Method for purifying radium from barium and impurities in aqueous solution

Abstract

The present invention relates to a method for separating radium from barium by selective chromatographic separation.

Description

[0001] DESCRIPTION

[0002] TITLE: PROCESS FOR PURIFYING RADIUM WITH RESPECT TO BARIUM AND IMPURITIES IN AQUEOUS SOLUTION

[0003] TECHNICAL FIELD

[0004] The invention relates to the field of separation and purification of metallic elements in solution. More specifically, the invention relates to a process for purifying radium from a solution in which it is present together with barium and optionally metallic or non-metallic impurities.

[0005] The invention finds particular application for the recovery of the radium-226 isotope which makes it possible to produce actinium-225, useful in nuclear medicine for the treatment of cancers by targeted alpha-therapy.

[0006] PREVIOUS STATE OF THE ART

[0007] Radium can occur naturally in various ores. It can also be present in processing residues resulting from the contact of an acidic leaching solution with an ore containing uranium.

[0008] In all cases, radium is usually present in conjunction with other elements such as barium and impurities.

[0009] Separations of radioisotopes, for example using ethylenediaminetetraacetic acid (EDTA), have been described. They generally demonstrate low selectivity in the separation of radium compared to other elements and / or are difficult to implement.

[0010] Thus, US2,554,649 describes a method for separating radium from a sample also containing barium, by chromatographic separation using a single eluent. However, the described chromatographic separation is performed using a sample with a very high radium concentration, present in a mass equal to that of the barium; moreover, the eluent used is concentrated and therefore does not guarantee good selectivity for radium separation, particularly when the initial sample contains low amounts of radium compared to the other elements, such as barium. The prior art therefore does not allow for high radium concentration from the very low initial concentrations in the sample.

[0011] It is therefore necessary to make available a process for purifying radium from samples in which radium is present in small quantities alongside other elements, including metallic impurities.

[0012] It is therefore particularly interesting to isolate the radium present in these residues in order to make use of it.

[0013] The Inventors therefore set themselves the goal of making available a process for isolating radium from other elements, particularly from barium and other impurities that may be present.

[0014] More specifically, they set themselves the goal of purifying radium from a sample in which it is weakly concentrated, for example an ore extraction residue, such as an extraction residue, which results from contacting an acidic leaching solution on an ore containing uranium.

[0015] DESCRIPTION OF THE INVENTION

[0016] These goals are achieved by the invention which proposes a chromatographic separation process of radium from barium, allowing a first selective elution of barium, then the elution of radium.

[0017] To this end, the invention relates to a process for separating radium from a sample S comprising radium and barium, said process comprising a chromatographic separation step SC comprising: loading the sample S onto a column C comprising a cation exchange stationary phase PS capable of retaining radium and barium; circulating an eluent E1 in said phase PS, E1 selectively eluting barium with respect to radium, leading to an eluate ELB3 enriched in barium; then circulating an eluent E2 in said phase PS, E2 eluting radium; and leading to an eluate ELR3 enriched in radium;

[0018] E1 and E2 each comprise a complexing agent, identical or different; characterized in that the concentration of said agent in eluent E1 ([E1]) is lower than the concentration of said agent in eluent E2 ([E2]). It was thus discovered that it was possible to selectively elute barium from radium under certain eluent concentration conditions.

[0019] The separation process according to the invention makes it possible to recover radium while maximizing its concentration and / or radiological and / or chemical purity.

[0020] In the context of the subsequent production of actinium-225, the process of the invention therefore makes it possible to limit the generation of irradiation products, which would be difficult to separate subsequently and which would therefore risk impacting the radiological purity of the actinium-225 produced.

[0021] According to other advantageous aspects of the invention, the method comprises one or more of the following features, taken individually or in all technically possible combinations:

[0022] In the above and below, radium may be in the form of one of its isotopes, particularly radioactive radium-226.

[0023] The term "radium" used here therefore also refers to radium-226.

[0024] The process according to the invention allows the separation of radium from a sample S comprising in particular radium and barium.

[0025] The said sample S may in particular be a solution, such as an aqueous solution.

[0026] Typically, this solution may be weakly concentrated in radium, with a radium concentration of less than 10⁻¹⁰ 2 g / L, in particular less than 10' 4g / L, and jointly a barium concentration greater than 10' 3 , in particular greater than 10' 2 g / L of solution.

[0027] The said sample S may include, in addition to radium and barium, one or more metallic or non-metallic impurities.

[0028] Metallic impurities may include selected impurities from the base metals, alkaline earth metals, actinides, metalloids, such as lead, uranium, arsenic.

[0029] Said stationary phase PS can be any cation exchange stationary phase material that is capable of retaining radium and barium.

[0030] Such a material may include a solid inorganic support (such as silica or alumina particles or a silica gel), an organic support (such as a polymer) or an inorganic-organic support, which is functionalized, by grafting or impregnation, by organic molecules capable of retaining, by ion exchange, molecular recognition or any other mechanism, the radium (Ra) and barium (Ba) ions present in the sample S.

