Method for separating rare earth elements from solution

Abstract

The present invention relates to a method for separating at least one rare earth element from a solution comprising said at least one rare earth element and optionally at least one further magnetic element, comprising the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone with different magnetic field values ​​in the solution, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and of said optional at least one further magnetic element in the second zone; b) increasing the pH of the solution in the first zone to precipitate said at least one rare earth element or to precipitate said optional at least one further magnetic element in the second zone; and c) recovering the precipitate.

Description

[Technical field]

[0001] The present invention relates to a method for separating at least one rare earth element from a solution containing said at least one rare earth element optionally in a mixture with other magnetic elements, in particular other rare earth elements. [Background technology]

[0002] The rare earth elements (REE), also called rare earth metals, are a set of 17 nearly indistinguishable, lustrous, silvery-white soft heavy metals. They consist of the 15 lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) plus scandium (Sc) and yttrium (Y).

[0003] Rare earth elements are widely used in a variety of applications.

[0004] As part of metal alloys, they are present, for example, in nickel metal hydride batteries, fuel cells, steel compositions, superalloys, or aluminum-magnesium alloys. They are also useful as catalysts (especially in oil refineries), in catalytic converters, as fuel additives, in various chemical processes, and even for air pollution control. Rare earth elements are also widely used for their magnetic properties, especially in computer hard drives, motors, turbines, microphones or speakers, and magnetic resonance imaging (MRI) equipment.

[0005] Contrary to what their name suggests, rare earth elements are quite widespread in the Earth's crust. However, their supply is problematic. In fact, there are only a limited number of suppliers of rare earth elements. Moreover, most of the suppliers are located in the same geographical region, mainly in China, making rare earth elements a strategic resource.

[0006] For these reasons, rare earth elements are listed by the European Union as being associated with high supply risks.

[0007] Therefore, there is a need to find alternative supply routes.

[0008] An important source that is currently underutilized is waste. Indeed, mining and industrial wastes contain large amounts of rare earth elements that are not yet evaluated. The reuse of commodities, especially magnets and / or electronics, is also a very promising alternative supply solution.

[0009] One of the biggest challenges associated with the recovery of rare earth elements from waste is the difficulty of separating certain earth elements from other metals, especially other rare earth elements. Indeed, rare earth elements have similar chemical and physical properties that make them difficult to separate individually.

[0010] Several separation methods are currently known.

[0011] Solvent extraction is one of the most widely used methods. It allows the separation of different rare earth elements based on the difference in their solubility in two different immiscible liquids. However, it is relatively time-consuming to carry out. In addition, it requires heating and the use of toxic solvents. Therefore, the implementation of this method requires very restrictive safety measures to ensure the safety of the operators and to prevent environmental pollution.

[0012] Another method is ion exchange chromatography. Based on the differences in the electrostatic properties of the rare earth elements, this method is very effective. However, it is slow and very expensive. For these reasons, ion exchange chromatography requires very high purity, typically greater than 99.9%, and is limited to high-profit applications.

[0013] The third method is molten salt electrolysis. The main drawback of this method is that it requires very high temperatures (about 400-900 °C), making it very expensive.

[0014] A fourth method is described in WO2021155224, in which rare earth elements are precipitated as carbonates, hydroxycarbonates, bicarbonates, phosphates, dihydrogen phosphates, hydrogen phosphates, or any combination thereof. However, this document does not describe a step of magnetically separating the rare earth elements. Furthermore, it does not describe a step of locally increasing the pH of the solution. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] International Publication No. 2021 / 155224 Summary of the Invention [Problem to be solved by the invention]

[0016] There is therefore a need to provide alternative methods for recovering rare earth elements from secondary sources, especially waste materials.

[0017] In particular, there is a need for methods that allow for the recycling of rare earth elements present in mining, industrial and / or electronic waste.

[0018] What is needed is a method for separating rare earth elements that is easy to implement and has significantly reduced associated costs.

[0019] There is also a need for a method for recovering rare earth elements that is environmentally friendly, particularly one that does not require the use of toxic solvents.

[0020] There is also a need for a method for recovering rare earth elements that minimizes risk to operators.

[0021] There is also a need for a method that allows for the isolation of a specific rare earth element from a mixture of rare earth elements. [Means for solving the problem]

[0022] The present invention relates to a method for separating at least one rare earth element from a solution containing said at least one rare earth element and optionally at least one further magnetic or magnetisable element, comprising the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone in the solution with different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and a concentration of said optional at least one further magnetic or magnetizable element in the second zone; b) precipitating said at least one rare earth element in a first zone or said optional at least one further magnetic or magnetisable element in a second zone; c) recovering the precipitate; The present invention relates to a method comprising the steps of:

[0023] According to a preferred embodiment, the precipitation of said at least one rare earth element is induced by increasing the pH of the solution in a first zone or the precipitation of said one further magnetic or magnetisable element is induced by increasing the pH of the solution in a second zone. In particular, the present invention relates to a method for separating at least one rare earth element from a solution comprising said at least one rare earth element and optionally at least one further magnetic element, comprising the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone in the solution with different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and of said optional at least one further magnetic element in the second zone; b) increasing the pH of the solution in the first zone, thereby inducing precipitation of said at least one rare earth element, or increasing the pH of the solution in the second zone, thereby inducing precipitation of said optional at least one further magnetic element; c) recovering the precipitate; The present invention relates to a method comprising the steps of:

[0024] Preferably, said at least one further magnetic or magnetisable element, more preferably said at least one further magnetic element, is selected from the group consisting of transition metals, rare earth elements different from said at least one rare earth element, and mixtures thereof.

[0025] According to a particular embodiment, the at least one rare earth element has a magnetic susceptibility χ REE and the further magnetic or magnetisable element, in particular the further magnetic element, has an absolute relative difference |(χ REE -χ ME ) / χ ME so that the magnetic susceptibility χ | is 1 or more, preferably 10 or more. ME has.

[0026] According to a first embodiment, χ REE χ ME The larger, first zone is the zone of solution having the highest magnetic field value.

[0027] According to a second embodiment, χ ME χ REE The larger, first zone is the zone of solution having the lowest magnetic field value.

[0028] Preferably, during step a), the solution has a pH value below 7, preferably in the range of 2-6.

[0029] Preferably, during step b) the pH is locally increased to a value greater than 7, preferably greater than 8. More preferably, during step b) the pH is increased to a value greater than 7, preferably greater than 8.

[0030] According to a first embodiment, during step b), the pH is adjusted to 0.1% by the addition of at least one chemical substance present in the solution, such as nitrate ions NO 3 -Preferably, during step b), the pH is increased locally by electrochemically reducing at least one chemical present in the solution, such as nitrate ions NO 3 - is increased by electrochemically reducing

[0031] Preferably, according to the first embodiment, said at least one chemical is electrochemically reduced at the surface of an electrode located in the solution.

[0032] Preferably the electrode is a mesh electrode, preferably a ferromagnetic mesh electrode.

[0033] According to a second embodiment, during step b), the pH is increased by local addition of a chemical base.

[0034] According to one embodiment, the method further comprises, before step c), an intermediate step of removing the inhomogeneous magnetic field.

[0035] Preferably, the precipitate is recovered in step c) by flushing with a purge solution, said purge solution preferably consisting of an optionally acidified aqueous solution.

[0036] According to one embodiment, the method comprises, before step a), a preliminary step of dissolving the solid comprising said at least one rare earth element and optionally at least one further magnetic element in a solvent, preferably an acidic solution.

