A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation...

Hydrometallurgy 98 (2009) 10–20

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Hydrometallurgy

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A literature review of the recovery of molybdenum and vanadium from spenthydrodesulphurisation catalystsPart II: Separation and purification

Li Zeng, Chu Yong Cheng ⁎Parker Centre for Integrated Hydrometallurgy Solutions/CSIRO Minerals, PO Box 7229, Karawara, WA 6152, Australia

⁎ Corresponding author. Tel.: +61 8 9334 8916; fax: +E-mail address: [email protected] (C. Yong Cheng)

0304-386X/$ – see front matter. Crown Copyright © 20doi:10.1016/j.hydromet.2009.03.012

a b s t r a c t
a r t i c l e i n f o
Article history:
Received 20 January 2009
Various methods for sepasolutions of spent catalysts

Revised 24 March 2009Accepted 24 March 2009Available online 31 March 2009

Keywords:MolybdenumVanadiumSeparationPurificationSolvent extraction

ration, purification and recovery of molybdenum and vanadium from leachare reviewed. The main methods include sulphide precipitation, ammonium salt

precipitation, carbon absorption, ion exchange and solvent extraction. These methods are briefly comparedand assessed for both purification of leach solutions and recovery of molybdenum and vanadium from thesolutions in terms of their selectivity, efficiency and product quality. The strategies for recovery of othervaluable metals including nickel and cobalt are also reviewed and discussed.Among these methods, precipitation offers low cost and simple operation, however, high purities (N99%) ofproducts of molybdenum and vanadium cannot be achieved. The loading capacities of activated carbon formolybdenum and vanadium are relatively low, resulting in no industrial application of this technology in theseparation of molybdenum and vanadium. Ion exchange offers a useful means for almost completeseparation of molybdenum and vanadium and for production of their high purity products, although thescale of application of ion exchange in industry is limited. Solvent extraction is highly selective for separationand recovery of molybdenum and vanadium, and is the most promising method recommended for futureresearch and development.

Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112. Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.1. Sulphide precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.2. Ammonium salt precipitation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.3. Other precipitation methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. Adsorption with activated carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124. Ion exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125. Solvent extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5.1. Solution chemistry of molybdenum and vanadium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.2. Extraction chemistry of molybdenum and vanadium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135.3. Separation and recovery of molybdenum and vanadium by solvent extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

5.3.1. SX of molybdenum and vanadium with extractants involving compound formation . . . . . . . . . . . . . . . . . . . . . . 145.3.2. SX of molybdenum and vanadium with extractants involving ion association . . . . . . . . . . . . . . . . . . . . . . . . . 165.3.3. SX of molybdenum and vanadium with extractants involving solvation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185.3.4. SX of molybdenum and vanadium with other extractants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185.3.5. The combination of SX and other technologies for separation and recovery of molybdenum and vanadium . . . . . . . . . . . 18

6. Summary and recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

61 8 9334 8001..

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Table 1Effect of different ammonium salts on the separation of Mo and V by precipitation(based on Rokukawa, 1993).

Ammoniumsalts

V Mo

Terminalconcentration (g/L)

Precipitation(%)

Terminalconcentration (g/L)

Precipitation(%)

NH4Cl 0.016 99.1 1.18 8.2(NH4)2SO4 0.014 97.9 1.16 9.5NH4NO3 0.003 98.4 1.23 4.1CH3COONH4 0.017 99.0 1.24 3.1

11L. Zeng, C.Y. Cheng / Hydrometallurgy 98 (2009) 10–20

1. Introduction

In Part I of this review, various metallurgical processes for spenthydrodesulphurisation (HDS) catalysts are reviewed. In most cases,spent catalysts are treated with hydrometallurgical leaching processessuch as acid leaching, caustic leaching, salt leaching and bioleachingtogether with roasting as a pre-treatment step. Most of the molybde-num and vanadium exist in the form of simple oxyanions or complexoxyanionic polymers depending on the pH of the leach solution. Nickeland cobalt enter into solutions accompanied with molybdenum andvanadium in acid leaching and bioleaching and stay in the residue inalkaline leaching processes. The methods of recovering metals fromsolutions usually include precipitation, solvent extraction, ionexchange, adsorption with activated carbon and biotechnologicaladsorption. Among them, solvent extraction is one of the wellestablished unit operations in hydrometallurgy for commercial produc-tion of high purity metals. It has certain inherent advantages such asease of continuous operation, high throughputs, improved economicscoupled with flexibility of handling a variety of metal solutions fromdiverse sources. Therefore, the separation and purification of molybde-numandvanadium from leach solutions of spent catalysts using solventextraction will be reviewed in more detail.

2. Precipitation

Chemical precipitation is the most common and simplest method torecover andseparatemetal values fromsolutions. Someauthors (Sebenikand Ference, 1982; Biswas et al., 1985; Park et al., 2006 a, b; Chen et al.,2007) studied the separation and purification of molybdenum andvanadium from other metal values in both acidic and alkaline leachsolutions of spent catalysts by selective precipitation. There are twomainapproaches to precipitation. One is sulphide precipitation in whichmolybdenum is precipitated as MoS3, leaving vanadium in the solution.This approach is usually applied to acidic leach solutions. The otheris ammonium salt precipitation in which vanadium is precipitated asNH4VO3 by addition of ammoniumsulphate or chloride. Generally, this isfollowed by precipitatingmolybdenumbyadjusting the solutionpH. Thesecond approach ismainly used for caustic or salt leach solutionsof spentcatalysts.

2.1. Sulphide precipitation

Suzuki and Gao (1982) reported a process in which H2S gas wasfirst injected into the acidic leachate (N40 °C) to precipitate MoS3.About 99% of the vanadiumwas then precipitated out in a pH range of4.5–5.5 adjusted by addition of calcium carbonate.

Sebenik and Ference (1982) proposed to precipitate MoS3 byaddition of H2S in an acidic solution. A known amount of H2SO4 wasadded to the solution to obtain a desired acid concentration and thesolutionwas then sparged with H2S for 20 min at 80 °C. The optimumseparation of molybdenum from vanadium occurred with a H2SO4

concentration range of 2–4 N. About 99.8% of the molybdenumreported to the precipitate and 99.8% of the vanadium remained in thesolution. The vanadium in the form of vanadyl cation (VO2+)was thenprecipitated as hydrated oxide, V(OH)4∙1.5H2O, by neutralisation ofthe solution, or as red cake, Na2H2V6O17, by oxidising the vanadium inthe solution with NaClO3 when the pH was adjusted with NaOH orNa2CO3.

