Study of the Relationship Between New Ionic Interaction Parameters and Salt Solubility in Electrolyte Solutions Based on Molecular Dynamics Simulation

Studying the relationship between ionic interactions and salt solubility in seawater has implications for seawater desalination and mineral extraction.In this paper,a new method of expressing ion-to-ion interaction is proposed by using molecular dynamics simulation,and the relationship between ion-to-ion interaction and salt solubility in a simulated seawater water-salt system is investigated.By analyzing the variation of distance and contact time between ions in an electrolyte solution,from both spatial and temporal perspectives,new parameters were proposed to describe the interaction between ions:interaction distance(ID),and interaction time ratio(ITR).The best correlation between characteristic time ratio and solubility was found for a molar ratio of salt-to-water of 10:100 with a correlation coefficient of 0.96.For the same salt,a positive correlation was found between CTR and the molar ratio of salt and water.For type 1-1,type 2-1,type 1-2,and type 2-2 salts,the correlation coefficients between CTR and solubility were 0.93,0.96,0.92,and 0.98 for a salt-to-water molar ratio of 10:100,respectively.The solubility of multiple salts was predicted by simulations and compared with experimental values,yielding an average relative deviation of 12.4%.The new ion-interaction parameters offer significant advantages in describing strongly correlated and strongly hydrated electrolyte solutions.

Minimum-Modified Debye-Hückel Theory for Size-Asymmetric Electrolyte Solutions with Moderate Concentrations

A minimum-modified Debye-Hückel(DH)theory for electrolytes with size asymmetry is developed.Com-pared with the conventional DH theory,the minimum-modified DH theory only introduces an extra surface charge density to capture the electrostatic effect of the size asymmetry of the electrolytes and hence facilitates a boundary element method for electrostatic potential calculation.This theory can distinguish the electrostat-ic energies and excess chemical potentials of ions with the same sizes but opposite charges,and is applied to a binary primitive electrolyte solution with moderate electrostatic coupling.Compared with the hyper-netted chain theory,the validity of this modified DH theory demonstrates significant improvement over the conventional DH theory.

Prediction of Activity Coefficients for Mixed Aqueous Electrolyte Solutions from the Data of Their Binary Solutions

The simple equation relating the activity coefficient of each solute in mixed electrolyte solution to its value in binary solutions under isopiestic equilibrium was tested by comparison with the experimental data for the 18 electrolyte solutions consisting of 1：1, 1：2, and 1：3 electrolytes. The isopiestic measurements were made on the quaternary system BaCl2-NH4Br-NaI-H2O and its ternary subsystems NaI-NH4Br-H2O, NaI-BaCl2-H2O, and NH4Br-BaCl2-H2O at 298.15K. The results were used to test the applicability of the Zdanovskii＇s rule to the mixed electrolyte solutions which contain no common ions, and the agreement is excellent. The activity coefficients of the solutes in the above quaternary and ternary systems calculated from the above-mentioned simple equation are in good agreement with the Pitzer＇s equation.

Effects of ion-ion correlations on surface charge inversion in mixture electrolyte solutions

As the structure of electrical double layer(EDL)is crucial for the transport properties of ions in micro/nanochannels,to demonstrate the effects of the ion-ion correlations on EDL structures in mixture electrolyte solutions,the interaction forces between two mica surfaces immersed in different volume fractions of LaCl3/KCl and LaCl3/MgCl2 mixture solutions with a total ionic strength of 10^-4 mol/L were measured using a surface forces apparatus(SFA).The results reveal that the surface charge of mica surfaces can be inversed at a critical concentration of La^3+ions in electrolyte solutions,due to the correlations between La^3+ions.The addition of monovalent has negligible effects on ion-ion correlations,while the charge inversion was slightly suppressed by introducing the divalent ions.The mechanism of charge inversion in mixture electrolyte solutions was analyzed based on the strongly correlated liquid(SCL)theory.These findings provide implications for understanding the effects of ion-ion correlations on EDL structures,surface charge properties,and ion transportation.

