Hydrometallurgy 105 (2011) 229–233

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Hydrometallurgy

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Precipitation of crystallized hydrated iron(III) vanadate from industrial vanadiumleaching solution

Liang Chen ⁎, Fengqiang Liu, Dabiao LiVanadium Products Manufactory, Panzhihua Steel and Vanadium Company Limited, Pangang Group, Panzhihua 617023, China

⁎ Corresponding author. Tel.: +86 812 3397502E-mail address: cougar365@163.com (L. Chen).

0304-386X/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.hydromet.2010.10.002

a b s t r a c t

a r t i c l e i n f o

Article history:Received 28 April 2010Received in revised form 14 July 2010Accepted 11 October 2010Available online 16 October 2010

Keywords:Iron vanadateFervaniteCrystallinePrecipitation

The crystalline Fe4(VO4)4·5H2O was synthesized at normal pressure frommixing vanadium leaching solutionwith Fe2(SO4)3. We investigated the effects of reaction temperature, pH and alkali type and characterized theprecipitate using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results showed thatthe V/Fe molar ratio and vanadium precipitation ratio decreased with the elevation of pH and reactiontemperature, but the addition of Ca(OH)2 increased the V/Fe molar ratio and the vanadium precipitation ratio,then a better crystallized precipitate was synthesized. The best conditions obtained are reaction temperatureat 90 °C, pH 2–3, reaction time of 72 h and the addition of Ca(OH)2. Under these conditions, the V/Fe molarratio of precipitate was close to 1.0 and over 98.5% of the vanadium was precipitated. XRD and SEM analysisshowed that the precipitate were conformed as crystalline Fe4(VO4)4·5H2O with grain size of 5–15 μm.

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© 2010 Elsevier B.V. All rights reserved.

1. Introduction

Fervanite is a common product in many hydrometallurgical opera-tions, and has been investigated for many years for its wide rangepotential applications. For example, fervanite is widely used as gas sensormaterial (Mangamma et al., 1996), electrodematerials for rechargeable Libatteries (Poizot et al., 2000), highly active heterogeneous Fenton-likecatalyst (Deng et al., 2008; Klissurski et al., 2004) and raw materials forsmelting ferrovanadium alloy (Liao and Bai, 1985). As a consequence,fervanite has been produced by a variety of methods. Fervanite thin filmswere prepared by sol–gel method (Surca-Vuk et al., 2002); single phasecrystalline fervanite(FeVO4) was synthesized by the solid state reactionbetween theα-Fe2O3 and V2O5 for 15 h at 773 K–1073 K (Klissurski et al.,2003); crystalline fervanite has been synthesized by a hydrothermalmethod from a solution of VOCl2 and FeCl3 when the solutions weresealed in Pyrex ampoules and treated hydrothermally at 280 °C for 40 h(Okaet al., 1996); the triclinic fervanitewaspreparedbymixed solutionofiron nitrate andammoniummetavanadate under stirring andmaintainedat 75 °C for 1 h, then the dried precipitate was calcined in a muffle at500 °C for 2 h (Deng et al., 2008). The crystallized FeVO4·1.5H2O waspreparedat low temperature frommixing aboiling solutionof ironnitratewith boiling solution of vanadium oxide, the mixture was maintainedunder stirring for several days at 85 °C (Melghit and Al-Mungi, 2007).

Most of the vanadium products manufactories in the world extractvanadiumoxide from the steel slag using the classic technology. The briefflow of the classic technology includes sodium carbonate roasting, water

leaching, precipitating with ammoniate and reduction process. Thevanadium oxide was produced by calcining process of ammoniumvanadate and the ammoniumvanadatewere extracted by an ammoniumsalt precipitation from the vanadium leaching solution, which mainlyconsist of sodium vanadate. About 85% of the vanadium is used for steelproduction and ferrovanadium alloy is the most important vanadiumproduct due to its physical properties such as tensile strength, hardnessand fatigue resistance (He et al., 2007). Compared with the traditionalammonium salt precipitation, the method of precipitation iron orthva-nadate with Fe3+ from vanadium leaching solution is economical andenvironmental friendly, for the wastewater is easy for treatment, for lackof NH4

+–N. Presently, increasing environmental concerns limited theapplication of the traditional technology, thus it is of great importance toprecipitate crystalline iron orthvanadate by coprecipitation of vanadateand iron(III) from leaching solutions at low temperature and pressure,which are efficient and economical for industrial production.

