Metastable phase equilibria for the quaternary system containing potassium, magnesium, rubidium and chloride at 323.15 K

Metastable phase equilibria for the quaternary system containing potassium, magnesium, rubidium and chloride at 323.15 K

Fluid Phase Equilibria 349 (2013) 67–70 Contents lists available at SciVerse ScienceDirect Fluid Phase Equilibria journal homepage: www.elsevier.com...

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Fluid Phase Equilibria 349 (2013) 67–70

Contents lists available at SciVerse ScienceDirect

Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid

Metastable phase equilibria for the quaternary system containing potassium, magnesium, rubidium and chloride at 323.15 K Dongbo Jiang a , Ying Zeng a,b,∗ , Xudong Yu a a b

College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, PR China Mineral Resources Chemistry Key Laboratory of Sichuan Higher Education Institutions, Chengdu 610059, PR China

a r t i c l e

i n f o

Article history: Received 9 January 2013 Received in revised form 31 March 2013 Accepted 5 April 2013 Available online 17 April 2013 Keywords: Metastable phase equilibrium Solubility Solid solution Rubidium Underground brine

a b s t r a c t By employing the method of isothermal evaporation, the metastable phase equilibria of the quaternary systems KCl + RbCl + MgCl2 + H2 O were researched at 323.15 K. In this paper, the solubilities and physicochemical properties, such as refractive indices and densities of the equilibrated solution, were determined. Through analysis of the experiments data, the metastable phase diagram, the water content diagram and physicochemical properties versus composition diagrams of the quaternary system were plotted. The study results indicated that in the metastable phase diagram, there were four invariant points (H1 , H2 , H3 , H4 ), nine univariant curves, and six crystallization fields. And the six crystallization fields were magnesium chloride hexahydrate (MgCl2 ·6H2 O) and potassium chloride (KCl) and rubidium chloride (RbCl) and a rubidium and magnesium chloride double salt named carnallite (RbCl·MgCl2 ·6H2 O) and a potassium and magnesium chloride double salt named carnallite (KCl·MgCl2 ·6H2 O) and a solid solution of potassium and rubidium chloride [(K, Rb)Cl]. The solid solution [(K, Rb)Cl] had the largest crystallization field. This showed that only by using evaporation and crystallization methods at 323.15 K, was it difficult to separate potassium from rubidium in chloride solution. The physicochemical properties of the quaternary system change regularly with the changes of composition in aqueous solutions. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Rubidium is mainly occurs in natural carnallite, cesium lithium mica, feldspar and brine [1]. The Pingleba brine located in the Sichuan Basin is famous for concentrations high sodium, potassium, lithium, bromine, borate and rubidium in the world. The Pingleba brine resource is of excellent quality, the rubidium content is as high as 32.55 mg/L. Its rubidium content is 3.75 times of the industrial mined grade, which is far higher than other world’s brine [2]. Underground brine is a complex water–salt coexisting system. Through studying the phase equilibrium of the corresponding brine system to explore the regular about the evaporation, concentration, and crystallization behavior of salts, we can obtain the necessary basic data for the comprehensive utilization of brine resources. Due to the lack of the phase equilibrium data of the containing rubidium salt water system, the development and utilization of Rubidium resources will be affected. In order to solve this problem, some scholars have carried out the study of the phase equilibrium for the partial containing rubidium brine system, and

ternary K2 SO4 + Rb2 SO4 + H2 O phase equilibrium for 298.15 K was studied by Kalink and Rumyantsev [3]; Merbach did on 298.15 K quaternary system of KCl + RbCl + CsCl + H2 O and its sub system phase equilibrium [4,5]; D’Ans and Brsch did on 298.15 K quaternary system of KCl + RbCl + (CsCl) + MgCl2 + H2 O and its sub systems [6,7]; Zeng completed the study for 298.15 K quaternary system of LiCl + KCl + RbCl + H2 O and its sub system phase equilibrium [8–10]. The quaternary system KCl + RbCl + MgCl2 + H2 O is an important subsystem for the complex multiple-system of Pingleba brine. So far the metastable equilibrium of the quaternary system KCl + RbCl + MgCl2 + H2 O at 323.15 K has not been reported. Zeng has completed the study of the ternary system KCl + MgCl2 + H2 O, KCl + RbCl + H2 O 323.15 K metastable phase equilibrium [11]. In this paper, the metastable phase equilibria of the system was presented and the solubilities, densities, and refractive index of the equilibrated solution in the systems were measured at 323.15 K.

