A method for recovering mixed acid waste liquid containing hydrofluoric acid

Abstract

The invention discloses a method for recovering mixed acid waste liquid containing hydrofluoric acid, comprising reacting a raw material with a sodium salt or a potassium salt, and then filtering to obtain a filtrate; the raw material is a mixed acid waste liquid containing hydrofluoric acid; the filtrate is sent to a diffusion dialysis device for treatment, the diffusion dialysis device includes a homogeneous anion exchange membrane; the recovered liquid obtained by the treatment of the diffusion dialysis device is sent to a membrane separation device, the membrane material of the membrane separation device is an acid-resistant metal ion removal membrane, and the recovered mixed acid is obtained on the permeation side of the membrane separation device. The invention can effectively remove impurities and metal ions in low-concentration waste acid solutions, so that the products meet the electronic grade reuse standard, improve the resource recovery rate, and have a simple process flow and low energy consumption, which is suitable for industrial promotion and application.

Description

Technical Field

[0001] The invention belongs to the technical field of ultra-clean and high-purity chemistry, and in particular relates to a method for recovering mixed acid waste liquid containing hydrofluoric acid. Background Art

[0002] In the electronics industry, etching processes often use mixed acids including hydrofluoric acid, which produces a large amount of mixed acid waste containing hydrofluoric acid. These waste liquids cannot be used directly because of excessive levels of fluorosilicic acid and metal impurities after use. At the same time, if the fluorine-containing waste liquid is discharged directly without treatment, it will cause serious pollution to the environment.

[0003] Traditional methods for treating waste acid include neutralization precipitation, distillation, adsorption, etc. However, simple neutralization treatment often makes it difficult to recycle and reuse the acid, resulting in a waste of resources. The ion exchange method uses ion exchange resins to adsorb impurity ions in waste acid, but it cannot completely remove all impurities, and the resin regeneration is frequent and the cost of use is high. The distillation method obtains waste acid by heating and evaporation. Due to the complex composition of the mixed acid waste liquid, a single distillation tower cannot achieve the purpose of purification. Multiple distillation towers lead to high investment costs and large equipment footprint.

[0004] In addition, the etching process uses a mixed acid containing hydrofluoric acid, nitric acid, etc. The existing technology only focuses on purifying and recovering the hydrofluoric acid, which is the most difficult to recycle. In the purification process, nitric acid and other components are often removed simultaneously with the removal of impurities. As a result, when the obtained hydrofluoric acid is used again in the etching process, fresh nitric acid and other acids need to be added for compounding. This process also causes a waste of resources.

[0005] Patent CN116873870 B proposes a method for recovering a solution containing hydrofluoric acid and refining hydrofluoric acid, and obtains a concentrated and purified mixed acid solution through pretreatment, distillation, adsorption and other steps, but the process flow is complicated and the distillation process has high energy consumption. Patent CN213387823 U recovers nitric acid-hydrofluoric acid through evaporation, condensation, filtration and other steps, but the recovery rate of this method is low, and the recovered acid is difficult to meet the electronic grade index requirements.

[0006] Although these patents provide new treatment ideas and technical solutions, in actual applications, how to further improve treatment efficiency and reduce costs, as well as how to maximize the utilization of mixed acid and waste acid resources and make the recycled mixed acid meet electronic grade reuse standards, are still challenges facing the industry. Therefore, it is urgent to develop more effective and environmentally friendly waste acid recycling technology to reduce environmental pollution, reduce production costs, and improve the recycling rate of resources. Summary of the invention

[0007] The purpose of the present invention is to provide an environmentally friendly and efficient method for recycling mixed acid waste liquid. The present invention effectively removes fluorosilicic acid, metal ions and other impurities in mixed acid waste acid through a series of optimized process steps and separation methods, improves the purity of the recycled mixed acid, makes it meet the electronic grade reuse standard, and reduces energy consumption and investment costs, and improves the resource recovery rate.

[0008] In order to achieve the above object, the present invention adopts the following technical solution:

[0009] A method for recovering mixed acid waste liquid containing hydrofluoric acid comprises the following steps:

[0010] (1) reacting a raw material with a sodium salt or a potassium salt, and then filtering to obtain a filtrate; the raw material is a mixed acid waste liquid containing hydrofluoric acid;

[0011] (2) sending the filtrate to a diffusion dialysis device for treatment, wherein the diffusion dialysis device comprises a homogeneous anion exchange membrane;

[0012] (3) The recovered liquid obtained by the diffusion dialysis device is sent to a membrane separation device. The membrane material of the membrane separation device is an acid-resistant metal ion removal membrane, and the recovered mixed acid is obtained on the permeation side of the membrane separation device.