The objective of our study was to search for the best conditions of theformation of crystalline iron(III) orthvanadate(V) with composition Fe/V=1.Theprecipitationexperiment,X-raydiffraction (XRD)andScanningElectronMicroscopy (SEM)were taken to investigate the parameters andmechanismof crystalline fervaniteprecipitation from industrial vanadiumleaching solution and the effects of the parameters, such as the reactiontemperature, pH value and alkali type were investigated.

2. Materials and methods

2.1. Chemical compositions of leaching solution

The industrial vanadium leaching solution was produced by theVanadium Products Manufactory of Panzhihua Steel and Vanadium

20 30 40 50 60 70 80 90 10095

96

97

98

99

100

V precipitation rate(%) V/Fe molar ratio

Temperature (oC)

V p

reci

pita

tion

rate

(%)

1.0

1.1

1.2

1.3

1.4

1.5V

/Fe m

olar ratio

Fig. 1. Precipitation rate of vanadium and V/Fe molar ratio of the precipitate at differenttemperature.

230 L. Chen et al. / Hydrometallurgy 105 (2011) 229–233

Company Limited. The solution was cleaned by addition of Al2(SO4)3and MgSO4 to eliminate the impurities, such as SiO4

4− and PO43−. After

the cleaning process, the pH value of the leaching solution is 10.0 andthe mainly species of vanadium in solution is sodium vanadate. Thechemical composition of the leaching solution was shown in Table 1.The pH of the suspensions was manually adjusted desired value with0.1 M NaOH or Ca (OH)2, which were freshly prepared every day.

2.2. Experimental approach

According to the previous conclusion that prolonged reaction timecan affect the product and probably leads to a crystalline phase, thereaction time was prolonged to 72 h. The precipitation experimentswere performed at normal pressure in 500 mL cleaned glass bottleswhich were sealed to avoid the air. 400 mL of industrial leachingsolution was added to the bottle and then the bottle was heated to thedesired temperature, and 45.9 g of Fe2(SO4)3 was subsequently added.Then, the pH was adjusted to desired value immediately, followingrotary shaking at 300 r/min for 72 h. When the Fe2(SO4)3 was mixedwith the vanadium leaching solution, the solution changes fromyellow to orange and become more acidic immediately. Since this is arapid kinetic reaction, an amorphous phasewas precipitated. After thepH was adjusted to desired value, orange yellowish precipitateappears immediately, indicating that a great amount of OH− arecoordinated to Fe3+. However, after 72 h of stirring, the color of themixture changed from orange to yellow-brown similar to that of thefervanite mineral. The pH was adjusted every 24 h, after 72 h ofreaction, the suspension was centrifuged and separated into a thicksolid phase and a clear supernatant. The supernatant was filteredusing 0.22 μm cellulose nitrate membrane filters, then the concentra-tions of Fe3+ and V5+ were analyzed. The solid phase was rinsed withdeionized water by allowing the solids to settle and then decantingthe supernatant. This process was repeated several times, and solidwas dried at room temperature in air, for analysis.

2.3. XRD and SEM characterizations

The solid phase was characterized by X-ray Diffraction (XRD) andScanning Electron Microscopy (SEM). The powder XRD patterns werecollected on a Rigaku D/Max 2500 PC X-ray diffractometer withgraphite monochromated CuKa1 radiation. The powder samples werescanned from 10 to 90° 2θ with increments of 0.04° 2θ. The ScanningElectron Microscopy (SEM) images of the samples were obtained in aJSM-5600LV electron microscopy operated at 20 kV.

3. Results and discussion

3.1. Effect of temperature on the precipitation

The rate of vanadium precipitation is one of the most importantparameter in the vanadic products manufacturing. The effect ofreaction temperature on precipitation rate was investigated attemperature from 30 °C to 90 °C, Fig. 1 shows that the vanadiumprecipitation rate decreased with the increase of reaction tempera-ture, possibly resulting from that the solubility of iron orthvanadateincrease with increase of temperature from 30 °C to 90 °C.

