Search Results (18)

In this study, thermodynamic properties such as water activity, osmotic coefficient, and saturation points of the aqueous mixture in the system D-Sucrose + Water + ammonium nitrate (AN) were determined at 298.15 K. The measurements were carried out on the mixtures of concentrations of NH₄NO₃ (ranging from 0.1 to 6 mol·kg⁻¹) and D-sucrose (from 0.1 to 4 mol·kg⁻¹) using our hygrometric method. Powder X-ray diffraction (XRD) and attenuated total reflection–Fourier transform infrared (ATR-FTIR) spectroscopy were used to characterize the solid phases crystallized during the supersaturation of the solution. Other thermodynamic quantities such as the solute activity coefficients, excess Gibbs energies, transfer energies, and solute solubilities were calculated using the Pitzer–Simonson–Clegg (PSC) model. The results obtained indicate that at an AN concentration lower than 1 mol·kg⁻¹, the system exhibits increasingly negative deviations from ideality, and that NH₄NO₃ promotes the salting-out effect of sucrose. Full article

A solubility model of SO₂ in multi-ion electrolyte solutions has been developed by the activity-fugacity relation at vapor-liquid equilibria. The fugacity coefficient of SO₂ in the vapor phase is calculated by the equation of state (EOS) of pure SO₂, and the activity coefficient of SO₂ in the liquid phase is calculated by the Pitzer activity coefficient theory. The model can reproduce the reliable solubility data of SO₂ in pure water and multi-ion electrolyte solutions (Na⁺, K⁺, Cl⁻, ${\mathrm{SO}}_4^{2-}$) within or close to experimental uncertainties. Although the second-order and third-order interaction parameters between SO₂ and Mg²⁺ and Ca²⁺ have been adopted by an approximation, the solubility model can also be extended to predict the SO₂ solubility in seawater. In addition, combining with the EOS of a CO₂-SO₂ fluid mixture, the model can be used to predict the solubility of a CO₂-SO₂ mixture in aqueous electrolyte solutions. The calculated results are consistent with experimental data, which indicates that the solubility model has certain predictive ability. Full article

Development of a defensible source-term model (STM), usually a thermodynamical model for radionuclide solubility calculations, is critical to a performance assessment (PA) of a geologic repository for nuclear waste disposal. Such a model is generally subjected to rigorous regulatory scrutiny. In this article, we highlight key guiding principles for STM model development and validation in nuclear waste management. We illustrate these principles by closely examining three recently developed thermodynamic models with the Pitzer formulism for aqueous H⁺—Nd³⁺—NO₃⁻(—oxalate) systems in a reverse alphabetical order of the authors: the XW model developed by Xiong and Wang, the OWC model developed by Oakes et al., and the GLC model developed by Guignot et al., among which the XW model deals with trace activity coefficients for Nd(III), while the OWC and GLC models are for concentrated Nd(NO₃)₃ electrolyte solutions. The principles highlighted include the following: (1) Principle 1. Validation against independent experimental data: A model should be validated against experimental data or field observations that have not been used in the original model parameterization. We tested the XW model against multiple independent experimental data sets including electromotive force (EMF), solubility, water vapor, and water activity measurements. The results show that the XW model is accurate and valid for its intended use for predicting trace activity coefficients and therefore Nd solubility in repository environments. (2) Principle 2. Testing for relevant and sensitive variables: Solution pH is such a variable for an STM and easily acquirable. All three models are checked for their ability to predict pH conditions in Nd(NO₃)₃ electrolyte solutions. The OWC model fails to provide a reasonable estimate for solution pH conditions, thus casting serious doubt on its validity for a source-term calculation. In contrast, both the XW and GLC models predict close-to-neutral pH values, in agreement with experimental measurements. (3) Principle 3. Honoring physical constraints: Upon close examination, it is found that the Nd(III)-NO₃ association schema in the OWC model suffers from two shortcomings. Firstly, its second stepwise stability constant for Nd(NO₃)₂⁺ (log K₂) is much higher than the first stepwise stability constant for NdNO₃²⁺ (log K₁), thus violating the general rule of (log K₂–log K₁) < 0, or $\frac{K_1}{K_2}>1$. Secondly, the OWC model predicts abnormally high activity coefficients for Nd(NO₃)₂⁺ (up to ~900) as the concentration increases. (4) Principle 4. Minimizing degrees of freedom for model fitting: The OWC model with nine fitted parameters is compared with the GLC model with five fitted parameters, as both models apply to the concentrated region for Nd(NO₃)₃ electrolyte solutions. The latter appears superior to the former because the latter can fit osmotic coefficient data equally well with fewer model parameters. The work presented here thus illustrates the salient points of geochemical model development, selection, and validation in nuclear waste management. Full article

