Solubilities, Densities and Refractive Indices in the Aqueous

Dec 23, 2016 - College of Chemistry and Materials Science, Northwest University, Xi'an ... K and 0.1 MPa were determined with isothermal dissolution m...
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Solubilities, Densities and Refractive Indices in the Aqueous Quaternary System of Lithium Sulfate, Lithium Metaborate, and Lithium Carbonate at 288.15, 298.15, 308.15 K and 0.1 MPa Yafei Guo,†,‡ Long Li,† Lina Cao,† Xiaoping Yu,†,‡ Shiqiang Wang,† and Tianlong Deng*,† †

Tianjin Key Laboratory of Marine Resources and Chemistry, College of Chemical Engineering and Materials Science, Tianjin University of Science and Technology, Tianjin, 300457, People’s Republic of China ‡ College of Chemistry and Materials Science, Northwest University, Xi’an 710127, People’s Republic of China ABSTRACT: Solubilities, densities and refractive indices of the aqueous quaternary system of lithium sulfate, lithium metaborate, and lithium carbonate at 288.15, 298.15, 308.15 K and 0.1 MPa were determined with isothermal dissolution method. According to the experimental results, the dry-salt phase diagrams, water-phase diagrams, and the diagrams of physicochemical properties including density, pH, and refractive index versus composition of lithium sulfate at three temperatures were plotted. In the dry-salt phase diagrams at three temperatures, there are four crystallization regions corresponding to lithium metaborate octahydrate (LiBO2· 8H2O, LB), lithium carbonate (Li2CO3, LC), and lithium sulfate monohydrate (Li2SO4·H2O, LS), and three univariant-solubility curves corresponding to minerals of LS, LB, and LC, and one invariant point of three coexisted minerals (LS + LB + LC). A comparison of the phase diagrams at 288.15, 298.15, and 308.15 K shows that the areas of lithium sulfate monohydrate and lithium metaborate octahydrate are decreased obviously and the area of lithium carbonate region is increased significantly with the increase of temperature from 288.15 to 308.15 K. Physicochemical properties of density and refractive index in the quaternary system change regularly with the increase of temperature and the dry-salt composition of Li2SO4 (g/100 g·S) in the solution. With the increase of Li2SO4 (g/100 g·S) in the solution, density and refractive index are increased first to reach the maximum values at the invariant points of three coexisted minerals and then decreased sharply. The calculated values of densities and refractive indices in the quaternary system at three temperatures with the empirical equations are in good agreement with the experimental values.

1. INTRODUCTION The demand of metallic lithium and its compounds has increased significantly with the development of the chemical industry and modern green energy. Because of the high cost for lithium recovery from solid ores, it is essential to recover lithium resource from the liquid salt lake brines around the world.1−3 Salt lakes distributed in western China are famous for their high concentrations of lithium, sulfate, carbonate, and boron resources. The composition of those salt lake brines belongs to the complex salt−water system (Na+ + K+ + Li+ + Mg2+ + Cl− + SO42− + CO32− + borate + H2O).4 In order to effectively separate lithium metaborate-containing mixture salts, some containing lithium and metaborate ternary systems (LiCl + LiBO2 + H2O) at 288.15, 298.15, and 308.15 K, (LiBO2 + Li2CO3 + H2O) at 288.15 and 298.15 K, (LiBO2 + CaB2O4 + H2O) at 288.15 and 298.15 K, (Li2SO4 + LiBO2 + H2O) at 288.15 and 298.15 K, and the quaternary system (LiCl + LiBO2 + Li2SO4 + H2O) at 298.15 K had been investigated previously.5−10 However, the phase equilibrium of the salt−water system (Li2SO4 + LiBO2 + Li2CO3 + H2O) is not reported in the literature, and it is valuable for the separation of lithiumcontaining mixture salts in the salt lake deposits. In this paper, the solubilities, densities, and refractive indices of the quaternary © XXXX American Chemical Society

system (Li2SO4 + LiBO2 + Li2CO3 + H2O) at 288.15, 298.15, and 308.15 K were presented for the first time.

