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

Abstract

The invention relates to a method for extracting at least one rare earth from an aqueous solution Al of an organic acid or of a mixture of organic acids comprising, in addition to one or more rare earths, one or more transition metals, which method comprises at least one step of bringing the aqueous solution Al into contact with a water-immiscible organic solution comprising, as an extractant, the diglycolamide of formula (I): dissolved in an organic diluent, followed by separating the aqueous solution Al from the organic solution, wherein the method is characterised in that the aqueous solution Al further comprises a salting-out agent. It also relates to a method for recovering, together or separately, the thus extracted rare earths.

Description

[0001] PROCESSES FOR THE EXTRACTION AND RECOVERY OF RARE EARTH ELEMENTS FROM AQUEOUS SOLUTIONS OF ORGANIC ACIDS

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The invention relates to the field of extraction and recovery of rare earths present in natural or urban ores.

[0005] More specifically, it relates to a process for extracting rare earths from an aqueous solution of one or more organic acids, with high extraction yields and high selectivity with respect to other metallic elements likely to also be present in this solution and, in particular, with respect to iron.

[0006] It also relates to a process for recovering, together or separately, the rare earths thus extracted.

[0007] The invention finds applications in particular in the production of rare earths from concentrates derived from “urban ores”, i.e. “mines” made up of industrial and domestic waste containing rare earths and, in particular, in the recycling of rare earths present in waste electrical and electronic equipment, also called “WEEE” or “D3E”.

[0008] More particularly, the invention finds an application in the recycling of rare earths contained in used or discarded permanent magnets, and, in particular, in permanent magnets of the Neodymium-Iron-Boron (or NdFeB) type.

[0009] However, it can also be used to produce rare earths from concentrates of natural ores such as monazites, bastnaesites, apatites or xenotimes, or from concentrates of natural ore residues such as, for example, tin slag.

[0010] STATE OF THE PRIOR ART

[0011] Rare earth elements (hereinafter "RE") are metals characterized by similar properties, namely scandium (Sc), yttrium (Y) and all the 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 lutetium (Lu).

[0012] The particular electronic configuration of TRs, and in particular their unsaturated 4f electronic subshell, gives them unique chemical, structural and physical properties. These properties are used in industrial applications as varied as they are sophisticated: glass and ceramics industries, polishing, catalysis, manufacturing of high-tech alloys, permanent magnets, optical devices, phosphors, rechargeable batteries for electric or hybrid vehicles, alternators for wind turbines, etc.

[0013] TRs are therefore part of the so-called “technological” metals whose supply is strategic.

[0014] However, as there are few countries producing rare earths from mineral deposits (China alone currently accounts for nearly 60% of the world's annual production of rare earths), there is a significant risk of a disruption in the supply of rare earths in the long term, hence the need to optimize all the ways in which they can be produced.

[0015] At the same time, growing environmental awareness is driving the constant search for alternatives to mining, such as substituting the chemicals used, reducing demand, or recycling used products or production waste. Recycling is emerging as a pillar of the circular economy, which involves optimizing the value generated by resources by reducing the need for primary resources and avoiding landfilling end-of-life products.

[0016] One of the first markets, in terms of volume and potential market value, for recycling WTs concerns NdFeB permanent magnets, which are present in various high-tech products such as electric or hybrid vehicles, wind turbines, hard drives and induction motors. This resource for WT recycling is particularly interesting to exploit because these magnets contain a significant quantity of light WTs (approximately 30% by mass of a neodymium / praseodymium mixture) and a smaller quantity of heavy WTs with high economic value, including dysprosium. In addition to containing a significant quantity of iron and a smaller quantity of boron, NdFeB permanent magnets are generally covered with a protective anti-corrosion coating based on nickel and other transition metals such as cobalt.

[0017] Most of the work aimed at recovering TRs present in natural or urban ores by liquid-liquid extraction has been carried out on aqueous solutions resulting from the treatment of these ores with inorganic acids such as nitric acid, hydrochloric acid, sulfuric acid or phosphoric acid.

[0018] Thus, for example, international application WO-A-2016 / 046179, hereinafter reference [1], describes the use of lipophilic diglycolamides such as N,N,N',N'-tetra-octyl-3-oxapentanediamide (or TODGA) and / V, / V, / \ / ', / \ / '-tetradodecyl-3-oxapentane-diamide (or TdDDGA) as extractants, to selectively recover TRs from aqueous solutions resulting from the leaching of a powder of used or discarded NdFeB permanent magnets by an inorganic acid, which is preferably nitric acid but which can also be sulfuric acid, hydrochloric acid or phosphoric acid.

