Process for recovering technetium and other metals from an aqueous solution

Abstract

The invention relates to a method for recovering one or more metals chosen from technetium, ruthenium, palladium and rhenium from an aqueous solution, which comprises precipitating the metal(s) in the solution by adding a reagent to the solution, then collecting the precipitate thus formed, and which is characterized in that the reagent comprises – or consists of – a mixture of 1,10-phenanthroline and a nickel(II) salt chosen from nickel(II) nitrate and nickel(II) sulfate. Applications: recovery of all or part of the technetium, ruthenium and / or palladium present in aqueous solutions of fission products, prior to operations aimed at conditioning the fission products by vitrification; recovery of all or part of the ruthenium, palladium and / or rhenium present in solutions resulting from an attack by nitric acid of industrial and / or urban waste.

Description

Title of the invention: Process for recovering technetium and other metals from an aqueous solution Technical field

[0001] The invention relates to the field of metal recovery from aqueous solutions.

[0002] More specifically, the invention relates to a process for selectively recovering one or more metals chosen from technetium, ruthenium, palladium and rhenium from an aqueous solution, in particular nitric acid, in which this metal or these metals are present together with other elements, in particular metallic elements.

[0003] The invention finds, firstly, application in the field of the treatment of spent nuclear fuels, in particular in the treatment of aqueous solutions of fission products resulting from the treatment of spent nuclear fuels with a view to recovering all or part of the technetium, ruthenium and / or palladium which they contain, prior to operations aimed at conditioning the fission products by vitrification.

[0004] However, it can also be used in the treatment of solutions resulting from an attack by nitric acid of industrial and / or urban waste, such as waste from electrical and electronic equipment, also known as WEEE and D3E, or catalytic converters from used vehicles, to recover the ruthenium, palladium and / or rhenium present in this waste with a view to recycling it. State of the prior art

[0005] The aqueous solutions of fission products (FPs) produced during the treatment of spent nuclear fuels are part of the ultimate waste from this treatment and are subjected to a set of operations - called vitrification - the objective of which is to condition the FPs in glass matrices that are stable over the very long term, which are themselves poured into steel containers for storage.

[0006] These PF solutions contain in particular technetium and light platinoids, in particular ruthenium and palladium, which can be used, in particular in the field of catalysis or electrocatalysis or even in the medical field.

[0007] It would therefore be desirable to have a process for recovering these metals from aqueous PF solutions before the latter are subjected to vitrification.

[0008] Furthermore, rhenium, ruthenium and palladium being part of the metals considered by the European Union as strategic and critical, the recycling of which has therefore become a major political and environmental issue, a process for recovering technetium, ruthenium and palladium from aqueous solutions of PFs could advantageously be used to recover rhenium, ruthenium and palladium from solutions resulting from an acid attack of industrial and / or urban waste containing them.

[0009] It has been proposed in patent RU 2513724 Cl to recover technetium from radioactive liquid waste for long-term storage in the form of a metal alloy. To do this, it is provided in this patent to precipitate the technetium by adding to the liquid waste an organometallic complex composed, on the one hand, of 1,10-phenanthroline or 2,2'-bipyridine or a mixture thereof or a mixture of these and one or more diamines such as ethylenediamine, and, on the other hand, of a divalent metal, then to subject the precipitate obtained to calcination at 600 °C-1200 °C, under a hydrogen atmosphere and in the presence of a low-melting metal such as tin or aluminum. The divalent metals used in this patent are copper, iron and cobalt.

[0010] RU 2513724 Cl teaches that, when the waste is an aqueous solution of nitric acid, then the nitric acid content of this solution must not exceed 3 mol / L, regardless of the divalent metal used, otherwise no precipitate is obtained.

[0011] Furthermore, all the examples of RU 2513724 Cl aim to recover technetium from aqueous nitric acid solutions which do not include any element other than technetium and this patent is totally silent on data which are nevertheless crucial when it comes to recovering a metal or metals from a medium in which it(they) is(are) found, namely those which concern the existence of a possible selectivity of this recovery with respect to other elements and, in particular, other metals likely to also be present in this medium.

