Fluorine removal pretreatment system based on zero-valent iron

Abstract

The invention is applied to the technical field of environmental engineering wastewater treatment, and discloses a zero-valent iron-based defluorination pretreatment system, which comprises a reaction tank, a PH regulating tank and a sludge sedimentation tank, the reaction tank main body is made of a corrosion-resistant material, a mechanical stirrer is arranged in the reaction tank, and a zero-valent iron feeding port, a nitric acid feeding pipeline and a pH monitor are arranged above one end of the reaction tank; the pH adjusting tank main body is made of a corrosion-resistant material. According to the defluorination pretreatment system based on zero-valent iron, a spiral feeder is mounted at a zero-valent iron feeding port of the reaction tank, and a flow meter and a regulating valve are mounted at the inlet end of a nitric acid feeding pipeline, so that the feeding amount of zero-valent iron and nitric acid can be accurately controlled, the reaction accuracy and stability are ensured, meanwhile, the feeding amount of the zero-valent iron is determined according to the fluorine content in wastewater, and the treatment effect is improved. And the fixed mass volume ratio of the adding amount of the zero-valent iron to the adding amount of the nitric acid is adopted, so that the predictability of the reaction process is high, and the stability of the treatment effect is improved.

Description

Technical Field

[0001] The invention relates to the technical field of environmental engineering wastewater treatment, and in particular to a fluorine removal pretreatment system based on zero-valent iron. Background Art

[0002] In today's era of rapid industrial development, the generation of fluorine-containing wastewater has become an environmental problem that cannot be ignored. Fluorine-containing wastewater mainly comes from many important industries, such as non-ferrous metallurgy, steel and aluminum processing and other metal processing fields. In the production process of these industries, raw materials or chemicals containing fluoride are often used, which inevitably leads to fluoride in the wastewater. In addition, traditional industries such as coke production, glass manufacturing, and ceramic manufacturing, high-tech industries such as the electronics industry and electroplating, agricultural-related industries such as fertilizer production and pesticide production, fluorine chemicals and fine chemical fields such as semiconductor processing are also important sources of fluorine-containing wastewater. Once fluorine-containing wastewater is discharged into the environment, it will bring serious consequences. First, it will cause soil and groundwater pollution. The sedimentation of fluorine-containing smoke or leaching by precipitation will pollute the soil and groundwater. These pollutants will also enter the bodies of plants and animals through the natural environment, thereby damaging the entire ecosystem and ultimately affecting human health. At the same time, we must realize that fluorine resources are limited. Fluorite, as the current main source of hydrofluoric acid, has limited reserves and is facing the crisis of depletion.

[0003] At present, the main treatment methods for fluoride-containing wastewater include chemical precipitation, coagulation sedimentation, adsorption and ion exchange. Among them, the chemical precipitation method is to separate fluoride from water by adding substances that can react with fluoride ions to form insoluble precipitates into the fluoride-containing wastewater. Commonly used precipitants include lime, carbide slag and calcium chloride. However, these traditional treatment methods often have some shortcomings in practical applications, such as unstable treatment effects, high costs, and secondary pollution. Summary of the invention

[0004] The object of the present invention is to provide a fluorine removal pretreatment system based on zero-valent iron to solve the problems of unstable treatment effect, high cost and secondary pollution proposed in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions: a zero-valent iron-based defluorination pretreatment system, comprising a reaction tank, a pH adjustment tank and a sludge sedimentation tank;

[0006] The reaction tank body is made of corrosion-resistant material, a mechanical stirrer is arranged in the reaction tank, and a zero-valent iron injection port, a nitric acid injection pipeline and a pH monitor are arranged above one end of the reaction tank;

[0007] The pH regulating tank body is made of corrosion-resistant material, a mechanical stirrer is arranged in the pH regulating tank, and a liquid alkali adding pipeline, a metering pump and a pH monitor are arranged above one end of the pH regulating tank;

[0008] The sludge sedimentation tank adopts one of an inclined plate sedimentation tank or a radial flow sedimentation tank, and a sludge scraper is installed in the sludge sedimentation tank, and an overflow weir is arranged above the sludge sedimentation tank, and the sludge discharge port of the sludge sedimentation tank is connected to the sludge conveying pipeline.

