Process for purifying boric acid by reverse osmosis membrane to prepare nuclear-grade boric acid

Abstract

The application belongs to the technical field of fine chemical industry, and specifically provides a process method for preparing nuclear-grade boric acid by reverse osmosis membrane purification of boric acid, which comprises the following process steps: pretreatment, complexation impurity removal, two-stage membrane separation, and rate control crystallization. The process method has the advantages of excellent impurity removal effect, simple process, easy operation and control, good reproducibility, low production cost, environmental friendliness, etc., and the prepared nuclear-grade boric acid is suitable for the field of nuclear industry, electronic-grade materials and other fields with high requirements for the purity of boric acid.

Description

Technical Field

[0001] This application belongs to the field of fine chemical technology, and in particular relates to a process for purifying boric acid using reverse osmosis membranes to prepare nuclear-grade boric acid. Background Technology

[0002] Boric acid is an important basic chemical raw material with a wide range of applications. Nuclear-grade boric acid refers to boric acid products with extremely high purity and strictly controlled impurity content, mainly used as a coolant and neutron absorber in nuclear reactors. In pressurized water reactor nuclear power plants, boric acid is used as a soluble neutron poison, and the nuclear reaction rate is controlled by adjusting the boron concentration to ensure the safe operation of the reactor. Industrially, boric acid is usually produced by neutralizing borax with sulfuric acid, but the purity of the resulting industrial boric acid is generally 99%~99.5%, containing a relatively large number of impurities, and requires deep purification to meet the requirements of high-end applications.

[0003] Traditional purification methods, such as recrystallization, suffer from low recovery rates, high energy consumption, and stringent requirements for raw material purity. Solvent extraction may introduce organic solvent residues and is complex. Ion exchange methods are susceptible to resin contamination by boric acid and are difficult to regenerate. Therefore, developing a novel process for preparing nuclear-grade boric acid that can efficiently and deeply remove impurities while ensuring long-term stable system operation, and boasts high yield and low energy consumption, is of great significance.

[0004] Patent application CN119240726A discloses an electronic-grade boric acid, its purification method, and its application. This technology achieves simultaneous removal of organic and metallic impurities through a two-step core process of oil removal and ion exchange, offering advantages such as low operational difficulty and comprehensive impurity removal. However, the ion exchange resin and pretreated activated carbon used are costly and have limited lifespan, resulting in high overall costs. Additionally, patent application CN103787349A discloses a method for preparing nuclear-grade high-purity boric acid. This technology directly uses abundant boromagnesia ore as raw material, overcoming the limitation of relying on high-grade raw materials such as borax and hard borate. However, this method involves cumbersome process steps, including water leaching, acid leaching, iron removal, hydrogen peroxide oxidation, and multiple recrystallization steps, resulting in a long process cycle and limited production efficiency. Summary of the Invention

[0005] To address the aforementioned issues and further optimize the purity, cost, and process flow of boric acid purification, this application provides a process for preparing nuclear-grade boric acid by purifying boric acid using a reverse osmosis membrane:

[0006] S1) Industrial boric acid and deionized water are mixed evenly and then passed through a filter and an activated carbon column to obtain boric acid solution A.

[0007] S2) Add dilute sulfuric acid to boric acid solution A to adjust the pH, add EDTA complexing agent to react, and then pass it through a fixed bed column packed with complex adsorbent to obtain boric acid solution B;

[0008] S3) Pass boric acid solution B through a reverse osmosis membrane module with an aromatic polyamide composite membrane to obtain a primary concentrate;

[0009] S4) The primary concentrate is passed through a nanofiltration membrane module with a polypiperazine amide composite membrane material to obtain a secondary concentrate and a secondary nanofiltration permeate. The secondary concentrate enters the S5 process for subsequent operations, and the secondary nanofiltration permeate is returned to the reverse osmosis membrane module in the S3 process for recycling.

