Metastable Phase Equilibrium in the Quaternary System LiCl + KCl +

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Metastable Phase Equilibrium in the Quaternary System LiCl + KCl + RbCl + H2O at 348.15 K Qinghong Yin,† Ying Zeng,†,‡,* Xudong Yu,† Pengtao Mu,† and Qi Tan† †

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 quaternary system LiCl + KCl + RbCl + H2O at 348.15 K was done by using an isothermal evaporation method. The solubilities, densities, and refractive indices of the equilibrated solution were determined experimentally. On the basis of the measured data, the stereo phase diagram, the metastable phase diagram, the water content diagram, and the physicochemical properties versus composition diagrams were constructed. Results show that the quaternary system is of a complex type with the solid solution of potassium chloride and rubidium chloride [(K, Rb)Cl] formed at 348.15 K. The metastable phase diagram consists of two invariant points, five univariant curves, and four crystallization fields corresponding to single salts potassium chloride (KCl), rubidium chloride (RbCl), lithium chloride monohydrate (LiCl·H2O), and a solid solution of potassium and rubidium chloride [(K, Rb)Cl]. Salt RbCl has the largest solubility among the coexisting salts and presents the smallest crystallization field in the phase diagram. The crystallization region of [(K, Rb)Cl] almost occupies the entire phase region, which shows that it is difficult to separate potassium from rubidium in chloride solution by only using evaporation and crystallization methods. This is compared with the metastable phase diagram of the quaternary system at 298.15 K that shows that the crystallization forms have not changed, while the crystallization fields have slightly change. The refractive index of the solution has been calculated using an empirical equation. The maximum absolute deviation between the calculated and experimental data of the refractive index is less than 0.007.

1. INTRODUCTION Rubidium is a very soft, silvery-white metallic element of the alkali metal group, and it was discovered by the newly developed method of flame spectroscopy by German chemists Bunsen RW and Kirchhoff GR in 1861.1 Rubidium is also an extremely important rare chemical element and widely used in the fields of photovoltaic cells, catalysts, biochemistry, ion propulsion rockets, laser conversion devices of electric power, and so on.2 Rubidium belongs to the typical scattered lithophile element group and cannot easily form an independent mineral in nature.3 Generally, pegmatite and pollucite are mainly solid deposits for rubidium; salt lake brine and underground brine are mainly liquid ore for rubidium. The Sichuan basin, located in the west of China, is one of the main regions abundant with the brine containing rubidium and is especially famous for the Pingluo underground brine. The Pingluo underground brine is of a chloride type and abounds with potassium and rubidium. The content of potassium (up to 54.66 g·L−1) and rubidium (up to 0.0375 g·L−1) is 40.97 and 3.75 times that of the industrial grade for comprehensive utilization, respectively.4 Therefore, it is more economical to extract these elements from brine than the traditional process of extracting them from solid ore. It is well-known that the solubility data of inorganic salts along with the phase diagram provide a very important basis for the comprehensive utilization of brine and provide theoretical © 2013 American Chemical Society

direction to establish the best production process and technology. On that basis, some phase equilibria focused on systems containing rubidium have been investigated. Norio studied the RbCl + 1-butanol + H2O system at 298.15 K and it was found that the solubility of rubidium chloride decreased with an increase of the 1-butanol content.5 Gao completed the system RbCl + EtOH + H2O at 298.15 and 323.15 K and Rb2SO4 + EtOH + H2O at 273.15 K to 333.15 K.6,7 The results show that ethanol has a strong salting-out effect on the rubidium salt, while also proving the feasibility of isolating and purifying the rubidium salt with ethanol. Hu studied CH3OH + Rb2CO3 + H2O and CH3CH2OH + Rb2CO3 + H2O at 298.15 K, 308.15 K, and 318.15 K.8 In all cases, the salting-out effect in the two mixed solvent systems was greater for ethanol than for methanol; however, the temperature had no significant effect on these two systems. Furthermore, some salt-water systems aimed at the rubidium system also have been researched. Song used the Pitzer equation to calculate the equilibrium solubility of the NaCl + RbCl + H2O.9 Merbach completed the quaternary system of KCl + RbCl + CsCl + H2O and its subsystems at 298.15 K.10,11 The experimental results show the solid solution [(K, Rb) Cl] was formed at 298.15 K. Received: July 11, 2013 Accepted: September 6, 2013 Published: September 18, 2013 2875

