Values Of Equilibrium Constants Research Articles

Remarks on the Evaluation of Thermodynamic Data for Sulfate Ion Protonation

A thorough search of the scientific literature under the auspices of the IUPAC Sub-Committee on Solubility and Equilibrium Data (SSED) has identified and compiled quantitative thermodynamic data for the first sulfate protonation step from about 270 papers, reports, books and electronic databases. A critical evaluation of these sources using well-defined criteria has rejected about half of them. The remaining (‘accepted’) data reveal that the standard state values of the first protonation constant of the sulfate ion, $$K_{1}^{\text{o}}$$, corresponding to the equilibrium: $${\text{SO}_{4}^{2 - }} ({\text{aq}}) + {\text{ H}}^{ + } \left( {\text{aq}} \right) \rightleftharpoons {{\text{HSO}}_{4}^{ - }}({\text{aq}})$$ at infinite dilution, are known to good levels of accuracy up to ~ 250 °C. However, at higher temperatures, and at all temperatures in the presence of added electrolytes, the equilibrium constant values are much less certain. The corresponding values for the enthalpy ($$\Delta_{\text{r}} H_{1}^{\text{o}}$$), entropy ($$\Delta_{\text{r}} S_{1}^{\text{o}}$$) and isobaric heat capacity ($$\Delta_{\text{r}} C_{p,1}^{\text{o}}$$) changes are also moderately well determined at near-ambient temperatures but are much more poorly defined both at higher temperatures and in the presence of even modest concentrations of added electrolytes. Comments on a number of aspects of the data and their evaluation are provided.

Determination of the hydrogen-bond acidity and basicity for un-dissociated hydrazoic acid, isocyanic acid and isothiocyanic acid

Literature values of water-solvent partition coefficients for un-dissociated hydrazoic acid, isocyanic acid and isothiocyanic acid have been used to obtain properties or ‘descriptors’ of the three acids. These descriptors can be used in linear free energy relationships that we have already obtained to predict further values of partition coefficients for a very large number of solvents. The descriptors include the hydrogen-bond acidity, A, and hydrogen-bond basicity, B, of the acids. We have also used literature values of equilibrium constants for 1:1 complexation of the acids with a number of bases to obtain values of our 1:1 hydrogen-bond acidity, αH2. There is very good agreement between the two sets of hydrogen-bond acidity. Isothiocyanic acid is a strong hydrogen-bond acid about the same as chloroacetic acid, isocyanic acid is about as strong as acetic acid and hydrogen azide is a moderate-to-weak hydrogen bond acid. The hydrogen-bond basicity of the three acids is very small.

Where to find equilibrium constants?

A crucial part of any equilibrium modelling calculation is the selection of equilibrium constants that quantify the strength of interactions between metals and ligands. For researchers new to the field of solution chemistry, locating suitable equilibrium constants that lead to reliable model results can be problematic. Numerous large compilations of equilibrium constant values have been published each having their own limitations, coverage and availability. This work surveys eleven major compilations of equilibrium constants including those from authoritative groups such as IUPAC, NIST, and NEA. For each compilation surveyed, details are given related to the historical background and underlying project, scope of the database with respect to range of included metals and ligands, and the present-day availability of publications or computer databases resulting from the project. The various methods employed by different data compilers in their critical assessment for each compilation are also discussed.

Explore the competency of natural diluents with Tri-n-octylamine for the extractive separation of malonic acid

Abstract Since last 50 years, the malonic acid is produced from petroleum feedstock while recently a patent is filed by Lygos, Inc., a lab in Berkeley, California to produce malonic acid through genetically natural yeast cells by biological fermentation. Like all fermentation process the proposed method is both environment and economically friendly. The study is explore the reactive extraction of malonic acid from aqueous phase with nontoxic natural diluents for instance sunflower oil, rice bran oil, sesame oil and tri-n-octylamine as an extractant in view of novel finding in fermentation technology. The physical extraction (extraction with diluents) failed to extract any acid from aqueous solution so the extracting power depends only on extractant. The results are tabulated in terms of distribution coefficient, δ (9.633–34.436 for sunflower oil, 12.089–33.014 for sesame oil, and 11.151–37.655 for rice bran oil), loading factor, φ (0.280–4.067 for sunflower oil, 0.280–4.086 for sesame oil, and 0.280–4.123 for rice bran oil) and extraction efficiency, ƞ (90.595–97.178% for sunflower oil, 92.360–97.060% for sesame oil, and 91.770–97.413% for rice bran oil). Further overall equilibrium constant values, ɛ are in the range of 0.213–0.670 L/mol for sunflower oil, 0.208–0.671 L/mol for sesame oil, and 0.212–0.673 L/mol for rice bran oil for 0.23–0.69 mol/L of TOA. The results show that up-to 30% TOA in nontoxic diluents is suitable for the reactive extraction of malonic acid. Further, water co-extraction phenomenon also discussed and found that water co-extraction was observed more for rice bran oil.

