Method for removing the actinium contained in a rare earth solution using a solvent derived from carboxylic acid and rare earth composition obtained by this method

Abstract

The invention relates to a method for removing the actinium contained in an initial aqueous solution of rare earth chlorides resulting from ore processing, the method comprising the following steps: bringing the initial aqueous solution into contact with a water-immiscible organic solvent, the organic solvent comprising at least one cationic extractant, separating, by liquid-liquid extraction, the rare earth elements and the actinium, all of the rare earth elements except for all or some of the lanthanum and / or yttrium being extracted in the organic solvent, bringing the organic solvent, comprising all of the rare earth elements except for all or some of the lanthanum, and / or yttrium, into contact with an acid solution to produce an aqueous composition having a mass concentration of actinium, lanthanum and / or yttrium, relative to the other earth elements, that is lower than the mass concentration of actinium, lanthanum and / or yttrium of the initial aqueous solution, wherein the cationic extractant comprises at least one C8 to C20 carboxylic acid of formula (I): in which: R1, R2 and R3 are independently selected from the group comprising hydrogen, C1-C14 linear or branched alkyl substituted with at least one halogen atom or being unsubstituted, at least one saturated or unsaturated C5-C6 ring, and mixtures thereof, wherein the sum of the carbon atoms contained in R1, R2 and R3 is between 6 and 18.

Description

[0001] METHOD FOR REMOVING ACTINIUM FROM A RARE EARTH SOLUTION BY A CARBOXYLIC ACID-DERIVED SOLVENT AND RARE EARTH COMPOSITION OBTAINED BY THIS METHOD

[0002] FIELD OF INVENTION

[0003] The invention falls within the general field of rare earth solution processing. More specifically, it relates to a process for removing a radioactive compound from an aqueous solution obtained from rare earth ore processing by liquid-liquid extraction. The invention also relates to a rare earth composition obtained by liquid-liquid extraction from an initial aqueous solution of rare earth chlorides.

[0004] PRIOR STATE OF TECHNOLOGY

[0005] The ores from which rare earth elements are extracted may contain radioactive compounds, which must be separated from the rare earth elements. For example, monazite contains all the radioactive isotopes of the thorium-232 families ( 232 Th), uranium 235 ( 235 U) and uranium 238 ( 238 U). Ores generally undergo an initial processing stage consisting of physical concentration (magnetic separation, flotation, etc.). However, during this stage, the radioactive isotopes present in the ore are not separated from the rare earth elements. In a second stage, the previously obtained concentrate undergoes chemical treatments. During these chemical treatments, the radioactive equilibrium of the three radioactive families below is disrupted, and each radioelement will evolve according to its own chemical properties independently of the other elements in the radioactive family.

[0006] Some isotopes decay rapidly, while others, which have a radioactive half-life exceeding a few days, must be disposed of to prevent contamination of rare earth elements. For example, the following isotopes have a relatively long radioactive half-life:

[0007] • Family of 232 Th: 232 Th, 228 Th, 228 Ra,

[0008] • Family of 238 U: 238 U, 234 U, 234 Th, 230 Th, 226 Ra, 210 Pb, 210 Po,

[0009] • Family of 235 U: 235 U, 231 Pa, 227 Ac. 223 Ra.

[0010] Most of these elements have chemical properties sufficiently different from those of rare earth elements that their removal can be achieved using conventional hydrometallurgical techniques, such as precipitation and filtration. This is the case, for example, for isotopes of thorium, uranium, radium (Ra), lead (Pb), polonium (Po), and protactinium (Pa). However, the case of the isotope 227Actinium-227, also known as Ac, with a radioactive half-life of 22 years, is unique because its chemical properties are similar to those of rare earth elements, particularly lanthanum. During the separation of rare earth elements, actinium follows lanthanum and risks accumulating in compounds containing lanthanum. It must then be disposed of through radioactive waste management, which incurs additional costs. Therefore, it is necessary to implement processes for separating rare earth elements and actinium, allowing for the efficient removal of the isotope. 227 Ac.