To check the compound stoichiometry, the V/Fe molar ratio wasmeasured. The effect of the reaction temperature on the Fe/V molarratio of the compoundwas shown in Fig. 1. It could be seen that the V/

Table 1Chemical compositions of leaching solution.

Element V5+ Cr6+ Si4+ P5+

Concentration g/L 29.23 1.47 0.06 0.005

Fe molar ratio decreased with the increase of reaction temperaturefrom 30 °C to 90 °C. The molar ratio of V/Fe was found to be close to1.0 at 90 °C, confirming the stoichiometry of FeVO4.

The X-ray diffraction (XRD) pattern of the sample obtained at 30 °Cand 90 °C are shown in Fig. 2. It shows poorly crystallized materialswere obtained compared to the triclinic iron orthovanadate phase. Thediffraction peaks A can be perfectly indexed to the Fe4(VO4)4·5H2OJCPDS NO.27-0257 and the diffraction peaks B can be perfectlyindexed to the NaHSO4·H2O JCPDS NO.22-1379 , indicating that theproduct is composedmainly of Fe4(VO4)4·5H2O andNaHSO4·H2O. Theexistent of NaHSO4·H2Owas resulted from the solution enwrapped bythe precipitate, thus it cannot be easily eliminated by rinsing process.Previous study found the formation of Na2Fe6(SO4)4(OH)12 precipitateat low pH conditions, however, we find no evidence of crystallineNa2Fe6(SO4)4(OH)12 from XRD data. This indicates that Fe3+ did notprecipitate via formation of an ordered crystalline phase. However, itshould benoted that aminor fraction of poorly orderedprecipitatewasnot detected. The V/Fe molar ratio of precipitate close to 1.4 at 30 °C,indicating that the precipitate consist of Fe4(VO4)4·5H2O andV2O5·XH2O, due to the V/Fe molar ratio of precipitate of 1.1 whichwas close to that of the crystalline Fe4(VO4)4·5H2O, indicating that themain phase of the precipitate was Fe4(VO4)4·5H2O. From the XRD(Fig. 2) pattern of precipitate samples at 30 °C and90 °C,we noticednosignificant difference of Bragg reflection position, but only change inpeak intensity. It suggests that increasing the reaction temperatureprobably improve crystalline of the precipitate and the reactiontemperature should be as high as practical, thus the reactiontemperature of the following experiment was fixed at 90 °C.

3.2. Effect of pH on the precipitation

These are twelve vanadium(V) species coexisting in solution. Thesecan be categorized as cationic species VO2

+ , neutral species VO(OH)3and anion species. The anion species are divided into decavanadatespecies V10O26(OH)24− , V10O27(OH)5−, and V10O28

6−), mono species (VO2

(OH)2−, VO3(OH)2−, and VO43−) and other polyvanadate species (V2O6

(OH)3−, V2O74−, V3O9

3−, and V4O124−) (Peacock and Sherman, 2004). The

vanadium species are highly dependent on the pH and vanadiumconcentration in solution, as shown in Fig. 3 (Hu et al., 2009). Vanadium(V) species in solution can include those of decavanadate andmetavanadate form at concentrations in excess of 0.1 mol/L (Peacockand Sherman, 2004). The vanadate in the alkali industrial solution ismostly in the forms of HV4O12

3−, because the concentration of theindustrial solution is 0.57 mol/L which exceeds 0.1 mol/L, and the pHvalue is close to 9.8. Since the pH of solution during the precipitationexperiment is in the range of 1.5–5.0, the decavanadate species (V10O26

10 20 30 40 50 60 70 80 90 1000

Rel

ativ

e in

tens

ity

B BBB

BBBB

B

AAA

A

A

90oC

30oC

2-theta (°)

A: Fe4 (VO4) 4 · 5H2O

B: Na HS O4 · H2O

A

B

Fig. 2. The powder X-ray diffraction pattern of precipitate at 30 °C and 90 °C.

231L. Chen et al. / Hydrometallurgy 105 (2011) 229–233

(OH)24− , V10O27(OH)5−, and V10O286−) are the main forms in the solution

during the precipitation experiment.The effect of pH from1.5 to 5.0 onprecipitation at 90 °Cwas studied

by using NaOH solution to adjust the pH. As shown in Fig. 4, the V/Femolar ratio and vanadium precipitation rate efficiency decreased withincrease of pH value. As the V/Fe ratio of the precipitate exceed 1.0with the pH from 1.5 to 2.0, implying incomplete reaction of V10O28

6−

and Fe3+ and hydrated sodium polyvanadate (xNa2O·yV2O5·nH2O)may precipitate, which has low solubility, inducing that superfluousFe3+ and little vanadium remained in the solution.

