PROCESS FOR THE SELECTIVE EXTRACTION OF BORON BY AN ORGANIC SOLVENT FROM SOLUTIONS DERIVED FROM THE ACID ATTACK OF PERMANENT MAGNETS COMPRISING RARE EARTHS

Abstract

This process for extracting boron contained in an aqueous solution comprising rare earth elements, consists of bringing said aqueous solution into contact and mixing it with an organic solvent, said organic solvent comprising at least one extraction compound consisting of an alcohol, comprising a chain of 6 to 18 carbon atoms, aliphatic or aromatic, linear or branched, bringing the aqueous solution and the organic solvent into contact and mixing it resulting in the transfer of boron from said aqueous solution to said organic solvent.

Description

Title of the invention: PROCESS FOR THE SELECTIVE EXTRACTION OF BORON BY AN ORGANIC SOLVENT FROM SOLUTIONS DERIVED FROM THE ACID ATTACK OF PERMANENT MAGNETS COMPRISING RARE EARTHS Field of invention

[0001] The invention falls within the general field of boron recycling, particularly from used or discarded permanent magnets. More specifically, it relates to a process for solvent extraction of boron contained in a solution resulting from the acid attack of permanent magnets comprising rare earth elements. Prior art

[0002] The use of rare earth magnets is increasing due to their application in electric car motors, electric scooters and wind turbines. Among the most widely used rare earth magnets are neodymium-iron-boron (NdFeB) permanent magnets. However, the scarcity of the chemical elements constituting these magnets and the pollution emitted during their extraction have made their recycling a critical issue.

[0003] Thus, the recovery of rare earths used in the composition of end-of-life magnets or still present in the production waste of these magnets, is a determining factor in view of the scarcity of traditional sources of supply of rare earths.

[0004] In order to recover these rare earths, it is essential to separate them from the boron during magnet reprocessing operations. Recycling boron followed by its return to the market is therefore an important operation. In addition, since boron is a toxic element, this operation avoids the costly management of residues classified as toxic which contain it and which are produced during magnet recycling.

[0005] Current recycling techniques are essentially based on two processes: - on the one hand, a so-called short loop process, in which the permanent magnets are reduced to powder and then reformed directly from this powder, - on the other hand, a so-called long loop process, which consists of dissolving the magnets and then separating the different constituent elements of the magnet.

[0006] The present invention falls within the scope of this second category of method.

[0007] To begin with, recycling begins by demagnetizing permanent magnets recovered from end-of-life devices, by heating them to a temperature above their Curie temperature. They are then ground into powder and then thermally oxidized.

[0008] The oxidized powder is then attacked using an acid, for example nitric acid, hydrochloric acid or sulfuric acid, causing all or part of the elements to go into solution.

[0009] The acid etching solution thus obtained comprises the constituents of permanent magnets, namely in the case of NdFeB magnets, neodymium, iron, boron and its traces of other minor constituents, for example other rare earth elements and / or elements such as iron, aluminum, cobalt, copper, zinc.

[0010] From this solution, boron recovery is based on the liquid-liquid extraction technique.

[0011] This dissolution process is described, for example, in WO 96 / 00698, in which the magnet is oxidized by heat treatment and then dissolved in a hydrochloric acid solution.

[0012] On the other hand, processes are known from the current state of the art in which boron is extracted from aqueous solutions free of rare earths, using an organic solvent composed of at least one alcohol, or a diol, diluted in a liquid mixture of hydrocarbons.

[0013] Such a process is for example described in the document “Boron extraction from aqueous medium using novel hydrophobic deep eutectic solvents”, Almustafa et al., 2020, which details the extraction of boron from aqueous solutions from wastewater, free of rare earths and iron, using eutectic solvents comprising a diol and a monoalcohol.

[0014] Similarly, in the document “Recovery of boron from unacidified salt lake brine by solvent extraction with 2,2,4-trimethyl-l,3-pentanediol”, Peng et al., 2021, boron extraction is carried out from an aqueous solution derived from brine free of rare earths and iron, using 2,2,4-trimethyl-l,3-pentanediol.

[0015] Such a diol-based extracting system has been applied to the reprocessing of magnets. After solutionization, a boron extraction step is described which is preceded by the recovery of the rare earths present in the magnet etching solution.

[0016] This process is set out in the document “Recovery and separation of rare earths and boron from spent Nd-Fe-B magnets”, Liu et al., 2020, which describes the extraction of boron using a solvent composed of 2-ethyl-l,3-hexanediol and sulfonated kerosene, after total precipitation of the rare earths in solution in the form of oxalate.