2. EXPERIMENTAL SECTION Reagents and Apparatus. The chemicals recrystallized before use are shown in Table 1. Doubly deionized water Table 1. Chemicals Used code

grade

initial puritya

purified method

final puritya

LBb

A.R.e

0.99

recrystallization

0.995

LSc

A.R.e

0.99

recrystallization

0.998

LCd

A.R.e

0.99

recrystallization

0.998

analytical method gravimetric method for BO2− gravimetric method for SO42− titration for CO32−

Purity in mass fraction. LB, lithium metaborate octahydrate, LiBO2· 8H2O. cLS, lithium sulfate monohydrate monohydrate, Li2SO4·H2O. d LC, lithium carbonate anhydrous, Li2CO3. eA.R., either from the Sinopharm Chemical Reagent Co. Ltd. or Tianjin Chemical Reagent Manufactory. a

b

Received: September 4, 2016 Accepted: December 12, 2016

A

DOI: 10.1021/acs.jced.6b00777 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

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Table 2. Solubilities of the Quaternary System (LiBO2 + Li2SO4 + Li2CO3 + H2O) at 288.15, 298.15, 308.15 K and 0.1 MPaa composition of liquid phase 100wb no. 288.15 K 1, Ad 2, Be 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20, E 21 22, C 298.15 K 1, A′d,e 2, B′e 3 4 5 6 7 8 9 10 11 12 13 14, E′ 15 16 17 18 19, C′ 308.15 K 1, A″ 2, B″ 3 4 5 6 7 8 9 10 11 12 13 14 15

composition of dry salt phase J (g/100 g dry salt)

LiBO2

Li2SO4

Li2CO3

LiBO2

Li2SO4

Li2CO3

H2O

equilibrium solid phasec

0.88 1.61 1.40 1.32 1.33 1.23 1.27 1.30 1.22 1.16 1.02 1.06 0.97 0.90 0.90 0.92 0.91 0.91 0.87 1.05 0.65 0.00

24.56 0.00 0.28 0.48 0.74 1.15 1.52 1.90 2.23 2.43 3.98 4.92 7.37 10.08 12.09 14.92 16.36 18.53 20.59 25.83 25.89 25.94

0.00 0.92 0.83 0.81 0.76 0.68 0.63 0.61 0.53 0.50 0.31 0.35 0.42 0.35 0.36 0.47 0.58 0.53 0.56 0.67 0.78 0.80

3.46 63.64 55.90 50.49 46.92 40.18 37.26 34.03 30.62 28.31 19.14 16.75 11.09 7.99 6.76 5.62 5.09 4.55 3.94 3.80 2.38 0.00

96.54 0.00 11.04 18.53 26.17 37.51 44.40 49.92 56.08 59.38 75.00 77.76 84.09 88.94 90.53 91.47 91.66 92.78 93.52 93.77 94.76 97.01

0.00 36.36 33.05 30.98 26.91 22.32 18.35 16.05 13.30 12.31 5.86 5.49 4.82 3.08 2.71 2.91 3.25 2.67 2.54 2.43 2.86 2.99

293.08 3852.57 3896.58 3734.46 3440.24 3159.68 2822.69 2524.57 2417.02 2339.26 1784.30 1479.79 1041.71 782.65 648.68 513.24 460.21 400.64 354.29 263.05 266.04 273.97

LB + LS LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB + LS LC + LS LC + LS

2.34 3.89 3.14 3.25 3.27 3.14 3.10 2.83 2.15 2.47 1.85 1.63 2.09 3.31 2.28 1.68 1.08 0.50 0.00

24.42 0.00 0.57 0.66 1.05 1.51 1.99 2.63 3.08 4.07 5.12 6.40 13.27 24.38 24.71 24.93 25.31 25.45 25.79

0.00 0.40 0.26 0.29 0.26 0.25 0.19 0.17 0.17 0.14 0.09 0.17 0.27 0.41 0.47 0.57 0.48 0.46 0.73

8.74 90.68 79.08 77.40 71.46 64.08 58.68 50.24 39.85 36.96 26.22 19.89 13.40 11.79 8.29 6.17 4.01 1.89 0.00

91.26 0.00 14.24 15.80 22.87 30.76 37.74 46.67 56.97 60.92 72.44 78.01 84.87 86.76 89.98 91.73 94.19 96.37 97.25

0.00 9.32 6.68 6.80 5.66 5.17 3.58 3.09 3.18 2.12 1.34 2.09 1.74 1.45 1.73 2.09 1.80 1.75 2.75