[0010] S5) Cool and stir the secondary concentrate to crystallize, then centrifuge to obtain high-purity boric acid crystals and mother liquor. Rinse the high-purity boric acid crystals with ultrapure water and then vacuum dry to obtain nuclear-grade boric acid. The mother liquor is returned to the reverse osmosis membrane module in the S3 process for recycling.

[0011] Furthermore, in the S2 process, the pH is adjusted to 3-6.5.

[0012] Furthermore, the concentration of the EDTA complexing agent in the S2 process is 0.05-0.1%.

[0013] Furthermore, the reaction time for the S2 process is 30-60 minutes.

[0014] Furthermore, the operating pressure in the S3 process is 1.5-3.0 MPa, and the temperature is 25-35℃.

[0015] Furthermore, in the S5 process, the cooling rate is 5-10℃ / h, and the crystallization temperature is 5-15℃.

[0016] Furthermore, the stirring time in step S5 is 1-4 hours.

[0017] Furthermore, the preparation method of the complex adsorbent includes the following steps:

[0018] ZrOCl2 was evenly dispersed in DMF, and trifluoroacetic acid and terephthalic acid were added to form a homogeneous solution. The temperature was then raised to react. After the reaction was completed, the mixture was cooled to room temperature, centrifuged to collect the precipitate, washed, and vacuum dried to obtain the defect intermediate.

[0019] Tetrabutyl titanate and methanol were mixed evenly, and the defect intermediate was added. The mixture was heated to react, and the precipitate was collected by centrifugation, washed, and dried under vacuum to obtain the complex adsorbent.

[0020] Furthermore, the volume ratio of tetrabutyl titanate to methanol is (1-3):8.

[0021] Furthermore, the volume ratio of trifluoroacetic acid to DMF is (2-3):25.

[0022] Compared with the prior art, this application has the following beneficial effects:

[0023] 1. In the preparation of the complex adsorbent in this application, the added trifluoroacetic acid, as a strong acid regulator, competes with terephthalic acid for Zr coordination sites, thus directionally forming ligand defects. This process not only exposes more metal active sites to improve reaction efficiency, but also induces the formation of richer pore structures, optimizes the specific surface area of ​​the material, and provides sufficient anchoring sites for the subsequent introduction of Ti, effectively avoiding Ti species aggregation and ensuring uniform loading.

[0024] 2. This application uses a solvothermal method to uniformly disperse Ti on the aforementioned ligand-deficient intermediate. The introduction of Ti brings stronger Lewis acid sites, significantly increasing the density of active sites; on the other hand, by utilizing the difference in electronegativity between Ti and Zr, the overall electron cloud distribution of the adsorbent is precisely adjusted, thereby strengthening the interaction between the adsorbent and the complex, and improving adsorption selectivity and stability.

[0025] 3. This application achieves the preparation of high-purity boric acid through integrated design including pretreatment, complexation and impurity removal, two-stage membrane separation, and rate-controlled crystallization, effectively reducing energy consumption and production costs in the production process. The two-stage membrane separation system, which circulates the mother liquor, can also improve the overall recovery rate. The synergistic design of the adsorbent and the two-stage membrane separation can efficiently remove small molecule EDTA complexes, while solving the problem that complexes are easy to adsorb and accumulate on the membrane surface, leading to flux attenuation, thus optimizing the process flow. Attached Figure Description

[0026] Figure 1 The flowcharts are for the process methods of Examples 1-3 and Control Groups 1-3 of this application.

[0027] Figure 2 This is a TEM image of the complex adsorbent prepared in Example 1 of this application.

[0028] Figure 3 The images show the BET curves of the complex adsorbents prepared in Example 1 and Control Group 2 of this application.

[0029] Figure 4 Infrared spectral images of nuclear-grade boric acid and boric acid standards prepared in Example 1 of this application. Detailed Implementation

[0030] To make the inventive objectives, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments described herein. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] When using “including,” “having,” and “contains” as described herein, the intention is to cover non-exclusive inclusion, unless an explicit qualifying term such as “only,” “consisting of,” etc., is used, in which case another component may be added.

