Pitzer Ion-interaction Model Research Articles

Advanced thermodynamic approach to adsorption of charged adsorbates from aqueous electrolyte solutions

This study present estimation of the thermodynamic parameters and the influence of ionic activity coefficient on the thermodynamic equilibrium constant of adsorption of phosphates on fly ash. The adsorption was conducted over a wide range of initial phosphate concentrations at different pH values pH = (3; 7; 10). The adsorption results were treated using the Langmuir, Freundlich and Sips adsorption isotherms, which provide information about the maximum adsorption capacity. The Langmuir and Sips isotherms were a satisfactory fit to the adsorption data, especially at pH = 3, with an acceptable regression coefficient over the entire concentration range, Langmuir (r2 = 0.9737) and Sips (r2 = 0.9969). The estimated maximum phosphate sorption capacity of fly ash was 6.21 ± 0.68 (mmol·g−1) according to Langmuir and 4.19 ± 0.16 (mmol·g−1) according to the Sips model, at pH = 3.0. However, there is no data in the published literature for estimating the thermodynamic parameters of the phosphate adsorption process using thermodynamic models for activity coefficients. Novel approach of this paper was determination of the thermodynamic equilibrium constant and Gibbs free energy, using the Pitzer ion-interaction model to predict the nature of adsorption. The Pitzer-ion interaction model was used for the mixed ionic systems, taking into consideration the effect of other present ions besides phosphates in the equilibrium solution resulting from fly ash desorption. The procedure for comprehensive estimation of the ion activity coefficient at maximum adsorption capacity and the dimensionless thermodynamic equilibrium constant using Langmuir's and Sips’s constants was presented. The calculated value of the phosphate activity coefficient in the equilibrium solution was γH2PO4,e = 0.7003 ± 0.0027 and the converted molar activity coefficient was γH2PO4,e = 0.6903 ± 0.0027. The estimated values of Gibbs free energy were: ΔGL = −6.788 ± 0.521 kJ·mol−1 based on Langmuir equilibrium constant and ΔGa = −7.707 ± 0.527 kJ·mol−1 based on activity and thermodynamic equilibrium constant. According to Sips model, the adsorption process is even more spontaneous, with the Gibbs free energy calculated using the phosphate activity coefficient and the thermodynamic equilibrium constant, ΔGa = −9.707 ± 0.617 kJ·mol−1. Consideration of the ionic activity coefficient is particularly important for large, charged adsorbates at higher concentrations, as the absolute difference in free energy for adsorption is app. 12 %. The scientific contribution is reflected in obtaining the necessary and more accurate information for the improvement of adsorption processes and possibly for the upgrading of fly ash in overall wastewater treatment technology.

Solid-liquid phase equilibria and theoretical simulation of the quaternary system NaBr + KBr + MgBr2 + H2O and its subsystem NaBr + MgBr2 + H2O at 308.2 K and 1–500 bar

Solid-liquid phase equilibria of bromine salt can be indicative of Br evolution in Br-rich underground brines of Sichuan Basin in China. Consequently, the solid–liquid phase equilibria of the ternary subsystem NaBr + MgBr2 + H2O and quaternary system NaBr + KBr + MgBr2 + H2O at 308.2 K are determined by the isothermal dissolution equilibrium method. Then, Pitzer ion interaction model and particle swarm optimal algorithm are used to predict the phase equilibria of the systems listed above. The calculated solubilities are in good agreement with the experimental data.Considering the pressure conditions in deep strata, furthermore, we develop a thermodynamic prediction model of the phase equilibria for the systems changing with pressure. The thermodynamic volume properties of solution at 308.2 K with increasing pressure (1–500 bar) are evaluated. The unreported parameters of pressure dependency (Av,V¯MX(aq)0,βMX(0),v,βMX(1),v,CMXv) in Pitzer model at 308.2 K in the studied systems of this work are fitted accordingly. As a result, the effects of pressure on the phase equilibria are investigated in detail, and phase diagrams of the systems at 1–500 bar are also drawn and discussed. This work can provide important thermodynamic data for the salt mineral exploitation of the actual deep strata brines.

