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Lithium iron phosphate (LiFePO4) recovered from waste LiFePO4 batteries inevitably contains impurity aluminium, which may affect material electrochemical performance. Nearly all references believe that aluminium-doped LiFePO4 is a solid solution and that the material capacity increases firstly before decreasing with aluminium content. However, their reported performance of the aluminium-free LiFePO4 as a comparison is far lower than commercial LiFePO4 currently manufactured at large scales. Thus, conclusions drawn based on such a comparison are questionable. To better understand the effects of aluminium on LiFePO4 electrochemical performance, we first tracked aluminium behaviour in FePO4·2H2O, FePO4 precursors and LiFePO4 product. In FePO4·2H2O prepared from aqueous solution, aluminium exists as AlPO4·2H2O in two types (monoclinic and orthorhombic systems) of solid solutions (Fe1-xAlxPO4·2H2O). In Fe1-xAlxPO4 dehydrated from Fe1-xAlxPO4·2H2O, trigonal AlPO4 and FePO4 firstly form a solid solution (Fe1-xAlxPO4, berlinite). At higher aluminium content (x ≥ 0.026), additional AlPO4 forms an independent phase in monoclinic system. In Li1-xFe1-xAlxPO4/C (x = 0–0.048), no evidence of solid solution formation was observed. Secondly, the effects of aluminium on Li1-xFe1-xAlxPO4/C electrochemical performance were studied. It is found that, material specific discharge capacity only decreases monotonically with addition of aluminium at optimal calcination temperature (as 760 °C), unlike references, which “increases firstly before decreasing”. Finally, it is found that aluminium has no remarkable impact on material cycling stability under 100 cycles at 1C rate using coin test.

Boron abundantly exists in salt lake brine system as various boron-containing aqueous species or minerals. The phase behavior of boron and other substances (Li, Na, K, Rb, Cs, Mg, Ca, Sr, Cl, S etc.) in the complicated salt brine system during the solar pool process needs to be simulated and predicted by models. Basic experimental data (e.g. solubility, etc.) of simple binary and ternary system are necessary for the model parameterizations. At present, the unavailability of solubility data in the H3BO3 + SrCl2 + H2O ternary system makes the model parameterization difficult. In this paper, we determined the solubility isotherms in the H3BO3 + SrCl2 + H2O ternary system at 273.15 K, 298.15 K, 323.15 K, 348.15 K and 363.15 K. The result show that the isotherms all consisted of the solubility branches H3BO3(cr) and SrCl2⋅nH2O(cr) (n = 6 and 2), and no new phase has been found. Then, a Pitzer–Simonson–Clegg (PSC) model in the ISLEC software package was used to simulate the thermodynamic properties of the H3BO3 + H2O, SrCl2 + H2O, and H3BO3 + SrCl2 + H2O systems, including solubility, water activity, activity coefficients, heat capacity and enthalpy of dilution. With the obtained model parameters, a complete polythermal phase diagram of the H3BO3 + SrCl2 + H2O system was predicted at temperatures from 255 to 373 K. The present work lays the foundation for the future simulations of complicated salt lake brine systems containing H3BO3 and SrCl2.

Although the Ca2+–F− association is of great importance for aqueous environments and industrial systems containing F−, as well as for defluorination processes, many details of the association solvation structures and behavior remain unclear. Herein, a combination of classical/ab initio molecular dynamics simulations and density functional theory calculations was used to investigate the structure and hydration of CaFx2−x (x = 1, 2) and the association/dissociation behavior of Ca2+–F− in aqueous CaF2 solutions. The primary shell of Ca2+ is found to be very flexible in the association of Ca2+–F−, with coordination numbers dynamically oscillating in the range of 6–9, with 6 and 7 being the most favorable. The calculations show that for CaF(H2O)14+, the contact ion pair (CIP) is more favorable and occurs with no energy barrier, whereas the formation of CaF2(aq.) must overcome a ∼3.6 kJ mol−1 energy barrier; moreover, the CIP and solvent shared ion pair (SSIP) dynamically coexist for CaF2(H2O)14 in aqueous CaF2 solutions. Calculations for the dissociation process of CaF(H2O)6+ show a dramatic energy increase going from SSIP to free Ca2+ and F−, ascribed to the surprisingly long-range electrostatic attraction between Ca2+ and F− rather than to special F⋯H interactions. The energy increase results in the estimated association constant of CaF+ being larger than that previously measured using fluoride ion selective electrodes. This is attributed to the fact that the latter value might correspond to the ligand reaction of free Ca2+ and F− to form the Ca2+–F− SSIP. The combination of these results with CaF2(s) solubility measurements suggests that the higher-order Ca2+–F− complexes are absent in aqueous CaF2 solutions.