[0031] This may include a material comprising silica particles grafted with molecules of an organic radium ligand, for example, an oxacryptand. A material particularly well-suited to the implementation of the invention is, for example, that offered by IBC Advanced Technologies, Inc. under the reference AnaLig® Ra-01. This stationary phase retains radium, regardless of its isotope.

[0032] According to one embodiment, the stationary phase PS also retains barium.

[0033] It has been observed that although the PS phase fixes radium and barium, it is possible to elute, under specific conditions, selectively barium and then radium in order to obtain a radium-rich eluate purified in barium.

[0034] Sample S is loaded at the top of the column; typically, a sample volume is loaded and fixed by circulation within the column's stationary phase. The sample volume generally depends on the column bed volume (or BV). The column bed volume is not limited and can be adjusted, in particular, according to the nature and volume of the samples to be separated. Typically, it can be between 10' 1 ml and 10 6 mL.

[0035] Typically, between 1 and 10,000 BVs from the sample are engaged, typically between 10 and 1,000 BVs, especially between 10 and 500 BVs, particularly between 10 and 300 BVs.

[0036] The sample circulation speed can be adjusted according to the operating conditions and can, for example, be between 1 and 100 BV / h, in particular between 1 and 30 BV / h.

[0037] After fixing, one or more washing steps can be carried out with one or more acidic solutions, typically aqueous solutions of nitric acid, in order to wash the impregnating agent or in other words the interstitial liquid of the resin.

[0038] The nitric acid content of the washing solution(s) is preferably within the range of acidities recommended by the supplier of the stationary phase material, for example from 0.01 mol / L to 4 mol / L of nitric acid for AnaLig® Ra-01 particles.

[0039] The term "eluent" used here refers to the mobile phase capable of transporting the element in question through the stationary phase. Eluents E1 and E2 are in the form of aqueous solutions comprising, as solute, a complexing or chelating agent for the element to be eluted (the two terms being considered synonymous here, and will be referred to as "complexing agent").

[0040] The complexing agent of the eluent E1 is chosen from among the agents capable of releasing the barium retained by the stationary phase PS, in particular by complexation or chelation (the two terms being considered here as synonyms).

[0041] The complexing agent of the eluent E2 is chosen from among the agents capable of releasing the radium retained by the stationary phase PS, in particular by complexation or chelation.

[0042] The complexing agents, i.e. the solutes, of the eluents E1 and E2 can be identical or different.

[0043] Depending on one embodiment, these complexing agents are different.

[0044] According to one embodiment, these complexing agents are identical, the eluents E1 and E2 differing by the respective concentration of said agent.

[0045] The pH of eluents E1 and E2, typically between 4 and 10, can optionally be adjusted using a buffering agent.

[0046] Advantageously, the pH of eluent E2 is slightly basic, specifically between 7 and 9.

[0047] According to the invention, the complexing agents of E1 and E2 are preferably chosen from an aminopolycarboxylic acid or a salt of an aminopolycarboxylic acid such as ethylenediaminetetraacetic acid (or EDTA), diethylenetriaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), tartaric acid or aqueous solutions of citric acid and its ammonium, alkali or alkaline-earth salts; of oxalic acid and its ammonium, alkali or alkaline-earth salts; and mixtures thereof.

[0048] Thus, it may include ammonium citrate, EDTA, citric acid, oxalic acid, sodium citrate, magnesium citrate, potassium citrate, calcium citrate, ammonium oxalate, sodium oxalate, magnesium oxalate, potassium oxalate, calcium oxalate, and their combinations, preferably ammonium citrate.

[0049] According to one embodiment, the concentration of E1 in complexing agent (here denoted [E1]) is less than the concentration of E2 in complexing agent (here denoted [E2]) to allow the selective elution of barium by E1, then that of radium by E2. Thus, according to one embodiment, the eluent E1 and the eluent E2 are such that [E1] < [E2] / 2, in particular [E1] < [E2] / 5, preferably [E1] = [E2] / 10.

[0050] For illustrative purposes, the concentration [E1] for elutating barium can be less than 1 M, in particular less than 0.5 M, preferably between 0.01 M and 0.5 M.

[0051] According to one embodiment, the concentration [E2] for eluting radium may be greater than 0.1 M, in particular greater than 1 M, preferably between 0.5 M and 3 M.

[0052] Circulation refers to the passage of the eluent through the stationary phase of the column. Generally, the volume of eluent involved depends on the volume of the column bed.

[0053] Typically, between 1 and 100 BV of each eluent are committed, especially between 10 and 50 BV.

[0054] Advantageously, the committed volume of E1 and the committed volume of E2 are identical.

[0055] The flow rate of each eluent can be adjusted according to the operating conditions and can, for example, be between 1 and 100 BV / h, in particular between 1 and 30 BV / h.

[0056] Advantageously, the traffic speed of E1 and the traffic speed of E2 are identical.

[0057] SC separation can be performed as long as the recovery yield of barium and / or radium in the eluate is less than or equal to a threshold value, relative to the respective amount of said element in the sample used. In other words, either elution step can be stopped as soon as the amount of barium and / or radium recovered exceeds this threshold value.

