Thermodynamics and Phase Equilibrium of the System CsClâMgCl2

Article pubs.acs.org/jced

Thermodynamics and Phase Equilibrium of the System CsCl−MgCl2− H2O at 298.15 K Lijiang Guo,*,†,‡ Yaxiao Wang,§ Lanying Tu,§ and Jianqiang Li‡ †

Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, People’s Republic of China National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China § College of Chemical Engineering, Qinghai University, Xining 810016, People’s Republic of China ‡

ABSTRACT: Water activities of the CsCl−MgCl2−H2O ternary system and its sub-binary systems were elaborately measured by an isopiestic method at 298.15 K. The solubility of this ternary system at 298.15 K was also measured by two different methods, namely isothermal method and Flow-Cloud-Point method. The solubilities measured by the two different methods were consistent with each other. A Pitzer model was used to represent the thermodynamic properties and calculate the solubility isotherms for the CsCl− MgCl2−H2O ternary system at 298.15 K. Both the equal water activity lines and the solubility isotherms are calculated with parameters reported in literature. It was found that only the calculated equal water activity lines with the parameters reported by Scharge et al. are consistent with the experimental values of this work. However, all the calculated solubility isotherms deviated from the experimental data in this work. New set of ternary parameters were obtained by fitting the water activities and solubility data of this work. Using the new parameters, the calculated equal water activity lines and solubility isotherms agreed with experimental values measured in this work. model14,15 was selected to correlate the measured water activities and solubility data, to evaluate the reliability of the reported solubility data and the validity of the model parameters.

1. INTRODUCTION The thermodynamic properties, solubility isotherms and their simulation by thermodynamic model of the CsCl−MgCl2− H2O ternary system at 298.15 K, are of significant importance for extracting cesium resource from salt lake, for example, the Chaerhan Salt Lake located in the Qaidam Basin of China. The water activity of its sub-binary systems MgCl2−H2O1−3 and CsCl−H2O4,5 have been reported. The water activity of the ternary system CsCl−MgCl2−H2O have also been reported,6 but unfortunately the isopiestic data are only available in graphical form and it is difficult to be evaluated. The solubility of the CsCl−MgCl2−H2O ternary system at 298.15 K was reported by different authors,6−8 however, the measured solubility data is inconsistent with each other. Using the Pitzer model, Christov et al.9 and Scharge et al.10 calculated the solubility isotherms for this ternary system but the model parameters and the log K for the double salt CsCl·MgCl2· 6H2O(s) are different. The calculated solubility isotherm for CsCl(s) and CsCl·MgCl2·6H2O(s) by Scharge et al.10 deviate from the reported experiment data.6−8 We measured the water activity for the CsCl−MgCl2−H2O ternary system and its sub-binary MgCl2−H2O and CsCl−H2O systems with the isopiestic method at 298.15 K. Meanwhile, the solubility of the CsCl−MgCl2−H2O ternary system at 298.15 K is also determined by two different methods, the isothermal method and the Flow-Cloud-Point method,11−13 which can make the measured solubility data reliable. The Pitzer © XXXX American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Materials. All the chemical agents used in the experiment are shown in Table 1, including the source of compounds, purification method, final purity, and so forth, and more detailed information are given as follows. The stock solutions of NaCl, H2SO4, MgCl2, and CsCl used in the isopiestic measurement and Flow-Cloud-Point method were prepared through the procedure described in our previous work.16,17 Water purified by deionization followed by double distillation (once with trace K2MnO4) with a conductance less than 1.5 × 10−4 S·m−1 was used for all sample purifications, preparations, and dilutions in the experiment. H2SO4 (G. R., Beijing Chemical Works) was used as a stock solution in the isopiestic measurement without further purification. The NaCl and MgCl2·6H2O (G. R., Sinopharm Chemical Reagent Co., Ltd.) were purified by triple recrystallization, and the contents of each main impurity element were detected to be less than 0.01%. CsCl (Aladdin, 99.95%, metals basis) was used without Received: November 15, 2016 Accepted: March 1, 2017

A

DOI: 10.1021/acs.jced.6b00952 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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Table 1. Chemical Agents Used in the Experimenta

a

agents

grade

sources

purification method

final purity

impurity analysis method

NaCl H2SO4 MgCl2·6H2O CsCl

G. R. G. R. G. R. metals basis

Sinopharm Chemical Reagent Co., Ltd. Beijing Chemical Works Sinopharm Chemical Reagent Co., Ltd. Aladdin

recrystallization no further purification recrystallization no further purification

99.99% 99.99% 99.90% 99.95%

ICP ICP ICP

The final impurity of the chemical agents were determined in this work, and the purity basis is mass.