2.2. Ammonium salt precipitation

Biswas et al. (1985) carried out the precipitation of vanadium asNH4VO3 by adding (NH4)2SO4 to the leach solution after NaCl–watervapour roasting with hot water at pH 8.6. The solution was thenheated for 1 h at 80 °C, ice-cooled and filtered. The filtrate wassubjected to solvent extraction to recover molybdenum.

Rokukawa (1993) studied the separation of molybdenum andvanadium by ammonium salt precipitation. Different kinds ofammonium salts (120 g/L) were tested with a solution containing2.17 g/LV and 1.28 g/LMo at pH 8.0. Some results are shown in Table 1.

In most cases, over 98% of the vanadium was precipitated.Although CH3COONH4 performed the best, the industry usually usesNH4Cl to precipitate vanadium due to its economic advantage. Muchmore than theoretical amount of NH4Cl is needed because theexcessive NH4Cl not only prompts the formation of vanadiumprecipitate, but also reduces the solubility of NH4VO3 due to thecommon ion effect. As a result, the solubility of NH4VO3 in NH4Clsolution decreases with increasing NH4Cl concentration (Table 2). Forexample, at 30 °C, with 0.21 g/L NH4Cl in the solution, the NH4VO3

solubility was 2.49 g/100 g H2O. When the NH4Cl concentrationincreased to 4.47 g/L, the NH4VO3 solubility largely decreased to0.006 g/100 g H2O.

Liu and Sui (2002) reported the precipitation of vanadium asNH4VO3 by adding NH4Cl to the solution from leaching Na2CO3-roasted spent catalysts with hot water. The following precipitationreaction occurred in a pH range of 8.0–9.0:

NaVO3 þ NH4Cl ¼ NH4VO3A þ NaCl ð1Þ

The molybdenum was then precipitated as molybdic acid byacidification with concentrated HNO3:

Na2MoO4 þ 2HNO3 þ H2O ¼ H2MoO4·H2O Aþ 2NaNO3 ð2Þ

Up to 99% of the vanadium was precipitated when the vanadiumconcentration (V2O5) in the solutionwas 25 g/L and the concentrationof NH4Cl exceeded 40 g/L.

Park et al. (2006a,b) studied the precipitation of molybdenum asammonium molybdate from a leach solution containing 22.0 g/L Mo,0.015 g/L Ni, 0.82 g/L Al and a small amount of V (8 mg/L). A MoO3

product of 97.3% purity was obtained. In the process, the solution wasfirst treated with HCl to adjust its pH to 2. The sodium molybdate wasconverted to molybdenum chloride as shown in the following reaction:

Na2MoO4 þ 8HCl ¼ MoCl6 þ 2NaCl þ 4H2O ð3Þ

The resultant solution was neutralised with ammonia to aroundpH 11 to convertmolybdenum as ammoniummolybdate. This solutionwas acidified by HCl to pH 2 and heated to 90 °C to allow the formationof ammonium molybdate precipitate:

MoCl6 þ 8NH4OH ¼ ðNH4Þ2MoO4 þ 6NH4Clþ 4H2O: ð4Þ

Ammonium salt precipitation is the primary method for theseparation of vanadium from molybdenum. Usually after vanadiumprecipitation, there is a small amount of molybdenum in the NH4VO3

crystal product and 30–100mg/kg vanadium in the filtrate containingmolybdenum (Shi and Wang, 2004). Solvent extraction and ionexchange are thereafter applied to completely separate molybdenumand vanadium.

Fig. 1. A conceptual process flow sheet for the recovery of molybdenum from spentcatalyst by oxidative soda ash leaching and carbon adsorption (based on Park, 2006a,b).

Table 2Solubility of NH4VO3 in NH4Cl solution (based on Shi and Wang, 2004).

Temperature/°C NH4Cl (g/L) NH4VO3 (g/100 g H2O)

12.5±2 0.261 0.0850.296 0.0490.550 0.018

30 0.210 2.4902.540 0.0264.470 0.0068.980 Minimum

60 0.551 1.34020.060 Minimum

12 L. Zeng, C.Y. Cheng / Hydrometallurgy 98 (2009) 10–20

2.3. Other precipitation methods

Chen et al. (2007) studied selective precipitation of vanadium andmolybdenum from an alkaline leach solution of spent catalysts by theaddition of barium hydroxide and barium aluminate, respectively,because of the low solubility of Ba3(VO4)2 and BaMoO4 in aqueoussolutions (Yoshio et al., 1995; Chang and Fuenzalida, 2003). At atemperature of 40 °C for a reaction time of 15minwith a stoichiometricquantity of Ba(OH)2, the precipitation of V reached 94.8%. In the case ofmolybdenum, 92.6%Mowas precipitated at a temperature of 80 °C for areaction time of 40 min with a stoichiometric quantity of BaAl2O4.

Complete separation and recovery of vanadium and molybdenumcannot be achieved by precipitation although its operation is simpleand costs are low. The precipitation of vanadium and molybdenum isfavoured when their concentrations in solution are very high (above30 g/L).

3. Adsorption with activated carbon

The activated carbon based purification route is well-known torecover precious metals like gold and silver from leach solutions(Laxen, 1984). It was tested as a unit process for the treatment ofrefractory metals such as molybdenum and vanadium (Mukherjeeet al., 1988a,b). In the field of hydrometallurgy, in addition to solventextraction and ion exchange, carbon adsorption emerges as animportant technology for metal purification and concentration. Inthe case of molybdenum and vanadium, the metal bearing anions areselectively adsorbed on activated charcoal by replacing the attachedhydroxyl ions. The metals are then freed from the loaded carbon bycontacting with suitable alkaline solutions. An alternative way to freethe adsorbed metals from the carbon is to use acidic solution, whichfavours formation of molybdenum and vanadium cations anddiscourages adsorption.

