A Zinc Nitrate–Calcium Nitrate–Water System: The Solubility of Solids

Article pubs.acs.org/jced

A Zinc Nitrate−Calcium Nitrate−Water System: The Solubility of Solids and the Density of Liquids in a Wide Range of Temperatures Ekaterina V. Belova, Nikita A. Brusinski, Mikhail N. Mamontov, and Irina A. Uspenskaya* Chemistry Department, Lomonosov MSU, Moscow, 119991, Russian Federation ABSTRACT: The equilibrium phase diagram of the Zn(NO3)2−Ca(NO3)2−H2O system at 251.85, 262.35, and 288.15 K was studied by the isothermal solution saturation method and wet residue analysis. Densities of ternary Zn(NO3)2− Ca(NO3)2−H2O solutions were measured at 298.15−321.35 K. For some solutions, pH measurements were provided at 298.15 K.

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INTRODUCTION Heavyweight brines are widely used in the oil and gas industries as workover and packer fluids. One should consider some technical and economic aspects to develop a new type of successful mixtures. Fluids should be stable at a wide temperature and pressure range of exploitation and storage conditions to minimize frictional pressure losses in slim hole drilling applications, do not have a corrosive action,1−3 and have a reasonable cost.3,4 Calcium and zinc salts due to their high density and rather low cost are widely used to prepare workover fluids.3,5 However, corrosion activity (i) and the loss of homogeneity (ii) of nonsolid heavy workover fluids under storage conditions at low temperatures may be a problem for the usage of calcium and zinc salts mixtures. The first problem (i) is solved by adding special corrosion inhibitors;4,6 in this case, information about the acidity of brines is necessary. The stability of saturated solutions can be predicted from a phase diagram, so corresponding investigations should be performed to solve the second (ii) problem. In most cases, industry is interested in information about multicomponent systems. An experimental investigation of quaternary or five-component phase diagrams is time-consuming and laborious. As alternative, the thermodynamic modeling of multicomponent systems may be performed. For the model parametrization, one should have experimental data on SLE from binary and ternary subsystems. The aim of the present work was to investigate a volumetric properties near room temperature and phase equilibria at subzero region of ternary system Zn(NO3)2−Ca(NO3)2−H2O; additional pH measurements were made for some mixtures with high density. Nitrates of zinc and calcium were chosen as an object of investigation because the Zn(NO3)2−H2O and Ca(NO3)2−H2O systems are characterized by rather low eutectic temperatures,7 so their ternary solutions can be stable at subzero temperatures. Although the system Zn(NO3)2− Ca(NO3)2−H2O is rather simple, we could not find any information about phase equilibria in this ternary system. The particular tasks of the work were to build cross sections of Zn(NO3)2−Ca(NO3)2−H2O phase diagrams at 251.85, 260.35, © 2017 American Chemical Society

and 288.15 K and to measure a liquid density at 298.15−321.35 K. Data achieved in this work for the studied system can be used in future to construct a thermal and caloric equation of liquid and to calculate SLE in a wide range of temperature and composition.

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METHODOLOGY To prepare Zn(NO3)2 and Ca(NO3)2 stock solutions, the following reagents were used: Zn(NO3)2·6H2O (p.a., >98%), Ca(NO3)2·4H2O (p.a., >98%); the names, CAS numbers, supplier, and mass fraction purities of salts used are listed in Table 1. Impurities in Ca(NO3)2·4H2O, according to supplier, Table 1. Purity, Supplier, and CAS Numbers of the Compounds compound

purity (%)

supplier

CAS

Ca(NO3)2·4H2O Zn(NO3)2·6H2O

>98 (p.a.) >98 (p.a.)

