs free energies have been calculated. The results have been interpreted in terms of ion−solvent and ion−ion interactions and structural factors of the ionic liquid. Experimental results of refractive indices for the binary system are reported and have been fitted by a polynomial expansion.

Prediction of the solubility of HCl-MgCl2-H2O system at −5°C using the ion-interaction model

The component solubilities of the HCl-MgCl2-H2O system at −5°C were predicted by using the Pitzer ion interaction model and its extended Harvie and Weare model. The results indicated that the model supplies a good prediction of the above-mentioned system. The values of parameters of β(0), β(1), and Cφ of HCl and MgCl2 were obtained by using the same optimization methods as in the literature, while those of θMgH and ΨMgHCl were derived by extrapolating the published data of 5, 15, 25, 35, and 45°C, as well as coupling the activity coefficients with the solubility data. The comparison between the calculated results and the experimental data indicated that the Pitzer ion interaction model and its extended Harvie and Weare model are quite reliable in the solubility prediction.

NH4Cl + NH4NO3 + H2O Ternary Mixed Electrolyte System: Thermodynamic Modeling Based on Potentiometric Measurements

This work reports the results of the thermodynamic modeling of NH4Cl salt in the ternary NH4Cl (m1) + NH4NO3 (m2) + H2O mixed electrolyte system based on potentiometric measurements. The electrochemical measurements were performed, at similar constant ionic strengths, in different series of mixed salt solutions, each characterized by a fixed salt molal ratio r (where r = m1/m2 = 0.05, 1, 5, 10, and m1, m2 are the molalities of NH4Cl and NH4NO3, respectively). The galvanic cell used for collecting the potentiometric data consisted of a solvent polymeric (PVC) NH4+ selective membrane electrode (NH4+ ISE) and an Ag/AgCl electrode. Pitzer ion-interaction equations for mixed salts were used for modeling the nonideal behavior of the system, over the ionic strength ranging from 0.01 mol·kg−1 up to about 6 mol·kg−1, at 298.15 K. On the basis of the obtained Pitzer ion-interaction parameters, the osmotic coefficients, solvent activities, and excess Gibbs free energies were also determined for these investigated te...

Influence of alkyl chain on the thermodynamic properties of aqueous solutions of ionic liquids 1-alkyl-3-methylimidazolium bromide at different temperatures

Osmotic coefficients ϕ, mean activity coefficients γ ±, vapor pressure p data, and excess Gibbs free energies G E of aqueous solutions of three ionic liquids 1-propyl-3-methylimidazolium bromide [PMIm]Br, 1-pentyl-3-methylimidazolium bromide [PnMIm]Br, and 1-hexyl-3-methylimidazolium bromide [HMIm]Br were determined by the vapor pressure osmometry method at four temperatures (298.15 K to 328.15 K) in intervals 10 K. From the comparison of osmotic coefficients it follows that aqueous solution of [PMIm]Br shows a more pronounced deviation from Debye–Hückel limiting law (DHLL) and vapor pressure depression more than the other studied ionic liquids which was interpreted in terms of hydrophobic interactions. The Pitzer-ion interaction and MNRTL electrolyte models satisfactorily correlate experimental osmotic coefficient data with good precision. The parameters of the Pitzer-ion interaction model are used to calculate the mean molal activity coefficients and excess Gibbs free energies.

Reactive transport modeling of column experiments on the evolution of saline–alkaline waste solutions

