Combined membrane treatment method and device for radioactive waste liquid treatment

Abstract

The invention belongs to the technical field of waste treatment in the nuclear industry, and particularly relates to a combined membrane treatment method and device for radioactive waste liquid treatment. Comprising the following steps: step 1, pretreatment; step 2, main processing; step 3, fine treatment; and 4, post-treatment is carried out. The invention has the following beneficial effects: (1) by integrating the pretreatment unit composed of active carbon and ultrafiltration, the main treatment unit of modified nanofiltration, the fine treatment unit of a special reverse osmosis membrane and the post-treatment unit of an adsorption membrane assembly, comprehensive removal of various forms of nuclides such as suspended solids, colloids, insoluble substances, ionic states and the like can be realized; the radioactive waste liquid up-to-standard discharge target is achieved. (2) a modified loose nanofiltration membrane and a cellulose reverse osmosis (RO) membrane assembly are adopted, so that the nuclide removal rate is guaranteed, and meanwhile, the transmittance of boric acid can be greatly improved, so that boron in the waste liquid is separated and recycled.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste treatment in the nuclear industry, and in particular relates to a combined membrane treatment method and device for treating radioactive waste liquid. Background Art

[0002] During the operation of nuclear power plants, large amounts of radioactive liquid waste are generated annually. This waste contains numerous radionuclides, such as Co, Sr, Cs, and Sb, which are highly hazardous and difficult to remove. Furthermore, borate ions or colloidal substances are present in the waste. Because the boron in the waste can undergo reactive chemical compensation, a boron recovery system is required for nuclear purification and reuse within the power plant. However, approximately 0.4 tons of boron is released into the environment per reactor per year. There is an urgent need to develop efficient treatment methods for radioactive liquid waste that can simultaneously remove radionuclides and recover boron.

[0003] Currently, conventional radioactive wastewater treatment technologies commonly include filtration + flocculation + ion exchange, or evaporation + ion exchange. However, these conventional technologies suffer from low removal efficiency, and can only treat radionuclides to a concentration of 100 to 1000 Bq / L, failing to meet process treatment requirements. CN 109513267 B discloses a radioactive wastewater treatment device that replaces the "coagulation sedimentation + filtration" treatment process with a combined process of "flocculation + centrifugation + residual chlorine removal + cavitation + combined filter element filtration" to pretreat nuclear, biological, and chemical decontamination wastewater. This device is capable of efficiently removing multiple nuclides, such as uranium, strontium, cesium, cobalt, and iodine, from the radioactive wastewater, achieving high-throughput, high-load continuous treatment of decontamination wastewater. However, this method primarily utilizes an adsorption filter element to adsorb the nuclides, and does not consider the regeneration and treatment of the adsorption filter element.

[0004] Membrane treatment processes separate impurities through the principles of physical retention or charge migration. Different membrane products have different molecular weight cutoffs, and membrane treatment has a good treatment effect even for extremely low concentrations of small colloidal nuclides. CN111863302A discloses a device and method for deep purification of radioactive waste liquid. This method uses a combination of powder / special media filters, membrane systems, multi-media ion exchange columns, and an electric desalination system to treat radioactive waste liquid with a large nuclide concentration range to below 30Bq / L. However, although this method can remove some radionuclides, it still cannot meet emission standards, and the process does not consider boron recovery, resulting in a waste of resources. Summary of the Invention

[0005] The present invention aims to provide a combined membrane treatment method and apparatus for treating radioactive wastewater. This method addresses the dual needs of radionuclide removal and boron recovery in existing nuclear industry radioactive wastewater. Utilizing a full membrane process, it boasts advantages such as high efficiency, energy conservation, resistance to clogging, simplified operation and maintenance, and minimal secondary waste, making it suitable for large-scale industrial production and widespread application. By designing membrane separation methods tailored to the scale of characteristic pollutants and integrating multiple membrane modules to form a combined membrane treatment process, the method not only effectively intercepts radionuclides but also improves boron recovery efficiency.

[0006] The technical solution of the present invention is as follows: A combined membrane treatment method for treating radioactive waste liquid comprises the following steps:

[0007] Step 1: Preprocessing;

[0008] Step 2: Main processing;

[0009] Step 3: fine processing;

[0010] Step 4: Post-processing.

