Hydrophobic membrane, preparation method of hydrophobic membrane and treatment method of high-salt radioactive wastewater

Abstract

The invention discloses a hydrophobic membrane, a preparation method of the hydrophobic membrane and a treatment method of high-salt radioactive wastewater. The hydrophobic membrane comprises a polymer, and the polymer comprises polyvinylidene fluoride; the hydrophobic membrane is a hydrophobic membrane subjected to CF4 plasma irradiation treatment. The hydrophobic membrane has high interception performance, the treatment method can achieve the volume minimization of radioactive waste, meanwhile, the purification liquid can reach the natural background radioactivity level, efficient treatment of salt-containing radioactive waste water is achieved, and the treatment method is simple and convenient to operate.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, specifically to a hydrophobic membrane, a method for preparing the hydrophobic membrane, and a method for treating high-salt radioactive wastewater. Background Technology

[0002] Nuclear safety has become a key concern in the development of nuclear energy. During the routine operation and accident conditions of nuclear facilities, large amounts of radioactive wastewater are typically generated. Radioactive wastewater is also generated in many other processes, such as spent fuel reprocessing and nuclear facility decommissioning. The radionuclides contained in this wastewater mainly originate from fission products, activation products, and corrosion products. For radionuclides with long half-lives, they need to be separated from the wastewater, isolated from the environment, and stored long-term until they decay to a harmless level.

[0003] The treatment methods for wastewater vary depending on its salinity. Low-salinity radioactive wastewater (less than 2 g / L) is often treated using ion exchange technology. Medium-salinity radioactive wastewater (2-10 g / L) is treated using mature technologies such as ion exchange and reverse osmosis. High-salinity radioactive wastewater (over 10 g / L) is much more difficult to treat. For high-salinity radioactive wastewater, evaporation is a relatively mature technology. Evaporation redistributes radionuclides in the evaporation residue and condensate, obtaining a evaporation residue containing the vast majority of radionuclides and a condensate with lower radionuclide content. However, this method involves large equipment investment, high energy consumption, and complex system maintenance. For wastewater with high salinity or corrosive components, the evaporation process can lead to corrosion and scaling. Furthermore, when the wastewater contains foaming agents or surfactants, liquid entrainment is likely to occur, resulting in poor separation of volatile nuclides such as iodine-131I, rubidium-86Rb, ruthenium-103Ru, and 106Ru. This significantly reduces the decontamination factor of the nuclides in the wastewater.

[0004] Therefore, how to achieve efficient treatment of high-salt radioactive wastewater has become an urgent technical problem to be solved. Summary of the Invention

[0005] This application provides a hydrophobic membrane, a method for preparing the hydrophobic membrane, and a method for treating high-salt radioactive wastewater. It can minimize the volume of radioactive waste, while also enabling the purified liquid to reach the natural background radioactivity level. The treatment method is simple and easy to operate.

[0006] In a first aspect, embodiments of this application propose a hydrophobic membrane, which includes a polymer, including polyvinylidene fluoride; the hydrophobic membrane is a hydrophobic membrane treated with CF4 plasma irradiation.

[0007] According to one aspect of the embodiments of this application, the water contact angle of the hydrophobic membrane is 113°-180°.

[0008] According to one aspect of the embodiments of this application, the hydrophobic membrane includes one or more of hollow fiber membranes and flat sheet membranes.

[0009] Secondly, embodiments of this application propose a method for preparing a hydrophobic membrane, comprising: providing a casting solution, preparing a base membrane material using a non-solvent phase separation method; the casting solution comprising a polymer, the polymer comprising polyvinylidene fluoride; and irradiating the base membrane material with CF4 plasma to obtain a hydrophobic membrane.

[0010] According to another aspect of the embodiments of this application, a casting solution is provided. In the step of preparing a base film material using a non-solvent phase separation method, the casting solution further includes a pore-forming agent and an organic solvent; optionally, based on the total mass of the casting solution as 100%, the polymer content is 15%-21% by mass, and the pore-forming agent content is 3%-5% by mass.

[0011] According to another aspect of the embodiments of this application, the organic solvent includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0012] According to another aspect of the embodiments of this application, the pore-forming agent includes one or more of polyvinylpyrrolidone and polyethylene glycol.

[0013] According to another aspect of the embodiments of this application, the casting solution includes polyvinylidene fluoride, N,N-dimethylacetamide, and polyvinylpyrrolidone.

[0014] According to another aspect of the embodiments of this application, the step of preparing a base film material by using a non-solvent phase separation method, including the preparation of a coagulation bath, further includes providing a casting solution.

[0015] According to another aspect of the embodiments of this application, the coagulation bath includes deionized water and ethanol.

[0016] According to another aspect of the embodiments of this application, with the total mass of the coagulation bath as 100%, the mass content of deionized water is 87%-93%, and the mass content of ethanol is 7%-13%.