[0037] Preferably, if cobalt Co, iron Fe and / or nickel Ni are present in the solution, they are removed prior to application of the inhomogeneous magnetic field.

[0038] According to one embodiment, the method further comprises purifying and / or metal converting the precipitate. [Brief description of the drawings]

[0039] [Figure 1]FIG. 1 is a schematic diagram of a first embodiment of the invention, in which a solution comprises one rare earth element to be extracted and one further magnetic or magnetisable element, in which the rare earth element precipitates and the further magnetic or magnetisable element remains in solution. [Diagram 2] FIG. 2 is a schematic diagram of a second embodiment of the invention, in which a solution comprises one rare earth element to be extracted and one further magnetic or magnetisable element, the further magnetic or magnetisable element precipitating whilst the rare earth element remains in solution; [Diagram 3] FIG. 1 is a schematic diagram of a device 10 adapted for carrying out step b) of forming an oxide of the rare earth element of interest. [Figure 4] FIG. 1 is a schematic diagram of a device 10 adapted for carrying out step c) of recovering the oxides of the rare earth elements of interest. [Diagram 5] FIG. 2 is a schematic diagram of the arrangement of radial rods used in Example 1 to generate a non-uniform magnetic field. [Figure 6] Photographs of three radial magnet arrays a) dry (before contact with starting solution), b) with starting solution added, and c) after injection of potassium hydroxide solution. [Figure 7] FIG. 11 is a cross-sectional view of a magnetic filter assembly used in Example 2. [Figure 8] FIG. 7 is a schematic diagram of the filtration chamber of the magnetic filter assembly shown in FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The present invention relates to a method for separating at least one rare earth element from a solution containing said at least one rare earth element and optionally at least one further magnetic or magnetisable element, comprising the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone in the solution with different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and a concentration of said optional at least one further magnetic or magnetizable element in the second zone; b) precipitating said at least one rare earth element in a first zone or said optional at least one further magnetic or magnetisable element in a second zone; c) recovering the precipitate; The present invention relates to a method comprising the steps of:

[0041] In particular, the present invention relates to a method for separating at least one rare earth element from a solution comprising said at least one rare earth element and optionally at least one further magnetic element, comprising the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone in the solution having different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and of said optional at least one further magnetic element in the second zone; b) increasing the pH of the solution in the first zone, thereby inducing precipitation of said at least one rare earth element, or increasing the pH of the solution in the second zone, thereby inducing precipitation of said optional at least one further magnetic element; c) recovering the precipitate; The present invention relates to a method comprising the steps of:

[0042] According to a preferred embodiment, the present invention relates to a method for separating at least one rare earth element from a solution comprising said at least one rare earth element and at least one further magnetic or magnetisable element, comprising the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone in the solution with different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and a concentration of said at least one further magnetic or magnetizable element in the second zone; b) precipitating said at least one rare earth element in a first zone or precipitating said at least one further magnetic or magnetisable element in a second zone; c) recovering the precipitate; The present invention relates to a method comprising the steps of:

[0043] According to a further preferred embodiment, the present invention relates to a method for separating at least one rare earth element from a solution containing said at least one rare earth element and at least one further magnetic element, comprising the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone in the solution having different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and a concentration of said at least one further magnetic element in the second zone; b) precipitating said at least one rare earth element in a first zone or precipitating said at least one further magnetic element; c) recovering the precipitate; The present invention relates to a method comprising the steps of:

[0044] The aim of the method according to the invention is to isolate and / or recover and / or separate at least one specific rare earth element present in a solution from other elements also present in the solution.

[0045] In particular, the aim of the method according to the invention is to isolate and / or recover and / or separate said at least one particular rare earth element from other elements that may be present in the solution, in particular other magnetic or magnetisable elements, in particular other magnetic elements such as other rare earth elements.

[0046] "Separating at least one rare earth element from a solution" refers in the context of the present invention to isolating said at least one rare earth element from at least one component of the solution, which may consist not only of other elements, in particular other magnetic or magnetizable elements, but also of the solvent itself.

[0047] According to a first embodiment, the rare earth elements are recovered as a precipitate.

[0048] Preferably, according to this first embodiment, the method comprises the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone in the solution having different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone; b) precipitating said at least one rare earth element in a first zone; c) recovering the precipitate of the at least one rare earth element of step b); Includes.

[0049] More preferably, according to this first embodiment, the method comprises the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone in the solution having different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone; b) increasing the pH of the solution in the first zone, thereby inducing precipitation of said at least one rare earth element; c) recovering the precipitate of the at least one rare earth element of step b); Includes.

[0050] According to a second embodiment, while said at least one rare earth element is maintained in solution, a further magnetic or magnetisable element, preferably a further magnetic element, is selectively precipitated.

[0051] Preferably, according to this second embodiment, the method comprises the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone with different magnetic field values ​​in the solution, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and of said at least one further magnetic or magnetisable element, preferably said at least one further magnetic element, in the second zone; b) precipitating said at least one further magnetic or magnetisable element in a second zone, preferably said at least one further magnetic element; c) recovering the precipitate of the at least one further magnetic element; Includes.

[0052] More preferably, according to this second embodiment, the method comprises the following steps: a) applying a non-uniform magnetic field to the solution, thereby creating at least one first zone and at least one second zone with different magnetic field values ​​in the solution, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element in the first zone and of said at least one further magnetic or magnetisable element, preferably said at least one further magnetic element, in the second zone; b) increasing the pH of the solution in the second zone, thereby inducing precipitation of said at least one further magnetic or magnetisable element, preferably said at least one further magnetic element; c) recovering the precipitate of the at least one further magnetic element; Includes.

[0053] solution A "solution" in the context of the present invention refers to a composition that is liquid at ambient conditions, in particular at a temperature of 25° C. and an ambient pressure of 1 bar.

[0054] The solution typically consists of a liquid solvent, in particular an aqueous solvent, in which the at least one rare earth element to be separated is dissolved.

[0055] Preferably, the at least one rare earth element separated from the solution is selected from the group consisting of lanthanum La, cerium Ce, praseodymium Pr, neodymium Nd, promethium Pm, samarium Sm, europium Eu, gadolinium Gd, terbium Tb, dysprosium Dy, holmium Ho, erbium Er, thulium Tm, ytterbium Yb, lutetium Lu, scandium Sc, yttrium Y and mixtures thereof.

[0056] According to a particular embodiment, the at least one rare earth element separated from the solution is selected from the group consisting of gadolinium Gd, terbium Tb, dysprosium Dy, holmium Ho, erbium Er, thulium Tm, and mixtures thereof. More preferably, the at least one rare earth element separated from the solution is selected from the group consisting of terbium Tb, dysprosium Dy, holmium Ho, erbium Er, and mixtures thereof.

[0057] According to an alternative embodiment, the at least one rare earth element separated from the solution is selected from the group consisting of neodymium (Nd), dysprosium (Dy) and mixtures thereof. Advantageously, the at least one rare earth element separated from the solution is neodymium (Nd).

[0058] Preferably, the solution is 1.10 -3 mol.L -1 ~2 mol.L -1 , more preferably 0.1 mol.L -1 ~1.0 mol.L -1 , typically 0.05 mol.L -1 ~0.5 mol.L -1 The at least one rare earth element is separated.

[0059] Preferably the solvent is an aqueous solvent, especially an acidic aqueous solution.

[0060] More preferably, the solvent is selected from the group consisting of nitric acid solution, chloride acid solution, sulfuric acid solution and mixtures thereof. Advantageously, the solvent consists of a nitric acid solution.

