Recovery of scandium from leaching solutions of tungsten residue using solvent extraction with Cyanex 572

Accepted Manuscript Recovery of scandium from leaching solutions of tungsten residue using solvent extraction with Cyanex 572

Huaping Nie, Yabing Wang, Yanliang Wang, Zeyuan Zhao, Yamin Dong, Xiaoqi Sun PII: DOI: Reference:

S0304-386X(17)30512-1 doi:10.1016/j.hydromet.2017.10.026 HYDROM 4685

To appear in:

Hydrometallurgy

Received date: Revised date: Accepted date:

21 June 2017 23 October 2017 25 October 2017

Please cite this article as: Huaping Nie, Yabing Wang, Yanliang Wang, Zeyuan Zhao, Yamin Dong, Xiaoqi Sun , Recovery of scandium from leaching solutions of tungsten residue using solvent extraction with Cyanex 572. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Hydrom(2017), doi:10.1016/j.hydromet.2017.10.026

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ACCEPTED MANUSCRIPT Recovery of scandium from leaching solutions of tungsten residue using solvent extraction with Cyanex 572 Huaping Nie a , Yabing Wanga,b,c, Yanliang Wangb,c, Zeyuan Zhaob,c, Yamin

School of Metallurgy and Chemical Engineering, Jiangxi University of Science & Technology,

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a

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Dongb,c and Xiaoqi Sunb,c*

Ganzhou 341000, China.

Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou,

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b

35002, China.

Xiamen Institute of Rare Earth Materials, Haixi Institute, Chinese Academy of Sciences, Xiamen

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c

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361021, China.

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*Corresponding author: X.Q. Sun. Tel./fax: +865926376370. E-mail address: [email protected].

ACCEPTED MANUSCRIPT ABSTRACT Cyanex 572 has been first studied for the extraction of scandium from trivalent rare earths (REs). The extraction mechanism of Cyanex 572 for Sc(III) was proposed to be cation-exchange, and the stoichiometry of Cyanex 572 with Sc(III) was

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indicated to be close to 3:1. The extractabilities of Sc(III) from leaching solution of

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tungsten residue with Cyanex 572, P507, Cyanex 923 and TBP were compared at

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different concentrations, which indicated that Cyanex 572 was the best among them to extract scandium under the same conditions. The loading capacity of Cyanex 572

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toward Sc(III) and stripping of loaded Sc(III) from the organic phase were also

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studied. By simple washing and stripping steps, the composition of scandium was

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increased more than eight hundred times.

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Keywords: Cyanex 572; scandium; rare earth; separation; tungsten residue

ACCEPTED MANUSCRIPT 1. Introduction Because of the excellent physical and chemical properties, scandium (Sc) has been one of the most important strategic materials (Wang et al., 2011a). Scandium and its compounds were widely used in various fields, such as metallurgy, chemical

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industry, aerospace, etc (Kerkove et al., 2014; Yin et al., 2011). Scandium was

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expensive due to its scarcity and the complicated metallurgical processes for its

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recovery and purification (Wang and Cheng, 2011). As the development of scandium products, more and more studies on the separation and recovery of scandium have

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been reported. Up to now, scandium has not been found in sufficient quantities to be

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considered as a reserve, but trace amount of scandium frequently occurred in many ores. Due to its low content, scandium was recovered as a by-product during the

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processes of tailings and residues of various sources, such as tungsten refinery residue,

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titanium pigment production waste liquor, uranium leach liquor, red mud, etc (Wang et al., 2013a; Xu and Li, 1996; Zhong, 2002). Scandium was always found in the tungsten minerals such as scheelite (calcium tungstate, CaWO 4 ) and wolframite

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(iron- manganese tungstate, FeWO 4 /MnWO4 ), which were mined and used to produce about 37,400 tonnes of tungsten concentrates per year (Smirnov and Molchanova, 1997). The residues from tungsten ores contained significant amounts of scandium. Scandium could be recovered via a number of processes, including solvent extraction, ion exchange, liquid membrane extraction, etc (Liao et al., 2001). Currently, hydrometallurgical processes, which mainly involve leaching, solvent extraction and precipitation have become the most commonly used methods for

ACCEPTED MANUSCRIPT scandium recovery (Wang et al., 2011a). Among the recovery processes, solvent extraction revealed advantages such as continuous operation, high processing capacity, and simple equipment on laboratory and industrial scales (Nazal et al., 2014). As can

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be seen in Table 1, some extractants were studied for the extraction of scandium.