Dilution enthalpies of the binary systems (LiBO2 + H2O) and (LiB5O8 + H2O) and the ion interactions at 308.15 K

Microcalorimeter measured the dilution enthalpies of the binary systems (LiBO2 + H2O) and (LiB5O8 + H2O) at 308.15 K and 0.1 MPa. Based on the Pitzer theory of electrolytes, their apparent molar enthalpies and the Pitzer single electrolyte parameters at 308.15 K were carried out by fitting the experimental data for the first time. Moreover, the calculated apparent molar enthalpies of LiBO2 and LiB5O8 aqueous solution according to the Pitzer ion-interaction model were consistent well with the experimental values, manifesting the high reliability of this study.

Phase Equilibrium of the Ternary System Na2SO3–Na2SO4–H2O at 293.15, 313.15, and 353.15 K

The phase equilibrium data of the ternary system Na2SO3–Na2SO4–H2O at 293.15, 313.15, and 353.15 K were determined by the isothermal dissolution method. There are one invariant point, two univariant isothermal dissolution curves, and three crystallization regions at each temperature. As the temperature increases from 293.15 to 313.15 K, the solubilities of both Na2SO4 and Na2SO3 increase. The single crystallization region of Na2SO4 decreases, while the single crystallization region of Na2SO3 increases. When the temperature increases from 313.15 to 353.15 K, the solubilities of both Na2SO4 and Na2SO3 decrease. The single crystallization region of Na2SO4 decreases, and the single crystallization region of Na2SO3 is basically unchanged. Furthermore, based on the solubility data, the Pitzer ion interaction model was used to calculate the relevant Pitzer parameters and then to calculate the solubilities of Na2SO3 and Na2SO4 theoretically. The calculated Na2SO3 and Na2SO4 solubilities basically agree with the experimental values. The data obtained in this work have important implications for the design and optimization of the Na2SO3 crystallization process from resorcinol production wastewater.

Apparent molar heat capacities of aqueous solutions of LiBO2, NaBO2, KBO2, Na2B4O7 and K2B4O7 at T = (298.12, 313.13 and 328.14) K using a Picker flow calorimeter

The apparent molar heat capacities of LiBO2(aq), NaBO2(aq), KBO2(aq), Na2B4O7(aq) and K2B4O7(aq) solutions at molalities from 0.01 to 2.6 mol·kg−1, and at temperatures T = (298.12, 313.13 and 328.14) K have been determined using a Picker flow calorimeter built in this work. Further, the standard heat capacities of these solutes were derived from the experimental data by extrapolation to infinite dilution using the Pitzer ion-interaction model. The group contribution method is used to calculate the standard molar heat capacities of tetraborate ion in three equilibria for different assumptions, among which the prediction on the assumption that the standard molar heat capacity of reaction for the association reaction is zero is the most reasonable, and the results are in good agreement with the experimental data.

Measurements and predictions of mineral solubilities in the quaternary systems NaCl + KCl + SrCl2 + H2O, NaCl + MgCl2 + SrCl2 + H2O and KCl + MgCl2 + SrCl2 + H2O at 308 K

This paper describes the measurements and predictions for mineral solubilities in the quaternary systems NaCl + KCl + SrCl2 + H2O, NaCl + MgCl2 + SrCl2 + H2O, KCl + MgCl2 + SrCl2 + H2O and subsystem MgCl2 + SrCl2 + H2O at 308 K in detail. The isothermal dissolution equilibrium method was used to determine the solubility of each salt in systems experimentally. Each stable phase diagram was constructed according to the measured results. The ternary system MgCl2 + SrCl2 + H2O has two invariant points, three solubility curves and three crystallization regions (MgCl2·6H2O, SrCl2·2H2O and SrCl2·6H2O). There is one invariant point, three solubility curves and three crystallization regions (NaCl, KCl and SrCl2·6H2O) in the quaternary system NaCl + KCl + SrCl2 + H2O. Two invariant points, five solubility curves and four crystallization regions (NaCl, MgCl2·6H2O, SrCl2·2H2O and SrCl2·6H2O) are included in the quaternary system NaCl + MgCl2 + SrCl2 + H2O. In the quaternary system KCl + MgCl2 + SrCl2 + H2O, the double salts KCl·MgCl2·6H2O were found as its ternary system KCl + MgCl2 + H2O, thus this quaternary system contains three invariant points, seven solubility curves and five crystallization regions (KCl + MgCl2·6H2O + KCl·MgCl2·6H2O + SrCl2·2H2O + SrCl2·6H2O). Using the fitted mixing parameter ΨMg, Sr, Cl and the Pitzer parameters available in literatures, the phase equilibria of four systems listed above were predicted with the Pitzer ion interaction model. The calculations are in adequate agreement with the experimental values.

