Article pubs.acs.org/jced
Phase Equilibria in the Quaternary Systems KCl−K2B4O7−K2SO4−H2O and MgCl2−MgB4O7−MgSO4−H2O at 273 K Xiang-Po Zhao,† Xue-Ping Zhang,† Yu-Yan Yang,† and Shi-Hua Sang*,†,‡ †
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: The method of isothermal dissolution equilibrium was used to study the solubilities of salts and the densities of saturated solutions in the two quaternary systems KCl−K2B4O7−K2SO4−H2O and MgCl2−MgB4O7−MgSO4− H2O at 273 K. The equilibrium solid phases were also determined by the method of X-ray diffraction. On the basis of experimental results, the phase diagrams and density versus composition diagrams of those quaternary systems at 273 K were plotted. The results indicate that both the phase diagrams of the two systems consist of one invariant point, three stable solubility isothermal curves, and three crystalline regions. The crystallization fields for the system KCl−K2B4O7−K2SO4− H2O correspond to K2B4O7·4H2O, KCl, and K2SO4. Those for the system MgCl2−MgB4O7−MgSO4−H2O correspond to MgB4O7·9H2O, MgCl2·6H2O and MgSO4·7H2O. MgCl2−MgB4O7−H2O at 323.15 K.10 Yan et al. have studied the ternary system KCl−K2B4O7−H2O at 298 K.11 In the previous study, we have investigated the quaternary system KCl−K2B4O7−K2SO4−H2O at 288 K.12 And Song et al. have studied the quaternary system MgCl2−MgB4O7−MgSO4−H2O at 298 K.13 Although the quaternary systems KCl−K2B4O7− K2SO4−H2O and MgCl2−MgB4O7−MgSO4−H2O at other temperatures have been reported, there is no paper that has described these quaternary systems at 273 K. The multicomponent system of Qinghai salt lakes can be simplified as the Li−K−Mg−Cl−SO4−B4O7−H2O system. The quaternary systems KCl−K2B4O7−K2SO4−H2O and MgCl2−MgB4O7− MgSO4−H2O belong to subsystems of this simplified system. The study at 273 K can perfect the thermodynamic data of the water−salt system at different temperatures and lay a foundation for our further study for the Li−K−Mg−Cl− SO4−B4O7−H2O system. In this paper, the solubilities and densities in the quaternary systems were measured at 273 K. The phase equilibria of the two quaternary systems KCl−K2B4O7−K2SO4−H2O and MgCl2−MgB4O7−MgSO4−H2O were studied at 273 K, which will be useful in exploiting the salt lake resources such as potassium, magnesium, and boron, and guiding the separation and extraction process in low temperature, especially in winter.
1. INTRODUCTION There are many salt lakes in China, especially in the Qinghai province. Among them, the salt lake in Qaidam Basin is famous for abundant potassium, magnesium, and borate resources.1 In recent years, owing to the reduction of land mineral resources, liquid mineral resources such as salt lakes and underground brine began to be explored. Therefore, to meet the growing demand for natural resources, development and utilization of salt lake resources has become increasingly important. It is well-known that the equilibrium theory for the water− salt system has been used to investigate the laws of natural salt deposits and transformation. According to the theory of phase diagram and phase diagram data, the change in concentrations and the salting sequence of the liquid can be determined in the process of brine evaporation. Through the material balance calculations, the composition of the liquid and solid for the each stage of concentration can be obtained in order to determine the appropriate process route and reasonable process conditions.2 It is widely acknowledged that the liquid boron resource of the salt lake is extremely