PROCESS FOR THE VALORIZATION OF RARE EARTHS CONTAINED IN IONIC CLAYS

Abstract

This process for the recovery of rare earths contained in ionic clays implements the leaching of said clays according to a continuous loop: in which said leaching is initiated by contacting fresh ionic clay with an aqueous leaching solution S1 comprising a dissolved salt of M1 / zCl or M2 / zSO4, where M is a cation chosen from the group consisting of Na+, NH4+ and Mg2+; and z = 1 or 2, representing the number of charges of the cation M, generating on the one hand, a leachate or aqueous solution S2 comprising rare earth cations and actinium, and on the other hand, a leached or exhausted clay; then in which, said solution S2 is subjected to a phase of extraction of the valued rare earths, generating on the one hand, an organic solution S3 or a solid S3 comprising the valued rare earths, and on the other hand a raffinate R comprising the salt of M1 / zCl or of M2 / zSO4, actinium in cationic form, and the non-valued rare earths;The raffinate R is brought into contact with a quantity of fresh ionic clay, forming a new solution S2; said new solution S2 is then subjected to a new phase of extraction of the valuable rare earths, generating a new raffinate R; the leaching solution constituted by the raffinate R resulting from the successive phases of extraction of the valuable rare earths, continuously circulating in connection with new quantities of fresh ionic clay. Figure 1;

Description

Title of the invention: METHOD FOR VALORIZING RARE EARTHS CONTAINED IN IONIC CLAYS Scope of the invention

[0001] The invention falls within the general field of rare earth recovery from ionic clays. More specifically, it relates to a process for recovering rare earths contained in ionic clays.

[0002] Prior art

[0003] Ionic clays consist of a layered structure of silicate and aluminosilicate sheets with a negatively charged surface. This charge is generally neutralized by cations, for example sodium, calcium, and magnesium cations, which are labilely attached to the surface of the sheets. In the upper layers of the soil, the progressive weathering of rare earth element-containing rocks, such as monazite or bastnaesite, leads to the migration of these rare earth elements to clays located in deeper layers, which consequently become enriched in rare earth elements. Trivalent rare earth element ions form stronger bonds with clays than divalent and monovalent ions, and therefore tend to replace the cations already adsorbed to the surface of the sheets. Thus, ionic clays become enriched in rare earth elements over time, particularly in so-called "heavy" rare earth elements.This category includes rare earth elements with an atomic number greater than or equal to that of samarium, as well as yttrium and scandium.

[0004] The trivalent cations on the surface of said ionic clays can be exchanged with other ions when the clays are brought into contact with solutions particularly concentrated in cations. These properties allow the extraction of rare earths by leaching the ionic clays with solutions containing sodium, magnesium, or ammonium cations. The high cation concentration of these solutions leads to their exchange with the rare earth cations labilely bound to the clays. This yields a solution with a relatively low rare earth concentration, typically less than 1 g / L. Conventionally, this solution is purified of non-rare earth elements, particularly Fe and Al, and then the rare earths are precipitated and recovered as a rare earth carbonate concentrate, also known as MREC (Mixed Rare Earths Carbonate).

[0005] The document Review On The Development And Utilization Of Ionie Rare Earth Ore, Luo Et Al., Minerals 2022, 12, 554, describes rare earth recovery processes and in particular a leaching process of ionic clays comprising the use of solutions of monovalent cation salts, such as Na+ and NH4+, or divalent salts such as Mg2+, exchanged with rare earth cations by adsorption on the surface of ionic clays.

[0006] Document WO 2018 / 162951 describes a method for recovering lanthanides from clays for the production of lanthanide oxides, the method comprising a step of precipitation of rare earths in the form of carbonates, using NH4HCO3.

[0007] One drawback of leaching ionic clays is that, like all rare earth deposits, they contain radioactive elements. This radioactivity must be removed during processing to prevent contamination of the rare earths produced. When rare earths are dissolved by ion exchange, some radioactive elements, whose behavior is similar to that of rare earths, are also released from the clays. Some isotopes decay rapidly, while others, which have a radioactive half-life exceeding a few days, must be removed to prevent contamination of the rare earths.

[0008] For example, the isotope 227Ac (a decay product of 235U), also known as actinium-227, which has a half-life of 22 years, is extremely radioactive. It is a unique case because its chemical properties are similar to those of lanthanum. Actinium therefore follows the rare earth elements and ends up in the MREC (Rare Earth Recycling Facility). It must then be treated in a downstream process and disposed of through the radioactive waste stream, which requires additional permits and costs.

[0009] Another problem related to the presence of actinium in rare earth concentrates concerns transportation. Indeed, above 1 Bq / g, the transport of such a mixture is subject to strict regulations concerning the transport of radioactive materials, known as "Class 7". This necessitates the use of specialized carriers, which constitutes a constraint and additional costs.

[0010] Known separation processes allow the removal of actinium. This type of extraction process, for example, liquid-liquid extraction, is described in particular in Applicant's documents FR 2311246 and FR 2411360. This process allows the removal of actinium as well as some of the lanthanum, and in some cases cerium and yttrium, without loss of the most valuable rare earth elements, namely Pr, Nd, Tb, and Dy. Since yttrium, cerium, and lanthanum have little economic value, this process also avoids significant additional costs, particularly during transport or separation from other high-value rare earth elements.

[0011] Current rare earth recovery techniques from ionic clays have the particularity of recycling the leaching solutions, depleted of rare earths after separation of the MREC, at the beginning of the process in order to save the leaching reagent. In the case of ionic clays, the actinium removal process This process has the drawback of progressively enriching the recycled leaching solution with actinium, lanthanum, and sometimes yttrium and cerium. The increased concentration of lanthanum, cerium, and yttrium, in turn, impacts the solvent extraction of rare earth elements in the liquid-liquid extraction process for removing actinium. Therefore, it is necessary to purge these solutions of actinium, lanthanum, and sometimes yttrium and cerium.

[0012] For environmental reasons, this purging requires the implementation of a process which allows the radioelements to be sequestered in a stable form to limit the risks of groundwater contamination. Description of the invention

[0013] One of the aims of the invention is to remove actinium during the rare earth recovery process from the treatment of ionic clays, thereby avoiding the production, transport, and subsequent processing of radioactive intermediate rare earth concentrates. This removal of actinium is advantageously accompanied by the removal of some of the lanthanum and, in some cases, yttrium and cerium. Since these rare earths have little commercial value, this significantly reduces the total mass of the intermediate rare earth concentrate to be transported and substantially lowers the cost of the separation processes.

[0014] This joint elimination of actinium and low-value rare earths according to the invention has the advantage of not having any adverse effect on the environment, nor on the overall recovery yield of the valuable rare earths, and, according to a certain method of implementation, of not producing any waste.

[0015] By "valued rare earths", for the purposes of the invention, means the lanthanides with an atomic number strictly greater than cerium, and typically praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, erbium, rhohnium, thulium, ytterbium and lutetium, to which is added scandium when the latter is associated with the rare earth group.

[0016] Furthermore, by "unvalued rare earths", we mean, in the sense of the invention, lanthanides with an atomic number less than or equal to that of cerium.

[0017] Yttrium can complement, according to the process used to implement the invention, either the group of valued rare earths or the group of non-valued rare earths.

[0018] Another object of the present invention is to recycle the raffinate resulting from the recovery process by removing the unrecovered actinium and rare earth elements in order to prevent their accumulation in the recycling loop, which will be described in more detail later. This reagent recycling is economically essential in the context of ionic clay processing.

