Methods for improved, magnetically assisted separation of rare earth elements

Abstract

Method for separating rare earth elements from a solid or aqueous phase (1), comprising the steps: a) Contact of the aqueous phase (1) with a second phase (2), selected from a solid or an organic liquid phase, such that a concentration gradient is created within the aqueous phase (1) due to the transfer of rare earth elements in the form of rare earth ions (3) from the second phase (2) into the aqueous phase (1) or from the aqueous phase (1) into the second phase (2), and b) Applying a magnetic field (4) using a magnet (5) during contact at the contact surface between aqueous phase (1) and second phase (2), wherein the magnetic field (4) is aligned such that a magnetic field gradient is antiparallel to the concentration gradient of the rare earth ions (3) in the aqueous phase (1) and where the product of the rare-earth-dependent magnetic susceptibility χ, calculated from the rare-earth concentration * rare-earth magnetic susceptibility, and the magnetic field gradient is greater than 0.002 T 2 / m is.

Description

[0001] The invention relates to a process for separating rare earths from a solid or an aqueous phase by leaching or solvent extraction.

[0002] The magnetic separation of rare earths is well known in the art (Lei et al. 2022).

[0003] DE 10 2014 211 289 A1 describes a device and a method for separating and concentrating components with magnetic properties from an ion-containing solution. An ion-containing solution is passed through a magnetic field and then divided into at least two partial liquid streams.

[0004] The effectiveness of separation using known methods is low.

[0005] US 2017 / 0001128 A1 discloses a process for the magnetically assisted demulsification of extraction phases, wherein a first solution containing a first solvent and a solvated paramagnetic metal ion are brought into contact with a second solvent. The first and second solutions are mixed to form an emulsion, with the phases of the emulsion containing different concentrations of the paramagnetic metal ion. An applied magnetic field gradient with a sufficient gradient strength causes the phases to separate more rapidly.

[0006] EP 4 273 284 A1 discloses a method for separating at least one rare earth element from a solution containing the at least one rare earth element and optionally at least one further magnetic element. A non-uniform magnetic field is applied to the solution, thereby creating at least one first zone and at least one second zone with a different magnetic field in the solution. The application of the non-uniform magnetic field value effects the concentration of the at least one rare earth element in the first zone and the concentration of the optional at least one further magnetic element in the second zone. Increasing the pH in the first or second zone induces precipitation of the at least one rare earth element or at least one further magnetic element, respectively, and the precipitate can be recovered.

[0007] US 2014 / 0166788 A1 discloses a method for separating rare earth element compounds from a slurry of mixed rare earth element compounds. The slurry flows through at least one first channel containing at least one first magnet. The individual rare earth element compounds or groups of rare earth element compounds separated from the slurry by the magnet according to their respective ratio of magnetic susceptibility (A / J) to specific density (Ap) are recovered.

[0008] Fan et al. (2022) discloses a method for separating rare earths based on differences in the magnetic moment. Rare earth solutions were exposed to a magnetic field, which accelerates the crystallization of the rare earths.

[0009] Higgins et al. demonstrate a method for separating rare earth elements based on the intrinsic magnetic properties of rare earth ions. Using an external Fe 14 Nd2B magnets and a concentration gradient created by decreasing temperature can effectively and selectively crystallize the rare earths.

[0010] The object of the invention is to provide a more effective process for the separation of rare earths in the form of their rare earth ions.

[0011] Complex structures such as membranes should be dispensed with.

[0012] The invention relates to a process for separating rare earths from a solid or an aqueous phase, comprising the steps: a) contacting an aqueous phase with a second phase selected from a solid or an organic (liquid) phase, so that a concentration gradient is created within the aqueous phase due to the transfer of the rare earths in the form of rare earth ions from or to the second phase, and b) Applying a magnetic field using a magnet during contact at the contact surface (between the aqueous phase and the second phase), wherein the magnetic field is aligned such that the magnetic field gradient is antiparallel to the concentration gradient of the rare earth ions in the aqueous phase and where the product of the rare earth-dependent magnetic susceptibility χ and the magnetic field gradient is greater than 0.002 T 2 / m is.

