CaCl2 H2O System Research Articles

Influence of Saline Fluids on the Electrical Conductivity of Olivine Aggregates at High Temperature and High Pressure and Its Geological Implications

The electrical conductivities of hydrous olivine (Ol) aggregates and Ol–H2O, Ol–NaCl–H2O (salinity: 1–21 wt%; fluid fraction: 5.1–20.7 vol%), Ol–KCl–H2O (salinity: 5 wt%; fluid fraction: 10.9–14.0 vol%) and Ol–CaCl2–H2O systems (salinity: 5 wt%; fluid fraction: 10.7–13.7 vol%) were measured at 2.0–3.0 GPa and 773–1073 K using a multi-anvil apparatus. The electrical conductivity of saline fluid-bearing olivine aggregates slightly increases with increasing pressure and temperature, and the electrical conductivities of both hydrous and saline fluid-bearing samples are well described by an Arrhenius relation. The dihedral angle of the saline fluids is approximately 50° in the Ol–NaCl–H2O system with 5 wt% NaCl and 5.1 vol% fluids, which implies that the fluids were interconnected along grain boundaries under the test conditions. The electrical conductivities of the Ol–NaCl–H2O system with 5 wt% NaCl and 5.1 vol% fluids are ∼two to four orders of magnitude higher than those of hydrous olivine aggregates. The salinity and fluid fraction moderately enhance the sample electrical conductivities owing to the interconnectivity of the saline fluids. The activation enthalpies of the electrical conductivities for the Ol–NaCl–H2O systems range from 0.07 to 0.36 eV, and Na+, Cl−, H+, OH−, and soluble ions from olivine are proposed to be the main charge carriers. For a fixed salinity and fluid fraction, the electrical conductivities of the Ol–NaCl–H2O system resemble the Ol–KCl–H2O system but are slightly higher than that of the Ol–CaCl2–H2O system. The Ol–NaCl–H2O system with a salinity of ∼5 wt% NaCl and fluid fraction larger than 1.8 vol% can be employed to reasonably explain the origin of the high-conductivity anomalies observed in mantle wedges.

Composition for rock grouting based on insoluble calcium salts for groundwater protection

Importance to reduce permeability of rocks arises safety of mining operations and protecting the soil and underground water in the area of industrial waste storage with high contents of water-soluble salts. Disadvantage of the existing methods of grouting rocks by soluble salts is either their dissolution with changing of the composition or diluting of the contacting solution. The paper considers the composition of the grouting mixture for the deposition of insoluble calcium salts and its effectiveness in laboratory conditions. The eutonic solution of a four-component KCl–NaCl–CaCl2–H2O system was used as the initial solution, while saturated solutions of sodium sulfate and carbonate, and sulfuric acid were applied as the precipitators. Efficiency of rock grouting was estimated according to the water or solution filtration rate through the rock (sand, sylvinite, and halite) before and after calcium salt crystallization. Laboratory experiments showed that the precipitation of calcium sulfate responds to the challenge of plugging rocks. The paper proposes some recommendations of protective screens at the bed of the salt tailing piles and slurry storage facilities.

Cryogenic Raman Spectroscopic Studies on Common Ore-forming Fluid Systems

The composition and properties of ore-forming fluids are key to understanding the mechanisms of mineralization in ore deposits. These characteristics can be understood by studying fluid inclusions. Hydrates in fluid inclusions containing NaCl–H2O and MgCl2–H2O were studied using cryogenic Raman spectroscopy. The intensity ratio of peaks at 3401, 3464, 3514, and 3090 cm−1 shows a positive correlation with the concentration of hydrates in the inclusions, as does the ratio of the total integrated area of the MgCl2 hydrate peak (3514 cm−1) to the 3090 cm−1 peak with the concentration of MgCl2 (correlation coefficient >0.90). These correlations are important in the quantitative analysis of MgCl2 in synthetic and natural NaCl–MgCl2–CaCl2–H2O-bearing fluid inclusions. Semi-quantitative analysis of NaCl–MgCl2–H2O solutions indicates that peaks at 3437 and 3537 cm−1 reflect the presence of NaCl in the solution. Further, a peak at 3514 cm−1 is indicative of the presence of MgCl2. The relative intensities of these peaks may be related to the relative abundances of NaCl and MgCl2. A quantitative attempt was made on NaCl–MgCl2–CaCl2–H2O system, but it was found that quantifying NaCl, MgCl2 and CaCl2 separately in NaCl–MgCl2–CaCl2–H2O system by the secondary freezing method is difficult.