[0011] Such actinium removal processes are described, for example, in document WO 2019 / 000014, where actinium is precipitated from solutions of rare-earth chlorides or nitrates, which come from the processing of monazite or xenotime ores, by adding sulfate salts. The drawback of this process is that it requires the addition of significant quantities of salt (on the order of hundreds of g / L) to induce precipitation. Furthermore, this process is relatively time-consuming. Moreover, it does not remove a sufficient amount of actinium.

[0012] Other methods describe the separation of rare earth elements and actinium by liquid-liquid extraction. This extraction is carried out using organic solvents containing rare earth element selective molecules, which are extracted into the organic phase while the actinium remains in the aqueous phase. Indeed, it is known to use cationic agents with a high affinity for rare earth elements, such as organophosphate acid derivatives, as extracellular agents.

[0013] As an example, document CN 85100148 describes a process for producing lanthanum oxides by separating lanthanum and actinium from a rare-earth nitrate solution. The liquid-liquid separation is carried out using an organic solvent comprising mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (HEHEHP) or di(2-ethylhexylphosphoric acid ester (HDEHP or D2EHPA).

[0014] Similarly, document KR 100351554 details a liquid-liquid separation method for rare earth elements and actinides contained in rare earth nitrate solutions derived from radioactive liquid waste. The process involves the use of tributyl phosphate and phosphoric acid esters in the form of metallic salts.

[0015] Document WO 2016 / 083739 describes a liquid / liquid extraction process in which, starting from a nitric or hydrochloric acid solution containing rare earth elements, Ac-227, and other impurities, all rare earth elements except lanthanum are extracted, leaving lanthanum, actinium, and other impurities in the unextracted portion, but without the remaining rare earth elements. The unextracted portion then undergoes a second separation step to extract all the La and Ac-227 for purification. The extractant can be a phosphoric acid, such as HDEHP, a phosphonic acid, such as HEHEHP, a phosphinic acid, or versatic acid.

[0016] Document GB 1, 180,922 describes a process for separating rare earth chlorides or nitrates by liquid / liquid extraction using a solvent. The solvent comprises a C8 to C20 carboxylic acid, preferably a mixture of Versatic™ 911, diluted in a hydrocarbon such as kerosene or xylene.

[0017] The document "Extraction of rare earths and yttrium with high molecular weight carboxylic acids," by Singh DK et al., describes the extraction of rare earths La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, and Y from a chloride solution. This extraction is carried out using a solvent comprising dodecane and a high molecular weight carboxylic acid extradant, selected from: isooctanoic acid, isononanoic acid, isodecanoic acid, naphthenic acid, neoheptanoic acid, and Versatic™ 10.

[0018] Another problem related to the presence of actinium in rare earth solutions concerns transportation. Indeed, an ore with a uranium content of 5000 ppm relative to the sum of its rare earth contents results in a quantity of 227 Ac, which generates an activity equivalent to approximately 2.4 Bq / g of rare earth elements. However, 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 represents an additional constraint and cost. It is therefore necessary to limit the transport steps for such products, particularly by directly processing the solutions derived from the ores, without resorting to intermediate steps.

[0019] Furthermore, during rare earth production operations, intermediate manufacturing concentrates are subject to strict radiation protection regulations. In particular, concentrates with an activity level of actinium-227 exceeding 0.1 Bq / g require special monitoring of workers.

[0020] Furthermore, other rare earth elements, such as yttrium and cerium, are of little economic interest, but their presence during the processing of base ores generates significant additional costs, particularly during transport. Moreover, during downstream processing aimed at purifying rare earth elements to produce high-value rare earth elements, such as praseodymium, neodymium, terbium, and dysprosium, the presence of yttrium and cerium again leads to increased costs. DESCRIPTION OF THE INVENTION

[0021] One of the aims of the invention is to remove actinium during the production of a rare earth solution from ore processing, thereby avoiding the costly production, transport, and subsequent processing of radioactive rare earth intermediate concentrates. This actinium removal is accompanied by the removal of all or part of the lanthanum and / or yttrium. Since these two 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 used by users of said concentrate.

