Article pubs.acs.org/jced
Phase Equilibria of Two Ternary Systems: Li2SO4−Li2B4O7−H2O and K2B4O7−K2SO4−H2O at 273 K Yu-yan Yang,† Xue-ping Zhang,† Dan Wang,† and Shi-hua Sang*,†,‡ †
College of Materials and Chemistry & Chemical Engineering, and ‡Mineral Resources Chemistry Key Laboratory of Sichuan Higher Education Institutions, Chengdu University of Technology, Chengdu 610059, P. R. China ABSTRACT: The isothermal dissolution equilibrium method was used to determine the solubilities of salts and the equilibrium solid phases in the two ternary systems: Li2SO4−Li2B4O7−H2O and K2B4O7−K2SO4−H2O at 273 K. These results are also used to construct phase diagrams of the two ternary systems. Both phase diagrams have an eutectic point, two univariant solubility curves, and two crystallization regions of single solid phase. At the eutectic point of the ternary system Li2SO4−Li2B4O7−H2O, the coexisting solid phases are Li2B4O7·3H2O and Li2SO4·H2O; at the eutectic point of the ternary system K2B4O7−K2SO4−H2O, the coexisting solid phases are K2B4O7· 4H2O and K2SO4.
1. INTRODUCTION Acting as a natural liquid mineral resource, one of the most striking features for a salt lake is high salinity. Salt lakes are widely distributed in western China. Among them, it is generally believed that the salt lake on the Qinghai−Tibet plateau is extremely rich and a source of economical value. Salt lake brine is rich in lithium resources.1 Lithium is the lightest metal in nature with strong chemical activity.2 Different kinds of brine have different characteristics with a high concentration of lithium, potassium, boron. Boron is one type of a main source of chemical material.3 Boron storage resources are rich in our country.4 Lake salt with abundant boron treated as a valuable liquid boron resource will be able to meet the increasing consumption of boron resources.5 It is necessary to conduct the research of concentrations of potassium, lithium, and boron in the salt lakes. By now, systematic work has been done by our group on phase equilibria of some brine-mineral systems, such as quaternary system Li−K−CO3−SO4−H2O at 273.15 K,6 quaternary system K−CO3−SO4−B4O7−H2O at 273.15 K,7 quaternary system Na−K−Li−B4O7−H2O at 273.15 K,8 and quaternary system K−Cl−SO4−B4O7−H2O at 298.15 K.9 Our group also measured the phase equilibria of several ternary systems containing lithium or potassium, such as Li2SO4− Li2B4O7−H2O at 288 K,10 NaBr−Na2B4O7−H2O at 298 K,11 Li2CO3−Li2B4O7−H2O and K2CO3−K2B4O7−H2O at 288 K,12 K2B4O7−KBr−H2O at 323 K,13 K2B4O7−K2SO4−H2O at 288 K10 and at 348.15 K.14 There are also some measurements of ternary phase equilibria involving lithium or potassium salts from other groups, such as those of Li2SO4−Li2B4O7−H2O at 298.1515 and 323.15 K,16 and KCl−K2B4O7−H2O at 298.15 K.17 To the best of our knowledge, the phase equilibrium measurements of those two systems at 273 K have not been reported. This work was conducted on the basis of our previous work. The article aims at expanding the temperature range in © XXXX American Chemical Society
offering basic solubility data, which can instruct the design of the extraction process.
