Separation of Vanadium and Tungsten from Sodium Molybdate

May 3, 2014 - Jialiang Zhang , Yuping Deng , Qiuyue Zhou , Peixin Qin , Yubo Liu , Chengyan Wang ... Honghu Tang , Wei Sun , Yuehua Hu , Haisheng Han...
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Separation of Vanadium and Tungsten from Sodium Molybdate Solution by Solvent Extraction Thi Hong Nguyen and Man Seung Lee* Department of Advanced Material Science and Engineering, Institute of Rare Metal, Mokpo National University, Chonnam 534-729, Republic of Korea S Supporting Information *

ABSTRACT: Solvent extraction experiments have been performed, to separate vanadium (V) and tungsten (W) from a synthetic solution containing macroamounts of molybdenum (Mo), in order to determine the effects of solution pH, extractant type and concentration, and stripping reagent. Only V was selectively extracted by 5,8-diethyl-7-hydroxydodecane-6-oxime (LIX 63) from the solution at the equilibrium pH 8.0. Stripping of the loaded LIX 63 with dilute NaOH solution led to complete stripping of V. After removal of V, the highest separation factor between W and Mo was obtained at the equilibrium pH 7.7, by extraction with Aliquat 336. The addition of tributyl phosphate (TBP) to the tricaprylmethylammonium chloride (Aliquat 336) had a profound effect on the separation of the W and Mo by stripping with sulfuric acid solution. In the same H2SO4 concentration range, Mo and W were not stripped from the loaded Aliquat 336 alone, while Mo was selectively stripped over W from the loaded mixture of Aliquat 336 and TBP. A process was proposed to separate V and W from Mo solution by solvent extraction. must be controlled to 18 °C,9 while hydrogen peroxide should be added to the solution as a complexing agent when using a mixture of TRPO and TBP.16 Primene JMT, TOA, and DIDA12,3,17 can extract Mo and W, but no information has been reported on the separation of these metals from each other. In the separation of Mo and V, Alamine 336 and Aliquat 336 are effective from acidic and alkaline solutions.2 However, Alamine 336 is employed in most commercial plants because it is possible to strip Mo and V from the loaded organic by using ammonia as a stripping reagent. In the case of Aliquat 336, ammonia cannot effectively strip the loaded metals. LIX 63 has the advantage of simultaneous extraction of Mo and V from sulfuric acid solution. Alamine 336 and Alamine 304 have been employed for the extraction of Mo from sulfuric acid solution, and a better performance is found for Alamine 304.20 In general, W, Mo, and V exist as anionic species in alkaline solution. Therefore, amines have been employed to separate Mo/V or Mo/W from the solution. Primene JMT has been employed to extract the three metals from the solution.17 However, little information has been reported regarding the separation of these three metals from each other. In this work, solvent extraction experiments have been performed to separate V and W from the leaching solution of Ni−Mo ores. A synthetic solution containing 10 g/L Mo, 1 g/L W, and 0.1 g/L V was prepared, based on the composition of the leaching solution of Ni−Mo ores.6 In solvent extraction, amines such as tertiary (TOA, Alamine 336) and ammonium salt (Aliquat 336) and a cationic extractant (LIX 63) were employed, and the extraction and separation behaviors of the three metals were

1. INTRODUCTION Molybdenum (Mo), tungsten (W), and vanadium (V) are strategic metals. Due to the rapidly growing demand for these metals in the manufacture of advanced materials, it is necessary to develop a process to recover them from diverse resources, such as ores and spent catalysts. Of these, the most important are the cobalt−molybdenum (Co−Mo) type of spent catalysts and nickel−molybdenum (Ni−Mo) ores. In the case of Co− Mo catalysts, other metals exist such as aluminum (Al), iron (Fe), Ni, and V, in addition to Co and Mo; and thus much work has been performed on the recovery of these metals.1−5 Unlike Co−Mo catalysts, Mo, V, and W coexist in the Ni−Mo ores; however, little work has been reported on the separation of these three metals from the leaching solution of the ores.6−8 The separation of V, Mo, and W is very difficult due to their similar chemical properties.2,9 Some work has been reported on the extraction of Mo, W, and V in the presence of other metals from the leaching solution, by employing precipitation,6,7 adsorption, 8 ion exchange, 4,10,11 and solvent extraction.1,3,9,12−16 Compared to other separation methods, solvent extraction has several advantages in the separation of these three metals, in terms of separation factor and the commercial applicability of the process.2 Various extractants, such as a C19−C23 primary amine derivative (N1923),9 another C18−C24 primary amine (Primene JMT),17 a mixture of trialkylphosphine oxide (TRPO) and tributyl phosphate (TBP),16 tertiary amine (trioctyl/dodecyl amine, Alamine 336; tri-n-octyl amine (TOA); tri-n-dodecyl amine, Alamine 304), quaternary ammonium salt (tricaprylmethylammonium chloride, Aliquat 336),2,12,13,18−20 secondary amine (diisododecylamine, DIDA),12,13 and 5,8-diethyl-7hydroxydodecane-6-oxime (LIX 63)1,3 have been employed for the separation of W, V, and Mo. In the separation of Mo and W using primary amine N1923, the reaction temperature © 2014 American Chemical Society

