Two-stage fluorine-containing wastewater treatment system and method

Abstract

The invention provides a two-stage system and method for treating fluorine-containing wastewater, the system comprises a first-stage defluorination procedure and a second-stage defluorination procedure, the pH value of the fluorine-containing wastewater is adjusted to be between weak acidity and weak alkalinity by using an alkaline compound in a first mixing tank to form first mixed wastewater; carrying out a first-stage fluorine removal procedure, mixing the first mixed wastewater containing high-concentration fluorine ions with calcium chloride, and stirring in a second mixing tank to obtain second mixed wastewater containing low-concentration fluorine ions; carrying out a second-stage fluorine removal procedure, mixing the second mixed wastewater with a deep fluorine removal agent, and stirring in a third mixing tank to form third mixed wastewater; and injecting the third mixed wastewater from the third mixing tank into a flocculation tank, and adding a polymer for flocculation and sedimentation to discharge precipitates and fluorine-removed wastewater, the fluorine ion content of the fluorine-removed wastewater being 15 ppm or less.

Description

Technical Field

[0001] The present invention relates to a fluorine-containing wastewater treatment technology, and in particular to a two-stage system for treating fluorine-containing wastewater using a deep defluorinating agent. Background Art

[0002] Semiconductor industrial wastewater is industrial wastewater generated during the wafer production process. When semiconductor factories make wafers, they use a large amount of hydrofluoric acid to clean the wafer surface. In addition to hydrofluoric acid, other acids such as sulfuric acid or phosphoric acid are often mixed in. In the process of liquid crystal display panels and solar energy industries, high-concentration hydrofluoric acid or hydrofluoric acid mixed acid is also used to clean TFT-LCD panels or solar silicon wafers. The pollutants contained in semiconductor industrial wastewater are mainly fluorides and other pollutants.

[0003] At present, the treatment methods of fluoride-containing wastewater are roughly divided into three methods in industry: chemical precipitation, flocculation precipitation, and adsorption. Among them, chemical precipitation is the most commonly used method in industry and has great economic benefits. Generally speaking, calcium salt precipitation is used for high-concentration fluoride-containing industrial wastewater, that is, calcium salts such as calcium chloride or calcium hydroxide are added to the industrial wastewater to make the fluoride ions in the wastewater react with the calcium ions provided by the agent to form calcium fluoride precipitation and then remove the fluoride ions in the water. Although the chemical precipitation method has a simple process, convenient treatment, and small equipment requirements, it has other effects such as excessive concentrations of chloride ions and calcium ions in the discharged water.

[0004] Please refer to Figure 1 , Figure 1 This is a comparison chart of the concentrations of fluoride ions and calcium chloride after the wastewater is treated by chemical precipitation. The traditional chemical precipitation method is to use calcium salts such as calcium chloride or calcium hydroxide to add into industrial wastewater to react fluoride ions with calcium ions in the wastewater to form calcium fluoride. However, when only calcium salts are used to remove fluoride to a concentration of 50ppm, the removal efficiency will drop significantly. Therefore, it is necessary to add excessive calcium salts for the reaction, resulting in excessive reagents, increased costs, and other problems. As a result, it is necessary to add excessive calcium chloride reagents to reduce the fluoride ion concentration in the wastewater to below 15ppm or even lower in order to meet the discharge water standards, resulting in increased costs, consumption of a large amount of calcium chloride, and environmental pollution. In addition, the addition of excessive calcium chloride will increase the chloride ion content and conductivity in the discharged water, and will also increase the amount of sludge produced.

[0005] In view of this, how to optimize the operating procedures of the fluoride-containing wastewater treatment system is an issue that needs to be addressed urgently. Summary of the invention

[0006] In view of the above-mentioned problems in the prior art, the present invention provides a two-stage system for treating fluoride-containing wastewater, which can reduce excessive addition of calcium chloride and the amount of sludge, and make the defluorination system have stable water output, reduce the fluoride ions in the fluoride-containing wastewater to below 15ppm, and achieve better effect in treating fluoride-containing wastewater, reduce the cost of the defluorination system, and facilitate the use of water treatment equipment and increase the service life of the equipment.