[0017] According to another aspect of the embodiments of this application, the temperature of the coagulation bath is 35-45°C.

[0018] According to another aspect of the embodiments of this application, the step of irradiating the base film material with CF4 plasma to obtain a hydrophobic film includes: the radio frequency power of the irradiation treatment is 475-525W.

[0019] According to another aspect of the embodiments of this application, the irradiation time for the irradiation treatment is 3-15 minutes.

[0020] According to another aspect of the embodiments of this application, the CF4 intake volume during the irradiation treatment is 50-70 sccm.

[0021] Thirdly, embodiments of this application propose a method for treating high-salt radioactive wastewater, comprising: treating the high-salt radioactive wastewater by membrane distillation to obtain a first concentrate and a first permeate; wherein the hydrophobic membrane used for membrane distillation includes the hydrophobic membrane of the first aspect of this application, or a hydrophobic membrane prepared by the preparation method of the second aspect of this application; solidifying the first concentrate; subjecting the first permeate to deep purification treatment to obtain a second concentrate and a second permeate; wherein the deep purification treatment employs continuous electro-desalination treatment; and re-treating the second concentrate by membrane distillation.

[0022] According to another aspect of the embodiments of this application, the step of solidifying the first concentrate includes: stirring the first concentrate with cement to form a solidified body, wherein the salt concentration in the first concentrate is greater than or equal to 200 g / L.

[0023] According to another aspect of the embodiments of this application, in the step of treating high-salt radioactive wastewater by membrane distillation to obtain a first concentrate and a first permeate, the membrane distillation treatment conditions include: the temperature on the feed side is 55-65°C, and the flow rate on the feed side is 0.06-0.12 m / s; and / or, the temperature on the freshwater side is 15-25°C, and the flow rate on the freshwater side is 0.8-1.2 m / s.

[0024] According to another aspect of the embodiments of this application, in the step of subjecting the first permeate to deep purification to obtain the second concentrate and the second permeate, the continuous electro-desalination process is performed in a single stage or in multiple stages.

[0025] According to another aspect of the embodiments of this application, the treatment method further includes pretreatment of the high-salt radioactive wastewater prior to membrane distillation treatment.

[0026] According to another aspect of the embodiments of this application, the pretreatment includes adding activated carbon and scale inhibitor to high-salt radioactive wastewater.

[0027] According to another aspect of the embodiments of this application, the pretreatment includes filtering high-salt radioactive wastewater using an ultrafiltration membrane.

[0028] According to another aspect of the embodiments of this application, the processing method further includes pretreating the first permeate before continuous electro-desalination;

[0029] Optionally, the pretreatment includes reverse osmosis or electrodialysis.

[0030] This application embodiment improves the retention performance of a hydrophobic membrane by selecting a suitable hydrophobic membrane, in which the polymer includes polyvinylidene fluoride, and by subjecting the hydrophobic membrane to CF4 plasma irradiation treatment. Combining membrane distillation and continuous electrostatic desalination to treat high-salt radioactive wastewater minimizes the volume of radioactive waste while ensuring the purified solution reaches natural background radioactivity levels. Furthermore, the treatment method is simple and easy to operate. Attached Figure Description

[0031] The features, advantages, and technical effects of exemplary embodiments of this application will now be described with reference to the accompanying drawings.

[0032] Figure 1 This is a schematic diagram of the process for treating high-salt radioactive wastewater according to an embodiment of this application. Detailed Implementation

[0033] The features and exemplary embodiments of various aspects of this application will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a comprehensive understanding of this application. However, it will be apparent to those skilled in the art that this application can be implemented without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of this application by illustrating examples. In the accompanying drawings and the following description, at least some well-known structures and techniques are not shown to avoid unnecessarily obscuring the application; and, for clarity, the dimensions of some structures may be exaggerated. Furthermore, the features, structures, or characteristics described below can be combined in any suitable manner in one or more embodiments.

[0034] It should be noted that, in this application, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0035] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application). Unless otherwise stated, the test temperature for all parameters mentioned in this application is 25°C and the test pressure is standard atmospheric pressure.

[0036] The list of items connected by the term "one or more" can mean any combination of the listed items. The term "multiple" means two or more.

[0037] Radioactive wastewater is usually treated by concentration or enrichment methods to minimize the volume of the resulting radioactive waste and ultimately seal the radionuclides in the wastewater, isolating them from the environment for a long period of time so that they can gradually decay.

