Phase Equilibria in the Quaternary Systems KClâPbCl2âZnCl2âH2O

Article pubs.acs.org/jced

Phase Equilibria in the Quaternary Systems KCl−PbCl2−ZnCl2−H2O and MgCl2−PbCl2−ZnCl2−H2O at 373 K Xue-ping Zhang,† Xiao-feng He,† Yu-yan Yang,† and Shi-hua Sang*,†,‡ †

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: In this work, the method of isothermal dissolution equilibrium was applied to investigating the phase equilibria of quaternary systems KCl−PbCl2−ZnCl2− H2O and MgCl2−PbCl2−ZnCl2−H2O at 373 K throughout the entire concentration range. Isothermal solubility and water content diagrams were constructed based on the measured solubility of components and the coexisting solid phase, respectively. The experimental results indicate that the phase diagram of the quaternary system KCl−PbCl2−ZnCl2−H2O at 373 K consists of three invariant points, seven univariant isothermal solubility curves, and five single solid-phase crystalline regions corresponding to KCl, PbCl2, KCl·2PbCl2, 2KCl·ZnCl2, and ZnCl2. It is shown that the phase diagram of the quaternary system MgCl2−PbCl2−ZnCl2−H2O at 373 K is made up of two invariant points, five univariant isothermal solubility curves, and four single solid-phase crystalline regions corresponding to MgCl2·6H2O, PbCl2, MgCl2·ZnCl2·5H2O, and ZnCl2.

1. INTRODUCTION The relationship between lead and zinc in nature is intimate and usually symbiotic. Because lead and zinc act as indispensable nonferrous metals, these mineral resources have been universally applied to various fields, such as the chemical industry, metallurgy, and the petroleum industry; thus, thermodynamics studies on lead and zinc have become increasingly important. It is widely acknowledged that the solubility of the salts is used to calculate the supersaturation and determine the optimum conditions for crystal growth.1 Moreover, it is necessary for the design and operation of solvent extraction.2 Owing to the economic importance of lead and zinc, studies involving the solubility of lead chloride and zinc chloride were carried out. The aqueous thermodynamics of PbSO4 in Na2SO4/H2SO4 systems has been expanded to high concentrations.3 Although it is difficult to study the aqueous thermodynamics of Pb(II) in high concentration solutions because of the significant presence of lead chloride species4,5 and the limited solubility of PbCl2.6 The solubilities of lead chloride in low concentrations of sodium chloride or calcium chloride aqueous solution were studied by Russian researchers.7 It was found that the solubility of lead chloride decreased first and then increased with increasing chloride concentration. The NaCl−ZnCl2−H2O aqueous system has been conducted at a variety of temperatures, such as 273.15,8 260.35, and 250.15 K.9 Because high density fluid is used as a petroleum drilling fluid, solubilities and densities of the ternary system CaCl2−ZnCl2− H2O have been carried out at 273.15 and 298.15 K10 and the © XXXX American Chemical Society

system CaCl2+ZnCl2+H2O (NaCl saturated) was studied at T = 288.15 K.11 The solubilities of ZnCl2 and CO(NH2)2 in HCl have been determined at T = 298.15 K.12 The phase equilibria of the ternary system ZnCl2−LiCl−H2O at 298 and 313 K have been conducted,13 and it was found that the double salt 2LiCl· ZnCl2·2.5H2O was observed. In a previous study, we analyzed phase equilibria involving zinc chloride in the ternary systems KCl−ZnCl2−H2O and CaCl2−ZnCl2−H2O14 and quaternary system KCl−MgCl2−ZnCl2−H2O.15 Furthermore, we determined water salt systems involving lead chloride at 373 K, including ternary systems CaCl2−PbCl2−H2O and PbCl2− ZnCl2−H2O16 and quaternary system KCl−MgCl2−PbCl2− H2O.15 To the best of our knowledge, this is the first report on phase equilibria in these two systems. The aim of this work is to investigate the experimental solubilities of potassium, magnesium, lead, and zinc chlorides in “hot” aqueous solutions at 373 K. The result attempts to explain the solid−liquid phase equilibria of salt minerals in the two quaternary systems KCl−PbCl2−ZnCl2−H2O and MgCl2− PbCl2−ZnCl2−H2O at 373 K. It can be also useful for understanding the formation, transportation of lead and zinc in hydrothermal solutions, and some ore-forming processes. Received: February 25, 2017 Accepted: June 8, 2017

