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The specific heat capacity of NaBO2(aq) solution was determined using a Calvet-type calorimeter at a temperature from 288.15 to 338.15 K and at a concentration from about 0.25 mol·kg–1 H2O to near ...

Solubility of sparingly soluble salts, i.e., CaF2(s), MgF2(s), and ZnF2(s), in ZnSO4 aqueous solution is necessary for the process design to remove Ca2+, Mg2+, and F– ions from zinc hydrometallurgi...

Solubility data for the reciprocal system Ca2+, Mn2+//F–, SO42– + H2O is very important for the removal of fluoride or calcium ions from the MnSO4 aqueous solution by CaF2(s) precipitation; however...

MgSO4 and (NH4)2SO4 are the main impurities in the hydrometallurgical systems of zinc and manganese. To understand their influences on MgF2(s) solubility, which the fluoride in these systems is expected to remove, we measured MgF2(s) solubility in NH4Cl, (NH4)2SO4 and MgSO4 aqueous solutions at 298.15 K. It was found that the MgF2(s) solubility exhibits salt-in effect in the (NH4)2SO4(aq) and NH4Cl(aq) solutions, but salt-out and salt-in effects in the MgSO4(aq) solution. Furthermore, the MgF2(s) solubility in (NH4)2SO4(aq) is higher than in NH4Cl(aq) solution. Ionic association reactions have been derived to interpret the above solubility phenomena.

Peritectic transformation of pure CaCl2·6H2O during its phase-change process limits its application as a phase change material (PCM). After modification by adding other salts, it may turn into eutectic material. In this work, the possibility of CaCl2·6H2O + NH4Cl + KCl as eutectic phase change material is studied by experiment combining computer simulation. At first, solubility isotherms of the quaternary system CaCl2 + NH4Cl + KCl + H2O was experimentally determined at T = 293.15 K. Secondly, phase diagrams of the quaternary system and its sub-system were simulated by a Pitzer-Simonson-Clegg model. The predicted solubility isotherms was found in good agreement with the experimental data at 293.15 K, which shows the model is reliable for this system. The solubility behavior of the system at other temperatures was predicted with the model, and an eutectic point (46.68 wt% CaCl2, 4.65 wt% NH4Cl, 2.70 wt% KCl and 45.97 wt% H2O) with melting temperature at 297.35 K was found existing in this system which is a promising PCM. At last, a heat storing and releasing experiment of 80 g PCM was carried out to check the possibility of the predicted material as PCM, it was found that the predicted material is an excellent PCM with latent heat of 149.6 J/g.

The solubility of MgF2, CaF2, and ZnF2 in aqueous solution is seldom studied. Their solubility data available in the literature conflict with each other, and their change tendency with temperature is hard to draw. In this work, we elaborately measured their solubility over the temperature range from 298.15 to 353.15 K. To guarantee the data reliability, various methods including ethylenediamine tetraacetic acid disodium salt dihydrate (EDTA) titration and fluoride ion selective electrode (FISE) have been used for ion content analysis in the saturated solutions and X-ray diffraction (XRD) for equilibrium solid phase identification. Besides, sufficient solid–liquid contact time has been taken to guarantee the equilibrium. The determined results were compared with those reported in the literature, and their differences have been discussed. It was found that the MgF2 solubility decreases; however, the CaF2 solubility increases with increasing temperature. In the ZnF2 + H2O system, the equilibrium solid phase ...

ABSTRAT Solubility isotherms as well as the corresponding solid phases of the quaternary system LiCl+MgCl 2 +KCl+H 2 O and the eutectic points for the ternary systems LiCl+MgCl 2 +H 2 O, LiCl+KCl+H 2 O and MgCl 2 +KCl+H 2 O at 323.15 K have been elaborately determined by an isothermal equilibrium method. Five crystallization fields including two double salts (LiCl·MgCl 2 ·7H 2 O(s) and KCl·MgCl 2 ·6H 2 O(s)), two hydrate salts (MgCl 2 ·6H 2 O(s) and LiCl·H 2 O(s)) and one single salt (KCl(s)) were detected in the quaternary system. The reliability of the experimental results were verified both by testing the phase diagram rule and comparing with the literature data. It was found that all of the results were accordance with the phase diagram rule, and moreover, the excellent agreement between the experimental data and the literature data was also obtained, which indicate that the solubility data obtained in this work are reliable. Based on the quaternary phase diagram, the example was provided for industrial application. The measured phase diagram reported in this work are the essential tool to guide industrial process of extracting Li from the salt lake brine containing MgCl 2 and LiCl using KCl reagent.

