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Solubility Investigations in the (NH4)2C2O4−NH4VO3−H2O System from 313.15 to 363.15 K Shaona Wang,† Xuemei Guo,‡ Hao Du,*,†,§ Shili Zheng,† Biao Liu,† and Yi Zhang† †

Key Laboratory of Green Process and Engineering, National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China ‡ School of Chemical Engineering, Tianjin University, Tianjin 300072, China § International College, University of Chinese Academy of Sciences, Beijing 100190, China ABSTRACT: The solubility of the (NH4)2C2O4−NH4VO3−H2O system has been measured over a temperature range from 313.15 to 363.15 K. On the basis of the results, a solubility diagram has been drawn. Additionally, the densities of the solutions have been measured. From analysis of the solubility data, a separation method for NH4VO3 from the (NH4)2C2O4−NH4VO3−H2O system was proposed, involving cooling and salting-out crystallization from (NH4)2C2O4 solution.

NH4VO3−NH4NO3−H2O system has been published by Trypuc and Druzynski. 21 Solubility of NH 4 VO 3 in NH4H2PO4−H2O and (NH4)3PO4−H2O systems has been published by Ning et al.22,23 These results are necessary to determine the optimal conditions for carrying out the ammonium precipitation process. Among the ammonium salts above, there appears to be no literature data concerning the (NH4)2C2O4−NH4VO3−H2O system. To make a comprehensive and reliable evaluation of the (NH4 ) 2C 2O 4−NH 4VO3 −H2 O system, solubility for the (NH4)2C2O4−NH4VO3−H2O system has been described over the desired temperature range from 313.15 to 363.15 K in this work. The investigated range of temperatures has been chosen on the basis of the operating parameters used in the two vanadium extraction technologies.

1. INTRODUCTION Vanadium is widely used in the iron and steel industries, the aeronautics industry, and the ceramic industry, in catalysts, and as an electrolyte in vanadium redox batteries.1−7 However, the primary use of vanadium is as an alloying element in the iron and steel industries, with the strength of steel being significantly improved upon the addition of vanadium. Due to the rapid growth of the iron and steel industries in China, the demand for vanadium is expected to increase in the future. Vanadiumbearing titanomagnetite is the most important ore for vanadium production,8,9 and vanadium slag, which is enriched with vanadium and produced from vanadium-bearing titanomagnetite during iron making process, is the major raw material for vanadium extraction. Roasting of vanadium slag with sodium salts followed by water leaching and ammonium precipitation (sodium roasting) is currently the most popular vanadium extraction process.10−12 Recently, a novel method featuring nonsalt roasting and ammonium leaching (nonsalt roasting) has been proposed and seems to be cleaner than the sodium roasting technology.13−16 In the ammonium precipitation process of the above two technologies, vanadium can be precipitated as NH4VO3 by the addition of ammonium salts such as NH4Cl, (NH4)2SO4, NH4HCO3, (NH4)2C2O4, (NH4)3PO4, and NH4H2PO4. Chen presented the equilibrium results of the NH4VO3−H2O system ranging from 273.15 to 343.15 K.17 Equilibrium studies for NH4HCO3−NH4VO3−H2O and (NH4)2HCO3−NH4VO3−H2O systems, respectively, have been published by Trypuc and Stefanowicz and Yan et al.,18,19 whereas the NH4HCO3−NH4VO3−H2O system has been partly reported by Zhao et al.20 Solubility of the © 2017 American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Apparatus and Reagents. Polypropylene bottles exhibiting good heat resistance and chemical stability (100 mL capacity) were used to prepare the samples. The bottles were placed in a HZ-9212S type thermostatic shaking water bath (manufactured by Hualida Experimental Equipment Co., Ltd., China) with a precision of 0.1 K to reach equilibrium at each predetermined temperature, respectively. The chemicals used in this study have been shown in Table 1 and were of analytical grade. (NH4)2C2O4·H2O (>99.5%) and NH4VO3 (>99.5%) were purchased from Xilong Chemical Received: April 18, 2017 Accepted: July 26, 2017 Published: August 11, 2017 3313

DOI: 10.1021/acs.jced.7b00362 J. Chem. Eng. Data 2017, 62, 3313−3318

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Table 1. Purities and Suppliers of Chemicals chemical name

source

initial mass fraction purity, %

CAS reg. no.

