A method for treating fluorine-containing wastewater and recycling large-particle fluorite powder

Abstract

The present invention discloses a method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, which relates to the technical field of fluorine-containing wastewater treatment and resource recovery. The method comprises the following steps: Step S1, raw material preparation; Step S2, seed crystal activation; Step S3, impurity removal treatment of the fluorine-containing wastewater; Step S4, precipitation reaction; and Step S5, subsequent treatment. This method achieves a higher removal rate of fluoride ions and total organic carbon in the fluorine-containing wastewater, and the recycled fluorite powder has higher purity and larger particle size.

Description

Technical Field

[0001] The present invention relates to the technical field of fluorine-containing wastewater treatment and resource recovery, and in particular to a method for treating fluorine-containing wastewater and recycling large-particle fluorite powder. Background Art

[0002] At present, the treatment methods of fluorine-containing waste liquid mainly include chemical precipitation, adsorption, membrane separation, etc. Chemical precipitation is a more commonly used method. By adding precipitants such as calcium salts to the fluorine-containing waste liquid, fluoride ions react with calcium ions to form calcium fluoride precipitates, thereby achieving the removal and recovery of fluoride ions. However, the fluorite powder precipitate obtained by the traditional chemical precipitation method has a small particle size, usually in the micron or even nanometer range. Small-particle calcium fluoride precipitates have problems such as difficulty in filtration, slow sedimentation rate, and low separation efficiency, which increases the subsequent processing cost and operational difficulty. Using recycled fluorite powder instead of fluorite ore powder to produce hydrofluoric acid has problems such as powder leakage and production line blockage.

[0003] To address the problem of small-particle fluorite precipitation, existing technologies attempt to increase the particle size by adjusting precipitation reaction conditions, such as changing the reaction temperature, pH value, and the amount of precipitant added. However, these improvements have been less than ideal. Furthermore, these improvements often affect the purity of the calcium fluoride, resulting in unstable quality of the recovered calcium fluoride product, making it difficult to meet the quality requirements of fluorite powder for industrial production.

[0004] To address the above-mentioned issues, a Chinese invention patent with authorization publication number CN116588963B discloses a method for recovering large-particle calcium fluoride from fluoride-containing wastewater. The method comprises: removing impurities from fluoride-containing acidic wastewater to obtain pure fluoride-containing wastewater; activating calcium fluoride seed crystals to obtain activated seed crystals; adding the activated seed crystals to the pure fluoride-containing wastewater, adding a calcium-containing regulator according to a preset calcium-fluoride ratio, and then adding a crystal growth promoter at a preset mass ratio to obtain a reaction solution; adjusting the pH of the reaction solution at a preset reaction temperature, stirring, and then settling, filtering, and drying to obtain large-particle calcium fluoride. The amount of activated seed crystals added is 5 to 10 times the fluoride ion concentration in the pure fluoride-containing wastewater. The method ensures that crystals in the activated seed crystals gradually grow and precipitate sufficient calcium fluoride, forming a large-particle calcium fluoride product, thereby recovering fluoride from fluoride-containing acidic wastewater while recovering a high-quality calcium fluoride product. However, the purity and particle size of the calcium fluoride recovered by this method still need to be further improved.

[0005] It can be seen that it is necessary to seek more effective methods for treating fluorine-containing wastewater and recycling large-particle fluorite powder to recover large-particle fluorite powder with high purity and large particle size. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for treating fluorine-containing wastewater and recycling large-particle fluorite powder with high purity and large particle size, so as to better apply it to the AHF production line. The method has a high pollutant removal rate.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, comprising the following steps:

[0008] Step S1, raw material preparation: prepare a calcium hydroxide slurry with a mass percentage concentration of 15%-30% of a calcium-containing substance; prepare a NaOH solution with a mass percentage concentration of 0.1%-1%;

[0009] Step S2, seed activation: Take fluorite powder seed crystals, place them in a dilute hydrochloric acid solution with a mass fraction of 3%-8% for 2-4 hours, then repeatedly rinse with deionized water until neutral, then place the seed crystals in a seed crystal activator solution, after energy field treatment, take out the seed crystals and dry them for later use;

[0010] Step S3, impurity removal treatment of fluorine-containing wastewater: Filter the fluorine-containing wastewater to remove large particles of impurities, then add a composite treatment agent thereto, mix evenly, and let it settle for 30-60 minutes to allow flocs to settle to the bottom of the water, then separate the supernatant from the sediment by filtration to obtain preliminarily treated fluorine-containing wastewater;

[0011] Step S4, precipitation reaction: using the NaOH solution described in step S1 as a reaction base liquid, adding the activated seed crystals prepared in step S2 thereto, starting stirring to uniformly disperse the seed crystals in the base liquid; using a peristaltic pump to simultaneously dropwise add the fluorine-containing wastewater obtained by the preliminary treatment in step S3 and the calcium hydroxide slurry prepared in step S1; and simultaneously controlling the dropwise addition of the fluorine-containing wastewater and the calcium hydroxide slurry within 1.5-4 hours depending on the concentration of the fluorine-containing wastewater. After the dropwise addition is completed, adding a crystal growth promoter, and continuing stirring for 0.5-1 hour to fully allow the calcium fluoride precipitation reaction to proceed;

[0012] Step S5, subsequent treatment: filtering the reaction solution through a vacuum drum filter; washing the filter cake obtained by filtration with deionized water 3-6 times, and then drying it in a vacuum drying oven at 80-90° C. to constant weight to obtain large-particle high-purity fluorite powder.

[0013] Preferably, the calcium-containing substance in step S1 is at least one of calcium hydroxide and calcium oxide.