Labtech Chimmed

13477-34-4 10196-18-6

do not exceed the following concentrations: nonsoluble particles 0.005 wt %, HNO30.02 wt %, SO42−less than 0.01 wt %, PO43−less than 0.002 wt %, Fe2+ and Fe3+ 0.0002 wt %, (Na+ + K+)0.05 wt %, Pb2+0.0005 wt %, Mg2+0.05 wt %. The supplier claims that the impurity content in Zn(NO3)2·6H2O does not exceed 0.005 wt % for nonsoluble particles, for SO42−0.003 wt %, Cl−0.001 wt %, Fe2+ and Fe3+0.0005 wt %, (sum of Na+, K+, and Ca2+) 0.005 wt %, Pb2+0.005 wt %, HNO30.025 wt %. The water used was previously distilled and degassed. The samples for density measurements were prepared by adding water to stock zinc−calcium nitrate solutions; to determine solubility, we used both stock solution and melted hydrates to Received: January 14, 2017 Accepted: March 22, 2017 Published: March 31, 2017 1544

DOI: 10.1021/acs.jced.7b00036 J. Chem. Eng. Data 2017, 62, 1544−1549

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The composition of solution over the solid phase was the same within the error of analysis if a time of raw mixture annealing was the same (with or without stirring or seeds). As a result, we were sure that all samples achieved an equilibrium state at 2−3 days. In this way we also estimated the reproducibility of measurements for a mixture with a fixed composition. The sum of Ca2+ and Zn2+ ion concentrations was analyzed by the complexometric titration method with 0.0500 M EDTA and eriochrome black as described by Schwarzenbach and Flaschka.11 The Ca2+ concentration was determined in the same way with ZnS precipitated by Na2S saturated solution prepared from fresh Na2S·9H2O (p.a., > 98%). We checked the quality of such a masking on a set of solutions with known concentrations of calcium and zinc prepared from the stock solutions. Amounts found matched within error of determination the amounts added. Diluted probes were titrated with the addition of diluted HNO3 (reagent grade) to prevent hydrolysis. The calcium concentration of every data point is an average of three titrations of calcium, and the standard deviation of these titrations was assumed as an error of calcium content in solution. As for zinc, we subtracted the calcium concentration from an average of three titrations of total zinc and calcium content, so the relative error of zinc content in solution results from the sum of relative standard deviations of both sets of titrations.

prepare raw mixtures. A complexometric titration method was applied to determine the concentrations of the solutions. Densities were measured with a VIP-2MP vibrating-tube densimeter as it was described in our previous work.8 The dependence of the resulting density from the square of the oscillation period is linear, so it possible to calibrate the densimeter measuring the oscillation periods of samples with known densities. The calibration was performed with following substances: ambient air, ultrapure water, and standard materials (produced and certificated by D. I. Mendeleyev Institute for Metrology, Russia, St. Petersburg, VNIIM): REP-2 [726.57 kg· m−3 at 298.15 K (25 °C), 707.50 kg·m−3 at 323.15 K (50 °C)], REP-5 [997.04 kg·m−3 at 298.15 K (25 °C), 988.03 kg·m−3 at 323.15 K (50 °C)], REP-7 [1315.56 kg·m−3 at 298.15 K (25 °C)], and REP-12 [1090.32 kg·m−3 at 298.15 K (25 °C)]. The standard uncertainty of the registered temperature was 0.02 °C. The standard deviation for measurement of one sample density is 0.1 kg·m−3. The relative standard uncertainty of density would be around 0.004 because of the uncertainty of Zn(NO3)2 and Ca(NO3)2 concentration in stock solution.9 For pH measurements we used a glass membrane electrode ESK-10604/7(Research and Production Association Izmeritelnaya Tekhnika IT, Russia). The standard uncertainty of EMF is 0.1 mV, and the relative standard uncertainty of pH measurement is 0.005. Phase equilibria investigation has been performed with the method of isothermal solution saturation and wet residue analysis.10 Prepared mixtures were held in a refrigerator camera at fixed temperature, which was measured by 100 Ω Pt resistance thermometer TSPV-1 137 (Iztech, Russia) with a multichannel precise thermometric direct current bridge. The standard uncertainty of temperature registered in refrigerator camera during the experiment was 0.2 °C for −10.8 °C/262.35 K and 0.5 °C for −21.3 °C/251.85 K. For the additional stabilization of the temperature regime in the refrigerator camera, samples were held inside the camera in baths with KCl−H2O and NaCl−H2O eutectic mixtures for −10.8 °C/ 262.35 K and −21.3 °C/251.85 K, respectively. As for 15 °C/ 288.15 K, the samples were held in a water thermostat, where the standard uncertainty of temperature registered was 0.1 °C. The precision of temperature measuring was ±0.05 °C. To prevent the possible influence of nucleation rate for equilibration procedure, most of the raw mixtures were homogenized at ambient temperature. To prepare samples with relatively high raw concentrations we used melted and stirred Zn(NO3)2·6H2O and Ca(NO3)2·4H2O with consequent titrations of the melts to determine their composition. Precipitation occurred during cooling of the sample in the thermostat or the refrigerator camera. The samples were kept during 2−3 days at subzero temperatures with periodic sampling to analyze a composition of liquid phase. The ratio of analyzed aliquots and solution volumes was such to neglect the changing of system composition during sampling (near 1:100). Probes were weighted in closed plastic tubes before and after dilution. The sampling time was less than a minute. Special procedures were performed to prove an achievement of equilibrium state; we checked the influence of stirring and addition of a seed. Tiny crystals of calcium or zinc nitrate hydrates were used to start crystallization in the latter case; the quantity of crystals was too small to influence the composition of the system. For some samples at subzero temperature we checked if stirring affects the results. We switched of stirring 1− 2 h before probing to provide sedimentation of solid phase.

