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Rapid selective extraction of V(V) from leaching solution using annular centrifugal contactors and stripping for NH4VO3
Accepted Manuscript Rapid selective extraction of V(V) from leaching solution using annular centrifugal contactors and stripping for NH4VO3 Xiaohua Jing, Jianyou Wang, Hongbin Cao, Pengge Ning, Zhi Sun PII: DOI: Reference:
S1383-5866(17)30985-1 http://dx.doi.org/10.1016/j.seppur.2017.06.078 SEPPUR 13856
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
29 March 2017 14 June 2017 30 June 2017
Please cite this article as: X. Jing, J. Wang, H. Cao, P. Ning, Z. Sun, Rapid selective extraction of V(V) from leaching solution using annular centrifugal contactors and stripping for NH4VO3, Separation and Purification Technology (2017), doi: http://dx.doi.org/10.1016/j.seppur.2017.06.078
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Rapid selective extraction of V(V) from leaching solution using annular centrifugal contactors and stripping for NH4VO3 Xiaohua Jing1,2, Jianyou Wang1*, Hongbin Cao2, Pengge Ning2*, Zhi Sun2 1. College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China 2. Beijing Engineering Research Centre for Process Pollution Control, Division of Environment Technology and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
*Corresponding authors at: No. 1, Beier Street, Zhongguancun, Haidian District, Beijing 100190, China (Pengge Ning). Tel/Fax: +86 10 82544845. No. 38, Tongyan Road, Haihe Education Park, Jinnan District, Tianjin 300350 (Jianyou Wang). Tel/Fax: +86 22 23501117 E-mail address:
pgning @ipe.ac.cn(P. Ning). [email protected] (J. Wang)
Abstract: The efficient and rapid selective extraction of V(V) from leaching solution with sulfated primary amine N1923 was demonstrated. In the single-stage extraction using annular centrifugal contactor (ACC), the influence of the total flow and the speed rotor on extraction percentage of V(V) was investigated using central composite design (CCD), and the results of experimental conditions were analyzed by analysis of variance. The current concentrations of V(V) and Cr(VI) in leaching solution were 23.70g/L and 1.52g/L, respectively. 99.6% of vanadium was extracted and separated from the aqueous solution by employing four-stage countercurrent extraction with annular centrifugal contactors (ACCs). The total contact/resident time of the two phases was 4.8 min, and the separation factor of V(V) and Cr(VI) was 273.9. The two metals in leaching solution can be separated primarily, and then 23.61g/L V(V) and 0.72g/L Cr(VI) in loaded organic phase can be further separated by the stripping. The NH4VO3 with purity of 99.7% was obtained by two steps of separations and studied by the analyses of XRD, SEM and particle size distribution (PSD). The reactions of extraction and stripping in the separation processes were investigated in order to 1
establish a firm conclusion. Keywords: Annular centrifugal contactors, Selective extraction, Stripping, Two-step separation, NH4VO3, Leaching solution
1. Introduction The industrial chromium-bearing vanadium slag (V-Cr slag) emitted from the production of yellow phosphorus, the company of special steel additive and hydrometallurgy, can be disposed to reach the targets of reducing environmental pollution and reusing metal resources by the salt roasting process (Fig. S1 in supplementary material) [1, 2]. High purity of NH4VO3/V2O5 was obtained by this industrial disposal method [3, 4]. NH4VO3 is promising materials for batteries and catalysts due to their excellent physicochemical properties [5-7]. The salt roasting process for the dispose of industrial V-Cr slag was successfully used in industrial application in Liaoning province of China [3]. Among all units, the solvent extraction is one of the most important and key steps, which can be used for the separation of V(V) from other ions in leaching solution. The primary separation of V(V) from leaching solution was reached by the solvent extraction. The extractant primary amine N1923 with high-cost can be reused after stripping, and the reuse efficiency of it is significantly important to the economic benefits for disposing the V-Cr slag. Considering the cost of disposing V-Cr slag and the economic benefits for the reuse of heavy metals, the efficiencies of extraction and reuse of extractants were called to meet the demand of sustainable development. Reducing the time of contact/resident and stratification is a better way to improve the extraction and separation efficiency of V(V) from in the leaching solution. Taking into account of the vanadium and chromium were the highest oxidation states (i.e., +5 and +6), the oxidation of primary amines extractants [8] is increased with increase of the contact time of the two phases (i.e., the organic phase and aqueous phase). Reducing the contact time of two phases or changing the extractants is essential to improve the efficiency of reuse of extractants in industrial application. The current extraction equipment of the multistage mixer-settlers used in industrial application 2
were insufficient to reach the rapid separation of V(V) from the leaching solution due to the long contact and stratification time. It is an urgent work to investigate a new kind of equipments with high extraction efficiency. The ACCs, with good characters of fast and excellent phase separation, high mass transfer efficiency in unit time, have been used in many separation processes. Firstly, the total partitioning process for high level liquid waste was improved by ACCs in the nuclear industry[9]. The deep separation of Nd3+ and Fe3+ was carried out by non-equilibrium solvent extraction with ACCs in order to find an efficient method to avoid third phase formation in the TRPO process[10]. Secondly, phenol and p-cresol in wastewater were efficiently extracted with ACCs [11, 12]. The extraction separations of aqua-/lipo-soluble bioactive compounds and many chiral molecules were studied by multistage countercurrent fractional extraction with ACCs [13-17]. To our concern, the deep separation of V(V) and Cr(VI) in leaching solution has been carried out by 21 stages countercurrent extraction using ACCs[4]. Recently, two-step method for separation of chemical compounds from liquid-liquid/solid phases was investigated in the field of chemical engineering [18, 19]. Although one-step method of extraction using ACCs can completely separate V(V) and Cr(V) with contact/resident time of 25.2min[4], more rapid separation method for the end-product of NH4VO3 will be considered to use for industrial application due to the economic benefits. In this paper, with the initial pH value of 5.0 in the leaching solution and extractant (sulfated primary amine N1923), the new methods of four-stage countercurrent extraction using ACCs was investigated to rapidly separate V(V) from leaching solution for recovering heavy metals from V-Cr slag. The 99.7 wt% NH4VO3 was obtained by stripping, which was a reactive crystallization process. The obtained NH4VO3 can also be used for making high purity (99.996 wt%) of commercial NH4VO3. This new separation method was studied to improve extraction efficiency with very short contact/resident time of the two phases. The advantages of the novel extraction and separation method were discussed in order to obtain more information with the aim of pilot-scale production.