Table 2. Measured Isopiestic Molalities m and Calculated Water Activities aw for the Ternary System CsCl−MgCl2−H2O at 298.15 K and 0.1 MPaa no.

mCsCl/mol·kg−1

mMgCl2/mol·kg−1

no.

−1

mCsCl/mol·kg−1

mMgCl2/mol·kg−1 −1

1

mNaCl = 1.7877 mol·kg , aw = 0.9393 ± 0.0009 2.0001 0 1.5467 0.2742 1.2730 0.4258 0.8995 0.6203 0.5824 0.7736 0.3033 0.9005 0.0646 1.0040 0 1.0309

2

mNaCl = 2.6652 mol·kg , aw = 0.9064 ± 0.0009 3.0764 0 2.3499 0.4165 1.9107 0.6391 1.3217 0.9114 0.8385 1.1138 0.4284 1.2719 0.0897 1.3949 0 1.4258

3

mNaCl = 4.9294 mol·kg−1, aw = 0.8101 ± 0.0008

4

mH2SO4 = 3.5084 mol·kg−1, aw = 0.7605 ± 0.0008

5

6.1137 0 4.5435 0.8054 3.6033 1.2052 2.3902 1.6482 1.4580 1.9368 0.7209 2.1402 0.1470 2.2857 0 2.3215 mH2SO4 = 5.0273 mol·kg−1, aw = 0.7016 ± 0.0007

6

7.7358 0 5.6638 1.0039 4.4508 1.4887 2.9013 2.0007 1.7439 2.3167 0.8520 2.5295 0.1723 2.6782 0 2.7118 mH2SO4 = 5.8651 mol·kg−1, aw = 0.6365 ± 0.0006

9.7395 7.0368 5.4611 3.4915 2.0650 0.9981 0.2001 0

0 1.2473 1.8266 2.4077 2.7432 2.9631 3.1096 3.1501

8.6948 6.6535 4.1631 2.4215 1.1560 0.2296 0

1.5412 2.2254 2.8708 3.2168 3.4320 3.5690 3.6093

a

The water activity is calculated by the eqs 1 and 2 with the parameters reported in ref 16. The uncertainty for the water activity is absolute uncertainty. m, molality, moles per kilogram of solvent (pure water). The relative standard uncertainty is ur(m) = 0.003, u(T) = 0.1 K, and ur(p) = 0.1.

controlled by the temperature control system that consists of thermostats, an electric-contact thermometer, and a light bulb, and the temperature accuracy can be controlled within ±0.1 K. A fan was used to stir the air in the oven. The transparent sample bottles were made of hexafluoropropene−tetrafluoroethylene copolymer, and the sample in the bottle was observed. A magneton was in each sample bottle so that the sample could be stirred by the multisite magnetic stirrer in the oven. The procedure of the solubility measurement is as follows. At first, a m series of different mole fraction of CsCl YCsCl = m +CsCl m

further purification. The salt impurities were analyzed by ICP emission spectrometry (Thermo Electron Corporation, ICAP 6500 DUO). The concentration of the H2SO4 stock solution was determined gravimetrically with BaCl2 as precipitant. The concentration of NaCl, MgCl2, and CsCl stock solutions were determined gravimetrically by precipitation with AgNO3. The largest relative deviation of the determination among three parallel samples was controlled below 0.05%. 2.2. Apparatus and Experimental Procedure. The isopiestic measurement setup and procedure in this work are the same as described in our previous work,16,17 and will not be described again. The Flow-Cloud-Point method11−13 was the same as our previous work,18 carried out in a large drying oven that has good heat preservation effect. The oven has two layers of door, the inner layer of which is made of glass and that can make it easy to observe the samples in the oven. The temperature was

CsCl

MgCl 2

mixture stock solutions were prepared by mixing the pure stock solutions of MgCl2 and CsCl, of which the concentration was already known. Then, a certain amount of the mixture stock solutions was put in the transparent sample bottle (magneton within, and the total weight already known). The bottle was then put on the multisite magnetic stirrer to stir the mixture solution. By keeping the bottle open, the water in the solution B



