Advanced treatment method for fluorine-containing wastewater in semiconductor / photovoltaic industry

Abstract

The invention relates to an advanced treatment method and system for fluorine-containing wastewater in semiconductor / photovoltaic industry. The treatment method comprises the following steps: pH adjustment: adding sodium hydroxide into pretreated fluorine-containing wastewater or fluorine-containing wastewater without silicon, and adjusting the pH value to 9.5-10.2, so that fluorine ions exist in the form of sodium fluoride; performing ceramic ultrafiltration membrane CUF treatment and reverse osmosis membrane RO treatment to obtain RO produced water and sodium fluoride concentrated water; deep purification: the RO produced water passes through a deep fluorine removal resin adsorption unit, so that the concentration of fluorine ions in the water is reduced to 1t; 1 ppm, so as to obtain recycled produced water; resourceful treatment: introducing the sodium fluoride concentrated water into a bipolar membrane electrodialysis system, and converting the sodium fluoride concentrated water into hydrofluoric acid and a sodium hydroxide solution; and refining and recycling.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment and resource utilization technology, specifically relating to a method for deep treatment of fluoride-containing wastewater from the semiconductor / photovoltaic industry. Background Technology

[0002] In the cleaning processes of the semiconductor / photovoltaic industry, ultrapure water is typically used for cleaning, resulting in relatively clean fluoride-containing wastewater with low impurity content, but a high concentration of fluoride ions, requiring strict treatment. Currently, the traditional treatment process for fluoride-containing wastewater mainly uses the lime-calcium chloride precipitation method, which removes fluoride ions by generating calcium fluoride precipitate, followed by the use of a deep defluorinating agent to reduce the fluoride ion concentration in the effluent to below the discharge standard (e.g., <1 ppm). However, this process has the following drawbacks: high reagent dosage and high treatment costs; the generation of large amounts of calcium fluoride solid waste sludge, which is difficult to dispose of and easily causes secondary pollution; and the inability to achieve water recycling, failing to meet zero-discharge requirements.

[0003] Another approach is to use evaporators for concentration to achieve zero emissions. However, this method is economically unsustainable and has extremely high operating costs, consuming 80-120 kWh / t of wastewater, making it unaffordable for manufacturing companies and unfeasible for industrial application. Therefore, developing an economical, efficient, and resource-recoverable advanced treatment process for fluoride-containing wastewater has become an urgent need for the semiconductor / photovoltaic industry.

[0004] Electronic-grade hydrofluoric acid, a key material in semiconductor manufacturing, has long been reliant on imports, with only a few domestic companies capable of producing high-end products. Achieving the recycling and reuse of these chemicals would significantly reduce production costs and mitigate environmental impact. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for the deep treatment of fluoride-containing wastewater from the semiconductor / photovoltaic industry. This method employs a membrane separation-bipolar membrane coupling process, which not only efficiently removes fluoride ions and achieves zero-discharge wastewater reuse, but also efficiently recovers resources such as hydrofluoric acid and sodium hydroxide, resulting in significant economic and environmental benefits. The technical solution is as follows:

[0006] 10. A method for deep treatment of fluoride-containing wastewater from the semiconductor / photovoltaic industry, comprising the following steps:

[0007] (6) pH adjustment: Add sodium hydroxide to the pretreated fluoride-containing wastewater or fluoride-containing wastewater without silicon to adjust the pH value to 9.5-10.2 so that fluoride ions exist in the form of sodium fluoride;

[0008] (7) Ceramic ultrafiltration membrane CUF treatment and reverse osmosis membrane RO treatment: The fluoride-containing wastewater obtained in step (2) after pH adjustment is passed through ceramic ultrafiltration membrane CUF treatment and reverse osmosis membrane RO treatment in sequence to separate water from sodium fluoride and obtain RO permeate and sodium fluoride concentrate.

[0009] (8) Deep purification: The RO permeate obtained in step (3) is passed through a deep defluorination resin adsorption unit to reduce the fluoride ion concentration in the water to <1ppm, and the permeate is reused.

[0010] (9) Resource recovery: The sodium fluoride concentrate obtained in step (3) is introduced into a bipolar membrane electrodialysis system to be converted into hydrofluoric acid and sodium hydroxide solution;

[0011] (10) Refining and reuse: The hydrofluoric acid obtained in step (5) is purified by distillation to obtain electronic grade hydrofluoric acid for reuse in production; the sodium hydroxide solution obtained in step (5) is purified and reused for pH adjustment in step (2).

