Metastable Phase Diagram of the Quaternary ... - ACS Publications

Article pubs.acs.org/jced

Metastable Phase Diagram of the Quaternary System Li+, Na+//Cl−, B4O72−−H2O at 273 K Jingqiang Zhang,† Ying Zeng,*,†,‡ Yun Peng,† and Bo Zong† †

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: Using an isothermal evaporation method, the metastable phase equilibrium of the quaternary system Li+, Na+//Cl−, B4O72−−H2O was investigated at 273 K. The useful data for solubilities, densities, and pH values were measured, based on which the metastable phase diagram, water content diagram, density vs composition diagram, and pH value vs composition diagram of this system were constructed. The metastable phase diagram of this quaternary system contains two invariant points, five univariant curves, and four crystallization fields. This quaternary system is of a simple cosaturation type, without double salt or solid solution formed. The four crystallization fields are corresponding to salts NaCl, LiCl·H2O, LiBO2·8H2O, and Na2B4O7·10H2O, respectively. The sequence of the crystallization field sizes of slats is salt Na2B4O7·10H2O > salt LiBO2·8H2O > salt NaCl > salt LiCl·H2O, which demonstrates that the borates, including salt Na2B4O7·10H2O and salt LiBO2·8H2O, can be more easily separated from the solution in this system at 273 K. The crystalloid form of lithium borate is LiBO2·8H2O in the given system at 273 K, instead of Li2B4O7·3H2O formed in the system containing with lithium borate at temperatures above 273 K.

■

INTRODUCTION Salt lake brine, abundant with minerals as sodium, potassium, lithium, and borate, is one kind of important natural liquid resource and acts as important raw material in modern industry. In China, most salt lakes are located in arid and rainless regions, especially in the Qinghai-Xizang (Tibet) Plateau, where the solar power and wind power can be utilized to exploit the salt lake brines.1Among those lakes, Zabuye Salt Lake is famous for its high concentration of lithium, potassium, and boron. Topics regarding how to comprehensively utilize this brine resource are drawing more and more researchers’ attention. As is wellknown, solubility data of salts and phase equilibria diagram are very important basic data for the comprehensive utilization of brine, which give guidance to establish the best production process and technology. Based on this, our research concerns the metastable phase relations investigation of different salt− water systems referring to the Zabuye Salt Lake. In the Zabuye Salt Lake region, the average annual temperature is about 273 K;2 meanwhile, the state of equilibria in the evaporation process of brines is always metastable.3 Therefore a research series focused on the metastable phase equilibria at 273 K have been reported, including our research group’s previous studies about the aqueous quaternary systems Li+, K+//CO32−, borate−H2O;4 Li+, K+//SO42−, borate−H2O;5 Na+, K+//Cl−, borate−H2O;6 Na+//Cl−, CO32−, borate−H2O;7 Li+//Cl−, SO42−, borate−H2O;8 and the quinary system Li+, K+, Na+//SO42−, borate−H2O.9 The main components of the Zabuye Salt Lake brine can be simplified as Li+, Na+, K+//Cl−, SO42−, CO32−, and borate− H2O systems.2 The quaternary system Li+, Na+//Cl−, B4O72−− H2O is an important subsystem of the complex system © 2013 American Chemical Society

mentioned above. So far, the metastable of this water-salt quaternary system has not been reported yet. With the hope to separate lithium and boron resources in the Zabuye Salt Lake brine, the metastable phase equilibrium of the system Li+, Na+//Cl−, B4O72−−H2O was investigated at 273 K and presented in this manuscript.

■

EXPERIMENTAL SECTION

Reagents and Apparatus. The chemicals referred to in our study were of analytical purity grade and purchased from the Kelong Chemical Reagent Plant, Chengdu, China. They were lithium tetraborate (Li2B4O7; 99.5 % (w/w)), sodium tetraborate decahydrate (Na2B4O7·10H2O; 99.5 % (w/w)), lithium chloride (LiCl; 98.5 % (w/w)), and sodium chloride (NaCl; 99.5 % (w/w)). In addition, doubly deionized water, with an electrical conductivity of κ ≤ 1.0·10−4 S·m−1 and pH ≈ 6.60, was required in the preparation of artificial solutions and analytical operations. Evaporation operations were performed inside a SHH-250 type thermostatic evaporator, with which the experimental temperature was controlled at 273 K and the range of deviation was ± 0.1 K. AL104 type analytical balance of a resolution of 0.0001 g was applied to determine the weight of solution samples. All pH values were measured with pXS-1+ ion activity meter, and the data displayed were of an uncertainty of 0.01. Received: October 26, 2012 Accepted: January 3, 2013 Published: January 10, 2013 441

dx.doi.org/10.1021/je301160b | J. Chem. Eng. Data 2013, 58, 441−445

Journal of Chemical & Engineering Data

Article

Table 1. Solubilities, pH Values, and Densities of the Equilibrated Solution in the Quaternary System Li+, Na+// Cl−, B4O72−− H2O at 273 Ka density

a

composition of equilibrium solution, w(B)·102

Jänecke index of dry salt, J(B)

no.

