METHOD FOR REMOVING ACTINIUM CONTAINED IN A RARE EARTH SOLUTION BY AN ORGANIC SOLVENT

Abstract

A process for removing actinium from an aqueous solution of rare earth sulfates or rare earth chlorides, said aqueous solution being obtained from ore processing, said process comprising the following steps: – contacting and mixing the aqueous solution with an organic solvent immiscible with water, said organic solvent comprising at least one cationic extraction agent, and – separating the rare earths and actinium by liquid-liquid extraction, to produce a rare earth solution having an actinium concentration lower than the actinium concentration of the aqueous solution of rare earth sulfates or rare earth chlorides.

Description

Title of the invention: PROCESS FOR ELIMINATING ACTINIUM CONTAINED IN A RARE EARTH SOLUTION BY AN ORGANIC SOLVENT Field of invention

[0001] The invention falls within the general field of the treatment of aqueous solutions of rare earths. More specifically, it relates to a method for removing a radioactive compound from an aqueous solution, resulting from the treatment of rare earth ores, by liquid-liquid extraction. Prior art

[0002] The ores from which rare earths are extracted may contain radioactive compounds, which must be separated from the rare earths. For example, monazite contains all the radioactive isotopes of the thorium 232 (232Th), uranium 235 (235U) and uranium 238 (238U) families. The ores first undergo a first processing step which consists of physical concentration (magnetic separation, flotation, etc.). However, during this step, the radioactive isotopes present in the ore are not separated from the rare earths. In a second step, a chemical attack is carried out on the concentrate obtained previously. This chemical treatment makes it possible to separate the radioactive elements from the minerals carrying the rare earths.

[0003] Some isotopes decay rapidly, while others, which have a half-life of more than a few days, must be removed to avoid contamination of rare earths. For example, the following isotopes have a relatively long half-life: - Family of 232Th: 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 the 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 the isotopes of thorium, uranium, radium (Ra), lead (Pb), polonium (Po) and protactinium (Pa).

[0005] On the other hand, the case of the isotope 227Ac, ​​whose radioactive period is 22 years, is unique because its chemical properties are close to those of rare earths, and in particular those of lanthanum. During the separation of rare earths, actinium will follow lanthanum and it risks accumulating in compounds which include lanthanum. It will then have to be disposed of in the radioactive waste stream, which requires additional costs. It is therefore necessary to implement processes for separating rare earths and actinium, allowing the 227Ac isotope to be efficiently removed.

[0006] Such methods for removing actinium are described, for example, in document WO 2019 / 000014 where actinium is precipitated from solutions of rare earth chlorides or sulfates, which come from the treatment of monazite or xenotime type ores, by adding sulfate salts. The disadvantage of this method is that it requires the addition of significant quantities of salt (of the order of a hundred g / L) to cause precipitation. In addition, this method is relatively time-consuming. Furthermore, it does not allow sufficient actinium to be removed.

[0007] Other methods describe the separation by liquid-liquid extraction of rare earths and actinium. This extraction is carried out using organic solvents comprising molecules selective for rare earths, which are extracted in the organic phase while the actinium remains in the aqueous phase. Indeed, it is known to use as extracting agents, cationic agents which have a strong affinity with rare earths, such as organophosphorus acid derivatives.

[0008] For example, document CN 85100148 describes a process for producing lanthanum oxides, by separating the lanthanum and actinium present in a solution of rare earth nitrates. The liquid-liquid separation is carried out using an organic solvent comprising the mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (HEHEHP) or the ester of di(2-ethylhexyl)phosphoric acid (HDEHP or D2EHPA).

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

[0010] Another problem related to the presence of actinium in rare earth solutions concerns their transport. Indeed, an ore with a uranium content of 1000 ppm in a mixture of rare earths results in a quantity of 227Ac which generates an activity equivalent to approximately 0.5 Bq / g of rare earths. However, beyond 0.1 Bq / g, the transport of such a mixture is subject to strict regulations concerning the transport of radioactive materials, known as "class 7". This requires the use of specialized transporters, which constitutes an additional constraint. It is therefore necessary to limit the stages of transport of such solutions, in particular by directly treating the solutions derived from the ores, without resorting to intermediate stages. Statement of the invention

[0011] One of the aims of the invention is to eliminate actinium from the production of a rare earth solution resulting from the processing of ore, to avoid the costly and time-consuming production and transport of radioactive intermediate concentrates of rare earths.