[0061] Preferably, the acidic aqueous solution is 0.1 mol.L -1 ~5 mol.L -1 , more preferably 0.5 mol.L -1 ~2 mol.L -1 The acid concentration ranges from 0.1 to 1.0.

[0062] Advantageously, the pH of the starting solution is lower than 7, preferably in the range 2-6.

[0063] If the solution has a pH value below 2, it is almost impossible to induce rapid precipitation of the magnetic elements.

[0064] If the solution has a pH value greater than 7, the rare earth elements are already in precipitated form. Therefore, it is not possible to induce selective precipitation.

[0065] Preferably, the pH of the starting solution is 5.0 or less, more preferably 4.9 or less, typically 2.0 to 4.0.

[0066] Thus, when the solvent is selected from an acidic aqueous solution, the at least one rare earth element to be separated is present in the starting solution in ionic form, typically as a cation.

[0067] The solution to be treated may further comprise additional elements and / or compounds different from the rare earth element to be separated. These additional elements and / or compounds correspond in the context of the present invention to impurities to be separated from the rare earth element of interest. In particular, the object of the present invention is to recover and / or isolate the rare earth element of interest without the additional elements or compounds.

[0068] These additional elements or compounds may, for example, be kept in solution while the rare earth element of interest precipitates. Alternatively, these additional elements or compounds may precipitate while the rare earth element of interest is kept in solution. Thus, the method allows for the separation of the rare earth element of interest from the additional elements or compounds directly and without additional steps.

[0069] However, some additional elements or compounds may not be isolated from the desired rare earth element by merely carrying out steps a), b) and c) of the method of the present invention, and therefore these specific impurities must be separated / removed during a pre-treatment step.

[0070] The need for one or more pretreatment steps depends on the specific properties of the impurities to be extracted, and in particular on their behavior in the magnetic field applied in step b).

[0071] Advantageously, the method of the invention comprises, before step a), a preliminary step of elemental analysis to identify additional elements optionally present in the solution, which allows the skilled person to determine the nature of the elements present in the solution and to identify any final pretreatment steps required.

[0072] According to certain embodiments, the solution further comprises at least one magnetic or magnetizable element, typically at least one further magnetic element, selected from the group consisting of transition metals, rare earth elements different from the at least one rare earth element to be separated, and mixtures thereof.

[0073] "Magnetic or magnetizable element" in the context of the present invention refers to a chemical element that can move when placed in a magnetic field gradient. Typical examples are ferromagnetic, paramagnetic and diamagnetic elements. These consist, for example, of rare earth elements or transition metals such as cobalt Co, nickel Ni, iron Fe, and their solubilized ionic forms.

[0074] Preferably, said at least one further magnetic or magnetisable element is selected from magnetisable elements.

[0075] "Magnetizable element" in the context of the present invention refers to a chemical element that has no spontaneous magnetization but acquires magnetization under the influence of an external magnetic field. Typical examples are paramagnetic and diamagnetic elements.

[0076] "Paramagnetic element" in the context of the present invention refers to a chemical element that has no spontaneous magnetization, but which, under the influence of an external magnetic field, acquires magnetization in the same direction as the exciting magnetic field. Paramagnetic elements have a positive value of magnetic susceptibility.

[0077] "Diamagnetic element" in the context of the present invention refers to a chemical element that does not have spontaneous magnetization, but acquires magnetization under the influence of an external magnetic field in the direction opposite to the exciting magnetic field. Diamagnetic elements have a negative value of magnetic susceptibility. "Further magnetic or magnetizable element" in the context of the present invention refers to a magnetic or magnetizable element different from the rare earth element of interest, typically a magnetizable element, preferably a paramagnetic or diamagnetic element. The further magnetic or magnetizable element may for example consist of a rare earth element different from the rare earth element of interest, or a transition metal such as cobalt Co, nickel Ni, iron Fe, and some of their solubilized ionic forms.

[0078] Depending on the difference in magnetic susceptibility between the rare earth element of interest and the further magnetic or magnetisable element, preferably the further magnetic element, the method of the present invention may allow separation of the rare earth element of interest from said further magnetic or magnetisable element, preferably said further magnetic element.

[0079] Otherwise, a preliminary step of purification is necessary to separate and / or eliminate the further magnetic or magnetisable elements, preferably the further magnetic elements, before carrying out the method of the invention.

[0080] According to a first variant, the at least one rare earth element of interest has a magnetic susceptibility χ REE and the further magnetic or magnetisable element, in particular the further magnetic element, has an absolute relative difference |(χ REE -χ ME ) / χ MEso that the magnetic susceptibility χ | is 1 or more, preferably 10 or more. ME has.

[0081] According to this variant, the method of the invention makes it possible to separate the rare earth element of interest simply by carrying out steps a) and b) as defined above. Indeed, by carrying out the method of the invention, the rare earth element of interest can be isolated from further magnetic or magnetisable elements, preferably from further magnetic elements.

[0082] Preferably, according to this variant, no pretreatment step is necessary to eliminate further magnetic or magnetisable elements, preferably further magnetic elements, in particular further rare earth elements.

[0083] Otherwise, the magnetic susceptibility χ of the target rare earth element REE and the magnetic susceptibility χ of further magnetic (or magnetizable) elements ME If they are too close, they cannot be separated by carrying out steps a) and b) of the method of the invention. A preliminary step of purification is necessary to separate and / or eliminate further magnetic (or magnetizable) elements before carrying out the method of the invention.

[0084] Mention may be made of cobalt Co, nickel Ni, iron Fe and boron B which are commonly present in mining wastes.

[0085] Cobalt (Co), nickel (Ni), iron (Fe) and boron (B) may be separated, for example, by selective precipitation in the presence of oxalic acid in the solution. Indeed, by adding magnesium oxide (MgO) to the solution, Cobalt (Co), nickel (Ni), iron (Fe) and / or boron (B) can be selectively precipitated while the rare earth elements remain in solution. The solution free of Co, nickel (Ni), iron (Fe) and / or boron (B) may then be recovered by filtration. Suitable methods of selective precipitation are described, for example, in EP 3180290.

[0086] Cobalt Co, nickel Ni and iron Fe are magnetic elements and depending on the difference between their magnetic susceptibility and that of the rare earth element of interest, they can be eliminated simply by carrying out steps a), b) and c) of the method of the invention, but their selective precipitation using magnesium oxide is easier.

[0087] "Free of element A" in the context of the present invention refers to a solution containing a very low concentration of element A. In particular, the concentration of element A in the solution is less than 0.001 mol.L. -1 Less than 0.0001 mol.L, preferably 0.0001 mol.L -1 The following is the result.

[0088] The starting solution typically results from the dissolution of a solid containing the at least one rare earth element to be separated.

[0089] According to a particular embodiment, the method of the invention comprises a preliminary step of preparing a solution of such a solid, preferably by dissolving it in an acidic solution.

[0090] Solids containing the rare earth elements of interest typically consist of mining waste, industrial waste, and / or recycled goods or equipment.

[0091] "Mining wastes", in the context of the present invention, refer to solid and liquid residues from coal mining, phosphogypsum tailings, uranium mine wastes, and acid mine drainage from polymetallic sources such as rare earth mining and Zn-Pb or pyrite-Cu mining.

[0092] "Industrial waste", in the context of this invention, refers to coal fly ash, which is the residual particulate matter from coal combustion, bauxite residues from bauxite processing for aluminum production, and electronic waste (e-waste) from home appliances and electric vehicles.

