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 one or more rare earth elements from other metals in columns 4 to 14 of the periodic table of elements, in a mixture in aqueous solution. The method uses a polyethylene-imine-CS2 adduct in salt form. (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 "rare earths" mixed with other metals 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] With the aim of promoting the transition to a circular economy (sharing, reusing, repairing, renovating and recycling existing products and materials for as long as possible so that they retain their value) and of having virtuous products, the recovery of these "rare earths" is a major objective for the coming years (battery recycling).

[0007] Separating the "rare earths" from the metals in groups 4 to 14 of the periodic table of elements is a challenge to be met in the coming years. Description of the invention

[0008] The Applicant has found and developed a simple, inexpensive process for separating "rare earths" mixed with other metals in aqueous solution.

[0009] More specifically, the invention is a method for separating one or more rare earth elements from other metals in columns 4 to 14 of the periodic table of elements, in an aqueous solution mixture SA, said method comprising at least the following successive steps:

[0010] a) add to the aqueous solution SA at least one polyethylene-hnine-CS2 adduct in the form of a salt (PELCS2);

[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) carry out a liquid / solid separation on the suspension S to obtain an aqueous solution L containing predominantly the elements among the rare earths initially present in the aqueous solution SA.

[0014] The solution SA subjected to the process of the invention contains at least 1 element 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.

[0015] Advantageously the rare earths in the SA solution are chosen from the following elements: neodymium, dysprosium, lanthanum, gadolinium, europium, yttrium, cerium and samarium.

[0016] According to a preferred embodiment of the invention, the SA solution contains at least two elements from among the rare earths.

[0017] 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.

[0018] Solution SA further comprises at least one other metal from columns 4 to 14 of the periodic table of elements. The metals from columns 4 to 14 of the periodic table are preferably iron, copper, chromium, manganese, cobalt, nickel, zinc, cadmium, mercury, tin, lead, vanadium, aluminum, gallium, selenium, and molybdenum.

[0019] The “periodic table of elements” refers to Mendeleev’s table (IUPAC update 2016).

[0020] In particular, the total concentration of other metals from columns 4 to 14 of the periodic table of elements, initially present in the SA solution, is between 1 and 10,000 ppm by weight.

[0021] By "a polyethylene-imine-CS2 adduct" is meant a product resulting from the reaction of a polyethylene-imine with carbon disulfide.

[0022] In particular, the reaction can be carried out in the presence of a base, allowing the polyethylene-imine-CS2 adduct to be obtained directly in salt form. For example, the reaction can be carried out in the presence of sodium hydroxide (NaOH) or potassium hydroxide (KOH) to obtain the polyethylene-imine-CS2 adduct in salt form (PEI-CS2), respectively as a sodium or potassium salt.

[0023] Preferably, the polyethylene-imine used to produce the polyethylene-imine-CS2 adduct in salt form in step a) of the process of the invention contains between 15 and 65% primary amine functions, between 25 and 60% secondary amine functions, and between 10 and 60% tertiary amine functions. More preferably, the polyethylene-imine contains between 25 and 45% primary amine functions, between 35 and 55% secondary amine functions, and between 20 and 40% tertiary amine functions.

[0024] Advantageously the polyethylene-imine at the origin of the polyethylene-imine-CS2 adduct in salt form used in step a) of the process of the invention has a molecular weight between 300 and 70,000 daltons.

[0025] The salt of polyethylene-imine-CS2 (PELCS2) adduct is an alkali metal salt, namely a potassium or sodium salt. Preferably, this salt is a sodium salt.

[0026] In particular, the polyethylene-imine-CS2 adduct in salt form (PELCS2) is such that all the CS2 functions are in a salt form.

[0027] Advantageously, a composition containing two different polyethylene-imine-CS2 adducts in the form of salts (PELCS2) can be used in step a) of the process. In other words, the composition contains two salts of (PELCS2) that differ because they were obtained from different polyethylene imines, but their counterions, i.e., an alkali metal cation, can be identical.

[0028] Preferably, for carrying out step a) of the process of the invention, the polyethylene-imine-CS2 adduct in salt form (PELCS2) is in aqueous solution at a concentration of between 0.5 and 60% by weight, said aqueous solution having a pH of between 10 and 14. The salt is in particular added in this form to the SA solution.

[0029] Advantageously, for step a) of the process of the invention, the polyethylene-imine-CS2 adduct in salt form (PELCS2) is the product of the reaction of a polyethylene-imine with carbon disulfide, with a proportion molar of carbon disulfide / sum of amine groups present in polyethylene imine between 0.5 and 1.1, preferably between 0.6 and 0.95.

[0030] The process according to the invention makes it possible, at the end of step d), to obtain an aqueous solution L containing predominantly the elements among the rare earths initially present in the aqueous solution SA.

[0031] In other words, the aqueous solution L, obtained at the end of step d), comprises a ratio (other metals from columns 4 to 14 of the periodic table of elements: elements among the rare earths) which is less than the ratio (other metals from columns 4 to 14 of the periodic table of elements: elements among the rare earths) of the aqueous solution SA.

