Fluidized bed treatment technology for fluorine-containing wastewater crystallization

Abstract

The invention relates to a fluorine-containing wastewater crystallization fluidized bed treatment technology, and belongs to the technical field of sewage treatment.The fluorine-containing wastewater is treated through a crystallization fluidized bed, a carbon dioxide aeration device is arranged at the bottom of a guide cylinder of the crystallization fluidized bed, acid-base adjustment is achieved through carbon dioxide, and stable control over the pH of sewage is achieved; by introducing carbon dioxide into the crystallization fluidized bed, growth of calcium fluoride crystals can be effectively intervened, calcium fluoride crystal particles are increased, and the separation difficulty of calcium fluoride is reduced; the dosage of the defluorinating agent can be reduced, and the purity of calcium fluoride crystals is also improved; according to the invention, the problems of small calcium fluoride crystal particles and difficulty in separation in the defluorination process of the existing crystallization fluidized bed are effectively solved, the defluorination treatment cost is reduced, the dosage of an acid-base neutralization agent is reduced, and the defluorination of fluorine can be realized at a relatively low temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and in particular relates to a fluorine-containing wastewater crystallization fluidized bed treatment technology. Background Art

[0002] Fluoride-containing wastewater is usually treated with chemical precipitation and coagulation precipitation to remove fluoride ions. The most commonly used precipitants in chemical precipitation are calcium salts, such as lime, calcium chloride, calcium carbonate, and carbide slag. Calcium salts have a good effect in removing fluoride, but the disadvantage in practical applications is that the calcium fluoride formed by calcium salts and fluorine will be wrapped on the surface of calcium hydroxide, which is not conducive to the complete reaction. This leads to a large amount of calcium salt added (the amount added is often 3 to 4 times the theoretical value), a high sludge yield and complex composition, a low calcium fluoride content, and low reuse value. In addition, the effluent from a simple chemical precipitation method cannot meet discharge requirements, and generally requires additional deep defluoridation, which increases production and operating costs.

[0003] Studies have shown that the use of crystallization fluidized bed equipment can improve the defluorination effect of chemical precipitation. For example, patent CN101941752B discloses a method and apparatus for treating fluorine-containing wastewater, proposing a process idea of extracting calcium fluoride from fluorine-containing wastewater using a solid-liquid two-phase fluidized bed as a crystallization reactor and calcium chloride as a crystal seed. This method is mainly used for fluorine-containing wastewater in the chemical, non-ferrous metallurgy, glass, electronics, photovoltaic and other industries. The pH of this type of wastewater is mostly between 1 and 2. Before entering the fluidized bed for calcium fluoride crystallization and precipitation, a large amount of NaOH or KOH reagents needs to be added for neutralization. The cost of adding the reagents is high, and the crystallization fluidized bed usually uses mechanical stirring to fluidize the calcium fluoride crystal nuclei. During the mechanical stirring process, the calcium fluoride crystal nuclei will collide with the crystal particles, resulting in unstable growth of the crystals, affecting the subsequent solid-liquid separation and screening process, and reducing the production efficiency of the equipment. In addition, in the prior art, during the addition of the calcium salt defluorinating agent, the pH value of the wastewater fluctuates, etc., resulting in the produced calcium fluoride crystals being small and easily encapsulating the calcium salt defluorinating agent, resulting in an increase in the amount of defluorinating agent used, low purity of the calcium fluoride crystals, and difficulty in recycling.

