System and method for treating uranium-containing nitric acid-containing waste liquid by coupling MVR (mechanical vapor recompression) with single-effect evaporation concentration
Through MVR coupled single-effect evaporation and concentration technology and cooling thick salt production technology, the problems of salt removal and uranium concentration improvement in wastewater with high salt content nitric acid system are solved, and efficient waste liquid treatment and energy consumption reduction are achieved.
Patent Information
- Application Number
- CN202411081230.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-08
- Publication Date
- 2024-12-13
AI Technical Summary
The prior art is difficult to effectively remove the salt in the uranium-containing wastewater of the nitric acid system with high salt content and increase the uranium concentration, and the evaporation and enrichment process has high energy consumption, resulting in an increase in treatment cost.
The MVR coupled single-effect evaporation and enrichment process is adopted, and MVR is used as the enrichment system, combining single-effect evaporation and cooling thick salt output technology to reduce system blockage by softening water and steam cleaning, achieving efficient salt removal and uranium concentration improvement.
The 80% salt removal rate and uranium concentration in the waste liquid are reduced to less than 50μg/L, meeting emission requirements, and reducing energy consumption through heat recovery.
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Figure CN119132681A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the technical field of uranium purification and conversion, and specifically to a system and method for treating uranium- and nitric acid-containing wastewater by MVR coupling single-effect evaporation and concentration. Background Art
[0002] During the uranium purification production process, uranium-containing wastewater of the nitric acid system, such as distillation residue, organic phase alkaline washing liquid and denitrification tail gas washing liquid, will be produced. The uranium-containing wastewater of this system has the characteristics of high salt content (about 60-70 kg of salt per cubic meter of waste liquid) and high organic impurity content. In the treatment process of this type of wastewater, uranium recovery is first required for the wastewater, but the wastewater after uranium recovery still does not meet the discharge requirements, so it is necessary to deeply remove the uranium in the uranium-containing wastewater of this system. In order to solve the problems of high salt content in the wastewater and substandard uranium concentration, it is necessary to find a suitable and efficient process.
[0003] At present, the commonly used desalination processes mainly include ion exchange adsorption, membrane separation and evaporation concentration. Since the salt content of uranium-containing wastewater in the nitric acid system after uranium recovery is mainly sodium nitrate, potassium nitrate and other impurity salts, the adsorption effect of this component in ion exchange adsorption is currently poor, that is, the ion exchange resin suitable for the nitric acid system is in the research stage, so this method is not suitable for the removal of salt in this type of wastewater. Due to the high salt content in uranium-containing wastewater in the nitric acid system, resulting in high osmotic pressure, it is difficult to remove salt using membrane separation. The evaporation concentration method can remove most of the salt in the wastewater, thus meeting the demand for salt removal in uranium-containing wastewater in the nitric acid system. At the same time, evaporation concentration can also solve the key problem of uranium concentration not meeting the standard. However, the energy consumption of this method is extremely high, resulting in an increase in the cost of waste liquid treatment. Therefore, a new energy-saving evaporation concentration method is needed to treat uranium-containing wastewater in the nitric acid system.
[0004] Therefore, the present invention provides a new energy-saving process of "MVR coupled single-effect evaporation concentration + cooling thickening + centrifugal salt removal" to treat high-salt uranium-containing and nitric acid-containing waste liquid, which aims to concentrate the impurity salts in the waste liquid and remove them by cooling and centrifugation. The centrifuge produced in the process will undergo further uranium recovery treatment; and the large amount of condensed water with low uranium concentration produced by the system will meet the discharge standards after testing. In order to reduce system blockage, the process uses two-stage evaporation to concentrate the feed liquid, in which MVR is a concentration system, and the subsequent formation of a nearly saturated solution is completed by single-effect evaporation, and softened water cleaning and steam cleaning are added to the evaporation and concentration system to reduce system blockage, ensuring that the process can operate efficiently and stably. Summary of the invention
[0005] The purpose of the present invention is to provide an MVR-coupled single-effect evaporation and concentration process, which can remove most of the salt in the uranium-containing and nitric acid-containing waste liquid, and at the same time, the clear liquid produced by the process can achieve standard discharge. In order to solve the problems of easy blockage and high energy consumption of single-system evaporation, this process is equipped with MVR-coupled single-effect evaporation, and MVR is used as the concentration system, which saves energy while satisfying a certain degree of concentration of the feed liquid; the process is also equipped with softened water cleaning and steam cleaning to reduce the problem of system blockage and ensure process stability. After the waste liquid is treated by this process, a large amount of impurity salts in the waste liquid can be removed, and the uranium concentration of the condensed water produced by the system is reduced to less than 50μg / L, meeting the final standard discharge requirements; on the other hand, after the concentrated liquid is cooled and desalted, the liquid is further recovered for uranium.
