Journal of Chemistry
Volume 2017 (2017), Article ID 2319635, 6 pages
https://doi.org/10.1155/2017/2319635

Research Article

Study of Phase Equilibrium of NaBr + KBr + H₂O and NaBr + MgBr₂ + H₂O at 313.15 K

Qing Chen, Jiping She, and Yang Xiao

College of Energy, Chengdu University of Technology, Chengdu, Sichuan 610059, China

Correspondence should be addressed to Jiping She; 437290779@qq.com

Received 28 March 2017; Revised 21 May 2017; Accepted 5 June 2017; Published 16 July 2017

Academic Editor: Christophe Coquelet

Copyright © 2017 Qing Chen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The phase equilibrium for the ternary systems NaBr + KBr + H₂O and NaBr + MgBr₂ + H₂O at 313.15 K was investigated by isothermal solution saturation method. The solubilities of salts and the densities of saturated solutions in these ternary systems were determined by chemical methods, while the equilibrium solid phases were analyzed by Schreinermarker wet residues method. Based on the experimental data, phase diagrams and density versus composition diagrams were plotted. The two ternary systems were type of simple common-saturation and without complex salt and solid solution. There are in all two crystalline regions, two univariant curves, and one invariant point in these phase diagrams of two ternary systems at 313.15 K. The equilibrium solid phases in the ternary system NaBr + KBr + H₂O are KBr and NaBr·2H₂O, and those in the ternary system NaBr + MgBr₂ + H₂O are NaBr·2H₂O and MgBr₂·6H₂O.

1. Introduction

Phase equilibrium in salt-water systems and phase diagram are the foundation of inorganic chemical production and salt mineral resources exploitation [1–4]. To extract relevant products from the potassium, magnesium, and bromine salt mine, it is essential to investigate the phase equilibrium of NaBr + KBr + H₂O and NaBr + MgBr₂ + H₂O. By now, a number of studies on the Br-bearing phase equilibria have been done, such as quaternary systems KCl−KBr−K₂SO₄−H₂O at 323 K, 348 K, and 373 K [5–7], NaBr−SrBr₂−MgBr₂−H₂O and KBr−SrBr₂−MgBr₂−H₂O at 323 K [8], and quinary system Na⁺, K⁺//Cl⁻, Br⁻, and −H₂O at 373 K [9]. The two ternary systems NaBr−KBr−H₂O and NaBr−MgBr₂−H₂O also have been reported at 323 K and 348 K [10–12]. However, the data provided is far from enough, so an extensive study at other temperatures needs to be done. The phase equilibrium of NaBr + KBr + H₂O and NaBr + MgBr₂ + H₂O at 313.15 K has not been reported yet. This paper is conducive to fill the blank of data. In this study, the solubility and density of the ternary systems were obtained. The equilibrium solid phases were analyzed, and the crystallization regions were determined. All results can offer fundamental data support for salt mineral resources exploitation and further theoretical studies.

2. Methodology

2.1. Materials and Apparatus

The sources and purity of the chemicals are listed in Table 1. Doubly deionized water (electrical conductivity ≤  S·m⁻¹) is used in the work. A HZS-H thermostatic water bath shaker is employed to carry out the experiments.

Table 1: Purities and suppliers of chemicals.

Chemical
Mass fraction purity
Source

NaBr
≥99.0%
Tianjin Bodi Chemical Holding Co. Ltd., China

KBr
≥99.0%
Tianjin Bodi Chemical Holding Co. Ltd., China

MgBr₂⋅6H₂O
≥99.0%
Tianjin Bodi Chemical Holding Co. Ltd., China

2.2. Experimental Methods

The method of isothermal solution saturation [13–15] was employed to determine the solubility of the ternary systems. The famous Schreinermarks method of moist residues [15–17] was applied to determine the equilibrium solid phase in the experiments.

Based on a fixed ratio and ensuring that one of the components is excessive, the experimental components are added to a series of conical flasks (125 mL) gradually, and the sealed flasks are placed into the oscillator. The oscillator vibrates continuously at 313.15 K (the standard uncertainty of 0.3 K). In a pre-experiment, the liquid phase of the samples is analyzed every 2 days, and it is shown that the phase equilibrium is reached in 10 days. After equilibrium, the oscillation is stopped and the system is allowed to stand for 4 days to make sure that all the suspended crystals settle. The wet residues and liquid phase are transferred to two volumetric flasks, respectively. Simultaneously, some other liquid phases are used to determine density individually. Finally, these samples are quantitatively analyzed by chemical methods.