ammonium oxalate ammonium metavanadate

Xilong Chemical Plant Xilong Chemical Plant

⩾99.5 ⩾99.5

1113-38-8 7803-55-6

3. RESULTS AND DISCUSSION 3.1. Solubility Data for the NH4VO3−H2O Systems. The comparison of available literature data with the present work for the binary systems NH4VO3−H2O in the temperature range from 313.15 to 363.15 K is summarized in Figure 1.17−19,23 As shown in Figure 1, the experimental solubility of NH4VO3 in pure water is in good agreement with the literature data reported with relative deviations of less than 5%, indicating that the procedure is acceptable and the results are reliable. 3.2. Solubility Data for the (NH4)2C2O4−H2O Systems. Solubility of the (NH4)2C2O4−H2O system has been published by Hill and Distler.24 The comparison of literature data with the present work for the (NH4)2C2O4−H2O system in the temperature range from 273.15 to 373.15 K is summarized in Figure 2.24 As shown in Figure 2, the experimental solubility of (NH4)2C2O4 in pure water is also in good agreement with the literature data reported with relative deviations of less than 5%, indicating that the results are reliable. 3.3. Solubility Data for the (NH4)2C2O4−NH4VO3−H2O Systems. The results concerning the salts solubility from the chemical analysis of the solutions ranging from 313.15 to 363.15 K are presented in Table 2. The concentration of each solution component is given both in mol·kg−1 and mass fractions. Table 2 presents also the solid-phase composition being in equilibrium with the studied solutions. The experimental values provided the basis for plotting a solubility curve of the examined solubility system, as shown in Figure 3. As shown in Figure 3, the solubility isotherms of NH4VO3 decrease steadily with an increase of the (NH 4 ) 2 C 2 O 4 concentration from 313.15 to 363.15 K. That is, the saltingout effect of (NH4)2C2O4 on NH4VO3 is very strong. More specifically, it decreases sharply when the (NH 4 ) 2C 2 O4 concentration increases from zero to about 0.3−0.5 mol·kg−1 at all temperatures investigated. A further increase in the (NH4)2C2O4 concentration did not appear to have a significant effect on the NH4VO3 solubility, which decreased only slightly when the (NH4)2C2O4 concentration further increased. For example, the solubility of NH4VO3 decreases 73.29% from 0.453 to 0.121 mol·kg−1 monotonically with the (NH4)2C2O4 concentration increases from 0 to 0.5 mol·kg−1 at 363.15 K. After that, the NH4VO3 solubility decreases only 26.71% from 0.121 mol·kg−1 to 0 with further increasing of the (NH4)2C2O4 concentration to 1.6796 mol·kg−1. At 353.15 K, the NH4VO3 solubility declines sharply from 0.3754 to 0.0709 mol·kg−1 with the (NH4)2C2O4 concentration increasing from 0 to 0.4227 mol·kg−1 just like what is present at 363.15 K, and then decreases slowly. From the analysis above, the solubility of NH 4 VO 3 shows obvious dependence with (NH 4 ) 2 C 2 O 4 concentration within the low (NH4)2C2O4 concentration range. Thus, it is possible to separate NH4VO3 through salting-out crystallization from (NH4)2C2O4 solution especially in the low (NH4)2C2O4 concentration region examined. It can also be seen from Figure 3 that the solubility of NH4VO3 decreases significantly with the decreasing of temperature. The difference of temperatures is more significant at relatively low (NH4)2C2O4 concentration. For example, the solubility of NH4VO3 decreases 0.3708 mol·kg−1 with the

