EA040373B1 - SEPARATION OF RARE EARTH METALS - Google Patents

Description

The invention relates to the extraction and separation of rare earth metals. In particular, the present invention relates to the extraction and separation of rare earth metals using specially designed ionic liquids.

State of the art of the present invention

Rare earth metals, which include the lanthanides (La to Lu), Y, and Sc, have unique physical and chemical properties that make them indispensable components of numerous high-tech products and environmentally friendly technologies, including wind turbines, liquid crystal/LED displays, phosphors, magnetic drives (hard drives) and other devices. These applications require a continuous industrial supply of high purity rare earth metals, which is currently provided by the extraction and processing of natural ores of these metals. However, there are problems that the exponential increase in demand for these metals will outpace their supply in the coming years, and thus the development of other secondary sources of these valuable metals becomes attractive. One such source is the recovery of rare earths from end-of-life products and industrial waste (often referred to as urban mining), which, although highly problematic, has the potential to provide a continuous supply of rare earths. One of the most important demands of urban mining is the development of economical and reliable separation processes/technologies that provide selective and efficient separation of rare earth metals from each other (intra-group separation) to produce high purity rare earth metals.

During the last five decades, a variety of processes have been developed such as liquid-liquid extraction (eg the Rhone-Poulenc process), ion exchange, and precipitation. Among the variety of available technologies, liquid-liquid extraction has proven to be the most suitable industrial process due to its scalability, adaptability and regenerability. In addition, industrial liquid-liquid extraction processes used to date have used industrial organophosphorus extractants, which do not have specific selectivity for individual rare earth metals, which leads to a number of stages of separation of rare earth metals from each other (see Table 1). In addition, additional processing steps are usually required to produce a high purity rare earth metal. These factors lead to a multiple increase in processing costs, which puts a burden on the overall cost of consumer products. In addition, in most of the methods used for the separation of rare earth metals, organic solvents are necessarily used, which, due to their toxicity, volatility and flammability, are not considered environmentally friendly.

In table. 1 compares some of the currently used industrial liquid-liquid extraction processes that are available for in-group separation of rare earth metals (for example, to separate dysprosium from neodymium).

The partition coefficient for a pair of individual rare earth metals is expressed as the ratio of distribution coefficients (DM) of rare earth metals, where the partition coefficient of an individual rare earth metal is defined as the ratio of its concentrations in the non-aqueous phase and in the aqueous phase, i.e. DM=[M] _N-Aq /[M] _Aq . For example, the separation factor of dysprosium with respect to neodymium is D _Dy /D _Nd .

Table 1. Comparison of separation factors of commonly used extractants of rare earth metals

Liquid-Main Component Coefficient Literature liquid extraction

Bis(2-ethylhexyl)phosphoric process

HDEHP acid

Process Bis(2,4,4Cyapex 272 trimethylpentyl)phosphinic acid

Process Bis(2,4,4-trimethylpentyl)Suapeh 302 monothiophosphinic acid

Mono-2-ethylhexyl eff] separation process

41.5 (Dy/Nd) S. K. Gupta, N. Krishnamurthy, Extractive Metallurgy of Rare Earths, CRC, New York, 2005, pp. 1-484.

1.36 (Dy/Nd) B. Swain, E.O. Otu, Separation and Purification Technology, 83, (2011), 82-90.

239.3 (Dy/Nd) M. Yuan, A. Luo, D. Li, Acta Metall. sin. 1995, 8, 10-14.

. 1.17 (Dy/Nd) N. Song, S. Tong, W. Liu, Q. Jia,

Synergist 2-ethylhexylphosphonic acid;

W. Zhoua, W. Liaob, J. Chem. Technol. Biotechnol., 2009, 84, sec-nonylphenoxyacetic 1798-1802.

acid

- 1 040373

Another of the most commonly used organophosphorus extractants is 2-ethylhexylphosphoric acid mono-2-ethylhexyl ester (P507), which also provides low separation factors, with selectivity for heavy rare earth metals generally being lower than for light rare earth metals (e.g. Tm/Er (3.34), Yb/Tm (3.56) and Lu/Yb (1.78)). Another significant disadvantage of many common rare earth extractants, such as P507, is that it is difficult to completely purify the heavy rare earth metals, in particular Tm(III), Yb(III) and Lu(III), even at elevated acidity. The low selectivity for rare earths leads to an excessively large number of steps required for efficient separation, and due to the low extractability of rare earths, the use of an extractant at higher concentrations is required. The production of organophosphorus extractants also requires complex synthetic procedures using hazardous starting materials, and said extractants have limited stability and regenerability. Another common problem is the emulsification and leaching of extractants.

Fryxell et al. (Inorganic Chemistry Communications, 2011, 14, 971-974) a chelating diamide extractant attached to a silica support has been proposed for separating lanthanides. However, this system proved unsuitable for the extraction of rare earth metals in an acidic environment (pH<5) and, most importantly, exhibited very low absorption coefficients for the separation of rare earth metals.

Ionic liquids have also been used as potential extractants for rare earth metals. In the works of Binnemans et al. (Green Chemistry, 2015, 17, 2150-2163; Green Chemistry, 2015, 17, 856-868) describes the extraction of Nd and Dy or Y and Eu from mixtures of transition metal compounds with an ionic liquid based on betaine bis(trifluoromethylsulfonyl)imide. However, this system turned out to be unsuitable for the selective intragroup separation of rare earth metals.

Chai et al. (Hydrometallurgy, 2015, 157(C), 256-260) describes the use of an ionic liquid based on 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (P507) with a trioctylmethylammonium cation for the separation of rare earth metals. In this case, only low partition coefficients and partition coefficients were observed, indicating insufficient extractability and selectivity. In addition, in the process of extracting the rare earth metal from the ionic liquid, the added acid will decompose the ionic liquid based on the acid and base pair, which must then be regenerated through an exchange reaction.

Schelter et al. describes the separation of Nd and Dy, and this separation was achieved by precipitation using a three-position nitroxide ligand, forming complexes of Nd and Dy having different solubilities in benzene. However, precipitation is not considered an industrially applicable process, and furthermore, this process requires the use of specific rare earth metal precursors and an inert anhydrous environment, which is largely impractical on an industrial scale. This method also requires the use of benzene, which is a highly toxic solvent, to achieve a high degree of separation.

Thus, there is a need to develop efficient methods that increase separation selectivity and extractability while minimizing environmental pollution.

By using an ionic liquid containing a cation having specific properties, it has been found that rare earth metals can be extracted and separated from each other with increased selectivity and extractability compared to known methods using various extractants. Because the process uses an ionic liquid, the extractant may also provide reduced volatility and flammability, potentially leading to safer and more environmentally friendly extraction of rare earth metals.

Thus, according to a first aspect, the present invention provides a method for extracting a rare earth metal from a mixture of one or more rare earth metals, said method comprising contacting an acidic solution of the rare earth metal with a composition that contains an ionic liquid to form an aqueous phase and a non-aqueous phase into which the rare earth metal is selectively extracted, and the ionic liquid has the formula [Cat ⁺ ][X ^- ], in which:

[Cat ⁺ ] is a cationic particle having the structure:

where [Y ⁺ ] contains a group selected from ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4diazabicyclo[2.2.2]octanium, diazabicycloundecenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium groups , indolinium, indolium, morpholine, oxaborolium, oxaphospholium, oxazinium, oxazolium, isooc

- 2 040373 sazolium, oxothiazolium, phospholium, phosphonium, phthalazinium, piperazinium, piperidinium, piranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinoline, isoquinoline, quinoxalinium, quinazolinium, quinuclidinium , isothiadiazolium, thiazinium, thiazolium, isothiazolium, thiophenium, thiuronium, triazinium, triazolium, isotriazolium and uronium;

each EDG is an electron donating group; And

L1 is a connecting group selected from C ₁ . ₁₀ alkanediyl, C ₂ _ ₁₀ alkenediyl, C ₁ . ₁₀ guαlkαnilefer and C ₁ . ₁₀ dialkanylketone groups;

each L2 is a connecting group independently selected from C ₁ . ₂ alkandiyl, C ₂ -alkenediyl, C ₁ . ₂ dialkanylether and C ₁ . ₂ dialkanylketone groups; And

[X ^- ] is an anionic species.

The term ionic liquid as used herein means a liquid that can be obtained by melting a salt, and when obtained in this way, it consists solely of ions. The ionic liquid may be formed from a homogeneous substance containing one type of cations and one type of anions, or it may contain more than one type of cations and/or more than one type of anions. Thus, an ionic liquid can be composed of more than one type of cation and one type of anion. In addition, the ionic liquid can be one type of cations and one or more types of anions. In addition, more than one type of cation and more than one type of anion may constitute an ionic liquid.

The term ionic liquid encompasses compounds having high melting points and compounds having low melting points, such as at or below room temperature. Thus, many ionic liquids have melting points below 200°C, in particular below 100°C, around room temperature (15 to 30°C) or even below 0°C. Ionic liquids having melting points below about 30° C. are commonly referred to by the term room temperature ionic liquids and are often prepared from organic salts having nitrogen-containing heterocyclic cations. In room temperature ionic liquids, the structures of the cation and anion prevent the formation of an ordered crystal structure, and thus the salt is liquid at room temperature.

