METHOD FOR SEPARING RARE EARTHS IN AQUEOUS SOLUTION MIXTURE

Abstract

METHOD FOR SEPARING RARE EARTH ELEMENTS IN A MIXTURE IN AQUEOUS SOLUTION The invention relates to a method for separating two elements E1 and E2, selected from rare earth elements, in a mixture in aqueous solution SA. The method uses at least one dithiocarbamate salt. (no figures)

Description

Title of the invention: METHOD FOR SEPARING RARE EARTHS IN AQUEOUS SOLUTION MIXTURE Scope of the invention

[0001] The present invention relates to a method for separating at least two elements selected from the lanthanides, scandium and yttrium, in a mixture in aqueous solution. prior state of the art

[0002] The “rare earths” consist of 17 elements: 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 lighter "rare earths" are used for their exceptional magnetic properties, and the heavier "rare earths" (the most valuable ones) are used to raise the temperature point at which magnets lose their magnetism.

[0003] They are omnipresent, especially in four industrial sectors which represent 10% of the world economy: digital (mobile phones, hard drives, screens); energy (offshore wind turbines, electric and hybrid car engines); medical (devices, robots); armaments.

[0004] Their uses are diverse: the first (31%) being permanent magnets (used in generators, flywheels, alternators, toy and clock motors); catalysts (18%) (used in catalytic converters for cars); metallurgical alloys (18%) (used in aeronautical, military, medical construction, etc.); polishing (13%) (used on the surface of many industrial products); glasses and ceramics (11%); the rest representing 9%.

[0005] Permanent magnets are experiencing unbridled growth. Wind power and low-carbon mobility consume 35% of the global market, with China accounting for 91% of production. Their rapid growth (consumption will triple by 2030 for wind power and increase tenfold for electric vehicles) could be hampered by a limited supply of rare earth elements.

[0006] Numerous methods exist for purifying an isolated rare earth element. For example, complexing agents such as diethyldithiocarbamate, pyrrolidine dithiocarbamate (see document FR2614213) can remove impurities such as iron and cobalt in aqueous solution. Extraction methods using organic solvents exist after complexing a rare earth element. It is also possible to react a rare earth element with a molecule (oxalate, carbonate, tris(2-aminoethyl)amine) to form an insoluble complex and proceed with a liquid-solid separation.

[0007] Rare earth elements have similar physical and chemical properties. Therefore, it is difficult to separate each element from a mixture containing several elements of the rare earth series. The methods described above do not allow the isolation of an element from a mixture of elements containing at least two rare earth elements. While some methods exist for isolating an element 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 documents JP5401497, JP5836349, JP6789910). Description of the invention

[0008] The Applicant has found and developed a simple, inexpensive process for separating two elements from the "rare earths" in a mixture in aqueous solution.

[0009] More specifically, the invention is a method for separating two elements El and E2, chosen from rare earths, in a mixture in aqueous solution SA, said method comprising the following successive steps:

[0010] a) add to the aqueous solution SA at least one dithiocarbamate salt of formula: R1R2NCS2 M+, in which M is an alkali metal cation, the RI and / or R2 groups are chosen from the group comprising a hydrogen atom, a methyl group, a carbon chain comprising 2 to 20 carbon atoms unsaturated or not, substituted or not, which may comprise one or more heteroatoms chosen from nitrogen and oxygen, linear, branched or cyclic, the RI and R2 groups being able to form a ring between them;

[0011] b) stir the aqueous solution obtained in step a) for at least 1 minute;

[0012] c) stop the agitation and wait at least 5 minutes for the formation of a suspension S

[0013] d) perform a liquid / solid separation on the suspension S to obtain a solid SO containing predominantly the element El relative to the element E2 and an aqueous solution SA' containing predominantly the element E2 relative to the element El.

[0014] By "mostly" means an E1 / E2 ratio, included in the solid SO, greater than 1 / 1, in particular greater than 1.5 / 1.

[0015] By "mostly" means an E2 / E1 ratio, included in the aqueous solution SA', greater than 1 / 1, in particular greater than 1.5 / 1.

