Method for the selective extraction of boron by means of an organic solvent from solutions derived from acid attack on permanent magnets comprising rare earths

Abstract

The invention relates to a method for extracting boron contained in an aqueous solution A1 comprising rare earth elements, wherein the method consists in bringing the aqueous solution A1, which results from the dissolution of powdered NdFeB magnets or machining scraps from the manufacture of permanent magnets, into contact with an organic solvent and mixing it therewith, the organic solvent comprising at least one extraction compound consisting of an alcohol, comprising an aliphatic or aromatic, linear or branched chain of 6 to 18 carbon atoms and wherein bringing the aqueous solution A1 into contact with the organic solvent and mixing it therewith causes the boron to be transferred from the aqueous solution A1 to the organic solvent.

Description

[0001] PROCESS FOR THE SELECTIVE EXTRACTION OF BORON BY AN ORGANIC SOLVENT FROM SOLUTIONS DERIVED FROM THE ACID ATTACK OF PERMANENT MAGNETS COMPRISING RARE EARTHS

[0002] FIELD OF THE INVENTION

[0003] 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.

[0004] PRIOR STATE OF THE ART

[0005] 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 that make up these magnets and the pollution emitted during their extraction have made their recycling a critical issue.

[0006] 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.

[0007] In order to recover these rare earths, it is essential to separate them from 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 containing it, which are produced during magnet recycling.

[0008] Current recycling techniques are essentially based on two processes:

[0009] • on the one hand a so-called “short loop” process, a process in which the permanent magnets are reduced to powder, then reformed directly from this powder,

[0010] • on the other hand, a so-called “long loop” process, which consists of dissolving the magnets, then separating the different constituent elements of the magnet. The present invention falls within the framework of this second category of process.

[0011] To begin, 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.

[0012] 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.

[0013] 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, aluminium, cobalt, copper, zinc.

[0014] From this solution, boron recovery is based on the liquid-liquid extraction technique.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] Similarly, in the paper “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 performed from an aqueous solution derived from rare earth and iron-free brine using 2,2,4-trimethyl-l,3-pentanediol. Such a diol-based extractant system has been applied to magnet reprocessing. After solutionization, a boron extraction step is described, which is preceded by the recovery of rare earths present in the magnet etching solution.

[0019] This process is outlined in the paper “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.

[0020] This boron extraction process applies to solutions not containing rare earths.

[0021] The paper "Separation of fission and corrosion products from boric acid solutions by solvent extraction", Narbutt J. et al., 1979, describes a process for the liquid-liquid extraction of boric acid dissolved in aqueous solutions from radioactive corrosion and fission products. It does not cover the extraction of boron from used or discarded permanent magnets.

[0022] 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.

[0023] According to the invention, boron is extracted from an attack solution containing rare earths, which gives complete freedom in the choice of the 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 may 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 may limit the parameters for implementing such processes.

[0024] STATEMENT OF THE INVENTION

[0025] The invention, by eliminating boron, which is considered toxic, allows easier management of the solid residues generated by the recycling of rare earth magnets. It thus contributes more to compliance with ecological constraints. The invention therefore relates to a method for extracting boron contained in an aqueous Al solution comprising rare earth elements, the aqueous Al solution being obtained from the dissolution of an NdFeB magnet powder, or from machining waste resulting from the manufacture of permanent magnets. In the method of the invention, the aqueous Al 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 Al solution and the organic solvent resulting in the transfer of boron from said aqueous Al solution to said organic solvent.

[0026] 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.

[0027] The steps of contacting and mixing the aqueous Al solution and the organic solvent result in the transfer of boron from said aqueous Al solution to said organic solvent.

[0028] By "boron" is included any compound comprising at least one boron atom, present in aqueous or organic phase. For example, boric acid is included in the definition of "boron" according to the invention.

[0029] For the purposes of the invention, the term “alcohol” denotes all compounds comprising at least one alcohol function, this includes monoalcohols and diols.

[0030] In the present invention, the term "borate" denotes a molecular compound comprising at least one boron atom and at least one oxygen atom. For example and without limitation, the metaborate ions BCh and tetraborate B4O? 2 “ are borates.

[0031] By "boron salt" is included borate salts. For example and without limitation, sodium metaborate NaBCh and sodium tetraborate Na2B4O7 are boron salts. Sodium tetraborate pentahydrate Na2B4O7*5H2O or decahydrate Na2B4O7*10H2O which are also called borax, are boron salts. Preferably, the extraction compound is selected from the group consisting of: 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.

[0032] The term "1-3 diol" refers to a chemical compound that contains two alcohol functions carried by two carbon atoms separated from each other by another carbon atom. These compounds are also called "P-diols".

[0033] The term "monoalcohol" refers to a chemical compound that contains a single alcohol function.

[0034] 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.

[0035] 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, paraffins, cycloparaffins, and mixtures thereof. As diluent compound, mention may be made, for example, of Shellsol®D70 (aliphatic hydrocarbon), Solvesso®150 (aromatic hydrocarbon).

[0036] Preferably, the diluting compound is a liquid substance in which the extraction compound is dissolved.

[0037] 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.

[0038] 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. For the purposes of the invention, the term "modifying compound" denotes a chemical species other than the extraction compound and the diluent compound, capable of modifying certain properties of the organic solvent.

[0039] For example, the modifying compound can delay the appearance of a third phase or aid in the settling of the organic solvent and the aqueous solution.

[0040] It can be dissolved in the diluent compound.

[0041] 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 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%.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] According to the invention, the organic solvent is brought into contact with the aqueous Al solution comprising rare earth elements and boron. According to the invention, this aqueous Al solution is a solution resulting from the acid attack of demagnetized neodymium-iron-boron (NdFeB) permanent magnets or from 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.

[0046] The term "solution resulting from the acid attack of magnets" refers to 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.

[0047] Machining scrap refers to the material left over from the manufacturing of permanent magnets. It contains the same components as magnets, namely iron, boron, and rare earth elements.

