Article pubs.acs.org/jced
Liquid−Solid Equilibria in the Quaternary System KCl−KBr−K2SO4− H2O at 348 K Kai-jie Zhang,†,‡,§ Shi-hua Sang,*,†,‡,§ Ting Li,†,‡,§ and Rui-zhi Cui†,‡,§ †
College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, P. R. China State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (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: The solubilities and densities of solid−liquid equilibria in the quaternary system KCl−KBr−K2SO4−H2O at 348 K were determined experimentally by using an isothermal solution saturation method. According to the experimental data, the phase diagram of the quaternary system was plotted. In the equilibrium phase diagram of the quaternary KCl−KBr− K2SO4−H2O system at 348 K, there are one univariant dissolution curve and two crystallization fields corresponding to K(Cl, Br) and K2SO4, and no invariant point has been found in this quaternary system. The quaternary system contained solid solution K(Cl, Br). The density values in the equilibrium solution increase with the increase of potassium bromide concentration and decrease with the increase of potassium chloride concentration.
1. INTRODUCTION Potash resources are lacking in China, and therefore China mainly relies on importing a great deal of potash resources to meet market demand.1 However, high-quality gas fields brines rich in potassium salt are widely distributed in the Sichuan basin of China. The brines contain many useful components such as potassium, bromine, iodine, boron, lithium, strontium, and rubidium, which fill urgent needs in the domestic market. Their contents generally meet the grades for mining. Therefore, the comprehensive utilization of the brine resources is of great economic significance.2 It has vital significance to develop gas fields brine resources and produce important potassium chemical raw materials. A large research project for underground gas field brines and salt lake brines has been recently carried out in our previous work.3−6 But few reports about solid solution system are reported and mainly focus on the temperature of 298 K.7 Solid−liquid equilibria studies of the NaCl−NaBr−H2O ternary system and a phase diagram for the ternary system of KCl−KBr−H2O at 298 K, 313 K, and 323 K have been completed.8−10 Otherwise, the phase equilibrium of KCl− KBr−K2SO4−H2O quaternary system at 323 K has also been reported.11 No data for the liquid−solid equilibrium in the quaternary system KCl−KBr−K2SO4−H2O at 348 K are reported in the literature. Liquid−solid equilibrium in quaternary system KCl−KBr− K2SO4−H2O at 348 K belongs to the solid solution system. In this work, solubilities of the quaternary system KCl−KBr− K2SO4−H2O are investigated by the isothermal method at 348 K. The phase diagram is plotted and discussed. © 2012 American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Reagents and Instruments. All chemical reagents we used are analytical purity grade. The conductivity of distilled water is less than 10−4 S·m−1, with pH 6.6. The electronic balance precision is 0.0001 g, type AL104, obtained from the company of Mettler-Toledo. A SHA-GW digital display constant temperature oil bath (± 0.1 K) is obtained from JinTan City Guowang Experimental Instrument Manufactory of China. 2.2. Experimental Method. The isothermal solution saturation method is used in this study. From ternary invariant points, we begin to add the third salt from low to high until the third salt is saturated. For example, in our system, from the invariant point of the ternary system K2SO4−KBr−H2O at 348 K we began to add the salt of KCl gradually. The appropriate quantity of salts and distilled water are calculated and mixed into glass bottles; then, the glass bottles are put into thermostatic oil bath vibrator. The clarifying solution is taken for chemical analysis periodically. When the compositions of the solution do not change, equilibrium is established. The experiment shows that the equilibrium is attained in 14 days at 348 K. The densities of the liquid samples were measured by the weighing bottle method, and the equilibrium solid phases were determined by wet slag method supplemented X-ray powder diffraction. Received: September 1, 2012 Accepted: December 13, 2012 Published: December 21, 2012 115
dx.doi.org/10.1021/je3009717 | J. Chem. Eng. Data 2013, 58, 115−117
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Table 1. Solubilities and Densities of the Quaternary System KCl−KBr−K2SO4−H2O at Temperature T = 348 K and Pressure p = 0.1 MPaa composition of solution 100w(b)
a
composition of dry salt [m(KCl + KBr + K2SO4) = 100 g]
density
no.
