USE OF LIPOPHILIC DERIVATIVES OF AMINOPOLYCARBOXYLIC ACIDS FOR THE EXTRACTION OF RARE EARTHS FROM AN ACIDIC AQUEOUS SOLUTION

Abstract

A lipophilic derivative of an aminopolycarboxylic acid may be used as an extractant to extract at least one rare earth from an acidic aqueous solution. Such a lipophilic derivative may be applied to the production of rare earths from concentrates derived from urban ores and, in particular, from concentrates from waste electrical and electronic equipment such as used or discarded NdFeB permanent magnets. Such a lipophilic derivative may be used in producing rare earths from concentrates derived from natural ores or from concentrates derived from residues of natural ores.

Claims

1. A method of extract at least one rare earth from an acidic aqueous solution, the method comprising: contacting (i) a first acidic aqueous solution (A1), comprising a rare earth metal, and (ii) an aminopolycarboxylic acid derivative, having formula (I) or (II): ##STR00003## wherein m is 0 or 1, R.sup.1 and R.sup.2 together form a saturated or unsaturated C.sub.5 or C.sub.6 ring, optionally comprising a substituent comprising linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, and R.sup.8 are independently H, a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, X.sup.1 and X.sup.2, identical to each other, and X.sup.3 and X.sup.4, identical to each other but different from X.sup.1 and X.sup.2, are a hydroxy, a NHR, or NRR, with R and R being a linear or branched C.sub.6 to C.sub.20 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, X.sup.5 and X.sup.6, identical to each other, are NHR or NRR, with R and R being a linear or branched C.sub.6 to C.sub.20 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, R.sup.9 is a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, a monocyclic aryl group, or a CH.sub.2CONHR or CH.sub.2CONRR group with R and Rbeing a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, and R.sup.10 is a COOH group, thereby extracting from the first acidic aqueous solution (A1) at least one of the rare earth metal, wherein the aminopolycarboxylic acid derivative functions as an extractant.

2. The method of claim 1, wherein m is 0.

3. The method of claim 1, wherein R.sup.1 and R.sup.2 together form a cyclohexyl or phenyl group, optionally comprising a substituent comprising a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group.

4. The method of claim 1, wherein the aminopolycarboxylic acid derivative has formula (Ib) or (Ic): ##STR00004## wherein R.sup.3, R.sup.4, R.sup.11, R.sup.12, R.sup.13, and R.sup.14 are independently H, a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group.

5. The method of claim 4, wherein X.sup.1 and X.sup.2 are NHR or NRR with R and R being a linear or branched C.sub.6 to C.sub.20 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, and X.sup.3 and X.sup.4 are a hydroxyl group.

6. The method of claim 5, wherein X.sup.1 and X.sup.2 are NRR with R and R identically being a linear or branched C.sub.8 to C.sub.20 and, more preferably, C.sub.8 to C.sub.12 alkyl group, preferably n-octyl, 2-ethylhexyl, n-decyl or n-dodecyl.

7. The method of claim 4, wherein the aminopolycarboxylic acid derivative has formula (Ib), wherein R.sup.3, R.sup.4, R.sup.11, R.sup.12, R.sup.13 and R.sup.14 are H, X and X.sup.2 are N(C.sub.12H.sub.25).sub.2, and X.sup.3 and X.sup.4 are a hydroxyl group.

8. The method of claim 1, wherein the aqueous solution (A1) comprises an inorganic acid in a range of from 0.1 mmol/L to 0.01 mol/L.

9. The method of claim 4, wherein the contacting comprises contacting the first aqueous solution (A1) and an organic solution immiscible with water, the organic solution comprising the aminopolycarboxylic acid derivative in an organic solvent, then separating the first aqueous solution (A1) from the organic solution.

10. The method of claim 9, wherein the organic solution comprises the aminopolycarboxylic acid derivative in a range of from 0.01 to 0.1 mol/L.

11. The method of claim 9, further comprising: back-extracting the rare earth from a second organic solution obtained after the extracting, the back-extracting comprising contacting the second organic solution and a second aqueous solution (A2), then separating the second organic solution from the second aqueous solution (A2).

