A multi-stage method and system for treating radioactive nuclear waste water

Abstract

The application discloses a multi-stage treatment method and system for radioactive nuclear wastewater, and belongs to the technical field of industrial wastewater treatment. The method comprises the following steps: after the radioactive nuclear wastewater is pre-concentrated through one-stage negative pressure evaporation, electrolytic oxidation is performed on the high-concentration chloride ions in the evaporated liquid, organic matters are synchronously degraded, ammonia nitrogen is removed, the wastewater is subjected to two-stage negative pressure evaporation for deep concentration, then is subjected to reverse osmosis desalination refining, and finally is subjected to microcrystalline adsorption to remove trace radioactive nuclides, so that the wastewater can be discharged up to the standard. The electrolytic oxidation unit is arranged between the two-stage evaporation, a self-oxidation system is constructed without the need of adding an oxidant, and coking of the organic matters is avoided; the two-stage evaporation shares a negative pressure system to realize energy cascade utilization, and the reverse osmosis concentrated water and the adsorption regeneration liquid are refluxed to realize zero discharge. The application is suitable for treatment of wastewater with high salt, high organic matter, high nitrogen and radioactive composite pollution, and has the advantages of short process, low cost and outstanding volume reduction effect.

Description

Technical Field

[0001] This application relates to the field of industrial wastewater treatment technology, specifically providing a multi-stage treatment method and system for radioactive nuclear wastewater. Background Technology

[0002] With the rapid development of nuclear energy, nuclear technology applications, and related chemical industries, processes such as nuclear fuel reprocessing, nuclear power plant operation, nuclear medicine diagnosis and treatment, and irradiation processing generate large amounts of radioactive wastewater with complex composition and extremely high treatment difficulty. This type of wastewater typically exhibits multiple characteristics, including high salinity (TDS reaching tens of thousands of mg / L), high concentrations of organic matter (COD thousands to tens of thousands of mg / L), high nitrogen content (total nitrogen hundreds to thousands of mg / L), and radioactive contamination (total α and total β activities tens to thousands of Bq / L). It poses a serious threat to the ecological environment and human health and must be strictly treated to meet discharge or reuse requirements.

[0003] Currently, the treatment of this type of complex polluted wastewater mainly faces the following technical bottlenecks. First, traditional biological treatment methods are completely ineffective: the extremely high salt content (Cl) in the wastewater... - High concentrations (up to tens of thousands of mg / L) of pollutants can strongly inhibit and toxicize microorganisms, causing traditional biological nitrogen removal and COD degradation processes such as activated sludge, nitrification, and denitrification to malfunction, making it difficult to establish or even causing the biological system to collapse. Secondly, single physicochemical methods have limited effectiveness or are prohibitively expensive: while evaporation crystallization technology can effectively desalinate and concentrate pollutants, and also has some effect on ammonia nitrogen removal, the simple evaporation process cannot effectively degrade high concentrations of recalcitrant organic pollutants in wastewater. The evaporation condensate still contains a large amount of organic matter, making it impossible to directly meet standards. Furthermore, if organic matter cokes in the evaporator, it will affect the stable operation of the equipment. Advanced oxidation technologies, such as electrochemical oxidation, especially electrocatalytic oxidation using boron-doped diamond (BDD) electrodes, can generate highly oxidizing hydroxyl radicals, effectively degrading recalcitrant organic matter. However, when directly treating extremely high-salt, high-COD raw water, on the one hand, a large amount of inorganic salt ions may lead to increased electrode side reactions, reduced current efficiency, and a surge in energy consumption; on the other hand, the high concentration of pollutants makes complete oxidation extremely time-consuming, making equipment investment and operating costs prohibitive. Furthermore, existing combined processes are not suitable for wastewater with multiple characteristics such as high salinity, high COD, high nitrogen content, and radioactive pollution. For example, although a simple combination of evaporation and reverse osmosis can achieve desalination and concentration, it cannot solve the problem of simultaneous removal of organic matter and ammonia nitrogen. Although a combination of chemical precipitation and ion exchange can remove nuclides, it will generate a large amount of chemical sludge and is difficult to cope with high salinity environments.

[0004] In the field of radioactive wastewater treatment, evaporation technology is widely used due to its high efficiency in retaining non-volatile nuclides, and the International Atomic Energy Agency (IAEA) has listed evaporation as one of the standard technologies for radioactive wastewater treatment. However, traditional evaporation processes suffer from problems such as high energy consumption, organic scaling, and secondary steam pollution. In recent years, boron-doped diamond (BDD) electrodes have attracted attention in the field of electrochemical oxidation. Existing technologies disclose methods for mineralizing organic acids in radioactive wastewater using BDD electrodes, but these methods are designed for specific wastewaters such as ion exchange resin regeneration liquids and employ a "stripping-BDD electrolysis" process. They do not address the evaporation and concentration process for high-salinity wastewater, nor do they solve the problem of ammonia nitrogen removal.

