Fluorine-containing wastewater treatment method

Abstract

The invention discloses a treatment method of fluorine-containing wastewater. The treatment method comprises the following steps: S1, adding acid to reduce the pH value of the wastewater to 1-2 before the wastewater enters a reaction tank; after the wastewater enters the reaction tank, lime milk is added into the reaction tank until the pH value of the wastewater reaches 12; s2, the supernate in the reaction tank overflows to a first flocculation tank, a PAM solution is added into the first flocculation tank, the supernate in the first flocculation tank overflows to a coagulation tank, acid is added into the coagulation tank to adjust the pH to 6.4-7.2, and then a PAC solution is added; s3, enabling the supernate in the coagulation tank to overflow to a second flocculation tank, adding the rest PAM into the second flocculation tank, and enabling the supernate to overflow to a sedimentation tank for sedimentation after the addition is finished. After the wastewater is treated by the treatment method disclosed by the invention, the fluorine ions in the wastewater can be finally reduced to be less than 15mg / L, and the process effects of two-stage chemical precipitation and coagulating sedimentation in the traditional method are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for treating fluorine-containing wastewater. Background Art

[0002] Fluoride-containing wastewater mainly comes from the production process of solar panels. In the manufacturing process of solar panels, a variety of fluorine-containing compounds are needed, such as hydrogen fluoride, ammonium fluoride, etc. These compounds will produce fluorine-containing wastewater during the reaction process. In addition, fluorine-containing cleaning agents are also used in the cleaning and etching processes of solar panels, and these cleaning agents will also form fluorine-containing wastewater after use.

[0003] Fluoride-containing wastewater has the following characteristics: (1) High fluoride content: The most notable feature of fluoride-containing wastewater is its high fluoride ion concentration. Due to the use of a large number of fluoride-containing compounds in the production process, the fluoride ion concentration in the wastewater is generally high, even up to thousands of milligrams per liter, far exceeding the emission standards of most countries and regions. (2) Strong acidity: Fluoride-containing wastewater is often highly acidic. This is because acidic substances are required for reaction and cleaning during the production of solar panels. Strongly acidic wastewater is not only corrosive, but also damages treatment equipment, increasing the difficulty of treatment. (3) Difficulty in treatment: Due to the high fluoride content and strong acidity of fluoride-containing wastewater, conventional sewage treatment methods are often difficult to effectively remove fluoride ions. In addition, fluoride salts are not easily biodegradable under natural conditions, which also increases the difficulty of wastewater treatment. (4) High treatment cost: Due to the difficulty in treating fluoride-containing wastewater, special agents, equipment and processes are required during the treatment process, resulting in high treatment costs. This undoubtedly increases production costs and environmental pressures for enterprises. (5) Strict emission standards: With the increasingly stringent environmental regulations, higher requirements have been put forward for the emission standards of fluorine-containing wastewater. Enterprises need to invest more funds and energy and adopt more advanced treatment technologies and equipment to ensure that wastewater discharge complies with relevant regulations.

[0004] The main treatment processes for fluoride-containing wastewater are as follows: 1. Chemical precipitation method For high-concentration fluoride-containing industrial wastewater, the calcium salt precipitation method is generally used, that is, adding lime, calcium chloride, carbide slag and other chemical precipitants to the wastewater to make fluoride ions and calcium ions generate CaF 2 The reaction formula is: Ca 2+ +F-=CaF 2 ↓ This process has the advantages of simple method, convenient treatment and low cost, but it has disadvantages such as it is difficult to meet the effluent standards after treatment, the sludge settles slowly and is difficult to dehydrate.

[0005] 2. Coagulation and sedimentation method This method is mainly used in conjunction with chemical precipitation, because the coagulation and sedimentation method is easily affected by fluoride, pH, and salinity during the defluorination process. The main principle is: in the coagulation and sedimentation tank, by adding coagulants and coagulants, floccules or colloids are adsorbed or exchanged with ligands, and then the sediment is separated from the water under the action of the sedimentation tank.