dx.doi.org/10.1021/je400649r | J. Chem. Eng. Data 2013, 58, 2875−2880

Journal of Chemical & Engineering Data

Article

Some metastable phase equilibria at different temperatures on salt-water systems of the rubidium system have been studied by our research group, such as ternary system LiCl + RbCl + H2O at 298.15 K,12 and KCl + RbCl + H2O at 298.15 K, 323.15 K, and 348.15 K.13−15 Results indicated that ternary system LiCl + RbCl + H2O is of a simple type; no double salt or solid solution is found in this ternary system, whereas the ternary system KCl + RbCl + H2O is of a complex type, the solid solution [(K, Rb)Cl] is formed at 298.15 K, 323.15 K, and 348.15 K. The quaternary system LiCl + KCl + RbCl + H2O at 298.15 K has been researched in our earlier study.16 The metastable phase diagram of this quaternary system consists of four crystallization fields corresponding to single salts LiCl·H2O, KCl, RbCl, and solid solution [(K, Rb)Cl]. As we know, temperature is one of the main affecting factors for the salt’s crystallization zone and crystallization form. To figure out the effect for the temperature, it was necessary to focus the research on the metastable phase equilibria about the system LiCl + KCl + RbCl + H2O at multitemperatures. Accordingly, the metastable phase equilibrium of the quaternary system LiCl + KCl + RbCl + H2O at 348.15 K is reported in detail. Also, the comparisons between the metastable phase diagrams at 298.15 K and 348.15 K are presented in this paper.

A = ρa

where ρa = 0.0012 g·cm , the density of dry air at 293.15 K and normal atmospheric pressure. The 2WAJ Abbe refractometer with a precision of 0.0001 was used to determine the refractive index of liquid phase. The solid phases were analyzed by DX-2700 X-ray diffractometer with Cu Kα radiation, and the operation conditions were 40 kV and 30 mA. 2.3. Analytical Methods. The concentration of Cl− was analyzed by AgNO3 volumetric method with a precision of ± 0.0030;18 the total amount of K+ and Rb+ was analyzed by sodium tetraphenylborate (STPB)hexadecyl trimethyl ammonium bromide (CTAB) back-titration with a precision of ± 0.0050; the concentration of Rb+ was analyzed by the 5300 type inductively coupled plasma optical emission spectrometry (ICP−OES: RF power was set to 1250 W, the coolant gas flow rate was 0.013 L·s−1, carrier gas flow rate was 0.25 L·s−1, auxiliary gas flow rate was 0.0033 L·s−1) with a precision less than ± 0.0050, and then the composition of K+ was calculated by the subtraction method. The concentration of Li+ was measured by an ICP−OES method with a precision of ± 0.0050.

3. RESULTS AND DISCUSSION Table 2 lists the solubilities and physicochemical properties (density and refractive index) of the quaternary system LiCl + KCl + RbCl + H2O at 348.15 K. The solubility data corresponding to the invariant points in the binary and ternary subsystems of this quaternary system are tabulated in Table 3. In Tables 2 and 3, the concentration of each solution component is expressed in molality mB, and the Jänecke index (dry salt mole index) is expressed by J(B). B can be LiCl, KCl, RbCl, or H2O. J(B) is calculated by (mLiCl + mKCl + mRbCl) with a benchmark that can be expressed as follows: mLiCl J(LiCl) = 100 mLiCl + mKCl + mRbCl (3)

Table 1. Solubility and Analytical Experimental Reagents

lithium chloride (LiCl) potassium chloride (KCl) rubidium chloride (RbCl) silver nitrate (AgNO3)

source Chengdu Kelong Chemical Reagent Plant Chengdu Kelong Chemical Reagent Plant Jiangxi Dongpeng New Materials Co., Ltd. Sinopharm Chemical Reagent Co., Ltd.

mass fraction purity 0.990 0.995 0.995 0.998

J(H 2O) =

m1 + A ρ m 2 ‐A 0

m H 2O mLiCl + mKCl + mRbCl

100

(4)