[0032] In particular, the ratio (other metals from columns 4 to 14 of the periodic table of elements: elements among the rare earths) in the aqueous solution L is 0, that is to say devoid of other metals from columns 4 to 14 of the periodic table of elements.

[0033] Rare earth elements, as well as other metals from columns 4 to 14 of the periodic table of elements, are notably present in the SA solution in a cationic form.

[0034] Furthermore, the process of the invention may preferably comprise two successive steps b1) and b2) between steps b) and c), said steps consisting of:

[0035] bl) Add to the aqueous solution obtained in step a) a water-soluble polymer P with an average molecular weight between 20,000 and 1 million daltons and stir for at least 1 minute,

[0036] b2) Add to the solution obtained in step bl) a water-soluble polymer P' of average molecular weight greater than 1 million daltons and shake for at least 1 minute.

[0037] One of the advantages of implementing steps bl) and b2) is a reduction in the time of step c).

[0038] 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.

[0039] Polymer P has a molecular weight between 50,000 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.

[0040] 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 graphical method consisting of taking the values ​​of reduced viscosity (ordinate axis) on the concentration (abscissa axis) and extrapolating the curve up to zero concentration.

[0041] 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:

[0042] [Math 1]

[0043] [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.

[0044] 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.

[0045] 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.

[0046] Advantageously, the polymer P is chosen from among poly(aluminum chloride), the product of the polycondensation reaction between epichlorohydrin and dimethylamine, homopolymers or copolymers of diallyldimethyl ammonium halide.

[0047] 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,

[0048] - 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, anhydride maleic, itaconic anhydride, itaconamide, vinylpyridine, hydroxyalkyl (meth)acrylate, thioalkyl (meth)acrylate, 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;

[0049] - the anionic hydrophilic monomer(s) being chosen from among the monomers acrylic acid, methacrylic acid, dimethylacrylic acid, itaconic acid, Cl-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;

[0050] - 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)a crylamides, such as methacrylamido-propyl trimethyl ammonium chloride (MAPTAC), acrylamido-propyl 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.

[0051] 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.

[0052] [Math.2] [rnoHowzère] . , ____ L ~ — \mommère\eau

[0053] The polymer P' can have a linear, branched, star-shaped (or "star") structure (in English) or in the shape of a comb. This structure can be obtained, depending on the general knowledge of a person skilled in the art.

[0054] 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.

[0055] 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 inverse); suspension polymerization; reactive extrusion polymerization; water-in-water polymerization; or micellar polymerization.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] 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.

[0060] The process of the invention may advantageously include the following steps after step d):

[0061] e) add to the aqueous solution L at least one polyethylene-imine-CS2 adduct in salt form (PELCS2);

[0062] f) stir the aqueous solution obtained in step d) for at least 1 minute

[0063] g) stop stirring and wait at least 5 minutes for the formation of a suspension S';

[0064] h) carry out a liquid / solid separation on the suspension S' to obtain a solid SO containing predominantly the elements among the rare earths initially present in the solution L.

[0065] The stirring time (step f)) and waiting time (step g)) are of the same order of magnitude as for steps b) and c). The stirring means in step f) is preferably identical to that of step b). The liquid / solid separation method h) is preferably identical to that of step d).

[0066] In particular, the total quantity of rare earth elements in the SO solid is greater than 80%, in particular greater than 90% by mass compared to the total quantity of rare earth elements initially present in the L solution.

[0067] The amount of polyethylene-imine-CS2 adduct in salt form (PELCS2) added in steps a) and e) is determined based on the cationic charge density of the aqueous solution SA. More precisely, it is determined such that the anionic charges of the polyethylene-imine / carbon disulfide salt (PELCS2) neutralize the cationic charges of the metallic elements present in the aqueous solution SA.

[0068] 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.

[0069] This cationic charge density allows the calculation of the quantity of polyethylene-imine-CS2 adduct in salt form 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 PELCS2 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%.

[0070] Preferably for step a) of the process of the invention, the stoichiometric dosage corresponding to the ratio between the anionic charge density of the polyethylene-imine-CS2 adduct in salt form (PELCS2) and the total cationic charge density of the metallic elements in solution SA is between 80 and 120%, even more preferably between 95% and 105%.

[0071] For step e) of the process of the invention, the stoichiometric dosage corresponding to the ratio between the anionic charge density of the polyethylene-imine-CS2 adduct in salt form (PELCS2) and the total cationic charge density of the metallic elements in solution SA is between 200 and 500%, more preferably between 250 and 400%.

[0072] The invention and its advantages will become more apparent in the light of the following examples and figures.

[0073] [Fig.1]

[0074] Figure 1 represents Mendeleev's periodic table. The grey cells represent the elements that can be analyzed by ICP-OES technology.

[0075] [Fig.2]

[0076] Fig. 2 represents the evolution of the concentration of europium and copper in the filtrate from the solution treated with PELCS2, according to example 6. The x-axis represents the stoichiometry, expressed in %, of PELCS2 added, the y-axis represents the concentration of cations in the solution, expressed in ppm.

[0077] [Fig.3]

[0078] Fig. 3 represents the evolution of the concentration of yttrium and iron in the filtrate from the solution treated with PELCS2, according to example 7. The x-axis represents the stoichiometry, expressed in %, of PELCS2 added, the y-axis represents the concentration of cations in the solution, expressed in ppm.

