Process for separating rare-earth metals in admixture in aqueous solution

Abstract

To provide a process for separating each element from a mixture containing several elements of rare-earth metals.SOLUTION: Provided is a process for separating two elements E1 and E2, chosen from rare-earth metals, in admixture in aqueous solution AS. The process uses at least one dithiocarbamate salt.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for separating at least two elements selected from the lanthanides, scandium and yttrium, which are admixed in an aqueous solution. [Background technology]

[0002] Rare earth metals are formed from 17 elements, namely the 15 lanthanides: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, as well as scandium and yttrium. The light rare earth metals are used for their exceptional magnetic properties, while the heavy rare earth metals (the most valuable) are used to raise the temperature point at which magnets lose their magnetism.

[0003] They are widespread, particularly in four industrial sectors representing 10% of the world economy: digital (mobile phones, hard disks, screens), energy (offshore wind turbines, electric and hybrid car engines), medicine (instruments, robots) and weapons.

[0004] Their uses are diverse, primarily (31%) permanent magnets (used in generators, flywheels, alternators, toy and watch motors), catalysts (18%) (used in catalytic converters in cars), metallurgical alloys (18%) (used in aeronautical, military and medical constructions, etc.), abrasives (13%) (used on the surfaces of many industrial products), glass and ceramics (11%), and the remaining 9%.

[0005] Permanent magnets are experiencing unstoppable growth. Wind power and low-carbon mobility consume 35% of the global market, with China accounting for 91% of manufacturing. Their rapid growth (wind power consumption is expected to triple by 2030, and electric vehicles tenfold) could challenge the finite supply of rare earth metals.

[0006] There are many methods for purifying elements isolated from rare earth metals. For example, complexing agents such as diethyldithiocarbamate and pyrrolidinedithiocarbamate (see FR2614213) make it possible to remove impurities such as iron and cobalt from aqueous solutions. There are methods for complexing rare earth metal elements and then extracting them using organic solvents. It is also possible to react rare earth metal elements with molecules (oxalate, carbonate, tris(2-aminoethyl)amine) to form insoluble complexes, followed by solid-liquid separation.

[0007] Rare earth metals have similar physical and chemical properties. As a result, it is difficult to separate individual elements from a mixture containing several elements of the rare earth metal system. Previously described methods cannot isolate elements from a mixture containing at least two elements of the rare earth metal system. While a few methods exist for isolating elements from a mixture of rare earth elements, they require complex and energy-intensive reaction conditions (e.g., heating, combustion, electrolysis, reaction with toxic chlorinated gases; see references JP5401497, JP5836349, and JP6789910). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] FR2614213 [Patent Document 2] JP5401497 [Patent Document 3] JP5836349 [Patent Document 4] JP6789910 Summary of the Invention [Means for solving the problem]

[0009] The applicant has discovered and developed a simple, low-cost method that allows for the separation of two elements of the rare earth metals that are mixed in an aqueous solution.

[0010] More specifically, the present invention relates to a method for separating two elements E1 and E2 selected from rare earth metals, admixed in an aqueous solution AS, comprising the following successive steps: a) Formula: R1R2NCS2 - M + adding at least one dithiocarbamate of the formula: (wherein M is an alkali metal cation, and the R1 and / or R2 groups are selected from the group comprising a hydrogen atom, a methyl group, a linear, branched or cyclic, saturated or unsaturated, substituted or unsubstituted carbon chain containing 2 to 20 carbon atoms, which may contain one or more heteroatoms selected from nitrogen and oxygen, and the R1 and R2 groups may together form a ring) to an aqueous solution AS; b) stirring the aqueous solution obtained in step a) for at least 1 minute; c) stopping the stirring and waiting for at least 5 minutes for the formation of a suspension S; d) performing solid-liquid separation on the suspension S to obtain a solid SO containing mainly the element E1 relative to the element E2, and an aqueous solution AS' containing mainly the element E2 relative to the element E1; The method includes:

[0011] The term "mainly" means that the solid SO contains an E1 / E2 ratio of more than 1 / 1, in particular more than 1.5 / 1.