Ionic liquids are most commonly known as solvents. It has been shown that many ionic liquids have low vapor pressure, low thermal stability, flammability, and regenerability. Due to the vast number of combinations of anions and cations available, it is possible to fine-tune the physical properties of the ionic liquid (eg, melting point, density, viscosity, and miscibility with water or organic solvents) to meet the requirements of a particular application.

Typically, when rare earth metals are extracted from sources such as ores or waste, the resulting product is a mixture of rare earth metals dissolved in an aqueous acidic solution. In the method according to the present invention, rare earth metals can be selectively extracted directly from an aqueous acidic source material, eliminating the need for significant processing of the source material before extraction.

It should be understood that in order to form an aqueous phase and a non-aqueous phase when contacted with an acidic solution, the composition containing the ionic liquid must be sufficiently hydrophobic such that phase separation of the aqueous solution and the composition occurs.

By using a composition containing an ionic liquid defined according to the first aspect, it has surprisingly been found that increased selectivity and extractability can be obtained by extracting rare earth metals from an acidic solution. The combination of high extractability (determined by Partition Ratio) and selectivity (determined by Partition Factors) is the key to a commercially efficient separation process because the number of separation steps required to obtain a product can be reduced without sacrificing purity. For example, in the process of the present invention, mixtures of dysprosium and neodymium can be separated at a selectivity (partition ratio) of greater than 1000:1 with a single contact. This represents a significant improvement over known systems, which are described in table. 1.

Without intending to be bound by any particular theory, the authors believe that the presence of a central donor nitrogen atom in the ionic liquid causes different binding strengths of different rare earth metals as a result of different ionic radii due to lanthanide contraction. Thus, some rare earth metals are preferentially bound by the hydrophobic ionic liquid extractant, resulting in efficient in-group separation of the rare earth metals. The configuration of this variable nitrogen binding as part of the ionic liquid is believed to provide the particularly efficient rare earth extraction described herein. However, it should be understood that an ionic liquid containing a nitrogen atom donor, in order to carry out the separation of various rare earth metals, must contain additional electron donor groups introduced in order to

- 3 040373 ensuring sufficient extractability.

Preferably, the method further comprises recovering the rare earth metal from the non-aqueous phase. This recovery may be carried out using any suitable means, however, it is preferred that the rare earth metal is recovered from the non-aqueous phase by washing with an acid wash solution.

It should be understood that the acidic wash solution can be any acidic solution that releases the rare earth metal from the ionic liquid. In most embodiments, the acid wash is an aqueous acid wash and the acid will substantially remain in the aqueous phase in contact with the ionic liquid. Preferably, the acid wash solution contains an aqueous solution of hydrochloric acid or nitric acid.

Washing of the rare earth metal can be carried out by any suitable method. Preferably, the ionic liquid is contacted with an acidic wash solution for two or more wash cycles to completely purify the rare earth metal, preferably 2 or 3 wash cycles. In some embodiments, a single wash cycle may be used. The term wash cycle as used herein typically includes contacting an acidic wash solution with the composition, reaching equilibrium over a period of time, such as 15 to 30 minutes, and separating the aqueous and organic phases. The second cycle can be carried out by contacting the composition with another acidic wash solution that is substantially free of rare earths.

One advantage of the ionic liquid as an extractant, as described in relation to the first aspect, is that the rare earth metal can be purified from the ionic liquid at a relatively high pH. This reduces the cost associated with the amount and strength of acid required to purify the rare earth metals from the ionic liquid and the equipment required to contain such strong acids. In addition, complete purification of rare earth metals from the ionic liquid at a relatively high pH is possible, while in the case of many known extractants, such as P507, complete purification of heavy rare earth metals (for example, Tm(III), Yb(III), Lu(III)) is difficult even at low pH.

Thus, the acid wash solution preferably has a pH value of 0 or more. In preferred embodiments, the acidic wash solution has a pH value of 1 or less.

According to preferred embodiments, the method includes extracting a rare earth metal from a mixture of two or more rare earth metals. Preferably, the acidic solution contains the first and second rare earth metal, and the method includes:

(a) preferably separating the first rare earth metal into a non-aqueous phase.

Preferably, the method further comprises in step (a) separating the non-aqueous phase from the acidic solution; and (b) contacting an acidic solution depleted of the first rare earth metal with the composition containing the ionic liquid and optionally recovering the second rare earth metal therefrom.

In some preferred embodiments, the first rare earth metal is recovered from the non-aqueous phase in step (a), and the aforementioned non-aqueous phase is recycled and used as the composition in step (b).

It should be understood that since the extractability (partition coefficient) for a particular rare earth metal varies with pH, it may be preferable to extract different rare earth metals at different pH values. For example, an acidic solution may have a lower pH in step (a) than in step (b). Preferably the acidic solution has a pH value of less than 3.5 in step (a) and the acidic solution has a pH value of more than 3.5 in step (b). As a rule, 2 or 3 extraction cycles are carried out at a certain pH value. Although the above embodiment only describes extraction at two different pH values, it should be understood that the separation of rare earth metals is generally carried out over a range of pH values with a gradual increase in pH over a plurality of extraction steps. For example, when separating three or more rare earth metals, multiple separation steps can be performed in a specific pH range, such as 1 to 4.

The acidic solution from which the rare earth metal is extracted may have any suitable pH value. Preferably, the rare earth metal is extracted at a pH greater than 1, more preferably at a pH of 2 to 4.

The pH of the acidic solution of the rare earth metal can be adjusted in any suitable manner, which is well known to those skilled in the art. For example, the pH of an acidic solution can be changed by adding acid neutralizers such as mildly alkaline solutions containing sodium carbonate, sodium bicarbonate, ammonia, CO ₂ , amines.

- 4 040373 or alcohols.

The above embodiments involve separating a particular rare earth metal from another rare earth metal directly from an acidic solution of the rare earth metal at varying pH levels. However, it should be understood that any suitable extraction sequence may be used to separate the rare earth metals. For example, two or more rare earth metals can be simultaneously extracted from an acidic solution into a non-aqueous phase at elevated pH, followed by back extraction from the nonaqueous phase with acidic solutions having a lower pH to separate the individual rare earth metals. Thus, all or only some of the rare earth metals that are present in the acidic solution may be initially extracted from the acidic solution using an ionic liquid containing composition.

It should be understood that the separation of certain pairs of rare earth metals is of particular importance due to their simultaneous recovery from valuable waste. For example, Nd and Dy are widely used in permanent magnets for numerous applications such as hard drives, MRI scanners, electric motors and generators. La and Eu are also an important pair due to their common use in fluorescent lamps, other phosphors contain Y and Eu (YOX phosphors); La, Ce and Tb (LAP phosphors); Gd, Ce and Tb (CBT phosphors); Ce and Tb (CAT phosphors).

Thus, in preferred embodiments, the first rare earth metal is dysprosium and the second rare earth metal is neodymium. According to other preferred embodiments, the first rare earth metal is lanthanum and the second rare earth metal is europium. According to further preferred embodiments, the first rare earth metal is terbium and the second rare earth metal is cerium.

The composition may be contacted with the acidic solution in any suitable manner and in any suitable ratio such that rare earths are exchanged between the aqueous and non-aqueous phases.

The composition is preferably added to the acidic solution in a volume ratio of 0.5:1 to 2:1, preferably 0.7:1 to 1.5:1, more preferably 0.8:1 to 1.2:1, for example, 1:1. However, it should be understood that the volume ratio will vary depending on the method of bringing the acidic solution into contact with the composition containing the ionic liquid.

Preferably, before contacting the composition with an acidic solution of the rare earth metal, the composition is conditioned to reach equilibrium with an acidic solution having the same pH as the acidic solution of the rare earth metal. Thus, the mixture of composition and acidic solution will generally remain at the desired pH during extraction.

The composition may be contacted with an acidic solution of the rare earth metal under any conditions suitable for the extraction of the rare earth metal.

It should be understood that the temperature used during contacting the acidic solution with the composition containing the ionic liquid may be any suitable temperature, which may vary depending on the viscosity of the composition containing the ionic liquid. For example, when a higher viscosity composition is used, a higher temperature may be required to obtain optimal results.

Preferably, the acidic solution is brought into contact with the composition at ambient temperature, i. without external heating or cooling. However, it should be understood that a natural change in temperature may occur during extraction as a result of contacting the composition with an acidic solution.

The composition may be contacted with an acidic solution of the rare earth metal for any suitable period of time to facilitate extraction of the rare earth metal into the non-aqueous phase. Preferably, this time period is determined such that equilibrium is reached and the proportions of the rare earth metal in the aqueous and non-aqueous phases remain constant. In preferred embodiments, the method comprises contacting an acidic rare earth metal solution and the composition for 10 to 40 minutes, preferably 15 to 30 minutes.

Preferably, the method includes contacting and physically mixing an acidic solution of the rare earth metal and the composition. Such agitation generally accelerates the extraction of the rare earth metal. Any suitable device can be used to achieve this goal, and a mixing device is well known in the art. For example, the mixture can be mixed using a blender or mixer. The mixing device may include equipment specifically designed for multi-phase mixing, such as high shear tools. Alternatively, agitation may include shaking the mixture, for example using a shaker that simulates a wrist movement.

