Smelting decontamination method for radioactive contaminated metal

Abstract

The invention relates to a radioactive contamination metal smelting decontamination method, which comprises the following steps of pretreating radioactive contamination metal, separating the radioactive contamination metal subjected to molten-state pretreatment through an electrochemical separation and / or magnetic separation technology, and separating the radioactive contamination metal by utilizing precipitation potential difference and Curie point difference between radionuclide and a metal main body, the metal main body and the radioactive contamination nuclide are separated, and a metal product after control releasing is obtained. According to the method provided by the invention, radionuclides and impurities in the radioactive pollution metal can be accurately separated, so that a metal product is effectively removed and controlled, effective recycling of waste metal in metal radioactive waste is realized, and the problems of storage pollution of the radioactive pollution metal and the like are solved. In addition, the method provided by the invention has the advantages that the operation process is simple, electrolysis raw materials are easy to obtain and low in price, the method is environment-friendly, and the operation cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of metal smelting decontamination, and in particular relates to a method for smelting decontamination of radioactively contaminated metal. Background Art

[0002] The large accumulation of radioactive metal waste is one of the key factors restricting the development of the nuclear industry. With the development of my country's decommissioning projects, a large amount of radioactive contaminated metals have been generated: zirconium (melting point 1852°C), platinum (melting point 1772°C), nickel (melting point 1453°C), gold (melting point 1064°C) and other metals and their alloys. Most of these scrap metals are currently stored in the factory, causing great storage pressure, and there are radiation risks and cross-contamination risks, which cannot meet the needs of waste safety management. At the same time, some early reactors have gradually entered the decommissioning stage. The decommissioning of reactors will also generate a large amount of metal waste, which will bring great storage pressure and radiation risks to the plant area, which is not conducive to the utilization of my country's resources and the sustainable development of nuclear energy.

[0003] At present, the nuclear industry often uses the smelting decontamination method. The main process is: adding metal raw materials containing nuclides into the reaction crucible, and removing radioactive impurities in the molten metal through oxidation-reduction and adsorption by mixing different decontaminants, and then slag separation. This method has the characteristics of low cost, etc. However, there are technical difficulties in the separation and purification process, such as the difficulty in separating some nuclides Co-60.

[0004] In the prior art, patent CN202111241478.X provides a method for smelting and decontaminating radioactive contaminated scrap metals, which includes the following steps: inspection, preparation, smelting, and testing. The method for making the decontaminant includes the following substances in mass percentage: CaO 10%-15%, Fe2O3 15%-25%, Al2O330%-40%, SiO2 10%-20%, and MgO 2%-5%. Patent CN92100288.2 discloses a method for smelting and decontaminating uranium-contaminated metals. The technical solution is to use an industrial frequency induction furnace as a smelting device, break the contaminated metal to be melted into small pieces, mix it with a flux, and then load it into the furnace together. The furnace is powered on and heated to 200-300°C higher than the melting point of the metal to be melted for smelting, so as to achieve the purpose of smelting and decontamination. The most prominent feature is the use of blast furnace slag from a steel plant as a flux. Patent CN115331861A discloses a method for decontamination, smelting and recycling of radioactive scrap metal, which includes the following steps: step 1: scrap metal pretreatment; step 2: pre-decontamination; step 3: scrap metal crushing and packaging; step 4: radioactive contaminated scrap metal smelting; step 5: product processing. The method of the present invention has good decontamination effect and high unlimited utilization rate, and has opened up a one-stop product process from radioactive scrap metal smelting to product production, realizing the true recycling of radioactive scrap metal. Summary of the invention

[0005] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for smelting and decontaminating radioactive contaminated metals. The purpose of decontaminating the metals can be achieved by adding the radioactive contaminated metals to molten salt for pretreatment, assembling an electrolytic cell for electrochemical separation and / or magnetically separating the molten metal. The method has the advantages of high recovery rate, maintaining metal properties, and simple operation.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: a method for smelting and decontaminating radioactive contaminated metal, the method comprising the following steps:

[0007] S1. Pretreatment of radioactive contaminated metal: After decontamination of the outer surface of the radioactive contaminated metal, the radioactive contaminated metal is cut, the cut radioactive contaminated metal and the molten salt are put into a crucible for smelting and decontamination, and the insoluble slag is separated to obtain the pretreated radioactive contaminated metal; the pretreated radioactive contaminated metal enters step S2 or S3;