[0012] The term "predominantly" means that the aqueous solution AS' contains an E2 / E1 ratio of more than 1 / 1, in particular more than 1.5 / 1.

[0013] The solution AS subjected to the method of the invention contains two elements E1 and E2 from the group of 17 rare earth metals, including the 15 lanthanides: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, and also scandium and yttrium.

[0014] According to one preferred embodiment, the two elements E1 and E2 are dysprosium and lanthanum, respectively. According to another preferred embodiment, the two elements E1 and E2 are europium and lanthanum, respectively. According to yet another preferred embodiment, the two elements E1 and E2 are yttrium and lanthanum, respectively.

[0015] For the purposes of the present invention, the rare earth elements are in particular present in the solution in the form of cations.

[0016] In particular, the total concentration of elements from rare earth elements that are originally present in the solution AS is in the range of 1 to 10,000 ppm by mass.

[0017] The dithiocarbamate used in step a) of the process of the present invention has the formula: R1R2NCS2 - M + wherein M is an alkali metal cation, the R1 and / or R2 groups are selected from the group comprising a hydrogen atom, a methyl group, a linear, branched, or cyclic, saturated or unsaturated, substituted or unsubstituted carbon chain containing 2 to 20 carbon atoms, which may contain one or more heteroatoms selected from nitrogen and oxygen, and the R1 and R2 groups may together form a ring.

[0018] Preferentially, the cation M is sodium or potassium.

[0019] Advantageously, the dithiocarbamate is chosen from the alkali metal salts of the following compounds: piperazine dithiocarbamic acid, piperidine dithiocarbamic acid, cyclohexylamine dithiocarbamic acid, dimethyl dithiocarbamic acid, diethyl dithiocarbamic acid, dipropyl dithiocarbamic acid, dibutyl dithiocarbamic acid, ethylenediamine dithiocarbamic acid. Preferentially, this compound is piperazine dithiocarbamic acid.

[0020] Preferentially, the dithiocarbamate is potassium piperazinedithiocarbamate.

[0021] Preferentially, to carry out step a) of the process of the invention, the dithiocarbamate is added to the aqueous solution in a concentration of between 0.5% and 60% by weight, and the AS is in the form of an aqueous solution.

[0022] In addition, the method of the invention may preferentially comprise, between steps b) and c), two successive steps b1) and b2), said steps comprising: b1) adding to the solution obtained at the end of step a) a water-soluble polymer P having an average molecular weight between 20,000 and 1,000,000 daltons and stirring for at least 1 minute; b2) adding a water-soluble polymer P' having an average molecular weight of more than 1 million daltons to the solution obtained in step b1) and stirring for at least 1 minute; It consists of:

[0023] One advantage of performing steps b1) and b2) is the reduction in the time required for step c).

[0024] The term "polymer" refers to a natural polymer or a chemically modified natural polymer, or a synthetic homopolymer or copolymer prepared from at least two different monomers.

[0025] Polymer P has a molecular weight between 20,000 and 1 million daltons. Polymer P' has a molecular weight of 1 million daltons or more, preferentially between 1 million and 40 million daltons, more preferentially between 3 million and 30 million daltons. The term "molecular weight" means the weight average molecular weight.

[0026] Molecular weight is determined by the intrinsic viscosity of the polymer, which may be measured via methods known to those skilled in the art and can be calculated from reduced viscosity values ​​for various polymer concentrations by a graphical method consisting of plotting reduced viscosity values ​​(Y-axis) against concentration (X-axis) and extrapolating the curve to zero concentration.

[0027] The intrinsic viscosity value is plotted on the Y-axis or using the least squares method. The molecular weight can then be determined by the Mark-Houink equation: [Number 1] [η]=KM α [η] represents the intrinsic viscosity of the polymer as determined via a method for measuring solution viscosity. K represents an empirical constant. M represents the molecular weight of the polymer. α represents the Mark-Howink coefficient. K and α depend on the particular polymer-solvent system.