[0019] The invention therefore relates to a process for recovering rare earth elements contained in ionic clays, by leaching said clays in a continuous loop. According to this process: - said leaching is initiated by bringing fresh ionic clay into contact with an aqueous leaching solution SI comprising a dissolved salt of Ml / zCl or M2 / zSO4, where M is a cation chosen from the group consisting of Na+, NH4+ and Mg2+; and z = 1 or 2, representing the number of charges of the cation M, the fresh ionic clay comprising rare earths and actinium in the form of trivalent cations fixed on anionic groups of this clay, said rare earths being exchanged by the cations M on this ionic clay, this leaching generating on the one hand, a leachate or aqueous solution S2 comprising rare earth cations and actinium, and on the other hand, a leached or exhausted clay, the solution S2 being advantageously purified of Fe and Al impurities by increasing the pH; - then said solution S2 is subjected to a phase of extraction of the valuable rare earths, defined as being made up of lanthanides of atomic number greater than that of Ce as well as Sc, where appropriate with added yttrium, by contacting an organic liquid phase or a solid phase generating on the one hand, an organic solution S3 or a solid S3 comprising the valuable rare earths, where appropriate with added yttrium, and on the other hand a raffinate R comprising the salt of Ml / zCl or of M2 / zSO4, actinium in cationic form, and the non-valued rare earths defined as being made up of rare earths of atomic number less than or equal to that of Ce, where appropriate with added yttrium, of which part of the lanthanum, in cationic form; the raffinat R becoming the leaching solution, being brought into contact with a quantity of fresh ionic clay, forming a new solution S2 enriched in Ac3+ cations and in unvalued rare earths, including La3+ compared to the concentrations of these same elements in the initial solution S2, said new solution S2 being subjected to a new phase of extraction of the valuable rare earths, generating a new raffinat R; the leaching solution consisting of the raffinate R resulting from the successive extraction phases of the recovered rare earths, rotating continuously in connection with new quantities of fresh ionic clay, constituting a so-called leaching loop, leading to a transient state with progressive enrichment in actinium and unrecovered rare earths in the solution S2, until reaching a stationary state in which the quantity of leached actinium and unrecovered rare earths becomes zero, these elements remaining fixed on the leached or exhausted clay, and consequently the concentration of these elements in said loop remaining constant.

[0020] According to an advantageous feature of the invention, the concentration of all or part of the solution S2 in actinium and unrecovered rare earths is controlled by precipitating Ac3+ cations and unrecovered rare earths, including La3+ and, where applicable, Y3+, contained in the raffinate R resulting from the successive extraction phases of the recovered rare earths; the carbonates resulting from this precipitation of Ac3+ cations and unrecovered rare earths are separated from the liquid phase of the portion of the raffinate R subjected to this precipitation step, the resulting filtrate, free of rare earths, being reused in the leaching solution.

[0021] According to one embodiment, carbonates are simple residues or waste, then stored.

[0022] According to another embodiment, the carbonates are dissolved by an acidic solution generating a solution S4; this solution S4 is brought into contact with the leached ionic clays, causing the re-adsorption by said leached or rare earth depleted ionic clays of the Ac3+ cations and unvalued rare earths, including La3+ and Y3+, resulting in the formation of a solution S5 comprising a salt of Ml / zCl or M2 / zSO4, the solution S5 being reintroduced into the continuously rotating leaching solution.

[0023] According to one embodiment, the contact of the leaching solution SI, then of the raffinate R, where appropriate supplemented with solution S5, with the fresh clay, is carried out by percolation through said fresh clays in-situ or in piles, to form solution S2.

[0024] According to another embodiment, the contact of the SI solution, then of the raffinate R, optionally supplemented with the S5 solution, with the fresh clay is carried out in a reactor to form the S2 solution, said S2 solution being separated from the fresh clays by a liquid-solid separation process.

[0025] Thus, the invention makes it possible to separate actinium and some of the unrecovered rare earth elements from the recovered rare earth elements. Specifically, the recovered rare earth elements are extracted while leaving the actinium and some of the unrecovered rare earth elements in solution. Consequently, the unrecovered rare earth elements and the actinium are completely reattached to the clay after the latter has been depleted.

[0026] In fact, in the case, for example, of the implementation of the process of the invention on site, the residual clay is recharged with actinium, lanthanum and even cerium and yttrium, the quantities of these elements re-adsorbed by the clay being able to reach 100% of the total quantities of all the rare earths initially contained in said clay before leaching.

[0027] According to the invention, "fresh clay" means clay obtained from ores and chosen for example from the group consisting of kaolinite, montmorillonite, illite and halloysite and not having undergone any leaching other than natural.

[0028] According to the invention, "activity" refers to the trivalent actinium cation content, Ac 3+. This activity is expressed in Bq / L or Bq / g.

[0029] Initiation of leaching

[0030] Leaching preferably takes place in a reactor, in a pile or in situ. It constitutes the initiation of the entire process of the invention.

[0031] According to one embodiment, the priming or initiation of leaching is carried out by a leaching solution SI, which percolates through fresh ionic clay in-situ or in a pile, to form the solution S2.

[0032] According to another embodiment, the contact of the SI solution with the fresh ionic clay is carried out in a reactor to form the S2 solution, said S2 solution being separated from the fresh ionic clay by a liquid-solid separation process, for example by decantation or filtration.

[0033] The aqueous leaching solution SI comprises a dissolved salt of Ml / zCl or M2 / zSO4, where M is a cation chosen from the group consisting of Na+, NH4+ and Mg2+; and z = 1 or 2, representing the number of charges of the cation M.

[0034] Preferably, the salt is a sodium chloride (NaCl), ammonium sulfate ((NH4)2SO4) or magnesium sulfate (MgSO4).

[0035] Advantageously, the molar concentration of Ml / zCl in the SI solution and then of the raffinate R, is between 1 and 2 mol / L. In particular, the molar concentration of NaCl is preferably equal to 1.5 mol / L.

[0036] Preferably, during the leaching of the clay, the molar concentration of M2 / zSO4 in the SI solution, and then in the raffinate R, is between 0.05 and 0.5 mol / L. In particular, the molar concentration of (NH4)2SO4 is preferably between 0.1 and 0.4 mol / L.

[0037] Advantageously, the specific concentration of cations in the SI solution is adjusted to allow for good rare earth leaching efficiency. An excessively high concentration of cations leads to unnecessary reagent losses.

[0038] When fresh ionic clay is brought into contact with the aqueous leaching solution SI, the high concentration of salt cations dissolved in the solution SI causes their exchange with the trivalent rare earth and actinium cations labilely fixed on the clay.

[0039] The trivalent cations of rare earths and actinium are thus found in solution, and form an aqueous solution S2 with the ions of the dissolved salt.

[0040] According to the invention, the trivalent rare earth cations included in the solution S2 are cations of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, erbium, yttrium, holmium, thulium, ytterbium, lutetium and also of scandium when this element is considered associated with the rare earth group.

[0041] The concentration of rare earth cations in solution S2 is advantageously between 0.1 and 5 g / L.

[0042] Examples of ionic clays include, but are not limited to, kaolinite, montmorillonite, illite and halloysite.

[0043] Ionic clays depleted of rare earths, both at the initiation of leaching and following successive leachings due to the implementation of a leaching loop, are preferably washed with water to remove the M cations. This washing has the advantage of increasing the quantity of M cations recycled upstream of the process and consequently improving the re-adsorption of actinium, lanthanum, yttrium, and even cerium by said depleted clays during any subsequent steps by eliminating competition with the M cations.

[0044] Extraction of valuable rare earths

[0045] Preferably, the S2 solution is purified by increasing the pH to remove aluminum and iron impurities. For example, the A13+ and Fe3+ ions can be precipitated using solutions of NH4HCO3, Na2CO3, NaOH, or NH3OH, which increase the pH of the solution, and then separated from the solution by solid-liquid separation.