[0048] In particular, we find mainly Nd (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%). We do not find Sc, Y, Tm, Yb, Lu, in NdFeB magnets. A typical composition of an NdFeB magnet is for example, by mass, is: 65% Fe, 24% Nd, 2.5% Pr, 4.25% Dy, 1% B, 5% Co.

[0049] This aqueous solution Al 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 boric acid form, from 0 to 20 g / L of iron in dissolved salt form, and from 0 to 5 g / L of metallic elements in dissolved salt form belonging to the group comprising cobalt, aluminum, zinc, copper, manganese and nickel.

[0050] 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.

[0051] In particular, the Al 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. In particular, the dissolved salts of rare earth elements belong to the group comprising rare earth nitrates, rare earth chlorides, rare earth sulfates, and mixtures thereof.

[0052] Ideally, the process according to the invention therefore comprises a step of bringing the organic solvent and the aqueous solution Al into contact, preferably with a ratio between their respective volumes of between 1 and 10.

[0053] 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.

[0054] The mixing is followed by a separation step carried out, for example, by decantation of the aqueous Al solution and the organic solvent.

[0055] Contacting and mixing are preferably carried out at a temperature between 20°C and 70°C, preferably between 40°C and 60°C.

[0056] This produces a solvent enriched in boron and an aqueous raffinate depleted in boron.

[0057] Advantageously, the concentration of boron in this solvent is between 1 g / L and 14 g / L.

[0058] 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.

[0059] This extraction operation is advantageously carried out counter-currently on several stages, in batteries of mixer-decanters or in agitated or pulsed columns.

[0060] 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 exiting in the raffinate are equal to those entering the initial aqueous Al solution. The target residual boron content is chosen according to environmental constraints. If necessary, the process can be adapted to have a boron content lower than 30 mg / L in the aqueous solvent.

[0061] 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, NH4OH, and mixtures thereof. The boron can then be recovered in the form of alkaline borate obtained from these solutions.

[0062] Generally, the base has a concentration between 0.1 and 2 mol / L.

[0063] For the purposes of the invention, the term "re-extraction" means a liquid-liquid extraction enabling the boron already extracted using said solvent to be transferred from the organic solvent to an aqueous phase.

[0064] Here, the boron contained in the organic solvent is transferred to the aqueous phase containing the base. Thus, the recovered solvent is virtually boron-free. Preferably, it has a boron concentration of less than 10 mg / L.

[0065] The method of the invention may further comprise a step of recovering boron in the form of boron salt from boric acid included in the organic solvent. This step of recovering boron comprises the following substeps: a) bringing a basic aqueous solution A2 into contact with the organic solvent to extract the boron in the form of solubilized borate into the basic aqueous solution A2; b) distillation of the basic aqueous solution A2 loaded with borate to concentrate the solution, generating a distillate; c) crystallization of the borate in the form of hydrated boron salt; d) solid-liquid separation of the crystallized hydrated boron salt, generating crystallization mother liquors; e) reintroduction of the distillate and the crystallization mother liquors into the step of bringing the basic aqueous solution A2 into contact with the organic solvent.Crystallized hydrated boron salt, recovered in solid form, can be reused in various industrial sectors, for example in the glass industry (borosilicate glass), ceramics (boron nitride), metallurgy (flux for steel), or medical products (antiseptics).

[0066] Steps a) to e) are advantageously carried out in a closed loop, to allow the continuous circulation of the aqueous solutions, with a view to their recycling. In this embodiment, the water introduced into the process circulates in a loop within it. In addition, the process does not consume any additional water other than that which is initially introduced and recycled.

[0067] At the same time, all traces of organic solvent present in the aqueous phase are fully recycled and revalued.

[0068] This allows the recovery, advantageously, of more than 99% of the boron contained in the organic solvent. The solid borate produced advantageously has a purity greater than 99%.

[0069] Sub-step a)

[0070] The organic solvent comprises, at this stage, boric acid at a boron concentration generally between 1 mg / L and 14 g / L, preferably between 1 g / L and 14 g / L.

[0071] Advantageously, the basic aqueous solution A2 is prepared by diluting a concentrated basic solution or by solubilizing a solid basic compound.

[0072] Preferably, it is a solution of NaOH, KOH, LiOH, or NH4OH. The choice of base depends on the boron salt to be produced, so a NaOH solution will allow the formation of sodium borate. Similarly, a KOH solution will be chosen to obtain potassium borate.

[0073] Preferably, the basic aqueous solution A2 is introduced in a stoichiometric amount relative to the amount of boron salt to be produced. Thus, the number of moles of alkali or ammonium added determines the structure of the final product. For example, to produce sodium tetraborate Na2B4O7, 0.5 moles of NaOH are introduced for 1 mole of boron included in the organic solvent. Similarly, 1 mole of NaOH must be introduced for 1 mole of boron to generate sodium metaborate NaBÛ2.

[0074] The basic solution is therefore not introduced in excess. In doing so, the consumption of alkaline product is reduced.

[0075] Advantageously, the ratio between the number of moles of alkali or ammonium in the basic solution and the number of moles of boron in the organic solvent is between 0.3 and 1.

[0076] During the step of bringing the basic aqueous solution A2 into contact with the organic solvent, the boric acid included in the solvent is transferred from the organic phase to the aqueous phase. A basic aqueous solution loaded with borate is then obtained.

[0077] Sub-step a) of bringing the basic aqueous solution A2 into contact with the organic solvent is preferably carried out in a device comprising several stages, where the organic solvent and the basic aqueous solution A2 circulate in counter-current.

[0078] For this purpose, the two liquids are circulated at different flow rates, such that the ratio of the flow rate of the basic aqueous solution and the flow rate of the organic solvent can be between 0.1 and 2, preferably between 0.1 and 1, and even more preferably between 0.1 and 0.5. These flow rate ratios make it possible to minimize the quantity of water circulating in the process and to optimize the energy consumption of the process.

