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During investigations of the formation of hydrated magnesium carbonates, a sample of the previously unknown magnesium carbonate hexahydrate (MgCO3·6H2O) was synthesized in an aqueous solution at 273.15 K. The crystal structure consists of edge-linked isolated pairs of Mg(CO3)(H2O)4 octahedra and noncoordinating water molecules, and exhibits similarities to NiCO3·5.5H2O (hellyerite). The recorded X-ray diffraction pattern and the Raman spectra confirmed the formation of a new phase and its transformation to magnesium carbonate trihydrate (MgCO3·3H2O) at room temperature.

For lithium halides, LiX (X = Cl, Br and I), hydrates with a water content of 1, 2, 3 and 5 moles of water per formula unit are known as phases in aqueous solid–liquid equilibria. The crystal structures of the monohydrates of LiCl and LiBr are known, but no crystal structures have been reported so far for the higher hydrates, apart from LiI·3H2O. In this study, the crystal structures of the di- and trihydrates of lithium chloride, lithium bromide and lithium iodide, and the pentahydrates of lithium chloride and lithium bromide have been determined. In each hydrate, the lithium cation is coordinated octahedrally. The dihydrates crystallize in the NaCl·2H2O or NaI·2H2O type structure. Surprisingly, in the tri- and pentahydrates of LiCl and LiBr, one water molecule per Li+ ion remains uncoordinated. For LiI·3H2O, the LiClO4·3H2O structure type was confirmed and the H-atom positions have been fixed. The hydrogen-bond networks in the various structures are discussed in detail. Contrary to the monohydrates, the structures of the higher hydrates show no disorder.

The title carbonate hydrate, Cs2Mg4(CO3)5·10H2O, was crystallized at room temperature out of aqueous solutions containing caesium bicarbonate and magnesium nitrate. Its monoclinic crystal structure (P21/n) consists of double chains of composition 1 ∞[Mg(H2O)2/1(CO3)3/3], isolated [Mg(H2O)(CO3)2]2– units, two crystallographically distinct Cs+ ions and a free water molecule. The crystal under investigation was twinned by reticular pseudomerohedry.

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...

A sample of pure, artificial hellyerite was synthesized in aqueous solution at 0 °C. The recorded X-ray diffraction pattern completely agrees with the reference data given for natural hellyerite. Laboratory high resolution X-ray powder diffraction, applying global optimization methods and Rietveld refinement, was employed to solve the crystal structure. Synthetic hellyerite was determined to crystallize in the primitive monoclinic space group P2/m (no. 10) with a = 10.769(2) A, b = 7.295(2) A, c = 9.343(2) A, and β = 94.042(2)°. The crystal structure consists of edge-linked, isolated pairs of Ni2(CO3)2(H2O)8 octahedra and non-coordinating water molecules. According to structure solution and thermal analysis the molecular formula of hellyerite was corrected from NiCO3·6H2O to NiCO3·5.5H2O. The title compound was characterized by scanning electron microscopy, IR-, Raman-, and UV/Vis spectroscopy.

The term oceanic salts concerns the salts, which can be formed from solutions containing the major ions of seawater, that is the hexary system Na+, K+, Mg++, Ca++, Cl–, SO4 ––H2O. Besides in geochemistry of evaporites and the potash extraction the solubility equilibria and properties of aqueous solutions containing these ions are of importance in many fields of science and technology in a wide range of temperature and composition. After a short introduction into the types of subsystems and the main features of their solubility diagrams the known salt phases, their properties and stability are listed and discussed with a focus on recent work and discoveries. The status of solubility data evaluation of the multi-component system is discussed from the view point of the data itself and the possibilities and limitations of applying thermodynamic modelling. This is demonstrated with the data compilation of Usdowski and Dietzel, the Pitzer models of Harvie, Möller and Weare as well as the model developed in the THEREDA project. Future work should be directed to improve accuracy of solubility data in multi-component solutions combined with modelling and to consider kinetics and mechanistic aspects in crystallization of phases like anhydrite or polyhalite.

The previously reported structures of the hydrates of simple inorganic salts that crystallize at room temperature are generally well determined. This is not true for water-rich hydrates, which crystallize at temperatures below 273 K. In this series, investigations of the crystal structures of water-rich hydrates crystallized from aqueous solutions at low temperatures are presented. Reported herein are the structures of a set of magnesium salts. Crystals of MgCl2·8H2O (magnesium dichloride octahydrate), MgCl2·12H2O (magnesium dichloride dodecahydrate), MgBr2·6H2O (magnesium dibromide hexahydrate), MgBr2·9H2O (magnesium dibromide nonahydrate), MgI2·8H2O (magnesium diiodide octahydrate) and MgI2·9H2O (magnesium diiodide nonahydrate) were grown from their aqueous solutions at temperatures below 298 K according to the solid–liquid phase diagrams. All structures are built up from Mg(H2O)6octahedra. Dimensions and angles in the hexaaqua cation complexes are very similar and variation is not systematic. The anions are incorporated into a specific network of O—H...Xhydrogen bonds.