2. EXPERIMENTS 2.1. Reagents and Instruments. All chemicals of analytical purity used in this work (Li2B4O7, K2B4O7·4H2O, Li2SO4·H2O, K2SO4 and auxiliary reagents) are listed in Table 1. Water for analytical laboratory use was purified by an ultrapure water purification system. Table 1. Samples chemical reagent
mole fraction purity
Li2SO4·H2O
≥99.5%
Li2B4O7
≥99.5%
K2B4O7·4H2O
≥99.5%
K2SO4
≥99.0%
manufacturer
analytical method
Chengdu Kelong Chemical Reagent Manufacture, China Sinopharm Chemical Reagent Co., Ltd. Sinopharm Chemical Reagent Co., Ltd. Chengdu Kelong Chemical Reagent Manufacture, China
barium chloride gravimetric method mannitol volumetric method mannitol volumetric method barium chloride gravimetric method
An Al104 type standard electronic balance with a level 1 standard calibration supplied by the Mettler Toledo Instruments Co., Ltd., was employed to determine the mass of the sample. A thermostat box with a resolution of 0.1 °C within −15 °C−60 °C (SHH-250, manufactured by the Chongqing Inbev Received: February 26, 2017 Accepted: May 22, 2017
A
DOI: 10.1021/acs.jced.7b00219 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Table 2. Solubilities of Salts in the Ternary System Li2SO4− Li2B4O7−H2O at 273 K and 94.77 kPaa
Experimental Instrument Co., Ltd.) was employed to control the experimental temperature. A DX-2700 X-ray powder crystal diffraction analyzer supplied by Dandong Fangyuan Instrument Co., Ltd. was employed to identify the equilibrium solid phases. 2.2. Experiment Methods. The samples were prepared by adding a certain proportion of two salts into 50 mL of pure water. It must be guaranteed that one of the salts is excessive and precipitated in aqueous solution. The dissolution reactions were conducted in 200 mL sealed galss reactors which were placed in the oscillator (HY-5). The temperature for mechanical agitation was controlled at (273 ± 0.1) K by incubator. In the whole process of equilibrium, the presence of a solid phase should always be maintained. After the system was stirred for 10 days, the sample was allowed to stand for 5 days to measure the liquid phase concentration. The equilibrium state of the sample was identified by the unchanging solution concentration. When the concentration difference of three successive samples was less than 1%, the system was considered to be fully balanced. To ensure the system achieved full solid− liquid phase equilibrium, the mixing time was selected as 30 days and the standing time was set to 10 days. The liquid phase concentration analysis was carried out by chemical methods as will be described later. And the solid phases were washed thoroughly and vacuum-dried for X-ray diffraction analysis. 2.3. Analytical Methods. The concentration of B4O72− was determined in the presence of mannitol by a neutral method using 0.02 mol·L−1 NaOH standard solution as titrant and 10g·L−1 phenolphthalein ethanol solution as indicator (with an uncertainty of 0.003). The concentration of K+ was measured by sodium tetraphenylborate volumetric method using 3.5 g·L−1 quaternary ammonium salt standard solution as titrant and 0.4 g·L−1 titrant yellow as indicator (uncertainty of 0.005). The Li+ content in saturated solution was determined by atomic absorption spectrophotometry (AAS) with an estimated relative error less than 1 %. The content of SO42− was determined by barium chloride weight titration method (with an uncertainty of 0.005). Each equilibrium sample was repeated three times, the three parallel experimental errors did not exceed 0.5%, and the average of the three measurements was taken as the final result.
liquid composition, 100·wB no.
Li2SO4
Li2B4O7
solid phases
1,A 2 3 4 5 6,E 7 8 9 10 11 12 13 14,B
0 5.47 8.32 12.19 20.75 23.57 23.87 24.63 24.22 24.35 25.06 25.20 25.19 26.58
1.81 1.65 1.31 1.00 0.70 0.57 0.56 0.55 0.57 0.56 0.49 0.41 0.38 0
Li2B4O7·3H2O Li2B4O7·3H2O Li2B4O7·3H2O Li2B4O7·3H2O Li2B4O7·3H2O Li2B4O7·3H2O + Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O Li2SO4·H2O
a Note: wB, mass fraction of component B in saturated solution. Standard uncertainties u are u(T) = 0.1 K, u(P) = 0.9 kPa, u[w(Li2B4O7)] = 0.003, u[w(Li2SO4)] = 0.005
3. RESULT DISCUSSIONS 3.1. Li2SO4−Li2B4O7−H2O at 273 K. The solubilities of two salts and solid phases in dissolution equilibrium of Li2SO4− Li2B4O7−H2O system at 273 K were listed in Table 2. Figure 1 is the phase diagram of this ternary system with partial enlargement in Figure 2. The X-ray diffraction photograph of the invariant point E of the ternary system is given in Figure 3. At point E, the solid phases are Li2B4O7·3H2O and Li2SO4· H2O. From the corresponding phase diagram we can see that the system is a simple ternary system, and no double salt and solid solution were found. The dissolution diagram contains an invariant point E and two univariant curves AE and BE standing for the solubility curves of Li2B4O7·3H2O and Li2SO4·H2O, respectively. The entire phase diagram can be divided into four regions. They include two crystallization fields in which the solid phases are lithium sulfate monohydrate (Li2SO4·H2O) and lithium borate trihydrate (Li2B4O7·3H2O), respectively. The other regions correspond to unsaturated liquid phase area (ABE) and a total crystallization area (CDE). The crystallization area of Li2B4O7·3H2O (ACE) is larger than that of
Figure 1. Equilibrium phase diagram of the ternary system Li2SO4− Li2B4O7−H2O at 273 K.