[0006] The commonly used flocculant is aluminum salt (PAC). After aluminum salt is added to water, Al 3+ With F - The complexation of aluminum salts and the intermediate products of aluminum salt hydrolysis and the final Al(OH) 3 (am) Alum flowers remove fluoride ions from water through ligand exchange, physical adsorption, and sweeping. The reaction formula can be expressed as: Al 13 O 4 (OH) 24 7 + + XF Al 13 O 4 (OH) 24 → XF X 7 + +XOH - Al(OH) 3 + XF - →Al(OH) 3 -XF X + OH - 3. Adsorption method This treatment method can be used to reduce the fluoride ion concentration to 10m / L through chemical precipitation, and then the adsorption method can be used for treatment. The main principle is: the fluoride ions in the water are adsorbed onto the surface of the porous material by mixing with the wastewater under the action of the adsorbent (activated alumina, etc.), or the wastewater is passed through its granular material to form a filter bed, thereby separating the fluoride ions from the water. The adsorption method generally loads the adsorbent into the filling column and adopts a dynamic adsorption method. It is easy to operate and has a stable defluorination effect.

[0007] Traditional fluoride-containing wastewater treatment processes usually use a combination of chemical precipitation and coagulation precipitation (such as Figure 1 As shown), process description: S1, add Ca(OH) into the reaction tank 2, the pH value is controlled between 8 and 9, and the supernatant flows to the flocculation tank through the overflow port; S2, the PAC metering pump directly and quantitatively adds coagulant PAC (polyaluminium chloride) in the flocculation tank (without adjusting the pH), adsorbs the sediment and agglomerates in the water into alum flowers, and the supernatant flows to the flocculation tank through the overflow port; S3, the PAM (polyacrylamide) metering pump quantitatively adds PAM polymer coagulant aid, so that the agglomerates are adsorbed and connected into larger alum flowers, and the supernatant flows to the sedimentation tank through the overflow port; S4, in the sedimentation tank, the agglomerate sediment and the wastewater are separated, and a scraper is installed in the tank to collect the precipitated sludge at the bottom of the tank body, and regularly transport it to the sludge thickening tank by a pneumatic diaphragm pump for sludge treatment.

[0008] When using the traditional chemical precipitation method + coagulation precipitation method combined process, since the solubility of calcium fluoride in water at 18°C ​​is 16.3 mg / L, which is 7.9 mg / L in terms of fluoride ions, calcium fluoride above this solubility will form precipitates. In actual operation, it was found that the speed of precipitate formation would be significantly slowed down when the residual fluoride was 30 mg / L. In actual fluoride-containing wastewater treatment projects, excessive addition of lime is usually used to further reduce the fluoride ion concentration, but the effect is poor. Usually, the fluoride content in wastewater treated with lime will not be lower than 30 mg / L. The reason is: since the amount of lime added is controlled by the pH linkage, and the addition of lime will quickly increase the pH, it is impossible to add enough lime in the first reaction tank, resulting in (Ca 2+ +F - =CaF 2 ↓) The reaction is incomplete; the solubility of lime is low. If powdered lime is added directly, a large amount of Ca cannot be formed in the water in a short time. 2+ , thus affecting the chemical reaction (Ca 2+ +F - =CaF 2 ↓) is carried out; the commonly used flocculant for flocculation and precipitation of fluoride ion wastewater is aluminum salt (PAC), and when aluminum salt is used, the optimal pH for coagulation is 6.4-7.2, and due to excessive addition of Ca(OH) 2 , which makes the pH in the flocculation tank higher, often above 10, so the flocculation effect is poor, thus affecting the fluoride ion removal efficiency. Summary of the invention

[0009] In view of the above technical problems, the present invention provides a method for treating fluorine-containing wastewater.

