A method for separating hafnium and zirconium tetrachloride by molten salt extraction distillation

Abstract

The application provides a molten salt extraction rectification separation method of zirconium hafnium tetrachloride, and is particularly suitable for a molten salt extraction rectification separation device. In the molten salt extraction rectification separation, main components such as a rectification tower, a sublimer, a reflux tank, a condenser, a reboiler and a circulating tank are connected first, then zirconium hafnium chloride raw materials to be separated and chloride salt for rectification are filled, and finally the device is started to realize the separation of zirconium hafnium chloride under rectification conditions. The separation device and method have good usability and process adaptability, and the prepared zirconium tetrachloride and hafnium tetrachloride meet the use requirements in the fields of atomic energy, aerospace, high-power laser and integrated circuit, and provide reference and guidance for the research and development and application of the molten salt rectification separation technology and equipment of zirconium hafnium tetrachloride.

Description

TECHNICAL FIELD

[0001] The present application relates to the chemical separation technology field of metal compounds, in particular, to a molten salt extraction rectification separation method of zirconium hafnium tetrachloride. BACKGROUND

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

[0003] At present, zirconium hafnium separation technology is divided into wet method and fire method, among which, zirconium hafnium fire separation technology mainly utilizes the oxidation-reduction reaction characteristics, volatility characteristics, and subtle differences between zirconium hafnium compounds at high temperature to realize separation and the subtle differences of electrochemical characteristics. Specifically, the molten salt extraction rectification process in zirconium hafnium fire separation technology realizes industrial production, and this technology utilizes the difference in volatility of zirconium hafnium tetrachloride in molten salt to realize rectification separation.

[0004] However, in the currently published literature, there is no systematic study on the process design and device design of molten salt rectification separation of zirconium hafnium tetrachloride. The technical details, process equipment and process parameters of this process are not clear, and the research and development of zirconium hafnium molten salt rectification separation technology and equipment, as well as industrial application, lack theoretical and practical guidance. Therefore, to realize the breakthrough of this technology, an exact and achievable molten salt extraction rectification separation method of zirconium hafnium tetrachloride needs to be proposed. SUMMARY

[0005] To solve the above problems, the present application provides a molten salt extraction rectification separation method of zirconium hafnium tetrachloride, which is clear in steps and detailed in details, and the reaction conditions, process parameters, etc. are clear, especially suitable for molten salt extraction rectification separation device, to realize the breakthrough of technology, provide reference and guidance.

[0006] In the first aspect, the present application provides a molten salt extraction rectification separation method of zirconium hafnium tetrachloride, which is suitable for a molten salt extraction rectification separation device, and the device comprises:

[0007] a rectification tower, a sublimator, a reflux tank, a condenser, a reboiler, a circulating tank and a gas preheater;

[0008] The method comprises:

[0009] S1, connecting the rectification tower with the reflux tank and the reboiler respectively, connecting the reflux tank with the condenser, connecting a gas pipeline on the rectification tower, inserting one end of the gas pipeline away from the rectification tower into the reflux tank, then connecting the circulating tank with the reboiler, connecting a molten salt circulating pipeline on the circulating tank, connecting the liquid outlet end of the molten salt circulating pipeline on the reflux tank, connecting a vapor pipeline on the molten salt circulating pipeline, then connecting one end of the vapor pipeline with the gas preheater and the other end with the bottom of the rectification tower;

[0010] S2, after loading zirconium hafnium tetrachloride into the sublimator, connecting the sublimator with the rectification tower, then loading chlorides into the reboiler, vacuumizing the device, after the vacuum degree reaches-0.1 MPa, filling nitrogen to replace the air in the device;

[0011] S3, controlling the temperature of the sublimator to be 200 ℃-300 ℃, the temperature of the circulating tank to be 480 ℃-600 ℃, the temperature of the reflux tank to be 300 ℃-400 ℃, the temperature of the molten salt circulating pipeline to be 300 ℃-400 ℃, the temperature of the gas preheater to be 500 ℃-650 ℃, and the temperature of the reboiler to be 400 ℃-600 ℃, so that the chlorides are in a molten state in the rectification tower, and molten salt is obtained;

[0012] S4, transporting an appropriate amount of the molten salt into the circulating tank, filling a protective gas with a pressure of 0.3 atm-1.0 atm into the gas preheater, the protective gas pressurizing the molten salt in the circulating tank along the molten salt circulating pipeline into the reflux tank, and the molten salt flowing along the reflux tank into the rectification tower;

[0013] S5, increasing the temperature of the sublimator to 400 ℃-450 ℃, so that the zirconium hafnium tetrachloride vaporizes, the vaporized zirconium hafnium tetrachloride enters the rectification tower to perform 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 hafnium tetrachloride vapor enters the condenser;

[0014] S6, after the rectification process is completed, cooling the reboiler and the circulating tank to 250 ℃-400 ℃, discharging the molten salt in the reflux tank into the reboiler and the circulating tank, condensing the hafnium tetrachloride vapor enriched in the rectification tower in the condenser, and obtaining an enriched hafnium tetrachloride;

[0015] S7, heating the reboiler to 550 ℃-600 ℃, so that the dissolved zirconium tetrachloride in the molten salt vaporizes, then filling the nitrogen into the gas preheater, and the nitrogen transports the vaporized zirconium tetrachloride to the condenser for recovery.

[0016] 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 into the circulating tank, and after the molten salt is stored in the circulating tank for 5-10 minutes, a small amount of zirconium hafnium chloride dissolved in the molten salt is vaporized and sent into the vapor pipeline, and the vaporized zirconium hafnium chloride enters the rectification tower for rectification treatment.

[0017] Preferably, in step S5, after the vaporized zirconium hafnium tetrachloride enters the rectification tower, it diffuses towards the top of the rectification tower, and gas-liquid phase contact occurs with the molten salt, and after multi-stage refining, it enters the reflux tank, wherein part of the hafnium tetrachloride vapor is dissolved in the molten salt in the reflux tank, and the other part of the undissolved hafnium tetrachloride vapor enters the condenser for condensation, and the molten salt in the rectification tower flows to the bottom and gas-liquid phase contact occurs with the rising zirconium tetrachloride vapor, thereby enriching the zirconium tetrachloride.

[0018] Preferably, in step S3, the sublimator temperature is controlled to be 250-280°C, the circulating tank temperature is controlled to be 500-550°C, the reflux tank temperature is controlled to be 320-350°C, the molten salt circulating pipeline temperature is controlled to be 320-350°C, the gas preheater temperature is controlled to be 550-600°C, and the reboiler temperature is controlled to be 450-500°C.