Water activities of the CuCl2−MCl2−H2O (M = Mg, Ca) ternary systems and their sub-binary systems have been measured by the isopiestic method at 298.15 K. The maximum concentrations of the CuCl2−H2O, MgCl2−H2O and CaCl2−H2O binary systems are 5.28 mol•kg−1, 5.25 mol•kg−1 and 6.61 mol•kg−1, respectively. The concentrations of mixture solution rang from 0.91 mol•kg−1 to 5.69 mol•kg−1 for CuCl2−MgCl2−H2O system, and 1.29 mol•kg−1 to 6.87 mol•kg−1 for CuCl2−CaCl2−H2O system. The measured water activities of the sub-binary systems are consistent with the experimental results reported in literature. The measured equal water activities in the ternary systems strongly deviate from the Zdanovskii-Stokes-Robinson (ZSR) lines. The Pitzer model, Pitzer-Simonson-Clegg (PSC) model and Reaction model were selected to correlate and predict the water activity obtained in this work and the solubility reported in literature for the CuCl2−MCl2−H2O (M = Mg, Ca) ternary systems at 298.15 K. It was found that, the Pitzer model and PSC model cannot consistently represent these thermodynamic properties, with the binary and mixing parameters that already reported or fitted in this work. However, the Reaction model, representing the different competition association ability of common-anions and water molecules with different cations, can successfully predictethe water activity and solubility isotherms in these ternary systems at 298.15 K with binary parameters only. Applying the Reaction model, some examples of the Cu-bearing species distribution as a function of MgCl2 (CaCl2) molalities are given and used to account for how the structure variation of a electrolyte solution influences its macroproperties.

The water activities of the systems MSO4 + H2O (M = Mn, Co, Ni, Cu, Zn) are essential data needed for simulating the hydrometallurgical process of these metals. In our previous work (J. Chem. Eng. Data, 2014, 59, 97–102), the experimental data of water activity for these binary systems have been reported at 323.15 K. As one part of this series of work, the experimental data of water activity for these systems are reported at 373.15 K. The reliability of the apparatus at 373.15 K was verified by measuring and comparing the water activities of the two reference systems, CaCl2 + H2O and LiCl + H2O. The results showed that the maximal relative deviation of the water activities between the reference systems was 0.054%. The water activities for the concerned five systems were found to be approximately the same at a certain salt molality below 1 M. The water activities of these systems decrease at a certain salt molality more than 1 M in the following sequence: aMnSO4 > aCuSO4(∼aZnSO4) > aCoSO4(∼aNiSO4). Further...

The water activities for the binary Li2SO4–H2O and MgSO4–H2O, as well as the ternary Li2SO4–MgSO4–H2O systems at 323.15 and 373.15 K were elaborately determined by isopiestic measurements. The relative deviation of the isopiestic molality of parallel samples in each experimental run is better than 0.2%. The experimental water activities in the binary systems were compared with literature data and good agreement was found. The results obtained show that at salt concentration below 3 m the isopiestic composition lines of the Li2SO4–MgSO4–H2O system obey the Zdanovskii rule, whereas above 3 m the composition lines positively deviate from the Zdanovskii rule.

Osmotic coefficients, water activities, and vapor pressures for the systems of LiCl + H2O, MgSO4 + H2O, and LiCl + MgSO4 + H2O over the ionic strength ranges from I = (0.5552 to 7.0004, 4.1028 to 22.6048, and 1.1982 to 20.5863) mol·kg–1 respectively at T = (273.15, 298.15, 323.15, 348.15, and 373.15) K were determined by the isopiestic method with an improved simple apparatus. Aqueous CaCl2 solution was chosen as a reference standard. The measured osmotic coefficients for the binary solutions of LiCl + H2O and MgSO4 + H2O were in agreement with those from the literature. The experimental data of osmotic coefficients for the ternary mixtures were represented by using the Pitzer ion-interaction model; the expressions for the temperature dependencies of the model parameters were given. The standard deviations of all the measured osmotic coefficient data from those calculated by using the model over the temperature range were estimated. A set of model equations of apparent molar enthalpy and excess heat capac...