Separation of the aqueous and non-aqueous phases may be accomplished by any suitable means, for example using a small scale device such as a separating funnel or

- 5 040373

Craig. It should be understood that the phases are usually kept to settle before separation. Settling can be carried out by gravity or preferably accelerated using additional equipment such as a centrifuge. Alternatively, the aqueous and non-aqueous phases may be separated using equipment that provides contact and phase separation, such as, for example, a centrifugal extractor, a pulse column, or a combined mixer-precipitator.

It should be understood that in order to extract or separate certain rare earth metals, multi-stage extraction and separation processes may be carried out. These may include several steps of extracting an acidic solution of the rare earth metal with the composition, or several steps of back-extraction of the non-aqueous phase with an aqueous acidic solution. The present invention requires fewer steps to separate the rare earth metals because the ionic liquid extractant provides separation factors and distribution factors that typically exceed those found in prior systems.

The term electron donor group (EDG) as used herein should be understood to mean any group having a pair of electrons available to form a coordination bond with an acceptor. In particular, an electron donating group as defined herein is to be understood to mean groups having an available electron pair capable of coordinating a rare earth metal to form a metal-ligand complex. In addition, it should be understood that EDGs typically have a single atom that is an electron donor for bond formation. However, in the alternative, the donor group may provide electrons for the formation of one or more bonds between atoms, i.e. EDG may be a ligand with a hapticity of 2 or more.

It should be understood that the arrangement of the EDG and the L ₂ connecting groups is such that the EDG and the central nitrogen atom are able to simultaneously coordinate the rare earth metal.

Preferably, when the metal simultaneously coordinates the nitrogen connecting L1 to each L ₂ and one of the EDGs, the ring formed by nitrogen, L ₂ , EDG and the metal is a 5- or 6-membered ring, preferably a 5-membered ring.

In preferred embodiments, [Y ⁺ ] is an acyclic cation selected from [-N(R ^a )(R ^b )(R ^c )] ⁺ , [-P(R ^a )(R ^b )(R ^c )] ⁺ and [-S(R ^a )(R ^b )] ⁺ , with each R ^a , R ^b and R ^c independently selected from optionally substituted C _1-30 alkyl, C _3-8 cycloalkyl and O _6-10 aryl groups.

According to other preferred embodiments, [Y ⁺ ] is a cyclic cation selected from

each R ^a , R ^b , R ^c , R ^d , R ^e and R ^f independently selected from hydrogen and optionally substituted C1-30αkyl, C3-8 cycloalkyl and O6-10 aryl groups, or any two of R ^a , R ^b , R ^c , R ^d , R ^e linked to adjacent carbon atoms form an optionally substituted methylene chain -(CH2)q- where q is from 3 to 6.

Accordingly, according to preferred embodiments, at least one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a C1-5 alkyl group substituted with -CO2R ^x , -OC(O)R ^x , -CS2R ^x , -SC(S)R ^x , -S(O)OR ^x , -OS(O)R ^x , -NR ^x C(O)NR ^y R ^z , -NR ^x C(O)OR ^y , -OC (O)NR ^y R ^z , -NR ^x C(S)OR ^y , -OC(S)NR ^y R ^z , -NR ^x C(S)SR ^y , -SC(S)NR ^y R ^z , -NR ^x C(S)NR ^y R ^z , -C(O)NR ^y R ^z , -C(S)NR ^y R ^z , wherein R ^x , R ^y and R ^z are independently selected from hydrogen or C _1-6 alkyl.

According to another preferred embodiment of the present invention, [Y ⁺ ] is a saturated heterocyclic cation selected from cyclic ammonium, 1,4

- 6 040373 diazabicyclo[2.2.2]octanium, morpholinium, cyclic phosphonium, piperazinium, piperidinium, quinuclidinium and cyclic sulfonium.

Preferably, [Y ⁺ ] is a saturated heterocyclic cation having the form

Preferably, at least one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a C1-3 alkyl group substituted with -CO2R ^x -C(O)NR ^y R ^z , each R ^x , R ^y and R ^z are independently selected from C3-6alkyl.

More preferably, at least one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a group selected from

and R ^y =R ^z , and each R ^x , R ^y and R ^z selected from C _3-6 alkyl, preferably C ₄ -alkyl, for example, i-Bu.

Even more preferably, at least one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a group selected from

wherein R ^y =R ^z , and wherein R ^y and R ^z are selected from C _3-6 alkyl, preferably C ₄ alkyl, eg iBu.

In preferred embodiments, one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a substituted C1-5 alkyl group and the others are R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is independently selected from H and unsubstituted C1-5 alkyl groups. Preferably the rest of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f are H.

Preferably, [Y ⁺ ] is a cyclic cation selected from

More preferably [Y ⁺ ] is a cyclic cation

While preferably R ^f represents a substituted C _1-5 alkyl group, and the rest

- 7 040373 of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f are independently selected from H and unsubstituted C _1-5 alkyl groups.

In preferred embodiments, L1 is a connecting group selected from C _1-10 alkanediyl and C _1-10 alkenediyl groups, more preferably selected from C _1-5 alkanediyl and C _2-5 alkenediyl groups, and most preferably selected from C _1-5 alkanediyl groups, for example a connecting group selected from -CH2-, -C2H4- and -C3H6-.

In preferred embodiments, each L2 is a connecting group independently selected from C _1-2 alkanediyl and C ₂ -alkenediyl groups, preferably selected from C _1-2 alkanediyl groups, eg independently selected from -CH2-, -C2H4-.

Each EDG may be any suitable electron donor group capable of coordinating with a rare earth metal to form a metal-ligand complex.

Preferably, each EDG is an electron donating group independently selected from -CO2R ^x , -OC(O)R ^x , -CS2R ^x , -SC(S)R ^x , -S(O)OR ^x , -OS(O)R ^x , -NR ^x C(O)NR ^y R ^z , -NR ^x C(O)OR ^y , -OC(O)NR ^y R ^z , -NR ^x C(S)OR ^y , -OC(S)NR ^y R ^z , -NR ^x C(S)SR ^y , -SC(S)NR ^y R ^z , -NR ^x C(S)NR ^y R ^z , -C(O)NR ^y R ^z , -C(S) NR ^y R ^z , wherein R ^x , R ^y and R ^z are independently selected from H or C1-6 alkyl. More preferably, each EDG is an electron donor group independently selected from -CO2R ^x , -C(O)NR ^y R ^z , with each R ^x , R ^y and R ^z independently selected from C3-6alkylα.

In preferred embodiments, each -L ₂ -EDG is an electron donor group independently selected from

and R ^y =R ^z , and each R ^x , R ^y and R ^z selected from C _3-6 alkyl, preferably C ₄ -alkyl, for example, i-Bu.

More preferably, each -L2-EDG is an electron donating group independently selected from

and R ^y =R ^z , and while R ^y and R ^z selected from C _3-6 alkyl, preferably C ₄ -alkyl, for example, iBu.

It should be understood that, as presented above, the extraction of rare earth metals provides a certain functionality of the cation of the ionic liquid. Thus, any suitable anionic species [X ^- ] can be used as part of the ionic liquid used in the method according to the present invention.

Preferably [X ^- ] is one or more anionic species selected from hydroxides, halides, perhalides, pseudohalides, sulfates, sulfites, sulfonates, sulfonimides, phosphates, phosphites, phosphonates, methides, borates, carboxylates, azolates, carbonates, carbamates, thiophosphates , thiocarboxylates, thiocarbamates, thiocarbonates, xanthates, thiosulfonates, thiosulphates, nitrate, nitrite, tetrafluoroborate, hexafluorophosphate, perchlorate, halometallates, amino acids, borates, polyfluoroalkoxyaluminates.

For example, [X ^- ] is preferably one or more anionic species selected from the following:

a) a halide anion selected from F ^- , Cl ^- , Br ^- , I ^- ;

b) perhalide anion selected from [I ₃ ] ^- , [I2Br] ^- , [IBr2] ^- , [Br3] ^- , [Br2C] ^- , [BrCl2] ^- , [ICl2] ^- , [I ₂ Cl] ^- , [Cl3] ^- ;

c) a pseudohalide anion selected from [N ₃ ] ^- , [NCS] ^- , [NCSe] ^- , [NCO] ^- , [CN] ^- ;

d) sulfate anion selected from [HSO ₄ ] ^- , [SO ₄ ] ^2- , [R2OSO2O] ^- ;

e) a sulfite anion selected from [HSO3] ^- , [SO3] ² , [R ² OSO2] ^- ;

f) a sulfonate anion selected from [R1SCO2O] ^- ;

g) a sulfonimide anion selected from [(R1SO ₂ ) ₂ N] ^- ;

h) a phosphate anion selected from [H2PO4] ^- , [HPO4] ^2- , [PO4] ^3- , [R2OPO3] ^2- , [(R ² O)2POJ ^- ;

i) a phosphite anion selected from [H2PO3] ^- , [HPO3] ^2- , [R ² OPO2] ^2- , [(R2O)2PO] ^- ;

j) a phosphonate anion selected from [R1PO3] ^2- , [R1P(O)(OR2)O] ^- ;

k) a methide anion selected from [(R1SO2) ₃ C] ^- ;

l) a borate anion selected from bisoxalatoborate, bismalonate borate, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, tetrakis(pentafluorophenyl)borate;

m) a carboxylate anion selected from [R2CO2] ^- ;

n) an azolate anion selected from 3,5-dinitro-1,2,4-triazolate, 4-nitro-1,2,3-triazolate, 2,4