Leakage of saline–alkaline tank waste solutions often creates a serious environmental contamination problem. To better understand the mechanisms controlling the fate of such waste solutions in the Hanford vadose zone, we simulated reactive transport in columns designed to represent local site conditions. The Pitzer ion interaction module was used, with principal geochemical processes considered in the simulation including quartz dissolution, precipitation of brucite, calcite, and portlandite, multi-component cation exchange, and aqueous complexation reactions. Good matches were observed between the simulated and measured column data at ambient temperature (∼ 21 °C). Relatively good agreement was also obtained at high temperature (∼ 70 °C). The decrease of pH at the plume front is examined through formation of secondary mineral phases and/or quartz dissolution. Substantial formation of secondary mineral phases resulting from multi-component cation exchange suggests that these phases are responsible for a decrease in pH within the plume front. In addition, a sensitivity analysis was conducted with respect to cation exchange capacity, selectivity coefficient, mineral assemblage, temperature, and ionic strength. This study could serve as a useful guide to subsequent experimental work, to thermodynamic models developed for the concentrated solutions at high ionic strength and to other types of waste plume studies.

Potentiometric investigation of the thermodynamic properties of the ternary mixed (NH 4Cl + CaCl 2 + H 2O) electrolyte system

In this work, the results of a potentiometric investigation of the thermodynamic properties of the ternary NH 4Cl + CaCl 2 + H 2O mixed electrolyte system are presented. The reported results are based on the experimental data of a galvanic cell, combining a solvent polymeric ammonium ion-selective membrane electrode (NH 4 + ISE), and an Ag/AgCl electrode. The potentiometric measurements were performed at 298 K by using different series of mixed salt solutions, each characterized by a fixed salt molal ratio ( r = m N H 4 Cl / m CaC l 2 = 0.1 , 0.2 , 1 , and 5 ), but with similar ionic strengths within the series. The semi-empirical Pitzer ion-interaction theory for mixed salts was used for modeling this ternary electrolyte system over the ionic strength ranging from about 0.05 to 5.5 mol/kg. Besides the determination of the mixed θ N H 4 Ca and Ψ N H 4 CaCl ion-interaction parameters, the impact of the effect of the higher order electrostatic terms were also analyzed for this mixed ternary electrolyte system. Finally, based on the potentiometric experimental data and the determined mixing parameters, the calculated values of the osmotic coefficients, the excess Gibbs free energies and the water activities ( a w) were determined for the whole series of the studied ternary mixed electrolyte system.

A Potentiometric, Spectrophotometric and Pitzer Ion-Interaction Study of Reaction Equilibria in the Aqueous H+-Al3+, H+-Oxalate and H+-Al3+-Oxalate Systems up to 5 mol⋅dm−3 NaCl

The aqueous speciation of the mixed H+-Al3+-oxalate (L) system at equilibrium was determined by potentiometry in solutions of 0.1, 1.6 and 3.0 mol⋅dm−3 NaCl and by spectrophotometry in solutions of 5.0 mol⋅dm−3 NaCl at 298.2 K. These experiments enabled the description of the ionic strength dependence of the AlL+,AlL2− and AlL33− species and the formulation of a Pitzer ion-interaction model. The accuracy of our aqueous speciation calculations for this mixed system was also strengthened by experimental validation of previously-established models for the protonation of oxalate in the H+-L system and of the hydrolysis of Al3+ in the H+-Al3+ system. The latter system also enabled the formulation of a new Pitzer ion-interaction model for the heptavalently-charged Al13O4(OH)247+ Keggin ion to 3.0 mol⋅dm−3 NaCl. The proposed set of parameters can be used to predict chemical speciation in the mixed H+-Al3+-L system in aqueous solutions of NaCl up to 5.0 mol⋅dm−3 (5.6 mol⋅kg−1 NaCl) at 298.2 K.

Chromium(III) Hydroxide Solubility in the Aqueous K+-H+-OH−-CO2-HCO 3 − -CO 3 2− -H2O System: A Thermodynamic Model

Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures of CO2(g) (0.003 or 0.03 atm.), and as functions of K2CO3 concentrations (0.01 to 5.8 mol⋅kg−1) in the presence of 0.01 mol⋅dm−3 KOH and KHCO3 concentrations (0.001 to 0.826 mol⋅kg−1) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions. A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used to interpret the solubility data. Only two aqueous species [Cr(OH)(CO3) 2 2− and Cr(OH)4CO 3 3− ] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO2(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log 10 K° values of reactions involving these species [{Cr(OH)3(am) + 2CO2(g)⇌Cr(OH)(CO3) 2 2− +2H+} and {Cr(OH)3(am) + OH−+CO 3 2− ⇌Cr(OH)4CO 3 3− }] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available for comparisons.

