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Article pubs.acs.org/jced

Phase Equilibria for the Aqueous Reciprocal Quaternary System K+, Mg2+//Cl−, Borate−H2O at 298 K Shanshan Guo,† Xudong Yu,†,‡ and Ying Zeng*,†,‡ †

College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, P. R. China Mineral Resources Chemistry Key Laboratory of the Higher Education Institutions of Sichuan Province, Chengdu 610059, P. R. China

‡

ABSTRACT: The phase equilibria of the quaternary system K+, Mg2+// Cl−, borate−H2O were studied at T = 298 K using an isothermal dissolution method. On the basis of the experimental data, the stable equilibrium phase diagram and the diagrams of the density versus composition and refractive indices versus composition of this quaternary system at 298 K were constructed. This phase diagram consists of three invariant points, seven univariant curves, and five crystallization fields corresponding to the single salt MgB4O7·9H2O, KCl, MgCl2·6H2O, K2B4O7·4H2O, and the double salt KCl·MgCl2·6H2O. The largest crystallization field is MgB4O7·9H2O; the smallest crystallization field is MgCl2·6H2O. By comparison with the stable phase diagram of system K+, Mg2+//Cl−, borate−H2O at 288, 298, and 323 K, the crystalline forms of salts are not changed, and the crystalline form of borate are B4O5(OH)42−. The crystallization field of MgB4O7·9H2O decrease obviously at 323 K. The crystallization region of KCl and K2B4O7·4H2O increases evidently, and the crystallization region of MgCl2·6H2O and KCl·MgCl2·6H2O changes slightly, meaning temperature has little impact on the solubility of KCl·MgCl2·6H2O and MgCl2·6H2O.

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equilibrium of the system K+, Mg2+//Cl−, borate−H2O at different temperatures are necessary.

INTRODUCTION The area of Sichuan basin is much larger than 20 × 104 km2, and underground brine are widely distributed in it. Pingluo underground brine,1 one of the most important liquid mineral resources located in Sichuan Basin, belongs to chloride type brine and is abundant with minerals such as potassium, lithium, rubidium, and borate.2 The concentration of potassium in Pingluo underground brine is as high as 53.267 g/L.3,4 It is well-known that phase equilibria are the base of the development in brine resource. Till now, a series of phase equilibria have been studied. Jin5−7 studied Na+, K+, Mg2+// Cl−, SO42−−H2O at 288, 298, and 308 K. Song8 argued solubility prediction in ternary system Na+, Rb+// Cl−−H2O at 298 K with the Pitzer equation. Some others phase equilibria at different temperatures studied by our team, such as the ternary systems K+, Rb+//Cl−−H2O, K+, Mg2+//Cl−−H2O at 298 K9 and LiCl + KCl (MgCl2) + H2O at 348 K,10 the quaternary systems Li+, K+, Mg2+//borate−H2O at 348 K,11 Rb+, Mg2+// Cl−, borate−H2O at 348 K,12 Li+, K+, Rb+//Cl−−H2O at 298, 323, and 348 K.13−15 The quaternary system K+, Mg2+//Cl−, borate−H2O is an important subsystem of Pingluo underground brine. Up to now, the quaternary system K+, Mg2+//Cl−, borate−H2O has been investigated at 28816 and 323 K.17 No report has been found to describe the stable phase equilibria of this system at 298 K. In order to figure out the effect of temperature on this quaternary system and provide basic data for the development of underground brine, researches focus on the stable phase © 2016 American Chemical Society