[0019] Recently, two studies have shown the possibility of effectively leaching NdFeB permanent magnet powders with organic acids.

[0020] These are:

[0021] - on the one hand, from a study published by M. Gergoric et al. in Journal of Sustainable Metallurgy 2019, 5(1), 85-96, hereinafter reference [2], and in which the organic acids used are glycolic acid, maleic acid and ascorbic acid, and

[0022] - 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 in which the organic acids used are acetic acid, formic acid, citric acid and tartaric acid.

[0023] The advantages of using organic acids over inorganic acids such as nitric, hydrochloric or sulfuric acids are numerous, namely that organic acids, which are generally derived from biological sources, are slightly or non-corrosive, generate fewer toxic gases than inorganic acids and are mostly biodegradable, which significantly reduces the ecological impact of leaching.

[0024] Having also been interested in the possibility of extracting TRs from glycolic acid and maleic acid leachates and having tested several types of extractants (tri-n-butyl phosphate or TBP, (2-ethylhexyl)phosphoric acid or D2EHPA, TODGA, Cyanex™ 1 and Cyanex™ 923), M. Gergoric et al. showed in reference [2] that TODGA, at a concentration of 1 mol / L in organic solution, allows the extraction of neodymium, dysprosium and praseodymium selectively with respect to iron, cobalt and boron but only from maleic acid leachate.

[0025] As part of their work on the recovery of TRs from acidic aqueous solutions resulting from the treatment of used or discarded NdFeB permanent magnets, the inventors observed:

[0026] - 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 TRs from an aqueous solution resulting 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);

[0027] - that in addition to the selectivity towards iron, cobalt, nickel and boron, TODGA has, in the context of this use, more affinity for heavy TRs such as dysprosium than for light TRs such as neodymium and praseodymium (unpublished data), which is interesting in the perspective of a selective recovery of these TRs; but

[0028] - that despite these advantages, the distribution coefficients of the TRs obtained during the extractions and, therefore, the extraction yields are relatively low (unpublished data), which is a disadvantage for implementation on an industrial scale.

[0029] The inventors therefore set themselves the goal of improving these distribution coefficients and, at the same time, these extraction yields.

[0030] However, still within the framework of their work, the inventors noted that, surprisingly, the distribution coefficients, the extraction yields as well as the extraction kinetics obtained during extractions by TODGA of TRs from an aqueous solution resulting from the leaching of a powder of NdFeB permanent magnets by an organic acid, such as acetic acid, are considerably improved when a release agent is added to this aqueous solution, without affecting the extraction selectivity with respect to other metallic elements (iron, cobalt, boron, etc.) or the preference that TODGA shows for heavy TRs.

[0031] And it is on the basis of these experimental findings that the invention was developed.

[0032] STATEMENT OF THE INVENTION

[0033] The invention therefore relates, firstly, to a process for extracting one or more rare earths from an aqueous solution Al of an organic acid or a mixture of organic acids comprising, in addition to the rare earth(s), one or more transition metals, which process comprises at least one contacting of the aqueous solution Al with an organic solution immiscible with water, comprising as extractant, TODGA, i.e. diglycolamide of formula: in solution in an organic diluent, followed by separation of the aqueous solution Al from the organic solution, and is characterized in that the aqueous solution Al further comprises a release agent.

[0034] In the foregoing and following, the expressions "from .... to ....", "ranging from .... to ...." and "between .... and ...." are equivalent and are intended to mean that the limits are included.

[0035] Likewise, the terms “solution” and “phase” are equivalent and perfectly interchangeable.

[0036] According to the invention, the concentration of the organic acid or mixture of organic acids in the aqueous solution Al can range from 0.1 mol / L to 16 mol / L, preferably a concentration of between 0.5 mol / L and 2 mol / L. This organic acid or the organic acids of the mixture can be chosen 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.

[0037] The salting out agent can be any electrolyte capable of improving the capacity of TODGA to extract TRs from an organic solution, in particular by a dehydrating power making it possible to reduce the quantity of free water molecules in the system and, consequently, the solubility of TRs in aqueous solution.

[0038] Preferably, the release 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.

[0039] Among these, every preference is given to a nitrate and, more particularly, to a nitrate of an alkali or alkaline-earth metal and, even more so, to lithium nitrate, sodium nitrate and potassium nitrate.

[0040] According to the invention, the release agent is added to the aqueous solution Al at a concentration preferably ranging from 0.25 mol / L to 1 mol / L, for example 0.6 mol / L, of aqueous solution Al.