[0093] Examples of reused goods or equipment can include, for example, electronic devices, magnets, mineral concentrates, rechargeable batteries such as Li-ion and nickel metal hydride (Ni-MH) batteries, and catalytic converters that are a source of cerium oxide.

[0094] In the context of recycling, prior to melting the solids, depending on the starting solids, it may be necessary to carry out preliminary steps of sorting, combustion and / or rejection of the polymeric material. The determination of these possible preliminary steps and how to carry them out belong to the general knowledge of the person skilled in the art.

[0095] Preferably, the acid solution is selected from the group consisting of nitric acid solutions, oxalic acid solutions, chloride acid solutions, sulphuric acid solutions and mixtures thereof. Advantageously, the acid solution consists of an aqueous solution of nitric acid.

[0096] Preferably, the concentration of the acid in the acidic solution is 0.1 mol.L -1 ~5 mol.L -1 , more preferably 0.5 mol.L -1 ~2 mol.L -1 The range is.

[0097] Advantageously, a preliminary step of dissolution of the solid is carried out by immersing the solid in a hot acidic solution.

[0098] Preferably, the acidic solution is contacted with the solid at a temperature in the range of from 30°C to 100°C, more preferably from 40°C to 80°C, typically from 50°C to 70°C.

[0099] Preferably, dissolving the solid in the acidic solution is carried out under stirring.

[0100] Advantageously, stirring and / or heating is maintained until all the starting solids are dissolved in solution. Preferably, stirring and / or heating is carried out for at least 1 minute, more preferably at least 5 minutes, even more preferably from 1 minute to 1 hour, typically from 5 minutes to 30 minutes.

[0101] According to a particular embodiment, after complete dissolution of the solids, a few drops of a basic solution are added to the solution to increase its pH. The purpose of this optional step is to reduce the overpotential required for local precipitation of at least one rare earth element to be separated.

[0102] Preferably, the base solution is selected from the group consisting of potassium hydroxide, sodium hydroxide, disodium phosphate, and mixtures thereof.

[0103] Preferably, the concentration of the base solution is 0.01 mol.L -1 ~1.0 mol.L -1 , e.g. 0.1 mol.L -1 The range is.

[0104] Advantageously, the base solution is added to the solution until the pH of the solution is in the range of a value between 3.0 and 4.9, typically between 4.0 and 4.5.

[0105] Elemental analysis of the solution is required to determine its topology as well as the operating conditions, particularly the magnetic field maxima and minima required to isolate the rare earth element of interest. This analysis includes X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), or inductively coupled plasma optical emission spectrometry (ICP-OES), all of which are applicable to liquids. If only optically active elements are known to be present, UV-visible absorbance spectroscopy of the solution can instead be used to identify which elements are present in the solution from their characteristic absorbance spectrum, as well as their concentrations using a calibration curve of absorbance according to the Beer-Lambert law.

[0106] magnetic field The method of the invention comprises a first step a) of applying a non-uniform magnetic field to the solution, whereby at least one first zone and at least one second zone with different magnetic field values ​​are created in the solution.

[0107] "Inhomogeneous magnetic field" in the context of the present invention refers to a magnetic field acting in a specific area and whose strength varies depending on the position within this specific area. The area typically comprises at least one low magnetic field area and at least one high magnetic field zone, whereby the strength of the magnetic field acting in said at least one high magnetic field zone is higher than the strength of the magnetic field acting in said at least one low magnetic field zone.

[0108] Preferably, the magnetic field strength of said at least one high magnetic field zone is more than 5 times, more preferably more than 10 times, even more preferably more than 20 times, the magnetic field strength of said at least one low magnetic field zone.

[0109] Preferably, the strength of the magnetic field acting in said at least one high magnetic field zone is in the range of 200 mT to 1.0 T, more preferably 500 mT to 0.9 T, typically 300 mT to 600 mT.

[0110] Preferably, the strength (absolute value) of the magnetic field acting in the at least one low magnetic field zone is in the range of 0.1 mT to 100 mT, more preferably 0.1 mT to 50 mT, typically 0.1 mT to 50 mT.

[0111] The magnetic field B applied to a material has the constitutive relationship B=μ 0 (H+M)(where μ 0 is the permeability of free space, and H is the auxiliary magnetic field. In free space, i.e., a vacuum, B=μ 0 H. In linear magnetic media, the induced magnetization M is related to a given magnetic field by H=χM, where χ is the dimensionless magnetic susceptibility. χ is a measure of the material's magnetizability to the magnetic field. A further useful quantity when dealing with substances of various concentrations c in a liquid is

[0112]

number

[0113] The molar magnetic susceptibility χ, defined as m If a given magnetic field B is inhomogeneous, i.e., if there is a magnetic field gradient ▽B, the magnetic field gradient force F ▽B teeth,

[0114]

number

[0115] Molar magnetic susceptibility χm It acts on substances that have

[0116] Paramagnetic material (χ m >0) are attracted to areas of high magnetic field (i.e., areas with the highest absolute value of the field strength), while diamagnetic materials (χ m <0) are repelled and are attracted to areas of low magnetic field, i.e., areas with the lowest absolute value of magnetic field strength).

[0117] Most rare earth elements are capable of forming paramagnetic ions, which means that under the influence of an external magnetic field, they acquire a magnetization oriented in the same direction as the applied magnetic field.

[0118] Molar magnetic susceptibility χ of a particular material mmay be determined according to several methods. In the case of solutions, for example, the Quincke method, which consists in placing one leg of a U-tube containing the target solution in a uniform magnetic field and measuring the change in height of the liquid in the magnetic field, or the NMR Evans method of chemical shift of the solvent peak due to paramagnetic species dissolved in the solvent, may be mentioned. These two methods are detailed in PW Selwood, Magnetochemistry, 2nd ed. (Interscience Publishers, 1956), and EM Schubert, Utilizing the Evans Method with a Superconducting NMR Spectrometer in the Undergraduate Laboratory, J. Chem. Educ. 69, 62 (1992). In the case of solids or liquids, for example, the Gouy magnetic balance, in which the sample is suspended under a mass balance and the change in effective mass is measured when a magnetic field gradient is applied, or magnetometers such as a vibrating sample magnetometer, which can measure the magnetization of the sample as a function of the applied magnetic field, may be mentioned. These methods are described in detail in PW Selwood, Magnetochemistry, 2nd ed. (Interscience Publishers, 1956) and JMD Coey, Magnetism and Magnetic Materials (Cambridge University Press, 2010).

[0119] The magnetic susceptibilities of the main rare earth elements in their most common ionic forms are reported in Table 1 below:

[0120] [Table 1]

[0121] Therefore, gadolinium (Gd 3+ , terbium Tb 3+ , Dysprosium Dy 3+ , Holmium Ho 3+ , ErbiumEr 3+ and Thulium Tm3+ The ions of the rare earth elements have a significantly higher magnetic susceptibility, χ m In addition, four other elements related to the rare earths, yttrium (Y), 3+ , Lantern La 3+ , Scandium Sc 3+ and lutetium Lu 3+ All ionic forms of gadolinium (Gd) are weakly diamagnetic. 3+ , terbium Tb 3+ , Dysprosium Dy 3+ , Holmium Ho 3+ , ErbiumEr 3+ and Thulium Tm 3+ Each of these has a unique magnetic susceptibility χ m They can be distinguished according to their magnetic properties.

[0122] Due to the induced magnetization, paramagnetic ions are attracted towards regions of high magnetic field. Thus, when placed in a non-uniform magnetic field, the most susceptible (most paramagnetic) ions will move towards the regions where the magnetic field is strongest. Conversely, the least susceptible ions (diamagnetic or least paramagnetic ions) will remain in the regions where the magnetic field is weakest.