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RESULTS AND DISCUSSION Phase Equilibria Data. To the best of our knowledge, any information about phase equilibria in the ternary system zinc nitrate−calcium nitrate−water and volumetric properties of solution is absent. For storage conditions of workover fluids in North Regions, the information about salts solubility under ambient temperature is crucial, so only low-temperature isothermal sections of ternary phase diagram were investigated in the present work. We performed experiments at 15 °C/ 288.15 K, −10.8 °C/262.35 K, and −21.3 °C/251.85 K; the results of chemical analysis of coexisting phases are presented in Table 2, Table 3, and Table 4, respectively. The isothermal sections of ternary phase diagram at 15 °C/288.15K, −10.8 °C/ Table 2. Mass Fraction Solubility of the Ternary Ca(NO3)2− Zn(NO3)2−H2O System at the Temperature 15.0 °C/288.15 K and Pressure 0.1 MPaa initial composition, 100wb

composition of liquid phase, 100wb

no.

Zn(NO3)2

Ca(NO3)2 Zn(NO3)2

Ca(NO3)2

1 2 3 4 5 6 7

1.93 8.40 8.91 18.87 26.8 37.55 48.99

60.20 50.35 50.38 39.54 32.2 20.9 11.02

5.01 15.38 15.21 22.4 31.4 41.01 41.02

48.51 37.18 37.50 31.98 25.37 16.3 16.9

8 9 10

49.02 50.72 56.24

7.29 5.52 1.66

46.98 48.20 50.52

7.86 6.04 2.88

equilibrium solid phase Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Zn(NO3)2·6H2O + Ca(NO3)2· 4H2O Zn(NO3)2·6H2O Zn(NO3)2·6H2O Zn(NO3)2·6H2O

a

Standard uncertainties u(T) = 0.1 K, u(p) = 1 kPa, ur(w(Zn(NO3)2)) = 0.004, ur(w(CaNO3)2)) = 0.002. bw, mass fraction. 1545

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Table 3. Mass Fraction Solubility of the Ternary Ca(NO3)2− Zn(NO3)2−H2O System at the Temperature −10.8 °C/ 262.35 K and Pressure 0.1 MPaa

no.

