Fused salt extractive distillation separation method of zirconium-hafnium tetrachloride

Abstract

The invention provides a fused salt extractive distillation separation method of zirconium-hafnium tetrachloride, which is particularly suitable for a fused salt extractive distillation separation device. When the fused salt extractive distillation separation is carried out, main components such as a distillation tower, a sublimator, a reflux tank, a condenser, a reboiler and a circulating tank are connected, then a zirconium and hafnium chloride raw material to be separated and chloride salt for distillation are filled, and finally the device is started to realize the separation of zirconium and hafnium chlorides under the distillation condition. The separation device and method have good usability and process adaptability, the prepared zirconium tetrachloride and hafnium tetrachloride meet the use requirements in the fields of atomic energy, aerospace, high-power laser, integrated circuits and the like, and reference and guidance are provided for research, development and application of zirconium and hafnium tetrachloride molten salt rectification separation technology and equipment.

Description

Technical Field

[0001] The present application relates to the technical field of chemical separation of metal compounds, and in particular to a molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride. Background Art

[0002] Zirconium (Zr) and hafnium (Hf) have good corrosion resistance, high temperature resistance and radiation resistance. They are widely used in atomic energy, aerospace, high-power lasers, integrated circuits and other fields. They are important strategic metal resources.

[0003] Currently, zirconium and hafnium separation technologies are divided into two categories: wet and pyrolysis. Pyrolysis primarily utilizes the redox reaction characteristics, volatility, and subtle differences between zirconium and hafnium compounds at high temperatures, as well as subtle differences in electrochemical properties, to achieve separation. Specifically, the molten salt extraction and distillation process within the pyrolysis technology has achieved industrial production. This technology utilizes the volatility differences between zirconium tetrachloride and hafnium in molten salt to achieve distillation separation.

[0004] However, currently available literature lacks systematic research on the process and equipment design for the molten salt distillation separation of zirconium and hafnium tetrachloride. The technical details, equipment, and parameters of this process remain unclear, and the research and development, as well as the industrial application, of this technology and equipment for molten salt distillation separation of zirconium and hafnium tetrachloride lack theoretical and practical guidance. Therefore, to achieve a breakthrough in this technology, a precise and feasible molten salt extraction and distillation method for zirconium and hafnium tetrachloride separation is needed. Summary of the Invention

[0005] To solve the above problems, the present application provides a molten salt extraction and distillation separation method for zirconium and hafnium tetrachloride. The method has clear steps and detailed details, and the reaction conditions and process parameters are clear. It is particularly suitable for molten salt extraction and distillation separation devices, providing reference and guidance for achieving technological breakthroughs.

[0006] In a first aspect, the present application provides a molten salt extraction and distillation separation method for zirconium and hafnium tetrachloride, the method being applicable to a molten salt extraction and distillation separation device, the device comprising: Distillation tower, sublimator, reflux tank, condenser, reboiler, circulation tank and gas preheater; The method comprises: S1. Connect the distillation tower to the reflux tank and the reboiler respectively, then connect the reflux tank to the condenser, connect a gas pipeline to the distillation tower, insert one end of the gas pipeline away from the distillation tower into the reflux tank, then connect the circulation tank to the reboiler, connect a molten salt circulation pipeline to the circulation tank, connect the liquid outlet end of the molten salt circulation pipeline to the reflux tank, connect a steam pipeline to the molten salt circulation pipeline, then connect one end of the steam pipeline to the gas preheater and the other end to the bottom of the distillation tower; S2. After the zirconium hafnium tetrachloride is loaded into the sublimator, the sublimator is connected to the distillation tower, and the chloride is loaded into the reboiler. The device is evacuated to a vacuum degree of -0.1 MPa, and nitrogen is filled in to replace the air in the device; S3, controlling the temperature of the sublimator to 200° C. to 300° C., the temperature of the circulation tank to 480° C. to 600° C., the temperature of the reflux tank to 300° C. to 400° C., the temperature of the molten salt circulation pipeline to 300° C. to 400° C., the temperature of the gas preheater to 500° C. to 650° C., and the temperature of the reboiler to 400° C. to 600° C., so that the chloride is in a molten state in the distillation tower to obtain molten salt; S4, delivering an appropriate amount of the molten salt to the circulation tank, charging the gas preheater with a shielding gas having a pressure of 0.3 atm-1.0 atm, the shielding gas pressing the molten salt in the circulation tank along the molten salt circulation pipeline into the reflux tank, and the molten salt flows into the distillation tower along the reflux tank; S5. Raising the temperature of the sublimator to 400° C. to 450° C. to vaporize the zirconium and hafnium tetrachloride. The vaporized zirconium and hafnium tetrachloride enter the distillation tower and undergo gas-liquid phase mass and heat transfer with the molten salt. The separated zirconium tetrachloride is enriched in the molten salt in the reboiler, and the hafnium tetrachloride-rich vapor enters the condenser. S6. After the distillation treatment is completed, the reboiler and the circulation tank are cooled to 250° C. to 400° C., the molten salt in the reflux tank is discharged into the reboiler and the circulation tank, and the hafnium tetrachloride-rich vapor in the distillation tower is condensed in the condenser to obtain an enriched hafnium tetrachloride; S7. Raise the temperature of the reboiler to 550° C. to 600° C. to vaporize the zirconium tetrachloride dissolved in the molten salt, and then fill the gas preheater with nitrogen. The nitrogen transports the vaporized zirconium tetrachloride to the condenser for recovery.

[0007] Preferably, in step S4, when the liquid level of the molten salt in the reboiler is greater than 1 / 2, an appropriate amount of the molten salt is transported to the circulation tank. After the molten salt is stored in the circulation tank for 5 min to 10 min, a small amount of zirconium and hafnium chloride dissolved in the molten salt is vaporized and sent to the steam pipeline. The vaporized zirconium and hafnium chloride enters the distillation tower for distillation treatment.

[0008] Preferably, in step S5, the vaporized zirconium hafnium tetrachloride enters the distillation tower and diffuses toward the top of the distillation tower, comes into gas-liquid contact with the molten salt, and enters the reflux tank after multi-stage refining, wherein a portion of the hafnium tetrachloride-rich vapor dissolves in the molten salt in the reflux tank, and another portion of the undissolved hafnium tetrachloride-rich vapor enters the condenser and is condensed, and the molten salt in the distillation tower flows to the bottom of the tower and comes into gas-liquid contact with the rising vapor rich in zirconium tetrachloride to concentrate the zirconium tetrachloride.

