Facile and Efficient Removal of Tungsten Anions Using Lysine

Feb 18, 2017 - We present a facile method for tungsten ion removal using lysine for the development of an environmentally friendly and sustainable rec...
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Facile and efficient removal of tungsten anions using lysinepromoted precipitation for recycling high-purity tungsten Takashi Ogi, Takahiko Makino, Satoshi Nagai, Wendelin J. Stark, Ferry Iskandar, and Kikuo Okuyama ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b02934 • Publication Date (Web): 18 Feb 2017 Downloaded from http://pubs.acs.org on March 1, 2017

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Facile and efficient removal of tungsten anions using lysinepromoted precipitation for recycling high-purity tungsten

Takashi Ogi,†,* Takahiko Makino,‡ Satoshi Nagai,† Wendelin J. Stark,§ Ferry Iskandar,# Kikuo Okuyama†



Department of Chemical Engineering, Hiroshima University, 1-4-1 Kagamiyama, Hiroshima

739-8527, Japan ‡

Cutting Tool R&D Division, Kyocera Corporation, Kagoshima Sendai Plant, 1810 Taki-cho,

Satsumasendai, Kagoshima 895-0292, Japan §

Institute for Chemical and Bioengineering, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093,

Zurich, Switzerland #

Department of Physics, Institute of Technology Bandung, Ganesha 10, Bandung 40132, West

Java, Indonesia

*Corresponding author: Takashi Ogi E-mail: [email protected] Tel/ Fax: +81-82-424-3765 Department of Chemical Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, 739-8527, Japan

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ABSTRACT We present a facile method for tungsten ion removal using lysine for the development of an environmentally friendly and sustainable recycling technique. Lysine addition to the tungsten solution achieved 100% tungsten removal within 5 min, as a white lysine–tungsten precipitate. Electrospray ionization mass spectrometry analyses of the tungsten and lysine mixed solutions showed that lysine promoted dehydration condensation reactions of anionic tungsten species such as HWO4− and W6O192− through the electrostatic interactions between positively charged lysine and negatively charged tungsten ions. Calcination of the lysine–tungsten precipitate produced tungsten oxide powder of high purity (99.6%) because the lysine is completely decomposed. This facile and useful metal removal method can be used for polyoxometalates of other metals such as molybdenum, tantalum, and niobium.

Keyword: Recovery of Rare Metal, Adsorption, Settling, Amino acid, Polyoxometalate, High purity recycling

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INTRODUCTION The development of cost-effective and environmentally benign techniques for the removal of useful or toxic metals from solutions has been attracting increasing attention in recent years to achieve environmental conservation and to secure resources.1-7 In particular, the development of techniques for recycling rare metals from waste products, so-called “urban mining”, based on the principles of green chemistry and green engineering should be accelerated to meet growing global demands and enable creation of a sustainable society.8-21 Recycling of the rare metal tungsten is essential because it is widely used in the manufacturing industry, e.g., in cutting tools for automobile parts, mill rollers, electric lamp filaments, thermal shield plates, and catalysts for the removal of organic materials.22-25 However, primary mining of tungsten is environmentally taxing and its deposits are geopolitically highly concentrated, endangering supplies to other regions. Tungsten is therefore defined as a critical raw material by Japan, the European Union, and the United States.26 More efficient use and recycling of tungsten is a crucial issue in reducing primary mining and supply risks. Conventional ion-exchange27, 28 and electroplating29 processes are used to remove tungsten from metal scrap wastewaters. Ion exchange is an effective method for tungsten removal and is widely used. However, ion exchange is costly, slow, and cumbersome, and a significant amount of ion-exchange resin must be used for the method to be effective. The cost and complexity of ion exchange also limit the resins available. Although electrolyte systems are available, electrolysis is expensive, requires significant maintenance, uses other resources, can create further waste disposal problems, and is energy-intensive. The development of cost-effective and environmentally friendly methods for tungsten recovery from wastewater is therefore important.

