Recovery of high-purity vanadium from aqueous solutions by a

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Recovery of high-purity vanadium from aqueous solutions by a reusable primary amines N1923 associated with semiquantitative understanding of vanadium species Jiawei Wen, Pengge Ning, Hongbin Cao, Zhi H.I. Sun, Yi Zhang, and Gaojie Xu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00445 • Publication Date (Web): 03 May 2018 Downloaded from http://pubs.acs.org on May 5, 2018

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ACS Sustainable Chemistry & Engineering

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Recovery of high-purity vanadium from aqueous solutions by a reusable

2

primary amines N1923 associated with semiquantitative understanding of

3

vanadium species

4 5

Jiawei Wena,b,c, Pengge Ning*a, Hongbin Caoa,b,c, Zhi Sun a, Yi Zhanga,b,c and Gaojie Xua

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a. Beijing Engineering Research Center of Process Pollution Control, Institute of

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Process Engineering, Chinese Academy of Sciences, Beijing 100190, PR China;

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b. School of Chemical Engineering & Technology, Tianjin University, Tianjin

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300072, PR China.

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c. Collaborative Innovation Center of Chemical Science and Engineering (Tianjin),

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Tianjin 300072, PR China.

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

Corresponding author：： Pengge Ning ([email protected]) Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences Tel: +86 10 82544844 Fax: +86 10 82544845 No. 1 Beierjie, Zhongguancun, Beijing, China

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ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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ABSTRACT

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The recovery of high-purity vanadium has attracted significant attention regarding both

38

sustainability and environmental protection necessities. However, insufficient understanding of

39

vanadium species in aqueous solution constrains further optimization of vanadium recovery

40

process. Here, a closed-loop technical route (extraction and stripping) was realized to recover

41

high-purity vanadium products by in-situ monitoring/controlling vanadium species. The evolution

42

of vanadium species in extraction reaction was semiquantitatively visualized by the system

43

combined with annular centrifugal contactors (ACCs) and electrospray ionization time-of-flight

44

mass spectrometry (ESI-TOF-MS), while the active (V4 and V10 species) and non-active (H2VO4-)

45

vanadium species were identified. In stripping process, the behaviors of vanadium species have

46

been described, which affected morphology of recycled NH4VO3 products. As a result, the

47

transformation pathway of vanadium species in the whole recovery process was performed. Under

48

deep studies of vanadium speciation, pilot-scale experiments have been carried out using actual

49

leaching solution, and high-purity V2O5 products (99.9%) were obtained.

50 51

KEYWORDS: vanadium recovery; high-purity NH4VO3; vanadium species; primary N1923;

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ESI-TOF-MS

53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 2


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INTRODUCTION

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Vanadium is a commercially strategic metal and widely applied in countless high-tech fields,

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such as catalysts, redox flow batteries, and biomedical drugs. Meanwhile, it is considered as an

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emerging contaminant in the Environmental Protection Agency’s candidate contaminant list

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(CCL4)1. Therefore, the recovery of vanadium from solid waste or wastewater has become

77

increasingly important considering both features of resource recycle and less environmental

78

hazard.

79

Solvent extraction is an effective method to recover vanadium from leaching solution, among

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them our group proposed a technical route to extract vanadium from V-Cr slag with pilot-scale

81

and industrial-scale experiments2 (Fig. 1). Nevertheless, most processes referring to vanadium

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recovery, including our route, succeed in effective extraction of vanadium. The purity was still

83

needed to be improved to cope with increasing demand of high-purified vanadium products3.

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Vanadium was extracted and separated from impurities based on the differences between

85

vanadium ions and other elemental ions. It was required to minimize the effects of impurities to

86

prepare high-purified vanadium products. Therefore, understanding these behaviors and

87

interactions of all elements in vanadium-bearing solution, especially that of vanadium ions, has

88

become essential. Iron slag salt roasting

V-Cr slag

leaching

sodium phosphate crystallization

recycling V 2O 5

stripping

precipitation

Cr2O3

89 90

solvent extraction

purification

reduction of chromium

Fig. 1 Flow chart for the resourceful utilization of chromium-bearing vanadium slag.