[0008] S2, electrochemical separation: two electrodes are set in the crucible that continues to be heated to construct an electrolytic cell, and direct current is applied between the two electrodes, and the radioactive nuclides are gradually enriched and precipitated and accumulated on the electrodes; when the radioactive nuclides accumulate to a certain extent, the electrodes are removed and the radioactive nuclides are collected to obtain the radioactive contaminated metal after electrochemical separation treatment; if the radioactive contaminated metal after electrochemical separation treatment meets the clearance standard, a metal product after clearance is obtained; if the radioactive contaminated metal after electrochemical separation treatment does not meet the clearance standard, then enter step S3 for magnetic separation;

[0009] S3, magnetic separation: placing the crucible that continues to be heated in a magnetic separation device, the crucible containing the radioactive contaminated metal after pretreatment or the radioactive contaminated metal after electrochemical separation treatment, setting the heating temperature between the Curie point of the metal body of the radioactive contaminated metal and the Curie point of the radioactive nuclide, stopping the heating after the magnetic separation is continued for a set time, and cooling to obtain a metal solid after magnetic separation;

[0010] S4, cutting one or both ends of the metal solid enriched with radioactive nuclides and impurities after the magnetic separation, and obtaining the middle section of the metal solid after the magnetic separation as the metal product after release.

[0011] Furthermore, before step S1, a step of preparing molten salt is also included: selecting a molten salt raw material, grinding the molten salt raw material into a uniform molten salt raw material powder, and obtaining the molten salt.

[0012] Furthermore, the particle size of the molten salt raw material powder is less than 1 mm.

[0013] Further, in step S1, the molten salt is selected from a combination of one or more of CaF2, AlF3, MgF2, CaCl2, Al(NO3)3, MgCl2, and CaSiO4.

[0014] Further, in step S1, the metal body of the radioactive contaminated metal is a combination of one or more of different types of steel, aluminum, zirconium, copper, nickel, and gold;

[0015] The radioactive nuclides in the radioactive contaminated metal are a combination of one or more of uranium, cobalt and nickel.

[0016] Furthermore, in step S1, the method of decontaminating the outer surface of the radioactive contaminated metal includes wiping, sandblasting, and electrochemical decontamination.

[0017] Furthermore, in step S2, the material of the electrode is selected from one or more combinations of tungsten, molybdenum, platinum, graphite, and glassy carbon.

[0018] Further, in step S2, when two electrodes are set in the crucible to construct an electrolytic cell, electrochemical testing is performed to determine whether the performance of each device is stable; the electrochemical testing method includes one or a combination of cyclic voltammetry, open circuit instantaneous potentiometry, square wave voltammetry, constant potential electrolysis, and constant current electrolysis.

[0019] Furthermore, in step S2, electrolysis is performed by constant potential electrolysis, wherein the potential is in the range between the radioactive nuclide electrode potential and the metal main electrode potential of the radioactive contaminated metal, so that the radioactive nuclides and impurities are enriched and precipitated on the electrode.

[0020] Further, in step S3, the magnetic separation device is selected from one of a Helmholtz coil, a uniform magnetic field generator, and a permanent magnet system.

[0021] Furthermore, the crucible is made of ceramic or quartz.

[0022] Furthermore, the radioactivity of the metal product after clearance meets the national clearance standard in GB / T17567-2009.

[0023] The beneficial effects of the present invention are as follows: A method for smelting and decontaminating radioactive contaminated metals provided by the present invention comprises the following steps: pretreating the radioactive contaminated metals, and separating the radioactive contaminated metals pretreated in the molten state by electrochemical separation and / or magnetic separation technology, and using the precipitation potential difference and Curie point difference between the radioactive nuclides and the metal body to separate the metal body and the radioactive contaminated nuclides to obtain the metal product after clearance. In the present invention, the molten metal is used as the substance participating in the electrode reaction in the electrochemical separation, the upper molten salt is used as the electrolyte, and the metal such as molybdenum or high temperature resistant graphite is used as the electrode or connecting wire, and constant potential / constant current electrolysis is performed. After electrolysis in the molten salt, the electrode containing the radioactive nuclide is taken out; magnetic separation is to apply a uniform magnetic field at both ends of the horizontal or vertical axis of the molten metal, and cut off the two ends after cooling, that is, to obtain metal that meets the clearance standard in the smelting furnace. The present invention can accurately separate the radioactive nuclides and impurities in the radioactive contaminated metal, thereby effectively clearing the metal product, realizing the effective recycling of scrap metal in metal radioactive waste, and solving the problems of storage pollution of radioactive contaminated metals.