Received: Revised: Accepted: Published: 8608

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investigated, by varying the solution pH and extractant concentration. Also, stripping of the metals from the loaded organic phases was examined, to find an optimum condition to separate the metals. Based on the results, a process together with optimum conditions to separate the three metals was proposed, by employing solvent extraction.

2. EXPERIMENTAL SECTION A synthetic solution containing Mo, W, and V was prepared by dissolving Na2MoO4 (Sigma Co.), Na2WO4 (Sigma), and Na3VO4 (Johnson Matthey Co.) in distilled water. The concentration of Mo, W, and V in the solution was maintained at 10.0, 1.0, and 0.1 g/L, respectively. The acidity of the solution was adjusted, by using NaOH or H2SO4 (Duksan Co.) solution. LIX 63 (BASF Co.), Aliquat 336 (BASF), Alamine 336 (BASF), TOA (Samchun Co.), trioctylphosphine oxide (TOPO; Sigma-Aldrich Co.), and TBP (BASF) were used as received. Kerosene (Daejung Co.) and decanol (Acros Co.) were employed as the diluent and modifier, respectively. Solvent extraction experiments were carried out by mixing the organic and aqueous phases in a 100 mL screw cap bottle and shaking the mixtures for 30 min (extraction and stripping equilibrium was reached within 30 min in initial tests), with a wrist action shaker. All of the experiments were performed at room temperature (25 ± 1 °C). After shaking, the organic and aqueous phases were separated using separating funnels for 5 min. The concentration of metal ions in the aqueous phase was determined by inductively coupled plasma−optical emission spectroscopy (ICP-OES; Spectro Arcos). The concentration of metal ions in the loaded organic phase was calculated by mass balance, and the extraction percentage was calculated as the mass of metal extracted in the organic phase to the initial mass of metal in the aqueous phase before extraction. The distribution ratio (D) was calculated as the concentration of metals present in the organic phase to that present in the aqueous phase at equilibrium. The errors associated with the extraction and stripping percentage of metals were within ±5%.

Figure 1. Effect of the equilibrium pH value on the extraction of metals by 0.1 M Aliquat 336 in kerosene. Solution: 10.0 g/L Mo, 1.0 g/L W, and 0.1 g/L V. O/A (the volume ratio of the organic to aqueous) = 1:1.

Figure 2. Effect of the equilibrium pH value on the extraction of metals using 0.1 M TOA in kerosene. Solution: 10.0 g/L Mo, 1.0 g/L W, and 0.1 g/L V. O/A = 1:1.

3. RESULTS AND DISCUSSION 3.1. Effect of Solution pH on the Extraction Behavior of Metals with Amines and LIX 63. According to the distribution diagram of Mo, W, and V reported in the literature,2,17 the anionic species of molybdenum are stable at pH > 1.0. Vanadium and tungsten are mostly in the form of anionic species at pH > 2.0. The cationic species of molybdenum and vanadium are stable in the pH range from zero to 3.0, while that of tungsten is nil in this pH range. Hence, it can be said that most W exists as anionic species, while some V and Mo exist as cationic species. Therefore, TOA, Alamine 336, and Aliquat 336 were used for the selective extraction of anionic species, and LIX 63 was chosen as a cationic extractant. The extraction behavior of Mo, W, and V with the above extractants was investigated as a function of pH. Since MoO3(s), WO3(s), and V2O5(s) may form when the solution pH is lower than 2.0,17 the initial pH of the solution was controlled to between 2.0 and 10. The concentrations of Mo, W, and V in the synthetic solution were 10.0, 1.0, and 0.1 g/L, respectively. In these experiments, the concentration of each extractant was fixed at 0.1 M. The variations in the extraction percentage of the three metals with equilibrium pH after extraction are presented in Figures 1−3.