[0009] Preferably, in step S3, the temperature of the sublimator is controlled to be 250°C~280°C, the temperature of the circulation tank is controlled to be 500°C~550°C, the temperature of the reflux tank is controlled to be 320°C~350°C, the temperature of the molten salt circulation pipeline is controlled to be 320°C~350°C, the temperature of the gas preheater is controlled to be 550°C~600°C, and the temperature of the reboiler is controlled to be 450°C~500°C.

[0010] Preferably, the temperature of the top of the distillation tower is the same as that of the reflux tank, and the temperature of the bottom of the distillation tower is the same as that of the reboiler; The temperature in the distillation tower decreases step by step from the bottom to the top.

[0011] Preferably, the chloride includes at least two of potassium chloride, aluminum chloride, cuprous chloride, sodium chloride, and ferric chloride.

[0012] Preferably, in step S2, the mass ratio of the zirconium hafnium tetrachloride to the chloride is 1:(10-100).

[0013] Preferably, in step S4, the protective gas is nitrogen or argon; The flow rate of the protective gas is 0.1 L / min~5 L / min.

[0014] Preferably, in step S4, when the molten salt flows into the distillation tower along the reflux tank, the flow rate of the molten salt is 0.05 L / min to 2 L / min; The number of plates in the distillation tower is 20 to 30.

[0015] In a second aspect, the present application provides zirconium tetrachloride and hafnium tetrachloride obtained by the molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride described in the first aspect.

[0016] In summary, this application includes at least one of the following beneficial technical effects: 1. The present application provides a molten salt extraction and distillation separation method for zirconium and hafnium tetrachloride, which is particularly suitable for a molten salt extraction and distillation separation device. The device has a simple connection method, is easy to operate, and has strong applicability. The present application uses protective gas as the conveying medium. After being heated by a gas preheater, the molten salt is pressurized from a circulation tank to a reflux tank to achieve reflux of the molten salt distillation. After the zirconium and hafnium chloride is vaporized, it enters a distillation tower and contacts the molten salt for distillation treatment. The method has a simple and convenient operation process and high separation efficiency, and solves the problems of unclear technical details and process equipment in the current molten salt distillation separation technology of zirconium and hafnium tetrachloride, providing a good reference and powerful guidance for achieving technological breakthroughs. 2. The device applicable to the method provided in this application includes a gas preheater, which is used to use the heated protective gas to pressurize the molten salt along the molten salt circulation pipeline into the reflux tank, and use the protective gas to control the circulation of the molten salt. Furthermore, by controlling the pressure and flow of the protective gas, the molten salt can be circulated simply and efficiently, thereby solving the problems of conventional conveying pumps being unable to convey high-temperature corrosive melts, the low transmission efficiency of gas lift pumps, and the high-temperature reliability degradation of molten salt pumps during long-term operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0018] Figure 1 A flow chart of a molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride proposed in an embodiment of the present application is shown; Figure 2 The schematic diagram of the structure of the molten salt extraction and distillation separation device proposed in the embodiment of the present application is shown; Figure 3 The minimum theoretical number of plates required to achieve the target separation effect (hafnium content in zirconium <0.01%, zirconium content in hafnium <0.5%) at different reflux ratios is shown using the phase equilibrium equation and operating line equation in Table 2 in the embodiments of the present application and the plate-by-plate calculation method.

[0019] Description of reference numerals: 1. Distillation tower; 11. Gas pipeline; 12. Distillation section; 13. Stripping section; 14. Feed inlet; 15. Throttle valve; 2. Sublimator; 3. Reflux tank; 4. Condenser; 41. Vacuum pump interface; 5. Reboiler; 6. Circulation tank; 61. Steam pipeline; 62. Molten salt circulation pipeline; 7. Gas preheater; 8. Heating furnace; 9. Molten salt emptying tank. DETAILED DESCRIPTION

[0020] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] In the drawings, the sizes of components, layer thicknesses, or regions may be exaggerated for clarity. Therefore, any implementation of the present disclosure is not necessarily limited to the dimensions shown in the drawings, and the shapes and sizes of components in the drawings do not reflect true proportions. Furthermore, the drawings schematically illustrate idealized examples, and any implementation of the present disclosure is not limited to the shapes or values ​​shown in the drawings.

[0022] Related technologies for zirconium and hafnium separation include wet and pyrolysis. Wet solvent extraction, exemplified by MIBK and other methods, is the most widely used technology for zirconium and hafnium separation. Westinghouse Electric and Huachang Electric in the United States, as well as domestic companies such as China National Nuclear Corporation (CNNC) Weike, China National Nuclear Corporation (CNNC) Jinghuan, and Nanjing Youtian all use wet solvent extraction to separate zirconium and hafnium. However, this wet solvent extraction technology is associated with significant environmental pollution, high production costs, and lengthy production processes.

[0023] Fire-processed zirconium and hafnium separation technologies primarily exploit the redox reaction characteristics, volatility, and subtle differences between zirconium and hafnium compounds at high temperatures, as well as subtle differences in electrochemical properties. These technologies include the Newnham process, the Chandler process, the Flengas process, the Xiao process, molten salt extraction and distillation, high-pressure distillation, and selective electrolysis. However, only the molten salt extraction and distillation process has achieved industrial production. This technology exploits the volatility differences between zirconium tetrachloride and hafnium in molten salt to achieve distillation separation. Since hafnium tetrachloride is more volatile than zirconium tetrachloride, hafnium tetrachloride concentrates at the top of the distillation column, while zirconium tetrachloride concentrates at the bottom. Compared to wet extraction, fire-processed molten salt extraction and distillation offers reduced environmental pollution and lower production costs. The separation of raw materials and products can be directly integrated into the existing carbon chlorination and magnesium thermal reduction distillation steps in the production process for zirconium and hafnium metals, significantly shortening the zirconium and hafnium manufacturing process and reducing production costs. French company Cezos is the only company in the world to have mastered this technology and achieved industrial production of nuclear-grade zirconium tetrachloride and hafnium. However, due to the unique nature and sensitivity of zirconium and hafnium in its applications, publicly available literature rarely contains process parameters and details regarding the molten salt distillation separation process. Furthermore, the domestic zirconium and hafnium industry is still in its infancy in developing molten salt distillation technology. With the continuous development of strategic emerging sectors in my country, such as energy, electronics, and aerospace, and the increasing demands for environmental protection and sustainable development, the zirconium and hafnium industry is also facing industrial upgrading. Compared to wet solvent extraction, zirconium and hafnium molten salt distillation offers advantages in terms of reducing the generation of "three wastes," streamlining production processes, and reducing chemical reagent consumption. Therefore, developing molten salt distillation separation technology for zirconium and hafnium in my country is essential for the industry's efficient, green, and sustainable development.