[0024] Compared with the existing water-based separation of radioactive nuclides, which has complex procedures and produces a large amount of secondary waste, the present invention uses an anhydrous dry method to treat radioactive contaminated metals, performs physical, chemical, electrical and / or magnetic treatment in the same container, and directly separates the radioactive nuclides from the metal body through the difference in potential and Curie point, so as to obtain metals with higher purity, and it is pollution-free to the environment, non-destructive to the metal body, and has a higher refining efficiency. In addition, the method provided by the present invention is treated and reacted under a molten salt layer at a relatively high temperature. The molten salt has a neutron shielding effect, which avoids the pollution hazard of radioactive nuclides, and the radioactive nuclides can be enriched in the subsequent electrical and / or magnetic separation process, thereby improving the safety of the treatment process. The method provided by the present invention has the advantages of simple operation process, easy availability and low price of electrolytic raw materials, environmental friendliness, and low operating cost, and is worthy of promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic flow chart of a method for smelting and decontaminating radioactive contaminated metal provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention are further clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The radioactive contaminated metal smelting and decontamination method provided in this embodiment applies electromagnetic separation technology to the decontamination of radioactive waste metals, and has the following advantages: (1) Electromagnetic separation technology is based on the magnetic difference between different substances in the magnetic field, and separates substances with different magnetic properties through the force of the magnetic field. This method can more effectively separate impurities and useful metals and improve the purity of the metal. (2) In the same time, electromagnetic separation technology usually only needs to consume less electrical energy, which is more advantageous in terms of energy consumption. (3) No harmful gas or waste residue is generated during the electromagnetic separation process, and the impact on the environment is relatively small.

[0028] like Figure 1 As shown, this embodiment provides a method for smelting and decontaminating radioactive contaminated metal, the method comprising the following steps:

[0029] S1. Pretreatment of radioactive contaminated metal: After decontamination of the outer surface of the radioactive contaminated metal, the radioactive contaminated metal is cut, the cut radioactive contaminated metal and the molten salt are put into a crucible for smelting and decontamination, and the insoluble slag is separated to obtain the pretreated radioactive contaminated metal; the pretreated radioactive contaminated metal enters step S2 for electrochemical separation or S3 for magnetic separation;

[0030] Optionally, in step S1, the metal body of the radioactive contaminated metal includes one or a combination of different types of steel, aluminum, zirconium, copper, nickel, gold, etc. The radioactive nuclides on the radioactive contaminated metal include one or a combination of uranium, cobalt, nickel, etc.

[0031] Specifically, before step S1, the method further includes the step of preparing molten salt: selecting a molten salt raw material, grinding the molten salt raw material into a uniform molten salt raw material powder, and obtaining the molten salt.

[0032] In the step of preparing molten salt, the molten salt uses different types of molten salt raw materials. By adjusting the types of molten salt raw materials and their composition ratios, molten salt with a melting point close to the melting point of the metal body of the radioactive contaminated metal can be accurately configured, thereby effectively reducing the molten salt consumption caused by evaporation and sublimation of the molten salt.

[0033] Optionally, the molten salt uses one or a combination of more than one of CaF2, AlF3, MgF2, CaCl2, Al(NO3)3, MgCl2, CaSiO4, etc. as the molten salt raw material.

[0034] Optionally, in the step of preparing the molten salt, when the metal body of the radioactive contaminated metal is stainless steel, the molten salt uses CaF2, AlF3 and MgF2 as molten salt raw materials, each molten salt raw material is ground into a uniform molten salt raw material powder, and the molten salt raw material powders are evenly mixed in a certain proportion (the proportion of each molten salt raw material powder is determined according to the specific stainless steel model) to obtain the molten salt CaF2-AlF3-MgF2.

[0035] Optionally, in the step of preparing the molten salt, when the metal main body of the radioactive contaminated metal is nickel, the molten salt raw material is CaSiO4. When the metal main body of the radioactive contaminated metal is gold, the molten salt raw material is CaCl2.

[0036] Specifically, in the step of preparing molten salt, the particle size of the molten salt raw material powder is less than 1 mm.