abundant in Qing-Tibet Plateau. Owing to the economic importance of boron in developing the industry, Chinese scholars have been committed to study the phase chemical behavior of boron extensively. For instance, Song et al. studied the solubilities of the systems Li+, Mg2+//B4O72−, SO42−−H2O,3 MgB4O7−MgSO4−MgCl2− H2O,4 Li2B4O7−Li2SO4−H2O,5 and MgB4O7−MgSO4−H2O6 at 298.15 K. Furthermore, the systems K2B4O7−Li2B4O7−H2O, Na2B4O7−Li2B4O7−H2O,7 and K2B4O7−Na2B4O7−H2O8 at 288.15 K, and the systems Li2B4O7−MgB4O7−H2O and K2B4O7−MgB4O7−H2O at 273.15 K9 have been studied by our group. Luo et al. have investigated the ternary system © XXXX American Chemical Society
Received: November 3, 2016 Accepted: February 22, 2017
A
DOI: 10.1021/acs.jced.6b00926 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
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SHH-250 incubator of ±0.1 K uncertainty supplied by Chongqing Yingbo Experimental Instrument Co., Ltd. was used to control the temperature at 273 ± 0.1 K. An electric thermal blowing drybox (101-0AB, supplied by the Beijing Zhongxing Weiye Instrument Co., LTD) was used to dry the solid samples. 2.2. Experimental Method. The method of isothermal dissolution equilibrium was taken to carry out our research for the quaternary systems KCl−K2B4O7−K2SO4−H2O and MgCl2−MgB4O7−MgSO4−H2O. Specific operations are as follows. First, a series of mixtures of three salts was prepared by a certain percentage based on the composition of invariant point for each ternary system. Then, 50 mL of distilled water was added to the mixture to dissolve the salts. However, at least two salts could not be dissolved completely for each sample. When finishing the preparation, the solid−liquid mixtures in bottles were shaken in the oscillator (HY-5) which was put in the incubator. The temperature was controlled to (273 ± 0.1) K. After one month of vibration, the oscillator was turned off. The liquid phase was obviously clarified in about 10 days, and a pipettor was used to take quickly 5 mL of supernatant. The composition of salts in the liquid was measured by chemical analysis. When the composition of all salts varied by no more than 0.3%, we assumed that dissolution equilibrium has been reached. A Siemens D500 X-ray diffraction analyzer was used for the X-ray diffraction analysis of the solids. The solid phases of the invariant point were determined by the X-ray diffraction photograph. A density bottle method with an uncertainty of 0.01 g·cm−3 was used to measure the densities of the equilibrium solution. In the experiment, the Eppendorf pipettor was used to take quickly 5 mL of saturated solution in a 100 mL volumetric flask. Then, the sample was weighed by using an analytical balance. The density was calculated by the ratio of mass to volume. 2.3. Analytical Methods. 15 The concentration of potassium ion (K+) was measured using the method of sodium tetraphenyl borate (STPB)−hexadecyl trimethylammonium bromide (CTAB) back-titration (uncertainty of 0.3 mass %). The concentration of magnesium ion (Mg2+) was determined at PH = 10 using the EDTA titration method and Eriochrome Black-T as indicator (uncertainty of 0.3 mass %). The concentration of chloride ion (Cl−) was determined by silver
2. EXPERIMENTS 2.1. Reagents and Instruments. The main chemical reagents used in the experiment were listed in Table 1. Table 1. Sample Description Table chemical reagent KCl MgCl2· 6H2O K2B4O7· 4H2O MgB4O7· 9H2O K2SO4 MgSO4
mole fraction purity ≥99.5% ≥98% ≥99.5% ≥98%
source
analysis method
