A method for treating high-fluoride acidic wastewater based on flotation / seed crystal coupling method

Abstract

The present invention relates to the technical field of high-fluoride acidic wastewater treatment, and particularly to a method for treating high-fluoride acidic wastewater based on a flotation / seed crystal coupling method. The present invention improves an existing high-fluoride acidic wastewater treatment system by coupling sludge after ultrasonic flotation with actual high-fluoride acidic wastewater and using the flotation sludge as a seed crystal to increase the fluorine removal ratio in CaF2 precipitation. The steps include ultrasonic treatment, flotation treatment, acid washing and seed crystal coupling. The improved method designed by the present invention can basically dissociate CaCO3 impurities in the sludge, and couple the dissociated sludge with high-fluoride acidic wastewater to further purify the calcium fluoride sludge, so that the CaF2 content in the final product CaF2 sludge is increased to 92.72% without introducing a new calcium source. Moreover, compared with traditional calcium salt precipitation defluoridation, the present invention consumes less calcium salt for defluoridation under sludge seed crystal conditions, has better defluoridation effect, and the prepared CaF2 sludge can meet the acid-grade fluorite FC-93 standard.

Description

Technical Field

[0001] The present invention relates to the technical field of high-fluoride acidic wastewater treatment, and in particular to a method for treating high-fluoride acidic wastewater based on a flotation / seed crystal coupling method. Background Art

[0002] Fluorine chemical, photovoltaic, and glass manufacturing companies generate large amounts of fluorine-containing sludge and wastewater during their production processes. If not properly treated, these wastewater can cause environmental pollution. Fluorine-containing sludge primarily consists of CaF2, a scarce, non-renewable resource in China. Therefore, fluorine-containing sludge has value in resource recovery.

[0003] Due to the stable production process and high purity of raw materials, the sludge generated by the photovoltaic industry usually has a high content of CaF2 and the types of impurities it contains are relatively stable, mainly CaCO3 and SiO2. It is possible to consider purifying fluorine-containing sludge as a substitute for fluorite.

[0004] Based on the characteristics of flotation technology that is efficient and economical, and the process is easy to scale up, as well as the advantages of the seed crystal method in inducing crystallization to produce high-quality calcium fluoride sludge, the inventors decided to design a method for treating high-fluoride acidic wastewater based on a flotation / seed crystal coupling method. By coupling the sludge after ultrasonic flotation with actual high-fluoride acidic wastewater, the flotation sludge is used as a seed crystal to increase the fluorine removal rate in the CaF2 precipitation, and a specific plan for the resource utilization of CaF2 sludge is designed, providing a technical reference for the large-scale resource utilization of CaF2 sludge in the photovoltaic industry. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for treating high-fluoride acidic wastewater based on a flotation / seed crystal coupling method, comprising the following steps:

[0006] collecting wastewater through a wastewater collection system, the wastewater collection system comprising a first regulating tank for collecting high-fluorine acidic wastewater, a second regulating tank for collecting low-fluorine dilute acid wastewater and dilute alkaline wastewater, a third regulating tank for collecting concentrated alkaline wastewater, and a fourth regulating tank for collecting domestic wastewater;

[0007] The wastewater collected from the first regulating tank, the second regulating tank and the third regulating tank is sequentially subjected to flocculation and impurity removal treatment, nitrification treatment and concentration treatment in the pretreatment system, the biochemical system and the terminal treatment system to obtain fluorine-containing sludge;

[0008] The wastewater collected from the fourth regulating tank is sequentially subjected to nitrification and concentration treatment in the biochemical system and the terminal treatment system to obtain fluorine-containing sludge;

[0009] The high-fluoride acidic wastewater is then collected from the first regulating tank for future use;

[0010] The present invention is an improvement on the above method in that it uses a flotation / seed crystal coupling method to treat fluorine-containing sludge and high-fluorine acidic wastewater, and the specific steps are as follows:

[0011] S1. Ultrasonic treatment: First, fluorine-containing sludge is prepared into slurry, then inhibitors and capture agents are added to the slurry, and finally ultrasonic treatment is used to obtain pretreated slurry;

[0012] S2, flotation treatment: using flotation process to treat the pre-treated sludge in S1 and separate the flotation sludge;

[0013] S3, acid washing and seed coupling:

[0014] S3-1. First, collect the flotation sludge in S2 as a seed crystal. Then, add the high-fluoride acidic wastewater from the first regulating tank to the flotation sludge while stirring to obtain a pickling sludge. Finally, add calcium salt to the pickling sludge and mix well to obtain System A.