Most Mo, W, and V were extracted by Aliquat 336 in the equilibrium pH range from 2.3 to 5.0 (see Figure 1). The extraction percentage of Mo decreased rapidly to 40%, while that of W and V remained constant, with the increase of pH value from 5.0 to 7.5. In the pH range between 7.5 and 7.9, the extraction percentage of Mo and W declined continuously to 30% and 25%, respectively, and was then constant with the further increase of pH value. The extraction percentage of V started to decrease rapidly when the pH increased from 7.9 to 9.0. It has been reported that Aliquat 336 has a stronger tendency to extract polynuclear than mononuclear anionic species.3,18 According to the distribution diagram of Mo, W, and V,2,3,17 the polynuclear anionic species of Mo, such as [Mo7O21(OH)3]3−, [Mo7O22(OH)2]4−, [Mo7O23(OH)]5−, and [Mo7O24]6−, are predominant in the pH range between 2.0 and 5.0 while mononuclear anionic species [MoO4]2− is predominant at pH > 5.0. The polynuclear anionic species of V, including [V10O26(OH)2]4−, [V10O27(OH)]5−, and [V10O28]6−, dominate in the range of 2.0 < pH < 7.0, while mononuclear anionic species [VO2(OH)2]− and [VO3(OH)]2− are predom8609

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10%, for any pH value. In contrast, a high extraction efficiency of V can also be observed in Figure 3. The extraction percentage of V increased steadily to 70% when the equilibrium pH value of the solution increased from 1.8 to 8.0. The extraction behavior of V in these results was similar to that reported in the literature.3 However, the solvent extraction reaction of V by LIX 63 at high pH range has not been reported in this literature. Since most V exists as anionic species in our experimental range, a solvation reaction may be responsible for the extraction of V by LIX 63.24 LIX 63 has a strong tendency to extract metal ions in a hydroxide form.17 According to the distribution diagram of Mo, W, and V,2,17 the V−OH species dominate at pH > 2.0, and their fraction increases with the increase of pH value. This can explain the increase of the extraction percentage of V when the equilibrium pH value increased from 1.8 to 8.0. Since Mo−OH species are predominant in the pH range from 2.0 to 6.0, the extraction of Mo decreased, with the increase of pH from 1.8 to 8.0. In the case of W, a small amount of [W6O20(OH)]5− formed in the range of 5.0 < pH < 8.0, and thus in our conditions, its extraction percentage by LIX 63 was almost negligible. From the data represented in Figures 1−3, a combination of LIX 63 and Aliquat 336 was chosen for the separation of W and V from Mo solution, and the following sequences were attempted. First, the use of LIX 63 would lead to selective extraction of V from the solution at the equilibrium pH 8.0 where the extraction percentage of Mo and W was negligible. After removing V, the pH of V free raffinate could be adjusted to a suitable pH value (equilibrium pH = 6.0−8.0) using H2SO4 solution. Finally, this raffinate was contacted with Aliquat 336 for the separation of W and Mo, and Mo solution with high purity could then be obtained. 3.2. Separation of V from the Solution. 3.2.1. Effect of LIX 63 Concentration. According to Figure 3, the highest extraction percentage of V was obtained using 0.1 M LIX 63 at the equilibrium pH 8.0, and this pH was chosen for further experiments. In order to investigate an optimum extractant concentration for the separation of V from Mo solution in the presence of W, the concentration of LIX 63 was varied from 0.1 to 1 M. As shown in Figure 4, little change was observed in the

Figure 3. Effect of the equilibrium pH value on the extraction of metals using 0.1 M LIX 63 in kerosene. Solution: 10.0 g/L Mo, 1.0 g/ L W, and 0.1 g/L V. O/A = 1:1.