Li2SO4·H2O (BDE). This indicates that the solubility of Li2B4O7 is smaller than that of Li2SO4 at 273.15 K. The concentration of lithium borate decreases with increasing concentration of lithium sulfate before reaching the invariant point E. At point E, the mass fraction composition of the liquid phase is w(Li2B4O7) = 0.57% and w(Li2SO4) = 23.57%. 3.2. Comparison of Phase Diagrams of the System Li2SO4−Li2B4O7−H2O at 273, 288,10 and 323 K.16 The phase diagrams of the system Li2SO4−Li2B4O7−H2O at 28810 and 323 K16 were also reported recently. Figure 4 is the comparison of salt solubilities of the ternary system Li2SO4− Li2B4O7−H2O at 273, 288, and 323 K. As shown in Figure 4, these two phase diagrams are similar to our results in topology. B
DOI: 10.1021/acs.jced.7b00219 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Figure 2. Enlarged partial diagram of the ternary system Li2SO4− Li2B4O7−H2O at 273 K.
Figure 4. Comparison of salt solubilities of the ternary system Li2SO4−Li2B4O7−H2O at 273, 288,10 and 323 K16
Table 3. Solubilities of Salts in the Ternary System K2B4O7− K2SO4−H2O at 273 K and 94.77 kPaa liquid composition, 100·wb
Figure 3. X−ray diffraction photograph of the eutectic point E [Li2B4O7·3H2O + Li2SO4·H2O] of the ternary system Li2SO4− Li2B4O7−H2O at 273 K.
no.
K2SO4
K2B4O7
solid phases
1,B1 2 3 4 5 6,E1 7 8 9 10 11,A1
6.92 6.75 6.38 5.69 4.92 4.91 4.51 3.91 1.91 0.91 0
0 0.66 1.65 4.09 5.64 6.17 6.38 6.17 6.78 6.95 7.36
K2SO4 K2SO4 K2SO4 K2SO4 K2SO4 K2SO4+K2B4O7·4H2O K2B4O7·4H2O K2B4O7·4H2O K2B4O7·4H2O K2B4O7·4H2O K2B4O7·4H2O
a Note: wB, mass fraction of component B in saturated solution. Standard uncertainties u are u(T) = 0.1 K, u(P) = 0.9 kPa, u[w(K2B4O7)] = 0.003, u[w(K2SO4)] = 0.005
That is, they all have an eutectic point, and two isothermal dissolution curves, as well as two solid regions of crystallization. Moreover, the solid phases are also the same, that is, Li2B4O7· 3H2O and Li2SO4·H2O. The main differences are in the size of crystallization area and end point positions of the univariant curves. At 323 K, the liquid composition of the invariant point is w(Li2B4O7) = 0.74% and w(Li2SO4) = 25.05%. At 288 K, the liquid composition of the invariant point is w(Li2B4O7) = 0.88% and w(Li2SO4) = 24.50%. At 273 K, the liquid composition of the invariant point is w(Li2SO4) = 23.57% and w(Li2B4O7) = 0.57%. Compared with the solubility data at other temperatures, our experimental data are consistent with them. 3.3. K2B4O7−K2SO4−H2O at 273 K. The solubilities of salts and equilibrium solid phases in the ternary system K2B4O7− K2SO4−H2O at 273 K were listed in Table 3. Figure 5 is the phase diagram of the ternary system K2B4O7−K2SO4−H2O at 273 K and the corresponding local enlarged drawing is shown in Figure 6. The X-ray diffraction photograph of the invariant point E1 in the ternary system is given in Figure 7. According to this figure, there are two salt precipitates in solution at the
