Closed-loop recovery method for unqualified sponge zirconium

Abstract

The invention discloses an unqualified sponge zirconium closed-loop recovery method, and relates to the technical field of nuclear fuel circulation and materials.The method comprises the following steps that S1, irregular and porous unqualified sponge zirconium is converted into zirconium oxide blocks or particles with stable chemical components and uniform physical forms through a high-temperature oxidation reaction; s2, processing zirconium oxide blocks or particles obtained after oxidation into powder meeting the feeding requirement of a chlorination process through a ball milling process; and S3, mixing the qualified zirconium oxide powder subjected to ball milling with a carbon-containing reducing agent according to a set proportion, putting the mixed material into a reaction device for chlorination reaction, and condensing a product to realize efficient recovery of ZrCl4. According to the method provided by the invention, the treatment problem caused by the porous and irregular physical properties of the unqualified sponge zirconium can be solved, the high purity and the quality consistency of a final product are ensured, and the method can be directly embedded into a recovery process of an existing production process, so that the high-valued recycling of the unqualified sponge zirconium is realized.

Description

Technical Field

[0001] This invention belongs to the field of nuclear fuel cycle and materials technology, specifically relating to a method for recycling and reusing substandard products (mainly surface oxides and filter media) generated during the production of nuclear-grade sponge zirconium. Background Technology

[0002] Zirconium, due to its excellent thermal neutron transparency and corrosion resistance, is a key material for nuclear reactor fuel cladding. With the rapid development of my country's nuclear power industry, the demand for nuclear-grade sponge zirconium continues to grow. In the domestic production process of nuclear-grade sponge zirconium, approximately 20% of the zirconium ingots are substandard during the peeling and filtration stages. Currently, these substandard products can only be disposed of at a low price of about 85,000 yuan / ton, far below the market price of 480,000 yuan / ton for qualified sponge zirconium, and even lower than the procurement cost of the raw material ZrO2. Based on the current annual production capacity of 200 tons, the direct economic loss reaches 2.45 million yuan annually; if the production capacity is increased to the planned 2,000 tons / year, the annual loss will reach as high as 24.5 million yuan, constituting a huge "value gap" for enterprises.

[0003] Currently, research on the recycling of substandard sponge zirconium mainly focuses on returning it to the starting point of zircon sand chlorination and purification. However, this faces challenges such as a long process flow, high energy consumption, and poor economic efficiency. Simply crushing and directly returning it to the chlorination process is problematic because the irregular shape and significant differences in physical properties between the substandard product and the main raw material can easily lead to uneven chlorination, low reaction efficiency, and difficulty in effectively removing the accumulated metallic impurities such as Cr, Ni, and Mn, which can contaminate the entire batch of product and affect the quality of the main product line. Even if some material is recovered, the recovery rate and product purity are difficult to guarantee consistently, making the entire recycling process economically and technically infeasible.

[0004] Therefore, there is an urgent need to find an economical and efficient recycling process that can be directly integrated into existing production processes to achieve high-value reuse of substandard sponge zirconium. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a closed-loop recycling method for substandard sponge zirconium. This method can solve the processing difficulties caused by the porous and irregular physical properties of substandard sponge zirconium, ensure the high purity and quality consistency of the final product, and can be directly integrated into the recycling process of existing production processes to achieve high-value reuse of substandard sponge zirconium.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A closed-loop recycling method for substandard sponge zirconium includes the following steps:

[0008] S1. Irregular, porous, substandard sponge zirconium is transformed into zirconium oxide blocks or particles with stable chemical composition and uniform physical morphology through high-temperature oxidation reaction.

[0009] S2. The zirconia blocks or particles obtained after oxidation are processed into powder that meets the feeding requirements of the chlorination process through ball milling.

[0010] S3. The qualified zirconium oxide powder after ball milling is mixed with a carbon-containing reducing agent in a set ratio. The mixture is placed in a reaction device for chlorination reaction. The product is condensed to achieve efficient recovery of ZrCl4.

[0011] Furthermore, in the closed-loop recycling method for substandard sponge zirconium described above, the oxidizing atmosphere in step S1 is a mixture of nitrogen and oxygen, wherein the oxygen volume concentration ranges from 20% to 80%.