inant when pH > 7.0. Thus, the extraction percentage of Mo decreased at pH > 5.0, and that of V declined sharply, with the increase of pH from 7.9 to 9.0. In the case of W, the polynuclear anionic species of W, such as [W12O39]6−, [W12O41]10−, and [W6O20(OH)]5−, are predominant in the range of 2.0 < pH < 8.0, and anionic species WO42− form as the pH increases. The decrease in the extraction percentage of W with the increase of solution pH is ascribed to a variation in the distribution of species, as solution pH increases from 7.5 to 9.0. During the extraction, a third phase was formed; and thus decanol was added to Aliquat 336 as a modifier in further experiments, to suppress the formation of a third phase.21,22 The extraction behavior of Mo, W, and V by TOA is presented in Figure 2. Most Mo, W, and V were extracted at equilibrium pH 4.4, and the extraction percentage of these metals decreased to zero, with the increase of the equilibrium pH from 4.4 to 6.0. When the solution pH was higher than 6.0, the extraction of Mo, V, and W with TOA was negligible. In the case of Alamine 336, similar extraction behavior of Mo and V was obtained under the same conditions. Unlike the ammonium salt (Aliquat 336), protonation is required, for tertiary amine to extract metal ions. Therefore, in the extraction of these metals with TOA and Alamine 336, amines react first with acid to form protonated amine; and then anionic species of metals are extracted by this protonated amine.23 Thus, the variation in the extraction percentage of the three metals with solution pH might be ascribed to the protonation reaction of the tertiary amines. At low pH, the concentration of acid is enough for the amines to be protonated, and the metals can be extracted by these protonated amines. However, with the increase of solution pH, the concentration of acid becomes low, so that the amines exist like themselves, without being protonated. Therefore, the extraction percentage of the three metals decreased rapidly with the increase of solution pH. Since the concentration of V in the solution was the lowest, the extraction percentage of V by TOA and Alamine 336 was the highest. Figure 2 indicates that the use of TOA (or Alamine 336) leads to coextraction of V and Mo from the solution, by careful control of solution pH. In the case of LIX 63 (Figure 3), the extraction percentage of Mo decreased from 35% to zero, with the increase of the equilibrium pH from 1.8 to 8.0 while that of W was lower than

Figure 4. Effect of LIX 63 concentration on the extraction of Mo, W, and V with LIX 63 in kerosene. Solution: 10.0 g/L Mo, 1.0 g/L W, and 0.1 g/L V. O/A = 1:1. Equilibrium pH 8.0. 8610

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extraction percentage of V (approximately 70%) with the increase of extractant concentration from 0.1 to 0.5 M, but V was completely extracted with the further increase of LIX 63 concentration up to 1 M. The extraction percentage of Mo increased from 0.2% to 13% with the increase of LIX 63 concentration while that of W was nil in the pH range. Figure 4 shows that 0.1 M LIX 63 is an optimum condition to separate V from Mo and W, at which condition 70% of V and 0.2% of Mo were extracted. 3.2.2. Stripping of V from the Loaded LIX 63. It has been reported that stripping of V from the loaded LIX 63 with concentrated sulfuric acid is difficult.3 Therefore, sodium hydroxide solution was used in the current study as a stripping solution. For this purpose, the loaded LIX 63 was prepared by contacting the aqueous solution containing 10.0 g/L Mo, 1.0 g/ L W, and 0.1 g/L V, with 0.1 M LIX 63 at O/A = 1:1. The concentrations of Mo, W, and V in the raffinate after extraction were 9.8, 1.0, and 0.03 g/L, respectively. The loaded organic phase containing 70 mg/L V and 20 mg/L Mo was employed in the stripping experiments. The concentration of NaOH in the stripping solution varied from 0.5 to 2 M. The results indicated that V was completely stripped from the LIX 63 when the concentration of sodium hydroxide solution was 0.5 M. With the further increase of NaOH concentration up to 2 M, the stripping percentage of V decreased slightly to 80%. In addition, in the NaOH concentration employed in this study, most of the Mo was stripped from the loaded LIX 63. When the concentration of Mo and V is low, ion exchange with AG1x8 resin could lead to complete separation of these metals from the stripping solution.4 3.3. Separation of W from the Raffinate after Removal of V. 3.3.1. Selection of pH Value for the Separation of W by Extraction with Aliquat 336. Figure 1 indicates that the separation of W from Mo solution is possible using Aliquat 336 when the equilibrium pH is in the range between 6.0 and 8.0. In order to investigate the effect of solution pH on the separation efficiency of W from the Mo solution after removing V, experiments were carried out in the equilibrium pH range from 6.0 to 8.0. The concentrations of Mo and W in the solution were kept at 10.0 and 1.0 g/L, respectively. The solution was contacted with 0.1 M Aliquat 336, in the presence of 10% (v/v) decanol. The extraction percentage of both Mo and W declined with the increase of the equilibrium pH from 6.0 to 7.8 and then remained constant with the further increase of pH (see Figure 5). Compared to Figure 1, the absence of V in the solution had a negligible effect on the extraction of W and Mo with Aliquat 336. According to the results, the separation of W from Mo in the equilibrium pH range from 7.5 to 7.7 is possible because W can be selectively extracted over Mo. The solution pH of 7.7 seems to be an optimum condition for the extraction of W from Mo solution. Compared to the extraction of Mo and V by Aliquat 336,19 no precipitates of solid phases were observed from the loaded Aliquat 336 during the extraction of W and Mo when decanol was added as a modifier. At the equilibrium pH 7.7, both [MoO4]2− and [WO4]2− are predominant in the solution,17 but the extraction percentage of W with Aliquat 336 was much higher than that of Mo. This can be explained by the difference in the electric charge densities (number of charge/thermochemical radius of ion) between the two metal ions.9 Since the charge density of [WO4]2− (7.78 nm−1) is smaller than that of [MoO4]2− (7.87 nm−1), the extraction percentage of W by Aliquat 336 was higher than that of Mo.

