A system and method for treating uranium-containing nitric acid waste solutions

Abstract

This invention relates to the field of uranium-containing nitric acid purification technology, and in particular to a system and method for treating uranium-containing nitric acid waste liquid. The system includes a pretreatment unit, a first-stage distillation unit, and a second-stage distillation unit connected sequentially. First, the uranium-containing nitric acid waste liquid is pretreated by centrifugation to remove waste residue. Then, the resulting uranium-containing nitric acid clear liquid undergoes first-stage distillation, exchanging heat with saturated steam after desuperheating and depressurization. Partially vaporized water and nitric acid leave the first-stage distillation unit in a mixed gaseous state, serving as the feed for the second-stage distillation unit. The non-volatile nitrates contained in the uranium-containing nitric acid clear liquid are concentrated and enriched in the first-stage distillation unit. Subsequently, the nitric acid and water mixed liquid phase in the second-stage distillation unit undergoes multiple partial vaporizations and multiple partial condensations. The light component water flows out from the top of the column in the form of water vapor, while the heavy component nitric acid flows out from the bottom of the column in liquid form, further improving the nitric acid recovery rate and realizing the resource recovery and utilization of uranium-containing nitric acid waste liquid.

Description

Technical Field

[0001] This invention relates to the field of uranium-containing nitric acid purification technology, and in particular to a system and method for treating uranium-containing nitric acid waste liquid. Background Technology

[0002] Uranium purification and conversion, encompassing processes such as uranium concentrate dissolution, solvent extraction purification, concentration and denitrification, hydration reduction, hydrofluorination, fluorination, condensation and liquefaction, and product receiving, is a crucial link in my country's nuclear fuel recycling process. In the "wet" solvent extraction purification process, the crude uranyl nitrate aqueous solution is extracted with an organic solvent. The uranyl nitrate enters the organic solvent, while unextracted metal salt ions, residual metallic uranium, and a certain concentration of nitric acid form the raffinate aqueous phase, i.e., uranium-containing nitric acid wastewater. Direct neutralization and discharge of this wastewater would not only cause significant environmental damage but also waste substantial amounts of nitric acid and alkali resources.

[0003] Chinese invention patent CN201611217555.7 discloses a process for recovering nitric acid from uranium-containing waste liquid. The process mainly employs vacuum distillation to recover nitric acid from the uranium-containing waste liquid. In this process, water vapor and non-condensable gases escape from the top of the distillation column and enter the top condenser, while nitric acid vapor enters the gas-phase acid condenser from the nitric acid vapor outlet on the side of the distillation column. However, periodic monitoring of the nitric acid and uranium concentrations in the distillation residue shows that the nitric acid concentration remains at 8-12 mol / L. Therefore, this process does not yet achieve the resource-based recovery and utilization of uranium-containing nitric acid waste liquid.

[0004] To address this problem, this invention proposes a novel system and method for treating uranium-containing nitric acid wastewater. Through a dual-tower vacuum distillation process, the uranium-containing nitric acid wastewater is treated to achieve harmlessness, and nitric acid and water in the wastewater can be efficiently recovered, significantly reducing the cost of uranium conversion production and meeting my country's requirements for green, environmentally friendly, and sustainable development. Summary of the Invention

[0005] The purpose of this invention is to provide a system and method for treating uranium-containing nitric acid waste liquid, which further improves the recovery rate of nitric acid and realizes the resource recycling of uranium-containing nitric acid waste liquid.

[0006] The present invention provides a uranium-containing nitric acid waste liquid treatment system, including a pretreatment unit, a first-stage distillation unit, and a second-stage distillation unit, wherein the pretreatment unit, the first-stage distillation unit, and the second-stage distillation unit are connected end to end in sequence.

[0007] In a preferred embodiment of this technical solution, the pretreatment mechanism includes a centrifuge and a clear liquid storage tank, wherein the centrifuge, the clear liquid storage tank, and the first-stage distillation mechanism are connected in sequence.