[0006] The technical scheme of the present invention is as follows: an MVR-coupled single-effect evaporation and concentration system for treating uranium-containing and nitric acid-containing waste liquid, comprising a feed buffer tank, the feed buffer tank is connected to a non-condensable gas preheater, the non-condensable gas preheater is connected to a plate heat exchanger, the plate heat exchanger is connected to an MVR evaporation and concentration unit, the MVR evaporation and concentration unit is connected to an MVR condensate water tank and a single-effect evaporation and concentration unit, the single-effect evaporation and concentration unit is connected to a thickening kettle, the thickening kettle is connected to a flat scraper centrifuge, and the MVR condensate water tank and the single-effect evaporation and concentration unit are connected to a condensate water buffer tank.
[0007] The MVR evaporation and concentration unit includes an MVR evaporator, an MVR heater, and a Roots compressor; the MVR evaporator is connected to the MVR heater, and the MVR heater is connected to the MVR condensed water tank.
[0008] The single-effect evaporation and concentration unit includes a single-effect evaporator, a single-effect heater, and a single-effect condenser; the MVR evaporator is connected to the single-effect evaporator, the single-effect evaporator is connected to the single-effect heater, the single-effect evaporator is connected to the single-effect condenser, and the single-effect evaporator is connected to the thickening kettle.
[0009] A method for treating uranium- and nitric acid-containing waste liquid by MVR coupling single-effect evaporation and concentration, comprising the following steps:
[0010] S1: feeding and preheating;
[0011] The waste liquid first enters the feed buffer tank, then enters the non-condensable gas preheater, where it is preheated once; the waste liquid enters the plate heat exchanger for heat exchange;
[0012] S2: MVR evaporation concentration
[0013] The waste liquid after S1 enters the MVR evaporator and begins to evaporate; the treated waste liquid is sent to the single-effect evaporation concentration unit.
[0014] S3: Single-effect evaporation concentration
[0015] The treated waste liquid is sent to the single-effect evaporator and forced to circulate between the single-effect heater and the single-effect evaporator;
[0016] S4: Cooling and thickening desalination
[0017] The waste liquid at the bottom of the single-effect evaporator is pumped to the thickening kettle, where the crystals are precipitated by cooling, and the slurry is separated into solid and liquid by a flat scraper centrifuge.
[0018] In the S1, the pH of the waste liquid is adjusted to 6-12, and the COD is <200 mg / L.
[0019] In S1, the non-condensable gas generated by the MVR evaporation and concentration unit and the single-effect evaporation and concentration unit enters the non-condensable gas preheater, and the waste liquid is preheated once in the non-condensable gas preheater, and the preheating temperature reaches 40-55°C; the waste liquid enters the plate heat exchanger, and then heat exchanges with the secondary steam condensate generated by the MVR evaporation and concentration unit in the plate heat exchanger, and the feed liquid temperature after the heat exchange is 70-80°C.
[0020] In S2, the temperature of the MVR evaporator is 90 to 95°C, and the pressure is -10 to -30 kPa.
[0021] In S2, the temperature of the separated secondary steam is increased after being compressed by the Roots compressor, and then it is introduced into the MVR heater to further heat the waste liquid, so that the waste liquid is accelerated to concentrate in the MVR separator after receiving sufficient heat and is recycled.