[0015] S3-2, after the acid washing reaction of system A in S3-1 is completed, the low-fluorine dilute acid wastewater generated is input into the second regulating tank, and the generated CaF2 sludge is input into the sedimentation tank;

[0016] When the processes in S1 to S3 meet the following constraints, the sludge CaF2 with a liquid-solid ratio greater than 50 can reach the target fluorite standard under the premise of reducing the amount of calcium source added. The constraints are:

[0017] In S2: the mass percentages of CaF2, CaCO3 and SiO2 in the flotation sludge are 75-76%, 19-20% and 4-5% respectively;

[0018] In S3: n is the multiplication coefficient and n∈R + , then the amount of high-fluoride acidic wastewater added to system A is n[25,30]mL, the amount of flotation sludge added is n[0.5,0.6]g; the amount of calcium salt added makes the molar ratio of calcium and fluorine in system A be 1:2;

[0019] The pH of system A is 3-4, and the pickling reaction time is 30-40 minutes.

[0020] Furthermore, the water quality data of high-fluoride acidic wastewater are: pH = 2-1, COD content of 180-200 mg / L, F- content of 18,000-20,000 mg / L, TP content of 74-80 mg / L, conductivity of 29-35 mS / cm, sulfate content of 130-150 mg / L, and chloride content of 170-200 mg / L.

[0021] Description: The industrial wastewater treated by the process of this invention has three characteristics:

[0022] 1. High fluoride ion content: The fluoride ions in the wastewater mainly come from the high-fluoride acidic wastewater produced by the use of hydrofluoric acid in the production process, with a fluoride ion content of up to 18,000 mg / L; followed by low-fluoride dilute acid wastewater, with a fluoride ion content of 800 mg / L, and dilute alkaline wastewater with a fluoride ion content of 50 mg / L. The rest of the wastewater basically does not contain fluoride ions;

[0023] 2. High ammonia nitrogen content: The total nitrogen in the wastewater mainly comes from the ammonia nitrogen in the washing wastewater, with an average ammonia nitrogen content of 4000 mg / L;

[0024] 3. Low COD: The organic pollutants in the wastewater mainly come from alcohol organic matter produced during the production process. Due to the low discharge frequency, the COD and BOD contents of the wastewater are low, and it is low-concentration organic wastewater;

[0025] 4. High salt content: Because a large amount of hydrofluoric acid, hydrochloric acid, sodium hydroxide and other inorganic salts are used in the production process, the salt content in the wastewater is high, which is high-salt chemical wastewater.

[0026] Furthermore, the ultrasonic parameters in S1 are: ultrasonic power of 80 to 200 W, ultrasonic frequency of 20 to 60 kHz, and ultrasonic duration of 10 to 60 min.

[0027] Description: When ultrasonic technology is applied to mineral flotation, it can significantly improve flotation efficiency and reagent utilization through the physical and chemical effects of ultrasound.

[0028] Furthermore, the capture agent in S1 is sodium oleate, and the inhibitor is acidified water glass.

[0029] Description: Description: When pH = 8-9, the adsorption strength of Si(OH)4 molecules, the main component of acidified water glass, on the surface of CaF2 is stronger than that on the surface of CaCO3. Ultrasonic treatment will make the desorption of Si(OH)4 molecules from CaF2 more complete, the inhibitory effect of water glass on CaF2 is weakened, and the desorption sites will be replaced by sodium oleate, and the floatability of CaF2 is improved. Therefore, more CaF2 is floated out overall, and the recovery rate of CaF2 shows an upward trend.