Plant. High-purity Milli-Q water, with a resistivity > 18.2 MΩ· cm at ambient temperature, was used to prepare all aqueous solutions. 2.2. Experimental Procedure. Solubility was determined via the isothermal solution saturation method.20 Standard uncertainties u are u(p) = 0.5 kPa, u(T) = 0.1 K, u(m((NH4)2C2O4)) = 0.01 mol·kg−1, u(m(NH4VO3)) = 0.01 mol·kg−1, and u(ρ) = 0.002 g·cm−3. Ammonium oxalate solutions with predetermined concentrations (see Table 2) were prepared in polypropylene bottles and positioned in a thermostatic shaking water bath at a certain temperature, at a shaking speed of 180 rpm. While maintaining these temperatures, small amounts of ammonium vanadate were added to the ammonium oxalate solutions every day until saturation was reached. Sampling of the liquid phase and examination of the solid phase were performed daily prior to further addition of NH4VO3 to the solutions. It was considered that equilibrium had been achieved when the composition of the liquid phase did not change with either time or with the further addition of NH4VO3 and when the vanadium-bearing phase was detected in the solid phase. Once the system had reached equilibrium, shaking was stopped and the samples were allowed to stand in the baths for 10 more days to allow the suspended particles to settle. After this time, the densities were measured using a pycnometer test method. Each data point represents an average of at least three individual measurements obtained with a precision of ±0.002 g·cm−3. The oxalate ion (C2O42−) content in the solution was determined using a standard manganometric method involving the titration of oxalate ions against permanganate solution.21 For this purpose, a sample of the solution (1 mL) was withdrawn, diluted with water to 10 mL, acidified to pH 1 using 1 M H2SO4, heated to ∼343 K, and titrated against KMnO4 to allow calculation of the oxalate content in the sample. The vanadate ion (VO3−) was titrated against ammonium ferrous sulfate solution using a solution of N-phenylanthranilic acid as the indicator. Taking an average of the oxalate and vanadate content measurements carried out in triplicate, the solubilities of (NH4)2C2O4 and NH4VO3 could be determined. To minimize the uncertainties in the calculated results, the ammonium ion (NH4+) content was also determined using ultraviolet−visible spectrophotometry (UV−vis, LabTechUV9100). This method was based on the theory that ammonium ion in water samples can react with potassium iodide mercury to generate amino mercury ionic complex iodine derivatives in alkaline conditions, and its color depth is proportional with the ammonium ion concentration of the solution. The measurements outlined in Table 2 represent the mean values obtained from the titrations carried out in triplicate. The solubilities expressed as molality and mass fraction were calculated using density data listed in Table 2. Finally, after drying the solid phases in an electrothermal air drying oven (DHG-9140A, Shanghai Yiheng Scientific Instrument Corp.), they were examined by X-ray diffraction (XRD, PW223/30 with Cu Kα radiation, 40 kV, and 100 mA, Philips). 3314

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Table 2. Solubilities and Liquid Densities for the System (NH4)2C2O4−NH4VO3−H2O at Pressure p = 100.7 kPaa,b composition of liquid phase (mol·kg−1) sample no.

(NH4)2C2O4

NH4VO3

1 2 3 4 5 6 7 8 9 10 11 12 13

0.0000 0.0160 0.0994 0.1469 0.1715 0.2207 0.2931 0.3632 0.4320 0.5090 0.5320 0.5560 0.5816

0.0948 0.0688 0.0398 0.0347 0.0297 0.0198 0.0148 0.0148 0.0137 0.0137 0.0117 0.0098 0.0000

1 2 3 4 5 6 7 8

0.0000 0.0399 0.1044 0.2079 0.2765 0.3593 0.4782 0.7808

0.1497 0.1036 0.0606 0.0267 0.0158 0.0148 0.0137 0.0000

1 2 3 4 5 6 7 8 9

0.0000 0.0866 0.1943 0.2699 0.3519 0.4934 0.6620 0.8126 1.0053

0.2116 0.0955 0.0525 0.0405 0.0256 0.0255 0.0146 0.0107 0.0000

1 2 3 4 5 6 7 8 9 10 11 12 13 14

0.0000 0.0499 0.0737 0.0986 0.1718 0.2211 0.3418 0.4866 0.6292 0.7875 0.9113 1.0275 1.0964 1.2112

0.2637 0.2134 0.1784 0.1454 0.1073 0.0783 0.0484 0.0442 0.0401 0.0380 0.0378 0.0155 0.0135 0.0000