This study is part of a series of studies on the development of a multi-temperature thermodynamically consistent model for salt lake brine systems. Under the comprehensive thermodynamic framework proposed in our previous study, the thermodynamic properties of the binary systems (i.e., NaCl+H2O, KCl+H2O, MgCl2+H2O and CaCl2+H2O) are simulated by the Pitzer–Simonson–Clegg (PSC) model. Various thermodynamic properties (i.e., water activity, osmotic coefficient, mean ionic activity coefficient, enthalpy of dilution and solution, relative apparent molar enthalpy, heat capacity of aqueous phase and solid phases) are collected and fitted to the model equations. The thermodynamic properties of these systems are reproduced or predicted by the obtained model parameters. Comparison to the experimental or model values in the literature suggests that the model parameters determined in this study can describe all of the thermodynamic and phase equilibria properties over wide temperature and concentration ranges. This modeling study of binary systems provides a solid basis for property predictions of salt lake brines under complicated conditions.

Solubility isotherms of the ternary Ca(NO3)2–LiNO3–H2O system were elaborately determined at T = (273.15, 298.15, and 323.15 K) by an isothermal equilibrium method, and the results showed that there are two stable solubility branches for the solid phases Ca(NO3)2·4H2O and LiNO3·3H2O at 273.15 K, and four stable solubility isotherms for the solid phases Ca(NO3)2·4H2O, Ca(NO3)2·3H2O, LiNO3·3H2O, and LiNO3 at 298.15 K, and solubility data corresponding to solid phases Ca(NO3)2·3H2O, Ca(NO3)2·2H2O, and LiNO3 at 323.15 K. The experimental data were correlated by a modified Brunauer–Emmett–Teller (BET) model to obtain the complete phase diagram of the ternary system over the temperature range from 273 to 373 K. On the basis of the simulated polytherms, an eutectic point Ca(NO3)2·4H2O + LiNO3·3H2O was recognized, and the melting temperature and fusion heat are 290.5 K and 139.8 J·g–1, respectively, measured by differential scanning calorimetry.

This paper is part of a series of studies on the development of a multi-temperature thermodynamically consistent model for salt lake brine systems. The objective of this study is to extend the binary thermodynamic models published in our previous studies to multicomponent systems. A revised general Pitzer–Simonson–Clegg (PSC) g E , ∗ equation for multicomponent system is proposed without limitation on the number of components. From the g E , ∗ equation, mathematical expressions of the activity coefficient of each component as well as the excess enthalpy and excess heat capacity of the aqueous phase are derived. Based on the multicomponent PSC equations and the CALPHAD-type thermodynamic framework, a generic command-line based program, named ISLEC, was developed for the thermodynamic modeling of aqueous system. The performance of the model and program were tested using three case studies based on typical systems. In the first case study, a temperature-dependent model for a six-component system of Li+-Na+-K+-Mg2+-Ca2+-Cl--H2O was developed based our previous published binary models and the regressed mixing parameters developed in this study. The model well represents the phase equilibrium and activity properties of all 10 sub-ternary systems well over a wide temperature range. These ternary models are generally valid from the lowest eutectic temperature to approximately 373.15 K. For most of the studied ternary systems, the original PSC model is valid for solubility isotherm and phase diagram modeling. However, for the LiCl + KCl + H2O and KCl + CaCl 2+ H2O ternary systems, the revised PSC equations are advantageous in describing the solid-liquid phase equilibria, especially at elevated temperatures. Using the parameters determined in binary and ternary systems, the Li+-Na+-K+-Mg2+-Ca2+-Cl--H2O model system reproduces the phase diagrams of its 10 sub-quaternary and two of its sub-quinary systems (LiCl + NaCl + KCl + MgCl2+H2O and NaCl + KCl + MgCl2+CaCl2+H2O) generally well at various temperatures. However, the reliability of our model predictions of the thermal properties of multicomponent aqueous mixture cannot be assured, and the differences from experimental data are usually large. Thus, the thermal data generated from our model should be used with caution for multicomponent systems. The evaporation and cooling crystallization processes of Dead Sea brine, which is a six-component Li+–Na+–K+–Mg2+-Ca2+-Cl--H2O system, were simulated to test the ISLEC program. The results demonstrate the satisfactory performance of the ISLEC program for solving multiphase equilibria in systems containing at least six components. In the second case study, the PSC equations were applied to model the solubility isotherms in a neutral-solute-containing system: H3BO3+NaCl + H2O. The results are excellent, but additional H3BO3-containing systems should be studied for further validation. In the last case study, mass and energy balance simulations were performed for the process of KCl production using sylvinite as the raw material, thus revealing the applications of ISLEC for process design and simulation.