91 92

To date, considerable efforts have been dedicated exclusively to probing on the behaviors of

93

vanadium in the recovery process. The acidity in aqueous/leaching solution was the main factor in 3



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vanadium extraction4. Zhao et al. demonstrated that ionic liquid-based synergistic extraction of

95

vanadium was strongly dependent on the acidity of aqueous solutions5. The acidity was an

96

important consideration in the formation and transition of different vanadium species6,7, where V1

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species oligomerized into tetramers (V4 species) and decamers (V10 species) with the increase of

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vanadium concentration and acidity

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combinations of vanadium concentration and pH. Hence it is strategic to monitor or control the

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transformation of vanadium species rather than controlling operation conditions of the recovery

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process. Numerous people concerned the role of vanadium species

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extraction paths of vanadium species were performed13 in the competitive extraction of vanadium

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and chromium through phase diagram. Meanwhile, the dynamic equilibrium between extraction

104

reaction and ionic reaction in the aqueous solution influenced the transformation of vanadium

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species, accordingly resulted in the variation of optimal reaction regions in recovery. Therefore,

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unveiling information of vanadium species provided us deep understanding of vanadium

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extraction in high yields, and be beneficial for economical design of vanadium recovery process as

108

well as high-purity vanadium products.

8-10

. The vanadium species may be the same in different

11, 12

, for example, the

109

Even though we knew that vanadium species affected extraction reaction and ultimate purity

110

of vanadium products, there is a lack of study that focuses on tracking transformation pathway of

111

vanadium species during vanadium recovery processes. In this paper, observation of vanadium

112

species transformation pathway in the extraction process was realized based on a novel online

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monitoring system combined with annular centrifugal contactors (ACCs) and electrospray

114

ionization time-of-flight mass spectrometry (ESI-TOF-MS). ACCs were employed to produce

115

intermediates relying on their momentary capacity of phase separation 14, 15. ESI-TOF-MS, a “soft”

116

ionization technique to characterize polyoxometalates (POMs) compounds in polar solvents

117

became a powerful tool for the detecting and tracking of vanadium species18. Furthermore, this

118

online monitoring system is also promising for other transition metal species, which can further

119

expose transform pathways of various transition metal species in secondary resource recovery.

4


16, 17

,

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120

EXPERIMENTAL

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Materials

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Sodium

metavanadate (NaVO3,

CAS 13718-26-8, 99.9%)

was

purchased

from

123

Sigma-Aldrich. Sulfuric acid (H2SO4, 98%) was purchased from Sinopharm Chemical Reagent

124

Co., Ltd. Primary amine N1923 (CH3(CH2)8-10CH(NH2)(CH2)8-10CH3, chemical purity of 93%)

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was supplied by Shanghai Laiya Shi Chemical Co. Ltd. Ammonia solution (NH3, CAS 1336-21-6,

126

25–28%) was purchased from Xilong Chemical Co., Ltd, and ethanol A.R. was purchased from

127

Beijing Chemical Works. 15 vol% of N1923 modified by 6 vol% LK-N21X diluted in kerosene

128

was defined as organic phase. The aqueous phase for lab-scale experiments was prepared using

129

ultra-pure water from a purification system (Milli-Q Direct 8, Millipore). While the aqueous

130

solution used for pilot experiments was actual leaching solution contained 24-25 g/L V (V), 16-18

131

g/L Cr (VI) and, 12 kinds of impurities.