A laboratory-scale investigation by Mukherjee et al. (1990)demonstrated the feasibility of producing high purity V2O5 fromBayer sludge through a carbon adsorption and desorption route. It issuggested that such a process could be adopted advantageously on alarger scale using either the carbon-in-solution or carbon-in-columntechnique.

Activated carbon was used to purify a sodium molybdate solutionprior to the recovery of pure ammonium polymolybdate andmolybdenum trioxide (Kar et al., 2004). The sodium molybdatesolutionwas first treated with hydrochloric acid to adjust the pH up to2. A calculated quantity of charcoal was then added to selectivelyadsorbmostmolybdate anions while the other impurities remained inthe solution. Thereafter, the molybdate-loaded charcoal was firstwashed with water and then treated with ammonia to desorb themolybdates. The purity of final MoO3 product reached up to 99.94%.

Park et al. (2006a,b) proposed an adsorption/desorption andselective precipitation method to separate and recover molybdenumas molybdenum trioxide after leaching spent HDS catalysts withsodium carbonate and hydrogen peroxide. Under optimum conditionsof adsorption (pH 0.75, 3 h, 40% pulp density), the amount of Mo

absorbed by a gram of carbonwas 48.8 mg.With 30% pulp density and15% (v/v) NH4OH at pH 9.5 for a fixed time of 3 h, almost all of themolybdenum was desorbed. The resultant desorption solution wasthen acidified to pH 2 with HCl and heated to 90 °C to precipitate theammoniummolybdate salt. The complete process flow sheet is shownin Fig. 1.

4. Ion exchange

Ion exchange is a well-known technology for metal separation andpurification. In the process to recycle spent hydroprocessing catalysts(Berrebi et al., 1994) after a preliminary purification of the alkalineleach solution to eliminate the elements which could affect theseparation, the purified solution was then sent to the ion exchangeunit for complete separation of molybdenum and vanadium. It wasreported that the recovery of molybdenum and vanadium reached90% with high purity.

In most cases, solutions from leaching spent HDS catalysts withacids, alkalis or salts contain high concentration of molybdenum andrelatively low concentration of vanadium. Although most of vanadiumcan be separated from molybdenum by precipitation, the purity ofammoniummolybdate product cannotmeet themarket requirement ifthe concentration of vanadium is over 0.1 g/L in the solution. Zeng et al.(2006) studied the removal of vanadium from ammonium molybdatesolution by ion exchange. Over 99.84% of the vanadium was removedusing a chelating resinD418 (function group:–NHCH2PO3Na2) at pH7.2for a contact time of 30 min. The concentration of molybdenum was50 g/L and the concentration of vanadium was 0.638 g/L. Aftercontacting10 bed volumes, the vanadiumconcentrationwas reduced to0.007 g/L, resulting in an increase in theMo/V concentration ratio from78 in the feed solution to 7140 in the molybdenum product solution.The desorption results were excellent with 2mol/L NaOH solution. Theprocess features stable re-usability of the resin when transformed byHCl. A complete removal of vanadium from ammonium molybdatesolution containing 60–80 g/L of molybdenum, 0.6 g/L of vanadium

Fig. 2. An illustration of three-compartment electrochemical ion exchange cell (basedon Henry and van Lierde, 1998).

Table 3Effect of different pH on the formations of predominant species of Mo and V (based onTangri et al., 1998).

Mo V

pH Species pH Species

N6.5 MoO42− N13 VO4

3−

4 Mo7O246− 9 V2O7

4−

2 Mo8O264− 8.5 VO3

−

≤1 MoO22+ 6 V3O9

3−

0.8 MoO3∙2H2O 2 V10O286−

b2 VO2+


and 20 g/L of chloride ions using a strong base resin D296was recentlyreported (Hu et al., 2009). In this study, it was found that the separationcanbeonly performed in thepHrangeof 6.5–8.5and, chloride ionshavean important influence on the separation. The loaded resinwas strippedand regenerated using 6 mol/L of HCl with the vanadium desorptionratio over 98.5%.

Henry and van Lierde (1998) proposed a method to separatevanadium from molybdenum by electrochemical ion exchange. Athree-compartment electrochemical cell was equipped with a RVC(Reticulated Vitreous Carbon) cathode mixed with an ion exchangeresin Amberlite IRA 94S and two Ti–Pt anodes separated by a Daramicdiaphragm. In the process, the pentavalent vanadyl anion wasselectively desorbed after its reduction to a tetravalent vanadyl cation(Fig. 2). At 50 °C, using 30 g/L H2SO4 as eluant and a decreasingcurrent intensity, 93% of V and only 7% of Mo were eluted from theinitially loaded resin containing 9.3 kg/m3 V and 130 kg/m3 Mo.Further elution of molybdenum with an alkaline solution led to therecovery of a pure molybdate solution with a molar Mo/V ratio of1000 after a post-precipitation at pH 8.

5. Solvent extraction

Due to the requirement for high purity molybdenum andvanadium, solvent extraction is used to replace precipitation inmetallurgical flow sheets. In recent decades, many researchers havestudied and developed solvent extraction processes for the separationand recovery of molybdenum and vanadium (Wilkomirsky et al.,1985; Bal et al., 1992; Hirai and Komasawa, 1990, 1993; Ho et al., 1994;Sadanandam et al., 1996; Muir et al., 1996; Tangri et al., 1998). Sincethe behaviour of molybdenum and vanadium in a solvent extractionprocess are strongly affected by the type of predominant speciespresent in the aqueous phase, it is necessary to understand thesolution chemistry of the two metals. It is noted that the nature ofspecies formed depends on pH, oxidation state and concentration ofthe metal and ligands in the solution.

5.1. Solution chemistry of molybdenum and vanadium

Being transition metals, both molybdenum and vanadium exhibitmultiple valencies. Vanadium belongs to the VB group of the periodictable and displays +2, +3, +4 and +5 valencies in solutions. Stablevalencies are +4 and +5 which are important for solvent extraction.Molybdenum belongs to the VIB group and displays valencies of +3,+4, +5 and +6. The stable valency of +6 is important for solventextraction. An interesting feature shown by molybdenum and vana-

dium is the phenomenon of polymerisation in the pH range of 2–6.5.Whenacid is added to their alkaline solution andpH is slowly decreasedfrom 6.5 to 2, simple metal ions start polymerising to give highmolecular weight isopolyanions. Cationic species of MoO2

2+, VO2+ and

VO2+ are formed at pHb2. Anionic complex species of VOCl3−, MoO2Cl3−

and MoO2 (SO4)22− are reported to be present in a solution with 2–3 Nacid concentration. Neutral complexes ofMoO2Cl2, VOCl2 andVO2Cl areformed in stronger acid solution (~6 N HCl) (Sato et al., 1977, 1986a,b;Tedesco and deRumi,1980). The various isopolyanions exist in dynamicequilibrium and the predominant species formed at different pH areshown in Table 3.