[0022] Thus, the invention relates to a process for removing actinium from an initial aqueous solution of rare-earth chlorides, said initial aqueous solution being obtained from the chemical treatment of ore. The process comprises the following steps:

[0023] • contacting and mixing the initial aqueous solution with an organic solvent immiscible with water, said organic solvent comprising at least one cationic extraction agent,

[0024] • separation by liquid-liquid extraction of rare earth elements and actinium, all rare earth elements except all or part of the lanthanum and / or yttrium being extracted in the organic solvent,

[0025] • contacting the organic solvent comprising all the rare earth elements, with the exception of all or part of the lanthanum and / or yttrium, with an acidic solution, to produce an aqueous composition having an actinium-related activity lower than the actinium-related activity of the initial aqueous solution, and a lanthanum and / or yttrium mass content relative to the other rare earths lower than the lanthanum and / or yttrium mass content relative to the other rare earths of the initial aqueous solution, the aqueous composition comprising all or part of the rare earth elements, wherein the cationic extraction agent comprises at least one C8 to C20 carboxylic acid of formula (I): in which R 1 , R 2 and R 3are independently chosen from the group comprising the hydrogen atom, a linear or branched C14 Cl alkyl substituted by at least one halogen atom or unsubstituted, at least one saturated or unsaturated C5 to C6 ring, and mixtures thereof, the sum of the carbon atoms contained in R 1 , R 2 and R 3 being between 6 and 18. The invention also relates to a rare earth composition obtained by the process according to the invention.

[0026] ORGANIC SOLVENT

[0027] According to the invention, the organic solvent comprises at least one cationic extraction agent which is a long-chain carboxylic acid.

[0028] A "long-chain carboxylic acid" is defined as a carboxylic acid that comprises at least 8 carbon atoms, including the carbon atom of the acid function, and at most 16 carbon atoms.

[0029] The chain can be linear or branched, or include aliphatic or aromatic rings and oxygen or halogen atoms.

[0030] These compounds are particularly effective at complexing trivalent cations, such as rare earth cations.

[0031] According to the invention, the rare earths are chosen from the group comprising: scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and mixtures thereof.

[0032] Preferably, the cationic extraction agent is a carboxylic acid of formula (I) chosen from the group comprising the neodecanoic acids of general formula CmlLml, where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, and the naphthenic acids of general formula Cml. n H2( n-z)O2 where n is an integer between 8 and 20 corresponding to the total number of carbon atoms and z is an integer between 0 and 4 corresponding to the number of rings, and their mixtures.

[0033] According to one embodiment, the extracellular agent is neodecanoic acid which is a synthetic mixture of acid isomers of general formula CmtLmCL where m is an integer between 9 and 11.

[0034] Versatic™ Acid 10 is an example of neodecanoic acid comprising a mixture of the two compounds given as examples below:

[0035] Advantageously, the cationic extrading agent is 2-ethylhexanoic acid with the formula:

[0036] Preferably, the cationic extrading agent is 2-bromooctanoic acid, which is an alpha-halogenated carboxylic acid, with the formula:

[0037] The cationic extrading agent can be a naphthenic acid with the general formula Cn H2( n -z)O2, which is a mixture of alicyclic carboxylic acids, in which n is an integer from 8 to 20, corresponding to the number of carbon atoms, and z is an integer from 0 to 4 corresponding to the total number of saturated aliphatic rings.

[0038] Preferably, naphthenic acid F has the formula (II): in which:

[0039] R 4 , R 5 , R 6 and R 7 are chosen independently from the group comprising the hydrogen atom and a linear or branched saturated alkyl chain, and x is between 0 and 13. For example, when R 4 , R 5 and R 7 , are hydrogen atoms, R 6 An alkyl group at C2 and x equals 1, naphthenic acid has the formula CiolIixO, comprising a pentane ring and represented by the following formula:

[0040] The cationic extraction agent can be a mixture of the molecules described above.

[0041] Additionally, the organic solvent may include a diluent compound, chosen from the group consisting of C5 to C16 hydrocarbons, linear or branched, aliphatic or aromatic.