[0012] However, in the context of their work, the inventors have found that a reagent comprising 1,10-phenanthroline and a nickel(II) salt such as nickel(II) nitrate - the use of which is neither described nor suggested in RU 2513724 Cl - makes it possible to precipitate technetium, rhenium, ruthenium and palladium present in aqueous solutions having a nitric acid content of up to 6 mol / L, or even higher, and, therefore, to recover these metals in solid form from these solutions, and this, selectively from the other elements, in particular metallic elements, also present therein.

[0013] And it is on these experimental observations that the present invention is based. Statement of the invention

[0014] The invention therefore relates to a process for recovering one or more metals chosen from technetium, rhenium, ruthenium and palladium from an aqueous solution A, which comprises the precipitation in the solution of the metal(s) by adding a reagent to the aqueous solution A, then the collection of the precipitate thus formed, characterized in that the reagent comprises - or consists of - a mixture of 1,10-phenanthroline and a nickel(II) salt chosen from nickel(II) nitrate and nickel(II) sulfate.

[0015] According to the invention, the reagent may be in a liquid form, that is to say typically in the form of an aqueous solution comprising the mixture of 1,10-phenanthroline and nickel(II) salt.

[0016] Alternatively and preferably because this makes it possible to avoid dilution of the aqueous solution A when adding the reagent to this solution, the reagent may be in a semi-solid form, that is to say typically in the form of an aqueous suspension, also called mud or slurry, of particles comprising - or consisting of - the mixture of 1,10-phenanthroline and nickel(II) salt, and, better still, in a solid form, that is to say typically in the form of a powder whose grains comprise - or are constituted by - the mixture of 1,10-phenanthroline and nickel(II) salt.

[0017] The semi-solid and solid forms of the reagent can be obtained by more or less extensive dehydration of an aqueous solution comprising the mixture of 1,10-phenanthroline and nickel(II) salt, for example by placing this solution in an oven at a temperature of 40°C to 60°C.

[0018] Whatever the form in which it is presented, the reagent has a 1,10-phenanthroline / nickel(II) salt molar ratio which is advantageously between 2.5 and 5 and, preferably, equal to 3.

[0019] Furthermore, whatever the form in which it is presented, the reagent is preferably added to the aqueous solution A in an amount such that the mixture of 1,10-phenanthroline and nickel(II) salt is in excess relative to the stoichiometric conditions of the precipitation reaction of the metal or metals that it is desired to recover, this excess being able to be easily determined by measuring this metal or these metals in the aqueous solution A to know the content before implementing the process of the invention.

[0020] The nickel(II) salt present in the reagent is preferably nickel(II) nitrate so that, preferably, the reagent comprises - or is constituted by - a mixture of 1,10-phenanthroline and nickel(II) nitrate.

[0021] Alternatively, the reagent may comprise - or consist of - a mixture of 1,10-phenanthroline and nickel(II) sulfate or a mixture of 1,10-phenanthroline, nickel(II) nitrate and nickel(II) sulfate.

[0022] According to the invention, the addition of the reagent to the aqueous solution A is, preferably carried out with stirring then the reaction medium is kept stirring, for example for 1 hour to 24 hours, at room temperature.

[0023] As known per se, the collection of the precipitate can be carried out by any technique making it possible to separate a solid phase from a liquid phase and, in particular, by filtration or centrifugation.

[0024] According to the invention, the aqueous solution A may be an aqueous solution which does not comprise nitric acid or any other acid.

[0025] However, since the process has proven very effective in recovering technetium, rhenium, ruthenium and / or palladium from aqueous nitric acid solutions, aqueous solution A may also be an aqueous solution which comprises nitric acid, in which case its nitric acid concentration is preferably at most 8 mol / L.

[0026] In particular, the aqueous solution A may, firstly, be an aqueous solution of PFs resulting from the treatment of spent nuclear fuels from which it is desired to recover all or part of the technetium, ruthenium and / or palladium present in this solution.

[0027] This aqueous solution of PFs can in particular be produced during the implementation of the treatment of spent fuels with the use of TBP as an extractant, such as the PUREX or COEX processes, or with other extractants such as amides. This aqueous solution of PFs can then be chosen from: - raffinates from the first cycle of uranium and plutonium extraction from these processes, - concentrates from the evaporators of raffinates from the plutonium and uranium purification cycles of these processes, and - mixtures of these.

[0028] Such an aqueous solution of PFs typically comprises from 1 mol / L to 3 mol / L of nitric acid.