[0033] The terms "preferred," "more preferably," "better," and "even better" used in this application refer to embodiments of this application that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this application. That is, in this application, "preferred," "more preferably," "better," and "even better" are merely descriptions of implementations or embodiments with better effects, but do not constitute a limitation on the scope of protection of this application.

[0034] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0035] In this application, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise explicitly specified. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise explicitly specified.

[0036] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0037] Unless otherwise specified, all steps in this application may be performed sequentially or randomly. For example, the method comprising steps (a) and (b) indicates that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc. Unless otherwise stated, singular terms may include plural forms and should not be construed as having a quantity of one.

[0038] In this application, "above" or "below" includes the number itself. For example, "below 1" includes 1.

[0039] In this application, room temperature refers to 0~40℃, including but not limited to 10~40℃, or further to 20~30℃.

[0040] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0041] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this application, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description in this application, any prior art methods, equipment, and materials similar to or equivalent to those described, used, or made by the methods, equipment, and materials in the embodiments of this application may be used to implement this application.

[0042] Example 1

[0043] This embodiment provides a process for purifying boric acid using reverse osmosis membranes to prepare nuclear-grade boric acid, specifically including the following steps:

[0044] S1) Mix 1 kg of industrial boric acid and 15 kg of deionized water at 50 °C until homogeneous, and then pass the mixture through a filter with a sieve size of 5-10 μm and an activated carbon column at a flow rate of 60 L / h to obtain boric acid solution A.

[0045] S2) Add boric acid solution A to 1% dilute sulfuric acid to adjust the pH to 4.5, add 0.075% EDTA complexing agent, and react for 45 min; then pass it through a fixed bed packed with complex adsorbent to obtain boric acid solution B.

[0046] S3) Under the conditions of operating pressure of 2MPa and temperature of 30℃, boric acid solution B is passed through a reverse osmosis membrane module with an aromatic polyamide composite membrane to obtain a primary concentrate.

[0047] S4) The primary concentrate is passed through a nanofiltration membrane module with an operating pressure of 1.0 MPa, a temperature of 40°C, and a membrane material of polypiperazine amide composite membrane to obtain secondary nanofiltration permeate and secondary concentrate; the secondary nanofiltration permeate is returned to the reverse osmosis membrane module for recycling treatment, and the secondary concentrate enters the S5 process;

[0048] S5) The temperature of the secondary concentrate is reduced to 10℃ at a cooling rate of 7.5℃ / h for crystallization, and stirred at a rate of 200r / min for 3h to obtain high-purity boric acid crystals and mother liquor; the high-purity boric acid crystals and mother liquor are separated by centrifugation, and the mother liquor is returned to the reverse osmosis membrane module of the S3 process for recycling; the high-purity boric acid crystals are washed with ultrapure water and then vacuum dried at 50℃ to obtain nuclear-grade boric acid.

[0049] The complex adsorbent in this embodiment:

[0050] 32 g of ZrOCl2 was vigorously stirred in 2.5 LDM for 20 min to ensure complete dissolution. Then, 16.1 g of terephthalic acid and 250 mL of trifluoroacetic acid were added to form a homogeneous solution, and the mixture was reacted at 120 °C for 36 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed with anhydrous ethanol, and dried under vacuum at 60 °C to obtain the defect intermediate.

[0051] Mix 200 mL of tetrabutyl titanate and 800 mL of methanol evenly, then add 10 g of defect intermediate and heat to 100°C for 24 h. Collect the precipitate by centrifugation, wash with methanol, and dry under vacuum at 60°C to obtain the complex adsorbent.

[0052] Example 2

[0053] This embodiment provides a process for purifying boric acid using reverse osmosis membranes to prepare nuclear-grade boric acid, specifically including the following steps:

[0054] S1) Mix 1 kg of industrial boric acid and 15 kg of deionized water at 50 °C until homogeneous, and then pass the mixture through a filter with a sieve size of 5-10 μm and an activated carbon column at a flow rate of 60 L / h to obtain boric acid solution A.