[0014] Preferably, the particle size of the fluorite powder seed crystals in step S2 is 50-80 μm.

[0015] Preferably, the seed crystal activator solution in step S2 comprises the following components in parts by weight: 0.1-0.3 parts of lanthanum nitrate, 0.3-0.6 parts of cerium nitrate, 0.2-0.5 parts of polyethylene glycol, 0.1-0.2 parts of amino acid, 0.1-0.3 parts of amphoteric organic ion salt, and 100 parts of water.

[0016] Preferably, the polyethylene glycol is polyethylene glycol PEG-1500; the amino acid is glycine; and the amphoteric organic ion salt is 1-benzylpyridine-3-carboxylate.

[0017] Preferably, the energy field treatment time in step S2 is 20-30 minutes; the energy field is at least one of ultrasound, microwave, and steady magnetic field; the frequency of the ultrasound is 140-180kHz, and the power is 200-300W; the frequency of the microwave treatment is 2.5-3.5GHz, and the power is 800-1500W; the magnetic field strength of the steady magnetic field is 8000-15000Gs.

[0018] Preferably, the mass ratio of the seed crystal to the seed crystal activator solution in step S2 is 1:(3-5).

[0019] Preferably, the composite treatment agent in step S3 is a mixture of polyferric sulfate, strong acid cation exchange resin, and polyacrylamide in a mass ratio of 3:(0.8-1.2):1; the strong acid cation exchange resin is strong acid cation exchange resin 001X7, provided by Basler Chemical Technology (Tianjin) Co., Ltd.; and the polyacrylamide is polyacrylamide A556PWG.

[0020] Preferably, the mass ratio of the composite treatment agent to the fluorine-containing wastewater is (0.3-0.5):1000.

[0021] Preferably, the mass of the reaction bottom liquid in step S4 is 15%-25% of the mass of the fluorine-containing wastewater after preliminary treatment, and the amount of the activated seed crystal added is 3%-8% of the amount of CaF2 generated.

[0022] Preferably, the molar flow rate of fluoride ions in the fluoride-containing wastewater after the preliminary treatment in step S4 is twice the molar flow rate of calcium ions in the calcium hydroxide slurry.

[0023] Preferably, the dripping in step S4 is carried out in a variable speed dripping manner of first slow and then fast, and the reaction temperature is maintained at 30-45°C during the dripping process.

[0024] Preferably, the crystal growth promoter in step S4 is a mixture of aminotrimethylenephosphonic acid and glycine in a mass ratio of 1:(0.8-1.2).

[0025] Preferably, the amount of the crystal growth promoter added in step S4 is 0.05‰ -0.2‰ of the mass of the fluorine-containing wastewater after preliminary treatment.

[0026] Preferably, the operating vacuum degree of the vacuum drum filter in step S5 is -0.06 to -0.08 MPa.

[0027] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0028] (1) The method disclosed in the present invention for treating fluorine-containing wastewater and recycling large-particle fluorite powder is to construct a large number of active sites on the surface of the seed crystals by immersing the seed crystals in dilute hydrochloric acid and synergistically activating the seed crystals with a seed activator, thereby providing extremely favorable nucleation conditions for the growth of calcium fluoride crystals. The seed crystal activator solution comprises the following components in parts by weight: 0.1-0.3 parts of lanthanum nitrate, 0.3-0.6 parts of cerium nitrate, 0.2-0.5 parts of polyethylene glycol, 0.1-0.2 parts of amino acids, 0.1-0.3 parts of amphoteric organic ion salts, and 100 parts of water. Through the mutual cooperation and joint action of the components, the activity of the fluorite powder seed crystals can be effectively improved, thereby promoting the production of large-particle, high-purity fluorite powder. Rare earth metal ions promote crystal nucleation and growth, polyethylene glycol improves mass transfer and crystal morphology, and amino acids and amphoteric organic ion salts enhance the ability to complex and regulate impurity ions. The combination of multiple functions not only improves the activity of the seed crystal, but also purifies the reaction environment, reduces the impact of impurities, and achieves comprehensive optimization of crystal growth. Compared with single-function activators, it can more effectively improve the particle size and purity of fluorite powder. Traditional seed crystal activators have a single component or lack synergy, while this formula scientifically combines multiple ingredients such as lanthanum nitrate and cerium nitrate. Lanthanum nitrate and cerium nitrate provide rare earth metal ions, which can change the electronic structure and active sites on the surface of the seed crystal; polyethylene glycol adjusts the solution viscosity and surface tension, optimizing ion diffusion and the crystal growth environment; amino acids and amphoteric organic ion salts interact with the seed crystal and solution ions through special functional groups. The components synergistically form a unique activation system, promoting the improvement of seed crystal activity from multiple dimensions.

[0029] (2) The method disclosed in the present invention for treating fluorine-containing wastewater and recycling large-particle fluorite powder uses an innovative composite treatment agent to pre-deeply purify the fluorine-containing waste liquid, thereby greatly optimizing the reaction environment. The composite treatment agent is composed of a mixture of polyferric sulfate, a strong acid cation exchange resin, and polyacrylamide in a mass ratio of 3: (0.8-1.2): 1. Through such a formula design, the various components work synergistically to efficiently remove suspended particles and organic pollutants in the fluorine-containing waste liquid, and can effectively reduce the negative impact on fluorine recovery during impurity removal; significantly reduce the impact of impurities on calcium fluoride precipitation; and at the same time, add a crystal growth promoter to further regulate the crystal growth rate and direction, so that the particle size of the obtained fluorite powder is significantly increased, greatly improving the separation performance of the precipitation.

