Extraction and recovery processes for rare earth elements present in an acidic aqueous solution, using a deep hydrophobic eutectic solvent

Abstract

The invention relates to a process for extracting rare earths from an aqueous solution A1, comprising contacting A1 with an organic solution and then separating the aqueous and organic solutions, the organic solution comprising an HDES consisting of: - a first compound of formula (I) or (II): in which: R1 to R4 = alkyl group in C1 to C18; R5 to R8 = H or alkyl group in C1 to C18; R9 to R12 = alkyl group in C1 to C18; R13 and R14 = H, alkyl group in C1 to C18 or –(CH2)nOR group in which n is an integer from 1 to 8 and R = alkyl group in C1 to C8; and the total number of carbon atoms is at least 24; and- a second compound of formula R'-OH or R'-COOH, in which R' = acyclic or cyclic hydrocarbon group, saturated or unsaturated, possibly comprising one or more branches and whose total number of carbon atoms ranges from 6 to 28.The invention also relates to a method for recovering rare earths by implementing this extraction process.

Description

Title of the invention: Processes for the extraction and recovery of rare earth elements present in an acidic aqueous solution, using a deep hydrophobic eutectic solvent. Technical field

[0001] The invention relates to the field of extraction and recovery of rare earths present in acidic aqueous solutions, with a view to recycling these rare earths.

[0002] More specifically, the invention relates to a method for selectively extracting one or more rare earths from an acidic aqueous solution which may include, in addition to this or these rare earths, other metallic elements such as iron, the extraction using as an organic solution, a solution comprising a deep hydrophobic eutectic solvent.

[0003] The invention also relates to a method for selectively recovering one or more rare earths from an acidic aqueous solution, implementing the extraction process.

[0004] The invention finds particular applications in the recycling of rare earths present in "urban ores", that is to say "mines" made up of industrial and domestic waste including rare earths and, in particular, waste electrical and electronic equipment (more simply noted "WEEE" or "D3E") such as used or discarded permanent magnets.

[0005] However, it can also be used to recover rare earths present in natural ores, such as monazites, bastnasites, apatites, xenotimes, eudialytes or allanites. Prior art

[0006] The particular physical and chemical properties of rare earths (scandium, yttrium and lanthanides) currently make them indispensable chemical elements in many industrial fields: glass and ceramics industries, catalysis, metallurgy, manufacture of permanent magnets, optical devices, phosphors etc.

[0007] Rare earths are therefore part of the so-called "technological" metals and constitute the majority of the elements of everyday technological objects, such as CDs, mobile phones, computer hard drives, etc.

[0008] While global demand for rare earths continues to increase, there is a significant risk of rare earth supply disruptions, particularly due to to a limited number of producing countries, with China currently monopolizing the global rare earth market.

[0009] Moreover, due to their limited availability, the increased use of certain metals and their high prices, it is necessary to optimize all avenues for the production and recovery of rare earths.

[0010] Recycling these rare earths present in used materials is increasingly preferred in view of political, economic and environmental concerns which are in particular linked to mining activities.

[0011] One of the largest markets, in terms of both volume and market value, for rare earth recycling concerns Neodymium-Iron-Boron (NdFeB) permanent magnets found in a number of WEEE (Waste Electrical and Electronic Equipment) waste streams. This resource for rare earth recycling has the advantage of containing significant and valuable rare earth elements, typically around 30% by mass. The composition of NdFeB permanent magnets varies depending on the application and the manufacturer, but they typically contain highly valuable heavy rare earth elements (dysprosium and, to a lesser extent, gadolinium and terbium) as well as light rare earth elements (notably neodymium and praseodymium).

[0012] The hydrometallurgical route, based on the liquid-liquid extraction technique, is commonly considered one of the most commercially suitable routes for recovering rare earths from the environment in which they are found.

[0013] Hydrometallurgical processes, which are currently used industrially to recover rare earths from an acidic aqueous solution, employ, for example, organophosphate extractants, such as phosphoric acids, phosphonic acids, phosphinic acids, carboxylic acids, and alkyl phosphates. These include, for example, trioctylphosphine oxide (or TOPO), di-2-ethylhexylphosphoric acid (or HDEHP), bis(trimethyl-2,4,4-pentyl)phosphinic acid (or Cyanex™ 272), and tri-n-butyl phosphate (or TBP).

[0014] Although these extractants allow for the efficient extraction of rare earths, they nevertheless have the disadvantage of co-extracting iron and other metallic elements - considered as impurities - in non-negligible quantities.

[0015] It was then proposed to use other types of extractants such as lipophilic symmetric diglycolamides, such as A / MAL / V'-tctraoctyl-3-oxapcntanc diamide (or TODGA) (see international application PCT WO 2016 / 046179, hereinafter reference [ 1 ]), to extract and selectively recover rare earths present in acidic aqueous solutions from the processing of used and discarded permanent magnets.

[0016] However, these extradants are conventionally diluted in volatile, toxic and flammable organic solvents in considerable volumes, which is a disadvantage, particularly in terms of human and environmental safety.

[0017] Furthermore, in the context of their use for liquid-liquid extractions, these volatile organic solvents sometimes require the simultaneous use of phase modifiers to avoid the formation of an undesirable third phase.