[0005] In summary, current technologies lack an integrated treatment process capable of efficiently, stably, and economically removing salt, recalcitrant organic matter, and nitrogen pollutants from radioactive high-salinity wastewater, ultimately achieving comprehensive and stable compliance with effluent standards. Particularly in high-salinity environments, key challenges remain: how to utilize the wastewater's inherent characteristics to construct a self-generating oxidation system; how to prevent scaling of evaporation equipment by organic matter; and how to achieve gradient enrichment and deep removal of radionuclides. Summary of the Invention

[0006] One of the purposes of this application is to develop a new multi-stage coupled treatment technology for radioactive wastewater, which has important practical significance and application value for improving the treatment level of radioactive wastewater, reducing treatment costs, and reducing secondary pollution.

[0007] To achieve the above objectives, this application adopts the following technical solution:

[0008] A multi-stage treatment method for radioactive nuclear wastewater includes the following steps:

[0009] (1) Radioactive nuclear wastewater is sent into a primary negative pressure evaporation unit for vapor-liquid separation to obtain primary distillate and primary concentrate;

[0010] (2) The primary distillate is fed into the electrolytic oxidation unit, where chloride ions in the primary distillate are used to generate active chloride species on the anode surface to oxidize and degrade organic pollutants in the wastewater, while ammonia nitrogen is removed by breakpoint chlorination.

[0011] (3) The effluent after electrolytic oxidation is sent to a secondary negative pressure evaporation unit for deep concentration to obtain secondary distillate and secondary concentrate;

[0012] (4) The secondary distillate is sent to the reverse osmosis unit for desalination to obtain reverse osmosis permeate and reverse osmosis concentrate;

[0013] (5) The reverse osmosis permeate is sent into a microcrystalline adsorption unit for deep adsorption treatment to remove trace radionuclides and obtain compliant discharge water.

[0014] Furthermore, the operating pressure of the single negative pressure evaporation in step (1) is -0.05~-0.09 MPa, the evaporation temperature is 45~85℃, the concentration ratio is 3~20 times, and a baffle plate demister is used at the top of the evaporator with a plate spacing of 20~50mm and a baffle plate angle of 45°~90°.

[0015] Furthermore, the electrode material used in the electrolytic oxidation step (2) is a boron-doped diamond electrode or a titanium-based coated electrode, and the current density is 10~100 mA / cm². 2 The hydraulic residence time is 30~120 min.

[0016] Furthermore, the operating pressure of the secondary negative pressure evaporation in step (3) is -0.05~-0.09 MPa, the evaporation temperature is 45~85℃, the concentration factor is 3~10 times, and the total dissolved solids in the effluent are ≤5000 mg / L.

[0017] Furthermore, the reverse osmosis unit in step (4) uses an anti-fouling spiral wound reverse osmosis membrane, with an operating pressure of 1.0~4.0 MPa, a recovery rate of 70%~85%, and a desalination rate of ≥90%.

[0018] Furthermore, the adsorption material used in the microcrystalline adsorption unit in step (5) includes at least one of modified zeolite molecular sieve, titanium silicon molecular sieve, silver-loaded zeolite, activated carbon-supported nano metal oxide or titanium ferrocyanide-based composite adsorption material, with a particle size of 0.5~5 mm and a hydraulic retention time of 10~60 min.

[0019] Furthermore, the reverse osmosis concentrate in step (4) is returned to the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit for reprocessing, and the regenerated liquid of the microcrystalline adsorption unit in step (5) is returned to the primary negative pressure evaporation unit.

[0020] A system for implementing the above-mentioned multi-stage treatment method for radioactive nuclear wastewater includes, in sequence along the water flow direction:

[0021] The single negative pressure evaporation unit is used to pre-concentrate radioactive wastewater and separate high-boiling-point organic matter and radionuclides. Its evaporation outlet is connected to the inlet of the electrolytic oxidation unit, and its concentrate outlet is connected to the external treatment system.

[0022] The electrolytic oxidation unit is used to electrolytically oxidize the primary distillate, and its outlet is connected to the inlet of the secondary negative pressure evaporation unit.

[0023] The secondary negative pressure evaporation unit is used to deeply concentrate the effluent after electrolytic oxidation. Its evaporator outlet is connected to the inlet of the reverse osmosis unit, and its concentrate outlet is connected to the external treatment system.

[0024] The reverse osmosis unit is used for desalination and removal of trace radionuclides. Its product water outlet is connected to the inlet of the microcrystalline adsorption unit, and its concentrate outlet is connected to the inlet of the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit.

[0025] The microcrystalline adsorption unit is used for deep removal of trace radionuclides, and its outlet is used to discharge the final treated water.

[0026] Furthermore, the primary negative pressure evaporation unit and the secondary negative pressure evaporation unit share a single negative pressure system and are equipped with a pressure gradient control device to achieve energy cascade utilization.

