A Novel Process for Simultaneous Extraction of Iron, Vanadium

Disposal of slags from alloy steelmaking is a serious problem as the toxic metals in the slag such as chromium and vanadium can be leached out. Recove...
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A Novel Process for Simultaneous Extraction of Iron, Vanadium, Manganese, Chromium, and Titanium from Vanadium Slag by Molten Salt Electrolysis Shiyuan Liu,†,‡ Lijun Wang,*,†,‡ and Kuochih Chou†,‡ †

State Key Laboratory of Advanced Metallurgy, and ‡Collaborative Innovation Center of Steel Technology, University of Science and Technology Beijing, Beijing 100083, China ABSTRACT: Disposal of slags from alloy steelmaking is a serious problem as the toxic metals in the slag such as chromium and vanadium can be leached out. Recovery of the valuable metals needs an effective, economically viable method with a minimum number of unit processes. In the present work, a novel process for simultaneous recovery of iron, vanadium, titanium, chromium, and manganese from vanadium slag is proposed including the chlorination of vanadium slag in molten salt and electrolysis of the salt bath. The optimal conditions for the chlorination are an AlCl3−slag mass ratio of 1.5:1 and a salt bath composition (NaCl−KCl)−AlCl3 mass ratio of 1.66:1, at 900 °C for 8 h. The chlorination ratio of iron, vanadium, chromium, and manganese can reach 90.3%, 76.5%, 81.9%, and 97.3%, respectively, and the titanium volatilization ratio was 79.9%. Metal chlorides in molten salts are electrolyzed at 900 °C with graphite electrodes. Valuable metals (Fe, V, Cr, Mn) were deposited on the cathode in terms of alloy or metal of granular shape. The possible mechanisms involved in these findings were explored. The main compositions of residue are Al2O3 and SiO2, which has the potential usage for landfilling and or building by mixing with other substances for instance.

1. INTRODUCTION Vanadium titanomagnetite ore is one of the main primary sources of vanadium, which is scattered in Australia, China, Russia, and South Africa.1 The main pyrometallurgical processes for producing vanadium slag include the shaking ladle process in South Africa,2 hot metal ladle process in New Zealand, and converter process in China and Russia.3 There are many valuable elements in vanadium slags, with an approximate composition of 30−40 mass % total Fe, 6.92−14.35 mass% TiO2, 13.52−19.03 mass% V2O3, 0.93−4.59 mass% Cr2O3, and 7.44−10.67 mass% MnO.4 Titanium is widely used in aircraft due to its particular properties of being lightweight, strong, and corrosion-resistant.5 Titanium dioxide is used widely as pigment, as filler in paper, plastics, and rubber industries, and as flux in the manufacture of glass.6 Vanadium and chromium are important alloying elements used largely in manufacturing microalloyed steel.7,8 Manganese being a deoxidizing and desulfurizing agent is used extensively in steelmaking.9 Thus, to fully utilize such resources is of great importance. The traditional vanadium extraction from the vanadium slag mainly consists of the following technologies: salt roasting,6,10,11 direct vanadium alloying by vanadium slag,12 and ferrovanadium by vanadium slag,12 The salt roasting is the key to the vanadium extraction, which includes the following procedures: salt (Na2CO3, NaCl, NaOH, Na2SO4, CaCO3 or CaO one or more mixed) roasting of vanadium slag under © XXXX American Chemical Society

oxidation conditions, then water leaching of the roasted products, vanadium isolation from the leachate and vanadium precipitation,13,14 calcination precipitation, and reduction of V2O5. The objective of salt roasting is to convert insoluble vanadium(III) from vanadium slag to water-soluble sodium vanadate(V),15 meanwhile, Cr3+ converts to Cr6+ under oxidizing conditions. Although the salt roasting was applied widely in an industrial production, there are some problems: (1) It is generally recognized that the biological action of vanadium depends on its oxidation state, and its toxicity increases as the valence increases (pentavalent compounds are the most toxic).16 The toxicity of Cr(VI) species, which is one of the most carcinogenic contaminants, is one hundred times higher than that of Cr(III).17 The hazardous vanadium(V) and chromium(VI) compounds in leaching lixivium and tailings, therefore, greatly threaten the environment.18,19 (2). Vanadium slag usually contains a large amount of valuable metals (Ti, Cr, Mn, and Fe), which are not simultaneously recovered during the vanadium roasting procedure. The smelting reduction of vanadium slag has been investigated.12 Vanadium slag was reduced by dissolved carbon and silicon in iron melt through Received: September 22, 2016 Revised: November 22, 2016 Accepted: November 23, 2016