[0024] At present, the process and technical details of the molten salt distillation separation technology of zirconium and hafnium, as well as the design and operating parameters of the distillation equipment are not clear, and there is an urgent need to carry out technical process and equipment research and development.

[0025] Based on the above problems, the invention concept proposed in this application is: by building a distillation device, obtaining key process parameters, and optimizing the process parameters, the molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride is made more systematic, the technical details are clearer, and the separation efficiency is improved.

[0026] See also Figure 1 , Figure 1 The flow chart of a molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride proposed in an embodiment of the present application is shown, which specifically includes: The method is applicable to a molten salt extraction and distillation separation device, which includes: Distillation tower, sublimator, reflux tank, condenser, reboiler, circulation tank and gas preheater; Methods include: S1. Connect the distillation tower to the reflux tank and the reboiler respectively, then connect the reflux tank to the condenser, connect the gas line to the distillation tower, insert the end of the gas line away from the distillation tower into the reflux tank, then connect the circulation tank to the reboiler, connect the molten salt circulation line to the circulation tank, connect the liquid outlet end of the molten salt circulation line to the reflux tank, connect the steam line to the molten salt circulation line, then connect one end of the steam line to the gas preheater and the other end to the bottom of the distillation tower; S2. After the zirconium hafnium tetrachloride is loaded into the sublimator, the sublimator is connected to the distillation column, and the chloride is loaded into the reboiler. The device is evacuated to a vacuum degree of -0.1 MPa, and then the air in the device is replaced by nitrogen; S3. Controlling the temperature of the sublimator to 200°C-300°C, the temperature of the circulation tank to 480°C-600°C, the temperature of the reflux tank to 300°C-400°C, the temperature of the molten salt circulation pipeline to 300°C-400°C, the temperature of the gas preheater to 500°C-650°C, and the temperature of the reboiler to 400°C-600°C, so that the chloride is in a molten state in the distillation tower to obtain molten salt; S4. A suitable amount of molten salt is transported to a circulation tank, and a protective gas having a pressure of 0.3 atm-1.0 atm is charged into the gas preheater. The protective gas presses the molten salt in the circulation tank into the reflux tank along the molten salt circulation pipeline, and the molten salt flows into the distillation tower along the reflux tank; S5. Raise the temperature of the sublimator to 400°C~450°C to vaporize the zirconium and hafnium tetrachloride. The vaporized zirconium and hafnium tetrachloride enter the distillation tower to conduct gas-liquid mass and heat transfer with the molten salt. The separated zirconium tetrachloride is enriched in the molten salt in the reboiler, and the hafnium tetrachloride-rich vapor enters the condenser. S6. After the distillation treatment is completed, the reboiler and the circulation tank are cooled to 250°C to 400°C, the molten salt in the reflux tank is discharged into the reboiler and the circulation tank, and the hafnium tetrachloride-rich vapor in the distillation tower is condensed in the condenser to obtain an enriched hafnium tetrachloride; S7. Raise the temperature of the reboiler to 550°C~600°C to vaporize the zirconium tetrachloride dissolved in the molten salt, and then fill the gas preheater with nitrogen. The nitrogen will transport the vaporized zirconium tetrachloride to the condenser for recovery.

[0027] In specific implementation, when performing molten salt extraction and distillation separation, the device is first installed, and then the device is used to achieve molten salt extraction and distillation separation. This application utilizes the difference in vapor pressure of zirconium and hafnium tetrachloride in chloride molten salt to enrich the more volatile hafnium tetrachloride at the top of the distillation tower, while the less volatile zirconium tetrachloride is enriched at the bottom of the distillation tower, specifically dissolved in the molten salt in the reboiler, to achieve the separation of zirconium and hafnium. This method system is complete and simple to operate. It can be used for the research of molten salt extraction and distillation separation processes and equipment, and can also be scaled up for the preparation and production of nuclear-grade zirconium and hafnium chloride. Its scope of application is wider and broader.

[0028] In some embodiments, see Figure 2 , shows a schematic structural diagram of the molten salt extraction and distillation separation device proposed in an embodiment of the present application, step S1 specifically includes: The distillation tower 1 is composed of a rectifying section 12 and a stripping section 13 connected to each other, wherein the top of the rectifying section 12 is connected to the first end of the reflux tank 3, the bottom of the stripping section 13 is connected to the first end of the reboiler 5, and the second end of the reflux tank 3 is connected to the condenser 4; The side of the rectifying section 12 close to the reflux tank 3 is connected to the gas pipeline 11, and the end of the gas pipeline 11 away from the rectifying section 12 extends into the reflux tank 3; The first end of the circulation tank 6 is connected to the second end of the reboiler 5, the second end of the circulation tank 6 is connected to the molten salt circulation pipeline 62, and the liquid outlet end of the molten salt circulation pipeline 62 is connected to the second end of the reflux tank 3; One end of the molten salt circulation pipeline 62 close to the circulation tank 6 is connected to the steam pipeline 61. The steam pipeline 61 is a four-way pipe. The first end of the steam pipeline 61 is connected to the gas preheater 7, and the second end is connected to the bottom of the stripping section 13; the third end is connected to the molten salt circulation pipeline 62, and the fourth end is connected to the circulation tank 6. In some embodiments, each component of the above device is placed in a corresponding heating furnace 8 to facilitate temperature control. The connection method of the device is simple, more systematic, easy to operate, and highly applicable.

[0029] In specific implementation, the sublimator 2 is connected to the connection between the distillation section 12 and the stripping section 13 and is communicated with the distillation tower 1 so as to transport the vaporized zirconium and hafnium tetrachloride to the distillation tower 1 for distillation treatment.

[0030] In some embodiments, the total number of stages of the distillation tower 1 is set to 20 to 30, and the distillation tower 1 is provided with a plurality of feed ports 14 connected to the sublimator 2 from top to bottom. Since hafnium tetrachloride evaporates more easily, when preparing hafnium tetrachloride of higher purity, the feed position is selected closer to the reboiler 5, and the number of plates of the distillation section 12 is relatively increased to evaporate as much hafnium tetrachloride as possible, so that the vapor flows upward and the hafnium tetrachloride therein is increasingly concentrated with each plate, thereby obtaining a higher purity. Zirconium tetrachloride is more difficult to volatilize. When obtaining zirconium tetrachloride of higher purity, the feed position is selected closer to the reflux tank 3, and the number of plates of the stripping section 13 is relatively increased, so that the liquid flows downward and the zirconium tetrachloride therein is gradually concentrated, thereby obtaining zirconium tetrachloride of higher purity.