12. The method of claim 11, wherein the second aqueous solution (A2) comprises a complexing agent.

13. The method of claim 1, wherein the rare earth metal comprises neodymium, praseodymium, and/or dysprosium.

14. The method of claim 1, wherein the first aqueous solution (A1) is an acid medium comprising, dissolved therein, a urban ore concentrate.

15. The method of claim 1, wherein the first aqueous solution (A1) is an acid medium comprising, dissolved therein, neodymium-iron-boron permanent magnet parts.

16. The method of claim 5, wherein X.sup.1 and X.sup.2 are NRR with R and R identically being a linear or branched C.sub.8 to C.sub.12 alkyl group.

17. The method of claim 5, wherein X.sup.1 and X.sup.2 are NRR with R and R identically being n-octyl, 2-ethylhexyl, n-decyl or n-dodecyl.

18. The method of claim 4, wherein the aminopolycarboxylic acid derivative has formula (Ib), wherein R.sup.3, R.sup.4, R.sup.11, R.sup.12, R.sup.13, and R.sup.14 are H, X.sup.1 and X.sup.2 are N(C.sub.8H.sub.17).sub.2, and X.sup.3 and X.sup.4 are a hydroxyl group.

19. A composition, comprising: a first acidic aqueous solution (A1) comprising a rare earth metal; and an aminopolycarboxylic acid derivative, having formula (I) or (II): ##STR00005## wherein m is 0 or 1, R.sup.1 and R.sup.2 together form a saturated or unsaturated C.sub.5 or C.sub.6 ring, optionally comprising a substituent comprising a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, and R.sup.8 are independently H, a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, X.sup.1 and X.sup.2, identical to each other, and X.sup.3 and X.sup.4, identical to each other but different from X.sup.1 and X.sup.2, are a hydroxy, a NHR, or NRR, with R and R being a linear or branched C.sub.6 to C.sub.20 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, X.sup.5 and X.sup.6, identical to each other, are NHR or NRR, with R and R being a linear or branched C.sub.6 to C.sub.20 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, R.sup.9 is a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, a monocyclic aryl group, or a CH.sub.2CONHR or CH.sub.2CONRR group with R and R being a linear or branched C.sub.1 to C.sub.40 alkyl group, a C.sub.5 or C.sub.6 cycloalkyl group, or a monocyclic aryl group, and R.sup.10 is a COOH group.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0068] FIG. 1 illustrates the influence of the initial pH of aqueous hydrochloric solutions on the extraction coefficient of neodymium(II), denoted E %.sub.Nd, as observed in extraction tests carried out using a lipophilic derivative of EDTA as an extractant, in solution in different solvents.

[0069] FIG. 2 illustrates the influence of the initial pH of aqueous hydrochloric solutions on the distribution coefficient of neodymium(II), denoted D.sub.Nd, as observed in extraction tests carried out using a lipophilic derivative of EDTA as an extractant, in solution in different solvents.

[0070] FIG. 3 illustrates the influence of the initial pH of aqueous nitric solutions on the extraction coefficient of neodymium(II), denoted E %.sub.Nd, as observed in extraction tests carried out using a lipophilic derivative of EDTA as an extractant, in solution in different solvents.

[0071] FIG. 4 illustrates the distribution isotherm of neodymium(III) as obtained following tests aimed at extracting this element from an aqueous solution comprising 0.01 mol/L of either hydrochloric or nitric acid and using a lipophilic derivative of EDTA as an extractant, in solution in 1,3-diisopropylbenzene.

[0072] FIG. 5 illustrates the influence of the initial pH of aqueous hydrochloric solutions on the extraction coefficient, denoted E %.sub.M, of neodymium(III), praseodymium(III) and dysprosium(III) as observed in extraction tests carried out using a lipophilic derivative of EDTA as an extractant, in solution in 1,3-diisopropylbenzene.

