Methods for extracting and recovering rare earths from aqueous solutions of organic acids

Abstract

A method may extract at least one rare earth from an aqueous solution A1 of an organic acid or of a mixture of organic acids including, in addition to one or more rare earths, one or more transition metals. Such a method may include bringing the aqueous solution A1 into contact with a water-immiscible organic solution, including as an extractant, diglycolamide of formula:dissolved in an organic diluent, followed by separating the aqueous solution A1 from the organic solution. The aqueous solution A1 may further include a salting out agent. The thus extracted rare earths may be recovered, together or separately.

Description

TECHNICAL FIELD

[0001] The invention relates to the field of the extraction and recovery of rare earths present in natural or urban minerals.

[0002] More specifically, it relates to a method making it possible to extract rare earths from an aqueous solution of one or more organic acids, and this, with high extraction yields and high selectivity with respect to other metal elements likely to also be present in this solution and, particularly, with respect to iron.

[0003] It also relates to a method making it possible to recover, together or separately, the thus extracted rare earths.

[0004] In particular, the invention applies to the production of rare earths from concentrates derived from “urban minerals”, that is to say “mines” consisting of industrial and domestic waste comprising rare earths and, particularly, in the recycling of rare earths present in waste electrical and electronic equipment, also known as “WEEE” or “W3E”.

[0005] More particularly, the invention applies to the recycling of rare earths contained in spent or scrapped permanent magnets, and, particularly, in permanent magnets of the Neodymium-Iron-Bore (or NdFeB) type.

[0006] However, it may also be used to produce rare earths from concentrates derived from natural minerals such as monazites, bastnaesites, apatites or xenotimes, or from concentrates derived from natural mineral residues such as, for example, tin slag.PRIOR ART

[0007] Rare earths (hereinafter referred to as “RE”) group metals that are characterized by neighboring properties, namely scandium (Sc), yttrium (Y) and all lanthanides, the latter corresponding to the 15 chemical elements listed in the periodic table of elements from atomic number 57 for lanthanum (La) to atomic number 71 for luteium (Lu).

[0008] The particular electronic configuration of the RE and, in particular, the unsaturated electronic sublayer 4f thereof, confers thereto unique chemical, structural and physical properties. These properties are used in industrial applications as varied as they are sophisticated: glass and ceramic industries, polishing, catalysis, manufacturing of high-tech alloys, of permanent magnets, of optical devices, of luminophores, of rechargeable batteries for electric or hybrid vehicles, of generators for wind turbines, etc.

[0009] RE therefore form part of the so-called “technological” metals the supply of which is strategic.

[0010] However, as few countries produce rare earths from mining deposits (China alone currently accounts for nearly 60% of the world annual RE production), there is a significant risk over time of a shortage of rare earth supplies, hence the need to optimize all avenues making it possible to produce them.

[0011] At the same time, increasing environmental awareness is driving the constant search for alternatives to mining such as substituting used chemicals, reducing needs or recycling spent products or production waste. Recycling appears to be a pillar of the circular economy, which involves maximizing the value generated by resources thus by reducing the need for primary resources and avoiding landfilling products at the end of life thereof.

[0012] One of the first markets, in volume and potential market value, for RE recycling concerns NdFeB permanent magnets that are present in various high-tech products such as electric or hybrid vehicles, wind turbines, hard drives and induction motors. This resource for recycling RE is particularly interesting to value because these magnets contain a significant amount of light RE (around 30% by mass of a neodymium / praseodymium mixture) and a lower amount of heavy RE of high economic value, including dysprosium. In addition to containing a large amount of iron and a smaller amount of boron, NdFeB permanent magnets are generally coated with a corrosion-protective coating based on nickel and other transition metals such as cobalt.

[0013] Most of the work aimed at recovering RE present in natural or urban minerals by liquid-liquid extraction has been carried out on aqueous solutions derived from the treatment of these minerals by inorganic acids of the nitric acid, hydrochloric acid, sulfuric acid or phosphoric acid type.

[0014] Thus, for example, international application WO-A-2016 / 046179, hereinafter reference [1], describes the use of lipophilic diglycolamides such as N,N,N′,N′-tetraoctyl-3-oxapentanediamide (or TODGA) and N,N,N′,N′-tetradodecyl-3-oxapentanediamide (or TdDDGA) as extractants, to selectively recover RE from aqueous solutions derived from the leaching of a powder of spent or scrapped NdFeB permanent magnets by an inorganic acid, which is preferably nitric acid but which may also be sulfuric acid, hydrochloric acid or phosphoric acid.

[0015] Recently, two studies have shown the possibility of effectively leaching powders of NdFeB permanent magnets with organic acids.

[0016] This concerns:

[0017] on the one hand, a study published by M. Gergoric et al. in Journal of Sustainable Metallurgy 2019, 5 (1), 85-96, hereinafter reference [2], and wherein the organic acids used are glycolic acid, maleic acid, and ascorbic acid, and

[0018] on the other hand, a study published by S. Belfqueh et al. in Journal of Rare Earths 2022, https: / / doi.org / 10.1016 / j.jre.2022.04,027, hereinafter reference [3], and wherein the organic acids used are acetic acid, formic acid, citric acid and tartaric acid.