[0031] In some embodiments, the molten salt circulation pipeline 62, the gas pipeline 11 and the steam pipeline 61 are also arranged in the heating furnace 8 to insulate the liquid or gas in the pipeline, so that the pipeline always remains in a liquid or gas state to ensure smooth distillation.

[0032] In some embodiments, the liquid level of the molten salt in the reflux tank 3 is higher than the end of the gas pipeline 11 extending into the reflux tank 3 to ensure that the vaporized zirconium and hafnium tetrachloride can contact the molten salt for distillation.

[0033] In some embodiments, a vacuum pump interface 41 is provided at the upper end of the condenser 4. After the interface 41 is connected to the vacuum pump, the vacuum pump is started to enhance the diffusion effect of the steam.

[0034] In some embodiments, the condenser 4 is provided with an opening connected to the distillation tower 1. After the distillation is completed, the condenser 4 and the sublimator 2 are removed, and the condenser 4 is installed at the position of the original sublimator 2. The material recovered in the condenser 4 is then transported to the distillation tower 1 for secondary distillation and purification to improve the purity of the separated product.

[0035] In some embodiments, the third end of the circulation tank 6 is connected to a molten salt emptying tank 9. When the gas in the molten salt is fully extracted, all the molten salt is discharged into the molten salt emptying tank 9 for cooling. When the next test is performed, the cooled molten salt is discharged into the reboiler 5 to achieve the repeated use of the molten salt.

[0036] In specific implementation, after the reboiler 5 is dismantled, the molten salt draining tank 9 is installed at the original position of the reboiler 5, so that the molten salt can be reused repeatedly.

[0037] In some embodiments, a throttle valve 15 is provided near the reflux tank 3 of the distillation tower 1. By controlling the throttle valve 15, the flow rate of the molten salt in the reflux tank 3 can be more accurately controlled to achieve a better reflux ratio and improve the separation efficiency.

[0038] In some embodiments, in step S2, the sublimator is placed in a glove box with a water and oxygen content of less than 1 ppm, and zirconium hafnium tetrachloride is then loaded into the sublimator. This reduces oxidation reactions of the raw materials during the loading process, ensures the stability of their chemical and physical properties, and reduces contamination of the raw materials by other impurities (such as water vapor and dust), thereby improving the purity of the raw materials.

[0039] In some embodiments, step S2 further includes: Load the sublimator and reboiler separately in a glove box with a water and oxygen content of less than 1 ppm. This minimizes deliquescence of the raw materials during loading, ensures their chemical and physical stability, and reduces contamination from other impurities (such as water vapor and dust), further improving raw material purity. After loading, install the reboiler and sublimator in their respective locations.

[0040] In some embodiments, in step S4, when the liquid level of the molten salt in the reboiler is greater than 1 / 2, an appropriate amount of molten salt is transported to a circulation tank. After the molten salt is stored in the circulation tank for 5 min to 10 min, a small amount of zirconium and hafnium chloride dissolved in the molten salt is vaporized and sent to the steam pipeline. The vaporized zirconium and hafnium chloride enters the distillation tower for distillation treatment.

[0041] By setting up a steam pipeline, a small amount of zirconium and hafnium tetrachloride enriched at the bottom of the tower can be collected and re-transported to the distillation tower for separation, which helps to improve the comprehensive recovery rate of zirconium and hafnium chloride.

[0042] In some embodiments, in step S5, the vaporized zirconium hafnium tetrachloride enters the distillation tower and diffuses toward the top of the distillation tower, comes into gas-liquid contact with the molten salt, and enters the reflux tank after multi-stage refining. A portion of the hafnium tetrachloride-rich vapor dissolves in the molten salt in the reflux tank, and another portion of the undissolved hafnium tetrachloride-rich vapor enters the condenser and is condensed. The molten salt in the distillation tower flows to the bottom of the tower and comes into gas-liquid contact with the rising vapor rich in zirconium tetrachloride to concentrate the zirconium tetrachloride.

[0043] By setting up a gas pipeline, part of the vaporized zirconium and hafnium tetrachloride is diverted to balance the gas pressure of the distillation tower, avoiding liquid flooding in the distillation tower to a certain extent, so that the distillation process can proceed more smoothly.

[0044] In some embodiments, in step S3, the sublimator temperature is controlled to be 250°C~280°C, the circulation tank temperature is 500°C~550°C, the reflux tank temperature is 320°C~350°C, the molten salt circulation pipeline temperature is 320°C~350°C, the gas preheater temperature is 550°C~600°C, and the reboiler temperature is 450°C~500°C.

[0045] In a specific implementation, after preheating the sublimator, the zirconium hafnium tetrachloride reaches or approaches its vaporization temperature, so that it vaporizes more easily and quickly in the subsequent heating and vaporization process, which helps to accelerate the distillation process and improve the overall separation efficiency.

[0046] In practice, the purpose of heating the circulation tank is to: 1) strip the zirconium and hafnium chloride dissolved in the molten salt, return it to the distillation tower, and produce it as a product; and 2) maintain the molten salt in a liquid state so that the conveying gas (i.e., shielding gas) can press the liquid chloride into the reflux tank, forming a stable reflux.

[0047] The purpose of heating the reflux tank is to ensure that the chloride in the reflux tank is liquid, but its temperature should be lower than that of the circulation tank, so that zirconium tetrachloride can be more dissolved in the molten salt and flow downward, and hafnium tetrachloride can be better evaporated in the form of steam.

[0048] The purpose of heating the molten salt circulation pipeline is to ensure that the chloride transported to the reflux tank remains in a molten state, so that the temperature of the transported molten salt and the molten salt entering the reflux tank are the same, avoiding the temperature difference affecting the solubility and selectivity of the molten salt and enhancing the effect of extraction distillation.

[0049] The heating gas preheater can preheat the decompressed cold gas (i.e., shielding gas) to prevent the cold gas from coming into contact with the molten salt, causing the molten salt to solidify or the temperature to drop, resulting in poor fluidity.

[0050] The purpose of heating the reboiler is to make the zirconium and hafnium chloride dissolved in the molten salt form rising vapor, which is used to concentrate the descending molten salt. The heating temperature is controlled at 450 ℃ ~ 500 ℃ to obtain the appropriate rising vapor flow rate and pressure, and promote sufficient bubbling contact between the gas and liquid phases.