[0079] According to a variant, this step is carried out at a temperature between 20°C and 70°C, preferably between 40°C and 60°C. These temperature ranges are optimized for a ratio of the flow rate of the basic aqueous solution and the flow rate of the organic solvent between 0.1 and 2. Sub-step b)

[0080] In sub-step b), the basic aqueous solution A2 comprising the solubilized borate is advantageously subjected to a concentration step by distillation generating a distillate. This step is carried out at a temperature between 20°C and 110°C, preferably between 30°C and 105°C, and at an absolute pressure between 2.10 4 Pa and 10 5 Pa, preferably. The concentration of the solution allows to obtain a saturated borate solution.

[0081] Sub-step c)

[0082] Sub-step c) of crystallization is advantageously carried out by distillation of the basic aqueous solution A2 concentrated in borate, or by cooling the basic aqueous solution A2 concentrated in borate.

[0083] The crystallized solid is then suspended in the solution. This distillation is carried out until the desired quantity of crystallized solid in suspension is obtained. This step is carried out at a temperature between 20°C and 110°C, preferably between 30°C and 105°C, and at an absolute pressure between 2.10 4 Pa and 10 5 No, preferably.

[0084] The temperature at which the distillation is carried out determines the degree of hydration of the boron salt produced. For example, at a temperature between 20°C and 60°C, borax decahydrate Na2B4O?.10H2O is obtained. On the other hand, borax pentahydrate Na2B4O?.5H2O is obtained at a temperature between 60°C and 100°C.

[0085] According to another variant of the invention, the crystallization of the borate is carried out by cooling the concentrated basic aqueous borate solution, so that the solubility of the boron salt in solution decreases. In this case, the solution is cooled according to a temperature gradient of 10°C to 40°C per hour.

[0086] The borate suspension can be reheated to obtain a partial re-solubilization of the borate and then re-subjected to cooling to reform a borate suspension, this operation constituting a crystallization cycle. Between 1 and 3 crystallization cycles can be carried out, preferably 1 to increase the purity of the crystallized borate. These two crystallization methods, respectively distillation and cooling, allow the elimination of traces of solvent remaining in the solid to the crystallization mother liquors.

[0087] By "traces of solvent" we mean small quantities of extraction compound, and / or modifying compound and / or diluting compound.

[0088] Furthermore, the distillation carried out during the concentration and possibly crystallization stage generates a distillate, which generally contains less than 1% by mass of traces of solvent.

[0089] This distillate is advantageously recirculated in the process and / or mixed with the basic aqueous solution A2 during the step of bringing the basic aqueous solution A2 into contact with the organic solvent. In fact, the distillate dilutes the concentrated basic solution or solubilizes the solid basic compound.

[0090] After the crystallization step, the borate crystal suspension can be subjected to a maturation step, the duration of which is 30 minutes to 2 hours, preferably 1 hour. This duration allows the solution to reach thermodynamic equilibrium.

[0091] Sub-step d)

[0092] According to sub-step d), the hydrated boron salt crystals are advantageously recovered by carrying out a solid-liquid separation step. Among the solid-liquid separation methods, mention may be made, but are not limited to, distillation, centrifugation and filtration.

[0093] Advantageously, the crystallized hydrated boron salt is filtered, generating crystallization mother liquors. These crystallization mother liquors may contain less than 1% by mass of traces of solvent.

[0094] Filtration can be carried out under vacuum or under positive pressure between 10 5 and 5.10 5 Pa, preferably 10 5 Pa, or under reduced pressure between 10 4 and 8.10 4 Pa. Sub-step e)

[0095] Advantageously, the crystallization mother liquors are recirculated in the process during the step of bringing the basic aqueous solution A2 into contact with the organic solvent. They are mixed with the basic aqueous solution A2 during this contacting step.

[0096] According to the invention, the solid thus recovered is a hydrated borate, the formula of which may be NaBCh yEEO, Na2B4O7 yEEO, Na2BsC>8 yEEO, Li2B4O? yEEO, K2B4O7 yEEO, or (NH4)2B4O? yEEO, where y is between 0 and 11.

[0097] After solid-liquid separation, the recovered solid can be washed to remove all traces of solvent.

[0098] In this case, the crystallized hydrated boron salt is washed with an aqueous solution and / or with the distillate from the distillation, generating wash waters. These wash waters may contain less than 1% by mass of traces of solvent.

[0099] The wash waters are advantageously recirculated in the process during the step of bringing the basic aqueous solution A2 into contact with the organic solvent. They can be mixed with the basic aqueous solution A2 during this contacting step.

[0100] Thus, the process according to the invention does not result in any loss of solvent and allows the obtaining of a very low residual carbon content, from the organic solvent, in the crystallized boron salt.

[0101] The reuse of the distillate, crystallization mother liquors and / or washing waters has the advantage of allowing the recovery of all aqueous flows and all of the solvent.

[0102] A drying step may be carried out after washing. In particular, drying may be carried out at a temperature between 50°C and 150°C, at an absolute pressure between 10 4 Pa and 10 5Pa. Depending on the drying temperature, hydrated or anhydrous borax will be obtained. For example, a drying temperature between 100°C and 150°C will produce anhydrous borax.

[0103] BRIEF DESCRIPTION OF THE FIGURES

[0104] The manner in which the invention can be implemented and the advantages which result therefrom will emerge more clearly from the following example of implementation, given for informational and non-limiting purposes, in support of the appended figure.

[0105] Figure 1 is a schematic representation of a battery of four mixer-settlers implementing the boron extraction process according to a particular embodiment of the invention.

[0106] Figure 2 is a schematic representation of the method according to a particular embodiment of the invention.

[0107] DETAILED DESCRIPTION OF THE FIGURES

[0108] A particular embodiment of the process implemented in a battery of four mixer-decanters is shown diagrammatically in Figure 1.

[0109] The process is carried out in a device comprising several stages, where the organic solvent and the basic aqueous solution circulate in countercurrent.

[0110] In particular, the process can be carried out in a battery of mixer-settlers or in liquid-liquid extraction columns. The number of stages in these devices is preferably between 3 and 10, preferably between 5 and 7.

[0111] The device of Figure 1 is a battery of mixer-decanters (e) of four stages (a, b, c, d), of a type known per se. At the level of a first stage (a) are fed an organic solvent loaded with boric acid (11) and a borax solution (12) resulting from the recycling of the crystallization mother liquors and optionally the washing waters.