[0013] The diffusion dialysis device can remove most of the metal ions in the filtrate and retain mixed acid components such as nitric acid and hydrochloric acid. The subsequent membrane separation device is used to further remove residual trace metal ions and particulate impurities.

[0014] Preferably, the raw material in step (1) further includes hydrochloric acid or nitric acid or a mixture of the two.

[0015] Preferably, the dosage of the sodium salt or potassium salt in step (1) is 2 to 20 times the molar number of the fluorosilicic acid impurities in the mixed acid waste liquid.

[0016] Preferably, the reaction temperature in step (1) is 0-30°C.

[0017] Preferably, the filtration in step (1) is performed in a filter, and the filter is a bag filter.

[0018] Preferably, the operating pressure of the filtration is controlled to be 0.15~0.4Mpa.

[0019] Preferably, the filter bag of the bag filter is made of PTFE, and the pore size of the filter bag is 0.1-1.0 um.

[0020] Preferably, the homogeneous anion exchange membrane in step (2) is a perfluorosulfonic acid functional membrane, and the thickness of the homogeneous anion exchange membrane is 50-100 um.

[0021] Preferably, the perfluorosulfonic acid functional membrane is obtained by sulfonation reaction of PTFE, PVDF or PVC.

[0022] Preferably, in the feed of the diffusion dialysis device described in step (2), the volume ratio of the filtrate to the process water is 1:0.8~1.2, the operating temperature of the diffusion dialysis device is controlled to be 20~35°C, and the operating pressure is controlled to be 0.1~0.3MPa.

[0023] Preferably, the operating pressure of the membrane separation device in step (3) is 0.2-1.0 Mpa, and the operating temperature is 20-45°C.

[0024] Preferably, the material of the acid-resistant metal ion removal membrane in step (3) is a perfluoro PMMD-CTFE membrane material, and the perfluoro PMMD-CTFE membrane material is prepared by the following method:

[0025] (1-1) Preparation of copolymer A:

[0026] Perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMMD) and chlorotrifluoroethylene (CTFE) are mixed in a perfluoro solvent and polymerized under the action of a catalyst to obtain a copolymer A;

[0027] (1-2) Preparation of acid-resistant metal ion removal membrane:

[0028] The copolymer A and acetone are mixed in a perfluorinated solvent at 60-80° C. to obtain a composite layer membrane liquid, and then the composite layer membrane liquid is coated on the surface of a polytetrafluoroethylene-based membrane, and dried to obtain the acid-resistant metal ion removal membrane.

[0029] Preferably, the perfluoro solvent is selected from one or more of Fluorinert FC-40, Fluorinert FC-72 or Fluorinert FC-75.

[0030] Preferably, the mass ratio of the perfluoro-2-methylene-4-methyl-1,3-dioxolane to the chlorotrifluoroethylene in step (1-1) is 1:5-7.

[0031] Preferably, in step (1-1), the total mass concentration of perfluoro-2-methylene-4-methyl-1,3-dioxolane and chlorotrifluoroethylene in the perfluoro solvent is 30% to 40%.

[0032] Preferably, the mixing in step (1-1) is carried out at 40-65°C.

[0033] Preferably, the catalyst in step (1-1) is perfluoropropionyl peroxide.

[0034] Preferably, the amount of the catalyst added in step (1-1) is 0.01% to 0.02% of the mass of the perfluoro-2-methylene-4-methyl-1,3-dioxolane.

[0035] Preferably, step (1-1) further comprises a step of removing the solvent after the polymerization reaction.

[0036] Preferably, in step (1-2), the mass concentration of the copolymer A in the composite layer membrane solution is 0.05% to 0.2%.

[0037] Preferably, the amount of acetone added in step (1-2) is 2.5% of the mass of the perfluoro solvent.

[0038] Preferably, the polytetrafluoroethylene-based membrane described in step (1-2) is prepared by hot pressing polyphenylene sulfide (PPS) non-woven fabric and polytetrafluoroethylene (PTFE).

[0039] Preferably, the pore size of the basement membrane described in step (1-2) is 10-15 nm.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The present invention proposes a method for recovering mixed acid waste liquid by combining diffusion dialysis and membrane separation. Fluorosilicic acid is removed through a pretreatment step, and then recovered by diffusion dialysis and membrane separation devices to effectively remove metal ions, particulate matter and other impurities while retaining mixed acid components such as nitric acid and hydrochloric acid to obtain a mixed acid liquid. The recovery rate of the mixed acid liquid can reach more than 90%, meeting the high standard requirements of electronic grade mixed acid and achieving the purpose of resource recycling. The entire process is simple, with low energy consumption, and has significant advantages in reducing pollution and production costs.