Fig. 4 shows that the V/Fe molar ratio decrease from 1.23 to near1.0 and precipitation rate of vanadium maintains above 97.7% whenthe pH increased from 1.5 to 3.0. The color of the precipitate becameyellow-brown similar to that of Fe4(VO4)4·5H2O after reaction (Poizotet al., 2000). The results conformed the main crystalline phase in theprecipitate as Fe4(VO4)4·5H2O, and the basic reaction for theprecipitation can be formulated as following equations:

5HV2O3−7 þ 11H

þ ¼ H2V10O4−28 þ 7H2O

0 2 4 6-6.0

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

VO3-

HVO3

VO2+

V10O286-

HV10O285-

LgC

v(to

tal)

V2O5

H2V10O284-

Fig. 3. Forms of vanadium(V) ex

2H2V10O4−28 þ 20Fe

3þ þ 52OH− ¼ 5Fe4ðVO4Þ4d5H2O þ 3H2O

When the pH of the solution was in the range of 4.0–5.0, the V/Femolar ratio decrease to near 0.75, while the precipitation rate ofvanadiumdecreased to below75%. The color of the precipitate changesfrom yellow-brown to yellow with the increase of pH from 3.0 to 4.0,indicating that the iron orthvanadate is gradually transformed intohydro ferric oxide with the increase of pH and vanadate was releasedinto the solution. Previous study shows that vanadiumcan be removedfrom solution bymetal (hydr)oxide adsorbents, Peacpck and Shermanhave identified the Fe2O2V(OH)2 and Fe2O2VO(OH)0 surface com-plexes. Adsorption occurs by the formation of inner-sphere surfacecomplexes resulting from bidentate corner-sharing between doublyand singly protonated VO4

3− tetrahedra and FeO6 polyhedra. Thereaction can be formulated as following equations:

2FeOHþ2 þ VO

þ2 ¼ Fe2O2VðOHÞþ2 þ 2H

þ

and 2FeOH+HVO42−=Fe2O2VO(OH)+2OH− (Peacock and Sherman,

2004).

8 10 12 14

VO43-

HVO42-

V2O74-

HV2O73-

V3O93-

V4O124-

pH

isting in aqueous solution.

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.060

70

80

90

100

vanadium precipitation rate(%) V/Fe molar ratio

pH

vana

dium

pre

cipi

tatio

n ra

te(%

)

0.6

0.8

1.0

1.2

1.4

V/F

e molar ratio

Fig. 4. V/Fe molar ratio of precipitate and vanadium precipitation rate at different pHvalue.

2 4 60

20

40

60

80

100

120

precipitation rate(NaOH) precipitation rate Ca(OH)2 V/Fe (NaOH) V/Fe Ca(OH)2

pH

vana

dium

pre

cipi

tatio

n ra

te(%

)

0.6

0.8

1.0

1.2

V/F

e molar ratio

Fig. 5. V/Fe molar ratio of precipitate and vanadium precipitation rate at different pH.

232 L. Chen et al. / Hydrometallurgy 105 (2011) 229–233

Vanadium adsorption decreases with increasing pH, and themaximum adsorption capacities was achieved at pH 3.0–4.0 (Naeemet al., 2007). Clearly, the pH had a significant effect on the precipitation

10 20 30 40

B

A

AA

Rel

ativ

e in

tens

ity

2-Th

A

B

Fig. 6. XRD patterns of precipitates at diff

rate and V/Femolar ratio. Since the stability of the adsorbed vanadiumand iron orthvanadate decreased with the increase of the pH,vanadium releases to the solution. As a result, there are two speciesof vanadiummay exist in the precipitate: vanadium adsorbed on FeO6

polyhedra and iron orthvanadate precipitate.