pH value

g·cm−3

w(Li+)

w(Na+)

w(Cl−)

w(B4O72−)

w (H2O)

J(Li22+)

J(Na22+)

J(Cl22−)

J(B4O72−)

J(H2O)

solid phase

1, A 2 3 4, E1 5, B 6, C 7 8 9 10 11 12, E2 13 14, D 15 16 17 18 19

6.00 5.52 5.78 5.76 5.93 8.73 7.95 8.27 8.20 8.18 8.05 7.83 7.23 9.82 9.10 9.64 9.29 9.26 9.06

1.2244 1.2470 1.2083 1.2108 1.1800 1.2039 1.1950 1.1900 1.1768 1.1714 1.1612 1.1610 1.1579 1.0145 1.0172 1.0185 1.0235 1.0333 1.0964

6.68 6.18 5.80 5.74 6.40 0.00 0.13 0.49 1.00 1.45 1.98 2.77 3.67 0.08 0.10 0.13 0.23 0.48 1.02

0.30 0.24 0.26 0.26 0.00 10.20 9.85 8.78 7.24 5.99 4.63 2.70 0.97 0.21 0.30 0.34 0.38 0.73 1.18

34.65 31.94 29.90 29.55 32.65 15.61 15.75 15.82 15.90 16.48 17.08 18.03 19.90 0.00 0.17 0.45 0.97 2.86 6.55

0.00 0.12 0.32 0.52 0.21 0.27 0.30 0.54 0.88 0.40 0.46 0.64 0.83 1.65 1.77 1.63 1.69 1.58 1.10

58.37 61.52 63.72 63.93 60.74 73.92 73.97 74.37 74.98 75.68 75.85 75.86 74.63 98.06 97.66 97.45 96.73 94.35 90.15

98.68 98.82 98.67 98.66 100.0 0.00 4.30 15.60 31.46 44.54 58.66 77.30 92.64 56.05 53.10 56.01 66.15 68.65 74.13

1.32 1.18 1.33 1.34 0.00 100.0 95.70 84.40 68.54 55.46 41.34 22.70 7.36 43.95 46.90 43.99 33.85 31.35 25.87

100.0 99.84 99.51 99.21 99.70 99.22 99.14 98.47 97.53 98.91 98.78 98.40 98.12 0.00 17.51 37.67 55.66 79.76 92.88

0.00 0.16 0.49 0.79 0.30 0.78 0.86 1.53 2.47 1.09 1.22 1.60 1.88 100.0 82.49 62.33 44.34 20.24 7.12

664.5 758.6 836.6 846.7 731.6 1853 1836 1826 1814 1791 1729 1633 1452 51261 39184 32047 21897 10386 5045

LI+NI LI+NI LI+NI LI+NI+LB LI+LB NI+NB NI+NB NI+NB NI+NB NI+NB NI+NB NI+NB+LB NI+LB LB+NB LB+NB LB+NB LB+NB LB+NB LB+NB

LI: LiCl·H2O; NI: NaCl; LB: LiBO2·8H2O; NB: Na2B4O7·10H2O; w(B): mass fraction of component B; J(B): Jänecke index of dry salt.

the Jänecke index is expressed by J(B); B can be Li+, Na+, Cl−, B4O72−, or H2O. The data of mass fraction and Jänecke index ought to observe the two formulas listed below.