Modeling Solubility of Anhydrite and Gypsum in Aqueous Solutions: Implications for Swelling of Clay-Sulfate Rocks

The swelling of clay-sulfate rocks is a well-known phenomenon often causing threats to the success of various geotechnical projects, including tunneling, road and bridge construction, and geothermal drilling. The origin of clay-sulfate swelling is usually explained by physical swelling due to clay expansion combined with chemical swelling associated with the transformation of anhydrite (CaSO4) into gypsum (CaSO4∙2H2O). The latter occurs through anhydrite dissolution and subsequent gypsum precipitation. Numerical models that simulate rock swelling must consider hydraulic, mechanical, and chemical processes. The simulation of the chemical processes is performed by solving thermodynamic equations, which usually contribute a significant portion of the overall computation time. This paper employs feed-forward neural network (FFNN) and cascade-forward neural network (CFNN) models trained with a Bayesian regularization (BR) algorithm as an alternative approach to determine the solubility of anhydrite and gypsum in the aqueous phase. The network models are developed using calcium sulfate experimental data collected from the literature. Our results indicate that the FFNN-BR is the most accurate model for the regression task. The comparison analysis with the Pitzer ion interaction model as well as previously published data-driven models shows that the FFNN-BR model is highly accurate in determining the solubility of sulfate minerals in acid and salt-containing solutions. We conclude from our results that the FFNN-BR model can be used to determine the solubility of anhydrite and gypsum needed to address typical subsurface engineering problems such as swelling of clay-sulfate rocks.

Volumetric Properties for the Aqueous Solution of Yttrium Trichloride at Temperatures from 283.15 to 363.15 K and Ambient Pressure

To effectively develop the rare earth elements resources from the geothermal waters, it is essential to understand the volumetric properties of the aqueous solution system to establish the relative thermodynamic model. In this study, densities of YCl3 (aq) at the molalities of 0.08837–1.60639 mol·kg−1 from 283.15 K to 363.15 K at 5 K intervals and ambient pressure were measured experimentally by an Anton Paar digital vibrating-tube densimeter. Based on experimental data, the volumetric properties including apparent molar volume (Vϕ) and the coefficient of thermal expansion of the solution (α) of the binary systems (YCl3 + H2O) were derived. The 3D diagram (mi, T, Vϕ) of apparent molar volumes against temperature and molality was plotted. On the basis of the Pitzer ion-interaction model of electrolyte, the Pitzer single-salt parameters ( β MX 0 v , β MX 1 v , and C MX v ) for YCl3 and temperature-dependence equation F(i, p, T) = a1 + a2ln(T/298.15) + a3(T-298.15) + a4/(620-T) + a5(T-227) as well as their coefficients ai (i = 1–5) in the binary system were obtained for the first time. The values of Pitzer single-salt parameters of YCl3 agree well with the calculated values corresponding to the temperature-dependence equations, indicating that single-salt parameters and temperature-dependent formula obtained in this work are reliable.

Measurement and modeling of mean activity coefficients in ternary electrolyte system (Nicl2/Triton X-100/H2O) at T=298.15 ± 0.1 K

In this work, the results relating to the thermodynamic properties for the ternary electrolyte system of (NiCl2 + Triton X-100 + water) using the potentiometric method were reported at T = 298.15 K. The electromotive force measurements were carried out on the galvanic cell without liquid junction of the type: Ni2+-ISE | NiCl2 (m), Triton X-100 (%wt.), H2O (100-%wt.) | AgCl|Ag over total ionic strengths from 0.0010 to 6.0000 mol.kg-1 for different percentage mass fraction of Triton X-100 (%wt. = 0.0, 1.0, 2.5, 5.0, 7.5 and 10.0). The mean activity coefficients of NiCl2 were determined by using potentiometric data. Then, the mean activity coefficients of NiCl2 were correlated with Pitzer ion interaction model and TCPC model. The Pitzer ion-interaction parameters (βo, β1 and C^∅) and the adjustable parameters (b and S) of TCPC model were determined by correlating of data for the series under investigated system. The Pitzer ion interaction parameters were used to calculating of thermodynamic properties such as the osmotic coefficients and the excess Gibbs energy of solution. The result showed that the Pitzer ion interaction model could be used to investigation of the system, successfully.