ACCEPTED MANUSCRIPT Table 1 Effects of various extractants on the extraction of scandium

Type

Structure

Effects

Reference (Singh and

P204 was the most commonly Dhadke, 2003; used extractant to concentrate Xue and Li, and separate Sc. 1991)

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P204

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P507 had similar or slower (Li et al., 1980;

extractability for Sc than P204, Wang and Li,

but the required acidity of 1994)

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stripping was also lower.

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P507

Acidic Extractant

The stripping ratios of Sc from

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Cyanex 272, Cyanex 301 and Cyanex 302 were much easier

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Cyanex 272

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Cyanex 301

than those of P204 and P507.

The maximal stripping ratios of

(Wang and Li,

Sc after a single contact with

1994; Wang and

Cyanex 272, Cyanex 301 and

Li, 1995)

Cyanex 302 were nearly 82%, 75% and 78% with 1.5 mol/L, 5.8 mol/L and 3.5 mol/L H2 SO4 solutions, respectively.

Cyanex 302

The acidity range for Cyanex 925 to separate Sc from iron was 6.0-8.0 mol/L H2 SO4 . Cyanex 925 ( Li and Wang,

Neutral

1998)

Extractant Sc extraction by Cyanex 923 was achieved in the acidity range of 2.0-7.0 mol/L H2 SO4 with good selectivity over iron.

ACCEPTED MANUSCRIPT Cyanex 923

The separation of Sc and Th could be accomplished in an (Peppard et al.,

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acidity range of 7.0-8.0 mol/L 1956)

HCl by the use of undiluted TBP solution.

had higher

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P350

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T BP

extraction

ability than T BP for scandium

(Zhao and Li,

extraction from HCl solutions,

1990)

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and better selectivity over many impurity elements.

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P350

ACCEPTED MANUSCRIPT Very recently, a novel extractant, CYANEX® 572 (a mixture of phosphonic and phosphinic acids), has been released by the Cytec Industries (Quinn et al., 2015; Wang et al., 2015). Cyanex 572 performed better than the common industrial extractant P507, especially for the enrichments of thulium, ytterbium, and lutecium.

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The extraction system consisting of Cyanex 572 and isooctanol in 260# kerosene

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revealed good selectivity to thorium over REs, the separation factor between thorium

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and REs reached 4.38×104 (Wang et al., 2017). Samarium and cobalt were also separated by solvent extraction with Cyanex 572 from the leach liquor of waste SmCo

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magnet (Sinha et al., 2017). In this article, the extraction of scandium using Cyanex

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572 were investigated. Moreover, the recovery of scandium from tungsten residue

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was studied using Cyanex 572 for the development of a novel separating process.

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2. Experimental

2.1 Reagents and apparatus

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Cyanex 572 (C572) and Cyanex 923 (C923) were supplied by Cytec Industries Inc, which were used without further purification or saponification. P507 and TBP were obtained from Luoyang Aoda Chemical Co., Ltd. (China), which were purified as described elsewhere (Xue and Li, 1992). Heptane was employed as the diluent during the extraction experiments. The individual RE stock solution including La-Lu plus Y was prepared by dissolving the corresponding oxides (>99.9%, Fujian Changting Golden Dragon Rare Earth Co., Ltd., China) with HCl acid and diluting with water. Tungsten residue was supplied by Chongyi Zhangyuan Tungsten Co., Ltd.

ACCEPTED MANUSCRIPT (China), which was produced in the decomposition process of wolframite with sodium hydroxide. The leaching solution was prepared by dissolving tungsten res idue with HCl acid. Inductively coupled plasma optical emission spectroscopy (ICP-OES, Horiba Ultima 2) was used to determine the concentrations of REs in aqueous phase.

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The concentrations of acidic extractants were titrated by standard solution of sodium

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hydroxide (Wang et al., 2011b). The total concentration of mixed REs and free H+

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were determined by volumetric titration with standard solution of EDTA and NaOH,

2.2 Characterization of Cyanex 572

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respectively.