Measurements and Modeling of the Phase Equilibria in AlCl3 + NaCl + CaCl2 + H2O and AlCl3 + CaCl2 + NH4Cl + H2O Systems

Solid–liquid phase equilibrium for chloride salt systems plays a vital role in the utilization of liquid wastes generated from soda ash production by the Solvay process. The equilibrium data for ternary systems AlCl3–NaCl–H2O, AlCl3–NH4Cl–H2O, and CaCl2–NH4Cl–H2O from 283 to 353 K were determined by a dynamic method. A chemical model for these systems was developed with the mixed-solvent electrolyte model parameterization with the average absolute relative deviation less than 5%. The new model is capable of calculating solubilities of NaCl and NH4Cl in the AlCl3–CaCl2–H2O system, and the average absolute relative deviation of predicted points is less than 6%. The experimental and calculated phase equilibria have been used in developing a recovery method for NaCl and CaCl2 in the liquid wastes from the Solvay process and the subsequent utilization of CaCl2.

Densities for Ternary System of CaCl2–H2O–CO2 at Elevated P-T: An Experimental and Modeling Approach

Very few thermodynamic models exist for estimation of density alteration due to solution of CO2 in a pure H2O and CaCl2–H2O system. All of these models require density of CaCl2 solution to estimate density of CaCl2–H2O–CO2 system. Similarly, models presented to calculate CaCl2 solution density need pure H2O density in advance. The main approach to model density of CaCl2–H2O–CO2 system is based on estimation of density alteration of CaCl2–H2O system due to the solution of CO2 mole fraction. Hence, to estimate CO2–CaCl2–H2O system density, density of CaCl2 solution is necessary, and to estimate density of CaCl2–H2O system, density of pure H2O is required in advance. Firstly in this paper, density of 0, 1.91, and 4.85 mol/kg CaCl2 solutions saturated with CO2 at 328.15 to 375.15 °K and 68.9 to 206.8 Bar were measured through laboratory experiments. Then, a new model is developed to estimate the density of CaCl2 solutions containing CO2 based on the experiments conducted in this study. The average and maximum absolute deviations of the new model from the experimental data are 0.0047 and 0.0177, respectively. Hence, the new model combined with other existing models to separately calculate density of the CaCl2 solution can be used to accurately predict density of the CaCl2–H2O–CO2 system in a wide range of P-T applicable for subsurface reservoirs.

Solution properties and salt-solution equilibria in the H-Li-Na-K-Ca-Mg-Cl-H2O system at 25 °C: A new thermodynamic model based on Pitzer's equations

A large part of Li production comes from the exploitation of saline lakes and salars. Industrial processes for Li recovery from such resources have to deal with highly saline waters. It is therefore necessary to develop the knowledge of Li chemistry adapted to these contexts. The present work aims to present a new set of Pitzer interaction parameters able to describe the chemical behavior of the H-Li-Na-K-Ca-Mg-Cl-H2O system up to salt solubility, at 25 °C. In a previous work, the model was limited to the H-Li-Na-K-Cl-H2O system. It is extended here by including Ca and Mg, taking into account recently revised parameters allowing the thermal properties of the binary CaCl2-H2O and MgCl2-H2O systems to be represented. The consistent extension of the thermodynamic database was made possible by the study of the binary CaCl2-H2O system up to the supersaturated metastable region and of nine ternary systems, namely X-Ca-Cl, X-Mg-Cl and Ca-Mg-Cl (where X = H, Li, Na, K). The model was finally tested on five quaternary systems.

