Ionic Liquids in selective extraction of Co from Ni

PUSHPA GAUTAM16MS06004MATERIALS SCIENCE & ENGG.SMMME, IIT BBS

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CONTENTS• Introduction to Ionic Liquids- definition, properties.• Types of ILs – TSIL, DES, MCIL• Application of Ionic Liquids• Literature review: Processing of metals in ILs• Selective separation of Co from Ni by Solvent extraction with undiluted

Phosphonium Ionic liquids- Objective, chemicals used, Batch-scale extraction experiment, Calculation, Results and discussion.

• Conclusion• Future perspective• Safety aspects• References

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Ionic Liquids(ILs)Definition: Ionic liquids are molten salts entirely composed of ions(+ve,-vely charged) that are liquid at or below room temperature, i.e. MP ˂ 100°C.

Example: 1-ethyl-3-methyl imidazolium bis(trifluoro methyl sulfonyl) limide- M.P.= -17°C.

Properties of ILs :• Non- flammable• Very low/negligible vapor pressure• Wide liquid range, high thermal stability• Wide electro-chemical window(> 4 V)• High ion conductivity• Designer solvents• Green solvents• Viscosity= 10cP to above 1000 cP• Density = 0.8-3.3 g/cc

Types of ILs1. Functional Ionic liquid/ Task-specific Ionic liquids (TSILs) :• Possess functional groups covalently bonded to IL ions.• Example- IL derived from anti fungal drug miconazol.• Used to modify solvent parameters, improve bio- degradability , for catalytic

activation of certain dissolved substrate.2. Deep eutectic solvents (DES):• Mixtures of two components- a quaternary ammonium halide salt + a hydrogen

bond donor (like amine , alcohol, acid).• Example- Mixture of choline chloride and urea3. Metal-containing ionic liquid (MCILs):• A metal ion or metal complex is part of either cation or anion.• Example- Chloro- aluminate IL (N-ethyl pyridinium bromide + Aluminium chloride)-

moisture sensitive • Used in spectroscopy, electro chemistry, organo metallic synthesis, catalyst,

electrolyte for electro deposition.

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Application of ILs• Electro deposition of metals/alloys• Electrolytic extraction of active metals at room tempr• Liquid-liquid extraction of metals• Electro-refining of metals• In electro chemical devices fuel cells, batteries• Electrolyte in Lithium-ion battery

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Literature review: Processing of metals in ILs

1. Dai et al. (1997)- Investigated solubility of uranium(VI) oxide in Imidazolium chloro-aluminate ionic liquids.

2. Bell et al. - reported dissolution of vanadium(V) oxide (V2O5) in Imidazolium chloro-aluminate .

3. Abbott and co-workers- were able to dissolve wide variety of metal oxide in Deep-Eutectic Solvent(DES). The reported solubility of copper(II) oxide, zinc(II) oxide and iron(II, III) oxide in three different Deep-Eutectic Solvents formed by mixture of Choline Chloride and a Carboxylic acid like Malonic acid, Oxalic acid and Phenyl Propionic acid.

4. Nockemann et al. used betainium bis(tri-fluoro-methyl-sulfonyl) imide for dissolution of metal oxides like rare-earth oxides, uranium(VI) oxide, Zinc(II) oxide(ZnO), Copper(II) oxide(CuO) and Nickel(II) oxide(NiO).

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Conti…..5. White-head et al. used 1-butyl-3-methyl imidazolium hydrogen-sulfate as leaching media for minerals like Pyrite and Chalcopyrite, in which an oxidative leach was applied to selectively extract gold and silver with iron(III) sulfate as oxidant and thio-urea as complexing agent.6. Dong et al. used the same IL in (5) and its aqueous solution containing oxygen as oxidant

for leaching of chalcopyrite.7. Rogers and co-workers first suggested the use of ILs as extraction phase for liq-liq

extraction in 1998.8. Visser et al. in 2001- used ionic liquids for which thio-ether, thio-urea and urea groups

were substituted on alkyl-imidazolium cation combined with a hexa-fluoro-phosphate anion and were able to extract heavy metal Hg2+ and Cd2+.

