Metastable Phase Equilibrium of the Quinary Aqueous System Li+ +

Based on the experimental data, the space metastable phase diagram and the projected phase diagram saturated with salt Li2CO3 of the quinary system at...
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Metastable Phase Equilibrium of the Quinary Aqueous System Li+ + K+ + Cl− + CO32− + B4O72− + H2O at 273.15 K Ruilin Wang† and Ying Zeng*,†,‡ †

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 metastable phase equilibrium of the quinary aqueous system Li+ + K+ + Cl− + CO32− + B4O72− + H2O was investigated at 273.15 K using an isothermal evaporation method. The solubilities and densities of the equilibrated solution were determined. Based on the experimental data, the space metastable phase diagram and the projected phase diagram saturated with salt Li2CO3 of the quinary system at 273.15 K were constructed. The projected phase diagram of this system consists of three invariant points, seven univariant curves, and five crystallization fields corresponding to the single salts LiCl· H2O, KCl, K2B4O7·4H2O, K2CO3·3/2H2O, and LiBO2·8H2O. Comparisons between the phase diagrams at 273.15 K and at 298.15 K show that the crystallization form of lithium borate is LiBO2·8H2O at 273.15 K, which formed as Li2B4O7·5H2O at 298.15 K.

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INTRODUCTION Potassium, as one of the three major agricultural fertilizers, is a nutrient essential for plant growth. It is mainly used in agriculture and the manufacturing fields of glass, ceramics, textiles, electrical, metallurgical, and other industrial sectors. Boron is an important chemical raw mineral for the production of borax, boric acid, and boron compounds. Recent years, boron and its compounds are widely used in computer hard drives, floppy drives, printer heads, and other core components. Lithium, a dilute alkali metal, is the lightest metal in nature, which density is 0.534 g·cm−3. With the recent development of technology, the use of lithium increasingly important and widespread, mainly used in traditional ceramic, metal smelting and alloys, battery materials, military industry, and other emerging areas. Salt lake brine and minerals are important sources of these elements, and extracting them from the brine is more economical. Brine, an important liquid mineral resource, is widely distributed in the area of the Qinghai-Xizang (Tibet) Plateau, and a series of salt lakes in Tibet, such as the Zabuye Lake, Dogai Coring Lake, and Dangxiongcuo Lake, are famous for abundant with sodium, potassium, and lithium, as well as chloride, borate, sulfate, and carbonate. In recent years, the government and researchers have paid great attention to the exploitation and comprehensive utilization of the brine. The Searles Lake (USA), Dead Sea (Israel), the Great Salt Lake (USA), and Atacama Lake (Chile) have been greatly exploited and utilized just after the related system equilibria have been studied. In addition, some researchers have tried to calculate the phase diagram for salt lake systems at lower temperatures by using Pitzer’s equation, but it was not possible because of the lack of Pitzer’s parameters at lower temperature. It is wellknown that phase diagrams are the basis and guidance of © 2014 American Chemical Society

utilization of saline lake brine and the separation technique of salts; in the meantime, from the determined solubility data of the related systems, the Pitzer’s parameters at lower temperature could be calculated. Therefore, studies on the phase equilibria of aqueous salt systems are necessary. The Zabuye Salt Lake, located in Tibet and with an area of 247 km2, has a significant economic value for its high concentrations of lithium, sodium, potassium, and borate. In the spring brine, the content of Li+ is 1.17 g·L−1, the content of K+ is 48.1 g·L−1, and the content of B2O3 is 10.3 g·L−1.1 The main components of the brines belong to the complex system (Li+ + Na+ + K+ + Cl− + CO32− + SO42− + borate + H2O).2−4 Because the climatic conditions in the Zabuye Salt Lake region are windy and arid, with high daily evaporation, to economically exploit salt lake brine resources, natural energies such as the energy of the sun or the wind are often used to evaporate the brines. As widely known, the metastable phase equilibrium research is essential to predict the crystallized path of evaporation of the salt lake brine, and therefore, the investigation of metastable equilibrium is of theoretical and practical importance. The metastable equilibrium phase diagram is also called the “solar phase diagram”, which to be studied in the early 1920s. Metastable equilibrium studies aiming at the seawater system Na+ + K+ + Mg2+ + Cl− + SO42− + H2O at 288.15 K, 298.15 K, and 308.15 K5−7 have been reported, respectively, and the results have been used to extract MgSO4·K2SO4·6H2O or K2SO4 from Chaidamu Saline Lake. The metastable equilibria of the quinary system Li+ + K+ + Cl− + CO32− + B4O72− + Received: December 13, 2013 Accepted: February 11, 2014 Published: February 20, 2014 903

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Journal of Chemical & Engineering Data