[0012] Thus, the invention relates to a method for removing actinium contained in an aqueous solution of rare earth sulfates or rare earth chlorides, said aqueous solution being obtained from the treatment of ore. The method comprises the following steps: - contacting and mixing the aqueous solution with a water-immiscible organic solvent, said organic solvent comprising at least one cationic extraction agent, and - separation by liquid-liquid extraction of rare earths and actinium, to produce a rare earth solution having an actinium concentration lower than the actinium concentration of the aqueous solution of rare earth sulfates or rare earth chlorides. Organic solvent

[0013] According to the invention, the organic solvent comprises at least one cationic extraction agent which is an organophosphorus acid.

[0014] Preferably, the cationic extraction agent is an organophosphorus acid chosen from the group comprising: - phosphoric acid esters, of formula I: [Chem.l] - phosphonic acid esters, of formula II: [Chem.2] - phosphinic acid esters, of formula III: [Chem. 3] O R1 .....f\ K / OH R2 and their mixtures, where R1 and R2 are the same or different, independently chosen from the group comprising linear or branched, aliphatic or aromatic alkyl or aryl radicals of 1 to 20 carbon atoms, preferably of 4 to 20 carbon atoms, and hydrogen atoms.

[0015] These compounds are particularly effective for complexing trivalent cations, such as rare earth cations. 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.

[0016] Advantageously, the cationic extracting agent may be selected from the group consisting of di(2-ethylhexyl)phosphoric acid ester, mono-2-ethylhexyl 2-ethylhexylphosphonic acid ester, bis(2,4,4-trimethylpentyl) phosphinic acid ester (known under the trade name CYANEX®272), CYANEX®572 (mixture of phosphonic acid and phosphinic acid), and mixtures thereof.

[0017] Additionally, the organic solvent may comprise a diluent compound, selected from the group consisting of hydrocarbons of 5 to 16 carbon atoms, linear or branched, aliphatic or aromatic.

[0018] For example, the diluent compound is chosen from the group comprising: 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.

[0019] As a diluting compound, we can cite for example, Shellsol®D70 (aliphatic hydrocarbon), Solvesso®150 (aromatic hydrocarbon).

[0020] The diluting compound allows the cationic extraction agent, and optionally the modifying compound, to be dissolved. It is in the liquid state and does not modify the chemical properties of the compounds it solubilizes. It is different from the cationic extraction agent.

[0021] In addition to the cationic extraction agent and the diluting compound, the solvent may comprise at least one modifying compound, chosen from the group consisting of phosphoric acid esters and linear or branched fatty alcohols, the total number of carbon atoms of which is between 6 and 12.

[0022] Preferably it is chosen from the group comprising: tributyl phosphate, decan-1-ol, octan-1-ol, isodecan-1-ol, hexan-1-ol, dodecan-1-ol, 2-ethylhexanol and mixtures thereof.

[0023] For the purposes of the invention, the term "modifying compound" means a chemical species other than the cationic extraction agent and the diluting compound, capable of modifying certain properties of the organic solvent. For example, the modifying compound can delay the appearance of a third phase or aid decantation.

[0024] According to a particular embodiment, the organic solvent comprises at least one cationic extraction agent and at least one diluting compound.

[0025] Alternatively, the organic solvent may comprise at least one cationic extractant, at least one diluent compound and at least one modifying compound.

[0026] Preferably, the organic solvent has a concentration of cationic extracting agent of between 0.1 and 2 mol / L, preferably between 0.5 and 1.5 mol / L. Such a concentration allows the solvent to retain a viscosity of less than 20 cP at room temperature.

[0027] In a particular embodiment of the invention, the organic solvent comprises: - from 15% to 55% of at least one cationic extraction agent, - from 45% to 85% of at least one diluting compound, by weight relative to the total weight of the organic solvent, the total being equal to 100%.