[0013] The skilled person recognizes that if the rare earths are present as rare earth ions in the aqueous phase, they are extracted using the principle of solvent extraction with a second, organic (liquid) phase; or that if the rare earths are present in the solid phase (e.g., as ore), they are transferred into the aqueous phase using the principle of leaching. The invention now relates to a possibility for intensifying the phase transition.

[0014] In the case of contact with a second, solid phase, the solid phase contains the rare earths (e.g. it is a rare earth-containing ore) and the aqueous phase should, as one skilled in the art will recognize, be very acidic so that the rare earths can migrate into the aqueous phase during the leaching process.

[0015] In the case of contact with a second, organic (liquid) phase, this is a solvent extraction, i.e. the rare earths are contained in the aqueous phase as rare earth ions and pass into the second, organic phase upon contact.

[0016] The concentration gradient that develops in the aqueous phase (experience shows that this occurs after at least 10 seconds of contact in step a)) is measured using a Mach-Zehnder interferometer.

[0017] The “magnetic field gradient” is also called “magnetic pressure gradient” and can be measured by determining the magnetic field strength with a conventional Hall probe (a Gaussian meter) at discrete points, from which a magnetic field gradient can be calculated.

[0018] “Antiparallel” in the sense of the invention means that the orientation of the magnetic field is chosen such that the gradient of the magnetic field is opposite to the concentration gradient of the rare earth ions in the aqueous phase. This means that the concentration in the aqueous phase decreases from left to right (relative to Figs. 1, left half towards the middle), the magnetic field must increase from left to right ( Figs. 1: left half toward the center). As a result, the magnetic Rayleigh number of the system becomes positive, and above the critical value specified in the invention (the product of the magnetic susceptibility of the respective rare earth ion and the magnetic field gradient), the instability leads to vortex-like flows in the liquid phase(s), which enhance the extraction.

[0019] This is equivalent to stating that the direction of rare earth ion depletion must be antiparallel to the direction of magnetic flux density reduction.

[0020] The inventive extension of the magnetic field leads to a positive Rayleigh number.

[0021] Examples of magnets include bar magnets or ring magnets to create an antiparallel alignment. However, electromagnets, clusters of permanent magnets, or any conceivable device that creates a magnetic field are also suitable, as long as the conditions mentioned above are met.

[0022] The invention allows, for example, the supplementation of solvent extraction by Kelvin-driven convection as a method to increase efficiency.

[0023] Advantageously, vortex formation occurs in the area of ​​the phase interface with the aqueous phase, significantly intensifying the transfer of rare earth ions from or into the aqueous phase. An improvement in extraction kinetics has been observed. This means that under the conditions / limits of the invention, a "situation" arises characterized by convection with large-scale circulation in the velocity field. The kinetic energy of the vortex controls the flow velocity at the interface. The vortex ensures a subsequent flow of rare earths from the distant region.

[0024] Advantageously, the invention achieves a selectively enhanced separation of the rare earth ions.

[0025] The invention works particularly well for trivalent rare earth ions with high magnetic susceptibility, such as Dy(III), Ho(III), Er(III), Tb(III) and Gd(III).

[0026] The following relationship resulting from the invention is important: The separation yield scales advantageously as a function of the second to third power of the magnetic field gradient (B VB). Preferred embodiments

[0027] In a preferred embodiment of the invention, the product of the magnetic susceptibility χ and the magnetic field gradient is at least 0.002 T 2 / m, or even at least 0.003 T 2 / m, or at least 0.0035 T 2 / m.

[0028] Preferably, the product is a maximum of 0.177, also a maximum of 0.088, or even a maximum of 0.030, or a maximum of 0.020.

[0029] In a preferred embodiment, the second, organic phase contains the extractant Pc88a in 0.25-1 mol / L (most preferably > 0.5 mol / L) (Pc88a = CAS 14802-03-0, mono-2-ethxylhexyl (2-ethylhexyl)phosphonate).

[0030] Preferably, the magnet is a 5 mm long (±10%) cylindrical NdFeB permanent magnet with a 4 mm diameter (±10%).