[0051] In some embodiments, the temperature of the top of the distillation column is the same as that of the reflux tank, and the temperature of the bottom of the distillation column is the same as that of the reboiler; The temperature in the distillation tower decreases gradually from the bottom to the top. Due to the different volatility of zirconium tetrachloride and hafnium tetrachloride in molten salt, the gradually decreasing temperature distribution allows the more volatile hafnium tetrachloride to be enriched in the lower temperature area (top of the tower), while the less volatile zirconium tetrachloride is enriched in the higher temperature area (bottom of the tower), thereby promoting the effective separation of zirconium tetrachloride and hafnium tetrachloride.

[0052] In some embodiments, the chloride comprises at least two of potassium chloride, aluminum chloride, cuprous chloride, sodium chloride, and ferric chloride.

[0053] Preferably, the chlorides are potassium chloride and aluminum chloride. Aluminum chloride can react with potassium chloride at high temperatures to form a KAlCl4 molten salt. KAlCl4 molten salt has the advantages of a low melting point, low viscosity, low vapor pressure, high solubility for zirconium and hafnium chloride, and good stripping properties for zirconium and hafnium chloride, thus facilitating efficient distillation separation of zirconium and hafnium.

[0054] In some embodiments, in step S2, the mass ratio of zirconium hafnium tetrachloride to chloride is 1:(10-100).

[0055] By controlling the mass ratio, it is possible to ensure a relatively wide reflux ratio adjustment range in the distillation process and avoid excessive chloride usage, which results in low difficulty of zirconium and hafnium chloride in molten salt and difficulty in stripping, and the molten salt pump is prone to high-temperature reliability degradation during long-term operation.

[0056] In some embodiments, in step S4, the protective gas is nitrogen or argon; The flow rate of protective gas is 0.1 L / min~5 L / min.

[0057] The protective gas is set to nitrogen because in step S2, the remaining air in the device is replaced with nitrogen, but it is more preferred to use argon for replacement and protection because the specific gravity of argon is greater than that of air, which makes it easier to replace the air cleanly and reduce the introduction of other impurity gases.

[0058] In the embodiment of the present application, the reflux of the molten salt distillation is controlled by the circulation of the molten salt, and the circulation of the molten salt is controlled by the flow rate of the shielding gas. Therefore, by reasonably setting the flow rate of the shielding gas, the reflux ratio can be adjusted to achieve simple and efficient circulation of the molten salt, thereby solving the problems of conventional conveying pumps being unable to convey high-temperature corrosive melts, low transmission efficiency of gas lift pumps, and decreased high-temperature reliability during long-term operation of molten salt pumps.

[0059] In some embodiments, in step S4, when the molten salt flows into the distillation tower along the reflux tank, the flow rate of the molten salt is 0.05 L / min to 2 L / min; The number of plates in the distillation tower is 20 to 30.

[0060] During specific implementation, in step S4, after the molten salt enters the reflux tank, the flow rate of the molten salt is controlled to 0.05 L / min~2 L / min. After the molten salt forms a stable liquid flow in the distillation tower, step S5 is performed. The stable molten salt liquid flow can ensure uniform heat transfer in all parts of the distillation tower, which helps to reduce heat loss and temperature fluctuations, thereby improving the thermal efficiency of the entire distillation process; after performing step S5, the contact area between the gas and liquid phases in the tower can be increased, the heat exchange effect can be enhanced, and the separation and purification of the substances in the tower can be accelerated. The stable molten salt liquid flow also helps to maintain the balance of the gas and liquid phases in the tower and reduce the occurrence of backmixing.

[0061] The present application also provides zirconium tetrachloride and hafnium tetrachloride obtained by the above-mentioned molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride.

[0062] The zirconium tetrachloride and hafnium tetrachloride separated by the method of the embodiment of the present application can be used in technical fields such as atomic energy, aerospace, high-power lasers, and integrated circuits.

[0063] In order to enable those skilled in the art to more clearly understand the present application, a molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride of the present application is now described in detail through the following examples.

[0064] Example First, the embodiment of the present application uses the vapor pressure data of zirconium tetrachloride and hafnium tetrachloride in KAlCl4 molten salt to perform process design, and calculates the core process parameters such as the number of theoretical plates and reflux ratio required for the target separation effect (hafnium content in zirconium <0.01%, zirconium content in hafnium <0.5%).

[0065] Table 1 shows the relative volatility in the temperature range of 350°C to 500°C calculated using the vapor pressure data of zirconium tetrachloride and hafnium tetrachloride in molten salt.

[0066] Table 1. Relative volatility of zirconium hafnium tetrachloride with different mole fractions of raw materials at different temperatures

[0067] It can be seen from Table 1 that the relative volatility changes with the changes in mole fraction and temperature. When the mole fraction increases, the relative volatility increases significantly, which means that in actual operation, increasing the feed rate while keeping the reflux ratio unchanged and properly controlling the temperature will help achieve efficient separation.

[0068] Table 2 shows the operating line equations for the zirconium-hafnium molten salt distillation process at different reflux ratios calculated based on the relative volatility data in Table 1.

[0069] Table 2. Operating line equations for the distillation of zirconium and hafnium molten salt at different reflux ratios

[0070] According to Table 2, as the reflux ratio increases, the slope of the operating line of the distillation section increases, thereby increasing the mass transfer driving force. Under the same theoretical plate number, the composition of the distillate (i.e., the enriched liquid after the hafnium tetrachloride at the top of the tower is condensed) is closer to the target product, thereby improving the separation efficiency. When the reflux ratio increases, the slope of the operating line of the distillation section becomes smaller, the mass transfer driving force increases, which is also conducive to the further separation of impurities. It can also reduce the hafnium content in the bottom enriched liquid (i.e., the molten salt enriched with zirconium tetrachloride in the reboiler) and improve the purity of the enriched zirconium tetrachloride.

[0071] Table 3 shows the minimum number of theoretical plates required to achieve the target separation effect (hafnium content in zirconium <0.01%, zirconium content in hafnium <0.5%) at different reflux ratios, calculated using the Fenske equation-Gilliland diagram method. Figure 3 The minimum number of theoretical plates required to achieve the target separation effect (hafnium content in zirconium <0.01%, zirconium content in hafnium <0.5%) at different reflux ratios is shown in the embodiments of the present application using the phase equilibrium equation and operating line equation in Table 2 and a plate-by-plate calculation method.

[0072] Table 3. Theoretical plate number calculated using the Gilliland diagram

[0073] According to the O'Connell model, the overall efficiency of the distillation tower is about 0.42, that is, when R / Rmin is 1.5-3.0, the actual number of plates required is 250-338. If the middle plate is used as the feed plate, 125-169 stages are required in both the distillation section and the stripping section to achieve the target separation effect.