273.69 2231.00 2420.74 2284.04 2082.93 1939.09 1793.98 1673.27 1752.42 1396.58 1315.34 1118.12 539.50 255.82 264.11 267.91 272.12 278.68 277.09

LB + LS LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB + LS LC + LS LC + LS LC + LS LC + LS LC + LS

3.48 5.95 5.01 4.99 5.13 4.72 4.92 4.45 4.90 4.88 4.23 4.59 4.41 4.31 3.93

24.23 0.00 0.99 1.20 2.72 4.68 5.68 6.15 7.07 9.39 9.89 12.50 14.20 16.04 19.40

0.00 0.112 0.108 0.109 0.130 0.134 0.140 0.129 0.132 0.143 0.110 0.106 0.096 0.091 0.096

12.55 98.15 81.99 79.26 64.26 49.48 45.83 41.46 40.50 33.84 29.72 26.70 23.57 21.09 16.77

87.45 0.00 16.24 19.01 34.10 49.11 52.87 57.34 58.41 65.17 69.51 72.68 75.92 78.47 82.82

0.00 1.85 1.77 1.73 1.63 1.41 1.30 1.20 1.09 0.99 0.77 0.62 0.51 0.45 0.41

260.92 1548.67 1535.61 1487.07 1153.51 949.39 831.05 832.34 725.72 593.66 602.90 481.45 434.72 389.05 327.00

LB + LS LC + LB LC + LB LC + LB LC + LB LC+LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB LC + LB

B

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Table 2. continued composition of liquid phase 100wb no. 308.15 K 16 17 18, E″ 19 20 21, C″

composition of dry salt phase J (g/100 g dry salt)

LiBO2

Li2SO4

Li2CO3

LiBO2

Li2SO4

Li2CO3

H2O

3.72 3.45 3.43 2.35 1.24 0.00

22.45 24.08 24.12 24.45 24.99 25.04

0.096 0.078 0.044 0.069 0.062 0.074

14.16 12.50 12.43 8.76 4.72 0.00

85.47 87.22 87.41 90.98 95.04 99.70

0.37 0.28 0.16 0.26 0.24 0.30

280.73 262.20 262.44 272.14 280.32 298.20

equilibrium solid phasec LC LC LC LC LC LC

+ + + + + +

LB LB LB + LS LS LS LS

a

Standard uncertainties for u(T) = 0.1 K and u(p) = 0.005 MPa. u(w) for LiBO2, Li2CO3 and Li2SO4 are 0.00058, 0.0036, and 0.00057 in mass fraction, respectively. bw, mass fraction. cLC, Li2CO3; LB, LiBO2·8H2O; LS, Li2SO4·H2O. dReference 9. eReference 7. fReference 10.

Figure 1. Phase diagram of the quaternary system (Li2SO4+ LiBO2+ Li2CO3 + H2O) at 288.15 K. Δ, liquid phase; , stable isotherm curve. J (Li2CO3), Janecke index of Li2CO3 in 100 g dry salt of (Li2SO4 + LiBO2 + Li2CO3); J (H2O), Janecke index of H2O with the unit of H2O g in 100 g of dry salt of (Li2SO4 + LiBO2 + Li2CO3). (a) Dry-salt phase diagram; (b) water-phase diagram.

Figure 2. Phase diagram of the quaternary system (Li2SO4+ LiBO2+ Li2CO3 + H2O) at 298.15K. ●, experimental point; , stable isotherm curve. J (Li2CO3), J (LiBO2), J (Li2SO4), and J (H2O) expressed Janecke index of Li2CO3, LiBO2, Li2SO4, and H2O, respectively, in 100 g of dry salt of (Li2SO4 + LiBO2 + Li2CO3). (a) Dry-salt phase diagram; (b) water-phase diagram.