[0016] The solution SA subjected to the process of the invention contains 2 elements El and E2 among the 17 "rare earths", said "rare earths" comprising 15 lanthanides: lanthanum; cerium; praseodymium; neodymium; promethium; samarium; europium; gadolinium; terbium; dysprosium; holmium; erbium; thulium; ytterbium and lutetium, as well as scandium and yttrium.

[0017] According to a preferred embodiment, the two elements El and E2 are dysprosium and lanthanum, respectively. According to another preferred embodiment, the two elements El and E2 are europium and lanthanum, respectively. According to yet another preferred embodiment, the two elements El and E2 are yttrium and lanthanum, respectively.

[0018] For the purposes of the invention, "rare earth elements" are notably present in the solution in a cationic form.

[0019] In particular, the total concentration of elements among the rare earths, initially present in the SA solution is between 1 and 10,000 ppm by weight.

[0020] The dithiocarbamate salt, used in step a) of the process of the invention, has the formula: R1R2NCS2 M+ in which M is an alkali metal cation, the RI and / or R2 groups are chosen from the group comprising a hydrogen atom, a methyl group, a carbon chain comprising 2 to 20 carbon atoms, unsaturated or not, substituted or not, which may comprise one or more heteroatoms chosen from nitrogen and oxygen, linear, branched or cyclic, the RI and R2 groups being able to form a ring between them.

[0021] Preferably, the cation M is sodium or potassium.

[0022] Advantageously, the dithiocarbamate salt is selected from the alkali metal salts of the following compounds: piperazine dithiocarbamate, piperidine dithiocarbamate, cyclohexylamine dithiocarbamate, dimethyl dithiocarbamate, diethyl dithiocarbamate, dipropyl dithiocarbamate, dibutyl dithiocarbamate, and ethylenediamine dithiocarbamate. Preferably, this compound is piperazine dithiocarbamate.

[0023] Preferably, the dithiocarbamate salt is potassium piperazine dithiocarbamate.

[0024] Preferably, for carrying out step a) of the process of the invention, the dithiocarbamate salt is added to the aqueous solution at a concentration of between 0.5 and 60% by weight, SA being in the form of aqueous solution.

[0025] Furthermore, the process of the invention may preferably comprise two successive steps b1) and b2) between steps b) and c), said steps consisting of:

[0026] bl) Add to the solution obtained at the end of step a) a water-soluble polymer P of average molecular weight between 20,000 and 1 million daltons and stir for at least 1 minute.

[0027] b2) Add to the solution obtained in step bl) a water-soluble polymer P' with an average molecular weight greater than 1 million daltons and shake for at least 1 minute.

[0028] One of the advantages of implementing steps bl) and b2) is the reduction of the time of step c).

[0029] By "polymer" is meant a natural polymer or a chemically modified natural polymer or a synthetic homopolymer or copolymer prepared from at least two different monomers.

[0030] Polymer P has a molecular weight between 20,000 and 1 million daltons. Polymer P' has a molecular weight greater than or equal to 1 million daltons, preferably between 1 and 40 million daltons, more preferably between 3 and 30 million daltons. Molecular weight is understood to be the average molecular weight by weight.

[0031] The molecular weight is determined by the intrinsic viscosity of the polymer. The intrinsic viscosity can be measured by methods known to those skilled in the art and can be calculated from the reduced viscosity values ​​for different polymer concentrations by a graphical method consisting of plotting the reduced viscosity values ​​(ordinate axis) on the concentration (abscissa axis) and extrapolating the curve down to zero concentration.

[0032] The intrinsic viscosity value is measured on the y-axis or using the least squares method. The molecular weight can then be determined using the Mark-Houwink equation:

[0033] [q] = KM" [q] represents the intrinsic viscosity of the polymer determined by the solution viscosity measurement method. K represents an empirical constant. M represents the molecular weight of the polymer. a represents the Mark-Houwink coefficient. K and a depend on the particular polymer-solvent system.