[0041] As for TODGA, it is present in the organic solution at a concentration preferably ranging from 0.05 mol / L to 1 mol / L, for example 0.25 mol / L.

[0042] The organic diluent in which the TODGA is dissolved may be any non-polar aliphatic organic diluent that has been proposed for use in performing liquid-liquid extractions such as an alcohol such as n-octanol, n-decanol or isodecanol, or a hydrocarbon or mixture of hydrocarbons, for example isooctane, n-dodecane, hydrogenated tetrapropylene (or TPH), kerosene, Isane™ IP-185T or Isane™ IP-175T, with preference given to n-dodecane.

[0043] The organic solution may further comprise a phase modifier capable of increasing the loading capacity of the TODGA in the organic diluent used, i.e. the maximum concentration of metallic elements that the organic solution may have without the formation of a third phase by demixing when it is brought into contact with an aqueous phase loaded with metallic elements.

[0044] The use of a phase modifier is, for example, indicated in the case where the organic diluent is n-dodecane.

[0045] This phase modifier may in particular be chosen 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 / V, / V-dihexyloctanamide (or DHOA), / V, / V-dibutyldecanamide (or DBDA), N,N-di(2-ethylhexyl)acetamide (or D2EHAA), / V, / V-di(2-ethylhexyl)propionamide (or D2EHPA), / V, / V-di(2-ethylhexyl)isobutyramide (or D2EHIBA) or / V, / V-dihexyldecanamide (or DHDA).

[0046] Furthermore, this phase modifier preferably represents no more than 15% by volume of the volume of the organic solution, or even no more than 10% by volume of the volume of this solution when it is an alcohol such as n-octanol.

[0047] According to the invention, the extraction process is preferably carried out at room temperature, i.e. at a temperature ranging from 20°C to 25°C.

[0048] This extraction process can advantageously be used to recover one or more rare earths from an aqueous solution of an organic acid or a mixture of organic acids and, in particular, to recover together or separately one or more light rare earths, i.e. with an atomic number at most equal to 61, and one or more heavy rare earths, i.e. with an atomic number at least equal to 62, from such an aqueous solution.

[0049] Also, the invention also relates to a process for recovering one or more rare earths from an aqueous solution Al of an organic acid or a mixture of organic acids comprising, in addition to the rare earth(s), one or more transition metals, which process comprises at least the following steps: a) extraction of the rare earth or co-extraction of the rare earths from the aqueous solution Al by implementing an extraction process as previously defined; then b) back-extraction of the rare earth or at least one of the rare earths from the organic solution obtained at the end of step a), the back-extraction comprising at least one contacting of the organic solution with an aqueous solution A2, followed by a separation of the organic solution from the aqueous solution A2.

[0050] According to the invention, the aqueous solution A2 may consist of water, that is to say that it only comprises water, preferably deionized.

[0051] Alternatively, the aqueous solution A2 may also be a solution comprising an agent complexing rare earths in aqueous media.

[0052] As previously mentioned, in the case where the aqueous solution A1 comprises at least one light rare earth, TRI, and at least one heavy rare earth, TR2, then the rare earths TRI and TR2 can be recovered in a grouped manner, in which case, in step b), these rare earths are co-extracted 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.

[0053] Alternatively, the rare earths TRI and TR2 may be recovered separately, in which case step b) comprises: bi) a back-extraction of the rare earth(s) TRI from the organic solution obtained at the end of step a) which is carried out with the aqueous solution A2, then b2) a back-extraction of the rare earth(s) TR2 from the organic solution obtained at the end of bi), the back-extraction comprising at least one contacting of the organic solution with an aqueous solution A3 different from the aqueous solution A2, followed by a separation of the organic solution from the aqueous solution A3.

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

[0055] The agent for complexing rare earths in aqueous media that can be used in the context of the invention may in particular be: - an aminopolycarboxylic acid such as ethylenediamine tetraacetic acid (or EDTA), / V-(2-hydroxyethyl)ethylenediamine triacetic acid (or HEDTA), nitrilotriacetic acid (or NTA) or diethylenetriamine pentaacetic acid (or DTPA) or a salt thereof, for example a sodium salt; or

[0056] - a hydrophilic diglycolamide, i.e. a compound corresponding to the formula: R 1 (R 2 )NC(O)-CH2-O-CH2-C(O)-N(R 3 )R 4 in which R 1 , R 2 , R 3 and R 4, identical or different, represent alkyl groups, linear or branched, and whose total number of carbon atoms is at most 20, such as / V, / V, / V', / V'-tetramethyldiglycolamide (or TMDGA), N, N, / V', / V'-tetraethyldiglycolamide (or TEDGA) or N,N,N',N'-tetrapropyldiglycolamide (or TPDGA), preference then being given to TEDGA.