[0112] Furthermore, an aqueous solution of NaOH (13) is fed countercurrently to the fourth stage (d). A distillate (20) obtained during the implementation of the invention is also fed countercurrently to the fourth stage (d).

[0113] The organic solvent loaded with boron (11) from the first stage (a) is then transferred to the second stage (b), then to the third stage (c) and finally to the fourth stage (d), mixed and decanted at each stage.

[0114] The aqueous phase which feeds the fourth stage (d), consisting of the aqueous solution of NaOH (13), is transferred via stages (c), (b), to the first stage (a) where it combines with the borax solution (12), in each stage the aqueous and solvent phases are mixed and decanted.

[0115] The aqueous alkali borate solution (14) is recovered at the outlet of the first stage (a). The extraction solvent (15) exits, free of boron, at the fourth stage (d).

[0116] Referring to Figure 2, the aqueous borate solution (14) leaving the mixer-settler battery (e) is recovered and treated to crystallize the borate.

[0117] The aqueous borate solution (14) is first distilled (g) by increasing the temperature and / or by modifying the pressure of the medium until a saturated borate solution and a distillate (20) are obtained. Crystallization (h) is then carried out either by distillation generating distillate (20) again, or by cooling resulting in both cases in the formation of a suspension of crystallized borate.

[0118] Finally, the boron salt suspension is filtered (i), allowing the recovery of the crystallization mother liquors (21) and the crystallized borate (16). If necessary, the borate can be washed (j), this generating wash waters (22). The distillate (20) is also used to wash the borate.

[0119] The distillate (20) is reused to dilute (f) a concentrated basic sodium hydroxide solution (17) to obtain the aqueous NaOH solution (13), which will be introduced into the battery of mixer-decanters (e) for the liquid-liquid extraction of boron.

[0120] The crystallization mother liquors (21) and the washing waters (22) are mixed to form the borax solution (12) which is reintroduced into the battery (e). EXAMPLES OF EMBODIMENT OF THE INVENTION

[0121] Examples 1 to 21 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.

[0122] Example 1: Extraction of boron by an EHD / octan-l-ol solvent

[0123] 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 is introduced. The solution has 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 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.

[0124] 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.

[0125] 20 mL of an organic extraction solvent composed of 30% by mass of 2-ethyl-1,3-hexanediol (EHD) as the extraction compound and 70% by mass of octan-1-ol as the diluting compound are introduced into the same flask.

[0126] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0127] The medium is stirred vigorously at 60°C for 15 minutes. Afterwards, the aqueous and organic phases are separated by decantation.

[0128] We then obtain a boron concentration of 0.25 g / L in the aqueous phase, 4.25 g / L in the organic phase and therefore a boron partition coefficient equal to 17. 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 neodymium partition coefficient is less than 10 -4 while the partition coefficient of copper is less than 0.05.

[0129] Example 2: Extraction of boron by an EHD / octan-l-ol solvent

[0130] 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.

[0131] The volume ratio between the aqueous phase and the organic phase is therefore 4.

[0132] We then obtain a boron partition coefficient equal to 5.

[0133] 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.

[0134] Example 3: Extraction of boron using an EHD / Solvesso® 150 / 2-EH solvent

[0135] In a 100 mL flask, 60 mL of an acidic aqueous solution resulting from the dissolution of oxidized permanent magnet powder in nitric acid is introduced. The solution has 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.

[0136] 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 the same flask. The volume ratio between the aqueous phase and the organic phase is therefore 6.

[0137] The medium is stirred vigorously at 60°C for 15 minutes. Afterwards, the aqueous and organic phases are separated by decantation.

[0138] We then obtain a boron partition coefficient equal to 6.

[0139] 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.

[0140] Example 4: Extraction of boron using an EHD / Solvesso® 150 / 2-EH solvent

[0141] 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.

[0142] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0143] We then obtain a boron partition coefficient equal to 32.

[0144] 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.

[0145] Example 5: Extraction of boron by a TPMD / kerosene / decanol solvent

[0146] In a 100 mL flask, 50 mL of an acidic aqueous solution obtained by dissolving oxidized permanent magnet powder in nitric acid is introduced, 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 includes traces of zinc. It has a pH of 2. 10 mL of an organic extraction solvent composed of 15% by mass of 2,2,4-trimethyl-,1,3-pentaediol (TPMD) as the extraction compound, 25% by mass of kerosene as the diluting compound, and 60% by mass of decanol as the modifying compound are introduced into the same flask.

[0147] The volume ratio between the aqueous phase and the organic phase is therefore 5.

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

[0149] We then obtain a boron partition coefficient equal to 1.7.

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

[0152] 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.

[0153] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0154] We then obtain a boron partition coefficient equal to 18.

[0155] 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. Example 7: Extraction of boron by a BEPD / kerosene / decanol solvent

[0156] In a 100 mL flask, 50 mL of an acidic aqueous solution obtained by dissolving oxidized permanent magnet powder in nitric acid is introduced, 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.

[0157] 10 mL of an organic extraction solvent composed of 15% by mass 2-butyl-2-ethylpropane-1,3-diol (BEPD) as the extraction compound, 25% by mass kerosene as the diluting compound, and 60% by mass decanol as the modifying compound are introduced into the same flask.

[0158] The volume ratio between the aqueous phase and the organic phase is therefore 5.

[0159] The medium is stirred vigorously at 60°C for 15 minutes. Afterwards, the aqueous and organic phases are separated by decantation.

[0160] We then obtain a boron partition coefficient equal to 1.65.

[0161] 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.

[0162] Example 8: Extraction of boron by a BEPD / kerosene / decanol solvent

[0163] 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.

[0164] The volume ratio between the aqueous phase and the organic phase is therefore 1. We then obtain a boron partition coefficient equal to 2.

[0165] 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.