2. Experimental 2.1. Reagents and apparatus

∗ Corresponding author. Tel.: +86 28 84079016; fax: +86 28 84079074. E-mail address: [email protected] (Y. Zeng). 0378-3812/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2013.04.005

The chemicals used were analytical purity grade: potassium chloride (KCl; 99.5%), rubidium chloride (RbCl; 99.5%), and magnesium chloride hexahydrate (MgCl2 ·6H2 O; 98.0%). Deionized water

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with an electrical conductivity less than 1 × 10−4 S m−1 and pH ≈6.60, was used in the experiments. A thermostatic evaporator (type SHH-250, Chongqing Inborn Instrument Corp., China) was used for metastable phase equilibrium experiments, the temperature precision is ±0.1 K. An inductively coupled plasma optical emission spectrometer (type 5300 V, Perkin-Elmer Instrument Corp., America) was used for the determination of the potassium and rubidium ion concentrations in solution. An Abbe refractometer (type 2WAJ, Shanghai Jingke Electronic Co., Ltd., China) was used for measuring the refractive index of the equilibrated solution with a precision of 0.0001. A standard analytical balance (type FA1204B, Shanghai Jingke Electronic Co., Ltd., China) of 110 g capacity and 0.0001 g resolution was used for determination of the density of solution. A Siemens D500 X-ray diffractometer with Ni-filtered Cu KR radiation and a Hitachi S-530 scanning electron microscope were used to analyze the crystalloid form of the solid phases and determining invariant points. The operating conditions of the X-ray diffractometer were 35 kV and 25 mA. 2.2. Analytical method The Rb+ and K+ ion composition was analyzed by inductively coupled plasma optical emission spectrometry (precision: less than 0.06 mass %, type ICP-OES 5300 V). The Mg2+ ion concentration was determined by titration with EDTA stand solution in the presence of indicator of K–B with a precision of 0.5% [12]. The Cl− concentration was measured by AgNO3 titration in the presence of indicator K2 CrO4 with a precision of 0.3% [13]. 2.3. Experimental method The metastable phase equilibria of the quaternary systems were studied at 323.15 K using the isothermal evaporation method. Depending on the solubility of salts in aqueous solution and the invariant point in the ternary subsystem at 323.15 K, the appropriate quantities of salts and deionized water were calculated and mixed into clean polyethylene containers. After salts completely dissolved, the container was placed in a thermostatic evaporator (SHH-250 type) for isothermal evaporation. The experimental conditions were a relative humidity of (20–30%) and evaporation rate of (4.0–5.5) mm d−1 . The temperature was controlled to [(323.15 ± 0.1) K] measured by a thermal resistance. When enough solid phases appeared, the solid were separated from the solution. For further identification, the salts were dried at 323.15 K and then analyzed by X-ray diffraction (XRD; Siemens D500 X-ray diffractometer) to determine the crystalloid form of the solid phase and determining invariant points. Meanwhile, a 5.0 mL sample of the clarified solution was taken from the liquid phase through a pipette and then diluted to a 100 mL final volume in a volumetric flask filled with deionized water to analyze the liquid-phase compositions. The densities of solution were measured with specific gravity bottle method with a precision of 0.0002 g cm−3 [14], the refractive index of equilibrated solution was determined by a 2WAJ. The remainder of the solution continued to be evaporated to reach the next measuring point. The same procedure was repeated until the solution was completely evaporated.

Fig. 1. Metastable phase diagram of the quaternary system KCl + RbCl + MgCl2 + H2 O at 323 K.

experimental data in Table 1, the experimental metastable phase diagram of the system at 323.15 K was constructed in Fig. 1. Fig. 2 is a partial enlarged diagram of Fig. 1. Fig. 3 is the relevant water diagram of the system at 323.15 K. In Figs. 1 and 2, points A, B, C, D, E and F are invariant points of the three ternary systems. Points S1 , S2 , S3 and S4 are invariant points of the quaternary system. The phase diagram consists of six crystallization fields, nine univariant curves, and four invariant points. The six crystallization fields correspond to single salts KCl, RbCl, MgCl2 ·6H2 O, and double salt KCl·MgCl2 ·6H2 O, RbCl·MgCl2 ·6H2 O and the solid solution [(K, Rb)Cl]. The salt’s crystallization region decreases in the order of KCl, RbCl, RbCl·MgCl2 ·6H2 O, KCl·MgCl2 ·6H2 O and MgCl2 ·6H2 O. The solid solution [(K, Rb)Cl] has the largest crystallization field almost occupies the entire phase region, the salt MgCl2 ·6H2 O has the smallest crystallization field, which shows that it is difficult to separate potassium from rubidium in chloride solution by only using evaporation and crystallization methods at 323 K. Four invariant points in this system are noted as S1 , S2 , S3 and S4 . Point S1 is a commensurate invariant point, cosaturated with three salts RbCl, RbCl·MgCl2 ·6H2 O and [(K, Rb)Cl]. The composition of the corresponding equilibrated solution is w(KCl) = 1.02%, w(MgCl2 ) = 11.97%, w(RbCl) = 30.01%. Point S2 is a commensurate invariant point, cosaturated with

3. Results and discussion The experimental results and the physicochemical property values such as densities and refractive indices of the quaternary system at 323.15 K are listed in Table 1. The ion concentration values of the metastable equilibrated solution were expressed both in mass fraction w (b) and Jänecke index J (b). According to the

Fig. 2. Partial enlarged diagram of Fig. 1.

