Ion-interaction Model Research Articles

Apparent molar volume and modeling of volumetric properties of ionic liquid aqueous solutions 1-butyl-3-metilmidazolium chloride [Bmim+][Cl-] at various temperatures

Densities of the aqueous solutions of ionic liquid 1-butyl-3 metilmidazolium chloride [Bmim + ][Cl - ] were determined using a vibrating tube densitometer Anton Paar DMA 5000 at a temperature range between (283.15 - 218.15) K. The apparent molar volumes V f of aqueous chloride1-butyl-3-methylimidazolium were calculated and adjusted to the Pitzer ion interaction model, obtaining the limiting apparent molar volumes V f and Pitzer volumetric parameters b (O) M V X , b (1) M V X , C V MX at temperatures of 283.15, 288.15, 293.15, 298.15, 303.15, 313.15 and 318.15K, proving that this model adequately represents the experimental volumetric data below an ionic strength of 0.6018 mol / kg. Finally the limiting apparent molar expansibilities f O E were calculated from the limiting apparent molar volumes at various temperatures and the results are discussed in terms of the interactions occurring in solution.

Reflections on my career as a marine physical chemist, and tales of the deep.

This is a personal review of how one can apply the principles of physical chemistry to study the ocean and other natural waters. Physical chemistry is the study of chemical thermodynamics, kinetics, and molecular structure. My long-term interest in the chemistry of seawater is an extension of my early work on water and the interactions that occur in aqueous electrolyte solutions, which I began as part of my PhD research on the thermodynamics of organic acids in water. Over the years, I have attempted to apply the tools of physical chemistry to elucidate the structures of seawater, brines, lakes, and rivers. I have developed and continue to work on ionic interaction models that can be applied to all natural waters. Here, I reflect on how my students, postdocs, research assistants, and scientific colleagues have influenced my life, my career, and the field of marine physical chemistry. My hope was and is to use these tools to understand the molecular structures of natural waters.

Isopiestic determination of the osmotic and activity coefficients of the {yK2SO4 + (1 − y)K2HPO4}(aq) system at T = 298.15 K

The molality-based osmotic coefficients of aqueous mixtures of K2SO4 and K2HPO4 have been measured at T=(298.15±0.01)K by the isopiestic method, at K2SO4 ionic strength fractions y=(0.21008, 0.39887, 0.60657, 0.80517, and 1) over the ionic strength range (1.3167 to 1.9587)mol·kg−1, using KCl(aq) as the reference standard solution. These osmotic coefficients were modeled with an extended form of Pitzer’s ion-interaction model equations, both with the usual Pitzer mixing terms and with Scatchard’s neutral-electrolyte solution mixing terms, and with the Clegg–Pitzer–Brimblecombe equations based on the mole-fraction-composition scale. There are no previously published isopiestic measurements for this ternary system. Model parameters for K2SO4(aq) at T=298.15K were also evaluated using the present results along with seven sets of osmotic coefficients taken from the published literature. For the {yK2SO4+(1−y)K2HPO4}(aq) system, few or no mixing terms were needed for the three models because the ionic strength dependences of the osmotic coefficients of K2SO4(aq) and K2HPO4(aq) are very similar and their curves nearly parallel, as are those of the mixtures which are intermediate and nearly equally spaced as a function of the ionic strength fraction.

Chemical speciation in fresh, saline and hyper-saline waters

AbstractA thermodynamic model is proposed, which combines the ion association and the ion interaction models using the extended database pit2010.dat for a more precise modeling of the chemical species of micro components in natural waters of varying ionic strength (fresh, saline and hyper-saline). Compared to the ion association model, the proposed combined model more adequately describes the complex character of the ionic interactions. The performance of the combined ion association/ion interaction model compared to that of the ion association model is illustrated in case studies of several Bulgarian natural water systems of different ionic strength and type of pollution. The results are interpreted in terms of the chemical behavior of the metals and of their chemical species in the water systems, which is defined by the redox potential, pH, cationic and anionic organic and inorganic composition of the water systems and by the ability of the metals to preferentially coordinate with some anions, as well as by the stability of the corresponding species. The affinity of the transition metals towards the ligands is explained by the “hardness-softness” factor and the crystal field stabilization energy (CFSE).