invariant point. The forms of precipitations are K2B4O7·4H2O and K2SO4. The dissolution diagram consists of an invariant point E1 and two univariant curves A1E1 and B1E1 representing the solubility curves of K2B4O7·4H2O and K2SO4, respectively. The whole phase diagram can be divided into four regions, which consist of two crystallization regions for single salt corresponding to potassium sulfate (K2SO4) and potassium borate tetrahydrate (K2B4O7·4H2O), an unsaturated liquid phase area (A1B1E1) and a total crystallization area (C1D1E1). The area of B1E1D1 represents the crystallization area of K2SO4. Similarly, the crystallization area of K2B4O7·4H2O was shown in Figure 6 corresponding to the area of A1E1C1. It shows that the sizes of them are almost the same. It also means the solubility of K2SO4 is similar to that of K2B4O7. Point E1 saturates with salts K2SO4 + K2B4O7·4H2O and the mass fraction composition of saturated solution is w(K2SO4) = 4.91% and w(K2B4O7) = 6.17%. 3.4. Comparison with the Phase Diagrams at (273, 288,10 and 348 K14) for the Ternary System K2B4O7− C
DOI: 10.1021/acs.jced.7b00219 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Figure 7. X-ray diffraction photograph of the eutectic point E1[K2B4O7·4H2O + K2SO4] of the ternary system K2B4O7−K2SO4− H2O at 273 K.
Figure 5. Equilibrium phase diagram of the ternary system K2B4O7− K2SO4−H2O at 273 K.
Figure 8. Comparison of salt solubilities of the ternary system K2B4O7−K2SO4−H2O at 273, 288,10 and 348 K.14
4.91% and w(K2B4O7) = 6.17%. At 288 K, it shifts to w(K2SO4) = 7.57% and w(K2B4O7) = 6.88%. When the temperature rises to 348 K, the invariant point continues to move and is at w(K2SO4) = 4.43%, w(K2B4O7) = 30.74%. It is concluded that the solubility of K2B4O7 at the invariant point is more affected by temperature and increases significantly with the rise in temperature.
Figure 6. Enlarged partial diagram of the ternary system K2B4O7− K2SO4−H2O at 273.15 K.
4. CONCLUSION The solubilities of salts and equilibrium solid phases in the systems Li2SO4−Li2B4O7−H2O and K2B4O7−K2SO4−H2O at 273 K were determined simultaneously. On the basis of experimental data, phase diagrams of the two systems were constructed. The equilibrium solid phases in the first system are Li2B4O7·3H2O and Li2SO4·H2O, and those of the second system are K2SO4 and K2B4O7·4H2O. The results show that there is no solid solution or double salts in the two systems, and each of the systems has an invariant point, two univariant curves, and two crystallization regions.
K2SO4−H2O. The phase diagrams of the ternary system K2B4O7−K2SO4−H2O have been studied at various temperatures. Figure 8 is the comparison of salt solubilities of the ternary system K2B4O7−K2SO4−H2O at 273, 288, and 348 K. Compared with the ternary system at different temperatures, they all have a common type of phase diagram. They all consist of one invariant point, two univariant curves, and two regions of crystallization. The equilibrium solid phases exist in the solid−liquid mixture in the forms of K2SO4 and K2B4O7·4H2O at these temperatures, revealing that the solid phases remain unchanged in the range of 273−348 K. Also, it is easy to observe that the size of the crystallization field has changed. At 273 K the liquid composition of invariant point is w(K2SO4) =
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel: 13032845233. D
DOI: 10.1021/acs.jced.7b00219 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
ORCID
(17) Yan, S. W.; Tang, M. L.; Deng, T. L. Phase equilibria in the ternary system KCl−K2B4O7−H2O at 298.15 K (In Chinese). J. Mineral. Petrol. 1994, 14, 101−103.