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 ...

The solution chemistry of Mo(VI) and W(VI) in mixtures of sulfuric and phosphoric acids is relevant to the development of practicable hydrometallurgical processes for the recovery and separation of these two elements from low-grade scheelite ores. The behavior of Mo(VI) and W(VI) in such mixtures has been studied using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), nuclear magnetic resonance (NMR), and small-angle X-ray scattering (SAXS) spectroscopies, along with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS). Where applicable, these techniques have produced a self-consistent picture of the similarities and differences between the chemical speciation of Mo(VI) and W(VI) as functions of solution composition, mostly at a constant phosphorous/metal (P/M; M = Mo(VI) or W(VI)) ratio of ∼1. In dilute acidic media (0.02 mol·kg-1 H+, without H2SO4), Mo(VI) exists mostly (∼60%) as P2Mo5O236- with the remaining ∼40% as β-Mo8O264-. Under the same conditions, W(VI) is largely present as NaPW11O396- (∼80%) and P2W5O236- (∼10%), with the remainder probably occurring as isopolytungstates such as W12O4212- and some tungstophosphate dimers such as P2W18O626-. At higher acid concentrations (≲5 mol·kg-1 H2SO4), polymeric Mo(VI) anions are broken down to form the oxocations MoO22+ and Mo2O52+ and their protonated forms, with the dimers becoming increasingly dominant at higher acidities (∼80% in 5 mol·kg-1 H2SO4). In stark contrast, W(VI) polyanions do not decompose at higher acidities but instead form (∼70% in 0.6 mol·kg-1 H2SO4) a Keggin ion, PW12O403-. Further acidification with H2SO4 results in the agglomeration of this Keggin ion, forming clusters of about 50 and 100 A in diameter that ultimately produce crystalline precipitates, which could be identified in part by their X-ray diffraction patterns. Possible application of these findings to the hydrometallurgical separation of Mo and W using acidic solutions is briefly discussed, based on a limited number of batch solvent extractions.

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...

A combination of electronic (UV-vis) and X-ray absorption (EXAFS, XANES) spectroscopies has been used to investigate the formation of copper(II)/chloride complexes in concentrated aqueous solutions. It is established that lowering the water activity by the addition of Mg(ClO4)2 at a constant Cl−/Cu(II) ratio results in the replacement of water molecules by Cl− ions in the primary coordination shell of Cu(II). This behavior closely parallels the effect of increasing the Cl−/Cu(II) ratio and demonstrates that full understanding of the stoichiometry and structures of the complexes formed in concentrated metal-ion chloride solutions requires explicit consideration of the role of the solvent.

Control of the morphology of carbonate crystals plays an indispensable role in mineralization process. We investigated the relationship between HPMC concentration and different molar ratios of Mg/Ca on the carbonate crystallization by monitoring crystal polymorph, crystal size, and morphology. In this experiment, the total molars of [Mg2+] and [Ca2+] were 50 mM. The results demonstrated that different molar ratio of Ma/Ca primarily can help different morphology form in multidimensional spline space, for instance, lens-like calcite, spindle shaped aragonite and polyhedron nesquehonite. Moreover, the metastable aragonite phase of CaCO3 can come into being with the existence of HPMC. Meanwhile, the Mg2+ would inhibit the growth of calcite and facilitate the production of the aragonite when the Mg2+ concentration is lower than 25 mM in solution. With increasing the molar ratio of Mg/Ca, the nesquehonite precipitation would be induced when the magnesium concentration is sufficiently high. The nesquehonite grew along the same (4 0 0) orientation in that the HPMC can be controlled by the basic units during the aggregation and reorientation process. The results of polarizing microscope also provided forceful support for the crystal growth mechanism. The thermodynamical stable phase of anhydrous calcium carbonate (CaCO3) was nucleated preferentially after the combination between Ca2+ and CO32−, then, the Mg2+ can bond with the oxygen atoms in HPMC due to electrostatic adherence and combine with CO32− and H2O to form a nesquehonite crystal phase. The results illustrated that the extent of binding affinity during HPMC with Ca2+ or Mg2+ was suggested to be in connection with the reconstructuring process and the morphology of final carbonate crystals.

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.

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 ...