[0046] According to one embodiment, the extraction phase of the valued rare earths, where appropriate supplemented with yttrium by contacting the solution S2 with the liquid phase, implements a liquid-liquid extraction process, said liquid phase comprising an organic solvent immiscible with water comprising at least one cationic extraction agent.

[0047] Advantageously, liquid-liquid extraction generates: - on the one hand, an aqueous solution S3 comprising the recovered rare earths as well as a small proportion of the unrecovered rare earths initially contained in solution S2, and - on the other hand, a raffinate R comprising the salt of Ml / zCl or M2 / zSO4, actinium as well as the majority of the unvalued rare earths, in cationic form.

[0048] Typically, the cationic extraction agent is preferably chosen from the group consisting of alkyl-phosphonic derivatives, alkyl-phosphinic derivatives and mixtures thereof, for example, mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (HEH(EH)P), bis(2,4,4-trimethylpentyl)phosphinic acid (known by trade name CYANEX®272), a mixture of phosphonic acid and phosphinic acid (known by trade name CYANEX®572), neodecanoic acids of general formula CmH2mO2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, naphthenic acids of general formula CnH2(nz)O2 where n is an integer between 8 and 20, and z is an integer between 0 and 4, and their mixtures.

[0049] The recovered rare earths contained in solution S3 are re-extracted by an acidic aqueous solution forming an aqueous extract E, the acid being able to be chosen from the group including hydrochloric acid, nitric acid and sulfuric acid and then possibly precipitated into a solid, the solution or the solid having an actinium activity of less than 0.1 Bq / g of rare earths contained.

[0050] According to another embodiment, the extraction phase of the valued rare earths is carried out by contacting the solution S2 with a solid phase capable of fixing the cations of said rare earths.

[0051] The solid phase is advantageously chosen from the group comprising: silicas with a high specific surface area, typically greater than 40 m2 / g, on which extracting molecules are grafted or adsorbed, titanium oxides on which extracting molecules are grafted or adsorbed, zirconium oxides on which extracting molecules are grafted or adsorbed, polymer matrices on which extracting molecules are grafted, and macroporous polymer matrices impregnated with extraction agents.

[0052] Advantageously, the grafted or adsorbed extracting molecules and the extraction agents are compounds capable of binding the valuable rare earth elements by ion exchange. The extracting molecules have active groups that are typically those of the cationic extraction agents used in the liquid-liquid extraction process, in particular phosphonic, phosphinic, or carboxylic groups. The extraction agents are those used in the liquid-liquid extraction process.

[0053] Preferably, the solid phase is stationary and located in a reservoir in which the solution S2 percolates, generating a solid S3. The recovered rare earths are fixed on the solid phase while the unrecovered earths are removed in the raffinate R.

[0054] After percolation of the solution S2, the solid S3 preferably undergoes a solid-liquid re-extraction using an acidic eluent, generating an aqueous extract E loaded with valuable rare earths, the acidic eluent being chosen from the group consisting of hydrochloric acid, sulfuric acid and nitric acid.

[0055] According to one embodiment, the aqueous extract E loaded with valuable rare earths is concentrated by evaporation.

[0056] According to another embodiment, the rare earths recovered, where appropriate with added yttrium contained in the aqueous extract E, are precipitated using a precipitating agent selected from the group including sodium carbonate, ammonium bicarbonate, sodium hydroxide, ammonia, oxalic acid and its alkali salts.

[0057] Advantageously, the raffinate R resulting from the successive extraction phases of the valorized rare earths has a total concentration of rare earth ions of between 0.1 and 5 g / L and an activity related to the Ac3+ content of between 0 and 30 Bq / L.

[0058] The raffinate R resulting from the extraction operation of the valuable rare earths is, preferably, divided into two streams Fl and F2, the Fl stream constituting the leaching solution rotating in a loop, and the F2 stream being subjected to the precipitation in the form of carbonates of the Ac3+ cations and the non-valued rare earths, the ratio Fl / (F1+F2) being between 0 and 1.

[0059] Leaching loop

[0060] As already indicated, the raffinate R resulting from the successive extraction phases of the recovered rare earths becomes the new leaching solution S2, and circulates continuously in contact with new quantities of fresh ionic clay, constituting a so-called leaching loop. This contact leads to the formation of new solutions S2 enriched, compared to the initial solution S2, in Ac3+ cations and in unrecovered rare earths, including La3+ and, where applicable, Y3+, constituting a transient state until reaching a stationary state in which, although the clay undergoing leaching is partially depleted of rare earths, the quantity of actinium and unrecovered rare earths recovered as a result of this leaching becomes zero.

[0061] In other words, the process implements a leaching loop, in which the leaching solution S2 is progressively enriched in Ac3+ cations and in unvalued rare earths, including La3+ and where applicable Y3+, due to its contact with new quantities of fresh ionic clay.

[0062] Lanthanum purging

[0063] Advantageously, the process of the invention implements the control of the lanthanum concentration of the solution S2 in order to optimize the extraction of valuable rare earths and to prevent the extraction of non-valued rare earths from competing with the extraction of valuable rare earths, so that the process would lose its interest.

[0064] For this purpose, the precipitation of Ac3+ cations and unvalued rare earths, including La3+ and where applicable Y3+, contained in the raffinate R in the form of carbonates, is generated.

[0065] Preferably, the precipitation of Ac3+ cations and rare earths not recovered in the form of carbonates is carried out by adding to the raffinate R resulting from the successive phases of extraction of the recovered rare earths, a solution of carbonate salt of M2 / zCO3 or Mz(HCO3)2, where M is a cation chosen from the group consisting of Na+, NH4+ and Mg2+ and z = 1 or 2.

[0066] Preferably, the carbonates are separated from the liquid phase of the raffinate R before their dissolution, resulting in a rare earth free filtrate, said filtrate being reused in the leaching solution. The carbonates separated from the liquid phase of the raffinate R are preferentially washed with water to remove the cations M.

[0067] Carbonates advantageously exhibit an activity between 0 and 50 Bq / g of dry carbonates, said carbonates comprising: - 20% to 60% lanthanum, by weight, relative to the total weight of carbonates considered dry, - 0 to 30% of other unvalued rare earths, including yttrium and cerium, by weight, relative to the total weight of carbonates considered dry.

[0068] Carbonates are either stored as residues or waste, or preferably subsequently dissolved by an acidic solution generating a solution S4. Advantageously, the acidic solution used to dissolve the carbonates resulting from the precipitation of Ac3+ cations and unrecovered rare earths comprises a Lewis acid selected from the group consisting of HCl and H2SO4. The acidic solution preferably has a molar concentration of Lewis acid between 0.001 and 1.5 mol / L.

[0069] Re-adsorption of unvalued rare earths and actinium

[0070] Advantageously, the process of the invention also aims at the re-adsorption of Ac3+ cations and unrecovered rare earth elements, in particular La3+ and Y3+, by the various quantities of leached ionic clay, which is then depleted of rare earth elements and results from different leaching processes. This re-adsorption is carried out by contacting the S4 solution with said quantities of leached clay.

[0071] The contacting of the S4 solution with the ionic clays depleted in rare earths is carried out in a reactor, by percolation over a filter, by percolation over a pile of leached clay or by percolation through a deposit of leached clays.

[0072] The M cations, which were adsorbed on the clay, are exchanged and pair with the Lewis acid anions to form a solution S5 of salt of Ml / zCl or of M2 / zSO4, the solution S5 being reintroduced into the leaching loop.

[0073] At the end of the re-adsorption operation, the ionic clay, depleted of valuable rare earths, is preferably washed with water to remove the M cations. This washing has the advantage of improving the recovery of the M cations and preventing their release into the environment. Brief description of the figures

[0074] The figures referred to below are purely illustrative. The process they represent can be implemented in other configurations.

[0075] Fig. 1 is a general schematic representation of the process according to the invention.

