Hydrofluoric acid-containing waste liquid treatment system and method

Abstract

The invention relates to the field of hydrofluoric acid-containing waste liquid treatment, in particular to a hydrofluoric acid-containing waste liquid treatment system and method.The hydrofluoric acid content in treated waste liquid is smaller than 6% through the hydrofluoric acid-containing waste liquid treatment system, and the hydrofluoric acid-containing waste liquid treatment system comprises a pretreatment reaction device provided with a waste liquid inlet and a fluorine-containing clear liquid outlet; the filtering device is provided with a liquid inlet and a filtrate outlet, and the liquid inlet is communicated with the fluorine-containing clear liquid outlet of the pretreatment reaction device; the membrane concentration device is provided with a membrane concentration liquid inlet and a concentrated liquid outlet, and the membrane concentration liquid inlet is communicated with the filtrate outlet; the evaporation device is provided with a liquid inlet and a gas outlet, and the liquid inlet is communicated with the concentrated liquid outlet; the evaporation device comprises a demister, and the demister is used for removing liquid drops in hydrofluoric acid steam in the evaporation device; the condensing device is provided with an air inlet communicated with the air outlet of the evaporation device, and the hydrofluoric acid steam is condensed in the condensing device to obtain the electronic-grade hydrofluoric acid. The system can avoid the problem of fluosilicic acid crystallization in waste liquid treatment.

Description

Technical Field

[0001] This application relates to the field of hydrofluoric acid wastewater treatment, and in particular to a hydrofluoric acid wastewater treatment system and method. Background Technology

[0002] In recent years, the new energy photovoltaic industry has developed rapidly, leading to a surge in demand for electronic chemicals, especially hydrofluoric acid, required for battery cell production. During photovoltaic manufacturing, hydrofluoric acid (HF) is typically used for texturing and cleaning silicon wafer surfaces. However, the actual amount of hydrofluoric acid involved in the reaction is relatively small, resulting in a large amount of wastewater containing hydrofluoric acid being discharged into wastewater treatment systems. This used acid is converted into waste acid, containing residual hydrofluoric acid, fluorosilicic acid, suspended particles, and metal cations such as boron, phosphorus, potassium, sodium, and aluminum. According to the "Emission Standard of Pollutants for Battery Industry" (GB30484-2013), since 2016, the fluoride concentration in wastewater from the battery industry must be below 8 mg / L, imposing strict limits on fluoride emissions.

[0003] For the recycling of hydrofluoric acid wastewater from the photovoltaic industry, existing technologies propose using evaporation to concentrate the wastewater and leveraging the azeotropic nature of HF and water to recover hydrofluoric acid through heating. This method achieves resource-based treatment of waste acid by staged recovery of HF aqueous solution and pure water. Current photovoltaic production lines, by introducing additives and concentrated acid downgrading technologies, reduce the amount of acid used at the source, lowering the concentration of hydrofluoric acid wastewater to below 6%, or even below 4% or lower, compared to previous photovoltaic production lines. However, due to the extremely low wastewater concentration, the original evaporation recovery process cannot solve the problems of system salt crystallization and excessive fluorosilicic acid impurities. Summary of the Invention

[0004] In view of this, in order to solve the above problems, this application provides a system and method for treating hydrofluoric acid-containing waste liquid.

[0005] The first aspect of this application is a hydrofluoric acid wastewater treatment system, wherein the hydrofluoric acid content in the wastewater is less than 6%, and the treatment system includes: a pretreatment reaction device, which is provided with a wastewater inlet and a fluorine-containing clear liquid outlet, wherein the pretreatment reaction device (1) is used to react with the wastewater by adding a desalination agent to precipitate and remove impurity ions to obtain a fluorine-containing clear liquid; a filtration device, which is provided with an inlet and a filtrate outlet, wherein the inlet is connected to the fluorine-containing clear liquid outlet of the pretreatment reaction device; a membrane concentration device, which is provided with a membrane concentration inlet and a concentrate outlet, wherein the membrane concentration inlet is connected to the filtrate outlet; an evaporation device, which is provided with an inlet and an outlet, wherein the inlet is connected to the concentrate outlet; the evaporation device includes a demister, which is used to remove droplets in the hydrofluoric acid vapor in the evaporation device; and a condensation device, which is provided with an inlet connected to the outlet of the evaporation device, wherein the hydrofluoric acid vapor is condensed in the condensation device to obtain electronic-grade hydrofluoric acid.

[0006] Regarding the first aspect of this application, in some embodiments, the membrane concentration apparatus includes: a primary concentration section communicating with the membrane concentration inlet; and a secondary concentration section having one end communicating with the primary concentration section and the other end communicating with the concentrate outlet.

[0007] In some embodiments, the ion-selective membranes of both the primary membrane concentration section and the secondary membrane concentration section are tetrafluoroethylene polymer membranes.

[0008] In some embodiments, the tetrafluorovinyl polymer includes at least one of ethylene-tetrafluoroethylene copolymer and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer; Regarding the first aspect of this application, in some embodiments of this application, the demister includes a wire mesh fiber bed, the wire mesh fiber bed having an interception efficiency of 98%~100% for 1μm droplets in gaseous hydrofluoric acid vapor; the diameter of the wire mesh fiber bed is 0.1mm~0.3mm; the material of the wire mesh fiber bed is an acid-resistant and heat-resistant fluoropolymer material above 120°C; the wire mesh fiber bed includes tetrafluoroethylene polymer.

[0009] In some embodiments of this application, the evaporation apparatus may include an evaporation tower, which may be a packed tower. The evaporation tower may include a bottom baffle, a packing layer, a demister layer, and a material inlet. The exterior of the evaporation tower may also include accessories such as a reboiler and a condenser.

[0010] The evaporation tower of this application uses a steam heat source to heat the concentrate, causing HF and water to evaporate in a certain proportion to produce hydrofluoric acid vapor. After the hydrofluoric acid vapor is purified by the wire mesh fiber bed of the mist generator, it is condensed by the heat exchanger to obtain electronic-grade hydrofluoric acid. During the evaporation process, by controlling the pressure and evaporation time, HF solutions of different concentrations can be obtained at the top of the tower, as well as residual evaporation liquid of different HF concentrations at the bottom of the tower.

[0011] Regarding the first aspect of this application, in some embodiments of this application, the hydrofluoric acid wastewater treatment system may further include a PLC (Programmable Logic Controller) system. The PLC system integrates the start-up, shutdown, and interlocking control of various devices and equipment, and performs real-time monitoring of parameters such as flow rate, fluoride ion concentration, pressure, and temperature. The PLC system may include a data acquisition and monitoring system and an alarm. The data acquisition system may include a flow meter, which may be an electromagnetic flow meter or an ultrasonic flow meter; the data acquisition system may include a fluoride ion concentration measuring meter; when the parameter exceeds a preset value, the alarm sounds.

[0012] Regarding the first aspect of this application, in some embodiments of this application, the hydrofluoric acid wastewater treatment system may further include a corrosion-resistant pump and a regulating valve; the corrosion-resistant pump includes a fluoropolymer-lined centrifugal pump or a magnetic pump; the regulating valve includes an electric or pneumatic regulating valve, and the regulating valve includes a fluoroplastic-lined butterfly valve.

[0013] Regarding the first aspect of this application, in some embodiments of this application, the hydrofluoric acid wastewater treatment system may further include a cooling water circulation system that provides cooling water to the condensation device.

[0014] Regarding the first aspect of this application, in some embodiments of this application, the hydrofluoric acid wastewater treatment system may further include a waste heat recovery system, which uses the waste heat generated by the condensation of steam from the evaporator to preheat the influent water, thereby reducing system energy consumption. Regarding the first aspect of this application, in some embodiments of this application, the hydrofluoric acid waste liquid treatment system may further include an uninterruptible power supply (UPS), which ensures that the PLC and key instruments continue to operate when the power is off, thereby preventing the system from going out of control.