Figure 5. Effect of the equilibrium pH on the extraction of Mo and W with 0.1 M Aliquat 336/10% decanol in kerosene. Solution: 10.0 g/L Mo and 1.0 g/L W. O/A = 1:1.

3.3.2. Effect of Adding Solvating Extractant to Aliquat 336 on the Separation of W from the Solution. In order to find an optimum condition for the separation of W from Mo solution at the equilibrium pH 7.7, three organic systems were tested: (1) Aliquat 336, (2) Aliquat 336 and 0.1 M TBP, and (3) Aliquat 336 and 0.1 M TOPO. In these experiments, the concentration of Aliquat 336 was varied from 0.02 to 0.2 M, and 10% v/v decanol was added to the organic phase to prevent the formation of a third phase. It can be seen in Figure 6 that

Figure 6. Effect of Aliquat 336 concentration on the extraction of Mo and W with Aliquat 336 alone, and the mixtures of Aliquat 336 and TBP/TOPO. Solution: 10.0 g/L Mo and 1.0 g/L W. O/A = 1:1. Equilibrium pH 7.7. Diluent: kerosene. Modifier: 10% decanol.

the extraction percentage of W slowly increased with the increase of Aliquat 336 from 0.02 to 0.2 M while that of Mo steadily increased. The extraction percentage of Mo and W by the mixture of Aliquat 336 and TBP/TOPO was a slightly higher than that by Aliquat 336 alone. Since the concentration of 0.02 M Aliquat 336 is not enough to extract Mo from the solution, the extraction percentage of Mo increased rapidly, with increasing Aliquat 336 concentration. When the concentration of Aliquat 336 increased from 0.02 to 0.2 M, 8611

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together with 10% decanol, with the aqueous solution. It can be seen in Supporting Information Table S4 that the stripping percentage of W was negligible with the increase of H2SO4 solution from 0.1 to 1 M, but that of Mo increased slowly from 4% to 23%. With the increase of H2SO4 concentration (1−7 M), the stripping percentage of Mo increased sharply to 87%, while a lower increase in the stripping percentage of W was obtained (see Figure 7). In the case of stripping with NaOH