With the data of Jänecke index J(B) in Tables 2 and 3, the stereo phase diagram of the system at 348.15 K was constructed in Figure 1. Figure 2 is the projected phase diagram of Figure 1. Figure 3 shows the projected phase diagrams of LiCl + KCl + RbCl + H2O at 298.15 K16 and 348.15 K. In the stereo phase diagram, points a, b, and c are invariant points of the three binary systems corresponding to LiCl + H2O, KCl + H2O, and RbCl + H2O, respectively; Points A, B, C, and D, cosaturated with two salts, are four invariant points of the three ternary systems corresponding to KCl + RbCl + H2O, LiCl + KCl + H2O, and LiCl + RbCl + H2O, respectively; Points E1 and E2, cosaturated with three salts, are two invariant points of the quaternary system LiCl + KCl + RbCl + H2O. As shown in Figure 1 and Figure 2, there is a solid solution of potassium and rubidium chloride [(K, Rb)Cl] formed in this system at 348.15 K. In the metastable phase diagram (Figure 2), there are four crystallization fields, five univariant curves, and two invariant points. The four crystallization fields correspond to single salts KCl, LiCl·H2O, RbCl and the solid solution [(K, Rb)Cl]. The salt’s crystallization region increases in the sequences of RbCl, LiCl·H2O, KCl, and [(K, Rb)Cl].

deionized water, with an electrical conductivity less than 1.0· 10−4 S·m−1 and pH ≈ 6.60, was used to prepare the solid− liquid phase equilibrium experiments and chemical analysis. 2.2. Experimental Method. The isothermal evaporation method was employed for the solubility experiments.16 The SHH-250 type thermostatic evaporator with the temperature controlling precision ± 0.10 K was employed in the metastable phase equilibrium experiments. The densities of solution were measured with a gravity bottle method with a precision of ± 0.0002 g·cm−3 and used for the mass fraction calculation of liquid components. The specific gravity bottle method with a correction of air buoyancy was used.17 The correction equation for density, ρ (g·cm−3) is,

ρ=

(2) −3

2. EXPERIMENTAL SECTION 2.1. Apparatus and Reagents. All inorganic salts used in our study were of analytical grade and tabulated in Table 1. The

chemical name

m2 ρ0 − ρa

(1) −3

where ρ0 = 0.9982 g·cm , the density of distilled water at 293.15 K, m1 is the mass of the gravity bottle filled with sample, and m2 is the mass of the gravity bottle filled with distilled water, A is the correction value of the air floating force, 2876



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Table 2. Solubilities and Physicochemical Property Values of the Quaternary System LiCl + KCl + RbCl + H2O at T = 348.15 K and Pressure p = 0.1 MPaa Jänecke index of dry salt composition of equilibrated solution, mB/(mol·kg−1) no.

density ρ/(g·cm−3)

refractive index

1,A 2 3 4 5 6 7 8 9 10 11 12 13 14 15,E1 16,B 17 18 19 20 21 22 23 24 25 26 27,E2 28,C 29 30 31 32,E1 33,D 34 35,E2

1.3143 1.3248 1.3353 1.3408 1.3406 1.3611 1.3502 1.3806 1.3779 1.4274 1.4254 1.4375 1.4956 1.5360 1.5768 1.7107 1.7220 1.6887 1.6405 1.6020 1.5679 1.5305 1.5366 1.5519 1.5734 1.6444 1.6896 1.5023 1.5150 1.5415 1.5615 1.5768 1.6879 1.6895 1.6896

1.3762 1.3692 1.3708 1.3705 1.3714 1.3724 1.3744 1.3765 1.3800 1.3864 1.3970 1.4045 1.4151 1.4230 1.4446 1.3906 1.3909 1.3914 1.3936 1.3976 1.4051 1.4050 1.4066 1.4126 1.4210 1.4345 1.4409 1.4478 1.4356 1.4409 1.4412 1.4446 1.4340 1.4406 1.4409

J(LiCl) + J(KCl) + J(RbCl) = 100

mLiCl

mKCl

mRbCl

mH2O

J(LiCl)

J(KCl)

J(RbCl)

J(H2O)

equilibrated solid phase

0.0000 0.2147 0.3161 0.5119 0.6157 0.8233 1.1323 1.4013 1.9533 2.9063 3.9137 4.7558 5.5768 6.3034 8.3416 0.0000 0.3444 0.5426 1.0097 2.0052 2.7908 3.6400 3.9231 4.7535 5.3385 6.2916 6.6266 10.9413 8.7874 8.7615 8.3958 8.3416 7.5466 6.6643 6.6266

4.0603 3.9745 3.7867 3.6311 3.4433 3.2246 3.0690 2.8477 2.5043 1.9570 1.7290 1.6056 1.5640 1.3937 0.5862 0.2253 0.1958 0.1811 0.1395 0.1100 0.0738 0.0738 0.0738 0.0671 0.0604 0.0657 0.0698 0.9014 0.7606 0.7257 0.6251 0.5862 0.0000 0.0429 0.0698