[0058] For example, this threshold value could be 80% and, even better, 90%.

[0059] At the end of the SC separation according to the invention, an ELR3 eluate enriched in radium is recovered compared to the sample S loaded on the C column.

[0060] The radium-rich ELRS eluate can then be regenerated with an acidic aqueous solution. Advantageously, the separation allows the radium purity to be increased by a factor of more than 100, particularly more than 1000, and especially more than 10,000.

[0061] Here, "chemical purity" refers to the mass ratio of radium to the sum of the masses of the elements present in the sample considered.

[0062] "Radiological purity" refers to the ratio of the radioactivity of the radionuclide in question to the total radioactivity of the sample in question, expressed as a percentage.

[0063] The separation may also include the usual steps, generally implemented in chromatography, such as packing the column with the dry or wet stationary phase, washing, conditioning, and possible pH adjustment.

[0064] According to one embodiment, the process according to the invention may comprise the successive conduct of several SC separations as described above.

[0065] The number of SC separations can be adjusted according to one or more parameters, such as the nature and volume of the sample to be separated and / or the desired chemical or radiological purity in radium and / or the desired yield at the end of the process, it being understood that the maximum number of SC separations is generally set according to the desired industrial optimization which ultimately depends on the cost and the duration in particular.

[0066] Typically, SC separation can be carried out n times, with n between 1 and 10, advantageously 2, 3, 4 or 5 times, advantageously 4, 5 or 6 times. Without wishing to be bound by the theory, the inventors identified that carrying out 4 or 5 successive SC separations could be particularly advantageous.

[0067] Each of the n SC separations can be carried out on said column C loaded with the stationary phase PS, by means of the eluents E1 and E2, as previously described, it being understood that said SC separation is carried out n times successively, with n being an integer between 1 and 10, on said column C loaded with the stationary phase PS, by means of the eluents E1 and E2, such that the (n- 1 ) ème SC separation leads to a radium-enriched eluate (ELR) a ) n -i, and the n ième SC separation is performed with (ELR a ) n -i and leads to a radium-enriched eluate (ELR a ) n .

[0068] Thus, the eluate (ELR3) obtained at the 1 ère separation is committed as a sample in the second separation.

[0069] Iteratively, the eluate (ELR a ) n -i from (n-1) ème separation is committed as a sample in the n èmeSeparation. Successive SC separations are typically conducted under the conditions described above.

[0070] The succession of at least 2 iterative separations (2 <n<10) sera désignée ici par les termes « cascade » ou « série » utilisés de façon interchangeable.

[0071] The particular way of implementing iterative separations is described here more specifically, by referring to one of the separations of said cascade according to its rank i in the cascade.

[0072] It is understood that in this embodiment, n is the total number of iterations performed, and n>2.

[0073] Here, "rank" refers to the respective position of the separation in the cascade, considered in the chronological order of the cascade's conduction.

[0074] Within the cascade, each of the iterative SC separations is designated by its rank i in the cascade (SCj), i being an integer between 2 and n.

[0075] Each of the i SCj separations can be conducted on a column Ci loaded with the stationary phase PSj, using the eluents E1j and E2j, such that Ci, PSj, E1j, E2j correspond respectively to C, PS, E1, E2 previously described, it being understood that said SO separation is conducted on said column Ci loaded with the stationary phase PS, using the eluents E1 and E2, such that the (i-1) ème SO-i separation leads to a radium-enriched eluate (ELR) a ii, and i ième Separation S is performed by engaging (ELR a )ii and leads to a radium-enriched eluate (ELR a )j.

[0076] Iteratively, the eluate (ELR a )ji from (i-1) ème separation is committed as a sample in the i ème separation.

[0077] In other words, the (i-1) ème SO-i separation leads to a radium-enriched eluate (ELR) a)ii, which is engaged as a sample of the i ième SO separation which leads to a radium-enriched eluate (ELR) a )j.

[0078] Advantageously, identical or different conditions can be implemented for each SC separation. Thus, typically the eluents E1 and E2 respectively can be identical with similar concentrations for each SC separation.

[0079] Advantageously, the volumes of PS committed and / or the volumes of eluents E1, respectively E2 can be different for each SC separation, in particular volumes lower at each successive SC iteration.

[0080] Thus, referring more specifically to a separation i: The stationary phase PSj and the eluents E1j, E2j, can be respectively identical or different for each iteration i considered, it being understood that each PSj, E1j, E2j is defined as for PS, E1, E2, respectively, previously described.

[0081] In particular, the volumes committed of each PSj and / or the volumes of each eluent E1j, respectively E2j may be identical or different, notably different for each iteration i considered.

[0082] According to this method of implementing cascade separations, the volume of the BV bed of column i (BVj) of the i ième SC separation (SCj) is less than or equal to the volume B ji of the anterior column (i-1) of the (i-1) ème SC separation (SC ) in the cascade.

[0083] Thus, B j

[0084] According to one embodiment, the ratio B j / BV-1 is between 0.05 and 1.5, in particular between 1 / 10 and 1 for each i.

