Method for upgrading rare earth elements contained in ionic clays

Abstract

This method for upgrading rare earth elements contained in ionic clays implements the leaching of said clays in a continuous loop: wherein said leaching is initiated by bringing fresh ionic clay into contact with an aqueous leaching solution S1 comprising a dissolved MlIzCI or M2 / zSO4 salt, wherein M is a cation selected 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 cations of rare earths elements and of actinium, and, on the other hand, a leached or depleted clay; and then wherein said solution S2 is subjected to a phase of extracting the upgraded rare earth elements, generating, on the one hand, an organic solution S3 or a solid S3 comprising the upgraded rare earth elements, and, on the other hand, a raffinate R comprising the MlIzCI or M2 / zSO4 salt, the actinium in cationic form, and the non-upgraded rare earth elements; the raffinate R being brought into contact with a quantity of fresh ionic clay, forming a new solution S2, said new solution S2 being subjected to a new phase of extracting the upgraded rare earth elements, generating a new raffinate R; the leaching solution formed by the raffinate R resulting from the successive phases of extracting the upgraded rare earth elements, going round continuously with new quantities of fresh ionic clay.

Description

[0001] METHOD FOR THE VALORIZATION OF RARE EARTHS CONTAINED IN IONIC CLAYS - FIELD OF THE INVENTION

[0002] 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.

[0003] PRIOR STATE OF TECHNOLOGY

[0004] Ionic clays are composed of layers of silicate and aluminosilicate sheets with a negatively charged surface. This charge is generally neutralized by cations, such as 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-containing rocks, such as monazite or bastnaesite, leads to the migration of these rare earths to clays located in deeper layers, which consequently become enriched in rare earths. Trivalent rare earth 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 earths over time, particularly in so-called "heavy" rare earths.This category includes rare earths whose atomic number is greater than or equal to that of samarium, as well as yttrium and scandium.

[0005] The trivalent cations on the surface of these 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 earth elements 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 results in 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 iron and aluminum, and then the rare earth elements are precipitated and recovered as a rare earth carbonate concentrate, also known as MREC (Mixed Rare Earths Carbonate).The document Review On The Development And Utilization Of Ionic Rare Earth Ore, Luo Et Al., Minerals 2022, 12, 554, describes rare earth recovery processes and in particular a leaching process of ionic clays including the use of monovalent cation salt solutions, such as Na. + and NH4 + , or divalents like Mg 2+ , exchanged with trivalent 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, with half-lives exceeding a few days, must be removed to avoid contamination of the rare earths.

[0008] For example, the isotope 227 Ac (descendant of 235Actinium-227 (also known as U), with 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 (Rapid Recycling and Energy Consumption) stream. It must then be processed downstream 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" materials. This necessitates the use of specialized carriers, which constitutes a constraint and additional costs. Known separation processes allow for the removal of actinium. This type of extraction process, for example, liquid-liquid extraction, is described in particular in Applicant documents FR 3 154 392 and FR 2411360. This process makes it possible to remove actinium as well as some of the lanthanum, and in some cases cerium and yttrium, without loss of the most valuable rare earths, namely Pr, Nd, Tb, and Dy.Since yttrium, cerium and lanthanum have little economic interest, this process also avoids significant additional costs, particularly during transport or separation from other high value rare earths.

[0010] Current rare earth recovery techniques from ionic clays are unique in that they recycle the leaching solutions, depleted of rare earths after MREC separation, at the beginning of the process to conserve the leaching reagent. In the case of ionic clays, the actinium removal 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 rare earth extraction by the solvent in the liquid-liquid extraction process. Therefore, it is necessary to purge these solutions of actinium, lanthanum, and sometimes yttrium and cerium.

[0011] For environmental reasons, this purging requires the implementation of a process that allows the radioelements to be sequestered in a stable form to limit the risks of groundwater contamination.

[0012] 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 rare earth intermediate concentrates. This removal of actinium is advantageously accompanied by the removal of some lanthanum and, in some cases, yttrium and cerium. Since these rare earths have little commercial value, this significantly reduces the total mass of the rare earth intermediate concentrate to be transported and substantially lowers the cost of the separation processes. This combined removal of actinium and low-value rare earths according to the invention has the advantage of having no adverse effects on the environment or on the overall recovery yield of the rare earths recovered, and, according to a certain implementation method, of producing no waste.

[0014] For the purposes of this invention, "valued rare earths" means lanthanides with an atomic number strictly greater than cerium, and typically praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, erbium, holmium, thulium, ytterbium and lutetium, to which scandium is added when the latter is associated with the rare earth group.

[0015] Furthermore, by "unvalued rare earths", we mean, for the purposes of the invention, lanthanides with an atomic number less than or equal to that of cerium.

[0016] Yttrium can complement, depending on the process used to implement the invention, either the group of valued rare earths or the group of non-valued rare earths.

[0017] Another objective of the present invention is to recycle the raffinate resulting from the recovery process by removing unrecovered actinium and rare earth elements to prevent their accumulation in the recycling loop, which will be described in more detail later. This reagent recycling is economically essential in the processing of ionic clays.

[0018] 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 contacting fresh ionic clay with an aqueous leaching solution SI comprising a dissolved salt of Mi / z Cl or NU / zSCL, where M is a cation chosen from the group consisting of Na + NH4 + and Mg 2+; 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 the 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 Mi / ; z Cl or M2 / ZSO4, actinium in cationic form, and unvalued rare earths defined as consisting of lanthanides with an atomic number less than or equal to that of Ce, possibly with added yttrium, including some lanthanum, in cationic form;

[0019] The raffinate R, becoming the leaching solution, is brought into contact with a quantity of fresh ionic clay, forming a new solution S2 enriched in Ac cations 3+ and in unvalued rare earths, including La 3+ 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 valued rare earths, generating a new raffinate R;

[0020] the leaching solution consisting of raffinat R resulting from successive extraction phases of the recovered rare earths, continuously rotating in conjunction 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,

[0021] • the liquid phase brought into contact with solution S2 during the extraction phase of the recovered rare earths, which employs a liquid-liquid extraction process, said liquid phase comprising an organic solvent immiscible with water, including at least one cationic extraction agent selected from the group consisting of alkylphosphonic derivatives, alkylphosphinic derivatives and mixtures thereof, for example, mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (HEH(EH)P), bis(2,4,4-trimethylpentyl)phosphinic acid, a mixture of phosphonic acid and phosphinic acid, neodecanoic acids of general formula C m H 2m O2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, naphthenic acids of general formula C n H2( n-z)O2 where n is an integer between 8 and 20, and z is an integer between 0 and 4, and their mixtures; • the solid phase brought into contact with the solution S2 during the extraction phase of the valued rare earths is capable of fixing the cations of said rare earths and is chosen 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, the extracting molecules and the extraction agents being compounds having the capacity to fix the valued rare earths by ion exchange;the extracting molecules have active groups comprising at least one cationic extracting agent selected 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, a mixture of phosphonic acid and phosphinic acid, neodecanoic acids of general formula C; m H 2m O2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, naphthenic acids of general formula C n H2(nz)O2 where n is an integer between 8 and 20, and z is an integer between 0 and 4, and their mixtures.

