Article pubs.acs.org/jced
Solubility Data in the Ternary NH4HCO3−NH4VO3−H2O and (NH4)2CO3−NH4VO3−H2O Systems at (40 and 70) °C Hong Yan,†,‡ Hao Du,† Shaona Wang,*,† Shili Zheng,† and Yi Zhang† †
National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China ‡ University of Chinese Academy of Sciences, No.19A Yuquan Road, Beijing 100049, China ABSTRACT: Effective separation of NH4VO3 from NH4HCO3 or (NH4)2CO3 solution is an important step in the newly proposed vanadium production process based on sodium salt roasting. The solubility data for NH4HCO3−NH4VO3−H2O and (NH4)2CO3−NH4VO3−H2O systems at (40 and 70) °C were studied, respectively; thus, a strategy for effective separation of NH4VO3 from NH4HCO3 or (NH4)2CO3 solution has been proposed.
1. INTRODUCTION Vanadium is a valuable strategic metal with diverse applications. About 85% of vanadium is used in iron and steel making industry to produce high strength steel due to its superior malleability and robustness.1 Further, it is widely used as alloying materials to fabricate titanium alloys for aerospace industries, as catalysts for the chemical and polymer industries, as electrolytes in electrochemical energy storage device, and as additives for pigments production.1,2 In addition, vanadium exhibits excellent properties to be utilized in the ceramic, special glass and medical fields.3−6 South Africa, Russia and China are major vanadium producers, accounting for 95% of the global vanadium production. Vanadium is found in over 50 different minerals, and vanadiumbearing titanomagnetite is the most important ore for vanadium production.2,7 Vanadium slag, which is produced during iron making using vanadium-bearing titanomagnetite, is the major raw material for vanadium extraction, accounts for 58% of the world’s vanadium production.8,9 The traditional process for the production of vanadium using vanadium slag as raw material is sodium salt roasting,10,11 which is widely applied because this process is easy to operate and the products obtained have high purity. However, this process is mostly limited due to the production of high salinity ammonium-rich wastewater (30−40 m3/t V2O5), which contains 4000−16 000 mg/L NH4+ and more than 20 g/L Na+. The ammonia−nitrogen wastewater was treated with evaporation-concentration process, accounting 15−20% of the cost for vanadium oxide production. Furthermore, the obtained sodium sulfate/ammonium sulfate mixed salts are difficult be further purified or used as industrial raw materials. In fact, deep burying is suggested as the only economical way to deal with the mixed salts, creating severe environmental pollution. In this regard, how to control the wastewater has become a major challenge for global vanadium production industries. The formation of high salinity ammonium-rich wastewater is due to the direct participation of vanadium using ammonium © XXXX American Chemical Society
salts from sodium vanadate solution, which is obtained via leaching of sodium salt roasted vanadium slag. And further, in order to increase the ammonium vanadate precipitation efficiency and decrease the consumption of ammonium salt, the operation is usually operated as acidic condition by addition of excessive amount of sulfuric acid. Therefore, in order to avoid the formation of such wastewater, alternative vanadium separation strategies have to be developed. Recently, a novel process for separating vanadium based on sodium salt roasting process has established by Institute of Process Engineering, Chinese Academy of Science. The detailed process is shown in Figure 1, as can be seen, vanadium slag is first roasted with sodium salt, then after being leached and separated with the residue, the leachate which contains Na3VO4
Figure 1. Flowchart for the new sodium salt roasting process. Received: December 13, 2015 Accepted: June 9, 2016
A