[0166] Example 9: Extraction of boron by a BEPD / kerosene / decanol solvent

[0167] In a 200 mL flask, 100 mL of an acidic aqueous solution resulting from the dissolution of oxidized permanent magnet powder in sulfuric acid is introduced, having a boron concentration of 0.6 g / L, neodymium of 14.7 g / L, praseodymium of 3.6 g / L, dysprosium of 0.9 g / L, cerium of 0.4 g / L, and other rare earths of less than 0.1 g / L, for a total of 20 g / L of rare earths. The solution has an iron concentration of 0.25 g / L, aluminum, cobalt and copper less than 0.1 g / L and it includes traces of zinc. It has a pH of 2.

[0168] 10 mL of an organic extraction solvent composed of 15% by mass 2-butyl-2-ethylpropane-1,3-diol (BEPD) as the extraction compound, 25% by mass kerosene as the diluting compound, and 60% by mass decanol as the modifying compound are introduced into the same flask.

[0169] The volume ratio between the aqueous phase and the organic phase is therefore 10.

[0170] The medium is stirred vigorously at 60°C for 15 minutes. Afterwards, the aqueous and organic phases are separated by decantation.

[0171] We then obtain a boron partition coefficient equal to 1.7.

[0172] 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 5*10' 4 while the partition coefficient of copper is less than 0.1. Example 10: Extraction of boron by a 2-PH / kerosene solvent

[0173] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of oxidized permanent magnet powder in nitric acid is introduced. The solution has 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.

[0174] 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 the same flask.

[0175] The volume ratio between the aqueous phase and the organic phase is therefore 5.

[0176] The medium is stirred vigorously at room temperature for 15 minutes. After which, the aqueous and organic phases are separated by decantation.

[0177] We then obtain a boron partition coefficient equal to 0.6.

[0178] 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.

[0179] Example 11: Extraction of boron by a 2-PH / kerosene solvent

[0180] The extraction of Example 10 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 10, and 50 mL of the organic extraction solvent of Example 10.

[0181] 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. The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so that the neodymium partition coefficient is less than 10' 4 while the partition coefficient of copper is less than 0.05.

[0182] Example 12: Extraction of boron by a pure 2-PH solvent

[0183] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of oxidized permanent magnet powder in nitric acid is introduced. The solution has 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.

[0184] 10 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) are introduced into this same flask as the extraction compound.

[0185] The volume ratio between the aqueous phase and the organic phase is therefore 5.

[0186] The medium is stirred vigorously at 60°C for 15 minutes. Afterwards, the aqueous and organic phases are separated by decantation.

[0187] We then obtain a boron partition coefficient equal to 0.56.

[0188] 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.

[0189] Example 13: Extraction of boron by a pure 2-PH solvent

[0190] The extraction process of Example 12 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 12, and 50 mL of the organic extraction solvent of Example 12. The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0191] We then obtain a boron partition coefficient equal to 0.58.

[0192] 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.

[0193] Example 14: Extraction of boron by a pure 2-PH solvent

[0194] In a 100 mL flask, 50 mL of an acidic aqueous solution obtained by dissolving oxidized permanent magnet powder in hydrochloric acid is introduced. The solution has a boron concentration of 4.5 g / L, neodymium concentration of 110 g / L, praseodymium concentration of 27 g / L, dysprosium concentration of 7 g / L, cerium concentration of 3 g / L, and other rare earths concentration 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 concentration of 0.5 g / L, cobalt concentration of 0.5 g / L, copper concentration of 0.2 g / L, and contains traces of zinc. It has a pH of 2.

[0195] 50 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) is introduced into this same flask as the extraction compound.

[0196] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0197] The medium is stirred vigorously at 50°C for 15 minutes. Afterwards, the aqueous and organic phases are separated by decantation.

[0198] We then obtain a boron partition coefficient equal to 0.63.

[0199] 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. Example 15: Extraction of boron by a pure 2-PH solvent

[0200] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of oxidized permanent magnet powder in sulfuric acid is introduced, having a boron concentration of 0.6 g / L, neodymium of 14.7 g / L, praseodymium of 3.6 g / L, dysprosium of 0.9 g / L, cerium of 0.4 g / L, and other rare earths of less than 0.1 g / L, for a total of 20 g / L of rare earths. The solution has an iron concentration of 0.25 g / L, aluminum, cobalt and copper less than 0.1 g / L and it includes traces of zinc. It has a pH of 2.

[0201] 50 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) is introduced into this same flask as the extraction compound.

[0202] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0203] The medium is stirred vigorously at 50°C for 15 minutes. Afterwards, the aqueous and organic phases are separated by decantation.

[0204] We then obtain a boron partition coefficient equal to 0.30.

[0205] 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.

[0206] Example 16: Extraction of boron by a pure 2-PH solvent from an aqueous solution before a rare earth concentration of 250 g / L

[0207] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of a powder of oxidized permanent magnets in nitric acid is introduced, 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. 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. 10 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) is introduced into this same flask as the extraction compound.

[0208] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0209] The medium is stirred vigorously at 60°C for 15 minutes. Afterwards, the mixture is centrifuged, and the aqueous and organic phases are separated by decantation.

[0210] We then obtain a boron partition coefficient equal to 0.65.

[0211] 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.

[0212] Example 17: Extraction of boron by a pure 2-PH solvent from an aqueous solution before a rare earth concentration of 350 g / L

[0213] In a 100 mL flask, 10 mL of an acidic aqueous solution obtained by dissolving oxidized permanent magnet powder in hydrochloric acid is introduced, having a boron concentration of 4.5 g / L, neodymium of 256 g / L, praseodymium of 63 g / L, dysprosium of 17 g / L, cerium of 7 g / L, and other rare earths of less than 7 g / L, for a total of 350 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 includes traces of zinc. It has a pH of 2.

[0214] 40 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) is introduced into this same flask as the extraction compound.

[0215] The volume ratio between the aqueous phase and the organic phase is therefore 0.25.

[0216] The medium is stirred vigorously at 60°C for 15 minutes. Afterwards, the mixture is centrifuged, and the aqueous and organic phases are separated by decantation.

[0217] This gives a boron partition coefficient of 2.46. The concentrations of total rare earths, iron, aluminum, cobalt, copper and zinc in the solvent are less than 10 mg / L, so the neodymium partition coefficient is less than 10' 4 while the partition coefficient of copper is less than 0.05.