[0028] In another embodiment of the invention, the organic solvent comprises: - from 15% to 55% of at least one cationic extraction agent, - from 45% to 85% of at least one diluting compound, - from 0% to 10% of at least one modifying compound, by weight relative to the total weight of the organic solvent, the total being equal to 100%. Aqueous solution of rare earths

[0029] The aqueous solution of rare earths, according to the invention, may be an aqueous solution of rare earth sulfates or an aqueous solution of rare earth chlorides.

[0030] The concentration of rare earths in the aqueous solution of rare earth sulfates or in the aqueous solution of rare earth chlorides may be between 100 mg / L and 450 g / , or between 0.001 and 0.20 mol / L. The concentration of rare earths in an aqueous solution of sulfates is preferably between 100 mg / L and 40 g / L. The concentration of rare earths in an aqueous solution of chlorides is preferably between 100 mg / L and 250 g / L.

[0031] Preferably, the aqueous solution of rare earth sulfates or the aqueous solution of rare earth chlorides is obtained from the chemical treatment of an ore concentrate of the xenotime, monazite, ionic clays and / or bastnaesite type. In practice, this concentrate is obtained by physical concentration of the ores. As methods of physical concentration, examples include magnetic separation and flotation, without the present invention being limited to these methods.

[0032] In the case of an aqueous solution of rare earth sulfates, this is obtained by treating a concentrate of xenotime, monazite and / or bastnaesite with sulfuric acid.

[0033] Alternatively, the aqueous solution of rare earth sulfates may be obtained from the treatment of ionic clays with ammonium sulfate, alkali sulfates or magnesium sulfate.

[0034] When it is an aqueous solution of rare earth chlorides, this preferably results from the treatment of ionic clays with chlorides of alkali or alkaline earth metals.

[0035] Depending on the nature of the ore from which the solution is derived, the activity of the aqueous solution linked to the 227Ac content is between 0.5 and 25 Bq / g of rare earths. Liquid-liquid extraction

[0036] In practice, the contacting and mixing of the aqueous solution of rare earth sulfates or rare earth chlorides with the organic solvent can be carried out in a device comprising several stages, for example a battery of mixer-decanters or an extraction column. In this device, the aqueous solution and the organic solvent advantageously circulate in countercurrent.

[0037] Advantageously, the process is carried out at a temperature between 20°C and 60°C, preferably between 30°C and 50°C.

[0038] Preferably, the device comprises an extraction section and a re-extraction section. It may further comprise a washing section. Each section may consist of 1 to 10 stages.

[0039] According to one embodiment, the solvent can be saponified by a basic solution (ammonia, sodium hydroxide, etc.) with an OH ion concentration of between 3 and 10 mol / L.

[0040] According to one embodiment, the organic solvent can be washed in the washing section using an acid solution (hydrochloric, sulfuric, nitric, etc.) with an H+ ion concentration of between 0.2 and 7 mol / L.

[0041] In practice, an aqueous extract is obtained at the end of the liquid-liquid extraction, comprising mainly the rare earths Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. This extract advantageously has an activity, linked to the 227Ac content, of less than 0.1 Bq / g of rare earths.

[0042] In general, an aqueous raffinate is also obtained whose rare earth content is more than 90% and advantageously more than 99% lanthanum. This raffinate comprises more than 99.9% of the 227Ac included in the aqueous rare earth solution. Detailed description of the figures

[0043] [Fig.l] is a schematic representation of the process according to Examples 1 and 2 of the invention, in a liquid-liquid extraction battery consisting of four sections.

[0044] [Fig.2] is a schematic representation of the method according to Example 2 of the invention, in a liquid-liquid extraction battery consisting of four sections.

[0045] [Fig. 3] is a schematic representation of the method according to Example 3 of the invention, in a liquid-liquid extraction battery consisting of four sections.