DOI: 10.1021/acs.jced.5b00985 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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2. EXPERIMENTAL SECTION 2.1. Apparatus and Reagents. Polypropylene bottles with good heat resistance and chemical stability (capacity of 250 mL) were used for preparing the samples. These bottles were placed in HZ-9212S type thermostatic shaking water baths with a precision of 0.1 °C to reach equilibrium at 40 and 70 °C, respectively. The concentration of VO3− in all samples was determined by measuring vanadium content using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES, PE Optima 5300DV, PerkinElmer). The NH4+ concentration was analyzed using ultraviolet−visible spectrophotometer (UV−vis, LabTechUV9100). In order to ensure the accuracy of measurement, the concentration of HCO3− and CO32− were determined by the titration method. The solid phases were first dried in electrothermal air drying oven (DHG-9140A, Shanghai Yiheng Scientific Instrument Corporation) and then examined by X-ray diffraction analysis (XRD, PW223/30 with Cu Kα radiation, 40 kV and 100 mA, Philips). The chemicals used in this study is shown in Table 1 and were of analytical grade. Ammonium bicarbonate, ammonium carbonate, and ammonium vanadate were purchased from Xilong Chemical Plant. The purities of these chemicals are above 99%. High-purity Milli-Q water, with a resistivity of above 18.2 MΩ·cm at ambient temperature, was used for preparing the solutions. 2.2. Experimental Procedure. The solubility was determined via the isothermal solution saturation method.14,15 The NH4HCO3/(NH4)2CO3 solutions with predetermined concentrations were prepared in polypropylene bottles and positioned in thermostatic shaking water bath at 40 and 70 °C, shaking with a speed of 180 rpm, then small amounts of NH4VO3 was added into the NH4HCO3/(NH4)2CO3 solutions every day at constant temperature 40 and 70 °C until the solution reached saturation. Sampling of the liquid phase and examining of the solid phase were performed every day before further addition of NH4VO3 to the solutions (see Table 2). The equilibrium state was considered to be achieved when the composition of liquid phase did not change with either time or further addition of salts, and the vanadium-bearing phase was presented in the solid phases. Once the system was in equilibrium state, the shaking was stopped, and the samples were kept in the baths for 10 more days in order for the suspended precipitates to settle. After the upper layer became clarified thoroughly, the densities were measured by pycnometer test method. Each data represents the average of at least three individual measurements with the precision of ±0.0002 g cm−3. Each equilibrium liquid phase sample of 1 mL was taken using a sampling gun and transferred into a volumetric flask, followed by dilution with high purity water for further analysis. The concentration of vanadium was determined using ICP-OES. The NH4+ concentration was analyzed using ultraviolet−visible spectrophotometer (UV−vis,
is obtained. Instead of direct reacting of sodium vanadate with ammonium salts, sodium vanadate is first converted to calcium vanadate by calcification as follows: 2Na3VO4 + 3CaO + 3H 2O → Ca3(VO4 )2 + 6NaOH
(1)
According to the reaction, the calcification process realizes the separation of vanadium from sodium.12 The obtained calcium vanadate can either be utilized as primary raw material for ferrovanadium production13 or be further converted to ammonium vanadate by reacting with ammonium salts. In addition, NH4HCO3/(NH4)2CO3 has been utilized as ammonium salts to separate vanadium instead of traditional NH4Cl/(NH4)2SO4 salts, so that the solution does not contain any difficult to evaporate anions, making it easy to recycle. The reactions are as follows: Ca3(VO4 )2 + 2NH4HCO3 + CO2 → 3CaCO3 + 2NH4VO3 + H 2O
(2)
Ca3(VO4 )2 + (NH4)2 CO3 + 2CO2 → 3CaCO3 + 2NH4VO3
(3)
The obtained CaCO3 can return to reaction 1 after being calcined to CaO. As shown in Figure 1, the calcification and carbonization-ammonium processes can realize zero waste discharge and cleaner production. From Figure 1, after separation of the reaction slurry, a mixed aqueous solution of NH4HCO3/(NH4)2CO3−NH4VO3−H2O at 70 °C is obtained. Consequently, it is necessary to study the equilibrium solubility of the ternary NH4HCO3−NH4VO3− H2O and (NH4)2CO3−NH4VO3−H2O system for designing separation methods of NH4VO3 from the solutions. For the NH4HCO3−NH4VO3−H2O and (NH4)2CO3−NH4VO3−H2O systems, 40 and 70 °C have been proposed to be the equilibrium temperatures by considering both the carbonizationammonization reaction temperature (70 °C) and ammonium metavanadate crystallization efficiency. The target of this research is to provide fundamental information for the design of NH4VO3 separation strategy from NH4HCO3/(NH4)2CO3 solutions. Table 1. Purities and Suppliers of Chemicals source
initial mole fraction purity
CAS no.