- 8 040373 dinitroimidazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4-nitroimidazolate, tetrazolate;

o) a sulfur-containing anion selected from thiocarbonates (for example, [R ² OCS2] ^- , thiocarbamates (for example, [R ² 2NCS ₂ ] ^- ), thiocarboxylates (for example, [R1CS2] ^- ), thiophosphates (for example, [(R ² O )2PS2] ^- ), thiosulfonates (eg [RS(O)2S] ^- ), thiosulfates (eg [ROS(O) ₂ S] ^- );

p) nitrate ([NO ₃ ] ^- ) or nitrite ([NO ₂ ] ^- ) anion;

q) tetrafluoroborate ([BF4] ^- ), hexafluorophosphate ([PF6] ^- ), hexafluoroantimonate ([SbF6] ^- ) or perchlorate ([ClO4] ^- ) anion;

r) a carbonate anion selected from [CO ₃ ] ^2- , [HCO3] ^- , [R ² CO3] ^- ; preferably [MeCO ₃ ] ^- ;

s) polyfluoroalkoxyaluminate anions selected from [Al(OR ^F )4] ^- , RF being selected from C1-6 alkyl substituted with one or more fluoride groups;

where R ¹ and R ² are independently selected from the group consisting of C1-C1o-alkyl, C6-aryl, C1-C10alkyl(C6)aryl and C6-aryl(C1-C10)alkyl, each of which may be substituted with one or several groups selected as fluorine, chlorine, bromine, iodine, C1-C6alkoxy, C2-C12alkoxyalkoxy, C3-C8-cycloalkyl, C6-C10-aryl, C7-C10-alkaryl, C7-C10-aralkyl, -CN , -OH, -SH, -NO2, -CO2R ^x , -OC(O)R ^x , -C(O)R ^x , -C(S)R ^x , -CS2R ^x , -SC(S)R ^x , -S(O)(C1-C6)alkyl, -S(O)O(C1-C6)alkyl, -OS(O)(Cr C ₆ )alkyl, -S(C ₁ -C ₆ )alkyl, -SS (C ₁ -C ₆ )alkyl), -NR ^x C(O)NR ^y R ^z , -NR ^x C(O)OR ^y , -OC(O)NR ^y R ^z , -NR ^x C(S)OR ^y , -OC(S)NR ^y R ^z , -NR ^x C(S)SR ^y , -SC(S)NR ^y R ^z , -NR ^x C(S)NR ^y R ^z , -C(O)NR ^y R ^z , -C(S)NR ^y R ^z , -NR ^y R ^z , or a heterocyclic group, wherein R ^x , R ^y and R ^z are independently selected from hydrogen or C ₁ -C ₆ alkyl and R ¹ may also be fluorine, chlorine, bromine or iodine.

Although [X ^- ] may be any suitable anion, it is preferred that [X ^- ] is a non-coordinating anion. The term non-coordinating anion, which is used herein and is common in the field of ionic liquid chemistry and metal coordination compounds, is intended to describe an anion that does not coordinate or only weakly coordinates a metal atom or ion. As a rule, non-coordinating anions contain their charge distributed over several atoms in the molecule, which significantly limits their coordinating ability. This limits the effective interaction of the anion with the selective coordination of the [Cat ⁺ ] cation and the rare earth metal.

Thus, more preferably, [X ^- ] is one or more non-coordinating anionic species selected from the following anions: bistriflomide, triflate, tosylate, perchlorate, [Al(OC(CF ₃ ) ₃ ) ₄ ] ^- , tetrakis[3,5 -bis(trifluoromethyl)phenyl]borate, tetrakis(pentafluorophenyl)borate, tetrafluoroborate, hexafluoroantimonate and hexafluorophosphate; and preferably from bistriflomide and triflate anions.

According to some preferred embodiments, [Cat ⁺ ] is one or more ionic species having the structure:

.EDG

1-2

I

4ZΊ 1<

EDG EDG where [Z ⁺ ] is a group selected from ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, boronium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4diazabicyclo[2.2.2]octanium, diazabicycloundecenium, dithiazolium, furanium, guanidinium, imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, isooxazolium, oxothiazolium, phospholium, phosphonium, phthalazolium, piperazinium, piperidinium, piranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, quinazolidinium, quinoline, isoquinoline, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, isothiadiazolium, thiazinium, thiazolium, isothiazolium, thiophenium, thiuronium, triazinium, triazolium, isotriazolium and uronium.

It should be understood that the composition may contain an ionic liquid as defined above in combination with a diluent. Typically, a diluent may be used to reduce the viscosity of the composition when the ionic liquid has a high viscosity, which limits its practical use in liquid-liquid extraction. The diluent can also be used to reduce costs when the diluent is cheaper to produce than the ionic liquid. It should be understood that any diluent added to the composition must be sufficiently hydrophobic such that separation of the composition and the acidic solution of the rare earth metal into aqueous and non-aqueous phases is required. In some embodiments, the diluent may enhance the hydrophobicity of the composition.

Thus, according to preferred embodiments, the composition further

- 9 040373 contains a low-viscosity ionic liquid. The term low-viscosity ionic liquid should be understood to mean that this ionic liquid has a lower viscosity than the above-described ionic liquid as an extractant. As mentioned above, it should be understood that the low viscosity ionic liquid must be sufficiently hydrophobic such that separation of the composition and the acidic solution of the rare earth metal into aqueous and non-aqueous phases is to be expected. In addition, it should be understood that the cation and/or anion of the low viscosity ionic liquid can provide hydrophobicity.

By using an ionic liquid as a diluent, the reduction in volatility and flammability provided by the ionic liquid as an extractant can be maintained, potentially making the rare earth extraction process safer and more environmentally friendly.

In preferred embodiments, the low viscosity ionic liquid cation is selected from the ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4-diazabicyclo[2.2.2]octanium, diazabicycloundecenium, dithiazolium, furanium, guanidinium, imidazolium groups. , indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, isooxazolium, oxothiazolium, phospholium, phosphonium, phthalazolium, piperazinium, piperidinium, piranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolinium, quinazolinium , isoquinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, isothiadiazolium, thiazinium, thiazolium, isothiazolium, thiophenium, thiuronium, triazinium, triazolium, isotriazolium and uronium.

Preferably, the low viscosity ionic liquid cation is selected from the phosphonium, imidazolium and ammonium groups.

According to some preferred embodiments, the low viscosity ionic liquid cation is selected from [N(R ³ )(R ⁴ )(R ⁵ )(R ⁶ )] ⁺ and [P(R ³ )(R ⁴ )(R ⁵ )(R ⁶ )] ⁺ , with each R ³ , R ⁴ , R ⁵ and R ⁶ independently selected from optionally substituted C ₁ . ₂₀ alkyl, O ₃ . ₈ cycloalkyl and C ₆ . ₁ aryl groups.

In more preferred embodiments, the low viscosity ionic liquid cation [P(R ³ )(R ⁴ )(R ⁵ )(R ⁶ )] ⁺ , wherein each R ³ , R ⁴ , R ⁵ is independently selected from C1.10αlkulα, preferably C2- 6 alkyl, and R ⁶ is selected from C4. ₂₀ alkyl, preferably C ₈ . ₁₄ alkyl. For example, the low viscosity ionic liquid cation can be selected from triethyloctylphosphonium ([P ₂₂₂ ( ₈ )] ⁺ ), tributyloctylphosphonium ([P444(8)] ⁺ ), trihexyloctylphosphonium ([P666( ₈ )]] ⁺ ), trihexyldecylphosphonium ([P ₆₆₆ ( ₁₀ )]] ⁺ ) and trihexyltetradecylphosphonium ([P666(14]]+).

In other more preferred embodiments, the low viscosity ionic liquid cation is [N(R ³ )(R ⁴ )(R ⁵ )(R ⁶ )] ⁺ , wherein R ³ , R ⁴ , R ⁵ are selected from C4.14αkyl, preferably C6 .10alkyl, and R ⁶ is selected from C1. ₄ alkyl, preferably C ₁ . ₂ alkyl. For example, the low viscosity ionic liquid cation may be selected from trioctylmethylammonium, tris(2-ethylhexyl)methylammonium, and tetrabutylammonium.

In other preferred embodiments, the low viscosity ionic liquid cation is selected from imidazolium cations substituted with one or more C1. ₂₀ alkyl, C ₃ . ₈ cycloalkyl and C ₆ . ₁₀ aryl groups, preferably two C ₁ . ₁₀ αalkyl groups, preferably one methyl group and one C ₁ . ₁₀ alkyl group. For example, the low viscosity ionic liquid cation may be selected from 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, and 1octyl-3-methylimidazolium.

It should be understood that any suitable anionic group can be used as the anion of the low viscosity ionic liquid. Preferably, the anion of the low viscosity ionic liquid is as described above with respect to the anionic group [X ^- ]. For example, it is most preferred that the low viscosity ionic liquid anion is a non-coordinating anion as described above. It should be understood that there may be an excess of anions from the low viscosity ionic liquid compared to the ionic liquid as the extractant. Thus, it is especially preferred that the anion of the low viscosity ionic liquid is a non-coordinating anion.

