Process for recovering technetium and other metals from aqueous solutions
By using a mixture of 1,10-phenanthroline and nickel(II) salt as a reagent, the problem of selectively recovering technetium, ruthenium, and palladium from aqueous nitric acid containing multiple metals was solved, achieving efficient metal recovery, especially with a technetium recovery rate of up to 99% at high nitric acid concentrations, and showing low precipitation rates for other elements.
Patent Information
- Application Number
- CN202480066856.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-10-19
- Filing Date
- 2024-10-18
- Publication Date
- 2026-05-15
AI Technical Summary
Existing technologies struggle to selectively recover technetium, ruthenium, and palladium from aqueous nitric acid solutions containing multiple metals, especially at high nitric acid concentrations, and lack methods for the selective recovery of other elements.
Using a mixture of 1,10-phenanthroline and nickel(II) salt as a reagent, the metal is precipitated by adding the mixture to an aqueous solution to form a solid precipitate, which is then separated by filtration or centrifugation. This method is applicable to different forms of reagent (liquid, semi-solid, or solid) to achieve selective recovery of technetium, ruthenium, and palladium.
High efficiency of technetium, ruthenium and palladium was achieved at nitric acid concentrations up to 8 mol/L, with technetium recovery reaching 99% in complex solutions. It also showed low precipitation rates for other elements, demonstrating selectivity and robustness.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of recovering metals from aqueous solutions.
[0002] More specifically, the present invention relates to a method for selectively recovering one or more metals selected from technetium, ruthenium, palladium and rhenium from an aqueous solution (particularly an aqueous solution of nitric acid), wherein the metal or these metals are present together with other elements (particularly metals).
[0003] This invention is primarily applicable to the field of spent nuclear fuel processing, and particularly to the processing of aqueous solutions of fission products derived from spent nuclear fuel processing, with the aim of recovering all or part of the technetium, ruthenium, and / or palladium contained therein before vitrification of the fission products.
[0004] However, the present invention can also be used to treat solutions generated from the acid washing of industrial and / or municipal waste (such as waste electrical and electronic equipment, also known as WEEE, or catalytic converters of scrapped vehicles) to recover ruthenium, palladium and / or rhenium present in the waste for recycling. Background Technology
[0005] The aqueous solution of fission products (FP) generated during spent nuclear fuel reprocessing is part of the final waste from the process and requires a series of operations—called vitrification—to encapsulate the FP in a glass matrix that is stable over a very long period of time, and then these matrices are cast into steel containers for storage.
[0006] Specifically, these FP solutions contain technetium and light platinum group elements, especially ruthenium and palladium, which can be recycled, particularly for applications in catalysis or electrocatalysis or in the medical field.
[0007] Therefore, a method is desired to recover these metals from aqueous FP solutions before vitrification.
[0008] Furthermore, since rhenium, ruthenium, and palladium are considered strategically important and crucial metals by the EU, their recycling has become an important political and environmental issue. A method capable of recovering technetium, ruthenium, and palladium from aqueous FP solutions could be advantageously used to recover rhenium, ruthenium, and palladium from solutions obtained by acid washing of industrial and / or municipal waste containing rhenium, ruthenium, and palladium.
[0009] Patent RU 2513724 C1 discloses a method for recovering technetium from radioactive liquid waste for long-term storage in the form of a metallic alloy. To this end, the patent provides a method for adding an organometallic complex to the liquid waste, the complex consisting of: on one hand, 1,10-phenanthroline or 2,2'-bipyridine or a mixture thereof, or a mixture thereof with one or more diamines (e.g., ethylenediamine); and on the other hand, a divalent metal. The resulting precipitate is then calcined in a hydrogen atmosphere at a temperature of 600°C to 1200°C in the presence of a low-melting-point metal (e.g., tin or aluminum). The divalent metals used in this patent are copper, iron, and cobalt.