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Cyanex 572 used in this study was characterized by NMR. 1 H NMR (400 MHz, CDCl3 ) δ 10.47–9.09 (m, 2H), 3.98–3.85 (m, 2H), 2.16–1.98 (br, 2H), 1.91–1.69 (m,

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4H), 1.69–1.65 (d, 1H), 1.65–1.49 (m, 3H), 1.49–1.15 (m, 20H), 1.15–1.10 (d, 6H),

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1.10–1.00 (m, 1H), 0.95–0.80 (m, 29H); 13C NMR (100 MHz, CDCl3 ) δ 66.31 (d, J = 7.4 Hz), 53.12 (d, J = 12.5 Hz), 40.08 (d, J = 7.0 Hz), 39.57 (d, J = 89.6 Hz), 34.01 (d, J = 3.8 Hz), 33.59 (d, J = 10.3 Hz), 31.23, 30.05, 30.01, 29.89 (d, J = 142.0 Hz), 28.90,

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28.46, 26.71 (d, J = 9.5 Hz), 24.36 (d, J = 4.6 Hz), 24.32, 24.25 (d, J = 5.2 Hz), 23.34, 22.97, 22.88, 14.06 (d, J = 5.9 Hz), 10.92, 10.33; 60.35–59.63 (m), 35.81–35.39 (m). Corresponding

31 P

31 P

NMR (160 MHz, CDCl3 ) δ

NMR peak at 35 and 60 ppm

with equal integral proportion indicated that the mole ratio of two components from Cyanex 572 (phosphonic and phosphinic acids) was 1:1. In this study, the concentration of Cyanex 572 was determined by means of titration with sodium hydroxide.

ACCEPTED MANUSCRIPT 2.3 Solvent extraction process The common extraction experiments were performed by shaking equal volumes (4 mL) of feed solution and organic phase for 30 min at 25℃.As for the scandium recovery experiment from leaching solution, the phase ratio of extrac tion was fixed at

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1 : 4 (organic phase was 1.5 mL, aqueous phase was 6 mL) volume ratio. The aqueous

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and organic phases were separated after centrifugation at 3500 rpm for 5 min. All the

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stripping experiments were conducted by mixing 4 mL of loaded organic phase with 4 mL of HCl with different concentrations in a vibrating mixer for 30 min at 25℃. The

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extraction efficiency (E), distribution ratio (D), separation factor (β), and stripping

E% 

[ M ]r 100 % [ M ]s  [ M ]r



Da Db

(3)

ED

(2)

S% 

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(1)

[ M ]s [ M ]r

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D

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ratio (S) are defined as follows:

[ M ]aq,r

[ M ]org , s

100%

(4)

where the equilibrium concentration of RE in aqueous phase ([M] r) was determined by titration method or ICP-OES. The amount of RE in organic phase ([M]s ) was calculated by mass balance. Da and D b denote the distribution ratios of REa and REb, respectively. [M]aq,r is the equilibrium concentration of RE in stripping acid and [M]org,s represents the initial concentration of RE in the loaded organic phase.

ACCEPTED MANUSCRIPT 3. Results and discussion 3.1 Effect of pH on the extraction The effect of aqueous pH on REs extraction was investigated when Cyanex 572 was used as the extractant. As shown in Fig. 1, the extraction efficiencies of

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lanthanides and yttrium increase with the increase of aqueous pH, and seldom exceed

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80% in the studied range of pH. Extraction sequence of Cyanex 572 fo r lanthanides

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followed the positive sequence, i.e., La(III) < Ce(III) < Pr(III) < Nd(III) < Sm(III) < Eu(III) < Gd(III) < Tb(III) < Dy(III) < Ho(III) < Er(III) < Tm(III) < Yb(III) < Lu(III).

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The sequence can be attributed to their ionic radii, i.e., the extraction efficiencies of

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lanthanides increased with their ionic radii were decreased. As the ionic radii were decreased, the coordination strengths of Cyanex 572 with REs were increased.

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Accordingly, the extraction efficiencies of Cyanex 572 for lanthanide were increased.

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Because Y(III) had a neighboring ionic radius between Ho(III) and Er(III), its extraction efficiency lied between Ho(III) and Er(III). Among the RE ions, Sc(III) had a minimum ionic radius and highest extraction efficiency. Unlike those of lanthanides

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and yttrium, the extraction efficiencies of Sc(III) reached above 99% under the extraction conditions.

