Extractant for rare earth extraction from aqueous phosphoric acid solutions and method of extraction

Abstract

An extractant which makes it possible to extract both light rare earths and heavy rare earths from an aqueous phosphoric acid solution, likely to be present in this solution, and which is characterised in that it comprises: a compound of formula (I) below: ##STR00001##
wherein R1 and R2, identical or different, are a hydrocarbon group, saturated or unsaturated, linear or branched, in C6 to C12; R3 is a hydrocarbon group, in C1 to C6, or a hydrocarbon group, saturated or unsaturated, monocyclic, in C3 to C8; R4 and R5, identical or different, are a hydrogen atom or a hydrocarbonate group, saturated or unsaturated, linear or branched, in C2 to C8; and a surfactant. Applications of this extractant include treatment of aqueous solutions from the leaching of natural phosphates by sulphuric acid and aqueous solutions from the leaching of urban minerals by phosphoric acid, in view of making profitable use of the rare earths present in these solutions.

Claims

1. An extractant comprising: a compound of formula (I): ##STR00004## where: R.sup.1 and R.sup.2, either identical or different, are a saturated or unsaturated, linear or branched hydrocarbon group having 6 to 12 carbon atoms; R.sup.3 is: a saturated or unsaturated, linear or branched hydrocarbon group having 1 to 12 carbon atoms and optionally one or more heteroatoms; or a saturated or unsaturated, monocyclic hydrocarbon group having 3 to 8 carbon atoms and optionally one or more heteroatoms; R.sup.4 and R.sup.5, either identical or different, are a hydrogen atom, or a saturated or unsaturated, linear or branched hydrocarbon group having 2 to 8 carbon atoms; and a surfactant.

2. The extractant of claim 1, in which R.sup.1 and R.sup.2, either identical or different, are a linear or branched alkyl group having 6 to 12 carbon atoms.

3. The extractant of claim 2, in which R.sup.1 and R.sup.2 are identical and are a branched alkyl group having 8 to 10 carbon atoms.

4. The extractant of claim 1, in which R.sup.3 is a linear or branched alkyl group having 1 to 12 carbon atoms, or a 6-membered monocyclic aromatic group.

5. The extractant of claim 1, in which R.sup.4 is a linear or branched alkyl group having 2 to 8 carbon atoms.

6. The extractant of claim 1, in which R.sup.5 is a hydrogen atom.

7. The extractant of claim 1, in which the compound is: ethyl 1-(N,N-diethylhexylcarbamoyl)ethylphosphonate of formula (I) where R.sup.1 and R.sup.2 are a 2-ethylhexyl group, R.sup.3 is a methyl group, R.sup.4 is an ethyl group and R.sup.5 is a hydrogen atom; ethyl 1-(N,N-diethylhexylcarbamoyl)nonylphosphonate of formula (I) where R.sup.1 and R.sup.2 are a 2-ethylhexyl group, R.sup.3 is an n-octyl group, R.sup.4 is an ethyl group and R.sup.5 is a hydrogen atom; butyl 1-(N,N-diethylhexylcarbamoyl)nonylphosphonate of formula (I) where R.sup.1 and R.sup.2 are a 2-ethylhexyl group, R.sup.3 is an n-octyl group, R.sup.4 is an n-butyl group and R.sup.5 is a hydrogen atom; butyl 1-(N,N-dioctylcarbamoyl)nonylphosphonate of formula (I) where R.sup.1, R.sup.2 and R.sup.3 are an n-octyl group, R.sup.4 is an n-butyl group and R.sup.5 is a hydrogen atom; or ethyl 1-(N,N-diethylhexylcarbamoyl)benzylphosphonate of formula (I) where R.sup.1 and R.sup.2 are a 2-ethylhexyl group, R.sup.3 is a phenyl group, R.sup.4 is an ethyl group and R.sup.5 is a hydrogen atom.

