Method for treating pickling wastewater in stainless steel production and recycling fluorine ions

Abstract

The invention discloses a method for treating pickling wastewater in stainless steel production and recycling fluorine ions. The method comprises a pickling wastewater pretreatment reaction, a primary precipitation reaction, a calcium fluoride crystallization fluidized bed structure, induced crystallization regulation, a seed crystal storage tank, a secondary precipitation reaction, a deep defluorination reaction and an online regulation system. According to the invention, through cooperative treatment of a plurality of steps of pretreatment, primary precipitation, calcium fluoride crystallization fluidized bed induced crystallization, secondary precipitation, deep fluorine removal and the like, oil stains, heavy metal ions and fluorine ions in the pickling wastewater can be effectively removed, the treated wastewater reaches the discharge standard, and the purification treatment of the wastewater is realized.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a method for treating pickling wastewater from stainless steel production and recovering and utilizing fluoride ions. Background Technology

[0002] Pickling is an essential step in the production of stainless steel, used to remove oxide scale and impurities from the surface to ensure surface quality and subsequent processing performance. However, the pickling process generates a large amount of pickling wastewater, which contains not only high concentrations of fluoride ions but also Fe²⁺. + Fe³ + Cr³ + Ni² + It contains various heavy metal ions, along with a certain amount of oil pollution. If discharged directly, it will cause serious pollution to water bodies, soil and other ecological environments, and endanger human health.

[0003] Currently, there are many methods for treating stainless steel pickling wastewater, such as chemical precipitation, adsorption, and ion exchange. Chemical precipitation is widely used due to its simple operation and low cost, but traditional chemical precipitation methods suffer from problems such as incomplete removal of fluoride ions, large amounts of precipitated sludge, and ineffective recovery of fluoride resources. Although adsorption and ion exchange methods can achieve deep fluoride removal, the regeneration costs of adsorbents and ion exchange resins are high, and the treatment capacity is limited, making them unsuitable for large-scale industrial wastewater treatment.

[0004] In addition, during the fluoride ion recovery process, traditional crystallization equipment is prone to problems such as difficulty in crystal sedimentation, equipment blockage, and low crystallization efficiency, resulting in low purity of calcium fluoride products that cannot meet the requirements of industrial applications.

[0005] Therefore, a method for treating pickling wastewater from stainless steel production and recovering fluoride ions is proposed. This method, which achieves efficient recovery and utilization of fluoride ions, is stable in operation, and has low cost, has significant practical significance and application value. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned problems by providing a method for treating and recovering fluoride ions from pickling wastewater in stainless steel production. This invention employs a multi-step process involving pretreatment, primary precipitation, fluidized bed induced crystallization with calcium fluoride, secondary precipitation, and deep defluorination. This synergistic treatment effectively removes oil, heavy metal ions, and fluoride ions from the pickling wastewater, ensuring that the treated wastewater meets discharge standards and achieving wastewater purification. To achieve the above-mentioned objective, the technical solution adopted by this invention is as follows: According to one aspect of the present invention, a method for treating pickling wastewater from stainless steel production and recovering fluoride ions is provided, comprising a pickling wastewater pretreatment reaction, a primary precipitation reaction, a calcium fluoride crystallization fluidized bed structure and induced crystallization control, seed crystal storage, a secondary precipitation reaction, a deep defluorination reaction, and an online control system.

[0007] Preferably, the pretreatment reaction of the pickling wastewater adopts the air flotation separation method to remove oil from the pickling wastewater. Specifically, the pickling wastewater is introduced into the pretreatment tank, and a large number of micro bubbles are generated by the air flotation equipment. The oil adheres to the surface of the bubbles and floats to the water surface. The oil is removed by the oil skimming device, thereby reducing the impact of oil on the subsequent treatment process.

[0008] Preferably, the primary sedimentation reaction specifically involves: introducing pretreated acidic wastewater (after oil removal) into a primary sedimentation tank; adding lime slurry to adjust the pH to 3-4; simultaneously activating the aeration device for thorough aeration for 30-60 minutes; then adding polyacrylamide (PAM) as a coagulant at a dosage of 2-5 mg / L; stirring thoroughly; and finally coagulation and sedimentation for 1-2 hours. This step removes a large amount of Fe²⁺ from the pickling wastewater. + Fe³ + Cr³ + In addition to other possible metal ions, this reduces the load on subsequent processing steps.