Volumetric properties of the ternary system (CsCl + Cs2SO4 + H2O) and its subsystems from 283.15 to 363.15 K and atmospheric pressure: Experimental and thermodynamic model

The salt-water interactions on single salt aqueous solutions of cesium sulfate and cesium chloride, as well as their mixing solutions, have been investigated by a combination of density measurements by an Anton Paar Digital vibrating-tube densimeter and the correction of the Pitzer model of electrolyte. The volumetric properties including apparent molar volume (Vϕ) and the coefficient of thermal expansion of the solution (α) of the binary systems (CsCl + H2O), (Cs2SO4 + H2O) and the ternary system (CsCl + Cs2SO4 + H2O) from 283.15 to 363.15 K at 5 K intervals and atmospheric pressure were derived. Variation trends of these volumetric properties against temperature and molality were revealed minutely. The Pitzer single salt parameters (βMX0v, βMX1v and CMXv, MX = CsCl and Cs2SO4), mixing ion-interaction parameters (θCl,SO4v and ψCs,Cl,SO4v) as well as the correlation coefficient ai in the temperature-dependence equation (F(i, p, j) = a1 + a2ln(T/298.15) + a3(T-298.15) + a4/(620-T) + a5/(T-227)) have been obtained according to Pitzer ion-interaction model of electrolytes. These results are helpful to understanding the ion-interaction of aqueous solutions.

Model development for estimating calcium sulfate dihydrate, hemihydrate, and anhydrite solubilities in multicomponent acid and salt containing aqueous solutions over wide temperature ranges

Thermodynamic solubility of calcium sulfate in multicomponent electrolyte aqueous solutions is of significant importance in many disciplines in science and engineering. A knowledge of environmental chemistry and aqueous solubility of calcium sulfate and several of its hydrates; anhydrite (CaSO4), hemihydrate (CaSO4.0.5H2O), and dihydrate (CaSO4.2H2O); in acid and salt-containing media is of huge practical and theoretical importance. In this study, a solubility calculation model was developed based on coupling of Least Squares Support Vector Machine and Coupled Simulated Annealing (CSA-LSSVM) to model the solubility of various forms of calcium sulfate in aqueous solutions over wide temperature ranges. Comparing the model results to 3079 experimental data gathered from the literature yields a correlation coefficient of 0.9897 and RMSE of 0.0068. The model is able to present accurate solubility results for calcium sulfate dihydrate (CaSO4.2H2O) in aqueous solutions containing H2SO4, ZnSO4, CuSO4, NiSO4, MnSO4, H3PO4, NaCl, CaCl2, MgCl2, KCl, FeCl2, Na2SO4, HNO3, Ca(NO3)2, HCl, AlCl3, Ca(HCO3)2, NaNO3, LiNO3, Li2SO4, MgSO4, Al2(SO4)3, NaClO4, NaOH, KOH at temperatures up to 100 °C, calcium sulfate hemihydrate (CaSO4.0.5H2O) in solutions containing NaCl, CaCl2, MgCl2, KCl, FeCl2, HCl at temperatures up to 125 °C, and calcium sulfate anhydrite (CaSO4) in solutions containing H2SO4, NaCl, CaCl2, MgCl2, Na2SO4, HNO3, HCl, NaNO3, LiNO3, NiSO4, MgSO4, Al2(SO4)3, Mg(NO3)2 at temperatures up to 350 °C. Comparison of the CSA-LSSVM model results to those of Pitzer ion interaction model as well as BR-ANN model in binary, ternary, and multicomponent mixtures reveals the superiority of the CSA-LSSVM model developed in this study in all cases.