8. The extractant of claim 7, in which the compound is butyl 1-(N,N-diethylhexylcarbamoyl)nonylphosphonate.

9. The extractant claim 1, in which the surfactant is an ionic surfactant.

10. The extractant of claim 9, in which the surfactant is a salt of a dialkyl(C.sub.6-C.sub.12)sulfosuccinate.

11. The extractant of claim 10, in which the dialkyl(C.sub.6-C.sub.12)sulfosuccinate is di(2-ethylhexyl)sulfosuccinate.

12. The extractant of claim 1, which has a molar ratio of the compound to the surfactant ranging from 20:80 to 80:20.

13. The extractant of claim 4, in which R.sup.3 is a methyl, n-octyl or phenyl group.

14. The extractant of claim 11, in which the surfactant is a sodium salt of di(2-ethylhexyl)sulfosuccinate.

15. A method for extracting at least one rare earth from an aqueous phosphoric acid solution, comprising contacting the aqueous solution with a non-water miscible organic solution comprising an extractant in an organic diluent, then separating the aqueous solution and the organic solution, in which the extractant comprises: a compound of formula (I): ##STR00005## where: R.sup.1 and R.sup.2, either identical or different, are a saturated or unsaturated, linear or branched hydrocarbon group having 6 to 12 carbon atoms; R.sup.3 is: a saturated or unsaturated, linear or branched hydrocarbon group having 1 to 12 carbon atoms and optionally one or more heteroatoms; or a saturated or unsaturated, monocyclic hydrocarbon group having 3 to 8 carbon atoms and optionally one or more heteroatoms; R.sup.4 and R.sup.5, either identical or different, are a hydrogen atom, or a saturated or unsaturated, linear or branched hydrocarbon group having 2 to 8 carbon atoms; and a surfactant.

16. The method of claim 15, in which the organic solution comprises from 0.005 mol/L to 1 mol/L of the extractant.

17. The method of claim 15, in which the aqueous phosphoric acid solution is a solution issued from a leaching of a natural phosphate with sulfuric acid.

18. The method of claim 15, in which the aqueous phosphoric acid solution is a solution issued from a leaching of industrial and domestic waste from equipment comprising rare earths.

19. A method for recovering at least one rare earth from an aqueous phosphoric acid solution, comprising: extracting the at least one rare earth from the aqueous solution by contacting the aqueous phosphoric acid solution with a non-water miscible organic solution comprising an extractant in an organic diluent, the extractant comprising: a compound of formula (I): ##STR00006## where: R.sup.1 and R.sup.2, either identical or different, are a saturated or unsaturated, linear or branched hydrocarbon group having 6 to 12 carbon atoms; R.sup.3 is: a saturated or unsaturated, linear or branched hydrocarbon group having 1 to 12 carbon atoms and optionally one or more heteroatoms; or a saturated or unsaturated, monocyclic hydrocarbon group having 3 to 8 carbon atoms and optionally one or more heteroatoms; R.sup.4 and R.sup.5, either identical or different, are a hydrogen atom, or a saturated or unsaturated, linear or branched hydrocarbon group having 2 to 8 carbon atoms; and a surfactant; separating the aqueous phosphoric acid solution and the organic solution; stripping the at least one rare earth from the organic solution by contacting the organic solution with an aqueous solution of oxalic acid or salt thereof; and separating the aqueous solution of oxalic acid or a salt thereof and the organic solution.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIGS. 1A and 1B illustrate the results of extraction tests performed on aqueous phosphoric phases containing five rare earths and iron, using organic phases comprising as extractant either DEHCNPB, or AOT, or a mixture of DEHCNPB and AOT in different DEHCNPB/AOT molar ratios; FIG. 1A shows the trend in the distribution coefficients of the rare earths and iron, denoted D.sub.M, as a function of the molar fraction of AOT, denoted x.sub.AOT, of the extractant, whilst FIG. 1B shows the trend in the selectivity coefficients of the rare earths over iron, denoted S.sub.Tr/Fe, as a function of x.sub.AOT.