[0028] The term "water-soluble polymer" refers to a polymer that is dissolved at 25°C and 10 g.L in deionized water. -1 This indicates a polymer that, when dissolved with stirring at a concentration of 0.1 to 1.25, results in an aqueous solution free of insoluble particles.

[0029] The water-soluble polymer P or P' may be a natural polymer or a chemically modified natural polymer, or a synthetic polymer or a semi-synthetic (or semi-natural) polymer.

[0030] Advantageously, the polymer P is chosen from poly(aluminum chloride), products of the polycondensation reaction of epichlorohydrin with dimethylamine, homopolymers or copolymers of diallyldimethylammonium halides.

[0031] the polymer P' is preferentially synthetic and is composed of at least one anionic hydrophilic monomer and / or at least one cationic hydrophilic monomer and / or at least one non-ionic hydrophilic monomer, nonionic hydrophilic monomers are water-soluble vinyl monomers, such as acrylamide, methacrylamide, N-alkylacrylamide, N-alkylmethacrylamide, N,N-dialkylacrylamide (e.g. N,N-dimethylacrylamide or N,N-diethylacrylamide), N,N-dialkylmethacrylamide, alkoxylated acrylic acid esters, alkoxylated methacrylic acid esters, N-vinylpyrrolidone, N-methylol (meth)acrylamide, N-vinylcaprolactam, N-vinylformamide (NVF), N-vinylacetamide, N-vinylimidazole, N-vinylsuccinic acid imide, acryloylmorpholine (ACMO), glycidyl methacrylate, glyceryl methacrylate, diacetone acrylamide, methacrylic anhydride, acrylonitrile, maleic anhydride, itaconic anhydride, itaconamide, vinylpyridine, hydroxyalkyl (meth)acrylate, thioalkyl (meth)acrylate, isoprenol and its alkoxylated derivatives, hydroxyethyl (meth)acrylate and its alkoxylated derivatives, hydroxypropyl acrylate and its alkoxylated derivatives, vinyl acetate, and mixtures thereof, wherein the alkyl group is a C1-C3 hydrocarbon chain; - Anionic hydrophilic monomers include the monomers acrylic acid, methacrylic acid, dimethylacrylic acid, itaconic acid, C1-C3 hemiesters of itaconic acid, acryloyl chloride, crotonic acid, maleic acid, fumaric acid, 3-acrylamido-3-methylbutanoic acid, vinyl sulfonic acid, vinylphosphonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethyl methacrylate, sulfopropyl methacrylate, sulfopropyl acrylate, allylphosphonic acid, ethylene glycol methacrylate phosphate, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (ATBS), 2-acrylamido-2-methylpropanedisulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and diethyl allylphosphonate (diethylallyl phosphonate), carboxyethyl acrylate; water-soluble salts of all these monomers, for example, their alkali metal, alkaline earth metal, or ammonium salts; and mixtures thereof; The cationic hydrophilic monomer is selected from diallyldialkylammonium salts, such as diallyldimethylammonium chloride (DADMAC); acidified or quaternized salts of dialkylaminoalkyl(meth)acrylamido, such as methacrylamidepropyltrimethylammonium chloride (MAPTAC), acrylamidopropyltrimethylammonium chloride (APTAC), acidified or quaternized salts of dialkylaminoalkyl acrylates, such as quaternized or chlorinated dimethylaminoethyl acrylate (ADAME), acidified or quaternized salts of dialkylaminoalkyl methacrylates, such as quaternized or chlorinated dimethylaminoethyl methacrylate (MADAME), and mixtures thereof.

[0032] The term "hydrophilic monomer" refers to a monomer having an octanol / water partition coefficient, Kow, characterized by log(Kow) of 1 or less, where the Kow partition coefficient is determined at 25°C in an octanol / water mixture having a volume ratio of 1 / 1 at a pH between 6 and 8. [Number 2]

[0033]

number

[0034] The polymer P' may have a linear, branched, star or comb structure, which can be obtained according to the general knowledge of a person skilled in the art.