[0085] According to one embodiment, the BV report n / BV n -i is between 0.2 and 0.5,

[0086] According to one embodiment, the BV report n / BVi is between 1 / 100 and 1.

[0087] ​Without wanting to be bound by the theory, the inventors identified that the radium purity of the final eluate (ELR) a ) n depends particularly on the total number of iterations n, and / or the ratio BVj / BVj-i, and / or the ratio BV n / BV n -i, and / or the BV report n / BVi ; and more specifically the total number of iterations n, the ratio B j / B ji, the ratio B n / B ni and the ratio BV n / BVi:

[0088] Thus, by properly adjusting these parameters, the inventors identified that radium purity could be increased, making it possible to obtain a radiological radium purity typically greater than 99%, and a chemical purity typically greater than 50%, such as between 50 and 99%, especially between 75 and 100% (by weight), particularly between 90 and 100%.

[0089] Advantageously, one or more washing steps can be conducted on column C after the loading and fixation of the eluate (ELR) a )ii , prior to the circulation of the eluent E1j for each iteration i.

[0090] According to one embodiment, each SC chromatographic separation step can be followed by a radium regeneration step by eluate treatment (ELR) a )ii with an acid solution, in particular a nitric acid solution HNO3, such as HNO3 10 N. This regeneration step is carried out prior to the SCj separation.

[0091] The conduct of the SCi separation with the eluate (ELR) a )ii is therefore understood as including the loading of the eluate (ELR a )ii possibly regenerated.

[0092] According to one embodiment, the process includes the additional step of evaporation-concentration of the final eluate (ELR3) subsequent to the chromatographic separation step.

[0093] According to an alternative embodiment, the process according to the invention includes an additional refining step by heat treatment of the final eluate (ELR3) subsequent to the chromatographic separation step.

[0094] This refining process is specifically aimed at removing silicon from the final eluate (ELR3).

[0095] Typically, refining includes a buffering step of the radium-enriched eluate, for example buffered at pH 8 with a 0.5 M citrate solution, followed by an evaporation step of the resulting solution, typically under mild conditions, for example around 100°C, to obtain a residue.

[0096] The residue then undergoes a calcination step by heat treatment. Typically, the heat treatment includes calcining said residue at a temperature between 100 and 1500°C, in particular between 300 and 1000°C, more specifically between 500 and 600°C.

[0097] The eluate (ELR3) obtained after chromatographic separation may contain, in addition to radium, traces of metals and organic impurities that could complex the radium. This heat treatment step allows, in particular, the oxidation of impurities and the elimination of any organic impurities that may be present in the eluate (ELR3).

[0098] Advantageously, this heat treatment step allows control of the chemical nature of the radium obtained in the end: thus, the radium is no longer obtained in organic form (i.e. complexed with organic ligands, such as aminopolycarboxylic acids such as citric, tartaric or EDTA for example) but in the form of a mineral residue (typically in the form of radium carbonate).

[0099] The heat treatment step is typically followed by a step of dissolving the resulting mineral residue in an acidic solution, such as a concentrated mineral acid solution (nitric HNO3 or hydrochloric HCl), typically with a concentration between 10' 1 M and 10M. Advantageously, this step allows the selective dissolution of radium from other mineral species possibly present in the residue, which are insoluble, such as silica or alumina which remains in suspension.

[0100] This selective dissolution step can then be followed by a filtration step of the oxidized particles to remove suspended and / or agglomerated oxide particles, typically SiC>2 silica particles. Typically, this filtration can be carried out with a syringe filter.

[0101] This refining process leads to a purified radium solution. Advantageously, it increases the chemical purity of radium, typically exceeding 90%, particularly exceeding 95%, and especially exceeding 96%.

[0102] Furthermore, this refining process allows radium to be obtained in a salt form.

[0103] The sample S used in the process according to the invention can ultimately be derived from a residue of ore extraction, in particular from an ore containing uranium.

[0104] More specifically, sample S may originate from a residue of uranium extraction from said ore.

[0105] Thus, typically, the sample S can be prepared from an extraction residue by processing the residue comprising the following steps: processing said residue by particle size separation, such as by hydrocyclone, to isolate a fine particle fraction; processing by leaching said fine particle fraction, by one or more acidic solutions resulting in a filtrate F; and purification of said filtrate F by SCo chromatography, giving rise to a raffinate R.

[0106] Typically, sample S comprises said raffinate R, in particular sample S consists of said raffinate R.

[0107] Typically, the F filtrate is a solution comprising radium, barium, and lead.

[0108] Advantageously, the treatment process makes it possible to valorize the ore residue.

[0109] Thus, hydrocyclone treatment makes it possible to obtain a fraction of fine particles enriched in radium, while the fraction of coarse particles can be enriched in other elements, notably arsenic.

[0110] The leaching process yields a radium-enriched filtrate F, separated from a filtrate that may be enriched in lead, among other things. The raffinate R obtained by purifying filtrate F using SCo chromatography is typically enriched in radium, while the eluate ELo obtained by said chromatography may be enriched in lead.