[0034] By "water-soluble polymer" is meant a polymer which gives an aqueous solution without insoluble particles when dissolved under stirring at 25°C and with a concentration of 10 gL 1 in deionized water.

[0035] The water-soluble polymers P or P' can be natural polymers or chemically modified natural polymers or synthetic polymers or semi-synthetic (or semi-natural) polymers.

[0036] Advantageously, polymer P is chosen from poly(aluminum chloride), the product of the polycondensation reaction between epichlorohydrin and dimethylamine, diallyldimethyl ammonium halide homopolymers or copolymers.

[0037] The polymer P' is preferably synthetic and 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,

[0038] - the non-ionic hydrophilic monomer(s) being chosen from the group including water-soluble vinyl monomers, such as acrylamide, methacrylamide, N-alkylacrylamides, N-alkylmethacrylamides, N,N-dialkyl acrylamides (e.g., N,N-dimethylacrylamide or N,N-diethylacrylamide), N,N-dialkylmethacrylamides, alkoxylated esters of acrylic acid, alkoxylated esters of methacrylic acid, N-vinylpyrrolidone, N-methylol(meth)acrylamide, N-vinyl caprolactam, N-vinylformamide (NVF), N-vinyl acetamide, N-vinyl imidazole, N-vinyl succinimide, acryloyl morpholine (ACMO), glycidyl methacrylate, glyceryl methacrylate, and diacetone acrylamide, methacrylic anhydride, acrylonitrile, maleic anhydride, itaconic anhydride, itaconamide, vinylpyridine, hydroxyalkyl (meth)acrylates, thioalkyl (meth)acrylates, isoprenol and its alkoxylated derivatives, hydroxyethyl (meth)acrylates and their alkoxylated derivatives, hydroxypropylacrylate and its alkoxylated derivatives,vinyl acetate, and mixtures thereof, the alkyl groups being C1-C3 hydrocarbon chains;

[0039] - the anionic hydrophilic monomer(s) being chosen from among the monomers acrylic acid, methacrylic acid, dimethylacrylic acid, itaconic acid, C1-C3 itaconic acid hemi-esters, acryloyl chloride, crotonic acid, maleic acid, fumaric acid, 3-acrylamido-3-methylbutanoic acid, vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, methallylsulfonic acid, 2-methylidenepropane-1,3-disulfonic acid, 2-sulfoethyl methacrylate, sulfopropyl methacrylate, sulfopropylacrylate, allylphosphonic acid, ethylene glycol methacrylate phosphate, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid (ATBS), 2-acrylamido-2-methylpropane disulfonic acid 3-allyloxy-2-hydroxypropane sulfonic acid, diethylallylphosphonate, carboxyethyl acrylate; water-soluble salts of all these monomers as their alkali metal, alkaline earth metal, or ammonium salts; and mixtures thereof;

[0040] - the cationic hydrophilic monomer(s) being chosen from the salts of diallyldialkyl ammonium such as diallyl-1-dimethyl ammonium chloride (DADMAC); acidified or quaternized salts of dialkyl-aminoalkyl(meth)acrylamides, such as methacrylamidopropyl trimethyl chloride ammonium (MAPTAC), acrylamidopropyl trimethyl ammonium chloride (APTAC), acidified or quaternized salts of dialkyl-aminoalkyl acrylate such as quaternized or salified dimethylaminoethyl acrylate (ADAME), acidified or quaternized salts of dialkyl aminoalkyl methacrylate such as quaternized or salified dimethylaminoethyl methacrylate (MADAME), and mixtures thereof.

[0041] By "hydrophilic monomer" is meant a monomer which has an octanol / water partition coefficient, Kow, less than or equal to 1, in which the partition coefficient Kow is determined at 25 °C in an octanol / water mixture having a volume ratio of 1 / 1, at a pH between 6 and 8.

[0042] [Math.2] \monomer\ Aow~ [monomer]^

[0043] The polymer P' can have a linear, branched, star-shaped or comb-shaped structure. This structure can be obtained, according to the general knowledge of a person skilled in the art.