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tration difference of two duplicated samples was ±0.3%, which can be attributed to the errors in weighing, equilibrium time, water transportation in the isopiestic chamber, and temperature difference between two cups, correspondingly, the largest deviation of water activities should be less than 0.005. 3.2. Solubility measurement results. 3.2.1. Flow-CloudPoint Measured Results. For the Flow-Cloud-Point measurement, the concentration of the saturated solution can be calculated according to the amount of the mixture solution added in the bottle and the final total weight of the bottle. Duplicate samples for some of the mixture solutions are used to check the reliability of the experimental results. Compared with the final mixture solution in the bottle (no less than 15 g), the difference between the picked out total weight (no more than three drops of water, about 0.15 g) is small, and we can assume that the average of the picked out total weight of the bottle was the right weight with that of saturated solution. The total uncertainty of the measured solubility by the Flow-Cloud-Point method should be less than 0.2%. The measured solubility for the CsCl−MgCl2−H2O ternary system at 298.15 K by the Flow-Cloud-Point method is tabulated in Table 3.

evaporated gradually. The transparent bottle continued to be carefully observed; when a few crystals appeared in the solution, the bottle was covered with the cap. The bottle was then taken out of the oven and put into the desiccator for an hour, after which the bottle was weighed. Two or three drops of water were added to the bottle and the bottle was covered and weighed again. The bottle was put back on the multisite magnetic stirrer for at least 1 h to ensure that the temperature of the solution in the bottle was consistent with the air in the oven. If there were still crystals in the solution, the bottle was taken out of the oven and two or three drops of water were added again. If the crystals disappeared, the bottle was opened and the water gradually evaporated. This procedure was repeated, so that one could get a series of total weight (including the weight of bottle, magneton, and the solution) with and without crystals. In the total weight data of the bottle, one can pick out the smallest with crystals and the biggest without crystals, and the concentration can be calculated according to the total weight of the sample bottle and the original amount mixture solution added in the bottle. The isothermal measurement, the same as the literature,19 was carried out in a thermostat (LAUDA E219, Germany) with temperature stability of ±0.02 K. The time for the solid−liquid equilibrium is no less than 6 days. The compositions of the liquid phases and their corresponding wet solid phases were analyzed by mass titration20 instead of volumetric methods, and the relative error could be controlled below 0.2%. The Mg2+ ion concentration was determined by EDTA complexometric titration, and Eriochrome black T was used as the indicator. The Cl− ion concentration was determined gravimetrically by precipitation with AgNO3, and the largest relative deviation among three parallel samples was controlled below 0.05%. The Cs+ was determined gravimetrically by precipitation with sodium tetraphenylboron, and the relative error could be controlled below 1.0%. To avoid the effect of the magneton on the electronic balance, mechanical balance was used in the weighing. The solid phases are analyzed by X-ray diffraction.

Table 3. Measured Solubility for the Ternary System CsCl− MgCl2−H2O by the Flow-Cloud-Point method at 298.15 K and 0.1 MPaa solubility in mixture aqueous solutions

3. RESULTS AND DISCUSSIONS 3.1. Isopiestic Experiment Results. NaCl(aq) and H2SO4(aq) solutions were used as references at higher and lower water activity in the isopiestic measurement, respectively. The osmotic coefficients ϕ of the references as a function of molalities (m) (eq 1) have been reported in our previous work16,17 and are used directly in this work

−ν × M w × m × ϕ 1000

mMgCl2/mol·kg−1

solid phaseb

1 2 3 4 5 6 7 8 9

1.1591 2.9050 5.3618 8.3207 9.9358 1.9018 4.0830 7.5735 8.9205

4.3549 3.8329 3.3481 1.9270 0.9969 4.0275 3.5799 3.3206 1.5514

A A A A A A B B B

m, molality, moles per kilogram of solvent (pure water). The relative standard uncertainty is ur(m) = 0.004, u(T) = 0.1 K, and ur(p) = 0.1. b The solid phases are estimated according to the Pitzer model calculated results, and not detected in the experiment. A = CsCl· MgCl2·6H2O(s); B = CsCl(s).