Pourbaix (1966) represented the conditions of thermodynamicequilibrium of themolybdenum–water system at 25 °C, in the absenceof complexing substances and substances forming insoluble salts.Molybdenum forms a large number of complexes such as hydro-chloric, oxalic, thiocyanic and phosphoric molybdates in differentvalences.

Among these complexes, the ones with hexavalent molybdenumare most important which are normally present as molybdenumtrioxide or molybdic anhydride MoO3, its hydrates (molybdic acids)and dissolved forms. Molybdate ion MoO4

2− is obtained by the actionof alkalis on MoO3. By varying the relative quantities of MoO3 andalkalis, a whole series of salts such as the di-, tri-molybdates can beobtained.

The distribution of molybdenum species produced by a prelimin-ary computer simulation is shown in Fig. 3 (Olazabal et al., 1992). Ascan be seen, cationic molybdenum(VI) species become predominantin the most acidic region (pHb1) and the polynuclear anionic speciesare predominant in the region 1bpHb6, while the mononuclearanionic species is the only one at pHN6.

Vanadium also exhibits a variety of complex speciation andoxidation states in aqueous solutions. In leach liquors from theprocessing of spent catalysts, ores and residues, vanadium(IV) and (V)predominate in acidic medium and vanadium(V) in alkaline medium.Between pH 2 to 12, vanadium(V) exists in a series of polyanions suchas decavanadate V10O28

6− or metavanadate V4O124− which are partially

protonated according to the pH value (Ho et al., 1994). Thepolymerisation of vanadium in the liquor lies on its concentrationand the pH value of the liquor. Colours of some vanadium species inaqueous solutions are shown in Table 4.

Olazabal et al. (1992) presented the distribution diagram (Fig. 4) ofvanadium species in water as a function of the pH by computersimulation. It can be seen from Fig. 4 that the cationic vanadium(V)species is predominant at pHb2. Polynuclear anionic species arepredominant in the range 2bpHb9, while mononuclear anionicspecies dominate at pHN9.

5.2. Extraction chemistry of molybdenum and vanadium

From Figs. 3 and 4, the different acid–base behaviour observed forboth metals suggested that three kinds of liquid extractants could beused for the separation of molybdenum and vanadium. Cationicextractants seemed to be suitable in the acidic range where the

Table 4Characteristics of some vanadium species in aqueous solutions (based on Li et al., 2007).

Oxidative state Species Medium Colour of species

V(II) [V(H2O)6]2+ Acidic PurpleV(III) [V(H2O)6]3+ Acidic GreenV(IV) VO2+ Acidic Blue

VO44− Acidic

V(V) VO43− pHN12.6 Achromaticity

V2O74− pH=9.6–10 Achromaticity

VO3− pH=7–7.5

V3O93− pH=7–7.5 Achromaticity

V4O124− pH=7–7.5

V10O286− pH=2.0–6.5 Orange-red

VO2+ pH=1–2 Yellow

Fig. 3. The distribution of molybdenum species in the Mo–H2O system as a function of pH with a total MoO42− concentration of 21.20 mM (based on Olazabal et al., 1992).


cationic vanadium(V) species are more stable than the correspondingmolybdenum(VI) species; basic long-chain alkylamines could be usedto extract anionic metal complexes in the acidic range where cationicspecies are expected to be non-predominant; quaternary long-chainalkylammonium salts can be used to extract anionic species in theneutral and basic regions, especially, where polynuclear complexes ofbothmetals are predominant. The extractants of solvation type (Ritceyand Ashbrook, 1984; Cox, 2004) could be also used to extract theneutral species of molybdenum and vanadium from their solutionswhen neutral species are predominantly present.

5.3. Separation and recovery of molybdenum and vanadium by solventextraction

A number of papers have been published in the past 30 yearsrelating to the solvent extraction of molybdenum and vanadium usinga variety of organic reagents from various aqueous solutions. Differentkinds of extractants for the separation and recovery of molybdenumand vanadium will be classified and reviewed.

5.3.1. SX of molybdenum and vanadium with extractants involvingcompound formation

Coleman et al. (1958) reported that kerosene solutions containing5–20% (v/v) D2EHPA extracted VO2+with fast kinetics in a pH range of1.5–2.5 and the extracted VO2+ species were readily stripped withdilute H2SO4. Mechanism studies carried out by Sato et al. (1978)indicated that the extracted species were polymeric involving severalD2EHPA molecules e.g. VOð ÞR2 � RHð Þ2 where RH=D2EHPA. Theextraction was proportional to the pH and the square root of D2EHPAconcentration (Ipinmoroti and Hughes, 1990). Tangri et al. (1998) alsoreported that D2EHPA can be used to extract the cationic species ofmolybdenum and vanadium like MoO2

2+ and VO2+ at pH 1 from their

solutions.The effect of concentrations of nitric and hydrochloric acids on the

extraction of molybdenum and vanadium using D2EHPAwas tested byLitz (1981). Molybdenum showed good extraction at low nitricnormalities whereas vanadium showed only slight extraction. Theeffect of hydrochloric acid concentration on their extraction was verysimilar to the nitric acid system except at high normalities. The effect ofpH on the extractions of the two elements from sulphate solutions byD2EHPA was also studied. Although both molybdenum and vanadiumcan be extracted readily at pH 2–3, the molybdenum extractiondecreased slightly with decreasing pH whereas the vanadium extrac-

tion decreased rapidly with decreasing pH. Moreover, D2EHPAextracted vanadium effectively only at pH lower than 3, but molybde-numeffectively at pHashigh as 6 (Ackermannet al.,1992). This allowedpreferential extraction of molybdenum from a vanadium-bearingsolution and separation using selective stripping. The separation ofmolybdenum and vanadiumwas best accomplished at pH 6, providedthat the molybdenum concentration was low (Chen et al., 2003).