[0019] Preferably, the temperature at the top of the rectification tower is the same as that of the reflux tank, and the temperature at the bottom of the rectification tower is the same as that of the reboiler.

[0020] The temperature in the rectification tower decreases step by step from the bottom to the top.

[0021] Preferably, the chlorides include at least two of potassium chloride, aluminum chloride, cuprous chloride, sodium chloride, and ferric chloride.

[0022] Preferably, in step S2, the mass ratio of the zirconium hafnium tetrachloride to the chlorides is 1: (10-100).

[0023] Preferably, in step S4, the protective gas is nitrogen or argon.

[0024] The flow rate of the protective gas is 0.1-5 L / min.

[0025] Preferably, in step S4, when the molten salt flows into the rectification tower from the reflux tank, the flow rate of the molten salt is 0.05-2 L / min.

[0026] The number of trays in the rectification tower is 20-30 stages.

[0027] In a second aspect, the application provides zirconium tetrachloride and hafnium tetrachloride obtained by the above-mentioned method for separating zirconium tetrachloride and hafnium tetrachloride by molten salt extractive rectification.

[0028] In summary, the application includes at least one of the following beneficial technical effects:

[0029] 1. The application provides a method for separating zirconium tetrachloride and hafnium tetrachloride by molten salt extractive rectification, which is particularly suitable for a molten salt extractive rectification separation device. The device has simple connection mode, easy operation, and strong applicability. In the application, protective gas is used as a conveying medium, and after heating by a gas preheater, the molten salt is pressurized from a circulating tank to a reflux tank to realize reflux of the molten salt. After the zirconium and hafnium chlorides are vaporized, they enter the rectification tower to contact with the molten salt for rectification treatment. The method has simple and convenient operation process and high separation efficiency, and solves the problem of unclear technical details and process equipment of the current molten salt rectification separation technology of zirconium tetrachloride and hafnium tetrachloride, thereby providing a good reference and strong guidance for realizing technical breakthrough.

[0030] 2. The device used in the method provided by the application includes a gas preheater, which is used to pressurize the molten salt along the molten salt circulating pipeline to the reflux tank by using the heated protective gas, and to control the circulation of the molten salt by using the protective gas. Furthermore, by controlling the pressure and flow of the protective gas, the molten salt is simply and efficiently circulated, thereby solving the problems of the conventional conveying pump that cannot transport high-temperature corrosive melt and the gas lift pump that has low transmission efficiency, and the problem of the molten salt pump that is prone to have high-temperature reliability decline during long-period operation. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the description of the embodiments of the application. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without any creative labor based on these drawings.

[0032] Figure 1 A flow chart of a method for separating zirconium tetrachloride and hafnium tetrachloride by molten salt extractive rectification is shown in the embodiments of the application.

[0033] Figure 2 A structure schematic diagram of a molten salt extractive rectification separation device is shown in the embodiments of the application.

[0034] 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%) under different reflux ratios is obtained by using the phase equilibrium equation and the operating line equation in Table 2 and using the plate-by-plate calculation method.

[0035] Explanation of reference signs:

[0036] 1 distillation column; 11 gas line; 12 rectification section; 13 stripping section; 14 feed inlet; 15 throttle valve;

[0037] 2 sublimator; 3 reflux tank;

[0038] 4 condenser; 41 vacuum pump interface;

[0039] 5 reboiler;

[0040] 6 circulating tank; 61 vapor line; 62 molten salt circulating line;

[0041] 7 gas preheater;

[0042] 8 heating furnace;

[0043] 9 molten salt emptying tank. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0045] In the drawings, the size of a constituent element, the thickness of a layer, or a region may be exaggerated for the sake of clearness and convenience in some cases. Therefore, the size of any one implementation of the present disclosure is not necessarily limited to the size shown in the drawings, and the shapes and sizes of the components in the drawings do not reflect true proportions. In addition, the drawings schematically show ideal examples, and any one implementation of the present disclosure is not limited to the shapes or values shown in the drawings.

[0046] In the related art, zirconium-hafnium separation technology is divided into wet and fire methods. The wet method for separating zirconium and hafnium is a solvent extraction technology represented by MIBK, which selectively extracts zirconium or hafnium into an organic phase to separate zirconium and hafnium, and is the most widely used zirconium-hafnium separation technology. Westinghouse, Huachang, domestic Guohe Weike, Zhonghe Jinghuan, Nanjing Youtian, etc. all use wet solvent extraction technology to separate zirconium and hafnium. However, this wet solvent extraction technology has problems such as serious environmental pollution, high production cost, and long production process.

[0047] Zirconium hafnium pyrogenic separation technology mainly uses the redox reaction characteristics, volatility characteristics, and fine differences between zirconium and hafnium compounds at high temperatures, and the fine differences in electrochemical characteristics to realize separation, including Newnham process, Chandler process, Flengas process, Xiao process, molten salt extraction rectification process, high-pressure rectification process, and selective electrolysis process. However, only the molten salt extraction rectification process among the above processes has realized industrialized production. This technology uses the volatility difference of zirconium tetrachloride / hafnium tetrachloride in molten salt to realize rectification separation. Since hafnium tetrachloride is more volatile than zirconium tetrachloride, hafnium tetrachloride will be enriched at the top of the rectification tower, and zirconium tetrachloride will be enriched at the bottom of the rectification tower. Compared with wet extraction, the molten salt extraction rectification technology has the advantages of small environmental pollution, low production cost, and the separation of raw materials and products can be directly connected with the carbon chlorination and magnesium reduction distillation processes in the current zirconium and hafnium production process, thereby significantly shortening the zirconium and hafnium manufacturing process and reducing production costs. Saizos Company in France is the only company in the world that masters this technology and realizes the industrialized production of nuclear-grade zirconium tetrachloride / hafnium tetrachloride. However, due to the particularity and sensitivity of zirconium and hafnium in application fields, there are few process parameters and details of the molten salt rectification separation process in the publicly reported literature. The research and development of the molten salt rectification technology in the domestic zirconium and hafnium industry is still in its infancy. With the continuous development of China's energy, electronics, aerospace and other strategic emerging fields, and the increasing demand for environmental protection and sustainable development, the zirconium and hafnium industry also faces industrial upgrading. Compared with the wet solvent extraction technology, the molten salt rectification separation technology of zirconium and hafnium has more advantages in terms of "three wastes" generation, production process simplification, and chemical reagent consumption. Therefore, developing the molten salt rectification separation technology of zirconium and hafnium in China is a necessary requirement for the efficient, green, and sustainable development of the industry.