[0035] The polymers P and P' may be added during steps b1) and b2) in various forms, in particular in liquid form, for example, independently of one another, as a solution, emulsion, dispersion or suspension, or in solid form. The polymers may be in the form of an aqueous solution, an inverse emulsion (water-in-oil), an aqueous suspension, a powder, or a dispersion of the polymer in oil. The polymer P is preferably in the form of an aqueous solution. The polymer P' is advantageously in the form of a powder or an inverse emulsion.

[0036] Generally, the water-soluble polymers P and P' do not require the development of any particular polymerization method. In particular, they can be obtained via any polymerization technique known to those skilled in the art. These can include, inter alia, solution polymerization, gel polymerization, precipitation polymerization, emulsion polymerization (aqueous or inverse), suspension polymerization, reactive extrusion polymerization, water-in-water polymerization, or micellar polymerization.

[0037] The amount of water-soluble polymers P and P' added during steps b1) and b2) is in particular between 1 and 10,000 ppm by weight, preferentially between 10 and 5,000 ppm by weight, in the solution obtained via the process of step a) or b1).

[0038] In step b) of the method of the present invention, the aqueous solution obtained in step a) is stirred for at least 1 minute. Preferentially, this solution is stirred for 1 to 5 minutes. A person skilled in the art knows how to select the appropriate stirring means. In steps b1) and / or b2), the stirring time is comparable to that in step b).

[0039] In step c) of the method of the invention, stirring of the solution obtained from step b) is stopped and the waiting time for the formation of suspension S is at least 5 minutes, in particular 10 or 15 minutes. Preferentially, the waiting time for the formation of suspension S is between 5 minutes and 2 hours.

[0040] In step d) of the process of the invention, the skilled person knows how to select a suitable solid-liquid separation method, which may be, by way of example, a filtration or decantation step.

[0041] In step a) of the method of the invention, the stoichiometric dose, corresponding to the ratio of the anionic charge density of the dithiocarbamate, in particular (PIP-CS2), to the total cationic charge density of the metal elements in the solution AS, is between 100% and 500%, more preferentially between 200% and 500%, and even more preferentially between 250% and 500%.

[0042] The amount of dithiocarbamate added in step a) is determined depending on the cationic charge density of the aqueous solution AS, more precisely, so that the anionic charge of the dithiocarbamate neutralizes the cationic charge of the metal elements present in the aqueous solution AS.

[0043] Aqueous AS solutions are analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the content of each metal element that makes up the solution. These contents, weighted by the molecular weight of each metal element, allow the cationic charge density of the solution to be determined.

[0044] This cationic charge density allows the calculation of the amount of dithiocarbamate to be used to neutralize all cationic charges of the metal element at 100% of the optimal content. Thus, the stoichiometric dosage corresponds to the ratio of the anionic charge density of the dithiocarbamate to the cationic charge density of the metal element solution. If necessary, a small or large amount may be applied relative to this 100% value.

[0045] The invention and its advantages will be more clearly understood in light of the following examples and drawings. [Brief explanation of the drawings]

[0046] [Figure 1] A diagram of Mendeleev's periodic table. The shaded cells represent elements that can be analyzed using ICP-OES techniques. [Figure 2] FIG. 1 shows the evolution of the concentrations of dysprosium and lanthanum in the filtrate obtained from the solution treated with PIP-CS2 according to Example 2. The x-axis represents the stoichiometry of the added PIP-CS2 (expressed as a percentage), while the y-axis represents the concentration of the cations in the solution (expressed in ppm). [Figure 3] FIG. 1 shows the evolution of europium and lanthanum concentrations in filtrates obtained from solutions treated with PIP-CS2 according to Example 3. The x-axis represents the stoichiometry of added PIP-CS2 (expressed as a percentage), while the y-axis represents the concentration of cations in solution (expressed in ppm). [Figure 4] FIG. 1 shows the evolution of yttrium and lanthanum concentrations in filtrates obtained from solutions treated with PIP-CS2 according to Example 4. The x-axis represents the stoichiometry of added PIP-CS2 (expressed as a percentage), while the y-axis represents the concentration of cations in solution (expressed in ppm). [Example]

[0047] ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) Analysis Method: ICP-OES technology is a technique that allows the analysis of most of the elements in Mendeleev's periodic table (Figure 1).