[0123] Therefore, in the context of the present invention, by applying a non-uniform magnetic field to a solution, the elements present in the solution will have their magnetic susceptibility χ m are spatially separated according to

[0124] In particular, the application of a non-uniform magnetic field increases the magnetic susceptibility χ of magnetic elements, especially rare earth elements, in the solution. m Therefore, the rare earth elements have a magnetic susceptibility χ m are spatially selected according to

[0125] The movement of the magnetic elements therefore results in the formation of a concentration gradient of said at least one rare earth element in the solution, which typically extends from a first zone having a higher concentration of said at least one rare earth element towards a second zone having a lower concentration of said at least one rare earth element.

[0126] Preferably, the concentration of said at least one rare earth element in the first zone is more than 5 times higher, more preferably more than 10 times higher, even more preferably more than 20 times higher than the concentration of said at least one rare earth element in the second zone.

[0127] The inhomogeneous magnetic field is typically applied by using an inhomogeneous magnetic field generating module.

[0128] The non-uniform magnetic field generating module may be disposed inside the solution or outside the solution near the solution.

[0129] When placed outside the solution, the inhomogeneous magnetic field generating module typically consists of a particular assembly of permanent magnets and / or electromagnets.

[0130] For example, the inhomogeneous magnetic field generating module may consist of a set of axially magnetized bar magnets arranged with parallel or alternating magnetization. Arrays of axially magnetized bars are described, inter alia, in P. Dunne, Near Electrode Effects in Magneto-Electrochemistry, Ph.D., Trinity College, University of Dublin, 2011; P. Dunne et al., Magnetic Structuring of Electrodeposits, Phys. Rev. Lett. 107, 024501(2011) and P. Dunne et al., Patterning Metallic Electrodeposits with Magnet Arrays, Physical Review B 85, ​​224411(2012).

[0131] Alternatively, the inhomogeneous magnetic field generating module may consist of a collection of radially magnetized bar magnets arranged with aligned or alternating magnetization (e.g., by alternating adjacent, rows and / or columns). Arrays of radially magnetized bars are described, inter alia, in O. Cugat et al., Permanent Magnet Variable Flux Sources, IEEE Transactions on Magnetics 30, 4602 (1994).

[0132] The non-magnetic magnetic field generating module may also consist of an assembly of prismatic magnets. A 1D linear assembly is disclosed in particular in JE Hilton et al., An Adjustable Linear Halbach Array, Journal of Magnetism and Magnetic Materials 324, 2051 (2012). The determination of the alignment of the magnets depends on the final magnetic field required and belongs to the general knowledge of the person skilled in the art.

[0133] When placed inside the solution, the inhomogeneous magnetic field generating module may consist of a wire, mesh or soft magnetic material that is magnetized by an external magnetic field source.

[0134] The strength of the magnetic field and the specific properties of the magnetic field generating module depend on the rare earth elements to be separated and also on the impurities present in the solution, in particular further magnetic elements. It is common knowledge of the person skilled in the art to determine the required magnetic field, knowing the composition of the solution.

[0135] An example method for determining the magnetic field B and magnetic field gradient ▽B required for a particular solution involves electroplating a mixed oxide onto a flat cathode in the presence of characterized spatially varying B and ▽B. The cathode is in contact with an array of permanent magnets, preferably backed by one or more magnets to provide a well-defined variation of both B and ▽B. The magnetic field of this magnet array can be simulated and / or measured with a scanning Hall probe, and the resulting magnetic field gradient can be calculated. Preferably, the cathode is a metal foil with a thickness <1 mm, ideally <100 μm. Typically, the cathode consists of a thin metal foil, or a metallized Si wafer. Elemental analysis of the deposit, such as by scanning X-ray fluorescence (XRF) or energy dispersive X-ray spectroscopy (EDX), allows elemental concentration ratios to be mapped and thus correlated with the spatial variations of B and ▽B.

[0136] In the context of the present invention, it is necessary to maintain the inhomogeneous magnetic field until the precipitate is formed. In particular, the inhomogeneous magnetic field should be maintained at least during part of step b), preferably until the end of step b).

[0137] According to a first embodiment, the inhomogeneous magnetic field is configured to attract, in a first zone of the solution, said at least one rare earth element to be separated.

[0138] This first embodiment is based on the idea that the rare earth element to be separated is the most paramagnetic ion present in the solution (i.e., the one with the highest magnetic susceptibility χ m It is particularly preferred when the cation is an ion having the formula:

[0139] More specifically, this first embodiment relates to a method for producing a magnetic material in which the at least one rare earth element of interest has a magnetic susceptibility χ REE and the solution has χ REE >χ ME So, the magnetic susceptibility χ ME It is particularly preferred when the magnetic material further comprises at least one further magnetic element having the formula:

[0140] Preferably, according to this first embodiment, the first zone is the zone of the solution having the highest magnetic field value.

[0141] According to a second embodiment, the inhomogeneous magnetic field is configured to magnetically attract additional rare earth elements, different from the at least one rare earth metal element, in a second zone of the solution. This second embodiment is advantageous in that the rare earth elements to be separated are the least paramagnetic or most diamagnetic rare earth ions present in the solution (i.e. with a magnetic susceptibility χ m It is particularly preferred when the cation is the ion with the lowest valence.

[0142] More specifically, this second embodiment relates to a method for producing a magnetic material having at least one rare earth element of interest having a magnetic susceptibility χ REE and the solution has χ ME >χ REE So, the magnetic susceptibility χ ME It is particularly preferred when the magnetic material further comprises at least one further magnetic element having the formula:

[0143] Preferably, according to this second embodiment, the first zone is the zone of the solution with the lowest magnetic field value.

[0144] If the rare earth element to be separated is neither the most nor the least paramagnetic rare earth element present in the solution, the magnetic susceptibility χ m The rare earth elements with higher magnetic susceptibility (χ m The sequence of steps a), b) and c) defined above must be repeated one or several times so as to recover successively the rare earth elements (lower rare earth elements) and then the target rare earth element.

[0145] In particular, the sequence of steps a), b) and c) is carried out to obtain a rare earth element having a magnetic susceptibility χ m Rare earth elements with higher magnetic susceptibility χ than the target rare earth element m It may be necessary to repeat the process as many times as necessary depending on the presence of rare earth elements with low

[0146] For example, χ m (RE 1 )>χm (RE 2 )>χ m (RE 3 )>χ m (RE 4 ) as the four different rare earth elements RE 1 , R.E. 2 , R.E. 3 and R.E. 4 Consider a starting solution containing RE 3 Since RE is neither the most nor the least paramagnetic rare earth element in the solution, it is not possible to directly recover it. 4 After that, RE 4 Once recovered from the solution, the RE is extracted by repeating the sequence of steps a), b) and c). 3 can be recovered.

[0147] Precipitation The method of the invention further comprises a step b) of precipitating the at least one rare earth element in a first zone in which the at least one rare earth element is enriched or a step b) of precipitating the at least one further magnetic or magnetisable element in a second zone in which the at least one further magnetic or magnetisable element is enriched.

[0148] The precipitation of said rare earth element or said at least one further magnetic or magnetisable element may be carried out according to known methods.

[0149] According to one embodiment, the rare earth elements are precipitated by injecting a sulfate solution, preferably a sodium sulfate solution, into the first zone.

[0150] According to a preferred embodiment, step b) consists of increasing the pH of the solution either in the first zone enriched with said at least one rare earth element or in the second zone enriched with said optional at least one further magnetic or magnetisable element.