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2．Materials and methods 2.1 Materials In this work the stock solution of V(V) and Cr(VI) was obtained from CITIC Jinzhou vanadium Industry Co., Ltd. (Liaoning Province, China). The main compositions of the leaching solution are listed in Table 1. Table 1.Chemcial components of the leaching solution Element
Na
Al
SiO2
Mo
Ti
Concentration, g/L
19.60
0.03
0.17
0.06
0.03
SO42-*
V
Cr
Element
Fe
1-*
Cl
Concentration, g/L 0.02 7.85 18.75 23.70 1.52 *The anions were determined by ion chromatography, the others were measured by ICP-OES
The extractant was consisted of 15vol.% sulfated primary amine , 5vol.% phase modifier，80vol.% sulfonated kerosene as diluents. Sulfated primary amine N1923 can be obtained by the reaction of primary amine N1923 (ChengDu Aike Chemical Reagent Co., Ltd, with a purity of 98%) and sulfuric acid solution (9.2mol/L), as shown in equation 1. 2RNH 2org H 2 SO4aq ( RNH3 )2 SO4org
(1)
where, R represents C19H39, C21H43 and C23H47, org represents organic phase, aq represents aqueous phase, and the average molar mass of N1923 is 310.30g/mol. N1923 is C19-C23 secondary alkyl primary amine. The commercial sulfonated kerosene is used as the diluents. The modifier LK-N21X is the mixture of ester and aliphatic alcohol (analytical grade) and its solubility is about 0.037g/100g water at 298.15K. The reagents (Table 2) are all of analytical grade and used without further purification. The water used in all experiments is ultra-pure water with specific resistance more than 18.2MΩcm (Millipore Milli-Q). The 25-28 wt% of ammonia solution is used for stripping. The pH value of the leaching solution is modulated with sulfuric acid solution (9.2mol/L).
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Table 2.Source and purity of chemicals used in the work Chemicals N1923
Source ChengDu Aike Chemical
Mass purity ≥98%
Reagent Co., Ltd (China) Sulfuric acid
Beijing Chemical works (China)
95%-98%
Sulfated kerosene
Beijing Chemical works (China)
98%
Ammonia solution
Xilong Chemical Co., Ltd (China)
25-28%
Ethanol
Beijing Chemical works (China)
≥99.8%
Acetone
Beijing Chemical works (China)
≥99.7%
Nitric acid
Beijing Chemical works (China)
65-68%
Hydrochloric acid
Beijing Chemical works (China)
36-38%
2.2 Analytical method The concentrations of anion in the leaching solution were analyzed by DX-500 ion Chromatography (DIONEX, USA). The concentrations of the vanadium and chromium in the leaching solution/raffinate were measured using an inductively coupled plasma-optical emission spectrometer (ICP-OES, iCAP6300, PerkinElmer, USA) at the corresponding wavelengths with the correlation degree of standard curve≧99.99%. The concentrations of these metallic ions in the organic phase were calculated from mass balance. The pH values of the leaching solutions were analyzed by a pH meter with an uncertainty of 0.01 (Delta320, Mettler, Switzerland). All the samples were carried out in the same conditions three times. The morphology was observed by a scanning electron micrometer (SEM, JSM-7610F, JEOL Ltd, Japan). The crystal structures of NH4VO3 powder was characterized by an X-ray diffractmeter with Cu Ka radiation (XRD, Smartlab, Rigaku Corportion, Japan) . The particle size distribution of NH4VO3 was analyzed by laser particle analysis instrument (Mastersizer 2000, Malvern Instrument, UK).
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2.3 Formulas The extraction percentages of V(V) and Cr(V) (EV and ECr), separation factor (βV/Cr), and recovery yield of V(V) [(RV)] were calculated as follows: EV
ECr
V / Cr
RV
VS CS V - VR CRV VS CS V
100
VS CS Cr - VRCRCr VS CS Cr
CS (V ) CR (V ) CR (V )
100
CR (Cr ) CS (Cr ) CR (Cr )
m( NH 4VO3 ) / M ( NH 4VO3 ) ( EV CS (V ) VS ) / M（V )
(2)
(3)
(4)
(5)
The VS and VR represent the volumes of the stock and raffinate solution, respectively. CS(V) (g/L), CR(V) (g/L), CS(Cr) (g/L) and CR(Cr) (g/L) represent the concentrations of vanadium and chromium in the stock and raffinate solution, respectively. The m(NH4VO3) represents the weight of powders (g). The M(NH4VO3) and M(V) represent the molar mass of NH4VO3 and V (g/mol), respectively.
2.4 Design of two-step separation processes The route of two-step separation to prepare NH4VO3 from leaching solution is shown in Fig. 1. In the first step of separation procedure, most of V(V) and part of Cr(VI) were extracted from leaching solution, and the ions and compound of Na+, SO42-, Cl-, SiO2, Mo2+ were remained in the raffinate. The powder of NH4VO3 were obtained by the second separation step of stripping (i.e., reactive crystallization), and the (NH4)2Cr2O7 was remained in the mother liquid due to the different solubilities of NH4VO3 and (NH4)2Cr2O7 in the mother liquor [20-22].
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Fig. 1.Flow chart of two-step separation
2.5 Apparatus Annular centrifugal contactors (ACCs) with 20mm rotor diameter were made at the Institute of Nuclear and New Technology[9]. The hold-up volume is about 20 ml, and the suggested rotor speed is from 2900 r/min to 5500 r/min. The main structures of the equipment are made of stainless steel (Fig. 2).
Fig. 2.ACC with 20-mm-diam; (a): housing module; (b): rotor module.
2.6 Extraction and stripping methods The 1-4 stages extraction with ACC/ACCs are shown in Figure 3(a)-(d), respectively. The stripping was shown in Figure 3(e). The extractions with ACC/ACCs (heavy-weir diameter of 10.5mm) were carried out at the initial pH of 5.0 in the leaching solution. The flow ratio of heavy phase to light phase is 1:1. The rotor speed of the ACC is from 3030 to 4869 r/min, Total flow rate of two phases is from 0.25 to 1.95 L/h. The 7
specific steps for operating ACC/ACCs were described in our published paper[4]. The loaded organic phase contained V(V) was stripped with 25-28 wt% of ammonia solution at the temperature of 318.15K for more than 21 min, and the stirring speed was 100-150 rpm. All the extraction experiments were carried out at normal atmospheric pressure and temperature of 298.15K unless stated otherwise.