With high figure of merits (FOMs) and intelligent responsiveness, flexible transparent electrodes (FTEs) based on one-dimensional nanomaterials (1DNMs), covering silver nanowires (AgNWs), copper nanowires (CuNWs) and carbon nanotubes (CNTs), are of great promise for smart flexible electronics. Inspired by directional collection of water droplets on wetted spider silks, we propose a universal strategy applicable to AgNW-based FTEs, CuNW-based FTEs and CNT-based FTEs. That is, the 1DNM-based FTEs are wetted by patch precursor mist and then, due to a synergism of surface energy gradient (making the 1DNMs preferentially capture patch precursor microdroplets) and anisotropic fast volatilization (producing a driving force for power-free microdroplet transport), are directionally patched in a mild way (ultraviolet-triggering). The directional formation of flexible conductive patches at the junctions of 1DNMs can significantly lower and stabilize the contact resistance of 1DNM-1DNM, and thus both high electri-optical and electri-mechanical FOMs of 1DNM-based FTEs are achieved. Moreover, because of the switchability of conducting polypyrrole (PPy) in the patches, the patched FTEs have a switching behavior of electrical conductivity in response to periodic electrical stimuli. Upon the electrical switch, the smart flexible electronic devices integrated with patched 1DNM-based FTEs are proved to be of practicability and reliability. The bioinspired universal strategy opens up a new avenue to achieve high FOMs of 1DNM-based FTEs of potential use in smart flexible electronics. This study also offers an attractive approach for directional repair or reconstruction of 1DNMs, as well as for precise intelligentization on solid surfaces or interfaces.

The solubilities of anhydrite in the ternary systems CaSO4 + MSO4 + H2O (M = Co, Ni) were determined through isothermal solution saturation at 348.1 K and 363.1 K. At low bivalent metal sulfate concentrations, anhydrite solubility decreases until it eventually reaches a minimum. Anhydrite solubility subsequently increases with the amount of heavy metal sulfate to a maximum. At this point, further increases in the concentration of metal sulfate decreases the solubility of anhydrite until saturation of the added bivalent metal sulfate. A Pitzer thermodynamic model was selected to predict isopiestic data including calcium sulfate solubilities of the ternary systems CaSO4 + MSO4 + H2O (M = Mn, Co, Ni, Cu, Zn) from 298.1 K to 373.1 K. The functional dependencies of the MSO4 (M = Ni, Cu, Zn) ion interaction parameters with temperature were determined, and the third virial parameters were given. The calculated solubilities are in agreement with the available experimental data. Using the Pitzer model and paramete...

The phase diagram of the quaternary system LiCl–NaCl–KCl–H2O have been predicted with a Pitzer–Simonson–Clegg thermodynamic model by combining the binary and ternary model parameters, which were determined by simulating reliable experimental data. The predicted phase diagram shows a good agreement with the available experiment data from the literature. The other thermodynamic properties (e.g. water activity) of the quaternary and its sub-ternary systems have been investigated by the model and compared with the experimental data in literature. Significant improvements have been made in comparison with assessments.

In this work, the water activities of the NaCl–CaCl2–H2O and KCl–CaCl2–H2O ternary systems and of their sub-binary systems NaCl–H2O and KCl–H2O were measured using an isopiestic method at 323.15 K. The isopiestic composition line for the NaCl–CaCl2–H2O system was found to obey the Zdanovskii rule very well, whereas the KCl–CaCl2–H2O system deviated slightly. The addition of NaCl to an aqueous solution of CaCl2 decreased its water activity for all CaCl2 molalities. However, KCl was found to decrease and increase the water activity at low and high CaCl2 molality, respectively. The turning point appears at 8.0 mol·kg–1 CaCl2 solution. The Pitzer–Simonson–Clegg (PSC) model was applied to represent the water activity of the two ternary systems, and the calculated results are discussed.