[0031] In a preferred embodiment, in step a), contact is made with a second, solid phase. This solid phase is a solid ore containing the rare earths, and the aqueous phase is acidic with a pH < 2. This process is known as leaching. Here, too, a faster transfer of the rare earth ions occurs due to the vortices formed within the aqueous phase.

[0032] In a further preferred embodiment of the process according to the invention, it is a process for separating the rare earths from the aqueous phase, wherein in step a) contact is made with a second, organic (liquid) phase and therefore step a) is: a) Solvent extraction using Contacting the aqueous phase with the second, organic phase (in the form of a single drop of the second, organic phase) so that a concentration gradient is created within the aqueous phase due to the transfer of the rare earths (in the form of rare earth ions) into the second phase.

[0033] Especially for such an extraction process, where the rare earth ion can form a complex with the extractant and form a depletion at the aqueous bulk interface (see Figs.1), a bar magnet can generate a magnetic field that decreases radially outward, which produces the minimum value essential to the invention. On the other hand, a ring magnet can be used in a stripping process (this is the preferred existing step c mentioned below), i.e., the expulsion after extraction in step a) for the transfer of the rare earth ions from the second, organic phase into a third, aqueous collecting solution.

[0034] Particularly preferred in this embodiment is a variant in which steps a) and b) are followed by the following step c): c) Expulsion to transfer the rare earth ions from the second phase, which is the organic phase (also called: second organic phase), into a third, aqueous collecting solution.

[0035] Preferably, a magnetic field according to the variant according to the invention is also applied here in step c), with the only difference being that, with respect to the concentration gradient, this must now be antiparallel to the concentration gradient of the rare earth ions in the third, aqueous collecting solution. This is because the ions pass from the second, organic phase into the third, aqueous collecting solution in step c). This expulsion in step c) is also referred to as "stripping." It can be seen that the concentration gradient (now in the third aqueous collecting solution) is oriented in the opposite direction, and the orientation of the magnetic field must also be changed so that it is antiparallel to the concentration gradient according to the invention.

[0036] It also corresponds to a preferred embodiment if the rare earths are selected from dysprosium, erbium, terbium, holmium and gadolinium.

[0037] In a further preferred embodiment of the invention (it is a process for separating the rare earths from the aqueous phase and it) is contacted in step a) with a second, organic phase and the aqueous phase has, before contacting in step a), a concentration of dysprosium(III) or erbium(III) or terbium(III) or holmium(III) or gadolinium(III) in the range of 450-550 mM each and the magnetic field gradient is at least 7 T 2 / m. In particular, it can be 7.3 T 2 / m for Dy or 9.3 T 2 / m for Er or 9.1 T 2 / m for Tb or 7.4 T 2 / m for Ho or 14 T 2 / m for Gd; each within the limits of ±10% of the value.

[0038] Advantageously, an even larger, active convection forms above this magnetic field gradient, which causes a significant increase in the transfer of the rare earth ions (both from the aqueous phase into the second, organic phase, and, if carried out subsequently, in a stripping step, as in step c) of the above-mentioned embodiment, if a magnetic field is also applied in this case.

[0039] The magnetic field gradient is particularly preferably in the range of 7-430 T 2 / m, or max. 215 T 2 / m, max. 72 T 2 / m or max. 48 T 2 / m.

[0040] In a further preferred embodiment of the method according to the invention, the magnet in step b) is a bar magnet, selected from bar-shaped permanent magnets, bar-shaped electromagnets, and bar-shaped superconducting magnets. These are particularly well suited for achieving a clear orientation of the magnetic field in relation to the laboratory geometry.

[0041] In a particularly preferred variant of the above-mentioned embodiment, for the separation of rare earths from the aqueous phase, wherein in step a) contact is made with a second, organic phase and step a) is: a) Solvent extraction using Contacting the aqueous phase with the second, organic phase, so that a concentration gradient is created within the aqueous phase due to the transfer of the rare earths in the form of rare earth ions into the second phase, and with the additional step following step b): c) expulsion to transfer the rare earth ions from the second phase, which is the organic phase, into a third, aqueous collecting solution, during the expulsion in step c), a magnetic field is also applied by means of a magnet to the contact surface between the second, organic phase and the third, aqueous collecting solution, wherein the magnetic field is aligned such that the magnetic field gradient is antiparallel to the concentration gradient of the rare earth ions within the third, aqueous collecting solution in step c) and also the product of the rare earth-dependent magnetic susceptibility χ and the magnetic field gradient is greater than 0.002 T 2 / m is.