Thermodynamic investigation of the ternary mixed electrolyte (NaCl + Na2HCit + H2O) system using potentiometric measurements at T = (298.2 and 308.2) K

In this work, the mean activity coefficients of NaCl in the (NaCl+Na2HCit+H2O) ternary mixed electrolyte system were determined using the potentiometric method. The potentiometric measurements were carried out on the galvanic cell without liquid junction of the type: Na-ISE/NaCl (m1), Na2HCit (m2), H2O/Ag–AgCl over total ionic strengths from (0.01 to 4.000)mol·kg−1. Different series of the salt molal ratios r (r=mNaCl/mNa2HCit=0.1, 1, 2.5, 5.0, 7.5, 10.0) and pure NaCl were used for the measurement at T=(298.2 and 308.2)K and P=0.1MPa. The results were interpreted by using Pitzer ion-interaction model with and without higher-order electrostatic effects. The mixing parameters obtained were used to calculate the values of the mean activity coefficients of Na2HCit, the osmotic coefficients, solvent activity and the excess Gibbs free energies for the whole series of the studied mixed electrolyte system.

Predicting the solubility of SrSO4 in Na–Ca–Mg–Sr–Cl–SO4–H2O system at elevated temperatures and pressures

Precipitation of strontium sulfate (or SrSO4) has already been distinguished as one of the most costly and critical problems which may occur in process industries and oilfield operations. Costs due to scaling and remedial actions that need to be taken afterward are generally high owing to low solubility of SrSO4 in aqueous solutions. Therefore, a thorough understanding of the SrSO4 thermodynamic behavior under various operating conditions is vital to predict or even avoid the overall damage caused by scaling. The primary aim of this work is to develop a model based on Least Squares Support Vector Machine (LSSVM) and Coupled Simulated Annealing (CSA) referred to as CSA-LSSVM to predict strontium sulfate solubility as a function of pressure, temperature and ionic compositions. In this context, we have employed almost 1641 experimental data regarding strontium sulfate solubility to build a comprehensive model and to evaluate its reliability. The results show that the proposed model has a better performance in comparison with pre-existing empirical correlations used for predicting SrSO4 solubility and it is also in well accordance with experimental measurements. A comparison was also drawn between predictions of Pitzer ion interaction model with CSA-LSSVM model forecasts in terms of sensitivity analysis and single point solubility predictions. The whole dataset was analyzed at the end to diagnose the possible outliers and to investigate the reliability of recorded measurements. Based on the results obtained from this study, developed model could successfully be used in predicting SrSO4 solubility in aqueous Na–Ca–Mg–Sr–Cl–SO4–H2O system over temperature ranges from 2 to 253.5°C, and pressures from 1 to 568.51atm.

Thermodynamic model for the solubility of BaSeO4(cr) in the aqueous Ba2+-SeO4 2−-Na+-H+-OH−-H2O system: Extending to high selenate concentrations

