Solubility of Calcium Carbonate in Ammonium Chloride Aqueous

Article pubs.acs.org/jced

Solubility of Calcium Carbonate in Ammonium Chloride Aqueous Solution at T = (298.15, 323.15, and 348.15) K Haipeng Zhao, Jia Chen, Chengqi Liu, Wei Shen, Chao Cai, and Yongsheng Ren* School of Chemistry & Chemical Engineering, Ningxia University, Yinchuan 750021, P. R. China ABSTRACT: Solubility and physicochemical properties (viscosity, density, and pH value) of calcium carbonate in ammonium chloride aqueous solution at (298.15, 323.15, and 348.15) K were investigated by using isothermal dissolution method. The solubility of calcium carbonate is 0.1521 mmol·kg−1 in water, but the solubility up to 10.5899 mmol·kg−1 when the molality of ammonium chloride aqueous solution is 1.5946 mol·kg−1 at 323.15 K, and the solubility increases with an increase on temperature and on molality of ammonium chloride. The reason for this result is interpreted by hydrolysis theory that hydrolysis of ammonium cause pH to decrease. The behavior about physicochemical properties is also analyzed, and the viscosity of the solution was predicted by the exponential model and extended Jones−Dole model. The solubility and physicochemical properties in this work is basically required for studying of calcium carbonate, which would provide a basis to optimize the process of calcium carbonate in the industrial production.

1. INTRODUCTION Calcium-based wastes is a class of common industrial byproduct, involves in many sectors, such as slag produced by steel manufacturing, lime mud produced pulp and paper industry, waste of nitrophosphate production, and residue of coating powder production process, etc. These slags usually are reused in different fields. Steel slag is used as aggregate for stone mastic asphalt1 and Portland cement clinker,2 and it could improve soil properties with increased dry weight and strength coupled with implied decreased permeability.3 Lime mud can remove heavy metals from metal finishing wastewater.4 Besides, it could be filler in industry5 and raw material for fabrication of anorthite ceramic.6 2CaCN2 + 2H 2O → Ca(HCN2)2 + Ca(OH)2

(1)

Ca(HCN2)2 + CO2 + H 2O → 2NH 2CN + CaCO3↓

(2)

2NH 2CN → (NH 2CN)2

(3)

calcium phosphate, and calcium chloride use of DCD waste. Gao13 studied the production of calcium oxide powder use of waste, and Li14 offered a method to produce lime use of waste. However, these are low-end products with low value-added; thus, it is a serious problem on how to make better use of DCD waste. Some commercial calcium carbonate with high value-added, such as light calcium carbonate (PCC) and calcium carbonate whiskers, is being widely used in many areas. PCC can increase the volume and improve the processing performance, dimensional stability, printing performance, and physical properties (such as heat resistance, matting properties, abrasion resistance, flame resistance, whiteness, and gloss). So PCC is widely used for paper,15,16 plastics,17 synthetic rubber,18 food, food colorants, pharmaceuticals, adhesives, and hygiene supplies. Calcium carbonate whisker is applied in many areas of production like composite materials,19 building materials, paint, friction materials, paper due to its performance about high strength and thermal insulation. The main ingredient is calcium carbonate in DCD slag. It not only solves the problem of environmental pollution but also can create high value-added if the residue can be used to produce calcium carbonate products. Therefore, it is necessary to investigate the method of preparing commercial calcium carbonate by the residue.

Dicyandiamide (DCD) waste is also a kind of calcium-based wastes during the production of DCD. The chemical reactions involved in the synthesis of DCD is shown in eqs 1, 2, and 3. Calcium carbonate residue produced in eq 2. Currently, DCD waste is often piled up due to many issues such as its huge amount and high freight. However, the waste will become dust after dried. The dust pollute the environment and take up much space. Researchers are trying to exploit a new technology to solve problem on how to take advantage of DCD waste. Of course, some results have been achieved, Xuan7 studied the DCD waste treatment by precipitation method. Jiang and Wu8 studied the harmful composition in dicyandiamide slag. Ding and Zhang9 studied the production of cement from the DCD waste instead of limestone. Zhang10−12 explored the method to produce dicyandiamide, industrial calcium sulfate, industrial © XXXX American Chemical Society

CaCO3 + 2HCl → CaCl 2 + CO2 + H 2O

(4)

CaCl 2 → Ca 2 + + 2Cl−

(5)