[0022] In S2, the density of the treated wastewater is increased to 1.25 g / cm 3 Finally, it is sent to the single-effect evaporation concentration unit.
[0023] In S3, the external environment heats the single-effect evaporator by supplementing steam to the single-effect heater.
[0024] In S3, the steam generated by the single-effect evaporator enters the single-effect condenser for cooling.
[0025] In S3, the waste liquid is cooled to 20-30° C. in a thickening kettle.
[0026] In the S3, the water content of the solid salt particles is less than 8%.
[0027] In S4, the solid salt particles are discharged from the lower part of the flat scraper centrifuge and barreled for further processing; and the centrifuged mother liquor enters the mother liquor tank and is pumped to the extraction and stripping system for uranium recovery.
[0028] It also includes S5: condensed water meets the discharge standards; the steam condensed water produced by the MVR evaporation concentration unit and the single-effect evaporation concentration unit enters the condensed water buffer tank, and is then sent to the plate heat exchanger, where it undergoes heat exchange and cools down to 35°C before being tested. It is then discharged after the uranium concentration meets the standards.
[0029] The remarkable effects of the present invention are:
[0030] (1) The present invention uses MVR as a concentration system. When the feed liquid concentration reaches a certain level, the feed is transferred to a single-effect system for further concentration. High-speed water cleaning and steam cleaning are provided in the single-effect system to reduce the problem of system blockage, so that the process can operate more efficiently and stably.
[0031] (2) The present invention targets waste liquid containing uranium and nitrate, and combines the three sections of "MVR evaporation concentration + single-effect evaporation concentration + cooling and thickening salt discharge" to remove a large amount of impurity salts in the waste liquid, and the desalination rate can reach 80%. At the same time, a large amount of uranium is enriched in the centrifuge liquid obtained during desalination, which can further realize uranium recovery and reduce the loss of nuclear materials. In addition, the uranium concentration of the condensed water generated during the salt concentration process is less than 50μg / L.
[0032] (3) The present invention adopts the method of "MVR coupled single-effect evaporation and concentration". This technology not only meets the treatment process of uranium-containing and nitric acid-containing waste liquid, but also generates secondary steam in the MVR evaporation process that can be recycled after compression. The condensed water and non-condensable gas generated by the system can be used for material preheating. At the same time, part of the condensed water can be used for the preparation of process reagents, fully recovering heat and reducing process energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Figure 1 This is the flow chart of MVR combined single-effect evaporation concentration and thickening desalination of uranium-containing wastewater;
[0034] Figure 2 Flow chart of MVR evaporation concentration system
[0035] Figure 3 Flow chart of single-effect evaporation concentration system
[0036] In the figure: feed buffer tank 1, non-condensable gas preheater 2, plate heat exchanger 3, MVR evaporation concentration unit 4, MVR condensate tank 5, single-effect evaporation concentration unit 6, thickening kettle 7, flat scraper centrifuge 8, condensate buffer tank 9;
[0037] MVR evaporator 4-1, MVR heater 4-2, Roots compressor 4-3;
[0038] Single-effect evaporator 6-1, single-effect heater 6-2, single-effect condenser 6-3. DETAILED DESCRIPTION
[0039] Many specific details are described in the following description to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present application, so the present application is not limited by the specific implementation disclosed below.
[0040] The terms used in one or more embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit one or more embodiments of the present application. The singular forms of "a", "said" and "the" used in one or more embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in one or more embodiments of the present application refers to and includes any or all possible combinations of one or more associated listed items.
[0041] It should be understood that, although the terms first, second, etc. may be used to describe various information in one or more embodiments of the present application, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of one or more embodiments of the present application, the first may also be referred to as the second, and similarly, the second may also be referred to as the first.
