Method for low-cost and efficient recovery of fluorine element from fluorine-containing wastewater

Abstract

The present application relates to the technical field of wastewater treatment, in particular to a method for low-cost and efficient recovery of fluorine element from fluorine-containing wastewater, comprising the following steps: determining the fluorine ion concentration and the type of coexisting ions in the fluorine-containing wastewater; selecting a pH regulator and a crystal inducer according to the type of coexisting ions; and passing the fluorine-containing wastewater containing coexisting ions into a nucleation granulation reactor, adding the pH regulator and the crystal inducer, so that the fluorine in the wastewater is converted into calcium fluoride. Compared with the prior art, the present application maximizes the fluorine element recovery benefit by optimizing the economic crystal inducer suitable for the essential physicochemical properties of fluorine-containing wastewater, effectively solves the problems of device fouling and cost increase caused by excessive addition of crystal inducer in the chemical precipitation method, and reduces the later device maintenance cost; compared with the traditional treatment process, the present application has the advantages of small occupied area, convenient operation, high automation degree, and effectively reduces the occupied area and labor cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, in particular to a method for low-cost and efficient recovery of fluorine elements in fluorine-containing wastewater. BACKGROUND

[0002] The main source of fluorine pollution in the water environment is the fluorine-containing "three wastes" discharged by industrial production, involving industries such as aluminum electrolysis, steel, cement, brick, ceramics, phosphate fertilizer, glass, semiconductor, pharmaceuticals, etc. The common feature of these industries is to use fluorine-containing minerals as the main raw material or auxiliary raw material. In the smelting and production process, fluorine is decomposed from the minerals and enters the environment, causing fluorine pollution. The existence of fluorine pollution has caused serious harm to human health and environmental safety. At present, the commonly used methods at home and abroad mainly include adsorption method and precipitation method. Among them, the chemical precipitation method is to add a certain amount of chemical reagent to the fluorine-containing wastewater, so that fluorine in the wastewater generates fluoride precipitate or adsorbs fluorine ions by co-precipitation, and then the precipitate is separated from water by filtration or natural sedimentation, so as to achieve the purpose of removing fluorine. Although the chemical precipitation method is simple in process and easy to operate, the amount of reagent used is large, which increases the water treatment cost. In addition, the sludge produced by this method has a high water content, which needs to be further coupled with a plate and frame filter pressing process, which also increases the equipment area and further increases the treatment cost. At the same time, this method cannot effectively recover fluorine ions in wastewater, causing waste of fluorine resources and loss of recovery benefits. Therefore, it is of great significance to find a new fluorine removal technology with stable fluorine removal effect, low treatment cost and effective recovery of fluorine ions in wastewater. SUMMARY

[0003] In order to overcome the above technical defects, the present application provides a method for low-cost and efficient recovery of fluorine elements in fluorine-containing wastewater, which realizes the balance between treatment cost and resource recovery benefit based on the principle of core crystal granulation technology.

[0004] The present application provides a method for low-cost and efficient recovery of fluorine elements in fluorine-containing wastewater, comprising the following steps:

[0005] S1. Determining the fluorine ion concentration and coexisting ion type of the fluorine-containing wastewater;

[0006] S2. Selecting a pH adjuster and a crystal inducer according to the coexisting ion type. Specifically, the pH adjuster can be selected from one or more of sodium hydroxide or calcium hydroxide; the crystal inducer can be selected from one or more of calcium chloride, calcium hydroxide or magnesium chloride;

[0007] S3. Passing the fluorine-containing wastewater containing coexisting ions into a core crystal granulation reactor, adding a pH adjuster and a crystal inducer, and converting fluorine in the wastewater into calcium fluoride.

[0008] In actual operation, according to the essential properties of the fluorine-containing wastewater, such as the pH of raw water, the concentration of fluoride ions and the types of coexisting ions, an economical crystallization inducer is optimized and adapted, and through precise control of the crystallization inducer, the water treatment cost is greatly reduced while ensuring the effluent quality and the recovery efficiency of fluoride ions. In addition, the recovered spherical granules have high purity, low water content and high solid-liquid separation efficiency, which can bring additional economic benefits to enterprises.