[0038] The treatment of high-salt radioactive wastewater is quite difficult, mainly in the following aspects: (1) High-salt radioactive wastewater may contain hundreds of nuclides such as Na-24, Cr-51, Mn-54, Fe-55, Fe-59, Co-58, Co-60, Zn-65, Sr-89, Sr-91, Zr-95, Nb-95, Mo-99, Tc-99m, Ru-103, Ru-106m, Ag-110m, Te-129m, Te-129, Te-131m, Te-131, Te-132, Cs-134, Cs-137, Ba-140, La-140, Ce-141, Ce-143, Ce-144, W-187, Np-239. The properties of each nuclide (e.g., form of existence, valence state, etc.) are complex and can change under different operating conditions (e.g., pH value, ionic strength, temperature, etc.), which makes it difficult to achieve nuclide concentration and enrichment using adsorption / ion exchange technology. (2) The mass concentration of nuclides in high-salt radioactive wastewater is extremely low, generally 10 -3 Below micrograms per liter; while coexisting non-radioactive ions such as K + Na + Ca 2+ Mg 2+ The concentration of these non-radioactive ions is high, and their presence seriously affects the removal of radionuclides by adsorption technology. (3) Evaporation method is not very effective in separating volatile nuclides (such as 131I, 86Rb, 103Ru, 106Ru). (4) Under the condition of simplifying the process as much as possible, it is difficult to coordinate and cooperate among the various treatment methods to efficiently concentrate nuclides in high-salt radioactive wastewater.

[0039] Membrane distillation technology is a novel membrane separation technology that has been extensively studied in recent years. The membrane distillation process uses a hydrophobic membrane as the medium. Under the influence of interfacial tension, volatile components can permeate through the membrane pores in gaseous form, driven by the vapor pressure difference across the membrane. Non-volatile nuclide ions are retained and concentrated on the feed side. Water is transported across the membrane in vapor form from the hot side to the cold side, where it is then condensed, achieving a deep purification effect.

[0040] Compared to evaporation, membrane distillation technology operates at lower temperatures and, through the interception effect of the membrane, effectively mitigates liquid entrainment during the evaporation process. Furthermore, membrane distillation technology can effectively reduce problems such as corrosion and explosion during evaporation, making it a more advantageous technology for treating high-salinity radioactive wastewater.

[0041] The detergency factor (DF) can be calculated using the following formula:

[0042] DF=C f / C p

[0043] Among them, C f C represents the concentration of the radionuclide in the feed solution. p This represents the concentration of the nuclide in the permeate.

[0044] In direct contact membrane distillation (DCMD), the permeate is diluted, C p It cannot be measured directly, but is obtained through the following formula:

[0045]

[0046] Wherein, C0 and C1 are the initial and final concentrations (mg / L) on the freshwater side, respectively, and m0 and m1 are the initial and final masses (g) on ​​the freshwater side, respectively.

[0047] This application provides a hydrophobic membrane, which includes a polymer, including polyvinylidene fluoride.

[0048] The hydrophobic membrane is a hydrophobic membrane that has been treated with CF4 plasma irradiation.

[0049] In this embodiment, by selecting a suitable hydrophobic membrane, the polymer in the hydrophobic membrane including polyvinylidene fluoride, and subjecting the hydrophobic membrane to CF4 plasma irradiation treatment, the retention performance of the hydrophobic membrane is improved.

[0050] In some embodiments, CF4 plasma irradiation treatment may include vacuum cryogenic CF4 plasma irradiation treatment.

[0051] It should be noted that the PVDF used in the embodiments of this application must have certain acid resistance and radiation resistance properties, and in addition to containing fluorine, it must meet the requirement of being halogen-free, that is, it must not contain elements such as chlorine, bromine, and iodine.

[0052] In some embodiments, the water contact angle of the hydrophobic membrane can be 113°-180°.

[0053] The water contact angle of a hydrophobic membrane can be measured using a contact angle meter (such as the SL200KS model from Krono, USA). The hydrophobic membrane sample is pre-dried, and its water contact angle is measured using a 1 μL droplet. The value at the 5th second is taken as the contact angle of the hydrophobic membrane sample. Each sample is measured at least five times at different locations, and the average value is taken.

[0054] In some embodiments, the hydrophobic membrane may include one or more of hollow fiber membranes and flat sheet membranes. Optionally, it may be a hollow fiber membrane, which can be assembled into a hollow fiber membrane module for use.

[0055] Hollow fiber membrane modules are asymmetrical, self-supporting filter membranes that can be backwashed. They consist of end caps, housings, etc.

[0056] This application provides a method for preparing a hydrophobic membrane, which includes the following steps:

[0057] A casting solution is provided, and a base film material is prepared by a solvent-free phase separation method; the casting solution includes a polymer, which includes polyvinylidene fluoride;

[0058] A hydrophobic membrane was obtained by irradiating the base membrane material with CF4 plasma.

[0059] It should be noted that the characteristics and advantages described for hydrophobic membranes also apply to this preparation method, and will not be repeated here.