[0010] RU 2513724 C1 discloses that when the waste is an aqueous solution of nitric acid, regardless of the divalent metal used, the nitric acid content of the solution must not exceed 3 mol / L, otherwise no precipitation will occur.
[0011] Furthermore, all instances of RU 2513724 C1 are intended to recover technetium from aqueous nitric acid solutions containing no elements other than technetium, and the patent makes no mention of crucial data regarding the selective nature of the recovery relative to other elements (particularly other metals that may be present in the medium) when recovering such metals from a medium containing one or more metals.
[0012] However, in their research, the inventors discovered that a reagent containing 1,10-phenanthroline and a nickel(II) salt (e.g., nickel(II) nitrate) (neither described nor recommended in RU 2513724 C1) can precipitate technetium, rhenium, ruthenium, and palladium present in aqueous solutions with nitric acid concentrations as high as 6 mol / L or even higher, thereby enabling the recovery of these metals from these solutions in solid form, and enabling the selective recovery of these metals in the presence of other elements (especially other metals).
[0013] This invention is based on these experimental results. Summary of the Invention
[0014] Therefore, the object of the present invention is a method for recovering one or more metals selected from technetium, rhenium, ruthenium and palladium from an aqueous solution A, the method comprising adding a reagent to the aqueous solution A to precipitate the metal in the solution, and then collecting the precipitate formed therefrom, 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.
[0015] According to the present invention, the reagent may be in liquid form, i.e., typically in the form of an aqueous solution containing a mixture of 1,10-phenanthroline and nickel(II) salt.
[0016] Alternatively, more preferably, this avoids diluting the aqueous solution A when adding the reagent, which may be in a semi-solid form, i.e., typically in the form of an aqueous suspension (also known as a slurry), whose particles comprise or consist of a mixture of 1,10-phenanthroline and nickel (II) salt; more preferably, the reagent may be in a solid form, i.e., typically in the form of a powder, whose particles comprise or consist of a mixture of 1,10-phenanthroline and nickel (II) salt.
[0017] The semi-solid and solid forms of the reagent can be obtained by dehydrating an aqueous solution containing a mixture of 1,10-phenanthroline and nickel(II) salt to varying degrees, for example by placing the solution in an oven at 40°C to 60°C.
[0018] Regardless of the form of the reagent, advantageously, 1,10-phenanthroline is in molar excess relative to the nickel(II) salt.
[0019] Preferably, the molar ratio of 1,10-phenanthroline / nickel(II) salt in the reagent is between 2.5 and 5, more preferably equal to 3.
[0020] Furthermore, regardless of its form, the amount of reagent preferably added to aqueous solution A is 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 one or more metals to be recovered. This excess can be readily determined by analyzing the content of this or these metals in aqueous solution A prior to implementing the method of the present invention.
[0021] Preferably, the nickel(II) salt present in the reagent is nickel(II) nitrate, and therefore, preferably, the reagent comprises or consists of a mixture of 1,10-phenanthroline and nickel(II) nitrate.
[0022] Alternatively, the reagent may contain 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.
[0023] According to the present invention, it is preferable to add the reagent to the aqueous solution A under stirring, and then keep the reaction medium under stirring at room temperature for, for example, 1 hour to 24 hours.
[0024] As is well known, the collection of precipitates can be carried out by any technique that can separate the solid phase from the liquid phase, especially by filtration or centrifugation.
[0025] According to the present invention, aqueous solution A may be an aqueous solution that does not contain nitric acid or any other acid.
[0026] However, since this method has been shown to recover technetium, rhenium, ruthenium and / or palladium from aqueous nitric acid solution very effectively, aqueous solution A can also be an aqueous solution containing nitric acid, in which case the nitric acid concentration is preferably at most 8 mol / L.
[0027] Specifically, the aqueous solution A can first be an aqueous FP solution obtained from processing spent nuclear fuel, with the aim of recovering all or part of the technetium, ruthenium and / or palladium present in the solution.