A Temperature-Dependent Thermodynamic Model Derived from Heat Capacity of Metal Chloride Aqueous Solutions

In this work, a temperature-dependent thermodynamic model based on heat capacity was proposed to predict the osmotic and mean ion activity coefficients of metal chloride aqueous solutions. The CaCl2–H2O system was used to verify the model and the results show the predicted values can well agree with the reported data, indicating that the proposed thermodynamic model is reliable. Meanwhile, the heat capacities at constant pressure of both CuCl2–H2O and NiCl2–H2O systems in the range from 298.15 to 363.15 K were calculated from the enthalpy changes determined by the calorimetric experiments. Therefore, the osmotic and mean ion activity coefficients of the two systems within 4 mol·kg–1 were predicted in a wide temperature range with the established model. The calculated results were well consistent with the data in the literature and further indicate the thermodynamic model was reliable and convenient.

An investigation of factors influencing freeze lining behaviour

ABSTRACTRecent studies have indicated that the steady state thicknesses and interface temperatures of freeze linings can be influenced by factors other than the thermal parameters of the systems. To explore these possibilities further cold modelling of freeze linings was undertaken in the CaCl2–H2O system using an experimental apparatus that enabled the variation of both the bath temperature and the fluid flow rate. Through in situ experimental observations, it was shown that the phases formed, the deposit/liquid interface temperature and the freeze lining thicknesses depend strongly on chemical parameters and elementary reaction steps, which are not considered by the conventional thermal treatment of freeze linings. These results indicate the need for further systematic investigation of various process parameters that influence the elementary reaction steps that may be active in these systems under dynamic steady state conditions.

Solubility in the diagonal sections of the 2KCl + Ca(NO3)2 ⇆ 2KNO3 + CaCl2–H2O system

Solubility data in the diagonal sections of the quaternary reciprocal 2KCl + Ca(NO3)2 → 2KNO3 + CaCl2–H2O system at 25 and 15°C are presented. It has been shown that the quaternary system has no stable diagonal at the studied temperatures, but contains a stable pair of salts, namely, potassium nitrate and calcium chloride. The obtained data can be used to optimize the thermal and concentrational parameters of the synthesis of potassium nitrate from calcium nitrate and potassium chloride.

Thermodynamic modeling of phases equilibrium in aqueous systems to recover potassium chloride from natural brines

Chemical fertilizers, such as potassium chloride, ammonium nitrate and other chemical products like sodium hydroxide and soda ash are produced from electrolyte solutions or brines with a high content of soluble salts. Some of these products are manufactured by fractional crystallization, when several salts are separated as solid phases with high purity (>90%). Due to the large global demand for potassium fertilizers, a good knowledge about the compositions of salts and brines is helpful to design an effective process. A thermodynamic model based on Pitzer and Harvie's model was used to predict the composition of crystallized salts after water removal by forced evaporation and cooling from multicomponent solutions or brines. Initially, the salts’ solubilities in binary systems (NaCl–H2O, KCl–H2O and MgCl2–H2O) and ternary system (KCl–MgCl2–H2O) were calculated at 20°C and compared with literature data. Next, the model was compared to our experimental data on the quinary system NaCl–KCl–MgCl2–CaCl2–H2O system at 20°C. The Pitzer and Harvie's model represented well both the binary and ternary systems. Besides, for the quinary system the fit was good for brine densities up to 1350kg/m3. The models were used to estimate the chemical composition of the solutions and salts produced by fractional crystallization and in association with material balance to respond to issues related to the production rates in a solar pond containing several salts dissolved, for instance, NaCl, KCl, MgCl2 and CaCl2.

Phase Equilibrium Study of the AlCl3–CaCl2–H2O System for the Production of Aluminum Chloride Hexahydrate from Ca-Rich Flue Ash

The study of the solid–liquid phase equilibrium for the AlCl3–CaCl2–H2O system is of significance to separate aluminum chloride hexahydrate from the leachate obtained by the reaction of Ca-rich fly ash and a waste hydrochloride from chemical plant. The phase equilibrium data for the binary AlCl3–H2O system and the ternary AlCl3–CaCl2–H2O system over the temperature range from 278.15 K to 363.15 K were measured. A rigorous and thermodynamically consistent model representing the AlCl3–CaCl2–H2O system developed on the basis of the Pitzer’s activity coefficient model embedded in the Aspen Plus. On the basis of this, the phase behavior of the ternary AlCl3–CaCl2–H2O system at different temperatures was visualized with lucidity on an equilateral triangle. The phase-equilibrium diagram generated by modeling was illustrated to identify the course of crystallization to recover AlCl3·6H2O from the solutions containing calcium chloride. All of these will provide a thermodynamic basis for the separation of aluminum ...