[0022] 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 precipitation of the Ac cations in the form of carbonates or hydroxides 3+ and untapped rare earth elements, including La 3+ and, where applicable, Y 3+ , contained in the raffinate R resulting from the successive extraction phases of the recovered rare earths; the carbonates or hydroxides resulting from this precipitation of the cations Ac 3+ and unvalued 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.

[0023] According to one embodiment, carbonates or hydroxides are simple residues or waste, which are then stored.

[0024] In another embodiment, the carbonates or hydroxides 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 of the Ac cations by said leached or depleted ionic clays. 3+ and untapped rare earth elements, including La 3+ and Y 3+ leading to the formation of a solution S5 comprising a salt of Mi / z Cl or M2 / ZSO4, the S5 solution being reintroduced into the continuously rotating leaching solution.

[0025] According to one embodiment, the leaching solution SI, then the raffinate R, possibly supplemented with solution S5, is brought into contact with the fresh clay by percolation through said fresh clays in-situ or in piles, to form solution S2.

[0026] 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.

[0027] Thus, the invention allows for the separation of 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. Subsequently, the unrecovered rare earth elements and the actinium are fully reattached to the clay after the clay has been depleted.

[0028] 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.

[0029] 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.

[0030] According to the invention, "activity" refers to the trivalent actinium cation content, Ac 3+ This activity is expressed in Bq / L or Bq / g. Initiation of leaching

[0031] Leaching preferably takes place in a reactor, in a pile or in situ. It constitutes the initiation of the entire process of the invention.

[0032] 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 solution S2.

[0033] According to another embodiment, the SI solution is brought into contact with the fresh ionic clay 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.

[0034] The aqueous leaching solution SI comprises a dissolved salt of Mi / z Cl or M2 / ZSO4, where M is a cation chosen from the group consisting of Na + NH4 + and Mg 2+; and z = 1 or 2, representing the number of charges of the cation M.

[0035] Preferably, the salt is a sodium chloride (NaCl), ammonium sulfate ((NEL SCL) or magnesium sulfate (MgSCL).

[0036] Advantageously, the molar concentration of Mi / z Cl in solution SI and then raffinate R, is between 1 and 2 mol / L. In particular, the molar concentration of NaCl is preferably equal to 1.5 mol / L.

[0037] Preferably, during clay leaching, 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 (NEL SCL is preferably between 0.1 and 0.4 mol / L.

[0038] Advantageously, the specific concentration of cations in solution S1 is adjusted to ensure good rare earth leaching efficiency. Excessive cation concentration leads to unnecessary reagent losses. When fresh ionic clay is brought into contact with the aqueous leaching solution SI, the high concentration of cations from the salt dissolved in solution SI causes their exchange with the trivalent rare earth and actinium cations labilely bound to 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 S2 solution are lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, erbium, yttrium, holmium, thulium, ytterbium, lutetium and also scandium when this element is considered associated with the rare earth group.

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

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

[0043] Ionic clays depleted of rare earth elements, 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 the said depleted clays during any subsequent steps by eliminating competition with the M cations. This washing also has the advantage of improving the recovery of M cations and preventing their release into the environment.

[0044] Extraction of valuable rare earth elements

[0045] Preferably, solution S2 is purified by increasing the pH to remove aluminum and iron impurities. For example, Al ions 3+ and Fe 3+can be precipitated using solutions of NH4HCO3, Na2CO3, NaOH or NH4OH, which increase the pH of the solution, then separated from the solution by solid-liquid separation. According to one embodiment, the extraction phase of the valued rare earths, where appropriately 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.

[0046] Advantageously, liquid-liquid extraction generates:

[0047] • 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

[0048] • on the other hand, a raffinate R comprising the salt of Mi / zCl or NL / zSC actinium as well as most of the unvalued rare earths, in cationic form.

[0049] The cationic extraction agent is chosen from the group consisting of alkylphosphonic derivatives, alkylphosphinic derivatives, and mixtures thereof, for example, mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (HEH(EH)P), bis(2,4,4-trimethylpentylphosphinic acid (known by the trade name CYANEX®272), a mixture of phosphonic acid and phosphinic acid (known by the trade name CYANEX®572), and neodecanoic acids of general formula C m H 2m O2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, naphthenic acids of general formula C n H2( n -z)O2 where n is an integer between 8 and 20, and z is an integer between 0 and 4, and their mixtures.

[0050] The rare earths recovered from the S3 solution 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.

[0051] According to another embodiment, the extraction phase of the recovered rare earths is carried out by contacting solution S2 with a solid phase capable of binding the cations of said rare earths. The solid phase is chosen from the group comprising: silicas with a high specific surface area, typically greater than 40 m² 2 / 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, including resins, impregnated with extracting molecules.

[0052] Advantageously, grafted, adsorbed, or impregnated extractant molecules are compounds capable of binding the valuable rare earth elements through ion exchange. These extractant molecules possess active groups that are typically those of the cationic extraction agents used in the liquid-liquid extraction process, particularly phosphonic, phosphinic, or carboxylic groups.

[0053] Extracting molecules have active groups comprising at least one cationic extraction agent selected 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, a mixture of phosphonic acid and phosphinic acid, neodecanoic acids of general formula CmH2mO2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromo-octanoic 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 mixtures thereof.

[0054] Preferably, the solid phase is stationary and located in a reservoir into which the solution S2 percolates, generating a solid S3. The recovered rare earths are fixed onto the solid phase, while the unrecovered earths are removed in the raffinate R.

[0055] After percolation of solution S2, the solid S3 preferably undergoes 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. 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 supplemented with yttrium contained in the aqueous extract E, are precipitated using a precipitating agent selected from the group comprising sodium carbonate, ammonium bicarbonate, sodium hydroxide, ammonia, magnesium oxide, oxalic acid and its alkali salts.

