Process for removing actinium from a rare earth solution using a carboxylic acid-derived solvent and the rare earth composition obtained by this process

Abstract

This process for removing actinium from an initial aqueous solution of rare earth sulfates or chlorides obtained from ore processing comprises 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, – separating the rare earth elements and actinium by liquid-liquid extraction, all rare earth elements except all or part of the lanthanum and / or yttrium being extracted into the organic solvent, – contacting the organic solvent, comprising all 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 rare earth elements, lower than the mass concentration of actinium.in lanthanum and / or yttrium of the initial aqueous solution, wherein the cationic extraction agent 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 the hydrogen atom, a linear or branched C1 to C14 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 R1, R2 and R3 being between 6 and 18.

Description

Title of the invention: Process for removing actinium from a rare earth solution using a carboxylic acid-derived solvent AND COMPOSITION OF RARE EARTHS OBTAINED BY THIS PROCESS Scope of the invention

[0001] The invention falls within the general field of the treatment of aqueous rare earth solutions. More specifically, it relates to a process for removing a radioactive compound from an aqueous solution obtained from the processing of rare earth ores, by liquid-liquid extraction. The invention also relates to a rare earth composition obtained from the liquid-liquid extraction of an initial aqueous solution of rare earth sulfates or chlorides. Prior state of the art

[0002] 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 (²³²Th), uranium-235 (²³⁵U), and uranium-238 (²³⁸U) series. The ores generally undergo a first processing step consisting of physical concentration (magnetic separation, flotation, etc.). However, during this step, the radioactive isotopes present in the ore are not separated from the rare earth elements. In a second step, chemical treatments are carried out on the concentrate obtained previously. During these chemical treatments, the radioactive equilibrium of the three radioactive series below is disrupted, and each radioelement will evolve according to its own chemical properties independently of the other elements in the radioactive series.

[0003] Some isotopes decay rapidly, while others, which have a radioactive half-life exceeding a few days, must be disposed of to avoid contamination of rare earth elements. For example, the following isotopes have a relatively long radioactive half-life: - 232Th family: 232Th, 228Th, 228Ra, - 238U family: 238U, 234U, 234Th, 230Th, 226Ra, 210Pb, 210Po, - 235U family: 235U, 231Pa, 227Ac, ​​223Ra.

[0004] Most of these elements have chemical properties sufficiently different from those of rare earths that their removal can be carried out using conventional hydrometallurgical techniques, such as precipitation and filtration. This is the case, for example, with for example, isotopes of thorium, uranium, radium (Ra), lead (Pb), polonium (Po) and protactinium (Pa).

[0005] In contrast, the case of the isotope 227Ac, ​​also known as actinium-227, which has a radioactive half-life of 22 years, is unique because its chemical properties are similar to those of rare earth elements, and in particular to those of lanthanum. During the separation of rare earth elements, actinium will follow lanthanum and risks accumulating in compounds containing lanthanum. It will then have to be disposed of through the radioactive waste stream, which entails additional costs. It is therefore necessary to implement processes for separating rare earth elements and actinium, enabling the efficient removal of the 227Ac isotope.

[0006] Such processes for removing actinium 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 allow for the removal of a sufficient amount of actinium.

[0007] Other processes 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 that have a high affinity for rare earth elements, such as organophosphate acid derivatives, as extracting agents.

[0008] By way of example, 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-ethylhexyl)phosphoric acid ester (HDEHP or D2EHPA).

[0009] Similarly, document KR 100351554 details a liquid-liquid separation method for rare earths and actinides contained in rare earth nitrate solutions from radioactive liquid waste. The process involves the use of tributyl phosphate and phosphoric acid esters in the form of metallic salts.

[0010] Another problem related to the presence of actinium in rare earth solutions concerns transport. Indeed, an ore having a uranium content of 5000 ppm relative to the sum of the rare earths contained results in a quantity of 227Ac which This 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" materials. 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.

[0011] Furthermore, during rare earth production operations, intermediate manufacturing concentrates are subject to strict radiation protection regulations. In particular, concentrates whose activity related to the presence of actinium-227 exceeds 0.1 Bq / g require special monitoring of workers.

