Measurements of the SolidâLiquid Equilibria in the Quaternary

Article pubs.acs.org/jced

Measurements of the Solid−Liquid Equilibria in the Quaternary Systems KBr−K2SO4−K2B4O7−H2O and NaBr−Na2SO4−Na2B4O7−H2O at 298 K Rui-zhi Cui,†,‡ Shi-hua Sang,*,†,‡ Qing-zhu Liu,†,‡ and Pan Wang†,‡ †

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

‡

ABSTRACT: According to the compositions of the underground gasfield brines in the west of Sichuan Basin, in China, solid− liquid equilibria in the quaternary systems KBr−K2SO4−K2B4O7−H2O and NaBr−Na2SO4−Na2B4O7−H2O at 298 K were measured by isothermal solution saturation method. The solubilities of salts and the densities of saturated solutions in these quaternary systems were determined. Using the experimental data, phase diagrams, water content diagrams, and solution density diagrams were constructed. The two phase diagrams were simple cosaturation type without complex salt and solid solution. The phase diagram of the quaternary system KBr−K2SO4−K2B4O7−H2O has one invariant point, three univariant curves as the boundary of KBr, K2SO4 and K2B4O7·4H2O crystallization fields. The quaternary system NaBr−Na2SO4−Na2B4O7−H2O at 298 K consisted of five univariant curves, two invariant points and four crystallization regions of Na2B4O7·10H2O, Na2SO4, Na2SO4· 10H2O, and NaBr·2H2O. Mg2SO4−H2O at 298 K,4 K2SO4−K2B4O7 at 288 and 373 K,5,6 Li−Na−K−CO 3 −B 4 O 7 −H 2 O at 288 and 298 K, 7 , 8 Na+,K+,Mg2+//SO42−,B4O72−−H2O at 288 K,9 and the metastable phase equilibria in the quaternary systems Na−K−CO3− B4O7−H2O at 273.15 K10 and Li2SO4−Li2CO3−Li2B4O7−H2O at 288 K.11 Recently, a systematic study on the underground brine in Western Sichuan basin has been carried out by our research work, such as the measurements and calculation of the phase equilibria of the quaternary systems KCl−K2SO4−K2B4O7−H2O at 298 K12,13 and Na−K−Br−SO4−H2O at 323 K,14,15 measurements of the solid−liquid equilibria in the quinary systems Na−K−Cl−SO4−B4O7−H2O at 298 and 323 K,16,17 KCl−KBr−K2SO4−K2B4O7−H2O at 323 and 348 K,18 as well as the quaternary systems KCl−KBr−K2SO4−H2O and NaCl− NaBr−Na2B4O7−H2O at 348 K have also been studied.19,20 The underground gasfield brines in the Western Sichuan Basin can be simplified as six-component brine system Na−K−Cl−

1. INTRODUCTION The underground brine resources are rare liquid mineral resource in the world, and China has very abundant liquid mineral resources, especially in the Sichuan Basin. In addition to NaCl, the brine resources in the Sichuan Basin also contain many other useful components, such as K+, Ca2+, Mg2+, Li+, Sr2+, SO42−, CO32−, B4O72−, and Br−, and all meet or exceed their corresponding industrial grades.1 With the gradual consumption of solid mineral resources, people have drawn more and more attention to the excellent liquid mineral resources. The brine recently found in the west of the Sichuan Basin has high potassium and boron contents and high concentrations of minerals. Particularly, the potassium and boron contents of the brines are unusually high, up to 53.3 g·L−1 and 4994.36 mg·L−1, respectively. These rare liquid mineral resources have very good exploitation and utilization prospect.2,3 Generally speaking, phase equilibria and phase diagrams are the theoretical basis of the exploitation and utilization of the underground brine resources. In view of the abundant borate resources, a series of studies have been conducted on the B4O72−bearing metastable and stable phase equilibria in underground brines, salt lake brines and seawater system, i.e., Mg2B4O7− © 2014 American Chemical Society