[0079] [Fig.4]

[0080] Fig. 4 represents the evolution of the concentration of neodynium and mercury in the filtrate from the solution treated with PELCS2, according to example 11. The x-axis represents the stoichiometry, expressed in %, of the PELCS2 added, the y-axis represents the concentration of the cations in the solution, expressed in ppm.

[0081] [Fig.5]

[0082] Fig. 5 represents the evolution of the concentration of dysprosium and mercury in the filtrate from the solution treated with PELCS2, according to example 13. The x-axis represents the stoichiometry, expressed in %, of PELCS2 added, the y-axis represents the concentration of cations in the solution, expressed in ppm.

[0083] [Fig.6]

[0084] Fig. 6 represents the evolution of the concentration of europium and copper in the filtrate from the solution treated with PELCS2, with the addition of two polymers, according to Example 14. The x-axis represents the stoichiometry, expressed in %, of the PELCS2 added, the y-axis represents the concentration of the cations in the solution, expressed in ppm.

[0085] [Fig.7]

[0086] Fig. 7 represents the evolution of the concentration of europium and copper in the filtrate from the solution treated with PELCS2, with the addition of two polymers, according to Example 15. The x-axis represents the stoichiometry, expressed in %, of the PELCS2 added, the y-axis represents the concentration of the cations in the solution, expressed in ppm. EXAMPLES#:

[0087] ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry) analysis method:

[0088] ICP-OES technology is a technique allowing the analysis of most of the elements of the Mendeleev periodic table ([Fig.1]).

[0089] 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.

[0090] 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.

[0091] 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 an X-ray wavelength according to the Planck-Einstein relation: [Math.3] E=

[0092] (E: energy of the photon (in Joules), h Planck constant (6.63.10 34 Js, c: speed of light in a vacuum, X: frequency (in hertz) of the electromagnetic wave associated with the photon considered).

[0093] Thanks to the optical sensors and detectors of the measuring device, these wavelengths are identified, thus enabling the identification and quantification of the compounds present.

[0094] Depending on each element considered and taking into account our specific matrices, here is the protocol put in place:

[0095] Sample preparation:

[0096] - 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.

[0097] - Samples after chelation: 2 drops of 69% by weight nitric acid are added to 10 ml of the samples.

[0098] The corresponding solutions are injected into the ICP-OES 5800 (Agilent), using the following parameters:

[0099] - ICP RF power of 1.2 kW

[0100] - Carrier gas: argon flow rate of 0.7 L / min.

[0101] The elements La, Ce, Pr, Nd, Sm, Gd, Dy, Fe, Hg, Cu 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.

[0102] Determination of the anionic charge density of a salt resulting from the reaction of a polyethyleneimine with carbon disulfide (called: PEI-CS2)

[0103] The charge density of PELCS2 is calculated from the colloidal charge (meq / g), determined by colloidal assay using methyl glycol chitosan (MGC) and potassium polyvinyl sulfate (PVSK).

[0104] A solution containing 5 g / L of PELCS2 is prepared by diluting, under magnetic stirring, 1.00 g of PELCS2 equivalent (dry extract) in a 200 mL beaker, the amount of deionized water added depending on the initial PELCS2 concentration. 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 to 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).

[0105] 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

[0106] The same measurement is carried out without the addition of PELCS2, and the quantity in millilitres of PVSK is noted as B.

[0107] The anionic charge density is calculated using the following formula:

[0108] [Math 4]

[0109] C(meq / g) = (BA) x NPVSk / (5 xm xlO3),

[0110] where m = mass of PELCS2 solution at 5 g / L

[0111] Npvsk = normality of the PVSK solution, = f / 400, with factor f given by the supplier WAKO.

[0112] Stoichiometric titration of an aqueous solution containing metallic elements

[0113] The solution is analyzed by 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.

[0114] This cationic charge density makes it possible to calculate the quantity of PEL CS2 polymer to be used to neutralize all cationic charges of the metallic elements to an optimal content of 100%. The stoichiometric dosage therefore corresponds to the ratio between the anionic charge density of PEI-CS2 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%.

[0115] Example to clarify the calculation of the stoichiometric %:

[0116] For an aqueous solution (1000 g) containing 20 ppm of copper (II), the amount of PEI-CS2 (with a charge density of 2.84 meq / g) required to achieve 100% stoichiometry is determined according to the following formula:

[0117] [Math 5]

[0118] Q= (ST / 100) * (Cmetal * VALmetal) / (MWmetal * D / 1000)

[0119] With ST = target stoichiometry (%)

[0120] Q = quantity of PEI-CS2 to be added (in ppm)

[0121] Cmetal = metal concentration (in ppm)

[0122] VALmetal = metal valence

[0123] MWmetal: molecular mass of metal (g / mol)

[0124] D = charge density of the PEI-CS2 polymer (meq / g)

[0125] Thus for 100% stoichiometry, 222 ppm of PEI-CS2 is required. PEI-CS2 Polymer Synthesis Example 1#: Polymer A

[0126] In a double-jacketed IL reactor equipped with a motor, a stirring blade, and a condenser, 248 g of water, 42 g of sodium hydroxide (50% by weight in water), and 50 g of Epomin® P 1050 (PEI from Nippon Shokubai, molar mass 70,000 daltons; molar proportions of primary / secondary / tertiary amines: 25 / 50 / 25) are loaded. The mixture is stirred for 15 minutes and maintained at 35 °C by a cooling unit via the reactor's double jacket.