[0037] Step S1 includes the following specific steps: after a certain degree of decontamination treatment is performed on the outer surface of the radioactive contaminated metal, the radioactive contaminated metal is cut to a size suitable for being placed in a crucible in a heating furnace, and then the cut radioactive contaminated metal and the molten salt are put into the crucible in the heating furnace, heated until they are uniformly dissolved, and after heating for a predetermined time, the insoluble slag is removed by slag removal to obtain the pre-treated radioactive contaminated metal;

[0038] In step S1, the method for pre-treating the radioactive contaminated metal includes technical means such as external surface decontamination (wiping, sandblasting, electrochemical decontamination, etc.), cutting, smelting decontamination, etc. of the radioactive contaminated metal.

[0039] Specifically, in step S1, the method of decontaminating the outer surface of the radioactive contaminated metal includes wiping, sandblasting, electrochemical decontamination, etc.

[0040] Specifically, in step S1, the molten salt in a molten state serves as both a slag-forming agent and a conductive medium in the electrolytic cell, and can reduce radioactive nuclides from a high potential to a low potential, so as to facilitate enrichment and precipitation on the electrode.

[0041] S2, electrochemical separation: two electrodes are arranged in a crucible to construct an electrolytic cell, direct current is applied between the two electrodes, and radioactive nuclides and impurities are gradually enriched and precipitated and accumulated on the electrodes under the action of electrolysis; when the radioactive nuclides and impurities accumulate to a certain extent, the electrodes are removed and the radioactive nuclides are collected to obtain radioactive contaminated metals after electrochemical separation treatment; if the radioactive contaminated metals after electrochemical separation treatment meet the clearance standards, the metal products after clearance are obtained and directly recycled; if the radioactive contaminated metals after electrochemical separation treatment do not meet the clearance standards, the process proceeds to step S3 for magnetic separation;

[0042] Among them, when the radioactive nuclides and impurities accumulate on the electrode to the point where they are completely attached to the electrode surface, the potential curve can be seen through the operation of the electrochemical workstation. The accumulation amount is also determined empirically to remove the electrode and collect the radioactive nuclides. Generally, the electrode is removed and the radioactive nuclides are collected 4 to 40 hours after electrolysis.

[0043] Specifically, in step S2, the specific method of constructing the electrolytic cell is as follows: two suitable electrodes are set in the crucible, and appropriate electrochemical tests are performed to determine the stability of the performance of each device. Depending on the electrolysis requirements, it is sometimes necessary to add appropriate molten salt.

[0044] Optionally, the electrochemical testing method includes one or a combination of cyclic voltammetry, open circuit instantaneous potentiometry, square wave voltammetry, constant potential electrolysis or constant current electrolysis.

[0045] In step S2, the electrode material and the connecting wire material are one or a combination of tungsten, molybdenum, platinum, graphite, glassy carbon, etc. The shape of the electrode material or the connecting wire includes the following types: one or a combination of wire, column, basket, sheet, etc.

[0046] Optionally, electrolysis is performed by constant potential electrolysis, wherein the potential is between the radionuclide electrode potential and the target metal (metal body of radioactive contaminated metal) electrode potential, and the radionuclide and impurities are simultaneously enriched and precipitated on the electrode (for example, the radionuclide is reduced from a high-valent state to a simple substance or forms a low-valent oxide at the positive electrode, and the ions in the molten salt are oxidized from a low-valent state to a high-valent state at the negative electrode), which helps to obtain a target metal with higher purity. The direct current is a constant potential direct current and / or a constant current direct current.

[0047] In a specific embodiment, the electrode material is one or a combination of tungsten sheet, molybdenum sheet or platinum sheet, and the time node for replacing the tungsten sheet, molybdenum sheet or platinum sheet is determined according to the changes in the constant potential and / or constant current curve.

[0048] In a specific embodiment, when radioactive contaminated stainless steel is electrolyzed by constant potential electrolysis and the radionuclide is cobalt-60, a DC voltage of 2.4 to 3.2 V is applied between the two electrodes and the electrolysis is performed for 4 to 40 hours. When radioactive contaminated copper is electrolyzed by constant current electrolysis and the radionuclide is uranium-238, a DC current of -3 to 3A is applied between the two electrodes and the electrolysis is performed for 4 to 40 hours.