[0048] At present, the process and technical details of the molten salt rectification separation technology of zirconium and hafnium, as well as the design and operating parameters of the rectification equipment, are not clear, and technical process and equipment research and development are urgently needed.

[0049] Based on the above problems, the application concept proposed in the present application is to build a rectification device, obtain key process parameters, and optimize the process parameters, so that the molten salt extraction rectification separation method of zirconium and hafnium tetrachloride is more systematic, the technical details are clearer, and the separation efficiency is improved.

[0050] Referring to Figure 1 , Figure 1 A flow chart of a molten salt extraction rectification separation method of zirconium and hafnium tetrachloride is shown, which specifically includes:

[0051] The method is suitable for a molten salt extraction rectification separation device, and the device includes:

[0052] a rectification tower, a sublimator, a reflux tank, a condenser, a reboiler, a circulating tank, and a gas preheater;

[0053] The method comprises the following steps:

[0054] S1, connecting the rectifying tower with the reflux tank and the reboiler respectively, connecting the reflux tank with the condenser, connecting the gas pipeline on the rectifying tower, inserting the end of the gas pipeline away from the rectifying tower into the reflux tank, and then connecting the circulating tank with the reboiler, connecting the molten salt circulating pipeline on the circulating tank, connecting the liquid outlet end of the molten salt circulating pipeline on the reflux tank, connecting the vapor pipeline on the molten salt circulating pipeline, and then connecting one end of the vapor pipeline with the gas preheater and the other end with the bottom of the rectifying tower;

[0055] S2, after the zirconium hafnium tetrachloride is loaded into the sublimator, connecting the sublimator with the rectifying tower, loading the chlorides into the reboiler, and then vacuumizing the device, and after the vacuum degree reaches-0.1 MPa, filling nitrogen to replace the air in the device;

[0056] S3, controlling the temperature of the sublimator to be 200 ℃-300 ℃, the temperature of the circulating tank to be 480 ℃-600 ℃, the temperature of the reflux tank to be 300 ℃-400 ℃, the temperature of the molten salt circulating pipeline to be 300 ℃-400 ℃, the temperature of the gas preheater to be 500 ℃-650 ℃, and the temperature of the reboiler to be 400 ℃-600 ℃, so that the chlorides are in a molten state in the rectifying tower, and the molten salt is obtained;

[0057] S4, transporting an appropriate amount of molten salt into the circulating tank, filling the gas preheater with a protective gas with a pressure of 0.3 atm-1.0 atm, and the protective gas pressurizes the molten salt in the circulating tank along the molten salt circulating pipeline into the reflux tank, and the molten salt flows into the rectifying tower along the reflux tank;

[0058] S5, increasing the temperature of the sublimator to 400 ℃-450 ℃, so that the zirconium hafnium tetrachloride is vaporized, and the vaporized zirconium hafnium tetrachloride enters the rectifying tower to perform gas-liquid phase mass and heat transfer with the molten salt, and the separated zirconium tetrachloride is enriched in the molten salt in the reboiler, and the hafnium tetrachloride vapor is enriched in the condenser;

[0059] S6, after the rectification is completed, cooling the reboiler and the circulating tank to 250 ℃-400 ℃, discharging the molten salt in the reflux tank into the reboiler and the circulating tank, condensing the hafnium tetrachloride vapor in the condenser, and obtaining the hafnium tetrachloride enrichment;

[0060] S7, increasing the temperature of the reboiler to 550 ℃-600 ℃, so that the dissolved zirconium tetrachloride in the molten salt is vaporized, and then filling the gas preheater with nitrogen, and the nitrogen transports the vaporized zirconium tetrachloride to the condenser for recovery.

[0061] In the implementation, the device is installed first, and then the molten salt extractive distillation separation is realized by using the device. The application is to use the difference in vapor pressure of zirconium hafnium tetrachloride in the chloride molten salt, so that the more volatile hafnium tetrachloride is enriched at the top of the rectifying column, and the less volatile zirconium tetrachloride is enriched at the bottom of the rectifying column. The method is complete in system, simple in operation, and can be used for research on molten salt extractive distillation separation process and equipment, and can be enlarged for preparation and production of nuclear grade zirconium hafnium chloride. The application range is wider and broader.

[0062] In some embodiments, referring to Figure 2 , a structure diagram of the molten salt extractive distillation separation device is shown, and step S1 specifically includes:

[0063] The rectifying column 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;

[0064] 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;

[0065] The first end of the circulating tank 6 is connected to the second end of the reboiler 5, the second end of the circulating tank 6 is connected to the molten salt circulating pipeline 62, and the liquid outlet end of the molten salt circulating pipeline 62 is connected to the second end of the reflux tank 3;

[0066] The end of the molten salt circulating pipeline 62 close to the circulating tank 6 is connected to the vapor pipeline 61, the vapor pipeline 61 is a four-way pipe, the first end of the vapor pipeline 61 is connected to the gas preheater 7, the second end is connected to the bottom of the stripping section 13; the third end is connected to the molten salt circulating pipeline 62, and the fourth end is connected to the circulating tank 6;

[0067] In some embodiments, each component in the above device is placed in a corresponding heating furnace 8 to facilitate temperature control. The connection mode of the device is simple and more systematic, which is convenient to operate and has strong applicability.

[0068] In the implementation, the sublimer 2 is connected at the connection of the rectifying section 12 and the stripping section 13, and is connected to the rectifying column 1 to facilitate the transportation of the vaporized zirconium hafnium tetrachloride to the rectifying column 1 for rectification.

[0069] In some embodiments, the total number of stages of the rectification tower 1 is set to 20-30, and a plurality of feed inlets 14 connected to the sublimator 2 are arranged from top to bottom on the rectification tower 1. Since hafnium tetrachloride is more easily evaporated, when hafnium tetrachloride of higher purity is to be prepared, the feeding position is selected at a position closer to the reboiler 5, the number of plates of the rectifying section 12 is relatively increased, and the hafnium tetrachloride is evaporated as much as possible, so that the vapor flows upward, and the hafnium tetrachloride in the vapor is gradually enriched from plate to plate, so that hafnium tetrachloride of higher purity is obtained. Since zirconium tetrachloride is more difficult to evaporate, when zirconium tetrachloride of higher purity is to be obtained, the feeding position is selected at a position closer to the reflux tank 3, the number of plates of the stripping section 13 is relatively increased, and the liquid flows downward, and the zirconium tetrachloride in the liquid is gradually enriched, so that zirconium tetrachloride of higher purity is obtained.