[0055] S2) Add boric acid solution A to 1% dilute sulfuric acid, adjust pH=3, add 0.05% EDTA complexing agent, and react for 30 min; then pass through a fixed bed packed with complex adsorbent to obtain boric acid solution B;

[0056] S3) Under the conditions of operating pressure of 1.5MPa and temperature of 25℃, boric acid solution B is passed through a reverse osmosis membrane module with an aromatic polyamide composite membrane to obtain a primary concentrate.

[0057] S4) The primary concentrate is passed through a nanofiltration membrane module with an operating pressure of 1.0 MPa, a temperature of 40°C, and a membrane material of polypiperazine amide composite membrane to obtain secondary nanofiltration permeate and secondary concentrate; the secondary nanofiltration permeate is returned to the reverse osmosis membrane module for recycling treatment, and the secondary concentrate enters the S5 process;

[0058] S5) The temperature of the secondary concentrate is reduced to 5℃ at a cooling rate of 5℃ / h for crystallization, and stirred at a rate of 200r / min for 1h to obtain high-purity boric acid crystals and mother liquor; the high-purity boric acid crystals and mother liquor are separated by centrifugation, and the mother liquor is returned to the reverse osmosis membrane module of the S3 process for recycling; the high-purity boric acid crystals are washed with ultrapure water and then vacuum dried at 50℃ to obtain nuclear-grade boric acid.

[0059] The complex adsorbent in this embodiment:

[0060] 32 g of ZrOCl2 was vigorously stirred in 2.5 LDM for 20 min to ensure complete dissolution. Then, 16.1 g of terephthalic acid and 200 mL of trifluoroacetic acid were added to form a homogeneous solution, and the mixture was reacted at 120 °C for 36 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed with anhydrous ethanol, and dried under vacuum at 60 °C to obtain the defect intermediate.

[0061] Mix 300 mL of tetrabutyl titanate and 800 mL of methanol evenly, then add 10 g of defect intermediate and heat to 100°C for 24 h. Collect the precipitate by centrifugation, wash with methanol, and dry under vacuum at 60°C to obtain the complex adsorbent.

[0062] Example 3

[0063] This embodiment provides a process for purifying boric acid using reverse osmosis membranes to prepare nuclear-grade boric acid, specifically including the following steps:

[0064] S1) Mix 1 kg of industrial boric acid and 15 kg of deionized water at 50 °C until homogeneous, and then pass the mixture through a filter with a sieve size of 5-10 μm and an activated carbon column at a flow rate of 60 L / h to obtain boric acid solution A.

[0065] S2) Add boric acid solution A to 1% dilute sulfuric acid, adjust pH to 6.5, add 0.1% EDTA complexing agent, and react for 60 min; then pass through a fixed bed packed with complex adsorbent to obtain boric acid solution B;

[0066] S3) Under the conditions of operating pressure of 3MPa and temperature of 35℃, boric acid solution B is passed through a reverse osmosis membrane module with an aromatic polyamide composite membrane to obtain a primary concentrate.

[0067] S4) The primary concentrate is passed through a nanofiltration membrane module with an operating pressure of 1.0 MPa, a temperature of 40°C, and a membrane material of polypiperazine amide composite membrane to obtain secondary nanofiltration permeate and secondary concentrate; the secondary nanofiltration permeate is returned to the reverse osmosis membrane module for recycling treatment, and the secondary concentrate enters the S5 process;

[0068] S5) The temperature of the secondary concentrate is reduced to 15℃ at a cooling rate of 10℃ / h for crystallization, and stirred at a rate of 200r / min for 4h to obtain high-purity boric acid crystals and mother liquor; the high-purity boric acid crystals and mother liquor are separated by centrifugation, and the mother liquor is returned to the reverse osmosis membrane module of the S3 process for recycling; the high-purity boric acid crystals are washed with ultrapure water and then vacuum dried at 50℃ to obtain nuclear-grade boric acid.