initial composition, 100wb

composition of liquid phase, 100wb

Zn(NO3)2 Ca(NO3)2

Zn(NO3)2 Ca(NO3)2

1 2 3 4 5 6 7 8 9

6.97 11.97 17.02 5.67 10.84 19.30 20.21 25.58 41.91

13.55 9.11 4.53 46.17 41.56 30.64 33.36 27.55 15.81

8.56 14.52 19.13 7.15 14.79 21.02 26.32 31.30 34.87

16.64 11.05 5.10 39.08 32.03 26.57 22.14 18.10 14.88

10

30.00

30.00

34.65

15.17

11 12 13

43.98 45.00 46.99

6.96 5.00 3.01

39.44 40.81 42.65

8.43 6.20 3.83

equilibrium solid phase ice ice ice Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Zn(NO3)2·6H2O + Ca(NO3)2· 4H2O Zn(NO3)2·6H2O + Ca(NO3)2· 4H2O Zn(NO3)2·6H2O Zn(NO3)2·6H2O Zn(NO3)2·6H2O

Figure 1. Equilibrium phase diagram of the ternary system Ca(NO3)2−Zn(NO3)2−H2O at 288.15 K. Black squares (■), the composition of coexisting phases according to analysis data, red circles (●) correspond to initial (raw) composition, and red triangles (▼) correspond to the pure substances; A, pure solid of Ca(NO3)2·4H2O; B, pure solid of Zn(NO3)2·6H2O. Solubility of Zn(NO3)2 in water: 52.70 wt %,13 solubility of Ca(NO3)2 in water 54.94 wt %,7 cosaturated point of Zn(NO3)2·6H2O and Ca(NO3)2·4H2O is 41 wt % Zn(NO3)2 and 16.9 wt % Ca(NO3)2. Thick lines are boundaries of liquid or three-phase area, and thin lines are nodes. Numbers near squares correspond to the numbers of mixtures in Table 2.

a

Standard uncertainties u(T) = 0.2 K, u(p) = 1 kPa, ur(w(Zn(NO3)2)) = 0.004, ur(w(CaNO3)2)) = 0.002. bw, mass fraction.

Table 4. Mass Fraction Solubility of the Ternary Ca(NO3)2− Zn(NO3)2−H2O System at the Temperature −21.3 °C/ 251.85 K and Pressure 0.1 MPaa

no. 1 2 3 4 5 6 7 8 9

initial composition, 100wb

composition of liquid phase, 100wb

Zn(NO3)2 Ca(NO3)2

Zn(NO3)2 Ca(NO3)2

8.57 14.53 19.13 5.07 10.42 15.01 20.01 25.01 40

16.63 11.03 5.1 44.94 39.58 34.97 29.96 24.97 20

12.52 20.2 26.64 7.2 13.92 19.4 24.95 29.77 32.16

24.3 15.33 7.11 36.59 30.62 25.53 21.04 17.15 14.02

10

30

30

32.07

14.63

11 12 13 14 15 16 17 18

43.97 44.99 47 43.40 43.70 46.26 47.22 47.68

36.78 38.74 40.45 38.72 40.74 42.76 42.96 42.20

9.85 6.94 4.26 7.46 4.59 1.91 0.96 0

6.96 5.02 3.02 6.01 4.11 1.34 0.43 0

equilibrium solid phase ice ice ice Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Ca(NO3)2·4H2O Zn(NO3)2·6H2O + Ca(NO3)2· 4H2O Zn(NO3)2·6H2O + Ca(NO3)2· 4H2O Zn(NO3)2·6H2O Zn(NO3)2·6H2O Zn(NO3)2·6H2O Zn(NO3)2·6H2O Zn(NO3)2·6H2O Zn(NO3)2·9H2O Zn(NO3)2·9H2O Zn(NO3)2·9H2O

Figure 2. Equilibrium phase diagram of the ternary system Ca(NO3)2−Zn(NO3)2−H2O at 262.35 K. Black squares (■), the composition of coexisting phases according to analysis data, red circles (●) correspond to initial (raw) composition, and red triangles (▼) correspond to the pure substances; A, pure solid of Ca(NO3)2·4H2O; B, pure solid of Zn(NO3)2·6H2O; W, water; solubility of Zn(NO3)2 in water: 46.0 wt %,13 solubility of Ca(NO3)2 in water: 47.5 wt %,7 cosaturated point of Zn(NO3)2·6H2O and Ca(NO3)2·4H2O is 34.76 wt % Zn(NO3)2 and 15.03 wt % Ca(NO3)2. Thick lines are the boundaries of the liquid or three-phase area, and thin lines are nodes. Numbers near squares correspond to the numbers of mixtures in Table 3.

a

Standard uncertainties u(T) = 0.5 K, u(p) = 1 kPa, ur(w(Zn(NO3)2)) = 0.004, ur(w(CaNO3)2)) = 0.002. bw, mass fraction.

