Methods for extracting and recovering rare earths present in an acidic aqueous solution using a hydrophobic deep eutectic solvent

Abstract

The invention relates to a method for extracting rare earths from an aqueous solution A1, comprising bringing A1 into contact 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), where: R1 to R4 = C1 to C18 alkyl group; R5 to R8 = H or C1 to C18 alkyl group; R9 to R12 = C1 to C18 alkyl group; R13 and R14 = H, C1 to C18 alkyl group or –(CH2)n-O-R group, where n is an integer from 1 to 8, and R = C1 to C8 alkyl group; and the total number of carbon atoms is at least equal to 24; and - a second compound of formula R'-OH or R'-COOH, where R' = acyclic or cyclic, saturated or unsaturated hydrocarbon group, optionally comprising one or more branches and of which the 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 method.

Description

[0001] PROCESSES FOR EXTRACTION AND RECOVERY OF RARE EARTHS PRESENT IN AN ACID AQUEOUS SOLUTION, IMPLEMENTING

[0002] A DEEP HYDROPHOBIC EUTECTIC SOLVENT

[0003] Description

[0004] TECHNICAL FIELD

[0005] 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.

[0006] More specifically, the invention relates to a process 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.

[0007] The invention also relates to a method for selectively recovering one or more rare earths from an acidic aqueous solution, implementing the extraction process.

[0008] The invention finds applications in particular 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.

[0009] However, it can also be used to recover rare earth elements present in natural ores, such as monazites, bastnasites, apatites, xenotimes, eudialytes or allanites.

[0010] PREVIOUS STATE OF THE ART

[0011] 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.

[0012] Rare earth elements are therefore part of the so-called "technological" metals and constitute the majority of the elements in everyday technological objects, such as CDs, mobile phones, computer hard drives, etc.

[0013] While global demand for rare earths continues to rise, there is a significant risk of rare earth supply disruptions, particularly due to a limited number of producing countries, with China currently monopolizing the global rare earth market.

[0014] Furthermore, 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.

[0015] Recycling these rare earths present in used materials is increasingly favoured in view of political, economic and environmental concerns which are in particular linked to mining activities.

[0016] One of the largest markets, in terms of both volume and market value, for rare earth recycling involves Neodymium-Iron-Boron (NdFeB) permanent magnets found in various WEEE (Waste Electrical and Electronic Equipment) materials. This resource for rare earth recycling offers 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).

[0017] The hydrometallurgical route, based on the liquid-liquid extraction technique, is commonly considered one of the most commercially suitable methods for recovering rare earth elements from their surrounding environment. Hydrometallurgical processes, which are currently used industrially to recover rare earth elements from acidic aqueous solutions, employ organophosphate extractants such as phosphoric acids, phosphonic acids, phosphinic acids, carboxylic acids, and alkyl phosphates. Examples include trioctylphosphine oxide (TOPO), di-2-ethylhexylphosphoric acid (HDEHP), bis(trimethyl-2,4,4-pentyl)phosphinic acid (Cyanex™ 272), and tri-n-butyl phosphate (TBP).

[0018] Although these extractants allow for the efficient extraction of rare earths, they have the disadvantage of co-extracting iron and other metallic elements - considered as impurities - in significant quantities.

[0019] It was then proposed to use other types of extractants such as lipophilic symmetric diglycolamides, such as / V / / V, / V' / / \ / '-tetraoctyl-3-oxapentane diamide (or TODGA) (cf. international application PCT WO 2016 / 046179, hereinafter reference [1]), for the selective extraction and recovery of rare earths present in acidic aqueous solutions from the processing of used and discarded permanent magnets.

[0020] However, these extractants are typically diluted in volatile, toxic and flammable organic solvents in considerable volumes, which is a drawback, particularly in terms of human and environmental safety.

[0021] Furthermore, when used 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.

[0022] 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 Eutectic 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. These solvents, immiscible with water, comprise a mixture of at least two compounds: a first compound called a "hydrogen bond acceptor" (or HBA for "Hydrogen Bond Acceptor") and a second compound called a "hydrogen bond donor" (or HBD for "Hydrogen Bond Donor").Hydrogen Bond Donor (in English), the first and second compounds interacting together through hydrogen bonds, allowing the production of a solvent whose melting point is significantly lower than that of the first and second compounds in their pure state and are therefore, for the most part, liquid at room temperature.