[0012] 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

[0013] 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 removal of actinium 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.

[0014] Thus, the invention relates to a process for removing actinium from an initial aqueous solution of rare earth sulfates or rare earth chlorides, said initial aqueous solution being obtained from ore processing. The process comprises the following steps: - contacting and mixing the initial aqueous solution with an organic solvent immiscible with water, said organic solvent comprising at least one cationic extraction agent, - 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, - 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, as well as 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): [Chem. 1] in which: R1, R2 and R3 are independently chosen from the group comprising the hydrogen atom, a linear or branched Cl-C14 alkyl substituted by at least one halogen atom or unsubstituted, at least one saturated or unsaturated C5-C6 ring, and mixtures thereof, the sum of the carbon atoms contained in R1, R2 and R3 being between 6 and 18.

[0015] The invention also relates to a rare earth composition obtained by the process according to the invention. Organic solvent

[0016] According to the invention, the organic solvent comprises at least one cationic extraction agent which is a long-chain carboxylic acid.

[0017] By "long chain carboxylic acid" is meant a carboxylic acid which comprises at least 8 carbon atoms, including the carbon atom of the acid function, and at most 16 carbon atoms.

[0018] The chain may be linear or branched, or include aliphatic or aromatic rings and oxygen or halogen atoms.

[0019] These compounds are particularly effective at complexing trivalent cations, such as rare earth cations.

[0020] 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.

[0021] Preferably, the cationic extraction agent is a carboxylic acid of formula (I) chosen from the group comprising neodecanoic acids of general formula CmH2mO2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, naphthenic acids of general formula CnH2(nz)O2 where n is an integer between 8 and 20 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.

[0022] According to one embodiment, the extracting agent is neodecanoic acid which is a synthetic mixture of acid isomers of general formula CmH2mO2 where m is an integer between 9 and 11.

[0023] Versatic™ Acid 10 is an example of neodecanoic acid comprising a mixture of the two compounds given as examples below: [Chem. 2] O ' 4 ' ' OH

[0024] [Chem.3] O

[0025] Advantageously, the cationic extracting agent is 2-ethylhexanoic acid of formula: [Chem. 4] O OH

[0026] Preferably, the cationic extracting agent is 2-bromo-octanoic acid, which is an alpha-halogenated carboxylic acid, of formula: [Chem. 5]

[0027] The cationic extrading agent can be a naphthenic acid of 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.

[0028] Preferably, naphthenic acid has the formula (II): [Chem. 6] in which: R4, R5, R6 and R7 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.

[0029] For example, when R4, R5 and R7 are hydrogen atoms, R6 a C2 alkyl and x is equal to 1, naphthenic acid has the formula Ci0Hi8O2, comprising a pentane ring and represented by the following formula: [Chem. 7]

[0030] The cationic extraction agent may be a mixture of the molecules described above.

[0031] Additionally, the organic solvent may include a diluent compound, selected from the group consisting of C5 to C16 hydrocarbons, linear or branched, aliphatic or aromatic.

[0032] For example, the diluent compound is chosen from the group comprising: decane and its isomers, dodecane and its isomers, kerosene, toluene, hydrocarbons aliphatics having between 10 and 14 carbon atoms, hydrocarbons of 10 carbon atoms comprising at least one aromatic function, and their mixtures.

[0033] 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).

[0034] The diluent compound allows the cationic extraction agent to dissolve. It is different from the cationic extraction agent.

[0035] 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 to Cl6 fatty alcohols, and sulfoxides.

[0036] Preferably, the modifying compound is chosen 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.

[0037] For the purposes of this invention, the term "modifying compound" refers to a chemical species other than the cationic extraction agent and the diluent compound, 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.

[0038] According to a particular embodiment, the organic solvent comprises at least one cationic extraction agent and at least one diluent compound.

[0039] Alternatively, the organic solvent may comprise at least one cationic extraction agent, at least one diluting compound and at least one modifying compound.

[0040] 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.

[0041] In a particular embodiment of the invention, the organic solvent comprises: - 15% to 70% of at least one cationic extraction agent, - 30% to 85% of at least one diluent compound, in weight relative to the total weight of the organic solvent, the total being equal to 100%.