Article

Table 1. Solubility and Analytical Experimental Reagents chemical name lithium chloride (LiCl) potassium chloride (KCl) lithium carbonate (Li2CO3) potassium carbonate (K2CO3) lithium tetraborate (Li2B4O7) potassium tetraborate tetrahydrate (K2B4O7·4H2O)

initial mass fraction purity

source Chengdu Kelong Reagent Plant Chengdu Kelong Reagent Plant Chengdu Kelong Reagent Plant Chengdu Kelong Reagent Plant Chengdu Kelong Reagent Plant Chengdu Kelong Reagent Plant

purification method

final mass fraction purity

analysis method

Chemical

0.995

none

0.995

Chemical

0.995

none

0.995 0.970

titration

0.995

titration

Chemical

0.995

evaporation recrystallization evaporation recrystallization none

0.995

Chemical

0.995

none

0.995

Chemical Chemical

H2O8 at 298.15 K and the quaternary system Li+ + K+ + Cl− + B4O72− + H2O at 298.15 K9 have also been completed, and the results of the research have been used to comprehensively utilize Searles Salt Lake. Although all of the mentioned research have played an important role in exploiting the salt lake brine resources, they are concentrated on temperatures above 298.15 K, whereas the climate conditions in the region of Zabuye Lake are windy and arid with little rainfall and great evaporating capacity, with an average annual temperature about 273.15 K.10 Consequently, studies on the phase equilibria at 273.15 K will be more related to reality and be of great use in the exploitation of the brine. Because the low temperature has higher requirements on the experimental conditions, there are few reports about the metastable equilibrium at 273.15 K. In previous research work, our group has completed a series of papers about the metastable phase equilibria of systems focused on Zabuye Lake at 273.15 K, such as research about the quaternary systems Na+ + K+ + Cl− + B4O72− + H2O,11 K+ + Cl− + SO42− + B4O72− + H2O,12 Na+ + K+ + Cl− + CO32− + H2O,13 and the quinary systems Li+ + Na+ + K+ + SO42− + B4O72− + H2O14 and Na+ + K+ + CO32− + SO42− + B4O72− + H2O.15 For the borate system, Churikov et al. have conducted related research,16−18 such as research about the ternary systems of Na+ + BO2− + OH− + H2O and K+ + BO2− + OH− + H2O at 263.15 K, 283.15 K, 298.15 K, and 323.15 K, and the ternary systems of Na+ + BH4+ + OH− + H2O and K+ + BH4+ + OH− + H2O at 263.15 K. The quinary system Li+ + K+ + Cl− + CO32− + B4O72− + H2O is one important subsystem of the Zabuye Salt Lake brines. The stable and metastable phase equilibria of this quinary system at 298.15 K have been reported.8,19 In this paper, the metastable equilibria of the quinary system Li+ + K+ + Cl− + CO32− + B4O72− + H2O at 273.15 K are presented; the solubilities and the physicochemical properties such as densities of the equilibrated solution in this system were measured. The comparisons between the metastable phase diagrams at different temperatures have also been made.

An inductively coupled plasma optical emission spectrometer (type 5300 V, PerkinElmer Instrument Corp. of America) was employed for the determination of the lithium ion concentration in solution. A Siemens D500 X-ray diffraction analyzer with Ni-filtered Cu KR radiation was used for the analysis of solid phases. The operating conditions are 35 kV and 25 mA.

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EXPERIMENTAL METHODS20 The isothermal evaporation method was used for the metastable phase equilibria experiments.21 The required amounts of reagent, calculated according to the solubility of the salt at 273.15 K and the solubility data of the invariant point in the quaternary subsystems, were dissolved into 1000 mL of deionized water and loaded into a clean opened polyethylene container (24 cm long, 14 cm wide, and 7 cm high). Then, the container was placed in a thermostatic evaporator for isothermal evaporation. The temperature was controlled to 273.15 ± 0.1 K, measured by a thermal resistance. Because of the low evaporation temperature, the time for reaching equilibrium was comparatively long. The measuring point depended on the changes of the solid phase in the process of evaporation. When enough new solid phases appeared in evaporating container, the solids were separated from the solutions. The wet crystals in the solid phase were separated from each other according to crystal shape as much as possible, dried at 273.15 K, pestled into a powder, and then analyzed by X-ray diffraction. Meanwhile, a 5.0 mL liquid sample was taken from the clarified solution, diluted to a 100 mL final volume with deionized water in a volumetric flask, and used to analyze the concentration of liquid phase components. Another 5.0 mL sample of the clarified solution was taken and placed in the weighing bottle to determine the density. The remainder of the solution continued to be evaporated to reach the next measuring point. The same procedure was repeated until the solution was fully evaporated. The densities of solution were determined with a gravity bottle method with a precision of 0.0002 g·cm−3 and used for mass fraction calculations of components. The specific gravity bottle method with a correction of air buoyancy was used.22 The specific gravity bottle method proceeded as follows: a flask made to hold a known volume of liquid at a specified temperature was used to weigh the bottle, with the stopper to the nearest 0.001 g. A 5.0 mL liquid sample was taken and transferred to the density bottle. The bottle was weighed with the stopper and the liquid sample. The difference in weights was divided by the volume of liquid to give the specific gravity of the liquid.