[0044] The polymers P and P' can be added in steps 1b) and 1b) in various forms, including liquid form, for example as a solution, emulsion, dispersion, or suspension, or solid form, independently of each other. The polymers can 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. Polymer P is preferably in the form of an aqueous solution. Polymer P' is advantageously in the form of a powder or an inverse emulsion.

[0045] In general, water-soluble polymers P and P' do not require the development of a specific polymerization process. Indeed, they can be obtained using all polymerization techniques well known to those skilled in the art. These may include, in particular, solution polymerization; gel polymerization; precipitation polymerization; emulsion polymerization (aqueous or reverse); suspension polymerization; reactive extrusion polymerization; water-in-water polymerization; or micellar polymerization.

[0046] The quantity of water-soluble polymers P and P' added during steps bl) and b2) is in particular from 1 to 10,000 ppm by weight in the solution obtained in step a) or bl) of the process, preferably between 10 and 5,000 ppm by weight.

[0047] For step b) of the process of the invention, the aqueous solution obtained in step a) is stirred for at least 1 minute. Preferably, this solution is stirred for between 1 and 5 minutes. A person skilled in the art will know how to choose the appropriate stirring method. For steps b1) and / or b2), the stirring times are of the same order of magnitude as for step b).

[0048] For step c) of the process of the invention), the stirring of the solution from step b) is stopped to wait at least 5 minutes, in particular 10 minutes or 15 minutes, for the formation of a suspension S. Preferably the waiting time for the formation of the suspension S is between 5 minutes and 2 hours.

[0049] For step d) of the process of the invention, a person skilled in the art would know how to choose the appropriate liquid / solid separation method. By way of example, this method could be a filtration or decantation step.

[0050] For step a) of the process of the invention, the stoichiometric dosage corresponding to the ratio between the anionic charge density of the dithiocarbamate salt, in particular of (PIP-CS2), and the total cationic charge density of the metallic elements in the SA solution is between 100 and 500%, more preferably between 200 and 500% and even more preferably between 250 and 500%.

[0051] The amount of dithiocarbamate salt added in step a) is determined as a function of the cationic charge density of the aqueous solution SA. More precisely, it is determined such that the anionic charges of the dithiocarbamate salt neutralize the cationic charges of the metallic elements present in the aqueous solution SA.

[0052] The aqueous solution SA is analyzed by Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) to determine the concentration of each metallic element it contains. These concentrations, weighted by the molecular weight of each metallic element, allow the cationic charge density of the solution to be determined.

[0053] This cationic charge density allows the calculation of the quantity of dithiocarbamate salt to be used to neutralize all cationic charges of the metallic elements to an optimal concentration of 100%. The stoichiometric titration therefore corresponds to the ratio between the anionic charge density of the dithiocarbamate salt and the cationic charge density of the metallic element solution. If necessary, an under-dosage or overdosage can be applied compared to this value of 100%.

[0054] The invention and its advantages will become more apparent in the light of the following examples and figures.

[0055] [Fig.1]

[0056] Figure 1 represents Mendeleev's periodic table. The shaded cells represent the elements that can be analyzed by ICP-OES technology.

[0057] [Fig.2]

[0058] Fig. 2 represents the evolution of the concentration of disprosium and lanthanum in the filtrate from the solution treated with PIP-CS2, according to example 2. The x-axis represents the stoichiometry, expressed in %, of the PIP-CS2 added, the y-axis represents the concentration of the cations in the solution, expressed in ppm.

[0059] [Fig.3]

[0060] Fig. 3 represents the evolution of the concentration of europium and lanthanum in the filtrate from the solution treated with PIP-CS2, according to example 3. The x-axis represents the stoichiometry, expressed in %, of the PIP-CS2 added, the y-axis represents the concentration of the cations in the solution, expressed in ppm.