[0030] (3) The present invention discloses a method for treating fluorine-containing wastewater and recycling large-particle fluorite powder. The crystal growth promoter is a mixture of aminotrimethylenephosphonic acid and glycine in a mass ratio of 1:(0.8-1.2). Aminotrimethylenephosphonic acid has excellent complexing properties and easily forms stable complexes with impurity ions such as magnesium and iron in the solution, reducing the interference of impurity ions on the growth of calcium fluoride crystals and reducing the probability of impurities entering the crystal lattice, thereby improving the purity of fluorite powder. Glycine molecules contain active functional groups such as amino and carboxyl groups, which can improve the surface activity of the seed crystals through chemical bonding with the surface of the seed crystals, promote the nucleation and growth of calcium fluoride crystals on the seed crystal surface, and increase the crystal growth rate. The two are mixed in a mass ratio of 1:(0.8-1.2) to produce a synergistic effect, making the effect of promoting crystal growth and improving purity far better than using either substance alone, breaking through the limitations of the traditional single promoter. The promoter mixed in this ratio can accurately control the growth direction and rate of calcium fluoride crystals. The adsorption of aminotrimethylenephosphonic acid on the crystal surface has a certain selectivity and can inhibit the growth of certain crystal faces; glycine can promote the growth of specific crystal faces. The combination of the two can prompt calcium fluoride crystals to grow in a direction that is conducive to the formation of large particle size, obtaining fluorite powder particles with uniform size and large particle size.

[0031] (4) The method disclosed in the present invention for treating fluorine-containing wastewater and recycling large-particle fluorite powder adopts energy field treatment, wherein the energy field is at least one of ultrasound, microwave, and a steady magnetic field. Energy field treatment can greatly improve the efficiency of the activation process. At the same time, the action of the energy field makes the activator more uniform on the surface and inside the seed crystal, avoiding the problems of localized insufficient or excessive activation that may occur in traditional immersion methods, ensuring the consistency of the overall activity of the seed crystal, facilitating the uniform growth of subsequent calcium fluoride crystals, and thus improving the stability of the quality of the fluorite powder product.

[0032] (5) The method for treating fluorine-containing wastewater and recycling large-particle fluorite powder disclosed in the present invention has a mass percentage concentration of 15%-30% in step S1. On the one hand, if the slurry is too thin, the wastewater discharge will increase. On the other hand, if the slurry concentration is too high, the calcium hydroxide will not be dispersed well enough, and the generated fluorite powder will easily cover the calcium hydroxide, resulting in reduced purity. The mass percentage concentration of the NaOH solution used as the reaction base liquid is 0.1%-1%. If the concentration is too low, it is necessary to increase the amount of base liquid or reduce the feeding rate of fluorine-containing wastewater to ensure the generation of larger particle size CaF2. If the concentration is too high, the OH in the base liquid will - The higher the ion concentration, the lower the F - With Ca 2+The selectivity of the reaction leads to a decrease in the purity of the generated fluorite powder. The mass of the reaction bottom liquid is 15%-25% of the mass of the fluorine-containing wastewater after preliminary treatment. If the amount of bottom liquid is too small, there will be too many nucleation points of CaF2 generated by the reaction, reducing the particle size; if the amount of bottom liquid is too large, the amount of wastewater generated will increase significantly, increasing the cost of wastewater treatment. The amount of activated seed added is 3%-8% of the amount of CaF2 generated. If it is too small, there will not be enough nucleation points, making the precipitated particles finer; if it is too large, the contribution to increasing the particle size of the recovered fluorite powder is limited, and at the same time, it causes waste of fluorite powder. The dripping described in step S4 adopts a variable speed dripping method of first slow and then fast to ensure the instantaneous F in the reaction system. - and Ca 2+ In a relatively stable state. Because the amount of bottom liquid in the early reaction system is small, slowly adding fluorine-containing wastewater and calcium hydroxide slurry can make the F in the system - and Ca 2+ At a lower concentration, the nucleation point is reduced, and the speed becomes faster in the later stage because the addition of fluorine-containing wastewater and calcium hydroxide slurry significantly increases the amount of bottom liquid. Instantaneous addition of more fluorine-containing wastewater and calcium hydroxide slurry can ensure the same F as the initial - and Ca 2+ Same concentration. DETAILED DESCRIPTION

[0033] The following description is intended to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are merely examples, and those skilled in the art may conceive of other obvious variations.

[0034] Example 1: A method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, comprising the following steps:

[0035] Step S1, raw material preparation: prepare a calcium hydroxide slurry with a mass percentage concentration of 15% by weight of a calcium-containing substance; prepare a NaOH solution with a mass percentage concentration of 0.1%;

[0036] Step S2, seed activation: Take fluorite powder seed crystals, place them in a 3% by mass dilute hydrochloric acid solution and soak them for 2 hours, then rinse them repeatedly with deionized water until neutral, then place the seed crystals in a seed crystal activator solution, after energy field treatment, take out the seed crystals and dry them for later use;

[0037] Step S3, impurity removal treatment of fluorine-containing wastewater: Filter the fluorine-containing wastewater to remove large particles of impurities, then add the composite treatment agent thereto, mix evenly, and let it settle for 30 minutes to allow the flocs to settle to the bottom of the water, and then separate the supernatant and the sediment by filtration to obtain the preliminarily treated fluorine-containing wastewater;

[0038] Step S4, precipitation reaction: using the NaOH solution described in step S1 as a reaction base liquid, adding the activated seed crystals prepared in step S2 thereto, starting stirring to uniformly disperse the seed crystals in the base liquid; using a peristaltic pump to simultaneously dropwise add the fluorine-containing wastewater obtained by the preliminary treatment in step S3 and the calcium hydroxide slurry prepared in step S1; and simultaneously controlling the dropwise addition of the fluorine-containing wastewater and the calcium hydroxide slurry within 1.5 hours based on the concentration of the fluorine-containing wastewater. After the dropwise addition is completed, adding a crystal growth promoter, and continuing stirring for 0.5 hours to allow the calcium fluoride precipitation reaction to proceed fully;

[0039] Step S5, subsequent treatment: filtering the reaction solution through a vacuum drum filter; washing the filter cake obtained by filtration with deionized water three times, and then drying it in a vacuum drying oven at 80° C. to constant weight to obtain large-particle high-purity fluorite powder.