[0070] In some embodiments, the molten salt circulating pipeline 62, the gas pipeline 11, and the vapor pipeline 61 are also arranged in the heating furnace 8 to heat the liquid or gas in the pipelines, so that the liquid or gas in the pipelines is always kept in a liquid or gaseous state, and the rectification is ensured to be carried out smoothly.

[0071] In some embodiments, the liquid level of the molten salt in the reflux tank 3 is higher than the end of the end of the gas pipeline 11 extending into the reflux tank 3, so as to ensure that the vaporized zirconium hafnium tetrachloride can contact the molten salt for rectification treatment.

[0072] In some embodiments, a vacuum pump interface 41 is arranged at the upper end of the condenser 4, and the condenser 4 is connected to a vacuum pump after the vacuum pump interface 41 is connected to the vacuum pump, and the vacuum pump is started to strengthen the diffusion effect of the vapor.

[0073] In some embodiments, an opening connected to the rectification tower 1 is arranged on the condenser 4, and after the rectification is completed, the condenser 4 and the sublimator 2 are removed, the condenser 4 is installed at the position of the original sublimator 2, and the material recovered in the condenser 4 is transported to the rectification tower 1 for secondary rectification and purification, so as to improve the purity of the separated product.

[0074] In some embodiments, the third end of the circulating tank 6 is connected to a molten salt emptying tank 9, and after the gas in the molten salt is sufficiently discharged, all the molten salt is discharged into the molten salt emptying tank 9 for cooling, and the cooled molten salt can be discharged into the reboiler 5 for reuse in the next test.

[0075] In specific implementation, after the reboiler 5 is removed, the molten salt emptying tank 9 is installed at the position of the original reboiler 5, and the molten salt can also be reused.

[0076] In some embodiments, a throttling valve 15 is arranged at a position close to the reflux tank 3 of the rectification tower 1, and the flow of the molten salt in the reflux tank 3 can be more accurately controlled by controlling the throttling valve 15, so as to achieve a better reflux ratio and improve the separation efficiency.

[0077] In some embodiments, in step S2, the sublimator is placed in a glove box with water-oxygen content <1 ppm, and the zirconium hafnium tetrachloride is loaded into the sublimator. Reducing the oxidation reaction of the raw material during the loading process ensures the stability of its chemical and physical properties, and reduces the pollution of other impurities (such as water vapor, dust, etc.) to the raw material, thereby improving the purity of the raw material.

[0078] In some embodiments, in step S2, further comprising:

[0079] The sublimator and the reboiler are respectively placed in a glove box with water-oxygen content <1 ppm for loading, which reduces the deliquescence of the raw material during the loading process, ensures the stability of its chemical and physical properties, and further reduces the pollution of other impurities (such as water vapor, dust, etc.) to the raw material, thereby further improving the purity of the raw material. After loading, the reboiler and the sublimator are installed at the corresponding positions.

[0080] 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 the circulating tank. After the molten salt is stored in the circulating tank for 5 min to 10 min, a small amount of zirconium hafnium chloride dissolved in the molten salt is vaporized and sent to the vapor pipeline. The vaporized zirconium hafnium chloride enters the rectification tower for rectification treatment.

[0081] By setting the vapor pipeline, a small amount of zirconium hafnium tetrachloride enriched in the tower bottom can be collected and re-transported to the rectification tower for separation, which helps to improve the comprehensive recovery rate of zirconium / hafnium chloride.

[0082] In some embodiments, in step S5, after the vaporized zirconium hafnium tetrachloride enters the rectification tower, it diffuses towards the top of the rectification tower and comes into contact with the molten salt. After multi-stage refining, it enters the reflux tank. Part of the hafnium tetrachloride vapor is dissolved in the molten salt in the reflux tank, and the other part of the undissolved hafnium tetrachloride vapor enters the condenser for condensation. The molten salt in the rectification tower flows to the bottom and comes into contact with the rising zirconium tetrachloride vapor, thereby enriching the zirconium tetrachloride.

[0083] By setting the gas pipeline, part of the vaporized zirconium hafnium tetrachloride is diverted to balance the gas pressure in the rectification tower, thereby avoiding liquid overflow in the rectification tower to a certain extent, and making the rectification process more smoothly.

[0084] In some embodiments, in step S3, the temperature of the sublimator is controlled to be 250 ℃ to 280 ℃, the temperature of the circulating tank is controlled to be 500 ℃ to 550 ℃, the temperature of the reflux tank is controlled to be 320 ℃ to 350 ℃, the temperature of the molten salt circulating pipeline is controlled to be 320 ℃ to 350 ℃, the temperature of the gas preheater is controlled to be 550 ℃ to 600 ℃, and the temperature of the reboiler is controlled to be 450 ℃ to 500 ℃.

[0085] In specific implementations, the sublimator is preheated to bring the zirconium hafnium tetrachloride to or close to its vaporization temperature, so that vaporization occurs more easily and more quickly in the subsequent heating and vaporization process, which helps to accelerate the rectification process and improve the overall separation efficiency.

[0086] In specific implementations, the purpose of heating the circulating tank is to: 1) strip the zirconium hafnium chlorides dissolved in the molten salt, return them to the rectification column and extract them as products; 2) maintain the liquid state of the molten salt to facilitate the delivery of the gas (i.e., the protective gas) to press the liquid chlorides into the reflux tank to form a stable reflux.

[0087] The reflux tank is heated to ensure that the chlorides in the reflux tank are in a liquid state, but their temperature is lower than that of the circulating tank, so that more zirconium tetrachloride can be dissolved in the molten salt to flow downward, and more hafnium tetrachloride can be vaporized in the form of vapor.

[0088] The molten salt circulating pipeline is heated to ensure that the chlorides delivered to the reflux tank maintain a molten state, so that the temperature of the delivered molten salt is the same as that of the molten salt entering the reflux tank, avoiding temperature differences that affect the solubility and selectivity of the molten salt, and enhancing the effect of extractive rectification.