[0042] For example, the diluent compound is chosen from the group including: decane and its isomers, dodecane and its isomers, kerosene, toluene, aliphatic hydrocarbons having between 10 and 14 carbon atoms, hydrocarbons of 10 carbon atoms comprising at least one aromatic function, and mixtures thereof.

[0043] Examples of diluent compounds include Shellsol®D70 (aliphatic hydrocarbon), Isopar®L (aliphatic hydrocarbon with a low content of cyclic molecules), Isopar®M (aliphatic hydrocarbon with a low content of cyclic molecules) or Solvesso®150 (aromatic hydrocarbon).

[0044] The diluent compound dissolves the cationic extraction agent. It is distinct from the cationic extraction agent itself.

[0045] In addition to the cationic extraction agent and the diluent compound, the solvent may include at least one modifying compound, selected from the group comprising neutral esters of phosphoric acid, neutral esters of phosphonic acid, phosphine oxides, linear or branched C6-C16 fatty alcohols, and sulfoxides.

[0046] Preferably, the modifying compound is selected from the group comprising tributyl phosphate, decan-l-ol, octan-l-ol, isodecan-l-ol, hexan-l-ol, dodecan-l-ol, 2-ethylhexanol, dibutyl sulfoxide, dihexyl sulfoxide, petroleum-derived sulfoxides, trioctylphosphine oxide (TOPO), and mixtures thereof. For the purposes of this invention, the term "modifying compound" refers to a chemical species, other than the cationic extraction agent and the diluent, capable of modifying certain properties of the organic solvent. For example, the modifying compound may delay the formation of a third phase or aid in decantation.

[0047] According to a particular embodiment, the organic solvent comprises at least one cationic extraction agent and at least one diluent compound.

[0048] Alternatively, the organic solvent may comprise at least one cationic extraction agent, at least one diluent compound and at least one modifying compound.

[0049] Preferably, the organic solvent has a molar concentration of cationic extraction agent between 0.1 and 2 mol / L, preferably between 0.3 and 1.5 mol / L. Such a concentration allows the solvent to maintain a viscosity of less than 20 cP at room temperature, i.e. between 20°C and 27°C, preferably at 25°C.

[0050] In a particular embodiment of the invention, the organic solvent comprises: from 15% to 70% of at least one cationic extraction agent, from 30% to 85% of at least one diluent compound, by weight relative to the total weight of the organic solvent, the total being equal to 100%.

[0051] In another embodiment of the invention, the organic solvent comprises: from 15% to 70% of at least one cationic extraction agent, from 10% to 85% of at least one diluent compound, from 0% to 20% of at least one modifying compound, by weight relative to the total weight of the organic solvent, the total being equal to 100%.

[0052] INITIAL AQUEOUS SOLUTION OF RARE EARTHS

[0053] The initial aqueous solution of rare earths, according to the invention, is an aqueous solution of rare earth chlorides.

[0054] The concentration of rare earths in the initial aqueous solution of rare earth chlorides can be between 100 mg / L and 250 g / L, or between 0.001 and 1.5 mol / L.

[0055] Preferably, the initial aqueous solution of rare earth chlorides is obtained by chemically treating a selected ore concentrate from the group consisting of xenotime, monazite, and mixtures thereof with hydrochloric acid. Alternatively, the aqueous solution of rare earth chlorides may be obtained by chemically treating ionic clays with chlorides of alkali metals, particularly sodium chloride, ammonium chloride, or alkaline earth metals such as magnesium.

[0056] Concentrates can be obtained by physical concentration of ores. Examples of physical concentration methods include magnetic separation and flotation, but the present invention is not limited to these methods.

[0057] Alternatively, the concentrates may be mixtures of rare earth hydroxides, carbonates, or oxides obtained by precipitation and optionally by calcination of rare earths and actinium present in a solution comprising the rare earths and actinium. The solution may be obtained in one or more physical and chemical processing steps from an ore selected from the group consisting of xenotime, monazite, and mixtures thereof, or ionic clays.

[0058] Depending on the nature of the ore from which the initial aqueous solution originates, its activity is linked to the content of 227 Ac, can be between 0.1 and 25 Bq / g of rare earths.