[0017] Thus, all the boron extraction processes known to date apply to solutions not containing rare earths.

[0018] There is therefore a need to develop a process for selectively extracting boron from an aqueous solution resulting from the attack of magnets and containing mainly rare earths, with some traces of other elements.

[0019] According to the invention, boron is extracted from an attack solution containing the rare earths, which gives complete freedom in the choice of processes subsequently implemented to recover and separate the rare earths without the possible disturbances which would be due to the presence of boron. Indeed, some of the processes of the prior art can present a risk of contamination of the rare earths by boron and moreover boric acid has a low solubility in these solutions compared to rare earth salts which can limit the parameters for implementing such processes. Statement of the invention

[0020] The invention, by eliminating boron, which is considered toxic, allows easier management of solid residues generated by the recycling of rare earth magnets. It thus contributes more to compliance with ecological constraints.

[0021] The invention therefore relates to a process for extracting boron contained in an aqueous solution comprising rare earth elements, in which said aqueous solution is brought into contact and mixed with an organic solvent comprising at least one extraction compound consisting of an alcohol, comprising a chain of 6 to 18 carbon atoms, aliphatic or aromatic, linear or branched, the contacting and mixing of the aqueous solution and the organic solvent resulting in the transfer of boron from said aqueous solution to said organic solvent.

[0022] The present invention can only be carried out with compounds comprising a number of carbon atoms greater than or equal to 6, or less than or equal to 18. Indeed, below 6 carbon atoms, hydrocarbons are gaseous, while above 18 carbon atoms, they are solid waxes or tars.

[0023] The steps of contacting and mixing the aqueous solution and the organic solvent result in the transfer of boron from said aqueous solution to said organic solvent.

[0024] For the purposes of the invention, the term “alcohol” denotes all compounds comprising at least one alcohol function, this includes monoalcohols and diols.

[0025] Preferably, the extraction compound is chosen from the group comprising: - 1-3 diols, preferably from 2-ethyl-1,3-hexanediol (EHD), 2-butyl-2-ethylpropane-1,3-diol (BEPD), 2,2,4-trimethyl-1,3-pentanediol (TMPD), 2-chloro-4-(1,1,3,3-tetramethylbutyl)-6-methylol-phenol (CTMP), and mixtures thereof; - monoalcohols of 6 to 18 carbon atoms, with a branched or linear aliphatic chain, preferably from 2-ethylhexanol (2-EH), 2-propylheptanol (2-PH), 2-butyloctanol, isodecanol, octanol, and mixtures thereof.

[0026] By "1-3 diol" is meant a chemical compound which comprises two alcohol functions carried by two carbon atoms separated from each other by another carbon atom. These compounds are also called "[3-diols".

[0027] By "monoalcohol" is meant a chemical compound which comprises a single alcohol function.

[0028] In addition to the extraction compound, the organic solvent may also comprise at least one diluent compound. The diluent compound preferably consists of a hydrocarbon chain of 6 to 18 carbon atoms, aliphatic or aromatic.

[0029] Preferably, the diluent compound is chosen from the group comprising: decane and its isomers, dodecane and its isomers, kerosene, toluene, hydrocarbons having between 6 and 18 carbon atoms, aliphatic or aromatic, and mixtures thereof. As diluent compound, mention may be made, for example, of Shellsol®D70 (aliphatic hydrocarbon), Solvesso®150 (aromatic hydrocarbon).

[0030] Preferably, the diluting compound is a liquid substance in which the extraction compound is dissolved.

[0031] According to one embodiment, the organic solvent further comprises a modifying compound, different from the extraction compound. The modifying compound preferably consists of an alcohol comprising an aliphatic chain of 6 to 18 carbon atoms.

[0032] Preferably, the modifying compound is chosen from the group comprising monoalcohols, preferably from decan-1-ol, octan-1-ol, isodecan-1-ol, hexan-1-ol, dodecan-1-ol, 2-propylheptanol, 2-ethylhexanol, and mixtures thereof.

[0033] For the purposes of the invention, the term “modifying compound” denotes a chemical species other than the extraction compound and the diluting compound, capable of modifying certain properties of the organic solvent.

[0034] For example, the modifying compound may delay the appearance of a third phase or aid in the settling of the organic solvent and the aqueous solution.