[0042] (2) The diffusion dialysis device of the present invention can efficiently remove metal ions from waste liquid while retaining hydrofluoric acid, nitric acid and hydrochloric acid by utilizing the selective permeability of the acid-resistant anion exchange membrane. The acid-resistant anion exchange membrane has excellent chemical stability and thermal stability and can be used for a long time under acidic conditions. With the concentration difference as the driving force, the membrane base is positively charged and can selectively pass through acid anions and drive smaller hydrogen ions H + Through this process, metal ions are intercepted and the purpose of mixed acid recovery and metal ion removal is achieved.

[0043] (3) The diffusion dialysis device used in the present invention is easy to operate, easy to control, and has low maintenance costs. By accurately setting operating conditions, it reduces energy consumption and is suitable for industrial-scale applications.

[0044] (4) In the membrane separation device of the present invention, trace metal ions in hydrofluoric acid are further removed by the acid-resistant PMMD-CTFE perfluoro membrane material, thereby improving the purity of the product and achieving the purpose of recycling electronic-grade hydrofluoric acid; the PMMD-CTFE membrane material not only has excellent mechanical properties and chemical stability, but also the dissolution rate of the membrane material is controlled at an extremely low level of less than 10 ppt, and the content of total organic carbon is less than 0.1 ppt, thereby avoiding the potential influence of membrane material dissolution on product purity and ensuring the purity and reliability of the final product. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments, so that those skilled in the art can fully understand the technical content of the present invention. It should be understood that the following examples are used to further illustrate the present invention and cannot be interpreted as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above content of the present invention belong to the scope of protection of the present invention, and the raw materials used in the present invention are commercial products that can be purchased on the market without special instructions. The specific process parameters of the following examples are also only an example in a suitable range, that is, those skilled in the art can make a selection within a suitable range according to the description herein, and are not limited to the specific numerical values ​​​​exemplified below.

[0046] Example 1

[0047] (1) Preparation of PMMD-CTFE membrane materials:

[0048] In a closed reactor, perfluoro-2-methylene-4-methyl-1,3-dioxolane and chlorotrifluoroethylene are added to a perfluoro solvent in a mass ratio of 1:6. The perfluoro solvent used is Fluorinert FC-72, and the sum of the mass concentrations of perfluoro-2-methylene-4-methyl-1,3-dioxolane and chlorotrifluoroethylene is 35%.

[0049] Heat and stir at 60°C to ensure that the raw materials are fully mixed and dissolved, then add the catalyst perfluoropropionyl peroxide (synthesized in the laboratory, the synthesis method is referenced in Zhejiang Chemical Industry, Vol. 36, No. 2, 2005, P31), the added mass of which is 0.015% of the mass of perfluoro-2-methylene-4-methyl-1,3-dioxolane. Then carry out polymerization reaction, and after removing the solvent by evaporation, copolymer A is obtained.

[0050] The prepared copolymer A was dissolved in a perfluoro solvent so that the mass concentration of the copolymer A was 0.18%. The perfluoro solvent was able to dissolve the copolymer A well during the dissolution process, ensuring the uniformity and stability of the composite membrane liquid. Subsequently, acetone of 2.5% of the mass of the perfluoro solvent was added to the solution, and the mixture was heated and stirred at 80°C for 20 hours to form a composite membrane liquid.

[0051] The prepared composite layer membrane liquid was coated on the surface of the PTFE base membrane and dried at 80°C for 11 hours to obtain an acid-resistant metal ion removal membrane. The PTFE base membrane was prepared by hot pressing polyphenylene sulfide (PPS) non-woven fabric and polytetrafluoroethylene (PTFE), and the pore size of the base membrane was 14 nm.

[0052] (2) The mixed acid waste liquid is fed into the reactor through the inlet, wherein the mass fraction of hydrofluoric acid contained in the waste liquid is 10%, the mass fraction of nitric acid is 1%, the mass fraction of hydrochloric acid is 0.5%, the mass fraction of fluorosilicic acid is 5000 mg / kg, and the total metal impurity content is less than 100 ppm. The amount of sodium chloride added is controlled to be twice the molar number of fluorosilicic acid in the mixed acid waste liquid, the reaction temperature of the reactor is 20°C, and the stirring speed is 100 r / min to ensure that the fluorosilicic acid in the waste acid liquid is fully reacted and removed.