[0076] Figure 2 is a schematic representation of the method according to the invention. including a leaching step in a reactor.

[0077] Fig. 3 is a schematic representation of the process according to the invention comprising an in-situ leaching step.

[0078] Fig. 4 is a schematic representation of the process according to the invention comprising a heap leaching step.

[0079] Detailed description of the figures

[0080] With reference to [Fig. 1], a quantity of fresh ionic clay (10), containing rare earth and actinium ions, is leached (11) by an aqueous leaching solution SI comprising a dissolved salt.

[0081] Leaching (11) generates, on the one hand, a leachate or aqueous solution S2 (12) comprising the recovered rare earth cations Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Sc as well as the unrecovered rare earths La, Ce and Y, and actinium. Consequently, leaching (11) produces a depleted or exhausted clay (24).

[0082] Solution S2 (12) is treated by adding a neutralizing agent (N) to precipitate impurities such as aluminum, iron and lead.

[0083] The treated solution S2 (12) is brought into contact with a liquid phase (13), which generates on the one hand, a solution S3 (14) comprising the recovered rare earths, and on the other hand a raffinate R (18) comprising the dissolved salt, actinium, lanthanum and, where appropriate, cerium and yttrium, in cationic form.

[0084] Solution S3 (14) is precipitated (15) in the form of valuable rare earth carbonates (16). The liquid phase (17) is separated from the precipitate and rejoins the raffinate R (18).

[0085] The raffinate R (18) is recycled to leach (11) a new quantity of fresh ionic clay (10), resulting in the formation of a solution S2 (12) enriched in actinium, lanthanum, and, where applicable, yttrium cations, relative to the concentrations of these same elements in the initial solution S2. The liquid phase (17) can rejoin the raffinate R (18) just before the leaching (11) of a new quantity of fresh ionic clay (10).

[0086] These leaching steps (11) and contact with a liquid phase (13) are carried out continuously, forming a leaching loop where new quantities of fresh ionic clays (10) are leached, until a steady state is reached such that the chemical equilibrium between the leached ionic clay (10) and the S2 solution (12) enriched in actinium, lanthanum and, where applicable, yttrium cations no longer varies.

[0087] Optionally, the actinium, lanthanum, and yttrium cations contained in the raffinate (18) are precipitated (19) as carbonates. The liquid phase (20) is separated from the precipitate and rejoins the raffinate R (18). The carbonates are subsequently dissolved (21) using an acidic solution. Their dissolution generates a solution S4 (22), which is brought into contact (23) with the depleted ionic clays (24). During this contact, the actinium, lanthanum, and yttrium cations are re-adsorbed onto the clays (24). The leachate from this contact, also called solution S5 (25) which includes the dissolved salt, is reintroduced into the leaching loop.

[0088] We thus recover a clay depleted in valuable rare earths (26), but recharged in actinium, lanthanum and yttrium.

[0089] Referring to [Fig. 2], an ionic clay (30), whose layers contain trivalent rare-earth cations, is fed into a leaching reactor (31). In this reactor (31), a first quantity of ionic clay is leached with an aqueous SI leaching solution, comprising a dissolved NaCl salt at a molar concentration of 1.5 mol / L. The trivalent rare-earth and actinium cations are exchanged for Na+ cations. The clay and the rare-earth-laden solution then form a pulp (32).

[0090] The pulp (32) is filtered in a filter press (33) to separate the liquid phase (35) corresponding to a first solution (S2) from the depleted clay (34). The latter is subsequently washed.

[0091] The first solution S2 (35) is treated by adding a neutralizing agent (NI), which is Na2CO3, allowing the precipitate impurities of aluminium, iron and lead.

[0092] After this treatment, the first solution S2 (35) is contacted with an organic solvent enabling the extraction of rare earths in an extraction battery (36), generating on the one hand a solution S3 (37) comprising the extracted rare earths, and on the other hand a raffinate R (41) comprising the rare earths not recovered in solution, including lanthanum, cerium, and actinium. The organic solvent is composed of mono-2-ethylhexyl ester of (2-ethylhexyl)phosphonic acid (PC88A) with a molar concentration of 1.0 M, in kerosene.

[0093] A Na2CO3 solution is added to a reactor (38) to precipitate the rare earths contained in solution S3, in the form of rare earth carbonates (39). The rare earth carbonates (39) have an activity of less than 0.1 Bq / g of rare earths.

[0094] The rare earth carbonates (39) are separated from the liquid phase (40). The latter is introduced into a buffer reactor (47) where its cation concentration is adjusted. It is then recycled to the leaching reactor (31).

[0095] The raffinate R (41) is partially precipitated by a solution of NH4HCO3 in the reactor (42), thus forming a solid consisting of unrecovered rare earth carbonates, including lanthanum, cerium, and actinium (43). The carbonates (43) are separated from the liquid phase (L1) and washed, the wash water being mixed with the liquid phase (L1) and sent to the buffer reactor (47).

[0096] The unprecipitated liquid phase (46) of the raffinate R is introduced into the buffer reactor (47) where its cation concentration is adjusted. It is then reintroduced into the leaching reactor (31).

[0097] Carbonates (43) are dissolved by an HCl solution in the reactor (44), generating a solution S4 (45) comprising the unrecovered rare earth elements, including lanthanum, cerium, and actinium. Solution S4 is brought into contact with a pile of depleted clays (48), resulting from several leachings.

[0098] This leads to the re-adsorption of the unrecovered rare earth elements by the depleted clays, where the Ac3+, La3+, and Ce3+ cations are again adsorbed onto the clay sheets, the depleted clays then being replenished with Ac, La, and Ce (A). This also results in the formation of a NaCl solution S5 (49) purified of all or part of the Ac3+, La3+, and Ce3+ cations. The S5 solution (49) resulting from this contact is recycled to the buffer reactor (47).

[0099] The process of the invention represented in [Fig.3] includes an in-situ leaching step which consists of injecting an aqueous leaching solution SI, comprising a dissolved salt of (NH4)2SO4 at a molar concentration of 0.18 mol / L, into an injection well (50) to bring it into contact with a deposit of ionic clays.

[0100] Percolation of the solution through the clay deposit results in the exchange of trivalent rare-earth and actinium cations by NH4+ cations, and the formation of a depleted ionic clay deposit (51), and an aqueous solution S2 (52), comprising the trivalent rare-earth cations and actinium. The solution (52) is extracted from the deposit via a production well or via a trench.

[0101] Solution S2 (52) is treated by adding a neutralizing agent (N2), which is NH4HCO3, allowing the precipitate impurities of aluminium, iron and lead.

[0102] After this treatment, solution S2 (52) is contacted with an organic solvent in an extraction battery (53), generating, on the one hand, a solution S3 (54) comprising the extracted rare earths, and on the other hand, a raffinate R (58) comprising the unextracted rare earths, not recovered in solution, including lanthanum, cerium, and actinium. The organic solvent is composed of naphthenic acid, aliphatic kerosene, and decanol at 31 / 62 / 7 vol%, respectively.

[0103] A solution of NH4HCO3 is added to a reactor (55) to precipitate the rare earths contained in the solution S3 in the form of rare earth carbonates (56) having an activity of less than 0.1 Bq / g of rare earths.

[0104] The rare earth carbonates (56) are separated from the liquid phase (57), the latter being introduced into a buffer reactor (64) for adjustment of the cation concentration, then reintroduced into the injection well (50).

[0105] The raffinate R (58) is partially precipitated by a solution of NH4HCO3 in the reactor (59), thus forming a solid consisting of unrecovered rare earth carbonates, including lanthanum, cerium and yttrium, and actinium (60). The carbonates (60) are separated from the liquid phase (L2) and washed, the wash water being mixed with the liquid phase (L2) and sent to the buffer reactor (64).