[0048] The principle of ICP-OES consists of introducing a sample containing the analyte of interest, which is then ionized by an argon plasma. By definition, plasma is a fully ionized but electrically neutral gas (free electrons and ions are present). It is sometimes likened to a flame and has a temperature that can be up to 10,000 K.

[0049] The sample first enters the chamber in liquid state and in the form of an aerosol. The function of the chamber is to produce a homogeneous aerosol at its exit, which is carried to the torch by the argon flow. The energy provided by the plasma then allows the vaporization, atomization, and ultimately ionization of the various elements in the injected sample.

[0050] These various elements (atoms) will therefore absorb the photons produced by the plasma, causing electrons in these elements to move to higher energy electron shells. When excited, atoms lose energy by emitting one or more photons depending on the state of excitation. These photons are characterized by an energy that can be related to the wavelength λ according to the Planck-Einstein relation:

[0051]

number

[0052] (E: photon energy (unit: joule), h: Planck's constant (6.63 x 10 -34 Js), c: the speed of light in a vacuum, λ: the wavelength (in meters) of the electromagnetic wave associated with the photon under consideration. Using the instrument's light sensors and detectors, these wavelengths are determined, allowing the identification and quantification of the compounds present.

[0053] Depending on each element under consideration and taking into account our specific matrix, a protocol has been developed:

[0054] Sample preparation: - Control sample: 1 mL of a solution containing 10 ppm of the salt of the element is diluted with 9 mL of 5% by weight nitric acid in water. - Chelation sample: Add 2 drops of 69% by weight nitric acid to 10 mL of sample.

[0055] The corresponding solutions are injected into an ICP-OES 5800 (Agilent) using the following parameters: - 1.2kW RF ICP power - Carrier gas: Argon flow rate 0.7 L / min

[0056] The elements La and Dy were analyzed by axial observation. The elements Y and Eu were analyzed by lateral observation with a measurement height of 8 mm. Calibration curves were obtained for each element from 0.1 ppm to 5 ppm using standard Agilent solutions.

[0057] Formula:R1R2NCS2 - M + Determination of the anionic charge density of dithiocarbamate of PIP-CS2 The charge density of the compound PIP-CS2 is calculated from the colloidal charge (meq / g), which is determined by a colloidal assay using methyl glycol chitosan (MGC) and potassium polyvinyl sulfate (PVSK).

[0058] A 5 g / L solution of PIP-CS2 was prepared by diluting 1.00 g of PIP-CS2 equivalent (dry extract) in a 200 mL beaker with magnetic stirring and adding deionized water in an amount appropriate for the initial PIP-CS2 concentration. Once the 5 g / L PIP-CS2 solution was homogenous, 0.25 g of the solution was weighed out and 100 mL of deionized water was added. The pH was adjusted accurately to 10.4-10.6 using 0.1 N acid or sodium hydroxide. While stirring, exactly 5 mL of MGC (1 / 200 N) was added, followed by 3 drops of toluidine blue, and the solution was assayed in PVSK (1 / 400 N).

[0059] When the blue color changes to purple and remains purple for 20 seconds, the equivalence point is reached, and the amount of PVSK introduced (unit: milliliter) is designated as A.

[0060] The same measurement was carried out without adding (PIP-CS2), and the amount of PVSK (unit: milliliter) was designated as B.

[0061] The anionic charge density is calculated using the following formula: [Number 3] C(meq / g)=(BA)×N PVSK / (5×m×10 -3 ) [In the formula, m = mass of PIP-CS2 solution at 5g / L N PVSK = normality of PVSK solution, = f / 400, the factor f is given by the supplier WAKO].