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EXPERIMENTS Reagents. The chemicals used in this work were of analytic purity grade, and key information is listed in Table 1. The deionized water, with electrical conductivity less than 1 × 10−4 S·m−1 and pH ≈ 6.60, was used for preparing the experimental samples and chemical analysis. Apparatus. The SHY-2 type thermostatic water bath oscillator (made by Jiangsu Jinchengguosheng Instrument Plant) was used in isothermal dissolution experiments, with the temperature controlling precision ±0.2 K. The WYA type Abbe refractometer was used for the measurement of refractive, with a precision of 0.0001. The AL104 type analytical balance of a resolution of 0.0002 g was applied to determine the weight of samples. The DX-2700 X-ray diffractometer with Cu K α radiation was confirmed for the crystalline form of the solid phase. Experimental Methods. The isothermal dissolution method was employed in this study. First, a series of appropriate quantity salts was dissolved in deionized water in a closed container and placed in a thermostatic water bath oscillator, which temperature was controlled at (298 K ± 0.2 Received: November 7, 2015 Accepted: February 26, 2016 Published: March 8, 2016 1566

DOI: 10.1021/acs.jced.5b00938 J. Chem. Eng. Data 2016, 61, 1566−1572

Journal of Chemical & Engineering Data

Article

Table 1. Chemical Reagents Used in the Experiment chemical name

initial purity

potassium tetraborate (K2B4O7·5H2O)

0.990

magnesium oxide (MgO)

0.998

boric acid (H3BO3)

0.990

hungchaoite (MgB4O5(OH)4·7H2O)

0.990

potassium chloride (KCl)

0.990

recrystallization

magnesium chloride hexahydrate(MgCl2·6H2O)

0.980

recrystallization

purified method

recrystallization

final purity

source Sinopharm Chemical Reagent Co., Ltd. Sinopharm Chemical Reagent Co., Ltd. Sinopharm Chemical Reagent Co., Ltd. synthesized in laboratory19 Chengdu Kelong Chemical Reagent Plant Chengdu Kelong Chemical Reagent Plant

0.990 0.998 0.998 0.990 0.998 0.990

analytical method18 alkalimetry in the presence of mannitol for B4O72− titration with EDTA stand solution for Mg2+ alkalimetry in the presence of mannitol alkalimetry in the presence of mannitol for B4O72− titration with AgNO3 stand solution for Cl− titration with AgNO3 stand solution for Cl−

Table 2. Solubility, Density, and Refractive Index of the Equilibria Solution in the Quaternary System K+, Mg2+//Cl−, Borate− H2O at 298 K and Pressure p = 0.1 MPaa Jänecke index of dry salt composition of equilibrated solution w(B) × 10

2

2+

J(Mg ) + J(K22+) = J(Cl22−) + J(B4O72−) = 100

no.

density/ (g·cm−3)

refractive index

w(Mg2+)

w(K+)

w(Cl−)

w(B4O72−)

w(H2O)

J(Mg2+)

J(K22+)

J(Cl22−)

J(B4O72−)

J(H2O)

1, A 2 3 4 5 6, B 7, F1 8 9 10 11 12 13 14 15, E 16 17 18 19 20 21, D 22 23 24, F3

1.1207 1.1258 1.1561 1.1692 1.1802 1.1982 1.2281 1.2346 1.2354 1.2385 1.2398 1.2408 1.2426 1.2538 1.3552 1.3548 1.3514 1.3433 1.3392 1.3193 1.3344 1.3495 1.3517 1.3520

1.3540 1.3588 1.3600 1.3600 1.3645 1.3728 1.3731 1.3757 1.3786 1.3825 1.3829 1.3847 1.3967 1.4026 1.4300 1.4296 1.4282 1.4260 1.4259 1.4170 1.4226 1.4278 1.4288 1.4301

0.01 0.12 0.10 0.11 0.10 0.00 0.25 0.49 1.27 2.00 2.34 2.90 4.40 5.27 8.70 9.25 9.16 8.84 8.67 8.13 8.60 8.98 8.74 8.91

1.98 5.54 5.99 6.50 9.99 14.24 14.65 13.67 11.75 9.97 9.92 8.29 5.22 3.45 0.00 0.14 0.17 0.23 0.27 0.82 0.16 0.12 0.10 0.09

0.00 1.00 2.05 2.72 7.46 11.98 12.12 12.61 13.18 13.45 14.39 14.56 15.88 16.95 25.12 26.83 26.56 25.71 25.22 24.11 25.24 26.26 25.38 25.82