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Recently, metal recovery through biosorption or biomineralization by microorganisms has been studied, with the aim of developing sustainable and environmentally friendly techniques.3046

We achieved 100% removal of tungsten by introducing Escherichia coli cells into a tungsten

aqueous solution.47 We also showed that E. coli cells have the potential to adsorb tungsten selectively from real wastewaters obtained from spent scrap (tungsten carbide).48 We performed a series of tungsten biosorption studies and found that amino acids exposed on the surfaces of heat-treated E. coli cells significantly enhanced the tungsten adsorption capacity.49 Detailed analyses using two-dimensional electrophoresis, liquid chromatography tandem mass spectrometry, and an amino acid analyzer showed that various amino acids, particularly lysine, were strongly related to the electrostatic adsorption of tungsten anions. The acid dissociation constant (pKa COOH) of lysine is 2.18.50 Lysine is therefore positively charged at low pH and can adsorb tungsten anions. Lysine is therefore potentially a strong, safe, and cost-effective adsorbent with minimum environmental impact. Based on this background, we focused on the use of lysine, but without E. coli cells, as a green adsorbent/precipitant for tungsten recovery; the concept is shown in Scheme 1. Lysine was introduced into a tungsten aqueous solution, and the interactions between lysine and tungsten ions were evaluated at various solution pHs, initial lysine and tungsten concentrations, and operating temperatures. Lysine was removed from the tungsten–lysine precipitates by atmospheric calcination. In terms of sustainable development, lysine has several advantages as an additive for metal removal: it is easy to obtain, inexpensive, and safe, and can be easily removed by calcination to give high-purity oxides. High-purity products are a critical element in achieving

efficient

recycling.

Although

a

wide

range

of

adsorbents/coagulants/flocculants/precipitants have been used for metal removal, this is the first

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report of the use of lysine. In addition, lysine was used to remove various other metal ions to determine its applicability.

HWO4-

Lysine

O H-N-H + H

-O

O

Dehydration

W O

OH

O

Condensation

W O

-H2O

W O

W

W

Condensation

W O

O

O

O O

OH

O

O

O

O

W

W O

O

O

OH

Condensation and Precipitation

O

Lysine

Precipitation

Calcination High-purity WO3 powder

Tungsten aqueous Solution (pH 2.0)

Scheme 1. Tungsten removal using lysine and production of high-purity tungsten oxide.

EXPERIMENTAL SECTION Materials. Lysine hydrochloride was purchased from the Ajinomoto Healthy Supply Co., Inc., Tokyo, Japan. Na2WO4·2H2O and hydrochloric acid were purchased from the Kanto Chemical Co., Inc., Tokyo, Japan. All chemicals were used as received. Tungsten removal tests using lysine. Test solutions were prepared by mixing ultrapure water, lysine hydrochloride, and 1 mol L−1 hydrochloric acid for pH adjustment; a 1 mol L−1 Na2WO4·2H2O aqueous solution was then added to a specified concentration. The total solution volume was 48 mL. After the start of the experiment, test samples were collected with a syringe at specified time intervals, and the samples were filtered (Whatman filter, pore size: 0.2 µm; GE

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Healthcare Life Sciences) before analysis. Experiments were conducted at various solution temperatures from 10 to 40 °C and the pH was adjusted from 1.36 to 8.03 using hydrochloric acid. The initial tungsten concentration in the mixed solution ranged from 1.8 to 239 mmol L−1, and the lysine concentration in the mixed solution ranged from 2.7 to 383 mmol L−1. When metal ions were introduced into the lysine solution, a white precipitate appeared immediately. The white precipitate was centrifuged at 7840 × g for 10 min and dried in a drying oven at 80 °C for 12 h. The dried sample was calcined in a furnace at 600 °C for 4 h under atmospheric (air) conditions. Characterization. The removal of tungsten ions with time was monitored by periodically withdrawing aliquots of the solution and determining the tungsten concentration using inductively coupled plasma-atomic emission spectrometry (ICP-AES; ICPE-9820, Shimadzu Corporation, Kyoto, Japan). The percentage of tungsten removed, Rw, was calculated as ܴ୵ =