3.3. Ca(OH)2 vs NaOH

It can be seen from Fig. 5, the V/Fe molar ratio and vanadiumprecipitation rate increased slightly in the presence of Ca2+ at pH 2.0–3.0, while the vanadium precipitation rate increased greatly at pH 4.0–5.0 in the presence of Ca2+, compared to that of the solution thatadjusted by NaOH solution. Previous studies showed that theprecipitate varies with the decreasing of the pH of the solution. Theprecipitate is Ca3(VO4)2 at pH from 10.8 to 10.0, Ca2V2O7 at pH 7.8 to9.3, and Ca(VO3)2 from 5.1 to 6.1 (Liao and Bai, 1985), However, themechanism of the precipitation reaction of Ca2+ and vanadate is notclear at pHb3. Fig. 5 shows the V/Fe molar ratio is below 1.0 in theprecipitate at pH 4.0–5.0. It reveals the formation of calciumvanadium precipitate, because the Fe3+ was replaced by Ca2+ withthe increasing of the pH from 3.0 to 5.0. And the Fe3+ precipitates viaformation of Ferric hydroxide. Thus the precipitation rate isdependent on the solubility of the calcium vanadium precipitate.

3.4. The X-ray diffraction pattern of the sample

To investigate the mechanism of the precipitation reaction, theXRD analysis of the precipitate was conducted under the flowingconditions: pH 2.0–3.0, and 90 °C. A comparison between the infraredspectra of the different precipitates produced from the solutionsadjusted by different alkali was shown in Fig. 6.

Fig. 6 shows that all diffraction peaks of the precipitate can beperfectly indexed to the crystalline Fe4(VO4)4·5H2O (JCPDS NO.27-0257) and NaHSO4·H2O (JCPDS NO.22-1379) when the solution wasadjusted by Ca(OH)2, and the intensity of the diffraction peaksincreased with the increasing of the pH. Compared with theprecipitate when the pH of the solution adjusted by NaOH, the poorlycrystalline Fe4(VO4)4·5H2O precipitate changed more crystallinewhen pH of the solution adjusted by Ca(OH)2, revealing that theaddition of Ca2+ promoted the crystallization of the precipitate.

50 60 70 80

BB

A: Fe4(VO4)4 · 5H2OB: NaHSO4 · H2O

eta (°)

Na OH pH=2.0

Na OH pH=2.5

Na OH pH=3.0

Ca (OH)2 pH=2.0

Ca (OH)2 pH=2.5

Ca (OH)2 pH=3.0

erent pH and different type of alkali.

Fig. 7. Scanning electron micrograph of the precipitate synthesized at pH 2.5.

233L. Chen et al. / Hydrometallurgy 105 (2011) 229–233

Analysis results of the iron orthvanadate precipitate at 90 °C andpH 2.5 is described as follow: the purity of the Fe4(VO4)4·5H2O was96.92% (SO3 1.28%, Na2O 1.67%, SiO2 0.08%, P2O5 0.002%, others 0.05%)with the addition of NaOH to adjust the pH of the solution. While thepH of the solution was adjusted by the Ca(OH)2, the purity of theproduct was 97.28%(SO3 1.39%, Na2O 1.15%, SiO2 0.084%, P2O5 0.004%,CaO 0.06%, others 0.04%). It suggests that the main impurities of theprecipitate were S and Na, which results from the incompletion of therinsing process. XRD conforms the main phase of the impurities wasNaHSO4·H2O in the precipitate.

It reveals that there is little effect on the content of impurities withthe addition of Ca(OH)2 to adjust the pH of the solution, thus theaddition of Ca(OH)2 to adjust the pH was optimal.

3.5. SEM image of the precipitate

In this study the SEMwas conducted to investigate themechanismof the effect of Ca2+ on the precipitation at pH 2.5. SEM image shownin Fig. 7 indicates that the precipitate were composed mainlycrystalline phase. From Fig. 7a, it reveals that the precipitate wasconsist of the small flakes with diameters ranging from 2 to 8 μmwiththe addition of NaOH to adjust the pH of the solution. Fig. 7b showsthe SEM image of precipitate with the addition of Ca(OH) 2. It revealsthat the precipitate are composedmainly of crystalline spherical grainwith size of 5–15 μm and its size is larger than that of the precipitatewith the addition of NaOH. Therefore, it can be accepted that theaddition of Ca(OH) 2 effect the iron vanadate on crystalline bypromoting the growth and agglomeration of the particles.