[0046] [Fig. 4] is a schematic representation of the method according to Example 4 of the invention, in a liquid-liquid extraction battery consisting of three sections. Examples of embodiments of the invention

[0047] The examples below were simulated using software, called “PAREX+”, developed by the Applicant, the basic data necessary for the calculations of which were previously obtained by laboratory tests according to the different chemical systems presented.

[0048] Two types of aqueous solutions resulting from the chemical attack of rare earth ores are considered: - an aqueous solution of rare earths resulting from the treatment of a raw material of the ionic clay type; - an aqueous solution of rare earths resulting from the processing of a xenotime-type raw material.

[0049] The examples below were calculated for a battery-type installation of mixer-decanters operating counter-currently, continuously and having the following performances: - the extraction yield of all rare earths with atomic numbers higher than cerium (Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) as well as that of yttrium is higher than 99.9%, - the purification rate of 227Ac compared to the extracted rare earths (ratio between 227 Ac found in the raffinate and 227Ac present in the initial aqueous solution of rare earths) is greater than 99.9%.

[0050] Example 1: Removal of 227Ac from a solution of rare earth chlorides obtained by leaching ionic clays with a NaCl solution The method according to the invention is carried out using the following device: a liquid-liquid extraction battery of the mixer-decanter type operating continuously in counter-current, consisting of a one-stage loading section (30), a two-stage extraction section (31), a one-stage washing section (32) and a seven-stage re-extraction section (33), these four sections being connected to each other.

[0051] The extraction section (31) is supplied with an aqueous solution (1) 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 181,200 L / h, the composition of which is detailed in Table 1.

[0052] A solvent SI (4), composed of 67% by volume of aliphatic kerosene and 33% by volume of HEHEHP (where HEHEHP is the cationic extraction agent), is injected at a flow rate of 9,000 L / h into the loading section (30). The solvent SI is saponified by a sodium hydroxide solution (2) with an OH concentration of 8 mol / L, at a flow rate of 396 L / h.

[0053] An aqueous raffinate (5) is obtained with a flow rate of 182,052 L / h. This aqueous raffinate (5) comprises mainly La, as well as almost all of the 227Ac contained in the aqueous solution (1). The measured activity is 28 Bq / g of rare earths.

[0054] The solvent SI is washed with a hydrochloric acid solution (6) at an H+ concentration of 4.5 mol / L, with a flow rate of 400 L / h. This step takes place at the washing section (32).

[0055] An aqueous solution of hydrochloric acid (3) with an H+ concentration of 5.5 mol / L is fed into the re-extraction section (33) with a flow rate of 584 L / h, to enable the re-extraction of the rare earths in the aqueous phase. This allows the solvent to be regenerated, to extract all traces of rare earths.

[0056] An aqueous extract (7) comprising mainly 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 584 L / h. This extract has a rare earth concentration of 140 g / L and an activity, linked to the 227Ac content, of 1.25.10 3 Bq / g of rare earths.

[0057] The purification rate of 227Ac relative to the extracted rare earths, which is equal to the ratio between the 227Ac content per gram of rare earths in the aqueous feed (1) and the 227Ac content per gram of rare earths in the extracted aqueous solution (7) is, under these conditions, equal to 5070.

[0058] The summary diagram of the process of example 1 according to the invention is shown in [Fig.l].

[0059] The quantities of rare earths and the flow rates are reported in Table 1.

[0060] [Tab.l] Stage Alita. Chsrg. Reex. SI Raff. Lav. Ext Flux ? s 4 S 6 7 Nature Aqueous Aqueous Aqueous Organic Aqueous Aqueous Aqueous Flow îL;5i} 181 200 396 584 9 CW 182 052 409 584 Flow TR. 106 24 82 0.21 OR 334 t Ce ^.1) 0.03 0.000 s 8.6 0.03 <o,ooo? 10,8 nd(g'l) 0,10 32..4 sm(g-l) 0,02 <9,0001 5,1 eu (g-l) <0,001 <o,qû<;1 0,4 gd 9,92 4,9 tb(g;l) <0,01 clp dy (gi) «9001 4,7 1,13 0,01 <9,0061 3,1 tùn yb (g-l} 2.2• lij (g l) 0,13 39.9 ^"ac oÿgst) 6,3 28 1,25.kh oh’ 08011) 8 h+ (næl'l) 0,001 5.5 0,018 4,5 2,1 hehehp j 33 kérosène ■67