[0018] These are the reasons why research has been conducted for some years on hydrophobic deep eutectic solvents (hereafter simply referred to as HDES for "Hydrophobic Deep Eutectical Solvents"), which have emerged as a promising alternative to the volatile organic solvents usually used in liquid-liquid extractions. Indeed, HDES exhibit advantageous properties, such as low volatility, low toxicity, near non-flammability, recyclability, and low production cost.

[0019] These water-immiscible solvents comprise a mixture of at least two compounds: a first compound called a "hydrogen bond acceptor" (or HBA for "Hydrogen Bond Acceptor" in English) and a second compound called a "hydrogen bond donor" (or HBD for "Hydrogen Bond Donner" in English), the first and second compounds interacting together by hydrogen bonds, allowing the obtaining of a solvent whose melting point is significantly lower than that of the first and second compounds in the pure state and are therefore, for the most part, liquid at room temperature.

[0020] In the context of a liquid-liquid extraction, one of the first or second compound of the HDES is typically suitable for extracting the element that one wishes to extract.

[0021] For example, a hydrophobic eutectic solvent comprising TOPO as HBA and n-decanoic acid as HBD has been proposed by UG Favero et al. (Separation and Purification Technology 2023, 34, 123592, hereafter [2]) for extracting lanthanides from an aqueous solution of nitric acid.

[0022] It has also been observed that, in liquid-liquid extraction, the formation of an undesirable third phase is avoided when an HDES is used, particularly thanks to the compound HBD, which also acts as a phase modifier. The use of an HDES therefore eliminates the need for an additional phase modifier.

[0023] With the demand for rare earths constantly increasing and environmental issues becoming increasingly important, inventors considered it desirable to broaden the range of HDES suitable for use in the extraction and recovery of rare earths from acidic aqueous solutions.

[0024] They have therefore set themselves the goal of providing HDES which make it possible to extract rare earths very efficiently from an acidic aqueous solution and with a high selectivity towards other metallic elements likely to be present in this aqueous solution and, in particular, iron. Description of the invention

[0025] The invention thus proposes, firstly, a method for extracting one or more rare earths from an acidic aqueous solution Al, the method comprising at least one contacting of the aqueous solution Al with an organic solution followed by a separation of the aqueous and organic solutions and being characterized in that the organic solution comprises an HDES consisting of: - of at least one first compound (as HBA) corresponding to one of the formulas (I) and (II):

[0026] [Chem.l] in which: R1 to R4 represent, independently of each other, an alkyl group, linear or branched, in C1 to C[8; R5 to R8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to C[8; R9 to R12 represent, independently of each other, an alkyl group, linear or branched, in Ci to Ci8; R13 and R14 represent, independently of each other, a hydrogen atom, an alkyl group, linear or branched, in C1 to C18, or a -(CH2)nOR group in which n is an integer from 1 to 8 and R represents an alkyl group, linear or branched, in C1 to C8; and the total number of carbon atoms is at least 24; and - of at least one second compound (as HBD) of formula R'-OH or R'-COOH, in which R' represents an acyclic or cyclic hydrocarbon group, saturated or unsaturated, possibly comprising one or more branches and whose total number of carbon atoms ranges from 6 to 28.

[0027] In the preceding and following, "alkyl group, linear or branched, in C j to C18" means any alkyl group (i.e. of formula CnH2n+i) which comprises at least one carbon atom but not more than 18 carbon atoms and whose chain is linear or has one or more branches when the alkyl group comprises at least 3 carbon atoms.

[0028] Similarly, the term "alkyl group, linear or branched, in C i to C 8" means any alkyl group which comprises at least one carbon atom but not more than 8 carbon atoms and whose chain is linear or has one or more branches when the alkyl group comprises at least 3 carbon atoms.

[0029] Furthermore, when R' is an acyclic hydrocarbon group, then it can be any group formed of a hydrocarbon chain comprising at least 6 carbon atoms but no more than 28 carbon atoms, this chain being linear or comprising one or more branches and / or one or more double or triple bonds.

[0030] When R' is a cyclic hydrocarbon group, then it may be of a single ring or of several rings (for example, of two rings), possibly condensed, this or these rings typically each comprising 5 or 6 carbon atoms and being able to include one or more branches, saturated or unsaturated, and / or one or more unsaturations (the said ring(s) being able in particular to be of aromatic nature), R' comprising in total at least 6 carbon atoms but not more than 28 carbon atoms and the -OH or -COOH group being borne by one of the carbon atoms of the ring(s).

[0031] In formula (I), it is preferred that R1 to R4 represent, independently of each other, an alkyl group, linear or branched, in C5 to Ci2 and, preferably, in C6 to C8 and / or that R5 to R8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to C8, it being understood that the compounds corresponding to this formula (I) have a total number of carbon atoms of at least 24.

[0032] More particularly, it is preferred that R1 to R4 be identical to each other and that they all represent a linear alkyl group in C6 to C8 and / or that R5 to R8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to C8.

[0033] Such a compound may, for example, be TODGA which corresponds to the formula (I) above, in which R1 to R4 all represent a linear C8 alkyl group while R5 to R8 all represent a hydrogen atom.