[0042] Since the concentration gradient is different here, the magnetic field must also be adjusted accordingly in terms of its orientation.

[0043] Statements concerning the application of the magnetic field in step b) therefore preferably also apply to step c), if present.

[0044] In a likewise preferred embodiment of the process, according to an embodiment mentioned above, in which contact is made with a second organic phase in step a), in the solvent extraction in step a) the second organic phase contains an extractant selected from • the cation exchangers neo-decanoic acid, benzamidine or naphthenic acid, and • the phosphorous acids bis-(2-ethylhexyl)phosphoric acid, mono-2-ethylhexyl (2-ethylhexyl)phosphonate, diisooctylphosphinic acid, diisooctylthiophosphinic acid, or diisooctyldithiophosphinic acid, and • the chelating ion exchanger 1-phenyldecane-1,3-dione, and • the solvent extraction agents tributyl phosphate, dibutyl butylphosphonate or trioctylphosphine oxide, and • the anion exchangers 16,16-dimethylheptadecan-1-amine or methyltrioctylammonium chloride.

[0045] These are particularly well-suited for quickly and effectively achieving a concentration gradient in the aqueous phase. It is particularly preferred if the extraction agent is mono-2-ethylhexyl (2-ethylhexyl)phosphonate and the rare earth ion is dysprosium(III).

[0046] In a similarly advantageous variant of the embodiment of the invention, in which contact is made with a second organic phase in step a), this phase comprises kerosene, 1-octanol, 2-ethylhexanol, paraffin, or mixtures thereof. It particularly preferably consists essentially of these, i.e., at least 80 wt.%. For example, at least 80 wt.% of the second organic phase is paraffin.

[0047] In another advantageous variant of the embodiment, in which contact is made with a second, organic phase in step a), both steps a) and b) are carried out in a Hele-Shaw cell.

[0048] A "Hele-Shaw cell" consists of two square, usually transparent discs (usually Plexiglas). One of them has a hole in the center. Both discs are pressed evenly together at the edges. If this is not the case, other means, such as a circle of filter paper, must be used to ensure even pressure distribution within the cell or equal spacing between the discs.

[0049] A "Hele-Shaw cell" in the sense of the preferred embodiment describes a cell whose thickness is significantly smaller than its length and width. This results in a quasi-two-dimensional state for some flow processes within the cell, depending on the viscosity of the fluid.

[0050] The second, organic phase is injected as droplets. The flow volume can preferably be approximately 1-4 mm in diameter, resulting in individual droplets. Table 1 below shows the magnetic susceptibility χ of various rare earth ions

[0051] Figs. 1 schematically shows an arrangement according to a preferred embodiment of the invention, in which the aqueous phase contains the rare earths as rare earth ions and is contacted with a second, organic (liquid) phase in step a).

[0052] The invention is not limited to the embodiments illustrated and described, but also encompasses all embodiments having the same effect within the meaning of the invention. Furthermore, the invention is not limited to the specifically described combinations of features, but can also be defined by any other combination of specific features of all the individual features disclosed as a whole, provided that the individual features are not mutually exclusive or a specific combination of individual features is not explicitly excluded.

[0053] The invention will be explained in more detail below using an exemplary embodiment, without being limited to this. Examples of implementation

[0054] Example 1 concerns the variant of solvent extraction with an aqueous and an organic phase.

[0055] The magnetic Rayleigh number is 10 6up to 10 7 . The magnetic gradient force (magnetic field gradient) is calculated as (B ·∇B) or (0.5 ∇B 2 ) than the value 7 T 2 / m. The product of the magnetic susceptibility and the magnetic field gradient is 0.002 T 2 / m.

[0056] In the example, the dysprosium(III) concentration in the aqueous phase is 0.5 M (mol / L), which corresponds to a force of χDy⋅cDyμ0. Magnetic field gradient with the value of 7 T2 / m⋅(5.8 / 2) / 1.256(N / A2)⋅100~1616 N / m3.