[0061] The abbreviations correspond to the following steps: Feed: feeding of the aqueous solution of rare earths (1) into the extraction section (31) Loading: loading the soda solution (2) into the loading section (30) Re-ex.: re-extraction of rare earths by adding an aqueous solution of hydrochloric acid (3) in the re-extraction section (33) Raff.: aqueous raffinate (5) from the loading section (30) Wash: washing for solvent regeneration using hydrochloric acid solution (6) in the washing section (32) Ext.: aqueous extract (7) from the re-extraction section (33) TR: rare earths Nature: nature of the flow gTR:gram of rare earths kgTR: kilogram of rare earths

[0062] Example 2: Removal of 227Ac from a solution of rare earth sulfates obtained by leaching ionic clays with a solution of (NH4)2SO4 The method according to the invention is carried out using the following device: a liquid-liquid extraction battery of the mixer-settler type operating in countercurrent, consisting of a one-stage loading section (34), a two-stage extraction section (35), a two-stage washing section (36) and a seven-stage re-extraction section (37), these four sections being interconnected.

[0063] The extraction section (35) is fed with an 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 2.

[0064] The SI solvent (11), composed of 67% by volume of aliphatic kerosene and 33% by volume of HEHEHP (where HEHEHP is the cationic extraction agent), is injected at a flow rate of 10,000 L / h into the loading section (34). The SI solvent is saponified by an ammonia solution (9) with an OH concentration of 4 mol / L, at a flow rate of 1,000 L / h.

[0065] An aqueous raffinate (12) comprising mainly La and almost all of the 227Ac is obtained with a flow rate of 126,323 L / h. The measured activity is 27 Bq / g of rare earths.

[0066] The solvent SI is washed with a sulfuric acid solution (13) at an H+ concentration of 0.7 mol / L, with a flow rate of 4,248 L / h in the washing section (36).

[0067] An aqueous solution of nitric acid (10) with an H+ concentration of 3.5 mol / L is fed into the re-extraction section (37) with a flow rate of 2,523 L / h, thus allowing the regeneration of the solvent.

[0068] An aqueous extract (14) comprising mainly 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 2,636 L / h. This extract has a rare earth concentration of 31 g / L and an activity, linked to the 227Ac content, of 1.3.10 3 Bq / g of rare earths.

[0069] The purification rate of 227Ac relative to the rare earths, which is equal to the ratio between the 227Ac content per gram of rare earths in the aqueous feed (8) and the 227Ac content per gram of rare earths in the extracted aqueous solution (14) is under these conditions equal to 4,920.

[0070] The summary diagram of the process of example 2 according to the invention is shown in [Fig.2],

[0071] The quantities of rare earths and the flow rates are reported in Table 2.

[0072] [Tab.2] Power stage Load. Reex. SI Raff Lav. Ext. : Flux g 9 10 H 12 13 14 Nature Aqueous Aqueous Aqueous Organic Aqueous Aqueous Aqueous Flow 120 800 1 000 2 523 10 000 126 323 424S 2 636 Flow TR (kg^'h) 106 25 81 La (g / L) 032 0.20 5.2 Ce (g;L) 0.04 0.0002 1.9 Pt ( g / L) 0.05 <0.0001 24 NdfeL} 0.16 <0.0001 7 7 Sm (g-'L) 0.02 <0.0001 1.12 Eu (g;L) «0.10 <0 0001 038 i Gd (g / L) 0.02 <0.0001 1.1 Tb (gL) <0.01 <0.0001 0.21 Dy (g / L) 0.02 <03001 1.05 Ho 0.01 <0.0001 0.25 Et (g / L) 0.01 <03001 0.68 Tm (gL) <0.091 <0.0001 0.08 Yb (s;L) 0.01 <0.0001 0.55 Lu (gtl) <0.001 <0.0001 0.0 SY(g / L) 0.19 <0.0001 8.8 21"Ac (Bq / gjoJ 6.3' 5 y7 L29W'3 OH' {îtsciI'L) 4 H+(moFL) 0.001 3.5 0.0Û59S 0.66 232 HEHEHP (%vol) 33 Ketoses ( 67