3.2.2. Isothermal Experiment Results. The isothermal measured solubility, the corresponding composition of wet solid phase and the kind of solid phases are presented in Table 4. 3.3. Discussion. The measured water activities for the binary systems MgCl2−H2O and CsCl−H2O at 298.15 K agree well with the values reported in literature,1−5 as shown in Figures 1 and 2, respectively. The experimental isopiestic points and equal water activity lines for the ternary system CsCl− MgCl2−H2O at 298.15 K are shown in Figure 3. The isopiestic composition points at equal water activity in the CsCl− MgCl2−H2O system at 298.15 K are not in straight lines and do not obey the Zdanovskii rule, which means there are strong ion association or the apparent constancy of interaction between the component electrolytes in the ternary aqueous solution. This conclusion can also be confirmed by the inference of Stewart and Zener21 that the formation of ion clusters in CsCl solutions.

(1)

where a, b, c, d, e, f, g, and h are empirical parameters. The osmotic coefficient of these reference solutions can be calculated using eq 1. The water activity aw of the reference solutions can be calculated by eq 2 ln a w =

mCsCl/mol·kg−1

a

ϕ = a + b(m)0.5 + c(m) + d(m)1.5 + e(m)2 + f (m)2.5 + g (m)3 + h(m)3.5

no.

(2)

where ν is the number of ions for the complete dissociation of one molecule of the reference solutions. Mw is the molar mass of H2O. The measured water activities for the CsCl−MgCl2−H2O ternary system at 298.15 K are tabulated in Table 2. In each run of the isopiestic measurements, the largest relative concenC



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Table 4. Measured Solubility for The Ternary System CsCl−MgCl2−H2O at 298.15 K by the Isothermal Methoda composition of solution no. 1 2 3 4 5 6 7 a

mCsCl/mol·kg

−1

1.5833 2.5100 4.3674 6.5738 5.8536 7.7850 8.8441

mMgCl2/mol·kg

composition of wet solid phase (100w) −1

4.1727 3.9553 3.6371 3.4118 3.4564 3.3342 1.7849

CsCl

38.3413 43.6048 45.3185

H2O

41.8262 37.7548 37.3293

MgCl2

solid phase

19.8325 18.6404 17.3522

A A A A A A+B B

w: mass fraction. A: CsCl·MgCl2·6H2O(s); B: CsCl(s). The relative standard uncertainty is ur(m) = 0.003, u(T) = 0.02 K, ur(p) = 0.1.

we have reasons to believe that the measured results of this work are reliable.

4. MODELING The Pitzer model14,15 was selected to correlate the measured water activity and the experimental solubility data for the CsCl−MgCl2−H2O ternary system at 298.15 K. The binary Pitzer model parameters of the MgCl2−H2O system at 298.15 K have been reported,9,10 as shown in Table 5. The calculated water activities for the MgCl2−H2O system at 298.15 K with these binary parameters are consistent with the experimental values, as shown in Figure 1. The binary parameters of the CsCl−H2O system at 298.15 K have been reported by Balarew et al.9 and Scharge et al.,10 as shown in Table 5. The calculated water activity with the binary parameters of Scharge et al. with the setting α1 = 2, α2 = 12 deviated from the experimental values at the concentration higher than 4 mol·kg−1. The calculated water activity of the CsCl−H2O system at 298.15 K with parameters of ref 10 (setting α1 = −1, α2 = 12) or of ref 9 are consistent with the experimental values reported in literature4,5 and measured in this work, as shown as the solid line in Figure 2. The mixture model parameters of CsCl−MgCl2−H2O ternary system have been reported by Balarew et al.9 and Scharge et al.,10 as shown in Table 6. The parameters of Balarew et al.9 were obtained by fitting the solubility data reported by D’Ans and Busch7 and disregarding the solubility data of Vaisfeld et al.8 Similarly, Scharge et al.10 obtained the ternary parameters by fitting the solubility data that Balarew et al. have chosen, together with the isopiestic data digitalized from the graph form reported by Skripin et al.6 We calculated the equal water activity lines of the ternary system at 298.15 K with the corresponding binary and mixture parameters reported by Balarew et al.9 and Scharge et al.10 respectively. The calculated results with parameters of Balarew et al.9 or Scharge et al.10 (setting α1 = 2, α2 = 12), deviated from the experimental values, as shown in Figure 3a. The calculated equal water activity lines with the parameters of Scharge et al.10 (setting α1 = −1, α2 = 12) are roughly consistent with the experiment results, as shown in Figure 3b. It seems that the Pitzer model parameters reported by Scharge et al. are valid, at least for representing the thermodynamic properties of this ternary system. We have no idea whether the reported parameters are valid or not for calculating the solubility isotherms. So we try to calculate the solubility isotherm with the reported parameters. First, the ln K parameters of different solid phase in the ternary system are investigated. The ln K parameter for pure MgCl2· 6H2O at 298.15 K was reported by Balarew,9 and the value is