[0015] Regarding the first aspect of this application, in some embodiments of this application, the hydrofluoric acid waste liquid treatment system may further include a safety protection system. The safety protection system may include an HF leak detection alarm, which is installed around the reaction device or evaporator. The safety protection system may include emergency spray equipment and explosion-proof electrical equipment.

[0016] A second aspect of this application provides a method for treating hydrofluoric acid-containing waste liquid, wherein the hydrofluoric acid content in the waste liquid is less than 6%, and the treatment method includes the following steps: Pretreatment step: Add a desalination agent to the hydrofluoric acid-containing waste liquid for pretreatment to obtain a fluoride-containing clear liquid; Filtration step: The fluoride-containing clear liquid is filtered to obtain filtrate; Membrane concentration step: The filtrate is subjected to membrane concentration treatment to obtain a concentrated solution; Evaporation and purification steps: The concentrated liquid is evaporated to obtain hydrofluoric acid vapor, the hydrofluoric acid vapor is demisted, and the hydrofluoric acid vapor obtained after the evaporation and demisting processes is condensed to obtain electronic grade hydrofluoric acid.

[0017] The method for treating hydrofluoric acid waste liquid in this application employs membrane concentration, utilizing an electric field to drive ion separation and sieving, and concentrating fluoride ions. This solves the problem of high energy consumption during the evaporation of low-concentration waste acid. By combining this method with an evaporation device containing a fiber demister, the method captures tiny droplets and mist in the gas after passing through the fiber demister. The evaporated gas, free of droplets and mist, is then condensed to obtain electronic-grade hydrofluoric acid. Electronic-grade hydrofluoric acid has higher economic value compared to hydrofluoric acid products obtained by conventional evaporation methods. Furthermore, because this application first uses membrane concentration to separate a large amount of water from the hydrofluoric acid waste liquid before evaporation, it avoids wasting energy by using a large amount of energy for water evaporation. The method in this application, which involves recycling the hydrofluoric acid waste liquid, can save more than 60% of energy consumption.

[0018] The electronic-grade hydrofluoric acid produced in this application can be recycled in the solar cell manufacturing process, significantly reducing hydrofluoric acid consumption during production. Because a large amount of hydrofluoric acid is recycled in this application, the method avoids the secondary pollution problems associated with precipitation methods for removing fluoride ions. Correspondingly, the hydrofluoric acid wastewater treatment system of this application reduces the amount of calcium fluoride sludge generated in wastewater treatment, achieving a reduction of over 70%, thereby lowering production costs and reducing waste generation. The waste acid treatment method in this application does not produce sludge or wastewater, and is characterized by high efficiency, environmental friendliness, and good economic benefits.

[0019] With regard to a second aspect of this application, in some embodiments of this application, membrane concentration includes multi-stage membrane concentration processing.

[0020] Regarding the second aspect of this application, in some embodiments of this application, the fluorine-containing liquid is filtered to obtain the filtrate by: performing hydrocyclone separation on the fluorine-containing liquid, and filtering the fluorine-containing liquid after hydrocyclone separation using a filter cartridge to obtain the filtrate, wherein the filtration accuracy of the filter cartridge is 0.1μm to 0.5μm.

[0021] Regarding the second aspect of this application, in some embodiments of this application, the desalination agent in the pretreatment step includes at least one of potassium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, potassium chloride, sodium chloride, magnesium chloride, aluminum chloride, potassium hydroxide, and sodium hydroxide. Preferably, potassium hydroxide is used as the desalination agent in this application. The resulting potassium fluorosilicate has lower solubility in hydrofluoric acid waste liquid and is more likely to precipitate, thereby removing fluorosilicate ions from the hydrofluoric acid waste liquid more thoroughly.

[0022] Regarding the second aspect of this application, in some embodiments of this application, the molar amount of the desalination agent added is equal to the amount of F in the hydrofluoric acid-containing waste liquid. - 0.1 to 1.2 times the molar amount of ions.

[0023] Preferably, the molar amount of the desalination agent added is equal to the amount of F in the hydrofluoric acid waste liquid. - 0.1 to 0.15 times the molar amount of ions.

[0024] Furthermore, the molar amount of the desalination agent added is equal to the amount of F in the hydrofluoric acid-containing waste liquid. - 0.12 times the molar amount of ions.

[0025] The desalination agent of this application forms a precipitate by adding one or more of potassium, sodium, magnesium, calcium salts or alkali to the waste acid to be treated, and then filtering it to obtain a solid fluorosilicate byproduct. Fluorosilicate has high value and can be sold as a byproduct after water washing and purification.

[0026] Regarding the second aspect of this application, in some embodiments of this application, the membrane concentration step involves performing membrane concentration treatment on the filtrate to obtain a concentrated solution, which includes: performing a first membrane concentration treatment on the filtrate to obtain a solution containing multivalent ions; and then performing a divalent anion separation treatment on the solution containing multivalent ions to obtain the concentrated solution.

[0027] Regarding the second aspect of this application, in some embodiments of this application, the current conditions for membrane concentration include: using a current density of 60A / m² to 120A / m²; Regarding the second aspect of this application, in some embodiments of this application, the voltage conditions for membrane concentration include: using a voltage of 35V~100V; Regarding the second aspect of this application, in some embodiments of this application, in the evaporation purification step, the evaporation temperature is 108℃~122℃, and the condensation temperature is 12℃~19℃.

[0028] Regarding the second aspect of this application, in some embodiments of this application, during the membrane concentration step, the concentration of hydrofluoric acid in the concentrate is 6.0% to 8.5%; Regarding the second aspect of this application, in some embodiments of this application, the concentration of electronic-grade hydrofluoric acid is 25% to 35%; In some embodiments of this application, during the purification step, the concentrate is evaporated to obtain an evaporation residue, the concentration of hydrofluoric acid in the evaporation residue being 36% to 38.4%; In some embodiments of this application, the evaporation residue is used as industrial-grade hydrofluoric acid.

[0029] Regarding the second aspect of this application, in some embodiments of this application, in the pretreatment step, the waste acid to be treated comes from the waste acid generated in the wet process of TOPCon solar cells.

[0030] Regarding the second aspect of this application, in some embodiments of this application, the treatment system for hydrofluoric acid waste liquid according to any one of the first aspects is employed.

[0031] Beneficial effects: This application provides a treatment system for hydrofluoric acid wastewater with a hydrofluoric acid content of less than 6%. The system includes a pretreatment reaction unit, a filtration unit, a membrane concentration unit, an evaporation unit, and a condensation unit connected in sequence. The hydrofluoric acid wastewater with a hydrofluoric acid content of less than 6% is processed sequentially through these units to obtain electronic-grade hydrofluoric acid. This system is particularly effective for treating wastewater containing hydrofluoric acid with a hydrofluoric acid content of less than 6%. Firstly, membrane concentration technology is used to concentrate fluoride ions in the low-concentration hydrofluoric acid wastewater, replacing traditional evaporation concentration technology and saving over 60% of energy. Secondly, the system utilizes a pretreatment reaction unit with added desalination agents, a filtration unit, a membrane concentration unit, and a demister in the evaporation unit to progressively remove fluorosilicic acid impurities from the low-concentration hydrofluoric acid wastewater, ensuring the quality of the final electronic-grade hydrofluoric acid, which has high economic value.