Shi-hua Sang: 0000-0002-5948-3882 Funding
This project was supported by the National Natural Science Foundation of China (U1407108), Scientific Research and Innovation Team in Universities in Sichuan Provincial Department of Education (15TD0009) and the Youth Science and Technology Innovation Team of Sichuan Province, China (2013TD0005). Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) Wang, B. C. Lithium-bearing brine resources status and its progress of development technology in China (in Chinese). Ind. Miner. Process. 2000, 29 (10), 13−15. (2) Zhong, H.; Zhou, Y. F.; Yin, H. A. Progress in technology for extracting lithium from Li-bearing brine resources (In Chinese). Multipurpose Utilization of Mineral Resources. 2003, 14 (1), 23−28. (3) Wang, W. X.; Yan, Z. L. The development and utilization of boron resource in Qinghai-tibet region (in Chinese). Qinghai Sci. Technol. 2002, 9 (2), 25−26. (4) Liu, R.; Xue, X. X.; Liu, X.; Wang, D. S.; Zha, F.; Huang, D. Progress on China’s boron resource and current situation of boronbearing materials (in Chinese). J. Bull. Chin. Ceram. Soc. 2006, 25, 102−107. (5) Hu, L. R.; Wang, S. J. Discussion on sustainable development of salt lake resources in Qinghai province (in Chinese). Technol. Chem. Ind. Miner. 2006, 35, 1−4. (6) Sang, S. H.; Zeng, X. X.; Wang, D.; Qu, S. D. Study on metastable equilibria in the quaternary system Li+, K+//CO32‑, SO42‑−H2O at 273 K (in Chinese). Journal of Sichuan University (Engineering Science Edition). 2011, 43 (4), 189−193. (7) Sang, S. H.; Qu, S. D. A study on metastable equilibria of the quaternary system K2SO4−K2B4O7−K2CO3−H2O at 273K (In Chinese). J. Miner. Petrol. 2010, 30 (4), 102−105. (8) Sang, S. H.; Yin, H. A.; Ni, S. J.; Zhang, C. J. Metastable equilibrium solubilities of solutions in the quaternary system of K2B4O7−Na2B4O7−Li2B4O7−H2O 273 K (in Chinese). Acta Phys.Chim. Sin. 2007, 23 (8), 1285−1287. (9) Zhang, Z. L.; Sang, S. H.; Li, M.; Hou, C. H. Study on metastable phase equilibrium of the quaternary system K2B4O7−K2SO4−KCl− H2O at 298 K (in Chinese). Chem. Eng. 2009, 37 (5), 46−48. (10) Sang, S. H.; Zhang, X. Solubility investigations in the systems Li2B4O7−Li2SO4−H2O and K2B4O7−K2SO4−H2O at 288 K. J. Chem. Eng. Data 2010, 55, 808−812. (11) Sang, S. H.; Yu, H. Y. Phase equilibria in the ternary system Na2B4O7−NaBr−H2O at 298 K (In Chinese). Journal of Sea-Lake Salt and Chemical Industry. 2006, 35, 4−5. (12) Sang, S. H.; Tang, M. L.; Yin, H. A.; et al. Phase equilibria in the ternary systems Li2CO3−Li2B4O7−H2O and K2CO3−K2B4O7−H2O at 288 K (In Chinese). Ind. Miner. Process. 2002, 31, 7−9. (13) Zhao, X. Y.; Sang, S. H.; Sun, M. L. Phase equilibria in the ternary system K2B4O7−KBr−H2O at 323 K (In Chinese). J. Salt Lake Res. 2011, 12, 35−38. (14) Cui, R. Z.; Sang, S. H.; Zhang, K. J.; Li, T. The phase equilibria in the ternary systems K2B4O7−K2SO4−H2O and Na2SO4−Na2B4O7− H2O at 348 K. J. Chem. Eng. Data 2012, 57, 3498−350. (15) Song, P. S.; Du, X. H.; Xu, H. C. Phase relationship and the physicochemical properties of solution in the ternary system Li2B4O7− Li2SO4−H2O at 298.15 K (In Chinese). Chin. Sci. Bull. 1983, 34 (2), 106−110. (16) Shi, X. Y.; Li, D.; Deng, T. L. Phase equilibria in the ternary system Li2B4O7−Li2SO4−H2O at 323.15 K (In Chinese). J. Salt Chem. Ind. 2009, 7, 22−24. E
DOI: 10.1021/acs.jced.7b00219 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