[0111] Thus, according to one embodiment, the process according to the invention includes prior to the SC separation, a step of isolating said sample S from a solution So comprising radium, barium and lead, by initial chromatographic separation (SCo) comprising: loading said solution So onto a Co column comprising a stationary phase PSo capable of retaining lead; collecting as a raffinate the sample S comprising radium and barium, S being depleted in lead compared to So.

[0112] Typically, the PSo stationary phase can be selected from cation exchange stationary phase materials that are capable of retaining lead.

[0113] Such a material may include a solid inorganic support (such as silica or alumina particles or a silica gel), an organic support (such as a polymer) or an inorganic-organic support, which is functionalized, by grafting or impregnation, by organic molecules capable of retaining, by ion exchange, molecular recognition or any other mechanism, the lead (Pb) ions present in the sample S.

[0114] This may include a material comprising silica particles grafted with molecules of an organic lead ligand, for example, a crown ether. Materials particularly well-suited to implementing the process of the invention include, for example, the Pb resins offered by Triskem™.

[0115] Typically the concentration of the So solution is between 0.1 and 5 N.

[0116] According to one embodiment, the chromatographic separation SCo can be carried out without eluent by circulation of the charged So solution, with radium and barium circulating through the stationary phase PSo and lead being retained by said phase.

[0117] The lead initially present in the So sample can be recovered by eluting the lead retained in the stationary phase PSo with a suitable eluent.

[0118] Thus, according to one embodiment, the SCo separation further comprises the circulation of a lead-complexing agent after collection of solution S, and the collection of a lead-enriched eluate ELo. The agents are capable of removing the lead retained by the stationary phase PSo, notably by complexation or chelation (the two terms being considered synonymous here). Advantageously, the lead-complexing agent is ammonium acetate, in aqueous solution with a concentration between 0.1 and 1 N, particularly acidified solutions, with a pH between 1 and 7.

[0119] The PSo phase can then be reconditioned to recover elements that would still be fixed on PSo after the elution of radium and lead.

[0120] According to one embodiment, the process further includes, prior to step SCo, an aqueous leaching step leading as filtrate F to said solution So comprising radium, barium and lead.

[0121] The said leaching step can advantageously be carried out on a fraction of an ore extraction residue, such as the aforementioned fine particle fraction and, more specifically, a fraction comprising particles whose average diameter (in number) is less than 25 pm, particularly less than 20 pm, particularly less than 17 pm.

[0122] Typically, the leaching step includes at least two successive acid treatments, and the collection of said filtrate F from the second acid treatment as solution So.

[0123] Advantageously, the first acid treatment comprises mixing said residue sample with an aqueous hydrochloric acid solution of acidity typically between 0.1 N and 8 N and collecting a solid, and the second acid treatment comprises mixing said solid with an aqueous nitric acid solution of acidity typically between 0.01 N and 10 N, and collecting said solution So as filtrate F.

[0124] Advantageously, the solid obtained at the end of the first acid treatment and the liquid filtrate obtained at the end of the second acid treatment are enriched in radium.

[0125] Advantageously, the liquid filtrate also obtained by the first acid treatment is enriched in lead.

[0126] Typically, acidic solutions are involved in a Liquid / Solid (by mass) ratio greater than 1, in particular about 4. Acid treatments in the leaching stage are advantageously carried out hot, at a temperature between 25°C and 70°C, in particular about 60°C.

[0127] According to one embodiment, the process further comprises, prior to the leaching step, a particle size separation step, typically comprising: one or more hydrocyclone treatments of an ore residue; the separation of a fine particle fraction, having an average diameter of less than 25 pm, in particular less than 20 pm, particularly less than 17 pm.

[0128] Advantageously, it has been shown that hydrocyclone separation allows the majority of the radium to be "concentrated," which is therefore found in the fine particle fraction resulting from the particle size separation.

[0129] Thus, the particle size separation of a fines fraction from the ore extraction residue makes it possible to multiply the radium content by at least 1.5, advantageously by at least 2.

[0130] Typically, ore extraction residue includes a radium content of between 100 and 10000 Bq / g relative to the mass of residue.

[0131] The said ore extraction residue comprises, in addition to radium and barium, one or more additional metallic impurities selected from uranium and arsenic, and / or one or more non-metallic impurities such as phosphorus.

[0132] Typically, the extraction residue can be chosen from among the extracted ore, waste, by-products of extraction, as well as concentrated materials from ore processing.

[0133] Examples of ores include uranium ores.

[0134] Concentrated material means any residue enriched in a radioactive element of interest, such as radium, relative to the natural ore (typically concentrated to a level of approximately 10⁻¹⁰). 8 %), for example, materials from the processing of uranium ore (typically with a concentration greater than 10' 8 %) including products used as a radioactive source for irradiation, such as radioactive needles or implants usable in brachytherapy, typically concentrated at around 90%.