A speciated, conventional Pitzer ion-interaction model for the aqueous Nd3+–H+–Na+–K+–Ca2+–Cl−–OH− system at 298 K and 0.1 MPa

A conventional, speciated Pitzer ion-interaction model at 298 K and 0.1 MPa is presented for the NdCl3 + H2O system and mixtures containing HCl, NaCl, KCl, and CaCl2. The model uses Nd3+, NdOH2+, Nd(OH)2+, Nd(OH)30, NdCl2+, and NdCl2+ solute species and was fitted to isopiestic, electromotive force (emf), and NdCl3·6H2O solubility data. The model was then extended to pH values at which Nd(OH)3, Nd(OH)2Cl, and a speculative double salt, Nd(OH)3·NdCl3, are stable. The two hydroxychloride salts enabled the model to join the stability fields of NdCl3·6H2O and Nd(OH)3 ensuring continuity in the range 2 < pH < 13. The activity coefficient model developed from the low pH [NdCl3 + NaCl](aq) system reproduces the solubility of solid Nd(OH)3(s) in water and NaCl(aq) with only the addition of standard state free energy terms for crystalline (cr) and amorphous (am) NdOH3(s) and the Nd(OH)2+ and Nd(OH)30 solute species. No Pitzer parameters involving NdOH2+, Nd(OH)2+ and Nd(OH)30 were necessary to reproduce the full body of thermodynamic data over an ionic strength range from infinite dilution to the solubility limits of NaCl, KCl, CaCl2·6H2O, Nd(OH)3(s), the hydroxychloride salts, and for mixtures containing up to 4.5 molal HCl(aq). The model adds only five ‘binary’ and three ‘ternary’ Pitzer ion-interaction parameters to the H-Na-K-Ca-Cl-OH parameters in Harvie et al. (1984; hereafter HMW). The model is simpler, compositionally broader, and more accurate than previously published Pitzer ion-interaction models for aqueous neodymium-chloride and -hydroxide solutions containing HCl, NaCl, KCl or CaCl2. The model has ramifications for geochemical modeling and uncertainty quantification of An(III) solubilities used to support certification of evaporite hosted nuclear waste repositories.

Thermodynamic properties for the aqueous solutions of cesium borates at 298.15 K and 101 kPa: Experimental and correlation by Pitzer ion-interaction model

As a new-type of liquid mineral resource of cesium including salt lake brine, geothermal water, underground water and seawater, the recovery of cesium is of great significance for its importance strategic purpose in modern industry, and the parameterization of ion-interaction model is essential to understand the ion-interaction of cesium borate solutions. In this paper, the dilution enthalpies on Cs2B4O7 aqueous solutions from 0.03900 to 0.54815 mol·kg−1 and CsB5O8 aqueous solutions from 0.02072 to 0.09889 mol·kg−1 at 298.15 K and 1.325 kPa were determined by the high-precision adiabatic microcalorimeter BT2.15 (Setaram, France), and the dissolution enthalpies for Cs2B4O7·5H2O and CsB5O8·4H2O were measured by the multi-channel microcalorimeter TAM-IV (TA, America). On the basis of experimental dilution enthalpies, the apparent molar enthalpies of Cs2B4O7 and CsB5O8 aqueous solutions were derived, and the diagrams of apparent molar enthalpy against molalities of Cs2B4O7 and CsB5O8 in aqueous solutions were plotted. And then, according to the Pitzer ion-interaction model of apparent molar enthalpy of electrolyte, Pitzer single parameters i.e. FMX (βMX0L, βMX1L, βMX2L and CMXL, M = Cs+, X = [B4O5(OH)4]2− or [B5O6(OH)4]−) were obtained for the first time. The calculated apparent molar enthalpies for Cs2B4O7 and CsB5O8 aqueous solutions agree well with the experiment values, indicating that the single salt parameters obtained for Cs2[B4O5(OH)4] and Cs[B5O6(OH)4] in this work are reliable.

