Cl

Article pubs.acs.org/jced

Salt−Water Phase Equilibria in Ternary Systems K+(Mg2+), NH4+//Cl−− H2O at T = 273 K Xudong Yu,*,†,‡,§ Lin Wang,† Jie Chen,† and Maolan Li† †

College of Materials and Chemistry & Chemical Engineering, Chengdu University of Technology, Chengdu 610059, P. R. China Collaborative Innovation Center of Panxi Strategic Mineral Resources Multi-Purpose Utilization, Chengdu 610059, P. R. China § Mineral Resources Chemistry, Key Laboratory of Sichuan Higher Education Institutions, Chengdu 610059, P. R. China ‡

ABSTRACT: Phase equilibria for two ternary systems K+, NH4+//Cl−−H2O, and Mg2+, NH4+//Cl−−H2O at T = 273 K were investigated by means of the isothermal saturation dissolution method. The density of each equilibrium liquid phase was determined by using the weighting bottle method. The compositions of the solid phases were confirmed using Scherinemakers’ wet residue method. The phase diagrams and the figures of density versus composition were plotted in accordance with the experimental data. The ternary system Mg2+, NH4+//Cl−−H2O is a type of complex with an incongruent type complex salt ammonium carnallite (NH4Cl·MgCl2·6H2O) formed at 273 K, which consists of two invariant points, three monovariant curves, and three solid phase crystallization fields. The ternary system of K+, NH4+//Cl−−H2O consists of three invariant points, four monovariant curves, and five solid phase crystallization fields and is also a type of complex with two solid solutions [(K, NH4)Cl] and [(NH4, K)Cl] found at 273 K. The comparison of obtained phase diagrams at 273 K in this work and 298 K has been deliberated. Ternary systems K+(Mg2+), NH4+//Cl−−H2O are two parts of the above system. The phase diagrams of K+(Mg2+), NH4+// Cl−−H2O at T = 298 K11,12 have been obtained by our research group; results show that the two systems belong to complex type with double salt or solid solution found. As is known to all, the double salt and hydrated salt crystal zone and crystallization morphology rely on the coexistence of ions and temperature.13 Therefore, the determination of the same system at different temperatures are necessary to obtain the crystalline information on the double salt, solid solution, and hydrated salt change with the temperature. As far as we know, there are no report about the phase equilibria for two ternary systems K+, NH4+//Cl−− H2O, and Mg2+, NH4+//Cl−−H2O at T = 273 K. In view of

1. INTRODUCTION Phase chemistry studies of the complex aqueous system are the foundation and direction of the comprehensive exploitation of brine.1 The phase separation technique have been widely used in many industrial processes such as precipitation, evaporation of water from brines, and extraction chemical products from liquid minerals (Searls Saline Lake, Qarhan Saline Lake, Dead Sea, Lop Nor Saline Lake, etc.).2 There is a wide range of saline lakes and oilfield brine spread in the Qinghai, Xinjiang, Tibet, and Inner Mongolia provinces in China.3 To scientifically exploit brine resources, the relevant phase equilibria and phase diagram focused on the composition of those brines are necessary.4−9 According to the composition characteristics (high content sodium, magnesium, potassium, ammonium, calcium, chloride, and borate) of oil field brine in Nanyishan, the seven-component system Na+, K+, NH4+, Ca2+, Mg2+//Cl−, and borate−H2O can be applicable to represent the phase equilibrium relationship of the brine.10 © XXXX American Chemical Society

Received: November 24, 2016 Accepted: March 17, 2017

A

DOI: 10.1021/acs.jced.6b00981 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Solubility and Analytical Experimental Reagents chemical name

CAS No.

initial purity (w/w %)

purified method

source

ammonium chloride (NH4Cl)

12125-02-9

99.0

recrystallization

magnesium chloride hexahydrate (MgCl2·6H2O) potassium chloride (KCl)

7791-18-6

99.0

recrystallization

7447-40-7

99.0

recrystallization

Chengdu Kelong Chemical Reagent Plant, China Sinopharm Chemical Reagent Co., Ltd., China Sinopharm Chemical Reagent Co., Ltd., China

final purity (w/w %)

analytical method17

99.5

titration with AgNO3 for Cl−

99.5

titration with EDTA stand solution for Mg2+ titration with AgNO3 for Cl−

99.5

Table 2. Experimental Values of Solubility and Densities in the Ternary System NH4Cl + MgCl2 + H2O at 273 K and Pressure p = 0.1 MPaa composition of equilibrated solution, w(B) × 102 no.