[0019] The advantages of using organic acids over inorganic acids such as nitric, hydrochloric or sulphuric acids are numerous, namely that organic acids, which are generally derived from biological sources, are low or non-corrosive, generate less toxic gasses than inorganic acids and are mostly biodegradable, which makes it possible to considerably reduce the ecological impact of leaching.

[0020] Being further interested in the possibility of extracting RE from glycolic acid and maleic acid leach and having tested a plurality of types of extractants (tri-n-butyl phosphate or TBP, (2-ethylhexyl)phosphoric acid or D2EHPA, TODGA, Cyanex™ 272 and Cyanex™ 923), M. Gergoric et al. showed in reference [2] that TODGA, at a concentration of 1 mol / L in organic solution, makes it possible to extract neodymium, dysprosium and praseodymium selectively with respect to iron, cobalt and boron but only from maleic acid leach.

[0021] Within the scope of their work on the recovery of RE from acidic aqueous solutions derived from the treatment of spent or scrapped NdFeB permanent magnets, the inventors found:

[0022] that the use of TODGA as an extractant, at a concentration ranging from 0.05 mol / L to 1 mol / L in the organic phase, makes it possible to extract RE from an aqueous solution derived from the leaching of a powder of NdFeB permanent magnets by acetic acid, and this, selectively with respect to iron, cobalt, nickel and boron also present in this solution (unpublished data);

[0023] that in addition to the selectivity towards iron, cobalt, nickel and boron, TODGA has, in the context of this use, more affinity for heavy RE such as dysprosium than for light RE such as neodymium and praseodymium (unpublished data), which is interesting in the perspective of selective recovery of these RE; but

[0024] that despite these advantages, the distribution coefficients of the RE obtained during extractions and, therefore, the extraction yields are relatively low (unpublished data), which penalizes implementation on an industrial scale.

[0025] The inventors have therefore set themselves the goal of achieving improvements in these distribution coefficients and thereby these extraction yields.

[0026] Yet, still within the scope of their work, the inventors found that, surprisingly, the distribution coefficients, the extraction yields as well as the extraction kinetics obtained during extractions of RE by TODGA from an aqueous solution derived from the leaching of a powder of NdFeB permanent magnets by an organic acid, such as acetic acid, are improved considerably when a salting out agent is added to this aqueous solution, and this, without affecting the extraction selectivity with respect to other metal elements (iron, cobalt, boron, etc.) or the preference of TODGA for heavy RE.

[0027] It is on the basis of these experimental findings that the invention was developed.DISCLOSURE OF THE INVENTION

[0028] Therefore, an object of the invention is, firstly, a method for extracting one or more rare earths from an aqueous solution A1 of an organic acid or of a mixture of organic acids comprising, in addition to the rare earth(s), one or more transition metals, which method comprises at least bringing the aqueous solution A1 into contact with a water-immiscible organic solution, comprising as an extractant, TODGA, that is to say the diglycolamide of formula:dissolved in an organic diluent, followed by separating the aqueous solution A1 from the organic solution, and is characterized in that the aqueous solution A1 further comprises a salting out agent.In the foregoing and the following, the expressions “from . . . to . . . ”, “ranging from . . . to . . . and” between . . . and . . . are equivalent and mean that the limits are included.

[0030] Likewise, the terms “solution” and “phase” are equivalent and perfectly interchangeable.

[0031] According to the invention, the concentration of the organic acid or of the mixture of organic acids in the aqueous solution A1 may range from 0.1 mol / L to 16 mol / L, preferably being given at a concentration between 0.5 mol / L and 2 mol / L.

[0032] This organic acid or the organic acids of the mixture may be selected from monocarboxylic acids such as formic acid, acetic acid, propionic acid, lactic acid or glycolic acid, dicarboxylic acids such as oxalic acid, malonic acid, maleic acid, tartaric acid, fumaric acid, mesoxalic acid, glutaric acid or diglycolic acid, and tricarboxylic acids such as citric acid, isocitric acid, tricarballylic acid or trimesic acid.

[0033] The salting out agent may, for its part, be any electrolyte capable of improving the ability of TODGA to extract RE from an organic solution, particularly by a dehydrating power allowing to decrease the amount of free water molecules in the system and, thereby, the solubility of RE in aqueous solution.

[0034] Preferably, the salting out agent is a salt, typically inorganic, and, more specifically, a salt of an alkali or alkaline earth metal such as lithium, sodium, potassium, calcium or magnesium chloride, lithium, sodium, potassium, calcium or magnesium nitrate, lithium, sodium, potassium, calcium or magnesium sulfate or lithium, sodium, potassium, calcium or magnesium phosphate, or an ammonium salt such as ammonium chloride, nitrate, sulfate or phosphate.

[0035] Among these, preference is given to a nitrate and, more particularly, to a nitrate of an alkali or alkaline earth metal and, more particularly, to lithium nitrate, sodium nitrate and potassium nitrate.

[0036] According to the invention, the salting out agent is added to the aqueous solution A1 at a concentration ranging, preferably, from 0.25 mol / L to 1 mol / L, for example 0.6 mol / L, of aqueous solution A1.