The 5300 V type inductively coupled plasma optical emission spectrometer (ICP-OES) was used to determine the lithium and sodium concentration in solution. Experimental Procedure. A certain amount of salts was dissolved into deionized water to make up the experimental solutions. The ratio of salts to water was dependent on the solubility of the invariant points of the subsystems at 273 K. Then, evaporation of the synthesized solutions proceeded in the SHH-250 type thermostatic evaporator, inside which the temperature of the solutions was (273 ± 0.1) K. The solutions were observed periodically, and newly appeared solids were separated from them by filtration. In the meantime, the concentrations of the components of the clarified solutions were measured by chemical or instrument analysis method. The pH values of those were determined with a pXS-1+ ion activity meter. The densities of the filtrates were obtained by a specific gravity bottle method,10 and the generated deviation was calibrated by multipoint temperature revision.11 With this, one sampling was completed. The solutions separated by filtration were evaporated again, and the next samples were taken as mentioned above. This operation was repeated, and the whole procedure ended when the solutions evaporated to dryness. Analytical Methods. The concentrations of Na+ and Li+ were determined by ICP-OES, with a precision less than 0.06 % (w/w). The chlorine ion concentration was measured by titration with a silver nitrate standard solution, with a precision of 0.3 % (w/w).12 The borate ion concentration was measured by neutralization titration in excessive mannitol conditions, with a precision of 0.3 % (w/w).12

w(Li+) + w(Na +) + w(Cl−) + w(B4O7 2 −) + w(H 2O) (1)

=1

J(Li 2 2 +) + J(Na 2 2 +) = J(Cl 2 2 −) + J(B4O7 2 −) = 100 (2)

On the basis of the Jänecke index displayed in Table 1, the metastable phase diagram of this system at 273 K is plotted in Figure 1, and Figure 2 is a partially enlarged diagram of Figure 1. In addition, the corresponding water-content diagram of this system and its partially enlarged diagram were constructed, as shown in Figures 3 and 4, respectively. As shown in Figures 1 and 2, the metastable phase diagram contains two invariant points, five univariant curves, and four crystallization fields. Solid solutions and double salts cannot be found in this system at 273 K, with that this system can be defined as a simple cosaturation type. There are six data points marked in phase diagram in total; they are A, B, C, D, E1, and E2. Points A, B, C, and D, cosaturated with two salts, are four invariant points of four ternary subsystems of this quaternary system at the investigated temperature, respectively. Unlike other four points, E1 and E2, cosaturated with three salts, are invariant points of the quaternary system Li+, Na+//Cl−, B4O72−−H2O at 273 K. The mass fraction compositions of E1 and E2 and regarding categories of saturated salts are listed below. At point E1, the mass fraction composition of the equilibrated solution is w(Li+) = 5.74 %, w(Na+) = 0.26 %, w(Cl−) = 29.55 %, and w(B4O72−) = 0.52 %, and the cosaturated salts are NaCl, LiCl·H2O, and LiBO2·8H2O. At point E2, the mass fraction composition of the equilibrated solution is w(Li+) = 2.77 %, w(Na+) = 2.70 %, w(Cl−) = 18.03

■

RESULTS AND DISCUSSION The experimental data are tabulated in Table 1, which includes solubilities, densities, and pH values of the equilibrium solution in the quaternary system Li+, Na+//Cl−, B4O72−−H2O at 273 K. In Table 1, the mass fraction of B is expressed by w(B), and 442



Article

Figure 3. Water content diagram of the quaternary system Li+, Na+// Cl−, B4O72−−H2O at 273 K. ●, experimental value; , experimental relationship curve.

Figure 1. Metastable phase diagram of the quaternary system Li+, Na+//Cl−, B4O72−−H2O at 273 K. ●, metastable experimental point; , metastable univariant curve.

Figure 4. Partially enlarged diagram of Figure 3. Figure 2. Partially enlarged diagram of Figure 1.

LiCl·H2O, and LiBO2·8H2O, so E1 is a commensurate invariant point. However, point E2 locates out of the triangle formed by corresponding solid-phase salts NaCl, Na2B4O7·10H2O and LiBO2·8H2O, so E2 belongs to an incommensurate invariant point. The two methods present consistent results. There are five univariant curves in phase diagram, labeled as AE1, BE1, CE2, DE2, and E1E2, respectively. These univariant solubility curves are cosaturated with two salts; for example, salt NaCl and LiCl·H2O are cosaturated at every point on curve AE1. The four crystallization fields correspond to the four single salts sodium chloride (NaCl), lithium chloride monohydrate (LiCl·H2O), lithium metaborate octahydrate (LiBO2·8H2O), and sodium tetraborate decahydrate (Na2B4O7·10H2O), respectively. In Figure 1, salts Na 2 B 4 O 7 ·10H 2 O and LiBO2·8H2O have larger crystallization areas and lower solubility than salts NaCl and LiCl·H2O. It means that salt Na2B4O7·10H2O and salt LiBO2·8H2O are easier to be saturated and crystallized than NaCl and LiCl·H2O at 273 K in the process of isothermal evaporation.