NITROGEN STEELS AND HIGH NITROGEN STEELS. INDUSTRIAL TECHNOLOGIES AND PROPERTIES

Nitrogen pressure can be a basis for the most general classification of steel, alloyed by nitrogen. Nitrogen steels are made under normal pressure, high nitrogen steels are made under pressure that is higher than atmospheric in special units. Nitrogen, as well as carbon, also strengthens austenite, but increases thermal stability of austenite, has the smaller sizes of ions and high solubility in γ- and α-phases. The result is smaller size of nitrides, smaller superficial energy, their higher strengthening effect and possibility of simultaneous increase in durability and corrosion resistance of austenite. The article considers the mechanisms of nitrogen influence on properties of steel, thermodynamics and kinetics of steels alloying with nitrogen, critical concentration of nitrogen and influence of nitrogen on properties of steel. There is no uniform balanced database and thermodynamic model now. Therefore any choice of values of equilibrium constant and parameters of interaction according to tabular data reduces the accuracy of calculations of nitrogen solubility in steel. In the circumstances it is better to use experimental data for concrete alloy from original works. At the choice of data it is necessary to be guided by the following control values: KN = 0,044, A ≥ 600. The nitrogen solubility in liquid metal, in α- and γ-phases is significantly various. Critical nitrogen concentration Nk, which excess leads to formation of bubbles and interstices at steel solidification, depends on composition of steel. Now the acceptable results when determining critical nitrogen concentration, can be received from the following condition: during the whole time of solidification the nitrogen content in residual liquid has to be less its equilibrium with the general pressure in the system of content in liquid metal at the same temperature T. Examples of nitrogen and high nitrogen steels, including steels with special properties, such as corrosion-resistant in bioactive environments, bactericidal steel, alloyed according on the scheme C + N steels, are given.

Synthesis of 1-benzyl-1H-benzimidazoles as galectin-1 mediated anticancer agents

In our pursuit to develop novel non-carbohydrate small molecule Galectin-1 Inhibitors, we have designed a series of 1-benzyl-1H-benzimidazole derivatives and demonstrated their anticancer activity. The compound 6g, 4-(1-benzyl-5-chloro-1H-benzo[d]imidazol-2-yl)-N-(4-hydroxyphenyl) benzamide was found to be most potent with an IC50 of 7.01 ± 0.20 µM and arresting MCF-7 cell growth at G2/M phase and S phase. Induction of apoptosis was confirmed by morphological changes like cell shrinkage, blebbing and cell wall deformation, dose dependent increase in the mitochondrial membrane potential (ΔΨm) and ROS levels. Further, dose dependent decrease in Gal-1 protein levels proves Gal-1 mediated apoptosis by 6g. Molecular docking studies were performed to understand the Gal-1 interaction with compound 6g. In addition, RP-HPLC studies showed 85.44% of 6g binding to Gal-1. Binding affinity studies by fluorescence spectroscopy and Surface Plasmon Resonance (SPR) showed that 6g binds to Gal-1 with binding constant (Ka) of 1.2 × 104 M−1 and equilibrium constant KD value of 5.76 × 10−4 M respectively.