[0074] The embodiments of this application are based on Table 1, Table 2, Table 3 and Figure 3 The obtained theory and calculation method are implemented in steps 1 to 3 as follows: Example 1 Step 1: Connect the distillation tower to the reflux tank, then connect the reflux tank to the condenser, connect the gas pipeline to the distillation tower, insert the end of the gas pipeline away from the distillation tower into the reflux tank, connect the molten salt circulation pipeline to the circulation tank, connect the liquid outlet end of the molten salt circulation pipeline to the reflux tank, connect the steam pipeline to the molten salt circulation pipeline, then connect one end of the steam pipeline to the gas preheater and the other end to the bottom of the distillation tower. After connection, place each component in the corresponding heating furnace; Step 2: Using zirconium hafnium tetrachloride with a hafnium content of 2% as a molten salt distillation raw material, in a glove box with a water and oxygen content of less than 1 ppm, take 100 g of zirconium hafnium tetrachloride and 2 kg of chloride salt, and load them into a sublimator and a reboiler, respectively. Connect the sublimator to the feed position in the middle of the distillation tower, connect the reboiler to the bottom of the distillation tower, and connect the circulation tank to the reboiler. Place the connected sublimator and reboiler in the corresponding heating furnace, respectively, and then evacuate the device to vacuum. After the vacuum reaches -0.1 MPa, use nitrogen to replace the air in the washing device. Step 3: Use a heating furnace to heat the sublimator to 250°C, the circulation tank to 550°C, the reflux tank to 350°C, the molten salt circulation pipeline to 350°C, the gas preheater to 600°C, the condenser to room temperature, and the reboiler to 500°C to melt the chloride to obtain molten salt. The top temperature of the distillation tower is controlled to be consistent with the reflux tank temperature, the bottom temperature is controlled to be consistent with the reboiler temperature, and the middle temperature is gradually cooled from the bottom to the top of the tower at 50°C / m according to the temperature difference between the top and bottom of the tower of 150°C; Step 4: 3 / 4 of the molten salt in the reboiler is transported to the circulation tank, and then nitrogen with a pressure of 0.6 atm is injected into the gas preheater. The nitrogen flow rate is set to 0.1 L / min, and 2 / 3 of the molten salt in the circulation tank is pressed into the reflux tank. The molten salt flow rate of the reflux tank is controlled to 0.05 L / min. Step 5. After the molten salt flow in the distillation tower stabilizes, the sublimator is heated to 450°C to vaporize the zirconium and hafnium tetrachloride. The vaporized zirconium and hafnium tetrachloride enters the distillation tower and undergoes distillation treatment with the molten salt. During the distillation process, whenever the liquid level of the molten salt in the reboiler exceeds 1 / 2, 3 / 4 of the molten salt is discharged into the circulation tank, which is kept in the circulation tank for 5 minutes to strip the dissolved zirconium and hafnium chloride and return it to the distillation tower along the steam pipeline. Then, 2 / 3 of the molten salt is pressed into the reflux tank, and it is ensured that the liquid level of the reflux tank is higher than the gas pipeline at the top of the tower. The separated zirconium tetrachloride flows into the reboiler and dissolves in the molten salt, and the hafnium tetrachloride enters the condenser. Step 6: After the distillation treatment is completed, the temperature of the reboiler and the circulation tank is lowered to 350°C, the molten salt in the reflux tank is discharged into the reboiler and the circulation tank, and enriched hafnium tetrachloride is obtained in the condenser; Step 7: Then replace the condenser, raise the temperature of the reboiler and the circulation tank to 550°C, fill the gas preheater with high-purity nitrogen, evaporate the zirconium tetrachloride enriched in the molten salt and transport it to the condenser for condensation, and recover zirconium tetrachloride.

[0075] Chemical composition analysis showed that the hafnium tetrachloride enriched at the top of the tower in Example 1 had a hafnium content of 3.15%, and the hafnium tetrachloride enriched at the bottom of the tower had a hafnium content of 1.72%, proving that after one distillation treatment, the zirconium and hafnium tetrachlorides had been significantly separated.

[0076] Example 2 Step 1: Connect the distillation tower to the reflux tank, then connect the reflux tank to the condenser, connect the gas pipeline to the distillation tower, insert the end of the gas pipeline away from the distillation tower into the reflux tank, connect the molten salt circulation pipeline to the circulation tank, connect the liquid outlet end of the molten salt circulation pipeline to the reflux tank, connect the steam pipeline to the molten salt circulation pipeline, then connect one end of the steam pipeline to the gas preheater and the other end to the bottom of the distillation tower. After connection, place each component in the corresponding heating furnace; Step 2: Using zirconium hafnium tetrachloride with a hafnium content of 2% as a molten salt distillation raw material, in a glove box with a water and oxygen content of <1 ppm, take 500 g of zirconium hafnium tetrachloride and 5 kg of chloride salt, and load them into a sublimator and a reboiler, respectively. Connect the sublimator to the feed position in the middle of the distillation tower, connect the reboiler to the bottom of the distillation tower, and connect the circulation tank to the reboiler. Place the connected sublimator and reboiler in the corresponding heating furnace, respectively, and then evacuate the device to vacuum. After the vacuum reaches -0.1 MPa, use nitrogen to replace the air in the washing device. Step 3: Use a heating furnace to heat the sublimator to 280°C, the circulation tank to 500°C, the reflux tank to 330°C, the molten salt circulation pipeline to 320°C, the gas preheater to 550°C, the condenser to room temperature, and the reboiler to 550°C to melt the chloride to obtain molten salt. The top temperature of the distillation tower is controlled to be consistent with the reflux tank temperature, the bottom temperature is controlled to be consistent with the reboiler temperature, and the middle temperature is gradually cooled from the bottom to the top of the tower at 50°C / m according to the temperature difference of 120°C between the top and bottom of the tower; Step 4: 3 / 4 of the molten salt in the reboiler is transported to the circulation tank, and then nitrogen with a pressure of 1.0 atm is injected into the gas preheater. The nitrogen flow rate is set to 5 L / min, and 2 / 3 of the molten salt in the circulation tank is pressed into the reflux tank. The molten salt flow rate of the reflux tank is controlled to 0.1 L / min. Step 5: After the flow rate of the molten salt in the distillation tower stabilizes, the sublimator is heated to 400°C to vaporize the zirconium and hafnium tetrachloride. The vaporized zirconium and hafnium tetrachloride enters the distillation tower and undergoes distillation treatment with the molten salt. During the distillation process, whenever the liquid level of the molten salt in the reboiler exceeds 1 / 2, 3 / 4 of the molten salt is discharged into the circulation tank, which is kept in the circulation tank for 10 minutes to strip the dissolved small amount of zirconium and hafnium chloride and return it to the distillation tower along the steam pipeline. Then, 2 / 3 of the molten salt is pressed into the reflux tank, and it is ensured that the liquid level of the reflux tank is higher than the gas pipeline at the top of the tower. The separated zirconium tetrachloride flows into the reboiler and dissolves in the molten salt, and the hafnium tetrachloride enters the condenser. Step 6: After the distillation treatment is completed, the temperature of the reboiler and the circulation tank is lowered to 350° C., the molten salt in the reflux tank is discharged into the reboiler and the circulation tank, and hafnium tetrachloride enriched at the top of the tower is obtained in the condenser; Step 7: Then replace the condenser, raise the temperature of the reboiler and the circulation tank to 550°C, and then fill the gas preheater with high-purity nitrogen to evaporate the zirconium tetrachloride enriched in the molten salt and transport it to the condenser for condensation to recover zirconium tetrachloride.