Abstract The aqueous solubility of BaSeO4(cr) was studied at 23 ± 2 ℃ as a function of Na2SeO4 concentrations (0.0001 to 4.1 mol kg –1) and equilibration periods (3 to 596 d). The equilibrium, approached from both the under- and over-saturation directions, in this system was reached rather rapidly (≤3 d). The SIT and Pitzer's ion-interaction models were used to interpret these data and the predictions based on both of these models agreed closely with the experimental data. Thermodynamic analyses of the data show that BaSeO4(cr) is the solubility-controlling phase for Na2SeO4 concentrations <0.59 mol kg –1. The log 10 K 0 value for the BaSeO4(cr) solubility product (BaSeO4(cr) ⇌ Ba2++ SeO4 2– ) calculated by the SIT and Pitzer models were very similar (− 7.32 ± 0.07 with Pitzer and − 7.25 ± 0.11 with SIT). Although the BaSeO4(cr) solubility product and Ba concentrations as a function of Na2SeO4 concentrations predicted by both the SIT and Pitzer models are similar, the models required different sets of fitting parameters. For examples, 1) interpretations using the SIT model required the inclusion of Ba(SeO4)2 2– species with log 10 K 0 = 3.44 ± 0.12 for the reaction (Ba2++ 2SeO4 2– ⇌ Ba(SeO4)2 2– ), whereas these species are not needed for Pitzer model, and 2) at Na2SeO4 concentrations >0.59 mol kg –1 it was also possible to calculate the value for log 10 K 0 for the solubility product of a proposed double salt (Na2Ba(SeO4)2(s) ⇌ 2Na++ Ba2++ 2SeO4 2– ) which for the SIT model is − (8.70 ± 0.29) whereas for the Pitzer model it is − (9.19 ± 0.19). The ion-interaction/ion-association parameters hitherto unavailable for both the SIT and Pitzer models required to fit these extensive data extending to as high ionic strengths as 12.3 mol kg –1 were determined. The model developed in this study is consistent with all of the reliable literature data, which was also used to extend the model to barium concentrations as high as 0.22 mol kg –1 and pH ranging from 1.4 to 13.8, in addition to selenium concentrations as high as 4.1 mol kg –1.

Prediction of the aqueous solubility of BaSO4 using pitzer ion interaction model and LSSVM algorithm

Deposition of barium sulfate (or BaSO4) has already been recognized as a devastating problem facing process industries and oilfield operations, mainly owing to its low solubility in aqueous solutions. Predicting and also preventing the overall damage caused by BaSO4 precipitation requires a profound knowledge of its solubility under different thermodynamic conditions. The main aim of this study is to develop a solubility prediction model based on a hybrid of least squares support vector nachines (LSSVM) and coupled simulated annealing (CSA) aiming to predict the solubility of barium sulfate over wide ranges of temperature, pressure and ionic compositions. Results indicate that predictions of the presented model are in well accordance with experimental measurements yielding overall correlation coefficient (R2) of 0.996 and total RMSE of 0.00077. Constructed model was also found to outperform a previously well-known correlation employed for predicting BaSO4 solubility in aqueous solutions. Solubility predictions based on Pitzer ion interaction model were also compared to CSA-LSSVM predictions in terms of single point estimations and sensitivity analysis. Results of this study suggest that CSA-LSSVM model could be implemented in assessing the solubility of BaSO4 in Na–Mg–Ca–K–Ba–Cl–SO4–H2O system over wide ranges of temperature from 0 to 279°C and pressures ranging from 1 to 1517 bars with an acceptable degree of accuracy.

Thermodynamic model for the solubility of Ba(SeO4, SO4) precipitates

Abstract The solubility of Ba(SeO4, SO4) precipitates was determined as a function of the BaSeO4 mole fractions, ranging from 0.0015 to 0.3830, and time with an equilibration period extending to as long as 302 days. Equilibrium/steady state conditions in this system are reached in ≤ 65 days. Pitzer's ion interaction model was used to calculate solid and aqueous phase activity coefficients. Thermodynamic analyses showed that the data do not satisfy Gibbs-Duhem equation, thereby demonstrating that a single-solid solution phase does not control both the selenate and sulfate concentrations. Our extensive data with log 10 [Ba] ranging from − 3.6 to −5.9 mol kg –1, log 10 [SeO4] ranging from − 3.6 to −5.2 mol kg –1, and log 10 [SO4] ranging from − 4.0 to −5.3 mol kg –1 can be explained with the formation of an ideal BaSeO4 solid solution phase that controls the selenium concentrations and a slightly disordered/less-crystalline BaSO4(s) (log 10 K ○ sp =− 9.5 instead of − 10.05 for barite) that controls the sulfate concentrations. In these experiments the BaSO4 component of the solid solution phase never reaches thermodynamic equilibrium with the aqueous phase. Thermodynamic interpretations of the data show that both the ideal BaSeO4 solid solution phase and less-crystalline BaSO4(s) phase are in equilibrium with each other in the entire range of BaSeO4 mole fractions investigated in this study.