[0073] The abbreviations correspond to the following steps: Feed: feeding of the aqueous solution of rare earths (8) into the extraction section (35) Loading: loading the ammonia solution (9) into the loading section (34) Re-ex.: re-extraction of rare earths by adding an aqueous solution of nitric acid (10) in the re-extraction section (37) Raff.: aqueous raffinate (12) from the loading section (34) Wash: washing, regeneration of the solvent 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 earths

[0074] Example 3: Removal of 227Ac from a solution of rare earth sulfates obtained by treatment of a xenotime concentrate with a sulfuric acid solution. The method according to the invention is carried out using the following device: a liquid-liquid extraction battery of the mixer-decanter type operating counter-currently, continuously, consisting of a one-stage loading section (38), a two-stage extraction section (39), a one-stage washing section (40) and a seven-stage re-extraction section (41), these four sections being connected to each other.

[0075] The extraction section (39) is fed with an 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, ​​with a flow rate of 7,927 L / h, the composition of which is detailed in Table 3.

[0076] The SI solvent (18), composed of 67% by volume of aliphatic kerosene and 33% by volume of HEHEHP (cationic extraction agent) is injected at a flow rate of 6,650 L / h into the loading section (38). The SI solvent is saponified by an ammonia solution (16) with an OH concentration of 4 mol / L at a flow rate of 665 L / h.

[0077] An aqueous raffinate (19) comprising mainly La and almost all of the 227Ac is obtained with a flow rate of 8,966 L / h. The measured activity is 167 Bq / g of rare earths

[0078] The solvent SI is washed with a sulfuric acid solution (20) at an H+ concentration of 0.4 mol / L with a flow rate of 84 L / h in the washing section (40).

[0079] An aqueous solution of nitric acid (17) with an H+ concentration of 3.5 mol / L is fed into the re-extraction section (41) with a flow rate of 2,671 L / h.

[0080] An aqueous extract (21) comprising mainly 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 2,798 L / h. It has a rare earth concentration of 37 g / L and an activity, linked to the 227Ac content, of 2.27.10 4 Bq / g of rare earths.

[0081] The purification rate of 227Ac, ​​which is equal to the ratio between the 227Ac content per gram of rare earths in the aqueous feed (15) and the 227Ac content per gram of rare earths in the extracted aqueous solution (21) is equal to 5,220.

[0082] The summary diagram of the process of example 3 according to the invention is shown in [Fig.3].

[0083] The quantities of rare earths and the flow rates are reported in Table 3.

[0084] [Tab.3] Aliîa. Cats. Reex. Solvent SI SafE Washing hxt Flow 15 16 17 18 19 20 XX Nature Aqueous Aqueous Aqueous Orgaœçue Aqueous Aqueous Aqueous Flow (Lh) 7 927 665 2 671 6 650 8 966 84 2 798 Flow TR CxgiR.'h) 104 1 103 la(gÆ.) 029 080 0.57 Ce (gL) 0.69 0.003 1.95 Pt (gL) 0.10 <0.0001 0.28 NdigZL; 0.46 <0.0001 1.31 Sm (ÿL) 0.30 0.85 EufeLJ 0^7 <0.0001 0.18 Gd (gl) 0.82 <03001 231 Tb(gÆ) 028 <0.0001 0.50 Dy (g / L) 1.20 <03001 3.41 Hofg-L) 0.26 <0.0001 0.73 Er (&1) 0.75 <0.0001 2.11 Tm (g / L) 0.10 <0.0001 ■0.29 Yb(gL) 0.61 <03001 1.73 Lu (gll) 0.08 <0.0001 0.24 Y(gL) 7.20 <0.0001 20.39 ^Ac (Bçets:) 1.18 167 2.27.10^ OH- (moliL) 4 H' (moLL) 0.001 3.5 0.02 0.4 2.34 HEHEHP (Kvol) 33 Kerosesis (%vc<5) 67