[0089] The gas preheater is heated to preheat the cold gas (i.e., the protective gas) after pressure reduction, preventing the molten salt from solidifying or the flowability from deteriorating due to contact with the cold gas.

[0090] The reboiler is heated to form rising vapor of zirconium hafnium chlorides dissolved in the molten salt, which is used to concentrate the descending molten salt, and the heating temperature is controlled at 450 ℃~500 ℃, which can obtain appropriate rising vapor flow and pressure to promote sufficient bubble contact between gas and liquid phases.

[0091] In some embodiments, the temperature at the top of the rectification column is the same as that of the reflux tank, and the temperature at the bottom of the rectification column is the same as that of the reboiler.

[0092] The temperature in the rectification column decreases step by step from the bottom to the top. Due to the different volatilities of zirconium tetrachloride and hafnium tetrachloride in the molten salt, the more volatile hafnium tetrachloride can be more enriched in the lower temperature area (the top of the column), while the less volatile zirconium tetrachloride can be enriched in the higher temperature area (the bottom of the column), to promote the effective separation of zirconium tetrachloride and hafnium tetrachloride.

[0093] In some embodiments, the chlorides include at least two of potassium chloride, aluminum chloride, cuprous chloride, sodium chloride, and ferric chloride.

[0094] Preferably, the chloride is potassium chloride and aluminum chloride. The aluminum chloride can form a KAlCl4 molten salt with the potassium chloride at high temperature. The KAlCl4 molten salt has the advantages of low melting point, small viscosity, small vapor pressure, large solubility of zirconium hafnium chloride, and good stripping characteristics of zirconium hafnium chloride, which helps to realize efficient rectification separation of zirconium hafnium.

[0095] In some embodiments, in step S2, the mass ratio of zirconium hafnium tetrachloride to chloride is 1: (10-100).

[0096] By controlling the mass ratio, it can not only ensure that the rectification process has a relatively wide reflux ratio adjustment range, but also avoid the problem that too much chloride causes the difficulty of zirconium hafnium chloride in the molten salt to be too low and the stripping to be difficult, and the problem that the molten salt pump is prone to high-temperature reliability decline during long-period operation.

[0097] In some embodiments, in step S4, the protective gas is nitrogen or argon.

[0098] The flow rate of the protective gas is 0.1 L / min-5 L / min.

[0099] The protective gas is set to nitrogen because nitrogen is used to replace the residual air in the device in step S2, but more preferably, argon is used for replacement and protection because the specific gravity of argon is greater than that of air, which makes it easier to replace the air completely and reduce the introduction of other impurity gases.

[0100] In the embodiment of the present application, the reflux of the molten salt rectification is controlled by the circulation of the molten salt, and the circulation of the molten salt is controlled by the flow rate of the protective gas. Therefore, by reasonably setting the flow rate of the protective gas, the reflux ratio can be adjusted, the molten salt can be simply and efficiently circulated, and the problems of conventional delivery pumps being unable to deliver high-temperature corrosive melts, the transmission efficiency of gas lift pumps being low, and the molten salt pump being prone to high-temperature reliability decline during long-period operation are solved.

[0101] In some embodiments, in step S4, when the molten salt flows into the rectification tower along the reflux tank, the flow rate of the molten salt is 0.05 L / min-2 L / min.

[0102] The number of trays in the rectification tower is 20-30 stages.

[0103] In the implementation, in step S4, after the molten salt enters the reflux tank, the flow rate of the molten salt is controlled to be 0.05 L / min to 2 L / min, and after the molten salt forms a stable liquid flow in the rectifying tower, step S5 is performed. The stable molten salt liquid flow can ensure uniform heat transfer at each part in the rectifying tower, which helps to reduce heat loss and temperature fluctuation, thereby improving the heat efficiency of the entire rectifying process; after step S5 is performed, the contact area of the gas-liquid phase 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-liquid phase in the tower and reduce the occurrence of back mixing.

[0104] The application also provides zirconium tetrachloride and hafnium tetrachloride obtained by the above-mentioned molten salt extractive distillation separation method of zirconium and hafnium tetrachloride.

[0105] The zirconium tetrachloride and hafnium tetrachloride obtained by the method of the application can be used in the technical fields of atomic energy, aerospace, high-power laser, integrated circuit, etc.

[0106] In order for those skilled in the art to more clearly understand the application, the application will now be described in detail through the following examples.

[0107] Embodiment

[0108] Firstly, the application utilizes the vapor pressure data of zirconium tetrachloride and hafnium tetrachloride in KAlCl4 molten salt to design the process, and calculates the required theoretical plate number and reflux ratio and other core process parameters for the target separation effect (hafnium content in zirconium <0.01%, zirconium content in hafnium <0.5%).

[0109] Table 1 shows the relative volatility of zirconium and hafnium tetrachloride in the temperature range of 350 ℃ to 500 ℃ calculated by using the vapor pressure data of zirconium tetrachloride and hafnium tetrachloride in molten salt.

[0110] Table 1. Relative volatility of zirconium and hafnium tetrachloride at different temperatures of different molar fractions of raw materials

[0111]

[0112] As can be seen from Table 1, the relative volatility will change with the change of molar fraction and temperature, and when the molar fraction increases, the relative volatility increases significantly, which means that in the actual operation process, by keeping the reflux ratio unchanged and increasing the feeding rate, and by appropriately controlling the temperature, high-efficiency separation can be achieved.

[0113] Table 2 shows the operating line equation of the zirconium and hafnium molten salt rectification process at different reflux ratios calculated according to the relative volatility data in Table 1.

[0114] Table 2. Operation line equation of hafnium-zirconium molten salt rectification process under different reflux ratios

[0115]

[0116] According to Table 2, it can be obtained that the slope of the operation line of the rectification section increases after the reflux ratio increases, thereby increasing the mass transfer driving force, so that the composition of the distillate (i.e. the enriched liquid after condensation of the top hafnium tetrachloride of the column) is closer to the target product under the same number of theoretical plates, and the separation efficiency is improved;

[0117] When the reflux ratio increases, the slope of the stripping section operation line becomes smaller, and the mass transfer driving force increases, which is also beneficial to the further separation of impurities, and can also reduce the content of hafnium in the bottom enriched liquid (i.e. the molten salt enriched with zirconium tetrachloride in the reboiler), thereby improving the purity of the enriched zirconium tetrachloride.

[0118] 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%) under different reflux ratios calculated by the Fenske equation-Gilliland chart 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%) under different reflux ratios calculated by the Fenske equation-Gilliland chart method is shown in Table 2.

