Article pubs.acs.org/jced
Solid−Liquid Phase Equilibria in the Ternary Systems (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K Shiqiang Wang,*,† Yafei Guo,† Dongchan Li,‡ Fengmin Zhao,† Wei Qiao,† and Tianlong Deng† †
Tianjin Key Laboratory of Marine Resources and Chemistry, College of Marine Science and Engineering, Tianjin University of Science and Technology, Tianjin 300457, P. R. China ‡ School of Marine Science and Engineering, Hebei University of Technology, Tianjin 300130, P. R. China ABSTRACT: Solubility as well as solution density in aqueous systems (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K have been studied using the isothermal dissolution method. In the ternary system (LiCl + MgCl2 + H2O) at 288.15 K, two invariant points, three isothermal dissolution curves and three crystallization regions including MgCl2·6H2O, LiCl·2H2O, and double salt LiCl·MgCl2·7H2O were detected. Experimental results compared with values of this system at (273.15, 348.15, and 323.15) K shows that the LiCl·MgCl2·7H2O crystallization region is increased slightly with the increasing of temperature, while that of MgCl2·6H2O and LiCl·2H2O are decreased obviously. In the ternary system (Li2SO4 + MgSO4 + H2O) at 288.15 K, there are one invariant point, two isothermal dissolution curves, and two crystallization regions corresponding to Li2SO4·H2O and MgSO4·7H2O. When this experimental phase diagram at 288.15 K was compared with that at (298.15, 303.15, and 348.15) K, it shows that the Li2SO4· H2O crystallization region is increased with the increasing of temperature, while that of MgSO4·7H2O is decrease obviously. A Pitzer and Harvie−Weare thermodynamic model were applied to calculate the solubility for this ternary system, and the calculated solubilities agree reasonably with the experimental results.
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INTRODUCTION Lithium and its compounds have been used extensively in many industries such as the battery, optics, metallurgy, nuclear energy, aerospace, and so on. As the solid ores drying up gradually and the high recoverable cost, to develop liquid lithium mineral resources has become an inevitable tendency in future. Liquid lithium mineral resources are mainly distributed in salt lake brine, seawater, geothermal water, and oil-field water, especially lithium resources reserves in salt lake brine are more than 80% in mass of the total reserves.1,2 Lots of salt lakes abundant with lithium resources are located in the Qinghai−Xizang Plateau, such as Dong-xi-taijinaier Salt Lake.3 However, lithium-containing salt lake brine always coexist with magnesium ion, resulting in increasing the difficulty of separation and extraction of lithium from brine for lithium and magnesium ion many similar chemical properties.4−6 In order to acquiring the thermodynamic behaviors and exploiting these valuable brine resources, the solid−liquid phase equilibria systems containing lithium have been studied, including three-, four-, and five-component systems (Li2SO4 + MgSO4 + H2O) at (348.15, 323.15, and 308.15) K,7−9 (Li2SO4 + Na2SO4 + H2O) at (348.15, 308.15, and 288.15) K,10,11 (LiCl + NaCl + Li2SO4 + Na2SO4 + H2O) at 273.15 K,12 and (LiCl + Li2SO4 + MgCl2 + MgSO4 + H2O) at (323.15 and 308.15) K,13−15 and (Li + Na + K + Cl + SO4 + H2O) at 308.15 K.16 © XXXX American Chemical Society
Although the ternary systems (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) over a wide temperature had been previously reported since the 1950s,17 the phase diagram and solution physicochemical properties are still not sufficient, and both of the systems at 288.15 K have not yet been reported. The average temperature of the Dong-xi-taijinaier Salt Lake region in summer is around 288.15 K, so the phase equilibrium study of these ternary systems at 288.15 K has significant value for separating and purifying lithium salts from the brines. In this paper, solubility of the ternary system (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K were presented experimentally and predicted by the Harvie−Weare (HW) model.
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EXPERIMENTAL SECTION Reagents. The reagents in the experiment include epsomite (MgSO4·7H2O, A.R. grade, purity by mass percentage > 0.995), bischofite (MgCl2·6H2O, A.R. grade, purity by mass percentage > 0.992), lithium chloride monohydrate (LiCl·H2O, A.R. grade, purity by mass percentage > 0.990), lithium sulfate monohydrate (Li2SO4·H2O, A.R. grade, purity by mass percentage > 0.991) purchased from Sinopharm Chemical Reagent Co. Ltd. The water was doubly deionized (electrical Received: October 7, 2014 Accepted: December 29, 2014
A
DOI: 10.1021/je500946w J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 1. Experimental Solubility and Solution Density in (LiCl + MgCl2 + H2O) at 288.15 K and Pressure p = 0.1 MPaa composition of solution 100wb
a
no.