[0007] To achieve the above object, the present invention provides a two-stage system for treating fluorine-containing wastewater, which includes a first defluorination process and a second defluorination process. The two-stage system for treating fluorine-containing wastewater includes a first mixing tank, a second mixing tank, a third mixing tank and a flocculation tank. The first mixing tank is connected to a fluorine-containing wastewater source, and is used for stirring and mixing the fluorine-containing wastewater from the fluorine-containing wastewater source and the alkaline compound added thereto, so as to adjust the pH value of the fluorine-containing wastewater to weak acidity, so as to form a first mixed wastewater; the second mixing tank is connected to the first mixing tank, and is used for stirring and mixing the first mixed wastewater from the first mixing tank and the calcium chloride added thereto, so as to form a second mixed wastewater; the third mixing tank is connected to the second mixing tank, and is used for stirring and mixing the second mixed wastewater from the second mixing tank and the deep defluorinating agent added thereto, so as to form a third mixed wastewater; and the flocculation tank connected to the third mixing tank, and is used for stirring and mixing the third mixed wastewater from the third mixing tank and the polymer added thereto for flocculation, so as to produce precipitate discharge and defluorinated wastewater, and the fluoride ion of the defluorinated wastewater is below 15ppm.

[0008] Preferably, the fluoride ion content of the second mixed wastewater is reduced to 30% to 85% of the fluoride ion content of the first mixed wastewater.

[0009] Preferably, the fluoride ion content of the third mixed wastewater is reduced to 85% to 99% of the fluoride ion content of the first mixed wastewater.

[0010] Preferably, the alkaline compound is sodium hydroxide.

[0011] Preferably, the deep defluorination agent comprises 40 wt% to 70 wt% of polyaluminium sulfate, 0.3 wt% to 30 wt% of hydroxyapatite and deionised water supplemented to 100 wt%.

[0012] Preferably, the deep defluorination agent includes 40wt% to 70wt% of polyaluminium sulfate, 5wt% to 6.5wt% of polyaluminium chloride, 5wt% to 30wt% of hydroxyapatite, 1wt% of polyferric sulfate, 1wt% of nano-aluminium, 1wt% of nano-iron, 1wt% of nano-calcium and deionized water supplemented to 100wt%.

[0013] Preferably, the polymer is polyacrylamide.

[0014] In addition, the present invention further provides a two-stage method for treating fluoride-containing wastewater, which comprises the following steps:

[0015] injecting fluoride-containing wastewater from a fluoride-containing wastewater source into a first mixing tank;

[0016] and adding an alkaline compound into the first mixing tank to adjust the pH value of the fluorine-containing wastewater to weak acidity to form first mixed wastewater;

[0017] The first stage of the defluorination process includes: injecting the first mixed wastewater from the first mixing tank into the second mixing tank, and adding calcium chloride to form second mixed wastewater;

[0018] Performing a second stage of defluorination procedure includes: injecting the second mixed wastewater from the second mixing tank into a third mixing tank, and adding a deep defluorination agent to form a third mixed wastewater; and

[0019] The third mixed wastewater is injected from the third mixing tank into the flocculation tank, and a polymer is added for flocculation and sedimentation to discharge the precipitate and the defluorinated wastewater, wherein the fluoride ion of the defluorinated wastewater is below 15 ppm.

[0020] Preferably, the deep defluorination agent comprises 40 wt% to 70 wt% of polyaluminium sulfate, 0.3 wt% to 30 wt% of hydroxyapatite and deionised water supplemented to 100 wt%.

[0021] Preferably, the deep defluorination agent includes 40wt% to 70wt% of polyaluminium sulfate, 5wt% to 6.5wt% of polyaluminium chloride, 5wt% to 30wt% of hydroxyapatite, 1wt% of polyferric sulfate, 1wt% of nano-aluminium, 1wt% of nano-iron, 1wt% of nano-calcium and deionized water supplemented to 100wt%.

[0022] The two-stage introduction of calcium chloride and deep defluoridation agent (also known as MU-RF501) provided by the present invention can not only avoid excessive addition of calcium chloride, but also reduce the chloride ion content in the discharge water and the conductivity of the water, further reducing the amount of sludge generated.

[0023] The following is a detailed description through specific embodiments and accompanying diagrams, which will make it easier to understand the purpose, technical content, characteristics and effects achieved by the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a comparison chart of the concentrations of fluoride ions and calcium chloride after wastewater is treated using chemical precipitation.