[0060] The non-solvent-induced phase separation method is well-known in the field. Its process mainly includes dissolving the polymer in an organic solvent to form a homogeneous solution, then slowly adding a reagent with stronger miscibility with the organic solvent to extract the organic solvent, forming a two-phase structure with the polymer as the continuous phase and the solvent as the dispersed phase, and then removing the solvent to obtain a polymer with a certain pore structure.

[0061] In some embodiments, in the step of preparing a base film material using a solvent-free phase separation method, the casting solution may further include a pore-forming agent and an organic solvent.

[0062] It is understood that the preparation process of the casting solution can involve first mixing the polymer and the porogen and then dissolving them in an organic solvent. Alternatively, the polymer can be dissolved in an organic solvent first, followed by the porogen, or vice versa. This application does not limit this to any particular method, as long as a mixture of polymer, porogen, and organic solvent can be obtained.

[0063] In some embodiments, the polymer content, based on 100% of the total mass of the casting solution, can be 15%-21%, for example, 15%, 16%, 17%, 18%, 19%, 20%, or 21%. The pore-forming agent content can be 3%-5%, for example, 3%, 3.5%, 4%, 4.5%, or 5%.

[0064] By setting the content of polymer and pore-forming agent in the casting solution within the above range, the porosity of the hydrophobic membrane can be adjusted, the pore structure of the hydrophobic membrane can be improved, and the relationship between the retention performance and flux of the hydrophobic membrane can be balanced, thereby improving the flux and retention performance of the hydrophobic membrane.

[0065] In some embodiments, the organic solvent may include one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methylpyrrolidone (NMP). Optionally, the organic solvent may include N,N-dimethylacetamide.

[0066] In some embodiments, the porogen may include one or more of polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG). Optionally, the porogen may include polyvinylpyrrolidone.

[0067] In some embodiments, the casting solution may include polyvinylidene fluoride, N,N-dimethylacetamide, and polyvinylpyrrolidone.

[0068] In some embodiments, the step of providing a casting solution and preparing a base film material using a non-solvent phase separation method may further include the preparation of a coagulation bath.

[0069] In some embodiments, the coagulation bath may include deionized water and ethanol.

[0070] In some embodiments, the deionized water content can be 87%-93% based on the total mass of the coagulation bath (100%), for example, 87%, 88%, 89%, 90%, 91%, 92%, or 93%, and the ethanol content can be 7%-13%, for example, 7%, 8%, 9%, 10%, 11%, 12%, or 13%.

[0071] In some embodiments, the temperature of the coagulation bath can be 35-45°C, and can be selected as 40°C. For example, it can be 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, or 45°C.

[0072] By setting the components, composition, or temperature of the coagulation bath within the aforementioned range, the pore structure of the base film material and the dissolution rate of the organic solvent can be adjusted in the embodiments of this application.

[0073] In some embodiments, the step of preparing the base membrane material using a non-solvent-induced phase separation method with a casting solution may further include steps such as setting spinneret parameters, soaking the membrane fibers, and drying the membrane fibers. It is understood that hollow fiber membranes are typically filamentous and are therefore also referred to as membrane fibers.

[0074] In some embodiments, the steps of setting the spinneret parameters may include: maintaining a pressure of 0.3 MPa above the liquid in the casting solution tank, setting the casting solution supply pump speed to 5.2 rpm, the core liquid flow rate to 3 mL / min, the drawing speed to 5.3 m / min, and setting the winding speed to 92%-100% of the drawing speed. The above parameters can be fine-tuned according to the specific conditions on site.

[0075] In some embodiments, the membrane fiber soaking step may include: soaking the membrane fiber in deionized water for one week, optionally changing the deionized water once a day, to fully leach out the organic solvents from the surface and pores of the membrane fiber.

[0076] In some embodiments, the step of drying the membrane fibers may include: hanging the membrane fibers vertically to dry in a shaded, dust-free room with a temperature of 20-40°C and a humidity of 15%-45% for several days, until the membrane fibers change from slightly yellow to pure white.

[0077] The embodiments of this application can adjust the pore structure of the base membrane material and the amount of organic solvent removed by adjusting steps such as setting the spinneret parameters, soaking the membrane fibers, and drying the membrane fibers.

[0078] In some embodiments, the step of irradiating the base film material with CF4 plasma to obtain a hydrophobic film includes: the radio frequency power of the irradiation treatment can be 475-525W, for example, 475W, 485W, 500W, 510W, or 525W.

[0079] In some embodiments, the irradiation time for the irradiation treatment can be 3-15 min, for example, 3 min, 5 min, 7 min, 9 min, 11 min, 13 min, or 15 min.

[0080] In some embodiments, the CF4 intake volume during irradiation can be 50-70 sccm, for example, 50 sccm, 55 sccm, 60 sccm, 65 sccm, or 70 sccm.