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EXPERIMENTAL SECTION Reagents and Apparatus. All inorganic salts used in our study were of analytical grade and are tabulated in Table 1. The deionized water, with an electrical conductivity less than 1·10−4 S·m−1 and pH = 6.60, was used in the experiments. An SHH-250 type thermostatic evaporator, made by the Chongqing Inborn Instrument Corp., China, was used for metastable phase equilibrium experiments. The range of the temperature is 258.15 K to 373.15 K, and the temperature uncertainty is ± 0.1 K. 904

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g·cm−3

1.2333 1.2302 1.2333 1.2364 1.2228 1.2365 1.2327 1.2441 1.2355 1.2428 1.2471 1.2433 1.2514 1.2358 1.2288 1.2162 1.2167 1.2213 1.2173 1.2226 1.2253 1.2208 1.2200 1.2234 1.2237 1.2235 1.4633 1.5008 1.5006 1.4984 1.5084 1.5007 1.5000 1.4951 1.5038 1.5050 1.5045 1.5023 1.5044 1.5092 1.0291

no.

1,M1 2 3 4 5 6 7 8 9 10 11 12 13 14 15,M4 16 17 18 19 20 21 22 23 24 25 26,K3 27,M3 28 29 30 31 32 33 34 35 36 37 38 39 40,K1 41,M8

density ρ

0.4891 0.5244 0.5129 0.5280 0.5410 0.4978 0.5230 0.4913 0.4877 0.5266 0.4956 0.5064 0.4711 0.5057 0.4697 0.4365 0.4416 0.4416 0.4106 0.4502 0.4365 0.4524 0.4553 0.4423 0.4617 0.4646 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0036 0.0151

m(Li+)

0.0000 0.0019 0.0026 0.0031 0.0038 0.0033 0.0037 0.0054 0.0054 0.0061 0.0059 0.0061 0.0073 0.0069 0.0115 0.0110 0.0110 0.0111 0.0111 0.0114 0.0111 0.0111 0.0111 0.0111 0.0113 0.0113 0.3518 0.3427 0.3451 0.3393 0.3435 0.3478 0.3463 0.3421 0.3462 0.3427 0.3490 0.3385 0.3467 0.3472 0.0308

m(K+) 0.4685 0.4779 0.4687 0.4759 0.4746 0.4786 0.4717 0.4773 0.4805 0.4707 0.4801 0.4767 0.4736 0.4780 0.4217 0.4281 0.4247 0.4243 0.4213 0.4283 0.4228 0.4172 0.4316 0.4288 0.4202 0.4227 0.0079 0.0080 0.0080 0.0086 0.0083 0.0087 0.0087 0.0085 0.0085 0.0082 0.0086 0.0075 0.0083 0.0080 0.0000

m(Cl−) 0.0207 0.0483 0.0468 0.0553 0.0702 0.0223 0.0553 0.0197 0.0128 0.0620 0.0218 0.0355 0.0052 0.0347 0.0603 0.0198 0.0282 0.0283 0.0002 0.0322 0.0238 0.0458 0.0328 0.0233 0.0512 0.0503 0.3482 0.3382 0.3402 0.3335 0.3382 0.3423 0.3400 0.3353 0.3392 0.3358 0.3418 0.3323 0.3393 0.3377 0.0323

m(CO32−) 0.0008 0.0007 0.0006 0.0006 0.0006 0.0010 0.0005 0.0006 0.0005 0.0006 0.0006 0.0008 0.0006 0.0008 0.0000 0.0006 0.0008 0.0011 0.0010 0.0017 0.0017 0.0015 0.0023 0.0023 0.0024 0.0037 0.0000 0.0010 0.0015 0.0017 0.0017 0.0015 0.0020 0.0029 0.0032 0.0033 0.0035 0.0033 0.0039 0.0061 0.0139

m(B4O72−)

composition of equilibrium solution, mB/(mol·kg−1) 3.2556 3.0939 3.1422 3.0711 3.0128 3.1894 3.0889 3.2028 3.2156 3.0578 3.1789 3.1356 3.2722 3.1294 3.2811 3.4128 3.3939 3.3911 3.5217 3.3500 3.4100 3.3483 3.3267 3.3789 3.3039 3.2822 2.8328 2.8961 2.8744 2.9183 2.8856 2.8528 2.8633 2.8906 2.8572 2.8833 2.8333 2.9167 2.8494 2.8350 5.1822

m(H2O) 104.21 109.14 108.70 110.11 112.92 103.09 109.90 101.66 100.26 110.31 101.86 104.71 97.83 104.11 108.41 99.28 101.17 101.17 94.73 102.00 100.19 105.24 102.30 100.02 106.44 106.15 1.00 1.02 1.02 1.03 1.02 1.01 1.01 1.02 1.01 1.02 1.00 1.03 1.00 1.00 33.82

J(Li22+) 0.00 0.40 0.54 0.64 0.80 0.69 0.78 1.11 1.10 1.29 1.21 1.27 1.51 1.42 2.66 2.50 2.52 2.55 2.57 2.58 2.55 2.59 2.50 2.52 2.59 2.57 97.80 97.42 97.32 97.06 97.15 97.13 96.99 96.79 96.75 96.76 96.65 96.92 96.60 96.10 68.90

J(K22+) 99.82 99.45 99.34 99.24 99.06 99.11 99.11 98.77 98.79 98.59 98.67 98.57 98.35 98.41 97.34 97.35 97.30 97.20 97.20 97.04 97.05 97.05 96.98 96.96 96.86 96.58 2.20 2.29 2.27 2.46 2.35 2.44 2.45 2.39 2.37 2.31 2.38 2.14 2.32 2.23 0.00