262.35 K, and −21.3 °C/251.85 K are shown in Figures 1, 2, and 3 (symbols correspond to initial (raw) and equilibria state of system, thick lines are phase boundaries, and thin lines are nodes). The cosaturated points at −21.3, −10.8, and 15 °C

were determined directly from the Zn(NO3)2·6H2O−Ca(NO3)2·4H2O−H2O area investigation. 1546

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9) stable hydrate at low temperatures is a moot point due to closeness of composition and problems with hydrate separation as a pure phase. According to refs 12 and 13 in the range −29 °C to −17.5 °C, nonahydrate is the stable solid phase. It melts with decomposition to liquid and hexahydrate, which is stable until 34 °C. But in a more recent work,14 authors cite Martre and Pouillen,15 who performed DTA experiment and supposed that the low-temperature Zn(NO3)2·nH2O to be octahydrate which melts at −13 °C and claimed that there is no nonahydrate reported by Funk12 and Sieverts and Petzold.13 We think that the isothermal solubility experiment data is more reliable due to possible supercooling before heating run at DTA and the composition of Zn(NO3)2·9H2O is more reliable that Zn(NO3)2·8H2O. According to our data, Zn(NO3)2·6H2O precipitates in a rather wide compositional range, and Zn(NO3)2·9H2O precipitates at very low calcium nitrate contents of the ternary system. The similar situation was observed by Ibnlfassi et al.14 for Zn(NO3)2−NH4NO3−H2O at −20 °C and −25 °C, although authors attribute that the octahydrate is a stable binary phase instead of nonahydrate. Volumetric Properties and Acidity. Volumetric properties of binary solutions for both Zn(NO3)2−H2O and Ca(NO3)2−H2O at 25 °C were studied by Spitzer et al.16 Ewing and Mikovsky17 measured volumetric properties in Ca(NO3)2−H2O in a wider temperature range (25−60 °C) from diluted solutions to rather concentrated ones (Ca(NO3)2 content up to 70 wt %). Roy et al.18 reported volumetric properties for calcium nitrate solutions at elevated temperatures (30−50 °C), but the concentrations are only up to 0.228 M, which corresponds to rather low densities (up to 1.03 g·cm−3). Vercher et al.19 studied Ca(NO3)2−H2O−propanol-1 system, and the authors revised data for Ca(NO3)2−H2O binary system at 25 °C in a wide compositional range (up to 49 wt % of calcium nitrate). Densities of fused zinc nitrtate hydrates and calcium nitrate tetrahydrate were reported by several authors.20−22 Brown et al.23 determined densities for rather diluted aqueous solutions of zinc nitrate (molalities up to 0.5 mol· kg−1) at the pressure 0.35 MPa from 3 to 95 °C. In the most of the other sources reported data was obtained at atmospheric pressure.24−26 Doan and Sangster24 reported densities at 25 °C for few aqueous zinc nitrate solutions (molalities up to 5 mol·

Figure 3. Equilibrium phase diagram of the ternary system Ca(NO3)2−Zn(NO3)2−H2O at 251.85 K. Black squares (■), the composition of coexisting phases according to analysis data, red circles (●) correspond to initial (raw) composition, and red triangles (▼) correspond to the pure substances; A, pure solid of Ca(NO3)2·4H2O; B, pure solid of Zn(NO3)2·6H2O; C, pure solid of Zn(NO3)2·9H2O; W, water; solubility of Zn(NO3)2 in water: 41.6 wt %13 (42.2 wt % this work), solubility of Ca(NO3)2 in water: 44.6 wt %,7 cosaturated point of Zn(NO3)2·6H2O and Ca(NO3)2·4H2O is 32.12 wt % Zn(NO3)2 and 14.33 wt % Ca(NO3)2. Thick lines are boundaries of the liquid or three-phase areas, and thin lines are nodes. Numbers near squares correspond to the numbers of mixtures in Table 4.