[0040] The calcium-containing substance in step S1 is calcium hydroxide; the particle size of the fluorite powder seed crystal in step S2 is 50 μm; the seed crystal activator solution in step S2 includes the following components in parts by weight: 0.1 parts of lanthanum nitrate, 0.3 parts of cerium nitrate, 0.2 parts of polyethylene glycol, 0.1 parts of amino acid, 0.1 parts of amphoteric organic ion salt, and 100 parts of water; the polyethylene glycol is polyethylene glycol PEG-1500; the amino acid is glycine; and the amphoteric organic ion salt is 1-benzylpyridine-3-carboxylate.

[0041] The energy field treatment time in step S2 is 20 minutes; the energy field is ultrasonic; the frequency of the ultrasonic wave is 140 kHz and the power is 200 W; the mass ratio of the seed crystal to the seed crystal activator solution in step S2 is 1:3; the composite treatment agent in step S3 is prepared by mixing polyferric sulfate, strong acid cation exchange resin, and polyacrylamide in a mass ratio of 3:0.8:1; the strong acid cation exchange resin is strong acid cation exchange resin 001X7, provided by Basler Chemical Technology (Tianjin) Co., Ltd.; and the polyacrylamide is polyacrylamide A556PWG.

[0042] The mass ratio of the composite treatment agent to the fluorine-containing wastewater is 0.3:1000; the mass of the reaction base liquid in step S4 is 15% of the mass of the fluorine-containing wastewater after preliminary treatment, and the amount of the activated seed crystal added is 3% of the amount of CaF2 generated; the molar flow rate of fluoride ions in the fluorine-containing wastewater after preliminary treatment in step S4 is twice the molar flow rate of calcium ions in the calcium hydroxide slurry; the dropwise addition in step S4 adopts a variable speed dropwise addition method of first slow and then fast, and the reaction temperature is maintained at 30°C during the dropwise addition process; the crystal growth promoter in step S4 is a mixture of aminotrimethylenephosphonic acid and glycine in a mass ratio of 1:0.8; the amount of the crystal growth promoter added in step S4 is 0.05‰ of the mass of the fluorine-containing wastewater after preliminary treatment; the operating vacuum degree of the vacuum drum filter in step S5 is -0.06MPa.

[0043] Example 2: A method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, comprising the following steps:

[0044] Step S1, raw material preparation: prepare a calcium hydroxide slurry with a mass percentage concentration of 20% by weight of a calcium-containing substance; prepare a NaOH solution with a mass percentage concentration of 0.3%;

[0045] Step S2, seed activation: Take fluorite powder seed crystals, place them in a 4% by mass dilute hydrochloric acid solution and soak them for 2.5 hours, then rinse them repeatedly with deionized water until neutral, then place the seed crystals in a seed crystal activator solution, after energy field treatment, take out the seed crystals and dry them for later use;

[0046] Step S3, impurity removal treatment of fluorine-containing wastewater: Filter the fluorine-containing wastewater to remove large particles of impurities, then add a composite treatment agent thereto, mix evenly, and let it settle for 40 minutes to allow flocs to settle to the bottom of the water, and then separate the supernatant and the sediment by filtration to obtain preliminarily treated fluorine-containing wastewater;

[0047] Step S4, precipitation reaction: using the NaOH solution described in step S1 as a reaction base liquid, adding the activated seed crystals prepared in step S2 thereto, starting stirring to uniformly disperse the seed crystals in the base liquid; using a peristaltic pump to simultaneously dropwise add the fluorine-containing wastewater obtained by the preliminary treatment in step S3 and the calcium hydroxide slurry prepared in step S1; and controlling the dropwise addition of the fluorine-containing wastewater and the calcium hydroxide slurry within 2 hours depending on the concentration of the fluorine-containing wastewater. After the dropwise addition is completed, adding a crystal growth promoter, and continuing stirring for 0.7 hours to allow the calcium fluoride precipitation reaction to proceed fully;

[0048] Step S5, subsequent treatment: the reaction solution is filtered through a vacuum drum filter; the filter cake obtained by filtration is washed with deionized water 4 times, and then placed in a vacuum drying oven at 83° C. to dry to constant weight to obtain large-particle high-purity fluorite powder.

[0049] The calcium-containing substance in step S1 is calcium oxide; the particle size of the fluorite powder seed crystal in step S2 is 60 μm; the seed crystal activator solution in step S2 includes the following components in parts by weight: 0.15 parts of lanthanum nitrate, 0.4 parts of cerium nitrate, 0.3 parts of polyethylene glycol, 0.13 parts of amino acid, 0.15 parts of amphoteric organic ion salt, and 100 parts of water; the polyethylene glycol is polyethylene glycol PEG-1500; the amino acid is glycine; and the amphoteric organic ion salt is 1-benzylpyridine-3-carboxylate.