0.1588 0.1414 0.1811 0.2630 0.3027 0.3738 0.4788 0.5607 0.5987 0.7931 0.9353 1.0750 1.1933 1.2355 1.8061 4.1356 4.0968 4.0157 4.0256 3.7329 3.6634 2.9415 2.9101 2.7405 2.9407 2.9307 3.2136 0.0000 1.1950 1.6324 1.8036 1.8061 2.8084 3.0540 3.2136

37.6722 37.6333 37.9167 37.5444 37.8111 37.7500 36.9611 36.6944 36.5556 35.2778 32.8944 30.4833 27.9222 26.6389 21.3500 26.8389 26.4111 26.5444 25.5556 25.3056 24.0667 26.9222 26.4611 25.6778 22.9778 20.7722 18.0667 26.0556 23.6833 20.9444 21.0778 21.3500 18.9167 19.1667 18.0667

0.00 4.96 7.36 11.63 14.14 18.61 24.18 29.12 38.64 51.37 59.50 63.95 66.91 70.57 77.72 0.00 7.43 11.46 19.50 34.28 42.76 54.69 56.80 62.87 64.01 67.74 66.87 92.35 81.80 78.79 77.56 77.72 73.16 68.27 66.87

96.24 91.77 88.41 82.40 78.92 72.94 65.58 59.21 49.51 34.61 26.29 21.59 18.77 15.61 5.46 5.17 4.23 3.82 2.70 1.87 1.13 1.10 1.07 0.88 0.73 0.71 0.70 7.65 7.08 6.53 5.78 5.46 0.00 0.44 0.70

3.76 3.27 4.22 5.98 6.94 8.45 10.24 11.67 11.85 14.02 14.21 14.46 14.32 13.83 16.82 94.83 88.34 84.72 77.79 63.85 56.11 44.21 42.12 36.25 35.26 31.55 32.43 0.00 11.13 14.68 16.66 16.82 26.84 31.29 32.43

892.90 868.94 885.39 851.96 866.66 853.72 789.69 762.97 722.84 623.65 500.05 409.95 335.01 298.24 198.92 615.43 569.59 560.00 493.90 432.75 368.67 404.59 383.03 339.70 275.51 223.59 182.31 220.01 220.49 188.37 194.69 198.92 182.68 196.34 182.31

KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl KCl + (K,Rb)Cl LiI + KCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl RbCl + (K,Rb)Cl LiI + RbCl +(K,Rb)Cl LiI + KCl LiI + KCl LiI + KCl LiI + KCl LiI + KCl + (K,Rb)Cl LiI + RbCl LiI + RbCl LiI + RbCl + (K,Rb)Cl

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(n) = 1.0·10−4; ur(LiCl) = 0.0030; ur(KCl) = 0.0050; ur(RbCl) = 0.0050; mB = molality of B; LiI, LiCl·H2O.

Comparisons between the metastable phase diagrams at 298.15 K16 and 348.15 K (in Figure 3) show that the crystallization forms of the salts are not changed with the change of temperature; while at 348.15 K, the crystallization zone of solid solution [(K, Rb)Cl] decreased, and the crystallization zones of single salts KCl, RbCl, and LiCl·H2O enlarged. Thus, pure salts KCl, RbCl, and LiCl·H2O can be easier to obtaine at high temperature. Figure 6 is the relevant water content diagram of the system at 348.15 K, with the Jänecke index of water as ordinate, and the Jänecke index of rubidium as abscissa. On the univariant curve AE1, the Jänecke index of water decreases with the increase of J(RbCl) and reaches the smallest value at the invariant point E1. On the univariant curve BE2, the concentration of RbCl decreases and the concentration of LiCl increases in the evaporation process. Salt LiCl has a higher solubility in the water at 348.15 K, thus with an increase of LiCl

The solid solution [(K, Rb)Cl] contains most of the crystallization field. The five isothermal evaporation univariant curves, namely, curves AE1, BE2, CE1, DE2, and E1E2, are cosaturated with two salts and an equilibrated solution, respectively. The composition of the invariant points E1 and E2 are listed in what follows. At point E1, the molality of the equilibrated solution is mLiCl = 8.3416, mKCl = 0.5862, mRbCl = 1.8061, mH2O = 21.3500. Figure 4 is the X-ray diffraction pattern of the salts corresponding to the invariant point E1. Figure 4 shows that point E1 cosaturated with salts KCl, LiCl·H2O and (K, Rb)Cl. At point E2, the molality of the equilibrated solution is mLiCl = 6.6266, mKCl = 0.0698, mRbCl = 3.2136, mH2O = 18.0667. Figure 5 is the X-ray diffraction pattern of the salts corresponding to the invariant point E2. Figure 5 shows that point E2 cosaturated with salts LiCl·H2O, RbCl and (K, Rb)Cl. 2877