[0028] Specifically, this aqueous FP solution may be generated during the treatment of spent fuel using TBP as an extractant, such as with the PUREX or COEX methods, or using other extractants, such as amides. This aqueous FP solution can be selected from: - The raffinate produced in the first uranium and plutonium extraction cycle in these processes - Concentrates derived from the raffinate evaporator in the plutonium and uranium purification cycles of these processes, and - A mixture of them.
[0029] This aqueous FP solution typically contains 1 mol / L to 3 mol / L of nitric acid.
[0030] Alternatively, aqueous solution A can also be a solution obtained by acid washing industrial and / or municipal waste with nitric acid, with the aim of recovering all or part of ruthenium, palladium, and / or rhenium. For example, such waste can be discarded electronic and electrical equipment (e.g., electronic circuit boards, computer hard drives, etc.), catalytic converters from scrapped vehicles, aircraft turbines, petroleum industry catalysts, resistor wires, and thermocouples.
[0031] In this case, the nitric acid content in aqueous solution A can be as high as 8 mol / L, depending on the nature of the waste being treated and the acid washing treatment being performed.
[0032] The method of the present invention has many advantages, especially its simplicity, low cost and robustness.
[0033] Other features and advantages of the method of the present invention will become apparent from the following additional description, which relates to tests used to verify the method.
[0034] However, it goes without saying that such additional description is merely for illustrating the subject matter of the invention and should in no way be construed as limiting the subject matter of the invention. Detailed Implementation
[0035] Example 1: Recovery of rhenium using a mixture of 1,10-phenanthroline and nickel(II) nitrate The purpose of the experiment was to recover rhenium from five aqueous solutions, each containing approximately 2.1 g / L of rhenium (added in the form of perrhenic acid HReO4), which differed in their nitric acid content.
[0036] Therefore, the first solution does not contain nitric acid, while the other four solutions contain 2.1 mol / L, 3.1 mol / L, 4.1 mol / L, and 6.2 mol / L of nitric acid, respectively.
[0037] All experiments were conducted under the same operating conditions, i.e., using the same reagents and under the same precipitation and precipitate collection conditions.
[0038] The reagent was prepared by the following steps: 2 g of 1,10-phenanthroline monohydrate (molar mass: 198.22 g / mol) and 981 mg of nickel nitrate hexahydrate (Ni(NO3)2) were mixed under stirring. Add 6H2O (molar mass: 290.7 g / mol) to 45 mL of water, stir for 2 hours, and then place the resulting mixture in an oven at 50°C for 48 hours to dehydrate it, thereby obtaining a dry powdered reagent.
[0039] Each experiment consisted of the following steps: 105 mg of reagent was added to one of five aqueous solutions in 4.5 mL with stirring, and the resulting mixture was kept stirred for 24 hours, followed by solid-liquid separation by filtration.
[0040] The concentration of rhenium in the filtered liquid phase was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). For each experiment, the percentage of precipitated rhenium (hereinafter referred to as Re) was recorded. s (%) is determined by the following formula (I):
[0041] in: This is the concentration of rhenium in the aqueous solution being tested, expressed in mg / L. This is the concentration of rhenium in the liquid phase obtained by filtration, expressed in mg / L.
[0042] The results of these experiments are shown in Table I below.
[0043] Table I
[0044] The table shows that using a mixture of 1,10-phenanthroline and nickel(II) nitrate as a precipitating agent, more than 90% of rhenium can be recovered from aqueous solutions with or without nitric acid. When nitric acid is present, the recovery rate exceeds 90% for nitric acid concentrations above 6 mol / L, and even reaches 99% at nitric acid concentrations of 3.1 mol / L and 4.1 mol / L.
[0045] Example 2: Recovery of technetium using a mixture of 1,10-phenanthroline and nickel(II) nitrate The purpose of the experiment was to recover technetium from seven aqueous solutions, each containing approximately 1 g / L of technetium-97 (added in the form of pertechnetic acid HTcO4), the difference being their nitrate content.
