Article Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Solid−Liquid Equilibrium of the Quaternary System Lithium, Potassium, Rubidium, and Borate at T = 323 K Xudong Yu,†,‡ Ying Zeng,*,†,‡ Peijun Chen,† and Longgang Li† †
College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, P. R. China Collaborative Innovation Center of Panxi Strategic Mineral Resources Multi-Purpose Utilization, Chengdu University of Technology, Chengdu 610059, P. R. China
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‡
ABSTRACT: The solid−liquid equilibrium (SLE) of electrolyte mixtures Li+, K+, Rb+//borate−H2O at T = 323 K was studied by the isothermal dissolution method, and the X-ray diffraction method was used to confirm the solid-phase compositions. The analysis of phase diagram shows that the graph consists of one three-salt cosaturation invariant point and three regions of crystallization corresponding to single salts Li2B4O7·3H2O, K2B4O7·4H2O, and RbB5O8·4H2O, respectively. From the comparison of phase diagrams of system Li+, K+, Rb+// B4O72−−H2O between 323 and 348 K, we can conclude that (1) the crystalline form of salts lithium borate, potassium borate, and rubidium borate did not change at 323 and 348 K and (2) the salt Li2B4O7·3H2O crystalline area decreases and the other two salt crystalline areas, K2B4O7·4H2O and RbB5O8·4H2O, increase at 323 K.
1. INTRODUCTION There is plenty of underground brine containing potassium, sodium, magnesium, borate, and other high-value elements such as lithium, rubidium, and cesium in the Sichuan Basin of China.1,2 For the present, a phase-separation technique has been applied to the development and utilization of high-value elements from underground brine. The seven-component system Li−Na−K−Mg−Rb−Cl−B4O7−H2O can be used to describe the principal composition of the Sichuan basin underground brine. Through the study of the multitemperature solid−liquid equilibrium (SLE) of the above-mentioned complex system and its related subsystems, the crystalline forms and areas of salt can be obtained, which is of significance in guiding the utilization process route formulation of underground brine in the Sichuan Basin. The solid−liquid equilibrium of the borate-containing system is an important part of the seven-component system because it can form various forms of boron such as BO2−, B4O72−, and B5O8− that appear in the solution. Accordingly, the study of the solid−liquid equilibrium of the boratecontaining system is beneficial to the construction of the phase diagrams of the seven-component complex system. For the borate-containing system, some phase equilibrium research has been done, for example, systems Na+//BO2−, OH−−H2O at (263, 283, 298, 323) K;3,4 Na+//Br−, SO42−, B4O72−−H2O and Na+//Br−, B4O72−−H2O at 323 K;5 Li+//Cl−(SO42−), BO2−− H2O at 323 K;6 Li+, Na+, K+//CO32−, B4O72−−H2O at (288 and 298) K;7 Mg2+//Cl−(SO42−), B6O102−−H2O at 308 K;8 Li+ (Na+), Mg2+//B4O72−−H2O at 298 K;9 Li+, Na+, Mg2+// B4O72−−H2O at 273 K10 and some phase equilibria on the subsystems of Li+, K+, Rb+, Mg2+//Cl−, B4O72−−H2O studied by our research group.11−14 © XXXX American Chemical Society
As for the system studied in this article, the corresponding phase diagram at 348 K has been completed by Yan,15 while the solid−liquid equilibrium (SLE) of system Li+, K+, Rb+// borate−H2O at 323 K has not been carried out. Consequently, on the basis of the results of ternary subsystems,16 the phase equilibrium of system Li+, K+, Rb+//borate−H2O at T = 323 K is reported in detail.