(DDW, pH = 6.60 and the conductivity = 1 × 10−4 S·m−1 at 298.15 K) was used. The precision electronic balance (0.01 mg, Mettler Toledo, New Classic M, Switzerland) with an uncertainty of 0.2 mg was used for weighing. Magnetic stirring thermostatic water bath (HXC-500-6A, Beijing Fortune Joy Science Technology Co. Ltd., China) was used, and the temperature precision was controlled within ±0.1 K. Density was measured using DMA 4500 M high precision of vibrating-tube densimeter (Anton Paar, Austria). The densimeter was calibrated with dry air and freshly deionized

distilled degassed water at 293.15 K and atmospheric pressure, and the densities of deionized distilled degassed water were in good agreement with the literature with the uncertainty within ±0.5 mg·cm−3 at 95% confidence level (k = 2).11 Refractive indices were measured by an Abbe refractometer (WAY-2S, Shanghai Yuguang Instrument Co. Ltd., China), which was connected with a thermostatic water-circulator bath (high-precision thermoregulation, cc-k12, German Huber Company, Germany) C

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to control the measured temperature. The standard uncertainty of Abbe refractometer, which was calibrated using double distilled water, was 1.3330 at 293.15 K and atmospheric pressure was ±0.001 (0.68 level of confidence). All physicochemical parameters of the aqueous solution in this study were measured in triplicate. Experimental Method. The isothermal dissolution equilibrium method was adopted, which was described by Deng et al.12,13 Generally, the synthetic series of brines for the ternary system were mixed by adding different ratios of the crystallized solid salts of lithium sulfate and lithium metaborate octahydrate in a series of sealed hard polyethylene bottles, and then the bottles were put into the magnetic stirring thermostatic water bath at a stationary temperature of either 288.15 ± 0.1, 298.15 ± 0.1, or 308.15 ± 0.1 K with 120 r/min stirring speed to accelerate the solubility equilibrium. After about one month, the supernatants of the liquid phases in each bottle were taken out at intervals for chemical analysis. During the course of analysis (each interval), the bottle was capped tightly and still kept in the magnetic stirring thermostatic water without stirring to ensure the composition of quaternary system maintained. When the content of each component in liquid phase did not change, those results demonstrated that the phase equilibrium in each bottle was achieved. After the synthetic brines reached equilibria, a series of liquid phase and solid phase samples were taken out for chemical analysis, and each solid phase sample was identified immediately with the BX51-type polarizing microscope (Olympus, Japan) and further identification with X-ray diffractometer (MSAL XD-3, Beijing Purkinje General Instrument Co. Ltd., China). Analytical Methods. The composition of the SO42− in liquids was analyzed by gravimetric methods of barium chloride with the standard uncertainty u(SO42−) = 0.0005 in mass fraction.14 The BO2− concentration was analyzed using gravimetric method with sodium hydroxide standard solution after carbonate in solution evicting in the presence of mixture indicators of methyl red plus phenolphthalein and the excessive mannitol conditions, and the standard uncertainty u(BO2−) was 0.0005

Figure 3. Phase diagram of the quaternary system (Li2SO4+ LiBO2+ Li2CO3 + H2O) at 308.15 K. ○, experimental point; , isotherm curve. J (Li2CO3), J (LiBO2), J (Li2SO4), and J (H2O) expressed Janecke index of Li2CO3, LiBO2, Li2SO4, and H2O, respectively, in 100 g of dry salt of (Li2SO4 + LiBO2 + Li2CO3). (a) Dry-salt phase diagram; (b) water-phase diagram.

Figure 4. X-ray diffractive diagram of the cosaturated solid phase (LiBO2·8H2O + Li2SO4·H2O + Li2CO3) in the invariant points E, E′, and E″. D

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in mass fraction.14 The CO32− concentration in liquids was obtained after neutralization titration and deducting the concentration of metaborate with the standard uncertainty u(CO32−) = 0.003 in mass fraction.14 The lithium ion concentration was calculated through ion balance and evaluated occasionally using inductively coupled plasma optical emission spectrometry (Prodigy, Leman Corporation, America). Then, the compositions of LiBO2, Li2CO3, and Li2SO4 in mass fraction were calculated corresponding to the analytical results of the BO2−, CO32−, and SO42− concentrations in the liquid phase, and the standard uncertainties u(w) for LiBO2, Li2CO3, and Li2SO4 were 0.00058, 0.0036, and 0.00057 in mass fraction, respectively.

3. RESULTS AND DISCUSSION Dry-Salt Diagrams and Water-Phase Diagrams at Three Temperatures. The experimental results on solubilities of the quaternary system (Li2SO4 + LiBO2 + Li2CO3 + H2O) at 288.15, 298.15, 308.15 K and 0.1 MPa are presented in Table 2. The composition of the liquid phase expressed in mass fraction in the quaternary system in Table 2 was converted into a dry basis composition, that is, J g/100 g dry salt of (Li2SO4 + LiBO2 + Li2CO3). According to the dry basis composition data in Table 2, the dry-salt phase diagrams and water-phase diagrams of the quaternary system at 288.15, 298.15, and 308.15 K are plotted in Figures 1−3, respectively.