[0025] Figure 2 It is a schematic diagram of the two-stage defluorination system disclosed in the present invention.

[0026] Figure 3It is a comparison chart of chloride ion concentrations of fluoride-containing wastewater after being treated by chemical precipitation method and the deep defluorination agent of the present invention.

[0027] Figure 4 The present invention is a flow chart for treating fluoride-containing wastewater using the two-stage defluorination system of the present invention.

[0028] Reference numerals:

[0029] 1. Fluorine-containing wastewater treatment system; 11. First mixing tank; 12. Second mixing tank; 13. Third mixing tank; 14. Flocculation tank; 21. Alkaline compound tank; 22. Calcium chloride agent tank; 23. Deep defluorination agent tank; 24. Polymer tank; FW, fluorine-containing wastewater source; MW1, first mixed wastewater; MW2, second mixed wastewater; MW3, third mixed wastewater; TW, defluorination wastewater; PPT, precipitate; S01-S04, steps. DETAILED DESCRIPTION

[0030] Several examples are listed below to illustrate the implementation of the two-stage system and method for treating fluorine-containing wastewater of the present invention, so those skilled in the art can simply understand the advantages and effects that can be achieved by the present invention through the contents of the following examples. It should be understood that the examples listed in this specification are only used to illustrate the implementation of the present invention, and are not used to limit the scope of the present invention. Those skilled in the art can make various modifications and changes based on common knowledge without departing from the spirit of the present invention to implement or apply the content of the present invention.

[0031] The fluorine-containing wastewater used in the embodiment of the present invention is industrial wastewater taken from a semiconductor factory as the fluorine-containing wastewater to be treated, wherein the pH value of the fluorine-containing wastewater to be treated is between 3 and 4, the fluorine ion concentration is 100ppm to 1000ppm, the chloride ion concentration is 5ppm to 60ppm, and the conductivity is 1ms / cm to 3ms / cm.

[0032] Please refer to Figure 2 , which is a schematic diagram of a two-stage system 1 for treating fluorine-containing wastewater disclosed in the present invention. The fluorine-containing wastewater treatment system 1 of the present invention comprises a first mixing tank 11, a second mixing tank 12, a third mixing tank 13 and a flocculation tank 14, which are specifically described as follows:

[0033] The first mixing tank 11 is connected to the fluorine-containing wastewater source FW by a pipeline, so that the fluorine-containing wastewater to be treated is injected into the first mixing tank 11, and is connected to the alkaline compound tank 21 by a pipeline, so that the alkaline compound is injected into the first mixing tank 11. The first mixing tank 11 is provided with a stirring assembly to mix the fluorine-containing wastewater and the alkaline compound to adjust the pH value of the fluorine-containing wastewater from weak acidity to weak alkalinity to form the first mixed wastewater MW1.

[0034] Examples of alkaline compounds include, but are not limited to, sodium hydroxide. The amount of the alkaline compound used depends on the amount required to adjust the initial pH value of the fluorine-containing wastewater to the target pH value. Those skilled in the art can measure the pH value and adjust the amount of the alkaline compound according to the prior art, and the present invention is not limited thereto.

[0035] The pH value of the fluorine-containing wastewater is adjusted to be weakly acidic to weakly alkaline in the first mixing tank 11 . The pH value of the weakly acidic to weakly alkaline pH value is preferably between 6 and 8. In this embodiment, the pH value of the fluorine-containing wastewater is adjusted to 6 (weakly acidic).

[0036] The second mixing tank 12 is connected to the first mixing tank 11 by a pipeline, so that the first mixed wastewater MW1 is injected into the second mixing tank 12, and is connected to the calcium chloride reagent tank 22 by a pipeline, so that calcium chloride is injected into the second mixing tank 12. The second mixing tank 12 is provided with a stirring assembly to mix the first mixed wastewater MW1 and calcium chloride, and stir at a speed of 50 rpm for 10 to 18 minutes to fully react to form the second mixed wastewater MW2.

[0037] The calcium chloride used in this example is commercially available calcium chloride.