density (g·cm−3)

w(NH4Cl)

w(MgCl2)

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

1.0698 1.0826 1.0954 1.1068 1.1174 1.1369 1.1553 1.1725 1.1853 1.1935 1.2043 1.2077 1.2155 1.2248 1.2401 1.2498 1.2636 1.2917 1.3165

23.08 22.28 19.97 18.22 16.47 13.59 10.85 9.14 8.29 8.12 6.71 6.41 5.39 4.12 2.51 0.79 0.22 0.05 0.00

0.00 2.23 4.47 5.69 7.91 11.57 14.36 16.81 18.07 19.09 20.82 21.19 23.34 24.99 26.12 28.01 30.07 34.03 34.13

composition of wet solid phase, w(B) × 102 w(NH4Cl)

w(MgCl2)

44.72 45.48 44.65 44.5 45.78 45.19 42.91 33.24 34.17 32.02 36.94

1.61 3.07 4.12 5.27 7.11 8.67 10.83 13.92 13.88 15.73 14.82

0.66

36.65

equilibrated solid phase NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl + NH4Cl·MgCl2·6H2O NH4Cl·MgCl2·6H2O NH4Cl·MgCl2·6H2O NH4Cl·MgCl2·6H2O MgCl2·6H2O + NH4Cl·MgCl2·6H2O MgCl2·6H2O MgCl2·6H2O MgCl2·6H2O

Note: w(B): mass fraction of B; standard uncertainties u are u(T) = 0.10 K, ur(p) = 0.05, u(ρ) = 2 × 10−4 g·cm−3, u(w(NH4Cl)) = 0.0050, and u(w(MgCl2)) = 0.0050.

a

Figure 1. Stable phase diagram of the ternary system NH4Cl + MgCl2 + H2O at 273 K.

B



Article

Figure 2. X-ray diffraction pattern of the invariant point E1.

Figure 3. X-ray diffraction pattern of the invariant point E2.

solubility equilibria. The equilibrium can be considered to be achieved when the content of the sample kept constant. The time required for equilibrium reached is nearly 30 days. When the solution at equilibrium, the stirring was stopped for at least 48 h until the liquid phase became clear, and then we took 5.0 mL for the determination of densities by using the weighting bottle method,15 as well as another 5.0 mL diluted to a final volume of 100 mL in a volumetric flask with double-deionized water for the measurement of the compositions of the liquid phases by a chemical analysis method. The solid phases were identified by Schreinemakers’ wet residue method16 and the Xray diffraction (XRD) method. 2.3. Analytical Methods.17 The methods used the following procedures: Mg2+: titration with EDTA stand solution, standard uncertainty of 0.50%; NH4+: formaldehyde method, standard uncertainty of 0.50%; Cl−: AgNO3 titration method, standard uncertainty of 0.30%; K+: CTAB−STPB titration method, standard uncertainty of 0.50%.

this, the salt−water phase equilibria data of the ternary systems at 273 K are reported in this study.

2. EXPERIMENTAL SECTION 2.1. Instruments and Chemicals. Double-deionized water with κ ⩽ 1 × 10−4 S·m−1 was used for phase equilibria experiments and analytical operations. All materials in this work are given in Table 1. The solubility experiments were carried out via the SHH-250 type thermostat. The crystalloid form of solid phase was identified with a DX-2700 type X-ray diffractometer. 2.2. Experimental Methods. The phase equilibrium experiments were carried out by means of an isothermal saturation dissolution method.14 Take the system Mg2+, NH4+//Cl−−H2O, for instance: a series of artificial samples in glass bottles were obtained by adding different amounts of NH4Cl, MgCl2·6H2O, and H2O, and then the samples were placed on the thermostat at 273 ± 0.1 K. The HY-8 oscillator with a 120 rpm stirring speed was used to accelerate the C



Article

The compositions of KCl, NH4Cl, and MgCl2 were acquired with the K+, NH4+, and Mg2+ concentrations, so the standard uncertainties of the KCl, NH4Cl, and MgCl2 were 0.50%.