[0135] All the steps of the process, which are detailed below, are preferably carried out at room temperature, i.e., at a temperature of 20°C to 25°C. According to another object, the present invention also relates to the ELR3 eluate obtainable by the process according to the invention, comprising a content of 226Ra between 0.1 and 500 GBq / L, more specifically between 1 and 200 GBq / L, and even more specifically between 10 and 50 GBq / L, and a chemical purity in 226 Ra between 50 and 99% more specifically between 75 and 95% (by mass).

[0136] BRIEF DESCRIPTION OF THE FIGURES

[0137] [Fig 1] Figure 1 schematically represents the process of valorizing radium from an ore extraction residue 1, to a radium-enriched extract (ELR3)2, including the separation process of the invention.

[0138] In the scheme in Figure 1, two successive chromatographic separations (SC)i and (SC)2 have been represented, it being understood that a lower or higher number of SC separations may be implemented, if appropriate.

[0139] [Fig 2] Figure 2 represents a heat treatment (TT) refining step of the radium-enriched eluate obtained at the end of the chromatographic separation step of the process according to the invention.

[0140] DETAILED DESCRIPTION OF SPECIFIC IMPLEMENTATION METHODS

[0141] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to Figure 1, illustrating the separation of radium from an ore extraction residue 1, which residue includes in particular radium, barium, lead, arsenic.

[0142] Residue 1 is first subjected to particle size separation A.

[0143] As previously described, said particle size separation A may include one or more hydrocyclone separations, in order to collect a fraction 2 of fine particles, in particular of average diameter (in number) less than 17 pm enriched in radium and a fraction 2' of coarse particles of greater average diameter which may for example be enriched in other impurities, for example arsenic.

[0144] Fraction 2 is then treated by leaching, first by treatment B with an aqueous solution of hydrochloric acid, resulting in a filtrate 3' enriched in lead and actinium, and a residual solid 3 enriched in radium. Solid 3 then undergoes a second acid treatment B' with a nitric acid solution, resulting in a filtrate 4 and a solid residue 4'.

[0145] Filtrate 4 corresponds to filtrate F, respectively the sample referenced above So.

[0146] The filtrate 4 obtained at the end of the HCl then HNO3 leaching steps is generally not pure enough to serve as a radiiferous solution for manufacturing targets for irradiation.

[0147] The radium present in the So solution resulting from the double leaching (B and B') is then isolated by implementing the following steps.

[0148] It is thus subjected to an initial chromatographic separation (SCo) to purify it of lead, using a resin comprising a stationary phase (PSo) that retains the lead, thereby recovering a raffinate (R) of equivalent radium concentration but purified of lead. Elution of the resin with, for example, ammonium acetate leads to an eluate (ELo) enriched in lead.

[0149] The raffinate R, corresponding to sample S above, is then used in the radium separation process according to the invention, which, by way of illustration, consists of two successive chromatographic separation steps (SC)i and (SC)2 in series, each carried out on a column C loaded with a radium-retaining stationary phase, such as AnaLig® Ra. Each separation (SC)i and (SC)2 comprises elution with eluent E1, which specifically elutes barium, followed by eluent E2, which elutes radium.

[0150] Thus, elution by E1 leads to a barium-enriched eluate (ELB3)I obtained after separation (SC)i and to a barium-enriched eluate (ELB3)2 obtained after separation (SC)2, respectively.

[0151] Thus, elution by E2 leads to a radium-enriched eluate (ELR3)I obtained at the end of the (SC)i separation and to a radium-enriched eluate (ELR3)2 obtained at the end of the (SC)2 separation, respectively.

[0152] Each of the eluents E1 and E2 is for example made up of an aqueous solution of ammonium citrate, with for example [E1]=0.05 M and [E2]=0.5 M.

[0153] The eluate (ELRS)I obtained at the end of (SC)i is committed to the top of the second column C for the second chromatographic separation (SC)2.

[0154] Each SC separation also leads to a raffinate R1 and R2, respectively.

[0155] The eluate (ELR3)2 can then be used for the valorization of radium, for example in the preparation of radium targets by electrodeposition.

[0156] EXAMPLES A residue from ore extraction (m = 1149 kg) having the following particle size composition is used to separate radium:

[0157] [Table 1] Analysis of the residue indicates that it contains a radium-226 content of approximately 2500 Bq / g of residue.

[0158] Particle size separation

[0159] A fraction of coarse particles (574 kg) is isolated from the residue by hydrocyclone:

[0160] [Table 2] a fraction of fine particles with a D90 (90% of the particles are smaller than 15.5 pm) for a mass of 574 kg:

[0161] [Table 3] The fine particle fraction has the following composition:

[0162] [Table 4]

[0163] Dissolution by leaching

[0164] The fine particle fraction is then attacked with hydrochloric acid HCl for 4h, at 60°C, in a Liquid / solid ratio L / S=4, by mixing 1318 L of water and 978 L of 37% HCl (1164 g).

[0165] Washing with 1613 L of water yields a filtrate (m=3592 g, v=3295 L, d=1.09) enriched in lead and actinium with the following composition:

[0166] [Table 5]

[0167] We also obtain a residual solid ("cake") enriched in radium, having the following composition:

[0168] [Table 6]

[0169] [Table 7]

[0170] The residual solid obtained is mixed with 525 L of water (m=525 kg) and then undergoes a second attack with nitric acid (604 L of water and 427 L of HNO3 65% (598 kg)) for 4h, at 60°C, in a Liquid / solid ratio L / S=4.