[0004] Alkaline fluoride-containing wastewater (pH between 12-13) generated in fields such as electrolytic aluminum, phosphorus chemical industry, semiconductors, and new energy also requires the addition of calcium salt defluoridation agents for defluorination. Before defluorination, large amounts of hydrochloric acid or sulfuric acid are added for neutralization. After neutralization, the addition of calcium salt defluoridation introduces large amounts of chloride ions, sulfate ions, and other ions into the effluent, causing secondary contamination. Furthermore, defluoridation using a crystallization fluidized bed for this type of wastewater also suffers from the problem of unstable crystal growth and small size. This results in large amounts of defluoridation agent, difficulty separating the resulting calcium fluoride crystals, low purity, and low recycling value. Summary of the Invention

[0005] In order to overcome the problems existing in the background technology, the present invention provides a crystallization fluidized bed treatment technology for fluorine-containing wastewater. By introducing carbon dioxide into the crystallization fluidized bed and utilizing carbon dioxide gas to achieve acid-base adjustment, the problem of small calcium fluoride crystal particles and difficult separation in the existing crystallization fluidized bed defluorination process is effectively overcome, the defluorination treatment cost is reduced, the amount of acid-base neutralization agent used is reduced, and efficient and low-cost treatment of fluorine-containing wastewater is achieved.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions: The fluorine-containing wastewater crystallization fluidized bed treatment technology is to add the fluorine-containing wastewater into the crystallization fluidized bed, and introduce carbon dioxide gas into the crystallization fluidized bed and add a defluorination agent.

[0007] Furthermore, the pH of the influent of the crystallization fluidized bed is 12-13.

[0008] Furthermore, in the initial reaction stage of 0-60 minutes, the pH of the sewage is controlled to be 9-10; in the crystallization stage of 60-180 minutes, the pH of the sewage is controlled to be 7-9; the reaction temperature is 20-40°C.

[0009] Furthermore, the defluorinating agent is a calcium salt that can react with fluoride ions to form calcium fluoride precipitate.

[0010] Furthermore, calcium salt is added at a molar ratio of 1.2-1.5:1 between calcium and fluoride ions in the wastewater.

[0011] Furthermore, the defluorination agent is calcium chloride.

[0012] Furthermore, the crystallization fluidized bed includes an outer cylinder, a crystallization cylinder and a guide cylinder arranged concentrically; the upper end of the guide cylinder is inserted into the crystallization cylinder; and a carbon dioxide aeration device is provided at the bottom of the guide cylinder.

[0013] Furthermore, the sewage inlet is opened at the lower part of the diversion tube.

[0014] Furthermore, the crystallization sulfurization bed is equipped with a pH online detection system; and a spiral guide plate is provided between the crystallization cylinder and the guide cylinder.

[0015] Furthermore, the carbon dioxide aeration device is a gas distributor.

[0016] Beneficial effects of the present invention: The present invention controls the inlet pH of sewage to 12-13 by introducing carbon dioxide into the crystallization fluidized bed, thereby greatly reducing the amount of acidic agents such as hydrochloric acid or sulfuric acid required to neutralize alkaline sewage, thereby reducing the increase of impurity ions in the sewage caused by the addition of neutralizers.

[0017] The present invention uses a crystallization fluidized bed to treat fluoride-containing wastewater. By introducing carbon dioxide into the crystallization fluidized bed, the carbon dioxide gas is used to achieve acid-base adjustment, thereby achieving stable control of the pH value of the wastewater. By introducing carbon dioxide into the crystallization fluidized bed, the growth of calcium fluoride crystals can be effectively intervened, the calcium fluoride crystal particles can be increased, and the difficulty of separating calcium fluoride can be reduced. At the same time, the intervention of carbon dioxide in the calcium fluoride crystallization process can not only reduce the amount of defluorinating agent used, but also improve the purity of the calcium fluoride crystals.