This study focuses on the thermodynamic modeling of the crystallization by the drowning process for two lithium salts: lithium hydroxide (LiOH) and lithium formate (CHLiO₂). The modeling involves utilizing thermodynamic properties, such as the activity, osmotic, and solubility coefficients, within the ternary systems of LiOH + cosolvent + water and CHLiO₂ + cosolvent + water, as well as their respective binary constituent systems. Ethanol is chosen as the cosolvent for both salts, facilitating a comparative analysis. Given the limited availability of thermodynamic data for lithium formate with different cosolvents, the study aims to address this gap. The modified Pitzer model was employed for the modeling process, where the parameters were successfully obtained for both systems, with a deviation of less than 1%. Additionally, the mass and energy balance for the drowning-out crystallization process of both salts was performed. Full article

Ventilation Air Methane (VAM) refers to the release of fugitive methane (CH₄) emissions into the atmosphere during underground coal mining operations. Growing concerns regarding the greenhouse effects of CH₄ have led to a worldwide effort in developing efficient and cost-effective methods of capturing CH₄. Among these, absorption-based processes, particularly those using Ionic Liquids (ILs) are appealing due to their advantages over conventional methods. In this study, the solubility of CH₄ in various ILs, expressed by Henry’s law constant, is first reviewed by examining a wide range of experimental techniques. This is followed by a review of thermodynamic modelling tools such as the extended Henry’s law model, extended Pitzer’s model, Peng–Robinson (PR) equation of state, and Krichevsky−Kasarnovsky (KK) equation of state as well as computational (Artificial Neural Network) modelling approaches. The comprehensive analysis presented in this paper aims to provide a deeper understanding of the factors that significantly influence the process of interest. Furthermore, the study provides a critical examination of recent advancements and innovations in CH₄ capture by ILs. ILs, in general, have a higher selectivity for methane compared to conventional solvents. This means that ILs can remove methane more effectively from VAM, resulting in a higher purity of the recovered methane. Overall, ILs offer several advantages over conventional solvents for the after treatment of VAM. They are more selective, less volatile, have a wider temperature range, are chemically stable, and can be made from renewable materials. As a result of their many advantages, ILs are becoming increasingly popular for the after treatment of VAM. They offer a more sustainable, efficient, and safe alternative to conventional solvents, and they are likely to continue gaining market share in the coming years. Full article

The comprehensive topological isomorphism of liquid–vapor, fusibility, and solubility diagrams in the proper sets of variables is proven with the aid of van der Waals equations of the shift in phase equilibrium. Analogues of Gibbs–Konovalov and Gibbs–Roozeboom laws are demonstrated in solubility diagrams of ternary and quaternary systems under crystallization of different types of solid solutions. For the demonstration, the quaternary reciprocal system ${\mathrm{K}}^{+},{\mathrm{NH}}_4^{+}\left|\right|{\mathrm{Cl}}^{-},{\mathrm{Br}}^{-}-{\mathrm{H}}_2\mathrm{O}$ and its ternary subsystems with modeling of the liquid phase within the framework of the classical Pitzer formalism are mainly used. An algorithm for calculating solubility equilibria in these systems is given. Full article

The fundamentals of scaling during waterflooding of an oilfield are presented. Mineral precipitation is described using both the kinetics approach, with the corresponding equations given, and the thermodynamic models’ theoretical foundation discussed—mainly specific ion interaction and Pitzer models. This paper focuses on the process of mixing incompatible waters during both water injection and production from an oilfield, as this was identified as a primary reason for barium sulphate precipitation. Two methods of minimizing the risk of solid phase deposition during the mixing of water using the addition of inhibitors and removal of sulfur compounds through a membrane system before water injection into the bed are shown. In addition, formation damage to the near-well zone is discussed with its implications for field operators. Using thermodynamics, especially equations based on the HKF-SRK modified model, this paper describes typical conditions for barium sulphate precipitation during hydrocarbon production on a Polish offshore oilfield. The case study is presented using scaling tendency (ST) and solid concentration values to distinguish the most vulnerable places of solid deposition, both topside and subsurface. The importance of avoiding the mixing of incompatible waters is documented and shown in comparison to a non-mixing scenario. Full article