1 2 3 4 5 6 7 8 9 10

0.0000 0.0439 0.0886 0.1441 0.2604 0.4227 0.6226 0.8419 1.2039 1.4288

0.3754 0.3320 0.2907 0.2296 0.1228 0.0709 0.0656 0.0593 0.0413 0.0000

composition of liquid phase (wt %) (NH4)2C2O4 T = 313.15 0.00 0.20 1.23 1.82 2.13 2.74 3.63 4.50 5.36 6.31 6.60 6.89 7.21 T = 323.15 0.00 0.49 1.29 2.58 3.43 4.46 5.93 9.68 T = 333.15 0.00 1.07 2.41 3.35 4.36 6.12 8.21 10.08 12.47 T = 343.15 0.00 0.62 0.91 1.22 2.13 2.74 4.24 6.03 7.80 9.77 11.30 12.74 13.60 15.02 T = 353.15 0.00 0.54 1.10 1.79 3.23 5.24 7.72 10.44 14.93 17.72

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NH4VO3

equilibrium solid phase

ρ (g·cm−3)

1.11 0.81 0.47 0.41 0.35 0.23 0.17 0.17 0.16 0.16 0.14 0.11 0.00

NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 (NH4)2C2O4·H2O

1.0023 1.0024 1.0058 1.0076 1.0085 1.0104 1.0132 1.0159 1.0186 1.0216 1.0225 1.0235 1.0247

1.75 1.21 0.71 0.31 0.18 0.17 0.16 0.00

NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 (NH4)2C2O4·H2O

1.0022 1.0037 1.0061 1.0100 1.0127 1.0158 1.0204 1.0323

2.48 1.12 0.61 0.47 0.30 0.30 0.17 0.12 0.00

NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 (NH4)2C2O4·H2O

1.0018 1.0049 1.0087 1.0114 1.0143 1.0195 1.0257 1.0313 1.0385

3.09 2.50 2.09 1.70 1.26 0.92 0.57 0.52 0.47 0.44 0.44 0.18 0.16 0.00

NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 (NH4)2C2O4·H2O

1.0012 1.0028 1.0036 1.0044 1.0068 1.0084 1.0124 1.0172 1.0219 1.0273 1.0315 1.0355 1.0379 1.0419

4.39 3.88 3.40 2.69 1.44 0.83 0.77 0.69 0.48 0.00

NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 (NH4)2C2O4·H2O

1.0016 1.0030 1.0044 1.0061 1.0098 1.0150 1.0215 1.0287 1.0407 1.0484

K

K

K

K

K

DOI: 10.1021/acs.jced.7b00362 J. Chem. Eng. Data 2017, 62, 3313−3318

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Table 2. continued composition of liquid phase (mol·kg−1) sample no.

(NH4)2C2O4

NH4VO3

1 2 3 4 5 6 7 8 9 10

0.0000 0.0439 0.1292 0.1391 0.2860 0.4676 0.6770 0.8915 1.2551 1.6796

0.4530 0.4325 0.3698 0.3230 0.1989 0.1211 0.0959 0.0865 0.0798 0.0000

composition of liquid phase (wt %) (NH4)2C2O4 T = 363.15 K 0.00 0.54 1.60 1.73 3.55 5.80 8.40 11.05 15.56 20.83

NH4VO3

equilibrium solid phase

ρ (g·cm−3)

5.30 5.06 4.33 3.78 2.33 1.42 1.12 1.01 0.93 0.00

NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 (NH4)2C2O4·H2O

1.0021 1.0034 1.0059 1.0061 1.0104 1.0158 1.0221 1.0286 1.0398 1.0532

a

Molalities of salts in water as a solvent are reported. bStandard uncertainties u are u(p) = 0.5 kPa, u(T) = 0.1 K, u(m((NH4)2C2O4)) = 0.01 mol· kg−1, u(m(NH4VO3)) = 0.01 mol·kg−1, and u(ρ) = 0.002 g·cm−3.

Figure 3. Solubility diagram of the (NH4)2C2O4−NH4VO3−H2O system from 313.15 to 363.15 K. Figure 1. Solubility data of the NH4VO3−H2O system from 313.15 to 363.15 K.

Figure 4. Density−mass fraction relationship of (NH4)2C2O4 in the (NH4)2C2O4−NH4VO3−H2O system from 313.15 to 363.15 K. Figure 2. Solubility data of the (NH4)2C2O4−H2O system from 273.15 to 373.15 K.