Water activity for binary KCl–H2O, NaCl–H2O and MgCl2–H2O, as well as two ternary NaCl–MgCl2–H2O and KCl–MgCl2–H2O, systems has been measured by using an isopiestic method at 323.15 K. The isopiestic results obtained show that the isopiestic composition lines of the NaCl–MgCl2–H2O system was found to obey the Zdanovskii rule, whereas the KCl–MgCl2–H2O system was observed to deviate slightly. The experimental water activities determined were applied to regress the parameters of the Pitzer model with a good agreement. The model with new parameters is validated by comparing water activity predictions with those given in the literature and not used in the parametrization process and calculating the solubility of the NaCl–MgCl2–H2O and KCl–MgCl2–H2O systems at various temperatures with the comparison of literature values.

A theoretical and experimental investigation of solubility of gypsum and anhydrite II in the complex system CaSO4 + MgSO4 + H2SO4 + H2O was conducted from 298.1 to 363.1 K. The solubility of anhydr...

Utilizing improvements in experimental equipment, analytical methods and the initial material, the solubility isotherms of the ternary system MgCl2–MgSO4–H2O were determined in detail at T = (323.15 and 348.15) K using an isothermal method of solid–liquid equilibrium. The results indicate that the solid phases MgSO4·nH2O(s) (n = 6, 1) and MgCl2·6H2O(s) are stable and MgSO4·nH2O(s) (n = 5, 4) are metastable at 323.15 K, which contradicts the results of a previous experimental study1 in which the phase MgSO4·4H2O(s) was reported as stable. The liquidus of the four solid phases MgSO4·nH2O(s) (n = 6, 4, 1) and MgCl2·6H2O(s) were measured at 348.15 K in this work. The findings indicate that the phases MgSO4·H2O(s) and MgCl2·6H2O(s) are stable and MgSO4·6H2O(s) and MgSO4·4H2O(s) are metastable at 348.15 K. Remarkable differences between this work and the literature solubility data for the phase MgSO4·H2O(s) at 348.15 K are observed. A Pitzer–Simonson–Clegg thermodynamic model was chosen to simulate the properti...

Solubility isotherms for the ternary system MgCl2–MgSO4–H2O and the quaternary reciprocal system Li+, Mg2+//Cl–, SO42––H2O were determined at 298.15 K by an isothermal dissolution method. In the ternary phase diagram, there are six solubility branches corresponding to the solid phases MgSO4·nH2O(s) (n = 7, 6, 5, 4, 1) and MgCl2·6H2O(s). In the quaternary equilibrium phase diagram, there are 16 solubility co-saturated lines corresponding to the solid phases MgSO4·nH2O(s) (n = 7, 6, 5, 4, 1), MgCl2·6H2O(s), Li2SO4·H2O(s), LiCl·MgCl2·7H2O(s), and LiCl·H2O(s). This report describes for the first time that the equilibrium solid phases MgSO4·H2O(s) and MgSO4·4H2O(s) have been found to exist in this quaternary system. However, the phase field of MgSO4·H2O(s) overlaps with the phase fields of MgSO4·4H2O(s) and MgSO4·5H2O(s), which indicates that MgSO4·4H2O(s) and MgSO4·5H2O(s) are metastable phases; MgSO4·H2O(s) is a relatively more stable phase in both the ternary and quaternary systems. A Pitzer–Simonson–Clegg ...

Solubility isotherms as well as the corresponding solid phases of the quaternary system MgCl2+LiCl+NH4Cl+H2O at 298.15 K have been elaborately measured by an isothermal equilibrium method. Four crystallization fields including two double salts (LiCl·MgCl2·7H2O(s) and NH4Cl·MgCl2·6H2O(s)), one hydrate salt (MgCl2·6H2O(s)), and one solid-solution (LiCl·H2O+NH4Cl)(ss) were detected in this system. A Pitzer-Simoson-Clegg (PSC) thermodynamic model was used to simulate and predict the thermodynamic properties of this quaternary system and its subsystems. The water activities of the ternary systems MgCl2+LiCl+H2O and LiCl+NH4Cl+H2O, as well as the solubility of the quaternary system MgCl2+LiCl+NH4Cl+H2O, were predicted by the PSC model, the results of which were compared with available literature data and the experimental results in this work. The excellent agreement between the predicted and experimental results indicates that the solubility results obtained in this work are reliable. On the basis of the quater...