Effect of external electric field on the terahertz transmission characteristics of electrolyte solutions

We fabricated a microfluidic chip with simple structure and good sealing performance,and studied the influence of the electric field on THz absorption intensity of liquid samples treated at different times by using THz time domain spectroscopy system.The tested liquids were deionised water and CuSO_(4),CuC_(l2),NaHCO_(3),Na_(2)CO_(3) and NaCl solutions.The transmission intensity of the THz wave increases as the standing time of the electrolyte solution in the electric field increases.The applied electric field alters the dipole moment of water molecules in the electrolyte solution,which affects the vibration and rotation of the whole water molecules,breaks the hydrogen bonds in the water,increases the number of single water molecules and leads to the enhancement of the THz transmission spectrum.

Effects of water on the structure and transport properties of room temperature ionic liquids and concentrated electrolyte solutions

Transport properties and the associated structural heterogeneity of room temperature aqueous ionic liquids and especially of super-concentrated electrolyte aqueous solutions have received increasing attention,due to their potential application in ionic battery.This paper briefly reviews the results reported mainly since 2010 about the liquid-liquid separation,aggregation of polar and apolar domains in neat RTILs,and solvent clusters and 3D networks chiefly constructed by anions in super-concentrated electrolyte solutions.At the same time,the dominating effect of desolvation process of metal ions at electrode/electrolyte interface upon the transport of metal ions is stressed.This paper also presents the current understanding of how water affects the anion-cation interaction,structural heterogeneities,the structure of primary coordination sheath of metal ions and consequently their transport properties in free water-poor electrolytes.

HIGH-PERFORMANCE GAS DIFFUSION POROUS STARVED OF ELECTROLYTE SOLUTION

The performance of gas diffusion porous electrode starved of electrolyte solution can be significantly increased by decreasing the thickness of uneven liquid film covering the catalyst agglomerates.

V-L EQUILIBRIUM OF WEAK ELECTROLYTE SOLUTION OF THE NH_3-CO2-H_2O,NH_3-H_2S-H_2O AND NH_3-SO_2-H_2O SYSTEM

In this paper we have systematically studied V-L equilibrium in ternary aqueous solutions containingvolatile electrolytes by introducing a ternary interaction term into Edwards generalized molecular thermody-namic model and optimizing several adjustable parameters.The program PARA9 with flexible functions ofdoing a series of calculations has been developed and carried out on a TQ-16 computer.It can be usedeither for directly calculating the V-L equilibrium or for optimizing the adjustable parameters.For the sys-toms（NH3-CO3-H2O3,NH3-H2S-H2O and NH3-SO2-H2O）satisfactory results have been obtained withrelative mean deviation of 5-10%.Besides,several sets of adjustable parameters and valuable information ofactivity coefficients,equilibrium concentrations of ions and molecules in solutions are obtained.

Correlation of the mean activity coefficient of aqueous electrolyte solutions using an equation of state

Accurate calculation of thermodynamic properties of electrolyte solution is essential in the design and optimization of many processes in chemical industries. A new electrolyte equation of state is developed for aqueous electrolyte solutions. The Carnahan-Starling repulsive model and an attractive term based on square-well potential are adopted to represent the short range interaction of ionic and molecular species in the new electrolyte EOS. The long range interaction of ionic species is expressed by a simplified version of Mean Spherical Approximation theory （MSA）. The new equation of state also contains a Born term for charging free energy of ions. Three adjustable parameters of new eEOS per each electrolyte solution are size parameter, square-well potential depth and square-well potential interaction range. The new eEOS is applied for correlation of mean activity coefficient and prediction of osmotic coefficient of various strong aqueous electrolyte solutions at 25℃ and 0.1 MPa. In addition, the extension of the new eEOS for correlation of mean activity coefficient and solution density of a few aqueous electrolytes at temperature range of 0 to 100℃ is carried out.

