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Solvent extraction of molybdenum and vanadium from sulphate solutions with Cyphos IL 101
Hydrometallurgy 154 (2015) 72–77
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Solvent extraction of molybdenum and vanadium from sulphate solutions with Cyphos IL 101 Zhaowu Zhu a, Karol Tulpatowicz b, Yoko Pranolo a, Chu Yong Cheng a,⁎ a b
CSIRO Minerals Resources National Research Flagship, Australia RMDSTEM Limited, Australia
a r t i c l e
i n f o
Article history: Received 25 November 2014 Received in revised form 4 March 2015 Accepted 10 March 2015 Available online 14 March 2015 Keywords: Cyphos IL 101 Molybdenum Vanadium Solvent extraction
a b s t r a c t Increasing demand for the rare metals of molybdenum and vanadium stimulates the research on their recovery from various resources. Solvent extraction of molybdenum and vanadium from sulphate solution with Cyphos IL 101 (trihexyl(tetradecyl)phosphonium chloride) in an aromatic diluent of ShellSol A150 was investigated in order to develop a more efficient separation method. It was found that molybdenum was extracted efficiently in the tested pH range of 0.5–2.0, while efficient vanadium extraction was at pH over 1.8. Effective separation of molybdenum from vanadium could be achieved at pH around 0.5. The separation of molybdenum and vanadium from impurities including iron(III) and aluminium was effective. The metal loading capacity was very high due to the formation of polyoxometallic ions during the extraction of molybdenum and vanadium. Chloride up to 10 g/L and sulphate up to 100 g/L had no significant effect on metal extraction. The extraction of molybdenum and vanadium was very fast, reaching equilibrium in 0.5 min. Vanadium could be stripped efficiently using 0.5 M sulphuric acid, while molybdenum could be stripped efficiently using 4–6 M sulphuric acid. The Cyphos IL 101 organic system has obvious advantages compared to the previously investigated solvent systems in terms of separation of molybdenum from vanadium and separation of vanadium from iron(III) and aluminium. Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.
1. Introduction Increasing demand for the rare metals of molybdenum and vanadium stimulates the research on their recovery from various resources (Ziyadanogullari and Aydın, 2004; He et al., 2007; Wang et al., 2009; Zeng and Cheng, 2009a, 2009b; Parhi et al., 2011). It is particularly true to recover them from spent catalysts owing to their value for sustainable supply and significant reduction of environmental pollution (Biswas et al., 1985; Villarreal et al., 1999; Valverde et al., 2008; Zeng and Cheng, 2009a; Rojas-Rodriguez et al., 2012; Banda et al., 2013). The leach of raw materials with sulphuric acid to recover molybdenum and vanadium is widely used due to its low corrosion and low cost (Valverde et al., 2008; Zeng and Cheng, 2009a; Sahu et al., 2013). Recovery of molybdenum and vanadium from sulphate leach solutions by solvent extraction has been widely investigated. A number of solvent systems have been reported which could be used for their recovery and separation. Among them, the acidic organo-phosphorus extractants including organophosphoric, organophosphonic and organophosphinic acids have been extensively investigated (Zhang et al., 1995; Li et al., 2012; Padhan and Sarangi, 2014; Tavakoli and Dreisinger, 2014). It was concluded that molybdenum could be separated from vanadium at low pH near 0 (Zhang et al., 1995). However, ⁎ Corresponding author. E-mail address: [email protected] (C.Y. Cheng).
http://dx.doi.org/10.1016/j.hydromet.2015.03.005 0304-386X/Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.
it was difficult to separate vanadium from the impurities usually present such as iron(III) and aluminium (Zhang et al., 1995; Tavakoli and Dreisinger, 2014). Long chain amine extractants including primary, tertiary amines and quaternary amine salts were also well investigated. Both molybdenum and vanadium(V) could be extracted efficiently at low pH by primary and tertiary amines. Good separations of molybdenum and vanadium(V) from iron(III) and aluminium was readily achieved using tertiary amines (Miller and Mooliman, 1985; Parhi et al., 2011; Lozano and Godinez, 2003; Sahu et al., 2013). However, it is difficult to separate molybdenum from vanadium(V) due to their similar extraction properties (Olazabal et al., 1992; Sahu et al., 2013). A quaternary amine salt of Aliquat 336 (methyltrioctylammonium chloride) could be used to separate vanadium(V) from molybdenum in a high pH range of 7–10 due to the high extraction of vanadium and very low extraction of molybdenum, but their separation in the pH range of 0.5–5 was very poor (Olazabal et al., 1992; Kushwaha et al., 2011). Furthermore, vanadium stripping was difficult using acid solution. Selective stripping of vanadium in the co-loaded Aliquat 336 system with molybdenum was only achieved by reducing vanadium(V) to vanadium(IV) (Hirai and Komasawa, 1993). A hydroxyoxime extractant, LIX 63 (5,8-diethyl-7-hydroxydodecane6-oxime) was investigated and showed good separation of molybdenum from vanadium(IV) at very low pH around 0 (Zhang et al., 1996). The separation of molybdenum and vanadium from the impurities including
Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77
73
Table 1 Composition of the synthetic solution and chemical purity used for the solution preparation. Metal
Mo
V
Fe
Al
Cu
Mn
Concentration (g/L) Chemicals
0.5 Na2MoO4·2H2O
0.5 Na3VO4
1.0 Fe2SO4·6H2O
1.0 Al2(SO4)3·16H2O
1.0 CuSO4·5H2O
1.0 MnSO4·4H2O
iron(III) and aluminium was efficient. However, the separation of molybdenum from vanadium(V) was very difficult since both of them were strongly extracted even at pH b 1, resulting in their poor separation in acidic solutions (Zeng and Cheng, 2010). Additionally, the stability of LIX 63 is a concern due to its degradation, particularly in the presence of the potential oxidant vanadium(V) (Barnard et al., 2010). In summary, either poor separation of molybdenum from vanadium(V), or poor separation of both from iron(III) and aluminium was generally shown with the solvent systems previously investigated. Additionally, alkaline solution was required to strip molybdenum, resulting in high risk of poor phase separation and solvent loss by high solubility in alkaline solutions (Zeng and Cheng, 2009b). In the present work, trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) was studied for the separation of molybdenum and vanadium(V) and separation of them from the impurities including iron(III) and aluminium in a synthetic sulphate solution.
2. Experimental 2.1. Reagents and solution preparation Cyphos IL 101 was kindly supplied by Cytec Industries Inc. (USA). The organic solutions were prepared by dissolving Cyphos IL 101 in an aromatic hydrocarbon diluent of ShellSol A150 provided by Shell Chemicals (Australia). This aromatic hydrocarbon diluent was used because Cyphos IL 101 has poor solubility in aliphatic hydrocarbon diluent. In regard to the most frequently associated metals in the raw materials of molybdenum and vanadium, an aqueous solution was prepared by dissolving corresponding metal salts in de-ionised water to a desired concentration as shown in Table 1. Although nickel and cobalt are commonly presented in catalysts used for petroleum hydrodesulphurisation, they were not included in this study because they are unable to form extractable anions in sulphate solutions and could not be extracted with Cyphos IL 101 system. All inorganic chemicals used were analytical grade.