[0106] The unprecipitated liquid phase (63) of the raffinate R is introduced into the buffer reactor (64), then recycled into the injection well (50).

[0107] Carbonates (60) are dissolved by a solution of H2SO4 in reactor (61), generating a solution S4 (62) comprising the unrecovered rare earth elements, including lanthanum, cerium, yttrium, and actinium. Solution S4 then percolates through a depleted clay deposit (65), where all or part of the La3+, Ce3+, Y3+, and Ac3+ cations bind to the clays, resulting in the formation of clays replenished with La, Ce, Y, and Ac (66). The resulting solution S5 (67) from this percolation is then recycled to the buffer reactor (64). The contents of the buffer reactor (64) are recycled to the injection well (50).

[0108] With reference to [Fig.4], ionic clays (70) are arranged in a pile (71) and leached by an aqueous leaching solution SI, comprising a dissolved salt of (NH4)2SO4 at a molar concentration of 0.18 mol / L.

[0109] The trivalent rare earth and actinium cations exchanged by the NH4+ cations then form an aqueous solution S2 (73) while the pile of clays is broken up (72).

[0110] Solution S2 (73) is treated by adding a neutralizing agent (N3), which is NH4HCO3, allowing the precipitate impurities of aluminium, iron and lead.

[0111] After this treatment, the solution S2 (73) is brought into contact with a solid phase composed of beads of a macroporous cross-linked polystyrene resin onto which aminomethylphosphonic acid is adsorbed in an extraction column (74), generating on the one hand a solid S3 (75) where the extracted rare earths are fixed and valued, and on the other hand a raffinate R (80) comprising the rare earths not extracted, not valued in solution, including lanthanum, cerium and yttrium, as well as actinium.

[0112] The solid S3 (75) is re-extracted using sulfuric acid H2SO4 at 200 g / L generating an aqueous extract E (76) comprising the extracted and recovered rare earths.

[0113] A solution of NH4HCO3 is added to a reactor (77) to precipitate the rare earths contained in the aqueous extract E (76) in the form of rare earth carbonates (78) having an activity of less than 0.1 Bq / g of rare earths.

[0114] The rare earth carbonates (78) are separated from the liquid phase (79), the latter being introduced into a buffer reactor (86) for adjustment of the cation concentration, then brought back into contact with the pile of clays (71).

[0115] The raffinate R (80) is partially precipitated by a solution of NH4HCO3 in the reactor (81), thus forming a solid consisting of unrecovered rare earth carbonates (82), including lanthanum, cerium and yttrium, and actinium. The carbonates (82) are separated from the liquid phase (L3) and washed, the wash water being mixed with the liquid phase (L3) and sent to the buffer reactor (86).

[0116] The unprecipitated liquid phase (85) of the raffinate R (80) is introduced into the buffer reactor (86) for adjustment of the cation concentration, then brought into contact with the clay pile (71).

[0117] Carbonates (82) are dissolved by a solution of H2SO4 in the reactor (83), generating a solution S4 (84) comprising the unrecovered rare earth elements, including lanthanum, cerium, yttrium, and actinium. Solution S4 is brought into contact with a pile of depleted clays (87). By percolation, all or part of the La3+, Ce3+, Y3+, and Ac3+ cations will bind to the clays, thus forming a pile of clays replenished with La, Ce, Y, and Ac (88). The resulting solution S5 (89) is recycled to the buffer reactor (86).

[0118] Examples of embodiments of the invention

[0119] As follows from the above, after the elimination of the recovered rare earths, according to the process of the invention, the leaching solution becomes enriched in unrecovered rare earths (La, Y, Ce, Ac), and is then recycled for further leaching of the clay.

[0120] Examples 1 to 3 below illustrate the influence of multiple recycling processes on clay leaching, leading to a progressive increase in the concentration of unrecovered rare earth elements in the leaching solution. The unrecovered rare earth elements consist primarily of lanthanum, due to the implementation of the separation process, which substantially extracts rare earth elements with atomic numbers higher than that of lanthanum. The leaching solutions are successively solutions of sodium chloride, ammonium sulfate, and magnesium sulfate.

[0121] Examples 1 to 4 correspond to an implementation of the process without implementation of lanthanum purging.

[0122] Example 1: Leaching of ionic clays using aqueous NaCl leaching solutions

[0123] Aqueous leaching solutions having a molar concentration of NaCl of 1.5 M and exhibiting variable concentrations of LaC13 and CeC13 are brought into contact with quantities of ionic clay from the same ore, and comprising rare earths, some of which are in cationic form.

[0124] Typically, the concentrations of lanthanum, cerium and neodymium are 580 ppm, 540 ppm and 400 ppm respectively.

[0125] A volume of 104 mL of each leaching solution is brought into contact with 70 g of dried clay which has been previously sieved to 1 mm.

[0126] The mixture is stirred at room temperature for 7 minutes and the pH is adjusted to 4.7 using a Na2CO3 solution to precipitate the Al impurities.

[0127] The mixture is stirred for a further 14 minutes, then filtered. The resulting wet clay cake is washed by piston with 100 mL of demineralized water.

[0128] The concentration of La, and of other rare earth elements in solution (Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) is measured before and after contact with the clay. The masses are listed in Table 1 below.

[0129] Four tests are carried out with increasing concentrations of La in the leaching solution so as to simulate the progressive enrichment in the loop.

[0130] [Table 1] Leaching Tests Leaching Solution (SI) Leaching Solution (S2) Leaching Ratio La La (mg) [La] (g / L) Total La present in 1 e leachate (mg) Other rare earths (mg) La leachate at Test Solution (mg) E1 0 0 16.3 30.9 16.3 1 E2 20.5 0.20 34.1 35.6 13.6 0.83 E3 71.3 0.69 81.6 38.4 10.3 0.63 E4 120 1.15 125 39.7 5.1 0.31 E5 168 1.62 172 41.2 3.9 0.24

[0131] The leaching ratio of La corresponds to the ratio between the mass of La leached after a leaching test En, n being equal to 1, 2, 3, 4 or 5, and the mass of La leached after the first leaching test EL

[0132] During the El test, 16.3 mg of La and 30.9 mg of other rare earths are leached.

[0133] During the E2 leaching trial or test, a total of 20.5 mg of La is included in the Leaching solution. The leaching solution contains a total of 34.1 mg of La. The leaching solution E2 also contains 35.6 mg of other rare earth elements.

[0134] The leaching tests El to E5 demonstrate that the more the quantity of La in the leaching solution (SI) is increased, the less La is recovered at each step in the leaching solution (S2).

[0135] Above a certain quantity, an equilibrium is reached at which La is no longer leached, meaning that the La remains bound to the ionic clay. In this example, equilibrium is reached for a mass of La in the leaching solution of 206 mg, corresponding to a mass concentration of 2.0 g / L. This value is obtained by linear regression from the values ​​in Table 1.

[0136] In addition, it is noted that the mass of other leached rare earths increases substantially from 30.9 mg to 41.2 mg when the concentration in La increases.

[0137] The leaching ratio La of 1 for the leaching test El is taken as a reference to demonstrate the implementation of the process.

[0138] In this example, the evolution of the leaching ratio is shown during the implementation of the invention with sodium chloride leaching and without any lanthanum purging.

[0139] Recycling raffinate R according to the invention gradually leads to equilibrium in the leaching loop when the La concentration reaches a certain value. At that point, the La leaching ratio is zero and the La concentration no longer changes during the leaching cycles.

[0140] Example 2: Leaching of ionic clays using aqueous leaching solutions of (NH4)2SO4

[0141] Aqueous leaching solutions having a molar concentration of (NH4)2SO4 of 0.18 M and exhibiting variable concentrations of La2(SO4)3 are brought into contact with quantities of ionic clay from the same ore, and containing rare earths, in particular in cationic form.