[0057] Advantageously, the raffinate R resulting from the successive extraction phases of the recovered rare earths has a total rare earth ion concentration between 0.1 and 5 g / L and an activity linked to the Ac content 3+ between 0 and 30 Bq / L.

[0058] The raffinate R resulting from the extraction of valuable rare earths is preferentially divided into two streams F1 and F2, with stream F1 constituting the leaching solution circulating in a loop, and stream F2 undergoing precipitation of Ac cations as carbonates or hydroxides 3+ and unvalued rare earths, the ratio F1 / (F1+F2) being between 0 and 1.

[0059] Leaching loop

[0060] As previously mentioned, the raffinate R resulting from the successive extraction phases of the recovered rare earths becomes the new leaching solution S2, and circulates continuously in conjunction with new quantities of fresh ionic clay, forming a so-called leaching loop. This contact leads to the formation of new S2 solutions enriched in Ac cations compared to the initial S2 solution. 3+ and in unvalued rare earths, including La 3+ and where applicable Y 3+, constituting a transitional state until reaching a stationary state in which, although the clay undergoing leaching is partially depleted of rare earths, the quantity of actinium and unvalued 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 Ac cations 3+ and in unvalued rare earths, including La 3+ and where applicable Y 3+ due to its contact with new quantities of fresh ionic clay. Lanthanum purging

[0062] Advantageously, the process of the invention implements the control of the lanthanum concentration of the S2 solution 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.

[0063] To this end, the precipitation of the cations Ac is induced 3+ and untapped rare earth elements, including La 3+ and where applicable Y 3+ contained in the raffinate R in the form of carbonates or hydroxides.

[0064] Preferably, the precipitation of Ac cations 3+ and unrecovered rare earths 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 M2 / ZCO3 carbonate salt or M z(HCO3)2, where M is a cation chosen from the group consisting of Na + NH4 + and Mg 2+ and z = 1 or 2.

[0065] Alternatively, the precipitation of Ac cations 3+ and rare earths not recovered in the form of hydroxides, is carried out by adding to the raffinate R resulting from the successive phases of extraction of the recovered rare earths, a solution or suspension of MgO or hydroxides M(OH) Z where M is a cation chosen from the group consisting of Na + NH4 + and Mg 2+ and z = 1 or 2 the charge of the cation considered.

[0066] Preferably, the carbonates or hydroxides are separated from the liquid phase of raffinate R before their dissolution, resulting in a rare earth-free filtrate, which is then reused in the leaching solution. The carbonates or hydroxides separated from the liquid phase of raffinate R are optionally washed with water to remove the cations M.

[0067] Carbonates or hydroxides advantageously exhibit an activity between 0 and 50 Bq / g of carbonates or hydroxides considered dry; said carbonates or hydroxides comprise:

[0068] ■ 20% to 60% lanthanum, by weight, relative to the total weight of carbonates or hydroxides considered dry,

[0069] ■ 0 to 30% of other unrecovered rare earth elements, including yttrium and cerium, by weight, relative to the total weight of carbonates or hydroxides considered dry. The carbonates or hydroxides 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 or hydroxides resulting from the precipitation of Ac cations 3+ and unvalued rare earths, includes a Lewis acid selected from the group consisting of HCl and H2SO4. The acid solution preferably has a molar concentration of Lewis acid between 0.001 and 1.5 mol / L.

[0070] Re-adsorption of unused rare earth elements and actinium

[0071] Advantageously, the process of the invention also targets the re-adsorption of Ac cations 3+ and untapped rare earth elements, including La 3+ and Y3+ This is achieved by the different quantities of leached ionic clay, which is then depleted of rare earth elements and results from the various leaching processes it has undergone. This re-adsorption is carried out by contacting solution S4 with these quantities of leached clay.

[0072] 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.

[0073] The M cations, which were adsorbed onto the clay, are exchanged and pair with the Lewis acid anions to form a Mi salt solution S5. z Cl or M2 / ZSO4, with the S5 solution being reintroduced into the leaching loop.

[0074] 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.

[0075] BRIEF DESCRIPTION OF THE FIGURES

[0076] The figures shown below are purely illustrative. The process they illustrate can be implemented in other configurations.

[0077] Figure 1 is a general schematic representation of the process according to the invention. Figure 2 is a schematic representation of the process according to the invention comprising a leaching step in a reactor.

[0078] Figure 3 is a schematic representation of the process according to the invention comprising an in-situ leaching step.

[0079] Figure 4 is a schematic representation of the process according to the invention comprising a heap leaching step.

[0080] DETAILED DESCRIPTION OF THE FIGURES

[0081] With reference to Figure 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.

[0082] 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).

[0083] Solution S2 (12) is treated by adding a neutralizing agent (N) to precipitate impurities such as aluminum, iron and lead.

[0084] 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 applicable, cerium and yttrium, in cationic form.

[0085] Solution S3 (14) is precipitated (15) as valuable rare earth carbonates (16). The liquid phase (17) is separated from the precipitate and joins the raffinate R (18).

[0086] 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 appropriate, yttrium cations, compared to the concentrations of these same elements in the initial solution S2. The liquid phase (17) can join the raffinat R (18) just before the leaching (11) of a new quantity of fresh ionic clay (10). These leaching (11) and contacting steps 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 solution S2 (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 returned to the raffinate R (18). The carbonates are then dissolved (21) using an acidic solution. Their dissolution generates 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 resulting 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 of valuable rare earths (26), but recharged with actinium, lanthanum and yttrium.

[0089] Referring to Figure 2, an ionic clay (30), whose layers contain divalent 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 divalent rare-earth and actinium cations are exchanged for Na+ cations. + . The clay and the rare earth 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), namely Na2CO3, which precipitates the impurities of aluminum, iron, and lead. After this treatment, the first solution S2 (35) is contacted with an organic solvent that allows the extraction of rare earth elements in an extraction battery (36), generating, on the one hand, a solution S3 (37) containing the extracted rare earth elements, and on the other hand, a raffinate R (41) containing the rare earth elements 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.

[0092] A Na2Cu3 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.

[0093] The rare earth carbonates (39) are separated from the liquid phase (40). This phase is introduced into a buffer reactor (47) where its cation concentration is adjusted. It is then recycled to the leaching reactor (31).

[0094] 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).