[0057] In a region around the interface (1 mm inside to 1 mm outside) the average magnetic field gradient should be at least in the order of 7 T 2 / m. In this case, Ra*, at which the transition from non-vortex to vortex flow in the aqueous phase occurs between O(10 6 ) and O(10 7 ).

[0058] For Ho(III), Er(III), Tb(III) and Gd(III) the minimum magnetic gradient force is 7.4 for Ho(III), 9.3 for Er(III), 9.1 for Tb(III) and 14 for Gd(III), respectively, each in the unit T 2 / m. This means that the Ra* number lies between O(10 6 ) and O(10 7 ). To achieve the same Ra* range, for example, for the rare earth ion Sm(III) a much larger magnetic field gradient of 420 T 2 / m required. Example 2:

[0059] The minimum magnetic field gradient (B ·∇B) causing large-scale convection depends on the dimensionless magnetic susceptibility χ of the solution in which the vortices due to the magnetic field are to arise. The product of χ and (B ·∇B) must be greater than 0.002 T 2 / m, preferably greater than 0.003 T 2 / m. This means that it depends on the rare earth concentration and that χ is calculated using the following formula: χ=rare earth concentration*rare earth magnetic susceptibility.

[0060] For a Dy(III) of 500 mM, χ = χ Dy · c Dy = 5.8 · 10 -7 · 500 = 0.0003. This results in a minimum magnetic field gradient (B · VB) of 7 - 10 T 2 / m. The same applies to Er(III), Ho(III), Gd(III), and Tb(III), as they have a high magnetic susceptibility similar to Dy(III).

[0061] Sm(III), on the other hand, would, under the same conditions, contain 400 - 580 T 2 / m required. Magnetic susceptibilities of various rare earth ions:

[0062] The following Table 1 shows the magnetic susceptibility χ of various rare earth ions, each for chloride salts in aqueous solution, measured at room temperature and atmospheric pressure. Table 1: Y(III) The(III) Ce(III) Nd(III) Sm(III) Gd(III) Tb(III) Dy(III) Ho(III) Er(III) Yb(III) x * 10 4 (M -1 ) -0,1 -0,1 0,2 0,6 0,1 3,0 4,6 5,8 5,7 4,5 0,9 Example 3:

[0063] This experiment was conducted in a Hele-Shaw cell (1 mm gap width, quartz) with a 1 mm cell depth. The second, organic phase was applied to the lower and upper plates. The organic phase contained low-viscosity paraffin with 0.25-0.75 mol / L Pc88a extractant. The aqueous phase contained 0.1 M HCl and 0 to 1 mol / L DyCl3.

[0064] Magnetless and ring-magnet configurations form stable concentration gradients of approximately equal strength. In these cases, the concentration field is stable over time. With the ring magnet, the field is somewhat stronger around the droplet interface (between the aqueous phase and the second, organic phase). Bar magnets cause instabilities and shifting concentration gradients parallel to the interface.

[0065] Vortex pairs in the cell plane were observed, reaching approximately 3 mm in diameter and caused by the instabilities induced by the magnetic field. Cited non-patent literature: Lei, Z.; Fritzsche, B.; Salikhov, R.; Schwarzenberger, K.; Hellwig, O.; Eckert, K. Magnetic Separation of Rare-Earth Ions: Property Database and Kelvin Force Distribution J. Phys. Chem. C, 2022, 126, 2226-2233. Fan, B.; Li, F., Cheng, Y., Wang, Z., Zhang, N., Wu, Q., Bai, L., Zhang, X.; Rare-earth separations enhanced by magnetic field; Separation and Purification Technology 301 (2022) 122025. Higgins RF, Cheisson T, Cole BE, Manor BC; Caroll, P.J.; Schelter, E. J.; Magnetic Field Directed Rare-Earth Separations; Angew. Chem. Int. Ed. 2020, 59, 1851 - 1856