Xilong Chemical Plant
≥99%
1066-33-7
Xilong Chemical Plant
≥99%
506-87-6
Xilong Chemical Plant
≥99%
7803-55-6
chemical name ammonium bicarbonate ammonium carbonate ammonium metavanate
Table 2. Comparison of NH4VO3 Solubility Data in Pure Water composition of NH4VO3 (mol kg−1) temperature (°C)
experiment (NH4HCO3 system)a
experiment ((NH4)2CO3 system)b
literaturec
40 70
0.0946 0.2563
0.0935 (contain 0.01g/L (NH4)2CO3) 0.2612
0.1032 (ref 17) 0.2643 (ref 18)
a
Experiment(NH4HCO3 system), NH4VO3 solubility data in pure water got from NH4HCO3 system experiment data. bExperiment((NH4)2CO3 system), NH4VO3 solubility data in pure water got from (NH4)2CO3 system experiment data. cLiterature, NH4VO3 solubility data in pure water got from ref 17 and 18. B
DOI: 10.1021/acs.jced.5b00985 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 3. Experimental Solubilities, Expressed in g L NH4VO3−H2O at Pressure p = 100.8 kPaa,b composition of liquid phase (g L−1) sample no.
NH4HCO3
NH4VO3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
0.01 1.21 2.87 4.01 5.39 7.52 8.12 9.92 12.17 14.18 18.81 23.04 24.89 28.15 35.31 39.88 46.00 48.12 60.57 70.01 73.09 80.00 94.52 110.45 120.13 131.86 139.07 155.55 169.99 178.40 185.11 191.25 203.73
10.97 9.87 9.03 7.99 6.76 6.03 4.96 3.87 3.37 2.83 2.51 2.41 2.38 2.26 2.31 2.50 2.52 2.53 2.57 2.61 2.77 2.85 3.01 3.09 3.14 3.16 3.18 3.21 3.37 3.49 3.58 3.66 3.78
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
0.00 2.12 2.79 3.95 5.60 6.12 6.33 6.53 9.27 13.45 16.52 19.57 23.14 28.26 33.85 37.00 45.82 51.29 62.55 75.91 80.97 93.21 105.01
30.02 27.55 27.14 26.01 24.22 21.97 20.15 18.79 17.40 15.22 13.98 12.70 11.02 9.55 8.60 8.15 7.76 7.52 7.41 6.74 6.44 6.23 6.21
−1
and in Molalities m, and Liquid Densities for the System NH4HCO3−
composition of liquid phase (mol kg−1) NH4HCO3 T = 40 °C 0.0001 0.0153 0.0362 0.0506 0.0680 0.0949 0.1023 0.1249 0.1530 0.1780 0.2360 0.2889 0.3117 0.3522 0.4386 0.4950 0.5708 0.5959 0.7493 0.8658 0.9034 0.9828 1.1532 1.3397 1.4574 1.5862 1.6708 1.8574 2.0225 2.0863 2.1434 2.1798 2.3204 T = 70 °C 0.0000 0.0268 0.0353 0.0499 0.0708 0.0774 0.0800 0.0825 0.1171 0.1699 0.2085 0.2469 0.2917 0.3562 0.4265 0.4660 0.5755 0.6438 0.7835 0.9458 1.0011 1.1409 1.2721 C
NH4VO3
equilibrium solid phase
ρ (g/cm3)
0.0935 0.0842 0.0770 0.0681 0.0576 0.0514 0.0422 0.0329 0.0286 0.0240 0.0213 0.0204 0.0201 0.0191 0.0194 0.0210 0.0211 0.0212 0.0215 0.0218 0.0231 0.0236 0.0248 0.0253 0.0257 0.0257 0.0258 0.0259 0.0271 0.0276 0.0280 0.0282 0.0291
NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3
1.0023 1.0024 1.0028 1.0031 1.0033 1.0034 1.0044 1.0051 1.0069 1.0083 1.0087 1.0096 1.0107 1.0118 1.0191 1.0199 1.0201 1.0222 1.0232 1.0236 1.0241 1.0304 1.0375 1.0436 1.0434 1.0523 1.0536 1.0601 1.0639 1.0824 1.0932 1.1106 1.1114
0.2563 0.2352 0.2317 0.2220 0.2067 0.1875 0.1720 0.1604 0.1484 0.1298 0.1191 0.1082 0.0938 0.0813 0.0732 0.0693 0.0658 0.0637 0.0627 0.0567 0.0538 0.0515 0.0508
NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3
1.0011 1.0013 1.0012 1.0013 1.0014 1.0014 1.0013 1.0014 1.0019 1.0021 1.0031 1.0035 1.0040 1.0044 1.0047 1.0051 1.0079 1.0084 1.0106 1.0159 1.0238 1.0342 1.0449
DOI: 10.1021/acs.jced.5b00985 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 3. continued composition of liquid phase (g L−1) sample no.