2.2. Metal extraction and stripping Metal extraction and stripping tests were carried out in a 300 mL hexagonal glass reactor immersed in a temperature controlled water bath (40 ± 1 °C) (temperature under which solvent extraction practices often operated). The aqueous and organic solutions were mixed using Eurostar Digital overhead stirrer coupled with a 40 mm diameter impeller at a stirring speed of around 1200 RPM. Mixing continued to 10 min for each sampling point except tests for kinetics study. The pH was monitored using a Hanna portable pH metre connected with a Ross Sure Flow electrode. The pH was adjusted with 4 M NaOH and 2 M H2SO4 solutions as required. For the tests of chloride and sulphate effect, sodium chloride and sodium sulphate were used, respectively to achieve the desired concentrations. 2.3. Extraction kinetics test A preliminary extraction test was conducted at an A/O ratio of 1:1, 40 °C and a selected pH to determine the amount of NaOH solution required for pre-equilibration. The organic solution was then preequilibrated with the pre-determined amount of NaOH solution. The synthetic solution and the pre-equilibrated organic solution were mixed at an A/O ratio of 1:1 and 40 °C. Timing started immediately once the two phases were mixed. Mixed solution samples were taken at 0.5, 1.0, 2.0, 3.0, 5.0 and 10 min for assay. 2.4. Sampling and analysis After the two phases were separated, the aqueous solution was filtered through a 0.45 μm Supor membrane filter. Metal concentrations in aqueous solutions were analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Metal concentrations in organic solutions were calculated based on the metal concentrations in the feed solution and the raffinate. 3. Results and discussion 3.1. Metal extraction pH isotherms
100.0
Metal extraction pH isotherms were measured in a pH range of 0.5 to 2 with 0.10 M Cyphos IL 101 in ShellSol A150 and the synthetic solution (Fig. 1). It was shown that the molybdenum extraction was very efficient with N 98% extraction in the pH range tested, while vanadium extraction started from 8% at pH 0.5 and increased to 93% at pH 1.8. Good separation of molybdenum from vanadium was achieved at pH 0.5 with the separation factor of 700. The extraction of iron was very low at pH lower than 1.5. It slightly increased to 7.4% and 11.4% at pH 1.8 and 2.0, respectively. The extraction of other metals including aluminium, manganese and copper were negligible, indicating very good separation of molybdenum and vanadium from these metals.
90.0
Extraction (%)
80.0 70.0 60.0 50.0 40.0 30.0
V
Mo
Fe
Cu
Mn
Al
20.0 10.0 0.0 0.0
0.5
1.0 1.5 Equilibrium pH
2.0
2.5
Fig. 1. Metal extraction pH isotherms with 0.10 M Cyphos IL 101 and the synthetic solution at A/O ratio of 1:1 and 40 °C.
Table 2 The pH change during metal extraction with 0.10 M Cyphos IL 101 and pre-neutralised synthetic solutions at A/O ratio of 1:1 and 40 °C. Initial pH Equilibrium pH Mo extraction (%) V extraction (%)
0.50 0.58 98.9 8.6
1.17 1.25 99.4 50.0
1.58 1.80 99.3 93.5
1.83 2.13 99.8 97.0
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Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77
100.0
100.0
90.0
90.0
80.0
80.0
V
60.0
70.0 Extraction (%)
Extraction (%)
70.0
Mo
50.0 Fe
40.0
60.0 Mo 50.0
30.0
20.0
20.0
10.0
10.0
0.0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 Cyphos 101 concentration (M)
The extraction mechanism of molybdenum and vanadium is very complicated due to the formation of various polyoxometallic species (Olazabal et al., 1992; Bal et al., 2002, 2004; Zeng and Cheng, 2009b). It is well known that many molybdenum anions of could form in the solution depending on the pH and its concentration. The possible anionic species should be H3Mo7O324−, H2Mo7O424−, HMo7O524−, HMo8O326−, Mo8O426− and H3Mo8O528− at pH below 2.5 based on Bal et al. (2004), but principally to be H3Mo7O324− based on Olazabal et al. (1992). The fraction of anionic species H3Mo7O324− increases from pH 0.5 to 2.5 where it becomes predominant. During the extraction, cationic ions convert to anions based on the Le Chatelier's principle shown in Eqs. (1)–(3). 0 3− 0 − 3 R3 R P Cl org þ H3 Mo7 O24 ⇔ R3 R P 3 H3 Mo7 O24 org þ 3Claq ð1Þ aq
−
2þ
þ
MoO2 þ 2H2 O⇔HMoO4 þ 3H −
þ
ð2Þ
3−
7HMoO4 þ 4H ⇔H3 Mo7 O24 þ 4H2 O
ð3Þ
where R3R′P ⋅ Cl represents Cyphos IL 101 in chloride form and subscripts of org and aq organic and aqueous phase, respectively. Due to very strong extraction of H3Mo7O324− species generated in Eq. (3) by Cyphos IL 101, these species are extracted immediately
Fe
40.0
30.0
Fig. 2. Effect of Cyphos 101 concentration on metal extraction at A/O ratio of 1:1, pH 1.80 and 40 °C.
V
0.0 0
20
40
80
100
Fig. 4. Effect of sulphate on metal extraction with 0.10 M Cyphos IL 101 at pH 1.80, A/O ratio of 1:1 and 40 °C.
after the formation, which makes Eqs. (2) and (3) move to the right side regardless of any acid generated. The pH change was determined during the metal extraction using pre-neutralised synthetic solutions as shown in Table 2. The organic solution of 0.10 M Cyphos IL 101 was pre-washed with de-ionised water to equilibrium pH of about 6. In Table 2, it is obvious that the aqueous equilibrium pH increased during the metal extraction due to the extraction of acid by Cyphos IL 101. Vanadium extraction increased with pH increase in Fig. 1, indicating that higher pH is favourable to the vanadium extraction. Olazabal et al. (1992) reported that the majority of vanadium(V) was present in the form of VO+ 2 at pH lower than 2 and polyoxovanadate only formed in the neutral solution. It was suggested that vanadium transformation from its cations to the anions also occurred according to the Le Chatelier's principle during the extraction since only anions could be extracted. Therefore, it is predicted that Cyphos IL 101 enabled the extractable vanadium anions forming in the aqueous phase at low pH. The most probable anionic vanadates were formed via Eqs. (3) to (5) according to the reported investigations (Miller and Mooliman, 1985; Olazabal et al., 1992; Bal et al., 2002; Lozano and Godinez, 2003). þ
þ
3−
VO2 þ 2H2 O⇔VO4 þ 4H þ
ð4Þ þ
4−
2VO2 þ 3H2 O⇔V2 O7 þ 6H þ
ð5Þ þ
4−
10VO2 þ 8H2 O⇔H2 V10 O28 þ 14H :
100.0 90.0
ð6Þ
All three kinds of vanadium anions formed via Eqs. (4)–(6) could be extracted with Cyphos IL 101 via an anion exchange mechanism. Based on the data reported by Olazabal et al. (1992), the fraction of H2V10O4− 28 species increased from pH 0.5 to 2, resulting in the increase in
80.0 70.0
Extraction (%)
60
Sulphate addition (g/L)
V 60.0 50.0
Mo
40.0
Fe
Table 3 Metal extraction and distribution with 0.10 M Cyphos IL 101 at pH 1.80 and 40 °C with various A/O ratios.
30.0 20.0 10.0
A/O ratio
Mo In aqueous (g/L)
In organic (g/L)
Extraction (%)
In aqueous (g/L)
In organic (g/L)
Extraction (%)
1:1 2:1 4:1 6:1
0.003 0.002 0.002 0.003
0.447 0.898 1.797 2.685
99.3 99.7 99.7 99.3
0.022 0.015 0.014 0.013
0.446 0.906 1.817 2.733
95.3 96.7 97.0 97.3
0.0 0.0
2.0
4.0 6.0 Chloride addition (g/L)
8.0
10.0
Fig. 3. Effect of chloride on metal extraction with 0.10 M Cyphos IL 101 at pH 1.80, A/O ratio of 1:1 and 40 °C.
V
Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77 100.0
100.0
90.0
90.0
80.0
80.0 V
70.0
70.0
60.0
Extraction (%)
Extraction (%)
75
Mo
50.0 40.0 30.0
60.0 V
50.0 40.0
Mo
30.0
20.0
20.0 10.0
10.0 0.0 1:1
2:1
4:1
6:1
0.0
A/O ratio
0.0
1.0
2.0
3.0
4.0
5.0
6.0
Time (min) Fig. 5. Metal extraction under various A/O ratios with 0.10 M Cyphos IL 101 and single metal solutions containing 9.6 g/L Mo and 4.8 g/L V, respectively, at pH 1.80 and 40 °C.