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Fig. 1 Effect of pH values on REs (La3+-Lu3+, Sc 3+, Y3+) extraction. Organic phase: 0.48 mol/L

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Cyanex572 in n-heptane. Aqueous phase: 0.16 (total) and 0.01 (individual) mol/L RE ion.

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As shown in Fig. 2, Sc(III) and Lu(III) exhibit similar extraction behaviors when

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the aqueous pH values were adjusted. However, the extraction efficiency of Sc(III) is still significantly higher than that of Lu(III) at a higher pH value. Accordingly, it can

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be confirmed that Cyanex 572 may be regarded as a powerful extractant for the separation of Sc(III) from other RE ions. With the increase of aqueous acidity, the extractability of Cyanex 572 for Sc(III) decreases. Therefore, it is possible to strip the extracted Sc(III) with hydrochloride acid effectively.

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Fig. 2. Effect of aqueous pH on Sc(III) and Lu(III) extraction. Organic phase: 0.05 mol/L Cyanex

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3.2 Extraction mechanism

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572 in n-heptane, aqueous phase: 0.0102 mol/L Sc(III) and 0.012 mol/L Lu(III).

As mentioned above, Cyanex 572 performed well for the extraction of Sc(III).

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Herein, further experiments were conducted to study the extraction mechanism of Sc(III) with Cyanex 572. To make a comparison, the extraction behaviors of Cyanex

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572 for Lu(III) and Yb(III) were also studied.

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Fig. 3. Relationship of equilibrium acidity value and the decrease of RE concentration in aqueous

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phase. Organic phase: 1.2 mol/L Cyanex 572 in n-heptane, initial aqueous phase pH = 3.

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By changing initial RE concentration, the relationship between the increase of H+ and the decrease of RE ion concentration in aqueous phase was investigated. Data in

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Fig. 3 show that the slopes of three lines are all around 3, which reveal that Cyanex 572 released 3 mol of protons when it extracted 1 mol of RE(III). Accordingly, the

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RE extraction mechanism using Cyanex 572 from hydrochloride media can be expressed as follows:

M 3 ( aq)  3HL( org )  ML3(org )  3H 

(5)

where M represents RE, HL denotes Cyanex 572 in organic phase. Infrared spectra analysis was performed to compare Cyanex 572 before and after the loading of Sc(III). As be seen from Table 2 and Fig. 4, the characteristic peak at 1172 cm-1 associated with the vibration of the P=O group was shifted to 1158 cm-1 ,

ACCEPTED MANUSCRIPT and 970 cm-1 associated with the vibration of the P-O-H group was shifted to 958 cm-1 after Sc(III) extraction. Meanwhile, the P-O-C stretching vibration of 1034 cm-1 was slightly shifted to 1036 cm-1 . The above changes further indicate that prono unced coordination interactions took place between Sc(III) and P=O, P-O-H groups from

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Cyanex 572 in the extraction process.

Fig. 4. Infrared spectra of blank Cyanex 572 and Sc(III)-loaded Cyanex 572.

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Table 2 Characteristic IR spectral data for Cyanex 572 and Sc(III)-loaded Cyanex 572 Wavenumber, cm-1

Probable

assignment

Cyanex 572

Sc(III)-loaded Cyanex 572

νP=O

1172

1158

νas P-O-C

1034

1036

νas P-O-H

970

958

νas C-H, νs C-H

2954, 2872

2954, 2872

δas CH3 -, δ s CH3 -

1464, 1364

1464, 1364

ACCEPTED MANUSCRIPT 3.3 Loading capacity In consideration of the fact that extraction capacity is important to evaluate an extractant, the extraction capacity of 0.083 mol/L Cyanex 572 for 0.021 mol/L Sc(III) at the pH value of 0.5 were investigated. To determine the extraction capacity,

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continuous extraction equilibriums between the same organic phase containing

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Cyanex 572 with fresh Sc(III)-containing aqueous solution were performed. As

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revealed in Fig. 5, the extraction capacity of Sc(III) increases with increasing the extraction times and reaches almost unchanged after three times of extraction.

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572 reached 1.25 g/L under this condition.