[0061] [Fig.4]

[0062] Figure 4 shows the evolution of the concentration of yttrium and lanthanum in the filtrate obtained from the solution treated with PIP-CS2, according to Example 4. The x-axis represents the stoichiometry, expressed as a percentage, of the PIP-CS2 added; the y-axis represents the concentration of the cations in the solution, expressed in ppm. EXAMPLES#:

[0063] ICP-OES (Inductively Coupled Plasma - Optical Emission) analysis method Spectrometry):

[0064] ICP-OES technology is a technique allowing the analysis of most of the elements of the Mendeleev periodic table ([Fig. 1]).

[0065] The principle of ICO-OES consists of introducing a sample containing the analytes of interest, which is then ionized by an argon plasma. By definition, a plasma is a fully ionized but electrically neutral gas (containing free electrons and ions). This can be likened to a flame with a temperature reaching 10,000 K.

[0066] The sample first enters a chamber in liquid and aerosol form. The chamber's function is to generate a homogeneous aerosol at the outlet, which is conveyed to the torch by a flow of argon. The energy then supplied by the plasma enables the vaporization, atomization, and finally ionization of the various elements of the injected sample.

[0067] These different elements (atoms) will therefore absorb photons generated by the plasma, which will cause the electrons of these elements to shift to more energetic electron shells. Once excited, the atoms will lose energy by emitting one or more photons, depending on their state of excitation. These photons are characterized by an energy that can be related to a wavelength λ, according to the Planck-Einstein relation E = λ / λ, where E is the energy of the photon (in wavelengths). Joules), h is Planck's constant (6.63 x 10³⁴ J·s, c is the speed of light in a vacuum, and 1 is the frequency (in hertz) of the electromagnetic wave associated with the photon in question). Thanks to the optical sensors and detectors of the measuring device, these wavelengths are identified, thus allowing the identification and quantification of the compounds present.

[0068] Depending on each element considered and taking into account our specific matrices, here is the protocol put in place:

[0069] Sample preparation:

[0070] - Control sample: 1 mL of the solution containing 10 ppm of the salt of the element is diluted with 9 ml of 5% by weight nitric acid in water.

[0071] - Samples after chelation: 2 drops of 69% by weight nitric acid are added to 10 ml of the samples.

[0072] The corresponding solutions are injected into the ICP-OES 5800 (Agilent), using the following parameters:

[0073] - ICP RF power of 1.2 kW

[0074] - Carrier gas: argon flow rate of 0.7 L / min.

[0075] Elements La, Dy were analyzed in axial view. Elements Y and Eu were analyzed in radial view with a measurement height of 8 mm. Calibration from 0.1 ppm to 5 ppm was obtained using the Agilent standard solution for each element.

[0076] Determination of the anionic charge density of a dithiocarbamate salt of formula: 1^1^ NCS2 M+ (called: PIP-CS2)

[0077] The charge density of the PIP-CS2 compound is calculated from the colloidal charge (meq / g), determined by colloidal assay using methyl glycol chitosan (MGC) and potassium polyvinyl sulfate (PVSK).

[0078] A solution containing 5 g / L of (PIP-CS2) is prepared by diluting, under magnetic stirring, 1.00 g of (PIP-CS2) equivalent (dry extract) in a 200 mL beaker, the amount of deionized water added depending on the initial concentration of PIP-CS2. When the 5 g / L PELCS2 solution is homogeneous, weigh out 0.25 g of the solution and add 100 mL of deionized water. Adjust the pH precisely between 10.4 and 10.6 with 0.1 N acid or sodium hydroxide. Under stirring, add exactly 5 mL of MGC (1 / 200 N), then 3 drops of toluidine blue, and titrate with PVSK (1 / 400 N).

[0079] The equivalence point is reached when the blue color changes to violet and remains violet for 20 seconds; the quantity in milliliters of PVSK introduced is denoted A

[0080] The same measurement is carried out without the addition of (PIP-CS2), and the quantity in millilitres of PVSK is noted as B

[0081] The anionic charge density is calculated using the following formula:

[0082] [Math 3]

[0083] C(meq / g) = (BA) x Npvsk / (5 xm xlO3)

[0084] Where m = mass of PIP-CS2 solution at 5 g / L

[0085] Npvsk = normality of the PVSK solution, = f / 400, with factor f given by the supplier WAKO.