[0030] Under the action of ultrasound, sodium oleate desorbs from the SiO2 surface, and the adsorption sites are replaced by acidified water glass, which strengthens the inhibitory effect of water glass, resulting in a decrease in the overall SiO2 content. The CaCO3 content also shows a certain downward trend. This is due to the existence of two hydrogen bonds between the hydrogen atoms of the Si(OH)4 molecule and the fluorine atoms on the CaF2 surface, and only one hydrogen bond between the hydrogen atoms of the Si(OH)4 molecule and the oxygen atoms on the CaCO3 surface. The interaction between the Si(OH)4 molecule and CaF2 is stronger than that between calcite, resulting in a greater adsorption capacity. Therefore, ultrasonic treatment has a more significant effect on the improvement of CaF2 floatability, that is, a more significant improvement in the recovery grade and efficiency of CaF2.

[0031] Furthermore, the configuration steps of acidified water glass are as follows:

[0032] SA1. Mix the water glass stock solution and water in a volume ratio of 1:10 and stir evenly to prepare a water glass solution;

[0033] SA2. Mix laboratory AR grade concentrated sulfuric acid and water in a volume ratio of 1:10 to make a sulfuric acid solution.

[0034] SA3. Mix the sulfuric acid solution in SA2 and the water glass solution in S2-C1 in a volume ratio of 1:1 and stir evenly to obtain acidified water glass as an inhibitor.

[0035] Furthermore, the stirring rate during the stirring in S3-1 is maintained at 600 to 800 r / min.

[0036] Furthermore, the calcium salt in S3-1 is CaCl2. The main reason for using CaCl2 as an external calcium source is to avoid introducing new difficult-to-remove elements.

[0037] Furthermore, the target fluorite standard in S4 is: the mass percentage of CaF2 is 93-99%, the mass percentage of CaCO3 is less than 2%, and the mass percentage of SiO2 is less than 3.5%.

[0038] Note: The above standards are the quality standards of the fluorite industry, namely the fluorite YB / T5217-2019 medium-acid grade fluorite FC-93 standard.

[0039] Compared with the existing high-fluoride acidic wastewater treatment, the beneficial effects of the present invention are:

[0040] (1) Compared with the existing high-fluoride acidic wastewater treatment system, the improved flotation / seed method coupling method designed by the present invention can basically dissociate the CaCO3 impurities in the sludge, and the CaCO3 content is reduced from 19.89% before dissociation to 3.42% after dissociation. The dissociated sludge is coupled with high-fluoride acidic wastewater to further purify the calcium fluoride sludge. Without introducing a new calcium source, the free CaCO3 after dissociation is reduced to 0.04%. 2+ It reacts with high-fluorine acidic wastewater and converts into CaF2, increasing the CaF2 content in the final product CaF2 sludge to 92.72%.

[0041] (2) Compared with the traditional calcium salt precipitation defluoridation, the improved flotation / seed method coupling method designed in the present invention consumes less calcium salt for defluoridation under the sludge seeding condition, has better defluoridation effect, and has better sludge precipitation effect. The prepared CaF2 sludge can meet the acid grade fluorite FC-93 standard.

[0042] (3) The improved flotation / seed method coupling method designed by the present invention was actually applied in a photovoltaic production enterprise with a daily sludge output of 10 tons. An economic benefit analysis was conducted based on the predicted results. Based on 300 days of normal operation per year, the annual output value reached 6 million yuan, which has good market application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a flow chart of the steps of the present invention;

[0044] Figure 2 is the SEM image of CaF2 in control group A;

[0045] Figure 3 is the SEM image of CaF2 in control group B;

[0046] Figure 4 is the SEM image of CaF2 in control group C;

[0047] Figure 5 This is a diagram of the wastewater quality after increasing the Ca / F ratio in the experimental example. DETAILED DESCRIPTION

[0048] In order to further illustrate the approach and effects achieved by the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with experiments.

[0049] Example 1: This example describes a method for treating high-fluoride acidic wastewater based on a flotation / seed crystal coupling method, as described below.