Chengdu Kelong Chemical Reagent Manufacture, China
silver nitrate volumetric method silver nitrate volumetric method mannitol volumetric method mannitol volumetric method barium chloride gravimetric method barium chloride gravimetric method
Chengdu Kelong Chemical Reagent Manufacture, China Sinopharm Chemical Reagent Co., Ltd. Laboratory Synthesis
≥99.0%
Chengdu Kelong Chemical Reagent Manufacture, China
≥99.0%
Chengdu Kelong Chemical Reagent Manufacture, China
Hungtsaoite (MgB4O7·9H2O) was obtained by the method of chemical synthesis.14 To obtain the hungtsaoite, analytical reagent grade H3BO3 and MgO were used as raw materials. Three substances MgO, H3BO3, and H2O were mixed in a ratio of 1:8:66 and then stirred continuously for 3 h at 298 K. The insoluble material was filtered off. After filtration, the liquid phase was further stirred until a large number of white precipitate was formed. The X-ray diffraction photograph of the synthesized product was seen in Figure 1. The chemical titration method was used to determine the purity of the MgB4O7·9H2O. The experimental solutions were prepared by using distilled water (conductivity less than 1 × 10−5 S·m−1, pH = 6.6). A standard analytical balance with 110 g capacity and less than 0.1% uncertainty (AL104, manufactured by the Mettler Toledo Instruments Co., Ltd.) was employed for the measurement of the solution density. An oscillator (HY-5, supplied by the Jintan Kexi Instrument Co., Ltd.) was employed for accelerating equilibration of the samples. A
Figure 1. X-ray diffraction photograph of the synthesized MgB4O7·9H2O. B
DOI: 10.1021/acs.jced.6b00926 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 2. Solubilities of Salts and Densities of Saturated Solution in the Quaternary System KCl−K2B4O7−K2SO4−H2O at 273 and 94.77 KPaa composition of the solution, 100·wb
density ρ
composition of dry salt, Jb, J(K2SO4+K2B4O7+KCl) = 100
no.
K2SO4
K2B4O7
KCl
K2SO4
K2B4O7
KCl
H2O
solid
(g·cm−3)
1,A 2 3 4 5 6 7 8,B 9 10 11 12 13 14 15 16,C 17 18 19 20 21 22 23,E
0.00 0.67 0.78 0.84 0.85 0.87 0.88 5.41 4.58 3.78 2.74 1.92 1.52 1.10 0.97 0.95 0.79 0.85 0.83 0.90 0.92 0.92 0.89
2.07 2.04 1.91 1.90 1.84 1.83 1.82 6.27 5.76 4.79 3.77 2.77 2.75 2.42 1.85 0.00 0.87 1.58 1.69 1.73 1.74 1.77 1.80
21.32 21.21 21.02 20.93 20.63 20.82 20.71 0.00 2.04 4.11 8.03 11.71 15.39 18.60 20.32 21.62 20.86 20.78 20.72 20.70 20.70 20.56 20.42
0.00 2.80 3.29 3.55 3.65 3.70 3.76 46.32 37.00 29.81 18.84 11.71 7.73 4.97 4.19 4.21 3.51 3.66 3.57 3.86 3.94 3.96 3.85
8.85 8.53 8.06 8.03 7.89 7.78 7.77 53.68 46.52 37.78 25.93 16.89 13.99 10.94 8.00 0.00 3.86 6.81 7.27 7.41 7.45 7.61 7.79
91.15 88.67 88.65 88.42 88.46 88.52 88.47 0.00 16.48 32.41 55.23 71.40 78.28 84.09 87.81 95.79 92.63 89.53 89.16 88.73 88.61 88.43 88.36
327.53 318.06 321.76 322.48 328.82 325.17 327.17 756.16 707.75 688.64 587.76 509.76 408.65 352.08 332.15 343.07 344.05 330.85 330.29 328.63 328.08 328.63 332.71
KB+KC KB+KC KB+KC KB+KC KB+KC KB+KC KB+KC KS+KB KS+KB KS+KB KS+KB KS+KB KS+KB KS+KB KS+KB KS+KC KS+KC KS+KC KS+KC KS+KC KS+KC KS+KC KS+KC+KB
1.166 1.162 1.163 1.164 1.163 1.160 1.159 1.064 1.083 1.092 1.100 1.119 1.125 1.140 1.157 1.159 1.159 1.159 1.159 1.156 1.160 1.158 1.159
a
Note: wb, mass fraction of component b in saturated solution. Jb, mass of component b in 100 g of dry salt. The experimental pressure is 94.77 KPa. Notation: KS, K2SO4; KB, K2B4O7·4H2O; KC, KCl. Standard uncertainties u are u(T) = 0.1 K, u(P) = 0.9 KPa, u(ρ) = 0.01 g·cm−3, u(w(KCl)) = 0.003, u(w(K2B4O7)) = 0.005, u(w(K2SO4)) = 0.005.