[0037] As for TODGA, it is present in the organic solution at a concentration ranging, preferably, from 0.05 mol / L to 1 mol / L, for example 0.25 mol / L.

[0038] The organic diluent wherein TODGA is in solution may be any non-polar aliphatic organic diluent the use of which has been proposed for carrying out liquid-liquid extractions such as an alcohol such as n-octanol, n-decanol or isodecanol, or a hydrocarbon or a mixture of hydrocarbons, for example isooctane, n-dodecane, hydrogenated tetrapropylene (or TPH), kerosene, Isane™ IP-185T or Isane™ IP-175T, preference being given to n-dodecane.

[0039] The organic solution may further comprise a phase modifier suitable for increasing the loading capacity of TODGA in the used organic diluent, that is to say the maximum concentration of metal elements that the organic solution may have without the occurrence of the formation of a third phase by demixing when it is brought into contact with an aqueous phase loaded with metal elements.

[0040] The use of a phase modifier is, for example, indicated in the case where the organic diluent is n-dodecane.

[0041] This phase modifier may particularly be selected from trialkyl phosphates such as tri-n-butylphosphate (or TBP) or tri-n-hexylphosphate (or THP), alcohols such as n-octanol, n-decanol or isodecanol, and monoamides such as N,N-dihexyloctanamide (or DHOA), N,N-dibutyldecanamide (or DBDA), N,N-di(2-ethylhexyl) acetamide (or D2EHAA), N,N-di(2-ethylhexyl) propionamide (or D2EHPA), N,N-di(2-ethylhexyl) isobutyramide (or D2EHiBA) or N,N-dihexyldecanamide (or DHDA).

[0042] Moreover, this phase modifier, preferably, does not represent more than 15% by volume of the organic solution, or no more than 10% in volume of volume of this solution when it is an alcohol such as n-octanol.

[0043] According to the invention, the extraction method is preferably implemented at room temperature, that is to say at a temperature ranging from 20° C. to 25° C.

[0044] This extraction method may advantageously be used to recover one or more rare earths from an aqueous solution of an organic acid or of a mixture of organic acids and, particularly, to recover together or separately one or more light rare earths, that is to say with an atomic number at most equal to 61, and one or more heavy rare earths, that is to say with an atomic number at least equal to 62, from such an aqueous solution.

[0045] In addition, another object of the invention is a method for recovering one or more rare earths from an aqueous solution A1 of an organic acid or of a mixture of organic acids comprising, in addition to the rare earth(s), one or more transition metals, which method comprises at least the following steps:

[0046] a) extracting the rare earth or co-extracting the rare earths of the aqueous solution A1 by implementing an extraction method as previously defined; then

[0047] b) stripping the rare earth or at least one of the rare earths from the organic solution obtained at the end of step a), stripping comprising at least bringing the organic solution into contact with an aqueous solution A2, followed by separating the organic solution from the aqueous solution A2.

[0048] According to the invention, the aqueous solution A2 may consist of water, that is to say that it comprises only water, preferably deionized.

[0049] Alternatively, the aqueous solution A2 may also be a solution comprising an agent complexing the rare earths in aqueous media.

[0050] As previously mentioned, in the case where the aqueous solution A1 comprises at least one light rare earth, RE1, and at least one heavy rare earth, RE2, then the rare earths RE1 and RE2 can be recovered in a grouped manner, in which case, in step b), these rare earths are co-stripped from the organic solution obtained at the end of step a), the aqueous solution A2 then preferably comprising an agent complexing the rare earths in an aqueous medium.

[0051] Alternatively, the rare earths RE1 and RE2 can be recovered separately, in which case step b) comprises:

[0052] b1) stripping the rare earth(s) RE1 from the organic solution obtained at the end of step a) that is carried out with the aqueous solution A2, then

[0053] b2) stripping the rare earth(s) RE2 from the organic solution obtained at the end of b1), stripping comprising at least one step of bringing the organic solution into contact with an aqueous solution A3 different from the aqueous solution A2, followed by separating the organic solution from the aqueous solution A3.

[0054] In this case, the aqueous solution A2, preferably, consists of water while the aqueous solution A3 is preferably a solution comprising an agent complexing the rare earths in an aqueous medium.

[0055] The agent complexing the rare earths in an aqueous media likely to be used according to the invention may in particular be:

[0056] an aminopolycarboxylic acid such as ethylenediamine tetraacetic acid (or EDTA), N-(2-hydroxyethyl)ethylenediamine triacetic acid (or HEDTA), nitrilotriacetic acid (or NTA) or diethylenediamine pentaacetic acid (or DTPA) or a salt thereof, for example a sodium salt; or

[0057] a hydrophilic diglycolamide, that is to say a compound having the formula: R1(R2)N—C(O)—CH2—O—CH2—C(O)—N(R3)R4 wherein R1, R2, R3 and R4, identical or different, represent alkyl groups, linear or branched, and of which the total number of carbon atoms is no more than 20, such as N,N,N′,N′-tetramethyldiglycolamide (or TMDGA), N,N,N′,N′-tetraethyldiglycolamide (or TEDGA) or N,N,N′,N′-tetrapropyldiglycolamide (or TPDGA), preference then being given to TEDGA.