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According to the investigation, the maximum loading capacity of Sc (III) by Cyanex

Fig. 5. Extraction capacity of Cyanex 572 toward Sc(III). Organic phase: 0.083 mol/L Cyanex 572 in n-heptane. Aqueous phase: 0.021 mol/L Sc(III), pH = 0.5.

3.4 Stripping studies

ACCEPTED MANUSCRIPT Because of the stronger coordination interaction between Sc(III) and extractant, the Sc(III)- loaded organic phase was always difficult to be stripped. As reported in some recent literatures, thorium and heavy REs were prone to be stripped from Cyanex 572 (Wang et al., 2015; Wang et al., 2017). Thus, the stripping of Sc(III) by

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Cyanex 572 was investigated in this study. As listed in Table 3, three different

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experiments were performed to study the stripping behaviors of Cyanex 572. All the

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stripping experiments were conducted for 5 times, and the total stripping ratios were calculated. As shown in Table 3, S(b)％ reached 89.9% after the organic phase was

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diluted by n-heptane, which was much higher than S(a)％ without dilution. The results

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revealed that the dilution of Sc(III) loaded organic phase was an effective method to achieve higher stripping ratio. Under the same conditions, the total stripping ratio of

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S(b) ％ was higher than that of S(c) ％, i.e., 89.9% vs. 57.4%. The comparison

P507.

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confirmed that the stripping property of Cyanex 572 for Sc(III) was better than that of

Table 3 Effect of Sc(III) stripping with HCl. Organic phase: (a) 0.15 mol/L Cyanex 572 loaded w ith 0. 0301 mol/L Sc(III). (b) 0.0375 mol/L Cyanex 572 loaded w ith 0. 0092 mol/L

HCl.

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Sc(III). (c) 0.0375 mol/l P507 loaded with 0.0077 mol/l Sc(III), stripping reagent: 3 mol/L

Stripping times

S(a)％

S(b)％

S(c)％

1st

23.5±0.2

52.3±2.2

30.3±1.3

2nd

9.3±0.8

22.1±1.1

11.2±0.02

3rd

6.3±0.2

8.5±0.5

7.5±1.2

4th

4.4±0.4

4.3±0.1

4.8±0.3

5th

3.1±0.1

2.7±0.1

3.7±0.02

Total

46.5±1.6

89.9±0.9

57.4±2.9

ACCEPTED MANUSCRIPT To optimize the stripping conditions, 0.0325 mol/L Cyane x 572 loaded with 0.0083 mol/L Sc(III) was stripped with 5 mol/L HCl. As showed in Fig. 6,

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the loaded Sc(III) can be fully stripped after 10 times of stripping.

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Fig. 6. Effect of stripping time on the total stripping ratio of Sc(III). Organic phase: 0.0325mol/L

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Cyanex 572 loaded with 0.0083 mol/L Sc(III), stripping reagent: 5 mol/L HCl.

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3.5 Recovery of scandium from tungsten residue Tungsten is an important resource for many high- tech products. With the booming utilization of tungsten resources, tungsten residue has become a kind of pollutant that cannot be ignored. The tungsten residue contained some critical elements such as scandium and some other REs, which can be fully utilized as a secondary resource. As can be seen in Fig. 7, a recovery process based on Cyanex 572 for scandium has been developed, and the major chemical composition of leaching solution from tungsten residue is listed in Table 4.

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Fig. 7. A conceptual flowsheet for scandium recovery from tungsten residue.

Table 4 The major chemical composition of leaching solution. Aqueous acidity: 1.38 mol/L H+. Composition

Sc

Th

Ti

mg/L

9.9

8.9

±

±

Mn

REs

Al

Ca

Mg

30.7

1.3

13091.4

9530.9

40.5

506.5

5591.1

221.1

±

±

±

±

±

±

±

±

0.1

142.2

260.7

0.4

4.7

20.6

0.7

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Fe

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0.1

Zr

0.3

0.2

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As revealed in Fig. 8, the extraction behaviors of Sc(III) from leaching solution of tungsten residue by Cyanex 572 and some other organophosphorus extractants such as TBP, Cyanex 923 and P507 were compared. Their extractabilities to Sc(III) decreases in the order of TBP < Cyanex923 < Cyanex572 < P507 under the same conditions. According to the previous literature (Zhu et al., 2017), the loaded Sc(III) was difficult to be stripped from P507. Thus, the better extracting and stripping properties of

ACCEPTED MANUSCRIPT Cyanex 572 for Sc(III) revealed its advantages for the recovery of scandium from the

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leaching solution of tungsten residue.