[0018] The present invention effectively overcomes the problems of small calcium fluoride crystal particles and difficult separation in the existing crystallization fluidized bed defluorination process, reduces the defluorination treatment cost, reduces the amount of acid-base neutralization agent used, and realizes efficient and low-cost treatment of fluoride-containing wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the crystallization fluidized bed of the present invention; In the figure, 1-guide tube, 2-crystallization tube, 3-outer tube, 4-water inlet, 5-carbon dioxide aeration device, 6-spiral guide plate, 7-exhaust hole, 8-overflow cofferdam, 9-drainage outlet, 10-crystallization discharge port. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and beneficial effects of the present invention more clear, the technical solution of the present invention will be described in detail below. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0021] The fluorine-containing wastewater crystallization fluidized bed treatment technology includes the following contents: The sewage is added to the crystallization fluidized bed, and a calcium salt defluorination agent is added to the crystallization fluidized bed. At the same time, carbon dioxide gas is introduced into the guide tube of the crystallization fluidized bed. The pH value of the sewage is controlled by the amount of carbon dioxide introduced. In the initial reaction stage of the reaction of 0-60 minutes, the pH value of the sewage is controlled to be 9-10; in the crystallization stage of 60-180 minutes, the pH value of the sewage is controlled to be 7-9.

[0022] By introducing carbon dioxide into the crystallization fluidized bed, the present invention controls the inlet pH of the sewage to 12-13, significantly reducing the amount of acidic agents such as hydrochloric acid or sulfuric acid required to neutralize alkaline sewage, and even eliminating the need for adding acidic agents. This further reduces the increase in impurity ions in the sewage caused by the addition of neutralizers. Furthermore, by introducing carbon dioxide into the crystallization fluidized bed, the carbon dioxide can produce a relatively mild acid-base neutralization reaction with the sewage, achieving stable control of the sewage pH value. Furthermore, it can effectively interfere with the growth of calcium fluoride crystals, increase the size of calcium fluoride crystal particles, and reduce the difficulty of calcium fluoride separation. Furthermore, through extensive experimental research, the inventors have found that the intervention of carbon dioxide in the calcium fluoride crystallization process not only reduces the amount of defluorinating agents used, but also improves the purity of the calcium fluoride crystals.

[0023] The dosage of the calcium salt defluorination agent is: calcium salt is added at a molar ratio of 1.2-1.5:1 between calcium and fluoride ions in the wastewater.

[0024] Control the reaction temperature in the fluidized bed: 20-40℃.

[0025] In order to illustrate the present invention more clearly, the following examples are provided for detailed description. Example 1

[0026] It should be noted that the crystallization fluidized bed used in the present invention can be any form of solid-liquid two-phase crystallization fluidized bed. The main difference between the present invention and the existing crystallization fluidized bed is that a carbon dioxide aeration device 5 is provided. This embodiment only lists one fluidized bed structure. The listed crystallization fluidized bed structure cannot be understood as a necessary technical limitation for the implementation of the method of the present invention.

[0027] The crystallization fluidized bed is a cylindrical structure, comprising a concentrically arranged guide tube 1, a crystallization tube 2 and an outer tube 3; the upper end of the guide tube 1 is inserted into the crystallization tube 2, with a gap left between the guide tube 1 and the crystallization tube 2.

[0028] The carbon dioxide aeration device 5 is arranged at the bottom of the guide tube 1 , and the water inlet 4 is opened at the lower part of the guide tube 1 .

[0029] The lower part of the crystallization cylinder 2 is further provided with a conical bottom, and a crystallization discharge port 10 is opened at the conical bottom.

[0030] The CO2 aeration device 5 includes a CO2 supply system and a gas distributor. The gas distributor utilizes a 316L stainless steel sintered plate with a pore size of 0.1-0.5mm and a porosity of 1-3%. This ensures uniform distribution of CO2 bubbles, increasing the gas-liquid contact area. The CO2 supply system provides CO2 to the gas distributor and is equipped with a gas flow meter and pressure regulating valve (the CO2 supply system utilizes conventional, mature technology and is not shown in the accompanying diagram). The supply pressure is controlled between 0.1-0.3 MPa.

[0031] As a preferred solution, a spiral guide plate 6 is provided between the crystallization cylinder 2 and the guide cylinder 1 to form a vortex in the fluid, thereby increasing the probability of crystal collision and improving the growth rate of crystal particles.