the separation factor between W and Mo decreased (see Supporting Information Table S1). It was also shown that the separation factor by the mixture of Aliquat 336 and TBP/ TOPO was higher than that by Aliquat 336 alone. The results indicated that the use of the 0.02 M Aliquat 336 led to the highest separation efficiency of W from Mo at the equilibrium pH 7.7. According to Figure 6, a little difference occurred in the extraction percentage of W and Mo by the mixture of Aliquat 336 and TBP/TOPO. Therefore, the mixture of Aliquat 336 and TBP was employed for further experiments. The extraction results by TBP alone (0.1 M) and the mixture of 0.02 M Aliquat 336 and TBP (0.1−1.0 M) are shown in Supporting Information Table S2. The extraction percentage of Mo and W with TBP alone was lower than 2% in the equilibrium pH range from 2.1 to 9.5. Since most Mo and W exist as anionic species in this pH range,2,17 the extraction percentage of the two metals by TBP alone is low. In addition, the extraction percentage of Mo and W was nearly constant with the increase of the TBP concentration in the mixture with 0.02 M Aliquat 336 when the equilibrium pH of the solution was 7.7. Since a slight increase in the extraction percentage of the two metals was observed using the mixture of Aliquat 336 and TBP/TOPO, the presence of TBP or TOPO in Aliquat 336 has a favorable effect on the extraction of W and Mo. More fundamental work needs to be carried out to elucidate the extraction mechanism by the mixture of Aliquat 336 and TBP/TOPO. 3.3.3. Stripping of W from the Loaded Aliquat 336. In order to investigate the stripping behavior of Mo and W from the loaded Aliquat 336 alone, the loaded Aliquat 336 was prepared by contacting a synthetic solution containing 10.0 g/L Mo and 1.0 g/L W with 0.02 M Aliquat 336. The concentrations of W and Mo in the loaded Aliquat 336 were 700 and 778 mg/L, respectively. The NaOH and H2SO4 solutions were tested as stripping solutions, and their concentrations were varied from 0.1 to 1 M. The results showed that, in our experimental ranges, Mo and W from the loaded Aliquat 336 alone were not stripped by the use of sulfuric acid solution. During the stripping process with H2SO4 solution, green-black precipitates were observed in the organic phase. The precipitates may be formed by the transformation of the extracted species of Mo and W to some other species, which are insoluble in the organic phase. The obtained results agree with the reported literature,19 where extracted species of Mo, including heptamolybdate and octamolybdate in the Aliquat 336, transform to hexamolybdate which precipitates as the green-yellow compound in the organic phase. This may be the reason why, in our conditions, the stripping of the Mo and W was negligible. With NaOH solution (see Supporting Information Table S3), the stripping percentage of Mo and W from the loaded Aliquat 336 increased steadily from 47.4% and 51.2% to 94.1% and 90.3%, respectively, with the increase of NaOH concentration from 0.1 to 1 M. In alkaline solution, mononuclear anionic species of W and Mo are predominant, and the stripping percentage of the two metals increased.3,18 Since the stripping behavior of W and Mo from the loaded Aliquat 336 was similar, it was difficult to separate the two metals by stripping from the loaded Aliquat 336. Since adding TBP to Aliquat 336 has some favorable effect on the extraction of W and Mo, further stripping experiments were performed with the loaded mixture of Aliquat 336 and TBP. For this purpose, a loaded organic phase was prepared by contacting the mixture of 0.02 M Aliquat 336 and 0.1 M TBP

Figure 7. Effect of H2SO4 concentration on the stripping of Mo and W, from the mixture of 0.02 M Aliquat 336 and 0.1 M TBP. O/A = 1:1. Loaded organic: 700 mg/L W and 778 mg/L Mo. Diluent: kerosene. Modifier: 10% decanol.

solution, when the NaOH concentration was higher than 0.7 M, the Mo and W were completely stripped from the loaded organic. The concentrations of W and Mo in the stripping solution were 700 and 778 mg/L, respectively. Compared to the stripping results from Aliquat 336 alone, the presence of TBP in the Aliquat 336 seemed to be more effective, in the separation of Mo and W by stripping from the loaded mixture. It might be said that TBP may play a role as a modifier, to suppress the formation of Mo and W precipitates with Aliquat 336 during the stripping process. In addition, the cationic species of Mo is predominant in concentrated acid solution (pH < 2.0), while the anionic species of W is formed.2,17 Thus, the stripping of Mo from the loaded Aliquat 336/TBP using H2SO4 solution was possible, while that of W was negligible in the same conditions. A higher separation factor between Mo and W was obtained during the stripping from the loaded mixture when H2SO4 concentration in the stripping solution was lower than 1.0 M (see Supporting Information Table S5). The stripping solution using 1.0 M H2SO4 solution contained 170 mg/L Mo and 0.5 mg/L W. A comparison of the results between the previously reported and current studies has been made (see Supporting Information Table S6), and a process flow sheet is proposed in Figure 8, which describes the separation of V and W from Mo solution, using solvent extraction. This process can be applied for the recovery of Mo, from the leaching solution of Ni−Mo ores that contain W and V.