132

Extraction process

133

The experimental setup was shown in Fig. 2. The extraction process was conducted in two

134

sets of ACCs with 20mL hold-up volume, which were made at the Institute of Nuclear and New

135

Technology19. The structure and principle of ACCs were explained in our previous work13. The

136

aqueous solution (0.01–0.08 mol/L V) and the organic phase were flowed into ACCs by two

137

peristaltic pumps, respectively. The phase ratio of the two phases was 1:1, which was in

138

accordance with our previous work20. The mass transferred rapidly under high centrifugal force in

139

ACCs, and then separated two phases flowed into their collectors and flowed out of ACCs through

140

output pipelines. The rotor speed was fixed at 3700 r/min, which was in the range of optimal

141

regions in similar extraction system13. The contact time was calculated by the ratio of liquid

142

hold-up volume (L) of ACCs and total flow rate of two phases (L/h).

143

Stripping process

144

The loaded organic phase contained vanadium was stripped using 2.5% ammonia solution

145

(vaq : vorg=1:3) at the temperature of 318.15 K. Ethanol and water were used to scrub the power. 5



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146

Finally, high-purity NH4VO3 power was obtained after drying in an oven at 328.15 K for ten

147

hours.

148

Characterizations

149

Concentrations of vanadium in aqueous solution were determined by inductive couple

150

plasma-optical emission spectrometry (ICP-OES, PerkinElmer Optima 6300DV), and the pH

151

values of aqueous phase were measured using a Mettler-Tolerdo Delta 320 pH meter. The

152

morphology was observed by a scanning electron micrometer (SEM, JSM-7610 F), and crystal

153

structures of solid materials were characterized by an X-ray diffractmeter (XRD, Smartlab (9)).

154

The concentrations of SO42- ions were detected by an ion chromatograph (ICS-5000+, Thermo).

155

Chemical speciation analyses of vanadium in aqueous solutions were carried out on a Waters

156

Xevo G2-XS TOF mass spectrometer through an electrospray ionization (ESI) interface. The

157

injection flow rate was 5 µL/min, and full scan mass spectra (m/z 50–1000) were operated in a

158

negative ion mode. The capillary voltage was 2.5 kV, and desolvation temperature was set at

159

150°C. Nitrogen (Airgas, >99.99% purity) was used for desolvation gas at 800 L/h. Optimized

160

cone voltage was decided at -20 V, while source temperature was 40°C.

161

Data analysis

162

The extraction yield of vanadium was calculated as follows, where V0 and Ve were initial, and

163

equilibrium volumes of aqueous solution and m0 and me were vanadium concentrations of aqueous

164

solution.

165

EV =

m0V0 − meVe m0V0

166

(1)

167

The vanadium species analysis included two steps. Firstly, different types of vanadium

168

species were verified with characteristic mass peaks coupled with isotope distribution patterns

169

(provided by Masslynx software), most of which were also reported in previous literatures 18, 21-24.

170

The identified vanadium species in aqueous solutions were concluded in Table S1. Secondly, the

171

relative percentages of different vanadium species were semi-quantified according to the relative 6


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172

intensity of vanadium clusters in MS results, which was similar with analysis process of aluminum

173

species 25, 26. The semi-quantified equation was performed as Eq. (2), where Ei and Ej represented

174

the intensity of cluster i, j, respectively. Then the relative mole concentration of interested peak i,

175

ci, was obtained. Details of the calculation process were shown in “Mass spectrometer data

176

analysis” section (Table S2, Fig. S1) of Supporting Information (SI).

ci (%) =

177

Ei ×100% ∑ Ej j =1

(2)

178 179

180 181

Fig. 2 The experimental setup included three parts: extraction part; stripping part; online

182

monitoring part.