DETERMINATION OF TYPE OF SOLVATE OF PHOSPHORIC ACID DURING ITS EXTRACTION BY TRIBUTYL PHOSPHATE

The extraction of phosphoric acid with a solution of tri-n-butyl phosphate (TBP) in toluene from its individual aqueous solutions in a concentration range of 0-11 M is investigated. The experiments are performed at room temperature (20 ± 1 °С). The isotherms of extraction of phosphoric acid under conditions of equality of the volumes of the saturating aqueous phase and the receiving organic phase are constructed. The extraction isotherm is nonlinear, but to an acid concentration in the aqueous phase of ~ 8 M, it is close to linear, and at higher concentrations, the amount of extracted acid increases harshly. To establish the mechanism of acid extraction in the system phosphoric acid – 0.1 M solution of TBP in toluene the method of combining a laboratory and computational experiment is proposed. The optimal parameters describing the extraction of phosphoric acid from natural aqueous solutions are determined. Calculations performed in two approximations were made. In the first approximation the condition of ideality of systems is accepted. In the second approximation the deviations of the properties of phosphoric acid solutions in aqueous solution are taken into account. For the two approximations the preferential extraction of phosphoric acid molecules in the form of H3PO4 ∙ nTBP type solvates (where n = 1, 3) is shown. In the range of concentrations of phosphoric acid in the aqueous phase from 6 to 11 M, the values of equilibrium constants are estimated, which describe the processes and reactions occurring in the system: stepwise dissociation of acid, distribution of TBP, formation of solvates of phosphoric acid, distribution of the resulting solvates of acid, displacement of ionic equilibria in aqueous phase. Mathematically these processes are taken into account using the law of mass action and the equations of material balance. It is believed that the system has established an equilibrium corresponding to a given temperature and pressure. The calculated values of solvate concentrations are in satisfactory agreement with experimental data.

Myristic acid based imidazoline derivative as effective corrosion inhibitor for steel in 15% HCl medium

There is a high demand of effective and eco-friendly corrosion inhibitor for industrial applications. In an attempt to prepare a benign and effective corrosion inhibitor for acidizing purpose, an imidazoline derivative, N-(2-(2-tridecyl-4,5-dihydro-1H-imidazol-1-yl)ethyl)tetradecanamide (NTETD) was synthesized from myristic acid and diethyleneamine. The characterization of the newly synthesized compound was done using 1H NMR, FTIR, and elemental analysis techniques. NTETD was examined as a corrosion inhibitor for low carbon steel in 15% HCl solution using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), linear polarization (LPR), scanning electron microscope (SEM), energy dispersive spectroscopy (EDAX), atomic force spectroscopy (AFM), and X-ray photoelectron spectroscopy (XPS) techniques. It was found that, the optimum concentration of NTETD is 300 mg/L. With this concentration, inhibition efficiency above 93% is achievable. Results from PDP show that, NTETD acted as a mixed type corrosion inhibitor but with principal effect on cathodic corrosion half reactions. The calculated value of the adsorption-desorption equilibrium constant (1.015 × 103) reveals a strong bonding between NTETD molecules and the steel surface. The EDAX, FTIR, and XPS results confirm the adsorption of NTETD molecules on the steel surface. SEM and AFM results agree with experimental findings that NTETD is effective in corrosion mitigation of steel in 15% HCl solution. The possible corrosion inhibition mechanism by NTETD has been proposed.

Model and Algorithm for Calculating the Formation of Phases in Aqueous Solutions of Metal Salts

An equilibrium model and an algorithm for processing experimental potentiometric titration data are developed that improve the reliability of results on phase formation in aqueous solutions of metal salts. In creating the model, it is proposed that the formation of polynuclear, heteroligand compounds and fluctuations of the system parameters be considered, and that the laws of molecular solubility, solubility over an intermediate, and identifying the main sediment be used. To derive the material balance equations of the studied systems, software is developed that allows calculations of the number of particles in the system, the values of equilibrium constants, and the composition of compounds, in addition to automatic selection of the functions that describe random processes when estimating the uncertainty of equilibrium constant values.