[0008] In a preferred embodiment of this technical solution, the first-stage distillation unit includes a first distillation column body, a first top condenser, a first reboiler, a distillate liquid storage tank, and a bottom liquid storage tank. Along the direction from the top to the bottom of the column, the first distillation column body is sequentially provided with a first distillate outlet, a first reflux inlet, a first feed inlet, a first reboiler vapor inlet, and a first bottom liquid outlet. The clear liquid storage tank is connected to the first feed inlet. The first distillate outlet, the first top condenser, the distillate liquid storage tank, and the first reflux inlet are sequentially connected. The first reboiler is connected to the first reboiler vapor inlet. The first bottom liquid outlet is connected to the bottom liquid storage tank.

[0009] In a preferred embodiment of this technical solution, the second-stage distillation unit includes a second distillation column body, a second top condenser, a second reboiler, a top product water storage tank, and a nitric acid storage tank. Along the direction from the top to the bottom of the column, the second distillation column body is sequentially provided with a second distillate outlet, a second reflux inlet, a second feed inlet, a second reboiler vapor inlet, and a second bottom liquid outlet. The distillate liquid storage tank is connected to the second feed inlet. The second distillate outlet, the second top condenser, the top product water storage tank, and the second reflux inlet are sequentially connected. The second reboiler is connected to the second reboiler vapor inlet. The second bottom liquid outlet is connected to the nitric acid storage tank. The top product water storage tank is also connected to the first reflux inlet.

[0010] As a preferred embodiment of this technical solution, it further includes an exhaust mechanism, wherein the distillate liquid phase storage tank and the top product water storage tank are respectively connected to the exhaust mechanism.

[0011] As a preferred embodiment of this technical solution, a liquid-phase acid cooler is provided between the second bottom liquid outlet and the nitric acid storage tank.

[0012] As a preferred embodiment of this technical solution, it further includes one or more condensate storage tanks, and the condensate outlets of the first reboiler and the second reboiler are both connected to the condensate storage tanks.

[0013] As a preferred embodiment of this technical solution, it further includes a negative pressure mechanism, which is connected to the distillate liquid phase storage tank, the top product water storage tank, the nitric acid storage tank, the first distillation column body, and the second distillation column body respectively; the negative pressure mechanism is a water ring vacuum pump.

[0014] The present invention also discloses a method for treating uranium-containing nitric acid waste liquid using the above-mentioned uranium-containing nitric acid waste liquid treatment system, specifically including the following steps:

[0015] S1. The uranium-containing nitric acid waste liquid is centrifuged to obtain a clear uranium-containing nitric acid liquid;

[0016] S2. The uranium-containing nitric acid solution is subjected to first-stage distillation. In the first-stage distillation column, the uranium-containing nitric acid solution is contacted with the upward steam for mass and heat transfer. The bottom of the column yields a nitrate-containing residue, and the mixed steam of nitric acid and water at the top of the column is condensed to obtain a nitric acid solution.

[0017] S3. The nitric acid solution undergoes a second-stage distillation process. In the second-stage distillation column, the nitric acid solution is contacted with the upward-moving steam for mass and heat transfer. A concentrated nitric acid solution is obtained at the bottom of the column, and the water vapor at the top of the column is condensed to obtain aquatic products.

[0018] The concentration of nitric acid in the nitrate-containing residual liquid is 2-4 mol / L.

[0019] The concentration of nitric acid in the concentrated nitric acid solution is 12-14 mol / L;

[0020] The concentration of nitric acid in the aquatic products is less than 0.01 mol / L.

[0021] As a preferred embodiment of this technical solution, in step S1, a disc centrifuge is used for centrifugation, and the rotation speed is controlled at 5500-6000 rpm, with a feed rate of 2-4 ml. 3 / h; In step S2, during the first-stage distillation, the pressure at the top of the column is controlled to be -70kPa to -60kPa, and the boiling point of the liquid phase at the bottom of the column is 93℃ to 98℃; In step S3, during the second-stage distillation, the pressure at the top of the column is controlled to be -70kPa to -60kPa, and the boiling point of the liquid phase at the bottom of the column is 85℃ to 90℃.