[0029] Alternatively, the aqueous solution A may also be a solution resulting from an attack by nitric acid of industrial and / or urban waste from which it is desired to recover all or part of the ruthenium, palladium and / or rhenium present in this solution. Such waste may, for example, be WEEE (electronic cards, computer hard drives, etc.), catalytic converters from used vehicles, turbines used in aeronautics, catalysts used in the petroleum industry, electrical resistance filaments and thermocouples.

[0030] In which case, the aqueous solution A can comprise up to 8 mol / L of nitric acid depending on the nature of the waste treated and the attack treatment to which it is subjected.

[0031] The method of the invention has numerous advantages, in particular its simplicity of implementation, its low cost of implementation and its robustness.

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[0044] Other characteristics and advantages of the method of the invention will emerge from the additional description which follows and which relates to tests which have enabled this method to be validated. It goes without saying, however, that this additional description is given only as an illustration of the subject of the invention and must in no case be interpreted as a limitation of this subject. Detailed presentation of specific implementation methods Example 1: Recovery of rhenium with a mixture of 1,10-phenanthroline and nickel(II) nitrate Tests are being carried out to recover rhenium from 5 aqueous solutions, each containing approximately 2.1 g / L of rhenium (provided in the form of per-rhenic acid HReO4) but differing from each other in their nitric acid content. Thus, the first solution is free of nitric acid while the other 4 comprise respectively 2.1 mol / L, 3.1 mol / L, 4.1 mol / L and 6.2 mol / L of nitric acid. All tests are carried out under the same operating conditions, i.e. with the same reagent and under the same precipitation and precipitate collection conditions. The reagent was prepared by adding, with stirring, 2 g of 1,10-phenanthroline and 981 mg of Ni(NO3)2 to 45 mL of water and then, after stirring the mixture thus obtained for 2 hours, placing this mixture in an oven heated to 50 °C for 48 hours to dehydrate it and thus obtain the reagent in the form of a dry powder. Each test consists of adding, with stirring, 105 mg of reagent to 4.5 mL of one of the 5 aqueous solutions and keeping the mixture thus obtained under stirring for 24 hours at the end of which a solid / liquid separation is carried out by filtration. The concentration of rhenium in the liquid phases obtained after filtration is measured by inductively coupled plasma equipped with an atomic emission spectrometer (ICP-AES) and, for each test, the percentage of rhenium having precipitated, noted Res (%) below, is determined by the formula (I) below: [Math.l] Res(%) = L Jîtù in which: [Re]ini is the concentration of rhenium in the aqueous solution under test, expressed in mg / L, while [Re]fin is the concentration of rhenium in the liquid phase resulting from filtration, expressed in mg / L. The results of these tests are presented in the table below. [HhKM of te sgW» aqyeü&e 0 2.1 3.1 6.2 [Reh» (w / U 136 147 21 29 154 Res(%| 94 93 99 95 93

[0046] This table shows that the use of a mixture of 1,10-phenanthroline and nickel(II) nitrate as precipitation reagent makes it possible to recover in solid form more than 90% of the rhenium present in an aqueous solution comprising or not nitric acid and, when nitric acid is present, for a nitric acid concentration greater than 6 mol / L, the recovery rate even reaching 99% for nitric acid contents of 3.1 mol / L and 4.1 mol / L.

[0047] Example 2: Recovery of technetium with a mixture of 1,10-phenanthroline and nickel(II) nitrate

[0048] Tests are carried out to recover technetium from 7 aqueous solutions, each comprising approximately 1 g / L of technetium-97 (provided in the form of pertechnetic acid HTcO4) but differing from each other in their nitric acid content.

[0049] Thus, the first solution is free of nitric acid while the other 6 comprise respectively 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L and 6 mol / L of nitric acid.

[0050] All tests are carried out following an operating protocol identical to that described in example 1 above.

[0051] The concentration of technetium in the liquid phases obtained after filtration is measured by ICP-AES and, for each test, the percentage of technetium having precipitated, noted Tcs(%) below, is determined by the formula (II) below:

[0052] [Math.2]

[0053] in which: [Tc]ini is the concentration of technetium in the aqueous solution under test, expressed in mg / L, while [Tc]fin is the concentration of technetium in the liquid phase resulting from filtration, expressed in mg / L.