‫ܥ‬଴ − ‫ܥ‬ୣ × 100% ‫ܥ‬଴

where C0 is the initial concentration of tungsten in the solution [mol L−1] and Ce is the tungsten concentration after lysine addition [mol L−1]. The calculated errors in the experimental results were less than 1.0%. The ionic states of pure tungsten, pure lysine, and the tungsten–lysine mixed aqueous solution were determined using electrospray ionization mass spectrometry (ESIMS; LTQ Orbitrap XL, Thermo Fisher Scientific). Samples of tungsten concentration 100 ppm were prepared for analysis and the pH was adjusted using hydrochloric acid. The crystal structure of the tungsten oxide powder obtained by calcination was examined using powder Xray diffraction (XRD; Bruker, D2 Phaser, Billerica, MA, USA, Cu Kα radiation). The tungsten concentration in the tungsten oxide powder was determined using ICP-AES.

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RESULTS AND DISCUSSION Figure 1(a) and (b) show the effect of solution pH (1.37–8.03) on tungsten removal by lysine at 25 °C. The initial concentrations of tungsten and lysine were kept at 177 and 92 mmol L−1, respectively. Figure 1(a) shows that the tungsten concentration rapidly decreased within 5 min when the solution pH was less than 2.15. Specifically, lysine removed 96% of tungsten from the tungsten solution at pH 1.37. In contrast, the tungsten concentration did not decrease at pH values greater than 3.61. Figure 1(b) shows digital photographs of the tungsten solution samples after exposure to lysine solution for 5 min. When the solution pH was adjusted to less than 2.15, a white sediment formed. We confirmed that the precipitation of insoluble tungstic acid does not started until pH 0.64 at the initial tungsten concentration of 170 mmol L−1 (see supporting information Figure S1). Figure 1(c) shows the percentage tungsten removal as a function of the ratio of the initial tungsten and lysine concentrations (lysine/W) at different initial tungsten concentrations (230, 17, and 1.8 mmol L−1). The solution pH and temperature were kept at 1.8 and 25 °C, respectively. When the lysine/W ratio increased, the percentage of tungsten removed also increased, for all initial tungsten concentrations. Tungsten removal increased with increasing initial tungsten concentration. In the case of 230 mmol L−1, 100% tungsten removal was achieved using an equimolar lysine concentration. These results imply that the solubility of the tungsten–lysine precipitate and the percentage of tungsten removed are strongly related. The effect of solution temperature on tungsten removal was then investigated. Figure 1(d) shows the percentage tungsten removal as a function of solution temperature (10–40 °C) for different initial lysine concentrations (48 and 36 mmol L−1). The solution pH and initial tungsten concentration were kept at 1.8 and 150 mmol L−1, respectively. The percentage of tungsten removed increased with decreasing solution temperature. At 15.5 °C, 96% tungsten was recovered from the solution.

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This high removal rate was a result of the decreased solubility of the tungsten–lysine precipitate. This result indicates that high removal rates can be achieved by decreasing the solution temperature.

Figure 1. (a) Changes in soluble tungsten ion concentration using lysine at 25 °C in solutions with different pHs. Na2WO4·2H2O and lysine concentrations were kept at 177 and 92 mmol L−1, respectively. (b) Digital photographs of samples after 5 min. (c) Relationship between lysine/W initial concentrations and percentage tungsten removal at 60 min for different initial tungsten

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concentrations; pH and temperature of solutions were kept at 1.8 and 25 °C, respectively. (d) Relationship between solution temperature and percentage tungsten removal at 30 min for different initial lysine concentrations; pH and initial tungsten concentration of solutions were kept at 1.8 and 150 mmol L−1, respectively.