[0034] It may also be a compound corresponding to the formula (I) above, in which R1 to R4 all represent a linear alkyl group at C8, R5 and R7 both represent a methyl group while R6 and R8 both represent a hydrogen atom.

[0035] In formula (II), it is preferred that R9 to R12 represent, independently of each other, an alkyl group, linear or branched, in Ci to Ci2 and, preferably, in Ci to C8 and / or that R13 and R14 represent, independently of each other, a hydrogen atom or a -(CH2)nOR group in which n and R are as described above, it being understood that the compounds corresponding to this formula (II) have a total number of carbon atoms of at least 24.

[0036] More particularly, it is preferred that R9 and R11 be identical to each other and that R10 and R12 be identical to each other but different from R9 and R11 and / or that R13 and R14 be different from each other, one representing a hydrogen atom and the other a -(CH2)nOR group in which n and R are such as previously defined, it being understood that the compounds corresponding to this formula (II) have a total number of carbon atoms of at least 24.

[0037] Such a compound may, for example, be A,A'-dimethyl-,A,A'-dioctylhexymethoxymalonamide (or DMDOHEMA), which corresponds to the formula (II) above, in which R9 and R11 both represent a linear C8 alkyl group, R10 and R12 both represent a methyl group, R13 represents a hydrogen atom while R14 represents a -(CH2)nOR group in which n is equal to 2 and R represents a linear C6 alkyl group.

[0038] As for the second compound, it is preferred that it be of formula R'-OH or R'-COOH, in which R' represents an alkyl group, linear or branched, preferably linear, in C6 to C12 or a cycloalkyl group whose ring is formed by 6 carbon atoms and possibly comprising one or more branches.

[0039] For example, the second compound can be chosen from n-decanoic acid, n-octanoic acid, 2-ethylhexanoic acid, lementhol and n-octanol, with any preference given to n-decanoic acid.

[0040] Preferably, the first compound is TODGA while the second compound is n-decanoic acid.

[0041] According to the invention, the HDES is preferably composed of 10% to 90% molar and, even better, 30% to 70% molar of each of the first and second compounds, the sum of the molar percentages of the first and second compounds being equal to 100.

[0042] In other words, the HDES can consist of a first compound / second compound molar ratio of between 10 / 90 and 90 / 10 and preferably between 30 / 70 and 70 / 30.

[0043] Preferably, the HDES consists of 30% to 60% molar of the first compound and 40% to 70% molar of the second compound, the sum of the molar percentages of the first and second compounds being equal to 100.

[0044] Advantageously, HDES consists of 45% to 50% molar of the first compound and 50% to 55% molar of the second compound, with preferred HBA / HBD molar ratios of 45 / 55 or 50 / 50.

[0045] For example, HDES can be made up of 45 molar percent of TODGA and 55 molar percent of n-decanoic acid.

[0046] Moreover, the HDES preferably represents at least 50% by mass and, even better, at least 80% by mass of the mass of the organic solution.

[0047] In the context of the invention, it is preferred that the organic solution be made up of HDES, that is to say that it comprises nothing other than this HDES, in which case HDES represents 100% by mass of the mass of the organic solution.

[0048] For example, the organic solution may consist of an HDES which itself consists of 45 molar % of TODGA and 55 molar % of n-decanoic acid.

[0049] As for the Al solution, it preferably comprises from 0.1 mol / L to 3 mol / L of an acid, which is advantageously chosen from nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, citric acid and tartaric acid, preferably nitric acid.

[0050] The organic solution and the Al solution as described above are brought into contact in a volume ratio O / Al of, preferably, between 1 and 10 and, even better, equal to 1 / 2.

[0051] Furthermore, prior to contacting the organic and Al solutions, the organic solution can advantageously be balanced with respect to water and acid. To do this, the organic solution can first be contacted with an acidic aqueous solution A2, which contains the same acid and at the same concentration as the Al solution intended for use in the extraction process, and then the organic solution and A2 are separated from each other. In this case, the organic solution and A2 are advantageously brought into contact in a volume ratio O / A2 preferably between 1 and 10 and, even better, equal to 1 / 2.

[0052] The extraction process as described above and, more specifically, the organic solution as described above, makes it possible to extract one or more rare earth elements from the Al solution, the rare earth element(s) being chosen, preferably, from lanthanum, praseodymium, neodymium, europium, gadolinium, dysprosium, holmium, yttrium, ytterbium and their mixtures.

[0053] In addition to very efficiently extracting one or more rare earths from an acidic aqueous solution, the organic solution as defined above has been shown to allow excellent separation of the rare earth(s) from other metallic elements - considered as impurities - likely to be present in the acidic aqueous solution.

[0054] More particularly, the organic solution as defined above allows excellent separation of one or more rare earths from iron.

[0055] Also, the extraction process as described above is advantageously implemented to extract one or more rare earths present in an acidic aqueous solution Al which includes, in addition to this or these rare earths, iron.

[0056] This Al solution may in particular be a solution from an acid leaching of an urban ore concentrate and, in particular, from a WEEE waste concentrate.