[0095] The unprecipitated liquid phase (46) of raffinate R is introduced into the buffer reactor (47) where its cation concentration is adjusted. It is then reintroduced into the leaching reactor (31).

[0096] Carbonates (43) are dissolved by an HCl solution in reactor (44), generating 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 leaching operations. This leads to the re-adsorption of the unrecovered rare earth elements by the depleted clays where the Ac cations 3+ , There 3+ , This 3+ are again adsorbed onto the clay sheets, the depleted clays then being recharged with Ac, La and Ce (A). This also leads to the formation of a NaCl S5 (49) solution purified of all or part of the Ac cations 3+ , There 3+ , This 3+. The S5 solution (49) resulting from this contact is recycled in the buffer reactor (47).

[0097] The process of the invention shown in Figure 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.

[0098] The 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 deposit of depleted ionic clays (51), and an aqueous solution S2 (52), comprising trivalent rare earth cations and actinium. Solution (52) is extracted from the deposit via a production well or via a trench.

[0099] Solution S2 (52) is treated by adding a neutralizing agent (N2), which is NH4HCO3, allowing the precipitate impurities of aluminium, iron and lead.

[0100] 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.

[0101] 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.

[0102] The rare earth carbonates (56) are separated from the liquid phase (57), which is then introduced into a buffer reactor (64) to adjust the cation concentration, and subsequently reintroduced into the injection well (50). The raffinate R (58) is partially precipitated by an NH4HCO3 solution in the reactor (59), thus forming a solid composed 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).

[0103] The unprecipitated liquid phase (63) of the raffinate R is introduced into the buffer reactor (64), then recycled into the injection well (50).

[0104] Carbonates (60) are dissolved by a solution of H2SO4 in the 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 cations... 3+ , This 3+ , Y 3+ and Ac 3+ will bind to the said clays, leading to the formation of clays recharged with La, Ce, Y and Ac (66). The S5 solution (67) resulting 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).

[0105] With reference to Figure 4, ionic clays (70) are arranged in a pile (71) and leached by an aqueous leaching solution SI, comprising a dissolved salt of (NH4)2SÜ4 at a molar concentration of 0.18 mol / L.

[0106] The divalent rare earth and actinium cations exchanged by the NH4 cations + then form an aqueous solution S2 (73) while the pile of clays is depleted (72).

[0107] Solution S2 (73) is treated by adding a neutralizing agent (N3), which is NH4HCO3, allowing the precipitate impurities of aluminium, iron and lead.

[0108] After this treatment, the S2 solution (73) is contacted with a solid phase composed of macroporous cross-linked polystyrene resin beads onto which bis-2,4,4-trimethylpentylphosphinic acid is adsorbed in an extraction column (74), generating on the one hand a solid S3 (75) in which the extracted and recovered rare earths are fixed, and on the other hand a raffinate R (80) comprising the unfixed rare earths, not recovered in solution, including lanthanum, cerium and yttrium, as well as actinium. The S3 solid (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.

[0109] 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.

[0110] 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 put back into contact with the pile of clays (71).

[0111] 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).

[0112] 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).

[0113] 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 cations... 3+ , This 3+ , Y 3+ and Ac 3+ will attach to the clays, thus forming a pile of clays recharged with La, Ce, Y and Ac (88). The S5 solution (89) resulting from this contact is recycled in the buffer reactor (86).

[0114] EXAMPLES OF THE INVENTION'S IMPLEMENTATION

[0115] As follows from the foregoing, after the removal of the recovered rare earth elements according to the process of the invention, the leaching solution becomes enriched in unrecovered rare earth elements (La, Y, Ce, Ac), and is then recycled for further clay leaching. Examples 1 to 3 below illustrate the influence of multiple recycling processes on clay leaching, which leads 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.

[0116] Examples 1 to 4 correspond to an implementation of the process without implementation of lanthanum purging.

[0117] Example 1: Leaching of ionic clays using aqueous NaCl leaching solutions

[0118] Aqueous leaching solutions having a molar concentration of NaCl of 1.5 M and exhibiting variable concentrations of LaCl3 and CeCl3 are brought into contact with quantities of ionic clay from the same ore, and comprising rare earths, some of which are in cationic form.

[0119] Typically, the concentrations of lanthanum, cerium and neodymium are 580 ppm, 540 ppm and 400 ppm respectively.

[0120] A volume of 104 mL of each leaching solution is brought into contact with 70 g of dried clay that has been previously sieved to 1 mm.

[0121] The mixture is stirred at room temperature for 7 minutes and the pH is adjusted to 4.7 using a Na2CO3 solution to precipitate Al impurities.

[0122] 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.

[0123] 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. Four tests are carried out with increasing concentrations of La in the leaching solution to simulate the progressive enrichment in the loop.

[0124] Table 1

[0125] Leaching solution Solution resulting from leaching

[0126] (SI) (S2)

[0127] Total

[0128] The Ratio Tests of The Others

[0129] leached by leaching leaching The [The] present lands

[0130] the outcome of the La (mg) (g / L) in the rare

[0131] test

[0132] leachate (mg)

[0133] (mg)

[0134] (mg)

[0135] El 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

[0136]

[0137] E5 168 1.62 172 41.2 3.9 0.24

[0138] The leaching ratio of La corresponds to the ratio between the mass of La leached after a leaching test E n , n being equal to 1, 2, 3, 4 or 5, and the mass of the leachate at the end of the first leaching test E1

[0139] During the El test, 16.3 mg of La and 30.9 mg of other rare earths were leached.

[0140] During the E2 leaching 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 E2 leaching solution also contains 35.6 mg of other rare earth elements.

[0141] The El to E5 leaching tests demonstrate that the more we increase the amount of La in the leaching solution (SI), the less La is recovered leached at each step in the leaching solution (S2).

[0142] Above a certain quantity, an equilibrium is reached at which La is no longer leached; that is, 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 was obtained by linear regression from the values ​​in Table 1. Furthermore, it is observed that the mass of the other leached rare earths increases significantly from 30.9 mg to 41.2 mg as the La concentration increases.

[0143] The leaching ratio La of 1 for the leaching test El is taken as a reference to demonstrate the implementation of the process.

[0144] This example shows the evolution of the leaching ratio during the implementation of the invention with sodium chloride leaching and without any lanthanum purging.

[0145] The recycling of raffinate R according to the invention gradually leads to equilibrium in the leaching loop when the concentration of La reaches a certain value. At this point, the La leaching ratio is zero and the La concentration no longer changes during the leaching cycles.