[0032] Specifically, this application employs a pretreatment reaction device to initially precipitate fluorosilicate ions, allowing them to form fluorosilicates through the pretreatment reaction. A filtration device further removes the fluorosilicate precipitate, and a membrane concentration device concentrates the waste liquid while simultaneously removing divalent anionic impurities such as fluorosilicate. The concentrated liquid obtained after membrane concentration further enters an evaporation device containing a demister. The evaporation device evaporates the concentrated liquid to obtain hydrofluoric acid vapor, which is then purified by demistering and condensed to finally obtain hydrofluoric acid. The evaporation process separates various salts from the hydrofluoric acid vapor, and the demister further prevents soluble impurities from entering the condensation device with droplets from the hydrofluoric acid vapor, further reducing the content of soluble impurities and salts in the condensed hydrofluoric acid. This device effectively solves the problems of salt crystallization and blockage, and excessive fluorosilicate impurities in traditional low-concentration hydrofluoric acid waste acid treatment processes. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the hydrofluoric acid waste liquid treatment system provided in the embodiments of this application.

[0034] Among them, 1-pretreatment reaction device; 2-filtration device; 3-membrane concentration device; 4-evaporation device; 41-demister; 5-condensation device; 6-hydrofluoric acid waste liquid storage tank; 7-product acid tank. Detailed Implementation

[0035] The following specific embodiments further illustrate the technical solution of the present invention. These specific embodiments do not represent a limitation on the scope of protection of the present invention. Non-essential modifications and adjustments made by others based on the concept of the present invention still fall within the scope of protection of the present invention.

[0036] In the recycling of hydrofluoric acid waste, the presence of fluorosilicic acid can affect product quality. Fluorosilicic acid begins to decompose significantly into silicon tetrafluoride gas under heating conditions of 60-80°C. If this gas is not removed before heating, it will condense along with the volatilized hydrofluoric acid and water vapor, ultimately entering the product as an impurity and causing the impurity content to exceed standards. Therefore, removing fluorosilicic acid from hydrofluoric acid waste is crucial for its recycling.

[0037] Metal cations are often introduced during the removal of fluorosilicic acid, and hydrofluoric acid wastewater itself contains various metal cations. These metal cations react with fluorosilicic acid to form fluorosilicic acid precipitates, such as sodium fluorosilicate and potassium fluorosilicate. However, the treated hydrofluoric acid wastewater still contains small amounts of dissolved salts, such as sodium fluorosilicate, potassium fluorosilicate, sodium fluoride, and potassium fluoride. In traditional subsequent evaporation and concentration processes, as the solution concentration increases, these soluble salts tend to crystallize and precipitate, thus affecting the stability of the treatment process.

[0038] For example, in an aqueous solution at 100°C, the solubility of sodium fluorosilicate is 5 g / 100 g, and the solubility of sodium fluoride is 1.2 g / 100 g; in hydrofluoric acid, the solubility of sodium fluorosilicate and sodium fluoride is even lower. If a low-concentration hydrofluoric acid waste liquid is directly concentrated by evaporation to increase the hydrofluoric acid content (usually from a concentration below 6% to a concentration above 30%), a large amount of water needs to be evaporated. This will lead to a significant concentration of impurity metal cations in the hydrofluoric acid waste liquid. Since sodium fluoride and sodium fluorosilicate themselves have low solubility, the large concentration factor will cause salts such as sodium fluoride and sodium fluorosilicate to crystallize and precipitate, resulting in equipment and pipeline blockage.

[0039] Experiments have shown that sodium fluoride crystallization can lead to the loss of fluoride ions in hydrofluoric acid waste liquid, resulting in a continuous decrease in the concentration of hydrogen fluoride and making it impossible to obtain hydrofluoric acid products with a concentration of more than 20% after evaporation and condensation.

[0040] Therefore, if the evaporation and concentration method is still used to concentrate low-concentration hydrofluoric acid waste liquid with a concentration of less than 6%, problems will arise such as fluorosilicate precipitation leading to equipment blockage, fluoride ion consumption resulting in low concentration of hydrofluoric acid, low fluoride recovery rate, and high energy consumption in treating hydrofluoric acid waste liquid.

[0041] To address one of the aforementioned problems, the first aspect of this application provides a treatment system for hydrofluoric acid-containing wastewater. The hydrofluoric acid content in the wastewater is less than 6%, and the wastewater originates from waste acid generated during the wet process of TOPCon (tunneling oxide passivated contact) solar cells. The waste acid mainly contains residual hydrofluoric acid, fluorosilicic acid, suspended particles, and metal cations such as boron, phosphorus, potassium, sodium, and aluminum, with the fluorosilicate ion content exceeding 50,000 ppm.

[0042] like Figure 1 The system for treating hydrofluoric acid waste liquid, as shown, includes a pretreatment reaction device 1, a filtration device 2, a membrane concentration device 3, an evaporation device 4, and a condensation device 5 connected in sequence. The pretreatment reaction device 1 has a waste liquid inlet and a fluorinated clear liquid outlet; the filtration device 2 has an inlet and a filtrate outlet, with the inlet connected to the fluorinated clear liquid outlet of the pretreatment reaction device 1 via a pipeline; the membrane concentration device 3 has a membrane concentration inlet and a concentrate outlet, with the membrane concentration inlet connected to the filtrate outlet of the filtration device 2 via a pipeline; the evaporation device 4 has an inlet and an outlet, with the inlet connected to the concentrate outlet of the membrane concentration device 3 via a pipeline; the evaporation device 4 includes a demister 41 for removing droplets from the hydrofluoric acid vapor within the evaporation device 4; the condensation device 5 has an inlet connected to the outlet of the evaporation device 4, and the hydrofluoric acid vapor is condensed in the condensation device 5 to obtain electronic-grade hydrofluoric acid.

[0043] In this application, hydrofluoric acid waste liquid flows into pretreatment reaction device 1 through the waste liquid inlet. In pretreatment reaction device 1, the hydrofluoric acid waste liquid is pretreated by adding a desalination agent, causing the fluorosilicate ions to react with the agent and form a precipitate. The pretreated hydrofluoric acid waste liquid yields a fluorine-containing clear liquid, which flows out through the fluorine-containing clear liquid outlet of pretreatment reaction device 1.

[0044] The filter device 2 is equipped with an inlet, which is connected to the outlet of the fluoride-containing clear liquid of the pretreatment reaction device 1 via a pipeline. Therefore, the fluoride-containing clear liquid flowing out of the outlet of the pretreatment reaction device 1 flows into the filter device 2, where it filters the fluoride-containing clear liquid to remove precipitates and other solid particles. After the fluoride-containing clear liquid passes through the filter device 2 to remove precipitates, a filtrate is obtained, with a significant reduction in fluorosilicate ions. The filter device 2 is equipped with a filtrate outlet, through which the filtrate flows out of the filter device 2.

[0045] The membrane concentration unit 3 is equipped with a membrane concentration inlet, which is connected to the filtrate outlet of the filtration unit 2 via a pipeline. The filtrate flowing out of the filtration unit 2 flows through the pipeline to the membrane concentration inlet and enters the membrane concentration unit 3. The membrane concentration unit 3 uses an electric field to drive ion separation and sieving, selectively separating specific ions and molecules in the filtrate based on the charge characteristics of the ions. After processing by the membrane concentration unit 3, the fluorosilicate ions in the filtrate are further separated, and the water molecules are also separated, resulting in a concentrated solution with high hydrofluoric acid concentration and low fluorosilicate content. The membrane concentration unit 3 has a concentrated solution outlet, through which the concentrated solution is discharged from the membrane concentration unit 3. The evaporation unit 4 is equipped with an inlet, which is connected to the concentrated solution outlet of the membrane concentration unit 3 via a pipeline. The concentrated solution discharged from the membrane concentration unit 3 flows through the pipeline to the evaporation unit 4, where the evaporation unit 4 heats the concentrated solution to achieve azeotropic reaction of HF and water, thereby forming hydrofluoric acid vapor. Hydrofluoric acid vapor often carries small droplets, which may contain water-soluble ionic impurities. Therefore, the evaporation device 4 also includes a demister 41, which is used to remove droplets from the hydrofluoric acid vapor in the evaporation device 4. The evaporation device 4 is provided with an outlet, and the condensation device 5 is provided with an inlet connected to the outlet of the evaporation device 4. After the droplets are removed by the demister 41, the hydrofluoric acid vapor flows out of the evaporation device 4 through the outlet. The hydrofluoric acid vapor flowing out of the evaporation device 4 flows to the inlet of the condensation device 5, where it is condensed to obtain electronic-grade hydrofluoric acid.