Fig. 6. Extraction kinetics of molybdenum and vanadium with 0.10 M Cyphos IL 101 and the synthetic solution at pH 1.80, A/O ratio of 1:1 and 40 °C.
vanadium(V) extraction with pH as indicated in Fig. 1. The extraction of H2V10O4− 28 species via anion exchange is shown in Eq. (7). 4− 0 − 4 R3 R P Cl org þ H2 V10 O28 ⇔ R3 R P 4 H2 V10 O28 org þ 4Claq ð7Þ 0
aq
The formation of polyoxovanadate and polyoxomolybdate could be verified by the over stoichiometrical extractions in the subsequent tests. However, further investigation is required to exactly determine the extracted species with Cyphos IL 101. 3.2. Effect of Cyphos 101 concentration The extraction of molybdenum, vanadium and iron was determined using various Cyphos IL 101 concentrations and the synthetic solution at pH 1.80 ± 0.01, A/O ratio of 1:1 and 40 °C (Fig. 2). It was shown that the concentration of Cyphos IL 101 in the range of 0.01–0.10 M had no effect on the extraction of molybdenum and vanadium, indicating that Cyphos IL 101 has very high extraction capacity. The total molar concentration of extracted molybdenum and vanadium was 0.014 M using 0.01 M Cyphos IL 101. The molar concentration of metal loading was higher than that of the Cyphos IL 101, indicating the formation of polyoxometallic anions during the extraction. The extraction of iron increased slightly with the increase in the organic concentration due to more available extractant. The very low iron extractions at low organic concentrations suggested high selectivity of vanadium and molybdenum over iron using low concentration of Cyphos IL 101. In order to evidence the variation of iron extraction, higher concentration of 0.10 M Cyphos IL 101 was selected for the subsequent test work.
vanadium and iron with 0.10 M Cyphos IL 101 and the synthetic solution was studied by adding sodium chloride in the initial synthetic solution. The results obtained at pH 1.80 ± 0.01, A/O ratio of 1:1 and 40 °C are shown in Fig. 3. It was shown that the addition of chloride up to 10 g/L has no significant effect on the extraction of molybdenum and iron. The extraction of vanadium slightly decreased with the increase in chloride concentration (Fig. 3), probably due to the combination of chloride with VO+ 2 which adversely affected the formations of extractable anions via Eqs. (4)–(6). Another possible reason could be attributed to the competitive extraction of chloride ions. Considering that sulphate could reach very high concentration in the leach solution due to possible high concentrations of impurities, the effect of sulphate concentration on the extraction of molybdenum, vanadium and iron was studied by adding sodium sulphate in the initial aqueous solution. The extraction was conducted at pH 1.80 ± 0.01, A/O ratio of 1:1 and 40 °C (in Fig. 4). It was also observed that sulphate concentration up to 100 g/L had no significant effect on the extraction of molybdenum and iron. The extraction of vanadium also decreased slightly with the increase in the sulphate concentration probably due to the combination of sulphate with VO+ 2 to adversely affect the polyoxovanadate formation. Similar to the effect of chloride, sulphate could also be competitively extracted by Cyphos IL 101, resulting in the decrease in vanadium extraction. The association of sulphate with Cyphos IL 101 has been reported elsewhere (Zhu et al., 2013). 100.0 90.0 80.0
Chloride is often presented in the raw materials and/or operation water. The effect of chloride on the extraction of molybdenum,
70.0
Table 4 Metal loading in the 0.10 M Cyphos IL 101 organic solution by contacting with single metal solutions at pH 1.80 and 40 °C. A/O ratio
1:1 2:1 4:1 6:1
Mo
V
In organic (g/L)
In organic (M)
[M]/[org]a
9.6 19.1 26.5 24.4
0.10 0.20 0.28 0.25
1.00 1.99 2.76 2.54
Stripping (%)
3.3. Effect of chloride and sulphate concentration
60.0 50.0 40.0 V 30.0 20.0
In organic (g/L)
In organic (M)
[M]/[org]
4.69 9.40 15.2 15.4
0.09 0.18 0.30 0.30
0.92 1.85 2.98 3.03
Mo
10.0
a [M] and [org] represent the molar concentrations of metal and Cyphos IL 101, respectively.
0.0 0.0
1.0
2.0
3.0
4.0
5.0
6.0
H2 SO4 [M] Fig. 7. Metal stripping with various concentrations of H2SO4 solution at A/O ratio of 1:1 and 40 °C.
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Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77
Table 5 Stripping efficiency of molybdenum and vanadium with NaCl in 0.1 M Cyphos IL 101. NaCl (M)
pH
Stripping of Mo (%)
Stripping of V (%)
Observation
0.5 1.0 2.0 3.0
7.17 7.21 7.85 7.95
27.8 54.2 44.0 46.4
23.6 54.2 53.8 47.3
Clear phases Clear phases Slight precipitation Slight precipitation
The effect of both chloride and sulphate on the extraction of molybdenum in the concentration range tested was too weak to be observed due to its very strong extraction with Cyphos IL 101. 3.4. Effect of A/O ratio The metal extraction was measured with 0.10 M Cyphos IL 101 and the synthetic solution at pH 1.80 ± 0.01 and 40 °C using various A/O ratios. The extraction and distribution of molybdenum and vanadium are shown in Table 3. As Cyphos IL 101 has very high capacity for the extraction of molybdenum and vanadium, the metal extraction was not affected by increasing A/O ratio from 1:1 to 6:1, resulting in the significant increase in the metal concentrations in the loaded organic solution. At A/O ratio of 6:1, about 2.7 g/L of each metal (0.08 M total Mo and V) was loaded in the 0.10 M Cyphos IL 101 solution without phase separation problem. To determine the maximum loading capacity of Cyphos IL 101 for the extraction of molybdenum and vanadium, solutions containing individual metal of 9.6 g/L Mo(0.100 M) and 4.8 g/L V (0.094 M), respectively, were prepared. Metal extractions with 0.10 M Cyphos IL 101 from these solutions at pH 1.80 ± 0.01 and 40 °C using various A/O ratios are shown in Fig. 5. It was shown that both molybdenum and vanadium were extracted efficiently at an A/O ratio of 1:1 and 2:1 with good phase separation. At high A/O ratio of 4:1 and 6:1, both organic phases were heavily emulsified, suggesting that the organic was over-loaded. The metal loading in organic solutions with various A/O ratios was calculated (Table 4). It was shown that the loading of molybdenum and vanadium reached about 20 g/L and 10 g/L at an A/O ratio of 2:1, respectively, corresponding to that one mole of Cyphos IL 101 was loaded with 1.99 mol of molybdenum or 1.85 mol of vanadium. This, again, suggested that polyoxometallic anions were formed during the extraction of both molybdenum and vanadium. 3.5. Kinetics of molybdenum and vanadium extraction The extraction kinetics of molybdenum and vanadium with 0.10 M Cyphos IL 101 pre-equilibrated to a neutral pH of about 6 and the synthetic solution was studied at pH 1.80 ± 0.01, A/O ratio of 1:1 and 40 °C (Fig. 6). It was found that the extraction of both molybdenum and vanadium was very fast and reached the equilibrium within 0.5 min. 3.6. Stripping of molybdenum and vanadium The pre-loaded 0.10 M Cyphos IL 101 containing 0.43 g/L Mo and 0.42 g/L V was stripped using various concentrations of H2SO4 solutions at an A/O ratio of 1:1 and 40 °C (Fig. 7). It was shown that the stripping of vanadium with sulphuric acid was easier than that of molybdenum. The stripping of vanadium reached 87.6% using 0.5 M H2SO4, while
molybdenum stripping was only 3.6%. This suggests that the separation of molybdenum from vanadium could also be obtained by selective stripping using 0.5 M H2SO4. Efficient molybdenum stripping was achieved using higher sulphuric acid solutions of 4–6 M with 78.3– 95.6% Mo stripping. It is suggested that the stripping of molybdenum and vanadium from the loaded Cyphos IL 101 is due to the large increase in H+ concentration and the competition of anionic species of SO2− 4 and HSO− 4 at high H2SO4 concentration. The stripping of molybdenum and vanadium in the pre-loaded Cyphos IL 101 solution using various NaCl concentration solutions were carried out at around neutral pH, A/O of 1:1 and 40 °C (Table 5). The stripping efficiency of both molybdenum and vanadium increased with the increase in NaCl concentration from 0.5 M to 1.0 M. Precipitation in the aqueous phase was observed when further increased NaCl concentration to over 2.0 M, indicating that it is difficult to apply NaCl for the stripping of molybdenum and vanadium. The stripping of molybdenum and vanadium by other selected agents was also studied as shown in Table 6. It was found that no other agents performed better than sulphuric acid in terms of metal stripping and selectivity.