In this work, the solubility behaviors of gypsum and anhydrite in the H2SO4-H3PO4-H2O system were investigated over the temperature range T = 30–80°C, and the results showed that the solubility of anhydrite was considerably lower than that of gypsum. On the basis of the differential solubilities of gypsum and anhydrite, a method was developed to remove calcium from the scheelite leaching solution by adding anhydrite as an inoculating crystal. The effects of the reaction time, concentration of the CaSO4 inoculating crystals, and temperature were investigated. With an addition of CaSO4 inoculating crystals at a concentration of 60 g/L, the Ca2+ concentration of the scheelite leaching solution decreased to a low level of approximately 0.76 g/L after 10 h at 70°C.

In this work, we apply static density functional theory (DFT) calculations, as well as classical and first-principles molecular dynamics (FPMD) simulations, using the free-energy perturbation method to study the protonation ability, active site and structures of W(VI) and Mo(VI) in acidic aqueous solution. Using FPMD simulations, utilizing the pKa's calculation technique, we concluded that the octahedral WO2(OH)2(H2O)2 is the true formula for tungstic acid (H2WO4), and the hydroxyl ligands are the acidic site. This aqueous structure of H2WO4 is analogous to the previously reported structure of molybdic acid (H2MoO4). The FPMD trajectories of the tungstic acid deprotonation show that the mono-protonated monotungstate ion (HWO4−) may partially exist as a five-coordinated WO3(OH)(H2O)− species except for the four-coordinated WO3(OH)− species. This result is supported by DFT calculations, with an isoenergetic point (ΔE = 1.9 kcal·mol−1) for the WO3(OH)(H2O)− and WO3(OH)− species, when explicit solvent molecules are taken into account. In contrast, for the H2MoO4 acid, FPMD trajectories during the deprotonation process show that two H2O ligands immediately escape from the first coordinated sphere of Mo(VI) to form the four-coordinated MoO3(OH)− species. This difference indicates that structural expansion of W(VI) began in the first protonated step, while that of Mo(VI) only occurs in the second step. In addition, our calculated first and second acid constants for tungstic acid are higher than previously reported values for molybdic acid. This result suggests that WO42− is more easily protonated than the MoO42− anion in the same acidic solution, which is further confirmed by DFT calculations of hydrated oxoanions and its protonated species, based upon the hydration energy., The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (Nos. 51334008 and 51704338) and the Research Foundation of Education Bureau of Hunan Province, China (No. 17C1639).

Solubility isotherms of the sparingly soluble salts CaF2(s) and CaSO4·2H2O(s) in their mixed aqueous solutions have been measured at 298.1 K. It was found that the CaF2(s) solubility decreases with increasing CaSO4 concentration in the solution and reaches about 1/3 of the CaF2(s) solubility in pure water in the CaSO4·2H2O(S) saturated solution. A thermodynamic model was developed to predict the CaF2(s) solubility isotherm in this system, in which the short range interactions of the species in the aqueous solution are represented by ion-association constants reported in literature, and the long range interaction, i.e., the electrostatic term, is represented by the well known Davies equation. The predicted solubility isotherm reasonably agrees with the experimental results. The contributions of the long-range term and the short-range term to the calculated solubility isotherm were investigated. It was concluded that the ionic association combining with the Davies equation is sufficient to represent the excess interaction of the CaF2 + CaSO4 aqueous solution at 298.15 K. This model approach could be applicable for other dilute mixed electrolyte systems in which component activity coefficients are lacking and model parameters are difficult to determine.

The solid solution–aqueous solution (SSAS) equilibria in the KCl + RbCl + H2O system were redetermined at 298.15 K. The experimental data for (K,Rb)Cl were consistent with the formation of a continuous solid solution without miscibility gaps. The Schreinemakers’ wet residues method and an XRD quantitative analysis technique based on the Vegard approach were applied to determine the chemical composition of the solid solution phase of (K,Rb)Cl. The compositions of (K,Rb)Cl derived from the Vegard approach are in accordance with those from the wet residues method. The thermodynamic properties of mixing of the (K,Rb)Cl solid solution were theoretically predicted using atomistic simulations. From these simulations, a regular solution behavior is recognized that is consistent with the knowledge of the thermodynamic properties of mixing of (K,Rb)Cl obtained from SSAS equilibrium studies, but the predicted regular solution model parameter A 0 is significantly larger than that regressed from the SSAS equilibrium data. Finally, a thermodynamic model was developed for representing the SSAS equilibria and element partitioning in the KCl + RbCl + H2O system as a function of temperature that can be used for predicting the SSAS equilibria in the studied system over the temperature range 273.15–373.15 K.