[0057] 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.

[0058] In accordance with the invention, step b) can be carried out hot, i.e. typically at a temperature ranging from 40°C to 60°C, to promote the de-extraction of the rare earth(s), in particular when the aqueous solution A2 consists of water.

[0059] The recovery process advantageously further comprises one or more washes of the organic solution obtained at the end of step b) with a view to its reuse.

[0060] Thus, the organic solution obtained at the end of step b) can in particular be subjected to:

[0061] - a first wash called “acid”, by at least one contact of the organic solution with a strongly acidic aqueous solution, for example a 4 mol / L sulfuric acid solution, followed by a separation of the organic solution from this acidic aqueous solution; and

[0062] - a second wash called "with water", by at least one contact of the organic solution resulting from the acid wash with water, preferably deionized, followed by a separation of the organic solution from this water.

[0063] In the context of the invention, the aqueous solution Al is preferably a solution resulting from the leaching of waste electrical and electronic equipment by an organic acid or a mixture of organic acids. In particular, the aqueous solution Al is a solution resulting from the leaching of a powder of used or discarded NdFeB permanent magnets by an organic acid or a mixture of organic acids, preferably by acetic acid as described in reference [3], so that this solution comprises neodymium, dysprosium and praseodymium.

[0064] By "scrap" permanent magnets we mean all waste from the manufacture of permanent magnets, regardless of the form in which this waste is presented (powders, shavings or more massive elements).

[0065] Other characteristics and advantages of the method of the invention will emerge from the additional description which follows, which relates to experimental tests which have made it possible to validate this method.

[0066] It goes without saying that this additional description is given only as an illustration of the subject of the invention and must in no case be interpreted as a limitation of this subject.

[0067] BRIEF DESCRIPTION OF THE FIGURES

[0068] Figure 1 illustrates the evolution of the distribution coefficients, denoted DM, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, as a function of the sodium nitrate concentration, denoted [NaNOs] and expressed in mol / L, as observed for extractions having been carried out using, on the one hand, aqueous phases corresponding to aliquots of a leachate resulting from a leaching of a NdFeB permanent magnet powder 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 an n-dodecane / n-octanol mixture (95 / 5, v / v).

[0069] Figure 2 is a figure similar to Figure 1 but for extractions carried out using organic phases comprising 0.1 mol / L of TODGA in the n-dodecane / n-octanol mixture.

[0070] Figure 3 is a figure similar to Figures 1 and 2 but for extractions carried out using organic phases comprising 0.25 mol / L of TODGA in the n-dodecane / n-octanol mixture. Figure 4, provided for comparison, illustrates the evolution of the distribution coefficients, noted DM, of neodymium, praseodymium and dysprosium, as a function of the TODGA concentration, noted [TODGA] and expressed in mol / L, as observed for extractions having been carried out using, on the one hand, aqueous phases corresponding to aliquot parts of a leachate resulting from a 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 mixture n-dodecane / n-octanol (95 / 5, v / v).

[0071] Figure 5 illustrates the evolution of the distribution coefficients, noted DM, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, as a function of the duration of the aqueous phase / organic phase contact, noted t and expressed in minutes, as observed for extractions having been carried out using, on the one hand, aqueous phases corresponding to aliquot parts of a leachate resulting from a 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 an n-dodecane / n-octanol mixture (95 / 5, v / v).

[0072] Figure 6 illustrates the distribution coefficients, denoted DM, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, as a function of the organic diluent as obtained for extractions having been carried out using, on the one hand, aqueous phases corresponding to aliquots of a leachate resulting from a 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 an n-dodecane / n-octanol mixture (95 / 5, v / v).

[0073] Figure 7 illustrates the evolution of the back-extraction yields, noted RM and expressed in %, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, as a function of the aqueous phase / organic phase volume ratio, noted A / O, as observed for back-extractions having been carried out using, on the one hand, organic phases loaded with metallic elements and comprising 0.25 mol / L of TODGA in an n-dodecane / n-octanol mixture (95 / 5, v / v), and, on the other hand, aqueous phases consisting of deionized water.

[0074] Figure 8 illustrates the evolution of the back-extraction yields, noted RM and expressed in %, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, as a function of the temperature, noted T and expressed in °C, as observed for back-extractions having been carried out using, on the one hand, organic phases loaded with metallic elements and comprising 0.25 mol / L of TODGA in a mixture n-dodecane / n-octanol (95 / 5, v / v) and, on the other hand, aqueous phases consisting of deionized water.