[0010] Technical solution: A method for treating fluoride-containing wastewater comprises the following steps: S1: Before the wastewater enters the reaction tank, a certain amount of acid is added to reduce the pH value of the wastewater and control the pH value at 1-2; after the wastewater enters the reaction tank, quicklime is added with water to prepare lime milk, and then lime milk is added to the reaction tank until the pH value of the wastewater reaches 12; S2: The supernatant in the reaction tank overflows to the first flocculation tank, and the PAM solution is added to the first flocculation tank. The supernatant in the first flocculation tank overflows to the coagulation tank, and acid is added to the coagulation tank to adjust the pH to 6.4-7.2, and then the PAC solution is added; S3: The supernatant in the coagulation tank overflows to the second flocculation tank, and the remaining PAM is added to the second flocculation tank. After the addition is completed, the supernatant overflows to the sedimentation tank for sedimentation.

[0011] S4: Part of the sludge in the sedimentation tank is returned to the reaction tank, and the rest of the sludge enters the filter press system for dehydration and then is discharged normally.

[0012] Furthermore, the fluoride content in the wastewater entering the reaction tank in S1 is greater than 200 mg / L (calculated as fluoride ions).

[0013] Furthermore, the acid added in S1 is sulfuric acid.

[0014] Furthermore, the mass concentration of the PAM solution added twice in S2 and S3 was 0.1%, and the volume concentration of the PAM solution in the first flocculation tank and the second flocculation tank was controlled to be 0.4% according to the influent water volume.

[0015] Furthermore, the amount of PAC added in S3 is: according to the influent water volume, the amount of PAC added is controlled so that the PAC concentration in the coagulation tank is controlled at 80±5 ppm%.

[0016] Furthermore, the sludge return volume in S4 is 20% of the total sludge discharge volume.

[0017] Beneficial effects: The present invention adds a certain amount of acid before the wastewater enters the reaction tank to reduce the pH value of the wastewater, thereby providing conditions for the subsequent addition of alkaline lime milk. When the same pH is reached as the reaction end point, for example, the addition of lime milk is stopped when the pH is set to 12. After the pH value is lowered, more lime milk needs to be added to reach pH = 12 due to the acid-base neutralization reaction. At this time, the wastewater contains more Ca 2+ and F - The reaction can further reduce the fluoride content of the treated wastewater. After this step of treatment with the traditional chemical precipitation + coagulation precipitation combination process, the fluoride content is generally not less than 50 mg / L. By adding acid to lower the pH, and stopping adding alkali when the pH reaches 12, the fluoride content can be reduced to below 30 mg / L.

[0018] In S1, quicklime is prepared into lime milk and then added to solve the problem that quicklime cannot form a large amount of Ca in a short time when it is directly added. 2+ , which can not only solve the problems that affect the reaction, but also help to keep the on-site environment clean.

[0019] Since the pH value when PAC is added needs to be controlled at 6.4-7.2, the pH value needs to be further adjusted. In the present invention, S2 adds PAM whose effect is not affected by pH value once before adding PAC, and then adds PAC after adjusting the pH value. After adding PAC, PAM is added for the second time. The system undergoes two coagulation reactions, thereby further reducing the fluoride ion content in the wastewater after the final treatment.

[0020] Sludge return can not only utilize the excess amount that is not converted into CaF 2 Ca(OH) 2 This reduces the amount of lime added. At the same time, the returned calcium fluoride sludge particles can act as flocculation seeds, and through sweeping, adsorption and other effects, they help coagulation, sedimentation and fluoride removal, ultimately reducing the fluoride ion in the effluent to less than 15 mg / L, generally reaching 8~10 mg / L, achieving the process effect of two-stage chemical precipitation + coagulation precipitation of the traditional method. In addition, the amount of PAC and lime used is less, and the calcium fluoride precipitate after coagulation has a better precipitation effect in the subsequent sedimentation tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a combined process diagram of traditional chemical precipitation method + coagulation precipitation method; Figure 2 This is the combined process diagram of the chemical precipitation method + coagulation precipitation method of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be described in detail below with reference to the accompanying drawings.