[0142] The protocol of Example 1 is repeated here, except that the pH is adjusted using a solution of NH4HCO3.

[0143] The concentration of La and other rare earth elements in solution is measured before and after contact with the clay. The masses are listed in Table 2 below.

[0144] [Table 2] Leaching Tests Leaching Solution (SI) Leaching Solution (S2) Leaching Ratio La La (mg) [La] (g / L) Total La present in the leachate (mg) Other rare earth elements (mg) La leachate at T from the test (mg) E1 0 0 15.8 28.5 15.8 1 E2 22.3 0.21 37.9 31.1 15.6 0.99 E3 44.6 0.43 58.6 32.4 14.0 0.88 E4 129 1.24 137 33.9 8.3 0.53 E5 255 2.45 256 32.1 0.64 0.04

[0145] During the first El leaching test, 15.8 mg of La and 28.5 mg of the other rare earths were leached.

[0146] During the second leaching test E2, a total of 22.3 mg of La is included in the leaching solution. The leaching solution comprises a total of 37.9 mg of La, of which 22.3 mg came from the leaching solution, and 15.6 mg from the leaching of the clay involved in test E2. The solution from leaching E2 also includes 31.1 mg of other rare earths.

[0147] The leaching tests El to E5 demonstrate that the more the quantity of La in the leaching solution (SI) is increased, the less La is recovered at each step in the leaching solution (S2).

[0148] Above a certain quantity, an equilibrium is reached at which La is no longer leached. In this example, this equilibrium is reached for an initial quantity of La in the solution of 274 mg, corresponding to a concentration of approximately 2.6 g / L. Furthermore, it is noted that the quantity of other leached rare earths increases slightly from 28.5 mg to 32.1 mg.

[0149] This example shows the evolution of the leaching ratio during implementation of the invention with ammonium sulfate leaching and without lanthanum purging.

[0150] Recycling raffinate R according to the invention, loaded with La, gradually leads to an equilibrium when the La concentration of raffinate R reaches a certain value. Then, the La leaching ratio is zero and the La concentration no longer changes during the leaching cycles.

[0151] Example 3: Leaching of ionic clays using aqueous leaching solutions of MgSO4

[0152] Aqueous leaching solutions of MgSO4 with a molar concentration of 0.18 M and containing different concentrations of La2(SO4)3 are brought into contact with quantities of ionic clay from the same ore, and containing rare earths, in particular in cationic form.

[0153] The protocol of Example 1 is repeated here, except that the pH is adjusted using an NH4HCO3 solution.

[0154] Three tests are carried out with increasing concentrations of La in the leaching solution.

[0155] The masses are listed in Table 3 below.

[0156] [Table 3] Leaching tests Leaching solution (SI) Leaching solution (S2) Leaching ratio La La (mg) [La] (g / L) Total La present in the leachate (mg) Other rare earths (mg) Leachate at the end of the test (mg) El 0 0 15.8 30.2 15.8 1 E2 21.6 0.21 35.8 36.5 14.1 0.89 E3 123 1.18 131 36.5 7.8 0.49

[0157] During the first El leaching test, 15.8 mg of La and 30.2 mg of other rare earths were leached.

[0158] During the second leaching test E2, a total of 21.6 mg of La is included in the leaching solution. The leaching solution comprises a total of 35.8 mg of La, of which 21.6 mg comes from the leaching solution and 14.1 mg from the leaching of the clay involved in test E2. The leaching solution E2 also comprises 36.5 mg of other rare earth elements.

[0159] The El to E3 leaching tests demonstrate that the more the quantity of La in the leaching solution (SI) is increased, the less La is recovered at each step in the leaching solution (S2).

[0160] In this example, it is determined that equilibrium is reached for an amount of La in the initial solution of 228 mg, i.e. a concentration of the order of 2.2 g / L.

[0161] So, the leaching ratio La is zero, and the concentration does not change during successive leaching cycles.

[0162] Example 4: Leaching of ionic clays using aqueous leaching solutions of (NH4)2SO4 comprising La and Y

[0163] This example illustrates the evolution of leaching solutions when the separation of rare earths is carried out by implementing the rare earth extraction process in which yttrium has a behavior almost identical to that of lanthanum and is therefore also not valued.

[0164] Salt leaching solutions of (NH4)2SO4 with a concentration of 0.18 M and containing different concentrations of La2(SO4)3 and Y2(SO4)3 are brought into contact with quantities of ionic clay from the same ore, and containing trivalent rare earth cations.

[0165] The protocol of Example 1 is repeated here, except that the pH is adjusted using a solution of NH4HCO3.

[0166] The concentration of La, Y and other rare earths in solution is measured before and after contact with the clay. The masses are listed in Table 4 below.

[0167] [Table 4] Leaching Tests Leaching Solution (S1) Leaching Solution (S2) Leaching Ratio La [La] Y [Y]( Total Total Other La leached Y leached La Y (mg) (g / L) (mg) g / L) La Y lands leached to T ied to the i (mg) (mg) rare ( mg) from test (mg) from test (mg) El 0 0 0 0 17.3 7.7 25.3 17.3 7.7 1 1 E2 22.1 0.21 9.5 0.09 36.4 16.4 25.2 14.3 6.9 0.83 0.89 E3 41.9 0.40 21.7 0.21 56.9 28.7 25.7 15.0 7.0 0.87 0.91 E4 128 1.23 52.9 0.51 136.8 58.3 25.0 9.2 5.4 0.53 0.69 E5 252 2.42 105.7 1.01 243.7 107.6 26.0 <0.1 mg 1.9 <0.01 0.25

[0168] During the first El leaching test, 17.3 mg of La, 7.7 mg of Y and 25.3 mg of the other rare earths were leached.

[0169] During the second leaching test E2, a total of 22.1 mg of La was included in the leaching solution. The leaching solution comprised a total of 36.4 mg of La, of which 22.1 mg came from the leaching solution and 14.3 mg from the leaching of the clay involved in test E2.

[0170] A total of 9.5 mg of Y is included in the leaching solution of the second leaching test E2. The solution obtained from the leaching comprises a total of 16.4 mg of Y, of which 9.5 mg comes from the leaching solution, and 6.9 mg comes from leaching of the clay involved in test E2.

[0171] At the fifth leaching test E5, 8.0 mg is reattached, which justifies the negative value in Table 4.

[0172] The El to E5 leaching tests demonstrate that the more the quantity of La and Y in the leaching solution (SI) is increased, the less La and Y are recovered leached at each step in the leaching solution (S2).

[0173] Above a certain quantity, an equilibrium is reached at which these elements are no longer leached. In this example, the equilibrium is reached: - in the case of La, for a quantity of La in the leaching solution of 273 mg, calculated by linear regression of the values ​​in table 4, i.e. a concentration of 2.6 g / L, identical to that of example 2 where yttrium is not added. - in the case of Y, for a quantity of Y in the leaching solution of 144 mg, i.e. a concentration of 1.4 g / L.

[0174] In addition, it is noted that the quantity of other leached rare earths changes little and remains between 25.3 mg and 26.0 mg.

[0175] Here, the leaching ratio of La or Y for the leaching step El is set at 1 as a reference to demonstrate the implementation of the process.

[0176] It is clear from Examples 1 to 4 that the recycling of raffinate R within the process gradually leads to an equilibrium, which is reached when the concentrations of La and / or Y in the raffinate R reach a certain value. Indeed, the raffinate R, which is obtained from the extraction of the solution resulting from leaching S2, becomes enriched in La and / or Y cations during the leaching of ionic clays. When equilibrium is reached, the leaching ratios of La and / or Y are negative, and their concentration no longer changes during the leaching cycles.