NH4HCO3 → NH4 + + HCO3−

(6)

Received: May 14, 2015 Accepted: October 7, 2015

A

DOI: 10.1021/acs.jced.5b00417 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

HCO3− ↔ H+ + CO32 −

(7)

Ca 2 + + CO32 − → CaCO3↓

(8)

NH4 + + Cl− → NH4Cl

(9)

2.2. Experimental Method. The samples for measuring the solubility of calcium carbonate in ammonium chloride aqueous solutions were prepared as follows: ammonium chloride was added into water, and the mixture was stirred until a transparent solution obtained, a surplus on calcium carbonate was added to the ammonium chloride aqueous solutions. In this experiment, the concentration of Ca2+ in the aqueous solutions remains constant after 24 h. The oscillator was stopped after stirring another 12 h in order to ensure no changes in solution. Then the temperature was kept at T = (298.15, 323.15, or 348.15) K for 24 h to allow any remaining solids to settle, and the actual temperature of the aqueous systems was monitored by a mercury thermometer. The saturated solution was removed into a 100 mL beaker at T = (298.15, 323.15, or 348.15) K when the system reached equilibrium. The liquid phase, after weighting accurately, added into a 100 mL volumetric flask and diluted with doubly deionized water immediately. At the same time, samples of the same batch were used to measure physicochemical properties (density, viscosity, and pH value) individually according to the analytical method. Finally, the chemical composition of solution was determined by chemical analysis. 2.3. Analysis. CaCO3 molality was determined by titration with EDTA standard solution26 in the presence of alkali and Ca-indicator.27,28 The average relative deviation of the determination was less than 0.3 % by this method. Ammonium chloride molality was determined by means of methanal titration method. The average relative deviation of the determination was less than 0.3 % by this method. A PB-10 precision pH meter supplied by the Sartorius Scientific Instruments (Beijing) Co., Ltd. was used to measure the pH of the solutions with a standard uncertainty of 0.02. Density (ρ) was measured with a specific weighing bottle method with a standard uncertainty of 0.005.29,30 An Ubbelohde capillary viscometer is used in the determination of the viscosity (η) with a standard uncertainty of 0.008. All of the measurements of the above physicochemical properties of the equilibrium solutions were made in a constant temperature bath maintained at the desired temperature ± 0.05 K.

Calcium ions are leached after a series of processes from DCD waste as eqs 4 and 5, and calcium carbonate is prepared by reaction bicarbonate with calcium ion as eqs 6, 7, 8, and 9. The commercial calcium carbonate was obtained from precipitation by filtering, and the major component in filtrate is ammonium chloride. The entire production process is carried out at 348.15 K. However, the problem emerged in this study that the solubility of calcium carbonate in ammonium chloride aqueous solution is significantly higher than its solubility in water. The yield of commercial calcium carbonate would reduce if calcium carbonate is dissolved in the solution. What’s more, the calcium carbonate that dissolved in ammonium chloride aqueous solutions might affect the quality of product. Such as, some furcation arise on the calcium carbonate whiskers sometimes. Therefore, it is essential to improve the production process of calcium carbonate products. Basic data about NH4Cl−CaCO3−H2O ternary system is necessary for optimizing production process. In the literature, Kendall20 provided the solubility of calcium carbonate in water at (298.15 and 323.15) K, which is 0.1431 mmol·kg−1 and 0.1521 mmol·kg−1, respectively, and the solubility at 348.15 K is 0.140 mmol·kg−1 that was reported in Konno’s paper.21 The solubility of calcium carbonate in ammonium chloride aqueous solutions has been reported in the literature,22−25 respectively. However, the data from these studies cannot meet demand for optimization of calcium carbonate production process. The solubility of calcium carbonate in ammonium chloride aqueous solutions at (298.15, 323.15, and 348.15) K is studied in this work. Meanwhile, some basic physicochemical properties of this solution were measured. The experimental data are compared with previous data in literature. The data is very close. We also found some regular trends during the study of mixed solution on density, viscosity, and pH value. Besides, the experimental data were simulated using the model in order to verify the correctness of the experimental data in this work.