Fig. 3.1-4 stages of extraction with ACCs and stripping
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3. Results and Discussion 3.1 Effect of rotor speed and total flow on extraction of vanadium with ACC The central composite design was used to estimate the contribution and coefficient of parameters and their interactions that screened by Analysis of Variance (ANOVA) at 95% confidence interval, which minimized the cost and errors[23]. The rotor speed (Rs) and total flow (v) are the significant factors that strongly influence the extraction percentage of V(V) when the flow ration (A/O) is 1. In this model, 13 random experiments (Table S1 in supplementary material) were selected to investigate the effect of the two variables on E V by ANOVA according to Fisher’s statistical analysis. As shown in Table S2 (supplementary material) the criterion for significant contribution of each variable was P-value less than 0.05 and F-value more than 0.05, which showed that the two factors had significant contribution in the model. When the flow ratio (A/O) is 1, analysis of results by response surface methodology (RSM) for plotting EV (%) versus the two variables is investigated and is shown in Fig. 4. Based on the data analysis, the semi-empirical expression for evaluation of E V (%) is obtained as equation 6:
Fig. 4.Effect of rotor speed and total flow on extraction efficiency with ACC (flow ratio (A/O) = 1)
EV=73.75+5.08Rs×10-3-8.56v 9
(6)
From equation 6, it is concluded that the extraction percentage of vanadium (V) is increased with the increase of Rs and the decrease of v. Two immiscible liquids are mixed by turbulent Taylor-vortex flow in the mixing zone of ACC[24]. Extraction reaction and mass transfer occur through the liquid-liquid interfacial area produced by the turbulent effect. In another word, extraction efficiency is determined by the degree of two immiscible phase turbulence. The degree of turbulence is increased with the increase of the rotor speed in the ACC. With the decrease of v, the contact/residence time of two phases in the annular zone is increased, resulting in high EV in the extraction process. Considering the operation stability of ACC and extraction efficiency per unit time, the Rs of 4600 r/min and the v of 1.0L/h were selected for the multistage countercurrent extraction with ACCs. If Rs=4600r/min and v=1.0L/h, the prediction value of EV was 88.6% from the equation 6.
3.2 Effect of stage number on the EV and βV/Cr with ACC/ACCs The experimental results of EV and βV/Cr with different stage numbers (i.e., one, two, three and four stages countercurrent extraction with ACC/ACCs) are presented in Fig. 5. The EV is 87.5% by the single-stage extraction with ACC, and the prediction value from equation 6 is 88.6 %. The error between the real value and prediction value is 1.2%, indicating the experiments of condition carried out in section 3.1 is good for guiding the extraction process. It is shown that the EV is increased with the increase of stage numbers of ACCs. With four stages countercurrent extraction using ACCs, EV can reach 99.6% and almost all vanadium (V) were extracted and separated from the leaching solution. The βV/Cr is increased with the increase of stage number, and the value of it can reach 273.9 with four stages countercurrent extraction using ACCs (Fig. 5b). The deep separation of V(V) and Cr(VI) is reached by extractions using ACCs.
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Fig. 5.Effect of stage number on EV and βV/Cr using ACC/ACCs (Error bars were calculated based on tripicate experiments)
3.3 Effect of four-stage countercurrent extraction on contact/resident time Separation of V(V) and Cr(VI) in leaching solution by four-stage countercurrent extraction using ACCs, the contact/resident time of two immiscible liquids was obtained by the following equation 7 [10]:
t
V 60 v
(7)
where t represents the contact time (min), V represents the liquid hold-up volume of the mixing zone in ACC (L), v represents the total flow rate of two phases (L/h). From Fig. 6, it was concluded that the EV and βV/Cr were reached 99.6% and 273.9 with the contact/resident time of 4.8 min. According to the previous paper [1], the biggest EV of 95.9% with βV/Cr of 495. To our interest, the EV obtained by this novel method was higher than the values used by the previous methods (i.e., multistage mixer-settlers used for industrial manufacture and oscillation extraction reported in published papers) although the βV/Cr was less than the other methods (Table 3). With the increase of the contact/resident time of two immiscible liquids in oscillation extraction, the extraction efficiency of V(V) was decreased.
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Fig. 6.Effect of contact time on EV and βV/Cr using ACC/ACCs
Table 3.Separation results for difference extraction methods Initial pH
Extractant
methods
Contact time, min
EV,%
ECr,%
βV/Cr
5.0
Sulphated primary amine N1923 Primary amine N1923 Primary amine LK-N21
ACCs
4.8
99.6
47.6
273.9
ACCs
25.1
95.1
0
∞
OE
45
94.5
2.91
573
6.1[4] 5.0[1]
OE-Oscillation extraction
As for extraction of V(V) and Cr(VI), the contact time with ACC/ACCs is the same with the resident time in the process of extraction when two phases begin to flow into the ACC. The contact/resident time of two phases in ACC/ACCs is equal to the time of mass transfer. The extraction efficiency of V(V) is greatly improved. Based on the published papers[1, 25], the total time of agitation and stratification for separating V(V) and Cr(VI) in unit volume of leaching/aqueous solution was 45 min with a separating funnel. As for four-stage countercurrent extraction using ACCs, the total contact/resident time per unit volume of leaching/aqueous solution was 4.8 min. The results indicated the contact/resident time for disposing per unit volume of leaching/aqueous solution can be saved 89% by detailed comparison between four-stage countercurrent extraction using ACCs and oscillation extraction. In other word, 12
separation efficiency per unit volume of leaching/aqueous solution has been improved.
3.4 Stripping for NH4VO3 According to the first step separation method of extraction using ACCs, 23.61g/L of vanadium and 0.72g/L of chromium were extracted in the organic phase. Vanadium in the loaded organic phase can be recovered with NH4VO3 by stripping (equations 9-10 in section 4.5), and chromium in the leaching/aqueous phase can be recovered by reduction reaction. Effect of the molar ratio of NH3·H2O to vanadium (V) on recovery yield (RV) are presented in supplementary material (Fig. S4). The highest RV was 68.5% by the molar ratio of 1.3. The XRD patterns of NH4VO3 are shown in Fig. 7(a) and it agrees well with the standard pattern peaks. The SEM image of the recovered NH4VO3 is presented in Fig. 7(b), and it was noticed that the plate-like crystals of NH4VO3 were solitary or aggregate state. The particle size distribution (Fig. 7(c)) of recovered NH4VO3 was presented and found the D(50) was 28.336 µm. To accurately calculate the purity of NH4VO3, the powder of recovered NH4VO3 was further dissolved by aqua regia and its purity was measured by ICP-OES (Table 4). The mass percentage of NH4VO3 was accounted for 99.7 wt %.