2. EXPERIMENTAL SECTION 2.1. Reagents and Apparatus. Doubly deionized water (DDW) with κ < 1 × 10−4 S·m−1 was used for sample preparation and dilution in the solubility experiments. Detailed information on the chemicals used in the experiment is shown in Table 1. The HSY-A-type thermostat oscillator (Changzhou Zhongbei Instrument Co., Ltd., China) was used in the solubility experiments. The WYA-type Abbe refractometer (Shanghai INESA Scientific Instrument Co., Ltd., China) with a precision of ±0.0001 at the 95% confidence level was used in determining the refractive index (nD). The weight of the sample was determined by a BSA124S-type standard analytical balance (Sartorius). The pycnometry method with a precision of ±0.0002 g·cm−3 at the 95% confidence level was used for the determination of the density. The concentrations of Rb+ and Li+ were determined with the 5300 V-type ICP-OES (PerkinElmer). The composition of the solid phase of the invariant point was determined with DX-2700-type X-ray Received: May 12, 2018 Accepted: July 11, 2018
A
DOI: 10.1021/acs.jced.8b00391 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 1. Solubility and Analytical Experimental Reagents initial purity (w/w %)
purification method
lithium tetraborate (Li2B4O7)
99.0
recrystallization
potassium tetraborate (K2B4O7·5H2O) boric acid (H3BO3)
99.0 99.0
rubidium carbonate (Rb2CO3)
99.8
rubidium pentaborate (RbB5O6(OH)4·2H2O)
99.0
chemical name
recrystallization
recrystallization
final purity (w/w %)
source Chengdu Kelong Chemical Reagent Plant, China Sinopharm Chemical Reagent Co., Ltd., China Sinopharm Chemical Reagent Co., Ltd., China Jiangxi Dongpeng new materials Co., Ltd., China synthesized in the laboratory21
99.5 99.0 99.8 99.8 99.8
analytical method17 alkalimetry in the presence of mannitol for boron alkalimetry in the presence of mannitol for boron alkalimetry in the presence of mannitol acid−base titration for CO32− alkalimetry in the presence of mannitol for boron
Table 2. Solid−Liquid Equilibrium and Physicochemical Properties of the Quaternary System Li+, K+, Rb+//B4O72−−H2O at 323 K and Pressure p = 0.1 MPaa Jänecke index of dry salt (g/100 g of salt) equilibrium solutions composition, w(B) × 10 no.
density/ (g·cm−3)
refractive index/nD
1, A 2 3 4 5 6, E 7, B 8 9, E 10, C 11 12 13 14 15 16 17 18 19 20 21 22 23, E
1.3661 1.3965 1.4353 1.4394 1.4436 1.4471 1.4235 1.4393 1.4471 1.1415 1.1571 1.1653 1.1691 1.1833 1.2069 1.2495 1.2635 1.2647 1.2855 1.3122 1.3463 1.4025 1.4471
1.3846 1.3882 1.3902 1.3938 1.3951 1.3969 1.3874 1.3938 1.3969 1.3472 1.3480 1.3490 1.3510 1.3547 1.3575 1.3632 1.3665 1.3685 1.3734 1.3769 1.3816 1.3907 1.3969
w(Li2B4O7) w(K2B4O7) w(RbB5O8) 4.62 4.02 3.85 3.80 3.48 3.23 0.00 1.72 3.23 3.61 3.22 3.18 3.30 3.28 3.14 3.35 3.16 2.90 3.13 3.34 3.03 3.68 3.23
27.29 26.92 25.98 25.97 26.42 25.28 25.14 25.20 25.28 0.00 1.02 1.49 2.45 3.75 6.98 10.55 12.70 13.52 17.27 18.23 19.22 23.89 25.28
0.00 2.38 4.78 7.02 9.34 11.21 12.69 11.93 11.21 7.32 6.88 6.99 7.47 7.55 7.24 7.70 7.06 7.41 7.47 7.98 8.19 10.09 11.21
2
J(K2B4O7) + J(Li2B4O7) + J(RbB5O8) = 100
w(H2O) J(Li2B4O7) J(K2B4O7) J(RbB5O8) 68.09 66.68 65.39 63.21 60.76 60.28 62.17 61.15 60.28 89.07 88.88 88.34 86.78 85.42 82.64 78.40 77.08 76.17 72.13 70.45 69.56 62.34 60.28
14.48 12.06 11.13 10.33 8.87 8.13 0.00 4.43 8.13 33.03 28.97 27.27 24.97 22.50 18.09 15.51 13.79 12.17 11.23 11.30 9.96 9.77 8.13
85.52 80.79 75.07 70.58 67.33 63.65 66.46 64.86 63.65 0.00 9.18 12.78 18.54 25.72 40.21 48.85 55.42 56.73 61.97 61.70 63.14 63.43 63.65