The significance of ion activity in transport through a porous concrete material sample with steel rebar in its center and bathing solution is presented. For the first time, different conventions and models of ion activity are compared in their significance and influence on the ion fluxes. The study closes an interpretational gap between ion activity in a stand-alone (stagnant) electrolyte solution and ion transport (dynamic) through concrete pores. Ionic activity models developed in stationary systems, namely, the Debye–Hückel (DH), extended DH, Davies, Truesdell–Jones, and Pitzer models, were used for modeling the transport of ions driven through the activity gradient. The activities of ions are incorporated into a frame of the Nernst–Planck–Poisson (NPP) equations. Calculations were done with COMSOL software for a real concrete microstructure determined by X-ray computed tomography. The concentration profiles of four ions (Na⁺, Cl⁻, K⁺, OH⁻), the ionic strength, and the electric potential in mortar (with pores) and concrete samples (with aggregates and pores) are presented and compared. The Pitzer equation gave the most reliable results for all systems studied. The difference between the concentration profiles calculated with this equation and with the assumption of the ideality of the solution is negligible while the potential profiles are clearly distinguishable. Full article

Lead–acid batteries are important to modern society because of their wide usage and low cost. The primary source for production of new lead–acid batteries is from recycling spent lead–acid batteries. In spent lead–acid batteries, lead is primarily present as lead pastes. In lead pastes, the dominant component is lead sulfate (PbSO₄, mineral name anglesite) and lead oxide sulfate (PbO•PbSO₄, mineral name lanarkite), which accounts for more than 60% of lead pastes. In the recycling process for lead–acid batteries, the desulphurization of lead sulfate is the key part to the overall process. In this work, the thermodynamic constraints for desulphurization via the hydrometallurgical route for recycling lead pastes are presented. The thermodynamic constraints are established according to the thermodynamic model that is applicable and important to recycling of lead pastes via hydrometallurgical routes in high ionic strength solutions that are expected to be in industrial processes. The thermodynamic database is based on the Pitzer equations for calculations of activity coefficients of aqueous species. The desulphurization of lead sulfates represented by PbSO₄ can be achieved through the following routes. (1) conversion to lead oxalate in oxalate-bearing solutions; (2) conversion to lead monoxide in alkaline solutions; and (3) conversion to lead carbonate in carbonate solutions. Among the above three routes, the conversion to lead oxalate is environmentally friendly and has a strong thermodynamic driving force. Oxalate-bearing solutions such as oxalic acid and potassium oxalate solutions will provide high activities of oxalate that are many orders of magnitude higher than those required for conversion of anglesite or lanarkite to lead oxalate, in accordance with the thermodynamic model established for the oxalate system. An additional advantage of the oxalate conversion route is that no additional reductant is needed to reduce lead dioxide to lead oxide or lead sulfate, as there is a strong thermodynamic force to convert lead dioxide directly to lead oxalate. As lanarkite is an important sulfate-bearing phase in lead pastes, this study evaluates the solubility constant for lanarkite regarding the following reaction, based on the solubility data, PbO•PbSO₄ + 2H⁺ ⇌ 2Pb²⁺ + SO₄²⁻ + H₂O(l). Full article

In this work, the adsorption behavior of Sr onto a synthetic iron(III) oxide (hematite with traces of goethite) has been studied. This solid, which might be considered a representative of Fe³⁺ solid phases (iron corrosion products), was characterized by X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS), and its specific surface area was determined. Both XRD and XPS data are consistent with a mixed solid containing more than 90% hematite and 10% goethite. The solid was further characterized by fast acid-base titrations at different NaCl concentrations (from 0.1 to 5 M). Subsequently, for each background NaCl concentration used for the acid-base titrations, Sr-uptake experiments were carried out involving two different levels of Sr concentration (1 × 10⁻⁵ and 5 × 10⁻⁵ M, respectively) at constant solid concentration (7.3 g/L) as a function of −log([H⁺]/M). A Surface Complexation Model (SCM) was fitted to the experimental data, following a coupled Pitzer/surface complexation approach. The Pitzer model was applied to aqueous species. A Basic Stern Model was used for interfacial electrostatics of the system, which includes ion-specific effects via ion-specific pair-formation constants, whereas the Pitzer-approach involves ion-interaction parameters that enter the model through activity coefficients for aqueous species. A simple 1-pK model was applied (generic surface species, denoted as >XOH^−1/2). Parameter fitting was carried out using the general parameter estimation software UCODE, coupled to a modified version of FITEQL2. The combined approach describes the full set of data reasonably well and involves two Sr-surface complexes, one of them including chloride. Monodentate and bidentate models were tested and were found to perform equally well. The SCM is particularly able to account for the incomplete uptake of Sr at higher salt levels, supporting the idea that adsorption models conventionally used in salt concentrations below 1 M are applicable to high salt concentrations if the correct activity corrections for the aqueous species are applied. This generates a self-consistent model framework involving a practical approach for semi-mechanistic SCMs. The model framework of coupling conventional electrostatic double layer models for the surface with a Pitzer approach for the bulk solution earlier tested with strongly adsorbing solutes is here shown to be successful for more weakly adsorbing solutes. Full article