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Fig. 8. The extraction of Sc(III) from leaching solution of tungsten residue.

To obtain a suitable extractant concentration for the scandium recovery, a series of

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experiments by adjusting the Cyanex 572 concentration from 0.04 mol/L to 0.28 mol/L were carried out. As shown in the Fig. 9, the extraction efficiency of Sc(III)

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increases pronouncedly with the increasing concentration of Cyanex 572. The extractability of Cyanex 572 for Sc(III) is far better than those for the impurities from the leaching solution. In the studied concentration range of Cyanex 572, the extraction efficiency of Sc(III) reaches 93% when the concentration of Cyanex 572 is 0.28 mol/L. The extraction sequence follows the order: Sc(Ⅲ) > Zr(Ⅳ) > Th(Ⅳ) > Ti(Ⅳ) ≈ Fe(Ⅲ) ≈ Mn(Ⅱ) ≈ Al(Ⅲ) ≈ Ca(Ⅱ) ≈ Mg(Ⅱ).

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Fig. 9. The extractabilities of Cyanex 572 for different elements.

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For studying the recovery of scandium, the purities of different elements in the

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leaching solution before extraction and after stripping were compared. As shown in Fig. 10, the content of impurity accounts for more than 99%, while the content of

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scandium accounts for only 0.035% in the leaching solution. After scrubbing with 1.5 mol/L HCl twice, the loaded organic phase was stripped with 3 mol/L HCl and the

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purity of scandium arrived at 28.623% in the enrichment solution. By the recovery process, the composition of scandium could be increased for eight hundred times. After 12 times of stripping, the yield of scandium was still 90.9%. These results mentioned above show that Cyanex 572 was efficient to recovery scandium from the leaching solution of tungsten residue.

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Fig. 10. Comparison of Sc in the leaching solution and enrichment

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4. Conclusions

Cyanex 572 was first studied for the extraction of scandium fro m REs, the

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recovery of scandium by Cyanex 572 fro m the leaching solution of tungsten residue was also investigated. The extraction sequence of Cyanex 572 for

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lanthanides followed the positive sequence, and the separation factors of Sc( III)

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toward other RE ions were larger under the lower pH values. By specific extraction experiments and IR spectra analysis, a cation exchange mechanism was

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proposed and the stoichiometry of Cyanex 572 to Sc(III) was indicated to be 3:1. Moreover, the extraction capacity of Cyane x 572 for Sc(III) was deter mined to be 1.25 g/L under the experimental conditions. Also the scandium could be effectively stripped with HCl. Because of its better extraction and stripping properties, Cyanex 572 performed better than P507, Cyanex 923 and TBP. As for the recovery of scandium from tungsten residue us ing Cyanex572, the composition of scandium increased nearly eight hundred times, and the yield of scandium reached 90.9%. The separation of Sc(III), Th(Ⅳ) and Zr(Ⅳ) are underway in this lab. In summary,

ACCEPTED MANUSCRIPT Cyanex 572 would be an effective extractant for the separation and enrichment of scandium from various resources.

Acknowledgments

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This work was supported by the “Hundreds Talents Program” fro m the

Science and

Technology Major Projects of Fujian Province

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(21571179),

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Chinese Academy of Sciences, National Natural Science Foundation of China

(2015HZ0001-3) and Natural Science Foundation of Fujian Province (2016J0102).

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The authors would like to thank Ganzhou Rare Earth Group Co., Ltd. for supplying

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rare earth feed and Chongyi Zhangyuan Tungsten Co., Ltd. for supplying tungsten

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residue.

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References

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Highlights 

Cyanex 572 revealed excellent extracting and separating properties for Sc.

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Cyanex 572 performed better than P507, Cyanex 923 and TBP for Sc

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extraction. A cation-exchange extraction mechanism of Cyanex 572 for Sc was proposed.

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Sc was effectively recovered from tungsten residue using Cyanex 572.

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The composition of Sc increased more than eight hundred times.

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