[0009] Preferably, the main body of the calcium fluoride crystallization fluidized bed structure is a cylinder with a conical bottom, made of HDPE (high-density polyethylene), which has advantages such as corrosion resistance, high strength, and long service life. The equipment internally includes a cylindrical overflow weir, a crystallization settling component, an acid washing control system, a blower system, a circular aeration disc, a reflux pump, an acid dosing pump, an observation port, an online pH sensor, an online liquid level sensor, and a total outlet for the packing material. The circular overflow weir is used to control the effluent water level and ensure stable equipment operation; the crystallization settling component promotes the crystallization of calcium fluoride. The system facilitates sedimentation of the wastewater, improving crystallization efficiency; the acid pickling control system is used to unclog the equipment through acid pickling; the blower system works in conjunction with the circular aeration disc to provide aeration and prevent packing caking; the reflux pump controls the wastewater return flow; the acid dosing pump adds acid solution; the equipment observation port allows operators to easily observe the internal operation of the equipment; the online pH sensor and online liquid level sensor are used to detect the pH value and liquid level of the wastewater in the equipment in real time, respectively, and transmit the detection data to the online control system; the equipment packing's main discharge port is used to discharge calcium fluoride crystals that meet the particle size requirements.

[0010] Preferably, the operation process and crystallization induction control of the calcium fluoride crystallization fluidized bed are as follows: The effluent from the primary precipitation reaction is introduced into the calcium fluoride crystallization fluidized bed. First, lime slurry is added to the influent to adjust the pH to 5-6.5. After stirring evenly, the effluent enters through the equipment inlet. The reflux flow rate is controlled at 150-300% using a reflux pump, and the upward flow velocity of the wastewater within the equipment is controlled at 0.01-0.05 m / s. Uniform seed crystals of 100-500 μm are used for crystallization induction. The seed crystals are added to the crystallization fluidized bed and react fully with the wastewater. The blower system is intermittently activated as needed for equipment operation, and aeration is performed through circular aeration discs at an aeration intensity of 0.5-1.0 m³ / (m²·h) to prevent packing caking. When a significant increase in reflux pressure is detected, the acid washing control system is activated, and acid solution is added through the acid dosing pump ⑧ for acid washing to resolve system blockage issues.

[0011] Preferably, the seed crystal storage specifically involves the following: During the operation of the calcium fluoride crystallization fluidized bed, the seed crystals continuously grow as the reaction proceeds, and the particle size gradually increases. When the seed crystal particle size is ≥1-2mm, it needs to be discharged externally. During operation, the particle size of the packing material in the tower is monitored weekly. When the particle size reaches 1mm or more, it is discharged in batches through the main outlet of the equipment packing material, with each discharge accounting for 10%. The discharged large seed crystal particles can be crushed to 100-500μm by a slurry pump and then reused in the system as inducing seed crystals. The portion of the seed crystals that have grown is transported to the packing material storage tank for storage. After acid treatment, the stored seed crystals yield calcium fluoride products with a purity >80%, meeting industrial application standards.

[0012] Preferably, the secondary precipitation reaction specifically involves: introducing the effluent from the calcium fluoride crystallization fluidized bed into the secondary sedimentation tank, adding quicklime to the tank to adjust the pH value of the wastewater to 9-10, stirring evenly, and then carrying out coagulation and sedimentation for 1-1.5 hours. This step can remove residual nickel and other heavy metal ions from the wastewater.

[0013] Preferably, the deep defluorination reaction specifically involves: introducing the effluent from the secondary precipitation reaction into a deep defluorination tank, adding a defluorinating agent (such as polyaluminum chloride, activated alumina, etc.) to the tank, with a dosage of 50-100 mg / L, adjusting the pH of the wastewater to 7-8, stirring evenly, and then carrying out coagulation and sedimentation for 1-2 hours. The fluoride ion concentration of the treated wastewater meets the discharge standards and can be discharged to the wastewater treatment center for further disposal.