A

DOI: 10.1021/acs.jced.7b00218 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

distilled water with the conductivity of less than 1 × 10−5 S m−1 into the solid samples. Water used in the experiments was polished by an ultrapure water purification system. A standard AL104 analytical balance manufactured by the Mettler Toledo Instruments Co., Ltd. was employed to evaluate the quality of the sample. The balance has a maximum measuring range of 110 g and resolution of 0.0001 g. A HZ9613Y high-temperature oil bath oscillator with a resolution of 0.1 K provided by the Jintan Jieruier Instrument Co., Ltd. was applied for thorough shaking so that dissolution equilibrium can be achieved faster at a constant temperature. A DX-2700 Xray powder crystal diffraction analyzer supplied by Dandong Fangyuan Instrument Co., Ltd. was employed to identify the equilibrium solid phases. 2.2. Experimental Method. The isothermal dissolution equilibrium method was utilized to carry out the phase equilibria of the quaternary systems at 373 K. The artificial geothermal brines for the simple quaternary system were prepared by adding the third component gradually based on the invariant points in three ternary subsystems. The samples were prepared by adding a certain proportion of two salts into 50 mL

2. EXPERIMENTS 2.1. Reagents and Instruments. A variety of analytical chemicals prepared for a series of samples are tabulated in Table 1. All of the water salt mixtures were prepared by adding Table 1. Description of the Samples chemical reagent

mole fraction purity

KCl

≥99.5%

Chengdu Kelong Chemical Reagent Manufacture, China

MgCl2· 6H2O

≥98%


ZnCl2

≥98%


PbCl2

≥99.5%


analysis method

source

chemical titration method chemical titration method chemical titration method chemical titration method

Table 2. Solubilities for Salts in Quaternary System KCl−PbCl2−ZnCl2−H2O at 373 K and 94.77 KPaa Jänecke index Jb (g/100 g of dry salt)

composition of the solution (100·wb) no.

ZnCl2

PbCl2

KCl

ZnCl2

PbCl2

KCl

H2O

solid phases

1, A 2 3 4 5 6 7 8, E3 9, B 10 11 12, E1 13 14 15, E2 16 17 18 19 20 21, C 22 23 24 25 26, D 27 28 29 30 31, F 32 33 34

0.00 9.56 21.85 35.71 44.25 48.98 62.63 73.53 0.00 10.12 19.21 22.54 27.95 39.50 43.62 50.49 63.68 64.23 67.61 69.53 37.74 36.93 35.72 34.07 31.40 61.85 59.03 57.58 55.50 51.84 76.93 77.14 76.95 76.00

2.14 2.15 2.02 1.94 1.73 1.63 1.49 1.34 6.89 4.50 3.09 2.78 2.32 1.86 1.72 1.78 1.69 1.67 1.45 1.30 0.00 1.01 1.14 1.22 1.75 0.00 0.54 0.88 1.06 1.42 3.35 2.71 2.52 2.23

10.02 12.42 13.65 12.22 10.99 9.76 8.98 8.54 34.84 30.53 27.46 25.96 24.89 21.86 20.03 18.98 15.23 14.47 14.01 12.36 43.14 42.86 41.72 40.65 36.36 29.33 28.61 27.55 26.50 24.57 0.00 1.04 2.54 4.51

0.00 39.62 58.24 70.61 77.67 81.13 85.68 88.15 0.00 22.41 38.61 43.95 50.67 62.48 66.73 70.86 79.01 79.92 81.39 83.58 46.66 45.71 45.46 44.86 45.17 67.83 66.94 66.95 66.82 66.61 95.83 95.36 93.83 91.85