An important question concerning the possibility of life under martian conditions is the existence of liquid water at low temperatures. On the martian surface, the existence of iron(III) sulfate is expected. The influence of iron(III) sulfate salt on ice deposits in respect to the formation of liquid salt brines was not investigated in the past. In this contribution, the investigation of the phase diagram of the system iron(III) sulfate–water and the influence of sulfuric acid to this system are presented. A new crystalline acidic iron(III) sulfate hydrate has been found in the ternary system iron(III) sulfate–water–sulfuric acid, which represents the most water-rich iron salt phase ever detected.

The determination of the phase diagram of the binary system sodium perchlorate – water is reported. Beside the eutectic point, two polymorph crystal structures of sodium perchlorate dihydrate were determined. The two crystal structures are discussed, compared to each other and to other known sodiumhalide dihydrate crystal structures. The two polymorphs of the perchlorate dihydrate represent the two variants of connected octahedra in the layer structure found for sodium halide dihydrates.

A sample of pure, artificial hellyerite was synthesized in aqueous solution at 0 °C. The recorded X-ray diffraction pattern completely agrees with the reference data given for natural hellyerite. Laboratory high resolution X-ray powder diffraction, applying global optimization methods and Rietveld refinement, was employed to solve the crystal structure. Synthetic hellyerite was determined to crystallize in the primitive monoclinic space group P2/m (no. 10) with a = 10.769(2) A, b = 7.295(2) A, c = 9.343(2) A, and β = 94.042(2)°. The crystal structure consists of edge-linked, isolated pairs of Ni2(CO3)2(H2O)8 octahedra and non-coordinating water molecules. According to structure solution and thermal analysis the molecular formula of hellyerite was corrected from NiCO3·6H2O to NiCO3·5.5H2O. The title compound was characterized by scanning electron microscopy, IR-, Raman-, and UV/Vis spectroscopy.

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.

Salts comprise a very large and important group of chemical compounds. Natural occurrence of salts and industrial processes of their recovery, conversion, purification, and use depend on solubility phenomena and their chemistry in aqueous solutions, mostly in multi-ion systems. Modeling of these processes as well as developing new ones requires knowledge of the properties of the aqueous salt solutions in extended T-p-x ranges including a growing number of components in solutions (CO2, SO2, lithium salts, salts of rare earth metals, actinides, etc.). At least for the thermodynamic properties, the general accepted methodology is to use thermodynamic databases of aqueous species and solids in combination with an appropriate ion-interaction model to perform equilibrium calculations for species distributions in solution and phase equilibria. The situation in respect to available thermodynamic models and data for their parameterization is discussed at selected examples. Thereby, the importance of accurate experimental determinations of phase equilibrium data for derivation of model parameters is emphasized. Furthermore, it is concluded that experimental investigations should follow a chemical systematic. Simple physical models or quantum chemical calculations cannot predict unknown quantities in the databases with sufficient accuracy. Finally, solubility changes in salt-water systems at enhanced temperatures are considered. Systems, which can be considered as molten hydrates, display interesting phase behavior and chemical reactivity as protic ionic liquids. The latter can be exploited in chemical syntheses to substitute mixtures of concentrated acids like HNO3/H2SO4 by simple salts like ferric nitrate. For an understanding of the chemical and phase behavior of water-salt systems in terms of structure–property relations, a renaissance of chemical guided basic investigations of such systems would be worthwhile.

Since the discovery of perchlorate salts on Mars and the known occurrence of ferric salts in the regolith, there is a distinct possibility that the title compound could form on the surface of Mars. [Fe(H2O)6](ClO4)3·3H2O was crystallized from aqueous solutions at low temperatures according to the solid–liquid phase diagram., Since the discovery of perchlorate salts on Mars and the known occurrence of ferric salts in the regolith, there is a distinct possibility that the title compound could form on the surface of Mars. [Fe(H2O)6](ClO4)3·3H2O was crystallized from aqueous solutions at low temperatures according to the solid–liquid phase diagram. It consists of Fe(H2O)6 octa­hedra (point group symmetry -3.) and perchlorate anions (point group symmetry .2) as well as non-coordinating water mol­ecules, as part of a second hydrogen-bonded coordination sphere around the cation. The perchlorate appears to be slightly disordered, with major–minor component occupancies of 0.773 (9):0.227 (9).