(2) FIGS. 2A and 2B illustrate the results of extraction tests performed on aqueous phosphoric phases containing five rare earths and iron, using organic phases comprising as extractant a mixture of DEHCNPB and AOT (DEHCNPB/AOT molar ratio: 60:40) at different concentrations; FIG. 2A shows the trend in the distribution coefficients of the rare earths and iron, denoted D.sub.M, as a function of the concentration of the DEHCNPB and AOT mixture, denoted [DEHCNPB+AOT] and expressed in mol/L, in organic phase, whilst FIG. 2B shows the trend in the selectivity coefficients of the rare earths over iron, denoted S.sub.Tr/Fe, as a function of [DEHCNPB+AOT], also expressed in mol/L.

(3) FIGS. 3A and 3B illustrate the results of extraction tests performed on aqueous acid phases containing five rare earths and iron and comprising as acid either nitric acid or hydrochloric acid or sulfuric acid or phosphoric acid, using organic phases comprising as extractant a mixture of DEHCNPB and AOT (DEHCNPB/AOT molar ratio: 60:40); FIG. 3A shows the distribution coefficients of the rare earths and iron, denoted D.sub.M, obtained as a function of the acid contained in the aqueous phase, whilst FIG. 3B gives the selectivity coefficients of the rare earths over iron, denoted S.sub.Tr/Fe, obtained as a function of the acid contained in the aqueous phase.

(4) FIGS. 4A and 4B illustrate the results of extraction tests performed on aqueous phases containing five rare earths and iron and comprising phosphoric acid at different concentrations, using organic phases comprising as extractant a mixture of DEHCNPB and AOT (DEHCNPB/AOT molar ratio: 60:40); FIG. 4A shows the trend in the distribution coefficients of the rare earths and iron, denoted D.sub.M, as a function of the concentration of phosphoric acid, denoted [H.sub.3PO.sub.4] and expressed in mol/L, in aqueous phase, whilst FIG. 4B shows the trend in the selectivity coefficients of the rare earths over iron, denoted S.sub.Tr/Fe, as a function of [H.sub.3PO.sub.4].

(5) FIG. 5 illustrates the results of extraction tests performed at different temperatures on aqueous phosphoric phases containing five rare earths and iron, using organic phases comprising as extractant a mixture of DEHCNPB and AOT (DEHCNPB/AOT molar ratio: 60:40); this Figure shows the trend in the distribution coefficients of the rare earths and iron, denoted D.sub.M, as a function of temperature, denoted T and expressed in ° C.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(6) The experimental results reported in the following examples were obtained using aqueous acid phases comprising two light rare earths, namely lanthanum (La) and neodymium (Nd), and three heavy rare earths, namely europium (Eu), dysprosium (Dy) and ytterbium (Yb).

(7) The distribution coefficients, extraction yields and selectivity coefficients reported in the following examples were determined in accordance with conventional practice in the field of liquid-liquid extractions, namely that: the distribution coefficient of a metal element M, denoted D.sub.M, between two phases respectively organic and aqueous, is determined by the following equation:

(8) $D_M=\frac{{\left[M\right]}_{\mathrm{org},f}}{{\left[M\right]}_{\mathrm{aq},f}}=\frac{{\left[M\right]}_{\mathrm{aq},i}-{\left[M\right]}_{\mathrm{aq},f}}{{\left[M\right]}_{\mathrm{aq},f}}$
where:

(9) [M].sub.org,f is the concentration of M in the organic phase after extraction,

(10) [M].sub.aq,f is the concentration of M in the aqueous phase after extraction, and

(11) [M].sub.aq,i is the concentration of M in the aqueous phase before extraction; the extraction yield of a metal element M, denoted R.sub.M, from an aqueous phase is determined by the following equation:

(12) $R_M=\frac{{\left[M\right]}_{\mathrm{org},f}}{{\left[M\right]}_{\mathrm{aq},i}}=\frac{D_M}{D_M+1}$
where [M].sub.org,f, [M].sub.aq,i and D.sub.M have the same meaning as previously; whilst the selectivity coefficient of a metal element M1 over a metal element M2, denoted S.sub.M1/M2, is determined by the equation:

(13) $S_{M1/M2}=\frac{D_{M1}}{D_{M2}}$
where:

(14) D.sub.M1 is the distribution coefficient of M1, and

(15) D.sub.M2 is the distribution coefficient of M2.