[0086] Stoichiometric titration of an aqueous solution containing metallic elements

[0087] The solution is analyzed by ICP-OES to determine the concentration of each metallic element it contains. This concentration, weighted by the molecular weight of each metallic element, allows the cationic charge density of the solution to be determined.

[0088] This cationic charge density allows the calculation of the quantity of (PIP-CS2) to be used to neutralize all cationic charges of the metallic elements to an optimal concentration of 100%. The stoichiometric dosage therefore corresponds to the ratio between the anionic charge density of (PIP-CS2) and the cationic charge density of the metallic element solution. If necessary, an under-dosage or overdosage can be applied compared to this optimal value of 100%.

[0089] Example to clarify the calculation of the stoichiometric %:

[0090] For an aqueous solution (1000 g) containing 20 ppm of copper II, the amount of (PIP CS2) (with charge density: 2.55 meq / g) required to achieve 100% stoichiometry is determined according to the following formula:

[0091] [Math 4]

[0092] Q = (ST / 100) * (Cmetal * VALmetal / (MWmetal * D / 1000)

[0093] With ST = target stoichiometry (%)

[0094] Q = quantity of (PIP-CS2) to be added (in ppm)

[0095] Cmetal = metal concentration (in ppm)

[0096] VALmetal = metal valence

[0097] MWmetal: molecular mass of metal (g / mol)

[0098] D = charge density of the compound (PIP-CS2) (meq / g)

[0099] Thus for 100% stoichiometry, 247 ppm of (PIP-CS2) is required.

[0100] Example 1: Synthesis of a compound (PIP-CS2) in the form of a salt of potassium

[0101] In a double-jacketed IL reactor equipped with a motor, a stirring blade, and a condenser, 51 g of water, 288 g of potassium hydroxide (50% by weight in water), and 112 g of solid piperazine (PIP) are loaded. The mixture is stirred for 15 minutes and maintained at 35 °C by a cooling unit via the reactor's double jacket.

[0102] A dropping funnel is loaded with 198 g of CS2 and fitted onto the IL reactor. The CS2 is added to the reactor dropwise for 80 min. The temperature of the reaction medium is maintained at 40°C, and water is supplied to the condenser to prevent CS2 loss. The reaction medium turns reddish, indicating the progress of the reaction. After the addition of CS2, the medium is maintained at 40°C with stirring for 120 min and then cooled to 25°C.

[0103] After adding 350 g of deionized water, the resulting solution is an aqueous solution containing 40% by weight of compound (PIP-CS2).

[0104] Treatment of solutions containing metallic elements Examples#!#:

[0105] In a 2 L volumetric flask containing a Teflon-coated magnetic stir bar, 2 L of deionized water is added in which 41 mg of dysprosium chloride hexahydrate (DyCl3.6H2O) and 53.5 mg of lanthanum chloride heptahydrate (LaCl3.7H2O) are dissolved to obtain a solution containing 10 ppm of dysprosium salt and 10 ppm of lanthanum salt. An ICP-OES analysis is performed to determine the initial quantity of each element in the solution (in order to eliminate the variability in hydration from one salt to another depending on its storage conditions).

[0106] The (PIP-CS2) solution (example 1) is diluted to 1% (by weight) by mixing 150 mg of it with 6 g of deionized water.

[0107] The aqueous solution containing dysprosium and lanthanum is stirred moderately, and the diluted (PIP-CS2) solution is added (amount adjusted to obtain the desired stoichiometry of (PIP-CS2).

[0108] The mixture is kept under agitation for 60 s and a precipitate appears.

[0109] The stirring is stopped and the suspension is left to settle naturally for 60 min. The resulting solution is filtered (Sartorius 0.45p filter) to perform a liquid-solid separation.

[0110] The filtrate is analyzed by ICP-OES to measure the concentration of dysprosium and lanthanum. The analysis of the filtrate during the treatment is represented by [Fig.2].