[0014] Preferably, the online control system is connected to an online pH sensor, an online liquid level sensor, and various dosing devices, reflux pumps, fans, and other equipment. It collects operating parameters such as pH value, liquid level, and reflux pressure of the wastewater in real time, and automatically adjusts the operating status of each device according to the preset parameter range. For example, it adjusts the dosage of lime slurry, PAM, and defluorinating agent, controls the reflux flow rate of the reflux pump, and turns the fan system on or off, thereby realizing the automated operation and stable control of the entire treatment process.

[0015] Preferably, all sludge generated by the process (including primary sedimentation sludge, secondary sedimentation sludge, deep defluorination sedimentation sludge, and unqualified sludge discharged from the calcium fluoride crystallization fluidized bed) must be transported to a sludge thickening tank for thickening, and then dewatered by a plate and frame filter press before being discharged to a professional sludge treatment facility for harmless disposal to avoid secondary pollution.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The present invention describes a method for treating and recovering fluoride ions from pickling wastewater in stainless steel production. Through a multi-step process including pretreatment, primary precipitation, fluidized bed induced crystallization of calcium fluoride, secondary precipitation, and deep defluorination, the method can effectively remove oil, heavy metal ions, and fluoride ions from pickling wastewater. The treated wastewater meets the discharge standards, thus achieving wastewater purification.

[0017] 2. The present invention describes a method for treating pickling wastewater from stainless steel production and recovering fluoride ions. This method employs a calcium fluoride crystallization fluidized bed combined with induced crystallization control technology. Uniform seed crystals of 100-500 μm are used to induce fluoride ions to crystallize and generate calcium fluoride. By controlling operating parameters such as reflux flow rate, upward flow rate, and pH value, the crystallization efficiency and the purity of the calcium fluoride product (purity > 80%) are improved, realizing the recovery and utilization of fluoride ions, turning waste into treasure, and reducing treatment costs.

[0018] 3. The present invention describes a method for treating pickling wastewater from stainless steel production and for recovering and utilizing fluoride ions. The calcium fluoride crystallization fluidized bed is made of HDPE material, which has good corrosion resistance and a long service life. The equipment is equipped with a crystal settling component, a blower aeration system, and a pickling control system, which effectively solves the problems of difficult crystal settling and equipment blockage in traditional crystallization equipment, and ensures the stable operation of the equipment.

[0019] 4. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions described in this invention achieves automated operation and real-time control of the entire treatment process by setting up an online control system, enabling precise dosing, reducing manual operation, and improving treatment efficiency and operational stability. Attached Figure Description

[0020] Figure 1This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram of the crystallization fluidized bed structure of the present invention; In the attached diagram: 1. Main body; 2. Overflow weir; 3. Crystal settling component; 4. Acid washing control system; 5. Blower system; 6. Aeration disc; 7. Return pump; 8. Acid dosing pump; 9. Equipment observation port; 10. Online pH sensor; 11. Online liquid level sensor; 12. Equipment packing main discharge port; 13. Inlet; 14. Outlet; 15. Return pipe. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of the invention, and these aspects of the invention can be achieved even without these specific details.

[0022] Please see Figures 1 to 2 This invention provides a method for treating pickling wastewater from stainless steel production and for recovering and utilizing fluoride ions. The technical solution is as follows: Example 1: A stainless steel manufacturing plant generates pickling wastewater at a rate of 2500 m³ / d. The wastewater quality is as follows: fluoride ion concentration of 800 mg / L, Fe²⁺ ions... + The concentration is 500 mg / L, Fe³ + The concentration is 300 mg / L, Cr³ + The concentration is 50 mg / L, Ni² + The concentration is 20 mg / L, the pH value is 1.5, and the oil content is 100 mg / L.

[0023] The specific steps of the processing method of the present invention are as follows: 1. Pickling wastewater pretreatment reaction: The pickling wastewater is introduced into the pretreatment tank, the air flotation equipment is turned on, and microbubbles are generated. Oil stains adhere to the surface of the bubbles and float to the surface. The oil stains are removed by the oil skimming device. After treatment, the oil content in the wastewater is reduced to below 5mg / L.

[0024] 2. Primary sedimentation reaction: The pretreated wastewater is introduced into the primary sedimentation tank, lime slurry is added to adjust the pH to 3.5, the aeration device is turned on for 45 minutes, then PAM (dosage 3 mg / L) is added, stirred evenly, and sedimentation is carried out for 1.5 hours. After sedimentation, Fe²⁺ in the wastewater is obtained. + Fe³ + Cr³ + The concentrations were reduced to below 10 mg / L, 8 mg / L, and 2 mg / L, respectively.

