Selective PGM Extraction with Simple Ionic Liquids

Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University

Director Prof. Atsushi MURAMATSU

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Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, created in part from the former Research Institute of Mineral Dressing and Metallurgy, has been researching all sorts of things through many different approaches and viewpoints. Our institute promotes the development of cutting edge research and new areas of study, while also re-concentrating new comprehensive knowledge of metal resource processing. We aim to be a leader in future training and the continued development of the metallurgical industry, and have established the Center for Mineral Processing and Metallurgy (CMPM) in order to fulfill these goals. This center will recreate the expertise of processing and metallurgy that will support social infrastructure, and pursue new metal resource processing in the future, starting with the processes of dressing and refining metals, but also including the process of recovering resources from waste, nuclear fuel processes, resources circulation and disposal processing, and urban mining processes.

Founded on April 1st, 2018

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Research field

Hiroyuki FUKUYAMA High-temperature Physical Chemistry of Materials

Shin-ya KITAMURA Base Materials Processing

Junya KANO Powder Processing for Functional Materials

Nobuaki SATO Energy System

Itaru HONMA Chemistry of Energy Conversion Devices

Etsuro SHIBATA Metallurgy and Recycling System for Metal Resources Circulation

Atsushi MURAMATSU Hybrid Nano-particle

Takahisa OMATA Atomic Site Control in Inorganic Materials

Field of cooperative

research

Hiroshi NOGAMI Environmental-Conscious Materials Processing*

Hiroyuki SHIBATA Materials Separation Processing*

Manager of Center: Itaru HONMA

*Principal “DIVISION OF PROCESS AND SYSTEM ENGINEERING”

1st Step:

Separation of Pt and Pd

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Ionic Liquids:Novel Extraction media

Platinum Group Metals (PGMs)

Widely used in various fields (e.g. automobile catalyst, electronic materials) Platinum Group Metals (PGMs)： Pd, Pt, Rh, Ir, Ru, Os

Problem: Depletion of PGMs Solution: recycle from urban mines

<Main recycle methods: Solvent Extraction with HCl solution>

H+ H+

Cl-Cl-PtCl62-

Cl-

Cl-

Cl-Cl-

Organicphase

Aq. phase

Solvent extraction system: Pt Extraction1)

[shaking]

NR R

R NR

RR

NHR

R

RPtCl62- HN

R

RR

PtCl62-NHR

R

RHN

R

RR

R : n-C8H17

High efficient extractionVolatile organic solvents (Non environmental friendly)Low selectivity

less toxic and high selectivity system is needed

1) B. Swain, J. Jeong, S. K. Kim and J. C. Lee, Hydrometallurgy, 104, 1 (2010).

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Solvent Extraction using Ionic Liquids

Ionic Liquids (ILs)Molten salts at room temperature

NS SO

CF3O

F3C

O

OPF6

BF4

Cl

( NTf2 )

cations anions

ILs have potential for new extraction media

ILs

Non-flammable, Non-volatile, and Non-harmful properties

Flexible molecular design

Suitable for extraction

Immiscible to water

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Basic scheme of IL synthesis

NNH3C

NNH3C

Cl−Cl

[C4mim][Cl]

LiTf2NR R Tf2N−

NNH3C

[C4mim][TFSI]

R

Evaluation of extraction

ICP-AES

Metal ions

Extract

Waterphase Shaking:

Temp. is kept.

Phase separation

*In the case of IL,extraction phase is under.

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The simpler, the better.

Cation Anion

Ionic Liquids

NS SO

CF3O

F3C

O

O PF6 BF4

OS

CF3O

O

Cl

Br

ClO4

( NTf2 )

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Design and synthesis of Ionic Liquids, which have phase separation against water, and have functions for extraction with affinity of target PGM.