w(KBr)
w(KCl)
w(K2SO4)
m(KBr)
m(KCl)
m(K2SO4)
m(H2O)
solid phase
ρ/g·cm−3
1(E1) 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17(E2)
0.00 7.07 12.33 21.23 22.15 24.66 26.60 29.20 29.45 30.61 30.90 31.06 33.99 34.89 38.17 41.23 46.88
34.68 28.20 24.78 19.23 18.76 17.60 16.15 14.43 10.67 10.76 10.23 13.39 8.06 7.22 5.65 4.22 0.00
1.67 1.26 1.11 0.86 0.84 0.78 0.72 0.64 1.20 1.29 1.19 0.60 1.30 1.28 1.11 1.29 1.60
0.00 19.35 32.26 51.38 53.05 57.30 61.19 65.96 71.27 71.75 73.02 68.95 78.41 80.41 84.95 88.21 96.70
95.41 77.20 64.84 46.54 44.93 40.89 37.15 32.60 25.82 25.22 24.17 29.72 18.59 16.64 12.58 9.03 0.00
4.59 3.45 2.90 2.08 2.01 1.81 1.66 1.45 2.90 3.02 2.81 1.33 3.00 2.95 2.47 2.76 3.30
117.02 118.43 122.87 125.10 125.32 123.71 124.78 129.71 103.38 114.27 114.96 110.60 111.03 109.87 110.18 107.84 108.12
KCl + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 K(Cl, Br) + K2SO4 KBr + K2SO4
1.417 1.466 1.504 1.514 1.537 1.572 1.574 1.581 1.586 1.600 1.610 1.614 1.618 1.625 1.646 1.674 1.688
Note: w(b) is the mass fraction of b. Standard uncertainties u are u(T) = 0.1 K, u(ρ) = 0.004 g·cm−3, and u(w) = 0.005.
2.3. Analytical Methods.12 The potassium ion concentration (K+) was determined by a sodium tetraphenylborate (STPB)−hexadecyl trimethylammonium bromide (CTAB) titration (uncertainty of 0.5 mass %). The compositions of sulfate ion (SO42−) in the liquid and their corresponding wet residues of the solid phases were determined by the gravimetric methods of barium chloride with the precisions within ± 0.5 mass %. The chlorine ion (Cl−) and bromine ion (Br−) total concentration were evaluated by the Mohr method (with a mass fraction uncertainty of 0.3 %). The bromide ion (Br−) was determined by the iodometry method. The chlorine ion (Cl−) concentration was determined by subtraction method, respectively. The components of the solid phase were determined by the wet residue method and were further identified by X-ray diffraction.
Figure 1. Equilibrium phase diagram of yjr KCl−KBr−K2SO4−H2O quaternary system at temperature T = 348 K and pressure p = 0.1 MPa.