[0035] In a particular embodiment of the invention, the organic solvent comprises: - 10% to 100% of at least one extraction compound, - 0% to 90% of at least one diluting compound, - 0% to 70% of at least one modifying compound, by weight relative to the total weight of the organic solvent, the total being equal to 100%.

[0036] According to one embodiment, the organic solvent comprises at least 5%, or even 20%, or even 30%, or even 40%, or even 50%, of at least one extraction compound. The organic solvent may comprise at most 90%, or even 80%, or even 70%, or even 60% of at least one extraction compound.

[0037] According to one embodiment, the organic solvent comprises at least 5%, or even 20%, or even 25%, or even 30%, or even 40%, or even 50%, of at least one diluent compound. The organic solvent may comprise at most 95%, or even 80%, or even 70%, or even 60%, or even 55% of at least one diluent compound.

[0038] According to one embodiment, the organic solvent comprises at least 5%, or even 10%, or even 20%, or even 25%, or even 30%, or even 40%, of at least one modifying compound. The organic solvent may comprise at most 80%, or even 70%, or even 60%, or even 50% of at least one modifying compound.

[0039] According to the invention, the organic solvent is brought into contact with the aqueous solution comprising rare earth elements and boron.

[0040] According to the invention, this aqueous solution is a solution resulting from the acid attack of demagnetized neodymium-iron-boron (NdFeB) permanent magnets or machining waste resulting from the manufacture of permanent magnets, reduced to powder and oxidized. Preferably, it has a pH between 0.5 and 3.5.

[0041] By "solution resulting from the acid attack of magnets" is meant a solution obtained following the dissolution of a magnet powder, in particular an NdFeB magnet, in an acid solution, for example nitric acid, hydrochloric acid or sulfuric acid. This powder results from the demagnetization, grinding and oxidation of permanent magnets.

[0042] "Machining waste" refers to the scrap material created during the manufacture of permanent magnets. It includes the same constituents as magnets, i.e. iron, boron and rare earth elements.

[0043] In particular, the majority of Nd is found by mass (from 14% to 26%), then Pr (from 0% to 9%), Dy (from 0% to 6%), Tb (from 0% to 1%), Ce (from 0% to 6%). Sc, Y, Tm, Yb, Lu are not found in NdFeB magnets. A typical composition of an NdFeB magnet is, for example, by mass: 65% Fe, 24% Nd, 2.5% Pr, 4.25% Dy, 1% B, 5% Co.

[0044] This aqueous solution preferably comprises: - from 20 to 450 g / L of rare earth elements in dissolved salt form, - from 1 to 9 g / L of boron in the form of boric acid, - from 0 to 20 g / L of iron in the form of dissolved salt, and - from 0 to 5 g / L of metallic elements in the form of dissolved salt belonging to the group including cobalt, aluminum, zinc, copper, manganese and nickel.

[0045] According to the invention, these rare earth elements are chosen from the group comprising: lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, and mixtures thereof.

[0046] In particular, the solution may comprise between 0 g / L and 1 g / L of cobalt, between 0 g / L and 1 g / L of copper, between 0 g / L and 1 g / L of aluminum and / or between 0 g / L and 0.5 g / L of zinc in the form of dissolved salt.

[0047] In particular, dissolved salts of rare earth elements belong to the group comprising rare earth nitrates, rare earth chlorides, rare earth sulfates, and mixtures thereof.

[0048] Ideally, the method according to the invention therefore comprises a step of bringing the organic solvent and the aqueous solution into contact, preferably with a ratio between their respective volumes of between 1 and 10.

[0049] The contacting and mixing are carried out in a liquid-liquid extraction apparatus. Preferably, the mixing time is between 1 and 15 minutes, preferably between 3 and 5 minutes.

[0050] The mixing is followed by a separation step carried out, for example, by decantation of the aqueous solution and the organic solvent.

[0051] The contacting and mixing are preferably carried out at a temperature between 20°C and 70°C, preferably between 40°C and 60°C.

[0052] This produces a solvent enriched in boron and an aqueous raffinate depleted in boron.

[0053] Advantageously, the concentration of boron in this solvent is between 1 g / L and 14 g / L.

[0054] The selectivity of boron extraction is such that the concentrations of rare earths, iron, aluminum, cobalt, copper and zinc are less than 10 mg / L.

[0055] This extraction operation is advantageously carried out counter-currently on several stages, in batteries of mixer-decanters or in stirred or pulsed columns.