Elucidation of Ionic Interactions in the Protic Ionic Liquid Solutions by Isothermal Titration Calorimetry

The strong hydrogen-bonded network noted in protic ionic liquids (PILs) may lead to stronger interactions of the ionic entities of PILs with solvents (water, methanol, ethylene glycol, dimethylsulfoxide (DMSO), N,N'-dimethylformamide (DMF)) as compared with those of aprotic ionic liquids (APILs). The PILs used in this work are 1-methylimidazolium tetrafluoroborate, 2-methylpyridinium tetrafluoroborate, and N-methylpyrrolodinium tetrafluoroborate in comparison to 1-butyl-3-methylimidazolium tetrafluoroborate, which is classified as an APIL. In this work, the excess partial molar enthalpy, H(E)IL obtained from isothermal calorimetric titrations at 298.15 K is used to probe the nature of interactions of the PIL cations with solvent molecules against those present in APIL-solvent systems. This work also reports interesting flip-flopping in the thermal behavior of these PIL-solvent systems depending upon the structure of the cationic ring of a PIL. In some cases, these flip-flops are the specific fingerprints for specific PILs in a common solvent environment. The excess partial molar enthalpy at infinite dilution, H(E,∞)IL, of these PILs bears a critical dependence on the solvent properties. An analysis of relative apparent molar enthalpies, ϕL, of the PIL solutions by the ion interaction model of Pitzer yields important information on ionic interactions of these systems.

Thermodynamic properties of binary aqueous solutions of orthophosphate salts, sodium, potassium and ammonium at T = 298.15 K

In this investigation, the thermodynamic properties of the aqueous solutions of orthophosphate salts M3−nHnPO4 H2O with n=0, 1, or 2 and M=Na+, K+ or NH4+ at 298.15K are determined. The water activity measurements for NaH2PO4(aq), Na2HPO4(aq), Na3PO4(aq); KH2PO4(aq), K2HPO4(aq), K3PO4(aq), (NH4)H2PO4(aq), (NH4)2HPO4(aq) and (NH4)3PO4(aq) are effectuated from dilution to saturated solution using the hygrometric method. The activity coefficients are evaluated using ionic-interaction model. The mineral solubility of these phosphate salts is investigated at T=298.15K. The prediction of solubility is made for minerals and other solid phases in aqueous solutions of phosphates. Correlating and predicting the phase behavior in such systems is a difficult task, partially caused by chemical reactions in the liquid phase but also due to the possible formation of one or more solid phases. Solid phases, molality of saturated binary solutions ms(exp) and logarithm of solubility product K°sp are also determined at 298.15K. The standard molar Gibbs energies of dissolution ΔG°diss, formation ΔGf Calc° and the literature ΔGf Ref°, of solid phases crystallizing from saturated phosphate salts solutions are evaluated.This investigation allows understanding physicochemical nature and structure of phosphate solutions, in particular, questions of anion or cation hydration, especially at higher concentrations, ion-pairing formation, and the possibility of phosphate complex formation.

Development of Monopole Interaction Models for Ionic Compounds. Part I: Estimation of Aqueous Henry's Law Constants for Ions and Gas Phase pKa Values for Acidic Compounds.

The SPARC (SPARC Performs Automated Reasoning in Chemistry) physicochemical mechanistic models for neutral compounds have been extended to estimate Henry's Law Constant (HLC) for charged species by incorporating ionic electrostatic interaction models. Combinations of absolute aqueous pKa values, relative pKa values in the gas phase, and aqueous HLC for neutral compounds have been used to develop monopole interaction models that quantify the energy differences upon moving an ionic solute molecule from the gas phase to the liquid phase. Inter-molecular interaction energies were factored into mechanistic contributions of monopoles with polarizability, dipole, H-bonding, and resonance. The monopole ionic models were validated by a wide range of measured gas phase pKa data for 450 acidic compounds. The RMS deviation error and R(2) for the OH, SH, CO2 H, CH3 and NR2 acidic reaction centers (C) were 16.9 kcal/mol and 0.87, respectively. The calculated HLCs of ions were compared to the HLCs of 142 ions calculated by quantum mechanics. Effects of inter-molecular interaction of the monopoles with polarizability, dipole, H-bonding, and resonance on acidity of the solutes in the gas phase are discussed.