[0027] Preferably, the concentrate outlet of the reverse osmosis unit is connected to the inlet of the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit via a reflux pipeline, and the regenerated liquid outlet of the microcrystalline adsorption unit is connected to the inlet of the primary negative pressure evaporation unit via a reflux pipeline.

[0028] Furthermore, the anode in the electrolytic oxidation unit is a boron-doped diamond electrode or a titanium-based coated electrode, and the cathode is a stainless steel electrode or a titanium electrode.

[0029] Preferably, the reverse osmosis unit is equipped with an anti-fouling spiral wound reverse osmosis membrane assembly;

[0030] Preferably, the microcrystalline adsorption unit includes an adsorption column, which is filled with at least one of modified zeolite molecular sieve, titanium silicon molecular sieve, silver-loaded zeolite, or activated carbon-supported nano-metal oxide. The particle size of the adsorption material is 0.5~5mm, and the height-to-diameter ratio of the adsorption column is 3:1~8:1.

[0031] The technical effects of this application are as follows:

[0032] This application achieves the synergistic and efficient removal of salt, organic matter, nitrogen pollutants, and radionuclides from radioactive high-salt wastewater through a specific process sequence coupling of "primary negative pressure evaporation → electrolytic oxidation → secondary negative pressure evaporation → reverse osmosis → microcrystalline adsorption".

[0033] (1) High synergistic removal efficiency and excellent effluent quality. The multi-stage coupling process achieves the tiered synergistic removal of high salt, high organic matter, high nitrogen and radionuclides. The first evaporation is a low-temperature pre-concentration of salt and nuclides under negative pressure; electrolytic oxidation utilizes natural chloride ions (≥1000 mg / L) in wastewater to generate active chloride species (500~2000 mg / L) in situ, simultaneously achieving a COD removal rate of 80%~95% and efficient conversion and removal of ammonia nitrogen, laying the foundation for total nitrogen removal in subsequent units without the need for external oxidants; the second evaporation further concentrates and ensures water quality; reverse osmosis and microcrystalline adsorption form a dual fine treatment barrier.

[0034] (2) Effectively solves the problem of equipment fouling and scaling, and has strong operational stability. The electrolytic oxidation unit is set between the two evaporation processes. After the first evaporation removes suspended solids and scale precursors, the electrolytic oxidation further removes more than 80% of COD, destroys the molecular structure of organic matter such as humic acid and protein, and significantly reduces the risk of coking in the secondary evaporator.

[0035] (3) Zero reagent addition and extremely low sludge production significantly reduce operating costs. No oxidant, flocculant, or acid-base regulator needs to be added throughout the process, and the reagent cost per ton of water is reduced by more than 80% compared to the Fenton oxidation process. The solid waste of the system comes only from the concentrate and saturated adsorption materials, and the total sludge production is reduced by 70% to 90% compared to the traditional process, and the comprehensive treatment cost per ton of water is reduced by 42% to 57%.

[0036] (4) Energy cascade utilization, resulting in significant energy saving. The two-stage evaporation uses a single negative pressure system, and energy cascade utilization is achieved through pressure gradient control, reducing energy consumption per ton of water by 15% to 25% compared to single-stage evaporation.

[0037] (5) The volume reduction effect of radioactive waste is outstanding, and the system has zero discharge through internal circulation. The primary evaporation concentrates the waste by 3 to 20 times, and the secondary evaporation concentrates it by 3 to 10 times, enriching most of the radionuclides in a small amount of concentrated liquid, reducing the waste volume by more than 85% compared with traditional processes. The reverse osmosis concentrate and the microcrystalline adsorption regeneration liquid are both returned to the evaporation unit for further treatment, achieving zero liquid discharge within the system.

[0038] In summary, the process described in this application is short, stable in operation, low in cost, and produces minimal secondary pollution. It is suitable for the advanced treatment of high-salt, high-organic, and high-nitrogen radioactive wastewater in fields such as nuclear fuel reprocessing, nuclear power plant operation, and nuclear medicine. Attached Figure Description

[0039] The various technical features of this application and their relationships will be further explained below with reference to the accompanying drawings. The drawings are exemplary; some technical features are not shown to scale, and some drawings may omit technical features commonly used in the art to which this application pertains that are not essential for understanding and implementing this application, or additionally show technical features that are not essential for understanding and implementing this application. In other words, the combination of various technical features shown in the drawings is not intended to limit this application. Furthermore, throughout this application, the same reference numerals refer to the same things. Specific descriptions of the drawings are as follows:

[0040] Figure 1 This is a process flow diagram of the multi-stage treatment method for radioactive wastewater proposed in this application. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solutions of this application, the technical solutions described in this application will be further described in detail below with reference to specific embodiments.

[0042] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0043] In this application, "preferred," "preferred," and "ideal" are optional, meaning they are selected from either "with" or "without" the other two parallel options. If multiple "preferred" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" option is independent.