Results of our experiments allow conclusions about the absence of mixed hydrates or double salts in this system. All solutions coexist with zinc or calcium hydrates. As known, calcium tetrahydrate precipitates in the temperature range from −26.7 to 42.4 °C; at higher temperatures Ca(NO3)2·nH2O with n = 2, 3 are the stable ones.7 Because the temperature of isothermal solubility experiment does not exceed 15 °C, tetrahydrate should be the stable one in the binary system. According to our results, it is the only calcium nitrate hydrate which precipitates in the ternary system at the temperature above −21 °C. The composition of Zn(NO3)2·nH2O (n = 8 or

Table 5. Densities of Ternary Solutions in the Ternary Ca(NO3)2−Zn(NO3)2−H2O System at Various Temperatures and the Pressure 0.1 MPa composition, 100wa

a

composition, 100wa

no.

Zn(NO3)2

Ca(NO3)2

density (kg·m−3)

Zn(NO3)2

Ca(NO3)2

density (kg·m−3)

1 2 3 4 5 6 7

3.29 11.92 24.26 38.77 2.65 10.04 20.49

47.94 38.14 25.97 14.80 38.60 32.12 21.93

1525.0 1524.5 1559.0 1644.7 1395.3 1417.6 1444.0

T = 298.15 K 8 9 10 11 12 13

31.87 42.85 38.06 33.64 28.79 24.16

12.16 4.98 9.90 14.78 19.70 24.69

1489.5 1548.4 1538.6 1534.3 1523.9 1516.8

1 2 3 4

3.29 11.92 24.26 38.77

47.94 38.14 25.97 14.80

1513.9 1513.5 1547.6 1632.2

T = 323.15 K 5 6 7 8

2.65 10.04 31.87 42.85

38.60 32.12 12.16 4.98

1385.7 1407.4 1434.0 1478.9

no.

w, mass fraction. Standard uncertainties u(T) = 0.02 K, u(p) = 1 kPa, ur(ρ) = 0.004,9 ur(w(Zn(NO3)2)) = 0.002, ur(w(CaNO3) 2)) = 0.002. 1547

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kg−1). Wahab et al. provided density measurements in a wider compositional (molalities up to 7.76 mol·kg−1) and temperature range (22−49 °C).25 The most complete data set was given in an earlier work by Jain et al.;26 in this investigation the compositional range is up to 21.6 mol·kg−1 at 22−77 °C. Temperatures in an oil well are higher than the environment temperatures and can reach 50−80 °C. Hydrostatic pressure created by a workover fluid depends on density of such a fluid, which is decreased with the temperature increase. So information about density at elevated temperatures is the most essential for industrial application. In the present work, we determined densities at 25 °C/298.15 K and 50 °C/323.15 K for different ternary compositions, mostly for the ones staying liquid at lower temperatures. The experimental results are listed in Table 5. We found no information in literature about the densities of ternary solutions. As was mentioned above, multicomponent systems are interesting for the development of new functional fluids, but their investigation is timeconsuming and laborious. So various methods of properties estimation were proposed at last; a Laliberte scheme27 is a perspective for the density prediction. In our previous work8 we revealed that the description of ternary solution properties with the use of only binary parameters is not excellent; the model provides mainly underestimated density values for the ternary aqua solution of zinc and sodium chloride. To test the applicability of Laliberte method for nitrate system a set of solutions (N = 9−13 from Table 5) were prepared with compositions which should give equal densities according to Laliberte scheme.27 But the resulting density slightly decreases with calcium nitrate addition. Therefore, the results of the present work can be useful to make some corrections in the density scheme of Laliberte. To compare two ternary systems, NaCl−ZnCl2−H2O and Ca(NO3)2−Zn(NO3)2−H2O, we can conclude that the maximum densities achieved in the nitrate system for mixtures stable at subzero temperatures are lower than the ones for mixtures with ZnCl2.8 For the samples N = 9−13 from Table 5, we additionally provided pH measurements. The standards used for calibration and the results are presented in Table 6. The results of such measurements are necessary to estimate the variation of the acidity of solutions with the highest density which stay homogeneous at subzero temperatures. As can be seen, partial substitution of zinc nitrate by calcium nitrate leads to a weak decrease of acidity. As the density of such solutions and their

homogeneity at subzero temperatures does not vary essentially, this result can be useful for a choice of packer fluid compositions with reduced corrosion action.