Received: March 11, 2014 Accepted: May 28, 2014 Published: June 10, 2014 2252

dx.doi.org/10.1021/je5002363 | J. Chem. Eng. Data 2014, 59, 2252−2257

Journal of Chemical & Engineering Data

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Table 1. Solubilities and Densities of Solution in the Quaternary System KBr−K2SO4−K2B4O7−H2O at 298 K and 0.1 MPaa Jänecke index composition of solution w(B) × 100b no. 1A1 2 3 4 5 6 7 8B1 9 10 11 12 13 14 15 16 17 C1 18 19 20 21 22 23E1

J(KBr) + J(K2SO4) + J(K2B4O7) = 100 g

w(KBr)

w(K2SO4)

w(K2B4O7)

J(KBr)

J(K2SO4)

J(K2B4O7)

J(H2O)

equilibrium solidsc

Solution density ρ/(g·cm−3)

39.48 39.31 39.24 39.01 38.77 38.62 38.27 0.00 1.97 5.67 8.02 13.28 20.17 26.83 33.96 38.26 38.96 38.86 38.81 38.79 38.62 38.58 38.32

1.02 0.94 0.81 0.72 0.66 0.63 0.62 7.26 6.47 5.56 4.80 3.48 2.19 1.42 0.99 0.64 0.00 0.07 0.13 0.24 0.34 0.46 0.61

0.00 0.17 0.45 0.87 1.26 1.59 1.99 11.27 10.29 8.66 7.69 5.97 4.22 3.17 2.56 1.99 2.14 2.10 2.00 1.98 1.98 1.97 1.97

97.49 97.26 96.90 96.09 95.30 94.56 93.61 0.00 10.53 28.50 39.09 58.41 75.89 85.37 90.54 93.57 94.79 94.71 94.80 94.59 94.34 94.07 93.69

2.51 2.33 2.00 1.78 1.62 1.55 1.53 39.20 34.54 27.98 23.42 15.33 8.22 4.53 2.63 1.57 0.00 0.18 0.31 0.59 0.82 1.13 1.48

0.00 0.41 1.11 2.13 3.09 3.89 4.87 60.80 54.93 43.53 37.49 26.27 15.89 10.10 6.82 4.86 5.21 5.11 4.89 4.82 4.84 4.80 4.82

146.92 147.43 146.91 146.35 145.83 144.86 144.60 439.63 433.71 402.87 387.50 339.91 276.22 218.25 166.59 144.31 143.28 143.71 144.25 143.86 144.29 143.85 144.51

KBr + KS KBr + KS KBr + KS KBr + KS KBr + KS KBr + KS KBr + KS KS + KB KS + KB KS + KB KS + KB KS + KB KS + KB KS + KB KS + KB KS + KB KBr + KB KBr + KB KBr + KB KBr + KB KBr + KB KBr + KB KBr + KB + KS

1.3762 1.3850 1.3951 1.3946 1.4010 1.4058 1.4069 1.1524 1.1567 1.1661 1.1744 1.1998 1.2398 1.2827 1.3451 1.3870 1.4040 1.4077 1.4057 1.4050 1.4036 1.4084 1.4088

w(B) is the mass fraction of component B. aUncertainties: T, ± 0.1 K; w(KBr): ± 0.3%; w(K2SO4): ± 0.5%; w(K2B4O7): ± 0.3%. cAbbreviations: KB: K2B4O7·4H2O; KS: K2SO4. b

Br−SO4−B4O7−H2O. The quaternary systems KBr−K2SO4− K2B4O7−H2O and NaBr−Na2SO4−Na2B4O7−H2O are two subsystems of the brines. So far, although the second quaternary system at 323 K has been reported by us,21 there is no research report about the phase equilibria of the two quaternarty subsystems at 298 K, which is just the object of this work. Two ternary subsystems KBr−K2B4O7−H2O and NaBr−Na2B4O7− H2O of them at 298 K have already been reported in our previous research,22,23 which is useful to provide the foundation for this work. In this article, the solubilities and densities in the equilibrium solution of the two quaternary systems were measured and the solid−liquid stable equilibria are presented in detail at 298 K.