[0044] In this application, terms such as "multiple", "various", "multiple times", and "multi-source" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "at least one" means one or more than or equal to two.

[0045] Primary negative pressure evaporation: refers to the preliminary evaporation and concentration operation of radioactive nuclear wastewater under negative pressure conditions (below normal pressure). By reducing the system pressure, the boiling point of the wastewater is lowered, thereby achieving vapor-liquid separation at a lower temperature to obtain primary distillate and primary concentrate enriched with salts and nuclides.

[0046] Electrolytic oxidation refers to the process of generating highly reactive oxidizing species (such as hydroxyl radicals ·OH, active chlorine Cl2 / ClO) through electrochemical reactions occurring on the anode surface under the influence of an applied DC electric field. - This process involves oxidizing and degrading organic pollutants in wastewater, while simultaneously removing ammonia nitrogen through oxidation.

[0047] Active chlorine species: These refer to chlorine-containing active substances with strong oxidizing properties generated during electrolytic oxidation when chloride ions lose electrons at the anode surface. They mainly include free chlorine (Cl2), hypochlorous acid (HClO), and hypochlorite ions (ClO2). - ) and chlorate (ClO3) - These species can effectively attack organic molecules and participate in the breakpoint chlorination reaction of ammonia nitrogen.

[0048] Breakpoint chlorination refers to the process by which ammonia nitrogen (NH3-N) in wastewater is gradually oxidized and eventually converted into nitrogen gas (N2) for removal under the action of chlorine-based oxidants (such as Cl2, HClO, ClO⁻). When the dosage of active chlorine reaches a specific molar ratio, the concentrations of residual chlorine and ammonia nitrogen in the water both drop to their lowest point; this point is called the "breakpoint." In this application, the breakpoint chlorination reaction is achieved by electrolytically oxidizing the active chlorine species generated in situ, without the need for external chlorinating agents.

[0049] Secondary negative pressure evaporation: refers to the negative pressure evaporation and concentration operation performed again on the effluent after electrolytic oxidation, which is used to further remove residual salts, concentrate nuclides, and ensure the quality of the influent entering the subsequent membrane system.

[0050] Reverse osmosis (RO) is a membrane separation technology that uses pressure difference as the driving force and the selective permeability of a semi-permeable membrane to separate water from solutes such as dissolved salts, organic matter, colloids, and microorganisms. In this application, the reverse osmosis unit is used for desalination and removal of trace radionuclides, and the permeate enters the subsequent microcrystalline adsorption unit.

[0051] Microcrystalline adsorption: refers to the process of using microcrystalline materials (such as modified zeolite molecular sieves, titanium-silicon molecular sieves, silver-loaded zeolite, activated carbon-supported nano-metal oxides, etc.) with regular pore structure, high specific surface area and specific adsorption sites to deeply remove trace pollutants (including recalcitrant organic matter, residual ammonia nitrogen and trace radionuclides) from water through physical adsorption, ion exchange or chemical adsorption.

[0052] Primary concentrate / secondary concentrate: These refer to the residual liquid discharged from the primary and secondary negative pressure evaporation units, respectively, which are enriched with most of the salts, high-boiling-point organic matter, and radioactive nuclides. This concentrate is discharged outside the system for further treatment (such as solidification, vitrification, etc.).

[0053] Reverse osmosis concentrate: refers to the concentrated liquid that fails to permeate through the membrane in the reverse osmosis unit, containing a high concentration of salt and trace contaminants. In this application, the reverse osmosis concentrate is returned to the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit through a return pipeline for further treatment, thereby achieving zero liquid discharge within the system.

[0054] Microcrystalline adsorption regeneration solution: refers to the liquid generated during the regeneration of saturated microcrystalline adsorption materials, which contains contaminants (including trace radionuclides) eluted from the adsorption material. This regeneration solution is returned to a primary negative pressure evaporation unit for further processing.

[0055] Energy cascade utilization: refers to the sharing of a negative pressure system between the primary negative pressure evaporation unit and the secondary negative pressure evaporation unit. Through a pressure gradient control device, steam or heat at different pressure levels can be utilized in a graded and orderly manner, thereby reducing overall energy consumption.

[0056] Autogenous oxidation system: refers to a reaction system that utilizes the high concentration of chloride ions (≥1000 mg / L) contained in radioactive nuclear wastewater to generate active chloride species in situ through electrochemical reactions in an electrolytic oxidation unit, achieving organic matter oxidation and ammonia nitrogen removal without the need for external oxidants.

[0057] like Figure 1As shown, this application provides a multi-stage treatment method for radioactive nuclear wastewater, defining a five-step core process: "primary negative pressure evaporation → electrolytic oxidation → secondary negative pressure evaporation → reverse osmosis → microcrystalline adsorption." It should be noted that this specific sequence is not a simple superposition of the units, but rather a coupling mechanism proposed based on an in-depth analysis of the characteristics of pollutants in high-salt radioactive wastewater.