[0022] The uranium-containing nitric acid waste liquid treatment system and method of the present invention have at least the following technical effects:

[0023] 1. The uranium-containing nitric acid waste liquid treatment system of the present invention includes a pretreatment unit, a first-stage distillation unit, and a second-stage distillation unit connected end to end in sequence. First, the uranium-containing nitric acid waste liquid is pretreated by centrifugation to remove waste residue. Then, the resulting uranium-containing nitric acid clear liquid is subjected to first-stage distillation, where it exchanges heat with saturated steam after de-cooling and depressurization. Partially vaporized water and nitric acid leave the first-stage distillation unit in a mixed gaseous state and serve as the feed for the second-stage distillation unit. The non-volatile nitrates contained in the uranium-containing nitric acid clear liquid are concentrated and enriched in the first-stage distillation unit. Then, the nitric acid and water mixed liquid phase in the second-stage distillation unit undergoes multiple partial vaporizations and multiple partial condensations. The light component water flows out from the top of the tower in the form of water vapor, and the heavy component nitric acid flows out from the bottom of the tower in a liquid state, further improving the nitric acid recovery rate and realizing the resource recycling of uranium-containing nitric acid waste liquid.

[0024] 2. This invention uses a dual-tower vacuum distillation method to treat uranium-containing nitric acid wastewater, which can effectively separate nitric acid, water and metal nitrates to obtain reusable and relatively pure nitric acid and water products, thereby reducing the cost of uranium conversion production by saving chemical raw materials. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the uranium-containing nitric acid waste liquid treatment system of the present invention;

[0027] Figure 2 This is a flowchart of the uranium-containing nitric acid waste liquid treatment method of the present invention.

[0028] 1: Centrifuge; 2: Clear liquid storage tank; 3: First distillation column body; 4: First column top condenser; 5: First reboiler; 6: Distillate liquid phase storage tank; 7: Bottom liquid storage tank; 8: Second distillation column body; 9: Second column top condenser; 10: Second reboiler; 11: Column top product water storage tank; 12: Nitric acid storage tank; 13: Exhaust system; 14: Liquid phase acid cooler; 15: Condensate storage tank. Detailed Implementation

[0029] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] like Figure 1 As shown, the present invention provides a uranium-containing nitric acid waste liquid treatment system, including a pretreatment unit, a first-stage distillation unit, and a second-stage distillation unit, wherein the pretreatment unit, the first-stage distillation unit, and the second-stage distillation unit are connected end to end in sequence.

[0034] First, the uranium-containing nitric acid waste liquid is pretreated by a pretreatment unit to remove insoluble solids, preventing them from entering the first-stage distillation unit and causing blockages that would affect distillation efficiency. Then, it enters the first-stage distillation unit, where the non-volatile nature of metal nitrates leads to their continuous enrichment in the bottom liquid phase, separating the nitrates from the volatile nitric acid and water to remove impurities. Finally, it enters the second-stage distillation unit, where the less volatile nitric acid is continuously concentrated and enriched compared to water, yielding both highly concentrated nitric acid and water products. Therefore, the uranium-containing nitric acid waste liquid treatment system of this invention significantly improves the nitric acid recovery rate and achieves the resource-based recycling of uranium-containing nitric acid waste liquid.

[0035] Uranium-containing nitric acid waste liquid, with an acidity of 1 mol / L to 3 mol / L, contains 1‰-10‰ insoluble solids. To prevent these insoluble solids from entering the distillation unit, they need to be removed. This invention does not strictly limit the specific form of the pretreatment unit; filtration or centrifugation can be used to separate the solids and liquids in the uranium-containing nitric acid waste liquid. In this embodiment, the pretreatment unit includes a disc centrifuge 1 and a clear liquid storage tank 2, which are sequentially connected to the first-stage distillation unit. The disc centrifuge 1 operates at a speed of 5900 rpm / min, with a feed rate of 2 m³ / h-4 m³ / h. Under centrifugal force, due to the density difference between the liquid and solid phases, the liquid phase is collected and discharged in the middle of the drum, while the solid phase is collected and discharged at the outer edge of the drum, completing the separation of the liquid and solid phases and achieving pretreatment of the waste liquid. The uranium-containing nitric acid solution obtained from the pretreatment enters the clear solution storage tank and serves as the raw material for the first-stage distillation unit.