[0011] After adjusting the pH of the wastewater in step 1, a flocculant is injected into the radioactive waste liquid and passed through a carbon fiber filter and an elastic fiber ultrafiltration component in sequence to remove suspended matter, colloids, insoluble matter, and polymer particles in the wastewater; in step 1, the solution for adjusting the pH of the wastewater is a sulfuric acid solution or a sodium hydroxide solution, and the flocculant is a positively charged polymer electrolyte.

[0012] In step 1, the pretreatment is carried out at a flux of not more than 1 to 5 m 3 / h, pressure 0.5 MPa, pH 1.0-11.0.

[0013] In step 2, the pretreated wastewater is passed through a loose nanofiltration membrane to intercept divalent and higher nuclides and increase the yield of boric acid; in step 2, the temperature is not more than 50° C., the pressure is 0 to 4 MPa, and the pH is 2 to 11.0.

[0014] In step 3, the wastewater after the main treatment is passed through a cellulose RO membrane assembly to remove cesium and strontium in the wastewater and increase the boric acid permeability; in step 3, the temperature does not exceed 45° C., the pressure is 0-4 MPa, and the pH is 2-11.0.

[0015] In step 4, the finely treated wastewater is sequentially passed through an ion fiber filter and a nuclide adsorption filter. In step 4, the temperature is not more than 45° C., the pressure is 0 to 0.6 MPa, and the pH is 1.0 to 11.0.

[0016] A combined membrane treatment device for treating radioactive waste liquid comprises four parts, namely a pre-treatment unit, a main treatment unit, a fine treatment unit and a post-treatment unit, which are connected in sequence.

[0017] The pretreatment unit includes a raw water tank, a raw water pump, a carbon fiber filter, and an elastic fiber ultrafiltration component connected in sequence. The outlet on one side of the elastic fiber ultrafiltration component is connected to the raw water tank, and the outlet on the other side of the elastic fiber ultrafiltration component is connected to the intermediate water tank.

[0018] The main treatment unit includes an intermediate water tank, an intermediate water pump, and a nanofiltration membrane assembly connected in sequence, wherein the outlet of one side of the nanofiltration membrane assembly is connected to the intermediate water tank, and the other side of the nanofiltration membrane assembly is connected to the nanofiltration water tank;

[0019] The fine treatment unit includes a nanofiltration water tank, a nanofiltration water pump, and a special reverse osmosis component connected in sequence, wherein the outlet of one side of the special reverse osmosis membrane component is connected to the nanofiltration water tank, and the outlet of the other side of the special reverse osmosis membrane component is connected to the ion fiber filter element;

[0020] The post-processing unit includes an ion fiber filter cartridge filter outlet connected to a nuclide adsorption filter cartridge filter inlet, the nuclide adsorption filter cartridge filter outlet is connected to the nanofiltration water tank, the nuclide adsorption filter cartridge filter outlet is connected to the special reverse osmosis membrane assembly outlet, and the nuclide adsorption filter cartridge filter outlet is connected to the device discharge port.

[0021] The beneficial effects of the present invention are as follows: (1) The present invention can achieve the comprehensive removal of various forms of radionuclides, such as suspended matter, colloids, insoluble matter, and ions, by integrating a pretreatment unit composed of activated carbon and ultrafiltration, a main treatment unit composed of modified nanofiltration, a fine treatment unit composed of a special reverse osmosis membrane, and a post-treatment unit composed of an adsorption membrane assembly, thereby achieving the goal of meeting the discharge standards for radioactive waste liquid. (2) The present invention adopts a modified loose nanofiltration membrane and a cellulose reverse osmosis RO membrane assembly, which can significantly increase the permeability of boric acid while ensuring the removal rate of radionuclides, thereby separating and recovering boron in the waste liquid. (3) The radioactive waste liquid combined membrane treatment device provided by the present invention has the advantages of high efficiency, energy saving, non-clogging, simple operation and maintenance, and small amount of secondary waste, and is suitable for large-scale industrial production and promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of a combined membrane treatment device for treating radioactive waste liquid provided by the present invention.