More details of the experimental method and the procedure are presented in the previous papers [12–14].

2.3. Analysis

The concentration of potassium ion was analyzed by a sodium tetraphenylborate (STPB) hexadecyl trimethyl ammonium bromide (CTAB) titration [18–20] (uncertainty of 0.0058); the concentration of magnesium ion was measured with an EDTA standard solution using the indicator Eriochrome Black-T [21] (uncertainty of 0.0072); the concentration of bromine ion was determined by Mohr’s method using a silver nitrate standard solution [21] (uncertainty of 0.0037); and the concentration of sodium was evaluated according to the ion charge balance. The density is measured using a pycnometer (uncertainty of 0.002). Each experimental result is achieved from the average value of three parallel measurements.

3. Results and Discussion

To compare with literature data [22, 23], the experimental data on the solubility for NaBr, KBr, or MgBr₂ in pure water at 313.15 K are in good agreement with the literature values, which demonstrates that the experimental devices and methods are feasible.

3.1. Solid-Liquid Phase Equilibrium for NaBr + KBr + H₂O

The experimental data were listed in Table 2. The ion concentration values were expressed in mass fraction in the equilibrium solution. The solution densities were given in grams per cubic centimeter. According to the experimental results, the phase diagram was plotted in Figure 1 and the relationship of the solution densities was plotted in Figure 2. In the ternary system NaBr + KBr + H₂O at 313.15 K, it contains one invariant point, two univariant curves, and two crystallization regions.

Table 2: Mass Fraction Solubility of the ternary NaBr + KBr + H₂O system at temperature = 313.15 K and pressure = 0.1 .

Number
Composition of liquid phase,
Composition of wet residue phase,
Densities of liquid phase
Equilibrium solid phase

ρ/(g⋅cm⁻³)

1, P
0.00
43.51

ND
1.4208
KBr

2
3.56
40.23
2.45
59.74
1.4247
KBr

3
7.23
36.77
5.43
53.13
1.4286
KBr

4
10.88
33.61
6.84
58.31
1.4351
KBr

5
14.88
30.33
9.60
55.30
1.4446
KBr

6
18.75
27.21
10.57
59.18
1.4546
KBr

7
21.68
24.98
12.22
57.81
1.4636
KBr

8
25.23
22.18
14.66
54.92
1.4738
KBr

9
29.28
19.08
15.63
56.89
1.4863
KBr

10
33.05
16.62
15.95
59.95
1.5034
KBr

11
37.45
13.87
18.97
56.55
1.5254
KBr

12
41.23
11.48
18.92
59.52
1.5439
KBr

13, S
46.12
8.20
49.09
20.61
1.5658
NaBr⋅2H₂O + KBr

14
47.31
4.97
59.53
2.84
1.5462
NaBr⋅2H₂O

15
49.56
2.36
54.95
1.91
1.5355
NaBr⋅2H₂O

16, H
51.43
0.00
ND
ND
1.5296
NaBr⋅2H₂O

uncertainties  K, , , , and . , mass fraction of NaBr; , mass fraction of KBr. , not determined. H, S, and P have the same meaning as described in Figure 2.

Figure 1: Equilibrium phase diagram of the ternary system NaBr + KBr + H₂O at 313.15 K. ●, equilibrium liquid phase composition; ■, moist solid phase composition; A, pure solid of NaBr; B, pure solid of KBr; C, pure solid of NaBr⋅2H₂O; W, water; H, solubility of NaBr in water; P, solubility of KBr in water; S, cosaturated point of NaBr⋅2H₂O and KBr.

Figure 2: Density versus (NaBr) in the ternary system (NaBr + KBr + H₂O). H, S, and P have the same meaning as described in Figure 1.

As indicated in Figure 1, A, B, C, and W denote solid NaBr, solid KBr, solid NaBr·2H₂O, and H₂O, respectively; point S, an invariant point, reflects the cosaturated solution of KBr and NaBr·2H₂O at 313.15 K, with (NaBr) = 0.4612 and (KBr) = 0.0820; P and H denote the solubility of KBr and NaBr in water at 313.15 K, respectively. Two univariant solubility curves of this ternary system are PS and HS. Curve PS corresponds to the saturated KBr solution and visualizes changes of the KBr concentration with increasing the NaBr concentration. Curve SH corresponds to the saturated NaBr solution and indicates changes of the NaBr concentration with the KBr concentration increasing in the equilibrating solution. The KBr concentration decreases sharply with increasing the NaBr concentration, which illustrates that NaBr has a strong salting-out effect on KBr.