9. Rajendran investigated extraction behaviour of heavy metal ions (Zn2+,Cu2+,Ni2+,Fe3+,Pb2+)

to tri-methyl-capryl-ammonium in combination with salicylate, benzoate and anthranilate anions.

10. Liu used (Cyphos IL 104) a combination of tri-hexyl (tetra decyl) phosphonium with bis-(2,4,4-trimethyl pentyl phosphinate in Soybean oil, methyl-ester and biodiesels as dilutant for rare earth extraction.

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Selective separation of Co from Ni by Solvent extraction with undiluted Phosphonium Ionic liquids

Objective: Development of an efficient solvent extraction process for separation of Co &

Ni from a chloride medium by using Phosphonium ionic liquids.

Chemicals used :1. Tri(hexyl)tetra decyl phosphonium chloride (Cyphos IL 101)2. Tri(butyl) tetra decyl phosphonium chloride (Cyphos IL 167)3. Tetra(octyl) phosphonium bromide (Cyphos IL 166)4. Tri(hexyl) tetra decyl phosphonium bromide (Cyphos IL 102)5. Methyl-tri octyl-ammonium chloride(Aliquat 336)6. CoCl2.6H2O, NiCl2.6H2O, CaCl2.2HO , MgCl2.6H2O, MnCl2 .4H2O7. Hydrogen chloride solution .

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Solvent Extraction: 1-Dissolution of metal source in acid/alkaline aqueous medium2-Ionic Liquid brought in contact with metal-loaded aqueous solution3-Metal ions enter ionic liquid phase preferentially 4-Separate/partition ionic liquid & aqueous phase layer5-Loaded-organic phase introduced to another aqueous phase---STRIPPING 6-Unloaded organic phase after purification sent for reuse.7-Metal is precipitated from metal-loaded aqueous phase.

Ion Exchange:1-Solid synthetic resin(small hard porous beads) made to absorb metal ion2-Absorbed ion brought into solution-ELUTION3-Metal is recovered from solution by precipitation.

Extraction batch test 1:Aqueous solution of 8M HCl + Co & Ni mixture + 250 ml Ionic Liquid[tri(hexyl)tetra decyl phosphonium chloride] poured in a jacketed reactor vessel (500ml) → Intensively stirred at 1040 rpm for 10 min at 60°C→Equilibrium was reached→ Phases were allowed to settle → Analysis of both phases.

Batch-scale extraction experiment:

Extraction batch test 2:Aqueous solution of 8M HCl (250ml) + 250 ml Ionic Liquid[tri(hexyl)tetra decyl phosphonium chloride] poured in a jacketed reactor vessel (500ml)→Intensively stirred at 1040 rpm for 10 min at 60°C→ Equilibrium was reached →Phases were allowed to settle→ organic phase (loaded with water & hydrochloride) was reused as extraction phase→ extraction was repeated as in batch test 1→ Metal content of 2 phases was analysed.

Extraction batch test 3: Aqueous 8 M HCl soln containing CoCl2.6H2O, NiCl2.6H2O, CaCl2.2HO & MgCl2.6H2O with a metal concentration of 5g/L was prepared (500 ml)→ Aqueous solution was poured in a jacketed reactor vessel (1 L)→Extraction phase(500 ml) was added → Intensive stirring at 1040 rpm for 10 min at 60°C → Equilibrium was reached →Phases were allowed to settle→ Metal content of 2 phases was analysed.

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Batch scale reactor before extraction batch test 2 Batch scale reactor after extraction batch test 2 : (upper phase = ionic liquid, lower phase = aqueous soln phase): [2]

Cobalt(II) is extracted as the dark blue tetracobaltate(II) complex to the ionic liquid phase, while the green hydrated Nickel(II) ions remains in the aqueous phase. 11

Stripping conditions :Water was poured in a jacketed reactor vessel (250 ml)→ Extraction phase from extraction batch test-2 containing Co(II) (5 g/L, 80 ml ) was added→ Intensively stirred at 1040 rpm for 10 min at 60°C→ Phases allowed to settle→ Cobalt-concentration in aqueous phase was measured after centrifugation (3000 rpm, 10 min)→ Organic phase recycled & reused.