[0059] LIQUID-LIQUID EXTRACTION

[0060] In practice, the contacting and mixing of the initial aqueous solution of rare-earth chlorides with the organic solvent can be carried out in a multi-stage device, for example, a bank of mixer-settlers or an extraction column. In this device, the aqueous solution and the organic solvent advantageously flow in counter-current flow.

[0061] Advantageously, the process is carried out at a temperature between 20°C and 60°C, preferably between 30°C and 50°C.

[0062] Preferably, the device includes an extraction section and a re-extraction section. It may also include a washing section. Each section may have 1 to 10 stages.

[0063] According to one embodiment, the solvent is saponified by a basic solution (ammonia, sodium hydroxide, magnesium oxide, etc.) with a molar concentration of OH" ions between 0.5 and 10 mol / L.

[0064] Once the rare earth elements have been extracted from the organic solvent, the solvent is contacted with an acidic solution chosen from the group consisting of hydrochloric acid, nitric acid, and sulfuric acid solutions. This contacting, or washing, of the organic solvent can be carried out in the washing section.

[0065] In practice, an aqueous composition of rare earths is obtained at the end of the liquid-liquid extraction comprising all or part of the rare earths initially present in the initial aqueous solution.

[0066] This aqueous composition, which is a solution of chlorides, nitrates or sulfates of rare earths, advantageously has an activity, linked to the actinium content, of less than 0.10 Bq / g of rare earths, preferably less than 0.01 Bq / g of rare earths.

[0067] The process according to the invention therefore has the advantage of reducing the relative content of La, Ce and or Y compared to the other rare earths contained in the rare earth composition, compared to the initial aqueous solution of rare earth chlorides.

[0068] In particular, the sum of the mass concentrations of lanthanum, cerium and yttrium can be reduced, for example by 50%, without this value being limiting for the process.

[0069] Preferably, the rare earth composition does not include lanthanum or yttrium.

[0070] This reduction in the La, Ce and Y content is important from an economic point of view because it allows on the one hand to reduce transport costs where applicable, and on the other hand it reduces the cost of separations of rare earths downstream, in particular the costs related to the purification of praseodymium, neodymium, terbium and dysprosium.

[0071] In general, an aqueous refinement is also obtained in which the sum of the mass concentrations of lanthanum, cerium and yttrium relative to other rare earths is greater than 90%.

[0072] RARE EARTHEN COMPOSITION

[0073] The rare earth composition exhibits a content of 227 Ac less than 0.10 Bq / g of rare earths, preferably less than 0.01 Bq / g of rare earths, the mass fraction of alkaline earths and lead contained in the composition being less than 1000 ppm, relative to the mass of rare earths, preferably less than 100 ppm relative to the mass of rare earths, the composition being in the form of a solid or aqueous solution.

[0074] Advantageously, the rare earth composition exhibits a total activity of less than 0.10 Bq / g of rare earths, preferably less than 0.01 Bq / g of rare earths. The total activity is related to the radioelement content in the composition, for example,226 Ra, 228 Ra, 232 Th, 238 U, 231 Pa, and their descendants. The rare earth composition may contain all or part of the rare earths and advantageously presents a reduced relative mass concentration of lanthanum, and / or yttrium compared to the other rare earth elements, with regard to their mass concentration in the initial aqueous solution.

[0075] According to one embodiment, the rare earth composition is precipitated using a precipitating agent selected from the group comprising sodium carbonate, ammonium bicarbonate, sodium hydroxide, ammonia, oxalic acid and its alkali salts.

[0076] When the composition is precipitated, it is in the form of a solid belonging to the group comprising carbonates, hydroxycarbonates, oxycarbonates, hydroxynitrates, hydroxides, oxides, oxalates, crystallized nitrates, anhydrous nitrates, crystallized chlorides and anhydrous rare earth chlorides.

[0077] Advantageously, the precipitated solids are calcined to obtain oxides.

[0078] According to another embodiment, the rare earth composition is crystallized or poured at high temperature, preferably between 110°C and 150°C, preferably at atmospheric pressure.