[0012] 11. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 1, characterized in that, if the fluoride-containing wastewater contains silicon dioxide, it further includes a pretreatment step, wherein a backwashing filter is set up for silicon removal pretreatment.

[0013] 12. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 2, characterized in that the backwash filter adopts a 5μm PP filter element, and a laser particle counter is provided to monitor silicon powder in real time during the silicon removal pretreatment process, so as to dynamically optimize the backwashing cycle of the backwash filter in real time.

[0014] 13. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 1, characterized in that, in step (3), the ceramic ultrafiltration membrane (CUF) treatment uses a ceramic ultrafiltration membrane with a molecular weight cutoff of 1000-10000 Daltons and an operating pressure of 0.1-0.2 MPa; the reverse osmosis membrane (RO) treatment uses a seawater desalination-grade reverse osmosis membrane with an operating pressure of 1.5-2.0 MPa and a recovery rate controlled at 65-75%.

[0015] 14. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 1, characterized in that, in step (4), the regeneration of the deep fluoride removal resin used in the deep fluoride removal resin adsorption unit is carried out using an aluminum sulfate or aluminum chloride solution with a concentration of 10%-15%.

[0016] 15. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 1, characterized in that, in step (6), in the distillation purification of hydrofluoric acid generated by the bipolar membrane electrodialysis system, based on the difference in boiling points between the components in the mixture, the hydrofluoric acid is first evaporated and then collected by condensation after passing through a distillation device to obtain electronic-grade hydrofluoric acid with a purity of SEMI G5.

[0017] 16. A system for implementing the deep treatment method for fluoride-containing wastewater according to any one of claims 1-6, characterized in that it comprises a pH adjustment unit, a ceramic ultrafiltration and reverse osmosis membrane separation unit, a deep fluoride removal resin adsorption unit, a bipolar membrane electrodialysis unit, and a distillation purification unit; the fluoride-containing wastewater after pH adjustment is treated by the ceramic ultrafiltration and reverse osmosis membrane separation unit to obtain RO permeate and sodium fluoride concentrate; the RO permeate is sent to the bipolar membrane electrodialysis unit for treatment, and the sodium fluoride concentrate is sent to the bipolar membrane electrodialysis system for treatment.

[0018] 17. The system according to claim 7, characterized in that it further comprises a pretreatment unit for performing silicon removal pretreatment through a backwash filter.

[0019] 18. The system according to claim 7, characterized in that a water quality monitoring instrument is provided between the ceramic ultrafiltration and reverse osmosis membrane separation unit and the deep fluoride removal resin adsorption unit for real-time monitoring of the fluoride ion concentration and conductivity of the RO permeate; and a purity detection device is provided between the bipolar membrane electrodialysis unit and the distillation purification unit to ensure that the initial purity of the hydrofluoric acid entering the distillation purification unit meets the requirements.

[0020] The advanced treatment method for fluoride-containing wastewater of the present invention has the following outstanding features:

[0021] (1) Zero discharge and resource recycling: This invention integrates membrane separation and resource recovery technologies to achieve full treatment and resource recovery of fluoride-containing wastewater, achieving zero discharge of wastewater and recovering high-value hydrofluoric acid and sodium hydroxide, forming a closed-loop recycling system.

[0022] (2) Significant cost advantages: Compared with the traditional lime precipitation method, this process reduces the consumption of chemical reagents and the cost of solid waste disposal; compared with the zero-discharge evaporation process, the operating energy consumption can be reduced by more than 60%; the recovered electronic-grade hydrofluoric acid and sodium hydroxide can be directly reused in production, significantly reducing the cost of raw material procurement;

[0023] (3) High treatment efficiency: The combined process of CUF+RO membrane separation and deep defluorination resin adsorption unit can stably control the fluoride ion concentration in the effluent to below 1ppm, which is far below the national standard; the conversion rate of sodium fluoride by bipolar membrane electrodialysis can reach more than 90%, and the hydrofluoric acid recovery rate is more than 50% higher than that of traditional processes.

[0024] (4) Strong adaptability: It is equipped with a silicon removal pretreatment unit, which can treat fluoride-containing wastewater generated by different processes in the semiconductor photovoltaic industry.

[0025] (5) High product quality: The recovered hydrofluoric acid can reach the SEMI G5 standard after distillation and purification, meeting the needs of high-end semiconductor manufacturing. Attached Figure Description

[0026] Figure 1 The process flow diagram of the deep treatment method for fluoride-containing wastewater in the semiconductor / photovoltaic industry of the present invention. Detailed Implementation

[0027] The technical approach of this invention will be described below.