[0151] The increase in pH in the first zone directly results in the precipitation of said at least one rare earth element.

[0152] The increase in pH in the second zone directly results in the precipitation of said at least one further magnetic or magnetisable element.

[0153] Preferably, said at least one rare earth element or said at least one further magnetic or magnetisable element is precipitated as an oxide, hydroxide or a mixture thereof, more preferably as an oxide.

[0154] "(Hydroxy)oxide" in the context of the present invention refers to an oxide, a hydroxide or a mixture thereof.

[0155] Preferably, during step b), the pH of the solution is locally increased to a value of 3 or more, preferably 6 or more, typically between 6 and 8.

[0156] According to the invention, the increase in pH is a local increase, which means that the increase in pH only concerns a certain area of ​​the solution and its vicinity. In particular, during step b), the pH of the rest of the solution remains unchanged. The local increase carried out in the method of the invention is achieved by the introduction of hydroxide ions OH only in the first zone or in the second zone. - As the pH increases, the rare earth element of interest (in the first zone) or further magnetic or magnetizable elements (in the second zone) immediately convert into hydroxide ions OH - to form the corresponding (hydr)oxide. This immediate reaction of the concentrated element prevents the diffusion of hydroxide ions and an overall increase in pH in the rest of the solution, at least until the precipitate is recovered in step c).

[0157] The local increase in pH may be carried out according to any known method, provided that the method chosen makes it possible to increase the pH of the solution only in a selected specific area.

[0158] According to a first embodiment, the pH of the solution can be locally increased, for example by local addition, in particular local injection, of a chemical base.

[0159] In the context of the present invention, the term "locally" is used to indicate that the increase in pH, in particular the addition or injection of a chemical base, is carried out only in one of the first and second zones of the solution.

[0160] According to one embodiment, the pH is increased only in a first zone of the solution and not in a second zone of the solution.

[0161] According to an alternative embodiment, the pH is increased only in the second zone of the solution and not in the first zone of the solution.

[0162] Preferably, according to this first embodiment, the pH of the solution is locally increased by chemical dissociation of a strong base.

[0163] A "strong base", in the context of the present invention, refers to a chemical base associated with an acid / base couple having a pKa value of 9 or greater.

[0164] The chemical base may be added to the solution in the form of a concentrated basic solution, in which case local injection may be performed, for example, using a micropipette.

[0165] The concentrated basic solution may consist, for example, of a solution of potassium hydroxide or other basic compound.

[0166] Preferably, the concentrated basic solution has a pH in the range of 7.5 to 14.0, typically 12.0 to 14.0.

[0167] Alternatively, the chemical base may be added to the solution in the form of a solid, for example a powder.

[0168] Examples of solid chemical bases include the compounds LiOH, NaOH, KOH, and Ca(OH). 2 The following can be mentioned.

[0169] According to a second embodiment, the local increase in pH is performed by electrochemical reduction. In particular, the pH of the solution is increased by reduction of a chemical species present in the solution. The chemical species to be reduced may already be present in the solution. Alternatively, the specific chemical species may be added to the solution before step a) or step b).

[0170] Examples of species that can be electrochemically reduced include nitrate, hydroxylamine, oxygen, hydrogen peroxide, and water.

[0171] According to a preferred embodiment, the local increase in pH is caused by the incorporation of nitrate ions NO 3 - Preferably, according to this embodiment, the solution was prepared by dissolving the solid in an aqueous solution of nitric acid. Thus, the nitrate ions are already present in the solution, since they were added during the dissolution step. In particular, no step of adding a species likely to be electrochemically reduced is necessary.

[0172] According to a particular embodiment, the chemical species, in particular the nitrate ions, are electrochemically reduced at the surface of an electrode located in the solution, in particular the electrode being placed in the region of the solution (first region or second region) where a precipitate needs to form.

[0173] Preferably, according to this embodiment, the pH of the solution is locally increased by using an electrochemical cell capable of inducing the reduction of species likely to be reduced.

[0174] Preferably, the electrochemical cell comprises at least one current generator connected to at least one cathode, at least one anode, and optionally at least one reference electrode.

[0175] The purpose of the cathode is to reduce a chemical species in solution. The purpose of the anode is to close an electric circuit. If present, the purpose of the reference electrode is to monitor and control the cathode potential via a thermodynamically stable reference reaction.

[0176] The cathode is typically selected from a planar, mesh or wire electrode. The cathode may be segmented or continuous, and may be magnetic or non-magnetic.

[0177] According to a particular embodiment, the cathode is a mesh electrode, preferably a ferromagnetic mesh electrode, such as a steel mesh electrode. Thus, according to this particular embodiment, the oxide of said at least one rare earth element is precipitated on the surface of the mesh electrode.

[0178] Examples of non-magnetic metals which can be used to form the cathode include platinum (Pt), austenitic stainless steel (particularly types 304 or 316), glassy carbon, graphite, and related materials.

[0179] Examples of magnetic metals that can be used to form the cathode include martensitic or ferritic steels, such as type 409 or 410 stainless steels, metal coated NdFeB permanent magnets, and the like.

[0180] An example of the reference electrode is a silver chloride electrode.

[0181] According to a first embodiment, the electrochemical cell is operated to induce a constant potential difference between the cathode and the anode (potentiostatic control).

[0182] Preferably, according to this first embodiment, the potential difference between the cathode and the anode is −1.0V or less, preferably in the range of −1.5V to −2.8V, and more preferably in the range of −2.0V to −2.5V.

[0183] According to a second embodiment, the electrochemical cell is operated to keep the current flowing between the cathode and the anode constant (galvanostatic control).

[0184] Preferably, according to this second embodiment, the current density value is −0.5 mA cm -2 ~-10mA cm -2 The range is.

[0185] According to a preferred embodiment, step b) is carried out at a temperature ranging from 30°C to 100°C, preferably from 60°C to 80°C.

[0186] Heating of the solution can typically be accomplished using any heating means known to those of skill in the art, including immersing the container containing the starting solution in a thermostatically controlled oil or water bath, or circulating a stream of insulated heated water through the solution.

[0187] Sediment recovery The method of the present invention further comprises a step c) of recovering the precipitate of said at least one rare earth element.

[0188] According to a preferred embodiment, the method of the invention further comprises an intermediate step prior to step c), in particular between steps b) and c), of removing the inhomogeneous magnetic field.

[0189] This preliminary step makes the precipitates mobile and therefore easier to recover.

[0190] Preferably, step c) comprises a first sub-step of draining the solution followed by effective recovery of the precipitate.

[0191] Draining the solution allows the precipitate to be isolated from the solution, thus facilitating its recovery.

[0192] Recovery of the oxides may be carried out according to any known method, for example, the oxides may be recovered by scraping the surface of the cathode.

[0193] According to a particular embodiment, the precipitate of at least one rare earth element is mechanically recovered, for example using a blade.

[0194] According to a preferred embodiment, the precipitate is recovered by flowing a flush solution inside the device, particularly over the cathode surface. If a mesh electrode is used, the flush solution is typically flowed through the holes in the mesh electrode. Flowing the flush solution can dislodge and optionally dissolve the precipitate, particularly if an acidified flush solution is used.

[0195] The precipitate is finally recovered by drying of the purged solution, typically at a temperature of 60° C. or greater.

[0196] This embodiment is particularly suitable when the cathode is selected from a mesh electrode.

[0197] The flush solution preferably consists of an optionally acidified aqueous solution.