[0046] In this application, the fluorosilicate ions in the hydrofluoric acid waste liquid are initially precipitated as fluorosilicates using a pretreatment reaction device 1 and a filtration device 2. The fluorosilicate precipitate is then separated to obtain a concentrated solution. The concentrated solution is further separated and sieved using a membrane concentration device 3, driven by an electric field. This separates the fluorosilicate ions and water molecules in the filtrate, resulting in a concentrated solution with a high concentration and low fluorosilicate content. The membrane concentration device 3 removes fluorosilicate ions from the hydrofluoric acid solution, preventing their formation as fluorosilicates and avoiding saturated crystallization of fluorosilicates during subsequent evaporation and purification, thus preventing crystallization from clogging the equipment. Furthermore, compared to evaporation concentration, membrane concentration solves the problem of high energy consumption in the evaporation concentration of low-concentration hydrofluoric acid waste liquid. In addition, by removing fluorosilicate ions through membrane concentration, the flow of fluorosilicate ions into the evaporation device 4 is prevented from being evaporated and forming silicon tetrafluoride gas. Therefore, the membrane concentration device 3 can reduce the silicon tetrafluoride gas content in the hydrofluoric acid vapor. By using an evaporation device 4 containing a demister 41, hydrofluoric acid in the concentrate obtained after treatment by the membrane concentration device 3 is evaporated to form hydrofluoric acid vapor. After the droplets in the hydrofluoric acid vapor are removed by the demister 41, the hydrofluoric acid vapor is further condensed to obtain electronic grade hydrofluoric acid.

[0047] The electronic-grade hydrofluoric acid obtained by condensation in this application has a price exceeding 6,000 yuan / ton, while the value of industrial-grade hydrofluoric acid is only half that of electronic-grade hydrofluoric acid. Therefore, the electronic-grade high-purity hydrofluoric acid recovered using the method described in this application has high value and economic benefits.

[0048] Since this application first uses membrane concentration to separate a large amount of water from the hydrofluoric acid waste liquid before evaporation and purification, it avoids converting a large amount of energy into heat energy and then using it for the evaporation and concentration process, thus avoiding energy waste.

[0049] In some further embodiments, the pretreatment reaction device 1 includes a pretreatment reaction tank equipped with a hydrocyclone separator. A desalination agent is added to the pretreatment reaction tank to cause fluorosilicate ions in the hydrofluoric acid waste liquid to precipitate. The fluorine-containing precipitate and the fluorine-containing clarified liquid are obtained through hydrocyclone separation. Using a hydrocyclone separator, based on the principle of centrifugal sedimentation, the fluorine-containing precipitate and the fluorine-containing clarified liquid in the hydrofluoric acid waste liquid can be initially separated, preventing excessive precipitate from entering subsequent steps and reducing the burden on subsequent steps in treating the fluorine-containing precipitate.

[0050] In some further embodiments, the filtration device is a fine filtration device. The fine filtration device includes a filter element, which can be made of tetrafluoroethylene polymer. The filter element has a filtration accuracy of 0.1 μm to 0.5 μm. That is, when the filter element's filtration accuracy is 0.1 μm, under standardized testing conditions, it can effectively intercept particles with a diameter of not less than 0.1 μm. In actual use, due to the deep filtration mechanism of the filter media and the formed filter cake layer effect, the filter element also has a certain interception capacity for some particles smaller than the nominal accuracy. Its filtration effect is affected by a combination of factors such as particle shape, material, and system operating pressure. Specifically, the filter element of filtration device 2 can have a filtration accuracy of 0.5 μm. The fluorinated clear liquid after treatment by the hydrocyclone separator may still contain some suspended fluorinated precipitates and other particulate matter. These suspended fluorinated precipitates and other particulate matter, due to their low specific gravity, cannot be separated in the hydrocyclone separator.

[0051] The fine filtration device selected in this application can filter and separate small-sized fluoride precipitates and other particulate matter in fluoride-containing liquids, preventing fluoride precipitates from entering downstream equipment and causing blockages, and avoiding the introduction of impurities into downstream equipment. Fluoride ions can penetrate most plastic molecules, thereby damaging the material's structural properties; therefore, conventional plastics cannot be used for the treatment of hydrofluoric acid wastewater. Compared to other types of filtration devices, this application uses tetrafluoroethylene vinyl polymer as the filter element material, which can withstand the corrosion of hydrofluoric acid in fluoride-containing liquids.

[0052] In some further embodiments, the membrane concentration apparatus 3 includes: a primary membrane concentration apparatus for concentrating the filtrate; and a secondary membrane concentration apparatus for separating divalent anions from the liquid treated by the primary membrane concentration apparatus. The membrane in the membrane concentration device 3 can be a tetrafluorovinyl polymer membrane; specifically, the tetrafluorovinyl polymer can include at least one of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer or ethylene-tetrafluoroethylene copolymer.

[0053] A membrane concentration unit 3 refers to a complete set of equipment that utilizes the selective separation characteristics of membranes to achieve the separation of solvents and solutes or different solutes under the drive of external energy (such as pressure or potential difference). This unit typically consists of membrane modules, pumps, pressure vessels, instruments, and a control system. Its core function is to effectively reduce the volume and impurity content of the liquid being processed through the separation process, thereby increasing the concentration of the target component. Membrane concentration units are existing technology and will not be described in detail here.

[0054] The membrane concentration unit 3 includes: a primary concentration section for concentrating the filtrate; and a secondary concentration section for separating divalent anions from the liquid processed by the primary membrane concentration unit.

[0055] The primary membrane concentration unit is equipped with a purified liquid outlet. Water molecules are discharged through the purified liquid outlet of the primary membrane concentration unit as purified liquid, while solutions containing multivalent ions, such as solutions containing fluorosilicate ions and hydrofluoric acid, enter the secondary membrane concentration unit through the liquid outlet of the primary membrane concentration unit.

[0056] The secondary membrane concentration unit separates divalent anions, such as fluorosilicate ions, from hydrofluoric acid in solutions containing multivalent ions. The solution containing fluorosilicate ions is discharged after separation by the secondary membrane concentration unit, which includes a concentrate outlet. The concentrated solution containing hydrofluoric acid is discharged through the concentrate outlet of the secondary membrane concentration unit and enters the evaporation unit 4.

[0057] The membrane concentration unit 3 can simultaneously concentrate and remove impurities from the filtrate, preventing impurities from entering subsequent treatment devices and avoiding equipment blockage due to the crystallization and precipitation of fluorosilicic acid impurities. At the same time, the membrane concentration unit 3 increases the concentration of hydrofluoric acid in the filtrate, featuring high concentration ratio and low energy consumption, significantly reducing the energy consumption required for treating hydrofluoric acid-containing wastewater.