[0023] In a liquid-liquid extraction, one of the first or second components of the HDES is typically suitable for extracting the element that one wishes to extract.

[0024] 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]) to extract lanthanides from an aqueous nitric acid solution.

[0025] It has also been observed that, in liquid-liquid extraction, the formation of an undesirable third phase is avoided when an HDES is used, notably 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.

[0026] With the demand for rare earths constantly increasing and environmental issues becoming more and more 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.

[0027] They have therefore set themselves the goal of providing HDES which allow the extraction of rare earths very efficiently from an acidic aqueous solution, with a high selectivity towards other metallic elements likely to be present in this aqueous solution and, in particular, iron.

[0028] DESCRIPTION OF THE INVENTION

[0029] The invention thus proposes, firstly, a method for extracting one or more rare earth elements 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:

[0030] - of at least one first compound (as HBA) corresponding to one of the formulas (I) and (II):

[0031] (I) (H) in which:

[0032] R 1 to R 4represent, independently of each other, an alkyl group, linear or branched, in Ci to Cis;

[0033] R 5 to R 8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to Cis;

[0034] R 9 to R 12 represent, independently of each other, an alkyl group, linear or branched, in Ci to Cis;

[0035] R 13 and R 14 represent, independently of each other, a hydrogen atom, an alkyl group, linear or branched, in the order Ci to Cis, 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 the order Ci to Cs; and the total number of carbon atoms is at least 24; and

[0036] - 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.

[0037] In the preceding and following text, the term "alkyl group, linear or branched, in the form C1 to C1s" means any alkyl group (i.e., of formula C1 n H2n+i) which includes 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 includes at least 3 carbon atoms.

[0038] Similarly, an "alkyl group, linear or branched, in C1 to C1" means any alkyl group which includes 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 includes at least 3 carbon atoms.

[0039] Furthermore, when R' is an acyclic hydrocarbon group, then it can be any group formed from a hydrocarbon chain comprising at least 6 carbon atoms but no more than 28 carbon atoms, this chain being linear or having one or more branches and / or one or more double or triple bonds.

[0040] When R' is a cyclic hydrocarbon group, then it can be a single ring or several rings (for example, two rings), possibly condensed, this or these rings typically each comprising 5 or 6 carbon atoms and can include one or more branches, saturated or unsaturated, and / or one or more unsaturations (the said ring(s) can notably be of aromatic nature), R' comprising in total at least 6 carbon atoms but no more than 28 carbon atoms and the -OH or -COOH group being carried by one of the carbon atoms of the ring(s).

[0041] In formula (I), we prefer that R 1 to R 4 represent, independently of each other, an alkyl group, linear or branched, in Cs to C12 and, preferably, in Ce to Cs and / or R 5 to R 8represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to Cs, it being understood that the compounds corresponding to this formula (I) have a total number of carbon atoms at least equal to 24.

[0042] More specifically, we prefer that R 1 to R 4 are identical to each other and that they all represent a linear alkyl group in Ce to Cs and / or that R 5 to R 8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to Cs.

[0043] Such a compound may, for example, be TODGA, which corresponds to formula (I) above, in which R 1 to R 4 all represent a linear Cs alkyl group while R 5 to R 8 each represent a hydrogen atom. It can also be a compound corresponding to formula (I) above, in which R 1 to R 4all represent a linear alkyl group in Cs, R 5 and R 7 both represent a methyl group while R 6 and R 8 both represent a hydrogen atom.

[0044] In formula (II), we prefer that R 9 to R 12 represent, independently of each other, an alkyl group, linear or branched, in C1 to C12 and, preferably, in C1 to Cs and / or R 13 and R 14 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 compounds corresponding to this formula (II) have a total number of carbon atoms of at least 24.

[0045] More specifically, we prefer that R 9 and R 11 are identical to each other and that R 10 and R 12 be identical to each other but different from R 9 and R 11 and / or that R13 and R 14 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 compounds conforming to this formula (II) have a total number of carbon atoms of at least 24.

[0046] Such a compound may, for example, be N, / V'-dimethyl-, / V,N'-dioctylhexymethoxymalonamide (or DMDOHEMA), which corresponds to formula (II) above, in which R 9 and R 11 both represent a linear alkyl group in Cs, R 10 and R 12 both represent a methyl group, R 13 represents a hydrogen atom while R 14 represents a -(CH2)nOR group in which n is equal to 2 and R represents a linear Ce alkyl group.