[0050] The energy field treatment time in step S2 is 23 minutes; the energy field is microwave; the frequency of the microwave treatment is 2.8 GHz and the power is 1000 W; the mass ratio of the seed crystal and the seed crystal activator solution in step S2 is 1:3.5; the composite treatment agent in step S3 is composed of polyferric sulfate, strong acid cation exchange resin, and polyacrylamide mixed in a mass ratio of 3:0.9:1; the strong acid cation exchange resin is strong acid cation exchange resin 001X7, provided by Basler Chemical Technology (Tianjin) Co., Ltd.; the polyacrylamide is polyacrylamide A556PWG; and the mass ratio of the composite treatment agent to fluorine-containing wastewater is 0.35:1000.

[0051] The mass of the reaction base liquid in step S4 is 18% of the mass of the fluorine-containing wastewater after preliminary treatment, and the amount of the activated seed crystal added is 4% of the amount of CaF2 generated; the molar flow rate of fluoride ions in the fluorine-containing wastewater after preliminary treatment in step S4 is twice the molar flow rate of calcium ions in the calcium hydroxide slurry; the dropwise addition in step S4 adopts a variable speed dropwise addition method of first slow and then fast, and the reaction temperature is maintained at 35°C during the dropwise addition process; the crystal growth promoter in step S4 is a mixture of aminotrimethylenephosphonic acid and glycine in a mass ratio of 1:0.9; the amount of the crystal growth promoter added in step S4 is 0.09‰ of the mass of the fluorine-containing wastewater after preliminary treatment; the operating vacuum degree of the vacuum drum filter in step S5 is -0.065MPa.

[0052] Example 3: A method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, comprising the following steps:

[0053] Step S1, raw material preparation: prepare a calcium hydroxide slurry with a mass percentage concentration of 22% by weight of a calcium-containing substance; prepare a NaOH solution with a mass percentage concentration of 0.6%;

[0054] Step S2, seed activation: Take fluorite powder seed crystals, place them in a 5% by mass dilute hydrochloric acid solution and soak them for 3 hours, then rinse them repeatedly with deionized water until neutral, then place the seed crystals in a seed crystal activator solution, after energy field treatment, take out the seed crystals and dry them for later use;

[0055] Step S3, impurity removal treatment of fluorine-containing wastewater: Filter the fluorine-containing wastewater to remove large particles of impurities, then add a composite treatment agent thereto, mix evenly, and let it settle for 45 minutes to allow flocs to settle to the bottom of the water, then separate the supernatant from the sediment by filtration to obtain preliminarily treated fluorine-containing wastewater;

[0056] Step S4, precipitation reaction: using the NaOH solution described in step S1 as a reaction base liquid, adding the activated seed crystals prepared in step S2 thereto, starting stirring to uniformly disperse the seed crystals in the base liquid; using a peristaltic pump to simultaneously dropwise add the fluorine-containing wastewater obtained by the preliminary treatment in step S3 and the calcium hydroxide slurry prepared in step S1; and simultaneously controlling the dropwise addition of the fluorine-containing wastewater and the calcium hydroxide slurry within 3 hours depending on the concentration of the fluorine-containing wastewater. After the dropwise addition is completed, adding a crystal growth promoter, and continuing stirring for 0.7 hours to allow the calcium fluoride precipitation reaction to proceed fully;

[0057] Step S5, subsequent treatment: the reaction solution is filtered through a vacuum drum filter; the filter cake obtained by filtration is washed with deionized water 5 times, and then placed in a vacuum drying oven at 85° C. to dry to constant weight to obtain large-particle high-purity fluorite powder.

[0058] The calcium-containing substance in step S1 is a mixture of calcium hydroxide and calcium oxide in a mass ratio of 1:3; the particle size of the fluorite powder seed crystal in step S2 is 65 μm; the seed crystal activator solution in step S2 includes the following components in parts by weight: 0.2 parts of lanthanum nitrate, 0.45 parts of cerium nitrate, 0.35 parts of polyethylene glycol, 0.15 parts of amino acid, 0.2 parts of amphoteric organic ion salt, and 100 parts of water; the polyethylene glycol is polyethylene glycol PEG-1500; the amino acid is glycine; and the amphoteric organic ion salt is 1-benzylpyridine-3-carboxylate.

[0059] The energy field treatment time in step S2 is 25 minutes; the energy field is a steady magnetic field; the magnetic field strength of the steady magnetic field is 12000 Gs; the mass ratio of the seed crystal and the seed crystal activator solution in step S2 is 1:4; the composite treatment agent in step S3 is composed of polyferric sulfate, strong acid cation exchange resin, and polyacrylamide mixed in a mass ratio of 3:1:1; the strong acid cation exchange resin is strong acid cation exchange resin 001X7, provided by Basler Chemical Technology (Tianjin) Co., Ltd.; the polyacrylamide is polyacrylamide A556PWG; the mass ratio of the composite treatment agent to fluorine-containing wastewater is 0.4:1000.

[0060] The mass of the reaction base liquid in step S4 is 20% of the mass of the fluorine-containing wastewater after preliminary treatment, and the amount of the activated seed crystal added is 6% of the amount of CaF2 generated; the molar flow rate of fluoride ions in the fluorine-containing wastewater after preliminary treatment in step S4 is twice the molar flow rate of calcium ions in the calcium hydroxide slurry; the dropwise addition in step S4 adopts a variable speed dropwise addition method of first slow and then fast, and the reaction temperature is maintained at 38°C during the dropwise addition process; the crystal growth promoter in step S4 is a mixture of aminotrimethylenephosphonic acid and glycine in a mass ratio of 1:1; the amount of the crystal growth promoter added in step S4 is 0.12‰ of the mass of the fluorine-containing wastewater after preliminary treatment; the operating vacuum degree of the vacuum drum filter in step S5 is -0.07MPa.