NH4HCO3
NH4VO3
24 25 26 27 28 29 30 31 32
117.07 133.46 137.69 140.15 149.23 160.55 170.62 178.94 189.68
6.14 6.15 6.19 6.18 6.20 6.23 6.15 6.12 6.09
composition of liquid phase (mol kg−1) NH4HCO3 T = 70 °C 1.4131 1.5943 1.6410 1.6691 1.7697 1.8788 1.9909 2.0773 2.2016
NH4VO3
equilibrium solid phase
ρ (g/cm3)
0.0500 0.0496 0.0498 0.0497 0.0496 0.0492 0.0485 0.0480 0.0477
NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3
1.0487 1.0596 1.0621 1.0629 1.0674 1.0817 1.0848 1.0904 1.0906
a
Molalities of salts in water as a solvent are reported. bStandard uncertainties u are u(p) = 0.5 kPa, u(T) = 0.05 K, ur(m(NH4HCO3)) = 0.02, ur(m(NH4VO3)) = 0.05, ur(ρ) = 0.001.
LabTechUV9100) and the concentration of HCO3− and CO32− were determined by the titration method.16 The equilibrium solid phases were first dried at 40 and 70 °C for 24 h and then grinded to powder in a mortar. The crystallography information was identified using X-ray diffraction with scanning range from 5° to 90°. To guarantee the accuracy of the analysis, each equilibrium system was sampled and analyzed at least three times, and the results hereafter were the average of multiple measurements with standard deviation of less than 5%.
3. RESULTS AND DISCUSSION 3.1. NH4HCO3−NH4VO3−H2O System. The solubility data of NH4HCO3−NH4VO3−H2O ternary system at 40 and 70 °C were measured and presented in Table 3. The solubility curve is plotted in Figure 2. The XRD patterns obtained from the Figure 3. XRD pattern of the NH4HCO3−NH4VO3−H2O system equilibrium solid phases at 40 °C.
in the NH4HCO3 concentration as the NH4HCO3 concentration changes from 0 to 2.2 mol/kg approximately. Closer observation suggests that there is a sharp decrease in NH4VO3 solubility when the NH4HCO3 concentration changes from 0 to 0.5 mol/kg. Further increase of NH4HCO3 concentration does not appear to have significant effect on the NH4VO3 solubility. At 40 °C,before the NH4HCO3 concentration reaches 0.25 mol/kg, the solubility of NH4VO3 presents a significant decrease with the increase of NH4HCO3 concentration, which is similar to that occurred at 70 °C. After that, the solubility NH4VO3 presents increases lightly with the increase of NH4HCO3 concentration. Besides, from Figure 2, it is clear that the NH4VO3 solubility exhibits significant difference at 40 and 70 °C. On the basis of this, a new method to separate NH4VO3 is proposed, which is cooling crystallization by decreasing the temperature from 70 to 40 °C, and thus NH4VO3 crystal can be obtained. Furthermore, NH4HCO3 can be utilized to enhance the vanadium separation efficiency via salting out effects. 3.2. (NH4)2CO3−NH4VO3−H2O System. The solubility of (NH4)2CO3−NH4VO3−H2O ternary system at 40 and 70 °C were measured preciously, and the results are presented in Table 4. The solubility curve is plotted in Figure 3. The XRD patterns obtained from the equilibrium solid phase at 40 and 70 °C indicates that NH4VO3 is the sole composition which is same as NH4HCO3−NH4VO3−H2O system. According to Figure 4, the solubility of NH4VO3 shows a trend of decrease with the increase of (NH4)2CO3 concentration
Figure 2. Solubility diagram of the NH4HCO3−NH4VO3−H2O system at 40 and 70 °C.
equilibrium solid phase at 40 and 70 °C indicate that the equilibrium solid phase is totally made up of NH4VO3 and the XRD pattern of 40 °C is shown in Figure 3. The data of NH4VO3 solubility in pure water obtained in this work was verified by comparing with refs 17 and 18 values. As is shown in Table 2, the experimental solubility of NH4VO3 in pure water at 40 and 70 °C is in good agreement with the literature data reported with relative deviations of less than 5%, indicating that the procedure is acceptable. As can be seen from Figure 2, at 70 °C, the solubility of NH4VO3 shows a trend of monotonic decrease with an increase D
DOI: 10.1021/acs.jced.5b00985 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 4. Experimental Solubilities, Expressed in g L −1 and in Molalities m, and Liquid Densities for the System (NH4)2CO3− NH4VO3−H2O at Pressure p = 100.7 kPaa,b composition of liquid phase (g L−1) sample no.