[0032] The crystallization fluidized bed is equipped with online pH and temperature monitoring equipment (the installation of monitoring instruments in the crystallization fluidized bed is a mature existing technology and is not described in detail in this embodiment). The detection probe of the online pH monitoring equipment is installed in the guide tube 1. The crystallization fluidized bed is also equipped with a defluorinating agent addition device, through which the defluorinating agent is added to the guide tube (conventional technical means, the installation location and structure of the defluorinating agent addition device are not described in detail in this embodiment).

[0033] As a preferred solution, the crystallization fluidized bed is equipped with a seed adding device, through which seeds are added into the flow guide tube 1 to accelerate the formation of crystals (conventional technical means, the setting position and structure are not described in detail in this embodiment).

[0034] Example of crystallization fluidized bed operation index control: Carbon dioxide is introduced continuously for aeration at a rate of 0.5-2m³ / (m³・h), the bubble diameter is controlled at 0.5-2mm, and the fluidized bed rising velocity is maintained at 0.1-0.5m / h.

[0035] Note: The following examples were all carried out in a fluidized bed crystallization. Example 2

[0036] Treatment of fluoride-containing wastewater from a lithium battery alkaline leaching waste residue: F content 820 mg / L.

[0037] The sewage was added to the crystallization fluidized bed, with an inlet pH of 12.6, an inlet temperature of 24°C, a carbon dioxide gas supply system pressure of 0.2 MPa, a carbon dioxide flow rate controlled at 1.2 m³ / (m³·h), and a 20% mass concentration CaCl2 aqueous solution as a defluorination agent, with the dosage controlled at 1.5 times the theoretical value (molar ratio of calcium to fluoride ions in sewage).

[0038] After the water intake is complete, the carbon dioxide aeration system is activated, controlling the wastewater pH at 9.0-9.5 for the first 45 minutes. The calcium chloride dosing system is then activated, continuously adding defluoridation agents to the flow tube. After 45 minutes, the wastewater pH is controlled at 7.5-8.5, and calcium fluoride seed crystals (approximately 0.18mm in diameter) are added at a dosage of 1.0g / L. The entire reaction process lasts for 2 hours, with the carbon dioxide aeration system operating continuously and the carbon dioxide flow rate adjusted in real time based on feedback from the pH meter.

[0039] After the reaction, analysis of the crystals discharged from the crystal discharge port revealed an average particle size of 2.5 mm, a calcium fluoride purity of 90.8%, an effluent pH of 8.1, a fluoride content of 9.5 mg / L, and a fluoride removal rate of 98.84%. The effluent met the discharge requirements of the national standard GB30484-2013.

[0040] Comparative Example 1 This comparative example uses a conventional crystallization fluidized bed without spiral guide plates, carbon dioxide aeration devices, and pH online monitoring systems. The wastewater treatment is the same as in Example 2.

[0041] The pH value of the wastewater in the early stage of crystallization was regulated at 8.0±0.5 by adding hydrochloric acid. The crystal granules were fluidized only by the inlet flow rate. The amount of calcium chloride added was the same as in Example 2. The amount of seed crystals (calcium fluoride with a particle size of about 0.18 mm) added was 1.0 g / L. The entire reaction process was maintained for 2 hours. Under these conditions, the effluent fluoride ion concentration and the effluent calcium fluoride particles were as follows: the effluent fluoride ion concentration was 25 mg / L, the chloride ion content was increased, and it did not meet the discharge requirements. Further treatment in an advanced treatment module was required. The average particle size of the calcium fluoride particles was 1.2 mm, the purity was 85.1%, and the product utilization value was low. Example 3

[0042] Alkaline high-concentration fluoride-containing wastewater from a chemical industry, with an F content of 580 mg / L.

[0043] The sewage was added to the crystallization fluidized bed, with an inlet pH of 13.1; an inlet temperature of 24°C, a carbon dioxide gas supply system pressure of 0.25 MPa, a carbon dioxide flow rate controlled at 1.8 m³ / (m³·h), and a 20% mass concentration CaCl2 aqueous solution as a defluorination agent, with the dosage controlled at 1.3 times the theoretical value (molar ratio of calcium to fluoride ions in sewage).