3.7. Performance comparison The performance of the Cyphos IL 101 system and other previously investigated systems were compared (Table 7). It is clear that all previously investigated systems have disadvantages either in poor separation of molybdenum from vanadium or in poor separation of vanadium from impurities including iron(III) and aluminium. Additionally, the stripping of molybdenum was only achieved using alkaline solutions, resulting in high risks of poor phase separation and organic loss due to high solubility in alkaline solutions (Zhang et al., 1995; Zeng and Cheng, 2009b). The Cyphos IL 101 system has obvious advantages for good separation of molybdenum from vanadium and good separation of vanadium from iron(III). Both vanadium(V) and molybdenum can be efficiently stripped using sulphuric acid solutions.
4. Conclusions Cyphos IL 101, trihexyl(tetradecyl)phosphonium chloride, has significant advantages for the recovery of molybdenum and vanadium from sulphate solutions compared to other investigated solvent systems. Molybdenum could be extracted efficiently in the pH range of 0.5–2.0, while efficient vanadium extraction was at pH over 1.8, leading to their good separation at pH around 0.5. The separation of molybdenum and vanadium from impurities including iron(III), aluminium, manganese, copper and possibly nickel and cobalt was very effective. As molybdenum and vanadium formed polyoxometallic anions during extraction, the loading capacity of Cyphos IL 101 was very high with 20 g/L Mo or 10 g/L V loaded in the 0.10 M organic solution without phase separation problem. Chloride up to 10 g/L and sulphate up to 100 g/L had no significant effect on the metal extraction and separation. The extraction of molybdenum and vanadium was very fast, reaching equilibrium in 0.5 min. Vanadium could be stripped using 0.5 M sulphuric acid solution and molybdenum could be efficiently stripped using 4–6 M sulphuric acid. The separation of molybdenum from vanadium also can be achieved by selective stripping vanadium using 0.5 M
Table 6 Stripping of molybdenum and vanadium from 0.10 M Cyphos IL 101 organic solution by other stripping solutions at an A/O ratio of 1:1 and 40 °C. Reagents
1.0 M HCl
1.0 M NH3·H2O
1.0 M (NH4)2CO3
1.0 M Na2CO3
1.0 M NaOH
V stripping (%) Mo stripping (%) Phase separation
54.8 4.0 Good
51.9 8.6 Poor
76.0 44.1 Good
71.0 55.9 Good
– – Precipitation
Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77
77
Table 7 Performance comparison of various solvent systems used in the recovery and separation molybdenum and vanadium in sulphate solutions. Solvent systems
Diluent
Mo/V separation
Separation from Fe(III)
Organo phosphoric acid Organo phosphonic acid Organo phosphinic acid Primary amine
Hydrocarbon compound
a
Only by reducing to Fe(II) No separation of vanadium
Hydrocarbon compound
Possible separation at pH b 1.0 Only by reducing to Fe(II) No separation of vanadium
Hydrocarbon compound
Possible separation at pH b 1.0 Only by reducing to Fe(II) Poor separation of vanadium No separation in pH range of No reference was found Possible separation due to 1–6 low Al extraction
Kerosene and isodecanol as the modifier
Possible separation at pH b 0.5
Separation from Al
Tertiary amine
Kerosene and isodecanol Possible at pH b 1.0 or as the modifier or toluene reducing V(V) to V(IV)
Good separation
Good separation
Quaternary amine
Kerosene and isodecanol Possible at pH b 0.5; as the modifier or toluene bGood in pH range of 7–10 Hydrocarbon compound Poor separation in acidic solution Aromatic hydrocarbon Good separation at pH b 0.5 compound
Good separation
Good separation
Good separation
Good separation
Good separation
Good separation
Oxime Cyphos IL 101 a b
Reference Zhang et al. (1995), Tavakoli and Dreisinger (2014) Zhang et al. (1995), Tavakoli and Dreisinger (2014) Zhang et al. (1995) Schrotterova and Nekovar (2000), Lozano and Godinez (2003); Olazabal et al. (1992), Hirai and Komasawa (1993), Parhi et al. (2011), Sahu et al. (2013). Olazabal et al. (1992), Kushwaha et al. (2011) Zhang et al. (1996), Park et al. (2010), Zeng and Cheng (2010) Present work
Possible separation with the estimated separation factor N100; Good separation with the estimated separation factor N1000.
sulphuric acid solution and bulk stripping molybdenum using 4–6 M sulphuric acid solution. Acknowledgements The authors would like to thank Drs Keith Barnard and Wensheng Zhang for reviewing the paper and providing valuable suggestions. The support of the CSIRO Mineral Resources National Research Flagship is gratefully acknowledged. References Bal, Y., Bal, K.E., Cote, G., 2002. Kinetics of the alkaline stripping of vanadium(V) previously extracted by Aliquat 336. Miner. Eng. 15, 377–379. Bal, Y., Bal, K.E., Cote, G., Lallam, A., 2004. Characterization of the solid third phases that precipitate from the organic solutions of AliquatR 336 after extraction of molybdenum(VI) and vanadium(V). Hydrometallurgy 75, 123–134. Banda, R., Nguyen, T.H., Sohn, S.H., Lee, M.S., 2013. Recovery of valuable metals and regeneration of acid from the leaching solution of spent HDS catalysts by solvent extraction. Hydrometallurgy 133, 161–167. Barnard, K.R., Turner, N.L., Shiers, D.W., 2010. LIX63 stability in the presence of Versatic 10 under proposed commercial extract and strip conditions, part III: Effect of manganese and cobalt loading on oxime stability at 30 °C. Hydrometallurgy 104, 268–277. Biswas, R.K., Wakihara, M., Taniguchi, M., 1985. Recovery of vanadium of and molybdenum from heavy oil desulphurisation waste catalyst. Hydrometallurgy 14, 219–230. He, D., Feng, Q., Zhang, G., Ou, L., Lu, Y., 2007. An environmentally-friendly technology of vanadium extraction from stone coal. Miner. Eng. 20, 1184–1186. Hirai, T., Komasawa, I., 1993. Electro-reductive stripping of vanadium in solvent extraction process for separation of vanadium and molybdenum using trinoctylmethylammonium chloride. Hydrometallurgy 33, 73–82. Kushwaha, J., Agrawal, A., Upadhyay, A.K., Mankhand, T.R., Sahu, K.K., 2011. Recovery of molybdenum from spent HDS catalyst leach liquor by solvent extraction using Aliquat 336. 15th International Conference on Non-ferrous Metals, July 8–9, Kolkata, India. Li, X., Wei, C., Wu, J., Li, M., Deng, Z., Li, C., Xu, H., 2012. Co-extraction and selective stripping of vanadium (IV) and molybdenum (VI) from sulphuric acid solution using 2ethylhexyl phosphonic acid mono-2-ethylhexyl ester. Sep. Purif. Technol. 86, 64–69. Lozano, L.J., Godinez, C., 2003. Comparative study of solvent extraction of vanadium from sulphate solutions by primene 81R and Alamine 336. Miner. Eng. 16, 291–294. Miller, J.D., Mooliman, M.B., 1985. A review of new developments in amine solvent extraction systems for hydrometallurgy. Sep. Sci. Technol. 19 (11–12), 895–909. Olazabal, M.A., Orive, M.M., Fernhdez, L.A., Madariaga, J.M., 1992. Selective extraction of vanadium(V) from solutions containing molybdenum(VI) by ammonium salts dissolved in toluene. Solvent Extraction Ion Exch. 10 (4), 623–635. Padhan, E., Sarangi, K., 2014. Separation of molybdenum and cobalt from spent catalyst using Cyanex 272 and Cyanex 301. Int. J. Miner. Process. 127, 52–61.