The influence of calcium chloride deicing salt on phase changes and damage development in cementitious materials

The conventional CaCl2–H2O phase diagram is often used to describe how calcium chloride behaves when it is used on a concrete pavement undergoing freeze-thaw damage. However, the chemistry of the concrete can alter the appropriateness of using the CaCl2–H2O phase diagram. This study shows that the Ca(OH)2 present in a hydrated portland cement can interact with CaCl2 solution creating a behavior that is similar to that observed in isoplethal sections of a ternary phase diagram for a Ca(OH)2–CaCl2–H2O system. As such, it is suggested that such isoplethal sections provide a reasonable model that can be used to describe the behavior of concrete exposed to CaCl2 solution as the temperature changes. Specifically, the Ca(OH)2 can react with CaCl2 and H2O resulting in the formation of calcium oxychloride. The formation of the calcium oxychloride is expansive and can produce damage in concrete at temperatures above freezing. Its formation can also cause a significant decrease in fluid ingress into concrete. For solutions with CaCl2 concentrations greater than about 11.3% (by mass), it is found that calcium oxychloride forms rapidly and is stable at room temperature (23 °C).

Water Activity Measurements by the Isopiestic Method for the MCl–CaCl2–H2O (M = Na, K) Systems at 323.15 K

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.

Solid–liquid phase equilibria of Ca(H2PO2)2–CaCl2–H2O and Ca(H2PO2)2–NaH2PO2–H2O ternary systems at 298.15 K

Calcium hypophosphite has been widely used as an anti-corrosive agent, flame retardant, fertilizer, assistant for Ni electroless plating, and animal nutrition supplements. High purity calcium hypophosphite can be synthesized via the replacement reaction of sodium hypophosphite and calcium chloride. In this work, the solid–liquid phase equilibria of Ca(H2PO2)2–CaCl2–H2O and Ca(H2PO2)2 –NaH2PO2–H2O ternary systems at 298.15K were studied experimentally via the classical isothermal solubility equilibrium method, and the phase diagrams for these two systems were obtained. It was found that two solid salts of Ca(H2PO2)2 and CaCl2∙6H2O, and three solid salts of Ca(H2PO2)2, NaCa(H2PO2)3, and NaH2PO2∙H2O can form in the corresponding systems under phase-equilibrium conditions. Ca(H2PO2)2 has low solubility in the Ca(H2PO2)2–CaCl2–H2O system. NaCa(H2PO2)3 occupies a large solid field in the ternary system of Ca(H2PO2)2 –NaH2PO2–H2O.

Salt efflorescence on pottery in the Athenian Agora: A closer look

Salt contamination in the ceramic collection of the Athenian Agora, American School of Classical Studies, Greece, was confronted for the first time by the fulltime conservation staff that was appointed in 1979. A review is presented of the examination and analysis of the salt contaminants for their identification and of simulation tests to determine their source(s) and mode of formation since 1990. In the analytical campaigns of 1992 and 1994, calclacite (Ca(CH3COO)Cl·5H2O) (ICCD 12-0869) and calcium acetate hemihydrate (Ca(CH3COO)2·0.5H2O) (ICCD 19-0199) were identified with X-ray diffraction and polarized light microscopy and examined with the environmental scanning electron microscope. The various means with which to mitigate the contamination and the crystallization-deliquescence cycles, e.g. consolidation, desalination, and climate control, were also studied. The article focuses on the processes involved in the formation of acetate salt compounds with the publication of the first solubility and deliquescence diagrams of the Ca(CH3COO)2–CaCl2–H2O system at 25°C. Comparisons are drawn with recent work carried out on thecotrichite (Ca3(CH3COO)3Cl(NO3)2·7H2O). The course of action adopted by the conservation staff of the Athenian Agora to combat efflorescence has been termination of cleaning with hydrochloric acid and desalination as a remedial measure in lieu of the costly replacement of wooden cabinets with enameled steel storage cases for the extensive ceramic collection (52,000 catalogued ceramics). Volatile acetic acid concentrations in wooden storage cases in the collection have been found to range from 1039 ± 20 to 1267 ± 20 µg/m3 (400 to 500 ppb) at 25°C. Since 1979, all newly excavated ceramics and all ceramics exhibiting efflorescence in the collection have been routinely desalinated. No efflorescence has formed on the desalinated objects. Various methods of mitigation such as controlling the RH are also discussed.