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Table 3. Experimental Solubility Values Corresponding to the Invariant Points of the Binary and Ternary Subsystems at 348.15 K and Pressure p = 0.1 MPaa Jänecke index of dry salt composition of equilibrated solution, mB/(mol·kg−1)

J(KCl) + J(LiCl) + J(RbCl) = 100

no.

system

mLiCl

mKCl

mRbCl

mH2O

J(LiCl)

J(KCl)

J(RbCl)

J(H2O)

equilibrated solid phase

a b c A B C D E1 E2

LiCl-H2O KCl-H2O RbCl-H2O KRbCl KRbCl LiKCl LiRbCl LiKRbCl LiKRbCl

12.0052 0.0000 0.0000 0.0000 0.0000 10.9413 7.5466 8.3416 6.6266

0.0000 4.3313 0.0000 4.0603 0.2253 0.9014 0.0000 0.5862 0.0698

0.0000 0.0000 4.4904 0.1588 4.1356 0.0000 2.8084 1.8061 3.2136

27.2833 37.6167 25.3889 37.6722 26.8389 26.0556 18.9167 21.3500 18.0667

100.00 0.00 0.00 0.00 0.00 92.39 72.88 77.71 66.87

0.00 100.00 0.00 96.24 5.17 7.61 0.00 5.46 0.70

0.00 0.00 100.00 3.76 94.83 0.00 27.12 16.83 32.43

227.26 868.48 565.38 892.90 615.43 220.01 182.68 198.90 182.31

LiCl·H2O KCl RbCl KCl + (K,Rb)Cl RbCl + (K,Rb)Cl LiCl·H2O + KCl LiCl·H2O + RbCl LiCl·H2O + KCl + (K,Rb)Cl LiCl·H2O + RbCl + (K,Rb)Cl

a Note: Standard uncertainties u are u(T) = 0.10 K; ur(p) = 0.05; ur(LiCl) = 0.0030; ur(KCl) = 0.0050; ur(RbCl) = 0.0050; mB = molality of B; KRbCl, KCl + RbCl + H2O; LiKCl, KCl + LiCl + H2O; LiRbCl, RbCl + LiCl + H2O; LiKRbCl, LiCl + KCl + RbCl + H2O.

Figure 1. Stereo diagram of the quaternary system LiCl + KCl + RbCl + H2O at 348.15 K.

Figure 3. The projected phase diagram of the quaternary system LiCl + KCl + RbCl + H2O at 298.15 K16 and 348.15 K: •, experimental point at 348.15 K; ▲, experimental point at 298.15 K; E1, E2, invariant points at 348.15 K; F1, F2, invariant points at 298.15 K.

Figure 2. The projected phase diagram of the quaternary system LiCl + KCl + RbCl + H2O at 348.15 K: •, experimental point.

Figure 4. X-ray diffraction pattern of the invariant point E1 (KCl, LiCl· H2O and [(K, Rb)Cl]).

in the solution, the Jänecke index of water decreases gradually until it reaches the invariant point E2. 2878



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was determined, and the data are shown in Table 2. On the basis of the experimental results in Table 2, the relationship between physicochemical properties (densities and refractive indices) and the composition of rubidium chloride in solution were constructed in Figure 7. Figure 7 shows that the densities and refractive indices of the equilibrated aqueous solution change regularly with the change of the content of J(RbCl). On the univariant curve AE1, with the increase of J(RbCl), the density and refractive index increase gradually until the invariant point E1 is reached.

4. EMPIRICAL CALCULATION OF THE REFRACTIVE INDICES According to the empirical equation for the refractive index of solutions developed in the previous study, the refractive indices of the equilibrated solutions were calculated:19 A × mi × Mi n ln =∑ i n0 1000 (5)

Figure 5. X-ray diffraction pattern of the invariant point E2 (RbCl, LiCl·H2O and [(K, Rb)Cl]).

where, n and n0 denote the refractive index of the solution and pure water at 348.15 K, respectively; Ai denotes the constants of the ith salt in the solution. The value of n0 is 1.32404,20 the data of Ai can be obtained from the saturated solubility of the binary system. In this quaternary system, Ai constants of LiCl, KCl, and RbCl at 348.15 K are 0.001726, 0.0010952, and 0.000889, respectively. Besides, mi is the molality of the ith salt in the solution, and Mi is the molar mass of the ith salt. All of the calculated results have a maximum absolute deviation less than 0.007.