0.00 7.15 13.80 19.09 23.80 28.22 33.54 30.71 28.22 66.97 61.85 59.95 56.49 51.78 41.70 35.64 30.79 31.10 26.80 27.00 26.90 26.80 28.22
J(H2O)
equilibrium solid phase
213.38 200.12 188.97 171.78 154.85 151.77 164.37 157.39 151.77 814.94 799.56 757.53 656.58 585.90 476.12 363.02 336.36 319.64 258.84 238.45 228.52 165.51 151.77
LiB + KB LiB + KB LiB + KB LiB + KB LiB + KB LiB + KB + RB KB + RB KB + RB LiB + KB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + RB LiB + KB + RB
a Note: Standard uncertainties u are u(T) = 0.20 K; ur(p) = 0.05; u(ρ) = 2.0 × 10−4 g·cm−3; u(nD) = 1.0 × 10−4; ur(Li2B4O7) = 0.0030; ur(K2B4O7) = 0.0050; ur(RbB5O8) = 0.0050; LiB-Li2B4O7·3H2O, RB-RbB5O8·4H2O, KB-K2B4O7·4H2O.
Li+: ICP-OES, standard uncertainty ±0.5% at the 95% confidence level.18 Rb+: ICP-OES, standard uncertainty ±0.5% at the 95% confidence level.19 K+: calculated by the subtraction method.
powder diffraction (Dandong Fangyuan Instrument Co., Ltd., China). 2.2. Experimental Procedure. A series of samples with different amounts of Li2B4O7, K2B4O7·5H2O, RbB5O8·4H2O, and H2O were put into 100 mL tightly sealed bottles and immersed in the HSY-A-type thermostat oscillator at 120 rpm and at (323 ± 0.2) K. After equilibration, the stirring was stopped, and afterward it was kept static for at least 24 h. A certain amount of clear solution was transferred into a 250 mL volumetric flask, diluted with doubly deionized water to volume, and mixed. It was then used for chemical or instrumentational analysis; the corresponding density and refractive index were measured. The solid phases were separated, dried at 323 K, and then ground into powder, which was used for the X-ray powder diffraction determination. 2.3. Analytical Methods. Borate: neutralization titration, standard uncertainty ±0.3% at the 95% confidence level.17
3. RESULTS AND DISCUSSION The experimental data for the solubility, refractive index (nD), and density (ρ) for the system Li+, K+, Rb+//borate−H2O at 323 K are given in Table 2. The composition of B (Li2B4O7, K2B4O7, RbB5O8, or H2O) in Table 2 is expressed by the Jänecke index J(B)(g/100 g of salt) and mass fraction w(B). Calculation formulas of the Jänecke index (eqs 1−5) are as follows: Letting ws = w(Li 2B4 O7 ) + w(K 2B4 O7 ) + w(RbB5O8) (1) B
DOI: 10.1021/acs.jced.8b00391 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Figure 1. Stable phase diagram of the quaternary system Li+, K+, Rb+//borate−H2O at 323 K.
Figure 2. X-ray diffraction pattern of invariant point E (Li2B4O7·3H2O, K2B4O5(OH)4·2H2O, and RbB5O6(OH)4·2H2O).
J(Li 2B4 O7 ) =
w(Li 2B4 O7 ) × 100 ws
(2)
J(K 2B4 O7 ) =
w(K 2B4 O7 ) × 100 ws
(3)
J(RbB5O8) =
w(RbB5O8) × 100 ws
(4)
J(H 2O) =
w(H 2O) × 100 ws
The phase diagram of Li+, K+, Rb+//borate−H2O at 323 K is presented as a right triangle in Figure 1 by using the values of J(K2B4O7) and J(Li2B4O7) as the abscissa and ordinate, respectively; the three vertices of the right triangle corresponded to the three pure compounds, and the three points on the triangle’s edge represented the composition of the three ternary subsystems. The phase diagram as shown in Figure 1 consists of one three-salt cosaturation invariant point, three isothermal dissolution curves, and three crystalline regions corresponding to lithium teraborate trihydrate (Li2B4O7·3H2O), potassium teraborate tetrahydrate (K2B4O7· 4H2O), and rubidium pentaborate tetrahydrate (RbB5O8· 4H2O). Among the three crystalline regions, K2B4O7·4H2O has
(5) C
DOI: 10.1021/acs.jced.8b00391 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Figure 5. Refractive index vs composition diagram for the quaternary system Li+, K+, Rb+//borate−H2O at 323 K.