For this reason, it is preferred to limit the total amount of halide or pseudohalide anions in the composition. For example, in preferred embodiments, the composition contains less than 25% halide or pseudohalide anions, preferably less than 20%, more preferably less than 15%, most preferably less than 10%, such as less than 5%, based on total anion content. In some embodiments, the composition is substantially free of halide or pseudohalide anions.

Alternatively or in addition, the composition may further comprise one or more non-ionic liquid diluents. For example, in some preferred embodiments, the composition further comprises one or more organic solvents. It should be understood that suitable organic solvents should include hydrophobic and non-coordinating solvents. The term non-coordinating

- 10 040373 solvent, which is used in this document and is common in the field of metal coordination compounds, is intended to describe a solvent that does not coordinate or only weakly coordinate metal atoms or ions.

Suitable organic solvents include, but are not limited to, hydrocarbon solvents such as C ₁ . ₂₀ alkanes, alkenes or cycloalkanes, aromatic solvents such as toluene or benzene, C ₆₊ alcohols such as n-hexanol, ether solvents such as diethyl ether, dipropyl ether, dibutyl ether and methyl tert-butyl ether, or halogenated solvents such as carbon tetrachloride, tetrachloroethane, chloroform, dichloromethane, chlorobenzene or fluorobenzene. Preferably the organic solvent is a hydrocarbon solvent.

The ionic liquid may be present in the composition at any concentration suitable for the extraction of rare earth metals, and it should be understood that this concentration will vary depending on the particular application and pH. In particular, it should be understood that competitive separation is desirable for the separation of rare earth metals. For example, the concentration of the ionic liquid must be low enough to prevent extraction of all rare earth metals present. Thus, the concentration of the ionic liquid will generally depend on the concentration of rare earth metals to be extracted and the pH value at which the separation is performed. In some preferred embodiments, the ionic liquid is present in the composition at a concentration of at least 0.001M, preferably 0.005M to 0.01M.

In other embodiments, the composition may consist primarily of an ionic liquid.

It should be understood that the concentration of the ionic liquid in the composition may be varied to achieve a certain target viscosity of the composition. In addition, it should be understood that the nature of the low-viscosity ionic liquid or other diluent can be changed in order to obtain a certain level of viscosity.

According to preferred embodiments, the viscosity of the composition is in the range of 50 to 500 mPa-s at 298 K when the composition contains a solution of an ionic liquid in a low-viscosity ionic liquid. When the ionic liquid is in an organic solvent solution, it should be understood that the composition will likely have a lower viscosity, for example, less than 50 mPa-s. Viscosity can be measured by any suitable method; for example, viscosity can be measured using a rotational disk viscometer at variable temperature.

In some embodiments, an acidic solution can be obtained by leaching the rare earth metal from its source using an acid, such as a mineral acid such as hydrochloric, nitric, perchloric, or sulfuric acid, typically hydrochloric or nitric acid. Preferably, the source of the rare earth metal is a mineral or waste. However, it should be understood that the rare earth acid solution or mixture of rare earth metals can be obtained by any suitable method from any source of the rare earth metal.

The concentration of rare earth metals in the acidic solution is typically between 60 ppm and up to 2000 ppm However, it should be understood that any suitable concentration of rare earth metals in acidic solution may be used.

As a rule, rare earth metals are obtained from rare earth ores, which are mined and processed in a variety of ways, depending on the particular ore. Such methods are well known in the art. Typically, after mining, these methods may include steps such as grinding, calcination to remove carbonates, chemical treatment (eg, alkali/hydroxide treatment), and finally acid leaching to produce an aqueous acidic solution containing a mixture of rare earth metals.

Examples of rare earth minerals that are present in rare earth ores are eschinite, allanite, apatite, bastnäsite, brannerite, britholite, eudialyte, euxenite, fergusonite, gadolinite, kainite, loparite, monazite, parisite, perovskite, pyrochlore, xenotime, yttrocerite, huanhoite, zebaite, florensite, synhisite, samarskite and knopit.

Rare earth metals can also be obtained in increasing quantities from recycled waste. As the global demand for rare earths grows, it becomes more and more attractive to obtain rare earths from recycled waste, in particular in those countries where there are no minable deposits of rare earth ores. Rare earth waste can be obtained from a variety of sources, such as direct processing of rare earth scrap/remains from industrial waste, urban mining of end-of-life items containing rare earth metals, or mining of municipal and industrial waste containing rare earth metals from landfills. As rare earths are increasingly used in consumer products, the number of rare earths is also on the rise.

- 11 040373 metals that can be obtained from such waste.

Wastes that may contain rare earths are magnetic chips and discarded magnets, rare earth containing residues from metal production/processing (e.g. residues from smelters and electric arc furnaces or industrial residues such as phosphogypsum and red mud), phosphors such as as phosphors which contain fluorescent lamps, LEDs, liquid crystal display backlights, plasma screens and cathode ray tubes, permanent magnets (such as NdFeB) such as those used by automobiles, mobile phones, hard disk drives, computers and peripherals , electronic kitchen appliances, hand tools, electric shavers, industrial electric motors, electric bicycles, electric and hybrid car motors, wind turbines, nickel-metal hydride batteries such as those using rechargeable batteries and electric vehicles and hybrid automotive batteries, glass polishing powders, fluidized bed cracking catalysts and optical glass. The main sources of end-of-life products containing rare earth metals, in terms of value, are permanent magnets, nickel-metal hydride batteries and fluorescent lamps, and scrap in the form of waste magnetic chips.

Rare earth metals are usually extracted from waste products by mineral acid leaching, with optional further treatment to remove impurities such as transition metals. As a result, an acidic solution of rare earth metals is obtained, which can be used as a starting material for separation and purification of individual rare earth metals.

Thus, it is an advantage of the present invention that rare earth metals can be extracted with high selectivity and extractability directly from an acidic solution of rare earth metal, which can be conveniently obtained in an ore or waste extraction process.

According to a further aspect of the present invention, an ionic liquid ([Cat ⁺ ][X ^- ]) is provided substantially as described above herein.

According to a further aspect of the present invention, there is provided a composition substantially as described herein above.

In some preferred embodiments, the composition further comprises a rare earth metal. It should be understood that a composition containing a rare earth metal can itself be a valuable resource, and it is not always desirable to separate the rare earth metal, for example, by washing with an acid.

For example, a composition further containing a rare earth metal can be used to electrodeposit a rare earth metal or deposit one or more rare earth metals (eg, with oxalic acid).

The electrodeposition of rare earth metals from ionic liquids and the precipitation of rare earth metals from solution are well known in the art and may be carried out in any suitable manner as will be understood by one skilled in the art.

According to a further aspect of the present invention, there is provided the use of a composition further containing a rare earth metal for electrodeposition of a rare earth metal.

According to a further aspect of the present invention, there is provided the use of a composition further comprising a rare earth metal for depositing a rare earth metal.

According to a further aspect of the present invention, there is provided a method for producing an ionic liquid according to claim 59, said method comprising the reaction /and .EDG

NH ₂ ^with LG where LG is the leaving group.

The term leaving group, as used herein, should be understood to mean a group that can be removed from a molecule by reaction with a nucleophilic center; in particular, the leaving group leaves with a pair of electrons upon heterolytic bond cleavage. The leaving group is typically one that is capable of stabilizing the extra electron density that results from heterolytic bond cleavage. Such groups are well known in the field of chemistry.

It should be understood that the [Z] group may be any group that is capable of replacing a leaving group to form the [Z ⁺ ] cation as defined above herein.

It should be understood that the leaving group as defined herein is such that the primary amine linked via L1 to [Z] can replace the leaving group to form a bond between the nitrogen atom and the L2 group, and such that the [Z] may replace the leaving group to form a bond between [Z] and the L ₂ group.

- 12 040373

The leaving group may, for example, be a group selected from dinitrogen, dialkyl ethers, perfluoroalkylsulfonates such as triflate, tosylate or mesylate, halogens such as Cl, Br and I, water, alcohols, nitrate, phosphate, thioethers and amines. Preferably the LG leaving group is selected from halogens, more preferably the LG leaving group is Cl.

Such substitution reactions, which are described herein, are well known in the art and can be carried out without difficulty by a person skilled in the art.

By producing an ionic liquid by this method, an ionic liquid having preferential extraction properties of a rare earth metal can be conveniently synthesized in one step, which reduces the increased cost associated with multi-step synthesis.

According to a further aspect of the present invention, the use of an ionic liquid or composition further containing a rare earth metal as described herein is provided for the extraction of rare earth metals. Preferably, the ionic liquid or composition is used to preferentially extract the first rare earth metal from a solution that contains the first and second rare earth metals.

Hereinafter, the present invention will be illustrated by means of the following examples with reference to the figures below, wherein:

in fig. 1 is a graph illustrating partition coefficients for extraction of a number of rare earth metals according to an embodiment of the present invention; and in FIG. 2 shows the crystal structure of the [MAIL] ⁺ cation in coordination with Nd after extraction from an acidic (HCl) solution containing NdCl ₃ -6H ₂ O.