[0028] The semiconductor / photovoltaic industry fluoride-containing wastewater deep treatment process of the present invention includes the following steps:

[0029] (1) Pretreatment: When fluoride-containing wastewater contains silicon dioxide (such as wastewater generated during semiconductor / photovoltaic silicon material processing), a pretreatment process is used to remove silicon. The process unit is equipped with an automatic backwash filter to remove silicon powder particles (residue from the cleaning process). This pretreatment process can effectively prevent silicon scale contamination of the subsequent membrane system. During the silicon removal pretreatment process, a laser particle counter is also used to monitor silicon powder in real time so as to dynamically optimize the backwashing cycle of the automatic backwash filter in real time.

[0030] (2) pH adjustment: Add sodium hydroxide to the pretreated fluoride-containing wastewater or fluoride-containing wastewater without silicon to adjust the pH value to 9.5-10.2, so that the fluoride ions in the wastewater are converted into sodium fluoride (NaF). The reaction formula is: HF+NaOH→NaF+H2O.

[0031] (3) CUF+RO treatment: The pH-adjusted wastewater is first passed through a ceramic ultrafiltration (CUF) system using a ceramic ultrafiltration membrane with a molecular weight cutoff of 1000-10000 Daltons and an operating pressure of 0.1-0.2 MPa to remove any trace colloids and particulate matter that may be present in the water, protecting the subsequent reverse osmosis (RO) membrane system. The ultrafiltration permeate then enters the reverse osmosis (RO) system using a seawater desalination-grade reverse osmosis membrane at an operating pressure of 1.5-2.0 MPa and a recovery rate controlled at 65-75%, achieving the separation of water and sodium fluoride to obtain RO permeate and sodium fluoride concentrate.

[0032] (4) Deep Purification: RO permeate enters a deep fluoride removal resin adsorption system. This system, equipped with deep fluoride removal resin, optimizes the reactor structure through CFD fluid simulation, improving water distribution uniformity by over 5% and reducing short-circuiting of the adsorption resin material. The deep fluoride removal resin deeply adsorbs residual fluoride ions, reducing the fluoride ion concentration in the permeate to <1 ppm. The deep fluoride removal resin is regenerated using aluminum sulfate or aluminum chloride solution. Through step optimization, the regeneration time is reduced by 10-15% compared to conventional processes. The regeneration wastewater, after treatment, can be disposed of in the sludge system. The treated permeate can meet RO water standards (conductivity <10 μS / cm) for direct reuse in production, or meet the raw water standards for ultrapure water systems to replace tap water.

[0033] (5) Resource recovery: The sodium fluoride concentrate and recycled permeate produced by the RO system are independently introduced into the bipolar membrane electrodialysis system. Within the bipolar membrane, the sodium fluoride solution is drawn away by the positive and negative electrodes of a direct current source. + F tends to pass through the anode membrane at the positive electrode. - The cathode membrane tends to pass through the negative electrode, while pure water, drawn by the positive and negative electrodes, flows through it. + Through the anolyte membrane, OH - Through the cathode membrane, the anode and cathode membranes, and the sodium fluoride solution and water are alternately superimposed, and finally Na... + +OH - Combine to form NaOH, H + +F - It combines to form HF. The resulting sodium hydroxide solution can be used for pH adjustment at the front end of the process, realizing the recycling of chemicals. The operating conditions of the bipolar membrane electrodialysis system are: temperature 25-35℃, current density 20-50mA / cm². 2 .

[0034] (6) Distillation and purification: The hydrofluoric acid produced by the bipolar membrane electrodialysis system enters the distillation and purification unit. Based on the difference in boiling points between the components in the mixture, the HF is first evaporated through a distillation device and then collected by a condenser to obtain electronic-grade hydrofluoric acid with a purity of SEMI G5. This hydrofluoric acid can be directly reused in the cleaning and texturing processes of semiconductor and photovoltaic production. The residual salt solution in the distillation device can be used again through the aforementioned RO system to prepare wastewater and reused in the workshop production line.

[0035] The system for implementing the above-mentioned process provided by the present invention includes: a pretreatment unit, a pH adjustment unit, a ceramic ultrafiltration and reverse osmosis membrane separation unit, a deep fluoride removal resin adsorption unit, a bipolar membrane electrodialysis unit, and a distillation purification unit; each unit is connected in sequence through pipelines.