Functionsfor extraction

Ionic Liquids+X－

PGMs +X－

TSILs, Task-Specific Ionic Liquids

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1st challenge IL-1

Shaking( 2600 rpm, 30 sec )

Pd, Au: Aqueous solution was changed to colorless．⇒Rapid and high extraction is expected．

Pd: red solid，Au: yellow solid．

Pt: no change in color and no precipitation．10

Pd Pt Au Pd Pt Au

Water phase

IL phase

ON NSO

NTf2

S

O

Extraction （ IL，2600 rpm, 30 sec ）

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Proton NMR

IL1

IL2

ON NSO

NTf2

ON NSO

NTf2

S

O

PdPt

IL

Pt, PdH2O

PtH2O

Pd, IL

Pd-SelectiveTHP-Deprotection

IL1 or IL2 O

R

S

S

Pd

Cl

Cl

[PtCl6]2-

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ON N

NTf2

S

S

Pd

L

L

ON N

NTf2

SPd

L

Cl L

ON N

NTf2

SPd

L

S LO

N N NTf2

and

IL-1 - Pd

IL-2 - Pd

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Difficulty in Rh extraction by conventional method

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Next step:Extraction of Rh

Amino-substituted task-specific ILs

N N N

NTf2R

REffects of Alkyl chains on the PGM extraction

Effect of anions and cations on the hydrophobicity as solvent of extraction

Molecular Design of the ILs

Behave as Pd, Pt extractants1)

Expectation for Rh extractants2),the difficult element to extract

Amino-substituted organic extractants are useful forPGM extraction in organic solvent systems

NN

O

N

OC6H13

C8H17

C8H17

C8H17

C8H17

1) B. Swain, J. Jeong, S. K. Kim and J. C. Lee, Hydrometallurgy, 104, 1 (2010).2) H. Narita, K. Morisaku and M. Tanaka, Chem. Commun., 5921(2008).

NOct

Oct Oct

Extractants with Amino groupRhPt

Pd

Design and Synthesis of Amino-substituted Hydrophobic ILs Investigation of Rh Extraction Ability into the ILs

This Work

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A Synthetic Route of Amino-substituted ILsSynthesis of Amino-substituted ILs

IL2IL1

IL5

IL3

IL4

Various types of amino-substituted ILs were Prepared

IL6 IL7

N N N

NTf2N N N

NTf2

N N N

NTf2Oct

Oct

N N N

NTf2Hex

HexN N N

NTf2Bu

BuN N N

NTf2Pr

PrN N N

NTf2Et

Et

Br N N

NTf2

N N N

NTf2R

RR2NH

MeCN85 °C

LiNTf2

H2Or.t., 1 h

NN

Br(CH2)3Br

Acetone45 °C, 20 h

Br N N

Br

IL1: R = c-HexIL2: R = 2-EthylhexylIL3: R = OctIL4: R = HexIL5: R = BuIL6: R = PrIL7: R = Et

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A Extraction Procedure of PGMs into ILs

100 ppm Pd, Pt, RhHCl 2.0 mL (C0)

Shaking, 1500 rpm, 15 min

ILs (ILn (n = 1~7), 0.40 g)

Centrifuged, 6000 rpm, 5 min

Micro tube

ICP-AES (Aq. phase: C)Extraction efficiency E (%)E = 100 x (C0-C)/C0

before after

Aq. phaseILsphase

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HCl conc. was increased

E of Pd and Pt was decreasedRh was not extracted

PGM Extraction Experiment • Aq. phase： 100 ppm Pd, Pt, Rh HCl 2.0 mL• ILs phase： IL1, IL2, 400 mg• Shaking： 1500 rpm, 15 min, 25 oC

IL1: R = c-HexIL2: R = 2-Ethylhexyl

Pd Pt Rh

N N N

NTf2R

R

Pd, Pt1.0-4.0 M HCl: [PdCl4]2-, [PtCl6]2-

Because Cl- competed with [PdCl4]2-, [PtCl6]2-, Cl- blocked ion pairs

Rh 1.0 M HCl: Complex species were changed from [RhCl5 (H2O)]2- to [RhCl6]3-

Effect of Steric Hinderance on the PGM Extraction

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Less steric hinderance of the amino-group enhanced the PGMs extraction ability