[0081] By setting one or more of the following conditions for CF4 plasma irradiation treatment—radio frequency power, irradiation time, or CF4 intake rate—within the aforementioned range, the resulting energy field can excite the transformation of CF4 from a gaseous state to a plasma state. The active species in the plasma can activate the surface of polymer materials, generating free radicals and introducing active groups. Then, by grafting fluorine atoms onto the material surface to form a new surface layer, the material surface is hydrophobically enhanced. This further improves the hydrophobicity of the hydrophobic film and enhances the removal rate of radionuclides from high-salt radioactive wastewater.

[0082] In some embodiments, the volume content of CF4 in the plasma can be 100%, that is, the plasma is pure CF4 gas.

[0083] Figure 1 This is a schematic diagram of the process for treating high-salt radioactive wastewater according to an embodiment of this application. Figure 1 As shown in the embodiment of this application, a method for treating high-salt radioactive wastewater is proposed, including the following steps:

[0084] S10: High-salt radioactive wastewater is treated by membrane distillation to obtain a first concentrate and a first permeate; wherein the hydrophobic membrane used for membrane distillation treatment includes the hydrophobic membrane of the first aspect of this application, or the hydrophobic membrane prepared by the preparation method of the second aspect of this application.

[0085] S20: Solidify the first concentrate;

[0086] S30: The first permeate is subjected to deep purification treatment to obtain a second concentrate and a second permeate; wherein, the deep purification treatment adopts continuous electro-deionization (CEDI).

[0087] S40: The second concentrate is returned to step S10 for membrane distillation.

[0088] This application combines membrane distillation and continuous electro-desalination to treat high-salinity radioactive wastewater, minimizing the volume of radioactive waste while ensuring the purified solution reaches natural background radioactivity levels. Furthermore, the treatment method is simple and easy to operate. In addition, solidifying the first concentrate allows for safe storage, and reprocessing the second concentrate using membrane distillation further reduces its volume.

[0089] In some embodiments, the membrane distillation process can be direct contact membrane distillation (DCMD).

[0090] Membrane distillation can improve the rejection rate of non-volatile nuclides, reduce the concentration of radionuclides in the first permeate, effectively concentrate high-salt radioactive wastewater, reduce the volume of its concentrate, and thus reduce the volume after solidification.

[0091] By performing continuous electro-desalination on the first permeate, a suitable optimized process can be established. The high selectivity and decontamination factor of continuous electro-desalination on volatile nuclides can be utilized to further remove residual nuclides in the first permeate, thereby further enhancing the decontamination factor on nuclides in high-salt radioactive wastewater, so as to achieve the purpose of "high concentration and deep purification".

[0092] In some embodiments, the first permeate is subjected to continuous electro-desalination to obtain a second concentrate and a second permeate.

[0093] Continuous electrodialysis (CEDI) is a novel membrane separation technology that organically combines electrodialysis and ion exchange.

[0094] Continuous electrostatic desalination can further improve the removal efficiency of monovalent nuclides in high-salt radioactive wastewater, thereby further enhancing the decontamination factor of nuclides in high-salt wastewater, while enabling the purified liquid to reach the natural background radioactivity level.

[0095] Since the treatment method of this application does not require the use of evaporation to concentrate high-salt radioactive wastewater, the system is highly simplified. The equipment used is smaller in size, more operable, more maintainable and repairable, and has lower energy consumption, which has obvious advantages over the evaporation method.

[0096] Membrane distillation can reduce the volume of the first concentrate and increase its salt content.

[0097] In some embodiments, the step of solidifying the first concentrate may include: mixing the first concentrate with cement to form a solidified body, wherein the salt concentration in the first concentrate is greater than or equal to 200 g / L, for example 200-300 g / L.

[0098] In some embodiments, in the step of treating high-salt radioactive wastewater by membrane distillation to obtain a first concentrate and a first permeate, the conditions for membrane distillation treatment may include: the temperature on the feed side is 55-65°C, and the flow rate on the feed side is 0.06-0.12 m / s.

[0099] In some embodiments, the conditions for membrane distillation may include: a freshwater temperature of 15-25°C and a freshwater flow rate of 0.8-1.2 m / s.

[0100] By setting one or more of the temperature and flow rate on the feed side and the temperature and flow rate on the fresh water side within the above range, membrane distillation can be carried out smoothly and the efficiency of membrane distillation treatment can be improved.

[0101] In some embodiments, in the step of subjecting the first permeate to deep purification to obtain the second concentrate and the second permeate, the continuous electro-desalination process may be single-stage or multi-stage. The specific stage can be set according to the processing requirements.

[0102] Normally, when the first permeate is subjected to continuous electro-desalination, a single stage of continuous electro-desalination is sufficient to achieve a good treatment effect on the radionuclides in the first permeate.