[0056] After boron transfer, the boron concentration in the aqueous raffinate is typically less than 30 mg / L. This corresponds to a boron extraction rate greater than 95%. The quantities of rare earths, iron, aluminum, cobalt, copper and zinc leaving in the raffinate are equal to those entering the initial aqueous solution. The target residual boron content is chosen according to environmental constraints.

[0057] If necessary, the process can be adapted so as to have a lower content than 30 mg / L of boron in the aqueous solvent.

[0058] Furthermore, the method comprises, after the transfer of the boron, a step of re-extraction of the boron included in the organic solvent. Preferably, this step of re-extraction of the boron is carried out by bringing a Brônsted base into contact with said solvent, the base being advantageously chosen from the group comprising: NaOH, KOH, LiOH, NH40H, and mixtures thereof. The boron can then be recovered in the form of alkaline borate obtained from these solutions.

[0059] Generally, the base has a concentration between 0.1 and 2 mol / L.

[0060] For the purposes of the invention, the term "re-extraction" means a liquid-liquid extraction making it possible to transfer from the organic solvent to an aqueous phase the boron already extracted using said solvent.

[0061] Here, the boron contained in the organic solvent is transferred to the aqueous phase containing the base. Thus, the recovered solvent is almost free of boron. preferably, it has a boron concentration of less than 10 mg / L. Examples of embodiments of the invention

[0062] Examples 1 to 14 aim to demonstrate different embodiments of the invention. They set out the basic data used to carry out a boron extraction process according to the invention, in the presence of rare earths in solution.

[0063] Examples 15 and 16 show a more complete implementation of the method.

[0064] Example 1: Extraction of boron by an EHD / octan-l-ol solvent

[0065] In a 50 mL flask, 20 mL of an aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets in nitric acid are introduced, the solution having a boron concentration of 4.5 g / L, neodymium of 110 g / L, praseodymium of 27 g / L, dysprosium of 7 g / L, cerium of 3 g / L, and other rare earths at less than 1 g / L, for a total of 150 g / L of rare earths. The solution has an iron concentration of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and it includes traces of zinc. It has a pH of 2.

[0066] The aqueous solution is prepared by demagnetizing neodymium-iron-boron NdFeB permanent magnets, grinding them into powder and finally thermally oxidizing them. The oxidized powder is then dissolved in a nitric acid solution.

[0067] 20 mL of an organic extraction solvent composed of 30% by mass of 2-ethyl-1,3-hexanediol (EHD), as extraction compound, and 70% by mass of octan-1-ol, as diluting compound, are introduced into this same flask.

[0068] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0069] The medium is stirred vigorously at 60°C for 15 minutes. After which, the aqueous and organic phases are separated by decantation.

[0070] We then obtain a boron concentration in the aqueous phase of 0.25 g / L, in the organic phase of 4.25 g / L and therefore a boron partition coefficient equal to 17.

[0071] The final concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0072] Example 2: Extraction of boron by an EHD / octan-l-ol solvent

[0073] The extraction process of Example 1 is repeated, but this time introducing into a flask, 40 mL of the acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets of Example 1, and 10 mL of the organic extraction solvent of Example 1.

[0074] The volume ratio between the aqueous phase and the organic phase is therefore 4.

[0075] We then obtain a boron partition coefficient equal to 5.

[0076] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the copper partition coefficient is less than 0.05.

[0077] Example 3: Extraction of boron by an EHD / Solvesso®150 / 2-EH solvent

[0078] In a 100 mL flask, 60 mL of an acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets are introduced, the solution having a boron concentration of 4.5 g / L, neodymium of 110 g / L, praseodymium of 27 g / L, dysprosium of 7 g / L, cerium of 3 g / L, and other rare earths of less than 1 g / L, for a total of 150 g / L of rare earths. The solution has an iron concentration of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and it includes traces of zinc. It has a pH of 2.

[0079] 10 mL of an organic extraction solvent composed of 30% by mass of 2-ethyl-1,3-hexanediol (EHD) as the extraction compound, 50% by mass of Solvesso®150 as the diluting compound, and 20% by mass of 2-ethylhexanol (2-EH) as the modifying compound are introduced into this same bottle.

[0080] The volume ratio between the aqueous phase and the organic phase is therefore 6.

[0081] The medium is stirred vigorously at 60°C for 15 minutes. After which, and the aqueous and organic phases are separated by decantation.

[0082] We then obtain a boron partition coefficient equal to 6.