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Fig. 7.XRD patterns of the recovered NH4VO3 and standard powder diffraction of NH4VO3 (a), SEM (b) and particle size distribution of the recovered NH4VO3 (c) (D-diameter)
Table 4.The purity of NH4VO3 recovered from leaching solution Content (wt. %)
(NH4)2Cr2O7
Na2SO4
Al2O3
SiO2
NH4VO3
FeCl3
MoO2
Recovered NH4VO3
0.276
0.002
0.008
0.011
99.68
0.016
0.005
3.5 Chemical reactions of extraction and stripping Chemical reactions in extraction and stripping are essential to optimize the whole separation technology. When the two phases start to contact, the extractant of sulfated primary amine N1923 can 14
react with the vanadium and chromium to form metal-organic compounds by an ion exchange reaction[26], and the chemical reaction is shown as equation 8. The metal-organic compounds can distribute over the organic phase but not the aqueous phase. Then vanadium can be selectively extracted from the aqueous phase with the separation of the two phases. However, a small part of the chromium compounds can be extracted into the organic phase too. MepOq (OH )r v 0.5v( RNH3 )2 SO4 ( RNH3 )v MepOq (OH )r 0.5vSO42
(8)
where, Me means V or Cr, p, q, r, m and ν are stoichiometric numbers in chemical reactions. According to diagram[26] of V(V)-OH- species and the species[27] of Cr(VI) in aqueous solution, the different pH values and concentrations of V(V) and Cr(VI) in the process of four-stage countercurrent extraction using ACCs are presented in Fig. 8 and Table 5, and the main chemical reactions are listed in Table 6.
Fig. 8.Process of 1-4 stages extraction with ACCs, (a): extraction of V(V); (b): extraction of Cr(VI)
Table 5.Concentrations of V(V) and Cr(VI), pH at the end of 1-4stage extraction Stage
pHe
CR(V) (g/L)
CR(Cr) (g/L)
1 2 3 4
8.1 8.0 7.9 7.8
2.96 1.78 0.92 0.09
0.58 0.68 0.77 0.80
pHe—the equilibrium pH at the end of extraction, CR(V )—the concentration of V(V) in the raffinate at the end of extraction, CR(Cr)—the concentration of Cr(VI) in the raffinate at the end of extraction.
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Table 6.Chemical reactions in extraction process Stage number 1
2
pH0
Main species
Main equations
5.0
V10O27(OH)5Cr2O72-
8.1
V3O93CrO42-
V10O27(OH)5- + 2.5(RNH3)2SO4 = (RNH3)5V10O27(OH) + 2.5SO42Cr2O72- + (RNH3)2SO4 = (RNH3)2Cr2O7 + SO425(RNH3)2Cr2O7 + 2V10O27(OH)5- = 2(RNH3)5V10O27(OH) + 5Cr2O72V3O93- + 1.5(RNH3)2SO4 = (RNH3)3V3O9 + 1.5SO42CrO42- + (RNH3)2SO4 = (RNH3)2CrO4 + SO423(RNH3)2CrO4 + 2V3O93- =2 (RNH3)3V3O9 + 3CrO42The same as stage 2 The same as stage 2
3 8.0 4 7.9 pH0= the initial pH
Considering the two species of (RNH3)5V10O27(OH) and (RNH3)3V3O9 after extraction, the acid-base neutralization of stripping are described by equations 9-10.
RNH3 5 V10O27 OH + 10NH3 H 2O 10NH4VO3 5RNH 2 8H 2O RNH3 3 V3O9 + 3NH3 H 2O 3NH 4VO3 3RNH 2 3H 2O
(9) (10)
4. Conclusions It was demonstrated that V(V) and Cr(VI) in the leaching solution were rapid separated by four-stage countercurrent extraction with ACCs using sulfated primary amine N1923 as extractant. The NH4VO3 with purity of 99.7 wt% was obtained by stripping. The V(V) and Cr(VI) can be firstly extracted and separated from leaching solution using the first step separation of four-stage countercurrent extraction with ACCs, and the separation of V(V) and Cr(VI) can be reached by the second step separation of stripping. Compared with the traditional extraction method (i.e., extraction with multistage mixer-settlers and stripping) used in industry, the contact time of two phases used this novel method was decreased sharply and the efficiency of mass transfer was greatly improved. The oxidation of extractant was effectively prevented with the decrease of the contact/resident time for two immiscible phases. In conclusion, the two-step separation method using ACCs has great potential in separating V(V) 16
from leaching/aqueous solution for the end-product of NH4VO3/V2O5. The efficiencies of extractive separation and repeated utilization of extractants were improved using this new method, thereby offering significant advantages over conventional processes.
Acknowledgments This work was financially supported by the Youth Innovation Promotion Association, CAS (No.2016042), National Natural Science Foundation (Grant No.51425405) and National Key Technology Support Program of China (No.2015BAB02B05).
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p-cresol using centrifugal extractors, Chinese Journal of Chemical Engineering, 15 (2007) 209-214. [13] Y. Cao, H. Xing, Q. Yang, B. Su, Z. Bao, R. Zhang, Y. Yang, Q. Ren, High performance separation of sparingly aqua-/lipo-soluble bioactive compounds with an ionic liquid-based biphasic system, Green Chemistry, 14 (2012) 2617-2625. [14] K. Tang, H. Zhang, Y. Liu, Experimental and simulation on enantioselective extraction in centrifugal contactor separators, AIChE Journal, 59 (2013) 2594–2602. [15] P. Zhang, Z. Hui, K. Tang, J. Yi, H. Yan, Influence of pH on enantioselective extraction of aromatic acid enantiomers in centrifugal contactor separators: experiments and simulation, Separation & Purification Technology, 141 (2015) 68-75. [16] K. Tang, Y. Wang, P. Zhang, Y. Huang, G. Dai, Process optimization of continuous liquid-liquid extraction in centrifugal contactor separators for separation of oxybutynin enantiomers, Separation & Purification Technology, 150 (2015) 170-178. [17] K. Tang, P. Wen, P. Zhang, Y. Huang, Studies on multistage enantioselective liquid–liquid extraction of amino-(4-nitro-phenyl)-acetic acid enantiomers using CuPF6{(S)-BINAP}: experiments and modeling, Separation & Purification Technology, 134 (2014) 100-109. [18] C. Zhang, P. Li, B. Cao, Fabrication of superhydrophobic–superoleophilic fabrics by an etching and dip-coating two-step method for oil–water separation, Industrial & Engineering Chemistry Research, 55 (2016) 5030-5035. [19] M. Yuliana, B.T. Nguyen-Thi, S. Faika, L.H. Huynh, F.E. Soetaredjo, Y.H. Ju, Separation and purification of cardol, cardanol and anacardic acid from cashew (Anacardium occidentale L.) nut-shell liquid using a simple two-step column chromatography, Journal of the Taiwan Institute of Chemical Engineers, 45 (2014) 2187-2193. [20] M. Trypuć, K. Białowicz, Solubility of NH4 VO3 in water + ammonia, Journal of Chemical & Engineering Data, 42 (1997) 318-320. [21] F. Liu, P. Ning, H. Cao, Z. Li, Y. Zhang, Solubilities of NH4VO3 in the NH3–NH4+–SO42––Cl––H2O system and modeling by the Bromley–Zemaitis Equation, Journal of Chemical & Engineering Data, 58 (2013) 1321-1328. [22] S.F. Kudryashov, O.S. Kudryashova, L.P. Filippova, Solubility in the Na 2Cr2O7-(NH4)2Cr2O7-K 2Cr2O7-H2O system, Russian Journal of Inorganic Chemistry, 55 (2010) 594-601. [23] M. Arabi, M. Ghaedi, A. Ostovan, J. Tashkhourian, H. Asadallahzadeh, Synthesis and application of molecularly imprinted nanoparticles combined ultrasonic assisted for highly selective solid phase extraction trace amount of celecoxib from human plasma samples using design expert (DXB) software, Ultrasonics Sonochemistry, 33 (2016) 67-76. [24] S. Vedantam, J.B. Joshi, Annular centrifugal contactors—a review, Chemical Engineering Research and Design, 84 (2006) 522-542. [25] P. Ning, H. Cao, X. Lin, Y. Zhang, The crud formation during the long-term operation of the V(V) and Cr(VI) extraction, Hydrometallurgy, 137 (2013) 133-139. [26] P. Nekovář, D. Schrötterová, Extraction of V(V), Mo(VI) and W(VI) polynuclear species by primene JMT, Chemical Engineering Journal, 79 (2000) 229-233. [27] D. Mohan, K.P. Singh, V.K. Singh, Trivalent chromium removal from wastewater using low cost activated carbon derived from agricultural waste material and activated carbon fabric cloth, Journal of Hazardous Materials, 135 (2006) 280-295.