J(Cl22−) 4.40 10.06 9.93 11.54 14.65 4.63 11.63 4.07 2.64 12.99 4.49 7.34 1.07 7.14 13.93 4.51 6.45 6.49 0.04 7.29 5.47 10.66 7.38 5.28 11.79 11.50 96.80 96.13 95.91 95.41 95.65 95.59 95.23 94.88 94.80 94.82 94.68 95.16 94.56 93.46 72.28

J(CO32−) 0.18 0.15 0.12 0.12 0.13 0.20 0.11 0.12 0.11 0.12 0.12 0.16 0.13 0.17 0.00 0.15 0.18 0.25 0.24 0.38 0.40 0.36 0.52 0.52 0.55 0.85 0.00 0.29 0.42 0.48 0.49 0.43 0.56 0.82 0.88 0.93 0.96 0.94 1.08 1.68 31.10

J(B4O72−) 693.58 643.91 665.97 640.44 628.85 660.54 649.10 662.77 661.06 640.53 653.32 648.33 679.51 644.26 757.36 776.14 777.61 776.92 812.47 758.94 782.62 778.90 747.50 764.08 761.61 749.88 787.56 823.27 810.47 834.91 816.19 796.61 801.98 817.85 798.59 814.09 784.73 835.12 794.02 784.71 11584.95

J(H2O)

Jänecke index of dry salt, mol/100 mol dry salt J(Cl22−) + J(B4O72−) + J(K22+) = 100 LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LCL+LC+LB LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL LICL+LC+KCL+LB LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL LC+KC+KCL+KB LC+LB+KB

equilibrium solid phasea

Table 2. Solubilities and Densities of Solutions in the Quinary System Li+ + K+ + Cl− + CO32− + B4O72− + H2O at T = 273.15 K and Pressure p = 0.1 MPaa

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g·cm−3

1.1064 1.1075 1.1338 1.1658 1.2073 1.1881 1.5293 1.4961 1.4991 1.5296 1.4993 1.4973 1.5080 1.5105 1.5190 1.5026 1.5087 1.4951 1.5267 1.5281 1.5244 1.5250 1.5526 1.5536 1.5494 1.5435 1.5516 1.5368 1.5158 1.5235 1.5212 1.5235 1.5079 1.1691 1.1721 1.1722 1.1775 1.1819 1.1815 1.1820 1.1839

no.

42 43 44 45 46 47,K2 48,M7 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63,M2 64 65 66 67 68 69 70 71 72 73 74 75,M6 76 77 78 79 80 81 82

density ρ

Table 2. continued

0.0295 0.0259 0.0288 0.0303 0.0339 0.0562 0.0079 0.0072 0.0072 0.0072 0.0072 0.0072 0.0079 0.0079 0.0079 0.0079 0.0079 0.0072 0.0079 0.0079 0.0079 0.0000 0.0036 0.0036 0.0036 0.0043 0.0043 0.0050 0.0050 0.0058 0.0058 0.0058 0.0065 0.0050 0.0050 0.0058 0.0058 0.0058 0.0065 0.0086 0.0094

m(Li+)

0.0692 0.0743 0.0908 0.1166 0.1405 0.1531 0.3472 0.3350 0.3357 0.3541 0.3402 0.3409 0.3591 0.3508 0.3581 0.3527 0.3609 0.3515 0.3788 0.3756 0.3820 0.3731 0.3655 0.4003 0.4043 0.4102 0.4020 0.3922 0.3949 0.3688 0.3638 0.3514 0.3657 0.1509 0.1621 0.1660 0.1673 0.1688 0.1712 0.1678 0.1729

m(K+) 0.0063 0.0071 0.0087 0.0117 0.0169 0.1377 0.0000 0.0100 0.0116 0.0127 0.0147 0.0151 0.0164 0.0155 0.0213 0.0219 0.0227 0.0265 0.0315 0.0336 0.0392 0.0063 0.0062 0.0063 0.0058 0.0065 0.0066 0.0072 0.0072 0.0072 0.0075 0.0072 0.0073 0.1453 0.1415 0.1447 0.1444 0.1453 0.1419 0.1402 0.1425

m(Cl−) 0.0670 0.0680 0.0815 0.1012 0.1280 0.0520 0.3522 0.3300 0.3287 0.3463 0.3303 0.3307 0.3480 0.3403 0.3425 0.3362 0.3438 0.3298 0.3525 0.3473 0.3485 0.3435 0.3552 0.3548 0.3585 0.3512 0.3603 0.3510 0.3542 0.3510 0.3485 0.3477 0.3467 0.0000 0.0145 0.0148 0.0155 0.0163 0.0197 0.0202 0.0222

m(CO32−) 0.0256 0.0255 0.0294 0.0345 0.0303 0.0203 0.0039 0.0033 0.0034 0.0035 0.0035 0.0035 0.0035 0.0035 0.0033 0.0035 0.0035 0.0035 0.0035 0.0036 0.0034 0.0242 0.0084 0.0434 0.0444 0.0578 0.0407 0.0401 0.0394 0.0171 0.0146 0.0035 0.0193 0.0114 0.0120 0.0126 0.0135 0.0135 0.0170 0.0163 0.0180