[0025] 3. Operation and Crystallization Induction Control of Calcium Fluoride Crystallization Fluidized Bed: Primary sedimentation effluent is introduced into the calcium fluoride crystallization fluidized bed, and lime slurry is added to adjust the pH to 6.0, entering through the equipment inlet. The reflux rate is controlled at 200%, and the upward flow velocity is 0.03 m / s. Uniform seed crystals of 100-500 μm are added. The blower system 5 is intermittently turned on, with an aeration intensity of 1.0 m³ / (m²·h), aerating 3 times a day for 30 minutes each time. The particle size of the packing material in the tower is monitored weekly. When the particle size reaches 1 mm or more, 10% is discharged in batches. The discharged large seed crystals are crushed by a slurry pump and reused. After acid treatment, the purity of the stored seed crystals is 82%.

[0026] 4. Secondary sedimentation reaction: The effluent from the crystallization fluidized bed is introduced into the secondary sedimentation tank, and quicklime is added to adjust the pH to 9.5. Sedimentation is carried out for 1.2 hours. After sedimentation, Ni²⁺ in the wastewater is obtained. + The concentration dropped to below 0.5 mg / L.

[0027] 5. Deep defluoridation reaction: The secondary sedimentation effluent is introduced into the deep defluoridation tank, polyaluminum chloride (dosage amount is 80mg / L) is added, the pH value is adjusted to 7.5, and sedimentation is carried out for 1.5 hours. After treatment, the fluoride ion concentration in the wastewater is reduced to below 10mg / L, which meets the discharge standards.

[0028] 6. Sludge disposal: The sludge generated by each process is concentrated, dewatered and then discharged for harmless treatment.

[0029] Example 2: A stainless steel manufacturing plant generates 1500 m³ / d of pickling wastewater. The wastewater quality is as follows: fluoride ion concentration is 1000 mg / L, Fe²⁺ ions are present. + The concentration is 600 mg / L, Fe³ + The concentration is 400 mg / L, Cr³ + The concentration is 60 mg / L, Ni² + The concentration is 30 mg / L, the pH value is 1.7, and the oil content is 80 mg / L. The specific steps of the treatment method of this invention are as follows: 1. Pickling wastewater pretreatment reaction: The pickling wastewater is introduced into the pretreatment tank, and the air flotation equipment is turned on to remove oil. After treatment, the oil content in the wastewater is reduced to below 5mg / L.

[0030] 2. Primary sedimentation reaction: The pretreated wastewater is introduced into the primary sedimentation tank, lime slurry is added to adjust the pH to 3.0, the aeration device is turned on for 60 minutes, then PAM (dosage 5 mg / L) is added, stirred evenly, and allowed to settle for 2 hours. After sedimentation, Fe²⁺ in the wastewater is obtained. + Fe³ + Cr³ + The concentrations were reduced to below 8 mg / L, 10 mg / L, and 3 mg / L, respectively.

[0031] 3. Operation and Crystallization Induction Control of Calcium Fluoride Crystallization Fluidized Bed: Primary sedimentation effluent is introduced into the calcium fluoride crystallization fluidized bed, and lime slurry is added to adjust the pH to 5.0, entering through the equipment inlet. The reflux rate is controlled at 100%, and the upward flow velocity is 0.01 m / s. Uniform seed crystals of 100-500 μm are added. The blower system 5 is intermittently turned on, with an aeration intensity of 0.8 m³ / (m²·h), aerating 4 times a day for 20 minutes each time. The particle size of the packing material in the tower is monitored weekly. When the particle size reaches 1 mm or more, 10% is discharged in batches. The discharged large seed crystals are crushed by a slurry pump and reused. The stored seed crystals are treated with acid to achieve a calcium fluoride purity of 80%.

[0032] 4. Secondary sedimentation reaction: The effluent from the crystallization fluidized bed is introduced into the secondary sedimentation tank, and quicklime is added to adjust the pH to 10.0. Sedimentation is carried out for 1.5 hours. After sedimentation, Ni²⁺ in the wastewater is obtained. + The concentration dropped to below 0.5 mg / L.