Figure 6. Physicochemical properties versus composition of the quaternary system (Li2SO4 + LiBO2 + Li2CO3 + H2O) at 288.15 K. −Δ−, 288.15 K; −●−, 298.15 K; −○−, 308.15 K. J(Li2SO4), Janecke index of Li2SO4 in 100 g of dry salt of (Li2SO4 + LiBO2 + Li2CO3). (a) Density versus composition; (b) refractive index versus composition.

From dry-salt diagrams in Figures 1a−3a, there are three crystallization regions corresponding to lithium metaborate octahydrate (LiBO2·8H2O), lithium carbonate (Li2CO3), and lithium sulfate monohydrate (Li2SO4·H2O), three univariant solubility isotherm curves at 288.15, 298.15, and 308.15 K corresponding to AE, A′E′, and A″E″ (Li2SO4·H2O + LiBO2· 8H2O), CE, C′E′, and C″E″(Li2SO4·H2O + Li2CO3), and BE, B′E′, and B″E″ (LiBO2·8H2O + Li2CO3), and one invariant point (points E, E′, or E″) with the three cosaturated solid phases (LiBO2·8H2O + Li2CO3 + Li2SO4·H2O). The compositions of LiBO2, Li2SO4, and Li2CO3 (in mass fraction 100w) in the invariant points E, E′ and E″ at 288.15, 298.15, and 308.15 K are (1.05, 25.83, 0.67), (3.31, 24.38, 0.41), and (3.43, 24.12, 0.044), respectively. As to the dry-salt diagram at each temperature, the area of crystal region of lithium carbonate is the largest, which indicates that Li2CO3 is of low solubility, and the areas of the crystallization zones decrease in the order of LiBO2·8H2O and Li2SO4·H2O. No solid solution and double salts were found at three temperatures in the system. The water-phase diagrams of the quaternary system at 288.15, 298.15, and 308.15 K are shown in Figures 1b−3b. It shows that the values of H2O (g/100 g·S) in the univariant solubility isotherm curves of BE, B′E′ and B″E″ at 288.15, 298.15, and 308.15 K are gradually decreased with increasing of Li2SO4 (g/100 g·S). At the invariant points E, E′ or E″, the water phase values reach the singularity values, and then the values of H2O(g/100 g·S) in the univariant solubility isotherm

Figure 5. Comparison of the equilibrium phase diagrams for the quaternary system (Li2SO4+ LiBO2+ Li2CO3 + H2O) at 288.15, 298.15, and 308.15 K. J (Li2CO3) and J (LiBO2), Janecke index of Li2CO3 and LiBO2 in 100 g of dry salt of (Li2SO4 + LiBO2 + Li2CO3); − Δ−, 288.15 K; −●−, 298.15 K; −○−, 308.15 K.

Table 3. Values of the Constants d0, nD0, and the Fitted Parameters of Density Constants Ai and Refractive Index Constants Bi for LiBO2, Li2SO4 and Li2CO3 at 288.15, 298.15, and 308.15 Ka parameters

288.15

298.15

308.15

d0 nD0 Ai (LiBO2) Ai (Li2SO4) Ai (Li2CO3) Bi (LiBO2) Bi (Li2SO4) Bi (Li2CO3)

0.99909 1.33339 0.028591 0.008314 −0.019356 0.004339 0.001379 −0.0006788

0.99704 1.33250 0.010918 0.007803 0.014678 0.002315 0.0011875 0.001951

0.99403 1.33131 0.01044 0.008188 0.0299 0.00264 0.00137 0.03171

a

d0, density values of the pure water at the three temperatures;15 nD0, the refractive indices in the pure water at the three temperatures.15 E

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Table 4. Experimental and Calculated Data of Density and Refractive Index for the Quaternary System (LiBO2 + Li2SO4 + Li2CO3 + H2O) at 288.15, 298.15, 308.15 K and 0.1 MPaa density, ρ/(g/cm3) no.b

exp. value

cal. value

1, Ac 2, Bd 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20, E 21 22, C

1.26407 1.02769 1.02698 1.02808 1.02899 1.03204 1.03281 1.03595 1.03734 1.04053 1.04950 1.05841 1.07780 1.10029 1.12175 1.14288 1.15519 1.17531 1.19491 1.24865 1.24337 1.23845