m(B4O72−)

composition of equilibrium solution, mB/(mol·kg−1) 4.7633 4.7378 4.5794 4.3439 4.1639 3.9567 2.8339 2.9267 2.9206 2.7778 2.8828 2.8772 2.7344 2.8000 2.7400 2.7800 2.7156 2.7878 2.5739 2.5967 2.5450 2.5556 2.6844 2.2328 2.1956 2.0756 2.2267 2.3039 2.2883 2.6039 2.6533 2.8072 2.6106 4.2256 4.1389 4.1028 4.0878 4.0739 4.0361 4.0594 4.0072

m(H2O) 29.19 24.27 22.34 18.58 18.03 18.07 2.26 2.07 2.05 1.95 2.01 2.00 2.09 2.14 2.07 2.10 2.05 1.89 1.92 1.92 1.87 0.00 0.95 0.80 0.79 0.91 0.96 1.15 1.14 1.47 1.49 1.59 1.65 1.64 1.60 1.78 1.77 1.76 1.96 2.67 2.81

J(Li22+) 68.38 69.53 70.40 71.61 74.86 49.22 98.90 96.18 95.73 95.63 94.92 94.83 94.75 94.86 93.56 93.28 93.22 92.12 91.54 90.99 89.96 92.44 96.15 88.95 88.96 86.46 89.47 89.25 89.45 93.83 94.29 97.05 93.22 49.06 51.38 51.35 51.44 51.53 51.87 51.74 51.87

J(K22+) 6.27 6.60 6.78 7.19 9.02 44.26 0.00 2.87 3.30 3.43 4.09 4.20 4.32 4.20 5.57 5.78 5.87 6.95 7.60 8.13 9.23 1.57 1.63 1.41 1.27 1.37 1.48 1.64 1.63 1.83 1.94 1.99 1.87 47.23 44.83 44.77 44.42 44.35 42.98 43.23 42.74

J(Cl22−) 66.23 63.64 63.19 62.12 68.18 16.72 100.32 94.74 93.73 93.54 92.18 91.98 91.82 92.04 89.49 88.91 88.82 86.44 85.19 84.15 82.08 85.10 93.44 78.86 78.88 74.01 80.18 79.87 80.23 89.30 90.32 96.02 88.36 0.00 4.59 4.59 4.77 4.99 5.96 6.22 6.65

J(CO32−) 25.34 23.87 22.82 21.20 16.13 6.52 1.10 0.94 0.97 0.94 0.99 0.97 0.93 0.94 0.88 0.94 0.92 0.93 0.86 0.87 0.80 5.98 2.22 9.63 9.76 12.18 9.06 9.12 8.92 4.34 3.77 0.96 4.91 3.71 3.80 3.89 4.14 4.13 5.15 5.03 5.39

J(B4O72−) 4708.42 4433.72 3550.62 2667.29 2217.93 1272.16 807.26 840.18 832.88 750.21 804.43 800.36 721.52 757.25 715.96 735.27 701.48 730.56 622.06 629.11 599.40 633.11 706.21 496.22 483.06 437.42 495.49 524.25 518.38 662.46 687.67 775.31 665.41 1373.84 1311.45 1269.20 1257.18 1243.55 1222.61 1251.87 1202.23

J(H2O)

Jänecke index of dry salt, mol/100 mol dry salt J(Cl22−) + J(B4O72−) + J(K22+) = 100 LC+LB+KB LC+LB+KB LC+LB+KB LC+LB+KB LC+LB+KB LC+LB+KB+KCL LC+KC+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB LC+KCL+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KC+KB KCL+KB+LB KCL+KB+LB KCL+KB+LB KCL+KB+LB KCL+KB+LB KCL+KB+LB KCL+KB+LB KCL+KB+LB

equilibrium solid phasea

Journal of Chemical & Engineering Data Article

906

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907

1.1820 1.1693 1.1810 1.2308 1.2012 1.1754 1.1800 1.1741 1.1753 1.1759 1.1749 1.1690 1.1769 1.1732 1.1740 1.1772 1.1721 1.1878 1.1866 1.1873 1.1882 1.1870 1.1884

83 84 85 86,M5 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105

0.0108 0.0158 0.0180 0.4048 0.3782 0.3551 0.3573 0.3508 0.3487 0.3436 0.3573 0.3479 0.3494 0.3465 0.3458 0.3487 0.3451 0.3422 0.3515 0.3422 0.3501 0.3451 0.3314

m(Li+)