[0036] The pretreatment unit includes an automatic backwashing filter (5μm PP filter element); the ceramic ultrafiltration and reverse osmosis membrane separation unit includes an ultrafiltration device and a reverse osmosis device connected in sequence; the deep fluoride removal resin adsorption unit includes a fluoride removal resin reactor and a regeneration system; the bipolar membrane electrodialysis unit mainly consists of a bipolar membrane electrodialysis unit; and the distillation purification unit includes a distillation purification device and a condensation device connected in sequence.

[0037] Water quality monitoring instruments are installed between the ceramic ultrafiltration and reverse osmosis membrane separation unit and the deep fluoride removal resin adsorption unit to monitor the fluoride ion concentration and conductivity of the RO permeate in real time; a purity detection device is installed between the bipolar membrane electrodialysis unit and the distillation purification unit to ensure that the initial purity of the hydrofluoric acid entering the distillation purification unit meets the requirements.

[0038] To enable those skilled in the art to better understand the process and advantages of this invention, the invention will be further described below in conjunction with the accompanying drawings and embodiments. Figure 1 This is a process flow diagram of the present invention. In the diagram: 1-Fluoride-containing wastewater collection device; 2-Pretreatment unit; 3-pH adjustment unit; 4-CUF system; 5-RO system; 6-RO permeate collection device; 7-RO concentrate collection device; 8-Deep fluoride removal resin adsorption unit; 9-RO water reuse point; 10-Bipolar membrane electrodialysis unit; 11-Regenerated sodium hydroxide collection device; 12-Regenerated hydrofluoric acid collection device; 13-Regenerated sodium hydroxide concentration device; 14-Regenerated hydrofluoric acid concentration device; 15-Distillation purification unit; 16-Electronic grade hydrofluoric acid collection device; 17-Production line hydrofluoric acid reuse point.

[0039] The attached diagram is for illustrative purposes only. In actual implementation, the equipment layout and connection method can be adjusted according to specific circumstances.

[0040] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. A semiconductor manufacturing plant generates fluoride-containing wastewater during its cleaning process, which enters a fluoride-containing wastewater collection device 1 with a fluoride ion concentration of 300 mg / L. The process of the present invention is used for treatment:

[0041] (1) Pretreatment: The fluoride-containing wastewater from the fluoride-containing wastewater collection device 1 undergoes silicon removal pretreatment in the pretreatment unit 2. The pretreatment unit 2 is equipped with an automatic backwash filter with a 5μm PP filter element, which can remove silicon powder particles larger than 5μm and residual particles from the cleaning process.

[0042] (2) pH adjustment: Add 5% sodium hydroxide solution to the wastewater in pH adjustment unit 3 to adjust the pH to 9.5 and stir evenly;

[0043] (3) CUF+RO treatment: The adjusted wastewater enters the CUF system 4 with a molecular weight cutoff of 5000 Da and an operating pressure of 0.15 MPa. The permeate enters the seawater desalination membrane of the RO system 5 with an operating pressure of 1.8 MPa and a recovery rate of 75%. The permeate of the RO system 5 has a fluoride ion concentration of about 10 mg / L and enters the RO permeate collection device 6. The concentrate effluent from the RO system 5 has a sodium fluoride concentrate concentration of 10% and enters the RO concentrate collection device 7.

[0044] (4) Deep purification: The RO permeate from the RO permeate collection device 6 enters the deep fluoride removal resin adsorption unit 8. After deep fluoride removal resin treatment, the fluoride ion concentration of the permeate is reduced to 0.5 ppm and the conductivity is 6 μS / cm. This permeate can be directly sent to the RO water reuse point 9 at the production end. The resin in the deep fluoride removal resin adsorption unit 8 is regenerated using a 5% aluminum sulfate solution, with a regeneration cycle of 3 days.

[0045] (5) Resource recovery treatment: In the resource recovery treatment process, the sodium fluoride concentrate from the RO concentrate collection unit 7 enters the bipolar membrane electrodialysis unit 10 and is treated at 30°C and a current density of 35 mA / cm2 to obtain 0.2% hydrofluoric acid and 1.4% sodium hydroxide solution, which are then fed into the regenerated hydrofluoric acid collection unit 12 and the regenerated sodium hydroxide collection unit 11, respectively. The low-concentration sodium hydroxide solution and hydrofluoric acid produced in the above steps are fed into the regenerated sodium hydroxide concentration unit 13 and the regenerated hydrofluoric acid concentration unit 14 for concentration treatment.