3. RESULTS AND DISCUSSION Mg2+, NH4+//Cl−−H2O Ternary System. The solubility data and composition of the wet residues (both expressed in

Figure 5. Stable phase diagram of the ternary system NH4Cl + KCl + H2O at 273 K.

confirmed by XRD pattern, as shown in Figure 2, consists of salts NH4Cl and NH4Cl·MgCl2·6H2O. Point E2 belongs to the commensurate type, which consists of w(NH4Cl) = 0.79% and w(MgCl2) = 28.01%. The solid phase of E2 confirmed by XRD pattern, as shown in Figure 3, consist of salts MgCl2·6H2O and NH4Cl·MgCl2·6H2O. Two invariants of ternary system and three isothermal dissolution curves divide the phase diagram into three parts, which correspond to three crystallization zones of NH4Cl, MgCl2·6H2O, and NH4Cl·MgCl2·6H2O. The crystallization zones decrease in the sequence of NH4Cl, NH4Cl·MgCl2· 6H2O, and MgCl2·6H2O, and the solubility of three salts are indicated in order of descending MgCl2·6H2O, NH4Cl·MgCl2· 6H2O, and NH4Cl. A variety of salt hydrate forms of magnesium chloride have been found, such as MgCl2·nH2O (n = 2, 4, 6, 8, 12). Previous

Figure 4. Density vs composition diagram for the ternary system NH4Cl + MgCl2 + H2O at 273 K.

100w) of the ternary system Mg2+, NH4+//Cl−−H2O at 273 K are listed in Table 2, and the ternary phase diagram was shown in Figure 1. In Figure 1, points A and B are invariant points of two binary systems NH4Cl + H2O and MgCl2 + H2O, and points E1 and E2 are two invariant points of the ternary system; curves AE1, E1E2, and BE2 are three isothermal dissolution curves. Invariant point E1 is the incommensurate type, which consists of w(NH4Cl) = 6.41% and w(MgCl2) = 21.19%. The solid phase of E1

Table 3. Experimental Values of Solubility and Densities in the Ternary System NH4Cl + KCl + H2O at 273 K and Pressure p = 0.1 MPab composition of equilibrated solution, w(B) × 102 no.

density (g·cm−3)

w(NH4Cl)

w(KCl)

1, A 2 3 4, H1 5 6 7 8 9 10, H2 11 12 13, H3 14 15 16 17 18, B

1.1511 1.1506 1.1434 1.1404 1.1360 1.1377 1.1342 1.1283 1.1204 1.1249 1.1225 1.0995 1.0996 1.0860 1.0852 1.0755 1.0771 1.0698

0.00 1.17 1.91 2.95 4.75 7.13 9.41 11.97 17.85 17.77 18.04 18.89 21.58 21.62 22.60 23.08 23.86 23.08

22.43 21.62 20.84 20.13 19.05 17.92 15.48 13.41 10.89 11.36 11.06 8.11 5.06 3.77 2.44 1.63 0.93 0.00

composition of wet solid phase, w(B) × 102 w(NH4Cl) 0.89 1.24 1.53 2.71 4.33 4.70 7.06 21.93 40.46 47.49 58.96 58.38 57.31 55.59 61.31 61.28

w(KCl)

equilibrated solid phase

68.49 64.67 79.86 78.36 75.98 77.54 73.97 51.76 16.24 12.68 6.30 3.31 2.54 1.67 1.10 0.59

KCl KCl KCl KCl + (K, NH4)Cl (K, NH4)Cl (K, NH4)Cl (K, NH4)Cl (K, NH4)Cl (K, NH4)Cl (K, NH4)Cl + (NH4, K)Cl (NH4, K)Cl (NH4, K)Cl NH4Cl + (NH4, K)Cl NH4Cl NH4Cl NH4Cl NH4Cl NH4Cl

Note: w(B): mass fraction of B; standard uncertainties u are u(T) = 0.10 K, ur(p) = 0.05, u(ρ) = 2 × 10−4 g·cm−3, u(w(NH4Cl)) = 0.0050, and u(w(KCl)) = 0.0050.

b

D



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11.36%, and salts [(NH4, K)Cl], [(K, NH4)Cl] coexist at the invariant point H2. Invariant point H3 is w(NH4Cl) = 21.58% and w(KCl) = 5.06%, and salts NH4Cl, [(NH4, K)Cl] coexist at the invariant point H3. Three invariants of the ternary system and four isothermal dissolution curves divide the phase diagram into five parts, which correspond to five crystallization zones of NH4Cl, KCl, [(NH4, K)Cl], [(K, NH4)Cl], and a crystallization zone of two kinds of solid solution [(K, NH4)Cl + (NH4, K)Cl] precipitation. The crystalline zone of solid solution is the largest in the system, which indicates that it is difficult to separate them only by crystallization methods at 273 K in chloride solution. A comparison of the solubility data of system K+, NH4+//Cl−−H2O at 298 K12 and 273 K shows that the influence of temperature of solubility is a positive correlation for NH4Cl and KCl but a negative correlation for the solid solution. The figure of density versus composition (Figure 6) is constructed using the density value as ordinate, w(KCl) as abscissa; as shown in Figure 6, the value of density increases with the increasing concentration of KCl.