LiCl
MgCl2
H2O
1,A 2 3 4 5,E 6 7 8 9 10 11 12,F 13 14 15 16 17 18,B
43.95 40.8 39.79 39.91 39.82 38.05 37.86 34.53 34.01 32.67 31.73 27.14 23.81 19.40 14.40 9.68 0.20 0.00
0.00 3.45 4.98 5.02 5.29 6.15 6.39 8.42 8.62 9.72 10.46 14.34 16.1 19.28 22.88 26.68 35.01 35.22
56.05 55.75 55.23 55.07 54.89 55.8 55.75 57.05 57.37 57.61 57.81 58.52 60.09 61.32 62.72 63.64 64.79 64.78
composition of wet solid phase 100w LiCl
MgCl2
58.59
1.20
57.62 42.50
2.01 13.48
23.65
25.08
22.86 22.41 13.78 8.21
25.48 25.38 34.35 36.44
6.70 5.17
35.88 36.17
density ρ/(g·cm−3)
equilibrium solid phase
1.2870 1.2978 1.3074 1.3107 1.3127 1.3092 1.3088 1.3057 c
LiCl·2H2O LiCl·2H2O LiCl·2H2O LiCl·2H2O LiCl·2H2O + LiCl·MgCl2·7H2O LiCl·MgCl2·7H2O LiCl·MgCl2·7H2O LiCl·MgCl2·7H2O LiCl·MgCl2·7H2O LiCl·MgCl2·7H2O LiCl·MgCl2·7H2O LiCl·MgCl2·7H2O + MgCl2·6H2O MgCl2·6H2O MgCl2·6H2O MgCl2·6H2O MgCl2·6H2O MgCl2·6H2O MgCl2·6H2O
1.3067 1.3104 1.3066 1.3078 1.3106 1.3153 1.3320 1.3339
Standard uncertainties u are u(T) = 0.02 K, u(ρ) = 0.0001, u(LiCl) = 0.003, and u(MgCl2) = 0.004. bw = mass fraction. c, means not detected.
conductivity κ < 1.0·10−4 S·m−1) for the experimental samples preparation and quantitative analysis. Apparatus. The equilibrium experimental instruments in this study include: a thermostatic bath with a temperature precision of 0.02 K, test equilibrium bottles, and an electric magnetic stirrer. The application of the Olympus BX51 professional microscope and MSAL XD-3 powder XRD (Beijing Puxi General Instrument Co. Ltd., China) were used to identify solid phase minerals. A Prodigy ICP-OES (Leman Co.) was employed in determining Li+ concentrations in solution. Experimental Method. The solid−liquid phase equilibrium experiment was studied with the isothermal dissolution equilibrium method.11,15 First, the appropriate salts (MgSO4· 7H2O, Li2SO4·H2O, LiCl·H2O, and MgCl2·6H2O) and doubly deionized water mixed in different mass ratios were placed and sealed in the equilibrium bottles, which must ensure the solid phases were not dissolved entirely and always existed in the whole equilibrium process. Then the sealed bottles were fixed in the magnetic stirring thermostatic bath (HXC-500-6A). The temperatures of the baths were set at 288.15 ± 0.02 K and with 150 rpm stirring speed. These artificial synthesized complexes were stirred with an electric magnetic stirrer, and the equilibration times were about (5 to 6) days. Before sampling, it took about 8 h for the clarification of an aqueous solution. Two samples were taken out from the bottles. One was used for determining solution densities, and the other is applied to quantitative analysis. In addition, the solids were determined by X-ray powder diffraction analysis combined with Schreinemakers’ method. Analytical Methods. The concentrations of Cl− and SO42− were measured, Cl− ion titrimetric analysis with AgNO3 standard solution using potassium chromate as an indicator, and SO42− ion gravimetric analysis with barium sulfate precipitation at a pH = 1.22. The precision of Cl− ion in triplicate could be less than 0.3 %, and the result deviation of SO42− ion in triplicate was within 0.1 %. The concentration of the Mg2+ in the liquid phases were analyzed by titration with
ethylenediamine tetraacetic acid disodium salt standard solution (NH3·H2O−NH4Cl buffer, pH = 9.5 to 10) using Eriochrome Black-T as the indicator. The significantly interference of Li+ ion was eliminated by adding anhydrous alcohol and n-butanol as a masking agent.18 The Li+ concentration was analyzed by ICP-OES.