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Graphical Abstract
Highlights 1. Rapid selective extraction of V(V) from leaching solution was reached using ACCs 2. The 99.7 wt% of NH4VO3was obtained by the two-step separation method 3. The sulfated primary amine N1923 was used for the extraction separation of V(V) and Cr(VI) 4. The second step of separation of stripping was investigated
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S1383-5866(17)30985-1 http://dx.doi.org/10.1016/j.seppur.2017.06.078 SEPPUR 13856
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
29 March 2017 14 June 2017 30 June 2017
Please cite this article as: X. Jing, J. Wang, H. Cao, P. Ning, Z. Sun, Rapid selective extraction of V(V) from leaching solution using annular centrifugal contactors and stripping for NH4VO3, Separation and Purification Technology (2017), doi: http://dx.doi.org/10.1016/j.seppur.2017.06.078
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Rapid selective extraction of V(V) from leaching solution using annular centrifugal contactors and stripping for NH4VO3 Xiaohua Jing1,2, Jianyou Wang1*, Hongbin Cao2, Pengge Ning2*, Zhi Sun2 1. College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China 2. Beijing Engineering Research Centre for Process Pollution Control, Division of Environment Technology and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
*Corresponding authors at: No. 1, Beier Street, Zhongguancun, Haidian District, Beijing 100190, China (Pengge Ning). Tel/Fax: +86 10 82544845. No. 38, Tongyan Road, Haihe Education Park, Jinnan District, Tianjin 300350 (Jianyou Wang). Tel/Fax: +86 22 23501117 E-mail address:
pgning @ipe.ac.cn(P. Ning). [email protected] (J. Wang)
Abstract: The efficient and rapid selective extraction of V(V) from leaching solution with sulfated primary amine N1923 was demonstrated. In the single-stage extraction using annular centrifugal contactor (ACC), the influence of the total flow and the speed rotor on extraction percentage of V(V) was investigated using central composite design (CCD), and the results of experimental conditions were analyzed by analysis of variance. The current concentrations of V(V) and Cr(VI) in leaching solution were 23.70g/L and 1.52g/L, respectively. 99.6% of vanadium was extracted and separated from the aqueous solution by employing four-stage countercurrent extraction with annular centrifugal contactors (ACCs). The total contact/resident time of the two phases was 4.8 min, and the separation factor of V(V) and Cr(VI) was 273.9. The two metals in leaching solution can be separated primarily, and then 23.61g/L V(V) and 0.72g/L Cr(VI) in loaded organic phase can be further separated by the stripping. The NH4VO3 with purity of 99.7% was obtained by two steps of separations and studied by the analyses of XRD, SEM and particle size distribution (PSD). The reactions of extraction and stripping in the separation processes were investigated in order to 1
establish a firm conclusion. Keywords: Annular centrifugal contactors, Selective extraction, Stripping, Two-step separation, NH4VO3, Leaching solution
1. Introduction The industrial chromium-bearing vanadium slag (V-Cr slag) emitted from the production of yellow phosphorus, the company of special steel additive and hydrometallurgy, can be disposed to reach the targets of reducing environmental pollution and reusing metal resources by the salt roasting process (Fig. S1 in supplementary material) [1, 2]. High purity of NH4VO3/V2O5 was obtained by this industrial disposal method [3, 4]. NH4VO3 is promising materials for batteries and catalysts due to their excellent physicochemical properties [5-7]. The salt roasting process for the dispose of industrial V-Cr slag was successfully used in industrial application in Liaoning province of China [3]. Among all units, the solvent extraction is one of the most important and key steps, which can be used for the separation of V(V) from other ions in leaching solution. The primary separation of V(V) from leaching solution was reached by the solvent extraction. The extractant primary amine N1923 with high-cost can be reused after stripping, and the reuse efficiency of it is significantly important to the economic benefits for disposing the V-Cr slag. Considering the cost of disposing V-Cr slag and the economic benefits for the reuse of heavy metals, the efficiencies of extraction and reuse of extractants were called to meet the demand of sustainable development. Reducing the time of contact/resident and stratification is a better way to improve the extraction and separation efficiency of V(V) from in the leaching solution. Taking into account of the vanadium and chromium were the highest oxidation states (i.e., +5 and +6), the oxidation of primary amines extractants [8] is increased with increase of the contact time of the two phases (i.e., the organic phase and aqueous phase). Reducing the contact time of two phases or changing the extractants is essential to improve the efficiency of reuse of extractants in industrial application. The current extraction equipment of the multistage mixer-settlers used in industrial application 2
were insufficient to reach the rapid separation of V(V) from the leaching solution due to the long contact and stratification time. It is an urgent work to investigate a new kind of equipments with high extraction efficiency. The ACCs, with good characters of fast and excellent phase separation, high mass transfer efficiency in unit time, have been used in many separation processes. Firstly, the total partitioning process for high level liquid waste was improved by ACCs in the nuclear industry[9]. The deep separation of Nd3+ and Fe3+ was carried out by non-equilibrium solvent extraction with ACCs in order to find an efficient method to avoid third phase formation in the TRPO process[10]. Secondly, phenol and p-cresol in wastewater were efficiently extracted with ACCs [11, 12]. The extraction separations of aqua-/lipo-soluble bioactive compounds and many chiral molecules were studied by multistage countercurrent fractional extraction with ACCs [13-17]. To our concern, the deep separation of V(V) and Cr(VI) in leaching solution has been carried out by 21 stages countercurrent extraction using ACCs[4]. Recently, two-step method for separation of chemical compounds from liquid-liquid/solid phases was investigated in the field of chemical engineering [18, 19]. Although one-step method of extraction using ACCs can completely separate V(V) and Cr(V) with contact/resident time of 25.2min[4], more rapid separation method for the end-product of NH4VO3 will be considered to use for industrial application due to the economic benefits. In this paper, with the initial pH value of 5.0 in the leaching solution and extractant (sulfated primary amine N1923), the new methods of four-stage countercurrent extraction using ACCs was investigated to rapidly separate V(V) from leaching solution for recovering heavy metals from V-Cr slag. The 99.7 wt% NH4VO3 was obtained by stripping, which was a reactive crystallization process. The obtained NH4VO3 can also be used for making high purity (99.996 wt%) of commercial NH4VO3. This new separation method was studied to improve extraction efficiency with very short contact/resident time of the two phases. The advantages of the novel extraction and separation method were discussed in order to obtain more information with the aim of pilot-scale production.