[0119] Table 3. Number of theoretical plates calculated by Gilliland chart

[0120]

[0121] According to the O'Connell model, the overall column efficiency of the rectification column is about 0.42, that is, when R / Rmin is 1.5-3.0, the actual number of plates required is 250-338, and if the middle plate is used as the feed plate, the rectification section and the stripping section both require 125-169 stages to achieve the target separation effect.

[0122] According to the theoretical and calculation methods obtained from Table 1, Table 2, Table 3 and Figure 3 Embodiments 1-3 are set up as follows:

[0123] Embodiment 1

[0124] Step 1, connect the rectification column with the reflux tank, then connect the reflux tank with the condenser, connect the gas pipeline on the rectification column, insert the end of the gas pipeline away from the rectification column into the reflux tank, connect the molten salt circulation pipeline on the circulation tank, connect the liquid outlet end of the molten salt circulation pipeline on the reflux tank, connect the vapor pipeline on the molten salt circulation pipeline, then connect one end of the vapor pipeline with the gas preheater and the other end with the bottom of the rectification column, and then place each part in the corresponding heating furnace.

[0125] Step 2, take hafnium content of 2% of hafnium zirconium tetrachloride as the raw material of molten salt rectification, in the glove box with water oxygen content <1 ppm, take hafnium zirconium tetrachloride 100 g, chloride salt 2 kg, respectively, into the sublimator and the reboiler, the sublimator is connected to the feed position in the middle of the rectification tower, the reboiler is connected with the bottom of the rectification tower, and the circulating tank is connected with the reboiler, then the connected sublimator and reboiler are respectively placed in the corresponding heating furnace, then the device is pumped to vacuum, after the vacuum reaches-0.1 MPa, the air in the device is washed by using nitrogen gas;

[0126] Step 3, use the heating furnace to heat the sublimator to 250 ℃, the circulating tank to 550 ℃, the reflux tank to 350 ℃, the molten salt circulating pipeline to 350 ℃, the gas preheater to 600 ℃, the condenser to room temperature, and the reboiler to 500 ℃, so that the chloride is melted to obtain the molten salt, the top temperature of the rectification tower is controlled to be consistent with the reflux tank, the bottom temperature is consistent with the reboiler temperature, and the middle temperature is gradually reduced from the bottom to the top of the tower according to 150 ℃, 50 ℃ / m.

[0127] Step 4, 3 / 4 of the molten salt in the reboiler is transported to the circulating tank, then nitrogen gas with a pressure of 0.6 atm is injected into the gas preheater, the nitrogen gas flow is set to 0.1 L / min, 2 / 3 of the molten salt in the circulating tank is pressed into the reflux tank, and the molten salt flow of the reflux tank is controlled to be 0.05 L / min;

[0128] Step 5, when the molten salt flow in the rectification tower is stable, heat the sublimator to 450 ℃ to vaporize the hafnium zirconium tetrachloride, and the vaporized hafnium zirconium tetrachloride enters the rectification tower to be rectified with the molten salt, during the rectification 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 circulating tank, the dissolved hafnium zirconium chloride is stripped in the circulating tank and returns to the rectification tower along the vapor pipeline, then 2 / 3 of the molten salt is pressed into the reflux tank, and the liquid level of the reflux tank is ensured to be 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 hafnium tetrachloride enters the condenser;

[0129] Step 6, when the rectification process is completed, the temperature of the reboiler and the circulating tank is reduced to 350 ℃, the molten salt in the reflux tank is discharged into the reboiler and the circulating tank, and the enriched hafnium tetrachloride is obtained in the condenser;

[0130] Step 7, then replace the condenser, raise the temperature of the reboiler and the circulating tank to 550 ℃, fill high-purity nitrogen gas into the gas preheater, evaporate and transport the enriched zirconium tetrachloride in the molten salt to the condenser to condense, and recover the zirconium tetrachloride.

[0131] After chemical composition analysis, hafnium content in hafnium-rich tetrachloride at the top of the column in Example 1 is 3.15%, and hafnium content in zirconium-rich tetrachloride at the bottom of the column is 1.72%, which proves that zirconium hafnium tetrachloride has been obviously separated after one rectification treatment.

[0132] Example 2

[0133] Step 1, connect the rectification column with the reflux tank, then connect the reflux tank with the condenser, connect the gas pipeline on the rectification column, insert the end of the gas pipeline away from the rectification column into the reflux tank, connect the molten salt circulation pipeline on the circulating tank, connect the liquid outlet end of the molten salt circulation pipeline on the reflux tank, connect the vapor pipeline on the molten salt circulation pipeline, then connect one end of the vapor pipeline with the gas preheater and the other end with the bottom of the rectification column, and then place each part in the corresponding heating furnace after connection;

[0134] Step 2, take 500 g of zirconium hafnium tetrachloride and 5 kg of chloride salt with hafnium content of 2% in the glove box with water and oxygen content <1 ppm, and then load them into the sublimator and the reboiler respectively, connect the sublimator to the feeding position in the middle of the rectification column, connect the reboiler with the bottom of the rectification column, and connect the circulating tank with the reboiler, then place the connected sublimator and reboiler in the corresponding heating furnaces, and then pump the device to vacuum, and then use nitrogen to replace the air in the device after the vacuum degree reaches-0.1 MPa;

[0135] Step 3, heat the sublimator to 280 ℃, the circulating tank to 500 ℃, the reflux tank to 330 ℃, the molten salt circulation pipeline to 320 ℃, the gas preheater to 550 ℃, the condenser to room temperature, and the reboiler to 550 ℃ using the heating furnace, so that the chloride is melted to obtain the molten salt, control the temperature of the top of the rectification column to be consistent with that of the reflux tank, the temperature of the bottom to be consistent with that of the reboiler, and the temperature in the middle to gradually decrease from the bottom to the top according to 50 ℃ / m according to the temperature difference of 120 ℃ between the top and the bottom of the column.

[0136] Step 4, transport 3 / 4 of the molten salt in the reboiler to the circulating tank, then flush nitrogen with a pressure of 1.0 atm into the gas preheater, set the nitrogen flow rate to 5 L / min, press 2 / 3 of the molten salt in the circulating tank into the reflux tank, and control the molten salt flow rate of the reflux tank to be 0.1 L / min.