[0057] As such, it may in particular be a solution resulting from an acid leaching of a material in divided form (powder, fragments, etc.) and resulting from a treatment of used or discarded NdFeB permanent magnets.

[0058] The invention also relates to a method for recovering one or more rare earth elements present in an acidic aqueous solution Al, the method comprising at least the following successive steps: a) extraction of the rare earth element(s) from the acidic aqueous solution Al by the extraction process as defined above; and b) deextraction of the rare earth(s) from the organic solution obtained at the end of step a), the deextraction comprising at least one contacting of the organic solution with an aqueous deextraction solution AD and then a separation of the organic and aqueous solutions.

[0059] In this process, the organic solution, the Al solution and the O / Al volume ratio used in step a) are advantageously the same as those previously defined.

[0060] Furthermore, the organic solution can, prior to its contact with the Al solution, be balanced in water and acid as defined above.

[0061] According to the invention, in step b), the organic solution obtained at the end of step a) is brought into contact with the solution AD in a volume ratio O / Ad of, preferably, between 1 and 10 and, even better, equal to 1 / 2.

[0062] The aqueous solution AD may consist only of water.

[0063] However, to promote the de-extraction of the rare earth(s), it is possible to provide that this AD solution includes: - the same strong mineral acid as that present in the aqueous solution Al (i.e., nitric acid, sulfuric acid, or hydrochloric acid), but at a concentration of no more than 0.01 mol / L; and / or - an agent that complexes the rare earth(s) in an aqueous environment.

[0064] The complexing agent that may be used in the context of the invention may, in particular, be: - a hydrophilic diglycolamide, that is to say a compound corresponding to formula (I) above but whose total number of carbon atoms is at most 16, such as N,N,N',A'-tetramethyldiglycolamide (or TMDGA), A,A,A',A'-tetraethyldiglycolamide (or TEDGA) or N,N,A',A'-tetrapropyldiglycolamide (or TPDGA); - a hydrophilic malonamide, that is to say a compound corresponding to formula (II) above but whose total number of carbon atoms is at most 15, such as A,A,A',A'-tetramethylmalonamide, A,A,A',A'-tetraethylmalonamide or A,A,A',A'-tetrapropylmalonamide; - an aminopolycarboxylic acid such as ethylenediamine tetraacetic acid (or EDTA), A-(2-hydroxyethyl)ethylenediamine triacetic acid (or HEDTA), nitrilotriacetic acid (or NTA), diethylenetriamine pentaacetic acid (or DTPA) or a salt of these, for example a sodium salt; - a mono-, di- or tri-carboxylic acid such as acetic acid, glycolic acid, diglycolic acid, malonic acid, citric acid, tartaric acid.

[0065] Preferably, the complexing agent is a hydrophilic diglycolamide and, more particularly, TEDGA.

[0066] This complexing agent is preferably present in the AD solution at a concentration ranging from 0.05 mol / L to 2 mol / L, preferably from 0.1 mol / L to 1 mol / L and, even better, equal to 1 mol / L.

[0067] Other features and advantages of the invention will become apparent from the following supplementary description.

[0068] It goes without saying that this additional description is given only as an illustration of the object of the invention and should in no case be interpreted as a limitation of this object. Brief description of the figures

[0069] [Fig. 1] illustrates the distribution coefficients DM of praseodymium, boron, neodymium, dysprosium, and iron, as obtained from extractions carried out on aqueous solutions, denoted Ali to Al5, obtained from the leaching of NdFeB permanent magnet powder by, respectively, nitric acid, sulfuric acid, hydrochloric acid, acetic acid, and a mixture of acetic acid and sodium nitrate, using, as organic solutions, solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70.

[0070] [Fig.2] illustrates the distribution coefficients DM of iron, lanthanum, neodymium, europium, dysprosium and yttrium, as obtained from extractions carried out on so-called synthetic aqueous solutions, denoted AlSi to A1S3, comprising respectively 0.1 mol / L, 1 mol / L and 3 mol / L of nitric acid, using, as organic solutions, solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70.

[0071] [Fig.3] is a figure analogous to [Fig.2] but for extractions carried out using, as organic solutions, solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 45 / 55.

[0072] [Fig.4] is a figure analogous to [Fig.2] but for extractions carried out using, as organic solutions, solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 70 / 30.

[0073] [Fig.5], which is given for comparison purposes, is a figure analogous to [Fig.2] but for extractions carried out using, as organic solutions, solutions comprising 0.25 mol / L of TODGA in n-dodecane with 5 vol% of n-octanol.

[0074] [Fig.6] is a figure analogous to [Fig.2] but for extractions carried out using, as organic solutions, solutions consisting of a TODGA / n-octanoic acid mixture in a molar ratio of 30 / 70.

[0075] [Fig.7] is a figure analogous to [Fig.2] but for extractions carried out using, as organic solutions, solutions consisting of a TODGA / 2-ethylhexanoic acid mixture in a molar ratio of 35 / 65.

[0076] [Fig.8] illustrates the distribution coefficients DM of dysprosium, europium, iron, lanthanum, neodymium and yttrium, as obtained from extractions carried out on aqueous solution A1S2 (i.e. comprising 1 mol / L of HNO3), using, as organic solution, a solution consisting of a TODGA / menthol mixture in a molar ratio of 40 / 60.