From the above analysis, it was clearly that the saturated solubility of NH4VO3 decreased significantly upon decreasing the temperature, which suggests that the separation of NH4VO3 via cooling crystallization could be feasible within the (NH4)2C2O4 concentration range examined herein. In addition, salting-out crystallization should also be suitable for the separation of NH4VO3 from the system due to the obvious

temperature decrease from 363.15 to 313.15 K when the (NH4)2C2O4 concentration is around 0.04 mol·kg−1. And it decreases only 0.1371 mol·kg −1 when the (NH4 ) 2C 2O4 concentration is around 0.4 mol·kg−1. 3316

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Figure 5. XRD pattern of the (NH4)2C2O4−NH4VO3−H2O system equilibrium solid phase from 313.15 to 363.15 K: (a) NH4VO3; (b) (NH4)2C2O4·H2O.

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differences in solubility upon varying the (NH 4 ) 2 C 2 O 4 concentration. Based on these observations, we propose a novel method for the separation of NH4VO3, involving cooling crystallization by decreasing the temperature from 363.15/ 353.15 to 313.15/323.15 K, while (NH4)2C2O4 can be utilized to enhance the vanadium separation efficiency via salting-out effects. Using data presented in Table 2, in Figure 4 the relation between the solution density and the concentration of (NH4)2C2O4 salt is shown for the given range of temperatures. From Figure 4, it can be seen that the solution densities increase linearly with the increase of (NH4)2C2O4 concentration, reaching the maximum values at the (NH4)2C2O4 saturated point. The major powder XRD pattern of the equilibrium solid phases obtained at 313.15 K are shown in Figure 5. Figure 5 shows that in the investigated temperature range from 313.15 to 363.15 K in the solid phase only NH4VO3, except (NH4)2C2O4·H2O in the (NH4)2C2O4·H2O saturated point. The solid phases obtained at 323.15−363.15 K from XRD pattern analysis is similar to that found at 313.15 K.

(1) Habashi, F. Two hundred years of vanadium. In Vanadium Geology, Processing and Applications, Proceedings of the International Symposium on Vanadium[C], 41st Annual Conference of Metallurgists of CIM, Montreal, Canada, Aug. 11−14, 2004; Tanner, M. F., Riveros, M. F., Gattrell, P. A., Gattrell, J. E., Gattrell, M., Perron, L., Eds.; Canadian Institute of Mining, Metallurgy and Petroleum: Montreal, Canada, 2002; pp 3−15. (2) Moskalyk, R. R.; Alfantazi, A. M. Processing of vanadium: a review. Miner. Eng. 2003, 16, 793−805. (3) Sengupta, P.; Dey, K. K.; Halder, R.; Ajithkumar, T. G.; Abraham, G.; Mishra, R. K.; Kaushik, C. P.; Dey, G. K. Vanadium in Borosilicate Glass. J. Am. Ceram. Soc. 2015, 98, 88−96. (4) Gupta, S.; Kirillova, M. V.; Guedes da Silva, M. F.; Pombeiro, A. J. L. Highly efficient divanadium(V) pre-catalyst for mild oxidation of liquid and gaseous alkanes. Appl. Catal., A 2013, 460−461, 82−89. (5) Wu, C. Z.; Xie, Y. Promising vanadium oxide and hydroxide nanostructures: from energy storage to energy saving. Energy Environ. Sci. 2010, 3, 1191−1206. (6) Franz, R.; Mitterer, C. Vanadium containing self-adaptive lowfriction hard coatings for high-temperature applications: A review. Surf. Coat. Technol. 2013, 228, 1−13. (7) Gambino, D. Potentiality of vanadium compounds as antiparasitic agents. Coord. Chem. Rev. 2011, 255, 2193−2203. (8) Taylor, P. R.; Shuey, S. A.; Vidal, E. E.; Gomez, J. C. Extractive Metallurgy of Vanadium Containing Titaniferous Magnetite Ores: A Review. Miner. Metall. Proc. 2006, 23, 80−86. (9) Chen, D. S.; Zhao, L. S.; Liu, Y. H.; Qi, T.; Wang, J. C.; Wang, L. N. A novel process for recovery of iron, titanium, and vanadium from titanomagnetite concentrates: NaOH molten salt roasting and water leaching processes. J. Hazard. Mater. 2013, 244-245, 588−595. (10) Sadykhov, G. Oxidation of titanium-vanadium slags with the participation of Na2O and its effect on the behavior of vanadium. Russ. Metall. 2008, 2008(6), 449−458. (11) Li, X. S.; Xie, B.; Wang, G. A.; Li, X. J. Oxidation process of lowgrade vanadium slag in presence of Na2CO3. Trans. Nonferrous Met. Soc. China 2011, 21, 1860−1867. (12) Wang, Z. H.; Zheng, S. L.; Wang, S. N.; Qin, Y. L.; Du, H.; Zhang, Y. Electrochemical decomposition of vanadium slag in concentrated NaOH solution. Hydrometallurgy 2015, 151, 51−55. (13) Zheng, S. L.; Du, H.; Wang, S. N.; Zhang, Y.; Li, M. A method of roasted raw materials containing vanadium leaching by ammonium bicarbonate solution. Chinese Patent 201410220685.0. (14) Du, H.; Zheng, S. L.; Wang, S. N.; Liu, B.; Zhang, Y.; Li, M. A method of roasted raw materials containing vanadium leaching by ammonia solution. Chinese Patent 201410162944.9. (15) Du, H.; Zheng, S. L.; Wang, S. N.; Liu, B.; Zhang, Y.; Li, M. A method of roasted raw materials containing vanadium leaching by ammonium oxalate solution. Chinese Patent 201610121140.3.