0.1680 0.1586 0.1597 0.0125 0.0114 0.0111 0.0118 0.0123 0.0129 0.0137 0.0132 0.0129 0.0128 0.0130 0.0127 0.0128 0.0130 0.0132 0.0130 0.0133 0.0129 0.0133 0.0133

m(K+) 0.1395 0.1416 0.1388 0.4144 0.3829 0.3605 0.3635 0.3570 0.3559 0.3513 0.3646 0.3551 0.3557 0.3535 0.3523 0.3557 0.3519 0.3491 0.3588 0.3492 0.3567 0.3523 0.3385

m(Cl−) 0.0223 0.0200 0.0240 0.0000 0.0035 0.0033 0.0033 0.0033 0.0033 0.0033 0.0033 0.0035 0.0033 0.0033 0.0035 0.0033 0.0033 0.0035 0.0033 0.0033 0.0033 0.0033 0.0033

m(CO32−) 0.0173 0.0131 0.0155 0.0039 0.0037 0.0033 0.0032 0.0031 0.0031 0.0036 0.0033 0.0031 0.0033 0.0035 0.0032 0.0033 0.0033 0.0034 0.0032 0.0033 0.0032 0.0033 0.0032

m(B4O72−)

composition of equilibrium solution, mB/(mol·kg−1) 4.0444 4.1178 4.0872 3.5228 3.6622 3.7733 3.7578 3.7878 3.7911 3.8050 3.7467 3.7944 3.7894 3.7978 3.8067 3.7906 3.8067 3.8189 3.7761 3.8183 3.7856 3.8044 3.8700

m(H2O) 3.33 5.06 5.74 93.96 95.03 94.72 94.41 94.22 93.76 93.21 93.75 93.74 93.96 93.64 93.91 93.78 93.70 93.57 93.74 93.52 93.90 93.52 93.34

J(Li22+) 51.74 50.62 50.87 2.91 2.86 2.97 3.11 3.30 3.47 3.71 3.46 3.48 3.44 3.52 3.44 3.44 3.54 3.60 3.48 3.63 3.46 3.60 3.75

J(K22+) 42.95 45.21 44.20 96.18 96.22 96.16 96.04 95.87 95.70 95.31 95.67 95.69 95.66 95.52 95.69 95.68 95.57 95.46 95.68 95.45 95.67 95.49 95.35

J(Cl22−) 6.88 6.38 7.64 0.00 0.88 0.89 0.88 0.90 0.90 0.90 0.87 0.94 0.90 0.90 0.95 0.90 0.91 0.96 0.89 0.91 0.89 0.90 0.94

J(CO32−) 5.32 4.17 4.92 0.91 0.92 0.88 0.85 0.83 0.83 0.98 0.88 0.83 0.90 0.96 0.87 0.88 0.89 0.93 0.84 0.92 0.86 0.91 0.91

J(B4O72−) 1245.26 1314.52 1301.81 817.64 920.19 1006.44 992.93 1017.26 1019.50 1032.20 983.07 1022.33 1019.08 1026.31 1033.84 1019.56 1033.77 1044.36 1006.92 1043.62 1015.34 1031.08 1090.06

J(H2O)

Jänecke index of dry salt, mol/100 mol dry salt J(Cl22−) + J(B4O72−) + J(K22+) = 100 KCL+KB+LB KCL+KB+LB KCL+KB+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB LCL+KCL+LB

equilibrium solid phasea

a Note: Standard uncertainties u are u(T) = 0.10 K; ur(p) = 0.05; ur(ρ) = 2.0·10−4 g·cm−3; ur(Li+) = 0.0050; ur(K+) = 0.0050; ur(Cl−) = 0.0030; ur(CO32−) = 0.0050; ur(B4O72−) = 0.0030; mB = molality of B; KC, K2CO3·3/2H2O; KCL, KCl; KB, K2B4O7·4H2O; LC, Li2CO3; LCL, LiCl·H2O; LB, LiBO2·8H2O.

g·cm−3

no.

density ρ

Table 2. continued

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Figure 1. Space phase diagram of the quinary system Li+ + K+ + Cl− + CO32− + B4O72− + H2O at 273.15 K; ●, experimental point. Bottom shows partial enlargements.

The chloride ion concentration was determined by AgNO3 titration with the uncertainty of ± 0.0030. The lithium ion concentration was determined by inductively coupled plasma optical emission spectrometry (uncertainty: ± 0.0050, type ICP-OES 5300 V). Each analysis was repeated three times with triplicate samples prepared for each data point, and the average value of three measurements was considered as the final value of the analysis.

The composition of potassium ion was measured by titration with a sodium tetraphenylborate−hexadecyl trimethyl ammonium bromide aqueous solution. The uncertainty of the determination was ± 0.0050. The borate ion concentration was determined by a neutralization titration in the presence of propanetriol, with the uncertainty of ± 0.0030. The carbonate ion concentration was determined by acid− base neutralization titration, with the uncertainty of ± 0.0050. The specific method was using the standard hydrochloric acid to titrate the carbonate and bicarbonate within the sample with the phenolphthalein−double methyl orange as the indicator. First, the phenolphthalein was used as an indicator; when the carbonate was converted to bicarbonate, the solution changed from purple to reddish at the end point. Then, adding methyl orange and continuing the titration, the solution suddenly from yellow to orange as the titration end point. Each sample was measured three times in parallel, and the precision was calculated as the following equation. precision/% =

Vexp − Vave Vave

·100 %

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RESULTS AND DISCUSSION

The solubilities and densities of the equilibrated solution in the quinary system at 273.15 K are tabulated in Table 2. In Table 2, the concentration of each solution component is expressed in molality mB, and J(B) is the Jänecke index values of B, with J(K22+) + J(Cl22−) + J(B4O72−) = 100. The Jänecke index, that is the mole percentage, can be calculated according to the following correlations. Let [M] = mK+ + mCl− + m B4O27−

(2)

(1)

J(K 22 +) =

where Vexp is the experimental data; Vave is the average data of the parallel samples. 908

m K+ ·100 [M]

(3)

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Figure 2. Projected diagram of the quinary system Li+ + K+ + Cl− + CO32− + B4O72− + H2O at 273.15 K(saturated with Li2CO3); ●, experimental point. Bottom shows partial enlarged diagrams.