[0038] The mixing ratio of the first mixed wastewater MW1 to calcium chloride is 1:300-1500, preferably 1:450. The amount of calcium chloride can be adjusted according to actual conditions until the fluoride ion content in the second mixed wastewater MW2 after the reaction drops to the target concentration or percentage.

[0039] The first mixed wastewater MW1 is stirred and mixed with calcium chloride to reduce the fluoride ion content in the second mixed wastewater MW2 to 80-420 ppm, that is, to reduce (remove) 30%-85% of the fluoride ions in the first mixed wastewater MW1.

[0040] The third mixing tank 13 is connected to the second mixing tank 12 by a pipeline, so that the second mixed wastewater MW2 is injected into the third mixing tank 13, and is connected to the deep defluorinating agent tank 23 by a pipeline, so that the deep defluorinating agent is injected into the third mixing tank 13. The third mixing tank 13 is provided with a stirring assembly to mix the second mixed wastewater MW2 and the deep defluorinating agent, and stir at a rotation speed of 50 rpm for 10 to 18 minutes to make them fully react to form the third mixed wastewater MW3.

[0041] The mixing ratio of the second mixed wastewater MW2 to the deep defluorination agent is 1:150-1000, preferably 1:380. The dosage of the deep defluorination agent can be adjusted according to actual conditions until the fluoride ion content in the third mixed wastewater MW3 after the reaction drops to the target concentration or percentage.

[0042] The second mixed wastewater MW2 is stirred and mixed with the deep defluorination agent to reduce the fluoride ion content in the third mixed wastewater MW3 to 15 ppm or below, that is, reduced (removed) to 85% to 99% of the fluoride ions in the first mixed wastewater MW1.

[0043] Please refer to Table 1, which shows the ingredients and proportions of the deep defluorination agent of the present invention. The ingredients in Table 1 are uniformly mixed to prepare the deep defluorination agents of Example 1 and Comparative Examples 1 to 6.

[0044] Table 1

[0045] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Polyaluminium Sulfate 40wt% 70wt% 40wt% 40wt% 40wt% 40wt% 40wt% Polyaluminium chloride 6wt% 0wt% 0wt% 6.5wt% 6wt% 5wt% 5.5wt% Hydroxyapatite 10wt% 0.7wt% 0.3wt% 30wt% 20wt% 15wt% 5wt% Polyferric Sulfate 1wt% 0wt% 0wt% 1wt% 1wt% 1wt% 1wt% Nano Aluminum 1wt% 0wt% 0wt% 1wt% 1wt% 1wt% 1wt% Nano Iron 1wt% 0wt% 0wt% 1wt% 1wt% 1wt% 1wt% Nano Calcium 1wt% 0wt% 0wt% 1wt% 1wt% 1wt% 1wt% Deionized water 40.0wt% 29.3wt% 59.7wt% 19.5wt% 30.0wt% 36.0wt% 45.5wt%

[0046] As shown in Table 1, the deep defluorination agent is composed of the following ingredients in weight percentage concentrations: 40% to 70% polyaluminium sulfate, 0.3% to 30% hydroxyapatite and deionized water supplemented to 100%. Further, the deep defluorination agent is composed of the following ingredients in weight percentage concentrations: 40% to 70% polyaluminium sulfate, 5% to 6.5% polyaluminium chloride, 5% to 30% hydroxyapatite, 1% polyferric sulfate, 1% calcium sulfate, 1% nano-aluminium, 1% nano-iron, 1% nano-calcium and deionized water supplemented to 100%.

[0047] Polyaluminum sulfate and polyferric sulfate are mainly used to remove fluoride ions in fluoride-containing wastewater and achieve flocculation effects; in addition, the matrix of polyaluminum sulfate and polyferric sulfate is sulfate ion, and its solubility in water is the same as that of sulfuric acid in water. The efficiency of polyaluminum sulfate and polyferric sulfate dissolving in water synergistically improves the reactivity with fluoride ions and improves the removal of fluoride ions.

[0048] The content of aluminum oxide in the polyaluminum sulfate is in the range of 15wt% to 20wt%, preferably 15.8wt%. The content of iron oxide in the polyferric sulfate is in the range of 0.2wt% to 0.8wt%, preferably 0.2wt%. The total iron content (in terms of Fe 3+ The mass fraction of the organic solvent (calculated) is 10% to 20%, preferably 19%.