[0073] FIG. 6 illustrates the influence of the initial pH of aqueous nitric solutions on the extraction coefficient, denoted E %.sub.M, of neodymium(III), praseodymium(III) and dysprosium(III) as observed in extraction tests carried out using a lipophilic derivative of EDTA as extractant, in solution in 1,3-diisopropylbenzene.

[0074] FIG. 7 illustrates the influence of the concentration, noted [RP2] and expressed in mol/L, of a first lipophilic derivative of CyDTA on the extraction coefficient, noted E %.sub.M, of neodymium(II), praseodymium(III) and dysprosium(III) as observed in tests aimed at extracting these three rare earths from an aqueous nitric solution using this derivative as an extractant, in solution in n-dodecane.

[0075] FIG. 8 illustrates the influence of the concentration, noted [RP4] and expressed in mol/L, of a second lipophilic derivative of CyDTA on the extraction coefficient, noted E %.sub.M, of neodymium(II), praseodymium(III) and dysprosium(III) as observed in tests aimed at extracting these three rare earths from an aqueous nitric solution using this derivative as an extractant, in solution in n-dodecane.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0076] The distribution coefficients, extraction coefficients, load capacities and separation factors reported in the following examples were determined in accordance with the conventions of the field of liquid-liquid extraction, namely that: [0077] the distribution coefficient between two phases, respectively organic and aqueous phases, of a metallic element M, noted D.sub.M and without unit, is determined by the following formula:

[00001]$D_M=\frac{{\left[M\right]}_{\mathrm{org},\mathrm{eq}}}{{\left[M\right]}_{\mathrm{aq},\mathrm{eq}}}$ [0078] wherein: [0079] [M].sub.org,eq is the concentration of M in the organic phase at equilibrium (in g/L or mol/L), and [0080] [M].sub.aq,eq is the concentration of M in the aqueous phase after extraction (in g/L or mol/L); [0081] the extraction coefficient of a metallic element M, noted E %.sub.M and without unit, is determined by the following formula:

[00002]$E{\%}_M=\frac{{\left[M\right]}_{\mathrm{org},\mathrm{eq}}}{{\left[M\right]}_{\mathrm{aq},\mathrm{init}}}$ [0082] wherein: [0083] [M].sub.org,eq has the same meaning as before (in g/L or mol/L), and [0084] [M].sub.aq,init is the initial concentration of M in the aqueous phase (in g/L or mol/L); [0085] the separation factor of a metallic element M1 with respect to a metallic element M2, noted FS.sub.M1/M2 and without unit, is determined by the following formula:

[00003]${\mathrm{FS}}_{M1/M2}=\frac{D_{M1}}{D_{M2}}$ [0086] wherein: [0087] D.sub.M1 is the distribution coefficient of M1, and [0088] D.sub.M2 is the distribution coefficient of M2.

Example 1: Use of a Lipophilic Derivative of EDTA

[0089] The liquid-liquid extraction tests reported below were carried out using as extractant a lipophilic derivative of EDTA, namely the derivative of particular formula (Ia) wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 represent a hydrogen atom, X.sup.1 and X.sup.2 represent a N(C.sub.10H.sub.21).sub.2 group while X.sup.3 and X.sup.4 represent an OH group.

1Synthesis of the Derivative:

[0090] The derivative was preliminarily synthesised by reacting EDTA dianhydride (commercially available) with an excess of didecylamine.

[0091] For this purpose, in a 100 mL flask, 1 g (3.9 mmol) of EDTA dianhydride and 2.55 g (8.58 mmol) of didecylamine were dissolved in 33 mL of anhydrous dimethylformamide (or DMF) under nitrogen and heated to 90 C. with vigorous stirring for 12 hours. After cooling, the mixture was poured into 330 mL of milli-Q water and the precipitate was collected by vacuum filtration. The solid was washed with 50 mL of milli-Q water then dissolved in 150 mL of methanol and evaporated under reduced pressure to a dry residue. The latter was recrystallised in 50 mL of ethyl acetate at 4 C. The crystals were collected by vacuum filtration, washed with cold ethyl acetate and dried under high vacuum. 2.6 g of the expected derivative were thus obtained in the form of a white solid (Yield: 78%).