[0218] Example 18: Extraction of boron by a pure 2-PH solvent from an aqueous solution before a rare earth concentration of 400 g / L

[0219] In a 100 mL flask, 50 mL of an acidic aqueous solution resulting from the dissolution of oxidized permanent magnet powder in nitric acid is introduced, 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 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.

[0220] 50 mL of an organic extraction solvent composed of 100% by mass of 2-propylheptanol (2-PH) is introduced into this same flask as the extraction compound.

[0221] The volume ratio between the aqueous phase and the organic phase is therefore 1.

[0222] The medium is stirred vigorously at 60°C for 15 minutes. Afterwards, the aqueous and organic phases are separated by decantation.

[0223] We then obtain a boron partition coefficient equal to 3.

[0224] 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.

[0225] Example 19 below shows the benefits of operating on concentrated rare earth solutions. Example 20 gives an example of operation in a battery of mixer-settlers including boron extraction and solvent recycling. Example 19: Boron extraction using a pure 2-PH solvent

[0226] The solubility of boron in the attack solutions is limited, and to benefit from this concentration effect (examples 13, 16, 18), the extraction should be carried out in two stages, first on the attack solution at approximately 150 g / L rare earths then on the solution partially depleted of boron and reconcentrated to approximately 400 g / L.

[0227] In a reactor, the following are introduced at a temperature of 50°C:

[0228] 300 mL of an organic solvent composed of pure 2-propylheptanol, as an extraction compound;

[0229] 75 mL of an aqueous solution resulting from the dissolution of an oxidized permanent magnet powder, the solution having a concentration of boron of 4.5 g / L, neodymium 110 g / L, praseodymium 27 g / L, dysprosium 7 g / L, cerium 3 g / L, and other rare earths at less than 1 g / 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.

[0230] After mixing for 15 minutes and decanting the phases, we recover:

[0231] 300 mL of an organic solvent with a boron concentration of 0.8 g / L.

[0232] 75 mL of an aqueous phase comprising rare earths, the solution having a boron concentration of 1.27 g / L, neodymium 110 g / L, praseodymium 27 g / L, dysprosium 7 g / L, cerium 3 g / L, and other rare earths at less than 1 g / 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.

[0233] The boron extraction rate for this first stage is 71.1%

[0234] 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. Then in a second reactor we introduce at a temperature of 50°C:

[0235] 56 mL of an organic solvent composed of pure 2-propylheptanol, as an extraction compound;

[0236] 28 mL of the concentrated solution obtained previously

[0237] We recover:

[0238] 56 mL of an organic solvent with a boron concentration of 1.37 g / L.

[0239] 28 mL of an aqueous phase comprising rare earths, the solution having a concentration of boron 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.

[0240] With this sequence of extraction-concentration-extraction operations, the aqueous phase was depleted of boron and the overall extraction rate compared to the initial solution is 95%.

[0241] Example 20: Extraction of boron by a BEPD / kerosene / decanol solvent in a battery of mixer-decanters

[0242] This example is an embodiment of the invention implemented in a countercurrent extraction battery. a) Bringing an aqueous solution and an organic solvent into contact

[0243] In a battery of six mixer-decanters operating in countercurrent, at a temperature of 50°C, the following are introduced: in 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 stage 6: water at a flow rate of 7 mL / h.

[0244] We recover: at 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; at 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.

[0245] 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.

[0246] The process allows the transfer of most of the boron initially contained in the aqueous solution to the organic solvent.

[0247] The aqueous raffinate thus obtained contains a quantity of boron less than 30 mg / L.

[0248] Rare earths, iron and other impurities are not present in the solvent, they are recovered in the aqueous raffinate. b) Re-extraction of boron from the boron-loaded solvent

[0249] In a second battery of four mixer-settlers operating in countercurrent, at a temperature of 50°C, the following are fed: in stage 1: the organic solvent loaded with boron, 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; in 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.

[0250] We recover: at 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; at stage 4: an organic solvent, at a flow rate of 145 mL / h, the solvent having a boron concentration of 30 mg / L.

[0251] 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.

[0252] 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).

[0253] The solvent thus regenerated has a low boron concentration, less than 30 mg / L, and is recycled during extraction.

[0254] Example 21: Regeneration of boron from an organic solvent loaded with boric acid and comprising BEPD

[0255] In a battery of five mixer-settlers operating in countercurrent, at a temperature of 50°C, the following are fed: in stage 1: an organic solvent consisting of 15% by mass of 2-butyl-2-ethylpropane-1,3-diol (BEPD), 25% by mass of kerosene and 60% by mass of decan-1-ol, the boron concentration of the solvent being 4.40 g / L, with a flow rate of 100 L / h; in stage 5: a NaOH solution, concentrated in sodium at 9.40 g / L, with a flow rate of 50 L / h.

[0256] We recover: at stage 1: an aqueous borate solution concentrated in boron at 8.78 g / L, and concentrated in sodium at 9.40 g / L, with 0.1% by mass of BEPD, with a flow rate of 50 L / h. The Na / B molar ratio is 0.5, i.e. the stoichiometry of the tetraborate ion Na2B4O7. at stage 5: an organic solvent with a residual boron concentration of less than 0.01 g / L, with a flow rate of 100 L / h.

[0257] Thus, 99.8% of the boron included in the extraction solvent is recovered.

[0258] Concentrations and flow rates are detailed in Table 1. Table 1

[0259] Example 22: Crystallization of sodium tetraborate pentah drate or borax (Na2B4O7 , 5H2O) from sodium tetraborate solution

[0260] 4.7 L of aqueous borax solution, or 4.8 kg, are obtained after extraction of boron from an organic extraction solvent consisting of BEPD, kerosene and decan-l-ol, and from a sodium hydroxide solution.

[0261] The aqueous solution has a boron concentration of 8.78 g / L, a sodium concentration of 9.40 g / L. It contains 0.1% by mass of BEPD, or 4.8 g of residual BEPD.