[0103] In some embodiments, the processing method may further include pretreatment of the first permeate prior to continuous electro-desalination.

[0104] In some embodiments, pretreatment may include reverse osmosis or electrodialysis.

[0105] In some embodiments, the treatment method may further include pretreatment of the high-salt radioactive wastewater prior to membrane distillation.

[0106] In some embodiments, pretreatment may include adding activated carbon and scale inhibitors to high-salt radioactive wastewater.

[0107] In some embodiments, pretreatment may include filtering high-salt radioactive wastewater using an ultrafiltration membrane.

[0108] Pretreatment of high-salt radioactive wastewater can remove suspended solids such as oil and particulate matter. Pretreatment of high-salt radioactive wastewater is beneficial for subsequent membrane distillation treatment, and pretreatment of the first permeate is beneficial for subsequent continuous electro-desalination treatment.

[0109] The hydrophobic membrane and treatment method prepared in this application can not only be used to treat high-salt radioactive wastewater, providing new technical support for the management of high-salt and low-radioactive waste, but also be used in fields such as industrial wastewater desalination and seawater desalination.

[0110] Example

[0111] The following embodiments describe the disclosure of this application in more detail. These embodiments are for illustrative purposes only, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0112] Example 1

[0113] (1) Preparation of hydrophobic membranes

[0114] A casting solution is provided, wherein the mass content of polymer PVDF is 18% and the mass content of pore-forming agent PVP K30 is 5% based on the total mass of the casting solution (100%). The above polymer PVDF and pore-forming agent PVP K30 are mixed and dissolved in DMAc, and hollow fiber membrane base material is prepared by a non-solvent phase separation method.

[0115] A hydrophobic membrane was obtained by irradiating hollow fiber membrane base material with CF4 plasma. The CF4 plasma irradiation conditions included a radio frequency power of 475W, an irradiation time of 3min, and a CF4 inlet flow rate of 60sccm.

[0116] (2) Treatment of high-salt radioactive wastewater

[0117] High-salt radioactive wastewater was treated using membrane distillation, and the wastewater entered the feed tank. The feed side flow rate was controlled at 0.1 m / s and the temperature at 60℃. The freshwater side flow rate was controlled at 1 m / s and the temperature at 20℃. When the feed solution in the feed tank was concentrated to ~224 g / L, the concentrations of Co, Sr, and Cs in the feed solution and the first permeate were measured. The concentrations of Co, Sr, and Cs in the feed solution were 18.70 mg / L, 12.47 mg / L, and 17.60 mg / L, respectively, and the concentrations of Co, Sr, and Cs in the first permeate were 0.04 mg / L, 0.04 mg / L, and 0.28 mg / L, respectively. The detergency factor reached above 50.

[0118] The first concentrate collected at the feed outlet of the membrane distillation system is directly used for cement solidification. To obtain the decontamination factors for Co, Sr, and Cs for the entire system, Co, Sr, and Cs are re-added to the first permeate obtained from the membrane distillation treatment, bringing the concentration of these three ions to approximately 5 mg / L, while the concentrations of other salts remain unchanged. The adjusted first permeate is then pretreated using RO (Reverse Oxidation), with a recovery rate of 90% in the RO process unit. Co, Sr, and Cs are then re-added to the RO permeate, bringing the concentration of these three ions to approximately 0.5 mg / L, while the concentrations of other salts remain unchanged. The adjusted RO permeate is then subjected to continuous electro-desalination treatment. The RO permeate becomes the second permeate. The concentrate from the RO process and the continuous electro-desalination is mixed to form the second concentrate, which is returned to the feed tank for re-treatment using membrane distillation.

[0119] After the re-addition of Co, Sr, and Cs, the concentrations of Co, Sr, and Cs in the first permeate were 5.12 mg / L, 5.30 mg / L, and 4.90 mg / L, respectively. The concentrations of Co, Sr, and Cs in the RO permeate were 0.031 mg / L, 0.088 mg / L, and 0.32 mg / L, respectively. After the re-addition of Co, Sr, and Cs, the concentrations of Co, Sr, and Cs in the RO permeate were 0.49 mg / L, 0.49 mg / L, and 0.46 mg / L, respectively. The concentrations of Co, Sr, and Cs in the second permeate were 0.0041 mg / L, 0.0045 mg / L, and 0.00001 mg / L, respectively.

[0120] Based on the above analysis data, the total detergency factor for Co, Sr, and Cs of the entire process system, including membrane distillation, reverse osmosis, and continuous electro-desalination, was calculated to be 2.12 × 10⁻⁶. 6 4.47×10 5 and 1.03×10 7 .

[0121] Example 2

[0122] (1) Preparation of hydrophobic membranes

[0123] A casting solution is provided, wherein the mass content of polymer PVDF is 18% and the mass content of pore-forming agent PVP K30 is 5% based on the total mass of the casting solution (100%). The above polymer PVDF and pore-forming agent PVP K30 are mixed and dissolved in DMAc, and hollow fiber membrane base material is prepared by a non-solvent phase separation method.