[0146] Example 2: Leaching of ionic clays using aqueous leaching solutions of (NH4)2SO4

[0147] 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, notably in cationic form.

[0148] The protocol from example 1 is repeated here, except that the pH is adjusted using an NH4HCO3 solution.

[0149] The concentration of La and other rare earth elements in solution was measured before and after contact with the clay. The masses are listed in Table 2 below.

[0150] Solution from the Solution resulting from the

[0151] leaching (SI) leaching (S2)

[0152] Total

[0153] Other tests of leaching. Leaching ratio. The [Leaching] present in the tissues. Tissue leaching. The (mg) (g / L) in the rare test.

[0154] leachate (mg) (mg)

[0155] (mg)

[0156] El 0 0 15.8 28.5 15.8 1

[0157] E2 22.3 0.21 37.9 31.1 15.6 0.99

[0158] E3 44.6 0.43 58.6 32.4 14.0 0.88

[0159] E4 129 1.24 137 33.9 8.3 0.53

[0160]

[0161] E5 255 2.45 256 32.1 0.64 0.04

[0162] During the first El leaching test, 15.8 mg of La and 28.5 mg of other rare earths were leached.

[0163] During the second leaching test E2, a total of 22.3 mg of La was included in the leaching solution. The leaching solution contained 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 leaching solution E2 also contained 31.1 mg of other rare earth elements.

[0164] The leaching tests El to E5 demonstrate that the more we increase the amount of La in the leaching solution (SI), the less La is recovered leached at each step in the leaching solution (S2).

[0165] Above a certain quantity, an equilibrium is reached at which La is no longer leached. In this example, this equilibrium is reached with an initial quantity of La of 274 mg, corresponding to a concentration of T of 2.6 g / L. Furthermore, the quantity of other leached rare earths increases slightly from 28.5 mg to 32.1 mg.

[0166] This example demonstrates the evolution of the leaching ratio during implementation of the invention with ammonium sulfate leaching and without lanthanum purging. Recycling raffinate R according to the invention, laden with La, gradually leads to equilibrium when the La concentration of raffinate R reaches a certain value. At this point, the La leaching ratio is zero, and the La concentration no longer changes during leaching cycles.

[0167] Example 3: Leaching of ionic clays using aqueous leaching solutions of MgSO4

[0168] 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, notably in cationic form.

[0169] The protocol from example 1 is repeated here, except that the pH is adjusted using an NH4HCO3 solution.

[0170] Three trials are carried out with increasing concentrations of La in the leaching solution.

[0171] The masses are listed in Table 3 below.

[0172] Table 3

[0173] Solution from leaching

[0174] leaching (SI) (S2)

[0175] Total

[0176] The Ratio Tests of The Others

[0177] leached at leaching The leaching The present lands

[0178] the outcome

[0179] (mg) (g / L) in the rare

[0180] of the test

[0181] leachate (mg)

[0182] (mg)

[0183] (mg)

[0184] El 0 0 15.8 30.2 15.8 1

[0185] E2 21.6 0.21 35.8 36.5 14.1 0.89

[0186]

[0187] E3 123 1.18 131 36.5 7.8 0.49

[0188] During the first leaching test (E1), 15.8 mg of La and 30.2 mg of other rare earth elements were leached. During the second leaching test (E2), a total of 21.6 mg of La was included in the leaching solution. The leaching solution contained a total of 35.8 mg of La, of which 21.6 mg came from the leaching solution and 14.1 mg from the leaching of the clay used in test E2. The leaching solution (E2) also contained 36.5 mg of other rare earth elements.

[0189] The El to E3 leaching tests demonstrate that the more we increase the amount of La in the leaching solution (SI), the less La is recovered leached at each step in the leaching solution (S2).

[0190] In this example, we determine 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.

[0191] Therefore, the leaching ratio La is zero, and the concentration does not change during successive leaching cycles.

[0192] Example 4: Leaching of ionic clays using aqueous leaching solutions of (NH4)2SO4 comprising La and Y

[0193] 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.

[0194] 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.

[0195] The protocol from example 1 is repeated here, except that the pH is adjusted using an NH4HCO3 solution.

[0196] The concentration of La, Y, and other rare earth elements in solution was measured before and after contact with the clay. The masses are listed in Table 4 below.

[0197] Table 4

[0198] Leaching Solution Ratio (SI) / Leaching Solution (S2)

[0199] leaching

[0200] Y

[0201] leachate

[0202] Other leaching tests

[0203] Total Total to

[0204] leaching The [The] Y [Y] lands at

[0205] The Y outcome The Y (mg) (g / L) (mg) (g / L) rare the outcome

[0206] (mg) (mg) of

[0207] (mg) of the test

[0208] test

[0209] (mg)

[0210] (mg)

[0211] 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

[0212] < 0.1

[0213] E5 252 2.42 105.7 1.01 243.7 107.6 26.0 1.9 0.25

[0214]

[0215] mg 0.01

[0216] During the first El leaching test, 17.3 mg of La, 7.7 mg of Y and 25.3 mg of other rare earths were leached.

[0217] During the second leaching test E2, a total of 22.1 mg of La was included in the leaching solution. The leaching solution contained 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.

[0218] A total of 9.5 mg of Y is included in the leaching solution of the second leaching test E2. The leaching solution comprises a total of 16.4 mg of Y, of which 9.5 mg comes from the leaching solution, and 6.9 mg from leaching of the clay involved in test E2.

[0219] At the fifth leaching test E5, 8.0 mg is reattached, which justifies the negative value in Table 4.

[0220] The leaching tests E1 to E5 demonstrate that the higher the quantity of La and Y in the leaching solution (S1), the less La and Y are recovered at each step in the leached solution (S2). Beyond a certain quantity, an equilibrium is reached at which these elements are no longer leached. In this example, the equilibrium is reached:

[0221] • 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.

[0222] • 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.

[0223] 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.

[0224] Here, the leaching ratio of La or Y for the leaching step El is set to 1 as a reference to demonstrate the implementation of the process.

[0225] Examples 1 through 4 show that recycling raffinate R within the process gradually leads to an equilibrium, which is reached when the concentrations of La and / or Y in raffinate R reach a certain value. Indeed, 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. Once equilibrium is reached, the leaching ratios of La and / or Y are negative, and their concentration no longer changes during subsequent leaching cycles.