[0042] In another embodiment of the invention, the organic solvent comprises: - 15% to 70% of at least one cationic extraction agent, - 10% to 85% of at least one diluent compound, - 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%. Initial aqueous solution of rare earths

[0043] The initial aqueous solution of rare earths, according to the invention, can be an aqueous solution of rare earth sulfates or an aqueous solution of rare earth chlorides.

[0044] The concentration of rare earth elements in the initial aqueous solution of rare earth sulfates or chlorides can be between 100 mg / L and 250 g / L, or between 0.001 and 1.5 mol / L. The mass concentration of rare earth elements in an aqueous solution of sulfates is preferably between 100 mg / L and 40 g / L. The mass concentration of rare earth elements in an aqueous solution of chlorides is preferably between 100 mg / L and 250 g / L.

[0045] Preferably, the initial aqueous solution of rare earth sulfates is obtained from the chemical treatment with sulfuric acid of an ore concentrate selected from the group consisting of xenotime, monazite, and mixtures thereof.

[0046] Alternatively, the initial aqueous solution of rare earth sulfates can be obtained from the treatment of ionic clays with sulfates of alkali metals, ammonium, or alkaline earth metals such as magnesium.

[0047] Preferably, the initial aqueous solution of rare earth chlorides is obtained from the chemical treatment with hydrochloric acid of an ore concentrate selected from the group consisting of xenotime, monazite, and mixtures thereof.

[0048] Alternatively, the aqueous solution of rare earth chlorides can be obtained from the treatment of ionic clays with chlorides of alkali metals, in particular sodium chloride, ammonium chloride, or alkaline earth metals such as magnesium.

[0049] 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.

[0050] Depending on the nature of the ore from which the initial aqueous solution is derived, its activity related to the 227Ac content can be between 0.1 and 25 Bq / g of rare earths. Liquid-liquid extraction

[0051] In practice, the contacting and mixing of the initial aqueous solution of rare earth sulfates or 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 directions.

[0052] Advantageously, the process is carried out at a temperature between 20°C and 60°C, preferably between 30°C and 50°C.

[0053] Preferably, the device comprises an extraction section and a re-extraction section. It may, in addition, comprise a washing section. Each section may comprise 1 to 10 stages.

[0054] 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.

[0055] Once the rare earths have been extracted in the organic solvent, the latter is brought into contact with an acidic solution which is chosen from the group consisting of hydrochloric acid, nitric acid and sulfuric acid solutions.

[0056] This contacting or washing of the organic solvent can be carried out in the washing section.

[0057] 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.

[0058] 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.

[0059] The process according to the invention therefore has the advantage of reducing the relative content of La, Ce and or Y with respect to the other rare earths contained in the rare earth composition, compared to the initial aqueous solution of rare earth sulfates or chlorides.

[0060] 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.

[0061] Preferably, the rare earth composition does not include lanthanum or yttrium.

[0062] 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.

[0063] In general, an aqueous raffinate 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%. Composition of rare earths

[0064] The rare earth composition has a 227Ac 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 relative to the mass of rare earths, the composition being in the form of a solid or aqueous solution.

[0065] Advantageously, the rare earth composition has 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 content of radioelements in the composition, for example, 226Ra, 228Ra, 232Th, 238U, 231Pa, and their decay products.

[0066] The rare earth composition may contain all or part of the rare earths and advantageously has 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.

[0067] 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.

[0068] 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 chlorides of rare earths.

[0069] Advantageously, the precipitated solids are calcined to obtain oxides.

[0070] According to another embodiment, the rare earth composition is crystallized or cast at high temperature, preferably between 110°C and 150°C, preferably at atmospheric pressure.

[0071] For example, the crystallization of solutions of nitrates or rare earth chlorides generates crystallized nitrates or crystallized chlorides, while the high-temperature pouring of these solutions and their subsequent cooling results in the formation of anhydrous nitrates or anhydrous chlorides.

[0072] 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.

[0073] Advantageously, the concentration of rare earth elements in the aqueous solution is between 10 g / L and 500 g / L. Preferably, the concentration of rare earth elements is between 50 and 450 g / L in a nitrate solution, and between 5 and 30 g / L in an aqueous solution of sulfates and between 50 and 200 g / L in an aqueous solution of chlorides. Brief detailed description of the figures

[0074] Fig. 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.