[0085] The abbreviations correspond to the following steps: Feed: feeding of the aqueous solution of rare earths (15) into the extraction section (39) Loading: loading the ammonia solution (16) into the loading section (38) Re-ex.: re-extraction of rare earths by adding an aqueous solution of nitric acid (16) in the re-extraction section (41) Raff.: aqueous raffinate (19) from the loading section (38) Ext.: aqueous extract (21) from the re-extraction section (41) TR: rare earths Nature: nature of the flow gTR:gram of rare earths kgTR: kilogram of rare earths

[0086] Example 4: Removal of 227Ac from a solution of rare earth sulfates obtained by treatment of a xenotime concentrate with a sulfuric acid solution. The method according to the invention is carried out using the following device: a liquid-liquid extraction battery of the mixer-decanter type operating countercurrently, continuously, consisting of a four-stage extraction section (42), a four-stage washing section (43) and a seven-stage re-extraction section (44), these three sections being connected to each other.

[0087] The extraction section (42) is fed with an aqueous solution (22) 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 7,927 L / h, the composition of which is detailed in Table 4.

[0088] A solvent S2 (24), composed of 70% by volume of aliphatic kerosene and 30% by volume of HDEHP, (where HDEHP is the cationic extraction agent), is injected at a flow rate of 56,000 L / h.

[0089] An aqueous raffinate (25) comprising mainly La as well as almost all of the 227Ac, ​​is obtained with a flow rate of 8,298 L / h. The measured activity is 105 Bq / g of rare earths.

[0090] The solvent S2 is washed with a sulfuric acid solution (26) at an H+ concentration of 3.1 mol / L with a flow rate of 162 L / h in the washing section (43).

[0091] An aqueous solution of nitric acid (23) with an H+ concentration of 5 mol / L is fed into the re-extraction section (44) with a flow rate of 36,000 L / h.

[0092] An aqueous extract (27) comprising mainly 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 38,775 L / h. This extract has a rare earth concentration of 2.7 g / L and an activity, linked to the 227Ac content, of 7.8.10 3 Bq / g of rare earths.

[0093] The 227Ac purification rate, which is equal to the ratio between the 227Ac content per gram of rare earths in the aqueous feed (22) and the 227Ac content per gram of rare earths in the extracted aqueous solution (27) is equal to 150.

[0094] The summary diagram of the process of example 4 according to the invention is shown in [Fig.4],

[0095] The quantities of rare earths and the flow rates are reported in Table 4.

[0096] [Tab.4] Stage ; Alku. Reex. S2 Raff. Lav. Ext. Flux ! ?? 24 25 2ô 77 Nature Aqueous Aqueous Organic Aqueous Aqueous Aqueous Flow (LA) 7 927 36 000 56 000 Ë29S 162 38 775 Flow TR: 164 1 103 La (g-'L) 0.29 0.130 0.03 Ce (gî.) ; 0.69 0.009 0.14 Pr (g / LJ 0.10 <0.0001 0.02 Nd (g / L) 0.46 <0.0001 0.09 Sirs (gL) 0.30 <0.0001 .................... 0.06 Eu (gi) i 0.07 <0.0001 0.01 Gd (g / L) 0.S2 <0.0001 0.17 Tb (gL) 0.18 <0.0001 0.04 Dy (gL) 1.20 <0.0001 0.25 Ho (g-'L) 0.26 <0.0001 0.05 Er (gjL) 0.75 <0.0001 0.15 Tœ; fg / L) 0.10 <0.0001 0.02 Yb (gL) 0.61 <0.0001 0.12 Lu (gL) i 0.08 <0.0001 0.02 Y(gL) 7.20 <0.0001 1.47 " ■ Ac (BqsgT®) LIS 105 7.83.10-3 H* (moFL); 0.001 s 0.40 3.1 4.6 HDEHP (Wol) Kerosene P'otoI) 7 G;