To clarify the mechanism of tungsten removal using lysine, the Na2WO4 aqueous solutions (pH 8.0 and 3.0), lysine solution, and tungsten–lysine mixed solution were analyzed using ESIMS. Although pH 1.8 was used in the removal experiments, pH 3.0 was used for the ESI-MS analysis because of instrumental limitations. Figure 2(a) shows that the main ionic species in the Na2WO4 aqueous solution at pH 8.0 was HWO4−. When the solution pH was reduced to 3.0 using hydrochloric acid, various ionic tungsten species, e.g., W6O192−, W7O222−, W3O102−, and HWO4−, were formed through condensation of HWO4− ions (Figure 2b). HWO4− undergoes dehydration by a proton (H+) supplied by the pH decrease to form tungsten polyoxometalates,51 e.g., 6HWO4− + 4H+ → W6O192− + 5H2O. Lysine is mainly positively charged in solution at pH 1.8 because its acid dissociation constant (pKa COOH) is 2.2. This is supported by the ESI-MS results (Figure 2c). Lysine therefore acts as a counter cation to the tungsten polyoxometalate in lysine–Na2WO4 mixed solutions at pH less than 1.8. The condensation of HWO4− ions can therefore be promoted by electrostatic interactions between the positively charged lysine and negatively charged tungsten oxoacid. Figure 2(d) and (e) show the ESI-MS results for a sample containing 100 ppm Na2WO4 aqueous solution and 100 ppm lysine aqueous solution. The results (Table 1) show the presence of various tungsten condensates in the tungsten–lysine mixed solution. The chemical formula of the main condensate was C6H13N2O5W, formed by a dehydration reaction of HWO4− and lysine (C6H14N2O2).

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100

HWO4-

(a)

80 60 40 20 0 100

W6O192-

80

(b)

HWO4- W3O102- W O 24 13

60 40

W7O222-

W8O252-

W5O162-

20 0 200

300

400

500

600

90

800

900

1000

(c)

L-lysine

80 Relativ e A bundanc e

700

m/z m/z

100

70 60 50 40 30 20 10 0 100

150

200

250

300 m/z

350

400

450

m/z

100

500

(d)

90

Relative Abundance

80

C6H13N2O5W

70 60 50 40

HW2O7-

30 20 10 0 360 380 400 FTMS - p ESI Full ms [80.00-1600.00] 100

90 80 Relative Abundance

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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C12H25N4O6W

420

m/z

440

460

480

m/z

C6H10N2O7W2

500

(e) C12H25N4O9W2

C6H12N2O8W2

70 60 50

C12H27N4O7W

40 30 20 10 0 500

550

600

m/z

650

700

750

m/z

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Figure 2. ESI-MS analyses of tungsten solution, lysine solution, and tungsten–lysine mixed solution. (a) Na2WO4 aqueous solution at pH 8.0; (b) Na2WO4 aqueous solution at pH 3.0; (c) lysine aqueous solution at pH 2.8; (d) tungsten–lysine mixed solution at pH 8.0; m/z range 360– 500; (e) tungsten–lysine mixed solution at pH 2.8; m/z range 500–750. (a), (b), (d), and (e) positive mode; (c) negative mode.

Table 1. Proposed chemical formulas of tungsten–lysine condensates based on ESI-MS analysis Structural formula

W : Lys

CH NOW

1: :1

C H NOW

1: :2

C H NOW

1: :2

CH NOW

2

2: :1

2

2: :1

6

12

12

6

13

2

25

4

27

10

5

6

4

2

7

7

CH NOW 6

12

2

8

Figure 3 shows a proposed mechanism for tungsten removal using lysine, based on the above results. The main ionic species in Na2WO4 aqueous solution at pH 8.0 is HWO4−. When lysine solution is added, the pH of the mixed solution changes from 8.0 to 7.0. Lysine is present as positively charged species at this pH; these react with negatively charged tungsten ions through ionic bonding to form tungsten–lysine condensates, i.e., tungsten polyoxometalates. Reduction of the solution pH to 2.0 using hydrochloric acid results in the various types of lysine-containing tungsten polyoxometalates in the solution reacting with each other through dehydrative condensation. A saturated solution of tungsten polyoxometalates is eventually formed, causing sedimentation of tungsten precipitates. These reactions occur at around pH 2.0.