[0137] Step 5, when the flow of molten salt in the rectification tower is stable, the sublimator is heated to 400 ℃, so that the zirconium hafnium tetrachloride is vaporized, and the vaporized zirconium hafnium tetrachloride enters the rectification tower to be rectified with the molten salt. During the rectification 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 circulating tank, and the molten salt is kept in the circulating tank for 10 minutes to strip the dissolved small amount of zirconium hafnium chloride and return to the rectification tower along the vapor pipeline. Then 2 / 3 of the molten salt is pressurized into the reflux tank, and the liquid level of the reflux tank is ensured to be 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;

[0138] Step 6, when the rectification process is completed, the temperature of the reboiler and the circulating tank is reduced to 350 ℃, and the molten salt in the reflux tank is discharged into the reboiler and the circulating tank. The enriched hafnium tetrachloride at the top of the tower is obtained in the condenser.

[0139] Step 7, then replace the condenser, raise the temperature of the reboiler and the circulating tank to 550 ℃, then fill high-purity nitrogen into the gas preheater, evaporate and transport the enriched zirconium tetrachloride in the molten salt to the condenser for condensation, and recover the zirconium tetrachloride.

[0140] Through chemical composition analysis, the hafnium content of the hafnium tetrachloride enriched at the top of the tower in Example 2 is 4.05%, and the hafnium content of the zirconium tetrachloride enriched at the bottom of the tower is 1.68%.

[0141] Example 3

[0142] Step 1, connect the rectification tower with the reflux tank, then connect the reflux tank with the condenser, connect the gas pipeline on the rectification tower, insert the end of the gas pipeline away from the rectification tower into the reflux tank, connect the molten salt circulating pipeline on the circulating tank, connect the liquid outlet end of the molten salt circulating pipeline to the reflux tank, connect the vapor pipeline on the molten salt circulating pipeline, then connect one end of the vapor pipeline with the gas preheater and the other end with the bottom of the rectification tower, and then place each part in the corresponding heating furnace;

[0143] Step 2, use zirconium hafnium tetrachloride with hafnium content of 2% as the raw material for molten salt rectification, take 300 g of zirconium hafnium tetrachloride and 4.5 kg of chloride salt in a glove box with water oxygen content <1 ppm, and place them in the sublimator and the reboiler respectively, connect the sublimator to the feed position in the middle of the rectification tower, connect the reboiler with the bottom of the rectification tower, and connect the circulating tank with the reboiler, then place the connected sublimator and reboiler in the corresponding heating furnace, then vacuumize the device, and after the vacuum degree reaches -0.1 MPa, use nitrogen to replace the air in the device;

[0144] Step 3, heat the sublimator to 280℃, the circulating tank to 550℃, the reflux tank to 340℃, the molten salt circulating pipeline to 350℃, the gas preheater to 600℃, the condenser to room temperature, and the reboiler to 520℃, melt the chloride to obtain molten salt, control the top temperature of the rectifying column to be consistent with the reflux tank, the bottom temperature to be consistent with the reboiler temperature, and the middle temperature to be 150℃ according to the temperature difference between the top and bottom of the column, gradually decrease the temperature from the bottom to the top of the column at 50℃ / m;

[0145] Step 4, transport 3 / 4 of the molten salt in the reboiler to the circulating tank, then inject nitrogen gas with a pressure of 1.0 atm into the gas preheater, set the nitrogen gas flow rate to 1.5 L / min, and press 2 / 3 of the molten salt in the circulating tank into the reflux tank, control the molten salt flow rate of the reflux tank to be 0.08 L / min;

[0146] Step 5, when the molten salt flow rate in the rectifying column is stable, heat the sublimator to 420℃ to vaporize the zirconium hafnium tetrachloride, the vaporized zirconium hafnium tetrachloride enters the rectifying column and is subjected to rectification treatment with the molten salt, during the rectification 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 circulating tank, the dissolved small amount of zirconium hafnium chloride is stripped in the circulating tank for 10 min and returns to the rectifying column along the vapor pipeline, then 2 / 3 of the molten salt is pressed into the reflux tank, and the liquid level of the reflux tank is ensured to be higher than the gas pipeline at the top of the column, the separated zirconium tetrachloride flows into the reboiler and dissolves in the molten salt, and hafnium tetrachloride enters the condenser;

[0147] Step 6, when the rectification treatment is completed, reduce the temperature of the reboiler and the circulating tank to 350℃, discharge the molten salt in the reflux tank into the reboiler and the circulating tank, and obtain the top-enriched hafnium tetrachloride in the condenser;

[0148] Step 7, then replace the condenser, increase the temperature of the reboiler and the circulating tank to 550℃, then fill high-purity nitrogen gas into the gas preheater, evaporate and transport the zirconium tetrachloride enriched in the molten salt to the condenser for condensation, and recover the zirconium tetrachloride.

[0149] Through chemical composition analysis, the hafnium content of the hafnium tetrachloride enriched in the top of the column in Example 3 is 2.96%, and the hafnium content of the zirconium tetrachloride enriched in the bottom of the column is 1.81%.

[0150] The zirconium tetrachloride enriched in Example 3 is used as raw material to continuously rectify 9 times according to the operation process of Example 3, and the hafnium content of the zirconium tetrachloride obtained at the bottom is 0.0084%, which proves that the hafnium in the zirconium tetrachloride is effectively separated and enriched after multiple rectifications, and higher-purity zirconium tetrachloride is obtained.

[0151] The hafnium content of the hafnium tetrachloride obtained after 9 rectifications is 12.15%, which is taken as raw material again, and 10 continuous rectifications are carried out, and the content of zirconium tetrachloride at the top of the tower is reduced to 0.47%. It is proved that after the enrichment of zirconium tetrachloride through multiple rectifications, the purity of hafnium tetrachloride is improved.

[0152] In combination with Table 3, in Example 3, the hafnium tetrachloride enriched at the top of the tower is continuously rectified for 10 times, the purity of hafnium tetrachloride at the top of the tower reaches the standard, and the total rectification stage number is 120; the zirconium tetrachloride enriched at the bottom of the tower is continuously rectified for 11 times, the purity of zirconium tetrachloride at the bottom of the tower reaches the standard, and the total rectification stage number is 132. It can be seen that the actual control reflux ratio in Example 3 is close to R / Rmin=3.0, and the test results are basically consistent with the theoretical calculation results.