[0036] In this embodiment, the first-stage distillation mechanism specifically includes a first distillation column body 3, a first top condenser 4, a first reboiler 5, a distillate liquid phase storage tank 6, and a bottom liquid storage tank 7. Along the direction from the top to the bottom of the column, the first distillation column body 3 is sequentially provided with a first distillate outlet, a first reflux inlet, a first feed inlet, a first reboiler vapor inlet, and a first bottom liquid outlet. The clear liquid storage tank 2 is connected to the first feed inlet. The first distillate outlet, the first top condenser 4, the distillate liquid phase storage tank 6, and the first reflux inlet are sequentially connected. The first reboiler 5 is connected to the first reboiler vapor inlet. The first bottom liquid outlet is connected to the bottom liquid storage tank 7.

[0037] The uranium-containing nitric acid solution in the clear liquid storage tank 2 enters the first distillation column body 3 through the first feed inlet via the clear liquid transfer pump. After mixing with the downward-flowing liquid phase in the first distillation column body 3, the uranium-containing nitric acid solution continues to flow downward, engaging in mass and heat transfer with the upward-flowing steam. The liquid phase flowing down to the bottom of the first-stage distillation column body enters the first reboiler 5. In the tube side of the first reboiler 5, it exchanges heat with the saturated steam at 0.23 MPa and 125°C in the shell side, becoming superheated steam. This superheated steam returns from the top of the first reboiler 5 to the first distillation column body 3, providing upward-flowing steam for the distillation process. The upward-flowing steam exchanges mass and heat with the downward-flowing liquid phase. Some of the nitric acid and water mixed steam flows out from the top of the first-stage distillation column body, enters the first cooler, is cooled into liquid phase, and flows into the distillate liquid phase storage tank 6.

[0038] After multi-stage distillation, the non-volatile nitrates in the uranium-containing nitric acid solution are continuously concentrated and enriched in the first distillation column 3. When the concentration ratio reaches 30-45 times, the nitrate-containing residual liquid is collected by the nitrate residue pump and enters the bottom liquid storage tank 7. The volatile nitric acid and water vapor mixture in the uranium-containing nitric acid solution is continuously distilled and condensed by the first condenser before entering the distillate liquid phase storage tank 6. The nitric acid solution in the distillate liquid phase storage tank 6 contains a large amount of water, with a concentration of 2mol / L-4mol / L, which does not meet the concentration requirements for reused nitric acid in the production line. Therefore, part of this nitric acid solution is pumped back to the first distillation column 3 as reflux liquid, and the other part is pumped back to the second distillation column 8 as feed.

[0039] The first distillation column body 3 is preferably a packed column, and both the column body and the packing are made of 304L stainless steel.

[0040] In this embodiment, the second-stage distillation unit includes a second distillation column body 8, a second top condenser 9, a second reboiler 10, a top product water storage tank 11, and a nitric acid storage tank 12. Along the direction from the top to the bottom of the column, the second distillation column body 8 is sequentially provided with a second distillate outlet, a second reflux inlet, a second feed inlet, a second reboiler vapor inlet, and a second bottom liquid outlet. The distillate liquid storage tank 6 is connected to the second feed inlet. The second distillate outlet, the second top condenser 9, the top product water storage tank 11, and the second reflux inlet are sequentially connected. The second reboiler 10 is connected to the second reboiler vapor inlet. The second bottom liquid outlet is connected to the nitric acid storage tank 12. The top product water storage tank 11 is also connected to the first reflux inlet.