[0058] If such a complexing agent is used, then it is preferably present in the aqueous solution A2 at a concentration ranging from 0.001 mol / L to 1 mol / L.

[0059] In accordance with the invention, step b) can be carried out hot, that is to say typically at a temperature ranging from 40° C. to 60° C., to favor the stripping of the rare earth(s), particularly when the aqueous solution A2 consists of water.

[0060] The recovery method advantageously comprises one or more washings of the organic solution obtained at the end of step b) with a view to the reuse thereof.

[0061] Thus, the organic solution obtained at the end of step b) may particularly be subjected to:

[0062] a first so-called “acid” washing, by at least one step of bringing the organic solution into contact with a strongly acidic aqueous solution, for example a sulfuric acid solution at 4 mol / L, followed by separating the organic solution from this acidic aqueous solution; and

[0063] a second so-called “water” washing, by at least one step of bringing the organic solution derived from the acid washing into contact with water, preferably deionized, followed by separating the organic solution from this water.

[0064] Within the scope of the invention, the aqueous solution A1 is preferably a solution derived from the leaching of waste electrical and electronic equipment by an organic acid or a mixture of organic acids.

[0065] In particular, the aqueous solution A1 is a solution derived from the leaching of a spent or scrapped powder of NdFeB permanent magnets by an organic acid or a mixture of organic acids, preferably by acetic acid as described in reference [3], such that this solution comprises neodymium, dysprosium and praseodymium.

[0066] “Scrapped” permanent magnets means all the scraps from the manufacturing of permanent magnets, and this, regardless of the form in which these scraps occur (powders, chips or more solid elements).

[0067] Other features and advantages of the method of the invention will emerge from the following additional description, which relates to experimental tests having made it possible to validate this method.

[0068] It goes without saying that this additional description is given only by way of illustration of the object of the invention and must under no circumstances be interpreted as a limitation of this object.BRIEF DESCRIPTION OF THE FIGURES

[0069] FIG. 1 illustrates the evolution of the distribution coefficients, noted DM, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, depending on the concentration of sodium nitrate, noted [NaNO3] and expressed in mol / L, as observed for extractions having been carried out by using, on the one hand, aqueous phases corresponding to aliquot parts of a leach resulting from leaching of a powder of NdFeB permanent magnets by acetic acid and comprising sodium nitrate at concentrations ranging from 0.25 mol / L to 1 mol / L and, on the other hand, organic phases comprising 0.05 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture.

[0070] FIG. 2 is a figure similar to FIG. 1 but for extractions having been carried out by using organic phases comprising 0.1 mol / L of TODGA in the n-dodecane / n-octanol mixture.

[0071] FIG. 3 is a figure similar to FIGS. 1 and 2 but for extractions having been carried out by using organic phases comprising 0.25 mol / L of TODGA in the n-dodecane / n-octanol mixture.

[0072] FIG. 4, provided by way of comparison, illustrates the evolution of the distribution coefficients, noted DM, of neodymium, praseodymium and dysprosium, depending on the concentration of TODGA, noted [TODGA] and expressed in mol / L, as observed for extractions having been carried out by using, on the one hand, aqueous phases corresponding to aliquot parts of a leach resulting from leaching of a powder of NdFeB permanent magnets by acetic acid and free of sodium nitrate and, on the other hand, organic phases comprising from 0.05 mol / L to 1 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture.

[0073] FIG. 5 illustrates the evolution of the distribution coefficients, noted DM, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, depending on the duration of the aqueous phase / organic phase contact, noted t and expressed in minutes, as observed for extractions having been carried out by using, on the one hand, aqueous phases corresponding to aliquot parts of a leach resulting from leaching of a powder of NdFeB permanent magnets by acetic acid and comprising sodium nitrate at a concentration of 0.6 mol / L and, on the other hand, organic phases comprising 0.25 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture.

[0074] FIG. 6 illustrates the distribution coefficients, noted DM, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, depending on the organic diluent as obtained for extractions having been carried out by using, on the one hand, aqueous phases corresponding to aliquot parts of a leach resulting from leaching of a powder of NdFeB permanent magnets by acetic acid and comprising sodium nitrate at a concentration of 0.6 mol / L and, on the other hand, organic phases comprising 0.25 mol / L of TODGA in isooctane, n-octanol, n-dodecane and a n-dodecane / n-octanol (95 / 5, v / v) mixture.

[0075] FIG. 7 illustrates the evolution of the stripping yields, noted RM and expressed in %, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, depending on the aqueous phase / organic phase volume ratio, noted A / O, as observed for strippings having been carried out by using, on the one hand, organic phases loaded with metal elements and comprising 0.25 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture, and, on the other hand, aqueous phases consisting of deionized water.

[0076] FIG. 8 illustrates the evolution of the stripping yields, noted RM and expressed in %, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, depending on the temperature, noted T and expressed in ° C., as observed for strippings having been carried out by using, on the one hand, organic phases loaded with metal elements and comprising 0.25 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture and, on the other hand, aqueous phases consisting of deionized water.