D. Jiang et al. / Fluid Phase Equilibria 349 (2013) 67–70

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Table 1 The solubilities, densities and refractive indices of the quaternary system KCl + RbCl + MgCl2 + H2 O at 323 K. No.

1A 2 3 4 5 6 7 8S1 9 10 11 12 13S2 14S3 15D 16S1 17B 18C 19S2 20F 21 22 23 24 25 26 27 28 29 30 31 32 33S4 34E 36 37S4

Refractive index

1.3921 1.3924 1.3953 1.3977 1.4006 1.4018 1.4049 1.4051 1.4057 1.4059 1.4105 1.4171 1.4299 1.4356 1.4336 1.4051 1.4076 1.4295 1.4311 1.3736 1.3764 1.3724 1.3782 1.3851 1.3864 1.3872 1.3912 1.3936 1.4028 1.4038 1.4043 1.4054 1.4133 1.409 1.4119 1.4133

Density

1.6463 1.6096 1.5863 1.5897 1.5667 1.5656 1.5612 1.5426 1.5279 1.4946 1.4691 1.4462 1.4358 1.4231 1.4883 1.5426 1.5590 1.4210 1.4358 1.2316 1.3073 1.3139 1.3107 1.3234 1.3316 1.3398 1.3485 1.3502 1.3861 1.3906 1.368 1.3646 1.3582 1.3767 1.3682 1.3582

Composition of equilibrium solution w(b) × 102

Equilibrated solid phase

Jänecke index of dry salt J(K2 Cl2 ) + J(MgCl2 ) + J(Li2 Cl2 ) = 100

KCl

MgCl2

RbCl

H2 O

KCl

MgCl2

RbCl

H2 O

1.17 1.26 1.16 1.43 1.36 1.36 1.32 1.02 0.48 0.34 0.25 0.22 0.15 0.16 0.20 1.02 0.00 0.00 0.15 27.13 25.26 25.10 22.30 18.73 18.54 17.01 12.77 12.45 7.51 3.64 3.13 2.59 1.49 4.60 2.43 1.49

0.00 2.17 4.25 6.29 7.26 8.93 10.71 11.97 12.54 16.60 25.42 25.44 30.71 30.04 37.11 11.97 12.78 35.82 30.71 0.00 1.64 2.01 3.59 7.01 7.64 8.78 11.17 12.41 17.26 20.49 21.08 22.25 24.69 25.68 23.08 24.69

48.15 46.83 42.10 41.98 39.60 39.55 37.22 33.01 24.98 17.53 9.15 2.01 0.23 0.08 0.00 33.01 31.43 0.36 0.23 1.73 1.82 2.00 2.68 3.93 4.21 4.63 5.44 5.97 7.61 6.97 4.34 1.84 0.06 0.00 0.14 0.06

50.68 49.74 52.49 50.30 51.78 50.16 50.75 54.00 62.00 65.53 65.18 72.33 68.91 69.72 62.69 54.00 55.79 63.82 68.91 71.14 71.28 70.89 71.43 70.33 69.61 69.58 70.62 69.17 67.62 68.90 71.45 73.32 73.76 69.72 74.35 73.76

3.79 3.76 3.44 3.85 3.68 3.43 3.22 2.54 1.36 0.92 0.55 0.54 0.32 0.33 0.34 2.54 0.00 0.00 0.32 96.22 87.29 85.15 75.45 58.34 56.07 50.68 38.05 35.06 19.18 9.11 8.08 6.23 3.72 10.27 6.30 3.72

0.00 10.10 19.68 26.46 30.54 35.12 40.81 46.66 55.20 69.92 87.07 96.45 99.39 99.56 99.66 46.66 50.78 99.61 99.39 0.00 8.84 10.66 18.96 34.11 36.09 40.83 51.96 54.56 68.84 80.14 86.02 91.04 96.19 89.73 93.47 96.19

96.21 86.14 76.88 69.69 65.78 61.45 55.97 50.80 43.44 29.16 12.38 3.01 0.29 0.11 0.00 50.80 49.22 0.39 0.29 3.78 3.87 4.19 5.59 7.55 7.84 8.49 9.99 10.38 11.98 10.75 5.90 2.73 0.09 0.00 0.23 0.09

1359 1228 1286 1120 1154 1045 1024 1114 1445 1461 1181 1450 1180 1222 890 1114 1172 939 1180 2088 2037 1990 1999 1812 1741 1713 1739 1610 1427 1425 1524 1574 1520 1288 1593 1520