3.97 9.56 8.07 7.64 4.11 2.05 4.16 2.67 2.58 3.09 3.16 3.10 3.71 3.39 0.58 0.62 0.64 0.63 0.66 0.78 0.00 0.10 0.42 0.54

94.04 83.78 83.79 83.02 78.35 71.73 68.82 70.56 71.21 71.48 70.20 71.14 70.79 70.94 65.60 63.16 63.48 64.59 65.18 66.16 65.99 64.53 65.36 64.64

8.67 6.48 5.25 5.13 2.98 0.00 5.24 10.39 25.79 39.17 43.20 52.95 73.06 83.10 100.00 99.54 99.44 99.19 99.05 96.95 99.16 99.58 99.64 99.70

91.33 93.52 94.75 94.87 97.02 100.00 94.76 89.61 74.21 60.83 56.80 47.05 26.94 16.90 0.00 0.46 0.56 0.81 0.95 3.05 0.84 0.42 0.36 0.30

0.00 18.68 35.67 43.82 79.89 92.74 86.44 90.17 91.79 90.49 90.89 91.15 90.37 91.62 98.96 98.96 98.92 98.90 98.81 98.55 100.00 99.83 99.24 99.05

100.0 81.32 64.24 56.18 20.11 7.24 13.56 8.83 8.21 9.51 9.11 8.85 9.63 8.38 1.04 1.04 1.08 1.10 1.19 1.45 0.00 0.17 0.76 0.95

20370 6130 5741 5249 3297 2188 1932 2008 1951 1892 1745 1752 1585 1509 1017 916 931 978 1005 1064 1029 965 1005 975

25, C 26 27, F2

1.2429 1.3012 1.3026

1.4038 1.4123 1.4127

6.48 6.84 6.88

2.34 1.92 1.85

21.03 21.36 21.69

0.00 0.74 0.10

70.15 69.14 69.49

91.59 91.98 92.28

8.41 8.02 7.72

100.00 98.44 99.80

0.00 1.56 0.20

1313 1254 1258

equilibrated solid KB+MB KB+MB KB+MB KB+MB KB+MB KB+KI KB+MB+KI MB+KI MB+KI MB+KI MB+KI MB+KI MB+KI MB+KI MB+Bis MB+Bis MB+Bis MB+Bis MB+Bis MB+Bis Bis+KI Bis+KI Bis+KI MB+Bis+KCar Bis+KI Bis+KI MB+KI+KCar

Note: Standard uncertainties u are u(T) = 0.20 K, ur(p) = 0.05, ur(ρ) = 2.0 × 10−4 g ·cm−3, ur(n) = 1.0 × 10−4; ur(K+) = 0.0050, ur(Mg2+) = 0.0050, ur(Cl−) = 0.0030, ur(B4O72−) = 0.0030. KB, K2B4O7·4H2O; KI, KCl; K-Car, KCl·MgCl2·6H2O; Bis, MgCl2·6H2O; MB, MgB4O7·9H2O.

a

K). Then stirred for 5−7 weeks to promote the establishing of the equilibrium and placed 2 days to keep the solution clearly. After that, the solid phase was separated from the liquid phase by filter. For the liquid phase, the densities of solution were measured using specific gravity bottle, with a precision of 0.002 g·cm3, and the refractive index of solution was determined using refractometer, with a precision of 0.0001. The density measured using specific gravity bottle in the room, we must adjust the temperature by air conditioner to control it. The refractometer link with the water bath oscillator, the water flows

in the refractometer, always keeps the temperature at 298 K, when we measured the refractive. Meantime, 5.0 mL of clarified solution was taken and diluted to analyze the composition. The crystallization forms of the salts in solid phase were tested using X-ray diffractometer. Analytical Methods. The composition of the liquid phase was determined by chemical analysis.18 Cl− was determined by AgNO3, with a precision of ±0.3%. B4O72− was determined by neutralization, with a precision of ±0.3%. Mg2+ was measured by ethylene diamine tetraacetic acid titration, with a precision 1567



