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The underground brines in the Sichuan Basin of China are rich in lithium, potassium, strontium, chlorine, etc. In order to fully develop and utilize these brine resources, it is necessary to carry out phase equilibrium research about the quaternary system LiCl–KCl–SrCl2–H2O and develop a reasonable lithium extraction process. The quaternary system LiCl–KCl–SrCl2–H2O at 273.2 K were determined using the isothermal dissolution equilibrium method. As a result, the corresponding phase diagrams were drawn based on the data. The phase diagram shows that the quaternary system LiCl–KCl–SrCl2–H2O has no double salt or solid solution at 273.2 K and there are two invariant points, five univariate curves and four solid phase crystallization fields, which are LiCl·2H2O, SrCl2·2H2O, SrCl2·6H2O and KCl. Furthermore, Pitzer's model was used to predict the solubility of salts in the quaternary system. The calculated values are in good agreement with the experimental ones. Finally, combined with isothermal evaporation method and the phase diagram of the quaternary system, a brine evaporation process was designed. [ABSTRACT FROM AUTHOR]

Sichuan Basin of China is a typical underground brine enrichment area. In order to develop and utilize the brine resource, it is necessary to study the phase equilibria and phase diagram of brine systems. In this work, the phase equilibria of the quinary system NaCl + KCl + MgCl2 + SrCl2 + H2O (saturated with NaCl) at 308.2 K of the underground brines in Sichuan Basin are measured experimentally by isothermal dissolution equilibrium method. The phase diagram, water content diagram, and sodium chloride content change diagram of the quinary system with NaCl saturated are also drawn, respectively. The results show that the phase diagram of the quinary system contains three invariant points, seven isothermal solubility curves, and five solid crystal zones at 308.2 K. In the phase diagram, the KCl crystallization area is the largest, followed by SrCl2·6H2O, KCl·MgCl2·6H2O, and SrCl2·2H2O, while MgCl2·6H2O has the smallest crystallization area. Magnesium chloride in the quinary system has the largest solubility and has strong salting‐out effect on other salts. Furthermore, the unreported mixed ion interaction parameters θMg, Sr and ΨMg, Sr, Cl of Pitzer model are fitted, respectively. Consequently, the solubilities of the quinary system NaCl + KCl + MgCl2 + SrCl2 + H2O at 308.2 K are predicted using the Pitzer model, and the calculated phase diagram at 308.2 K is also plotted in detail. The predicted solubilities of the quinary system were in good agreement with the experimental solubilities. Finally, the study on the phase equilibrium of the quinary system can provide phase equilibrium data for the development and utilization of liquid mineral resources. [ABSTRACT FROM AUTHOR]

The solubility diagram of the ternary system GdCl3–TbCl3–H2O is studied by means of isothermal saturation in ampules at 25°С. A continuous series of solid solutions of isovalent substitution crystallizes in the system The diagram of solubility in the three-component system GdCl3–TbCl3–H2O at 25°C is calculated according to the classical Pitzer model. Results from experiments agree convincingly with ones from thermodynamic modeling. [ABSTRACT FROM AUTHOR]

In this work, the isothermal dissolution equilibrium method was used to investigate the solid-liquid equilibrium of the quaternary system NaBr–KBr–CaBr2–H2O at 273.15 K. The isothermal solubility of three bromides in aqueous solution was measured, and the dry salt phase diagram and water diagram were constructed. The determination results indicate that the system is a simple co-saturation type, and the equilibrium crystals are all simple salts. The isothermal phase diagram of the quaternary system NaBr–KBr–CaBr2–H2O at 273.15 K contains three isothermal dissolution lines intersecting at an invariant point. The saturated salts at this point are: NaBr⋅2H2O, KBr, and CaBr2⋅6H2O. The entire phase space of the dry salt phase diagram is divided into three parts by three isotherms, that is, the crystalline region of NaBr⋅2H2O that occupies most, the larger crystalline region of KBr and the narrow crystalline region of CaBr2⋅6H2O. The invariant point characteristics of the system at different temperatures were compared, and the Pitzer model was used to theoretically predict the isothermal solubility of the quaternary system at 273.15 K. Since the selected parameters in the calculation program come from the temperature correlation equation reported in the literature, the reliability of the parameters is relatively strong. The predicted value of solubility has a small deviation from the experimental value, and the result proves that the reliability of the experimental data is strong. The results of the phase equilibrium study not only reveal the dissolution and crystallization rules of bromine salts in the brine of oil and gas fields in the Sichuan Basin, but also verify the applicability of the Pitzer model in predicting the solubility of low-temperature bromine-containing system. [ABSTRACT FROM AUTHOR]

Neodymium (Nd), a rare earth element (REE), is critical to numerous industries. Neodymium can be extracted from ore concentrates, waste materials, or recycled materials such as recycled Nd-Fe-B permanent magnets. In a standard process, concentrated sulfuric acid (H2SO4) is used as an extraction/leaching agent. Therefore, knowledge of Nd(III)–sulfate interaction at high ionic strengths is important for optimization of the extraction process. In addition, sulfate is also a major species in natural surface waters and present in nuclear waste streams. Nd(III) has been used a chemical analog to trivalent actinides in nuclear waste research and development. Consequently, knowledge of Nd(III)-sulfate interactions is also impactful to the field of nuclear waste management. In this study, we have developed a thermodynamic model that can describe the interaction of Nd(III) with sulfate to ionic strengths up to ~ 16.5 mol·kg–1 and to temperatures up to 100 °C. The model adopts the Pitzer formulation to describe activity coefficients of aqueous species. This model can be used to design and optimize a chemical process for REE recovery from ore concentrates, recycled materials, and acid mine drainage (AMD) and to understand the mobility of REEs and actinides in the environment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Alkaline leaching is an effective method for dealing with arsenic-containing resources. Arsenic is dissolved in an alkaline solution in the form of arsenate, but the lack of relevant basic data has caused difficulties in the theoretical analysis during production and research. The dissolution behavior of arsenic in the solution was systematically studied in this paper. The solubility behavior of the self-made sodium arsenate in water and NaOH solution were measured. The research on sodium arsenate solution was carried out to obtain the quasi-solubility product using the Pitzer model, and the effect of temperature and NaOH concentration on the solubility and quasi-solubility product of sodium arsenate was clarified.