Experimental and Modeling Study of Vapor Liquid Equilibrium for a Methyldiethanolamine–CO2–H2S–Water Quaternary System Using Activity Coefficient Models with Corrected Equilibrium Constants

The solubilities of CO2 and H2S mixtures in methyldiethanolamine aqueous solutions were investigated in the wide temperature range from 313.15 (absorption range) to 403.15 K (stripping range) using the static method. The values of equilibrium constants for amine protonation (K1), activity coefficients (γi), and fugacity coefficients (Φi) were regressed from the newly obtained experimental solubility data to correct nonideality. In order to obtain the equilibrium constants for amine protonation, modified Kent–Eisenberg model was applied. Then, two kinds of activity coefficient models, the Deshmukh–Mather model and the electrolyte nonrandom two-liquid model, were applied to minimize the gaps between experimental data and predicted values with newly obtained equilibrium constants. In this study, six thermodynamic models were presented by combining (1) equilibrium model and (2) activity coefficient models. Based on the best fitted solubility results, the mole fractions of all electrolytes, the pH in the liqui...

Silver(I) chlorides speciation and its relationship to the design, construction and evaluation of true Ag(s)/[AgCln]1−n reference electrodes for their use in bis(trifluoromethylsulfonyl)imide room temperature ionic liquids

This study describes a methodology for the design of true reference electrodes of the second kind based on the chemical speciation of the system AgCl(s)/[AgCln]1−n in both homogeneous and heterogeneous systems in bis(trifluoromethylsulfonyl)imide room temperature ionic liquids (RTIL), based on measurements of the open circuit potential (OCP) of Ag(s) or Ag(s)|AgCl(s) indicator electrodes immersed in solutions of Ag [NTf2] and [C2mim]Cl in RTIL, as well as on representative potentiometric titrations of Ag(I) or of chloride ions in the same media. The found values of the apparent equilibrium constants of the chemical equilibrium processes associated to the electrode potential at the metal|RTIL interface, lay the foundation for the design of true reference electrode systems. To test the usefulness of the information collected during the chemical speciation of these systems, four true reference electrodes were built for their use in four imidazolium-based bis(trifluoromethylsulfonyl) RTIL, and their electrode potentials were determined over time using the [Co(Cp)2]+/0 or [Fe(Cp)2]+/0 redox couples as internal redox references. The aim of this work is to provide a simple method for the development and characterization of true reference electrodes for their use in RTIL, thus averting the use of QRE and enabling the construction of comparable potential scales in RTIL.

Mass Balance Simulation for Steam Reformer in Direct Reduction of Iron Ore by Hyl III Process.

HYL direct reduction of iron ore process uses a reducing gas composed of a mixture of H2 and CO in order to reduce iron oxide pellets to metallic iron (DRI). This process is mainly dependent on a reformer to supply the reducing gas. In the reformer, natural gas is catalytically converted into reducing gas by reaction with steam at a temperature of 800 to 850°C and pressure between 8 and 8.5 bars in the presence of Nickel based catalyst. In order to analyze the reformer operation, it is necessary to estimate the reformed gas composition for some specific process conditions.The present work is based on the solution of a set of non-linear equations describing mass balances of carbon, hydrogen, oxygen and higher hydrocarbons, to enable the calculation of reformed gas composition for a steam reformer. The procedure can assist both process engineers tackling the problem of estimating output from a primary reformer at the design stage and plant operating engineers. The mass balance equations are solved by using the equilibrium constants for the reforming and water gas shift reactions. This includes simultaneously solving non-linear equations relating to the composition of reactants and other variables as temperature and pressure at which reactions take place. In addition, amount of carbon contained in natural gas compared to amount of steam used in steam reforming reaction is also considered during calculations. The basic requirements to establish the model are a set of reactions and values of equilibrium constants for the reforming and water gas shift reactions.

Fluorescence correlation spectroscopy for multiple-site equilibrium binding: a case of doxorubicin-DNA interaction.

Quantitative description of the interaction between doxorubicin (DOX), a broadly used anticancer drug, and DNA is the key to understand the action mechanism and side effects of its clinical use. However, the reported equilibrium constants of DOX-DNA interaction obtained using a range of different analytical methods vary even by several orders of magnitude. Herein, we propose a novel application of a single-molecule technique - fluorescence correlation spectroscopy (FCS) - to probe the interaction between DOX and two types of DNA (pUC19 and calf thymus DNA), taking advantage of intrinsic self-fluorescence of DOX. We provide an analytical formula for autocorrelation analysis to determine the equilibrium constant of DOX-DNA complex-formation, where binding of multiple DOX molecules to a DNA chain is included in the reaction-diffusion model. Our FCS-based method not only quantitatively revealed the values of equilibrium constant, but also implied that the stability of DOX-DNA complex is related to the types of base pair rather than the length or structure of the DNA. This work opens a promising pathway toward quantitative determination of molecular interactions in complex systems such as living cells or organisms at single-molecule level.