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Table 3. Composition of the Invariant Points for the Subsystems of the Quaternary System K+, Mg2+//Cl−, Borate−H2O at 298 K, and Pressure p = 0.1 MPaa composition of equilibrated solution

Jänecke index of dry salt

w(B) × 102

J(Mg2+) + J(K22+) = J(Cl22−) + J(B4O72−) = 100

no.

system

w(K+)

w(Mg2+)

w(Cl−)

w(B4O72−)

w(H2O)

J(K22+)

J(Mg2+)

J(Cl22−)

J(B4O72−)

JH2O)

equilibrated solid phase

a b c d A B C D E F1 F2 F3

KCl−H2O MgCl2−H2O K2B4O7−H2O MgB4O7−H2O K+, Mg2+//borate−H2O K+//Cl−, borate−H2O K+, Mg2+// Cl−−H2O

15.11 0.00 4.43 0.00 0.01 14.28 6.48 8.60 0.00 14.65 1.85 0.09

0.00 9.00 0.00 0.12 1.99 0.00 2.35 0.16 8.70 0.25 6.88 8.91

13.72 26.30 0.00 0.00 0.00 11.99 21.06 25.28 25.16 12.12 21.69 25.82

0.00 0.00 8.80 0.78 3.97 2.05 0.00 0.00 0.58 4.16 0.10 0.54

71.17 64.70 86.77 99.10 94.04 71.68 70.12 65.96 65.56 68.82 69.49 64.64

100.0 0.00 100.0 0.00 91.33 100.0 8.41 0.84 0.00 94.76 7.72 0.30

0.00 100.0 0.00 100.0 8.67 0.00 91.59 99.16 100.0 5.24 92.28 99.70

100.0 100.0 0.00 0.00 0.00 92.74 100.0 100.0 98.96 86.44 99.80 99.05

0.00 0.00 100.0 100.0 100.0 7.26 0.00 0.00 1.04 13.56 0.20 0.95

2041 958.5 8487 110111 20369 2181 1313 1029 1017 1932 1258 975

KI Bis KB MB KB+MB KB+KI KI+K-Car Bis+K-Car Bis+MB KI+MB+KB KI+MB+K-Car Bis+MB+K-Car

a

Mg2+//Cl−, borate−H2O K+, Mg2+//Cl−, borate− H2O

KB, K2B4O7·4H2O; KI, KCl; K-Car, KCl·MgCl2·6H2O; Bis, MgCl2·6H2O; MB, MgB4O7·9H2O.

of ±0.5%. K+ was analyzed by sodium tetraphenylborate (STPB)−hexadecyl trimethy lammonium bromide (CTAB) back-titration with a precision of ±0.5%.

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EXPERIMENTAL RESULTS AND DISCUSSION

The data of solubilities, densities, and refractive indices of the equilibrium solution and its corresponding solid phases of the

Figure 2. Planar projection diagram of the quaternary system K+, Mg2+//Cl−, borate−H2O at 298 K. ●, experimental point. −, univariant curve.

Figure 3. Partial enlarged diagram of Figure 2.

quaternary system K+, Mg2+//Cl−, borate−H2O at 298 K were listed in Table 2. The component corresponding to the invariant points of the binary and ternary subsystems of this quaternary system were

Figure 1. Stereodiagram of the quaternary system K+, Mg2+//Cl−, borate−H2O at 298 K. 1568



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Figure 4. X-ray diffraction pattern of the cosaturated salts corresponding to the invariant point F1 (K2B4O7· 4H2O + MgB4O7· 9H2O + KCl).