[0069] The complex adsorbent in this embodiment:

[0070] 32 g of ZrOCl2 was vigorously stirred in 2.5 LDM for 20 min to ensure complete dissolution. Then, 16.1 g of terephthalic acid and 300 mL of trifluoroacetic acid were added to form a homogeneous solution, and the mixture was reacted at 120 °C for 36 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed with anhydrous ethanol, and dried under vacuum at 60 °C to obtain the defect intermediate.

[0071] Mix 100 mL of tetrabutyl titanate and 800 mL of methanol evenly, then add 10 g of defect intermediate and heat to 100°C for 24 h. Collect the precipitate by centrifugation, wash with methanol, and dry under vacuum at 60°C to obtain the complex adsorbent.

[0072] Control group 1

[0073] This control group provides a process for purifying boric acid using reverse osmosis membranes to prepare nuclear-grade boric acid, specifically including the following steps:

[0074] S1) Mix 1 kg of industrial boric acid and 15 kg of deionized water at 50 °C until homogeneous, and then pass the mixture through a filter with a sieve size of 5-10 μm and an activated carbon column at a flow rate of 60 L / h to obtain boric acid solution A.

[0075] S2) Add boric acid solution A to 1% dilute sulfuric acid to adjust the pH to 4.5, add 0.075% EDTA complexing agent, and react for 45 min; then pass it through a fixed bed packed with complex adsorbent to obtain boric acid solution B.

[0076] S3) Under the conditions of operating pressure of 2MPa and temperature of 30℃, boric acid solution B is passed through a reverse osmosis membrane module with an aromatic polyamide composite membrane to obtain a primary concentrate.

[0077] S4) The primary concentrate is passed through a nanofiltration membrane module with an operating pressure of 1.0 MPa, a temperature of 40°C, and a membrane material of polypiperazine amide composite membrane to obtain secondary nanofiltration permeate and secondary concentrate; the secondary nanofiltration permeate is returned to the reverse osmosis membrane module for recycling treatment, and the secondary concentrate enters the S5 process;

[0078] S5) The temperature of the secondary concentrate is reduced to 10℃ at a cooling rate of 7.5℃ / h for crystallization, and stirred at a rate of 200r / min for 3h to obtain high-purity boric acid crystals and mother liquor; the high-purity boric acid crystals and mother liquor are separated by centrifugation, and the mother liquor is returned to the reverse osmosis membrane module of the S3 process for recycling; the high-purity boric acid crystals are washed with ultrapure water and then vacuum dried at 50℃ to obtain nuclear-grade boric acid.

[0079] The complex adsorbent used in this control group:

[0080] 32 g of ZrOCl2 was vigorously stirred in 2.5 LDM for 20 min to ensure complete dissolution. Then, 16.1 g of terephthalic acid and 250 mL of trifluoroacetic acid were added to form a homogeneous solution, and the mixture was reacted at 120 °C for 36 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed with anhydrous ethanol, and dried under vacuum at 60 °C to obtain the complex adsorbent.

[0081] Control group 2

[0082] This control group provides a process for purifying boric acid using reverse osmosis membranes to prepare nuclear-grade boric acid, specifically including the following steps:

[0083] S1) Mix 1 kg of industrial boric acid and 15 kg of deionized water at 50 °C until homogeneous, and then pass the mixture through a filter with a sieve size of 5-10 μm and an activated carbon column at a flow rate of 60 L / h to obtain boric acid solution A.

[0084] S2) Add boric acid solution A to 1% dilute sulfuric acid to adjust the pH to 4.5, add 0.075% EDTA complexing agent, and react for 45 min; then pass it through a fixed bed packed with complex adsorbent to obtain boric acid solution B.

[0085] S3) Under the conditions of operating pressure of 2MPa and temperature of 30℃, boric acid solution B is passed through a reverse osmosis membrane module with an aromatic polyamide composite membrane to obtain a primary concentrate.