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2．Materials and methods 2.1 Materials In this work the stock solution of V(V) and Cr(VI) was obtained from CITIC Jinzhou vanadium Industry Co., Ltd. (Liaoning Province, China). The main compositions of the leaching solution are listed in Table 1. Table 1.Chemcial components of the leaching solution Element
Na
Al
SiO2
Mo
Ti
Concentration, g/L
19.60
0.03
0.17
0.06
0.03
SO42-*
V
Cr
Element
Fe
1-*
Cl
Concentration, g/L 0.02 7.85 18.75 23.70 1.52 *The anions were determined by ion chromatography, the others were measured by ICP-OES
The extractant was consisted of 15vol.% sulfated primary amine , 5vol.% phase modifier，80vol.% sulfonated kerosene as diluents. Sulfated primary amine N1923 can be obtained by the reaction of primary amine N1923 (ChengDu Aike Chemical Reagent Co., Ltd, with a purity of 98%) and sulfuric acid solution (9.2mol/L), as shown in equation 1. 2RNH 2org H 2 SO4aq ( RNH3 )2 SO4org
(1)
where, R represents C19H39, C21H43 and C23H47, org represents organic phase, aq represents aqueous phase, and the average molar mass of N1923 is 310.30g/mol. N1923 is C19-C23 secondary alkyl primary amine. The commercial sulfonated kerosene is used as the diluents. The modifier LK-N21X is the mixture of ester and aliphatic alcohol (analytical grade) and its solubility is about 0.037g/100g water at 298.15K. The reagents (Table 2) are all of analytical grade and used without further purification. The water used in all experiments is ultra-pure water with specific resistance more than 18.2MΩcm (Millipore Milli-Q). The 25-28 wt% of ammonia solution is used for stripping. The pH value of the leaching solution is modulated with sulfuric acid solution (9.2mol/L).
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Table 2.Source and purity of chemicals used in the work Chemicals N1923
Source ChengDu Aike Chemical
Mass purity ≥98%
Reagent Co., Ltd (China) Sulfuric acid
Beijing Chemical works (China)
95%-98%
Sulfated kerosene
Beijing Chemical works (China)
98%
Ammonia solution
Xilong Chemical Co., Ltd (China)
25-28%
Ethanol
Beijing Chemical works (China)
≥99.8%
Acetone
Beijing Chemical works (China)
≥99.7%
Nitric acid
Beijing Chemical works (China)
65-68%
Hydrochloric acid
Beijing Chemical works (China)
36-38%
2.2 Analytical method The concentrations of anion in the leaching solution were analyzed by DX-500 ion Chromatography (DIONEX, USA). The concentrations of the vanadium and chromium in the leaching solution/raffinate were measured using an inductively coupled plasma-optical emission spectrometer (ICP-OES, iCAP6300, PerkinElmer, USA) at the corresponding wavelengths with the correlation degree of standard curve≧99.99%. The concentrations of these metallic ions in the organic phase were calculated from mass balance. The pH values of the leaching solutions were analyzed by a pH meter with an uncertainty of 0.01 (Delta320, Mettler, Switzerland). All the samples were carried out in the same conditions three times. The morphology was observed by a scanning electron micrometer (SEM, JSM-7610F, JEOL Ltd, Japan). The crystal structures of NH4VO3 powder was characterized by an X-ray diffractmeter with Cu Ka radiation (XRD, Smartlab, Rigaku Corportion, Japan) . The particle size distribution of NH4VO3 was analyzed by laser particle analysis instrument (Mastersizer 2000, Malvern Instrument, UK).
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2.3 Formulas The extraction percentages of V(V) and Cr(V) (EV and ECr), separation factor (βV/Cr), and recovery yield of V(V) [(RV)] were calculated as follows: EV
ECr
V / Cr
RV
VS CS V - VR CRV VS CS V
100
VS CS Cr - VRCRCr VS CS Cr
CS (V ) CR (V ) CR (V )
100
CR (Cr ) CS (Cr ) CR (Cr )
m( NH 4VO3 ) / M ( NH 4VO3 ) ( EV CS (V ) VS ) / M（V )
(2)
(3)
(4)
(5)
The VS and VR represent the volumes of the stock and raffinate solution, respectively. CS(V) (g/L), CR(V) (g/L), CS(Cr) (g/L) and CR(Cr) (g/L) represent the concentrations of vanadium and chromium in the stock and raffinate solution, respectively. The m(NH4VO3) represents the weight of powders (g). The M(NH4VO3) and M(V) represent the molar mass of NH4VO3 and V (g/mol), respectively.
2.4 Design of two-step separation processes The route of two-step separation to prepare NH4VO3 from leaching solution is shown in Fig. 1. In the first step of separation procedure, most of V(V) and part of Cr(VI) were extracted from leaching solution, and the ions and compound of Na+, SO42-, Cl-, SiO2, Mo2+ were remained in the raffinate. The powder of NH4VO3 were obtained by the second separation step of stripping (i.e., reactive crystallization), and the (NH4)2Cr2O7 was remained in the mother liquid due to the different solubilities of NH4VO3 and (NH4)2Cr2O7 in the mother liquor [20-22].