183

RESULTS AND DISCUSSION

184

Performances of vanadium species in extraction process

185

The liquid-liquid extraction reaction of vanadium and primary amines N1923 was expressed

186

as Eq. (3) 27. To further study the mechanism and optimize the reaction, liquid-liquid extractions

187

of vanadium from aqueous solutions (0.01–0.08 mol·L-1 V) by 15% primary amines N1923 were

188

conducted, and the results were shown in Fig. 3. The relative ratio of mole quantity of acid and

189

vanadium (n (H)/n (V)) replaced pH values as variables because n (H)/n (V) was more

190

controllable in lab-studies than pH values. 7



m R N H 2 + V x O y n − + n H + → ( R N H 2 )m ( H n V x O y )

191

(3)

192 193

(a)

100 (b) 0.01 mol/L V

36 s 72 s 144 s 216 s

80

0.02 mol/L V 0.04 mol/L V 0.08 mol/L V

80

E x tr a c tio n y ie ld /%

100

E x tr a c tio n y ie ld /%

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 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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60

60 40

40

20

20 0 00.5 194

0.6

0.7

0.8

n(H)/n(V)

0.9

1.0

1.1

0.4

0.6

0.8

1.0

1.2

n(H)/n(V)

195

Fig. 3 (a): effect of reaction time (36–216 s) on the extraction yield at 0.01 mol/L vanadium

196

concentration; (b): effect of vanadium concentration (0.01–0.08 mol/L) on the extraction yield at

197

the same contact time (36 s).

198 199

The reaction time was confirmed in Fig. 3 (a). The extraction yield (Fig. 3(a)) and

200

equilibrium pH (Fig. S2 (a)) were almost the same at 36 s, 72 s, 144 s and 216 s, meaning the

201

reaction almost finished within 36 s. It is different from the condition that occurred in vanadium

202

and chromium coexisted aqueous solution13, indicating that vanadium extraction is much quicker

203

in individual vanadium aqueous solution than mixed vanadium and chromium aqueous solution.

204

The extraction process within 216 s was paid main attention according to above results.

205

The pH values before and after extraction were shown in Table S3 and Fig. S2 (b). The

206

values of initial pH were 2–6, and those of equilibrium pH were 5–7. The equilibrium pH

207

increased sharply when n (H) /n (V) was 1.2 at higher vanadium concentration because high

208

extraction yield resulted in much less dissociative H+ left in aqueous solution. When n (H) /n (V)

209

was 0.4, and initial pH was above 6, the extraction reaction almost did not occur.

210

The extraction yield increased with the addition of acid as shown in Fig. 3 (b). Additional 8


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211

acids were consumed to generate more vanadic acid molecules in the reaction, so additional

212

quantity of acids was in agreement with the trend of extraction yield. The extraction yield in

213

different vanadium concentrations was the same with the increase of n (H) /n (V), which means

214

that n (H) /n (V) was the key factor in the extraction. Furthermore, n (H) /n (V) in aqueous

215

solution decided the distribution of vanadium species, so vanadium chemical speciation was a

216

crucial factor in extraction process.

217

In vanadium extraction process, three changes occurred with the addition of sulfuric acid:

218

firstly, the concentration of SO42- ions increased; secondly, the amount of H+ increased, and pH

219

decreased; and thirdly, distribution of vanadium species changed. That is to say, the concentrations

220

of SO42- ions, H+ and the distribution of vanadium species were three possible factors acted in the

221

reaction. The concentrations of SO42- ions were detected (Fig. S3) during the reaction (0 s, 72 s,

222

144 s and 216 s), which changed little before and after reaction. Thus, the SO42- ions had little

223

effect in vanadium extraction.

224

The increase of H+ and variation of vanadium species occurred synchronously. The H+

225

provided enough acids to form vanadium acid molecules, on the other hand, it also affected the

226

distribution of vanadium species. The extraction yield was more than 96% when n (H) /n (V) was

227

1.2 in different vanadium concentrations, indicating active vanadium species may exist in that

228

condition related to a certain ratio of acid and vanadium concentrations.

229

The vanadium species during extraction reaction were measured and identified by

230

ESI-TOF-MS in different levels of n (H) /n (V) (0.6, 0.8 and 1.0) (Table S4, Fig. S4-S12). It

231

reported that V6O162- species was a novel smaller species, not the products of gas-phase

232

fragmentation or thermal degradation in MS 28. However, it was detected in normal acidic aqueous

233

solution and seemed stable under various conditions, making us difficult to believe it as a novel

234

species due to complete accepted vanadium aqueous solution chemistry (H2VO4-, V2, V4, V5, and

235

V10 were major species). The V6 species were supposed to be a fragment of V10 species, which

236

occurred in detecting process. The framework of V10 species was too large29, and it can break into

237

two small fragments before reaching the analyzer. The fragment of V6 species was more stable

238

than another one, so it was charged, and then detected by an analyzer. In following section, all

239

proportions of V6 species were attributed to those of V10 species.