[0127] A dropping funnel is loaded with 44 g of CS2 and fitted onto the IL reactor. The CS2 is then 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 between 40 and 50°C with stirring for 120 min.

[0128] A further addition of 7 g of Epomin® P 1050 and 32 g of water is then made to the reaction medium. The medium is maintained at the same temperature for 400 min and is then cooled to 25°C.

[0129] The pH is then adjusted with sodium hydroxide (50% by weight in water) to a value between 10.0 and 12.0. The resulting solution is an aqueous solution containing 20% ​​by weight of polymer A (PELCS2). Example 2#: Polymer B

[0130] The PELCS2 polymer is obtained according to the same protocol as Example 1, with the following in the IL reactor: 165 g of water, 86 g of sodium hydroxide, and 50 g of Epomin® SP 200 (PEI from Nippon Shokubai, molar mass 10,000 daltons, molar proportions of primary / secondary / tertiary amines: 35 / 35 / 30). The dropping funnel is loaded with 82 g of CS2. Final addition: 3 g of Epomin® SP 200 and 11 g of water. The resulting solution is an aqueous solution containing 40% by weight of polymer B (PELCS2). Example 3#: Polymer C

[0131] The PELCS2 polymer is obtained according to the same protocol as Example 1, with the following in the IL reactor: 165 g of water, 86 g of sodium hydroxide, and 50 g of Epomin® SP 018 (PEI from Nippon Shokubai, molar mass 18000 daltons, molar proportions of primary / secondary / tertiary amines: 35 / 35 / 30). The dropping funnel is loaded with 82 g of CS2. Final addition: 3 g of Epomin® SP 018 and 11 g of water. The resulting solution is an aqueous solution containing 40 wt% of polymer C (PELCS2). Example 4#: Polymer D

[0132] The PELCS2 polymer is obtained according to the same protocol as in Example 1, with the following in the IL reactor: 98 g of water, 121 g of sodium hydroxide, and 50 g of tetraethylene pentamine (TEPA). The dropping funnel is loaded with 115 g of CS2. Final addition: 2 g of TEPA and 7 g of water. The resulting solution is an aqueous solution containing 50% by weight of polymer D (PELCS2). Example 5#: Polymer E

[0133] The PELCS2 polymer is obtained according to the same protocol as Example 1, with the following in the IL reactor: 159 g of water, 102 g of sodium hydroxide, 25 g of TEPA, and 50 g of Epomin® P 1050. The dropping funnel is loaded with 115 g of CS2. Final addition: 3 g of TEPA and 10 g of water. The resulting solution is an aqueous solution containing 40% by weight of polymer E.

[0134] Treatment of solutions containing metallic elements Examples#6#:

[0135] In a 2 L volumetric flask containing a Teflon-coated magnetic stir bar, 2 L of deionized water is added in which 40 mg of hydrated europium chloride (EuCl3.6H2O) and 96.4 mg of pentahydrated copper sulfate (Cu(SO4)2.5H2O) are dissolved to obtain a solution containing 10 ppm of europium salt and 10 ppm of copper 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).

[0136] The polymer E solution (example 5) is diluted to 1% (by weight) by mixing 40 mg of it with 1.41 g of deionized water.

[0137] The aqueous solution containing europium and copper is stirred moderately, and the diluted polymer E solution is added (amount adjusted to obtain 100% stoichiometry of polymer E).

[0138] The mixture is kept under agitation for 60s and a precipitate appears.

[0139] 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.

[0140] The filtrate is analyzed by ICP-OES to measure the concentration of europium and copper. The analysis of the filtrate during the treatment is represented by [Fig. 2].

[0141] 1998 g of filtrate solution are recovered. The filtrate contains 5.43 ppm of element Dissolved europium and 0 ppm of copper.

[0142] On the filter, 2g of solid are recovered. It contains 12,000 ppm of copper (analysis by ICP-OES).

[0143] Polymer E therefore allows an enrichment of copper in the precipitate formed (very rapidly).

[0144] The filtrate is again added with 300% in stoichiometry of polymer E. After formation of a precipitate, the resulting suspension is filtered (Sartorius 0.45p filter).

[0145] 2.5 g of solid are recovered on the filter. They contain 9400 ppm of europium (ICP-OES analysis).

[0146] The double treatment with polymer E therefore makes it possible to obtain a solid enriched in europium. Examples#?#:

[0147] 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 hydrated yttrium chloride (YC13·xH2O) and 178 mg of iron chloride (FeCl3) are dissolved to obtain a solution containing 10 ppm of yttrium salt and 10 ppm of ferric 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).

[0148] The polymer E solution (example 5) is diluted to 1% (by weight) by mixing 50 mg of it with 1.91 g of deionized water.