[0061] Example 4: A method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, comprising the following steps:

[0062] Step S1, raw material preparation: prepare a calcium hydroxide slurry with a mass percentage concentration of 28% by weight of a calcium-containing substance; prepare a NaOH solution with a mass percentage concentration of 0.9%;

[0063] Step S2, seed activation: Take fluorite powder seed crystals, place them in a 7% by mass dilute hydrochloric acid solution and soak them for 3.5 hours, then repeatedly rinse them with deionized water until they are neutral, then place the seed crystals in a seed crystal activator solution, after energy field treatment, take out the seed crystals and dry them for later use;

[0064] Step S3, impurity removal treatment of fluorine-containing wastewater: Filter the fluorine-containing wastewater to remove large particles of impurities, then add the composite treatment agent thereto, mix evenly, and let it settle for 55 minutes to allow the flocs to settle to the bottom of the water, and then separate the supernatant and the sediment by filtration to obtain the preliminarily treated fluorine-containing wastewater;

[0065] Step S4, precipitation reaction: using the NaOH solution described in step S1 as a reaction base liquid, adding the activated seed crystals prepared in step S2 thereto, starting stirring to uniformly disperse the seed crystals in the base liquid; using a peristaltic pump to simultaneously dropwise add the fluorine-containing wastewater obtained by the preliminary treatment in step S3 and the calcium hydroxide slurry prepared in step S1; and controlling the dropwise addition of the fluorine-containing wastewater and the calcium hydroxide slurry to be completed within 3.5 hours depending on the concentration of the fluorine-containing wastewater. After the dropwise addition is completed, adding a crystal growth promoter, and continuing stirring for 0.9 hours to allow the calcium fluoride precipitation reaction to proceed fully;

[0066] Step S5, subsequent treatment: the reaction solution is filtered through a vacuum drum filter; the filter cake obtained by filtration is washed with deionized water 5 times, and then placed in a vacuum drying oven at 88° C. to dry to constant weight to obtain large-particle high-purity fluorite powder.

[0067] The calcium-containing substance in step S1 is calcium hydroxide; the particle size of the fluorite powder seed crystal in step S2 is 70 μm; the seed crystal activator solution in step S2 includes the following components in parts by weight: 0.25 parts of lanthanum nitrate, 0.55 parts of cerium nitrate, 0.45 parts of polyethylene glycol, 0.18 parts of amino acid, 0.25 parts of amphoteric organic ion salt, and 100 parts of water; the polyethylene glycol is polyethylene glycol PEG-1500; the amino acid is glycine; the amphoteric organic ion salt is 1-benzylpyridine-3-carboxylate; the energy field treatment time in step S2 is 28 minutes; the energy field includes ultrasound, microwave, and steady magnetic field; the frequency of the ultrasound is 170 kHz and the power is 290 W; the frequency of the microwave treatment is 3.3 GHz and the power is 1400 W; the magnetic field strength of the steady magnetic field is 14000 Gs; the mass ratio of the seed crystal to the seed crystal activator solution in step S2 is 1:4.5.

[0068] The composite treatment agent in step S3 is a mixture of polyferric sulfate, strong acid cation exchange resin, and polyacrylamide in a mass ratio of 3:1.1:1; the strong acid cation exchange resin is strong acid cation exchange resin 001X7, provided by Basler Chemical Technology (Tianjin) Co., Ltd.; the polyacrylamide is polyacrylamide A556PWG; the mass ratio of the composite treatment agent to the fluorine-containing wastewater is 0.45:1000; the mass of the reaction base liquid in step S4 is 23% of the mass of the fluorine-containing wastewater after preliminary treatment, and the amount of the activated seed crystal added is the amount of CaF2 generated. 7%; the molar flow rate of fluoride ions in the fluoride-containing wastewater after preliminary treatment in step S4 is twice the molar flow rate of calcium ions in the calcium hydroxide slurry; the dropwise addition in step S4 adopts a variable speed dropwise addition method of first slow and then fast, and the reaction temperature is maintained at 43°C during the dropwise addition process; the crystal growth promoter in step S4 is a mixture of aminotrimethylenephosphonic acid and glycine in a mass ratio of 1:1.1; the amount of the crystal growth promoter added in step S4 is 0.18‰ of the mass of the fluoride-containing wastewater after preliminary treatment; the operating vacuum degree of the vacuum drum filter in step S5 is -0.075MPa.

[0069] Example 5: A method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, comprising the following steps:

[0070] Step S1, raw material preparation: prepare a calcium hydroxide slurry with a mass percentage concentration of 30% by weight of a calcium-containing substance; prepare a NaOH solution with a mass percentage concentration of 1%;

[0071] Step S2, seed activation: Take fluorite powder seed crystals, place them in a dilute hydrochloric acid solution with a mass fraction of 8% for 4 hours, then repeatedly rinse with deionized water until neutral, then place the seed crystals in a seed crystal activator solution, after energy field treatment, take out the seed crystals and dry them for later use;

[0072] Step S3, impurity removal treatment of fluorine-containing wastewater: Filter the fluorine-containing wastewater to remove large particles of impurities, then add a composite treatment agent thereto, mix evenly, and let it settle for 60 minutes to allow flocs to settle to the bottom of the water, then separate the supernatant from the sediment by filtration to obtain preliminarily treated fluorine-containing wastewater;

[0073] Step S4, precipitation reaction: using the NaOH solution described in step S1 as a reaction base liquid, adding the activated seed crystals prepared in step S2 thereto, starting stirring to uniformly disperse the seed crystals in the base liquid; using a peristaltic pump to simultaneously dropwise add the fluorine-containing wastewater obtained by the preliminary treatment in step S3 and the calcium hydroxide slurry prepared in step S1; and simultaneously controlling the dropwise addition of the fluorine-containing wastewater and the calcium hydroxide slurry within 4 hours depending on the concentration of the fluorine-containing wastewater. After the dropwise addition is completed, adding a crystal growth promoter, and continuing stirring for 1 hour to fully allow the calcium fluoride precipitation reaction to proceed;

[0074] Step S5, subsequent treatment: filtering the reaction solution through a vacuum drum filter; washing the filter cake obtained by filtration with deionized water 6 times, and then drying it in a vacuum drying oven at 90° C. to constant weight to obtain large-particle high-purity fluorite powder.