240

The variations of main species (V1, V4, and V10 species) in aqueous solution were depicted in 9



241

Fig. 4(a)-(c). It is noted that relative ratio of V4 species increased while that of V10 species

242

decreased when n (H)/n (V) was 0.6 compared with others because there was not enough H+ to

243

form V10 species at that condition. The variations in different levels of n (H) /n (V) (0.6, 0.8 and

244

1.0) were summarized in Fig. 4(d), and three main points were discussed and concluded as

245

follows.

246

(1) The extraction reaction and ionic equilibrium reaction of vanadium happened at the same

247

time. The process was described as follows: at the initial condition, there was a lot of V4 and V10

248

species and almost none V1 species. After contact with primary amines, the vanadium extraction

249

reacted quickly, the concentrations of H+, V4, and V10 species decreased quickly. At the same time,

250

V4 and V10 species dissociated into V1 species, so vanadium ionic equilibrium reactions occurred

251

nearly at the same time. After 72s, the H2VO4- species polymerized into polyoxovanadate species

252

for the extraction due to continual contact of extractant, indicating vanadium species reached a

253

new balance in aqueous solution.

254

(2) The V10 and V4 species were active species in extraction reaction, while V10 species were

255

much more active. During first 72 s, the decreased slope ratio was different for different species

256

(V10 > V4). Concentrations of V10 species decreased sharply, meaning that V10 species were much

257

more active in the extraction. Moreover, with the contact of extractant after 72 s, the V10 species

258

increased even with invariable extraction yield (not enough H+ can provide for reaction),

259

indicating V10 species were more easy to form. Another hypothesis was that V10 species could

260

produce more H+ in ionic equilibrium reaction, so it was more preferable in the reaction.

261

(3) The H2VO4- species was non-active species in extraction reaction, but it acted in ionic

262

equilibrium reaction. It illustrated above that extraction reaction did not occur when initial pH was

263

above 6, where H2VO4- species existed obviously in aqueous solution1. When n (H) /n (V) was 0.8,

264

the reaction yield increased a lot, and the percentage of H2VO4- species was less than 0.5%. In

265

other words, the H2VO4- species did not exist in optimal reaction region. Moreover, V10 species

266

dissociated into H2VO4- species during first 72 s, then the percentages of H2VO4- species remained

267

unchanged until the reaction almost finished (within 72 s). All these phenomena indicated that

268

H2VO4- species were non-active in extraction reaction, it only took part in the vanadium ionic

269

equilibrium reaction to adjust the equilibrium of vanadium species and H+.

270 10


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25

(a)

34

65

(b)

60

(c)

20 15

R e lative ra tio /%

R e la tiv e ra tio /%

R e la tiv e ra tio /%

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 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


32

10

30

55 50 45 40

5 35

28

0 0

72

(d)

Time/s

144

216

30

0

72

Time/s

144

216

0

72

Time/s

144

216

new balance

V10 V4

V1 271

extraction reaction equilibrium reaction 0

72

extraction reaction

144

216

Time/s

272

Fig. 4 The relative ratio variation for V1 species(a) V4 species(b) and V10 species(c) during

273

extraction process (0 s, 72 s, 144 s and 216 s) with different acid/vanadium ratio (0.6 (dot), 0.8

274

(dash) and 1.2 (line)) in 0.01 mol/L vanadium aqueous solution; (d): The variation trend for V1, V4

275

and V10 species during extraction process (0 s, 72 s, 144 s and 216 s).