[0149] The aqueous solution containing yttrium and iron is stirred moderately, and the dilute polymer E solution is added (amount adjusted to obtain 100% stoichiometry of polymer E).

[0150] The mixture is kept under agitation for 60s and a precipitate appears.

[0151] 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.

[0152] The filtrate is analyzed by ICP-OES to measure the concentration of europium and copper. The analysis of the filtrate during the treatment is represented by [Fig. 3].

[0153] 1997.5 g of filtrate solution are recovered. The filtrate contains 5.90 ppm of element dissolved yttrium and 0 ppm iron.

[0154] On the filter, 2.5g of solid are recovered. It contains 24490 ppm of iron (analysis by ICP-OES).

[0155] Polymer E therefore allows an enrichment of iron in the precipitate formed (very rapidly).

[0156] As in example 6, the addition of 300% in stoichiometry of polymer E in the filtrate allows in a second step to enrich the solid obtained after precipitation and filtration in yttrium. Examples#8#:

[0157] In a 2 L volumetric flask containing a Teflon®-coated magnetic stir bar, 2 L of deionized water is added, in which the following metal salts (Table 1) are dissolved to obtain a mixture containing 10 ppm of each metal 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).

[0158] [Tables 1] Salt Molecular weight (g / mol) Weighing mass (mg) Neodymium (III) chloride 250.6 45.1 Dysprosium (III) chloride 268.9 40.9 Lanthanum (III) chloride, heptahydrate 371.43 53.5 Gadolinium (III) chloride, heptahydrate 371.7 47.3 Europium (III) chloride 258.3 40.1 Yttrium (III) chloride 195.3 49.5 Cerium (III) chloride, heptahydrate 372.6 53.2 Samarium(III) chloride 256.8 41.9 Copper(II) sulfate pentahydrate 249.6 96.4 Mercury(II) chloride 271.5 33.2 Iron(II) chloride 162.2 178.2

[0159] Table 1: quantities of salts added

[0160] The polymer E solution (example 5) is diluted to 1% (by weight) by mixing 180 mg of it with 6.93 g of deionized water.

[0161] The aqueous solution containing the various metallic elements is stirred moderately, and the diluted polymer E solution is added (quantity adjusted to obtain 100% stoichiometry of polymer E).

[0162] The mixture is kept under agitation for 60s and a precipitate appears.

[0163] The agitation is stopped and the suspension is left to settle naturally during 60 min. The resulting solution is filtered (Sartorius 0.45p filter) to perform a liquid-solid separation.

[0164] The filtrate is analyzed by ICP-OES to measure the concentration of the different metallic elements. The analysis of the filtrate is described in Table 2.

[0165] At 100% stoichiometry, the filtrate contains between 4 and 6 ppm of dissolved lanthanides and 0 ppm of heavy metals. Polymer E allows for heavy metal enrichment in the precipitate and lanthanide enrichment of the filtrate.

[0166] [Tables2] Element 0% stoichiometry 100% stoichiometry neodymium 9.03 4.03 dysprosium 8.1 4.1 lanthanum 8.69 4.06 gadolinium 8.07 4.12 europium 8.1 5.43 yttrium 5.89 4.45 cerium 11.32 4.73 samarium 9.1 4.25 copper 10.09 0 mercury 12.93 0 iron 8.02 0

[0167] Table 2: ICP-OES analysis of the filtrate (quantities in ppm) Example #9:

[0168] In a 2 L volumetric flask containing a Teflon®-coated magnetic stir bar, 2 L of deionized water is added, in which the following lanthanide salts (Table 3) are dissolved to obtain a mixture containing 10 ppm of each lanthanide 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).

[0169] [Tables3] Salt Molecular weight (g / mol) Weighing mass (mg) Neodymium (III) chloride 250.6 45.1 Dysprosium (III) chloride 268.9 40.9 Lanthanum (III) chloride, heptahydrate 371.4 53.5 Gadolinium (III) chloride, heptahydrate 371.7 47.3 Europium (III) chloride 258.3 40.1 Yttrium (III) chloride 195.3 49.5 Cerium (III) chloride, heptahydrate 372.6 53.2 Samarium (III) chloride 256.8 41.9

[0170] Table 3: quantities of lanthanide salts added

[0171] The polymer E solution (example 5) is diluted to 1% (by weight) by mixing 480 mg of it with 18.74 g of deionized water.

[0172] The aqueous solution containing the different lanthanides is stirred moderately, and the diluted polymer E solution is added (quantity adjusted to obtain the desired stoichiometry in polymer E).

[0173] The mixture is kept under agitation for 60s and a precipitate appears.

[0174] The agitation is stopped and the suspension is left to settle naturally during 60 min. The resulting solution is filtered (Sartorius 0.45p filter) to perform a liquid-solid separation.

[0175] The filtrate is analyzed by ICP-OES to measure the concentration of the different metallic elements. The analysis of the filtrate is described in Table 4.

[0176] At 400% stoichiometry, the filtrate contains between 0.3 and 1.1 ppm of each lanthanide. Polymer E, at a high concentration, therefore allows for the efficient chelation of all lanthanides and yields a solid after precipitation and filtration enriched in lanthanides.