[0198] Examples of the acidified aqueous solution include, for example, citric acid solution, hydrochloric acid solution, nitric acid solution, and mixtures thereof. Preferably, the acidified aqueous solution comprises a nitric acid solution.

[0199] Preferably, the acidified aqueous solution is 0.1 to 1 mol.L -1 , typically 0.5 mol.L -1 The acid has a concentration in the range of

[0200] According to one embodiment, the flush solution may be heated, for example at a temperature in the range of 50° C. to 90° C., to facilitate dissolution of the oxides.

[0201] According to a particular embodiment, the method of the invention further comprises a step of magnetic filtration between steps b) and c).

[0202] In particular, according to this particular embodiment, both the solution and the precipitate obtained at the end of step b) are transferred to a second magnetic field device and magnetically captured. The purpose of this optional step is either i) to capture the paramagnetic precipitates in situ, so that they can be washed with water, removing the residual raw solution, or ii) to separate the different precipitates formed during step b). The solution is then drained and the precipitates are recovered according to any of the methods detailed above.

[0203] Optional post-processing According to a particular embodiment, the method of the invention further comprises at least one step of purification and / or metal transformation of the precipitate.

[0204] For example, if several elements precipitate together in step c), a purification step may be required. Examples of purification methods include solvent extraction and ion exchange chromatography.

[0205] The precipitates may also be converted to the corresponding metals by any known method, such as annealing in a reducing atmosphere using an inlet gas consisting of a mixture of 5% dihydrogen and 95% nitrogen.

[0206] The solution depleted of said at least one rare earth element can be reused in the method of the invention in order to recover other rare earth elements still present in the solution, in such a case it is necessary to carry out the method defined above again, in particular by repeating the sequence of steps a), b) and c).

[0207] FIG. 1 is a schematic diagram of a first embodiment of the invention, in which a solution comprises one rare earth element to be extracted and one further magnetic or magnetisable element, in which the rare earth element precipitates and the further magnetic or magnetisable element remains in solution.

[0208] FIG. 2 is a schematic diagram of a second embodiment of the invention, in which a solution comprises one rare earth element to be extracted and one further magnetic or magnetisable element, the further magnetic or magnetisable element being precipitated whilst the rare earth element is maintained in solution.

[0209] In Figs. 1 and 2, χ A Gaχ B Think bigger.

[0210] 1 and 2, a starting solution 2 comprising one rare earth element A and one further magnetic or magnetisable element B is subjected to the method according to the invention. A device 3 comprises magnets 4A, 4B making it possible to create an inhomogeneous magnetic field. Under the effect of the inhomogeneous magnetic field, the rare earth element A is concentrated in the high magnetic field region 5, whilst the further magnetic or magnetisable element B is concentrated in the low magnetic field region 6.

[0211] The device further comprises at least one electrochemical unit 7 making it possible to locally increase the pH of the solution.

[0212] In FIG. 1, an electrochemical unit 7 is located in the high magnetic field region 5 , thereby inducing the formation of a precipitate 8 of rare earth elements in the high magnetic field region 5 .

[0213] Conversely, in FIG. 2 an electrochemical unit 7 is located in the low magnetic field region 6 , thereby inducing the formation of a precipitate 8 of a further magnetic or magnetisable element in the low magnetic field region 6 .

[0214] A device 10 suitable for carrying out the method according to the invention is shown diagrammatically in FIGS.

[0215] The device 10 includes a reservoir 12 adapted to receive a flow of an aqueous solution 14 comprising at least one rare earth element A in admixture with impurities B, C and D. The solution further comprises at least one species E that is likely to be reduced (not shown). The reservoir 12 includes an inlet 16 for introducing the solution 14 into the reservoir 12, and an outlet 18 for collecting the solution 14 at an outlet of the reservoir 12.

[0216] The device 10 further includes a pair of magnets 20, 22 located on either side of the reservoir 12, said magnets 20, 22 being capable of creating a non-uniform magnetic field inside the reservoir 12. A mesh electrode 24 is located inside the reservoir 12 so as to be in contact with the solution 14 when injected into the reservoir 12. In particular, the mesh electrode 24 is disposed between the two magnets 20, 22. Another electrode 26 is located between the reservoir 12 and the inlet 16.

[0217] The value of the applied magnetic field is configured to specifically attract the at least one rare earth element A in the vicinity of the mesh electrode 24 .

[0218] Mesh electrode 24 and other electrode 26 are connected to each other by an external current generator 28, which is capable of inducing a potential difference between mesh electrode 24 and other electrode 26. Device 10 is further connected to a heating means (not shown) that allows for temperature control of solution 14.

[0219] The device 10 also includes an inlet 29 for injecting a flush / purge solution 30 into the interior of the reservoir 12 and an outlet 32 ​​for withdrawing the flush / purge solution 30 at the outlet of the reservoir 12 .

[0220] The method according to the invention will now be described with reference to the device 10 .

[0221] Referring to Figure 3:

[0222] A solution 14 containing at least one rare earth element A, and further magnetic or magnetisable elements B, C and D, is circulated inside the reservoir 12 while a non-uniform magnetic field is applied inside the reservoir 12 by magnets 20, 22. In particular, the solution 14 is injected into the interior of the reservoir 12 as a stream flowing from the inlet 16 towards the outlet 18. Under the effect of the non-uniform magnetic field, the at least one rare earth element A is retained in the vicinity of the mesh electrode 24, whereas the remainder of the solution 14, in particular the further magnetic or magnetisable elements B, C and D, are carried away by the flow of the solution 14 towards the outlet 18.

[0223] The current generator 28 is then turned on to induce a potential difference between the mesh electrode 24 and the other electrode 26. Under the influence of the potential difference, the species E oxidizes at the surface of the mesh electrode 24, thereby locally increasing the pH of the solution in the vicinity of the mesh electrode 24. As a result, the at least one rare earth element A precipitates as an oxide on the surface of the mesh electrode 24.

[0224] Referring to Figure 4:

[0225] Thereafter, the current generator 28 and, optionally, the inhomogeneous magnetic field are turned off and the reservoir 12 is emptied of solution 14 .

[0226] Then, a flush / purge solution 30 is injected into the reservoir 12 through an inlet 28. Upon contact with the flush / purge solution 30, oxides deposited on the surface of the mesh electrode 24 are peeled off from the mesh electrode 24 and discharged together with the flush / purge solution 30. The flush / purge solution 30 containing the at least one rare earth element A is then collected at an outlet 32. EXAMPLES

[0227] Example 1 Recovery of dysprosium oxide from solutions that also contain cerium ions (static method, involving chemical precipitation) The starting solution was 50.10 -3 mol.L -1 Cerium nitrate (Ce(NO3 ) 3 and 40.10 -3 mol.L -1 Dysprosium nitrate Dy(NO 3 ) 3 It is an aqueous solution containing

[0228] An open array of aligned radial rods (N42 magnetic rods with 4 mm radius and 20 mm length) with an “alternate adjacent” configuration is used to generate a non-uniform magnetic field, as shown in Figure 5. The light zones represent high-field regions, while the dark zones represent low-field regions.

[0229] The open array was immersed in the starting solution. Then, 0.1 mol.L -1 2 ml of potassium hydroxide KOH solution (pH 12.86) was locally injected into the area of ​​highest magnetic field value (light zone). This induced the precipitation of Dy-rich oxides, which remained in the high magnetic field area and were repelled from the zero magnetic field area. After waiting 2 min until no further changes were observed, the solution was slowly removed from around the magnet and replaced with water. The precipitate was then pipetted out of the magnet and allowed to settle in a glass vial placed on a strong permanent magnet. After settling, the supernatant liquid was removed and fresh deionized water was added. The suspension was remixed by stirring the vial and allowed to settle again. This was repeated 10 times, after which the solution was heated to evaporate the water, thereby drying the powder.