[0044] During the first 45 minutes, the wastewater pH was controlled at 9.0-9.5. The calcium chloride dosing device was activated, and defluorination agent was continuously added to the flow tube. After 45 minutes, the wastewater pH was controlled at 7.8-9.0. Calcium fluoride seed crystals were added to the flow tube at a dose of 0.8g / L. Carbon dioxide was continuously introduced throughout the reaction to adjust or maintain the pH. The entire reaction process lasted 2.5 hours.

[0045] After the reaction, analysis of the crystals discharged from the crystal discharge port revealed an average particle size of 2.2 mm, a calcium fluoride purity of 90.4%, an effluent pH of 7.8, a fluoride content of 9.2 mg / L, and a fluoride removal rate of 98.41%. The effluent met the discharge requirements of the national standard GB30484-2013.

[0046] Comparative Example 2: This comparative example was carried out in a conventional crystallization fluidized bed (without spiral guide plates, without carbon dioxide aeration system, and equipped with a stirring device), and the wastewater was treated in the same manner as in Example 3. The pH value in the pre-crystallization stage was adjusted to 8.0±0.5 by adding hydrochloric acid. The amounts of calcium chloride and seed crystals added were the same as in Example 3. The reaction was carried out for 2.5 hours. The fluoride ion concentration in the effluent and the effluent calcium fluoride particles were as follows: the fluoride ion concentration in the effluent was 15.5 mg / L, which did not meet the discharge requirements and required further treatment in an advanced treatment module. The average size of the calcium fluoride particles was 1.1 mm, and the purity was 82.6%. The product had a low utilization value.

[0047] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A fluorine-containing wastewater crystallization fluidized bed treatment technology, characterized in that: The fluorine-containing wastewater is added to a crystallization fluidized bed, and carbon dioxide gas is introduced into the crystallization fluidized bed and a defluorination agent is added.

2. The fluorine-containing wastewater crystallization fluidized bed treatment technology according to claim 1, characterized in that: The inlet water pH of the crystallization fluidized bed is 12-13.

3. The fluorine-containing wastewater crystallization fluidized bed treatment technology according to claim 2, characterized in that: In the initial reaction stage of 0-60 minutes, the pH of the sewage is controlled at 9-10; in the crystallization stage of 60-180 minutes, the pH of the sewage is controlled at 7-9; the reaction temperature is 20-40°C.

4. The fluorine-containing wastewater crystallization fluidized bed treatment technology according to claim 1, characterized in that: The defluorinating agent is a calcium salt that can react with fluoride ions to generate calcium fluoride precipitate.

5. The fluorine-containing wastewater crystallization fluidized bed treatment technology according to claim 4, characterized in that: Calcium salt is added at a molar ratio of 1.2-1.5:1 between calcium and fluoride ions in the wastewater.

6. The fluorine-containing wastewater crystallization fluidized bed treatment technology according to claim 4 or 5, characterized in that: The defluorinating agent is calcium chloride.

7. The crystallization fluidized bed used in the fluorine-containing wastewater crystallization fluidized bed treatment technology according to any one of claims 1 to 6, characterized in that: The crystallization fluidized bed comprises an outer cylinder, a crystallization cylinder and a guide cylinder which are arranged concentrically; the upper end of the guide cylinder is inserted into the crystallization cylinder; and a carbon dioxide aeration device is provided at the bottom of the guide cylinder.

8. The crystallization fluidized bed according to claim 7, characterized in that The sewage inlet is opened at the lower part of the diversion tube.

9. The crystallization fluidized bed according to claim 7, characterized in that The crystallization sulfurization bed is equipped with a pH online detection system; a spiral guide plate is provided between the crystallization cylinder and the guide cylinder.

10. The crystallization fluidized bed according to claim 7, characterized in that The carbon dioxide aeration device is a gas distributor.

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