nitrate volumetric method (uncertainty of 0.3 mass %). Borate ion was determined using the mannitol volumetric method (uncertainty of 0.5 mass %). The concentration of sulfate was determined by barium chloride gravimetric method (uncertainty of 0.5 mass %). Each sample was measured three times in parallel, and ion concentrations of the sample are calculated using the average of three determinations.
3. RESULTS AND DISCUSSION 3.1. The Quaternary System KCl−K2B4O7−K2SO4−H2O at 273 K. Experimental solubilities of salts and densities of saturated solutions in the quaternary system KCl−K2B4O7− K2SO4−H2O at 273 K were listed in Table 2. According to the mass fraction of salts, the composition of dry salts noted as J(g/ 100g dry salt) was calculated. The phase diagram of the quaternary system KCl−K2B4O7−K2SO4−H2O at 273 K was plotted in Figure 2 based on the determined experimental data. Furthermore, a corresponding water content diagram was drawn in Figure 3. In Table 2 and Figure 2, the points A, B, and C are the invariant points of the ternary systems KCl−K2SO4− H2O, K2B4O7−K2SO4−H2O, and KCl−K2B4O7−H2O. As can be observed in Table 2 and Figure 2, neither double salt nor solid solution was produced at 273 K. The phase diagram consists of one invariant point, three solubility curves, and three crystalline areas. The area CEAD in Figure 2 represents the crystallization field of potassium chloride (KCl). Similarly, the area BEAG shows the crystallization field of potassium sulfate (K2SO4). And the area BECF stands for the crystallization field of potassium tetraborate tetrahydrate (K2B4O7·4H2O). The crystallization area of K2SO4 is largest, while the crystallization area of K2B4O7·4H2O is relatively small. The smallest area is the
Figure 2. Phase diagram of the quaternary system KCl−K2B4O7− K2SO4−H2O at 273 K.
crystallization area of KCl. It can be seen from the size of the crystallization area that the solubility of KCl is far greater than K2SO4. The salt KCl has salt-out effect on K2SO4 and K2B4O7. Therefore, the salt K2SO4 is more easily separated from the mixed solution which contains KCl, K2B4O7, and K2SO4 at 273 K. Curves AE, BE, and CE stand for three solubility curves. Point E is the invariant point for the system KCl−K2B4O7− K2SO4 at 273 K at w(K2SO4) = 0.89%, w(K2B4O7) = 1.80%, and w(KCl) = 20.42% where three salts KCl, K2SO4, and K2B4O7·4H2O reach saturation. In Figure 3, water content increases with the increasing J(K2B4O7) at the univariant curve C
DOI: 10.1021/acs.jced.6b00926 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Figure 5. Density of saturated solution composition diagram for the quaternary system KCl−K2B4O7−K2SO4−H2O at 273 K.
Figure 3. Water content diagram of the quaternary system KCl− K2B4O7−K2SO4−H2O at 273 K.