As indicated in Figure 1, along the curve PS, we connect the composition points of wet residue phase with liquid phase and then extend the intersection of these straight lines which is approximately the equilibrium solid phase for KBr. The same method is utilized to analyze the equilibrium solid phase of SH, and the intersection is NaBr·2H₂O. WPSH denotes unsaturated region at 313.15 K. BPS denotes crystallization region of KBr, while SHC denotes crystallization region of NaBr·2H₂O. Zone BSC represents the mixed crystalline region of KBr + NaBr·2H₂O. It is obvious that the crystalline region of NaBr·2H₂O is much smaller than that of KBr.

The phase diagrams of the ternary system NaBr + KBr + H₂O at 323 and 348 K have been reported [10]. Apparently, the three phase diagrams have very similar shapes, each of them having an invariant point, two univariant curves, and two crystallization regions. The equilibrium solid phases in the ternary system NaBr + KBr + H₂O are potassium bromide (KBr) and sodium bromide dihydrate (NaBr·2H₂O) at 313 K and 323 K, and those are potassium bromide (KBr) and sodium bromide (NaBr) at 348 K.

Figure 2 indicates the relationship between the mass fraction of NaBr and the density in the solution. With increasing the NaBr concentration, the density first increases and then the density declines afterwards. At the invariant point S, the density reaches a maximum value.

3.2. Solid-Liquid Phase Equilibrium for NaBr + MgBr₂ + H₂O

The phase equilibrium experimental data is shown in Table 3, and the ternary phase diagram is drawn in Figure 3.

Table 3: Mass Fraction Solubility of the ternary NaBr + MgBr₂ + H₂O system at temperature = 313.15 K and pressure = 0.1 .

Number
Composition of liquid phase,
Composition of wet residue phase,
Densities of liquid phase
Equilibrium solid phase

ρ/(g⋅cm⁻³)

1, H
51.43
0.00

ND
1.5296
NaBr⋅2H₂O

2
45.58
4.98
59.07
2.67
1.5391
NaBr⋅2H₂O

3
40.05
10.49
60.65
4.21
1.5496
NaBr⋅2H₂O

4
34.65
15.45
57.84
6.50
1.5663
NaBr⋅2H₂O

5
30.38
20.43
59.93
6.71
1.5843
NaBr⋅2H₂O

6
23.82
26.87
56.46
9.52
1.6049
NaBr⋅2H₂O

7
17.41
32.79
55.09
11.08
1.6242
NaBr⋅2H₂O

8
10.80
38.47
53.04
12.91
1.6488
NaBr⋅2H₂O

9
6.76
43.23
50.73
15.14
1.6723
NaBr⋅2H₂O

10, Q
4.18
47.81
7.78
51.15
1.6846
NaBr⋅2H₂O + MgBr₂⋅6H₂O

11
2.72
48.95
2.01
52.78
1.6795
MgBr₂⋅6H₂O

12
1.32
50.28
0.98
54.15
1.6705
MgBr₂⋅6H₂O

13, N
0.00
51.62
ND
ND
1.6584
MgBr₂⋅6H₂O

uncertainties  K, , , , and . , mass fraction of NaBr; , mass fraction of MgBr₂. , not determined. N, Q, and H have the same meaning as described in Figure 4.

Figure 3: Equilibrium phase diagram of the ternary system NaBr + MgBr₂ + H₂O at 313.15 K. ●, equilibrium liquid phase composition; ■, moist solid phase composition; A, pure solid of NaBr; D, pure solid of MgBr₂; C, pure solid of NaBr⋅2H₂O; M, pure solid of MgBr₂⋅6H₂O; W, water; H, solubility of NaBr in water; N, solubility of MgBr₂ in water; Q, cosaturated point of MgBr₂⋅6H₂O and NaBr⋅2H₂O.

As indicated in Figure 3, A, M, D, C, and W denote solid NaBr, solid MgBr₂·6H₂O, solid MgBr₂, solid NaBr·2H₂O, and H₂O, respectively; point Q, an invariant point, reflects the cosaturated solution of MgBr₂·6H₂O and NaBr·2H₂O at 313.15 K, with (NaBr) = 0.0418 and (MgBr₂) = 0.4781; N and H represent the solubility of MgBr₂ and NaBr in water at 313.15 K, respectively. Two univariant solubility curves of this ternary system are PS and HS. Curve NQ corresponds to the saturated MgBr₂ solution and visualizes changes of the MgBr₂ concentration with increasing the NaBr concentration. Curve QH corresponds to the saturated NaBr solution and indicates changes of the NaBr concentration with increasing the MgBr₂ concentration. The solubility of NaBr decreases sharply with increasing the MgBr₂ concentration.