17.60 8.91 5.38 3.89 3.04 2.70 2.04 1.61 16.51 9.97 6.21 5.42 4.21 2.94 2.63 2.50 2.10 2.08 1.75 1.56 0.00 1.25 1.45 1.60 2.52 0.00 0.61 1.02 1.28 1.82 4.17 3.35 3.07 2.70

82.40 51.47 36.38 25.50 19.29 16.17 12.28 10.24 83.49 67.62 55.18 50.63 45.03 34.58 30.64 26.64 18.89 18.00 16.86 14.86 53.34 53.04 53.09 53.54 52.31 32.17 32.45 32.03 31.90 31.57 0.00 1.29 3.10 5.45

722.37 314.42 166.52 100.52 75.53 65.65 36.80 19.89 139.64 121.48 100.96 95.01 81.29 58.18 52.98 40.35 24.07 24.42 20.38 20.21 23.64 23.76 27.26 31.68 43.86 9.67 13.40 16.27 20.39 28.49 24.56 23.62 21.94 20.86

KP+P KP+P KP+P KP+P KP+P KP+P KP+P KP+P+Z KP+K KP+K KP+K KP+K+KZ KP+KZ KP+KZ KP+KZ+Z KP+Z KP+Z KP+Z KP+Z KP+Z KZ+K KZ+K KZ+K KZ+K KZ+K KZ+Z KZ+Z KZ+Z KZ+Z KZ+Z P+Z P+Z P+Z P+Z

a

wb, mass fraction of component b in saturated solution; Jb, mass of component b in 100 g of dry salt. K−KCl, Z−ZnCl2, P−PbCl2, KP−KCl·2PbCl2, KZ−2KCl·ZnCl2; standard uncertainties u are u(T) = 0.1 K, u(P) = 0.9 KPa, u(w(KCl)) = 0.005, u(w(PbCl2)) = 0.005, and u(w(ZnCl2)) = 0.003. B



Article

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 glass reactors, which were placed in the high-temperature oil bath oscillator (HZ-9613Y). The temperature for mechanical agitation was controlled at 373 ± 0.1 K by an oil bath oscillator. In the whole process of equilibrium, the presence of a solid phase should always be maintained. After 3 days of vibration, the solid−liquid mixtures were left to stand for 2 days until the liquid phase was clearly clarified, and a pipet was used to quickly remove 5 mL of the supernatant. The composition of salts in the liquid was measured by chemical analysis. When the composition of the liquid phase did not change, we assumed that dissolution equilibrium had been reached, and the solid phases were thoroughly washed and vacuum-dried for X-ray diffraction analysis by a DX-2700 X-ray diffraction analyzer. The solid phases of the invariant point were determined by the X-ray diffraction photograph. 2.3. Analytical Methods. Because of the occurrence of lead chloride and zinc chloride hydrolysis in aqueous solution, a few drops of hydrochloric acid were added to prevent such phenomenon, which made it difficult to measure the concentration of chloride ions. The concentration of metal cations instead of the chloride ion in the coexisting solution were determined. The sodium tetraphenylborate volumetric method was used to determine the content of potassium using 3.5 g L−1 hyamine standard solution as a titrant and titan yellow as indicator (uncertainty of 0.005). Total Zn2+, Pb2+, and Mg2+ were determined using the EDTA titration method at pH 10 with Eriochrome Black-T as indicator and ammonia as buffer solution (uncertainty of 0.003). Total Zn2+ and Pb2+ were determined by the EDTA volumetric method at pH 4.5 using xylenol orange as the indicator (uncertainty of 0.003). The concentration of Mg2+ was determined by subtracting the lead and zinc concentration from the total concentration of magnesium lead and zinc (uncertainty of 0.003). The concentration of Pb2+ was determined at pH 4.5 using xylenol orange as the indicator in the conditions that Pb2+ was separated by adding H2SO4 to form PbSO4 (uncertainty of 0.005). The concentration of Zn2+ was evaluated by subtracting the lead concentration from the total concentration of lead and zinc (uncertainty of 0.003). The composition of the samples was taken as the average of three analysis results.

Figure 1. Dry salt diagram of quaternary system KCl−PbCl2−ZnCl2− H2O at 373 K.