Ion Association versus Ion Interaction Models in Examining Electrolyte Solutions: Application to Calcium Hydroxide Solubility Equilibrium

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 descri...

Solubility in K+-Na+-Mg2−4 aqueous solution at T = 298.15 K

In the salt solubility predictions for K+-Na+-Mg 4 2− aqueous solution the treatment of thermodynamic data of three-component systems at T = 298.15 K involved the application of the Extended Pitzer’s ion-interaction model for the pure and mixed electrolyte solutions and criteria of phase equilibrium. Osmotic coefficients data of three-component systems were revised according to recently published parameters of the solutions NaCl(aq) and KCl(aq) that served as reference standards in isopiestic measurements. Parameters of the extended ion-interaction model of K2SO4(aq) are determined by treatment of experimental and predicted values of osmotic coefficient in supersaturated region obtained by the Zdanovskii-Stokes-Robinson rule. Results of salt solubility prediction were compared to experimental solubility data from literature. The agreement between calculated and experimental solubility data in the systems K2SO4 + MgSO4 + H2O, Na2SO4 + MgSO4 + H2O, and Na2SO4 + K2SO4 + H2O at T = 298.15 K, was excellent.

Isopiestic Studies on Rare Earth Chloride Quaternary System (H2O + LaCl3 + PrCl3 + NdCl3) and Ternary Subsystems

Isopiestic measurements have been carried out for the quaternary system H2O + LaCl3 + PrCl3 + NdCl3 and its ternary subsystems H2O + LaCl3 + PrCl3, H2O + LaCl3 + NdCl3, and H2O + PrCl3 + NdCl3 at 298.15 K. The results are well represented by the partial ideal solution model and the modified Pitzer ion-interaction model extending to C(3) over full concentration range.

Surface-Enhanced Raman Spectroscopy Detection of Ionic Solutes by Surfactant-Mediated Adsorption to a Hydrophobic Surface

Chemical modification of the surfaces of surface-enhanced Raman spectroscopy (SERS)-active metals with thin molecular layers expands the variety of molecular species that can be attracted to the SERS surface from solution. This approach can provide selective detection of new classes of molecules that would not otherwise be detectable through direct interaction with a SERS-active metal. For example, polycyclic aromatic compounds can be attracted from aqueous solution to gold or silver SERS substrates that are modified with alkylsilanes or alkanethiols. While n-alkane monolayers attract hydrophobic solutes to a SERS-active surface, they are not well suited to adsorbing more water-soluble, ionized species from solution. In this work, we address SERS detection of ionic solutes by applying the principles of ion-interaction chromatography, where a charged surfactant is added to solution and adsorbs to an n-alkane-modified, SERS-active surface. The adsorbed charged surfactant serves to attract an ionic solute of opposite charge to the surface, where it can be detected. This concept was tested with a model anionic solute, 3-nitrobenzenesulfonate (NBS(-)), with a cationic surfactant, cetylpyridinium (CP(+)), that adsorbs to a 1-dodecanethiol (C12)-modified silver surface. The interfacial populations of both the surfactant and anionic solute can be determined simultaneously from SERS spectra. The adsorption equilibrium of CP(+) to the C12 surface was fit to a Langmuir model, and the effect of supporting electrolyte on its adsorption equilibria was also investigated by SERS. The retention of NBS(-) at the C12 surface depends on the concentration of CP(+). The binding of NBS(-) to adsorbed CP(+) is described by an ion-interaction model that includes competition for the NBS(-) population due to association with surfactant ions in solution. While the strength of this binding interaction is not as great as the hydrophobic interactions that drive aromatic hydrocarbons to hydrophobic SERS surfaces, SERS detection of analyte ions by this approach could be accomplished at concentrations two orders of magnitude lower compared with Raman detection in free solution.