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Figure 3. Proposed mechanism for tungsten removal using lysine.

To clarify the role of the amino function in lysine, different types of amino acid, i.e., glycine, monosodium glutamate, histidine, and arginine, were added to the tungsten solution. The amino acid properties and tungsten removal rates are shown in Figure S2 in the supporting information. The percentage of tungsten removed increased with increasing number of nitrogen atoms. This indicates that positively charged amino groups are important in the formation of tungsten polyoxometalates. From above result, we named this method a Charged Amino group Assisted Precipitation (CAAP) method. Plattes et al. reported tungsten removal from industrial wastewater by precipitation, coagulation, and flocculation using an inorganic precipitant, namely

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ferric chloride.52 They suggested that the main mechanism for tungsten removal was adsorption of negatively charged tungsten oxyanions on the positively charged iron hydroxide generated on the surface of ferric hydroxide at low pH. In the case of lysine, the same phenomena probably occur in the solution. However, lysine is an organic and can be easily removed. When ferric chloride was used as the additive, the inorganic component (iron) remains as a contaminant in the tungsten concentrates, resulting in difficulties in recycling pure tungsten from urban mining. To determine the potential applicability of this CAAP method to real wastewater in the near future, tungsten concentrates were prepared by drying the tungsten–lysine precipitates at 80 °C for 12 h. The digital photographs in Figure 4(a) show the dried powder samples obtained from the tungsten–lysine precipitates. The concentration of tungsten in the dried sample, calculated from the amount of tungsten removed per unit of dried precipitate, was 51.4% (w/w), i.e., 12 times the concentration of tungsten in the initial solution (239 mmol L−1). We prepared tungsten oxide by calcination. First, we used thermogravimetry to identify the optimum temperature for lysine removal. We used both lysine and tungsten–lysine precipitates for this analysis. Figure S3 in the supporting information shows that the weights of both samples decreased with increasing temperature, and the sample weights were constant above 600 °C. Based on these results, a dried powder sample of tungsten–lysine precipitate was calcined at 600 °C for 4 h in a furnace. The calcined powder was yellow, as shown in Figure 4(b), indicating generation of WO3 crystals.53, 54 ICP-AES showed that the solid condensate produced contained 99.6% WO3 (w/w); this is 21 times the tungsten concentration in the initial solution (239 mmol L−1). Figure 4(c) shows the XRD patterns of the tungsten–lysine powder after drying and calcination. The pattern of pure lysine powder was also obtained as a reference. After drying, the tungsten–lysine precipitate showed a broad peak at 20–30°. This amorphous structure is different from those of pure lysine

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powder and Na2WO4. The XRD pattern of the tungsten–lysine powder sample after calcination at 600 °C indicates the presence of high-purity crystalline WO3. We calculated the cost of lysine per mass of tungsten recovered. The results in Figure 1(c) show that the mass of lysine needed per kilogram of tungsten recovered is around 0.5 kg for an initial tungsten concentration of 230 mmol L−1. If we use the price of industrial-grade lysine from Alibaba.com (US$ 0.7/kg), the calculated cost of lysine per kilogram of tungsten recovered is 0.4 US$. A comparison of this price with that of tungsten itself (US$ 70/kg, from Alibaba.com) shows that the cost of lysine is 0.6% that of tungsten (= US$-Lys/US$-W). This cost evaluation indicates that this method is feasible even if the lysine is lost by burning.