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RESULTS AND DISCUSSION LiCl + MgCl2 + H2O. Experimental solubilities as well as solution densities for the aqueous ternary system (LiCl +
Figure 1. Phase diagram for the ternary system (LiCl + MgCl2 + H2O) at 288.15 K. ●, liquid phase; , isothermal curve; ◀, wet solid phases; Bis, MgCl2·6H2O; Lic, LiCl·MgCl2·7H2O; Lc, LiCl·2H2O.
MgCl2 + H2O) at 288.15 K were determined and listed in Table 1. The stable phase diagram based on the solubility results was plotted in Figure 1 with a square coordinate. B
DOI: 10.1021/je500946w J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Figure 2. Comparison of phase diagram in the ternary system (LiCl + MgCl2 + H2O) at (273.15, 288.15, 323.15, and 348.15) K. −■−, phase diagram at 273.15 K; ···□···, phase diagram at 288.15 K; −▲−, phase diagram at 323.15 K; ···◊···, phase diagram at 348.15 K.
Figure 3. Phase diagram for the ternary system (Li2SO4 + MgSO4 + H2O) at 288.15 K. ●, liquid phase; , isothermal curve; ◀, wet solid phases; Eps−MgSO4·7H2O; Ls−Li2SO4·H2O.
In the stable phase diagram (Figure 1), there are two invariant points corresponding to E (MgCl2·6H2O + LiCl· MgCl2·7H2O) and F (LiCl·MgCl2·7H2O + LiCl·2H2O); three isothermal dissolution curves of AE, EF, and BF, which are saturated with a single salt (LiCl·2H2O, LiCl·MgCl2·7H2O, and MgCl2·6H2O); and three crystallization fields corresponding to bischofite (MgCl2·6H2O), lithium chloride dihydrate (LiCl· 2H2O), and lithium carnallite (LiCl·MgCl2·7H2O), respectively. In the binary system LiCl−H2O, the transition between LiCl·H2O and LiCl·2H2O is at 292.15 K, and the equilibrium solid phase present at 288.15 K is LiCl·2H2O which was determined by Schreinemakers’ method. The size of crystallization fields followed MgCl2·6H2O > LiCl·MgCl2·7H2O > LiCl·2H2O. This ternary system belongs to incongruent double salt type, which is a complex type due to the incongruent double salt LiCl·MgCl2·7H2O that are formed.
Solubilities of single salt LiCl and MgCl2 in the liquid phase with mass fraction corresponding to w(LiCl) = 43.95 % (A) and w(MgCl2) = 35.22 % (B). Points E and F represent cosaturation with two salts. At the invariant point E, the compositions in the liquid phase are w(LiCl) = 39.82 % and w(MgCl2) = 5.29 %, and the compositions are w(LiCl) = 27.14 % and w(MgCl2) = 14.34 % at point B. The solubility of the system (LiCl + MgCl2 + H2O) over a wide temperature had been reported; the phase diagram at (273.15, 323.15, and 348.15) K17 compared with that at 288.15 K (this study) is shown in Figure 2. It was found that (1) the solid phase numbers are the same; (2) the mineral LiCl·2H2O is dehydrated and transformed into LiCl·H2O, and the area of crystallization region decreased obviously as temperature increasing from (273.15 to 348.15) K; (3) lithium carnallite
Table 2. Experimental Solubility and Density in (Li2SO4 + MgSO4 + H2O) at 288.15 K and Pressure p = 0.1 MPaa composition of solution 100wb
a
composition of wet solid phase 100w
no.