[0262] The crystallization of borax pentahydrate from the aqueous solution is carried out according to the following steps: i. distillation of the aqueous solution at 100°C until 0.7 kg of solution is obtained, with a boron concentration of 6.0% by mass (approximately 60 g / L) and 4.1 kg of distillate; ii. cooling of the solution obtained from 100°C to 65°C in one hour to crystallize the borax pentahydrate; iii. maturation of the crystals for one hour at 65°C resulting in the formation of a suspension of borax pentahydrate; iv. filtration of the suspension of borax pentahydrate under 10 5 No positive pressure; v. washing the boron salt with 110 g of distilled water at 5°C; vi. drying the boron salt in a ventilated oven at 65°C until constant mass. We obtain:

[0263] 0.55 kg of crystallization mother liquors comprising 3.8% by mass of boron and comprising less than 50 ppm of solvent;

[0264] 4.1 kg of distillate comprising 0.12% by mass BEPD, or 4.8 g of BEPD

[0265] 130 g of wash water comprising 3.6% by mass of boron;

[0266] 106 g of borax pentahydrate with a purity greater than 99.8%; less than 350 mg / kg of residual organic carbon in the borax;

[0267] 24 g of borax pentahydrate impregnation water.

[0268] Of the 41.3 g of boron contained in the initial aqueous solution, 15.7 g are recovered in the form of borax pentahydrate. Thus, 38% of the boron initially contained in the aqueous phase is crystallized. The 62% of borate contained in the mother liquors is recycled at the stage of contacting the boron-laden organic solvent and the basic aqueous solution.

[0269] The same result can be obtained by distilling the boron-laden solution at 65°C under reduced pressure, between 10 4 Pa and 7.10 4Pa, until 106 g of borax pentahydrate is suspended before filtration.

[0270] The 4.1 kg of distillate contains more than 99% of the BEPD extractant from the initially aqueous-soluble solvent. The distillate is recycled for the production of the basic aqueous solution.

[0271] Borax decahydrate can be obtained by the same process, by concentrating the initial aqueous solution under vacuum at 60°C, and cooling it to 5°C within one hour before filtration. The masses are detailed in Table 2.

[0272] Table 2

[0273] Example 23: Regeneration of boron from a 2-propylheptanol (2PH) solvent loaded with boric acid

[0274] In a battery of six mixer-settlers operating in countercurrent, at a temperature of 50°C, the following are fed: on stage 1: an organic solvent comprising an extraction compound consisting of pure 2-propylheptanol, the boron concentration of the solvent being 1.5 g / L, with a flow rate of 100 L / h; on stage 6: a concentrated sodium NaOH solution at 12.28 g / L, with a flow rate of 10 L / h.

[0275] We recover: - at stage 1: an aqueous borate solution concentrated in boron at 14.9 g / L, concentrated in sodium at 12.28 g / L, and concentrated in 2-propylheptanol at 70 mg / L, with a flow rate of 10 L / h. The Na / B molar ratio is 0.39. at stage 6: a solvent whose residual boron concentration is less than 0.01 g / L, with a flow rate of 100 L / h.

[0276] Thus, 99.3% of the boron included in the extraction solvent is recovered.

[0277] Concentrations, flow rates and masses are detailed in Table 3.

[0278] Table 3

[0279] In a battery of five mixer-settlers operating in counter-current, at a temperature of 50°C, the following are fed: at stage 1: an organic solvent consisting of 15% by mass of BEPD, 25% by mass of kerosene and 60% by mass of decan-l-ol, the solvent has a boron concentration of 3.52 g / L and is introduced with a flow rate of 576 L / h and a borax solution concentrated in boron at 39.7 g / L and in sodium at 42.3 g / L, resulting from the recycling of the mother liquors from the crystallization of the borax produced, the description of which follows, with a flow rate of 39.6 L / h. at stage 5: a NaOH solution concentrated in sodium at 11.5 g / L introduced at a flow rate of 187.8 L / h. This solution is made from 3.76 kg of solid NaOH and 187.8 L of distillate. We recover: at stage 1: an aqueous solution with a boron concentration of 15.4 g / L, a sodium concentration of 16.4 g / L and comprising 0.1% by mass of solvent, with a flow rate of 233.3 L / h because the conversion of boric acid into borax generates 5.9 L of water.The Na / B molar ratio is 0.5, which is the stoichiometry of the tetraborate ion Na2B4O7; at stage 5: a solvent with a boron concentration of less than 0.01 g / L, with a flow rate of 576 L / h.

[0280] Thus, 99.7% of the boron included in the extraction solvent is recovered.

[0281] The crystallization of borax pentahydrate from the aqueous solution recovered in stage 1 is carried out according to the following steps: i. distillation of the aqueous solution recovered in stage 1 under vacuum at 65°C, during which the borax pentahydrate precipitates, until a solution is obtained with a concentration of total boron (solid boron and solubilized boron) of 73.1 g / L and sodium of 77.9 g / L, with a flow rate of 49.2 L / h and 187.8 L / h of distillate; ii. maturation of the crystals for one hour resulting in the formation of a suspension of borax pentahydrate; iii. filtration of the suspension of borax pentahydrate under 10 5No positive pressure; iv. drying of the boron salt in a ventilated oven at 65°C until constant mass.

[0282] We obtain:

[0283] 187.8 L / h of distillate containing 0.12% solvent, which will be recycled to the battery;

[0284] 39.6 L / h of crystallization mother liquors with a boron concentration of 39.7 g / L and sodium concentration of 42.3 g / L;

[0285] 14.4 kg / h of borax pentahydrate comprising 5% by mass of water or 13.7 kg / h of borax pentahydrate, with less than 50 ppm of BEPD or less than 0.035 g / kg of residual organic carbon.

[0286] The resulting borax pentahydrate is more than 99.8% pure.

[0287] The crystallization mother liquors contain 44% of the total boron.

[0288] The distillate contains all of the aqueous-soluble solvent contained in the boron solution recovered in stage 1. The concentrations and flow rates of the liquid-liquid extraction and crystallization are detailed in Tables 4 and 5.