2Nd(III) Extraction Test:

[0092] A first series of extraction tests was carried out using: [0093] as aqueous solutions, solutions comprising from 0.1 mmol/L to 0.1 mol/L of hydrochloric acid or nitric acid and 0.01 mol/L of neodymium(II) in the form of chloride (in the case of HCl) or nitrate (in the case of HNO.sub.3) in water; and [0094] as organic solutions, solutions comprising 0.01 mol/L of the derivative in one of the following solvents: 1,3-diisopropylbenzene, chloroform, 10-undecen-1-ol, MIBK, 3-heptanone, TBP and a mixture of n-dodecane/1-octanol (93/7, v/v).

[0095] Each test was performed by placing 2 mL of an aqueous solution and 2 mL of an organic solution (that is to say an O/A ratio of 1) in a tube and subjecting the tube to vigorous stirring (400 rpm) for 30 minutes at room temperature, followed by centrifugation at 11,000 g for 5 minutes.

[0096] Afterwards, the concentrations of Nd(III) remaining in the aqueous solutions were determined by inductively coupled plasma emission spectroscopy (or ICP-OES) on aliquots of these solutions after dilution in 1 M hydrochloric or nitric acid. The calibration range was established from ICP standards (PlasmaCAL) at 1,0045 g/mL.

[0097] The concentrations of Nd(III) present in organic solutions were deduced from those obtained for aqueous solutions after a simple mass balance.

[0098] The extraction coefficients, E %.sub.Nd, and distribution coefficients, D.sub.Nd, of Nd(III) were calculated from the concentrations thus determined.

[0099] FIGS. 1 to 3 illustrate: [0100] FIG. 1: the extraction coefficients of Nd(III) obtained as a function of the initial pH of the aqueous hydrochloric solutions; [0101] FIG. 2: the distribution coefficients of Nd(III) obtained as a function of the initial pH of the aqueous hydrochloric solutions; and [0102] FIG. 3: the extraction coefficients of Nd(III) obtained as a function of the initial pH of the aqueous nitric solutions.

[0103] Moreover, FIG. 4 illustrates the distribution isotherm of neodymium(III) in the form of a curve which shows the equilibrium relationship existing between the concentration of Nd(III) in organic solution, noted [Nd].sub.org,eq and expressed in g/L, and the initial concentration of this same element in aqueous solution, noted [Nd].sub.aq,init and expressed in g/L, as obtained for the tests wherein neodymium(III) was extracted from an aqueous solution comprising 0.01 mol/L of hydrochloric acid or nitric acid (pH 2) using as organic solution, a solution comprising 0.015 mol/L in 1,3-diisopropyl benzene.

3Nd(III) Back-Extraction Tests:

[0104] The back-extraction tests were carried out using: [0105] as organic solutions, solutions loaded with neodymium(II) as obtained following the extraction tests reported in point 2 above; and [0106] as aqueous solutions, solutions comprising 0.01 mol/L of DTPA in water.

[0107] Each test was carried out following an operating protocol similar to that described in point 2 above.

[0108] The analysis of Nd(III) concentrations in aqueous and organic solutions after their separation was also carried out as described in point 2 above.

[0109] These tests showed that it is possible to extract almost all of the neodymium(II) from an organic solution wherein it has been previously extracted, using an aqueous solution containing DTPA at a level of 0.01 mol/L.

4Nd (III), Pr(III) and Dy(III) Extraction Tests:

[0110] In order to get as close as possible to an acid leaching medium for NdFeB permanent magnets, a second series of extraction tests was carried out using: [0111] as aqueous solutions, solutions comprising from 0.1 mmol/L to 0.01 mol/L of hydrochloric acid or nitric acid and from 0.01 mol/L to 1.5 mol/L of each of the rare earths (neodymium(II), praseodymium(II) and dysprosium(III)) in the form of chlorides (in the case of HCl) or nitrates (in the case of HNO.sub.3) in water; and [0112] as organic solutions, solutions comprising 0.01 mol/L of the derivative in 1,3-diisopropylbenzene or a mixture n-dodecane/1-octanol (93/7, v/v).