Table 3. Comparison of Invariant Points between the Quaternary System KCl−K2B4O7−K2SO4−H2O at 273 and 288 K12
BE and reaches maximum value at the point B, while there is no obvious change at the other univariant curves. Figure 4 is the X-ray diffraction photograph of the invariant point E. As can be seen from the Figure 4, three solid phases KCl, K2SO4, and K2B4O7·4H2O were found at point E. Figure 5 is the density vs composition diagram of potassium borate in the quaternary system KCl−K2B4O7−K2SO4−H2O at 273 K. According to Figure 5, the density decreases with the increasing J(K2B4O7) at the univariant curve BE. 3.2. Comparison of the Quaternary System KCl− K2B4O7−K2SO4−H2O at 273 and 288 K.12 The invariant points of the quaternary system KCl−K2B4O7−K2SO4−H2O at 273 and 288 K were listed in Table 3. As regard to this system, solubilities curves have the same tendency at two different temperatures. Moreover, the same solid phases can be formed at 273 and 288 K. The three salts KCl, K2SO4, and K2B4O7· 4H2O were determined at two temperatures. However, the size of the crystallization area is slightly different at 273 K compared with 288 K. The invariant point at 273 K is at w(KCl) = 20.42%, w(K2SO4) = 0.89% and w(K2B4O7) = 1.80%. While, the invariant point is shifted to w(KCl) = 22.32%, w(K2SO4) = 0.27% and w(K2B4O7) = 2.28% at 288 K. 3.3. The Quaternary System MgCl 2 −MgB 4 O 7 − MgSO4−H2O at 273 K. Experimental solubilities of salts and
composition of the invariant point (100·w(b)) T/K
invariant point
b = KCl
273 288
E E0
20.42 22.32
a
b = K2SO4 b = K2B4O7 0.89 0.27
1.80 2.28
solid phasea KS+KB+KC KS+KB+KC
Notation: KS, K2SO4; KB, K2B4O7·4H2O; KC, KCl.
densities of saturated solutions of the ternary system MgCl2− MgB4O7−MgSO4−H2O at 273 K were listed in Table 4. The phase diagram of the quaternary system MgCl2−MgB4O7− MgSO4−H2O at 273 derived from experimental data was drawn in Figure 6. At the same time, the water diagram of the quaternary system MgCl2−MgB4O7−MgSO4−H2O at 273 K was plotted in Figure 7. In Table 4 and Figure 6, the points A1, B1, and C1 are the invariant points of the ternary systems MgB4O7−MgSO4−H2O, MgCl2−MgSO4−H2O, and MgCl2− MgB4O7−H2O. It can be seen from Table 4 and Figure 6 that neither double salt nor solid solution was found at the investigated temperature. The phase diagram contains one invariant point, three univariant curves, and three crystalline areas. The three crystallization fields A1D1C1E1, A1E1B1G1, and
Figure 4. X-ray diffraction diagram of the invariant point E in the quaternary system KCl−K2B4O7−K2SO4−H2O at 273 K. D
DOI: 10.1021/acs.jced.6b00926 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 4. Solubilities of Salts and Densities of Saturated Solution in the Quaternary System MgCl2−MgB4O7−MgSO4−H2O at 273 and 94.77 KPaa composition of dry salt, Jb, J(MgSO4+MgB4O7+ MgCl2) = 100
composition of the solution, 100·wb
density ρ
no.
MgCl2
MgB4O7
MgSO4
MgCl2
MgB4O7
MgSO4
H2O
solid
(g·cm−3)
1,A1 2 3 4 5 6 7,E1 8,B1 9 10 11 12 13 14,C1 15 16 17 18 19 20
0.00 6.47 14.81 23.20 27.17 29.32 31.68 33.55 33.29 33.23 33.12 32.69 32.35 33.81 33.24 32.86 32.42 32.32 32.24 32.08