[0171] Washing with 1161 L of water yields a filtrate (m=2251 kg, v=2052 L, d=1.1) enriched in radium with the following composition: [Table s]

[0172] The radium yield from the dissolution is therefore 78.9%.

[0173] The solid residue obtained also has the following composition:

[0174] [Table 9]

[0175] Lead purification

[0176] The radium-enriched filtrate obtained above is fixed onto a column loaded with Triskem™ Pb resin:

[0177] [Table 10]

[0178] The following solutions are used: Washing:

[0179] [Table 11]

[0180] Lead elution:

[0181] [Table 12]

[0182] Reconditioning: [Table 13]

[0183] This yields a lead-enriched eluate: [Table 14]

[0184] The raffinate and washes, enriched with radium, are collected:

[0185] [Table 15]

[0186] The radium yield from this separation is therefore 73.1%.

[0187] Purification of radium by successive chromatographic separations

[0188] First purification: The radium-enriched solution obtained above is fixed onto a column loaded with AnaLig® Ra resin:

[0189] [Table 16]

[0190] We use the following solutions:

[0191] [Table 17]

[0192] This yields two eluates:

[0193] [Table 18]

[0194] [Table 19] By treating the radium-enriched eluate with 65% nitric acid (18.4 kg), a regenerated eluate is obtained:

[0195] [Table 20]

[0196] Second purification:

[0197] This regenerated eluate is then subjected to a second chromatographic separation (SC2) on the following column: [Table 21] using the following solutions:

[0198] [Table 22]

[0199] This yields two eluates:

[0200] [Table 23]

[0201] [Table 24]

[0202] By treating the radium-enriched eluate with 65% nitric acid (18.4 kg), a regenerated eluate is obtained:

[0203] [Table 25]

[0204] Third purification: This regenerated eluate is then subjected to a third chromatographic separation (SC3) on the following column:

[0205] [Table 26]

[0206] And the following solutions:

[0207] [Table 27]

[0208] This yields two eluates:

[0209] [Table 28] [Table 29] By treating the radium-enriched eluate with 65% nitric acid (4.1 kg), a regenerated eluate is obtained:

[0210] [Table 30]

[0211] Fourth purification:

[0212] This regenerated eluate is then subjected to a fourth chromatographic separation (SC4) on the following column: [Table 31]

[0213] And the following solutions:

[0214] [Table 32]

[0215] This yields two eluates:

[0216] [Table 33]

[0217] [Table 34]

[0218] By treating the radium-enriched eluate with 65% nitric acid (0.368 kg), a regenerated eluate is obtained:

[0219] [Table 35]

[0220] Fifth purification: This regenerated eluate is then subjected to a fifth chromatographic separation (SC5) on the following column:

[0221] [Table 36]

[0222] And the following solutions:

[0223] [Table 37]

[0224] This yields two eluates:

[0225] [Table 38] [Table 39] The radium-enriched eluate is then concentrated by evaporation-concentration (FCV=3), leading to the following concentrate:

[0226] [Table 40]

[0227] The concentrate is mixed with 1.220 L of alcohol to form the following target by electrodeposition:

[0228] [Table 41]

[0229] Heat treatment (TT) refining of the eluate (ELR3)

[0230] This step is illustrated in Figure 2, which is referred to here.

[0231] ATT step: Placement in buffered solution

[0232] We prepare a solution of approximately 10 mL by mixing the radium-enriched eluate with a 0.5 M citrate solution, buffered at pH 8, and with a radium concentration in complexed form between 100-300 mg / L.

[0233] BTT Stage: Evaporation

[0234] Then the solution obtained in step ATT is evaporated, typically under mild conditions, at approximately 100°C. Fractions of the eluate (2 mL) are successively evaporated, removing the aqueous phase (b), to obtain a residue. Step CTT: Calcination

[0235] The residue obtained in the BTT step is placed in an inert platinum crucible, under an inert platinum lid, and then in a calcination furnace for heating, for example at a rate of 2°C / min, to reach a temperature between approximately 500 and 600°C. This decomposition step leads to the decomposition of the organic phase, in this case citrate (c), and to the formation of radium in mineral form, in this case radium carbonate (RaCOs).

[0236] DTT step: Selective dissolution of Ra

[0237] The radium in mineral form is reconstituted with a concentrated acid solution, such as nitric acid HNO3 or hydrochloric acid HCl 6N. This prepares a suspension with a volume between 1 and 5 mL.

[0238] ETT step: Filtration of oxidized particles

[0239] The suspension thus obtained is filtered with a syringe filter (volume <40pm) in order to remove suspended and / or agglomerated oxide particles (e), typically silica particles SIO2.

[0240] FTT step: Purified radium solution

[0241] We thus recover the purified FTT solution.