Figure 5. X-ray diffraction pattern of the cosaturated salts corresponding to the invariant point F2 (KCl + MgB4O7 · 9H2O + KCl·MgCl2·6H2O).

tabulated in Table 3. In Tables 2 and 3, the concentration of solution component was expressed in mass fraction w(B), with w(K+) + w(Mg2+) + w(Cl−) + w(B4O72−) + w(H2O) = 100%. J(B) is the Jänecke index values of B, B can be K22+, Mg2+, Cl22−, B4O72− or H2O, the data of J(B) ought to comply with J(K22+) + J(Mg2+) = J(Cl22−) + J(B4O72−) = 100. Letting w(Mg 2 +) w(K+) w(Cl−) 1 1 + = × [M] = × 2 39.10 24.31 2 35.45 w(B4 O72 −) + 155.24 J(K 22 +) =

w(K+) 1 × × 100 2 39.10[M]

J(Cl 22 −) =

w(Cl−) 1 × × 100 2 35.45[M]

(3)

J(H 2O) =

w(H 2O) × 100 18.02[M]

(4)

Figure 1 is the space phase diagram of the quaternary system at 298 K. Figure 2 is the planar projection diagram of Figure 1. Figure 3 is the partial enlarged diagram of Figure 2. As shown in Figure 1 to Figure 3, the quaternary system K+, Mg2+//Cl−, borate−H2O is of a complex type, with double salt KCl·MgCl2· 6H2O formed at 298 K. The stable phase diagram consists of three invariant points, seven univariant curves, and five crystallization zones. The five crystallization fields correspond to four single salts MgB4O7·9H2O, KCl, MgCl2·6H2O, K2B4O7· 4H2O, and one double salt KCl·MgCl2·6H2O.

(1)

(2) 1569



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Figure 6. X-ray diffraction pattern of the cosaturated salts corresponding to the invariant point F3 (MgCl2·6H2O + MgB4O7 · 9H2O + KCl·MgCl2· 6H2O).

Figure 7. Water content vs J(Mg2+) diagram of the quaternary system K+, Mg2+//Cl−, borate−H2O at 298 K. ●, experimental value; −, experimental relationship curve.

Figure 8. Refractive indices vs J(Mg2+) diagram for the quaternary system K+, Mg2+//Cl−, borate−H2O at 298 K. ●, experimental value; −, experimental relationship curve.

Among the five crystallization fields, the crystallization zone of salt MgCl2·6H2O is the smallest, and that of salt MgB4O7· 9H2O is the largest, which means that salt MgCl2·6H2O has the largest solubility in water than the other coexisted salts, whereas salt MgB4O7·9H2O has the smallest solubility and can be easier to separate from solution in this system at 298 K. Figure 4, Figure 5, and Figure 6 are the X-ray diffraction patterns of the cosaturated salts corresponding the three invariant points F1, F2, and F3, respectively, with the abscissa ordinate 2θ from 10° to 60°. At the invariant points F1, the three cosaturated salts are KCl + K2B4O7·4H2O + MgB4O7· 9H2O, and the mass fraction composition of the equilibrated solution is w(K+) = 14.65%, w(Mg2+) = 0.25%, w(Cl−) = 12.12%, w(B4O72−) = 4.16%, w(H2O) = 68.82%. At the invariant points F2, the three cosaturated salts are KCl + KCl· MgCl2·6H2O + MgB4O7·9H2O, and the mass fraction

composition of the equilibrated solution is w(K+) = 1.85%, w(Mg2+) = 6.88%, w(Cl−) = 21.69%, w(B4O72−) = 0.10%, w(H2O) = 69.49%. At the invariant points F3, the three cosaturated salts are MgCl2·6H2O + KCl·MgCl2·6H2O + MgB4O7·9H2O, and the mass fraction composition of the equilibrated solution is w(K+) = 0.09%, w(Mg2+) = 8.91%, w(Cl−) = 25.82%, w(B4O72−) = 0.54%, w(H2O) = 64.64%. The water content vs composition diagram of this system at 298 K was listed in Figure 7, with J(Mg2+) as abscissa, J(H2O) as ordinate. It shows that at the univariant curve AF1, the water content changes obviously, while at the other univariant curves, the water content changes slightly. Based on the data in Table 2, the diagrams of the density vs J(Mg2+) and the refractive index vs J(Mg2+) were plotted in Figures 8 and 9. The density and refractive index values changes regularly, both of density and refractive index values on 1570