Inoue et al. (1993) carried out extraction and separation ofmolybdenum and vanadium in acidic sulphate solutions containingnickel, cobalt, iron and a large amount of aluminium using threeextractants: Cyanex 272, PC88A and TR-83. Figs. 5–7 show therelationship between the extractions of each metal and the initialpH of the aqueous phase. From the comparison of these figures,molybdenum can be well extracted even at low pH with all of theseextractants; especially, it can be highly selectively extracted over othermetals at pH=0 with Cyanex 272 and TR-83. Vanadium can beselectively extracted over aluminiumwith TR-83 and PC-88A. It can beconcluded that Cyanex 272 is most suitable for the separation ofmolybdenum and vanadium from the large amount of aluminium.Based on the fundamental data on the extraction of a singlecomponent, the authors subsequently carried out the experimentsof extraction of a multi-component system using synthetic solutioncontaining metal ions with the similar components of the real processsolution and 40% (v/v) Cyanex 272 in EXXSOL D80 as the solvent.Table 5 shows the extractions of themetals from themulti-componentaqueous solution at varying pH.

It was shown thatmolybdenum could be separated fromvanadium,iron, nickel, cobalt and aluminium at pH around 0 while, at pH=1.51,

Fig. 4. The distribution of vanadium species in water as a function of pH with a total VO2+ concentration of 14.33 mM. The dashed line represents the sum of the distribution

percentages of the decavanadates (based on Olazabal et al., 1992).


nearly all of the molybdenum, vanadium and iron were co-extractedleaving nearly all of the aluminium in the raffinate. In order to removethe co-extracted vanadium frommolybdenum, the loaded solvent wasscrubbed with 0.85 N H2SO4 at O/A ratio of 1:1. About 94.4% of thevanadium was scrubbed off while only 0.16% of the molybdenum wasco-scrubbed. It was found that stripping molybdenum from the loadedsolvent was the key in the recovery of molybdenum by solventextraction with acidic organo-phosphorus extractants. The best pHrange of the stripping solution for good phase separation and withoutturbid phenomenonwas between 8.0–8.4. In this pH range, more than90% stripping of molybdenum can be achieved by one batch operationusing ammonia solution. The scrubbed solution containing vanadiumand iron was contacted with Cyanex 272 again. Complete selectivestripping of vanadium excluding iron can be accomplished by usingaqueous ammonia solution. Zhang et al. (1995) studied the recovery ofmolybdenum and vanadium from the acidic solutionwith a novel typeof commercial extractant PIA-8 (bis (2-ethylhexyl) phosphinic acid)and the results were very close to those obtained using Cyanex 272. Acommercially available extractant of oxime-LIX 63 was also used toinvestigate the extraction of molybdenum(VI) and vanadium(IV) fromleach solution of spent hydrodesulphurisation catalysts with sulphuricacid in the presence of various other metals, such as aluminium(III),cobalt(II), nickel(II) and iron(III) (Zhang et al., 1996). It was found thatmolybdenum(VI) and vanadium(IV) were extracted preferentially and

Fig. 5. Extraction of metals with 20% (v/v) Cyanex 272 in EXXSOL D80 (based on Inoueet al., 1993).

separated completely from the co-existingmetals at a lowpHof around1.5 with LIX 63 dissolved in Exxsol D80. 2 M H2SO4 was used toselectively strip vanadium(IV) in the loaded organic phase. Molybde-numwas easily and completely stripped by 10% ammonia solution afterthe removal of vanadium(IV). After stripping, LIX 63 can be recycled tothe extraction by regeneration with a 2 M H2SO4. After the recovery ofmolybdenum and vanadium, Inoue et al. (1997) also investigated theselective recovery of the small amounts of cobalt and nickel from theraffinate containing a large amount of aluminium at low pH using twotypes of synergistic mixtures. One is a mixture of LIX 63 in combinationwith acidic organophosphinate such Cynnex 272 and PIA-8, andanother is that of picolylamines in combination with DNNSA. Bothmixtures were able to selectively extract nickel and cobalt at a low pHaway from a large excess of aluminium. However, the former mixturesuffered from a very slow extraction rate of nickel, while the lattermixture from poor phase disengagement particularly in stripping.

Olazabal et al. (1992) studied selective extraction of vanadium(V)from solutions containing molybdenum(VI) by a liquid chelatingextractant (LIX 26). Fig. 8 shows the extraction of both metals as afunction of pH when the aqueous solution was equilibrated with anorganic solution containing 2% LIX 26 and 10% n-octanol in hexane.

As can be seen, LIX 26/n-octanol/hexane mixtures could not beused for selective extraction in any pH range. Moreover, molybdenum(VI) was preferred over vanadium(V) although the cationic aqueous

Fig. 6. Extraction of metals with 20% (v/v) PC-88A in EXXSOL D80 (based on Inoue et al.,1993).

Fig. 7. Extraction of metals with 20% (v/v) TR-83 in EXXSOL D80 (based on Inoue et al.,1993).

Fig. 8. Extraction as a function of pH for the systems of V(V) (730 ppm)/LIX 26 (2%)-n-octanol (10%)-hexane and Mo(VI) (2000 ppm)/LIX 26 (2%)-n-octanol (10%)-hexane(based on Olazabal et al. 1992).


species of Mo(VI) are less predominant than that of V(V), because thecatonic vanadate species VO2

+ were readily hydrolysed even in diluteacid solutions above pH 1.5 to form oxyanions. These oxyanionspolymerised and protonated to form a series of anions with thegeneral formula HyV2xO5x+2

y−4 (Eq. (5)) or HyV2xO5x+3y−6 (Eq. (6)) (Ho

et al., 1994), where x usually takes the value of 1, 2 or 5 (Gupta andKrishnamurthy, 1992; Rakib and Durand, 1996).