[0177] [Tables4] Stoichiometry (polymer E) Element 0% 100% 200% 300% 400% neodymium 8.44 7.13 3.38 0.89 0.41 dysprosium 7.94 6.93 3.7 0.84 0.37 lanthanum 9.59 8.41 5.22 2.07 1.09 gadolinium 9.71 8.82 5.34 1.51 0.73 europium 7.66 6.72 3.5 0.86 0.39 yttrium 6.88 6.31 4.13 1.2 0.58 cerium 8.92 7.25 3.24 0.93 0.43 samarium 9.46 8.21 5.27 1.98 0.95

[0178] Table 4: ICP-OES analysis of the filtrate (quantities in ppm)

[0179] Example 10:

[0180] In a 2 L volumetric flask containing a Teflon®-coated magnetic stir bar, 2 L of deionized water is added in which the lanthanide salts are dissolved (Table 3 of Example 9) to obtain a mixture containing 10 ppm of each lanthanide 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).

[0181] The polymer solution B (example 2) is diluted to 1% (by weight) by mixing 480 mg of it with 18.74 g of deionized water.

[0182] The aqueous solution containing the different lanthanides is stirred moderately, and the diluted polymer B solution is added (quantity adjusted to obtain the desired stoichiometry in polymer B).

[0183] The mixture is kept under agitation for 60s and a precipitate appears.

[0184] 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.

[0185] The filtrate is analyzed by ICP-OES to measure the concentration of the different metallic elements. The analysis of the filtrate is described in Table 5.

[0186] At 300% stoichiometry, the filtrate contains between 2 and 3 ppm of each lanthanide. Polymer B, at high dosage, therefore allows for the efficient chelation of all lanthanides and yields a solid after precipitation and filtration enriched in lanthanides.

[0187] [Tables 5] Stoichiometry (polymer B) Element 0% 100% 200% 300% neodymium 8.87 4.48 3.23 2.34 dysprosium 8.54 4.55 3.24 2.01 lanthanum 8.32 4.51 3.36 2.6 gadolinium 9.56 4.57 3.39 2.46 europium 9.64 5.88 4.97 2.98 yttrium 7.02 4.9 4.55 2.27 cerium 10.21 5.18 3.18 2.59 samarium 9.87 4.7 3.38 2.62

[0188] Table 5: ICP-OES analysis of the filtrate (quantities in ppm) Examples#! 1#:

[0189] In a 2 L volumetric flask containing a Teflon-coated magnetic stir bar, 2 L of deionized water is added in which 45.1 mg of hydrated neodymium chloride (NdCl3·xH2O) and 33.2 mg of mercury chloride (FeCl3) are dissolved to obtain a solution containing 10 ppm of neodymium salts and 10 ppm of mercury 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).

[0190] The polymer solution B (example 2) is diluted to 1% (by weight) by mixing 22 mg of it with 0.85 g of deionized water.

[0191] The aqueous solution containing neodymium and mercury is stirred moderately, and the diluted polymer B solution is added (amount adjusted to obtain 100% stoichiometry of polymer B).

[0192] The mixture is kept under agitation for 60s and a precipitate appears.

[0193] 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.

[0194] The filtrate is analyzed by ICP-OES to measure the concentration of neodymium and mercury. The analysis of the filtrate during the treatment is represented by [Fig. 4].

[0195] 1997.5 g of filtrate solution are recovered. The filtrate contains 4.48 ppm of element dissolved neodymium and 0 ppm mercury.

[0196] On the filter, 2.5 g of solid are recovered. The solid contains 8000 ppm (by weight) of mercury (analysis by ICP-OES).

[0197] Polymer B therefore allows an enrichment of mercury in the precipitate formed (very rapidly).

[0198] As in example 6, the addition of 300% stoichiometrically of polymer B in the filtrate allows in a second step to enrich the solid obtained after precipitation and filtration in neodymium. Examples#12#:

[0199] In a 2 L volumetric flask containing a Teflon®-coated magnetic stir bar, 2 L of deionized water is added in which the lanthanide salts are dissolved (Table 3 of Example 9) to obtain a mixture containing 10 ppm of each lanthanide 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).

[0200] The polymer C solution (example 3) is diluted to 1% (by weight) by mixing 480 mg of it with 18.74 g of deionized water.

[0201] The aqueous solution containing the different lanthanides is stirred moderately, and the dilute polymer C solution is added (quantity adjusted to obtain the desired stoichiometry in polymer C).

[0202] The mixture is kept under agitation for 60 s and a precipitate appears.

[0203] The stirring is stopped and the suspension is left to settle naturally for 60 min. The resulting solution is filtered (Sartorius 0.45 p filter) to perform a liquid-solid separation.

[0204] The filtrate is analyzed by ICP-OES to measure the concentration of the different metallic elements. The analysis of the filtrate is described in Table 6.

[0205] At 300% stoichiometry, the filtrate contains between 0.8 and 1.8 ppm of each lanthanide. Polymer C, at a high dosage, therefore allows for the efficient chelation of all the lanthanides and yields a solid after precipitation and filtration, enriched in lanthanides.