Figure 3. Water-content diagram of the quaternary system Li+, K+, Rb+//borate−H2O at 323 K.
convenient description of the concentration of boron in solution. The composition of the solid phase in point E was analyzed by the X-ray diffraction method and the XRD pattern given in Figure 2. The identification is performed by a comparison of the diffraction pattern to databases showing that salts Li2B4O7·3H2O (PDF no. 50-0564), K2B4O7·4H2O (PDF no. 29-0987), and RbB5O8·4H2O (PDF no. 43-0415) coexist in invariant point E. The liquid composition of point E is w(Li2B4O7) = 3.23%, w(K2B4O7) = 25.28%, w(RbB5O8) = 11.21%, and w(H2O) = 60.28%. The comparison of the phase diagrams of system Li+, K+, Rb+//borate−H2O between 323 and 348 K15 shows that (1) the system at 323 and 348 K is simple, and the phase diagram is composed of one three-salt cosaturation invariant point, three isothermal dissolution curves, and three crystalline regions; (2) the crystalline forms have not changed with temperature, and the crystalline region of Li2B4O7·3H2O decreased, while the crystalline regions of the other two salts, K2B4O7·4H2O and RbB5O8·4H2O, enlarged at 323 K. Thus, pure salts K2B4O7·4H2O and RbB5O8·4H2O can be more easily obtained at high temperature. Figures 3−5 were constructed with J(K2B4O7) as the abscissa and J(H2O), the density, or the refractive index of the sample as the ordinate. As Figure 3 shows, the water content decreases on the CE curve (with the coexistence of RbB5O8·4H2O and Li2B4O7·3H2O) with J(K2B4O7) incrementally until it reaches the smallest value at point E; however, there are no obvious changes on the AE (with the coexistence of K2B4O7·4H2O and Li2B4O7·3H2O) and BE (cosaturation of K2B4O7·4H2O and RbB5O8·4H2O) curves. The solubility of K2B4O7 is largest in this system, thus the concentration of K2B4O7 in solution is the major influencing factor of the values of density and refractive index, which can be proven from Figures 4 and 5. The values of density (ρ) and refractive index (nD) increase with J(K2B4O7) incrementally until they reach the maximum values at point E.
Figure 4. Density vs composition diagram for the quaternary system Li+, K+, Rb+//borate−H2O at 323 K.