[0062] Stoichiometric assay of aqueous solutions containing metal elements The solution is analyzed by ICP-OES to determine the content of each metal element that makes up the solution, which is weighted by the molecular weight of each metal element, allowing the cationic charge density of the solution to be determined.

[0063] This cationic charge density allows the calculation of the amount of (PIP-CS2) to be used to neutralize all cationic charges of the metal element at an optimal content of 100%. The stoichiometric dose therefore corresponds to the ratio of the anionic charge density of (PIP-CS2) to the cationic charge density of the metal element solution. If necessary, a small or large dose may be applied relative to this optimal 100% value.

[0064] Example to clarify calculation of stoichiometric percentage: For an aqueous solution (1000 g) containing 20 ppm copper(II), the amount of (PIP-CS2) with 100% stoichiometry (charge density: 2.55 meq / g) is determined according to the following formula: [Number 4] Q = (TS / 100) * (C 金属 *VAL 金属 ) / (MW 金属 * D / 1000) [In the formula, TS=Target stoichiometry (%) Q = Amount of (PIP-CS2) to be added (unit: ppm) C 金属 = Metal concentration (unit: ppm) VAL 金属 = Metal valence MW 金属 : Molecular weight of metal (g / mol) D = charge density of compound (PIP-CS2) (meq / g)]

[0065] Thus, for 100% stoichiometry, 247 ppm of (PIP-CS2) is required.

[0066] Example 1 Synthesis of the potassium salt of the compound (PIP-CS2) 51 g of water, 288 g of potassium hydroxide (50% by weight in water), and 112 g of solid piperazine (PIP) are introduced into a 1 L double-jacketed reactor equipped with a motor, a stirring paddle, and a condenser. The resulting mixture is mixed for 15 minutes and maintained at 35°C using a cold air generator through the double jacket of the reactor.

[0067] The dropping funnel is charged with 198 g of CS2 and attached to a 1 L reactor. The CS2 is added dropwise to the reactor in this way over a period of 80 minutes. The temperature of the reaction medium is maintained at 40°C, and water is supplied to the condenser to prevent loss of CS2. The reaction medium acquires a reddish color, which reflects the progress of the reaction. After the addition of CS2, the medium is maintained at 40°C for 120 minutes with stirring, then cooled to 25°C.

[0068] After adding 350 g of deionized water, the resulting solution is an aqueous solution containing 40% by weight of the compound (PIP-CS2).

[0069] Treatment of solutions containing metal elements

[0070] Example 2 To a 2 L volumetric flask containing a Teflon®-coated magnetic bar, add 2 L of deionized water containing 41 mg of dysprosium chloride hexahydrate (DyCl3·6H2O) and 53.5 mg of lanthanum chloride heptahydrate (LaCl3·7H2O) to obtain a solution containing 10 ppm of dysprosium salts and 10 ppm of lanthanum salts. Perform ICP-OES analysis to determine the initial amount of each element in the solution (to avoid variability in hydration between salts due to storage conditions).

[0071] The (PIP-CS2) solution (Example 1) is diluted to 1% (by weight) by mixing 150 mg with 6 g of deionized water.

[0072] The aqueous solution containing dysprosium and lanthanum is gently stirred and the diluted (PIP-CS2) solution is added (amount adjusted to obtain the desired stoichiometry of (PIP-CS2)).

[0073] The mixture is stirred for 60 seconds and a precipitate appears.

[0074] The stirring is stopped and the suspension is left to settle for 60 minutes. The resulting solution is filtered (0.45 μ Sartorius filter) to separate the solid and liquid.

[0075] The filtrate is analyzed by ICP-OES to determine the concentrations of dysprosium and lanthanum elements. The analysis of the filtrate during processing is shown in Figure 2.