A

DOI: 10.1021/acs.iecr.6b03682 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research the injection of pulverized vanadium slag into the converter slag. The main shortcomings of the direct alloying are the low degree of recovery of vanadium, the complication of the steelmaking operation, and the contamination of steel. A process is provided for the production of ferrovanadium from vanadium slag.20 This process has a high energy consumption. To utilize the vanadium slag in China efficiently, a new process based on the novel metallurgical process for recycling valuable metals is proposed by the authors. The general flow sheet of this process is shown in Figure 1. In this process (1)

Figure 2. XRD Pattern of Original Vanadium Slag.

55 SEM. Anhydrous aluminum chloride can be used as the chlorinating agent.21 The solid reagents of sodium chloride, potassium chloride, and anhydrous aluminum chloride of analytical grade were used in this work. 2.2. Apparatus and Procedures of Valuable Metals Extraction. 2.2.1. The Chlorination of Vanadium Slag. In each experiment, 4.0 g of vanadium slag after drying was mixed sufficiently with a certain amount of NaCl−KCl and AlCl3, heated in an alumina crucible with a lid to the targeted temperature, and held for various time. Graded argon (with the purity of 99.9%) was introduced as the protective gas. After that, the crucible was taken out of the furnace, cooled down in air, and then the sample was crushed to collect all the substances. The products of the experiment were immersed in 200 mL of deionized water contained in a beaker with glass cover for 30 min. After that the beaker solution was filtered through Whatman GF-A membrane. The volume of the filtrate was measured, and the concentrations of valuable metals (Fe, Mn, V, and Cr) were analyzed by ICP-AES. The residue was subjected to chemical analysis. The percentage of chlorinated valuable metals (Fe, Mn, V, Ti, and Cr) was calculated based on eq 1 and 2):

Figure 1. Flowchart of a new process for the efficient utilization of the vanadium slag.

the hazardous vanadium(V) compounds and chromium(VI) compounds are not produced; (2) the vanadium slag is first chlorinated by chlorinating agent, and then separated to produce TiCl4 and chlorinating slag. The next step is electrolysis of the chlorinating slag to obtain the metal or alloy directly used to steelmaking; (3) the new process would realize the simultaneous high recovery of vanadium, titanium, iron, chromium, and manganese from vanadium slag and reduce energy and material costs and alleviate environmental problem.

2. EXPERIMENTAL SECTION 2.1. Materials. The vanadium slag from a Chinese steel plant was crushed, dried, ground, and sieved. The sample with particle size 49−74 μm was dried at 105 °C for 4 h and kept in a desiccator. The composition of vanadium slag was chemically analyzed using inductively couple plasma optical emission spectroscopy (ICP-AES, SPECTRO ARCOS EOP, SPECTRO Analytical Instruments GmbH) as shown in Table 1. As can be seen, valuable metals (Ti, Cr, V, Mn, and Fe) contents in vanadium slags are above 50 mass%. X-ray diffraction (XRD) patterns of the powder of the sample were recorded with a Rigaku TTRIII X-ray diffractometer equipped with a Cu Kα radiation source (λ = 0.15405 nm). The XRD patterns in Figure 2 indicate that the main crystalline phase of the vanadium slag are fayalite, manganoan ((Fe,Mn)2SiO4), titanomagnetite (Fe2.5Ti0.5O4), and vuorelainenite ((Mn,Fe)(V,Cr)2O4). SEM observation was performed with a Zeiss Ultra

V (Fe, Mn and Cr) chlorination (%) =

[V ] × V × 100 Wv (1)

where Wv was the mass of element (V, Fe, Mn, and Cr) in mg from the original vanadium slag; [V] was the concentration of corresponding element (V, Fe, Mn and Cr) from the filtrate in mg/L; V was the volume of the filtrate in liter. ⎛ m ⎞ Ti chlorination (%) = ⎜1 − ⎟ × 100 WTi ⎠ ⎝

(2)

where WTi was the mass of titanium in mg from the original vanadium slag; m was the mass of titanium in mg from the residue. 2.2.2. Electrolysis of Salt Bath. Graphite rods were used as cathode and anode materials. Iron wire was used as the lead wire; 20.0 g of the chlorinated vanadium slag and 80.0 g of salt

Table 1. Main Chemical Composition of the Vanadium Slag in wt % composition

V2O3

Cr2O3

FeO

SiO2

TiO2

MnO

Al2O3

MgO

CaO

content

10.05

5.84

37.00

20.88

11.38

5.93

3.39

3.15

2.38

B

DOI: 10.1021/acs.iecr.6b03682 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 3. Plots of standard Gibbs free energy change as a function of temperature (reactions 3−10: normalized by 1 mol AlCl3).