Figure 2. Partial enlarged dry salt diagram of quaternary system KCl− PbCl2−ZnCl2−H2O at 373 K.

3. RESULTS AND DISCUSSION 3.1. Quaternary System KCl−PbCl2−ZnCl2−H2O at 373 K. The experimental solubilities of salts and coexisting equilibrium solid phases in the quaternary system KCl− PbCl2−ZnCl2−H2O at 373 K are listed in Table 2. On the basis of the experimental data, the isothermal sections of the dry salt diagram for the quaternary system KCl−PbCl2−ZnCl2−H2O at 373 K are shown in Figure 1. The corresponding partial enlarged diagram is presented in Figure 2. In Table 2 and Figure 1, points A and B present the invariant points of the ternary system KCl−PbCl2−H2O. Similarly, the invariant points of the ternary system KCl−ZnCl2−H2O were marked as points C and D. The cosaturated point of ternary system PbCl2−ZnCl2−H2O was distinguished as point F. The results indicate that this quaternary system is a type of complex owing to the formation of double salts KCl·2PbCl2 and 2KCl·ZnCl2. The isothermal solubility diagram consists of three invariant points, seven univariant curves, and five regions of crystallization corresponding to KCl, PbCl2, KCl·2PbCl2, 2KCl·ZnCl2,

Figure 3. Water content diagram of quaternary system KCl−PbCl2− ZnCl2−H2O at 373 K.

and ZnCl2. It was shown that most of the crystalline areas were occupied by lead chloride. The fields of potassium chloride, zinc chloride, potassium lead double salt, and potassium zinc double salt existence are very narrow. This indicates that the salt PbCl2 has the smallest solubility and precipitates from mixed solution in a wide concentration range. The seven C



Article

Figure 4. X-ray diffraction photograph of invariant point E1 [KCl+KCl·2PbCl2+2KCl·ZnCl2] of the quaternary system KCl−PbCl2−ZnCl2−H2O at 373 K.

Figure 5. X-ray diffraction photograph of invariant point E2 [ZnCl2+2KCl·ZnCl2+KCl·2PbCl2] of the quaternary system KCl−PbCl2−ZnCl2−H2O at 373 K.

Figure 6. X-ray diffraction photograph of invariant point E3 [ZnCl2+KCl·2PbCl2+PbCl2] of the quaternary system KCl−PbCl2−ZnCl2−H2O at 373 K.

ing liquid phase are w(ZnCl2) = 22.54%, w(PbCl2) = 2.78%, and w(KCl) = 25.96%. Point E2 saturates with salts ZnCl2+KCl· 2PbCl2+2KCl·ZnCl2, and the mass fraction compositions of the corresponding liquid phase are w(ZnCl2) = 43.62%, w(PbCl2) = 1.72%, and w(KCl) = 20.03%. Point E3 saturates with salts ZnCl2+PbCl2+KCl·2PbCl2, and the mass fraction compositions

isothermal dissolution curves are AE3, BE1, CE1, DE2, FE3, E1E2, and E2E3. It is clear that curve AE3 is considered to be the longest solubility curve among them. Points E1, E2, and E3 are the invariant points for the system KCl−PbCl2−ZnCl2−H2O at 373 K. Point E1 saturates with salts KCl+KCl·2PbCl2+2KCl· ZnCl2, and the mass fraction compositions of the correspondD



Article

Table 3. Solubilities for Salts in the Quaternary System MgCl2−PbCl2−ZnCl2−H2O at 373 K and 94.77 KPaa Jänecke index Jb (g/100 g of dry salt)

composition of the solution (100·wb) no.