[0049] Polyaluminium chloride mainly provides the effect of flocculation and removal of fluoride ions.

[0050] When the hydroxyapatite in the deep defluorination agent of the present invention reacts with the fluoride-containing wastewater, the OH in the hydroxyapatite - Ions can react with fluoride ions in fluoride-containing wastewater to achieve the effect of ion exchange. At the same time, hydroxyapatite can also adsorb fluoride ions. Therefore, hydroxyapatite can remove fluoride ions in two ways: ion exchange and adsorption. It can shorten the removal reaction time and reduce the stirring time. The chemical reaction formula of ion exchange is: Ca 10(PO4)6(OH)2+2F - →Ca 10 (PO4)6F2+2OH - . This further improves the removal rate and effect of fluoride ions. In addition, OH in hydroxyapatite - After ion exchange, the ions enter the wastewater, which can maintain the pH value of the wastewater between pH 6 and 8 and reduce the use of alkaline compounds.

[0051] The flocculation tank 14 is connected to the third mixing tank 13 by a pipeline, so that the third mixed solution is injected into the flocculation tank 14, and is connected to the polymer tank 24 by a pipeline, so that the polymer is injected into the flocculation tank 14. The flocculation tank 14 is provided with a stirring assembly to mix the third mixed solution and the polymer for flocculation, and stir at a rotation speed of 30 rpm for 10 to 18 minutes to make them fully react to generate a precipitate PPT for discharge and defluoridation wastewater TW, and the fluoride ion of the defluoridation wastewater TW is less than 15 ppm.

[0052] The mixing ratio of the third mixed solution to the polymer is 1:200-1250, preferably 1:800.

[0053] Examples of polymers include, but are not limited to, polyacrylamide.

[0054] The stirring components of the first mixing tank 11, the second mixing tank 12, the third mixing tank 13 and the flocculation tank 14 of the present invention can be any components with stirring function, such as: paddle stirrers, turbine stirrers, anchor stirrers, ribbon stirrers, magnetic stirrers, side-entry stirrers, etc.

[0055] Example 1: Determination of fluorine removal efficiency of a two-stage defluorine removal system

[0056] The two-stage system 1 for treating fluorine-containing wastewater of the present invention treats 500mL of fluorine-containing wastewater source FW to obtain treated defluorinated wastewater TW. In the first defluorination procedure, the addition amount of 37wt% calcium chloride is 0.4-1.6mL. In the second defluorination procedure, the mixing ratio of deep defluorinating agent and deionized water is 1:5-50, so as to prepare a deep defluorinating agent solution with a weight percentage concentration of 5%-50%. The above dilution ratio can be adjusted according to demand or not diluted, and the present invention is not limited to this. In this example, the deep defluorinating agent in Table 1 is prepared into a solution with a weight percentage concentration of 40% in deionized water, and added to the second mixed wastewater MW2 in an amount of 0.5-2.9mL, and the supernatant is extracted and the fluoride ion concentration is detected by a fluoride electrode, wherein the fluoride ion detection method is based on the "Fluoride Salt Detection Method in Water-Fluoride Selective Electrode Method" (NIEA W413.52A), and the results are shown in Table 2.

[0057] Table 2

[0058]

[0059] As shown in Table 2, after the fluorine-containing wastewater is treated with the deep defluorination agent of Table 1 of the present invention, the fluoride ion concentration is reduced to 9.5-13.4 ppm, and the defluorination efficiency is 90.4%-99.7%. Among them, the deep defluorination agent of Example 1 has the best defluorination effect, overcoming the above problems. Figure 1 The traditional chemical precipitation method has exceeded the limit of fluoride removal efficiency, and the fluoride ion concentration in fluoride-containing wastewater is reduced by effectively utilizing minimal reagents, thereby solving the technical problem of the traditional chemical precipitation method requiring the addition of excessive calcium chloride, reducing costs and avoiding the problem of deriving new chemical pollution.

[0060] It can be seen that the deep defluorination agent of the present invention can meet the requirement that the discharge standard of low-concentration fluorine-containing wastewater must be lower than 15 ppm.