NaCl−KCl (NaCl−KCl = 50.6:49.4 mol %) were mixed evenly, and heated in an alumina crucible with a lid to the targeted temperature under the protection of argon gas. The electrodes were held 3 cm above the salt melt during the heating process. Once the melting and homogenization of molten salts and slag were completed, electrolysis was started under 3.0 V supplied by a TEKTRONIX 2460. The experiments were conducted about 4−7 h. After the electrolysis, electrodes were taken out of the salt melt and cooled down under the protection of argon gas. The deposited products on the cathode were washed using deionized water and dried before being subjected to SEM/EDS and XRD analysis.

3. RESULTS AND DISCUSSION 3.1. The Possibility of Chlorination of Various Elements by AlCl3. According to the XRD pattern of

Figure 5. Effect of temperature on chlorination of iron, vanadium, manganese, chromium, and titanium from the molten salt roasting samples (AlCl3-slag mass ratio of 1.5:1, mixture salt (NaCl-KCl)-AlCl3 mass ratio of 1.66:1 and 8h).

difficult than in the case of reactions 3−5. It can be seen from reaction 10 that TiO2 could also react with AlCl3 to produce TiCl4. The change of vapor pressure of TiCl4 with temperature was presented in Figure 4, from which it can be seen that TiCl4 can easily volatilize and be separated from the molten slag in the temperature range of 700 to 950 °C. From the above analysis, AlCl3 can chlorinate the valuable elements, such as Fe, Mn, V, Ti, and Cr presented in vanadium slag. In the case of Ti, the chlorinating product of TiCl4 can be easily separated from the slag phase due to the high volatility of TiCl4.

Figure 4. Change of vapor pressure of TiCl4 with temperature.

vanadium slag, the possibilities of Fe2SiO4, FeV2O4, Fe2TiO4, and FeCr2O4 reacting with chlorinating agent AlCl3 were evaluated from the thermodynamic viewpoint as shown in eqs 3−10. The standard Gibbs free energies of these reactions were obtained from the FactSage 6.4 program. The data were plotted against the temperature change shown in Figure 3. First of all, the chlorination of various elements by AlCl3 can happen in the temperature range of 0 to 1000 °C. Chlorination of Fe and Mn is easier than chlorination of Cr, V, and Ti. After Fe and Mn chlorination, V2O3, TiO2, and Cr2O3 would react with AlCl3 (shown in reactions 8−10). From the thermodynamic equilibrium, chlorination in the case of reaction 6 was more

AlCl3 +

3 3 1 3 Fe2SiO4 = FeCl 2 + Al 2O3 + SiO2 4 4 2 2

(3)

AlCl3 +

3 3 1 3 FeV2O4 = FeCl 2 + Al 2O3 + V2O3 2 2 2 2

(4)

AlCl3 +

3 3 1 3 Fe2TiO4 = FeCl 2 + Al 2O3 + TiO2 4 4 2 2

(5)

AlCl3 +

3 3 1 3 FeCr2O4 = FeCl 2 + Al 2O3 + Cr2O3 2 2 2 2 (6)

C

AlCl3 +

3 1 3 MnO = Al 2O3 + MnCl 2 2 2 2

(7)

AlCl3 +

1 1 V2O3 = VCl3 + Al 2O3 2 2

(8)

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Figure 6. XRD patterns of the samples obtained at different roasting temperature.

Figure 9. Plot of chlorination kinetics under different reaction temperatures.

Figure 7. Plots of standard Gibbs free energy change as a function of temperature (reactions 11−13: normalized by 1 mol VCl3).

Figure 8. Effect of time on chlorination of iron, vanadium, manganese, chromium, and titanium from the molten salt roasting samples (AlCl3−slag mass ratio of 1.5:1, mixture salt (NaCl−KCl)−AlCl3 mass ratio of 1.66:1 and 900 °C).

Figure 10. Nature logarithm of reaction rate constant vs reciprocal temperature.