[0046] Therefore, the first solution does not contain nitric acid, while the other six solutions contain 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L and 6 mol / L of nitric acid, respectively.
[0047] All tests were conducted in accordance with the same operating procedures described in Example 1 above.
[0048] The concentration of technetium in the filtered liquid phase was determined by ICP-AES. The percentage of technetium precipitated in each experiment (hereinafter referred to as Tc) was also measured. s (%) is determined by the following formula (II):
[0049] in: [Tc] ini This is the concentration of technetium in the aqueous solution being tested, expressed in mg / L. [Tc] fin This is the concentration of technetium in the liquid phase obtained by filtration, expressed in mg / L.
[0050] The results of these experiments are shown in Table II below.
[0051] Table II
[0052] The table shows that solid technetium can be recovered from aqueous solution, optionally containing nitric acid, using a mixture of 1,10-phenanthroline and nickel(II) nitrate as a precipitating agent. Recovery rates are above 95% when the nitric acid concentration is 2 mol / L to 6 mol / L; and even reach 99% or 100% when the nitric acid concentration is 3 mol / L to 5 mol / L.
[0053] Example 3: Recovery of rhenium, ruthenium, and palladium using a mixture of 1,10-phenanthroline and nickel(II) nitrate The objective of the experiment was to recover rhenium, ruthenium, and palladium from an aqueous nitric acid solution, which is representative of an aqueous FP solution, with rhenium serving as a simulant for technetium.
[0054] Therefore, the tested aqueous solution contained 2.5 mol / L nitric acid and 34 non-radioactive elements (added as metals, nitrates, or oxides), including rhenium, ruthenium, and palladium, as well as rhodium, lanthanides (Ce, Gd, La, Nd, Pr, Sm, etc.), alkali metals (Cs, Li, Na, and Rb), alkaline earth metals (Ba, Mg, and Sr), transition metals (Cu, Fe, Mn, Mo, Ni, Zr, etc.) and other elements.
[0055] The concentrations of these elements in the solution are denoted as [M]. ini The values are expressed in g / L, as shown in Table III below.
[0056] The experiment consisted of the following steps: 1062 mg of the reagent prepared as described in Example 1 above was added to 15 mL of aqueous solution under stirring, and the resulting mixture was kept under stirring for 1 hour, and then solid-liquid separation was performed by filtration.
[0057] The concentrations of 34 elements in the filtered liquid phase were determined by ICP-AES, and the precipitation percentage of each element (hereinafter referred to as M) was calculated. s (%) is determined by the following formula (III):
[0058] in: [M] ini It is the concentration of the element in the aqueous solution to be tested, expressed in g / L, while [M] fin It is the concentration of elements in the liquid phase obtained by filtration, expressed in g / L.
[0059] The results of this experiment are shown in Table III below.
[0060] Table III
[0061] The table shows that, in the presence of a considerable number of elements (some of which are present in high concentrations, such as Ce, Cs, and Li), using a mixture of 1,10-phenanthroline and nickel(II) nitrate as a precipitating agent, 97% of rhenium, nearly 60% of palladium, and over 10% of ruthenium can be recovered in solid form from an aqueous nitric acid solution. This recovery is selective relative to other elements present in the solution, as the precipitation percentages of other elements are mostly zero, or at least very low or extremely low.
[0062] The table also shows that, since rhenium is a good analog of technetium, a large portion of the technetium present in multimetallic aqueous solutions (such as the aqueous solution used in this experiment) can be recovered.
[0063] Example 4: Comparison of the rhenium recovery effects of a mixture of 1,10-phenanthroline and nickel(II) nitrate with a mixture of 1,10-phenanthroline and nickel(II) sulfate. Experiments were conducted to recover rhenium from an aqueous solution containing 2.1 g / L rhenium (added in the form of perrhenic acid HReO4) and 3 mol / L nitric acid.