the smallest crystal area, which indicates that it has the highest solubility in this system, while Li2B4O7·3H2O has the greatest crystal area, which shows that the solubility of Li2B4O7 in this system is minimized and that it can be precipitated more easily than can the other two salts. Detailed information about the cosaturated salts for isothermal dissolution curves AE, BE, and CE is listed below. AE: K 2B4 O7 ·4H 2O + Li 2B4 O7 ·3H 2O
(6)
BE: K 2B4 O7 · 4H 2O + RbB5O8 ·4H 2O
(7)
CE: Li 2B4 O7 · 3H 2O + RbB5O8 · 4H 2O
(8)
Multiple forms of boron ions exist in solution, likely BO2−, B5O8−, and B4O72−,20 thus they can be precipitated as different crystalloid forms. Accordingly, B4O72− was chosen for a more D
DOI: 10.1021/acs.jced.8b00391 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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(10) Yang, L.; He, X. F.; Gao, Y. Y.; Cui, R. Z.; Sang, S. H. Studies on phase equilibria in the quaternary systems LiCl - KCl - MgCl2 H2O and Li2B4O7 - Na2B4O7 - MgB4O7 - H2O at 273 K. J. Chem. Eng. Data 2018, 63, 1206−1211. (11) Duan, X.; Zeng, Y.; Luo, J.; Tao, Y.; Yu, X. D. Stable phase equilibrium of aqueous quaternary system Li+, Rb+, Mg2+ // Borate H2O at 298.2 K. J. Chem. Eng. Jpn. 2017, 50, 470−475. (12) Guo, S. S.; Yu, X. D.; Zeng, Y. Phase equilibria for the aqueous reciprocal quaternary system K+, Mg2+ // Cl−, Borate - H2O at 298 K. J. Chem. Eng. Data 2016, 61, 1566−1572. (13) Yu, X. D.; Luo, Y. L.; Wu, L. T.; Cheng, X. L.; Zeng, Y. Solidliquid equilibrium on the reciprocal aqueous quaternary system Li+, Mg2+ // Cl−, and Borate - H2O at 323 K. J. Chem. Eng. Data 2016, 61, 3311−3316. (14) Yu, X. D.; Zeng, Y.; Guo, S. S.; Zhang, Y. J. Stable phase equilibrium and phase diagram of the quinary system Li+, K+, Rb+, Mg2+ // Borate - H2O at T = 348.15 K. J. Chem. Eng. Data 2016, 61, 1246−1253. (15) Yan, F. P.; Yu, X. D.; Yin, Q. H.; Zhang, Y. J.; Zeng, Y. The solubilities and physicochemical properties of the aqueous quaternary system Li+, K+, Rb+ // Borate - H2O at 348 K. J. Chem. Eng. Data 2014, 59, 110−115. (16) Feng, S.; Yu, X. D.; Cheng, X. L.; Zeng, Y. Phase diagrams and physicochemical properties of Li+, K+(Rb+) // Borate - H2O systems at 323 K. Russ. J. Phys. Chem. A 2017, 91, 2149−2156. (17) Institute of Qinghai Salt Lakes, Chinese Academy of Sciences. Analytical Methods of Brines and Salts, 2nd ed; Chines Science Press: Beijing, 1988. (18) Yuan, H. Z.; Zhu, Y. J.; Wu, L. P.; Zhang, X. Determination of High-Content of Lithium in Natural Saturated Brines by Inductively Coupled Plasma-Atomic Emission Spectrometry. Rock Miner. Anal. 2011, 30, 87−89. (19) Shang, C. S.; An, L. Y.; Hu, Z. W. ICP-OES Determination of Rubidium in Bitter. Chem. Res. Appl. 2012, 24, 642−645. (20) Li, J.; Gao, S. Y. Chemistry of Borates. J. Salt Lake Science 1993, 1, 62−66. (21) Zeng, Y.; Yu, X. D.; Liu, L. L.; Yin, Q. H. Method for Preparation Rubidium Pentaborate Tetrahydrate. CN 103172078A, 2013.
4. CONCLUSIONS The experimental values of solubility, refractive index (nD), and density (ρ) of the system Li+, K+, Rb+//borate−H2O at T = 323 K were measured. The system belongs to a simple cosaturation type without the formation of a double salt or solid solution, and there are three solid-phase crystalline regions corresponding to pure salts Li2B4O7·3H2O, K2B4O7· 4H2O, and RbB5O8·4H2O. The analysis of the phase diagram of Li+, K+, Rb+//borate− H2O at 323 and 348 K shows that the crystalline forms have not changed with temperature; the crystalline region of Li2B4O7·3H2O decreased, while the crystalline regions of the other two salts, K2B4O7·4H2O, and RbB5O8·4H2O, enlarged at 323 K. On curve CE, the water content decreases while the values of density and refractive index increase with J(K2B4O7) incrementally.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected];
[email protected]. ORCID
Xudong Yu: 0000-0002-3848-9484 Peijun Chen: 0000-0001-6067-6502 Funding
This work is funded by the NSFC (U1507111, U1607121, and 41473059), the Science & Technology Department of Sichuan Province (2017JY0191), and the Sichuan Provincial Education Department (16ZA0083). Notes
The authors declare no competing financial interest.
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REFERENCES
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DOI: 10.1021/acs.jced.8b00391 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