Parhi, P.K., Park, K.H., Kim, H.I., Park, J.T., 2011. Recovery of molybdenum from the sea nodule leach liquor by solvent extraction using Alamine 304-I. Hydrometallurgy 105, 195–200. Park, K.H., Kim, H.I., Parhi, P.K., 2010. Recovery of molybdenum from spent catalyst leach solutions by solvent extraction with LIX 84-I. Sep. Purif. Technol. 74, 294–299. Rojas-Rodriguez, A.D., Flores-Fajardo, O., Gonzalez, F.S.A., Castillo, N.N.L., Gomez, M.J.C., 2012. Chemical treatment to recover molybdenum and vanadium from spent heavy gasoil hydrodesulfurization catalyst. Adv. Chem. Eng. Sci. 2, 408–412. Sahu, K.K., Agrawal, A., Mishra, D., 2013. Hazardous waste to materials: recovery of molybdenum and vanadium from acidic leach liquor of spent hydroprocessing catalyst using alamine 308. J. Environ. Manag. 125, 68–73. Schrotterova, D., Nekovar, P., 2000. Extraction of Cr(VI), Mo(VI), and W(VI) from sulfate solutions by primary amine. 27th International Conference of the Slovak Society of Chemical Engineering, 22–26 May, 2000, Tatranske, Matliare. Tavakoli, M.R., Dreisinger, D.B., 2014. Separation of vanadium from iron by solvent extraction using acidic and neutral organophosphorus extractants. Hydrometallurgy 141, 17–23. Valverde Jr., I.M., Paulino, J.F., Afonso, J.C., 2008. Hydrometallurgical route to recover molybdenum, nickel, cobalt and aluminum from spent hydro treating catalysts in sulphuric acid medium. J. Hazard. Mater. 160, 310–317. Villarreal, M.S., Kharisov, B.I., Torres-Martinez, L.M., Elizondo, V.N., 1999. Recovery of vanadium and molybdenum from spent petroleum catalyst of PEMEX. Ind. Eng. Chem. Res. 38, 4624–4628. Wang, M., Wang, X., Liu, W., 2009. A novel technology of molybdenum extraction from low grade Ni–Mo ore. Hydrometallurgy 97, 126–130. Zeng, L., Cheng, C.Y., 2009a. A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation catalysts: part I: metallurgical processes. Hydrometallurgy 98 (1–2), 1–9. Zeng, L., Cheng, C.Y., 2009b. A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation catalysts: part II: separation and purification. Hydrometallurgy 98 (1–2), 10–20. Zeng, L., Cheng, C.Y., 2010. Recovery of molybdenum and vanadium from synthetic sulphuric acid leach solutions of spent hydrodesulphurisation catalysts using solution extraction. Hydrometallurgy 101, 141–147. Zhang, P., Inoue, K., Tsuyama, H., 1995. Recovery of metal values from spent hydrodesulfurization catalysts by liquid–liquid extraction. Energy Fuels 9, 231–239. Zhang, P., Inoue, K., Yoshizuka, K., Tsuyama, H., 1996. Extraction and selective stripping of molybdenum and vanadium(IV) from sulphuric acid solution containing aluminium(III), cobalt(II), nickel(II) and iron(III) by LIX 63 in Exxsol D80. Hydrometallurgy 41, 45–53. Zhu, Z., Pranolo, Y., Chu, Y.C., 2013. Uranium recovery from alkaline leach solution using a new reagent of Cyphos IL 101. ALTA 2013 Uranium-REE Conference, 30–31. Perth, Australia. Ziyadanogullari, R., Aydın, I., 2004. Recovery of uranium, nickel, molybdenum and vanadium from floated asphaltite ash. Sep. Sci. Technol. 39 (13), 3113–3125.
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Solvent extraction of molybdenum and vanadium from sulphate solutions with Cyphos IL 101 Zhaowu Zhu a, Karol Tulpatowicz b, Yoko Pranolo a, Chu Yong Cheng a,⁎ a b
CSIRO Minerals Resources National Research Flagship, Australia RMDSTEM Limited, Australia
a r t i c l e
i n f o
Article history: Received 25 November 2014 Received in revised form 4 March 2015 Accepted 10 March 2015 Available online 14 March 2015 Keywords: Cyphos IL 101 Molybdenum Vanadium Solvent extraction
a b s t r a c t Increasing demand for the rare metals of molybdenum and vanadium stimulates the research on their recovery from various resources. Solvent extraction of molybdenum and vanadium from sulphate solution with Cyphos IL 101 (trihexyl(tetradecyl)phosphonium chloride) in an aromatic diluent of ShellSol A150 was investigated in order to develop a more efficient separation method. It was found that molybdenum was extracted efficiently in the tested pH range of 0.5–2.0, while efficient vanadium extraction was at pH over 1.8. Effective separation of molybdenum from vanadium could be achieved at pH around 0.5. The separation of molybdenum and vanadium from impurities including iron(III) and aluminium was effective. The metal loading capacity was very high due to the formation of polyoxometallic ions during the extraction of molybdenum and vanadium. Chloride up to 10 g/L and sulphate up to 100 g/L had no significant effect on metal extraction. The extraction of molybdenum and vanadium was very fast, reaching equilibrium in 0.5 min. Vanadium could be stripped efficiently using 0.5 M sulphuric acid, while molybdenum could be stripped efficiently using 4–6 M sulphuric acid. The Cyphos IL 101 organic system has obvious advantages compared to the previously investigated solvent systems in terms of separation of molybdenum from vanadium and separation of vanadium from iron(III) and aluminium. Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.
1. Introduction Increasing demand for the rare metals of molybdenum and vanadium stimulates the research on their recovery from various resources (Ziyadanogullari and Aydın, 2004; He et al., 2007; Wang et al., 2009; Zeng and Cheng, 2009a, 2009b; Parhi et al., 2011). It is particularly true to recover them from spent catalysts owing to their value for sustainable supply and significant reduction of environmental pollution (Biswas et al., 1985; Villarreal et al., 1999; Valverde et al., 2008; Zeng and Cheng, 2009a; Rojas-Rodriguez et al., 2012; Banda et al., 2013). The leach of raw materials with sulphuric acid to recover molybdenum and vanadium is widely used due to its low corrosion and low cost (Valverde et al., 2008; Zeng and Cheng, 2009a; Sahu et al., 2013). Recovery of molybdenum and vanadium from sulphate leach solutions by solvent extraction has been widely investigated. A number of solvent systems have been reported which could be used for their recovery and separation. Among them, the acidic organo-phosphorus extractants including organophosphoric, organophosphonic and organophosphinic acids have been extensively investigated (Zhang et al., 1995; Li et al., 2012; Padhan and Sarangi, 2014; Tavakoli and Dreisinger, 2014). It was concluded that molybdenum could be separated from vanadium at low pH near 0 (Zhang et al., 1995). However, ⁎ Corresponding author. E-mail address: [email protected] (C.Y. Cheng).
http://dx.doi.org/10.1016/j.hydromet.2015.03.005 0304-386X/Crown Copyright © 2015 Published by Elsevier B.V. All rights reserved.