[0047] 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 Ce to C12 or a cycloalkyl group whose ring is formed by 6 carbon atoms and possibly including one or more branches.

[0048] For example, the second compound can be chosen from n-decanoic acid, n-octanoic acid, 2-ethylhexanoic acid, menthol, and n-octanol, with preference given to n-decanoic acid. Preferably, the first compound is TODGA while the second compound is n-decanoic acid.

[0049] According to the invention, HDES is preferably made up 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.

[0050] In other words, HDES can consist of a first compound / second compound molar ratio between 10 / 90 and 90 / 10 and preferably between 30 / 70 and 70 / 30.

[0051] Preferably, 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.

[0052] 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.

[0053] For example, HDES may consist of 45 molar percent of TODGA and 55 molar percent of n-decanoic acid.

[0054] Furthermore, HDES preferably represents at least 50% by mass and, even better, at least 80% by mass of the mass of the organic solution.

[0055] 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.

[0056] For example, the organic solution may consist of an HDES which is made up of 45 molar percent of TODGA and 55 molar percent of n-decanoic acid.

[0057] As for the Al solution, it preferably comprises 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. The organic solution and the Al solution as described above are brought into contact in an O / Al volume ratio preferably between 1 and 10, and even better, equal to 1 / 2.

[0058] Furthermore, prior to contacting the organic and Al solutions, the organic solution can advantageously be balanced in water and acid. To do this, the organic solution can first be contacted with an aqueous acidic solution A2, which contains the same acid and at the same concentration as the Al solution intended for use in the extraction process. Then, the organic solution and A2 are separated. In this case, the organic solution and A2 are advantageously contacted in a volume ratio O / A2 preferably between 1 and 10, and even better, equal to 1 / 2.

[0059] The extraction process as described above and, more specifically, the organic solution as described above, allows one or more rare earths to be extracted from the Al solution, the rare earth(s) being chosen, preferably, from lanthanum, praseodymium, neodymium, europium, gadolinium, dysprosium, holmium, yttrium, ytterbium and mixtures thereof.

[0060] 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 - that may be present in the acidic aqueous solution.

[0061] More specifically, the organic solution as defined above allows for excellent separation of one or more rare earths from iron.

[0062] 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.

[0063] This Al solution can notably be a solution resulting from the acid leaching of an urban ore concentrate and, in particular, from a WEEE waste concentrate. As such, it can notably be a solution resulting from the acid leaching of a material in a divided form (powder, fragments, etc.) and resulting from the processing of used or discarded NdFeB permanent magnets.

[0064] The invention also relates to a process for recovering one or more rare earths present in an acidic aqueous solution Al, the process comprising at least the following successive steps: a) extraction of the rare earth(s) from the acidic aqueous solution Al by the extraction process as defined above; and b) des-extraction of the rare earth(s) from the organic solution obtained at the end of step a), the des-extraction comprising at least one contacting of the organic solution with an aqueous des-extraction solution AD and then a separation of the organic and aqueous solutions.

[0065] 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.

[0066] Furthermore, the organic solution can, prior to its contact with the Al solution, be balanced in water and acid as defined above.

[0067] 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.

[0068] The aqueous solution AD may consist of only water.

[0069] 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 complexing the rare earth(s) in aqueous medium.

[0070] The complexing agent that can 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 / V' / V' / VS / V'-tetramethyldiglycolamide (or TMDGA), N, N, / V', / V'-tetraethyldiglycolamide (or TEDGA) or A / A / A / ^ / V'-tetrapropyldiglycolamide (or TPDGA);

[0071] - 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 / V' / V' / VS / V'-tetramethylmalonamide, A / A / A / ^ / V'-tetraethylmalonamide or / V' / V' / VS / V'-tetrapropylmalonamide;

[0072] - an aminopolycarboxylic acid such as ethylenediamine tetraacetic acid (or EDTA), / V-(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;

[0073] - a mono-, di- or tri-carboxylic acid such as acetic acid, glycolic acid, diglycolic acid, malonic acid, citric acid, tartaric acid.

[0074] Preferably, the complexing agent is a hydrophilic diglycolamide and, more particularly, TEDGA.

[0075] 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.

[0076] Other features and advantages of the invention will become apparent from the supplementary description that follows.

[0077] It goes without saying that this additional description is given only as an illustration of the object of the invention and should in no way be interpreted as a limitation of this object.