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CONCLUSIONS Isothermal cross sections of the phase diagram of the ternary Zn(NO3)2−Ca(NO3)2−H2O system was studied in 251.85− 288.11 K temperature range with the method of isothermal solution saturation and wet residue analysis. Tetrahydrate Ca(NO3)2·4H2O appeared to precipitate in a wider compositional range than Zn(NO3)2 hydrates. The homogeneity area with the temperature is decreased mostly because of ice precipitation field, similar to the NaCl−ZnCl2− H2O system.8 As expected, Zn(NO3)2 and Ca(NO3)2 do not form mixed hydrates at subzero temperatures. It was shown that the field of Zn(NO3)2 nonahydrate stability in the ternary system at 251.85 is rather small and Zn(NO3)2 hexahydrate stays more stable in the ternary system at this temperature. The densities of ternary mixtures at 298.15 and 321.35 K were measured. Partial substitution of zinc nitrate by calcium nitrate can slightly decrease the acidity, maintaining the same density of solution and its homogeneity at subzero temperatures. These results allow determining the concentrations of heavy solutions stable at low temperatures for use as a base for workover fluids which can be transported and kept at these conditions.

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*E-mail: [email protected]. Tel.: +7-495-9392280. Fax: +7495-9391205. ORCID

Irina A. Uspenskaya: 0000-0001-6271-1316 Author Contributions

The manuscript was written through equal contributions of all authors. Funding

The work is performed at User Facilities Center of M. V. Lomonosov Moscow State University. The investigations were partially supported by the URALCHEM OJSC. Notes

The authors declare no competing financial interest.

EMF (mV)

pH

b

■

−12.02 156.78 184.99 288.00

6.86 4.01 3.56 1.65

■

Table 6. pH of Standard and Ternary Solutions in the Ternary Ca(NO3)2−Zn(NO3)2−H2O System at 298.1 K a

no. 1 2 3 4

1 2 3 4 5 a

standard, KH2PO4 standard, KHC8H4O4 standard, KHC4H4O6 standard, KH3(C2O4)2*2H2O composition, 100wa

AUTHOR INFORMATION

Corresponding Author

Zn(NO3)2

Ca(NO3)2

EMFa (mV)

pHb

42.85 38.06 33.64 28.79 24.16

4.98 9.90 14.78 19.70 24.69

279.64 275.18 267.63 259.46 259.03

1.85 1.93 2.06 2.20 2.21

ACKNOWLEDGMENTS The authors thank the M. V. Lomonosov Moscow State University Program of Development. REFERENCES

(1) Ramsey, M. S.; Shipp, J. A.; Lang, B. J.; Black, A.; Curry, D. Cesium Formate: Results and Analysis of Drilling with a New High Density Unweighted Brine. SPE 1996, 36425, 95−104. (2) Howard, S. K. Formate Brines for Drilling and Completion: State of the Art. SPE 1995, 30498, 483−496. (3) Piccolo, E. L.; Scoppio, L.; Nice, P. I.; Nodland, S. Corrosion and Environmental Cracking Evaluation of High Density Brines for Use in HPHT Fields. SPE 2005, 97593, 1−12. (4) Smart, N. G.; Bhardwaj, R. C.; Bockris, J. O’M. Kinetic, Solution, and Interfacial Aspects of Iron Corrosion in Heavy Brine Solutions. Corrosion 1992, 48, 764−779.

u(EMF) = 0.1 mV. bur(pH) = 0.005; u(T) = 0.01 K. 1548

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DOI: 10.1021/acs.jced.7b00036 J. Chem. Eng. Data 2017, 62, 1544−1549