IL1: R = c-HexIL2: R = 2-Ethylhexyl

IL2 extracted Pd and Pt efficientlyRh was slightly extracted

Pd Pt Rh

N N N

NTf2R

R

Less steric hinderancethan IL1

PGMs extraction in IL phase• Aq. phase： 100 ppm Pd, Pt, Rh HCl 2.0 mL• ILs phase： IL1, IL2, 400 mg• Shaking： 1500 rpm, 15 min, 25 oC

Effect of Steric Hinderance on the PGM Extraction

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Alkyl Chain Length (Oct-Bu) DependencePGMs extraction in IL phase• Aq. phase： 100 ppm Pd, Pt, Rh HCl 2.0 mL• ILs phase： IL3-IL5, 400 mg• Shaking： 1500 rpm, 15 min, 25 oC

IL3: R = OctIL4: R = HexIL5: R = Bu

Increase in the hydrophobicity that was turned by the alkyl chain length is a key factor for effective extraction of Rh ions

IL3-IL5 show high extraction ability toward Pd and Pt

The alkyl side chain enhanced hydrophobicity

Pd Pt

Rh

N N N

NTf2R

R

HCl conc. was increased

E of Pd and Pt was decreasedE of Rh was increased

IL3, IL4 exhibit high extraction ability to Rh

The amino-moiety was protonated, then captured PGM ions

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PGMs extraction in IL phase• Aq. phase： 100 ppm Pd, Pt, Rh HCl 2.0 mL• ILs phase： IL5-IL7, 400 mg• Shaking： 1500 rpm, 15 min, 25 oC

IL5: R = BuIL6: R = PrIL7: R = Et

N N N

NTf2R

R

At HCl 1.0-4.0 M, Increase of the hydrophobicity is the key factor to improve E

HCl 1.0- 4.0 M

High Hydrophobicity of the ammonium cation moiety is important

Non-protonated ILs coordinate with PGM ionsHCl 0.3 M

Rh

Pd

E of all elements tend to decreaseE: IL5 > IL6 > IL7

IL7 indicated extraction ability towards Pd and Rh

Pt

Alkyl Chain Length (Bu-Et) Dependence

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PGMs Extraction in the Presence of Multi Metal Ions

Cu, Ni, Al, Mg Basically Inactive

PGMs extraction in IL phase• Aq. phase： 100 ppm Pd, Pt, Rh, Zn, Fe, Cu,

Ni, Al, Mg HCl 2.0 mL• ILs phase： IL4, IL5, 400 mg• Shaking： 1500 rpm, 15 min, 25 oC

N N N

NTf2R

R

IL4 IL5

IL4: R = HexIL5: R = Bu

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IL4 Pd, Pt, Rh were selectively extracted

PGMs could be extracted with high selectivity

N N N

NTf2R

R

IL5 Only Pd and Pt were highly extracted

IL5

IL4: R = HexIL5: R = Bu

IL4

PGM solvent extraction• Aq. phase： 100 ppm Pd, Pt, Rh, Zn, Fe, Cu,

Ni, Al, Mg HCl 2.0 mL• ILs phase： IL4, IL5, 400 mg• Shaking： 1500 rpm, 15 min, 25 oC

Solvent Extraction for Multi Metal Ions

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Back Extraction of PGMs into HNO3 aq. Solution PGM back extraction• Aq. phase：HNO3 2.0 mL• ILs phase： IL3-IL5

(after 100 ppm Pd, Pt, Rh from 2.0 M HCl 2.0 mL extracted)• Shaking： 1500 rpm, 15 min, 25 oC