[0083] The concentrations of total rare earth, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0084] Example 4: Extraction of boron by an EHD / Solvesso®150 / 2-EH solvent

[0085] The extraction process of Example 3 is repeated, but this time introducing into a flask, 50 mL of an acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets of Example 3, and 50 mL of the organic extraction solvent of Example 3.

[0086] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0087] We then obtain a boron partition coefficient equal to 32.

[0088] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0089] Example 5: Extraction of boron by a TPMD / kerosene / decanol solvent

[0090] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets, having a boron concentration of 4.5 g / L, neodymium of 110 g / L, praseodymium of 27 g / L, dysprosium of 7 g / L, cerium of 3 g / L, and other rare earths of less than 1 g / L, for a total of 150 g / L of rare earths, are introduced. The solution has an iron concentration of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and it includes traces of zinc. It has a pH of 2.

[0091] 10 mL of an organic extraction solvent composed of 15% by mass of 2,2,4-trimethyl-,1,3-pentaediol (TPMD), as extraction compound, 25% by mass of kerosene, as diluting compound, and 60% by mass of decanol, as modifying compound, are introduced into this same flask.

[0092] The volume ratio between the aqueous phase and the organic phase is therefore 5.

[0093] The medium is stirred vigorously at 60°C for 15 minutes. After which, and the aqueous and organic phases are separated by decantation.

[0094] We then obtain a boron partition coefficient equal to 1.7.

[0095] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0096] Example 6: Extraction of boron by a TPMD / kerosene / decanol solvent

[0097] The extraction of Example 5 is repeated but this time introducing into a flask, 50 mL of the acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets of Example 5, and 50 mL of the organic extraction solvent of Example 5.

[0098] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0099] We then obtain a boron partition coefficient equal to 18.

[0100] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0101] Example 7: Extraction of boron using a BEPD / kerosene / decanol solvent

[0102] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of an oxidized permanent magnet powder, having a boron concentration of 4.5 g / L, neodymium of 110 g / L, praseodymium of 27 g / L, dysprosium of 7 g / L, cerium of 3 g / L, and other rare earths of less than 1 g / L, for a total of 150 g / L of rare earths, are introduced into a 100 mL flask. The solution has an iron concentration of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and it includes traces of zinc. It has a pH of 2.

[0103] 10 mL of an organic extraction solvent composed of 15% by mass 2-butyl-2-ethylpropane-1,3-diol (BEPD) as extraction compound, 25% by mass kerosene as diluting compound, 60% by mass decanol as modifying compound are introduced into this same flask.

[0104] The volume ratio between the aqueous phase and the organic phase is therefore 5.

[0105] The medium is stirred vigorously at 60°C for 15 minutes. After which, the aqueous and organic phases are separated by decantation.

[0106] We then obtain a boron partition coefficient equal to 1.2.

[0107] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0108] Example 8: Extraction of boron by a BEPD / kerosene / decanol solvent

[0109] The extraction of Example 7 is repeated but by introducing into a flask, 50 mL of the acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets of Example 7, and 50 mL of the organic extraction solvent of Example 7.

[0110] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0111] We then obtain a boron partition coefficient equal to 4.

[0112] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0113] Example 9: Extraction of boron by a 2-PH / kerosene solvent

[0114] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets are introduced, the solution having a boron concentration of 4.5 g / L, neodymium of 110 g / L, praseodymium of 27 g / L, dysprosium of 7 g / L, cerium of 3 g / L, and other rare earths of less than 1 g / L, for a total of 150 g / L of rare earths. The solution has an iron concentration of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and it includes traces of zinc. It has a pH of 2.

[0115] 10 mL of an organic solvent composed of 60% by mass of 2-propylheptanol (2-PH) as the extraction compound and 40% by mass of kerosene as the diluting compound are introduced into this same flask.

[0116] The volume ratio between the aqueous phase and the organic phase is therefore 5.

[0117] The medium is stirred vigorously at room temperature for 15 minutes. After which, the aqueous and organic phases are separated by decantation.

[0118] We then obtain a boron partition coefficient equal to 0.6.

[0119] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0120] Example 10: Extraction of boron by a 2-PH / kerosene solvent

[0121] The extraction of example 9 is repeated, but by introducing into a flask 50 mL of the acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets from Example 9, and 50 mL of the organic extraction solvent from Example 9.

[0122] The volume ratio between the aqueous phase and the organic phase is therefore 1. We then obtain a boron partition coefficient equal to 0.6.