1.25664 1.02769 1.02570 1.02546 1.02897 1.03113 1.03649 1.04107 1.04316 1.04371 1.05690 1.06559 1.08325 1.10722 1.12566 1.15067 1.16172 1.18401 1.20239 1.25972 1.24337 1.22051

1, A′c,e 2, B′d 3 4 5 6 7 8 9

1.26407 1.03942 1.04087 1.04323 1.04426 1.04588 1.05286 1.05667 1.05337

1.25319 1.03931 1.04038 1.04282 1.04576 1.04788 1.05043 1.05227 1.04816

relative err./% 288.15 K 0.00 0.00 −0.12 −0.25 −0.00 −0.088 0.36 0.49 0.56 0.31 0.71 0.68 0.51 0.63 0.35 0.68 0.56 0.74 0.62 0.89 0.00 −1.44 298.15 K −0.85 0.01 −0.047 −0.040 0.14 0.19 −0.23 −0.42 −0.50

density, ρ/(g/cm3)

refractive index, nD exp. value

cal. value

relative err./%

1.3846 1.3419 1.3475 1.3477 1.3480 1.3481 1.3489 1.3490 1.3492 1.3500 1.3511 1.3537 1.3570 1.3611 1.3651 1.3691 1.3708 1.3742 1.3780 1.3874 1.3852 1.3812

1.3846 1.3419 1.3413 1.3412 1.3418 1.3420 1.3430 1.3439 1.3441 1.3442 1.3464 1.3483 1.3523 1.3570 1.3608 1.3661 1.3687 1.3728 1.3765 1.3874 1.3850 1.3812

0.00 0.00 −0.46 −0.48 −0.46 −0.45 −0.44 −0.38 −0.38 −0.43 −0.35 −0.40 −0.35 −0.30 −0.32 −0.22 −0.16 −0.10 −0.11 0.00 −0.01 0.00

1.3881 1.3459 1.3438 1.3443 1.3446 1.3449 1.3456 1.3465 1.3458

1.3881 1.3461 1.3440 1.3445 1.3451 1.3454 1.3459 1.3460 1.3446

0.00 0.01 0.01 0.02 0.04 0.04 0.02 −0.03 −0.09

no.b

exp. value

cal. value

10 11 12 13 14, E′ 15 16 17 18 19, C′

1.06554 1.06594 1.07350 1.13968 1.25789 1.25001 1.24536 1.23859 1.23700 1.23244

1.05952 1.06025 1.06958 1.13583 1.25788 1.24812 1.24393 1.23784 1.23101 1.23243

1, A″ 2, B″ 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18, E″ 19 20 21, C″

1.25699 1.06128 1.07037 1.07521 1.08338 1.09793 1.10111 1.10423 1.11521 1.13194 1.13621 1.16141 1.17311 1.18577 1.21469 1.24271 1.25759 1.25504 1.24525 1.23738 1.22294

1.25701 1.06128 1.05935 1.06098 1.07651 1.08939 1.10084 1.09931 1.11294 1.13442 1.13025 1.15888 1.17256 1.18894 1.21745 1.24550 1.25801 1.25688 1.24708 1.23792 1.22293

relative err./% 298.15 K −0.56 −0.53 −0.37 −0.34 −0.00 −0.15 −0.12 −0.06 −0.48 −0.00 308.15 K 0.00 0.00 −1.0 −1.3 −0.63 −0.78 −0.02 −0.45 −0.20 0.22 −0.52 −0.22 −0.047 0.27 0.23 0.22 0.033 0.15 0.15 0.043 −0.00

refractive index, nD exp. value

cal. value

relative err./%

1.3483 1.3478 1.3489 1.3615 1.3833 1.3811 1.3797 1.3784 1.3770 1.3759

1.3471 1.3467 1.3483 1.3610 1.3835 1.3808 1.3795 1.3779 1.3762 1.3759

−0.09 −0.08 −0.05 −0.03 0.01 −0.02 −0.01 −0.03 −0.06 0.00

1.3892 1.3572 1.3580 1.3583 1.3601 1.3625 1.3641 1.3653 1.3666 1.3689 1.3695 1.3725 1.3746 1.3772 1.3818 1.3864 1.3890 1.3891 1.3865 1.3841 1.3812