[0058] The demister 41 includes a wire mesh fiber bed, which has an interception efficiency of 98%~100% for droplets larger than 1μm in hydrofluoric acid vapor. The diameter of the wire mesh fiber bed is 0.1mm~0.3mm. The material of the wire mesh fiber bed is an acid-resistant fluoropolymer material that can withstand temperatures above 120℃. The wire mesh fiber bed includes tetrafluoroethylene polymer. The demister 41 uses a wire mesh fiber bed with specially sized and materiald fibers to efficiently intercept droplets larger than 1μm in hydrofluoric acid vapor, thereby preventing dissolved ionic impurities in the droplets from entering the condensation device, thus reducing impurities in the condensed hydrofluoric acid. In this application, an acid-resistant fluoropolymer material such as tetrafluoroethylene polymer that can withstand temperatures above 120℃ is selected as the wire mesh fiber bed material, avoiding corrosion of the wire mesh fiber bed by high temperature and hydrofluoric acid. The wire mesh fiber bed of this application is durable.

[0059] In this application, the evaporation device 4 may include an evaporation tower, which may be a packed tower. The packed tower uses a steam heat source to heat the fluorine-containing concentrate under a certain pressure, causing HF and water to evaporate in a certain proportion. By controlling the pressure and evaporation time, hydrofluoric acid vapor of different concentrations can be obtained at the top of the tower, as well as residual evaporation liquid at the bottom of the tower. The packed tower may include a bottom baffle, a packing layer, and a demister layer. The bottom baffle is located at the bottom of the packed tower and is used to support the packing layer and prevent the packing from falling into the bottom of the tower. The packing layer is composed of packing material that can promote the separation of hydrofluoric acid and water. The demister layer is located at the top of the packed tower and is used to intercept droplets entrained in the hydrofluoric acid vapor.

[0060] like Figure 1 The treatment system for hydrofluoric acid waste liquid shown may also include a hydrofluoric acid waste liquid storage tank 6. The outlet of the hydrofluoric acid waste liquid storage tank 6 is connected to the inlet of the pretreatment reaction device 1 through a pipeline. The hydrofluoric acid waste liquid storage tank 6 is used to store hydrofluoric acid waste liquid, and hydrofluoric acid is flowed from the hydrofluoric acid waste liquid storage tank 6 to the pretreatment reaction device 1 through a connecting pipeline.

[0061] like Figure 1 The treatment system for hydrofluoric acid waste liquid shown may also include a product acid tank 7. The inlet of the product acid tank 7 is connected to the outlet of the condensation device 5 through a pipeline. The product acid tank 7 is used to store the electronic-grade hydrofluoric acid obtained by condensation.

[0062] Hydrofluoric acid products are generally classified into industrial-grade hydrofluoric acid, reagent-grade hydrofluoric acid, and electronic-grade hydrofluoric acid based on their impurity content. Industrial-grade hydrofluoric acid has a relatively high impurity content and is suitable for non-precision applications. Reagent-grade hydrofluoric acid has a relatively low impurity content and is suitable for some industrial applications where purity requirements are not extremely high. The electronic-grade hydrofluoric acid obtained in this application refers to hydrofluoric acid with extremely low impurity content, meeting the impurity content requirements of "Electronic-grade Hydrofluoric Acid for Solar Cells" (GB / T 31369-2015). This electronic-grade hydrofluoric acid can be used in solar cell production lines, reducing reagent costs in the solar cell production process.

[0063] The second aspect of this application also provides a method for treating hydrofluoric acid waste liquid, comprising the following steps: a pretreatment step: adding a desalination agent to the hydrofluoric acid waste liquid for pretreatment to obtain a fluorine-containing clear liquid; a filtration step: filtering the fluorine-containing clear liquid to obtain a filtrate; a membrane concentration step: performing membrane concentration on the filtrate to obtain a concentrate; and an evaporation purification step: evaporating the concentrate to obtain hydrofluoric acid vapor and evaporation residue, performing demisting treatment on the hydrofluoric acid vapor, and condensing the hydrofluoric acid vapor obtained after evaporation and demisting treatment to obtain electronic-grade hydrofluoric acid.

[0064] This application employs pretreatment and filtration steps to initially precipitate fluorosilicate ions from hydrofluoric acid wastewater into fluorosilicate precipitates. The fluorosilicate precipitates are then separated to obtain a concentrated solution. This concentrated solution is further treated with a membrane concentration step. The membrane concentration step utilizes an electric field to drive ion separation and sieving, separating fluorosilicate ions and water molecules from the filtrate. This results in a concentrated solution with a high concentration and low fluorosilicate content. In the membrane concentration step, divalent fluorosilicate ions are separated and removed from the hydrofluoric acid solution, preventing the formation of fluorosilicate ions in subsequent processes and avoiding saturated crystallization of fluorosilicate during subsequent evaporation and purification, thus preventing crystallization from clogging the equipment. Furthermore, compared to other concentration methods, membrane concentration solves the problem of high energy consumption in the evaporation and concentration of low-concentration hydrofluoric acid wastewater. In addition, by removing fluorosilicate ions through membrane concentration, it prevents fluorosilicate ions from flowing into the evaporation and purification step and being evaporated to form silicon tetrafluoride gas. Therefore, membrane concentration can reduce the impurity content in hydrofluoric acid vapor. The hydrofluoric acid vapor obtained by evaporating the concentrate is demisted to remove droplets from the hydrofluoric acid vapor. Finally, the demisted hydrofluoric acid vapor is condensed to obtain electronic-grade hydrofluoric acid.

[0065] In hydrofluoric acid wastewater not treated by the method described in this application, the concentration of metal ions (such as potassium, sodium, calcium, magnesium, aluminum, etc.) mostly exceeds 2000 ppb, and the concentration of non-metallic fluorosilicate ions also exceeds 50,000 ppm. In this application, pretreatment can precipitate fluorosilicate ions as salts, and after removing the precipitate by filtration, a fluoride-containing clear liquid is obtained. Membrane concentration can effectively separate the anions and cations in the fluoride-containing clear liquid, thereby further separating and removing divalent fluorosilicate ions from the hydrofluoric acid solution. After pretreatment, filtration, and membrane concentration, the fluorosilicate ion concentration in the hydrofluoric acid wastewater of this application is reduced to below 100 ppm.

[0066] This application first employs pretreatment and filtration steps to remove a large amount of fluorosilicate impurities, then uses a membrane concentration step to separate a large amount of water and fluorosilicate from the hydrofluoric acid waste liquid, followed by an evaporation and purification step. This not only systematically solves the problems of fluorosilicate crystallization and excessive fluorosilicate impurities, but also avoids converting a large amount of energy into heat energy for use in the evaporation and concentration process, thus avoiding energy waste. At the same time, it obtains electronic-grade hydrofluoric acid with high utilization value, improving the economic efficiency of the hydrofluoric acid waste liquid treatment method.

[0067] In some further embodiments, the desalination agent includes at least one of potassium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, potassium chloride, sodium chloride, magnesium chloride, aluminum chloride, potassium hydroxide, and sodium hydroxide. In some further embodiments, the molar amount of the desalination agent added is equal to the amount of F in the hydrofluoric acid-containing waste liquid. - The amount of desalination agent added is 0.1 to 1.2 times the molar amount of F in the hydrofluoric acid waste liquid. In some embodiments of this application, the molar amount of desalination agent added can be the same as that added to the hydrofluoric acid waste liquid. - The multiples of the ion molar amount can be 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, and any two of the aforementioned values.

[0068] In some further embodiments, the membrane concentration step, wherein the membrane concentration treatment of the filtrate to obtain the concentrate includes: performing a first membrane concentration treatment on the filtrate to obtain a solution containing multivalent ions; and then performing a divalent anion separation treatment on the solution containing multivalent ions to obtain the concentrate.

[0069] Specifically, the first membrane concentration process separates water from the filtrate, resulting in a concentrated solution with lower water content and higher hydrofluoric acid content, as well as a purified solution (fresh water) with lower ion content; the first-stage membrane concentration saves energy costs required for concentration.