[0053] (3) The treated waste acid liquid is sent to a bag filter. The filter bag is made of PTFE and the operating pressure is controlled at 0.4 MPa. Under the action of the filter, the clear liquid of the reaction liquid is further sent to the diffusion dialysis device through the side outlet.

[0054] (4) A diffusion dialysis device was used to control the feed volume ratio of waste acid liquid and process water to 1:0.8, the operating temperature to 20°C, and the operating pressure to 0.1 MPa. A perfluorosulfonic acid PTFE membrane (provided by Shandong Tianwei Membrane Technology Co., Ltd.) was used as the anion exchange membrane. Under the action of the anion exchange membrane, the recovered liquid in the waste acid liquid was effectively collected into the recovery tank, with a recovery rate of more than 90%. At the same time, more than 80% of the metal ions were effectively removed.

[0055] (5) The mixed acid recovery liquid treated in the above steps is further sent to a membrane separation device, and the operating pressure of the membrane separation device is controlled to be 0.2 MPa and the operating temperature is controlled to be 20°C. Under the action of the PMMD-CTFE membrane material, the metal ions in the recovery liquid are further removed, and finally the electronic grade mixed acid product is collected on the permeate side of the membrane separation device.

[0056] After the above steps, the mass fraction of hydrofluoric acid in the mixed acid is 9.5%, the mass fraction of nitric acid is 0.95%, and the mass fraction of hydrochloric acid is 0.45%. The detection results of metal ions and fluorosilicic acid are shown in Table 1.

[0057] Example 2

[0058] (1) Same as Example 1.

[0059] (2) The mixed acid waste liquid is fed into the reactor through the inlet, wherein the mass fraction of hydrofluoric acid contained in the waste acid liquid is 15%, the mass fraction of nitric acid is 3%, the mass fraction of fluorosilicic acid is 8000 mg / kg, and the metal impurity content is less than 100 ppm. The amount of sodium carbonate added is controlled to be 5 times the molar number of fluorosilicic acid impurities in the mixed acid waste liquid, the reaction temperature is 0℃, and the stirring speed is 110 r / min to ensure that the fluorosilicic acid in the waste acid liquid is fully reacted and removed.

[0060] (3) The treated waste acid liquid is sent to a bag filter. The filter bag is made of PTFE and the operating pressure is controlled at 0.15 MPa. Under the action of the filter, the clear liquid of the reaction liquid is further sent to the diffusion dialysis device through the side outlet.

[0061] (4) A diffusion dialysis device was used to control the feed volume ratio of waste acid liquid and process water to 1:1, the operating temperature to 25°C, and the operating pressure to 0.2 MPa. A perfluorosulfonic acid PVDF membrane (provided by Shandong Tianwei Membrane Technology Co., Ltd.) was used as the anion exchange membrane. Under the action of the anion exchange membrane, the recovered liquid in the waste acid liquid was effectively collected into the recovery tank, with a recovery rate of more than 90%. At the same time, more than 80% of the metal ions were effectively removed.

[0062] (5) The mixed acid recovery liquid treated in the above steps is further sent to the membrane separation device. The operating pressure of the membrane separation device is controlled to be 0.4 MPa and the operating temperature is controlled to be 42.5°C. Under the action of the PMMD-CTFE membrane material, the metal ions in the recovery liquid are further removed, and finally the electronic grade mixed acid product is collected on the permeate side of the membrane separation device.

[0063] The mass fraction of hydrofluoric acid in the mixed acid after treatment in the above steps is 14.5%, and the mass fraction of nitric acid is 2.8%. The detection results of metal ions and fluorosilicic acid are shown in Table 1.

[0064] Example 3

[0065] (1) Same as Example 1.

[0066] (2) The mixed acid waste liquid is fed into the reactor through the inlet, wherein the mass fraction of hydrofluoric acid contained in the waste acid liquid is 20%, the mass fraction of hydrochloric acid is 5%, the mass fraction of fluorosilicic acid is 10000 mg / kg, and the metal impurity content is less than 100 ppm. The amount of potassium chloride added is controlled to be 20 times the molar number of fluorosilicic acid impurities in the mixed acid waste liquid, the reaction temperature is 30°C, and the stirring speed is 120r / min to ensure that the fluorosilicic acid in the waste acid liquid is fully reacted.