[0077] FIG. 9 schematically illustrates the four steps of each cycle of a 9-cycle test intended to verify the recyclability of an organic phase comprising 0.25 mol / TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture and used to extract RE from a leach obtained by leaching of a powder of NdFeB permanent magnets by acetic acid and comprising sodium nitrate at a concentration of 0.6 mol / L; in this figure, PO means organic phase while PA means aqueous phase.

[0078] FIG. 10 illustrates the evolution of the distribution coefficients, noted DM, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, depending on the number of cycles, as observed for the 9-cycle test shown schematically in FIG. 9.

[0079] FIG. 11 illustrates the evolution of the stripping yields, noted RM and expressed in %, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, depending on the number of cycles, as observed for the 9-cycle test shown schematically in FIG. 9.DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTSExample I: Extraction of RE

[0080] The liquid-liquid extractions, the results of which are reported hereinafter, were carried out by using:

[0081] as aqueous phases loaded with metal elements: aliquot parts of a leach obtained by leaching of a powder of NdFeB permanent magnets by acetic acid at 1.6 mol / L, the leach being added (for the extractions in accordance with the invention) or not (for the extractions carried out by way of comparison) with sodium nitrate (NaNO3) as a salting out agent, and

[0082] as organic extraction phases: solutions comprising TODGA in an organic diluent.

[0083] Leaching of the powder of NdFeB permanent magnets was conducted for 24 hours, with a solid / liquid ratio of 0.5% and at a temperature of 60° C.

[0084] The concentrations of RE and other metal elements present in the leach are presented in Table 1 hereinafter.TABLE 1ConcentrationsElementsppmmMol / LFe3 25858.3 Nd1 3079.1Dy  620.4Pr  1671.2Co  802.9Ni  250.4B  555.1

[0085] Each extraction was carried out by bringing, in a 5 mL vial stirred at 400 rpm in a thermostatic stirrer (20° C.), an aqueous phase into contact with an organic phase. Unless otherwise indicated, the aqueous phase / organic phase (A / O) volume ratio was 1 and the contact time was 60 minutes. At the end of the stirring period, the mixture was centrifuged (10 000 rpm-5 minutes) and the aqueous and organic phases were separated from one another.

[0086] The aqueous phases obtained at the end of the extractions were diluted in 1% nitric acid and analyzed by inductively coupled plasma emission spectroscopy (ICP-OES) while the organic phases were mineralized in the microwave in a mixture comprising 69% nitric acid and 35% hydrogen peroxide (HNO3 / H2O2=9 / 1, v / v) then diluted in 1% nitric acid and analyzed by inductively coupled plasma mass spectrometry (ICP-MS).

[0087] From the results of these analyses, the distribution coefficients were determined in accordance with the conventions in the field of liquid-liquid extractions, namely that the distribution coefficient of a metal element M, noted DM, between two phases, organic and aqueous respectively, is equal to:DM=[M]org,eq[M]aq,eqwith:[M]org,eq=concentration of the metal element in the organic phase at extraction equilibrium (in g / L or mol / L), and[M]aq,eq=concentration of the metal element in the aqueous phase at extraction equilibrium (in g / L or mol / L).

[0090] All extractions were carried out in triplicate in order to evaluate the statistical reliability of the results.I.1—Influence of the Presence of NaNO3 in the Aqueous Phases on the Extraction of RE by TODGA

[0091] The influence of the presence of NaNO3 in the aqueous phases on the extraction of RE was demonstrated:

[0092] by carrying out extractions with aqueous phases comprising from 0.25 mol / L to 1 mol / L of NaNO3 and organic phases comprising either 0.05 mol / L or 0.1 mol / L or 0.25 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture, n-octanol serving as a phase modifier, and

[0093] by comparing the distribution coefficients of the RE obtained at the end of these extractions with those obtained for extractions carried out with aqueous phases free of NaNO3 and organic phases comprising from 0.05 mol / L to 1 mol / L of TODGA, also in the n-dodecane / n-octanol mixture.

[0094] FIGS. 1 to 4 respectively illustrate:

[0095] FIG. 1: the evolution of the distribution coefficients DM of the RE (Nd, Pr and Dy) as well as the other metal elements (Fe, B, Co and Ni) depending on the concentration of NaNO3 as observed for the extractions carried out with aqueous phases comprising NaNO3 and organic phases comprising 0.05 mol / L of TODGA;

[0096] FIG. 2: the evolution of the distribution coefficients DM of the RE as well as of the other metal elements depending on the concentration of NaNO3 as observed for the extractions carried out with aqueous phases comprising NaNO3 and organic phases comprising 0.1 mol / L of TODGA;

[0097] FIG. 3: the evolution of the distribution coefficients DM of the RE as well as of the other metal elements depending on the concentration of NaNO3 as observed for the extractions carried out with aqueous phases comprising NaNO3 and organic phases comprising 0.25 mol / L of TODGA;

[0098] FIG. 4: the evolution of the distribution coefficients DM of the RE depending on the concentration of TODGA as observed for extractions carried out with aqueous phases free of NaNO3.