[0058] Step (1) The radioactive nuclear wastewater is sent into a primary negative pressure evaporation unit for vapor-liquid separation to obtain primary distillate and primary concentrate.

[0059] In some embodiments, the operating pressure of the single negative pressure evaporation in step (1) is -0.05 to -0.09 MPa, the evaporation temperature is 45 to 85°C, and the concentration ratio is 3 to 20 times. The steam condensation temperature is 30 to 50°C, and the heat source is steam, hot water, or a heat pump. A baffle-type demister is used at the top of the evaporator, with a baffle spacing of 20 to 50 mm and a baffle angle of 45° to 90°.

[0060] The primary negative pressure evaporation step is located at the very beginning of the process. Its purpose is to utilize the negative pressure and low temperature (45~85℃) conditions to concentrate most of the salts, high-boiling-point organic matter, and radionuclides in the radioactive wastewater into a primary concentrate (concentration factor 3~20 times), while simultaneously obtaining a primary distillate containing low-boiling-point organic matter, ammonia nitrogen, and salts. This step effectively reduces the inorganic salt load on the subsequent electrolytic oxidation unit and avoids the impact of high concentrations of suspended solids and scale-forming substances on the electrolytic reactor.

[0061] Step (2) The primary distillate is fed into the electrolytic oxidation unit, where chloride ions in the primary distillate are used to generate active chloride species on the anode surface to oxidize and degrade organic pollutants in the wastewater, while breakingpoint chlorination is used to remove ammonia nitrogen.

[0062] In some embodiments, the electrode material used in step (2) of electrolytic oxidation is a boron-doped diamond electrode or a titanium-based coated electrode, and the current density is 10~100 mA / cm². 2 The hydraulic retention time is 30–120 min. The reaction temperature is 20–50 °C, the pH of the reaction is 6–9, and the electrode spacing is 5–20 mm.

[0063] The electrolytic oxidation unit, which receives the primary distillate, has a key advantage: it fully utilizes the high chloride ion content of the primary distillate to construct a self-generating oxidation system without the need for external oxidants. Furthermore, by removing over 80% of COD pre-treatment, it effectively achieves deep mineralization of organic matter and breakpoint chlorination of ammonia nitrogen, preventing the adhesion and coking of organic matter in the subsequent secondary evaporator and ensuring long-term stable system operation. This design cleverly transforms the wastewater's inherent "high salinity disadvantage" into an "oxidative advantage."

[0064] The following main processes occur simultaneously during electrolytic oxidation:

[0065] Organic matter mineralization: Strongly oxidizing active species oxidize and decompose organic pollutants (COD) in wastewater into CO2 and H2O, achieving efficient removal of COD;

[0066] Ammonia nitrogen removal: Ammonia nitrogen (NH3-N) in wastewater undergoes breakpoint chlorination under the action of active chlorine, or is directly electrochemically oxidized on the anode surface, converting into N2 for removal. The synergistic removal of total nitrogen in the system is further achieved through subsequent secondary evaporation and reverse osmosis.

[0067] Step (3) The effluent after electrolytic oxidation is sent to the secondary negative pressure evaporation unit for deep concentration to obtain secondary distillate and secondary concentrate.

[0068] In some embodiments, the operating pressure of the secondary negative pressure evaporation in step (3) is -0.05 to -0.09 MPa, the evaporation temperature is 45 to 85°C, the concentration factor is 3 to 10 times, and the total dissolved solids in the effluent are ≤5000 mg / L. The steam condensation temperature is 30 to 50°C, and the heat source is steam, hot water, or a heat pump.

[0069] The secondary negative pressure evaporation system is set after electrolytic oxidation. Besides further concentrating residual salts, its more important function is that electrolytic oxidation removes most organic matter (especially surfactants and scale precursors), significantly reducing the risk of steam entrainment during the secondary evaporation process and drastically decreasing the tendency for coking and scaling on the heat exchange surface. Examples show that the secondary evaporator operated continuously for 60 days without significant scaling, and the heat transfer coefficient decreased by less than 5%.

[0070] Step (4) The secondary distillate is sent to the reverse osmosis unit for desalination to obtain reverse osmosis permeate and reverse osmosis concentrate.

[0071] In some embodiments, the reverse osmosis unit in step (4) uses a fouling-resistant spiral wound reverse osmosis membrane made of polyamide composite material, with an operating pressure of 1.0~4.0 MPa and a membrane flux of 15~25 L / (m²). 2 The influent temperature is 15~35℃, the recovery rate is 70%~85%, the product water TDS ≤ 50 mg / L, and the concentrate is returned to the primary or secondary evaporation.

[0072] The reverse osmosis unit desalinates and refines the secondary distillate, achieving a desalination rate of ≥90% and a retention rate of over 75% for trace radionuclides. Preferably, the reverse osmosis concentrate can be returned to the primary or secondary evaporation unit for further treatment, achieving zero liquid discharge within the system.