276

277

Performances of vanadium species in stripping process for high-purity NH4VO3

278

The loaded organic phase was stripped using 2.5% aqueous ammonia solution (vaq : vorg=1:3)

279

at 318.15 K. In stripping process (Fig. S13), the organic phase was orange at first, after stirring

280

with ammonia solution for 10 min, its color changed light, and it was white after 60 min. Finally,

281

NH4VO3 solid precipitated and obtained for analysis. The organic phase was recycled for next

282

time. It has been reported that the key procedure in stripping process was the transformation from

283

V10 species to V1 species

284

attributed to the existence of V10 species31. In our studies, the color of stripped solution was

285

yellow at first (Fig. S13), indicating polyoxovanadate species existed in aqueous solution. With

286

the decrease of pH (Fig. S14), the polyoxovanadate species dissociated into H2VO4- species and

287

precipitated out NH4VO3 solid. If there was not enough ammonia, the aqueous solution was

288

yellow, and no powder precipitated out (Fig. S15), meaning that only H2VO4- species could

289

precipitate out in alkaline solution.

30

. Simultaneously, the orange/yellow color in aqueous solution was

11



290

XRD patterns of obtained solids agreed well with standard pattern peaks of NH4VO3

291

(01-076-0191) (Fig. 5(a)–(c)). The mass fractions of impurities in obtained NH4VO3 solids were

292

investigated detailedly (Table S5). Concentrations of 20 common metals were measured by

293

ICP-OES, and that of SO42- was measured by an ion chromatograph. Purity of NH4VO3 power was

294

almost 99.93%, and it only decreased a little by recycled extractant. The overall recovery rate was

295

about 93% (Table S6), meaning 93 g of 100 g vanadium in initial aqueous solution was recovered

296

in final high-purity NH4VO3 (Eq. (4)). The loss rate of vanadium was less than 0.7% in extraction

297

process, but about 5% in stripping process. The NH4VO3 solubility was about 0.5 g/100 mL

298

(20 ℃)32 in water, and lower vanadium in organic phase led to high loss rate due to invariable

299

solubility. So this recovery process was more suitable for large-scale industrial application because

300

concentration of vanadium was high in actual leaching solution.

301 302

Fig. 5 XRD patterns of the NH4VO3 solid: (a): obtained from different vanadium concentration

303

(0.08–0.16 mol/L) in organic phase(n(H)/n(V) was 1.2); (b): obtained from different n(H)/n(V)

304

(0.6 and 1.2) in initial aqueous solution (0.10 mol/L V); (c): obtained using recycled extractant

305

N1923 for first, second and third time (0.10 mol/L V, n(H)/n(V) was 1.2); SEM images of the

306

NH4VO3 solid: (d): obtained from n(H)/n(V) was 1.2 in initial aqueous solution (0.10 mol/L V); 12


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307

(e): obtained from n(H)/n(V) was 0.6 in initial aqueous solution (0.10 mol/L V); (f): obtained

308

using recycled extractant N1923 for third time (0.10 mol/L V, n(H)/n(V) was 1.2); (g): obtained

309

from 0.12 mol/L V solution (n(H)/n(V) was 1.2).

310

rate(%) =

311

mV ( NH4VO3(s) )

mV (wastewater(aq) ) (4)

312 313 314

Concentrations of vanadium in initial aqueous solutions (Fig. 5(a) and 5(g)), and recycle time

315

of primary amine N1923 (Fig. 5(c) and 5(f)) cannot influence the crystallographic structure and

316

morphology of obtained solid. However, pH values in initial aqueous solution obviously effected

317

the crystal structure and morphology of obtained NH4VO3. The intensities of (001) and (020)

318

peaks seemed different in different XRD results of NH4VO3 obtained from different pHs (Fig.

319

5(b)), indicating crystal structure depended on initial acidity of vanadium aqueous solution.