1.3889 1.3572 1.3555 1.3559 1.3601 1.3625 1.3653 1.3640 1.3675 1.3722 1.3694 1.3754 1.3775 1.3804 1.3856 1.3907 1.3920 1.3905 1.3883 1.3849 1.3810

−0.02 0.00 −0.18 −0.18 0.00 0.00 0.09 −0.09 0.06 0.24 −0.01 0.21 0.21 0.24 0.28 0.31 0.22 0.10 0.13 0.06 −0.01

Standard uncertainties u are u(T) = 0.1 K, u(p) = 0.005 MPa. u(x) for nD and ρ are 0.001 and 0.5 mg·cm−3, respectively. bThe number column corresponds to the number column in Table 2. cReference 9. dReference 7. eReference 10. a

curves of EC, E′C′, and E″C″ are increased slightly with the increase of Li2SO4 (g/100 g·S). On the univariant solubility isotherm curves of EA, E′A′, and E″A″, that is, Li2SO4·H2O + LiBO2·8H2O, changes of H2O (g/100 g·S) are minor. Figure 4 shows the typical X-ray diffractive diagram of the cosaturated solid phase (LiBO2·8H2O + Li2SO4·H2O + Li2CO3 in the invariant points in the invariant points E, E′, and E″ at three temperatures. A comparison of the dry-salt diagrams of the quaternary system (Li2SO4 + LiBO2 + Li2CO3 + H2O) at 288.15, 298.15, and 308.15 K is shown in Figure 5. Figure 5 shows that the areas of lithium sulfate monohydrate and lithium metaborate octahydrate are decreased obviously and the area of the phase regions of lithium carbonate is increased significantly with the increase of temperature from 288 to 308 K. This information on area change for the crystallized phase regions can be adapted for separating and purifying those three kinds of lithium salts from the concentrated brines. Density and Refractive Index at Three Temperatures. On the basis of density and refractive index data at 288.15, 298.15, 308.15 K and 0.1 MPa in Table 3, the diagrams of the density and refractive index versus dry-salt composition of

lithium sulfate (g/100 g·S) in the solution are plotted in Figure 6. Figure 6a is the diagram of density versus lithium sulfate in solution at 288.15, 298.15, and 308.15 K. Figure 6a shows that densities in the univariant crystalline line of (LiBO2·8H2O + Li2CO3) (curves BE, B′E′, and B″E″) in the quaternary system increase significantly with the increasing of lithium sulfate to reach the maximum values of 1.24865, 1.25789, and 1.25504 g·cm−3 at the invariant points E, E′, or E″ at 288.15, 298.15, and 308.15 K, respectively. Densities in the unvariant crystalline lines (Li2SO4·H2O + Li2CO3) and (Li2SO4·H2O + LiBO2·8H2O) at 288.15, 298.15, and 308.15 K decrease sharply with the increase of lithium sulfate. Generally, densities in the quaternary system are increased with the increase of temperature in Figure 6a. Figure 6b presents the relationship between refractive index versus lithium sulfate in solution at 288.15, 298.15, and 308.15 K. Similarly, it was found that the solution refractive index from point B to point E at 288.15 K and point B″ to point E″ at 308.15 K in the solubility curves of (LiBO2·8H2O + Li2CO3) in the quaternary system increases obviously with the increase of lithium sulfate, and the solution refractive index from points E, E′, or E″ to points C, C′, or C″ F

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three temperatures were correlated successfully using the empirical equations of density and refractive index. In addition, more works on thermodynamic properties for the lithiumcontaining quaternary system from 288.15 to 308.15 K such as osmotic coefficient, heat capacity, dissolution heat, dilution heat, and mixing heat are ongoing in our laboratory for future understanding of the ion-interaction in the salt−water system.