The co-saturation line for the solid phases NaCl(s) and MgCl2 · 6H2O(s) in aqueous solution has been measured by a phase equilibrium at various temperatures. It was found that the Y b (Y b = w(NaCl)/(w(NaCl) + w(MgCl2))) value of the co-saturation line increase with increasing temperature. A new recrystallization approach has been suggested for the purification of MgCl2 · 6H2O(s) containing quite amount of impurity NaCl, i.e., dissolving the crude sample at low temperatures, followed by evaporating and phase separating at high temperatures. Applying the proposed approach a crude MgCl2 · 6H2O(s) sample can be purified to the level of Y b = 0.17% by only one crystallization process.

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.

Knowledge of the structure and speciation of aqueous Cu(II)-chloride complexes is important for understanding Cu(II) behavior in the deep removal technology of Cu impurity from nickel electrolysis anolytes containing chloride. In this paper, X-ray absorption spectroscopic measurements are reported for dissolved copper in lithium chloride (up to ~ 16 mol kg −1 ) solutions at room temperature. The speciation and structure of corresponding solutions has been probed by performing a combined ab initio XANES theoretical and experimental analysis. The EXAFS spectrum was analyzed as well within this approach. Our XAS data and ab initio XANES calculations favored the five-coordinated [Cu(H 2 O) 5 ] 2+ with square pyramidal configuration over the four-(square planar and tetrahedron, [Cu(H 2 O) 4 ] 2+ ) and six-coordinated (octahedron, [Cu(H 2 O) 6 ] 2+ ) structure in dilute Cl − solution (~ 0.55 mol kg −1 ). This is also supported by the EXAFS refinement with the [CuO 5 ] model having the lowest statistical error. In the highest Cl − concentration solution, the results of both methods show that tetrahedral [CuCl 4 ] 2– complexes are predominant. Upon manually adjusting its geometric parameter to the distortion degree α of ~ 18° and average Cu Cl bond distance of 2.25 A of a squashed tetrahedral model, not only does the calculated XANES spectrum well reproduce the experimental spectrum, but also the statistical error in the EXAFS refinements is lowest.

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.

Water activity for the binary H2SO4–H2O and H3PO4–H2O systems, as well as the ternary H2SO4–H3PO4–H2O system has been measured using an isopiestic method at 298.15 K. The results for binary systems obtained in this work agree well with literature data. The results show that the isopiestic composition lines of the H2SO4–H3PO4–H2O system obey Zdanovskii’s rule at low concentrations, whereas at higher concentrations the isopiestic lines are observed to have positive deviations. The relative uncertainties of isopiestic molalities of parallel samples in each experimental run are better than 0.2 %. The measured water activities reported in this work can be used to parameterize thermodynamic models for chemical engineering of phosphorus and heavy metal hydrometallurgical processes.

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.

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 is generally considered to affect ionic association in aqueous electrolyte solutions; however, it is usually ignored when the association reactions or constants are discussed. In this work, the effect of water activity on the association reaction $$ {\text{Ni}}_{{ ( {\text{aq}})}}^{2 + } + n{\text{Cl}}_{{ ( {\text{aq)}}}}^{ - } \rightleftharpoons {\text{NiCl}}_{{n{\text{ (aq)}}}}^{2 - n} $$ was investigated by EXAFS and UV–Vis spectroscopy measurements on NiCl2 aqueous solutions at room temperature with constant Cl−/Ni2+ ratio (~66) and various water activities; the latter were adjusted by adding MgCl2 and Mg(ClO4)2. Both the EXAFS and the UV–Vis spectra measurements indicated that the extent of Ni–Cl association increases in decreasing water activity environments, independent on the Cl−/Ni2+ ratio. Thus, the effect of water activity on the ionic association should not be ignored and more emphasis should be paid on it, especially, when the water activity is very low.

The solubility data and pH of the ZnSO4-Zn(OH)2-H2O system were elaborately measured at T = 291.15, 298.15, 308.15, and 323.15 K, and the solid phases were determined by XRD to be ZnSO4 · 3Zn(OH)2 · 5H2O. The Pitzer model was applied to simulate thermodynamically and predict the relationship between mass percent of ZnSO4 and pH in the ZnSO4-Zn(OH)2-H2O system taking account of the equilibrium of ions over the temperature from 273.15 to 323.15 K. Based on the experimental data and the calculation results, a theoretical direction of avoiding base zinc sulfate forming in industrial processes was advised.