Figure 1. Measured water activities of the system MgCl2−H2O at 298.15 K and their comparison with the results in literatures. All symbols are experimental values: ▽, ref 1; ○, ref 2; ◊, ref 3; ■, this work; , calculated values by Pitzer model with the parameters in literature.9

Figure 2. Water activity of the binary system CsCl−H2O at 298.15 K. All symbols are experimental values: ■, experimental values reported by Rard;5 □, recommended values.5 All lines are Pitzer model values: ····, with parameters of ref 10 (setting α1 = 2, α2 = 12); , with parameters of ref 10 (setting α(1) = −1, α(2) = 12) or with parameters of ref 9.

The solubilities measured by isothermal method and FlowCloud-Point method are consistent with each other but deviate from the experimental values reported in literature,6−8 as shown in Figure 4. Considering the consistency of the solubility data measured with two completely different methods in this work, D



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Figure 3. Experimental isopiestic points and calculated equal water activity lines in the MgCl2−CsCl−H2O system at 298.15 K. ●, isopiestic experiment point; (a) ---, calculated water activity lines with parameters of Christov;9 − , calculated equal water activity lines with parameters of Scharge10 setting α(1) = 2, α(2) = 12; (b) ---, calculated water activity lines with parameters of Scharge10 setting α(1) = −1, α(2) = 12; , calculated equal water activity lines with parameters of this work.

Table 6. Mixture Parameters for the System MgCl2−CsCl− H2O at 298.15 K

a

θMN

ψMNX

−0.1260 −0.35098a −0.30045b −0.38374

0 0.00694a −0.01090b 0.007005

Setting α

(1)

= −1 and α

(2)

ref

= 12. Setting α b

9 10 this work (1)

= 2 and α(2) = 12.

With corresponding model parameters and ln K parameters reported by Balarew et al.9 and Scharge et al.,10 the solubility isotherms were calculated and compared with the experiment values, as shown in Figure 4. The calculated solubility isotherms deviated from the experiment values of this work. Reasonable mixture parameters are needed to calculate the solubility isotherms with the Pitzer model. In order to make the calculating work simple, we chose the set of binary parameters of Balarew et al.9 without that of β(2). The mixture parameters are obtained by fitting the water activity and solubility data measured in this work, as shown in Table 6. The equal water activity lines and the solubility isotherms at 298.15 K are calculated with the binary9 and mixture parameters obtained in this work. The ln K parameter for CsCl(s) solid phase was the same with Balarew.9 The fitted ln K parameter for CsCl·MgCl2· 6H2O(s) is 9.2. The calculated equal water activity lines were consistent with the measured values, as shown in Figure 3b. The calculated solubility isotherm for CsCl·MgCl2·6H2O(s) agreed well with the experiment values measured in this work, and the calculated solubility isotherm for CsCl(s) is roughly consistent with the experiment values of this work, as shown in Figure 4.

Figure 4. Solubility of the CsCl−MgCl2−H2O system at 298.15 K. All symbols are experimental values. Reference 6: ○, CsCl(s); ◓, CsCl(s) + CsCl·MgCl2·6H2O(s); ⊕, CsCl·MgCl2·6H2O(s); ●, MgCl2·6H2O(s). Reference 7: (pentagon bottom solid), CsCl(s) + CsCl·MgCl2·6H2O(s); (pentagon with cross), CsCl·MgCl2·6H2O(s); (pentagon top solid), MgCl2·6H2O(s) + CsCl·MgCl2·6H2O(s). Reference 8: □, CsCl(s); ⬓, CsCl + CsCl·MgCl2·6H2O(s); ⊞, CsCl·MgCl2·6H2O(s); ⬒, MgCl2· 6H2O + CsCl·MgCl2·6H2O(s); ■, MgCl2·6H2O(s). Flow-Cloud-Point method in this work, △; isothermal method in this work: ★, CsCl· MgCl2·6H2O(s); ☆, CsCl(s); (star top solid), CsCl·MgCl2·6H2O(s) + CsCl(s). All lines are calculated solubility isotherms by Pitzer model. With parameters of ref 9: − ••−, for CsCl·MgCl2·6H2O; ---, for CsCl(s). With parameters of ref 10: − •−, for CsCl·MgCl2·6H2O(s); ····, for CsCl(s). With parameters of this work: , for CsCl·MgCl2· 6H2O(s); − − , for CsCl(s).