Table 2. Titanium Chlorination Rate vs Time at 900 °C Fitted by Three Kinetics Equations kinetics equations

R2

k

x = k1t 1 −3(1 − x)(2/3) + 2(1 − x) = k2t 1 − (1 − x)(1/3) = k3t

0.605 0.997 0.837

0.116 0.0471 0.0571

AlCl3 +

1 1 Cr2O3 = CrCl3 + Al 2O3 2 2

AlCl3 +

3 1 3 TiO2 = Al 2O3 + TiCl4(g) 4 2 4

(9)

(10)

3.2. Effect of Temperature on Chlorination Ratio. The effect of the chlorinating temperature, viz. 700−950 °C, at an AlCl3-slag mass ratio of 1.5:1, mixture salt (NaCl-KCl)-AlCl3 mass ratio of 1.66:1 and 8h on the chlorination of valuable D

DOI: 10.1021/acs.iecr.6b03682 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 11. Effect of AlCl3−slag mass ratio on chlorination of iron, vanadium, manganese, chromium, and titanium from the molten salt roasting samples (mixture salt (NaCl−KCl)−AlCl3 mass ratio of 1.66:1, 900 °C, and 8 h).

Figure 13. XRD patterns of the deposited product under different electrolysis time.

Table 3. A Mass Balance Regarding AlCl3 [wt %] (AlCl3− Slag Mass Ratio of 1.5:1, Mixture Salt (NaCl−KCl)−AlCl3 Mass Ratio of 1.66:1 and 900°C) time (h)

chlorination

molten salt

evaporation

1 2 4

61.99 62.17 65.81

29.04 22.76 17.62

8.97 15.07 16.57

of FeCl2, and then it is suggested that Fe2SiO4 and FeTiO3 from the original vanadium slag disappeared at 900 °C, which would explain the fact that the chlorination ratio of Fe reached 90.3%. From the thermodynamic equilibrium, chlorination in the case of reaction 6 was more difficult than in the case of reactions 3−5, thus the chlorination ratio of Cr was lower than the chlorination ratio of Fe, Mn, and V in the temperature range 700 to 800 °C. The chlorination ratio of V increased quickly as the chlorination temperature increased from 700 to 800 °C. No significant effect on the chlorination ratio of V was observed when the chlorination temperature was further increased to 900 °C. The chlorination ratio of V was higher than Cr in the temperature range of 700 to 800 °C. However, the chlorination ratio of V was lower than Cr at 900 °C, which could be attributed to the VCl3 as the chlorination agent can react with TiO2, Cr2O3, and FeCr2O4 at high temperature. Changes with temperature in the standard Gibbs free energy of reactions 11−13 were calculated by the FactSage 6.4 program and results were shown in Figure 7. The optimal temperature for the entire process was found to be 900 °C. 3 3 1 3 VCl3 + FeCr2O4 = FeCl 2 + V2O3 + Cr2O3 (11) 2 2 2 2

Figure 12. Effect of mixture salt (NaCl−KCl)−AlCl3 mass ratio on chlorination of iron, vanadium, manganese, chromium, and titanium from the molten salt roasting samples (AlCl3−slag mass ratio of 1.5:1, 900 °C, and 8 h).

metals in vanadium slag was investigated. The results are presented in Figure 5. The chlorination ratio of the valuable metals (Mn, Cr, and Fe) and the volatilization of Ti is remarkably enhanced with the elevating temperature after which the chlorination ratio reached a steady state in the region of 900 to 950 °C. XRD patterns of vanadium slag roasted at different temperatures are given in Figure 6. It was observed that the Fe2SiO4 and FeTiO3 still existed at 800 °C, leading to the relative low chlorination ratio

VCl3 +

1 1 Cr2O3 = V2O3 + CrCl3 2 2

(12)

VCl3 +

3 1 3 TiO2 = V2O3 + TiCl4(g) 4 2 4

(13)

3.3. Effect of Time on Chlorination Ratio. Here the chlorinating time varying from 0.5 to 8 h was investigated at 900 when the mass ratio of AlCl3−slag and salt mixture-AlCl3 were kept as 1.5:1 and 1.66:1, respectively. Figure 8 presents the effect of time on the chlorination ratio of iron, vanadium, manganese, chromium, and titanium. It is apparent that chlorinations of Fe and Mn are not strongly dependent on time since the chlorination ratio of Fe

Table 4. Theoretical Decomposition Voltage of Different Metal Chlorides at 900 °C metal chlorides

CrCl3

FeCl2

VCl3

MnCl2

AlCl3

NaCl

KCl

theoretical decomposition voltage (V)

0.98

1.08

1.11

1.77

1.80

3.17

3.31

E

DOI: 10.1021/acs.iecr.6b03682 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 14. SEM morphologies of deposited product under different electrolysis time: (a) 4 h; (b) 7 h.