We studied the thermodynamic properties of the lithium perchlorate (LiClO4) + ethylene carbonate (EC) +water ternary system by using cell potential measurements. Thermodynamic properties reported were obtained using the electrochemical cell: Li-ISE|LiClO4(m)|ClO4-ISE in a variety of mixed solvent systems containing 0, 10, 20 and 30% mass fractions of ethylene carbonate in water + EC mixtures (wEC/wmixture% = 0, 10, 20 and 30) on the wide range of ionic strength from 0.0090 to 2.4900 mol.kg−1 at T = (298.2, 308.2 and 318.2) K. The obtained results were analysed using Extended Debye-Huckel equation and Pitzer model. The values of Pitzer ion-interaction parameters β(0), β(1) and Cϕ were used to drive the values of thermodynamic properties such as the excess Gibbs free energy, the solvent activity, mean activity coefficients, the osmotic coefficients and diffusion coefficients for this system. [ABSTRACT FROM AUTHOR]

The inland natural brine of Algerian chotts is known to contain considerable quantities of oceanic salts; hence, it becomes vital to estimate their mining and economic potential viability. This was done by carrying out an integrated geochemical simulation approach. It has been investigated how density and ionic composition change during isothermal evaporation experimentation (IEE) at 308.15°K. The crystallization path during the isothermal evaporation process is predicted using the Jänecke quinary diagram of the system Na+, K+, Mg2+//Cl–, and SO42–-H2O at 308.15°K and PHREEQC software (with Pitzer database). An integrated approach that is provided combines these two models with an experimental design. The nature and the crystallization sequence of the precipitated salts during the isothermal evaporation were determined by X-ray diffraction. The PHREEQC simulation, as well as Jänecke theoretical and experimental sequences, and the sequence provided by the real crystallization experiment all showed good agreement and confirmed the crystallization of halite, leonite, and sylvite minerals. At the end of the IEE, there was a minor deviation in the occurrence of epsomite in the recovered solids assemblage. The current study established that PHREEQC with Pitzer's database and Jänecke quinary diagram are powerful tools recommended for the characterization and evaluation of unknown brines involving the Na+, K+, Mg2+//Cl–, and SO42–-H2O system at 308.15°K. [ABSTRACT FROM AUTHOR]

To better use rare earth element resources in geothermal water, it is essential to understand the volumetric property and the ion-interaction of the rare earth element aqueous solution systems. In this paper, the densities of aqueous Y2(SO4)3 from 0.00405 to 0.04071 mol kg−1 at 283.15 to 363.15 K were measured using an Anton Paar Digital vibrating-tube densimeter. Apparent molar volumes (Vϕ) and the coefficient of thermal expansion (α) were obtained based on the experimental density data, and the diagrams of the apparent molar volume and coefficient of thermal expansion of Y2(SO4)3(aq) against temperature (T) and molality (m) in the binary system were revealed. The Pitzer single-salt parameters for Y2(SO4)3 and their temperature-dependent correlation F(i, p, T) = a1 + a2ln(T/298.15) + a3(T − 298.15) + a4/(620 − T) + a5/(T − 227) (where T is temperature in Kelvin, ai are the correlation coefficients) for Y2(SO4)3 were obtained for the first time. [ABSTRACT FROM AUTHOR]

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.

In this study, the isothermal saturation method was applied to obtain the data for solid–liquid equilibria in a system consisting of four solids (LiCl + NaCl + Li2SO4 + Na2SO4) and water at 288.15 K. The chemical composition of the liquid phase was experimentally determined, and the corresponding phase diagrams were constructed. The obtained diagram exhibited 6 crystallization areas, 10 univariant curves, and 5 invariant points. The 6 crystallization regions consisted of LiCl·2H2O, Li2SO4·H2O, NaCl, Na2SO4·10H2O, Li2SO4·3Na2SO4·12H2O and Li2SO4·Na2SO4. The solid-phase solubilities and phase equilibria were derived from the experimental data at 288.15 K using Pitzer's equations. The calculated data were compared with the experiment, and the corresponding phase diagrams for both datasets were calculated. Experimental and theoretical diagrams were in good agreement. [ABSTRACT FROM AUTHOR]

The evaporative-crystallization process (ECP) is a frequently used approach for complete nutrient recovery from human urine, and crystallization sequence is related to the selection of seed and the optimization of crystallization process. In this study, three hydrolyzed urine (HU) samples, which were acidified to an initial pH of 4 with HCl, H2SO4, and H3PO4, were used to recover crystallized products by ECP, their crystallization process and thermodynamic properties during ECP were compared, and the detailed crystallization sequence was analyzed using the PHREEQC-2 simulation. The results showed that the pH-adjusted acid has a significant effect on crystal precipitation, and the new crystal in HCl-4-HU, H2SO4-4-HU, and H3PO4-4-HU first appeared at volume concentration factors (CFV) of 19.61, 9.90, and 9.96, respectively. Furthermore, the simulated crystallization process characteristics of HU by PHREEQC-2 have a good fit with the actual experimental data, and crystallization sequence of HCl-4-HU, H2SO4-4-HU, H3PO4-4-HU during ECP were NH4Cl (CFV from 10.25 to 100) / NaCl (CFV from 71.43 to 100), NH4NaSO4 (CFV from 10.25 to 55.56) / NH4Cl (CFV from 20 to 100) / (NH4)2SO4 (CFV from 40.45 to 100), NH4H2PO4 (CFV from 10.25 to 100) / NaH2PO4 (CFV from38.46 to 55.5) / NaCl (CFV from 45.46 to 100), respectively. The present study clearly reveals the crystallization sequence and thermodynamic properties of nutrient elements in acidified HU, which provides an important theoretical basis for the optimization of crystallized products obtained from HU for future study. [ABSTRACT FROM AUTHOR]