[0061] Example 2: Conductivity measurement of defluoridation wastewater after treatment with a two-stage defluoridation system

[0062] The supernatant of the defluorinated wastewater TW treated by the two-stage system 1 for treating fluorinated wastewater of the present invention was extracted, and the conductivity was detected by a conductivity meter, wherein the conductivity detection method refers to the "Method for Determining Conductivity in Water - Conductivity Meter Method" (NIEAW203.51B), and compared with the traditional chemical precipitation method (i.e., only adding calcium chloride), the conductivity of the original fluorinated wastewater in this example is 2.65ms / cm, and the comparison results are shown in Table 3.

[0063] Table 3

[0064]

[0065] As shown in Table 3, the deep defluorination agent of the present invention reduces the conductivity of fluorine-containing wastewater to 3.63-4.07 ms / cm, which is 38.3%-57.0% lower than that of the traditional chemical precipitation method. The calculation formula is shown in Mathematical Formula 1, among which the deep defluorination agent of Example 1 has the best effect, the smallest increase in conductivity, and the highest reduction ratio.

[0066]

[0067] Example 3: Determination of chloride ion concentration in defluoridation wastewater after treatment with a two-stage defluoridation system

[0068] The supernatant of the defluorinated wastewater TW treated by the two-stage fluorinated wastewater treatment system 1 of the present invention was extracted, and the chloride ion concentration was detected. The chloride ion detection method refers to the "Chloride Salt Detection Method in Water" (NIEA W407.51C), and compared with the traditional chemical precipitation method (i.e., only adding 3 grams of calcium chloride), the chloride ion concentration of the original fluorinated wastewater in this example is 55.2ppm. The results are as follows: Figure 3 As shown in Table 4.

[0069] Table 4

[0070]

[0071] like Figure 3 As shown in Table 4, after the fluorine-containing wastewater is treated by chemical precipitation, the chloride ion concentration in the fluorine-containing wastewater is as high as 1557.3ppm. On the contrary, after the deep defluorination agents of Example 1 and Comparative Examples 1 to 4 of the present invention are used to treat the fluorine-containing wastewater, the chloride ion concentration in the fluorine-containing wastewater is only 341.7 to 1055.2ppm, with a reduction ratio of 33.4% to 80.9%, among which the deep defluorination agent of Example 1 has the best effect.

[0072] It can be seen that the two-stage defluorination system of the present invention can effectively reduce the conductivity of fluorine-containing wastewater and reduce the chloride ion content in the wastewater while achieving a better defluorination effect. The deep defluorination agent of the present invention does have a synergistic effect.

[0073] See also Figure 4 The present invention also provides a two-stage method for treating fluoride-containing wastewater, comprising the following steps:

[0074] Step S01: injecting fluorine-containing wastewater from a fluorine-containing wastewater source into a first mixing tank, and adding an alkaline compound into the first mixing tank to adjust the pH value of the fluorine-containing wastewater to be weakly acidic to weakly alkaline, so as to form first mixed wastewater;

[0075] Step S02: performing a first stage of defluorination procedure, including: injecting the first mixed wastewater from the first mixing tank into the second mixing tank, and adding calcium chloride to form a second mixed wastewater;

[0076] Step S03: performing a second defluorination procedure, including: injecting the second mixed wastewater from the second mixing tank into the third mixing tank, and adding a deep defluorination agent to form a third mixed wastewater; and

[0077] Step S04: injecting the third mixed wastewater from the third mixing tank into the flocculation tank, and adding polymer to perform flocculation and sedimentation, so as to discharge the precipitate and the defluorinated wastewater, wherein the fluoride ion of the defluorinated wastewater is less than 15 ppm.

[0078] In summary, the two-stage defluorination system of the present invention includes a first defluorination procedure and a second defluorination procedure. In the first defluorination procedure, calcium chloride is used to remove most of the fluoride ions in the fluoride-containing water, and in the second defluorination procedure, a deep defluoridation agent is used to remove the remaining trace fluoride ions that are difficult to remove, so that the fluoride ion content of the treated fluoride-containing wastewater is lower than 15ppm, which overcomes the technical problem that the traditional technology needs to use excessive chemical reagents. In addition, while achieving a better defluorination effect, it can effectively reduce the conductivity of the fluoride-containing wastewater and reduce the chloride ion content in the wastewater, and reduce the amount of sludge generated. Therefore, the two-stage defluorination system of the present invention does have a synergistic effect, has environmental protection and economic benefits, and increases the recycling of wastewater after defluorination.