The polarization of ions has a certain effect on the dissolution of ionic crystals. The results show that the ionic dipole intensity in the solution depends on the electric field strength. In this study, the electrolyte concentration increased with the higher solubility of MgBr₂ added to the solution; also, the polarity of the solution increases, and the dielectric coefficient of the dielectric medium is reduced, while the ionic electric field strength increases, making it easy to bound more water to its surrounding, so that the reduction of water in the dissolution of other substances leads to enhanced salting out. In this system, it illustrates that MgBr₂ has a strong salting-out effect on NaBr.

In Figure 3, the same method used in Figure 1 is utilized to analyze the equilibrium solid phase of the system NaBr + MgBr₂ + H₂O. Consequently, curve NQ corresponding equilibrium solid phase is MgBr₂·6H₂O and curve HQ corresponding equilibrium solid phase is NaBr·2H₂O. WNQH denotes unsaturated region at 313.15 K. NQM denotes crystallization region of MgBr₂·6H₂O, while HQC denotes crystallization region of NaBr·2H₂O. Zone MQC denotes the mixed crystalline region of MgBr₂·6H₂O + NaBr·2H₂O. It is obvious that crystallization region of MgBr₂·6H₂O is much smaller than that of NaBr·2H₂O.

The phase diagram of the ternary system NaBr + MgBr₂ + H₂O has been studied at 323 K and 348 K [11, 12]. Compared with the three phase diagrams at different temperatures, the result shows that the solubility of MgBr₂·6H₂O is highest at three temperatures. But the numbers of invariant points, crystallization fields, and univariant curves are different. The quaternary systems at 313 K and 348 K are all simple cosaturation type without complex salt and solid solution. They all include one invariant point, two univariant curves, and two crystallization regions (MgBr₂·6H₂O and NaBr·2H₂O at 313 K, MgBr₂·6H₂O and NaBr at 348 K). The phase diagram at 323 K includes two invariant points, three univariant curves, and three crystallization regions, where the solids are NaBr·2H₂O, NaBr, and MgBr₂·6H₂O, respectively.

Figure 4 indicates the relationship between the mass fraction of MgBr₂ and the density in the solution. With an increase of the MgBr₂ concentration, the density first increases and then, the density declines afterwards. At the invariant point Q, the density reaches a maximum value.

Figure 4: Density versus (MgBr₂) in the ternary system (NaBr + MgBr₂ + H₂O). N, Q, and H have the same meaning as described in Figure 3.

4. Conclusions

The phase equilibria in the NaBr + KBr + H₂O and NaBr + MgBr₂ + H₂O ternary systems at 313.15 K were investigated. The solubility and density data of the ternary systems were obtained. The diagrams of density versus composition and the ternary phase diagrams were plotted. The equilibrium solid phases were analyzed and the crystalline regions were determined. In ternary system NaBr + KBr + H₂O, the crystalline region of KBr is much larger than that of NaBr·2H₂O and NaBr has a strong salting-out effect on KBr. In ternary system NaBr + MgBr₂ + H₂O, the crystalline region of NaBr·2H₂O is much larger than that of MgBr₂·6H₂O and MgBr₂ has a strong salting-out effect on NaBr. There are in all two crystalline regions, one invariant point, and two univariant curves in the ternary phase diagrams. All results can offer fundamental data support for optimizing the processes and further theoretical studies.

Conflicts of Interest

The authors declare that there are no financial conflicts of interest.

References

J. Zhang, X. W. Shi, S. L. Zhao, X. F. Song, and J. G. Yu, “Progress in study on phase equilibria of salt-water systems,” Journal of Chemical Industry and Engineering(China), vol. 67, pp. 379–389, 2016.

S. B. Shu, Y. L. Xu, E. X. Xu, and C. W. Xiao, “Study on the occurrence of potassium-rich brine in a geological structure in west Sichuan and the analytical patterns,” China Well and Rock Salt, vol. 34, pp. 23–26, 2003.

Y. T. Lin and S. X. Cao, “Rare gas field brines rich in potassium and boron of western Sichuan basin,” Geology in China, vol. 28, pp. 45–47, 2001.

T. L. Deng, H. Zhou, and X. Chen, The Phase Diagram of Salt-Water System and Its Application, Chemical Industry Press, Beijing, China, 2013.