[0042] A MVR-coupled single-effect evaporation and concentration system for treating uranium-containing and nitric acid-containing waste liquid, comprising a feed buffer tank 1, a non-condensable gas preheater 2, a plate heat exchanger 3, an MVR evaporation and concentration unit 4, an MVR condensed water tank 5, a single-effect evaporation and concentration unit 6, a thickening kettle 7, a flat scraper centrifuge 8, and a condensed water buffer tank 9; wherein the feed buffer tank 1 is connected to the non-condensable gas preheater 2, the non-condensable gas preheater 2 is connected to the plate heat exchanger 3, the plate heat exchanger 3 is connected to the MVR evaporation and concentration unit 4, the MVR evaporation and concentration unit 4 is connected to the MVR condensed water tank 5 and the single-effect evaporation and concentration unit 6, the single-effect evaporation and concentration unit 6 is connected to the thickening kettle 7, the thickening kettle 7 is connected to the flat scraper centrifuge 8, and the MVR condensed water tank 5 and the single-effect evaporation and concentration unit 6 are connected to the condensed water buffer tank 9;
[0043] The MVR evaporation concentration unit 4 includes an MVR evaporator 4-1, an MVR heater 4-2, and a Roots compressor 4-3; the MVR evaporator 4-1 is connected to the MVR heater 4-2, and the MVR heater 4-2 is connected to the MVR condensed water tank 5
[0044] The single-effect evaporation concentration unit 6 includes a single-effect evaporator 6-1, a single-effect heater 6-2, and a single-effect condenser 6-3; the MVR evaporator 4-1 is connected to the single-effect evaporator 6-1, the single-effect evaporator 6-1 is connected to the single-effect heater 6-2, the single-effect evaporator 6-1 is connected to the single-effect condenser 6-3, and the single-effect evaporator 6-1 is connected to the thickening kettle 7
[0045] A method for treating uranium- and nitric acid-containing waste liquid by MVR coupling single-effect evaporation and concentration, comprising the following steps:
[0046] S1: Feeding and preheating
[0047] The waste liquid (pH adjusted to 6-12, COD < 200 mg / L) first enters the feed buffer tank 1, and then enters the non-condensable gas preheater 2. The non-condensable gas generated by the MVR evaporation and concentration unit 4 and the single-effect evaporation and concentration unit 6 enters the non-condensable gas preheater 2. The waste liquid is preheated once in the non-condensable gas preheater 2, and the preheating temperature reaches 40-55°C. The waste liquid enters the plate heat exchanger 3, and then exchanges heat with the secondary steam condensate generated by the MVR evaporation and concentration unit 4 in the plate heat exchanger 3. After the secondary preheating (heat exchange), the feed liquid temperature can reach 70-80°C.
[0048] S2: MVR evaporation concentration
[0049] After two preheatings in S1, the waste liquid enters the MVR evaporator 4-1 (maintaining the evaporator temperature at 90-95°C and the pressure at -10-30kPa) and begins to evaporate. The generated steam and entrained tiny droplets rise in the MVR evaporator 4-1, and the entrained droplets are well separated after passing through the baffle. The separated secondary steam is compressed by the Roots compressor 4-3 (the compressor frequency is set to 35-42Hz) and the temperature is increased (the compressor outlet steam temperature is 100-110°C and the pressure is 20-30kPa), and then passed into the MVR heater 4-2 to further heat the waste liquid, so that the waste liquid is accelerated to concentrate in the MVR separator 4-1 after sufficient heat is obtained, and recycled. The density of the treated waste liquid is increased to 1.25g / cm 3 After that, it is sent to the single-effect evaporation and concentration unit 6; the condensed water of the secondary steam generated by the MVR evaporation and concentration unit 4 can preheat the waste liquid.