320

Subsequently, morphology of obtained NH4VO3 was also controlled by acidity. The shuttle-like

321

NH4VO3 microcrystals (Fig. 5(d, f, g)) were obtained when n (H) /n (V) was 1.2 no matter what

322

vanadium concentrations were or how many times extractant recycled. The filaments-like

323

NH4VO3 microcrystals (Fig. 3(e)) were obtained when n (H) /n (V) was 0.6.

324

The acidity in aqueous solution obviously played a key role in the control of morphology of 33

or V2O534 architectures. Zakharova. et.

325

NH4VO3, which was consistent with those of NH4V3O8

326

al. reported that different forms of vanadium precursors and different reactions (olation or

327

oxolation reactions) resulted in different vanadium oxide networks in the transformation from

328

NH4VO3 to NH4V3O8

329

vanadium species were intrinsic property of vanadium aqueous solution with different acidities.

330

The V10 species were made of 10 edge-sharing [VO6] octahedral37 while V4 species were chain

331

structures38, so the morphology of NH4VO3 was more sharp with more V4 species involved (Fig.

332

5(e)). The vanadium chemical speciation was an essential factor in vanadium recovery process for

333

high-value vanadium products.

33

. Similarly, the synthesis of BiVO4 was also affected by pH

13


35, 36

. The


334

335

Transformation pathway of vanadium species in vanadium recovery process

NaVO 3 (s)+H 2 O ⇔ H 2 VO 4 − + Na +

(5)

336 337

4H 2 VO 4 − +3H + ⇔ HV4 O 11− + 5H 2 O

(6)

338 339

10H 2 VO 4 − +8H + ⇔ V10 O 26 2 − + 14H 2 O

(7)

340 341

5HV4 O 11 − +H + ⇔ 2V10 O 26 2 − + 3H 2 O

(8)

342 343

V10 O 26 2 − +2H + + x R N H 2 ⇔ ( R N H 2 ) x H 2 V10 O 26

(9)

344 345

H V4 O 11 − +H + + x RN H 2 ⇔ ( R NH 2 ) x H 2 V 4 O 11

(10)

346 347

V10 O 26 2 − +14H 2 O ⇔ 10H 2 VO 4 − + 8H +

(11)

348 349

HV4 O 11 − +5H 2 O ⇔ 4H 2 VO 4 − + 3H +

(12)

350 351

( RNH 2 )m ( H 2 V4 O 11 ) +NH 3 ⋅ H 2 O → m RNH 2 +HV4 O 11− + H 2 O+NH 4 + (13)

352 353

( RNH 2 )m ( H 2 V10 O 26 ) +2NH 3 ⋅ H 2 O → m RNH 2 +V10 O 26 2 − + 2H 2 O+2NH 4 + (14)

354 355

Page 14 of 22

H 2 V O 4 - + N H 4 + → N H 4 V O 3(s ) + H 2 O (15)

356

14


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357 358

Fig. 6 The transformation pathway of vanadium species in vanadium recovery process.

359

The transformation pathway of vanadium speciation in recovery process was performed in

360

Fig. 6. The NaVO3 dissolved in water and formed H2VO4- (Eq. (5)), with addition of acid, the

361

aqueous solution turned to orange and polyoxovanadate species formed (Eq. (6)–(8)). Then after

362

contact with primary amine N1923, the aqueous phase changed colorless (Eq. (11)–(12)) and

363

organic phase turned into orange (Eq. (9)–(10)). The organic phase contained (RNH2)x-Vi (i=4, 6,

364

10) species were stripped by aqueous ammonia solution, then hydrogen bonds in vanadium

365

complexes were broken and polyoxovanadate species formed (Eq. (13)–(14)). The

366

polyoxovanadate species dissociated into H2VO4- species in stripping (Eq. (11) –(12)), and then,

367

H2VO4- species precipitated out NH4VO3 powder with different morphologies (Eq. (15)). Primary

368

amines were recycled for a next extraction.