[0009] Further, in the S2, when the coexisting ion is sulfate ion, the pH regulator is sodium hydroxide, and the crystallization inducer is magnesium chloride.

[0010] Further, in the S2, when the coexisting ion is chloride ion or nitrate ion, the pH regulator is calcium hydroxide, and the crystallization inducer is calcium hydroxide and calcium chloride.

[0011] Further, in the S1, the initial concentration of the fluorine-containing wastewater is 100-10000 mg / L, and the initial pH value of the fluorine-containing wastewater is 1-4; in the S3, the final adjusted pH value of the fluorine-containing wastewater is 6-8.

[0012] Further, in the S3, when the concentration of fluoride ions is 100-1000 mg / L, the crystallization inducer is calcium hydroxide.

[0013] Further, in the S3, when the concentration of fluoride ions is 1000-5000 mg / L, the crystallization inducer is calcium hydroxide and calcium chloride.

[0014] Further, in the S3, the molar ratio of calcium hydroxide to fluoride ions is (0.35-0.45):1.

[0015] In a preferred embodiment, the molar ratio of calcium hydroxide to fluoride ions is (0.35-0.42):1; the molar ratio of calcium hydroxide to fluoride ions is (0.35-0.40):1; the molar ratio of calcium hydroxide to fluoride ions is (0.35-0.38):1.

[0016] Further, in the S3, the molar ratio of calcium hydroxide, calcium chloride and fluoride ions is (0.1-0.2):(0.15-0.25):1.

[0017] In a preferred embodiment, the molar ratio of calcium hydroxide, calcium chloride and fluoride ions is (0.1-0.15):

[0018] (0.2-0.25):1; or the molar ratio of the calcium hydroxide, calcium chloride and fluoride ions is (0.15-0.2):(0.15-0.2):1; or the molar ratio of the calcium hydroxide, calcium chloride and fluoride ions is (0.12-0.18):(0.15-0.2):1; or the molar ratio of the calcium hydroxide, calcium chloride and fluoride ions is (0.15-0.2):(0.2-0.22):1; or the molar ratio of the calcium hydroxide, calcium chloride and fluoride ions is (0.12-0.18):(0.15-0.2):1.

[0019] Further, in the S3, the fluorine special seed crystal is filled in the core crystal prilling reactor, the particle size of the fluorine special seed crystal is 100-140 mesh, and the filling height is 10%-30% of the effective height of the device.

[0020] Specifically, the special seed crystal for recovering fluoride ions is pre-filled in the core crystal prilling reactor as the crystal nucleus of fluoride ion crystallization growth, so as to reduce the nucleation energy barrier of calcium fluoride, under the driving of the economic inducer, it can be attached and precipitated in the metastable zone, and finally the densification of the prilling body is realized, the spherical crystalline product formed realizes the efficient recovery of the fluorine resource in the wastewater, and great economic benefits are created.

[0021] Further, in the S2, the fluorine special seed crystal is one or more of dolomite, quartz sand and brucite.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. The prilling body formed by the present application has high purity, low water content and high solid-liquid separation efficiency, can be directly applied to the three industries of metallurgy, chemical industry and building materials, has great market capacity, and creates considerable resource recovery benefits;

[0024] 2. The present application effectively solves the problems of device scaling and cost increase caused by excessive addition of inducer in the chemical precipitation method, and reduces the later device maintenance cost;

[0025] 3. Compared with the traditional treatment process, the present application has the advantages of small occupied area, convenient operation, high automation, and effectively reduces the occupied area and labor cost. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The process flow chart of the present application. DETAILED DESCRIPTION

[0027] In order to better understand the technical solutions of the present application, the present application will be described in detail below in conjunction with specific embodiments. The experimental methods in the following examples, unless otherwise specified, are generally in accordance with the conventional conditions or in accordance with the conditions recommended by the manufacturers. The test materials used in the following examples, unless otherwise specified, are all purchased from conventional biochemical reagent stores. Unless otherwise specified, percentages and parts are calculated by weight. Unless otherwise defined, all professional and scientific terms used herein have the same meaning as understood by those skilled in the art. In addition, any method and material similar or equivalent to those described can be applied in the present application. The preferred implementation methods and materials described herein are only for demonstration.