Examples

Example 1. Synthesis of an ionic liquid.

General procedure for synthesizing an ionic liquid according to embodiments of the present invention.

The reaction mixture containing 3 mol of N,N-dialkyl-2-chloroacetamide and a substrate having the structure H2N-L ₁ -[Z] was stirred in a halogenated solvent (eg CHCl ₃ , CH ₂ Cl ₂ etc.) or aromatic solvent (eg, toluene, xylene, etc.) at a temperature of 60 to 70°C for 7 to 15 days. After cooling, the solid was filtered off and the organic phase was repeatedly washed with a solution of 0.1-0.2 M HCl until the aqueous phase showed moderate acidity (pH>2). The organic phase was then washed 2-3 times with a 0.1 M Na ₂ CO ₃ solution and finally washed with deionized water until the aqueous phase showed a neutral pH. The solvent was removed under high vacuum to give an ionic liquid (with chloride anion) as a highly viscous liquid. This ionic liquid can be used as it is, or the chloride anion can be replaced with other anions (such as, for example, bistriflomide, triflate, hexafluorophosphate, etc.) using conventional substitution methods, for example, by reacting an alkali metal salt containing the desired anion , with an ionic liquid in an organic solvent.

Synthesis of an ionic liquid with an imidazolium cation

[MA11/]SG

1-(3-Aminenopropyl)imidazole (0.05 mol) was added to N,N-diisobutyl-2-chloroacetamide (0.15 mol) in a 500 ml three neck round bottom flask. Triethylamine (0.11 mol) was then added along with chloroform (200 ml). The reaction mixture was stirred for 6 hours at room temperature and then stirred at 60 to 70°C for 7 days. The reaction mixture was then cooled and, after filtration, washed successively with solutions of 0.1 M HCl, 0.1 M Na ₂ CO ₃ and deionized water (as described in the general procedure). The solvent was removed from the neutralized organic phase at a pressure of 8 mbar (6 mm Hg) and finally at a temperature of 60° C. and a pressure of 0.067 mbar (0.05 mm Hg). [MAIL ⁺ ]CΓ ionic liquid was obtained in the form of a highly viscous yellow liquid.

The ionic liquid [MAIL ⁺ ]Cl- (0.025 mol) was dissolved in chloroform and lithium bis(trifluoromethane)sulfonamide (LiNTf2) (0.03 mol) was added. The reaction mixture was stirred for 1 hour and then the organic phase was washed several times with deionized water. Finally, the solvent was removed from the organic phase in vacuo (0.13 mbar, 0.1 mmHg) at 65° C. to give the bistrilimide anion-containing ionic liquid [MAIL ⁺ ][NTf2-].

Example 2 Liquid-liquid extraction of rare earth metals using [MAIL ⁺ ][NTf ₂ -].

- 13 040373

General extraction procedure for rare earth metals.

Equal volumes (from 2 to 5 ml) of the extractant in the form of an ionic liquid ([MAIL ⁺ ][NTf2 ^- ] in [P666( ₁₄ ) ⁺ ] [NTf ₂ ^- ]) and an acidic aqueous stock solution containing rare earth metals in HCl were shaken until equilibrium is reached for 15-30 minutes, using a shaker that simulates the movement of the wrist. The phases were centrifuged and the aqueous phase was analyzed for rare earths by inductively coupled plasma optical emission spectroscopy (ICP-OES), although it should be understood that any suitable analysis method could be used. The content of rare earth metals extracted into the organic phase of the ionic liquid was determined by mass balance using OES-ICP measurements.

The distribution coefficient of an individual rare earth metal was determined as the ratio of its concentration in the ionic liquid phase and its concentration in the aqueous phase (raffinate). DM=[M] _IL /[M] _Aq where IL is the ionic liquid phase and Aq is the aqueous phase (raffinate).

The partition factor (SF) for an individual pair of rare earth metals is the ratio of the partition coefficient of the first rare earth metal and the partition coefficient of the second rare earth metal. For example, the separation factor of dysprosium with respect to neodymium is D _Dy /D _Nd . It should be understood that separation factors estimated from independently derived partition factors are lower than the actual separation factors obtained during the separation of mixtures of rare earth metals in the process of competitive separation (see examples below).

Partition coefficients of individual rare earth metals were obtained by separate extraction according to the general procedure above using 0.0075 M [MAIL ⁺ ][NTf2 ^- ] in [P666( ₁₄ ) ⁺ ][NTf ₂ ^- ] and hydrochloric acid solution 200 mg/l (h ./million) chloride of the corresponding rare earth metal (where 200 hours/million means the concentration of the solution based on the elemental metal). In FIG. 1 is a plot of distribution coefficients for each rare earth metal versus pH, showing that the ionic liquid of the present invention can be used to extract rare earth metals over a pH range.

Separation of Dy and Nd.

An aqueous HCl solution containing DyCl ₃ -6H ₂ O (60 mg/l (ppm) Dy) and NdCl ₃ -6H ₂ O (1400 mg/l (ppm) Nd) at pH 3 was extracted ionic liquid extractant (0.005 M [MAIL ⁺ ][NTf2 ^- ] in [P666( ₁₄ ) ⁺ ][NTf2 ^- ]) according to the general procedure above. As a result of a single contact (extraction), DDy=13.45, D _Nd =0.0124, SF _Dy - _Nd =1085 were obtained.

This split ratio (1085) is significantly higher than the split ratios obtained with Dy/Nd separation by prior art systems shown in Table 1 (maximum ratio 239).

Separation of Eu and La.

An aqueous HCl solution containing EuCl ₃ -6H ₂ O (65 mg/l (ppm) Eu) and LaCl ₃ -7H ₂ O (470 mg/l (ppm) La) at pH 3 was extracted ionic liquid extractant (0.005 M [MAIL ⁺ ][NTf2 ^- ] in [P666( ₁₄ ) ⁺ ][NTf2 ^- ]) according to the general procedure above. As a result of a single contact (extraction) we got DEu=9.3,

DLa=0.044, SFEu-La=211.

Separation of Tb and Ce.

An aqueous solution of HCl containing TbCl ₃ -6H ₂ O (530 mg/l (ppm) Tb) and CeCl ₃ -6H ₂ O (950 mg/l (ppm) Ce) at pH 3 was extracted with an extractant , which is an ionic liquid (0.0075 M [MAIL ⁺ ][NTf2 ^- ] in [P666( ₁₄ ) ⁺ ][NTf2 ^- ]), according to the general procedure above. As a result of a single contact (extraction), DTb=11.2, DCe=0.068, SF _Tb - _Ce =162 were obtained.

Example 3 Purification of rare earth metals from [MAIL ⁺ ] [NTf ₂ ^- ].

At pH 3, Dy(III) (200 ppm) was purified from the organic phase containing [MAIL ⁺ ][NTf2 ^- ] in [P666( ₁₄ ) ⁺ ][NTf ₂ ^- ] (0.005 M) by performing two successive contact. The organic phase was contacted with an equal volume of aqueous HCl (0.2 M) and shaken to equilibrium for 15-30 minutes using a shaker simulating a wrist movement. In the first contact, 140 ppm was purified. Dy(III), and in the second contact was purified 55 ppm. Dy(III).

Similarly, from observing the distribution coefficients in FIG. 1 it is clear that for heavy rare earth metals such as Tm, Yb and Lu, the distribution coefficients decrease significantly with increasing acidity. Thus, the authors also suggest that heavy rare earth metals can be purified from the ionic liquid according to the present invention at relatively high pH values.

The above examples show that a significant increase in separation ratios in rare earth base pairs can be obtained by using the ionic liquid of the present invention (e.g., Nd/Dy: Nd-Dy magnet, Eu/La: white lamp phosphor, Tb/Ce: phosphor green lamp). In addition, rare earth metals may be advantageous

-

Claims (22)