Kinetic and thermodynamic study of magnesium obtaining as sulfate monohydrate from nickel laterite leach waste by crystallization

According to the European Union, magnesium is considered as a critical metal, which can also be found in nickel laterite waste processing, where it is a strategic element with nickel, copper, and cobalt. For this reason, the goal of this work was to study the parameters for crystallization of magnesium sulphate under pressure based on nickel laterite leach solution through a reactor designed with separation system where monohydrate crystals were not decomposed. A magnesium monoelementary solution was used for the present study. After the reaction, the solid phase was separated with the reactor still under pressure to avoid crystals decomposition. Magnesium sulphate solubility was determined to complement the data already published in the literature and to define the solubility product from 30 to 230 °C. Pitzer interaction model made possible the Kps values were obtained at high-temperatures. The crystallization of magnesium sulphate reached the equilibrium in 5 h. At pH 5.7 and 230 °C, 81% of the magnesium crystallized. The particles presented a spherical morphology. The reactor here designed allowed the realization of crystallization at high-temperature, without crystals decomposition. The flowchart here proposed represents the novelty since it could be used for critical metals recovery from mining waste.

A general model for prediction of BaSO4 and SrSO4 solubility in aqueous electrolyte solutions over a wide range of temperatures and pressures

The aqueous solubility of BaSO4 and SrSO4 in salt-containing solutions plays a crucial role in process industries and oilfield operations. Small variations in thermodynamic conditions result in precipitation and co-precipitation of these salts, mainly owing to their limited solubility in aqueous solutions. Understanding the environmental chemistry of BaSO4 and SrSO4 requires accurate knowledge of their solubility and thermodynamic behaviors. In this study, a general solubility prediction model based on a least square support vector machine and differential evolution algorithm was developed that is able to handle solubility predictions for BaSO4 in single salt solutions containing NaCl, CaCl2, MgCl2, KCl, KBr, Na2SO4, and Na2B4O7, and for SrSO4 solubility, it can handle predictions for single, binary, and ternary salt solutions containing NaCl, CaCl2, and MgCl2 over a wide range of temperatures and pressures. Model predictions agree excellently with experimental measurements, yielding an overall correlation coefficient (R2) of 0.9911 and an Average Absolute Error of 6.24%. A comparison of the general solubility prediction model with the Pitzer ion-interaction model revealed that both the models perform well in single salt solutions, while the Pitzer model fails to produce accurate solubility predictions when the aqueous system is extended to binary and ternary electrolyte mixtures.

Volumetric properties and the ion-interaction parameters of the binary system (CsB5O8 + H2O) at temperatures from (283.15 to 363.15) K and 101 kPa

This paper reports the densities of CsB5O8 (aq) in the range of salt concentrations from 0.02526 to 0.08148 mol·kg−1, which were determined by an accurate Anton Paar Digital vibrating-tube densimeter at 5 K intervals from 283.15 to 363.15 K and 101 kPa. The apparent molar volume (Vϕ), the coefficient of thermal expansion (α), apparent molar expansibility of the solute (ϕE) were calculated and variations of these properties against temperature and concentration were revealed minutely. According to Pitzer ion-interaction apparent molar volume model of aqueous electrolyte system, the Pitzer single salt parameters i.e. FMX (βMX0v, βMX1v and CMXv, M = Cs+, X = [B5O6(OH)4]-), the temperature-dependence equation [FMX (i, p, T) = a1 + a2ln(T/298.15) + a3(T-298.15) + a4/(620-T) + a5(T-227), i = βMX0v, βMX1v and CMXv] as well as their coefficients ai (i = 1 to 5) in the binary system were obtained, which is not reported in the literature. The fitted results of single salt parameters βMX0v, βMX1v and CMXv were in good agreement with the experiment values, indicating that the single salt parameters and temperature relational coefficients for Cs[B5O6(OH)4] obtained in this work are reliable.

Apparent molar volumes for Cs2B4O7 aqueous solution at temperatures from (283.15 to 363.15) K and 101 kPa

Densities for aqueous solutions of Cs2B4O7 at the molalities of (0.16635–0.69694) mol·kg−1 were measured with an Anton Paar Digital vibrating-tube densimeter at temperatures from 283.15 K to 363.15 K and 101 kPa. According to experimental data, apparent molar volume (Vϕ), partial molar volume (V¯ϕ), and the coefficient of thermal expansion (α) of the Cs2B4O7 aqueous solution were calculated, and their distributive behaviors against temperature and molality have been discussed in details. Considering the structure of Cs2B4O7 in aqueous solution system is in the form of Cs2[B4O5(OH)4], the Pitzer single-salt parameters (βM,X0v, βM,X1v, βM,X2v and CM,Xv) for Cs2[B4O5(OH)4] as well as temperature-dependence correlations were obtained for the first time on the basis of Pitzer ion-interaction apparent molar volume model of electrolytes. The deviations between the Pitzer single-salt parameters of Cs2[B4O5(OH)4] fitted at each temperatures based on the experimental data and those of the calculated values corresponding to the temperature-dependence equations on Pitzer single-salt parameters are all within ±0.1, indicating that the single-salt parameters and their temperature-dependence equations obtained in this work are reliable.