[0023] In the figure: 1 raw water tank, 2 raw water pump, 3 carbon fiber microfilter, 4 elastic fiber ultrafiltration membrane assembly, 5 intermediate water tank, 6 intermediate water pump, 7 nanofiltration membrane assembly, 8 nanofiltration water tank, 9 nanofiltration water pump, 10 special reverse osmosis membrane assembly, 11 ion fiber filter element filter, 12 nuclide adsorption filter element filter. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings, specific implementation methods and examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] The present invention provides a combined membrane treatment method and device for treating radioactive waste liquid, which can effectively remove various forms of nuclides in radioactive waste liquid, and at the same time, pass through the boric acid in the waste liquid, thereby ensuring that the discharge meets the standards while achieving the goal of boron recovery.

[0026] A combined membrane treatment method for treating radioactive waste liquid comprises the following steps:

[0027] Step 1: Preprocessing

[0028] After adjusting the pH of the wastewater, a flocculant is injected into the radioactive waste liquid and passed through a carbon fiber filter and an elastic fiber ultrafiltration assembly in sequence to remove suspended matter, colloids, insoluble matter, and polymer particles in the wastewater.

[0029] In a preferred embodiment, in step 1, the solution for adjusting the pH of the wastewater is a sulfuric acid solution or a sodium hydroxide solution, and the flocculant is a positively charged polymer electrolyte.

[0030] In another preferred embodiment, in step 1, the pretreatment is carried out at a flux of not more than 1 to 5 m 3 / h, pressure 0.5Mpa, pH 1.0~11.0.

[0031] Step 2: Main Processing

[0032] The pretreated wastewater is passed through a loose nanofiltration membrane to intercept divalent and higher nuclides and increase the yield of boric acid;

[0033] In step 2, the process is carried out under the conditions of temperature not exceeding 50° C., pressure 0-4 MPa, and pH 2-11.0.

[0034] Step 3: Finishing

[0035] The wastewater after primary treatment is passed through the cellulose RO membrane module to remove cesium and strontium in the wastewater and increase the boric acid permeability;

[0036] In step 3, the process is carried out under the conditions of temperature not exceeding 45° C., pressure 0 to 4 MPa, and pH 2 to 11.0.

[0037] Step 4: Post-processing

[0038] The finely treated wastewater is passed through the ion fiber filter and the radionuclide adsorption filter in sequence, and ion exchange and adsorption are used to ensure that the waste liquid meets the discharge standards.

[0039] In step 4, the reaction is carried out under the conditions of temperature not exceeding 45° C., pressure 0-0.6 MPa, and pH 1.0-11.0.

[0040] In view of the occurrence form and morphological characteristics of radioactive nuclides in wastewater, a pretreatment unit is composed of a carbon fiber microfilter and an elastic fiber ultrafiltration device to separate most of the suspended solids, colloids, and insoluble substances in the radioactive wastewater. A loose nanofiltration membrane is used as the main treatment unit to remove divalent and above ionized nuclides in the radioactive wastewater and improve the permeability of boric acid. A high-pressure and high-desalination reverse osmosis membrane is used to form a fine treatment unit to remove non-radioactive ionized nuclides in the wastewater and improve the permeability of boric acid. An ion fiber filter and a nuclide adsorption filter are used to form a post-treatment unit to remove the remaining nuclides in the wastewater through ion exchange and adsorption, thereby achieving the purification of nuclides in the wastewater and the separation and recovery of boron.

[0041] like Figure 1 As shown, the present invention provides a combined membrane treatment device for treating radioactive liquid waste, comprising a pretreatment unit, a main treatment unit, a finishing unit, and a post-treatment unit connected in sequence. The specific equipment includes: a raw water tank 1, a raw water pump 2, a carbon fiber microfilter 3, an elastic fiber ultrafiltration membrane assembly 4, an intermediate water tank 5, an intermediate water pump 6, a nanofiltration membrane assembly 7, a nanofiltration water tank 8, a nanofiltration water pump 9, a special reverse osmosis membrane assembly 10, an ion fiber filter cartridge 11, and a nuclide adsorption filter cartridge 12.