[0009] Preferably, the corrosion-resistant material used in the reaction tank and the pH adjustment tank is PP or an alloy.

[0010] Preferably, a screw feeder is installed at the zero-valent iron addition port of the reaction tank, and a flow meter and a regulating valve are installed at the inlet end of the nitric acid addition pipeline.

[0011] Preferably, the treatment process of the defluorination pretreatment system comprises the following steps:

[0012] S1. Use sulfuric acid or hydrochloric acid to adjust the pH value of raw water;

[0013] S2. Add zero-valent iron according to the fluoride content in the wastewater until the zero-valent iron is completely dissolved to form divalent ferrous ions Fe 2+ ;

[0014] S3, add nitric acid, the mass volume ratio of zero-valent iron addition M (kg) to nitric acid addition V (L) is 1:4.5-5, oxidizing the divalent iron into trivalent iron Fe 3+ , reaction time 0.5h;

[0015] The solutions in S4 and S3 enter the pH adjustment tank and add liquid alkali to the pH adjustment tank to adjust the pH and react for 0.5h;

[0016] The solutions in S5 and S4 enter the sludge sedimentation tank for mud-water separation.

[0017] Preferably, the pH of the raw water after treatment in S1 is less than 1.5.

[0018] Preferably, the zero-valent iron in S2 is elemental iron with a purity of >95%, and the mass ratio of the added amount of zero-valent iron to fluorine is 1.1-2:1.

[0019] Preferably, the concentration of nitric acid added in S3 is 25%.

[0020] Preferably, the concentration of the liquid alkali added in S4 is 30%, and the pH of the solution after adjustment in S4 is 3.5-4.5.

[0021] Compared with the prior art, the beneficial effects of the present invention are: the defluorination pretreatment system based on zero-valent iron:

[0022] 1. By installing a spiral feeder at the zero-valent iron dosing port of the reaction pool and a flow meter and a regulating valve at the inlet of the nitric acid dosing pipeline, the dosage of zero-valent iron and nitric acid can be accurately controlled to ensure the accuracy and stability of the reaction. At the same time, the dosage of zero-valent iron is determined according to the fluorine content in the wastewater, and the fixed mass volume ratio of the dosage of zero-valent iron to the dosage of nitric acid is determined, so that the reaction process is highly predictable, thereby improving the stability of the treatment effect;

[0023] Furthermore, adjusting the pH value of the raw water to a specific range creates stable conditions for subsequent reactions. In each reaction step, the reaction time is clearly specified, such as 0.5 h for the ferric iron generation reaction and the reaction after pH adjustment, so that the reaction can proceed fully and the consistency of the treatment effect can be ensured;

[0024] Furthermore, the reaction tank and pH adjustment tank are made of corrosion-resistant materials, which ensures the stability and durability of the equipment and reduces the fluctuation of treatment effect caused by equipment corrosion. The sludge sedimentation tank adopts an inclined plate sedimentation tank or a radial flow sedimentation tank and is equipped with a scraper to ensure the stability of the mud-water separation effect and improve the reliability of the overall treatment system.

[0025] 2. Zero-valent iron is cheaper than the precipitant in the traditional treatment method and elemental iron is easy to obtain. The dosage of nitric acid and liquid alkali is within a reasonable range, which ensures the reaction effect and reduces the cost of chemical reagents;

[0026] Furthermore, the equipment used in the system, such as the reaction tank and pH adjustment tank, has a relatively simple structure, uses common corrosion-resistant materials, has a low manufacturing cost, and has strong equipment durability and relatively low maintenance costs. The conventional design of the sludge sedimentation tank also reduces the equipment investment cost;

[0027] Furthermore, through precise dosing control and strict reaction conditions, the fluorine removal efficiency is improved and the waste of reagents is reduced. At the same time, the reaction time is shorter, which improves the processing efficiency and reduces the operating cost.