[0075] Fig. 2 is a schematic representation of the process according to Example 2 of the invention, in a liquid-liquid extraction battery consisting of four sections.

[0076] Figure 3 is a schematic representation of the process according to Example 3 of the invention, in a liquid-liquid extraction battery consisting of four sections. Examples of embodiments of the invention

[0077] The examples below were simulated using software called “PAREX +”, implemented by the Applicant, the basic data for which were previously obtained from laboratory tests according to the different chemical systems presented.

[0078] Three types of initial aqueous solutions resulting from chemical treatments of rare earth ores are considered: - an aqueous solution of rare earth sulfates obtained from the treatment of an ionic clay type ore with ammonium sulfate; - an aqueous solution of rare earth sulfates obtained from the treatment of a xenotime type ore with sulfuric acid; - an aqueous solution of rare earth chlorides obtained from the treatment of an ionic clay type ore with sodium chloride.

[0079] Examples 1 to 3 below were calculated for a counter-current, continuous, mixer-settler battery type installation with the following performance: - the extraction yield of all rare earths with atomic number greater than praseodymium (Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) is greater than 99%; - the 227Ac removal rate, which is equal to the ratio between the activity related to the mass flow rate of Ac from the raffinate and the activity related to the mass flow rate of Ac from 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 raffinate 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 raffinate and the mass flow rate of yttrium present in the initial aqueous solution, is greater than 70%.

[0080] Example 1: Removal of ractinium-227, lanthanum and yttrium contained in an initial aqueous solution of rare earth sulfates, obtained by treating ionic clays with an ammonium sulfate solution

[0081] 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 single-stage solvent loading section (34), an eight-stage extraction section (35), a five-stage washing section (36) and a four-stage re-extraction section (37), these four sections being connected to each other.

[0082] The extraction section (35) is supplied with an initial aqueous solution (8) comprising a mixture of rare earth sulfates, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, and 227Ac, ​​with a flow rate of 120,800 L / h, the composition of which is detailed in Table 1. This initial aqueous solution (8) is obtained by treating ionic clays with an ammonium sulfate solution.

[0083] The solvent SI (11), composed of naphthenic acid, aliphatic kerosene and decan-l-ol at 31 / 62 / 7 vol% respectively, is injected at a rate of 70,000 L / h into the loading section (34).

[0084] The solvent SI is saponified by an ammonia solution (9) with a molar concentration of OH of 4 mol / L, at a flow rate of 7,000 L / h.

[0085] An aqueous raffinate (12) comprising mainly La, Ce and Y, as well as almost all of the 227Ac is obtained with a flow rate of 172,110 L / h.

[0086] The calculated activity, linked to the 227Ac content, is 1.25 Bq / g of rare earths.

[0087] The solvent SI is washed by a sulfuric acid solution (13) at a sulfuric acid concentration of 0.319 mol / L, with a flow rate of 43,372 L / h in the washing section (36).

[0088] An aqueous solution of nitric acid (10) with a molar concentration in H+ of 5 mol / L is fed into the re-extraction section (37) with a flow rate of 233 L / h, thus allowing the regeneration of the solvent.

[0089] An aqueous extract (14) consisting mainly of the rare earths Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y is obtained with a flow rate of 227 L / h. This extract has a mass concentration of rare earths of 211 g / L and an activity, related to the 227Ac content, below the detection limit which is 2.10 5 Bq / g of rare earths.

[0090] The relative mass percentage of La compared to other rare earths is 0.05% by weight, and the relative mass percentage of Y compared to other rare earths is 14.2% by weight.

[0091] The 227Ac removal rate with respect to rare earths, which is equal to the ratio of the 227Ac content per gram of rare earths in the initial aqueous solution (8) to the content of 227Ac per gram of rare earths in the aqueous extract (14) is, under these conditions, greater than 34,000.

[0092] The lanthanum removal rate, which is equal to the ratio between the mass flow rate of La in the initial aqueous solution (8) and the mass flow rate of La in the aqueous raffinate (12) is, under these conditions, equal to 99.9%.