369

Development of this vanadium recovery process

370

15



140

1 2 3

120 100

Percentage/%

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 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 22

80 60 40 20 0

Extraction yield

purity

recovery rate

371 372

Fig. 7 Recycled efficiency (extraction yield; purity; recovery rate) of N1923 for first, second and

373

third time (black: first time; orange: second time; blue: third time).

374 375

The extraction yield, purity of NH4VO3 powder, and recovery rate of vanadium were almost

376

the same after three recycled times (Fig. 7). Under guidance of vanadium speciation, the recovery

377

process exhibited well-performances for high-purity vanadium products in pilot-scale experiments.

378

The actual V-rich leaching solution containing 24-25 g/L V (V) and 16-18 g/L Cr (VI) and 12

379

kinds of impurities were separated by ACCs with a speed of 50 L/h. After one month continuous

380

operation, the purity of final V2O5 was more than 99.9%, while mass loss of primary amines

381

N1923 was only 0.1%.

382

Zhang et al. developed a synergistic solvent extraction of vanadium by D2EHPA and PC88A,

383

and the purity of final V2O5 product was 99.07% 3. Meanwhile, they also applied P507 in

384

N235-based extraction system, where the extraction yield of vanadium was approximate 90%39.

385

Zhang et al. reported that the extraction yield of vanadium was more than 98% by N235 from

386

leaching solution40. Therefore, the purity of vanadium product, extraction yield, and recovery rate

387

of this vanadium recovery process was all in the top level among present literature. As one of

388

potential technologies, this closed-loop vanadium recovery technical route not only showed great

389

promise in large-scale industries but also acted as a valuable study case of transformation pathway 16


Page 17 of 22 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 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


390

of transition metal species.

391

CONCLUSIONS

392

In summary, this paper investigated the relationship between vanadium species and vanadium

393

recovery process through in suit monitoring/controlling vanadium species by ESI-TOF-MS. More

394

attention of transition metal species should be paid in their recovery process, and the studies of

395

vanadium and chromium species in solvent extraction will be investigated in our subsequent

396

research. Three main aspects were focused and concluded as follows.

397

(1) A closed-loop process has been developed to recover vanadium from aqueous/leaching

398

solution. The primary amine N1923 was identified as a high-effective extractant with more than

399

96% extraction yield of vanadium within 36s, and purity of recycled NH4VO3 was more than

400

99.92%. The global rate of vanadium was 93%, while reutilization efficiency of extractant

401

performed well.

402

(2) The transformation pathway of vanadium species in whole recovery process has been

403

characterized and concluded in the text. Meanwhile, active and non-active vanadium species were

404

discussed based on this in-situ monitored technique, which was potentially devoted to the insights

405

of transition metal speciation in hydrometallurgy field.

406

(3) Under guidance of vanadium speciation studies, pilot-scale experiments have been carried

407

out in actual leaching solution, and the purity of final V2O5 products was 99.9%.

408

SUPPORTING INFORMATION

409

Supporting Information. Brief statement in non-sentence format listing the contents of the material

410

supplied as Supporting Information.

411

AUTHOR INFORMATION

412

Corresponding Author

413

*Pengge Ning. E-mail: [email protected] ; Tel: +86 10 82544844

414

Fax: +86 10 82544845.

415

Notes

416

The authors declare no competing financial interest 17



417

ORCID

418

Jiawei Wen: 0000-0003-1105-8024

419

Pengge Ning: 0000-0002-6617-202X

420

Hongbin Cao: 0000-0001-5968-9357

421

Zhi Sun: 0000-0001-7183-0587

422

ACKNOWLEDGMENTS

423

This work was supported by National Natural Science Foundation of China (No.51425405), 1000

424

Talents Program of China (Z.S.) and Youth Innovation Promotion Association, CAS [No.

425

2016042].

426

REFERENCES

427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451

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576 577 578 579

Synopsis: We proposed a closed-loop technical route to recover high-purity vanadium products from aqueous/leaching solution based on in-situ monitoring/controlling vanadium species.

22


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Recovery of high-purity vanadium from aqueous solutions by a

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