ZnCl2

PbCl2

MgCl2

ZnCl2

PbCl2

MgCl2

H2O

solid phases

1, A1 2 3, E4 4 5 6 7 8 9, E5 10, B1 11 12 13 14 15, C1 16 17 18 19 20, D1 21 22 23 24 25

0.00 7.19 12.10 12.94 27.56 53.15 59.29 59.63 60.26 11.34 11.42 11.50 11.71 11.86 62.51 60.96 60.63 60.52 60.47 76.93 75.38 71.95 71.39 69.48 61.58

7.23 3.87 3.23 2.96 2.05 1.14 0.96 0.90 0.87 0.00 0.13 0.34 0.54 1.66 0.00 0.34 0.58 0.67 0.73 3.35 1.92 1.76 1.68 1.51 1.02

38.07 37.06 36.36 35.96 29.29 18.83 14.93 14.82 14.58 39.54 39.08 38.99 38.77 37.47 15.14 14.86 14.83 14.72 14.65 0.00 2.23 5.12 5.48 7.45 13.69

0.00 14.94 23.41 24.95 46.79 72.69 78.86 79.14 79.59 22.29 22.56 22.62 22.95 23.26 80.50 80.04 79.73 79.73 79.72 95.83 94.78 91.27 90.88 88.58 80.72

15.96 8.04 6.25 5.71 3.48 1.56 1.28 1.19 1.15 0.00 0.26 0.67 1.06 3.26 0.00 0.45 0.76 0.88 0.96 4.17 2.41 2.23 2.14 1.93 1.34

84.04 77.02 70.34 69.34 49.73 25.75 19.86 19.67 19.26 77.71 77.18 76.71 75.99 73.48 19.50 19.51 19.51 19.39 19.32 0.00 2.81 6.50 6.98 9.49 17.94

120.75 107.81 93.46 92.83 69.78 36.76 33.01 32.71 32.08 96.54 97.51 96.73 96.00 96.12 28.78 31.30 31.51 31.73 31.84 24.56 25.74 26.86 27.31 27.49 31.08

Bis+P Bis+P Bis+P+MZ MZ+P MZ+P MZ+P MZ+P MZ+P MZ+P+Z Bis+MZ Bis+MZ Bis+MZ Bis+MZ Bis+MZ MZ+Z MZ+Z MZ+Z MZ+Z MZ+Z P+Z P+Z P+Z P+Z P+Z P+Z

wb, mass fraction of component b in saturated solution; Jb, mass of component b in 100 g of dry salt. P−PbCl2, Bis−MgCl2·6H2O, MZ−MgCl2· ZnCl2·5H2O, Z−ZnCl2; standard uncertainties u are u(T) = 0.1 K, u(P) = 0.9 KPa, u(w(MgCl2)) = 0.003, u(w(PbCl2)) = 0.005, and u(w(ZnCl2)) = 0.003. a

Figure 7. Dry salt diagram of quaternary system MgCl2−PbCl2− ZnCl2−H2O at 373 K.

Figure 8. Water content diagram of quaternary system MgCl2− PbCl2−ZnCl2−H2O at 373 K.

of the corresponding liquid phase are w(ZnCl2) = 73.53%, w(MgCl2) = 1.34%, and w(KCl) = 8.54%. Figure 3 is the water content diagram of the quaternary system KCl−PbCl2−ZnCl2−H2O at 373 K. It reveals that the water content decreases with the increase in zinc chloride content on the univariant curves except for curve FE3 and reaches minimum value at point D (J = 9.67). This means that the total salt concentration is the highest at point D. The maximum value of water content appears at point A (J = 722.37). Compared with point D, the water content at point A is significantly larger, which shows that the solution concentration reaches a minimum at point A.

Figure 4 is the X-ray diffraction photograph at invariant point E1 where KCl, KCl·2PbCl2, and 2KCl·ZnCl2 were determined. Figure 5 is the X-ray diffraction photograph at invariant point E2 where ZnCl2, KCl·2PbCl2, and 2KCl·ZnCl2 were found. Figure 6 is the diffraction photograph at invariant point E3. As can be seen from Figure 6, PbCl2, ZnCl2, and KCl·2PbCl2 were determined at invariant point E3. 3.2. Quaternary System MgCl2−PbCl2−ZnCl2−H2O at 373 K. The experimental solubilities in the quaternary system MgCl2−PbCl2−ZnCl2−H2O at 373 K are tabulated in Table 3. Figure 7 is the dry salt diagram of the quaternary system MgCl2 −PbCl2−ZnCl2−H2 O at 373 K that was drawn E



Article

Figure 9. X-ray diffraction photograph of invariant point E4 [Bis+PbCl2+MgCl2·ZnCl2·5H2O] of quaternary system MgCl2−PbCl2−ZnCl2−H2O at 373 K.