RI + KRI RI + KRI RI + KRI RI + KRI RI + KRI RI + KRI RI + KRI RI + KRI + Rb-Car KRI + Rb-Car KRI + Rb-Car KRI + Rb-Car KRI + Rb-Car Bis + KRI + Rb-Car Bis + KRI + K-Car Bis + K-Car RI + KRI + Rb-Car RI + Rb-Car Bis + Rb-Car Bis + KRI + Rb-Car KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI KI + KRI + K-Car KI + K-Car KI + K-Car KI + KRI + K-Car

RI: RbCl; KI: KCl; Bis: MgCl2 ·6H2 O; K-Car: KCl·MgCl2 ·6H2 O; Rb-Car: RbCl·MgCl2 ·6H2 O; (K, Rb)Cl: KRI.

three salts MgCl2 ·6H2 O, RbCl·MgCl2 ·6H2 O and [(K, Rb)Cl]. The composition of the corresponding equilibrated solution is w(KCl) = 0.15%, w(MgCl2 ) = 30.71%, w(RbCl) = 0.23%. Point S3 is a commensurate invariant point, cosaturated with three salts MgCl2 ·6H2 O, KCl·MgCl2 ·6H2 O and [(K, Rb)Cl]. The composition

Fig. 3. Water content diagram of the quaternary system KCl + RbCl + MgCl2 + H2 O at 323 K.

of the corresponding equilibrated solution is w(KCl) = 0.16%, w(MgCl2 ) = 30.04%, w(RbCl) = 0.08%. Point S4 is a commensurate invariant point, cosaturated with three salts KCl, KCl·MgCl2 ·6H2 O and [(K, Rb)Cl]. The composition of the corresponding equilibrated solution is w(KCl) = 1.49%, w(MgCl2 ) = 24.69%, w(RbCl) = 0.06%. According to Table 1 and Fig. 3, the ordinate is the Jänecke index of water, and the abscissa is the Jänecke index of magnesium. Fig. 3 shows that the water content changes regularly with the Jänecke index change of magnesium chloride. The water decreased with the increase of J(MgCl2 ) on the univariant curve AS1 , S3 D. While the water increased with the decrease of J(MgCl2 ) on the univariant curve S1 B, ES4 and S2 C. Fig. 4 is the density versus composition diagram of this system. Fig. 5 is the refractive index versus composition diagram of this system. The ordinate is the values of physicochemical properties (density or refractive index), and the abscissa is the Jänecke index of magnesium chloride. Figs. 4 and 5 show that the density and refractive index changes regularly with the Jänecke index change of magnesium chloride. The density and refractive index increases with increasing concentration of J(MgCl2 ) on the univariant curve FS4 and S1 B. The density and refractive index increases with increasing concentration of J(MgCl2 ) on the univariant curve FS4 and S1 B. The density decreased with the increase of J(MgCl2 ),while the refractive index increased with the increase of J(MgCl2 ) on the univariant curve AS1 and ES4 . The density and the refractive index decrease with increasing concentration of J(MgCl2 ) on the univariant curve CS2 . The density increases with increasing concentration

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the diagram of water and the composition diagram of physical and chemical properties were all worked out. The research results showed that the metastable phase diagram at 323.15 K of this system consists of six crystalline phase areas, nine univariant curves, and four invariant points. The phase diagram of the quaternary system is composed of six crystallization fields and four invariant points. The six crystallization fields correspond to single salts KCl, RbCl, MgCl2 ·6H2 O, and double salt KCl·MgCl2 ·6H2 O, RbCl·MgCl2 ·6H2 O and the solid solution [(K, Rb)Cl], the crystalline phase areas of [(K, Rb)Cl] is maximum, while the crystalline phase areas of MgCl2 ·6H2 O is minimum. The water content and physicochemical properties of equilibrium liquid phase change regularly with changes of the liquid phase composition. Acknowledgements

Fig. 4. Density versus composition KCl + RbCl + MgCl2 + H2 O 323 K.

diagram

of

the

quaternary

system

The authors thank the National High Technology Research and Development Program of China (2012AA061704), China National Nature Science Foundation (No. 41173071), China Geological Survey (1212011085523), and the Research Fund for the Doctoral Program of Higher Education from the Ministry of Education of China (20115122110001) for financial support. References

Fig. 5. Refractive index versus composition diagram of the quaternary system KCl + RbCl + MgCl2 + H2 O 323 K.

of J(MgCl2 ) on the univariant curve CS2 , while the refractive index almost unchanged. 4. Conclusion In this paper, through the isothermal evaporation experiment, the data for the metastable phase equilibrium of quaternary system KCl + RbCl + MgCl2 + H2 O at 323 K and equilibrium liquid physicochemical properties were obtained. The metastable phase diagram,

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