[0078] BRIEF DESCRIPTION OF THE FIGURES

[0079] Figure 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 Als, from the leaching of a powder of NdFeB permanent magnets 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.

[0080] Figure 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 Als3, 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.

[0081] Figure 3 is a figure analogous to Figure 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.

[0082] Figure 4 is a figure analogous to Figure 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.

[0083] Figure 5, which is given for comparison, is a figure analogous to Figure 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.

[0084] Figure 6 is a figure analogous to Figure 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.

[0085] Figure 7 is a figure analogous to Figure 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.

[0086] Figure 8 illustrates the distribution coefficients DM of dysprosium, europium, iron, lanthanum, neodymium and yttrium, as obtained from extractions carried out on aqueous Al2 solution (i.e. comprising 1 mol / L of HNO3), using, as the organic solution, a solution consisting of a TODGA / menthol mixture in a molar ratio of 40 / 60. Figure 9 illustrates the distribution coefficients DM of dysprosium, europium, iron, lanthanum, neodymium and yttrium, as obtained from extractions carried out on aqueous solution Als2 (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.

[0087] Figure 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 in %, of neodymium, europium, yttrium, gadolinium, dysprosium, ytterbium, lanthanum and iron, as obtained from extractions carried out on a synthetic acidic aqueous solution Al4 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.

[0088] Figure 11 illustrates the neodymium de-extraction yields, denoted RNd and expressed as %, obtained from de-extractions on organic solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70 and including previously extracted metallic elements (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.

[0089] Figure 12 illustrates the extraction coefficients, denoted E%M and expressed as %, of neodymium, europium, iron, yttrium, gadolinium, dysprosium, ytterbium, and lanthanum, as obtained after various extraction / deextraction cycles. Extractions were performed on aqueous Al4 solution, using organic solutions consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70, while deextractions were performed using aqueous solutions containing 1 mol / L of TEDGA as the deextraction aqueous solutions. DETAILED DESCRIPTION OF SPECIFIC PROCEDURES

[0090] 1. Preparation of deep hydrophobic eutectic solvents:

[0091] 1.1. General principle:

[0092] 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 then stirred for approximately 1 hour at 60 °C until a homogeneous mixture is obtained.

[0093] Next, the mixture is cooled to room temperature for about a day.

[0094] 1.2. Characterization:

[0095] 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.

[0096] The melting temperature of each of the HDES, as indicated in the following Table I, is measured by differential scanning calorimetry (DSC) with a temperature rise rate of 5 °C / min, over a temperature range of -100 °C to 150 °C.

[0097] Table I

[0098] 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.

[0099] 2. General principle of rare earth extraction:

[0100] 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 from such an acid leaching;

[0101] 2) preparation of an HDES according to the synthesis described in point 1.1 above;

[0102] 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;

[0103] 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.

[0104] 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.

[0105] The mass concentrations of these elements present in HDES after extraction are thus deduced from those obtained for the Al solution after a simple mass balance.

[0106] The distribution coefficient of each element, 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: in which:

[0107] [M] HDES - is the concentration of M in the HDES after extraction (in g / L);

[0108] [M] aq ,f est L a concentration of M in the Al solution after extraction (in g / L);

[0109] [M] aq f is the concentration of M in the Al solution before extraction (in g / L); and V aq and V HDES are the respective volumes (in L) of the Al solution and the HDES brought into contact.

[0110] Furthermore, the extraction coefficient of each of the elements M, denoted E%M and expressed as a percentage, is determined by the following formula: in which:

[0111] [M] H DEs,f a L a same meaning as before; and

[0112] [M] H DES,I est the concentration of M in the HDES before extraction (in g / L).

[0113] 3. Extractions of rare earth elements from acidic aqueous solutions obtained by leaching NdFeB permanent magnet powder:

[0114] In this example, five acidic aqueous solutions, denoted Ali to Als, are first prepared by performing acid leaching of a powder of ground NdFeB permanent magnets.

[0115] Ali, AI2 and Alî 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 4000 rpm for 20 minutes. The supernatants are then collected and filtered (Vivaspin™ 20 PES, 30 kDa MWCO).

[0116] AI4 is obtained by dissolving the magnet powder in acetic acid (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).

[0117] Solution AI5, on the other hand, is obtained by adding sodium nitrate (at 0.6 mol / L) to a sample of solution AI4.