Claims

1. A two-stage system for treating fluoride-containing wastewater, characterized in that: Include: A first mixing tank is connected to a fluorine-containing wastewater source and is used to stir and mix the fluorine-containing wastewater from the fluorine-containing wastewater source and the alkaline compound added thereto, so as to adjust the pH value of the fluorine-containing wastewater to between weak acidity and weak alkalinity, so as to form a first mixed wastewater; a second mixing tank connected to the first mixing tank, for stirring and mixing the first mixed wastewater from the first mixing tank and the calcium chloride added therein to form a second mixed wastewater; a third mixing tank connected to the second mixing tank, for stirring and mixing the second mixed wastewater from the second mixing tank and the deep defluorination agent added therein to form a third mixed wastewater; as well as The flocculation tank is connected to the third mixing tank and is used to stir and mix the third mixed wastewater from the third mixing tank and the polymer added therein for flocculation to produce precipitate discharge and defluoridated wastewater, wherein the fluoride ion in the defluoridated wastewater is below 15 ppm.

2. The two-stage system for treating fluorine-containing wastewater according to claim 1, characterized in that: The fluoride ion content of the second mixed wastewater is reduced to 30% to 85% of the fluoride ion content of the first mixed wastewater.

3. The two-stage system for treating fluorine-containing wastewater according to claim 1, characterized in that: The fluoride ion content of the third mixed wastewater is reduced to 85% to 99% of the fluoride ion content of the first mixed wastewater.

4. The two-stage system for treating fluorine-containing wastewater according to claim 1, characterized in that: The alkaline compound is sodium hydroxide.

5. The two-stage system for treating fluorine-containing wastewater according to claim 1, characterized in that: The deep defluorination agent comprises 40wt% to 70wt% of polyaluminium sulfate, 0.3wt% to 30wt% of hydroxyapatite and deionized water supplemented to 100wt%.

6. The two-stage system for treating fluorine-containing wastewater according to claim 1, characterized in that: The deep defluorination agent comprises 40wt% to 70wt% of polyaluminium sulfate, 5wt% to 6.5wt% of polyaluminium chloride, 5wt% to 30wt% of hydroxyapatite, 1wt% of polyferric sulfate, 1wt% of nano-aluminium, 1wt% of nano-iron, 1wt% of nano-calcium and deionized water supplemented to 100wt%.

7. The two-stage system for treating fluorine-containing wastewater according to claim 1, characterized in that: The polymer is polyacrylamide.

8. A two-stage method for treating fluoride-containing wastewater, characterized in that: The following steps are involved: Injecting fluorine-containing wastewater from a fluorine-containing wastewater source into a first mixing tank, and adding an alkaline compound into the first mixing tank to adjust the pH value of the fluorine-containing wastewater to be weakly acidic to weakly alkaline, so as to form first mixed wastewater; The first stage of the defluorination process includes: injecting the first mixed wastewater from the first mixing tank into the second mixing tank, and adding calcium chloride to form second mixed wastewater; Performing a second stage of defluorination procedure, including: injecting the second mixed wastewater from the second mixing tank into a third mixing tank, and adding a deep defluorination agent to form a third mixed wastewater; and The third mixed wastewater is injected from the third mixing tank into the flocculation tank, and a polymer is added for flocculation and sedimentation to discharge the precipitate and the defluorinated wastewater, wherein the fluoride ion of the defluorinated wastewater is less than 15 ppm.

9. The method according to claim 8, characterized in that The deep defluorination agent comprises 40wt% to 70wt% of polyaluminium sulfate, 0.3wt% to 30wt% of hydroxyapatite and deionized water supplemented to 100wt%.

10. The method according to claim 8, characterized in that The deep defluorination agent comprises 40wt% to 70wt% of polyaluminium sulfate, 5wt% to 6.5wt% of polyaluminium chloride, 5wt% to 30wt% of hydroxyapatite, 1wt% of polyferric sulfate, 1wt% of nano-aluminium, 1wt% of nano-iron, 1wt% of nano-calcium and deionized water supplemented to 100wt%.

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