Existing molal-based Pitzer activity coefficient models for (H + Nd + NO 3){aq} mixtures are either inaccurate, ill-formed, or do not span the ionic strength (I) range of the solid solubility data for the (H + Nd + ox + NO 3){aq} system. As a precedential step in developing a thermodynamic model for aqueous neodymium-oxalate-bearing systems, a speciated, conventional Pitzer model was fitted to the osmotic coefficient and solid solubility data for the (H + Nd + NO 3){aq} system at 298 K and 0.1 MPa. The presented HNO 3 {aq} model spans the range, 0 < I < 30 mol·kg−1, using fewer parameters than previously published molal-based conventional Pitzer models for the speciated system. The Nd(NO 3) 3 {aq} and novel (H + Nd + NO 3){aq} models reproduce the fitted isopiestic and solid solubility data within their accuracy between infinite dilution and stoichiometric ionic strengths up to ∼40 mol·kg−1. • Speciated Pitzer ion-interaction model for H + Nd + NO 3 + OH system at 298 K, 0.1 MPa. • Accurate solute and solvent activities and solid solubility for I < 40 mol·kg−1. • Important step for modeling aqueous neodymium oxalate systems. • Protocol described for determining model parameters within Pitzer formalism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Separation and extraction of brominated salts by crystallization from wastewater. • Solubility was measured of the NaCl-NH 4 Cl-NaBr-NH 4 Br-H 2 O system at 298 K and 323 K. • The solubility of the NaCl-NH 4 Cl-NaBr-NH 4 Br-H 2 O system at 298 K was calculated. • The separation of bromide by crystallization was experimentally verified. Brominated wastewater from the propyl bromide pesticide production rich in ammonium, sodium and bromine salts at a high concentration of 11 %. For the recycling of chemical resources of this mixed brine salt system, this paper proposes a method for the separation of bromide from bromine-containing chemical wastewater by crystallization. According to the process design needs of the new method, and because 298 K and 323 K are two common temperatures in industrial practice, in this paper, the solubility data of the NaCl-NH 4 Cl-NaBr-NH 4 Br-H 2 O quaternary system at 298 K and 323 K, as well as its ternary subsystems, NaBr-NH 4 Br-H 2 O and NH 4 Cl-NH 4 Br-H 2 O at 323 K were determined by the isothermal solubilization method, and the corresponding phase diagrams were drawn. The solubility of the NaCl-NH 4 Cl-NaBr-NH 4 Br-H 2 O quaternary system at 298 K was also calculated using the Pitzer model, and the calculated results were in good agreement with the experimental measurements. Finally, based on the theoretical analysis of the phase diagrams of the 298 K and 323 K NaCl-NH 4 Cl-NaBr-NH 4 Br-H 2 O quaternary systems and combined with the phase diagrams of the 298 K NaBr-NaCl-CH 3 OH system, this paper proposes and designs a salt extraction process route for the brominated wastewater of the propyl bromide pesticide production. Through the separation experiment, the new process proved to be technically feasible and produced NaCl with 100 % purity, Na(Br,Cl) with 98.23 % NaBr, and NH 4 (Cl,Br) with 99.18 % and 97.57 % NH 4 Cl, respectively. The new process realizes the resourceful utilization of bromine-containing wastewater, and has the significant advantages of production safety and no emission of three wastes. [ABSTRACT FROM AUTHOR]

The phase equilibria of quaternary systems LiCl+KCl+NaCl+H 2 O and LiCl+KCl+MgCl 2 +H 2 O at 308.2 K were investigated by isothermal dissolution equilibrium method. The results reveal that the phase diagram of the quaternary system LiCl+KCl+NaCl+H 2 O consists of one invariant point, three univariable curves and three equilibrium solid crystallization fields (LiCl·H 2 O, NaCl and KCl). Two double salts appear in the quaternary system LiCl+KCl+MgCl 2 +H 2 O, namely KCl·MgCl 2 ·6H 2 O and LiCl·MgCl 2 ·7H 2 O, and the phase diagram is composed of three invariant points, seven univariable curves and five crystallization fields (LiCl·MgCl 2 ·7H 2 O, MgCl 2 ·6H 2 O, LiCl·H 2 O, KCl and KCl·MgCl 2 ·6H 2 O). Moreover, the solubilities of salts in two quaternary systems are predicted by applying the Pitzer model. The calculated phase diagrams were in good accordance with the experimental phase diagrams. The results clearly show that lithium chloride crystallizes as LiCl·2H 2 O at low temperatures; however, it is precipitated as LiCl·H 2 O at 308.2 K. Compared with KCl·MgCl 2 ·6H 2 O, LiCl·MgCl 2 ·7H 2 O has a smaller crystallization zone. The phase equilibria in invariant points of quaternary systems LiCl+KCl+NaCl+H 2 O and LiCl+KCl+MgCl 2 +H 2 O at 308.2 K have been explored for the first time. [ABSTRACT FROM AUTHOR]

• Solid-liquid phase equilibrium of NH 4 + //SO 4 2−, H 2 PO 4 −–H 2 O system aiming at salt-containing wastewater treatment in lithium-ion batteries industry. • Constructing the Pitzer thermodynamic model of the ternary system. • Calculating solubilities of the ternary system being in good agreement with the experimental results. A tremendous amount of wastewater containing ammonium salts, mainly NH 4 H 2 PO 4 and (NH 4) 2 SO 4 , has been produced in the production of cathode material of lithium iron phosphate (LFP). However, as an important basis for salt separation, the solid–liquid phase equilibrium (SLPE) of these two salts has been investigated by few studies. In this study, SLPE of the ternary system (NH 4 + //SO 4 2−, H 2 PO 4 −–H 2 O) from 313.15 K to 343.15 K at 101.2 kPa were investigated by isothermal dissolution method, and the corresponding physicochemical properties (density, viscosity, and pH) of saturated solution were measured. The phase diagram is composed of one invariant point, two univariant curves, and two single-salt crystallization fields for NH 4 H 2 PO 4 and (NH 4) 2 SO 4. Comparing the phase diagrams from 263.15 K to 343.15 K, it is obvious that two single-salt crystallization fields shrink with increasing temperature. And the area reduction of NH 4 H 2 PO 4 in two salts is more significant. When the temperature drops below 268.15 K, the ice crystallization field would appear. Neither single-salt solid solution, hydrous salt nor double salt was found in the whole temperature range. Furthermore, Pitzer model was successfully applied to describe the SLPE of the ternary system at temperatures from 273.15 K to 343.15 K. The lacking Pitzer-model parameters of mixed electrolytes (θ SO4-H2PO4 and ψ NH4-SO4-H2PO4) were calculated, and the temperature coefficients of model parameters and dissolution equilibrium constant were obtained. The importance of this study is that it supplies basic data and theoretical references for the separation and resource utilization of two ammonium salts from wastewater in the LFP batteries industry. [ABSTRACT FROM AUTHOR]

The solubilities, densities and refractive indices of the ternary KCl + PEG8000 + H2O system were determined at 288.2, 298.2, and 308.2 K. In terms of phase diagrams at 288.2, 298.2, and 308.2 K, they are all made up of three areas, where the homogeneous area (L) contains unsaturated liquid, area (L + S) contains one saturated liquid and one solid (KCl), and area (L + 2S) contains one saturated liquid and two solids (KCl and PEG8000). The results of these experiments showed that with an addition of PEG8000 to the liquid, the solubility of KCl and density of the liquid phase decreased, whereas the refractive index inceased. By comparing the phase diagrams at 288.2, 298.2, and 308.2 K, it is seen that with an increase of temperature, the areas of (L) and (L + S) enlarged, whereas the area of (L + 2S) reduced. The phase diagrams of the ternary systems KCl + PEG1000/4000/6000/8000 + H2O were also compared and showed that with an increase of the molar mass of PEG, the ovedrall phase diagrams did not change although the areas of each part varied in size. Also, a modified Pitzer model was adopted as the equilibrium thermodynamics model to correlate the experimental data. [ABSTRACT FROM AUTHOR]