Li2SO4
MgSO4
H2O
Li2SO4
1,A 2 3 4 5 6 7 8 9 10 11,E 12 13 14 15 16 17 18,B
25.98 25.17 24.69 24.06 23.25 22.88 21.57 19.72 19.18 17.27 16.64 16.77 14.87 13.23 7.13 4.61 2.43 0.00
0.00 1.41 2.1 2.85 3.79 4.43 7.18 9.66 11.13 14.07 14.93 14.93 15.78 16.33 19.67 21.03 22.71 24.62
74.02 73.42 73.21 73.09 72.96 72.69 71.25 70.62 69.69 68.66 68.43 68.3 69.35 70.44 73.2 74.36 74.86 75.38
c 63.01
0.57
66.36
1.02
63.82
2.42
57.53
5.97
29.36
23.63
6.38 4.85 2.61 1.80 0.87
35.11 36.80 37.82 38.48 39.40
MgSO4
density ρ/(g·cm−3)
equilibrium solid phase
1.2376 1.2461 1.248 1.2517 1.2583 1.2626 1.2781 1.2943 1.3042 1.3223 1.3328 1.3284 1.3185 1.3131 1.291 1.2809 1.2768 1.2691
Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O + MgSO4·7H2O MgSO4·7H2O MgSO4·7H2O MgSO4·7H2O MgSO4·7H2O MgSO4·7H2O MgSO4·7H2O MgSO4·7H2O
Standard uncertainties u are u(T) = 0.02 K, u(ρ) = 0.0001, u(Li2SO4) = 0.003, and u(MgSO4) = 0.015. bw = mass fraction. c, means not detected. C
DOI: 10.1021/je500946w J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 3. Calculated and Experimental Densities in (LiCl + MgCl2 + H2O) at 288.15 K
Figure 4. Comparison of phase diagram of the system (Li2SO4 + MgSO4 + H2O) at (288.15, 298.15, 303.15, and 348.15) K. −■−, phase diagram at 288.15 K; ···○···, phase diagram at 298.15 K; −▲−, phase diagram at 303.15 K; ···◊···, phase diagram at 348.15 K. a
no.
experimental value
calculated value
relative deviation /%
1,A 2 3 4 5,E 6 7 8 9 10 11 12,F 13 14 15 16 17 18,B
1.2870 1.2978 1.3074 1.3107 1.3127 1.3092 1.3088 1.3057 a
1.2870 1.3002 1.3090 1.3104 1.3126 1.3085 1.3096 1.3063 1.3045 1.3062 1.3070 1.3141 1.3078 1.3087 1.3096 1.3149 1.3331 1.3339
0.00 −0.18 −0.13 0.02 0.01 0.06 −0.06 −0.04
1.3067 1.3104 1.3066 1.3078 1.3106 1.3153 1.3320 1.3339
−0.03 −0.28 −0.09 −0.07 0.07 0.03 −0.08 0.00
, means not determined.
Table 4. Calculated and Experimental Densities in (Li2SO4 + MgSO4 + H2O) at 288.15 K
Figure 5. Diagram of the density versus composition of the systems (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K. (a) ···△···, in ternary system (LiCl + MgCl2 + H2O); (b) −▲−, in ternary system (Li2SO4 + MgSO4 + H2O).
(LiCl·MgCl2·7H2O) is incongruent, and the LiCl·MgCl2·7H2O crystallization area is increased with the increasing temperature, while that of MgCl2·6H2O is decreased significantly. (Li2SO4 + MgSO4 + H2O). Experimental solubilities as well as solution densities for an aqueous system (Li2SO4 + MgSO4 + H2O) at 288.15 K were determined and listed in Table 2. The stable phase diagram based on the solubility results is plotted in Figure 3. In the stable phase diagram (Figure 3), there are one invariant points E; two isothermal dissolution curves of AE and BE; and two hydrate salts Li2SO4·H2O and MgSO4·7H2O. The Li2SO4·H2O crystallization area is relatively larger than MgSO4· 7H2O. Solubilities of single salt Li2SO4 and MgSO4 with mass percentage corresponding to w(Li2SO4) = 25.98 % (A) and w(MgSO4) = 24.62 % (B). Points E represent cosaturation with two salts; the compositions in the liquid phase are w(Li2SO4) = 16.64 % and w(MgSO4) = 14.93 %.
no.