[0077] [Fig.9] illustrates the distribution coefficients DM of dysprosium, europium, iron, lanthanum, neodymium and yttrium, as obtained from extractions carried out on aqueous solution A1S2 (i.e. comprising 1 mol / L of HNO3), using, as organic solutions, solutions consisting of a TODGA / n-octanol mixture in molar ratios of 20 / 80, 35 / 65 or 45 / 55.

[0078] [Fig. 10] illustrates the influence of the contact time of an organic solution with an acidic aqueous solution on the extraction coefficients, denoted E%M and expressed as %, of neodymium, europium, yttrium, gadolinium, dysprosium, ytterbium, lanthanum and iron, as obtained from extractions carried out on a synthetic acidic aqueous solution A1S4 comprising 1 mol / L of HNO3, using as organic solutions solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70; in this figure, the ordinate axis represents the extraction coefficients while the abscissa axis represents the contact time of the organic and aqueous solutions, denoted t and expressed in minutes.

[0079] [Fig. 11] illustrates the neodymium de-extraction yields, denoted RNd and expressed in %, as obtained from de-extractions on organic solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70 and comprising metallic elements which have been previously extracted (including neodymium), using, as aqueous de-extraction solutions, solutions denoted ADi to AD6 and comprising respectively pure deionized water, 0.1 mol / L of TEDGA, 0.5 mol / L of TEDGA, 1 mol / L of TEDGA, 1 mol / L of sodium carbonate and 0.1 mol / L of EDTA.

[0080] [Fig. 12] illustrates the extraction coefficients, denoted E%M and expressed as %, of neodymium, europium, iron, yttrium, gadolinium, dysprosium, ytterbium and lanthanum, as obtained after different extraction / deextraction cycles; the extractions were carried out on aqueous solution A1S4, using, as organic solutions, solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70 while the deextractions were carried out using, as aqueous deextraction solutions, aqueous solutions comprising 1 mol / L of TEDGA.

[0081] Detailed description of particular embodiments

[0082] 1. Preparation of deep hydrophobic eutectic solvents

[0083] 1.1. General principle

[0084] In the following examples, the HDES are all prepared by mixing the first compound (HBA) with the second compound (HBD) in the desired HBA / HBD molar ratio. The mixture is stirred for approximately 1 hour at 60 °C until a homogeneous mixture is obtained.

[0085] Next, the mixture is cooled to room temperature for approximately one day.

[0086] 1.2. Characterization

[0087] Different HDES consisting of a mixture of TODGA / n-decanoic acid are prepared according to the synthesis described above and according to the molar ratios as indicated in Table I below.

[0088] The melting temperature of each of the HDES, as indicated in Table I below, is measured by differential scanning calorimetry (or DSC) analysis. for "Differential Scanning Calorimetry" in English) with a temperature rise rate of 5 °C / min, over a temperature range from -100 °C to 150 °C. [Tables 1] Table i TODGA / n-Decanoic Acid (mI / mI) 90 / 10 80 / 20 70 / 30 60 / 40 50 / 50 45 / 55 30 / 70 20 / 80 10 / 90 Melting Point (pC) 10.24 5.56 4.45 0.75 -8.01 -0.83 10.94 20.40 29.07

[0089] The above results confirm that HDES are liquid at room temperature since they have a low melting point (from -8.01 °C to 29.07 °C) and can therefore be used as organic solutions in liquid-liquid extractions.

[0090] 2. General principle of rare earth extraction

[0091] The extractions described below are all carried out according to the following steps: 1) preparation of an acidic aqueous solution Al, either by carrying out an acid leaching of NdFeB permanent magnet powders or by preparing a solution, called synthetic, simulating a solution resulting from such an acid leaching; 2) preparation of an HDES according to the synthesis described in point 1.1 above; 3) contacting the prepared HDES with an acidic aqueous solution A2 in a volume ratio HDES / A2 of 1 / 2, the solution A2 comprising the same acid and at the same concentration as the solution Al. The whole is then subjected to agitation at 250 rpm for 1 h at 25 °C and then centrifuged at 5,000 rpm for 10 minutes, to separate the HDES from the solution A2; 4) The HDES thus "equilibrated" is brought into contact with the Al solution in a volume ratio HDES / A1 of 1 / 2, then the mixture is stirred at 250 rpm for 1 h at 25 °C and centrifuged at 5,000 rpm for 10 minutes, to separate the HDES from the aqueous solution.

[0092] The mass concentrations of the elements present in the Al solution before and after extraction are determined by inductively coupled plasma spectrometry (more simply noted ICP-OES), after dilution of said Al solution in 1% nitric acid.

[0093] The mass concentrations of these elements present in the HDES after extraction are thus deduced from those obtained for the Al solution after a simple material balance.

[0094] The distribution coefficient of each of the elements, denoted M, between the Al solution and the HDES is calculated from the concentrations thus determined. This coefficient, denoted Dm and dimensionless, is calculated according to the conventions of the field of liquid-liquid extraction, that is to say by the following formula:

[0095] [Math.l] MffDES / Va; 1*1,, - v »™ x [U

[0096] in which: is 'a concentration of M in HDES after extraction (in g / L); is the concentration of M in the Al solution after extraction (in g / L); is the concentration of M in the Al solution before extraction (in g / L); and Vaq and Vhdes are the respective volumes (in L) of the Al solution and the HDES brought into contact.