Solubility equilibria are relevant to many aspects of chemistry and chemical engineering. Studies on solubility phenomena are of importance in understanding chemistry and in the development of chemical technology. Solubility equilibria are especially useful for geochemists investigating the formation and evolution of natural salt deposits. China possesses an enormous variety of such resources, including salt lakes, underground brines, oilfield brines, and natural soda and borate deposits, etc. With the ongoing economic development of China, the exploitation and comprehensive utilization of these kinds of mineral resources are making great progress. Although much research on aqueous salt systems has been published, solubility equilibria studies have long been an active research field in China. This paper presents a review of solubility research on salt/water systems, encompassing more than 200 papers from Chinese researchers.

The solubility isotherms of gypsum and insoluble anhydrite in the ternary system CaSO 4 –H 2 SO 4 –H 2 O were determined at T =(298.1, 323.1, 348.1, and 363.1) K using the isothermal method. The kinetics of the transformation between gypsum and insoluble anhydrite in H 2 SO 4 aqueous solutions at 298.1 and 363.1 K were also studied. Our measured solubility isotherms for gypsum are generally in good agreement with the literature solubility data. However, the solubilities of anhydrite measured in this work are much lower than those reported by Zdanovskii and Vlasov (1968b) [Zdanovskii, A.B., Vlasov, G.A., 1968b. Russ. J. Inorg. Chem. 13, 1418–1420.]. Kinetic experiments showed that the complete transformation from gypsum to anhydrite at 363.1 K takes at least 120 h in 0.5 mol kg −1 H 2 SO 4 aqueous solution and over 6 h for higher concentrations of H 2 SO 4 . Furthermore, much more time is needed for the Ca 2+ concentration in the solutions to equilibrate with the end solid phase “insoluble anhydrite” than for the complete transformation of gypsum to insoluble anhydrite. These kinetic results were used to identify why the insoluble anhydrite solubilities in H 2 SO 4 aqueous solution in the literature were higher than those in our results. A Pitzer thermodynamic model was chosen to simulate and predict the solubility isotherms of gypsum and insoluble anhydrite in this ternary system, and the good agreement between the experimental results and the model supports the reliability of the experimental solubility data obtained in this work. Finally, the stable fields for gypsum and insoluble anhydrite as a function of temperature and H 2 SO 4 concentration were constructed by the thermodynamic model.

A Pitzer–Simonson–Clegg model has been applied to calculate the isotherms of the system KNO3–LiNO3–NaNO3–H2O and its subsystems. The model parameters are fitted against experimental solubility and water activity in the sub-binary and sub-ternary systems of the titled quaternary system. The solubility of the system KNO3–LiNO3–NaNO3–H2O at 298.1 and 308.5 K and its subsystems KNO3–LiNO3–H2O at 283.1 K and LiNO3–NaNO3–H2O at 323.1 K are elaborately measured for verifying the reliability of the model prediction. Comparisons indicated that the calculated values are in agreement with our experimental data and literature data.

The solubility isotherms for the ternary system Li2SO4–MgSO4–H2O and the quaternary system Li2SO4–K2SO4–MgSO4–H2O at T = 273.15 K were determined by the isothermal equilibrium method. A Pitzer–Simonson–Clegg (PSC) model was used to simulate the properties of the binary and ternary systems of the quaternary title system. The binary model parameters were fitted against selected reliable experimental data of water activity. The mixture model parameters were obtained by fitting them to the ternary solubility isotherms taken from the literature and determined in this work. The solubility isotherms of the quaternary title system were predicted by the PSC model and compared with the experimental results in this work. The excellent agreement between the predicted and experimental results indicates that the experimental results obtained in this work are reliable.

A reaction model was developed to describe the thermodynamic properties of aqueous electrolyte solutions. In the model various types of association (ion–solvent, ion–ion) are incorporated using as much as possible structure information. In the framework of the model, an electrolyte aqueous solution is treated as a mixture of charged or neutral associated species consisting of cations, anions and the solvent water, among the species the short range interactions are assumed to be equal. The abundance of each species is determined by its specific Gibbs energy of formation related to the assumed master species. The total Gibbs energy of mixing consists of a long range electrostatic term and short range interaction terms, the latter are sum of Gibbs energy of all species. Based on the total Gibbs energy of mixing, activity expressions for each species were derived. The Gibbs energy of formation of each associated species is correlated by its stepwise formation Gibbs energies, thus reducing the number of necessary adjustable parameters. At the example systems CuCl 2 –MCln–H 2 O (M = Li, Ca, Mg) model parameters were determined by fitting experimental data of water activities and solubilities on the basis of ion associates in agreement with available structure information. Component activities, solubility isotherms and species abundances were calculated and compared with experimental results. This facilitates an understanding of structure–property relationships in the titled systems.