experimental value
calculated value
relative deviation/%
1,A 2 3 4 5 6 7 8 9 10 11,E 12 13 14 15 16 17 18,B
1.2376 1.2461 1.248 1.2517 1.2583 1.2626 1.2781 1.2943 1.3042 1.3223 1.3328 1.3284 1.3185 1.3131 1.291 1.2809 1.2768 1.2691
1.2376 1.2457 1.2495 1.2523 1.2557 1.2599 1.2811 1.2934 1.3068 1.3248 1.3293 1.3306 1.3210 1.3105 1.2884 1.2790 1.2774 1.2691
0.00 0.03 −0.12 −0.04 0.20 0.21 −0.24 0.07 −0.20 −0.19 0.26 −0.17 −0.19 0.20 0.20 0.14 −0.05 0.00
Solubility of the ternary system (Li2SO4 + MgSO4 + H2O) over a wide temperature had been reported; the phase diagram at (298.15, 303.15 and 348.15) K17 compares with that at 288.15 K (this study) is shown in Figure 4. It was found that the solid phase numbers are the same, while mineral MgSO4· 7H2O is dehydrated and transformed into MgSO4·H2O at 348.15 K, and the area of crystallization region of MgSO4·7H2O decreased obviously as temperature increasing from (288.15 to 348.15) K, while that Li2SO4·H2O increased with the increasing temperature. These changes indicate that the solubility of magnesium sulfate is positively correlated with temperature, whereas the solubilities of lithium sulfate is negative correlated with temperature. Solution Density in the Ternary System. On the basis of the experimental results in Tables 1 and 2, the solution density versus composition of (LiCl + MgCl2 + H2O) with solid lines D
DOI: 10.1021/je500946w J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 5. Single and Mixing Model Parameters in the System (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K species
β(0)
β(1)
LiCl Li2SO4 MgCl2 MgSO4 Li, Mg Li, Mg, Cl Li, Mg, SO4
0.1500 0.1306 0.3560 0.1095
0.3006 1.1550 1.6502 3.0049
β(2)
Cϕ
0.7250
0.004211 −0.001547 0.007589 0.06739
θ
ψ
ref
0.0023289 0.013152
27 28 29, 30 29, 30 this work this work this work
−0.034927
and (Li2SO4 + MgSO4 + H2O) with dashed lines at 288.15 K was plotted in Figure 5. In Figure 5a, the density curves in the ternary system (LiCl + MgCl2 + H2O) at 288.15 K were decreased first and then increased gradually with the increasing concentration of LiCl from point B to E, and the singular values of (1.3127 and 1.3104) g·cm−3 appear at the invariant points E and F. Then the solution densities were decreased sharply with the decreasing concentration of LiCl at the saturated region of LiCl·2H2O (curve EA). In Figure 5b, density curves in the ternary system (Li2SO4 + MgSO4 + H2O) were increased rapidly with the MgSO4 concentration at the saturated region of Li2SO4·H2O (curve AE), and reached the maximum value of 1.3328 g·cm−3 at the invariant point E, and solution densities decreased gradually with the increasing concentration of MgSO4 at the saturated region of MgSO4·7H2O (curve EB). The electrolyte solution empirical equation of density has been widely used in brine systems.19 The following empirical equation was used to calculate the density: ρ = ∑ Ai wi ln ρ0 (1)
Figure 6. Comparison of the calculated and experimental phase diagram in the system (LiCl + MgCl2 + H2O) at 288.15 K. −●−, experimental phase diagram; ···○···, calculated phase diagram; Bis, MgCl2·6H2O; Lic, LiCl·MgCl2·7H2O; Lc, LiCl·2H2O.
In the above equation, where ρ is solution density, ρ0 is the pure water density (0.99909 g·cm−3 at 288.15 K20); Ai is the coefficient of each salt, which calculated in the present work; wi is the weight percentage of each salt. Coefficients Ai of LiCl, MgCl2, Li2SO4, and MgSO4 are 0.005808, 0.008264, 0.008287, and 0.01003 at 288.15 K. Calculated values and experimental results are listed in Tables 3 and 4. The maximum relative error between calculated and experimental data is no more than 0.3%.
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SOLUBILITY CALCULATED The Pitzer and Harvie−Weare thermodynamic model,21−24 which give osmotic coefficients of the solution and mean Table 6. Solubility Equilibrium Constants (ln K) of Solid Phases in the System (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K solid phase
ln K
ref
MgCl2·6H2O MgSO4·7H2O LiCl·2H2O Li2SO4·H2O LiCl·MgCl2·7H2O
10.8098 −4.6193 12.1433 1.2168 24.3589
29, 30 29, 30 this work this work this work
Figure 7. Comparison of the calculated and experimental phase diagram in the system (Li2SO4 + MgSO4 + H2O) at 288.15 K. −●−, experimental phase diagram; ···○···, calculated phase diagram; Eps− MgSO4·7H2O; Ls−Li2SO4·H2O.