• Pitzer activity coefficient model for Nd3+–H+–Na+–K+–Ca2+–Cl−–OH− at 298 K. • Addition of 8 parameters to HMW reproduces data over 2 < pH < 13 and 0 < I < 23 mol·kg−1. • Published models for Nd3+–H+–Na+–Ca2+–Cl−–OH− critiqued. • Appropriate parameterization methods recommended. • Proposed resolutions to inter-laboratory discrepancies in Nd(OH) 3 solubility data. A conventional, speciated Pitzer ion-interaction model at 298 K and 0.1 MPa is presented for the NdCl 3 + H 2 O system and mixtures containing HCl, NaCl, KCl, and CaCl 2. The model uses Nd3+, NdOH2+, Nd(OH) 2 +, Nd(OH) 3 0, NdCl2+, and NdCl 2 + solute species and was fitted to isopiestic, electromotive force (emf), and NdCl 3 ·6H 2 O solubility data. The model was then extended to pH values at which Nd(OH) 3 , Nd(OH) 2 Cl, and a speculative double salt, Nd(OH) 3 ·NdCl 3 , are stable. The two hydroxychloride salts enabled the model to join the stability fields of NdCl 3 ·6H 2 O and Nd(OH) 3 ensuring continuity in the range 2 < pH < 13. The activity coefficient model developed from the low pH [NdCl 3 + NaCl](aq) system reproduces the solubility of solid Nd(OH) 3 (s) in water and NaCl(aq) with only the addition of standard state free energy terms for crystalline (cr) and amorphous (am) NdOH 3 (s) and the Nd(OH) 2 + and Nd(OH) 3 0 solute species. No Pitzer parameters involving NdOH2+, Nd(OH) 2 + and Nd(OH) 3 0 were necessary to reproduce the full body of thermodynamic data over an ionic strength range from infinite dilution to the solubility limits of NaCl, KCl, CaCl 2 ·6H 2 O, Nd(OH) 3 (s), the hydroxychloride salts, and for mixtures containing up to 4.5 molal HCl(aq). The model adds only five 'binary' and three 'ternary' Pitzer ion-interaction parameters to the H-Na-K-Ca-Cl-OH parameters in Harvie et al. (1984; hereafter HMW). The model is simpler, compositionally broader, and more accurate than previously published Pitzer ion-interaction models for aqueous neodymium-chloride and -hydroxide solutions containing HCl, NaCl, KCl or CaCl 2. The model has ramifications for geochemical modeling and uncertainty quantification of An(III) solubilities used to support certification of evaporite hosted nuclear waste repositories. [ABSTRACT FROM AUTHOR]

Uranyl ion, UO22+, and its aqueous complexes with organic and inorganic ligands can be the dominant species for uranium transport on the Earth surface or in a nuclear waste disposal system if an oxidizing condition is present. As an important biodegradation product, oxalate, C2O42−, is ubiquitous in natural environments and is known for its ability to complex with the uranyl ion. Oxalate can also form solid phases with uranyl ion in certain environments thus limiting uranium migration. Therefore, the determination of stability constants for aqueous and solid uranyl oxalate complexes is important not only to the understanding of uranium mobility in natural environments, but also to the performance assessment of nuclear waste disposal. Here we developed a thermodynamic model for the UO22+–Na+–H+–Cl––ClO4––C2O42––NO3––H2O system to ionic strength up to ∼11 mol•kg−1. We constrained the stability constants for UO2C2O4(aq) and UO2(C2O4)22− at infinite dilution based on our evaluation of the literature data over a wide range of ionic strengths up to ∼11 mol•kg−1. We also obtained the solubility constants at infinite dilution for solid uranyl oxalates, UO2C2O4•3H2O, based on the solubility data over a wide range of ionic strengths. The developed model will enable for the accurate stability assessment of oxalate complexes affecting uranium mobility under a wide range of conditions including those in deep geological repositories. [ABSTRACT FROM AUTHOR]

• The Pitzer model was applied to calculate activity coefficients of sulfuric acid ions. • Simple equilibrium calculations for sulfuric acid give correct pH for molality <0.2 M. • Addition of sulfate salts breaks the ideal behavior of dilute sulfuric acid solutions. • Engulfment model of micromixing was used to simulate activities during test reaction. • Guichardon Law should not be coupled with partial dissociation models for sulfuric acid. The Villermaux–Dushman test reaction for micromixing characterization has been used by many researchers to investigate homogeneous mixing systems. Due to the complexity of the iodine-forming reaction, the strong effect of ionic strength of reaction medium on its reaction rate constant, as well as the dependence of the sulfuric acid dissociation on its concentration, the kinetic model of the iodide/iodate test reaction with sulfuric acid is complicated. Therefore, a quantitative evaluation of such a test reaction is challenging and remains an open problem. In this paper, the pH of the sulfuric acid solutions with different values of ionic strength is investigated using the model of Pitzer. The numerical results of the simulation are compared with the experimental data and good agreement is obtained. It is also shown that simple equilibrium calculations for sulfuric acid do not give correct pH results when the ionic strength of its solution is increased by the addition of sulfate salts. However, such an assumption yields satisfactory results for the cases without additional salt and with an acid concentration lower than 0.2 M. Finally, the engulfment model of micromixing using activities to calculate proton concentrations is applied to analyze the experimental results from previous papers employing the iodide/iodate method. [ABSTRACT FROM AUTHOR]

Densities of the sodium arsenate aqueous solution with the molality varied from (0.04165 to 0.37306) mol · kg−1 were determined experimentally at temperature intervals of 5 K from 283.15 K to 363.15 K and ambient pressure using a precise Anton Paar Digital vibrating-tube densimeter. The apparent molar volumes (Vϕ), thermal expansion coefficient (α) and partial molar volume (V ¯ B) $({\bar V_{\rm{B}}})$ were obtained based on the results of density measurement. The 3D diagram of apparent molar volume against temperature and molality as well as the diagram of thermal expansion coefficient and partial molar volume against molality were plotted, respectively. On the basis of the Pitzer ion-interaction equation of apparent molar volume model, the Pitzer single-salt parameters ( (β M,X (0) v , β M,X (1) v , β M,X (2) v and C M,X v , M X = N a 3 A s O 4) $(\beta _{{\rm{M,X}}}^{(0)v},\beta _{{\rm{M,X}}}^{(1)v},{\rm{ }}\beta _{{\rm{M,X}}}^{(2)v}{\rm{ and }}C_{{\rm{M,X}}}^v,MX = N{a_3}As{O_4})$ and their temperature-dependent correlation F(i, p, T) = a1 + a2ln(T/298.15) + a3(T – 298.15) + a4/(620 – T) + a5/(T – 227) (where T is temperature in Kelvin, ai is the correlation coefficient) for Na3AsO4 were obtained on account of the least-squares method. Predictive apparent molar volumes agree well with the experimental values, and those results indicate that the single-salt parameters and their relational coefficients of temperature-dependence for Na3AsO4 obtained are reliable. [ABSTRACT FROM AUTHOR]