[0097] Furthermore, the extraction coefficient of each of the elements M, denoted E%M and expressed as a percentage, is determined by the following formula:

[0098] [Math.2]

[0099] in which: [A / L.,,,... has the same meaning as before; and . is the concentration of M in the HDES before extraction (in g / L). HDhS /

[0100] 3. Extraction of rare earth elements from acidic aqueous solutions obtained from a leaching of NdFeB permanent magnet powder

[0101] In this example, five acidic aqueous solutions, denoted Ali to Al5, are first prepared by carrying out acid leachings of a powder of ground NdFeB permanent magnets.

[0102] Ali, Al2 and Al3 are obtained respectively by dissolving the magnet powder in nitric acid (1 mol / L), sulfuric acid (1 mol / L) and hydrochloric acid (1 mol / L), then stirring them at 200 rpm for 16 hours at 25 °C and centrifuging them at 4,000 rpm for 20 minutes. The supernatants are then collected and filtered (Vivaspin™ 20 PES, 30 kDa MWCO).

[0103] Al4 is obtained by dissolving the magnet powder in acetic acid (at 1.6 mol / L), then stirring and heating the solution at 60 °C for 24 hours and centrifuging it at 10,000 rpm for 5 minutes. The supernatant is collected and filtered through cellulose (0.45 µm).

[0104] The Al5 solution, on the other hand, is obtained by adding sodium nitrate (at 0.6 mol / L) to a sample of the Al4 solution.

[0105] A first series of extraction tests is then carried out on each of the Ali solutions at A15 and using, as organic solutions, an HDES consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70.

[0106] Fig. 1 illustrates the distribution coefficients of praseodymium, boron, neodymium, dysprosium and iron, as obtained at the end of each of the extractions.

[0107] Extractions carried out with the solutions Ali(nitric acid) and Al5 (acetic acid-sodium nitrate mixture) gave better results, in particular due to the presence of nitrates.

[0108] 4. Extraction of rare earth elements from synthetic acidic aqueous solutions

[0109] 4.1 Influence of the HBA / HBD molar ratio and influence of the acid concentration in the solution Al on the distribution coefficients of the elements M

[0110] In this example, three acidic aqueous solutions, referred to as synthetic and denoted respectively AlSià A1S3, are first prepared. [YES] Alsi is obtained by dissolving iron(III) nitrate, lanthanum, neodymium, europium, dysprosium, and yttrium nitrates (simulating holmium) in water to obtain an aqueous solution containing 500 mg / L of iron and 500 mg / L of each of the rare earth elements. Concentrated nitric acid (69%) is then added to obtain a solution containing 0.1 mol / L of HNO3.

[0112] A1S2 and AlS3 are prepared in the same way, except that A1S2 comprises 1 mol / L of HNO3 and A1S3 comprises 3 mol / L of HNO3.

[0113] A second series of extractions is carried out by contacting each of the AlSi to AlS3 solutions with each of the following HDES: - TODGA / n-decanoic acid 30 / 70 (mol / mol); - TODGA / n-decanoic acid 45 / 55 (mol / mol); and - TODGA / n-decanoic acid 70 / 30 (mol / mol).

[0114] Figures 2 to 4 illustrate the distribution coefficients of rare earths and iron, as obtained at the end of each of the extractions.

[0115] These figures show that iron is extracted only very little compared to rare earths (whose extraction coefficient is between 96.77% and 99.99%) for all extractions carried out, thus demonstrating the effectiveness of an HDES for selectively extracting rare earths, with respect to iron, from an aqueous solution of nitric acid.

[0116] Furthermore, it should be noted that the higher the concentration of HNO3 in the aqueous solution, the higher the distribution coefficient of rare earths, and this is true for any HDES.

[0117] Further extractions are carried out by contacting each of the AlSi to Alss solutions with an organic solution used as a comparative example. This organic solution comprises 0.25 mol / L of TODGA in n-dodecane with 5 vol% of n-octanol (acting here as a phase modifier).

[0118] Fig. 5 illustrates the distribution coefficients of rare earths and iron, as obtained from extractions carried out using the "comparative" organic solution.

[0119] It follows that, for these extractions, the distribution coefficients of rare earths are much less important than those obtained from extractions carried out using, as organic solutions, an HDES.

[0120] 4.2 Influence of the nature of the HBD compound on the distribution coefficients of M elements

[0121] In this example, a third series of extractions is carried out by contacting each of the AlSi to A1S3 solutions (as described above) with each of the following HDES: - TODGA / n-octanoic acid 30 / 70 (mol / mol); and - TODGA / 2-ethylhexanoic acid 35 / 65 (mol / mol).

[0122] Figures 6 and 7 illustrate the distribution coefficients of rare earths and iron, as obtained at the end of this third series of extractions.

[0123] The results obtained for these extractions are also compared to those shown in [Fig.2].