isothermal dissolution equilibrium method. The system points of the quaternary system were prepared by adding the third salt component gradually on the basis of the ternary invariant points at 298 K. The prepared mixtures were placed in sealed glass bottles and dissolved into 50 mL of deionized water. In this way, all brine samples can be synthesized artificially. The bottles were then placed in a thermostated vibrator (HZS-H). The sample temperature was maintained at (298 ± 0.1) K. The solutions were taken out periodically for chemical analysis. The criterion for judging the equilibrium state of the system was the unchanging concentration of the solution. After equilibrium, the solution and wet crystals can be taken out for physicochemical analysis. The liquid phases were analyzed quantitatively by chemical methods, while the wet crystals were analyzed by X-ray diffraction to ascertain their crystalloid form. For experimental details, Niu et al. can be referenced.24 2.3. Analytical Methods. Potassium ion (K+) concentration was determined using sodium tetraphenyl borate−hexadecyl trimethylammonium bromide titration (with a precision of 0.5 wt %). Bromide ion (Br−) concentrations were determined by Mohr’s method using a silver nitrate standard solution (with a precision of 0.3 wt %). Borate ion (B4O72−) was determined by basic titration in the presence of mannitol with phenolphthalein solution as indicator (with a precision of 0.3 wt %). Sulfate ion (SO42−) concentration was measured by a method of alizarin red S volumetry (precision: 0.5 wt %). Sodium ion (Na+) concentration was evaluated according to the ion charge balance. The densities of the saturated solutions were determined using the pycnometer method (with a precision of 0.0002 g·cm−3).25

2. EXPERIMENTS 2.1. Reagents and Instruments. Deionized water, with a conductivity less than 1.2 × 10−4 S·m−1 and pH 6.60 at 298 K, was used to prepare synthesized brines and for chemical analysis. The chemicals used in this work are all analytically pure (ChengDu KeLong Chemical Reagent Factory). They are KBr (⩾ 99.0 wt %), K2SO4 (⩾ 99.0 wt %), K2B4O7·5H2O (⩾ 99.0 wt %), NaBr (⩾ 99.0 wt %), Na2SO4 (⩾ 99.0 wt %), and Na2B4O7· 10H2O (⩾ 99.0 wt %). A standard analytical balance of 110 g capacity and 0.0001 g resolution (AL104, the Mettler Toledo Instruments Co., Ltd.) was used to determine the solution densities. An HZS-H type thermostated vibrator with a precision ± 0.1 K was used for the equilibrium measurements. Its temperature control accuracy is ± 0.1 K after secondary calibration using a precise thermometer. 2.2. Experimental Methods. The phase equilibria in the two quaternary systems at 298 K were investigated using the 2253



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Figure 1. Dry-salt solubility diagram and its enlarged bottom of quaternary system KBr−K2SO4−K2B4O7−H2O at 298 K and 0.1 MPa.

3. RESULTS AND DISCUSSIONS 3.1. KBr−K2SO4−K2B4O7−H2O System. The measured values of salt solubilies and solution densities of the quaternary system KBr−K2SO4−K2B4O7−H2O at 298 K are presented in Table 1, where ion concentrations are expressed in mass fraction w(B), J(B) is the Janeäcke index values of B, with J(KBr) + J(K2SO4) + J(K2B4O7) = 100 g, and ρ is the density in g·cm−3. With the data in Table 1, a stable equilibrium phase diagram of the system at 298 K is given in Figure 1. The quaternary system KBr−K2SO4−K2B4O7−H2O at 298 K has no complex salt and solid solution. There are one invariant point, three univariant curves, and three regions of crystallization in this system. The three crystallization fields correspond to potassium borate tetrahydrate (K2B4O7·4H2O), potassium bromide (KBr), and potassium sulfate (K2SO4), respectively. The crystallization area of potassium sulfate (K2SO4) is larger than that of other salts. It means that K2SO4 has lower solubility than other salts in the quaternary system. Three univariant curves are A1E1, B1E1, and C1E1. Point E1 is the invariant point for the system KBr−K2SO4−K2B4O7−H2O at 298 K, which is saturated with KBr, K2SO4, and K2B4O7·4H2O, and the composition of the corresponding liquid phase is at w(KBr) = 0.3832, w(K2SO4) = 0.0061, and w(K2B4O7) = 0.0197. Figure 2 is the water content diagram of the quaternary system KBr−K2SO4−K2B4O7−H2O at 298 K, and the abscissa is the