Example 1: Synergic Effect of a Mixture of DEHCNPB and AOT on the Extraction of Rare Earths from an Aqueous Phosphoric Acid Solution and Impact of the DEHCNPB/AOT Molar Ratio of this Mixture on the Extracting Properties Thereof

(16) The synergic effect of a mixture of DEHCNPB and AOT on the extraction of rare earths from an aqueous phosphoric acid solution and the impact of the DEHCNPB/AOT molar ratio of this mixture on its extracting properties were assessed by extraction tests performed using: as aqueous phases: phases obtained by dissolving five salts of rare earths in oxidation state (Ill) in the respective forms: La(NO.sub.3).sub.3, Nd(NO.sub.3).sub.3, Eu(NO.sub.3).sub.3, Dy(NO.sub.3).sub.3 and Yb(NO.sub.3).sub.3, in a proportion of 0.25 g/L of each of these salts, in solutions comprising 5 mol/L of phosphoric acid in ultrapure water (i.e. Milli-Q water, having resistivity of >18 MΩ/cm at 25° C.); and as organic phases: phases comprising 0.1 mol/L of an extractant in isooctane, this extractant being composed either solely of DEHCNPB, or solely of AOT, or of a mixture of DEHCNPB and AOT for which the molar ratio of DEHCNPB to AOT was varied.

(17) Since iron is naturally contained as major impurity in ores and, in particular, in natural ores, the aqueous phases also comprised 2.5 g/L of iron(III) nitrate.

(18) The extraction tests were conducted using an aqueous phase/organic phase volume ratio (A/O) of 1. The aqueous and organic phases were placed in contact for 1 hour at constant temperature (20° C.), after which they were separated from each other via centrifugation (4 000 rpm) for 20 minutes at 20° C.

(19) The concentrations of the rare earths and iron in the aqueous phases were measured by inductively coupled plasma optical emission spectrometry (ICP-OES) before and after extraction.

(20) The results of these tests are given in Table 1 below indicating the extraction yields of the rare earths and iron, denoted R.sub.M, as a function of the AOT molar fraction, denoted x.sub.AOT, of the extractant system, as well as in FIGS. 1A and 1B showing the trend in the distribution coefficients of the rare earths and iron, denoted D.sub.M, as a function of x.sub.AOT (FIG. 1A), and the trend in the selectivity coefficients of the rare earths over iron, denoted S.sub.Tr/Fe, as a function of x.sub.AOT (FIG. 1B).

(21) In this Table and in these Figures, the results given for x.sub.AOT=0 correspond to the results obtained for the extractant composed solely of DEHCNPB, whilst the results given for x.sub.AOT=1 correspond to the results obtained for the extractant composed solely of AOT.

(22) TABLE-US-00001 TABLE 1 R.sub.M x.sub.AOT La Nd Eu Dy Yb Fe 0 0.01 0.03 0.04 0.04 0.04 0.02 0.2 0.66 0.54 0.38 0.25 0.15 0.06 0.4 0.87 0.77 0.64 0.46 0.24 0.10 0.6 0.82 0.70 0.55 0.38 0.18 0.09 0.8 0.69 0.53 0.39 0.25 0.09 0.06 1 0.44 0.27 0.21 0.18 0.08 0.09

(23) These results show that, for all the rare earths, the extraction yields obtained with an extractant composed of a mixture of DEHCNPB and AOT are higher than the sum of the extraction yields obtained with an extractant composed solely of DEHCNPB and an extractant composed solely of AOT, thereby indicating a synergic effect of the mixture of DEHCNPB and AOT on the extraction of all these rare earths (Table 1).