[0177] Example 5: Leaching of ionic clays with refixation of La and Ce onto the clay: Total removal of lanthanum with refixation onto the clay

[0178] This example illustrates the implementation of lanthanum purging by treating all of a raffinate R from the process of separating the recovered rare earths and refixing it on the depleted clay by a mixing operation in a stirred reactor and separation.

[0179] 500 g of ionic clay is leached by contacting it with a NaCl leaching solution of molar concentration equal to 1.5 M, the clay being washed afterwards.

[0180] Solutions of CeC13 and LaC13 are prepared at different concentrations, by dissolving a solid of La and Ce carbonates, precipitated from a raffinate obtained from liquid-liquid extraction.

[0181] 100 mL of a CeCl3 and LaCl3 solution is contacted with 92.5 g of the depleted clay for 20 minutes. The resulting solution is filtered. The clay is washed by piston with 100 mL of demineralized water. The amounts of La, Ce, and Na in the filtrate, which also contains the wash water, are measured.

[0182] Five tests are carried out corresponding to S4 solutions having an increasing concentration of La and Ce.

[0183] The quantities of La, Ce and Na are listed in Table 5 below.

[0184] [Table 5] Refixation tests Solution (S4) Filtrate (solutio n S5) La+Ce refixed (mg) La+Ce refixed (%) La+Ce (mg) La+Ce (mg) Na (mg) El 0 0 9.51 - - E2 3.09 <0.04 15.8 3.09 100 E3 15.1 <0.04 21.0 15.1 100 E4 29.6 <0.04 28.5 29.6 100 E5 131 61.9 49.6 69.2 53 E6 269 198 49.8 71.1 26

[0185] The clay used allows the reattachment of up to 0.76 g of La and Ce per kg of wet clay, or 5.4 moles of rare earth elements per tonne of wet clay. This corresponds to 1.1 g of La and Ce per kg of dry clay, or 7.7 moles of rare earth elements per tonne of dry clay. Beyond this point, the clay is saturated.

[0186] This example demonstrates the ability of depleted clay to quantitatively re-adsorb La and Ce from a La and Ce chloride solution.

[0187] Example 6: Extraction of rare earths from ionic clays with refixation of La and Ce on the clay, via the chloride route: Total purging with refixation on the clay (implementation on a filter by percolation through the depleted clay)

[0188] This example illustrates the implementation of lanthanum purging in the context of the process of the invention by treating all of a raffinate R from the process of separating the recovered rare earths, and refixing it on the depleted clay by a forced percolation operation through a bed of clay.

[0189] An ionic clay is leached by contacting 100 g of dry clay with a NaCl solution of concentration equal to 1.5 M. After filtration, 140 g of wet clay, of thickness equal to 2 centimeters, is obtained.

[0190] La and Ce chloride solutions are prepared at different total concentrations by dissolving La and Ce carbonates, obtained by precipitation of a raffinate from liquid-liquid extraction. These solutions percolate through the moist clay.

[0191] Percolation is accelerated by applying a pressure difference: either under vacuum using a Buchner funnel, or by pushing with compressed air through a pressure filter. The resulting solution is percolated several times over the damp clay bed, which is thus progressively enriched in rare earth elements.

[0192] A total of 10 percolations (or passes) are carried out. The residual concentration of La and Ce after each percolation is detailed in Table 6 below.

[0193] [Table 6] [La+Ce] (mg / L) [Na] (mg / L) [La+Ce] (mg / L) [Na] (mg / L) [La+Ce] (mg / L) [Na] (mg / L) Initial solution e(S4) 487 0 1017 0 4341 0 Buchner under vacuum (-850 mbarg) 1 pass 32 168 218 253 2 passes 16 192 137 312 3 passes 1.6 196 112 315 4 passes <0.3 201 114 320 5 passes <0.2 201 112 322 Filter under pressure (6 barg) 1 pass 184 296 2507 502 2 passes 136 336 2801 455 3 passes 127 344 2723 417 4 passes 122 353 2858 408 5 passes 121 360 2843 410 La+Ce refixed (mol / T sec) 5.0 9.0 9.5

[0194] It is observed that the refixation capacity of the clay used is on the order of 9.5 mol of La and Ce refixed / tonne of dry clay, i.e. about 1400 g of Le and Ce refixed / tonne of dry clay.

[0195] This example illustrates the fixation of unrecovered La and Ce rare earth elements onto depleted ionic clay during solvent extraction. It is demonstrated here that it is possible to reattach La and Ce by percolating solution S4 over the filter loaded with the clay cake used for the solid / liquid separation of the leached clay.

[0196] Example 7: Extraction of rare earths from an ionic clay with refixation of La and Ac and Ce on the clay, via the sulfate route: Total purging with refixation on the clay via the sulfate route (implementation on a filter by percolation through the depleted clay)

[0197] This example illustrates the refixation of Ac contained in raffinat R with a behavior in the process identical to that of lanthanum.

[0198] An ionic clay is leached with a (NH4)2SO4 solution of concentration equal to 0.18 M. The clay is subsequently washed.

[0199] A La sulfate solution is brought into contact with the depleted clay by percolating the solution through a bed of wet, depleted, and washed clay.

[0200] Percolation is accelerated by applying a pressure difference by drawing under vacuum using a Buchner. The resulting solution is percolated several times over the clay bed, which thus becomes progressively enriched in La and Ac.

[0201] The residual concentrations of La, Ce and Ac in the solution after depletion by three successive percolations on the clay bed are detailed in Table 7 below.

[0202] [Table 7] [La] (mg / L) [Ce] (mg / L) Ac-227 (Bq / L) In the initial solution (S4) 5700 80 38 After 3 percolations 4137 64 18

[0203] This example illustrates the refixation of lanthanum and actinium by the same process as in Example 6, via the sulfate route. It is demonstrated that it is possible to refix La and Ac by percolating the solution through the depleted clay, for example over the filter used for the solid-liquid separation of the depleted clay.

Claims

1. Demands A process for recovering rare earths contained in ionic clays by leaching said clays in a continuous loop: wherein said leaching is initiated by contacting fresh ionic clay with an aqueous leaching solution SI comprising a dissolved salt of Ml / zCl or M2 / zSO4, where M is a cation chosen from the group consisting of Na+, NH4+ and Mg2+; and z = 1 or 2, representing the number of charges of the cation M, the fresh ionic clay comprising rare earths and actinium in the form of trivalent cations attached to anionic groups of this clay, said rare earths being exchanged by the cations M on this ionic clay, this leaching generating on the one hand, a leachate or aqueous solution S2 comprising rare earth cations and actinium, and on the other hand, a leached or exhausted clay; then in which, said solution S2 is subjected to a phase of extraction of the valuable rare earths, defined as being made up of lanthanides of atomic number greater than that of cerium as well as Sc, where appropriate with added yttrium, by contacting an organic liquid phase or a solid phase generating on the one hand, an organic solution S3 or a solid S3 comprising the valuable rare earths, where appropriate with added yttrium, and on the other hand a raffinate R comprising the salt of Ml / zCl or of M2 / zSO4, actinium in cationic form, and the non-valued rare earths defined as being made up of rare earths of atomic number less than or equal to that of cerium, where appropriate with added yttrium, of which a part of the lanthanum, in cationic form; the raffinat R becoming the leaching solution, being brought into contact with a quantity of fresh ionic clay, forming a new solution S2 enriched in Ac3+ cations and in unvalued rare earths, including La3+ compared to the concentrations of these same elements in the initial solution S2, said new solution S2 being subjected to a new phase of extraction of the valuable rare earths, generating a new raffinat R; the leaching solution consisting of raffinate R resulting from successive extraction phases of the recovered rare earths, continuously rotating in conjunction with new quantities of ionic clay fresh, constituting a so-called leaching loop, leading to a transitional state with progressive enrichment in actinium and unvalued rare earths in the S2 solution, until reaching a stationary state in which the quantity of leached actinium and unvalued rare earths becomes zero, these elements remaining fixed on the leached or exhausted clay and consequently the concentration of these elements in said loop remaining constant.