Liquidus Temperatures and Thermodynamic Properties of the KCl– $$\mathrm{{KNO}}_{2}$$ KNO 2 , NaCl– $$\mathrm{{NaNO}}_{2}$$ NaNO 2 , and $$\mathrm{{KNO}}_{2}$$ KNO 2 – $$\mathrm {NaNO}_{2}$$ NaNO 2 Systems

Potassium nitrite is very sensitive to temperature, humidity, and the atmosphere, so few studies have been made in this field for the thermodynamic properties of molten salt with nitrite salt. In this article, the liquidus curves of NaCl– $$\mathrm{{NaNO}}_{2}$$ , KCl– $$\mathrm{{KNO}}_{2}$$ , and $$\mathrm {NaNO}_{2}$$ – $$\mathrm{{KNO}}_{2}$$ are calculated by a simple “hard-sphere” ionic interaction model. The calculated liquidus temperatures show good agreement with experimental values, which implies an ideal mixing enthalpy and entropy for the liquid binary systems. In addition to the phase equilibrium data and experimental thermochemical properties of molten salt systems, the activities of these binary systems are determined by the phase diagrams and the analytical integration of the classical Gibbs–Duhem equation.

Effect of composition and nonideal solution behavior on desalination calculations for mixed electrolyte solutions with comparison to seawater

Proper evaluation of physical properties of aqueous solutions is essential in the analysis of desalination systems. While standard seawater property data are readily accessible, they are generally not accurate for aqueous solutions requiring desalination that have significantly different composition than seawater. Since experimental data for a given solution may be unavailable under the conditions of interest, thermodynamic models are needed for relevant physical properties, particularly, activity and fugacity coefficients. Effects of composition and nonidealities in mixed electrolyte solutions are considered through a parametric study of the least work of separation. Conditions under which existing single electrolyte solution models, including ideal solution approximation, Debye–Hückel theory (Davies equation), and Pitzer's ionic interaction model, are valid when analyzing mixed electrolyte solutions are examined by comparing them to the Pitzer–Kim mixed electrolyte model. It is found that single electrolyte models often result in greater error than the ideal solution approximation when studying all but the most dilute mixed electrolyte solutions. Additionally, an effective molality can be used with the Pitzer model to increase the accuracy of the single electrolyte model as applied to mixed electrolytes. Finally, composition is a significant variable in the overall work of separation requirements.

ZnO Nanoparticles as Ethanol Gas Sensors and the Effective Parameters on Their Performance

ZnO nanoparticles are synthesized and applied as ethanol gas sensors. In some cases, the sensitivity and response time of these particles are shown to be higher than that has been reported in the literature. It has been investigated that the most possible reason for this higher gas sensing performance can be attributed to the quantity of the activity coefficient of its initial components. However, other effects such as pH and thermal decomposition are of importance as well. Specific ion interaction (SIT) model is applied to derive the mean activity coefficient values of the additives used in synthesis of ZnO nanoparticles.

Isopiestic determination of the osmotic and activity coefficients of the {yKBr + (1 – y)K2HPO4}(aq) system at T = 298.15 K

The molality-based osmotic coefficients of aqueous mixtures of KBr and K2HPO4 have been measured at T=(298.15±0.01)K by the isopiestic method at KBr ionic strength fractions y=(0.18328, 0.38241, 0.58031, 0.79186, and 1) and over the ionic strength range (2.5452 to 10.0418)mol·kg−1, using KCl(aq) and CaCl2(aq) as the reference standard solutions. These experiments were performed using glass sample dishes because preliminary experiments showed that some corrosion of our usual gold-plated silver dishes occurred with dissolution of silver, presumably by “pinhole” corrosion at imperfections in the gold layer. These osmotic coefficients were modeled with an extended form of Pitzer’s ion-interaction model equations, both with the usual Pitzer mixing terms and with Scatchard’s neutral-electrolyte mixing terms, and with the Clegg–Pitzer–Brimblecombe equations based on the mole-fraction-composition scale. There are no previously published isopiestic measurements for this ternary system. The present assessment yields mixing parameters for these models. Model parameters for KBr(aq) at T=(298.15±0.01)K were also evaluated using the present results along with four sets of osmotic coefficients taken from the published literature. For the {yKBr+(1−y)K2HPO4}(aq) system, the model with five Scatchard mixing terms gave a significantly better representation of the osmotic coefficients than any of the other models and is therefore recommended for calculation of osmotic and activity coefficients.