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were determined at 298 K. The phase diagram of this quaternary system consists of three invariant points, seven univariant curves, and five crystallization fields. This system is of a complex type, with the double salt KCl·MgCl2·6H2O formed. By comparisons with the stable phase diagram of system K+, Mg2+//Cl−, borate−H2O at T = 288, 298, and 323 K, the crystalline forms of salts are the same at the observed temperature, whereas the crystallization fields change with the temperature. The crystallization field of MgB4O7·9H2O decreases obviously, while the crystallization region of K2B4O7·4H2O increases evidently with the increases of temperature, and the crystallization region of MgCl2·6H2O and KCl·MgCl2·6H2O changes slightly. Salt MgB4O7·9H2O has the smallest solubility and more easily separated from solution than the other coexisting salts.

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AUTHOR INFORMATION

Corresponding Author

Figure 9. Densities vs J(Mg2+) diagram for the quaternary system K+, Mg2+//Cl−, borate−H2O at 298 K. ●, experimental value; −, experimental relationship curve.

*E-mail: [email protected]. Funding

Supported by the National High Technology Research and Development Program of China (2012AA061704), the National Natural Science Foundation of China (41173071, 41473059), the Sichuan youth science and technology innovation research team funding scheme (2013TD0005), and Innovation Team of Chengdu University of Technology (KYTD201405). Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Lin, Y. T.; Pan, Z. R. Give Full Play To Brine Resources Superiority in Sichuan Basin, Carry Out a Great Plan for the Development of West China. J. Acta Geologica Sichuan 2001, 1, 26−31 (in Chinese). (2) Lin, Y. T. Resource Advantages of the Underground Brines of Sichuan Basin and the Outlook of Their Comprehensive Exploitation. J. Salt. Lake Res. 2006, 14, 1−8 (in Chinese). (3) Chen, Y. H. Sequence of Salt Separation and Regularity of Some Trace Elements Distribution During Isothermal Evaporation (25 °C) of the Huanghai Sea Water. J. Acta Geol. Sin. 1983, 4, 379−382 (in Chinese). (4) Lin, Y. T.; Li, W. J. Improving Utilization Level of Liquid Mineral Resources of Potassium, Boron, Iodine, and Bromine in Sichuan Sustainable Development for Mining Industry. J. Chengdu Univ.Technol. 2000, 27, 45−50 (in Chinese). (5) Jin, Z. M.; Zhou, H. N.; Wang, L. S. Studies on the Metastable Phase Equilibrium of Na+, K+, Mg2+ // Cl−, SO42‑- H2O Quinary System at 288 K. Chem. J. Chin. Univ. 2002, 23, 690−694 (in Chinese). (6) Jin, Z. M.; Xiao, X. Z.; Liang, S. M. Studies of the Metastable Equilibrium for Quinary System of (Na+, K+, Mg2+), (Cl−, SO42‑), H2O. Acta. Chim. Sin. 1980, 38, 313−321 (in Chinese). (7) Jin, Z. M.; Zhou, H. N.; Wang, L. S. Studies on the Metastable Phase Equilibrium of (Na+, K+, Mg2+), (Cl−, SO42‑), H2O Quinary System at 308.15 K. Chem. J. Chin. Univ. 2001, 22, 634−638 (in Chinese). (8) Hu, B.; Song, P. S.; Li, Y. L. Solubility Prediction in the Ternary Systems NaCl−RbCl−H2O, KCl−CsCl−H2O and KBr−CsCl−H2O 25 °C Using the Ion−Interaction Model. CALPHAD: Comput. Coupling Phase Diagrams Thermochem. 2007, 31, 541−544. (9) Yu, X. D.; Zeng, Y.; Yao, H. X.; Yang, J. Y. Mesastable Phase Equilibria in the Aqueous Ternary System KCl + MgCl2 + H2O and KCl + RbCl + H2O at 298.15 K. J. Chem. Eng. Data 2011, 56, 3384− 3391.