[0226] Example 5: Leaching of ionic clays with reattachment of La and Ce to the clay: Total removal of lanthanum with reattachment to the clay

[0227] This example illustrates the implementation of lanthanum purging by treating all of a raffinate R from the process of separating the valued rare earths and refixing it on the depleted clay by a mixing operation in a stirred reactor and separation.

[0228] 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. Solutions of CeCl and LaCh are prepared at different concentrations, by dissolving a solid of La and Ce carbonates, precipitated from a raffinate obtained from liquid-liquid extraction.

[0229] One hundred mL of a CeCl3 and LaCl3 solution is contacted with 92.5 g of depleted clay for 20 minutes. The resulting solution is filtered. The clay is then 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.

[0230] Five tests are carried out corresponding to S4 solutions having an increasing concentration of La and Ce.

[0231] The quantities of La, Ce and Na are listed in Table 5 below.

[0232] Table 5

[0233] Filtrate

[0234] Solution (S4) The+This The+This Trials of (solution S5)

[0235] refixed refixed refixing La+Ce La+Ce Na

[0236] (mg) (%) (mg) (mg) (mg)

[0237] 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

[0238]

[0239] E6 269 198 49.8 71.1 26

[0240] The clay used can fix up to 0.76 g of La and Ce per kg of wet clay, which is equivalent to 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.

[0241] This example demonstrates the ability of depleted clay to quantitatively re-adsorb La and Ce from a La and Ce chloride solution. Example 6: Extraction of rare earths from ionic clays with reattachment of La and Ce to the clay, via the chloride route: Total purging with reattachment to the clay (implementation on a filter by percolation through the depleted clay)

[0242] This example illustrates the implementation of lanthanum purging in 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.

[0243] Ionic clay is leached by contacting 100 g of dry clay with a NaCl solution of concentration equal to 1.5 M.

[0244] After filtration, 140 g of wet clay, with a thickness of 2 centimeters, is obtained.

[0245] La and Ce chloride solutions at different total concentrations are prepared by dissolving La and Ce carbonates, obtained by precipitation of a raffinate from liquid-liquid extraction. These solutions percolate through the moist clay.

[0246] Percolation is accelerated by applying a pressure difference: either under vacuum using a Büchner funnel, or by pushing with compressed air using a pressure filter.

[0247] The resulting solution is percolated several times over the bed of damp clay, which thus gradually becomes enriched in rare earth elements.

[0248] A total of 10 percolations (or passes) were performed. The residual concentration of La and Ce after each percolation is detailed in Table 6 below. Table 6

[0249] [La+Ce] [Na] [La+Ce] [Na] [La+Ce] [Na] (mg / L) (mg / L) (mg / L) (mg / L) (mg / L) (mg / L) Solution

[0250] 487 0 1017 0 4341 0 initial (S4)

[0251] 1 passage 32 168 218 253

[0252] Büchner 2 passes 16 192 137 312

[0253] vacuum sealed 3 times 1.6 196 112 315

[0254] (-850 mbarg) 4 passes < 0.3 201 114 320

[0255] 5 passages < 0.2 201 112 322

[0256] 1 pass 184 296 2507 502 Filter under 2 passes 136 336 2801 455 pressure 3 passes 127 344 2723 417 (6 barg) 4 passes 122 353 2858 408

[0257] 5 passages 121 360 2843 410

[0258]

[0259] La+Ce refixed (mol / T sec) 5.0 9.0 9.5

[0260] We observe 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, or about 1400 g of Le and Ce refixed / tonne of dry clay.

[0261] This example illustrates the fixation of La and Ce rare earth elements onto depleted ionic clay, elements not recovered during solvent extraction. It demonstrates here that it is possible to reattach La and Ce by percolating solution S4 through a filter loaded with the clay cake used for the solid / liquid separation of the leached clay.

[0262] Example 7: Extraction of rare earths from an ionic clay with refixation of La, Ac and Ce onto the clay, via the sulfate route: Total purging with refixation onto the clay via the sulfate route (implementation on a filter by percolation through the depleted clay)

[0263] This example illustrates the refixation of Ac contained in raffinat R with a behavior in the process identical to that of lanthanum.

[0264] An ionic clay is leached with a (NH4)2SO4 solution of concentration equal to 0.18 M. The clay is then washed. 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.

[0265] Percolation is accelerated by applying a pressure difference by drawing under vacuum using a Büchner funnel. The resulting solution is percolated several times over the clay bed, which thus becomes progressively enriched in La and Ac.

[0266] 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.

[0267] Table 7

[0268] [The] [This] Ac-227

[0269] (mg / L) (mg / L) (Bq / L)

[0270] In the initial solution (S4) 5700 80 38

[0271] After 3 percolations 4137 64 18

[0272]

[0273] 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, through the filter used for the solid / liquid separation of the depleted clay.

[0274] Example 8: Extraction of rare earth elements from an ion-exchange resin using a sulfate solution obtained by leaching an ionic clay with an ammonium sulfate solution

[0275] This example illustrates the extraction of rare earth elements from a sulfate solution obtained by leaching an ionic clay with ammonium sulfate. In particular, this example demonstrates the observed selectivity between the absorption of La or Ce and that of rare earth elements with higher atomic numbers, as well as Y.

[0276] An ionic clay is leached with a solution of (NH-QiSO-t) of concentration equal to 0.18 M. A leachate, or solution of rare earth and ammonium sulfates of pH equal to 4.7, is obtained, the composition of which is given in Table 8 below.

[0277] Table 8: Composition of the rare earth and ammonium sulfate solution

[0278] Rare earth elements Concentration (mg / L)

[0279] The 197

[0280] This 10

[0281] Pr 44

[0282] Nd 155

[0283] Sm 20

[0284] Eu 2.2

[0285] Gd 13

[0286] Tb 1.6

[0287] Dy 11

[0288] Ho 2.0

[0289] Er 5.8

[0290] Tm 0.8

[0291] Yb 4.2

[0292] Read 0.6

[0293]

[0294] Y 61

[0295] A 10 mL column is loaded with 5.6 g of Lewatit® TP 272 resin, a polystyrene resin impregnated with bis-(2,4,4-trimethylpentyl-)phosphinic acid.

[0296] The resin is conditioned with 60 bed volumes (or BV, for bed volume) at a flow rate of 0.05 BV / min with a 0.18 M ammonium sulfate solution, at a pH of 4.3.