(or to points A, A′, or A″ at 288.15, 298.15, and 308.15 K in the solubility curves of (Li2SO4·H2O + Li2CO3) and (Li2SO4·H2O + LiBO2·8H2O) decreases slowly with the increase of dry-salt composition of lithium sulfate in the solution. Calculated Density and Refractive Index. The following empirical equations of density and refractive index with the composition of electrolyte solution were used15 ln

d = d0

∑ A i × wi

n ln D = n D0

■

(1)

AUTHOR INFORMATION

Corresponding Author

∑ Bi × wi

*E-mail: [email protected]. Tel/Fax: 86-22-60602963. ORCID

(2)

Shiqiang Wang: 0000-0002-6733-7076 Tianlong Deng: 0000-0002-1728-2943

where d and d0 express the density values of the solution and the pure water at the same temperature, respectively. Accordingly, nD and nD0 show the refractive index values in the electrolyte solution and the pure water at the same temperature, respectively. The d0 and nD0 of the pure water at 288.15, 298.15, and 308.15 K are presented in Table 3. wi is the ith component in the electrolyte solution, which is expressed in mass fraction. Ai and Bi are the constants of density and refractive index for the ith component in the electrolyte solution, respectively. Ai and Bi at each temperature can be obtained from the density or refractive index versus composition of the three binary subsystems, that is, LiBO2 + H2O, Li2SO4 + H2O, and Li2CO3 + H2O at the same temperature, respectively. Density constants Ai and refractive index constants Bi for LiBO2, Li2SO4, and Li2CO3 at 288.15, 298.15, and 308.15 K are listed in Table 3, respectively. The calculated and experimental data for density and refractive index in this system (Li2SO4 + LiBO2 + Li2CO3 + H2O) at 288.15, 298.15, and 308.15 K are shown in Table 4. According to the relative errors between the experimental and the calculated values for the physicochemical properties of the electrolyte solution being less than 2%, the predictive results were acceptable.16 In this work, the relative errors for densities and refractive indices in the quaternary system at three temperatures are within 1.44% and 0.31%, respectively, and those results indicate that the calculated results agree with the experimental values.

Funding

Financial support from the National Natural Science Foundation of China (21276194, 21306136, U1407113, U15071092, U1607123 and U1607129), the Training Program for Yangtze Scholars and Innovative Research Team in University of China (2013-373), the Innovative Research Team of Tianjin Municipal Education Commission of China (TD12-5004), and the Chinese Postdoctoral Science Foundation (2016M592827 and 2016M592828) is acknowledged. Notes

The authors declare no competing financial interest.

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REFERENCES

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4. CONCLUSION With the demand increasing for lithium salts around the world, the solubilities and the physicochemical properties of lithiumcontaining salt-water system are essential to effectively separate lithium-containing mixture salts. On the basis of solubilities and physicochemical properties including densities and refractive indices of the aqueous quaternary system (Li2SO4 + LiBO2 + Li2CO3 + H2O) at 288.15, 298.15, and 308.15 K, it was found that there are two kinds of hydrates existing as lithium sulfate monohydrate and lithium metaborate octahydrate, and the areas of hydrates Li2SO4·H2O and LiBO2·8H2O are decreased obviously and the area of anhydrous lithium carbonate region is increased significantly with the increase of temperature from 288.15 to 308.15 K. Those results demonstrate that the crystallization behavior of anhydrous lithium carbonate is in inverse correlation with temperature. This information on area change for the crystallized phase regions can be adapted for separating and purifying those three kinds of lithium salts from the concentrated brines. Considering that the phase equilibrium physiochemical property parameters of brine system are useful for solar pond process, the physicochemical properties including density and refractive index of the aqueous quaternary system at G

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(13) Deng, T. L. Stable and metastable phase equilibria in the salt− water systems. In Advance in Crystallization Processes; Yitzhak, M., Ed.; InTech Publisher: Croatia, 2012; Chapter 16, pp 399−430. (14) Qinghai institute of salt lakes of CAS. Analytical methods of brines and salts, 2nd ed.; Chinese Science Press: Beijing, 1988. (15) Deng, T. L.; Meng, L. Z.; Sun, B. Metastable phase equilibria of the reciprocal quaternary system containing sodium, potassium, chloride, and borate ions at 308.15 K. J. Chem. Eng. Data 2008, 53, 704−709. (16) Bespyatov, W. A.; Chernyaikin, I. S.; Naumov, V. N.; Stabnikov, P. A.; Gelfon, N. V. Low-temperature heat capacity of Al(C11H19O2)3. Thermochim. Acta 2014, 596, 40−41.

H

DOI: 10.1021/acs.jced.6b00777 J. Chem. Eng. Data XXXX, XXX, XXX−XXX