%, and w(B4O72−) = 0.64 %, and the cosaturated salts are NaCl, Na2B4O7·10H2O, and LiBO2·8H2O. Then, we try to judge the types of E1 and E2. Method 1: Composition Method. At point E1, the order of the ion concentrations in equilibrated solution is Cl− > Li+ > B4O72− > Na+, and it shows that the concentration of Cl− comes first. The corresponding equilibrated solid phases containing Cl− include NaCl and LiCl·H2O, so point E1 is a commensurate invariant point. At point E2, the order of the ion concentrations in equilibrated solution is also Cl− > Li+ > Na+ > B4O72−; however, though the concentration of Cl− is higher than other ions in the liquid phase, Cl− only presents in the salt NaCl among the corresponding equilibrated solid phases. Therefore, point E2 is an incommensurate invariant point. Method 2: Graphic Method. In the phase diagram, if the invariant point locates in the triangle, the vertices of which correspond to the cosaturated solid-phase salts, it can be defined as a commensurate invariant point. Point E1 locates in the triangle formed by corresponding solid-phase salts NaCl, 443



Article

As we know, borates often exist in the form of polyanions in solution, such as B(OH)4−, B4O5(OH)42−, B3O3(OH)4−, B5O6(OH)4−, and so forth, and they can be crystallized in different solid forms.5 According to the previous reports, taking for instance the quaternary system Li+//Cl−, SO42−, B4O72− H2O, the equilibrium solid phases of lithium borate correspond to LiBO2·8H2O at 273 K,8 288 K,13 and Li2B4O7·3H2O at 298 K14 in this system, respectively. Besides the experimental temperature, metastable or stable conditions may also influence the crystalloid form of lithium borate. Compared the metastable and stable phase diagrams of the quinary system Li+, Na+, K+//SO42−, B4O72−H2O at the same temperature 288 K, the results show that the crystalloid form of lithium borate is LiBO2·8H2O in the metastable condition, whereas that is Li2B4O7·3H2O in the stable condition.15 Therefore, the equilibrium solid phase of lithium borate in the given system can be affected by temperature and metastable or stable condition. In this study, lithium borate is crystallized in the form of LiBO2·8H2O in the given system at 273 K, and the formation of this crystal is probably influenced by the temperature and metastable state. However, which one is the main factor needs further investigation. Table 1 shows that the solubilities of sodium chloride and lithium chloride are greater than those of sodium tetraborate decahydrate and lithium tetraborate; thus in solution, the physicochemical properties are mainly affected by the chloride ion content. Figure 3 is the water content diagram of this quaternary system. The water content of the system decreases obviously with the increase of chloride ion content on the univariant curve DE2, whereas the change of water content becomes slightly in the region abutting invariant point E1 or E2. Figure 5 is the density versus composition diagram of the equilibrated solution, and Figure 6 is a partially enlarged

Figure 6. Partially enlarged diagram of Figure 5.

Figure 7. pH value vs composition diagram of the equilibrated solutions in the quaternary system Li+, Na+//Cl−, B4O72−−H2O at 273 K. ●, experimental value; , experimental relationship curve.

Figure 5. Density vs composition diagram of the equilibrated solutions in the quaternary system Li+, Na+//Cl−, B4O72−−H2O at 273 K. ●, experimental value; , experimental relationship curve.

diagram of it. On the univariant curve DE2, the density increases with the increase of chloride ion content. On the curve CE2, meanwhile, the density presents a trend of decrease with the decrease of chloride ion content. There are no obvious change on the curves AE1 and BE1. Figure 7 is the pH value versus composition diagram of the system, and Figure 8 is a partially enlarged diagram of it. The

Figure 8. Partially enlarged diagram of Figure 7.

pH value decreases with the increase of chloride ion content on the univariant curve DE2. With the decrease of chloride ion 444