0.75 0.92 1.28 1.48 1.69 1.75 1.85 0.00 0.37 0.51 0.60 0.88 1.23 1.59 1.58 1.63 1.68 1.70 1.71 1.75
20.92 13.25 7.43 4.62 3.45 2.99 2.33 1.50 1.51 1.55 1.64 1.89 1.95 0.00 1.26 1.66 2.01 2.05 2.07 2.11
0.00 31.35 62.97 79.18 84.09 86.08 88.34 95.72 94.65 94.16 93.67 92.19 91.05 95.51 92.13 90.90 89.78 89.60 89.51 89.26
3.46 4.46 5.44 5.05 5.23 5.14 5.16 0.00 1.05 1.45 1.70 2.48 3.46 4.50 4.38 4.51 4.65 4.71 4.75 4.87
96.54 64.19 31.59 15.77 10.68 8.78 6.50 4.28 4.30 4.39 4.63 5.33 5.49 0.00 3.49 4.59 5.57 5.69 5.74 5.87
361.47 384.50 325.17 241.30 209.50 193.60 178.86 185.31 184.33 183.37 182.81 182.01 181.45 182.49 177.16 176.63 176.93 177.24 177.62 178.24
MB+MS MB+MS MB+MS MB+MS MB+MS MB+MS MB+MS+Bis Bis+MS Bis+MS Bis+MS Bis+MS Bis+MS Bis+MS Bis+MB Bis+MB Bis+MB Bis+MB Bis+MB Bis+MB Bis+MB
1.221 1.183 1.209 1.266 1.305 1.331 1.334 1.279 1.281 1.291 1.297 1.314 1.318 1.325 1.322 1.327 1.330 1.329 1.331 1.330
a
Notation: wb, mass fraction of component b in saturated solution; Jb, mass of component b in 100 g of dry salt. The experimental pressure is 94.77 KPa. Bis, MgCl2·6H2O; MB, MgB4O7·9H2O; MS, MgSO4·7H2O. Standard uncertainties u are u(T) = 0.1 K, u(P) = 0.9 KPa, u(ρ) = 0.01 g·cm−3, u(w(MgCl2)) = 0.003, u(w(MgB4O7)) = 0.005, u(w(MgSO4)) = 0.005.
Figure 6. Phase diagram of the quaternary system MgCl2−MgB4O7− MgSO4−H2O at 273 K. Figure 7. Water content diagram of the quaternary system MgCl2− MgB4O7−MgSO4−H2O at 273 K.
B1E1C1F1 correspond to potassium tetraborate tetrahydrate (MgB4O7·9H2O), magnesium sulfate heptahydrate (MgSO4· 7H2O), and magnesium chloride hexahydrate (MgCl2·6H2O), respectively. The crystallization area of MgB4O7·9H2O is relatively large, while the crystallization area of MgSO4·7H2O is relatively small. The salt MgCl2·6H2O has the smallest crystallization area. It can be seen from the size of the crystallization area that the salt MgB4O7·9H2O is less soluble than MgSO4·7H2O and MgCl2·6H2O. The salt MgCl2·6H2O has a salt-out effect on MgSO4·7H2O and MgB4O7·9H2O. Therefore, the salt MgB4O7·9H2O is more easily separated from the mixed solution. Curves A1E1, B1E1, and C1E1 represent three univariant curves. Point E1 is the invariant point for the system MgCl2−MgB4O7−MgSO4−H2O at 273 K. It saturates with salts MgB4O7·9H2O, MgSO4·7H2O, and MgCl2·6H2O and
at w(MgCl2) = 31.68%, w(MgB4O7) = 1.85%, w(MgSO4) = 2.33%. In Figure 7, water content increases slightly and then reduces obviously with the increasing J(MgCl2) at the univariant curve A1E1 and reaches minimum value at the point E1. However, it changes slightly at the other univariant curves. Figure 8 is the X-ray diffraction photograph of the eutectic point E1 where three salts MgB4O7·9H2O, MgSO4·7H2O, and MgCl2·6H2O reach saturation. Figure 9 is the density vs composition diagram of the magnesium chloride in the quaternary system MgCl2−MgB4O7−MgSO4−H2O at 273 K. According to Figure 9, the density decreases slightly and then increases with increasing w(MgCl2). At the invariant point E1, E
DOI: 10.1021/acs.jced.6b00926 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Figure 8. X-ray diffraction diagram of the invariant point E1 in the quaternary system MgCl2−MgB4O7−MgSO4−H2O at 273 K.