[0113] Each test was carried out following an operating protocol similar to that described in point 2 above.

[0114] The analysis of the concentrations of the three rare earths in the aqueous and organic solutions after their separation was also carried out as described in point 2 above.

[0115] Their extraction coefficients, E %.sub.M, and distribution coefficients, D.sub.M, were calculated from the concentrations thus determined, then the factors of separation of neodymium(II) from praseodymium(III) on the one hand, and dysprosium(II) on the other hand, FS.sub.Nd/Pr and FS.sub.Nd/Dy, were calculated from the D.sub.M thus obtained.

[0116] The results are illustrated in FIGS. 5 and 6 and in Table I below which show: [0117] FIG. 5: the extraction coefficients of Nd(III), Pr(III) and Dy(III) obtained as a function of the initial pH of the aqueous hydrochloric solutions for the extractions carried out with the derivative in solution in 1,3-diisopropylbenzene; [0118] FIG. 6: the extraction coefficients of Nd(III), Pr(III) and Dy(III) obtained as a function of the initial pH of the aqueous nitric solutions for the extractions carried out with the derivative in solution in 1,3-diisopropylbenzene; [0119] Table I: the separation factors of neodymium(III) from praseodymium(III) on the one hand, and dysprosium(III) on the other hand, obtained for the extractions carried out on aqueous solutions comprising 0.1 mmol/L of hydrochloric or nitric acid (pH 4) with the derivative in solution in 1,3-diisopropylbenzene or the n-dodecane/1-octanol mixture (93/7, v/v).

TABLE-US-00001 TABLE I FS Solvent FS.sub.Nd/Pr FS.sub.Nd/Dy FS.sub.Nd/Pr FS.sub.Nd/Dy 1,3-diisopropylbenzene 1.38 1.47 1.14 1.37 n-dodecane/1-octanol 1.26 1.07 1.27 1.23 (93/7, v/v) Acid of aqueous solutions HCL HNO.sub.3

[0120] These results show that the derivative allows the extraction of neodymium(III), praseodymium(III) and dysprosium(III) from an aqueous hydrochloric or nitric solution with a pH ranging from 2 to 4.

[0121] They also show that the derivative has more affinity for neodymium (111) than for the other two rare earths, this affinity being in the order: Nd>Pr>Dy for the extractions carried out with the derivative in solution in 1,3-diisopropylbenzene while it is in the order: Nd>Dy>Pr for the extractions carried out with the derivative in solution in the n-dodecane/1-octanol mixture (93/7, v/v).

Example 2: Use of Two Lipophilic Derivatives of CyDTA

[0122] The liquid-liquid extraction tests reported below were carried out using as extractant, two lipophilic derivatives of CyDTA, in n-dodecane, namely: [0123] the derivative of particular formula (Ib) wherein R.sup.3, R.sup.4 and R.sup.11 to R.sup.14 represent a hydrogen atom, X.sup.1 and X.sup.2 represent a N(C.sub.12H.sub.25).sub.2 group while X.sup.3 and X.sup.4 represent an OH group, hereinafter called derivative RP2; and [0124] the derivative of particular formula (Ib) wherein R.sup.3, R.sup.4 and R.sup.11 to R.sup.14 represent a hydrogen atom, X.sup.1 and X.sup.2 represent a N(C.sub.8H.sub.17).sub.2 group while X.sup.3 and X.sup.4 represent an OH group, hereinafter called derivative RP4.

1Synthesis of Derivatives:

[0125] The derivatives were preliminarily synthesised by reacting the dianhydride of CyTDA with an excess of didodecylamine for the derivative RP2 and dioctylamine for the derivative RP4.