Radionuclides are inorganic substances, and the solubility of inorganic substances is a major factor affecting the disposal of radioactive waste and the release of concentrations of radionuclides. The degree of solubility determines whether a nuclide source migrates to the far field of a radioactive waste disposal site. Therefore, the most effective method for retarding radionuclide migration is to reduce the radionuclide solubility in the aqueous geochemical environment of subsurface systems. In order to assess the performance of disposal facilities, thermodynamic data regarding nuclides in water–rock systems and minerals in geochemical environments are required; the results obtained from the analysis of these data can provide a strong scientific basis for maintaining safety performance to support nuclear waste management. The pH, Eh and time ranges in the environments of disposal sites cannot be controlled, in contrast to those under experimental conditions in laboratories. Using a hypothetical error mechanism for the safety assessment of disposal sites may engender incorrect assessment results. Studies have focused on radionuclide reactions in waste disposal, and have offered evidence suggesting that these reactions are mainly affected by the geochemical environment. However, studies have not examined the thermodynamics of chemical reactions or interactions between water and minerals, such as the surface complexation and adsorption of various nuclide-ion species. Simple coefficient models have usually been applied in order to obtain empirical formulas for deriving Kd to describe nuclide distributions in the solid or liquid phase in water–rock geochemical systems. Accordingly, this study reviewed previous research on the applications of geochemical models, including studies on the development of geochemical models, sources of thermodynamic databases (TDBs) and their applications in programs, the determination of the adequacy of TDBs in surface complexation models and case studies, and the selection and application of activity coefficient equations in geochemical models. In addition, the study conducted case studies and comparisons of the activity coefficients derived by different geochemical models. Three activity coefficient equations, namely the Davies, modified Debye–Hückel, and Pitzer equations, and four geochemical models, namely PHREEQC, MINEQL+, MINTEQA2, and EQ3/6, were used in the study. The results demonstrated that when the solution’s ionic strength was <0.5 m, the differences in the activity coefficients between the Davies and modified Debye–Hückel equations were <5%. The difference between the Pitzer and Davies equations, or between the Pitzer and modified Debye–Hückel equations in terms of the calculated activity coefficients was <8%. The effect of temperature on the activity coefficient slightly influenced the modeling outputs of the Davies and modified Debye–Hückel equations. In the future, the probability distribution and uncertainty of parameters of Kd and the equilibrium constant can be used in geochemical and reactive transport models to simulate the long-term safety of nuclear waste disposal sites. The findings of this study can provide a strong scientific basis for conducting safety assessments of nuclear waste disposal repositories and developing environmental management or remediation schemes to control sites marred by near-surface contamination. Full article

Understanding of CO₂ hydrate–liquid water two-phase equilibrium is very important for CO₂ storage in deep sea and in submarine sediments. This study proposed an accurate thermodynamic model to calculate CO₂ solubility in pure water and in seawater at hydrate–liquid water equilibrium (HL_WE). The van der Waals–Platteeuw model coupling with angle-dependent ab initio intermolecular potentials was used to calculate the chemical potential of hydrate phase. Two methods were used to describe the aqueous phase. One is using the Pitzer model to calculate the activity of water and using the Poynting correction to calculate the fugacity of CO₂ dissolved in water. Another is using the Lennard–Jones-referenced Statistical Associating Fluid Theory (SAFT-LJ) equation of state (EOS) to calculate the activity of water and the fugacity of dissolved CO₂. There are no parameters evaluated from experimental data of HL_WE in this model. Comparison with experimental data indicates that this model can calculate CO₂ solubility in pure water and in seawater at HL_WE with high accuracy. This model predicts that CO₂ solubility at HL_WE increases with the increasing temperature, which agrees well with available experimental data. In regards to the pressure and salinity dependences of CO₂ solubility at HL_WE, there are some discrepancies among experimental data. This model predicts that CO₂ solubility at HL_WE decreases with the increasing pressure and salinity, which is consistent with most of experimental data sets. Compared to previous models, this model covers a wider range of pressure (up to 1000 bar) and is generally more accurate in CO₂ solubility in aqueous solutions and in composition of hydrate phase. A computer program for the calculation of CO₂ solubility in pure water and in seawater at hydrate–liquid water equilibrium can be obtained from the corresponding author via email. Full article