Predictions of salt solubility, brine vapor pressure and density are necessary to plan subsurface and surface operations. In this work, a comparative study was conducted to investigate prediction capabilities for salt solubility, equilibrium and volumetric properties of several minerals in "Formation" water by the Pitzer model (a commonly used industrial model) and by the ePC-SAFT equation of state (EOS). To achieve this, several validation and comparison steps were considered for reliable implementation of both models. Firstly, solubility, brine densities and vapor pressures for single-salt solutions were predicted. Afterward, the models' applications were extended to several mixtures of two salts to predict solubility compared to experimental data from available literature. ePC-SAFT shows promising accuracy. The average relative deviation for prediction of liquid density (which cannot be estimated with the Pitzer model) for single-salt solutions of NaBr, KCl, NaCl and Na2SO4 are 1.13%, 0.70%, 1.02% and 0.36%, respectively. The average relative deviation from experimental data of vapor pressure for mixtures of NaCl and KBr is 0.75% and for mixtures of NaBr and KCl is 0.74% for systems with different concentrations. Moreover, a stochastic regression procedure is presented to evaluate the ePC-SAFT parameters. This technique is used for strontium in different salt solutions. The average relative deviation for mean ionic activity coefficients calculated by ePC-SAFT from experimental data using the ePC-SAFT parameters of strontium from the work of Held et al. [1] for single-salt solutions of strontium chloride, strontium bromide, strontium iodide, strontium nitrate and strontium perchlorate are 19.73%, 19.96%, 15.15%, 14.95% and 25.70%, respectively. These values using the ePC-SAFT parameters of strontium regressed in this work are 6.98%, 10.13%, 8.33%, 9.59% and 10.08%, respectively. Finally, the solubility of different salts was studied for mixing of formation water (FW) and injection water (SW). [ABSTRACT FROM AUTHOR]

The solubilities in the quaternary system (LiCl + NaCl + KCl + H2O) at 288.15 K were investigated with the method of isothermal dissolution equilibrium. The phase diagram includes one cosaturated point, three isotherm dissolution curves, and three crystallization regions corresponding to sodium chloride, potassium chloride, and lithium chloride dihydrate. The area of the crystallization region of LiCl · 2H2O is the smallest, and it has a strong salting-out effect to NaCl and KCl. Comparing the phase diagrams of the quaternary system at 288.15 and 298.15, 373.15 K, it was found that solid mineral LiCl · 2H2O at 288.15 K transformed to LiCl · H2O at 298.15 K and LiCl at 373.15 K. Moreover, the area of the crystallization region of lithium chloride and sodium chloride increase with the increasing temperature, while that of potassium chloride decrease dramatically. Meanwhile, on the base of Pitzer model and its extended HW model, the solubilities in this quaternary system at 288.15 K were calculated and it shows that the predicted solubility result agree well with the experimental data. [ABSTRACT FROM AUTHOR]

In this study, I present experimental results on the equilibrium between boracite [Mg3B7O13Cl(cr)] and kurnakovite [chemical formula, Mg2B6O11·15H2O(cr); structural formula, MgB3O3(OH)5·5H2O(cr)] at 22.5 ± 0.5 °C from a long-term experiment up to 1629 days, approaching equilibrium from the direction of supersaturation, Mg3B7O13Cl(cr) + H+ + 2B(OH)4– + 18H2O(1) ⇌ 3MgB3O3(OH)5·5H2O(cr) + Cl–. Based on solubility measurements, the 10-based logarithm of the equilibrium constant for the above reaction at 25 °C is determined to be 12.83 ± 0.08 (2s). Based on the equilibrium constant for dissolution of boracite, Mg3B7O13Cl(cr) + 15H2O(l) = 3Mg2+ + 7B(OH)–4+ Cl– + 2H+ at 25 °C measured previously (Xiong et al. 2018) and that for the reaction between boracite and kurnakovite determined here, the equilibrium constant for dissolution of kurnakovite, MgB3O3(OH)5·5H2O(cr) = Mg2+ + 3B(OH)–4+ H+ + H2O(1) is derived as –14.11 ± 0.40 (2s). Using the equilibrium constant for dissolution of kurnakovite obtained in this study and the experimental enthalpy of formation for kurnakovite from the literature, a set of thermodynamic properties for kurnakovite at 25 °C and 1 bar is recommended as follows: Δ H f 0 = − 4813.24 ± 4.92 kJ / mol , Δ G f 0 = $\Delta H_{f}^{0}=-4813.24\pm 4.92\,{\text{kJ}}/{\text{mol}}\;,\Delta G_{f}^{0}=$ − 4232.0 ± 2.3 kJ / mol, and S 0 = 414.3 ± 0.9 J / mol ⋅ K . $-4232.0\pm 2.3\,{\text{kJ}}/{\text{mol,}}\;\,\text{and}\,{{S}^{0}}=414.3\pm 0.9\,{\text{J}}/{\left(\text{mol}\cdot \text{K} \right)}\;.$ Among them, the Gibbs energy of formation is based on the equilibrium constant for kurnakovite determined in this study; the enthalpy of formation is from the literature (Li et al. 1997), and the standard entropy is calculated internally with the Gibbs-Helmholtz equation in this work. The thermodynamic properties of kurnakovite estimated using the group contribution method for borate minerals based on the sums of contributions from the cations, borate polyanions, and structural water to the thermodynamic properties from the literature (Li et al. 2000) are consistent, within their uncertainties, with the values listed above. Since kurnakovite usually forms in salt lakes rich in sulfate, studying the interactions of borate with sulfate is important to modeling kurnakovite in salt lakes. For this purpose, I have re-calibrated our previous model (Xiong et al. 2013) describing the interactions of borate with sulfate based on the new solubility data for borax in Na2SO4 solutions presented here. [ABSTRACT FROM AUTHOR]

A set of Pitzer parameters was obtained to accurately describe the thermodynamic properties of solutions in the H2O–UO2(NO3)2–Th(NO3)4–HNO3 system at 25°С and represent the thermodynamic properties of liquid phases in the H2O–Th(NO3)4–HNO3 subsystem in the temperature range 25–50°С. Solubility products were calculated for crystal hydrates Th(NO3)4 · 6H2O and UO2(NO3)2 · 3H2O to predict the solubilities of these compounds in those solutions over a wide concentration range. [ABSTRACT FROM AUTHOR]