(24) They also show that the highest synergic effect of the DEHCNPB and AOT mixture is observed with an AOT molar fraction of 0.4 (i.e. a DEHCNPB/AOT molar ratio of 60:40) with the obtaining of distribution coefficients for lanthanum, neodymium, europium, dysprosium and ytterbium of respectively 6.4, 3.4, 1.74, 0.81 and 0.32 (FIG. 1A) and of extraction yields of these same elements of respectively 0.87, 0.77, 0.64, 0.46 and 0.24 (Table 1).

(25) They further show that the highest selectivity of the DEHCNPB and AOT mixture for rare earths over iron is also obtained with the AOT molar fraction of 0.4, with the obtaining of selectivity coefficients S.sub.La/Fe, S.sub.Nd/Fe, S.sub.Eu/Fe, S.sub.Dy/Fe and D.sub.Yb/Fe of respectively 59, 28.7, 15.0, 6.8 and 2.3.

Example 2: Impact of the Concentration of a Mixture of DEHCNPB and AOT in Organic Phase on the Efficiency of this Mixture for the Extraction of Rare Earths from an Aqueous Phosphoric Acid Solution

(26) The impact of the concentration of a DEHCNPB and AOT mixture in organic phase on the efficiency of this mixture for the extraction of rare earths from an aqueous phosphoric acid solution was assessed with extraction tests performed using: as aqueous phases: the same aqueous phases as used in Example 1 above; and as organic phases: phases comprising from 0.003 mol/L to 0.5 mol/L of a DEHCNPB and AOT mixture, in a DEHCNPB/AOT molar ratio of 60:40, in isooctane.

(27) Extractions were conducted under the same conditions as those described in Example 1 above.

(28) The results of these tests are given in Table 2 below, indicating the extraction yields of rare earths and iron, denoted R.sub.M, as a function of the molar concentration of the DEHCNPB and AOT mixture, denoted [DEHCNPB+AOT] and expressed in mol/L, and in FIGS. 2A and 2B showing the trend in the distribution coefficients of the rare earths and iron, denoted D.sub.M, as a function of [DEHCNPB+AOT] (FIG. 2A) and the trend in the selectivity coefficients of the rare earths over iron, denoted S.sub.Tr/Fe, as a function of [DEHCNPB+AOT] (FIG. 2B).

(29) TABLE-US-00002 TABLE 2 [DEHCNPB + AOT] R.sub.M (mol/L) La Nd Eu Dy Yb Fe 0.003 0.06 0.06 0.03 0.02 0.01 0.03 0.006 0.13 0.12 0.07 0.04 0.03 0.04 0.009 0.19 0.16 0.08 0.05 0.01 0.03 0.015 0.31 0.27 0.16 0.10 0.05 0.05 0.05 0.64 0.58 0.43 0.27 0.16 0.07 0.1 0.80 0.77 0.64 0.48 0.35 0.08 0.2 0.88 0.87 0.76 0.63 0.52 0.10 0.5 0.94 0.93 0.89 0.82 0.78 0.28

(30) These results show that the extraction of rare earths and iron increases with the concentration of the DEHCNPB and AOT mixture in the organic phase, with the obtaining of distribution coefficients for lanthanum, neodymium, europium, dysprosium, ytterbium and iron of respectively 7.08, 6.90, 3.17, 1.68, 1.08 and 0.11 for a concentration of this mixture of 0.2 mol/L (FIG. 2A).

(31) They also show that it is possible to obtain even higher distribution coefficients when using a DEHCNPB and AOT mixture at a molar concentration higher than 0.2 mol/L, e.g. 0.5 mol/L, but that a drop in the selectivity of this mixture for the rare earths over iron is then observed (FIG. 2B).

Example 3: Impact of the Type of Acid Contained in an Aqueous Solution on the Efficiency of the Mixture of DEHCNPB and AOT for the Extraction of Rare Earths from this Solution

(32) The impact of the type of acid contained in an aqueous solution on the efficiency of a DEHCNPB and AOT mixture for the extraction of rare earths from this solution was assessed with extraction tests performed using: as aqueous phases: phases obtained by dissolving 0.25 g/L of each of the following salts La(NO.sub.3).sub.3, Nd(NO.sub.3).sub.3, Eu(NO.sub.3).sub.3, Dy(NO.sub.3).sub.3 and Yb(NO.sub.3).sub.3, and 2.5 g/L of Fe(NO.sub.3).sub.3, in solutions comprising 5 mol/L of an acid in ultrapure water, this acid being either nitric acid, or hydrochloric acid, or sulfuric acid or phosphoric acid; and as organic phases: phases comprising 0.1 mol/L of a mixture of DEHCNPB and AOT, in a DEHCNPB/AOT molar ratio of 60:40, in isooctane.