Jänecke index values of K2SO4. Figure 2 shows that the water content increases at the uninvariant curves E1B1, and remains unchanged at the uninvariant curves A1E1 and C1E1 with an increase of the Jänecke index values of J(K2SO4). It reaches the biggest value at the point B1. In order to reflect the changes in the density, the density diagram of the system is constructed in Figure 3. According to Figure 3, the density of the system decreases with the content increases of K2SO4.

Figure 3. Density−composition relations of the solutions in quaternary system KBr−K2SO4−K2B4O7−H2O at 298 K and 0.1 MPa.

In comparison with the quaternary system KCl−K2SO4− K2B4O7−H2O26 and the quaternary system KBr−K2SO4− K2B4O7−H2O at 298 K, we can see that the two phase diagrams have very similar shapes, each of them having an invariant point, three univariant curves, and three crystallization regions. The crystallization field of the salt K2SO4 is the largest, whereas the crystallization field of halide is obviously smaller. This fact implied that the halide has higher solubility in the equilibrium solution. But the crystallization fields of halide are different. The crystallization field of the salt KBr is apparently smaller than that of KCl. The reason is that the KBr has higher solubility than KCl at the same temperature. It is also found that halide has the salting-out effect on sulfates and borate. 3.2. NaBr−Na2SO4−Na2B4O7−H2O System. The experimental data on the solubilities and densities of the quaternary system NaBr−Na2SO4−Na2B4O7−H2O at 298 K are presented

Figure 2. Water contents of saturated solutions in quaternary system KBr−K2SO4−K2B4O7−H2O at 298 K and 0.1 MPa. 2254



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Table 2. Solubilities and densities of solution in the quaternary system NaBr−Na2SO4−Na2B4O7−H2O at 298 K and 0.1 MPa.a Jänecke index composition of solution w(B) × 100b no. 1A2 2 3 4 5 6 7 8B2 9 10 11 12 13 14 15 16E2 17 C2 18 19 20 21 22 23 24D2 25 26 27 28 29 30F2

J(NaBr) + J(Na2SO4) + J(Na2B4O7) = 100 g

w(NaBr)

w(Na2SO4)

w(Na2B4O7)

J(NaBr)

J(Na2SO4)

J(Na2B4O7)

J(H2O)

equilibrium solidsc

solution density ρ/(g·cm−3)

48.87 48.46 48.22 48.12 47.56 47.25 47.31 0.00 5.38 10.19 11.69 19.67 30.90 40.34 46.86 47.31 49.36 48.97 48.75 48.69 48.01 47.77 47.45 24.71 24.44 25.19 25.02 24.87 25.12 24.87

0.58 0.58 0.56 0.55 0.54 0.53 0.51 19.92 17.81 15.51 14.98 12.61 7.82 2.92 0.70 0.52 0.00 0.23 0.38 0.43 0.51 0.51 0.51 10.67 10.40 10.45 10.36 10.17 10.18 10.00

0.00 0.20 0.47 0.52 0.58 0.68 0.69 1.09 0.99 0.87 0.86 0.82 0.79 0.75 0.71 0.70 0.72 0.71 0.71 0.70 0.71 0.70 0.70 0.00 0.13 0.42 0.65 0.69 0.74 0.77

98.82 98.42 97.90 97.81 97.70 97.49 97.53 0.00 22.24 38.34 42.46 59.43 78.22 91.67 97.06 97.49 98.57 98.12 97.82 97.72 97.54 97.53 97.51 69.85 69.88 69.86 69.45 69.59 69.69 69.79