[0041] Furthermore, a liquid-phase acid cooler 14 is provided between the second bottom liquid outlet and the nitric acid storage tank 12.

[0042] The nitric acid aqueous solution in the distillate liquid phase storage tank 6 is pumped through the second feed port to the second distillation column body 8 as feed to begin the second-stage distillation process. In the second distillation column body 8, the liquid nitric acid solution mixes with the downward-flowing liquid phase and continues to flow downwards, engaging in mass and heat transfer with the upward-flowing steam. The liquid phase flowing down to the bottom of the second distillation column body 8 enters the second reboiler 10, where it exchanges heat with the saturated steam at 0.23 MPa and 125°C in the shell side of the reboiler 10, becoming superheated steam. This superheated steam returns from the top of the second reboiler 10 to the second distillation column body 8, providing upward-flowing steam for the distillation process. The upward-flowing steam undergoes mass and heat transfer with the downward-flowing liquid phase. A portion of the nitric acid and water mixed steam flows out from the second distillate outlet at the top of the second distillation column body 8, enters the second cooler, is cooled to become liquid, and flows into the top product water storage tank 11.

[0043] Compared to water, nitric acid, which is less volatile, is continuously concentrated and enriched in the body of the second distillation column 8. When the concentration factor reaches 2-4 times, its acidity reaches 12 mol / L to 14 mol / L. Under the negative pressure (-70 kPa to -60 kPa) provided by the vacuum pump, it enters the liquid-phase acid cooler 14, is cooled, and flows into the nitric acid storage tank 12. At this point, the nitric acid concentration has reached the reuse requirement of the production line (>7 mol / L) and can be returned to the production line for reuse via the nitric acid transfer pump.

[0044] The water in the top product water storage tank 11 has three destinations: it is pumped to the first distillation column body 3 as top reflux liquid, pumped to the second distillation column body 8 as top reflux liquid, and then pumped to the production line for reuse.

[0045] The first reboiler 5 and the second reboiler 10 are important sites for heat exchange during the liquid phase heating and vaporization process in the distillation process, providing a continuous supply of gas phase for distillation. In the shell side of the first reboiler 5 and the second reboiler 10, the saturated vapor condenses and releases the latent heat of phase change, while in the tube side, the liquid phase in the bottom of the column circulates naturally using the thermosiphon effect and is heated and boils into the gas phase.

[0046] Based on the above technical solution, it further includes an exhaust mechanism 13 to collect non-condensable gases in the mixed phase in a timely manner. The distillate liquid phase storage tank 6 and the top product water storage tank 11 are respectively connected to the exhaust mechanism 13.

[0047] In addition, a gas-liquid separator can be used to remove non-condensable gases. The liquid condensed by the first or second cooler first enters the gas-liquid separator. After gas-liquid separation, the liquid phase enters the distillate liquid phase storage tank 6 or the column top product water storage tank 11, while the gas phase is directly discharged or used to provide the required compressed air for the distillation column.

[0048] In addition, to facilitate the recovery of condensate from the first reboiler 5 and the second reboiler 10, the system in this embodiment also includes one or more condensate storage tanks 15, with the condensate outlets of both the first reboiler 5 and the second reboiler 10 connected to the condensate storage tanks 15. Saturated steam at 0.23 MPa and 125°C undergoes a phase change after heat exchange in the first reboiler 5 and the second reboiler 10, becoming steam condensate. The condensate enters the condensate storage tanks, and multiple condensate tanks are used alternately. To prevent corrosion or leakage during equipment operation that could affect the quality of the condensate, samples of the condensate in the tanks are analyzed to ensure that the acid and uranium content is within acceptable limits before the condensate is discharged using the condensate transfer pump.