4. CONCLUSION The separation of V and W by solvent extraction from a synthetic solution, in the presence of Mo, was investigated as a 8612

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Figure 8. Schematic process flowsheet for the separation of V and W from Mo solution by solvent extraction.

S6). This material is available free of charge via the Internet at http://pubs.acs.org.

function of pH, and the nature and concentrations of the extractants. The obtained results indicated that V can be selectively extracted over W and Mo, by extraction with LIX 63 at the equilibrium pH 8.0 where the extraction percentage of W and Mo was negligible. V was completely stripped from the loaded LIX 63 using NaOH as a stripping reagent. After separating V, W was extracted over Mo from the raffinate by Aliquat 336 alone, or the mixture of Aliquat 336 and TBP. A higher separation factor between W and Mo was obtained at the equilibrium pH 7.7 by employing a lower concentration of Aliquat 336. Both W and Mo loaded in the organic phase were easily stripped by NaOH solution. The obtained results also indicated that the presence of TBP in Aliquat 336 improved the extraction and stripping efficiency. In particular, the coextracted Mo in the W extraction process by the Aliquat 336/TBP system was separated in the stripping step using H2SO4 solution. The separation factor between Mo and W in the stripping process was found to be 403. Based on the results, a solvent extraction process has been proposed to separate Mo, V, and W from the leaching solution of Ni−Mo ores.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +82 61 45 02492. Fax: +82 61 450 2498. E-mail: mslee@ mokpo.ac.kr. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a grant operated by KEITI, of the Ministry of Environment of Korea. We are thankful for the financial support. We are grateful to the Gwangju branch of the Korea Basic Science Institute (KBSI), for supplying ICP data.

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REFERENCES

(1) Zhang, P.; Inoue, K.; Yoshizuka, K.; Tsuyama, H. Extraction and Selective Stripping of Molybdenum (VI) and Vanadium (IV) from Sulfuric Acid Solution containing Aluminum (III), Cobalt (II), Nickel (II) and Iron (III) by LIX 63 in Exxsol D80. Hydrometallurgy 1996, 41, 45. (2) Zeng, L.; Cheng, C. Y. A Literature Review of the Recovery of Molybdenum and Vanadium from Spent Hydrodesulphurization Catalysts. Part II: Separation and Purification. Hydrometallurgy 2009, 98, 10. (3) Zeng, L.; Cheng, C. Y. Recovery of Molybdenum and Vanadium from Sulphuric Acid Leach Solutions of Spent Hydrosulphurization Catalysts using Solvent Extraction. Hydrometallurgy 2010, 101, 141. (4) Nguyen, T. H.; Lee, M. S. Separation of Molybdenum and Vanadium from Acid Solutions by Ion Exchange. Hydrometallurgy 2013, 136, 65. (5) Banda, R.; Nguyen, T. H.; Sohn, S. H.; Lee, M. S. Recovery of Valuable Metals and Regeneration of Acid from the Leaching Solution of Spent HDS Catalysts by Solvent Extraction. Hydrometallurgy 2013, 133, 161.

ASSOCIATED CONTENT

S Supporting Information *

Separation factors between W and Mo with Aliquat 336 alone and the mixture of Aliquat 336 and TOPO/TBP (Table S1), extraction behavior of Mo and W with TBP alone and the mixture of Aliquat 336 and TBP (Table S2), effect of NaOH concentration on the stripping of Mo and W from the loaded Aliquat 336 alone (Table S3), effect of H2SO4/NaOH concentration on the stripping of Mo and W from loaded Aliquat 336 containing TBP (Table S4), separation factor between Mo and W in the stripping process from the mixture of Aliquat 336 and TBP (Table S5), and comparison of the extraction and stripping of Mo, V, and W by some extractants between the reported literatures and the current study (Table 8613

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dx.doi.org/10.1021/ie500486y | Ind. Eng. Chem. Res. 2014, 53, 8608−8614