[0076] 1998.5 g of filtrate solution is recovered (after filtration at 500% stoichiometry). The filtrate contains 1.1 ppm dysprosium and 6.8 ppm lanthanum.

[0077] On the filter, 1.5 g of solid is recovered, which contains 9200 ppm of dysprosium and 3600 ppm of lanthanum (analysis by ICP-OES).

[0078] In this way, the compound (PIP-CS2) enriches dysprosium in the precipitates formed.

[0079] Example 3 To a 2 L volumetric flask containing a Teflon®-coated magnetic bar, add 2 L of deionized water containing 41 mg of hydrated europium chloride (EuCl3·xH2O) and 53.5 mg of lanthanum chloride heptahydrate (LaCl3.7H2O) to obtain a solution containing 10 ppm europium salts and 10 ppm lanthanum iron. Perform ICP-OES analysis to determine the initial amount of each element in the solution (to avoid variability in hydration between salts due to storage conditions).

[0080] The (PIP-CS2) solution (Example 1) is diluted to 1% (by weight) by mixing 160 mg with 6.17 g of deionized water.

[0081] The aqueous solution containing europium and lanthanum is gently stirred and the diluted (PIP-CS2) solution is added (amount adjusted to obtain the desired stoichiometry of (PIP-CS2)).

[0082] The mixture is stirred for 60 seconds and a precipitate appears.

[0083] The stirring is stopped and the suspension is left to settle for 60 minutes. The resulting solution is filtered (0.45 μ Sartorius filter) to separate the solid and liquid.

[0084] The filtrate is analyzed by ICP-OES to determine the concentration of europium and lanthanum elements. The analysis of the filtrate during processing is shown in Figure 3.

[0085] 1998.3 g of filtrate solution is recovered (after filtration at 500% stoichiometry). The filtrate contains 1.73 ppm europium and 6.8 ppm lanthanum.

[0086] On the filter, 1.7 g of solid is recovered, which contains 3176 ppm of lanthanum and 7141 ppm of europium (analysis by ICP-OES).

[0087] In this way, the compound (PIP-CS2) enriches europium in the precipitate formed.

[0088] Example 4 To a 2 L volumetric flask containing a Teflon-coated magnetic bar, add 2 L of deionized water containing 49.5 mg of hydrated yttrium chloride (Yl3 xHO) and 53.5 mg of lanthanum chloride heptahydrate (LaCl3.7HO) to obtain a solution containing 10 ppm yttrium salt and 10 ppm lanthanum salt equivalents. Perform ICP-OES analysis to determine the initial amount of each element in the solution (to avoid variability in hydration between salts due to storage conditions).

[0089] The (PIP-CS2) solution (Example 1) is diluted to 1% (by weight) by mixing 210 mg with 8.25 g of deionized water.

[0090] The aqueous solution containing yttrium and lanthanum is gently stirred and the diluted (PIP-CS2) solution is added (amount adjusted to obtain the desired (PIP-CS2) stoichiometry).

[0091] The mixture is stirred for 60 seconds and a precipitate appears.

[0092] The stirring is stopped and the suspension is left to settle for 60 minutes. The resulting solution is filtered (0.45 μ Sartorius filter) to separate the solid and liquid.

[0093] The filtrate is analyzed by ICP-OES to determine the concentration of yttrium and lanthanum elements. The analysis of the filtrate during processing is presented in Figure 4.

[0094] 1997.9 g of filtrate solution is recovered (after filtration at 500% stoichiometry). The filtrate contains 2.15 ppm yttrium and 6.8 ppm lanthanum.

[0095] On the filter, 2.12 g of solid is recovered, which contains 2665 ppm of lanthanum and 4504 ppm of yttrium (analysis by ICP-OES).

[0096] In this way, the compound (PIP-CS2) enriches yttrium in the precipitates formed.

[0097] Example 5 The operating conditions of Example 2 are repeated. The (PIP-CS2) solution (Example 1) is diluted to 1% (by weight) by mixing 150 mg with 6 g of deionized water.