Figure 6. Density vs composition diagram for the ternary system NH4Cl + KCl + H2O at 273 K.

research results show that the MgCl2 crystallizes in the form of MgCl2·6H2O at 269.75−389.85 K.18 In this work, the crystal form of magnesium chloride is MgCl2·6H2O, which is in agreement with the previous experimental result. In carnallite KCl·MgCl2·6H2O, K+ can be replaced by alkali metal elements (Rb+, Cs+) and NH4+ to form a series of different types’ carnallite.19 In this ternary system, in addition to single salts NH4Cl and MgCl2·6H2O, the double salt NH4Cl·MgCl2·6H2O is simultaneously formed at 273 K. Double salt has two types: congruent and incongruent. The simple way of identifying the types of double salt relies on whether the ray curve and the solubility curve of double salt intersect. The double salt belongs to congruent type when these two curves intersect, whereas it belongs to incongruent type.20 In Figure 2, the ray curve and the solubility curve of double salt do not intersect; therefore, double salt NH4Cl· MgCl2·6H2O belongs to the incongruent type. The stable and metastable phase diagrams of the system Mg2+, NH4+//Cl−−H2O at 298 K11,12 have been studied in our group; the difference of the phase diagram at 298 and 273 K shows that, as the temperature increases, the crystallization zones of single salts NH4Cl and MgCl2·6H2O decrease, while the crystallization zone of double salt NH4Cl·MgCl2·6H2O increases. Figure 2 indicates that MgCl2 has the highest solubility and NH4Cl solubility decreased with MgCl2 addition; thus, the mass fraction of MgCl2 in the solution is the main factor influencing of the density. Based on this, the figure of density versus composition (Figure 4) is constructed using w(MgCl2) and the value of density as abscissa and ordinate; as shown in Figure 4, the densities of the solution at equilibrium are positively correlated with the mass fraction of MgCl2. K+, NH4+//Cl−−H2O Ternary System. The solubility data and composition of the wet residues (both expressed in 100w) of the ternary system K+, NH4+//Cl−−H2O at 273 K are listed in Table 3, and the ternary phase diagram was shown in Figure 5. Three invariants (H1, H2, and H3), five crystallization zones, and four isothermal dissolution curves AH1, H1H2, H2H3, and BH3 constitute the phase diagram of K+, NH4+//Cl−−H2O. The crystallization morphology of H1 to H3 was confirmed with Schreinemakers’ wet residue method. Invariant point H1 consists of w(NH4Cl) = 2.95% and w(KCl) = 20.13%, and salts KCl, [(K, NH4)Cl] coexist at the invariant point H1. Invariant point H2 consists of w(NH4Cl) = 17.77% and w(KCl) =

4. CONCLUSIONS The salt−water phase equilibria of K+(Mg2+), NH4+//Cl−− H2O at T = 273 K were investigated via the isothermal saturation dissolution method. Ternary system Mg2+, NH4+// Cl−−H2O at 273 K is a type of complex with an incongruent type complex salt NH4Cl·MgCl2·6H2O formed. Two invariant points and three unvariant curves divide the phase diagram into three crystallization fields. MgCl2·6H2O has been found at 273 K, and it has the largest solubility among three salts. NH4Cl can be easily separated from the solution this system at 273 K on account of it has the largest crystallization region. The ternary system of K+, NH4+//Cl−−H2O is also a type of complex with two solid solutions [(K, NH4)Cl] and [(NH4, K)Cl] found at 273 K, and the crystalline zone of solid solution is the largest in this system, which indicates that it is difficult to separate them only by crystallization methods at 273 K. A comparison of the phase diagrams at 298 and 273 K show that the influence of temperature of solubility is positive correlation for single salts, while a negative correlation for solid solution and double salt.

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AUTHOR INFORMATION

Corresponding Author

*E-mail address: [email protected], [email protected]. cn. ORCID

Xudong Yu: 0000-0002-3848-9484 Funding

This project was supported by the NSFC (U1507111), the Research Fund from the Science and Technology Department of Sichuan Province (2017JY0191), the Scientific research fund of Sichuan Provincial education department (16ZA0083), the scientific research and innovation team in universities of Sichuan provincial department of education (15TD0009), innovation and entrepreneurship training program (201610616097), and youth foundation of CDUT(2017QJ04). Notes

The authors declare no competing financial interest. E



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REFERENCES

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