[0153] In summary, the zirconium hafnium tetrachloride molten salt extraction rectification separation method provided by the embodiments of the present application is simple in applicable device, easy to install, and the method applicable to the device is more systematic, the technical details are more specific, and the process parameters are more specific. It can be well applied to industrial and laboratory zirconium hafnium tetrachloride molten salt extraction rectification separation technology. And the embodiments of the present application adopt the protection gas pressure conveying mode, realize the simple and efficient circulation of the molten salt by controlling the gas pressure and flow, and solve the problems that the conventional conveying pump cannot convey the high-temperature corrosive melt and the gas lift pump has low transmission efficiency.

[0154] Each of the embodiments in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same and similar parts between the embodiments can be referred to each other.

[0155] Although the preferred embodiments of the embodiments of the present application have been described, those skilled in the art can make additional changes and modifications to the embodiments once they know the basic creative concept. Therefore, the appended claims are intended to include the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present application.

[0156] Finally, it is to be understood that the phraseology or terminology such as "first" and "second" etc. used herein is merely intended to differentiate one entity or operation from another without necessarily requiring or implying any actual such relationship or order between such entities or operations. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0157] The above describes in detail the method for separating zirconium hafnium tetrachloride by molten salt extraction rectification provided by the present application, and the principle and implementation mode of the present application are described by using specific examples. The above description of the examples is only used to help understand the method of the present application and its core idea. Meanwhile, according to the idea of the present application, the specific implementation mode and application range will be changed by the person skilled in the art, and the above description should not be understood as a limitation on the present application.

Claims

1. A method for separating hafnium and zirconium tetrachlorides by molten salt extraction rectification, characterized by, The method is suitable for a molten salt extractive distillation separation device, the device comprising: a distillation column, a sublimator, a reflux tank, a condenser, a reboiler, a circulating tank and a gas preheater; The method comprises: S1, connecting the distillation column with the reflux tank and the reboiler respectively, connecting the reflux tank with the condenser, connecting a gas pipeline on the distillation column, inserting one end of the gas pipeline away from the distillation column into the reflux tank, then connecting the circulating tank with the reboiler, connecting a molten salt circulating pipeline on the circulating tank, connecting the liquid outlet end of the molten salt circulating pipeline on the reflux tank, connecting a vapor pipeline on the molten salt circulating pipeline, connecting one end of the vapor pipeline with the gas preheater and the other end with the bottom of the distillation column; S2, after loading zirconium hafnium tetrachloride into the sublimator, connecting the sublimator with the distillation column, loading the chloride into the reboiler, evacuating the device to vacuum, after the vacuum degree reaches-0.1 MPa, filling nitrogen to replace the air in the device; S3, controlling the sublimator temperature to be 200 ℃-300 ℃, the circulating tank temperature to be 480 ℃-600 ℃, the reflux tank temperature to be 300 ℃-400 ℃, the molten salt circulating pipeline temperature to be 300 ℃-400 ℃, the gas preheater temperature to be 500 ℃-650 ℃, and the reboiler temperature to be 400 ℃-600 ℃, so that the chloride is in a molten state in the distillation column, and molten salt is obtained; S4, transporting an appropriate amount of the molten salt into the circulating tank, filling a protective gas with a pressure of 0.3 atm-1.0 atm into the gas preheater, the protective gas pressing the molten salt in the circulating tank along the molten salt circulating pipeline into the reflux tank, and the molten salt flowing along the reflux tank into the distillation column; S5, increasing the temperature of the sublimator to 400 ℃-450 ℃, so that the zirconium hafnium tetrachloride vaporizes, the vaporized zirconium hafnium tetrachloride enters the distillation column to perform gas-liquid phase mass and heat transfer with the molten salt, and the separated zirconium tetrachloride is enriched in the molten salt in the reboiler, and hafnium tetrachloride vapor enters the condenser; S6, after the distillation process is completed, cooling the reboiler and the circulating tank to 250 ℃-400 ℃, discharging the molten salt in the reflux tank into the reboiler and the circulating tank, condensing the hafnium tetrachloride vapor in the condenser, and obtaining an enriched hafnium tetrachloride; S7, heating the reboiler to 550 ℃-600 ℃, so that the dissolved zirconium tetrachloride in the molten salt vaporizes, and then filling the nitrogen into the gas preheater, the nitrogen transporting the vaporized zirconium tetrachloride to the condenser for recovery.

2. The method of claim 1, wherein the zirconium hafnium tetrachloride is separated by the molten salt extraction rectification method, characterized by, In step S4, when the liquid level of the molten salt in the reboiler is greater than 1 / 2, a proper amount of the molten salt is transported into the circulating tank, and after the molten salt is stored in the circulating tank for 5-10 minutes, a small amount of zirconium hafnium chloride dissolved in the molten salt is vaporized and sent into the vapor pipeline, and the vaporized zirconium hafnium chloride enters the rectification tower for rectification treatment.

3. The method of claim 1, wherein the zirconium hafnium tetrachloride is separated by the molten salt extraction rectification process, characterized in that, In step S5, after the vaporized zirconium hafnium tetrachloride enters the rectification tower, it diffuses towards the top of the rectification tower, and gas-liquid phase contact occurs with the molten salt, and after multi-stage refining, it enters the reflux tank, part of the hafnium tetrachloride vapor is dissolved in the molten salt in the reflux tank, and the other part of the undissolved hafnium tetrachloride vapor enters the condenser for condensation, the molten salt in the rectification tower flows to the bottom and gas-liquid phase contact occurs with the rising zirconium tetrachloride vapor, and the zirconium tetrachloride is enriched.

4. The method of claim 1, wherein the zirconium hafnium tetrachloride is separated by the molten salt extraction rectification process, characterized in that, In step S3, the sublimator temperature is controlled to be 250-280°C, the circulating tank temperature is controlled to be 500-550°C, the reflux tank temperature is controlled to be 320-350°C, the molten salt circulating pipeline temperature is controlled to be 320-350°C, the gas preheater temperature is controlled to be 550-600°C, and the reboiler temperature is controlled to be 450-500°C.

5. The method of claim 1 or 4, wherein the method is characterized by, The temperature at the top of the rectification tower is the same as that of the reflux tank, and the temperature at the bottom of the rectification tower is the same as that of the reboiler. The temperature in the rectification tower decreases step by step from the bottom to the top.

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

7. The method of claim 1 or 6, wherein the method is characterized by, In step S2, the mass ratio of the zirconium hafnium tetrachloride to the chlorides is 1: (10-100).

8. The molten salt extraction distillation separation method for zirconium 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 0.1-5 L / min.

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

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

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