A set of Pitzer interaction parameters is proposed to describe thermodynamic properties of the H2O–UO2(NO3)2–HNO3 solution within the temperature range of 15 to 50°C and ranges of concentrations of HNO3 and UO2(NO3)2 of 0 to 40 and 0 to 8 mol/kg, respectively. The experimental data on the vapor pressures of the volatile components of the system, degree of dissociation of nitric acid, and solid–liquid equilibria are used to determine these parameters. [ABSTRACT FROM AUTHOR]

Removing the pollutants from oilfield wastewater and reinjecting the wastewater to the formation are conducive to the protection of the local environment. Silicate is a kind of common pollutant of oilfield wastewater. And the accurate prediction of its solubility is beneficial to the formulation of wastewater treatment schemes. To predict the silicic acid solubility in varying temperature, multi-component aqueous solutions, a prediction model applicable to such solution is proposed in this paper based on Pitzer electrolyte solution theory and in consideration of the long-range and short-range Coulomb electrostatic interaction and dispersion interaction between cations and anions. For Na+-K+-Ca2+-Mg2+-Cl--SO42--HCO3--F--SiO32- solution, the prediction model is used to calculate the silicic acid solubility at different temperature and ion concentration, then the range analysis is used to analyze the factors affecting the solubility of silicic acid. The result indicate that temperature, Ca2+ and SO42- are the main factors, with the range R of 11.1, 7.8 and 6.9, respectively. The effects of these factors on the enthalpy change, potential energy and single point energy in silicate reaction have been studied by using quantum chemistry method. The research results agree with the range analysis results, which further checks the correctness of the prediction model. Therefore, this prediction model can be used to predict the silicate solubility in the temperature-varying multi-component silicate solution. [ABSTRACT FROM AUTHOR]

The development of LA-ICP-MS and other microanalytical techniques for in situ analysis of single fluid inclusions has made it possible to quantify the elemental concentration of major elements, trace metals, sulfur and halogens in fluid inclusions from a wide range of geological environments. The established quantification methods typically interpret the LA-ICP-MS and microthermometric data (melting points of ice, salt and hydrate phases) in terms of simple binary or ternary model systems (e.g., H 2 O-NaCl and H 2 O-NaCl-CaCl 2), which can be inaccurate for complex natural geofluids such as multi-solute basinal brines, magmatic-hydrothermal fluids or pegmatitic fluids. Another approach uses mass or charge balance constraints along with the elemental ratios obtained from LA-ICP-MS. This improves the quantification of more complex fluids to some extent, but because it is based on the equivalent concentration of NaCl from the NaCl-H 2 O binary system, it typically introduces systematic uncertainty in the concentrations of all elements analyzed. These limitations can be fundamentally overcome by combining microthermometric and LA-ICP-MS data with thermodynamic modeling. In this approach, elemental ratios (element/Na) are directly calculated from the LA-ICP-MS data and then the unknown Na concentration is calculated by modeling the chemical equilibrium between the aqueous solution and the last melting solid phase (e.g., ice, hydrohalite, sylvite) of the fluid inclusion using a Pitzer model for the aqueous solution. Comparison between modeled and experimental data of chloride systems (including salt-solution equilibria and synthetic fluid inclusion data) demonstrates excellent agreement over wide ranges of temperature and composition. Our new model, accompanied by a new approach for quantifying uncertainty, is more general than previous methods and makes it possible to quantify complex multi-element fluid inclusions from diverse geological environments including magmatic, metamorphic, sedimentary and various ore-forming hydrothermal fluids. • Application of the Pitzer model for quantifying fluid inclusions of high salinity brines. • Interpreting fluid inclusions within the extended multicomponent Li-Na-K-Rb-Cs-Mg-Ca-Sr-Fe-Cl-O-H system. • Uncertainty analysis and demonstration of the model's good performance. • Model implementation and provision of a code package (PyPitzer) for reuse. [ABSTRACT FROM AUTHOR]

The stable phase equilibrium of the ternary system K+, Mg2+//Cl−-H 2 O at 293.15, 298.15, 303.15, and 308.15 K were determined by isothermal dissolution equilibrium method. A kind of incongruent double salt, KCl·MgCl 2 ·6H 2 O, is found in this ternary system. Therefore, phase diagrams at each temperature all consist of two invariant points, three univariant curves and three crystallization regions for KCl·MgCl 2 ·6H 2 O, MgCl 2 ·6H 2 O, and KCl, respectively. Strong salting out effect of MgCl 2 on KCl leads to the order of crystallization areas, KCl > KCl·MgCl 2 ·6H 2 O > MgCl 2 ·6H 2 O. Meanwhile, with temperature decreasing, crystallization region of KCl becomes larger. Thus, the high MgCl 2 concentration and low temperature are beneficial to KCl preparation from carnallite ores. Furthermore, an approach combing density functional theory (DFT) and Pitzer model was proposed, which can predict solubility data in complex systems containing incongruent double salts. The calculated solubilities have a good agreement with experimental values. All the results involved in this paper provide basic thermodynamic data and theoretical guidance to fully utilize potassium resource stored in carnallite ores. [ABSTRACT FROM AUTHOR]

• The CuSO 4 – H 2 SO 4 – H 2 O system is vital for copper cathode and copper sulfate pentahydrate production. • Models for the ionic speciation and thermochemical properties in CuSO 4 – H 2 SO 4 – H 2 O system from 273.15 K to 373.15 K. • Pitzer model adapted to include the interaction parameters of sulfate complexes as HSO 4 - , H 2 S O 4 0 and CuSO 4 0. • Thermochemical model of CuSO 4 – H 2 SO 4 – H 2 O system from 273.15 K to 373.15 K including Pitzer ionic speciation approach. In this work, models have been developed that allow to estimate the ionic speciation and solution properties, such as: water activities, solubilities, densities, and ionic conductivities in the ternary system CuSO 4 – H 2 SO 4 – H 2 O in the temperature range 273.15 – 373.15 K, which constitutes the basis of hydrometallurgical processes to produce copper cathodes by electrowinning and copper sulfate pentahydrate by crystallization. For this, a parameterization of the required mathematical models was carried out, such as: the Pitzer ionic interaction model, the HKFmoRR equation of state (EOS), and the Appelo model, using the hydrogeochemical code PHREEQC in coupling with the optimization software PEST. These models allowed standard deviations of 0.3 %, 1.2 %, 0.3 % and 9.6 % for water activities, copper sulfate pentahydrate solubilities (CuSO 4 ·5H 2 O), densities, and ionic conductivities, respectively, in the ternary system studied. The calculated ionic speciation results showed that the main dissolved species were: Cu 2 + , SO 4 2 - , Cu SO 4 0 , H + , and HSO 4 -. The concentration of free sulfate ion (SO 4 2 -) decreases as the total concentration of sulfuric acid increases, due to the ion association and formation of complexes HSO 4 - , Cu SO 4 0 , and H 2 S O 4 0. This work provides new values of the Pitzer interaction parameters as a function of temperature, mainly those related to the neutral complex Cu SO 4 0 and H 2 S O 4 0 (λ ni and ζ nij). [ABSTRACT FROM AUTHOR]