[0042] The pretreatment unit includes a raw water tank 1, a raw water pump 2, a carbon fiber filter 3, and an elastic fiber ultrafiltration membrane assembly 4 connected in sequence. One outlet of the elastic fiber ultrafiltration membrane assembly 4 is connected to the raw water tank 1, and the other outlet of the elastic fiber ultrafiltration membrane assembly 4 is connected to the intermediate water tank 5.

[0043] The main treatment unit includes an intermediate water tank 5, an intermediate water pump 6, and a nanofiltration membrane assembly 7 connected in sequence. One side outlet of the nanofiltration membrane assembly 7 is connected to the intermediate water tank 5, and the other side of the nanofiltration membrane assembly 7 is connected to the nanofiltration water tank 8;

[0044] The fine treatment unit includes a nanofiltration water tank 8, a nanofiltration water pump 9, and a special reverse osmosis component 10 connected in sequence. The outlet of one side of the special reverse osmosis membrane component 10 is connected to the nanofiltration water tank 8, and the outlet of the other side of the special reverse osmosis membrane component 10 is connected to the ion fiber filter element 11;

[0045] The post-processing unit includes an ion fiber filter cartridge filter 11 outlet connected to a nuclide adsorption filter cartridge filter 12 inlet, the nuclide adsorption filter cartridge filter 12 outlet is connected to the nanofiltration water tank 8, the nuclide adsorption filter cartridge filter 11 outlet is connected to the special reverse osmosis membrane assembly 10 outlet, and the nuclide adsorption filter cartridge filter 12 outlet is connected to the device discharge port;

[0046] In another preferred embodiment, the raw water tank 1, the intermediate water tank 5, and the nanofiltration water tank 8 are connected to a deionized water pipeline, and the raw water tank 1 is connected to a pharmaceutical pipeline;

[0047] In another preferred embodiment, the elastic fiber ultrafiltration membrane assembly 4 is configured with 1 to 6 elastic fiber assemblies. The membrane fibers used in the elastic fiber ultrafiltration membrane assembly 4 have a high-strength membrane pore expansion function. During backwashing, the membrane pores are greatly expanded to achieve high-flow jet backwashing.

[0048] In another preferred embodiment, the nanofiltration membrane assembly 7 uses 6 to 8 component units, each of which contains 3 nanofiltration membranes. The nanofiltration membrane uses an interfacial polymerization method to introduce nanomaterials into a polyamide separation layer to obtain a loose nanofiltration membrane with high permeability. The nanomaterials include zeolite, TiO2, mesoporous SiO2, and alumina.

[0049] In another preferred embodiment, the special reverse osmosis membrane assembly 10 uses 8 to 12 component units, each of which contains 3 reverse osmosis membranes, and the reverse osmosis membrane uses a high-pressure, high-desalination cellulose RO membrane;

[0050] In another preferred embodiment, the ion fiber filter 11 is formed by pressing and folding cation, anion and chelate ion exchange fibers to form a filter element, the filtration method is dead-end filtration, the filter element flux is 4000-5000 L / h, and the compression ratio is 8:1-9:1;

[0051] In another preferred embodiment, the nuclide adsorption filter element 12 is formed by pressing and folding an adsorbent, wherein the adsorbent is based on polyacrylonitrile (PAN), cross-linked chitosan (CTS) or cross-linked alginate (ALG), and is made of inorganic ion exchangers such as synthetic potassium cobalt ferrocyanide (KCoCF), potassium titanium ferrocyanide (KTiCF), potassium nickel ferrocyanide (KNiCF), sodium titanosilicate (NaTS), potassium titanate (KTiO) and ternary layered metal sulfide as active ingredients.

[0052] Example 1:

[0053] A nuclear power plant Figure 1 The 5m 3 / h radioactive waste liquid combined membrane treatment device, which treats radioactive waste liquid.

[0054] (1) Material properties

[0055] The waste liquid contains Cr, Co, Sr, Cs, Sb, Ag, Li, I, borate (radical) and other plasma or colloidal chemical compositions, including 5050 Bq / L of radioactive nuclides and 1250 ppm of boron concentration.

[0056] (2) Process conditions

[0057] The flow rate of radioactive waste liquid is 4m 3 / h, waste liquid temperature 40 ° C, pressure 0.5 MPa, pH = 4.5, using 5% NaOH solution to adjust the waste liquid pH.