significantly free of ionic liquid at relatively high pH compared to prior art systems. Without intending to be bound by any particular theory, the authors believe that heavy rare earth metals exhibit a more pronounced increase in distribution coefficients than light rare earth metals, as a result of increased formation of the more hydrophobic doubly coordinated rare earth metal particle M-([MAIL ⁺ ][NTf2']) 2 compared to the singly coordinated particle M-([MAIL ⁺ ][NTf2']). The authors believe that the more hydrophobic particle will be more easily extracted into the organic phase during the separation process, resulting in increased partition coefficients. NMR, IR spectroscopy, and mass spectrometry studies have shown that doubly coordinated species are present to a greater extent in Lu and ionic liquid solutions than in La and ionic liquid solutions, demonstrating the differentiation between heavy and light rare earth metals achieved by ionic liquid according to the present invention. In addition, the optimized geometry of the LaCl ₃ -([MAIL ⁺ ][Cl'])2 and LuCl ₃ -([MAIL ⁺ ][Cl'])2 complexes shows that the distance between the tertiary central nitrogen atom of the ionic liquid cation and the metal atom significantly greater in the case of La (~2.9 A, no bond) than in the case of Lu (~2.6 A, presence of bond), which also confirms the weakened binding of the ionic liquid in the case of light rare earth metals. At the same time, the electron donor groups, in this case the amide groups attached to the nitrogen atom, bind to the metal in a very similar way in both cases. This result indicates that the ionic liquid cation core containing a donor tertiary nitrogen atom is important for the resulting differentiation between heavy and light rare earth metals and the resulting improved selectivity. CLAIM 1. A method for extracting a rare earth metal from a mixture of one or more rare earth metals, the above method comprising contacting an acidic solution of a rare earth metal with a composition that contains an ionic liquid to form an aqueous phase and a non-aqueous phase into which the rare earth metal is selectively extracted, wherein the ionic the liquid has the formula [Cat ⁺ ][X ^- ], in which [Cat ⁺ ] is a cationic particle having the structure: I N l ₂ l ₂ I I EDG EDG where [Y ⁺ ] contains a group selected from ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4diazabicyclo[2.2.2]octanium, diazabicycloundecenium, dithiazolium, furanium, guanidinium, imidazolium groups , indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, isooxazolium, oxothiazolium, phospholium, phosphonium, phthalazolium, piperazinium, piperidinium, piranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolinium, quinazolinium , isoquinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, isothiadiazolium, thiazinium, thiazolium, isothiazolium, thiophenium, thiuronium, triazinium, triazolium, isotriazolium and uronium; each EDG is C(O)NR ^y R ^z , with R ^y and R ^z independently selected from H or C1_6 alkyl; And L ₁ is a connecting group selected from C _1-10 alkanediyl and C ₂ _ ₁₀ alkenediyl groups; each L2 is a connecting group independently selected from C ₁ -6alkanediyl and C ₂ -alkenediyl groups; And [X ^- ] represents one or more anionic species selected from hydroxides, halides, perhalides, pseudohalides, sulfates, sulfites, sulfonates, sulfonimides, phosphates, phosphites, phosphonates, methides, borates, carboxylates, azolates, carbonates, carbamates, thiophosphates, thiocarboxylates, thiocarbamates, thiocarbonates, xanthates, thiosulfonates, thiosulphates, nitrate, nitrite, tetrafluoroborate, hexafluorophosphate, perchlorate, halometallates, amino acids, borates, polyfluoroalkoxyaluminates. 2. The method of claim 1, wherein the method comprises recovering the rare earth metal from the non-aqueous phase, preferably by washing with an acidic wash solution, preferably an aqueous hydrochloric acid solution or a nitric acid solution, wherein the acidic wash solution preferably has a pH of between 0 to 1. - 15 040373 3. A method according to any one of claims 1 or 2, wherein the method comprises extracting a rare earth metal from a mixture of two or more rare earth metals. 4. The method according to any one of claims 1 to 3, wherein the acidic solution contains the first and second rare earth metal, and the method includes: (a) preferentially isolating the first rare earth metal into the non-aqueous phase and preferentially separating the non-aqueous phase from the acidic solution; and (b) contacting an acidic solution depleted of the first rare earth metal with a composition that contains the ionic liquid and optionally recovering the second rare earth metal therefrom; wherein preferably the first rare earth metal is recovered from the non-aqueous phase in step (a), and the aforementioned non-aqueous phase is returned and used as the composition in step (b). 5. The method according to claim 4, wherein the first rare earth metal is dysprosium and the second rare earth metal is neodymium, or wherein the first rare earth metal is lanthanum and the second rare earth metal is europium; and/or wherein the acidic solution has a pH value of less than 3.5 in step (a) and the acidic solution has a pH value of more than 3.5 in step (b). 6. The method according to any one of claims 1 to 5, wherein the acidic solution from which the rare earth metal is extracted has a pH value of 2 to 4, and/or wherein the composition is aged before contacting the composition with the acidic rare earth metal solution. until equilibrium is reached with an acidic solution having the same pH value as an acidic solution of a rare earth metal. 7. The method according to any one of claims 1 to 6, wherein the composition is added to the acidic solution in a volume ratio of 0.5:1 to 2:1, preferably 0.7:1 to 1.5:1, preferably 0 .8:1 to 1.2:1, preferably 1:1. 8. A method according to any one of claims 1 to 7, wherein the method comprises contacting an acidic solution of the rare earth metal and the composition for 10 to 40 minutes, preferably 15 to 30 minutes, and/or the method comprising contacting and physically agitating acid solution of rare earth metal and composition. 9. The method according to any one of claims 1 to 8, wherein when the metal simultaneously coordinates the nitrogen connecting L1 to each L2 and one of the EDGs, the ring formed by nitrogen, L ₂ , EDG and the metal is a 5- or 6- a membered ring, preferably a 5-membered ring. 10. The method according to any one of claims 1 to 9, wherein [Y ⁺ ] is an acyclic cation selected from [-N(R ^a )(R ^b )(R ^c )] ⁺ , [-P(R ^a ) (R ^b )(R ^c )] ⁺ and [-S(R ^a )(R ^b )] ⁺ , with each R ^a , R ^b and R ^c independently selected from C _1-30 alkyl, C _3-8 cycloalkyl and C _6-10 aryl groups; or a cyclic cation selected from wherein each R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is independently selected from hydrogen and C1-30 alkyl, C3-8 cycloalkyl and C6-10 aryl groups, or any two of R ^a , R ^b , R ^c , R ^d , R ^e associated with adjacent carbon atoms form a methylene chain -(CH2)q-, where q is from 3 to 6; or a saturated heterocyclic cation selected from cyclic ammonium, 1,4-diazabicyclo[2.2.2]octanium, morpholinium, cyclic phosphonium, piperazinium, piperidinium, quinuclidinium and cyclic sulfonium, with [Y ⁺ ] being preferably a saturated heterocyclic cation having the formula - 16 040373 keel and C _6-10 aryl groups, or any two of R ^a , R ^b , R ^c , R ^d , R ^e linked to adjacent carbons form a methylene chain -(CH ₂ )q- where q is from 3 until 6; wherein preferably at least one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a C1-5 alkyl group substituted with -CO2R ^x , -OC(O)R ^x , -CS2R ^x , -SC (S)R ^x , -S(O)OR ^x , -OS(O)R ^x , -NR ^x C(O)NR ^y R ^z , -NR ^x C(O)OR ^y , -OC(O)NR ^y R ^z , -NR ^x C(S)OR ^y , -OC(S)NR ^y R ^z , -NR ^x C(S)SR ^y , -SC(S)NR ^y R ^z , -NR ^x C(S )NR ^y R ^z , -C(O)NR ^y R ^z , -C(S)NR ^y R ^z , wherein R ^x , R ^y and R ^z are independently selected from hydrogen or C 1-6 alkyl; preferably at least one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a C1-3 alkyl group substituted with -CO2R ^x , -C(O)NR ^y R ^z , each R ^x R ^y and R ^z are independently selected from C3-6alkyl; more preferably at least one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a group selected from most preferably and R ^y =R ^z , and each R ^x R ^y and R ^z selected from C _3-6 alkyl, preferably C ₄ -alkyl, preferably i-Bu. 11. The method of claim 10 wherein one of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f is a C1-5 alkyl group substituted with -CO2R ^x or -C(O)NR ^y R ^z , wherein R ^x , R ^y and R ^z are each independently selected from C3-6 alkyl and the remainder of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f are independently selected from H and unsubstituted C _1-5 alkyl groups , and preferably the rest of R ^a , R ^b , R ^c , R ^d , R ^e and R ^f are H. wherein preferably R ^f is a C1-5 alkyl group substituted with -CO2 R ^x or -C(O)NR ^y R ^z , wherein R ^x , R ^y and R ^z are each independently selected from C3-6 alkyl and the remainder from R ^a , R ^b , R ^c , R ^d , R ^e and R ^f are independently selected from H and unsubstituted C _1-5 alkyl groups. 