[0028] 3. The sludge generated by this system mainly comes from the sludge sedimentation tank. Compared with the traditional treatment method, the content of harmful substances in the sludge is relatively low. The sludge sedimentation tank adopts a mature design, and the scraper is convenient for the collection and treatment of sludge, reducing the risk of secondary pollution of the sludge to the environment;

[0029] Furthermore, zero-valent iron is converted into ferrous ions and ferric ions during the reaction, and combined with fluoride ions to form a stable precipitate, which is not easy to produce harmful reagent residues. Most of the nitric acid and liquid alkali are consumed or converted into harmless substances after the reaction, reducing potential harm to the environment. The sodium hexafluoroferrate produced by the reaction can be recycled and utilized as a resource;

[0030] Furthermore, during the entire treatment process, no traditional precipitants or complex chemical reagent combinations that may cause serious secondary pollution are used. The system design focuses on environmental protection, and the reaction products of each link are relatively stable, reducing the risk of secondary pollution to the soil, groundwater and ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the reaction flow of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] See also Figure 1 The present invention provides a technical solution: a fluorine removal pretreatment system based on zero-valent iron.

[0034] Embodiment 1:

[0035] Defluorination process when the acid in fluoride-containing wastewater is hydrofluoric acid

[0036] 1. Add zero-valent iron according to the fluoride content in the wastewater until the zero-valent iron is completely dissolved to form divalent ferrous ions Fe 2+ , the equation is Fe+2HF=FeF2+H2↑;

[0037] 2. Add nitric acid, the mass volume ratio of zero-valent iron addition M (kg) to nitric acid addition V (L) is 1:4.5-5, oxidizing divalent ferrous iron into trivalent iron Fe 3+ , reaction time 0.5h, the equation is 3FeF2+4HNO3=2FeF3+Fe(NO3)3+NO↑+2H2O;

[0038] 3. The solution enters the pH adjustment tank and liquid alkali is added to the pH adjustment tank to adjust the pH and react for 0.5h;

[0039] 4. The solution enters the sludge sedimentation tank for mud and water separation.

[0040] Embodiment 2:

[0041] Fluoride removal process when the raw water of fluoride-containing wastewater does not meet the acidic conditions by adjusting the pH value with hydrochloric acid

[0042] 1. Use hydrochloric acid to adjust the pH value of raw water;

[0043] 2. Add zero-valent iron according to the fluoride content in the wastewater until the zero-valent iron is completely dissolved to form divalent ferrous ions Fe 2+ , the equation is Fe+2HCl=FeCl2+H2↑;

[0044] 3. Add nitric acid, the mass volume ratio of zero-valent iron addition M (kg) to nitric acid addition V (L) is 1:4.5-5, oxidizing divalent ferrous iron into trivalent iron Fe 3+ , react for 0.5h, the equation is 3FeCl2+4HNO3=2FeCl3+Fe(NO3)3+NO↑+2H2O;

[0045] 4. The solution enters the pH adjustment tank and liquid alkali is added to the pH adjustment tank to adjust the pH and react for 0.5h;

[0046] 5. The solution enters the sludge sedimentation tank for mud and water separation.

[0047] Embodiment three:

[0048] Fluoride removal process when the raw water of fluoride-containing wastewater does not meet the acidic conditions by adjusting the pH value with sulfuric acid

[0049] 1. Use sulfuric acid to adjust the pH value of raw water;

[0050] 2. Add zero-valent iron according to the fluoride content in the wastewater until the zero-valent iron is completely dissolved to form divalent ferrous ions Fe 2+ , the equation is Fe+H2SO4=FeSO4+H2↑;

[0051] 3. Add nitric acid, the mass volume ratio of zero-valent iron addition M (kg) to nitric acid addition V (L) is 1:4.5-5, oxidizing divalent ferrous iron into trivalent iron Fe 3+ , react for 0.5h, the equation is 3FeSO4+4HNO3=Fe2(SO4)3+Fe(NO3)3+NO↑+2H2O;

[0052] 4. The solution enters the pH adjustment tank and liquid alkali is added to the pH adjustment tank to adjust the pH and react for 0.5h;

[0053] 5. The solution enters the sludge sedimentation tank for mud and water separation.