[0012] Furthermore, in the closed-loop recycling method for substandard sponge zirconium described above, the oxidation temperature range in step S1 is 500℃~1000℃.

[0013] Furthermore, in the closed-loop recycling method for substandard sponge zirconium described above, the oxidation temperature range in step S1 is 700℃~1000℃.

[0014] Furthermore, in the closed-loop recycling method for substandard sponge zirconium described above, the oxidation reaction time in step S1 is 1-8 hours.

[0015] Furthermore, in the closed-loop recycling method for unqualified sponge zirconium described above, a ball mill is used in step S2. The optimal combination of ball milling process parameters is determined by adjusting the rotation speed, milling time, material, size ratio, and loading amount of the grinding media.

[0016] Furthermore, in the closed-loop recycling method for unqualified sponge zirconium described above, the optimal combination of ball milling process parameters determined in step S2 is as follows: ball mill speed is 300 rpm, ball milling time is 2 h, and grinding ball material is zirconium oxide.

[0017] Furthermore, in the closed-loop recycling method for unqualified sponge zirconium as described above, the proportion of -200 mesh particles in the ball milling product in step S2 is ≥95%, and the proportion of -400 mesh particles is ≥65%.

[0018] Furthermore, in the closed-loop recovery method for unqualified sponge zirconium described above, step S3 specifically involves: placing the mixture in a fixed-bed or fluidized-bed chlorination furnace to react with chlorine gas, with the reaction formula being: ZrO2 + 2Cl2 + 2C → ZrCl4 + 2CO. By precisely controlling the chlorination temperature, chlorine flow rate, and carbon ratio, and utilizing the significant difference in volatility between the target product and the impurity element chlorides, efficient separation and deep impurity removal are achieved.

[0019] Furthermore, in the closed-loop recycling method for substandard sponge zirconium described above, the chlorination reaction temperature in step S3 is set to 800-1000℃.

[0020] Compared with existing technologies, the closed-loop recycling method for substandard sponge zirconium provided by this invention has the following beneficial effects:

[0021] This method utilizes the synergistic effect of high-temperature oxidation, customized ball milling, and chlorination purification. In the high-temperature oxidation stage, irregular, porous sponge zirconium is transformed into uniform and stable zirconium oxide. In the ball milling stage, an adaptive process is used to treat the zirconium oxide to a specific particle size that meets the requirements of existing chlorination feedstocks. In the chlorination stage, the difference in volatility characteristics between impurity chlorides and ZrCl4 is utilized to achieve deep purification. Through precise design and synergistic effects of each step, this process solves the processing challenges posed by the porous and irregular nature of substandard sponge zirconium, ensuring high purity and consistent quality of the final product. Furthermore, this process can be directly integrated into existing production processes for recycling, enabling the high-value reuse of substandard sponge zirconium, significantly reducing the generation and disposal costs of solid waste for enterprises, and providing a stable and low-cost internal recycling zirconium resource for the production of nuclear-grade zirconium materials.

[0022] In summary, this process has the advantages of high recovery rate, high product purity, good compatibility with existing production lines, and low operating cost, making it suitable for large-scale industrial recycling. Attached Figure Description

[0023] To further illustrate the above and other advantages and features of this application, the specific embodiments of this application will be described in more detail below with reference to the accompanying drawings. The accompanying drawings, together with the following detailed description, are included in and form a part of this specification. It should be understood that these drawings only depict typical examples of this application and should not be considered as limiting the scope of this application.

[0024] Figure 1 The flowchart below shows a closed-loop recycling method for substandard sponge zirconium provided in a specific embodiment of the present invention. Detailed Implementation

[0025] Exemplary embodiments of this application will be described below with reference to the accompanying drawings. For clarity and brevity, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the development of any such actual embodiment to achieve the developer's specific goals, such as complying with constraints related to the system and business, and these constraints may vary depending on the implementation. Furthermore, it should be understood that while development work can be very complex and time-consuming, such development work is merely a routine task for those skilled in the art who benefit from the content of this application.

[0026] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the equipment structure and / or processing steps closely related to the solution according to this application are shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0027] The embodiments or examples disclosed below are used to implement this application. To simplify the disclosure of this application, the components and methods of specific examples are described below. Of course, they are merely examples and are not intended to limit this application.