[0070] Since fluorosilicate ions contain two electrons, divalent anion separation removes them. The membrane concentration method described above removes fluorosilicate ions, preventing impurities from entering subsequent processing steps and avoiding equipment blockage due to the crystallization of fluorosilicic acid impurities.

[0071] In this application, hydrofluoric acid-containing wastewater, after membrane concentration treatment, yields purified water, divalent ion enriched water, and concentrated water. The purified water is almost salt-free fresh water, and the concentrated water is hydrofluoric acid-containing wastewater with a concentration of 6.0% to 8.5%. The fresh water obtained after membrane concentration has a very low content of charged ions. In this application, the fresh water obtained after membrane treatment has a conductivity of less than 5 μS / cm and a fluoride ion concentration of less than 8 ppm, which meets the reuse standards for treated water in the factory and can be used directly.

[0072] In some further embodiments, the ion-selective membrane is a tetrafluoroethylene polymer membrane; the tetrafluoroethylene polymer membrane is resistant to hydrofluoric acid corrosion, thereby improving the durability of the ion-selective membrane.

[0073] In some further embodiments, the tetrafluoroethylene vinyl polymer includes at least one of ethylene-tetrafluoroethylene copolymer or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

[0074] In some further embodiments, the current conditions for membrane concentration include a current density of 60 A / m² to 120 A / m²; in some specific embodiments, the applicable current densities include 60 A / m², 65 A / m², 70 A / m², 75 A / m², 80 A / m², 85 A / m², 90 A / m², 95 A / m², 100 A / m², 105 A / m², 110 A / m², 115 A / m², 120 A / m², and any value between any two of the aforementioned values. In some further embodiments, the voltage conditions for membrane concentration include: using a voltage of 35V to 100V; in some specific embodiments, the voltage that can be used can be 35V, 36V, 37V, 38V, 39V, 40V, 45V, 50V, 55V, 60V, 65V, 70V, 75V, 80V, 85V, 90V, 95V, 100V, and any value between any two of the aforementioned values.

[0075] When concentrating the filtrate through a membrane, due to F -Due to its high electronegativity, its ionization coefficient is low at low solution concentrations, and it mainly exists in the form of HF molecules. Therefore, it requires treatment under conditions of low current density and high voltage. In this application, a voltage of 35~100V and a current density of 60~120A / m² are used for treatment, resulting in good membrane concentration effect.

[0076] In some further embodiments, in the evaporation purification step, the evaporation temperature is 108℃~122℃, and the condensation temperature is 12℃~19℃. In some specific embodiments, in the evaporation purification step, the evaporation temperature can be 108℃, 109℃, 110℃, 111℃, 112℃, 113℃, 114℃, 115℃, 116℃, 117℃, 118℃, 119℃, 120℃, 121℃, 122℃, or any value between any two of the aforementioned values, or a range thereof; in some specific embodiments, the condensation temperature can be 12℃, 13℃, 14℃, 15℃, 16℃, 17℃, 18℃, 19℃, or any value between any two of the aforementioned values.

[0077] In some embodiments of this application, the hydrofluoric acid content of the hydrofluoric acid waste liquid in the treatment method is less than 6%; specifically, it can be 1%, 2%, 3%, 4%, 5%, 5.5%, 5.9%, or any value between any two of the aforementioned values.

[0078] In this application, the concentration of hydrofluoric acid in the hydrofluoric acid-containing waste liquid is low (as low as 1%). Membrane concentration is used to purify it while removing fluorosilicate ions, thereby avoiding the problem of equipment blockage caused by the precipitation and crystallization of fluorosilicate ions. Compared with the concentration method of direct evaporation purification, membrane concentration saves more than 60% of energy.

[0079] In some further embodiments, during the membrane concentration step, the concentration of hydrofluoric acid in the concentrate is 6.0% to 8.5%; specifically, it can be 6%, 7%, 8%, 8.5%, or any value between the aforementioned two. In this application, membrane concentration effectively concentrates the filtrate. Membrane concentration is highly efficient in the low concentration range. In the waste liquid concentration at the concentration levels described in this application, membrane concentration requires significantly less energy than evaporation, saving energy needed for the concentration step.

[0080] In some further embodiments, the concentration of the electronic-grade hydrofluoric acid in the evaporation and purification step is 25% to 35%; specifically, it can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or any value between any two of the aforementioned values.

[0081] In some further embodiments, the concentration of hydrofluoric acid in the evaporation residue is 36% to 38.4%; specifically, it can be 36%, 37%, 38%, 38.4% or any value between the two aforementioned values. In some specific embodiments, the evaporation residue can be used as industrial-grade hydrofluoric acid.

[0082] In some further embodiments, the evaporation and purification step further includes: condensing the hydrofluoric acid vapor obtained after the evaporation and demisting treatment to obtain the electronic-grade hydrofluoric acid and dilute acid products, wherein the concentration of hydrofluoric acid in the dilute acid products is 1.0% to 3.0%.

[0083] In some further embodiments, the pretreatment step involves a waste liquid containing hydrofluoric acid originating from the wet process of TOPCon solar cells. This waste liquid typically consists of a mixture of hydrochloric acid, sulfuric acid, and phosphoric acid, along with other impurities, and generally only yields industrial-grade hydrofluoric acid, which has low processing value. This application collects the waste acid generated from the wet process of TOPCon solar cells separately and then treats it specifically, avoiding the problem of mixing acids from various processes together, which would make impurity separation difficult. By optimizing the selection of acid sources, this application effectively avoids the following problem: because HF and HCl have similar boiling points, they are difficult to separate by evaporation / distillation, resulting in an excessively high chloride ion content in the obtained hydrofluoric acid product, failing to meet the purity requirements for electronic-grade hydrofluoric acid.

[0084] The concentration of fluorosilicic acid impurities in the electronic-grade hydrofluoric acid obtained after processing is less than 30 ppm.

[0085] In some further embodiments, the hydrofluoric acid waste liquid is treated using the hydrofluoric acid waste liquid treatment system mentioned in the first aspect.

[0086] Example 1 Application of hydrofluoric acid waste liquid treatment methods and systems in the field of photovoltaic waste acid treatment.

[0087] Wastewater from the wet process at a TOPCon solar cell production base was used as a raw material for treating and recovering hydrofluoric acid. In this embodiment, the hydrofluoric acid content in the wastewater was 1.2%, and the treatment capacity was 60 L / h. The treatment process is shown in the attached figure. Figure 1 As shown, the details are as follows: The hydrofluoric acid waste liquid stored in the hydrofluoric acid waste liquid storage tank 6 is piped from the outlet of the storage tank 6 to the inlet of the pretreatment reaction device 1 for pretreatment. Pretreatment in the pretreatment reaction device 1 includes adding a desalination agent to the hydrofluoric acid waste liquid. In this embodiment, the desalination agent is potassium hydroxide, wherein the amount of potassium hydroxide added is equal to the amount of F in the hydrofluoric acid waste liquid. - The amount of potassium hydroxide added in this example is 53.1 g / h, which is 0.12 times the molar amount of ions, and the purity of potassium hydroxide is 95%.

[0088] When potassium hydroxide is added to hydrofluoric acid waste liquid, the fluorosilicate ions in the waste liquid react with potassium ions to form potassium fluorosilicate precipitate. Compared with precipitates such as sodium fluorosilicate, potassium fluorosilicate has lower solubility. Therefore, more fluorosilicate ions in the hydrofluoric acid waste liquid can precipitate under the action of potassium-containing desalination agents, thus reducing the amount of fluorosilicate ions dissolved in the water.