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant variations. Various

[0029] Based on the present application, a process flow as shown in Figure 1 is established. First, fluorine special seeds with a particle size of 100-140 mesh are filled in the core crystal granulation reaction device, and the filling height is 10%-30% of the effective height of the device. Raw water is injected into the core crystal granulation reactor through a raw water lifting pump, so that the filled seeds in the reactor are in a fluidized state. Then, a nucleation agent, which is calcium hydroxide emulsion, is injected into the core crystal granulation reactor through a dosing pump. The effluent after reaction is overflowed through the overflow weir at the top of the device, and finally discharged into the effluent storage tank.

[0030] Based on the present application, the fluorine special seeds are pre-filled in the core crystal granulation reactor as the crystal nucleus for the crystallization growth of fluoride ions, so that the nucleation energy barrier of calcium fluoride in the fluorine-containing wastewater is reduced. Then, according to the water quality characteristics of the fluorine-containing wastewater, such as the fluoride ion concentration, the raw water pH, and the coexisting ion characteristics, the type and stoichiometric ratio of the nucleation agent are optimized. Under the driving of the nucleation agent, the fluoride ions in the fluorine-containing wastewater entering the core crystal granulation reactor can be attached and precipitated in the metastable zone, and finally the densification of the granules is realized, forming a spherical crystalline product with high purity, low water content, and high solid-liquid separation efficiency.

[0031] Based on the present application, the fluoride ion concentration in the fluorine-containing wastewater to be treated is in the range of 100-10000 mg / L, the wastewater pH is acidic, and the value range is 1-4. The coexisting ions are one or more of sulfate ions, nitrate ions, and chloride ions.

[0032] Based on the present application, the particle size of the fluorine special seed crystal filled in the core crystal prilling reactor is 100-140 mesh, and the filling height is 10%-30% of the effective height of the device; the fluorine special seed crystal is one or more of dolomite, quartz sand and brucite.

[0033] Based on the present application, the core crystal prilling reaction pH interval in the core crystal prilling reactor is pH=6-8, and the raw water pH regulator is one or more of sodium hydroxide or calcium hydroxide; the selection of the pH regulator depends on the coexisting ions in the wastewater, if the coexisting ions in the wastewater are sulfate ions, sodium hydroxide is used for pH adjustment; if the coexisting ions in the wastewater are chloride ions or nitrate ions, calcium hydroxide is used for pH adjustment, and the pH adjustment process is carried out simultaneously in the core crystal prilling reactor.

[0034] Based on the present application, the crystal inducer is one or more of calcium chloride, calcium hydroxide or magnesium chloride; and when sulfate ions coexist, magnesium chloride is used as the crystal inducer; if chloride ions or nitrate ions are the coexisting ions, calcium hydroxide is compounded with calcium chloride as the crystal inducer; at this time, when the fluoride ion concentration is 100-1000 mg / L, only calcium hydroxide is used as the crystal inducer, and the molar ratio of the crystal inducer to the fluoride ion concentration is (0.35-0.45):1; when the fluoride ion concentration is 1000-5000 mg / L, calcium hydroxide is compounded with calcium chloride as the crystal inducer, and the molar ratio between the dosages of calcium hydroxide and calcium chloride and the fluoride ion concentration is (0.1-0.2):(0.15-0.25):1; when the fluoride ion concentration is 5000-10000 mg / L, the molar ratio between the dosages of calcium hydroxide and calcium chloride and the fluoride ion concentration is (0.15-0.5):(0.15-0.5):1; when sulfate coexists in the wastewater, sodium hydroxide is compounded with magnesium chloride in the form of sodium hydroxide to recover magnesium fluoride spherical particles, wherein the dosage of sodium hydroxide depends on the pH of the wastewater, i.e. the pH of the wastewater is adjusted to 6-8, and the molar ratio between the dosage of magnesium chloride and the fluoride ion concentration is (0.6-0.9):1.