2VOþ2 þ 3H2O ¼ H3V2O

−7 þ 3H

þ ð5Þ

5H3V2O−7 ¼ H5V10O

−28 þ 4OH

− þ 3H2O ð6Þ

5.3.2. SX of molybdenum and vanadium with extractants involving ionassociation

Extractants involving ion association include primary, secondaryand tertiary amines and quaternary ammonium salts. The tertiaryamine Alamine 336 and the quaternary ammonium salt Aliquat 336are usually the preferred basic extractants, which are used forextraction of anionic complexes of molybdenum and vanadium fromtheir HCl, H2SO4 or HNO3 solutions (2–3 N) (Miura et al., 2001).

Olazabal et al. (1992) studied the separation of vanadium(V) fromsolutions containingmolybdenum(VI) by a basic alkylamine (Alamine336) and a quaternary ammonium salt (Aliquat 336) dissolved intoluene. The extractions of Mo(VI) and V(V) as a function of pH whenthe aqueous solution was equilibrated with 0.1 mol/L Alamine 336and 0.1 mol/L Aliquat 336 in toluene, respectively, are shown in Figs. 9and 10.

As can be seen, for the Alamine 336/toluene system, molybdenumis quantitatively extracted in the region pHb4 and the extraction issuppressed at pHN7. Vanadium is extracted in the range of 1bpHb8although quantitative extraction is only reached in the region3bpHb4.5. For the Aliquat 336/toluene system, vanadium isquantitatively extracted in the range 3.5bpHb9 while the extractionof molybdenum is quantitatively extracted at pHb5 and is suppressed

Table 5Extraction of metals from multi-component aqueous feed solution with 40% (v/v)Cyanex 272 in EXXSOL D80 at 40 °C (O/A ratio=1:1) (based on Inoue and Zhang,1993).

pH Metal in feed solution (g/L) Extraction (%)

[Mo] [V] [Fe] [Al] [Co] [Ni] Mo V Fe Al Co Ni

0.03 2.57 0.724 0.029 13.16 0.96 0.162 99.5 9.8 3.45 0.15 0 00.21 2.62 0.747 0.029 13.40 0.99 0.165 99.6 16.1 3.45 0.22 0 00.35 2.70 0.755 0.030 13.84 1.08 0.170 99.7 22.5 16.7 1.44 0 00.51 2.70 0.755 0.030 13.84 1.08 0.170 99.7 32.2 33.3 0.27 0 01.00 2.78 0.769 0.032 14.30 1.10 0.180 99.8 80.4 84.4 1.05 0 01.51 2.78 0.769 0.032 14.30 1.10 0.180 99.7 92.5 100 1.89 0 0

at pHN8. The extraction mechanism of vanadium(V) by Aliquat 336 atpH 9 is represented in Eqs. (7) and (8) (Sadanandam et al., 1996):

4R4NCl + V2O4−7 = R4Nð Þ4 V2O7ð Þ + 4Cl− ð7Þ

4R4NCl + V4O4−12 = R4Nð Þ4 V4O12ð Þ + 4Cl− ð8Þ

Thus, it is suggested that the separation of vanadium(V) andmolybdenum(VI) can be carried out in two ways. In the most acidicrange (pHb1), the Alamine 336/toluene system can be used to extractmolybdenum in the presence of vanadium. In the slight basic range(8bpHb9), the Aliquat 336/toluene system can be used to selectivelyextract vanadium in the presence of molybdenum.

Although Aliquat 336 is more versatile than Alamine 336 in that itcan extract molybdenum and vanadium both from acidic and alkalinesolutions (Ritcey and Lucas, 1979), Alamine 336 is the preferred choicein most commercial plants because it is possible to use ammonia asstripping reagent in both cases to give respective ammonium saltswhich can be easily crystallised and calcined to give their high purityoxides. In the case of Aliquat 336, ammonia is not a very efficientstripping reagent, particularly for vanadium since its kinetics ofstripping reaction is extremely low (Hirai and Komasawa,1997; Lozanoand Juan, 2001). Bal et al. (2002) investigated the kinetics of thealkaline stripping of vanadium(V) extracted by Aliquat 336. In thisstudy, the limiting step of the stripping process was found to be theslow transformation of the extracted polyoxometallate species(H2V10O28

4−) into HVO42− or/and VO4

3− ions. The stripping rate and thevalues of the corresponding kinetic constants are similar to those

Fig. 9. Extraction as a function of pH for the systems of V(V) (730 ppm)/0.1 M Alamine336-toluene and Mo(VI) (2000 ppm)/0.1 M Alamine 336-toluene (based on Olazabalet al. 1992).

Fig. 10. Extraction as a function of pH for the systems of V(V) (730 ppm)/0.1 M Aliquat336-toluene and Mo(VI) (2000 ppm)/0.1 M Aliquat 336-toluene (based on Olazabalet al. 1992).

Table 6Calculated vanadium loadings on 10% (v/v) (0.22 M) Aliquat 336 according tospeciation, charge and pH (based on Ho et al., 1994).

pH Species V: charge Saturated loading (g/L)

2.6–3.9 H2V10O284− decavanadate 2.50 29.6

3.9–6.0 HV10O285− decavanadate 2.00 23.7

6.0–6.2 V10O286− decavanadate 1.67 19.7

6.2–9.0 V4O124− metavanadate 1.00 11.8

9.0–13.0 V2O74− or VO3(OH)2− metavanadate 0.50 5.9

N13.0 VO43− orthovanadate 0.33 3.95


observed for the alkaline decomposition of decavanate in homoge-neous phase, although the stripping reaction is biphasic. Moreover, itwas reported that solid third phases precipitated from certain organicsolutions of Aliquat 336 after extraction of molybdenum(VI) and/orvanadium(V) (Kertes, 1965; Osseo-Asare, 1991; Vasudeva Rao andKolarik, 1996). Bal et al. (2004) characterised the isolated precipitatesand elucidated the mechanism of precipitation using elementalanalysis and IR and Raman spectroscopies. With respect to molybde-num(VI), various heptamolybdate and octamolybdate anions wererapidly extracted by anion exchange from acidic media in the pH rangeof 1–4 by Aliquat 336 in kerosene or n-heptanemodified by n-decanol,but such extracted species then transformed within several hours intohexamolybdate which precipitated as the greenish-yellow compoundR3R′Nð Þ2Mo6O19 (Karagiozov and Vasilev, 1981; Bal et al., 1992), whenAliquat 336 was highly loaded in molybdenum. Mixed-valence speciessuch as Mo5VIMoVO19