[0118] A first series of extraction tests is then carried out on each of the Ali solutions at AI5 and using, as organic solutions, an HDES consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70.

[0119] Figure 1 illustrates the distribution coefficients of praseodymium, boron, neodymium, dysprosium, and iron, as obtained after each extraction. Extractions performed with the Ali (nitric acid) and Als (acetic acid-sodium nitrate mixture) solutions yielded better results, primarily due to the presence of nitrates.

[0120] 4. Extractions of rare earth elements from synthetic acidic aqueous solutions:

[0121] 4.1 Influence of the HBA / HBD molar ratio and influence of the acid concentration in the Al solution on the distribution coefficients of the elements M:

[0122] In this example, three acidic aqueous solutions, called synthetic and denoted respectively Alsi to Als3, are first prepared.

[0123] 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.

[0124] A1S2 and A1S3 are prepared in the same way, except that Als2 comprises 1 mol / L of HNO3 and Alss comprises 3 mol / L of HNO3.

[0125] A second series of extractions is performed by contacting each of the Alsi to Alss solutions with each of the following HDES:

[0126] - TODGA / n-decanoic acid 30 / 70 (mol / mol);

[0127] - TODGA / n-decanoic acid 45 / 55 (mol / mol); and

[0128] - TODGA / n-decanoic acid 70 / 30 (mol / mol).

[0129] Figures 2 to 4 illustrate the distribution coefficients of rare earths and iron, as obtained at the end of each of the extractions.

[0130] These figures show that iron is extracted 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 to selectively extract rare earths, with respect to iron, from an aqueous solution of nitric acid.

[0131] Furthermore, it should be noted that the higher the HNO3 concentration in the aqueous solution, the higher the rare earth element distribution coefficient, regardless of the HDES. Additional extractions were performed by contacting each of the Alsi solutions with Al1S3 with an organic solution used as a comparative example. This organic solution comprised 0.25 mol / L of TODGA in n-dodecane with 5% by volume of n-octanol (acting as a phase modifier).

[0132] Figure 5 illustrates the distribution coefficients of rare earths and iron, as obtained from extractions carried out using the "comparative" organic solution.

[0133] As a result, for these extractions, the distribution coefficients of rare earths are much less important than those obtained from extractions carried out using HDES as organic solutions.

[0134] 4.2 Influence of the nature of the HBD compound on the distribution coefficients of the M elements:

[0135] In this example, a third series of extractions is performed by contacting each of the Alsi to Als3 solutions (as described above) with each of the following HDES:

[0136] - TODGA / n-octanoic acid 30 / 70 (mol / mol); and

[0137] - TODGA / 2-ethylhexanoic acid 35 / 65 (mol / mol).

[0138] Figures 6 and 7 illustrate the distribution coefficients of rare earths and iron, as obtained from this third series of extractions.

[0139] The results obtained for these extractions are also compared to those shown in Figure 2.

[0140] Furthermore, a fourth and fifth series of extractions are carried out on the Als2 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.

[0141] Figures 8 and 9 illustrate the distribution coefficients of rare earths and iron, as obtained from the fourth and fifth series of extractions.

[0142] Figures 2 and 6 to 9 show that rare earth elements are selectively extracted relative 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).

[0143] 4.3 Extraction kinetics:

[0144] In this example, different extractions are performed using:

[0145] - as aqueous solutions, a synthetic Als4 solution that simulates a solution obtained from the acid leaching of NdFeB permanent magnets and 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

[0146] - as organic solutions, an HDES consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70.

[0147] The extractions are carried out according to the general principle described in point 2 above, with the difference that the HDES and the Al$4 solution are brought into contact, under agitation 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.

[0148] Figure 10 illustrates the extraction coefficients of rare earths and iron as a function of the contact time between HDES and Als4. 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%.

[0149] 5. Rare earth extraction:

[0150] Deextraction tests are carried out using:

[0151] - 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 Al4 solution described above; and

[0152] - as aqueous deextraction solutions, the solutions noted ADI to Aoe 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.

[0153] For each deextraction test, HDES is contacted with one of the aqueous ADI to AD6 solutions in an HDES / AD volume ratio of 1:2. The mixture is then stirred at 250 rpm for 60 minutes at 25°C and centrifuged at 10,000 rpm for 5 minutes to separate the HDES from the aqueous solution. The mass concentrations of the metallic elements in the ADI to AD6 solutions after deextraction are measured by ICP-OES, and the deextraction yield of these elements is determined.