(33) Extractions were conducted under the same conditions as those described in Example 1 above.

(34) The results of these tests are illustrated in FIGS. 3A and 3B giving the distribution coefficients of the rare earths and iron, denoted D.sub.M, obtained for each acid (FIG. 3A) and the selectivity coefficients of the rare earths over iron, denoted log(S.sub.Tr/Fe), obtained for each acid (FIG. 3B).

(35) These results show that the highest efficiency of the DEHCNBE/AOT mixture to extract rare earths from an aqueous acid solution is obtained when the acid contained in this solution is phosphoric acid (FIG. 3A).

(36) The extraction of rare earths from an aqueous solution of nitric acid, hydrochloric acid or sulfuric acid is very low and non-selective over iron (FIG. 3B).

Example 4: Impact of the Phosphoric Acid Concentration in an Aqueous Solution on the Efficiency of a Mixture of DEHCNPB and AOT for the Extraction of Rare Earths from this Solution

(37) The impact of the phosphoric acid concentration in an aqueous solution on the efficiency of a DEHCNPB and AOT mixture for the extraction of rare earths from this solution was assessed with extraction tests performed using: as aqueous phases: phases obtained by dissolving 0.25 g/L of each of the following salts: La(NO.sub.3).sub.3, Nd(NO.sub.3).sub.3, Eu(NO.sub.3).sub.3, Dy(NO.sub.3).sub.3 and Yb(NO.sub.3).sub.3, and 2.5 g/L of Fe(NO.sub.3).sub.3 in solutions comprising 2 mol/L to 7 mol/L of phosphoric acid in ultrapure water; and as organic phases: phases comprising 0.2 mol/L of a DEHCNPB and AOT mixture, in a DEHCNPB/AOT molar ratio of 60:40, in isooctane.

(38) The extractions were conducted under the same conditions as those described in Example 1 above.

(39) The results of these tests are given in Table 3 below, indicating the extraction yields of the rare earths and iron, denoted R.sub.M, as a function of the molar concentration of phosphoric acid, denoted [H.sub.3PO.sub.4] and expressed in mol/L, and in FIGS. 4A and 4B showing the trend in the distribution coefficients of the rare earths and iron, denoted D.sub.M, as a function of [H.sub.3PO.sub.4], expressed in mol/L (FIG. 4A), and the trend in the selectivity coefficients of the rare earths over iron, denoted S.sub.Tr/Fe, as a function of [H.sub.3PO.sub.4], also expressed in mol/L (FIG. 4B).

(40) TABLE-US-00003 TABLE 3 [H.sub.3PO.sub.4] R.sub.M (mol/L) La Nd Eu Dy Yb Fe 2 0.98 0.98 0.97 0.94 0.94 0.57 3 0.97 0.97 0.95 0.90 0.90 0.48 4 0.96 0.95 0.92 0.86 0.84 0.31 5 0.94 0.93 0.88 0.80 0.74 0.25 7 0.92 0.89 0.81 0.70 0.56 0.16

(41) These results show that in accordance with reporting in the literature for cationic exchanger extractants (R. Turgis et al., Solvent Extr. Ion Exch. 2014, 32(7), 685-702, referenced [5] below), the efficiency of the DEHCNBE and AOT mixture for the extraction of rare earths from an aqueous acid phase decreases with the increase in acidity of this phase.

(42) Nevertheless, extraction remains efficient even at a phosphoric acid concentration of 7-8 mol/L, with distribution coefficients for lanthanum, neodymium, europium, dysprosium, ytterbium and iron of respectively 12.27, 7.90, 4.22, 2.28, 1.29 and 0.20 (FIG. 4A).