[0086] S4) The primary concentrate is passed through a nanofiltration membrane module with an operating pressure of 1.0 MPa, a temperature of 40°C, and a membrane material of polypiperazine amide composite membrane to obtain secondary nanofiltration permeate and secondary concentrate; the secondary nanofiltration permeate is returned to the reverse osmosis membrane module for recycling treatment, and the secondary concentrate enters the S5 process;

[0087] S5) The temperature of the secondary concentrate is reduced to 10℃ at a cooling rate of 7.5℃ / h for crystallization, and stirred at a rate of 200r / min for 3h to obtain high-purity boric acid crystals and mother liquor; the high-purity boric acid crystals and mother liquor are separated by centrifugation, and the mother liquor is returned to the reverse osmosis membrane module of the S3 process for recycling; the high-purity boric acid crystals are washed with ultrapure water and then vacuum dried at 50℃ to obtain nuclear-grade boric acid.

[0088] The complex adsorbent used in this control group:

[0089] 32 g of ZrOCl2 was vigorously stirred in 2.5 LDM for 20 min to ensure complete dissolution. Then 16.1 g of terephthalic acid was added to form a homogeneous solution, and the mixture was reacted at 120 °C for 36 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed with anhydrous ethanol, and dried under vacuum at 60 °C to obtain the defect intermediate.

[0090] Mix 200 mL of tetrabutyl titanate and 800 mL of methanol evenly, then add 10 g of defect intermediate and heat to 100°C for 24 h. Collect the precipitate by centrifugation, wash with methanol, and dry under vacuum at 60°C to obtain the complex adsorbent.

[0091] Control group 3

[0092] This control group provides a process for purifying boric acid using reverse osmosis membranes to prepare nuclear-grade boric acid, specifically including the following steps:

[0093] S1) Mix 1 kg of industrial boric acid and 15 kg of deionized water at 50 °C until homogeneous, and then pass the mixture through a filter with a sieve size of 5-10 μm and an activated carbon column at a flow rate of 60 L / h to obtain boric acid solution A.

[0094] S2) Add boric acid solution A to 1% dilute sulfuric acid to adjust the pH to 4.5, add 0.075% EDTA complexing agent, and react for 45 min to obtain boric acid solution B;

[0095] S3) Under the conditions of operating pressure of 2MPa and temperature of 30℃, boric acid solution B is passed through a reverse osmosis membrane module with an aromatic polyamide composite membrane to obtain a primary concentrate.

[0096] S4) The primary concentrate is passed through a nanofiltration membrane module with an operating pressure of 1.0 MPa, a temperature of 40°C, and a membrane material of polypiperazine amide composite membrane to obtain secondary nanofiltration permeate and secondary concentrate; the secondary nanofiltration permeate is returned to the reverse osmosis membrane module for recycling treatment, and the secondary concentrate enters the S5 process;

[0097] S5) The temperature of the secondary concentrate is reduced to 10℃ at a cooling rate of 7.5℃ / h for crystallization, and stirred at a rate of 200r / min for 3h to obtain high-purity boric acid crystals and mother liquor; the high-purity boric acid crystals and mother liquor are separated by centrifugation, and the mother liquor is returned to the reverse osmosis membrane module of the S3 process for recycling; the high-purity boric acid crystals are washed with ultrapure water and then vacuum dried at 50℃ to obtain nuclear-grade boric acid.

[0098] Performance testing

[0099] The purity of boric acid was tested in accordance with the national standard GB / T628-2011 Boric Acid Chemical Reagents. The final product was tested for anions and cations using ion chromatography and inductively coupled plasma atomic emission spectrometry, respectively. The test results are summarized in Table 1.

[0100] Table 1. Test Results of Nuclear-Grade Boric Acid Product Quality Performance

[0101]

[0102] The "-" indicates that the value is below the detection limit.