A review and comparison of fracture mineral investigations and their application to radioactive waste disposal

Abstract A compilation and comparison of fracture mineral studies from the Canadian and Fennoscandian Shields and the French Massif Central shows many similarities indicating larger external control over fracture mineral deposition, with different rock types exerting local controls. The sites investigated represent a wide range of geological settings, and host rock types ranging from felsic intrusive and extrusives to ultramafic intrusives and volcanics that span an age range from 2.5 to 0.36 Ga. Typical fracture minerals found at Canadian Shield sites include calcite, quartz, chlorite and clays, and these do not appear to be dependant on age, erosional depth or geological environment. The Fennoscandian Shield has a much larger variety of fracture filling minerals with epidote, zeolites, prehnite, fluorite, pyrrhotite, Fe oxides, serpentine, graphite, magnesite and barite in addition to the minerals typically found at Canadian Shield sites. The major control on fracture mineral type is most likely variations in rock type, and fluid chemistry and temperature. The C and O isotopic range of calcite is very similar among sites. Late-stage hydrothermal calcite, with strongly depleted δ18O values, is common at many sites. All of the sites have calcite with δ18O isotopic values in the range of −5 to −20‰ PDB, indicative of formation from meteoric water or basinal brines that have undergone varying degrees of water/rock interaction. One Canadian and a few Swedish sites have calcite in the shallower portion of the rock that shows isotopic evidence of dissolution and re-precipitation in equilibrium with the present-day waters. There are some striking similarities in fluid inclusion data among sites. Most sites have an elevated temperature (100–300 °C), low salinity group of fluid inclusions within the NaCl–H2O system, and a lower temperature (50–150 °C), higher salinity group of fluid inclusions within the NaCl–CaCl2–H2O system. Fluid inclusion density plots show some evidence of simple cooling, but most sites show two or more fluids were responsible for calcite formation. The origin of most of these fluids was magmatic/hydrothermal or meteoric water that had undergone varying degrees of water/rock interaction, but basinal brines and seawater were also possible sources. Several techniques and methods have been used to further characterize calcites. Strontium isotopes and rare earth elements can be useful to recognize different families of calcite. Uranium–Th dating has found many old calcites beyond the useful range of the technique, but also some relatively young calcites that may be related to interglacial periods. Where fluid inclusion data exists, formation temperatures were not consistent with a glacial water origin. Crush and leach experiments (with ion and gas chromatography and thermal ion mass spectrometry) have characterized inclusion fluids, but special care must be used to ensure only one generation is sampled at a time. Cathodoluminescence and scanning electron microscopy with energy-dispersive spectrometry has been useful in identifying multiple fluid generations within single calcite samples. Laser ablation and Raman spectrometry are additional techniques that are useful in determining individual fluid inclusion chemistry and isotopes.

The structure, dynamics and solvation mechanisms of ions in water from long time molecular dynamics simulations: a case study of CaCl2 (aq) aqueous solutions