[0124] Furthermore, a fourth and fifth series of extractions are carried out on the A1S2 solution and using, as an organic solution, an HDES consisting of a TODGA / menthol mixture in a molar ratio of 40 / 60 for the fourth series and HDES consisting of a TODGA / n-octanol mixture in molar ratios of 20 / 80, 35 / 65 and 45 / 55 for the fifth series.

[0125] Figures 8 and 9 illustrate the distribution coefficients of rare earths and iron, as obtained from the fourth and fifth series of extractions.

[0126] Figures 2 and 6 to 9 show that rare earth elements are selectively extracted with respect to iron in all extractions performed. These results therefore indicate that rare earth element extraction is primarily linked to the nature of the HBA compound (in this case, TODGA).

[0127] 4.3 Extraction kinetics

[0128] In this example, different extractions are performed using: - as aqueous solutions, a synthetic A1S4 solution that simulates a solution obtained from the acid leaching of NdFeB permanent magnets and that comprises 1 mol / L of HNO3 and 500 mg / L of the following metallic elements: Nd, Eu, Y, Gd, Dy, Yb, La and Fe; and - as organic solutions, an HDES consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70.

[0129] The extractions are carried out according to the general principle described in point 2 above, with the difference that the HDES and the A1S4 solution are brought into contact, under stirring at 250 rpm, for: 1, 5, 10, 20, 30, 45, 60 or 120 minutes, then the whole is subjected to centrifugation at 8,000 rpm for 1 minute to separate the HDES from the aqueous solution.

[0130] Figure 10 illustrates the extraction coefficients of rare earths and iron as a function of the contact time between HDES and A1S4. It shows that after only one minute of contact, the extraction coefficient of rare earths reaches 90% while that of iron is less than 1%. 5. Rare earth extraction

[0131] Deextraction tests are carried out using: - as organic solutions: an HDES consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70, having been previously loaded with Nd, Eu, Y, Gd, Dy, Yb, La and Fe by extraction of these elements from the Als 4 solution described above; and - as aqueous deextraction solutions, the solutions noted AD i to AD6 and comprising respectively pure deionized water, 0.1 mol / L of TEDGA, 0.5 mol / L of TEDGA, 1 mol / L of TEDGA, 1 mol / L of sodium carbonate and 0.1 mol / L of EDTA.

[0132] For each deextraction test, the HDES is brought into contact with one of the aqueous solutions AD i to AD6 in a volume ratio HDES / Ad of 1 / 2, then the mixture is stirred at 250 rpm for 60 minutes at 25°C, then centrifuged at 10,000 rpm for 5 minutes, to separate the HDES from the aqueous solution.

[0133] The mass concentrations of the metallic elements in the AD i to AD6 solutions after deextraction are measured by ICP-OES and the deextraction yield of these elements is determined.

[0134] By way of example, [Fig.1 1] illustrates the neodymium de-extraction yields for each de-extraction carried out.

[0135] This figure shows that aqueous solutions of TEDGA allow neodymium to be efficiently extracted.

[0136] In particular, the aqueous solution of TEDGA at 1 mol / L allows obtaining a neodymium deextraction yield of the order of 90%.

[0137] Next, five successive extraction / deextraction cycles are carried out.

[0138] Extractions are carried out on the A1S4 solution and using, as organic solutions, an HDES consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70.

[0139] As for the de-extractions, they are carried out using, as organic solutions, the HDES from the extractions and, as aqueous de-extraction solutions, solutions comprising 1 mol / L of TEDGA.

[0140] Fig. 12 illustrates the extraction coefficient of metallic elements, as obtained at the end of each extraction / de-extraction cycle.

[0141] This figure shows that even after five cycles, HDES remains effective since the rare earth extraction coefficients are between approximately 75% (for lanthanum) and approximately 95% (for Nd, Gd, Eu, Dy, Y, and Yb), while iron is extracted only to a very low degree (its coefficient being on the order of only a few percent). References cited

[0142] [1]WO 2016 / 046179 [2] UG Favero et al., Separation and Purification Technology 2023, 34, 123592.

Claims

1. Demands A process for extracting one or more rare earth elements from an acidic aqueous solution Al, the process comprising at least one contact of the aqueous solution Al with an organic solution followed by a separation of the aqueous and organic solutions, characterized in that the organic solution comprises a deep eutectic solvent consisting of: - of at least one first compound corresponding to one of the formulas (I) and (II): [Chem 1]

2. in which: R1 to R4 represent, independently of each other, an alkyl group, linear or branched, in Ci to Ci8; R5 to R8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to Ci8; R9 to R12 represent, independently of each other, an alkyl group, linear or branched, in Ci to Ci8; R13 and R14 represent, independently of each other, a hydrogen atom, an alkyl group, linear or branched, in C1 to C18 or a -(CH2)nOR group in which n is an integer from 1 to 8 and R represents an alkyl group, linear or branched, in C1 to C8; and the total number of carbon atoms is at least 24; and - of at least a second compound of formula R'-OH or R'-COOH, in which R' represents an acyclic or cyclic hydrocarbon group, saturated or unsaturated, possibly comprising one or more branches and whose total number of carbon atoms is from 6 to 28. Extraction process according to claim 1, wherein the first compound meets the following requirements: - to formula (I), in which R1 to R4 represent, independently of each other, an alkyl group, linear or branched, in C5 to Ci2 and, preferably, in C6 to C8 and / or wherein R5 to R8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to C8; or - to formula (II), wherein R9 to R12 represent, independently of each other, an alkyl group, linear or branched, in Ci to Ci2 and, preferably, in Ci to C8 and / or wherein R13 and R14 represent, independently of each other, a hydrogen atom or a -(CH2)nOR group in which n is an integer from 1 to 8 and R represents an alkyl group, linear or branched, in Ci to C8.