[0028] To address the problems of high economic losses, lack of efficient recovery methods, and incompatibility with main processes in the disposal of substandard nuclear-grade sponge zirconium in existing technologies, this invention provides a closed-loop recovery process combining high-temperature oxidation, customized ball milling, and chlorination purification, known as "oxidation-ball milling-chlorination." The process flow diagram is shown below. Figure 1 As shown, the method mainly includes the following steps:

[0029] S1. Irregular, porous, substandard sponge zirconium is transformed into chemically stable and physically uniform zirconium oxide blocks or particles through a high-temperature oxidation reaction.

[0030] The high-temperature oxidation stage aims to transform irregular, porous, substandard sponge zirconium into chemically stable and physically uniform zirconium oxide (ZrO2), laying the foundation for subsequent ball milling and chlorination.

[0031] The high-temperature oxidation reaction mechanism is as follows: In the lower temperature range (500-700℃), the oxidation reaction is controlled by chemical reaction and is mild; in the higher temperature range (700-1000℃), the oxidation reaction rate is controlled by the diffusion of oxygen ions in the oxide layer, and the reaction is vigorous and thorough, significantly shortening the processing time. The oxidation atmosphere is a mixture of nitrogen and oxygen. Studies have shown that introducing an appropriate amount of nitrogen (20%-80%) has a significant "catalytic" effect on the oxidation process. The mechanism is that a small amount of zirconium nitride (ZrN) mesophase is formed in the early stage of oxidation. When this phase is converted to ZrO2 in subsequent oxidation, it induces microcracks in the dense oxide layer, providing more channels for the internal diffusion of oxygen, thereby accelerating the overall oxidation kinetics and ensuring that even irregular thick-walled materials can achieve uniform and thorough oxidation.

[0032] S2. The oxidized zirconia blocks or particles are processed into powder that meets the feeding requirements of the chlorination process through ball milling.

[0033] The customized ball milling stage aims to process ZrO2 blocks or particles obtained after oxidation, which have high hardness and may contain sintered hard agglomerates, into fine powder that meets the feed requirements of existing chlorination processes. Since the recovered ZrO2 differs from the virgin ZrO2 obtained from calcined Zr(OH)4 in hardness and brittleness, directly using existing ball milling parameters would lead to low efficiency, excessive energy consumption, and substandard particle size. Therefore, this invention develops a customized ball milling process. By systematically adjusting the ball mill's rotation speed, milling time, and the material, size ratio, and loading of the grinding media (such as zirconia balls), the optimal parameter combination is determined, ensuring that the proportion of -200 mesh (75μm) particles in the ball milling product is ≥95%, and the proportion of -400 mesh (38μm) particles is ≥65%. This particle size distribution ensures that the material has sufficient specific surface area in the chlorination furnace for rapid reaction, while effectively avoiding the loss of fine powder due to airborne particles and system blockage.

[0034] S3. The qualified zirconium oxide powder after ball milling is mixed with a carbon-containing reducing agent in a set ratio. The mixture is placed in a reaction device for chlorination reaction. The product is condensed to achieve efficient recovery of ZrCl4.

[0035] The chlorination purification stage is crucial for achieving high purity in the entire recovery process. Qualified ZrO2 powder after ball milling is mixed with a carbon-containing reducing agent in a specific ratio. In a fixed-bed or fluidized-bed chlorination furnace at 800-1000℃, the mixture reacts with chlorine gas, the reaction being: ZrO2 + 2Cl2 + 2C → ZrCl4 + 2CO. This invention achieves efficient separation and deep impurity removal by precisely controlling the chlorination temperature, chlorine flow rate, and carbon ratio, utilizing the significant difference in volatility between the target product and the chlorides of impurity elements. The sublimation temperature of ZrCl4 is approximately 331℃, while the chlorides of key impurity elements, such as Cr, Ni, and Mn, have extremely low vapor pressures at the ZrCl4 sublimation temperature, making them difficult to volatilize. Therefore, within the condensation temperature range for collecting ZrCl4 (typically controlled at 300-400℃), most of these impurity chlorides remain in the residue, thus achieving efficient separation of impurity chlorides from gaseous ZrCl4. This targeted design ensures that the content of key impurities (such as Cr≤0.007%, Ni≤0.004%, Mn≤0.003%) in the final recycled ZrCl4 product does not exceed the qualified product standard.