3. RESULTS AND DISCUSSION Since the molality of ammonium chloride in the filtrate after the preparation of calcium chloride is relatively low, the molality of ammonium chloride aqueous solutions in experiment is low, relatively. The experimental points are more intensive from 0.1 mol·kg−1 to 1.0 mol·kg−1. However, there are less points at high molality in our experiment, because the solubility of calcium carbonate in low molality of ammonium chloride aqueous solutions is crucial data in industries. Of course, this experiment also explored several experimental points that high molality of ammonium chloride solution which is close to the saturated solution at each temperature in order to make a more comprehensive basic data. 3.1. Solubility of Calcium Carbonate in Ammonium Chloride Aqueous Solution. In this experiment, the experimental data were determined in various molalities at each experimental temperature. Solubility, density, viscosity, and pH

2. EXPERIMENTAL SECTION 2.1. Materials and Apparatus. The water used to prepare solutions was doubly deionized water (electrical conductivity ≤ 1·10−4 S·m−1) in this experiment. The sources and purity of the materials are listed in Table 1. All chemicals used were of analytical-purity grade, and the crystalline form of calcium carbonate is calcite. A constant temperature bath oscillator (SHZ-C, Shanghai Langgan Laboratory Equipment Co. Ltd., China) with a temperature range from (293.15 to 373.15) K was used for the phase equilibrium measurement. The temperature of this oscillator could be controlled to 0.05 K. Table 1. Chemical reagents used in this study chemical

CAS No.

ammonium chloride

12125-02-9

calcium carbonate

471-34-1

mass fraction purity

purification method

Tianjin Kermel Chemicals

0.995

recrystallization

Yantai Shuangshuang Chemicals

0.99

recrystallization

source

B

analytical method Volhard method (Cl−); methanal titration method (NH4+) EDTA titration method



Article

Table 2. Solubility and Physicochemical Properties of Calcium Carbonate (2) in Solutions of Ammonium Chloride (1) at T = (298.15, 323.15, and 348.15) K and P = 88.4 kPaa m1b /mol·kg−1 1 2 3 4 5 6 7 8 9 10

0.1283 0.2131 0.3496 0.4576 0.6546 0.8576 1.1388 1.8939 3.8441 4.8123

1 2 3 4 5 6 7 8 9 10 11

0.1044 0.2061 0.2937 0.4568 0.7449 0.9063 1.1559 1.5946 2.2643 4.1216 6.1213

1 2 3 4 5 6 7 8 9 10 11

0.0971 0.2041 0.3531 0.4284 0.7679 0.8725 1.2283 1.7809 2.3545 5.3807 6.7351

m2/mmol·kg−1 298.15 K 3.0609 3.8054 4.1909 5.2187 5.8858 6.8064 7.1201 8.0012 9.1095 9.5490 323.15 K 3.4305 4.5299 5.2009 5.6823 7.6390 8.0675 8.9828 10.5899 13.4130 15.0318 15.3040 348.15 K 4.3557 7.0448 8.8781 9.0819 11.7264 12.2137 15.7130 16.7878 17.8200 18.9622 19.4117

η/mPa·s

ρ/g·cm−3

pH

0.8801 0.8820 0.8876 0.8923 0.8963 0.8978 0.9031 0.9047 0.9433 0.9933

1.0003 1.0012 1.0043 1.0072 1.0093 1.0114 1.0163 1.0276 1.0623 1.1085

7.63 7.48 7.43 7.40 7.33 7.23 7.18 7.03 6.85 6.67

0.5558 0.5574 0.5661 0.5665 0.5680 0.5732 0.5738 0.5756 0.5783 0.6304 0.7813

0.9927 0.9933 0.9939 0.9971 1.0018 1.0112 1.0128 1.0188 1.0282 1.0571 1.1951

7.05 6.92 6.89 6.86 6.72 6.62 6.59 6.55 6.47 6.24 6.02

Figure 1. Solubility of calcium carbonate (2) in different molality of ammonium chloride (1) aqueous solutions. Blue □, 298.15 K; red ○, 323.15 K; △, 348.15 K.