[0049] Based on the above technical solution, and more preferably, it further includes a negative pressure mechanism, which is connected to the distillate liquid phase storage tank 6, the top product water storage tank 11, the nitric acid storage tank 12, the first distillation column body 3, and the second distillation column body 8 respectively, to provide negative pressure thereon; specifically, the pressure at the top of the first distillation column body 3 is controlled at -70kPa to -60kPa, and the boiling point of the liquid phase at the bottom of the column is reduced from 120℃-126℃ to 93℃-98℃. The pressure at the top of the second distillation column body is controlled at -70kPa to -60kPa, and the boiling point of the liquid phase at the bottom of the column is reduced from 106-112℃ to 85℃-90℃.

[0050] The negative pressure mechanism is preferably a water ring vacuum pump.

[0051] The corrosion rate of stainless steel by nitric acid is affected by both acidity and temperature. The acidity of nitric acid within the distillation system is limited by the input and output conditions of the materials and cannot be arbitrarily changed. However, by using vacuum distillation to lower the temperature of the gas and liquid phases within the distillation system, the corrosion rate of stainless steel by nitric acid can be slowed down.

[0052] Example 2

[0053] The treatment of uranium-containing nitric acid waste liquid with an acidity of 1 mol / L to 3 mol / L and containing 1‰ to 10‰ insoluble solids using the most preferred uranium-containing nitric acid waste liquid treatment system described above specifically includes the following steps ( Figure 2 ):

[0054] S1. A disc centrifuge is used, with the rotation speed controlled at 5500-6000 rpm and the feed rate at 2-4 m³ / min. 3 / h, the uranium-containing nitric acid waste liquid is centrifuged to obtain uranium-containing nitric acid clear liquid;

[0055] S2. The uranium-containing nitric acid solution is subjected to a first-stage distillation process with a feed rate of 2 m3 / h-4 m3 / h, and the pressure at the top of the column is controlled at -70 kPa to -60 kPa. The boiling point of the liquid phase at the bottom of the column is 93℃-98℃. In the first-stage distillation column, the uranium-containing nitric acid solution is subjected to mass and heat transfer in contact with the upward-moving steam. The bottom of the column is obtained as a nitrate-containing residue, and the mixed steam of nitric acid and water at the top of the column is condensed to obtain a nitric acid solution.

[0056] S3. The nitric acid solution is subjected to a second-stage distillation process with a feed rate of 2 m3 / h-4 m3 / h, and the pressure at the top of the column is controlled at -70 kPa to -60 kPa. The boiling point of the liquid phase at the bottom of the column is 85℃-90℃. In the second-stage distillation column, the nitric acid solution and the upward-flowing steam are in contact for mass and heat transfer. The concentrated nitric acid solution is obtained at the bottom of the column, and the water vapor at the top of the column is condensed to obtain aquatic products.

[0057] Finally, the concentrations of nitric acid in the nitrate-containing residual liquid, concentrated nitric acid solution, and aquatic products were analyzed. The concentration of nitric acid in the nitrate-containing residual liquid was 2 mol / L-4 mol / L, the concentration in the concentrated nitric acid solution was 12 mol / L-14 mol / L, and the concentration of nitric acid in the aquatic products was less than 0.01 mol / L. Therefore, the uranium-containing nitric acid wastewater treatment system of this invention significantly improves the nitric acid recovery rate and realizes the resource-based recycling of uranium-containing nitric acid wastewater.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for treating uranium-containing nitric acid waste liquid, characterized in that, It includes a pretreatment unit, a first-stage distillation unit, and a second-stage distillation unit. The pretreatment unit, the first-stage distillation unit, and the second-stage distillation unit are connected sequentially from end to end; The pretreatment unit includes a centrifuge (1) and a clear liquid storage tank (2). The centrifuge (1), the clear liquid storage tank (2), and the first-stage distillation mechanism are connected in sequence; The first-stage distillation unit includes a first distillation column body (3), a first column top condenser (4), a first reboiler (5), a distillate liquid phase storage tank (6), and a bottom liquid storage tank (7). Along the direction from the top to the bottom of the column, the first distillation column body (3) is provided with a first distillate outlet, a first reflux liquid inlet, a first feed inlet, a first reboiler steam inlet and a first bottom liquid outlet in sequence; The clear liquid storage tank (2) is connected to the first feed inlet; The first distillate outlet, the first top condenser (4), the distillate liquid storage tank (6), and the first reflux inlet are connected in sequence; The first reboiler (5) is connected to the first reboiler steam inlet; The first bottom liquid outlet is connected to the bottom liquid storage tank (7); The second-stage distillation unit includes a second distillation column body (8), a second top condenser (9), a second reboiler (10), a top product water storage tank (11), and a nitric acid storage tank (12). Along the direction from the top to the bottom of the column, the second distillation column body (8) is provided with a second distillate outlet, a second reflux liquid inlet, a second feed inlet, a second reboiler steam inlet, and a second bottom liquid outlet in sequence; The distillate liquid phase storage tank (6) is connected to the second feed inlet; The second distillate outlet, the second top condenser (9), the top product water storage tank (11), and the second reflux inlet are connected in sequence; The second reboiler (10) is connected to the second reboiler steam inlet; The outlet of the second bottom liquid is connected to the nitric acid storage tank (12); The product water storage tank (11) at the top of the tower is also connected to the first reflux liquid inlet.