TERNARY NaCl+LiCl+H2O MIXED ELECTROLYTE SYSTEM: DETERMINATION OF ACTIVITY COEFFICIENTS BASED ON POTENTIOMETRIC METHOD

The mean activity coefficients for NaCl in a ternary electrolyte system were determined by the potentiometric method, at 25°C, using a solvent polymeric (PVC) sodium-selective membrane electrode (Na+ ISE), containing N,N′-dibenzyl-N,N′-diphenyl-1,2-phenylenedioxydiacetamide as ionophore, and combined with an Ag/AgCl electrode. The potentiometric measurements were performed at the same ionic strengths in different series of mixed salt solutions, each characterized by a fixed salt molal ratio r (where r = m1/m2 = 1, 10, 50, 100). The nonideal behavior of the ternary NaCl(m1) + LiCl(m2) + H2O electrolyte system was described based on the Pitzer ion-interaction model for mixed salts over the ionic strength ranging from 0.01 up to about 4 mol/kg. Two- and three-particle Pitzer interaction parameters for a mixed electrolyte system were determined based on potentiometric data, and the critical role of potentiometric selectivity coefficient (K 12) of ISE as limiting factor in the potentiometric measurements was analyzed.

An improved model incorporating Pitzer’s equations for calculation of thermodynamic properties of pore solutions implemented into an efficient program code

Salts in porous building materials are not only considered as a major cause of damage but also strongly affect the hygric and capillary transport properties of such materials. This paper describes a model implemented into an efficient computer code that can be used for predicting the non-ideal behavior of pore solutions of complex composition. The model is based on the Pitzer ion interaction approach. Model parameters are provided and validated for the system Na+–K+–Cl-–NO3-–SO42-–H2O in the temperature range relevant to most buildings, i.e. from the temperature of freezing to 45 °C. This offers a number of potential applications including the incorporation in chemical equilibrium and humidity and moisture transport models.

Dissociation constants of protonated methionine species in seawater media

The dissociation constants (p K 1 ⁎ and p K 2 ⁎) for methionine have been measured in artificial seawater as a function of salinity ( S = 5 to 35) and temperature (5 to 45 °C). The seawater p K 2 ⁎ values were lower than the values in NaCl at the same ionic strength while the p K 1 ⁎ values in seawater were lower only at S = 35. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been used to determine the formation of Mg 2+ complexes and Pitzer interaction parameters for Mg 2+ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of p K 1 ⁎ and p K 2 ⁎ between NaCl and seawater. This study demonstrates that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.

Thermodynamic investigation of KCl in the ternary KCl/LiCl/ H 2 O mixed electrolyte system based on potentiometric method

The results of a thermodynamic investigation of KCl salt in the ternary KCl+LiCl+H 2O electrolyte system by potentiometric method are reported in this work. The experimental potentiometric data were obtained from a galvanic cell by combining a solvent polymeric (PVC) potassium-selective membrane electrode (K + ISE), containing Valinomycin as ionophore, and an Ag/AgCl electrode. The measurements were performed, at similar constant ionic strengths, in different series of mixed salt solutions, each characterized by a fixed salt molal ratio r (where r = m 1 / m 2 = 0.1 , 0.2 , 1 , 5 , 10 , and m 1 , m 2 are the molalities of KCl and LiCl, respectively). The non-ideal behaviour of the system was described on the base of the Pitzer ion-interaction model for mixed salts, over the ionic strength ranging from 0.01 up to about 5 mol/kg, at 298.15 K. Based on the obtained Pitzer ion-interaction parameters, the osmotic coefficients, solvent activities, and excess Gibbs free energies were determined for these investigated ternary electrolyte systems.