Claims

[1] Process for the separation of rare earths from a solid or an aqueous phase (1), comprising the steps: a) contacting the aqueous phase (1) with a second phase (2) selected from a solid or an organic liquid phase, so that due to the transfer of the rare earths in the form of rare earth ions (3) from the second phase (2) into the aqueous phase (1) or from the aqueous phase (1) into the second phase (2), a concentration gradient is created within the aqueous phase (1), and b) applying a magnetic field (4) by means of a magnet (5) during contact at the contact surface between the aqueous phase (1) and the second phase (2), wherein the magnetic field (4) is aligned such that a magnetic field gradient is antiparallel to the concentration gradient of the rare earth ions (3) in the aqueous phase (1) and where the product of the rare earth dependent magnetic susceptibility χ, calculated from the rare earth concentration * rare earth magnetic susceptibility, and the magnetic field gradient greater than 0.002 T 2 / m is. [2] Process according to claim 1, wherein in step a) contact is made with a second, solid phase (2) and the solid phase (2) is a solid ore containing the rare earths and the aqueous phase (1) is acidic with pH < 2. [3] Process according to claim 1, for separating the rare earths from the aqueous phase (1), wherein in step a) contact is made with a second, organic phase (2) and step a) is: a) Solvent extraction using Contacting the aqueous phase (1) with the second, organic phase (2) so that a concentration gradient is created within the aqueous phase (1) due to the transfer of the rare earth in the form of rare earth ions (3) from the aqueous phase (1) to the second phase (2). [4] A method according to claim 3, comprising the additional step following step b): c) Expulsion for the transfer of the rare earth ions (3) from the second phase (2), which is the organic phase, into a third, aqueous collecting solution. [5] Method according to one of claims 1 to 4, wherein the product of the rare earth-dependent magnetic susceptibility χ and the magnetic field gradient is greater than 0.003 T 2 / m is. [6] A method according to any one of claims 1 to 5, wherein the rare earths are selected from dysprosium, erbium, terbium, holmium and gadolinium. [7] Method according to one of claims 3 to 6, wherein in step a) contact is made with a second, organic phase (2) and the aqueous phase (1) before contacting in step a) has a concentration of dysprosium(III) or erbium(III) or terbium(III) or holmium(III) or gadolinium(III) in the range of 450-550 mM and the magnetic field gradient is at least 7 T 2 / m. [8] Method according to one of claims 1 to 7, wherein the magnet (5) in step b) is a bar magnet selected from bar-shaped permanent magnets, bar-shaped electromagnets and bar-shaped superconducting magnets. [9] Method according to claim 4, wherein also during the expulsion in step c) a magnetic field is applied by means of a magnet (5) to the contact surface between the second, organic phase (2) and the third, aqueous collecting solution, wherein the magnetic field is aligned such that the magnetic field gradient is antiparallel to the concentration gradient of the rare earth ions (3) within the third, aqueous collecting solution in step c) and also in this case the product of the rare earth-dependent magnetic susceptibility χ and the magnetic field gradient is greater than 0.002 T 2 / m is. [10] Process according to one of claims 3 to 9, wherein in step a) contact is made with a second, organic phase (2) and in the solvent extraction in step a) the second, organic phase (2) contains an extractant selected from • the cation exchangers neo-decanoic acid, benzamidine or naphthenic acid, and • the phosphorous acids bis-(2-ethylhexyl)phosphoric acid, mono-2-ethylhexyl (2-ethylhexyl)phosphonate, diisooctylphosphinic acid, diisooctylthiophosphinic acid, or diisooctyldithiophosphinic acid, and • the chelating ion exchanger 1-phenyldecane-1,3-dione, and • the solvent extraction agents tributyl phosphate, dibutyl butylphosphonate or trioctylphosphine oxide, and • the anion exchangers 16,16-dimethylheptadecan-1-amine or methyltrioctylammonium chloride. [11] The process of claim 10, wherein the extractant is mono-2-ethylhexyl (2-ethylhexyl)phosphonate and the rare earth ion is dysprosium(III). [12] Process according to one of claims 3 to 11, wherein in step a) contact is made with a second, organic phase (2), which comprises kerosene, 1-octanol, 2-ethylhexanol, paraffin, or mixtures thereof. [13] Process according to one of claims 3 to 12, wherein in step a) contact is made with a second, organic phase (2) and the two steps a) and b) are carried out in a Hele-Shaw cell.

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