[0230] In Figure 6 we report three photographs of the radial magnet array taken at different stages of the method.

[0231] FIG. 6a is a photograph of the array in its dry state, before contact with the starting solution.

[0232] FIG. 6b is a photograph of the array in contact with the starting solution.

[0233] FIG. 6c is a photograph of the array after potassium hydroxide solution injection.

[0234] When an aqueous solution of potassium hydroxide was injected, a white precipitate was observed to form in the high magnetic field region (between the magnetic bars).

[0235] The elemental composition of the precipitates was determined by ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy).

[0236] The powder obtained contains 84 atomic % dysprosium Dy and 16 atomic % cerium Ce.

[0237] Example 2 Recovery of dysprosium oxide from solutions further containing cerium ions (continuous flow method involving chemical precipitation) The starting solution was 50.10 -3 mol.L -1 Cerium nitrate (Ce(NO 3 ) 3 and 40.10 -3 mol.L -1 Dysprosium nitrate Dy(NO 3 ) 3 It is an aqueous solution containing

[0238] A peristaltic pump is used to recirculate the starting solution from the glass vial through the magnetic filtration device shown in FIGS.

[0239] FIG. 7 is a schematic diagram of a magnetic filter assembly 100.

[0240] The magnetic filter assembly 100 includes a filtration chamber 110 surrounded by eight prismatic magnets 120. The filtration chamber 110 traverses the magnets 120 from one side to the other.

[0241] The configuration of the filtration chamber 110 is illustrated in Figure 8. The filtration chamber 110 includes an inlet 130 for introducing a starting solution (not shown) into the filtration chamber, a magnetic mesh 140 located at the height of the magnet 120, and an outlet 150 for collecting the starting solution. The filtration chamber further includes an inlet 160 for introducing a basic solution for precipitating rare earth elements.

[0242] Masterflex silicone transfer tubing with an internal diameter of 1.6 mm was used to connect all fluid elements. The remaining fluid volume of the system was 11 ml, excluding the maximum volume of the glass vial, which was 23 ml. The basic solution was 0.1 mol.L -1 It is a solution of potassium hydroxide (KOH) solution (pH 12.86).

[0243] The process was as follows: 1.20 ml of working solution was added to the reservoir of a glass vial 2. The solution was circulated through the reservoir and system at 32 ml / min. 3. 1.0 ml of KOH solution was added at 0.25 ml / min. 4. Wait 60 seconds 5. 1.0 ml of KOH solution was added at 1 ml / min. 6. Wait 60 seconds 7. Drain the solution from the system 8. Rinse the system with 100ml of deionized water. 9. Remove the filtration chamber from the magnet 10. Pump 1 ml of water from the chamber into the vial at 2 ml / sec. 11. Pump 1 ml of water from the chamber into the same vial at 2 ml / sec.

[0244] The method involves obtaining rare earth oxide powders in a 2 ml water suspension.

[0245] The elemental composition of the obtained powder was determined by ICP-OES (Inductively Coupled Plasma-Optical Emission Spectroscopy).

[0246] The powder obtained contains 74 atomic % dysprosium Dy and 26 atomic % cerium Ce. [Explanation of symbols]

[0247] 2. Starting solution 3 Devices 4A Magnet 4B Magnet 5 High magnetic field region 6 Low magnetic field region 7. Electrochemistry Unit 8. Precipitation 10 Devices 12 Reservoir 14 solution 16 Inlet 18 Outlet 20. Magnet 22 Magnet 24 Mesh Electrode 26 electrodes 28 Current Generator 29 Inlet 30 Flush / Purge Solution 32 Outlet 100 Magnetic Filter Assembly 110 Filtration chamber 120 Magnet 130 Inlet 140 Magnetic Mesh 150 Outlet 160 Inlet

Claims

1. A method for separating at least one rare earth element (A) from a solution (2) containing said at least one rare earth element (A) and at least one magnetic or magnetizable element (B), comprising the following steps: a) applying a non-uniform magnetic field to the solution (2), thereby creating in the solution at least one first zone (5) and at least one second zone (6) with different magnetic field values, the application of the non-uniform magnetic field value inducing a concentration of said at least one rare earth element (A) in the first zone (5) and a concentration of said at least one further magnetic or magnetisable element (B) in the second zone (6), The process and b) precipitating said at least one rare earth element (A) in a first zone (5) or said at least one further magnetic or magnetisable element (B) in a second zone (6); c) recovering the precipitate (8); A method comprising:

2. 2. The method of claim 1, wherein the at least one further magnetic or magnetizable element (B) is selected from the group consisting of transition metals, rare earth elements different from the at least one rare earth element, and mixtures thereof.

3. The at least one rare earth element (A) has a magnetic susceptibility χ ＲＥＥ and the further magnetic or magnetizable element (B) has an absolute relative difference |(χ ＲＥＥ -X ＭＥ ) / X ＭＥ is 1 or more, preferably 10 or more, so that the magnetic susceptibility χ ＭＥ The method of claim 2, comprising:

4. χ ＲＥＥ Gaχ ＭＥ 4. The method according to claim 3, wherein the first zone (5) is the zone of the solution having the highest magnetic field value.

5. χ ＭＥ Gaχ ＲＥＥ 4. The method according to claim 3, wherein the first zone (5) is the zone of the solution having the lowest magnetic field value.

6. 6. The method according to any one of claims 1 to 5, wherein during step a) the solution (2) has a pH value below 7, preferably in the range of 2 to 6.

7. 7. The method according to any one of claims 1 to 6, wherein the precipitation of the at least one rare earth element (A) is induced by increasing the pH of the solution in a first zone (5) or the precipitation of the one further magnetic or magnetisable element (B) is induced by increasing the pH of the solution in a second zone (6).

8. 8. The method according to claim 7, wherein during step b) the pH is greater than 7, preferably greater than 8.

9. During step b), the pH is adjusted according to the concentration of at least one chemical substance present in solution (2), such as nitrate ions NO ３ － The method according to claim 7 or 8, wherein the amount of the metal oxide is increased by electrochemically reducing

10. 10. The method of claim 9, wherein the at least one chemical is electrochemically reduced at the surface of an electrode (24) located in the solution (2).

11. The method of claim 10, wherein the electrode (24) is a mesh electrode, preferably a ferromagnetic mesh electrode.

12. 12. The method according to any one of claims 7 to 11, wherein during step b) the pH is increased by localized addition of a chemical base.

13. 13. The method according to claim 1, further comprising, before step c), an intermediate step of removing the inhomogeneous magnetic field.

14. 14. The method according to any one of the preceding claims, wherein the precipitate (8) is recovered in step c) by flowing a purge solution (30), said purge solution (30) preferably consisting of an optionally acidified aqueous solution.

15. 15. The method according to any one of claims 1 to 14, comprising, prior to step a), a preliminary step of dissolving the solid comprising the at least one rare earth element (A) and at least one further magnetic or magnetisable element (B) in a solvent, preferably an acidic solution.

16. 16. The method according to any one of claims 1 to 15, wherein cobalt Co, iron Fe and / or nickel Ni, if present, are removed from the solution (2) before the application of the inhomogeneous magnetic field.

17. 17. The method according to any one of claims 1 to 16, further comprising a step of purifying and / or metal converting the precipitate (8).

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