[0050] collecting wastewater through a wastewater collection system, the wastewater collection system comprising a first regulating tank for collecting high-fluorine acidic wastewater, a second regulating tank for collecting low-fluorine dilute acid wastewater and dilute alkaline wastewater, a third regulating tank for collecting concentrated alkaline wastewater, and a fourth regulating tank for collecting domestic wastewater;

[0051] The wastewater collected from the first regulating tank, the second regulating tank and the third regulating tank is sequentially subjected to flocculation and impurity removal treatment, nitrification treatment and concentration treatment in the pretreatment system, the biochemical system and the terminal treatment system to obtain fluorine-containing sludge;

[0052] The wastewater collected from the fourth regulating tank is sequentially subjected to nitrification and concentration treatment in the biochemical system and the terminal treatment system to obtain fluorine-containing sludge;

[0053] The high-fluoride acidic wastewater was then collected from the first regulating tank for later use. The water quality data of the high-fluoride acidic wastewater were as follows: pH = 2, COD content of 180 mg / L, F- content of 18,000 mg / L, TP content of 74 mg / L, conductivity of 29 mS / cm, sulfate content of 130 mg / L, and chloride content of 170 mg / L.

[0054] The improvement is to use the flotation / seed crystal coupling method to treat fluorine-containing sludge and high-fluorine acidic wastewater. The specific steps are:

[0055] S1. Ultrasonic treatment: First, the fluorine-containing sludge is prepared into a slurry, then acidified water glass and sodium oleate are added to the slurry, and finally ultrasonic treatment is used to obtain a pretreated slurry;

[0056] The configuration steps of acidified water glass are:

[0057] SA1. Mix the water glass stock solution and water in a volume ratio of 1:10 and stir evenly to prepare a water glass solution;

[0058] SA2. Mix laboratory AR grade concentrated sulfuric acid and water in a volume ratio of 1:10 to make a sulfuric acid solution.

[0059] SA3, mixing the sulfuric acid solution in SA2 and the water glass solution in S2-C1 in a volume ratio of 1:1 to obtain acidified water glass as an inhibitor;

[0060] The ultrasonic parameters were as follows: ultrasonic power 80 W, ultrasonic frequency 20 kHz, and ultrasonic duration 10 min;

[0061] S2, flotation treatment: Use flotation process to treat the pre-treated mud in S1 and separate the flotation sludge; the specific flotation machine model used is WXFDIV-1L, with a processing capacity of 0.2~0.4m 3 / min;

[0062] S3, acid washing and seed coupling:

[0063] S3-1. First, collect the flotation sludge in S2 as a seed crystal. Then, while maintaining the stirring rate at 600 r / min, add the high-fluoride acidic wastewater from the first regulating tank to the flotation sludge to obtain a pickling sludge. Finally, add CaCl2 to the pickling sludge and mix well to obtain a system A with a pH of 3.

[0064] S3-2: After the acid washing reaction of system A in S3-1 for 30 minutes, the low-fluorine dilute acid wastewater generated is fed into the second regulating tank, and the generated CaF2 sludge is fed into the sedimentation tank;

[0065] When the processes in S1 to S3 meet the following constraints, the sludge CaF2 with a liquid-solid ratio greater than 50 can reach the target fluorite standard under the premise of reducing the amount of calcium source added. The constraints are:

[0066] In S2: the mass percentages of CaF2, CaCO3 and SiO2 in the flotation sludge are 75%, 19% and 4% respectively;

[0067] In S3: the ratio of the added amount of high-fluoride acidic wastewater and flotation sludge in system A is 25 mL:0.5 g; the added amount of CaCl2 makes the molar ratio of calcium and fluorine elements in system A be 1:2.

[0068] Example 2: This example describes a method for treating high-fluoride acidic wastewater based on a flotation / seed crystal coupling method under another parameter, the content of which is shown below.

[0069] collecting wastewater through a wastewater collection system, the wastewater collection system comprising a first regulating tank for collecting high-fluorine acidic wastewater, a second regulating tank for collecting low-fluorine dilute acid wastewater and dilute alkaline wastewater, a third regulating tank for collecting concentrated alkaline wastewater, and a fourth regulating tank for collecting domestic wastewater;

[0070] The wastewater collected from the first regulating tank, the second regulating tank and the third regulating tank is sequentially subjected to flocculation and impurity removal treatment, nitrification treatment and concentration treatment in the pretreatment system, the biochemical system and the terminal treatment system to obtain fluorine-containing sludge;

[0071] The wastewater collected from the fourth regulating tank is sequentially subjected to nitrification and concentration treatment in the biochemical system and the terminal treatment system to obtain fluorine-containing sludge;

[0072] The high-fluoride acidic wastewater is then collected from the first regulating tank for later use. The water quality data of the high-fluoride acidic wastewater are as follows: pH = 1, COD content of 200 mg / L, F- content of 20,000 mg / L, TP content of 80 mg / L, conductivity of 35 mS / cm, sulfate content of 150 mg / L, and chloride content of 200 mg / L.