[0067] (3) The treated waste acid liquid is sent to a bag filter. The filter bag is made of PTFE and the operating pressure is controlled at 0.3 MPa. Under the action of the filter, the clear liquid of the reaction liquid is further sent to the diffusion dialysis device through the side outlet.

[0068] (4) A diffusion dialysis device was used to control the feed volume ratio of waste acid liquid and process water to 1:1.2, the operating temperature to 35°C, and the operating pressure to 0.3 MPa. A perfluorosulfonic acid PVC membrane (provided by Shandong Tianwei Membrane Technology Co., Ltd.) was used as the anion exchange membrane. Under the action of the anion exchange membrane, the recovered liquid in the waste acid liquid was effectively collected into the recovery tank, with a recovery rate of more than 90%. At the same time, more than 80% of the metal ions were effectively removed.

[0069] (5) The mixed acid recovery liquid treated in the above steps is further sent to a membrane separation device, and the operating pressure of the membrane separation device is controlled to be 1.0 MPa and the operating temperature is controlled to be 45°C. Under the action of the PMMD-CTFE membrane material, the metal ions in the recovery liquid are further removed, and finally the electronic grade mixed acid product is collected on the permeate side of the membrane separation device.

[0070] The mass fraction of hydrofluoric acid in the mixed acid after the treatment in the above steps is 19.5%, and the mass fraction of hydrochloric acid is 4.9%. The detection results of metal ions and fluorosilicic acid are shown in Table 1.

[0071] The analysis results of the electronic grade mixed acid products in the above Examples 1-3 are shown in Table 1:

[0072] Table 1 Analysis results of the mixed acid products obtained in Examples 1 to 3

[0073]

[0074] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the attached claims.

Claims

1. A method for recovering mixed acid waste liquid containing hydrofluoric acid, characterized in that: The steps include: (1) reacting a raw material with a sodium salt or a potassium salt, and then filtering to obtain a filtrate; the raw material is a mixed acid waste liquid containing hydrofluoric acid; (2) sending the filtrate to a diffusion dialysis device for treatment, wherein the diffusion dialysis device comprises a homogeneous anion exchange membrane; (3) sending the recovered liquid obtained by the diffusion dialysis device to a membrane separation device, wherein the membrane material of the membrane separation device is an acid-resistant metal ion removal membrane, and recovering the mixed acid on the permeation side of the membrane separation device; The material of the acid-resistant metal ion removal membrane is a perfluoro PMMD-CTFE membrane material, and the perfluoro PMMD-CTFE membrane material is prepared by the following method: (1-1) Preparation of copolymer A: Perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMMD) and chlorotrifluoroethylene (CTFE) are mixed in a perfluoro solvent and polymerized under the action of a catalyst to obtain a copolymer A; (1-2) Preparation of acid-resistant metal ion removal membrane: The copolymer A and acetone are mixed in a perfluorinated solvent at 60-80° C. to obtain a composite layer membrane liquid, and then the composite layer membrane liquid is coated on the surface of a polytetrafluoroethylene-based membrane, and dried to obtain the acid-resistant metal ion removal membrane.

2. The recycling method according to claim 1, characterized in that: The dosage of the sodium salt or potassium salt in step (1) is 2 to 20 times the molar number of the fluorosilicic acid impurities in the mixed acid waste liquid.

3. The recycling method according to claim 1, characterized in that: The reaction temperature in step (1) is 0-30°C.

4. The recycling method according to claim 1, characterized in that: The filtration described in step (1) is carried out in a filter, and the filter is a bag filter. The material of the filter bag of the bag filter is PTFE, and the pore size of the filter bag is 0.1~1.0 um.

5. The recycling method according to claim 1, characterized in that: The operating pressure of the filtration described in step (1) is controlled to be 0.15~0.4Mpa.

6. The recycling method according to claim 1, characterized in that: The homogeneous anion exchange membrane described in step (2) is a perfluorosulfonic acid functional membrane, and the thickness of the homogeneous anion exchange membrane is 50-100 um.

7. The recycling method according to claim 6, characterized in that: The perfluorosulfonic acid functional membrane is obtained by sulfonation reaction of PTFE, PVDF or PVC.

8. The recycling method according to claim 1, characterized in that: In the feed of the diffusion dialysis device described in step (2), the volume ratio of the filtrate to the process water is 1:0.8~1.2, the operating temperature of the diffusion dialysis device is controlled to be 20~35°C, and the operating pressure is controlled to be 0.1~0.3MPa.

9. The recycling method according to claim 1, characterized in that: The operating pressure of the membrane separation device in step (3) is 0.2~1.0Mpa, and the operating temperature is 20~45°C.

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