(NH4)2CO3
NH4VO3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
0.00 1.25 2.46 3.56 5.52 7.23 8.39 10.21 13.17 14.74 18.94 25.62 32.27 41.20 53.04 59.18 65.31 76.62 84.75 104.58 106.46 115.36 123.54 140.19 153.26 171.24 175.15 183.56 189.25 190.33 212.75
11.09 10.38 8.29 6.69 5.77 5.01 4.81 4.52 3.93 4.00 3.36 3.00 2.89 2.94 2.97 3.15 3.21 3.32 3.42 3.65 3.68 3.69 3.74 3.85 3.91 3.94 4.02 4.07 4.09 4.11 4.23
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
0.00 0.88 2.23 5.35 7.11 8.83 10.41 12.97 15.34 19.52 25.39 34.64 39.38 51.78 57.81 65.31 70.78 78.56 86.88 101.11 105.71 123.52 131.05 137.92 148.24
30.60 29.94 28.91 27.65 26.58 22.57 21.35 19.09 17.98 16.47 14.97 14.05 13.24 12.01 11.25 10.32 9.12 9.95 10.01 10.31 10.33 10.34 10.35 10.33 10.32
composition of liquid phase (mol kg−1) (NH4)2CO3 T = 40 °C 0.0000 0.0130 0.0256 0.0370 0.0574 0.0751 0.0871 0.1058 0.1361 0.1521 0.1947 0.2620 0.3275 0.4163 0.5341 0.5926 0.6520 0.7590 0.8335 1.0043 1.0227 1.0999 1.1696 1.3221 1.4440 1.6100 1.6465 1.7231 1.7752 1.7855 1.9931 T = 70 °C 0.0000 0.0092 0.0232 0.0556 0.0739 0.0918 0.1081 0.1347 0.1593 0.2026 0.2632 0.3589 0.4077 0.5313 0.5921 0.6660 0.7168 0.7932 0.8749 1.0079 1.0518 1.2228 1.2964 1.3589 1.4482 E
NH4VO3
equilibrium solid phase
ρ (g/cm3)
0.0946 0.0885 0.0707 0.0571 0.0492 0.0427 0.0410 0.0384 0.0333 0.0339 0.0283 0.0252 0.0241 0.0244 0.0245 0.0259 0.0263 0.0270 0.0276 0.0288 0.0290 0.0289 0.0291 0.0298 0.0302 0.0304 0.0310 0.0313 0.0315 0.0316 0.0325
NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3
1.0021 1.0021 1.0018 1.0016 1.0020 1.0023 1.0029 1.0053 1.0083 1.0096 1.0134 1.0185 1.0263 1.0308 1.0344 1.0402 1.0435 1.0516 1.0592 1.0847 1.0843 1.0925 1.1003 1.1045 1.1056 1.1079 1.1081 1.1097 1.1105 1.1104 1.1119
0.2612 0.2556 0.2467 0.2360 0.2268 0.1924 0.1820 0.1627 0.1532 0.1402 0.1274 0.1194 0.1125 0.1011 0.0945 0.0863 0.0758 0.0824 0.0827 0.0843 0.0843 0.0840 0.0840 0.0835 0.0827
NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3
1.0013 1.0013 1.0014 1.0015 1.0017 1.0024 1.0028 1.0027 1.0030 1.0038 1.0047 1.0055 1.0061 1.0152 1.0171 1.0215 1.0286 1.0317 1.0344 1.0450 1.0469 1.0522 1.0530 1.0572 1.0663
DOI: 10.1021/acs.jced.5b00985 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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Table 4. continued composition of liquid phase (g L−1) sample no.
(NH4)2CO3
NH4VO3
26 27 28 29 30 31
152.29 164.42 176.55 184.39 189.20 205.49
10.29 10.26 10.23 10.19 10.16 10.17
composition of liquid phase (mol kg−1) (NH4)2CO3 T = 70 °C 1.4806 1.5847 1.6897 1.7602 1.8018 1.9454
NH4VO3
equilibrium solid phase
ρ (g/cm3)
0.0821 0.0811 0.0803 0.0798 0.0794 0.0790
NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3 NH4VO3
1.0714 1.0808 1.0884 1.0912 1.0938 1.1003
a
Molalities of salts in water as a solvent are reported. bStandard uncertainties u are u(p) = 0.5 kPa, u(T) = 0.05 K, ur(m((NH4)2CO3)) = 0.03, ur(m(NH4VO3)) = 0.02, ur(ρ) = 0.002.