0.3772 0.3778 0.3816 0.3833 0.3856 0.3894 0.3923 0.4064 0.4127 0.4831 0.5685

0.9794 0.9823 0.9861 0.9877 0.9923 0.9948 1.0004 1.0148 1.0198 1.0671 1.1037

6.77 6.74 6.68 6.50 6.35 6.27 6.19 6.12 6.05 5.85 5.58

Table 3. Solubility of the Calcium Carbonate (2) in Ammonium Chloride (1) Aqueous Solutions at Different Temperature in Literature

Therefore, some facts must be acknowledged that that solubility of calcium carbonate in ammonium chloride aqueous solution never be ignored during the calcium carbonate production. 3.2. Comparison of Experimental Solubility with Reported Data. The solubility data about calcium carbonate in ammonium chloride aqueous solutions reported in the literature22−25 are shown in Table 3. The solubility of calcium

ref

T/K

m1a/mol·kg−1

m2a/mmol·kg−1

22

298.15

23

288.15

24

291.15

25

333.15

0.1259 0.2531 0.5109 1.0418 1.0567 2.0772 4.6736 0.2018 1.0403 2.1673 0.0204 0.1021 0.2049 0.5183 1.0572 3.4602

2.874 3.772 5.124 7.068 4.394 6.491 7.659 3.25 6.86 9.53 1.674 3.420 4.679 6.966 10.046 14.398

a

Standard uncertainties u are u(T) = 0.05 K, u(P) = 0.5 kPa, ur(m1) = 0.01, ur(m2) = 0.03, ur(η) = 0.008, ur(ρ) = 0.005, and ur(pH) = 0.02. b m1, molality of ammonium chloride; m2, molality of calcium carbonate.

value of the ternary aqueous solutions of calcium carbonate and ammonium chloride over a range of T = (298.15 to 348.15) K are presented in Table 2. The relationship of solubility of calcium carbonate and molality of ammonium chloride aqueous solutions is shown in Figure 1. As shown in Figure 1 and Table 2, at the same temperature, the variation range of calcium carbonate solubility is very large in different ammonium chloride aqueous solutions. A clear trend can also be observed that solubility of calcium carbonate increases with an increase on the molality of ammonium chloride aqueous solutions when the temperature is constant, and the line of solubility is gradually smooth with an increase on the molality of ammonium chloride aqueous solutions. Moreover, the solubility of calcium carbonate trends to increase with an increase on temperature. In Figure 1, we can find that the solubility of calcium carbonate at 348.15 K is much higher than solubility at (298.15 and 323.15) K. In the industry, the process temperature of calcium carbonate products must be maintained at 348.15 K.

a

m1, molality of ammonium chloride; m2, molality of calcium carbonate.

carbonate in this work is contrasted to literature values22 has been reported at 298.15 K, a significant feature is that every data about this work is very close to previous data at 298.15 K, and the variation of solubility is consistent with each other. This fully explain our experimental data is reliable. Meanwhile, the relationship between solubility and temperature in references is shown in Figure 2, and the experimental data in this paper is shown in Figure 2 to compare the solubility better. Observing Table 3 and Figure 2a, it is clear that the solubility at 288.15 K in ref 23 is lower than other temperatures. For the solubility at 291.15 K in ref 24, there are two groups’ data close C



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Figure 2. Comparison on solubility of calcium carbonate (2) in ammonium chloride (1) aqueous solutions in this work and literature. Literature data:22−25 □, 288.15 K; red ○, 291.15 K; purple ▽, 298.15 K; blue △, 333.15 K); this work: pink ▲, 298.15 K; green ◆, 323.15 K; blue ■, 348.15 K.

It is really clear that the trend of viscosity of solution increases with an increase on the molar molality of ammonium chloride. The viscosity of aqueous solution at low molality is close to viscosity of water at the same temperature, but the viscosity of solution at high molality is much higher than water. At 298.15 K, the viscosity of ammonium chloride aqueous solution with 4.8123 mol·kg−1 is 0.9933 mPa·s, the viscosity of water is only 0.8937 mPa·s. At 323.15 K, the viscosity of ammonium chloride aqueous solution with 6.1213 mol·kg−1 is 0.7813 mPa·s, the viscosity of water is 0.5494 mPa·s. At 348.15 K, the viscosity of ammonium chloride aqueous solution with 6.7351 mol·kg−1 is 0.5685 mPa·s, the viscosity of water is 0.3799 mPa·s. As we all know, a close relationship exists between the viscosity and density of solution that high density means high viscosity sometimes. The viscosity necessarily increases due to that the density increases with molality of ammonium chloride increasing. Figure 3c indicates that the pH value of solution obviously decreases with an increase on the molality of ammonium chloride at the same temperature. The pH value reduces from 7.63 to 6.67 at 298.15 K. The pH value generally reduces from 7.02 to 6.05 at 323.15 K and reduces from 6.77 to 5.58 at 348.15 K. The higher temperature, the smaller pH value of the solution is. The result can be explained by the reasons as follows: ammonium chloride is a kind of strong acidic−weak salt according to the Bronsted-Lowry acid−base theory,31 so NH4+ will be hydrolyzed in water as eq 10, and H+ generated during this process. Based on the theory, at a constant temperature, the degree of hydrolysis is more intense when the molality of NH4+ increases. Therefore, the pH value of ammonium chloride aqueous solution decreases with an increase on the molality. In addition, an hydrolysis equilibrium constant will increase with temperature rising. The phenomenon that the pH in solution of the high temperature is smaller than low temperature may be interpreted by reason above.