[0124] A hydrophobic membrane was obtained by irradiating hollow fiber membrane base material with CF4 plasma. The CF4 plasma irradiation conditions included a radio frequency power of 525W, an irradiation time of 3min, and a CF4 inlet flow rate of 60sccm.

[0125] (2) Treatment of high-salt radioactive wastewater

[0126] Membrane distillation was used to treat high-salt radioactive wastewater, which entered the feed tank. The feed side flow rate was controlled at 0.1 m / s and the temperature at 60℃. The freshwater side flow rate was controlled at 1 m / s and the temperature at 20℃. When the feed solution in the tank was concentrated to ~275 g / L, the concentrations of Co, Sr, and Cs in the first concentrate and the first permeate were measured. The concentrations of Co, Sr, and Cs in the feed solution were 9.73 mg / L, 13.48 mg / L, and 20.17 mg / L, respectively. The concentrations of Co, Sr, and Cs in the first permeate were 0.01 mg / L, 0.02 mg / L, and 0.13 mg / L, respectively. The detergency factor reached 10. 2 above.

[0127] The first concentrate is collected at the feed outlet of the membrane distillation and directly used for cement solidification. The first permeate obtained from the membrane distillation is pretreated by RO and then subjected to continuous electro-desalination. The effluent from the continuous electro-desalination is the second permeate. The concentrate from the RO and the continuous electro-desalination is mixed to form the second concentrate. The second concentrate is returned to the feed tank for re-treatment by membrane distillation.

[0128] Example 3

[0129] (1) Preparation of hydrophobic membranes

[0130] A casting solution is provided, wherein the mass content of polymer PVDF is 18% and the mass content of pore-forming agent PVP K30 is 5% based on the total mass of the casting solution (100%). The above polymer PVDF and pore-forming agent PVP K30 are mixed and dissolved in DMAc, and hollow fiber membrane base material is prepared by a non-solvent phase separation method.

[0131] A hydrophobic membrane was obtained by irradiating hollow fiber membrane base material with CF4 plasma. The CF4 plasma irradiation conditions included a radio frequency power of 500W, an irradiation time of 15min, and a CF4 inlet flow rate of 60sccm.

[0132] (2) Treatment of high-salt radioactive wastewater

[0133] Membrane distillation was used to treat high-salt radioactive wastewater, which entered the feed tank. The feed side flow rate was controlled at 0.1 m / s and the temperature at 60℃. The freshwater side flow rate was controlled at 1 m / s and the temperature at 20℃. When the feed solution in the tank was concentrated to ~292 g / L, the concentrations of Co, Sr, and Cs in the feed solution and the first permeate were measured. The concentrations of Co, Sr, and Cs in the feed solution were 59.02 mg / L, 15.89 mg / L, and 15.51 mg / L, respectively. The concentrations of Co, Sr, and Cs in the first permeate were 0.02 mg / L, 0.02 mg / L, and 0.07 mg / L, respectively. The detergency factor reached 2 × 10⁻⁶. 2 above.

[0134] The first concentrate is collected at the feed outlet of the membrane distillation and directly used for cement solidification. The first permeate obtained from the membrane distillation is pretreated by RO and then subjected to continuous electro-desalination. The effluent from the continuous electro-desalination is the second permeate. The concentrate from the RO and the continuous electro-desalination is mixed to form the second concentrate. The second concentrate is returned to the feed tank for re-treatment by membrane distillation.

[0135] Comparative Example 1

[0136] Except for not treating the hollow fiber membrane with CF4 during the preparation of the hydrophobic membrane, the rest of the hollow fiber membrane preparation process and the high-salt radioactive wastewater treatment process are the same as in Example 1.

[0137] High-salt radioactive wastewater was treated using membrane distillation, and the wastewater entered the feed tank. The feed side flow rate was controlled at 0.1 m / s and the temperature at 60℃. The freshwater side flow rate was controlled at 1 m / s and the temperature at 20℃. When the feed solution in the feed tank was concentrated to ~224 g / L, the concentrations of Co, Sr, and Cs in the first concentrate and the first permeate were measured. The concentrations of Co, Sr, and Cs in the first concentrate were 8.94 mg / L, 6.60 mg / L, and 6.84 mg / L, respectively, and the concentrations of Co, Sr, and Cs in the first permeate were 0.23 mg / L, 0.07 mg / L, and 0.11 mg / L, respectively. The detergency factor reached above 10.

[0138] The first concentrate in the feed tank is directly subjected to cement solidification treatment. The first permeate obtained by membrane distillation is subjected to continuous electro-desalination treatment to obtain the second permeate and the second concentrate. The second concentrate needs to be treated again by membrane distillation.