J(Cl 2 2 −) =

mCl− ·100 [M]

J(B4 O7 2 −) =

J(H 2O) =

m B4O7 2− [M]

m H 2O [M]

Figure 2, the projected diagram saturated with salt Li2CO3, clearly shows that the metastable phase diagram of the quinary system Li+ + K+ + Cl− + CO32− + B4O72− + H2O at 273.15 K consists of five crystallization fields, seven univariant curves, and three invariant points. The five crystallization fields correspond to lithium chloride monohydrate (LiCl·H2O), anhydrous potassium chloride (KCl), potassium borate tetrahydrate (K2B4O7·4H2O), potassium carbonate hydrate (K2CO3·3/ 2H2O), and lithium metaborate octahydrate (LiBO2·8H2O). According to the phase rule, the invariant point represents the point which the variable is equal to zero. In this system, the invariant point is cosaturated with four salts and solution. The four cosaturated salts for the invariant points are: invariant point K1 is cosaturated with KCl, K2B4O7·4H2O, Li2CO3 and K2CO3·3/2H2O, invariant point K2 is cosaturated with KCl, K2B4O7·4H2O, Li2CO3 and LiBO2·8H2O, and invariant point K3 is cosaturated with KCl, Li2CO3, LiCl·H2O, and LiBO2· 8H2O, respectively. The univariant curve represents a line which the variable is equal to 1. In this system, the univariant curves are cosaturated with three salts and solution. The cosaturated salts for the univariant curves are listed below. K1M7, saturated with Li2CO3, K2B4O7·4H2O, K2CO3·3/ 2H2O. M3K1, saturated with Li2CO3, K2CO3·3/2H2O, KCl. K2K1, saturated with Li2CO3, K2B4O7·4H2O, KCl. K2M8, saturated with Li2CO3, K2B4O7·4H2O, LiBO2·8H2O. K2K3, saturated with Li2CO3, KCl, LiBO2·8H2O. K3M1, saturated with Li2CO3, LiCl·H2O, LiBO2·8H2O.

(4)

·100

·100

(5)

(6)

On the basis of the experimental data, the space diagram is shown in Figure 1. According to Table 2, the projected phase diagram which saturated with salt Li2CO3, letting the J(Cl22−) as the X axis and the J(B4O72−) as the Y axis, was constructed in Figure 2. The bottom sections of Figures 1 and 2 show the partial enlarged diagrams of the figures. In Figure 1, the six apexes of the regular three-prism denote six pure salts that are KCl, K2B4O7, K2CO3, LiCl, Li2B4O7, and Li2CO3, respectively. The nine touchlines express the nine ternary subsystems, and the nine points A to I correspond to the invariant points for these ternary subsystems. The upper regular triangle denotes the simple quaternary system K2CO3 + KCl + K2B4O7 + H2O, with the invariant point M1. The down regular triangle denotes the quaternary system Li2CO3 + LiCl + Li2B4O7 + H2O, with the invariant point M2. The three squares denote the three reciprocal quaternary subsystems Li2CO3 + K2CO3 + LiCl + KCl + H2O, LiCl + KCl + Li2B4O7 + K2B4O7 + H2O, and Li2CO3 + K2CO3 + Li2B4O7 + K2B4O7 + H2O, respectively. 909

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shows that, in this system and its corresponding quaternary subsystem, the lithium borate was in the form of LiBO2·8H2O, the potassium borate formed as K2B4O7·4H2O, but the mechanism of formation needs to be studied further. Comparison with the Metastable Phase Diagram at 298.15 K. The metastable phase diagram of Li+ + K+ + Cl− + CO32− + B4O72− + H2O at 298.15 K has been reported.7 Comparisons between the metastable phase diagrams of this quinary system at 273.15 K and 298.15 K show that the crystallization form of lithium borate was LiBO2·8H2O at 273.15 K, whereas that was in the form of Li2B4O7·5H2O at 298.15 K; the crystallization forms of the other salts (KCl, K2CO3, K2B4O7, LiCl, and Li2CO3) have not changed with the change of the temperature. In 273.15 K, the size of the area of K2B4O7·4H2O and LiCl·H2O were smaller than the regions in 298.15 K, while the area of the crystallization fields of KCl and K2CO3·3/2H2O has very little variation at different temperatures. As a comparison of different temperatures, the higher temperature is conductive to the precipitation of K2B4O7·4H2O and LiCl·H2O; thus the change of temperature can control the process of salting out during the comprehensive utilization of brines.