3−, Mo4VIMoVO194− or Mo3VMo3VIO18H2− (Ostrowetsky,

1964a,b; Che et al., 1979) also precipitated in very small quantities as ared-garnet solid, as a result of the partial reduction of molybdenum(VI). In the case of vanadium(V), the reddish extracted species of acidicdecavanadate rapidly extracted at pH 1.5–2 and turned olive-greenwithin a few days at room temperature while a black-greenish solidprecipitated. This solid third phase is composed of mixed-valence

decavanadate compounds such as R3R′Nð Þ4 HVIV3 VV

7O26

� �and/or

R3R′Nð Þ4 HVIV7 VV

3O24

� �(Ostrowetsky, 1964a,b). It is of interest that

when cyclohexanol and ethyl-4-phenol were used as phase modifiersinstead ofn-decanol, the precipitation ofmixed-valence decavanadateswas no longer observed, but a compoundmainly composed of an oxideof vanadium separated from the loaded organic phase after severalmonths of aging at room temperature.

Ho et al. (1994) studied the recovery of vanadium from spentcatalysts and alumina residues. The author focussed on the extractionof V(IV) as VO2+ from acidic solutions using D2EHPA and theextraction of V(V) as one of its many anionic species using tertiary orquaternary amines. It appeared that the quaternary amine extractantwas versatile to acidic, neutral and alkaline solutions and regarded asthe reagent of choice to extract vanadium(V) from a variety of processoptions and liquors, which may be obtained from treating spentcatalysts. Table 6 summarises the predominant vanadium species intheir pH range and the theoretical maximum V(V) extraction by 10%(v/v) Aliquat 336.

Isotherms test results confirmed that the maximum loading wasclose to that calculated. However higher loadings of vanadium thanthe predicted were observed at pH 9–11, indicating that thedecavanadate rather than the metavanadate species was extracted.Lower loading was observed at pH 13.4 (10 g/L NaOH), indicatingsome competition between the hydroxide and orthovanadate ions.Thus, attention to temperature and contact timewas required in acidic

media to inhibit degradation of vanadic acid while attention tohydroxide ion concentration was required in strong alkaline media toinhibit competition with orthovanadate species. In the presence ofmolybdenum(VI), selective extraction of vanadium was achieved atpH 9 and selective stripping was possible if co-extraction occurred atlower pH.

Tangri et al. (1998) studied the extraction of molybdenum andvanadium by Alamine 336 and the separation of them from thestripping solution by selective crystallisation based on the differencein the solubility of ammonium metavanadate and ammoniumparamolybdate. The solvent system applied was Alamine 336 alongwith isodecanol in kerosene. The mechanism of the extraction ofmolybdenum and vanadium by Alamine 336 is indicated below:

4R3NH � HSO4 + Mo8O4−26 = R3NHð Þ4�Mo8O26 + 4HSO−

4 ð9Þ

4R3NH � HSO4 + H2V10O4−28 = R3NHð Þ4�H2V10O28 + 4HSO−

4 ð10Þ

The loaded amine was easily stripped with ammonia solution togenerate solutions of their ammonium salts. Ammonium metavana-date (AMV)was the least soluble (0.6 g/100 g of H2O at 298K) and canbe easily crystallised out at pH 8–8.5. Ammonium molybdate washighly soluble in ammoniacal solutions at pHN8. In the evaporativecrystallisation process, NH3 was driven out and the molybdenumcrystallised out as ammonium paramolybdate (APM) at pH 4–5. Thisdifference can be used for the separation of molybdenum andvanadium.

A process for the extraction of vanadium resulting from sulphuricacid leaching of dolomitic shale was developed by Brooks and Potter(1974). A number of reagents were tested. Adogen 363 (tri-dodecylamine) performed the best, followed by Amberlitela-2 (asecondary amine) and Adogen 381 (Tri-isooctylamine) and PrimeneJMT (a primary amine) performed the worst.

The extraction of U(VI), Mo(VI), V(V), Ce(IV), Zr(IV), Fe(III) and Al(III) with Primene JMT in sulphate media was studied by Schroetter-ova et al. (1994) and Nekovar et al. (1997). Results showed that thepredominant species of vanadium in this media were decavanadates.Lozano and Juan (2001) also studied the solvent extraction ofpolyvanadates from acidic sulphate solutions by Primene 81R (aprimary amine) dissolved in kerosene. The presence of a modifier wasnecessary in order to avoid the formation of cruds or third phase andpH must be kept in the range of 2–2.5. Experimental data obtainedconfirmed that predominant polymeric species of vanadium in the pHrange of 2–2.5 was HV10O28

5− and the overall extraction was proposedto be:

5RNH2 + 5H + + HV10O5 −28 = RNH3ð Þ +

5 �HV10O5−28 ð11Þ

The stripping of vanadium can be achieved with ammoniasolution. In order to obtain a criterion for choosing more versatile

Table 7Comparison of some extractants for extraction of molybdenum and vanadium.

Extractants Selectivity

Extractants involvingcompound formation

D2EHPA Extraction of Mo over V at pHb1Cyanex 272 Extraction of Mo over V, Ni, Co, Fe, Al at

pH=0; extraction of Mo, V, Fe over Ni,Co, Al at pH=1.5

PC-88A Extraction of Mo over V at pHb1;extraction of Mo, V, Fe, Al over Ni,Co in the range of 2bpHb3.5

TR-83 Extraction of Mo over V, Fe, Ni, Co, Al atpH=0; extraction of Mo, V, Fe, Al over Ni,Co in the range of 2bpHb3

LIX 63 Extraction of Mo and V over Ni, Co, Fe andAl at pHb1.5

Basic extractants Alamine 336 Extraction of Mo over V at pHb1Aliquat 336 Extraction of V over Mo in the range of

7bpHb9Neutral extractants TBP No selectivity for Mo over VOthers Acetylacetone+

Kelex 100First extraction of V by acetylacetone, thenextraction of Mo by Kelex 100


extraction reagents, Lozano and Godinez (2003) further studied thebehaviour of amines Primene 81R and Alamine 336 under the sameconditions for the extraction of vanadium(V) in sulphate media.Extraction isotherms confirmed higher loading capacity in broad pHrange for the primary amine Primene 81R.