1.18 1.17 1.14 1.12 1.12 1.10 1.04 94.81 73.65 58.36 54.41 38.08 19.79 6.63 1.46 1.06 0.00 0.45 0.76 0.86 1.03 1.04 1.05 30.15 29.73 28.98 28.74 28.46 28.25 28.05

0.00 0.40 0.95 1.06 1.19 1.41 1.43 5.19 4.11 3.29 3.13 2.48 1.99 1.70 1.48 1.44 1.43 1.43 1.42 1.41 1.43 1.44 1.44 0.00 0.39 1.16 1.82 1.94 2.06 2.16

102.20 103.10 103.03 103.29 105.40 106.33 106.14 375.97 313.63 276.28 263.26 202.09 153.17 127.26 107.12 106.06 99.69 100.36 100.68 100.71 103.17 104.14 105.51 182.68 185.98 177.37 177.51 179.86 177.41 180.60

NBr + NS NBr + NS NBr + NS NBr + NS NBr + NS NBr + NS NBr + NS NS + NB NS + NB NS + NB NS + NB NS + NB NS + NB NS + NB NS + NB NS+NB+NBr NBr + NB NBr + NB NBr + NB NBr + NB NBr + NB NBr + NB NBr + NB S10 + NS S10 + NS S10 + NS S10 + NS S10 + NS S10 + NS S10 + NS + NB

1.5614 1.5710 1.5709 1.5675 1.5749 1.5800 1.5683 1.2249 1.2587 1.2852 1.2948 1.3508 1.3978 1.4718 1.5419 1.5703 1.5508 1.5556 1.5544 1.5632 1.5551 1.5574 1.5669 1.3227 1.3415 1.3289 1.3325 1.3421 1.3331 1.3521

Uncertainties: T, ± 0.1 K; w(NaBr): ± 0.3%; w(Na2SO4): ± 0.5%; w(Na2B4O7): ± 0.3%. bw(B) is the mass fraction of component B. Abbreviations: NB: Na2B4O7·10H2O, NS: Na2SO4, S10: Na2SO4·10H2O, NBr: NaBr·2H2O

a c

Figure 4. Dry-salt solubility diagram and its enlarged bottom of quaternary system NaBr−Na2SO4−Na2B4O7−H2O at 298 K and 0.1 MPa.

and point F2), five univariant curves (C2E2, A2E2, E2F2, D2F2, F2B2) and four crystallization regions, where the solids are NaBr· 2H2O, Na2SO4, Na2B4O7·10H2O and Na2SO4·10H2O, respectively. The crystallization field of NaBr·2H2O has the smallest crystallization area, whereas the salt Na2B4O7·10H2O has the biggest crystallization field in the quaternary system. It means

in Table 2. According to the experimental data in Table 2, the solubility diagram, water content diagram and densitycompoistion diagram of the quaternary system are shown in Figures 4−6 at 298 K. The quaternary system NaBr−Na2SO4−Na2B4O7−H2O at 298 K also belongs to simple cosaturation type. Figure 4 shows that this quaternary system has two invariant points (point E2 2255



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complex salt and solid solution. The crystallization field of Na2SO4·10H2O has disappeared at 323 K. The phase diagram at 323 K includes one invariant point, three univariant curves and three crystallization regions corresponding to solid solution NaBr·2H2O, Na2SO4, and Na2B4O7·10H2O. The shape of the each crystallization region is nearly identical. The solubility of NaBr·2H2O is highest among the salts, and that of Na2B4O7· 10H2O is lowest in this quaternary system at (298 and 323) K.

that Na2B4O7·10H2O has the smaller solubility, and it can be easiest separated from solution. Invariant point E2 is saturated with salts NaBr·2H2O + Na2SO4 + Na2B4O7·10H2O, and the mass fraction composition of the corresponding liquid phase is w(NaBr) = 0.4731, w(Na2SO4) = 0.0052, and w(Na2B4O7) = 0.0070. Invariant point F2 is saturated with salts Na2SO4 + Na2SO4· 10H2O + Na2B4O7·10H2O, and the mass fraction composition of the corresponding liquid phase is w(NaBr) = 0.2487, w(Na2SO4) = 0.1000, and w(Na2B4O7) = 0.0077.