[0103] Analysis of Examples 1-3 and Control Groups 1-3 and in combination Figure 1-4As can be seen from the test data in Table 1, the process for preparing nuclear-grade boric acid in this application has advantages such as excellent impurity removal effect, simple process, and controllable cost. Compared with Examples 1-3, the complex adsorbent prepared in Control Group 1 did not introduce Ti active sites, resulting in an increase in the content of metal impurities in the boric acid product, indicating that Ti loading plays a key role in improving the performance of the adsorbent. Compared with Examples 1-3, the complex adsorbent prepared in Control Group 2 did not undergo defect induction treatment, and the purity of the final product decreased significantly, confirming that defect induction can enable the adsorbent to form a richer pore structure and a larger specific surface area, thereby enhancing the adsorption capacity of EDTA complex. Compared with Examples 1-3, the nuclear-grade boric acid purification process in Control Group 3 deleted the complex adsorption unit. Although EDTA can remove metal ion impurities, the membrane module has a limited rejection rate for complexes, making it difficult to guarantee the purity of the final product; at the same time, complexes will accumulate on the membrane surface, leading to membrane fouling and affecting the long-term stable operation of the system.

[0104] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A process for purifying boric acid using reverse osmosis membranes to prepare nuclear-grade boric acid, characterized in that, Includes the following steps: S1) Industrial boric acid and deionized water are mixed evenly and then passed through a filter and an activated carbon column to obtain boric acid solution A. S2) Add dilute sulfuric acid to boric acid solution A to adjust the pH, add EDTA complexing agent to react, and then pass it through a fixed bed column packed with complex adsorbent to obtain boric acid solution B; the preparation method of the complex adsorbent includes the following steps: ZrOCl2 is evenly dispersed in DMF, trifluoroacetic acid and terephthalic acid are added to form a homogeneous solution, and the temperature is raised to react. After the reaction is completed, the solution is cooled to room temperature, centrifuged to collect the precipitate, washed, and vacuum dried to obtain the defect intermediate; tetrabutyl titanate and methanol are evenly mixed, the defect intermediate is added, the temperature is raised to react, centrifuged to collect the precipitate, washed, and vacuum dried to obtain the complex adsorbent; S3) Pass boric acid solution B through a reverse osmosis membrane module with an aromatic polyamide composite membrane to obtain a primary concentrate; S4) The primary concentrate is passed through a nanofiltration membrane module with a polypiperazine amide composite membrane material to obtain a secondary concentrate and a secondary nanofiltration permeate. The secondary concentrate enters the S5 process for subsequent operations, and the secondary nanofiltration permeate is returned to the reverse osmosis membrane module in the S3 process for recycling. S5) Cool and stir the secondary concentrate to crystallize, then centrifuge to obtain high-purity boric acid crystals and mother liquor. Rinse the high-purity boric acid crystals with ultrapure water and then vacuum dry to obtain nuclear-grade boric acid. The mother liquor is returned to the reverse osmosis membrane module in the S3 process for recycling.

2. The process for preparing nuclear-grade boric acid by purifying boric acid using a reverse osmosis membrane according to claim 1, characterized in that: In the S2 process, the pH is adjusted to 3-6.

5.

3. The process for preparing nuclear-grade boric acid by purifying boric acid using a reverse osmosis membrane according to claim 1, characterized in that: The mass concentration of the EDTA complexing agent in the S2 process is 0.05-0.1%.

4. The process for preparing nuclear-grade boric acid by purifying boric acid using a reverse osmosis membrane according to claim 1, characterized in that: The operating pressure in the S3 process is 1.5-3.0 MPa, and the temperature is 25-35℃.

5. The process for preparing nuclear-grade boric acid by purifying boric acid using a reverse osmosis membrane according to claim 1, characterized in that: The cooling rate in the S5 process is 5-10℃ / h, and the crystallization temperature is 5-15℃.

6. The process for preparing nuclear-grade boric acid by purifying boric acid using a reverse osmosis membrane according to claim 1, characterized in that: The stirring time in the S5 process is 1-4 hours.

7. The process for preparing nuclear-grade boric acid by purifying boric acid using a reverse osmosis membrane according to claim 1, characterized in that: The volume ratio of tetrabutyl titanate to methanol is (1-3):

8.

8. The process for preparing nuclear-grade boric acid by purifying boric acid using a reverse osmosis membrane according to claim 1, characterized in that: The volume ratio of trifluoroacetic acid to DMF is (2-3):25.

Images