Solubility of gypsum in the quaternary systems CaSO4–HMSO4–H2SO4–H2O (HM = Cu, Zn, Ni, Mn) are predicted up to saturated concentrations of heavy metal sulfates and to a H2SO4 concentration of 2 m by a Pitzer thermodynamic model. Experimental solubility and water activity in the subbinary and subternary systems from the literature were used for model parametrization. Then the solubility phase diagrams for the quaternary systems were predicted directly with these obtained binary and ternary model parameters. In order to verify the reliability of the predicted results, a series of solubility measurements of gypsum in these quaternary systems have been carried out at 298.15 K and the measured results were compared with the predicted ones. It was shown that the Pitzer thermodynamic model can perfectly predict the solubilities of gypsum in the quaternary systems. Meanwhile, the newly obtained experimental data were compared with limited literature data in some of the quaternary systems; good agreement was found...

The phase diagram of the quaternary system KNO3–LiNO3–Mg(NO3)2–H2O was simulated over the temperature range from 273 to 333 K by a Pitzer–Simonson–Clegg model, whose parameters were determined by fitting to experimental solubility and water activity data of the binary systems KNO3–H2O, LiNO3–H2O, Mg(NO3)2–H2O and the ternary systems KNO3–LiNO3–H2O, KNO3–Mg(NO3)2–H2O, LiNO3–Mg(NO3)2–H2O. Three new eutectic points with melting points within room temperatures were found in these systems, which could be used as candidates for storing heat from low temperature heat resources. Exothermal and endothermal behaviors of the predicted phase change materials were measured. Results show that the predicted phase change materials possess excellent heat storage and release ability.

Solubility isotherms of the ternary system (NH4Cl+CaCl2+H2O) were elaborately determined at T = (273.15 and 298.15) K by using the isothermal method. In the equilibrium phase diagram, there are two solubility branches corresponding to the solid phases CaCl2⋅6H2O and NH4Cl. Invariant point compositions are 36.32 wt% CaCl2 and 3.4 wt% NH4Cl at 273.15 K, and 45.86 wt% CaCl2 and 5.22 wt% NH4Cl at 298.15 K. A Pitzer–Simonson–Clegg thermodynamic model was applied to represent the thermodynamic properties of this ternary system and to construct a partial phase diagram of the ternary system at temperatures between (273.15 and 323.15) K. It was found in the predicted solubility phase diagram that the double salt 2NH4Cl⋅CaCl2⋅3H2O, found by other authors at (323.1 and 348.1) K, will disappear at temperatures below 298.15 K. Besides, it was found that there are two peritectic points in the ternary system with peritectic temperatures at 299.65 K and 298.15 K, and the former peritectic point falls just on the line between the composition points of NH4Cl and CaCl2⋅6H2O. According to phase rule, a solution made of this point will begin to crystallize at 299.65 K and end at 298 K and therefore can be acted as a “pseudo eutectic” phase change material (PCM). A heat storing and releasing experiment of 50 grams of the PCM was carried out, obtaining a satisfying result.

Deposit of CaSO4 in hydrometallurgical processes involving heavy metals usually decreases production quality and harms the production process. To avoid its formation at false time and sites, a sound understanding of the solubility behavior of CaSO4 in the quaternary systems CaSO4 + H2SO4 + (heavy metal)SO4 + H2O over large ranges of temperature and concentration is a prerequisite. Up to now, although a large amount of solubility data has been reported in these systems, little information is available on the solubility of anhydrite, especially at salt concentrations near saturation points. In this paper, we introduce the effect of CaSO4 in hydrometallurgical processes involving heavy metals, review published solubility data of calcium sulfate and its hydrate in relevant systems, and report our newly determined solubility results involving anhydrite in the quaternary systems CaSO4 + H2SO4 + MSO4 + H2O (M = Cu,Zn,Mn) at 348.1 and 363.1 K. Based on the newly obtained data some application examples were given. On account of the complexity of the solubility phase diagram of these quaternary systems, where the calcium sulfate solubility is a function of its crystal type, temperature, compositions of sulfuric acid, and heavy metal sulfate, a complete solubility phase diagram is not available until some basic data measurement, for instance, water activity at temperatures higher than 298 K, and final modeling has been finished.