[0093] The yttrium removal rate, which is equal to the ratio between the mass flow rate of Y in the initial aqueous solution (8) and the mass flow rate of Y in the aqueous raffinate (12) is, under these conditions, equal to 70.8%.

[0094] The quantities of rare earths and the flow rates are reported in Table 1.

[0095] [Table 1] Power supply ÇWg. Reex. Sc^wt SI RÆ Wash Sxt. S « 10 11 13 13 14 Nature A^aew Aqueous Aqmax OrgwqK® Aqsous Aqueous (Ùh) n$Sûo 7838 233 70 800 172 no 43 372 ^2 Î5Ô 58 43 032 0^ 03^7 37 87 8.05 Ce 804 8318 1838 8.05 <0.881 27;54 03« «8.801 §3.84 0.03 <081 123« 0.00 <081 8.97 CWL) 0.02 <0381 1233 W) 838 <8801 23-3 832 <0.881 12.19 KM5<3 0.01 <0.881 290 Br(gA) 031 <0 081 732 Ta(^L) 0.00 <7 88; 038 W) 831 <8.881 635 Lufgl) 83« <8.881 132 Y» 030 8396 28.93 32 2S 14 TmiTR(gA) os 834 211 Flow La-0^) 3833 832 Deit¥^g&) 233? 10.48 8.78 -¾ 7 77 125 <2.181 DH- (msIA) 4 HîSQsCmaÆ) 8381 8323 0.319 5 7.03 Na^&têmque (btecS) 31 Ktosèæe a Dec^L»! (%voi) 7

[0096] The abbreviations correspond to the following steps: Feed: supplying the initial aqueous solution of rare earths (8) to the extraction section (35) Loading: loading the ammonia solution (9) into the loading section (34) Reex.: re-extraction of rare earths by adding an aqueous solution of nitric acid (10) to the re-extraction section (37) Raff.: aqueous raffinate (12) from the extraction section (35) Wash: washing, solvent regeneration using a sulfuric acid solution (13) in the washing section (36) Ext.: aqueous extract (14) from the re-extraction section (37) TR: rare earths Nature: nature of the flow gTR .gram of rare earths kgTR: kilogram of rare earth elements

[0097] The aqueous extract (14) has an activity in 227Ac of less than 2.105 Bq / g of rare earths, which is less than the detection threshold, and corresponding to 3.106 Bq / g of solution.

[0098] This extract is precipitated as a carbonate by the addition of ammonium bicarbonate. After filtration, a wet rare earth carbonate is obtained containing 30% water and 42.7% rare earths. This solid has a 227Ac activity of less than 2 x 10⁵ Bq / g of rare earths, i.e., below the detection limit, which is less than 8 x 10⁶ Bq / g of solid.

[0099] This solid is then calcined at 900°C.

[0100] An oxide is then obtained comprising 83.1% rare earths. This oxide has an activity in 227Ac below the detection threshold, i.e. less than 2.10 5 Bq / g of rare earths, or 1.6.105 Bq / g of solid.

[0101] Example 2: Removal of 222Ac, lanthanum and yttrium from an initial aqueous solution of rare earth sulfates obtained by treating a xenotime concentrate with a sulfuric acid solution

[0102] 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 single-stage solvent loading section (38), an eight-stage extraction section (39), a five-stage washing section (40) and a four-stage re-extraction section (41), these four sections being connected to each other.

[0103] The extraction section (39) is fed with an initial aqueous solution (15) comprising a mixture of rare earth sulfates, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, and 227Ac, ​​at a flow rate of 7,927 L / h, the composition of which is detailed in Table 2. The initial aqueous solution (15) is obtained by treating a xenotime concentrate with a sulfuric acid solution.

[0104] The solvent SI (18), composed of naphthenic acid, aliphatic kerosene and decan-l-ol at 31 / 62 / 7 vol% respectively, is injected at a flow rate of 68,000 L / h into the loading section (38).

[0105] The solvent SI is then saponified by an ammonia solution (16) with an OH concentration of 4 mol / L, at a flow rate of 6,800 L / h.