to the solubility at 298.15 K. But it is visible that the solubility of calcium carbonate is 9.53 mmol·kg−1 at 291.15 K when the molality of ammonium chloride is 2.1673 mol·kg−1, which is higher than the solubility of this work at 298.15 K. The trend of solubility variation in ref 22 at 298.15 K is consistent with this work, and two solubility values are close to the solubility values at 298.15 K. So, third values at 291.15 K may be doubtful, after all, it is not suitable for the trend of solubility at other different temperatures in Figure 2a. In Figure 2a,b, the solubility of calcium carbonate at 333.15 K in ref 25 is higher than the value of this work at 323.15 K, but lower than the value at 348.15 K, and the change of solubility at these three temperatures is similar. The difference is that the solubility of calcium carbonate is 14.398 mmol·kg−1 at 333.15 K when the molality of ammonium chloride is 2.1673 mol·kg−1 in ref 25. The sixth value may be higher than itself now if it follows the variation of top five groups’ data in ref 25. 3.3. Physicochemical Properties in Solution. Figure 3a shows the density in different molalities of ammonium chloride aqueous solutions at T = (298.15, 323.15, and 348.15) K. It can be seen that the trend of density of solution increases with the molality of ammonium chloride increasing. The density of the solution gradually rises from 1.0003 g·cm−3 to 1.1085 g·cm−3 at 298.15 K, from 0.9927 g·cm−3 to 1.1951 g·cm−3 at 323.15 K, and from 0.9794 g·cm−3 to 1.1037 g·cm−3 at 348.15 K, respectively. A paramount reason for increasing of density is to increase the concentration of ammonium chloride in solution. The density of solution decreases with an increase on the temperature, and variation could be interpreted in two parts. On the one hand, the density of water decreases with an increase on temperature when it is higher than 277.15 K; it is undeniable that the density of water makes a primary contribution to the density of the solution, hence the density at low temperature is higher than high temperatures at the same molality. On the other hand, the density of solution increases as the molality of the salt increasing in a binary system. The NH4Cl−CaCO3− H2O ternary system can be regarded as a simple binary system owing to the small solubility of calcium carbonate in the solution. Therefore, it is easy to understand that the density of aqueous solution increases with an increase on the molality. The viscosity of mixed solutions in different molalities at T = (298.15, 323.15, and 348.15) K is shown in Figure 3b.

NH4Cl + H 2O ↔ NH3·H 2O + Cl− + H+

CaCO3 + H+ ↔ Ca 2 + + HCO3−

HCO3− ↔ H+ + CO32 − D

K = 1.79· 10−5 (10)

K = 4.96· 10−9

K = 4.69·10−11

(11) (12)



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Figure 3. Diagrams of physicochemical properties of calcium carbonate (2) in ammonium chloride (1) aqueous solution. Blue □, 298.15 K; red ○, 323.15 K; △, 348.15 K.

where a (10−3 Pa·s), b (kg·mol−1), and f (kg2·mol−2) are adjustable parameters and m is the molality of solution. The adjustable parameters were calculated by experimental data, which are listed in Table 5. The calculated viscosity is shown in Table 4. The relative deviation (RD) and root-mean-square error (RMSE) were calculated using eqs 14 and 15, respectively.