[0077] According to chemical composition analysis, the hafnium content of the hafnium tetrachloride enriched at the top of the tower in Example 2 was 4.05%, and the hafnium content of the zirconium tetrachloride enriched at the bottom of the tower was 1.68%.

[0078] Example 3 Step 1: Connect the distillation tower to the reflux tank, then connect the reflux tank to the condenser, connect the gas pipeline to the distillation tower, insert the end of the gas pipeline away from the distillation tower into the reflux tank, connect the molten salt circulation pipeline to the circulation tank, connect the liquid outlet end of the molten salt circulation pipeline to the reflux tank, connect the steam pipeline to the molten salt circulation pipeline, then connect one end of the steam pipeline to the gas preheater and the other end to the bottom of the distillation tower. After connection, place each component in the corresponding heating furnace; Step 2: Using zirconium hafnium tetrachloride with a hafnium content of 2% as a molten salt distillation raw material, in a glove box with a water and oxygen content of <1 ppm, take 300 g of zirconium hafnium tetrachloride and 4.5 kg of chloride salt, and load them into a sublimator and a reboiler, respectively. Connect the sublimator to the feed position in the middle of the distillation tower, connect the reboiler to the bottom of the distillation tower, and connect the circulation tank to the reboiler. Place the connected sublimator and reboiler in the corresponding heating furnace, respectively, and then evacuate the device to vacuum. After the vacuum reaches -0.1 MPa, use nitrogen to replace the air in the washing device; Step 3: Use a heating furnace to heat the sublimator to 280°C, the circulation tank to 550°C, the reflux tank to 340°C, the molten salt circulation pipeline to 350°C, the gas preheater to 600°C, the condenser to room temperature, and the reboiler to 520°C to melt the chloride to obtain molten salt. The top temperature of the distillation tower is controlled to be consistent with the reflux tank temperature, the bottom temperature is controlled to be consistent with the reboiler temperature, and the middle temperature is gradually cooled from the bottom to the top of the tower at 50°C / m according to the temperature difference between the top and bottom of the tower of 150°C; Step 4: 3 / 4 of the molten salt in the reboiler is transported to the circulation tank, and then nitrogen with a pressure of 1.0 atm is injected into the gas preheater. The nitrogen flow rate is set to 1.5 L / min, and 2 / 3 of the molten salt in the circulation tank is pressed into the reflux tank. The molten salt flow rate of the reflux tank is controlled to 0.08 L / min. Step 5. After the flow rate of the molten salt in the distillation tower stabilizes, the sublimator is heated to 420°C to vaporize the zirconium and hafnium tetrachloride. The vaporized zirconium and hafnium tetrachloride enters the distillation tower for distillation with the molten salt. During the distillation process, whenever the liquid level of the molten salt in the reboiler exceeds 1 / 2, 3 / 4 of the molten salt is discharged into the circulation tank. The circulating tank is kept for 10 minutes to strip the dissolved small amount of zirconium and hafnium chloride and return it to the distillation tower along the steam pipeline. Then, 2 / 3 of the molten salt is pressed into the reflux tank, and it is ensured that the liquid level of the reflux tank is higher than the gas pipeline at the top of the tower. The separated zirconium tetrachloride flows into the reboiler and dissolves in the molten salt, and the hafnium tetrachloride enters the condenser. Step 6: After the distillation treatment is completed, the temperature of the reboiler and the circulation tank is lowered to 350°C, the molten salt in the reflux tank is discharged into the reboiler and the circulation tank, and hafnium tetrachloride enriched at the top of the tower is obtained in the condenser; Step 7: Then replace the condenser, raise the temperature of the reboiler and the circulation tank to 550°C, and then fill the gas preheater with high-purity nitrogen to evaporate the zirconium tetrachloride enriched in the molten salt and transport it to the condenser for condensation to recover zirconium tetrachloride.

[0079] According to chemical composition analysis, the hafnium content of the hafnium tetrachloride enriched at the top of the tower in Example 3 was 2.96%, and the hafnium content of the zirconium tetrachloride enriched at the bottom of the tower was 1.81%.

[0080] The zirconium tetrachloride enriched in Example 3 was used as the raw material and subjected to nine consecutive distillations according to the operating procedures of Example 3. The resulting zirconium tetrachloride product had a hafnium tetrachloride content of 0.0084% at the bottom of the column. This demonstrated that the multiple distillations effectively separated and enriched the hafnium in the zirconium tetrachloride, resulting in zirconium tetrachloride of higher purity.

[0081] After nine rounds of distillation, hafnium tetrachloride with a hafnium content of 12.15% was fed back as raw material. After ten consecutive rounds of distillation, the zirconium tetrachloride content at the top of the tower was reduced to 0.47%. This demonstrates that multiple distillations effectively separate the zirconium tetrachloride from the enriched hafnium tetrachloride, increasing the purity of the hafnium tetrachloride.

[0082] Combined with Table 3, in Example 3, the hafnium tetrachloride-enriched material at the top of the tower was continuously distilled 10 times, the purity of the hafnium tetrachloride at the top of the tower met the standard, and the total number of distillation stages was 120; the zirconium tetrachloride-enriched material at the bottom of the tower was continuously stripped 11 times, the purity of the zirconium tetrachloride at the bottom of the tower met the standard, and the total number of stripping stages was 132. It can be seen that the actual controlled reflux ratio in Example 3 is close to R / Rmin = 3.0, and the experimental results are basically consistent with the theoretical calculation results.