5.3.3. SX of molybdenum and vanadium with extractants involvingsolvation

With solvating extractants, the metal ion becomes solvated byelectron donor-containing extractants. TBP (Tributylphosphate), aneutral extractant, was reported for extraction of molybdenum assolvated complexes of the type MoO2Cl2 � 2TBP in the loaded solventfrom 6 N HCl solution (Sato and Sato, 1995). Neutral VOCl2 species isextracted from chloride solution by TBP/TOPO (trioctylphosphineoxide).

Litz (1981) studied the effect of concentrations of nitric, hydro-chloric and sulphuric acids on the extraction of molybdenum andvanadium by TBP. Both molybdenum and vanadium were readilyextracted by TBP from the three acidic solutions. It was showed thatTBP cannot be used to separate molybdenum and vanadium.

5.3.4. SX of molybdenum and vanadium with other extractantsKim and Cho (1997) studied the effect of adding acetylacetone

solution to a liquid phase containing molybdenum and vanadiumfrom leaching spent desulphurisation catalyst with Na2CO3. It wasfound that all of the vanadium was extracted to the organic phase.Kelex 100, 7-(4-Ethyl-1-methyloctyl)-8-hydroxyquinoline, was thenadded to the aqueous phase, which led to the extraction of all of themolybdenum to the organic phase. However, there is no furtherinformation about details of the solvent extraction.

5.3.5. The combination of SX and other technologies for separation andrecovery of molybdenum and vanadium

In some cases, due to their low concentrations of molybdenum andvanadium in leach solutions, the current solvent extraction process inconventional mixer–settler reactors becomes economically inapplic-able. Therefore, in recent years, recovering of these metals from thesekinds of solutions by supported liquid membranes has becomean attractive technique (Yang and Cussler, 2000; Park et al., 2001;Valenzuela et al., 2000; Alguacil et al., 2000). Liquidmembrane presentsa high ability of separating metal ions in aqueous solutions using amicroporous solid support and a minimum quantity of expensiveorganic solvent (Sato et al., 1990).

Basualto et al. (2003) studied the extraction of molybdenum(VI)by Alamine 336, determined the permeation conditions through apoly microporous flat liquid membrane and examined a possibleextraction mechanism. It was concluded that the maximal apparentpermeability of molybdenum was achieved when the pH of feedsolution was adjusted around a value of 2.0 with sulphuric acid if a1.0 mol/L Na2CO3 was employed as stripping solution. The molybde-num(VI) permeation through the liquid membrane was enhancedwhen a 0.02 mol/L concentration of the amine carrier in the organicfilm was used. It was not possible to increase it indiscriminatelybecause a lower transport of metal-complex species occurred due tothe critical increase in viscosity of the organic phase.

Chen et al. (2003) presented a new type of metal ion selective resinbased on phosphoric acid functionality and its application to theseparation of molybdenum and vanadium. The resin was prepared byimmobilising D2EHPA as high as 2.5 mmol/g of resin onto the surfaceof porous Amberlite XAD-4 resin, employing a solvent-nonsolventprocess. Adsorption isotherm test results showed that D2EHPA-modified Amberlite XAD-4 resin can also adsorb more molybdenumthan vanadium ions. In the experiments conducted, the amount ofadsorbed molybdenum ions reached as high as 0.04 M of Mo per moleof D2EHPA, while this value of vanadium was less than 0.01 M in acondition that the initial concentration of molybdenum ions should be

lower than 0.01 M to achieve effective separation. This was because ofthe decrease in molybdenum distribution ratio between the modifiedresin and the liquid phase with increasing molybdenum concentra-tion. The selective extraction results using a series of contacts ofsolution mixtures further demonstrated the feasibility of this methodfor the separation of molybdenum and vanadium in solutions. Afteronly seven contacts, the relative concentration of vanadium increasedfrom 67% to more than 96%, while that of molybdenum decreasedfrom 33% to less than 4%.

A comparison of some extractants mentioned above for theseparation of molybdenum from vanadium and the separation ofmolybdenum and vanadium from other metals is shown in Table 7.

6. Summary and recommendations

Precipitation, carbon adsorption, ion exchange and solvent extrac-tion are the main technologies for the separation and purification ofmolybdenum and vanadium in spent catalyst leach solutions.Precipitation offers low cost and simple operation, however, highpurities (N99%) of products of molybdenum and vanadium cannot beachieved by this technology. The loading capacities of activated carbonfor molybdenum and vanadium are relatively low, resulting in noindustrial application of this technology in separation of molybdenumand vanadium. The scale of application of ion exchange in industry islimited although it can be used to separate molybdenum andvanadium almost completely and to produce high purity products.Solvent extraction is the well established unit operation for purifica-tion of molybdenum and vanadium in their aqueous solutions.

With almost all common acidic extractants, molybdenum, vana-dium, iron and aluminium can be extracted over nickel and cobalt inthe pH range of 1.5–3 from the leach solution of spent HDS catalysts.Vanadium, iron and aluminium in the loaded organic can be scrubbedoff by H2SO4 and separated from molybdenum which can then beeasily stripped by ammonia solution. Vanadium can be recovered fromscrub solution. With a kind of oxime extractant, LIX 63, molybdenumand vanadium can be preferentially extracted over iron, aluminium,nickel and cobalt around pH 1.5 and then separated by selectivestripping with excellent phase separation. With extractants involvingion association, Alamine 336 can be used to extract molybdenum overvanadium in the most acidic range (pHb1). In the slight basic range(8bpHb9), Aliquat 336 can be used to extract vanadium overmolybdenum. So far, there is no report regarding to neutral extractantfor the separation of molybdenum and vanadium. Further investiga-tion of solvent extraction to separate and purify molybdenum andvanadium is warranted.


Acknowledgements

The authors would like to thankMs. Sue Cook, Dr. Xianwen Dai andMr. Yoko Pranolo for collecting some reference papers, and Dr.Wensheng Zhang and Dr. Matthew Jeffrey for reviewing this paper andproviding valuable comments.

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A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation...

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Transcript of A literature review of the recovery of molybdenum and vanadium from spent hydrodesulphurisation...