2. The uranium-containing nitric acid wastewater treatment system according to claim 1, characterized in that, It also includes an exhaust system (13), and the distillate liquid phase storage tank (6) and the top product water storage tank (11) are respectively connected to the exhaust system (13).

3. The uranium-containing nitric acid wastewater treatment system according to claim 1, characterized in that, A liquid-phase acid cooler (14) is provided between the second bottom liquid outlet and the nitric acid storage tank (12).

4. The uranium-containing nitric acid wastewater treatment system according to claim 1, characterized in that, It also includes one or more condensate storage tanks (15), and the condensate outlets of the first reboiler (5) and the second reboiler (10) are connected to the condensate storage tanks (15).

5. The uranium-containing nitric acid wastewater treatment system according to claim 1, characterized in that, It also includes a negative pressure mechanism, which is connected to the distillate liquid phase storage tank (6), the top product water storage tank (11), the nitric acid storage tank (12), the first distillation column body (3), and the second distillation column body (8), respectively; The negative pressure mechanism is a water ring vacuum pump.

6. A method for treating uranium-containing nitric acid waste liquid using the uranium-containing nitric acid waste liquid treatment system according to any one of claims 1-5, characterized in that, Includes the following steps: S1. The uranium-containing nitric acid waste liquid is centrifuged to obtain a clear uranium-containing nitric acid liquid; S2. The uranium-containing nitric acid solution is subjected to first-stage distillation. In the first-stage distillation column, the uranium-containing nitric acid solution is contacted with the upward steam for mass and heat transfer. The bottom of the column yields a nitrate-containing residue, and the mixed steam of nitric acid and water at the top of the column is condensed to obtain a nitric acid solution. S3. The nitric acid solution undergoes a second-stage distillation process. In the second-stage distillation column, the nitric acid solution is contacted with the upward-moving steam for mass and heat transfer. A concentrated nitric acid solution is obtained at the bottom of the column, and the water vapor at the top of the column is condensed to obtain aquatic products. The concentration of nitric acid in the nitrate-containing residual liquid is 2-4 mol / L. The concentration of nitric acid in the concentrated nitric acid solution is 12-14 mol / L; The concentration of nitric acid in the aquatic products is less than 0.01 mol / L.

7. The method according to claim 6, characterized in that, In step S1, during the centrifugation process, a disc centrifuge (1) is used, and the rotation speed is controlled at 5500-6000 rpm, with a feed rate of 2-4 m³. 3 / h; In step S2, during the first-stage distillation process, the pressure at the top of the column is controlled to be -70 kPa to -60 kPa, and the boiling point of the liquid phase at the bottom of the column is 93℃ to 98℃. In step S3, during the second-stage distillation process, the pressure at the top of the column is controlled to be -70 kPa to -60 kPa, and the boiling point of the liquid phase at the bottom of the column is 85℃-90℃.

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