[0289] Table 4 Table 5

[0290] In a battery of five mixer-settlers operating in countercurrent, at a temperature of 50°C, the following are fed: on stage 1: an organic solvent consisting of 2-propylheptanol, with a boron concentration of 1.5 g / L, it is introduced with a flow rate of 1352 L / h and a borax solution concentrated in boron at 39.7 g / L and in sodium at 42.3 g / L resulting from the recycling of the mother liquors from the crystallization of the borax produced, the description of which follows, with a flow rate of 39.6 L / h. on stage 5: a NaOH solution concentrated in sodium at 11.5 g / L introduced at a flow rate of 187.8 L / h. This solution is produced from 3.76 kg of solid NaOH and 187.8 L of distillate.

[0291] We recover: at stage 1: an aqueous solution with a boron concentration of 15.4 g / L, a sodium concentration of 16.4 g / L and comprising 70 ppm by mass of solvent, with a flow rate of 233.3 L / h because the conversion of boric acid into borax generates 5.9 L of water. The Na / B molar ratio is 0.5; at stage 5: a solvent with a boron concentration of less than 0.01 g / L, with a flow rate of 1352 L / h.

[0292] Thus, 99.3% of the boron included in the extraction solvent is recovered.

[0293] The crystallization of borax pentahydrate from the aqueous solution recovered in stage 1 is carried out according to the following steps: i. distillation of the aqueous solution recovered in stage 1 under vacuum at 65°C, during which the borax pentahydrate precipitates, until a solution is obtained with a total boron concentration (solid boron and solubilized boron) of 73.1 g / L and sodium of 77.9 g / L, with a flow rate of 49.2 L / h and 187.8 L / h of distillate; ii. maturation of the crystals for one hour resulting in the formation of a suspension of borax pentahydrate; iii. filtration of the suspension of borax pentahydrate under 10 5 No pressure; iv. drying of the boron salt in a ventilated oven at 65°C until constant mass. We obtain:

[0294] 187.8 L / h of distillate containing 87 ppm of solvent, which will be recycled to the battery;

[0295] 39.6 L / h of crystallization mother liquors with a boron concentration of 39.7 g / L and sodium at 42.3 g / L;

[0296] 14.4 kg / h of borax pentahydrate comprising 5% by mass of water or 13.7 kg / h of borax pentahydrate with less than 50 ppm of 2PH or less than 0.037 g / kg of residual organic carbon.

[0297] The resulting borax pentahydrate has a purity greater than 99.8%. The crystallization mother liquors contain 44% of the total boron.

[0298] The distillate contains all of the aqueous-soluble solvent contained in the boron solution recovered in stage 1.

[0299] The concentrations and flow rates of liquid-liquid extraction and crystallization are detailed in Tables 6 and 7.

[0300] Table 6 Table 7

[0301] Lithium, potassium and ammonium tetraborates as well as sodium tetraborate decahydrate can be manufactured using the process according to the invention.

[0302] Since the solubility of these salts in water is different from that of sodium tetraborate pentahydrate, the amount of distillate, mother liquors, and boron salt produced during crystallization varies accordingly.

Claims

CLAIMS 1. Method for extracting boron contained in an aqueous Al solution comprising rare earth elements, the aqueous Al solution being obtained from the dissolution of an NdFeB magnet powder or machining waste resulting from the manufacture of permanent magnets, method in which said aqueous Al 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 Al solution and the organic solvent resulting in the transfer of boron from said aqueous Al solution to said organic solvent.

2. 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. Method for extracting boron according to claim 1 or 2, in which 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. Method for extracting boron according to claim 3, in which 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 their mixtures.

5. Method for extracting boron according to one of claims 1 to 4, in which 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. Method for extracting boron according to claim 5, in which 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.

7. Method for extracting boron according to one of claims 1 to 6, in which 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%.

8. Method for extracting boron according to one of claims 1 to 7, in which the aqueous solution Al 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. Method for extracting boron according to one of claims 1 to 8, in which 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. Method for 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. Method for extracting boron according to claim 11, in which the re-extraction of boron is carried out by bringing a Brônsted base into contact with said solvent, the base being chosen from the group comprising: NaOH, KOH, LiOH, NH4OH, and mixtures thereof.

13. A method for extracting boron according to one of claims 1 to 12, further comprising a step of recovering boron in the form of boron salt from boric acid included in the organic solvent, said step of recovering boron comprising the following sub-steps: a) contacting a basic aqueous solution A2 with said organic solvent to extract boron in the form of solubilized borate to the basic aqueous solution A2; b) distillation of the basic aqueous solution A2 loaded with borate to concentrate said solution, generating a distillate; c) crystallization of the borate in the form of hydrated boron salt; d) solid-liquid separation of the crystallized hydrated boron salt, generating crystallization mother liquors; e) reintroduction of the distillate and the crystallization mother liquors to the step of contacting the basic aqueous solution A2 with said organic solvent.

14. Method for extracting boron according to claim 13, in which the crystallization of the borate is carried out by distillation of the basic aqueous solution A2 concentrated in borate, or by cooling the basic aqueous solution A2 concentrated in borate.

15. Method for extracting boron according to claim 13 or 14, in which the contacting of the basic aqueous solution A2 with the organic solvent is carried out in a device comprising several stages, where the organic solvent and the basic aqueous solution A2 circulate in countercurrent.

16. Method for extracting boron according to one of claims 13 to 15, in which the basic aqueous solution A2 is prepared by dilution of a concentrated basic solution or by solubilization of a solid basic compound.

17. A method of extracting boron according to claim 16, wherein the distillate dilutes the concentrated basic solution or solubilizes the solid basic compound.

18. Method for extracting boron according to one of claims 13 to 17, in which the basic aqueous solution A2 is introduced in a stoichiometric quantity relative to the quantity of boron salt to be produced.

19. A method of extracting boron according to one of claims 13 to 18, wherein the crystallized hydrated boron salt is washed with an aqueous solution and / or with the distillate, generating wash water.

20. Method for extracting boron according to claim 19, in which the wash waters are recirculated in the method, during the step of bringing the basic aqueous solution A2 into contact with the organic solvent.

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