The values of ΔfG°T(Aln) (n = 3–10 atoms, T ≤ 3000 K), determined using the ROCBS-QB3 values of S°T(Aln) and of the corrected values of ΔfH°T(Aln)

In the present work, the values of ΔfG°T(kAln)CORR have been determined on the basis of the thermochemistry of atomization reactions (ΔrG°T(kAln → n2Al) = ΔrH°T(kAln → n2Al) − TΔrS°T(kAln → n2Al)), calculated using the ROCBS-QB3 values of S°T(kAln) and corrected values of ΔfH°T(kAln)CORR as well as of the tabulated values of 2Al. The values of ΔfH°T(kAln)CORR have been determined using the temperature dependencies of ROCBS-QB3 values of ΔfH°T(kAln), calculated at T ≤ 3000 K, and the corrected values of ΔfH°298.15(kAln, 2 < n ≤ 10 atoms)CORR, determined using the perfect linear correlation dependence, proposed in the present work for the clusters Xm (m ≤ 8 atoms), formed by the elements of the third row of the periodic table of elements (X = Na, Mg, Si, S, P and Cl, m ≥ 2 atoms).The values of ΔfH°298.15(kAln, 2 < n ≤ 10 atoms)CORR and ΔfH°0(kAln, 2 < n ≤ 10 atoms)CORR have been in good agreement, respectively, with the values of ΔfH°298.15(kAln, 2 < n ≤ 10 atoms), determined using the ROCBS-QB3 and CBS-Q thermochemistry of isodesmic and non isodesmic reactions, as well as with the theoretical values of the cohesive energies, reported previously. The CBS-Q and CBS-QB3 approaches have not been used for the calculations of the values of ΔfH°T(kAln, 2 < n ≤ 10 atoms) due to the spin contamination problems.At the same time, the effect of the spin contamination on the values of S°298.15(Xm) has not been significant, and has not been expected for the values of S°298.15(kAln). The values of S°298.15(Xm) and S°298.15(kAln), calculated using the different QM approaches (CBS-Q, RO/CBS-QB3, LSDA, PBEPBE, MP2) have been in the agreement each with the others. However, the more consistent values of S°298.15(kAln) have been determined using the correlation dependencies between the tabulated and calculated values of S°298.15(Xm).The values of ΔfG°T(kAln, n > 4 atoms), calculated in the present work, have been up to 250 kJ/mol higher those theoretical values, reported previously. The corresponding values of equilibrium constants (K°p)n−1 of reactions kAln = 2Al + k±1Aln−1 (n > 3 atoms) indicate that the contribution of the kAln clusters to the gas phase oxidation of 2Al is insignificant.

Study on a Microreaction Process for Synthesis of Polyaniline

ABSTRACTA catalytic continuous microreaction process for synthesis of polyaniline (PANI) under solar light was investigated. The polymerization of aniline was conducted via a photochemical method. The photopolymerization method yields a polymeric material that has been characterized by Fourier-transform infrared spectroscopy analysis and by scanning electron microscopy. It is shown that the functional groups and surface morphology are affected by solar incident energy where the PANI main vibrational bands become wider, resulting in higher concentration of rings. Results showed that solar intensity enhanced the average yield by 5% over that of indirect solar, while the average time of polymerization is reduced by 17%. The polymerization time was reduced by 20–​27% while the temperature was increased from 5°C​ to 25°C under indirect solar and direct solar, respectively. The yield of PANI is reduced from 94.0% to 84.2% as liquid hour space velocity (LHSV) is increased from 0.145 to 0.385 min−1. An optimum molar ratio of about 1.25 is found to give the maximum yield of PANI. Kinetic analysis revealed that a pseudo-first-order Langmuir–​Hinshelwood model is well expressing the oxidation rate of aniline over TiO2. The values of the adsorption equilibrium constant, , and the kinetic rate constant of surface reaction, , are 0.0209 and 0.791 (L−1g min−1), respectively. Comparison between microreactor's performance and performance of batch reactors from published literature was presented. The comparison confirmed the unique characteristics of the microreactor.