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Figure 4. (a) Digital photograph of tungsten–lysine precipitate after drying at 80 °C. (b) Digital photograph of tungsten–lysine precipitate after calcination at 600 °C for 4 h. (c) XRD patterns of powder samples of tungsten–lysine precipitate after drying and calcination.

The removal of various metal ions by lysine was investigated to determine the applicability of this method. As shown in Table 2, high percentage removals of tungsten, molybdenum, tantalum, and niobium ions were achieved. This indicates that lysine can be used to remove metals that form polyoxometalates. The results suggest that lysine promotes dehydration condensation reactions of tungsten, molybdenum, tantalum, and niobium oxoacids. They also imply that lysine-assisted removal has the advantage of selectively removing metals that form polyoxometalates. This is a great advantage in applications for industrial waste treatment and recycling.

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Table 2. Removal rates of various metal ions using lysine Lysine conc.

Metal conc. [mmol L ]

[mmol L ]

Lysine /metal [-]

170

94

0.6

26

1.8

94

18.0

25

1.4

24

1.8

94

1.7

3.0

1.8

24

1.8

71

182

96

0.5

24

1.8

99

44

48

1.1

27

1.7

89

10

114

11.4

27

1.7

99

2.0

11

5.7

27

1.7

19

Nb

11

57

5.2

25

1.5

96

Ni

9.2

240

26.1

27

1.9

1

Cs

3.7

240

64.9

27

1.7

5

Na

17.5

137

7.8

26

1.4-1.8

0

Al

14.9

137

9.2

26

1.4-1.8

3

Zn

7.1

137

19.3

26

1.4-1.8

0

Co

8.5

137

16.1

26

1.4-1.8

0

Si

12.5

137

11.0

26

1.4-1.8

0

Au

3.8

137

36.1

23

0.25

2

3.4

137

40.3

26

11

5

4.0

137

34.3

26

0.5

5

Metal

-1

W

-1

[ C]

pH [-]

Removal ratio at 5 min [%]

Temp. о

Mo

Ta

Pt

CONCLUSION In this paper, we report a facile and effective method for tungsten recovery from Na2WO4 aqueous solution using lysine. Lysine addition to the tungsten aqueous solution at pH less than

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2.15 caused sedimentation of white precipitates within 5 min, and 100% tungsten removal from the tungsten solution can be achieved. ESI-MS showed that lysine reacted with tungsten ions through electrostatic interactions and promoted the precipitation of tungsten polyoxometalates. Calcination of tungsten–lysine precipitates at 600 °C for 4 h yielded a solid condensate containing 99.6% tungsten (w/w), 21 times the concentration of tungsten in the initial solution. This facile method using lysine can be applied to polyoxometalates of other metals such as molybdenum, tantalum, and niobium. In the near future, we will use this facile method for industrial tungsten wastewater treatment.

ASSOCIATED CONTENT Supporting Information Additional data on digital photographs of tungsten solution samples at various pH in the absence of lysine, properties of amino acids and tungsten removal rates, and thermogravimetric analysis for powder samples of tungsten-lysine precipitate and lysine are provided in the supporting information section.

AUTHOR INFORMATION Corresponding Author *Telephone: +81-82-424-3765; e-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS

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This work was supported by JSPS KAKENHI Grant Number 26709061, Steel Foundation for Environmental Protection Technology. This work is partly supported by the Center for Functional Nano Oxide at Hiroshima University. The authors also thank Y. Sakamoto, T. Kondo, and H. Horiuchi for help with experiments and measurements.

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Table of Contents Graphic

Facile and efficient removal of tungsten anions using lysine-promoted precipitation for recycling high-purity tungsten Takashi Ogi*, Takahiko Makino, Satoshi Nagai, Wendelin J. Stark, Ferry Iskandar, Kikuo Okuyama Synopsis A sustainable resource recovery process using lysine assisted tungsten polyoxometalate precipitation are highlighted.

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