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.

Specific heat capacity of Rb2SO4(aq) and Cs2SO4(aq) solutions was determined using a Calvet-type calorimeter from 288.15 K to 338.15 K and from about 0.25 mol·kg−1 to concentration near room temperature solubility limits. For both Rb2SO4(aq) and Cs2SO4(aq) solutions, the specific heat capacity decreases with the increase of molality at constant temperature. Combining the heat capacity data determined in this study and other thermodynamic properties (i.e. water activity, osmotic coefficient, mean ionic activity coefficient, enthalpy of dilution and solubility) reported in literature, thermodynamic and phase equilibria properties of the binary Rb2SO4 + H2O and Cs2SO4 + H2O systems were modelled using a comprehensive thermodynamic framework, in which a Pitzer-Simonson-Clegg model was applied to represent the non-ideality of aqueous phases. The models can represent all the properties over wide temperature and concentration ranges. This study forms a basis for solubility prediction in multi-component systems containing Rb and Cs sulfates.

In this work, a thin-film UV-visible spectroscopic technique has been developed and combined with time-dependent density functional theory (TD-DFT) calculations for the study of the chemical speciation in concentrated aqueous solutions of Cu(II) + Cl-. When the CuCl2 concentration changed from 0.05 mol·kg- 1 to 5 mol·kg- 1, the UV peak shifted from ~ 250 nm to ~ 262 nm. Similar shifts were recorded for CuCl2 solutions containing up to 5 mol·kg- 1 NaCl. Combination of the spectral data with our previous TD-DFT calculations provided a consistent model of the chemical speciation in the Cu(II)/Cl- system up to high concentrations of both components. The results obtained indicate that many of the previous conclusions regarding these solutions, drawn from a variety of techniques are unreliable. Under the present conditions, the only species detected were innersphere complexes with one or two Cl- ions bound to the aquated Cu(II) ion. For all the solutions, no remarkable peaks at ~ 280 nm or 380 nm, indicative of CuCl3 - (aq) and CuCl4 2 - (aq) respectively, were observed.

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 ...

Knowledge of the thermodynamic properties of aqueous copper(II) chloride complexes is important for understanding and quantitatively modeling trace copper behavior in hydrometallurgical extraction processing. In this paper, UV–Vis spectra data of Cu(II) chloride solutions with various salinities (NaCl, 0–5.57 mol·kg−1) are collected at 25 °C. The concentration distribution of Cu–Cl species is in good agreement with those calculated by a reaction model (RM). The simple hydrated ion, Cu2+, is dominant at low concentration, whereas [CuCl]+, [CuCl2]0 and [CuCl3]− become increasingly important as the chloride concentration rises. Moreover, the RM calculation suggests the present of a small amount of [CuCl4]2−. The de-convoluted molar spectrum of each species is in excellent agreement with our previous theoretical results predicted by time-dependent density functional theory treatment of aqueous Cu-containing systems. The formation constants for these copper chloride complexes have been reported and are to be preferred, except log10 K 2 ([CuCl2]0).

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.

Water activity in the ternary system LiCl–SrCl2–H2O and its sub-binary systems has been elaborately measured by the isopiestic method. The measured water activities were used to justify the reliability of solubility isotherms reported in literature by correlating them with two thermodynamic models, that is, the extended Pitzer model and the Pitzer–Simonson–Clegg model. It was found that the extended Pitzer model cannot correlate consistently the water activities measured and either set of the solubility isotherms reported in literature for this concerned system, no matter how its parameters were adjusted. However, the Pitzer–Simonson–Clegg model can correlate consistently our measured water activities and the solubility isotherms reported by the literature (Kydynov et al. Issled. Obl. Khim. Tekhnol. Miner. Solei Okislov1965, 146–150), which should be more reliable than solubility data reported in other references.

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.

This work presents an assessment of solubility data for rare earth metal fluorides (generally of trivalent metals and of CeF4) in water and in aqueous ternary systems. Compilations of all available experimental data are introduced for each rare earth metal fluoride with a corresponding critical evaluation. Every such evaluation contains a collection of all solubility results in water, a selection of suggested solubility data, and a brief discussion of the multicomponent systems. Because the ternary systems were seldom studied more than once, no critical evaluations of such data were possible. Only simple fluorides (no complexes or binary salts) are treated as the input substances in this report. The literature has been covered through the end of 2013.

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.

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.