See Table 2 and Figure 3c for a discussion of the variety of solubility calcium carbonate in ammonium chloride aqueous solutions. The pH value decreases with molality of ammonium chloride aqueous solution increasing, and the solubility of calcium carbonate in ammonium chloride aqueous solution increases correspondingly. It is very reasonable to believe that the hydrolysis of ammonium chloride leads to increase the solubility of calcium carbonate as eqs 10, 11, and 12. Therefore, controlling the pH of solution may improve the quality of the calcium carbonate product better. 3.4. Model of Viscosity. Viscosity increases may influence the migration of Ca2+ in the solution, and the settling time of calcium carbonate could also be extended. This may have an impact on the quality of product. In fact, the viscosity of aqueous solutions was correlated and predicted using different models. In this work, the exponential model and extended Jones−Dole model32 were chosen to correlate the viscosity data, and two models were proved to be effective in refs 33 and 34. 3.4.1. Exponential Model. Since the molality of calcium carbonate in the NH4Cl−CaCO3−H2O ternary system is very low, the mixed solution can be regarded as a binary system. At a high molality of salts, the semiempirical exponential model is reported to be a successful model in predicting the viscosity of binary solutions.35,36 The exponential model is shown as eq 13.

η = a exp(bm + fm2)

RD =

(ηexp − ηcal ) ηexp

(14)

⎡ ∑n (η − η )2 ⎤1/2 exp ⎥ i = 1 cal RMSE = ⎢ ⎢⎣ ⎥⎦ n

(15)

Comparison of the calculated and experimental values, the RD values between the calculated values and experimental values at every temperature are less than 0.03 which in the allowable range, and the RMSE value is smaller. The correlation coefficient of R2 about calculated data obtained by exponential model is 0.9689, 0.9880, and 0.9908 at T = (298.15, 323.15, and 348.15) K, respectively. The relationship about the molality of solution and the calculated values used by exponential model is shown in Figure 4. 3.4.2. Extended Jones−Dole Model. The extended Jones− Dole model was successfully used to correlate the viscosity of

(13) E



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Table 4. Comparison of Experimental and Calculated Viscosity Data at Different Temperatures exponential model m1a/mol·kg−3

ηb/mPa·s

1 2 3 4 5 6 7 8 9 10

0.1283 0.2131 0.3496 0.4576 0.6546 0.8576 1.1388 1.8939 3.8441 4.8123

0.8801 0.882 0.8876 0.8923 0.8963 0.8978 0.9031 0.9047 0.9433 0.9933

1 2 3 4 5 6 7 8 9 10 11

0.1044 0.2061 0.2937 0.4568 0.7449 0.9063 1.1559 1.5946 2.2643 4.1216 6.1213

0.5558 0.5574 0.5661 0.5665 0.568 0.5732 0.5738 0.5756 0.5783 0.6304 0.7813

1 2 3 4 5 6 7 8 9 10 11

0.0971 0.2041 0.3531 0.4284 0.7679 0.8725 1.2283 1.7809 2.3545 5.3807 6.7351

0.3772 0.3778 0.3816 0.3833 0.3856 0.3894 0.3923 0.4064 0.4127 0.4831 0.5685

ηE/mPa·s 298.15 K 0.8870 0.8876 0.8885 0.8893 0.8910 0.8930 0.8961 0.9072 0.9536 0.9872 323.15 K 0.5660 0.5655 0.5650 0.5645 0.5644 0.5648 0.5660 0.5699 0.5805 0.6423 0.7773 348.15 K 0.3807 0.3814 0.3825 0.3831 0.3862 0.3872 0.3912 0.3988 0.4085 0.4962 0.5619

extended Jones−Dole model RD

ηJ/mPa·s

RD

0.0078 0.0063 0.0010 −0.0034 −0.0059 −0.0053 −0.0078 0.0028 0.0109 −0.0061

0.8960 0.8968 0.8979 0.8986 0.8996 0.9003 0.9010 0.9029 0.9435 0.9933

0.0180 0.0168 0.0116 0.0071 0.0036 0.0028 −0.0024 −0.0019 0.0002 0.0000

0.0184 0.0145 −0.0019 −0.0035 −0.0063 −0.0147 −0.0136 −0.0099 0.0038 0.0189 −0.0051

0.5507 0.5516 0.5525 0.5542 0.5578 0.5604 0.5645 0.5735 0.5890 0.6293 0.7813

−0.0091 −0.0104 −0.0241 −0.0217 −0.0180 −0.0223 −0.0163 −0.0036 0.0186 −0.0018 0.0000

0.0093 0.0095 0.0024 −0.0005 0.0016 −0.0056 −0.0028 −0.0187 −0.0102 0.0271 −0.0116

0.3808 0.3815 0.3825 0.3832 0.3866 0.3878 0.3929 0.4029 0.4149 0.4830 0.5685

0.0095 0.0097 0.0025 −0.0004 0.0025 −0.0040 0.0014 −0.0087 0.0054 −0.0001 0.0000

a m1, the molality of ammonium chloride; η, experimental viscosity in this work; ηE, calculated viscosity by exponential model; ηJ, calculated viscosity by extended Jones−Dole model. bStandard uncertainties u are ur(m1) = 0.01 and ur(η) = 0.05.