Figure 10. Phase diagram of the quaternary system K+, Mg2+//Cl−, borate−H2O at 298, 288, and 323 K: ●, 298 K; ◆, 288 K, and ▲, 323 K).

the univariant curve BF1, F1F2, F2F3 increases with the increase of J(Mg2+). At the invariant point F3, the refractive index reaches the maximum value. The comparisons among the stable phase diagrams of the quaternary system K+, Mg2+//Cl−, borate− H2O at (298, 288, and 323 K) have been made, as shown in Figure 10. The crystalline forms of salts have not changed, whereas the solubilities of salts have changed with the temperature, which reflected on the changes of the crystallization fields. The crystallization field of MgB4O7·9H2O decreases obviously, while the crystallization region of K2B4O7·4H2O increases evidently with the increases of temperature, and the crystallization region of KCl, MgCl2·6H2O and KCl·MgCl2·6H2O change slightly. At different temperature, the crystallization field of salt MgB4O7· 9H2O is keeping the largest, indicates that MgB4O7·9H2O has the smallest solubility and more easily separated from solution than the other coexisting salts.

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CONCLUSIONS The solubility, the density and refractive index of the equilibria solution in the quaternary system K+, Mg2+//Cl−, borate−H2O 1571



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(10) Mu, P. T.; Tan, Q.; Yu, X. D.; Li, Q.; Zeng, Y. Thermodynamics Phase Equilibria of the Aqueous Ternary Systems LiCl + KCl (MgCl2) + H2O at 348 K. J. Chem. Eng. Data 2015, 60, 574−579. (11) Tan, Q.; Zeng, Y.; Mu, P. T.; Yu, X. D.; Zhang, Yu. J. Stable Phase Equilibrium of Aqueous Quaternary System Li+, K+, Mg2+ // Borate - H2O at 348 K. J. Chem. Eng. Data 2014, 59, 4173−4178. (12) Yin, Q. H.; Mu, P. T.; Tan, Q.; Yu, X. D.; Li, Z. Q.; Zeng, Y. Phase Equilibria for the Aqueous Reciprocal Quaternary System Rb+, Mg2+ // Cl−, Borate - H2O at 348 K. J. Chem. Eng. Data 2014, 59, 2235−2241. (13) Yu, X. D.; Zeng, Y.; Yang, J. Y. Solid - Liquid Isothermal Evaporation Metastable Phase Equilibria in the Aqueous Quaternary System LiCl + KCl + RbCl + H2O at 298.15 K. J. Chem. Eng. Data 2012, 57, 127−132. (14) Li, Z. Q.; Yu, X. D.; Yin, Q. H.; Zeng, Y. Thermodynamics Metastable Phase Equilibria of Aqueous Quaternary System LiCl + KCl + RbCl + H2O at 323.15 K. Fluid Phase Equilib. 2013, 358, 131− 136. (15) Yin, Q. H.; Zeng, Y.; Yu, X. D.; Mu, P. T.; Tan, Q. Metastable Phase Equilibrium in the Quaternary System LiCl + KCl + RbCl + H2O at 323.15 K. J. Chem. Eng. Data 2013, 58, 2875−2880. (16) Sang, S. H.; Peng, J.; Wei, L. N. Solid - Liquid Phase Equilibrium of the Quaternary System Mg2+, K+ // Cl−, B4O72‑-H2O at 288 K. Acta Phys. Chim. Sin. 2009, 25, 331−335. (17) Yu, X. D. Phase Equilibria for Aqueous Quinary Systems Focused on Pingluo Underground Brine Enriched with Potassium, Rubidium, and Borate. Doctor thesis, Chengdu University of Technology, ChengDu, SiChuan, China, 2014 (in Chinese). (18) Institute of Qinghai Salt-Lake of Chinese Academy of Sciences, Analytical Methods of Brines and Salts, 2nd ed.; Chinese Science Press: Beijing, China, 1988 (in Chinese). (19) Jing, Y. A New Synthesis Method for Magnesium Borate. SeaLake Salt Chem. Ind. 2000, 29, 24−25 (in Chinese).

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