K3M4, saturated with Li2CO3, KCl, LiCl·H2O. Borates can form different polyanions in aqueous solution. The various species of boron in aqueous solution depend on the pH value, the total concentration of boron and salts, and the kinds of coexistent salts.23 B4O72− is just a traditional stoichiometric expression for various boric species in solution. In this metastable system at the studied temperature, the equilibrium solid phase of potassium borate exists as a tetraborate, with the crystallization form K2B4O5(OH)4·2H2O, and lithium borate exists as a borate, with the crystallization form LiBO2·8H2O. Figure 3 shows that the invariant point K2 cosaturated with salts KCl, K2B4O7·4H2O, Li2CO3 and LiBO2· 8H2O.

■

CONCLUSIONS An isothermal evaporation method was adopted to investigate the solubilities and densities of the aqueous quinary system Li+ + K+ + Cl− + CO32− + B4O72− + H2O at 273.15 K. According to the experimental data, the space gram and the projected phase diagram were plotted. The projected phase diagram saturated with salt Li2CO3 of this system at 273.15 K consists of three invariant points, seven univariant curves, and five crystallization fields corresponding to the single salts LiCl· H2O, KCl, K2CO3·3/2H2O, K2B4O7·4H2O and LiBO2·8H2O. In contrast to the subsystems containing potassium carbonate, the crystallization form of potassium carbonate is K2CO3·3/ 2H2O in this quinary system at research temperatures. The comparison was made between the metastable phase diagrams at 273.15 K and at 298.15 K. Results show that the crystallization form of lithium borate was LiBO2·8H2O at 273.15 K, whereas that was Li2B4O7·5H2O at 298.15 K; the crystallization forms of salts KCl, K2CO3, K2B4O7, LiCl, and Li2CO3 have not changed when the temperature changed to 298.15 K. Simultaneously, the size of salts crystallization area change with the change of temperature. Thus we can control the crystalline form and the order of salting out by controlling the temperature.

Figure 3. X-ray diffraction pattern of the invariant point K2 (KCl + LiBO2·8H2O + K2B4O7·4H2O + Li2CO3).

The three invariant points labeled as K1, K2, and K3 are cosaturated with four salts. The saturated salts and the mass fraction composition for the invariant points in this system are listed below. K1, saturated with salts Li2CO3 + K2CO3·3/2H2O + K2B4O7· 4H2O + KCl, with m(Li+) 0.0036 mol·kg−1, m(K+) 0.3472 mol· kg−1, m(Cl−) 0.0080 mol·kg−1, m(CO32−) 0.3377 mol·kg−1, m(B4O72−) 0.0061 mol·kg−1. K2, saturated with salts Li2CO3 + LiBO2·8H2O + K2B4O7· 4H2O + KCl, with m(Li+) 0.0562 mol·kg−1, m(K+) 0.1531 mol· kg−1, m(Cl−) 0.1377 mol·kg−1, m(CO32−) 0.0520 mol·kg−1, m(B4O72−) 0.0203 mol·kg−1. K3, saturated with salts LiCl·H2O + Li2CO3 + KCl + LiBO2· 8H2O, with m(Li+) 0.4646 mol·kg−1, m(K+) 0.0113 mol·kg−1, m(Cl −) 0.4227 mol·kg −1 , m(CO 3 2− ) 0.0503 mol·kg −1 , m(B4O72−) 0.0037 mol·kg−1. On the basis of the measured density data of the equilibrated solution tabulated in Table 2, we concluded that, at the univariant curves, the density of the solution smoothly changes with the J(Cl22−). Comparisons among this system and the ternary or quaternary subsystems containing K2CO3 show that the crystal form of salt potassium carbonate is K2CO3·3/2H2O at 273.15 K.24 Borates Present Forms in the Solution. Borates can form different polyanion ions in aqueous solution. The forms of the polyboron ions vary with the pH value, the concentration of the total boron, solvent, and the other coexisting ions in the solution. [B4O5(OH)4]2− is just the traditional stoichiometric expression for various polyboron ions in solution. The research of the quinary system of the metastable equilibria at 273.15 K

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: 86-28-84079074. Tel.: 8628-84079079. Funding

Financial support for this work was provided by the National Nature Science Foundation of China (no. 40673050 and 41173071), the National High Technology Research and Development Program of China (2012AA061704), the Research Fund for the Doctoral Program of Higher Education from the Ministry of Education of China (20115122110001), the Sichuan youth science and technology innovation research team funding scheme (2013TD0005), the Research Fund from the Sichuan Provincial Education Department (11ZZ009), and the Project of China Geological Survey (12120113087700). 910

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Notes

(21) Zeng, Y.; Lin, X. F.; Yu, X. D. Study on the Solubility of the Aqueous Quaternary System Li2SO4 + Na2SO4 + K2SO4 + H2O at 273.15 K. J. Chem. Eng. Data 2012, 57, 3672−3676. (22) Chemical Reagent General Method for the Determination of Density. China Patent GB 611-88-1988, 1988. (23) Farmer, J. B. Metal borates. In Advances in Inorganic Chemistry and Radiochemistry; Emeleus, H. J., Sharpe, A. G., Eds.; Academic Press: New York, 1982. (24) Zheng, Z. Y. Studies on the Metastable Phase Equilibrium in the Quinary System K+, Na+//CO32−, SO42−, B4O72−-H2O at 273 K. Master Thesis of Chengdu University of Technology: Chengdu, 2008.

The authors declare no competing financial interest.

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REFERENCES

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