[0046] (6) Refining and reuse: The 2% hydrofluoric acid produced by the bipolar membrane electrodialysis unit 10 and the regenerated hydrofluoric acid concentration unit 14 is sequentially fed into the distillation purification unit 15 and the condensation unit 16 to obtain electronic grade hydrofluoric acid with a purity of SEMI G5 and sent to the hydrofluoric acid reuse point 17 of the production line; the sodium hydroxide solution produced by the regenerated sodium hydroxide concentration unit 13 is sent to the pH adjustment unit 3 at the front end of the process to realize the recycling of chemicals.

Claims

1. A method for deep treatment of fluoride-containing wastewater from the semiconductor / photovoltaic industry, comprising the following steps: (1) pH adjustment: Add sodium hydroxide to the pretreated fluoride-containing wastewater or fluoride-containing wastewater without silicon to adjust the pH value to 9.5-10.2 so that fluoride ions exist in the form of sodium fluoride; (2) Ceramic ultrafiltration membrane CUF treatment and reverse osmosis membrane RO treatment: The fluoride-containing wastewater obtained in step (2) after pH adjustment is passed through ceramic ultrafiltration membrane CUF treatment and reverse osmosis membrane RO treatment in sequence to separate water from sodium fluoride and obtain RO permeate and sodium fluoride concentrate. (3) Deep purification: The RO permeate obtained in step (3) is passed through a deep defluorination resin adsorption unit to reduce the fluoride ion concentration in the water to <1ppm, thus obtaining reusable permeate; (4) Resource recovery: The sodium fluoride concentrate obtained in step (3) is introduced into a bipolar membrane electrodialysis system to be converted into hydrofluoric acid and sodium hydroxide solution; (5) Refining and reuse: The hydrofluoric acid obtained in step (5) is purified by distillation to obtain electronic grade hydrofluoric acid for reuse in production; the sodium hydroxide solution obtained in step (5) is purified and reused for pH adjustment in step (2).

2. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 1, characterized in that, If the fluoride-containing wastewater contains silica, a pretreatment step is also included, in which a backwashing filter is installed for silica removal pretreatment.

3. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 2, characterized in that, The backwash filter uses a 5μm PP filter element, and a laser particle counter is installed during the silicon removal pretreatment process to monitor silicon powder in real time, so as to dynamically optimize the backwashing cycle of the backwash filter in real time.

4. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 1, characterized in that, In step (3), the ceramic ultrafiltration membrane (CUF) treatment uses a ceramic ultrafiltration membrane with a molecular weight cutoff of 1,000-10,000 Daltons and an operating pressure of 0.1-0.2 MPa; the reverse osmosis membrane (RO) treatment uses a seawater desalination grade reverse osmosis membrane with an operating pressure of 1.5-2.0 MPa and a recovery rate controlled at 65-75%.

5. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 1, characterized in that, In step (4), the deep fluoride removal resin used in the deep fluoride removal resin adsorption unit is regenerated using an aluminum sulfate or aluminum chloride solution with a concentration of 10%-15%.

6. The method for deep treatment of fluoride-containing wastewater in the semiconductor / photovoltaic industry according to claim 1, characterized in that, In step (6), the hydrofluoric acid produced by the bipolar membrane electrodialysis system is purified by distillation. Based on the difference in boiling points between the components in the mixture, the hydrofluoric acid is first evaporated and then collected by condensation through a distillation device to obtain electronic-grade hydrofluoric acid with a purity of SEMI G5.

7. A system for implementing the deep treatment method for fluoride-containing wastewater according to any one of claims 1-6, characterized in that, It includes a pH adjustment unit, a ceramic ultrafiltration and reverse osmosis membrane separation unit, a deep fluoride removal resin adsorption unit, a bipolar membrane electrodialysis unit, and a distillation purification unit. After pH adjustment, the fluoride-containing wastewater is treated by the ceramic ultrafiltration and reverse osmosis membrane separation unit to obtain RO permeate and sodium fluoride concentrate. The RO permeate is sent to the bipolar membrane electrodialysis unit for treatment, and the sodium fluoride concentrate is sent to the bipolar membrane electrodialysis system for treatment.

8. The system according to claim 7, characterized in that, It also includes a pretreatment unit that performs silicon removal pretreatment through a backwash filter.

9. The system according to claim 7, characterized in that, Water quality monitoring instruments are installed between the ceramic ultrafiltration and reverse osmosis membrane separation unit and the deep fluoride removal resin adsorption unit to monitor the fluoride ion concentration and conductivity of the RO permeate in real time; a purity detection device is installed between the bipolar membrane electrodialysis unit and the distillation purification unit to ensure that the initial purity of the hydrofluoric acid entering the distillation purification unit meets the requirements.

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