[0049] S3, magnetic separation: placing the crucible that continues to be heated in a magnetic separation device, the crucible containing the radioactive contaminated metal after pretreatment or the radioactive contaminated metal after electrochemical separation treatment, setting the heating temperature between the Curie point of the metal body of the radioactive contaminated metal and the Curie point of the radioactive nuclide, stopping the heating after the magnetic separation is continued for a set time, cooling to obtain a metal solid after magnetic separation, wherein the radioactive nuclide and impurities are enriched at one or both ends of the metal solid after magnetic separation, and the metal body of the radioactive contaminated metal is concentrated in the middle section of the metal solid after magnetic separation;

[0050] Optionally, in step S3, the magnetic separation device includes the following types: a Helmholtz coil, a uniform magnetic field generator, a permanent magnet system, etc., or a combination of more than one of them.

[0051] Optionally, in step S3, the molten radioactive contaminated metal is placed in a magnetic field, and the magnetic field parameters (such as magnetic field strength, magnetic field gradient, etc.) are adjusted so that the metal body of the radioactive contaminated metal and the radioactive nuclides are subjected to different magnetic field forces in the magnetic field, thereby achieving separation. This step is the core of the electromagnetic separation technology, and the direction of the magnetic separation can be selected from one of the horizontal direction and the vertical direction.

[0052] In step S3, the material of the crucible needs to have electromagnetic transparency. Electromagnetic separation technology relies on the effect of magnetic field on metal, so the crucible material should be electromagnetic transparent, that is, it will not interfere with the magnetic field or affect the magnetic field distribution. Non-metallic materials such as ceramics and quartz usually have good electromagnetic transparency, so the material of the crucible is one of ceramics or quartz.

[0053] S4. Cut one or both ends of the metal solid enriched with radioactive nuclides and impurities after the magnetic separation, and the obtained middle section of the metal solid after the magnetic separation is the metal product after the control is released, which meets the control standards.

[0054] Specifically, the metal product after release can be directly recycled as technical purity metal; wherein, the technical purity metal specifically refers to a purity of about 90%, corresponding to the purity of pig iron.

[0055] Specifically, in step S4, the clearance standard is: the radioactivity of the metal product after clearance meets the clearance standard in the national GB / T 17567-2009.

[0056] The method provided in this embodiment adopts electrochemical and / or magnetic separation means in a high-temperature molten state, and uses potential difference and Curie point difference to separate the metal body and radioactive contamination nuclides to obtain the final non-metallic product, which can accurately separate radioactive nuclides and impurities in radioactive contaminated metals, effectively release and control products, and solve the problems of storage pollution of radioactive contaminated metals. The existing water-based separation of radioactive nuclides has complicated procedures and produces a large amount of secondary waste. This embodiment uses an anhydrous dry method to treat radioactive contaminated metals, and performs physical, chemical, electrical and / or magnetic treatment in the same container. Through the difference in potential and Curie point, the radioactive nuclides are directly separated from the metal body, and a high-purity metal can be obtained, which is pollution-free to the environment, non-destructive to the metal body, and has a high refining efficiency. In addition, the method provided in this embodiment is processed and reacted under a molten salt layer at a relatively high temperature. The molten salt has a neutron shielding effect, which avoids the pollution hazard of radioactive nuclides, and the radioactive nuclides can be enriched in the subsequent electrical and / or magnetic separation process, which improves the safety of the treatment process.

[0057] In summary, the steps of the method provided in this embodiment are scientific and reasonable, complementary, and highly operational. They can effectively separate and enrich radionuclides in radioactive contaminated metals, without causing environmental pollution or being destructive to metals. They are low in cost, high in refining efficiency, and simplify the processing process, saving reagent consumption. The effect is remarkable and worthy of promotion and application.

[0058] The specific implementation modes of the present invention are further described below through examples.

[0059] Example 1 Radioactive contamination of Fe (radionuclide is cobalt-60)

[0060] S11. Pretreatment of radioactive contaminated metal: After the radioactive contaminated Fe is sandblasted on the surface, it is mechanically cut to meet the size and dimensions of the crucible. CaF2-AlF3-MgF2 molten salt is prepared, dried in a vacuum muffle furnace for 72 hours, and placed in a crucible with radioactive contaminated steel and heated at 1650°C. The insoluble slag is removed by slag removal to obtain the pretreated radioactive contaminated metal;