[0073] Step (5) The reverse osmosis permeate is sent into the microcrystalline adsorption unit for deep adsorption treatment to remove trace radionuclides and obtain compliant discharge water.

[0074] In some embodiments, the microcrystalline adsorption unit in step (5) uses at least one of the following adsorption materials: modified zeolite molecular sieve, titanium-silicon molecular sieve, silver-loaded zeolite, activated carbon-supported nano-metal oxide, or titanium ferrocyanide-based composite adsorption material, with a particle size of 0.5~5 mm and a hydraulic retention time of 10~60 min. The filtration flow rate is 2~10 BV / h, the height-to-diameter ratio of the adsorption column is 3:1~8:1, the operating temperature is 10~40℃, the operating pressure is ≤0.3MPa, and the adsorption material is regenerated using an acid-base method.

[0075] The microcrystalline adsorption unit, serving as the final purification barrier, utilizes microcrystalline materials (such as silver-loaded zeolite and titanium-silicon molecular sieves) with high specific surface area, regular pore structure, and specific adsorption sites to achieve a selective removal rate of over 90% for trace radionuclides, ensuring that the final effluent radioactivity concentration is below the detection limit. Examples show that the total α and total β decontamination factors can reach 10. 4 .

[0076] In some embodiments, the reverse osmosis concentrate in step (4) is returned to the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit for reprocessing, and the regenerated liquid of the microcrystalline adsorption unit in step (5) is returned to the primary negative pressure evaporation unit.

[0077] Preferably, the reverse osmosis concentrate is returned to the primary negative pressure evaporation unit to maintain the system's salinity balance and ensure long-term operational stability.

[0078] Through the reflux design, apart from the final concentrate, no other liquid waste is directly discharged from the system. All process wastewater is either circulated within the system or concentrated and disposed of in solid / semi-solid form, complying with the principle of minimizing radioactive waste. Simultaneously, the reverse osmosis concentrate still contains a certain amount of salt and trace nuclides, which can be further concentrated after returning to the evaporation unit, improving the overall recovery rate. Desorbed nuclides in the microcrystalline adsorption regeneration solution are reintroduced into the concentrate through a single evaporation, avoiding secondary pollution. Furthermore, the reflux pipeline design creates a closed-loop material flow between units, ensuring stable treatment performance even with fluctuations in influent water quality through self-circulation.

[0079] This application provides a system for implementing the above-mentioned multi-stage treatment method for radioactive wastewater, comprising, in sequence along the water flow direction:

[0080] The single negative pressure evaporation unit is used to pre-concentrate radioactive wastewater and separate high-boiling-point organic matter and radionuclides. Its evaporation outlet is connected to the inlet of the electrolytic oxidation unit, and its concentrate outlet is connected to the external treatment system.

[0081] The electrolytic oxidation unit is used to electrolytically oxidize the primary distillate, and its outlet is connected to the inlet of the secondary negative pressure evaporation unit.

[0082] The secondary negative pressure evaporation unit is used to deeply concentrate the effluent after electrolytic oxidation. Its evaporator outlet is connected to the inlet of the reverse osmosis unit, and its concentrate outlet is connected to the external treatment system.

[0083] The reverse osmosis unit is used for desalination and removal of trace radionuclides. Its product water outlet is connected to the inlet of the microcrystalline adsorption unit, and its concentrate outlet is connected to the inlet of the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit.

[0084] The microcrystalline adsorption unit is used for deep removal of trace radionuclides, and its outlet is used to discharge the final treated water.

[0085] In some implementations, the primary negative pressure evaporation unit and the secondary negative pressure evaporation unit share a single negative pressure system and are equipped with a pressure gradient control device to achieve energy cascade utilization.

[0086] In some implementations, the concentrate outlet of the reverse osmosis unit is connected to the inlet of the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit via a reflux pipeline, and the regenerated liquid outlet of the microcrystalline adsorption unit is connected to the inlet of the primary negative pressure evaporation unit via a reflux pipeline.

[0087] The present application is further described below with reference to specific embodiments. The advantages and features of the present application will become clear from the description. The embodiments described are merely exemplary and do not constitute any limitation on the scope of the present application. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present application without departing from the spirit and scope of the present application, but such modifications and substitutions all fall within the protection scope of the present application.

[0088] Example 1:

[0089] The intermediate-level waste liquid generated by a nuclear fuel reprocessing plant (after preliminary pretreatment) has a processing capacity of 10 tons / day. Its main water quality conditions are shown in Table 1.

[0090] Table 1. Main water quality information of the waste liquid from the intermediate discharge process.

[0091]

[0092] Major nuclides include 238 Pu、 241 Am、 137 Cs、 90 Sr, organic matter mainly comes from extractant residues (such as TBP, kerosene degradation products), and total nitrogen exists in the form of nitrate and ammonia nitrogen.

[0093] The process parameters for each processing unit are configured as shown in Table 2.