[0097] The abbreviations correspond to the following steps: Feed: feed of the aqueous solution of rare earths (22) into the extraction section (42) Re-ex.: re-extraction of rare earths by adding an aqueous solution of nitric acid (23) in the re-extraction section (44) Raff.: aqueous raffinate (25) from the extraction section (42) Wash: washing, regeneration of the solvent (24) using a sulfuric acid solution (26) in the washing section (43) Ext.: aqueous extract (27) from the re-extraction section (44) TR: rare earths Nature: nature of the flow gTR:gram of rare earths

[0098] In addition to the disadvantages of the state of the art listed above, it appears that certain methods of the prior art, such as that described in the publication “Cleaning rare earth elements from actinium”, Journal of Alloys and Compounds, vol. 225 (1995), pages 320-323, can only be implemented if the initial aqueous solution of rare earths is a solution of rare earth nitrates. This is also the case for the process described in document CN 85100148, which is carried out to purify solutions of lanthanum nitrates only.

[0099] Furthermore, example 3 of document WO 2019 / 000014, which describes a process for purifying actinium by precipitation, applicable to solutions of rare earth sulfates or chlorides, has a precipitation rate of 227Ac for high 227Ac contents (70 Bq / L) of approximately 47%, for a precipitation rate of rare earths of 2%. The purification rate of 227Ac is therefore:

[0100] [Formula 1] (l-2%) / (147%)= 1.85

Claims

1.

2. Claims Process for removing actinium from an aqueous solution of rare earth sulfates or rare earth chlorides, said aqueous solution being obtained from ore processing, said process comprising the following steps: - contacting and mixing the aqueous solution with a water-immiscible organic solvent, said organic solvent comprising at least one cationic extraction agent, and - separation by liquid-liquid extraction of rare earths and actinium, to produce a rare earth solution having an actinium concentration lower than the actinium concentration of the aqueous solution of rare earth sulfates or earth chlorides rare. The actinium removal method of claim 1, wherein the cationic extractant is an organophosphorus acid selected from the group comprising: - phosphoric acid esters, of formula I: [Chem.l] - phosphonic acid esters, of formula II: [Chem. 2] - phosphinic acid esters, of formula III: [Chem. 3] and mixtures thereof, where R1 and R2 are identical or different, independently chosen from the group comprising linear or branched, aliphatic or aromatic alkyl or aryl radicals of 1 to 20 carbon atoms, and hydrogen atoms.

3. The actinium removal method of claim 1 or 2, wherein the cationic extractant is selected from the group consisting of di(2-ethylhexyl)phosphoric acid ester, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, phosphinic acid bis(2,4,4-trimethylpentyl) ester, and mixtures thereof.

4. Method for removing actinium according to one of claims 1 to 3, in which the organic solvent further comprises a diluent compound, chosen from the group consisting of hydrocarbons of 5 to 16 carbon atoms, linear or branched, aliphatic or aromatic.

5. A method for removing actinium according to one of claims 1 to 4, wherein the organic solvent has a concentration of cationic extractant of between 0.1 and 2 mol / L.

6. A method for removing actinium according to one of claims 1 to 5, wherein the aqueous solution of rare earth sulfates is obtained from the treatment of a concentrate of xenotime, monazite and / or bastnaesite with sulfuric acid.

7. A method of removing actinium according to one of claims 1 to 5, wherein the aqueous solution of rare earth sulfates is obtained from the treatment of ionic clays with ammonium sulfate, alkali sulfates or magnesium sulfate.

8. A method for removing actinium according to one of claims 1 to 5, in which the aqueous solution of rare earth chlorides is obtained from the treatment of ionic clays with chlorides of alkali or alkaline earth metals.

9. A method for removing actinium according to one of claims 1 to 8, wherein the concentration of rare earths in the aqueous solution of rare earth sulfates or rare earth chlorides is between 0.001 and 0.20 mol / L.

10. Method for removing actinium according to one of claims 1 to 9, in which the contacting of the aqueous solution of rare earth sulfates or rare earth chlorides with the organic solvent is carried out in a device comprising several stages, where said aqueous solution and the organic solvent circulate in countercurrent.

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