[0111] 1998.5 g of filtrate solution are recovered (after filtration with stoichiometry of 500%). The filtrate contains 1.1 ppm of dysprosium and 6.8 ppm of lanthanum.

[0112] 1.5 g of solid is recovered from the filter. It contains 9200 ppm dysprosium and 3600 ppm lanthanum (analysis by ICP-OES)

[0113] The compound (PIP-CS2) therefore allows an enrichment of dysprosium in the precipitate formed. Example #3:

[0114] In a 2 L volumetric flask containing a Teflon®-coated magnetic stir bar, 2 L of deionized water is added in which 41 mg of hydrated europium chloride (EuCl3·xH2O) and 53.5 mg of lanthanum chloride heptahydrate (LaCl3·7H2O) are dissolved to obtain a solution containing 10 ppm of europium salt and 10 ppm of lanthanum salt. An ICP-OES analysis is performed to determine the initial quantity of each element in the solution (in order to eliminate the variability in hydration from one salt to another depending on its storage conditions).

[0115] The (PIP-CS2) solution (example 1) is diluted to 1% (by weight) by mixing 160 mg of it with 6.17 g of deionized water.

[0116] The aqueous solution containing europium and lanthanum is stirred moderately, and the dilute (PIP-CS2) solution is added (amount adjusted to obtain the desired stoichiometry of (PIP-CS2)).

[0117] The mixture is kept under agitation for 60s and a precipitate appears.

[0118] The stirring is stopped and the suspension is left to settle naturally for 60 min. The resulting solution is filtered (Sartorius 0.45p filter) to perform a liquid-solid separation.

[0119] The filtrate is analyzed by ICP-OES to measure the concentration of europium and lanthanum. The analysis of the filtrate during the treatment is represented by [Fig. 3].

[0120] 1998.3 g of filtrate solution are recovered (after filtration with a stoichiometry of 500%). The filtrate contains 1.73 ppm of europium and 6.8 ppm of lanthanum.

[0121] On the filter, 1.7 g of solid are recovered. It contains 3176 ppm of lanthanum and 7141 ppm of europium (analysis by ICP-OES).

[0122] The compound (PIP-CS2) therefore allows an enrichment of europium in the precipitate formed. Examples #4:

[0123] In a 2 L volumetric flask containing a Teflon-coated magnetic stir bar, 2 L of deionized water is added in which 49.5 mg of yttrium chloride hydrate (YCl3·xH2O) and 53.5 mg of lanthanum chloride heptahydrate (LaCl3·7H2O) are dissolved to obtain a solution containing 10 ppm of yttrium salt and 10 ppm of lanthanum salt equivalent. An ICP-OES analysis is performed to determine the initial quantity of each element in the solution (in order to eliminate the variability in hydration from one salt to another depending on its storage conditions).

[0124] The solution (PIP-CS2) (example 1) is diluted to 1% (by weight) by mixing 210 mg of it with 8.25 g of deionized water.

[0125] The aqueous solution containing yttrium and lanthanum is stirred moderately, and the dilute (PIP-CS2) solution is added (amount adjusted to obtain the desired stoichiometry of (PIP-CS2)).

[0126] The mixture is kept under agitation for 60s and a precipitate appears.

[0127] The stirring is stopped and the suspension is left to settle naturally for 60 min. The resulting solution is filtered (Sartorius 0.45p filter) to perform a liquid-solid separation.

[0128] The filtrate is analyzed by ICP-OES to measure the concentration of yttrium and lanthanum. The analysis of the filtrate during the treatment is represented by [Fig. 4].

[0129] 1997.9 g of filtrate solution are recovered (after filtration with stoichiometry of 500%). The filtrate contains 2.15 ppm of yttrium and 6.8 ppm of lanthanum.

[0130] On the filter, 2.12 g of solid are recovered. It contains 2665 ppm of lanthanum and 4504 ppm of yttrium (analysis by ICP-OES).