[0064] Two experiments were conducted, the difference being the different reagent components added to the aqueous solution.
[0065] Reagent 1 was prepared by the following steps: 223 mg of 1,10-phenanthroline monohydrate and 109 mg of Ni(NO3)2 were mixed under stirring. Add 6H2O to 5 mL of water, stir for 2 hours, and then place the resulting mixture in an oven at 50°C for 48 hours to dehydrate it, thereby obtaining a dry powdered reagent.
[0066] Reagent 2 was prepared by the following steps: 446 mg of 1,10-phenanthroline monohydrate and 197 mg of nickel sulfate hexahydrate (NiSO4) were mixed under stirring. Add 6H2O (molar mass: 262.84 g / mol) to 5 mL of water, stir for 2 hours, and then place the resulting mixture in an oven at 50°C for 48 hours to dehydrate it, thereby obtaining a dry powdered reagent.
[0067] Both experiments were conducted under the same operating conditions, namely the same precipitation and precipitate collection conditions.
[0068] Each test consists of the following steps: 245 mg of one of the reagents is added to 10 mL of aqueous solution with stirring, and the resulting mixture is kept with stirring for 30 minutes, followed by solid-liquid separation by filtration.
[0069] The concentration of rhenium in the filtered liquid phase was measured by ICP-AES. For each experiment, the percentage of precipitated rhenium (hereinafter referred to as Re) was recorded. s (%) indicates that it is determined by formula (I) in Example 1 above.
[0070] The results of these experiments are shown in Table IV below.
[0071] Table IV
[0072] The table shows that using a mixture of 1,10-phenanthroline and nickel(II) nitrate as a precipitating agent can achieve a higher rhenium recovery rate than using a mixture of 1,10-phenanthroline and nickel(II) sulfate.
[0073] References RU 2513724 C1.
Claims
1. A process for the recovery of one or more metals selected from the group consisting of technetium, rhenium, ruthenium and palladium from an aqueous solution A, which comprises adding to said aqueous solution A a reagent to precipitate said one or more metals from the solution, and then collecting the precipitate thus formed, characterised in that, Said 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 according to claim 1, wherein said reagent is in the form of an aqueous solution comprising said mixture of 1,10-phenanthroline and a nickel (II) salt.
3. The method according to claim 1, wherein said reagent is in the form of an aqueous suspension whose microparticles comprise or consist of said mixture of 1,10-phenanthroline and a nickel (II) salt.
4. The method according to claim 1, wherein said reagent is in the form of a powder whose granules comprise or consist of said mixture of 1,10-phenanthroline and a nickel (II) salt.
5. The method according to any one of claims 1 to 4, wherein the molar ratio of 1,10- phenanthroline / nickel (II) salt in said reagent is between 2.5 and 5, preferably equal to 3.
6. The method according to any one of claims 1 to 5, wherein said reagent is added to said aqueous solution A in an amount such that said mixture of 1,10-phenanthroline and nickel (II) salt is in excess with respect to the stoichiometric conditions of the precipitation reaction of the one or more metals to be recovered.
7. The method according to any one of claims 1 to 6, wherein said reagent comprises or consists of a mixture of 1,10-phenanthroline and nickel (II) nitrate.
8. The method according to any one of claims 1 to 7, wherein said aqueous solution A is a fissile product aqueous solution resulting from the treatment of spent nuclear fuel.
9. The method according to claim 8, wherein said aqueous solution A comprises technetium, ruthenium and / or palladium, and from 1 mol / L to 3 mol / L of nitric acid.
10. The method according to any one of claims 1 to 7, wherein said aqueous solution A is an aqueous solution obtained by nitric acid pickling of industrial and / or municipal waste.
11. The method according to claim 10, wherein said aqueous solution A comprises ruthenium, palladium and / or rhenium, and up to 8 mol / L of nitric acid.