[0089] The pretreatment reaction device 1 includes a pretreatment reaction tank, which is equipped with a hydrocyclone separator. The hydrocyclone separator uses centrifugal force to separate the heterogeneous potassium fluorosilicate precipitate with density difference from the hydrofluoric acid waste liquid. In this embodiment, the hydrocyclone separator is a baffle-type hydrocyclone separator.

[0090] In this embodiment, the hydrofluoric acid waste liquid containing potassium fluorosilicate precipitate is initially separated by a baffle-type hydrocyclone to obtain potassium fluorosilicate precipitate and fluorine-containing clear liquid.

[0091] In this embodiment, before adding the desalting agent to the pretreatment reaction device 1, the total concentration of fluorosilicate in the hydrofluoric acid waste liquid is 51429 ppm. After adding the desalting agent to the pretreatment reaction device 1, the concentration of fluorosilicate in the fluorinated clear liquid discharged from the fluorinated clear liquid outlet of the pretreatment reaction device 1 drops to below 25714 ppm.

[0092] The filter device 2 is equipped with an inlet, which is connected to the outlet of the fluoride-containing clarified liquid of the pretreatment reaction device 1. After pretreatment, the hydrofluoric acid waste liquid becomes the fluoride-containing clarified liquid, which flows into the filter device 2 through the inlet. Since the baffle-type hydrocyclone separator relies on centrifugal force to initially separate the potassium fluorosilicate precipitate and the fluoride-containing clarified liquid, the resulting fluoride-containing clarified liquid may still contain potassium fluorosilicate precipitates with small particle sizes suspended in it. Therefore, in this embodiment, the filter device 2 is also used to further filter the potassium fluorosilicate precipitate in the fluoride-containing clarified liquid to obtain filtrate.

[0093] In this embodiment, the filter device 2 includes a filter element with a filtration accuracy of 0.5 μm; the filter element is made of PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), and there are two filter elements.

[0094] When the fluoride-containing liquid is filtered through the filter element, the potassium fluorosilicate precipitate in the filtrate is further reduced; the filter device 2 is provided with an outlet, and the filtrate flows to the membrane concentration device 3 through the outlet of the filter device 2.

[0095] After filtration using filter device 2, the concentration of potassium fluorosilicate precipitate particles with a diameter of 0.5 μm or larger in the fluorinated solution decreased from 3500 mg / L to 90 mg / L.

[0096] The potassium fluorosilicate precipitate obtained by the baffle hydrocyclone separator and the filter residue obtained by filtration can be further utilized as fluorosilicate by-products. In this embodiment, the amount of potassium fluorosilicate by-product that can be recovered is 1.0 kg / h, and the purity is 96.33%.

[0097] The membrane concentration device 3 is provided with a membrane concentration inlet and a concentrate outlet, the membrane concentration inlet being connected to the filtrate outlet; the membrane concentration device 3 includes: a primary concentration section connected to the membrane concentration inlet; and a secondary concentration section, one end connected to the primary concentration section and the other end connected to the concentrate outlet; the membrane concentration device 3 is used to perform membrane concentration treatment on the filtrate to obtain a concentrate, specifically including: performing a first membrane concentration treatment on the filtrate to obtain a solution containing multivalent ions; and then performing a divalent anion separation treatment on the solution containing multivalent ions to obtain the concentrate.

[0098] In this embodiment, the membrane concentration device 3 includes an ion-selective membrane, which is a tetrafluoroethylene polymer membrane. In this embodiment, the tetrafluoroethylene polymer is an ethylene-tetrafluoroethylene copolymer.

[0099] The membrane concentration device 3 includes a primary membrane concentration section and a secondary membrane concentration section. The primary membrane concentration section separates water molecules from the filtrate to obtain fresh water and a solution containing multivalent ions. The secondary membrane concentration section separates divalent anions such as fluorosilicate ions from other ions and molecules in the solution containing multivalent ions, thereby obtaining a concentrated solution.

[0100] Based on the amount of hydrofluoric acid waste liquid to be treated, in this embodiment, the membrane area of ​​the ion-selective membrane for membrane concentration is set to 0.055 m², the membrane concentration voltage is 35 V, the membrane concentration current is 3.5 A, and the current density is 63 A / m².

[0101] In this embodiment, the membrane concentration device 3 and method described above are used to concentrate the filtrate, which can significantly increase the hydrofluoric acid concentration of the filtrate. In this embodiment, the hydrofluoric acid concentration of the filtrate is concentrated from 0.61 mol / L (i.e. 1.2%) to 4.1 mol / L (i.e. 8.22%) of the concentrate at the outlet.

[0102] In this application, primary membrane concentration yields a solution containing multivalent ions and fresh water. This fresh water has a conductivity of less than 5 μS / cm, a fluoride ion concentration of less than 8 ppm, and contains few impurities, making it suitable for use as treated water in a factory. The solution containing multivalent ions is then concentrated using a secondary membrane to obtain a divalent ion enrichment solution and a concentrate. Since fluorosilicate is a divalent ion, by adjusting the charge density of the ion-selective membrane in the secondary membrane concentration to match the fluorosilicate ion concentration, the secondary membrane concentration can separate fluorosilicate ions from the solution containing multivalent ions, thereby obtaining a concentrate with a low fluorosilicate ion concentration.

[0103] The membrane concentration device 3 is provided with a concentrated liquid outlet, and the evaporation device 4 is provided with a liquid inlet. The liquid inlet is connected to the concentrated liquid outlet. The concentrated liquid obtained after membrane concentration flows through the concentrated liquid outlet to the liquid inlet of the evaporation device 4 and thus enters the evaporation device 4.

[0104] Evaporation purification is performed using an evaporation device 4 and a condensation device 5. The evaporation device 4 includes a demister 41, which is used to remove mist droplets from the hydrofluoric acid vapor inside the evaporation device 4. The evaporation device 4 includes an evaporation tower, which is a packed tower. The evaporation tower contains a reboiler, a reboiler baffle, a packing layer, a demister layer, and a material inlet. The exterior of the evaporation tower also includes accessories such as a reboiler and a condenser. The demister layer is located at the top of the packed tower, and the demister 41 is located in the demister layer of the packed tower. The demister 41 is a fiber demister, which includes a wire mesh fiber bed. The wire mesh fiber bed is made of ETFE (ethylene-tetrafluoroethylene copolymer) material. The wire mesh fiber bed has an interception efficiency of more than 98% for liquid droplets larger than 1μm in the gas phase, and the fiber diameter is 0.1-0.3mm.

[0105] The concentrate obtained after membrane concentration flows through the concentrate outlet to the inlet of evaporator 4, and then enters the bottom of the packed tower. The bottom of the packed tower is located at the bottom of the packed tower. The bottom of the packed tower is heated and evaporated by an electric heater with a power of 60kW. During evaporation, the temperature of the bottom of the packed tower is controlled at 112℃. At this temperature, the hydrogen fluoride in the concentrate azeotropically reacts with water to form hydrofluoric acid vapor.

[0106] Normally, hydrofluoric acid vapor contains some tiny droplets, which contain water-soluble ionic impurities. Directly condensing hydrofluoric acid vapor containing these droplets would cause the water-soluble ionic impurities to enter the condensed hydrofluoric acid. Therefore, in order to reduce the ionic impurities in the condensed hydrofluoric acid, this embodiment uses a demister with a gas phase interception efficiency of more than 98% for liquid droplets larger than 1 μm to remove droplets from the hydrofluoric acid vapor.

[0107] Evaporation device 4 is equipped with an outlet, and condensation device 5 is equipped with an inlet connected to the outlet of evaporation device 4. Condensation device 5 is located near the top of the packed tower and uses 7-12℃ low-temperature water for cooling, thereby controlling the condensation temperature at 15℃. Hydrofluoric acid vapor, after being de-misted by demister 41, is condensed in condensation device 5, yielding dilute acid product and electronic-grade hydrofluoric acid product respectively. After evaporation, the bottom of evaporation device 4 still contains residual evaporation liquid with a hydrofluoric acid concentration of 36%-38.4%; this residual evaporation liquid can be used as industrial-grade hydrofluoric acid.