Table 5. EDS Analysis of Deposited Product (in Figure 14)

1 − 3(1 − x)2/3 + 2(1 − x) =

EDS Analysis of the Deposited Product [wt %] phase

V

Fe

Al

Cr

Si

Mn

O

a-1 a-2 b-1 b-2

9.17 9.23 1.98 4.16

73.28 75.04 53.99 62.72

0.42 0.32 13.93 14.11

12.09 11.94 20.29 7.15

0 0 0 1.07

2.60 2.36 5.96 3.73

2.44 1.10 3.85 7.06

1 − (1 − x)1/3 =

3k mMC0 t σρR 0

t (16)

k reaMC0 t σρR 0

(17)

To reveal the controlling step of titanium chlorination, the conversion data of titanium at 900 °C are fitted into eqs 15, 16, and 17 as shown in Table 2. The experimental data shows a good agreement with eq 16, which means that the solid product layer diffusion control is the rate-determine step. The volatilization rates of Ti with different temperatures are fitted (Figure 9) and the value of k is obtained. Then the specific apparent activation energy can be calculated based on the Arrhenius equation as shown in Figure 10 ln k = ln A −

E RT

(18)

where E is the apparent activation energy, A is the preexponential factor, and R is the gas constant. The apparent activation energy of Ti chlorination is obtained as E = 59.95 kJ/ mol. 3.4. Effect of AlCl3 (w)/Slag (w) Ratio on Chlorination Ratio. The influence of AlCl3/slag mass ratio on the chlorination ratio of V, Cr, Mn, and Fe or the volatilization of Ti from the molten salt roasting samples was also investigated. As indicated in Figure 11, the chlorination of Fe and Mn are maintained steadily in 83.7−96.1% for Fe, 97.3− 99.5% for Mn across the AlCl3/slag mass ratio range considered because Fe and Mn are easily chlorinated compared with V, Cr, and Ti. Regarding Cr, V, and Ti, the chlorination percentage significantly increased with increasing AlCl3/slag ratio and reached a plateau after AlCl3/slag was 1.5. Assuming V2O3, Cr2O3, FeO, TiO2, MnO, CaO, and MgO in vanadium slag completely reacted with AlCl3 to form the corresponding chlorides (VCl3, CrCl3, FeCl2, TiCl4, MnCl2, CaCl2, and MgCl2), the theoretical mass ratio of AlCl3/ vanadium slag is 1.17. However, due to the volatilization of AlCl3 in nature, an excess amount of AlCl3 should be supplied. A mass balance regarding AlCl3 under different chlorination time is shown at Table 3. The volatilization of AlCl3 remarkably increased with time up to 2 h and then maintained steadily between 2 h and 4 h. The chlorination ratio of vanadium and chromium decreased slightly with increasing AlCl3/slag ratio from 1.5 to 3.0, which is attributed to the volatilization of vanadium. Thus, the optimal AlCl3/slag mass ratio is 1.5.

(14)

where x is the chlorination rate of titanium, km is the mass transfer coefficient of the reactant from molten salt in liquid boundary layer, R0 is the radius of the vanadium slag particle, De is the mass-transfer coefficient of the reactant in the product layer, krea is the reaction ratio constant, t is the reaction time, M is the molar weight of vanadium slag, C0 is the concentration of the reactant at t = 0, ρ is the density of vanadium slag, and σ is the coefficient of AlCl3. Under different process control, the kinetics equations can be simplified as22 (1) Liquid boundary layer diffusion control x=

σρR 0 2

(3) Surface reaction control

and Mn maintained above the 90%. The chlorination ratio of Cr increases with time up to 4 h and then reached a plateau between 4h and 8h. In the case of V, the chlorination ratio decreases as the chlorination time increased from 0.5h to 2h, which could be attributed to VCl3 as chlorinating agent to react with Cr and Ti. Titanium chlorination is influenced greatly by reaction time as shown in Figure 8. The reaction of Ti chlorination is a liquid−solid reaction type, which can be described by the unreacted shrinking core model. The basic equation as shown in eq 14 is used to describe the titanium chlorination macrokinetics of vanadium slag.22 R 1 x + 0 [1 − 3(1 − x)2/3 + 2(1 − x)] 3k m 6De 1 [1 − (1 − x)1/3 ] + k rea MC0 t = σρR 0