RELATIONSHIPS BETWEEN IONIC RADII AND PITZER'S PARAMETERS IN 1:1 TYPE ELECTROLYTE SOLUTIONS

A new expression for the osmotic and activity coefficients in single electrolyte solution is developed by reforming the Pitzer's osmotic equation.As a result,the correlations between the oMX,the sum of the"hard core"radii of ionsβ^(0)_(MX)andβ^(1)X_(MX),and the second virial coefficients/jjJx and'n Pitzer's equations are obtained.Furthermore,an"ionic overlap"model and its relevant equation are suggested.The relationships between the thermodynamic properties of aqueous electrolytes and the characteristic of their ions(ionic radii and ionic hydration)are discussed quantitatively.

Mixing of two different electrolyte solutions in electromagnetic rectangular mixers

This study proposes a new electromagnetic rectangular mixer, and numerically examines the mixing characteristics of two different electrolyte solutions in the device under a uniform magnetic field. The mixer consists of a conduit with electrodes equipped on its top and bottom walls. The difference in the electric potentials applied to the sets of electrodes induces the current. The combination of the induced current and magnetic field yields Lorentz force, resulting in the fluid motion for pumping and mixing of the two different fluids. The numerical simulation is carried out with the use of commercial software CFX. The present numerical model is validated by an existing numerical work. The effect of different variables on mixing efficiency is investigated in many different cases with two different heights of the duct and various input voltages of the electrodes. The current simulation results indicate that the mixing performance can be enhanced by using multiple sets of electrodes and applying higher input voltages（absolute values） to the electrodes.

Recent Advances in the Use of Statistical Mechanics to Establish Molecular Thermodynamic Models for Electrolyte Solutions

Based on statistical mechanics, a review of recent theoretical studies of real electrolyte solutions is presented from three aspects, namely, molecular simulation, mean spherical approximation (MSA), and perturbation theory. Recent advances in studies of three kinds of electrostatic potentials of mean force, three kinds of internal energies (ion-ion, ion-dipole, and dipole-dipole interactions), and three kinds of electro-lyte models (primitive, non-primitive, and solvent primitive models) are introduced. The advantages and dis-advantages between primitive and non-primitive models, and between MSA and perturbation theory are dis-cussed. Some new equations of state (EOSs) based on MSA and perturbation theory for real electrolyte so-lutions are introduced. The one-Yukawa EOS and the two-Yukawa EOS for charged colloid systems are presented.

Mixing features in an electromagnetic rectangular micromixer for electrolyte solutions

In this study, a new magnetohydrodynamic（MHD） mixer for electrolyte solutions with pumping function is reported, and the mixing performance of the device for two different electrolyte solutions is numerically examined in a uniform magnetic field. Application of different potentials to different electrodes allows the current to be induced. The combination of the induced current and magnetic field yields Lorentz force, resulting in the fluid motion. The numerical simulation for the flows in the device is carried out with commercial software CFX. The validity of CFX code for the present numerical model is presented. The mixing performance of the fluids is investigated in many different cases with different combinations of input voltage of the electrode. This study shows that the mixing performance can be enhanced by applying spatially alternating positive and negative voltages to the electrodes. The present simulation results show that with a magnetic field intensity lower than 0.5 T, a voltage difference smaller than 2.0 V, and an electric conductivity of electrolyte solution of 1.5 S/m the pumping capabilities ranging 1.6×10^（-7）-3.6×10^（-6） kg/s and the mixing indexes higher than 0.90 can be obtained with sophisticated designs of the micromixer.

Split-dose vs same-day reduced-volume polyethylene glycol electrolyte lavage solution for morning colonoscopy

AIM: To compare same-day whole-dose vs split-dose of 2-litre polyethylene glycol electrolyte lavage solution (PEG-ELS) plus bisacodyl for colon cleansing for morning colonoscopy.

Calculation of CO_2, CH_4 and H_2S Solubilities in Aqueous Electrolyte Solution at High Pressure and High Temperature

This paper reports an investigation into the characterisation of liquidaivapor electrolyte solutions at high pressure and high temperature. A procedure to enable calcuIations of methane, carbon dioxide and hydrogen sulphide solubilities in brines (0-6 m.) for temperature from 25 to 350℃ and for pressures from 1 to 1800 bar is presented. The model is based on Helgeson, Kirkham and Flowers modified equations of state (HKF) and on the semi-empirical interaction model introduced by Pitzer. HKF modified equations of state are used to calculate the reference fugacity of gas species, and the Pitzer ionic interaction model is used to calculate the activity coefficient of dissolved species (i.e. ionic or neutral).The efficiency of the combination of the two models is confirmed by several comparisons with data in the literature.