The search for literature data in the ternary systems M2+, Ca2+ + SO42− + H2O (M = Mg, Mn, Co, Ni, Cu, Zn) revealed a lack of data. A reason might be the difficulties of Ca analysis at high concentrated bivalent metal solutions. The solubility of gypsum was determined in MSO4 solutions (M = Mg, Mn, Co, Ni, Cu, Zn) over a broad concentration range at T = 298.15 K and T = 313.15 K. With increasing magnesium and heavy metal sulfate, respectively, the gypsum solubility decreases to a minimum and rises afterward to a maximum at about 1.2 mol MSO4/kg. Above that concentration, the solubility of gypsum decreases again until saturation with MSO4. At both temperatures and in the whole concentration range, no double salt formation was noticed. With increasing temperature, the solubility of gypsum increases also.

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.

[SnCl4(H2O)2]·6H2O is crystallized from a cold aqueous solution (53.39 wt% SnCl4) according to the solid-liquid phase diagram (263 K, 2 d).

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.

The solubility data for lithium sulfate and its double salts in water are reviewed. Where appropriate, binary, ternary, and multicomponent systems are critically evaluated. The best values were selected on basis of these evaluations and presented in tabular form. Fitting equations and plots are provided. The quantities, units, and symbols used are in accord with IUPAC recommendations. The original data have been reported and, if necessary, transferred into the units and symbols recommended by IUPAC. The literature on solubility data is covered up to the end of 2015.

Single crystals of calcium bromide enneahydrate, CaBr2·9H2O, calcium iodide octahydrate, CaI2·8H2O, calcium iodide heptahydrate, CaI2·7H2O, and calcium iodide 6.5-hydrate, CaI2·6.5H2O, were grown from their aqueous solutions at and below room temperature according to the solid–liquid phase diagram. The crystal structure of CaI2·6.5H2O was redetermined. All four structures are built up from distorted Ca(H2O)8antiprisms. The antiprisms of the iodide hydrate structures are connected eitherviatrigonal-plane-sharing or edge-sharing, forming dimeric units. The antiprisms in calcium bromide enneahydrate are monomeric.

Crystals of MgCl2·8H2O (I), MgCl2·12H2O (II), MgBr2·6H2O (III), MgBr2·9H2O (IV), MgI2·8H2O (V), and MgI2·9H2O (VI) are grown from their aqueous solutions at below 298 K according to their solid-liquid phase diagrams.

The ternary system LiCl−MgCl2−H2O has been investigated at eight different solution compositions and at 155 5°C. Isopiestic measurements have been made for total equilibrium molalities ranging up to 16.6 mol-kg−1, using MgCl2(aq) as the reference electrolyte. A description of the osmotic coefficients by the ion interaction model of Pitzer gave an overall standard error of 0.006 for the whole data set. The binary Pitzer parameters for MgCl2(aq) were taken from Valyashko and co-workers, whereas the parameters for LiCl(aq) have been determined by the authors in a previous work. It was necessary to use both mixing parameters θMgLi and ψMgLiCl for the fit. The regression gave values of 0.075626 for θMgLi and −7.1392×10−3 for θMgLiCl. The modified B.E.T. equation according to Stokes and Robinson was applied succesfully for water activities lower than 0.4. Using only a linear relationship between the LiCl salt mole fraction and the B.E.T. parameters r and ΔE it was possible to describe the water activities to within 0.36%.

Isopiestic measurements have been made for LiCl (aq) and CsCl (aq) at a temperature of 155°C. Equilibrium molalities ranged up to 21 mol-kg−1. MgCl2(aq) was chosen as the reference electrolyte. The apparatus used for the isopiestic experiments is an enhanced version of that developed by Grjotheim and co-workers. To test its precision osmotic coefficients of CaCl2 (aq) have also been determined and compared with previously reported vapor pressure measurements at high concentrations. The results show a very good coincidence. The data can be described by the ion interaction model of Pitzer. The resulting set of parameters allows a fit of the experimental osmotic coefficients with a standard error of 0.0078 and 0.0114 for LiCl(aq) and CsCl (aq), respectively. The osmotic coefficients of LiCl are consistent with data at lower molalities, but there are discrepancies for the CsCl solutions.

Isopiestic measurements have been performed for mixed aqueous solutions of the two reciprocal salt pairs MgCl 2 −KBr and MgBr 2 −KCl and for all common ion subsystems of the reciprocal system Mg 2+ , K + /Cl − , Br − /H 2 O at 100.3°C. As reference solution CaCl 2(aq) was used

Etude de la variation de l'energie standard de Gibbs pour les reactions reciproques haute temperature: AX+BY=AY+BX