[0023] As attached Figure 2 As shown, Embodiment 1: A method for treating fluoride-containing wastewater comprises the following steps: S1: The water volume of a factory is: 100m 3 / h, before the wastewater (the fluorine content is 300mg / L calculated as fluoride ions) enters the reaction tank, a certain amount of sulfuric acid is added to lower the pH value of the wastewater and control the pH at 1-2; after the wastewater enters the reaction tank, quicklime is added with water to prepare lime milk, and then lime milk is added to the reaction tank until the pH of the wastewater reaches 12; at this time, the fluorine content in the wastewater sampled in the reaction tank is 28mg / L.

[0024] S2: The supernatant in the reaction tank overflows to the first flocculation tank, into which 0.1% mass concentration of PAM is quantitatively added, and the addition amount is 0.4% of the influent volume. The supernatant in the first flocculation tank overflows to the coagulation tank, and acid is added to the coagulation tank to adjust the pH to 6.4-7.2, and then 80 mg / L (8 kg / h) of PAC is added; S3: The supernatant in the coagulation tank overflows to the second flocculation tank, into which 0.1% mass concentration of PAM is quantitatively added, and the addition amount is 0.4%. After the addition is completed, the supernatant overflows to the sedimentation tank for sedimentation. At this time, the fluoride content in the wastewater sampled from the sedimentation tank is 12 mg / L.

[0025] S4: 80% of the sludge at the bottom of the sedimentation tank enters the sludge filter press system through the valve opening control, and 20% flows back to the reaction tank.

[0026] Embodiment 2: A method for treating fluoride-containing wastewater comprises the following steps: S1: The water volume of a factory is: 100m 3 / h, before the wastewater (the fluorine content is 280 mg / L calculated as fluoride ions) enters the reaction tank, a certain amount of sulfuric acid is added to lower the pH value of the wastewater and control the pH at 1-2; after the wastewater enters the reaction tank, quicklime is added with water to prepare lime milk, and then lime milk is added to the reaction tank until the pH of the wastewater reaches 12; at this time, the fluorine content in the wastewater sampled in the reaction tank is 25 mg / L.

[0027] S2: The supernatant in the reaction tank overflows to the first flocculation tank, into which 0.1% mass concentration of PAM is quantitatively added, and the addition amount is 0.4% of the influent volume. The supernatant in the first flocculation tank overflows to the coagulation tank, and acid is added to the coagulation tank to adjust the pH to 6.4-7.2, and then 80 mg / L (8 kg / h) of PAC is added; S3: The supernatant in the coagulation tank overflows to the second flocculation tank, into which 0.1% mass concentration of PAM is quantitatively added, and the addition amount is 0.4%. After the addition is completed, the supernatant overflows to the sedimentation tank for sedimentation. At this time, the fluoride content in the wastewater sampled from the sedimentation tank is 9 mg / L.

[0028] S4: 80% of the sludge at the bottom of the sedimentation tank enters the sludge filter press system through the valve opening control, and 20% flows back to the reaction tank.

[0029] Embodiment 3: A method for treating fluoride-containing wastewater comprises the following steps: S1: The water volume of a factory is: 100m 3 / h, before the wastewater (the fluorine content is 335 mg / L calculated as fluoride ions) enters the reaction tank, a certain amount of sulfuric acid is added to lower the pH value of the wastewater to control the pH at 1-2; after the wastewater enters the reaction tank, quicklime is added with water to prepare lime milk, and then lime milk is added to the reaction tank until the pH of the wastewater reaches 12; at this time, the fluorine content in the wastewater sampled in the reaction tank is 32 mg / L.