Figure 10. X-ray diffraction photograph of invariant point E5 [ZnCl2+PbCl2+MgCl2·ZnCl2·5H2O] of quaternary system MgCl2−PbCl2−ZnCl2− H2O at 373 K.

Table 4. Invariant Points of Subsystems in Quaternary System KCl−PbCl2−ZnCl2−H2O at 373 and 298 K composition of the invariant point (100·wb) T (K)

b = KCl

b = PbCl2

b = ZnCl2

298

6.37 18.77 26.52 10.02 34.84 0 0 43.14 61.85

0.15 0.29 0.52 2.14 6.89 2.58 3.35 0 0

0 0 0 0 0 76.74 76.93 37.74 29.33

373 298 373 373

system KCl−PbCl2−H2O

PbCl2−ZnCl2−H2O KCl−ZnCl2−H2O

solid phase

ref

PbCl2+KCl·2PbCl2 KCl·2PbCl2+KCl·PbCl2·1/3H2O KCl+KCl·PbCl2·1/3H2O PbCl2+KCl·2PbCl2 KCl+KCl·2PbCl2 PbCl2+ZnCl2 PbCl2+ZnCl2 KCl+2KCl·ZnCl2 ZnCl2+2KCl·ZnCl2

17

this work 17 16 15

and ZnCl2. As can be seen from Figure 7, the crystallization area of PbCl2 is the largest. However, the crystallization area of ZnCl2 is the smallest. It shows that the salt PbCl2 has the smallest solubility, whereas salt ZnCl2 has the largest solubility. Five univariant curves are A1E4, B1E4, C1E5, D1E5, and E4E5. Points E4 and E5 are the invariant points for the system MgCl2−PbCl2−ZnCl2−H2O at 373 K. Point E4 saturates with salts MgCl2·6H2O + PbCl2+MgCl2·ZnCl2·5H2O, and the mass fraction compositions of the corresponding liquid phase are w(ZnCl2) = 12.10%, w(PbCl2) = 3.23%, and w(MgCl2) = 36.36%. Point E5 saturates with salts ZnCl2+PbCl2+MgCl2·

according to the experimental data. In Table 3 and Figure 7, the point A1 is the invariant point of the ternary system MgCl2− PbCl2−H2O. Similarly, points B1 and C1 are the invariant points of the ternary system MgCl2−ZnCl2−H2O, and point D1 is the invariant point of ternary system PbCl2−ZnCl2−H2O. It is seen from Table 3 and Figure 8 that this quaternary system is a type of complex and has double salts MgCl2·ZnCl2·5H2O generated at the investigated temperature. There are two invariant points, five univariant curves, and four regions of crystallization in the phase diagram. The four crystallization fields correspond to PbCl2, MgCl2·6H2O, MgCl2·ZnCl2·5H2O, F



Article

Table 5. Invariant Points of Subsystems in Quaternary System MgCl2−PbCl2−ZnCl2−H2O at 373 and 298 K composition of the invariant point (100·wb) T (K)

b = MgCl2

b = PbCl2

b = ZnCl2

system

solid phase

298

37.76 30.91 38.07 0 0 11.34 62.51

0.35 4.57 7.23 2.58 3.35 0 0

0 0 0 76.74 76.93 39.54 15.14

MgCl2−PbCl2−H2O

Bis+PbCl2·3MgCl2·19H2O PbCl2+PbCl2·3MgCl2·19H2O PbCl2+Bis PbCl2+ZnCl2 PbCl2+ZnCl2 Bis+MgCl2·ZnCl2·5H2O ZnCl2+MgCl2·ZnCl2·5H2O