[0106] An aqueous raffinate (19) comprising predominantly La, Ce and Y, as well as almost all of the 227Ac, ​​is obtained with a flow rate of 58,913 L / h. The measured activity is 2.32 Bq / g of rare earths

[0107] The solvent SI is washed by a sulfuric acid solution (20) at an H2SO4 concentration of 0.319 mol / L with a flow rate of 43,265 L / h in the washing section (40).

[0108] An aqueous solution of nitric acid (17) with an H+ concentration of 5 mol / L is fed into the re-extraction section (41) with a flow rate of 300 L / h.

[0109] An aqueous extract (21) consisting mainly of the rare earths Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y is obtained with a flow rate of 238 L / h. It has a rare earth concentration of 215 g / L and an activity, related to the 227Ac content, below the detection limit, i.e. less than 2.105 Bq / g of rare earths.

[0110] The relative content of La compared to other rare earths is 0.003% by weight and the relative content of Y compared to other earths is 20.8% by weight.

[0111] The purification rate of 227Ac with respect to rare earths, which is equal to the ratio of the content of 227Ac per gram of rare earths in the initial aqueous solution (15) to the content of 227Ac per gram of rare earths in the aqueous extract (21) is, under these conditions, greater than 34,000.

[0112] The lanthanum removal rate, which is equal to the ratio between the mass flow rate of lanthanum in the raffinate (19) and the mass flow rate of lanthanum in the initial aqueous solution (15) is, under these conditions, equal to 99.9%.

[0113] The yttrium removal rate, which is equal to the ratio of the yttrium mass flow rate in the raffinate (19) to the yttrium mass flow rate in the initial aqueous solution (15), is, under these conditions, equal to 81.30%. The quantities of rare earths and the flow rates are reported in Table 2.

[0114] [Table 2] Alita. Load. Next If RaS Lavàgé Ext. Low 55 56 17 18 19 20 21 Farewell Arreux Api» Orgaas^ae À^eœx Â^assx AqaÈ»x Debit 7 927 W >00 «ssoœ 5£ 913 43265 230 Debit TR W4 S 51 ü(g&) 0.29 0332 0305 z 4j4 0303 Ce W 065 734 <3301 3.29 OO A03Ô1 L.35 Sa (g A) ^■ô <3301 09 <030i 23? G4 (g&J 0.82 <o.ôg1 2uï oo <s3û1 536 iis <0301 <3.04 eo <3301 es ^'l) o? 2438 tm(ga) vô s 15 : a ,4 «los ?n 7^0 g3s7 4437 53 80 21 t««tr(g&) ims 039 21539 débit la (1¾¾} 231 s;9q ÿ&0) 37.05 46,38 wa u? 2.32 <2.ï9-s oh- (saoll) 4 0323 0.319 tc (msi l) a s3? kérasèns décwl-$5 (zz) ____________________1_____________________ 5 —l......................1.................. zz

[0115] The abbreviations correspond to the following steps: Feed: supplying the initial aqueous solution of rare earths (15) to the extraction section (39) Loading: loading of the ammonia solution (16) into the loading section (38) Re-extraction: re-extraction of rare earths by adding an aqueous solution of nitric acid (17) into the re-extraction section (41) Raff.: aqueous raffinate (19) from the extraction section (39) Ext.: aqueous extract (21) from the re-extraction section (41) TR: rare earths Nature: nature of the flux gTR .gram of rare earths kgTR: kilogram of rare earths

[0116] The aqueous extract (14) has an activity in 227Ac below the detection threshold, i.e. less than 2.105 Bq / g of rare earths, i.e. 3.106 Bq / g of solution.

[0117] This solution is precipitated as oxalate by the addition of oxalic acid.

[0118] After filtration, a wet rare earth oxalate is obtained containing 30% water and 35.6% rare earths.

[0119] This solid has an activity in 227Ac below the detection threshold, i.e. less than 2.10 5Bq / g of rare earths, i.e. 7106 Bq / g of solid.

[0120] The solid is then calcined at 900°C.

[0121] We then obtain an oxide containing 84.92% of rare earths, having an activity in 227 Ac of less than 2.10 5Bq / g of rare earths, i.e. 1.7.105 Bq / g of solid.