[0030] S2: The supernatant in the reaction tank overflows to the first flocculation tank, into which 0.1% mass concentration of PAM is quantitatively added, and the addition amount is 0.4% of the influent volume. The supernatant in the first flocculation tank overflows to the coagulation tank, and acid is added to the coagulation tank to adjust the pH to 6.4-7.2, and then 80 mg / L (8 kg / h) of PAC is added; S3: The supernatant in the coagulation tank overflows to the second flocculation tank, into which 0.1% mass concentration of PAM is quantitatively added, and the addition amount is 0.4%. After the addition is completed, the supernatant overflows to the sedimentation tank for sedimentation. At this time, the fluoride content in the wastewater sampled from the sedimentation tank is 13 mg / L.

[0031] S4: 80% of the sludge at the bottom of the sedimentation tank enters the sludge filter press system through the valve opening control, and 20% flows back to the reaction tank.

[0032] Comparative Example 1: S1: water inlet volume: 100m 3 / h, (the fluorine content calculated as fluoride ions is 300 mg / L) after entering the reaction tank, quicklime is added into the reaction tank until the pH value of the wastewater reaches 12; at this time, the fluorine content in the wastewater sampled in the reaction tank is 60 mg / L.

[0033] S2: The supernatant in the reaction tank overflows into the flocculation tank, and then 80 mg / L (8 kg / h) PAC is added; S3: The supernatant in the flocculation tank overflows into the coagulation tank, into which PAM is added (0.1% mass concentration of PAM is added, the addition amount is 0.4%). After the addition is completed, the supernatant overflows into the sedimentation tank for sedimentation. At this time, the fluoride content in the wastewater sampled from the sedimentation tank is 40 mg / L.

[0034] Although the present invention has been disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Anyone skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims of this application.

Claims

1. A method for treating fluorine-containing wastewater, characterized in that: The following steps are involved: S1: Before the wastewater enters the reaction tank, a certain amount of acid is added to reduce the pH value of the wastewater and control the pH value at 1-2; after the wastewater enters the reaction tank, quicklime is added with water to prepare lime milk, and then lime milk is added to the reaction tank until the pH value of the wastewater reaches 12; S2: The supernatant in the reaction tank overflows to the first flocculation tank, and the PAM solution is added to the first flocculation tank. The supernatant in the first flocculation tank overflows to the coagulation tank, and acid is added to the coagulation tank to adjust the pH to 6.4-7.2, and then the PAC solution is added; S3: The supernatant in the coagulation tank overflows to the second flocculation tank, and the remaining PAM is added to the second flocculation tank. After the addition is completed, the supernatant overflows to the sedimentation tank for sedimentation.

2. The method for treating fluorine-containing wastewater according to claim 1, characterized in that: The method further includes the following step S4: returning part of the sludge in the sedimentation tank to the reaction tank, and the rest of the sludge enters the filter press system for dehydration and then is discharged normally.

3. A method for treating fluorine-containing wastewater according to claim 1 or 2, characterized in that: The fluoride content in the wastewater entering the reaction tank in S1 is greater than 200 mg / L (calculated as fluoride ions).

4. A method for treating fluorine-containing wastewater according to claim 1 or 2, characterized in that: The acid added in S1 is sulfuric acid.

5. The method for treating fluorine-containing wastewater according to claim 4, characterized in that: The mass concentration of the PAM solution added twice to S2 and S3 was 0.1%. According to the influent water volume, the volume concentration of the PAM solution in the first flocculation tank and the second flocculation tank was controlled to be 0.4%.

6. The method for treating fluorine-containing wastewater according to claim 5, characterized in that: Dosage of PAC added in S3: According to the influent water volume, control the amount of PAC added so that the PAC concentration in the coagulation tank is controlled at 80±5 ppm%.

7. The method for treating fluorine-containing wastewater according to claim 2, characterized in that: The sludge return volume in S4 is 20% of the total sludge discharge volume.

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