2. A process for recovering rare earths contained in ionic clays according to claim 1, wherein the concentration of all or part of the solution S2 in actinium and unrecovered rare earths is controlled by precipitating Ac3+ cations and unrecovered rare earths contained in the raffinate R resulting from successive extraction phases of recovered rare earths, and wherein the carbonates resulting from the precipitation of Ac3+ cations and unrecovered rare earths are separated from the liquid phase of the portion of the raffinate R subjected to the precipitation step, resulting in a rare earth-free filtrate, said filtrate being reused in the leaching solution.

3. A process for recovering rare earths contained in ionic clays according to claim 2, wherein said carbonates are stored as residues.

4. A process for recovering rare earths contained in ionic clays according to any one of claims 2, wherein said carbonates are dissolved by an acidic solution generating a solution S4, said solution S4 being brought into contact with the leached ionic clays causing the re-adsorption by said leached or depleted rare earth ionic clays of Ac3+ cations and unrecovered rare earths +, resulting in the formation of a solution S5 comprising a salt of Ml / zCl or M2 / zSO4, the solution S5 being reintroduced into the continuously rotating leaching solution.

5. A process for valorizing rare earths contained in ionic clays according to any one of claims 1 to 4, characterized in that the contact of the leaching solution SI, then of the raffinate R, optionally supplemented with solution S5, with the fresh clay, is carried out by percolation through said fresh clays in-situ or in piles, to form solution S2.

6. A process for recovering rare earth elements contained in ionic clays according to any one of claims 1 to 4, characterized in that the The SI solution, then the R raffinate, possibly supplemented with the S5 solution, is brought into contact with the fresh clay in a reactor to form the S2 solution, said S2 solution being separated from the fresh clays by a liquid-solid separation process.

7. A process for valorizing rare earths contained in ionic clays according to any one of claims 1 to 6, characterized in that the molar concentration of Ml / zCl in the SI solution, and then of the raffinate R, is between 1 and 2 mol / L.

8. A process for recovering rare earths contained in ionic clays according to any one of claims 1 to 6, characterized in that during the leaching of the clay, the molar concentration of M2 / zSO4 in the SI solution, and then in the raffinate R, is between 0.05 and 0.5 mol / L.

9. A process for recovering rare earths contained in ionic clays according to any one of claims 1 to 8, characterized in that the raffinate R resulting from successive extraction phases of the recovered rare earths, optionally supplemented with yttrium, has a total concentration of rare earth ions including La3+ and Y3+ of between 0.1 and 5 g / L and an activity related to the Ac3+ content of between 0 and 30 Bq / L.

10. A process for valorizing rare earths contained in ionic clays according to any one of claims 2 to 9, characterized in that the precipitation in the form of carbonates of the Ac3+ cations and the unvalorized rare earths is carried out by adding to the raffinate R resulting from the successive phases of extraction of the valorized rare earths, a solution of carbonate salt of M2 / zCO3 or Mz(HCO3)2, where M is a cation chosen from the group consisting of Na+, NH4+ and Mg2+ and z = 1 or 2.

11. A process for recovering rare earths contained in ionic clays according to claim 10, characterized in that the carbonates are separated from the liquid phase of the raffinate R and washed with water to remove the cations M.

12. A process for recovering rare earths contained in ionic clays according to any one of claims 4 to 11, characterized in that the acidic solution used to dissolve the carbonates resulting from the precipitation of Ac3+ cations and unrecovered rare earths comprises a Lewis acid selected from the group consisting of HCl and H2SO4.

13. A process for recovering rare earths contained in ionic clays according to claim 12, characterized in that the acidic solution has a molar concentration of Lewis acid between 0.001 and 1.5 mol / L.

14. A process for recovering rare earths contained in ionic clays according to any one of claims 2 to 13, characterized in that the carbonates have an activity of between 0 and 50 Bq / g of carbonates considered dry, said carbonates comprise: from 20% to 60% of lanthanum, by weight, relative to the total weight of carbonates considered dry, from 0 to 30% of other unrecovered rare earths, including yttrium and cerium, by weight, relative to the total weight of carbonates considered dry.

15. A process for recovering rare earths contained in ionic clays according to any one of claims 1 to 14, characterized in that the ionic clays depleted of rare earths are washed with water, to remove the M cations.

16. A method for recovering rare earths contained in ionic clays according to any one of claims 4 to 15, characterized in that the contact of the S4 solution with the ionic clays depleted of rare earths is carried out in a reactor, by percolation over a filter, by percolation over a pile of leached clay, or by percolation through a deposit of leached clays.

17. A process for recovering rare earths contained in ionic clays according to any one of claims 4 to 16, characterized in that the raffinate R is divided into two streams Fl and F2, the Fl stream constituting the leaching solution rotating in a loop, and the F2 stream being subjected to the precipitation in the form of carbonates of the Ac3+ cations and the unrecovered rare earths, the ratio F1 / (F1+F2) being between 0 and 1.

18. A process for recovering rare earths contained in ionic clays according to any one of claims 1 to 17, characterized in that the extraction phase of the recovered rare earths, by contacting the solution S2 with the liquid phase, implements a liquid-liquid extraction process, said liquid phase comprising an organic solvent immiscible with water comprising at least one cationic extraction agent.

19. A process for recovering rare earths contained in ionic clays according to claim 18, characterized in that the recovered rare earths, optionally supplemented with yttrium contained in solution S3, are re-extracted by an acidic aqueous solution, the acid being able to be chosen from the group including hydrochloric acid, nitric acid and sulfuric acid and then optionally precipitated into a solid, the solution or the solid having an actinium activity of less than 0.1 Bq / g of rare earths contained.

20. A process for recovering rare earths contained in ionic clays according to any one of claims 1 to 17, characterized in that the extraction phase of the recovered rare earths, optionally supplemented with yttrium, is carried out by contacting the solution S2 with a solid phase capable of fixing the cations of said rare earths.

21. A process for valorizing rare earths contained in ionic clays according to claim 20, wherein the solid phase is selected from the group comprising: silicas with a high specific surface area on which extracting molecules are grafted or adsorbed, titanium oxides on which extracting molecules are grafted or adsorbed, zirconium oxides on which extracting molecules are grafted or adsorbed, polymer matrices on which extracting molecules are grafted, and macroporous polymer matrices impregnated with extraction agents.

22. A method for recovering rare earths contained in ionic clays according to claim 21, wherein the extracting molecules and the extraction agents are compounds having the capacity to fix the recovered rare earths by ion exchange.

23. A method for valorizing rare earths contained in ionic clays according to any one of claims 20 to 22, wherein the solid phase is stationary and located in a reservoir within which the solution S2 percolates generating a solid S3.

24. A process for recovering rare earth elements contained in ionic clays according to claim 23, wherein the solid S3 undergoes solid-liquid re-extraction with an acidic eluent, generating an aqueous extract E loaded with recovered rare earth elements, optionally with added yttrium, the acidic eluent being selected from the group consisting of hydrochloric acid, sulfuric acid and nitric acid.

25. A process for valorizing rare earths contained in ionic clays according to claim 24, wherein the aqueous extract E loaded with valorized rare earths, optionally supplemented with yttrium, is concentrated by evaporation.

26. A process for valorizing rare earths contained in ionic clays according to claim 24, wherein the valorized rare earths, optionally supplemented with yttrium contained in the aqueous extract E, are precipitated using a precipitating agent selected from the group consisting of: sodium carbonate, ammonium bicarbonate, sodium hydroxide, ammonia, oxalic acid and its alkali salts.

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