4. Conclusions

In summary, spherical grain of crystalline Fe4(VO4)4·5H2O wassuccessfully synthesized using Ca(OH)2 to adjust the pH of thesolution. This is an economical and mild solution with clearadvantages compared to the traditional high-temperature approachfor the large-scale crystalline Fe4(VO4)4·5H2O. The results of the studyshow that the reaction temperature, pH and alkali type exert strongeffect on the precipitation rate, V/Fe molar rate and particle size of theprecipitate. Increasing the reaction temperature promote the forma-tion of crystalline iron orthvanadate. A pH range of approximately2.0–3.0 is favorable for synthesis of crystalline Fe4(VO4)4·5H2O,

which is consistent with the electrostatic attraction betweenvanadate and strongly anionic metal specie. The ability of thehydrolyzing of Fe3+ increases as the pH increases above 4.0,suppressing the precipitation of iron orthvanadate. The calcium ionhas remarkable influence on the precipitation ratio and particle size ofthe precipitate at pH 2.0–3.0. However, the mechanism of the effect ofcalcium ion is not clear at present. The Ca(OH)2 is an importantadditive in the ferrovanadium alloy smelting process. This indicatesthat it is economical and efficient to use the Ca(OH)2 to adjust the pHof the solution in the precipitation process in industry.

References

Deng, J.H., Jiang, J.Y., Zhang, Y.Y., Lin, X.P., Du, C.M., Xiong, Y., 2008. FeVO4 as a highlyactive heterogeneous Fenton-like catalyst towards the degradation of orange II.Appl. Catal., B 84, 468–473.

He, D.S., Feng, Q.M., Zhang, G.F., Ou, L.M., Lu, Y.P., 2007. An environmentally-friendlytechnology of vanadium extraction from stone coal. Miner. Engneering 20,1184–1186.

Hu, J., Wang, X.W., Xiao, L.S., Song, S.R., Zhang, B.Q., 2009. Removal of vanadium frommolybdate solution by ion exchange. Hydrometallurgy 95, 203–206.

Klissurski, D., Iordanova, R., Radev, D., Kassabov, St., Milanova, M., Chakarova, K., 2004.Mechanochemically assisted synthesis of FeVO4 catalysts. J. Mater. Sci. 39 (16/17),5375–5377.

Klissurski, D., Radev, D., Iordanova, R., Milanova, M., 2003. Synthesis of iron(III)vanadate from mechanically activated precursors. Chim. inorganique 56 (6),27–30.

Liao, S.M., Bai, D.L., 1985. Foreign Vanadium Metallurgy. Metallurgy industrial press,Beijing, China.

Mangamma, G., Prabhu, E., Gnanasekaran, T., 1996. Investigations on FeVO4 as a gassensor material. Bull. Electrochem. 12 (11–12), 696–699.

Melghit, K., Al-Mungi, A.S., 2007. New form of iron orthovanadate FeVO4·1.5H2Oprepared at normal pressure and low temprerature. Mater. Sci. Eng., B 136,177–181.

Naeem, A., Westerhoff, P., Mustafa, S., 2007. Vanadium removal by metal (hydr)oxideadsorbents. water reseach 41, 1596–1602.

Oka, Y., Yao, T., Yamamoto, N., Ueda, Y., Kawasaki, S., Azuma, M., Takano, M., 1996.Hydrothermal synthesis, crystal structure, and magnetic properties of FeVO4-II. J.Solid State Chem. 123, 54–59.

Peacock, C.L., Sherman, D.M., 2004. Vanadium(V) adsorption onto goethite (α-FeOOH)at pH 1.5 to 12:A surface complexation model based on ab initio moleculargeometries and EXAFS spectroscopy. Geochim. Cosmochim. Acta 68 (8),1723–1733.

Poizot, P., Baudrin, E., Laruelle, S., Dupont, L., Touboul, M., Tarascon, J.M., 2000. Lowtemperature synthesis and electrochemical performance of cristalized FeVO4·1.1-H2O. Solid State Ionics 138, 31–40.

Surca-Vuk, A., Orel, B., Drazic, G., Decker, F., Colomban, P., 2002. UV–Visible and IRspectroelectrochemical studies of fevo4 sol–gel films for electrochromic applica-tions. J. Sol Gel Sci. Technol. 23 (2), 165–181.