[0075] The calcium-containing substance in step S1 is calcium hydroxide; the particle size of the fluorite powder seed crystal in step S2 is 80 μm; the seed crystal activator solution in step S2 includes the following components in parts by weight: 0.3 parts of lanthanum nitrate, 0.6 parts of cerium nitrate, 0.5 parts of polyethylene glycol, 0.2 parts of amino acid, 0.3 parts of amphoteric organic ion salt, and 100 parts of water; the polyethylene glycol is polyethylene glycol PEG-1500; the amino acid is glycine; the amphoteric organic ion salt is 1-benzylpyridine-3-carboxylate; the energy field treatment time in step S2 is 30 minutes; the energy field includes ultrasound, microwave, and steady magnetic field; the frequency of the ultrasound is 180 kHz and the power is 300 W; the frequency of the microwave treatment is 3.5 GHz and the power is 1500 W; the magnetic field strength of the steady magnetic field is 15000 Gs; the mass ratio of the seed crystal to the seed crystal activator solution in step S2 is 1:5.

[0076] The composite treatment agent in step S3 is a mixture of polyferric sulfate, strong acid cation exchange resin, and polyacrylamide in a mass ratio of 3:1.2:1; the strong acid cation exchange resin is strong acid cation exchange resin 001X7, provided by Basler Chemical Technology (Tianjin) Co., Ltd.; the polyacrylamide is polyacrylamide A556PWG; the mass ratio of the composite treatment agent to the fluorine-containing wastewater is 0.5:1000; the mass of the reaction base liquid in step S4 is 25% of the mass of the fluorine-containing wastewater after preliminary treatment, and the amount of the activated seed crystal added is the amount of CaF2 generated. 8%; the molar flow rate of fluoride ions in the fluoride-containing wastewater after preliminary treatment in step S4 is twice the molar flow rate of calcium ions in the calcium hydroxide slurry; the dropwise addition in step S4 adopts a variable speed dropwise addition method of first slow and then fast, and the reaction temperature is maintained at 45°C during the dropwise addition process; the crystal growth promoter in step S4 is a mixture of aminotrimethylenephosphonic acid and glycine in a mass ratio of 1:1.2; the amount of the crystal growth promoter added in step S4 is 0.2‰ of the mass of the fluoride-containing wastewater after preliminary treatment; the operating vacuum degree of the vacuum drum filter in step S5 is -0.08MPa.

[0077] Comparative Example 1

[0078] This example provides a method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, which is basically the same as Example 1, except that lanthanum nitrate and amphoteric organic ion salts are not added to the seed activator solution, and strong acid cation exchange resin is not added to the composite treatment agent.

[0079] Comparative Example 2

[0080] This example provides a method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, which is basically the same as Example 1, except that the crystal growth promoter is sodium glycocholate, and immersion treatment is used instead of energy field treatment.

[0081] In order to further illustrate the beneficial technical effects of the methods for treating fluorine-containing wastewater and recycling large-particle fluorite powder involved in various embodiments of the present invention, relevant performance tests were conducted on the large-particle fluorite powder obtained by the methods for treating fluorine-containing wastewater and recycling large-particle fluorite powder involved in each example, and the fluorine-containing wastewater before and after treatment. The test results are shown in Table 1. The test method is as follows:

[0082] (1) Particle size detection: A laser particle size analyzer (Model: Malvern Mastersizer 3000) was used to measure the particle size distribution D90 of the prepared fluorite powder samples according to GB / T19077-2016 "Particle size analysis by laser diffraction method". The samples were dispersed in anhydrous ethanol and ultrasonically dispersed for 6 minutes before measurement. Each sample was measured four times and the average value was taken.

[0083] (2) Purity test: The purity of fluorite powder samples was tested using an X-ray fluorescence spectrometer (model: PANalytical Axios Max) in accordance with GB / T5195.1-2017 "Fluorite - Determination of calcium fluoride content - EDTA titration method". The samples were ground to a particle size of less than 74 μm and dried at 105°C for 2.5 h before measurement.

[0084] (3) Pollutant removal rate detection: An ion chromatograph (model: Dion ICS-5000+) was used to detect the fluoride ion concentration in the fluoride-containing wastewater before and after treatment in accordance with HJ 84-2016 "Determination of inorganic anions in water quality - Ion chromatography method" and the fluoride ion removal rate was calculated. Fluoride ion removal rate = (fluoride ion concentration before treatment - fluoride ion concentration after treatment) / fluoride ion concentration before treatment × 100%. A total organic carbon analyzer (model: Shimadzu TOC-L CPH) was used to detect the total organic carbon content in the fluoride-containing wastewater in accordance with HJ 501-2009 "Determination of total organic carbon in water quality - Combustion oxidation-non-dispersive infrared absorption method" and the pollutant removal rate was calculated. The fluoride-containing wastewater tested was pickling wastewater with a fluoride ion concentration of 120 mg / L discharged from the cold rolling section of a steel plant.

[0085] Table 1

[0086]

[0087] As can be seen from the above table, the methods for treating fluorine-containing wastewater and recycling large-particle fluorite powder involved in the embodiments of the present invention have higher fluoride ion and total organic carbon removal rates than the control example. The fluorite powder recycled has higher purity and larger particle size, and can be better applied to the AHF production line.