[0036] Through the close integration and synergistic optimization of the above three stages, this invention ultimately achieves the goal of a comprehensive zirconium recovery rate of no less than 90% in substandard sponge zirconium, and forms a complete material closed loop of "substandard product → zirconium oxide → zirconium chloride → qualified sponge zirconium". Compared with the prior art, the beneficial effects of this process are reflected in:

[0037] 1) Compared with selling defective products directly at low prices, this process transforms them into high-value qualified products, directly eliminating economic losses and reducing dependence on external raw material purchases;

[0038] 2) A complete recycling process of "oxidation-ball milling-chlorination" for porous sponge zirconium is proposed. Oxidation is used to control and stabilize physical properties, customized ball milling is used to solve the feed compatibility problem, and optimized chlorination is used to achieve deep impurity removal, forming a complete technical closed loop.

[0039] 3) This process is highly compatible with existing sponge zirconium production lines. Recycled materials can be directly returned to the main process as intermediate products without the need to build new complex back-end processing facilities. It has low investment costs and is easy to implement and promote.

[0040] Example 1

[0041] The process for recycling substandard sponge zirconium using this embodiment comprises the following steps:

[0042] 1) Take 1 kg of surface oxides and filter materials (unqualified sponge zirconium) generated during the production process of CNNC Crystal Ring Zirconium Industry, place them in a high-temperature furnace, and carry out high-temperature oxidation for 4 hours in an air atmosphere (about 21% oxygen). The oxidation temperatures are set at 500℃, 600℃, 700℃, 800℃, 900℃, and 1000℃ respectively, and completely convert them into zirconium oxide.

[0043] 2) The zirconia product obtained in step 1 was fed into a laboratory ball mill. The milling time was controlled at 2 hours and the rotation speed at 300 rpm. Zirconia grinding balls were used to obtain a powder product. The particle size distribution was measured by a laser particle size analyzer and met the requirements of -200 mesh ≥ 95% and -400 mesh ≥ 65%.

[0044] 3) Mix the qualified zirconium oxide powder obtained in step 2 with excess carbon powder, place the mixture in a tube furnace, and introduce chlorine gas at 800°C to carry out a chlorination reaction. Control the reaction conditions and collect the condensed ZrCl4 product.

[0045] 4) The collected ZrCl4 products were sampled and analyzed. The contents of Cr, Ni and Mn were determined by ICP-MS. The results were all lower than the qualified sponge zirconium standard (Cr≤0.007%, Ni≤0.004%, Mn≤0.003%).

[0046] Example 2

[0047] The process for recycling substandard sponge zirconium using this embodiment comprises the following steps:

[0048] 1) Take 1 kg of unqualified sponge zirconium and oxidize it at 800℃ for 4 h. Set nitrogen and oxygen ratios of 0-100%, 10-90%, 20-80%, 30-70%, 40-60%, and 50-50% respectively to study the effects of different atmospheres on oxidation rate and product properties.

[0049] 2) Zirconia products are ball-milled using existing production line ball milling equipment. By adjusting the feed rate and ball milling time, the product particle size reaches the target of ≥95% for -200 mesh.

[0050] 3) The ball-milled zirconium oxide was fed into a small chlorination furnace for chlorination reaction. The resulting ZrCl4 was reduced, and the sponge zirconium sample was tested. Its chemical composition and mechanical properties met the requirements of qualified products.

[0051] Example 3

[0052] The process for recycling substandard sponge zirconium using this embodiment comprises the following steps:

[0053] 1) Take 100 kg of substandard sponge zirconium and oxidize it at a high temperature of 900℃ for 4 hours in an atmosphere of 50% nitrogen + 50% oxygen.

[0054] 2) The oxidation products are ball-milled using a dedicated ball milling production line, with strict control of process parameters to ensure that the powder after ball milling has a particle size of ≥97% for -200 mesh and ≥70% for -400 mesh.

[0055] 3) The ball-milled zirconium oxide powder was mixed with coke and fed into an industrial chlorination furnace for chlorination. The generated ZrCl4 was collected and condensed to obtain high-purity ZrCl4 crystals. Based on overall material balance, the total recovery rate of zirconium in this batch of substandard sponge zirconium reached 92%.