3. RESULTS AND DISCUSSION The experimental results for the solubilities and the solution densities of the quaternary system KCl−KBr−K2SO4−H2O at 348 K were tabulated in Table 1. The ion concentration values are expressed in mass fraction in the equilibrium solution. The solution densities were given in grams per cubic centimeter. The composition of dry salts are expressed in m(b), with J(KCl) + J(KBr) + J(K2SO4) = 100 g. According to the experimental results in Table 1, the phase diagram of the quaternary system at 348 K is plotted in Figure 1, and the relationship diagram of the solution densities is plotted in Figure 2. It can be found from Table 1 and Figure 1 that the quaternary system KCl−KBr−K2SO4−H2O at 348 K belongs to the solid solution system, which only contains one univariant curve (E1E2) and has no quaternary invariant point. In the stable phase diagram, there are two crystallization fields: K(Cl, Br) and K2SO4. The crystallization field of K2SO4 is bigger, and its solubility is lower in the system. On the contrary, the crystallization field of K(Cl, Br) is smaller, and its solubility is greater in the system. Otherwise, as the potassium bromide concentration increased in solution, the potassium chloride concentration decreased, which indicated that potassium
bromide has a strong salt-out effect on potassium chloride. Compared with the stable solubility data from the quaternary system KCl−KBr−K2SO4−H2O at 323 K,11 it can be found that the compositions of the invariant points for the ternary system KCl−K2SO4−H2O in our system with mass fraction are (34.68, 1.67) vs (29.30, 1.26) and (46.88, 1.60) vs (42.99, 1.63) for the ternary system KBr−K2SO4−H2O. The experimental result shows that the solubilities of KCl and KBr increase with an obvious increase in temperature. Potassium sulfate has a low solubility and is easy to crystallize from the equilibrium solution. Otherwise, those results demonstrate that the system belongs to solid solution system and that is has no quaternary invariant point at 323 K and 348 K. From Table 1 and Figure 2, we can find that the density values of solution are increasing with the increase of the content of potassium bromide, and the density values of solution are decreasing with the increase of the content of potassium chloride. The maximum value of the density of the solution is 1.688 g·cm−3, where the potassium bromide concentration is 46.88 % at point E2. The minimum of density 116
dx.doi.org/10.1021/je3009717 | J. Chem. Eng. Data 2013, 58, 115−117
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Figure 2. Density and composition of the KCl−KBr−K2SO4−H2O quaternary system at temperature T = 348 K and pressure p = 0.1 MPa.
of the solution is 1.417 g·cm−3 when the potassium chloride concentration is 34.68 % at point E1.
(7) Ren, B. S.; Cao, J. L. Thermodynamics Correlation of the Phase Equilibrium for the Brine-Salt System Containing Solid Solution. J. Chem. Eng. Chin. Univ. 2003, 17 (2), 119−122. (8) Weng, Y. B.; Wang, J. K.; Yin, Q. X.; Wang, Y. F. Solid-Liquid Equilibrium of NaCl-NaBr-H2O Ternary System (in Chinese). J. Petrochem. Technol. 2007, 36 (4), 358−361. (9) Zhang, K. J.; Sang, S. H.; Wang, D.; Zhang, J. J. Phase Diagram for the Ternary System of KCl−KBr−H2O at 323 K (in Chinese). J. Salt Chem. Ind. 2011, 40 (6), 5−7. (10) Weng, Y. B.; Wang, J. K.; Yin, Q. X.; Wang, Y. F. Phase Diagram for the Ternary System of K+/Cl−, Br−−H2O at 298 K, 313 K and 333 K (in Chinese). J. Chem. Eng. Chin. Univ. 2007, 21 (4), 695−699. (11) Wang, D.; Sang, S. H.; Zeng, X. X.; Ning, H. Y. Phase Equilibrium of KCl−KBr−K2SO4−H2O Quaternary System at 323 K (in Chinese). J. Petrochem. Technol. 2011, 40 (3), 285−288. (12) Qinghai Institute of Salt Lakes of CAS. Analytical Methods of Brines and Salts, 2nd ed. (in Chinese); Science Press: Beijing, 1988.
4. CONCLUSION The quaternary system KCl−KBr−K2SO4−H2O at 348 K was studied by the isothermal solution saturation method. Solubilities and densities were determined experimentally. On the basis of the experimental data, a phase diagram was plotted. The experimental results show that the quaternary system belongs to a solid solution system, and no double salts are formed. In the phase diagram of KCl−KBr−K2SO4−H2O at 348 K, there is one univariant curve and two regions of crystallization. The potassium bromide has a salting-out effect on the potassium chloride.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Funding
This project was supported by Open Fund (PLC201204) of State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Chengdu University of Technology), the National Nature Science Foundation of China (no. 40973047), and the Youth Science Foundation of Sichuan Province in China (08ZQ026-017). Notes
The authors declare no competing financial interest.
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REFERENCES
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