[0123] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0124] Example 11: Extraction of boron by a pure 2-PH solvent

[0125] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets are introduced, the solution having a boron concentration of 4.5 g / L, neodymium of 110 g / L, praseodymium of 27 g / L, dysprosium of 7 g / L, cerium of 3 g / L, and other rare earths of less than 1 g / L, for a total of 150 g / L of rare earths. The solution has an iron concentration of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and it includes traces of zinc. It has a pH of 2.

[0126] 10 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) are introduced into this same flask as extraction compound.

[0127] The volume ratio between the aqueous phase and the organic phase is therefore 5.

[0128] The medium is stirred vigorously at 60°C for 15 minutes. After which, the aqueous and organic phases are separated by decantation.

[0129] We then obtain a boron partition coefficient equal to 0.56.

[0130] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0131] Example 12: Extraction of boron by a pure 2-PH solvent

[0132] The extraction process of Example 11 is repeated, but by introducing into a flask 50 mL of the acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets of Example 11, and 50 mL of the organic extraction solvent of Example 11.

[0133] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0134] We then obtain a boron partition coefficient equal to 0.58.

[0135] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0136] Example 13: Extraction of boron by a pure 2-PH solvent from an aqueous solution having a rare earth concentration of 250 g / L

[0137] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets, having a boron concentration of 4.5 g / L, neodymium of 183 g / L, praseodymium of 45 g / L, dysprosium of 12 g / L, cerium of 5 g / L, and other rare earths of less than 5 g / L, for a total of 250 g / L of rare earths, are introduced. The solution has an iron concentration of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and includes traces of zinc. It has a pH of 2.

[0138] 10 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) are introduced into this same flask as extraction compound.

[0139] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0140] The medium is stirred vigorously at 60°C for 15 minutes. After which, the mixture is centrifuged, and the aqueous and organic phases are separated by decantation.

[0141] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0142] We then obtain a boron partition coefficient equal to 0.65.

[0143] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0144] Example 14: Extraction of boron by a pure 2-PH solvent from an aqueous solution having a rare earth concentration of 400 g / L

[0145] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets, having a boron concentration of 4.5 g / L, neodymium of 293 g / L, praseodymium of 72 g / L, dysprosium of 19 g / L, cerium of 8 g / L, and other rare earths of less than 8 g / L are introduced for a total of 400 g / L of rare earths. The solution has an iron concentration of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and it includes traces of zinc. It has a pH of 2.

[0146] 50 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) are introduced into this same flask as extraction compound.

[0147] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0148] The medium is stirred vigorously at 60°C for 15 minutes. After which, the aqueous and organic phases are separated by decantation.

[0149] We then obtain a boron partition coefficient equal to 3.

[0150] The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the partition coefficient of neodymium is less than 10 4 while the partition coefficient of copper is less than 0.05.

[0151] Example 15 which follows shows the interest of operating on concentrated solutions of rare earths. Example 16 gives an example of operation in a battery of mixer-decanters including the extraction of boron and the recycling of the solvent.

[0152] Example 15: Extraction of boron using a pure 2-PH solvent

[0153] The solubility of boron in the attack solutions is limited, and to benefit from this concentration effect (examples 12, 13, 14), it is advisable to carry out the extraction in two stages, firstly on the attack solution at approximately 150g / l rare earths then on the solution partially depleted of boron and reconcentrated to approximately 400 g / l.

[0154] In a reactor, the following are introduced at a temperature of 50°C: - 300 mL of an organic solvent composed of pure 2-propylheptanol, as an extraction compound; - 75 mL of an aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets, the solution having a concentration of boron of 4.5 g / L, neodymium HOg / L, praseodymium 27g / L, dysprosium 7g / L, cerium 3g / L, and other rare earths at less than 1g / L for a total of 150 g / L of rare earth, iron of 2 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, copper of 0.2 g / L and including traces of zinc. It has a pH of 2.

[0155] After mixing for 15 minutes and decanting the phases, we recover: - 300 mL of an organic solvent with a boron concentration of 0.8 g / L; - 75 mL of an aqueous phase comprising rare earths, the solution having a boron concentration of 1.27 g / L, neodymium HOg / L, praseodymium 27g / L, dysprosium 7g / L, cerium 3g / L, and other rare earths less than 1g / L for a total of 150 g / L of rare earth, iron 1 g / L, aluminum 0.5 g / L, cobalt 0.5 g / L and including traces of zinc.