[0054] In the above embodiments, the hydrogen generated after the monovalent iron is added is collected and used as energy.

[0055] The generated nitric oxide is collected separately and reacts with air. The nitric oxide is absorbed by water to form dilute nitric acid, which is then concentrated to a concentration of 25% for use as a defluorination agent. The equation is 4NO+3O2+2H2O=4HNO3.

[0056] The sludge sedimentation tank is used to separate mud and water. The main component of the sludge is sodium hexafluoroferrate (Na3FeF6). The formula for generating sodium hexafluoroferrate is Fe(NO3)3+6NaOH+6HF=Na3FeF6+3NaNO3+6H2O. Sodium hexafluoroferrate can be recycled and used for the production of battery positive electrode materials.

[0057] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and do not limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A defluorination pretreatment system based on zero-valent iron, characterized in that: Including reaction tank, pH adjustment tank and sludge sedimentation tank; The reaction tank body is made of corrosion-resistant material, a mechanical stirrer is arranged in the reaction tank, and a zero-valent iron injection port, a nitric acid injection pipeline and a pH monitor are arranged above one end of the reaction tank; The pH regulating tank body is made of corrosion-resistant material, a mechanical stirrer is arranged in the pH regulating tank, and a liquid alkali adding pipeline, a metering pump and a pH monitor are arranged above one end of the pH regulating tank; The sludge sedimentation tank adopts one of an inclined plate sedimentation tank or a radial flow sedimentation tank, and a sludge scraper is installed in the sludge sedimentation tank, and an overflow weir is arranged above the sludge sedimentation tank, and the sludge discharge port of the sludge sedimentation tank is connected to the sludge conveying pipeline.

2. A zero-valent iron-based defluorination pretreatment system according to claim 1, characterized in that: The corrosion-resistant material used in the reaction tank and the pH adjustment tank is one of PP or alloy.

3. A zero-valent iron-based defluorination pretreatment system according to claim 1, characterized in that: A screw feeder is installed at the zero-valent iron addition port of the reaction tank, and a flow meter and a regulating valve are installed at the inlet end of the nitric acid addition pipeline.

4. A zero-valent iron-based defluorination pretreatment system according to claim 1, characterized in that: The treatment process of the defluorination pretreatment system includes the following steps: S1. Use sulfuric acid or hydrochloric acid to adjust the pH value of raw water; S2. Add zero-valent iron according to the fluoride content in the wastewater until the zero-valent iron is completely dissolved to form divalent ferrous ions Fe 2+ ; S3, add nitric acid, the mass volume ratio of zero-valent iron addition M (kg) to nitric acid addition V (L) is 1:4.5-5, oxidizing the divalent iron into trivalent iron Fe 3+ , reaction time 0.5h; The solutions in S4 and S3 enter the pH adjustment tank and add liquid alkali to the pH adjustment tank to adjust the pH and react for 0.5h; The solutions in S5 and S4 enter the sludge sedimentation tank for mud-water separation.

5. A zero-valent iron-based defluorination pretreatment system according to claim 4, characterized in that: The pH of the raw water after treatment in S1 is less than 1.

5.

6. A zero-valent iron-based defluorination pretreatment system according to claim 4, characterized in that: The zero-valent iron in the S2 is elemental iron with a purity of >95%, and the mass ratio of the added amount of zero-valent iron to fluorine is 1.1-2:

1.

7. A zero-valent iron-based defluorination pretreatment system according to claim 4, characterized in that: The concentration of nitric acid added to S3 is 25%.

8. A zero-valent iron-based defluorination pretreatment system according to claim 4, characterized in that: The concentration of the liquid alkali added in S4 is 30%, and the pH of the solution after adjustment in S4 is 3.5-4.5.

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