it was difficult to separate vanadium from the impurities usually present such as iron(III) and aluminium (Zhang et al., 1995; Tavakoli and Dreisinger, 2014). Long chain amine extractants including primary, tertiary amines and quaternary amine salts were also well investigated. Both molybdenum and vanadium(V) could be extracted efficiently at low pH by primary and tertiary amines. Good separations of molybdenum and vanadium(V) from iron(III) and aluminium was readily achieved using tertiary amines (Miller and Mooliman, 1985; Parhi et al., 2011; Lozano and Godinez, 2003; Sahu et al., 2013). However, it is difficult to separate molybdenum from vanadium(V) due to their similar extraction properties (Olazabal et al., 1992; Sahu et al., 2013). A quaternary amine salt of Aliquat 336 (methyltrioctylammonium chloride) could be used to separate vanadium(V) from molybdenum in a high pH range of 7–10 due to the high extraction of vanadium and very low extraction of molybdenum, but their separation in the pH range of 0.5–5 was very poor (Olazabal et al., 1992; Kushwaha et al., 2011). Furthermore, vanadium stripping was difficult using acid solution. Selective stripping of vanadium in the co-loaded Aliquat 336 system with molybdenum was only achieved by reducing vanadium(V) to vanadium(IV) (Hirai and Komasawa, 1993). A hydroxyoxime extractant, LIX 63 (5,8-diethyl-7-hydroxydodecane6-oxime) was investigated and showed good separation of molybdenum from vanadium(IV) at very low pH around 0 (Zhang et al., 1996). The separation of molybdenum and vanadium from the impurities including
Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77
73
Table 1 Composition of the synthetic solution and chemical purity used for the solution preparation. Metal
Mo
V
Fe
Al
Cu
Mn
Concentration (g/L) Chemicals
0.5 Na2MoO4·2H2O
0.5 Na3VO4
1.0 Fe2SO4·6H2O
1.0 Al2(SO4)3·16H2O
1.0 CuSO4·5H2O
1.0 MnSO4·4H2O
iron(III) and aluminium was efficient. However, the separation of molybdenum from vanadium(V) was very difficult since both of them were strongly extracted even at pH b 1, resulting in their poor separation in acidic solutions (Zeng and Cheng, 2010). Additionally, the stability of LIX 63 is a concern due to its degradation, particularly in the presence of the potential oxidant vanadium(V) (Barnard et al., 2010). In summary, either poor separation of molybdenum from vanadium(V), or poor separation of both from iron(III) and aluminium was generally shown with the solvent systems previously investigated. Additionally, alkaline solution was required to strip molybdenum, resulting in high risk of poor phase separation and solvent loss by high solubility in alkaline solutions (Zeng and Cheng, 2009b). In the present work, trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) was studied for the separation of molybdenum and vanadium(V) and separation of them from the impurities including iron(III) and aluminium in a synthetic sulphate solution.
2. Experimental 2.1. Reagents and solution preparation Cyphos IL 101 was kindly supplied by Cytec Industries Inc. (USA). The organic solutions were prepared by dissolving Cyphos IL 101 in an aromatic hydrocarbon diluent of ShellSol A150 provided by Shell Chemicals (Australia). This aromatic hydrocarbon diluent was used because Cyphos IL 101 has poor solubility in aliphatic hydrocarbon diluent. In regard to the most frequently associated metals in the raw materials of molybdenum and vanadium, an aqueous solution was prepared by dissolving corresponding metal salts in de-ionised water to a desired concentration as shown in Table 1. Although nickel and cobalt are commonly presented in catalysts used for petroleum hydrodesulphurisation, they were not included in this study because they are unable to form extractable anions in sulphate solutions and could not be extracted with Cyphos IL 101 system. All inorganic chemicals used were analytical grade.
2.2. Metal extraction and stripping Metal extraction and stripping tests were carried out in a 300 mL hexagonal glass reactor immersed in a temperature controlled water bath (40 ± 1 °C) (temperature under which solvent extraction practices often operated). The aqueous and organic solutions were mixed using Eurostar Digital overhead stirrer coupled with a 40 mm diameter impeller at a stirring speed of around 1200 RPM. Mixing continued to 10 min for each sampling point except tests for kinetics study. The pH was monitored using a Hanna portable pH metre connected with a Ross Sure Flow electrode. The pH was adjusted with 4 M NaOH and 2 M H2SO4 solutions as required. For the tests of chloride and sulphate effect, sodium chloride and sodium sulphate were used, respectively to achieve the desired concentrations. 2.3. Extraction kinetics test A preliminary extraction test was conducted at an A/O ratio of 1:1, 40 °C and a selected pH to determine the amount of NaOH solution required for pre-equilibration. The organic solution was then preequilibrated with the pre-determined amount of NaOH solution. The synthetic solution and the pre-equilibrated organic solution were mixed at an A/O ratio of 1:1 and 40 °C. Timing started immediately once the two phases were mixed. Mixed solution samples were taken at 0.5, 1.0, 2.0, 3.0, 5.0 and 10 min for assay. 2.4. Sampling and analysis After the two phases were separated, the aqueous solution was filtered through a 0.45 μm Supor membrane filter. Metal concentrations in aqueous solutions were analysed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Metal concentrations in organic solutions were calculated based on the metal concentrations in the feed solution and the raffinate. 3. Results and discussion 3.1. Metal extraction pH isotherms
100.0
Metal extraction pH isotherms were measured in a pH range of 0.5 to 2 with 0.10 M Cyphos IL 101 in ShellSol A150 and the synthetic solution (Fig. 1). It was shown that the molybdenum extraction was very efficient with N 98% extraction in the pH range tested, while vanadium extraction started from 8% at pH 0.5 and increased to 93% at pH 1.8. Good separation of molybdenum from vanadium was achieved at pH 0.5 with the separation factor of 700. The extraction of iron was very low at pH lower than 1.5. It slightly increased to 7.4% and 11.4% at pH 1.8 and 2.0, respectively. The extraction of other metals including aluminium, manganese and copper were negligible, indicating very good separation of molybdenum and vanadium from these metals.
90.0
Extraction (%)
80.0 70.0 60.0 50.0 40.0 30.0
V
Mo
Fe
Cu
Mn
Al
20.0 10.0 0.0 0.0
0.5
1.0 1.5 Equilibrium pH
2.0
2.5
Fig. 1. Metal extraction pH isotherms with 0.10 M Cyphos IL 101 and the synthetic solution at A/O ratio of 1:1 and 40 °C.
Table 2 The pH change during metal extraction with 0.10 M Cyphos IL 101 and pre-neutralised synthetic solutions at A/O ratio of 1:1 and 40 °C. Initial pH Equilibrium pH Mo extraction (%) V extraction (%)
0.50 0.58 98.9 8.6
1.17 1.25 99.4 50.0
1.58 1.80 99.3 93.5
1.83 2.13 99.8 97.0
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Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77
100.0
100.0
90.0
90.0
80.0
80.0
V
60.0
70.0 Extraction (%)
Extraction (%)
70.0
Mo
50.0 Fe
40.0
60.0 Mo 50.0
30.0
20.0
20.0
10.0
10.0
0.0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 Cyphos 101 concentration (M)
The extraction mechanism of molybdenum and vanadium is very complicated due to the formation of various polyoxometallic species (Olazabal et al., 1992; Bal et al., 2002, 2004; Zeng and Cheng, 2009b). It is well known that many molybdenum anions of could form in the solution depending on the pH and its concentration. The possible anionic species should be H3Mo7O324−, H2Mo7O424−, HMo7O524−, HMo8O326−, Mo8O426− and H3Mo8O528− at pH below 2.5 based on Bal et al. (2004), but principally to be H3Mo7O324− based on Olazabal et al. (1992). The fraction of anionic species H3Mo7O324− increases from pH 0.5 to 2.5 where it becomes predominant. During the extraction, cationic ions convert to anions based on the Le Chatelier's principle shown in Eqs. (1)–(3). 0 3− 0 − 3 R3 R P Cl org þ H3 Mo7 O24 ⇔ R3 R P 3 H3 Mo7 O24 org þ 3Claq ð1Þ aq
−
2þ
þ
MoO2 þ 2H2 O⇔HMoO4 þ 3H −
þ
ð2Þ
3−
7HMoO4 þ 4H ⇔H3 Mo7 O24 þ 4H2 O
ð3Þ
where R3R′P ⋅ Cl represents Cyphos IL 101 in chloride form and subscripts of org and aq organic and aqueous phase, respectively. Due to very strong extraction of H3Mo7O324− species generated in Eq. (3) by Cyphos IL 101, these species are extracted immediately
Fe
40.0
30.0
Fig. 2. Effect of Cyphos 101 concentration on metal extraction at A/O ratio of 1:1, pH 1.80 and 40 °C.