[0206] [Tableauxô] Stoichiometry (polymer C) Element 0% 100% 200% 300% neodymium 9.2 4.23 2.98 1.14 dysprosium 8.65 4.3 2.99 0.81 lanthanum 9.32 4.26 3.11 1.4 gadolinium 8.67 4.32 3.14 1.26 europium 8.91 5.63 4.72 1.78 yttrium 6.84 4.65 4.3 1.07 cerium 10.54 4.93 2.93 1.39 samarium 9.58 4.45 3.13 1.42

[0207] Table 6: ICP-OES analysis of the filtrate (quantities in ppm) Examples#13#:

[0208] In a 2 L volumetric flask containing a Teflon®-coated magnetic stir bar, 2 L of deionized water is added in which 40.9 mg of hydrated dysprosium chloride (DyCl3·xH2O) and 33.2 mg of mercury chloride (FeCl3) are dissolved to obtain a solution containing 10 ppm of dysprosium salts and 10 ppm of mercury salts. 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).

[0209] The polymer C solution (example 3) is diluted to 1% (by weight) by mixing 20 mg of it with 0.78 g of deionized water.

[0210] The aqueous solution containing dysprosium and mercury is stirred moderately, and the dilute polymer C solution is added (amount adjusted to obtain 100% stoichiometry of polymer C).

[0211] The mixture is kept under agitation for 60 s and a precipitate appears.

[0212] 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.

[0213] The filtrate is analyzed by ICP-OES to measure the concentration of dysprosium and mercury. The analysis of the filtrate during the treatment is represented by [Fig. 5].

[0214] 1998.2 g of filtrate solution are recovered. The filtrate contains 4.3 ppm of element dissolved dysprosium and 0 ppm mercury.

[0215] On the filter, 2.2 g of solid are recovered. The solid contains 9090 ppm (by weight) of mercury (analysis by ICP-OES).

[0216] Polymer C therefore allows an enrichment of mercury in the precipitate formed (very rapidly).

[0217] As in example 6, the addition of 300% stoichiometrically of polymer C in the filtrate allows in a second step to enrich the solid obtained after precipitation and filtration in dysprosium. Examples#14#:

[0218] Two 2 L volumetric flasks containing a Teflon®-coated magnetic stir bar are filled with 2 L of deionized water in which 40 mg of hydrated europium chloride (EuCl₃·6H₂O) and 96.4 mg of pentahydrated copper sulfate (Cu(SO₄)₂·5H₂O) are dissolved to obtain a solution containing 10 ppm of europium salt and 10 ppm of copper salt. An ICP-OES analysis is performed to determine the initial quantity of each element in the solution (to eliminate the variability in hydration from one salt to another depending on its storage conditions).

[0219] The polymer E solution (example 5) is diluted to 1% (by weight) by mixing 40 mg of it with 1.41 g of deionized water.

[0220] The same procedure is followed for the polymer solution A (example 1) which is diluted to 1% (by weight) by mixing 72 mg of it with 1.37 g of deionized water.

[0221] The aqueous solutions containing europium and copper are stirred moderately, and the diluted polymer E and polymer A solutions are added separately (amount adjusted to obtain 100% stoichiometry of polymer A or E) into one of the two volumetric flasks.

[0222] The mixtures are kept under agitation for 60 s and precipitates appear.

[0223] The stirring is stopped and the suspensions are left to settle naturally for 60 min. The solutions obtained are filtered (Sartorius 0.45p filter) to perform a liquid-solid separation.

[0224] The filtrates are analyzed by ICP-OES to measure the concentration of europium and copper. The analysis of the filtrates during the treatment is represented by [Fig. 6].

[0225] For polymers A and E, copper is efficiently removed from the precipitate at 100% stoichiometry. The europium content in the filtrates is equivalent.

[0226] At high stoichiometry, polymer E allows the precipitate to be enriched a little more in europium. Examples#15#:

[0227] Two 2 L volumetric flasks containing a Teflon®-coated magnetic stir bar are filled with 2 L of deionized water in which 40 mg of hydrated europium chloride (EuCl₃·6H₂O) and 96.4 mg of pentahydrated copper sulfate (Cu(SO₄)₂·5H₂O) are dissolved to obtain a solution containing 10 ppm of europium salt and 10 ppm of copper salt. An ICP-OES analysis is performed to determine the initial quantity of each element in the solution (to eliminate the variability in hydration from one salt to another depending on its storage conditions).

[0228] The polymer E solution (example 5) is diluted to 1% (by weight) by mixing 40 mg of it with 1.41 g of deionized water.

[0229] The same procedure is followed for the polymer D solution (example 4) which is diluted to 1% (by weight) by mixing 32 mg of it with 1.25 g of deionized water.

[0230] The aqueous solutions containing europium and copper are stirred moderately, and the diluted polymer E and polymer D solutions are added separately (amount adjusted to obtain 100% stoichiometry of polymer D or E) into one of the two volumetric flasks.

[0231] The mixtures are kept under agitation for 60 s and precipitates appear.

[0232] The stirring is stopped and the suspensions are left to settle naturally for 60 min. The solutions obtained are filtered (Sartorius 0.45p filter) to perform a liquid-solid separation.

[0233] The filtrates are analyzed by ICP-OES to measure the concentration of europium and copper. The analysis of the filtrates during the treatment is represented by [Fig.7].