Calculation :Distribution coefficient for Cobalt : where [Co]O = initial Co-concn in aqueous phase before extraction [Co]aq=Co-concn in aqueous phase after extraction

Distribution coefficient for Ni : where [Ni]O = initial Ni-concn in aqueous phase before extraction [Ni]aq= Ni-concn in organic phase after extraction

Efficiency of separation of Co from Ni, β :

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Structure of tri (hexyl) tetra decyl phosphonium chloride (P 66614Cl)

Distribution coefficient of cobalt(II) as a function of the HCl concentration [2]

Extraction efficiency of Co increases with increasing Chloride concn, with a maximum at a chloride concn of 8 M.

Results & Discussion

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Absorption spectrum of the ionic liquid phase after extraction,containing bis(tri(hexyl)tetradecylphosphonium) tetrachlorocobaltate(II).The absorption spectrum is typical for the [CoCl4]2− anion. [2]

Distribution coefficient of Nickel(II) as a function of the HCl concn. [2]

[CoCl4]2- + 2[P66614]Cl → [P66614]2 [CoCl4] + 2Cl-

Increases linearly, low absolute value

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Anion Exchange mechanism

Results of the extraction after extraction batch tests 1 and 2 : [2]

Batch test 1 Batch test 2a

[Co]aq (mg L−1) 11 (±0.5) 14 (±1.4)

[Ni]org (mg L−1) 44 (±2.7) 43 (±3.6)

DCo 460 (±21) 360 (±32)

DNi 0.0088 (±0.0006) 0.0087 (±0.0007)

βCoNi 52 000 (±2800) 41 000 (±3300)

a --Using an ionic liquid phase, saturated with water and HCl.

Physical properties of the ionic liquid before and after extraction batch test 1 and batch test 2 (at 60 °C) : [2]

Batch test 1 Batch test 2

Before-extrctn After-extrctn Before-extrctn After-extrctn

Water content (wt%) 0.1 7.7 8.7 6.9

HCl content (wt%) 0 5.2 6.0 5.8

Viscosity (cP) 280 101 95 101

Density (g mL−1) 0.87 0.91 0.90 0.91

Phase separation time (s) — 90 — 90 15

Distribution coefficients D for cobalt(II), nickel(II), manganese(II), magnesium(II), and calcium(II) for Batch test-3 : [2]

Element DCo 450Ni 0.0062Mn 30Mg 0.0014Ca 0.0056

Percentage of cobalt that is stripped to aqueous phase from IL : [2]

Stripping step Amount of cobalt stripped(%)

1 2.5

2 28

3 52

4 17.5

Total 100

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Extraction results for extraction of cobalt and nickel from aqueous feed solutions containing 4 M NaCl to tri(hexyl)- tetradecyl phosphonium chloride: [2][Co]aq (mg L−1) 21 (±3)[Ni]org (mg L−1) 98 (±4.6)DCo 240 (±29)DNi 0.020 (±0.0010)βCo

Ni 12 000 (±1000)

Extraction efficiency of Co & Ni increasing with increasing Chloride concn

Advantage of using NaCl soln in place of HCl acid soln – •less aggressive media •cheaper •lower concentrations of Chloride needed

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Extraction results for the separation of cobalt and nickel using different ionic liquids as the extractant phase : [2]

P8888Br P44414Cl P66614Br P66614Cl

[Co]aq (mg L−1) 11 180 11 11

[Ni]org (mg L−1) 23 300 39 44

DCo 450 27 450 460

DNi 0.0046 0.064 0.0078 0.0088

βCoNi 98000 420 58000 52000

Water content of IL after extraction(%O)

3.8 23.4 7.3 7.7

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Extraction results after extraction using Aliquat 336 and Cyphos IL 101 as extraction phase : [2]

Aliquat 336 Cyphos IL 101

[Co]aq (mg L−1) 60 11

[Ni]org (mg L−1) 160 44

DCo 80 460

DNi 0.03 0.0088

βCoNi 2500 52000

Separation factor is 20 times higher in Phosphonium IL than Aliquat 336 due to increased hydrophobicity of Phosphonium IL.

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Conclusion• Co can be selectively separated from Ni, Mg & Ca with solvent extraction using

Phosphonium -based IL as extraction reagent.• After extraction Co can be easily stripped using water in 4 stripping steps. After

stripping the IL can be reused as extraction phase which makes it possible to do extraction in a Continuous process.

• Instead of Hydrochloric acid, Sodium Chloride can be used as a chloride source.• Advantage of using Phosphonium IL as extraction phase is that volatile organic

compounds are avoided and this offers a greener approach to solvent extraction leading to environment friendlier and healthy working conditions.

• By doing extraction on a Batch-scale setup, the practical implementation of IL as extraction phase has been proved.

• 3 Phosphonium and 1 Ammonium ILs were compared for their extraction capabilities where Tri(hexyl) tetra decyl phosphonium chloride seems to be superior and the best option as the IL phase.

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Future perspective• Replacement of organic solvents by Ionic liquids can increase the metal

loading in extraction phase and lead to a clean technology.

• Platinum group metals (PGMs) are processed from a chloride medium after leaching with hydrochloric acid with added chlorine. Here, Cyphos IL 101 could have potential as an extraction medium for separation of PGMs. Feeds other than chlorides can also be used.

• By replacing chlorides with nitrates there are opportunities to selectively extract lanthanides from a concentrated aqueous nitrate soln. This can be used for Rare earth recycling.

• Ionic liquid technology can be applied in re-processing of spent nuclear fuels for separation of residual Uranium and newly formed Plutonium from fission products and higher actinides.

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Safety aspects• Code of practice for Safety in lab should be followed while performing

experimental works with ILs .

• Specific caution is necessary for working with E4 products with clearance and hazardous lab equipment (like Bromine).

• Co & Ni are carcinogenic and can cause genetic defects and allergic symptoms; may damage fertility.

• Although ILs are green solvents still the safety of each individual IL should be evaluated before use.

• The author has reported an accident in which the Protic Ionic Liquid, Pyrrolidinium nitrate, exploded while drying it under reduced pressure at 110°C, using a rotary evaporator with an oil bath.

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References1. A. Stojanovic, C. Morgenbesser, D. Kogelnig, R. Krachler, and B.K. Keppler. Quaternary ammonium and

phosphonium ionic liquids in chemical and environmental engineering. In A. Kokorin, editor, Ionic Liquids: Theory, Properties, New Approaches, volume 1, pages 657–680. InTech, 2011.

2. Sil Wellens, Ben Thijs and Koen Binnemans, An environmentally friendlier approach to hydrometallurgy: highly selective separation of cobalt from nickel by solvent extraction with undiluted phosphonium ionic liquids, Green. Chem.,2012.

3. Sil Wellens, Remi Goovaerts, ClaudiaMoeller, Jan Luyten, Ben Thijs and Koen Binnemans, Continuous ionic liquid extraction process for the separation of cobalt from nickel , Green. Chem., 2013.

4. SilWellens, Tom Vander Hoogerstraete, Claudia Möller, Ben Thijs, Jan Luyten and Koen Binnemans, Dissolution of metal oxides in an acid-saturated ionic liquid solution and investigation of the back-extraction behaviour to the aqueous phase, Hydrometallurgy, 2014.

5. C.J. Bradaric, A. Downard, C. Kennedy, A.J. Robertson, and Y.H. Zhou. Industrial preparation of phosphoniumionic liquids. Green Chem.

6. M.G. Freire, P.J. Carvalho, R.L. Gardas, L.M. Santos, I.M. Marrucho, and J.A. Coutinho. Solubility of water in tetradecyltrihexylphosphonium-based ionic liquids. J. Chem. Eng. Data.

7. J. Rydberg, C. Musikas, and G.R. Choppin. Principles and Practices of Solvent Extraction, volume 1. Marcel Dekker, inc., 1st edition, 1992.

8. A.P. Abbott, G. Frisch, J. Hartley, and K.S. Ryder. Processing of metals and metal oxides using ionic liquids. Green Chem.

9. How safe are protic ionic liquids? Explosion of pyrrolidinium nitrate, Sil Wellens, Ben Thijsb and Koen Binnemans

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THANK YOU.

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