[0061] S12. Electrochemical separation: After the composition of the radioactive contaminated metal after pretreatment is uniform, two graphite rods are inserted into the crucible, one in the metal liquid surface and the other in the molten salt layer, with an inter-electrode distance of 30 mm. Then, the voltage is maintained at -2.0V to -2.4V for 10 minutes to remove impurities. After replacing the electrodes, they are maintained for 30 minutes and appropriate electrochemical tests are performed to determine the stability of the performance of each device. The constant potential electrolysis method is used to control the potential at -2.4V to -3.2V for 4 to 40 hours. The radioactive nuclide cobalt-60 is reduced from +3 valence at the cathode to a single substance or an iron-cobalt alloy deposited at the bottom of the cathode. The fluoride anions (F-) in the molten salt are discharged on the anode surface to form gaseous and solid carbon fluoride compounds CF x , where x represents the number of fluorine atoms, such as CF4 and C2F6; remove the electrode and collect the radioactive nuclide cobalt to obtain the radioactive contaminated metal after electrochemical separation treatment; the radioactive contaminated metal after electrochemical separation treatment exceeds 5.2Bq / g, which does not meet the clearance standard, and enters step S13;

[0062] S13, magnetic separation: continue to heat the radioactive contaminated metal after electrochemical separation to keep it in a molten state, and start cooling from 1600°C. Apply 1-5T magnetic field strength in the Helmholtz coil within the range of 770-1150°C (the Curie point of Fe is 770°C, and the Curie point of the radioactive nuclide cobalt is 1150°C) to perform magnetic separation to below 770°C for about 0.5 hour. After cooling, cut the radioactive nuclide cobalt enriched at one end of the metal solid after magnetic separation. The dose rate of the middle section of the metal solid after magnetic separation is 2.8Bq / g, which does not exceed 4Bq / g and meets the clearance standard, that is, the metal product after clearance is obtained, and the recovered metallic iron content is 87%.

[0063] Example 2 Radioactive contamination of Fe (radionuclide is nickel-63)

[0064] S21. Pretreatment of radioactive contaminated metal: After the radioactive contaminated Fe is sandblasted on the surface, it is mechanically cut to meet the size and dimensions of the crucible. CaSiO4 molten salt is prepared, dried in a vacuum muffle furnace for 72 hours, and placed in a crucible with radioactive contaminated Fe and heated at 1600°C. The insoluble slag is removed by slag removal to obtain the pretreated radioactive contaminated metal;

[0065] S22. Magnetic separation: After the composition of the pretreated radioactive contaminated metal is uniform, continue to heat the pretreated radioactive contaminated metal to keep it in a molten state, and cool it down from 1600°C. Within the range of 358-770°C (the Curie point of Fe is 770°C, and the Curie point of the radioactive nuclide nickel is 358°C), place it together with the crucible on a Helmholtz coil stand, apply a 1-5T magnetic field strength for magnetic separation for 1-2 hours, and after cooling, cut the radioactive nuclide nickel enriched at one end of the metal solid after magnetic separation. The radioactivity of the middle section of the metal solid after magnetic separation is 8000Bq / g, which does not exceed 10000Bq / g, and meets the clearance standard, that is, the metal product after clearance is obtained, and the recovered metallic iron content is 92%.

[0066] Example 3 Radioactive contamination Cu (radioactive nuclide is uranium-238)

[0067] S31. Pretreatment of radioactive contaminated metal: After the radioactive contaminated Cu is sandblasted on the surface, it is mechanically cut to meet the size and dimensions of the crucible. CaCl2 molten salt is prepared, dried in a vacuum muffle furnace for 72 hours, and placed in a crucible with the radioactive contaminated Cu and heated at 1100°C. The insoluble slag is removed by slag removal to obtain the pretreated radioactive contaminated metal;

[0068] S32. Electrochemical separation: After the composition of the radioactive contaminated metal after pretreatment is uniform, two molybdenum rods are inserted into the crucible as cathode and anode respectively, one is located in the metal liquid surface, and the other is located in the molten salt layer, with an inter-electrode distance of 30 mm. Then, the current is maintained at -2 to 2A for 10 minutes to remove impurities; after replacing the electrodes, it is maintained for 30 minutes, and appropriate electrochemical tests are carried out to determine the stability of the performance of each device; the constant current electrolysis method is used to control the current to -3 to 3A for 4 to 40 hours. The radioactive nuclide uranium is reduced from +6 valence to simple substance / alloy at the positive electrode, and the fluoride anion (F-) in the molten salt is discharged on the anode surface to form gaseous and solid carbon fluoride compounds CF x , wherein x represents the number of fluorine atoms, such as CF4 and C2F6; removing the electrode and collecting the radioactive nuclide uranium to obtain the radioactive contaminated metal after electrochemical separation treatment; the radioactivity of the radioactive contaminated metal after electrochemical separation treatment is 120Bq / g, not exceeding 200Bq / g, which meets the clearance standard, that is, the copper content in the metal product after clearance is 96%.