V
0.0 0
20
40
80
100
Fig. 4. Effect of sulphate on metal extraction with 0.10 M Cyphos IL 101 at pH 1.80, A/O ratio of 1:1 and 40 °C.
after the formation, which makes Eqs. (2) and (3) move to the right side regardless of any acid generated. The pH change was determined during the metal extraction using pre-neutralised synthetic solutions as shown in Table 2. The organic solution of 0.10 M Cyphos IL 101 was pre-washed with de-ionised water to equilibrium pH of about 6. In Table 2, it is obvious that the aqueous equilibrium pH increased during the metal extraction due to the extraction of acid by Cyphos IL 101. Vanadium extraction increased with pH increase in Fig. 1, indicating that higher pH is favourable to the vanadium extraction. Olazabal et al. (1992) reported that the majority of vanadium(V) was present in the form of VO+ 2 at pH lower than 2 and polyoxovanadate only formed in the neutral solution. It was suggested that vanadium transformation from its cations to the anions also occurred according to the Le Chatelier's principle during the extraction since only anions could be extracted. Therefore, it is predicted that Cyphos IL 101 enabled the extractable vanadium anions forming in the aqueous phase at low pH. The most probable anionic vanadates were formed via Eqs. (3) to (5) according to the reported investigations (Miller and Mooliman, 1985; Olazabal et al., 1992; Bal et al., 2002; Lozano and Godinez, 2003). þ
þ
3−
VO2 þ 2H2 O⇔VO4 þ 4H þ
ð4Þ þ
4−
2VO2 þ 3H2 O⇔V2 O7 þ 6H þ
ð5Þ þ
4−
10VO2 þ 8H2 O⇔H2 V10 O28 þ 14H :
100.0 90.0
ð6Þ
All three kinds of vanadium anions formed via Eqs. (4)–(6) could be extracted with Cyphos IL 101 via an anion exchange mechanism. Based on the data reported by Olazabal et al. (1992), the fraction of H2V10O4− 28 species increased from pH 0.5 to 2, resulting in the increase in
80.0 70.0
Extraction (%)
60
Sulphate addition (g/L)
V 60.0 50.0
Mo
40.0
Fe
Table 3 Metal extraction and distribution with 0.10 M Cyphos IL 101 at pH 1.80 and 40 °C with various A/O ratios.
30.0 20.0 10.0
A/O ratio
Mo In aqueous (g/L)
In organic (g/L)
Extraction (%)
In aqueous (g/L)
In organic (g/L)
Extraction (%)
1:1 2:1 4:1 6:1
0.003 0.002 0.002 0.003
0.447 0.898 1.797 2.685
99.3 99.7 99.7 99.3
0.022 0.015 0.014 0.013
0.446 0.906 1.817 2.733
95.3 96.7 97.0 97.3
0.0 0.0
2.0
4.0 6.0 Chloride addition (g/L)
8.0
10.0
Fig. 3. Effect of chloride on metal extraction with 0.10 M Cyphos IL 101 at pH 1.80, A/O ratio of 1:1 and 40 °C.
V
Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77 100.0
100.0
90.0
90.0
80.0
80.0 V
70.0
70.0
60.0
Extraction (%)
Extraction (%)
75
Mo
50.0 40.0 30.0
60.0 V
50.0 40.0
Mo
30.0
20.0
20.0 10.0
10.0 0.0 1:1
2:1
4:1
6:1
0.0
A/O ratio
0.0
1.0
2.0
3.0
4.0
5.0
6.0
Time (min) Fig. 5. Metal extraction under various A/O ratios with 0.10 M Cyphos IL 101 and single metal solutions containing 9.6 g/L Mo and 4.8 g/L V, respectively, at pH 1.80 and 40 °C.
Fig. 6. Extraction kinetics of molybdenum and vanadium with 0.10 M Cyphos IL 101 and the synthetic solution at pH 1.80, A/O ratio of 1:1 and 40 °C.
vanadium(V) extraction with pH as indicated in Fig. 1. The extraction of H2V10O4− 28 species via anion exchange is shown in Eq. (7). 4− 0 − 4 R3 R P Cl org þ H2 V10 O28 ⇔ R3 R P 4 H2 V10 O28 org þ 4Claq ð7Þ 0
aq
The formation of polyoxovanadate and polyoxomolybdate could be verified by the over stoichiometrical extractions in the subsequent tests. However, further investigation is required to exactly determine the extracted species with Cyphos IL 101. 3.2. Effect of Cyphos 101 concentration The extraction of molybdenum, vanadium and iron was determined using various Cyphos IL 101 concentrations and the synthetic solution at pH 1.80 ± 0.01, A/O ratio of 1:1 and 40 °C (Fig. 2). It was shown that the concentration of Cyphos IL 101 in the range of 0.01–0.10 M had no effect on the extraction of molybdenum and vanadium, indicating that Cyphos IL 101 has very high extraction capacity. The total molar concentration of extracted molybdenum and vanadium was 0.014 M using 0.01 M Cyphos IL 101. The molar concentration of metal loading was higher than that of the Cyphos IL 101, indicating the formation of polyoxometallic anions during the extraction. The extraction of iron increased slightly with the increase in the organic concentration due to more available extractant. The very low iron extractions at low organic concentrations suggested high selectivity of vanadium and molybdenum over iron using low concentration of Cyphos IL 101. In order to evidence the variation of iron extraction, higher concentration of 0.10 M Cyphos IL 101 was selected for the subsequent test work.
vanadium and iron with 0.10 M Cyphos IL 101 and the synthetic solution was studied by adding sodium chloride in the initial synthetic solution. The results obtained at pH 1.80 ± 0.01, A/O ratio of 1:1 and 40 °C are shown in Fig. 3. It was shown that the addition of chloride up to 10 g/L has no significant effect on the extraction of molybdenum and iron. The extraction of vanadium slightly decreased with the increase in chloride concentration (Fig. 3), probably due to the combination of chloride with VO+ 2 which adversely affected the formations of extractable anions via Eqs. (4)–(6). Another possible reason could be attributed to the competitive extraction of chloride ions. Considering that sulphate could reach very high concentration in the leach solution due to possible high concentrations of impurities, the effect of sulphate concentration on the extraction of molybdenum, vanadium and iron was studied by adding sodium sulphate in the initial aqueous solution. The extraction was conducted at pH 1.80 ± 0.01, A/O ratio of 1:1 and 40 °C (in Fig. 4). It was also observed that sulphate concentration up to 100 g/L had no significant effect on the extraction of molybdenum and iron. The extraction of vanadium also decreased slightly with the increase in the sulphate concentration probably due to the combination of sulphate with VO+ 2 to adversely affect the polyoxovanadate formation. Similar to the effect of chloride, sulphate could also be competitively extracted by Cyphos IL 101, resulting in the decrease in vanadium extraction. The association of sulphate with Cyphos IL 101 has been reported elsewhere (Zhu et al., 2013). 100.0 90.0 80.0
Chloride is often presented in the raw materials and/or operation water. The effect of chloride on the extraction of molybdenum,
70.0
Table 4 Metal loading in the 0.10 M Cyphos IL 101 organic solution by contacting with single metal solutions at pH 1.80 and 40 °C. A/O ratio
1:1 2:1 4:1 6:1
Mo
V
In organic (g/L)
In organic (M)
[M]/[org]a
9.6 19.1 26.5 24.4
0.10 0.20 0.28 0.25
1.00 1.99 2.76 2.54
Stripping (%)
3.3. Effect of chloride and sulphate concentration
60.0 50.0 40.0 V 30.0 20.0
In organic (g/L)
In organic (M)
[M]/[org]
4.69 9.40 15.2 15.4
0.09 0.18 0.30 0.30
0.92 1.85 2.98 3.03
Mo
10.0
a [M] and [org] represent the molar concentrations of metal and Cyphos IL 101, respectively.
0.0 0.0
1.0
2.0
3.0
4.0
5.0
6.0
H2 SO4 [M] Fig. 7. Metal stripping with various concentrations of H2SO4 solution at A/O ratio of 1:1 and 40 °C.