3. An extraction process according to claim 1 or 2, wherein the first compound meets the following requirements: - to formula (I), in which R1 to R4 are identical to each other and all represent a linear alkyl group in C6 to C8 and / or R5 to R8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in C1 to C8; or - to formula (II), in which R9 and R11 are identical to each other and R10 and R12 are identical to each other but different from R9 and R11 and / or R13 and R14 are different from each other, one representing a hydrogen atom and the other a -(CH2)nOR group in which n is an integer from 1 to 8 and R represents an alkyl group, linear or branched, in C1 to C8.

4. An extraction process according to any one of claims 1 to 3, wherein the first compound meets the following requirements: - to formula (I), in which R1 to R4 all represent a linear C8 alkyl group while R5 to R all represent a hydrogen atom; or - to formula (I), in which R1 to R4 each represent a linear C8 alkyl group, R5 and R7 each represent a methyl group, while R6 and R8 each represent a hydrogen atom; or - to formula (II), in which R9 and R11 both represent a linear C8 alkyl group, R10 and R12 both represent a methyl group, R13 represents a hydrogen atom while R14 represents a -(CH2)nOR group in which n is equal to 2 and R represents a linear C6 alkyl group.

5. Extraction process according to any one of claims 1 to 4, wherein the second compound is of formula R'-OH or R'-COOH, with R' representing a linear or branched alkyl group, in C6 to Ci2 or a cycloalkyl group in C6 and optionally comprising one or more branches.

6. Extraction process according to any one of claims 1 to 5, wherein the second compound is selected from n-decanoic acid, n-octanoic acid, 2-ethylhexanoic acid, menthol and n-octanol, preferably n-decanoic acid.

7. Extraction process according to any one of claims 1 to 6, wherein the first compound corresponds to formula (I), in which R1 to R4 all represent a linear C8 alkyl group and R5 to R all represent a hydrogen atom and the second compound is n-decanoic acid.

8. An extraction process according to any one of claims 1 to 7, wherein the deep eutectic solvent represents at least 50% by mass and, preferably, at least 80% by mass of the mass of the organic solution.

9. Extraction process according to any one of claims 1 to 8, wherein the deep eutectic solvent represents 100% by mass of the mass of the organic solution.

10. An extraction process according to any one of claims 1 to 9, wherein the deep eutectic solvent consists of 10% to 90% molar and preferably 30% to 70% molar of each of the first and second compounds, the sum of the molar percentages of the first and second compounds being equal to 100.

11. An extraction process according to any one of claims 1 to 10, wherein the deep eutectic solvent consists of 30% to 60% mol, preferably 45% to 50% mol of the first compound and 40% to 70% mol, preferably 50% to 55% mol of the second compound, the sum of the mol percentages of the first and second compounds being equal to 100.

12. Extraction process according to any one of claims 1 to 11, wherein the aqueous solution Al comprises from 0.1 mol / L to 3 mol / L of an acid selected from nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, citric acid and tartaric acid, preferably nitric acid.

13. A method according to any one of claims 1 to 12, wherein the rare earth(s) are selected from lanthanum, praseodymium, neodymium, europium, gadolinium, dysprosium, rhohnium, yttrium, ytterbium and mixtures thereof.

14. Extraction process according to any one of claims 1 to 13, wherein the aqueous Al solution comprises, in addition to the rare earth(s), iron.

15. Extraction process according to claim 13 or 14, wherein the aqueous solution Al is obtained from an acid leaching of a concentrate of waste electrical and electronic equipment.

16. Extraction process according to claim 13 or 14, wherein the acidic aqueous solution Al is obtained from an acid leaching of a material in divided form resulting from the treatment of used or discarded Neodymium-Iron-Boron permanent magnets.

17. A process for recovering one or more rare earths from an acidic aqueous solution Al, comprising at least the following successive steps: a) extraction of the rare earth(s) from the acidic aqueous solution Al by the extraction process according to any one of claims 1 to 16; and b) desalting of the rare earth(s) from the organic solution obtained at the end of step a), the desalting comprising at least contacting the organic solution with an aqueous desalting solution AD and then separating the organic and aqueous solutions.

18. Recovery process according to claim 17, wherein the aqueous solution AD comprises an agent complexing the rare earth(s) in aqueous medium, preferably N,N,N',A'-tetraethyldiglyco lamide.

19. A recovery process according to claim 18, wherein the complexing agent is present in the AD solution at a concentration ranging from 0.05 mol / L to 2 mol / L, preferably from 0.1 mol / L to 1 mol / L and, even better, equal to 1 mol / L.

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