[0156] The boron extraction rate for this first stage is 71.1%.

[0157] In a second step, the previous aqueous phase is concentrated by distillation to obtain a rare earth concentration of 400 g / L, i.e. a boron concentration of 3.40 g / L, neodymium of 293 g / L, praseodymium of 72 g / L, dysprosium of 19 g / L, cerium of 8 g / L, and other rare earths at less than 3 g / L, iron of 2.6 g / L, aluminum of 1.3 g / L, cobalt of 1.3 g / L and including traces of zinc and a solution volume of 28 mL.

[0158] Then in a second reactor we introduce at a temperature of 50°C: - 56 mL of an organic solvent composed of pure 2-propylheptanol, as an extraction compound; - 28 mL of the concentrated solution obtained previously

[0159] We recover: - 56 mL of an organic solvent with a boron concentration of 1.37 g / L; - 28 mL of an aqueous phase comprising rare earths, the solution having a boron concentration of 0.62 g / L, neodymium 293 g / L, praseodymium 72 g / L, dysprosium 19 g / L, cerium 8 g / L, and other rare earths less than 3 g / L, iron 2.6 g / L, aluminum 1.3 g / L, cobalt 1.3 g / L and including traces of zinc.

[0160] With this sequence of extraction-concentration-extraction operations the aqueous phase has been depleted of boron and the overall extraction rate compared to the initial solution is 95%.

[0161] Example 16: Extraction of boron by a BEPD / kerosene / decanol solvent in a battery of mixer-decanters

[0162] This example is an embodiment of the invention implemented in a countercurrent extraction battery.

[0163] a) Bringing an aqueous solution and an organic solvent into contact

[0164] In a battery of six mixer-decanters operating in counter-current, at a temperature of 50°C, the following are introduced: - at stage 1: an organic solvent at a flow rate of 145 mL / h, the solvent being composed of 15% by mass of BEPD, as extraction compound, 25% by mass of kerosene, as diluting compound, and 60% by mass of decanol, as modifying compound; - on stage 5: an acidic aqueous solution resulting from the dissolution of an oxidized permanent magnet powder, at a flow rate of 145 mL / h, the solution having a boron concentration of 4.60 g / L, neodymium of 110 g / L, praseodymium of 25 g / L, dysprosium of 6 g / L, cerium of 3 g / L, and other rare earths of less than 1 g / L, for a total of 137 g / L of rare earths. The solution has an iron concentration of 1 g / L, aluminum of 0.5 g / L, cobalt of 0.5 g / L, and it includes traces of zinc. It has a pH of 1.5; - on floor 6: water at a flow rate of 7 mL / h.

[0165] We recover: - on stage 1: an aqueous rare earth raffinate at a flow rate of 152 mL / h, the raffinate having a boron concentration of 16 mg / L, rare earths of 131 g / L, iron of 0.95 g / L, aluminum of 0.48 g / L, cobalt of 0.48 g / L and including traces of zinc; - on stage 6: an organic solvent loaded with boron at a flow rate of 145 mL / h, the solvent having a boron concentration of 4.58 g / L.

[0166] The boron extraction rate is therefore 99.6%. This rate corresponds to the mass of boron recovered in the solvent over the total mass of boron introduced into the feed.

[0167] The process makes it possible to transfer the majority of the boron initially contained in the aqueous solution to the organic solvent.

[0168] The aqueous raffinate thus obtained comprises a quantity of boron less than 30 mg / L.

[0169] The rare earths, iron and other impurities are not present in the solvent, they are recovered in the aqueous raffinate.

[0170] b) Re-extraction of boron from the boron-loaded solvent

[0171] In a second battery of four mixer-decanters operating in counter-current, at a temperature of 50°C, the following are supplied: - in stage 1: the boron-loaded organic solvent, recovered at the outlet of stage 6 during the previous contacting step, at a flow rate of 145 mL / h, the solvent being composed of 15% by mass of BEPD, 25% by mass of kerosene, 60% by mass of decanol, and having a boron concentration of 4.58 g / L; - on stage 4: an aqueous solution of NaOH, at a flow rate of 79 mL / h, the solution having a concentration of 0.40 mol / L.

[0172] We recover: - on stage 1: a basic solution, at a flow rate of 79 mL / h, having a boron concentration of 8.35 g / L and a sodium concentration of 9.2 g / L, i.e. a sodium boron molar ratio of 0.52; - on stage 4: an organic solvent, at a flow rate of 145 mL / h, the solvent having a boron concentration of 30 mg / L.