4. CONCLUSIONS The solid−liquid equilibria in the quaternary systems KBr− K2SO4−K2B4O7−H2O and NaBr−Na2SO4−Na2B4O7−H2O at 298 K were studied by the isothermal solution saturation method. Solubilities, densities and corresponding equilibrium solids were determined. The results show that these two quaternary systems belong to the simple cosaturation type. The quaternary system KBr−K2SO4−K2B4O7−H2O at 298 K has an invariant point, three univariant curves and three crystallization regions. The three crystallization regions correspond to KBr, K2SO4 and K2B4O7·4H2O. In the quaternary system NaBr− Na2SO4−Na2B4O7−H2O at 298 K, the equilibrium phase diagram was constructed in which there were two invariant points, five univariant curves and four crystallization fields (NaBr·2H2O, Na2SO4, Na2B4O7·10H2O, and Na2SO4·10H2O).

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Figure 5. Water contents of saturated solutions in quaternary system NaBr−Na2SO4−Na2B4O7−H2O at 298 K and 0.1 MPa.

Funding

This project was supported by open the National Natural Science Foundation of China (Grant No. 41373062), the Specialized Research Fund (20125122110015) for the Doctoral Program of Higher Education of China, the fund of Key Laboratory of Salt Lake Resources and Chemistry (KLSLRC-KF-13-DX-1), and the youth science and technology innovation team of Sichuan Province, China (2013TD0005).

In Figures 5 and 6, the Jänecke index of water gradually increases with increasing Na2SO4 index, and the density decreases with the increase of the Na2SO4 concentration at the univariant curves.

Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Lin, Y. T.; Cao, S. X. The utilization prospects of potassium-enrich and boron-enrich bittern in the west of the Sichuan basin (in Chinese). Conserv. Util. Miner. Resour. 1998, 1, 41−43. (2) Lin, Y. T. Study on Sustainable Development of Potassium Boron Iodine and Bromine in Brine of Sichuan Basin (in Chinese). J. Salt Lake Res. 2001, 9, 56−60. (3) Lin, Y. T. Resource advantages and comprehensive exploitation prospect of the underground brines in Sichuan basin (in Chinese). J. Salt Lake Res. 2006, 14, 1−8. (4) Song, P. S.; Du, X. H.; Sun, B. Study on the Ternary System Mg2B4O7−Mg2SO4−H2O at 25°C. Chin. Sci. Bull. 1988, 33, 1971− 1973. (5) Sang, S. H.; Zhang, X. Solubility Investigations in the Systems Li2SO4+Li2B4O7+H2O and K2SO4+K2B4O7+H2O at 288 K. J. Chem. Eng. Data 2010, 2, 808−812. (6) Cui, R. Z.; Sang, S. H.; Zhang, K. J.; Li, T. Phase equilibria in the ternary systems K2SO4−K2B4O7−H2O and Na2SO4−Na2B4O7−H2O at 348 K. J. Chem. Eng. Data 2012, 57, 3498−3501. (7) Sang, S. H.; Yin, H. A.; Tang, M. L. (Liquid + Solid) Phase Equilibria in the Quinary System Li+,Na+,K+//CO32−,B4O72−−H2O at 288 K. J. Chem. Eng. Data 2005, 50, 1557−1559. (8) Deng, T. L. Phase Equilibrium for the Aqueous System Containing Lithium, Sodium, Potassium, Chloride, and Borate Ions at 298.15 K. J. Chem. Eng. Data 2004, 49, 1295−1299.

Figure 6. Density−composition relations of the solutions in quaternary system NaBr−Na2SO4−Na2B4O7−H2O at 298 K and 0.1 MPa.

The phase diagram of the quaternary system NaBr−Na2SO4− Na2B4O7−H2O has been studied at 323 K.21 Compared with the two phase diagrams at different temperatures, the result shows that the numbers of invariant points, crystallization fields, and unvariant curves are different. The quaternary systems at two different temperatures are all simple cosaturation type without 2256



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