[0075] Figure 9 schematically illustrates the four steps of each cycle of a 9-cycle test designed to verify the recyclability of an organic phase comprising 0.25 mol / L of TODGA in an n-dodecane / n-octanol mixture (95 / 5, v / v) and used to extract TRs from a leachate obtained by leaching a NdFeB permanent magnet powder with 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.

[0076] Figure 10 illustrates the evolution of the distribution coefficients, noted DM, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, as a function of the number of cycles, as observed for the 9-cycle test schematically illustrated in Figure 9.

[0077] Figure 11 illustrates the evolution of the extraction yields, noted RM and expressed in %, of neodymium, praseodymium, dysprosium, iron, boron, cobalt and nickel, as a function of the number of cycles, as observed for the 9-cycle test schematically illustrated in Figure 9.

[0078] DETAILED PRESENTATION OF SPECIFIC IMPLEMENTATION METHODS

[0079] Example I: Extraction of TRs

[0080] The liquid-liquid extractions whose results are reported below were carried out using:

[0081] - as aqueous phases loaded with metallic elements: aliquot parts of a leachate obtained by leaching a powder of NdFeB permanent magnets with acetic acid at 1.6 mol / L, the leachate being supplemented (for the extractions in accordance with the invention) or not (for the extractions carried out for comparative purposes) with sodium nitrate (NaNOs) as a release agent, and

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

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

[0084] The concentrations of TRs and other metallic elements present in the leachate are presented in Table 1 below.

[0085] Table 1

[0086] Each extraction was carried out by placing, in a 5 mL flask shaken at 400 rpm in a thermostatically controlled shaker (20 °C), an aqueous phase in 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 subjected to centrifugation (10,000 rpm - 5 minutes) and the aqueous and organic phases were separated from each other.

[0087] The aqueous phases obtained from 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).

[0088] From the results of these analyses, the distribution coefficients were determined in accordance with the conventions of the field of liquid-liquid extractions, namely that the distribution coefficient of a metallic element M, noted DM, between two phases, respectively organic and aqueous, is equal to: with :

[0089] [M]org,eq = concentration of the metallic element in the organic phase at extraction equilibrium (in g / L or mol / L), and

[0090] [M] aq ,eq = concentration of the metallic element in the aqueous phase at extraction equilibrium (in g / L or mol / L).

[0091] All extractions were performed in triplicate to assess the statistical reliability of the results.

[0092] 1.1- Influence of the presence of NaNOs in the aqueous phases on the extraction of TRs by TODGA

[0093] The influence of the presence of NaNOs in the aqueous phases on the extraction of TRs was highlighted:

[0094] - by carrying out extractions with aqueous phases comprising from 0.25 mol / L to 1 mol / L of NaNOs and organic phases comprising either 0.05 mol / L or 0.1 mol / L or 0.25 mol / L of TODGA in an n-dodecane / n-octanol mixture (95 / 5, v / v), the n-octanol serving as a phase modifier, and

[0095] - by comparing the distribution coefficients of the TRs obtained at the end of these extractions with those obtained for extractions carried out with aqueous phases free of NaNOs and organic phases comprising from 0.05 mol / L to 1 mol / L of TODGA, also in the n-dodecane / n-octanol mixture.

[0096] Figures 1 to 4 illustrate respectively:

[0097] - figure 1: the evolution of the DM distribution coefficients of TR (Nd, Pr and Dy) as well as of the other metallic elements (Fe, B, Co and Ni) as a function of the concentration of NaNOs as observed for the extractions carried out with aqueous phases comprising NaNOs and organic phases comprising 0.05 mol / L of TODGA;

[0098] - figure 2: the evolution of the DM distribution coefficients of TRs as well as other metallic elements as a function of the concentration of NaNOs as observed for the extractions carried out with aqueous phases comprising NaNOs and organic phases comprising 0.1 mol / L of TODGA;

[0099] - figure 3: the evolution of the DM distribution coefficients of TRs as well as of the other metallic elements as a function of the concentration of NaNOs as observed for the extractions carried out with aqueous phases comprising NaNOs and organic phases comprising 0.25 mol / L of TODGA;

[0100] - figure 4: the evolution of the DM distribution coefficients of the TRs as a function of the TODGA concentration as observed for the extractions carried out with aqueous phases free of NaNOs.