[0058] (3) Application effect

[0059] Obtained 2.5m3 of purified waste liquid 3 / h, the volume reduction ratio reaches 62.5, the radioactivity in the purified wastewater is 0.005Bq / L, the purification coefficient reaches 1.01E6, and it meets the emission requirements; the boric acid (root) concentration in the purified wastewater is 1820ppm, and the transmittance reaches 91%

[0060] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A combined membrane treatment method for treating radioactive waste liquid, characterized in that: The steps include: Step 1: Preprocessing; Step 2: Main processing; Step 3: fine processing; Step 4: Post-processing.

2. The combined membrane treatment method for treating radioactive liquid waste according to claim 1, wherein: After adjusting the pH of the wastewater in step 1, a flocculant is injected into the radioactive waste liquid and passed through a carbon fiber filter and an elastic fiber ultrafiltration component in sequence to remove suspended matter, colloids, insoluble matter, and polymer particles in the wastewater; in step 1, the solution for adjusting the pH of the wastewater is a sulfuric acid solution or a sodium hydroxide solution, and the flocculant is a positively charged polymer electrolyte.

3. The combined membrane treatment method for treating radioactive waste liquid according to claim 2, characterized in that: In step 1, the pretreatment is carried out at a flux of not more than 1 to 5 m 3 / h, pressure 0.5Mpa, pH 1.0~11.

0.

4. The combined membrane treatment method for treating radioactive waste liquid according to claim 1, wherein: In step 2, the pretreated wastewater is passed through a loose nanofiltration membrane to intercept divalent and higher nuclides and increase the yield of boric acid; in step 2, the temperature is not more than 50° C., the pressure is 0 to 4 MPa, and the pH is 2 to 11.

0.

5. The combined membrane treatment method for treating radioactive waste liquid according to claim 1, wherein: In step 3, the wastewater after the main treatment is passed through a cellulose RO membrane assembly to remove cesium and strontium in the wastewater and increase the boric acid permeability; in step 3, the temperature does not exceed 45° C., the pressure is 0 to 4 MPa, and the pH is 2 to 11.

0.

6. The combined membrane treatment method for treating radioactive waste liquid according to claim 1, characterized in that: In step 4, the finely treated wastewater is sequentially passed through an ion fiber filter and a nuclide adsorption filter. In step 4, the temperature is not more than 45° C., the pressure is 0 to 0.6 MPa, and the pH is 1.0 to 11.

0.

7. A combined membrane treatment device for treating radioactive waste liquid, characterized in that: The utility model comprises four parts which are connected in sequence: a pre-processing unit, a main processing unit, a fine processing unit and a post-processing unit.

8. The combined membrane treatment device for treating radioactive liquid waste according to claim 7, characterized in that: The pretreatment unit includes a raw water tank, a raw water pump, a carbon fiber filter, and an elastic fiber ultrafiltration component connected in sequence. The outlet on one side of the elastic fiber ultrafiltration component is connected to the raw water tank, and the outlet on the other side of the elastic fiber ultrafiltration component is connected to the intermediate water tank.

9. The combined membrane treatment device for treating radioactive liquid waste according to claim 7, characterized in that: The main processing unit includes an intermediate water tank, an intermediate water pump, and a nanofiltration membrane assembly connected in sequence. One side outlet of the nanofiltration membrane assembly is connected to the intermediate water tank, and the other side of the nanofiltration membrane assembly is connected to the nanofiltration water tank.

10. The combined membrane treatment device for treating radioactive liquid waste according to claim 7, characterized in that: The fine treatment unit includes a nanofiltration water tank, a nanofiltration water pump, and a special reverse osmosis component connected in sequence, wherein the outlet of one side of the special reverse osmosis membrane component is connected to the nanofiltration water tank, and the outlet of the other side of the special reverse osmosis membrane component is connected to the ion fiber filter element; The post-processing unit includes an ion fiber filter cartridge filter outlet connected to a nuclide adsorption filter cartridge filter inlet, the nuclide adsorption filter cartridge filter outlet is connected to the nanofiltration water tank, the nuclide adsorption filter cartridge filter outlet is connected to the special reverse osmosis membrane assembly outlet, and the nuclide adsorption filter cartridge filter outlet is connected to the device discharge port.

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