[0234] For polymers A and D, copper is efficiently removed from the precipitate at 100% stoichiometry. The europium content in the filtrates is equivalent.

[0235] At high stoichiometry, polymer E allows for more efficient enrichment of the precipitate in europium. Examples#16#:

[0236] The operating conditions of Example 6 are repeated. The polymer E solution (Example 5) is diluted to 1% (by weight) by mixing 40 mg of it with 1.41 g of deionized water.

[0237] The aqueous solution containing europium and copper is stirred moderately, and the diluted polymer E solution is added (amount adjusted to obtain 100% polymer E stoichiometry). The solution is stirred for 1 minute. Then, 0.5 mL of an aqueous solution containing 1% coagulant (PAC 18 (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 solution containing 0.5 g / L of anionic flocculant (Flopam® AN 934 VHM, average molecular weight greater than 1 million daltons) is added and the solution is left to stir for 1 minute.

[0238] The mixture is kept under agitation at 200 rpm for 60 s then at 50 rpm for 5 min for floc formation.

[0239] 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.

[0240] The copper and europium contents of the solid and the filtrate remain equivalent to those obtained in Example 6. However, the processing times (sedimentation, liquid-solid separation) are shorter than those of Example 6.

Claims

Demands

1. A process for separating one or more rare earth elements from other metals in columns 4 to 14 of the periodic table of elements, in aqueous solution SA, said process comprising at least the following successive steps: a) adding to aqueous solution SA at least one polyethylene-imine-CS2 adduct in the form of a salt (PEI-CS2); b) stirring the aqueous solution obtained in step aj for at least 1 minute; c) stopping stirring and waiting at least 5 minutes for the formation of a suspension S; d) performing a liquid / solid separation on the suspension S to obtain an aqueous solution L containing predominantly the rare earth elements initially present in aqueous solution SA.

2. A process according to claim 1, characterized in that it contains between steps b) and c) the following successive steps: b1) Adding to the aqueous solution obtained in step a) a water-soluble polymer P of average molecular weight between 20,000 and 1 million daltons and stirring for at least 1 minute, b2) Adding to the solution obtained in step bl) a water-soluble polymer P' of average molecular weight greater than 1 million daltons and stirring for at least 1 minute.

3. A process according to claim 1, characterized in that the salt of the polyethylene-imine-CS2 adduct is a sodium salt. [Claimate 4] A process according to the preceding claims, characterized in that the polyethylene-imine at the origin of the polyethylene-imine -CS2 adduct in salt form used in step a) contains between 15 and 65% primary amine functions, between 25 and 60% secondary amine functions and between 10 and 60% tertiary amine functions. [Claimate 5] A process according to the preceding claims, characterized in that the polyethylene-imine at the origin of the polyethylene-imine -CS2 adduct in salt form used in step a) has a molecular weight between 300 and 70,000 daltons.

6. A process according to the preceding claims, characterized in that for step a) a composition containing two polyethylene-imine-CS2 adducts in different salt forms is used.

7. A process according to the preceding claims, characterized in that the polyethylene-imine-CS2 adduct in the form of a salt is in aqueous solution at a concentration of between 0.5 and 60 wt%, the aqueous solution having a pH of between 10 and 14.

8. A process according to the preceding claims, characterized in that, after step d), the process comprises at least the following steps: e) adding to the aqueous solution L at least one polyethylene-imine-CS2 adduct in the form of a salt (PEI-CS2); f) stirring the aqueous solution obtained in step d) for at least 1 minute; g) stopping the stirring and waiting at least 5 minutes for the formation of a suspension S'; h) performing a liquid / solid separation on the suspension S' to obtain a solid SO containing predominantly the elements among the rare earths initially present in the solution L.

9. A process according to the preceding claims, characterized in that the SA solution contains at least two elements from among the rare earths.

10. A process according to the preceding claims, characterized in that the rare earths in the SA solution are selected from the following: neodymium, dysprosium, lanthanum, gadolinium, europium, yttrium, cerium and samarium.

11. A method according to the preceding claims, characterized in that the metals of columns 4 to 14 of the periodic table are iron, copper, chromium, manganese, cobalt, nickel, zinc, cadmium, mercury, tin, lead, vanadium, aluminum, gallium, selenium and molybdenum.

12. A process according to the preceding claims, characterized in that, for step a), the polyethylene-imine-CS2 adduct in salt form (PEI-CS2) is the product of the reaction of a polyethylene-imine with carbon disulfide, with a molar proportion of carbon disulfide / sum of amine groups present in polyethylene imine between 0.5 and 1.

1.

13. A process according to the preceding claims, characterized in that for step a) of the process the stoichiometric dosage corresponding to the ratio between the anionic charge density of the polyethylene-imine-CS2 adduct in salt form (PEI-CS2) and the total cationic charge density of the metallic elements in the SA solution is between 80 and 120%.

14. A process according to claim 8, characterized in that for step e) of the process the stoichiometric dosage corresponding to the ratio between the anionic charge density of the polyethylene-imine-CS2 adduct in salt form (PEI-CS2) and the total cationic charge density of the metallic elements in the SA solution is between 200 and 500%.

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