[0131] The compound (PIP-CS2) therefore allows an enrichment of yttrium in the precipitate formed. Examples #5:

[0132] The operating conditions of Example 2 are repeated. The (PIP-CS2) solution (Example 1) is diluted to 1% (by weight) by mixing 150 mg of it with 6 g of deionized water.

[0133] The aqueous solution containing dysprosium and lanthanum is stirred moderately, and the diluted polymer solution (PIP-CS2) is added (amount adjusted to obtain 100% stoichiometry of (PIP-CS2)). The solution is stirred for 1 minute. Then, 0.5 mL of a 1% PAC 18 coagulant solution (polyaluminum chloride, average molecular weight between 20,000 and 1 million daltons) is added, and the solution is stirred for 1 minute. Finally, 0.5 mL of a 0.5 g / L anionic flocculant solution (Flopam AN 934 VHM, average molecular weight greater than 1 million daltons) is added, and the solution is left to stir for 1 minute.

[0134] The mixture is kept under agitation at 200 rpm for 60s then slowed down to 50 rpm for 5 min for floc formation.

[0135] The stirring is stopped and the suspension is left to settle naturally for 10 min. The resulting solution is filtered (Sartorius 0.45p filter) to perform a liquid-solid separation.

[0136] The dysprosium and lanthanum contents of the solid and the filtrate remain equivalent to those obtained in Example 2. However, the treatment times (sedimentation, liquid-solid separation) are shorter than those of Example 2.

Claims

Demands

1. A process for separating two elements E1 and E2, selected from rare earth elements, in a mixture in aqueous solution SA, said process comprising the following successive steps: a) adding to the aqueous solution SA at least one dithiocarbamate salt of formula: R1R2NCS2 M+, in which M is an alkali metal cation, the RI and / or R2 groups are selected from the group comprising a hydrogen atom, a methyl group, a carbon chain comprising from 2 to 20 carbon atoms, unsaturated or not, substituted or not, which may comprise one or more heteroatoms selected from nitrogen and oxygen, linear, branched or cyclic, the RI and R2 groups being able to form a ring between them; b) stirring the aqueous solution obtained in step a) for at least 1 minute; c) stopping the stirring and waiting at least 5 minutes for the formation of a suspension S;d) perform a liquid / solid separation on the suspension S to obtain a solid SO containing predominantly the element El compared to the element E2 and an aqueous solution SA' containing predominantly the element E2 compared to the element El.;

2. A method according to claim 1, characterized in that the cation M is sodium or potassium.

3. A process according to the preceding claims, characterized in that the dithiocarbamate salt is selected from the alkali metal salts of the following compounds: piperazine dithiocarbamate, piperidine dithiocarbamate, cyclohexylamine dithiocarbamate, dimethyl dithiocarbamate, diethyldithiocarbamate, dipropyldithiocarbamate, dibutyldithiocarbamate, ethylenediamine dithiocarbamate

4. A process according to claims 1 and 2, characterized in that the dithiocarbamate salt is potassium piperazine dithiocarbamate.

5. A process according to claim 1, characterized in that for step a) the dithiocarbamate salt is in aqueous solution at a concentration between 0.5 and 60% by weight.

6. A method according to the preceding claims, characterized in that the 2 elements El and E2 are respectively dysprosium and lanthanum.

7. A method according to the preceding claims, characterized in that the 2 elements El and E2 are respectively europium and lanthanum.

8. A method according to the preceding claims, characterized in that the 2 elements El and E2 are respectively yttrium and lanthanum.

9. A process according to the preceding claims, characterized in that between steps b) and c) it comprises two successive steps b1) and b2), said steps consisting of: b1) Adding to the solution a water-soluble polymer P of average molecular weight between 20,000 and 1 million daltons and leaving under stirring for at least 1 minute. b2) Adding to the solution a water-soluble polymer P' of average molecular weight greater than 1 million daltons and leaving under stirring for at least 1 minute.

10. A process according to the preceding claims, characterized in that for step a) of the process the stoichiometric titration corresponding to the ratio between the anionic charge density of the dithiocarbamate salt and the total cationic charge density of the rare earths of the SA solution is between 100 and 500%.

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