6DeMC0

(15)

(2) Solid product layer diffusion control F

DOI: 10.1021/acs.iecr.6b03682 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research 3.5. Effect of Salt (w)/AlCl3 (w) on Chlorination Ratio. Figure 12 gives the dependence of the chlorination ratio of each valuable metal on the salt/AlCl3 mass ratio. Apparently, the chlorination ratio of Mn, Fe, and Cr kept steadily across the salt (w)/AlCl3 (w) mass ratio range. The chlorination ratio of V increases when the salt/AlCl3 mass ratio increases from 1.38 to 1.66, whereas it has no a significant effect on the volatilization of Ti. The chlorination ratio of V and volatilization of Ti decrease remarkably with the increasing salt (w)/AlCl3 (w) mass ratio from 1.66 to 4.15, which could be attributed to decrease concentration of AlCl3. Thus, the optimal salt/AlCl3 mass ratio is 1.66. 3.6. Electrolysis of Molten Slat. After the chlorinating process, V, Fe, Cr, and Mn elements are presented in the molten salt in their chlorides. The corresponding ionic states for the cations are likely to be V3+, Fe2+, Cr3+, Mn2+ along with cations Na+, K+, and Al3+ in the molten salt. The current molten salt became a complex ionic solution. Changes with temperature in the standard Gibbs free energy of metal chlorides were calculated by the FactSage 6.4 program. According to the Nernst equations, the theoretical decomposition voltage of metal at 900 °C was obtained in Table 4. The sequence of electrical reduction was CrCl3 > FeCl2 > VCl3 > MnCl2 > AlCl3 > NaCl > KCl at 900 °C. Due to the polarization, a higher cell voltage than the theoretical decomposition voltage was necessary for electrolysis of metal chlorides. In view of this, a cell voltage of 3.0 V was chosen for the electrolysis of molten salt. The electrolysis of molten salt mixture was performed for 4 h and 7 h, respectively. The XRD patterns in Figure 13 indicate that the deposited products are V3Fe7, Cr, and an impurity of Al2O3. The scanning micrograph and EDS analysis of the deposited product under different electrolysis times are shown in Figure 14 and Table 5. It can be seen that the deposited product exhibits a cubic shape at 4 h, while at 7 h it shows a sintered granular shape. The deposited product and impurity can provide the active growth zone, especially the included angle and closed angle zone, in which the surface energy is lower and the nucleation of metal ion has a lower energy barrier.23 The EDS analysis of the deposited product indicated that the impurities including Al, Si, and O increased as the electrolysis time increased to 7 h. Thus, the optimal time is chosen as 4 h.

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metals (Fe, V, Cr, Mn) were deposited in the cathode in terms of alloy or metal of cubic shape. When the electrolysis time is prolonged, the impurity contents of Al, O, and Si in the deposited product will be increased accordingly.

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Lijun Wang: 0000-0003-2094-3228 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for the financial support for this work from National Nature Science Foundation of China (No.51474141), China Postdoctoral Science Foundation (2014M560046), and Beijing Higher Education Young Elite Teacher Project (YETP0349), as well as the Fundamental Research Funds for the Central Universities (FRF-TP-15052A3).

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REFERENCES

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4. CONCLUSIONS Valuable elements (V, Cr, Mn, Fe, and Ti) have been simultaneous extracted from vanadium slags by molten salt electrolysis. The following conclusions can be drawn: (1) In the molten salt chlorinating process, AlCl3 can chlorinate the valuable elements, such as Fe, Mn, V, Ti, and Cr presented in vanadium slag. In the case of Ti, the chlorinating product of TiCl4 can be easily separated from the slag phase due to the high volatility of TiCl4. Under the optimal conditions (AlCl3−slag mass ratio of 1.5:1, mixture salt (NaCl−KCl)−AlCl3 mass ratio of 1.66:1, 900 °C, and 8 h), the iron, vanadium, chromium, and manganese chlorination ratio was 90.3%, 76.5%, 81.9%, and 97.3%, respectively, and the titanium volatilization ratio was 79.9%. (2) In the molten salt electrolysis process, under the optimal conditions (chlorinated vanadium slag−(NaCl−KCl) mass ratio of 1:4, 3.0 V, 900 °C, and 4 h) the valuable G

DOI: 10.1021/acs.iecr.6b03682 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.iecr.6b03682 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX