IONIC LIQUIDS AND THEIR USE IN THE EXTRACTION OF RARE EARTH ELEMENTS AND/OR GALLIUM

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit, under 35 U.S.C. § 119(e), of U.S. provisional application Serial No. 62/265,563, filed on December 10, 2015.

FIELD OF THE INVENTION

[001] The present invention relates to ionic liquids. More specifically, the present invention is concerned with ionic liquids that are useful in the extraction of rare earth elements and/or gallium from various liquid or solid matrices.

BACKGROUND OF THE INVENTION

[002] The rare earth elements (REEs), also called rare earth metals (REMs), as defined by lUPAC, are scandium and yttrium as well as the fifteen lanthanides: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

[003] REEs are important strategic resources and have a wide range of applications owing to their peculiar physical and chemical properties; they are used in industries as diverse as industrial equipment, health, energy, automotive and aircraft and electronic equipment, resulting in an increase of the global demand for REEs. This increased demand resulted in the search and valorization of REEs from various sources, which complicates their extraction especially when they are found in trace amounts in complex matrices such as mining residues, spent electronics or magnets, which also contains many other metals. Furthermore, due to their chemical similarities, REEs extraction is a technically complicated process, requiring intense processing.

[004] One potential source of REEs is red muds. These are a side-product of the Bayer process, the principal means of refining bauxite into alumina. Compared to the starting bauxite, red muds are enriched in REEs by a factor of two. Further, after the processing of bauxite by the Bayer process, typically all the rare earth elements (heavy, medium, and light) can be found in the red muds. Given the scarcity of REEs supply globally, red muds are attractive as a source of REE. However, red muds contain elevated concentrations of iron, aluminium and other metals, and thus the separation of individual REEs is very challenging.

[005] Most REEs are obtained by hydrometallurgical processes which include thermal treatment of an ore in the presence of acidic reagents. Optimal reaction conditions and reagents used have to be matched specifically with each targeted ore. Different factors influence the reaction, for example, the presence of iron oxide and refractory metals such as aluminium, leading to an increased consumption of acid and energy (increase temperature). Unfortunately, the REEs composition and concentration in red muds varies widely according to the type of bauxite (gibbsite, boehmite, diaspore) used for Bayer process. Therefore, it is difficult to recover REEs from red muds and there remains a need for a versatile and adaptable REEs extraction method. [006] One suggested process is liquid-liquid extraction (LLE) using an organic solvent containing a dissolved extractant, where both components, the solvent and the extractant, can be varied to fulfill the above requirements.

[007] To date, much effort has been devoted to replace the volatile organic compounds (VOCs) typically used in such LLE processes with new solvents that could perform better, be more versatile and be recuperated/recycled more easily. Ionic liquids (ILs), when tailored to have negligible vapor pressure and high stability, have been used as solvents replace the VOCs in LLE. In fact, LLE studies on ionic liquids applied to REE extraction have mostly focused on the members of the imidazolium-IL family, most likely because of their low viscosity, availability and well established properties.

[008] A number of extractants have been used for REEs extraction. Extractants, which are viewed as the agent responsible for the extraction selectivity and efficiency, are dissolved in the solvent to form an extraction phase. Many researchers have attempted to develop novel extractants that are compatible with ionic liquids.

[009] Such extractants include those based on organophosphoric acids such as di-(2-ethylhexyl)phosphoric acid (HDEHP) and di-isodecyl phosphoric acid (DIDPA), dihexyl-N,N-diethylcarbamoylmethylphosphonate (DHDECMP), octylphenyl-N N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and trialkyl phosphine oxides

such as Cyanex™ 923 ( ) and tri-n-butylphosphate (TBP), and carboxylic acids, such as

o

C - C - R

Η - θ' _R2

(Versatic™ Acid 10: , wherein R ¹ and R ² are alkyl groups) as well as some mixtures of the above. However, these extractants have some limitations, such as slow kinetics, low solubility in the solvent, and they are effective only at low acid concentrations in the aqueous phase. When it comes to extraction of REEs from red muds lixiviates, their main drawbacks are that they undesirably co-extract other metals, such as iron and aluminium. Also, they are not effective in highly acidic conditions (>3M HNO3). There thus remains a need for other extractants.

[0010] Various diglycolamides have been suggested for use as REE extractants dissolved in various solvents. For example, tetra(2-ethyl hexyl) diglycolamide (TEHDGA), Ν,Ν,Ν',Ν'-tetraoctyl diglycolamide (TODGA) and didodecyl-dioctyl diglycolamide (D ³ DODGA) were used dissolved in n-dodecane. Unsymmetrical DGAs containing an octyl moiety in one arm and, on the other arm, an alkyl group varying from hexyl to dodecyl, were also suggested for the separation of europium. A/,A/-dioctyldiglycolamic acid (DODGAA) and methyl 2-(2- (dioctylamino)-2-oxoethoxy)acetate (MDODGA) have also been used as a REE extractant dissolved in ionic liquids. SUMMARY OF THE INVENTION

[0011] According to the invention, there is provided herein:

An ionic liquid of formula:

A

(I)

wherein:

R ¹ is a hydrogen atom, alkyi, or aryl;

each R ² is independently alkyi or aryl,

or both R ² together with the nitrogen atom to which they are attached form a heterocycloalkyl unsubstituted or substituted with one or more R ⁴ , or

or both R ² together with R ¹ and with the nitrogen atom to which they are attached form with a heteroaryl unsubstituted or substituted with one or more R ⁵ ;

R ³ is a hydrogen atom or alkyi unsubstituted or substituted with one or more alkoxy and/or halogen atom (F being a preferred halogen atom);

R ⁴ and R ⁵ are independently alkyi, aryl, or a halogen atom (F being a preferred halogen atom), and A ^" is an anion,

the aryl in R ¹ , R ² , R ⁴ and R ⁵ being unsubstituted or substituted with one or more alkyi, alkoxy and/or halogen atom (F being a preferred halogen atom),

the alkyi in R ¹ , R ² , R ⁴ and R ⁵ being unsubstituted or substituted with one or more alkyi, alkoxy, halogen atom (F being a preferred halogen atom), and/or aryl, said aryl being unsubstituted or substituted with one or more alkyi, alkoxy and/or halogen atom (F being a preferred halogen atom).

The ionic liquid of item 1 , wherein R ¹ is preferably an hydrogen atom or Ci-salkyl unsubstituted or substituted with one or more alkyi, alkoxy, halogen, and/or aryl, said aryl being unsubstituted or substituted with one or more alkyi, alkoxy and/or a halogen atom.

The ionic liquid of item 1 or 2, wherein R ¹ is a hydrogen atom or Ci-salkyl unsubstituted.

The ionic liquid of any one of items 1 to 3, wherein R ¹ is a hydrogen atom.

The ionic liquid of any one of items 1 to 4, wherein each R ² is independently, or both R ² are the same and are alkyi or aryl. 6. The ionic liquid of any one of items 1 to 5, wherein each R ² is independently, or both R ² are the same and are Ci-ealkyl or phenyl.

7. The ionic liquid of any one of items 1 to 6, wherein both R ² are the same and are methyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, octyl, or phenyl.

8. The ionic liquid of any one of items 1 to 7, wherein both R ² are the same and are propyl, isopropyl, butyl, sec-butyl, isobutyl, octyl, or phenyl, preferably both R ² are octyl.

9. The ionic liquid of any one of items 1 to 7, wherein one R ² is methyl and the other is phenyl.

10. The ionic liquid of any one of items 1 to 4, wherein both R ² together with the nitrogen atom to which they are attached form a heterocycloalkyl unsubstituted or substituted with one or more R ⁴ .

11. The ionic liquid of any one of items 1 to 4 and 10, wherein the heterocycloalkyl has 5 or 6 ring atoms forming one ring; one or two ring atoms being nitrogen atoms, the remaining ring atoms being carbon atoms.

12. The ionic liquid of any one of items 1 to 4, 10 and 11, wherein the heterocycloalkyl is pyrrolidin-1-yl or piperidin-1 -yl, both of which being independently unsubstituted or substituted with one or more R ⁴ .

13. The ionic liquid of any one of items 1 to 4 and 10 to 12, wherein heterocycloalkyl is pyrrolidin-1-yl unsubstituted or substituted with one or more R ⁴ .

14. The ionic liquid of any one of items 1 to 4 and 10 to 13, wherein the heterocycloalkyl is unsubstituted pyrrolidin-1-yl.

15. The ionic liquid of any one of items 1 to 4 and 10 to 12, wherein the heterocycloalkyl is piperidin-1 -yl unsubstituted or substituted with one or more R ⁴ .

16. The ionic liquid of any one of items 1 to 4, 10 to 12, and 15, wherein the heterocycloalkyl is piperidin-1 -yl substituted with one or more R ⁴ .

17. The ionic liquid of any one of items 1 to 4, 10 to 12 and 15 to 16, wherein the heterocycloalkyl is piperidin- 1 -yl substituted with two R ⁴ , preferably at positions 2 and 6.

18. The ionic liquid of any one of items 1 to 4, wherein both R ² together with R ¹ and with the nitrogen atom to which they are attached form with a heteroaryl unsubstituted or substituted with one or more R ⁵ .

19. The ionic liquid of any one of items 1 to 4 and 18, wherein the heteroaryl has 5 or 6 ring atoms forming one ring, preferably 5; one or two, preferably two, ring atoms being nitrogen atoms, the remaining ring atoms being carbon atoms.

20. The ionic liquid of any one of items 1 to 4, 18 and 19, wherein the heteroaryl is imidazolyl unsubstituted or substituted with one or more R ⁵ . The ionic liquid of any one of items 1 to 4, and 18 to 20, wherein the heteroaryl is imidazolyl substituted with one R ⁵ , preferably on the nitrogen atom.

The ionic liquid of any one of items 1 to 21 , wherein R ³ is Ci-ialkyl.

The ionic liquid of any one of items 1 to 22, wherein R ³ is methyl or butyl

The ionic liquid of any one of items 1 to 23, wherein R ⁴ is alkyl.

The ionic liquid of any one of items 1 to 24, wherein R ⁴ is Ci-ialkyl.

The ionic liquid of any one of items 1 to 25, wherein R ⁴ is methyl.

The ionic liquid of any one of items 1 to 26, wherein R ⁵ is alkyl.

The ionic liquid of any one of items 1 to 27, wherein R ⁵ is Cualkyl.

The ionic liquid of any one of items 1 to 28, wherein R ⁵ is methyl.

The ionic li uid of item 1, being:

The ionic liquid of any one of items 1 to 30, wherein A ^" is CI ^" , HS0 ₄ ^" , BF ₄ ^" , PF ₆ ^" , TFSI ^" , FSI ^" , DCA ^" or R ⁶ - SO3 ^" , wherein R ⁶ is alk(en/yn)yl, cycloalk(en/yn)yl, aryl, heteroaryl, each of which being optionally substitued by one or more alk(en/yn)yl, aryl, arylalk(en/yn)yl, and alk(en/yn)ylaryl, nitro, cyano, hydroxyl, halogen atom, alk(en/yn)oxy, alk(en/yn)oxycarbonyl, alk(en/yn)ylamino, and/or alk(en/yn)ylamido.

The ionic liquid of any one of items 1 to 31 , wherein A ^" is TFSI ^" , FSI ^" , DCA ^" , and R ⁶ -S03 ^" .

The ionic liquid of any one of items 1 to 32, wherein A ^" is R ⁶ -SC>3 ^" .

The ionic liquid of any one of items 31 to 33, wherein R ⁶ is

The ionic liquid of any one of items 34, wherein R ⁶ is Cialkyl or Ci haloalkyl.

The ionic liquid of any one of items 31 to 35, wherein the haloalkyl is perhaloalkyl.

The ionic liquid of any one of items 31 to 36, wherein the haloalkyl is perfluoroalkyl.

The ionic liquid of any one of items 1 to 37, wherein A ^" is CH3-SO3 ^" or CF3-SO3 ^" . A method of extracting one or more rare earth element and/or gallium from a matrix, the method comprising the step of contacting the matrix with an ionic liquid as defined in any one of items 1 to 38. The method of item 39, wherein the ionic liquid is immobilized on a solid support; the contacting step thereby resulting in the retention of the one or more rare earth element and/or gallium onto the solid support.

The method of item 39, wherein the ionic liquid is in liquid form; the contacting step thereby resulting in the dissolution of the one or more rare earth element and/or gallium into the ionic liquid.

The method of item 39 or 41 , wherein the matrix is solid.

The method of any one of items 39, 41 and 42, wherein the matrix is:

· a clay, in particular an aluminum-containing clays, for example an aluminous clay,

• an industrial waste, such as a slag, a sludge, a gangue, tailings, dumps, refuse, serpentine residues, red muds, flying ashes, or mixtures thereof,

• a pure or refined ore, in particular an aluminum-containing pure or refined ore, such as an aluminosillicate mineral, argillite, nepheline, mudstone, beryl, cryolite, garnet, spinel, bauxite, carbonatite, kyanite, kaolin, serpentine or mixtures thereof,

• an electronic component or an electronic waste (including consumer electronics),

• an alloy,

• a magnet,

• a batterie,

· a catalytic converter,

• residues from incineration, and/or

• a material used in fluorescent lights.

The method of any one of items 39 to 41 , wherein the matrix is liquid.

The method of any one of items 39 to 41 and 44, wherein the matrix is an aqueous solution or suspension resulting from mining and/or refining operations, or from the transformation and/or production of electronic components, alloys, magnets, batteries, catalytic converters and/or fluorescent lights.

The method of any one of items 39 to 41 and 44, wherein the matrix is a lixivium/leachate of a solid matrix as defined in claim 43, preferably a lixivium/leachate of red muds or of flying ashes.

The method of any one of items 39 to 41, 44 and 46, wherein the matrix is a lixivium/leachate obtained during mining and/or refining of an ore that contains the one or more rare earth elements and/or gallium, preferably a lixivium/leachate of red muds. 48. The method of any one of items 39 to 47, wherein the contacting step is carried out under agitation.

49. The method of any one of items 39 to 48, wherein the contacting step is carried out at a temperature ranging from about 0 to about 150 °C.

50. The method of any one of items 39 to 49, wherein the contacting step is carried out at a temperature of:

· about 0, about 5, about 10, about 15, about 20, about 25, about 30, about 35, about 40, about 45, about 50, about 55, about 60, about 65, about 70, about 75°C or more and/or

• about 150, about 140, about 130, about 120, about 110, about 100, about 95, about 90, about 85, about 80, about 75, about 70, about 60, about 65, or about 60°C or less.

51. The method of any one of items 39 to 50, wherein the contacting step is carried out at a temperature ranging from about 60 and about 80 °C.

52. The method of any one of items 39 to 50, wherein the contacting step is carried out at about room temperature.

53. The method of any one of items 39 to 52, wherein the contacting step lasts for:

• about 2, about 5, about 10, about 15, about 20, about 25, about 30, about 45 minutes or more, and /or

• about 60, about 45, about 30, about 25, about 20, about 15, about 10, or about 5 minutes or less.

54. The method of any one of items 39 to 53, wherein the contacting step lasts for about 30 minutes or less.

55. The method of any one of items 39 to 54, wherein the contacting step lasts for about 15 minutes or less.

56. The method of any one of items 39 to 55, wherein the contacting step lasts for about 5 minutes or less. 57. The method of any one of items 39 to 56, wherein the contacting step results in the extraction of about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 93%, about 95%, about 96%, about 97%, about 98%, about 99% or more or about 100% of the one or more rare earth element and/or gallium.

58. The method of any one of items 39 to 57, wherein the contacting step results in the extraction of about 90% or more of the one or more rare earth element and/or gallium.

59. The method of any one of items 39 to 58, wherein the contacting step is carried out at an ionic liquid:matrix weight ratio of:

• about 1 : 100, about 1 :90, about 1 : 80, about 1 :75, about 1 :60, about 1 :50, about 1 :45, about 1 :40, about 1:30, about 1 :25, about 1 :20, about 1 :15, or about 1 :10 or less, and/or

· about 1 :1 , about 1 :2, about 1 :3, about 1 :4, about 1 :5, about 1 :6, about 1 :7, about 1 :8, about 1 :9, about 1:10, about 1 :15, about 1:20, about 1 :25, about 1 :30, about 1 :35 or more. 60. The method of any one of items 39 to 59, wherein the contacting step is carried out at an ionic liquid:matrix weight ratio ranging from 1 : 10 to 1 :50.

61. The method of any one of items 39 to 60, wherein the contacting step is carried out at an ionic liquid:matrix weight ratio of is about 1 :30.

62. The method of any one of items 39 to 61 , wherein the one or more rare earth elements and/or gallium are preferentially extracted from the matrix.

63. The method of any one of items 39 to 62, wherein the one or more rare earth elements and/or gallium are selectively extracted from the matrix.

64. The method of any one of items 39 to 61 , further comprising the step of isolating the one or more rare earth element and/or gallium from the ionic liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the appended drawings:

Figure 1 is the reaction scheme for the synthesis of IL-1 and IL-2;

Figure 2 is the percentage of REE extracted by IL-1 and IL-2 as a function of the extraction time;

Figure 3 is the percentage of REE extracted as a function of ionic liquid:aqueous solution volumnic ratio for IL-1 ;

Figure 4 is the percentage of REE extracted as a function of ionic liquid:aqueous solution volumnic ratio for IL-2;

Figure 5 shows the water uptake from the atmosphere for the two ionic liquids;

Figure 6 shows the extraction efficiency of Sc ³⁺ as a function of extraction time;

Figure 7 shows the variation of the %E of REEs as a function of DODGAA and Cyanex 923;

Figure 8 shows the IR spectra of pure [Nni4][N(Tf)2], pure DODGAA, and the solid film precipitated out of the IL after the extraction process, showing losses of DODGAA;

Figure 9 shows the extraction of REEs with DODGAA or MDODGA in different ionic liquids;

Figure 10 shows the variation on the amount of water content in [Νιιι ₄ ][Ν(Ττ) ₂ ] as function of time and concentration of MDODGA exposed to ambient air at room temperature;

Figure 11 shows the extraction efficiency of a) 1 -DGA-IL and b) 2-DGA-IL at 0.3 M or 6 M HCI;

Figure 12 shows Sc extraction efficiency (after 20 min) by 1-DGA-IL (black) and 2-DGA-IL (gray) as a function of the volume ratio of the two phases (solution of 0.007 M Sc at 6 M HCI);

Figure 13 shows the extraction efficiency of Ga ³⁺ for various systems (1-DGA-IL, 2-DGA-IL, MDODGA and CYANEX 923) at 0.3 M or 6 M of HNO3 or HCI. Aqueous phase: 47ppm Ga ³⁺ . Aqueous/organic phase volume ratio 1 :3. Equilibrium time was 30 minutes;

Figure 14 shows the extraction efficiency of Ga ³⁺ by 2-DGA-IL as a function of time. Aqueous phase: 47ppm Ga ³⁺ in 6 M HNO3. Aqueous/organic phase volume ratio 1:3; Figure 15 shows the efficiency of extraction of gallium, some rare earth elements and some other metals from a clay by MDODGA (30 Nm IN N1114TFSI) under (A) mechanical stirring and (B) acoustic resonance mixing. The aqueous phase/organic phase volume ratio was 1 : 3;

Figure 16 shows the efficiency of extraction of gallium and rare earth elements from a red mud leachate by A) 1- DGA-IL and B) under various conditions;

Figure 17 shows the efficiency of extraction of gallium and rare earth elements from a fly ashes leachate by A) 1 - DGA-IL and B) under various conditions;

Figure 18 shows the efficiency of extraction of gallium and rare earth elements from another fly ashes leachate by A) 1 -DGA-IL and B) under various conditions;

Figure 19 shows the efficiency of extraction of gallium and rare earth elements from a clay leachate by A) 1- DGA-IL and B) under various conditions;

Figure 20 is identical to Figure 19 except that the vertical axis starts at 95% rather than 0%;

Figure 21 shows (A) the efficiency of Sc stripping from 1-DGA-IL using of HCI (squares) or HNO3 (circles) aqueous solutions as a function of acid concentration after mechanical stirring for 60 min and (B) the evolution of extraction efficiency when repeating extraction-stripping cycles with the ionic liquid. "After washing" is an extraction carried out with the ionic liquid after it has been reused for the 6 cycles and after it has been washed with water and dried.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Turning now to the invention in more details, there is provided an ionic liquid of formula:

wherein:

R ¹ is a hydrogen atom, alkyl, or aryl;

each R ² is independently alkyl or aryl,

or both R ² together with the nitrogen atom to which they are attached form a heterocycloalkyl unsubstituted or substituted with one or more R ⁴ , or

or both R ² together with R ¹ and with the nitrogen atom to which they are attached form with a heteroaryl unsubstituted or substituted with one or more R ⁵ ;

R ³ is a hydrogen atom or alkyl unsubstituted or substituted with one or more alkoxy and/or halogen atom (F being a preferred halogen atom);

R ⁴ and R ⁵ are independently alkyl, aryl, or a halogen atom (F being a preferred halogen atom), and A ^" is an anion,

the aryl in R ¹ , R ² , R ⁴ and R ⁵ being unsubstituted or substituted with one or more alkyi, alkoxy and/or halogen atom (F being a preferred halogen atom),

the alkyi in R ¹ , R ² , R ⁴ and R ⁵ being unsubstituted or substituted with one or more alkyi, alkoxy, halogen atom (F being a preferred halogen atom), and/or aryl, said aryl being unsubstituted or substituted with one or more alkyi, alkoxy and/or halogen atom (F being a preferred halogen atom).

[0014] Above, all the substituents are independent from one another. Hence, if, for example, the heterocycloalkyl or the heteroaryl is substituted with more than one R ⁴ , each is R ⁴ independent from the others. Similarly, if the alkyi (or aryl) group in any of R ¹ , R ² , R ³ , R ⁴ and R ⁵ bears more than one substituent, these substituents are independent from one another.

[0015] Herein, an "ionic liquid" is a salt comprising a cation and an anion, and that is a liquid at ambient or near ambient temperatures (i.e. having a melting point, or melting range, less than about 100°C).

[0016] Herein, "alk(en/yn)yl" means alkyi, alkenyl, or alkynyl. Herein, the terms "alkyi", "alkylene", "alkenyl", "alkynyl", and "alkenynyl" have their ordinary meaning in the art. Further, unless otherwise specified, the hydrocarbon chains of in any and all of the alkyi, alkenyl, and alkynyl groups, whether that are alone, part of a functional group (e.g. alkoxy), are substituted, or are in any other form, can be linear or branched. Further, unless otherwise specified, these hydrocarbon chains can contain between 1 and 12 carbon atoms, more specifically between 1 and 8 carbon atoms, more specifically between 1 and 6 carbon atoms, between 1 and 4 carbon atoms, between 1 and 3 carbon atoms, or contain 1 or 2 carbon atoms.

[0017] For more certainty, herein, an "alkyi" is a saturated aliphatic hydrocarbon monovalent substituent of general formula CnH _2n +i. An "alkenyl" is a monovalent aliphatic hydrocarbon radical, similar to alkyi except that it comprises at least one double bond. An "alkynyl" is a monovalent aliphatic hydrocarbon radical, similar to alkyi except that it comprises at least one triple bond.

[0018] Herein, an "alkoxy" is a monovalent substituent of formula -O-alkyl. An "alkenoxy" is a monovalent substituent of formula -O-alkenyl. An "alkynoxy" is a monovalent substituent of formula -O-alkynyl.

[0019] Herein, a "haloalkyl" is an alkyi group substituted with at least one halogen atom. In embodiments, the haloalkyl may be a "perhaloalkyl", which is an alkyi group as defined above in which all the hydrogen atoms have been replaced halogen atoms. For example, a perfluoroalkyl is an alkyi group with all its hydrogen atoms replaced by fluorine atoms.

[0020] Herein, halogen atoms include fluorine, chlorine, bromine, and iodine. A preferred halogen atom in any and all embodiments independently, including any subset thereof, is fluorine.

[0021] Herein, the terms "cycloalkyl ", "heterocycloalkyl", "aryl", and "heteroaryl" have their ordinary meaning in the art. For more certainty, herein, a "cycloalkyl" is a saturated aliphatic hydrocarbon monovalent substituent of general formula C _n H _2n -i, wherein the carbon atoms are linked into one or more loops, also called rings. Unless otherwise specified, the cycloalkyl can contain a total of 5 to 12 ring atoms forming one or two rings, or more specifically contain 5 or 6 ring atoms forming a single ring.

[0022] Herein, a "heterocycloalkyi" is a cycloalkyl wherein at least one ring carbon atom is replaced by a heteroatom. Unless otherwise specified, up to 4 ring atoms, more specifically up to 3 ring atoms, 2 ring atoms or a single ring atom can be a heteroatom.

[0023] Herein, an "aryl" is an unsaturated aromatic hydrocarbon monovalent substituent of general formula CnHn-1, wherein the carbon atoms are linked into one or more rings. Unless otherwise specified, the aryl can contain a total of 5 to 12 ring atoms forming one or two rings, more specifically it may contain 5 or 6 ring atoms forming one ring, preferably 6 ring atoms forming 1 ring.

[0024] Herein, a "heteroaryl" is an aryl wherein at least one ring carbon atom is replaced by a heteroatom. Unless otherwise specified, up to 4 ring atoms, more specifically up to 3 ring atoms, 2 ring atoms or a single ring atom can be a heteroatom.

[0025] Herein, a "heteroatom" is nitrogen, oxygen, sulphur, and chlorine. A preferred heteroatom in any and all embodiments independently, including any subset thereof, is nitrogen.

[0026] In embodiments, R ¹ is preferably an hydrogen atom or Ci. ₈ alkyl unsubstituted or substituted with one or more alkyl, alkoxy, halogen, and/or aryl, said aryl being unsubstituted or substituted with one or more alkyl, alkoxy and/or a halogen atom (F being a preferred halogen atom). In more preferred embodiments, R ¹ is a hydrogen atom or Ci-ealkyl unsubstituted. In more preferred embodiments, R ¹ is a hydrogen atom.

[0027] In embodiments, both R ² are independent from one another. Therefore, in other embodiments, both R ² are different. In other embodiments, both R ² are the same. In embodiments, each R ² is independently, or both R ² are the same and are: alkyl, preferably Ci-salkyl, or aryl, preferably phenyl. In embodiments, each R ² is independently, or both R ² are the same and are: methyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, octyl, or phenyl. In embodiments, both R ² are the same and are propyl, isopropyl, butyl, sec-butyl, isobutyl, octyl, or phenyl. In embodiments, both R ² are the same and are octyl. In embodiments, one R ² is methyl and the other is phenyl.

[0028] In embodiments, both R ² together with the nitrogen atom to which they are attached form a heterocycloalkyi unsubstituted or substituted with one or more R ⁴ . In embodiments, the heterocycloalkyi has 5 or 6 ring atoms forming one ring; one or two ring atoms being nitrogen atoms, the remaining ring atoms being carbon atoms. In embodiments, the heterocycloalkyi is pyrrolidin-1-yl or piperidin-1-yl both of which being independently unsubstituted or substituted with one or more R ⁴ .

• In preferred embodiments, heterocycloalkyi is pyrrolidin-1-yl unsubstituted or substituted with one or more R ⁴ . In more preferred embodiments, the heterocycloalkyi is unsubstituted pyrrolidin-1-yl. In other preferred embodiments, the heterocycloalkyl is piperidin-1-yl unsubstituted or substituted with one or more R ⁴ . In more preferred embodiment, the heterocycloalkyl is piperidin-1-yl substituted with one or more R ⁴ . In yet more preferred embodiment, the heterocycloalkyl is piperidin-1-yl substituted with two R ⁴ , preferably at positions 2 and 6 ( ) or 3 and 5 (*

In any of these embodiments, R ⁴ is as defined above. In preferred embodiments, R ⁴ is alkyl, preferably C^alkyl, Ci-3alkyl, Ci-2alkyl, preferably methyl.

[0029] In embodiments, both R ² together with R ¹ and with the nitrogen atom to which they are attached form with a heteroaryl unsubstituted or substituted with one or more R ⁵ . In embodiments, the heteroaryl has 5 or 6 ring atoms, preferably 5, forming one ring; one or two, preferably two, ring atoms being nitrogen atoms, the remaining ring atoms being carbon atoms. In preferred embodiments, the heteroaryl is imidazolyl ( ) unsubstituted or substituted with one or more R ⁵ . In more preferred embodiments, the heteroaryl is imidazolyl substituted with one R ⁵ , preferably on the nitrogen atom (i.e. the nitrogen atom at position 3 bearing the hydrogen atom in unsubstituted imidazolyl). Again, in any of these embodiments, R ⁵ is as defined above. In preferred embodiments, R ⁵ is alkyl, preferably preferably methyl.

[0030] In preferred embodiments, R ³ is 0-4alkyl. In more preferred embodiments, R ³ is methyl or butyl.

[0031] In any and all of the above embodiments, any one (independently), any subset, or all of the heteroatoms in the heterocycloalkyl and the heteroaryl is preferably a nitrogen atom.

[0032] In any and all of the above embodiments, any one (independently), any subset, or all of the halogen atoms is preferably a fluorine atom.

[0033] In preferred embodiments, the ionic liquid is of formula:

H

. H ₃

-N

, or

wherein A ^" is an anion.

[0034] In all of the above embodiments, A ^" may be any anion know as useful in ionic liquids. Non-limiting examples of suitable anions include CI ^" , HSO4 ^" , BF4 ^" , PF6 ^" , TFSI ^" (which is CF3-SO2-N-SO2-CF3 ^" and is called bis(trifluoromethanesulfonyl)imide), FSI ^" (which is FSO2-N-SO2F ^" and is called bis(fluorosulfonyl)imide), R ⁶ -S03~, and DCA ^" (which is dicyanamide). In preferred embodiments, A ^" is TFSI, FSI, DCA, and R ⁶ -S03~. In more preferred embodiments, A ^" is R ⁶ -S03~.

[0035] Above (i.e. in R ⁶ -S0 ³ -), R ⁶ is alk(en/yn)yl, cycloalk(en/yn)yl, aryl, heteroaryl, each of which being optionally substitued by one or more alk(en/yn)yl, aryl, arylalk(en/yn)yl (i.e. aryl-alk(en/yn)yl), and alk(en/yn)ylaryl (i.e. alk(en/yn)yl-aryl-), nitro (NO2), cyano (-CN), hydroxyl (-OH), halogen atom, alk(en/yn)oxy (i.e. aik(en/yn)yl-0- ), alk(en/yn)oxycarbonyl (i.e. alk(en/yn)yl-0-CO-), alk(en/yn)ylamino (i.e. alk(en/yn)yl-NR ⁷ -), and/or alk(en/yn)ylamido (i.e alk(en/yn)yl-NR ⁷ -CO-). In embodiments of the alk(en/yn)ylamino and alk(en/yn)ylamido, R7 represents a hydrogen atom, alk(en/yn)yl, aryl, arylalk(en/yn)yl, or alk(en/yn)ylaryl. In preferred embodiments, R ⁶ is Cwalkyl or Ci haloalkyl, preferably Ci-3alkyl or Ci-3haloalkyl, preferably Ci-2alkyl or preferably Cialkyl or Cihaloalkyl (i.e. methyl or halomethyl). In embodiments of any of the above, the haloalkyl is perhaloalkyl, preferably perfluoroalkyl. In preferred embodiments, C(R ⁶ )3-S03 ^" represents CH3-SO3 ^" (i.e. mesylate) or CF3-SO3 ^" (i.e. triflate). In preferred embodiments, C(R ⁶ )3-SC>3 ^" represents CH3-SO3 ^" . In preferred embodiments, C(R ⁶ )3-SC>3~ represents CF3-SO3 ^" .

Use of the Ionic Liquids

[0036] The above ionic liquids can be used for the extraction of rare earth elements as well as gallium from various matrices. Therefore, there is provided a method of extracting one or more rare earth element and/or gallium from a matrix, the method comprising the step of contacting the matrix with an ionic liquid as defined above.

[0037] As noted above, the rare earth elements (REEs), as defined by lUPAC, are scandium and yttrium as well as the fifteen lanthanides: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium.

[0038] In embodiments, the ionic liquid is in liquid form. In such embodiments, the contacting step thus results in the dissolution of the one or more rare earth element and/or gallium into the ionic liquid. Also, in such embodiments, the matrix may be either solid or liquid (or both, for example, a slurry). In consequence, the extraction is either a solid-liquid extraction and/or a liquid-liquid extraction.

[0039] In other embodiments, the ionic liquid may be immobilized on a solid support for flow-through bed extraction. In such embodiments, the contacting step results in the retention of the one or more rare earth element and/or gallium onto the ionic liquid immobilized on the solid support. Also, in such embodiments, the matrix is liquid. In consequence, the extraction is a solid-liquid extraction.

[0040] The solid supports on which the ionic liquid may be immobilized may be any solid support that is inert toward the matrix and allows for the immobilization of the ionic liquid. The immobilization of the ionic liquid will depend on the exact nature of the support. This immobilization may be carried according to immobilization techniques well known in the art, sometimes referred to as supported ionic liquids (SIL). Non-limiting examples of solid supports include glass beads, porous silica beads, polymeric beads, and polysiloxane beads. Non- limiting examples of immobilization techniques include ionic liquid adsorption on surfaces, absorption in pores, imprisonment in a polymer matrix, polymerization of functional groups added to the ionic liquid which may include but are not limited to vinyl or alkoxysilane groups, and covalent immobilization.

[0041] The ionic liquids can be used for the extraction of rare earth element(s) and/or gallium from various solid or liquid matrices. Aluminum-containing matrices appear to be of particular interest, since at least some of the ionic liquid of the invention do not extract aluminum, extract little aluminum, extract aluminum with an efficiency smaller than their extraction efficiency for rare earth element(s) and/or gallium. In other words, the ionic liquid appears to be useful to separate rare earth element(s) and/or gallium from aluminum.

[0042] Non-limiting examples of solid matrices include:

• clays, in particular aluminum-containing clays, for example aluminous clays,

• industrial wastes, such as slag, sludge, gangue, tailings, dumps, refuse, serpentine residues, red muds and flying ashes,

• pure or refined ores, in particular aluminum-containing ores, such as aluminosillicate minerals, argillite, nepheline, mudstone, beryl, cryolite, garnet, spinel, bauxite, carbonatite, kyanite, kaolin, serpentine or mixtures thereof,

• electronic components/wastes (including consumer electronics),

• alloys,

• magnets,

• batteries,

• catalytic converters,

• residues from incineration, and

• materials used in fluorescent lights.

[0043] Non-limiting examples of liquid matrices that can be extracted by a method according to any of the above embodiments, include aqueous solutions or suspensions, such as those resulting from mining and/or refining operations, transformation and/or production of electronic components and materials like alloys, magnets, and fluorescent lights. In particular, the liquid matrix may be a lixivium (i.e. a liquid obtained by lixiviation) or leachate of any of the above solid matrices, preferably a lixivium/leachate obtained during mining and/or refining of an ore that contains one or more rare earth elements and/or gallium (wherein the ore may or may not be primarily mined/refined to produce an element other than a rare earth and/or gallium, for example aluminum). A preferred liquid matrix is a lixivium/leachate of red muds. Another preferred liquid matrix is a lixivium/leachate of fly ashes. [0044] Of note, it is not required to add a separate extractant or solvent to the ionic liquid. Indeed, the ionic liquid plays a double role: solvent (when in liquid form) and extractant simultaneously. This is advantageous. Indeed, in conventional rare earth extractions, increasing the concentration of the extractant in the extraction solvent typically results in an increased extraction efficiency (i.e. a higher percentage of the element-to-extract is extracted). However, the concentration of the extractant is limited by its solubility in the solvent. Here, as the ionic liquid is both solvent and extractant, the extractant concentration is at its highest possible value, and thus extraction efficiency is maximized. Nevertheless, if desired the ionic liquid may be used in admixture with one or more organic solvents and/or other conventional ionic liquid. In a preferred embodiment, the ionic liquid is used alone, i.e. in pure form, i.e. not in admixture with another ionic liquid, an extractant or a solvent.

[0045] In any and all of these embodiments, it is contemplated to use a mixture of two or more ionic liquids of the invention.

[0046] Another advantage of some embodiments of the above ionic liquids is that they are not miscible with water. This allows extracting rare earth elements/gallium from aqueous solutions or suspensions. Furthermore, this limits the loss of extractant in such aqueous phases. Indeed, in conventional rare earth extractions involving a solvent and a separate extractant, the extractant may at least partially become solubilized in these aqueous phases. This limits the extraction efficiency and increases material costs. Furthermore, this is not environmentally desirable when the extractant is toxic (which is the case of, for example, phosphines based extractants).

[0047] The immiscibility of the ionic liquids with water allows performing the extraction on an aqueous matrix without contaminating it (or with reduced contamination compared to e.g. organic solvents), which eases the environmentally-friendly disposal of this matrix after the extraction.

[0048] Another advantage is that the above ionic liquids are typically less expensive than the ionic liquids of the imidazolium family typically used for rare earth/gallium extraction.

[0049] Finally, the ionic liquids can be tailored via their pendent arms (R ¹ to R ³ as defined above) and their anion.

[0050] The contacting step may occur under a variety of conditions (temperature, contact time, agitation, ionic liquid:matrix weight ratio, etc.). These will be easily tailored by the skilled person according to the matrix at hand.

[0051] In embodiments, the contacting step is carried out under agitation. Regarding agitation, it should be noted that it generally increases the rate of extraction and is therefore preferred. Various well known conventional stirring means typically used for solid-liquid and liquid-liquid extractions (stirrers, paddles and the like) can be used. Other stirring means such as acoustic resonance are also envisioned.

[0052] With regard to the temperature, it should be noted that the present ionic liquids, in embodiments, are generally significantly less volatile than the organic solvents conventionally used in such applications since their vapour pressure is several orders of magnitude lower. Therefore, they are advantageously more versatile as they can be used up to relatively higher temperatures. For example, in embodiments, the contacting step is carried out at a temperature ranging from about 0 to about 150°C. In embodiments, the contacting step is carried out at a temperature of:

• about 0, about 5, about 10, about 15, about 20, about 25, about 30, about 35, about 40, about 45, about 50, about 55, about 60, about 65, about 70, about 75°C or more and/or

• about 150, about 140, about 130, about 120, about 110, about 100, about 95, about 90, about 85, about 80, about 75, about 70, about 60, about 65, or about 60°C or less,

preferably at a temperature ranging from about 60 and about 80 °C or at about room temperature. This flexibility in the extraction temperature eases the use of the extraction in pre-existing industrial processes as it often eliminates the need for cooling or heating the matrix before performing the extraction. Of note, the use of higher temperatures in the above ranges may advantageously speed the extraction by lowering the viscosity of the ionic liquid.

[0053] The reduced volatility of the ionic liquid (compared to organic solvents) also means that they may be easier to reuse. Further, this may mean less air/work environment contamination than with volatile organic solvents.

[0054] With regard to the contact time, it should be noted that, in typical extractions, longer contact times typically result in increased extraction efficiency (i.e. a higher percentage of the element-to-extract is extracted). This is also true of the present method. It should also be noted that the results shown in the Examples below generally indicate a very quick and yet nearly complete extraction. This constitutes another advantage of some embodiments of the invention. In embodiments, the contacting step of the method lasts:

• about 2, about 5, about 10, about 15, about 20, about 25, about 30, about 45 minutes or more, and /or

• about 60, about 45, about 30, about 25, about 20, about 15, about 10, or about 5 minutes or less.

[0055] In embodiments, the contacting step results in the extraction of about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, about 93%, about 95%, about 96%, about 97%, about 98%, about 99% or more or about 100% of any one or more, all, or any subset of the one or more rare earth elements and/or gallium.

[0056] Advantageously, in embodiments, the method allows the preferential extraction of the one or more rare earth elements and/or gallium over other metals present in the matrix. This means that the one or more rare earth elements and/or gallium is extracted with a greater efficiency compared to other metals present in the matrix. Such a preferential extraction results in the desirable concentration of the rare earth elements and/or gallium. In embodiments, the method allows the selective extraction of the one or more rare earth elements and/or gallium over other metals present in the matrix. This means that other metals present in the matrix are not significantly extracted from the matrix. Such a selective extraction results in the more or less complete separation of the rare earth elements and/or gallium from the other metals present in the matrix. [0057] With regard to the ionic liquid:matrix weight ratio used, generally speaking the extraction efficiency will increase with the ionic liquid:matrix weight ratio. The minimum ionic liquid:matrix weight ratio required will depend on the quantity of rare earth/gallium to be extracted and the solubility of the rare earth/gallium in the ionic liquid. Indeed, an amount of ionic liquid vs. matrix as low as possible is desirable to increase the enrichment factor and to achieve the highest concentration in REE and/or gallium as possible in ionic liquid. However, there should preferably be enough ionic liquid to allow achieving the highest possible extraction efficiency. Depending on the type of extraction and on the concentration of the REE, a ionic liquid:matrix weight ratio ranging from 1:1 to 1 :100. In embodiments, the ionic liquid:matrix weight ratio is:

• about 1 :100, about 1 :90, about 1 : 80, about 1 :75, about 1 :60, about 1 :50, about 1 :45, about 1 :40, about 1 :30, about 1 :25, about 1 :20, about 1 : 15, or about 1 : 10 or less, and/or

• about 1 :1, about 1 :2, about 1 :3, about 1 :4, about 1 :5, about 1 :6, about 1:7, about 1 :8, about 1:9, about 1 :10, about 1 :15, about 1:20, about 1 :25, about 1 :30, about 1 :35 or more.

In preferred, embodiment, the ionic liquid:matrix weight ratio is about 1 :30.

[0058] In embodiments, the method further comprises the step of isolating the rare earth element and/or gallium from the ionic liquid. This can be achieved by back-extracting (stripping) the rare earth/gallium in a second aqueous phase, by precipitating directly the rare earth/gallium from the ionic liquid via the addition of reagents, by electrodepositing the rare earth/gallium from the ionic liquid (N.B. this specific technique cannot be used with ionic liquids immobilized on a solid support), or by pyrolysing the ionic liquid containing the rare earth/gallium. A preferred method is stripping, preferably using a concentrated acidic aqueous solution (such as HN0 ₃ at 4M or more).

Definitions

[0059] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

[0060] The terms "comprising", "having", "including", and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to") unless otherwise noted.

[0061] Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All subsets of values within the ranges are also incorporated into the specification as if they were individually recited herein.

[0062] Similarly, herein a general chemical structure with various substituents and various radicals enumerated as choices for these substituents is intended to serve as a shorthand method of referring individually to each and every molecule obtained by the combination of any of the radicals for any of the substituents. Each individual molecule is incorporated into the specification as if it were individually recited herein. Further, all subsets of molecules within the general chemical structures are also incorporated into the specification as if they were individually recited herein.

[0063] Herein, "substituted" as in the phrase "alkyl substituted with ..." means that any one or more of the hydrogen atoms of the e.g. alkyl group, including those at both ends of the group, may be independently replaced by the atoms or functional groups listed after the phrase.

[0064] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.

[0065] The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed.

[0066] No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0067] Herein, the term "about" has its ordinary meaning. In embodiments, it may mean plus or minus 10% or plus or minus 5% of the numerical value qualified.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0069] Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0070] The present invention is illustrated in further details by the following non-limiting examples.

Glossary

PIP +

13

, also called PP13 herein,

PYR13,

PYR ₁₄ ⁺

Nlll4 ⁺ , also called N1114 herein,

N(Tf) ₂ also called TFSI herein,

DODGAA

MDODGA , and

Cyanex 923 -Example 1 - Synthesis of Ionic Liquids

[0071] The following Ionic liquids were synthesized:

called 1-DGA-IL In Examples 3 and 4, and

[0072] The reaction synthesis is shown in Figure 1.

[0073] Synthesis of IL-1. A weight of 5.00 g (13.98 mmol) of MDODGAA (prepared as described in Comparative Example 1) was stirred and placed in an ice bath. Then, 1240 μΐ (14 mmol) of trifluoromethanesulfonic acid was added dropwise carefully to the solution for 3 hours. The solution was diluted in 100 mL dichloromethane, washed with deionized water to remove the acid excess, dried over sodium sulfate, filtered, and vacuum dried to remove the dichloromethane. Yield: 90% (4.48 g).

[0074] Synthesis of IL-2. The synthesis of IL-2 was similar to that of IL-1 except that 1-butanol was used for IL-2 instead of methanol used for IL-1.

-Example 2 - Extraction of Rare Earth Elements

[0075] The performances of IL-1 and IL-2 for the extractions of rare earth elements were tested as follows.

[0076] The extraction of REE was studied by equilibrating 0.5 mL of the ionic liquid phase with a given volume of an aqueous phase containing the REEs at 1 ppm (Figure 2) or 10 ppm (Figures 3 and 4) and both Fe ³⁺ and Al ³⁺ at 5000 ppm each. The extraction was done by wrist-type agitation using a Brunell, Model 75 shaker. The stirring time was varied. Then, an aliquot of the aqueous phase was removed and diluted with an aqueous solution of HNC-3 at 2% to a total volume of 6 mL for analysis of the remaining elements in the aqueous phase.

[0077] Figure 2 shows the percentage of REE extracted as a function of extraction time. It shows that the extraction is very complete and very quick; more than 90% of all REEs were extracted at the first measured point (at 5 minutes). The length of the alkyl chain in R ³ did not impact the extraction efficacy.

[0078] Figures 3 and 4 show the percentage of REE extracted as a function of ionic liquid:aqueous solution volumic ratio for IL-1 (Figure 3) and IL-2 (Figure 4). This means that the ionic liquids are able to achieve an enrichment of the phase in REE, by a factor given by the volumic ratio. For example, the 100% extraction of 10 ppm of scandium with a volumetric ratio of 1 :5 means that the final [Sc] in the ionic liquid is 50 ppm. [0079] Figure 5 shows that the water uptake from the atmosphere for the two ionic liquids is around 1500 ppm at equilibrium. This is lower than most ionic liquids.

Comparative Example 1 -Various Extractants Dissolved in Various Conventional Ionic Liquids

[0080] The extraction of Sc ³⁺ and Y ³⁺ in the presence of other rare earth elements (REEs) (La ³⁺ , Ce ³⁺ ) and other ions (Al ³⁺ , Fe ³⁺ ) from acidic aqueous phases was studied using ionic liquid composed of 1-butyl-methyl- pyrrolidinium [PYRi4] ⁺ , 1 -methyl-1 -propyl-piperidinium [PIP13] ^" , or 1-butyl-trimethyl ammonium [Nni4] ⁺ cations with a common anion, bis(trifluoromethylsulfonyl) amide [NfTfy] ^" . These ionic liquids are non-miscible with water and can thus be used for liquid-liquid extraction purposes. The four REEs selected are representative of light and heavy elements.

[0081] The extraction in ionic liquids was assisted by dissolving the extractants Ν,Ν-dioctyldiglycolamic acid (DODGAA), Cyanex 923 or methyl 2-(2-(dioctylamino)-2-oxoethoxy)acetate (MDODGA). DODGAA is known from the art. MDODGA is similar to DODGAA, the carboxyl acid group is replaced by a methoxyl group. Cyanex 923 is a commercial phosphonyl-based extractant.

Experimental

Materials and reagents

[0082] All the chemicals and reagents used in the study were of analytical grade and used as received. The nitric, hydrochloric, sulfuric acids, methanol (99.99%), diglycolic anhydride (90%), dioctylamine, chloroform-d, (>99.8 atom % D,), Iron(lll) chloride FeCh and aluminium(lll) chloride AICI3 were obtained from Sigma Aldrich. Trialkylphosphine oxide mixture (Cyanex 923 from Cytec, Canada) and dichloromethane (Alfa Aesar) were used as received. The ionic liquids [Nni4][N(Tf)2] (butyltrimethylammonium bis(trifluoromethane)sulfonamide), [PYRi ₄ ][N(Tf) ₂ ] (butylmethylpyrrolidinium bis(trifluoromethane)sulfonamide), [PIPi3][N(Tf) ₂ ]

(propylmethylpiperidnium bis(trifluoromethane)sulfonamide) (99%, from loLiTec) were used as-received.. The standard solutions of REEs were obtained from Inorganic Ventures as follows: scandium Sc(N03)3 (>99.9%), yttrium Y(N03)3, lanthanum La(N03)3, cerium Ce(N03)3 at 10 ppm and iron Fe(NOs)3 and aluminium AI(N03)3 at 10000 ppm.

Synthesis of DODGAA

[0083] Diglycolic anhydride, 4.62 g (35.9 mmol) was suspended in 40 mL of dichloromethane. Separately, 6.99 g (28.4 mmol) of dioctylamine was dissolved in 10 mL of dichloromethane. While stirring, the dioctylamine solution was added dropwise carefully to the diglycolic anhydride suspension placed in an ice bath. Stirring was continued at room temperature until the solution became clear as a result of dissolution of diglycolic anhydride. The solution was placed in a flask for reflux overnight. Thereafter, the reaction solution was washed with deionized water containing 1 M of HCI to remove the water-soluble impurities, dried over sodium sulfate, filtered, and vacuum-dried to remove the dichloromethane. Recrystallization was done with using 70 mL of n-hexane, obtaining 9.44 g (yield 95%) of the reaction product. ¹ H-NMR (CDCI3, δ, ppm): 0.88 (d, 6H, 2 x CH ₃ ); 1.28 (s, 20 H, 10 x CH ₂ ); 41.55 (s, 4 H, 2 x CH ₂ ); 3.08 (t, 2 H, CH ₂ ); 3.35 (t, 2 H, CH ₂ ); 4.20 (s, 2H, CH ₂ ); 4.38 (s, 2H, CH ₂ ). C NMR (CDCIs, δ, ppm): 14.19 (CH ₃ ); 14.21 (CH ₃ ); 22.72 (CH ₂ ); 22.75(CH ₂ ); 26.95 (CH ₂ ); 27.06 (CH ₂ ); 27.54 (CH ₂ ); 28.76 (CH ₂ ); 29.26 (CH ₂ ); 29.32 (CH ₂ ); 29.33 (CH ₂ ); 29.40 (CH ₂ ); 47.00 (CH ₂ ); 47.03 (CH ₂ ); 71.46; (CH ₂ ); 73.36 (CH ₂ ); 170.80 (CO); 171.88 (CO).

Synthesis ofMDODGA

[0084] A weight of 5.00 g (13.98 mmol) of DODGAA was dissolved in 50 mL methanol. Then 300 μΐ (6 mmol) of 4 M sulfuric acid was added dropwise carefully to the solution which was placed in an ice bath and then refluxed for 3 hours. The solution was diluted in 80 mL dichloromethane, washed with deionized water to remove the acid excess, dried over sodium sulfate, filtered, and vacuum dried to remove the dichloromethane. Yield: 95% (4.72 g). ¹ H-NMR (CDCI3, δ, ppm): 0.88 (d, 6H, 2 x CH ₃ ); 1.28 (s, 20 H, 10 x CH ₂ ); 41.55 (s, 4 H, 2 x CH ₂ ); 3.08 (t, 2 H, CH ₂ ); 3.35 (t, 2 H, CH ₂ ); 3.75(s, 3H, CH3), 4.20 (s, 2H, CH ₂ ); 4.38 (s, 2H, CH ₂ ). ¹³ C NMR (CDCI ₃ , δ, ppm): 14.19 (CH ₃ ); 14.21 (CH ₃ ); 22.72 (CH ₂ ); 22.75(CH ₂ ); 26.95 (CH ₂ ); 27.06 (CH ₂ ); 27.54 (CH ₂ ); 28.76 (CH ₂ ); 29.26 (CH ₂ ); 29.32 (CH ₂ ); 29.33 (CH ₂ ); 49.61 (CH ₂ ); 46.60 (CH ₂ ); 51.93 (CH ₃ ); 67.16; (CH ₂ ); 69.36 (CH ₂ ); 166.80 (CO); 169.88 (CO).

Extraction procedure

[0085] All the extraction studies were carried out at room temperature. The extraction of Sc ³⁺ , Y ³⁺ , La ³⁺ and Ce ³⁺ was studied by equilibrating 0.5 mL of the ionic liquid phase with 1.5 mL of an aqueous phase containing the REEs at 1 ppm and both Fe ³⁺ and Al ³⁺ at 5000 ppm each. The extraction was done by wrist-type agitation using a Brunell, Model 75 shaker. The stirring time was varied as described below. Then, an aliquot of the aqueous phase was removed and diluted with an aqueous solution of HNO3 at 2% to a total volume of 6 mL for analysis of the remaining elements in the aqueous phase.

[0086] The distribution ratio (D) was determined using the following equation:

where C, and Q are the concentration of the metal ions in the aqueous phase before and after extraction, respectively. ¼, is the volume of the aqueous phase and ¼. is the volume of the ionic liquid phase. The extraction efficiency (%E) was determined by using Equation 2:

and the separation factor (SF) was calculated as follow:

'REl

SF = 3

'RE2

where D _RE i and DRE2 are the distribution ratios of the rare earth ions 1 and 2. Instrumentation and analyses

[0087] The concentrations of rare earths in the aqueous phase were determined using inductively coupled plasma mass spectrometry (ICP-MS, Perkin Elmer, NexlON 300X) following the liquid-liquid extraction step. The concentration of the other metal ions (Fe ³⁺ and Al ³⁺ ) in the aqueous phase was determined using atomic absorption spectroscopy (AAS, Thermo Scientific, Series S AA spectrometer). For the analysis of Fe and Al, the aliquot was diluted to approximatively 10 ppm. Some extractions at various conditions were selected for reproducibility evaluation. Extractions done in triplicate provided uncertainties of 5% at the most. ¹ H NMR and ¹³ C NMR spectra of ionic liquids were recorded on a Bruker Advance 300 spectrometer operating at 300 MHz for ¹ H. CDCI ₃ was used as the solvent for recording all the NMR spectra and the data were analyzed with the SpinWorks 3 software package. The water content of the ionic liquid phase before and after the extraction was determined with a Mettler-Toledo C30 coulometric Karl Fischer titrator.

Results

Extraction kinetics

[0088] To determine the equilibration time, the extraction efficiency, %E, was measured over a period of three hours period for Sc ³⁺ in the different ionic liquids (Figure 6). For the DODGAA system (Figure 6A), it is observed that the %Es _c increases from its initial value to reach close to 100% after 45 minutes. For CYANEX 923 (Figure 6B), the %Esc increases from its initial value to 100% after 30 minutes regardless of the ILs used.

[0089] Of note, in Figure 6, the organic phase was 40 mM A) DODGAA or B) CYANEX 923 in [Νιιι ₄ ][Ν(Ττ) ₂ ], [PIPi ₃ ][N(Tf) ₂ ] or [PYRu][N(Tf) ₂ ]; the aqueous phase contained 1 ppm Sc ³⁺ with 0.3 M HCI or HNO3 at pH=1 and the organic:aqueous phase ratio was 1 :3.

Extraction of REEs by DODGAA and CYANEX 923 in ILs

[0090] The extraction efficiency of DODGAA for four rare earth metals, Sc ³⁺ , Y ³⁺ , La ³⁺ and Ce ³⁺ was compared to that of commercial extractant CYANEX 923. As indicated in Figure 7, the DODGAA-ILs system shows a higher selectivity for all heavier REEs (Sc ³⁺ and Y ³⁺ ) than the CYANEX 923-ILs system. The affinity of DODGAA for heavier REEs is not affected by the high concentration of Fe ³⁺ and Al ³⁺ (5000 ppm each).

[0091] The extraction efficiencies of Fe ³⁺ and Al ³⁺ with DODGAA are low compared to REEs. In contrast, these metal ions are more easily extracted from a hydrochloric acid solution than they are from a nitric acid solution.

[0092] The REEs patterns of extraction with CYANEX 923 differ significantly from those of DODGAA. In the case of the CYANEX 923-ILs system, high extraction efficiency is observed only in the case of Sc ³⁺ . Also, in most cases, the extraction efficiency of Al ⁺³ and Fe ⁺³ reaches 50-70%, causing a drastic decrease of the separation factor between REEs and non-REE metals.

[0093] Of note, in Figure 7, the columns from left to right are in the same order as the legend items from top to bottom in the legend of the figure. Also, the organic phase contained 40 mM DODGAA or CYANEX 923 in ILs; in the aqueous phase, [Sc ³⁺ ]= [Y ³⁺ ]= [La ³⁺ ]= [Ce ³⁺ ]=1 ppm and [AI ³⁺ ]= [Fe ³⁺ ]=5000 ppm with A) 0.3 M HN0 ₃ and B) 0.3 M HQ; and the organic:aqueous phase ratio was 1 :3.

Hydrophobicity of the organic phase

[0094] The transfer of water molecules from the aqueous phase to the hydrophobic IL phases is a well-known phenomenon. The first column in Table 1 shows the water content in ppm of the pure IL phases (without any extractant) as a function of time exposure to the atmosphere. Water uptake is quite rapid and increases from ca. 50 ppm (stored in glovebox) to above 1000 ppm after a few hours. An increase by 100 fold is noted after 3 days of exposure to air. The water concentration achieved in neat [Nni4][N(Tf)2] is greater than in neat [PIPi3][N(Tf)2] and [PYRi4][N(Tf) ₂ ] ILs. Although they are often said to be immiscible with water, all ILs used in this work are known to be highly hygroscopic and the solubility of water in the ILs increase with the hygroscopicity of the cation: [Νιιι ₄ ][Ν(Τί) ₂ ]> [ΡΙΡι ₃ ][Ν(Ττ) ₂ ]> [PYRu][N(Tf) ₂ ].

[0095] The water uptake is more severe after a 45 min of extraction and the water content reached about 12000 ppm. The addition of a ligand to the IL phase has no significant effect on the water uptake of the extracting phase. The water transfer to the IL phase appears to be independent of the type of acid although there is a difference in the hydration energy of CI ^" and NO3 ^" ions.

Table 1: Water uptake of the ionic liquids after exposition to the atmosphere and after shaking during 45 minutes. The aqueous phase contained 0.3M of the selected acid. The organic: aqueous phase ratio was 1 :3.

H2O (ppm) as function time (hours), After shaking with H2O

before shaking acidified t = 0 t = 8 t = 24 t = 72 HNOs HCI

[PYRi ₄ ][N(Tf) ₂ ] 47.4 1180 2810 4489 13105 12894

[PIPi ₃ ][N(Tf) ₂ ] 51.2 1624 2130 4548 12354 12585

[Niii ₄ ][N(Tf) ₂ ] 48.8 2548 3989 5814 11255 12688

[PYRi ₄ ][N(Tf) ₂ ] 13202 13546

[PIPi ₃ ][N(Tf) ₂ ] 11215 11354

11385 11849 [PYRi4][N(Tf) ₂ ] 13347 12987

[PIPi3][N(Tf) ₂ ] 11110 12554

[Niii4][N(Tf) ₂ ] 11025 12103

[0096] There is an important modification of the visual aspect of both phases during the extraction. Fist, DODGAA was completely dissolved in the three ionic liquids and they appear clear in each case. After contact with the aqueous phase, the IL phases became cloudy as a result of significant water uptake. Also, one could note the presence of a thin layer between both liquid phases, resulting from the precipitation of some compounds out of the aqueous or IL phase.

[0097] To obtain further insight into the nature of the thin-layer formed between the aqueous and the ILs phase, IR spectra of the IL-DODGAA system were taken, including the initial IL phase, the pure DODGAA and the precipitated phase observed after extraction with aqueous phase containing 0.3 M HNO3. A comparison of curves (1) and (3) in Figure 8 shows clearly the characteristic peaks of DODGAA (1500 cm- ¹ - 1750 cnr ¹ region), demonstrating losses of DODGAA from the extracting phase. This interaction with water may undermine the ability of DODGAA to be completely miscible with ionic liquids and may also interact with the hydroxyl group of extractant by hydrogen bonding and affect extraction properties.

[0098] To increase the hydrophobicity of DODGAA and prevent its leaching to the aqueous phase, an esterification of the carboxylic moiety was carried out (see scheme below). The extractant obtained, MDODGA, has an extracting group that is analogue to that of DODGAA, but the carboxylic acid group was replaced by a methoxyl group.

DODGAA MDODGA

Extraction ofREEs by MDODGA in ILs

[0099] Figure 9 compares the extraction results of REEs from HNO3 aqueous solutions using DODGAA or MDODGA. It is clear that the extraction efficiency of MDODGA for light REEs is much higher than DODGAA for all IL systems. Also, the extraction of REEs present at 1ppm is not affected by the presence of Fe ³⁺ and Al ³⁺ which are 5000 times each more concentrated. These Fe ³⁺ and Al ³⁺ ions are transferred to the IL phase to a smaller extent with MDODGA, their extraction efficiency decreasing from above 10% to less than 5%.

[00100] Of note, in Figure 9, the columns from left to right are in the same order as the legend items from top to bottom in the legend of the figure. Also, the organic phase contained 40 mM DODGAA or MDODGA in ILs; the aqueous phase contained [Sc ³⁺ ]= [Y ³⁺ ]= [La ³⁺ ]= [Ce ³⁺ ]=1 ppm and [AI ³⁺ ]= [Fe ³⁺ ]=5000 ppm with 0.3 M HN0 ₃ at pH=1 and the organic:aqueous phase ratio was 1 :3.

[00101] Another effect of the esterification of the extractant is that all extraction phases remained homogeneous and clear after extraction. Interestingly, the more hydrophobic MDODGA extractant also reduces significantly the amount of water uptake by the IL phase during the extraction as demonstrated in Figure 10 for the MDODGA- [Niii4][N(Tf)2] system. The water concentration reached in the 60 mM MDODGA solution in this IL is more than 13 times lower than that in the neat IL after 72h at ambient temperature.

[00102] In addition, the equilibration time for extractions with MDODGA is reduced to only 15 minutes compared to 40 minutes with DODGAA. These results indicate that the better solubilisation of the extractant in IL and lower H2O uptake are providing better extraction efficiencies.

Comparison with Examples 1 and 2

[00103] A first significant difference between Examples 1/2 and Comparative Example 1 is the extraction efficiency for La et Ce. In Comparative Example 1, these two REE were extracted at 80% at the most (see Figure 9) after an extraction time of 40 minutes with a volumic ratio of 1:3. In contrast, the ionic liquids IL-1 and IL-2 of Examples 1 and 2 allowed a 100% extraction of La and Ce (along with Sc and Y) within 10 minutes at the same volumic ratio (see Figures 3 and 4).

[00104] A second improvement is that the minimum extraction time to reach equilibrium is reduced in Examples 1 and 2. This is made clear by a comparison of Figures 1 and 6. Indeed, the ionic liquids IL-1 and IL-2 of Examples 1 and 2 provided a 100% extraction in 10 minutes, vs. 30 or even 40 minutes in Comparative Example 1.

[00105] A third improvement is that the ionic liquids IL-1 and IL-2 of Examples 1 and 2 are more efficient in extracting the rare earth elements. Indeed, Figure 9 shows that Sc and Y are extracted at 98 and 97%, respectively from an aqueous solution with a starting concentration of 1 ppm. Using the same volumic ratio, ionic liquids IL-1 and IL-2 of Examples 1 and 2 extracted >99 % of Sc and Y from an aqueous solution with a starting concentration of 10 ppm (Figure 3).

Example 3 - Synthesis of Ionic Liquids and Rare Earth Extraction and Isolation

Synthesis of Ionic Liquids

[00106] Two ionic liquids were synthesized:

1-DGA-IL (same as IL-1 above), and

[00107] The synthesis of the ionic liquid was divided into several steps. First, the DODGAA precursor was synthesized from anhydrous diglycol and dioctylamine. The following steps were an esterification of DODGAA in DODGA followed by protonation with a strong acid to generate the ionic liquid.

First Step: DODGAA Synthesis

[00108] 24.30 g of 97% anhydrous diglycol and 80 mL of dichloromethane (DCM) were added to a 500 mL flask. Dissolution was effected with ultrasound and was achieved after about 30-60 minutes depending on the size of the crystals (caution gaseous release, use a latex balloon on the flask and monitor).

[00109] Dioctylamine was heated in boiling water. 50mL of dioctylamine were added to the 500mL flask on ice (release of heat + gas). The reaction was allowed to proceed overnight at reflux under argon.

[00110] The next day, the product was washed (3 to 5 times) with 2% HCI and then dried with Na2S0 for 15 minutes. The mixture was filtered and the DCM evaporated. Hexane was added to the flask (about the content of a Pasteur pipette). The mixture was heated to 70°C under reflux. The mixture was well stirred, then allowed to cool to room temperature. The mixture was allowed to recrystallize in the fridge overnight.

[00111 ] The next day, the crystals were vacuum filtered and washed with a few drops of cold hexane.

[00112] Yield: more than 90%. Purity: more than 95%.

[00113] RMN 1H (300 MHz, CDCI3) δ: 4.347 (s, 2H); 4.148 (s, 2H); 3.169 (dt, J=65.1 MHz, 7.5 MHz, 4H); 1,490 (s, 4H); 1.221 (s, 20H); 0.821 (s, 6H)

[00114] RMN 1¾ (300 MHz, CDCI3) δ: 172.196, 170.543, 77.553, 77.126, 76.702, 72.293, 70.946, 46.856, 31.645, 29.134, 26.874, 22.546, 14.006

Second Step: MDODGA Synthesis

[00115] 30 g of DODGAA and 17.4 g of K2CO3 were dissolved in 140 mL of ultradry dimethylformamide (DMF) in a 500 mL flask. 14.28 g of CH ₃ I were added. The mixture was allowed to react overnight at 50°C under argon.

[00116] The next day, 40 mL of 1M HCI were slowly added to the 500 mL flask. The mixture was stirred for 15 minutes. The mixture was washed 2-3 times with 2% HCI (otherwise, the phases did not separate) and DCM. A final wash was performed with 40% sodium bisulfite. The organic phase was dried with Na2S0 ₄ for 15 minutes and then filtered. The DCM was evaporated using a rotovap. The MDODGA was purified using a silica flash column with 98% DCM, 2% methanol. (In general, 500mL of eluent were sufficient for a column of 250mL, the DODGAA remained at the top of the column). The resulting liquid was evaporated using a rotovap and allowed to dry under vacuum at 65°C at least 24 hours before the next step.

[00117] Yield: 51% (5g batch), 78.9% (10g batch), and 87.6% (~160g batch)

[00118] Purity: 83,3% - 97,1%

[00119] RMN ¹ H (300 MHz, CDCI ₃ ) δ: 4.243 (s, 2H); 4.213 (s, 2H); 3.706 (s, 3H); 3.201 (dt, J=28.5 MHz, 7.8 MHz, 4H); 1 ,482 (s, 4H); 1.228 (s, 20H); 0.830 (s, 6H)

[00120] RMN ¹³ C (300 MHz, CDCI ₃ ) δ: 170.459, 167.860, 77.517, 77.092, 76.667, 69.280, 67.901 , 51.718, 46.951, 45.763, 31.713, 29.133, 26.746, 22.545, 13.991

Third Step: DGA-TSIL Synthesis

[00121] Prepare a 250 mL three-necked flask with an inlet for a chloride calcium tube, an inlet for a dripper (linked to an argon inlet), and an argon outlet.

[00122] The MDODGA (49.18g in one batch and 102.87g in another batch) was added to the three-necked flask with a little anhydrous DCM. The mixture was stirred at -78°C and purged with argon for 15 minutes. Some DCM anhydride was introduced in the dripper with a syringe. A stoichiometric amount of acid was added to the dripper and then slowly added (1 drop per second) to the reaction mixture. The mixture was stirred at 0°C, then at room temperature in intervals of 15 minutes. The mixture was washed with water once, the DCM was evaporated, and the mixture was dried in a vacuum oven for 48h.

F

F

[00123] The acid was with triflic acid ( ^O Γ ^H ) when producing 1-DGA-IL and methanesulfonic acid ( o

H3C-S-0H

⁰ ) when producing 2-DGA-IL.

[00124] Yield (1-DGA-IL): 95,0%

[00125] Purity (1-DGA-IL): 76,0% - 93,2%

[00126] Water concentration, after drying 3 days at 65°C in a vacuum oven (1 -DGA-IL): 151 ppm

[00127] Purity (2-DGA-IL): 82,2% - 83,0%

[00128] Water concentration, after drying 3 days at 65°C in a vacuum oven (2-DGA-IL): 60ppm

Characterization (1-DGA-IL)

[00129] RMN ¹ H (300 MHz, CDCI3) δ: 4.211 (s, 2H); 4.177 (s, 2H); 3.670 (s, 3H); 3.168 (dt, J=27.9 MHz, 15.0 MHz, 4H); 1 ,449 (s, 4H); 1.195 (s, 20H); 0.794 (s, 6H)

[00130] RMN 13C (300 MHz, CDCI3) δ: 170.402, 167.830, 77.576, 77.151 , 76.726, 69.234, 67.850, 51.654, 45.720, 31.679, 29.083-26.899, 22. 509, 13.946 Characterization (2-DGA-IL)

[00131] RMN 1H (300 MHz, CDCI3) δ: 4.217 (s, 2H) ; 4.179 (s, 2H) ; 3.672 (s, 3H) ; 3.176 (dt, J=27.0 MHz, 7.5 MHz, 4H) ; 1,460 (s, 4H) ; 1.199 (s, 20H) ; 0.798 (s, 6H)

[00132] RMN 13C (300 MHz, CDCI3) δ: 171.721 , 170.407, 167.956, 77,574, 77.149, 76.724,69.233, 67.863, 51.671, 46.960, 31.686, 29.113, 26.701 , 22.513, 13.954

Comments on Synthesis

[00133] The NMR analyzes show that the only contaminant in 1-DGA-IL and 2-DGA-IL is MDODGA which was not protonated in the last step. The presence of this compound is not necessarily detrimental to extraction (it is immiscible with water and capable of complexing rare earth metals).

[00134] We also note that the yield increased with batch size.

Extractions

[00135] Extractions were made on synthetic solution and, various leachate samples (both liquid-liquid (LL) extractions) using mechanical stirring and acoustic resonance methods.

Extraction of Synthetic Solutions

[00136] 1-DGA-IL and 2-DGA-IL were brought into contact with a synthesized acidic aqueous solution of rare earth elements (all of them except promethium) and different other metals (i.e. non rare earth elements) typically present in mining waste. These "other metals" were Na ²⁺ , Al ³⁺ , Ca ²⁺ , Mn ²⁺ , Co ²⁺ , Zn ²⁺ , Fe ³⁺ , and Sn ²⁺ . The concentration of each rare earth element was 0.007 mM, while each other metal was present at a concentration of 0.1 M. The rare earth elements / other metals molar ratio was therefore about 1/14000. The organic phase to aqueous phase volume ratio was 1/10. The hydrochloric acid concentration in the synthetic solution was either 0.3 M or 6 M. The extractions were carried out at room temperature for 30 minutes. The results are shown in Figure 11.

[00137] The extraction efficiencies (% of element extracted) for scandium, yttrium, heavy rare earths elements (Tb to Lu) were greater than 95%, while they were greater than 70% for the light rare earth elements (La to Gd).

[00138] 1-DGA-IL was more efficient at a HCI concentration of 6 M. 2-DGA-IL showed less sensitivity to acid concentration, which broadens its potential applications. For both ionic liquids, lanthanum had a 10% increased extraction efficiency when decreasing acid concentration. For all other elements, the extraction efficiencies were either roughly unaffected by acid concentration or showed a loss of efficiency with increasing acid concentration. More specifically, for 2-DGA-IL, only the extraction efficiencies for Ce, Pr, and Nd were affected by the change in acid concentration and showed a loss of more than about 10% with increased concentration. For 1-DGA-IL, all rare earth elements showed differences in extraction efficiencies ranging from about 5 for scandium to about 10% for yttrium and heavy rare earth elements and of about 15% for light and medium rare earth elements, when changing acid concentration. [00139] We investigated the effect of the organic phase to aqueous phase volume (V _or A aq) ratio on the extraction efficiencies of 1-DGA-IL and 2-DGA-IL for Sc (solution of 0.007 M Sc at 6M HCI). The results are shown in Figure 12.

[00140] Increasing the V _or /Vaq ratio increased the extraction efficiencies up to a maximum ratio of 1/30 for both ionic liquids. The extraction efficiency was greater than 90% for the 1/50 ratio for both 1-DGA-IL and 2-DGA-IL and the 1/70 ratio for 1-DGA-IL. The ratio 1/30 suggests that a concentration increase factor of 30 is expected (at least for Sc). The ratio 1/50 remains interesting because it makes possible the use of very low volumes of ionic liquid (vs. the aqueous phase).

[00141] Table 2 shows the extraction efficiency for the various other metals present in the aqueous phase containing the rare earth elements. At 0.3 M HCI, 2-DGA-IL is more selective for rare earth elements (i.e. extract less of the other metals) than 1-DGA-IL. Conversely, at 6 M HCI, 1-DGA-IL is more selective than 2-DGA-IL. This suggests that 2-DGA-IL is more appropriate for use with less acidic solutions. Indeed, in these conditions, it had low extraction efficiencies for Fe and Al (the main "contaminants" in mining residues), while the extraction efficiencies for the rare earth elements was quite good - see Figure 11.

Table 2. Extraction efficiency of 1-DGA-IL and 2-DGA-IL for various other metals at different concentrations of HCI (0.3 M or 6 M). Concentration of rare earth elements = 0.007 mM. Concentration of the other metals = 0.1 M. [00142] Figure 13 shows the extraction efficiency for Ga by our two ionic liquids compared to a commercial extraction agent, CYANEX 923 (phosphine oxide with C8 alkyl chains), and MDODGA. Both CYANEX 923 and MDOGGA were used pure, i.e. not mixed with any ionic liquid or other solvent. This is possible since CYANEX 923 and MDOGGA are liquid at room temperature and immiscible with water. They were used pure so as to have a concentration comparable to our ionic liquids (also used pure). Figure 13 shows that 2-DGA-IL provides near complete extraction of gallium after 20 mln under various conditions (type and concentration of acid). In comparison, 1-DGA-IL was more sensitive to the type and concentration of acid. MDODGA did not allow extraction of gallium in these conditions. CYANEX 923 was also sensitive to the type and concentration of acid, and at most allowed extracting only about 70% of the gallium.

[00143] Figure 14 shows that 2-DGA-IL provides near complete extraction of gallium after only 20 min under various conditions.

Extraction of Leachates

[00144] Our ionic liquids were used to extract rare earth elements and/or gallium from industrial leachates of various natures:

· Leachate of red mud (ID. No.: NI130430-012, density = 1.226 kg/L);

• Leachate of fly ashes no.1 (ID. No.: NI130315-000, density = 1.135 kg/L);

• Leachate of fly ashes no. 2 (ID. No.: NI130430-017/18, density = 1.112 kg/L); and

• Leachate of degraded clay (ID. No.: SP-01-035, density = 1.196 kg/L).

[00145] Extractions were carried out with a volume ratio of 1 :10 (0.3 mL of ionic liquid per 3 mL of leachate). Both 1-DGA-LI and 2-DGA-LI were tested. The extractions were carried out stirring with a magnetic bar for each of the following three conditions:

• 10 minutes at 25°C

• 30 minutes at 25°C

• 30 minutes at 80°C

[00146] The results are shown in Figures 16 to 20. We note that 2-DGA-IL is generally more efficient than 1- DGA-IL. Also, the extraction efficiency was sensitive to the nature of the matrix, with the clay showing the best results.

Stripping Using an Aqueous Phase and Reuse of the Ionic Liquid

[00147] Stripping allows isolating the rare earth elements from the ionic liquid (after extraction) and concentrating them in an aqueous phase for future use.

[00148] Figure 21 A shows the stripping efficiency (% of element recovered from the 1-DGA-IL) of scandium using two acidic aqueous solutions (HCI and HN0 ₃ ) at different concentrations. The composition of the aqueous phase greatly affected the stripping efficiency. At a high HN0 ₃ concentration, it was possible to isolate more than 95% of the Sc from the ionic liquid. As the aqueous phase/ionic liquid volume ratio was 1:3, the scandium was therefore more concentrated in the aqueous phase than in the original liquid phase.

[00149] After the Sc was stripped from the ionic liquid, the ionic liquid was reused for extraction. Thus, several consecutive extraction-stripping cycles were done, reusing each time the same ionic liquid. Figure 21 B shows a gradual loss of extraction efficiency with each cycle. After using the Ionic liquid for 6 extraction-stripping cycles, It was possible to return to the original extraction efficiency by washing the ionic liquid with water and drying it in a vacuum oven (see "After washing" data in Figure 21 B).

[00150] The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

REFERENCES

[00151] The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety. These documents include, but are not limited to, the following:

Benrazek et al. Selective Extraction of Scandium from Aqueous Acidic Solutions Using Mixtures of Ionic Liquids and Extractants, 2 ^nd International Conference on Ionic Liquids in Separation, Toronto, Canada,

June 30, 2014

- Sun, X.; Peng, B.; Ji, Y.; Chen, J.; Li, D. Separation and Purification Technology 2008, 63, 61.

Baba, Y.; Kubota, F.; Kamiya, N.; Goto, M. Journal of Chemical Engineering of Japan 2011, 44, 679.

- Kubota, F.; Baba, Y.; Goto, M. Solvent Extraction Research and Development-Japan 2012, 19, 17. - Kubota, F.; Koyanagi, Y.; Nakashima, K.; Shimojo, K.; Kamiya, N.; Goto, M. Solvent Extraction Research and Development-Japan 2008, 15, 81.

Yang, F.; Baba, Y.; Kubota, F.; Kamiya, N.; Goto, M. Solvent Extraction Research and Development- Japan 2012, 19, 69.

- Yang, F.; Kubota, F.; Baba, Y.; Kamiya, N.; Goto, M. Journal of Hazardous Materials 2013, 254-255, 79.

- Villemin D, D. M. A. Orient J Chem 2013, 29, 4.

- Xie, F.; Zhang, T. A.; Dreisinger, D.; Doyle, F. Minerals Engineering 2014, 56, 10.

Billard, I. In Handbook on the Physics and Chemistry of Rare Earths; Jean-Claude, G. B., Vitalij, K. P., Eds.; Elsevier: 2013; Vol. Volume 43, p 213.

- Kubota, F.; Shimobori, Y.; Baba, Y.; Koyanagi, Y.; Shimojo, K.; Kamiya, N.; Goto, M. Journal of Chemical Engineering of Japan 2011 , 44, 307.

- Shimojo, K.; Nakai, A.; Okamura, H.; Saito, T.; Ohashi, A.; Naganawa, H. Analytical sciences : the international journal of the Japan Society for Analytical Chemistry 2014, 30, 513.

- Shimojo, K.; Naganawa, H.; Noro, J.; Kubota, F.; Goto, M. Analytical Sciences 2007, 23, 1427.

- Naganawa, H.; Shimojo, K.; Mitamura, H.; Sugo, Y.; Noro, J.; Goto, M. Solvent Extraction Research and Development-Japan 2007, 14, 151.