[0035] The technical solutions of the present application are further described in detail in combination with specific embodiments and the accompanying tables, and it should be understood that the following embodiments are only used to explain the present application and do not limit the present application.

[0036] Example 1

[0037] The method for low-cost and efficient recovery of fluorine elements in fluorine-containing wastewater comprises the following steps: filling white cloudstone with a particle size of 100 mesh into a nucleation granulation reactor, the filling height being 10% of the effective height of the device, injecting raw water into the nucleation granulation reactor through a raw water lifting pump, so that the filled seed crystals in the reactor are in a fluidized state, then injecting a nucleating agent into the nucleation granulation reactor through a dosing pump, the nucleating agent being calcium hydroxide emulsion, the effluent after reaction overflowing through an overflow weir at the top of the device, and finally being discharged into a water storage tank.

[0038] In this embodiment, the fluorine ion concentration in the fluorine-containing wastewater is 100 mg / L, the raw water pH is 1, the coexisting nitrate ion concentration is 1000 mg / L, the nucleation granulation process is used to treat the above fluorine-containing wastewater, the calcium hydroxide dosage is 155.79 mg / L, the effluent fluorine ion concentration is 6.5 mg / L, the fluorine ion recovery rate is 90.5%, the purity of the formed granules is 92.5%, and the treatment cost is 0.452 yuan / m 3 , more than 90% of the calcium fluoride recovery price is 2000 yuan / ton, and the economic benefits generated by the recovery of the granules are 0.82 yuan / m 3 .

[0039] Example 2

[0040] The method for low-cost and efficient recovery of fluorine elements in fluorine-containing wastewater comprises the following steps: filling white cloudstone with a particle size of 100 mesh into a nucleation granulation reactor, the filling height being 10% of the effective height of the device, injecting raw water into the nucleation granulation reactor through a raw water lifting pump, so that the filled seed crystals in the reactor are in a fluidized state, then injecting a nucleating agent into the nucleation granulation reactor through a dosing pump, the nucleating agent being calcium hydroxide emulsion, the effluent after reaction overflowing through an overflow weir at the top of the device, and finally being discharged into a water storage tank.

[0041] In this embodiment, the fluorine ion concentration in the fluorine-containing wastewater is 1000 mg / L, the raw water pH is 2, the coexisting sulfate ion concentration is 2000 mg / L, the nucleation granulation process is used to treat the above fluorine-containing wastewater, the sodium hydroxide dosage is 2500 mg / L, the magnesium chloride dosage is 2004.5 mg / L, the effluent fluorine ion concentration is 16.8 mg / L, the fluorine ion recovery rate is 90.2%, the purity of the formed granules is 92.8%, and the treatment cost is 17.64 yuan / m 3 , more than 90% of the magnesium fluoride recovery price is 6000 yuan / ton, and the economic benefits generated by the recovery of the granules are 19.58 yuan / m 3 .

[0042] Example 3

[0043] The method for low-cost and efficient recovery of fluorine elements in fluorine-containing wastewater comprises the following steps: filling white dolomite with a particle size of 140 mesh into a nucleation granulation reactor, the filling height being 30% of the effective height of the device, injecting raw water into the nucleation granulation reactor through a raw water lifting pump, so that the filled seed crystals in the reactor are in a fluidized state, then injecting a nucleating agent into the nucleation granulation reactor through a dosing pump, the nucleating agent being calcium hydroxide emulsion, the effluent after reaction overflowing through an overflow weir at the top of the device, and finally being discharged into a water storage tank;

[0044] In this embodiment, the fluorine ion concentration in the fluorine-containing wastewater is 5000 mg / L, the raw water pH is 2, and the coexisting chloride ion concentration is 3000 mg / L. The nucleation granulation process is used to treat the fluorine-containing wastewater. The calcium hydroxide dosage is 4500 mg / L, the calcium chloride dosage is 6000 mg / L, the effluent fluorine ion concentration is 25.6 mg / L, the fluorine ion recovery rate is 80.6%, the purity of the formed granules is 94.6%, and the treatment cost is 26.25 yuan / m 3 . The economic benefit generated by the recovery of the granules is 36.4 yuan / m 3 .