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Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77
Table 5 Stripping efficiency of molybdenum and vanadium with NaCl in 0.1 M Cyphos IL 101. NaCl (M)
pH
Stripping of Mo (%)
Stripping of V (%)
Observation
0.5 1.0 2.0 3.0
7.17 7.21 7.85 7.95
27.8 54.2 44.0 46.4
23.6 54.2 53.8 47.3
Clear phases Clear phases Slight precipitation Slight precipitation
The effect of both chloride and sulphate on the extraction of molybdenum in the concentration range tested was too weak to be observed due to its very strong extraction with Cyphos IL 101. 3.4. Effect of A/O ratio The metal extraction was measured with 0.10 M Cyphos IL 101 and the synthetic solution at pH 1.80 ± 0.01 and 40 °C using various A/O ratios. The extraction and distribution of molybdenum and vanadium are shown in Table 3. As Cyphos IL 101 has very high capacity for the extraction of molybdenum and vanadium, the metal extraction was not affected by increasing A/O ratio from 1:1 to 6:1, resulting in the significant increase in the metal concentrations in the loaded organic solution. At A/O ratio of 6:1, about 2.7 g/L of each metal (0.08 M total Mo and V) was loaded in the 0.10 M Cyphos IL 101 solution without phase separation problem. To determine the maximum loading capacity of Cyphos IL 101 for the extraction of molybdenum and vanadium, solutions containing individual metal of 9.6 g/L Mo(0.100 M) and 4.8 g/L V (0.094 M), respectively, were prepared. Metal extractions with 0.10 M Cyphos IL 101 from these solutions at pH 1.80 ± 0.01 and 40 °C using various A/O ratios are shown in Fig. 5. It was shown that both molybdenum and vanadium were extracted efficiently at an A/O ratio of 1:1 and 2:1 with good phase separation. At high A/O ratio of 4:1 and 6:1, both organic phases were heavily emulsified, suggesting that the organic was over-loaded. The metal loading in organic solutions with various A/O ratios was calculated (Table 4). It was shown that the loading of molybdenum and vanadium reached about 20 g/L and 10 g/L at an A/O ratio of 2:1, respectively, corresponding to that one mole of Cyphos IL 101 was loaded with 1.99 mol of molybdenum or 1.85 mol of vanadium. This, again, suggested that polyoxometallic anions were formed during the extraction of both molybdenum and vanadium. 3.5. Kinetics of molybdenum and vanadium extraction The extraction kinetics of molybdenum and vanadium with 0.10 M Cyphos IL 101 pre-equilibrated to a neutral pH of about 6 and the synthetic solution was studied at pH 1.80 ± 0.01, A/O ratio of 1:1 and 40 °C (Fig. 6). It was found that the extraction of both molybdenum and vanadium was very fast and reached the equilibrium within 0.5 min. 3.6. Stripping of molybdenum and vanadium The pre-loaded 0.10 M Cyphos IL 101 containing 0.43 g/L Mo and 0.42 g/L V was stripped using various concentrations of H2SO4 solutions at an A/O ratio of 1:1 and 40 °C (Fig. 7). It was shown that the stripping of vanadium with sulphuric acid was easier than that of molybdenum. The stripping of vanadium reached 87.6% using 0.5 M H2SO4, while
molybdenum stripping was only 3.6%. This suggests that the separation of molybdenum from vanadium could also be obtained by selective stripping using 0.5 M H2SO4. Efficient molybdenum stripping was achieved using higher sulphuric acid solutions of 4–6 M with 78.3– 95.6% Mo stripping. It is suggested that the stripping of molybdenum and vanadium from the loaded Cyphos IL 101 is due to the large increase in H+ concentration and the competition of anionic species of SO2− 4 and HSO− 4 at high H2SO4 concentration. The stripping of molybdenum and vanadium in the pre-loaded Cyphos IL 101 solution using various NaCl concentration solutions were carried out at around neutral pH, A/O of 1:1 and 40 °C (Table 5). The stripping efficiency of both molybdenum and vanadium increased with the increase in NaCl concentration from 0.5 M to 1.0 M. Precipitation in the aqueous phase was observed when further increased NaCl concentration to over 2.0 M, indicating that it is difficult to apply NaCl for the stripping of molybdenum and vanadium. The stripping of molybdenum and vanadium by other selected agents was also studied as shown in Table 6. It was found that no other agents performed better than sulphuric acid in terms of metal stripping and selectivity.
3.7. Performance comparison The performance of the Cyphos IL 101 system and other previously investigated systems were compared (Table 7). It is clear that all previously investigated systems have disadvantages either in poor separation of molybdenum from vanadium or in poor separation of vanadium from impurities including iron(III) and aluminium. Additionally, the stripping of molybdenum was only achieved using alkaline solutions, resulting in high risks of poor phase separation and organic loss due to high solubility in alkaline solutions (Zhang et al., 1995; Zeng and Cheng, 2009b). The Cyphos IL 101 system has obvious advantages for good separation of molybdenum from vanadium and good separation of vanadium from iron(III). Both vanadium(V) and molybdenum can be efficiently stripped using sulphuric acid solutions.
4. Conclusions Cyphos IL 101, trihexyl(tetradecyl)phosphonium chloride, has significant advantages for the recovery of molybdenum and vanadium from sulphate solutions compared to other investigated solvent systems. Molybdenum could be extracted efficiently in the pH range of 0.5–2.0, while efficient vanadium extraction was at pH over 1.8, leading to their good separation at pH around 0.5. The separation of molybdenum and vanadium from impurities including iron(III), aluminium, manganese, copper and possibly nickel and cobalt was very effective. As molybdenum and vanadium formed polyoxometallic anions during extraction, the loading capacity of Cyphos IL 101 was very high with 20 g/L Mo or 10 g/L V loaded in the 0.10 M organic solution without phase separation problem. Chloride up to 10 g/L and sulphate up to 100 g/L had no significant effect on the metal extraction and separation. The extraction of molybdenum and vanadium was very fast, reaching equilibrium in 0.5 min. Vanadium could be stripped using 0.5 M sulphuric acid solution and molybdenum could be efficiently stripped using 4–6 M sulphuric acid. The separation of molybdenum from vanadium also can be achieved by selective stripping vanadium using 0.5 M
Table 6 Stripping of molybdenum and vanadium from 0.10 M Cyphos IL 101 organic solution by other stripping solutions at an A/O ratio of 1:1 and 40 °C. Reagents
1.0 M HCl
1.0 M NH3·H2O
1.0 M (NH4)2CO3
1.0 M Na2CO3
1.0 M NaOH
V stripping (%) Mo stripping (%) Phase separation
54.8 4.0 Good
51.9 8.6 Poor
76.0 44.1 Good
71.0 55.9 Good
– – Precipitation
Z. Zhu et al. / Hydrometallurgy 154 (2015) 72–77
77
Table 7 Performance comparison of various solvent systems used in the recovery and separation molybdenum and vanadium in sulphate solutions. Solvent systems
Diluent
Mo/V separation
Separation from Fe(III)
Organo phosphoric acid Organo phosphonic acid Organo phosphinic acid Primary amine
Hydrocarbon compound
a
Only by reducing to Fe(II) No separation of vanadium
Hydrocarbon compound
Possible separation at pH b 1.0 Only by reducing to Fe(II) No separation of vanadium
Hydrocarbon compound
Possible separation at pH b 1.0 Only by reducing to Fe(II) Poor separation of vanadium No separation in pH range of No reference was found Possible separation due to 1–6 low Al extraction
Kerosene and isodecanol as the modifier
Possible separation at pH b 0.5
Separation from Al
Tertiary amine
Kerosene and isodecanol Possible at pH b 1.0 or as the modifier or toluene reducing V(V) to V(IV)
Good separation
Good separation
Quaternary amine
Kerosene and isodecanol Possible at pH b 0.5; as the modifier or toluene bGood in pH range of 7–10 Hydrocarbon compound Poor separation in acidic solution Aromatic hydrocarbon Good separation at pH b 0.5 compound
Good separation
Good separation
Good separation
Good separation
Good separation
Good separation
Oxime Cyphos IL 101 a b
Reference Zhang et al. (1995), Tavakoli and Dreisinger (2014) Zhang et al. (1995), Tavakoli and Dreisinger (2014) Zhang et al. (1995) Schrotterova and Nekovar (2000), Lozano and Godinez (2003); Olazabal et al. (1992), Hirai and Komasawa (1993), Parhi et al. (2011), Sahu et al. (2013). Olazabal et al. (1992), Kushwaha et al. (2011) Zhang et al. (1996), Park et al. (2010), Zeng and Cheng (2010) Present work
Possible separation with the estimated separation factor N100; Good separation with the estimated separation factor N1000.
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