system (Na + K + Ca + Mg + H + Cl + SO4 + CO2 + B(OH)4 + H2O) from low to high concentrations at 298.15 K and is applied to Searles Lake.25,26 Parameterizations. We obtained Pitzer’s single-salt parameters β(0), β(1), and Cϕ of LiCl, MgCl2, Li2SO4, and
activity coefficients of electrolyte expressions, has widely applied in predicting the solubility and thermodynamic property of electrolyte solution.11,16 Harvie and Weare have reliably predicted the mineral solubilities in complex brine E
DOI: 10.1021/je500946w J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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MgSO4 from the literature.27−30 The mixing ion-interaction parameters of θLi,Mg, ψLi,Mg,Cl, and ψLi,Mg,SO4 which have not been acquired from literature at 288.15 K, were determined by fitting the solubilities results by the least-square method. The Debye− Hückel parameter Aϕ = 0.3856 at 288.15 K,29,30 and the coefficients a1 and a2 for the MgSO4 is set 1.4 and 12. Pitzer single and mixing parameters used in this system are listed in Table 5. The solubility equilibrium constants ln K for miners LiCl· 2H2O(s), Li2SO4·H2O(s), LiCl·MgCl2·7H2O(s), MgCl2·6H2O(s), and MgSO 4·7H2 O(s) were acquired by calculating the component activities in their saturated solutions according to eq 2. The obtained ln K parameters are listed in Table 6.
Article
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +86-22-60601156. Funding
The work was financial supported from Program of the National Natural Science Foundation of China (Grant No. 21106103, 21276194, 21306136, and 21406048), the Training Program for Changjiang Scholars and Innovative Research Team in University ([2013]373), the Innovative Research Team of Tianjin Municipal Education Commission (TD125004), the Natural Science Foundation of Tianjin (12JCQNJC03400), and the Specialized Research Fund for the Doctoral Program of Chinese Higher Education (Grant No. 20111208120003).
M υMX υX ·υOH 2O = υM Mν + + υX X ν ‐ + υOH 2O
Notes
The authors declare no competing financial interest. ln K = υM ln(aM) + υX ln(aX ) + υO ln αH2O
■
(2)
Solubility Prediction for the Ternary System. On the basis of Pitzer and Harvie−Weare thermodynamic model for electrolytes, the solubilities of these ternary systems (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K have been calculated, respectively. The calculated and experimental phase diagrams were plotted in Figures 6 and 7, respectively. According to the comparison of phase diagram, the predicted solubilities are in good agreement with the experimental values. These results indicate that the single and mixing model parameters and the solubility equilibrium constants for the solid phases acquired this work are reliable.
REFERENCES
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CONCLUSIONS Phase equilibrium of ternary systems (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K including experimental solubilities and solution densities are determined using the isothermal dissolution equilibrium method. (1) LiCl + MgCl2 + H2O. There are two invariant points, three isothermal dissolution curves and three crystallization regions including MgCl2·6H2O, LiCl·2H2O, and double salt LiCl·MgCl2·7H2O. Phase diagram of this system at (273.15, 288.15, 323.15, and 348.15) K shows that LiCl·MgCl2·7H2O crystallization area is increased slightly with the increasing of temperature, while that of MgCl2·6H2O is decreased obviously. (2) Li2SO4 + MgSO4 + H2O. There are one invariant point, two isothermal dissolution curves, and two crystallization regions (Li2SO4·H2O and MgSO4·7H2O). When experimental phase diagram at 288.15 K was compared with that at (298.15, 303.15, and 348.15) K, it shows that the Li2SO4·H2O crystallization area is increased with the increasing of temperature, while that of MgSO 4·7H 2O is decreased obviously. (3) Solution density. Density values change regularly with increasing composition at 288.15 K, and the calculated density with empirical equation agree well with the experimental result. (4) Solubility calculated. Based on the Pitzer and Harvie− Weare thermodynamic model, the solubilities of (LiCl + MgCl2 + H2O) and (Li2SO4 + MgSO4 + H2O) at 288.15 K were calculated. The predicted and experimental solubilities are in good agreement. The single and mixing model parameters and the solubility products for the solid phases acquired in this work are reliable. F
DOI: 10.1021/je500946w J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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DOI: 10.1021/je500946w J. Chem. Eng. Data XXXX, XXX, XXX−XXX