[0297] The resin is then loaded by injection with 42 BV of rare earth and ammonium sulfate solution at a flow rate of 0.5 BV / min.

[0298] At the outlet of the column, 10 mL fractions (1 BV) are collected and each 10 mL fraction is then analyzed by inductively coupled plasma optical spectrometry (ICP-OES) to determine the rare earth concentration.

[0299] Finally, the resin is eluted by injection of 7 BV of 5 mol / L HCl, at a flow rate of 0.1 BV / min. Similarly, each 10 mL fraction, recovered at the column outlet during this phase, is analyzed by ICP-OES.

[0300] Tables 9, 10, 11 and 12 below summarize the rare earth concentrations measured in the 10 mL fractions (BV) collected during the different phases of the protocol, as well as the ratios between these concentrations and the initial concentrations in the rare earth and ammonium sulfate solution.

[0301] Table 9: Rare earth element concentration of the different fractions (BV) collected

[0302] Rare earth concentration (mg / L)

[0303] Lands

[0304] Loading Elution

[0305] rare

[0306] BV0 BV1 BV2 BV3 BV4 BV5 BV10 BV1 BV2 BV3 BV5 BV7 La 197 47 156 161 164 180 189 153 12 4.4 1.8 1.0 Ce 10 0.7 4.21 5.7 6.0 7.0 8.3 28 4.3 2.9 1.3 1.4 Pr 44 1.5 11 16 18 21 28 200 33 16 7.7 4.5 Nd 155 4.2 28 45 50 62 87 955 168 79 38 22 Dy 11 0.2 0.4 0.4 0.5 0.4 0.5 242 51 28 10 5.5

[0307]

[0308] Y 61 0.2 2.3 2.7 2.7 2.9 2.9 1058 269 111 55 29

[0309] Table 10: Ratio between the rare earth concentration at the column outlet and the initial concentration in the different collected fractions

[0310] Ratio between column outlet concentration and initial concentration (%) Soils

[0311] Loading

[0312] rare

[0313] BV0 BV1 BV2 BV3 BV4 BV5 BV10 BV14 BV21 BV28 BV35 BV42 La 100 24 79 82 83 91 96 90 91 88 91 94 Ce 100 6.9 42 57 60 69 82 87 97 92 98 104 Pr 100 3.5 24 37 41 49 65 68 76 78 85 92 Nd 100 2.7 18 29 33 40 56 58 69 74 82 91 Dy 100 1.8 4.0 3.9 4.2 4.1 4.9 10 18

[0314]

[0315] Table 11: Quantities of rare earth elements fixed on the resin

[0316] Amount of rare earth elements fixed on the resin (mg)

[0317] Land Loading

[0318] rare BVO BV1 BV2 BV3 BV4 BV5 BV10 BV14 BV21 BV28 BV35 BV42 La 0 1.5 1.9 2.3 2.6 2.8 3.6 3.9 4.0 4.3 4.5 4.6 Ce 0 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.4 0.4 0.4 0.4 Pr 0 0.4 0.8 1.0 1.3 1.5 2.4 2.6 2.7 2.8 2.9 2.9 Nd 0 1.5 2.8 3.9 4.9 5.8 9.9 10.6 11.0 11.4 11.7 11.9 Dy 0 0.1 0.2 0.3 0.4 0.5 1.1 1.2 1.3 1.4 1.5 1.6

[0319]

[0320] Y 0 0.6 1.2 1.8 2.4 2.9 5.6 6.2 6.7 7.3 7.9 8.4

[0321] The analyses clearly show a selectivity that allows up to 95% of heavy rare earths to be fixed while purifying up to 75% of the lanthanum in the first volumes of solution.

[0322] By setting the value for La to 1, we can define an enrichment factor in a given rare earth as corresponding to the following ratio:

[0323] -resin

[0324] L TR

[0325] -resin

[0326] There

[0327] -PLS

[0328] TR

[0329] -PLS

[0330] There

[0331] Or:

[0332] • c^ ine corresponds to the mass concentration of rare earth elements fixed on the resin, • c has Sme corresponds to the mass concentration of La fixed on the resin,

[0333] • c scorresponds to the mass concentration of rare earths in the solution of rare earth and ammonium sulfates,

[0334] • c There S corresponds to the mass concentration of La in the solution of rare earth and ammonium sulfates.

[0335] The calculated enrichment factors are shown in Table 12 below. Above 10 BV, there is a noticeable 5 to 6 times greater enrichment in Y and Dy compared to La, versus 2 times greater enrichment for Ce. Table 12: Enrichment Factors

[0336] Land Enrichment Factor

[0337] rare BVO BV1 BV2 BV3 BV4 BV5 BV10 BV14 BV21 BV28 BV35 BV42 La 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Ce 1.0 1.2 1.6 1.7 1.8 1.9 2.1 2.1 2.0 2.0 2.0 2.0 Pr 1.0 1.3 1.8 2.0 2.2 2.4 3.0 3.0 3.0 3.0 3.0 3.0 Nd 1.0 1.3 1.8 2.2 2.4 2.7 3.5 3.5 3.5 3.5 3.5 3.5 Dy 1.0 1.3 2.0 2.5 2.9 3.4 5.2 5.4 5.7 5.8 6.0 6.2

[0338]

[0339] Y 1.0 1.3 2.0 2.5 2.9 3.4 5.0 5.2 5.4 5.5 5.7 5.9

[0340] Knowing the variation in relative affinity of bis-(2,4,4-trimethylpentyl-)phosphinic along the series including actinium (less fixed than rare earths) and rare earths, one can deduce the possibility of removing actinium from the solution of rare earth and ammonium sulfates.