[0073] The improvement is to use the flotation / seed crystal coupling method to treat fluorine-containing sludge and high-fluorine acidic wastewater. The specific steps are:

[0074] S1. Ultrasonic treatment: First, the fluorine-containing sludge is prepared into a slurry, then acidified water glass and sodium oleate are added to the slurry, and finally ultrasonic treatment is used to obtain a pretreated slurry;

[0075] The configuration steps of acidified water glass are:

[0076] SA1. Mix the water glass stock solution and water in a volume ratio of 1:10 and stir evenly to prepare a water glass solution;

[0077] SA2. Mix laboratory AR grade concentrated sulfuric acid and water in a volume ratio of 1:10 to make a sulfuric acid solution.

[0078] SA3, mixing the sulfuric acid solution in SA2 and the water glass solution in S2-C1 in a volume ratio of 1:1 to obtain acidified water glass as an inhibitor;

[0079] The ultrasonic parameters were as follows: ultrasonic power 200 W, ultrasonic frequency 60 kHz, and ultrasonic duration 60 min;

[0080] S2, flotation treatment: Use flotation process to treat the pre-treated mud in S1 and separate the flotation sludge; the specific flotation machine model used is WXFDIV-1L, with a processing capacity of 0.2~0.4m 3 / min;

[0081] S3, acid washing and seed coupling:

[0082] S3-1. First, collect the flotation sludge in S2 as a seed crystal. Then, while maintaining the stirring rate at 600-800 r / min, add the high-fluoride acidic wastewater from the first regulating tank to the flotation sludge to obtain a pickling sludge. Finally, add CaCl2 to the pickling sludge and mix well to obtain a system A with a pH of 4.

[0083] S3-2: After the acid washing reaction of system A in S3-1 for 40 minutes, the low-fluorine dilute acid wastewater generated is fed into the second regulating tank, and the generated CaF2 sludge is fed into the sedimentation tank;

[0084] When the processes in S1 to S3 meet the following constraints, the sludge CaF2 with a liquid-solid ratio greater than 50 can reach the target fluorite standard under the premise of reducing the amount of calcium source added. The constraints are:

[0085] In S2: the mass percentages of CaF2, CaCO3 and SiO2 in the flotation sludge are 76%, 20% and 5% respectively;

[0086] In S3: the ratio of the added amount of high-fluoride acidic wastewater and flotation sludge in system A is 30 mL:0.6 g; the added amount of CaCl2 makes the molar ratio of calcium and fluorine elements in system A be 1:2.

[0087] Experimental Example: The description of this experimental example is based on the scheme described in Example 1, and is intended to illustrate the practical application effect of the present invention.

[0088] 1. Experimental Design

[0089] In this experimental example, the wastewater used was fluoride-containing wastewater generated during the production process of a photovoltaic enterprise in Jiangsu Province. It originated from the same company as the sewage sludge. The coupling wastewater used was highly fluoride-containing acidic wastewater. Compared to other production wastewaters, this wastewater has the highest fluoride content, reaching a concentration of up to 18,000 mg / L, indicating significant potential for resource recovery. The specific water quality is shown in Table 1.

[0090] Table 1 Water quality of high-fluoride acidic wastewater

[0091]

[0092] After acid washing, the impurity calcium salt is basically removed from the flotation sludge, and the Ca 2+ In the mud, this part of Ca 2 + It can be used as a calcium source to react with high-fluoride acidic wastewater to further produce the target product. No additional calcium salt is added, which means that only the impurity calcium from the sludge acid washing is used as the sole calcium source to couple with high-fluoride acidic wastewater. The purpose is to evaluate the feasibility of coupling crystal seeds to the flotation process.