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Fig. 1.Flow chart of two-step separation
2.5 Apparatus Annular centrifugal contactors (ACCs) with 20mm rotor diameter were made at the Institute of Nuclear and New Technology[9]. The hold-up volume is about 20 ml, and the suggested rotor speed is from 2900 r/min to 5500 r/min. The main structures of the equipment are made of stainless steel (Fig. 2).
Fig. 2.ACC with 20-mm-diam; (a): housing module; (b): rotor module.
2.6 Extraction and stripping methods The 1-4 stages extraction with ACC/ACCs are shown in Figure 3(a)-(d), respectively. The stripping was shown in Figure 3(e). The extractions with ACC/ACCs (heavy-weir diameter of 10.5mm) were carried out at the initial pH of 5.0 in the leaching solution. The flow ratio of heavy phase to light phase is 1:1. The rotor speed of the ACC is from 3030 to 4869 r/min, Total flow rate of two phases is from 0.25 to 1.95 L/h. The 7
specific steps for operating ACC/ACCs were described in our published paper[4]. The loaded organic phase contained V(V) was stripped with 25-28 wt% of ammonia solution at the temperature of 318.15K for more than 21 min, and the stirring speed was 100-150 rpm. All the extraction experiments were carried out at normal atmospheric pressure and temperature of 298.15K unless stated otherwise.
Fig. 3.1-4 stages of extraction with ACCs and stripping
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3. Results and Discussion 3.1 Effect of rotor speed and total flow on extraction of vanadium with ACC The central composite design was used to estimate the contribution and coefficient of parameters and their interactions that screened by Analysis of Variance (ANOVA) at 95% confidence interval, which minimized the cost and errors[23]. The rotor speed (Rs) and total flow (v) are the significant factors that strongly influence the extraction percentage of V(V) when the flow ration (A/O) is 1. In this model, 13 random experiments (Table S1 in supplementary material) were selected to investigate the effect of the two variables on E V by ANOVA according to Fisher’s statistical analysis. As shown in Table S2 (supplementary material) the criterion for significant contribution of each variable was P-value less than 0.05 and F-value more than 0.05, which showed that the two factors had significant contribution in the model. When the flow ratio (A/O) is 1, analysis of results by response surface methodology (RSM) for plotting EV (%) versus the two variables is investigated and is shown in Fig. 4. Based on the data analysis, the semi-empirical expression for evaluation of E V (%) is obtained as equation 6:
Fig. 4.Effect of rotor speed and total flow on extraction efficiency with ACC (flow ratio (A/O) = 1)
EV=73.75+5.08Rs×10-3-8.56v 9
(6)
From equation 6, it is concluded that the extraction percentage of vanadium (V) is increased with the increase of Rs and the decrease of v. Two immiscible liquids are mixed by turbulent Taylor-vortex flow in the mixing zone of ACC[24]. Extraction reaction and mass transfer occur through the liquid-liquid interfacial area produced by the turbulent effect. In another word, extraction efficiency is determined by the degree of two immiscible phase turbulence. The degree of turbulence is increased with the increase of the rotor speed in the ACC. With the decrease of v, the contact/residence time of two phases in the annular zone is increased, resulting in high EV in the extraction process. Considering the operation stability of ACC and extraction efficiency per unit time, the Rs of 4600 r/min and the v of 1.0L/h were selected for the multistage countercurrent extraction with ACCs. If Rs=4600r/min and v=1.0L/h, the prediction value of EV was 88.6% from the equation 6.
3.2 Effect of stage number on the EV and βV/Cr with ACC/ACCs The experimental results of EV and βV/Cr with different stage numbers (i.e., one, two, three and four stages countercurrent extraction with ACC/ACCs) are presented in Fig. 5. The EV is 87.5% by the single-stage extraction with ACC, and the prediction value from equation 6 is 88.6 %. The error between the real value and prediction value is 1.2%, indicating the experiments of condition carried out in section 3.1 is good for guiding the extraction process. It is shown that the EV is increased with the increase of stage numbers of ACCs. With four stages countercurrent extraction using ACCs, EV can reach 99.6% and almost all vanadium (V) were extracted and separated from the leaching solution. The βV/Cr is increased with the increase of stage number, and the value of it can reach 273.9 with four stages countercurrent extraction using ACCs (Fig. 5b). The deep separation of V(V) and Cr(VI) is reached by extractions using ACCs.
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Fig. 5.Effect of stage number on EV and βV/Cr using ACC/ACCs (Error bars were calculated based on tripicate experiments)
3.3 Effect of four-stage countercurrent extraction on contact/resident time Separation of V(V) and Cr(VI) in leaching solution by four-stage countercurrent extraction using ACCs, the contact/resident time of two immiscible liquids was obtained by the following equation 7 [10]:
t
V 60 v
(7)
where t represents the contact time (min), V represents the liquid hold-up volume of the mixing zone in ACC (L), v represents the total flow rate of two phases (L/h). From Fig. 6, it was concluded that the EV and βV/Cr were reached 99.6% and 273.9 with the contact/resident time of 4.8 min. According to the previous paper [1], the biggest EV of 95.9% with βV/Cr of 495. To our interest, the EV obtained by this novel method was higher than the values used by the previous methods (i.e., multistage mixer-settlers used for industrial manufacture and oscillation extraction reported in published papers) although the βV/Cr was less than the other methods (Table 3). With the increase of the contact/resident time of two immiscible liquids in oscillation extraction, the extraction efficiency of V(V) was decreased.
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Fig. 6.Effect of contact time on EV and βV/Cr using ACC/ACCs
Table 3.Separation results for difference extraction methods Initial pH
Extractant
methods
Contact time, min
EV,%
ECr,%
βV/Cr
5.0
Sulphated primary amine N1923 Primary amine N1923 Primary amine LK-N21
ACCs
4.8
99.6
47.6
273.9
ACCs
25.1
95.1
0
∞
OE
45
94.5
2.91
573
6.1[4] 5.0[1]
OE-Oscillation extraction
As for extraction of V(V) and Cr(VI), the contact time with ACC/ACCs is the same with the resident time in the process of extraction when two phases begin to flow into the ACC. The contact/resident time of two phases in ACC/ACCs is equal to the time of mass transfer. The extraction efficiency of V(V) is greatly improved. Based on the published papers[1, 25], the total time of agitation and stratification for separating V(V) and Cr(VI) in unit volume of leaching/aqueous solution was 45 min with a separating funnel. As for four-stage countercurrent extraction using ACCs, the total contact/resident time per unit volume of leaching/aqueous solution was 4.8 min. The results indicated the contact/resident time for disposing per unit volume of leaching/aqueous solution can be saved 89% by detailed comparison between four-stage countercurrent extraction using ACCs and oscillation extraction. In other word, 12
separation efficiency per unit volume of leaching/aqueous solution has been improved.