[0154] As an example, Figure 11 illustrates the neodymium deextraction yields for each deextraction performed.

[0155] This figure shows that aqueous solutions of TEDGA allow for the efficient extraction of neodymium.

[0156] In particular, the aqueous solution of TEDGA at 1 mol / L allows obtaining a neodymium deextraction yield of around 90%.

[0157] Next, five successive extraction / deextraction cycles are carried out.

[0158] Extractions are carried out on the Als4 solution and using, as organic solutions, an HDES consisting of a TODGA / n-decanoic acid mixture in a molar ratio of 30 / 70.

[0159] 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.

[0160] Figure 12 illustrates the extraction coefficient of metallic elements, as obtained at the end of each extraction / de-extraction cycle.

[0161] This figure shows that even after five cycles, HDES remains effective since the rare earth extraction coefficients are between about 75% (for lanthanum) and about 95% (for Nd, Gd, Eu, Dy, Y and Yb) while iron is only very slightly extracted (its coefficient being on the order of only a few percent).

[0162] REFERENCES CITED

[0163] [1] WO 2016 / 046179

[0164] [2] UG Favero et al., Separation and Purification Technology 2023, 34, 123592.

Claims

Demands 1. 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): in which: R 1 to R 4 represent, independently of each other, an alkyl group, linear or branched, in Ci to Cis; R 5 to R 8 represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in Ci to Cis; R 9 to R 12 represent, independently of each other, an alkyl group, linear or branched, in Ci to Cis; R 13 and R14 represent, independently of each other, a hydrogen atom, an alkyl group, linear or branched, in the order Ci to Cis, 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 the order Ci to Cs; and the total number of carbon atoms is at least 24; and - of at least one 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 ranges from 6 to 28.

2. Extraction process according to claim 1, wherein the first compound meets the following requirements: - to formula (I), in which R 1 to R 4 represent, independently of each other, an alkyl group, linear or branched, in Cs to C12 and, preferably, in Ce to Cs and / or in which R 5 to R 8represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in C1 to C1; or - to formula (II), in which R 9 to R 12 represent, independently of each other, an alkyl group, linear or branched, in C1 to C12 and, preferably, in C1 to Cs and / or in which R 13 and R 14 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 C1 to C1.

3. Extraction process according to claim 1 or 2, wherein the first compound meets the following requirements: - to formula (I), in which R 1 to R 4 are identical to each other and all represent a linear alkyl group in Ce to Cs and / or R 5 to R 8represent, independently of each other, a hydrogen atom or an alkyl group, linear or branched, in C1 to C1; or - to formula (II), in which R 9 and R 11 are identical to each other and R 10 and R 12 are identical to each other but different from R 9 and R 11 and / or R 13 and R 14 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 C1.

4. Extraction process according to any one of claims 1 to 3, wherein the first compound meets the following requirements: - to formula (I), in which R 1 to R 4 all represent a linear Cs alkyl group while R 5 to R 8 each represent a hydrogen atom; or - to formula (I), in which R 1 to R4 all represent a linear alkyl group in Cs, R 5 and R 7 both represent a methyl group while R 6 and R 8 both represent a hydrogen atom; or - to formula (II), in which R 9 and R 11 both represent a linear alkyl group in Cs, R 10 and R 12 both represent a methyl group, R 13 represents a hydrogen atom while R 14 represents a -(CH2)nOR group in which n is equal to 2 and R represents a linear Ce 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 Ce to C12 or a cycloalkyl group in Ce 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. An extraction process according to any one of claims 1 to 6, wherein the first compound corresponds to formula (I), in which R 1 to R 4 all represent a linear alkyl group in Cs and R 5 to R 8 they all represent a hydrogen atom and the second compound is n-decanoic acid.

8. 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 mol% and, of 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. 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, holmium, 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 earth elements from an acidic aqueous solution Al, 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 according to any one of claims 1 to 16; and b) de-extraction of the rare earth element(s) from the organic solution obtained at the end of step a), the de-extraction comprising at least contacting the organic solution with an aqueous de-extraction solution AD and then separating the organic and aqueous solutions.

18. A recovery process according to claim 17, wherein the aqueous solution AD comprises an agent that complexes the rare earth element(s) in aqueous medium, preferably N,N,N', / V'-tetraethyldiglycolamide.

19. 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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