IL3: R = OctIL4: R = HexIL5: R = Bu

Back extraction efficiency Eback (%) Eback = 100 × Cback/(C0 – C)

Cback : Aq. phase PGM conc. afterback extraction

HNO3 conc. was increased

IL4, 1 M HNO3

PGMs can recover from ILs phaseChange in HNO3 conc. allow selective back extraction

IL5IL4IL3

N N N

NTf2R

R

Eback was increased

Only Rh and Pd could be extracted

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HNO3 ammonia

urea water

N N N

NTf2Hex

Hex

IL4: R = Hex

PGMs were successfully back-extracted into aq. HNO3 and ammonia.

Back Extraction of PGMs into aq. Solutions

PGM back extractionAq. phase：2.0 mLILs phase： IL4(after 100 ppm PGMs extraction)Shaking： 1500 rpm, 15 min, 25 oC

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【Extractant】 IL4 400mg

【Extraction】 100 ppm Pt, Pd, and Rh in 3.0 M HCl, 2.0 mL

【Back-extraction】 8 M HNO3 or 1% (wt%) NH3·H2O

N N N

NTf2Hex

Hex

IL4

Back-extraction： 8 M HNO3 Back-extraction： 1% （wt%） NH3·H2O

fresh C6 second-hand C6 third-hand C60

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40

60

80

100

E (%

)

Pt Pd Rh

fresh C6 second-hand C6 third-hand C60

20

40

60

80

100

E (%

)

Pt Pd Rh

IL4 was recycled and exhibited high E after back-extraction with ammonia solution.The decrease in E was due to decrease in the IL4 amount by dissolution into the aqueous phase.

IL4 2nd-handIL4

3rd-handIL4

Recycle of Amino-substituted ILs for Extraction

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【Extractant】 IL4 400mg (fresh: 200 mg/used: 200 mg)

【Extraction】 100 ppm Pt, Pd, and Rh in 3.0 M HCl, 2.0 mL

【Back-extraction】 8 M HNO3 or 1% (wt%) NH3·H2O

fresh C6 fresh C6 (200 mg)+second-hand C6 (200mg)

fresh C6 (200mg)+third-hand C6 (200mg)

0

20

40

60

80

100

E (%

)

Pt Pd Rh

Back-extraction： 8 M HNO3 Back-extraction： 1% （wt%） NH3·H2O

fresh C6 fresh C6 (200 mg)+second-hand C6 (200mg)

fresh C6 (200mg)+third-hand C6 (200mg)

0

20

40

60

80

100

E (%

)

Pt Pd Rh

N N N

NTf2Hex

Hex

IL4

Usage of ammonia solution was an efficient back-extraction and recycle system.

Recycle of Amino-substituted ILs for Extraction

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1H-NMR Sprctra of IL4 After Treatment with HNO3

IL4

IL43.0 M HCl

IL4 after back-extraction

by HNO3(8 M)

IL4 after back-extraction

by ammonia(1 wt%)

water

8 M HNO3: Decomposition of IL4 was observed1 wt% NH3: IL4 was stable for the treatment with aq. NH3. 30

Towards Practical Usage of ILs for Extraction of PGMs

Kg-scale synthesis is readily possible.

Large-scale synthesis of ILs (500 g x 4 bottles）

A simple three-step route

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S. Ma, K. Funaki, A. Miyazaki, A. Muramatsu, K. Kanie, Chem. Lett., 46, 1422 (2017).

Synthesis of Amino-substituted IL with high hydrophobicity Investigation of PGM Extraction Ability into the ILs

ObjectivesSummary

Amino-substituted IL showed high extraction ability towards PGMmetals. Especially, the IL exhibits Rh extraction ability.

Only PGMs were selectively extracted from a model waste. Recycle of the ILs by the back extraction into NH3 phase was achieved.

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THANK YOU !Mr. Hanzawa, our graduate student, will present the recent results in our laboratory in his poster.

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