4. CONCLUSIONS Solubility data for the ternary (NH4)2C2O4−NH4VO3−H2O system ranging from 313.15 to 363.15 K were determined and studied. A significant difference in NH4VO3 solubility was observed with the change of temperature and (NH4)2C2O4 concentration, thus providing a theoretical basis for effective NH4VO3 separation by means of cooling and salting-out crystallization from an (NH4)2C2O4 solution.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 10 82544856. Fax: +86 10 82544856. E-mail: hdu@ ipe.ac.cn. ORCID

Shaona Wang: 0000-0001-7055-586X Funding

We gratefully acknowledge financial support from the Science and Technology Service Network Initiative Program of the Chinese Academy of Sciences under Grant No. KFJ-SW-STS148 and the National Natural Science Foundation of China under Grant No. 51404227. Notes

The authors declare no competing financial interest. 3317

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(16) Li, M.; Liu, B.; Zheng, S. L.; Wang, S. N.; Du, H.; Dreisinger, D. B.; Zhang, Y. A cleaner vanadium extraction method featuring non-salt roasting and ammonium bicarbonate leaching. J. Cleaner Prod. 2017, 149, 206−217. (17) Chen, J. Y. Handbook of hydrometallurgy; Metallurgical Industry Press: Beijing, China, 2005 (in Chinese). (18) Yan, H.; Du, H.; Wang, S. N.; Zheng, S. L.; Zhang, Y. Solubility data for the ternary NH4HCO3-NH4VO3-H2O and (NH4)2CO3NH4VO3-H2O systems at (40 and 70) °C. J. Chem. Eng. Data 2016, 61, 2346−2352. (19) Trypuc, M.; Stefanowicz, D. I. Solubility in the KVO3+NH4VO3+H2O system. J. Chem. Eng. Data 1997, 42, 1140− 1144. (20) Zhao, C.; Feng, M.; Wang, S. N.; Du, H.; Zheng, S. L.; Xie, H. Solubility investigation of NH4VO3 in the ternary NH4HCO3NH4VO3-H2O system at 40 and 70 °C. Chem. Ind. Eng. Prog. 2014, 33 (6), 1408−1412 (in Chinese). (21) Trypuc, M.; Druzynski, S. Investigation of Mutual Solubility in the NH4VO3-NH4NO3- H2O system. Ind. Eng. Chem. Res. 2009, 48, 5058−5063. (22) Liu, F.; Ning, P. G.; Cao, H. B.; Li, Z. B.; Zhang, Y. Solubilities of NH4VO3 in the NH3−NH4+−SO42−−Cl−−H2O System and Modeling by the Bromley−Zemaitis Equation. J. Chem. Eng. Data 2013, 58, 1321−1328. (23) Gong, X. L.; Zhang, C. Q.; Ning, P. G.; Cao, H. B.; Zhang, Y. Solubility of NH4VO3 in NH4H2PO4-H2O and (NH4)3PO4-H2O systems. Acta Phys.-Chin. Sin 2016, 32 (5), 1134−1142. (24) Hill, A. E.; Distler, E. F. The solubility of ammonium oxalate in water. J. Am. Chem. Soc. 1935, 57, 2203−2204.

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