[0054] The results of these tests are presented in the table below. [HNO5] of h aqueous solution ] mol / L) 0 1 3 4 5 6 lû 252 84 6 1 14 36 Tc4%| 99 76 92 99 1ÔÛ 99 96

[0056] This table shows that the use of a mixture of 1,10-phenanthroline and nickel(II) nitrate as precipitation reagent makes it possible to recover in solid form the technetium present in an aqueous solution comprising or not nitric acid, with a recovery rate greater than 95% for nitric acid contents ranging from 2 mol / L to 6 mol / L and which even reaches 99%, or even 100%, for nitric acid contents ranging from 3 mol / L to 5 mol / L.

[0057] Example 3: Recovery of rhenium, ruthenium and palladium with a mixture of 1,10-phenanthroline and nickel(II) nitrate

[0058] A test is carried out to recover rhenium, ruthenium and palladium from an aqueous nitric acid solution representative of an aqueous PFs solution, the rhenium acting as a technetium simulant.

[0059] Therefore, the aqueous solution subjected to the test comprises 2.5 mol / L of nitric acid and 34 non-radioactive elements (provided in metallic form, nitrates or oxides) including rhenium, ruthenium and palladium but also rhodium, lanthanides (Ce, Gd, La, Nd, Pr, Sm, ...), alkali metals (Cs, Li, Na and Rb), alkaline earth metals (Ba, Mg and Sr), transition metals (Cu, Fe, Mn, Mo, Ni, Zr, ...) and other elements.

[0060] The concentration of these elements in this solution, noted [M]ini and expressed in g / L, is presented in Table III below.

[0061] The test consists of adding, with stirring, 1062 mg of a reagent prepared as described in Example 1 above to 15 mL of the aqueous solution and keeping the mixture thus obtained with stirring for 1 hour at the end of which a solid / liquid separation is carried out by filtration.

[0062] The concentration of the 34 elements in the liquid phase obtained after filtration is measured by ICP-AES and the percentage of each element having precipitated, noted Ms(%) below, is determined by the formula (III) below:

[0063] [Math.3]

[0064] in which: [M]ini is the concentration of the element in the aqueous solution under test, expressed in g / L, while [M]fin is the concentration of the element in the liquid phase resulting from filtration, expressed in g / L.

[0065] The results of this test are presented in the table below. Cements [MU tb / M [ M ]end WM M4%^ Ag 0.003 0.003 0 Ai 13 1.9 0: B 0.12 0.12 0 Ba 2 5 25 fs ce 6.7 6.6 1.5 Cr 0.17 0.17 0 Cs 7.7 7.5 2.6 Cu 0.05 0.05 0 Eu 0.49 0.49 o Fe 0.6 0.6 0 Gd 1.8 1.8 0 La 3.7 3.6 2.7 Mg 0.057 0.057 0 Mn 0.031 0.031 0' Mo 0.67 0.63 5.9 Ma 3.9 3.8 2.5 Md 11 0 NS 0.17 0.17 0 Pd 33 1.5 58.3 Pr 3.4 3.4 0 Rb 1.1 1.1 Q: Re 6.1 0.18 97.04 Rh 0.95 0.90 5.26 Ru S? 2 4.6 11.53 sb 0.004 0.004 0 5m 2.4 2.4 0 Sn 0.025 0.025 0 Sr 1.3 1.9 0 Te 0.15 0.15 Ô ü 1 î ¥ 1.2 1.2 G Zn 0.13 0.13 0 Zî 0.9 0.9 ô LJ 4.6 4.6 0'

[0067] This table shows that in the presence of a large number of elements, some of which are at high contents (e.g., Ce, Cs and Li), the use of a mixture of 1,10-phenanthroline and nickel(II) nitrate as a precipitation reagent makes it possible to recover in solid form 97% of the rhenium, almost 60% of the palladium and more than 10% of the ruthenium present in an aqueous nitric acid solution, and this, selectively from the other elements also present in this solution since the percentage of precipitation is most often zero and, when it is not, is low to very low.

[0068] This table also shows that, since rhenium is a good simulant of technetium, it will be possible to recover a high fraction of the technetium present in a multi-metallic aqueous solution such as that on which the present test was carried out.