[0050] S3: Single-effect evaporation concentration
[0051] The density of the liquid in the MVR evaporator 4-1 reaches 1.25 g / cm 3 After that, it is sent to the single-effect evaporator 6-1, and then the circulating pump is used to force the liquid to circulate between the single-effect heater 6-2 and the single-effect evaporator 6-1; the outside world is supplemented with steam (the steam flow rate is 200-600 kg / h) to the single-effect heater 6-2, so as to heat the single-effect evaporator 6-1, and the vacuum pump frequency is set to 25-30 Hz to pump the negative pressure of the evaporator to -45--65 kPa to reduce the boiling point of the liquid, and the temperature of the single-effect evaporator 6-1 is maintained at 70-85 ° C to make the waste liquid easier to evaporate, thereby accelerating the concentration of the waste liquid, and the density of the waste liquid in the single-effect evaporator 6-1 can be increased to 1.50-1.55 g / cm 3 The steam generated by the single-effect evaporator 6-1 enters the single-effect condenser 6-3 for cooling;
[0052] S4: Cooling and thickening desalination
[0053] The bottom of the single-effect evaporator 6-1 is pumped to the thickening kettle 7 through the salt outlet pump. The saturated liquid is cooled to 20-30°C in the thickening kettle 7 to precipitate crystals. The slurry is separated from the solid by the flat scraper centrifuge 8 (the feeding time is 5-20 minutes, and the de-liquidation time is 10-20 minutes). The solid salt particles (water content <8%) are discharged from the bottom of the flat scraper centrifuge 8 and barreled for further treatment; the centrifuged mother liquor enters the mother liquor tank and is pumped to the extraction and stripping system for uranium recovery (the average uranium concentration of the mother liquor is 850 mg / L).
[0054] S5: Condensate discharge meets standards
[0055] The secondary steam condensate produced by the MVR evaporation concentration unit 4 and the single-effect evaporation concentration unit 6 enters the condensate buffer tank 9 and is then sent to the plate heat exchanger 3. After heat exchange in the plate heat exchanger 3 and cooling to 35°C, it is tested and discharged after the uranium concentration reaches the standard (density is less than 50μg / L).
[0056] S6: Softened water and steam cleaning
[0057] Steps S2 and S3 are equipped with high-speed softened water cleaning and steam cleaning to clear and clean pipes that are prone to blockage and crystallization during the evaporation process, ensuring that the process can run more efficiently and stably.
[0058] The above description is only a preferred embodiment of this patent and is not intended to limit this patent. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this patent should be included in the scope of protection of this patent.
[0059] It should be noted that, for the convenience of description, the aforementioned method embodiments are all described as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the described action sequence, because according to the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and units involved are not necessarily required by the present application.
[0060] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.
[0061] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The optional embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of the present application. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can understand and use the present application well.
Claims
1. A MVR coupled single-effect evaporation and concentration system for treating uranium-containing and nitric acid-containing wastewater, characterized in that: The invention comprises a feed buffer tank (1), wherein the feed buffer tank (1) is connected to a non-condensable gas preheater (2), the non-condensable gas preheater (2) is connected to a plate heat exchanger (3), the plate heat exchanger (3) is connected to an MVR evaporation and concentration unit (4), the MVR evaporation and concentration unit (4) is connected to an MVR condensate tank (5) and a single-effect evaporation and concentration unit (6), the single-effect evaporation and concentration unit (6) is connected to a thickening kettle (7), the thickening kettle (7) is connected to a flat scraper centrifuge (8), and the MVR condensate tank (5) and the single-effect evaporation and concentration unit (6) are connected to a condensate buffer tank (9).
2. The MVR coupled single-effect evaporation and concentration system for treating uranium-containing and nitric acid-containing waste liquid according to claim 1, characterized in that: The MVR evaporation concentration unit (4) comprises an MVR evaporator (4-1), an MVR heater (4-2), and a Roots compressor (4-3); the MVR evaporator (4-1) is connected to the MVR heater (4-2), and the MVR heater (4-2) is connected to the MVR condensed water tank (5).
3. The MVR coupled single-effect evaporation and concentration system for treating uranium-containing and nitric acid-containing wastewater according to claim 2, characterized in that: The single-effect evaporation concentration unit (6) comprises a single-effect evaporator (6-1), a single-effect heater (6-2), and a single-effect condenser (6-3); the MVR evaporator (4-1) is connected to the single-effect evaporator (6-1), the single-effect evaporator (6-1) is connected to the single-effect heater (6-2), the single-effect evaporator (6-1) is connected to the single-effect condenser (6-3), and the single-effect evaporator (6-1) is connected to the thickening kettle (7).