(43) Regarding the selectivity of the DEHCNBE and AOT mixture for rare earths over iron, FIG. 4B shows that it is very little impacted by the concentration of phosphoric acid in aqueous phase.

Example 5: Impact of Extraction Temperature on the Efficiency of a Mixture of DEHCNPB and AOT for the Extraction of Rare Earths from an Aqueous Phosphoric Acid Solution

(44) The impact of the temperature at which extraction is performed on the efficiency shown by a DEHCNPB and AOT mixture to extract rare earths from an aqueous phosphoric acid solution was assessed with extraction tests performed using: as aqueous phases: the same aqueous phases as those used in Example 1 above; and as organic phases: phases comprising 0.2 mol/L of a mixture of DEHCNPB and AOT, in a DEHCNPB/AOT molar ratio of 60:40, in isooctane.

(45) The extractions were conducted under the same conditions as those described in Example 1 above, with the exception that they were conducted at temperatures of 30° C., 40° C., 50° C. and 60° C.

(46) The results of these tests are given in Table 4 below indicating the extraction yields of the rare earths and iron, denoted R.sub.M, as a function of temperature, denoted T and expressed in ° C., and in FIG. 5 showing the trend in the distribution coefficients of the rare earths and iron, denoted D.sub.M, as a function of T.

(47) TABLE-US-00004 TABLE 4 T (° C.) Fe La Nd Eu Dy Yb 30 0.29 0.94 0.94 0.91 0.84 0.81 40 0.29 0.95 0.95 0.91 0.86 0.81 50 0.25 0.95 0.94 0.90 0.84 0.77 60 0.23 0.94 0.93 0.89 0.82 0.74

(48) These results show that the extraction of rare earth and iron only appears to be scarcely dependent on the temperature at which this extraction is performed.

(49) An extraction peak at 40° C. was nonetheless observed, allowing distribution coefficients to be reached for lanthanum, neodymium, europium, dysprosium, ytterbium and iron of respectively 20.04, 18.66, 10.74, 6.01, 4.30 and 0.4.

(50) The selectivity of the DEHCNPE and AOT mixture for the rare earths over iron was also very little impacted by the temperature at which extraction was performed since the extraction itself is scarcely dependent on this temperature.

Example 6: Stripping Tests

(51) Stripping tests were performed using: a plurality of organic phases comprising from 0.01 mol/L to 0.5 mol/L of a DEHCNPB and AOT mixture, in a DEHCNPB/AOT molar ratio of 60:40, in n-dodecane, previously loaded with La, Nd, Eu, Dy, Yb and Fe via contact with an aqueous solution comprising 0.25 g/L of each of these rare earths, 2.5 g/L of iron and 8 mol/L of phosphoric acid; and an aqueous phase comprising 0.2 mol/L of ammonium oxalate C.sub.2H.sub.8N.sub.2O.sub.4.

(52) For this test, 2 mL of each of the organic phases (containing most of the rare earths initially present in the aqueous solution and traces of iron) were placed in contact and left under agitation, for 1 hour at ambient temperature (24° C.), with 2 mL of the aqueous phase. After settling of the organic and aqueous phases, a white precipitate was formed containing the rare earths complexed by the oxalate.

(53) Rare earths can therefore be stripped in an aqueous phase in the form of oxalates and later converted to oxides by calcining these oxalates.

CITED REFERENCES

(54) [1] M. Krea and H. Khalaf, Hydrometallurgy 2000, 58(3), 215-225. [2] International application PCT WO 2013/167516. [3] “Chemistry and Technology of Surfactants”, Richard J. Farn, 2006 Blackwell Publishing Ltd, ISBN-13: 978-14051-2696-0. [4] “Self-Organized Surfactant Structures”, Tharwat F Tadros, 2011, John Wiley & Sons, ISBN: 978-3-527-63265-7. [5] R. Turgis et al., Solvent Extr. Ion Exch. 2014, 32(7), 685-702.