Table 5 that the different solid phases can be formed at 273 and 298 K. Three solid phases, MgB4O7·9H2O, MgSO4·7H2O, and MgCl2·6H2O, were determined at 273 K. However, because of the appearance of metastable and dehydration phenomena, in addition to MgB4O7·9H2O, MgSO4·7H2O, and MgCl2·6H2O, three more solid phases MgSO4·4H2O, MgSO4·5H2O, and MgSO4·6H2O can precipitate at 298 K. The phase diagram for the system MgCl2−MgB4O7−MgSO4−H2O at 273 K consists of one invariant point E1 whose composition is w(MgCl2) = 31.68%, w(MgSO4) = 2.33% and w(MgB4O7) = 1.85%. While, there are four invariant points for this system at 288 K. Point E2 is at w(MgCl2) = 27.36%, w(MgSO4) = 4.13% and w(MgB4O7) = 2.70%. Point E3 is at w(MgCl2) = 39.31%, w(MgSO4) = 4.14% and w(MgB4O7) = 3.51%. Similarly, the mass fraction of point E4 is w(MgCl2) = 32.40%, w(MgSO4) = 4.42% and w(MgB4O7) = 4.29%. Moreover, that for point E5 is w(MgCl2) = 32.05%, w(MgSO4) = 1.60% and w(MgB4O7) = 6.39%.
4. CONCLUSIONS Measurement of mineral solubilities in the two quaternary systems KCl−K2B4O7−K2SO4−H2O and MgCl2−MgB4O7− MgSO4−H2O were carried out at 273 K by the isothermal dissolution equilibrium method. On the basis of the experimental data, the phase diagrams of the two systems were drawn, as well as the density−composition diagrams. Gao et al. found that the existing form of borate in brine is mainly [B4O5(OH)4]2−.16 Because of such a complex structure, it is not only hard to form solid solution, but also difficult to generate a double salt with Cl−, CO32−, SO42− and cations.17 The results show that these two quaternary systems belong to the simple eutonic type, neither double salts nor solid solution are formed, and both systems contain one invariant point, three univariant curves, and three crystallization regions. The three crystallization regions of the first quaternary system at 273 K correspond to KCl, K2SO4, and K2B4O7·4H2O, and those in the second quaternary system are MgB4O7·9H2O, MgSO4·7H2O, and MgCl2·6H2O at 273 K.
Figure 9. Density of saturated solution composition diagram for the quaternary system MgCl2−MgB4O7−MgSO4−H2O at 273 K.
the density rises to a maximum value which is equal to 1.334 g· cm−3. 3.4. Comparison of the Ternary System MgCl2− MgB4O7−MgSO4−H2O at 273 and 298 K.13 The invariant points of the quaternary system MgCl2−MgB4O7−MgSO4− H2O at 273 and 298 K were listed in Table 5. It is seen from Table 5. Comparison of Invariant Points between the Quaternary System MgCl2−MgB4O7−MgSO4−H2O at 273 and 298 K13 composition of the invariant point (100·w(b)) T/K 273 298
invariant point
b= MgCl2
b= MgSO4
b= MgB4O7
solid phasea
E1 E2 E3 E4 E5
31.68 27.36 39.31 32.40 32.05
2.33 4.13 4.14 4.42 1.60
1.85 2.70 3.51 4.29 6.39
MB+MS+Bis M5+M6+MS M5+M4+MS Bis+M4+MS MB+MS+Bis
■
AUTHOR INFORMATION
Corresponding Author
*Tel: 13032845233. E-mail:
[email protected]. ORCID
Notation: Bis, MgCl2·6H2O; MB, MgB4O7·9H2O; MS, MgSO4· 7H2O; M6, MgSO4·6H2O; M5, MgSO4·5H2O; M4, MgSO4·4H2O.
a
Shi-Hua Sang: 0000-0002-5948-3882 F
DOI: 10.1021/acs.jced.6b00926 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Funding
This project was supported by the National Natural Science Foundation of China-Qaidam Saline Lake chemical engineering science research joint fund of Qinghai Provincial People’s Government (U1407108) and scientific research and innovation team in Universities of Sichuan Provincial Department of Education (15TD0009). Notes
The authors declare no competing financial interest.
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DOI: 10.1021/acs.jced.6b00926 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