A MODEL FOR THE ACTIVITY COEFFICIENTS OF WATER IN THE AQUEOUS SOLUTION OF HCl-MCl_n (M=Ni, Cu, Na AND Fe) WITHCONSTANT CONCENTRATION RATIO XHCl/XMCl_n

In orber to calculate the activity coefficients of water in the aqueous solution systems of double electrolytes, HCl and MCln (M=Ni, Cu,Na and Fe), a simplified regular solution model has been derived based on the assumption that the electrolytes in the aqueous solution are treated as independent particles instead of their ion forms, and that the interaction of the component pair HCl-MCln in the aqueous solution is very weak as compared with the component pairs HCl-H2O and H2 O-MCln. The interchange energies of the component pairs in the discussed systems, ωWCl-H2o, ωH2o-NiCl2,ωH2o-CuCl2, ωH2o-NaCl and ωH2O-FeCl3, have been evaluated from the experimental data to be-69800, -212600, -90550, -42450 and -198310J·mol-1.

Calculating models of mass action concentrations for NaBr(aq), LiNO_3(aq), HNO_3(aq), and KF(aq) binary solutions

The calculating models of mass action concentrations for electrolyte aqueous solutions NaBr-H2O, LiNO3-H2O, HNO3-H2O, and KF-H2O have been developed at 298.15 K and their molalities ranging from 0.1 mol/kg to saturation according to the ion and molecule coexistence theory as well as mass action law. The calculated mass action concentration is based on pure species as the standard state and the mole fraction as the concentration unit, and the reported activities are usually based on infinite dilution as the standard state and molality as the concentration unit. Hence, the calculated mass action concentration must be transformed to the same standard state and concentration unit. The transformation coefficients between calculated mass action concentrations and reported activities of the same component fluctuate in a very narrow range. Thus, the transformed mass action concentrations not only agree well with reported activities, but also strictly obey mass action law. The calculated results show that the new developed models can embody the intrinsic structure of investigated four electrolyte aqueous solutions. The results also indicate that mass action law has its widespread applicability to electrolyte binary aqueous solutions.

Physical Diffusion and Electron-transfer Dynamics of Electroactive Solutes in Polymer Electrolytes Ⅲ. Effect of the Polymer Solvents

The diffusion coefficients(Dapp) and the heterogeneous electron transfer rate constants(ks)for ferrocene in several polymer solvents were determined by using steady-stae voltammetry. Thetemperature dependence of the two parameters indicates Arrhenius behavior. The polymer solventeffects on diffusion and electron transfer dynamics of ferrocene were discussed

Physical Diffusion and Electron-transfer Dynamics of Electroactive Solutes in Polymer Electrolytes Ⅰ. Effect of the Nature of Electroactive Solutes

The diffusion coefficients(Dapp) and the heterogeneous electron-transfer rate constants(ks)for ferrocene and its seven derivatives in MPEG/LiClO4 electrolyte were determined by using steadystate voltammetry. The two parameters increase with increasing temperature, indicating Arrhenius behavior. The effects of the nature of electroactive solute molecules on Dapp, ks, and the half-wave potentials(E1/2) are discussed.

Physical Diffusion and Electron-transfer Dynamics of Electroactive Solutes in Polymer Electrolytes Ⅱ. Effect of the Ionic Size of Supporting Electrolytes

The ditheion coefficients(Dapp) and the heterogeneous electron-transfer rate constan(ks)for ferrocene in MPEG/salt electrolytes were determined by using Steady-stae voltammetry. The temperature dependence of the two parameters obeys the Arrhenius equstion. The effect of the ionic size of sir supporting electrolytes on diffusion and electron transfer dynamics of fermcene was discussed