[0033] 5. Deep defluoridation reaction: The secondary sedimentation effluent is introduced into the deep defluoridation tank, activated alumina is added (dosage is 85mg / L), the pH value is adjusted to 7.0, sedimentation is carried out for 2.5h, and the fluoride ion concentration in the wastewater is reduced to below 8mg / L after treatment. The effluent is then discharged to the sewage treatment center.

[0034] 6. Sludge disposal: The sludge generated by each process is concentrated, dewatered and then discharged for harmless treatment.

[0035] Example 3: A stainless steel manufacturing plant generates pickling wastewater at a rate of 1900 m³ / d. The wastewater quality is as follows: fluoride ion concentration is 1120 mg / L, Fe²⁺ ions are present. + The concentration is 700 mg / L, Fe³ + The concentration is 300 mg / L, Cr³ + The concentration is 45 mg / L, Ni² + The concentration is 40 mg / L, the pH value is 1.1, and the oil content is 150 mg / L. The specific steps of the treatment method of this invention are as follows: 1. Pickling wastewater pretreatment reaction: The pickling wastewater is introduced into the pretreatment tank, and the air flotation equipment is turned on to remove oil. After treatment, the oil content in the wastewater is reduced to below 5mg / L.

[0036] 2. Primary sedimentation reaction: The pretreated wastewater is introduced into the primary sedimentation tank, lime slurry is added to adjust the pH to 4.0, the aeration device is turned on for 60 minutes, then PAM (dosage 6 mg / L) is added, stirred evenly, and allowed to settle for 2 hours. After sedimentation, Fe²⁺ in the wastewater is obtained. + Fe³ + Cr³ +The concentrations were reduced to below 5 mg / L, 7 mg / L, and 2 mg / L, respectively.

[0037] 3. Operation and Crystallization Induction Control of Calcium Fluoride Crystallization Fluidized Bed: Primary sedimentation effluent is introduced into the calcium fluoride crystallization fluidized bed, and lime slurry is added to adjust the pH to 6.5, entering through the equipment inlet. The reflux rate is controlled at 300%, and the upward flow velocity is 0.05 m / s. Uniform seed crystals of 100-500 μm are added. The blower system 5 is intermittently turned on, with an aeration intensity of 1.0 m³ / (m²·h), aerating 4 times a day for 20 minutes each time. The particle size of the packing material in the tower is monitored weekly. When the particle size reaches 1 mm or more, 10% is discharged in batches. The discharged large seed crystals are crushed by a slurry pump and reused. After acid treatment, the purity of the stored seed crystals is 84%.

[0038] 4. Secondary sedimentation reaction: The effluent from the crystallization fluidized bed is introduced into the secondary sedimentation tank, and quicklime is added to adjust the pH to 10.0. Sedimentation is carried out for 1.5 hours. After sedimentation, Ni²⁺ in the wastewater is obtained. + The concentration dropped to below 0.5 mg / L.

[0039] 5. Deep defluoridation reaction: The secondary sedimentation effluent is introduced into the deep defluoridation tank, activated alumina (dosage is 100mg / L) is added, the pH value is adjusted to 8.0, and sedimentation is carried out for 2 hours. After treatment, the fluoride ion concentration in the wastewater is reduced to below 8mg / L, and the effluent is discharged to the sewage treatment center.

[0040] 6. Sludge disposal: The sludge generated by each process is concentrated, dewatered and then discharged for harmless treatment.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating pickling wastewater from stainless steel production and recovering fluoride ions, characterized in that, include: The system includes a pretreatment reaction for pickling wastewater, a primary precipitation reaction, a fluidized bed structure for calcium fluoride crystallization and control of induced crystallization, a seed storage tank, a secondary precipitation reaction, a deep defluorination reaction, and an online control system.

2. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 1, characterized in that: The pickling wastewater pretreatment tank uses air flotation separation to remove oil.

3. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 1, characterized in that: The pretreated acidic wastewater is adjusted to pH 3-4 with lime slurry and thoroughly aerated. An appropriate amount of PAM is added for coagulation and sedimentation to remove large amounts of Fe²⁺ from the acid washing wastewater. + Fe³ + Cr³ + And other possible metal ions.

4. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 1, characterized in that: The calcium fluoride crystallization fluidized bed structure includes a main body (1), an overflow weir (2), a crystal settling component (3), an acid washing control system (4), a blower system (5), an aeration disc (6), a reflux pump (7), an acid dosing pump (8), an equipment observation port (9), an online pH sensor (10), an online liquid level sensor (11), and a total outlet for the equipment packing (12). The main body (1) is a cylindrical body with a conical bottom and is made of HDPE. The main body (1) has an inlet (13) at the bottom and an outlet (14) at the top on the same side. The main body (1) is equipped with an acid washing control system (4) and a blower system (5). The acid washing control system (4) is connected to the inlet (13) through a connecting pipe and the acid dosing pump (8). The blower system (5) is connected to the bottom of the main body (1) through a duct. Next, the bottom of the main body (1) is provided with a total outlet (12) for the equipment packing, and the outer side of the upper end of the main body (1) is provided with a return pipe (15). The other end of the return pipe (15) is connected to the total outlet (12) for the equipment packing, and a return pump (7) is provided on the end of the return pipe (15) near the total outlet (12) for the equipment packing. The top of the main body (1) is provided with an equipment observation port (9), and pH online detection sensor (10) and liquid level online detection sensor (11) are respectively provided on both sides of the equipment observation port (9). The upper part of the inside of the main body (1) is provided with a cylindrical overflow weir (2), and pH online detection sensor (10) and liquid level online detection sensor (11) extend downward into the overflow weir (2). The middle section of the inside of the main body (1) is provided with a crystal precipitation component (3), and the lower part of the inside of the main body (1) is provided with a circular aeration disc (6).

5. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 4, characterized in that: The seed storage tank is connected to the equipment packing outlet (12) at the bottom of the calcium fluoride crystallization fluidized bed, so as to discharge the seed crystals in a timely manner. The seed storage tank is equipped with a slurry pump, which can crush the seed crystals to the target particle size and reuse them in the crystallization fluidized bed system.

6. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 1, characterized in that: The calcium fluoride crystal fluidized bed is prepared by adding lime milk to tap water to adjust the pH to 5-6.

5. After thorough mixing, the water enters through the inlet (13) with a return flow rate of 150-300% and an upward flow velocity controlled at 0.01-0.05 m / s. The blower system (5) is turned on intermittently as needed to prevent packing from caking. The blower aerates for 10 minutes every 6 hours. Under extreme conditions, when the return pressure rises significantly and the inner wall of the fluidized bed is significantly scaled (>1 cm), the acid washing system is turned on to solve the system blockage problem.

7. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 1, characterized in that: The induced crystallization control is achieved by using seed crystals with a particle size of 100-500μm to induce crystallization. The influent is primary sedimentation effluent, and the pH is adjusted to 5-6.5 with quicklime. After thorough mixing, it is fed into the calcium fluoride crystallization fluidized bed. As the equipment operates, the calcium fluoride particles adsorb and crystallize, and the particle size increases. When the particle size is ≥1-2mm, it needs to be discharged. During operation, the particle size of the packing material in the tower is monitored weekly. When it reaches 1mm or more, it is discharged in batches (10% each time). At the same time, large particles of packing material can be crushed with a slurry pump and reused for induced crystallization in the system. The increased portion of the packing material is stored in a packing storage tank and then treated with acid. The purity of the calcium fluoride is >80%, which meets the industrial application standards.

8. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 1, characterized in that: The effluent from the calcium fluoride crystallization fluidized bed is adjusted to pH 9-10 with quicklime, and an appropriate amount of PAM is added for secondary coagulation and sedimentation to remove other heavy metals, such as nickel.

9. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 1, characterized in that: The secondary coagulation and sedimentation effluent from the secondary sedimentation reaction is treated by adding an appropriate amount of defluoridating agent according to the actual water quality, adjusting the pH, and coagulating and settling to ensure that the effluent fluoride meets the standard (<10 mg / L) before being discharged to the wastewater treatment center.

10. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 1, characterized in that: All sludge generated from the processes must be discharged externally for harmless treatment.

11. The method for treating pickling wastewater from stainless steel production and recovering fluoride ions according to claim 4, characterized in that: The online monitoring system can accurately add chemicals based on pH and related parameters. The online liquid level detection sensor (11) is equipped with a function to measure the inner diameter of the fluidized bed, thereby assessing the degree of scaling in the fluidized bed and performing regular acid washing and descaling maintenance of the system.

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