[0101] These figures show that the presence in the aqueous phase of a release agent such as NaNOs leads to a significant increase in the distribution coefficients of the TRs compared to those obtained in the absence of a release agent. This increase is most marked in the case where TODGA is used in the organic phase at a level of 0.25 mol / L (figure 3) and where the presence in the aqueous phase of NaNOs at a level of 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.

[0102] Figures 1 to 3 further show that, regardless of the concentration of TODGA in the organic phase, an increase in the concentration of NaNOs in the aqueous phase leads to obtaining increasingly higher TR distribution coefficients. Thus, at 1 mol / L of NaNOs, a single aqueous phase / organic phase contact allows the quantitative extraction of all TRs (Nd, Pr and Dy).

[0103] The presence of NaNOs in the aqueous phase leads to the extraction of other metallic 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 NaNOs used. The extraction selectivity of TRs with respect to other metallic elements therefore tends to increase for increasing concentrations of NaNOs in the aqueous phase. Thus, the presence of a salting agent such as NaNOs does not change the selective nature of TR extraction by TODGA with respect to other metallic elements.

[0104] Finally, Figures 1 to 3 show that depending on the conditions of implementation of the extraction, it should be possible to extract dysprosium selectively with respect to didymium ( / .e. Nd + Pr).

[0105] 1.2- Influence of the presence of NaNOs in the aqueous phases on the kinetics of TR extraction by TODGA

[0106] The influence of the presence of NaNOs in the aqueous phases on the extraction kinetics of TRs by TODGA was demonstrated by carrying out extractions with aqueous phases comprising 0.6 mol / L of NaNOs and organic phases comprising 0.25 mol / L of TODGA in an n-dodecane / n-octanol mixture (95 / 5, v / v), and by varying the duration of the aqueous phase / organic phase contact from 1 minute to 60 minutes.

[0107] The results are presented in Figure 5 which shows the evolution of the DM distribution coefficients of TRs as well as other metallic elements, as a function of the duration of contact between the aqueous and organic phases.

[0108] As visible in this figure, thermodynamic equilibrium is reached in less than 5 minutes for TRs and other metallic elements with the exception of nickel for which equilibrium is only reached after 10 minutes of contact.

[0109] 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 are found in the organic phase while more than 99% of the other metallic elements remain in the aqueous phase.

[0110] 1.3 - Influence of organic diluent on TR extraction by TODGA

[0111] The influence of the organic diluent on the extraction of TRs by TODGA was demonstrated by carrying out extractions with aqueous phases comprising 0.6 mol / L of NaNOs and organic phases comprising 0.25 mol / L of TODGA in an aliphatic diluent chosen from isooctane, n-octanol, hydrogenated tetrapropylene (or TPH) and an n-dodecane / n-octanol mixture (95 / 5, v / v). For these extractions, the duration of the aqueous phase / organic phase contact was 5 minutes.

[0112] The results are presented in Figure 6 which illustrates, in the form of a bar diagram, the DM distribution coefficients obtained for TRs and other metallic elements as a function of the organic diluent used.

[0113] This figure shows that TRs can be extracted very efficiently by TODGA from an aqueous phase comprising a salting agent such as NaNOs, regardless of the organic diluent in which the TODGA is dissolved, the highest TR distribution coefficients being obtained, however, when the diluent is an n-dodecane / n-octanol mixture (95 / 5, v / v).

[0114] It should be noted that the addition of n-octanol to n-dodecane is necessary to avoid the appearance of a third phase. In the case of other diluents, the addition of n-octanol is not useful, which can simplify the implementation of the process of the invention on an industrial scale.

[0115] Example II: TR extraction

[0116] The liquid / liquid extractions whose results are reported below were carried out using:

[0117] - as organic phases loaded with metallic elements: the organic phases resulting from extractions having been carried out with aqueous phases comprising 0.6 mol / L of NaNOs, organic phases comprising 0.25 mol / L of TODGA in an n-dodecane / n-octanol mixture (95 / 5, v / v) and a contact time of 5 minutes (see point 1.2 above), and

[0118] - as aqueous de-extraction phases: either an aqueous solution of EDTA or TEDGA (point II.1 below) or deionized water (point 11.2 below).

[0119] The concentrations of TRs and other metallic elements present in the organic phases are presented in Table 2 below. Table 2

[0120] Each back-extraction was carried out by placing, in a 5 mL flask shaken at 400 rpm in a thermostatically controlled shaker (20 °C-60 °C), an aqueous phase in contact with an organic phase. At the end of the shaking period, the mixture was subjected to centrifugation (10,000 rpm - 5 min) and the aqueous and organic phases were separated from each other.