Table 5. Values of Coefficients a, b, and f of eq 13 and the RMSE Value of Calculated at the Studied Temperatures T/K

a

b

f

RMSE

298.15 323.15 348.15

0.8863 0.5667 0.3801

0.0035 0.0106 0.0063

0.0057 0.0135 0.0158

0.0058 0.0068 0.0054

the binary and ternary system in previous literature.33,37 In this work, the extended Jones−Dole model is used to calculate the viscosity of the mixed solution. η = η0(1 + Ac 0.5 + Bc + Dc 2 + Ec 3.5 + Fc 7)

(16)

T The extended Jones−Dole model is shown as eq 16, where η0 is the viscosity of water, c is the molar molality of ammonium chloride aqueous solution, A and B values were referenced in previous paper,37,38 and the other coefficients of the model are calculated by experimental data in this work. The all coefficients of this model are listed in Table 6. The molality in this work must be converted to molar concentration in order to use the extended Jones−Dole model successfully. The viscosity was calculated by extended

Figure 4. Experimental data and correlated values of viscosity of mixed solution. Blue △, 298.15 K; green ▽, 323.15 K; pink ◇, 348.15 K. The dotted line is the exponential model, and solid lines are the extended Jones−Dole model. F



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Table 6. Coefficients of Extended Jones−Dole Model for Ammonium Chloride Aqueous Solution at Each Temperature T/K

A

B

D

104 E

105 F

RMSE

298.15 K 323.15 K 348.15 K

0.0050 0.0050 0.0050

0.0065 0.0065 0.0065

0.0226 0.0226 0.0238

−0.0027 −0.0019 −0.0014

5.0111 2.0495 9.1430

0.0080 0.0089 0.0021

Notes

Jones−Dole model is indicated in Table 4; the RD values between the calculated values and experimental values at every temperature are less than 0.03, and the RMSE value is the allowable range. The correlation coefficient of R2 about calculated data obtained by the extended Jones−Dole model is 0.9700, 0.9867, and 0.9980 at T = (298.15, 323.15, and 348.15) K, respectively. Likewise, the relationship about the molality of solution and the calculated value is shown in Figure 4. Analysis of the results of the two models, it can predict the viscosity of the mixed solution well. Not overlooked is that different advantage they involved when the correlation coefficient of R2 values are compared. The extended Jones−Dole model is more suitable for temperature at (298.15 and 348.15) K. Conversely, the exponential model is more convincing for temperature at 323.15 K.

The authors declare no competing financial interest.

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4. CONCLUSION Solubility and physicochemical properties of calcium carbonate in ammonium chloride aqueous solutions (0.1 mol·kg−1 to 6.7 mol·kg−1) was measured at T = (298.15, 323.15, and 348.15) K. The relationship between solubility of calcium carbonate and molality of ammonium chloride is found, and the change of physicochemical properties in aqueous solutions is summarized. (1) The solubility of calcium carbonate in the ammonium chloride aqueous solution increases with an increase on molality of the ammonium chloride and on temperature, which may affect quality and the yield of calcium carbonate product. (2) The density and viscosity of aqueous solution increase with an increase on the molality of solution, but the value decreases if temperature increases. The pH value will decrease when the temperature and molality of aqueous solution increase, and the result can be explained by eq 10. (3) The viscosity of aqueous solution was predicted using two simple models. The extended Jones−Dole model is more suitable for temperature at 298.15 K and 348.15 K, and the exponential model is more convincing for temperature at 323.15 K. The experimental data in this work is supplementary to research data approved of calcium carbonate and could provide some available data to the production of calcium carbonate products. The data may also be referential when the solubility of calcium carbonate is studied in other systems, and it may play an important role in improving the production of ammonium chloride in the future.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected], [email protected]. Address: No. 539, West Helanshan Road, Xixia District, Yinchuan, 750021, P. R. China. (School of Chemistry & Chemical Engineering, Ningxia University). Funding

The authors are grateful for financial support from Natural Science Foundation of Ningxia Hui Autonomous Region, China (NZ14039). G



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Solubility of Calcium Carbonate in Ammonium Chloride Aqueous

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