[0056] 4) The recovered high-purity ZrCl4 was mixed with ZrCl4 from the main process line and subjected to magnesothermic reduction to successfully prepare nuclear-grade sponge zirconium products.

[0057] This invention provides a closed-loop recycling method for substandard sponge zirconium, utilizing the synergistic effects of high-temperature oxidation, customized ball milling, and chlorination purification. In the high-temperature oxidation stage, irregular, porous sponge zirconium is transformed into uniform and stable zirconium oxide. In the ball milling stage, an adaptive process is used to treat the zirconium oxide to a specific particle size that meets the requirements of existing chlorination feedstocks. In the chlorination stage, the difference in volatility characteristics between impurity chlorides and ZrCl4 is utilized to achieve deep purification. This process, through precise design and synergistic effects of each step, solves the processing challenges posed by the porous and irregular nature of substandard sponge zirconium, ensuring high purity and consistent quality of the final product. Furthermore, this process can be directly integrated into existing production processes, enabling high-value reuse of substandard sponge zirconium, significantly reducing the generation and disposal costs of solid waste for enterprises, and providing a stable and low-cost internal recycling zirconium resource for nuclear-grade zirconium material production. In summary, this process has advantages such as high recovery rate, high product purity, good compatibility with existing production lines, and low operating costs, making it suitable for large-scale industrial recycling.

[0058] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A closed-loop recycling method for substandard sponge zirconium, comprising the following steps: S1. Irregular, porous, substandard sponge zirconium is transformed into zirconium oxide blocks or particles with stable chemical composition and uniform physical morphology through high-temperature oxidation reaction. S2. The zirconia blocks or particles obtained after oxidation are processed into powder that meets the feeding requirements of the chlorination process through ball milling. S3. The qualified zirconium oxide powder after ball milling is mixed with a carbon-containing reducing agent in a set ratio. The mixture is placed in a reaction device for chlorination reaction. The product is condensed to achieve efficient recovery of ZrCl4.

2. The closed-loop recycling method for substandard sponge zirconium according to claim 1, characterized in that, In step S1, the oxidizing atmosphere is a mixture of nitrogen and oxygen, wherein the oxygen volume concentration ranges from 20% to 80%.

3. The closed-loop recycling method for substandard sponge zirconium according to claim 2, characterized in that, The oxidation temperature range in step S1 is 500℃~1000℃.

4. The closed-loop recycling method for substandard sponge zirconium according to claim 3, characterized in that, The oxidation temperature range in step S1 is 700℃~1000℃.

5. The closed-loop recycling method for substandard sponge zirconium according to claim 4, characterized in that, The oxidation reaction in step S1 lasts for 1-8 hours.

6. The closed-loop recycling method for substandard sponge zirconium according to any one of claims 1-5, characterized in that, In step S2, a ball mill is used. The optimal combination of ball mill process parameters is determined by adjusting the ball mill's rotation speed, milling time, grinding media material, size ratio, and loading amount.

7. The closed-loop recycling method for substandard sponge zirconium according to claim 6, characterized in that, The optimal combination of ball milling process parameters determined in step S2 is as follows: ball mill speed is 300 rpm, ball milling time is 2 h, and grinding ball material is zirconium oxide.

8. The closed-loop recycling method for substandard sponge zirconium according to claim 7, characterized in that, In step S2, the proportion of -200 mesh particles in the ball milling product is ≥95%, and the proportion of -400 mesh particles is ≥65%.

9. The closed-loop recycling method for substandard sponge zirconium according to claim 1, characterized in that, Step S3 specifically involves placing the mixture in a fixed-bed or fluidized-bed chlorination furnace to react with chlorine gas. The reaction formula is: ZrO2 + 2Cl2 + 2C → ZrCl4 + 2CO. By precisely controlling the chlorination temperature, chlorine flow rate, and carbon ratio, and utilizing the significant difference in volatility between the target product and the impurity element chlorides, efficient separation and deep impurity removal are achieved.

10. The closed-loop recycling method for substandard sponge zirconium according to claim 9, characterized in that, In step S3, the chlorination reaction temperature is set to 800-1000℃.

Images