Effect of hydrophobicity and H-bonding abilities of ions on osmotic coefficients of aqueous diethylammonium based protic ionic liquid solutions at 298.15 K

The osmotic and activity coefficients of aqueous solutions of diethylammonium based protic ionic liquids (PILs) were determined experimentally using vapor pressure osmometry in the concentration range of (~0.02 to ~0.5) mol·kg−1 at 298.15 K. Osmotic coefficient data show positive deviation from Debye-Hückel limiting law for all the studied PILs. Also a minimum in osmotic coefficient data was observed at higher concentrations and is explained in terms of ion-pair formation. Data of experimental osmotic coefficient were used to obtain activities (aw) and activity coefficients (γ1) of water, mean molal activity coefficient (γ±) of PILs and excess Gibbs free energy change (ΔGE) due to mixing. Observed variations in osmotic coefficients data were explained in terms of hydrophobicity as well as H-bonding. The data of osmotic and activity coefficients were further subjected to analysis through Pitzer ion-interaction model to get an information of ion-ion and ion-solvent interaction to understand ion-pairing, ion hydration and hydrophobic effects in aqueous solutions of PILs. For this, Pitzer ion interaction parameters β(0) and β(1) were estimated and compared with literature data available for other relevant systems. Finally, the results are interpreted in terms ion-ion, ion-solvent interaction along with effect of hydrophobicity on ion-pairing and further discussed the effect of alkyl chain length of anions on solvation behavior of protic ionic liquids in aqueous solutions.

Determination and Modeling the Activity Coefficients of 1-Propyl-3- methylimidazolium Bromide in the Ethanol + Water Mixtures at T = (298.2, 308.2 and 318.2) K

In this work, the results relating to the mean activity coefficient measurements for ionic liquid of 1- propyl -3 methylimidazolium bromide, [PMIm]Br in ethanol+ water mixtures have been reported using potentiometric measurements at T=( 298.2, 308.2 and 318.2)K. The electromotive force (emf) measurements were performed on the galvanic cell of the type:Br-ISE│[PrMIm] (m) ethanol (wt.%), H2O (1−wt) %│ [PrMIm] -ISE, in mixed solvent system containing 0, 10, 20, 30% mass fractions of ethanol over ionic strength ranging from 0.0010 to 2.0000 mol•kg−1. The Pitzer ion-interaction model was used to analyze the activity coefficients for studied system. The Pitzer ion-interaction parameters (β(0), β(1) and Cϕ) were determined and employed to calculate the mean activity coefficients, the osmotic coefficients and excess Gibbs free energies for the whole series the studied system.

Stable Phase Equilibria of the Quaternary System Na+//Cl–, NO3–, SO42––H2O at 353.15 K

The phase equilibria of the quaternary system Na+//Cl–, NO3–, SO42––H2O and the subsystems Na+//Cl–, SO42––H2O, Na+//Cl–, NO3––H2O, Na+//NO3–, SO42––H2O at 353.15 K were studied by the isothermal dissolution method. There are one invariant point, three univariant curves, three crystallization fields of single salt, three cocrystallization fields for two salts, and one cocrystallization field for three salts in the quaternary system. Neither double salt nor solid solution is found in the system at 353.15 K. At the invariant point of Na+//Cl–, NO3–, SO42––H2O system, the composition of the solution is NaCl 7.00 wt %, Na2SO4 1.59 wt %, NaNO3 47.79 wt %. The order of the solubility in the mixing solution of the single salts is Na2SO4 < NaCl < NaNO3. Moreover, the solubilities of the systems at 353.15 K were calculated theoretically by using the Pitzer ion interaction model. The high ionic strength was found to be a critical factor, which influenced the calculation accuracy significantly. All data and results ...