Article

(9) Zeng, Y.; Lin, X. F. Solubility and density measurements of concentrated Li2B4O7 + Na2B4O7 + Li2SO4 + Na2SO4 + K2SO4 + H2O solution at 273.15 K. J. Chem. Eng. Data 2009, 54, 2054−2059. (10) Zeng, Y.; Zheng, Z. Y. Metastable phase equilibria for the quaternary system Na+ + K+ + CO32− + B4O72− + H2O at 273.15 K. J. Chem. Eng. Data 2010, 55, 1623−1627. (11) Xu, G. L. The determination and application of the temperature correction coefficient for the density of Vinyl Acetate. Fujian Anal. Test 1999, 8, 1104−1108. (12) Institute of Qinghai Salt-lake of Chinese Academy of Science. Analytical Methods of Brines and Salts, 2nd ed.; Chinese Science Press: Beijing, China, 1984. (13) Li, M.; Sang, S. H.; Zhang, Z. L.; Zhang, X. A study on phase equilibrium of quaternary system Li2B4O7−Li2SO4−LiCl−H2O at 288 K. Salt Ind. 2009, 41, 21−23. (14) Song, P. S.; Du, X. H. A study on the equilibrium phase diagram and solution properties of quaternary system Li2B4O7−Li2SO4−LiCl− H2O at 298 K. Chin. Sci. Bull. 1986, 3, 209−213. (15) Zeng, Y.; Lin, X. F.; Ni, S. J.; Zhang, C. J. Study on the metastable equilibrium of the salt lake brine system Li2SO4 + Na2SO4 + K2SO4 + Li2B4O7 + Na2B4O7 + K2B4O7 + H2O at 288 K. J. Chem. Eng. Data 2007, 52, 164−167.

content, the pH value decreases on curve CE2 and alters slightly on curves AE1 and BE1, respectively.

■

CONCLUSIONS The results of the isothermal evaporation experiments demonstrate that the quaternary system Li+, Na+//Cl−, B4O72−−H2O at 273 K belongs to a simple cosaturation type. According to the experimental data, we plotted the metastable phase diagram and physicochemical property versus composition diagrams. There are two invariant points, five univariant curves, and four crystallization fields corresponding to NaCl, LiCl·H2O, LiBO2·8H2O, and Na2B4O7·10H2O in the phase diagram. By two different judgmental methods, we can draw the same conclusion that point E1 is a commensurate invariant point and point E2 is an incommensurate invariant point. In the view of crystallization area, the crystallization field of salt Na2B4O7·10H2O occupies the largest part, whereas salt LiCl·H2O has the smallest crystallization area. The salts Na2B4O7·10H2O and LiBO2·8H2O have larger crystallization areas and lower solubility than salts NaCl and LiCl·H2O, so the borates can be more easily separated from the solution in this system at 273 K. On account of lower temperature and metastable conditions, the crystalloid form of lithium borate in the equilibrium solid phase is LiBO2·8H2O, and Li2B4O7·3H2O is not found in the given system at 273 K.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: 86-28-84079016. Fax: 8628-84079074. Funding

Financial support for this work was provided by the National Natural Science Foundation of China (Grant No. 40673050, 41173071), National High Technology Research and Development Program of China (2012AA061704), the Project of China Geological Survey (1212011085523), and the Research Fund for the Doctoral Program of Higher Education from the Ministry of Education of China (20115122110001). Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Song, P. S. Utilization of salt lake resources. J. Salt Lake Sci. 1993, 1, 68−80. (2) Zheng, M. P.; Liu, W. G.; Xiang, J. Qinghai-Xizang Plateau Saline Lakes; Beijing Science and Technology Press: Beijing, China, 1989. (3) Gao, S. Y.; Shen, B. S.; Xia, S. P.; Zheng, M. P. Chemistry of the Salt Lake; Beijing Science and Technology Press: Beijing, China, 2007. (4) Zeng, Y.; Lin, X. F.; Meng, S. J. Study on metastable phase equilibrium of quaternary system Li+, K+//CO32−, B4O72−−H2O at 273 K. Chem. Eng. (China) 2008, 36, 47−50. (5) Zeng, Y.; Lin, X. F.; Zheng, Z. Y. An experimental study on the metastable equilibrium in quaternary system Li+, K+//SO42−, B4O72−− H2O at 273 K. J. Chem. Eng. Chin. Univ. 2009, 23, 7−11. (6) Zeng, Y.; Wang, R. L.; Lin, X. F.; Peng, Y. Metastable phase equilibrium in quaternary system Na+, K+//Cl−, B4O72−−H2O at 273 K. Acta Phys.−Chim. Sin. 2008, 24, 471−474. (7) Wang, R. L.; Zeng, Y. Study on metastable phase equilibrium of quaternary system Na+//Cl−, CO32−, B4O72−−H2O at 273 K. J. Miner. Pet. 2008, 28, 109−112. (8) Yang, H. X.; Zeng, Y. Metastable phase equilibrium in the aqueous quaternary system LiCl + Li2SO4 + Li2B4O7 + H2O at 273 K. J. Chem. Eng. Data 2011, 56, 53−57. 445


Metastable Phase Diagram of the Quaternary ... - ACS Publications

Recommend Documents