[0108] Evaporation purification is carried out using the aforementioned evaporation device 4 and condensation device 5. During this process, the concentration of hydrofluoric acid in the concentrated liquid entering the evaporation device 4 is 8.22%, and the volume is 8.76 L / h. During evaporation, when the concentration of hydrofluoric acid in the liquid in the bottom of the evaporation device 4 is low, the hydrofluoric acid obtained by condensation is a dilute acid product with a concentration of 2.77% and a volume of 6.0 L / h. Continuing to evaporate and purify the product, when the concentration of hydrofluoric acid in the liquid in the bottom of the evaporation device 4 increases, electronic-grade hydrofluoric acid is obtained by condensation with a concentration of 30.65% and a volume of 1.39 L / h. After evaporation, the liquid in the bottom of the evaporation device 4 is the evaporation residue, with a hydrofluoric acid concentration of 37.0% and a volume of 0.36 L / h. This evaporation residue can be used as industrial-grade hydrofluoric acid.

[0109] In this embodiment, the electronic-grade hydrofluoric acid obtained by condensation was tested and found to have a purity that meets the E2 grade of "Electronic-grade hydrofluoric acid for solar cells" (GB / T 31369-2015).

[0110] In this embodiment, the overall recovery rate of fluorine reached 76.4%, where the overall recovery rate of fluorine = (volume of hydrofluoric acid at the top of the tower × volume concentration of hydrofluoric acid at the top of the tower + volume of hydrofluoric acid at the bottom of the tower × volume concentration of hydrofluoric acid at the bottom of the tower) / (hydrogen fluoride content in the waste acid to be treated × treatment volume) = (1.39 × 30.65% + 6.01 × 2.06%) / (60 × 1.2%) = 76.4%.

[0111] In this embodiment, an electric field is used to drive ion separation and sieving, and fluoride ions are concentrated, solving the problems of high energy consumption, salt crystallization, and excessive fluorosilicic acid impurities in low-concentration waste acid evaporation. By combining pretreatment, filtration, membrane concentration, and evaporation purification, electronic-grade hydrofluoric acid products are obtained, which have higher economic value compared to hydrofluoric acid products obtained by conventional evaporation methods.

[0112] Testing revealed that the fluorosilicate content in the electronic-grade hydrofluoric acid obtained in this application was less than 13 ppm.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for treating hydrofluoric acid-containing waste liquid, wherein the hydrofluoric acid content in the waste liquid is less than 6%, characterized in that, The processing system includes: The pretreatment reaction device (1) is equipped with a waste liquid inlet and a fluoride-containing clear liquid outlet; The filtration device (2) is provided with an inlet and a filtrate outlet, and the inlet is connected to the fluoride-containing clear liquid outlet of the pretreatment reaction device (1). The membrane concentration device (3) is provided with a membrane concentration inlet and a concentrate outlet, wherein the membrane concentration inlet is connected to the filtrate outlet; The evaporation device (4) is provided with a liquid inlet and a gas outlet, the liquid inlet being connected to the concentrated liquid outlet; the evaporation device (4) includes a demister (41), the demister (41) being used to remove droplets from the hydrofluoric acid vapor inside the evaporation device (4); The condensing device (5) is provided with an air inlet that is connected to the air outlet of the evaporating device (4). The hydrofluoric acid vapor is condensed in the condensing device (5) to obtain electronic grade hydrofluoric acid.

2. The hydrofluoric acid wastewater treatment system as described in claim 1, characterized in that, The membrane concentration device (3) includes: a primary concentration section connected to the membrane concentration inlet; and a secondary concentration section connected at one end to the primary concentration section and at the other end to the concentrate outlet. And / or, the demister (41) includes a wire mesh fiber bed, the wire mesh fiber bed having an interception efficiency of 98%~100% for droplets larger than 1μm in the hydrofluoric acid vapor; the diameter of the wire mesh fiber bed is 0.1mm~0.3mm; the material of the wire mesh fiber bed is an acid-resistant and heat-resistant fluoropolymer material above 120℃; the wire mesh fiber bed includes a tetrafluoroethylene polymer; And / or, the pretreatment reaction device (1) includes a pretreatment reaction tank, and the pretreatment reaction tank is provided with a cyclone separator; And / or, the filtration device (2) includes a filter element with a filtration accuracy of 0.1 μm to 0.5 μm; the material of the filter element includes a tetrafluoroethylene polymer.

3. A method for treating hydrofluoric acid-containing waste liquid, wherein the hydrofluoric acid content in the waste liquid is less than 6%, characterized in that, The processing method includes the following steps: Pretreatment step: Add a desalination agent to the hydrofluoric acid-containing waste liquid for pretreatment to obtain a fluoride-containing clear liquid; Filtration step: The fluoride-containing clear liquid is filtered to obtain filtrate; Membrane concentration step: The filtrate is subjected to membrane concentration treatment to obtain a concentrated solution; Evaporation and purification steps: The concentrated liquid is evaporated to obtain hydrofluoric acid vapor, the hydrofluoric acid vapor is demisted, and the hydrofluoric acid vapor obtained after the evaporation and demisting processes is condensed to obtain electronic grade hydrofluoric acid.

4. The processing method as described in claim 3, characterized in that, In the filtration step, the step of filtering the fluoride-containing liquid to obtain filtrate includes: performing hydrocyclone separation on the fluoride-containing liquid, and filtering the fluoride-containing liquid after hydrocyclone separation using a filter cartridge to obtain filtrate, wherein the filtration accuracy of the filter cartridge is 0.1μm to 0.5μm.

5. The processing method as described in claim 3, characterized in that, In the pretreatment step, the desalination agent includes at least one of potassium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, potassium chloride, sodium chloride, magnesium chloride, aluminum chloride, potassium hydroxide, and sodium hydroxide. Preferably, the molar amount of the desalination agent added is equal to the amount of F in the hydrofluoric acid-containing waste liquid. - 0.1 to 1.2 times the molar amount of ions.

6. The processing method as described in claim 3, characterized in that, In the membrane concentration step, the process of concentrating the filtrate to obtain a concentrate includes: performing a first membrane concentration on the filtrate to obtain a solution containing multivalent ions; and then performing a divalent anion separation process on the solution containing multivalent ions to obtain the concentrate. Preferably, the current conditions for membrane concentration include a current density of 60 A / m² to 120 A / m². Preferably, the voltage conditions for membrane concentration include: a voltage of 35V to 100V.

7. The processing method as described in claim 3, characterized in that, In the evaporation and purification step, the evaporation temperature is 108℃~122℃, and the condensation temperature is 12℃~19℃.

8. The processing method according to any one of claims 3-7, characterized in that, In the membrane concentration step, the concentration of hydrofluoric acid in the concentrate is 6.0% to 8.5%. In the evaporation and purification step, the concentration of the electronic-grade hydrofluoric acid is 25% to 35%. And / or, in the evaporation and purification step, the concentrate is evaporated to obtain an evaporation residue, the concentration of hydrofluoric acid in the evaporation residue being 36% to 38.4%; the evaporation residue is used as industrial-grade hydrofluoric acid.

9. The processing method according to any one of claims 3-7, characterized in that, In the pretreatment step, the hydrofluoric acid-containing waste liquid comes from the waste liquid generated in the wet process of TOPCon solar cells.

10. The processing method as described in claim 3, characterized in that, The treatment system for hydrofluoric acid waste liquid as described in any one of claims 1-2 was adopted.

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