Systematic long time (5–20 ns) molecular dynamics (MD) simulations have been carried out to study the structural and dynamical properties of CaCl2 aqueous solutions over a wide range of concentrations (≤9.26 m) in this study. Our simulations reveal totally different structural characteristics of those yielded from short time (≤1 ns) MD simulations [A.A. Chialvo and J.M. Simonson, J. Chem. Phys. 119, 8052 (2003); T. Megyes, I. Bako, S. Balint, T. Grosz, and T. Radnai, J. Mol. Liq. 129, 63 (2006)]. An apparent discontinuity was found at 4–5 m of CaCl2 in various properties including ion–water coordination number and self-diffusion coefficient of ions, which were first noticed by Phutela and Pitzer in their thermodynamic modelling [R.C. Phutela and K.S. Pitzer, J. Sol. Chem. 12, 201 (1983)]. In this study, residence time was first taken into consideration in the study of Ca2+–Cl− ion pairing, and it was found that contact ion pair and solvent-sharing ion pair start to form at the CaCl2(aq) concentrations of about 4.5 and 4 m, respectively, which may be responsible for the apparent discontinuity. In addition, the residence time of water molecules around Ca2+ or Cl− showed that the hydration structures of Ca2+ and Cl− are flexible with short residence time (<1 ns). It needs to be pointed out that it takes much longer simulation time for the CaCl2–H2O system to reach equilibrium than what was assumed in previous studies.

Correlation of Thermodynamic Data for Aqueous Electrolyte Solutions to Very High Ionic Strength Using INSIGHT: Vapor Saturated Water Activity in the System CaCl2-H2O to 250°C and Solid Saturation

Osmotic coefficients for the CaCl2-H2O system between 25 and 250°C and from the dilute region to solid saturation or beyond (i.e., to ≈ 12 mCaCl2 at the lowest temperature and ≈32 mCaCl2 at the highest) have been correlated using the following permutations and modifications of the basic Pitzer ion-interaction equation: (1) the basic Pitzer equation, (2) the Pitzer equation augmented by an ionic strength-dependent third virial contribution, (3) the Pitzer equation together with equilibria involving the formation of CaCl+ and CaCl20, and (4) the simultaneous combination of all of the above. The effectiveness, accuracy, and practicality of each approach are reviewed.

A theoretical evaluation of mineral stability in Don Juan Pond, Wright Valley, Victoria Land

Don Juan Pond, located in the Wright Valley, Victoria Land, is unique for several reasons. It is the most saline of the Antarctic lakes, being a near-saturated CaCl2 solution. As a consequence of this high salinity, Don Juan Pond generally remains unfrozen in winter, even at temperatures below -50°C. Don Juan Pond is the site where antarcticite (CaCl2·6H2O) was first identified forming naturally. The objective of this paper is to demonstrate the utility of a chemical thermodynamic model (FREZCHEM) by developing theoretical stability diagrams for ice, halite (NaCl), hydrohalite (NaCl·2H2O), and antarcticite in Don Juan Pond, using experimental data collected on 34 days between 1961 and 1983. The composition of Don Juan Pond at the calculated eutectic temperature (-51.8°C) was CaCl2 = 3.72 mol kg−1 and NaCl = 0.50 mol kg−1, which is similar but not identical to a pure NaCl–CaCl2–H2O system. The low eutectic temperature and high CaCl2 concentrations of Don Juan Pond account for lack of freezing during winter. The model is compatible with the experimental data, and predicts the formation of ice during rare high water periods, halite, and antarcticite. These solid phases have all been reported from Don Juan Pond. The model also predicts the formation of hydrohalite at subzero temperatures; hydrohalite has never been observed at Don Juan Pond, but this may simply reflect that most sampling was done during the summer when halite is thermodynamically more stable than hydrohalite. The FREZCHEM model may prove useful in elucidating the physicochemical behaviour, the origin of salinity, and the evolution of Antarctic lakes.

Thermodynamic properties of mixtures of dipolar and quadrupolar hard spheres: Theory and simulation

We report a comprehensive study of the thermodynamic properties (the Helmholtz energy, configurational energy, compressibility factor, and chemical potentials) for mixtures of dipolar hard spheres and quadrupolar hard spheres by computer simulation and from perturbation theory based on the Padé approximation. The dipole moment of dipolar component is fixed at μA*2=3.0 and the quadrupole moment of quadrupolar component is varied up to QB*2=3.0. The results show that the Padé approximation gives a good description of the Helmholtz energy and configuration energy of the mixtures, but some discrepancies are found for their derivatives, especially for compressibility factor. In view of very large deviations for the system from simple mixtures, the Padé approximation is rather successful for the system. These results are being used as a reference system in our effort to develop an equation of state for the CaCl2–H2O system.