Solubility isotherms of the ternary system (LiCl + NH4Cl + H2O) were elaborately determined at T = (273.15, 298.15, and 323.15) K by an isothermal method. In the equilibrium phase diagram, there are two solubility branches at 273.15 K, corresponding to the solid phase LiCl·2H2O and NH4Cl. The invariant point composition at 273.15 K is w = 0.401 for LiCl, w = 0.024 for NH4Cl, and w = 0.575 for H2O. However, there are three solubility branches at (298.15 and 323.15) K, corresponding to the solid phase LiCl·H2O, NH4Cl, and a new found solid solution phase (NH4Cl)x(LiCl·H2O)1−x. A Pitzer−Simonson−Clegg thermodynamic model was selected to represent the thermodynamic properties of this system. Thermodynamic consistence between our solubility data and water activity from other research groups shows that these concerned experimental data are reliable.

Solubility data of CaCl 2 · n H 2 O ( n = 2, 4, 6) were predicted and evaluated by a Stokes and Robinson's adjusted BET-model using the vapor pressures of saturated solution as criteria. Prior to the prediction, the BET model was parameterized with the most recently reported experimental osmotic coefficients. The comparison with other models showed that, despite of fewer model parameters, the BET model could represent the activities in the system CaCl 2 + H 2 O as good as the Pitzer model in a large temperature range from 298.15 to 523.15 K. Meanwhile, experimental vapor pressure data of the saturated CaCl 2 solution were critically evaluated and some of them are selected as criteria for solubility prediction. In principle, the predicted solubility has higher accuracy than an average set of various experimental data and therefore is recommended for use in relevant cases.

Solubility data of LiCl·nH2O (n = 0, 1, 2) was evaluated by checking the consistency of evaluated vapor pressures with the experimental data. This process includes the following: (1) A series of vapor pressure data above the LiCl·nH2O saturated solution were evaluated, and reliable data were selected as “standard” data. (2) A BET model was selected to fit the selected experimental data of water activity at salt concentrations below 20 mol·kg-1 and at temperatures ranging from 273.15 K to 428.65 K. (3) Vapor pressures for the solubility data given by different authors were calculated with the BET model and further compared with the standard data. (4) Those solubility data at which vapor pressures calculated with the BET model obviously deviate from the standard data were considered to be unreliable.

From water activity data within the concentration range of molten salt hydrates the parameters ri and ei of the modified Brunauer, Emmett and Teller (BET) equation have been determined for several salts i. The parameters were used to model the solid–liquid phase diagrams and to extract the temperature functions of the Gibbs energy of formation of all occurring solid phases with respect to pure liquid water and anhydrous molten salts as reference states. Applying the multi-component formulation of the BET model according to Ally and Braunstein, phase diagrams of aqueous ternary systems composed of the salts LiNO3, NaNO3, Mg(NO3)2, Ca(NO3)2, Zn(NO3)2, LiCl, CaCl2, LiClO4, and Ca(ClO4)2 were predicted and compared with available experimental data. Good agreement with the experimental data was found, when the presumptions of the BET model in respect to water activity and chemical interactions are satisfied. Based on the BET calculations, a list of new eutectic temperatures and compositions of salt hydrate mixtures is given.

Enthalpy of melting can be used to store heat in a simple way for time periods of hours and days. Knowledge of the solid –liquid equilibria represents the most important presumption for systematic evaluations of the suitability of hydrated salt mixtures. In this paper, two approaches for predicting solid–liquid equilibria in ternary or higher component systems are discussed using the limited amount of thermodynamic data available for such systems. One method is based on the modified Brunauer–Emmett–Teller (BET) model as formulated by Ally and Braunstein. In cases of a strong tendency toward complex formation of salt components, the BET model is no longer applicable. Reaction chain models have been used to treat such systems. Thereby, the reaction chain represents a method to correlate step-wise hydration or complexation enthalpies and entropies and, thus, reduce the number of adjustable parameters. Results are discussed for systems containing MgCl2, CaCl2, ZnCl2, and alkali metal chlorides.