4. A method for treating uranium-containing and nitric acid-containing waste liquid by MVR coupling single-effect evaporation and concentration, using the MVR coupling single-effect evaporation and concentration system for treating uranium-containing and nitric acid-containing waste liquid as claimed in claim 3, characterized in that: The following steps are involved: S1: feeding and preheating; The waste liquid first enters the feed buffer tank (1), and then enters the non-condensable gas preheater (2), where it is preheated once; the waste liquid enters the plate heat exchanger (3) where it undergoes heat exchange; S2: MVR evaporation concentration The waste liquid after S1 enters the MVR evaporator (4-1) and begins to evaporate; the treated waste liquid is sent to the single-effect evaporation concentration unit (6); S3: Single-effect evaporation concentration The treated waste liquid is sent to the single-effect evaporator (6-1) and forced to circulate between the single-effect heater (6-2) and the single-effect evaporator (6-1); S4: Cooling and thickening desalination The waste liquid at the bottom of the single-effect evaporator (6-1) is pumped to a thickening kettle (7), where crystals are precipitated by cooling the temperature, and the slurry is separated into solid and liquid by a flat scraper centrifuge (8).
5. The method for treating uranium-containing and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 4, characterized in that: In the S1, the pH of the waste liquid is adjusted to 6-12, and the COD is <200 mg / L.
6. The method for treating uranium-containing and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 5, characterized in that: In the S1, the non-condensable gas generated by the MVR evaporation and concentration unit (4) and the single-effect evaporation and concentration unit (6) enters the non-condensable gas preheater (2), and the waste liquid is preheated once in the non-condensable gas preheater (2), and the preheating temperature reaches 40 to 55° C.; the waste liquid enters the plate heat exchanger (3), and then heat exchanges with the secondary steam condensate generated by the MVR evaporation and concentration unit (4) in the plate heat exchanger (3), and the feed liquid temperature after the heat exchange is 70 to 80° C.
7. The method for treating uranium-containing and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 4, characterized in that: In S2, the temperature of the MVR evaporator (4-1) is 90 to 95°C, and the pressure is -10 to -30 kPa.
8. The method for treating uranium- and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 7, characterized in that: In S2, the temperature of the separated secondary steam is increased after being compressed by the Roots compressor (4-3), and then it is passed into the MVR heater (4-2) to further heat the waste liquid, so that the waste liquid is accelerated to concentrate in the MVR separator (4-1) after receiving sufficient heat and is recycled.
9. The method for treating uranium-containing and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 7, characterized in that: In S2, the density of the treated wastewater is increased to 1.25 g / cm 3 Then, it is sent to the single-effect evaporation concentration unit (6).
10. The method for treating uranium-containing and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 4, characterized in that: In S3, the outside world supplies supplementary steam to the single-effect heater (6-2), thereby heating the single-effect evaporator (6-1).
11. The method for treating uranium- and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 10, characterized in that: In S3, the steam generated by the single-effect evaporator (6-1) enters the single-effect condenser (6-3) for cooling.
12. The method for treating uranium- and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 10, characterized in that: In the above S3, the waste liquid is cooled to 20-30°C in the thickening kettle (7).
13. The method for treating uranium- and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 10, characterized in that: In the S3, the water content of the solid salt particles is less than 8%.
14. The method for treating uranium- and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 4, characterized in that: In S4, the solid salt particles are discharged from the lower part of the flat scraper centrifuge (8) and barreled for further processing; while the centrifuged mother liquor enters the mother liquor tank and is pumped to the extraction and stripping system for uranium recovery.
15. The method for treating uranium- and nitric acid-containing waste liquid by MVR-coupled single-effect evaporation and concentration according to claim 4, characterized in that: The method further comprises S5: discharging condensed water after the condensed water meets the standards; the steam condensed water generated by the MVR evaporation concentration unit (4) and the single-effect evaporation concentration unit (6) enters the condensed water buffer tank (9), and is then sent to the plate heat exchanger (3), where the water is cooled to 35° C. by heat exchange in the plate heat exchanger (3), and then tested, and discharged after the uranium concentration meets the standards.