10.397. The ln K parameter for pure CsCl(s) reported by Balarew et al.9 and Scharge et al.10 was 3.50 and 3.52, respectively. The reported ln K parameters for CsCl·MgCl2· 6H2O(s) by Balarew et al.9 and Scharge et al.10 are 10.40 and 8.31, respectively, and they are quite different. Table 5. Binary Pitzer Model Parameters at 298.15 K system

β(0)

β(1)

MgCl2−H2O

0.3511 0.35235 0.0390 0.03676 0.03945

1.6512 1.68148 −0.0374 −0.00050 −0.00875

CsCl−H2O

β(2)

Cϕ

α(1)

0.3259 0.33175

0.0065 0.00519 −0.0012 0.00024 −0.00242

2 2 2 −1 2

E

α(2)

12 12

ref 9 9 9 10



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(9) Balarew, C.; Christov, C.; Valyashko, V.; Petrenko, S. Thermodynamics of Formation of Carnallite Type Double Salts. J. Solution Chem. 1993, 22, 173−181. (10) Scharge, T.; Muñoz, A. G.; Moog, H. C. Activity Coefficients of Fission Products in Highly Salinary Solutions of Na+, K+, Mg2+, Ca2+, Cl−, and SO42−: Cs+. J. Chem. Eng. Data 2012, 57, 1637−1647. (11) Zhang, L. Z.; Gui, Q. L.; Lu, X. H.; Wang, Y. R.; Shi, J. Measurement of Solid-Liquid Equilibria by a Flow-Cloud-Point Method. J. Chem. Eng. Data 1998, 43, 32−37. (12) Zhang, L. Z.; Gui, Q. L.; Lu, X. H.; Wang, Y. R.; Shi, J. Measurement of Solid-Liquid Equilibrium for the System Containing Salts by a Flow Cloud-Point Method. J. Nanjing Univ. Chem. Technol., Nat. Sci. Ed. (in Chinese) 1997, 19, 19−24. (13) Shi, X. D.; Lu, X. H.; Wang, Y. R.; Shi, J. Measurement and Prediction of Liquid-liquid Equilibrium of Water-1-butanol in the Presence of Calcium Chloride. J. Nanjing Univ. Chem. Technol., Nat. Sci. Ed. (in Chinese) 2001, 23, 49−51. (14) Pitzer, K. S. Thermodynamics of Electrolytes. I. Theoretical Basis and General Equations. J. Phys. Chem. 1973, 77, 268−277. (15) Pitzer, K. S.; Mayorga, G. Thermodynamics of Electrolytes. II. Activity and Osmotic Coefficients for Strong Electrolytes with One or Both Ions Univalent. J. Phys. Chem. 1973, 77, 2300−2308. (16) Guo, L. J.; Sun, B.; Zeng, D. W.; Yao, Y.; Han, H. J. Isopiestic Measurement and Solubility Evaluation of the Ternary System LiCl− SrCl2−H2O at 298.15 K. J. Chem. Eng. Data 2012, 57, 817−827. (17) Guo, L. J.; Zeng, D. W.; Yao, Y.; Han, H. J. Isopiestic Measurement and Solubility Evaluation of the Ternary System (CaCl2 + SrCl2 + H2O) at T = 298.15 K. J. Chem. Thermodyn. 2013, 63, 60− 66. (18) Guo, L. J.; Han, H. J.; Dong, O. Y.; Yao, Y. Thermodynamics and Phase Equilibrium of the High Concentration Solid SolutionAqueous Solution System KCl−RbCl−H2O from T= 298.15 K to T = 323.15 K. J. Chem. Thermodyn. 2017, 106, 285−294. (19) Dong, O. Y.; Zeng, D. W.; Zhou, H. Y.; Han, H. J.; Yin, X.; Du, Y. Phase Change Materials in the Ternary System NH4Cl + CaCl2 + H2O. CALPHAD: Comput. Coupling Phase Diagrams Thermochem. 2011, 35, 269−275. (20) Li, H. X.; Dong, O. Y.; Yao, Y.; Wang, H. Y.; Zeng, D. W. The Mass Titration Analytical Method and Its Application. J. Salt Lake Res. (in Chinese) 2011, 19, 31−36. (21) Stewart, R. F.; Zener, C. Cluster Formation in Aqueous Solutions of Strong Electrolytes. J. Phys. Chem. 1988, 92, 1981−1985.