[0093] In order to illustrate the effect of the flotation / seed method coupling improvement method designed in this method, the following experimental groups were designed:

[0094] Control group A: 25 mL of high-fluoride acidic wastewater was directly reacted with CaCl2 under natural conditions, with a calcium-fluoride ratio of 0.5;

[0095] Control group B: 0.5 g of flotation sludge was added as seed crystals to control group A;

[0096] Control group C: 0.02% polyacrylamide was added to the control group A; polyacrylamide is abbreviated as PAM, which is a water-soluble high molecular polymer and a commonly used flocculant in industry.

[0097] 2. Related performance experiments

[0098] 2-1. SEM inspection

[0099] The CaF2 sludge in the three samples of control group A, B and C was dried and observed under 3000 times SEM. Figures 2 to 4 .

[0100] Depend on Figure 2 It is obvious that the CaF2 particles are small in size and dispersed with each other. Figure 3 It can be clearly seen that the relative particle size of CaF2 particles under seed crystal conditions is larger than that of CaF2 particles formed under natural conditions, and the distribution of CaF2 particles under seed crystal conditions is more aggregated, which explains why the precipitation effect of CaF2 particles under seed crystal conditions is better than that under natural conditions. Figure 4 As can be seen in the figure, only a small amount of CaF2 crystals are observed under the action of PAM, while the majority of the area exhibits a wavy, viscous state. This indicates that PAM has a strong cohesive effect, allowing CaF2 particles to quickly condense and settle. However, the addition of PAM makes the reaction solution and calcium fluoride precipitate viscous, increasing the difficulty of CaF2 separation and introducing new impurities, which is not conducive to sludge purification.

[0101] In summary, the CaF2 sludge in control group B using flotation sludge as seed had a better sedimentation effect than the CaF2 sludge in control group A, but a worse sedimentation effect than the CaF2 sludge in control group C with the addition of PAM. Although the sedimentation effect of the seed method was worse than that of the flocculant addition, the sludge sediment obtained had greater resource potential.

[0102] 2. Analysis of fluoride content in wastewater

[0103] The wastewater after reaction under the conditions of control group A and control group B was analyzed, and three parallel experiments were performed respectively.

[0104] Before the reaction, the F concentration in the wastewater was 18,000 mg / L, the total volume was 100 ml, the calcium-fluoride ratio was 0.5, the calcium source additive was CaCl2, and the control group B was additionally added with 2 g of flotation sludge as a seed. The experimental results are shown in Table 2.

[0105] The average fluoride concentration in wastewater under natural conditions dropped to 982.96 mg / L, and the average fluoride concentration in wastewater under seed crystal conditions dropped to 272.38 mg / L. It can be clearly seen that the calcium salt removal efficiency under seed crystal conditions is higher. Figure 5 As shown. With the continuous increase of the calcium-fluoride ratio, the fluoride concentration in the wastewater also decreases, and the downward trend slows down as the calcium-fluoride ratio increases. When the calcium-fluoride ratio is 0.7, the fluoride concentration in the wastewater is 298.89 mg / L. At this time, the fluoride removal efficiency of calcium salt under natural conditions is close to the fluoride removal efficiency under seed conditions when the calcium-fluoride ratio is 0.5. This is because the seed method can reduce the supersaturation of the calcium fluoride precipitation reaction and improve the crystallization efficiency of calcium fluoride. Therefore, to achieve the same fluoride removal effect, compared with calcium salt fluoride removal under natural conditions, using flotation sludge as a seed to couple with fluoride-containing wastewater requires less calcium salt additives, which means that the operating cost can be reduced in the actual production process.

[0106] Table 2 Fluoride content in wastewater

[0107]

[0108] 3. Analysis of sludge sedimentation under seed conditions

[0109] The sludge precipitate after the reaction under seeding conditions was analyzed, and the results are shown in Table 3, where all contents are by mass. This analysis compares the results of the sludge analysis after coupling the free calcium produced by calcium carbonate in the acid-washed dissociation sludge with the fluoride-containing wastewater without the addition of additional calcium reagent. It is clear that the introduction of an additional calcium source further reacts with the fluoride-containing wastewater, producing more high-quality CaF2 product, with a fluoride recovery rate of 90±1%. This shows that using flotation sludge as seed crystals to couple with fluoride-containing wastewater can fully utilize the fluoride-containing wastewater while further increasing the CaF2 content in the sludge.