[0099] These figures show that the presence in the aqueous phase of a salting out agent such as NaNO3 leads to a substantial increase in the distribution coefficients of the RE in relation to those obtained in the absence of a salting out agent. This increase is most marked in the case where TODGA is used in the organic phase of up to 0.25 mol / L (FIG. 3) and where the presence in the aqueous phase of NaNO3 of up to 0.25 mol / L leads to a multiplication of the distribution coefficients of Dy, Nd and Pr by factors of 80, 116 and 200 respectively.

[0100] In addition, FIGS. 1 to 3 show that, regardless of the concentration of TODGA in the organic phase, an increase in the concentration of NaNO3 in the aqueous phase leads to obtaining increasingly higher distribution coefficients of RE. Thus, at 1 mol / L of NaNO3, a single aqueous phase / organic phase contact makes it possible to extract quantitatively all the RE (Nd, Pr and Dy).

[0101] The presence of NaNO3 in the aqueous phase results in the extraction of other metal elements (Fe, B, Co and Ni). However, the distribution coefficients of these metals remain very low (DM<0.1) regardless of the concentrations of TODGA and NaNO3 used. The selectivity of RE extraction with respect to other metal elements therefore tends to increase for increasing concentrations of NaNO3 in the aqueous phase. Thus, the presence of a salting out agent such as NaNO3 does not change the selective nature of the extraction of RE by TODGA with respect to the other metal elements.

[0102] Finally, FIGS. 1 to 3 show that, depending on the extraction implementation conditions, it should be possible to extract dysprosium selectively with respect to didymium (i.e. Nd+Pr).I.2—Influence of the Presence of NaNO3 in the Aqueous Phases on the Kinetics of Extracting RE by TODGA

[0103] The influence of the presence of NaNO3 in the aqueous phases on the kinetics of extracting RE by TODGA was demonstrated by carrying out extractions with aqueous phases comprising 0.6 mol / L of NaNO3 and organic phases comprising 0.25 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture, and by varying the contact time of the aqueous phase / organic phase from 1 minute to 60 minutes.

[0104] The results are presented in FIG. 5 that shows the evolution of the distribution coefficients DM of the RE as well as the other metal elements, depending on the contact time between the aqueous and organic phases.

[0105] As shown on this figure, the thermodynamic equilibrium is reached in less than 5 minutes for RE and other metal elements with the exception of nickel, for which the equilibrium is only reached after 10 minutes of contact.

[0106] Thus, in less than 5 minutes, 99% of the dysprosium, 96% of the neodymium and 94% of the praseodymium initially present in the aqueous phases return to the organic phase, while more than 99% of the other metal elements remain in the aqueous phase.I.3—Influence of the Organic Diluent on the Extraction of RE by TODGA

[0107] The influence of the organic diluent on the extraction of RE by TODGA was demonstrated by carrying out extractions with aqueous phases comprising 0.6 mol / L of NaNO3 and organic phases comprising 0.25 mol / L of TODGA in an aliphatic diluent selected from isooctane, n-octanol, hydrogenated tetrapropylene (or TPH) and a n-dodecane / n-octanol (95 / 5, v / v) mixture.

[0108] For these extractions, the aqueous phase / organic phase contact time was 5 minutes.

[0109] The results are presented in FIG. 6 that illustrates, in the form of a bar chart, the distribution coefficients DM obtained for the RE and other metal elements depending on the organic diluent used.

[0110] This figure shows that the RE can be extracted very efficiently by TODGA from an aqueous phase comprising a salting out agent such as NaNO3, and this, regardless of the organic diluent in which TODGA is dissolved, the highest distribution coefficients of RE being however obtained when the diluent is a n-dodecane / n-octanol (95 / 5, v / v) mixture.

[0111] It should be noted that the addition of n-octanol to the n-dodecane is necessary to avoid the appearance of a third phase. In the case of other diluents, the addition of n-octanol has no usefulness, which may simplify the implementation of the method of the invention on an industrial scale.Example II: Stripping of RE

[0112] The liquid / liquid strippings, the results of which are reported hereinafter, were carried out by using:

[0113] as organic phases loaded with metal elements: the organic phases derived from extractions having been carried out with aqueous phases comprising 0.6 mol / L of NaNO3, organic phases comprising 0.25 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture and a contact time of 5 minutes (see point 1.2 above), and

[0114] as aqueous stripping phases: either an aqueous solution of EDTA or TEDGA (point II.1 hereinafter) or deionized water (point II.2 hereinafter).

[0115] The concentrations of RE and other metal elements present in the organic phases are presented in Table 2 hereinafter.TABLE 2ConcentrationsElementsppmmMol / LFe 1913.4Nd11748.1Dy 600.4Pr 1441.0Co  70.2Ni  2 0.03B——

[0116] Each stripping was carried out by bringing, in a 5 mL vial stirred at 400 rpm in a thermostatic stirrer (20° C.-60° C.), an aqueous phase into contact with an organic phase. At the end of the stirring period, the mixture was subjected to a centrifugation (10 000 rpm-5 min) and the aqueous and organic phases were separated from one another.

[0117] The conditions under which the aqueous and organic phases obtained at the end of the strippings were analyzed are identical to those mentioned in Example 1 above for the extractions.