[0069] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for smelting and decontaminating radioactive contaminated metals, characterized in that: The method comprises the following steps: S1. Pretreatment of radioactive contaminated metal: After decontaminating the outer surface of the radioactive contaminated metal, the radioactive contaminated metal is cut, the cut radioactive contaminated metal and the molten salt are put into a crucible for smelting and decontamination, and the insoluble slag is separated to obtain the pretreated radioactive contaminated metal; The radioactive contaminated metal after pretreatment enters step S2 or S3; S2. Electrochemical separation: two electrodes are set in a continuously heated crucible to construct an electrolytic cell, and direct current is applied between the two electrodes. The radioactive nuclides are gradually enriched and precipitated on the electrodes. When the radioactive nuclides accumulate to a certain extent, the electrodes are removed and the radioactive nuclides are collected to obtain the radioactive contaminated metals after electrochemical separation. If the radioactive contaminated metals after electrochemical separation meet the clearance standards, the metal products after clearance are obtained. If the radioactive contaminated metals after electrochemical separation do not meet the clearance standards, proceed to step S3 for magnetic separation; S3, magnetic separation: placing the crucible that continues to be heated in a magnetic separation device, the crucible containing the radioactive contaminated metal after pretreatment or the radioactive contaminated metal after electrochemical separation treatment, setting the heating temperature between the Curie point of the metal body of the radioactive contaminated metal and the Curie point of the radioactive nuclide, stopping the heating after the magnetic separation is continued for a set time, and cooling to obtain a metal solid after magnetic separation; S4, cutting one or both ends of the metal solid enriched with radioactive nuclides and impurities after the magnetic separation, and obtaining the middle section of the metal solid after the magnetic separation as the metal product after release.

2. A method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: Before step S1, the method also includes the step of preparing molten salt: selecting a molten salt raw material, grinding the molten salt raw material into a uniform molten salt raw material powder, and obtaining the molten salt.

3. A method for smelting and decontaminating radioactive contaminated metal according to claim 2, characterized in that: The particle size of the molten salt raw material powder is less than 1 mm.

4. A method for smelting and decontaminating radioactive contaminated metal according to claim 2, characterized in that: In step S1, the molten salt is selected from one or more combinations of CaF2, AlF3, MgF2, CaCl2, Al(NO3)3, MgCl2, and CaSiO4.

5. The method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: In step S1, the metal body of the radioactive contaminated metal is a combination of one or more of different types of steel, aluminum, zirconium, copper, nickel, and gold; The radioactive nuclides in the radioactive contaminated metal are a combination of one or more of uranium, cobalt and nickel.

6. The method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: In step S1, the method of decontaminating the outer surface of the radioactively contaminated metal includes wiping, sandblasting, and electrochemical decontamination.

7. A method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: In step S2, the material of the electrode is selected from one or more combinations of tungsten, molybdenum, platinum, graphite, and glassy carbon.

8. The method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: In step S2, when two electrodes are set in the crucible to construct an electrolytic cell, electrochemical testing is performed to determine whether the performance of each device is stable; the electrochemical testing method includes one or a combination of cyclic voltammetry, open circuit instantaneous potentiometry, square wave voltammetry, constant potential electrolysis, and constant current electrolysis.

9. A method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: In step S2, electrolysis is performed by constant potential electrolysis, wherein the potential is in the range between the radioactive nuclide electrode potential and the metal main electrode potential of the radioactive contaminated metal, so that the radioactive nuclides and impurities are enriched and precipitated on the electrode.

10. The method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: In step S3, the magnetic separation device is selected from one of a Helmholtz coil, a uniform magnetic field generator, and a permanent magnet system.

11. A method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: The crucible is made of ceramic or quartz.

12. A method for smelting and decontaminating radioactive contaminated metal according to claim 1, characterized in that: The radioactivity of the metal product after clearance meets the national clearance standard in GB / T 17567-2009.

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