[0110] Table 3 Sludge precipitation analysis under seed conditions

[0111]

Claims

1. A method for treating high-fluoride acidic wastewater based on a flotation / seed crystal coupling method, comprising the following steps: collecting wastewater through a wastewater collection system, the wastewater collection system comprising a first regulating tank for collecting high-fluorine acidic wastewater, a second regulating tank for collecting low-fluorine dilute acid wastewater and dilute alkaline wastewater, a third regulating tank for collecting concentrated alkaline wastewater, and a fourth regulating tank for collecting domestic wastewater; The wastewater collected from the first regulating tank, the second regulating tank, and the third regulating tank is sequentially subjected to flocculation and impurity removal treatment, nitrification treatment, and concentration treatment in a pretreatment system, a biochemical system, and a terminal treatment system to obtain fluorine-containing sludge; The wastewater collected from the fourth regulating tank is sequentially subjected to nitrification treatment and concentration treatment in a biochemical system and a terminal treatment system to obtain fluorine-containing sludge; The high-fluoride acidic wastewater is then collected from the first regulating tank for future use; The method is characterized in that the fluorine-containing sludge and high-fluorine acidic wastewater are treated by a flotation / seed crystal coupling method, and the specific steps are: S1. Ultrasonic treatment: first, the fluorine-containing sludge is prepared into slurry, then an inhibitor and a capture agent are added to the slurry, and finally, ultrasonic treatment is performed to obtain pretreated slurry; S2, flotation treatment: Use flotation process to treat the pretreated sludge in S1 and separate the flotation sludge; S3, acid washing and seed coupling: S3-1, first collecting the flotation sludge in S2 as a seed crystal, then adding the high-fluoride acid wastewater from the first regulating tank to the flotation sludge while stirring to obtain a pickling sludge, and finally adding calcium salt to the pickling sludge and mixing uniformly to obtain System A; S3-2. After the acid washing reaction of system A in S3-1 is completed, the low-fluorine dilute acid wastewater generated is fed into the second regulating tank, and the generated CaF2 sludge is fed into the sedimentation tank; When the processes in S1 to S3 meet the following constraints, the sludge CaF2 with a liquid-to-solid ratio greater than 50 can reach the target fluorite standard under the premise of reducing the amount of calcium source added. The constraints are: In S1: the capture agent is sodium oleate, and the inhibitor is acidified water glass; In S2: the mass percentages of CaF2, CaCO3 and SiO2 in flotation sludge are 75~76%, 19~20% and 4~5% respectively; In S3: n is the multiplication factor and , then the amount of high-fluoride acidic wastewater added to system A is [25n, 30n] mL, the amount of flotation sludge added is [0.5n, 0.6n] g; the amount of calcium salt added makes the molar ratio of calcium to fluorine in system A 1:2; The pH of system A is 3~4, and the pickling reaction time is 30~40 min.

2. The method for treating high-fluoride acidic wastewater based on flotation / seed crystal coupling method according to claim 1, characterized in that: The water quality data of the high-fluoride acidic wastewater are: pH=2~1, COD content is 180~200 mg / L, F - The content is 18000~20000 mg / L, TP content is 74~80 mg / L, conductivity is 29~35 mS / cm, sulfate content is 130~150 mg / L, and chloride content is 170~200 mg / L.

3. The method for treating high-fluoride acidic wastewater based on flotation / seed crystal coupling method according to claim 1, characterized in that: The ultrasonic parameters described in S1 are: ultrasonic power of 80-200 W, ultrasonic frequency of 20-60 kHz, and ultrasonic duration of 10-60 min.

4. The method for treating high-fluoride acidic wastewater based on flotation / seed crystal coupling method according to claim 1, characterized in that: The stirring rate during the stirring in S3-1 is maintained at 600-800 r / min.

5. The method for treating high-fluoride acidic wastewater based on flotation / seed crystal coupling method according to claim 1, characterized in that: The calcium salt in S3-1 is CaCl2.

6. The method for treating high-fluoride acidic wastewater based on flotation / seed crystal coupling method according to claim 1, characterized in that: The target fluorite standard described in S4 is: the mass percentage of CaF2 is 93~99%, the mass percentage of CaCO3 is less than 2%, and the mass percentage of SiO2 is less than 3.5%.

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