[0122] Example 3: Removal of — Ac, lanthanum and yttrium from an initial aqueous solution of rare earth chlorides obtained by treatment of a concentrate of ionic clays with a sodium chloride solution.

[0123] 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.

[0124] 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 227Ac, ​​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.

[0125] The solvent SI (25), composed of naphthenic acid, aliphatic kerosene, and decanol at 31 / 62 / 7 vol% respectively, is injected at a rate of 46,000 L / h into the loading section (42). The solvent SI is saponified by a sodium hydroxide (NaOH) solution (23) with an OH concentration of 8 mol / L, at a rate of 2,300 L / h.

[0126] An aqueous raffinate (26) comprising predominantly La and Y and almost all of the 227Ac is obtained with a flow rate of 127,286 L / h. The measured activity is 1.25 Bq / g of rare earths

[0127] The solvent SI is washed with a hydrochloric acid solution (27) at an H+ concentration of 4.5 mol / L with a flow rate of 3,855 L / h in the washing section (44).

[0128] An aqueous solution of hydrochloric acid (24) with an H+ concentration of 5 mol / L is fed into the re-extraction section (45) with a flow rate of 216 L / h.

[0129] 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 227Ac content, below the detection limit which is 2.105 Bq / g of rare earths.

[0130] 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.

[0131] The purification rate of 227Ac with respect to rare earths, which is equal to the ratio of the content of 227Ac per gram of rare earths in the initial aqueous solution (22) to the content of 227Ac per gram of rare earths in the aqueous extract (28) is, under these conditions, greater than 34,000.

[0132] The lanthanum removal rate, which is equal to the ratio between the mass flow rate of lanthanum in the raffinate (26) and the mass flow rate of lanthanum in the initial aqueous solution (22) is, under these conditions, equal to 99.8%.

[0133] The yttrium removal rate, which is equal to the ratio of the yttrium mass flow rate in the raffinate (26) to the yttrium mass flow rate in the initial aqueous solution (22), is, under these conditions, equal to 70.5%. The quantities of rare earths and the flow rates are reported in Table 3.

[0134] [Table 3] Alim. dmg. Rée®. SWsat SI Rsû'. Lawge Ext 32 33 24 35 26 2" 2S Nsftss-e Atgoew ÀqtSSBK Aqss«ux OtgWus ÀqaeB® A Déiil (bed) 120 §88 2 300 210 4§ 000 Ï27 206 3 855 2h DMTRM 150 143 a La (gA) 0J2 0.385 8.332 MJ $7.3 03? <gj1 13,822 wd 0,00 <0,01 1.020 <0x4 13,108 w) 8j0 <0.01 2,537 pyw 0,02 12,088 0,01 3,041 mw <801 83ü 8,80 <gj1 b îx'4 l»^l) 8j0 <0 01 1,071 yw 0,10 0,1.38 31,333 tr (%) su 3s,4 14,3 total tr. fg l) ass o,« j??,)? 3w q0§ débit ¥{^) 23,37 m,4ô os as 1,33 <3,w$ œ wa) s hcl (mw 3 01)001 4,38 8.803 31 62 dtoa-l-rf ]               •■y

[0135] The abbreviations correspond to the following steps: Feed: supplying the initial aqueous solution of rare earths (22) to the extraction section (43) Loading: loading of the sodium hydroxide solution (23) into the loading section (42) Re-extraction: re-extraction of rare earths by adding an aqueous hydrochloric acid solution (24) into the re-extraction section (45) Raff.: aqueous raffinate (26) from the extraction section (43) Ext.: aqueous extract (28) from the re-extraction section (45) TR: rare earths Nature: nature of the flow gTR .gram of rare earths kgTR: kilogram of rare earth elements

[0136] The aqueous extract (28) has a 227Ac activity of less than 2 x 10⁵ Bq / g of rare earths, i.e., 3 x 10⁶ Bq / g of solution. This solution is precipitated as hydroxides by the addition of sodium hydroxide.

[0137] After filtration, a wet rare earth hydroxide is obtained containing 40% water and 44.3% rare earths. This solid has a 227Ac activity of less than 2 x 10⁵ Bq / g of rare earths, or 8 x 10⁶ Bq / g of solid.