[0118] The stripping yields were also determined in accordance with the conventions in the field of liquid-liquid extractions, namely that the extraction yield of a metal element M, noted RM and expressed in %, of an organic phase is equal to:RM=Maq,fMorg,i×1⁢0⁢0with:Mag,f=amount of M in the aqueous phase after stripping (in g or mol), andMorg,i=amount of M in the organic phase before stripping (in g or mol).

[0121] All the strippings were carried out in triplicate in order to evaluate the statistical reliability of the results.II.1—Stripping of RE without Intra-RE Selectivity

[0122] The possibility of stripping all the RE of an organic phase comprising TODGA was verified by using as aqueous stripping phases, aqueous phases comprising either EDTA or TEDGA at concentrations of 0.001 mol / L, 0.01 mol / L and 0.1 mol / L.

[0123] The strippings were carried out at 20° C. with an A / O ratio of 1 and a contact time of 60 minutes.

[0124] The aqueous phases of EDTA at 0.01 mol / L and of TEDGA at 0.1 mol / L made it possible to strip almost all (>95%) of all of the rare earths in a single organic phase / water phase contact, and this, selectively with respect to the other metal elements present in the organic phase.II.2—Stripping of RE with Intra-RE Selectivity

[0125] The possibility of stripping the RE, selectively from one another, from an organic phase comprising TODGA was verified by using deionized water as the aqueous stripping phases.

[0126] The strippings were carried out:

[0127] on the one hand, at 20° C. with an A / O ratio ranging from 0.3 to 10 and a contact time of 5 minutes, and

[0128] on the other hand, at a temperature ranging from 20° C. to 60° C. with an A / O ratio of 0.5 and a contact time of 5 minutes.

[0129] The results obtained in terms of stripping yields RM are illustrated in FIGS. 7 and 8.

[0130] These figures show that, under the stripping conditions used, the stripping of light rare earths RE (Nd and Pr: didymium) is favored in relation to that of dysprosium. This can be explained by the more pronounced affinity of TODGA for the heavy rare earths, resulting in more difficult stripping of the latter.

[0131] By using deionized water as the aqueous phase of stripping, a maximum intra-RE selectivity of the stripping can be achieved by using a A / O ratio of about 0.5.

[0132] In addition, the extraction step having an exothermic nature, the increase in temperature favors the stripping of all the rare earths and disadvantages the selective stripping between didymium and dysprosium.

[0133] Finally, deionized water stripping makes it possible to maintain an excellent selectivity with respect to other metal elements (Fe, Co, Ni and B), the majority of which (>99%) remains in the organic phase.Example III: Recyclability of the Organic Phase Used for the Extraction of RE

[0134] In order to assess the recyclability of an organic phase used to extract RE from a leach obtained by leaching of a powder of NdFeB permanent magnets by acetic acid (1.6 mol / L) and comprising 0.6 mol / L NaNO3, 9 cycles were carried out each comprising a step of extracting the RE, a step of stripping the RE and two steps of washing, respectively acid and water, of the organic phase as illustrated in FIG. 9.

[0135] As shown in this figure, wherein PO means organic phase and PA means aqueous phase, the difference existing between the first cycle and the second to ninth cycles lies in the fact that the extraction step of the first cycle was carried out with a “fresh” organic phase, comprising 0.25 mol / L of TODGA in a n-dodecane / n-octanol (95 / 5, v / v) mixture, while the extraction step of each of the second to ninth cycles was carried out with the organic phase derived from the water washing step of the previous cycle.

[0136] Apart from this difference, the operating conditions under which the 9 cycles were conducted were the same, namely that:

[0137] each extraction step was carried out by bringing an aliquot part of the leach into contact with an organic phase (fresh or recycled), at a temperature of 20° C., with an A / O ratio of 1 and a contact time of 5 minutes, then separating the aqueous and organic phases;

[0138] each stripping step was carried out by bringing the organic phase derived from the preceding extraction step into contact with an aqueous phase comprising 0.01 mol / L of EDTA, at a temperature of 20° C., with an A / O ratio of 1 and a contact time of 5 minutes, then separating the organic and aqueous phases;

[0139] each acid washing step was carried out by bringing the organic phase derived from the preceding stripping step into contact with an aqueous solution of sulfuric acid at 4 mol / L, at a temperature of 40° C., with an A / O ratio of 1 and a contact time of 30 minutes, then separating the organic and aqueous phases;

[0140] each water washing step was carried out by bringing the organic phase derived from the preceding acid washing step into contact with deionized water, at a temperature of 40° C., with an A / O ratio of 1 and a contact time of 30 minutes, then separating the organic and aqueous phases.

[0141] The aqueous and organic phases obtained at the end of the extractions and strippings were analyzed under conditions identical to those mentioned in Example 1 above.

[0142] The distribution coefficients DM obtained for the extraction step of each of the 9 cycles are illustrated in FIG. 10 while the stripping yields RM obtained for the stripping step of each of the 9 cycles are illustrated in FIG. 11.

[0143] FIG. 10 shows that the distribution coefficients of the rare earths remain high and in the same order of magnitude for all the cycles without loss of selectivity with respect to the other metal elements.