373 298 373 373

PbCl2−ZnCl2−H2O MgCl2−ZnCl2−H2O

ZnCl2·5H2O, and the mass fraction compositions of the corresponding liquid phase are w(ZnCl2) = 60.26%, w(PbCl2) = 0.87%, and w(MgCl2) = 14.58%. Figure 8 is the water content diagram of the quaternary system MgCl2−PbCl2−ZnCl2−H2O at 373 K; it shows that the water content changes regularly with the increase in zinc chloride content on the univariant curves. Water content decreases with increasing J (ZnCl2) at the univariant curves A1E4, D1E5, and E4E5 and reaches a minimum value at point D1, whereas there is no obvious change at the other univariant curves. Figure 9 shows the X-ray diffraction photograph of invariant point E4. Compared with the standard cards of three salt minerals, MgCl2·6H2O, PbCl2, and MgCl2·ZnCl2·5H2O were determined. Figure 10 is the X-ray diffraction photograph of invariant point E5. It demonstrates that ZnCl2, PbCl2, and MgCl2·ZnCl2·5H2O reached saturation. 3.3. Discussion. The solubilities for the ternary systems PbCl2−ZnCl2−H2O, MgCl2−PbCl2−H2O and KCl−PbCl2− H2O at 298 K have been reported by Hagemann.17 The invariant points of subsystems in the quaternary system KCl− PbCl2−ZnCl2−H2O and MgCl2−PbCl2−ZnCl2−H2O at 373 and 298 K are listed in Tables 4 and 5, respectively. The form of complex salt is largely influenced by temperature. Regarding system KCl−PbCl2−H2O, it was found that two different double salts KCl·2PbCl2 and KCl·PbCl2·1/3H2O were formed at 298 K,17 whereas at 373 K, the double salt KCl·PbCl2·1/ 3H2O was not identified. Similarly, aiming at ternary system MgCl2−PbCl2−H2O, the double salt PbCl2·3MgCl2·19H2O was found at 298 K.17 When the temperature rises to 373 K, double salt disappeared in the equilibrium solid phase. For ternary system PbCl2−ZnCl2−H2O, double salt was absent at 298 and 373 K. In this system, the crystallization of zinc chloride at 373 K is anhydrous zinc chloride.16 According to Blidin,13 ZnCl2·1.5H2O is stable at 298 K in saturated aqueous solution. When the temperature increased to 313 K, ZnCl2 acted as an extant precipitate in the solid−liquid equilibrium.

ref 17 this work 17 16 this work

building the phase diagram for quaternary system MgCl2− PbCl2−ZnCl2−H2O. It was shown that most of the crystalline areas were occupied by lead chloride in both systems. These results offer basic thermodynamic data for guiding comprehensive utilization of the lead and zinc mineral resources.

■

AUTHOR INFORMATION

Corresponding Author

*Tel: 13032845233. E-mail: [email protected]. ORCID

Shi-hua Sang: 0000-0002-5948-3882 Funding

Financial support by the National Natural Science Foundation of China (Grants 41373062, U1407108) and the scientific research and innovation team at the Sichuan University Provincial Department of Education Grant 15TD0009) are greatly acknowledged. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) Torrent-Burgus, J.; Veintemillas-Verdaguer, S. Solubility and activity coefficients of lead chloride in potassium nitrate solutions at 25°C and at boiling. Calculation of the supersaturation. Can. J. Chem. 1993, 71, 1259−1263. (2) Holdich, R. G.; Lawson, G. J. The solvent extraction of lead using commercially available extractants. Soc. Chem. Ind. 1986, 1. (3) Paige, C. R.; Kornicker, W. A.; Hileman, O. E., Jr.; et al. Modeling solution equilibrium for uranium ore processing: The PbSO4− H2SO4−H2O and PbSO4−Na2SO4−H2O systems. Geochim. Cosmochim. Acta 1992, 56, 1165−1173. (4) Byrne, R. H.; Young, R. W.; Miller, W. L. Lead chloride complexation using ultraviolet molar absorptivity characteristics. J. Solution Chem. 1981, 10, 243−251. (5) Millero, F. J.; Byrne, R. H. Use of Pitzer’s equations to determine the media effect on the formation of lead chloro complexes. Geochim. Cosmochim. Acta 1984, 48, 1145−1150. (6) Holdich, R. G.; Lawson, G. J. The solubility of aqueous lead chloride solutions. Hydrometallurgy 1987, 19, 199−208. (7) Chizhikov, D. M. Lead smelting learns; The Higher Education Press, 1954. (8) Adiguzel, V.; Erge, H.; Alisoglu, V.; Necefoglu, H. Study of the solubility, viscosity and density in Na+,Zn2+/Cl−−H2O, Na+−Zn2+− (H2PO2)−−H2O, Na+, Cl−/(H2PO2)−−H2O, and Zn2+,Cl−/(H2PO2)− − H2O ternary systems, and in Na+, Zn2+/Cl−, (H2PO2)−//H2O reciprocal quaternary system at 273.15 K. J. Chem. Thermodyn. 2014, 75, 35−44. (9) Belova, E. V.; Mamontov, M. N.; Uspenskaya, I. A. A sodium chloride-zinc chloride-water system: solubility of solids and density of liquid in wide range of temperatures. J. Chem. Eng. Data 2016, 61, 2426−2432.