[0069] Example 4: Comparison of a mixture of 1,10-phenanthroline and nickel(II) nitrate with a mixture of 1,10-phenanthroline and nickel(II) sulfate for the recovery of rhenium

[0070] Tests are carried out to recover rhenium from an aqueous solution comprising 2.1 g / L of rhenium (provided in the form of perrhenic acid HReO4) and 3 mol / L of nitric acid.

[0071] Two tests are carried out, differing in the composition of the reagent which is added to the aqueous solution.

[0072] Reagent 1 was prepared by adding, with stirring, 223 mg of 1,10-phenanthroline and 109 mg of Ni(NO3)2 to 5 mL of water and then, after stirring the mixture thus obtained for 2 hours, placing this mixture in an oven heated to 50°C for 48 hours to dehydrate it and thus obtain the reagent in the form of a dry powder.

[0073] Reagent 2 was prepared by adding, with stirring, 446 mg of 1,10-phenanthroline and 197 mg of NiSO4 to 5 mL of water and then, after stirring the mixture thus obtained for 2 hours, placing this mixture in an oven heated to 50°C for 48 hours to dehydrate it and thus obtain the reagent in the form of a dry powder.

[0074] The two tests are carried out under the same operating conditions, that is to say under the same conditions of precipitation and collection of the precipitate.

[0075] Each test consists of adding, with stirring, 245 mg of one of the reagents to 10 mL of aqueous solution and keeping the mixture thus obtained stirring for 30 minutes at the end of which a solid / liquid separation is carried out by filtration.

[0076] The concentration of rhenium in the liquid phases obtained after filtration is measured ICP-AES and, for each test, the percentage of rhenium having precipitated, noted Res(%) below, is determined by formula (I) of example 1 above.

[0077] The results of these tests are presented in the table below. Reagent used Reagent 1 (Ni(NO3)2) Reagent 2 (NISO4 [Re]S!> 119 221 Res(%| 943 893

[0079] This table shows that the use of a mixture of 1,10-phenanthroline and nickel(II) nitrate as a precipitation reagent allows a higher recovery of rhenium than that obtained with the mixture of 1,10-phenanthroline and nickel(II) sulfate. Reference cited

[0080] RU 2513724 Cl

Claims

Claims

1. A process for recovering one or more metals selected from technetium, rhenium, ruthenium and palladium from an aqueous solution A, comprising precipitating the metal(s) in the solution by adding a reagent to the aqueous solution A, then collecting the precipitate thus formed, characterized in that the reagent comprises - or consists of - a mixture of 1,10-phenanthroline and a nickel(II) salt selected from nickel(II) nitrate and nickel(II) sulfate.

2. The method of claim 1, wherein the reagent is in the form of an aqueous solution comprising the mixture of 1,10-phenanthroline and nickel(II) salt.

3. A method according to claim 1, wherein the reagent is in the form of an aqueous suspension of particles comprising - or consisting of - the mixture of 1,10-phenanthroline and nickel(II) salt.

4. A method according to claim 1, wherein the reagent is in the form of a powder whose grains comprise - or are constituted by - the mixture of 1,10-phenanthroline and nickel(II) salt.

5. A method according to any one of claims 1 to 4, wherein the reagent has a 1,10-phenanthroline / nickel(II) salt molar ratio of between 2.5 and 5, preferably equal to 3.

6. A method according to any one of claims 1 to 5, wherein the reagent is added to the aqueous solution A in an amount such that the mixture of 1,10-phenanthroline and nickel(II) salt is in excess relative to the stoichiometric conditions of the precipitation reaction of the metal(s) to be recovered.

7. A method according to any one of claims 1 to 6, wherein the reagent comprises - or consists of - a mixture of 1,10-phenanthroline and nickel(II) nitrate.

8. A method according to any one of claims 1 to 7, wherein the aqueous solution A is an aqueous solution of fission products from the processing of spent nuclear fuels.

9. The method of claim 8, wherein the aqueous solution A comprises technetium, ruthenium and / or palladium and from 1 mol / L to 3 mol / L of nitric acid.

10. A method according to any one of claims 1 to 7, wherein the aqueous solution A is an aqueous solution resulting from an attack of industrial and / or urban waste by nitric acid.

11. A method according to claim 10, wherein the aqueous solution A comprises ruthenium, palladium and / or rhenium and up to 8 mol / L of nitric acid.