Synthesis of CyTDA Dianhydride:

[0126] 12.64 g (36.7 mmol) of trans-1,2-diaminocyclohexane tetraacetic acid monohydrate (CyDTA.Math.H.sub.2O) and 11 mL of pyridine were introduced into a 250 mL single-necked flask. Then, 66 mL of acetic anhydride was added and the mixture was left stirring overnight. The solution obtained was poured dropwise into 350 mL of diethyl ether and the suspension formed was then filtered through a sintered glass of porosity 3. The precipitate was washed with diethyl ether (3100 mL) then dried under vacuum. 7.27 g of the expected dianhydride were thus obtained in the form of a yellowish powder (Yield: 69%).

Synthesis of the Derivative RP2:

[0127] 1 g (3.22 mmol) of the dianhydride of the previously obtained CyDTA and 2.51 g (2.2 eq., 7.08 mmol) of didodecylamine were introduced into a 100 mL two-necked flask equipped with a septum, topped with a condenser and placed under an argon atmosphere. Then, 40 mL of DMF was added, the mixture was brought to 60 C. and left stirring overnight. The DMF was then evaporated under vacuum and the residual crude was solubilised in 100 mL of dichloromethane (or DCM) and poured into a 250 mL separating funnel. The organic phase was washed with a 3 M hydrochloric acid solution (2100 mL) then with deionized water (Milli-Q2100 mL). The organic phase was then dried over sodium sulphate (Na.sub.2SO.sub.4) and filtered under reduced pressure. The hydrated salts were rinsed with DCM (340 mL) and the filtrate was evaporated under reduced pressure. The oily residue was purified by reverse-phase flash chromatography (C18 column) and elution by methanol/isopropanol gradient (from 100/0 to 80/20). 2.19 g of the derivative RP2 were thus obtained in the form of a white paste (Yield: 67%).

Synthesis of the Derivative RP4:

[0128] 1.43 g of the derivative RP4 in the form of a yellowish oil were obtained by following a protocol similar to that described for the synthesis of the derivative RP2, except that 1 g (3.22 mmol) of the CyDTA dianhydride was reacted with 1.71 g (2.2 eq., 7.08 mmol) of dioctylamine and that the elution of the C18 column used for the purification was carried out by a methanol/water gradient from 95/5 to 100/0 (Yield: 56%).

2Extraction Tests:

[0129] Extraction tests were carried out using: [0130] as aqueous solutions, solutions comprising 1 mmol/L nitric acid and from 0.01 mol/L to 0.1 mol/L neodymium(II), praseodymium(II) and dysprosium(II) as nitrate in water; and [0131] as organic solutions, solutions comprising from 0.01 mol/L to 0.1 mol/L of the derivative RP2 or the derivative RP4, in n-dodecane.

[0132] Each test was carried out following an operating protocol similar to that described in point 2 of Example I above.

[0133] The analysis of the concentrations of the three rare earths in the aqueous and organic solutions after their separation was also carried out as described in point 2 of Example I above.

[0134] Their extraction coefficients, E %.sub.M, were calculated from the concentrations thus determined.

[0135] The results are illustrated in FIGS. 7 and 8 which present the extraction coefficients thus obtained as a function of the concentrations of RP2 (FIG. 7) and RP4 (FIG. 8) of the organic solutions.

[0136] These figures show that, unlike the lipophilic derivative of EDTA tested in Example I above, the two lipophilic derivatives of CyDTA, in solution in n-dodecane, have an identical or almost identical affinity for neodymium(II), praseodymium(III) and dysprosium(II).

[0137] These results are extremely interesting because they mean that the invention offers a panel of extractants capable of enabling both an extraction of neodymium(III) selective with respect to praseodymium(II) and dysprosium(III)if such extraction is soughtand an extraction of all three rare earths.

REFERENCES MENTIONED

[0138] EP-A-3 323 899 [0139] WO-A-2016/046179 [0140] WO-A-2019/197792 [0141] U.S. Pat. No. 5,762,910 [0142] WO-A-2016/135523 [0143] Erne et al., Helv. Chem. Acta 1980, 63(8), 2264-2270 [0144] U.S. Pat. No. 8,785,691 [0145] WO-A-2014/064587