[0144] FIG. 11 shows, for its part, that the use of an EDTA solution at 0.01 mol / L as an aqueous stripping phase makes it possible for each cycle to recover 90% of the RE previously extracted in the organic phase, and this, again, selectively with respect to the other metal elements that have been extracted in the trace state.

[0145] It can therefore be deduced therefrom that the organic phase is perfectly reusable at least 9 times.REFERENCES CITED[1] WO-A-2016 / 046179

[0147] [2] M. Gergoric et al., Journal of Sustainable Metallurgy 2019, 5 (1), 85-96

[0148] [3] S. Belfqueh et al., Journal of Rare Earths 2022, https: / / doi.org / 10.1016 / j.jre.2022.04.027.

Claims

1. A method for extracting at least one rare earth from an aqueous solution A1, the method comprising:bringing the aqueous solution A1 into contact with a water-immiscible organic solution, comprising as an extractant, a diglycolamide of formula (I): dissolved in an organic diluent, in an organic phase; followed byseparating the aqueous solution A1 from the organic phasewherein the organic acid comprises formic acid, acetic acid, propionic acid, lactic acid, glycolic acid, oxalic acid, malonic acid, maleic acid, tartaric acid, fumaric acid, mesoxalic acid, glutaric acid, diglycolic acid, citric acid, isocitric acid, tricarballylic acid, and / or trimesic acid, andwherein the aqueous solution A1 further comprises a salting out agent, the salting out agent being a salt of an alkali metal, a salt of an alkaline earth metal, or an ammonium saltwherein the aqueous solution A1, prior to the bringing into contact, comprises an organic acid, a rare earth, and a transition metal.

2. The method of claim 1, whereinthe aqueous solution A1 comprises the organic acid in a range of from 0.1 to 16 mol / L.

3. The method of claim 1, wherein the salting out agent islithium, sodium, potassium, calcium, or magnesium chloride,lithium, sodium, potassium, calcium, or magnesium nitrate,lithium, sodium, potassium, calcium, or magnesium sulfate,lithium, sodium, potassium, calcium, or magnesium phosphate, orammonium chloride, nitrate, sulfate or phosphate.

4. The method of claim 1, wherein the aqueous solution A1 comprises the salting out agent in a range of from 0.25 to 1 mol / L.

5. The method of claim 1, wherein the organic phase comprises the diglycolamide in a range of from 0.05 to 0.4 mol / L.

6. A method for recovering one or more rare earths from a first aqueous solution A1, the method comprising:(a) extracting the rare earth or co-extracting the rare earths from the aqueous solution A1 by the method of claim 1; then(b) stripping the rare earth or at least one of the rare earths from the organic solution obtained after the extracting (a), the stripping comprising bringing the organic solution into contact with a second aqueous solution A2, followed by separating the organic solution from the second aqueous solution A2.

7. The method of claim 6, wherein the second aqueous solution A2 comprises an agent complexing the rare earths in an aqueous medium.

8. The method of claim 6, wherein the first aqueous solution A1 comprisesa first rare earth RE1, with an atomic number at most equal to 61, anda second rare earth RE2, with an atomic number at least equal to 62,wherein, in the stripping (b), the first and second rare earths RE1 and RE2 are co-stripped from the organic solution obtained after the extracting (a).

9. The method of claim 8, wherein the second aqueous solution A2 comprises an agent complexing the rare earths in an aqueous medium.

10. The method of claim 6, wherein the first aqueous solution A1 comprisesa first rare earth RE1, with an atomic number at most equal to 61, anda second rare earth RE2, with an atomic number at least equal to 62,wherein the stripping (b) comprises:(b1) stripping the first rare earth(s) RE1 from the organic solution obtained after the extracting (a) with the second aqueous solution A2; then(b2) stripping the second rare earth(s) RE2 from the organic solution obtained after the stripping (b1), stripping comprising bringing the organic phase into contact with a third aqueous solution A3 different from the second aqueous solution A2, followed by separating the organic phase from the third aqueous solution A3.

11. The method of claim 10, wherein the second aqueous solution A2 consists of water, andwherein the third aqueous solution A3 comprises an agent complexing the rare earths in an aqueous medium.

12. The method of claim 7, wherein the agent complexing the rare earths in an aqueous medium is an aminopolycarboxylic acid or a hydrophilic diglycolamide.

13. The method of claim 6, further comprising:washing the organic phase obtained after the stripping (b) for reuse thereof.

14. The method of claim 1, wherein the aqueous solution A1 is derived from leaching waste electrical and electronic equipment by an organic acid or a mixture of organic acids.

15. The method of claim 14, wherein the aqueous solution A1 is derived from leaching a spent or scrapped neodymium-iron-boron permanent magnet powder by at least one organic acid, andwherein the aqueous solution A1 comprises neodymium, dysprosium, and praseodymium.

16. The method of claim 14, wherein the organic acid is acetic acid.

17. The method of claim 1, wherein the aqueous solution A1 comprises the organic acid in a range of from 0.5 to 2 mol / L.

18. The method of claim 1, wherein the organic acid comprises plural organic acids.

19. The method of claim 1, wherein the salting out agent comprises lithium, sodium, and / or potassium nitrate.

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