[0139] As shown in Examples 1-3 and Comparative Example 1, CF4 plasma irradiation treatment of hydrophobic membranes can improve their retention performance. Combining membrane distillation and continuous electro-desalination to treat high-salt radioactive wastewater can minimize the volume of radioactive waste, while simultaneously bringing the purified solution to the natural background radioactivity level. Furthermore, the treatment method is simple and easy to operate.

[0140] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A hydrophobic membrane, characterized by, The hydrophobic membrane comprises a polymer, and the polymer comprises polyvinylidene fluoride; The hydrophobic membrane is a hydrophobic membrane that has been treated with CF4 plasma irradiation.

2. The hydrophobic membrane of claim 1, wherein, The hydrophobic membrane has a water contact angle of 113°-180°; and / or, The hydrophobic membrane includes one or more of hollow fiber membranes and flat sheet membranes.

3. A method for producing a hydrophobic film, characterized by, The preparation method includes: A casting solution is provided, and a base film material is prepared by a solvent-free phase separation method; the casting solution includes a polymer, and the polymer includes polyvinylidene fluoride. The base film material was irradiated with CF4 plasma to obtain a hydrophobic film.

4. The production method according to claim 3, characterized by, In the step of preparing a base film material by providing a casting solution and using a solvent-free phase separation method, the casting solution further includes a pore-forming agent and an organic solvent. Optionally, based on the total mass of the casting solution as 100%, the polymer content is 15%-21% by mass, and the pore-forming agent content is 3%-5% by mass.

5. The production method according to claim 4, characterized by, The casting solution satisfies one or more of the following conditions (1)-(3): (1) The organic solvent includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide and N-methylpyrrolidone; (2) The pore-forming agent includes one or more of polyvinylpyrrolidone and polyethylene glycol; (3) The casting solution includes polyvinylidene fluoride, N,N-dimethylacetamide, and polyvinylpyrrolidone.

6. The preparation method according to claim 3, characterized in that, The step of preparing the base film material by providing a casting solution and using a non-solvent phase separation method also includes the preparation of a coagulation bath; Optionally, the coagulation bath comprises deionized water and ethanol. Optionally, based on the total mass of the coagulation bath as 100%, the mass content of the deionized water is 87%-93%, and the mass content of the ethanol is 7%-13%. Optionally, the temperature of the coagulation bath is 35-45°C.

7. The preparation method according to claim 3, characterized in that, The step of irradiating the base film material with CF4 plasma to obtain a hydrophobic film satisfies one or more of the following conditions (1)-(3): (1) The radio frequency power of the irradiation treatment is 475-525W; (2) The irradiation time for the irradiation treatment is 3-15 min; (3) The CF4 intake volume in the irradiation treatment is 50-70 sccm.

8. A method for treating high-salinity radioactive wastewater, characterized by, include: High-salt radioactive wastewater is treated by membrane distillation to obtain a first concentrate and a first permeate; wherein the hydrophobic membrane used in the membrane distillation treatment includes the hydrophobic membrane described in claim 1 or 2, or a hydrophobic membrane prepared by any one of the preparation methods in claims 3-7; The first concentrate is solidified. The first permeate is subjected to deep purification treatment to obtain a second concentrate and a second permeate; wherein, the deep purification treatment adopts continuous electro-desalination treatment. The second concentrate was then treated again by membrane distillation.

9. The processing method according to claim 8, characterized in that, The steps for solidifying the first concentrate include: The first concentrate is mixed with cement to form a solidified body, wherein the salt concentration in the first concentrate is greater than or equal to 200 g / L.

10. The processing method according to claim 8, wherein In the step of treating high-salt radioactive wastewater using membrane distillation to obtain a first concentrate and a first permeate, the membrane distillation treatment conditions include: The temperature on the feed side is 55-65℃, and the flow rate on the feed side is 0.06-0.12 m / s; and / or, The temperature on the freshwater side is 15-25℃, and the flow velocity on the freshwater side is 0.8-1.2m / s.

11. The treatment method of claim 8, wherein, In the step of performing deep purification treatment on the first permeate to obtain the second concentrate and the second permeate, the continuous electro-desalination process can be single-stage or multi-stage.

12. The treatment method of claim 8, wherein, The treatment method also includes pretreatment of the high-salt radioactive wastewater prior to membrane distillation. Optionally, the pretreatment includes adding activated carbon and scale inhibitors to the high-salt radioactive wastewater; and / or, The pretreatment includes filtering the high-salt radioactive wastewater using an ultrafiltration membrane.

13. The processing method of claim 8, wherein, The processing method further includes pretreatment of the first permeate before continuous electro-desalination; Optionally, the pretreatment includes reverse osmosis or electrodialysis.

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