5. CONCLUSIONS The solubilities and physicochemical properties of the quaternary system LiCl + KCl + RbCl + H2O at 348.15 K were investigated by using the isothermal evaporation method. The stereo phase diagram, projected phase diagram, water content diagram, and the physicochemical properties versus composition diagrams were plotted according to the experimental data. The solid phases of the quaternary systems were found as LiCl·H2O, KCl, RbCl, and the solid solution [(K, Rb)Cl]. It is found that [(K, Rb)Cl] salt contains almost all of the crystallization field. Comparisons between the metastable phase diagrams at 298.15 K and 348.15 K show that the

Figure 6. Water-content diagram of the quaternary system LiCl + KCl + RbCl + H2O at 348.15 K.

Refractive index is a basic and important physicochemical property of electrolyte solutions and always changes with the temperature, component, and composition of solution. To ensure the change rule of the refractive index is in accordance with the composition variation of solution, the refractive index

Figure 7. Physicochemical properties vs composition diagrams for the quaternary system LiCl + KCl + RbCl + H2O at 348.15 K: (a) density vs composition; (b) refractive index vs composition. 2879



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(12) Yu, X. D.; Zeng, Y.; Zhang, J. Q.; Yang, J. Y. Metastable Phase Equilibria for the Aqueous Ternary System containing Lithium, Rubidium and Chloride at 298.15 K. Miner. Mag. 2011, 75, 2233. (13) Yu, X. D.; Zeng, Y. Metastable Phase Equilibria in the Aqueous Ternary Systems KCl + MgCl2 + H2O and KCl + RbCl + H2O at 298.15 K. J. Chem. Eng. Data 2011, 56, 3384−3391. (14) Yu, X. D.; Zeng, Y. Metastable Phase Equilibria in the Aqueous Ternary Systems KCl + MgCl2 + H2O and KCl + RbCl + H2O at 323.15 K. J. Chem. Eng. Data 2010, 55, 5771−5776. (15) Yu, X. D.; Zeng, Y.; Yin, Q. H.; Mu, P. T. Solubilities, Densities, and Refractive Indices of the Ternary Systems KCl + RbCl + H2O and KCl + MgCl + H2O at 348.15 K. J. Chem. Eng. Data 2012, 57, 3658− 3663. (16) Yu, X. D.; Zeng, Y.; Yang, J. Y. Solid−Liquid Isothermal Evaporation Metastable Phase Equilibria in the Aqueous Quaternary System LiCl + KCl + RbCl + H2O at 298.15 K. J. Chem. Eng. Data 2012, 57, 127−132. (17) Chen, H. Y.; Chen, H. Chemical reagent−General method for the determination of density(GB/T 611−2006); China Standards Press: Beijing, 2006. (18) Institute of Qinghai Salt-Lake of Chinese Academy of Sciences. Analytical Methods of Brines and Salts, 2nd ed.; Chinese Science Press: Beijing, China, 1988. (19) Song, P. S.; Du, X. H.; Xu, H. C. Study on Phase Diagram of Ternary System Li2B4O7 + Li2SO4 + H2O at 298.15 K. Chin. Sci. Bull. 1983, 2, 106−110. (20) Liu, G. Q.; Ma, L. X.; Liu, J. Handbook of Chemistry & Chemical Property Data (Inorganic Vol.); Chemical Industry Press: Beijing, China, 2002.

crystallization zone of solid solution [(K, Rb)Cl] decreased at 348.15 K, while the crystallization zones of single salts KCl, RbCl, and LiCl·H2O enlarged. The calculated refractive indices using empirical equations agree well with the experimental values. The maximum absolute deviation between the calculated and experimental values is less than 0.007.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]; [email protected]. Tel.: 8628-84078940. Fax: 86-28-84079074. Funding

This project was supported by National High Technology Research and Development Program of China (2012AA061704), China National Nature Science Foundation (No. 41173071), the Research Fund from the Sichuan Provincial Education Department (11ZZ009), the Sichuan youth science and technology innovation research team funding scheme (2013TD0005), and the Research Fund from the Science and Technology Department of Sichuan Province (2009GZ0238). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the associate editor and the anonymous reviewers for their critical comments and kind help on the manuscript.

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REFERENCES

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Metastable Phase Equilibrium in the Quaternary System LiCl + KCl +

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