[0045] Example 4

[0046] The method for low-cost and efficient recovery of fluorine elements in fluorine-containing wastewater comprises the following steps: filling white dolomite with a particle size of 140 mesh into a nucleation granulation reactor, the filling height being 30% of the effective height of the device, injecting raw water into the nucleation granulation reactor through a raw water lifting pump, so that the filled seed crystals in the reactor are in a fluidized state, then injecting a nucleating agent into the nucleation granulation reactor through a dosing pump, the nucleating agent being calcium hydroxide emulsion, the effluent after reaction overflowing through an overflow weir at the top of the device, and finally being discharged into a water storage tank;

[0047] In this embodiment, the fluorine ion concentration in the fluorine-containing wastewater is 5000 mg / L, the raw water pH is 2, and the coexisting chloride ion concentration is 3000 mg / L. The nucleation granulation process is used to treat the fluorine-containing wastewater. The calcium hydroxide dosage is 4500 mg / L, the calcium chloride dosage is 6000 mg / L, the effluent fluorine ion concentration is 25.6 mg / L, the fluorine ion recovery rate is 80.6%, the purity of the formed granules is 94.6%, and the treatment cost is 26.25 yuan / m 3 . The economic benefit generated by the recovery of the granules is 36.4 yuan / m 3 .

[0048] Finally, it should be noted that the above description is only the preferred embodiment of the present application, and those skilled in the art can make various similar expressions under the inspiration of the present application without departing from the purpose and scope of the present application. Such changes fall within the scope of the present application.

Claims

1. A low-cost and efficient method for recovering fluorine from fluoride-containing wastewater, characterized in that, Includes the following steps: S1. Determine the fluoride ion concentration and coexisting ion types in fluoride-containing wastewater; S2. Select pH adjusters and crystal inducers based on the types of coexisting ions; S3. Fluorine-containing wastewater with an initial concentration of 100-10000 mg / L containing coexisting ions is introduced into a nucleation granulation reactor. A pH adjuster and a crystal inducer are added to adjust the initial pH of the fluorine-containing wastewater (1-4) to a pH of 6-8, so that the fluorine in the wastewater is converted into calcium fluoride or magnesium fluoride. Wherein, when the coexisting ion is sulfate ion, the pH adjuster is sodium hydroxide and the crystal inducer is magnesium chloride; when the coexisting ion is chloride ion or nitrate ion, the pH adjuster is calcium hydroxide and the crystal inducer is calcium hydroxide and calcium chloride; when the fluoride ion concentration is 100-1000 mg / L, the crystal inducer is calcium hydroxide; when the fluoride ion concentration is 1000-5000 mg / L, the crystal inducer is calcium hydroxide and calcium chloride. The nucleogranulation reactor is filled with fluorine-specific seed crystals, the particle size of which is 100-140 mesh, and the filling height is 10%-30% of the effective height of the device; the fluorine-specific seed crystals are one or more of dolomite, quartz sand, and brucite.

2. The method for low-cost and high-efficiency recovery of fluoride from fluoride-containing wastewater according to claim 1, characterized in that, When the fluoride ion concentration is 100-1000 mg / L, the molar ratio of calcium hydroxide to fluoride ions is (0.35-0.45):

1.

3. The method for low-cost and high-efficiency recovery of fluoride from fluoride-containing wastewater according to claim 1, characterized in that, When the fluoride ion concentration is 1000-5000 mg / L, the molar ratio of calcium hydroxide, calcium chloride and fluoride ions is (0.1-0.2):(0.15-0.25):1.

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