[0121] The conditions under which the aqueous and organic phases obtained at the end of the back-extractions were analyzed are identical to those mentioned in Example I above for the extractions.

[0122] The extraction yields were also determined in accordance with the conventions of the field of liquid-liquid extractions, namely that the extraction yield of a metallic element M, noted RM and expressed in %, from an organic phase is equal to: 100 with :

[0123] M aq>f= quantity of M in the aqueous phase after back-extraction (in g or mol), and M org i = quantity of M in the organic phase before back-extraction (in g or mol).

[0124] All extractions were performed in triplicate to assess the statistical reliability of the results. 11.1 - Extraction of TRs without intra-TR selectivity

[0125] The possibility of back-extracting all TRs from an organic phase comprising TODGA was verified using as back-extraction aqueous phases, aqueous phases comprising either EDTA or TEDGA at concentrations of 0.001 mol / L, 0.01 mol / L and 0.1 mol / L.

[0126] The extractions were carried out at 20°C with an A / O ratio of 1 and a contact time of 60 minutes.

[0127] The aqueous phases of 0.01 mol / L EDTA and 0.1 mol / L TEDGA made it possible to back-extract almost all (> 95%) of all the rare earths in a single organic phase / aqueous phase contact, and this, selectively with respect to the other metallic elements present in the organic phase.

[0128] 11.2 - TR de-extraction with intra-TR selectivity

[0129] The possibility of back-extracting TRs, selectively with respect to each other, from an organic phase comprising TODGA was verified using deionized water as aqueous back-extraction phases.

[0130] The extractions were carried out:

[0131] - 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

[0132] - 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.

[0133] The results obtained in terms of RM extraction efficiencies are illustrated in Figures 7 and 8.

[0134] These figures show that, under the back-extraction conditions used, the back-extraction of light rare earths (Nd and Pr: didymium) is favored compared to that of dysprosium. This can be explained by the more pronounced affinity of TODGA for heavy rare earths, resulting in a more difficult back-extraction of these.

[0135] Using deionized water as the aqueous back-extraction phase, maximum intra-TR back-extraction selectivity can be achieved using an A / O ratio close to 0.5. In addition, since the extraction step has an exothermic character, increasing the temperature favors the back-extraction of all rare earths and discourages selective back-extraction between didymium and dysprosium.

[0136] Finally, de-extraction with deionized water allows excellent selectivity to be maintained with respect to other metallic elements (Fe, Co, Ni and B), the majority of which (> 99%) remains in the organic phase.

[0137] Example III: Recyclability of the organic phase used for the extraction of TRs

[0138] In order to assess the recyclability of an organic phase used to extract TRs from a leachate obtained by leaching a powder of NdFeB permanent magnets with acetic acid (1.6 mol / L) and comprising 0.6 mol / L of NaNOs, 9 cycles were carried out, each comprising a TR extraction step, a TR back-extraction step and two washing steps, respectively acid and water, of the organic phase as illustrated in Figure 9.

[0139] As shown in this figure, in which PO stands for organic phase and PA stands for aqueous phase, the difference between the first cycle and the second to ninth cycles is that the extraction step of the first cycle was carried out with a “fresh” organic phase, comprising 0.25 mol / L of TODGA in an n-dodecane / n-octanol mixture (95 / 5, v / v), while the extraction step of each of the second to ninth cycles was carried out with the organic phase from the water washing step of the previous cycle.

[0140] Apart from this difference, the operating conditions under which the 9 cycles were conducted were the same, namely that:

[0141] - each extraction step was carried out by contacting an aliquot of the leachate 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 separation of the aqueous and organic phases;

[0142] - each back-extraction step was carried out by bringing the organic phase from the extraction step preceding it 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 separation of the organic and aqueous phases; - each acid washing step was carried out by bringing the organic phase from the back-extraction step preceding it 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 separation of the organic and aqueous phases;

[0143] - each water washing step was carried out by contacting the organic phase from the preceding acid washing step 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.

[0144] The aqueous and organic phases obtained after the extractions and back-extractions were analyzed under conditions identical to those mentioned in Example I above.

[0145] The DM distribution coefficients obtained for the extraction step of each of the 9 cycles are illustrated in Figure 10 while the RM de-extraction efficiencies obtained for the de-extraction step of each of the 9 cycles are illustrated in Figure 11.

[0146] Figure 10 shows that the distribution coefficients of rare earths remain high and in the same order of magnitude for all cycles without loss of selectivity with respect to other metallic elements.

[0147] Figure 11 shows that the use of a 0.01 mol / L EDTA solution as the aqueous back-extraction phase allows each cycle to recover 90% of the TRs previously extracted in the organic phase, and this, again, in a selective manner with respect to the other metallic elements having been extracted in trace amounts.