[0079] For example, the crystallization of nitrate or rare earth chloride solutions generates crystallized nitrates or crystallized chlorides, while the high-temperature pouring of these solutions followed by their cooling results in the formation of anhydrous nitrates or anhydrous chlorides.

[0080] When the composition is in the form of an aqueous solution, the rare earth composition is an aqueous solution belonging to the group comprising aqueous solutions of rare earth sulfates, chlorides and nitrates.

[0081] Advantageously, the concentration of rare earths in the aqueous solution is between 10 g / L and 500 g / L. Preferably, the concentration of rare earths is between 50 and 450 g / L in a nitrate solution, between 5 and 30 g / L in an aqueous sulfate solution, and between 50 and 200 g / L in an aqueous chloride solution.

[0082] BRIEF DETAILED DESCRIPTION OF THE FIGURE

[0083] Figure 1 is a schematic representation of the process according to Example 1 of the invention, in a liquid-liquid extraction battery consisting of four sections. EXAMPLE OF AN EMBODIMENT OF THE INVENTION

[0084] The example below was simulated using software called "PAREX+", implemented by the Applicant, whose basic data necessary for the calculations were previously obtained through laboratory tests according to the different chemical systems presented.

[0085] We consider an aqueous solution of rare earth chlorides obtained from the treatment of an ionic clay type ore with sodium chloride.

[0086] Example 1 below was calculated for a counter-current, continuous mixer-settler battery-type installation with the following performance: the extraction efficiency of all rare earth elements with atomic numbers greater than praseodymium (Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) is greater than 99%; the removal rate of the 227 Ac, which is equal to the ratio between the activity related to the mass flow rate of 227 Refined AC and activity related to mass flow rate227 The Ac of the initial aqueous solution of rare earths, is greater than 99.9%; the lanthanum removal rate, which is equal to the ratio between the mass flow rate of La in the refiner and the mass flow rate of La in the initial aqueous solution, is greater than 99.8%; the yttrium removal rate, which corresponds to the ratio between the mass flow rate of yttrium in the refiner and the mass flow rate of yttrium present in the initial aqueous solution, is greater than 70%.

[0087] Example 1: Elimination of 227 Ac, lanthanum and yttrium from an initial aqueous solution of rare earth chlorides obtained by treating a concentrate of ionic clays with a sodium chloride solution.

[0088] The process according to the invention is carried out using the following device: a liquid-liquid extraction battery of the mixer-decanter type operating in counter-current, continuous operation, consisting of a one-stage loading section (42), a six-stage extraction section (43), a five-stage washing section (44) and a four-stage re-extraction section (45), these four sections being connected to each other.

[0089] The extraction section (43) is fed with an initial aqueous solution (22) comprising a mixture of rare earth chlorides, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, and 227 Ac, with a flow rate of 120,800 L / h, the composition of which is detailed in Table 3. The initial aqueous solution of rare earth chlorides (22) is obtained by treating a concentrate of ionic clays with a sodium chloride solution.

[0090] The solvent SI (25), composed of naphthenic acid, aliphatic kerosene and decan-l-ol at 31 / 62 / 7 vol % respectively, is injected at a rate of 46,000 L / h into the loading section (42).

[0091] The solvent SI is saponified by a sodium hydroxide solution NaOH (23) with an OH" concentration of 8 mol / L, at a flow rate of 2,300 L / h.

[0092] An aqueous refiner (26) comprising mostly La and Y as well as almost all of 227 Ac est o b(enu with a flow rate of 127,286 L / h. The measured activity is 1.25 Bq / g of rare earths

[0093] The solvent SI is washed with a hydrochloric acid solution (27) at a concentration of H + of 4.5. mol / L with a flow rate of 4,186 L / h in the washing section (44).

[0094] An aqueous solution of hydrochloric acid (24) with a concentration of H + 5 mol / L is fed into the re-extraction section (45) with a flow rate of 216 L / h.

[0095] An aqueous extract (28) comprising the rare earths La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y is obtained with a flow rate of 216 L / h. It has a rare earth concentration of 223 g / L and an activity, related to the content of 227 Ac, below the detection threshold which is 2.10' 5 Bq / g of rare earths.