Claims

DEMANDS 1. Process for recovering rare earth elements contained in ionic clays by leaching said clays according to a continuous loop: • wherein said leaching is initiated by contacting fresh ionic clay with an aqueous leaching solution S1 comprising a dissolved salt of Mi / zCl or M2 / ZSO4, where M is a cation selected from the group consisting of Na + NH4 + and Mg 2+ ; 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; • then in which, said solution S2 is subjected to a phase of extraction of the valuable rare earths, defined as being composed of lanthanides of atomic number greater than that of cerium as well as Sc, where applicable 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 applicable with added yttrium, and on the other hand a raffinate R comprising the salt of Mi / z Cl or M2 / ZSO4, actinium in cationic form, and unrecovered rare earth elements defined as lanthanides with an atomic number less than or equal to that of cerium, possibly with the addition of yttrium, including some lanthanum, in cationic form; the raffinate R becoming the leaching solution, being brought into contact with a quantity of fresh ionic clay, forming a new solution S2 enriched in Ac cations 3+ and unvalued rare earth elements, including La 3+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 recovered rare earths, generating a new raffinate R; the leaching solution constituted by the raffinate R resulting from the successive phases of extraction of the recovered rare earths, running continuously in conjunction 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 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, • the liquid phase brought into contact with solution S2 during the extraction phase of the recovered rare earths, which employs a liquid-liquid extraction process, said liquid phase comprising an organic solvent immiscible with water, including at least one cationic extraction agent selected from the group consisting of alkylphosphonic derivatives, alkylphosphinic derivatives and mixtures thereof, for example, mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (HEH(EH)P), bis(2,4,4-trimethylpentyl)phosphinic acid, a mixture of phosphonic acid and phosphinic acid, neodecanoic acids of general formula C m H 2m O2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, naphthenic acids of general formula C n H2( n -z)O2 where n is an integer between 8 and 20, and z is an integer between 0 and 4, and their mixtures; • the solid phase brought into contact with solution S2 during the extraction phase of the recovered rare earths is capable of binding the cations of said rare earths and is chosen from the group comprising: silicas with a high specific surface area onto which extracting molecules are grafted or adsorbed, titanium oxides onto which extracting molecules are grafted or adsorbed, zirconium oxides onto which extracting molecules are grafted or adsorbed, polymer matrices onto which extracting molecules are grafted, and macroporous polymer matrices impregnated with extracting molecules, the extracting molecules being compounds having the capacity to bind the recovered rare earths by ion exchange, the extracting molecules having active groups comprising at least one cationic extraction agent chosen from the group consisting of alkyl-phosphonic derivatives,alkyl-phosphinic derivatives and their mixtures, for example mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (HEH(EH)P), bis(2,4,4-trimethylpentyl)phosphinic acid, a mixture of phosphonic acid and phosphinic acid, neodecanoic acids of general formula C, m H 2m O2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, naphthenic acids of general formula C n H2( n -z)O2 where n is an integer between 8 and 20, and z is an integer between 0 and 4, and their mixtures.

2. A process for recovering rare earth elements contained in ionic clays according to claim 1, wherein the concentration of all or part of the solution S2 in actinium and unrecovered rare earth elements is controlled by precipitation of Ac cations as carbonates or hydroxides 3+and unrecovered rare earths contained in the raffinate R resulting from successive extraction phases of recovered rare earths, and in which the carbonates or hydroxides resulting from the precipitation of the cations Ac 3+ and unvalued rare earths are separated from the liquid phase of the portion of 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 or hydroxides are stored as residues.

4. A process for recovering rare earth elements contained in ionic clays according to any one of claim 2, wherein said carbonates or hydroxides 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 the Ac cations 3+ and untapped rare earth elements + leading to the formation of a solution S5 comprising a salt of Mi / z Cl or Nh / zSCh, the S5 solution being reintroduced into the continuously rotating leaching solution.

5. A process for recovering 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 contact of solution SI, then of raffinate R, optionally supplemented with solution S5, with fresh clay is carried out in a reactor to form solution S2, said solution S2 being separated from the fresh clays by a liquid-solid separation process.

7. A process for recovering rare earth elements contained in ionic clays according to any one of claims 1 to 6, characterized in that the molar concentration of Mi / z Cl in the SI solution, then 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, then in the raffinate R, is between 0.05 and 0.5 mol / L.

9. A process for recovering rare earth elements 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 earth elements, optionally with the addition of yttrium, has a total concentration of rare earth ions of which La 3+ and Y 3+ , ranging between 0.1 and 5 g / L and an activity linked to the Ac content 3+ between 0 and 30 Bq / L.

10. A process for recovering rare earth elements contained in ionic clays according to any one of claims 2 to 9, characterized in that the precipitation of the Ac cations in the form of carbonates or hydroxides 3+ and unrecovered rare earths, is carried out by adding to the raffinate R resulting from the successive phases of extraction of the recovered rare earths, a solution or suspension of MgO or of carbonate salt M2 / ZCO3 or of hydrogen carbonate salt M z (HCO3)2 or hydroxides M(OH) Z , where M is a cation chosen from the group consisting of Na + NH4 + and Mg 2+ and z = 1 or 2 is the charge number of the cation considered.

11. A process for recovering rare earths contained in ionic clays according to claim 10, characterized in that the carbonates or hydroxides 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 earth elements contained in ionic clays according to any one of claims 4 to 11, characterized in that the acidic solution used to dissolve the carbonates or hydroxides resulting from the precipitation of the cations Ac 3+ and unvalued rare earths includes a Lewis acid selected from the group consisting of HCl and H2SO4.

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

14. A process for recovering rare earth elements contained in ionic clays according to any one of claims 2 to 13, characterized in that the carbonates or hydroxides have an activity of between 0 and 50 Bq / g of carbonates or hydroxides considered dry, said carbonates or hydroxides comprising: ■ 20% to 60% lanthanum, by weight, relative to the total weight of carbonates or hydroxides considered dry, ■ 0 to 30% of other unvalued rare earths, including yttrium and cerium, by weight, relative to the total weight of carbonates or hydroxides 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 process 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 earth elements contained in ionic clays according to any one of claims 4 to 16, characterized in that the raffinate R is divided into two streams F1 and F2, stream F1 constituting the leaching solution circulating in a loop, and stream F2 being subjected to precipitation in the form of carbonates or hydroxides of the cations Ac 3+ and unvalued 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 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.

19. A process for valorizing rare earths contained in ionic clays according to any one of claims 1 to 18, wherein the solid phase is stationary and located in a reservoir within which the solution S2 percolates generating a solid S3.

20. A process for valorizing rare earths contained in ionic clays according to claim 19, wherein the solid S3 undergoes a solid-liquid re-extraction using an acidic eluent, generating an aqueous extract E loaded with valorized rare earths, optionally with added yttrium, the acidic eluent being chosen from the group consisting of hydrochloric acid, sulfuric acid and nitric acid.

21. A process for valorizing rare earths contained in ionic clays according to claim 20, wherein the aqueous extract E loaded with valorized rare earths, optionally supplemented with yttrium, is concentrated by evaporation.

22. A process for valorizing rare earths contained in ionic clays according to claim 20, 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, magnesium oxide, oxalic acid and its alkali salts.

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