[0098] The aqueous solution containing dysprosium and lanthanum is gently stirred, and a diluted polymer (PIP-CS2) solution is added (adjusted to obtain 100% stoichiometry of (PIP-CS2)). The solution is stirred for 1 minute. Next, 0.5 mL of a solution containing 1% of the coagulant PAC 18 (polyaluminum chloride, average molecular weight between 20,000 and 1,000,000 daltons) is added, and the solution is stirred for 1 minute. Finally, 0.5 mL of a solution containing 0.5 g / L of an anionic flocculant (FlopamAN 934 VHM, average molecular weight greater than 1,000,000 daltons) is added, and the solution is left stirring for 1 minute.

[0099] The mixture is stirred at 200 rpm for 60 seconds, then reduced to 50 rpm and continued for 5 minutes to allow flocs to form.

[0100] The stirring is stopped and the suspension is left to settle for 10 minutes. The resulting solution is filtered (0.45 μ Sartorius filter) to separate the solid and liquid.

[0101] The dysprosium and lanthanum contents in the solid and in the filtrate remain comparable to those obtained in Example 2. However, the processing times (sedimentation, solid-liquid separation) are shorter than those in Example 2.

Claims

1. A method for separating two elements E1 and E2 selected from rare earth metals admixed in an aqueous solution AS, comprising the following successive steps: a) Formula: R1R2NCS2 - M + adding at least one dithiocarbamate of formula (I) to an aqueous solution AS, wherein M is an alkali metal cation and the R1 and / or R2 groups are selected from the group comprising a hydrogen atom, a methyl group, a linear, branched or cyclic, saturated or unsaturated, substituted or unsubstituted carbon chain containing from 2 to 20 carbon atoms, which may contain one or more heteroatoms selected from nitrogen and oxygen, and the R1 and R2 groups may together form a ring; b) stirring the aqueous solution obtained in step a) for at least 1 minute; c) stopping the stirring and waiting for at least 5 minutes for the formation of a suspension S; d) performing solid-liquid separation on the suspension S to obtain a solid SO containing mainly the element E1 relative to the element E2, and an aqueous solution AS' containing mainly the element E2 relative to the element E1; A method comprising:

2. 2. The method according to claim 1, wherein the cation M is sodium or potassium.

3. 3. The method according to claim 1 or 2, characterized in that the dithiocarbamate is selected from the alkali metal salts of the following compounds: piperazine dithiocarbamic acid, piperidine dithiocarbamic acid, cyclohexylamine dithiocarbamic acid, dimethyl dithiocarbamic acid, diethyl dithiocarbamic acid, dipropyl dithiocarbamic acid, dibutyl dithiocarbamic acid, ethylene diamine dithiocarbamic acid.

4. 3. The method according to claim 1, wherein the dithiocarbamate is potassium piperazinedithiocarbamate.

5. 3. The method according to claim 1, wherein in step a) the dithiocarbamate is present in aqueous solution at a concentration of between 0.5% and 60% by weight.

6. 3. The method according to claim 1 or 2, characterized in that the two elements E1 and E2 are dysprosium and lanthanum, respectively.

7. 3. The method according to claim 1, wherein the two elements E1 and E2 are europium and lanthanum, respectively.

8. 3. The method according to claim 1, wherein the two elements E1 and E2 are yttrium and lanthanum, respectively.

9. The method comprises, between steps b) and c), two sequential steps b1) and b2), which steps b1) adding a water-soluble polymer P having an average molecular weight between 20,000 and 1,000,000 Daltons to the solution and stirring for at least 1 minute; b2) adding a water-soluble polymer P' having an average molecular weight of more than 1 million daltons to the solution and stirring for at least 1 minute; 3. The method according to claim 1 or 2, characterized in that it comprises:

10. 3. The method according to claim 1 or 2, characterized in that in step a) of the method, the stoichiometric dosage, corresponding to the ratio of the anionic charge density of the dithiocarbamate to the total cationic charge density of the rare earth metals in the solution AS, is between 100% and 500%.

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