Solubility prediction in the ternary systems NaCl–RbCl–H 2O, KCl–CsCl–H 2O and KBr–CsBr–H 2O at 25 ∘C using the ion-interaction model

The component solubilities in NaCl–RbCl–H 2O, KCl–CsCl–H 2O and KBr–CsBr–H 2O systems at 25 ∘C were calculated by using the Pitzer ion interaction model and its extended HW models. Excellent agreement with experimental solubilities indicated that the models can be successfully used to calculate the component solubilities. This study affords the necessary parameters for solubility predictions of complicated systems containing rubidium and caesium and establishes a theoretical basis for the separation of these valuable metals from salt lake brine.

Application of the Pitzer ion interaction model to isopiestic data for the Fe 2(SO 4) 3–H 2SO 4–H 2O system at 298.15 and 323.15 K

Recent isopiestic studies of the Fe 2(SO 4) 3–H 2SO 4–H 2O system at 298.15 K are represented with an extended version of Pitzer’s ion interaction model. The model represents osmotic coefficients for aqueous {(1 − y)Fe 2(SO 4) 3 + yH 2SO 4} mixtures from 0.45 to 3.0 m at 298.15 K and 0.0435 ⩽ y ⩽ 0.9370. In addition, a slightly less accurate representation of a more extended molality range to 5.47 m extends over the same y values, translating to a maximum ionic strength of 45 m. Recent isopiestic data for the system at 323.15 K are represented with the extended Pitzer model over a limited range in molality and solute fraction. These datasets are also represented with the usual “3-parameter” version of Pitzer’s model so that it may be incorporated in geochemical modeling software, but is a slightly less accurate representation of thermodynamic properties for this system. Comparisons made between our ion interaction model and available solubility data display partial agreement for rhomboclase and significant discrepancy for ferricopiapite. The comparisons highlight uncertainty remaining for solubility predictions in this system as well as the need for additional solubility measurements for Fe 3+-bearing sulfate minerals. The resulting Pitzer ion interaction models provide an important step toward an accurate and comprehensive representation of thermodynamic properties in this geochemically important system.

Thermodynamic investigation of a ternary mixed electrolyte (NaCl/MgCl 2/H 2O) system using Na + solvent polymeric membrane ion-selective electrode

This work reports the results of a thermodynamic investigation of the ternary NaCl–MgCl 2–H 2O mixed electrolyte system. The potentiometric measurements were performed at 298 K, using a galvanic cell by combining a solvent polymeric sodium ion-selective membrane electrode (Na + ISE), containing a mixture of N, N′-dibenzyl- N, N′-diphenyl-1,2-phenylene-dioxydiacetamide as ionophore, and an Ag/AgCl electrode. Different series of mixed salt solutions, each characterized by a fixed salt molal ratio r ( r = m NaCl / m MgC l 2 = 0.100 , 0.199, 0.995, 4.990 and 10.364) but with similar ionic strengths, were used in this investigation. The modeling of the ternary electrolyte system was based on the Pitzer ion-interaction semi-empirical theory for mixed salts, over the ionic strength ranging from 0.05 to 4.3 mol/kg. Pitzer ion-interaction parameters for mixed salts including the effect of the higher-order electrostatic terms were determined for this system. Moreover, based on the potentiometric experimental data and the determined mixing parameters, the values of the mean activity coefficients, the osmotic coefficients, the excess Gibbs free energies and the water activities ( a w) were reported for the whole series of the studied ternary mixed electrolyte systems. Finally, the impact of the magnitude of the potentiometric selectivity coefficient of this Na + ISE on the quality of the potentiometric data revealed that Nernst equation could suitably be used for the evaluation of mean activity coefficients (with at least 3 decimal numbers), for the ionic strength beyond 0.25 mol/kg and for mixed electrolyte systems with molal salt ratio higher than r = m NaCl / m MgC l 2 ≥ 5 .