Predicting the electrokinetic properties of the crude oil/brine interface for enhanced oil recovery in low salinity water flooding

The low-salinity waterflooding (LSWF) technique during enhanced oil recovery has received increasing attention over the last decade. Several studies have attempted to understand the effects of LSWF through both experiments and modelling, but their results are inconsistent due to a lack of understanding of the crude oil/brine and brine/rock interfaces. In this paper, the crude oil/brine interface was studied by developing a triple-layer surface complexation model. The carboxyl groups (–COOH) were attributed to the surface charge and electrical triple-layer development of the crude oil in LSWF. The zeta potentials of the emulsion at various pH levels and the calcium and magnesium concentrations were measured to examine the interface. These data were then directly fitted to the simulated zeta potentials to determine the surface site density of –COOH and the associated equilibrium constants for the dissociation and adsorption of calcium and magnesium. The –COOH site density was determined by fitting the pH-independent zeta potential, while the equilibrium constant values were estimated from the variations in the zeta potential with the changes in pH and the concentrations of calcium and magnesium. The determined surface complexation parameters were validated by comparing the experimental zeta potential data from different ionic solutions. The developed surface complexation model was used along with the estimated parameters to predict the interface of crude oil in seawater, formation water, and their dilutions. The simulated zeta potential results agreed well with the experimental data, demonstrating that the model is applicable to understand the crude oil/brine interface in LSWF. Finally, the importance of the prediction of the surface and zeta potentials in the evaluation of the interface and the estimation of electrostatic forces, and thus the wettability alteration, was discussed.

Determination of maximum loading capacity of polyamidoamine (PAMAM) dendrimers and evaluation of Cu55 dendrimer‐encapsulated nanoparticles for catalytic activity

AbstractSpectrophotometric titrations provide information about the interior of the polyamidoamine (PAMAM) dendrimers, and therefore how nanoparticles are encapsulated. In this work, binding studies were performed to determine maximum loading capacities (N) of hydroxyl terminated G4, G5, and G6 PAMAM dendrimers with Cu2+ ions. The values of N found via spectrophotometric titrations were 16.22, 31.86, and 57.36 for G4‐OH, G5‐OH, and G6‐OH, respectively. The determination of loading capacity was also done using Viva spin filtration, and the results were found to be in agreement with those found via spectrophotometric titrations. From the binding isotherm, the values of equilibrium constant (K′) were determined and found to be 0.0488 (G4‐OH), 0.0291 (G5‐OH), and 0.0158 (G6‐OH). Owing to instability of G4‐OH (Cu16), G5‐OH (Cu32), and G6‐OH (Cu57) dendrimer‐encapsulated nanoparticles (DENs) synthesized, G6‐OH (Cu55) DENs of average size 2.6 ± 0.3 nm were prepared and were found to be relatively stable. Thus G6‐OH (Cu55) catalyst was evaluated for the reduction of 4‐nitrophenol and was found to be catalytically active toward reduction of 4‐nitrophenol. Reaction kinetics of 4NP reduction was thoroughly studied in light of the Langmuir‐Hinshelwood kinetic model, and surface rate k, and the adsorption rates K4NP, and KBH4 were determined. The reaction was performed at different temperatures, which further expanded the study into determination of thermodynamic (ΔH‡, ΔS‡, ΔG‡, and EA) parameters.

Thermodynamic investigation of Hoechst 33258-poly(A).poly(U) binding through calorimetric studies

Abstract Interaction of the important minor groove binder Hoechst 33258 with poly(A).poly(U) was studied using isothermal titration calorimetry. The equilibrium constant of the association was calculated to be (4.00 ± 0.80) 106 M−1 at 298.15 K. The Hoechst RNA binding was driven by large negative enthalpy contributions. The equilibrium constant values for the binding reaction decreased with increasing [Na+] concentration. Parsing of the standard molar Gibbs energy change revealed that non-polyelectrolytic forces dominated the complexation process at all the salt concentrations studied. Temperature dependent calorimetric studies revealed that the equilibrium constant decreased in magnitude with increasing temperature in the range (288.15 ± 0.10)–(308.15 ± 0.10) K. Furthermore, there were significant alterations in the thermodynamic parameters with change in temperature; the binding became increasingly enthalpy driven and the standard molar entropic contribution decreased in magnitude and became unfavourable as the temperature was increased. Negative heat capacity change and an enthalpy-entropy compensation phenomenon were also observed. The data observed may be useful for developing structure selective RNA-based therapeutics.