[0094] Table 2 Process parameter configuration of each processing unit

[0095]

[0096] The processing results of each processing unit are shown in Table 3.

[0097] Table 3. Processing effect of each processing unit

[0098]

[0099] Based on Table 3 and the actual treatment, the results are as follows: (1) The total COD removal rate was 99.97%, and the effluent COD was 6 mg / L; (2) The total nitrogen removal rate was 99.84%, and the effluent total nitrogen was 5 mg / L, of which the nitrate removal rate was 99.96%; (3) The removal rates of total α and total β radioactivity reached 99.99%, and the radioactivity of the effluent was below the detection limit; (4) The BDD electrode was at 80 mA / cm 2 Under the conditions of 500 hours of operation, the electrode decay rate is <2%; (5) The two-stage evaporation uses a shared negative pressure system, and the energy consumption of evaporation per ton of water is reduced by 22% compared with single-stage evaporation; (6) Compared with the traditional “evaporation + chemical precipitation + ion exchange” process, the final volume of radioactive waste is reduced by 85% and the treatment cost is reduced by 48%.

[0100] Example 2:

[0101] A nuclear power plant produces radioactive waste liquid with a daily treatment capacity of 20 tons. The main water quality conditions are shown in Table 4.

[0102] Table 4. Main Water Quality Information of Radioactive Waste Liquid

[0103]

[0104] The main nuclides are 137 Cs、 60 Co、 90 Sr, organic matter mainly comes from cleaning agents and ion exchange resin regeneration waste liquid, while total nitrogen mainly comes from ammonia nitrogen and organic amines.

[0105] The process parameters for each processing unit are configured as shown in Table 5.

[0106] Table 5. Process parameter configuration for each processing unit

[0107]

[0108] The processing results of each processing unit are shown in Table 6.

[0109] Table 6. Processing effect of each processing unit

[0110]

[0111] According to Table 6 and the actual treatment situation, the results are as follows: (1) The total COD removal rate is 99.94%, and the COD of the effluent is 5 mg / L; (2) The total nitrogen removal rate is 99.67%, and the total nitrogen of the effluent is 4 mg / L; (3) The total α and total β of radioactivity are both lower than the national emission limits (total α≤1 Bq / L, total β≤10 Bq / L); (4) No obvious scaling was observed in the secondary evaporator after 60 days of continuous operation, and the heat exchange coefficient decreased by <5%; (5) The comprehensive treatment cost per ton of water is reduced by 42% compared with the traditional "evaporation + Fenton + ion exchange" process.

[0112] Example 3:

[0113] The total wastewater generated by a nuclear medicine and irradiation processing center has a treatment capacity of 15 tons / day. The main water quality characteristics are shown in Table 7.

[0114] Table 7. Main Water Quality Information of Radioactive Waste Liquid

[0115]

[0116] The main nuclides are 131 I, 99m Tc, 137 Cs, organic matter mainly comes from cleaning wastewater and organic scintillation liquid residue, and total nitrogen is mainly ammonia nitrogen (accounting for about 80%).

[0117] The process parameters for each processing unit are configured as shown in Table 8.

[0118] Table 8. Process parameter configuration for each processing unit

[0119]

[0120] The processing results of each processing unit are shown in Table 9.

[0121] Table 9. Processing effect of each processing unit

[0122]

[0123] Based on Table 9 and the actual processing situation, the results are as follows: (1) 131 I removal rate > 99.98%, effluent 131(1) The total nitrogen removal rate is 99.33%, and the total nitrogen in the effluent is 3 mg / L, which meets the requirements of the "Water Quality Standard for Wastewater Discharge into Urban Sewers"; (3) The electrolytic oxidation unit uses natural chloride ions in the wastewater to generate active chlorine, without the need for external oxidants, and the cost of reagents per ton of water is reduced by 85% compared with the Fenton process; (4) The system only produces primary concentrate, secondary concentrate and saturated microcrystalline adsorbent, and the total sludge production (dry basis) is reduced by 78% compared with the traditional "coagulation + activated carbon" process; (5) The comprehensive treatment cost per ton of water in the whole process is about RMB28 / ton, which is 57% lower than the traditional process (about RMB65 / ton).

[0124] Unless otherwise defined, all technical and scientific terms used throughout this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In case of any inconsistency, the meaning as stated in this application or derived from the content described herein shall prevail. Furthermore, the terminology used in this description is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0125] Note that the above are merely preferred embodiments and the technical principles employed in this application. Those skilled in the art will understand that this application is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of this application. Therefore, although this application has been described in detail through the above embodiments, this application is not limited to the above embodiments. Many other equivalent embodiments may be included without departing from the technical concept of this application, all of which fall within the scope of protection of this application.