D. Wang, S. H. Sang, X. X. Zeng, and H. Y. Ning, “Phase equilibria of quaternary system KCl-KBr-K₂SO₄-H₂O at 323 K,” Petrochemical Technology, vol. 40, pp. 285–288, 2011.

K. J. Zhang, S. H. Sang, T. Li, and R. Z. Cui, “Liquid–Solid Equilibria in the Quaternary System at 348 K,” Jounal of Chemical and Engineering Data, vol. 58, pp. 115–117, 2013.

R. Z. Cui, S. H. Sang, and Y. X. Hu, “Solid–Liquid Equilibria in the Quaternary Systems KCI-KBr-K₂B₄O₇-H₂O and KCI-KBr-K₂SO₄-H₂O at 373 K,” Jounal of Chemical and Engineering Data, vol. 58, pp. 477–481, 2013.

Q. Liu, Y. Y. Gao, S. H. Sang, R. Z. Cui, and X. P. Zhang, “Solid−liquid equilibria in the quaternary systems NaBr−SrBr₂−MgBr₂−H₂O and KBr−SrBr₂−MgBr₂−H₂O at 323 K,” Jounal of Chemical and Engineering Data, vol. 63, pp. 1305–1318, 2016.

R. Z. Cui, S. H. Sang, and Q. Liu, “Solid-liquid equilibria in the quinary system Na⁺, K⁺//Cl–, Br–, SO₄2––H₂O at 373 K,” Jounal of Chemical and Engineering Data, vol. 61, pp. 444–449, 2016.

A. Zdanovskii, E. Soloveva, E. Liahovskaia et al., Khimiizdat, St. Petersburg, Russia, 1973.

C. Christov and J. Chem, “Study of bromide salts solubility in the (m₁NaBr + m₂MgBr₂)(aq) system at T = 323.15 K, thermodynamic model of solution behavior and solid-liquid equilibria in the (Na + K + Mg + Br + H₂O) system to high concentration and temperature,” Journal of Chemical Thermodynamics, vol. 47, pp. 335–340, 2012.

J. Hu, S. Sang, M. Zhou, and W. Huang, “Phase equilibria in the ternary systems KBr-MgBr₂-H₂O and NaBr-MgBr₂-H₂O at 348.15 K,” Fluid Phase Equilibria, vol. 392, pp. 127–131, 2015.

W. Liu, Y. Xiao, Y. S. Liu, F. X. Zhang, and J. F. Qu, “Phase equilibrium for the ternary system K₂SO₄ + KCl + H₂O in aqueous solution at 303.15 K,” Jounal of Chemical and Engineering Data, vol. 60, no. 4, pp. 1202–1205, 2015.

X. R. Zhang, Y. S. Ren, P. Li, H. J. Ma, and W. J. Ma, “Solid–liquid equilibrium for the ternary systems (Na₂SO₄ + NaH₂PO₄ + H₂O) and (Na₂SO₄ + NaCl + H₂O) at 313.15 K and atmospheric pressure,” Jounal of Chemical and Engineering Data, vol. 59, no. 12, pp. 3969–3974, 2014.

Z. D. Niu and F. Q. Cheng, The Phase Diagram of Salt-Water System and Its Application, Tianjin University Press, Tianjin, China, 2002.

H. Schott, “A mathematical extrapolation for the method of wet residues,” Jounal of Chemical and Engineering Data, vol. 6, pp. 324–324, 1961.

F. A. H. Schreinemakers, “Graphical deductions from the solution isotherms of a double salt and its components,” Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics, vol. 11, pp. 109–765, 1893.

X. B. Si and Y. L. Gao, “Improvement of determination of potassium in fertilizers—gravimetric sodium tetraphenylborate method,” Jounal of Chemical and Engineering Data, vol. 1, pp. 49-50, 2002.

C. J. Zhao, “Determination of potassium in fertilizers—gravimetric sodium tetraphenylborate method,” China Quality Supervision, vol. 4, pp. 40-41, 2008.

SN/T 0736.7-1999. Dongying City Agricultural Bureau: China, 1999.

Qinghai Institute of Salt Lakes, Chinese Academy of Science. Analytical Methods of Brines and Salts, Chinese Science Press, Beijing, China, 2nd edition, 1988.

A. Seidell, Solubilities of Inorganic and Metal-Organic Compounds, American Chemical Society, Washington, DC, USA, 1940.

G. Q. Liu, L. X. Ma, and J. Liu, Physical Property Data Handbook of Chemistry and Chemical Engineering: Inorganic Volume, Chemical Industry Press, Beijing, China, 2002.