4. CONCLUSIONS Phase diagrams in quaternary systems KCl−PbCl2−ZnCl2− H2O and MgCl2−PbCl2−ZnCl2−H2O were investigated at 373 K by isothermal dissolution equilibrium method and X-ray powder diffraction. On the basis of the determined mineral solubility, the phase and water content diagrams of the two systems were drawn, respectively. It is concluded that these two quaternary systems are complex, having generated double salts. Not only were three single salts KCl, PbCl2, and ZnCl2 in mixed solid phases determined, but two double salts KCl· 2PbCl2, 2KCl·ZnCl2 were found in quaternary system KCl− PbCl2−ZnCl2−H2O. Furthermore, four precipitates, MgCl2· 6H2O, PbCl2, MgCl2·ZnCl2·5H2O, and ZnCl2, were involved in G



Article

(10) Hudgins, C. M. Solubility and density studies of the CaCl2− ZnCl2−H2O System at 0°C and 25°C. J. Chem. Eng. Data 1964, 9, 434−436. (11) Helvenston, E. P.; Cuevas, E. A. A study of the system CaCI2ZnCI2-H2O (NaCl Saturated) at l5°C. J. Chem. Eng. Data 1964, 9, 321−323. (12) Erkasov, R. S.; Nesmeyanova, R. M.; Orazbaeva, R. S.; et al. Solubility in the ZnCl2-CO(NH2)2-HCl-H2O system at 25°C. Russ. J. Inorg. Chem. 2013, 58, 213−215. (13) Bildin, V. P. Heterogeneous equilibria in systems containing lithium chloride and chlorides of group II metals. Bull. Acad. Sci. USSR, Div. Chem. Sci. 1954, 3, 337−345. (14) Zhang, X. P.; Wen, X. H.; He, X. F.; Sang, S.-H.; et al. Measurement of mineral solubilities in the ternary systems CaCl2− ZnCl2−H2O and KCl−ZnCl2−H2O at 373 K. J. Solution Chem. 2016, 45, 1504−1515. (15) Zhang, X. P.; Wang, W.; Yang, Y. Y.; et al. Measurement of mineral solubilities in the quaternary systems KCl−MgCl2−PbCl2− H2O and KCl−MgCl2−ZnCl2−H2O at 373 K. J. Chem. Eng. Data 2017, 62, 1403−1410. (16) Zhang, X. P.; Cui, R. Z.; Liu, Q.; et al. Phase equilibria of the ternary systems PbCl2−ZnCl2−H2O and PbCl2−CaCl2−H2O at 373 K (in Chinese). CIESC Journal. 2016, 67, 4552−4557. (17) Hagemann, S. Thermodynamische Eigenschaften des Bleis in Lösungen der ozeanischen Salze[D]. Ph.D. Thesis, Braunschweig, Germany, 1999.

H


Phase Equilibria in the Quaternary Systems KClâPbCl2âZnCl2âH2O

Recommend Documents

Phase Equilibria in the Quaternary Systems KClâPbCl2âZnCl2âH2O