[0083] In summary, the molten salt extraction and distillation separation method for zirconium and hafnium tetrachloride provided in the embodiments of the present application utilizes a simple and easy-to-install device. The method applicable to this device is more systematic, with clearer technical details and more specific process parameters. This method is well-suited for both industrial-grade and laboratory-grade molten salt extraction and distillation separation of zirconium and hafnium tetrachloride. Furthermore, the embodiments of the present application utilize pressure-delivered shielding gas. By controlling gas pressure and flow, this method achieves simple and efficient circulation of the molten salt, resolving the issues of conventional delivery pumps being unable to transport high-temperature corrosive melts and the low transmission efficiency of gas lift pumps.

[0084] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0085] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0086] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or terminal device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or terminal device that includes the element.

[0087] The above is a detailed introduction to the molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core ideas of the present application. At the same time, for those skilled in the art, according to the ideas of the present application, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride, characterized in that: The method is applicable to a molten salt extraction and distillation separation device, which comprises: Distillation tower, sublimator, reflux tank, condenser, reboiler, circulation tank and gas preheater; The method comprises: S1. Connect the distillation tower to the reflux tank and the reboiler respectively, then connect the reflux tank to the condenser, connect a gas pipeline to the distillation tower, insert one end of the gas pipeline away from the distillation tower into the reflux tank, then connect the circulation tank to the reboiler, connect a molten salt circulation pipeline to the circulation tank, connect the liquid outlet end of the molten salt circulation pipeline to the reflux tank, connect a steam pipeline to the molten salt circulation pipeline, then connect one end of the steam pipeline to the gas preheater and the other end to the bottom of the distillation tower; S2, after the zirconium hafnium tetrachloride is loaded into the sublimator, the sublimator is connected to the distillation tower, and the chloride is loaded into the reboiler, the device is evacuated to vacuum, and after the vacuum degree reaches -0.1 MPa, nitrogen is filled in to replace the air in the device; S3, controlling the temperature of the sublimator to 200°C-300°C, the temperature of the circulation tank to 480°C-600°C, the temperature of the reflux tank to 300°C-400°C, the temperature of the molten salt circulation pipeline to 300°C-400°C, the temperature of the gas preheater to 500°C-650°C, and the temperature of the reboiler to 400°C-600°C, so that the chloride is in a molten state in the distillation tower to obtain molten salt; S4, transporting an appropriate amount of the molten salt to the circulation tank, charging the gas preheater with a protective gas with a pressure of 0.3 atm-1.0 atm, the protective gas presses the molten salt in the circulation tank into the reflux tank along the molten salt circulation pipeline, and the molten salt flows into the distillation tower along the reflux tank; S5, raising the temperature of the sublimator to 400°C-450°C to vaporize the zirconium and hafnium tetrachloride, the vaporized zirconium and hafnium tetrachloride enters the distillation tower to perform gas-liquid phase mass transfer and heat transfer with the molten salt, the separated zirconium tetrachloride is enriched in the molten salt in the reboiler, and the hafnium tetrachloride-rich vapor enters the condenser; S6. After the distillation treatment is completed, the reboiler and the circulation tank are cooled to 250° C. to 400° C., the molten salt in the reflux tank is discharged into the reboiler and the circulation tank, and the hafnium tetrachloride-rich vapor in the distillation tower is condensed in the condenser to obtain an enriched hafnium tetrachloride; S7, raising the temperature of the reboiler to 550°C-600°C to vaporize the zirconium tetrachloride dissolved in the molten salt, and then filling the gas preheater with the nitrogen, which transports the vaporized zirconium tetrachloride to the condenser for recovery.

2. The molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride according to claim 1, characterized in that: In step S4, when the liquid level of the molten salt in the reboiler is greater than 1 / 2, an appropriate amount of the molten salt is transported to the circulation tank. After the molten salt is stored in the circulation tank for 5 min to 10 min, a small amount of zirconium and hafnium chloride dissolved in the molten salt is vaporized and sent to the steam pipeline. The vaporized zirconium and hafnium chloride enters the distillation tower for distillation treatment.

3. The molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride according to claim 1, characterized in that: In step S5, the vaporized zirconium-hafnium tetrachloride enters the distillation tower and diffuses toward the top of the distillation tower, contacts the molten salt in a gas-liquid phase, and enters the reflux tank after multi-stage refining, wherein a portion of the hafnium tetrachloride-rich vapor is dissolved in the molten salt in the reflux tank, and another portion of the undissolved hafnium tetrachloride-rich vapor enters the condenser for condensation, and the molten salt in the distillation tower flows to the bottom of the tower and contacts the rising vapor of zirconium tetrachloride-rich vapor in a gas-liquid phase to concentrate the zirconium tetrachloride.

4. The molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride according to claim 1, characterized in that: In step S3, the temperature of the sublimator is controlled to be 250°C~280°C, the temperature of the circulation tank is controlled to be 500°C~550°C, the temperature of the reflux tank is controlled to be 320°C~350°C, the temperature of the molten salt circulation pipeline is controlled to be 320°C~350°C, the temperature of the gas preheater is controlled to be 550°C~600°C, and the temperature of the reboiler is controlled to be 450°C~500°C.

5. The molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride according to claim 1 or 4, characterized in that: The temperature of the top of the distillation tower is the same as that of the reflux tank, and the temperature of the bottom of the distillation tower is the same as that of the reboiler; The temperature in the distillation tower decreases step by step from the bottom to the top.

6. The molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride according to claim 1, characterized in that: The chloride includes at least two of potassium chloride, aluminum chloride, cuprous chloride, sodium chloride and ferric chloride.

7. The molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride according to claim 1 or 6, characterized in that: In step S2, the mass ratio of the zirconium hafnium tetrachloride to the chloride is 1:(10-100).

8. The molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride according to claim 1, characterized in that: In step S4, the protective gas is nitrogen or argon; The flow rate of the protective gas is 0.1 L / min~5 L / min.

9. The molten salt extraction and distillation separation method of zirconium and hafnium tetrachloride according to claim 1, characterized in that: In step S4, when the molten salt flows into the distillation tower along the reflux tank, the flow rate of the molten salt is 0.05 L / min~2 L / min; The number of plates in the distillation tower is 20 to 30.

10. Zirconium tetrachloride and hafnium tetrachloride obtained by the molten salt extraction and rectification separation method of zirconium and hafnium tetrachloride according to any one of claims 1 to 9.

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