13. The method according to any one of claims 1-12, wherein L1 is a connecting group selected from C _1-5 alkanediyl and C _2-5 alkenediyl groups, preferably C _1-5 alkanediyl groups, preferably a connecting group selected from - CH ₂ -, -C ₂ H ₄ - and -C ₃ H ₆ -. 14. The method according to any one of claims 1 to 13, wherein each L2 is a connecting group independently selected from C _1-2 alkanediyl groups, preferably a connecting group independently selected from -CH ₂ - and -C ₂ H ₄ -. - 17 040373 15. The method according to any one of claims 1 to 14, wherein each R ^y and R ^z are independently selected from C _3-6 alkyl, preferably each -L2-EDG is an electron donor group independently selected from wherein R ^y =R ^z , and wherein each R ^y and R ^z is selected from C _3-6 alkyl, preferably C ₄ alkyl, preferably i-Bu. 16. The method according to any one of claims 1 to 15, wherein [X ^- ] is one or more anionic species selected from the following: a) a halide anion selected from F ^- , Cl ^- , Br ^- , I ^- ; b) perhalide anion selected from [I ₃ ] ^- , [I2Br] ^- , [IBr2] ^- , [Br3] ^- , [Br2C] ^- , [BrCl2] ^- , [ICl2] ^- , [I ₂ Cl] ^- , [Cl3] ^- ; c) a pseudohalide anion selected from [N ₃ ] ^- , [NCS] ^- , [NCSe] ^- , [NCO] ^- , [CN] ^- ; d) sulfate anion selected from [HSO ₄ ] ^- , [SO ₄ ] ^2- , [R2OSO2O] ^- ; e) a sulfite anion selected from [HSO ₃ ] ^- , [SO ₃ ] ² , [R2OSO2] ^- ; f sulfonate anion selected from [R1SCO2O] ^- ; g) a sulfonimide anion selected from [(R1SO ₂ ) ₂ N] ^- ; h) a phosphate anion selected from [H2PO4] ^- , [HPO4] ^2- , [PO4] ^3- , [R2OPO3] ^2- , [(R ² O)2PO2] ^- ; i) a phosphite anion selected from [H ₂ PO ₃ ] ^- , [HPO3] ^2- , [R2OPO2] ^2- , [(R2O) ₂ PO] ^- ; j) a phosphonate anion selected from [R1PO ₃ ] ^2- , [R1P(O)(OR2)O] ^- ; k) a methide anion selected from [(R1SO ₂ ) ₃ C] ^- ; l) a borate anion selected from bisoxalatoborate, bismalonate borate, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, tetrakis(pentafluorophenyl)borate; m) a carboxylate anion selected from [R2CO2] ^- ; n) an azolate anion selected from 3,5-dinitro-1,2,4-triazolate, 4-nitro-1,2,3-triazolate, 2,4-dinitroimidazolate, 4,5-dinitroimidazolate, 4,5-dicyanoimidazolate, 4 -nitroimidazolate, tetrazolate; o) a sulfur-containing anion selected from thiocarbonates (eg [R2OCS2] ^- , thiocarbamates (eg [R ² 2NCS2] ^- X thiocarboxylates (eg [R1CS2] ^- ), thiophosphates (eg [(R ² O)2PS ₂ ] ^- X thiosulfonates (eg [RS(O)2S] ^- ), thiosulphates (eg [ROS(O)2S] ^- ); p) nitrate ([NO ₃ ] ^- ) or nitrite ([NO2] ^- ) anion; q) tetrafluoroborate ([BF4] ^- ), hexafluorophosphate ([PF6] ^- ), hexafluoroantimonate ([SbF6] ^- ) or perchlorate ([ClO4] ^- ) anion; r) a carbonate anion selected from [CO ₃ ] ^2- , [HCO3] ^- , [R ² CO3] ^- ; preferably [MeCO ₃ ] ^- ; s) polyfluoroalkoxyaluminate anions selected from [Al(OR ^F )4] ^- , R ^F being selected from C1-6 alkyl substituted with one or more fluoride groups; where R ¹ and R ² are independently selected from the group consisting of C1-C10 alkyl, C6 aryl, C1-C10 alkyl(C6) aryl and C6 aryl(C1-C10) alkyl, each of which may be substituted with one or several groups selected as fluorine, chlorine, bromine, iodine, C1-C6-alkoxy, C2-C12alkoxyalkoxy, C3-C8-cycloalkyl, C6-C10-aryl, C7-C10-alkaryl, C7-C10-aralkyl, -CN, -OH, -SH, -NO2, -CO2R ^x , -OC(O)R ^x , -C(O)R ^x , -C(S)R ^x , -CS2R ^x , -SC(S)R ^x , -S(O)(C1-C6)alkyl, -S(O)O(C1-C6)alkyl, -OS(O)(C1C6)alkyl, -S(C1-C6)alkyl, -SS(C1 -C6)alkyl), -NR ^x C(O)NR ^y R ^z , -NR ^x C(O)OR ^y , -OC(O)NR ^y R ^z , -NR ^x C(S)OR ^y , -OC (S)NR ^y R ^z , -NR ^x C(S)SR ^y , -SC(S)NR ^y R ^z , -NR ^x C(S)NR ^y R ^z , -C(O)NR ^y R ^z , -C(S)NR ^y R ^z , -NR ^y R ^z , or a heterocyclic group, wherein R ^x , R ^y and R ^z are independently selected from hydrogen or C1-C ₆ alkyl, and R ¹ may also be fluorine, chlorine, bromine or iodine; wherein [X ^- ] is preferably one or more anionic species selected from the following anions: bistriflomide, triflate, tosylate, perchlorate, [Al(OC(CF ₃ ) ₃ ) ₄ ] ^- , tetrakis[3,5bis(trifluoromethyl)phenyl ]borate, tetrakis(pentafluorophenyl)borate, tetrafluoroborate, hexafluoroantimonate and hexafluorophosphate; and preferably from bistriflomide and triflate anions. 17. The method according to any one of claims 1 to 16, wherein [Cat ⁺ ] is one or more ionic species having the structure: - 18 040373 where [Z ⁺ ] is a group selected from ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnoline, diazabicyclodecenium, diazabicyclononenium, 1,4diazabicyclo[2.2.2]octanium, diazabicycloundecenium, dithiazolium, furanium, guanidinium groups , imidazolium, indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, isooxazolium, oxothiazolium, phospholium, phosphonium, phthalazolium, piperazinium, piperidinium, piranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, quinine , quinoline, isoquinoline, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, isothiadiazolium, thiazinium, thiazolium, isothiazolium, thiophenium, thiuronium, triazinium, triazolium, isotriazolium and uronium. 18. The method according to any one of paragraphs.1-17, in which the composition further comprises a low-viscosity ionic liquid; more preferably, the cation of the low-viscosity ionic liquid is selected from the groups of ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, boronium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4-diazabicyclo[2.2.2]octanium, diazabicycloundecenium, dithiazolium, furanium, guanidinium, imidazolium , indolinium, indolium, morpholine, oxaborolium, oxaphospholium, oxazinium, oxazolium, isooxazolium, oxothiazolium, phospholium, phosphonium, phthalazolium, piperazinium, piperidinium, piranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolium, quinazolinium, quinazolinium , quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, isothiadiazolium, thiazinium, thiazolium, isothiazolium, thiophenium, thiuronium, triazinium, triazolium, isotriazolium and uronium; preferably phosphonium, imidazolium and ammonium groups, preferably the low viscosity ionic liquid cation is selected from [N(R ³ )(R ⁴ )(R ⁵ )(R ⁶ )] ⁺ and [P(R ³ )(R ⁴ )(R ⁵ )(R ⁶ )] ⁺ , with each R ³ , R ⁴ , R ⁵ and R ⁶ independently selected from C1.20 alkyl, C3_8 cycloalkyl and C6.1o aryl groups; preferably [P(R ³ )(R ⁴ )(R ⁵ )(R ⁶ )] ⁺ , wherein each R ³ , R ⁴ , R ⁵ is independently selected from Cl.loalkulα, preferably _C2-6 alkyl, and R ⁶ is selected from _C4 . ₂ oalkyl, preferably C ₈ . ₁₄ alkyl or Cl. ₄ alkylα, preferably C ₁ . ₂ alkyl; or the low viscosity ionic liquid cation is selected from imidazolium cations substituted with one or more C ₁ . ₂₀ alkyl, C ₃ . ₈ cycloalkyl and C ₆ . ₁₀ aryl groups, preferably two C ₁ . ₁ oαalkyl groups. 19. The method according to item 18, in which the anion of low-viscosity ionic liquid is defined in item 16; and/or the composition contains less than 25% halide or pseudohalide anions relative to the total anion content; and/or wherein the composition further comprises one or more organic solvents. 20. The method according to claim 18 or 19, wherein the ionic liquid is present in the composition at a concentration of at least 0.001 M, preferably 0.005 M to 0.01 M, preferably 0.0075 M. 21. The method according to any one of claims 1 to 20, wherein the acidic solution can be obtained by leaching the rare earth metal from its source using an acid, preferably the source of the rare earth metal is a mineral or waste. 22. Ionic liquid having the formula: in which [Cat ⁺ ] is a cationic particle having the structure: /[ΥΊ 1' N. l ₂ l ₂ I I EDG EDG where [Y ⁺ ] contains a group selected from ammonium, benzimidazolium, benzofuranium, benzothiophenium, benzotriazolium, borolium, cinnolinium, diazabicyclodecenium, diazabicyclononenium, 1,4diazabicyclo[2.2.2]octanium, diazabicycloundecenium, dithiazolium, furanium, guanidinium, imidazolium groups , indazolium, indolinium, indolium, morpholinium, oxaborolium, oxaphospholium, oxazinium, oxazolium, isooxazolium, oxothiazolium, phospholium, phosphonium, phthalazolium, piperazinium, piperidinium, piranium, pyrazinium, pyrazolium, pyridazinium, pyridinium, pyrimidinium, pyrrolidinium, pyrrolinium, quinazolinium , isoquinolinium, quinoxalinium, quinuclidinium, selenazolium, sulfonium, tetrazolium, thiadiazolium, isothiadiazolium, thiazinium, thiazolium, isothiazolium, thiophenium, thiuronium, triazinium, triazolium, isotriazolium and uronium; each EDG is C(O)NR ^y R ^z , with R ^y and R ^z independently selected from H or C ₁ . ₆ alkyl; And L1 is a connecting group selected from C ₁ . ₁₀ alkanediyl and C ₂ . ₁₀ alkenediyl groups; each L2 is a connecting group independently selected from C ₁ . ₂ alkanediyl and C ₂ -alkenediyl groups; And [X ^- ] is an anionic species. 23. A composition comprising an ionic liquid according to claim 22 and a low viscosity ionic liquid. -