[0148] We can therefore deduce that the organic phase is perfectly reusable at least 9 times.

[0149] REFERENCES CITED

[0150] [1] WO-A-2016 / 046179

[0151] [2] M. Gergoric et al., Journal of Sustainable Metallurgy 2019, 5(1), 85-96

[0152] [3] S. Belfqueh et al., Journal of Rare Earths 2022, https: / / doi.org / 10.1016 / j.jre.2022.04.027.

Claims

CLAIMS 1. Process for extracting at least one rare earth from an aqueous solution Al of an organic acid or a mixture of organic acids comprising, in addition to one or more rare earths, one or more transition metals, which comprises at least one contacting of the aqueous solution Al with an organic solution immiscible with water, comprising as extractant, diglycolamide of formula: in solution in an organic diluent, followed by separation of the aqueous solution Al from the organic solution, and in which: - the organic acid(s) is (are) chosen from 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 trimesic acid, and - the aqueous solution Al further comprises a release agent, the release agent being a salt of an alkali metal, a salt of an alkaline earth metal or an ammonium salt.

2. Method according to claim 1, wherein the aqueous solution Al comprises from 0.1 mol / L to 16 mol / L of the organic acid or mixture of organic acids, preferably from 0.5 mol / L to 2 mol / L.

3. A method according to claim 1 or claim 2, wherein the salting-out agent is lithium, 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, or lithium, sodium, potassium, calcium or magnesium chloride, ammonium nitrate, sulfate or phosphate, preferably lithium, sodium or potassium nitrate.

4. Method according to any one of claims 1 to 3, in which the aqueous solution Al comprises from 0.25 mol / L to 1 mol / L of release agent.

5. Process according to any one of claims 1 to 4, in which the organic phase comprises from 0.05 mol / L to 0.4 mol / L of diglycolamide.

6. A method for recovering one or more rare earths from an aqueous solution Al of an organic acid or a mixture of organic acids comprising, in addition to the rare earth(s), one or more transition metals, which method comprises: a) an extraction of the rare earth or a co-extraction of the rare earths from the aqueous solution Al by implementing an extraction method according to any one of claims 1 to 5; then b) a back-extraction of the rare earth or at least one of the rare earths from the organic solution obtained at the end of step a), the back-extraction comprising at least one contacting of the organic solution with an aqueous solution A2, followed by a separation of the organic solution from the aqueous solution A2.

7. Recovery method according to claim 6, in which the aqueous solution A2 consists of water or comprises an agent for complexing rare earths in an aqueous medium.

8. Recovery method according to claim 6 or claim 7, in which the aqueous solution Al comprises at least one rare earth TRI, with an atomic number at most equal to 61, and at least one rare earth TR2, with an atomic number at least equal to 62, and in which, in step b), the rare earths TRI and TR2 are co-extracted from the organic solution obtained at the end of step a).

9. Recovery method according to claim 8, in which the aqueous solution A2 comprises an agent complexing rare earths in an aqueous medium.

10. Recovery method according to claim 6 or claim 7, in which the aqueous solution Al comprises at least one rare earth TRI, with an atomic number at most equal to 61, and at least one rare earth TR2, with an atomic number at least equal to 62, and in which step b) comprises: bi) a back-extraction of the rare earth(s) TRI from the organic solution obtained at the end of step a) with the aqueous solution A2, then b2) a back-extraction of the rare earth(s) TR2 from the organic solution obtained at the end of bi), the back-extraction comprising at least one contacting of the organic solution with an aqueous solution A3 different from the aqueous solution A2, followed by a separation of the organic solution from the aqueous solution A3.

11. Recovery method according to claim 10, in which the aqueous solution A2 consists of water and the aqueous solution A3 comprises an agent for complexing rare earths in an aqueous medium.

12. Recovery method according to any one of claims 7, 9 or 11, in which the agent complexing rare earths in aqueous medium is an aminopolycarboxylic acid or a hydrophilic diglycolamide.

13. Recovery method according to any one of claims 6 to 12, which further comprises one or more washes of the organic solution obtained at the end of step b) for its reuse.

14. Method according to any one of claims 1 to 13, in which the aqueous solution Al comes from the leaching of 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 Al is obtained from the leaching of a powder of used or discarded neodymium-iron-boron permanent magnets by at least one organic acid and comprises neodymium, dysprosium and praseodymium.

16. A recovery process according to claim 14 or claim 15, wherein the organic acid is acetic acid.

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