5. CONCLUSION Water activities of the CsCl−MgCl2−H2O ternary system and its sub-binary systems at 298.15 K were measured by the isopiestic method. The measured water activities for the binary systems are consistent with the values reported in literature. The solubility of the CsCl−MgCl2−H2O ternary system at 298.15 K is measured with two different methods, namely the isothermal method and the Flow-Cloud-Point method. Though deviated from the reported solubility data reported in literature, the measured solubility by the two different methods are consistent with each other, which indicates that the measured solubility data is more reliable than that of literature. The Pitzer model was used to correlate the measured water activities and the solubility data at 298.15 K. The calculated solubility isotherms with the parameters reported in literature all deviated from the experiment values measured in this work. A new set of mixture parameters are obtained by fitting the water activities and solubility data measured in this work. With the mixture parameters obtained in this work, the equal water activity lines and solubility isotherms of the CsCl−MgCl2− H2O ternary system at 298.15 K are calculated, and the results are consistent with the values measured in this work.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Lijiang Guo: 0000-0002-1018-4646 Funding

This work was financially supported by the National Natural Science Foundation of China under Contract No. 21303239 and U1507122. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Goldberg, R. N.; Nuttall, R. L. Evaluated Activity and Osmotic Coefficients for Aqueous Solutions: the Alkaline Earth Metal Halides. J. Phys. Chem. Ref. Data 1978, 7, 263−310. (2) Rard, J. A.; Mlller, D. G. Isopiestic Determination of the Osmotic and Activity Coefficients of Aqueous MgCl2 Solutions at 25 °C. J. Chem. Eng. Data 1981, 26, 38−43. (3) Yao, Y.; Sun, B.; Song, P. S.; Zhang, Z.; Wang, R. L.; Chen, J. Q. Thermodynamics of Aqueous Electrolyte Solution-Isopiestic Determination of Osmotic and Activity Coefficients in LiCl−MgCl2−H2O at 25 °C. Acta Chim. Sinica. 1992, 50, 839−848. (4) Makarov, L. L.; Evstropev, K. K.; Vlasov, Y. G. The Osmotic and Activity Coefficiences of RbCl, CsCl and KI in Highly Concentrated Aqueous Solutions. Russ. J. Phys. Chem. 1958, 32, 1618−1621. (5) Rard, J. A.; Miller, D. G. Isopiestic Determination of the Osmotic and Activity Coefficients of Aqueous CsCl, SrCl2, and Mixtures of NaCl and CsCl at 25 °C. J. Chem. Eng. Data 1982, 27, 169−173. (6) Skripin, M. Y.; Rumyantsev, A. V.; Solechnik, N. D. Thermodynamic Study of Rb+, Mg2+//Cl−−H2O and Cs+, Mg2+// Cl−−H2O Ternary Systems at 25 °C. Russ. J. Appl. Chem. 1993, 66, 983−986. (7) D’Ans, J.; Busch, W. Uber die Fraktionierung Inkongruent Löslicher Isomorpher Doppelsalze-Die Quaternären Systeme KCl− RbCl−(CsCl)−MgCl2−H2O Bei 25 °C. Z. Anorg. Allg. Chem. 1937, 232, 337−368. (8) Vaisfeld, M.; Schevchuk, V. Equilibrium in the system CsCl− MgCl2−H2O and CsCl−Cs2SO4−H2O at 25 °C. Russ. J. lnorg. Chem. 1967, 9, 2497−2499. F


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