[0096] The relative content of La compared to other rare earths is 0.17%, by weight, and the relative content of Y compared to other rare earths is 14.3%, by weight.

[0097] The purification rate of 227 Ac relative to rare earths, which is equal to the ratio between the content of 227 Ac per gram of rare earths in the initial aqueous solution (22) on the content of 227 Ac per gram of rare earths in the aqueous extract (28) is, under these conditions, greater than 34,000.

[0098] The lanthanum removal rate, which is equal to the ratio between the mass flow rate of lanthanum in the refiner (26) and the mass flow rate of lanthanum in the initial aqueous solution (22) is, under these conditions, equal to 99.8%.

[0099] The yttrium removal rate, which is equal to the ratio of the yttrium mass flow rate in the refiner (26) to the yttrium mass flow rate in the initial aqueous solution (22), is, under these conditions, 70.5%. The quantities of rare earth elements and the flow rates are reported in Table 1. Table 1 The abbreviations correspond to the following steps:

[0100] Feed: supplying the initial aqueous solution of rare earths (22) to the extraction section (43)

[0101] Loading: loading of the sodium hydroxide solution (23) into the loading section (42)

[0102] Reex.: re-extraction of rare earths by adding an aqueous solution of hydrochloric acid (24) to the re-extraction section (45)

[0103] Raff.: aqueous refiner (26) from the extraction section (43)

[0104] Ext.: aqueous extract (28) from the re-extraction section (45)

[0105] TR: rare earths

[0106] Nature: nature of the flux gTR: gram of rare earths kgTR: kilogram of rare earths

[0107] The aqueous extract (28) has an activity in 227 AC less than 2.10' 5 Bq / g of rare earths, or 3.10' 6 Bq / g of solution.

[0108] This solution is precipitated in the form of hydroxides by the addition of sodium hydroxide.

[0109] After filtration, a moist rare earth hydroxide is obtained containing 40% water and 44.3% rare earths. This solid has an activity in 227 AC less than 2.10' 5 Bq / g of rare earths, or 8.10'6 Bq / g of solid.

[0110] This solid is then calcined at 900°C.

[0111] This yields an oxide containing 84.92% rare earth elements, with an activity in 227 AC less than 2.10' 5 Bq / g of rare earths, i.e. 1.7 x 10⁻¹⁰ 5 Bq / g of solid.

[0112] It follows from this example that when the initial ore consists of ionic clays, the aqueous extract from the re-extraction solution has an actinium-227 content of less than 0.10 Bq / g of rare earths, but also a lanthanum mass fraction of less than 5% by weight relative to the total rare earth mass fraction and a yttrium mass fraction of less than 30% by weight relative to the total rare earth mass fraction.

[0113] The invention therefore proves to be particularly effective in the broader context of rare earth extraction.

Claims

DEMANDS 1. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore, the process comprising the following steps: ■ contacting the initial aqueous solution with an organic solvent immiscible with water, the organic solvent comprising at least one cationic extraction agent, ■ Separation by liquid-liquid extraction of rare earth elements and F actinium, all rare earth elements except all or part of the lanthanum, and / or yttrium being extracted in the organic solvent, ■ contacting the organic solvent, comprising all the rare earth elements except all or part of the lanthanum, and / or yttrium, with an acidic solution to produce an aqueous composition having a mass concentration of actinium, lanthanum, and / or yttrium, relative to the other earth elements, lower than the mass concentration of actinium, lanthanum and / or yttrium of the initial aqueous solution, the aqueous composition comprising all or part of the rare earth elements, wherein the cationic extraction agent comprises at least one C8 to C20 carboxylic acid of formula (I): in which: R 1 , R 2 and R 3are independently chosen from the group comprising the hydrogen atom, a linear or branched C14 Cl alkyl substituted by at least one halogen atom or unsubstituted, at least one saturated or unsaturated C5 to C6 ring, and mixtures thereof, the sum of the carbon atoms contained in R 1 , R 2 and R 3 being between 6 and 18.