Calcium–sodium exchange equilibria in two soils of Chambal Command Area of Rajasthan, India

AbstractCalcium–sodium exchange equilibria were studied at 15 and 25 °C in 2 smectite dominant soils belonging to Typic Haplustalf (Bundi Series) and Typic Pellustert (Chambal series) of Chambal Command Area of Rajasthan (India). These soils had preference for Na+ over Ca2+; however, the soil of Bundi Series at low Na saturation (10%) showed a preference for Ca2+ at lower temperature only. Higher specificity for Na+ in Chambal Series was related to the presence of zeoloites. The relationship between exchangeable sodium ratio and sodium adsorption ratio was nonlinear, and Chambal Series could maintain relatively lower sodium adsorption ratio even at higher exchangeable sodium ratio. Among different calculated selectivity coefficients, Gapon selectivity coefficient (KG) registered the lowest coefficient of variation. The values of thermodynamic equilibrium constant (K) were greater than unity indicating higher preference for Na+, especially in Chambal Series. The Ca↔Na exchange reaction was associated with an increase in the entropy of the system in these soils.

A Thermodynamic Model for ZrO2(am) Solubility at 25 °C in the Ca2+–Na+–H+–Cl−–OH−–H2O System: A Critical Review

Zirconium is an important element in the nuclear fuel cycle. Thermodynamic data and models to reliably predict Zr–OH system behavior in various conditions including high ionic strengths are required and currently are unavailable. Most available experimental data are rather old, obtained using inadequate methodologies, and provide equilibrium constant values that differ by many orders of magnitude. Previous reviews have recommended values based on available data. These reviews used all of the available data, including poor quality data, in a global fit to determine these values. This has resulted in recommended thermodynamic models with a large number of polynuclear species and a number of mononuclear species with values of thermodynamic constants for the solubility product of ZrO2(am) and Zr–OH hydrolysis constants that are many orders of magnitude different from those for the reliable analogous Hf reactions. In this critical review, we have evaluated the quality of the available data, selected only those data that are of high quality, and reinterpreted all of the high quality data using SIT and Pitzer models for applications to high ionic strength solutions. Herein for 25 °C we (1) present formation constant values for ZrOH3+, $$ {\text{Zr}}\left( {\text{OH}} \right)_{2}^{2 + } $$ , Zr(OH)4(aq), $$ {\text{Zr}}\left( {\text{OH}} \right)_{5}^{ - } $$ , and $$ {\text{Zr}}\left( {\text{OH}} \right)_{6}^{2 - } $$ , and the solubility product for ZrO2(am) which are consistent with the Hf system, (2) report a revised value for the formation constant of $$ {\text{Ca}}_{3} {\text{Zr}}\left( {\text{OH}} \right)_{6}^{4 + } $$ , (3) show that several hypothetical polynuclear species ( $$ {\text{Zr}}_{3} \left( {\text{OH}} \right)_{9}^{3 + } $$ , Zr4(OH) 15 + , and Zr4(OH)16(aq)) proposed in previous reviews are not needed, and (4) show that polynuclear species ( $$ {\text{Zr}}_{3} \left( {\text{OH}} \right)_{4}^{8 + } $$ and $$ {\text{Zr}}_{4} \left( {\text{OH}} \right)_{8}^{8 + } $$ ) are not important in a very extensive H+ concentration range (0.1–10−15.4 mol·kg−1). Our review has also resulted in SIT and Pitzer ion-interaction parameters applicable to as high ionic strength solutions as 5.6 mol·kg−1 in NaCl, 2.11 mol·kg−1 in CaCl2, and 23.5 mol·kg−1 in NaOH.