The solubility in triple water-salt systems containing NdCl₃, PrCl₃, YCl₃, TbCl₃ chlorides, and water-soluble fullerenol C₆₀(OH)₂₄ at 25 °C was studied by isothermal saturation in ampoules. The analysis for the content of rare earth elements was carried out by atomic absorption spectroscopy, for the content of fullerenol—by electronic spectrophotometry. The solubility diagrams in all four ternary systems are simple eutonic, both consisting of two branches, corresponding to the crystallization of fullerenol crystal-hydrate and rare earth chloride crystal-hydrates, and containing one nonvariant point corresponding to the saturation of both solid phases. On the long branches of C₆₀(OH)₂₄*18H₂O crystallization, a C₆₀(OH)₂₄ decreases by more than 2 orders of magnitude compared to the solubility of fullerenol in pure water (salting-out effect). On very short branches of crystallization of NdCl₃*6H₂O, PrCl₃*7H₂O, YCl₃*6H₂O, and TbCl₃*6H₂O, the salting-in effect is clearly observed, and the solubility of all four chlorides increases markedly. The four diagrams cannot be correctly approximated by the simple one-term Sechenov equation (SE-1), and very accurately approximated by the three-term modified Sechenov equation (SEM-3). Both equations for the calculation of nonelectrolyte solubility in electrolyte solutions (SE-1 and SEM-3 models) are obtained, using Pitzer model of virial decomposition of excess Gibbs energy of electrolyte solution. It is shown that semi-empirical equations of SE-1 and SEM-3 models may be extended to the systems with crystallization of crystal-solvates. Full article

The interactions of epinephrine ((R)-(−)-3,4-dihydroxy-α-(methylaminomethyl)benzyl alcohol; Eph⁻) with different toxic cations (methylmercury(II): CH₃Hg⁺; dimethyltin(IV): (CH₃)₂Sn²⁺; dioxouranium(VI): UO₂²⁺) were studied in NaCl_aq at different ionic strengths and at T = 298.15 K (T = 310.15 K for (CH₃)₂Sn²⁺). The enthalpy changes for the protonation of epinephrine and its complex formation with UO₂²⁺ were also determined using isoperibolic titration calorimetry: ΔH_HL = −39 ± 1 kJ mol⁻¹, ΔH_H2L = −67 ± 1 kJ mol⁻¹ (overall reaction), ΔH_ML = −26 ± 4 kJ mol⁻¹, and ΔH_M2L2(OH)2 = 39 ± 2 kJ mol⁻¹. The results were that UO₂²⁺ complexation by Eph⁻ was an entropy-driven process. The dependence on the ionic strength of protonation and the complex formation constants was modeled using the extended Debye–Hückel, specific ion interaction theory (SIT), and Pitzer approaches. The sequestering ability of adrenaline toward the investigated cations was evaluated using the calculation of pL_0.5 parameters. The sequestering ability trend resulted in the following: UO₂²⁺ >> (CH₃)₂Sn²⁺ > CH₃Hg⁺. For example, at I = 0.15 mol dm⁻³ and pH = 7.4 (pH = 9.5 for CH₃Hg⁺), pL_0.5 = 7.68, 5.64, and 2.40 for UO₂²⁺, (CH₃)₂Sn²⁺, and CH₃Hg⁺, respectively. Here, the pH is with respect to ionic strength in terms of sequestration. Full article

In this work, a thermodynamic model of CO₂-H₂O-NaCl-MgCO₃ systems is developed. The new model is applicable for 0–200 °C, 1–1000 bar and halite concentration up to saturation. The Pitzer model is used to calculate aqueous species activity coefficients and the Peng–Robinson model is used to calculate fugacity coefficients of gaseous phase species. Non-linear equations of chemical potentials, mass conservation, and charge conservation are solved by successive substitution method to achieve phase existence, species molality, pH of water, etc., at equilibrium conditions. From the calculated results of CO₂-H₂O-NaCl-MgCO₃ systems with the new model, it can be concluded that (1) temperature effects are different for different MgCO₃ minerals; landfordite solubility increases with temperature; with temperature increasing, nesquehonite solubility decreases first and then increases at given pressure; (2) CO₂ dissolution in water can significantly enhance the dissolution of MgCO₃ minerals, while MgCO₃ influences on CO₂ solubility can be ignored; (3) MgCO₃ dissolution in water will buffer the pH reduction due to CO₂ dissolution. Full article