The reactive solid-liquid equilibrium (SLE) in the quinary system 2-keto- l -gulonic acid (HKGA) + sodium-2-keto- l -gulonate (NaKGA) + hydrochloric acid (HCl) + sodium chloride (NaCl) + water was studied experimentally at 298 K and ambient pressure. The precipitation of three solid species was observed: HKGA monohydrate (HKGA ⋅ H 2 O), NaKGA monohydrate (NaKGA ⋅ H 2 O), and NaCl. A thermodynamic model based on the Pitzer model to calculate the activity coefficients in the liquid phase for the SLE was developed and unreported Pitzer parameters were fitted to the experimental data of this work. The equilibrium constant for the dissociation of HKGA and the solubility products of HKGA ⋅ H 2 O and NaKGA ⋅ H 2 O at 298 K were calculated from experimental data, whereas the equilibrium constant for the autoprotolysis of water and the solubility product of NaCl were adopted from literature data. The agreement between the experimental data and the results from the model is excellent, both regarding the liquid phase composition and the solid species in solid-liquid equilibrium. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Experimental results of the osmotic coefficients of aqueous solutions of 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO 4 ], 1-ethyl-3-methylimidazolium methylsulfate [EMIM][MeSO 4 ], 1-ethyl-3-methylimidazolium tosylate [EMIM][Tos], 1,3-dimethylimidazolium methylsulfate [MMIM][MeSO 4 ], tributylmethylphosphonium methylsulfate [TBMP][MeSO 4 ] and triisobutylmethylphosphonium tosylate [(iBu) 3 MP][Tos] obtained by vapor pressure osmometry (VPO) at 298.15 K and at atmospheric pressure are reported in this work. From this data water activity (a w), vapor pressure (p), mean molal activity coefficients (γ ±), Gibbs free energy due to mixing (ΔG mix) and excess Gibbs free energy change (ΔGE) are calculated. The activity coefficient data obtained are correlated with McMillan-Mayer theory and Pitzer model. The results obtained are elucidated in terms of ion association and structural characteristics of ILs. Graphical abstract Unlabelled Image Highlights • The Osmotic coefficients for aqueous imidazolium and phosphonium based ILs are reported at 298.15 K. • Deviation of ILs from Debye-Hückel limiting law has been discussed. • Gibbs free energy change due to mixing and the excess Gibbs free energy change have been calculated. • McMillan-Mayer theory and Pitzer model are applied to data. [ABSTRACT FROM AUTHOR]

Abstract Research on mechanisms of chloride ion transport in cement-based materials is relevant to improve the durability of reinforced concrete structures. Conventional chloride-transport models consider a linear diffusion equation, only valid for fully saturated and non-reactive concrete. This work proposes a model of chloride and other ions penetration in saturated concrete considering diffusion, chloride binding, chemical activity and migration. The model uses intrinsic diffusion coefficients. The influence of the ionic pore solution on chloride penetration into concrete is also studied. Chemical activity is introduced by coupling the transport equations to the Pitzer model. The migration is accounted for by imposing the electro-neutrality condition of the pore solution. It is shown that fitting the well known error function to experimentally obtained chloride profiles present results which are difficult to interpret. Moreover, it is shown that, by accounting for solely diffusion and chloride binding, good results are obtained. Contemplating chemical activity and migration slightly improves such results and allows concentration profiles of the present ionic species in the pore solution to be determined. Such profiles are involved in the degradation processes of cement-based materials exposed to aggressive environments. [ABSTRACT FROM AUTHOR]

The water activities of the MgCl2–RbCl–H2O ternary system and its sub-binary systems have been measured with the isopiestic method at 323.15 K. The measured water activities for the MgCl2–H2O and RbCl–H2O sub-binary systems agree well with the results reported in literature. The measured equal water activity lines of the MgCl2–RbCl–H2O ternary system are not straight lines, which means the mixing behavior of the solutions do not obey Zdanovskii's rule. The solubility of the MgCl2–RbCl–H2O ternary system has been determined with the Flow-Cloud-Point method at 323.15 K, and the measured results are roughly consistent with values reported in the literature. The Pitzer model was selected to correlate the water activity and solubility data measured in this work. The predicted water activities and solubility isotherm for the MgCl2–RbCl–H2O ternary system at 323.15 K, with binary solution parameters only, both deviated from the experiment values. The ternary solution Pitzer model parameters were obtained by fitting the measured water activities in the ternary system. The water activities and solubility isotherms of the MgCl2–RbCl–H2O ternary system at 323.15 K were calculated including both binary and ternary solution parameters. The calculated water activities are consistent with the experimental values. The calculated solubility isotherms are roughly consistent with experiment values, except they deviate somewhat in the RbCl crystallization region. [ABSTRACT FROM AUTHOR]

Abstract The osmotic and activity coefficients of aqueous solutions of diethylammonium based protic ionic liquids (PILs) were determined experimentally using vapor pressure osmometry in the concentration range of (~0.02 to ~0.5) mol·kg−1 at 298.15 K. Osmotic coefficient data show positive deviation from Debye-Hückel limiting law for all the studied PILs. Also a minimum in osmotic coefficient data was observed at higher concentrations and is explained in terms of ion-pair formation. Data of experimental osmotic coefficient were used to obtain activities (a w) and activity coefficients (γ 1) of water, mean molal activity coefficient (γ ±) of PILs and excess Gibbs free energy change (Δ G E ) due to mixing. Observed variations in osmotic coefficients data were explained in terms of hydrophobicity as well as H-bonding. The data of osmotic and activity coefficients were further subjected to analysis through Pitzer ion-interaction model to get an information of ion-ion and ion-solvent interaction to understand ion-pairing, ion hydration and hydrophobic effects in aqueous solutions of PILs. For this, Pitzer ion interaction parameters β (0) and β (1) were estimated and compared with literature data available for other relevant systems. Finally, the results are interpreted in terms ion-ion, ion-solvent interaction along with effect of hydrophobicity on ion-pairing and further discussed the effect of alkyl chain length of anions on solvation behavior of protic ionic liquids in aqueous solutions. Graphical abstract Unlabelled Image Highlights • Osmotic properties for aqueous diethylammonium based protic ionic liquids (PILs) are reported. • Effect of hydrogen bonding and hydrophobicity on ion-pairing in aqueous PIL solutions. • The Pitzer ion-interaction parameters suggest that the interaction between unlike charges is favorable. • All obtained parameters support that interaction in aqueous solutions of PILs favors kosmotropic behavior. [ABSTRACT FROM AUTHOR]