Claims

1. A multi-stage treatment method for radioactive nuclear wastewater, characterized in that, Includes the following steps: (1) Radioactive nuclear wastewater is sent into a primary negative pressure evaporation unit for vapor-liquid separation to obtain primary distillate and primary concentrate; (2) The primary distillate is fed into the electrolytic oxidation unit, where chloride ions in the primary distillate are used to generate active chloride species on the anode surface to oxidize and degrade organic pollutants in the wastewater, while ammonia nitrogen is removed by breakpoint chlorination. (3) The effluent after electrolytic oxidation is sent to a secondary negative pressure evaporation unit for deep concentration to obtain secondary distillate and secondary concentrate; (4) The secondary distillate is sent to the reverse osmosis unit for desalination to obtain reverse osmosis permeate and reverse osmosis concentrate; (5) The reverse osmosis permeate is sent into a microcrystalline adsorption unit for deep adsorption treatment to remove trace radionuclides and obtain compliant discharge water.

2. The method according to claim 1, characterized in that, The operating pressure of the single negative pressure evaporation in step (1) is -0.05~-0.09 MPa, the evaporation temperature is 45~85℃, the concentration ratio is 3~20 times, and a baffle plate demister is used at the top of the evaporator with a plate spacing of 20~50mm and a baffle plate angle of 45°~90°.

3. The method according to claim 1, characterized in that, The electrode material used in step (2) of electrolytic oxidation is a boron-doped diamond electrode or a titanium-based coated electrode, and the current density is 10~100 mA / cm². 2 The hydraulic residence time is 30~120 minutes.

4. The method according to claim 1, characterized in that, The operating pressure of the secondary negative pressure evaporation in step (3) is -0.05~-0.09 MPa, the evaporation temperature is 45~85℃, the concentration factor is 3~10 times, and the total dissolved solids in the effluent are ≤5000 mg / L.

5. The method according to claim 1, characterized in that, The reverse osmosis unit in step (4) uses an anti-fouling spiral wound reverse osmosis membrane, with an operating pressure of 1.0~4.0 MPa, a recovery rate of 70%~85%, and a desalination rate of ≥90%.

6. The method according to claim 1, characterized in that, The microcrystalline adsorption unit in step (5) uses at least one of the following adsorption materials: modified zeolite molecular sieve, titanium silicon molecular sieve, silver-loaded zeolite, activated carbon-supported nano metal oxide or titanium ferrocyanide-based composite adsorption material, with a particle size of 0.5~5 mm and a hydraulic retention time of 10~60 min.

7. The method according to claim 1, characterized in that, The reverse osmosis concentrate in step (4) is returned to the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit for reprocessing, and the regenerated liquid of the microcrystalline adsorption unit in step (5) is returned to the primary negative pressure evaporation unit.

8. A system for implementing the multi-stage treatment method for radioactive nuclear wastewater according to any one of claims 1 to 7, characterized in that, Along the direction of water flow, the following are included in sequence: The single negative pressure evaporation unit is used to pre-concentrate radioactive wastewater and separate high-boiling-point organic matter and radionuclides. Its evaporation outlet is connected to the inlet of the electrolytic oxidation unit, and its concentrate outlet is connected to the external treatment system. The electrolytic oxidation unit is used to electrolytically oxidize the primary distillate, and its outlet is connected to the inlet of the secondary negative pressure evaporation unit. The secondary negative pressure evaporation unit is used to deeply concentrate the effluent after electrolytic oxidation. Its evaporator outlet is connected to the inlet of the reverse osmosis unit, and its concentrate outlet is connected to the external treatment system. The reverse osmosis unit is used for desalination and removal of trace radionuclides. Its product water outlet is connected to the inlet of the microcrystalline adsorption unit, and its concentrate outlet is connected to the inlet of the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit. The microcrystalline adsorption unit is used for deep removal of trace radionuclides, and its outlet is used to discharge the final treated water.

9. The system according to claim 8, characterized in that, The primary negative pressure evaporation unit and the secondary negative pressure evaporation unit share a single negative pressure system and are equipped with a pressure gradient control device to achieve energy cascade utilization. Preferably, the concentrate outlet of the reverse osmosis unit is connected to the inlet of the primary negative pressure evaporation unit or the secondary negative pressure evaporation unit via a reflux pipeline, and the regenerated liquid outlet of the microcrystalline adsorption unit is connected to the inlet of the primary negative pressure evaporation unit via a reflux pipeline.

10. The system according to claim 8, characterized in that, The anode in the electrolytic oxidation unit is a boron-doped diamond electrode or a titanium-based coated electrode, and the cathode is a stainless steel electrode or a titanium electrode. Preferably, the reverse osmosis unit is equipped with an anti-fouling spiral wound reverse osmosis membrane assembly; Preferably, the microcrystalline adsorption unit includes an adsorption column, which is filled with at least one of modified zeolite molecular sieve, titanium silicon molecular sieve, silver-loaded zeolite, or activated carbon-supported nano-metal oxide. The particle size of the adsorption material is 0.5~5 mm, and the height-to-diameter ratio of the adsorption column is 3:1~8:1.

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