3.4 Stripping for NH4VO3 According to the first step separation method of extraction using ACCs, 23.61g/L of vanadium and 0.72g/L of chromium were extracted in the organic phase. Vanadium in the loaded organic phase can be recovered with NH4VO3 by stripping (equations 9-10 in section 4.5), and chromium in the leaching/aqueous phase can be recovered by reduction reaction. Effect of the molar ratio of NH3·H2O to vanadium (V) on recovery yield (RV) are presented in supplementary material (Fig. S4). The highest RV was 68.5% by the molar ratio of 1.3. The XRD patterns of NH4VO3 are shown in Fig. 7(a) and it agrees well with the standard pattern peaks. The SEM image of the recovered NH4VO3 is presented in Fig. 7(b), and it was noticed that the plate-like crystals of NH4VO3 were solitary or aggregate state. The particle size distribution (Fig. 7(c)) of recovered NH4VO3 was presented and found the D(50) was 28.336 µm. To accurately calculate the purity of NH4VO3, the powder of recovered NH4VO3 was further dissolved by aqua regia and its purity was measured by ICP-OES (Table 4). The mass percentage of NH4VO3 was accounted for 99.7 wt %.
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Fig. 7.XRD patterns of the recovered NH4VO3 and standard powder diffraction of NH4VO3 (a), SEM (b) and particle size distribution of the recovered NH4VO3 (c) (D-diameter)
Table 4.The purity of NH4VO3 recovered from leaching solution Content (wt. %)
(NH4)2Cr2O7
Na2SO4
Al2O3
SiO2
NH4VO3
FeCl3
MoO2
Recovered NH4VO3
0.276
0.002
0.008
0.011
99.68
0.016
0.005
3.5 Chemical reactions of extraction and stripping Chemical reactions in extraction and stripping are essential to optimize the whole separation technology. When the two phases start to contact, the extractant of sulfated primary amine N1923 can 14
react with the vanadium and chromium to form metal-organic compounds by an ion exchange reaction[26], and the chemical reaction is shown as equation 8. The metal-organic compounds can distribute over the organic phase but not the aqueous phase. Then vanadium can be selectively extracted from the aqueous phase with the separation of the two phases. However, a small part of the chromium compounds can be extracted into the organic phase too. MepOq (OH )r v 0.5v( RNH3 )2 SO4 ( RNH3 )v MepOq (OH )r 0.5vSO42
(8)
where, Me means V or Cr, p, q, r, m and ν are stoichiometric numbers in chemical reactions. According to diagram[26] of V(V)-OH- species and the species[27] of Cr(VI) in aqueous solution, the different pH values and concentrations of V(V) and Cr(VI) in the process of four-stage countercurrent extraction using ACCs are presented in Fig. 8 and Table 5, and the main chemical reactions are listed in Table 6.
Fig. 8.Process of 1-4 stages extraction with ACCs, (a): extraction of V(V); (b): extraction of Cr(VI)
Table 5.Concentrations of V(V) and Cr(VI), pH at the end of 1-4stage extraction Stage
pHe
CR(V) (g/L)
CR(Cr) (g/L)
1 2 3 4
8.1 8.0 7.9 7.8
2.96 1.78 0.92 0.09
0.58 0.68 0.77 0.80
pHe—the equilibrium pH at the end of extraction, CR(V )—the concentration of V(V) in the raffinate at the end of extraction, CR(Cr)—the concentration of Cr(VI) in the raffinate at the end of extraction.
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Table 6.Chemical reactions in extraction process Stage number 1
2
pH0
Main species
Main equations
5.0
V10O27(OH)5Cr2O72-
8.1
V3O93CrO42-
V10O27(OH)5- + 2.5(RNH3)2SO4 = (RNH3)5V10O27(OH) + 2.5SO42Cr2O72- + (RNH3)2SO4 = (RNH3)2Cr2O7 + SO425(RNH3)2Cr2O7 + 2V10O27(OH)5- = 2(RNH3)5V10O27(OH) + 5Cr2O72V3O93- + 1.5(RNH3)2SO4 = (RNH3)3V3O9 + 1.5SO42CrO42- + (RNH3)2SO4 = (RNH3)2CrO4 + SO423(RNH3)2CrO4 + 2V3O93- =2 (RNH3)3V3O9 + 3CrO42The same as stage 2 The same as stage 2
3 8.0 4 7.9 pH0= the initial pH
Considering the two species of (RNH3)5V10O27(OH) and (RNH3)3V3O9 after extraction, the acid-base neutralization of stripping are described by equations 9-10.
RNH3 5 V10O27 OH + 10NH3 H 2O 10NH4VO3 5RNH 2 8H 2O RNH3 3 V3O9 + 3NH3 H 2O 3NH 4VO3 3RNH 2 3H 2O
(9) (10)
4. Conclusions It was demonstrated that V(V) and Cr(VI) in the leaching solution were rapid separated by four-stage countercurrent extraction with ACCs using sulfated primary amine N1923 as extractant. The NH4VO3 with purity of 99.7 wt% was obtained by stripping. The V(V) and Cr(VI) can be firstly extracted and separated from leaching solution using the first step separation of four-stage countercurrent extraction with ACCs, and the separation of V(V) and Cr(VI) can be reached by the second step separation of stripping. Compared with the traditional extraction method (i.e., extraction with multistage mixer-settlers and stripping) used in industry, the contact time of two phases used this novel method was decreased sharply and the efficiency of mass transfer was greatly improved. The oxidation of extractant was effectively prevented with the decrease of the contact/resident time for two immiscible phases. In conclusion, the two-step separation method using ACCs has great potential in separating V(V) 16
from leaching/aqueous solution for the end-product of NH4VO3/V2O5. The efficiencies of extractive separation and repeated utilization of extractants were improved using this new method, thereby offering significant advantages over conventional processes.
Acknowledgments This work was financially supported by the Youth Innovation Promotion Association, CAS (No.2016042), National Natural Science Foundation (Grant No.51425405) and National Key Technology Support Program of China (No.2015BAB02B05).
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Graphical Abstract
Highlights 1. Rapid selective extraction of V(V) from leaching solution was reached using ACCs 2. The 99.7 wt% of NH4VO3was obtained by the two-step separation method 3. The sulfated primary amine N1923 was used for the extraction separation of V(V) and Cr(VI) 4. The second step of separation of stripping was investigated
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