Claims

DEMANDS 1. A process for separating radium from a sample S comprising radium and barium, said process comprising a chromatographic separation step SC comprising: loading the sample S onto a column C comprising a cation-exchange stationary phase PS capable of retaining radium and barium; circulating an eluent E1 in said phase PS, E1 selectively eluting barium from radium, leading to an eluate EI_Ba enriched in barium; then circulating an eluent E2 in said phase PS, E2 eluting radium; and leading to an eluate ELR3 enriched in radium; E1 and E2 each comprising a complexing agent, identical or different; characterized in that the concentration of said agent in eluent E1 ([E1]) is less than the concentration of said agent in eluent E2 ([E2]).

2. A method according to claim 1, wherein said SC separation comprises the iteration of i successive chromatographic separations SCi, such that 2 <i<n et n<10 n représentant le nombre total de séparations chromatographiques, chaque séparation SCi étant conduite sur une colonne Ci comprenant une phase stationnaire PSi, au moyen des éluants E1j et E2j, tels que Ci, PSi, E1i, E2i correspondent respectivement à C, PS, E1 , E2 tels que définis en revendication 1 , et tel que la i ième SCi separation includes eluate loading (EI_R a )ji obtained at the end of the SCi-i separation, and leads to a radium-enriched eluate (EL Ra )i.

3. A process according to claim 1, further comprising, after the SC chromatographic separation step, a refining of the radium-enriched ELR3 eluate, said refining comprising: - a step of dissolving the ELR3 eluate in a buffered solution; - an evaporation step of said buffered solution leading to a residue; - a calcination step of said residue leading to a mineral residue of radium; - a step of selectively dissolving radium by suspending the radium mineral residue in an acidic solution; and - a step of filtering suspended particles.

4. A method according to claim 1, 2 or 3 comprising prior to the SC separation, an isolation step of said sample S from a solution So comprising radium, barium and lead, by initial chromatographic separation SCo comprising loading said solution So onto a Co column comprising a stationary phase PSo suitable for retaining lead; collecting as a raffinate the sample S comprising radium and barium, S being depleted in lead compared to So.

5. A process according to claim 4 comprising prior to step SCo an aqueous leaching step leading as a filtrate to said solution So comprising radium, barium and lead.

6. A method according to any one of the preceding claims, wherein radium is in isotope form 226 Ra.

7. A process according to any one of the preceding claims wherein the eluents E1 and E2 each contain an identical complexing agent.

8. A process according to any one of the preceding claims wherein the eluent E1 and the eluent E2 are such that [E1] < [E2] / 2, in particular [E1] < [E2] / 5, preferably [E1] = [E2] / 10.

9. A process according to any one of the preceding claims wherein the eluent E1 and the eluent E2 are selected from aqueous solutions of citric acid and its ammonium, alkali or alkaline earth salts; of oxalic acid and its ammonium, alkali or alkaline earth salts; EDTA; and mixtures thereof.

10. A process according to any one of the preceding claims, wherein the eluent E1 and the eluent E2 are selected from ammonium citrate, EDTA, citric acid, oxalic acid, sodium citrate, magnesium citrate, potassium citrate, calcium citrate, ammonium oxalate, sodium oxalate, magnesium oxalate, potassium oxalate, calcium oxalate, and combinations thereof, preferably ammonium citrate.

11. A process according to any one of the preceding claims wherein the concentration [E1] is between 0.01 M and 0.5 M and the concentration [E2] is between 0.5 M and 3 M.

12. A process according to claim 4 wherein step SCo further comprises the circulation of a lead complexing agent after collection of solution S, and the collection of a lead-enriched eluate ELo.

13. A process according to claim 5 wherein the leaching step is carried out on a fraction of an ore extraction residue, said fraction comprising particles whose average diameter (in number) is less than 25 pm.

14. A process according to claim 13 wherein the leaching step comprises at least two successive acid treatments of said fraction, and the collection of said filtrate F from the second acid treatment as a solution So.

15. A process according to claim 14 wherein the first acid treatment comprises mixing said extraction residue sample with an aqueous solution of hydrochloric acid and collecting a solid, and the second acid treatment comprises mixing said solid with an aqueous solution of nitric acid, and collecting said solution So as a filtrate F.

16. A process according to claim 13 or 14 wherein said fraction is a fine particle fraction obtained by particle size separation of an ore extraction residue.

17. Process according to claim 16 wherein said residue comprises a radium content of between 100 and 10000 Bq / g relative to the mass of residue.

18. A process according to claim 16 or 17 wherein said ore extraction residue is selected from the extracted ore, the waste and by-products of the extraction, as well as the concentrated materials from the processing of the ore, and mixtures thereof.

19. Process according to claim 16, 17 or 18 wherein said ore extraction residue comprises one or more additional metallic impurities selected from uranium and arsenic, and / or one or more non-metallic impurities such as phosphorus.

20. Eluate EI_Ra obtainable by the process according to any one of claims 1 to 19, wherein it comprises a content of 226 Ra between 1 and 500 GBq / L, in particular between 1 and 200 GBq / L, preferably between 10 and 50 GBq / L, and a chemical purity in 226 Ra between 50 and 99% (by weight).

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