2. A process for removing actinium from an initial aqueous solution of rare-earth chlorides obtained from the chemical treatment of ore according to claim 1, wherein the cationic extraction agent F is a carboxylic acid of formula (I) selected from the group comprising neodecanoic acids of general formula C m I hmO 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)O2OÙ n is an integer between 8 and 20, corresponding to the total number of carbon atoms and z is an integer between 0 and 4, corresponding to the number of rings, and their mixtures.

3. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to claim 1 or 2, wherein the organic solvent further comprises a diluent compound selected from the group comprising C5 to C16 hydrocarbons, linear or branched, aliphatic or aromatic.

4. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 3, wherein the organic solvent further comprises a modifying compound selected from the group comprising neutral esters of phosphoric acid, neutral esters of phosphonic acid, phosphine oxides, linear or branched C6 to Cl6 fatty alcohols, and sulfoxides.

5. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 4, wherein the organic solvent has a molar concentration of cationic extraction agent between 0.1 and 2 mol / L.

6. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 5, wherein the initial aqueous solution of rare earth chlorides is obtained from the treatment with hydrochloric acid of an ore concentrate selected from the group consisting of xenotime, monazite, and mixtures thereof, or from the treatment of ionic clays with chlorides of alkali metals, ammonium, or alkaline earth metals such as magnesium.

7. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 6, wherein the molar concentration of rare earths in the initial aqueous solution is between 0.001 and 1.5 mol / L 8. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 7, wherein the acidic solution brought into contact with the organic solvent is selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid solutions.

9. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 8, wherein the aqueous composition is an aqueous solution of rare earth chlorides, nitrates or sulfates.

10. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 9, wherein the aqueous composition has an activity related to the actinium-227 content of less than 0.10 Bq / g of rare earths, preferably less than 0.01 Bq / g of rare earths.

11. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 10, wherein the aqueous composition is precipitated using a precipitating agent selected from the group comprising sodium carbonate, ammonium bicarbonate, sodium hydroxide, ammonia, oxalic acid and its alkali salts.

12. A process for removing actinium from an initial aqueous solution of rare earth chlorides obtained from the chemical treatment of ore according to any one of claims 1 to 10, wherein the aqueous composition is crystallized or poured at high temperature, preferably between 110°C and 150°C.

13. Rare earth composition obtained by the process according to any one of claims 1 to 12, having an activity related to the actinium-227 content of less than 0.10 Bq / g of rare earths, preferably less than 0.01 Bq / g of rare earths, the mass fraction of alkaline earths and lead contained in the composition being less than 1000 ppm, relative to the mass of rare earths, preferably less than 100 ppm, the composition being in the form of a solid or aqueous solution.

14. Rare earth composition according to claim 13, wherein the total activity is less than 0.10 Bq / g of rare earths, preferably less than 0.01 Bq / g of rare earths.

15. Rare earth composition according to claim 13 or 14, wherein the composition is in the form of a solid selected from the group comprising rare earth carbonates, hydroxycarbonates, oxycarbonates, hydroxynitrates, hydroxides, oxides, oxalates, crystallized nitrates, anhydrous nitrates, crystallized chlorides and anhydrous chlorides.

16. Rare earth composition according to claim 13 or 14, wherein the composition is an aqueous solution selected from the group comprising aqueous solutions of rare earth sulfates, chlorides and nitrates.

17. Rare earth composition according to claim 16, wherein the mass concentration of rare earths in the aqueous solution is between 10 g / L and 500 g / L.

18. A rare earth composition according to any one of claims 13 to 17, wherein said composition is obtained from the processing of xenotime, and wherein the lanthanum mass fraction is less than 0.5% by weight relative to the total rare earth mass fraction and the yttrium mass fraction is less than 30% by weight relative to the total rare earth mass fraction.

19. A rare earth composition according to any one of claims 13 to 17, wherein said composition is obtained from the processing of ionic clays, and wherein the lanthanum mass fraction is less than 5% by weight relative to the total rare earth mass fraction and the yttrium mass fraction is less than 30% by weight relative to the total rare earth mass fraction.

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