Abstract We present a transport-reaction model (TRACTION) specifically designed to account for non-ideal transport effects in the presence of thermodynamic (e.g. salinity or temperature) gradients. The model relies on the most fundamental concept of solute diffusion, which states that the chemical potential gradient (Maxwell's model) rather than the concentration gradient (Fick's law) is the driving force for diffusion. In turn, this requires accounting for species interactions by applying Pitzer's method to derive species chemical potentials and Onsager coefficients instead of using the classical diffusion coefficients. Electrical imbalances arising from varying diffusive fluxes in multicomponent systems, like seawater, are avoided by applying an electrostatic gradient as an additional transport contribution. We apply the model to pore water data derived from the seawater mixing zone at the submarine Mercator mud volcano (MMV) in the Gulf of Cadiz. Two features are particularly striking at this site: (i) Ascending halite-saturated fluids create strong salinity (NaCl) gradients in the seawater mixing zone that result in marked chemical activity, and thus chemical potential gradients. The model predicts strong transport-driven deviations from the mixing profile derived from the commonly used Fick's diffusion model, and is capable of matching well with the profile shapes observed in the pore water concentration data. Even better agreement to the observed data is achieved when ion pairs are transported separately. (ii) The formation of authigenic gypsum (several wt%) occurs in the surface sediments, which is typically restricted to evaporitic surface processes. Very little is known about the gypsum paragenesis in the subseafloor and we first present possible controls on gypsum solubility, such as pressure, temperature, and salinity (pTS), as well as the common ion and ion pairing effects. Due to leaching of deep diapiric salt, rising fluids of the MMV are saturated with respect to gypsum (as well as celestite and barite). Several processes that could drive these fluids towards gypsum supersaturation and hence precipitation were postulated and numerically quantified. In line with the varied morphology of the observed gypsum crystals, gypsum paragenesis at the MMV is likely a combination of two temperature-related processes. Gypsum solubility increases with increasing temperature, especially in strong electrolyte solutions and the first mechanism involves the cooling of saturated fluids along the geothermal gradient during their ascent. Secondly, local temperature changes, i.e. cooling during the transition from MMV activity towards dormancy results in the cyclic build-up of gypsum. The model showed that the interpretation of field data can be majorly misguided when ignoring non-ideal effects in extreme diagenetic settings. While at first glance the pore water profiles at the Mercator mud volcano would indicate strong reactive influences in the seawater mixing zone, our model shows that the observed species distributions are in fact primarily transport-controlled. The model results for SO 4 are particularly intriguing, as SO 4 is shown to diffuse into the sediment along its increasing (!) concentration gradient. Also, a pronounced gypsum saturation peak can be observed in the seawater mixing zone. This peak is not related to the dissolution of gypsum but is simply a result of the non-ideal transport forces acting on the activity profile of SO 4 and Ca profiles. [ABSTRACT FROM AUTHOR]

• Phase equilibria of NaBr+MgBr 2 +H 2 O and NaBr+KBr+MgBr 2 +H 2 O systems are determined experimentally at 308.2 K. • The thermodynamic volume properties of solution with high pressure are investigated preliminarily. • The thermodynamic prediction model of the phase equilibria is developed with high pressure. Solid-liquid phase equilibria of bromine salt can be indicative of Br evolution in Br-rich underground brines of Sichuan Basin in China. Consequently, the solid–liquid phase equilibria of the ternary subsystem NaBr + MgBr 2 + H 2 O and quaternary system NaBr + KBr + MgBr 2 + H 2 O at 308.2 K are determined by the isothermal dissolution equilibrium method. Then, Pitzer ion interaction model and particle swarm optimal algorithm are used to predict the phase equilibria of the systems listed above. The calculated solubilities are in good agreement with the experimental data. Considering the pressure conditions in deep strata, furthermore, we develop a thermodynamic prediction model of the phase equilibria for the systems changing with pressure. The thermodynamic volume properties of solution at 308.2 K with increasing pressure (1–500 bar) are evaluated. The unreported parameters of pressure dependency (Av , V ¯ MX(aq) 0 , β MX (0) , v , β MX (1) , v , C MX v) in Pitzer model at 308.2 K in the studied systems of this work are fitted accordingly. As a result, the effects of pressure on the phase equilibria are investigated in detail, and phase diagrams of the systems at 1–500 bar are also drawn and discussed. This work can provide important thermodynamic data for the salt mineral exploitation of the actual deep strata brines. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermodynamic properties of KBr in PEG 4000 + H 2 O were studied at (288.2, 298.2, and 308.2) K. • Experimental data were fitted to the extended Debye-Hückel and Pitzer models. • Good agreement between experimental and correlated data was obtained by both models. • Activity coefficients, the standard free energy of transference, and primary hydration number were reported. The goal of this research is to evaluate the mean ion activity coefficients (γ ±) of the mixtures containing KBr + PEG 4000 + H 2 O (PEG stands for poly(ethylene glycol)) as well as some other thermodynamic quantities including solvent osmotic coefficients (φ), excess Gibbs energies (G E), standard Gibbs energies of transference (Δ G t 0), and primary hydration number (n hydr). The experiment was employed by potentiometric measurement using the cell with two ion-selective electrodes (abbreviated as ISE) at (288.2, 298.2, and 308.2) K, and the mass fraction of PEG 4000 ranged from w = (0 to 0.20) with an increment of 0.05. The type of the cell is as follows: K–ISE | KBr (m), PEG 4000 (w), H 2 O (1- w) | Br–ISE. Nernst's equation was used to combine the Debye-Hückel and Pitzer models with potentiometric values. Pitzer ion interaction parameters (β 0, β 1, and C φ) and Debye-Hückel model parameter (a) were evaluated. Moreover, the Bjerrum parameter (q) was calculated. [ABSTRACT FROM AUTHOR]

• Microcalorimeter measured the dilution enthalpies of the systems (LiBO 2 + H 2 O) and (LiB 5 O 8 + H 2 O). • Apparent molar enthalpies of the two aqueous systems were derived via Debye-Hückel limiting law. • The single salt parameters of LiB(OH) 4 and LiB 5 O 6 (OH) 4 were obtained by the Pitzer model. Microcalorimeter measured the dilution enthalpies of the binary systems (LiBO 2 + H 2 O) and (LiB 5 O 8 + H 2 O) at 308.15 K and 0.1 MPa. Based on the Pitzer theory of electrolytes, their apparent molar enthalpies and the Pitzer single electrolyte parameters at 308.15 K were carried out by fitting the experimental data for the first time. Moreover, the calculated apparent molar enthalpies of LiBO 2 and LiB 5 O 8 aqueous solution according to the Pitzer ion-interaction model were consistent well with the experimental values, manifesting the high reliability of this study. [ABSTRACT FROM AUTHOR]