[0173] The boron re-extraction rate is 99.3%. This rate corresponds to the mass of boron recovered in the basic solution over the mass of boron contained in the charged organic solvent.

[0174] The boron recovery rate is 98.9%. This rate corresponds to the mass of boron recovered in the basic solution over the mass of boron contained in the acidic aqueous solution resulting from the dissolution of a magnet powder (i.e. the mass of boron introduced into the process).

[0175] The solvent thus regenerated has a low boron concentration, less than 30 mg / L, and is recycled to extraction.

Claims

Claims

1. A method for extracting boron contained in an aqueous solution comprising rare earth elements, the aqueous solution being obtained from the dissolution of an NdFeB magnet powder, or from machining waste resulting from the manufacture of permanent magnets, in which said aqueous solution is brought into contact and mixed with an organic solvent, said organic solvent comprising at least one extraction compound consisting of an alcohol, comprising a chain of 6 to 18 carbon atoms, aliphatic or aromatic, linear or branched, the contacting and mixing of the aqueous solution and the organic solvent resulting in the transfer of boron from said aqueous solution to said organic solvent.

2. A method for extracting boron according to claim 1, wherein the extraction compound is selected from the group comprising: - 1-3 diols, preferably from 2-ethyl-1,3-hexanediol (EHD), 2-butyl-2-ethylpropane-1,3-diol (BEPD), 2,2,4-trimethyl-1,3-pentanediol (TMPD), 2-chloro-4-(1,1,3,3-tetramethylbutyl)-6-methylol-phenol (CTMP), and mixtures thereof; - monoalcohols of 6 to 18 carbon atoms, with a branched or linear aliphatic chain, preferably from 2-ethylhexanol (2-EH), 2-propylheptanol (2-PH), 2-butyloctanol, isodecanol, octanol, and mixtures thereof.

3. A method of extracting boron according to claim 1 or 2, wherein the organic solvent further comprises at least one diluent compound consisting of a hydrocarbon chain of 6 to 18 carbon atoms, aliphatic or aromatic.

4. A method of extracting boron according to claim 3, wherein the diluent compound is selected from the group comprising: decane and its isomers, dodecane and its isomers, kerosene, toluene, hydrocarbons having between 6 and 18 carbon atoms, aliphatic or aromatic, and mixtures thereof.

5. A method of extracting boron according to one of claims 1 to 4, wherein the organic solvent further comprises a modifying compound different from the extraction compound, the modifying compound consisting of an alcohol comprising an aliphatic chain of 6 to 18 carbon atoms.

6. A method of extracting boron according to claim 5, wherein the modifying compound is selected from the group comprising monoalcohols, preferably from decan-1-ol, octan-1-ol, isodecan-1-ol, hexan-1-ol, dodecan-1-ol, 2-propylheptanol, 2-ethylhexanol, and mixtures thereof.

7. A method of extracting boron according to one of claims 1 to 6, wherein the organic solvent comprises: - 10% to 100% of at least one extraction compound, - 0% to 90% of at least one diluent compound, - 0% to 70% of at least one modifying compound, by weight relative to the total weight of the organic solvent, the total being equal to 100%.

8. A method for extracting boron according to one of claims 1 to 7, in which the aqueous solution comprises: - from 20 to 450 g / L of rare earth elements in the form of dissolved salt, - from 1 to 9 g / L of boron in the form of boric acid, - from 0 to 20 g / L of iron in the form of dissolved salt, and - from 0 to 5 g / L of metallic elements belonging to the group comprising cobalt, aluminum, zinc, copper, manganese and nickel.

9. A method of extracting boron according to one of claims 1 to 8, wherein the dissolved salts of rare earth elements belong to the group comprising rare earth nitrates, rare earth chlorides, rare earth sulfates, and mixtures thereof.

10. A method of extracting boron according to one of claims 1 to 9, in which the contacting and mixing are carried out at a temperature between 20°C and 70°C, preferably between 40°C and 60°C.

11. Method for extracting boron according to one of claims 1 to 10, in which the method further comprises, after the transfer of the boron, a step of re-extracting the boron included in the organic solvent.

12. A method of extracting boron according to claim 11, wherein the re-extraction of boron is carried out by contacting a Brônsted base with said solvent, the base being selected from the group comprising: NaOH, KOH, LiOH, NH4OH, and mixtures thereof.