Figure 4. Solubility diagram of the (NH4)2CO3−NH4VO3−H2O system at 40 and 70 °C.
Figure 5. Solubility diagrams of the NH4HCO3−NH4VO3−H2O system and (NH4)2CO3−NH4VO3−H2O system at 70 and 40 °C.
at 70 °C. When the concentration of (NH4)2CO3 is below 1.0 mol/kg, a sharp decrease in NH4VO3 solubility has been observed with the increase of (NH4)2CO3 concentration. In addition, a plateau has formed when the (NH4)2CO3 concentration is above 1.0 mol/kg. At 40 °C, the solubility of NH4VO3 decreases with the increased of (NH4)2CO3 concentration until it reached 0.3 mol/kg, and the solubility increase slightly when the (NH4)2CO3 concentration is more than 0.3 mol/kg. Furthermore, similar to that observed in NH4HCO3− NH4VO3−H2O system, Figure 4 suggests that there is a significant difference in NH4VO3 solubility between 40 and 70 °C. In this regard, cooling crystallization is also theoretically possible in this NH4VO3 separation process and the specific method is as follows: carbonization-ammoniation reaction is conducted with (NH4)2CO3 as reactant at 70 °C, followed by cooling the solution to 40 °C, and the NH4VO3 crystal will be formed. Likewise, adjusting the (NH4)2CO3 concentration properly in this system can improve the vanadium separation efficiency. 3.3. Comparison of NH4VO3 Solubility in NH4HCO3− NH4VO3−H2O and (NH4)2CO3−NH4VO3−H2O Systems. Figure 5 shows the solubility diagrams of the NH4HCO3− NH4VO3−H2O and (NH4)2CO3−NH4VO3−H2O systems at (40 and 70)°C. Solubility curves in the two systems were compared and unitized by NH4+ concentration. As presented in Figure 5, the NH4VO3 solubility curves show almost the same trends in NH4HCO3−NH4VO3−H2O and (NH4)2CO3− NH4VO3−H2O systems at 70 °C. However, the NH4VO3 solubility in (NH4)2CO3−NH4VO3−H2O system is significantly higher than that in NH4HCO3−NH4VO3−H2O system.
A slight difference shows between the NH4HCO3−NH4VO3− H2O and (NH4)2CO3−NH4VO3−H2O system at 40 °C when the concentration of NH4+ is lower than 0.6 mol/kg. In this range, the NH4VO3 solubility in (NH4)2CO3−NH4VO3−H2O system is higher than that in the NH4HCO3−NH4VO3−H2O system, and the difference maximizes when the NH4+ concentration reaches 0.3 mol/kg. However, these two curves are almost overlapped afterward in a wider NH4+ concentration range. In cooling crystallization operation, the greater the difference in NH4VO3 solubility between the high and low temperature appears, the higher the NH4VO3 crystallization efficiency is. From Figure 5, the (NH4)2CO3−NH4VO3−H2O system appears to exhibit larger NH4VO3 solubility difference between 70 and 40 °C, and therefore it is more favorable for the separation of NH4VO3 from (NH4)2CO3−NH4VO3−H2O system.
4. CONCLUSIONS Solubility data for the ternary NH4HCO3−NH4VO3−H2O and (NH4)2CO3−NH4VO3−H2O systems at (40 and 70) °C were studied. The result shows that both the two systems exhibit significant difference in NH4VO3 solubility as temperature changes, thus providing a theoretical basis for effectively NH4VO3 separation by means of cooling the slurry from 70 to 40 °C. In addition, because of a larger NH4VO3 solubility gap between 70 and 40 °C, NH4VO3 is more likely to get higher crystallization efficiency when cooling crystallization is conducted in the (NH4)2CO3− NH4VO3−H2O system. F
DOI: 10.1021/acs.jced.5b00985 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
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AUTHOR INFORMATION
Corresponding Author
*Tel.: +86 10 82544856; fax: +86 10 82544856. E-mail:
[email protected]. Funding
The authors gratefully acknowledge the financial support from the Major State Basic Research Development Program of China (973 program) under grant No. 2013CB632605, National Natural Science Foundation of China under Grant No. 51404227 and 51274179, Science and Technology ServiceNetwork Initiative of Chinese Academy of Sciences No. KFJ-SW-STS-148. Notes
The authors declare no competing financial interest.
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DOI: 10.1021/acs.jced.5b00985 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