[0138] This solid is then calcined at 900°C.

[0139] An oxide containing 84.92% rare earths is then obtained, having an activity in 227 Ac of less than 2.105 Bq / g of rare earths, i.e. 1.7105 Bq / g of solid.

[0140] It follows from these different examples that: - when the base ore consists of xenotime, 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 0.5% 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; - 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.

[0141] The invention therefore proves to be particularly effective in the more general context of rare earth extraction.

Claims

Demands

1. A process for removing actinium from an initial aqueous solution of rare earth sulfates or chlorides obtained from ore processing, 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, - separating the rare earth elements and actinium by liquid-liquid extraction, all rare earth elements except all or part of lanthanum and / or yttrium being extracted into the organic solvent, - contacting the organic solvent, comprising all rare earth elements except all or part of 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 rare 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): [Chem. 1] ^R2 h°y\3 0 (1) wherein: R1, R2 and R3 are independently selected from the group comprising the hydrogen atom, a linear or branched Cl to C14 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 R1, R2 and R3 being between 6 and 18.

2. A process for removing actinium from an initial aqueous solution of rare earth sulfates or chlorides obtained from the ore processing of claim 1, wherein the agent cationic extraction is a carboxylic acid of formula (I) chosen from the group including neodecanoic acids of general formula CmH2mO2 where m is an integer between 9 and 11, 2-ethylhexanoic acid, 2-bromooctanoic acid, naphthenic acids of general formula CnH2(nz)O2 where n is an integer between 8 and 20, 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 sulfates or chlorides from ore processing 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 sulfates or chlorides from ore processing 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 C6-C16 branched fatty alcohols, and sulfoxides.

5. A process for removing actinium from an initial aqueous solution of rare earth sulfates or chlorides from ore processing 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 sulfates or chlorides obtained from ore processing according to any one of claims 1 to 5, wherein the initial aqueous solution of rare earth sulfates is obtained from the processing with sulfuric acid of an ore concentrate selected from the group consisting of xenotime, monazite and mixtures thereof, or from the processing of ionic clays with sulfates 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 sulfates or chlorides obtained from ore processing 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.

8. A process for removing actinium from an initial aqueous solution of rare earth sulfates or chlorides obtained from ore processing according to any one of claims 1 to 7, wherein the molar concentration of rare earths in the initial aqueous solution is between 0.001 and 1.5 mol / L

9. A process for removing actinium from an initial aqueous solution of rare earth sulfates or chlorides from ore processing according to any one of claims 1 to 8, wherein the acid solution brought into contact with the organic solvent is selected from the group consisting of hydrochloric acid, nitric acid and sulfuric acid solutions.

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

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

12. A process for removing actinium from an initial aqueous solution of rare earth sulfates or chlorides from ore processing according to any one of claims 1 to 11, 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.

13. A process for removing actinium from an initial aqueous solution of rare earth sulfates or chlorides obtained from ore processing according to any one of claims 1 to 11, wherein the aqueous composition is crystallized or poured at high temperature, preferably between 110°C and 150°C.

14. Rare earth composition obtained by the process according to any one of claims 1 to 13, having an actinium-227 content-related activity 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 solid or aqueous solution form.

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

16. Rare earth composition according to claim 14 or 15, 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.

17. Rare earth composition according to claim 14 or 15, wherein the composition is an aqueous solution selected from the group comprising aqueous solutions of rare earth sulfates, chlorides and nitrates.

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

19. Rare earth composition according to any one of claims 14 to 18, wherein said composition is obtained from the treatment of xenotime, and wherein the mass fraction of lanthanum is less than 0.5% by weight relative to the total rare earth mass fraction and the mass fraction of yttrium is less than 30% by weight relative to the total rare earth mass fraction.

20. A rare earth composition according to any one of claims 14 to 18, wherein said composition is obtained from the processing of ionic clays, and wherein the mass fraction of lanthanum is less than 5% by weight relative to the mass fraction of rare earths rare earths total and the mass fraction of yttrium is less than 30% by weight relative to the total mass fraction of rare earths.

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