[0088] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for treating fluorine-containing wastewater and recycling large-particle fluorite powder, characterized in that: The steps include: Step S1, raw material preparation: prepare a calcium hydroxide slurry with a mass percentage concentration of 15%-30% of a calcium-containing substance; prepare a NaOH solution with a mass percentage concentration of 0.1%-1%; Step S2, seed activation: taking fluorite powder seed crystals, placing them in a dilute hydrochloric acid solution with a mass fraction of 3%-8% and soaking them for 2-4 hours, then repeatedly rinsing them with deionized water until neutral, and then placing the seed crystals in a seed crystal activator solution. After energy field treatment, the seed crystals are taken out and dried for later use; the seed crystal activator solution comprises the following components in parts by weight: 0.1-0.3 parts of lanthanum nitrate, 0.3-0.6 parts of cerium nitrate, 0.2-0.5 parts of polyethylene glycol, 0.1-0.2 parts of amino acids, 0.1-0.3 parts of amphoteric organic ion salts, and 100 parts of water; Step S3, impurity removal treatment of fluorine-containing wastewater: Filter the fluorine-containing wastewater to remove large particles of impurities, then add a composite treatment agent thereto, mix evenly, and let it settle for 30-60 minutes to allow flocs to settle to the bottom of the water, then separate the supernatant from the sediment by filtration to obtain preliminarily treated fluorine-containing wastewater; Step S4, precipitation reaction: using the NaOH solution described in step S1 as a reaction base liquid, adding the activated seed crystals prepared in step S2 thereto, starting stirring to uniformly disperse the seed crystals in the base liquid; using a peristaltic pump to simultaneously dropwise add the fluorine-containing wastewater obtained by the preliminary treatment in step S3 and the calcium hydroxide slurry prepared in step S1; and simultaneously controlling the dropwise addition of the fluorine-containing wastewater and the calcium hydroxide slurry within 1.5-4 hours depending on the concentration of the fluorine-containing wastewater. After the dropwise addition is completed, adding a crystal growth promoter, and continuing stirring for 0.5-1 hour to fully allow the calcium fluoride precipitation reaction to proceed; the crystal growth promoter is a mixture of aminotrimethylenephosphonic acid and glycine in a mass ratio of 1:(0.8-1.2); Step S5, subsequent treatment: filtering the reaction solution through a vacuum drum filter; washing the filter cake obtained by filtration with deionized water 3-6 times, and then drying it in a vacuum drying oven at 80-90° C. to constant weight to obtain large-particle high-purity fluorite powder.

2. The method for treating fluorine-containing wastewater and recovering large-particle fluorite powder as a resource according to claim 1, characterized in that: The calcium-containing substance in step S1 is at least one of calcium hydroxide and calcium oxide.

3. The method for treating fluorine-containing wastewater and recovering large-particle fluorite powder as a resource according to claim 1, characterized in that: The particle size of the fluorite powder seed crystals in step S2 is 50-80 μm.

4. The method for treating fluorine-containing wastewater and recycling large-particle fluorite powder according to claim 1, characterized in that: The polyethylene glycol is polyethylene glycol PEG-1500; the amino acid is glycine; and the amphoteric organic ion salt is 1-benzylpyridine-3-carboxylate.

5. The method for treating fluorine-containing wastewater and recycling large-particle fluorite powder according to claim 1, characterized in that: The energy field treatment in step S2 lasts for 20-30 minutes; the energy field is at least one of ultrasound, microwave, and a steady magnetic field; the frequency of the ultrasound is 140-180 kHz and the power is 200-300 W; the frequency of the microwave treatment is 2.5-3.5 GHz and the power is 800-1500 W; the magnetic field strength of the steady magnetic field is 8000-15000 Gs; The mass ratio of the seed crystal to the seed crystal activator solution in step S2 is 1:(3-5).

6. The method for treating fluorine-containing wastewater and recovering large-particle fluorite powder as a resource according to claim 1, characterized in that: The composite treatment agent in step S3 is prepared by mixing polyferric sulfate, strong acid cation exchange resin, and polyacrylamide in a mass ratio of 3:(0.8-1.2):1; the strong acid cation exchange resin is strong acid cation exchange resin 001X7; the polyacrylamide is polyacrylamide A556PWG; and the mass ratio of the composite treatment agent to the fluorine-containing wastewater is (0.3-0.5):1000.

7. The method for treating fluorine-containing wastewater and recovering large-particle fluorite powder as a resource according to claim 1, characterized in that: The mass of the reaction bottom liquid in step S4 is 15%-25% of the mass of the fluorine-containing wastewater after preliminary treatment, and the amount of the activated seed crystal added is 3%-8% of the amount of CaF2 generated; the molar flow rate of fluoride ions in the fluorine-containing wastewater after preliminary treatment in step S4 is twice the molar flow rate of calcium ions in the calcium hydroxide slurry.

8. The method for treating fluorine-containing wastewater and recycling large-particle fluorite powder according to claim 1, characterized in that: The dropwise addition in step S4 is carried out in a variable speed dropwise addition manner of first slow and then fast, and the reaction temperature is maintained at 30-45°C during the dropwise addition process; the amount of the crystal growth promoter added in step S4 is 0.05‰-0.2‰ of the mass of the fluorine-containing wastewater after preliminary treatment.

9. The method for treating fluorine-containing wastewater and recovering large-particle fluorite powder as a resource according to claim 1, characterized in that: The vacuum drum filter in step S5 operates at a vacuum degree of -0.06 to -0.08 MPa.

Images